KR20200145748A - Method, apparatus and recording medium for encoding/decoding image - Google Patents

Abstract

Disclosed are a method, an apparatus, and a recording medium for encoding/decoding an image performing efficient deblocking filtering. According to the present invention, in an image decoding method, it is determined whether or not to perform filtering on a boundary of a target block, and the filtering strength for the boundary of the target block and the number of samples used for filtering are determined. Based on the determination, filtering is performed on the boundary of the target block. In determining the filtering strength and the number of samples, coding parameters related to the target block and a neighboring block, such as a block size and a prediction mode, are used.

Description

Method, apparatus, and recording medium for video encoding/decoding {METHOD, APPARATUS AND RECORDING MEDIUM FOR ENCODING/DECODING IMAGE}

The present invention relates to a method, an apparatus and a recording medium for encoding/decoding an image. Specifically, the present invention relates to a method, apparatus, and recording medium for video encoding/decoding using an improved deblocking filter.

Through the continuous development of the information and communication industry, broadcast services with high definition (HD) resolution have spread worldwide. Through this proliferation, many users have become accustomed to high-resolution and high-definition images and/or videos.

In order to satisfy the demands of users for high image quality, many organizations are spurring the development of next-generation imaging devices. Users' interest in High Definition TV (HDTV) and Full HD (FHD) TV, as well as Ultra High Definition (UHD) TV, which has a resolution of 4 times or more compared to FHD TV This has increased, and as interest increases, an image encoding/decoding technology for an image having a higher resolution and quality is required.

As an image compression technology, there are various technologies such as inter prediction technology, intra prediction technology, transform and quantization technology, and entropy coding technology.

The inter prediction technique is a technique for predicting a value of a pixel included in a current picture by using a picture before and/or after a picture of the current picture. Intra prediction technology is a technology that predicts a value of a pixel included in a current picture by using information about a pixel in the current picture. The transform and quantization technique is a technique for compressing the energy of a residual signal. In the entropy encoding technique, a short code is assigned to a value with a high frequency of occurrence, and a long code is assigned to a value with a low frequency of occurrence.

Using such an image compression technique, data for an image can be effectively compressed, transmitted, and stored.

The conventional video encoding/decoding method and the filtering method used in the apparatus have limitations in performing encoding/decoding because the application method is limited.

An embodiment may provide an image decoding/encoding method and apparatus for performing efficient deblocking filtering.

In one side, determining whether to perform filtering on the target boundary of the target block; If it is determined that the filtering is to be performed, determining a filtering strength for a target boundary of the target block and the number of samples used for filtering; And if it is determined that the filtering is to be performed, performing filtering on a target boundary of the target block based on the filtering strength and the number of samples used for the filtering.

The number of samples used for the filtering may be determined based on at least one of a size of the target block and a size of a neighboring block adjacent to the target block.

Whether to perform the filtering may be determined based on a component of the target block.

The filter length of the filtering may be determined based on the size of the target block and a component of the target block.

The filtering strength of the filtering may be determined based on prediction modes of a plurality of blocks adjacent to the target boundary.

The filtering strength of the filtering may be determined based on a difference between motion vectors of a plurality of blocks adjacent to the target boundary.

If the target boundary is a picture boundary, filtering may not be performed on the target boundary.

If the target boundary is a slice boundary, filtering on the target boundary may not be performed.

The filtering may be performed based on a quantization parameter for the target block.

Information indicating whether the filtering is performed may be included in the parameter set.

If the information indicates that the filtering is not performed, it may be determined not to perform the filtering.

The parameter set may be referenced for a sub-picture.

In the other side, determining whether to perform filtering on the target boundary of the target block; If it is determined that the filtering is to be performed, determining a filtering strength for a target boundary of the target block and the number of samples used for filtering; And when it is determined that the filtering is to be performed, performing filtering on a target boundary of the target block based on the filtering strength and the number of samples used for the filtering.

The filtering strength of the filtering may be determined based on prediction modes of a plurality of blocks adjacent to the target boundary.

The filtering may be performed based on a quantization parameter for the target block.

Information indicating whether the filtering is performed may be included in a parameter set referenced for a sub-picture.

If the information indicates that the filtering is not performed, it may be determined not to perform the filtering.

In yet another aspect, a recording medium for recording a bitstream generated by an image encoding method is provided.

In another aspect, in a computer-readable recording medium including a bitstream representing image data used in an image decoding method, a target block is decoded using the image data, and the target block is Whether to perform filtering on the boundary is determined, and when it is determined that the filtering is to be performed, the filtering strength for the target boundary of the target block and the number of samples used for filtering are determined, and when it is determined that the filtering is performed And a computer-readable recording medium in which filtering is performed on a target boundary of the target block based on the filtering strength and the number of samples used for the filtering.

The filtering strength of the filtering may be determined based on prediction modes of a plurality of blocks adjacent to the target boundary.

The filtering may be performed based on a quantization parameter for the target block.

Information indicating whether the filtering is performed may be included in a parameter set referenced for a sub-picture.

If the information indicates that the filtering is not performed, it may be determined not to perform the filtering.

The embodiment may provide various filtering methods performed in each step of image encoding/decoding in order to improve the encoding/decoding efficiency of an image.

According to the embodiment, prediction efficiency may be improved by generating a prediction image using a reference sample closer to the original image.

The embodiment can improve the encoding/decoding efficiency of an image.

The embodiment can reduce the computational complexity of an image encoding apparatus and a decoding apparatus.

1 is a block diagram showing a configuration according to an embodiment of an encoding apparatus to which the present invention is applied.
2 is a block diagram showing a configuration according to an embodiment of a decoding apparatus to which the present invention is applied.
3 is a diagram schematically illustrating a split structure of an image when encoding and decoding an image.
4 is a diagram illustrating a form of a prediction unit that a coding unit may include.
5 is a diagram showing a form of a transform unit that may be included in a coding unit.
6 illustrates block division according to an example.
7 is a diagram for describing an embodiment of an intra prediction process.
8 is a diagram for describing a reference sample used in an intra prediction process.
9 is a diagram for describing an embodiment of an inter prediction process.
10 shows spatial candidates according to an example.
11 is a diagram illustrating a sequence of adding motion information of spatial candidates to a merge list according to an example.
12 illustrates a process of transformation and quantization according to an example.
13 shows diagonal scanning according to an example.
14 shows horizontal scanning according to an example.
15 shows vertical scanning according to an example.
16 is a structural diagram of an encoding apparatus according to an embodiment.
17 is a structural diagram of a decoding apparatus according to an embodiment.
18 illustrates vertical boundary filtering for adjacent block boundaries according to an embodiment.
19 illustrates horizontal boundary filtering for adjacent block boundaries according to an embodiment.
20 shows a deblocking filter according to an embodiment.
21 is a flowchart illustrating a method of determining whether to perform filtering according to an embodiment.
22 illustrates a boundary on which filtering is not performed according to an embodiment.
23 is a flowchart illustrating a method of determining a filtering strength according to an embodiment.
24 and 25 illustrate a method of determining a filtering strength according to a prediction mode according to an embodiment.
26 illustrates determination of a filtering strength for a block on which OBMC is performed, according to an embodiment.
27 illustrates filtering according to block division according to an embodiment.
28 illustrates a plurality of transform regions according to an embodiment.
29 shows six planes constructed by projecting a 360-degree image in the form of a cube map according to an example.
30 and 31 show rearrangements of six planes projected in the form of a cube map according to an example.
32 illustrates syntax and semantics for a PPS defined in connection with signaling whether or not filtering is performed for each boundary and a method of filtering according to an example.
33 shows positions of reconstructed samples in a block adjacent to a block boundary according to an example.
34 is a first syntax for signal adaptive deblocking filtering according to an example.
35 is a second syntax for signal adaptive deblocking filtering according to an example.
36 is a third syntax for signal adaptive deblocking filtering according to an example.
37 is a fourth syntax for signal adaptive deblocking filtering according to an example.
38 is a table showing a relationship between a quantization parameter and a value related to filtering according to an example.
39 illustrates an image decoding method according to an embodiment.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

For a detailed description of exemplary embodiments described below, reference is made to the accompanying drawings, which illustrate specific embodiments as examples. These embodiments are described in detail sufficient to enable a person skilled in the art to practice the embodiments. It should be understood that the various embodiments are different from each other but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. In addition, it is to be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the embodiment. Accordingly, the detailed description to be described below is not intended to be taken in a limiting sense, and the scope of exemplary embodiments, if properly described, is limited only by the appended claims, along with all scope equivalents to those claimed by the claims.

Like reference numerals in the drawings refer to the same or similar functions over several aspects. The shapes and sizes of elements in the drawings may be exaggerated for clearer explanation.

In the present invention, terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term “and/or” may include a combination of a plurality of related described items or any of a plurality of related described items.

When a component is referred to as being "connected" or "connected" to another component, the two components may be directly connected to each other or may be connected, but the above 2 It should be understood that other components may exist in the middle of the components. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle of the two components. something to do.

Components shown in the embodiments of the present invention are independently illustrated to represent different characteristic functions, and does not mean that each component is formed of separate hardware or a single software component unit. That is, each component is listed and included as each component for convenience of explanation, and at least two components of each component are combined to form one component, or one component is divided into a plurality of components to function. It is possible to perform, and integrated embodiments and separate embodiments of each of these components are also included in the scope of the present invention unless departing from the essence of the present invention.

In addition, the description of "including" a specific configuration in the exemplary embodiments does not exclude configurations other than the specific configurations described above, and additional configurations are not limited to the implementation of the exemplary embodiments or the technical idea of the exemplary embodiments. It means that it can be included in the scope.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance. That is, the description of "including" a specific configuration in the present invention does not exclude configurations other than the corresponding configuration, and means that additional configurations may also be included in the scope of the practice of the present invention or the technical idea of the present invention.

Some of the components of the present invention are not essential components for performing essential functions in the present invention, but may be optional components for improving performance only. The present invention may be implemented by including only essential elements in implementing the essence of the present invention, except for elements used for improving performance. A structure including only essential components excluding optional components used for performance improvement is also included in the scope of the present invention.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings in order to allow those of ordinary skill in the art to easily implement the embodiments. In describing the embodiments, when it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the present specification, a detailed description thereof will be omitted. In addition, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

Hereinafter, an image may refer to one picture constituting a video, and may refer to a video itself. For example, "encoding and/or decoding of an image" may mean "encoding and/or decoding of a video", and may mean "encoding and/or decoding of one image among images constituting a video" May be.

Hereinafter, the terms "video" and "motion picture(s)" may be used with the same meaning, and may be used interchangeably.

Hereinafter, the target image may be an encoding target image that is an encoding target and/or a decoding target image that is a decoding target. In addition, the target image may be an input image input through an encoding device or an input image input through a decoding device. In addition, the target image may be a current image that is currently a target of encoding and/or decoding. For example, the terms "target image" and "current image" may be used with the same meaning, and may be used interchangeably.

Hereinafter, the terms “image”, “picture”, “frame” and “screen” may be used with the same meaning, and may be used interchangeably.

Hereinafter, the target block may be an encoding target block that is an object of encoding and/or a decoding object block that is an object of decoding. Also, the target block may be a current block that is a target of current encoding and/or decoding. For example, the terms "target block" and "current block" may have the same meaning, and may be used interchangeably. The current block may mean an encoding object block to be encoded during encoding and/or a decoding object block to be decoded during decoding. In addition, the current block may be at least one of a coding block, a prediction block, a residual block, and a transform block.

Hereinafter, the terms "block" and "unit" may be used with the same meaning, and may be used interchangeably. Or “block” may represent a specific unit.

Hereinafter, the terms "region" and "segment" may be used interchangeably.

Hereinafter, the specific signal may be a signal indicating a specific block. For example, the original signal may be a signal representing a target block. The prediction signal may be a signal representing a prediction block. The residual signal may be a signal indicating a residual block.

In embodiments, each of the specified information, data, flag, index, element, attribute, etc. may have a value. A value of "0" such as information, data, flags, indexes, elements, and attributes may represent a logical false or a first predefined value. That is to say, the value "0", false, logical false, and the first predefined value may be replaced with each other and used. A value "1" of information, data, flags, indexes, elements, and attributes, etc. may represent a logical true or a second predefined value. That is to say, the value "1", true, logical true and the second predefined value may be used interchangeably.

When a variable such as i or j is used to indicate a row, column, or index, the value of i may be an integer greater than or equal to 0, or may be an integer greater than or equal to 1. That is to say, in embodiments, rows, columns, and indexes may be counted from 0, and may be counted from 1.

In embodiments, the term “one or more” or the term “at least one” may mean the term “plural”. "One or more" or "at least one" may be used interchangeably with "plural".

In the following, terms used in the embodiments are described.

Encoder: An encoder may refer to a device that performs encoding. In other words, the encoder may mean an encoding device.

Decoder: A decoder may mean a device that performs decoding. In other words, the decoder may mean a decoding device.

Unit: A unit may represent a unit for encoding and/or decoding an image. The terms "unit" and "block" may be used with the same meaning, and may be used interchangeably.

-The unit may be an MxN array of samples. M and N may each be a positive integer. A unit can often mean an arrangement of two-dimensional samples.

-In encoding and decoding of an image, a unit may be an area generated by division of one image. In other words, a unit may be a specified area within one image. One image may be divided into a plurality of units. Alternatively, the unit may mean the divided part when one image is divided into subdivided parts and encoding or decoding of the divided part is performed.

-In encoding and decoding of an image, a predefined process for a unit may be performed according to the type of the unit.

-Depending on the function, the type of unit is a macro unit, a coding unit (CU), a prediction unit (PU), a residual unit, a transform unit (TU), etc. It can be classified as Alternatively, depending on the function, the unit is a block, a macroblock, a coding tree unit, a coding tree block, a coding unit, a coding block, and a prediction unit. It may mean a (Prediction Unit), a prediction block, a residual unit, a residual block, a transform unit, and a transform block. For example, the target unit may be at least one of a CU, a PU, a residual unit, and a TU that are targets of encoding and/or decoding.

-A unit may refer to information including a luma component block, a chroma component block corresponding thereto, and a syntax element for each block, in order to distinguish it from a block.

-The size and shape of the unit can vary. In addition, the unit may have various sizes and various shapes. In particular, the shape of the unit may include not only a square, but also a geometric figure that can be expressed in two dimensions such as a rectangle, a trapezoid, a triangle, and a pentagon.

-Also, the unit information may include at least one of a unit type, a unit size, a unit depth, a unit encoding order, and a unit decoding order. For example, the type of the unit may indicate one of CU, PU, residual unit and TU.

-One unit can be further divided into sub-units with a smaller size than the unit.

Depth: Depth may mean the degree of division of a unit. Further, the depth of the unit may indicate the level at which the unit exists when the unit(s) is expressed as a tree structure.

-The unit division information may include depth related to the depth of the unit. Depth may indicate the number and/or degree to which a unit is divided.

-In the tree structure, the depth of the root node is the shallowest and the depth of the leaf node is the deepest. The root node may be the highest node. The leaf node may be the lowest node.

-One unit may be hierarchically divided into a plurality of sub-units while having depth information based on a tree structure. In other words, a unit and a sub-unit generated by the division of the unit may correspond to a node and a child node of the node, respectively. Each divided sub-unit can have a depth. Since the depth represents the number and/or degree of division of the unit, the division information of the sub-unit may include information on the size of the sub-unit.

-In the tree structure, the highest node may correspond to the first undivided unit. The highest node may be referred to as a root node. Also, the highest node may have a minimum depth value. In this case, the uppermost node may have a depth of level 0.

-A node with a depth of level 1 may indicate a unit created as the first unit is divided once. A node with a depth of level 2 may represent a unit created as the first unit is divided twice.

-A node having a depth of level n may indicate a unit generated when the first unit is divided n times.

-The leaf node may be the lowest node and may be a node that cannot be further divided. The depth of the leaf node may be at the maximum level. For example, a predefined value of the maximum level may be 3.

-QT depth may indicate the depth for quad division. BT depth can represent the depth for binary division. The TT depth may indicate the depth for the three-way division.

Sample: A sample may be a base unit constituting a block. A sample may be expressed as values from 0 to 2 ^Bd -1 according to a bit depth (Bd).

-The sample can be a pixel or a pixel value.

-Hereinafter, the terms "pixel", "pixel" and "sample" may be used with the same meaning, and may be used interchangeably.

Coding Tree Unit (CTU): A CTU may consist of one luma component (Y) coding tree block and two chroma component (Cb, Cr) coding tree blocks related to the luma component coding tree block. have. Also, the CTU may mean including the above blocks and a syntax element for each block of the above blocks.

-Each coding tree unit is a quad tree (QT), a binary tree (BT), and a ternary tree (TT) to construct sub-units such as a coding unit, a prediction unit, and a transform unit. It can be divided using one or more division methods. The quad tree may mean a quaternary tree. In addition, each coding tree unit may be divided using a multitype tree (MTT) using one or more partitioning schemes.

-CTU may be used as a term for referring to a pixel block, which is a processing unit in a process of decoding and encoding an image, as in splitting an input image.

Coding Tree Block (CTB): A coding tree block may be used as a term to refer to any one of a Y coding tree block, a Cb coding tree block, and a Cr coding tree block.

Neighbor block: A neighboring block may mean a block adjacent to a target block. The neighboring block may mean a reconstructed neighboring block.

-Hereinafter, the terms "neighbor block" and "adjacent block" may be used with the same meaning, and may be used interchangeably.

-The neighboring block may mean a reconstructed neighbor block.

Spatial neighbor block: The spatial neighboring block may be a block spatially adjacent to the target block. The neighboring block may include a spatial neighboring block.

-The target block and the spatial neighboring block may be included in the target picture.

-The spatial neighboring block may mean a block having a boundary contact with the target block or a block located within a predetermined distance from the target block.

-The spatial neighboring block may mean a block adjacent to the vertex of the target block. Here, the block adjacent to the vertex of the target block may be a block vertically adjacent to a neighboring block horizontally adjacent to the target block or a block horizontally adjacent to a neighboring block vertically adjacent to the target block.

Temporal neighbor block: The temporal neighbor block may be a block that is temporally adjacent to the target block. The neighboring block may include a temporal neighboring block.

-The temporal neighboring block may include a co-located block (col block).

-The collocated block may be a block in a co-located picture (col picture) that has already been reconstructed. The position of the collocated block in the collocated picture may correspond to the position in the target picture of the target block. Alternatively, the position of the collocated block in the collocated picture may be the same as the position in the target picture of the target block. The collocated picture may be a picture included in the reference picture list.

-The temporal neighboring block may be a block that is temporally adjacent to the spatial neighboring block of the target block.

Prediction mode: The prediction mode may be information indicating a mode encoded and/or decoded for intra prediction or a mode encoded and/or decoded for inter prediction.

Prediction unit: The prediction unit may mean a base unit for prediction such as inter prediction, intra prediction, inter compensation, intra compensation, and motion compensation.

-One prediction unit may be divided into a plurality of partitions or sub prediction units having a smaller size. The plurality of partitions may also be a base unit for performing prediction or compensation. A partition generated by division of a prediction unit may also be a prediction unit.

Prediction unit partition: A prediction unit partition may mean a form in which a prediction unit is divided.

Reconstructed neighboring unit: The reconstructed neighboring unit may be a unit that has already been decoded and reconstructed in a neighbor of the target unit.

-The reconstructed neighboring unit may be a spatial neighboring unit or a temporal neighboring unit to the target unit.

-The reconstructed spatial neighboring unit may be a unit in the target picture and already reconstructed through encoding and/or decoding.

-The reconstructed temporal neighboring unit may be a unit in the reference image and already reconstructed through encoding and/or decoding. The position of the reconstructed temporal neighboring unit in the reference image may be the same as the position in the target picture of the target unit, or may correspond to the position in the target picture of the target unit. Alternatively, the reconstructed temporal neighboring unit may be a neighboring block of a corresponding block in the reference image. Here, the position of the corresponding block in the reference image may correspond to the position of the target block in the target image. Here, if the positions of the blocks correspond, it may mean that the positions of the blocks are the same, it may mean that one block is included in another block, and one block occupies a specific position of another block. It can mean doing.

Sub-picture: A picture can be divided into one or more sub-pictures. A sub-picture may consist of one or more tile rows and one or more tile columns.

-A sub-picture may be a region having a square shape or a rectangle (ie, non-square) shape in the picture. Further, the sub-picture may include one or more CTUs. .

-One sub-picture may include one or more tiles, one or more bricks, and/or one or more slices.

Tile: A tile may be an area having a square shape or a rectangle (ie, a non-square shape) in the picture.

-A tile may contain one or more CTUs.

-A tile can be divided into one or more bricks.

Brick: A brick can mean one or more CTU rows in a tile.

-A tile can be divided into one or more bricks. Each brick can contain one or more CTU rows.

-Tiles that are not divided into two or more can also mean bricks.

Slice: A slice may include one or more tiles in a picture. Alternatively, a slice may include one or more bricks within a tile.

Parameter set: The parameter set may correspond to header information among structures in the bitstream.

-The parameter set is a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), and a decoding parameter. It may include at least one of a set (Decoding Parameter Set; DPS).

Information signaled through the parameter set may be applied to pictures referring to the parameter set. For example, information in the VPS may be applied to pictures referencing the VPS. Information in the SPS can be applied to pictures referencing the SPS. Information in the PPS may be applied to pictures referencing the PPS.

The parameter set may refer to an upper parameter set. For example, PPS may refer to SPS. SPS may refer to VPS.

-Also, the parameter set may include a tile group, slice header information, and tile header information. The tile group may mean a group including a plurality of tiles. In addition, the meaning of the tile group may be the same as the meaning of the slice.

The adaptation parameter set may mean a parameter set that can be shared by referring to different pictures, sub-pictures, slices, tile groups, tiles, or bricks. In addition, sub-pictures, slices, tile groups, tiles, or bricks in a picture may use information in different adaptation parameter sets by referring to different adaptation parameter sets.

In addition, the adaptation parameter sets may refer to different adaptation parameter sets by using identifiers of different adaptation parameter sets in sub-pictures, slices, tile groups, tiles, or bricks within a picture.

In addition, in a slice, a tile group, a tile, or a brick in a sub-picture, different adaptation parameter sets may be referenced using identifiers of different adaptation parameter sets.

In addition, in tiles or bricks in a slice, different adaptation parameter sets may be referenced using identifiers of different adaptation parameter sets.

Also, in a brick within a tile, different adaptation parameter sets may be referenced using identifiers of different adaptation parameter sets.

Information on the identifier of the adaptation parameter set may be included in the parameter set or header of the sub-picture, and the adaptation parameter set corresponding to the included adaptation parameter set identifier may be used in the sub-picture.

Information on the adaptation parameter set identifier may be included in the parameter set or header of the tile, and the adaptation parameter set corresponding to the included adaptation parameter set identifier may be used in the tile.

Information on the adaptation parameter set identifier may be included in the header of the brick, and the adaptation parameter set corresponding to the included adaptation parameter set identifier may be used in the brick.

Rate-distortion optimization: The encoding apparatus uses a combination of the size of the coding unit, the prediction mode, the size of the prediction unit, the motion information, and the size of the transform unit to provide high coding efficiency. You can use distortion optimization.

-The rate-distortion optimization method can calculate the rate-distortion cost of each combination in order to select an optimal combination among the above combinations. The rate-distortion cost can be calculated using the formula "D+λ*R". In general, a combination in which the rate-distortion cost is minimized according to the equation "D+λ*R" may be selected as an optimal combination in the rate-distortion optimization method.

-D can represent distortion. D may be a mean square error of difference values between original transform coefficients and reconstructed transform coefficients in the transform unit.

-R can represent a rate. R may represent a bit rate using related context information.

-λ can represent a Lagrangian multiplier. R may include coding parameter information such as prediction mode, motion information, and coded block flags, as well as bits generated by encoding transform coefficients.

-The encoding apparatus may perform processes such as inter prediction, intra prediction, transformation, quantization, entropy encoding, inverse quantization, and/or inverse transformation in order to calculate accurate D and R. These processes can greatly increase the complexity of the encoding device.

Bitstream: A bitstream may mean a sequence of bits including encoded image information.

Parameter set: The parameter set may correspond to header information among structures in the bitstream.

Parsing: Parsing may mean determining a value of a syntax element by entropy decoding a bitstream. Alternatively, parsing may mean entropy decoding itself.

Symbol: may mean at least one of a syntax element, a coding parameter, a transform coefficient, and the like of the encoding target unit and/or the decoding target unit. Further, the symbol may mean an object of entropy encoding or a result of entropy decoding.

Reference picture: The reference picture may mean an image referenced by a unit for inter prediction or motion compensation. Alternatively, the reference picture may be an image including a reference unit referenced by the target unit for inter prediction or motion compensation.

Hereinafter, the terms "reference picture" and "reference image" may be used with the same meaning, and may be used interchangeably.

Reference picture list: The reference picture list may be a list including one or more reference pictures used for inter prediction or motion compensation.

-The types of reference picture lists are List Combined (LC), List 0 (List 0; L0), List 1 (List 1; L1), List 2 (List 2; L2), and List 3 (List 3; L3). ), etc.

-One or more reference picture lists may be used for inter prediction.

Inter prediction indicator: The inter prediction indicator may indicate the direction of inter prediction for the target unit. Inter prediction may be one of one-way prediction and two-way prediction. Alternatively, the inter prediction indicator may indicate the number of reference pictures used when generating the prediction unit of the target unit. Alternatively, the inter prediction indicator may mean the number of prediction blocks used for inter prediction or motion compensation for a target unit.

Prediction list utilization flag: The prediction list utilization flag may indicate whether a prediction unit is generated by using at least one reference picture in a specific reference picture list.

-An inter prediction indicator can be derived using the prediction list utilization flag. Conversely, a prediction list utilization flag may be derived using the inter prediction indicator. For example, if the prediction list utilization flag indicates a first value of 0, it may indicate that a prediction block is not generated using a reference picture in a reference picture list for a target unit. When the prediction list utilization flag indicates the second value of 1, it may indicate that a prediction unit is generated using a reference picture list for the target unit.

Reference picture index: The reference picture index may be an index indicating a specific reference picture in the reference picture list.

Picture order count (POC): The POC of a picture may indicate the display order of the picture.

Motion Vector (MV): The motion vector may be a two-dimensional vector used for inter prediction or motion compensation. The motion vector may mean an offset between the target image and the reference image.

-For example, MV can be expressed in the form (mv _x , mv _y ). mv _x may represent a horizontal component, and mv _y may represent a vertical component.

Search range: The search region may be a two-dimensional region in which MV is searched during inter prediction. For example, the size of the search area may be MxN. M and N may each be a positive integer.

Motion vector candidate: A motion vector candidate may mean a block as a prediction candidate or a motion vector of a block as a prediction candidate when predicting a motion vector.

-The motion vector candidate may be included in the motion vector candidate list.

Motion vector candidate list: The motion vector candidate list may mean a list formed by using one or more motion vector candidates.

Motion vector candidate index: The motion vector candidate index may mean an indicator indicating a motion vector candidate in the motion vector candidate list. Alternatively, the motion vector candidate index may be an index of a motion vector predictor.

Motion information: Motion information includes not only motion vector, reference picture index and inter prediction indicator, but also reference picture list information, reference picture, motion vector candidate, motion vector candidate index, merge candidate, merge index, etc. It may mean information including at least one of.

Merge candidate list: The merge candidate list may mean a list formed by using one or more merge candidates.

Merge candidate: The merge candidate is a spatial merge candidate, a temporal merge candidate, a combined merge candidate, a combined bi-prediction merge candidate, a candidate based on history, a candidate based on the average of two candidates, and zero. May mean merge candidates, etc. The merge candidate may include an inter prediction indicator, and may include motion information such as a reference picture index for each list, a motion vector, a prediction list utilization flag, and an inter prediction indicator.

Merge index: The merge index may be an indicator indicating a merge candidate in the merge candidate list.

-The merge index may indicate a reconstructed unit that induces a merge candidate among reconstructed units spatially adjacent to the target unit and reconstructed units temporally adjacent to the target unit.

-The merge index may indicate at least one of motion information of the merge candidate.

Transform unit: The transform unit may be a basic unit in residual signal encoding and/or residual signal decoding such as transform, inverse transform, quantization, inverse quantization, transform coefficient encoding and transform coefficient decoding. One transform unit may be divided into a plurality of lower transform units having a smaller size. Here, the transform may include one or more of a first-order transform and a second-order transform, and the inverse transform may include one or more of a first-order inverse transform and a second-order inverse transform.

Scaling: Scaling may mean a process of multiplying a transform coefficient level by a factor.

-As a result of scaling on the transform coefficient level, a transform coefficient may be generated. Scaling may also be referred to as dequantization.

Quantization Parameter (QP): The quantization parameter may mean a value used when generating a transform coefficient level for a transform coefficient in quantization. Alternatively, the quantization parameter may mean a value used when generating a transform coefficient by scaling a transform coefficient level in inverse quantization. Alternatively, the quantization parameter may be a value mapped to a quantization step size.

Delta quantization parameter: The delta quantization parameter may mean a difference value between a predicted quantization parameter and a quantization parameter of a target unit.

Scan: Scan may mean a method of arranging the order of coefficients in a unit, block, or matrix. For example, arranging a two-dimensional array into a one-dimensional array may be referred to as a scan. Alternatively, alignment of a one-dimensional array into a two-dimensional array may also be referred to as a scan or an inverse scan.

Transform coefficient: The transform coefficient may be a coefficient value generated by performing transformation in the encoding apparatus. Alternatively, the transform coefficient may be a coefficient value generated by performing at least one of entropy decoding and inverse quantization in the decoding apparatus.

-A quantized level generated by applying quantization to a transform coefficient or a residual signal or a quantized transform coefficient level may also be included in the meaning of the transform coefficient.

Quantized level: The quantized level may mean a value generated by quantizing a transform coefficient or a residual signal in an encoding apparatus. Alternatively, the quantized level may mean a value targeted for inverse quantization when performing inverse quantization in the decoding apparatus.

-The quantized transform coefficient level resulting from transform and quantization may also be included in the meaning of the quantized level.

Non-zero transform coefficient: The non-zero transform coefficient may mean a transform coefficient having a non-zero value or a transform coefficient level having a non-zero value. Alternatively, the non-zero transform coefficient may mean a transform coefficient whose value is not zero or a transform coefficient level whose value is not zero.

Quantization matrix: The quantization matrix may mean a matrix used in a quantization process or an inverse quantization process to improve subjective or objective quality of an image. The quantization matrix may also be referred to as a scaling list.

Quantization matrix coefficient: The quantization matrix coefficient may mean each element in the quantization matrix. The quantization matrix coefficient may also be referred to as a matrix coefficient.

Default matrix: The default matrix may be a quantization matrix predefined by an encoding device and a decoding device.

Non-default matrix: The non-default matrix may be a quantization matrix that is not predefined in an encoding apparatus and a decoding apparatus. The non-default matrix may mean a quantization matrix signaled from an encoding device to a decoding device by a user.

Most Probable Mode (MPM): MPM may indicate an intra prediction mode that is likely to be used for intra prediction of a target block.

-The encoding device and the decoding device may determine one or more MPMs based on a coding parameter related to the target block and an attribute of an entity related to the target block.

-The encoding apparatus and the decoding apparatus may determine one or more MPMs based on the intra prediction mode of the reference block. There may be a plurality of reference blocks. The plurality of reference blocks may include a spatial neighboring block adjacent to the left side of the target block and a spatial neighboring block adjacent to the upper end of the target block. That is, one or more different MPMs may be determined according to which intra prediction modes are used for the reference blocks.

-One or more MPMs may be determined in the same manner in an encoding apparatus and a decoding apparatus. In other words, the encoding device and the decoding device can share an MPM list including one or more identical MPMs.

MPM list: The MPM list may be a list including one or more MPMs. The number of one or more MPMs in the MPM list may be predefined.

MPM indicator: The MPM indicator may indicate an MPM used for intra prediction of a target block among one or more MPMs in the MPM list. For example, the MPM indicator may be an index for the MPM list.

-Since the MPM list is determined in the same manner in the encoding device and the decoding device, the MPM list itself may not need to be transmitted from the encoding device to the decoding device.

-The MPM indicator may be signaled from the encoding device to the decoding device. As the MPM indicator is signaled, the decoding apparatus may determine an MPM to be used for intra prediction for a target block among MPMs in the MPM list.

MPM usage indicator: The MPM usage indicator may indicate whether or not the MPM usage mode is used for prediction of a target block. The MPM use mode may be a mode for determining an MPM to be used for intra prediction for a target block using an MPM list.

-The MPM usage indicator may be signaled from the encoding device to the decoding device.

Signaling: Signaling may indicate that information is transmitted from an encoding device to a decoding device. Alternatively, signaling may mean including information in a bitstream or a recording medium. Information signaled by the encoding device may be used by the decoding device.

-The encoding device may generate encoded information by performing encoding on the signaled information. The encoded information may be transmitted from the encoding device to the decoding device. The decoding apparatus may obtain information by performing decoding on the transmitted encoded information. Here, encoding may be entropy encoding, and decoding may be entropy decoding.

Statistical value: Variables, coding parameters, and constants may have values that can be calculated. The statistical value may be a value generated by an operation on values of these specified objects. For example, the statistical value is an average value for values such as a specified variable, a specified coding parameter and a specified constant, a weighted average value, a weighted sum, a minimum value, a maximum value, and a mode. It may be one or more of a value, an intermediate value, and an interpolation value.

1 is a block diagram showing a configuration according to an embodiment of an encoding apparatus to which the present invention is applied.

The encoding device 100 may be an encoder, a video encoding device, or an image encoding device. A video may include one or more images. The encoding apparatus 100 may sequentially encode one or more images of a video.

Referring to FIG. 1, the encoding apparatus 100 includes an inter prediction unit 110, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, and entropy encoding. A sub 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190 may be included.

The encoding apparatus 100 may perform encoding on a target image using an intra mode and/or an inter mode. In other words, the prediction mode for the target block may be one of an intra mode and an inter mode.

Hereinafter, the terms "intra mode", "intra prediction mode", "in-screen mode" and "in-screen prediction mode" may be used in the same meaning, and may be used interchangeably.

Hereinafter, the terms "inter mode", "inter prediction mode", "inter-screen mode", and "inter-screen prediction mode" may have the same meaning, and may be used interchangeably.

Hereinafter, the term "image" may only refer to a part of an image and may refer to a block. Also, processing for "image" may indicate sequential processing for a plurality of blocks.

In addition, the encoding apparatus 100 may generate a bitstream including information encoded by encoding a target image, and may output and store the generated bitstream. The generated bitstream may be stored in a computer-readable recording medium, and may be streamed through wired and/or wireless transmission media.

When an intra mode is used as the prediction mode, the switch 115 may be switched to intra. When an inter mode is used as the prediction mode, the switch 115 may be switched to inter.

The encoding apparatus 100 may generate a prediction block for a target block. Also, after the prediction block is generated, the encoding apparatus 100 may encode the residual block for the target block by using a residual of the target block and the prediction block.

When the prediction mode is an intra mode, the intra prediction unit 120 may use a pixel of an already encoded and/or decoded block adjacent to the target block as a reference sample. The intra prediction unit 120 may perform spatial prediction for the target block using the reference sample, and may generate prediction samples for the target block through spatial prediction. A prediction sample may mean a sample in a prediction block.

The inter prediction unit 110 may include a motion prediction unit and a motion compensation unit.

When the prediction mode is the inter mode, the motion prediction unit can search for an area that best matches the target block from the reference image in the motion prediction process, and derives a motion vector for the target block and the searched area using the searched area can do. In this case, the motion prediction unit may use the search region as a region to be searched.

The reference picture may be stored in the reference picture buffer 190, and when the reference picture is encoded and/or decoded, the coded and/or decoded reference picture may be stored in the reference picture buffer 190.

As the decoded picture is stored, the reference picture buffer 190 may be a decoded picture buffer (DPB).

The motion compensation unit may generate a prediction block for the target block by performing motion compensation using a motion vector. Here, the motion vector may be a 2D vector used for inter prediction. In addition, the motion vector may represent an offset between the target image and the reference image.

When the motion vector has a non-integer value, the motion prediction unit and the motion compensation unit may generate a prediction block by applying an interpolation filter to a partial region of the reference image. In order to perform inter prediction or motion compensation, a method of motion prediction and motion compensation of a PU included in the CU based on the CU is a skip mode, a merge mode, and an advanced motion vector prediction. Prediction (AMVP) mode or a current picture reference mode may be determined, and inter prediction or motion compensation may be performed according to each mode.

The subtractor 125 may generate a residual block, which is a difference between the target block and the prediction block. The residual block may also be referred to as a residual signal.

The residual signal may mean a difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming or quantizing, or transforming and quantizing a difference between the original signal and the predicted signal. The residual block may be a residual signal for each block.

The transform unit 130 may generate a transform coefficient by performing transform on the residual block, and may output the generated transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing transform on the residual block.

In performing the conversion, the conversion unit 130 may use one of a plurality of predefined conversion methods.

The plurality of predefined transformation methods may include Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), and Karhunen-Loeve Transform (KLT) based transformation. have.

A transform method used for transforming the residual block may be determined according to at least one of coding parameters for a target block and/or a neighboring block. For example, the transformation method may be determined based on at least one of an inter prediction mode for a PU, an intra prediction mode for a PU, a size of a TU, and a shape of a TU. Alternatively, transformation information indicating a transformation method may be signaled from the encoding device 100 to the decoding device 200.

When the transform skip mode is applied, the transform unit 130 may omit the transform of the residual block.

By applying quantization to a transform coefficient, a quantized transform coefficient level or a quantized level may be generated. Hereinafter, in embodiments, a quantized transform coefficient level and a quantized level may also be referred to as transform coefficients.

The quantization unit 140 may generate a quantized transform coefficient level (ie, a quantized level or a quantized coefficient) by quantizing the transform coefficient according to the quantization parameter. The quantization unit 140 may output the generated quantized transform coefficient level. In this case, the quantization unit 140 may quantize the transform coefficient using a quantization matrix.

The entropy encoding unit 150 may generate a bitstream by performing entropy encoding according to a probability distribution based on values calculated by the quantization unit 140 and/or coding parameter values calculated during an encoding process. . The entropy encoder 150 may output the generated bitstream.

The entropy encoder 150 may perform entropy encoding on information about pixels of an image and information for decoding an image. For example, information for decoding an image may include a syntax element or the like.

When entropy coding is applied, a small number of bits may be allocated to a symbol having a high probability of occurrence, and a large number of bits may be allocated to a symbol having a low probability of occurrence. As symbols are represented through such allocation, the size of a bitstring for symbols to be encoded may be reduced. Accordingly, compression performance of image encoding may be improved through entropy encoding.

In addition, the entropy encoding unit 150 includes exponential golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding for entropy encoding. A coding method such as Arithmetic Coding; CABAC) can be used. For example, the entropy encoding unit 150 may perform entropy encoding using a variable length encoding (VLC) table. For example, the entropy encoder 150 may derive a binarization method for a target symbol. In addition, the entropy encoder 150 may derive a probability model of a target symbol/bin. The entropy encoder 150 may perform arithmetic encoding using the derived binarization method, a probability model, and a context model.

The entropy encoder 150 may change a coefficient of a form of a two-dimensional block into a form of a one-dimensional vector through a transform coefficient scanning method in order to encode a quantized transform coefficient level.

The coding parameter may be information required for encoding and/or decoding. The coding parameter may include information that is encoded by the encoding device 100 and transmitted from the encoding device 100 to the decoding device, and may include information that can be derived during an encoding or decoding process. For example, as information transmitted to the decoding device, there is a syntax element.

A coding parameter, like a syntax element, may include information (or flags and indexes, etc.) that is encoded by the encoding device and signaled from the encoding device to the decoding device, as well as information derived during the encoding process or the decoding process. have. In addition, the coding parameter may include information required for encoding or decoding an image. For example, the size of the unit/block, the shape of the unit/block, the depth of the unit/block, the division information of the unit/block, the division structure of the unit/block, information indicating whether the unit/block is divided in a quad tree shape, Information indicating whether a unit/block is divided into a binary tree type, a division direction of a binary tree type (horizontal or vertical direction), a division type of a binary tree type (symmetrical division or asymmetrical division), and a unit/block is a triangular tree type Information indicating whether or not it is divided into, the direction of division in the form of a ternary tree (horizontal or vertical direction), the type of division in the form of a ternary tree (symmetrical or asymmetrical division, etc.), and a unit/block is a multi-type tree Information indicating whether or not it is divided into shapes, combinations and directions of divisions in the form of a multi-type tree (horizontal or vertical direction, etc.), division types of divisions in the form of a multi-type tree (symmetric division or asymmetric division), and multi-type Tree-shaped split tree (binary tree or ternary tree), prediction mode type (intra prediction or inter prediction), intra prediction mode/direction, intra luma prediction mode/direction, intra chroma prediction mode/direction, intra split information, inter Split information, coding block split flag, prediction block split flag, transform block split flag, reference sample filtering method, reference sample filter tap, reference sample filter coefficient, prediction block filtering method, prediction block filter tap, prediction block filter coefficient , Prediction block boundary filtering method, prediction block boundary filter tap, prediction block boundary filter coefficient, inter prediction mode, motion information, motion vector, motion vector difference, reference picture index, inter prediction direction, inter prediction indicator, prediction list utilization ) Flag, reference picture list, reference picture, POC, motion vector predictor, motion vector prediction index, motion vector prediction candidate, motion vector candidate list, information indicating whether to use the merge mode, merge index, merge candidate, merge candidate list , Whether to use skip mode Information indicating whether or not, type of interpolation filter, filter tab of interpolation filter, filter coefficient of interpolation filter, motion vector size, motion vector expression accuracy, transform type, transform size, information indicating whether to use first-order transform, add( Secondary) information indicating whether to use transformation, first-order transformation selection information (or first-order transformation index), second-order transformation selection information (or, second-order transformation index), information indicating the presence or absence of a residual signal, coded Coded block pattern, coded block flag, quantization parameter, residual quantization parameter, quantization matrix, information on intra-loop filter, information indicating whether to apply intra-loop filter, intra- The coefficient of the loop filter, the filter tab of the intra-loop, the shape/form of the intra-loop filter, information indicating whether to apply the deblocking filter, the coefficient of the deblocking filter, the filter tab of the deblocking filter, Deblocking filter strength, shape/shape of deblocking filter, information indicating whether to apply adaptive sample offset, adaptive sample offset value, adaptive sample offset category, adaptive sample offset type, adaptive in-loop ( In-loop) information indicating whether to apply the filter, coefficients of the adaptive intra-loop filter, filter tap of the adaptive intra-loop filter, shape/shape of the adaptive intra-loop filter, binarization/inverse binarization method, context Model, context model determination method, context model update method, information indicating whether to perform regular mode, information indicating whether to perform bypass mode, significant coefficient flag, last significant coefficient flag, coefficient group coding flag , Last significant count position, flag indicating whether the count value is greater than 1, flag indicating whether the count value is greater than 2, flag indicating whether the count value is greater than 3, remaining count value information, sign ) Information, reconstructed luma sample, reconstructed chroma sample, context bean, Bypass bin, residual luma sample, residual chroma sample, transform coefficient, luma transform coefficient, chroma transform coefficient, quantized level, luma quantized level, chroma quantized level, transform coefficient level, luma transform coefficient level, chroma transform coefficient level , Transform coefficient level scanning method, the size of the motion vector search region from the side of the decoding device, the shape of the motion vector search region from the side of the decoding device, the number of motion vector search from the side of the decoding device, CTU size, minimum block size , Maximum block size, maximum block depth, minimum block depth, image display/output order, slice identification information, slice type, slice division information, tile group identification information, tile group type, tile group division information, tile identification information, tile Type, tile segmentation information, picture type, bit depth, input sample bit depth, reconstructed sample bit depth, residual sample bit depth, transform coefficient bit depth, quantized level bit depth, information about luma signal, and chroma signal At least one of information, a color space of a target block, and a color space of a residual block, a combined form, or statistics may be included in the coding parameter. In addition, information related to the above-described coding parameter may also be included in the coding parameter. Information used to calculate and/or derive the above-described coding parameter may also be included in the coding parameter. Information calculated or derived using the above-described coding parameter may also be included in the coding parameter.

The prediction method may represent one of an intra prediction mode and an inter prediction mode.

The first-order transformation selection information may indicate a first-order transformation applied to the target block.

The second-order transform selection information may indicate a second-order transform applied to the target block.

The residual signal may represent a difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming a difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming and quantizing a difference between the original signal and the predicted signal. The residual block may be a residual signal for the block.

Here, signaling information may mean that the encoding apparatus 100 includes entropy-encoded information generated by performing entropy encoding on a flag or index in a bitstream, and , It may mean that the decoding apparatus 200 acquires information by performing entropy decoding on entropy-encoded information extracted from a bitstream. Here, the information may include flags and indexes.

The bitstream may include information according to the specified syntax. The encoding apparatus 100 may generate a bitstream including information according to the specified syntax. The encoding apparatus 200 may obtain information from the bitstream according to the specified syntax.

Since encoding through inter prediction is performed by the encoding apparatus 100, the encoded target image may be used as a reference image for other image(s) to be processed later. Accordingly, the encoding apparatus 100 may reconstruct or decode the encoded target image again, and store the reconstructed or decoded image as a reference image in the reference picture buffer 190. Inverse quantization and inverse transformation of a target image encoded for decoding may be processed.

The quantized level may be inversely quantized by the inverse quantization unit 160 and may be inversely transformed by the inverse transform unit 170. The inverse quantization unit 160 may generate an inverse quantized coefficient by performing inverse quantization on the quantized level. The inverse transform unit 170 may generate inverse quantized and inverse transformed coefficients by performing inverse transform on the inverse quantized coefficient.

The inverse quantized and inverse transformed coefficients may be summed with the prediction block through the adder 175, and a reconstructed block may be generated by summing the inverse quantized and inverse transformed coefficients and the prediction block. Here, the inverse quantized and/or inverse transformed coefficient may mean a coefficient in which at least one or more of dequantization and inverse-transformation is performed, and may mean a reconstructed residual block. Here, the reconstructed block may mean a recovered block or a decoded block.

The reconstructed block may pass through the filter unit 180. The filter unit 180 includes at least one of a deblocking filter, a sample adaptive offset (SAO), an adaptive loop filter (ALF), and a non-local filter (NLF). One or more may be applied to a reconstructed sample, a reconstructed block, or a reconstructed picture. The filter unit 180 may also be referred to as an in-loop filter.

The deblocking filter may remove block distortion occurring at the boundary between blocks. In order to determine whether to apply the deblocking filter, it may be determined whether to apply the deblocking filter to the target block based on the pixel(s) included in several columns or rows included in the block.

When applying the deblocking filter to the target block, the applied filter may differ according to the required strength of the deblocking filtering. In other words, a filter determined according to the strength of the deblocking filtering among different filters may be applied to the target block. When the deblocking filter is applied to the target block, one of a strong filter and a weak filter may be applied to the target block according to the required strength of the deblocking filtering.

In addition, when vertical filtering and horizontal filtering are performed on the target block, horizontal filtering and vertical filtering may be processed in parallel.

SAO may add an appropriate offset to a pixel value of a pixel to compensate for a coding error. The SAO may perform correction using an offset for a difference between an original image and an image to which the deblocking is applied in a pixel unit of an image to which deblocking is applied. To perform offset correction for an image, a method of dividing pixels included in an image into a certain number of areas, determining an area to be offset among the divided areas, and applying an offset to the determined area can be used. In addition, a method of applying an offset in consideration of edge information of each pixel of an image may be used.

The ALF may perform filtering based on a value obtained by comparing the reconstructed image and the original image. After the pixels included in the image are divided into predetermined groups, a filter to be applied to each divided group may be determined, and filtering may be performed differentially for each group. Information related to whether to apply the adaptive loop filter may be signaled for each CU. This information can be signaled for the luma signal. The shape and filter coefficient of ALF to be applied to each block may be different for each block. Alternatively, regardless of the characteristics of the block, a fixed ALF may be applied to the block.

The non-local filter may perform filtering based on reconstructed blocks similar to the target block. In the reconstructed image, an area similar to the target block may be selected, and filtering of the target block may be performed using statistical properties of the selected similar area. Information related to whether to apply the non-local filter may be signaled to the CU. In addition, shapes and filter coefficients of the non-local filter to be applied to the blocks may be different depending on the block.

The reconstructed block or reconstructed image that has passed through the filter unit 180 may be stored in the reference picture buffer 190 as a reference picture. The reconstructed block passing through the filter unit 180 may be a part of the reference picture. In other words, the reference picture may be a reconstructed picture composed of reconstructed blocks that have passed through the filter unit 180. The stored reference picture can then be used for inter prediction or motion compensation.

2 is a block diagram showing a configuration according to an embodiment of a decoding apparatus to which the present invention is applied.

The decoding device 200 may be a decoder, a video decoding device, or an image decoding device.

Referring to FIG. 2, the decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, an inter prediction unit 250, and a switch 245. , An adder 255, a filter unit 260, and a reference picture buffer 270 may be included.

The decoding apparatus 200 may receive a bitstream output from the encoding apparatus 100. The decoding apparatus 200 may receive a bitstream stored in a computer-readable recording medium, and may receive a bitstream streamed through a wired/wireless transmission medium.

The decoding apparatus 200 may perform intra-mode and/or inter-mode decoding on a bitstream. Further, the decoding apparatus 200 may generate a reconstructed image or a decoded image through decoding, and may output the generated reconstructed image or a decoded image.

For example, switching to an intra mode or an inter mode according to a prediction mode used for decoding may be performed by the switch 245. When the prediction mode used for decoding is an intra mode, the switch 245 may be switched to intra. When the prediction mode used for decoding is an inter mode, the switch 245 may be switched to inter.

The decoding apparatus 200 may obtain a reconstructed residual block by decoding the input bitstream, and may generate a prediction block. When the reconstructed residual block and the prediction block are obtained, the decoding apparatus 200 may generate a reconstructed block to be decoded by adding the reconstructed residual block and the prediction block.

The entropy decoder 210 may generate symbols by performing entropy decoding on a bitstream based on a probability distribution on the bitstream. The generated symbols may include symbols in the form of a quantized transform coefficient level (ie, a quantized level or a quantized coefficient). Here, the entropy decoding method may be similar to the entropy encoding method described above. For example, the entropy decoding method may be a reverse process of the entropy encoding method described above.

The entropy decoder 210 may change a coefficient in the form of a one-dimensional vector into a form of a two-dimensional block through a transform coefficient scanning method in order to decode the quantized transform coefficient level.

For example, the coefficients may be changed into a 2D block shape by scanning the coefficients of a block using a diagonal scan at the upper right. Alternatively, it may be determined which of the upper-right diagonal scan, vertical scan, and horizontal scan will be used according to the size of the block and/or the intra prediction mode.

The quantized coefficient may be inverse quantized by the inverse quantization unit 220. The inverse quantization unit 220 may generate an inverse quantized coefficient by performing inverse quantization on the quantized coefficient. In addition, the inverse quantized coefficient may be inversely transformed by the inverse transform unit 230. The inverse transform unit 230 may generate a reconstructed residual block by performing an inverse transform on an inverse quantized coefficient. As a result of performing inverse quantization and inverse transformation on the quantized coefficients, a reconstructed residual block may be generated. In this case, the inverse quantization unit 220 may apply a quantization matrix to the quantized coefficients in generating the reconstructed residual block.

When the intra mode is used, the intra prediction unit 240 may generate a prediction block by performing spatial prediction on the target block using pixel values of an already decoded block adjacent to the target block.

The inter prediction unit 250 may include a motion compensation unit. Alternatively, the inter prediction unit 250 may be referred to as a motion compensation unit.

When the inter mode is used, the motion compensation unit may generate a prediction block by performing motion compensation on a target block using a motion vector and a reference image stored in the reference picture buffer 270.

When the motion vector has a non-integer value, the motion compensation unit may apply an interpolation filter to a partial region in the reference image, and may generate a prediction block using the reference image to which the interpolation filter is applied. The motion compensation unit may determine which of a skip mode, merge mode, AMVP mode, and current picture reference mode is the motion compensation method used for the PU included in the CU based on the CU to perform motion compensation, and the determined mode According to the motion compensation can be performed.

The reconstructed residual block and prediction block may be added through an adder 255. The adder 255 may generate a reconstructed block by adding the reconstructed residual block and the prediction block.

The reconstructed block may pass through the filter unit 260. The filter unit 260 may apply at least one of the deblocking filter, SAO, ALF, and non-local filter to the reconstructed block or the reconstructed image. The reconstructed image may be a picture including a reconstructed block.

The filter unit 260 may output the reconstructed image.

The reconstructed block and/or the reconstructed image that has passed through the filter unit 260 may be stored in the reference picture buffer 270 as a reference picture. The reconstructed block that has passed through the filter unit 260 may be a part of the reference picture. In other words, the reference picture may be a reconstructed image composed of reconstructed blocks that have passed through the filter unit 260. The stored reference picture can then be used for inter prediction and/or motion compensation.

3 is a diagram schematically illustrating a split structure of an image when encoding and decoding an image.

3 may schematically show an example in which one unit is divided into a plurality of sub-units.

In order to efficiently divide an image, a coding unit (CU) may be used in encoding and decoding. A unit may be a term referring to a combination of 1) a block including image samples and 2) a syntax element. For example, "dividing a unit" may mean "dividing a block corresponding to a unit".

A CU may be used as a base unit for image encoding and/or decoding. In addition, the CU may be used as a unit to which a selected one of an intra mode and an inter mode is applied in image encoding and/or decoding. In other words, in image encoding and/or decoding, it may be determined which of an intra mode and an inter mode is applied to each CU.

In addition, the CU may be a base unit in encoding and/or decoding of prediction, transformation, quantization, inverse transformation, inverse quantization, and transformation coefficients.

Referring to FIG. 3, an image 300 may be sequentially divided into units of a largest coding unit (LCU). For each LCU, a partitioning structure can be determined. Here, LCU may be used in the same meaning as a coding tree unit (CTU).

The division of a unit may mean division of a block corresponding to a unit. The block division information may include depth information on the depth of the unit. The depth information may indicate the number and/or degree of division of the unit. One unit may be hierarchically divided into a plurality of sub-units with depth information based on a tree structure.

Each divided sub-unit may have depth information. The depth information may be information indicating the size of the CU. Depth information may be stored for each CU.

Each CU can have depth information. When a CU is divided, CUs generated by the division may have a depth that is increased by 1 from the depth of the divided CU.

The split structure may mean distribution of CUs in the LCU 310 for efficiently encoding an image. This distribution may be determined depending on whether to divide one CU into a plurality of CUs. The number of divided CUs may be a positive integer equal to or greater than 2 including 2, 4, 8, 16, and the like.

The horizontal size and the vertical size of the CU generated by division may be smaller than the horizontal size and the vertical size of the CU before division, depending on the number of CUs generated by division. For example, the horizontal size and the vertical size of the CU generated by division may be half the horizontal size and half the vertical size of the CU before division.

The divided CU may be recursively divided into a plurality of CUs in the same manner. By recursive partitioning, at least one of a horizontal size and a vertical size of a divided CU may be reduced compared to at least one of a horizontal size and a vertical size of the CU before division.

The partitioning of the CU can be recursively performed up to a predefined depth or a predefined size.

For example, the depth of the CU may have a value of 0 to 3. The size of the CU may range from 64x64 to 8x8 depending on the depth of the CU.

For example, the depth of the LCU 310 may be 0, and the depth of the Smallest Coding Unit (SCU) may be a predefined maximum depth. Here, as described above, the LCU may be a CU having the largest coding unit size, and the SCU may be a CU having the smallest coding unit size.

Segmentation may be started from the LCU 310, and the depth of the CU may increase by one whenever the horizontal size and/or the vertical size of the CU is reduced by the division.

For example, for each depth, a CU that is not divided may have a size of 2Nx2N. In addition, in the case of a divided CU, a CU having a size of 2Nx2N may be divided into four CUs having a size of NxN. The size of N can be halved for each increase in depth by 1.

Referring to FIG. 3, an LCU having a depth of 0 may be 64x64 pixels or 64x64 blocks. 0 can be the minimum depth. An SCU with a depth of 3 may be 8x8 pixels or 8x8 blocks. 3 can be the maximum depth. In this case, a CU of a 64x64 block that is an LCU may be expressed as a depth of 0. A CU of a 32x32 block can be expressed as a depth of 1. The CU of 16x16 blocks may be expressed as depth 2. A CU of an 8x8 block, which is an SCU, can be expressed as a depth of 3.

Information on whether the CU is divided may be expressed through partition information of the CU. The division information may be 1-bit information. All CUs except the SCU may include partition information. For example, a value of partition information of a CU that is not partitioned may be a first value, and a value of partition information of a CU to be partitioned may be a second value. When the split information indicates whether the CU splits, the first value may be 0, and the second value may be 1.

For example, when one CU is divided into 4 CUs, the horizontal size and the vertical size of each CU of the 4 CUs generated by the division are half the horizontal size and half the vertical size of the CU before division, respectively. I can. When a 32x32 CU is divided into 4 CUs, the sizes of the divided 4 CUs may be 16x16. When one CU is divided into four CUs, it can be said that the CU is divided into a quad-tree form. In other words, it can be considered that a quad-tree partition is applied to the CU.

For example, when one CU is divided into two CUs, the horizontal size or the vertical size of each CU of the two CUs generated by the division is half the horizontal size or half the vertical size of the CU before division, respectively. I can. When a 32x32 CU is vertically divided into two CUs, the sizes of the divided two CUs may be 16x32. When a 32x32 CU is horizontally divided into two CUs, the sizes of the divided two CUs may be 32x16. When one CU is divided into two CUs, it can be said that the CU is divided in a binary-tree form. In other words, it can be considered that a binary-tree partition is applied to the CU.

For example, when one CU is divided into three CUs, three divided CUs may be generated by dividing the horizontal size or the vertical size of the CU before being divided by a ratio of 1:2:1. For example, when a CU having a size of 16x32 is divided into three CUs in the horizontal direction, the three divided CUs may have sizes of 16x8, 16x16, and 16x8, respectively, from above. For example, when a 32x32 CU is divided into 3 CUs in the vertical direction, the divided 3 CUs may have sizes of 8x32, 16x32, and 8x32 from the left, respectively. When one CU is divided into three CUs, it can be said that the CU is divided in a ternary-tree form. In other words, it can be considered that a ternary-tree partition is applied to the CU.

In the LCU 310 of FIG. 3, both quad-tree type division and binary-tree type division are applied.

In the encoding apparatus 100, a coding tree unit (CTU) having a size of 64x64 may be divided into a plurality of smaller CUs by a recursive quad-cre structure. One CU can be divided into 4 CUs having the same sizes. CUs can be recursively partitioned, and each CU can have a quad tree structure.

Through recursive partitioning for the CU, the optimal partitioning method that generates the minimum rate-distortion ratio can be selected.

The CTU 320 of FIG. 3 is an example of a CTU to which quad-tree division, binary tree division, and ternary tree division are all applied.

As described above, in order to partition the CTU, at least one of quad tree partitioning, binary tree partitioning, and ternary tree partitioning may be applied to the CTU. Splits can be applied based on a specified priority.

For example, quad tree division may be preferentially applied to the CTU. CUs that can no longer be divided into quad trees may correspond to leaf nodes of the quad tree. A CU corresponding to a leaf node of a quad tree may be a root node of a binary tree and/or a ternary tree. That is, the CU corresponding to the leaf node of the quad tree may be divided into a binary tree type or a ternary tree type, or may not be divided any more. At this time, the quad-tree division is not applied again to the CU generated by applying binary tree division or triple tree division to the CU corresponding to the leaf node of the quad tree, so that block division and/or block division information signaling It can be done effectively.

The division of the CU corresponding to each node of the quad tree may be signaled using quad division information. Quad partition information having a first value (eg, "1") may indicate that the CU is divided into a quad tree form. Quad splitting information having a second value (eg, “0”) may indicate that the CU is not split in a quad tree form. The quad division information may be a flag having a specified length (eg, 1 bit).

Priority may not exist between binary tree division and ternary tree division. That is, the CU corresponding to the leaf node of the quad tree may be divided into a binary tree form or a ternary tree form. In addition, the CU generated by binary tree division or ternary tree division may be divided into a binary tree shape or a ternary tree shape, or may not be divided any more.

Partitioning when there is no priority between binary tree partitioning and ternary tree partitioning may be referred to as a multi-type tree partition. That is, a CU corresponding to a leaf node of a quad tree may be a root node of a multi-type tree. The splitting of the CU corresponding to each node of the multi-type tree may be signaled using at least one of information indicating whether the multi-type tree is split, split direction information, and split tree information. Information indicating whether to sequentially divide the CU corresponding to each node of the multi-type tree, information about the division direction, and information about the division tree may be signaled.

For example, information indicating whether a multi-type tree having a first value (eg, "1") is divided may indicate that the corresponding CU is divided into a multi-type tree. Information indicating whether a multi-type tree having a second value (eg, “0”) is divided may indicate that the corresponding CU is not divided into a multi-type tree form.

When the CU corresponding to each node of the multi-type tree is divided into a multi-type tree type, the corresponding CU may further include division direction information.

The splitting direction information may indicate the splitting direction of the multi-type tree splitting. The division direction information having the first value (eg, “1”) may indicate that the corresponding CU is divided in the vertical direction. The division direction information having the second value (eg, “0”) may indicate that the corresponding CU is divided in the horizontal direction.

When the CU corresponding to each node of the multi-type tree is divided into a multi-type tree form, the corresponding CU may further include partition tree information. The split tree information may indicate a tree used for splitting a multi-type tree.

For example, the partitioned tree information having a first value (eg, "1") may indicate that the corresponding CU is divided into a binary tree form. The partitioned tree information having a second value (eg, "0") may indicate that the corresponding CU is divided into a triplet tree.

Here, each of the above-described information indicating whether to be divided, the divided tree information, and the divided direction information may be flags having a specified length (eg, 1 bit).

At least one of the above-described quad split information, information indicating whether the multi-type tree is split, split direction information, and split tree information may be entropy-encoded and/or entropy-decoded. For entropy encoding/decoding of such information, information of a neighboring CU adjacent to the target CU may be used.

For example, it may be considered that the split shape of the left CU and/or the upper CU (that is, whether or not to split, the split tree and/or split direction) and the split shape of the target CU are likely to be similar to each other. Accordingly, context information for entropy encoding and/or entropy decoding of information of a target CU may be derived based on the information of the neighboring CU. In this case, the information of the neighboring CU may include at least one of 1) quad partition information, 2) information indicating whether the multi-type tree is partitioned, 3) partition direction information, and 4) partition tree information of the neighbor CU.

As another embodiment, among binary tree division and ternary tree division, binary tree division may be performed preferentially. That is, binary tree division may be applied first, and a CU corresponding to a leaf node of the binary tree may be set as the root node of the ternary tree. In this case, quad-tree partitioning and binary tree partitioning may not be performed for CUs corresponding to nodes of the three-dimensional tree.

CUs that are no longer split by quad tree splitting, binary tree splitting, and/or triple tree splitting may be a unit of coding, prediction, and/or transformation. That is, for prediction and/or transformation, the CU may no longer be partitioned. Accordingly, a split structure and split information for splitting a CU into a prediction unit and/or a transform unit may not exist in the bitstream.

However, when the size of the CU serving as the unit of partitioning is larger than the size of the maximum transform block, the CU may be recursively partitioned until the size of the CU becomes less than or equal to the size of the maximum transform block. For example, if the size of the CU is 64x64 and the size of the maximum transform block is 32x32, the CU may be divided into four 32x32 blocks for transform. For example, when the size of the CU is 32x64 and the size of the maximum transform block is 32x32, the CU may be divided into two 32x32 blocks for conversion.

In this case, information on whether the CU is divided for conversion may not be separately signaled. Without signaling, whether or not the CU is divided may be determined by comparison between the horizontal size (and/or vertical size) of the CU and the horizontal size (and/or vertical size) of the maximum transform block. For example, if the horizontal size of the CU is larger than the horizontal size of the maximum transform block, the CU may be vertically divided into two. Also, if the vertical size of the CU is larger than the vertical size of the maximum transform block, the CU may be horizontally divided into two.

Information about the maximum size and/or minimum size of the CU, and information about the maximum size and/or minimum size of the transform block may be signaled or determined at a higher level for the CU. For example, the higher level may be a sequence level, a picture level, a tile level, a tile group level, and a slice level. For example, the minimum size of the CU may be determined to be 4x4. For example, the maximum size of the transform block may be determined to be 64x64. For example, the minimum size of the transform block may be determined to be 4x4.

Information about the minimum size of the CU corresponding to the leaf node of the quad tree (say, the minimum size of the quad tree) and/or the maximum depth of the path from the root node of the multi-type tree to the leaf node (say, the maximum depth of the multi-type tree). Depth) information may be signaled or determined at a higher level for the CU. For example, the higher level may be a sequence level, a picture level, a slice level, a tile group level, and a tile level. Information about the minimum quad tree size and/or the maximum depth of the multi-type tree may be separately signaled or determined for each of the intra slice and the inter slice.

Difference information about the size of the CTU and the maximum size of the transform block may be signaled or determined at a higher level for the CU. For example, the higher level may be a sequence level, a picture level, a slice level, a tile group level, and a tile level. Information on the maximum size of the CU corresponding to each node of the binary tree (that is, the maximum size of the binary tree) may be determined based on the size and difference information of the CTU. The maximum size of the CU corresponding to each node of the ternary tree (that is, the maximum size of the ternary tree) may have a different value depending on the type of the slice. For example, within an intra slice, the maximum size of the ternary tree may be 32x32. In addition, for example, in the inter slice, the maximum size of the ternary tree may be 128x128. For example, the minimum size of the CU corresponding to each node of the binary tree (say, the minimum size of a binary tree) and/or the minimum size of the CU corresponding to each node of the ternary tree (say, the minimum size of the ternary tree) of the CU It can be set to the minimum size.

As another example, the maximum size of the binary tree and/or the maximum size of the ternary tree may be signaled or determined at the slice level. In addition, the binary tree minimum size and/or the ternary tree minimum size may be signaled or determined at the slice level.

Based on the above-described various block sizes and various depths, quad split information, information indicating whether to split a multi-type tree, split tree information, and/or split direction information may or may not exist in the bitstream.

For example, if the size of the CU is not larger than the quad tree minimum size, the CU may not include quad partition information, and the quad partition information for the CU may be inferred as a second value.

For example, the size of the CU corresponding to the node of the multi-type tree (horizontal and vertical size) is less than the maximum size of the binary tree (horizontal and vertical size) and/or the maximum size of the ternary tree (horizontal and vertical size). In a larger case, the CU may not be divided into a binary tree shape and/or a ternary tree shape. According to this determination method, information indicating whether to split the multi-type tree may not be signaled and may be inferred as a second value.

Alternatively, the size of the CU corresponding to the node of the multi-type tree (horizontal size and vertical size) is the same as the minimum size of the binary tree (horizontal size and vertical size), or the size of the CU (horizontal and vertical size) is a ternary tree If it is equal to twice the minimum size (horizontal size and vertical size), the CU may not be divided into a binary tree shape and/or a ternary tree shape. According to this determination method, information indicating whether to split the multi-type tree may not be signaled and may be inferred as a second value. This is because, when the CU is divided into a binary tree shape and/or a ternary tree shape, a CU smaller than the minimum binary tree size and/or the ternary tree minimum size is generated.

Alternatively, the binary tree division or the ternary tree division may be limited based on the size of the virtual pipeline data unit (ie, the pipeline buffer size). For example, when the CU is divided into sub-CUs not suitable for the pipeline buffer size by binary tree division or ternary tree division, binary tree division or ternary tree division may be limited. The pipeline buffer size may be equal to the size of the maximum transform block (eg, 64X64).

For example, when the pipeline buffer size is 64X64, the following partitions may be limited.

-Three-dimensional tree division for NxM (N and/or M is 128) CU

-Split horizontal binary tree for 128xN (N <= 64) CU

-Split vertical binary tree for Nx128 (N <= 64) CU

Alternatively, when the depth in the multi-type tree of the CU corresponding to the node of the multi-type tree is equal to the maximum depth of the multi-type tree, the CU may not be divided into a binary tree form and/or a ternary tree form. According to this determination method, information indicating whether to split the multi-type tree may not be signaled and may be inferred as a second value.

Or, for a CU corresponding to a node of a multi-type tree, a multi-type tree is possible only when at least one of vertical binary tree division, horizontal binary tree division, vertical ternary tree division, and horizontal ternary tree division is possible. Information indicating whether or not is divided may be signaled. Otherwise, the CU may not be divided into a binary tree shape and/or a ternary tree shape. According to this determination method, information indicating whether to split the multi-type tree may not be signaled and may be inferred as a second value.

Or, only when both vertical binary tree division and horizontal binary tree division are possible for the CU corresponding to the node of the multi-type tree, or when both vertical and horizontal ternary tree divisions are possible, the division direction information Can be signaled. Otherwise, the division direction information may not be signaled and may be inferred as a value indicating the direction in which the CU can be divided.

Or, split tree information only when both vertical binary tree division and vertical ternary tree division are possible for the CU corresponding to the node of the multi-type tree, or both horizontal binary tree division and horizontal ternary tree division are possible. Can be signaled. Otherwise, the split tree information may not be signaled and may be inferred as a value indicating a tree applicable to the splitting of the CU.

4 is a diagram illustrating a form of a prediction unit that a coding unit may include.

A CU that is no longer divided among CUs divided from the LCU may be divided into one or more prediction units (PUs).

PU may be a basic unit for prediction. The PU may be encoded and decoded in any one of a skip mode, an inter mode, and an intra mode. The PU can be divided into various forms according to each mode. For example, the target block described above with reference to FIG. 1 and the target block described above with reference to FIG. 2 may be a PU.

The CU may not be divided into PUs. If the CU is not divided into PUs, the size of the CU and the size of the PU may be the same.

In the skip mode, partitioning may not exist in the CU. In the skip mode, a 2Nx2N mode 410 having the same PU and CU sizes without division may be supported.

In the inter mode, 8 types of divided types may be supported within the CU. For example, in inter mode, 2Nx2N mode 410, 2NxN mode 415, Nx2N mode 420, NxN mode 425, 2NxnU mode 430, 2NxnD mode 435, nLx2N mode 440 and nRx2N Mode 445 may be supported.

In the intra mode, the 2Nx2N mode 410 and the NxN mode 425 may be supported.

In the 2Nx2N mode 410, a PU having a size of 2Nx2N may be encoded. A PU having a size of 2Nx2N may mean a PU having the same size as the CU. For example, a PU having a size of 2Nx2N may have a size of 64x64, 32x32, 16x16, or 8x8.

In the NxN mode 425, a PU having a size of NxN may be encoded.

For example, in intra prediction, when the size of a PU is 8x8, four divided PUs may be encoded. The size of the divided PU may be 4x4.

When a PU is encoded by an intra mode, the PU may be encoded using one of a plurality of intra prediction modes. For example, in High Efficiency Video Coding (HEVC) technology, 35 intra prediction modes may be provided, and a PU may be coded in one of 35 intra prediction modes.

Which of the 2Nx2N mode 410 and NxN mode 425 the PU is to be encoded may be determined by a rate-distortion cost.

The encoding apparatus 100 may perform an encoding operation on a PU having a size of 2Nx2N. Here, the encoding operation may be encoding a PU in each of a plurality of intra prediction modes that can be used by the encoding apparatus 100. An optimal intra prediction mode for a PU having a size of 2Nx2N may be derived through an encoding operation. The optimal intra prediction mode may be an intra prediction mode that incurs a minimum rate-distortion cost for encoding a PU having a size of 2Nx2N among a plurality of intra prediction modes that can be used by the encoding apparatus 100.

Also, the encoding apparatus 100 may sequentially perform an encoding operation on each PU of the PUs divided by NxN. Here, the encoding operation may be encoding a PU in each of a plurality of intra prediction modes that can be used by the encoding apparatus 100. An optimal intra prediction mode for a PU of NxN size may be derived through an encoding operation. The optimal intra prediction mode may be an intra prediction mode that incurs a minimum rate-distortion cost for encoding a PU having an NxN size among a plurality of intra prediction modes that can be used by the encoding apparatus 100.

The encoding apparatus 100 may determine which of a 2Nx2N size PU and an NxN size PU to encode based on a comparison of the rate-distortion cost of a 2Nx2N size PU and the rate-distortion costs of NxN size PUs.

One CU may be divided into one or more PUs, and a PU may also be divided into a plurality of PUs.

For example, when one PU is divided into four PUs, the horizontal size and vertical size of each PU of the four PUs generated by the division are half the horizontal size and half the vertical size of the PU before division, respectively. I can. When a 32x32 PU is divided into 4 PUs, the sizes of the divided 4 PUs may be 16x16. When one PU is divided into four PUs, it can be said that the PU is divided into a quad-tree form.

For example, when one PU is divided into two PUs, the horizontal size or vertical size of each PU of the two PUs generated by the division is half the horizontal size or half the vertical size of the PU before division I can. When a 32x32 PU is vertically divided into two PUs, the sizes of the divided two PUs may be 16x32. When a 32x32 PU is horizontally divided into two PUs, the sizes of the divided two PUs may be 32x16. When one PU is divided into two PUs, it can be said that the PU is divided into a binary-tree form.

5 is a diagram showing a form of a transform unit that may be included in a coding unit.

A transform unit (TU) may be a basic unit used for a process of transformation, quantization, inverse transformation, inverse quantization, entropy encoding, and entropy decoding in a CU.

The TU may have a square shape or a rectangular shape. The shape of the TU may be determined depending on the size and/or shape of the CU.

Among CUs divided from the LCU, CUs that are no longer divided into CUs may be divided into one or more TUs. In this case, the split structure of the TU may be a quad-tree structure. For example, as shown in FIG. 5, one CU 510 may be divided once or more according to the quad-tree structure. Through partitioning, one CU 510 may be composed of TUs of various sizes.

When one CU is divided two or more times, the CU can be regarded as being divided recursively. Through partitioning, one CU can be composed of TUs having various sizes.

Alternatively, one CU may be divided into one or more TUs based on the number of vertical lines and/or horizontal lines dividing the CU.

A CU may be divided into symmetric type TUs and may be divided into asymmetric type TUs. In order to divide into asymmetric TUs, information on the size and/or shape of the TU may be signaled from the encoding apparatus 100 to the decoding apparatus 200. Alternatively, the size and/or shape of the TU may be derived from information on the size and/or shape of the CU.

The CU may not be divided into TUs. If the CU is not divided into TUs, the size of the CU and the size of the TU may be the same.

One CU may be divided into one or more TUs, and a TU may also be divided into a plurality of TUs.

For example, when one TU is divided into four TUs, the horizontal size and vertical size of each TU of the four TUs generated by the division are half the horizontal size and half the vertical size of the TU before division, respectively. I can. When a TU of a size of 32x32 is divided into 4 TUs, the sizes of the divided 4 TUs may be 16x16. When one TU is divided into four TUs, it can be said that the TU is divided into a quad-tree form.

For example, when one TU is divided into two TUs, the horizontal size or vertical size of each TU of the two TUs generated by the division is half the horizontal size or half the vertical size of the TU before division, respectively. I can. When a TU of a size of 32x32 is vertically divided into two TUs, the sizes of the divided two TUs may be 16x32. When a TU of a size of 32x32 is horizontally divided into two TUs, the sizes of the divided two TUs may be 32x16. When one TU is divided into two TUs, it can be said that the TU is divided into a binary-tree form.

The CU may be divided in a manner other than that shown in FIG. 5.

For example, one CU can be divided into three CUs. The horizontal size or the vertical size of the three divided CUs may be 1/4, 1/2, and 1/4 of the horizontal size or vertical size of the CU before division, respectively.

For example, when a 32x32 CU is vertically divided into 3 CUs, the sizes of the divided 3 CUs may be 8x32, 16x32, and 8x32, respectively. In this way, when one CU is divided into three CUs, it can be considered that the CU is divided in the form of a ternary tree.

One of the exemplified quad tree type division, binary tree type division, and ternary tree type division may be applied for CU division, and a plurality of division methods may be combined together to be used for CU division. . In this case, a case where a plurality of partitioning schemes are combined and used may be referred to as partitioning in the form of a complex tree.

6 illustrates block division according to an example.

In the process of encoding and/or decoding an image, a target block may be divided as shown in FIG. 6. For example, the target block may be a CU.

For segmentation of a target block, an indicator indicating segmentation information may be signaled from the encoding apparatus 100 to the decoding apparatus 200. The division information may be information indicating how the target block is divided.

Split information includes a split flag (hereinafter referred to as "split_flag"), a quad-binary flag (hereinafter referred to as "QB_flag"), a quad tree flag (hereinafter referred to as "quadtree_flag"), a binary tree flag (hereinafter referred to as "binarytree_flag"). It may be at least one of "") and a binary type flag (hereinafter, "Btype_flag").

split_flag may be a flag indicating whether a block is divided. For example, a value of 1 of split_flag may indicate that the block is split. A value of 0 of split_flag may indicate that the block is not split.

QB_flag may be a flag indicating whether a block is divided into a quad tree form or a binary tree form. For example, a value of 0 of QB_flag may indicate that the block is divided into a quad tree. A value of 1 of QB_flag may indicate that the block is divided in the form of a binary tree. Alternatively, a value of 0 of QB_flag may indicate that the block is divided in the form of a binary tree. A value of 1 of QB_flag may indicate that the block is divided in the form of a quad tree.

quadtree_flag may be a flag indicating whether a block is divided into a quad tree shape. For example, a value of 1 of quadtree_flag may indicate that the block is divided into a quadtree shape. A value of 0 for quadtree_flag may indicate that the block is not divided into a quadtree form.

binarytree_flag may be a flag indicating whether a block is divided into a binary tree shape. For example, a value of 1 binarytree_flag may indicate that the block is divided into a binary tree. A value of 0 of binarytree_flag may indicate that the block is not divided into a binary tree shape.

Btype_flag may be a flag indicating whether a block is divided into a vertical or horizontal division when the block is divided in the form of a binary tree. For example, the value 0 of Btype_flag may indicate that the block is divided in the horizontal direction. A value of 1 of Btype_flag may indicate that the block is divided in the vertical direction. Alternatively, a value of 0 of Btype_flag may indicate that the block is divided in the vertical direction. A value of 1 of Btype_flag may indicate that the block is divided in the horizontal direction.

For example, split information for the block of FIG. 6 can be derived by signaling at least one of quadtree_flag, binarytree_flag, and Btype_flag as shown in Table 1 below.

[Table 1]

For example, split information for the block of FIG. 6 can be derived by signaling at least one of split_flag, QB_flag, and Btype_flag as shown in Table 2 below.

[Table 2]

The partitioning method may be limited only to a quad tree or a binary tree depending on the size and/or shape of the block. When such a limitation is applied, the split_flag may be a flag indicating whether to be divided into a quad-tree form or a flag indicating whether to divide into a binary tree form. The size and shape of the block may be derived according to the depth information of the block, and the depth information may be signaled from the encoding device 100 to the decoding device 200.

When the size of the block falls within a specified range, only quad-tree division may be possible. For example, the specified range may be defined by at least one of a maximum block size and a minimum block size in which only quadtree-type division is possible.

Information indicating a maximum block size and/or a minimum block size that can only be divided in the form of a quart tree may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. In addition, this information may be signaled for at least one unit of a video, a sequence, a picture, a parameter, a tile group, and a slice (or segment).

Alternatively, the maximum block size and/or the minimum block size may be a fixed size predefined by the encoding apparatus 100 and the decoding apparatus 200. For example, when the size of the block is 64x64 or more and 256x256 or less, only quadtree type division may be possible. In this case, split_flag may be a flag indicating whether to split into a quad tree.

When the block size is larger than the maximum transform block size, only quadtree-type division may be possible. In this case, the divided block may be at least one of a CU and a TU.

In this case, split_flag may be a flag indicating whether to split into a quad tree.

When the size of the block falls within a specified range, only a binary tree type or a ternary tree type can be divided. Here, for example, the specified range may be defined by at least one of a maximum block size and a minimum block size that can be divided only in a binary tree form or a ternary tree form.

Information indicating the maximum block size and/or the minimum block size in which only the binary tree type split or the triple tree type is possible may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. Also, this information may be signaled for at least one unit of a sequence, a picture, and a slice (or segment).

Alternatively, the maximum block size and/or the minimum block size may be a fixed size predefined by the encoding apparatus 100 and the decoding apparatus 200. For example, when the size of the block is 8x8 or more and 16x16 or less, only binary tree-type partitioning may be possible. In this case, split_flag may be a flag indicating whether to split into a binary tree form or a ternary tree form.

The above description of the division of the code tree type can be equally applied to the division of the binary tree type and/or the ternary tree type.

The division of the block may be limited by the previous division. For example, when a block is divided into a specified binary tree shape to generate a plurality of divided blocks, each divided block may be further divided only in a specified tree shape. Here, the specified tree form may be at least one of a binary tree form, a ternary tree form, and a quad tree form.

When the horizontal size or the vertical size of the divided block corresponds to a size that cannot be further divided, the above-described indicator may not be signaled.

Arrows from the center to the outside of the graph of FIG. 7 may indicate prediction directions of directional intra prediction modes. Also, a number displayed close to the arrow may indicate an example of an intra prediction mode or a mode value assigned to a prediction direction of the intra prediction mode.

In FIG. 7, the number 0 may indicate a planar mode, which is a non-directional intra prediction mode. Numeral 1 may indicate a DC mode, which is a non-directional intra prediction mode.

Intra encoding and/or decoding may be performed using reference samples of neighboring units of the target block. The neighboring block may be a reconstructed neighboring block. The reference sample may mean a neighboring sample.

For example, intra encoding and/or decoding may be performed using a reference sample value or a coding parameter included in a reconstructed neighboring block.

The encoding apparatus 100 and/or the decoding apparatus 200 may generate a prediction block by performing intra prediction on a target block based on information on a sample in the target image. When performing intra prediction, the encoding apparatus 100 and/or the decoding apparatus 200 may generate a prediction block for a target block by performing intra prediction based on information on a sample in the target image. When performing intra prediction, the encoding apparatus 100 and/or the decoding apparatus 200 may perform directional prediction and/or non-directional prediction based on at least one reconstructed reference sample.

The prediction block may mean a block generated as a result of performing intra prediction. The prediction block may correspond to at least one of CU, PU, and TU.

The unit of the prediction block may be the size of at least one of CU, PU, and TU. The prediction block may have a square shape having a size of 2Nx2N or NxN. The size of NxN may include 4x4, 8x8, 16x16, 32x32, 64x64, and the like.

Alternatively, the prediction block may be a square block having a size such as 2x2, 4x4, 8x8, 16x16, 32x32, or 64x64, and may be a rectangular block having sizes such as 2x8, 4x8, 2x16, 4x16, and 8x16. have.

Intra prediction may be performed according to an intra prediction mode for a target block. The number of intra prediction modes that the target block may have may be a predefined fixed value, and may be differently determined according to the property of the prediction block. For example, the properties of the prediction block may include the size of the prediction block and the type of the prediction block. In addition, the property of the prediction block may indicate a coding parameter for the prediction block.

For example, the number of intra prediction modes may be fixed to N regardless of the size of the prediction block. Alternatively, for example, the number of intra prediction modes may be 3, 5, 9, 17, 34, 35, 36, 65, 67 or 95.

The intra prediction mode may be a non-directional mode or a directional mode.

For example, the intra prediction mode may include two non-directional modes and 65 directional modes corresponding to numbers 0 to 66 shown in FIG. 7.

For example, when the specified intra prediction method is used, the intra prediction mode may include two non-directional modes and 93 directional modes, corresponding to numbers -14 to 80 shown in FIG. 7.

The two non-directional modes may include a DC mode and a planar mode.

The directional mode may be a prediction mode having a specific direction or a specific angle. The directional mode may also be referred to as an argular mode.

The intra prediction mode may be represented by at least one of a mode number, a mode value, a mode angle, and a mode direction. That is to say, the terms “(mode) number of intra prediction mode”, “(mode) value of intra prediction mode”, “(mode) angle of intra prediction mode” and “(mode) direction of intra prediction mode) mean the same And can be used interchangeably.

The number of intra prediction modes may be M. M may be 1 or more. In other words, the intra prediction modes may be M numbers including the number of non-directional modes and the number of directional modes.

The number of intra prediction modes may be fixed to M regardless of the block size and/or color component. For example, the number of intra prediction modes may be fixed to one of 35 or 67 regardless of the size of the block.

Alternatively, the number of intra prediction modes may be different according to the shape, size and/or type of color component of the block.

For example, in FIG. 7, the directional prediction modes shown by dotted lines can be applied only to prediction for a non-square block.

For example, as the size of the block increases, the number of intra prediction modes may increase. Alternatively, as the size of the block increases, the number of intra prediction modes may decrease. When the block size is 4x4 or 8x8, the number of intra prediction modes may be 67. When the block size is 16x16, the number of intra prediction modes may be 35. When the block size is 32x32, the number of intra prediction modes may be 19. When the block size is 64x64, the number of intra prediction modes may be 7.

For example, the number of intra prediction modes may vary depending on whether a color component is a luma signal or a chroma signal. Alternatively, the number of intra prediction modes of the luma component block may be greater than the number of intra prediction modes of the chroma component block.

For example, in the case of a vertical mode having a mode value of 50, prediction may be performed in a vertical direction based on a pixel value of a reference sample. For example, in the case of a horizontal mode having a mode value of 18, prediction may be performed in a horizontal direction based on a pixel value of a reference sample.

Even in a directional mode other than the above-described mode, the encoding apparatus 100 and the decoding apparatus 200 may perform intra prediction on a target unit using reference samples according to an angle corresponding to the directional mode.

The intra prediction mode located to the right of the vertical mode may be referred to as a vertical-right mode. The intra prediction mode located at the lower end of the horizontal mode may be referred to as a horizontal-below mode. For example, in FIG. 7, intra prediction modes having a mode value of 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65 and 66 are vertical It can be the right modes. Intra prediction modes having a mode value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17 may be horizontal lower modes.

The non-directional mode may include a DC mode and a planar mode. For example, the mode value of the DC mode may be 1. The mode value of the planner mode may be 0.

The directional mode may include an angular mode. Among the plurality of intra prediction modes, a mode other than the DC mode and the planar mode may be a directional mode.

When the intra prediction mode is the DC mode, a prediction block may be generated based on an average of pixel values of a plurality of reference samples. For example, the pixel value of the prediction block may be determined based on an average of pixel values of a plurality of reference samples.

The number of intra prediction modes and the mode values of each intra prediction mode described above may be merely exemplary. The number of intra prediction modes and the mode values of the intra prediction modes described above may be defined differently according to embodiments, implementations, and/or needs.

In order to perform intra prediction on the target block, a step of checking whether samples included in the reconstructed neighboring block can be used as reference samples of the target block may be performed. A value generated by copying and/or interpolation using at least one sample value of samples included in the reconstructed neighboring block when there is a sample that cannot be used as a reference sample of the target block among samples of the neighboring block This can be replaced with a sample value of a sample that cannot be used as a reference sample. If the value generated by copying and/or interpolation is replaced with the sample value of the sample, the sample can be used as a reference sample of the target block.

When intra prediction is used, a filter may be applied to at least one of a reference sample or a prediction sample based on at least one of an intra prediction mode and a size of a target block.

The type of filter applied to at least one of the reference sample or the prediction sample may be different according to at least one of an intra prediction mode of the target block, the size of the target block, and the shape of the target block. The types of filters may be classified according to one or more of a length of a filter tap, a value of a filter coefficient, and a filter strength. The length of the filter taps may mean the number of filter taps. In addition, the number of filter taps may mean the length of the filter.

When the intra prediction mode is the planar mode, in generating the prediction block of the target block, the upper reference sample of the target sample, the left reference sample of the target sample, and the upper right reference sample of the target block according to the position in the prediction block of the prediction target sample And a sample value of the prediction target sample may be generated using a weight-sum to which the lower left reference sample of the target block is assigned.

When the intra prediction mode is the DC mode, in generating the prediction block of the target block, an average value of upper reference samples and left reference samples of the target block may be used. Also, filtering using values of reference samples may be performed on specified rows or specified columns in the target block. The specified rows may be one or more top rows adjacent to the reference sample. The specified columns may be one or more left columns adjacent to the reference sample.

When the intra prediction mode is a directional mode, a prediction block may be generated using an upper reference sample, a left reference sample, an upper right reference sample, and/or a lower left reference sample of the target block.

Real unit interpolation may be performed to generate the above-described prediction samples.

The intra prediction mode of the target block may be predicted from the intra prediction mode of a neighboring block of the target block, and information used for prediction may be entropy encoded/decoded.

For example, if the intra prediction modes of the target block and the neighboring block are the same, it may be signaled that the intra prediction modes of the target block and the neighboring block are the same using a predefined flag.

For example, an indicator indicating an intra prediction mode identical to an intra prediction mode of a target block among intra prediction modes of a plurality of neighboring blocks may be signaled.

If the intra prediction modes of the target block and the neighboring block are different from each other, information on the intra prediction mode of the target block may be encoded and/or decoded using entropy encoding and/or decoding.

8 is a diagram for describing a reference sample used in an intra prediction process.

The reconstructed reference samples used for intra prediction of the target block are lower-left reference samples, left reference samples, upper-left corner reference samples, and upper reference samples. And the above-right reference samples.

For example, the left reference samples may mean a reconstructed reference pixel adjacent to the left side of the target block. The upper reference samples may refer to a reconstructed reference pixel adjacent to the upper end of the target block. The upper left corner reference sample may mean a reconstructed reference pixel located at the upper left corner of the target block. In addition, the lower left reference samples may mean a reference sample located at the lower end of the left sample line among samples located on the same line as the left sample line composed of the left reference samples. The upper right reference samples may mean reference samples located to the right of the upper pixel line among samples located on the same line as the upper sample line composed of the upper reference samples.

When the size of the target block is NxN, each of the lower left reference samples, the left reference samples, the upper reference samples, and the upper right reference samples may be N.

A prediction block may be generated through intra prediction of the target block. Generation of the prediction block may include determining values of pixels of the prediction block. The size of the target block and the prediction block may be the same.

A reference sample used for intra prediction of the target block may vary according to the intra prediction mode of the target block. The direction of the intra prediction mode may indicate a dependency relationship between reference samples and pixels of the prediction block. For example, the value of the specified reference sample may be used as the value of the specified one or more pixels of the prediction block. In this case, the specified reference sample and the specified one or more pixels of the prediction block may be samples and pixels specified by a straight line in the direction of the intra prediction mode. In other words, the value of the specified reference sample may be copied to the value of the pixel located in the reverse direction of the direction of the intra prediction mode. Alternatively, the value of the pixel of the prediction block may be a value of a reference sample located in the direction of the intra prediction mode based on the location of the pixel.

For example, when the intra prediction mode of the target block is the vertical mode, upper reference samples may be used for intra prediction. When the intra prediction mode is a vertical mode, a value of a pixel of the prediction block may be a value of a reference sample vertically positioned above the pixel position. Accordingly, upper reference samples adjacent to the target block to the upper end may be used for intra prediction. Also, values of pixels in one row of the prediction block may be the same as values of upper reference samples.

For example, when the intra prediction mode of the target block is the horizontal mode, left reference samples may be used for intra prediction. When the intra prediction mode is a horizontal mode, a value of a pixel of the prediction block may be a value of a reference sample located horizontally to the left of the pixel. Accordingly, left reference samples adjacent to the left of the target block may be used for intra prediction. Also, values of pixels in one column of the prediction block may be the same as values of left reference samples.

For example, when the mode value of the intra prediction mode of the target block is 34, at least a part of left reference samples, an upper left corner reference sample, and at least a part of the upper reference samples may be used for intra prediction. When the mode value of the intra prediction mode is 34, the value of the pixel of the prediction block may be a value of a reference sample located diagonally to the upper left of the pixel.

In addition, when an intra prediction mode having a mode value of 52 to 66 is used, at least some of the upper right reference samples may be used for intra prediction.

In addition, when an intra prediction mode having a mode value of 2 to 17 is used, at least some of the lower left reference samples may be used for intra prediction.

In addition, when an intra prediction mode having a mode value of 19 to 49 is used, an upper left corner reference sample may be used for intra prediction.

The number of reference samples used to determine the pixel value of one pixel of the prediction block may be one or two or more.

As described above, the pixel value of the pixel of the prediction block may be determined according to the location of the pixel and the location of the reference sample indicated by the direction of the intra prediction mode. When the location of the reference sample indicated by the pixel location and the direction of the intra prediction mode is an integer location, the value of one reference sample indicated by the integer location may be used to determine the pixel value of the pixel of the prediction block.

When the position of the reference sample indicated by the position of the pixel and the direction of the intra prediction mode is not an integer position, an interpolated reference sample may be generated based on the two reference samples closest to the position of the reference sample. have. The value of the interpolated reference sample can be used to determine the pixel value of the pixel of the prediction block. That is, when the position of the pixel of the prediction block and the position of the reference sample indicated by the direction of the intra prediction mode represent between two reference samples, an interpolated value is generated based on the values of the two samples. I can.

The prediction block generated by prediction may not be the same as the original target block. That is, a prediction error, which is a difference between the target block and the prediction block, may exist, and a prediction error may exist between a pixel of the target block and a pixel of the prediction block.

Hereinafter, the terms "difference", "error" and "residual" may be used in the same meaning, and may be used interchangeably.

For example, in the case of directional intra prediction, a larger prediction error may occur as the distance between a pixel of a prediction block and a reference sample increases. A discontinuity may occur between a prediction block and a neighboring block generated by such a prediction error.

Filtering on the prediction block may be used to reduce the prediction error. Filtering may be adaptively applying a filter to a region considered to have a large prediction error among prediction blocks. For example, an area considered to have a large prediction error may be a boundary of a prediction block. In addition, a region considered to have a large prediction error among prediction blocks may be different according to the intra prediction mode, and filter characteristics may be different.

As illustrated in FIG. 8, for intra prediction of a target block, at least one of reference lines 0 to 3 may be used. Each reference line may represent a reference sample line. The smaller the number of the reference line, the closer the reference sample line to the target block may be.

The samples of segment A and segment F may be obtained through padding using the closest samples of segment B and segment E, respectively, instead of being obtained from the reconstructed neighboring block.

Index information indicating a reference sample line to be used for intra prediction of a target block may be signaled. The index information may indicate a reference sample line used for intra prediction of a target block among a plurality of reference sample lines. For example, the index information may have a value of 0 to 3.

If the upper boundary of the target block is the boundary of the CTU, only the reference sample line 0 can be used. Therefore, in this case, index information may not be signaled. When a reference sample line other than the reference sample line 0 is used, filtering on a prediction block described later may not be performed.

In the case of inter-color intra prediction, a prediction block for a target block of the second color component may be generated based on a corresponding reconstructed block of the first color component.

For example, the first color component may be a luma component, and the second color component may be a chroma component.

For intra prediction between color components, a parameter of a linear model between the first color component and the second color component may be derived based on the template.

The template may include an upper reference sample and/or a left reference sample of the target block, and may include an upper reference sample and/or a left reference sample of the reconstructed block of the first color component corresponding to these reference samples. have.

For example, the parameters of the linear model are 1) a value of a sample of a first color component having a maximum value among samples in a template, 2) a value of a sample of a second color component corresponding to a sample of the first color component, 3) The value of the sample of the first color component having the minimum value among samples in the template and 4) the value of the sample of the second color component corresponding to the sample of the first color component can be derived.

When the parameters of the linear model are derived, a prediction block for the target block may be generated by applying the corresponding reconstructed block to the linear model.

Depending on the image format, sub-sampling may be performed on neighboring samples of the reconstructed block of the first color component and the corresponding reconstructed block. For example, when one sample of the second color component corresponds to four samples of the first color component, one corresponding sample may be calculated by sub-sampling the four samples of the first color component. have. When sub-sampling is performed, derivation of a parameter of a linear model and intra prediction between color components may be performed based on the sub-sampled corresponding sample.

Whether to perform intra prediction between color components and/or a range of a template may be signaled as an intra prediction mode.

The target block may be divided into two or four sub-blocks in a horizontal direction and/or a vertical direction.

The divided sub-blocks may be sequentially reconstructed. That is, as intra prediction is performed on a sub-block, a sub-prediction block for the sub-block may be generated. In addition, as inverse quantization and/or inverse transformation is performed on the sub-block, a sub residual block for the sub-block may be generated. A reconstructed subblock may be generated by adding the sub prediction block to the sub residual block. The reconstructed sub-block may be used as a reference sample for intra prediction of a sub-block of a later order.

The sub-block may be a block including a specified number (eg, 16) or more samples. Thus, for example, when the target block is an 8x4 block or a 4x8 block, the target block may be divided into two sub-blocks. In addition, when the target block is a 4x4 block, the target block cannot be divided into sub-blocks. When the target block has a size other than that, the target block may be divided into four sub-blocks.

Information about whether intra prediction based on such sub-blocks is performed and/or a division direction (horizontal or vertical direction) may be signaled.

Such sub-block-based intra prediction may be limited to be performed only when the reference sample line 0 is used. When subblock-based intra prediction is performed, filtering on a prediction block to be described later may not be performed.

The final prediction block may be generated by performing filtering on the prediction block generated by intra prediction.

Filtering may be performed by applying a specific weight to a filtering target sample, a left reference sample, an upper reference sample, and/or an upper left reference sample to be filtered.

A weight and/or a reference sample (or a range of a reference sample or a location of a reference sample, etc.) used for filtering may be determined based on at least one of a block size, an intra prediction mode, and a location of a sample to be filtered within a prediction block. have.

For example, filtering may be performed only for a specified intra prediction mode (eg, DC mode, planar mode, vertical mode, horizontal mode, diagonal mode and/or adjacent diagonal mode).

The adjacent diagonal mode may be a mode having a number in which k is added to the number of the diagonal mode, and may be a mode in which k is subtracted from the number of the diagonal mode. In other words, the number of the adjacent diagonal mode may be the sum of the number of the diagonal mode and k, and may be the difference between the number of the diagonal mode and k. For example, k may be a positive integer of 8 or less.

The intra prediction mode of the target block may be derived using an intra prediction mode of a neighboring block existing around the target block, and the derived intra prediction mode may be entropy-encoded and/or entropy-decoded.

For example, if the intra prediction mode of the target block and the intra prediction mode of the neighboring block are the same, information indicating that the intra prediction mode of the target block and the intra prediction mode of the neighboring block are the same may be signaled using specified flag information. .

In addition, for example, among intra prediction modes of a plurality of neighboring blocks, indicator information on a neighboring block having the same intra prediction mode as that of the target block may be signaled.

For example, if the intra prediction mode of the target block and the intra prediction mode of the neighboring block are different from each other, entropy encoding and/or entropy decoding based on the intra prediction mode of the neighboring block is performed to provide information on the intra prediction mode of the target block. Entropy encoding and/or entropy decoding may be performed.

9 is a diagram for describing an embodiment of an inter prediction process.

The square shown in FIG. 9 may represent an image (or picture). In addition, arrows in FIG. 9 may indicate a prediction direction. An arrow from the first picture to the second picture may indicate that the second picture refers to the first picture. That is, the image may be encoded and/or decoded according to the prediction direction.

Each picture may be classified into an I picture (Intra Picture), a P picture (Uni-prediction Picture), and a B picture (Bi-prediction Picture) according to an encoding type. Each picture may be encoded and/or decoded according to the encoding type of each picture.

When the target image to be encoded is an I picture, the target image may be encoded using data in the image itself without inter prediction referencing other images. For example, an I picture can be coded only by intra prediction.

When the target image is a P picture, the target image may be encoded through inter prediction using only a reference picture existing in one direction. Here, the unidirectional may be forward or reverse.

When the target image is a B picture, the target image may be encoded through inter prediction using reference pictures existing in both directions or inter prediction using a reference picture existing in one of forward and reverse directions. Here, both directions may be forward and reverse.

A P picture and a B picture that are encoded and/or decoded using a reference picture may be regarded as an image using inter prediction.

In the following, inter prediction in an inter mode according to an embodiment will be described in detail.

Inter prediction or motion compensation may be performed using a reference image and motion information.

In the inter mode, the encoding apparatus 100 may perform inter prediction and/or motion compensation on a target block. The decoding apparatus 200 may perform inter prediction and/or motion compensation corresponding to the inter prediction and/or motion compensation in the encoding apparatus 100 on the target block.

Motion information on the target block may be derived during inter prediction by each of the encoding apparatus 100 and the decoding apparatus 200. The motion information may be derived using motion information of a reconstructed neighboring block, motion information of a collocated block, and/or motion information of a block adjacent to the collocated block.

For example, the encoding apparatus 100 or the decoding apparatus 200 may perform prediction and/or motion compensation by using motion information of a spatial candidate and/or a temporal candidate as motion information of a target block. Can be done. The target block may mean a PU and/or a PU partition.

The spatial candidate may be a reconstructed block spatially adjacent to the target block.

The temporal candidate may be a reconstructed block corresponding to a target block in a collocated picture (col picture) that has already been reconstructed.

In inter prediction, the encoding apparatus 100 and the decoding apparatus 200 may improve encoding efficiency and decoding efficiency by using motion information of a spatial candidate and/or a temporal candidate. Motion information of a spatial candidate may be referred to as spatial motion information. The motion information of the temporal candidate may be referred to as temporal motion information.

Hereinafter, motion information of a spatial candidate may be motion information of a PU including a spatial candidate. The motion information of the temporal candidate may be motion information of the PU including the temporal candidate. The motion information of the candidate block may be motion information of a PU including the candidate block.

Inter prediction may be performed using a reference picture.

The reference picture may be at least one of a picture before the target picture or a picture after the target picture. The reference picture may mean an image used for prediction of a target block.

In inter prediction, a region within a reference picture may be specified by using a reference picture index (or refIdx) indicating a reference picture and a motion vector to be described later. Here, the specified area in the reference picture may represent a reference block.

In inter prediction, a reference picture may be selected, and a reference block corresponding to a target block may be selected within the reference picture. In addition, inter prediction may generate a prediction block for a target block using the selected reference block.

Motion information may be derived during inter prediction by each of the encoding apparatus 100 and the decoding apparatus 200.

The spatial candidate may be a block that 1) exists in the target picture, 2) has already been reconstructed through encoding and/or decoding, and 3) is adjacent to the target block or located at a corner of the target block. Here, the block located at the corner of the target block may be a block vertically adjacent to a neighboring block horizontally adjacent to the target block or a block horizontally adjacent to a neighboring block vertically adjacent to the target block. “A block located at the corner of the target block” may have the same meaning as “a block adjacent to the corner of the target block”. The "block located at the corner of the target block" may be included in the "block adjacent to the target block".

For example, the spatial candidate is a reconstructed block located to the left of the target block, a reconstructed block located at the top of the target block, a reconstructed block located at the lower left corner of the target block, and the upper right corner of the target block. It may be a reconstructed block or a reconstructed block located in the upper left corner of the target block.

Each of the encoding apparatus 100 and the decoding apparatus 200 may identify a block present at a location spatially corresponding to the target block in the coll picture. The position of the target block in the target picture and the position of the identified block in the collocated picture may correspond to each other.

Each of the encoding apparatus 100 and the decoding apparatus 200 may determine a coll block existing in a predetermined relative position with respect to the identified block as a temporal candidate. The predefined relative position may be an internal position and/or an external position of the identified block.

For example, the call block may include a first call block and a second call block. When the coordinates of the identified block are (xP, yP) and the size of the identified block is (nPSW, nPSH), the first collocated block may be a block located at the coordinates (xP + nPSW, yP + nPSH). The second collocated block may be a block located at coordinates (xP + (nPSW >> 1), yP + (nPSH >> 1)). The second call block may be selectively used when the first call block is not available.

The motion vector of the target block may be determined based on the motion vector of the collocated block. Each of the encoding apparatus 100 and the decoding apparatus 200 may scale a motion vector of a collocated block. The scaled motion vector of the collocated block may be used as the motion vector of the target block. Also, a motion vector of motion information of a temporal candidate stored in the list may be a scaled motion vector.

The ratio of the motion vector of the target block and the motion vector of the collocated block may be the same as the ratio of the first temporal distance and the second temporal distance. The first temporal distance may be a distance between a reference picture of a target block and a target picture. The second temporal distance may be a distance between a reference picture of a collocated block and a collocated picture.

The method of deriving motion information may vary according to the inter prediction mode of the target block. For example, as an inter prediction mode applied for inter prediction, an advanced motion vector predictor (AMVP) mode, a merge mode and a skip mode, a merge mode having a motion vector difference, There may be a sub-block merge mode, a triangulation mode, an inter-intra combined prediction mode, an affine inter mode, and a current picture reference mode. The merge mode may also be referred to as a motion merge mode. In the following, each of the modes is described in detail.

1) AMVP mode

When the AMVP mode is used, the encoding apparatus 100 may search for a similar block in the neighborhood of the target block. The encoding apparatus 100 may obtain a prediction block by performing prediction on a target block using motion information of the searched similar block. The encoding apparatus 100 may encode a residual block, which is a difference between the target block and the prediction block.

1-1) Creation of a predicted motion vector candidate list

When the AMVP mode is used as the prediction mode, each of the encoding apparatus 100 and the decoding apparatus 200 may generate a prediction motion vector candidate list using a motion vector of a spatial candidate, a motion vector of a temporal candidate, and a zero vector. have. The predicted motion vector candidate list may include one or more predicted motion vector candidates. At least one of a motion vector of a spatial candidate, a motion vector of a temporal candidate, and a zero vector may be determined and used as a predicted motion vector candidate.

Hereinafter, the terms “predicted motion vector (candidate)” and “motion vector (candidate)” may be used with the same meaning, and may be used interchangeably.

Hereinafter, the terms "prediction motion vector candidate" and "AMVP candidate" may be used with the same meaning, and may be used interchangeably.

Hereinafter, the terms "prediction motion vector candidate list" and "AMVP candidate list" may be used with the same meaning, and may be used interchangeably.

The spatial candidate may include reconstructed spatial neighboring blocks. In other words, the reconstructed motion vector of the neighboring block may be referred to as a spatial prediction motion vector candidate.

The temporal candidate may include a call block and a block adjacent to the call block. In other words, a motion vector of a collocated block or a motion vector of a block adjacent to the collocated block may be referred to as a temporal prediction motion vector candidate.

The zero vector may be a (0, 0) motion vector.

The predicted motion vector candidate may be a motion vector predictor for prediction of a motion vector. In addition, in the encoding apparatus 100, the predicted motion vector candidate may be an initial motion vector search position.

1-2) Search for motion vectors using the predicted motion vector candidate list

The encoding apparatus 100 may determine a motion vector to be used for encoding a target block within a search range by using the predicted motion vector candidate list. Also, the encoding apparatus 100 may determine a predicted motion vector candidate to be used as a predicted motion vector of a target block from among the predicted motion vector candidates of the predicted motion vector candidate list.

The motion vector to be used for encoding the target block may be a motion vector that can be coded at a minimum cost.

In addition, the encoding apparatus 100 may determine whether to use the AMVP mode in encoding the target block.

1-3) Transmission of inter prediction information

The encoding apparatus 100 may generate a bitstream including inter prediction information required for inter prediction. The decoding apparatus 200 may perform inter prediction on a target block using inter prediction information of a bitstream.

The inter prediction information includes 1) mode information indicating whether the AMVP mode is used, 2) a predicted motion vector index, 3) a motion vector difference (MVD), 4) a reference direction, and 5) a reference picture index. can do.

Hereinafter, the terms "predicted motion vector index" and "AMVP index" may be used with the same meaning, and may be used interchangeably.

In addition, the inter prediction information may include a residual signal.

When the mode information indicates that the AMVP mode is used, the decoding apparatus 200 may obtain a predicted motion vector index, a motion vector difference, a reference direction, and a reference picture index from the bitstream through entropy decoding.

The predicted motion vector index may indicate a predicted motion vector candidate used for prediction of a target block among predicted motion vector candidates included in the predicted motion vector candidate list.

1-4) Inter prediction in AMVP mode using inter prediction information

The decoding apparatus 200 may derive a predicted motion vector candidate using the predicted motion vector candidate list, and may determine motion information of a target block based on the derived predicted motion vector candidate.

The decoding apparatus 200 may determine a motion vector candidate for the target block from among the predicted motion vector candidates included in the predicted motion vector candidate list by using the predicted motion vector index. The decoding apparatus 200 may select a predicted motion vector candidate indicated by the predicted motion vector index from among predicted motion vector candidates included in the predicted motion vector candidate list as the predicted motion vector of the target block.

The encoding apparatus 100 may generate an entropy-coded predicted motion vector index by applying entropy encoding to the predicted motion vector index, and may generate a bitstream including an entropy-coded predicted motion vector index. The entropy-encoded prediction motion vector index may be signaled from the encoding device 100 to the decoding device 200 through a bitstream. The decoding apparatus 200 may extract an entropy-coded predictive motion vector index from a bitstream, and obtain a predicted motion vector index by applying entropy decoding to the entropy-coded predicted motion vector index.

The motion vector actually used for inter prediction of the target block may not coincide with the predicted motion vector. A motion vector to be actually used for inter prediction of a target block and MVD may be used to indicate a difference between the predicted motion vectors. The encoding apparatus 100 may derive a predicted motion vector similar to a motion vector to be actually used for inter prediction of a target block in order to use an MVD having a size as small as possible.

The MVD may be a difference between the motion vector of the target block and the predicted motion vector. The encoding apparatus 100 may calculate the MVD, and may generate an entropy-encoded MVD by applying entropy encoding to the MVD. The encoding apparatus 100 may generate a bitstream including an entropy-encoded MDV.

The MVD may be transmitted from the encoding device 100 to the decoding device 200 through a bitstream. The decoding apparatus 200 may extract the entropy-encoded MVD from the bitstream, and obtain the MVD by applying entropy decoding to the entropy-encoded MVD.

The decoding apparatus 200 may derive a motion vector of a target block by adding the MVD and the predicted motion vector. In other words, the motion vector of the target block derived from the decoding apparatus 200 may be the sum of the MVD and the motion vector candidate.

Also, the encoding apparatus 100 may generate entropy-encoded MVD resolution information by applying entropy encoding to the calculated MVD resolution information, and may generate a bitstream including entropy-encoded MVD resolution information. The decoding apparatus 200 may extract entropy-encoded MVD resolution information from the bitstream, and obtain MVD resolution information by applying entropy decoding to the entropy-encoded MVD resolution information. The decoding apparatus 200 may adjust the resolution of the MVD using the MVD resolution information.

Meanwhile, the encoding apparatus 100 may calculate MVD based on the affine model. The decoding apparatus 200 may derive the affine control motion vector of the target block through the sum of the MVD and the affine control motion vector candidates, and derive the motion vector for the sub-block using the afine control motion vector. have.

The reference direction may indicate a reference picture list used for prediction of a target block. For example, the reference direction may indicate one of the reference picture list L0 and the reference picture list L1.

The reference direction only indicates a reference picture list used for prediction of a target block, and may not indicate that directions of reference pictures are limited to a forward direction or a backward direction. That is to say, each of the reference picture list L0 and the reference picture list L1 may include pictures in the forward direction and/or the reverse direction.

When the reference direction is uni-direction, it may mean that one reference picture list is used. When the reference direction is bi-direction, it may mean that two reference picture lists are used. In other words, the reference direction can point to one of only the reference picture list L0, only the reference picture list L1, and two reference picture lists.

The reference picture index may indicate a reference picture used for prediction of a target block among reference pictures in the reference picture list. The encoding apparatus 100 may generate an entropy-encoded reference picture index by applying entropy encoding to the reference picture index, and may generate a bitstream including an entropy-encoded reference picture index. The entropy-encoded reference picture index may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. The decoding apparatus 200 may extract the entropy-coded reference picture index from the bitstream, and obtain the reference picture index by applying entropy decoding to the entropy-coded reference picture index.

When two reference picture lists are used for prediction of the target block. One reference picture index and one motion vector may be used for each reference picture list. In addition, when two reference picture lists are used for prediction of a target block, two prediction blocks may be specified for the target block. For example, the (final) prediction block of the target block may be generated through an average of two prediction blocks with respect to the target block or a weighted sum (weighed-sum).

The motion vector of the target block may be derived by the predicted motion vector index, MVD, reference direction, and reference picture index.

The decoding apparatus 200 may generate a prediction block for the target block based on the derived motion vector and the reference picture index. For example, the prediction block may be a reference block indicated by a motion vector derived in the reference picture indicated by the reference picture index.

As the motion vector of the target block itself is not encoded, the predicted motion vector index and the MVD are encoded, the amount of bits transmitted from the encoding apparatus 100 to the decoding apparatus 200 may be reduced, and encoding efficiency may be improved.

Motion information of a neighboring block reconstructed for the target block may be used. In a specific inter prediction mode, the encoding apparatus 100 may not separately encode motion information for a target block. The motion information of the target block is not encoded, and other information capable of inducing the motion information of the target block through motion information of the reconstructed neighboring block may be encoded instead. As other information is instead encoded, the amount of bits transmitted to the decoding apparatus 200 may be reduced, and encoding efficiency may be improved.

For example, as an inter prediction mode in which motion information of the target block is not directly encoded, there may be a skip mode and/or a merge mode. In this case, the encoding apparatus 100 and the decoding apparatus 200 may use an identifier and/or an index indicating which motion information of the reconstructed neighboring units is used as motion information of the target unit.

2) merge mode

As a method of deriving motion information of a target block, there is a merge. Merge may mean merging motions for a plurality of blocks. Merge may mean applying motion information of one block to another block. In other words, the merge mode may mean a mode in which motion information of a target block is derived from motion information of a neighboring block.

When the merge mode is used, the encoding apparatus 100 may perform prediction on motion information of a target block using motion information of a spatial candidate and/or motion information of a temporal candidate. The spatial candidate may include reconstructed spatial neighboring blocks that are spatially adjacent to the target block. The spatial neighboring block may include a left neighboring block and an upper neighboring block. The temporal candidate may include a call block. The terms "spatial candidate" and "spatial merge candidate" may be used with the same meaning, and may be used interchangeably. The terms "temporal candidate" and "temporal merge candidate" may be used with the same meaning, and may be used interchangeably.

The encoding apparatus 100 may obtain a prediction block through prediction. The encoding apparatus 100 may encode a residual block that is a difference between the target block and the prediction block.

2-1) Preparation of merge candidate list

When the merge mode is used, each of the encoding apparatus 100 and the decoding apparatus 200 may generate a merge candidate list using motion information of a spatial candidate and/or motion information of a temporal candidate. The motion information may include 1) a motion vector, 2) a reference picture index, and 3) a reference direction. The reference direction may be one-way or two-way. The reference direction may mean an inter prediction indicator.

The merge candidate list may include merge candidates. The merge candidate may be motion information. In other words, the merge candidate list may be a list in which motion information is stored.

The merge candidates may be motion information such as a temporal candidate and/or a spatial candidate. In other words, the merge candidate list may include motion information such as a temporal candidate and/or a spatial candidate.

In addition, the merge candidate list may include a new merge candidate generated by a combination of merge candidates already existing in the merge candidate list. In other words, the merge candidate list may include new motion information generated by a combination of motion information already existing in the merge candidate list.

In addition, the merge candidate list may include a history-based merge candidate. The history-based merge candidate may be motion information of a block encoded and/or decoded before the target block.

Also, the merge candidate list may include a merge candidate based on an average of two merge candidates.

The merge candidates may be specified modes for inducing inter prediction information. The merge candidate may be information indicating a specific mode for inducing inter prediction information. Inter prediction information of the target block may be derived according to the specified mode indicated by the merge candidate. In this case, the specified mode may include a process of inducing a series of inter prediction information. This specified mode may be an inter prediction information induction mode or a motion information induction mode.

Inter prediction information of a target block may be derived according to a mode indicated by a merge candidate selected by a merge index among merge candidates in the merge candidate list.

For example, the motion information induction modes in the merge candidate list may be at least one of 1) a subblock-based motion information induction mode and 2) an affine motion information induction mode.

Also, the merge candidate list may include motion information of a zero vector. The zero vector may be referred to as a zero merge candidate.

In other words, the motion information in the merge candidate list includes: 1) motion information of a spatial candidate, 2) motion information of a temporal candidate, 3) motion information generated by a combination of motion information already existing in the merge candidate list, and 4) zero vector. It may be at least one of.

The motion information may include 1) a motion vector, 2) a reference picture index, and 3) a reference direction. The reference direction may be referred to as an inter prediction indicator. The reference direction may be one-way or two-way. The unidirectional reference direction may indicate L0 prediction or L1 prediction.

The merge candidate list may be generated before prediction by the merge mode is performed.

The number of merge candidates in the merge candidate list may be predefined. The encoding apparatus 100 and the decoding apparatus 200 may add a merge candidate to the merge candidate list according to a predefined method and a predefined ranking so that the merge candidate list has a predefined number of merge candidates. The merge candidate list of the encoding apparatus 100 and the merge candidate list of the decoding apparatus 200 may be the same through a predefined method and a predefined ranking.

Merge can be applied in units of CU or PU. When the merge is performed in units of CU or PU, the encoding apparatus 100 may transmit a bitstream including predefined information to the decoding apparatus 200. For example, the predefined information includes: 1) information indicating whether to perform a merge for each block partition, and 2) a block to be merged with a block among spatial and/or temporal candidate blocks for the target block. Can include information about whether it is.

2-2) Search for motion vectors using merge candidate list

The encoding apparatus 100 may determine a merge candidate to be used for encoding the target block. For example, the encoding apparatus 100 may perform predictions on a target block by using merge candidates in the merge candidate list and generate residual blocks for the merge candidates. The encoding apparatus 100 may use a merge candidate that requires a minimum cost in prediction and encoding of a residual block for encoding a target block.

In addition, the encoding apparatus 100 may determine whether to use the merge mode in encoding the target block.

2-3) Transmission of inter prediction information

The encoding apparatus 100 may generate a bitstream including inter prediction information required for inter prediction. The encoding apparatus 100 may generate entropy-encoded inter prediction information by performing entropy encoding on the inter prediction information, and may transmit a bitstream including entropy-encoded inter prediction information to the decoding apparatus 200. Entropy-encoded inter prediction information may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through the bitstream. The decoding apparatus 200 may extract entropy-encoded inter prediction information from a bitstream, and obtain inter-prediction information by performing entropy decoding on the entropy-encoded inter prediction information.

The decoding apparatus 200 may perform inter prediction on a target block using inter prediction information of a bitstream.

The inter prediction information may include 1) mode information indicating whether a merge mode is used, 2) a merge index, and 3) correction information.

In addition, the inter prediction information may include a residual signal.

The decoding apparatus 200 may acquire the merge index from the bitstream only when the mode information indicates that the merge mode is used.

The mode information may be a merge flag. The unit of mode information may be a block. The information on the block may include mode information, and the mode information may indicate whether a merge mode is applied to the block.

The merge index may indicate a merge candidate used for prediction of a target block among merge candidates included in the merge candidate list. Alternatively, the merge index may indicate which block of neighboring blocks spatially or temporally adjacent to the target block is to be merged.

The encoding apparatus 100 may select a merge candidate having the highest encoding performance among merge candidates included in the merge candidate list, and may set a value of a merge index to indicate the selected merge candidate.

The correction information may be information used for correction of a motion vector. The encoding apparatus 100 may generate correction information. The decoding apparatus 200 may correct the motion vector of the merge candidate selected by the merge index based on the correction information.

The correction information may include at least one of information indicating whether or not to be corrected, information on a correction direction, and information on a correction size. A prediction mode for correcting a motion vector based on signaled correction information may be referred to as a merge mode having a motion vector difference.

2-4) Inter prediction in merge mode using inter prediction information

The decoding apparatus 200 may perform prediction on a target block by using a merge candidate indicated by a merge index among merge candidates included in the merge candidate list.

The motion vector of the target block may be specified by the motion vector of the merge candidate indicated by the merge index, a reference picture index, and a reference direction.

3) Skip mode

The skip mode may be a mode in which motion information of a spatial candidate or motion information of a temporal candidate is applied as it is to a target block. Also, the skip mode may be a mode that does not use a residual signal. That is to say, when the skip mode is used, the reconstructed block may be the same as the prediction block.

The difference between the merge mode and the skip mode may be whether a residual signal is transmitted or used. In other words, the skip mode can be similar to the merge mode except that no residual signal is transmitted or used.

When the skip mode is used, the encoding apparatus 100 transmits information indicating which of the spatial candidate or temporal candidate blocks the motion information of the target block is used as the motion information of the target block to the decoding apparatus 200 through a bitstream. Can be transmitted. The encoding apparatus 100 may generate entropy-encoded information by performing entropy encoding on such information, and may signal the entropy-encoded information to the decoding apparatus 200 through a bitstream. The decoding apparatus 200 may extract entropy-encoded information from a bitstream, and obtain information by performing entropy decoding on the entropy-encoded information.

In addition, when the skip mode is used, the encoding apparatus 100 may not transmit other syntax element information such as MVD to the decoding apparatus 200. For example, when the skip mode is used, the encoding apparatus 100 may not signal to the decoding apparatus 200 a syntax element related to at least one of an MVD, a coded block flag, and a transform coefficient level.

3-1) Preparation of merge candidate list

The skip mode can also use a merge candidate list. In other words, the merge candidate list can be used in both the merge mode and the skip mode. In this respect, the merge candidate list may be referred to as “skip candidate list” or “merge/skip candidate list”.

Alternatively, the skip mode may use a separate candidate list different from the merge mode. In this case, in the following description, the merge candidate list and the merge candidate may be replaced with a skip candidate list and a skip candidate, respectively.

The merge candidate list may be generated before prediction by the skip mode is performed.

3-2) Search for motion vectors using merge candidate list

The encoding apparatus 100 may determine a merge candidate to be used for encoding the target block. For example, the encoding apparatus 100 may perform predictions on a target block by using merge candidates of a merge candidate list. The encoding apparatus 100 may use a merge candidate that requires a minimum cost in prediction for encoding a target block.

In addition, the encoding apparatus 100 may determine whether to use the skip mode in encoding the target block.

3-3) Transmission of inter prediction information

The encoding apparatus 100 may generate a bitstream including inter prediction information required for inter prediction. The decoding apparatus 200 may perform inter prediction on a target block using inter prediction information of a bitstream.

The inter prediction information may include 1) mode information indicating whether a skip mode is used and 2) a skip index.

The skip index may be the same as the merge index described above.

When the skip mode is used, the target block may be encoded without a residual signal. Inter prediction information may not include a residual signal. Alternatively, the bitstream may not include a residual signal.

The decoding apparatus 200 may obtain the skip index from the bitstream only when the mode information indicates that the skip mode is used. As described above, the merge index and skip index may be the same. The decoding apparatus 200 may obtain the skip index from the bitstream only when the mode information indicates that the merge mode or the skip mode is used.

The skip index may indicate a merge candidate used for prediction of a target block among merge candidates included in the merge candidate list.

3-4) Inter prediction in skip mode using inter prediction information

The decoding apparatus 200 may perform prediction on a target block by using a merge candidate indicated by a skip index among merge candidates included in the merge candidate list.

The motion vector of the target block may be specified by the motion vector of the merge candidate indicated by the skip index, the reference picture index, and the reference direction.

4) Current picture reference mode

The current picture reference mode may mean a prediction mode using a pre-rebuilt region in a target picture to which the target block belongs.

A motion vector for specifying the pre-rebuilt region may be used. Whether or not the target block is coded in the current picture reference mode may be determined using a reference picture index of the target block.

A flag or index indicating whether the target block is a block coded in the current picture reference mode may be signaled from the encoding apparatus 100 to the decoding apparatus 200. Alternatively, whether the target block is a block coded in the current picture reference mode may be inferred through the reference picture index of the target block.

When the target block is encoded in the current picture reference mode, the target picture may exist at a fixed position or at an arbitrary position in the reference picture list for the target block.

For example, the fixed position may be a position where the value of the reference picture index is 0 or the last position.

When the target picture exists at an arbitrary position in the reference picture list, a separate reference picture index indicating such an arbitrary position may be signaled from the encoding apparatus 100 to the decoding apparatus 200.

5) subblock merge mode

The sub-block merge mode may mean a mode in which motion information is derived for a sub-block of a CU.

When the sub-block merge mode is applied, motion information of the collocated sub-block of the target sub-block in the reference image (ie, sub-block based temporal merge candidate) and/or affine control point motion vector A subblock merge candidate list may be generated using a merge candidate (affine control point motion vector merge candidate).

6) triangle partition mode

In the triangulation mode, divided target blocks may be generated by dividing the target block in a diagonal direction. For each divided target block, motion information of each divided target block may be derived, and a prediction sample for each divided target block may be derived using the derived motion information. A prediction sample of the target block may be derived through a weighted sum of the prediction samples of the divided target blocks.

7) Inter intra combined prediction mode

The inter-intra combined prediction mode may be a mode in which a prediction sample of a target block is derived using a weighted sum of a prediction sample generated by inter prediction and a prediction sample generated by intra prediction.

In the above-described modes, the decoding apparatus 200 may perform self-correction on the derived motion information. For example, the decoding apparatus 200 may search for a specific area based on a reference block indicated by the derived motion information to search for motion information having a sum of absolute differences (SAD). In addition, the searched motion information can be derived as corrected motion information.

In the above-described modes, the decoding apparatus 200 may perform compensation for a prediction sample derived through inter prediction using an optical flow.

In the above-described AMVP mode, merge mode, skip mode, and the like, motion information to be used for prediction of a target block among motion information in a list may be specified through an index on a list.

In order to improve encoding efficiency, the encoding apparatus 100 may signal only an index of an element that causes the least cost in inter prediction of a target block among the elements of the list. The encoding apparatus 100 may encode the index and may signal the encoded index.

Accordingly, the above-described lists (ie, the prediction motion vector candidate list and the merge candidate list) may be derived in the same manner based on the same data in the encoding apparatus 100 and the decoding apparatus 200. Here, the same data may include a reconstructed picture and a reconstructed block. Also, in order to specify an element by index, the order of the elements in the list may need to be constant.

10 shows spatial candidates according to an example.

In Fig. 10, the locations of spatial candidates are shown.

The large block in the middle can represent the target block. Five small blocks can represent spatial candidates.

The coordinates of the target block may be (xP, yP), and the size of the target block may be (nPSW, nPSH).

The spatial candidate A ₀ may be a block adjacent to the lower left corner of the target block. A ₀ may be a block occupying a pixel of coordinates (xP-1, yP + nPSH + 1).

The spatial candidate A ₁ may be a block adjacent to the left side of the target block. A ₁ may be the lowest block among blocks adjacent to the left of the target block. Alternatively, A ₁ may be a block adjacent to the top of A ₀ . A ₁ may be a block occupying a pixel of coordinates (xP-1, yP + nPSH).

The spatial candidate B ₀ may be a block adjacent to the upper right corner of the target block. B ₀ may be a block occupying a pixel of coordinates (xP + nPSW + 1, yP-1).

Spatial candidate B ₁ may be a block adjacent to the top of the target block. B ₁ may be the rightmost block among blocks adjacent to the top of the target block. Alternatively, B ₁ may be a block adjacent to the left side of B ₀ . B ₁ may be a block occupying a pixel of coordinates (xP + nPSW, yP-1).

Spatial candidate B ₂ may be a block adjacent to the upper left corner of the target block. B ₂ may be a block occupying a pixel of the coordinates (xP-1, yP-1).

Determination of the availability of spatial and temporal candidates

In order to include motion information of a spatial candidate or motion information of a temporal candidate in a list, it is necessary to determine whether motion information of a spatial candidate or motion information of a temporal candidate is available.

Hereinafter, the candidate block may include a spatial candidate and a temporal candidate.

For example, the determination may be made by sequentially applying steps 1) to 4) below.

Step 1) If the PU including the candidate block is outside the boundary of the picture, the availability of the candidate block may be set to false. "Availability is set to false" may have the same meaning as "availability is set to not available".

Step 2) If the PU including the candidate block is outside the boundary of the slice, the availability of the candidate block may be set to false. When the target block and the candidate block are located in different slices, the availability of the candidate block may be set to false.

Step 3) If the PU including the candidate block is outside the boundary of the tile, the availability of the candidate block may be set to false. When the target block and the candidate block are located in different tiles, the availability of the candidate block may be set to false.

Step 4) If the prediction mode of the PU including the candidate block is the intra prediction mode, the availability of the candidate block may be set to false. If the PU including the candidate block does not use inter prediction, the availability of the candidate block may be set to false.

11 is a diagram illustrating a sequence of adding motion information of spatial candidates to a merge list according to an example.

As illustrated in FIG. 11, in adding motion information of spatial candidates to the merge list, an order of A ₁ , B ₁ , B ₀ , A ₀ and B ₂ may be used. That is, motion information of available spatial candidates may be added to the merge list in the order of A ₁ , B ₁ , B ₀ , A ₀ and B ₂ .

How to derive a merge list in merge mode and skip mode

As described above, the maximum number of merge candidates in the merge list may be set. The set maximum number is displayed as N. The set number may be transmitted from the encoding device 100 to the decoding device 200. The slice header of a slice may include N. In other words, the maximum number of merge candidates in the merge list for the target block of the slice may be set by the slice header. For example, by default, the value of N may be 5.

Motion information (ie, merge candidate) may be added to the merge list in the order of steps 1) to 4) below.

Step 1) Among the spatial candidates, available spatial candidates may be added to the merge list. Motion information of available spatial candidates may be added to the merge list in the order shown in FIG. 10. In this case, when motion information of an available spatial candidate overlaps with other motion information already existing in the merge list, the motion information may not be added to the merge list. Checking whether or not it overlaps with other motion information existing in the list may be abbreviated as a "redundancy check".

The number of motion information to be added may be at most N.

Step 2) If the number of motion information in the merge list is smaller than N and a temporal candidate is available, motion information of the temporal candidate may be added to the merge list. In this case, when motion information of an available temporal candidate overlaps with other motion information already existing in the merge list, the motion information may not be added to the merge list.

Step 3) If the number of motion information in the merge list is smaller than N and the type of the target slice is "B", the combined motion information generated by combined bi-prediction will be added to the merge list. I can.

The target slice may be a slice including the target block.

The combined motion information may be a combination of L0 motion information and L1 motion information. The L0 motion information may be motion information referring only to the reference picture list L0. The L1 motion information may be motion information referring only to the reference picture list L1.

In the merge list, there may be one or more L0 motion information. Also, in the merge list, there may be one or more L1 motion information.

The combined motion information may be one or more. In generating the combined motion information, which L0 motion information and which L1 motion information among one or more L0 motion information and one or more L1 motion information are to be used may be predefined. One or more combined motion information may be generated in a predefined order by combined bidirectional prediction using a pair of different motion information in the merge list. One of the pairs of different motion information may be L0 motion information and the other may be L1 motion information.

For example, the combined motion information added with the highest priority may be a combination of L0 motion information having a merge index of 0 and L1 motion information having a merge index of 1. If the motion information having a merge index of 0 is not L0 motion information or the motion information having a merge index of 1 is not L1 motion information, the combined motion information may not be generated and added. The motion information added next may be a combination of L0 motion information having a merge index of 1 and L1 motion information having a merge index of 0. The following specific combinations may follow other combinations of video encoding/decoding fields.

In this case, when the combined motion information overlaps with other motion information already existing in the merge list, the combined motion information may not be added to the merge list.

Step 4) If the number of motion information in the merge list is smaller than N, zero vector motion information may be added to the merge list.

The zero vector motion information may be motion information in which the motion vector is a zero vector.

There may be one or more zero vector motion information. Reference picture indices of one or more zero vector motion information may be different from each other. For example, a value of the reference picture index of the first zero vector motion information may be 0. The value of the reference picture index of the second zero vector motion information may be 1.

The number of zero vector motion information may be the same as the number of reference pictures in the reference picture list.

The reference direction of the zero vector motion information may be bidirectional. Both motion vectors may be zero vectors. The number of zero vector motion information may be the smaller of the number of reference pictures in the reference picture list L0 and the number of reference pictures in the reference picture list L1. Alternatively, when the number of reference pictures in the reference picture list L0 and the number of reference pictures in the reference picture list L1 are different from each other, a unidirectional reference direction may be used for a reference picture index that can be applied only to one reference picture list.

The encoding apparatus 100 and/or the decoding apparatus 200 may sequentially add zero vector motion information to the merge list while changing the reference picture index.

When the zero vector motion information overlaps with other motion information already existing in the merge list, the zero vector motion information may not be added to the merge list.

The order of steps 1) to 4) described above is merely exemplary, and the order of steps may be interchanged. In addition, some of the steps may be omitted according to predefined conditions.

Derivation method of predicted motion vector candidate list in AMVP mode

The maximum number of predicted motion vector candidates in the predicted motion vector candidate list may be predefined. The predefined maximum number is denoted by N. For example, the predefined maximum number may be 2.

Motion information (ie, a predicted motion vector candidate) may be added to the predicted motion vector candidate list in the order of steps 1) to 3) below.

Step 1) Available spatial candidates among the spatial candidates may be added to the prediction motion vector candidate list. Spatial candidates may include a first spatial candidate and a second spatial candidate.

The first spatial candidate may be one of A ₀ , A ₁ , scaled A _0, and scaled A ₁ . The second spatial candidate may be one of B ₀ , B ₁ , B ₂ , scaled B ₀ , scaled B _1, and scaled B ₂ .

Motion information of the available spatial candidates may be added to the prediction motion vector candidate list in the order of the first spatial candidate and the second spatial candidate. In this case, when motion information of an available spatial candidate overlaps with other motion information already existing in the predicted motion vector candidate list, the motion information may not be added to the predicted motion vector candidate list. That is, when the value of N is 2, if the motion information of the second spatial candidate is the same as the motion information of the first spatial candidate, the motion information of the second spatial candidate may not be added to the predicted motion vector candidate list.

The number of motion information to be added may be at most N.

Step 2) If the number of motion information in the predicted motion vector candidate list is smaller than N and a temporal candidate is available, motion information of the temporal candidate may be added to the predicted motion vector candidate list. In this case, when motion information of an available temporal candidate overlaps with other motion information already existing in the predicted motion vector candidate list, the motion information may not be added to the predicted motion vector candidate list.

Step 3) If the number of motion information in the predicted motion vector candidate list is smaller than N, zero vector motion information may be added to the predicted motion vector candidate list.

There may be one or more zero vector motion information. Reference picture indices of one or more zero vector motion information may be different from each other.

The encoding apparatus 100 and/or the decoding apparatus 200 may sequentially add zero vector motion information to the predicted motion vector candidate list while changing the reference picture index.

When the zero vector motion information overlaps with other motion information already existing in the predicted motion vector candidate list, the zero vector motion information may not be added to the predicted motion vector candidate list.

The description of the zero vector motion information described above for the merge list may also be applied to the zero vector motion information. Redundant descriptions are omitted.

The order of steps 1) to 3) described above is merely exemplary, and the order between steps may be interchanged. In addition, some of the steps may be omitted according to predefined conditions.

12 illustrates a process of transformation and quantization according to an example.

As shown in FIG. 12, a quantized level may be generated by performing a transform and/or quantization process on the residual signal.

The residual signal may be generated as a difference between the original block and the prediction block. Here, the prediction block may be a block generated by intra prediction or inter prediction.

The residual signal may be transformed into the frequency domain through a transformation process that is part of a quantization process.

The transformation kernel used for transformation may include a variety of DCT kernels such as Discrete Cosine Transform (DCT) type 2 (DCT-II) and a Discrete Sine Transform (DST) kernel. .

These transform kernels may perform a separable transform or a 2D (2D) non-separable transform on the residual signal. The separable transform may be a transform that performs a 1D (1D) transform on the residual signal in each of a horizontal direction and a vertical direction.

DCT type and DST type adaptively used for 1D conversion may include DCT-V, DCT-VIII, DST-I and DST-VII in addition to DCT-II as indicated in Tables 3 and 4 below. have.

[Table 3]

[Table 4]

As shown in Tables 3 and 4, a transform set may be used to derive a DCT type or a DST type to be used for transformation. Each transform set may include a plurality of transform candidates. Each transformation candidate may be a DCT type or a DST type.

Table 5 below shows an example of a transform set applied to a horizontal direction and a transform set applied to a vertical direction according to an intra prediction mode.

[Table 5]

In Table 5, the number of the vertical direction transform set applied to the horizontal direction of the residual signal and the number of the horizontal direction transform set are displayed according to the intra prediction mode of the target block.

As illustrated in Table 5, transform sets applied in the horizontal direction and the vertical direction may be predefined according to the intra prediction mode of the target block. The encoding apparatus 100 may perform transform and inverse transform on the residual signal by using transforms included in a transform set corresponding to the intra prediction mode of the target block. Also, the decoding apparatus 200 may perform inverse transform on the residual signal by using a transform included in a transform set corresponding to the intra prediction mode of the target block.

In this transform and inverse transform, a transform set applied to the residual signal may be determined as exemplified in Tables 3, 4, and 5, and may not be signaled. The transformation indication information may be signaled from the encoding device 100 to the decoding device 200. The transformation indication information may be information indicating which transformation candidate is used among a plurality of transformation candidates included in the transformation set applied to the residual signal.

For example, when the size of the target block is 64x64 or less, all three transform sets may be configured according to the intra prediction mode. An optimal transform method may be selected from among 9 multiple transform methods due to a combination of three transforms in the horizontal direction and three transforms in the vertical direction. Encoding efficiency can be improved by encoding and/or decoding the residual signal using such an optimal transformation method.

In this case, for at least one of the vertical transformation and the horizontal transformation, information on which transformation among transformations belonging to the transformation set is used may be entropy encoded and/or decoded. Truncated unary binarization may be used to encode and/or decode such information.

The method using various transforms as described above can be applied to a residual signal generated by intra prediction or inter prediction.

The transformation may include at least one of a first order transformation and a second order transformation. A transform coefficient may be generated by performing a first-order transform on the residual signal, and a second-order transform coefficient may be generated by performing a second-order transform on the transform coefficient.

The primary transformation may be referred to as a primary transformation. In addition, the first-order transform may be referred to as an adaptive multiple transform (AMT). As described above, AMT may mean that different transformations are applied to each of the 1D directions (ie, vertical and horizontal directions).

The second-order transform may be a transform for improving the energy concentration of the transform coefficient generated by the first-order transform. Like the first-order transform, the second-order transform may be a separable transform or a non-separable transform. The non-separable transform may be a Non-Separable Secondary Transform (NSST).

The first-order transformation may be performed using at least one of a plurality of predefined transformation methods. For example, a plurality of predefined transformation methods include Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), and Karhunen-Loeve Transform (KLT) based transformation. It may include.

In addition, the first-order transformation may be a transformation having various types according to a kernel function defining DCT or DST.

For example, the first-order transform includes transforms such as DCT-2, DCT-5, DCT-7, DST-7, DST-1, DST-8, and DCT-8 according to the transform kernel shown in Table 6 below. can do. In Table 6, various transform types and transform kernel functions for Multiple Transform Selection (MTS) are illustrated.

MTS may mean that a combination of one or more DCT and/or DST conversion kernels is selected for conversion of the residual signal in the horizontal and/or vertical directions.

[Table 6]

In Table 6, i and j may be integer values of 0 or more and N-1 or less.

A secondary transform may be performed on transform coefficients generated by performing the first transform.

As with the first-order transform, a transform set can be defined in the second-order transform. Methods for deriving and/or determining a transform set as described above can be applied not only to a first order transform but also to a second order transform.

The first and second transformations can be determined for a specified object.

For example, a first order transform and a second order transform may be applied to a signal component of one or more of a luma component and a chroma component. Whether to apply the first-order transform and/or the second-order transform may be determined according to at least one of coding parameters for the target block and/or the neighboring block. For example, whether to apply a first-order transform and/or a second-order transform may be determined by the size and/or shape of the target block.

In the encoding apparatus 100 and the decoding apparatus 200, transformation information indicating a transformation method used for an object may be derived by using specified information.

For example, the transformation information may include an index of a transformation to be used for a first order transformation and/or a second order transformation. Alternatively, the transformation information may indicate that the first transformation and/or the second transformation are not used.

For example, when the target of the first transformation and the second transformation is the target block, the transformation method(s) applied to the first transformation and/or the second transformation indicated by the transformation information is applied to the target block and/or a neighboring block. It may be determined according to at least one of the coding parameters for.

Alternatively, transformation information indicating a transformation method for a specified object may be signaled from the encoding device 100 to the decoding device 200.

For example, for one CU, whether a first-order transformation is used, an index indicating a first-order transformation, whether a second-order transformation is used, an index indicating a second-order transformation, etc. may be derived from the decoding apparatus 200 as transformation information. have. Alternatively, for one CU, transformation information indicating whether a first-order transformation is used, an index indicating a first-order transformation, whether a second-order transformation is used, an index indicating a second-order transformation, and the like may be signaled.

Quantized transform coefficients (ie, quantized levels) may be generated by performing quantization on a residual signal or a result generated by performing a first-order transform and/or a second-order transform.

13 shows diagonal scanning according to an example.

14 shows horizontal scanning according to an example.

15 shows vertical scanning according to an example.

The quantized transform coefficients may be scanned according to at least one of (up-right) diagonal scanning, vertical scanning, and horizontal scanning according to at least one of an intra prediction mode, a block size, and a block shape. The block may be a transform unit.

Each scan can start at a specified start point and end at a specified end point.

For example, quantized transform coefficients may be changed into a one-dimensional vector form by scanning coefficients of a block using diagonal scanning of FIG. 13. Alternatively, horizontal scanning of FIG. 14 or vertical scanning of FIG. 15 may be used instead of diagonal scanning according to a block size and/or intra prediction mode.

Vertical scanning may be scanning a two-dimensional block shape coefficient in a column direction. Horizontal scanning may be scanning a two-dimensional block shape coefficient in a row direction.

That is, it may be determined which of diagonal scanning, vertical scanning and horizontal scanning will be used according to the size of the block and/or the inter prediction mode.

As shown in FIGS. 13, 14, and 15, quantized transform coefficients may be scanned in a diagonal direction, a horizontal direction, or a vertical direction.

The quantized transform coefficients can be expressed in a block form. The block may include a plurality of sub-blocks. Each sub-block may be defined according to a minimum block size or a minimum block type.

In scanning, the scanning order according to the type or direction of scanning may be first applied to sub-blocks. In addition, a scanning order according to a scanning direction may be applied to quantized transform coefficients in a sub-block.

For example, as shown in FIGS. 13, 14, and 15, when the size of the target block is 8x8, transform coefficients quantized by the first-order transformation, the second-order transformation, and quantization of the residual signal of the target block are Can be created. Thereafter, one of three scanning orders may be applied to four 4x4 sub-blocks, and quantized transform coefficients may be scanned for each 4x4 sub-block according to the scanning order.

The encoding apparatus 100 may generate entropy-coded quantized transform coefficients by performing entropy encoding on the scanned quantized transform coefficients, and may generate a bitstream including entropy-coded quantized transform coefficients. .

The decoding apparatus 200 may extract entropy-coded quantized transform coefficients from the bitstream, and generate quantized transform coefficients by performing entropy decoding on the entropy-coded quantized transform coefficients. Quantized transform coefficients may be arranged in a two-dimensional block form through inverse scanning. In this case, as a method of reverse scanning, at least one of a (top right) diagonal scan, a vertical scan, and a horizontal scan may be performed.

In the decoding apparatus 200, inverse quantization may be performed on quantized transform coefficients. Depending on whether or not the second-order inverse transform is performed, the second-order inverse transform may be performed on the result generated by performing the inverse quantization. Also, depending on whether or not the first-order inverse transform is performed, the first-order inverse transform may be performed on the result generated by the second-order inverse transform. A reconstructed residual signal may be generated by performing a first-order inverse transform on a result generated by performing a second-order inverse transform.

For the luma component reconstructed through intra prediction or inter prediction, inverse mapping of a dynamic range may be performed before in-loop filtering.

The dynamic range can be divided into 16 equal pieces, and a mapping function for each piece can be signaled. The mapping function may be signaled at the slice level or the tile group level.

The inverse mapping function for performing inverse mapping may be derived based on the mapping function.

In-loop filtering, storage of a reference picture, and motion compensation may be performed in the demapped region.

The prediction block generated through inter prediction may be converted into a mapped region by mapping using a mapping function, and the converted prediction block may be used to generate a reconstructed block. However, since intra prediction is performed in the mapped region, a prediction block generated by intra prediction may be used to generate a reconstructed block without mapping and/or demapping.

For example, when the target block is a chroma component residual block, the residual block may be converted into an inversely mapped area by performing scaling on the chroma component of the mapped area.

Whether scaling is available may be signaled at the slice level or the tile group level.

For example, scaling can be applied only when mapping for luma components is available, and division of luma components and division of chroma components follow the same tree structure.

Scaling may be performed based on an average of values of samples of the luma prediction block corresponding to the chroma prediction block. In this case, when the target block uses inter prediction, the luma prediction block may mean a mapped luma prediction block.

A value required for scaling may be derived by referring to the look-up table using the index of a piece to which the average of the values of the samples of the luma prediction block belongs.

By performing scaling on the residual block using the finally derived value, the residual block can be converted into an inversely mapped region. Thereafter, for the chroma component block, reconstruction, intra prediction, inter prediction, in-loop filtering, and storage of a reference picture may be performed in the demapped region.

For example, information indicating whether mapping and/or inverse mapping of the luma component and chroma component is available may be signaled through a sequence parameter set.

The prediction block of the target block may be generated based on a block vector. The block vector may represent a displacement between a target block and a reference block. The reference block may be a block in the target image.

In this way, a prediction mode for generating a prediction block with reference to a target image may be referred to as an Intra Block Copy (IBC) mode.

The IBC mode can be applied to a CU of a specified size. For example, the IBC mode can be applied to the MxN CU. Here, M and N may be 64 or less.

The IBC mode may include a skip mode, a merge mode, and an AMVP mode. In the case of a skip mode or a merge mode, a merge candidate list may be configured, and a merge index may be signaled to specify one merge candidate among merge candidates of the merge candidate list. The specified merge candidate block vector may be used as the block vector of the target block.

In the case of the AMVP mode, a differential block vector may be signaled. In addition, the prediction block vector may be derived from a left neighboring block and an upper neighboring block of the target block. In addition, an index on which neighboring block is to be used may be signaled.

The prediction block of the IBC mode may be included in the target CTU or the left CTU, and may be limited to a block within a previously reconstructed region. For example, the value of the block vector may be limited so that the prediction block of the target block is located within a specified region. The specified area may be an area of three 64x64 blocks that are encoded and/or decoded prior to the 64x64 block including the target block. By limiting the value of the block vector as described above, memory consumption and device complexity according to the implementation of the IBC mode may be reduced.

16 is a structural diagram of an encoding apparatus according to an embodiment.

The encoding device 1600 may correspond to the encoding device 100 described above.

The encoding apparatus 1600 includes a processing unit 1610, a memory 1630, a user interface (UI) input device 1650, a UI output device 1660, and a storage that communicate with each other through a bus 1690. (1640) may be included. In addition, the encoding apparatus 1600 may further include a communication unit 1620 connected to the network 1699.

The processing unit 1610 may be a semiconductor device that executes processing instructions stored in a central processing unit (CPU), a memory 1630 or the storage 1640. The processing unit 1610 may be at least one hardware processor.

The processing unit 1610 may generate and process signals, data, or information input to the encoding device 1600, output from the encoding device 1600, or used inside the encoding device 1600. Inspection, comparison, and judgment related to data or information can be performed. That is to say, in the embodiment, generation and processing of data or information, and inspection, comparison, and determination related to data or information may be performed by the processing unit 1610.

The processing unit 1610 includes an inter prediction unit 110, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, and inverse quantization. A unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190 may be included.

Inter prediction unit 110, intra prediction unit 120, switch 115, subtractor 125, transform unit 130, quantization unit 140, entropy encoding unit 150, inverse quantization unit 160, At least some of the inverse transform unit 170, the adder 175, the filter unit 180, and the reference picture buffer 190 may be program modules and may communicate with an external device or system. Program modules may be included in the encoding apparatus 1600 in the form of an operating system, an application program module, and other program modules.

Program modules may be physically stored on various known storage devices. In addition, at least some of these program modules may be stored in a remote storage device capable of communicating with the encoding device 1600.

Program modules are routines, subroutines, programs, objects, components, and data that perform functions or operations according to an embodiment or implement abstract data types according to an embodiment. The structure (data structure) may be included, but is not limited thereto.

The program modules may be composed of an instruction or code executed by at least one processor of the encoding apparatus 1600.

The processing unit 1610 includes an inter prediction unit 110, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, and inverse quantization. Commands or codes of the unit 160, the inverse transform unit 170, the adder 175, the filter unit 180, and the reference picture buffer 190 may be executed.

The storage unit may represent the memory 1630 and/or the storage 1640. The memory 1630 and the storage 1640 may be various types of volatile or nonvolatile storage media. For example, the memory 1630 may include at least one of a ROM 1631 and a RAM 1632.

The storage unit may store data or information used for the operation of the encoding device 1600. In an embodiment, data or information of the encoding apparatus 1600 may be stored in the storage unit.

For example, the storage unit may store pictures, blocks, lists, motion information, inter prediction information, and bitstreams.

The encoding apparatus 1600 may be implemented in a computer system including a recording medium that can be read by a computer.

The recording medium may store at least one module required to operate the encoding apparatus 1600. The memory 1630 may store at least one module, and may be configured to execute at least one module by the processor 1610.

A function related to communication of data or information of the encoding apparatus 1600 may be performed through the communication unit 1620.

For example, the communication unit 1620 may transmit the bitstream to the decoding apparatus 1700 to be described later.

17 is a structural diagram of a decoding apparatus according to an embodiment.

The decoding device 1700 may correspond to the decoding device 200 described above.

The decoding apparatus 1700 includes a processing unit 1710, a memory 1730, a user interface (UI) input device 1750, a UI output device 1760, and a storage that communicate with each other through a bus 1790. (1740) may be included. Also, the decoding apparatus 1700 may further include a communication unit 1720 connected to the network 1799.

The processing unit 1710 may be a central processing unit (CPU), a semiconductor device that executes processing instructions stored in the memory 1730 or the storage 1740. The processing unit 1710 may be at least one hardware processor.

The processing unit 1710 may generate and process signals, data, or information input to the decoding device 1700, output from the decoding device 1700, or used inside the decoding device 1700. Inspection, comparison, and judgment related to data or information can be performed. That is to say, in the embodiment, generation and processing of data or information, and inspection, comparison, and determination related to data or information may be performed by the processing unit 1710.

The processing unit 1710 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, an inter prediction unit 250, a switch 245, an adder 255, and a filter. It may include a sub 260 and a reference picture buffer 270.

Entropy decoding unit 210, inverse quantization unit 220, inverse transform unit 230, intra prediction unit 240, inter prediction unit 250, switch 245, adder 255, filter unit 260 and At least some of the reference picture buffers 270 may be program modules and may communicate with an external device or system. Program modules may be included in the decoding apparatus 1700 in the form of an operating system, an application program module, and other program modules.

Program modules may be physically stored on various known storage devices. In addition, at least some of these program modules may be stored in a remote storage device capable of communicating with the decoding device 1700.

Program modules are routines, subroutines, programs, objects, components, and data that perform functions or operations according to an embodiment or implement abstract data types according to an embodiment. The structure (data structure) may be included, but is not limited thereto.

The program modules may be composed of instructions or codes executed by at least one processor of the decoding apparatus 1700.

The processing unit 1710 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, an inter prediction unit 250, a switch 245, an adder 255, and a filter. Commands or codes of the unit 260 and the reference picture buffer 270 may be executed.

The storage unit may represent the memory 1730 and/or the storage 1740. The memory 1730 and the storage 1740 may be various types of volatile or nonvolatile storage media. For example, the memory 1730 may include at least one of a ROM 1173 and a RAM 1732.

The storage unit may store data or information used for the operation of the decoding apparatus 1700. In an embodiment, data or information of the decoding apparatus 1700 may be stored in a storage unit.

For example, the storage unit may store pictures, blocks, lists, motion information, inter prediction information, and bitstreams.

The decoding apparatus 1700 may be implemented in a computer system including a recording medium that can be read by a computer.

The recording medium may store at least one module required for the decoding apparatus 1700 to operate. The memory 1730 may store at least one module, and at least one module may be configured to be executed by the processing unit 1710.

A function related to data or information communication of the decoding apparatus 1700 may be performed through the communication unit 1720.

For example, the communication unit 1720 may receive a bitstream from the encoding device 1600.

Hereinafter, a filter according to an embodiment will be described.

For a block and a boundary between blocks, whether to perform filtering, a filtering boundary strength, and a filtering method (or type) may be determined, and filtering may be performed according to the determination.

The filtering method may mean performing filtering using different filter lengths or different filter coefficients.

The filter may mean a deblocking filter. The filter of the embodiment may correspond to the filter unit 180 described above with reference to FIG. 1 and/or the filter unit 260 described above with reference to FIG. 2.

The block to which the filter is applied is a picture, a sub-picture, a slice, a tile, a brick, a coding tree unit (CTU), a coding unit (CU), a prediction unit (PU), and a transform unit ( Transform Unit; TU), a coding block, a prediction block, a transform block, a sub-block, and the like, which may mean at least one of units determined according to division of an image. Here, the sub-block may be a unit generated by further dividing at least one of a CU, a PU, and a TU, such as a sub-CU, a sub-PU, and a sub-TU.

Hereinafter, the target block may be a block to which filtering is currently performed. Alternatively, the target block may be a block including a boundary that is the target of the current filtering. Alternatively, the boundary of the target block may be the target of filtering. The neighboring block may be a block adjacent to the target block. The neighboring block may be a block spatially adjacent to the target block or a block temporally adjacent to the target block.

The deblocking filter according to an embodiment may reduce blocking artifacts occurring at a block boundary caused by at least one of prediction, transformation, and quantization.

Meanwhile, the filter according to the embodiment may perform filtering using information on at least one of prediction, transformation, and quantization types signaled together with the reconstructed target block. Information on at least one of the prediction, transform, and quantization types may be transferred to the adder by the inverse quantization unit and the inverse transform unit, and may be transferred from the adder to the filter unit again.

As a method for removing blocking artifacts as described above, a deblocking filter may be used. Deblocking filtering may be performed through the form of a loop filter.

The deblocking filter may perform filtering on a block and a boundary between blocks or a sub-block within a block and a boundary between sub-blocks.

Here, the block may have a shape of MㅧN. M and N may each be a positive integer. The shape of MㅧN may mean a square or rectangular (or, non-square) block shape.

Blocking artifacts can occur by performing prediction, transformation, or quantization on a block. In order to reduce such blocking artifacts, a deblocking filter may be applied to at least one of boundaries of units of CTU, CU, PU, TU, coding tree block, coding block, prediction block, transform block, and sub-block.

Meanwhile, as a filtering method for reducing such blocking artifacts, filtering tailored to the size of the block may be performed by considering all the boundaries of the MxN block.

The deblocking filtering process according to the embodiment may be performed as follows.

First, with respect to the vicinity of a vertical boundary of a picture, sub-picture, slice, tile, brick, CTU, or block, horizontal 1-dimensional filtering may be performed on reconstructed signals near the vertical boundary. Next, for the vicinity of the horizontal boundary of the picture, sub-picture, slice, tile, brick, CTU or block, the vertical direction for the filtered reconstructed signals (by horizontal direction one-dimensional filtering) near the horizontal boundary. One-dimensional filtering can be performed.

Alternatively, first, with respect to the vicinity of a horizontal boundary of a picture, sub-picture, slice, tile, brick, CTU, or block, vertical 1-dimensional filtering may be performed on reconstructed signals near the horizontal boundary. . Next, for the vicinity of the vertical boundary of the picture, sub-picture, slice, tile, brick, CTU or block, the horizontal direction for the filtered reconstructed signals (by vertical one-dimensional filtering) near the vertical boundary. One-dimensional filtering can be performed.

The deblocking filtering method for the horizontal boundary may be similar to the deblocking filtering method for the vertical boundary. The embodiment will be described based on a vertical boundary deblocking filtering method, but a horizontal boundary deblocking filtering method may be performed and implemented in a similar manner.

18 illustrates vertical boundary filtering for adjacent block boundaries according to an embodiment.

19 illustrates horizontal boundary filtering for adjacent block boundaries according to an embodiment.

18 illustrates filtering on vertical boundaries between blocks adjacent to each other. In FIG. 18, horizontal filtering may be performed on a vertical boundary between a target block (block B) and a left block (block A).

19 illustrates filtering on a horizontal boundary between blocks adjacent to each other. In FIG. 19, vertical filtering may be performed on a horizontal boundary between a target block (block B) and an upper block (block A).

Meanwhile, in FIGS. 18 and 19, blocks A and B may be one of CTU, CU, PU, TU, coding tree block, coding block, prediction block, transform block, and sub-block. The sub-block can be a sub-CU, sub-TU or sub-PU.

20 shows a deblocking filter according to an embodiment.

1) at least one of the coding parameters of the target block and the coding parameters signaled from the higher level parameter set or the header, and 2) reconstructed pixels used for filtering may be used as inputs of deblocking filtering. The coding parameter input to the deblocking filter of the embodiment may mean the coding parameter described above with reference to FIG. 1.

A filtering boundary to which filtering is applied and whether to perform filtering may be determined using the information input to the deblocking filtering. In addition, a filtering strength and a filtering type for a filtering boundary may be determined by using information input for deblocking filtering. After these determinations, deblocking filtering may be performed, and pixels to which filtering has been applied by deblocking filtering may be output.

Referring to FIG. 20, a deblocking filter according to an embodiment may include a filtering determination unit, a filtering configuration unit, and a filtering execution unit.

The filtering decision unit can select any of the boundary on which deblocking filtering is performed is a boundary of a block, a boundary of a tile, a boundary of a sub-picture, a boundary of a brick, and a boundary of a slice, and can determine whether to perform filtering on the selected boundary. have.

The filtering configuration unit may determine a filtering strength and a filtering type of filtering applied to a boundary on which filtering is determined to be performed.

The filtering type may indicate at least one of the number of samples used for filtering, a location of a sample used for filtering, the number of samples to be filtered, a location of filtered samples, and a filter length.

The filtering execution unit may perform filtering on the selected boundary.

Meanwhile, since the tile is a technology for supporting parallel processing, an additional post-processing operation may be required for performing filtering on the boundary of the tile. Accordingly, information indicating whether to perform filtering on the boundary of a tile may be signaled through a higher level so that filtering on the boundary of a tile can be selectively used, apart from whether to perform filtering on the boundary of a block.

Filtering on the boundary of the tile may be described below. In this case, instead of a tile, filtering for a boundary to be described later may be applied to at least one of a picture, a sub-picture, a slice, and a brick.

21 is a flowchart illustrating a method of determining whether to perform filtering according to an embodiment.

In FIG. 21, blocks A and B may be blocks adjacent to each other. Blocks A and B may be blocks A and B described above with reference to FIGS. 18 and 19.

Hereinafter, the target boundary may mean a boundary that is the target of filtering, and may mean a boundary of the target block. In an embodiment, the target boundary may mean a boundary between blocks A and B.

In step 2110, when deblock_enabled_flag is 0, it may be determined that filtering is not possible, and filtering may be terminated according to the determination (2110-true). Conversely, when deblock_enabled_flag is 1, it may be determined that filtering can be performed, and step 2120 may be performed according to the determination (2110-false).

deblock_enabled_flag may be information indicating whether deblocking filtering can be performed. That is, deblock_enabled_flag may mean information on whether to perform deblocking filtering.

When deblock_enabled_flag is 1, it may indicate that deblocking filtering can be performed. Conversely, deblock_enabled_flag of 0 may indicate that deblocking filtering is not possible.

The deblock_enabled_flag may be determined in a sequence unit, a picture unit, a sub-picture unit, a slice unit, a tile group unit, a brick unit, or a tile unit, and may be signaled for this unit using a bitstream. In addition, the deblock_enabled_flag may be signaled in at least one of a parameter set and a header.

In an embodiment, a slice may be replaced with at least one of a picture, a sub-picture, a tile, and a brick.

In step 2120, if loop_filter_across_slice is 1, it may be determined that filtering can be performed on a slice boundary, and step 2140 may be performed according to the determination (2120-true). Conversely, when loop_filter_across_slice is 0, it may be determined that filtering is not possible to perform even on a slice boundary, and step 2130 may be performed according to the determination (2120-false).

The loop_filter_across_slice may be information indicating whether deblocking filtering for a slice boundary can be performed.

When loop_filter_across_slice is 0, it may indicate that deblocking filtering cannot be performed on a slice boundary. When loop_filter_across_slice is 1, it may indicate that deblocking filtering can be performed even on a slice boundary.

When deblock_enabled_flag is 1, loop_filter_across_slice may be determined in units of sequence, picture unit, sub-picture unit, slice unit, tile group unit, brick unit, or tile unit, and may be signaled using a bitstream for each unit.

In step 2130, it may be determined whether the target boundary is a slice boundary.

When the target boundary is a slice boundary (2130-true), filtering may be terminated. That is, it is determined that filtering cannot be performed on a slice boundary (loop_filter_across_slice==0), and when the target boundary is a slice boundary, filtering may be terminated.

Conversely, if the target boundary is not a slice boundary, step 2140 may be performed (2130-false).

In an embodiment, a tile may be replaced with at least one of a picture, a sub-picture, a slice, and a brick.

In step 2140, when the target boundary is the vertical boundary of the tile and enable_loop_filter_across_tile_col is 0, filtering may be terminated (2140-true). Conversely, when the target boundary is not a vertical boundary of a tile or if enable_loop_filter_across_tile_col is 1, step 2150 may be performed (2140-false).

enable_loop_filter_across_tile_col may be information indicating whether filtering is performed on the left boundary or the right boundary of the target tile. The target tile may be a tile to be filtered.

enable_loop_filter_across_tile_col may be derived from syntax elements signaled through at least one of a parameter set and a header. The syntax element may be information on whether filtering is performed on the boundary of each tile. When filtering to be performed currently is an operation on a vertical boundary, whether to perform filtering may be determined using enable_loop_filter_across_tile_col.

In step 2150, when the target boundary is the horizontal boundary of the tile and enable_loop_filter_across_tile_row is 0, filtering may be terminated (2150-true). Conversely, when the target boundary is not the horizontal boundary of the tile or if enable_loop_filter_across_tile_row is 1, step 2160 may be performed (2150-false).

enable_loop_filter_across_tile_row may be information indicating whether filtering is performed on the upper boundary or the lower boundary of the target tile.

enable_loop_filter_across_tile_row may be derived from syntax elements signaled through at least one of a parameter set and a header. The syntax element may be information on whether filtering is performed on the boundary of each tile. When filtering to be performed currently is an operation on a horizontal boundary, whether to perform filtering may be determined using enable_loop_filter_across_tile_row.

If deblock_enabled_flag is 0 or loop_filter_across_tile is 0, values of enable_loop_filter_across_tile_col and enable_loop_filter_across_tile_row may be derived to 0. If deblock_enabled_flag is 1 and loop_filter_across_tile is 1, the values of enable_loop_filter_across_tile_col and enable_loop_filter_across_tile_row may be derived using a syntax element signaled through at least one of a parameter set and a header. The syntax element may be information on whether filtering is performed on the boundary of each tile.

In step 2160, it may be determined whether the target boundary is the boundary of the block. When the target boundary is the boundary of a block, filtering on the target boundary may be performed (2160-true). Conversely, if the target boundary is not the boundary of the block, filtering may be terminated without being performed (2160-false). Here, the block may mean CTU, CU, PU, TU, coding tree block, coding block, prediction block, transform block, or sub-block.

In FIG. 21, it is determined that filtering cannot be performed on a slice boundary (ie, loop_filter_across_slice==0), and when the target boundary is a slice boundary, it has been described that filtering is not performed. This description can also be applied to the boundaries of bricks, tile groups and CTUs (not slice boundaries).

For example, it is determined that filtering cannot be performed on the brick boundary (ie, loop_filter_across_brick==0), and when the target boundary is a brick boundary, it may be determined that filtering is not performed.

Also, when the boundary between blocks is a vertical boundary and the left boundary of the target block coincides with the boundary of the picture, it may be determined that filtering is not performed. In addition, when a boundary between blocks is a horizontal boundary and an upper boundary of a target block coincides with a boundary of a picture, it may be determined that filtering is not performed.

Meanwhile, whether to perform filtering according to an embodiment may be determined based on the size of the block. Here, the size of the block may be at least one of a horizontal size, a vertical size, and an area of the block.

When the block size is MxN, filtering may not be performed if M or N is smaller than the threshold min_deblock_size.

For example, when the block size is 4x16 and min_deblock_size is 8, filtering may not be performed on the vertical boundary of the block.

Alternatively, for example, when the block size is 16x4 and the min_deblock_size is 8, filtering may not be performed on the horizontal boundary of the block.

22 illustrates a boundary on which filtering is not performed according to an embodiment.

In FIG. 22, the threshold value min_deblock_size is set to be 8.

Referring to FIG. 22, filtering may not be performed on vertical boundaries of a 4x32 block and a 4x16 block.

Hereinafter, a method of determining a filtering strength according to an embodiment will be described.

The filtering strength may be determined in consideration of at least one of 1) a coding parameter of a target block, 2) a coding parameter of a neighboring block, 3) a size of a target block, and 3) a size of a neighboring block.

The filtering strength may be changed according to an expression using at least one value among samples belonging to the target block. For example, the filtering strength may be changed according to a gradient calculated using sample values adjacent to the boundary between blocks.

As deblocking filtering, 1) vertical filtering may be performed after horizontal filtering or 2) horizontal filtering may be performed after vertical filtering for a target block.

When vertical filtering is performed after horizontal filtering or horizontal filtering is performed after vertical filtering, since nonlinear filtering is applied to samples on which the two filtering is performed, the result may vary according to the order of the filtering.

Therefore, in order to induce the same result in the encoding apparatus 1600 and the decoding apparatus 1700 (or to prevent a discrepancy between the encoding apparatus 1600 and the decoding apparatus 1700), the encoding apparatus 1600 and the decoding apparatus ( 1700) may be performed in a predetermined filtering order (the order of vertical filtering after horizontal or the order of horizontal filtering after vertical). The filtering order may be implicitly determined by the encoding apparatus 1600 and the decoding apparatus 1700, and may be determined explicitly by signaling information such as a flag.

In an embodiment, the filtering strength may have the same meaning as the boundary strength (BS). As the value of the filtering strength for the boundary increases, it may mean that strong filtering is performed on the boundary. When the value of the filtering strength for the boundary is 0, it may mean that filtering is not performed on the boundary.

23 is a flowchart illustrating a method of determining a filtering strength according to an embodiment.

In FIG. 23, blocks A and B may be blocks adjacent to each other. Blocks A and B may be blocks A and B described above with reference to FIGS. 18 and 19.

In step 2310, when the areas of both block A and block B are equal to or greater than inloop_large_block_threshold, it may be determined that the strongest filtering strength is used for filtering (eg, BS = 5) (2310-true). Conversely, when the area of block A or block B is smaller than inloop_large_block_threshold, step 2320 may be performed (2310-false).

The inloop_large_block_threshold may be a value predefined by the encoding apparatus 1600 and the decoding apparatus 1700. Alternatively, inloop_large_block_threshold may be information signaled to the encoding device 1600 and the decoding device 1700.

If the size of the block is MxN, the area of the block may be M*N. Both M and N may be 2n, and n may be a positive integer.

When at least one of the area of the block A and the area of the block B is equal to or greater than the predefined constant inloop_large_block_threshold, it may be determined that the strongest filtering strength is used for filtering (eg, BS = 5).

In an embodiment, at least one of a horizontal size and a vertical size of the block may be used instead of the area of the block to determine the filtering strength.

In addition, the depth of the block may be used instead of the area of the block to determine the filtering strength. For example, the deeper the block, the smaller the size of the block.

Also, in an embodiment, the strongest filtering strength does not only mean that the BS is 5, but may indicate that a filter having a length greater than J is used in one block. J may be a positive integer of 3 or more. That is, in this case, the length of the entire filter may be 2 x J or more.

The strongest filtering strength (eg, BS == 5) is at least V samples among samples belonging to block A or block B by performing filtering using at least U samples among samples belonging to block A or block B. It can mean changing the values of

For example, U and V can each be a positive integer. (U, V) can be (4, 3), (5, 4), (6, 4), (7, 4), (6, 5), (5, 3) or (6, 3) . U can be greater than or equal to V. That is, the U value may be greater than or equal to the V value.

In addition, when the value of the filtering strength is in the range of 0 to 3, the strongest filtering strength may be set through assignment of “BS = 3”.

In addition, when the range of the value of the filtering strength is 0 to 2, the strongest filtering strength may be set through assignment of “BS = 2”.

As described above, the filtering strength may be determined based on the size of the block (or at least one of an area, a horizontal size, a vertical size, and a depth).

The larger the block size, the higher the correlation between samples of the block may be probabilistic. Accordingly, when the block size is large, blocking artifacts can be efficiently removed by using strong filtering.

In step 2320, when the size of block A or size of block B is smaller than min_deblock_size, it may be determined that the weakest filtering strength is used for filtering (eg, BS = 0) (2320-true). Conversely, when the size of the block A and the size of the block B are greater than or equal to min_deblock_size, step 2330 may be performed (2320-false).

For example, when horizontal sizes of horizontally adjacent blocks A and B are smaller than min_deblock_size, it may be determined that the weakest filtering strength is used for filtering on a vertical boundary between blocks (e.g., BS = 0 ).

For example, when the vertical sizes of horizontally adjacent blocks A and B are smaller than min_deblock_size, it may be determined that the weakest filtering strength is used for filtering on a vertical boundary between blocks (e.g., BS = 0 ).

For example, when vertical sizes of vertically adjacent blocks A and B are smaller than min_deblock_size, it may be determined that the weakest filtering strength is used for filtering on a horizontal boundary between blocks (e.g., BS = 0 ).

For example, when the horizontal sizes of vertically adjacent blocks A and B are smaller than min_deblock_size, it may be determined that the weakest filtering strength is used for filtering on a horizontal boundary between blocks (e.g., BS = 0 ).

Alternatively, at least one of a picture, a sub-picture, a slice, a tile group, a tile, a brick, a CTU, a CU, a PU, a TU, a coding block, a prediction block, a transform block, and a sub-block may be divided in units of min_block_size ㅧ min_block_size. . If the vertical boundary or the horizontal boundary between blocks A and B does not correspond to the boundary of the divided unit, filtering may not be performed on the vertical boundary or the horizontal boundary.

Alternatively, at least one of a picture, sub-picture, slice, tile group, tile, brick, CTU, CU, PU, TU, coding block, prediction block, transform block, and sub-block may be divided by min_block_size x min_block_size units. . If the vertical or horizontal boundary between blocks A and B corresponding to the boundary of the divided unit corresponds to the boundary of the divided unit, filtering may be performed on the vertical boundary or the horizontal boundary.

Here, min_block_size is the minimum size of CU, minimum size of PU, minimum size of TU, minimum size of coding block, minimum size of prediction block, minimum size of transform block, minimum size of subblock, or deblocking filtering It can indicate the minimum size, etc. In addition, min_block_size may be a positive integer such as 1, 2, 4, and 8.

The min_deblock_size may be information signaled from the encoding device 1600 to the decoding device 1700. min_deblock_size is a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), and a decoding parameter set ( Decoding Parameter Set; DPS), a picture header, a sub-picture header, a slice header, a tile header, a brick, or a CTU.

The min_deblock_size may be a value preset in the encoding device 1600 and the decoding device 1700.

The weakest filtering strength (eg, BS == 0) is at least V samples among samples belonging to block A or block B by performing filtering using at least U samples among samples belonging to block A or block B. It can mean changing the values of For example, U and V may each be an integer. (U, V) may be (0, 0), (1, 1), (2, 1), (2, 2) or (3, 2). U can be greater than or equal to V.

The value of at least one attribute of U and V when BS == 0 may be different from the value of the above attribute when BS == 1. In the case of BS == 0, the value of at least one of U and V may be smaller than the value of the above-described attribute in case of BS == 1.

The weakest filtering strength (eg, BS == 0) may mean that no filtering is performed.

In step 2330, when at least one of the block A and the block B is a block encoded by intra prediction, it may be determined to use a strong filtering strength for filtering (eg, BS = 4) (2330-true) . Conversely, when both blocks A and B are encoded by inter prediction, step 2340 may be performed (2330-false).

The probability of generating a blocking artifact due to quantization in a block encoded with intra prediction may be higher than a probability of generating a blocking artifact due to quantization in a block encoded by inter prediction. Accordingly, strong filtering may be performed on a block in which intra prediction is used to efficiently remove blocking artifacts (eg, BS = 4).

24 and 25 illustrate a method of determining a filtering strength according to a prediction mode according to an embodiment.

Hereinafter, the intra prediction block may mean a block coded using intra prediction. The inter prediction block may mean a block coded using inter prediction.

As shown in FIG. 24, when block A is a block coded by intra prediction and block B is a block coded by inter prediction, filtering with strong filtering strength is performed for block A but weak filtering strength for block B. Filtering of can be performed.

In an intra prediction block, as the area within the block is closer to the right or the bottom of the block, the probability of occurrence of a prediction error for the area may be higher. Further, in the inter prediction block, a relatively smaller prediction error may occur compared to the intra prediction block. Therefore, when the prediction method of block A is intra prediction and the prediction method of block B is inter prediction, by applying a lower filtering strength to block B than to block A with respect to filtering on the boundary between block A and block B Blocking artifacts can be effectively reduced.

As illustrated in FIG. 25, when block A is a block coded by inter prediction and block B is a block coded by intra prediction, filtering with strong filtering strength may be applied to blocks A and B.

Intra prediction for block B, which is an intra prediction block, may be performed with reference to samples adjacent to the right boundary of block A. Therefore, if there is a quantization error in block A, there may be a high probability that the quantization error will propagate to block B as it is. In addition, if there is no quantization error in block A, there may be a high probability that a quantization error occurs in the vicinity of a boundary adjacent to block A in block B.

Also, the filtering strength may be determined according to whether the prediction modes of the block A and the block B are different from each other.

For example, if the prediction modes of block A and block B are different from each other, a weak filtering strength may be determined to be used (eg, BS = 1).

Filtering for block A when the horizontal sizes of block A and block B are all 32, the conversion mode of block A is DCT-II horizontal conversion, and the conversion mode of block B is DST-VII horizontal conversion or DCT-VIII horizontal conversion The filtering strength for block B may be determined higher than the strength. When the transform modes of the block A and the block B are opposite to each other, the filtering strength for the block A may be determined higher than the filtering strength for the block B.

The strong filtering strength (for example, BS == 4) is performed by performing filtering using at least U samples of samples belonging to block A or block B, so that at least V samples of samples belonging to block A or block B It can mean changing values.

For example, U and V can each be a positive integer. (U, V) is (3, 2), (4, 3), (5, 4), (6, 4), (7, 4), (6, 5), (5, 3) or (6 , 3). U can be greater than or equal to V.

In the case of BS == 4, the value of at least one attribute of U and V may be different from the value of the attribute in case of BS == 5. In the case of BS == 4, the value of at least one attribute of U and V may be smaller than the value of the attribute in case of BS == 5.

In addition, when the value of the filtering strength is in the range of 0 to 3, a strong filtering strength may be set through assignment of “BS = 2”.

In addition, when the value of the filtering strength is in the range of 0 to 2, a strong filtering strength may be set through assignment of “BS = 2”.

See FIG. 23 again.

In step 2340, if the transform coefficient of block A or transform coefficient of block B is more than one, it may be determined to use an intermediate filtering strength for filtering (eg, BS = 3) (2340-true). Conversely, if there is no transform coefficient of block A and no transform coefficient of block B, step 2350 may be performed (2340-false).

Here, the absence of a transform coefficient may mean that information on the transform coefficient does not exist in the bitstream. Alternatively, the absence of a transform coefficient may mean that a residual block for the target block is not derived.

The intermediate filtering strength (e.g., BS == 3) is performed by performing filtering using at least U samples of samples belonging to block A or block B, so that at least V samples of samples belonging to block A or block B are It can mean changing values.

For example, U and V can each be a positive integer. (U, V) is (2, 1), (2, 2), (3, 2), (4, 3), (5, 4), (6, 4), (7, 4), (6 , 5), (5, 3) or (6, 3). U can be greater than or equal to V.

In the case of BS == 3, the value of at least one attribute of U and V may be different from the value of the attribute in case of BS == 4. In the case of BS == 3, the value of at least one attribute of U and V may be smaller than the value of the attribute in case of BS == 4.

In addition, when the value of the filtering strength is in the range of 0 to 3, the intermediate filtering strength may be set through assignment of “BS = 1”.

In addition, when the value of the filtering strength is in the range of 0 to 2, the intermediate filtering strength may be set through assignment of “BS = 1”.

In step 2350, when the reference picture of block A and the reference picture of block B are different from each other, it may be determined that an intermediate filtering strength is used for filtering (eg, BS = 2) (2350-false). Conversely, when the reference picture of block A and the reference picture of block B are the same, step 2360 may be performed (2350-true).

The intermediate filtering strength (e.g., BS == 2) is performed by performing filtering using at least U samples of samples belonging to block A or block B, so that at least V samples of samples belonging to block A or block B are It can mean changing values.

For example, U and V can each be a positive integer. (U, V) is (1, 1), (2, 1), (2, 2), (3, 2), (4, 3), (5, 4), (6, 4), (7 , 4), (6, 5), (5, 3) or (6, 3). U can be greater than or equal to V.

In the case of BS == 2, the value of at least one attribute of U and V may be different from the value of the attribute in case of BS == 3. In the case of BS == 2, the value of at least one attribute of U and V may be different from the value of the attribute in case of BS == 3.

In addition, when the value of the filtering strength is in the range of 0 to 3, the intermediate filtering strength may be set through assignment of “BS = 1”.

In addition, when the value of the filtering strength is in the range of 0 to 2, the intermediate filtering strength may be set through assignment of “BS = 1”.

In step 2360, when at least one of condition 1, condition 2, and condition 3 below is satisfied, it may be determined that a weak filtering strength is used for filtering (eg, BS = 1) 2360- true). Conversely, when none of the conditions 1, 2, and 3 below are satisfied, it may be determined that the weakest filtering strength is used for filtering (eg, BS = 0) (2360-false). Here, T may be a positive integer. For example, T may be 16.

Condition 1) The motion vector difference (MVD) for the motion vectors of blocks A and B in units of 1/16 pixels is greater than the predefined T.

Condition 2) Block B does not perform Overlapped Block Motion Compensation (OBMC) using motion information of block A.

Condition 3) Block A does not perform OBMC using the motion information of block B.

The filtering strength according to the embodiment may be determined based on whether OBMC is used for the block.

If an OBMC using motion information of an adjacent block A is used for the target block B, blocking artifacts may occur less at the boundary between the block A and the block B than when the OBMC is not used. Therefore, in this case, the image quality can be improved by using a lower filtering strength.

For example, as in step 2360, when OBMC is used, the filtering strength BS may be determined to have a value of zero. When OBMC is not used, the filtering strength BS may be determined to have a value of 1.

On the other hand, when OBMC is used only for the Y component (or luma component), the filtering strength may be determined lower only for filtering for the Y component, and for filtering for the U and V components (or chroma components). For this, filtering strength can be maintained.

For example, when OBMC is used only for the luminance component, the filtering strength BS for the luma component may be determined to have a value of 0, and the filtering strength BS for the chroma component may be determined to have a value of 1.

26 illustrates determination of a filtering strength for a block on which OBMC is performed, according to an embodiment.

When OBMC using motion information of block A is performed for block B, it may be determined that the lowest filtering strength is used for boundary 0 between blocks A and B (eg, BS = 0).

Even if OBMC is performed for block B, since OBMC is performed using the motion information of block A, it is determined that a lower filtering strength is used for boundary 1 between blocks B and C and boundary 2 between blocks B and D. Can (eg BS = 1).

Weak filtering strength (e.g., BS == 1) is performed by performing filtering using at least U samples of samples belonging to block A or block B, so that at least V samples of samples belonging to block A or block B It can mean changing values.

For example, U and V can each be a positive integer. (U, V) is (1, 1), (2, 1), (2, 2), (3, 2), (4, 3), (5, 4), (6, 4), (7 , 4), (6, 5), (5, 3) or (6, 3). U can be greater than or equal to V.

In the case of BS == 1, the value of at least one attribute of U and V may be different from the value of the attribute in case of BS == 2. In the case of BS == 1, the value of at least one attribute of U and V may be smaller than the value of the attribute in case of BS == 2.

In addition, when the value of the filtering strength is in the range of 0 to 3, a weak filtering strength may be set through assignment of “BS = 1”.

In addition, when the range of the value of the filtering strength is 0 to 2, the weak filtering strength may be set through assignment of “BS = 1”.

It has been described that the steps 2310 to 2350 described above with reference to FIG. 23 are performed sequentially. However, each step of the steps 2310 to 2350 may not be limited to the order illustrated in FIG. 23, and may be performed independently or according to a different order.

In addition, the conditions of each step of steps 2310 to 2350 of FIG. 23 are not only the determination of the filtering strength, but also whether filtering is performed, the number of samples used for filtering, the location of the samples used for filtering, and the number of filtered samples. It may be used to determine the number and/or type of filtering.

For example, whether or not OBMC is used can be used to determine the filter type. When OBMC using motion information of block A is performed for block B, it is determined to use a filter type of low intensity for the boundary between block B and block A, or only a small number of samples within a close distance of the boundary This can be used for filtering.

When it is determined that the weakest filtering strength is used for filtering (e.g., BS = 0), deblocking filtering is not performed, or deblocking filtering where the weakest filtering strength (e.g., BS == 0) is used Can be done.

Weak filtering strength (e.g., BS == 0) is performed by filtering using at least U samples of samples belonging to block A or block B, and thus at least V samples of samples belonging to block A or block B. It can mean changing values.

For example, U and V can each be a positive integer. (U, V) is (1, 1), (2, 1), (2, 2), (3, 2), (4, 3), (5, 4), (6, 4), (7 , 4), (6, 5), (5, 3) or (6, 3). U can be greater than or equal to V.

The value of at least one attribute of U and V when BS == 0 may be different from the value of the above attribute when BS == 1. In the case of BS == 0, the value of at least one of U and V may be smaller than the value of the above-described attribute in case of BS == 1.

The number and/or positions of samples used for filtering in a block adjacent to the target boundary may be determined using at least one of horizontal sizes or vertical sizes of two blocks forming a block boundary.

In an embodiment, two blocks may refer to adjacent blocks forming a block boundary.

The number of samples used for filtering may be determined according to the size of a block having a smaller horizontal size or a smaller vertical size among the two blocks.

In order to determine the number of samples used for filtering, the area of the block or the depth of the block may be used instead of the size of the block.

27 illustrates filtering according to block division according to an embodiment.

In FIG. 27, square and rectangular CU #0, CU #1, CU #2, CU #3, CU #4, CU #5, and CU #6 generated by dividing the 64x32 area are illustrated.

In FIG. 27, a CU is illustrated, but an embodiment may not be limited only to a CU. An embodiment may be applied to a PU, a TU, a coding block, a prediction block, a transform block, a sub-CU, or a sub-TU instead of a CU.

CU #0 may be a 32x16 block in which a 32x16 size transformation is used. CU #1, CU #2, and CU #4 may be 16x8 blocks in which 16x8 size transformation is used. CU #3 and CU #5 may be 8x8 blocks in which 8x8 size transformation is used. CU #6 may be a 32x32 block in which a 32x32 size transformation is used.

Since CU #0 and CU #6 are adjacent in a horizontal direction, a vertical boundary may exist between CU #0 and CU #6. Since CU #0 and CU #1 are adjacent in the vertical direction, a horizontal boundary exists between CU #0 and CU #1.

The number and/or positions of samples used for filtering the vertical boundary between CU #0 and CU #6 may be determined based on a horizontal size of at least one of CU #0 and CU #6.

When filtering on the vertical boundary between CU #0 and CU #6 is performed, if the horizontal size or vertical size of at least one of CU #0 and CU #6 is greater than inloop_large_block_threshold, U samples within CU #0 Filtering may be performed on the V samples by using the V samples, and filtering may be performed on the V samples by using the U samples in CU #6. The U samples may be continuous horizontally from the vertical boundary.

For example, U and V can each be a positive integer. (U, V) can be (4, 3), (5, 4), (6, 4), (7, 4), (6, 5), (5, 3) or (6, 3) . U can be greater than or equal to V.

If the horizontal size of CU #0 and the horizontal size of CU #6 are the same, the number of samples used for the deblocking filter in CU #0 and the number of samples used for the deblocking filter in CU #6 are the same. can do. In addition, when the horizontal size of CU #0 and the horizontal size of CU #6 are the same, the number of samples subjected to deblocking filtering in CU #0 and the number of samples subjected to deblocking filtering in CU #6 may be the same. have.

The number and/or positions of samples used for filtering on the horizontal boundary between CU #0 and CU #1 may be determined based on the vertical size of at least one of CU #0 and CU #1.

When filtering on the horizontal boundary between CU #0 and CU #1 is performed, if the horizontal or vertical size of at least one of CU #0 and CU #1 is greater than inloop_large_block_threshold, then U samples within CU #0 Filtering may be performed on the V samples by using the values, and filtering may be performed on the V samples by using the U samples in CU #1. The U samples may be continuous from the horizontal boundary in the vertical direction.

For example, U and V can each be a positive integer. (U, V) is (0, 0), (1, 1), (2, 1), (2, 2), (3, 2), (4, 3), (5, 4), (6 , 4), (7, 4), (6, 5), (5, 3) or (6, 3). U can be greater than or equal to V.

When the vertical size of CU #0 and the vertical size of CU #1 are different, the number of samples used for the deblocking filter in CU #0 and the number of samples used for the deblocking filter in CU #1 are They can be different. For example, when the vertical size of CU #1 is smaller than the vertical size of CU #0, the number of samples used for the deblocking filter in CU #1 is used for the deblocking filter in CU #0. It may be smaller than the number of samples.

When the vertical size of CU #0 and the vertical size of CU #1 are different, the number of deblocking-filtered samples in CU #0 and the number of deblocking-filtered samples in CU #1 may be different. . For example, when the vertical size of CU #1 is smaller than the vertical size of CU #0, the number of samples subjected to deblocking filtering in CU #1 is less than the number of samples subjected to deblocking filtering in CU #0. Can be smaller.

The filtering strength for the target boundary may be determined using at least one of horizontal sizes or vertical sizes of the two blocks forming the block boundary.

In an embodiment, the filtering strength may be determined based on the area of the block or the depth of the block instead of the size of the block.

The number and/or positions of samples used for filtering in a block adjacent to the target boundary may be determined using at least one of horizontal sizes or vertical sizes of two blocks forming a block boundary.

The number of samples used for filtering may be determined according to the size of a block having a smaller horizontal size or a vertical size among the two blocks. Alternatively, the number of samples used for filtering may be determined according to the size of a block having a larger horizontal size or vertical size among the two blocks.

The number and/or positions of samples used for filtering on the vertical boundary between CU #5 and CU #6 may be determined based on the horizontal size of at least one of CU #5 and CU #6.

When filtering on the vertical boundary between CU #5 and CU #6 is performed, if the horizontal size or vertical size of at least one of CU #5 and CU #6 is greater than inloop_large_block_threshold, U samples within CU #5 Filtering may be performed on the V samples using s, and filtering may be performed on the V samples using U samples in CU #6. The U samples may be continuous horizontally from the vertical boundary.

For example, U and V can each be a positive integer. (U, V) is (0, 0), (1, 1), (2, 1), (2, 2), (3, 2), (4, 3), (5, 4), (6 , 4), (7, 4), (6, 5), (5, 3) or (6, 3). U can be greater than or equal to V.

When the horizontal size of CU #5 and the horizontal size of CU #6 are different, the number of samples used for the deblocking filter in CU #5 and the number of samples used for the deblocking filter in CU #6 are They can be different. For example, if the horizontal size of CU #5 is smaller than the horizontal size of CU #6, the number of samples used for the deblocking filter in CU #5 is used for the deblocking filter in CU #6. It may be smaller than the number of samples.

When the horizontal size of CU #5 and the horizontal size of CU #6 are different, the number of samples subjected to deblocking filtering in CU #5 and the number of samples subjected to deblocking filtering in CU #6 may be different. . For example, when the horizontal size of CU #5 is smaller than the horizontal size of CU #6, the number of samples subjected to deblocking filtering in CU #5 is less than the number of samples subjected to deblocking filtering in CU #6. Can be smaller.

When the filtering strength for a vertical boundary between CU #0 and CU #6 is determined, a horizontal size or a vertical size of at least one of CU #0 and CU #6 may be used.

When the filtering strength for a horizontal boundary between CU #0 and CU #1 is determined, a horizontal size or a vertical size of at least one of CU #0 and CU #1 may be used.

The filtering strength for samples in a block having a larger size may be greater than the filtering strength for samples in a block having a smaller size. For example, the filtering strength for the vertical boundary between CU #0 and CU #6 may be greater than the filtering strength for the horizontal boundary between CU #0 and CU #1.

Meanwhile, transformation of a rectangular shape such as 32x16 and 16x8 may be performed on a rectangular block. Filtering may also be performed on such a rectangular block or transform boundary.

28 illustrates a plurality of transform regions according to an embodiment.

For a rectangular CU having a large difference in ratio between width and height, such as CU #1 or CU #2 of FIG. 27, several transform regions may be determined as shown in FIG. 28 in order to increase conversion efficiency.

Deblocking filtering may be performed on boundaries between several transform regions using at least one of the coding parameters for the determined transform regions.

Filtering may be performed on samples adjacent to a block boundary using at least one of a filtering strength determined as in the description of FIGS. 18 to 28 and the number and/or positions of samples used for filtering.

Hereinafter, a detailed filtering method according to the filtering strength BS according to an embodiment will be described.

When the filtering strength range is 0 to 5, when the size of the BS is smaller than 4, filtering using Equation 1 may be performed. If the BS is 4, filtering using Equation 2 may be performed. If the BS is 5, filtering using Equation 3 and/or Equation 4 may be performed.

[Equation 1]

Δ = Clip[-tc, tc, {(q0-p0) << 2 + (p1-q1) + 4} / 8]

p'0 = p0 + Δ

q'0 = q0 + Δ

Equation 1 may be an example of filtering when the value of BS is less than 4.

Here, the value of tc is |p2-p0|, |q2-q0| And β. β may be determined by a quantization parameter (QP).

The Clip[a, b, c] function outputs a if c is less than a, outputs b if c is greater than b, and outputs c if c is greater than a and less than b. In other words, the Clip[a, b, c] function may be a function that adjusts the output value of c so as not to exceed a range between a and b. That is, the Clip of Equation 1 can be adjusted so that the value of ((q0-p0) << 2 + (p1-q1) + 4)/8 does not deviate between -tc and tc.

As shown in Equation 1, values of p'0 and q'0 may be calculated through 4-tap filtering using q1, q0, p0, and p1. Filtering on samples p'1 and q'1 may be performed through a method similar to a method of calculating p'0 and q'0.

As illustrated in FIG. 27, pn and qn may indicate the location of the n-th sample. Here, n may be an integer greater than or equal to 0.

[Equation 2]

q'0 = (1×q2 + 2×q1 + 2×q0 + 2×p0 +1×p1 + 4)/8

Equation 2 may illustrate a method of calculating q'0 when the value of BS is 4.

In Equation 2, values of the filtering coefficients may be (1, 2, 2, 2, 1). In Equation 2, 5-tap filtering using filtering coefficients of (1, 2, 2, 2, 1) may be applied.

With α and β determined by the quantization parameter, it may be determined whether samples around the boundary correspond to real edges.

The number of samples filtered by the filtering according to Equation 2 may also be limited to a maximum of J samples. (The number of samples may be J for the luma signal and K for the chroma signal.) According to this limitation, filtering may be applied to a maximum of L samples for each block adjacent to the boundary.

Each of J, K and L may be a positive integer. For example, J may be 6, K may be 4, and L may be 3. Here, J may be greater than or equal to K. Further, J may be greater than or equal to L. Also, K may be greater than or equal to L.

In an embodiment, a filtering method in which a filtering strength (eg, BS == 5) for a boundary adjacent to a block having a relatively larger size is additionally included may be provided.

Equations 3 and 4 may be used for filtering the boundary of a block having a relatively large size.

Whether the block size is large may be determined through comparison between the block size and the threshold value T. Here, T may be a positive integer. For example, T may be 32. For example, when the horizontal size of the target block is greater than or equal to T, it may be determined that the target block is a block having a large size. As another example, if the vertical size of the target block is greater than or equal to T, it may be determined that the target block is a block having a large size.

For example, at least one of the number of samples used in filtering and the number of filtered samples represented by Equation 3 or 4 may be larger than the number of samples in the filtering using Equation 2. That is, Equation 3 or Equation 4 may represent an example of a filtering method using more samples.

[Equation 3]

q'0=(1×q3 + 2×q2 + 3×q1 + 4×q0 + 3×p0 + 2×p1 + 1×p2 + 8)/16

According to Equation 3, q'0 may be calculated for a boundary adjacent to a block having a relatively large size. In Equation 3, compared to Equation 2, the number of samples used for filtering may be increased. In Equation 3, 7-tap filtering using the filtering coefficients of (1, 2, 3, 4, 3, 2, 1) may be applied.

According to Equation 3, in filtering a block having a relatively large size, blocking artifacts can be effectively reduced by increasing the number of samples adjacent to the boundary of the block.

[Equation 4]

q'4=(4×q5 + 3×q4 + 3×q3 + 2×q2 + 2×q1 + 1×q0 + 8)/16

Equation 4 may be used for filtering samples of q'4. According to Equation 4, blocking artifacts can be reduced by performing filtering on q'4 adjacent to the boundary of a block having a relatively large size.

Blocking artifacts may be reduced by increasing the number of samples used for filtering as the block size further increases. Specifically, filtering using a 7-tap filter such as Equation 3 may be performed on a boundary adjacent to a block having a relatively large size.

For example, when the horizontal size of the target block is 32 or more, a 7 tap filter may be used for the vertical boundary. Conversely, when the horizontal size of the target block is less than 32, a filter with a tap smaller than 7 for the vertical boundary may be used.

As another example, when the vertical size of the target block is 32 or more, a 7 tap filter may be used for the horizontal boundary. Conversely, when the vertical size of the target block is less than 32, a filter with a tap smaller than 7 for the horizontal boundary may be used.

In an embodiment, the number of samples used for filtering and the number of samples to be filtered may not be limited to the methods exemplified in the above-described equations, and various other filtering methods in addition to the illustrated methods include the size and area of the block. And it may be applied differently according to at least one of the depth.

When the range of the filtering strength is 0 to 3, when the BS is 1, filtering using Equation 1 may be performed. If the BS is 2, filtering using Equation 2 may be performed. If the BS is 3, filtering using Equation 3 and/or Equation 4 may be performed.

The number of samples used for filtering and the number of filtered samples may be determined based on a quantization parameter of a block on which filtering is performed.

For example, quantization parameters of blocks A and B adjacent to each other may be compared. According to this comparison, filtering for V samples using U samples may be performed for a block having a larger quantization parameter, and X samples may be used for a block having a smaller quantization parameter. Filtering may be performed on Y samples. Here, U may be greater than or equal to X, and V may be greater than or equal to Y. Each of U, V, X and Y may be positive integers. U can be at least V and X can be at least Y.

The number of samples used for filtering and the number of filtered samples may be determined according to at least one of coding parameters of a target block and an adjacent block.

Samples used for filtering may be limited to samples belonging to two blocks.

The filtering strength may be determined based on the prediction mode.

For example, when a block including a sample adjacent to a block boundary is encoded/decoded in an intra block copy (IBC) mode, it may be determined to use a weak filtering strength for filtering (e.g., BS = 1).

As another example, when a block boundary is a boundary of a transform block and a block including a sample adjacent to the block boundary is encoded/decoded with Combined Intra Inter Prediction (CIIP), a strong filtering strength is used for filtering. Can be determined (eg BS = 2).

The filtering strength may be determined based on the conversion mode.

For example, when a secondary transform is performed on a block including samples adjacent to the block boundary, it may be determined that a specific filtering strength for filtering is used (eg, BS = 2).

When secondary transformation is performed, a probability of occurrence of an error in a high frequency component of a residual signal may increase. Thus, it can be determined that a high filtering strength is used for filtering.

The filtering strength may be determined in consideration of the block size and whether a secondary transform is used.

The number of samples used for filtering may be determined based on the size and transformation mode of the target block and the neighboring block.

For example, if the horizontal sizes of block A and block B are all 32, the conversion mode of block A is DCT-2 horizontal conversion, and the conversion mode of block B is DST-7 horizontal conversion or DCT-8 horizontal conversion, block The number of samples used for filtering in A may be determined to be smaller than the number of samples used for filtering in block B.

The filtering strength may be determined according to types of two blocks adjacent to the boundary. The filtering strength may be determined according to a boundary among 1) a boundary between a transform block and a transform block, 2) a boundary between a coding block and a transform block, and 3) a boundary between a coding block and a coding block.

The filtering strength may be determined according to the transform and quantization type of the block.

For example, when the size of transform and quantization is 64×32 or 32×64 or more, the strongest filtering strength may be used.

The larger the unit of transformation and quantization is, the more the number of samples used for filtering may increase.

At least one of the embodiments may be used for deblocking filtering on a luma signal or deblocking filtering on a chroma signal.

When filtering is performed, the number of samples used for filtering may be determined differently according to the size of the block. As the size of at least one of the coding block, the prediction block, and the transform block increases, the number of samples used for filtering may increase.

When filtering is performed, the number of filtered samples may be differently determined according to the size of the block, and the number of filtered samples may be further increased as the size of at least one of the coding block, the prediction block, and the transform block increases.

The filtering strength applied to the luma component can be applied equally to the chroma component. Alternatively, the filtering strength applied to the luma component and the filtering strength applied to the chroma component may be independent of each other.

The number of samples used for filtering the luma component and the number of samples used for filtering the chroma component may be independent of each other. Alternatively, the number of samples used for filtering the chroma component may be less than or equal to the number of samples used for filtering the luma component.

At least one of 1) whether to perform filtering, 2) a filtering strength, and 3) a filtering method may be additionally determined by using samples around a target boundary to be filtered.

Using the slope of the samples around the boundary, it can be determined whether the samples around the boundary correspond to the real edge of the image, and whether or not blocking artifacts occur due to the encoding/decoding process of the block. Can be judged. Whether to perform filtering may be determined using the results of these determinations. Instead of a slope, a result calculated by using an operation using at least one value of samples belonging to at least one of block A and block B may be used for the above determinations.

Hereinafter, filtering for a tile boundary according to an embodiment will be described. In this case, filtering described below may be used for at least one boundary among pictures, sub-pictures, slices, and bricks, instead of the tile boundary.

Tiles can be used in a variety of applications, and can be particularly useful in encoding/decoding high-resolution 360-degree images.

A 360-degree image may be generated by projecting a 3D space onto 2D-shaped faces. Projection methods such as Cube Map Projection (CMP) other than EquiRectangular Projection (ERP) can rearrange multiple faces. Thus, the planes created by these projection methods may not be spatially continuous with each other. Alternatively, picture boundaries may be continuous with a certain tile boundary, and picture boundaries may be continuous with each other. In general, the encoding apparatus 1600 may set one surface as one tile. Accordingly, whether or not filtering is performed on the boundary of a tile and a filtering method may be an important issue.

If filtering is performed on all boundaries, image quality deterioration may occur as filtering is performed on the boundary of two discontinuous surfaces. Conversely, if filtering is not performed on all boundaries, filtering is not performed on the boundary of two consecutive faces, and thus blocking artifacts may occur. In addition, if filtering is not performed on the boundary of the picture, blocking artifacts may occur even when the decoded picture is output to the user in 3D format.

In order to solve these problems, whether to perform filtering on a picture boundary and a tile boundary of each tile and a filtering method may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through at least one of a parameter set and a header. . The encoding apparatus 1600 may generate entropy-encoded information by performing entropy encoding on whether to perform filtering on a picture boundary and a tile boundary of each tile and a filtering method. Entropy-encoded information may be included in at least one of a parameter set and a header. The decoding apparatus 1700 may perform entropy decoding on entropy-encoded information to derive whether to perform filtering on a picture boundary and a tile boundary of each tile and a filtering method.

Here, at least one of the parameter set and the header may include a sequence parameter set, a picture parameter set, an adaptation parameter set, a picture header, a slice header, a tile header, a brick header, and the like.

The projection method and rearrangement method of the 360-degree image may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through at least one of a parameter set and a header. The encoding apparatus 1600 may generate entropy-encoded information by performing entropy encoding for a projection method and a rearrangement method of a 360-degree image. Entropy-encoded information may be included in at least one of a parameter set and a header. The decoding apparatus 1700 may obtain a projection method and a rearrangement method of a 360-degree image by performing entropy decoding on entropy-encoded information. The encoding device 1600 and the decoding device 1700 may implicitly derive whether or not to perform filtering on the picture boundary and the tile boundary of each tile through signaling for the projection method and rearrangement method of the 360-degree image.

Here, at least one of the parameter set and the header may include a sequence parameter set, a picture parameter set, an adaptation parameter set, a picture header, a slice header, a tile header, a brick header, and the like.

As described above, filtering may not be implicitly performed on the boundary of discontinuous tiles, and filtering may be implicitly performed on the boundary of continuous tiles.

For the boundary of a picture in a tile, filtering is performed by using reconstructed pixels located at the boundary of consecutive surfaces in 3D space before projecting in 2D form and encoded/decoded information on these reconstructed pixels Can be.

For such filtering, the encoding apparatus 1600 may signal information indicating whether to perform filtering by using the boundary of which position of a certain tile to the decoding apparatus 1700 through at least one of a parameter set and a header. The decoding apparatus 1700 may determine whether to perform filtering on a picture boundary within a specified tile by using the signaled information, and determine whether to perform filtering on a boundary of a position of a tile.

By signaling a projection method and a rearrangement method of a 360-degree image through at least one of a parameter set and a header, the encoding apparatus 1600 and/or the decoding apparatus 1700 implicitly determine whether to perform filtering on the picture boundary within each tile. It can be derived, and it is possible to implicitly derive whether to perform filtering by using the boundary of which position of which tile.

Here, the filter for filtering may include, in addition to the deblocking filter, a loop filter that performs filtering using pixels reconstructed across a boundary or encoded/decoded information. The loop filter may include an adaptive sample offset and an adaptive loop filter.

29 shows six planes constructed by projecting a 360-degree image in the form of a cube map according to an example.

Inputs and outputs of the encoding apparatus 1600 and/or the decoding apparatus 1700 may have a rectangular shape. Thus, the six faces generated by the projection can be rearranged in the form of a rectangle with no space. Information on six faces can be compressed through such rearrangement.

30 and 31 show rearrangements of six planes projected in the form of a cube map according to an example.

30 and 31 may show rearrangement of six planes projected in the form of a cube map.

30 may show rearrangement using CMP.

31 may show rearrangement using a rotated sphere projection (RSP).

In the planes shown in FIG. 30, the planes that were spatially continuous in a three-dimensional space may be as follows: 1) a left face and a front face, 2) a front and a right face, 3 ) Top face and front.

Other surfaces may be spatially discontinuous surfaces in a three-dimensional space.

If the faces are each encoded/decoded as tiles, the boundary C11, the boundary C12, and the boundary R11 are tile boundaries, but may be spatially continuous boundaries, and the boundary R10, boundary R12, boundary C01, and boundary C02 are tile boundaries and spatial May be a discontinuous boundary.

Filtering may be performed on the boundary C11, the boundary C12, and the boundary R11, which are tile boundaries but spatially continuous boundaries. By filtering, blocking artifacts for these boundaries may be removed or image quality may be improved.

Filtering may not be performed on the boundary R10, the boundary R12, the boundary C01, and the boundary C02, which are tile boundaries but spatially discontinuous boundaries. It may be preferable in terms of image quality that filtering is not performed on these boundaries.

{Border C00 and Boundary C13} and {Border R00 and Boundary R01} and the like are picture boundaries, but may be continuous boundaries. Borders that are picture boundaries but are continuous with each other may be assumed to be borders adjacent to each other. Under this assumption, filtering may be performed on borders that are picture boundaries and are continuous with each other. Image quality may be improved through filtering on these boundaries.

In the faces shown in FIG. 31, the top face, back face and bottom face were rotated 90 degrees to the right.

By this rotation, only the boundary R10, the boundary R11, and the boundary R12 among the boundaries between the planes shown in FIG. 31 may be spatially discontinuous, and the remaining boundaries may be spatially continuous.

Filtering may not be performed on the boundary R10, boundary R11, and boundary R12 that are discontinuous boundaries. It may be more preferable not to perform filtering on discontinuous boundaries in terms of image quality.

{Border C00 and Boundary R11} and {Border R00 and Boundary R12}, etc. are picture boundaries, but may be continuous boundaries. Borders that are picture boundaries but are continuous with each other may be assumed to be adjacent borders. Under this assumption, filtering may be performed on borders that are picture boundaries and are continuous with each other. Image quality may be improved through filtering on these boundaries.

When the projection method and rearrangement method illustrated in FIG. 31 are used, the projection method and rearrangement method may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through at least one of a parameter set and a header. Also, whether filtering is performed only on the right or left boundary of the tile and the filtering method may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through at least one of a parameter set and a header. The encoding apparatus 1600 may generate entropy-encoded information by performing 1) a projection method and a rearrangement method, 2) whether to perform filtering on the right or left boundary of the tile, and entropy encoding on the filtering method. . Entropy-encoded information may be included in at least one of a parameter set and a header. The decoding apparatus 1700 may perform entropy decoding on entropy-encoded information to derive 1) a projection method and a rearrangement method, and 2) whether to perform filtering on a right or left boundary of a tile, and a filtering method. . Filtering for the upper and lower boundaries of the tile may not be performed (implicitly).

Alternatively, when the projection method and rearrangement method shown in FIG. 31 are used, the projection method and rearrangement method may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through at least one of a parameter set and a header. . Also, whether filtering is performed on only picture boundaries may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through at least one of a parameter set and a header. The encoding apparatus 1600 may generate entropy-encoded information by performing 1) a projection method and a rearrangement method, and 2) entropy encoding for whether to perform filtering on picture boundaries. Entropy-encoded information may be included in at least one of a parameter set and a header. The decoding apparatus 1700 may induce whether to perform entropy decoding on entropy-encoded information, 1) a projection method and a rearrangement method, and 2) filtering for picture boundaries. The decoding apparatus 1700 may implicitly determine whether to perform filtering by using a boundary of a certain position of a certain tile, and through this determination, may perform filtering on a picture boundary within a tile.

32 shows syntax and semantics for a PPS defined in connection with signaling whether or not filtering is performed for each boundary and a method of filtering according to an example.

Whether filtering is performed on the picture boundary and the tile boundary of each tile through loop_filter_across_tile_col[i][j] and loop_filter_across_tile_row[i][j], and a filtering method can be signaled from the encoding apparatus 1600 to the decoding apparatus 1700. have.

loop_filter_across_tile_upper_boundary[i] and loop_filter_across_tile_left_boundary[i] may be syntax elements indicating a tile on which filtering is performed and a boundary of the tile with respect to the picture boundary of each tile.

Here, loop_filter_across_tile_upper_boundary[i] may mean location information of the i-th upper boundary, and location information of the i-th upper boundary may mean location information about the upper boundary of the i-th tile.

In addition, loop_filter_across_tile_left_boundary[i] may mean location information of the i-th left border, and location information of the i-th left border may mean location information of the left border of the i-th tile.

If the image is not a 360 degree image, filtering for a picture boundary may not be required. Therefore, if the image is not a 360-degree image, loop_filter_across_tile_col[i][0], loop_filter_across_tile_row[i][0], loop_filter_across_tile_upper_boundary[i] and loop_filter_across_tile_left_boundary[i] may not be signaled, and the encoding device 1600 and decoding It may be implicitly derived that filtering is not performed in the device 1700.

Whether to perform filtering on a tile boundary and a filtering method may be signaled for a CTU or a unit of a predefined size. The unit of the predefined size may be fixed to the same value in the encoding apparatus 1600 and the decoding apparatus 1700, and information indicating the unit of the predefined size is a sequence parameter set, a picture parameter set, an adaptation parameter set, and a picture. It may be signaled through a header, a slice header, a tile header, and a brick header.

For this operation, filtering performance information may be signaled from the encoding device 1600 to the decoding device 1700. The filtering performance information may be a flag or bit.

The filtering performance information may be information indicating whether to collectively perform filtering on the boundaries of all blocks included in the tile boundary.

The filtering performance information may be signaled through a sequence parameter set, a picture parameter set, an adaptation parameter set, a picture header, a slice header, a tile header, and a brick header.

The encoding apparatus 1600 may generate entropy-encoded information by performing entropy encoding on the filtering performance information. Entropy-encoded information may be included in at least one of a parameter set and a header. The decoding apparatus 1700 may derive filtering performance information by performing entropy decoding on entropy-encoded information.

When filtering is performed, individual filtering performance information may be signaled from the encoding device 1600 to the decoding device 1700.

The individual filtering performance information may include indication information equal to or less than the number of CTUs (or blocks of a predefined size) located at the tile boundary. For example, the indication information may be a flag or bit. The individual filtering performance information may indicate whether to perform filtering and/or a filtering method for a tile boundary in which each CTU (or a block having a predetermined size) is located. In other words, the indication information of the individual filtering performance information may indicate whether to perform filtering and/or a filtering method for a tile boundary in which a corresponding CTU (or a block having a predefined size) is located.

The encoding apparatus 1600 may generate entropy-encoded information by performing entropy encoding on individual filtering performance information. Entropy-encoded information may be included in at least one of a parameter set and a header. The decoding apparatus 1700 may derive individual filtering performance information by performing entropy decoding on entropy-encoded information.

The decoding apparatus 1700 may perform the same tile boundary filtering on boundaries within the tile by using the individual filtering performance information. Alternatively, the decoding apparatus 1700 may determine whether to perform filtering and a filtering method for each CTU (or a block having a predefined size) located at a tile boundary using the individual filtering performance information.

Signal adaptive deblocking filtering

As a method of filtering block boundaries, signal adaptive deblocking filtering may be performed. The signal may be at least one or more of a luma component signal and a chroma signal component.

Signal adaptive deblocking filtering may be performed based on a value of a reconstructed signal component.

Signal adaptive deblocking filtering may determine whether to perform deblocking filtering based on a value of a reconstructed signal component.

The signal adaptive deblocking filtering may determine a filtering strength based on a value of a reconstructed signal component.

In the signal adaptive deblocking filtering, a quantization parameter may be determined based on a value of a reconstructed signal component, and deblocking filtering may be performed using the determined quantization parameter.

There may be one or more values of the reconstructed signal component. If more than one value is used, a statistical value for the reconstructed signal component may be calculated. The calculated statistical value can be used for signal adaptive deblocking filtering.

In deblocking filtering, filtering may be performed based on at least one of tc and β. tc and β may be threshold values applied when determining the strength of the filter or performing filtering.

tc and β may be determined based on the quantization parameter. The quantization parameter may be quantization parameters of one or more blocks adjacent to a block boundary of the target block.

When quantization parameters of one or more blocks are used, a statistical value for the quantization parameters may be calculated, and the calculated statistical value may be determined as a quantization parameter for a block boundary.

For example, when a quantization parameter is determined based on the value of the reconstructed signal component and signal adaptive deblocking filtering is performed, the quantization parameter for the block boundary is added by adding a quantization parameter offset to the quantization parameter for the block boundary. Can be determined. The quantization parameter offset may be calculated based on a value of the reconstructed signal component.

33 shows positions of reconstructed samples in a block adjacent to a block boundary according to an example.

A value of a reconstructed signal component or a statistical value of a reconstructed signal component may be calculated using at least one of samples reconstructed within a block adjacent to the block boundary.

For example, as shown in Equation 5 below, a statistical value compLevel for the reconstructed signal component may be calculated.

[Equation 5]

compLevel = (p _0,0 + p _0,3 + q _0,0 + q _0,3 ) >> M

The reconstructed sample calculated based on the statistical value of the reconstructed signal component may not be limited as shown in Equation (5). In p _i,k and q _i,k , i and k may each have a value of 0 to N.

N may represent the maximum number of horizontal/vertical samples used for deblocking filtering. In addition, N may be a positive integer. For example, N may be 3.

M may be log2(m). m may be the number of reconstructed signal samples used to calculate the statistical value compLevel for the reconstructed signal component. M can be a positive integer. For example, in Equation 5, M may be 2. M may be changed according to the number of reconstructed signal samples.

A quantization parameter offset value qPOffset may be calculated based on the statistical value compLevel for the reconstructed signal component. In this case, qPOffset may be determined for each section of sections in which the value of compLevel may belong.

For example, a value of qPOffset may be calculated based on qPOffsets preset in the encoding apparatus 1600 and/or the decoding apparatus 1700 for ranges in which the value of compLevel may belong.

For example, for each range of ranges for the value of compLevel, at least one of a minimum value, a maximum value, and a size of the range may be signaled from the encoding device 1600 to the decoding device 1700. The size may be the difference between the maximum value of the previous range and the maximum value of the next range. The decoding apparatus 1700 may derive ranges for a value of compLevel using at least one of a minimum value, a maximum value, and a size of the signaled range.

The encoding apparatus 1600 may generate entropy-encoded information by performing entropy encoding on at least one of a minimum value, a maximum value, and a size of a range. Entropy-encoded information may be signaled from the encoding device 1600 to the decoding device 1700. The decoding apparatus 1700 may derive at least one of a minimum value, a maximum value, and a size of a range by performing entropy decoding on entropy-encoded information.

Also, a value of qPOffset for each range may be signaled from the encoding device 1600 to the decoding device 1700. The decoding apparatus 1700 may calculate qPOffset for each range of the ranges using the signaled value of qPOffset.

The encoding apparatus 1600 may generate entropy-encoded information by performing entropy encoding on a value of qPOffset for each range. Entropy-encoded information may be signaled from the encoding device 1600 to the decoding device 1700. The decoding apparatus 1700 may derive a value of qPOffset for each range by performing entropy decoding on entropy-encoded information.

For example, as shown in Equation 6 below, a quantization parameter qP _BlockEdge for a block boundary may be calculated using a quantization parameter offset value qPOffset calculated based on the reconstructed signal component value.

[Equation 6]

qP _BlockEdge = ((Qp _Q + Qp _P + 1) >> 1) + qPOffset

When the block boundary is a vertical boundary, Qp _P may represent a quantization parameter of a block to the left of the block boundary. Qp _Q may represent a quantization parameter of a block to the right of a block boundary.

When the block boundary is a horizontal boundary, Qp _P may represent a quantization parameter of a block above the block boundary, and Qp _Q may represent a quantization parameter of a block below the block boundary. That is, Qp _P may represent a quantization parameter of a block including the reconstructed sample p _i,k , and Qp _Q may represent a quantization parameter of a block including the reconstructed sample q _i,k .

At least one of tc and β for the block boundary may be determined using the quantization parameter qP _BlockEdge for the block boundary, and deblocking filtering may be performed through this determination.

In signal adaptive deblocking filtering, at least one prediction mode among blocks around a boundary, color component, size, shape, type of one-dimensional transform, combination of two-dimensional transform, whether transform is used, filtering strength, sample Deblocking at least one of different quantization parameter offset values (qPOffsets) and quantization parameters for different block boundaries (qP _BlockEdges ) based on at least one of a value, a statistical value for samples, and a coding block flag It can be used in the process of filtering.

Prediction mode, color component, size, shape, type of 1D transformation, combination of 2D transformation, whether transformation is used, filtering intensity, sample value, statistical value of samples of at least one of the blocks around the boundary And at least one of a quantization parameter offset value qPOffset and a quantization parameter qP _BlockEdge for a block boundary used according to at least one of the coding block flags.

The prediction mode may indicate a prediction mode of a block. The prediction mode may indicate whether a block has been coded/decoded using any of an intra prediction mode, an inter prediction mode, and an intra block copy mode.

The color component may represent the color component of the block. The color component may represent a luma (Y) component or a chroma component.

The size may represent at least one of a block size and a transform size.

The shape may represent at least one of a block type and a transform type.

The first-order transform may indicate the type of transform performed on the residual block to generate transform coefficients. The first transform may represent at least one of DCT-J-based integer transforms such as DCT-2, DCT-8, DST-7, DCT-4, and DST-4, and DST-K-based integer transforms. have. Each of J and K may be a positive integer.

The quadratic transform may represent at least one of transforms rotating at least one of the transform coefficients based on an angle. The second order transformation may be performed after performing the first order transformation.

Whether to use the transform may indicate whether at least one of a first transform and a second transform is used for the residual block. Whether to use the transformation may include at least one of whether to use the first transformation or whether to use the second transformation.

The coded block flag may indicate whether a coded transform coefficient (or a quantized level) for a block exists in the bitstream.

In signal adaptive deblocking filtering, different quantization parameter offset values (qPOffsets) and quantization for different block boundaries based on at least one coding parameter for at least one block among blocks existing around a boundary At least one of the parameters (qP _BlockEdges ) may be selected for the process of deblocking filtering.

At least one of a quantization parameter offset value qPOffset and a quantization parameter qP _BlockEdge for a block boundary may change according to at least one coding parameter for at least one block among blocks existing around the boundary.

In the following, a syntax element required to implement signal adaptive deblocking filtering in the encoding apparatus 1600 and/or the decoding apparatus 1700, semantics of the syntax element, and encoding/decoding processes are illustrated.

34, 35, 36, and 37 illustrate syntax element information required for signal adaptive deblocking filtering.

At least one syntax element required for signal adaptive deblocking filtering may be encoded/decoded within at least one of a parameter set, a header, and a brick. Hereinafter, encoding may mean entropy encoding. Decryption may mean entropy decoding.

At least one of the parameter set, header, or brick is a video parameter set, a decoding parameter set, a sequence parameter set, an adaptation parameter set, a picture parameter set, a picture header, a sub-picture header, a slice header, a tile group header, a tile header, or a brick. It may be at least one of and the like.

In at least one of the units of the signaled parameter set, header, and brick, signal adaptive deblocking filtering using a syntax element for signal adaptive deblocking filtering may be used.

For example, when a syntax element for signal adaptive deblocking filtering is encoded/decoded within a sequence parameter set, signal adaptive deblocking filtering may be performed using a syntax element having the same value for a unit of a sequence.

For example, when a syntax element for signal adaptive deblocking filtering is encoded/decoded in a slice header, signal adaptive deblocking filtering using a syntax element having the same value for a unit of the slice may be performed.

For example, when a syntax element for signal adaptive deblocking filtering is encoded/decoded in an adaptation parameter set, signal adaptive deblocking filtering using a syntax element of the same value for units referencing the same adaptation parameter set is performed. Can be done.

The adaptation parameter set may refer to a parameter set that different pictures, different sub-pictures, different slices, different tile groups, different tiles, or different bricks can refer to and share. . Sub-pictures, slices, tile groups, tiles, or bricks in a picture may each refer to different adaptation parameter sets, and may use information in the adaptation parameter set that they refer to.

34 is a first syntax for signal adaptive deblocking filtering according to an example.

ladf_enabled_flag may be information indicating whether signal adaptive deblocking filtering is used by using a signal adaptive deblocking filtering syntax element in a unit of a signaled parameter set, header or brick.

The signal adaptive deblocking filtering syntax element may be at least one of num_ladf_intervals_minus2, ladf_lowest_interval_qp_offset, ladf_qp_offset[i], and ladf_delta_threshold_minus1[i].

num_ladf_intervals_minus2 + 2 may indicate the number of signal adaptive deblocking filtering syntax elements in a signaled parameter set, header, or brick unit.

The signal adaptive deblocking filtering syntax element may be at least one of ladf_qp_offset[i] and ladf_delta_threshold_minus1[i].

num_ladf_intervals_minus2 may have a value from 0 to N. Here, N may be a positive integer. For example, N may be 3.

ladf_lowest_interval_qp_offset may represent a quantization parameter offset value qPOffset for inducing a quantization parameter qP _BlockEdge for a block boundary.

ladf_lowest_interval_qp_offset may represent a quantization parameter offset value qPOffset for the first section to which the reconstructed signal component statistical value compLevel belongs.

ladf_lowest_interval_qp_offset can have a value from 0 to N. Here, N may be a positive integer. For example, N may be 63. In addition, N may represent a maximum value that a quantization parameter can have.

ladf_qp_offset[i] may represent an array of quantization parameter offset values qPOffsets for inducing a quantization parameter qP _BlockEdge for a block boundary.

ladf_qp_offset[i] may represent a quantization parameter offset value qPOffset for each section of sections to which the reconstructed signal component statistics value compLevel belongs.

ladf_qp_offset[ i] can have a value from 0 to N. Here, N may be a positive integer. For example, N may be 63. In addition, N may represent a maximum value that a quantization parameter can have.

ladf_delta_threshold_minus1[ i] may be a value used to calculate LadfIntervalLowerBound[ i ]. It may represent the minimum value for the i-th section in which the reconstructed signal component statistical value compLevel can belong.

LadfIntervalLowerBound[ i] can have a value from 0 to N. Here, N may be a positive integer. For example, N may be 2 ^BitDepth -3. BitDepth may represent a bit depth of a signal with respect to a luma component or a chroma component.

35 is a second syntax for signal adaptive deblocking filtering according to an example.

ladf_delta_prec_minus1 + 1 may represent the number of bits required to signal/express all ladf_delta_threshold_minus1[i].

ladf_delta_prec_minus1 can have a value from 0 to N. Here, N may be a positive integer. For example, N may be BitDepth-M. M can be a positive integer. For example, M may be 2.

36 is a third syntax for signal adaptive deblocking filtering according to an example.

ladf_delta_prec_minus1[ i] + 1 may represent the number of bits required to signal/express each ladf_delta_threshold_minus1[ i ].

ladf_delta_prec_minus1[ i] can have a value from 0 to N. Here, N may be a positive integer. For example, N may be BitDepth-M. M can be a positive integer. For example, M may be 2.

37 is a fourth syntax for signal adaptive deblocking filtering according to an example.

ladf_delta_bit_depth may represent the number of bits required to signal/express ladf_delta_threshold_minus1[i].

The ladf_delta_bit_depth value can have a value from 0 to BitDepth.

The value of LadfIntervalLowerBound[ 0] may be set to 0.

When i has a value from 0 to num_ladf_intervals_minus2, LadfIntervalLowerBound[ i + 1] may be calculated using at least one of Equation 7 and Equation 8 below.

[Equation 7]

LadfIntervalLowerBound[ i + 1] = LadfIntervalLowerBound[ i] + ladf_delta_threshold_minus1[ i] + 1

[Equation 8]

LadfIntervalLowerBound[ i + 1] = LadfIntervalLowerBound[ i] + (ladf_delta_threshold_minus1[ i] << (BitDepth-ladf_delta_bit_depth)) + 1

The following binarization, debinarization, entropy encoding method and/or entropy for at least one of the syntax elements for signal adaptive deblocking filtering signaled from the encoding device 1600 to the decoding device 1700 At least one or more of the decoding methods may be used.

-Signed 0-order Exp_Golomb binarization/inverse binarization method (se(v))

-Signed K-order Exp_Golomb binarization/inverse binarization method (sek(v))

-Zero-order exponent for unsigned positive integers-Golom binarization/inverse binarization method (ue(v))

-K-order exponent-Golom binarization/inverse binarization method for positive integers with no sign (uek(v))

-Fixed-length binarization/inverse binarization method (f(n))

-Truncated rice binarization/reverse binarization method or truncated unary binarization/reverse binarization method (tu(v))

-Truncated binary binarization/reverse binarization method (tb(v))

-Context-adaptive arithmetic encoding/decoding method (ae(v))

-Bit string in bytes (b(8))

-Signed integer binarization/inverse binarization method (i(n))

-Unsigned positive integer binarization/inverse binarization method (u(n))

-Unary binarization/inverse binarization method

As described below, the quantization parameter for the block boundary may be determined by adding a quantization parameter offset value calculated based on the reconstructed signal component value to the quantization parameter value for the block boundary.

First, a quantization parameter offset value qPOffset may be calculated.

When the value of ladf_enabled_flag is the second value (for example, "1"), steps 1) and 2) below may be performed.

Process 1) As described in Equation 5 above, compLevel may be calculated.

Step 2) The quantization parameter offset value qPOffset may be set as ladf_lowest_interval_qp_offset, and may be changed according to Code 1 below after setting.

[Code 1]

for( i = 0; i <num_ladf_intervals_minus2 + 1; i++) {

if( compLevel> LadfIntervalLowerBound[ i + 1])

qPOffset = ladf_qp_offset[ i]

else

break

}

Instead of step 2, the quantization parameter offset value qPOffset may be set to ladf_lowest_interval_qp_offset, and may be changed according to Code 2 below after setting.

[Code 2]

for( i = 0; i <num_ladf_intervals_minus2 + 1; i++) {

if( compLevel <LadfIntervalLowerBound[ i + 1])

qPOffset = ladf_qp_offset[ i]

else

break

}

Alternatively, instead of step 2, the quantization parameter offset value qPOffset may be set to ladf_lowest_interval_qp_offset, and may be changed according to code 3 below after setting.

[Code 3]

for( i = 0; i <num_ladf_intervals_minus2 + 1; i++) {

if( compLevel <= LadfIntervalLowerBound[ i + 1])

qPOffset = ladf_qp_offset[ i]

else

break

}

When the value of ladf_enabled_flag is a first value (eg, “0”), ladf_enabled_flag may be set to a quantization parameter offset value qPOffset.

38 is a table showing a relationship between a quantization parameter and a value related to filtering according to an example.

As shown in Equation 6 above, a quantization parameter qP _BlockEdge for a block boundary may be calculated.

In addition, at least one of β and tc may be determined, and deblocking filtering may be performed using at least one of β and tc.

β may be calculated by calculating the final quantization parameter Q for the block boundary as shown in Equation 9 below, and substituting the calculated final quantization parameter Q into the table of FIG. 38.

[Equation 9]

Q = Clip3( 0, 63, qP _BlockEdge + (beta_offset_div2 << 1))

beta_offset_div2 may represent an offset for a value of β signaled through at least one of a parameter set, a header, and a brick.

β may be a value for an 8-bit image. Scaling of β as shown in Equation 10 may be performed according to the bit depth of the image. The final value of β used for filtering can be calculated as in Equation 10 below.

[Equation 10]

β = β * (1 << (BitDepth-8))

tc may be calculated by calculating the final quantization parameter Q for the block boundary as shown in Equation 11 below, and substituting the calculated final quantization parameter Q into the table of FIG. 38.

[Equation 11]

Q = Clip3( 0, 65, qP _BlockEdge + 2 * (BS-1) + (tc_offset_div2 << 1))

tc_offset_div2 may represent an offset for a value of tc signaled in at least one of a parameter set, a header, and a brick.

tc may be a value for an 8-bit image. Scaling for tc as shown in Equation 10 may be performed according to the bit depth of the image. The final value of tc used for filtering can be calculated as in Equation 12 below.

[Equation 12]

tc = tc * (1 << (BitDepth-8))

39 is a flowchart of a filtering method according to an embodiment.

The filtering method may be performed by the encoding apparatus 1600 and the decoding apparatus 1700. Hereinafter, the processing unit may mean the processing unit 1610 of the encoding apparatus 1600 and/or the processing unit 1710 of the decoding apparatus 1700.

In step 3910, the processing unit may determine whether to perform filtering on the boundary of the target block.

Whether to perform filtering may be determined based on whether the boundary of the target block corresponds to at least one of a picture boundary, a sub-picture boundary, a slice boundary, a tile boundary, and a brick boundary.

In step 3920, the processor may determine a filtering strength for the boundary of the target block and the number of samples used for filtering.

The number of samples used for filtering may be determined based on at least one of a size of a target block and a size of a neighboring block adjacent to the boundary of the target block.

When the boundary of the target block is a vertical boundary, the number of samples used for filtering may be determined based on at least one of a horizontal size of a target block and a horizontal size of a neighboring block.

When the boundary of the target block is a horizontal boundary, the number of samples used for filtering may be determined based on at least one of a vertical size of a target block and a vertical size of a neighboring block.

The number of samples used for filtering may be determined by comparing at least one of a size of a target block and a size of a neighboring block with a predefined value.

For example, a predefined value that is compared with at least one of the size of the target block and the size of the neighboring block may be 32.

The number of samples used for filtering may be independently determined for the luma component and the chroma component of the target block.

The filtering strength may be determined based on a prediction mode of a target block and a prediction mode of a neighboring block.

For example, when a prediction mode of a target block and a prediction mode of a neighboring block are different from each other, it may be determined to use a weak filtering strength for filtering. Here, when a weak filtering strength is used, it may be BS = 1.

In operation 3930, the processor may perform filtering on the boundary of the target block based on the filtering strength and the number of samples used for filtering.

The filtering method according to the embodiment may be performed by the encoding apparatus 1600 and the decoding apparatus 1700 to generate a reconstructed image.

The embodiment may include a computer-readable non-transitory recording medium that stores image data for an image used in a decoding method. Here, the image data may be a bitstream. The bitstream may represent image data.

The image data may include the information and coding parameters described above for filtering. The target block may be decoded using the image data.

The information indicating whether to perform filtering in the bitstream indicates whether to perform filtering on the boundary of the target block by the encoding device 1600, and the decoding device 1700 determines whether to perform filtering on the boundary of the target block. Can be used.

In the above-described embodiments, the boundary of a target block may mean a boundary of a target block and/or a boundary of a neighboring block.

In the above-described embodiments, the neighboring block may mean a block adjacent to the boundary of the target block.

Using the aforementioned examples, unnecessary filtering may be prevented from being performed on a boundary where a blocking artifact does not occur, and a blocking artifact generated by at least one of prediction, transformation, and quantization may be removed.

When performing the filtering, samples used for filtering may be limited to samples belonging to two blocks.

When performing the filtering, different filtering strengths may be determined for transform and transform boundaries, blocks and transform boundaries, and blocks and blocks.

When performing the filtering, filtering may be performed when there is no actual edge at the boundary, and a filtering strength may be determined according to a transform and quantization type.

When performing the filtering, when the transform and quantization type is greater than or equal to 64×32 or 32×64, the strongest filtering strength may be used.

When performing the filtering, the number of samples used for filtering may be differently determined according to the size of the block, and the number of samples used for the filtering may increase as the size of the transform and quantization unit increases.

At least one of the above examples of the present invention may be used for luminance signal deblocking filtering or color difference signal deblocking filtering.

Using the above examples of the present invention, unnecessary filtering may be prevented from being performed on a boundary without a blocking phenomenon, and filtering may be performed on a block boundary where a blocking phenomenon has occurred by at least one of prediction, transformation, and quantization. .

In the embodiments of the present invention, the block may mean at least one of a coding block, a prediction block, and a transform block. In addition, the above block may mean a sub-block divided from blocks.

It is limited to only one of the above embodiments and is not applied to the deblocking filtering process, but a specific embodiment or at least one combination of the above embodiments may be applied to the deblocking filtering process.

The embodiments may be performed in the same manner in the encoding apparatus 1600 and the decoding apparatus 1700.

An image may be encoded/decoded using at least one or a combination of at least one of the above embodiments.

The order of applying the above embodiment may be different in the encoding apparatus 1600 and the decoding apparatus 1700, and the order of applying the above embodiment may be the same in the encoding apparatus 1600 and the decoding apparatus 1700.

The above embodiments may be performed for each of a luma signal and a chroma signal, and the above embodiments may be similarly performed for a luma signal and a chroma signal.

The shape of the block to which the above embodiments of the present invention are applied may have a square shape or a non-square shape.

The embodiments of the present invention may be applied according to the size of at least one of a target block, a coding block, a prediction block, a transform block, a block, a current block, a coding unit, a prediction unit, a transform unit, a unit, and a current unit. The size here may be defined as a minimum size and/or a maximum size in order to apply the embodiments, or may be defined as a fixed size to which the embodiments are applied. In addition, in the above embodiments, the first embodiment may be applied to the first size, and the second embodiment may be applied to the second size. That is, the always-on embodiments can be applied in combination according to the size. Further, the above embodiments of the present invention may be applied only when the size is greater than or equal to the minimum size and less than or equal to the maximum size. That is, the above embodiments may be applied only when the block size is within a certain range.

For example, the above embodiments can be applied only when the size of the target block is 8x8 or more. For example, the above embodiments can be applied only when the size of the target block is 4x4. For example, the above embodiments can be applied only when the size of the target block is 16x16 or less. For example, the above embodiments can be applied only when the size of the target block is 16x16 or more and 64x64 or less.

The above embodiments of the present invention can be applied according to a temporal layer. A separate identifier may be signaled to identify a temporal layer to which the above embodiments are applicable, and the above embodiments may be applied to a temporal layer specified by the corresponding identifier. Here, the identifier may be defined as the lowest layer and/or the highest layer to which the embodiment is applicable, or may be defined to indicate a specific layer to which the embodiment is applied. In addition, a fixed temporal layer to which the above embodiment is applied may be defined.

For example, the above embodiments can be applied only when the temporal layer of the target image is the lowest layer. For example, the above embodiments can be applied only when the temporal layer identifier of the target image is 1 or more. For example, the above embodiments can be applied only when the temporal layer of the target image is the highest layer.

A slice type or tile group type to which the above embodiments of the present invention are applied may be defined, and the above embodiments of the present invention may be applied according to the corresponding slice type or tile group type.

In the above-described embodiments, in applying the specified processing to a specified object, a specified condition may be required, and when the specified processing is described as being processed under a specified determination, the specified coding parameter If it is determined whether or not a specified condition is satisfied based on or has been described that a specified determination is made based on a specified coding parameter, it may be interpreted that the above specified coding parameter can be replaced with another coding parameter. That is to say, a coding parameter that affects a specified condition or a specified decision can be considered merely exemplary, and it will be understood that the combination of one or more other coding parameters in addition to the specified coding parameter plays the role of the above specified coding parameter. I can.

In the above-described embodiments, the methods are described on the basis of a flow chart as a series of steps or units, but the present invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps as described above. I can. In addition, those of ordinary skill in the art understand that the steps shown in the flowchart are not exclusive, other steps are included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention. You can understand.

The above-described embodiments include examples of various aspects. Not all possible combinations for representing various aspects may be described, but those of ordinary skill in the art will recognize that other combinations are possible in addition to the explicitly described combinations. Accordingly, the present invention will be said to include all other replacements, modifications and changes falling within the scope of the following claims.

The embodiments according to the present invention described above may be implemented in the form of program instructions that can be executed through various computer components and recorded in a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded in the computer-readable recording medium may be specially designed and configured for the present invention, or may be known and usable to those skilled in the computer software field.

The computer-readable recording medium may contain information used in embodiments according to the present invention. For example, a computer-readable recording medium may include a bitstream, and the bitstream may include information described in embodiments according to the present invention.

The computer-readable recording medium may include a non-transitory computer-readable medium.

Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magnetic-optical media such as floptical disks. media), and a hardware device specially configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of the program instructions include not only machine language codes such as those produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device may be configured to operate as one or more software modules to perform processing according to the present invention, and vice versa.

In the above, the present invention has been described by specific matters such as specific elements and limited embodiments and drawings, but this is provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. , Anyone with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations from these descriptions.

Therefore, the spirit of the present invention is limited to the above-described embodiments and should not be defined, and all modifications that are equally or equivalent to the claims as well as the claims to be described later fall within the scope of the spirit of the present invention. I would say.

Claims (20)

Determining whether to perform filtering on the target boundary of the target block;
If it is determined that the filtering is to be performed, determining a filtering strength for a target boundary of the target block and the number of samples used for filtering; And
And if it is determined that the filtering is to be performed, performing filtering on a target boundary of the target block based on the filtering strength and the number of samples used for the filtering. The method of claim 1,
The number of samples used for the filtering is determined based on at least one of a size of the target block and a size of a neighboring block adjacent to the target block. The method of claim 1,
Whether to perform the filtering is determined based on a component of the target block. The method of claim 1,
The filter length of the filtering is determined based on a size of the target block and a component of the target block. The method of claim 1,
The filtering strength of the filtering is determined based on prediction modes of a plurality of blocks adjacent to the target boundary. The method of claim 1,
The filtering strength of the filtering is determined based on a difference between motion vectors of a plurality of blocks adjacent to the target boundary. The method of claim 1,
If the target boundary is a picture boundary, filtering is not performed on the target boundary. The method of claim 1,
If the target boundary is a slice boundary, filtering on the target boundary is not performed. The method of claim 1,
The filtering is performed based on a quantization parameter for the target block. The method of claim 1,
Information indicating whether to perform the filtering is included in the parameter set,
If the information indicates that the filtering is not performed, it is determined not to perform the filtering. The method of claim 10,
The parameter set is referenced for a sub-picture. Determining whether to perform filtering on the target boundary of the target block;
If it is determined that the filtering is to be performed, determining a filtering strength for a target boundary of the target block and the number of samples used for filtering; And
If it is determined that the filtering is to be performed, performing filtering on a target boundary of the target block based on the filtering strength and the number of samples used for the filtering. The method of claim 13,
The filtering strength of the filtering is determined based on prediction modes of a plurality of blocks adjacent to the target boundary. The method of claim 12,
The filtering is performed based on a quantization parameter for the target block. The method of claim 1,
Information indicating whether to perform the filtering is included in a parameter set referenced for a sub-picture,
If the information indicates that the filtering is not performed, it is determined not to perform the filtering. A recording medium for recording a bitstream generated by the video encoding method according to claim 15. A computer-readable recording medium comprising a bitstream representing image data used in an image decoding method, comprising:
A target block is decoded using the image data,
Whether to perform filtering on the target boundary of the target block is determined,
When it is determined that the filtering is to be performed, the filtering strength of the target boundary of the target block and the number of samples used for filtering are determined
When it is determined that the filtering is to be performed, filtering is performed on the target boundary of the target block based on the filtering strength and the number of samples used for the filtering. The method of claim 17,
The filtering strength of the filtering is determined based on prediction modes of a plurality of blocks adjacent to the target boundary. The method of claim 17,
The filtering is performed based on a quantization parameter for the target block. The method of claim 17,
Information indicating whether to perform the filtering is included in a parameter set referenced for a sub-picture,
If the information indicates that the filtering is not performed, it is determined not to perform the filtering.

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