KR20210003604A - Method and apparatus for intra prediction - Google Patents

Abstract

Provided are a method and a device for video encoding/decoding which can improve efficiency of intra prediction coding. The method for video decoding comprises the steps of: deriving an intra prediction mode for a current block; determining at least one reconstructed sample line for the current block based on the derived intra prediction mode; constructing a reference sample using the at least one reconstructed sample included in the determined reconstructed sample line; and performing intra prediction on the current block based on the intra prediction mode and the reference sample.

Description

In-screen prediction method and apparatus {METHOD AND APPARATUS FOR INTRA PREDICTION}

The present invention relates to a video encoding/decoding method, an apparatus, and a recording medium storing a bitstream. Specifically, the present invention relates to a method and apparatus for encoding/decoding an image based on a plurality of reference sample lines.

Recently, the demand for high-resolution and high-quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various application fields. The higher the resolution and quality of the video data, the higher the amount of data is compared to the existing video data. Therefore, if the video data is transmitted using a medium such as a wired/wireless broadband line or stored using an existing storage medium, the transmission cost and The storage cost increases. High-efficiency image encoding/decoding technology for an image having a higher resolution and image quality is required to solve these problems that occur as image data becomes high-resolution and high-quality.

An inter-screen prediction technology that predicts pixel values included in the current picture from a picture before or after the current picture with an image compression technology, an intra prediction technology that predicts a pixel value included in the current picture using pixel information in the current picture, Various technologies exist, such as transformation and quantization technology for compressing the energy of the residual signal, and entropy coding technology that allocates short codes to values with a high frequency of appearance and long codes to values with low frequency of appearance. Image data can be effectively compressed and transmitted or stored.

In the conventional intra-prediction, since reference samples are constructed from neighboring reconstructed sample lines immediately adjacent to the current block, there is a limitation in further improving the compression performance.

An object of the present invention is to provide a video encoding/decoding method and apparatus using a plurality of reference sample lines.

Another object of the present invention is to provide a video encoding/decoding method and apparatus for implicitly deriving encoding parameters required for intra prediction from encoding parameters of neighboring blocks.

It is also an object of the present invention to provide a recording medium storing a bitstream generated by the video encoding/decoding method or apparatus of the present invention.

According to the present invention, the method includes: inducing an intra prediction mode for a current block; Determining at least one reconstructed sample line for the current block based on the derived intra prediction mode; Constructing a reference sample using at least one reconstructed sample included in the determined reconstructed sample line; And performing intra prediction on the current block based on the intra prediction mode and the reference sample.

In the video decoding method according to the present invention, the current block may include a sub-block of the current block.

In the image decoding method according to the present invention, the at least one reconstructed sample line may be determined based on a position of the current block in a coding tree block.

In the image decoding method according to the present invention, the at least one reconstructed sample line may be determined based on whether the derived intra prediction mode is directional.

In the image decoding method according to the present invention, the at least one reconstructed sample line may be determined based on at least one of the size and division information of the current block.

The image decoding method according to the present invention may further include obtaining information on the at least one reconstructed sample line from a bitstream.

The video decoding method according to the present invention may further include reconstructing an MPM candidate list of the current block based on the determined reconstructed sample line.

In the video decoding method according to the present invention, further comprising the step of deriving information on a reconstructed block adjacent to the current block, and performing intra prediction on the current block, the derived current block It may include the step of deriving an encoding parameter of the reconstructed block based on information on the adjacent reconstructed block.

In the image decoding method according to the present invention, information on a reconstructed block adjacent to the current block may include information indicating a reconstructed block adjacent to the current block for applying an intra-screen merge mode.

In the image decoding method according to the present invention, the encoding parameter of the reconstructed block may include at least one of a luminance component intra prediction mode, a multi reference line index, transform information, and a color difference component intra prediction mode.

In addition, according to the present invention, the method includes: determining an intra prediction mode for a current block; Determining at least one reconstructed sample line for the current block based on the derived intra prediction mode; Constructing a reference sample using at least one reconstructed sample included in the determined reconstructed sample line; And performing intra prediction on the current block based on the intra prediction mode and the reference sample.

In the image encoding method according to the present invention, the current block may include a sub-block of the current block.

In the image encoding method according to the present invention, the at least one reconstructed sample line may be determined based on a position of the current block in a coding tree block.

In the image encoding method according to the present invention, the at least one reconstructed sample line may be determined based on whether the derived intra prediction mode is directional.

In the image encoding method according to the present invention, the at least one reconstructed sample line may be determined based on at least one of the size and division information of the current block.

The image encoding method according to the present invention may further include encoding information on the at least one reconstructed sample line.

The video encoding method according to the present invention may further include reconstructing an MPM candidate list of the current block based on the determined reconstructed sample line.

In the video encoding method according to the present invention, further comprising the step of deriving information on a reconstructed block adjacent to the current block, and performing intra prediction on the current block, the derived current block It may include the step of deriving an encoding parameter of the reconstructed block based on information on the adjacent reconstructed block.

In the video encoding method according to the present invention, the encoding parameter of the reconstructed block may include at least one of a luminance component intra prediction mode, a multi reference line index, transform information, and a color difference component intra prediction mode.

Further, the recording medium according to the present invention can store a bitstream generated by the video encoding method according to the present invention.

According to the present invention, a method and apparatus for encoding/decoding an image using a plurality of reference sample lines may be provided.

In addition, according to the present invention, a video encoding/decoding method and apparatus for implicitly deriving encoding parameters required for intra prediction from encoding parameters of neighboring blocks can be provided.

In addition, according to the present invention, video encoding/decoding that reduces transmission bits and improves intra-prediction encoding efficiency by implicitly deriving encoding parameters of neighboring blocks, such as a merge mode of inter-picture encoding, for encoding parameters necessary for intra-picture encoding. Methods and apparatus can be provided.

In addition, according to the present invention, a video encoding/decoding method and apparatus for reducing the amount of bits generated of encoding parameters necessary for an intra prediction mode by using a signaling method for an intra-merge mode and an intra-merge list construction method can be provided. have.

Further, according to the present invention, a recording medium storing a bitstream generated by the video encoding/decoding method or apparatus of the present invention can be provided.

Further, according to the present invention, it is possible to improve the encoding and/or decoding efficiency of an image.

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 showing an image segmentation structure when an image is encoded and decoded.
4 is a diagram illustrating a shape of a prediction unit PU that may be included in the encoding unit CU according to an embodiment of the present invention.
5 is a diagram illustrating a shape of a transform unit TU that may be included in the encoding unit CU according to an embodiment of the present invention.
6 is a diagram illustrating a process of performing a quadratic transformation according to an embodiment of the present invention.
7 is a diagram illustrating neighboring blocks referenced to construct an MPM candidate list according to an embodiment of the present invention.
8 is a diagram illustrating an intra prediction mode according to an embodiment of the present invention.
9 is a diagram illustrating a process of performing intra prediction using a reference sample line adjacent to a current block according to an embodiment of the present invention.
10 is a diagram illustrating a process of configuring an intra-screen merge mode candidate list according to an embodiment of the present invention.
11 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.
12 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention. In the drawings, like reference numerals 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. For a detailed description of exemplary embodiments to be described later, reference is made to the accompanying drawings illustrating specific embodiments as an example. These embodiments are described in detail enough to enable those skilled in the art to practice the embodiments. It should be understood that the various embodiments are different from each other but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. In addition, it is to be understood that the position or arrangement of individual components in 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.

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

When a component of the present invention is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but other components exist in the middle. It should be understood that there may be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

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

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

Some of the constituent elements of the present invention are not essential constituent elements that perform essential functions in the present invention, but may be optional constituent elements merely for improving performance. The present invention can be implemented by including only the components essential to implement the essence of the present invention excluding components used for performance improvement, and a structure including only essential components excluding optional components used for performance improvement Also included in the scope of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In describing the embodiments of the present specification, if it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the present specification, the detailed description will be omitted, and the same reference numerals are used for the same components in the drawings. Used and redundant descriptions for the same components are omitted.

In addition, 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 image among images constituting a video" May be. Here, a picture may have the same meaning as an image.

Glossary of terms

Encoder: It may mean a device that performs encoding.

Decoder: May mean a device that performs decoding.

Parsing: Entropy decoding may mean determining a value of a syntax element, or entropy decoding itself.

Block: An MxN array of samples, where M and N mean positive integer values, and a block can often mean a two-dimensional sample array.

Sample: A basic unit that composes a block, and can represent a value from 0 to 2 ^Bd -1 according to the bit depth (Bd). In the present invention, pixels and pixels may be used in the same sense as samples.

Unit: It may mean a unit of image encoding and decoding. In encoding and decoding of an image, the unit may be an area generated by division of one image. Further, a unit may mean a divided unit when one image is divided into subdivided units and encoded or decoded. In encoding and decoding of an image, a predefined process may be performed for each unit. One unit may be further divided into sub-units having a smaller size than the unit. Depending on the function, the units are Block, Macroblock, Coding Tree Unit, Coding Tree Block, Coding Unit, Coding Block, and Prediction. It may mean a unit (Prediction Unit), a prediction block (Prediction Block), a transform unit (Transform Unit), a transform block (Transform Block), and the like. In addition, the unit may mean including a luminance component block, a chrominance component block corresponding thereto, and a syntax element for each block in order to distinguish it from the block. The unit may have various sizes and shapes, and in particular, the shape of the unit may include a geometric figure that can be expressed in two dimensions, such as a square, trapezoid, triangle, and pentagon, as well as a rectangle. Also, the unit information may include at least one of a type of a unit indicating a coding unit, a prediction unit, a transformation unit, etc., a size of a unit, a depth of a unit, an order of encoding and decoding of the unit, and the like.

Reconstructed Neighbor Unit: This may mean a unit that has already been encoded or decoded in a spatial/temporal manner around the encoding/decoding target unit and then reconstructed.

Unit Depth: It means the degree to which the unit is divided. In a tree structure, the root node has the shallowest depth, and the leaf node has the deepest depth.

Symbol: may mean a syntax element to be encoded/decoded, a coding parameter, a value of a transform coefficient, and the like.

Parameter Set: It may correspond to header information among structures in the bitstream, and is a video parameter set, sequence parameter set, picture parameter set, and adaptation parameter set. At least one or more of (adaptation parameter set) may be included in the parameter set. In addition, the parameter set may have a meaning including slice header and tile header information.

Bitstream: May mean a sequence of bits including coded image information.

Prediction Unit: A basic unit when inter prediction or intra prediction and compensation are performed, and one prediction unit may be divided into a plurality of small sized partitions. In this case, each of the plurality of partitions becomes a basic unit when performing the prediction and compensation, and a partition in which the prediction unit is divided may also be referred to as a prediction unit. The prediction unit may have various sizes and shapes, and in particular, the shape of the prediction unit may include not only a rectangle but also a geometric figure that can be expressed in two dimensions, such as a square, a trapezoid, a triangle, and a pentagon.

Prediction Unit Partition: This may mean a form in which a prediction unit is divided.

Reference Picture List: This may mean a list including one or more reference pictures used for inter prediction or motion compensation. The types of the reference image list may include LC (List Combined), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3), and more than one reference image for inter prediction. Lists can be used.

Inter prediction indicator (Inter Prediction Indicator): Can mean an inter prediction direction (unidirectional prediction, bidirectional prediction, etc.) of an encoding/decoding target block during inter prediction, and the encoding/decoding target block generates a prediction block. It may refer to the number of reference images used when the encoding/decoding target block performs inter prediction or motion compensation, and may refer to the number of prediction blocks used when performing inter prediction or motion compensation.

Reference Picture Index: It may mean an index for a specific reference picture in the reference picture list.

Reference picture: It may mean an image referenced by a specific unit for inter prediction or motion compensation, and the reference image may also be referred to as a reference picture.

Motion Vector: A two-dimensional vector used for inter prediction or motion compensation, and may mean an offset between an encoding/decoding target image and a reference image. For example, (mvX, mvY) may represent a motion vector, mvX may represent a horizontal component, and mvY may represent a vertical component.

Motion Vector Candidate including at least one of information, reference image, motion vector candidate, motion vector candidate index, etc.: It can mean a unit that is a prediction candidate when predicting a motion vector or a motion vector of the unit. have.

Motion Vector Candidate List: This may mean a list constructed using motion vector candidates.

Motion Vector Candidate Index: An indicator indicating a motion vector candidate in a motion vector candidate list, and may also be referred to as an index of a motion vector predictor.

Motion Information: This may refer to information on a motion vector, a reference image index, an inter prediction indicator, as well as a reference image list.

Merge Candidate List: This may mean a list constructed using merge candidates.

Merge Candidate: may include a spatial merge candidate, a temporal merge candidate, a combined merge candidate, a combined two-prediction merge candidate, a zero merge candidate, etc., and the merge candidate includes prediction type information, each It may include motion information such as a reference picture index and a motion vector for the list.

Merge Index: This may mean information indicating a merge candidate in the merge candidate list. Also, the merge index may indicate a block from which a merge candidate is derived from among blocks reconstructed spatially/temporally adjacent to the current block. In addition, the merge index may indicate at least one or more of motion information of the merge candidate.

Transform Unit: It may mean a basic unit when encoding/decoding a residual signal, such as transform, inverse transform, quantization, inverse quantization, and transform coefficient encoding/decoding, and one transform unit is It can be divided into a plurality of conversion units having a small size. The conversion unit may have various sizes and shapes, and in particular, the shape of the conversion unit may include a geometric figure that can be expressed in two dimensions, such as a square, trapezoid, triangle, and pentagon, as well as a rectangle.

Scaling: It may mean a process of multiplying the level of a transform coefficient by a factor, and a transform coefficient may be generated as a result. Scaling can also be called dequantization.

Quantization Parameter: This may mean a value used when scaling a transform coefficient level in quantization and inverse quantization. In this case, the quantization parameter may be a value mapped to a quantization step size.

Residual quantization parameter (Delta Quantization Parameter): This may mean a differential value between a predicted quantization parameter and a quantization parameter of an encoding/decoding target unit.

Scan: It can mean a method of sorting the order of coefficients in a block or matrix. For example, sorting a two-dimensional array into a one-dimensional array is called a scan, and a one-dimensional array into a two-dimensional array. Alignment can also be called a scan or an inverse scan.

Transform Coefficient: A coefficient value generated after performing transformation, and in the present invention, a quantized transform coefficient level obtained by applying quantization to a transform coefficient may also be included in the meaning of the transform coefficient.

Non-zero transform coefficient (Non-zero Transform Coefficient): It may mean a transform coefficient in which the size of the transform coefficient value is not 0 or a transform coefficient level in which the size of the value is not 0.

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

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

Default matrix: This may mean a predetermined quantization matrix defined in advance in an encoder and a decoder.

Non-default Matrix: This may mean a quantization matrix that is not predefined in an encoder and a decoder, but is transmitted/received by a user.

Coding Tree Unit: It may be composed of one luminance component (Y) and two color difference component (Cb, Cr) coded tree blocks related to a coded tree block. Each coding tree unit may be divided using one or more partitioning methods such as a quad tree and a binary tree in order to construct sub-units such as coding units, prediction units, and transform units. Like segmentation of an input image, it can be used as a term to refer to a pixel block that becomes a processing unit in an image decoding/encoding process.

Coding Tree Block: It can be used as a term for referring to any one of a Y-coded tree block, a Cb-coded tree block, and a Cr-coded tree block.

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 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 according to time.

1, the encoding apparatus 100 includes a motion prediction unit 111, a motion compensation unit 112, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, and a quantization unit. A unit 140, an entropy encoder 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 an input image in an intra mode and/or an inter mode. In addition, the encoding apparatus 100 may generate a bitstream through encoding of an input image, and may output the generated bitstream. When the intra mode is used as the prediction mode, the switch 115 may be switched to intra, and when the inter mode is used as the prediction mode, the switch 115 may be switched to inter. Here, the intra mode may refer to an intra prediction mode, and the inter mode may refer to an inter prediction mode. The encoding apparatus 100 may generate a prediction block for an input block of an input image. Also, after the prediction block is generated, the encoding apparatus 100 may encode a residual between the input block and the prediction block. The input image may be referred to as a current image that is a current encoding target. The input block may be referred to as a current block or a current block to be encoded.

When the prediction mode is an intra mode, the intra prediction unit 120 may use a pixel value of a block already coded around the current block as a reference pixel. The intra prediction unit 120 may perform spatial prediction using a reference pixel, and may generate prediction samples for an input block through spatial prediction. Here, intra prediction may mean intra prediction.

When the prediction mode is the inter mode, the motion prediction unit 111 may search for an area that best matches the input block from the reference image in the motion prediction process, and may derive a motion vector using the searched area. . The reference image may be stored in the reference picture buffer 190.

The motion compensation unit 112 may generate a prediction block by performing motion compensation using a motion vector. Here, the motion vector may be a 2D vector used for inter prediction. Also, the motion vector may represent an offset between the current image and the reference image. Here, inter prediction may mean inter prediction.

When the motion vector value does not have an integer value, the motion prediction unit 111 and the motion compensation unit 112 may generate a prediction block by applying an interpolation filter to a partial region of a reference image. . In order to perform inter prediction or motion compensation, the motion prediction and motion compensation method of the prediction unit included in the corresponding coding unit based on the coding unit is skip mode, merge mode, and AMVP mode. ), it is possible to determine which method is among the current picture reference modes, and to perform inter prediction or motion compensation according to each mode. Here, the current picture reference mode may mean a prediction mode using a pre-restored region in the current picture to which the encoding target block belongs. A motion vector for a current picture reference mode may be defined to specify the pre-restored region. Whether the encoding object block is encoded in the current picture reference mode may be encoded using a reference image index of the encoding object block.

The subtractor 125 may generate a residual block by using a difference between the input block and the prediction block. The residual block may be referred to as a residual signal.

The transform unit 130 may transform the residual block to generate a transform coefficient, and may output a transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing transform on the residual block. 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 may be generated. Hereinafter, in embodiments, a quantized transform coefficient level may also be referred to as a transform coefficient.

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

The entropy encoding unit 150 may generate a bitstream by performing entropy encoding according to a probability distribution on values calculated by the quantization unit 140 or values of a coding parameter calculated during an encoding process. Yes, and can output a bitstream. The entropy encoder 150 may perform entropy encoding on information for decoding an image in addition to information on pixels of 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 are allocated to a symbol having a high probability of occurrence, and a large number of bits are allocated to a symbol having a low probability of occurrence, and the symbol is expressed. The size of the column can be reduced. Therefore, compression performance of image encoding may be improved through entropy encoding. The entropy encoding unit 150 may use an encoding method such as exponential golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding. For example, the entropy encoding unit 150 may perform entropy encoding using a variable length encoding (VLC) table. In addition, the entropy encoder 150 derives a binarization method of a target symbol and a probability model of a target symbol/bin, and then performs arithmetic coding using the derived binarization method or a probability model. You may.

The entropy encoder 150 may change a two-dimensional block shape coefficient into a one-dimensional vector shape through a transform coefficient scanning method in order to encode a transform coefficient level. For example, by scanning the coefficients of a block using upright scanning, it can be changed to a one-dimensional vector form. Depending on the size of the transform unit and the intra prediction mode, instead of upright scan, a vertical scan that scans a two-dimensional block shape coefficient in a column direction and a horizontal scan that scans a two-dimensional block shape coefficient in a row direction may be used. That is, depending on the size of the transform unit and the intra prediction mode, it is possible to determine which scan method is to be used among upright scan, vertical scan, and horizontal scan.

The coding parameter, like a syntax element, may include information that can be inferred during the encoding or decoding process, as well as information that is encoded by the encoder and transmitted to the decoder, and refers to information required when encoding or decoding an image. can do. For example, intra prediction mode, inter prediction mode, intra prediction direction, motion information, motion vector, reference image index, inter prediction direction, inter prediction indicator, reference image list, motion vector predictor, motion merge candidate , Transform type, transform size, use of additional transform, filter information in the loop, presence of residual signal, quantization parameter, context model, transform coefficient, transform coefficient level, coded block pattern, coded block flag Flag), image display/output order, slice information, tile information, picture type, whether motion merge mode is used, skip mode is used, block size, block depth, block segmentation information, unit size, unit depth, unit segmentation information, etc. At least one or more of values and/or statistics may be included in the encoding parameter.

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 a difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming and quantizing the difference between the original signal and the predicted signal. The residual block may be a residual signal in units of blocks.

When the encoding apparatus 100 performs encoding through inter prediction, the encoded current image may be used as a reference image for other image(s) to be processed later. Accordingly, the encoding apparatus 100 may re-decode the encoded current image and store the decoded image as a reference image. Inverse quantization and inverse transformation of the current image encoded for decoding may be processed.

The quantized coefficient may be dequantized in the inverse quantization unit 160. It may be inverse transformed by the inverse transform unit 170. The inverse quantized and inverse transformed coefficients may be summed with the prediction block through the adder 175, and a reconstructed block may be generated by summing the inverse quantized and inverse transformed coefficients and the prediction block.

The restoration block may pass through the filter unit 180. The filter unit 180 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) to a reconstructed block or a reconstructed image. I can. The filter unit 180 may also be referred to as an in-loop filter.

The deblocking filter can remove block distortion occurring at the boundary between blocks. In order to determine whether to perform the deblocking filter, it may be determined whether to apply the deblocking filter to the current block based on the pixels included in several columns or rows included in the block. When applying a deblocking filter to a block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, horizontal filtering and vertical filtering may be processed in parallel when performing vertical filtering and horizontal filtering.

The sample adaptive offset may add an appropriate offset value to a pixel value to compensate for an encoding error. The sample adaptive offset may correct an offset from the original image in pixel units of the deblocking image. In order to perform offset correction for a specific picture, the pixels included in the image are divided into a certain number of areas, and then the area to be offset is determined and the offset is applied to the area, or offset by considering the edge information of each pixel. You can use the method of applying.

The adaptive loop filter 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, one filter to be applied to the group may be determined, and filtering may be performed differentially for each group. Information regarding whether to apply the adaptive loop filter may be transmitted for each coding unit (CU) of the luminance signal, and the shape and filter coefficients of the adaptive loop filter to be applied may vary according to each block. In addition, the same type (fixed type) adaptive loop filter may be applied regardless of the characteristics of the block to be applied.

The reconstructed block that has passed through the filter unit 180 may be stored in the reference picture buffer 190.

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 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, a motion compensation unit 250, and 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 perform decoding on a bitstream in an intra mode or an inter mode. In addition, the decoding apparatus 200 may generate a reconstructed image through decoding, and may output a reconstructed image.

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

The decoding apparatus 200 may obtain a reconstructed residual block from the input bitstream, and may generate a prediction block. When the reconstructed residual block and the prediction block are obtained, the decoding apparatus 200 may generate a reconstructed block that is a decoding object block by adding the reconstructed residual block and the prediction block. The block to be decoded may be referred to as a current block.

The entropy decoding unit 210 may generate symbols by performing entropy decoding according to a probability distribution for a 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 one-dimensional vector form coefficient into a two-dimensional block form through a transform coefficient scanning method in order to decode a transform coefficient level. For example, by scanning the coefficients of a block using up-right scanning, it can be changed into a two-dimensional block shape. Vertical scan and horizontal scan may be used instead of upright scan according to the size of the transform unit and the intra prediction mode. That is, depending on the size of the transform unit and the intra prediction mode, it is possible to determine which scan method is to be used among upright scan, vertical scan, and horizontal scan.

The quantized transform coefficient level may be inverse quantized in the inverse quantization unit 220 and may be inverse transformed in the inverse transform unit 230. As a result of inverse quantization and inverse transformation of the quantized transform coefficient level, a reconstructed residual block may be generated. In this case, the inverse quantization unit 220 may apply a quantization matrix to the quantized transform coefficient level.

When the intra mode is used, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using a pixel value of an already decoded block around the decoding object block.

When the inter mode is used, the motion compensation unit 250 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 does not have an integer value, the motion compensation unit 250 may generate a prediction block by applying an interpolation filter to a partial region of a reference image. In order to perform motion compensation, the motion compensation method of the prediction unit included in the coding unit based on the coding unit is among the skip mode, merge mode, AMVP mode, and current picture reference mode. It is possible to determine what kind of method it is, and motion compensation may be performed according to each mode. Here, the current picture reference mode may mean a prediction mode using a pre-restored region in the current picture to which the decoding object block belongs. A motion vector for a current picture reference mode may be used to specify the pre-restored region. A flag or index indicating whether the decoding target block is a block encoded in the current picture reference mode may be signaled, or may be inferred through the reference image index of the decoding target block. In the current picture reference mode, the current picture may exist at a fixed position (eg, a position where refIdx = 0 or the last position) in a reference image list for a decoding object block. Alternatively, it may be variably located in the reference image list, and for this purpose, a separate reference image index indicating the position of the current picture may be signaled.

The reconstructed residual block and prediction block may be added through an adder 255. As the reconstructed residual block and the prediction block are added, the generated block may pass through the filter unit 260. The filter unit 260 may apply at least one of a deblocking filter, a sample adaptive offset, and an adaptive loop filter to the reconstructed block or reconstructed image. The filter unit 260 may output a reconstructed image. The reconstructed image may be stored in the reference picture buffer 270 and used for inter prediction.

3 is a diagram schematically showing an image segmentation structure when an image is encoded and decoded.

3 schematically shows an embodiment 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. Here, the coding unit may mean a coding unit. A unit may be a term that refers to a block including 1) a syntax element and 2) an image sample. For example, "dividing a unit" may mean "dividing a block corresponding to a unit". The block division information may include information on the depth of the unit. The depth information may indicate the number and/or degree of division of the unit.

Referring to FIG. 3, an image 300 is sequentially segmented in units of a largest coding unit (LCU), and a segmentation structure is determined in units of an LCU. Here, the LCU may be used in the same meaning as a coding tree unit (CTU). One unit may be hierarchically divided with depth information based on a tree structure. Each divided sub-unit may have depth information. Since the depth information indicates the number and/or degree of division of the unit, it may include information on the size of the sub-unit.

The split structure may mean a distribution of a coding unit (CU) within the LCU 310. The CU may be a unit for efficiently encoding an image. This distribution may be determined according to whether or not to divide one CU into a plurality (a positive integer of 2 or more including 2, 4, 8, 16, etc.). The horizontal and vertical dimensions of the CU generated by the division are either half the horizontal size and half the vertical size of the CU before division, or a size smaller than the horizontal size and the vertical size of the CU before division, depending on the number of divisions. Can have. The divided CU may be recursively divided into a plurality of CUs whose horizontal size and vertical size are reduced in the same manner.

In this case, the partitioning of the CU may be recursively performed up to a predefined depth. The depth information may be information indicating the size of the CU and may be stored for each 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 coding unit having the largest coding unit size, and the SCU may be a coding unit having the smallest coding unit size.

The division starts from the LCU 310, and the depth of the CU increases by one whenever the horizontal size and the vertical size of the CU are reduced by the division. For each depth, a CU that is not divided may have a size of 2Nx2N. In the case of a divided CU, a CU having a size of 2Nx2N may be divided into a plurality of CUs having a size of NxN. The size of N decreases by half for every 1 increase in depth.

For example, when one coding unit is split into four coding units, the horizontal and vertical sizes of the four split coding units may each have a size of half compared to the horizontal and vertical sizes of the coding units before being split. have. For example, when a 32x32 coding unit is divided into four coding units, each of the divided four coding units may have a size of 16x16. When one coding unit is split into four coding units, it can be said that the coding unit is split in a quad-tree form.

For example, when one coding unit is split into two coding units, the horizontal or vertical size of the two split coding units may have a size of half compared to the horizontal or vertical size of the coding unit before being split. . For example, when a 32x32 coding unit is vertically split into two coding units, each of the two split coding units may have a size of 16x32. For example, when a 32x32 coding unit is horizontally split into two coding units, the split two coding units may each have a size of 32x16. When one coding unit is split into two coding units, it can be said that the coding unit is split in a binary-tree form.

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

Also, 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, if the value of the partition information is 0, the CU may not be partitioned, and if the value of the partition information is 1, the CU may be partitioned.

4 is a diagram illustrating a shape of a prediction unit PU that may be included in the encoding unit CU according to an embodiment of the present invention.

Among CUs divided from the LCU, CUs that are no longer divided may be divided into one or more prediction units (PUs). This treatment can also be referred to as division.

PU may be a basic unit for prediction. The PU may be encoded and decoded in any one of a skip mode, an inter-screen mode, and an intra-screen mode. The PU can be divided into various types according to the mode.

Also, the coding unit is not divided into prediction units, and the coding unit and the prediction unit may have the same size.

As shown in FIG. 4, in the skip mode, partitioning may not exist in the CU. In the skip mode, a 2Nx2N mode 410 having the same size as the CU without division may be supported.

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

One coding unit may be divided into one or more prediction units, and one prediction unit may be divided into one or more prediction units.

For example, when one prediction unit is divided into 4 prediction units, the horizontal and vertical sizes of the divided four prediction units may have a size of half each compared to the horizontal and vertical sizes of the prediction units before being divided. have. For example, when a prediction unit having a size of 32x32 is divided into four prediction units, each of the divided four prediction units may have a size of 16x16. When one prediction unit is divided into four prediction units, it can be said that the prediction unit is divided into a quad-tree form.

For example, when one prediction unit is divided into two prediction units, the horizontal or vertical size of the divided two prediction units may have a size of half compared to the horizontal or vertical size of the prediction unit before being divided. . For example, when a prediction unit having a size of 32x32 is vertically divided into two prediction units, each of the divided prediction units may have a size of 16x32. For example, when a prediction unit having a size of 32x32 is horizontally divided into two prediction units, the divided prediction units may each have a size of 32x16. When one prediction unit is divided into two prediction units, it can be said that the prediction unit is divided in a binary-tree form.

5 is a diagram illustrating a shape of a transformation unit (TU) that may be included in the encoding unit (CU) according to an embodiment of the present invention.

A transform unit (TU) may be a basic unit used for processes of transformation, quantization, inverse transformation, and inverse quantization in the CU. The TU may have a shape such as a square shape or a rectangle. 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 quadtree structure. When one CU is divided more than once, it can be said to be recursively divided. Through partitioning, one CU 510 may be composed of TUs of various sizes. Alternatively, the CU may be divided into one or more TUs based on the number of vertical lines and/or horizontal lines dividing the CU. The CU may be divided into symmetric type TUs or asymmetric type TUs. Information about the size/shape of the TU may be signaled for division into an asymmetric TU, or may be derived from information about the size/shape of the CU. Also, the encoding unit is not divided into transformation units, and the encoding unit and the transformation unit may have the same size.

One encoding unit may be divided into one or more transform units, and one transform unit may be divided into one or more transform units.

For example, when one transform unit is divided into four transform units, the horizontal and vertical sizes of the divided four transform units may each have a size of half compared to the horizontal and vertical sizes of the transform units before being divided. have. As an example, when a 32x32 transform unit is divided into four transform units, each of the divided four transform units may have a size of 16x16. When one transform unit is divided into four transform units, it can be said that the transform unit is divided into a quad-tree form.

For example, when one conversion unit is divided into two conversion units, the horizontal or vertical size of the two divided conversion units may have a size of half compared to the horizontal or vertical size of the conversion unit before division. . For example, when a 32x32 transform unit is vertically divided into two transform units, the divided two transform units may each have a size of 16x32. For example, when a 32x32 transform unit is horizontally divided into two transform units, the divided two transform units may each have a size of 32x16. When one transform unit is divided into two transform units, it can be said that the transform unit is divided into a binary-tree form.

When performing transformation, the residual block may be transformed using at least one of a plurality of pre-defined transformation methods. For example, as a plurality of pre-defined transformation methods, Discrete Cosine Transform (DST), Discrete Sine Transform (DST), or KLT may be used. Which transformation method is applied to transform the residual block may be determined using at least one of inter-prediction mode information, intra-prediction mode information, and size/type of the transform block of the prediction unit. Information can be signaled.

A residual signal generated after intra- or inter- prediction may be converted into a frequency domain through a transformation process as part of a quantization process. In this case, a variety of DCT and DST kernels other than DCT type 2 (DCT-II) can be used for transformation, and these transformation kernels may perform Separable transforms that perform 1D transform for the residual signal in the horizontal and vertical directions, respectively, Alternatively, 2D Non-separable transform may be performed.

As an example, DCT and DST types used for transformation can be adaptively used when converting DCT-V, DCT-VIII, DST-I, and DST-VII to 1D in addition to DCT-II as shown in Table 1. Transform set The DCT or DST type used for conversion can be derived by configuring. For example, after pre-defining different transform sets for the horizontal and vertical directions according to the intra prediction mode, the encoder/decoder uses the intra prediction mode of the current block and the transform included in the corresponding transform set. Thus, transformation and inverse transformation can be performed. In this case, the transform set is not transmitted and is mapped by the encoder/decoder according to the same rules as shown in the figure below, but information indicating which transform is used among transforms belonging to the corresponding transform set may be transmitted. This method of using various transforms can be applied to a residual signal through intra- or inter-screen prediction.

Multiple Transform Selection (MTS) can be applied to the residual signal by applying a different transform for each of the primary transform (Primary transform, or 1D direction (vertical, horizontal)), and whether to apply MTS to the current coding block Indicative flag (tu_mts_flag) and MST index (mts_idx) information indicating which transform is used in the horizontal and/or vertical direction as shown in Table 1 is explicitly transmitted or implicitly derived from at least one neighboring restoration block. I can.

6 is a diagram illustrating a process of performing a quadratic transformation according to an embodiment of the present invention.

After the MTS transform described above in Table 1 and related contents is performed, secondary transform may be performed to increase the energy concentration for the transform coefficient. Like the first transform, the second transform may be applied through a separable or non-separable secondary transform (NSST), and flag and index information about whether the second transform is used or not may be transmitted.

According to an embodiment of the present invention, the intra prediction encoding/decoding of the current coding block may include an intra prediction mode derivation step, a reference sample construction step, and an intra prediction operation step.

In deriving the intra prediction mode for the current block, a method of deriving using the intra prediction mode of one or more neighboring blocks, a method of deriving the intra prediction mode of the current block by entropy encoding/decoding, and encoding of neighboring blocks The intra prediction mode of the current block may be derived by using at least one of the parameters using methods. At this time, the neighboring block may be one or more blocks restored before encoding/decoding of the current block, and the neighboring block is outside the boundary of at least one predetermined unit among pictures, slices, tiles, and coding tree units (CTU). Or, if it corresponds to an inter-screen encoding/decoding block and is not available, the intra prediction mode corresponding to the neighboring block may be replaced with a DC mode, a planar mode, or a predetermined intra prediction mode. At this time, the size of the current block may be W x H, and W and H may be positive integers, respectively, for example, at least one of 2, 4, 8, 16, 32, 64, 128, 256, 512 have.

In using the intra prediction mode of the neighboring block, the intra prediction mode of the current block may be derived by combining one or more modes of the neighboring block. For example, the average value, median value, maximum value, minimum value, or average value, median value, maximum value, minimum value of one or more in-screen prediction modes of neighboring blocks corresponds to +N or -N in the in-screen prediction mode. The intra prediction mode can be derived as the intra prediction mode of the current block. In this case, the intra prediction mode may be expressed by at least one of a mode number, a mode value, and a mode angle. For example, the average of two intra prediction modes may mean at least one of an intermediate number of two mode numbers, an intermediate value of two mode values, and an intermediate angle between two mode angles. In this case, N may mean a positive integer.

In using the intra prediction mode of the neighboring block, the intra prediction mode of the current block may be derived using the Most Probable Mode (MPM). In using the MPM, an MPM list may be configured, and an intra prediction mode included in the MPM list may be configured based on an intra prediction mode of a neighboring block. The number of candidate modes included in the list may be a predetermined amount of N. The number of MPM candidate modes may vary according to the size/type of a block. At this time, the at least one or more intra prediction modes included in the MPM list can be configured by designating an intra prediction mode and/or an arbitrary intra prediction mode of at least one spatial neighboring block on which encoding/decoding has been completed. have.

An indicator intra_luma_mpm_flag indicating whether the same mode as the intra prediction mode of the current block exists in the derived MPM list may be encoded/decoded.

When the indicator indicates that the same mode exists in the MPM list, intra_luma_mpm_idx information indicating which mode is included in the MPM list may be encoded/decoded to induce an intra prediction mode of the current block.

When the MPM flag is 0, a secondary MPM candidate list may be configured for one or more intra prediction modes, and an intra prediction mode may be derived through a secondary MPM index (intra_luma_second_mpm_idx). When the second MPM flag (intra_luma_second_mpm_flag) is 1, the intra prediction mode of the luminance component may be derived using at least one of a second MPM index (intra_luma_second_mpm_idx) and an intra prediction mode of encoded/decoded adjacent units. have.

In order to configure the MPM for encoding/decoding the intra prediction mode and one or more intra prediction candidate modes included in the 2nd MPM list, surrounding coded information may be used.

When the indicator indicates that the same mode does not exist in the MPM list, the intra prediction mode of the current block may be derived by encoding/decoding the intra prediction mode of the current block. In this case, intra prediction modes not included in the MPM list may be sorted in at least one of an ascending order or a descending order.

The intra prediction mode of the chrominance component may be derived using at least one of an intra_chroma_pred_mode index of the chrominance component and/or an intra prediction mode of a corresponding luminance block.

Alternatively, a predetermined candidate of the derived MPM list may be derived into an intra prediction mode of the current block. For example, the intra prediction mode of the current block may be derived to a mode corresponding to list 0, which is the first of the MPM list. Alternatively, by encoding/decoding an index corresponding to a predetermined mode in the list, the corresponding mode may be derived as an intra prediction mode of the current block.

If the intra prediction mode of the current coding block is not included in the MPM list, the remaining intra prediction modes excluding the intra prediction modes included in the MPM list are arranged in a random order and correspond to the intra prediction mode of the current coding block. The index (intra_luma_mpm_remainder) can be explicitly transmitted.

If the intra prediction mode of the current coding block is not included in the MPM list and the 2nd MPM list, the remaining intra prediction modes excluding the intra prediction modes included in the MPM list and/or the 2nd MPM list are arranged in a random order. An index (intra_luma_mpm_remainder) corresponding to the intra prediction mode of the current coding block may be explicitly transmitted.

When the current block is encoded in an intra prediction mode, at least one or more intra prediction modes included in the MPM list are an intra prediction mode of at least one or more spatial neighboring blocks for which encoding/decoding is completed and/or an arbitrary intra prediction. You can configure the MPM list by specifying the mode.

7 is a diagram illustrating neighboring blocks referenced to construct an MPM candidate list according to an embodiment of the present invention.

For example, assuming that the number of intra prediction modes constituting the MPM list is 6, as in the example of FIG. 7, up to 5 intra prediction modes included in the MPM list can be sequentially derived from spatial neighboring blocks. have. At this time, the order of inducing the intra prediction mode from the neighboring blocks can be arbitrarily set by the encoder/decoder, for example, left (L), above (A), below left (BL), above right (AR), and It can be derived in the above left (AL) order. In this case, the planar and/or DC mode, which is a non-directional mode, can be regarded as an intra prediction mode with a high probability of occurrence, so planar and/or DC mode are included in the five intra prediction modes derived from the spatial neighboring blocks. If not, it is possible to configure the MPM list by including the planar and/or DC mode. At this time, the order in which the planar and/or DC mode are located on the MPM list can be arbitrarily set by the encoder/decoder, and for example, the order of left, above, planar, DC, below left, above right, and above left. In addition, it is possible to perform a redundancy check on whether intra prediction modes in the configured MPM list have different prediction mode values.

8 is a diagram illustrating an intra prediction mode according to an embodiment of the present invention.

In FIG. 7 and related contents, the number of intra prediction modes in the MPM list configured after the redundancy check described above is smaller than the maximum number (eg, 6) of intra prediction modes included in the MPM list allowed by the encoder/decoder. In this case, an intra prediction mode corresponding to a value of +1 or -1 may be allocated to an intra prediction mode having a directionality among intra prediction modes included in the MPM list. If 6 MPMs cannot be filled through the above process, the vertical, horizontal, mode 2, and diagonal modes shown in FIG. 8 are filled in order to construct an MPM list having up to 6 different intra prediction modes. I can. At this time, if the number of intra prediction modes allowed by the encoder/decoder is up to 67, in addition to Planar (mode 0) and DC (mode 1), modes 2 to 66 represent intra prediction modes for directionality, and vertical is mode 50, horizontal may indicate mode 18, diagonal may indicate mode 34.

When performing intra prediction on a current block or a subblock having a size/shape smaller than that of the current block based on the intra prediction mode, a reference sample used for prediction may be configured. In the following description, the current block may mean a sub-block. The reference sample may be configured through one or more reconstructed samples or a combination of samples, and filtering may be applied to the configured reference sample. The number and position of reconstructed sample lines used in the reference sample configuration may vary according to the position of the current block in the coding tree block. In this case, each of the reconstructed samples on the plurality of reconstructed sample lines may be used as it is, or may be used for calculation for generating a reference sample after filtering between samples on the same reconstructed sample line or filtering between samples on different reconstructed sample lines. The configured reference sample may be represented by ref[m, n], and a reconstructed sample or a filtered sample may be represented by rec[m,n], and m or n may be a predetermined integer value. If the current block's horizontal (W) and vertical (H) sizes are (W x H), the closest upper left reference to the sample position when the upper left sample position in the current block is (0, 0) You can set the relative position of the sample to (-1, -1).

9 is a diagram illustrating a process of performing intra prediction using a reference sample line adjacent to a current block according to an embodiment of the present invention.

During intra prediction, at least one reconstructed sample line among at least one reconstructed sample line adjacent to the current block may be set as a reference sample for a current block or a subblock of the current block. For example, a positive integer N reconstructed sample lines for which peripheral restoration has been completed for the current block are set as reference sample line candidates for intra prediction for the current block, and among them, the most optimal reference in terms of rate-distortion A sample line can be configured as a reference sample line of the current block. In this case, the index for the reference sample line may be explicitly transmitted or may be implicitly derived. As an example, referring to FIG. 9, the number of reference sample lines may be 4, and the current block signals index information on an optimal reference sample line for intra prediction to a decoder, or intra prediction mode information of the current block and/or It can be implicitly derived using information such as the size/depth of the current coding block.

According to an embodiment of the present invention, intra prediction using multi-reference lines can be applied only under specific conditions. For example, in order to reduce the amount of bits for the reference sample line index, after multi-reference line-based intra prediction is additionally performed on only the current block determined as MPM, index information on the multi-reference line may be signaled.

According to an embodiment of the present invention, intra prediction coding/decoding for a current coding block based on a multi-reference line may be applied under a predetermined condition and/or an encoding environment.

For example, the multi-reference line-based intra prediction encoding/decoding may or may not be applied in a specific intra prediction mode such as a DC and/or Planar mode.

As another example, multi-reference line-based intra prediction coding/decoding may or may not be applied only to intra prediction coding methods such as wide angle prediction and/or position dependent intra prediction combination (PDPC).

As another example, the multi-reference line-based intra prediction coding/decoding is performed based on the values of at least one coding parameter among the horizontal and/or vertical size, binary depth, and ternary depth coding parameters of a currently coded block (CU). It may or may not be applied conditionally accordingly.

As another example, multi-reference line-based intra prediction may or may not be applied according to the CTU and/or CU size.

As another example, intra prediction using multi-reference lines may or may not be applied based on the minimum value (MinQTSize) of a quaternary tree leaf node.

As another example, intra prediction using multi-reference lines may or may not be applied based on the maximum value (MaxBtSize) of the binary tree root node.

As another example, intra prediction using multi-reference lines may or may not be applied based on the minimum value (MinBtSize) of the binary tree root node.

As another example, intra prediction using multi-reference lines may or may not be applied based on the maximum value (MaxTtSize) of the ternary tree root node.

As another example, intra prediction using multi-reference lines may or may not be applied based on the minimum value (MinTtSize) of the ternary tree root node.

As another example, intra prediction using multi-reference lines may or may not be applied based on the maximum hierarchical depth value (MaxMttDepth) of multi-type tree segmentation.

According to an embodiment of the present invention, when intra prediction encoding a current coding block based on a multi-reference line, an MPM candidate list may be reconstructed based on a reference line index selected from the current coding block. Meanwhile, the optimal multi-reference line index of the current block is the minimum rate-distortion cost value after rate-distortion optimization is performed for each of the multi-reference lines for intra prediction allowed for the current block. May mean a reference line index having.

For example, after constructing an MPM candidate list by inducing an intra prediction mode according to a predefined scanning order for neighboring reconstructed blocks shown in FIG. 7, a reference line index equal to the optimal multi-reference line index of the current block is determined. The branch can exchange the intra prediction mode of an arbitrary neighboring block with the intra prediction mode set at the first index of the MPM candidate list.

As another example, after constructing an MPM candidate list by inducing an intra prediction mode according to a predefined scanning order for neighboring reconstructed blocks shown in FIG. 7, a reference line index equal to the optimal multi-reference line index of the current block is determined. Branches set the intra prediction mode of an arbitrary neighboring block as the intra prediction mode indicated by the first index of the MPM candidate list, and the existing intra prediction mode indicated by the first index as the intra prediction mode indicated by the second index. By setting, the MPM candidate list can be reconstructed.

As another example, when constructing an MPM candidate list by inducing an intra prediction mode for neighboring reconstructed blocks shown in FIG. 7 according to an arbitrary scanning order, the MPM candidate is an intra prediction mode and a multi-reference line of the neighboring block. The index can be derived from the intra prediction mode of the current coding block and the multi-reference line index. In this case, when a specific MPM idx does not indicate a neighboring restoration block, the multi-reference line index may set a randomly defined multi-reference line index value as a default value.

According to an embodiment of the present invention, when intra prediction encoding a current coded block based on a multi-reference line, a coding parameter for intra prediction of the current coded block may be derived using a neighboring reconstructed block. For example, by defining an arbitrary flag (imm_flag), encoding parameters used for intra prediction encoding of neighboring blocks may be implicitly derived according to the corresponding flag. The name of the flag may be different.

As an example, when the MPM flag is 1, if imm_flag is 1, at least one of information from the intra prediction mode of the neighboring block indicated by the MPM idx, a reference line index, a first transform flag and index, a second transform flag, and index information It can be implicitly derived during the intra prediction encoding process of the current block.

As another example, if imm_flag is 1, at least one of the intra prediction mode, reference line index, primary transformation flag and index, secondary transformation flag, and index information of the neighboring block indicated by MPM idx without the need to transmit the MPM flag It can be implicitly derived in the process of intra prediction coding of a block.

According to an embodiment of the present invention, when the current coding block is intra-/decoded, an intra-prediction mode for a luminance component required for intra/decoding from at least one reconstructed block among neighboring blocks that has been reconstructed ( At least one of intra_luma_pred_mode), multi reference line index (intra_luma_ref_idx), transform information (tu_mts_flag, mts_idx), and intra_chroma_pred_mode of color difference component encoding/decoding information may be derived.

For example, after explicitly and/or implicitly defining a flag (imm_flag) for an intra_merge_mode (IMM), encoding/decoding information for intra prediction may be derived from a neighboring reconstructed block. In this case, imm_flag may be information indicating a neighboring reconstructed block for inducing encoding/decoding information for intra prediction, and imm_idx may be explicitly transmitted or implicitly derived. Meanwhile, when explicitly encoding/decoding, at least one or more of the following entropy encoding methods may be used, and after being binarized, the final encoding/decoding may be performed as CABAC (ae(v)).

Truncated Rice Binaryization Method

K-th order Exp_Golomb binarization method

Constrained K-th order Exp_Golomb binarization method

Fixed-length binarization method

Unary binarization method

Truncated Unary Binaryization Method

A method of applying the intra_merge_mode (IMM) to the current coding block will be described later.

According to an embodiment of the present invention, imm_flag may be signaled only for an arbitrary condition (eg, an arbitrary intra prediction mode, the same multi-reference line index).

As an example, imm_flag may be transmitted only when the current coding block is determined as the MPM mode based on a rate-distortion optimization process. In this case, since imm_flag is not transmitted for all blocks encoded by intra prediction, the amount of bits for imm_flag can be reduced.

As another example, even if the current coding block is determined as the MPM mode based on the rate-distortion optimization process, intra_luma_mpm_idx does not indicate a spatial neighboring block and is filled with an arbitrary intra prediction mode (e.g., Planar, DC). In this case, imm_flag may not be transmitted.

As another example, even if the current coding block is determined as the MPM mode based on the rate-distortion optimization process, intra_luma_mpm_idx does not indicate a spatial neighboring block and is filled with an arbitrary intra prediction mode (e.g., Planar, DC). In the case of, at least one encoding parameter among the multi-reference line index (intra_luma_ref_idx), transform information (tu_mts_flag, mts_idx), and intra_chroma_pred_mode of the color difference component may have a randomly set default value.

As another example, when the current coding block is determined as the MPM mode based on the rate-distortion optimization process and the spatial neighboring block indicated by intra_luma_mpm_idx is not in the angular mode, imm_flag may not be transmitted.

As another example, imm_flag may or may not be applied only when a multi-reference line is used.

10 is a diagram illustrating a process of configuring an intra-screen merge mode candidate list according to an embodiment of the present invention.

According to an embodiment of the present invention, after imm_flag is transmitted, imm_idx may be implicitly derived. At this time, the intra-screen merge mode candidate list (IMMCL: IMM candidate list) indicated by imm_idx may have a positive integer K number of candidates, and IMMCL may be configured by limiting to neighboring restoration blocks according to a predefined scanning order. have. For example, when K is 5, referring to FIG. 10, IMMCL can be configured in the order of A1 → B1 → B0 → A0 → B2, and the same intra prediction mode as the intra prediction mode included in the IMMCL is used. Branched spatial neighboring blocks may not be duplicated in IMMCL. In this case, IMMCL may be configured for an intra prediction mode having an arbitrary condition, and for example, IMMCL may be configured only for spatial neighboring blocks having an angular mode.

As an example, after imm_flag is signaled as on (“1”), imm_idx may implicitly indicate the first spatial neighboring block constituting the IMMCL, and the internal/decoding information of the corresponding neighboring block is displayed within the screen of the current block. It can be derived from encoding/decryption information.

As another example, after imm_flag is signaled as on (“1”), when the number of neighboring blocks of the current coding block is K, if all of at least M neighboring blocks have the same intra prediction mode, imm_idx is implicitly The intra prediction encoding/decoding information of the first block on the imm list can be used as the encoding/decoding information of the current block. In this case, M is a positive integer, and M may have a value equal to or smaller than K.

11 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

Referring to FIG. 11, the decoder may derive an intra prediction mode for a current block (S1101).

Meanwhile, the current block may include a sub-block of the current block.

Also, the decoder may determine at least one reconstructed sample line for the current block based on the derived intra prediction mode (S1102).

Meanwhile, at least one or more reconstructed sample lines may be determined based on a location of a current block in a coding tree block.

Meanwhile, at least one reconstructed sample line may be determined based on whether the derived intra prediction mode is directional.

Meanwhile, at least one reconstructed sample line may be determined based on at least one of the size of the current block and partition information.

In addition, the decoder may construct a reference sample using at least one or more reconstructed samples included in the determined reconstructed sample line (S1103).

Also, the decoder may perform intra prediction for the current block based on the intra prediction mode and the reference sample (S1104).

Also, the decoder may obtain information on at least one reconstructed sample line from the bitstream.

Also, the decoder may reconstruct the MPM candidate list of the current block based on the determined reconstructed sample line.

In addition, the decoder may derive information on a reconstructed block adjacent to the current block. In this case, the decoder may derive encoding parameters of the reconstructed block based on the derived information on the reconstructed block adjacent to the current block.

Meanwhile, the information on the reconstructed block adjacent to the current block may include information indicating a reconstructed block adjacent to the current block for applying the intra-screen merge mode.

Meanwhile, the encoding parameter of the reconstructed block may include at least one of a luminance component intra prediction mode, a multi reference line index, transform information, and a color difference component intra prediction mode.

12 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

Referring to FIG. 12, the encoder may determine an intra prediction mode for a current block (S1201).

Meanwhile, the current block may include a sub-block of the current block.

Also, the encoder may determine at least one reconstructed sample line for the current block based on the derived intra prediction mode (S1202).

Meanwhile, at least one or more reconstructed sample lines may be determined based on a location of a current block in a coding tree block.

Meanwhile, at least one reconstructed sample line may be determined based on whether the derived intra prediction mode is directional.

Meanwhile, at least one reconstructed sample line may be determined based on at least one of the size of the current block and partition information.

In addition, the encoder may construct a reference sample using at least one reconstructed sample included in the determined reconstructed sample line (S1203).

In addition, the encoder may perform intra prediction on the current block based on the intra prediction mode and the reference sample (S1204).

Also, the encoder may encode information on at least one reconstructed sample line.

Also, the encoder may reconstruct the MPM candidate list of the current block based on the determined reconstructed sample line.

In addition, the encoder may derive information on a reconstructed block adjacent to the current block. In this case, the encoder may derive encoding parameters of the reconstructed block based on the derived information on the reconstructed block adjacent to the current block.

Meanwhile, the information on the reconstructed block adjacent to the current block may include information indicating a reconstructed block adjacent to the current block for applying the intra-screen merge mode.

Meanwhile, the encoding parameter of the reconstructed block may include at least one of a luminance component intra prediction mode, a multi reference line index, transform information, and a color difference component intra prediction mode.

Further, a computer-readable recording medium storing a bitstream generated by the above-described video encoding method or used in the video decoding method may be provided.

According to the present invention, an image encoding/decoding method for reducing transmission bits and improving intra-prediction encoding efficiency by implicitly deriving encoding parameters of neighboring blocks, such as a merge mode of inter-encoding, for encoding parameters necessary for intra-encoding, and An apparatus may be provided.

In addition, according to the present invention, a video encoding/decoding method and apparatus for reducing the amount of bits generated of encoding parameters necessary for an intra prediction mode by using a signaling method for an intra-merge mode and an intra-merge list construction method can be provided. have.

In addition, according to the present invention, encoding parameters required for intra prediction (eg, at least one of a luminance and/or intra prediction mode, a multi-reference line index, a transform transform flag, and a transform index) are used as neighboring blocks. An image encoding/decoding method and apparatus for reducing the amount of encoding generated bits by implicitly inducing in may be provided.

The intra-screen encoding/decoding process may be performed for each of the luminance and color difference signals. For example, in the intra-screen encoding/decoding process, at least one or more methods of inducing an intra prediction mode, segmenting a block, configuring a reference sample, and performing intra prediction may be applied differently to the luminance signal and the color difference signal.

The intra-screen encoding/decoding process for the luminance and color difference signals may be performed in the same manner. For example, in the intra-screen encoding/decoding process applied to the luminance signal, at least one of inducing an intra prediction mode, segmenting a block, configuring a reference sample, and performing intra prediction may be equally applied to the color difference signal.

The above methods can be performed in the same way in an encoder and a decoder. For example, at least one method of deriving an intra prediction mode, segmenting a block, configuring a reference sample, and performing intra prediction in the intra-picture encoding/decoding process may be applied equally to the encoder and the decoder. In addition, the order of applying the above methods may be different between the encoder and the decoder. For example, in performing the intra prediction/decoding of the current block, the encoder may configure a reference sample and then perform one or more intra prediction to encode the determined intra prediction mode.

The above embodiments of the present invention may be applied according to the size of at least one of a coding block, a prediction block, a transform block, a block, and a unit. The size here may be defined as a minimum size and/or a maximum size in order to apply the embodiments, or may be defined as a fixed size to which the embodiments are applied. In addition, in the above embodiments, the first embodiment may be applied to the first size, and the second embodiment may be applied to the second size. That is, the always-on embodiments may be applied in combination according to the size. Further, the above embodiments of the present invention can be applied only when the size is greater than or equal to the minimum size and less than or equal to the maximum size. That is, the above embodiments can be applied only when the block size is within a certain range.

For example, the above embodiments can be applied only when the size of the encoding/decoding target block is 8x8 or more.

For example, the above embodiments can be applied only when the size of the encoding/decoding object block is 16x16 or less.

For example, the above embodiments can be applied only when the size of the encoding/decoding target block is 8x8 or more and 16x16 or less.

The above embodiments of the present invention may be applied according to a temporal layer. A separate identifier is signaled to identify a temporal layer to which the above embodiments are applicable, and the above embodiments may be applied to a temporal layer specified by the corresponding identifier. Here, the identifier may be defined as a minimum layer and/or a maximum layer to which the embodiment is applicable, or may be defined as indicating the specific layer to which the embodiment is applied.

For example, the above embodiments can be applied only when the temporal layer of the current image is the lowest layer.

For example, the above embodiments can be applied only when the temporal layer of the current image is the highest layer.

According to the above embodiment of the present invention, when calculating a boundary strength in a deblocking filter, an intra prediction mode of an encoding/decoding target block may be used.

When performing intra prediction, prediction samples using a reference sample are integer-pel units, 1/2-pixel units, and 1/4-pixel units (1/4-pel). ) Unit, 1/8-pixel (1/8-pel) unit, 1/16-pixel (1/16-pel) unit, 1/32-pixel (1/32-pel) unit, 1/64-pixel The above embodiments of the present invention may be applied even when at least one of the (1/64-pel) units is used.

A slice type to which the above embodiments of the present invention are applied is defined, and the above embodiments of the present invention may be applied according to the corresponding slice type. For example, when the slice type is I-slice, intra prediction may be performed by dividing the current block into sub-blocks and deriving an intra prediction mode for each sub-block from neighboring blocks.

The shape of the block to which the above embodiments of the present invention are applied may have a square shape or a non-square shape.

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 those described above. have. In addition, those of ordinary skill in the art understand that the steps shown in the flowchart are not exclusive, other steps are included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention. You can understand.

The above-described embodiments include examples of various aspects. Although not all possible combinations for representing the various aspects can be described, those of ordinary skill in the art will recognize that other combinations are possible. Accordingly, the present invention will be said to include all other replacements, modifications and changes falling within the scope of the following claims.

The embodiments according to the present invention described above may be implemented in the form of program instructions that can be executed through various computer components and recorded in a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded in the computer-readable recording medium may be specially designed and configured for the present invention, or may be known and usable to those skilled in the computer software field. 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 processing according to the present invention, and vice versa.

In the above, the present invention has been described by specific matters such as specific components 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, Those of ordinary skill in the art 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 determined, and all modifications that are equally or equivalent to the claims as well as the claims to be described later fall within the scope of the spirit of the present invention I would say.

Claims (20)

In the video decoding method,
Deriving an intra prediction mode for the current block;
Determining at least one reconstructed sample line for the current block based on the derived intra prediction mode;
Constructing a reference sample using at least one reconstructed sample included in the determined reconstructed sample line; And
And performing intra prediction on the current block based on the intra prediction mode and the reference sample. The method of claim 1,
The image decoding method wherein the current block includes a sub-block of the current block. The method of claim 1,
The at least one reconstructed sample line is determined based on a position of the current block in a coding tree block. The method of claim 1,
The at least one reconstructed sample line is determined based on whether the derived intra prediction mode is directional. The method of claim 1,
The at least one reconstructed sample line is determined based on at least one of the size and segmentation information of the current block. The method of claim 1,
And obtaining information on the at least one reconstructed sample line from a bitstream. The method of claim 1,
And reconstructing an MPM candidate list of the current block based on the determined reconstructed sample line. The method of claim 1,
Further comprising the step of deriving information on the reconstructed block adjacent to the current block,
The step of performing intra prediction on the current block,
And deriving encoding parameters of the reconstructed block based on the derived information on the reconstructed block adjacent to the current block. The method of claim 8,
The information on the reconstructed block adjacent to the current block includes information indicating a reconstructed block adjacent to the current block for applying an intra-screen merge mode. The method of claim 8,
The encoding parameter of the reconstructed block includes at least one of a luminance component intra prediction mode, a multi reference line index, transform information, and a color difference component intra prediction mode. In the video encoding method,
Determining an intra prediction mode for the current block;
Determining at least one reconstructed sample line for the current block based on the derived intra prediction mode;
Constructing a reference sample using at least one reconstructed sample included in the determined reconstructed sample line; And
And performing intra prediction on the current block based on the intra prediction mode and the reference sample. The method of claim 11,
The image encoding method wherein the current block includes a sub-block of the current block. The method of claim 11,
The at least one reconstructed sample line is determined based on a position of the current block in a coding tree block. The method of claim 11,
The at least one reconstructed sample line is determined based on whether the derived intra prediction mode is directional. The method of claim 11,
The at least one reconstructed sample line is determined based on at least one of a size and split information of the current block. The method of claim 11,
Encoding information about the at least one reconstructed sample line. The method of claim 11,
And reconstructing an MPM candidate list of the current block based on the determined reconstructed sample line. The method of claim 11,
Further comprising the step of deriving information on the reconstructed block adjacent to the current block,
The step of performing intra prediction on the current block,
And deriving an encoding parameter of the reconstructed block based on the derived information on the reconstructed block adjacent to the current block. The method of claim 18,
The encoding parameter of the reconstructed block includes at least one of a luminance component intra prediction mode, a multi reference line index, transform information, and a color difference component intra prediction mode. Determining an intra prediction mode for the current block;
Determining at least one reconstructed sample line for the current block based on the derived intra prediction mode;
Constructing a reference sample using at least one reconstructed sample included in the determined reconstructed sample line; And
A computer-readable recording medium storing a bitstream generated by a video encoding method comprising the step of performing intra prediction on the current block based on the intra prediction mode and the reference sample.

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