Video encoding / decoding method and apparatus, and recording medium storing bit stream

Abstract

Provided are a video encoding / decoding method, an apparatus, and a recording medium storing a bitstream. An image decoding method of the present invention may comprise the steps of: deriving an intra prediction mode of a current luminance block; deriving an intra prediction mode of the current chroma block based on the intra prediction mode of the current luma block; and generating a prediction block of the current chroma block based on the intra prediction mode of the current chroma block, in which the step of deriving the intra prediction mode of the current chroma block may include determining whether CCLM (Cross-Component Linear Mode) may be performed for the current chroma block.

Description

[0001] This application is a divisional application of a patent application with an application date of December 27, 2019, application number 201980086940.8, and titled “Video encoding / decoding method, device, and recording medium storing bit stream”. Technical Field

[0002] The present invention relates to a method and apparatus for encoding / decoding an image. In particular, the present invention relates to a method and apparatus for efficiently encoding / decoding an image and signaling an intra-frame prediction mode. Background Art

[0003] Recently, in various applications, the demand for high-resolution and high-quality images such as high-definition (HD) or ultra-high-definition (UHD) images has increased. As the resolution and quality of images increase, the amount of data increases accordingly. This is one of the reasons for the increase in transmission cost and storage cost when image data is transmitted through existing transmission media such as wired or wireless broadband channels or when image data is stored. In order to solve these problems of high-resolution and high-quality image data, efficient image encoding / decoding technology is required.

[0004] There are various video compression techniques, such as inter-frame prediction techniques that predict the values ​​of pixels in a current picture from the values ​​of pixels in a previous picture or a subsequent picture, intra-frame prediction techniques that predict the values ​​of pixels in an area of ​​the current picture from the values ​​of pixels in another area of ​​the current picture, transformation and quantization techniques for compressing the energy of residual signals, and entropy coding techniques that assign shorter codes to frequently occurring pixel values ​​and longer codes to less frequently occurring pixel values. Summary of the invention

[0005] Technical issues

[0006] An object of the present invention is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0007] Another object of the present invention is to provide an image encoding / decoding method and apparatus for efficiently signaling an intra prediction mode.

[0008] Another object of the present invention is to provide a recording medium storing a bit stream generated by the image encoding method / apparatus of the present invention.

[0009] Another object of the present invention is to provide a recording medium storing a bit stream received, decoded and used by the image decoding apparatus according to the present invention to reconstruct an image.

[0010] Technical Solution

[0011] An image decoding method according to an embodiment of the present invention may include: deriving an intra-frame prediction mode of a current luminance block, deriving an intra-frame prediction mode of a current chrominance block based on the intra-frame prediction mode of the current luminance block, and generating a prediction block of the current chrominance block based on the intra-frame prediction mode of the current chrominance block, and the step of deriving the intra-frame prediction mode of the current chrominance block may include: determining whether CCLM (cross-component linear mode) can be performed for the current chrominance block.

[0012] In the image decoding method of the present invention, whether CCLM can be performed on the current chrominance block can be determined based on the size of the current luminance block.

[0013] In the image decoding method of the present invention, when the current luminance block has a predetermined size, it may be determined that CCLM can be performed on the current chrominance block.

[0014] In the image decoding method of the present invention, when the current luminance block is a 64×64 block, it may be determined that CCLM can be performed on the current chrominance block.

[0015] In the image decoding method of the present invention, whether CCLM can be performed on the current chrominance block can be determined based on the size of the coding tree block.

[0016] In the image decoding method of the present invention, when the coding tree block is smaller than a 64×64 block, it may be determined that CCLM can be performed on the current chrominance block.

[0017] In the image decoding method of the present invention, when the intra prediction mode of the current chrominance block is CCLM, the parameters of the linear model of CCLM can be derived based on the downsampled neighboring sample values ​​obtained by downsampling multiple reconstructed neighboring samples of the current luminance block.

[0018] In the image decoding method of the present invention, the parameters of the linear model of CCLM may be derived based on the maximum value and the minimum value derived from the down-sampled adjacent sample point values.

[0019] In the image decoding method of the present invention, the maximum value can be derived as the average of the first maximum value and the second maximum value among the downsampled adjacent sample values, and the minimum value can be derived as the average of the first minimum value and the second minimum value among the downsampled adjacent sample values.

[0020] In the image decoding method of the present invention, when an indicator showing whether the intra-frame prediction mode of the current luminance block is the planar mode is a first value, the planar mode can be derived as the intra-frame prediction mode of the current luminance block, and when the indicator is a second value, the MPM list of the current luminance block can be configured, and the mode indicated by the index for the MPM list can be derived as the intra-frame prediction mode of the current luminance block.

[0021] An image encoding method according to another embodiment of the present invention may include: determining an intra-frame prediction mode of a current luminance block, determining an intra-frame prediction mode of a current chrominance block, generating a prediction block of the current chrominance block based on the intra-frame prediction mode of the current chrominance block, and encoding the intra-frame prediction mode of the current chrominance block based on the intra-frame prediction mode of the current luminance block, and the step of determining the intra-frame prediction mode of the current chrominance block may include: determining whether CCLM (cross-component linear mode) can be performed for the current chrominance block.

[0022] In the image encoding method of the present invention, whether CCLM can be performed on the current chrominance block can be determined based on the size of the current luminance block.

[0023] In the image encoding method of the present invention, when the current luminance block has a predetermined size, it may be determined that CCLM can be performed on the current chrominance block.

[0024] In the image encoding method of the present invention, when the current luminance block is a 64×64 block, it may be determined that CCLM can be performed on the current chrominance block.

[0025] In the image encoding method of the present invention, whether CCLM can be performed on the current chrominance block can be determined based on the size of the coding tree block.

[0026] In the image encoding method of the present invention, when the coding tree block is smaller than a 64×64 block, it may be determined that CCLM can be performed on the current chrominance block.

[0027] In the image encoding method of the present invention, when the intra prediction mode of the current chrominance block is CCLM, the parameters of the linear model of CCLM can be derived based on the downsampled neighboring sample values ​​obtained by downsampling multiple reconstructed neighboring samples of the current luminance block.

[0028] In the image encoding method of the present invention, the parameters of the linear model of CCLM may be derived based on the maximum value and the minimum value derived from the down-sampled neighboring sample point values.

[0029] In the image encoding method of the present invention, the maximum value may be derived as the average of a first maximum value and a second maximum value among the downsampled adjacent sample values, and the minimum value may be derived as the average of a first minimum value and a second minimum value among the downsampled adjacent sample values.

[0030] A computer-readable recording medium according to another embodiment of the present invention may store a bitstream received, decoded and used to reconstruct an image by an image decoding device. The bitstream may include information about an intra-frame prediction mode of a current luminance block and information about an intra-frame prediction mode of a current chrominance block, the information about the intra-frame prediction mode of the current luminance block may be used to derive the intra-frame prediction mode of the current luminance block, the intra-frame prediction mode of the current luminance block and the information about the intra-frame prediction mode of the current chrominance block may be used to derive the intra-frame prediction mode of the current chrominance block, the intra-frame prediction mode of the current chrominance block may be used to generate a prediction block of the current chrominance block, and the intra-frame prediction mode of the current chrominance block may be derived based on determining whether CCLM (cross-component linear mode) can be performed for the current chrominance block.

[0031] A computer-readable recording medium according to another embodiment of the present invention may store a bit stream generated by the image encoding method and / or apparatus according to the present invention.

[0032] Beneficial Effects

[0033] According to the present invention, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0034] Furthermore, according to the present invention, an image encoding / decoding method and apparatus for efficiently signaling an intra prediction mode can be provided.

[0035] Furthermore, according to the present invention, there can be provided a recording medium storing a bit stream generated by the image encoding method / apparatus of the present invention.

[0036] Furthermore, according to the present invention, there can be provided a recording medium storing a bit stream received, decoded, and used by the image decoding apparatus according to the present invention to reconstruct an image. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a block diagram showing a configuration of an encoding device according to an embodiment to which the present invention is applied.

[0038] Figure 2 is a block diagram showing a configuration of a decoding device according to an embodiment to which the present invention is applied.

[0039] Figure 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded.

[0040] Figure 4 is a diagram illustrating an intra prediction process.

[0041] Figure 5 is a diagram illustrating an embodiment of an inter-frame prediction process.

[0042] Figure 6 is a diagram illustrating transform and quantization processing.

[0043] Figure 7 is a diagram showing reference samples that can be used for intra prediction.

[0044] Figure 8 is a diagram illustrating an embodiment of performing intra prediction by partitioning a current block.

[0045] Fig. 9 is a diagram for explaining a method of configuring an MPM list according to an embodiment of the present invention.

[0046] Fig.10 is a diagram for explaining an example of configuring an MPM list.

[0047] Fig.11 is a diagram for explaining another example of configuring an MPM list.

[0048] Fig.12 is a diagram for explaining another example of configuring an MPM list.

[0049] Fig.13 is a diagram for explaining another example of configuring an MPM list.

[0050] Fig.14 is a diagram for explaining another example of configuring an MPM list.

[0051] Fig.15 is a diagram for explaining another example of configuring an MPM list.

[0052] Fig.16 is a diagram for explaining another example of configuring an MPM list.

[0053] Fig.17 is a diagram for explaining another example of configuring an MPM list.

[0054] Fig.18 is a diagram for explaining another example of configuring an MPM list.

[0055] Fig.19 is a diagram for explaining the position of a luma block used for configuring a candidate mode of a current chroma block according to an embodiment of the present invention.

[0056] Fig. 20 A diagram for explaining a reference line of a current chrominance block and a reference line of a corresponding luminance block in the YUV4:4:4 format.

[0057] Fig.21 is a diagram for explaining neighboring sample points used to derive a linear regression model or a linear model in the YUV4:2:0 format. DETAILED DESCRIPTION

[0058] Various modifications may be made to the present invention, and there are various embodiments of the present invention, wherein examples of various embodiments of the present invention will now be provided with reference to the accompanying drawings and described in detail. However, the present invention is not limited thereto, although the exemplary embodiments may be interpreted as including all modifications, equivalents or substitutions within the technical concept and technical scope of the present invention. In various aspects, similar figure numerals refer to the same or similar functions. In the accompanying drawings, the shapes and sizes of the elements may be exaggerated for clarity. In the following detailed description of the present invention, reference is made to the accompanying drawings that illustrate specific embodiments of the present invention in a graphical manner. These embodiments are described in sufficient detail to enable those skilled in the art to implement the present disclosure. It should be understood that the various embodiments of the present disclosure, although different, are not necessarily mutually exclusive. For example, without departing from the spirit and scope of the present disclosure, the specific features, structures and characteristics described herein in conjunction with one embodiment may be implemented in other embodiments. In addition, it should be understood that the position or arrangement of each element within each disclosed embodiment may be modified without departing from the spirit and scope of the present disclosure. Therefore, the following detailed description should not be regarded as having a limiting meaning, and the scope of the present disclosure is limited only by the appended claims (when properly interpreted, together with the full range of equivalents claimed by the claims).

[0059] The terms "first", "second", etc. used in the specification may be used to describe various components, but the components should not be interpreted as being limited to these terms. These terms are only used to distinguish one component from other components. For example, without departing from the scope of the present invention, a "first" component may be named a "second" component, and a "second" component may also be similarly named a "first" component. The term "and / or" includes a combination of multiple items or any one of the multiple items.

[0060] It will be understood that in this specification, when an element is simply referred to as being “connected to” or “coupled to” another element rather than being “directly connected to” or “directly coupled to” another element, the element may be “directly connected to” or “directly coupled to” another element, or connected to or coupled to another element with other elements interposed therebetween. Conversely, it will be understood that when an element is referred to as being “directly coupled to” or “directly connected to” another element, there are no intervening elements.

[0061] In addition, the components shown in the embodiments of the present invention are shown independently to represent the characteristic functions that are different from each other. Therefore, this does not mean that each component is composed of a separate hardware or software component unit. In other words, for convenience, each component includes each component in the listed components. Therefore, at least two components of each component can be combined to form a component, or a component can be divided into multiple components to perform each function. If it does not depart from the essence of the present invention, the embodiment in which each component is combined and the embodiment in which a component is divided are also included in the scope of the present invention.

[0062] The terms used in this specification are only used to describe specific embodiments and are not intended to limit the present invention. Unless there is a significantly different meaning in the context, the expression used in the singular includes the expression in the plural form. In this specification, it will be understood that terms such as "including", "having" etc. are intended to indicate the presence of features, numbers, steps, actions, elements, parts or combinations thereof disclosed in the specification, and are not intended to exclude the possibility that one or more other features, numbers, steps, actions, elements, parts or combinations thereof may exist or may be added. In other words, when a particular element is referred to as "included", it does not exclude elements other than the corresponding element, but may include other elements in an embodiment of the present invention or in the scope of the present invention.

[0063] In addition, some components may not be essential components for performing the basic functions of the present invention, but rather selective components that only improve its performance. The present invention may be implemented by including only essential components for implementing the essence of the present invention without including components for improving performance. Structures that include only essential components without including selective components that only improve performance are also included within the scope of the present invention.

[0064] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. When describing the exemplary embodiments of the present invention, well-known functions or constructions will not be described in detail because they may unnecessarily obscure the understanding of the present invention. The same constituent elements in the accompanying drawings are represented by the same reference numerals, and repeated descriptions of the same elements will be omitted.

[0065] Hereinafter, an image may refer to a picture constituting a video, or may refer to the video itself. For example, "encoding or decoding an image or both encoding and decoding" may refer to "encoding or decoding a moving picture or both encoding and decoding", and may refer to "encoding or decoding one of the images of the moving picture or both encoding and decoding".

[0066] Hereinafter, the terms "motion picture" and "video" may be used as the same meaning and may be replaced with each other.

[0067] Hereinafter, a target image may be an encoding target image as an encoding target and / or a decoding target image as a decoding target. In addition, a target image may be an input image input to an encoding device, and an input image input to a decoding device. Here, the target image may have the same meaning as the current image.

[0068] Hereinafter, the terms "image", "picture", "frame" and "screen" may be used as the same meaning and may be replaced with each other.

[0069] Hereinafter, the target block may be an encoding target block as an encoding target and / or a decoding target block as a decoding target. In addition, the target block may be a current block as a target of current encoding and / or decoding. For example, the terms "target block" and "current block" may be used as the same meaning and may be replaced with each other.

[0070] Hereinafter, the terms "block" and "unit" may be used as the same meaning and may be replaced with each other. Alternatively, a "block" may refer to a specific unit.

[0071] In the following, the terms "region" and "segment" are used interchangeably.

[0072] Hereinafter, a specific signal may be a signal representing a specific block. For example, an original signal may be a signal representing a target block. A prediction signal may be a signal representing a prediction block. A residual signal may be a signal representing a residual block.

[0073] In an embodiment, each of the specific information, data, flags, indexes, elements, attributes, etc. may have a value. The value of the information, data, flags, indexes, elements, and attributes equal to "0" may represent a logical false or a first predefined value. In other words, the value "0", false, logical false, and the first predefined value may be replaced with each other. The value of the information, data, flags, indexes, elements, and attributes equal to "1" may represent a logical true or a second predefined value. In other words, the value "1", true, logical true, and the second predefined value may be replaced with each other.

[0074] When the variable i or j is used to represent a column, row, or index, the value of i may be an integer equal to or greater than 0, or an integer equal to or greater than 1. That is, the column, row, index, etc. may be counted from 0, or may be counted from 1.

[0075] Description of terms

[0076] Encoder: This refers to a device that performs encoding. In other words, it refers to an encoding device.

[0077] Decoder: Refers to a device that performs decoding. In other words, it refers to a decoding device.

[0078] Block: is an M×N sample array. Here, M and N may represent positive integers, and a block may represent a sample array in a two-dimensional form. A block may refer to a unit. A current block may represent an encoding target block that becomes a target at the time of encoding, or a decoding target block that becomes a target at the time of decoding. In addition, the current block may be at least one of a coding block, a prediction block, a residual block, and a transform block.

[0079] Sample: It is the basic unit of a block. d ), the sample point can be represented from 0 to 2 Bd In the present invention, a sample point may be used as the meaning of a pixel. That is, a sample point, a pel, and a pixel may have the same meaning as each other.

[0080] Unit: may refer to a coding and decoding unit. When encoding and decoding an image, a unit may be a region generated by partitioning a single image. In addition, when a single image is partitioned into sub-division units during encoding or decoding, a unit may represent a sub-division unit. That is, an image may be partitioned into a plurality of units. When encoding and decoding an image, a predetermined process for each unit may be performed. A single unit may be partitioned into sub-units having a size smaller than that of the unit. According to the function, a unit may represent a block, a macroblock, a coding tree unit, a coding tree block, a coding unit, a coding block, a prediction unit, a prediction block, a residual unit, a residual block, a transform unit, a transform block, and the like. In addition, in order to distinguish a unit from a block, a unit may include a luminance component block, a chrominance component block associated with the luminance component block, and a syntax element for each color component block. A unit may have various sizes and shapes, and specifically, the shape of a unit may be a two-dimensional geometric figure such as a square, a rectangle, a trapezoid, a triangle, a pentagon, and the like. Also, the unit information may include at least one of a unit type indicating a coding unit, a prediction unit, a transformation unit, etc., and a unit size, a unit depth, an order of encoding and decoding of the unit, and the like.

[0081] Coding tree unit: A single coding tree block configured with a luminance component Y and two coding tree blocks associated with chrominance components Cb and Cr. In addition, the coding tree unit may represent a syntax element including a block and each block. Each coding tree unit may be partitioned by using at least one of a quadtree partitioning method, a binary tree partitioning method, and a ternary tree partitioning method to configure a lower-level unit such as a coding unit, a prediction unit, a transform unit, etc. The coding tree unit may be used as a term for specifying a sample block that becomes a processing unit when encoding / decoding an image as an input image. Here, the quadtree may represent a quadtree.

[0082] When the size of the coding block is within a predetermined range, it can be divided using only quadtree partitioning. Here, the predetermined range may be defined as at least one of the maximum size and the minimum size of the coding block that can be divided using only quadtree partitioning. Information indicating the maximum / minimum size of the coding block that allows quadtree partitioning may be signaled through a bitstream, and the information may be signaled in at least one unit of a sequence, a picture parameter, a parallel block group, or a slice (fragment). Optionally, the maximum / minimum size of the coding block may be a fixed size predetermined in the encoder / decoder. For example, when the size of the coding block corresponds to 256×256 to 64×64, it is possible to divide using only quadtree partitioning. Optionally, when the size of the coding block is larger than the size of the maximum conversion block, it is possible to divide using only quadtree partitioning. Here, the block to be divided may be at least one of a coding block and a transform block. In this case, the information indicating the division of the coding block (e.g., split_flag) may be a flag indicating whether quadtree partitioning is performed. When the size of the coding block falls within a predetermined range, it is possible to divide using only binary or ternary tree partitioning. In this case, the above description of the quadtree partition can be applied to the binary tree partition or the ternary tree partition in the same manner.

[0083] Coding tree block: may be used as a term used to designate any one of a Y coding tree block, a Cb coding tree block, and a Cr coding tree block.

[0084] Neighboring block: may refer to a block adjacent to the current block. The block adjacent to the current block may refer to a block that touches the boundary of the current block or a block that is located within a predetermined distance from the current block. The neighboring block may refer to a block adjacent to a vertex of the current block. Here, the block adjacent to a vertex of the current block may refer to a block that is vertically adjacent to a neighboring block that is horizontally adjacent to the current block or a block that is horizontally adjacent to a neighboring block that is vertically adjacent to the current block.

[0085] Reconstructed neighboring block: may represent a neighboring block that is adjacent to the current block and has been encoded or decoded in space / time. Here, the reconstructed neighboring block may represent a reconstructed neighboring unit. The reconstructed spatial neighboring block may be a block that is within the current picture and has been reconstructed by encoding or decoding or both encoding and decoding. The reconstructed temporal neighboring block is a block at a position corresponding to the current block of the current picture within the reference image or a neighboring block of the block.

[0086] Unit depth: can represent the degree of partitioning of a unit. In a tree structure, the highest node (root node) can correspond to the first unit that is not partitioned. In addition, the highest node can have a minimum depth value. In this case, the depth of the highest node can be level 0. A node with a depth of level 1 can represent a unit generated by partitioning the first unit once. A node with a depth of level 2 can represent a unit generated by partitioning the first unit twice. A node with a depth of level n can represent a unit generated by partitioning the first unit n times. A leaf node can be the lowest node and a node that cannot be further partitioned. The depth of a leaf node can be the maximum level. For example, the predefined value of the maximum level can be 3. The depth of the root node can be the lowest, and the depth of the leaf node can be the deepest. In addition, when a unit is represented as a tree structure, the level at which the unit exists can represent the unit depth.

[0087] Bitstream: can represent a stream of bits including coded image information.

[0088] Parameter set: corresponds to header information among the configurations in the bitstream. At least one of a video parameter set, a sequence parameter set, a picture parameter set, and an adaptation parameter set may be included in the parameter set. In addition, the parameter set may include a slice header, a tile group header, and tile header information. The term "tile group" means a group of tiles and has the same meaning as a slice.

[0089] The adaptation parameter set may represent a parameter set that can be shared by being referenced in different pictures, sub-pictures, slices, tile groups, tiles, or bricks. In addition, information in the adaptation parameter set may be used by referring to different adaptation parameter sets for sub-pictures, slices, tile groups, tiles, or bricks within a picture.

[0090] Furthermore, regarding adaptation parameter sets, different adaptation parameter sets may be referenced by using identifiers of different adaptation parameter sets for a sub-picture, a slice, a tile group, a tile, or a partition within a picture.

[0091] Furthermore, regarding adaptation parameter sets, different adaptation parameter sets may be referenced by using identifiers of different adaptation parameter sets for slices, tile groups, tiles, or partitions within a sub-picture.

[0092] Furthermore, regarding adaptation parameter sets, different adaptation parameter sets may be referenced by using identifiers of different adaptation parameter sets for tiles or partitions within a slice.

[0093] Furthermore, with respect to adaptation parameter sets, different adaptation parameter sets may be referenced by using identifiers of different adaptation parameter sets for partitions within a tile.

[0094] Information about the adaptation parameter set identifier may be included in a parameter set or a header of a sub-picture, and an adaptation parameter set corresponding to the adaptation parameter set identifier may be used for the sub-picture.

[0095] Information about the adaptation parameter set identifier may be included in a parameter set or a header of a tile, and an adaptation parameter set corresponding to the adaptation parameter set identifier may be used for the tile.

[0096] Information about the adaptation parameter set identifier may be included in a header of the tile, and an adaptation parameter set corresponding to the adaptation parameter set identifier may be used for the tile.

[0097] A picture may be partitioned into one or more tile rows and one or more tile columns.

[0098] A sub-picture may be partitioned into one or more parallel block rows and one or more parallel block columns within a picture. A sub-picture may be an area having a rectangular / square form within a picture and may include one or more CTUs. In addition, at least one or more parallel blocks / blocks / strips may be included in a sub-picture.

[0099] A tile may be an area having a rectangular / square form within a picture and may include one or more CTUs. In addition, a tile may be partitioned into one or more partitions.

[0100] A partition may represent one or more CTU rows within a tile. A tile may be partitioned into one or more partitions, and each partition may have at least one or more CTU rows. A tile that is not partitioned into two or more may represent a partition.

[0101] A slice may include one or more tiles within a picture, and may include one or more partitions within a tile.

[0102] Parsing: may mean determining the value of a syntax element by performing entropy decoding, or may mean the entropy decoding itself.

[0103] Symbol: At least one of a syntax element, a coding parameter, and a transform coefficient value that can represent a coding / decoding target unit. In addition, the symbol can represent an entropy coding target or an entropy decoding result.

[0104] Prediction mode: may be information indicating a mode for encoding / decoding using intra prediction or a mode for encoding / decoding using inter prediction.

[0105] Prediction unit: may represent a basic unit when performing prediction (such as inter prediction, intra prediction, inter compensation, intra compensation, and motion compensation). A single prediction unit may be partitioned into multiple partitions of smaller size, or may be partitioned into multiple prediction units of lower levels. Multiple partitions may be basic units when performing prediction or compensation. Partitions generated by splitting a prediction unit may also be prediction units.

[0106] Prediction unit partition: may represent a shape obtained by partitioning a prediction unit.

[0107] A reference picture list may refer to a list including one or more reference pictures used for inter prediction or motion compensation. There are several types of available reference picture lists, including LC (List Combination), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3).

[0108] The inter prediction indicator may refer to the direction of inter prediction of the current block (unidirectional prediction, bidirectional prediction, etc.). Alternatively, the inter prediction indicator may refer to the number of reference pictures used to generate the prediction block of the current block. Alternatively, the inter prediction indicator may refer to the number of prediction blocks used when performing inter prediction or motion compensation on the current block.

[0109] The prediction list utilization flag indicates whether at least one reference picture in a specific reference picture list is used to generate a prediction block. The prediction list utilization flag may be used to derive the inter prediction indicator, and conversely, the inter prediction indicator may be used to derive the prediction list utilization flag. For example, when the prediction list utilization flag has a first value of zero (0), it indicates that the reference picture in the reference picture list is not used to generate the prediction block. On the other hand, when the prediction list utilization flag has a second value of one (1), it indicates that the reference picture list is used to generate the prediction block.

[0110] The reference picture index may refer to an index indicating a specific reference picture in a reference picture list.

[0111] A reference picture may refer to a reference picture referenced by a specific block for the purpose of inter-frame prediction or motion compensation of the specific block. Alternatively, a reference picture may be a picture including a reference block referenced by a current block for inter-frame prediction or motion compensation. Hereinafter, the terms "reference picture" and "reference image" have the same meaning and are interchangeable.

[0112] A motion vector may be a two-dimensional vector used for inter-frame prediction or motion compensation. A motion vector may represent an offset between a coding / decoding target block and a reference block. For example, (mvX, mvY) may represent a motion vector. Here, mvX may represent a horizontal component, and mvY may represent a vertical component.

[0113] The search range may be a two-dimensional area that is searched during inter prediction to retrieve a motion vector. For example, the size of the search range may be M×N. Here, M and N are both integers.

[0114] The motion vector candidate may refer to a prediction candidate block or a motion vector of the prediction candidate block when predicting a motion vector. In addition, the motion vector candidate may be included in a motion vector candidate list.

[0115] The motion vector candidate list may mean a list consisting of one or more motion vector candidates.

[0116] The motion vector candidate index may represent an indicator indicating a motion vector candidate in the motion vector candidate list. Alternatively, it may be an index of a motion vector predictor.

[0117] The motion information may represent information including at least one of items including a motion vector, a reference picture index, an inter prediction indicator, a prediction list utilization flag, a reference picture list information, a reference picture, a motion vector candidate, a motion vector candidate index, a merge candidate, and a merge index.

[0118] The merge candidate list may mean a list consisting of one or more merge candidates.

[0119] The merge candidate may represent a spatial merge candidate, a temporal merge candidate, a combined merge candidate, a combined bi-prediction merge candidate, or a zero merge candidate. The merge candidate may include motion information such as an inter prediction indicator, a reference picture index for each list, a motion vector, a prediction list utilization flag, and an inter prediction indicator.

[0120] The merge index may represent an indicator indicating a merge candidate in the merge candidate list. Alternatively, the merge index may indicate a block in a reconstructed block that is spatially / temporally adjacent to the current block, from which the merge candidate has been derived. Alternatively, the merge index may indicate at least one piece of motion information of the merge candidate.

[0121] Transform unit: may represent a basic unit when encoding / decoding (such as transform, inverse transform, quantization, inverse quantization, transform coefficient encoding / decoding) is performed on a residual signal. A single transform unit may be partitioned into a plurality of lower-level transform units having a smaller size. Here, the transform / inverse transform may include at least one of a first transform / first inverse transform and a second transform / second inverse transform.

[0122] Scaling: may refer to the process of multiplying the level of quantization by a factor. Transform coefficients may be generated by scaling the level of quantization. Scaling may also be referred to as inverse quantization.

[0123] Quantization parameter: may indicate a value used when a transform coefficient is used to generate a quantized level during quantization. The quantization parameter may also indicate a value used when a transform coefficient is generated by scaling the quantized level during inverse quantization. The quantization parameter may be a value mapped to a quantization step size.

[0124] Delta quantization parameter: may represent the difference between the predicted quantization parameter and the quantization parameter of the encoding / decoding target unit.

[0125] Scan: may refer to a method of ordering coefficients within a cell, block, or matrix. For example, changing a two-dimensional matrix of coefficients to a one-dimensional matrix may be called scanning, and changing a one-dimensional matrix of coefficients to a two-dimensional matrix may be called scanning or inverse scanning.

[0126] Transform coefficient: may refer to a coefficient value generated after performing a transform in an encoder. Transform coefficient may refer to a coefficient value generated after performing at least one of entropy decoding and inverse quantization in a decoder. A quantization level obtained by quantizing a transform coefficient or a residual signal or a quantized transform coefficient level may also fall within the meaning of a transform coefficient.

[0127] Quantization level: may represent a value generated by quantizing a transform coefficient or a residual signal in an encoder. Alternatively, the quantization level may represent a value that is a dequantization target subjected to dequantization in a decoder. Similarly, the quantized transform coefficient level as a result of transformation and quantization may also fall within the meaning of the quantization level.

[0128] Non-zero transform coefficient: may refer to a transform coefficient having a value other than zero, or a transform coefficient level or quantization level having a value other than zero.

[0129] Quantization matrix: may refer to a matrix used in a quantization process or an inverse quantization process performed to improve subjective image quality or objective image quality. The quantization matrix may also be referred to as a scaling list.

[0130] Quantization matrix coefficients: can represent each element in the quantization matrix. Quantization matrix coefficients can also be called matrix coefficients.

[0131] Default matrix: may represent a predetermined quantization matrix predefined in an encoder or a decoder.

[0132] Non-default matrix: may denote a quantization matrix that is not predefined in the encoder or decoder but is signaled by the user.

[0133] Statistical value: The statistical value for at least one of a variable, a coding parameter, a constant value, etc. having a calculable specific value can be one or more of the average value, summed value, weighted average value, weighted sum value, minimum value, maximum value, most frequently occurring value, median value, and interpolation value of the corresponding specific value.

[0134] Figure 1 is a block diagram showing a configuration of an encoding device according to an embodiment to which the present invention is applied.

[0135] The encoding device 100 may be an encoder, a video encoding device, or an image encoding device. A video may include at least one image. The encoding device 100 may sequentially encode at least one image.

[0136] Reference Figure 1 , the encoding device 100 may include a motion prediction unit 111, a motion compensation unit 112, an intra-frame prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180 and a reference picture buffer 190.

[0137] The encoding device 100 may perform encoding of an input image by using an intra mode or an inter mode or both an intra mode and an inter mode. In addition, the encoding device 100 may generate a bit stream including encoding information by encoding the input image, and output the generated bit stream. The generated bit stream may be stored in a computer-readable recording medium, or may be streamed through a wired / wireless transmission medium. When the intra mode is used as a prediction mode, the switch 115 may switch to the intra mode. Alternatively, when the inter mode is used as a prediction mode, the switch 115 may switch to the inter mode. Here, the intra mode may represent an intra prediction mode, and the inter mode may represent an inter prediction mode. The encoding device 100 may generate a prediction block for an input block of the input image. In addition, the encoding device 100 may encode the residual block using the residual of the input block and the prediction block after generating the prediction block. The input image may be referred to as a current image as a current encoding target. The input block may be referred to as a current block as a current encoding target, or may be referred to as an encoding target block.

[0138] When the prediction mode is the intra mode, the intra prediction unit 120 may use samples of a block that has been encoded / decoded and is adjacent to the current block as reference samples. The intra prediction unit 120 may perform spatial prediction on the current block by using the reference samples, or may generate prediction samples of the input block by performing spatial prediction. Here, intra prediction may refer to prediction within a frame.

[0139] When the prediction mode is the inter mode, the motion prediction unit 111 may retrieve the area that best matches the input block from the reference image when performing motion prediction, and derive a motion vector by using the retrieved area. In this case, the search area may be used as the area. The reference image may be stored in the reference picture buffer 190. Here, when encoding / decoding the reference image is performed, the reference image may be stored in the reference picture buffer 190.

[0140] The motion compensation unit 112 may generate a predicted block by performing motion compensation on the current block using a motion vector. Here, inter prediction may refer to prediction or motion compensation between frames.

[0141] When the value of the motion vector is not an integer, the motion prediction unit 111 and the motion compensation unit 112 may generate a prediction block by applying an interpolation filter to a partial area of ​​a reference picture. In order to perform inter-picture prediction or motion compensation on a coding unit, it may be determined which mode among the skip mode, merge mode, advanced motion vector prediction (AMVP) mode, and current picture reference mode is used for motion prediction and motion compensation of a prediction unit included in the corresponding coding unit. Then, inter-picture prediction or motion compensation may be performed differently according to the determined mode.

[0142] The subtractor 125 may generate a residual block by using the difference between the input block and the prediction block. The residual block may be referred to as a residual signal. The residual signal may represent the difference between the original signal and the prediction signal. In addition, the residual signal may be a signal generated by transforming or quantizing the difference between the original signal and the prediction signal, or by transforming and quantizing the difference between the original signal and the prediction signal. The residual block may be a residual signal of a block unit.

[0143] The transform unit 130 may generate a transform coefficient by performing a transform on the residual block and output the generated transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing a transform on the residual block. When the transform skip mode is applied, the transform unit 130 may skip the transform on the residual block.

[0144] The quantized level may be generated by applying quantization to a transform coefficient or to a residual signal. Hereinafter, the quantized level may also be referred to as a transform coefficient in an embodiment.

[0145] The quantization unit 140 may generate a quantization level by quantizing the transform coefficient or the residual signal according to the parameter and output the generated quantization level. Here, the quantization unit 140 may quantize the transform coefficient by using a quantization matrix.

[0146] The entropy encoding unit 150 may generate a bitstream by performing entropy encoding on the value calculated by the quantization unit 140 or the encoding parameter value calculated when encoding is performed according to the probability distribution, and output the generated bitstream. The entropy encoding unit 150 may perform entropy encoding on sample information of the image and information for decoding the image. For example, the information for decoding the image may include a syntax element.

[0147] When entropy coding is applied, symbols are represented so that a smaller number of bits are assigned to symbols with a high probability of generation, and a larger number of bits are assigned to symbols with a low probability of generation, and therefore, the size of the bit stream for the symbol to be encoded can be reduced. The entropy coding unit 150 may use a coding method for entropy coding such as exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. For example, the entropy coding unit 150 may perform entropy coding by using a variable length coding / code (VLC) table. In addition, the entropy coding unit 150 may derive a binarization method of a target symbol and a probability model of a target symbol / binary bit, and perform arithmetic coding by using the derived binarization method and context model.

[0148] In order to encode a transform coefficient level (quantized level), the entropy encoding unit 150 may change a coefficient in a two-dimensional block form into a one-dimensional vector form by using a transform coefficient scanning method.

[0149] The coding parameters may include information such as syntax elements (flags, indexes, etc.) that are encoded in the encoder and sent to the decoder by signaling, as well as information derived when performing encoding or decoding. The coding parameters may represent information required when encoding or decoding an image. For example, at least one value or combination of the following items may be included in the coding parameters: unit / block size, unit / block depth, unit / block partition information, unit / block shape, unit / block partition structure, whether to perform quadtree partitioning, whether to perform binary tree partitioning, binary tree partition direction (horizontal or vertical), binary tree partition form (symmetric partitioning or asymmetric partitioning), whether the current coding unit is partitioned by ternary tree partitioning, the direction of ternary tree partitioning (horizontal or vertical), the type of ternary tree partitioning (symmetric type or asymmetric type), whether the current coding unit is partitioned by multi-type tree partitioning, and the type of multi-type tree partitioning. direction (horizontal or vertical), type of multi-type tree partition (symmetric or asymmetric), tree (binary tree or ternary tree) structure of multi-type tree partition, prediction mode (intra-frame prediction or inter-frame prediction), luminance intra-frame prediction mode / direction, chrominance intra-frame prediction mode / direction, intra-frame partition information, inter-frame partition information, coding block partition flag, prediction block partition flag, transform block partition flag, reference sample filtering method, reference sample filter taps, reference sample filter coefficients, prediction block filtering method, prediction block filter taps, prediction block filter coefficients, prediction block boundary filtering method, prediction block boundary filter taps, prediction block boundary filter coefficients, intra-frame prediction mode , inter prediction mode, motion information, motion vector, motion vector difference, reference picture index, inter prediction angle, inter prediction indicator, prediction list utilization flag, reference picture list, reference picture, motion vector predictor index, motion vector predictor candidate, motion vector candidate list, whether to use merge mode, merge index, merge candidate, merge candidate list, whether to use skip mode, interpolation filter type, interpolation filter tap, interpolation filter coefficient, motion vector size, representation accuracy of motion vector, transform type, transform size, information on whether primary (first) transform is used, information on whether secondary transform is used, primary transform index, secondary transform index , information on whether a residual signal exists, coding block pattern, coding block flag (CBF), quantization parameter, quantization parameter residual, quantization matrix, whether to apply an intra-frame loop filter, intra-frame loop filter coefficients, intra-frame loop filter taps, intra-frame loop filter shape / form, whether to apply a deblocking filter, deblocking filter coefficients, deblocking filter taps, deblocking filter strength, deblocking filter shape / form, whether to apply adaptive sample offset, adaptive sample offset value, adaptive sample offset category, adaptive sample offset type, whether to apply an adaptive loop filter, adaptive loop filter coefficients, adaptive loop filter taps, adaptive loop filter shape / form,Binarization / debinarization method, context model determination method, context model update method, whether to execute normal mode, whether to execute bypass mode, context binary bit, bypass binary bit, valid coefficient flag, last valid coefficient flag, encoding flag for unit of coefficient group, position of last valid coefficient, flag on whether the value of coefficient is greater than 1, flag on whether the value of coefficient is greater than 2, flag on whether the value of coefficient is greater than 3, information on remaining coefficient values, sign information, reconstructed luminance sample, reconstructed chrominance sample, residual luminance sample, residual chrominance sample, luminance transform coefficient, chrominance transform coefficient, quantized luminance level, quantized chrominance level, transform coefficient level scanning method, motion vector search area at decoder side domain size, shape of a motion vector search area at a decoder side, number of motion vector searches at a decoder side, information on a CTU size, information on a minimum block size, information on a maximum block size, information on a maximum block depth, information on a minimum block depth, image display / output order, slice identification information, slice type, slice partition information, tile identification information, tile type, tile partition information, tile group identification information, tile group type, tile group partition information, picture type, bit depth of input samples, bit depth of reconstructed samples, bit depth of residual samples, bit depth of transform coefficients, bit depth of quantization levels, and information on a luminance signal or information on a chrominance signal.

[0150] Here, signaling a flag or an index may mean entropy encoding the corresponding flag or index by an encoder and including it in a bitstream, and may mean entropy decoding the corresponding flag or index from the bitstream by a decoder.

[0151] When the encoding apparatus 100 performs encoding by inter-frame prediction, the encoded current image may be used as a reference image for another image that is subsequently processed. Therefore, the encoding apparatus 100 may reconstruct or decode the encoded current image, or store the reconstructed or decoded image as a reference image in the reference picture buffer 190.

[0152] The quantized level may be dequantized in the dequantization unit 160 or may be inversely transformed in the inverse transform unit 170. The dequantized or inversely transformed coefficient or the dequantized and inversely transformed coefficient may be added to the prediction block by the adder 175. By adding the dequantized or inversely transformed coefficient or the dequantized and inversely transformed coefficient to the prediction block, a reconstructed block may be generated. Here, the dequantized or inversely transformed coefficient or the dequantized and inversely transformed coefficient may mean a coefficient on which at least one of dequantization and inverse transformation is performed, and may mean a reconstructed residual block.

[0153] The reconstructed block may pass through the filter unit 180. The filter unit 180 may apply at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) to the reconstructed sample, the reconstructed block, or the reconstructed image. The filter unit 180 may be referred to as an in-loop filter.

[0154] The deblocking filter may remove block distortion generated in the boundary between blocks. In order to determine whether to apply the deblocking filter, it may be determined whether to apply the deblocking filter to the current block based on the samples included in the number of rows or columns included in the block. When the deblocking filter is applied to the block, another filter may be applied according to the required deblocking filter strength.

[0155] In order to compensate for the coding error, a suitable offset value may be added to the sample value by using sample adaptive offset. Sample adaptive offset can correct the offset of the deblocked image from the original image in units of samples. A method of applying the offset in consideration of edge information about each sample may be used, or a method of partitioning the samples of the image into a predetermined number of regions, determining the region to which the offset is applied, and applying the offset to the determined region may be used.

[0156] The adaptive loop filter may perform filtering based on a comparison result of a filtered reconstructed image and an original image. Samples included in an image may be partitioned into predetermined groups, a filter to be applied to each group may be determined, and differential filtering may be performed on each group. Information on whether ALF is applied may be signaled by a coding unit (CU), and the form and coefficient of ALF to be applied to each block may vary.

[0157] The reconstructed block or the reconstructed image that has passed through the filter unit 180 may be stored in the reference picture buffer 190. The reconstructed block processed by the filter unit 180 may be a part of the reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks processed by the filter unit 180. The stored reference image may be used later in inter-frame prediction or motion compensation.

[0158] Figure 2 is a block diagram showing the configuration of a decoding device according to an embodiment and to which the present invention is applied.

[0159] The decoding device 200 may be a decoder, a video decoding device, or an image decoding device.

[0160] Reference Figure 2 , the decoding device 200 may include an entropy decoding unit 210, a dequantization unit 220, an inverse transform unit 230, an intra-frame prediction unit 240, a motion compensation unit 250, an adder 255, a filter unit 260 and a reference picture buffer 270.

[0161] The decoding device 200 may receive a bit stream output from the encoding device 100. The decoding device 200 may receive a bit stream stored in a computer-readable recording medium, or may receive a bit stream streamed through a wired / wireless transmission medium. The decoding device 200 may decode the bit stream by using an intra mode or an inter mode. In addition, the decoding device 200 may generate a reconstructed image or a decoded image generated by decoding, and output the reconstructed image or the decoded image.

[0162] When the prediction mode used in decoding is the intra mode, the switch may be switched to the intra mode. Alternatively, when the prediction mode used in decoding is the inter mode, the switch may be switched to the inter mode.

[0163] The decoding device 200 can obtain a reconstructed residual block by decoding the input bit stream and generate a prediction block. When the reconstructed residual block and the prediction block are obtained, the decoding device 200 can generate a reconstructed block that becomes a decoding target by adding the reconstructed residual block to the prediction block. The decoding target block may be referred to as a current block.

[0164] The entropy decoding unit 210 may generate symbols by entropy decoding the bit stream according to the probability distribution. The generated symbols may include symbols in the form of quantized levels. Here, the entropy decoding method may be an inverse process of the above entropy encoding method.

[0165] In order to decode the transform coefficient levels (quantized levels), the entropy decoding unit 210 may change the coefficients in the form of a one-way vector into a two-dimensional block form by using a transform coefficient scanning method.

[0166] The quantized level may be dequantized in the dequantization unit 220, or the quantized level may be inversely transformed in the inverse transform unit 230. The quantized level may be a result of dequantization or inverse transformation or both, and may be generated as a reconstructed residual block. Here, the dequantization unit 220 may apply a quantization matrix to the quantized level.

[0167] When the intra mode is used, the intra prediction unit 240 may generate a predicted block by performing spatial prediction on the current block, wherein the spatial prediction uses sample values ​​of a block that is adjacent to the decoding target block and has been decoded.

[0168] When the inter mode is used, the motion compensation unit 250 may generate a prediction block by performing motion compensation on the current block, wherein the motion compensation uses a motion vector and a reference image stored in the reference picture buffer 270 .

[0169] The adder 255 can generate a reconstructed block by adding the reconstructed residual block to the prediction block. The filter unit 260 can apply at least one of a deblocking filter, a sample adaptive offset, and an adaptive loop filter to the reconstructed block or the reconstructed image. The filter unit 260 can output the reconstructed image. The reconstructed block or the reconstructed image can be stored in the reference picture buffer 270 and used when performing inter-frame prediction. The reconstructed block processed by the filter unit 260 can be a part of the reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks processed by the filter unit 260. The stored reference image can be used later in inter-frame prediction or motion compensation.

[0170] Figure 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded. Figure 3 An example of partitioning a single cell into a plurality of lower-level cells is schematically shown.

[0171] In order to effectively partition an image, a coding unit (CU) may be used when encoding and decoding. A coding unit may be used as a basic unit when encoding / decoding an image. In addition, a coding unit may be used as a unit for distinguishing an intra prediction mode from an inter prediction mode when encoding / decoding an image. A coding unit may be a basic unit for prediction, transformation, quantization, inverse transformation, inverse quantization, or encoding / decoding processing of a transform coefficient.

[0172] Reference Figure 3 , the image 300 is partitioned sequentially according to the maximum coding unit (LCU), and the LCU unit is determined as a partition structure. Here, the LCU may be used in the same meaning as the coding tree unit (CTU). Unit partitioning may mean partitioning a block associated with the unit. In the block partition information, information about the unit depth may be included. The depth information may indicate the number or degree of the unit being partitioned or both the number and degree of the unit being partitioned. A single unit may be partitioned into a plurality of lower-level units hierarchically associated with the depth information based on a tree structure. In other words, the unit and the lower-level units generated by partitioning the unit may correspond to a node and a child node of the node, respectively. Each of the partitioned lower-level units may have depth information. The depth information may be information indicating the size of a CU and may be stored in each CU. The unit depth indicates the number and / or degree associated with partitioning the unit. Therefore, the partition information of the lower-level unit may include information about the size of the lower-level unit.

[0173] The partition structure may represent the distribution of coding units (CUs) within the LCU 310. Such distribution may be determined according to whether a single CU is partitioned into multiple (including 2, 4, 8, 16, etc., positive integers equal to or greater than 2) CUs. The horizontal size and vertical size of the CU generated by partitioning may be half of the horizontal size and vertical size of the CU before partitioning, respectively, or may have sizes smaller than the horizontal size and vertical size before partitioning, respectively, according to the number of partitioning. The CU may be recursively partitioned into multiple CUs. By recursive partitioning, at least one of the height and width of the CU after partitioning may be reduced compared to at least one of the height and width of the CU before partitioning. The partitioning of the CU may be recursively performed until a predefined depth or a predefined size. For example, the depth of the LCU may be 0, and the depth of the minimum coding unit (SCU) may be a predefined maximum depth. Here, as described above, the LCU may be a coding unit having a maximum coding unit size, and the SCU may be a coding unit having a minimum coding unit size. Partitioning starts from the LCU 310, and when the horizontal size or the vertical size or both the horizontal size and the vertical size of the CU are reduced by partitioning, the CU depth increases by 1. For example, for each depth, the size of the non-partitioned CU may be 2N×2N. In addition, in the case of a partitioned CU, a CU of size 2N×2N may be partitioned into four CUs of size N×N. As the depth increases by 1, the size of N may be halved.

[0174] In addition, information on whether a CU is partitioned may be indicated by using the partition information of the CU. The partition information may be 1-bit information. All CUs except the SCU may include partition information. For example, when the value of the partition information is a first value, the CU may not be partitioned, and when the value of the partition information is a second value, the CU may be partitioned.

[0175] Reference Figure 3 , an LCU with a depth of 0 may be a block of 64×64. 0 may be the minimum depth. An SCU with a depth of 3 may be a block of 8×8. 3 may be the maximum depth. A CU of a block of 32×32 and a CU of a block of 16×16 may be represented as depth 1 and depth 2, respectively.

[0176] For example, when a single coding unit is partitioned into four coding units, the horizontal size and vertical size of the four coding units partitioned may be half the size of the horizontal size and vertical size of the CU before being partitioned. In one embodiment, when a coding unit of size 32×32 is partitioned into four coding units, each of the four coding units partitioned may have a size of 16×16. When a single coding unit is partitioned into four coding units, it can be said that the coding unit can be partitioned into a quadtree form.

[0177] For example, when one coding unit is partitioned into two sub-coding units, the horizontal size or vertical size (width or height) of each of the two sub-coding units may be half of the horizontal size or vertical size of the original coding unit. For example, when a coding unit of size 32×32 is partitioned vertically into two sub-coding units, each of the two sub-coding units may have a size of 16×32. For example, when a coding unit of size 8×32 is partitioned horizontally into two sub-coding units, each of the two sub-coding units may have a size of 8×16. When one coding unit is partitioned into two sub-coding units, the coding unit may be said to be partitioned into two or partitioned according to a binary tree partition structure.

[0178] For example, when one coding unit is partitioned into three sub-coding units, the horizontal size or the vertical size of the coding unit may be partitioned at a ratio of 1:2:1, thereby generating three sub-coding units having a ratio of 1:2:1 in the horizontal size or the vertical size. For example, when a coding unit having a size of 16×32 is partitioned horizontally into three sub-coding units, the three sub-coding units may have sizes of 16×8, 16×16, and 16×8, respectively, in order from the uppermost sub-coding unit to the lowermost sub-coding unit. For example, when a coding unit having a size of 32×32 is partitioned vertically into three sub-coding units, the three sub-coding units may have sizes of 8×32, 16×32, and 8×32, respectively, in order from the left sub-coding unit to the right sub-coding unit. When one coding unit is partitioned into three sub-coding units, the coding unit may be said to be partitioned into three sub-coding units or partitioned according to a ternary tree partition structure.

[0179] exist Figure 3 , a coding tree unit (CTU) 320 is an example of a CTU to which a quadtree partition structure, a binary tree partition structure, and a ternary tree partition structure are all applied.

[0180] As described above, in order to partition a CTU, at least one of a quadtree partition structure, a binary tree partition structure, and a ternary tree partition structure may be applied. Various tree partition structures may be sequentially applied to a CTU according to a predetermined priority order. For example, a quadtree partition structure may be preferentially applied to a CTU. Coding units that can no longer be partitioned using a quadtree partition structure may correspond to leaf nodes of a quadtree. Coding units corresponding to leaf nodes of a quadtree may be used as root nodes of a binary and / or ternary tree partition structure. That is, coding units corresponding to leaf nodes of a quadtree may be further partitioned according to a binary tree partition structure or a ternary tree partition structure, or may not be further partitioned. Therefore, by preventing the coding blocks obtained from binary tree partitions or ternary tree partitions of coding units corresponding to leaf nodes of a quadtree from undergoing further quadtree partitions, block partitioning operations and / or operations of signaling partition information may be effectively performed.

[0181] The fact that the coding unit corresponding to the node of the quadtree is partitioned may be signaled using the four partition information. The four partition information having a first value (e.g., '1') may indicate that the current coding unit is partitioned according to the quadtree partition structure. The four partition information having a second value (e.g., '0') may indicate that the current coding unit is not partitioned according to the quadtree partition structure. The four partition information may be a flag having a predetermined length (e.g., one bit).

[0182] There may be no priority between binary tree partitioning and ternary tree partitioning. That is, the coding unit corresponding to the leaf node of the quadtree may further undergo any partitioning of the binary tree partitioning and the ternary tree partitioning. In addition, the coding unit generated by the binary tree partitioning or the ternary tree partitioning may undergo further binary tree partitioning or further ternary tree partitioning, or may not be further partitioned.

[0183] A tree structure in which there is no priority between binary tree partitions and ternary tree partitions is called a multi-type tree structure. A coding unit corresponding to a leaf node of a quadtree may be used as a root node of a multi-type tree. At least one of multi-type tree partition indication information, partition direction information, and partition tree information may be used to signal whether to partition a coding unit corresponding to a node of a multi-type tree. In order to partition a coding unit corresponding to a node of a multi-type tree, multi-type tree partition indication information, partition direction information, and partition tree information may be sequentially signaled.

[0184] The multi-type tree partition indication information having a first value (eg, '1') may indicate that the current coding unit will undergo multi-type tree partitioning. The multi-type tree partition indication information having a second value (eg, '0') may indicate that the current coding unit will not undergo multi-type tree partitioning.

[0185] When a coding unit corresponding to a node of a multi-type tree is further partitioned according to a multi-type tree partition structure, the coding unit may include partition direction information. The partition direction information may indicate in which direction the current coding unit will be partitioned for the multi-type tree partition. The partition direction information having a first value (e.g., "1") may indicate that the current coding unit will be partitioned vertically. The partition direction information having a second value (e.g., "0") may indicate that the current coding unit will be partitioned horizontally.

[0186] When the coding unit corresponding to the node of the multi-type tree is further partitioned according to the multi-type tree partition structure, the current coding unit may include partition tree information. The partition tree information may indicate a tree partition structure to be used to partition the node of the multi-type tree. The partition tree information having a first value (e.g., "1") may indicate that the current coding unit will be partitioned according to a binary tree partition structure. The partition tree information having a second value (e.g., "0") may indicate that the current coding unit will be partitioned according to a ternary tree partition structure.

[0187] The partition indication information, the partition tree information and the partition direction information may all be flags having a predetermined length (eg, one bit).

[0188] At least any one of the quadtree partition indication information, the multi-type tree partition indication information, the partition direction information, and the partition tree information may be entropy encoded / decoded. In order to entropy encode / decode those types of information, information about neighboring coding units adjacent to the current coding unit may be used. For example, there is a high probability that the partition type (partitioned or not partitioned, partition tree, and / or partition direction) of the left neighboring coding unit and / or the upper neighboring coding unit of the current coding unit is similar to the partition type of the current coding unit. Therefore, context information for entropy encoding / decoding the information about the current coding unit may be derived from the information about the neighboring coding units. The information about the neighboring coding units may include at least any one of the quadtree partition information, the multi-type tree partition indication information, the partition direction information, and the partition tree information.

[0189] As another example, among binary tree partitioning and ternary tree partitioning, binary tree partitioning may be preferentially performed. That is, the current coding unit may first undergo binary tree partitioning, and then the coding unit corresponding to the leaf node of the binary tree may be set as the root node for the ternary tree partitioning. In this case, for the coding unit corresponding to the node of the ternary tree, neither quadtree partitioning nor binary tree partitioning may be performed.

[0190] A coding unit that cannot be partitioned according to a quadtree partition structure, a binary tree partition structure, and / or a ternary tree partition structure becomes a basic unit for encoding, prediction, and / or transformation. That is, the coding unit cannot be further partitioned for prediction and / or transformation. Therefore, partition structure information and partition information for partitioning a coding unit into a prediction unit and / or a transformation unit may not exist in the bitstream.

[0191] However, when the size of the coding unit (i.e., the basic unit for partitioning) is larger than the size of the maximum transform block, the coding unit may be recursively partitioned until the size of the coding unit is reduced to be equal to or smaller than the size of the maximum transform block. For example, when the size of the coding unit is 64×64 and when the size of the maximum transform block is 32×32, the coding unit may be partitioned into four 32×32 blocks for transforming. For example, when the size of the coding unit is 32×64 and the size of the maximum transform block is 32×32, the coding unit may be partitioned into two 32×32 blocks for transforming. In this case, the partitioning of the coding unit for transforming is not separately signaled, and the partitioning of the coding unit for transforming may be determined by comparison between the horizontal size or vertical size of the coding unit and the horizontal size or vertical size of the maximum transform block. For example, when the horizontal size (width) of the coding unit is larger than the horizontal size (width) of the maximum transform block, the coding unit may be vertically divided into two equal parts. For example, when the vertical size (height) of the coding unit is larger than the vertical size (height) of the maximum transform block, the coding unit may be horizontally divided into two equal parts.

[0192] Information on the maximum and / or minimum size of a coding unit and information on the maximum and / or minimum size of a transform block may be signaled or determined at a higher level of the coding unit. The higher level may be, for example, a sequence level, a picture level, a slice level, a tile group level, a tile block level, etc. For example, the minimum size of a coding unit may be determined as 4×4. For example, the maximum size of a transform block may be determined as 64×64. For example, the minimum size of a transform block may be determined as 4×4.

[0193] Information on the minimum size of the coding unit corresponding to the leaf node of the quadtree (quadtree minimum size) and / or information on the maximum depth from the root node of the multi-type tree to the leaf node (maximum tree depth of the multi-type tree) may be signaled or determined at a higher level of the coding unit. For example, the higher level may be a sequence level, a picture level, a slice level, a tile group level, a tile level, etc. Information on the minimum size of the quadtree and / or information on the maximum depth of the multi-type tree may be signaled or determined for each of the intra-picture slice and the inter-picture slice.

[0194] The difference information between the size of the CTU and the maximum size of the transform block may be signaled or determined at a higher level of the coding unit. For example, the higher level may be a sequence level, a picture level, a slice level, a parallel block group level, a parallel block level, etc. The information of the maximum size of the coding unit corresponding to each node of the binary tree (hereinafter referred to as the maximum size of the binary tree) may be determined based on the size of the coding tree unit and the difference information. The maximum size of the coding unit corresponding to each node of the ternary tree (hereinafter referred to as the maximum size of the ternary tree) may vary according to the type of the slice. For example, for an intra-picture slice, the maximum size of the ternary tree may be 32×32. For example, for an inter-picture slice, the maximum size of the ternary tree may be 128×128. For example, the minimum size of the coding unit corresponding to each node of the binary tree (hereinafter referred to as the minimum size of the binary tree) and / or the minimum size of the coding unit corresponding to each node of the ternary tree (hereinafter referred to as the minimum size of the ternary tree) may be set to the minimum size of the coding block.

[0195] As another example, the maximum size of the binary tree and / or the maximum size of the ternary tree may be signaled or determined at the slice level. Alternatively, the minimum size of the binary tree and / or the minimum size of the ternary tree may be signaled or determined at the slice level.

[0196] According to the sizes and depth information of the above-mentioned various blocks, quad partition information, multi-type tree partition indication information, partition tree information and / or partition direction information may or may not be included in the bitstream.

[0197] For example, when the size of the coding unit is not greater than the minimum size of the quadtree, the coding unit does not include the quad partition information. Therefore, the quad partition information may be inferred from the second value.

[0198] For example, when the size (horizontal size and vertical size) of the coding unit corresponding to the node of the multi-type tree is greater than the maximum size (horizontal size and vertical size) of the binary tree and / or the maximum size (horizontal size and vertical size) of the ternary tree, the coding unit may not be partitioned into two or three partitions. Therefore, the multi-type tree partition indication information may not be signaled, but the multi-type tree partition indication information may be inferred from the second value.

[0199] Optionally, when the size (horizontal size and vertical size) of the coding unit corresponding to the node of the multi-type tree is the same as the maximum size (horizontal size and vertical size) of the binary tree and / or is twice as large as the maximum size (horizontal size and vertical size) of the ternary tree, the coding unit may not be further partitioned into two or three partitions. Therefore, the multi-type tree partition indication information may not be signaled, but may be derived from the second value. This is because when the coding unit is partitioned according to the binary tree partition structure and / or the ternary tree partition structure, a coding unit smaller than the minimum size of the binary tree and / or the minimum size of the ternary tree is generated.

[0200] Optionally, the binary tree partition or ternary tree partition may be limited based on the size of the virtual pipeline data unit (hereinafter, the pipeline buffer size). For example, when the coding unit is divided into sub-coding units that do not fit the pipeline buffer size by binary tree partition or ternary tree partition, the corresponding binary tree partition or ternary tree partition may be limited. The pipeline buffer size may be the size of the maximum transform block (e.g., 64×64). For example, when the pipeline buffer size is 64×64, the following division may be limited.

[0201] - N×M (N and / or M is 128) ternary tree partitions for coding units

[0202] - 128×N (N<=64) binary tree partitions in the horizontal direction for coding units

[0203] - N×128 (N<=64) binary tree partitions in the vertical direction for coding units

[0204] Optionally, when the depth of the coding unit corresponding to the node of the multi-type tree is equal to the maximum depth of the multi-type tree, the coding unit may not be further partitioned into two and / or three partitions. Therefore, the multi-type tree partition indication information may not be sent by a signal, but the multi-type tree partition indication information may be inferred from the second value.

[0205] Optionally, only when at least one of vertical binary tree partitioning, horizontal binary tree partitioning, vertical ternary tree partitioning, and horizontal ternary tree partitioning is possible for a coding unit corresponding to a node of a multi-type tree, a multi-type tree partition indication information may be signaled. Otherwise, the coding unit may not be partitioned into two and / or three partitions. Therefore, the multi-type tree partition indication information may not be signaled, but may be inferred from the second value.

[0206] Optionally, partition direction information may be signaled only when both vertical binary tree partitioning and horizontal binary tree partitioning or both vertical ternary tree partitioning and horizontal ternary tree partitioning are possible for a coding unit corresponding to a node of a multi-type tree. Otherwise, partition direction information may not be signaled, but may be derived from a value indicating a possible partition direction.

[0207] Optionally, partition tree information may be signaled only when both vertical binary tree partitioning and vertical ternary tree partitioning or both horizontal binary tree partitioning and horizontal ternary tree partitioning are possible for a coding tree corresponding to a node of a multi-type tree. Otherwise, partition tree information may not be signaled but may be derived from a value indicating a possible partition tree structure.

[0208] Figure 4 is a diagram illustrating an intra prediction process.

[0209] Figure 4 The arrows from the center to the outside in FIG. 1 represent the prediction direction of the intra prediction mode.

[0210] Intra-frame encoding and / or decoding may be performed by using reference samples of neighboring blocks of the current block. The neighboring blocks may be reconstructed neighboring blocks. For example, intra-frame encoding and / or decoding may be performed by using encoding parameters or values ​​of reference samples included in the reconstructed neighboring blocks.

[0211] The prediction block may represent a block generated by performing intra prediction. The prediction block may correspond to at least one of a CU, a PU, and a TU. The unit of the prediction block may have a size of one of a CU, a PU, and a TU. The prediction block may be a square block of a size of 2×2, 4×4, 16×16, 32×32, or 64×64, etc., or may be a rectangular block of a size of 2×8, 4×8, 2×16, 4×16, and 8×16, etc.

[0212] Intra-prediction may be performed according to an intra-prediction mode for the current block. The number of intra-prediction modes that the current block may have may be a fixed value, and may be a value determined differently according to properties of the prediction block. For example, the properties of the prediction block may include the size of the prediction block, the shape of the prediction block, and the like.

[0213] Regardless of the block size, the number of intra-frame prediction modes can be fixed to N. Alternatively, the number of intra-frame prediction modes can be 3, 5, 9, 17, 34, 35, 36, 65 or 67, etc. Optionally, the number of intra-frame prediction modes can vary according to the block size or the color component type or both the block size and the color component type. For example, the number of intra-frame prediction modes can vary depending on whether the color component is a luminance signal or a chrominance signal. For example, as the block size becomes larger, the number of intra-frame prediction modes can increase. Optionally, the number of intra-frame prediction modes of the luminance component block can be greater than the number of intra-frame prediction modes of the chrominance component block.

[0214] The intra prediction mode may be a non-angle mode or an angle mode. The non-angle mode may be a DC mode or a planar mode, and the angle mode may be a prediction mode having a specific direction or angle. The intra prediction mode may be represented by at least one of a mode number, a mode value, a mode number, a mode angle, and a mode direction. The number of intra prediction modes may be M, which is greater than 1, including non-angle modes and angle modes. In order to perform intra prediction on a current block, a step of determining whether a sample included in a reconstructed neighboring block can be used as a reference sample of the current block may be performed. When there are samples that cannot be used as reference samples of the current block, a value obtained by copying or interpolating at least one sample value of the samples included in the reconstructed neighboring block, or by both copying and interpolating, may be used to replace the unavailable sample value of the sample, so that the replaced sample value is used as the reference sample of the current block.

[0215] Figure 7 is a diagram showing reference samples that can be used for intra prediction.

[0216] like Figure 7 As shown, at least one of the reference sample line 0 to the reference sample line 3 can be used for intra prediction of the current block. Figure 7 In the example, the samples of fragment A and fragment F may be filled with the samples of the closest fragment B and fragment E, respectively, instead of being retrieved from the reconstructed neighboring blocks. Index information indicating the reference sample line to be used for intra prediction of the current block may be signaled. When the upper boundary of the current block is the boundary of the CTU, only the reference sample line 0 may be available. Therefore, in this case, the index information may not be signaled. When reference sample lines other than the reference sample line 0 are used, filtering for the prediction block, which will be described later, may not be performed.

[0217] When intra prediction is performed, a filter may be applied to at least one of a reference sample and a prediction sample based on an intra prediction mode and a current block size.

[0218] In the case of the planar mode, when generating a prediction block of the current block, according to the position of the prediction target sample within the prediction block, the sample value of the prediction target sample may be generated by using the weighted sum of the upper reference sample and the left reference sample of the current sample and the upper right reference sample and the lower left reference sample of the current block. In addition, in the case of the DC mode, when generating the prediction block of the current block, the average value of the upper reference sample and the left reference sample of the current block may be used. In addition, in the case of the angular mode, the prediction block may be generated by using the upper reference sample, the left reference sample, the upper right reference sample and / or the lower left reference sample of the current block. In order to generate the prediction sample value, interpolation of real number units may be performed.

[0219] In the case of intra prediction between color components, a prediction block of a current block of a second color component may be generated based on a corresponding reconstruction block of a first color component. For example, the first color component may be a luminance component, and the second color component may be a chrominance component. For intra prediction between color components, parameters of a linear model between the first color component and the second color component may be derived based on a template. The template may include the upper and / or left neighboring samples of the current block and the upper and / or left neighboring samples of the reconstruction block of the first color component corresponding thereto. For example, the sample value of the first color component having the maximum value among the samples in the template and the sample value of the second color component corresponding thereto, and the sample value of the first color component having the minimum value among the samples in the template and the sample value of the second color component corresponding thereto may be used to derive the parameters of the linear model. When deriving the parameters of the linear model, the corresponding reconstruction block may be applied to the linear model to generate a prediction block of the current block. Depending on the video format, subsampling may be performed on the reconstruction block of the first color component and the neighboring samples of the corresponding reconstruction block. For example, when one sample of the second color component corresponds to four samples of the first color component, the four samples of the first color component may be subsampled to calculate one corresponding sample. In this case, parameter derivation of the linear model and intra prediction between color components may be performed based on the corresponding subsampled samples. Whether to perform intra prediction between color components and / or the range of the template may be signaled as an intra prediction mode.

[0220] The current block may be partitioned into two sub-blocks or four sub-blocks in the horizontal direction or the vertical direction. The partitioned sub-blocks may be reconstructed sequentially. That is, intra prediction may be performed on the sub-block to generate a sub-prediction block. In addition, inverse quantization and / or inverse transformation may be performed on the sub-block to generate a sub-residual block. The reconstructed sub-block may be generated by adding the sub-prediction block to the sub-residual block. The reconstructed sub-block may be used as a reference sample for intra prediction of a subsequent sub-block. The sub-block may be a block including a predetermined number (e.g., 16) or more samples. Thus, for example, when the current block is an 8×4 block or a 4×8 block, the current block may be partitioned into two sub-blocks. In addition, when the current block is a 4×4 block, the current block may not be partitioned into sub-blocks. When the current block has other sizes, the current block may be partitioned into four sub-blocks. Information on whether intra prediction is performed based on sub-blocks and / or partition directions (horizontal or vertical) may be sent by a signal. Intra prediction based on sub-blocks may be performed only when reference sample line 0 is used. When subblock-based intra prediction is performed, filtering for a prediction block, which will be described later, may not be performed.

[0221] The final prediction block may be generated by performing filtering on the prediction block predicted by the intra-frame. The filtering may be performed by applying a predetermined weight to the filtering target sample, the left reference sample, the upper reference sample, and / or the upper left reference sample. The weight and / or reference sample (range, position, etc.) used for filtering may be determined based on at least one of the block size, the intra-frame prediction mode, and the position of the filtering target sample in the prediction block. The filtering may be performed only in the case of a predetermined intra-frame prediction mode (e.g., DC, plane, vertical, horizontal, diagonal, and / or adjacent diagonal mode). The adjacent diagonal mode may be a mode in which k is added to the diagonal mode or subtracted from the diagonal mode. For example, k may be a positive integer of 8 or less.

[0222] The intra-frame prediction mode of the current block may be entropy encoded / decoded by predicting the intra-frame prediction mode of a block existing adjacent to the current block. When the intra-frame prediction mode of the current block is the same as that of the neighboring block, information that the intra-frame prediction mode of the current block is the same as that of the neighboring block may be signaled by using predetermined flag information. In addition, indicator information of the intra-frame prediction mode that is the same as the intra-frame prediction mode of the current block among the intra-frame prediction modes of multiple neighboring blocks may be signaled. When the intra-frame prediction mode of the current block is different from that of the neighboring block, the intra-frame prediction mode information of the current block may be entropy encoded / decoded by performing entropy encoding / decoding based on the intra-frame prediction mode of the neighboring block.

[0223] Figure 5 is a diagram illustrating an embodiment of an inter-picture prediction process.

[0224] exist Figure 5 In , a rectangle can represent a picture. Figure 5In FIG. 1 , the arrow indicates the prediction direction. According to the encoding type of the picture, the picture can be classified into an intra picture (I picture), a predicted picture (P picture) and a bi-predicted picture (B picture).

[0225] An I picture may be encoded by intra prediction without requiring inter-picture prediction. A P picture may be encoded by inter-picture prediction using a reference picture existing in one direction (i.e., forward or backward) relative to the current block. A B picture may be encoded by inter-picture prediction using a reference picture existing in two directions (i.e., forward and backward) relative to the current block. When inter-picture prediction is used, the encoder may perform inter-picture prediction or motion compensation, and the decoder may perform corresponding motion compensation.

[0226] Hereinafter, embodiments of inter-picture prediction will be described in detail.

[0227] Reference pictures and motion information may be used to perform inter-picture prediction or motion compensation.

[0228] The motion information of the current block may be derived during inter-picture prediction by each of the encoding device 100 and the decoding device 200. The motion information of the current block may be derived by using the motion information of a reconstructed neighboring block, the motion information of a co-located block (also referred to as a col block or a co-located block), and / or the motion information of a block adjacent to the co-located block. The co-located block may represent a block in a previously reconstructed co-located picture (also referred to as a col picture or a co-located picture) that is spatially located at the same position as the current block. The co-located picture may be one of one or more reference pictures included in a reference picture list.

[0229] The derivation method of motion information may be different according to the prediction mode of the current block. For example, the prediction modes applied to inter prediction include AMVP mode, merge mode, skip mode, merge mode with motion vector difference, sub-block merge mode, triangle partition mode, inter-intra combined prediction mode, affine mode, etc. Here, the merge mode may be referred to as motion merge mode.

[0230] For example, when AMVP is used as a prediction mode, at least one of a motion vector of a reconstructed neighboring block, a motion vector of a co-located block, a motion vector of a block adjacent to the co-located block, and a (0,0) motion vector may be determined as a motion vector candidate for the current block, and a motion vector candidate list may be generated by using the motion vector candidate. The motion vector candidate for the current block may be derived by using the generated motion vector candidate list. The motion information of the current block may be determined based on the derived motion vector candidate. The motion vector of the co-located block or the motion vector of a block adjacent to the co-located block may be referred to as a temporal motion vector candidate, and the motion vector of the reconstructed neighboring block may be referred to as a spatial motion vector candidate.

[0231] The encoding device 100 may calculate a motion vector difference (MVD) between a motion vector of a current block and a motion vector candidate, and may perform entropy coding on the motion vector difference (MVD). In addition, the encoding device 100 may perform entropy coding on a motion vector candidate index and generate a bitstream. The motion vector candidate index may indicate the best motion vector candidate among the motion vector candidates included in the motion vector candidate list. The decoding device may perform entropy decoding on the motion vector candidate index included in the bitstream, and may select a motion vector candidate of a decoding target block from the motion vector candidates included in the motion vector candidate list by using the entropy-decoded motion vector candidate index. In addition, the decoding device 200 may add the entropy-decoded MVD to the motion vector candidate extracted by entropy decoding, thereby deriving a motion vector of the decoding target block.

[0232] In addition, the encoding apparatus 100 may perform entropy encoding on the resolution information of the calculated MVD. The decoding apparatus 200 may adjust the resolution of the entropy-decoded MVD using the MVD resolution information.

[0233] In addition, the encoding device 100 calculates a motion vector difference (MVD) between a motion vector in the current block and a motion vector candidate based on an affine model, and performs entropy encoding on the MVD. The decoding device 200 derives a motion vector based on each sub-block by deriving an affine controlled motion vector of a decoding target block according to the sum of the entropy-decoded MVD and the affine controlled motion vector candidate.

[0234] The bitstream may include a reference picture index indicating a reference picture. The reference picture index may be entropy encoded by the encoding apparatus 100 and then signaled as a bitstream to the decoding apparatus 200. The decoding apparatus 200 may generate a prediction block of a decoding target block based on the derived motion vector and the reference picture index information.

[0235] Another example of a method of deriving motion information of a current block may be a merge mode. The merge mode may represent a method of merging motions of a plurality of blocks. The merge mode may represent a mode of deriving motion information of a current block from motion information of a neighboring block. When the merge mode is applied, the motion information of the reconstructed neighboring block and / or the motion information of the same-position block may be used to generate a merge candidate list. The motion information may include at least one of a motion vector, a reference picture index, and an inter-picture prediction indicator. The prediction indicator may indicate unidirectional prediction (L0 prediction or L1 prediction) or bidirectional prediction (L0 prediction and L1 prediction).

[0236] The merge candidate list may be a list of stored motion information. The motion information included in the merge candidate list may be at least one of the following: motion information of a neighboring block adjacent to the current block (spatial merge candidate), motion information of a co-located block of the current block in a reference picture (temporal merge candidate), new motion information generated by combining motion information present in the merge candidate list, motion information of a block encoded / decoded before the current block (historical-based merge candidate), and a zero merge candidate.

[0237] The encoding device 100 may generate a bitstream by performing entropy encoding on at least one of a merge flag and a merge index, and may signal the bitstream to the decoding device 200. The merge flag may be information indicating whether a merge mode is performed for each block, and the merge index may be information indicating which neighboring block among neighboring blocks of the current block is a merge target block. For example, the neighboring blocks of the current block may include a left neighboring block located on the left side of the current block, an upper neighboring block arranged above the current block, and a temporal neighboring block temporally adjacent to the current block.

[0238] In addition, the encoding device 100 performs entropy encoding on the correction information for correcting the motion vector in the motion information of the merge candidate, and transmits it to the decoding device 200 by signal. The decoding device 200 may correct the motion vector of the merge candidate selected by the merge index based on the correction information. Here, the correction information may include at least one of information on whether to perform correction, correction direction information, and correction size information. As described above, the prediction mode in which the motion vector of the merge candidate is corrected based on the correction information transmitted by the signal may be referred to as a merge mode with a motion vector difference.

[0239] The skip mode may be a mode in which the motion information of the neighboring blocks is applied to the current block as it is. When the skip mode is applied, the encoding apparatus 100 may perform entropy encoding on information of the fact of which block's motion information is to be used as the motion information of the current block to generate a bitstream, and may signal the bitstream to the decoding apparatus 200. The encoding apparatus 100 may not signal a syntax element regarding at least any one of the motion vector difference information, the coded block flag, and the transform coefficient level to the decoding apparatus 200.

[0240] The sub-block merge mode may represent a mode for deriving motion information in units of sub-blocks of a coding block (CU). When the sub-block merge mode is applied, the sub-block merge candidate list may be generated using motion information of a sub-block co-located with the current sub-block in a reference image (sub-block based temporal merge candidates) and / or affine control point motion vector merge candidates.

[0241] The triangular partition mode may denote a mode of deriving motion information by partitioning the current block into diagonal directions, deriving each prediction sample using each of the derived motion information, and deriving the prediction sample of the current block by weighting each of the derived prediction samples.

[0242] The inter-intra combined prediction mode may mean a mode of deriving a prediction sample of a current block by weighting a prediction sample generated by inter prediction and a prediction sample generated by intra prediction.

[0243] The decoding apparatus 200 may correct the derived motion information by itself. The decoding apparatus 200 may search for a predetermined area based on a reference block indicated by the derived motion information, and derive motion information having a minimum SAD as the corrected motion information.

[0244] The decoding apparatus 200 may compensate for prediction samples derived through inter-frame prediction using optical flow.

[0245] Figure 6 is a diagram illustrating transform and quantization processing.

[0246] like Figure 6 As shown in , a transform process and / or a quantization process is performed on the residual signal to generate a quantized level signal. The residual signal is the difference between the original block and the prediction block (i.e., an intra-frame prediction block or an inter-frame prediction block). The prediction block is a block generated by intra-frame prediction or inter-frame prediction. The transform can be a primary transform, a secondary transform, or both a primary transform and a secondary transform. The primary transform of the residual signal generates a transform coefficient, and the secondary transform of the transform coefficient generates a secondary transform coefficient.

[0247] At least one scheme selected from various predefined transform schemes is used to perform the primary transform. For example, examples of the predefined transform schemes include discrete cosine transform (DCT), discrete sine transform (DST) and Karhunen-Loève transform (KLT). The transform coefficients generated by the primary transform may undergo a secondary transform. The transform scheme for the primary transform and / or the secondary transform may be determined based on the coding parameters of the current block and / or the neighboring blocks of the current block. Optionally, transform information indicating the transform scheme may be sent by a signal. DCT-based transforms may include, for example, DCT-2, DCT-8, etc. DST-based transforms may include, for example, DST-7.

[0248] A quantized level signal (quantized coefficient) may be generated by performing quantization on a residual signal or on a result of performing a primary transform and / or a secondary transform. Depending on the intra prediction mode of the block or the block size / shape, the quantized level signal may be scanned according to at least one of a diagonal upper right scan, a vertical scan, and a horizontal scan. For example, when the coefficients are scanned according to a diagonal upper right scan, the coefficients in block form are changed to a one-dimensional vector form. In addition to the diagonal upper right scan, a horizontal scan that scans the coefficients in a two-dimensional block form horizontally or a vertical scan that scans the coefficients in a two-dimensional block form vertically may be used according to the intra prediction mode and / or the size of the transform block. The scanned quantized level coefficients may be entropy encoded for insertion into a bitstream.

[0249] The decoder performs entropy decoding on the bit stream to obtain quantized level coefficients. The quantized level coefficients can be arranged in a two-dimensional block form by inverse scanning. For the inverse scanning, at least one of diagonal upper right scanning, vertical scanning, and horizontal scanning can be used.

[0250] The quantized level coefficients may then be dequantized, then inversely transformed secondary if necessary, and finally inversely transformed primary if necessary to generate a reconstructed residual signal.

[0251] Inverse mapping in the dynamic range can be performed for the luminance component reconstructed by intra-frame prediction or inter-frame prediction before in-loop filtering. The dynamic range can be divided into 16 equal segments, and the mapping function for each segment can be sent by signal. The mapping function can be sent by signal at the slice level or parallel block group level. The inverse mapping function for performing inverse mapping can be derived based on the mapping function. In-loop filtering, reference picture storage and motion compensation are performed in the inverse mapping area, and the prediction block generated by inter-frame prediction is converted to the mapping area via mapping using the mapping function, and then used to generate the reconstructed block. However, since intra-frame prediction is performed in the mapping area, the prediction block generated by intra-frame prediction can be used to generate the reconstructed block without mapping / inverse mapping.

[0252] When the current block is a residual block of a chroma component, the residual block can be converted to an inverse mapping area by performing scaling on the chroma component of the mapping area. The availability of scaling can be signaled at the slice level or the parallel block group level. Scaling can be applied only when mapping for the luminance component is available and the division of the luminance component and the division of the chroma component follow the same tree structure. Scaling can be performed based on the average value of the sample value of the luminance prediction block corresponding to the chroma block. In this case, when the current block uses inter-frame prediction, the luminance prediction block can represent the mapped luminance prediction block. The value required for scaling can be derived by using the index reference lookup table of the fragment to which the average value of the sample value of the luminance prediction block belongs. Finally, the residual block can be converted to an inverse mapping area by scaling the residual block using the derived value. Then, chroma component block recovery, intra-frame prediction, inter-frame prediction, in-loop filtering, and reference picture storage can be performed in the inverse mapping area.

[0253] Information indicating whether mapping / inverse mapping of luma components and chroma components is available may be signaled through a sequence parameter set.

[0254] The prediction block of the current block may be generated based on a block vector indicating the displacement between the current block and the reference block in the current picture. In this way, the prediction mode for generating the prediction block with reference to the current picture is called an intra-block copy (IBC) mode. The IBC mode may be applied to M×N (M<=64, N<=64) coding units. The IBC mode may include a skip mode, a merge mode, an AMVP mode, and the like. In the case of a skip mode or a merge mode, a merge candidate list is constructed, and a merge index is signaled so that a merge candidate can be specified. The block vector of the specified merge candidate may be used as the block vector of the current block. The merge candidate list may include at least one of a spatial candidate, a history-based candidate, a candidate based on the average of two candidates, and a zero merge candidate. In the case of the AMVP mode, a difference block vector may be signaled. In addition, a prediction block vector may be derived from the left neighboring block and the upper neighboring block of the current block. The index of the neighboring block to be used may be signaled. The prediction block in the IBC mode is included in the current CTU or the left CTU and is limited to blocks in the reconstructed area. For example, the value of the block vector may be limited so that the prediction block of the current block is located in the region of three 64×64 blocks preceding the 64×64 block to which the current block belongs in the encoding / decoding order. By limiting the value of the block vector in this way, the memory consumption and device complexity of the implementation according to the IBC mode may be reduced.

[0255] Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings.

[0256] The input image may be encoded / decoded by being partitioned into block units. Here, the unit block of encoding / decoding may be CTU (Coding Tree Unit), CU (Coding Unit), TU (Transform Unit), etc.

[0257] The image encoding device may generate an MPM list and entropy encode information about the intra prediction mode by using the generated MPM list. The image decoding device may entropy decode information about the intra prediction mode, generate an MPM list, and then reconstruct the intra prediction mode by using the decoded information and the MPM list.

[0258] In this specification, an image encoding device may be referred to as an encoder. In addition, an image decoding device may be referred to as a decoder.

[0259] Generation of MPM List

[0260] The encoder / decoder can generate a prediction block of the current block by using information about the current block and neighboring blocks that are adjacent to the current block and have been encoded / decoded. The information of the block used in this case can represent the pixel value of the block and / or the prediction mode (intra-frame prediction mode) of the block.

[0261] The neighboring block adjacent to the current block may represent at least one of an upper block, a lower block, a left block, a right block, an upper left block, an upper right block, and a lower left block that are n pixels away from the boundary of the current block. n may be 0 or any positive integer.

[0262] like Figure 7 As shown in , multiple (e.g., N) reference sample lines (reference lines) may be referenced to predict a current block. A prediction block of the current block may be generated by selecting at least one reference sample line from the multiple reference sample lines. N may be any positive integer. The reference sample line may be a set of samples in adjacent neighboring blocks that are equidistant from the current block. Information about which reference sample is used in each reference sample line may be signaled, and an index for restoring the corresponding information may be IntraLumaRefLineIdx.

[0263] For example, when IntraLumaRefLineIdx is a first value (e.g., 0), a sample set (i.e., a first reference sample line (reference line 0)) that is one pixel away from the current block may be indicated. Similarly, when IntraLumaRefLineIdx is a second value (e.g., 1), a second reference sample line (reference line 1) may be indicated. When IntraLumaRefLineIdx is a third value (e.g., 2), a third reference sample line (reference line 2) may be indicated. When IntraLumaRefLineIdx is an Nth value (e.g., N-1), an Nth reference sample line may be indicated.

[0264] The probability that the intra prediction mode of the current block is the same as the intra prediction mode of the adjacent neighboring block is high. Therefore, the intra prediction mode of the current block can be determined, encoded or decoded by using the intra prediction mode of the neighboring block. The encoder / decoder can derive the MPM (most probable mode) candidate mode with a high probability of being the same as the intra prediction mode of the current block based on the intra prediction mode of the neighboring block. The derived MPM candidate mode can be included in the MPM list. The encoder / decoder can configure the MPM list according to each reference sample line used for prediction.

[0265] Intra prediction of the current block may be performed by combining reference samples located in a direction indicated by the intra prediction mode of the current block.

[0266] For example, when the intra prediction mode of the current block is a diagonal mode, the prediction samples of the current block may be generated by combining the samples of the neighboring blocks located in the corresponding diagonal direction. For example, when the intra prediction mode of the current block is a vertical mode, the prediction samples of the current block may be generated by combining the samples of the neighboring blocks located above. For example, when the intra prediction mode of the current block is a horizontal mode, the prediction samples of the current block may be generated by combining the samples of the neighboring blocks located on the left.

[0267] When the intra prediction mode of the current block is a non-directional mode, the prediction samples of the current block may be generated by combining one or more samples of neighboring blocks.

[0268] The prediction mode of the current block may be generated by combining samples of the neighboring blocks with a predetermined matrix or vector. The size of the neighboring blocks may be increased or decreased for combination with the matrix or vector. The matrix or vector may be configured by using at least one of the size of the current block and the intra prediction mode of the current block.

[0269] For example, the size of the neighboring block may be reduced to 2×2, 4×4, or 8×8. The average value of the samples of the neighboring block may be used to reduce the size of the neighboring block. However, instead of the average value, different statistical values ​​described in this specification may be used.

[0270] A matrix or a vector used to generate a prediction block for the current block may be configured based on the size of the current block and / or the intra prediction mode of the current block.

[0271] For example, when the intra prediction mode of the current block is a non-directional mode and the current block is at least one of a 4×4 block, a 4×8 block, an 8×4 block, and an 8×8 block, a matrix or a vector may be configured.

[0272] Alternatively, when the intra prediction mode of the current block is a directional mode and the current block is at least one of a 4×4 block, a 4×8 block, an 8×4 block, and an 8×8 block, a matrix or a vector may be configured.

[0273] Optionally, when the current block is larger than an 8×8 block and the intra prediction mode of the current block is a non-directional mode, a matrix or a vector may be configured.

[0274] On the other hand, when the current block is larger than an 8×8 block and the intra prediction mode of the current block is a directional mode, a matrix or a vector may be configured.

[0275] In order to generate an intra prediction block of the current block, an interpolation filter may be adaptively used based on the location of a prediction target sample of the current block.

[0276] Figure 8 is a diagram illustrating an embodiment of performing intra prediction by partitioning a current block.

[0277] like Figure 8 As shown in , the current block may be partitioned into at least one or more sub-blocks. Here, the partitioning of the current block may be performed in at least one direction among horizontal, vertical, diagonal, and counter-diagonal directions.

[0278] Intra-frame prediction can be performed on each sub-block generated by partitioning. Figure 8 As shown in FIG. 1A , the current block may be partitioned in the horizontal direction to generate four subblocks. In this case, intra prediction may be performed from top to bottom (e.g., from subblock 1 to subblock 4 in sequence). Alternatively, intra prediction may be performed from bottom to top (e.g., from subblock 4 to subblock 1 in sequence).

[0279] Intra-frame prediction can be performed by using samples adjacent to the intra-frame prediction target block. Figure 8 In the example shown in A, when intra prediction is performed from top to bottom, intra prediction for subblock 1 may be performed by using samples of an upper neighboring block and samples of a left neighboring block. In addition, intra prediction for subblock 2 may be performed by using samples of an upper neighboring block, samples of a left neighboring block, and samples of reconstructed subblock 1. Therefore, intra prediction for the current subblock may be performed by using at least one of samples of an upper neighboring block, samples of a left neighboring block, and samples of a reconstructed neighboring subblock.

[0280] like Figure 8 As shown in FIG. 2B , the current block may be partitioned in the vertical direction to generate four sub-blocks. In this case, intra prediction may be performed from left to right (e.g., from sub-block 1 to sub-block 4 in sequence). Alternatively, intra prediction may be performed from right to left (e.g., from sub-block 4 to sub-block 1 in sequence). Figure 8 As explained in A, intra prediction for the current subblock may be performed by using at least one of samples of an upper neighboring block, samples of a left neighboring block, and samples of a reconstructed neighboring subblock.

[0281] Fig. 9is a diagram for explaining a method of configuring an MPM list according to an embodiment of the present invention.

[0282] The encoder / decoder may determine a method of configuring the MPM list based on at least one of a component of the current block and a reference sample line index. The component of the current block may be represented as cIdx. When cIdx has a first value, it may represent a luma component. When cIdx has a second value, it may represent a chroma component.

[0283] The intra prediction mode of the chroma block may be one of a plane mode, a DC mode, a horizontal mode, a vertical mode, a vertical diagonal mode, a direct mode (DM), and a linear mode (LM). The mode values ​​of the plane mode, the DC mode, and the horizontal mode may be represented as 0, 1, and 18, respectively. The mode values ​​of the vertical mode and the vertical diagonal mode may be represented as 50 and 66, respectively. The mode value of the LM may be represented as 81, 82, or 83.

[0284] Information about linear mode (LM) prediction may be signaled at a higher level. For example, information indicating whether linear mode (LM) is available (e.g., ccm_enabled_flag) may be signaled at a higher level of a block. For example, the value of ccm_enabled_flag may be determined at a higher level (e.g., sequence, picture, slice, tile, and CTU). When ccm_enabled_flag is a first value, it may indicate that LM is not available. When ccm_enabled_flag is a second value, it may indicate that LM is available.

[0285] For example, if the component of the current block is a luma component (Yes at S910) and the 0th reference sample line is used (Yes at S920), the first method of configuring the MPM list may be used. Fig.10 , Fig.16 , Fig.17 and Fig.18 Explains how to configure the MPM list.

[0286] For example, if the component of the current block is a luma component (Yes at S910) and reference sample lines other than the 0th reference sample line are used (No at S920), the second method of configuring the MPM list may be used. Figures 11 to 18 Explains how to configure the MPM list.

[0287] For example, if the component of the current block is a chroma component (No at S910) and LM is not available (Yes at S950), the third method of configuring the MPM list may be used. When the third method of configuring the MPM list is used, the method of configuring the MPM list explained with reference to Table 1 may be used.

[0288] For example, if the component of the current block is a chroma component (No at S910) and LM is available (No at S950), the fourth method of configuring the MPM list may be used. When the fourth method of configuring the MPM list is used, the method of configuring the MPM list explained with reference to Table 2 may be used.

[0289] In the above embodiment, the first value may represent 0, and the second value may represent 1.

[0290] In the embodiments described in this specification, the encoder / decoder may derive the MPM candidate mode from the intra prediction mode of the neighboring block adjacent to the current block. In the intra prediction mode of the neighboring block, the first prediction mode may be indicated by candIntraPredModeA, and the second prediction mode may be indicated by candIntraPredModeB. When intra prediction of the neighboring block is not available, candIntraPredModeA or candIntraPredModeB may be set to a planar mode.

[0291] For example, the first prediction mode may be an intra-frame prediction mode of a left neighboring block, and the second prediction mode may be an intra-frame prediction mode of an upper neighboring block. Alternatively, the first prediction mode may be an intra-frame prediction mode of an upper right neighboring block, and the second prediction mode may be an intra-frame prediction mode of a lower left neighboring block.

[0292] The encoder / decoder may generate an MPM list by using the derived MPM candidate mode. Generating the MPM list may mean adding or including the MPM candidate mode in the MPM list.

[0293] Fig.10 is a diagram for explaining an example of configuring an MPM list.

[0294] When, for example, the current block is a luminance block and the 0th reference line is used, the Fig.10 Method for configuring MPM list in .

[0295] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1010 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1020 ), the first method of generating an MPM list may be used ( S1021 ).

[0296] For example, according to the first method of generating the MPM list, at least one of the corresponding prediction mode (first prediction mode), the planar mode as a non-directional mode, and the DC mode may be included in the MPM list. In addition, at least one prediction mode of the prediction modes adjacent to the corresponding prediction mode (first prediction mode) may be included in the MPM list.

[0297] In this specification, the adjacent prediction mode may refer to a mode corresponding to a result obtained by adding an offset n to a specific prediction mode value or subtracting an offset n from a specific prediction mode value. Here, the offset n may be a positive integer and may be less than a specific value m. For example, the offset n may be 1 or 2.

[0298] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the plane mode, the DC mode, the (first prediction mode-1) mode, the (first prediction mode+1) mode, and the (first prediction mode-2) mode. Here, when a mode adjacent to the first prediction mode or the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0299] In the present specification, minAB may represent a mode having a smaller value between the first prediction mode and the second prediction mode. In addition, maxAB may represent a mode having a larger value between the first prediction mode and the second prediction mode.

[0300] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1010 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1020 ), the fifth method of generating an MPM list may be used ( S1022 ).

[0301] For example, according to the fifth method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, when the corresponding prediction mode (first prediction mode) is a plane mode, a DC mode may be included in the MPM list. In addition, when the corresponding prediction mode (first prediction mode) is a DC mode, a plane mode may be included in the MPM list. In addition, the MPM list may include at least one of a vertical mode, a horizontal mode, a (vertical-4) mode, and a (vertical+4) mode. The vertical mode may have a value of 50, the horizontal mode may have a value of 18, the (vertical-4) mode may have a value of 46, and the (vertical+4) mode may have a value of 54.

[0302] For example, when the first prediction mode is different from the second prediction mode (No at S1010) and both the first prediction mode and the second prediction mode are non-directional modes (Yes at S1030, Yes at S1040), the difference (maxAB-minAB) between the first prediction mode and the second prediction mode is calculated, and it may be confirmed whether the difference is within a predetermined range (e.g., from 2 to 62) (S1050). If the difference is within the predetermined range (Yes at S1050), the second method of generating the MPM list may be used (S1051).

[0303] For example, according to the second method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of the planar mode and the DC mode as non-directional modes may be included in the MPM list. In addition, at least one prediction mode of the prediction modes adjacent to the maxAB mode may be included in the MPM list.

[0304] For example, at S1040, if the difference (maxAB-minAB) between the first prediction mode and the second prediction mode is not within a predetermined range (eg, from 2 to 62) (No at S1050), the third method of generating an MPM list may be used (S1052).

[0305] For example, according to the third method of generating the MPM list, at least one of the neighboring patterns of the maxAB mode and the neighboring patterns of the minAB mode may be included in the MPM list.

[0306] For example, the MPM list generated according to the third method of generating the MPM list may include at least one of the first prediction mode, the second prediction mode, the planar mode, the DC mode, the (maxAB-2) mode, and the (maxAB+2) mode.

[0307] For example, when the first prediction mode is different from the second prediction mode (No in S1010), at least one of the two modes is a directional mode (Yes in S1030), and one of the two modes is a non-directional mode (No in S1040), the fourth method (S1041) for generating an MPM list can be used.

[0308] For example, according to the fourth method of generating the MPM list, the MPM list may include at least one of the first prediction mode and the second prediction mode. In addition, when the non-directional mode included in the MPM list is the planar mode, the DC mode may be included in the MPM list. In addition, when the non-directional mode included in the MPM list is the DC mode, the planar mode may be included in the MPM list. In addition, at least one adjacent mode of the adjacent modes of the non-directional mode included in the MPM list may be included in the MPM list.

[0309] For example, according to the fourth method of generating the MPM list, when the first prediction mode is a planar mode and the second prediction mode is a directional mode, the MPM list may include at least one of the planar mode and the second prediction mode. In addition, the MPM list may include at least one of a DC mode and a mode adjacent to the maxAB mode. The adjacent mode of the maxAB mode may be at least one of a (maxAB-1) mode, a (maxAB+1) mode, and a (maxAB-2) mode. When the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list. Here, the second prediction mode may represent the maxAB mode.

[0310] For example, when the first prediction mode is different from the second prediction mode (No at S1010 ) and both modes are non-directional modes (No at S1030 ), the fifth method of generating the MPM list may be used ( S1031 ).

[0311] For example, according to the fifth method of generating the MPM list, the MPM list may include at least one of the first prediction mode and the second prediction mode. In addition, the MPM list may include at least one of the vertical mode, the horizontal mode, the (vertical mode-4) mode, and the (vertical mode+4) mode. The vertical mode may have a value of 50, the horizontal mode may have a value of 18, the (vertical mode-4) mode may have a value of 46, and the (vertical mode+4) mode may have a value of 54. For example, the first prediction mode may be a planar mode, and the second prediction mode may be a DC mode.

[0312] For example, when one of the first prediction mode and the second prediction mode is a directional mode and the other is a non-directional mode, the mode with a larger value (maxAB) among the first prediction mode and the second prediction mode may be determined as the directional mode. Alternatively, the mode with a smaller value (minAB) among the first prediction mode and the second prediction mode may be determined as the non-directional mode.

[0313] For example, in the fourth method of generating the MPM list, the mode having a larger value (maxAB) among two modes may be determined as the directional mode.

[0314] Fig.11 is a diagram for explaining another example of configuring an MPM list.

[0315] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.11 Method for configuring MPM list in .

[0316] Here, the MPM list may include only the directional mode and / or the DC mode. In addition, the MPM list may not include the planar mode.

[0317] Furthermore, the MPM list may consist of unique intra prediction modes that do not overlap with each other.

[0318] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1110 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1120 ), the first method of generating an MPM list may be used ( S1121 ).

[0319] For example, according to the first method of generating the MPM list, at least one of the corresponding prediction mode (first prediction mode) and a neighboring mode of the corresponding prediction mode may be included in the MPM list.

[0320] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, (first prediction mode-1) mode, (first prediction mode+1) mode, (first prediction mode-2) mode, (first prediction mode+2) mode, and (first prediction mode-3) mode. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5. Here, when a mode adjacent to the first prediction mode or the second prediction mode is a non-directional mode, at least one directional mode among the directional modes located in the opposite direction may be included in the MPM list.

[0321] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1110 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1120 ), the seventh method of generating an MPM list may be used ( S1122 ).

[0322] For example, according to the seventh method of generating the MPM list, at least one of the DC mode, the vertical mode, the horizontal mode, the (vertical mode-4) mode, and the (vertical mode+4) mode may be included in the MPM list. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5. The DC mode may have a value of 1, the vertical mode may have a value of 50, the horizontal mode may have a value of 18, the (vertical mode-4) mode may have a value of 46, and the (vertical mode+4) mode may have a value of 54. The MPM list generated according to the seventh method of generating the MPM list may include at least one of the modes.

[0323] For example, when the first prediction mode is different from the second prediction mode (No at S1110) and both prediction modes are directional modes (Yes at S1130, Yes at S1140), the MPM list may include at least one of the first prediction mode and the second prediction mode. In addition, the difference (maxAB-minAB) between the two prediction modes may be obtained. If the difference is 1 (Yes at S1150), the second method of generating the MPM list may be used (S1151).

[0324] For example, according to the second method of generating the MPM list, the MPM list may include at least one of a neighboring pattern of the maxAB mode and a neighboring pattern of the minAB mode.

[0325] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (maxAB+1) mode, the (minAB-2) mode, and the (maxAB+2) mode. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5.

[0326] For example, when the difference (maxAB-minAB) between the two prediction modes is 2 (Yes at S1160), the third method of generating the MPM list may be used (S1161).

[0327] According to the third method of generating the MPM list, at least one of the neighboring patterns of the minAB mode and the neighboring patterns of the maxAB mode may be included in the MPM list.

[0328] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB+1) mode, the (minAB-1) mode, the (maxAB+1) mode, and the (minAB-2) mode. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5.

[0329] For example, when the difference value (maxAB-minAB) between the two prediction modes is 62 or more (Yes at S1170), the fourth method of generating the MPM list may be used (S1171).

[0330] According to the fourth method of generating the MPM list, at least one of the neighboring patterns of the maxAB mode and the neighboring patterns of the minAB mode may be included in the MPM list.

[0331] For example, according to the fourth method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB+1) mode, the (maxAB-1) mode, the (minAB+2) mode, and the (maxAB-2) mode. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5.

[0332] For example, when the difference value (maxAB-minAB) between the two prediction modes is equal to or greater than 3 and equal to or less than 61 (No in S1170), the fifth method of generating the MPM list may be used (S1172).

[0333] According to the fifth method of generating the MPM list, at least one of the neighboring patterns of the maxAB mode and the neighboring patterns of the minAB mode may be included in the MPM list.

[0334] For example, according to the fifth method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (minAB+1) mode, the (maxAB-1) mode, and the (maxAB+1) mode. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5.

[0335] For example, when the first prediction mode is different from the second prediction mode (No at S1110) and only one of the two modes is a directional mode (Yes at S1130, No at S1140), the sixth method of generating an MPM list may be used (S1141).

[0336] According to the sixth method of generating the MPM list, the directional mode in the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one neighboring mode of the included directional mode may be included in the MPM list.

[0337] For example, according to the sixth method of generating the MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include the second prediction mode. Here, the mode with a larger value among the first prediction mode and the second prediction mode may be determined as a directional mode, and the MPM list may include at least one of the (maxAB-1) mode, the (maxAB+1) mode, the (maxAB-2) mode, the (maxAB+2) mode, and the (maxAB-3) mode. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0338] For example, when the first prediction mode is different from the second prediction mode (No at S1110 ) and both modes are non-directional modes (No at S1130 ), the seventh method of generating the MPM list may be used ( S1131 ).

[0339] For example, according to the seventh method of generating the MPM list, at least one of the DC mode, the vertical mode, the horizontal mode, the (vertical mode-4) mode, and the (vertical mode+4) mode may be included in the MPM list. In this case, among these modes, only N modes may be included. Here, N may be a positive integer and may be 5. Here, the DC mode may have a value of 1, the vertical mode may have a value of 50, the horizontal mode may have a value of 18, the (vertical mode-4) mode may have a value of 46, and the (vertical mode+4) mode may have a value of 54. According to the seventh method of generating the MPM list, the MPM list may include at least one of the modes.

[0340] In the present specification, when at least one of the first prediction mode and the second prediction mode is a directional mode and the other is a non-directional mode, whether the mode is a directional mode or a non-directional mode may be determined based on a comparison of mode values. For example, a mode with a larger mode value may be determined as a directional mode.

[0341] Fig.12 is a diagram for explaining another example of configuring an MPM list.

[0342] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.12 Method for configuring MPM list in .

[0343] Here, the MPM list may include only the directional mode and / or the DC mode.

[0344] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1210 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1220 ), the first method of generating an MPM list may be used ( S1221 ).

[0345] For example, according to the first method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, at least one neighboring mode of the corresponding prediction mode may be included in the MPM list.

[0346] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, (first prediction mode-1) mode, (first prediction mode+1) mode, (first prediction mode-2) mode, (first prediction mode+2) mode, and (first prediction mode-3) mode. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0347] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1210 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1220 ), the fourth method of generating an MPM list may be used ( S1222 ).

[0348] For example, according to the fourth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0349] For example, when the first prediction mode is different from the second prediction mode (No at S1210) and both modes are directional modes (Yes at S1230, Yes at S1240), the second method of generating the MPM list may be used (S1241).

[0350] For example, according to the second method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of the adjacent mode of the minAB mode and the adjacent mode of the maxAB mode may be included in the MPM list. Here, when the minAB mode and the maxAB mode are adjacent modes, at least one mode in the MPM list may be repeated. In other words, the MPM list may include repeated identical prediction modes. Here, the identical prediction mode may be a directional mode.

[0351] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (minAB+1) mode, the (maxAB-1) mode, and the (maxAB+1) mode.

[0352] For example, when minAB is mode 4 and maxAB is mode 5, the MPM list may include at least one of the minAB mode, the maxAB mode, the (minAB-1) mode, the (minAB+1) mode, the (maxAB-1) mode, and the (maxAB+1) mode. Here, since minAB+1 is mode 5 and maxAB-1 is mode 4, the MPM list may include repeated modes 4 and 5.

[0353] For example, when at least one of (maxAB-minAB==1), (maxAB-minAB==2), and (maxAB-minAB>61) is satisfied, the MPM list may include at least one repeated pattern.

[0354] For example, when the first prediction mode is different from the second prediction mode (No in S1210) and one of the two prediction modes is a non-directional mode and the other is a directional mode (Yes in S1230, No in S1240), the third method of generating an MPM list (S1242) may be used.

[0355] For example, according to the third method of generating the MPM list, the directional pattern may be included in the MPM list. In addition, at least one adjacent pattern of the included directional pattern may be included in the MPM list.

[0356] For example, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include at least one of the second prediction mode, (maxAB-1) mode, (maxAB+1) mode, (maxAB-2) mode, (maxAB+2) mode, and (maxAB-3) mode. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0357] For example, when the first prediction mode is not the same as the second prediction mode (No at S1210 ) and both modes are non-directional modes (No at S1230 ), the fourth method of generating the MPM list may be used ( S1231 ).

[0358] For example, according to the fourth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0359] For example, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of a vertical mode, a horizontal mode, a horizontal diagonal mode, a diagonal mode, a vertical diagonal mode, and mode26.

[0360] In reference Fig.12 In the illustrated embodiment, the MPM list may include repeated directional patterns if a predetermined condition is met.

[0361] Fig.13 is a diagram for explaining another example of configuring an MPM list.

[0362] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.13 Method for configuring MPM list in .

[0363] Here, the MPM list may include only the directional mode and / or the DC mode.

[0364] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1310 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1320 ), the first method of generating an MPM list may be used ( S1321 ).

[0365] For example, according to the first method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, at least one neighboring mode of the corresponding prediction mode may be included in the MPM list.

[0366] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, (first prediction mode-1) mode, (first prediction mode+1) mode, (first prediction mode-2) mode, (first prediction mode+2) mode, and (first prediction mode-3) mode. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0367] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1310 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1320 ), the fifth method of generating an MPM list may be used ( S1322 ).

[0368] For example, according to the fifth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0369] For example, when the first prediction mode is different from the second prediction mode (No at S1310) and both modes are directional modes (Yes at S1330, Yes at S1340), the difference (maxAB-minAB) between the two modes may be obtained. When the difference between the two modes is 1 (Yes at S1350), the second method of generating an MPM list may be used (S1351).

[0370] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the neighboring mode of the maxAB mode, and the neighboring mode of the minAB mode.

[0371] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (maxAB+1) mode, the (minAB-2) mode, and the (maxAB+2) mode.

[0372] For example, when the difference (maxAB-minAB) between the two prediction modes is a predetermined integer (eg, 2 or more) (No at S1350), the third method of generating the MPM list may be used (S1352).

[0373] For example, according to the third method of generating the MPM list, at least one of the neighboring patterns of the maxAB mode and the neighboring patterns of the minAB mode may be included in the MPM list.

[0374] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (minAB+1) mode, the (maxAB-1) mode, and the (maxAB+1) mode.

[0375] For example, when at least one of (maxAB-minAB==2) and (maxAB-minAB>61) is satisfied, the MPM list may include at least one repeated pattern. Here, the repeated pattern may be a directional pattern.

[0376] For example, when the first prediction mode is different from the second prediction mode (No in S1310) and one of the two prediction modes is a non-directional mode and the other is a directional mode (Yes in S1330, No in S1340), the fourth method of generating an MPM list (S1341) may be used.

[0377] For example, according to the fourth method of generating the MPM list, the MPM list may include at least one of a directional pattern and a pattern adjacent thereto.

[0378] For example, according to the fourth method of generating the MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include the second prediction mode. In addition, the MPM list may include at least one of a (maxAB-1) mode, a (maxAB+1) mode, a (maxAB-2) mode, a (maxAB+2) mode, and a (maxAB-3) mode. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0379] For example, when the first prediction mode is different from the second prediction mode (No at S1310 ) and both modes are non-directional modes (No at S1330 ), the fifth method of generating the MPM list may be used.

[0380] For example, according to the fifth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0381] For example, according to the fifth method of generating the MPM list, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of a vertical mode, a horizontal mode, a horizontal diagonal mode, a diagonal mode, a vertical diagonal mode and mode 26.

[0382] Fig.14 is a diagram for explaining another example of configuring an MPM list.

[0383] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.14 Method for configuring MPM list in .

[0384] Here, the MPM list may include only the directional mode and / or the DC mode.

[0385] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1410 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1420 ), the first method of generating an MPM list may be used ( S1421 ).

[0386] According to the first method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, at least one neighboring mode of the corresponding prediction mode (first prediction mode) may be included in the MPM list.

[0387] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, (first prediction mode-1) mode, (first prediction mode+1) mode, (first prediction mode-2) mode, (first prediction mode+2) mode, and (first prediction mode-3) mode. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0388] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1410 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1420 ), the sixth method of generating an MPM list may be used ( S1422 ).

[0389] According to the sixth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0390] For example, when the first prediction mode is different from the second prediction mode (No at S1410) and both modes are directional modes (Yes at S1430, Yes at S1440), the difference (maxAB-minAB) between the two modes may be obtained. When the difference between the two modes is 1 (Yes at S1450), the second method of generating an MPM list may be used (S1451).

[0391] According to the second method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of the neighboring mode of the maxAB mode and the neighboring mode of the minAB mode may be included in the MPM list.

[0392] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (maxAB+1) mode, the (minAB-2) mode, and the (maxAB+2) mode.

[0393] For example, when the difference (maxAB-minAB) between the two prediction modes is 2 (Yes at S1460), the third method of generating the MPM list may be used (S1461).

[0394] According to the third method of generating the MPM list, at least one of the neighboring patterns of the minAB mode and the neighboring patterns of the maxAB mode may be included in the MPM list.

[0395] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB+1) mode, the (minAB-1) mode, the (maxAB+1) mode, and the (minAB-2) mode.

[0396] When the difference (maxAB-minAB) between the two prediction modes is 3 or more (No at S1460), the fourth method of generating the MPM list may be used (S1462).

[0397] According to the fourth method of generating the MPM list, at least one of the neighboring patterns of the maxAB mode and the neighboring patterns of the minAB mode may be included in the MPM list.

[0398] For example, according to the fourth method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (minAB+1) mode, the (maxAB-1) mode, and the (maxAB+1) mode.

[0399] For example, in the case of (maxAB-minAB>61), the MPM list may include at least one repeated pattern. Here, the repeated pattern may be a directional pattern.

[0400] For example, when the first prediction mode is different from the second prediction mode (No at S1410) and one of the two prediction modes is a non-directional mode and the other is a directional mode (Yes at S1430, No at S1440), the fifth method of generating an MPM list (S1441) may be used.

[0401] According to the fifth method of generating the MPM list, the directional pattern may be included in the MPM list. In addition, at least one neighboring pattern among neighboring patterns of the included directional pattern may be included in the MPM list.

[0402] For example, according to the fifth method of generating the MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include at least one of the second prediction mode, (maxAB-1) mode, (maxAB+1) mode, (maxAB-2) mode, (maxAB+2) mode, and (maxAB-3) mode. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0403] For example, when the first prediction mode is different from the second prediction mode (No at S1410 ) and both modes are non-directional modes (No at S1430 ), the sixth method of generating the MPM list may be used ( S1431 ).

[0404] According to the sixth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0405] For example, according to the sixth method of generating the MPM list, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of a vertical mode, a horizontal mode, a horizontal diagonal mode, a diagonal mode, a vertical diagonal mode and mode 26.

[0406] Fig.15 is a diagram for explaining another example of configuring an MPM list.

[0407] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.15 Method for configuring MPM list in .

[0408] Here, the MPM list may include only the directional mode and / or the DC mode.

[0409] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1510 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1520 ), the first method of generating an MPM list may be used ( S1521 ).

[0410] According to the first method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, at least one neighboring mode of the corresponding prediction mode (first prediction mode) may be included in the MPM list.

[0411] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, (first prediction mode-1) mode, (first prediction mode+1) mode, (first prediction mode-2) mode, (first prediction mode+2) mode, and (first prediction mode-3) mode. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0412] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1510 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1520 ), the sixth method of generating an MPM list may be used ( S1522 ).

[0413] According to the sixth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0414] For example, when the first prediction mode is different from the second prediction mode (No at S1510) and both modes are directional modes (Yes at S1530, Yes at S1540), the difference (maxAB-minAB) between the two modes may be obtained. When the difference is 1 (Yes at S1550), the second method of generating the MPM list may be used (S1551).

[0415] According to the second method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of a neighboring mode of the maxAB mode and a neighboring mode of the minAB mode may be included in the MPM list.

[0416] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (maxAB+1) mode, the (minAB-2) mode, and the (maxAB+2) mode.

[0417] For example, when the difference (maxAB-minAB) between the two prediction modes is 62 or more (Yes at S1560), the third method of generating the MPM list may be used (S1561).

[0418] According to the third method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of a neighboring mode of the maxAB mode and a neighboring mode of the minAB mode may be included in the MPM list.

[0419] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB+1) mode, the (maxAB-1) mode, the (minAB+2) mode, and the (maxAB-2) mode.

[0420] For example, when the difference between the two prediction modes (maxAB-minAB) is equal to or greater than 2 and equal to or less than 61 (No at S1560), the fourth method of generating the MPM list may be used (S1562).

[0421] According to the fourth method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of a neighboring mode of the maxAB mode and a neighboring mode of the minAB mode may be included in the MPM list.

[0422] For example, according to the fourth method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (minAB-1) mode, the (minAB+1) mode, the (maxAB-1) mode, and the (maxAB+1) mode.

[0423] For example, in the case of (maxAB-minAB==2), the MPM list may include at least one repeated pattern. Here, the repeated pattern may be a directional pattern.

[0424] For example, when the first prediction mode is different from the second prediction mode (No at S1510) and one of the two prediction modes is a non-directional mode and the other is a directional mode (Yes at S1530, No at S1540), the fifth method of generating an MPM list (S1541) may be used.

[0425] According to the fifth method of generating the MPM list, the directional pattern may be included in the MPM list. In addition, at least one neighboring pattern among neighboring patterns of the included directional pattern may be included in the MPM list.

[0426] For example, according to the fifth method of generating the MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include at least one of the second prediction mode, (maxAB-1) mode, (maxAB+1) mode, (maxAB-2) mode, (maxAB+2) mode, and (maxAB-3) mode. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0427] For example, when the first prediction mode is different from the second prediction mode (No at S1510 ) and both modes are non-directional modes (No at S1530 ), the sixth method of generating the MPM list may be used ( S1531 ).

[0428] According to the sixth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the horizontal diagonal mode, the diagonal mode, the vertical diagonal mode, and mode 26 may be included in the MPM list.

[0429] For example, according to the sixth method of generating the MPM list, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of a vertical mode, a horizontal mode, a horizontal diagonal mode, a diagonal mode, a vertical diagonal mode and mode 26.

[0430] Fig.16 is a diagram for explaining another example of configuring an MPM list.

[0431] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.16 Method for configuring MPM list in .

[0432] Here, the MPM list may include at least one of a non-directional mode or a directional mode.

[0433] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1610 ) and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1620 ), the first method of generating an MPM list may be used ( S1621 ).

[0434] According to the first method of generating the MPM list, at least one of the corresponding prediction mode (first prediction mode), the planar mode as a non-directional mode, and the DC mode may be included in the MPM list. In addition, at least one adjacent mode of the adjacent modes of the corresponding prediction mode (first prediction mode) may be included in the MPM list.

[0435] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the plane mode, the DC mode, the (first prediction mode-1) mode, the (first prediction mode+1) mode, and the (first prediction mode-2) mode. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0436] For example, when the first prediction mode is the same as the second prediction mode (Yes at S1610 ) and the corresponding prediction mode (first prediction mode) is a non-directional mode (No at S1620 ), the fifth method of generating an MPM list may be used ( S1622 ).

[0437] According to the fifth method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, when the corresponding prediction mode (first prediction mode) is the plane mode, the DC mode may be included in the MPM list. In addition, when the corresponding prediction mode (first prediction mode) is the DC mode, the plane mode may be included in the MPM list. In addition, at least one of the vertical mode, the horizontal mode, the (vertical-4) mode, and the (vertical+4) mode may be included in the MPM list.

[0438] For example, when the first prediction mode is different from the second prediction mode (No at S1610) and both modes are directional modes (Yes at S1630, Yes at S1640), at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of the planar mode and the DC mode as non-directional modes may be included in the MPM list. In addition, the difference (maxAB-minAB) between the two prediction modes may be obtained. When the difference is equal to or greater than 2 and equal to or less than 62 (Yes at S1650), the second method (S1651) for generating the MPM list may be used.

[0439] According to the second method of generating the MPM list, at least one neighboring mode among the neighboring modes of the maxAB mode may be included in the MPM list.

[0440] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the planar mode, the DC mode, the (maxAB-1) mode, and the (maxAB+1) mode.

[0441] When the difference (maxAB-minAB) between the two prediction modes is equal to or less than 1 or equal to or greater than 63 (No at S1650), the third method of generating the MPM list may be used (S1652).

[0442] According to the third method of generating the MPM list, at least one of the neighboring patterns of the maxAB mode and the neighboring patterns of the minAB mode may be included in the MPM list.

[0443] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the planar mode, the DC mode, the (maxAB-2) mode, and the (maxAB+2) mode.

[0444] For example, when the first prediction mode is different from the second prediction mode (No at S1610) and one of the two prediction modes is a non-directional mode and the other is a directional mode (No at S1640), the fourth method of generating an MPM list may be used (S1641).

[0445] According to the fourth method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, when the non-directional mode included in the MPM list is the planar mode, the DC mode may be included in the MPM list. In addition, when the non-directional mode included in the MPM list is the DC mode, the planar mode may be included in the MPM list. In addition, at least one of the adjacent modes of the maxAB mode may be included in the MPM list.

[0446] For example, according to the fourth method of generating the MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include at least one of a plane mode, a second prediction mode, a DC mode, a (second prediction mode-1) mode, a (second prediction mode+1) mode, and a (second prediction mode-2) mode. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list.

[0447] For example, when the first prediction mode is different from the second prediction mode (No at S1610 ) and both modes are non-directional modes (No at S1630 ), the fifth method of generating the MPM list may be used ( S1631 ).

[0448] According to the fifth method of generating the MPM list, at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, at least one of the vertical mode, the horizontal mode, the (vertical-4) mode, and the (vertical+4) mode may be included in the MPM list.

[0449] For example, according to the fifth method of generating the MPM list, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of the planar mode, the DC mode, the vertical mode, the horizontal mode, the (vertical -4) mode, and the (vertical +4) mode.

[0450] In the embodiments described in this specification, a flag indicating whether the planar mode is used may be sent by a signal. The corresponding flag may be represented as intra_luma_not_planar_flag. When intra_luma_not_planar_flag is a first value, it may indicate that the planar mode is used. When intra_luma_not_planar_flag is a second value, it may indicate that the planar mode is not used. Here, the first value may be 0, and the second value may be 1.

[0451] In the embodiments described in this specification, when intra_luma_not_planar_flag is signaled, the planar mode may be processed differently from the MPM candidate modes included in the MPM list. For example, the MPM list may be configured by removing the planar mode. When the MPM mode is applied to the current block, intra_luma_not_planar_flag may be reconstructed with priority so that it may be determined whether the mode of the current block is the planar mode. When the mode of the current block is not the planar mode, the MPM list excluding the planar mode may be configured by one of the embodiments described in this specification.

[0452] Intra_luma_not_planar_flag may be signaled only when reference line 0 is referenced. For example, when reference line 1 or greater is referenced, intra_luma_not_planar_flag may not be signaled through the bitstream. In this case, intra_luma_not_planar_flag may be inferred to be a second value. In other words, when reference line 1 or greater is referenced, the intra prediction mode of the current block may not be planar mode.

[0453] When the current block is in ISP mode, the method for generating an MPM list according to the embodiment described in this specification can be applied in the same manner. Figure 8 As shown in , when a current block is partitioned into a plurality of subblocks and intra prediction is sequentially performed for each subblock, an MPM list for the current block may be generated by one of the embodiments explained with reference to the accompanying drawings of the present invention.

[0454] Fig.17 is a diagram for explaining another example of configuring an MPM list.

[0455] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.17 Method for configuring MPM list in .

[0456] Here, the MPM list may include at least one of a non-directional mode and a directional mode. Here, the MPM list may not include a planar mode.

[0457] Furthermore, the MPM list may consist of unique intra prediction modes that do not overlap with each other.

[0458] For example, when the first prediction mode is the same as the second prediction mode and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1710 ), the first method of generating an MPM list may be used ( S1711 ).

[0459] According to the first method of generating the MPM list, at least one of the corresponding prediction mode (first prediction mode) and the DC mode as a non-directional mode may be included in the MPM list. In addition, at least one adjacent mode of the adjacent modes of the corresponding prediction mode (first prediction mode) may be included in the MPM list.

[0460] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the DC mode, the (first prediction mode-1) mode, the (first prediction mode+1) mode, and the (first prediction mode-2) mode. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list. Optionally, for example, according to the first method of generating the MPM list, the MPM list may be configured to include only the first prediction mode and the modes adjacent thereto. For example, the MPM list may include at least one of the first prediction mode, the (first prediction mode-1) mode, the (first prediction mode+1) mode, the (first prediction mode-2) mode, and the (first prediction mode+2) mode.

[0461] For example, when the first prediction mode is different from the second prediction mode and both modes are directional modes (No at S1710, Yes at S1720, Yes at S1730), at least one of the first prediction mode and the second prediction mode may be included in the MPM list. Alternatively, the DC mode as a non-directional mode may be included in the MPM list.

[0462] In addition, a difference value (maxAB-minAB) between two prediction modes may be obtained. When the difference value is equal to or greater than 2 and equal to or less than 62 (Yes at S1740), a second method of generating an MPM list may be used.

[0463] When the second method of generating the MPM list is used, the MPM list may include at least one of the neighboring patterns of the maxAB pattern.

[0464] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the DC mode, the (maxAB-1) mode, and the (maxAB+1) mode in sequence. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above examples. For example, the second prediction mode may be included before the first prediction mode. Optionally, the (maxAB+1) mode may be included before the (maxAB-1) mode. Optionally, for example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode and the second prediction mode, and may also include three modes of the (minAB+1) mode, the (minAB-1) mode, the (maxAB+1) mode, and the (maxAB-1) mode.

[0465] For example, when the difference (maxAB-minAB) between the two prediction modes is equal to or less than 1 or equal to or greater than 63 (No at S1740), the third method of generating the MPM list may be used (S1742).

[0466] According to the third method of generating the MPM list, at least one neighboring mode among the neighboring modes of the maxAB mode may be included in the MPM list.

[0467] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the DC mode, the (maxAB-2) mode, and the (maxAB+2) mode in sequence. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the second prediction mode may be included before the first prediction mode. Optionally, the (maxAB+2) mode may be located before the (maxAB-2) mode. Optionally, for example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode and the second prediction mode, and may also include the (minAB-1) mode, the (minAB+1) mode, and the (minAB-2) mode. Optionally, the MPM list may be configured to include at least one of the first prediction mode, the second prediction mode, the (minAB+1) mode, the (maxAB-1) mode, and the (minAB+2) mode.

[0468] For example, when the first prediction mode is different from the second prediction mode and one of the two prediction modes is a non-directional mode and the other is a directional mode (No in S1710, Yes in S1720, No in S1730), the fourth method of generating an MPM list (S1731) may be used.

[0469] According to the fourth method of generating the MPM list, the directional mode in the two prediction modes may be included in the MPM list. In addition, the DC mode as a non-directional mode may be included in the MPM list. In addition, at least one adjacent mode of the adjacent modes of the directional mode may be included in the MPM list.

[0470] For example, according to the fourth method of generating an MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include at least one of the second prediction mode, the DC mode, the (second prediction mode-1) mode, the (second prediction mode+1) mode, and the (second prediction mode-2) mode in sequence. Here, when the mode adjacent to the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the (second prediction mode+1) mode may be included before the (second prediction mode-1) mode. Alternatively, for example, according to the fourth method of generating an MPM list, the MPM list may be configured to include only directional modes. In this case, the MPM list may also be configured to include the second prediction mode, the (second prediction mode-1) mode, the (second prediction mode+1) mode, the (second prediction mode-2) mode, and the (second prediction mode+2) mode.

[0471] For example, when the first prediction mode is different from the second prediction mode and both modes are non-directional modes (No in S1710 , No in S1720 ), the fifth method of generating the MPM list may be used ( S1721 ).

[0472] According to the fifth method of generating the MPM list, the DC mode of the two prediction modes may be included in the MPM list. In addition, at least one of the vertical mode, the horizontal mode, the (vertical-4) mode, and the (vertical+4) mode may be included in the MPM list.

[0473] For example, according to the fifth method of generating the MPM list, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of the DC mode, the vertical mode, the horizontal mode, the (vertical-4) mode, and the (vertical+4) mode in sequence. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the (vertical+4) mode may be included before the (vertical-4) mode.

[0474] In an embodiment disclosed in the present specification, a flag indicating whether the intra prediction mode of the current block is a DC mode may be sent by a signal. The corresponding flag may be represented as intra_luma_not_dc_flag. When intra_luma_not_dc_flag is a first value, it may indicate that the DC mode is used. When intra_luma_not_dc_flag is a second value, it may indicate that the DC mode is not used. Here, the first value may be 0, and the second value may be 1.

[0475] In the embodiments described in this specification, when intra_luma_not_dc_flag is signaled, the DC mode may be processed differently from the MPM candidate modes included in the MPM list. For example, the MPM list may be configured by removing the DC mode. When the MPM mode is applied to the current block, intra_luma_not_dc_flag may be reconstructed with priority so that it may be determined whether the mode of the current block is the DC mode. When the mode of the current block is not the DC mode, the MPM list excluding the DC mode may be configured by one of the embodiments described in this specification.

[0476] Fig.18 is a diagram for explaining another example of configuring an MPM list.

[0477] When, for example, the current block is a luminance block and uses the 0th reference line or higher, the Fig.18 Method for configuring MPM list in .

[0478] Here, the MPM list may include only the directional mode and / or the DC mode.

[0479] Here, only the DC mode may be included as a non-directional mode, and any mode may not be excluded.

[0480] For example, when the first prediction mode is the same as the second prediction mode and the corresponding prediction mode (first prediction mode) is a directional mode (Yes at S1810 ), the first method of generating an MPM list may be used ( S1811 ).

[0481] According to the first method of generating the MPM list, the corresponding prediction mode (first prediction mode) may be included in the MPM list. In addition, at least one mode among modes adjacent to the corresponding prediction mode (first prediction mode) may be included in the MPM list.

[0482] For example, according to the first method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the (first prediction mode-1) mode, the (first prediction mode+1) mode, and the (first prediction mode-2) mode in sequence. Here, when the adjacent mode of the first prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the (first prediction mode+1) mode may be located before the (first prediction mode-1) mode.

[0483] For example, when the first prediction mode is different from the second prediction mode (No at S1810) and both modes are directional modes (Yes at S1820, Yes at S1830), at least one of the first prediction mode and the second prediction mode may be included in the MPM list. In addition, the difference (maxAB-minAB) between the two prediction modes may be obtained. When the difference is equal to or greater than 2 and equal to or less than 62 (Yes at S1840), the second method of generating the MPM list may be used.

[0484] According to the second method of generating the MPM list, at least one neighboring mode among the neighboring modes of the maxAB mode may be included in the MPM list.

[0485] For example, according to the second method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (maxAB-1) mode, and the (maxAB+1) mode in sequence. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the second prediction mode may be included before the first prediction mode. Optionally, the (maxAB+1) mode may be included before the (maxAB-1) mode.

[0486] For example, when the difference (maxAB-minAB) between the two prediction modes is equal to or less than 1 or equal to or greater than 63 (No at S1840), the third method of generating the MPM list may be used (S1842).

[0487] According to the third method of generating the MPM list, at least one neighboring mode among the neighboring modes of the maxAB mode may be included in the MPM list.

[0488] For example, according to the third method of generating the MPM list, the MPM list may include at least one of the first prediction mode, the second prediction mode, the (maxAB-2) mode, and the (maxAB+2) mode in sequence. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the second prediction mode may be included before the first prediction mode. Alternatively, the (maxAB+2) mode may be included before the (maxAB-2) mode.

[0489] For example, when the first prediction mode is different from the second prediction mode (No in S1810) and one of the two prediction modes is a non-directional mode and the other is a directional mode (Yes in S1820, No in S1830), the fourth method of generating an MPM list (S1831) may be used.

[0490] According to the fourth method of generating the MPM list, the directional modes in the two prediction modes may be included in the MPM list. In addition, at least one of the neighboring modes of the maxAB mode may be included in the MPM list.

[0491] For example, according to the fourth method of generating an MPM list, when the first prediction mode is a non-directional mode and the second prediction mode is a directional mode, the MPM list may include at least one of the second prediction mode, the (second prediction mode-1) mode, the (second prediction mode+1) mode, and the (second prediction mode-2) mode in sequence. Here, when the adjacent mode of the second prediction mode is a non-directional mode, at least one directional mode of the directional modes located in the opposite direction may be included in the MPM list. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the (second prediction mode+1) mode may be included before the (second prediction mode-1) mode.

[0492] For example, when the first prediction mode is different from the second prediction mode (No at S1810 ) and both modes are non-directional modes (No at S1820 ), the fifth method of generating the MPM list may be used ( S1821 ).

[0493] According to the fifth method of generating the MPM list, at least one of the vertical mode, the horizontal mode, the (vertical-4) mode, and the (vertical+4) mode may be included in the MPM list.

[0494] For example, according to the fifth method of generating the MPM list, when the first prediction mode is the planar mode and the second prediction mode is the DC mode, the MPM list may include at least one of the vertical mode, the horizontal mode, the (vertical-4) mode, and the (vertical+4) mode in sequence. Here, the order in which the MPM candidate modes are included in the MPM list is not limited to the above example. For example, the (vertical+4) mode may be included before the (vertical-4) mode.

[0495] In the embodiments described in the present specification, when the current block is a luminance block and uses the 0th reference line or higher, this may mean that configuring the MPM list in the mode using multiple reference lines and configuring the MPM list in the general intra prediction mode may be performed by the same method as configuring the MPM list. In the embodiments described in the present specification, the method of configuring the MPM list in the mode using multiple reference lines may be the same as the method of configuring the MPM list in the general intra prediction mode.

[0496] In the embodiments described in this specification, the MPM list may include MPM candidate modes in the following order.

[0497] For example, the first prediction mode may be included before a mode (low value index) adjacent to it. For example, the modes adjacent to the first prediction mode may be included in ascending order of the difference with the first prediction mode. For example, the first prediction mode may be included before the DC mode, which is a non-directional mode. For example, the DC mode, which is a non-directional mode, may be included between a mode having a difference of 1 with the first prediction mode and a mode having a difference of 2 with the first prediction mode among the adjacent modes of the first prediction mode. For example, an adjacent mode having a difference of -1 with the first prediction mode may be included before an adjacent mode having a difference of +1 with the first prediction mode. For example, an adjacent mode having a difference of +1 with the first prediction mode may be included before an adjacent mode having a difference of -1 with the first prediction mode.

[0498] For example, the DC mode as a non-directional mode may be included in the foremost position. For example, the maxAB mode may be included in the foremost position. For example, the adjacent mode of the minAB mode may be included before the adjacent mode of the maxAB mode. For example, the adjacent mode of the maxAB mode may be included between the adjacent mode of the minAB mode and another adjacent mode of the minAB mode. For example, the maxAB mode may be included before the adjacent mode of the maxAB mode.

[0499] For example, the first prediction mode may be located before the second prediction mode. For example, the second prediction mode may be located before the first prediction mode. For example, the first prediction mode and the second prediction mode may be located before the adjacent mode of the maxAB mode. For example, the first prediction mode and the second prediction mode may be located before the DC mode as a non-directional mode. For example, the DC mode as a non-directional mode may be located before the adjacent mode of the maxAB mode. For example, in the adjacent mode of the maxAB mode, the prediction mode with a difference of -1 may be located before the prediction mode with a difference of +1. For example, in the adjacent mode of the maxAB mode, the prediction mode with a difference of +1 may be located before the prediction mode with a difference of -1. For example, in the adjacent mode of the maxAB mode, the prediction mode with a difference of -2 may be located before the prediction mode with a difference of +2. For example, in the adjacent mode of the maxAB mode, the prediction mode with a difference of +2 may be located before the prediction mode with a difference of -2.

[0500] For example, the first prediction mode and the second prediction mode may be located before the adjacent modes of the directional mode. For example, the adjacent modes of the directional mode may be located in ascending order of the difference values ​​with the directional mode. For example, among the adjacent modes of the directional mode, the prediction mode with a difference of -1 may be located before the prediction mode with a difference of +1. For example, among the adjacent modes of the directional mode, the prediction mode with a difference of +1 may be located before the prediction mode with a difference of -1.

[0501] For example, the DC mode as a non-directional mode may be located before the directional mode. For example, the vertical mode may be located before the horizontal mode. For example, the vertical mode and the horizontal mode may be located before the adjacent mode of the vertical mode. For example, in the adjacent mode of the vertical mode, the prediction mode with a difference of -4 may be located before the prediction mode with a difference of +4. For example, in the adjacent mode of the vertical mode, the prediction mode with a difference of +4 may be located before the prediction mode with a difference of -4.

[0502] Being included in front of the MPM list may indicate that the index value for the MPM list is smaller. For example, in the MPM list, the first mode may be included before the second mode.

[0503] When the current block is a chroma block and LM (linear mode) is unavailable, in other words, when cclm_enabled_flag is the first value, DM (direct mode) may be used to derive a candidate mode of an intra prediction mode of the current block.

[0504] DM may be a candidate mode of the current chroma block derived by using an intra prediction mode of a luma block corresponding to a position of the current chroma block.The luma block and the chroma block may be partitioned into the same structure or different structures.

[0505] Fig.19is a diagram for explaining the position of a luma block used for configuring a candidate mode of a current chroma block according to an embodiment of the present invention.

[0506] exist Fig.19 In this case, the dark dashed line represents the current chrominance block as the prediction target, and the thick solid line represents the corresponding luminance block. In addition, the thin solid line represents the partition structure of the luminance block.

[0507] exist Fig.19 In the example shown in , in order to configure the candidate mode of the current chroma block, at least one of the sample positions A, B and C of the corresponding chroma block may be used.

[0508] The prediction mode of the luma block may be expressed as IntraPredModeY. For example, the prediction mode of the luma block sample corresponding to position A may be expressed as IntraPredModeY[xCb][yCb], and the prediction mode of the luma block sample corresponding to position B may be expressed as IntraPredModeY[xCb+cbWidth / 2][yCb+cbHeight / 2]. The prediction mode of the luma block sample corresponding to position C may be expressed as IntraPredModeY[xCb+cbWidth / 2-1][yCb+cbHeight / 2-1]. Here, xCb and yCb may represent the upper left position of the chroma block corresponding to the upper left position of the luma block within the current picture. In addition, cbWidth and cbHeight may represent the width and height of the luma block corresponding to the current chroma block.

[0509] For example, if the size of the current chroma block is 16×8 in the YUV4:2:0 format, cbWidth and cbHeight may be calculated as 32×16, respectively.

[0510] Table 1 represents candidate modes of a chroma block according to a prediction mode of a luminance block corresponding to a current chroma block.

[0511] Table 1

[0512]

[0513] For example, when the prediction mode of the corresponding luminance block is planar mode, the candidate mode list of the current chrominance block may include vertical diagonal mode (mode 66), vertical mode (mode 50), horizontal mode (mode 18), DC mode (mode 1) and planar mode (mode 0).

[0514] For example, when the prediction mode of the corresponding luma block is the vertical mode, the candidate mode list of the current chroma block may include at least one of a planar mode, a vertical diagonal mode, a horizontal mode, a DC mode, and a vertical mode.

[0515] The encoder / decoder may generate a prediction block by using a candidate mode list of a current chroma block and a reference line index of a luma block corresponding to the current chroma block.

[0516] for Fig. 20 At least one of the positions of the corresponding luminance block shown in , the reference line index of the luminance block can be used to determine the reference line to be used for prediction of the current chrominance block. Here, the position of the neighboring block to be used can be determined differently according to the color format.

[0517] The reference line index of the luma block may be represented as IntraLumaRefLineIdx. The reference line index of the current chroma block may be represented as IntraChromaRefLineIdx. IntraLumaRefLineIdx and IntraChromaRefLineIdx may be any positive integer including 0, respectively.

[0518] For example, in the YUV4:4:4 format or the YUV4:2:2 format, IntraChromaRefLineIdx may be derived as IntraLumaRefLineIdx. Here, the current chroma block and the corresponding luma block may use the same number of reference lines. In addition, the maximum values ​​of the reference line indexes may also be the same. In this case, information about IntraChromaRefLineIdx may not be signaled through the bitstream. IntraChromaRefLineIdx may be implicitly derived by using IntraLumaRefLineIdx.

[0519] For example, in the YUV4:2:0 format, IntraChromaRefLineIdx may be derived as a floor(IntraLumaRefLineIdx / 2) value. Floor() may represent a function that discards the decimal portion of a number. Here, the number of reference lines of the current chroma block may be 1 / 2 of the number of reference lines of the corresponding luminance block. In addition, the maximum value of the reference line index of the current chroma block may be 1 / 2 of the maximum value of the reference line index of the corresponding luminance block. In this case, information about IntraChromaRefLineIdx may not be signaled through the bitstream. IntraChromaRefLineIdx may be implicitly derived by using IntraLumaRefLineIdx.

[0520] Fig. 20 A diagram for explaining a reference line of a current chrominance block and a reference line of a corresponding luminance block in the YUV4:4:4 format.

[0521] For example, when the prediction mode of the corresponding luma block is the planar mode and the first reference line is used, in other words, when IntraPredModeY is the planar mode and IntraLumaRefLineIdx is the first value, the candidate mode list of the current chroma block may be configured by including at least one of the vertical diagonal mode, the vertical mode, the horizontal mode, the DC mode, and the planar mode. In addition, the first reference line (reference line 0) of the current chroma block may be used for prediction.

[0522] For example, when the prediction mode of the corresponding luma block is a vertical mode and a second reference line is used, in other words, when IntraPredModeY is a vertical mode and IntraLumaRefLineIdx is a second value, the candidate mode list of the current chroma block may be configured by including at least one of a plane mode, a vertical diagonal mode, a horizontal mode, a DC mode, and a vertical mode. In addition, a second reference line (reference line 1) of the current chroma block may be used for prediction.

[0523] For example, when the prediction mode of the corresponding luma block is a horizontal mode and a third reference line is used, in other words, when IntraPredModeY is a horizontal mode and IntraLumaRefLineIdx is a third value, the candidate mode list of the current chroma block may be configured by including at least one of a plane mode, a vertical mode, a vertical diagonal mode, a DC mode, and a horizontal mode. In addition, the third reference line (reference line 2) of the current chroma block may be used for prediction.

[0524] For example, when the prediction mode of the corresponding luminance block is the DC mode and the fourth reference line is used, in other words, when IntraPredModeY is the DC mode and IntraLumaRefLineIdx is the fourth value, the candidate mode list of the current chrominance block may be configured by including at least one of the plane mode, the vertical mode, the horizontal mode, the vertical diagonal mode, and the DC mode. In addition, the fourth reference line (reference line 3) of the current chrominance block may be used for prediction.

[0525] Table 2 shows a method of configuring the candidate mode list of the current chroma block when the current chroma block is LM (linear mode) (ie, when cclm_enabled_flag is the second value).

[0526] Table 2

[0527]

[0528] Referring to Table 2, in order to configure the candidate mode of the current chrominance block, at least one of LM and DM using the prediction mode of the corresponding luminance block may be used.

[0529] LM is a mode for predicting pixel values ​​of a current chrominance block by using encoded / decoded pixel values ​​of a corresponding luminance block corresponding to the current chrominance block.

[0530] Prediction according to LM can be performed by using the following equation (1).

[0531] Equation (1): pred C (i,j)=a*rec L (i,j)+b

[0532] In equation (1), pred C (i, j) can represent the current chrominance block, and rec L (i, j) may represent a corresponding luma block reconstructed. a and b may be derived based on neighboring blocks adjacent to the current chroma block and neighboring blocks of the corresponding luma block. Specifically, a and b may be derived by using a correlation between neighboring pixels of the corresponding luma block and neighboring pixels of the current chroma block or by using a maximum value and a minimum value of neighboring pixels to derive a and b, respectively, to derive a linear regression pattern or a linear model.

[0533] To derive a and b, information about at least one of neighboring samples of the current chrominance block, neighboring samples of the corresponding luma block, and a reference line index of the corresponding luma block may be used. Here, the position of the neighboring block to be used may be determined differently according to the color format.

[0534] For example, in the YUV4:4:4 format or the YUV4:2:2 format, a reference line at the same position as a reference line of a corresponding luma block indicated by a reference line index of the corresponding luma block may also be used for the current chroma block.

[0535] For example, in the YUV4:2:0 format, the reference line index (IntraChromaRefLineIdx) of the current chroma block may be derived as a value of floor(IntraLumaRefLineIdx / 2). In addition, when only some samples (e.g., even-numbered samples) in the corresponding reference line are used, the number of luma samples and the number of chroma samples may be consistent with each other. In other words, when four luma samples correspond to one chroma sample, one luma sample may be extracted from the four luma samples and used. Alternatively, the value of one representative luma sample may be derived by using statistical values ​​of some or all of the four luma samples. Here, the statistical value may be at least one of an average value, a maximum value, a minimum value, and a median value.

[0536] For example, by deriving an average value or a weighted average value for a plurality of luma samples, downsampling may be performed on the plurality of luma samples. The sample values ​​obtained by downsampling may be representative luma sample values ​​for the plurality of luma samples. The plurality of luma samples may include a luma sample at a target position and two luma samples located to the left and to the right of the luma sample. Alternatively, the plurality of luma samples may include a luma sample at a target position and two luma samples located above and below the luma sample. Alternatively, the plurality of luma samples may include a luma sample at a target position and four luma samples located to the left, to the right, above and below the luma sample. However, the above examples are not exhaustive, and the plurality of luma samples may include a luma sample at a target position and N neighboring samples.

[0537] Downsampling may also be applied to neighboring samples of a luma block corresponding to the current chroma block. In addition, among the sample values ​​obtained by downsampling the neighboring samples of the luma block, the maximum value and the minimum value may be used to derive parameters a and b of the linear model. Here, an average value of a first maximum value and a second maximum value among the downsampled sample values ​​may be determined as the maximum value. In addition, an average value of a first minimum value and a second minimum value among the downsampled samples may be determined as the minimum value.

[0538] Fig.21 is a diagram for explaining neighboring sample points used to derive a linear regression model or a linear model in the YUV4:2:0 format.

[0539] Reference Fig.21 , to derive parameters a and b of a linear regression model or a linear model, the encoder / decoder may use a reference line indicated by the same index as the reference line index N for the corresponding luma block of the current chroma block.

[0540] For example, when the corresponding luminance block uses the first reference line (reference line 0) or the second reference line (reference line 1), that is, when IntraLumaRefLineIdx is the first value or the second value, a and b can be derived by using the first reference line of the current chrominance block.

[0541] For example, when the corresponding luminance block uses the third reference line (reference line 2) or the fourth reference line (reference line 3), that is, when IntraLumaRefLineIdx is the third value or the fourth value, a and b can be derived by using the second reference line of the current chrominance block.

[0542] For example, when predicting by using reference line 0 Fig.21When a luma block is obtained, a linear regression mode or a linear mode may be derived by using a reference line 0 of the luma block and a reference line 0 of the chroma block. Here, the luma samples corresponding to the neighboring sample c0,0 of the current chroma block may be (y0,0), (y0,1), (y1,0), and (y1,1). As described above, a representative luma sample value may be derived from the four luma samples.

[0543] Here, according to the intra prediction mode of the current chroma block, the method of predicting LM can be determined differently. The intra prediction mode of the current chroma block can be represented as IntraPredModeC. For example, when IntraPredModeC is a first value, the LT_CCLM prediction method can be implemented. In addition, when IntraPredModeC is a second value, the L_CCLM prediction method can be implemented. In addition, when IntraPredModeC is a third value, the T_CCLM prediction method can be implemented. In Table 2, the first value, the second value, and the third value can be 81, 82, and 83, respectively.

[0544] The LT_CCLM prediction method may represent a method of deriving parameters of a linear mode by using the upper neighboring block and the left neighboring block of the current chroma block and the upper neighboring block and the left neighboring block of the corresponding luminance block. The L_CCLM prediction method may represent a method of deriving parameters of a linear mode by using the left neighboring block of the current chroma block and the left neighboring block of the corresponding luminance block. The T_CCLM prediction method may represent a method of deriving parameters of a linear mode by using the upper neighboring block of the current chroma block and the upper neighboring block of the corresponding luminance block.

[0545] For example, when the current chroma block uses the L_CCLM prediction method and the corresponding luminance block uses the first reference line or the second reference line, that is, when IntraPredMode is the second value and IntraLumaRefLineIdx is the first value or the second value, the parameters a and b of the linear model can be derived by using the first reference line adjacent to the left side of the current chroma block.

[0546] For example, when the current chroma block uses the T_CCLM prediction method and the corresponding luminance block uses the third reference line or the fourth reference line, that is, when IntraPredMode is the third value and IntraLumaRefLineIdx is the third value or the fourth value, the parameters a and b of the linear model can be derived by using the second reference line adjacent to the upper end of the current chroma block.

[0547] For intra prediction of the current luminance block, some of the reference lines 0 to 3 may be used. In addition, some of the reference lines 0 to 3 may be used to derive parameters a and b of CCLM.

[0548] In this case, the available reference lines for intra prediction of the current luminance block may be the same as the available reference lines for deriving the parameters of the CCLM. For example, in both cases, only three reference lines of reference line 0 to reference line 2 may be used. In other words, the available reference lines for intra prediction of the current luminance block may be reference lines 0 to reference line 2, and the available reference lines for deriving the parameters of the CCLM may be reference lines 0 to reference line 2.

[0549] Hereinafter, signaling (entropy encoding / decoding) of information about an intra prediction mode will be explained.

[0550] The encoder / decoder may entropy encode / decode information about the intra prediction mode. The information about the intra prediction mode may include at least one of a reference line index, an MPM flag, the remaining modes, and an MPM index. The encoder / decoder may entropy encode / decode a reference line index representing a reference line for prediction of the current block. The corresponding index may be represented as intra_luma_ref_idx. The maximum value of the reference line index may be determined based on the number of available reference lines. When the number of reference lines is N (an arbitrary positive integer), if the reference line index is the Nth value, it may indicate that the Nth reference line is used.

[0551] The encoder / decoder may entropy encode / decode an MPM flag indicating whether there is a mode identical to the prediction mode of the current block in the MPM list. The corresponding flag may be represented as intra_luma_mpm_flag. When intra_luma_mpm_flag is a first value, it may indicate that there is no mode identical to the prediction mode of the encoding / decoding target block in the MPM list. When intra_luma_mpm_flag is a second value, it may indicate that there is a mode identical to the prediction mode of the encoding / decoding target block in the MPM list.

[0552] When intra_luma_mpm_flag is present and the corresponding flag value is the first value, the encoder / decoder may additionally entropy encode / decode the remaining modes. The remaining modes may represent modes that do not belong to the MPM list. The remaining modes may be represented as intra_luma_mpm_remainder. The encoder / decoder may derive the prediction mode of the current block by using the MPM flag, the remaining modes, and the MPM list.

[0553] When intra_luma_mpm_flag is present and the corresponding flag value is the second value, the encoder / decoder may additionally entropy encode / decode the MPM index. The MPM index is an index indicating which candidate mode among the modes in the MPM list is the same as the prediction mode of the encoding / decoding target block. The MPM index may be represented as intra_luma_mpm_idx. The encoder / decoder may derive the prediction mode of the current block by using the MPM flag, the MPM index, and the MPM list.

[0554] In the above embodiment, the first value may represent 0, the second value may represent 1, the third value may represent 2, and the Nth value may represent N-1.

[0555] Whether to perform CCLM for the current chroma block may be determined based on at least one of the size (area) of the current block, the height and the width of the current block. CCLM (cross-component linear mode) may represent LM (linear mode). CCLM may include at least one of LT_CCLM, L_CCLM and T_CCLM.

[0556] LT_CCLM is a mode for deriving parameters (a and b) of a linear mode by using at least one sample of the reconstructed left neighboring block and at least one sample of the reconstructed upper neighboring block. LT_CCLM may also be expressed as INTRA_LT_CCLM.

[0557] L_CCLM is a mode for deriving parameters of a linear mode by using at least one sample of samples of a reconstructed left neighboring block. L_CCLM may also be expressed as INTRA_L_CCLM.

[0558] T_CCLM is a mode for deriving parameters of a linear mode by using at least one sample of samples of a reconstructed upper neighboring block. T_CCLM may also be expressed as INTRA_T_CCLM.

[0559] In each of LT_CCLM, L_CCLM, and T_CCLM, the current chrominance block may be predicted from the reconstructed corresponding luminance block by using the derived linear model.

[0560] Whether CCLM can be performed on the current block may be determined based on various encoding / decoding information.

[0561] For example, when information signaled through a parameter set (SPS, PPS, etc.) or a header indicates that CCLM is unavailable, CCLM may not be performed on all blocks that refer to the corresponding parameter set.

[0562] When the chroma block and the luma block are partitioned into a single tree structure, it may be determined that the CCLM is applicable to the current block.

[0563] In addition, whether CCLM is available may be determined based on the type of the slice to which the current block belongs. For example, when the slice to which the current block belongs is a P slice or a B slice, it may be determined that CCLM is available for the current block.

[0564] In addition, when the size of the coding tree block is smaller than 64×64, it may be determined that CCLM is applicable to the current block.

[0565] When the chroma block and the luminance block are partitioned into a single tree structure, if the chroma block obtained by partitioning is smaller than the minimum chroma block size, partitioning may not be performed for the chroma block. For example, the minimum chroma block size may be 16 samples. In other words, the minimum chroma block may be a block including 16 samples. Information about the size of the minimum chroma block may be predefined in the encoder / decoder. Optionally, information about the size of the minimum chroma block may be sent by a signal and included in the bitstream. Information about the minimum chroma block size may be expressed in at least one form of a block area, the number of samples included in the block, the width and / or the height of the block.

[0566] For example, when the current block is an 8×4 chroma block, if the current block is partitioned into a ternary tree structure, a 2×4 chroma block can be obtained. In other words, a chroma block including 8 samples less than 16 samples can be obtained. Therefore, ternary tree partitioning for an 8×4 chroma block can be prohibited.

[0567] For example, when the current block is an 8×4 chroma block, if the current block is partitioned into a binary tree structure, two 4×4 chroma blocks can be obtained. Therefore, the two obtained chroma blocks each include 16 samples. Therefore, binary tree partitioning for 8×4 chroma blocks may not be prohibited.

[0568] In the above example, the restriction on partitioning may not apply to the luma block corresponding to the current chroma block. In other words, according to the restriction on partitioning of the chroma block, the partition structures of the chroma block and the luma block may be determined differently.

[0569] When the chroma block and the luminance block are partitioned into a dual tree structure, the partitioning for the chroma block whose size is smaller than the predetermined size may be performed restrictively. Information about the predetermined size may be predefined in the encoder / decoder. Optionally, the information about the predetermined size may be included in the bitstream and sent with a signal. The information about the predetermined size may be expressed in the form of at least one of a block area, the number of samples included in the block, and the width and / or height of the block.

[0570] For example, when the width (or height) of the current chroma block is 4, quadtree partitioning may be prohibited. For example, when the current chroma block includes 16 or fewer samples, binary tree partitioning may be prohibited. For example, when the current chroma block includes 32 or fewer samples, ternary tree partitioning may be prohibited.

[0571] The intra prediction mode may be signaled only when the size of the current chroma block is greater than a predetermined size. When the size of the current chroma block is equal to or less than a predetermined size, the intra prediction mode of the block may be determined as a DC mode. Here, the predetermined size may be the size of a block including 8 samples.

[0572] As described above, in the single tree structure and the dual tree structure, 2×2, 4×2, or 2×4 chroma blocks can be removed by limiting the partitioning of the chroma blocks. In other words, the chroma blocks partitioned into 2×2, 4×2, or 2×4 can be prohibited. Therefore, the complexity of the hardware can be reduced.

[0573] In addition, compared with a predetermined threshold, it can be determined whether CCLM prediction is performed for the current block. For example, CCLM may not be performed for blocks whose size is equal to or less than the predetermined threshold. The predetermined threshold may be predefined in the encoder / decoder. Optionally, information about the predetermined threshold may be signaled at a higher level (parameter set or header) of the block. For example, the predetermined threshold may be signaled, wherein the predetermined threshold is included in at least one of a VPS, a DPS, a SPS, a PPS, an APS, a parallel block group, a parallel block header, and a slice header. The predetermined threshold may be compared with the size of the current block or the area of ​​the current block. Optionally, the predetermined threshold may be compared with the height and width of the current block and / or the height of the shorter side. Optionally, the predetermined threshold may be compared with at least one of the block area, the number of samples included in the block, the width and / or the height of the block.

[0574] For example, when the threshold is smaller, CCLM may be performed for the corresponding block. In addition, when the threshold is equal to or larger, CCLM may not be performed for the corresponding block. For example, when both the width and height of the block are 64, CCLM may be applied to the corresponding block. Alternatively, when the width of the block is 64 and the height is 32, CCLM may be applied to the corresponding block.

[0575] For example, the threshold value may be defined as a formula log2(A) or log2(A)-log2(M). When the area of ​​the current chroma block or the corresponding luminance block is less than A or equal to or less than A, CCLM prediction for the current chroma block may be skipped. A may be the area of ​​the luminance block or the area of ​​the chroma block for which CCLM will be prohibited. The area of ​​the block may be calculated by multiplying the width and height of the block. M may be the area of ​​the smallest available block. A and M may be positive integers including 0, respectively.

[0576] Whether CCLM is performed according to the size (area) of each block may be signaled through a parameter set or a header. Alternatively, whether CCLM is performed according to the size of a block may be predefined in an encoder / decoder and may be used, thus being predetermined.

[0577] For example, the threshold may be defined as a formula log2(A) or log2(A)-log2(M). When the shorter of the width and height of the current chroma block or the corresponding luminance block is less than A or equal to or less than A, CCLM prediction for the current chroma block may be skipped. A may be the width or height of the chroma block or the luminance block, and M may be the width or height of the smallest available block or the shorter of the width and height.

[0578] Whether CCLM is performed according to the shorter of the width and height of each block may be signaled through a parameter set or a header. Alternatively, a predetermined whether CCLM is performed according to the width (or height) of a block may be used.

[0579] In the above embodiment, whether CCLM prediction is performed can be indicated by a flag indicating whether CCLM prediction is allowed. For example, when CCLM prediction is not performed, the flag indicating whether CCLM prediction is allowed may have a first value (e.g., 0). In addition, when CCLM prediction is performed, the flag indicating whether CCLM prediction is allowed may have a second value (e.g., 1).

[0580] For example, when the size (area) of the current chrominance block or the corresponding luminance block is less than N×M, equal to N×M, or equal to or less than N×M (a predefined value), the encoder / decoder may skip CCLM prediction. Here, N and M may be positive integers other than 0, respectively. Here, N×M may be, for example, 4×2, 4×4, or 2×4.

[0581] For example, when the shorter of the width and height of the current chroma block or the corresponding luma block is less than N or equal to or less than N (which is a predefined value), the encoder / decoder may skip CCLM prediction.

[0582] Skipping CCLM prediction may mean that CCLM prediction is not performed. Alternatively, skipping CCLM prediction may mean that CCLM is set not to be performed in the encoder / decoder. When CCLM prediction is not skipped, this may mean that CCLM is performed for the corresponding block.

[0583] When entropy encoding / decoding the intra chroma prediction mode, entropy encoding / decoding of information about at least one or more CCLMs may be skipped according to the size (area) of a block or the height and width of the block.

[0584] Skipping entropy encoding / decoding may mean that information about CCLM of the corresponding block is not entropy encoded / decoded. In addition, if it is not a corresponding block, it may mean that information about CCLM is entropy encoded / decoded.

[0585] For example, when entropy encoding / decoding is performed for a block having an area equal to or less than a threshold, at least one of binarization / debinarization and entropy encoding / decoding may be performed in addition to at least one CCLM in the intra chroma prediction mode. For a block having a size greater than the threshold, at least one of binarization / debinarization and entropy encoding / decoding may be performed without excluding at least one CCLM in the intra chroma prediction mode.

[0586] For example, when entropy encoding / decoding is performed for a block whose width, height, or the shorter of both width and height is less than a threshold value or is equal to or less than a threshold value, at least one of binarization / debinarization and entropy encoding / decoding may be performed in addition to at least one CCLM in the intra chroma prediction mode. In the opposite case, at least one of binarization / debinarization and entropy encoding / decoding may be performed without excluding at least one or more CCLMs in the intra chroma prediction mode.

[0587] The threshold may be signaled by being defined in a parameter set or header, or may be a predefined value in the encoder / decoder.

[0588] Table 3 is an embodiment showing the relationship between the index of the intra prediction mode and the intra prediction mode.

[0589] Table 3

[0590] Intra prediction mode Associated name 0 Intraplane 1 Intra-frame DC 2..66 In-frame angle 2..In-frame angle 66 81..83 Intra LT CCLM, Intra L CCLM, Intra T CCLM

[0591] For example, when the index for the intra chroma prediction mode is 0, a planar prediction mode may be indicated. For example, when the index for the intra chroma prediction mode is 1, a DC prediction mode may be indicated. For example, when the index for the intra chroma prediction mode is 2 to 66, a prediction mode according to a corresponding direction may be indicated. For example, when the index for the intra chroma prediction mode is 81 to 83, INTRA LT CCLM, INTRA L CCLM, INTRA T CCLM may be indicated.

[0592] Table 4 is an embodiment showing the value of the syntax element (intra_chroma_pred_mode) for the intra chroma prediction mode (the value encoded / decoded in the entropy encoding / decoding process) and the index for the corresponding intra chroma prediction mode. Here, the index for the intra chroma prediction mode may represent the index present in Table 3.

[0593] Table 4

[0594]

[0595] Table 5 shows an embodiment of the index of the intra prediction mode for the chroma block and the corresponding binary bit string when CCLM is indicated as unavailable at the sequence, picture, tile, slice or CTU level.

[0596] Table 5

[0597] When sps_cclm_enabled_flag is equal to 0, the binarization of intra_chroma_pred_mode

[0598]

[0599] For example, when the intra prediction mode of the chroma block is DM (intra_chroma_pred_mode=4), the shortest binary bit string may be allocated. When the intra prediction mode of the chroma block is not DM (intra_chroma_pred_mode≠4), a binary bit string of equal length may be allocated. In other words, the length of the binary bit string corresponding to a mode other than DM may be greater than the length of the binary bit string corresponding to DM.

[0600] Table 6 is an example showing an index of an intra prediction mode for a chroma block and a corresponding binary bit string when CCLM is shown as available at a sequence, picture, tile, slice, or CTU level and whether CCLM is performed is restricted according to the area of ​​the block.

[0601] Table 6 Binarization for intra_chroma_pred_mode when sps_cclm_enabled_flag is equal to 1

[0602]

[0603] The second column of Table 6 is an embodiment of a binary bit string corresponding to an intra-frame chroma prediction mode when the current block is a relatively large block (i.e., the area of ​​the chroma block exceeds the threshold value (α)) and at least one CCLM in the CCLM is allowed. When CCLM is allowed, this means that the encoder / decoder can use CCLM for chroma blocks whose size exceeds the threshold. In this case, the encoder / decoder can entropy encode / decode the intra-frame chroma prediction mode including at least one CCLM in the CCLM for the corresponding block.

[0604] The third column of Table 6 is an embodiment in which the binary bit string corresponds to the intra-frame chroma prediction mode when the current block is a relatively small block (i.e., the area of ​​the chroma block is equal to or less than the threshold value (α)) and at least one CCLM in the CCLM is restricted. When the CCLM is restricted, this means that the encoder / decoder may not use the CCLM for chroma blocks equal to or less than the threshold value. In this case, the encoder / decoder may entropy encode / decode the intra-frame chroma prediction mode that does not include at least one CCLM in the CCLM for the corresponding block.

[0605] Since CCLM is not performed for a relatively small block, a binary bit string as a binarization result of modes 0 to 3 (planar, vertical, horizontal, DC, or INTRA_ANGULAR66) may be changed. In other words, as shown in Table 6, a binary bit string of a corresponding mode for a relatively small block may be shorter than a binary bit string of a corresponding mode for a relatively large block.

[0606] Table 7 is an embodiment of describing an entropy encoding / decoding method of a binary bit string for intra chroma prediction mode.

[0607] Table 7

[0608]

[0609] As described in Table 7, the entropy encoding / decoding method (whether bypass encoding or normal encoding) for the binary bit string may be determined differently based on information about whether CCLM signaled at the sequence, picture, tile, slice, or CTU level is available (sps_cclm_enabled_flag), whether the area of ​​the chroma block (nTbW*nTbH) is equal to or less than the threshold (α), and / or whether bin 2 is 0 (i.e., whether the mode of the current block is INTRA_L_CCLM or INTRA_T_CCLM). For example, in the case of normal encoding, there may be a value corresponding to each binIdx, and a context model may be adaptively selected by using the value.

[0610] Table 8 is another embodiment showing the relationship between ccm_mode_flag, ccm_mode_idx, intra_chroma_pred_mode, and lumaIntraPredMode, which are entropy encoded / decoded when sps_cclm_enabled_flag is 1.

[0611] Table 8

[0612]

[0613] In Table 8, ccm_mode_flag is 0, intra_chroma_pred_mode=4 is DM, ccm_mode_flag is 1, ccm_mode_idx=0 is LT_CCLM, ccm_mode_flag is 1, ccm_mode_idx=1 is L_CCLM, ccm_mode_flag is 1, and ccm_mode_idx=2 may indicate T CCLM.

[0614] As another example of Table 5, Table 9 is another embodiment showing the index of the intra prediction mode for the chroma block and the corresponding binary bit string.

[0615] Table 9 is generally applicable to the cases where sps_cclm_enabled_flag is 0 and 1 respectively.

[0616] Table 9

[0617] Value of intra_chroma_pred_mode Binary bit string 0 100 1 101 2 110 3 111 4 0

[0618] In Table 9, the first bit indicates whether the intra prediction mode is DM (0) or not DM (1). When the intra prediction mode is a mode but not DM, the next bit is the same as explained with reference to Table 5.

[0619] In the block partitioning method, the present invention can be applied to implicitly perform encoding / decoding not only in a dual tree structure or a separate tree structure (wherein the block partitioning method for the luminance component and the chrominance component can have a tree structure independent of each other) but also in a single tree structure. Alternatively, the present invention can be applied only in a dual tree structure or a separate tree structure. According to the present invention, the encoding / decoding throughput for relatively small blocks can be improved.

[0620] The above-described embodiments may be performed in the same manner in an encoder and a decoder.

[0621] At least one embodiment or a combination of the above embodiments may be used to encode / decode a video.

[0622] The order in which the above-described embodiments are applied may be different between an encoder and a decoder, or the order in which the above-described embodiments are applied may be the same in an encoder and a decoder.

[0623] The above-described embodiments may be performed on each luminance signal and each chrominance signal, or may be performed identically on the luminance signal and the chrominance signal.

[0624] The block form to which the above-described embodiment of the present invention is applied may have a square form or a non-square form.

[0625] The above-mentioned 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, a current block, a coding unit, a prediction unit, a transform unit, a unit, and a current unit. Here, the size may be defined as a minimum size or a maximum size or both a minimum size and a maximum size so that the above-mentioned embodiments are applied, or the size may be defined as a fixed size to which the above-mentioned embodiments are applied. In addition, in the above-mentioned embodiments, the first embodiment may be applied to a first size, and the second embodiment may be applied to a second size. In other words, the above-mentioned embodiments may be applied in combination according to the size. In addition, the above-mentioned embodiments may be applied when the size is equal to or greater than the minimum size and equal to or less than the maximum size. In other words, the above-mentioned embodiments may be applied when the block size is included in a specific range.

[0626] For example, when the size of the current block is 8×8 or larger, the above embodiment may be applied. For example, when the size of the current block is only 4×4, the above embodiment may be applied. For example, when the size of the current block is 16×16 or smaller, the above embodiment may be applied. For example, when the size of the current block is equal to or larger than 16×16 and equal to or smaller than 64×64, the above embodiment may be applied.

[0627] The above-described embodiments of the present invention may be applied according to time layers. In order to identify the time layers to which the above-described embodiments may be applied, a corresponding identifier may be signaled, and the above-described embodiments may be applied to the specified time layers identified by the corresponding identifier. Here, the identifier may be defined as the lowest layer or the highest layer or both the lowest layer and the highest layer to which the above-described embodiments may be applied, or may be defined as a specific layer to which the embodiments may be applied. In addition, a fixed time layer to which the embodiments may be applied may be defined.

[0628] For example, when the temporal layer of the current image is the lowest layer, the above embodiment may be applied. For example, when the temporal layer identifier of the current image is 1, the above embodiment may be applied. For example, when the temporal layer of the current image is the highest layer, the above embodiment may be applied.

[0629] A slice type or a tile group type to which the above-described embodiments of the present invention are applied may be defined, and the above-described embodiments may be applied according to the corresponding slice type or tile group type.

[0630] In the above embodiments, the method is described based on a flowchart having a series of steps or units, but the present invention is not limited to the order of the steps, but some steps may be performed simultaneously with other steps or in a different order. In addition, it should be understood by those skilled in the art that the steps in the flowchart are not mutually exclusive, and other steps may be added to the flowchart, or some steps may be deleted from the flowchart without affecting the scope of the present invention.

[0631] The embodiments include various aspects of the examples. All possible combinations for various aspects may not be described, but those skilled in the art will be able to recognize different combinations. Therefore, the present invention may include all substitutions, modifications and changes within the scope of the claims.

[0632] Embodiments of the present invention can be implemented in the form of program instructions that can be executed by various computer components and recorded in a computer-readable recording medium. The computer-readable recording medium may include a separate program instruction, a data file, a data structure, etc. or a combination of program instructions, data files, data structures, etc. The program instructions recorded in the computer-readable recording medium may be specially designed and constructed for the present invention, or known to those of ordinary skill in the field of computer software technology. Examples of computer-readable recording media include magnetic recording media (such as hard disks, floppy disks, and tapes), optical data storage media (such as CD-ROMs or DVD-ROMs), magneto-optical media (such as floppy disks), and hardware devices (such as read-only memory (ROM), random access memory (RAM), flash memory, etc.) that are specifically constructed to store and implement program instructions. Examples of program instructions include not only machine language codes formatted by a compiler, but also high-level language codes that can be implemented by a computer using an interpreter. The hardware device may be configured to be operated by one or more software modules to perform processing according to the present invention, or vice versa.

[0633] Although the present invention has been described according to specific items such as detailed elements and limited embodiments and drawings, they are provided only to help a greater understanding of the present invention, and the present invention is not limited to the above embodiments. It will be appreciated by those skilled in the art that various modifications and changes can be made from the above description.

[0634] Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and the entire scope of the claims and their equivalents will fall within the scope and spirit of the present invention.

[0635] Industrial Applicability

[0636] The present invention can be used to encode or decode images.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising: deriving a value of a first flag indicating whether an intra prediction mode of a current block is a planar mode; Derivation of an intra prediction mode of the current block based on a value of the first flag; generating a prediction block of the current block by performing intra prediction for the current block based on the intra prediction mode; and generating a reconstructed block of the current block based on the predicted block of the current block, The step of deriving the value of the first flag is performed based on whether the reference sample line used for intra-frame prediction of the current block is a first reference sample line directly adjacent to the current block.

2. The image decoding method according to claim 1, in, In the case where the reference sample line used for intra prediction of the current block is the first reference sample line, the step of deriving the value of the first flag is performed by decoding the first flag obtained from the bitstream.

3. The image decoding method according to claim 1, in, In a case where the reference sample line used for intra prediction of the current block is not the first reference sample line, the first flag is not obtained from the bitstream, and the value of the first flag is inferred to indicate that the intra prediction mode of the current block is not the planar mode.

4. The image decoding method according to claim 1, in, When the first flag indicates that the intra-frame prediction mode of the current block is not a planar mode, the step of deriving the intra-frame prediction mode of the current block includes: deriving a predetermined number of MPM candidate modes based on a first intra-frame prediction mode of a first neighboring block of the current block and a second intra-frame prediction mode of a second neighboring block of the current block.

5. The image decoding method according to claim 4, in, In case that the first intra prediction mode of the first neighboring block or the second intra prediction mode of the second neighboring block is unavailable, the planar mode is used instead of the unavailable intra prediction mode of the neighboring blocks.

6. The image decoding method according to claim 4, in, In the case where both the first intra prediction mode and the second intra prediction mode are non-directional modes, the predetermined number of MPM candidate modes include a DC mode, a vertical mode, a horizontal mode, a mode of vertical mode-4, and a mode of vertical mode+4.

7. The image decoding method according to claim 4, in, In a case where both the first intra prediction mode and the second intra prediction mode are different directional modes from each other, the predetermined number of MPM candidate modes include the first intra prediction mode and the second intra prediction mode, and The predetermined number of MPM candidate modes further includes an additional MPM candidate mode determined based on a difference between the first intra prediction mode and the second intra prediction mode.

8. The image decoding method according to claim 4, in, In a case where one of the first intra prediction mode and the second intra prediction mode is a directional mode and the other is a non-directional mode, the predetermined number of MPM candidate modes include the directional mode and modes adjacent to the directional mode, but do not include the non-directional mode.

9. An image encoding method performed by an image encoding device, the image encoding method comprising: Determining an intra prediction mode for a current block; generating a prediction block of the current block by performing intra prediction for the current block based on the intra prediction mode; generating a residual block of the current block based on the prediction block of the current block; encoding a first flag indicating whether the intra prediction mode of the current block is a planar mode; and encoding the intra prediction mode of the current block based on the value of the first flag, The step of encoding the first flag is performed based on whether the reference sample line used for intra-frame prediction of the current block is the first reference sample line directly adjacent to the current block.

10. A non-transitory computer-readable recording medium storing a bit stream generated by an image encoding method performed by an image encoding device, the image encoding method comprising: Determining an intra prediction mode for a current block; generating a prediction block of the current block by performing intra prediction for the current block based on the intra prediction mode; generating a residual block of the current block based on the prediction block of the current block; encoding a first flag indicating whether the intra prediction mode of the current block is a planar mode; and encoding the intra prediction mode of the current block based on the value of the first flag, The step of encoding the first flag is performed based on whether the reference sample line used for intra-frame prediction of the current block is the first reference sample line directly adjacent to the current block.

Images