KR102242675B1 - Method and apparatus for quantization - Google Patents

Abstract

Disclosed are a video decoding method, a decoding device, an encoding method, and an encoding device. In quantization and inverse quantization, a plurality of quantization methods and a plurality of inverse quantization methods may be used. The plurality of quantization methods include a variable-rate step quantization method and a fixed-rate step quantization method. The variable-rate step quantization method is a quantization method in which an increase rate of a quantization step as a value of a quantization parameter increases by 1 is not fixed. The fixed-rate step quantization method is a quantization method in which the increase rate of the quantization step is fixed as the value of the quantization parameter increases by 1.

Description

Quantization method and apparatus TECHNICAL FIELD

The following embodiments relate to a video decoding method, a decoding apparatus, an encoding method, and an encoding apparatus, and to a method and apparatus for performing quantization in encoding and decoding a video.

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 users' demands 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.

An image encoding/decoding apparatus and method is an inter prediction technology, an intra prediction technology, and an entropy encoding technology, etc. to perform encoding/decoding for high-resolution and high-definition images. Can be used. The inter prediction technique may be a technique for predicting a value of a pixel included in a target picture using a temporally previous picture and/or a temporally later picture. The intra prediction technique may be a technique for predicting a value of a pixel included in a target picture using information on a pixel in the target picture. The entropy encoding technique may be a technique of allocating a short code to a symbol with a high frequency of appearance and a long code to a symbol having a low frequency of appearance.

Various quantization and inverse quantization methods have been developed to improve the efficiency of image encoding/decoding.

An image encoding/decoding technique may determine optimal coding parameters based on objective image quality. The decision to use such objective image quality can improve the efficiency of image encoding/decoding. However, the decision to use the objective picture quality may produce a result different from the perceptual picture quality that the viewer actually feels. In particular, when the bit rate of compressed data generated by encoding is low, it may not be easy to control the amount of information and perceptual quality.

An embodiment may provide an encoding apparatus, an encoding method, a decoding apparatus, and a decoding method using scaling of a residual signal.

An embodiment may provide an encoding device, an encoding method, a decoding device, and a decoding method that determine a quantization parameter and a quantization step.

In one side, the quantization method includes performing quantization using a quantization method, wherein the quantization method is a variable-rate step quantization method, and the variable-rate step quantization method is a quantization step according to an increase in a value of a quantization parameter by 1. An encoding method is provided, which is a quantization method in which the increase rate of is not fixed.

As the value of the quantization parameter is smaller, the increase rate of the quantization step of the variable-rate step quantization method may be greater as the value of the quantization parameter increases by 1.

The encoding method may further include selecting the quantization method from among a plurality of quantization methods.

The plurality of quantization methods may include a fixed-rate step quantization method and the variable-rate step quantization method.

The fixed-rate step quantization method may be a quantization method in which an increase rate of the quantization step as the value of the quantization parameter increases by 1 is fixed.

In a region in which the value of the quantization parameter is relatively larger, an increase rate of a quantization step of the variable-rate step quantization method is smaller than an increase rate of a quantization step of the fixed-rate step quantization method.

In the other side, it includes performing inverse quantization using an inverse quantization method, wherein the inverse quantization method is a variable-rate step inverse quantization method, and the variable-rate step inverse quantization method has a quantization parameter value 1 A decoding method is provided, which is an inverse quantization method in which an increase rate of a quantization step is not fixed.

As the value of the quantization parameter is smaller, the increase rate of the quantization step of the variable-rate step inverse quantization method may be greater as the value of the quantization parameter increases by 1.

The decoding method may further include selecting the inverse quantization method from among a plurality of inverse quantization methods.

The plurality of inverse quantization methods may include a fixed-rate step inverse quantization method and the variable-rate step inverse quantization method.

The fixed-rate step inverse quantization method may be an inverse quantization method in which an increase rate of the quantization step is fixed as the value of the quantization parameter increases by 1.

In a region in which the value of the quantization parameter is relatively larger, an increase rate of the quantization step of the variable-rate step inverse quantization method may be smaller than the increase rate of the quantization step of the fixed-rate step inverse quantization method.

A quantization parameter of the fixed-rate step inverse quantization method corresponding to the quantization parameter of the variable-rate step inverse quantization method may be determined.

A quantization step corresponding to a quantization parameter of the fixed-rate step inverse quantization method may be used for the inverse quantization.

According to the fixed-rate step inverse quantization method, a quantization step of the fixed-rate step inverse quantization method corresponding to the quantization parameter is determined, and a quantization step ratio is applied to the quantization step of the fixed-rate step inverse quantization method. A quantization step for the variable-rate step inverse quantization method may be determined.

The quantization step ratio may be a ratio between a quantization step of the variable-rate step inverse quantization method and a quantization step of the fixed-rate step inverse quantization method.

The decoding method may further include obtaining a quantization method indicator.

The quantization method indicator may indicate one inverse quantization method used for inverse quantization of a target block among the plurality of inverse quantization methods.

The quantization method indicator may indicate an inverse quantization method applied to a specific unit.

The specified unit may be a video, a sequence, a picture, or a slice.

The quantization method indicator may indicate whether the variable-rate step inverse quantization method is applied to the specified unit.

The decoding method may further include obtaining a quantization parameter using a quantization parameter difference value.

The quantization parameter may be used for the inverse quantization.

The quantization parameter difference value may be a difference between an intermediate value and a value of the quantization parameter.

The intermediate value may be an intermediate value of a range of a quantization parameter of the variable-rate step inverse quantization method.

The quantization parameter may be applied to a specific unit.

The decoding method may further include obtaining a quantization parameter using a quantization parameter difference value.

The quantization parameter difference value may be a difference between a quantization parameter value of an upper unit and a quantization parameter value of a lower unit.

The obtained quantization parameter may be used for the inverse quantization of the sub-unit.

The quantization parameter difference value may be included in the header of the lower unit.

The upper unit may be a picture, and the lower unit may be a slice.

In another aspect, in a computer-readable recording medium storing a bitstream for decoding an image, the bitstream includes information on a target block, information on the target block, and the inverse quantization method Inverse quantization using is performed, and the inverse quantization method is a variable-rate step inverse quantization method, and the variable-rate step inverse quantization method is an inverse rate of increase of the quantization step as the value of the quantization parameter increases by 1. A computer-readable recording medium as a quantization method is provided.

An encoding apparatus, an encoding method, a decoding apparatus, and a decoding method using scaling of a residual signal are provided.

An encoding apparatus, an encoding method, a decoding apparatus, and a decoding method for determining a quantization parameter and a quantization step are provided.

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 shape of a prediction unit PU that may be included in the coding unit CU.
5 is a diagram showing a form of a transform unit (TU) that may be included in the coding unit (CU).
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 location of 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 illustrates an addition order of 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 shows traditional distortion and perceptual distortion according to an example.
19 is a graph showing a relationship between a quantization parameter and a quantization step in a fixed-rate step quantization method according to an example.
20 is a graph showing a relationship between a quantization parameter and an SNR of a fixed-rate step quantization method according to an example.
21 is a flowchart of a quantization method according to an embodiment.
22 is a flowchart of an inverse quantization method according to an embodiment.
23 illustrates a quantization step according to a quantization parameter according to an example.
24 illustrates a quantization parameter and a quantization step ratio according to an example.
25 shows a table of quantization parameters and quantization steps of a variable-rate step quantization method according to an example.
26 illustrates a syntax of a video parameter set according to an example.
27 shows the syntax of a sequence parameter set according to an example.
28 illustrates syntax of a picture parameter set according to an example.
29 shows syntax of a slice segment header according to an example.

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 should 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 should 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 appropriately described, is limited only by the appended claims, along with all scopes equivalent 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. The above 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 includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, the above two components may be directly connected or connected to each other, but the above 2 It should be understood that other components may exist in the middle of the components of the dog. 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 between the two components.

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 a single component, or one component is divided into a plurality of components to perform a 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 as long as they do not depart 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 used only 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 a combination 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, in the present invention, the description of "including" a specific configuration does not exclude configurations other than the corresponding configuration, and means that additional configurations may also be included in the scope of the implementation of the present invention or the technical idea of the present invention.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings in order to enable 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 elements in the drawings, and redundant descriptions of the same elements are omitted.

Hereinafter, an image may mean one picture constituting a video, and may represent 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 of the images constituting a video" May be.

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

Hereinafter, the target image may be an encoding target image that is a target of encoding and/or a decoding target image that is a target of decoding. Also, the target image may be an input image input through an encoding device or an input image input through a decoding device.

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, which is an object of encoding, and/or a decoding object block, which is an object of decoding. In addition, the target block may be a current block that is currently a target of encoding and/or decoding. For example, the terms "target block" and "current block" may be used with the same meaning, and may be used interchangeably.

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 and element, attribute, etc. may have a value. A value of "0" such as information, data, flags, 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 of "1" such as information, data, flags, elements, 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 the following, terms used in the embodiments are described.

Encoder: refers to a device that performs encoding.

Decoder: refers to a device that performs decoding.

Unit: A unit may represent a unit for encoding and 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. Each of M and N may 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, the 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 processing for a unit may be performed according to the type of the unit.

-Depending on the function, the type of the 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, a transform block, and the like.

-A unit may mean 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 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. In addition, the unit depth may indicate the level at which the unit exists when the unit is expressed in a tree structure.

-The unit division information may include the 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.

-One unit may be hierarchically divided into a plurality of sub-units while having depth information based on a tree structure. That is to say, 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 indicates 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, the 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 ranging ^{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 be composed of one luminance component (Y) coding tree block and two chrominance component (Cb, Cr) coding tree blocks related to the luminance component coding tree block. have. In addition, the CTU may mean including the blocks and a syntax element for each block of the 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 partitioned 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 for referring 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 the target block. The neighboring block may mean a reconstructed neighboring block.

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

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

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

-Spatial neighboring blocks may refer to blocks whose boundaries are in contact with the target block or blocks located within a predetermined distance from the target block.

-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 blocks may include temporal neighboring blocks.

-Temporal neighboring blocks may include co-located blocks (col blocks).

-The collocated block may be a block in a co-located picture (col picture) that has already been restored. The position of the collocated block within the collocated picture may correspond to the position within 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 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 the prediction unit may also be a prediction unit.

Prediction unit partition: This 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 around 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 within 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.

Parameter set: The parameter set may correspond to header information among structures in the bitstream. For example, the parameter set may include a video parameter set, a sequence parameter set, a picture parameter set, and an adaptation parameter set.

In addition, the parameter set may include slice header information and tile header information.

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, 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. Rate-distortion cost can be calculated using Equation 1 below. In general, a combination in which the rate-distortion cost is minimized may be selected as an optimal combination in the rate-distortion optimization method.

[Equation 1]

-D can represent distortion. D may be a mean square error of the difference values between the original transform coefficients and the 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 Lagrangian multiplier. R may include not only coding parameter information such as prediction mode, motion information, and coded block flag, but also bits generated by encoding transform coefficients.

-The encoding apparatus may perform processes such as inter prediction and/or intra prediction, transformation, quantization, entropy encoding, inverse quantization, and 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.

-The parameter set may include at least one of a video parameter set, a sequence parameter set, a picture parameter set, and an adaptation parameter set. In addition, the parameter set may include information on a slice header and information on a tile header.

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

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

Reference picture: A 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 the reference picture list are List Combined (LC), List 0 (List 0; L0), List 1 (List 1; L1), 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.

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

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 _{of (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. Each of M and N may 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 constructed 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 and merge index, etc. It may mean information including at least one of.

Merge candidate list: The merge candidate list may mean a list constructed using merge candidates.

Merge candidate: The merge candidate may mean a spatial merge candidate, a temporal merge candidate, a combined merge candidate, a combined bi-prediction merge candidate, and a zero merge candidate. The merge candidate may include prediction type information, a reference picture index for each list, and motion information such as a motion vector.

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 transform units having a smaller size.

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 can 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 means a differential value between a predicted quantization parameter and a quantization parameter of a target unit.

Scan: Scan may refer to 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, arranging a one-dimensional array in 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 that is an object of inverse quantization in 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 in which the size of a value is not 0 or a transform coefficient level in which the size of a 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 device and a decoding device. The non-default matrix 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.

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 encode a target image using an intra mode and/or an inter mode.

Also, the encoding apparatus 100 may generate a bitstream including encoding information through encoding on a target image, and may output the generated bitstream. The generated bitstream may be stored in a computer-readable recording medium, and may be streamed through a wired/wireless transmission medium.

When an intra mode is used as the prediction mode, the switch 115 may be switched to intra. When the 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 a residual between 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 coded/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.

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.

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

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 and 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 that is a difference between the target block and the prediction block. The residual block may 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, 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 transform the residual block to generate a transform coefficient, 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.

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

The transform method used for transforming the residual block may be determined according to at least one of coding parameters for the target block and/or the 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 or a quantized level by quantizing a transform coefficient according to a quantization parameter. The quantization unit 140 may output the generated quantized transform coefficient level or the generated quantized 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 Coding/Code (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 encoding unit 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 the 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 inferred during an encoding or decoding process. For example, as information transmitted to the decoding device, there is a syntax element.

The coding parameter, like a syntax element, may include information (or flags, 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 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 into a quad tree, and the unit/block is binary. Information indicating whether the tree is divided, the direction of division of the binary tree type (horizontal or vertical direction), the division type of the binary tree type (symmetrical division or asymmetrical division), and whether the unit/block is divided into a ternary tree shape. Information represented, split direction in the form of a ternary tree (horizontal or vertical direction), prediction method (intra prediction or inter prediction), intra prediction mode/direction, reference sample filtering method, prediction block filtering method, prediction block boundary filtering method, filtering Filter tap, filter coefficient of filtering, inter prediction mode, motion information, motion vector, reference picture index, inter prediction direction, inter prediction indicator, reference picture list, reference picture, motion vector predictor, motion vector prediction candidate, motion vector candidate List, information indicating whether to use merge mode, merge candidate, merge candidate list, information indicating whether to use skip mode, type of interpolation filter, filter tap of interpolation filter, filter coefficient of interpolation filter, motion Vector size, motion vector expression accuracy, transform type, transform size, information indicating whether to use a first-order transform, information indicating whether to use an additional (second-order) transform, a first-order transform index, a second-order transform index, and residual Information indicating the presence or absence of a signal, a coded block pattern, a coded block flag, a quantization parameter, a quantization matrix, information about an intra-loop filter, whether or not an intra-loop filter is applied. Information, intra-loop filter coefficients, intra-loop filter taps, intra-loop filter shape/form, information indicating whether to apply a deblocking filter, deblocking filter coefficients, deblocking filter Tap, deblocking filter strength, deblocking filter shape/type Information indicating whether to apply adaptive sample offset, adaptive sample offset value, adaptive sample offset category, adaptive sample offset type, whether to apply adaptive in-loop filter, adaptive In-loop filter coefficient, adaptive intra-loop filter tap, adaptive intra-loop filter shape/shape, binarization/inverse binarization method, context model, context model determination method, context model update method, whether to perform regular mode, Whether to perform bypass mode, context bin, bypass bin, transform coefficient, transform coefficient level, transform coefficient level scanning method, image display/output order, slice identification information, slice type, slice division information, tile identification information, At least one of a tile type, tile division information, picture type, bit depth, information on a luminance signal, and information on a color difference signal, a combined form, or statistics may be included in the coding parameter. The prediction method may represent one of an intra prediction mode and an inter prediction mode.

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 a flag or index means that the encoding apparatus 100 transmits an entropy-encoded flag or entropy-encoded index generated by performing entropy encoding on the flag or index into a bitstream. It may mean to include, and the decoding apparatus 200 may mean obtaining a flag or index by performing entropy decoding on an entropy-encoded flag or entropy-encoded index extracted from the bitstream. .

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 in the reference picture buffer 190 as a reference image. Inverse quantization and inverse transformation of a target image encoded for decoding may be processed.

The quantized level may be inversely quantized in the inverse quantization unit 160 and may be inversely transformed in the inverse transform unit 170. The inverse quantized and/or inverse transformed coefficient may be summed with the prediction block through the adder 175, and a reconstructed block may be generated by summing the inverse quantized and/or inverse transformed coefficient and the prediction block. Here, the inverse quantized and/or inverse transformed coefficient may mean a coefficient in which at least one of dequantization and inverse-transformation has been performed, and may mean a reconstructed residual block.

The reconstructed block may pass through the filter unit 180. The filter unit 180 reconstructs at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF). It can be applied to a 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 the deblocking filter is applied to the target block, the applied filter may be different 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 the original image and the 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 dividing the pixels included in the image into predetermined groups, a filter to be applied to each divided group may be determined, and filtering may be performed differentially for each group. For the luminance signal, information related to whether to apply the adaptive loop filter may be signaled for each CU. 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 reconstructed block or reconstructed image that has passed through the filter unit 180 may be stored in the reference picture buffer 190. The reconstructed block that has passed 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 be used for inter prediction later.

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. In addition, 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 the 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 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 a symbol in the form of a quantized transform coefficient level. 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 the block using the upper right diagonal scan. 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. Also, 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 the 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 using pixel values of an already decoded block around 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 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 of 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, a merge mode, an AMVP mode, and a 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, and ALF to the reconstructed block or the reconstructed image. The reconstructed image may be a picture including a reconstructed block.

The reconstructed image that has passed through the filter unit 260 may be output by the encoding device 100 and may be used by the encoding device 100.

The reconstructed image that has passed through the filter unit 260 may be stored as a reference picture in the reference picture buffer 270. 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 an image composed of reconstructed blocks that have passed through the filter unit 260. The stored reference picture can then be used for inter prediction.

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".

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

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

Referring to FIG. 3, an image 300 may be sequentially divided into units of a largest coding unit (LCU). For each LCU, a partition 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 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 according to whether to divide one CU into a plurality of CUs. The number of divided CUs may be a positive integer of 2 or more including 2, 4, 8, 16, and the like. The horizontal size and the vertical size of the CU generated by the 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 the division.

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

The partitioning of the CU may 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 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 every 1 increase in depth.

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, which is an LCU, may be expressed as a depth of 0. A CU of 32x32 blocks can be expressed as a depth of 1. A 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 0, and a value of partition information of a CU to be partitioned 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.

For example, when one CU is divided into two CUs, the horizontal size or 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 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 size. 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.

4 is a diagram illustrating a shape of a prediction unit PU that may be included in the coding unit CU.

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 the PU is encoded by the intra mode, the PU may be encoded using one of the 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 encoded in one of 35 intra prediction modes.

Which of the 2Nx2N mode 410 and NxN mode 425 the PU is to be coded 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 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 an NxN-sized PU 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 an NxN-sized PU 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 the 2Nx2N size PU and the rate-distortion costs of the 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 the vertical size of each PU of the four PUs generated by the division are half of the horizontal size and half of 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, respectively. 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 illustrating a form of a transform unit (TU) that may be included in the coding unit (CU).

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, or 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 having 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.

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

Split information is 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 one or more of a "") and a binary type flag (hereinafter, "Btype_flag").

split_flag may be a flag indicating whether the 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 shape. 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 the block is divided into a quadtree 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 of 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 of binarytree_flag may indicate that the block is divided into a binary tree shape. 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 the block is divided into a vertical or horizontal division when the block is divided in the form of a binary tree. For example, a value of 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, partition 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 according to the size and/or shape of the block. When this 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, 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 form.

If the size of the block falls within a specified range, only binary tree-type partitioning may be possible. 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 only be divided in the form of a binary tree.

Information indicating a maximum block size and/or a minimum block size that can only be divided in the form of a binary tree may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. In addition, such 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 division may be possible. In this case, split_flag may be a flag indicating whether to split into a binary tree.

The division of the block may be limited by the previous division. For example, when a block is divided into a binary tree shape and a plurality of divided blocks are generated, each divided block may be further divided only in a binary tree shape.

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.

7 is a diagram for describing an embodiment of an intra prediction process.

Arrows from the center to the outside of the graph of FIG. 7 may indicate prediction directions of intra prediction modes. Also, a number displayed adjacent 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.

Intra encoding and/or decoding may be performed using reference samples of units adjacent to the target block. The surrounding block may be a reconstructed block around it. For example, intra encoding and/or decoding may be performed using a value of a reference sample or a coding parameter included in a neighboring reconstructed 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.

For example, the number of intra prediction modes may be fixed to 35 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 or 36.

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 33 directional modes as shown in FIG. 6.

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

The directional modes may be prediction modes having a specific direction or a specific angle.

The intra prediction mode may be represented by at least one of a mode number, a mode value, and a mode angle. 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 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. 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 a block size and/or a color component type.

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 differ depending on whether the 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 color difference component block.

For example, in the case of a vertical mode having a mode value of 26, 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 10, 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 a reference sample 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 bottom of the horizontal mode may be referred to as a horizontal-below mode. For example, in FIG. 6, intra prediction modes having a mode value of 27, 28, 29, 30, 31, 32, 33, and 34 may be vertical right modes 613. Intra prediction modes having a mode value of 2, 3, 4, 5, 6, 7, 8, and 9 may be horizontal lower modes 616.

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, other modes excluding 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 described above and the mode value of each intra prediction mode may be exemplary only. 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. If there is a sample that cannot be used as a reference sample of the target block among the samples of the neighboring block, the value generated by copying and/or interpolation using at least one sample value of the samples included in the restored neighboring block is It may 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.

During intra prediction, 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, a size of the target block, and a shape of the target block. Filter types may be classified according to one or more of the number of filter taps, filter coefficient values, and filter strength.

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. In addition, 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-level 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 the 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 location of a reference sample used in an intra prediction process.

8 shows positions of reference samples used for intra prediction of a target block. Referring to FIG. 8, reconstructed reference samples used for intra prediction of a target block are lower-left reference samples 831, left reference samples 833, and upper left reference samples. left) corner reference samples 835, upper reference samples 837, upper-right reference samples 839, and the like.

For example, the left reference samples 833 may mean a reconstructed reference pixel adjacent to the left side of the target block. The upper reference samples 837 may mean a reconstructed reference pixel adjacent to the upper end of the target block. The upper left corner reference sample 835 may mean a reconstructed reference pixel located at the upper left corner of the target block. Further, the lower left reference samples 831 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 833. The upper right reference samples 839 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 837.

When the size of the target block is NxN, each of the lower left reference samples 831, the left reference samples 833, the upper reference samples 837, and the upper right reference samples 839 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.

The 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 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 a vertical mode having a mode value of 26, upper reference samples 837 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 837 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 837.

For example, when the intra prediction mode of the target block is a horizontal mode having a mode value of 10, left reference samples 833 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 833 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 833.

For example, when the mode value of the intra prediction mode of the target block is 18, at least some of the left reference samples 833, the upper left corner reference sample 835, and at least some of the upper reference samples 837 are performed. Can be used. When the mode value of the intra prediction mode is 18, 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 27, 28, 29, 30, 31, 32, 33, or 34 is used, at least some of the upper right reference samples 839 may be used for intra prediction.

In addition, when an intra prediction mode having a mode value of 2, 3, 4, 5, 6, 7, 8, or 9 is used, at least some of the lower left reference samples 831 may be used for intra prediction.

In addition, when an intra prediction mode having a mode value of 11 to 25 is used, the upper left corner reference sample 835 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, and may be 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 reference sample indicated by the location of the pixel and the direction of the intra prediction mode. When the position of the reference sample indicated by the position of the pixel and the direction of the intra prediction mode is an integer position, the value of one reference sample indicated by the integer position may be used to determine the pixel value of the pixel of the prediction block.

If the location of the reference sample indicated by the location of the pixel and the direction of the intra prediction mode is not an integer location, an interpolated reference sample may be generated based on the two reference samples closest to the location 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. Due to such a prediction error, discontinuity may occur between a prediction block and a neighboring block generated by such 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. Also, 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.

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. 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 one-way direction may be a forward direction or a reverse direction.

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 may be performed using 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. You can do it. 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, the motion information of the spatial candidate may be motion information of the PU including the 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 by 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 at 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 position 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 at 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 distance and the second distance. The first distance may be a distance between a reference picture of a target block and a target picture. The second distance may be a distance between the reference picture of the collocated block and the 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, there may be an advanced motion vector predictor (AMVP) mode, a merge mode, a skip mode, and a current picture reference mode. have. 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 around 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 that 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 motion vector of the reconstructed 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. Also, in the encoding apparatus 100, the predicted motion vector candidate may be an initial motion vector search position.

1-2) Search for a motion vector using a 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.

Also, 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 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 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 entropy encode the MVD.

The MVD may be transmitted from the encoding device 100 to the decoding device 200 through a bitstream. The decoding apparatus 200 may decode the received MVD. The decoding apparatus 200 may derive the motion vector of the target block by adding the decoded 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 entropy-decoded MVD and the motion vector candidate.

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 refers to 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. In other words, 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. That is to say, the reference direction can point to one of only a reference picture list L0, only a 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 reference picture index may be entropy-encoded by the encoding apparatus 100. The entropy-encoded reference picture index may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream.

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. Also, 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 and 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 neighboring blocks 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 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 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. Also, 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.

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 motion information induction mode in units of sub-blocks 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) a 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 merging is performed in units of CUs or units of PUs, 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. It can contain 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 using merge candidates in a merge candidate list and generate residual blocks for merge candidates. The encoding apparatus 100 may use a merge candidate that requires a minimum cost in prediction and encoding of the residual block for encoding the 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 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 and 2) a merge index.

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 the merge index to indicate the selected merge candidate.

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 in which the residual signal is not used. That is to say, when the skip mode is used, the reconstructed block may be a prediction block.

The difference between the merge mode and the skip mode may be whether the 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.

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 used with a skip mode, the encoding apparatus 100 may not signal a syntax element related to at least one of MVC, a coded block flag, and a transform coefficient level to the decoding apparatus 200.

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 in 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-restored region in a target picture to which the target block belongs.

A motion vector for specifying the pre-restored region may be used. Whether 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 encoded 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.

In the above-described AMVP mode, merge mode, and skip mode, 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 predicted 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 upper end 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 the 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 can 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 illustrates an addition order of motion information of spatial candidates to a merge list according to an example.

As shown in FIG. 11, in adding motion information of spatial candidates to the merge list, the 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 maximum number set is displayed as N. The set number may be transmitted from the encoding device 100 to the decoding device 200. The slice header of the 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) Available spatial candidates among the 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, if 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 a maximum of N pieces.

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. In addition, 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 are to be used among one or more L0 motion information and one or more L1 motion information 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 that is preferentially added 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 motion information having a merge index of 0 is not L0 motion information or 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 in the field of video encoding/decoding.

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 between 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 predicted 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 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 a maximum of N pieces.

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 the 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 the quantization process.

The transformation kernel used for transformation may include various 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 shown in Table 3 below.

[Table 3]

As shown in Table 3, 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 4 below shows an example of a transform set applied in the horizontal direction according to the intra prediction mode.

[Table 4]

In Table 4, the number of transform sets applied to the horizontal direction of the residual signal according to the intra prediction mode of the target block is indicated.

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

[Table 5]

As illustrated in Tables 4 and 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.

As described above, a method using various transforms 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, the vertical direction and the horizontal direction).

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. As an example, a plurality of predefined transformation methods include Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), and Karhunen-Loeve Transform (KLT) based transformation. Can include.

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

The first and second transformations may be applied to one or more signal components of a luminance component and a chrominance 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.

The transform method(s) applied to 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. The determined transformation method may indicate that the first order transformation and/or the second order transformation are not used.

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

A quantized level 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 the 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.

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 may 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 transform, the second-order transform, and quantization of the residual signal of the target block are Can be created. Thereafter, one of three scanning orders may be applied to the four 4x4 sub-blocks, and quantized transform coefficients may be scanned for each 4x4 sub-block according to the scanning order.

The scanned quantized transform coefficients may be entropy-coded, and the bitstream may include entropy-coded quantized transform coefficients.

The decoding apparatus 200 may generate quantized transform coefficients through entropy decoding of a bitstream. 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 diagonal scan, a vertical scan, and a horizontal scan at the top right corner may be performed.

Inverse quantization may be performed on the quantized transform coefficients. With respect to the result generated by performing the inverse quantization, the second-order inverse transformation may be performed depending on whether or not the second-order inverse transformation is performed. In addition, with respect to the result generated by performing the second-order inverse transform, the first-order inverse transform may be performed depending on whether or not the first-order inverse transform is performed. 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.

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 processor 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, in the embodiment, the generation and processing of data or information, and inspection, comparison, and determination related to the 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 instructions or codes 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 for the encoding apparatus 1600 to operate. The memory 1630 may store at least one module, and at least one module may be configured to be executed by the processing unit 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. In addition, the decoding apparatus 1700 may further include a communication unit 1720 connected to the network 1799.

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

The processor 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 communication of data or information 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.

Quantization method and apparatus for improving perceptual image quality

18 shows traditional distortion and perceptual distortion according to an example.

In Fig. 18, the relationship between the bit rate and distortion of the video is shown.

As shown in Fig. 18, traditional distortion is represented as a curve. On the other hand, perceptual distortion is expressed in the form of steps.

Perceptual distortion may be a distortion that a viewer feels about a video that is actually decoded and output by a viewer.

For traditional distortion, a statistically lossy area and a statistically lossless area are shown.

For perceptual distortion, perceptually lossy regions and perceptually lossless regions are shown.

According to the perceptual distortion graph, the viewer can suddenly perceive a large distortion at the point where the bit rate is a. On the other hand, the viewer may not recognize that the degree of distortion changes between the point where the bit rate is a and the point where the bit rate is b. Therefore, in the areas a to b, it may be advantageous in terms of perceptual image quality to finely adjust the bit rate and perform encoding of the bit rate a if possible.

In addition, particularly for a video having a low bit rate, fine adjustment for perceptual image quality may be required according to the principle of perceptual distortion.

19 is a graph showing a relationship between a quantization parameter and a quantization step in a fixed-rate step quantization method according to an example.

In the following embodiment, a plurality of quantization methods are described.

The plurality of quantization methods may include 1) a fixed-rate step quantization method and 2) a variable-rate step quantization method.

The fixed-rate step quantization method may be a quantization method in which an increase rate of a quantization step is fixed as a value of a quantization parameter increases by 1. For example, the fixed-step quantization method may be a quantization method in which a quantization step increases by about 12% every time a value of a quantization parameter increases by one.

For example, as shown in FIG. 19, when a fixed-rate step quantization method is used, when the quantization parameter increases by 6, the quantization step may increase by 2 times.

When the fixed-rate step quantization method is used, an increase amount of the quantization step in a region in which the value of the quantization parameter is relatively smaller may be smaller.

Hereinafter, the terms "increased amount of quantization step" and "increased amount of quantization step" may have the same meaning and may be used interchangeably.

An area in which the value of the quantization parameter is relatively smaller may generally be a high-definition area having a high bit rate. Therefore, when a fixed-rate step quantization method is used, a change in perceptual image quality according to a change in a value of a quantization parameter may be less in a range of a high bit rate. In addition, since the change in perceptual image quality is less, it is easy to control the image quality in detail, but the change in image quality may be insignificant.

In addition, when the fixed-rate step quantization method is used, the amount of increase in the quantization step in a region in which the value of the quantization parameter is relatively larger may be greater.

A region in which the value of the quantization parameter is relatively larger may be a low-quality region having a low bit rate in general. Accordingly, when a fixed-rate step quantization method is used, a change in perceptual image quality according to a change in a value of a quantization parameter may be greater in a range of a low bit rate. Also, since the change in perceptual image quality is larger, it may be difficult to finely control the image quality.

The variable-rate step quantization method may be a quantization method in which an increase rate of a quantization step as a value of a quantization parameter increases by 1 is not fixed. Alternatively, the variable-rate step quantization method may be a quantization method in which an increase rate of the quantization step as the value of the quantization parameter increases by 1 changes according to the value of the quantization parameter.

Since the increase rate of the quantization step as the value of the quantization parameter increases by 1 changes according to the value of the quantization parameter, when the variable-rate step quantization method is used, perceptual quality can be easily controlled in all bit rate regions. From this point of view, the variable-rate step quantization method can be regarded as a quantization method for the viewpoint of perceptual image quality.

For example, as the value of the quantization parameter is smaller, the increase rate of the quantization step of the variable-rate step quantization method may be greater as the value of the quantization parameter increases by 1.

For example, in a region in which the value of the quantization parameter is relatively smaller, the increase rate of the quantization step of the variable-rate step quantization method may be greater than the increase rate of the quantization step of the fixed-rate step quantization method.

For example, in a region in which the value of the quantization parameter is relatively larger, the increase rate of the quantization step of the variable-rate step quantization method may be smaller than the increase rate of the quantization step of the fixed-rate step quantization method.

20 is a graph showing a relationship between a quantization parameter and an SNR of a fixed-rate step quantization method according to an example.

20 shows that the quantization parameter and the signal-to-noise ratio (SNR) of the fixed-rate step quantization method have a linear relationship. Linear control can be made possible by this relationship, and SNR can be easily controlled.

Hereinafter, the description of the quantization method may also be applied to the inverse quantization method. Quantization and inverse quantization are processes performed by the encoding apparatus 100 and the decoding apparatus 200 respectively for encoding and decoding of a target block, and may be understood to correspond to each other. For example, the plurality of inverse quantization methods may include a fixed-rate step inverse quantization method and a variable-rate step inverse quantization method. The description of the variable-rate step quantization method can also be applied to the variable-rate step inverse quantization method. The description of the fixed-rate step quantization method can also be applied to the fixed-rate step inverse quantization method.

21 is a flowchart of a quantization method according to an embodiment.

In step 2110, the quantization unit 140 may select a quantization method.

The quantization unit 140 may select a quantization method to be used for a transform coefficient of a target block among a plurality of quantization methods.

The plurality of quantization methods may include a fixed-rate step quantization method and a variable-rate step quantization method.

The quantization method indicator may indicate a quantization method selected from among a plurality of quantization methods.

Hereinafter, the selected quantization method may be a variable-rate step quantization method.

In step 2120, the quantization unit 140 may perform quantization using the selected quantization method.

The quantization unit 140 may generate a quantized transform coefficient level by performing quantization using a selected quantization method on the transform coefficient.

In step 2130, the entropy encoder 150 may store information on quantization.

The entropy encoder 150 may generate a bitstream including information on quantization. Alternatively, the entropy encoder 150 may include information on quantization in a bitstream generated by the encoding apparatus 100.

The information on quantization may include 1) quantization method indicator information, 2) quantization parameter information, and 3) quantized transform coefficient level information.

The quantization method indicator information may indicate a quantization method indicator. The quantization parameter information may indicate a quantization parameter. The quantized transform coefficient level information may indicate the quantized transform coefficient level.

The entropy encoder 150 may generate quantization method indicator information by performing entropy encoding on the quantization method indicator. The quantization method indicator information may be generated between steps 2110 and 2120, and may be stored in a bitstream.

The entropy encoding unit 150 may generate quantization parameter information by performing entropy encoding on the quantization parameter. Quantization parameter information may be generated before step 2110 or between steps 2110 and 2120, and may be stored in a bitstream.

The entropy encoder 150 may generate quantized transform coefficient level information by performing entropy encoding on the quantized transform coefficient level.

22 is a flowchart of an inverse quantization method according to an embodiment.

The entropy decoder 210 may receive a bitstream.

The bitstream may include information on a target block. Information on the target block may include information on quantization.

As described above with reference to FIG. 21, information on quantization may include 1) quantization method indicator information, 2) quantization parameter information, and 3) quantized transform coefficient level information.

The quantization method indicator may also be referred to as an inverse quantization method indicator. Also, the quantization parameter may be referred to as an inverse quantization parameter.

In step 2210, the entropy decoding unit 210 may obtain a quantization method indicator.

The quantization method indicator may indicate one inverse quantization method used for inverse quantization of a target block among a plurality of inverse quantization methods.

The entropy decoding unit 210 may obtain a quantization method indicator by performing entropy decoding on the quantization method indicator information.

In step 2220, the entropy decoder 210 may obtain a quantization parameter.

The quantization parameter can be used for inverse quantization of the target block.

The entropy decoding unit 210 may obtain a quantization parameter by performing entropy decoding on the quantization parameter information. Alternatively, the entropy decoder 210 may obtain a quantization parameter by using a quantization parameter difference value to be described later.

In step 2230, the inverse quantization unit 220 may select an inverse quantization method.

The inverse quantization unit 220 may select an inverse quantization method indicated by a quantization method indicator among a plurality of inverse quantization methods.

In step 2240, the inverse quantization unit 220 may perform inverse quantization using the selected inverse quantization method.

The inverse quantization unit may perform inverse quantization using information on the target block and an inverse quantization method.

The inverse quantization unit 220 may generate a transform coefficient by performing inverse quantization using a selected inverse quantization method with respect to the quantized transform coefficient level.

23 illustrates a quantization step according to a quantization parameter according to an example.

23 may show modeling of a relationship between a quantization parameter and a quantization step in a variable-rate step quantization method.

In FIG. 23, the relationship between the quantization parameter and the quantization step of the fixed-rate step quantization method is shown as a graph.

In the graph, the x-axis represents the value of the quantization parameter of the fixed-rate step quantization method. The y-axis represents the value of the quantization step.

In FIG. 23, symbols "O" denote values of quantization steps corresponding to values of the quantization parameter with respect to integer values of the quantization parameter of the fixed-rate step quantization method. In other words, coordinates of one symbol "O" may be (a value of a quantization parameter of a fixed-rate step quantization method, a value of a quantization step corresponding to a value of a quantization parameter of the fixed-rate step quantization method). Since the value of the quantization parameter of the fixed-rate step quantization method is an integer, and the x-axis of the graph represents the value of the quantization parameter of the fixed-rate step quantization method, the symbols "O" are shown above the integer positions of the x-axis.

In FIG. 23, symbols "X" denote values of quantization steps corresponding to integer values of a quantization parameter of the variable-rate step quantization method. However, the symbol "X" is arranged to be located on a curve composed of the symbols "O" (for comparison with the fixed-rate step quantization method). In other words, the x-coordinate of the symbol "X" may not represent the value of the quantization parameter of the variable-rate step quantization method. Two symbols "X" adjacent to each other may correspond to integer values of a quantization parameter of a variable-rate step quantization method having a difference of values by one.

As shown in FIG. 23, in the fixed-rate step quantization method, as the value of the quantization parameter increases by 1, the quantization step may increase by about 12%. In other words, the difference between the quantization steps of adjacent symbols "O" may be about 12%.

As illustrated in FIG. 23, in a range in which the value of the quantization parameter is relatively smaller, the spacing between symbols "X" may be wider than the spacing between symbols "O". This may mean that the increase amount of the quantization step of the adjacent symbols "X" is greater than the increase amount of the quantization step of the adjacent symbols "O". That is to say, in a range in which the value of the quantization parameter is relatively smaller, when the value of the quantization parameter increases by 1, the increase amount of the quantization step of the variable-rate step quantization method is more than the increase of the quantization step of the fixed-rate step quantization method. It can be big.

Further, in a range in which the value of the quantization parameter is relatively larger, the spacing between symbols "X" may be narrower than the spacing between symbols "O". This may mean that the increase amount of the quantization step of adjacent symbols "X" is smaller than the increase amount of the quantization step of adjacent symbols "O". That is to say, in a range in which the value of the quantization parameter is relatively larger, when the value of the quantization parameter increases by 1, the increase amount of the quantization step of the variable-rate step quantization method is more than the increase amount of the quantization step of the fixed-rate step quantization method. It can be small.

24 illustrates a quantization parameter and a quantization step ratio according to an example.

In the graph of FIG. 24, the x-axis may represent a value of a quantization parameter. The y-axis may represent a value of the quantization step ratio. The quantization step ratio may be a ratio between a quantization step of a variable-rate step quantization method and a quantization step of a fixed-rate step quantization method.

The quantization step ratio can be derived by a gamma function, a calorie function, or a function having a shape and/or characteristic similar to these functions.

According to the graph of FIG. 24, the quantization step ratio increases in a range in which the value of the quantization parameter is relatively smaller. That is, in a range in which the value of the quantization parameter is relatively smaller, the quantization step of the variable-rate step quantization method may increase faster than the quantization step of the fixed-rate step quantization method.

Also, according to the graph of FIG. 24, the quantization step ratio decreases in a range in which the value of the quantization parameter is relatively larger. In other words, in a range in which the value of the quantization parameter is relatively larger, the quantization step of the fixed-rate step quantization method may increase faster than the quantization step of the variable-rate step quantization method.

The quantization method according to the viewpoint of perceptual image quality may be implemented by defining and/or adjusting the rate of increase of the value of the quantization step as the value of the quantization parameter increases by 1 as described above. This definition and/or adjustment may be implemented through the following methods 1) and 2).

1) A quantization parameter of the fixed-rate step quantization method corresponding to the quantization parameter of the variable-rate step quantization method is determined, and a quantization step corresponding to the determined quantization parameter of the fixed-rate step quantization method may be used for quantization.

2) According to the fixed-rate step quantization method, a quantization step corresponding to a quantization parameter is determined, and a quantization step for the variable-rate step quantization method may be determined by applying a quantization step ratio to the determined quantization step. In other words, the determined quantization step may be a product of the quantization step and the quantization step ratio of the fixed-rate step quantization method.

Below, an example of a method of determining a quantization parameter of a fixed-rate step quantization method corresponding to a quantization parameter of a variable-rate step quantization method, and using a quantization step corresponding to the quantization parameter of the determined fixed-rate step quantization method is shown. Is explained.

Hereinafter, the quantization parameter of the variable-rate step quantization method is denoted by QP _perceptual , and the quantization parameter of the fixed-rate step quantization method is denoted by QP.

In order to use the variable-rate step quantization method, which is a quantization method according to the perspective of perceptual image quality, QP _perceptual and QP can be mapped to each other through various methods. In addition, an equation or relationship between the QP and the quantization step used in the fixed-rate step quantization method may be defined and used. According to this mapping, and the relationship, the quantization staff corresponding to QP _perceptual and defined and / or can be derived according to QP _perceptual, there is quantization staff corresponding to the _perceptual QP may be used.

Equation 2 below is a gamma function representing a relationship between QP _perceptual and QP according to an example.

[Equation 2]

The QP _perceptual corresponding to the specified QP may be determined according to the relationship indicated by the gamma function of Equation 2.

When QP _perceptual is used for quantization and/or inverse quantization, a value of QP corresponding to a value of QP _perceptual may be derived through a gamma function such as Equation 2. The gamma function may have gamma function parameters (α, γ). The value of QP corresponding to the value of QP _perceptual may be determined by gamma function parameters (α, γ).

Fixed predefined values may be used in the encoding apparatus 100 and the decoding apparatus 200 as gamma function parameters (α, γ). In other words, the encoding apparatus 100 and the decoding apparatus 200 may share the same gamma function parameters (α, γ).

Alternatively, parameters (α, γ) of the gamma function may be signaled from the encoding device 100 to the decoding device 200 through a bitstream.

For example, the above-described quantization information may include gamma function parameters information. The entropy encoder 150 may generate gamma function parameter information by performing entropy encoding on gamma function parameters of the gamma function. The entropy decoding unit 210 may obtain gamma function parameters by performing entropy decoding on gamma function parameters information.

Among the gamma function parameters, α may be a parameter that allows a value of QP existing within a certain range to be issued with respect to the input QP _perceptual. α may have an integer value or a value scaled to an integer.

Among the parameters of the gamma function, γ may be a parameter for determining a QP corresponding to an input QP _perceptual. γ may have an integer value or a value scaled to an integer.

In general, QP may have an integer value in the range of 0 to 51. On the other hand, the QP value corresponding to the input QP _perceptual may be a real value within the range of 0 to 51. However, the value of the quantization step actually applied to scaling of the transform coefficient may be an integer. The value of the quantization step may be a value approximated in the form of an integer through scaling. In other words, even if the QP value derived through the above-described method can be expressed as a real number instead of an integer, the integer value of the quantization step may be determined in various ways.

For example, the value of the quantization step may be scaled and approximated to an integer value using a relation function between the QP and the quantization step. Alternatively, the value of the quantization step may be determined through a table look-up.

25 shows a table of quantization parameters and quantization steps of a variable-rate step quantization method according to an example.

In FIG. 25, values of a quantization parameter qP and a quantization step q_step used in quantization and inverse quantization using a variable-rate step quantization method are shown.

In FIG. 25, a value of a quantization step q_step for a value of a specified quantization parameter qP is illustrated. For example, when the value of the quantization parameter is 0, the value of the quantization step may be 40.

QP and q_step illustrated in FIG. 25 may represent quantization steps corresponding to _{QP perceptual} and QP _{perceptual, respectively.} That is to say, the table shown in FIG. 25 can be used for a look-up to determine the value of the quantization step described above.

The quantization parameter may be used for each unit for encoding and/or decoding a video. For example, a quantization parameter may be determined for a slice. In the case of a luminance component, a quantization parameter determined for a slice may be SliceQpY. The quantization parameter qP for the target block in the slice may be determined by the quantization parameter determined for the slice.

The value of the quantization step corresponding to the quantization parameter qP may be determined by 1) a table look-up for a table as shown in FIG. 25, 2) a relational expression between the quantization parameter and the quantization step, and 3) various other methods. .

For example, the value of the quantization step may be derived using a relation function of a quantization parameter and an increase rate of the value of the quantization step.

For example, the value of the quantization step may be determined by referring to a predefined value as shown in FIG. 25 through a table look-up. The value of the quantization step may be determined through a table look-up as shown in Equation 3 below.

[Equation 3]

q_step = q_step_table[qP]

Here, q_step_table may represent a table.

For example, the value of the quantization step may be determined as in Equation 4 using a relational expression between the quantization parameter and the quantization step.

[Equation 4]

q_step = q_function(qP, param1, param2, ...)

The input parameters of q_function for determining the value of the quantization step are 1) the value of the quantization parameter qP of the variable-rate step quantization method and 2) the value of the quantization parameter value qP of the variable-rate step quantization method as the value of the corresponding quantization step. It may be one or more parameters of the function to convert. For example, one or more parameters may be α and γ described above.

As these input parameters are input, the q_function can derive the value of the quantization step.

q_function may be implemented as a fixed-point operation in order to determine a value scaled by an integer type of a quantization type for a value qP of an input quantization parameter.

The inverse quantization method using the value of the quantization step may be performed as shown in Equation 5 below.

[Equation 5]

dq_transCoeffLevel = TransCoeffLevel * m * q_step

TransCoeffLevel may be one quantized transform coefficient. m may be a scaling factor. q_step may be a quantization step.

Scaling for one quantized transform coefficient TransCoeffLevel may be performed by the scaling factor m.

The dequantized transform coefficient dq_transCoeffLevel may be a product of the scaled quantized transform coefficient and the quantization step q_step. Alternatively, the dequantized transform coefficient dq_transCoeffLevel may be a product of a quantized transform coefficient TransCoeffLevel, a scaling factor m for the quantized transform coefficient, and a quantization step.

The inverse quantized transformation coefficient may be converted or determined into an integer type through an operation that considers the data type of each value and the dynamic range of each value according to the implementation of the encoding apparatus 100 and the decoding apparatus 200. have. Here, values may include TransCoeffLevel, m and q_step described above. The operation may include a clipping operation and a rounding operation.

The inverse quantization described above may be performed by the inverse quantization unit 160 of the encoding apparatus 100 and/or the inverse quantization unit 220 of the decoding apparatus 200. Further, quantization corresponding to the above-described inverse quantization may be performed by the quantization unit 140 of the encoding apparatus 100.

26 illustrates a syntax of a video parameter set according to an example.

27 shows the syntax of a sequence parameter set according to an example.

28 illustrates syntax of a picture parameter set according to an example.

29 shows syntax of a slice segment header according to an example.

In performing inverse quantization, a quantization method to be applied to a specified unit may be indicated through a higher level syntax. Here, the indicated quantization method may be one of a plurality of quantization methods. The higher-level syntax may include a quantization method indicator, and the quantization method indicator included in the higher-level syntax may indicate a quantization method to be applied to a specific unit that is an object of the higher-level syntax.

Alternatively, the high-level syntax may indicate whether the variable-rate step quantization method is applied to a specific unit. For example, the quantization method indicator included in the high-level syntax may indicate whether the variable-rate step quantization method is applied to a specific unit that is the target of the high-level syntax.

Alternatively, the higher-level syntax may indicate a quantization method applied to the specified unit among a plurality of quantization methods for the specified unit.

For example, the specified unit may be a video, a sequence, a picture, or a slice.

For example, the video parameter set may indicate a quantization method to be applied to an object of the video parameter set. The video parameter set may include the quantization method indicator information described above. The quantization method indicator information may indicate a quantization method to be applied to an object of a video parameter set among a plurality of quantization methods. Alternatively, the quantization method indicator information may indicate whether the variable-rate step quantization method is applied to an object of the video parameter set.

As quantization method indicator information for the above video parameter set, vps_perceptual_qp_enabled_flag is illustrated in FIG. 26. The quantization method indicator information may be a 1-bit flag.

For example, the sequence parameter set may indicate a quantization method to be applied to an object of the sequence parameter set. The sequence parameter set may include the quantization method indicator information described above. The quantization method indicator information may indicate a quantization method to be applied to an object of a sequence parameter set among a plurality of quantization methods. Alternatively, the quantization method indicator information may indicate whether the variable-rate step quantization method is applied to an object of the sequence parameter set.

As the quantization method indicator information for the above sequence parameter set, sps_perceptual_qp_enabled_flag is illustrated in FIG. 27. The quantization method indicator information may be a 1-bit flag.

For example, the picture parameter set may indicate a quantization method to be applied to an object of the picture parameter set. The picture parameter set may include the above-described quantization method indicator information. The quantization method indicator information may indicate a quantization method to be applied to an object of a picture parameter set among a plurality of quantization methods. Alternatively, the quantization method indicator information may indicate whether the variable-rate step quantization method is applied to an object of the picture parameter set.

As quantization method indicator information for the above picture parameter set, pps_perceptual_qp_enabled_flag is illustrated in FIG. 28. The quantization method indicator information may be a 1-bit flag.

For example, the slice segment header may indicate a quantization method to be applied to an object of the slice segment header. The slice segment header may include the above-described quantization method indicator information. The quantization method indicator information may indicate a quantization method to be applied to an object of a slice segment header among a plurality of quantization methods. Alternatively, the quantization method indicator information may indicate whether the variable-rate step quantization method is applied to an object of the picture parameter set.

As the quantization method indicator information for the slice segment header, slice_segment_header_perceptual_qp_enabled_flag is illustrated in FIG. 29. The quantization method indicator information may be a 1-bit flag.

In performing inverse quantization, a quantization parameter to be applied to a specified unit may be indicated through a higher level syntax. For example, the higher level syntax may be a video parameter set, a sequence parameter set, a picture parameter set, or a slice segment header.

For example, the video parameter set may include a quantization parameter applied to an object of the video parameter set. The sequence parameter set may include a quantization parameter applied to an object of the sequence parameter set. The picture parameter set may include quantization parameters applied to an object of the picture parameter set. The slice segment header may include a quantization parameter applied to an object of the slice segment header.

The high-level syntax may include additional syntax elements for variable-rate step inverse quantization when the value of the quantization method indicator information is a predefined value (eg, "1"). Additional syntax elements can be used to construct values used in the variable-rate step quantization method described above. For example, additional syntax elements may include gamma function parameters (α, γ).

A specified number of bits may be required to indicate the quantization parameter of the variable-rate step quantization method. Instead of directly signaling the value of the quantization parameter to reduce the number of required bits, substitute information indicating the value of the quantization parameter may be used instead. Such replacement information may be used for a specified unit, and may be included in a higher level syntax applied to the specified unit and signaled for each specified unit. Alternatively, the information on quantization described above with reference to FIGS. 21 and 22 may include such substitute information.

For example, replacement information for indicating the value of the quantization parameter may be a quantization parameter difference value.

For example, the quantization parameter difference value may be a difference between an intermediate value and a value of the quantization parameter. The intermediate value may be an intermediate value of a range of quantization parameters of the variable-rate step quantization method.

The quantization unit 140 may generate quantization parameter difference value information by performing entropy encoding using a signed exponential Golomb on the quantization parameter difference value.

Alternatively, the quantization parameter difference value may be a difference between a quantization parameter value of an upper unit and a quantization parameter value of a lower unit. For example, the upper unit may be a picture, and the lower unit may be a slice. The quantization parameter value of each unit may be signaled through the above-described signed exponential Golomb method. The quantization parameter obtained by using the quantization parameter difference value may be used for quantization for sub-units.

The quantization parameter difference value may be included in the header of the lower unit.

For the target picture, picture quantization parameter difference value information may be signaled. For example, the picture parameter set may include a picture quantization parameter difference value. The picture quantization parameter difference value may be information used to derive a quantization parameter applied to a picture.

In addition, slice quantization parameter difference value information may be signaled for each slice of one or more slices of the target picture. The slice header of each slice may include a slice quantization parameter difference value.

The slice quantization parameter difference value may represent a difference between a value of a quantization parameter applied to a picture and a value of a quantization parameter applied to a slice.

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 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, and the like 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, the 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 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 the 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 having 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 equivalently or equivalently 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 (22)

Performing quantization using a quantization method that generates a quantization parameter difference value
Including,
The quantization method is a variable-rate step quantization method,
The variable-rate step quantization method is a quantization method in which an increase rate of a quantization step is not fixed as the value of the quantization parameter increases by 1,
The quantization parameter difference value is a difference between an intermediate value and a value of the quantization parameter,
The intermediate value is an intermediate value of a range of quantization parameters of the variable-rate step quantization method. The method of claim 1,
As the value of the quantization parameter is smaller, the increase rate of the quantization step of the variable-rate step quantization method is higher as the value of the quantization parameter increases by 1. The method of claim 1,
Selecting the quantization method from among a plurality of quantization methods
Including more,
The plurality of quantization methods include a fixed-rate step quantization method and the variable-rate step quantization method,
The fixed-rate step quantization method is a quantization method in which an increase rate of the quantization step as the value of the quantization parameter increases by 1 is fixed. The method of claim 3,
In a region in which the value of the quantization parameter is relatively larger, an increase rate of a quantization step of the variable-rate step quantization method is smaller than an increase rate of a quantization step of the fixed-rate step quantization method. Obtaining a quantization parameter using the quantization parameter difference value
Steps to perform inverse quantization using the inverse quantization method
Including,
The inverse quantization method is a variable-rate step inverse quantization method,
The variable-rate step inverse quantization method is an inverse quantization method in which an increase rate of a quantization step is not fixed as the value of the quantization parameter increases by 1,
The quantization parameter is used for the inverse quantization,
The quantization parameter difference value is a difference between an intermediate value and a value of the quantization parameter,
The intermediate value is an intermediate value of a quantization parameter range of the variable-rate step inverse quantization method. The method of claim 5,
As the value of the quantization parameter is smaller, the increase rate of the quantization step of the variable-rate step inverse quantization method is higher as the value of the quantization parameter increases by 1. The method of claim 5,
Selecting the inverse quantization method from among a plurality of inverse quantization methods
Including more,
The plurality of inverse quantization methods include a fixed-rate step inverse quantization method and the variable-rate step inverse quantization method,
The fixed-rate step inverse quantization method is an inverse quantization method in which an increase rate of the quantization step as the value of the quantization parameter increases by 1 is fixed. The method of claim 7,
In a region in which the value of the quantization parameter is relatively larger, an increase rate of the quantization step of the variable-rate step inverse quantization method is smaller than the increase rate of the quantization step of the fixed-rate step inverse quantization method. The method of claim 7,
A quantization parameter of the fixed-rate step inverse quantization method corresponding to the quantization parameter of the variable-rate step inverse quantization method is determined,
A decoding method in which a quantization step corresponding to a quantization parameter of the fixed-rate step inverse quantization method is used for the inverse quantization. The method of claim 7,
According to the fixed-rate step inverse quantization method, a quantization step of the fixed-rate step inverse quantization method corresponding to the quantization parameter is determined, and a quantization step ratio is applied to the quantization step of the fixed-rate step inverse quantization method. The quantization step for the variable-rate step inverse quantization method is determined,
The quantization step ratio is a ratio between a quantization step of the variable-rate step inverse quantization method and a quantization step of the fixed-rate step inverse quantization method. The method of claim 5,
Obtaining a quantization method indicator
Including more,
The quantization method indicator indicates one inverse quantization method used for inverse quantization of a target block among the plurality of inverse quantization methods. The method of claim 11,
The quantization method indicator indicates an inverse quantization method applied to a specific unit. The method of claim 12,
The specified unit is a video, a sequence, a picture, or a slice. The method of claim 12,
The quantization method indicator indicates whether the variable-rate step inverse quantization method is applied to the specified unit. delete The method of claim 5,
The quantization parameter is a decoding method applied to a specific unit. The method of claim 5,
Obtaining a quantization parameter using a quantization parameter difference value; And
Steps to perform inverse quantization using the inverse quantization method
Including,
The inverse quantization method is a variable-rate step inverse quantization method,
The variable-rate step inverse quantization method is an inverse quantization method in which an increase rate of a quantization step is not fixed as the value of the quantization parameter increases by 1,
The quantization parameter difference value is a difference between a quantization parameter value of an upper unit and a quantization parameter value of a lower unit,
The obtained quantization parameter is used for the inverse quantization of the sub-unit. The method of claim 17,
The quantization parameter difference value is included in the header of the lower unit. The method of claim 17,
The upper unit is a picture, and the lower unit is a slice. A computer-readable recording medium storing a bitstream for decoding an image, wherein the bitstream comprises:
Information on the target block including the quantization parameter difference value
Including,
Inverse quantization using the information on the target block and the inverse quantization method is performed,
The inverse quantization method is a variable-rate step inverse quantization method,
The variable-rate step inverse quantization method is an inverse quantization method in which an increase rate of a quantization step is not fixed as the value of the quantization parameter increases by 1,
The quantization parameter is obtained using the quantization parameter difference value,
The quantization parameter difference value is a difference between an intermediate value and a value of the quantization parameter,
The intermediate value is an intermediate value of a range of quantization parameters of the variable-rate step inverse quantization method. Performing quantization using a quantization method that generates a quantization parameter difference value
Including,
The quantization method is a variable-rate step quantization method,
The variable-rate step quantization method is a quantization method in which an increase rate of a quantization step as a value of a quantization parameter increases by 1 is not fixed,
The quantization parameter difference value is a difference between a quantization parameter value of an upper unit and a quantization parameter value of a lower unit,
The obtained quantization parameter is used for the inverse quantization of the sub-unit. A computer-readable recording medium storing a bitstream for decoding an image, wherein the bitstream comprises:
Information on the target block including the quantization parameter difference value
Including,
Inverse quantization using the information on the target block and the inverse quantization method is performed,
The inverse quantization method is a variable-rate step inverse quantization method,
The variable-rate step inverse quantization method is an inverse quantization method in which the increase rate of the quantization step is not fixed as the value of the quantization parameter increases by 1,
The quantization parameter is obtained using the quantization parameter difference value,
The quantization parameter difference value is a difference between a quantization parameter value of an upper unit and a quantization parameter value of a lower unit,
The obtained quantization parameter is a computer-readable recording medium used for the inverse quantization of the sub-unit.

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