Image encoding / decoding method and method for transmitting bit stream

Abstract

Disclosed herein are an image encoding / decoding method and a method of transmitting a bitstream. An image decoding method according to the present invention comprises: acquiring symmetric motion vector difference mode available information from a bitstream; obtaining first prediction direction zero motion vector difference information from the bit stream; acquiring symmetric motion vector difference mode information of the current block from the bitstream based on the symmetric motion vector difference mode available information and the first prediction direction zero motion vector difference information; obtaining first prediction direction reference picture index information, second prediction direction reference picture index information and a first prediction direction motion vector difference value based on the symmetric motion vector difference mode information; and generating a prediction block of the current block by using at least one of the first prediction direction reference picture index information, the second prediction direction reference picture index information, and the first prediction direction motion vector difference.

Description

[0001] This application is a divisional application of a patent application with application date of March 6, 2020, application number 202080019697.0, and titled “Image encoding / decoding method and method for sending bit stream”. Technical Field

[0002] The present invention relates to an image encoding / decoding method and device, and a recording medium for storing a bit stream. 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, which predict the values ​​of pixels in the current image from the values ​​of pixels in previous or subsequent images; intra-frame prediction techniques, which predict the values ​​of pixels in one area of ​​the current image from the values ​​of pixels in another area of ​​the current image; transform and quantization techniques, which compress the energy of the residual signal; and entropy coding techniques, which assign short codes to frequently occurring pixel values ​​and long codes to less frequently occurring pixel values). Summary of the invention

[0005] Technical issues When a symmetric MVD derivation method is used to improve encoding / decoding efficiency, the present invention may provide a method and apparatus for deriving an MVD by considering an enhanced performance condition.

[0006] An object of the present invention is to provide a method and apparatus for encoding and decoding a picture that improves encoding and decoding efficiency.

[0007] Another object of the present invention is to provide a recording medium storing a bit stream generated by the image decoding method or apparatus according to the present invention.

[0008] Technical Solution An image decoding method according to an embodiment of the present invention includes: obtaining symmetric motion vector difference mode availability information from a bitstream; obtaining zero motion vector difference information in a first prediction direction from the bitstream; obtaining symmetric motion vector difference mode information of a current block from the bitstream based on the symmetric motion vector difference mode availability information and the zero motion vector difference information in the first prediction direction; obtaining reference picture index information in the first prediction direction, reference picture index information in the second prediction direction, and a motion vector difference value in the first prediction direction based on the symmetric motion vector difference mode information; and generating a prediction block of the current block by using at least one of the reference picture index information in the first prediction direction, the reference picture index information in the second prediction direction, and the motion vector difference value in the first prediction direction, wherein the step of obtaining the reference picture index information in the first prediction direction, the reference picture index information in the second prediction direction, and the motion vector difference value in the first prediction direction is obtained by deriving the reference picture index information in the first prediction direction, the reference picture index information in the second prediction direction, and the motion vector difference value in the first prediction direction from the bitstream instead of decoding the bitstream when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode.

[0009] In the image decoding method of the present invention, the first prediction direction is an L1 prediction direction, and the second prediction direction is an L0 prediction direction.

[0010] In the image decoding method of the present invention, the zero motion vector difference information of the first prediction direction indicates that the motion vector difference value of the first prediction direction is not decoded but is derived as (0, 0).

[0011] In the image decoding method of the present invention, zero motion vector difference information of the first prediction direction is obtained at the picture level.

[0012] In the image decoding method of the present invention, symmetric motion vector difference mode availability information is obtained at the sequence level.

[0013] In the image decoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the motion vector difference value in the first prediction direction is derived based on the motion vector difference value in the second prediction direction of the current block.

[0014] In the image decoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0015] In the image decoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0016] In the image decoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the reference picture index information of the first prediction direction and the reference picture index information of the second prediction direction are derived as the index of the short-term reference picture.

[0017] An image encoding method according to an embodiment of the present invention includes: determining symmetric motion vector difference mode availability information; determining zero motion vector difference information in a first prediction direction; encoding the symmetric motion vector difference mode information of a current block based on the symmetric motion vector difference mode availability information and the zero motion vector difference information in the first prediction direction; and determining whether to encode reference picture index information in the first prediction direction, reference picture index information in the second prediction direction, and motion vector difference value in the first prediction direction based on the symmetric motion vector difference mode information, wherein the step of determining whether to encode reference picture index information in the first prediction direction, reference picture index information in the second prediction direction, and motion vector difference value in the first prediction direction is determined as not encoding the reference picture index information in the first prediction direction, reference picture index information in the second prediction direction, and motion vector difference value in the first prediction direction when the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode.

[0018] In the image encoding method of the present invention, the first prediction direction is an L1 prediction direction, and the second prediction direction is an L0 prediction direction.

[0019] In the image encoding method of the present invention, the zero motion vector difference information of the first prediction direction indicates that the motion vector difference value of the first prediction direction is not encoded but is derived as (0, 0).

[0020] In the image encoding method of the present invention, the zero motion vector difference information of the first prediction direction is encoded at the picture level.

[0021] In the image encoding method of the present invention, the symmetric motion vector difference mode availability information is encoded at the sequence level.

[0022] In the image encoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the motion vector difference value in the first prediction direction is derived based on the motion vector difference value in the second prediction direction of the current block.

[0023] In the image encoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0024] In the image encoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0025] In the image encoding method of the present invention, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the reference picture index information of the first prediction direction and the reference picture index information of the second prediction direction are derived as the index of the short-term reference picture.

[0026] A non-temporary computer-readable recording medium storing a bit stream generated by an image encoding method according to an embodiment of the present invention, wherein the image encoding method includes: determining symmetric motion vector difference mode availability information; determining zero motion vector difference information in a first prediction direction; encoding the symmetric motion vector difference mode information of a current block based on the symmetric motion vector difference mode availability information and the zero motion vector difference information in the first prediction direction; and determining whether to encode reference picture index information in the first prediction direction, reference picture index information in the second prediction direction, and motion vector difference value in the first prediction direction based on the symmetric motion vector difference mode information, wherein the step of determining whether to encode the reference picture index information in the first prediction direction, the reference picture index information in the second prediction direction, and the motion vector difference value in the first prediction direction is determined as not encoding the reference picture index information in the first prediction direction, the reference picture index information in the second prediction direction, and the motion vector difference value in the first prediction direction when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode.

[0027] Beneficial Effects According to the present invention, an image encoding / decoding method and apparatus with improved compression efficiency can be provided. When a symmetric MVD derivation method is used, the present invention can improve image encoding / decoding efficiency by providing an MVD derivation method and apparatus taking into account enhanced performance conditions.

[0028] According to the present invention, an image encoding / decoding method and apparatus with enhanced encoding and decoding efficiency can be provided.

[0029] In addition, according to the present invention, a recording medium storing a bit stream generated by the image encoding method or apparatus of the present invention can be provided.

[0030] In addition, according to the present invention, there can be provided a recording medium storing a bit stream received and decoded by the picture decoding apparatus of the present invention and used to reconstruct a picture. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a block diagram showing a configuration of an encoding device according to an embodiment to which the present invention is applied.

[0032] Figure 2 is a block diagram showing a configuration of a decoding device according to an embodiment to which the present invention is applied.

[0033] Figure 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded.

[0034] Figure 4 is a diagram illustrating an intra prediction process.

[0035] Figure 5 is a diagram illustrating an embodiment of an inter-picture prediction process.

[0036] Figure 6 is a diagram illustrating transform and quantization processing.

[0037] Figure 7 is a diagram showing reference samples that can be used for intra prediction.

[0038] Figure 8 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

[0039] Fig. 9 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

[0040] Fig.10 is a diagram showing spatially neighboring blocks of an encoding target block / decoding target block.

[0041] Fig.11 is a diagram showing temporally neighboring blocks of an encoding target block / decoding target block.

[0042] Fig.12 is a diagram for explaining history-based motion vector candidate derivation.

[0043] Figures 13 to 18 is a diagram for explaining various embodiments of the syntax and semantics related to the symmetric MVD mode according to the present invention.

[0044] Fig.19 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.

[0045] Fig. 20 is a diagram for explaining an image encoding method according to an embodiment of the present invention. Detailed Description of the Invention

[0046] Various modifications can be made to the present invention, and there are various embodiments of the present invention. Herein, examples of various embodiments of the present invention will now be provided and described in detail with reference to the accompanying drawings. However, the present invention is not limited thereto. Although the exemplary embodiments may be interpreted as including all modifications, equivalents, or alternatives within the technical concept and technical scope of the present invention. In all aspects, similar reference numerals refer to the same or similar functions. In the drawings, for clarity, the shapes and sizes of elements may be exaggerated. In the following detailed description of the present invention, reference is made to the accompanying drawings, in which specific embodiments in which the present invention may be practiced are shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present disclosure. It should be understood that the various embodiments of the present disclosure, although different, are not necessarily mutually exclusive. For example, specific features, structures, and characteristics described herein in connection with one embodiment may be implemented in other embodiments without departing from the spirit and scope of the present disclosure. Additionally, it should be understood that, without departing from the spirit and scope of the present disclosure, the positions or arrangements of the respective elements within each disclosed embodiment may be modified. Therefore, the following detailed description should not be considered limiting, and the scope of the present disclosure is defined only by the appended claims (along with the full scope of equivalents claimed by the claims, when appropriately interpreted).

[0047] The terms "first", "second", etc. used in the specification may be used to describe various components, but the components should not be construed 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 be similarly named a "first" component. The term "and / or" includes combinations of multiple items or any one of the multiple items.

[0048] 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.

[0049] 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 of the listed components. Therefore, at least two components of each component can be combined to form a component, or a component can be partitioned 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 partitioned are also included in the scope of the present invention.

[0050] 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 elements, but may include additional elements in an embodiment of the present invention or in the scope of the present invention.

[0051] In addition, some components may not be indispensable components for performing the basic functions of the present invention, but rather selective components that only improve the performance thereof. The present invention may be implemented by including only indispensable components for realizing the essence of the present invention without including components for improving performance. Structures that include only indispensable components without including selective components that only improve performance are also included within the scope of the present invention.

[0052] 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.

[0053] 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".

[0054] Hereinafter, the terms "motion picture" and "video" may be used as the same meaning and may be replaced with each other.

[0055] 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 picture.

[0056] Hereinafter, the terms "image", "picture", "frame" and "screen" may be used as the same meaning and may be replaced with each other.

[0057] 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.

[0058] 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.

[0059] In the following, the terms "region" and "segment" are used interchangeably.

[0060] 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.

[0061] 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.

[0062] 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 1.

[0063] Terminology Description Encoder: This refers to the device that performs encoding. In other words, it refers to the encoding device.

[0064] Decoder: refers to a device that performs decoding. In other words, it refers to a decoding device.

[0065] Block: is an M×N array of samples. Here, M and N may represent positive integers, and a block may represent an array of samples 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 when encoding, or a decoding target block that becomes a target when 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.

[0066] Sample: It is the basic unit of a block. According to the bit depth (Bd), a sample can be represented as a number from 0 to 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.

[0067] 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-partition units during encoding or decoding, a unit may represent a sub-partition 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. Depending on 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. In addition, 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.

[0068] 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.

[0069] When the size of the coding block is within a predetermined range, it can be partitioned 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 partitioned 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 partition 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 partition using only quadtree partitioning. Here, the block to be partitioned may be at least one of a coding block and a transform block. In this case, information indicating the partitioning 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 partition using only binary or ternary tree partitioning. In this case, the above description of the quadtree partition may be applied to the binary tree partition or the ternary tree partition in the same manner.

[0070] 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.

[0071] 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.

[0072] 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 picture or a neighboring block of the block.

[0073] 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 first partitioning the first unit. 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.

[0074] Bitstream: can represent a stream of bits including coded image information.

[0075] 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.

[0076] 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 partitions. In addition, information in the adaptation parameter set may be used by referencing different adaptation parameter sets for sub-pictures, slices, tile groups, tiles, or partitions within a picture.

[0077] In addition, 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.

[0078] In addition, regarding the 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.

[0079] In addition, regarding the 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.

[0080] In addition, 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.

[0081] 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.

[0082] Information about the adaptation parameter set identifier may be included in a parameter set or a header of the tile, and an adaptation parameter set corresponding to the adaptation parameter set identifier may be used for the tile.

[0083] 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.

[0084] A picture may be partitioned into one or more tile rows and one or more tile columns.

[0085] 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 one sub-picture.

[0086] 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.

[0087] A partition may represent one or more CTU rows within a tile. A tile may be partitioned into one or more blocks, and each block may have at least one or more CTU rows. A tile that is not partitioned into two or more may represent a partition.

[0088] A slice may include one or more tiles within a picture, and may include one or more partitions within a tile.

[0089] Parsing: may mean determining the value of a syntax element by performing entropy decoding, or may mean the entropy decoding itself.

[0090] 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.

[0091] Prediction mode: may be information indicating a mode for encoding / decoding using intra prediction or a mode for encoding / decoding using inter prediction.

[0092] 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 partitioning a prediction unit may also be prediction units.

[0093] Prediction unit partition: may represent a shape obtained by partitioning a prediction unit.

[0094] 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 reference picture lists available, including LC (List Combination), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3).

[0095] 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.

[0096] 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.

[0097] The reference picture index may refer to an index indicating a specific reference picture in a reference picture list.

[0098] 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 picture" have the same meaning and may be interchangeable.

[0099] 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 target block / 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.

[0100] 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.

[0101] The motion vector candidate may refer to a prediction candidate block or a motion vector of a prediction candidate block when predicting a motion vector. In addition, the motion vector candidate may be included in a motion vector candidate list.

[0102] The motion vector candidate list may mean a list consisting of one or more motion vector candidates.

[0103] 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.

[0104] The motion information may represent information including at least one of 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.

[0105] The merge candidate list may refer to a list consisting of one or more merge candidates.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] Quantization parameter: may represent a value used when a transform coefficient is used to generate a quantized level during quantization. The quantization parameter may also represent 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 on a quantization step size.

[0111] Delta quantization parameter: may represent the difference between the predicted quantization parameter and the quantization parameter of the encoding / decoding target unit.

[0112] Scan: can 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 can be called scanning, and changing a one-dimensional matrix of coefficients to a two-dimensional matrix can be called scanning or inverse scanning.

[0113] Transform coefficient: may refer to a coefficient value generated after performing a transform in an encoder. A 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] Quantization matrix coefficients: can represent each element in the quantization matrix. Quantization matrix coefficients can also be called matrix coefficients.

[0118] Default matrix: may represent a predetermined quantization matrix predefined in an encoder or a decoder.

[0119] Non-default matrix: may denote a quantization matrix that is not predefined in the encoder or decoder but is signaled by the user.

[0120] 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.

[0121] Figure 1 is a block diagram showing a configuration of an encoding device according to an embodiment to which the present invention is applied.

[0122] 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.

[0123] 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.

[0124] 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 the current picture as the current encoding target. The input block may be referred to as the current block as the current encoding target, or may be referred to as the encoding target block.

[0125] 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.

[0126] When the prediction mode is the inter-frame mode, the motion prediction unit 111 may retrieve the area that best matches the input block from the reference picture when performing motion prediction, and derive the motion vector by using the retrieved area. In this case, the search area may be used as the area. The reference picture may be stored in the reference picture buffer 190. Here, when encoding / decoding of the reference picture is performed, the reference picture may be stored in the reference picture buffer 190.

[0127] The motion compensation unit 112 may generate a prediction 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.

[0128] 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, depending on the determined mode, inter-picture prediction or motion compensation may be performed differently.

[0129] 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.

[0130] 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.

[0131] The quantization level may be generated by applying quantization to a transform coefficient or to a residual signal. Hereinafter, the quantization level may also be referred to as a transform coefficient in an embodiment.

[0132] 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.

[0133] The entropy encoding unit 150 may generate a bit stream 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 bit stream. 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.

[0134] When entropy coding is applied, symbols are represented so that a smaller number of bits are allocated to symbols with a high probability of generation, and a larger number of bits are allocated 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.

[0135] 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.

[0136] 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 samples, reconstructed chrominance samples, residual luminance samples, residual chrominance samples, luminance transform coefficient, chrominance transform coefficient, quantized luminance level, quantized chrominance level, transform coefficient level scanning method, motion vector search area at decoder side size, shape of a motion vector search area at a decoder side, number of motion vector searches at a decoder side, information about a CTU size, information about a minimum block size, information about a maximum block size, information about a maximum block depth, information about 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 about a luminance signal or information about a chrominance signal.

[0137] 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.

[0138] When the encoding apparatus 100 performs encoding by inter-frame prediction, the encoded current picture may be used as a reference picture for another image that is subsequently processed. Therefore, the encoding apparatus 100 may reconstruct or decode the encoded current picture, or store the reconstructed or decoded image as a reference picture in the reference picture buffer 190.

[0139] 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.

[0140] 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.

[0141] The deblocking filter can remove block distortion generated in the boundary between blocks. In order to determine whether to apply the deblocking filter, it can 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 can be applied according to the required deblocking filter strength.

[0142] 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.

[0143] 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.

[0144] 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 a reference picture. That is, the reference picture is a reconstructed image composed of the reconstructed blocks processed by the filter unit 180. The stored reference picture may be used later in inter-frame prediction or motion compensation.

[0145] 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.

[0146] The decoding device 200 may be a decoder, a video decoding device, or an image decoding device.

[0147] 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.

[0148] 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-frame mode or an inter-frame 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.

[0149] 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.

[0150] 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 as 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.

[0151] 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.

[0152] In order to decode the transform coefficient level (quantized level), the entropy decoding unit 210 may change the coefficient in the form of a one-way vector into a two-dimensional block form by using a transform coefficient scanning method.

[0153] 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.

[0154] 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 blocks that are adjacent to the decoding target block and have been decoded. 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 picture stored in the reference picture buffer 270 .

[0155] The adder 225 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 a reference picture. That is, the reference picture is a reconstructed image composed of the reconstructed blocks processed by the filter unit 260. The stored reference picture can be used later in inter-frame prediction or motion compensation.

[0156] 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.

[0157] In order to efficiently 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 transformation coefficient.

[0158] 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.

[0159] 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 a plurality of (positive integers equal to or greater than 2, including 2, 4, 8, 16, etc.) 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 according to the number of partitions. The CU may be recursively partitioned into a plurality of 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 predetermined depth or a predetermined size. For example, the depth of the LCU may be 0, and the depth of the minimum coding unit (SCU) may be a predetermined 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 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. Also, 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.

[0160] 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.

[0161] 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.

[0162] 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 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.

[0163] 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 having a size of 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 having a size of 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 by a binary tree partition structure.

[0164] 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 the horizontal size or the vertical size of 1:2:1. 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.

[0165] 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.

[0166] 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 coding units 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.

[0167] 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).

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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 current coding unit may include partition tree information. The partition tree information may indicate a tree partition structure to be used to partition the nodes 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.

[0173] The partition indication information, the partition tree information, and the partition direction information can all be flags having a predetermined length (e.g., one bit).

[0174] 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 can be entropy-coded / entropy-decoded. In order to entropy-code / entropy-decode those types of information, information about neighboring coding units adjacent to the current coding unit can be used. For example, the 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 is very high. Therefore, context information for entropy-coding / entropy-decoding information about the current coding unit can be derived from information about the neighboring coding units. The information about the neighboring coding units can include at least any one of the quad-partition information, the multi-type tree partition indication information, the partition direction information, and the partition tree information.

[0175] As another example, in binary tree partitioning and ternary tree partitioning, binary tree partitioning can be preferentially performed. That is, the current coding unit can first undergo binary tree partitioning, and then the coding unit corresponding to the leaf node of the binary tree can be set as the root node for 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 can be performed.

[0176] 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 coding, prediction, and / or transformation. That is, the coding unit cannot be further partitioned for prediction and / or transformation. Therefore, there may be no partition structure information and partition information in the bitstream for partitioning the coding unit into a prediction unit and / or a transformation unit.

[0177] However, when the size of the coding unit (ie, 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 partition of the coding unit for transforming is not separately signaled, and the partition 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.

[0178] 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 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.

[0179] 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 parallel block group level, a parallel block 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.

[0180] 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 depending on 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.

[0181] 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.

[0182] Depending on 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.

[0183] 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 as the second value.

[0184] 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 by the binary tree or the ternary tree. Therefore, the multi-type tree partition indication information may not be signaled, but the multi-type tree partition indication information may be inferred as the second value.

[0185] 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 sent by a signal, but the multi-type tree partition indication information may be derived from the second value. This is because when the coding unit is partitioned by 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.

[0186] 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 partitioned into sub-coding units that do not fit into the pipeline buffer size by the 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 (eg, 64×64). For example, when the pipeline buffer size is 64×64, the following partition may be limited.

[0187] - N×M (N and / or M is 128) ternary tree partitions for coding units - 128×N (N<=64) binary tree partitions in the horizontal direction for coding units - N×128 (N<=64) binary tree partitions in the vertical direction for coding units 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 as the second value.

[0188] 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 sent by a signal. 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 sent by a signal, but the multi-type tree partition indication information may be inferred as a second value.

[0189] 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.

[0190] Optionally, the 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, the partition tree information may not be signaled but inferred as a value indicating a possible partition tree structure.

[0191] Figure 4 is a diagram illustrating an intra prediction process.

[0192] Figure 4 The arrows from the center to the outside in FIG. 1 represent the prediction direction of the intra prediction mode.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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 performing both copying and interpolation, 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.

[0198] Figure 7 is a diagram showing reference samples that can be used for intra prediction.

[0199] 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 samples of fragment A and fragment F can be filled with the samples of the closest fragment B and fragment E, respectively, instead of retrieving from the reconstructed neighboring blocks. The index information indicating the reference sample line to be used for intra prediction of the current block can be signaled. For example, in Figure 7 In the example, reference sample line indicators 0, 1, and 2 may be signaled as index information indicating reference sample lines 0, 1, and 2. When the upper boundary of the current block is the boundary of the CTU, only reference sample line 0 may be available. Therefore, in this case, index information may not be signaled. When a reference sample line other than reference sample line 0 is used, filtering for a prediction block, which will be described later, may not be performed.

[0200] When intra prediction is performed, a filter may be applied to at least one of reference samples and prediction samples based on the intra prediction mode and the current block size / shape.

[0201] In the case of the planar mode, when generating a prediction block of a current block, according to the position of a predicted target sample within the prediction block, the sample value of the predicted target sample can be generated by using the weighted sum of the upper reference sample and the left reference sample of the current block and the upper-right reference sample and the lower-left reference sample of the current block. Additionally, in the case of the DC mode, when generating a prediction block of a current block, the average value of the upper reference sample and the left reference sample of the current block can be used. Additionally, in the case of the angular mode, a prediction block can 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. To generate a predicted sample value, interpolation of real number units can be performed.

[0202] In the case of intra prediction between color components, a prediction block of the current block of the second color component can be generated based on the corresponding reconstructed block of the first color component. For example, the first color component can be a luminance component, and the second color component can be a chrominance component. For intra prediction between color components, the parameters of a linear model between the first color component and the second color component can be derived based on a template. The template can include the upper and / or left neighboring samples of the current block and the upper and / or left neighboring samples of the corresponding reconstructed block of the first color component. For example, the sample value of the first color component with the maximum value among the samples in the template and the corresponding sample value of the second color component, and the sample value of the first color component with the minimum value among the samples in the template and the corresponding sample value of the second color component can be used to derive the parameters of the linear model. When deriving the parameters of the linear model, the corresponding reconstructed block can be applied to the linear model to generate a prediction block of the current block. According to the video format, subsampling can be performed on the reconstructed block of the first color component and the neighboring samples of the corresponding reconstructed 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 can be subsampled to calculate one corresponding sample. In this case, the parameter derivation of the linear model and the intra prediction between color components can be performed based on the corresponding subsampled samples. Whether to perform intra prediction between color components and / or the range of the template can be signaled as an intra prediction mode.

[0203] 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 the sub-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 signaling. It may be limited to performing sub-block-based intra prediction 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.

[0204] The final prediction block can be generated by performing filtering on the prediction block predicted by the intra-frame. Filtering can be performed by applying predetermined weights to the filtering target samples, the left reference samples, the upper reference samples and / or the upper left reference samples. The weights and / or reference samples (range, position, etc.) used for filtering can be determined based on at least one of the block size, the intra-frame prediction mode and the position of the filtering target samples in the prediction block. Filtering can 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 can be a mode in which k is added to the diagonal mode or k is subtracted from the diagonal mode. For example, k can be a positive integer of 8 or less.

[0205] The intra-frame prediction mode of the current block can be entropy encoded / decoded by predicting the intra-frame prediction mode of the block adjacent to the current block. When the intra-frame prediction mode of the current block is the same as that of the neighboring block, the information that the intra-frame prediction mode of the current block is the same as that of the neighboring block can be sent by signaling 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 can be sent by signaling. 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 can be entropy encoded / decoded by performing entropy encoding / decoding based on the intra-frame prediction mode of the neighboring block.

[0206] Figure 5 is a diagram illustrating an embodiment of an inter-picture prediction process.

[0207] 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).

[0208] I pictures may be encoded by intra prediction without the need for inter-picture prediction. P pictures may be encoded by inter-picture prediction using reference pictures that exist in one direction (i.e., forward or backward) for the current block. B pictures may be encoded by inter-picture prediction using reference pictures that exist in two directions (i.e., forward and backward) for 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.

[0209] Hereinafter, embodiments of inter prediction will be described in detail.

[0210] Reference pictures and motion information may be used to perform inter-picture prediction or motion compensation.

[0211] 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 the one or more reference pictures included in the reference picture list.

[0212] The derivation method of motion information may be different depending on 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, geometric partition mode, combined inter-frame intra-frame prediction mode, affine mode, etc. Here, the merge mode may be referred to as motion merge mode.

[0213] 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 of 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 the 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.

[0214] 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 encoding on the motion vector difference (MVD). In addition, the encoding device 100 may perform entropy encoding 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 for 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 the motion vector of the decoding target block.

[0215] 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.

[0216] In addition, the encoding device 100 calculates a motion vector difference (MVD) between a motion vector in a 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 through the sum of the entropy-decoded MVD and the affine controlled motion vector candidate.

[0217] 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.

[0218] Another example of a method of deriving motion information of a current block may be a merge mode. The merge mode may indicate a method of merging motions of a plurality of blocks. The merge mode may indicate a mode of deriving motion information of a current block from motion information of a neighboring block. When the merge mode is applied, a merge candidate list may be generated using motion information of reconstructed neighboring blocks and / or motion information of co-located blocks. 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).

[0219] 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 a combination of 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.

[0220] 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.

[0221] 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 sends it to the decoding device 200 with a signal. The decoding device 200 can 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 sent with the signal can be referred to as a merge mode with a motion vector difference.

[0222] 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.

[0223] The subblock merge mode may indicate a mode for deriving motion information in units of subblocks of a coding block (CU). When the subblock merge mode is applied, the subblock merge candidate list may be generated using motion information of a subblock co-located with the current subblock in a reference picture (subblock-based temporal merge candidates) and / or affine control point motion vector merge candidates.

[0224] The geometric partition mode may denote a mode of deriving motion information by partitioning the current block into predefined 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.

[0225] 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.

[0226] 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 corrected motion information.

[0227] The decoding apparatus 200 may compensate for prediction samples derived through inter-frame prediction using optical flow.

[0228] Figure 6 is a diagram illustrating transform and quantization processing.

[0229] 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 transform coefficients, and the secondary transform of the transform coefficients generates secondary transform coefficients.

[0230] At least one scheme selected from various predefined transform schemes is used to perform the primary transform. For example, examples of the predetermined transform scheme 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.

[0231] A quantized level signal (quantized coefficient) may be generated by performing quantization on a residual signal or 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 scanning coefficients in 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 depending on 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.

[0232] 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 reverse scanning. For reverse scanning, at least one of diagonal upper right scanning, vertical scanning, and horizontal scanning can be used.

[0233] The quantized level coefficients may then be dequantized, then inversely transformed twice as needed, and finally inversely transformed once as needed to produce a reconstructed residual signal.

[0234] 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 partitioned into 16 equal segments, and the mapping function of each segment can be sent with a signal. The mapping function can be sent with a signal at the slice level or the 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 a reconstructed block. However, since intra-frame prediction is performed in the mapping area, the prediction block generated via intra-frame prediction can be used to generate a reconstructed block without mapping / inverse mapping.

[0235] 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 the mapping of the luminance component is available and the partitioning 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.

[0236] Information indicating whether mapping / inverse mapping of luma components and chroma components is available may be signaled through a sequence parameter set.

[0237] The prediction block of the current block can 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 can 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 sent with a signal so that a merge candidate can be specified. The block vector of the specified merge candidate can 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 sent with a signal. 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 sent with a signal. 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 can be limited so that the prediction block of the current block is located in the region of three 64×64 blocks before 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 scheme according to the IBC mode can be reduced.

[0238] In the following, reference will be made to Figures 8 to 20 Embodiments of the present invention are described.

[0239] Figure 8 is a flowchart showing an image encoding method according to an embodiment of the present invention, Fig. 9is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

[0240] [E1 / D1] Derivation of motion vector candidates Deriving motion vector candidates [E1 / D1] may include at least one or more of deriving spatial motion vector candidates [E1-1 / D1-1], deriving temporal motion vector candidates [E1-2 / D1-2], and deriving motion vector candidates based on history [E1-3 / D1-3]. Here, when the current block is in IBC (Intra Block Copy) mode, the motion vector may represent a block vector.

[0241] [E1-1 / D1-1] Derivation of spatial motion vector candidates The encoder / decoder may derive a motion vector candidate from a reconstructed block spatially adjacent to the encoding target block / decoding target block.

[0242] For example, Fig.10 As shown, the encoder / decoder can determine the spatial motion vector candidates of the encoding target block / decoding target block by deriving the spatial motion vectors in block B1 adjacent to the top of the encoding target block / decoding target block X, block A1 adjacent to the left side of the encoding target block / decoding target block, block B0 adjacent to the upper right corner of the encoding target block / decoding target block, block B2 adjacent to the upper left corner of the encoding target block / decoding target block, and block A0 adjacent to the lower left corner of the encoding target block / decoding target block.

[0243] In addition, the encoder / decoder can determine whether there is a motion vector in each block according to the predetermined order of the blocks included in the positions A0, A1, B0, B1 and B2. If there is a motion vector, the encoder / decoder can determine the motion vector of the corresponding block as a spatial motion vector candidate.

[0244] When the encoding target block / decoding target block is an IBC (Intra Block Copy) mode referring to the current picture, only neighboring blocks encoded in the IBC mode may be determined as spatial motion vector candidates. Here, the spatial motion vector candidate may be a spatial block vector candidate.

[0245] When the encoding target block / decoding target block is an inter prediction mode instead of an IBC mode, if a neighboring block is encoded as the IBC mode, the encoder / decoder may not use a motion vector of the corresponding block as a spatial motion vector candidate.

[0246] In other words, only when the spatially neighboring block has the same prediction mode as the current block, the encoder / decoder may determine the motion vector of the spatially neighboring block as the spatial motion vector candidate.

[0247] In addition, when the reference picture of at least one or more blocks included in the positions A0, A1, B0, B1, and B2 is different from the reference picture of the encoding target block / decoding target block, the encoder / decoder may scale the motion vector of the corresponding block and determine the motion vector of the corresponding block as a spatial motion vector candidate by using the distance between the encoding / decoding target picture and the reference picture of the corresponding block and the distance between the encoding / decoding target picture and the reference picture of the encoding target block / decoding target block. Here, the encoder / decoder may scale the motion vector based on a reference picture index instead of a reference picture.

[0248] In addition, when performing scaling, the encoder / decoder may determine a spatial motion vector candidate by scaling at least one or more motion vectors of blocks included in positions A0, A1, B0, B1, and B2 based on a reference picture corresponding to a reference picture index having a specific value. Here, the specific value may be a positive integer including 0.

[0249] In addition, the encoder / decoder may derive spatial motion vector candidates based on at least one or more encoding parameters.

[0250] In addition, the encoder / decoder may determine the motion vectors of spatially neighboring blocks as spatial motion vector candidates based on the size or area of ​​the current block.

[0251] For example, the encoder / decoder may determine the motion vector of the neighboring block as the spatial motion vector candidate only when the area of ​​the current block is greater than a predefined value.

[0252] For another example, if the current block is in IBC mode, the encoder / decoder may determine the block vector of the neighboring block as a spatial block vector candidate only when the area of ​​the current block is greater than a predefined value.

[0253] Here, the predefined value may be 16.

[0254] [E1-2 / D1-2] Derivation of temporal motion vector candidates The encoder / decoder may derive a motion vector candidate from a reconstructed block in a co-located picture temporally adjacent to the encoding target block / decoding target block.

[0255] For example, Fig.11As shown, the encoder / decoder may derive a temporal motion vector candidate in the order of a block in position H and a block in position C3, wherein position H is spatially outside the co-located block C corresponding to the encoding target block / decoding target block X, and position C3 is in the co-located picture of the encoding target picture / decoding target picture. Here, when a motion vector can be derived from a block in position H, the encoder / decoder may derive a temporal motion vector candidate in a block located at H. On the other hand, when a motion vector cannot be derived from a block located at H, the encoder / decoder may derive a temporal motion vector candidate in position C3. If H or C3 as a predetermined position is intra-coded using the current picture as a reference picture or is coded into an IBC (Intra-block Copy) mode, the encoder / decoder may not derive a temporal motion vector candidate. In this case, the temporal motion vector candidate may represent a motion vector of the co-located block.

[0256] In other words, only when the temporally neighboring block has the same prediction mode as the current block, the encoder / decoder may determine the motion vector of the temporally neighboring block as the temporal motion vector candidate.

[0257] Additionally, the encoder / decoder may derive a temporal motion vector candidate based on at least one or more encoding parameters.

[0258] When the distance between the picture including the encoding target block / decoding target block and the reference block of the encoding target block / decoding target block is different from the distance between the picture including the co-located block and the reference picture of the co-located block, the encoder / decoder may derive a temporal motion vector candidate by scaling the motion vector of the co-located block. Here, the encoder / decoder may scale the motion vector based on a reference picture index instead of a reference picture.

[0259] [E1-3 / D1-3] Deriving history-based motion vector candidates At least one piece of information used for an encoding / decoding process in an encoder / decoder or generated after the encoding / decoding process may be included in the history-based candidate list (ie, the HMVP candidate list).

[0260] Here, the information of the block may be at least one of encoding parameters such as an intra prediction mode and motion information.

[0261] When the current block is not an affine mode or does not use a temporal motion vector candidate in a sub-block, at least one piece of block information of the current block may be included in the HMVP candidate list.

[0262] When the current block is in IBC (Intra Block Copy) mode using the current picture as a reference picture, it may be included in a separate HMVP candidate list. Here, the separate candidate list may be an IBC HMVP candidate list.

[0263] Unlike conventional candidate lists (motion vector candidate lists and merge candidate lists) configured in block units, the HMVP candidate list is maintained when encoding / decoding is performed in units of pictures, slices, parallel blocks, CTUs, CTU rows, and CTU columns. Therefore, it can be used in units of pictures, slices, parallel blocks, CTUs, CTU rows, and CTU columns. In addition, the HMVP candidate list may include at least one piece of block information from multiple pieces of block information of blocks that were encoded / decoded in units of pictures, slices, parallel blocks, CTUs, CTU rows, and CTU columns before the current block. In addition, the HMVP candidate list may include at least one piece of block information from multiple pieces of block information of blocks that were previously encoded / decoded in units of pictures, slices, parallel blocks, CTUs, CTU rows, and CTU columns.

[0264] like Fig.12 As shown in the example of , the encoder / decoder may determine at least one piece of block information of a candidate in the HMVP candidate list for encoding / decoding processing of the current block. The encoder / decoder may perform encoding / decoding processing of the current block by using at least one piece of block information of the selected candidate.

[0265] The encoder / decoder may include at least one piece of block information used during the encoding / decoding process of the current block or at least one piece of block information used after the encoding / decoding process of the current block in the HMVP candidate list. Here, including at least one of the block information, the candidate, and the block in the candidate list may mean adding at least one of the block information, the candidate, and the block to the HMVP candidate list.

[0266] When at least one piece of block information of the current block is included in the HMVP candidate list, the piece of block information of the current block may be added to the HMVP candidate list first or last.

[0267] The maximum number of candidates in the HMVP candidate list may be determined as P. Here, P may be a positive integer including 0. P may be determined based on at least one of the encoding parameters of the current block and the encoding parameters of the candidate block. In addition, P may be a value that has been set in the encoder / decoder or a value that is signaled from the encoder to the decoder.

[0268] Candidates in the HMVP candidate list may be used to configure at least one of an intra prediction mode candidate list, a first MPM (Most Probable Mode) list, a second MPM list, a residual intra prediction mode candidate list, a motion vector candidate list, a merge candidate list, and an IBC candidate list.

[0269] In the multiple pieces of block information, the intra prediction coding mode may be included in the HMVP candidate list. The candidates in the HMVP candidate list including the intra prediction coding mode may be used to configure the intra prediction mode candidate list (e.g., the first MPM list, the second MPM list, the residual mode list, etc.). The candidate may be included in the intra prediction mode candidate list.

[0270] Among the multiple pieces of block information, inter-frame coding information (e.g., motion vector, reference picture index, reference picture list information, bidirectional prediction weight information (bcwIdx), 1 / 2 interpolation filter information (HpelIfIdx), etc.) may be included in the HMVP candidate list. Candidates in the candidate list including inter-frame coding information may be used to configure a motion vector candidate list. Candidates may be included in the motion vector candidate list.

[0271] Among the multiple pieces of block information, inter-frame coding information (e.g., motion vector, reference picture index, reference picture list information, bidirectional prediction weight information (bcwIdx), 1 / 2 interpolation filter information (HpelIfIdx), etc.) may be included in the HMVP candidate list. Candidates in the HMVP candidate list including inter-frame coding information may be used to configure a merge candidate list. Candidates may be included in the merge candidate list.

[0272] In this step, a history-based motion vector candidate list can be configured, wherein the history-based motion vector candidate list includes inter-frame coding information in multiple block information (for example, motion vector, reference picture index, reference picture list information, bidirectional prediction weight information (bcwIdx), 1 / 2 interpolation filter information (HpelIfIdx), etc.).

[0273] [E2 / D2] Configure motion vector candidate list Configuring the motion vector candidate list [E2 / D2] may include generating a combined motion vector candidate and adding it to the motion vector candidate list [E2-1 / D2-1].

[0274] The encoder / decoder may configure the motion vector candidate list by adding the derived motion vector candidate to the motion vector candidate list or by removing the motion vector candidate included in the motion vector candidate list.

[0275] The derived spatial motion vector candidates, temporal motion vector candidates, and history-based motion vector candidate lists may be added to a motion vector candidate list mvpListLX in a predetermined order. mvpListLX may represent a motion vector candidate list corresponding to at least one or more reference picture lists such as L0, L1, L2, and L3. For example, a motion vector candidate list corresponding to reference picture list L0 may be represented as mvpListL0.

[0276] Hereinafter, an embodiment of configuring a motion vector candidate list will be described.

[0277] For example, the encoder / decoder may sequentially add the derived spatial motion vector candidates, the temporal motion vector candidates, and the history-based motion vector candidate list to the motion vector candidate list.

[0278] For example, the encoder / decoder may sequentially add the derived spatial motion vector candidate, the history-based motion vector candidate list, and the temporal motion vector candidate to the motion vector candidate list.

[0279] For example, the encoder / decoder may add a history-based motion vector candidate list to the derived spatial motion vector candidates, and then add the temporal motion vector candidate to the motion vector candidate list. Specifically, the encoder / decoder may sequentially add N spatial motion vector candidates, a history-based motion vector candidate list, M spatial motion vector candidates, and a temporal motion vector candidate to the motion vector candidate list. Here, N and M may be positive integers equal to or greater than 0.

[0280] Alternatively, the encoder / decoder may add the spatial motion vector candidates, the temporal motion vector candidates, and the history-based motion vector candidate list to the motion vector candidate list in a predetermined order.

[0281] When configuring a motion vector candidate list, the encoder / decoder can determine whether the motion information is the same only in the spatial motion vector candidates. In the case where the number of candidates in the list does not meet the maximum number of motion vector candidates and thus a temporal motion vector candidate or a history-based motion vector candidate is added, the encoder / decoder may not check for redundancy with previous candidates.

[0282] In the case where the encoder / decoder adds a history-based motion vector candidate when configuring a motion vector candidate list, the encoder / decoder may add information that the maximum number of candidate blocks in the history-based candidate list is N to the motion vector candidate list. N may be greater than 0 and equal to the maximum number of candidates in the history-based candidate list.

[0283] In the case where the encoder / decoder adds a history-based motion vector candidate when configuring a motion vector candidate list, the encoder / decoder may add information that the maximum number of candidate blocks in the history-based candidate list is N to the motion vector candidate list. N may be greater than 0 and equal to the maximum number of candidates in the history-based candidate list. In the case where the maximum number of candidates in the history-based candidate list is greater than 4, information of up to 4 candidate blocks may be added to the motion vector candidate list.

[0284] In the case where the encoder / decoder adds a history-based motion vector candidate when configuring the IBC candidate list, the encoder / decoder may add information of P candidate blocks in the history-based candidate list to the IBC candidate list. Here, P may be 1, and the motion vector candidate may be a block vector candidate.

[0285] In addition to the derived spatial motion vector candidates, the history-based motion vector candidate list, and the temporal motion vector candidates, the encoder / decoder may add a vector having a predetermined value to the motion vector candidate list mvpListLX.

[0286] [E2-1 / D2-1] Generate a combined motion vector candidate and add it to the motion vector candidate list The encoder / decoder can generate a combined motion vector candidate by using at least one or more of the spatial motion vector candidates in the motion vector candidate list, the history-based motion vector candidate list, the temporal motion vector candidates, and the zero motion vector candidates, and can also add the combined motion vector candidate to the motion vector candidate list.

[0287] In addition, the encoder / decoder may generate a combined motion vector candidate based on at least one or more encoding parameters. In addition, the encoder / decoder may add the combined motion vector candidate to the motion vector candidate list based on at least one or more encoding parameters.

[0288] [E3 / D3] Determine the predicted motion vector from the motion vector candidate list The encoder / decoder may determine a motion vector candidate in the motion vector candidate list mvpListLX corresponding to the motion vector candidate index as the predicted motion vector.

[0289] The encoder may calculate the motion vector difference by calculating the difference between the motion vector and the predicted motion vector, and the decoder may calculate the motion vector by adding the predicted motion vector to the motion vector difference.

[0290] [E4 / D4] Perform motion compensation In the encoder / decoder, inter-frame prediction or motion compensation can be performed by using the motion vector thus determined.

[0291] [E5 / D5] Entropy encoding / entropy decoding of information about motion compensation of the current encoding target block / decoding target block.

[0292] The encoder / decoder may entropy encode / decode the motion compensation information from the bitstream. Here, the motion compensation information may include at least one of the following multiple information.

[0293] -inter_pred_idc indicates inter-frame prediction indicator - Reference picture index (ref_idx_l0, ref_idx_l1, ref_idx_l2, ref_idx_l3) - Motion vector candidate index (mvp_l0_flag, mvp_l1_flag, mvp_l2_flag, mvp_l3_flag) - Motion vector difference - cu_skip_flag, indicating whether to use the skip mode - merge_flag, indicating whether to use the merge mode - merge_idx (merge_index), indicating the merge candidate - Weighting factor (wf_l0, wf_l1, wf_l2, wf_l3) - Offset value (offset_l0, offset_l1, offset_l2, offset_l3) The inter - frame prediction indicator may refer to the direction of inter - frame prediction (such as uni - directional prediction, bi - directional prediction, tri - directional prediction, quad - directional prediction, etc.) of the current block during inter - frame prediction. This may indicate the number of reference pictures used by the current block to generate the prediction block. Optionally, one reference picture may be used for multi - directional prediction. In this case, M - direction prediction may be performed by using N reference pictures (N < M). Optionally, the inter - frame prediction indicator may refer to the number of prediction blocks used by the current block to perform inter - frame prediction or motion compensation. Additionally, it may represent the number of prediction blocks used by the current block when performing inter - frame prediction or motion compensation through at least one or more reference picture lists (such as L0, L1, L2, and L3). Here, L0, L1, L2, and L3 may refer to list 0, list 1, list 2, and list 3 respectively. Additionally, the inter - frame prediction indicator may be information on whether the current block refers to a reference picture list with a maximum number of N. Here, N may be 1, 2, 3, 4, and above, or a positive integer equal to or greater than 1. The current block may perform motion compensation by using one or more reference picture lists.

[0294] For example, the encoder / decoder may perform motion compensation by using reference picture lists L0 and L1 to generate at least one or more prediction blocks.

[0295] For example, the encoder / decoder may perform motion compensation by using reference picture lists L0, L1, and L2 to generate at least one prediction block.

[0296] For example, the encoder / decoder may perform motion compensation by using reference picture lists L0, L1, and L2 to generate at least one or more prediction blocks.

[0297] For example, the encoder / decoder may perform motion compensation by using reference picture lists L0, L1, and L2, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks N. Here, N may be 3 or a positive integer equal to or greater than 2.

[0298] For example, the encoder / decoder may perform motion compensation by using reference picture lists L0, L1, L2, and L3, thereby generating one prediction block.

[0299] For example, the encoder / decoder may perform motion compensation by using the reference picture lists L0, L1, L2, and L3, thereby generating at least one or more prediction blocks.

[0300] For example, the encoder / decoder may perform motion compensation by using reference picture lists of L0, L1, L2, and L3, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 4 or a positive integer equal to or greater than 2.

[0301] The available inter prediction directions may be determined based on the inter prediction indicator. Some or all of the available inter prediction directions may be selectively used based on the size and / or shape of the current block.

[0302] The inter-frame prediction indicator may be information indicating whether the inter-frame prediction uses unidirectional prediction of L0 (list 0), unidirectional prediction of L1 (list 1), or bidirectional prediction of both L0 and L1. The inter-frame prediction indicator may be represented by a prediction list utilizing a flag form, wherein the prediction list utilizing a flag form includes a flag indicating whether to use directional L0 prediction and a flag indicating whether to use directional L1 prediction.

[0303] Here, the prediction list utilization flag may indicate whether the corresponding reference picture list is used to generate the prediction block. For example, when the prediction list utilization flag indicates the first value (1), it may indicate that the corresponding reference picture list is used to generate the prediction block. On the other hand, when the prediction list utilization flag indicates the second value (0), it may indicate that the corresponding reference picture list is not used to generate the prediction block. In other words, the prediction block of the current block may be generated only by using the motion information of the prediction list utilization flag indicating that the corresponding reference picture list can be used to generate the prediction block. In addition, the prediction block of the current block may be generated using the corresponding motion information only when the prediction list utilization flag has the first value. In addition, the prediction list utilization flag may be set based on the inter-frame prediction indicator, and the inter-frame prediction indicator may be set based on the prediction list utilization flag.

[0304] In addition, num_ref_idx_l0_active_minus1, num_ref_idx_l1_active_minus1, num_ref_idx_l2_active_minus1, and num_ref_idx_l3_active_minus1 may refer to the numbers of reference pictures of reference picture lists L0, L1, L2, and L3, respectively.

[0305] The reference picture index may indicate a reference picture referenced by the current block in each reference picture list. For each reference picture list, one or more reference picture indexes may be entropy decoded. The encoder / decoder may perform motion compensation by using one or more reference picture indexes.

[0306] For example, the encoder / decoder may perform motion compensation by using one reference picture index, thereby generating at least one or more prediction blocks.

[0307] For example, the encoder / decoder may perform motion compensation by using two reference picture indices, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 2 or a positive integer equal to or greater than 2.

[0308] For example, the encoder / decoder may perform motion compensation by using three reference picture indices, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 3 or a positive integer equal to or greater than 3.

[0309] For example, the encoder / decoder may perform motion compensation by using four reference picture indices, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 4 or a positive integer equal to or greater than 4.

[0310] The motion vector candidate index may indicate a motion vector candidate used by a current block in a motion vector candidate list generated from each reference picture list and / or each reference picture index. For each reference picture list and / or each reference picture index, one or more motion vector candidate indexes may be entropy decoded. The encoder / decoder may perform motion compensation by using one or more motion vector candidate indexes.

[0311] For example, the encoder / decoder may perform motion compensation by using one motion vector candidate index, thereby generating at least one or more prediction blocks.

[0312] For example, the encoder / decoder may perform motion compensation by using two motion vector candidate indices, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 2 or a positive integer equal to or greater than 2.

[0313] For example, the encoder / decoder may perform motion compensation by using three motion vector candidate indices, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 3 or a positive integer equal to or greater than 3.

[0314] For example, the encoder / decoder may perform motion compensation by using four motion vector candidate indices, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 4 or a positive integer equal to or greater than 4.

[0315] The motion vector difference may represent the difference between the motion vector and the predicted motion vector. For the current block, one or more motion vector differences in each reference picture list and / or each reference picture index may be entropy decoded. The encoder / decoder may perform motion compensation by using one or more motion vector differences.

[0316] For example, the encoder / decoder may perform motion compensation by using a motion vector difference, thereby generating at least one or more prediction blocks.

[0317] For example, the encoder / decoder may perform motion compensation by using two motion vector differences, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 2 or a positive integer equal to or greater than 2.

[0318] For example, the encoder / decoder may perform motion compensation by using three motion vector differences, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 3 or a positive integer equal to or greater than 3.

[0319] For example, the encoder / decoder may perform motion compensation by using four motion vector differences, thereby generating at least one or more prediction blocks and a maximum number of prediction blocks of N. Here, N may be 4 or a positive integer equal to or greater than 4.

[0320] cu_skip_flag may indicate information about whether to use the skip mode, and may be entropy encoded / decoded in at least one or more units of the coding block and the prediction block. For example, when the information about whether to use the skip mode has a first value (1), it may indicate that the skip mode is used. When the information about whether to use the skip mode has a second value (0), it may not indicate that the skip mode is used.

[0321] merge_flag may indicate information on whether to use the merge mode, and may be entropy encoded / decoded in at least one or more units of the coding block and the prediction block. For example, when the information on whether to use the merge mode has a first value (1), it may indicate that the merge mode is used. When the information on whether to use the merge mode has a second value (0), it may not indicate that the merge mode is used.

[0322] merge_idx may represent information indicating a merge candidate within a merge candidate list, and may be entropy encoded / decoded in at least one or more units of a coding block and a prediction block. In addition, merge_idx may represent merge index information. In addition, merge_idx may indicate a block from which a merge candidate is derived from a reconstructed block that is spatially / temporally adjacent to a current block. In addition, merge_idx may indicate at least one or more pieces of motion information of a merge candidate. For example, when the merge index information has a first value (0), it may indicate a first merge candidate within a merge candidate list. When the merge index information has a second value (1), it may indicate a second merge candidate within a merge candidate list. When the merge index information has a third value (2), it may indicate a third merge candidate within a merge candidate list. Similarly, when it has a fourth value or an nth value, it may indicate a merge candidate having a corresponding value according to an order in the merge candidate list. Here, N may be a positive integer including 0.

[0323] When motion compensation is performed, at least two or more prediction blocks may be generated, and then a weighted sum may be calculated by using at least one or more of the weighting factors and offsets for each prediction block. The weighted sum thus calculated may be used for inter-frame prediction or motion compensation of the current block. At least one or more of the weighting factors and offsets of the prediction block may be entropy encoded / decoded in at least one or more units of the coding block and the prediction block. Here, at least one or more of the weighting factors and offsets of each prediction block may be entropy encoded / decoded for at least one or more of the reference picture list, the reference picture, the motion vector candidate index, the motion vector difference, the motion vector, the information on whether the skip mode is used, the information on whether the merge mode is used, and the merge index information. In addition, at least one or more of the weighting factors and offset values ​​of each prediction block may be entropy encoded / decoded based on the inter-frame prediction indicator.

[0324] At least one or more of the above-mentioned multiple pieces of information about motion compensation may be entropy encoded / decoded in at least one or more units of a CTU and a sub-CTU. Here, the sub-CTU may include at least one or more of a sub-CTU, a CU, and a PU.

[0325] For example, when at least one or more pieces of information about motion compensation are entropy encoded / decoded in a CTU, motion compensation may be performed using at least one or more pieces of information about motion compensation present in all blocks in the CTU.

[0326] For example, when at least one or more pieces of information about motion compensation are entropy encoded / decoded in a CTU or a sub-CTU, at least one or more pieces of information about motion compensation for a specific block size or a specific block depth may be entropy encoded / decoded. Here, information about a specific block size or a specific block depth may be entropy encoded / decoded in addition. In addition, a block size or block depth pre-set in an encoder / decoder may be used as a specific block size or a specific block depth. In addition, information about a specific block size or a specific block depth may be determined based on a coding parameter. In addition, information about a specific block size or a specific block depth may be determined based on another encoded / decoded syntax element value. The blocks in a sub-CTU may have a square or non-square shape.

[0327] Here, in a block including a specific block size or having a block size larger than the specific block size, at least one or more pieces of information about motion compensation may be entropy encoded / decoded. In a block having a block size smaller than the specific block size, at least one or more pieces of information about motion compensation may not be entropy encoded / decoded.

[0328] In a block having a smaller block size within a specific block size, motion compensation may be performed based on at least one or more pieces of entropy encoding / decoding information about motion compensation in the specific block size. Here, in a block having a smaller block size within the specific block size, at least one or more of a motion vector candidate, a motion vector candidate list, a merge candidate, a merge candidate list, or other information included in the information about motion compensation may be shared.

[0329] Here, in a block including a specific block depth or having a block depth shallower than the specific block depth, at least one or more pieces of information about motion compensation may be entropy encoded / decoded. In a block having a block depth deeper than the specific block depth, at least one or more pieces of information about motion compensation may not be entropy encoded / decoded.

[0330] In a block having a deeper block depth than a specific block depth, motion compensation may be performed based on at least one or more entropy decoding information regarding motion compensation at the specific block depth. In a block having a deeper block depth than a specific block depth, motion compensation may be performed based on at least one or more information regarding motion compensation at the specific block depth, and the information regarding motion compensation at the specific block depth may be entropy encoded. Here, in a block having a deeper block depth than a specific block depth, at least one or more of motion vector candidates, motion vector candidate lists, merge candidates, merge candidate lists, or other information included in the information regarding motion compensation may be shared.

[0331] For example, when the block size of a CTU is 64×64 and at least one or more information regarding motion compensation in a 32×32 block as a sub-CTU is entropy encoded / decoded, motion compensation in a block belonging to the 32×32 block but having a smaller size may be performed based on at least one or more entropy encoded / decoded information regarding motion compensation in the 32×32 block unit.

[0332] For example, when the block size of a CTU is 128×128 and at least one or more information regarding motion compensation in a 16×16 block as a sub-CTU is entropy encoded / decoded, motion compensation in a block belonging to the 16×16 block but having a size less than or equal to the 16×16 block unit may be performed based on at least one or more entropy encoded / decoded information regarding motion compensation in the 16×16 block unit.

[0333] For example, when the block depth of a CTU is 0 and at least one or more information regarding motion compensation in a block having a block depth of 1 in a sub-CTU is entropy encoded / decoded, motion compensation in a block belonging to the block having a block depth of 1 but having a deeper block depth may be performed based on at least one or more entropy encoded / decoded information regarding motion compensation in the block having a block depth of 1.

[0334] For example, when the block depth of a CTU is 0 and at least one or more information regarding motion compensation in a block having a block depth of 2 in a sub-CTU is entropy encoded / decoded, motion compensation in a block belonging to the block having a block depth of 2 but having a deeper or equal block depth may be performed based on at least one or more entropy encoded / decoded information regarding motion compensation in the block having a block depth of 2.

[0335] Here, as the positive integer of the depth increases, the depth may increase. As the depth value decreases, the depth may become shallower. Additionally, as the depth increases, the block size may decrease. On the other hand, as the depth decreases, the block size may increase. Also, the sub-depth of a specific block depth may represent a depth deeper than the specific block depth. The sub-depth of a specific block depth may represent a deeper depth within the block size corresponding to the specific block depth.

[0336] In addition, at least one or more pieces of information regarding motion compensation may be calculated by using index information within a set predetermined in the encoder and the decoder.

[0337] Furthermore, in at least one or more of a video parameter set, a sequence parameter set, a picture parameter set, an adaptation parameter set, a picture header, and a slice header, at least one or more pieces of information about motion compensation may be entropy encoded / decoded.

[0338] In addition, at least one or more pieces of information on motion compensation in at least one or more units of CTU, sub-CTU, CU, and PU may be entropy encoded / decoded by using at least one or more pieces of information on motion compensation of a higher level such as a parameter set, a picture header, and a slice header as a prediction value. The value of at least one or more pieces of information on motion compensation may be calculated by adding the prediction value of at least one or more pieces of information on motion compensation to the difference value of at least one or more pieces of information on motion compensation.

[0339] Optionally, at least one or more pieces of information about motion compensation in at least one or more of the CTU, sub-CTU, CU, and PU may be entropy encoded / decoded by using at least one or more pieces of information about motion compensation in a specific area within a picture, a slice, a tile, or a CTU as a prediction value. The value of the at least one or more pieces of information about motion compensation may be calculated by adding the prediction value of the at least one or more pieces of information about motion compensation to the difference value of the at least one or more pieces of information about motion compensation.

[0340] In addition, at least one or more pieces of information about motion compensation of the prediction block may be entropy encoded / decoded in at least one or more specific regions within a picture, a slice, a tile, or a CTU.

[0341] In addition, the encoder / decoder may entropy encode / decode the difference value of at least one or more pieces of information on motion compensation by using the at least one or more pieces of information on motion compensation as the predicted value of at least one or more pieces of information on motion compensation of the encoded / decoded neighboring block. The encoder / decoder may calculate the value of at least one or more pieces of information on motion compensation by adding the predicted value of at least one or more pieces of information on motion compensation to the difference value of at least one or more pieces of information on motion compensation.

[0342] In addition, the encoder / decoder may use at least one or more pieces of information about motion compensation of an encoded / decoded neighboring block as values ​​of at least one or more pieces of information about motion compensation of a current block without performing entropy encoding / decoding on the at least one or more pieces of information about motion compensation.

[0343] In addition, the encoder / decoder may derive at least one or more pieces of information regarding motion compensation based on at least one or more of the encoding parameters.

[0344] In addition, the encoder / decoder may entropy decode at least one or more pieces of information about motion compensation from the bitstream based on at least one or more of the encoding parameters. The encoder / decoder may entropy encode at least one or more pieces of information about motion compensation into the bitstream based on at least one or more of the encoding parameters.

[0345] In addition, the information about motion compensation may also include at least one or more of motion vector, motion vector resolution information, overlapped block motion compensation information, local illumination compensation information, affine motion compensation information, decoder-side motion vector derivation information, and bidirectional optical flow information. Here, the decoder-side motion vector derivation may refer to pattern matching motion vector derivation.

[0346] The motion vector resolution information may be information about whether a specific resolution is used for at least one or more of a motion vector and a motion vector difference. Here, the resolution may indicate accuracy. In addition, the specific resolution may be at least one or more of a 16-pixel (16-pel) unit, an 8-pixel (8-pel) unit, a 4-pixel (4-pel) unit, an integer pixel (integer-pel) unit, a 1 / 2-pixel (1 / 2-pel) unit, a 1 / 4-pixel (1 / 4-pel) unit, a 1 / 8-pixel (1 / 8-pel) unit, a 1 / 16-pixel (1 / 16-pel) unit, a 1 / 32-pixel (1 / 32-pel) unit, and a 1 / 64-pixel (1 / 64-pel) unit.

[0347] The overlapped block motion compensation information may be information about whether a subblock constructed by using motion information of a spatially neighboring block of the encoding target block / decoding target block is used to construct a prediction block of the encoding target block / decoding target block when compensating the motion of the encoding target block / decoding target block.

[0348] The local illumination compensation information may be information on whether to apply at least one or more of a weighting factor and an offset value when constructing a prediction block of an encoding target block / decoding target block. Here, the weighting factor and the offset value may be values ​​calculated based on a reference block.

[0349] The affine motion compensation information may be information about whether an affine motion model is used for motion compensation of an encoding target block / decoding target block. Here, the affine motion model may be a method of partitioning a block into multiple sub-blocks by multiple parameters and calculating motion vectors of the partitioned sub-blocks from representative motion vectors.

[0350] The decoder side motion vector derivation information may be information about whether a motion vector required for motion compensation is derived and used from the decoder. Here, the information about the motion vector may not be entropy encoded / decoded. Here, when the merge mode is used, the decoder side motion vector derivation may be performed.

[0351] The bidirectional optical flow information may be information about whether motion compensation is performed by correcting the motion vector in the pixel. Here, the motion vector in the pixel may not be entropy encoded / decoded. In addition, the motion vector correction may change the motion vector value in the block to the pixel.

[0352] The current block may perform motion compensation by using at least one or more pieces of entropy-decoded information about motion compensation. The current block may perform motion compensation by using at least one or more pieces of information about motion compensation, and may entropy encode at least one or more pieces of information about motion compensation.

[0353] When entropy encoding / decoding is performed on information related to motion compensation of a current encoding target block / decoding target block, the encoder / decoder may not perform entropy encoding / decoding on at least one or more pieces of information related to motion compensation by using encoding information of a current picture to which the current encoding target block / decoding target block belongs and a reference picture in a reference picture list.

[0354] Here, the encoding information of the current picture and the reference picture may be POC (Picture Order Count) information. The encoder / decoder may not perform entropy encoding / decoding on at least one or more pieces of information about motion compensation by using the POC information of the current picture and the reference picture in the reference picture list.

[0355] When the POC information between the current picture and the reference picture in the reference picture list satisfies the following conditions, the encoder / decoder may entropy encode / decode information (e.g., sym_mvd_flag) indicating whether to perform entropy encoding / entropy decoding on the L0 and L1 reference picture index information (ref_idx_l0 and ref_idx_l1) and the unidirectional (L0 or L1) motion vector difference information (MvdL0 or MvdL1) of the current encoding target block / decoding target block.

[0356] [Condition 1] The current encoding target block / decoding target block is in bidirectional prediction mode, and there are L0 reference pictures and L1 reference pictures.

[0357] [Condition 2-1] At least one or more of the N reference pictures in the L0 reference picture list has a POC smaller than the current picture POC, and at least one or more of the M reference pictures in the L1 reference picture list has a POC larger than the current picture POC (N and M may be natural numbers greater than 0 and may be equal to or different from each other).

[0358] [Condition 2-2] At least one or more of the N reference pictures in the L0 reference picture list has a POC greater than the current picture POC, and at least one or more of the M reference pictures in the L1 reference picture list has a POC less than the current picture POC (N and M may be natural numbers greater than 0 and may be equal to or different from each other).

[0359] When there is no reference picture satisfying [Condition 2-1], [Condition 2-2] may be performed. Conversely, when there is no reference picture satisfying [Condition 2-2] after performing [Condition 2-2], [Condition 2-1] may be performed.

[0360] If conditions are met, L0 and L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information may be always derived without entropy encoding / decoding, regardless of information indicating whether entropy encoding / decoding is performed (e.g., “sym_mvd_flag”).

[0361] When the condition is satisfied and the encoded / decoded 'sym_mvd_flag' has the first value (0), entropy encoding / decoding may be performed on L0 and L1 reference picture index information and MVD (motion vector difference) information of L0 and L1.

[0362] When the condition is satisfied and the encoded / decoded 'sym_mvd_flag' has the second value (1), L0 and L1 reference picture index information and MVD information of one direction (L0 or L1) may not be entropy encoded / decoded but derived as follows.

[0363] When [Condition 2-1] is met, if the POC of at least one or more of the N reference pictures in the L0 reference picture list is smaller than the POC of the current picture, the position information of such a reference picture in the L0 reference picture list can be derived as the L0 reference picture index value: the reference picture is a short-term reference picture, and the POC of the reference picture is smaller than the POC of the current picture and has the minimum difference with the POC of the current picture.

[0364] For example, when the second reference picture POC of the L0 reference picture list has the minimum difference with the current picture POC, a value of '1' indicating the second reference picture in the L0 reference picture list may be derived as the L0 reference picture index.

[0365] When [Condition 2-1] is met, if the POC of at least one or more reference pictures among the M reference pictures in the L1 reference picture list is greater than the POC of the current picture, the position information of such a reference picture in the L1 reference picture list can be derived as the L1 reference picture index value: the reference picture is a short-term reference picture, and the POC of the reference picture is greater than the POC of the current picture and has the minimum difference with the POC of the current picture.

[0366] For example, when the third reference picture POC of the L1 reference picture list has the smallest difference with the current picture POC, a value of '2' indicating the third reference picture in the L1 reference picture list may be derived as the L1 reference picture index.

[0367] When [Condition 2-2] is met, if the POC of at least one or more of the N reference pictures in the L0 reference picture list is greater than the POC of the current picture, the position information of such a reference picture in the L0 reference picture list can be derived as the L0 reference picture index value: the reference picture is a short-term reference picture, and the POC of the reference picture is greater than the POC of the current picture and has the smallest difference with the POC of the current picture.

[0368] For example, when the second reference picture POC of the L0 reference picture list has the minimum difference with the current picture POC, a value of '1' indicating the second reference picture in the L0 reference picture list may be derived as the L0 reference picture index.

[0369] When [Condition 2-2] is met, if the POC of at least one or more of the M reference pictures in the L1 reference picture list is smaller than the POC of the current picture, the position information of such a reference picture in the L1 reference picture list can be derived as the L1 reference picture index value: the reference picture is the current short-term reference picture, and the POC of the reference picture is smaller than the POC of the current picture and has the minimum difference with the POC of the current picture.

[0370] For example, when the third reference picture POC of the L1 reference picture list has the smallest difference with the current picture POC, a value of '2' indicating the third reference picture in the L1 reference picture list may be derived as the L1 reference picture index.

[0371] After configuring a reference picture list of a current picture or slice including an encoding target block / decoding target block, checking of conditions [2-1] and [2-2] and a derivation process of an L0 / L1 reference picture index may be performed.

[0372] Without considering the POC difference between the current picture POC, the L0 reference picture POC, and the L1 reference picture POC indicated by the derived L0 reference picture index and L1 reference picture index information, the encoder / decoder may always derive a motion vector difference value of a direction that is not entropy encoded / decoded as follows.

[0373] When entropy encoding / decoding the motion vector difference (MVD0) in the direction L0, the motion vector difference (MVD1) in the direction L1 can be derived as -MVD0. In other words, the horizontal and vertical motion vector differences in the direction L1 are as follows. (MVD1_x=-MVD0_x, MVD1_y=-MVD0_y) When entropy encoding / decoding the motion vector difference (MVD1) in the direction L1, the motion vector difference (MVD0) in the direction L0 can be derived as -MVD1. In other words, the horizontal and vertical motion vector differences in the direction L0 are as follows. (MVD0_x=-MVD1_x, MVD0_y=-MVD1_y) The encoder / decoder may derive a motion vector difference value of a direction that is not encoded / decoded by considering the current picture POC, the L0 reference picture POC indicated by the derived L0 reference picture index information, and the L1 reference picture POC indicated by the derived L1 reference picture index information.

[0374] For example, when entropy encoding / decoding the motion vector difference value (MVD0) in the direction L0, the motion vector difference value in the direction L1 may be derived as the scaled MVD0 value by the following Equation 1.

[0375] Equation 1

[0376] currPic is the POC of the current picture, RefPicList0[RefIdx10] is the reference picture POC indicated by the derived L0 reference picture index information, and RefPicList1[refIdxL1] is the reference picture POC indicated by the derived L1 reference picture index information.

[0377] DiffPicOrderCnt() is the POC difference between the current picture POC and the reference picture POC.

[0378] For example, when entropy encoding / decoding the motion vector difference value (MVD1) in the direction L1, the motion vector difference value in the direction L0 may be derived as the scaled MVD1 value through Equation 1.

[0379] The encoder / decoder may determine the direction of the entropy-encoded / decoded motion vector difference value by considering the POC difference between the current picture POC, the L0 reference picture POC, and the L1 reference picture POC indicated by the derived L0 reference picture index and L1 reference picture index information.

[0380] For example, when the difference between the current picture POC and the derived L0 reference picture POC is greater than the difference between the current picture POC and the derived L1 reference picture POC, the motion vector difference (MVD0) in the direction L0 can be entropy encoded / decoded, and the motion vector difference in the direction L1 can be derived as a scaled MVD0 value.

[0381] For example, when the difference between the current picture POC and the derived L1 reference picture POC is greater than the difference between the current picture POC and the derived L0 reference picture POC, the motion vector difference (MVD1) in the direction L1 can be entropy encoded / decoded, and the motion vector difference in the direction L0 can be derived as a scaled MVD1 value.

[0382] As another example, when the POC information between the current picture and the reference picture in the reference picture list satisfies the following conditions, the encoder / decoder may entropy encode / decode information (e.g., sym_mvd_flag) indicating whether to perform entropy encoding / decoding on the L0 and / or L1 reference picture index information and the unidirectional (L0 or L1) motion vector difference (MVD) information of the current encoding target block / decoding target block.

[0383] [Condition 1] The current encoding target block / decoding target block is in bidirectional prediction mode, and there are L0 reference pictures and L1 reference pictures.

[0384] [Condition 2-1] At least one or more reference picture POCs of the N reference pictures in the L0 reference picture list are smaller than the current picture POC, and at least one or more reference picture POCs of the M reference pictures in the L1 reference picture list are larger than the current picture POC (N>0, M>0).

[0385] [Condition 2-2] At least one or more reference picture POCs among the N reference pictures in the L0 reference picture list are greater than the current picture POC, and at least one or more reference picture POCs among the M reference pictures in the L1 reference picture list are less than the current picture POC (N>0, M>0).

[0386] When there is no reference picture satisfying [Condition 2-1], [Condition 2-2] may be performed. Conversely, when there is no reference picture satisfying [Condition 2-2] after performing [Condition 2-2], [Condition 2-1] may be performed.

[0387] [Condition 3] The POC difference between the L0 reference picture having the minimum POC difference with the current picture POC and the L1 reference picture satisfies the following Equation 2.

[0388] Equation 2

[0389] currPic is the POC of the current picture, RefPicList0[refIdx0] is the reference picture POC with the minimum POC difference with the current picture in the L0 reference picture list, and RefPicList1[refIdx1] is the reference picture POC with the minimum POC difference with the current picture in the L1 reference picture list.

[0390] When the condition is satisfied and the encoded / decoded 'sym_mvd_flag' has the first value (0), the encoder / decoder may perform entropy encoding / decoding on L0 and L1 reference picture index information and MVD (motion vector difference) information of L0 and L1.

[0391] When the condition is met and the encoded / decoded 'sym_mvd_flag' has the second value (1), the encoder / decoder may not perform entropy encoding / decoding but derive L0 and / or L1 reference picture index information and MVD information of one direction (L0 or L1) as described below.

[0392] If the conditions are met, the encoder / decoder may not perform entropy encoding / decoding, but may always derive L0 and / or L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information, regardless of the information indicating whether to perform entropy encoding / decoding (e.g., "sym_mvd_flag").

[0393] The L0 reference picture index may be derived from the location information of a reference picture having a minimum POC difference with the current picture in the L0 reference picture list.

[0394] For example, when the second reference picture POC of the L0 reference picture list has the minimum difference with the current picture POC, the encoder / decoder may derive a value of '1' indicating the second reference picture in the L0 reference picture list as the L0 reference picture index.

[0395] The L1 reference picture index may be derived from the location information of a reference picture having a minimum POC difference with the current picture in the L1 reference picture list.

[0396] For example, when the second reference picture POC of the L0 reference picture list has the minimum difference with the current picture POC, the encoder / decoder may derive a value of '1' indicating the second reference picture in the L0 reference picture list as the L0 reference picture index.

[0397] After configuring the reference picture list of the current picture or slice including the encoding target block / decoding target block, checking of condition [2-1], condition [2-2], and condition [3] and derivation processing of the L0 / L1 reference picture index may be performed.

[0398] When entropy encoding / decoding the motion vector difference (MVD0) in the direction L0, the motion vector difference (MVD1) in the direction L1 can be derived as -MVD0. In other words, the horizontal and vertical motion vector differences in the direction L1 are as follows. (MVD1_x=-MVD0_x, MVD1_y=-MVD0_y) When entropy encoding / decoding the motion vector difference (MVD1) in the direction L1, the motion vector difference (MVD0) in the direction L0 can be derived as -MVD1. In other words, the horizontal and vertical motion vector differences in the direction L0 are as follows. (MVD0_x=-MVD1_x, MVD0_y=-MVD1_y) As another example, when the POC information between the current picture and the reference picture in the reference picture list satisfies the following conditions, the encoder / decoder may entropy encode / decode information (e.g., sym_mvd_flag) indicating whether to perform entropy encoding / decoding on L0 and / or L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information of the current encoding / target block decoding target block.

[0399] [Condition 1] The current encoding target block / decoding target block is in bidirectional prediction mode, and there are L0 reference pictures and L1 reference pictures.

[0400] [Condition 2] The POC difference between the current picture POC, the Nth reference picture POC of the L0 reference picture list, and the Mth reference picture POC of the L1 reference picture list satisfies the following Equation 3.

[0401] Equation 3

[0402] currPic is the POC of the current picture, RefPicList0[N-1] is the Nth reference picture POC of the L0 reference picture list, and RefPicList1[M-1] is the Mth reference picture POC of the L1 reference picture list.

[0403] Here, N and M may be natural numbers greater than 0, and have the same value or different values.

[0404] For example, when N and M have a value of '1', they may represent the first reference picture POC in the L0 / L1 reference picture list.

[0405] When the condition is satisfied and the encoded / decoded 'sym_mvd_flag' has the first value (0), the encoder / decoder may perform entropy encoding / decoding on L0 and L1 reference picture index information and MVD (motion vector difference) information of L0 and L1.

[0406] When the condition is met and the encoded / decoded 'sym_mvd_flag' has the second value (1), the encoder / decoder may not perform entropy encoding / decoding but derive L0 and / or L1 reference picture index information and MVD information of one direction (L0 or L1) as described below.

[0407] The L0 reference picture index may be derived as a value of "N-1," indicating the Nth reference picture of the L0 reference picture list.

[0408] For example, in case N=1, the L0 reference picture index may be derived as "0", indicating the first reference picture of the L0 reference picture list.

[0409] The L1 reference picture index may be derived as a value of "M-1", indicating the Mth reference picture of the L1 reference picture list.

[0410] For example, in case of M=1, the L1 reference picture index may be derived as "0", thereby indicating the first reference picture of the L1 reference picture list.

[0411] After configuring the reference picture list of the current picture or slice including the encoding target block / decoding target block, the check of condition [2] and the derivation process of the L0 / L1 reference picture index may be performed.

[0412] When entropy encoding / decoding the motion vector difference (MVD0) in the direction L0, the motion vector difference (MVD1) in the direction L1 can be derived as -MVD0. In other words, the horizontal and vertical motion vector differences in the direction L1 are as follows. (MVD1_x=-MVD0_x, MVD1_y=-MVD0_y) When entropy encoding / decoding the motion vector difference (MVD1) in the direction L1, the motion vector difference (MVD0) in the direction L0 can be derived as -MVD1. In other words, the horizontal and vertical motion vector differences in the direction L0 are as follows. (MVD0_x=-MVD1_x, MVD0_y=-MVD1_y) If conditions are met, L0 and / or L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information may be always derived without entropy encoding / decoding, regardless of information indicating whether entropy encoding / decoding is performed (e.g., “sym_mvd_flag”).

[0413] When the current picture is a B slice and the current picture POC and the POC information in the reference picture in the reference picture list satisfy at least one or more of the above conditions, the encoder can entropy encode information (e.g., smvd_mvd_flag) indicating the possibility of sending entropy decoding of "L0 and / or L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information" indicating all encoding target blocks in the current slice (e.g., smvd_mvd_flag), and send the information to the decoder at the level of sequence parameter set (SPS), picture parameter set (PPS), adaptation parameter set (APS), picture header, parallel block group header, slice header and CTU.

[0414] The decoder may entropy decode the corresponding information (e.g., smvd_enabled_flag) transmitted from the encoder, and may decode the 'sym_mvd_flag' information of the current decoding target block based on the corresponding information. Here, the smvd_enabled_flag indicating that the sym_mvd_flag may be transmitted may be signaled at the level of a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a picture header, a tile group header, a slice header, and a CTU.

[0415] Accordingly, when the following conditions are met, the encoder / decoder may perform entropy encoding / entropy decoding on information (e.g., sym_mvd_flag) indicating whether entropy encoding / entropy decoding is performed on the L0 and L1 reference picture index information (ref_idx_l0 and ref_idx_l1) and unidirectional (L0 or L1) motion vector difference information (MvdL0 or MvdL1) of the current encoding target block / decoding target block.

[0416] [Condition 1] The current encoding target block / decoding target block is in bidirectional prediction mode, and there are L0 reference pictures and L1 reference pictures.

[0417] [Condition 2-1] At least one or more of the N reference pictures in the L0 reference picture list has a POC smaller than the current picture POC, and at least one or more of the M reference pictures in the L1 reference picture list has a POC larger than the current picture POC (N and M may be natural numbers greater than 0 and may be equal to or different from each other).

[0418] [Condition 2-2] At least one or more of the N reference pictures in the L0 reference picture list has a POC greater than the current picture POC, and at least one or more of the M reference pictures in the L1 reference picture list has a POC less than the current picture POC (N and M may be natural numbers greater than 0 and may be equal to or different from each other).

[0419] [Condition 3] smvd_enabled_flag has a value indicating that sym_mvd_flag can be transmitted (for example, smvd_enabled_flag is '1') When there is no reference picture satisfying [Condition 2-1], [Condition 2-2] may be performed. Conversely, when there is no reference picture satisfying [Condition 2-2] after performing [Condition 2-2], [Condition 2-1] may be performed.

[0420] For example, the encoder / decoder may decode the "sym_mvd_flag" information only when the "tile_group_smvd_enabled_flag" transmitted from the tile group header has the second value (1) and the decoding target block is in the bidirectional prediction mode. When the "sym_mvd_flag" has the second value (1), the encoder / decoder may derive the L0 and / or L1 reference picture index information and the unidirectional motion vector difference (MVD) information of the corresponding block by using at least one or more of the above methods.

[0421] For example, when the 'tile_group_smvd_enabled_flag' transmitted from the tile group header has the first value (0), the encoder / decoder may not decode the 'sym_mvd_flag' information of all decoding target blocks, but infer the corresponding information as the first value (0), thereby performing entropy decoding on the 'L0 and L1 reference picture index information and L0 motion vector difference / L1 motion vector difference' information.

[0422] The first value and the second value are not limited to the above examples. The present invention may include a case where the same definition as in the above embodiment is applied when the first value is 1 and the second value is 0.

[0423] When the current picture is a B slice and the current picture POC and the POC information in the reference picture in the reference picture list satisfy at least one or more of the above conditions, the encoder can entropy encode information (e.g., "tile_group_smvd_enabled_flag") indicating the possibility of entropy decoding of "L0 and / or L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information" indicating all encoding target blocks in the current slice at at least one level of a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a picture header, a tile group header, a slice header, a CTU, and a CU, and can send the information to the decoder.

[0424] The decoder may entropy-decode the corresponding information (eg, 'tile_group_smvd_enabled_flag') transmitted from the encoder, and may decode 'sym_mvd_flag' information of the current decoding target block based on the corresponding information.

[0425] In addition, when at least one or more of the above-mentioned POC conditions are met, the encoder may entropy encode the location information of the L0 and / or L1 reference pictures at at least one level of the picture header, tile group header, slice header and CTU, and send the information to the decoder.

[0426] For example, Fig.13 As shown, when the "tile_group_smvd_enabled_flag" entropy-decoded in the tile group header has a second value ("1"), the decoder can entropy-decode reference picture index information (e.g., smvd_ref_idx0, smvd_ref_idx1) that is generally applicable to all target blocks included in the tile group. When the "sym_mvd_flag" information entropy-decoded in the decoding target block has a second value ("1"), the decoder can derive the reference picture of the corresponding block from the reference picture index information (e.g., smvd_ref_idx0 or smvd_ref_idx1) entropy-decoded in the tile group header. Fig.13 The groups of parallel blocks in can represent stripes.

[0427] The first value and the second value are not limited to the above examples. The present invention may include a case where the same definition as in the above embodiment is applied when the first value is 1 and the second value is 0.

[0428] When the current picture is a B slice and the current picture POC and the POC information in the reference picture in the reference picture list satisfy at least one or more of the above conditions, the encoder can entropy encode information (e.g., 'sym_mvd_flag') indicating the possibility of sending entropy decoding of "L0 and / or L1 reference picture index information and unidirectional (L0 or L1) motion vector difference (MVD) information" for all encoding target blocks in the current parallel block group at at least one level of a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a picture header, a tile group header, a slice header, a CTU, and a CU, and can send the information to the decoder.

[0429] The decoder may decode 'sym_mvd_flag' information of a current decoding target block based on corresponding information (eg, 'tile_group_smvd_enabled_flag') transmitted from the encoder.

[0430] In addition, when at least one or more of the above-mentioned POC conditions are met, the encoder may entropy encode the location information of the L0 and / or L1 reference pictures at at least one level of the tile group header, the slice header, and the CTU, and send the information to the decoder.

[0431] For example, Fig.14 As shown, when the 'tile_group_smvd_enabled_flag' entropy-decoded in the tile group header has a second value ('1'), the decoder may entropy-decode information indicating whether to use default reference picture index information generally applicable to all target blocks included in the tile group (e.g., 'default_smvd_refIdx_flag'). In addition, when the 'default_smvd_refIdx_flag' has a second value ('1'), the decoder may apply a reference picture index indicating an L0 / L1 reference picture in a predetermined position defined by an encoder / decoder to all target blocks. Fig.14 The groups of parallel blocks in can represent stripes.

[0432] For example, the reference picture index indicating a predetermined position defined in the encoder / decoder may be "0" indicating the first reference picture in the L0 reference picture list and the L1 reference picture list. When the corresponding flag ("default_smvd_refIdx_flag") has a first value (0), reference picture index information (e.g., smvd_ref_idx0 and / or smvd_ref_idx1) generally applicable to all target blocks in the parallel block group may be additionally entropy decoded. When the "sym_mvd_flag" information entropy decoded in the decoding target block has a second value ("1"), the reference picture of the corresponding block may be derived from the reference picture index (e.g., smvd_ref_idx0 and / or smvd_ref_idx1) entropy decoded in the parallel block group header.

[0433] Fig.15 sps_smvd_enable_flag is information transmitted at a sequence level. This may be information indicating whether to use a symmetric MVD mode, wherein the symmetric MVD mode is derived without entropy decoding unidirectional motion vector difference information and bidirectional reference picture index information of a coding target block / decoding target block.

[0434] Fig.16 mvd_l1_zero_flag of may be information indicating that the motion vector difference value in the L1 direction is not decoded but derived as (0, 0). When mvd_l1_zero_flag has a first value (1), it may indicate that the motion vector difference value in the L1 direction is not decoded but derived as (0, 0). When mvd_l1_zero_flag has a second value (0), it may indicate that the motion vector difference value in the L1 direction is not derived as (0, 0).

[0435] Accordingly, when the following conditions are met, the encoder / decoder may perform entropy encoding / entropy decoding on information (e.g., sym_mvd_flag) indicating whether entropy encoding / entropy decoding is performed on the L0 and L1 reference picture index information (ref_idx_l0 and ref_idx_l1) and unidirectional (L0 or L1) motion vector difference information (MvdL0 or MvdL1) of the current encoding target block / decoding target block.

[0436] [Condition 1] The current encoding target block / decoding target block is in bidirectional prediction mode, and there are L0 reference pictures and L1 reference pictures.

[0437] [Condition 2-1] At least one or more of the N reference pictures in the L0 reference picture list has a POC smaller than the current picture POC, and at least one or more of the M reference pictures in the L1 reference picture list has a POC larger than the current picture POC (N and M may be natural numbers greater than 0 and may be equal to or different from each other).

[0438] [Condition 2-2] At least one or more of the N reference pictures in the L0 reference picture list has a POC greater than the current picture POC, and at least one or more of the M reference pictures in the L1 reference picture list has a POC less than the current picture POC (N and M may be natural numbers greater than 0 and may be equal to or different from each other).

[0439] [Condition 3] sps_smvd_enabled_flag has a value indicating that sym_mvd_flag can be transmitted (eg, sps_smvd_enabled_flag is '1').

[0440] [Condition 4] mvd_l1_zero_flag has a value indicating that the motion vector difference value in the L1 direction is not derived as (0, 0) (for example, mvd_l1_zero_flag is “0”).

[0441] When there is no reference picture satisfying [Condition 2-1], [Condition 2-2] may be performed. Conversely, when there is no reference picture satisfying [Condition 2-2] after performing [Condition 2-2], [Condition 2-1] may be performed.

[0442] In addition, when the 'mvd_l1_zero_flag' information has the second value (1), at least one or more of the above-mentioned 'tile_group_smvd_enabled_flag', 'default_smvd_refIdx_flag', 'smvd_ref_idx0', 'smvd_ref_idx1', and 'sym_mvd_flag' may not be entropy encoded / decoded. In addition, although 'mvd_l1_zero_flag' is described as being encoded / decoded in the tile group header, it may be encoded / decoded at least one level of a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a picture header, a slice header, a CTU, and a CU.

[0443] Figures 16 to 18 are other embodiments of the symmetric MVD mode.

[0444] exist Fig.16, 'sym_mvd_ref_idx[i]' entropy-decoded in the tile group header may be signaled only when each reference picture list has at least one or more reference pictures.

[0445] For example, when there is one reference picture in the L0 reference picture list and there are two or more reference pictures in the L1 reference picture list, "sym_mvd_ref_idx[1]" may be entropy decoded only for the L1 direction and "sym_mvd_ref_idx[0]" may be inferred to be 0 for the L0 direction.

[0446] For another example, only one "sym_mvd_ref_idx" applied to both L0 / L1 reference picture lists may be entropy decoded.

[0447] For example, when 'tile_group_smvd_enabled_flag' has the second value (1), the decoder may entropy decode only one 'sym_mvd_ref_idx' and use L0 and L1 reference pictures indicated by the corresponding value.

[0448] When the decoder needs to generate Fig.17 When a bit stream satisfies at least one or more of [Condition A], [Condition B] and [Condition C] described in the specification, the decoder should be able to decode the bit stream that satisfies at least one or more of these conditions.

[0449] [Condition A] The POC difference between the current picture and the reference picture indicated by "sym_mvd_ref_idx[0]" and the POC difference between the current picture and the reference picture indicated by "sym_mvd_ref_idx[1]" should have different encodings, the POC difference between the current picture and the reference picture indicated by "sym_mvd_ref_idx[0]" in the L0 reference picture list should be minimized, and the POC difference between the current picture and the reference picture indicated by "sym_mvd_ref_idx[1]" in the L1 reference picture list should be minimized.

[0450] [Condition B] The POC difference between the current picture and the reference picture indicated by "sym_mvd_ref_idx[0]" and the POC difference between the current picture and the reference picture indicated by "sym_mvd_ref_idx[1]" should have different encodings.

[0451] [Condition C] The POC difference between the current picture and the reference picture indicated by “sym_mvd_ref_idx[0]” and the POC difference between the current picture and the reference picture indicated by “sym_mvd_ref_idx[1]” should be equal to each other, and the reference picture indicated by “sym_mvd_ref_idx[0]” and the reference picture indicated by “sym_mvd_ref_idx[1]” should be located in the opposite direction to the current picture.

[0452] in addition, Fig.16 and Fig.17 The groups of parallel blocks in can represent stripes.

[0453] Fig.19 is a diagram for explaining an image decoding method according to an embodiment of the present invention.

[0454] The decoder may obtain symmetric motion vector difference mode availability information from a bitstream ( S1901 ).

[0455] Here, the symmetric motion vector difference mode availability information may be a sps_smvd_enable flag obtained at a sequence level. Since the sps_smvd_enable flag has been described above, the detailed description of the sps_smvd_enable flag is omitted here.

[0456] In addition, the decoder may obtain zero motion vector difference information of the first prediction direction from the bitstream (S1902). Specifically, the zero motion vector difference information of the first prediction direction may indicate that the motion vector difference value of the first prediction direction is not decoded but is derived as (0,0).

[0457] Here, the zero motion vector difference information of the first prediction direction may be mvd_l1_zero_flag obtained at the picture level. Since mvd_l1_zero_flag has been described above, the description of mvd_l1_zero_flag is omitted in the detailed description.

[0458] In addition, the decoder may obtain symmetric motion vector difference mode information of the current block from the bitstream based on the symmetric motion vector difference mode availability information and the zero motion vector difference information of the first prediction direction ( S1903 ).

[0459] Here, the motion vector difference mode information may be the above-mentioned sym_mvd_flag.

[0460] In addition, the decoder may obtain reference picture index information of the first prediction direction, reference picture index information of the second prediction direction, and a motion vector difference value of the first prediction direction based on the symmetric motion vector difference mode information (S1904). Specifically, when the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the decoder may obtain the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction by deriving from the bitstream instead of decoding the bitstream.

[0461] When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the motion vector difference value in the first prediction direction may be derived based on the motion vector difference value in the second prediction direction of the current block.

[0462] When the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction can be derived as the index of the backward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction can be derived as the index of the forward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0463] When the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction can be derived as the index of the forward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction can be derived as the index of the backward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0464] In addition, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the reference picture index information of the first prediction direction and the reference picture index information of the second prediction direction may be derived as indexes of short-term reference pictures.

[0465] In addition, the decoder may generate a prediction block of the current block by using at least one of reference picture index information of the first prediction direction, reference picture index information of the second prediction direction, and a motion vector difference value of the first prediction direction ( S1905 ).

[0466] Here, the first prediction direction may be an L1 prediction direction, and the second prediction direction may be an L0 prediction direction.

[0467] Fig. 20 is a diagram for explaining an image encoding method according to an embodiment of the present invention.

[0468] The encoder may determine symmetric motion vector difference mode availability information (S2001).

[0469] Here, the symmetric motion vector difference mode availability information may be a sps_smvd_enable flag encoded at the sequence level. Since the sps_smvd_enable flag has been described above, the detailed description of the sps_smvd_enable flag is omitted here.

[0470] In addition, the encoder may determine zero motion vector difference information of the first prediction direction (S2002). Specifically, the zero motion vector difference information of the first prediction direction may indicate that the motion vector difference value of the first prediction direction is not encoded but is derived as (0, 0).

[0471] Here, the zero motion vector difference information of the first prediction direction may be mvd_l1_zero_flag encoded at the picture level. Since the mvd_l1_zero_flag flag has been described above, the description of the mvd_l1_zero_flag flag is omitted here in the detailed description.

[0472] In addition, the encoder may encode symmetric motion vector difference mode information of the current block based on the symmetric motion vector difference mode availability information and the zero motion vector difference information of the first prediction direction (S2003). Here, the motion vector difference mode information may be the above-mentioned sym_mvd_flag.

[0473] In addition, the encoder may determine whether to encode the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction based on the symmetric motion vector difference mode information (S2004). Specifically, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the encoder may determine the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction as not to be encoded.

[0474] When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the motion vector difference value in the first prediction direction may be derived based on the motion vector difference value in the second prediction direction of the current block.

[0475] When the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction can be derived as the index of the backward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction can be derived as the index of the forward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0476] When the symmetric motion vector difference mode information of the current block indicates a symmetric motion vector difference mode, the reference picture index information of the first prediction direction can be derived as the index of the forward reference picture closest to the current picture in the reference picture list of the first prediction direction, and the reference picture index information of the second prediction direction can be derived as the index of the backward reference picture closest to the current picture in the reference picture list of the second prediction direction.

[0477] In addition, when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the reference picture index information of the first prediction direction and the reference picture index information of the second prediction direction may be derived as indexes of short-term reference pictures.

[0478] Here, the first prediction direction may be an L1 prediction direction, and the second prediction direction may be an L0 prediction direction.

[0479] pass Fig. 20 The bit stream generated by the image encoding method described in the embodiment can be stored in a non-transitory computer-readable recording medium.

[0480] When entropy encoding / decoding at least one or more pieces of information about motion compensation, at least one or more of the following binarization methods may be used.

[0481] Truncated Rice Binarization Method k-order Exp_Golomb binarization method Finite k-order Exp_Golomb binarization method Fixed-length binarization method Unary Binarization Method Truncated Unary Binarization Method When entropy encoding / decoding at least one or more pieces of information about motion compensation, the encoder / decoder may determine a context model by using at least one or more pieces of information about motion compensation of neighboring blocks, at least one or more pieces of information about previously encoded / decoded motion information, information about a current unit / block depth, or information about a current unit / block size.

[0482] The encoder / decoder may entropy encode / decode at least one or more pieces of information about motion compensation by using at least one or more pieces of information about motion compensation of a neighboring block, at least one or more pieces of information about previously encoded / decoded motion information, information about a current unit / block depth, or information about a current unit / block size as a prediction value of the information about motion compensation of the current block.

[0483] As described in the embodiments of the present invention, a reference picture set used for reference picture list construction and reference picture list modification may use at least one or more reference picture lists of L0, L1, L2, and L3.

[0484] When calculating the boundary strength in the deblocking filter according to an embodiment of the present invention, 1 to N motion vectors of the encoding target block / decoding target block can be used. Here, N represents a positive integer of 1 or more, and can be 2, 3, 4, etc.

[0485] When the motion vector used for motion vector prediction has at least one or more of a 16-pixel (16-pel) unit, an 8-pixel (8-pel) unit, a 4-pixel (4-pel) unit, an integer pixel (integer-pel) unit, a 1 / 2-pixel (1 / 2-pel) unit, a 1 / 4-pixel (1 / 4-pel) unit, a 1 / 8-pixel (1 / 8-pel) unit, a 1 / 16-pixel (1 / 16-pel) unit, a 1 / 32-pixel (1 / 32-pel) unit, and a 1 / 64-pixel (1 / 64-pel) unit, the embodiment of the present invention may also be applied. In addition, when performing motion vector prediction, the motion vector may be selectively used for each pixel unit.

[0486] A stripe type to which the embodiment of the present invention is applied may be defined, and the embodiment of the present invention may be applied according to the corresponding stripe type.

[0487] For example, when the slice type is a T (tri-prediction) slice, at least three or more motion vectors may be used to generate a prediction block, and a weighted sum of at least three or more prediction blocks may be calculated and used as a final prediction block of an encoding target block / decoding target block. For example, when the slice type is a Q (quad-prediction) slice, at least four or more motion vectors may be used to generate a prediction block, and a weighted sum of at least four or more prediction blocks may be calculated and used as a final prediction block of an encoding target block / decoding target block.

[0488] The above embodiments of the present invention can be applied not only to inter-frame prediction and motion compensation methods using motion vector prediction but also to inter-frame prediction and motion compensation methods using skip mode and merge mode.

[0489] The above embodiments may be performed in the same way in an encoder and a decoder.

[0490] At least one or a combination of the above embodiments may be used to encode / decode a video.

[0491] The order in which the above embodiments are applied may be different between the encoder and the decoder, or the order in which the above embodiments are applied may be the same in the encoder and the decoder.

[0492] The above embodiments may be performed on each of the luminance signal and the chrominance signal, or may be performed identically on the luminance and chrominance signals.

[0493] The block form to which the above embodiment of the present invention is applied may have a square form or a non-square form.

[0494] The above embodiments of the present invention may be applied according to the size of at least one of a coding block, a prediction block, a transform block, a block, 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 embodiments are applied, or may be defined as a fixed size to which the above embodiments are applied. In addition, in the above 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 embodiments may be applied according to size combinations. In addition, the above 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 embodiments may be applied when the block size is included in a specific range.

[0495] 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.

[0496] The above embodiments of the present invention may be applied in accordance with time layers. In order to identify the time layers to which the above embodiments may be applied, a corresponding identifier may be signaled, and the above embodiments may be applied to the specified time layers identified by the corresponding identifiers. 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 embodiments may be applied, or may be defined as a specific layer indicating the application of the embodiments. In addition, a fixed time layer to which the embodiments may be applied may be defined.

[0497] For example, when the temporal layer of the current image is the lowest layer, the above embodiment can be applied. For example, when the temporal layer identifier of the current image is 1, the above embodiment can be applied. For example, when the temporal layer of the current image is the highest layer, the above embodiment can be applied.

[0498] A slice type or a tile group type to which the above embodiments of the present invention are applied may be defined, and the above embodiments may be applied depending on the corresponding slice type or tile group type.

[0499] 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 can 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 can be added to the flowchart, or some steps can be deleted from the flowchart without affecting the scope of the present invention.

[0500] 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.

[0501] The embodiments of the present invention may 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 independent program instructions, data files, data structures, 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 a person 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 optical floppy disks); and hardware devices (such as read-only memory (ROM), random access memory (RAM), flash memory, etc.) that are specially 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.

[0502] Although the present invention has been described according to specific items such as detailed elements and limited embodiments and drawings, they are only provided to help a more comprehensive understanding of the present invention, and the present invention is not limited to the above embodiments. It should be understood by those skilled in the art that various modifications and changes can be made based on the above description.

[0503] Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and the full scope of the appended claims and their equivalents will fall within the scope and spirit of the present invention.

[0504] Industrial Applicability The present invention can be used to encode or decode images.

Claims

1. A method for decoding an image, the method comprising: include: Obtaining symmetric motion vector difference mode availability information from a bitstream; Obtain zero motion vector difference information in a first prediction direction from a bitstream; obtaining symmetric motion vector difference mode information of a current block from a bitstream based on the symmetric motion vector difference mode availability information and the zero motion vector difference information of the first prediction direction; Obtaining reference picture index information of a first prediction direction, reference picture index information of a second prediction direction, and a motion vector difference value of the first prediction direction based on the symmetric motion vector difference mode information; as well as generating a prediction block of the current block by using at least one of reference picture index information of a first prediction direction, reference picture index information of a second prediction direction, and a motion vector difference value of the first prediction direction, The step of obtaining the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction is performed by deriving the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction from the bitstream instead of decoding the bitstream when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode. The zero motion vector difference information of the first prediction direction indicates that the motion vector difference value of the first prediction direction is not decoded but is derived as (0, 0). wherein zero motion vector difference information of a first prediction direction is sent by signal at picture level, The bitstream includes a picture parameter set, a video parameter set and a sequence parameter set.

2. The method according to claim 1, in, The first prediction direction is an L1 prediction direction, and the second prediction direction is an L0 prediction direction.

3. The method according to claim 1, in, Symmetric motion vector difference mode availability information is obtained at sequence level.

4. The method according to claim 1, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the motion vector difference value in the first prediction direction is derived based on the motion vector difference value in the second prediction direction of the current block.

5. The method according to claim 1, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, The reference picture index information of the first prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the first prediction direction, and The reference picture index information of the second prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the second prediction direction.

6. The method according to claim 1, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, The reference picture index information of the first prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the first prediction direction, and The reference picture index information of the second prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the second prediction direction.

7. The method according to claim 5, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the reference picture index information of the first prediction direction and the reference picture index information of the second prediction direction are derived as indexes of the short-term reference pictures.

8. A method for encoding an image, the method comprising: include: determining symmetric motion vector difference mode availability information; Determining zero motion vector difference information of a first prediction direction; as well as encoding symmetric motion vector difference mode information of the current block based on the symmetric motion vector difference mode availability information and the zero motion vector difference information of the first prediction direction, Wherein, based on the symmetric motion vector difference mode information, whether to encode the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction is determined, The step of determining whether to encode the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction is determined as not encoding the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, The zero motion vector difference information of the first prediction direction indicates that the motion vector difference value of the first prediction direction is not encoded but is derived as (0, 0). Wherein, the zero motion vector difference information of the first prediction direction is encoded at the picture level, The bitstream includes a picture parameter set, a video parameter set and a sequence parameter set.

9. The method according to claim 8, in, The first prediction direction is an L1 prediction direction, and the second prediction direction is an L0 prediction direction.

10. The method according to claim 8, in, Symmetric motion vector difference mode availability information is encoded at sequence level.

11. The method according to claim 8, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the motion vector difference value in the first prediction direction is derived based on the motion vector difference value in the second prediction direction of the current block.

12. The method according to claim 8, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, The reference picture index information of the first prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the first prediction direction, and The reference picture index information of the second prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the second prediction direction.

13. The method according to claim 8, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, The reference picture index information of the first prediction direction is derived as the index of the forward reference picture closest to the current picture in the reference picture list of the first prediction direction, and The reference picture index information of the second prediction direction is derived as the index of the backward reference picture closest to the current picture in the reference picture list of the second prediction direction.

14. The method according to claim 12, in, When the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, the reference picture index information of the first prediction direction and the reference picture index information of the second prediction direction are derived as indexes of the short-term reference pictures.

15. A method of sending a bit stream, include: determining symmetric motion vector difference mode availability information; Determining zero motion vector difference information of a first prediction direction; encoding symmetric motion vector difference mode information of the current block into the bitstream based on the symmetric motion vector difference mode availability information and the zero motion vector difference information of the first prediction direction; as well as sending the bit stream, Wherein, based on the symmetric motion vector difference mode information, whether to encode the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction is determined, The step of determining whether to encode the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction is determined as not encoding the reference picture index information of the first prediction direction, the reference picture index information of the second prediction direction, and the motion vector difference value of the first prediction direction when the symmetric motion vector difference mode information of the current block indicates the symmetric motion vector difference mode, The zero motion vector difference information of the first prediction direction indicates that the motion vector difference value of the first prediction direction is not encoded but is derived as (0, 0). Wherein, the zero motion vector difference information of the first prediction direction is encoded at the picture level, The bitstream includes a picture parameter set, a video parameter set and a sequence parameter set.

Images