Image encoding / decoding method and device, and recording medium storing bit stream

Abstract

Disclosed in the present specification are an image encoding / decoding method and apparatus, and a recording medium storing a bit stream. An image decoding method according to the present invention comprises the steps of: acquiring prediction information and residual signal information on a current block from a bitstream, the prediction information being acquired by entropy decoding, and the residual signal information being acquired, and restoring the current block on the basis of the acquired prediction information and the acquired residual signal information; and determining a context model for entropy decoding the prediction information based on a prediction mode of a neighboring block of the current block.

Description

[0001] This application is a divisional application of an invention patent application with an application date of December 27, 2019, application number 201980086971.3, and invention name “Image encoding / decoding method and device and recording medium storing bit stream”. Technical Field

[0002] The present invention relates to a method and apparatus for encoding / decoding an image, and more particularly, to a method and apparatus for adaptively performing entropy encoding / decoding using prediction information of spatially neighboring blocks. Background Art

[0003] Recently, the demand for high resolution and quality images such as high definition (HD) or ultra high definition (UHD) images has increased in various applications. 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 transmitting image data through existing transmission media such as wired broadband channels or wireless broadband channels or when storing image data. In order to solve these problems of high resolution and high quality image data, efficient image encoding / decoding technology is required.

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

[0005] There are various inter prediction modes for improving the prediction performance of image encoders / decoders. As a result, data for expressing detailed information for performing inter prediction modes and intra prediction modes increases, resulting in a bit amount overhead for compression.

[0006] Conventional encoders / decoders use each inter-frame prediction mode indicator according to a sequence to express various inter-frame prediction information. However, since the predetermined sequence does not match the sequence of the frequency of the inter-frame prediction modes that actually occur, the binary bits are allocated inefficiently, resulting in a performance loss in encoding / decoding.

[0007] In addition, in a conventional encoder / decoder, since inter-frame prediction modes performing similar functions are divided into different indicators, there is a problem of increased bit overhead for the indicators and probability dispersion, resulting in performance loss of probability-based entropy coding. Summary of the invention

[0008] Technical issues

[0009] An object of the present invention is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0010] Another object of the present invention is to provide an image encoding / decoding method and device, which is used to reduce bit overhead by arranging a series of parsing sequences used to represent inter-frame prediction information in order from highest to lowest frequency of occurrence when expressing inter-frame prediction mode information, and allocating smaller bits in order of high frequency of occurrence.

[0011] Another object of the present invention is to improve entropy coding performance by combining similar inter-frame prediction modes and expressing them in one mode to reduce bits and concentrate the probability of occurrence of prediction modes.

[0012] Another object of the present invention is to perform entropy encoding / decoding on prediction determination information of a current coding block based on prediction information of spatially neighboring blocks.

[0013] Another object of the present invention is to provide a recording medium storing a bit stream generated by the image encoding method / device of the present invention.

[0014] Technical Solution

[0015] According to an embodiment of the present invention, a method for decoding an image may include: obtaining prediction information and residual signal information for a current block from a bit stream, and reconstructing the current block based on the obtained prediction information and the residual signal information, wherein the prediction information is obtained by entropy decoding, and wherein a context model for entropy decoding the prediction information is determined based on a prediction mode of a neighboring block of the current block.

[0016] In the image decoding method of the present invention, the prediction information is used to determine the prediction mode of the current block, and the prediction information includes at least one of the following items: general merge mode information, MMVD (merge mode with motion vector difference) mode information, triangle partition mode information, CIIP (combined inter-frame and intra-frame prediction) mode information, IBC (intra-frame block copy) mode information and sub-block merge mode information.

[0017] In the image decoding method of the present invention, the MMVD mode information is decoded based on the general merge mode information.

[0018] In the image decoding method of the present invention, the MMVD mode information is decoded based on the IBC mode information.

[0019] In the image decoding method of the present invention, the triangle partitioning mode information is decoded based on the general merge mode information, the CIIP mode information and the sub-block merge mode information.

[0020] In the image decoding method of the present invention, the step of obtaining the residual signal information includes: obtaining the residual signal information of the current block when the horizontal size or the vertical size of the current block is greater than a predetermined size.

[0021] In the image decoding method of the present invention, the predetermined size is determined based on maximum transform block size information obtained from the bit stream.

[0022] In the image decoding method of the present invention, the neighboring block is at least one block located on the left side or the top of the current block.

[0023] In the image decoding method of the present invention, the context model is determined based on whether the prediction mode of the neighboring block is an intra-frame prediction mode.

[0024] According to an embodiment of the present invention, a method for encoding an image may include: generating prediction information and residual signal information for a current block, and reconstructing the current block based on the prediction information and the residual signal information, wherein the prediction information includes at least one of the following items: general merge mode information, MMVD (merge mode with motion vector difference) mode information, triangle partition mode information, CIIP (combined inter-frame and intra-frame prediction) mode information, IBC (intra-frame block copy) mode information and sub-block merge mode information, and wherein the MMVD mode information is encoded based on the general merge mode information.

[0025] In the image encoding method of the present invention, the MMVD mode information is encoded based on the general merge mode information.

[0026] In the image encoding method of the present invention, the triangle partitioning mode information is encoded based on the general merge mode information, the CIIP mode information and the sub-block merge mode information.

[0027] In the image encoding method of the present invention, when the horizontal size or the vertical size of the current block is larger than the maximum transform block size, the step of generating the residual signal information is performed.

[0028] A computer-readable recording medium according to an embodiment of the present invention may be a non-temporary computer-readable recording medium storing a bit stream decoded by an image decoding device, wherein the bit stream includes prediction information and residual signal information for a current block, wherein the prediction information is used to determine a prediction mode of the current block, wherein the current block is reconstructed based on the prediction information and the residual signal information, wherein the prediction information is obtained through entropy decoding in the image decoding device, and wherein a context model for entropy decoding the prediction information is determined based on the prediction mode of a neighboring block of the current block.

[0029] Beneficial Effects

[0030] According to the present invention, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0031] Furthermore, according to the present invention, it is possible to provide an image encoding / decoding method and apparatus capable of adjusting a signal transmission order in the order of frequency of inter prediction information when transmitting a signal for inter prediction mode information.

[0032] In addition, according to the present invention, by combining similar inter-frame prediction modes, the performance of an entropy encoder and an entropy decoder for an inter-frame prediction mode can be improved.

[0033] Furthermore, according to the present invention, there can be provided a recording medium storing a bit stream generated by the image encoding method / apparatus of the present invention.

[0034] Furthermore, according to the present invention, there can be provided a recording medium storing a bit stream, wherein the bit stream is received, decoded, and used by the image decoding apparatus according to the present invention to reconstruct an image. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a block diagram showing a configuration of an encoding device according to an embodiment to which the present invention is applied.

[0036] Figure 2 is a block diagram showing a configuration of a decoding device according to an embodiment to which the present invention is applied.

[0037] Figure 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded.

[0038] Figure 4 is a diagram illustrating an intra prediction process.

[0039] Figure 5 is a diagram illustrating an embodiment of an inter-frame prediction process.

[0040] Figure 6is a diagram illustrating transform and quantization processing.

[0041] Figure 7 is a diagram showing reference samples that can be used for intra prediction.

[0042] Figure 8 is a flowchart illustrating an encoding / decoding process of a skip indicator according to one embodiment of the present invention.

[0043] Fig. 9 is a flowchart illustrating an encoding / decoding process of a prediction mode indicator according to an embodiment of the present invention.

[0044] Fig.10 and Fig.11 is a diagram illustrating an embodiment of an encoding / decoding process for single inter prediction mode information according to multiple inter prediction mode information.

[0045] Fig.12 is a diagram illustrating one embodiment of an inter prediction mode according to multiple inter prediction mode information.

[0046] Fig.13 is a diagram illustrating one embodiment of an inter prediction mode according to inter prediction mode information including combined inter prediction mode information.

[0047] Fig.14 is a diagram for explaining a process of performing entropy encoding / decoding of inter prediction mode information independently of previously encoded / decoded inter prediction mode information according to one embodiment of the present invention.

[0048] Fig.15 is a diagram for explaining a process of performing entropy encoding / decoding of inter prediction mode information according to previously encoded / decoded inter prediction mode information according to one embodiment of the present invention.

[0049] Fig.16 and Fig.17 is a diagram illustrating one embodiment of combining detailed inter prediction mode information.

[0050] Fig.18 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.

[0051] Fig.19 is a diagram for explaining an image encoding method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] Various modifications may be made to the present invention, and there are various embodiments of the present invention, and examples of various embodiments of the present invention will now be provided and described in detail with reference to the accompanying drawings. However, although the exemplary embodiments may be interpreted as including all modifications, equivalents or alternative forms within the technical concept and technical scope of the present invention, the present invention is not limited thereto. Similar reference numerals refer to the same or similar functions in various aspects. In the accompanying drawings, the shapes and sizes of the elements may be exaggerated for clarity. In the following detailed description of the present invention, reference is made to the accompanying drawings that illustrate specific embodiments in which the present invention may be implemented by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to implement the present disclosure. It should be understood that the various embodiments of the present disclosure, although different, are not necessarily mutually exclusive. For example, without departing from the spirit and scope of the present disclosure, the specific features, structures and characteristics described herein in conjunction with one embodiment may be implemented in other embodiments. In addition, it should be understood that without departing from the spirit and scope of the present disclosure, the position or arrangement of each element within each disclosed embodiment may be modified. Therefore, the following detailed description should not be understood in a limiting sense, and the scope of the present disclosure is limited only by the appended claims (in the case of appropriate interpretation, together with the full range of equivalent forms claimed by the claims).

[0053] The terms "first", "second", etc. used in the specification may be used to describe various components, but these components are not interpreted as being limited to these terms. These terms are only used to distinguish one component from other components. For example, without departing from the scope of the present invention, the "first" component may be referred to as the "second" component, and the "second" component may also be similarly referred to as the "first" component. The term "and / or" includes a combination of multiple items or any one of the multiple items.

[0054] It will be understood that, in this specification, when an element is merely referred to as being “connected to” or “coupled to” another element rather than being “directly connected to” or “directly coupled to” the other element, the element may be “directly connected to” or “directly coupled to” the other element, or connected to or coupled to the other element with other elements between the element and the other element. Conversely, it should be understood that when an element is referred to as being “directly coupled to” or “directly coupled to” another element, there are no intervening elements.

[0055] In addition, the components shown in the embodiments of the present invention are shown independently to present characteristic functions different from each other. Therefore, this does not mean that each component is composed of a component unit of separate hardware or software. In other words, for convenience, each component includes each of the enumerated components. Therefore, at least two components in each component can be combined to form a component, or a component can be divided into a plurality of components for performing each function. Without departing from the essence of the present invention, the embodiment in which each component is combined and the embodiment in which a component is divided are also included in the scope of the present invention.

[0056] The terms used in this specification are only used to describe specific embodiments, and are not intended to limit the present invention. Unless the expression used in the singular has a significantly different meaning in the context, it includes plural expressions. In this specification, it will be understood that terms such as "including ... ", "having ... ", etc. are intended to indicate that there are features, quantities, 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, quantities, 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", the elements other than the corresponding elements are not excluded, but additional elements may be included in embodiments of the present invention or in the scope of the present invention.

[0057] In addition, some components may not be indispensable components for performing the necessary functions of the present invention, but optional components that only improve their performance. The present invention can be implemented by only including the indispensable components for implementing the essence of the present invention and excluding the components used when improving performance. The structure that only includes the indispensable components and excludes the optional components used when only improving performance is also included in the scope of the present invention.

[0058] 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 structures may unnecessarily obscure the understanding of the present invention, and therefore they will not be described in detail. 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.

[0059] 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.”

[0060] Hereinafter, the terms "motion picture" and "video" may be used as the same meaning and may be replaced with each other.

[0061] Hereinafter, a target image may be an encoding target image as a target of encoding and / or a decoding target image as a target of decoding. In addition, a target image may be an input image input to an encoding device, and an input image input to a decoding device. Here, the target image may have the same meaning as the current image.

[0062] Hereinafter, the terms "image", "picture", "frame" and "screen" may be used as the same meaning and replaced with each other.

[0063] Hereinafter, the target block may be an encoding target block as a target of encoding and / or a decoding target block as a target of decoding. 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.

[0064] Hereinafter, the terms "block" and "unit" may be used as the same meaning and replaced with each other. Alternatively, a "block" may refer to a specific unit.

[0065] In the following, the terms "region" and "segment" are used interchangeably.

[0066] 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.

[0067] 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.

[0068] 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 columns, rows, indexes, etc. may be counted from 0 or 1.

[0069] Description of terms

[0070] Encoder: This refers to a device that performs encoding. In other words, it refers to an encoding device.

[0071] Decoder: Refers to a device that performs decoding. In other words, it refers to a decoding device.

[0072] Block: is an M×N sample array. Here, M and N may represent positive integers, and a block may represent a sample array in a two-dimensional form. A block may refer to a unit. A current block may represent an encoding target block that becomes a target at the time of encoding, or a decoding target block that becomes a target at the time of decoding. In addition, the current block may be at least one of a coding block, a prediction block, a residual block, and a transform block.

[0073] Sample: It is the basic unit of a block. According to the bit depth (Bd), the sample can be expressed from 0 to 2 Bd In the present invention, a sample point may be used as the meaning of a pixel. That is, a sample point, a pel, and a pixel may have the same meaning as each other.

[0074] Unit: may refer to a coding and decoding unit. When encoding and decoding an image, a unit may be a region generated by partitioning a single image. In addition, when a single image is partitioned into sub-division units during encoding or decoding, a unit may represent a sub-division unit. That is, an image may be partitioned into a plurality of units. When encoding and decoding an image, a predetermined process may be performed for each unit. 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 the unit may be a two-dimensional geometric figure, such as a square shape, a rectangular shape, a trapezoidal shape, a triangular shape, a pentagonal shape, and the like. Also, the unit information may include at least one of a unit type indicating a coding unit, a prediction unit, a transformation unit, etc., and a unit size, a unit depth, an order of encoding and decoding of the unit, and the like.

[0075] 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.

[0076] When the size of the coding block is within a predetermined range, it can be divided using only quadtree partitioning. Here, the predetermined range may be defined as at least one of the maximum size and the minimum size of the coding block that can be divided using only quadtree partitioning. Information indicating the maximum / minimum size of the coding block that allows quadtree partitioning may be transmitted by signaling through a bitstream, and the information may be transmitted by signaling 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 may be divided using only quadtree partitioning. Optionally, when the size of the coding block is larger than the size of the maximum conversion block, it may be divided using only quadtree partitioning. Here, the block to be divided may be at least one of a coding block and a transform block. In this case, the information indicating the division of the coding block (e.g., split_flag) may be a flag indicating whether quadtree partitioning is performed. When the size of the coding block falls within a predetermined range, it may be divided using only binary tree partitioning or ternary tree partitioning. In this case, the above description of the quadtree partition can be applied to the binary tree partition or the ternary tree partition in the same manner.

[0077] Coding tree block: may be used as a term for designating any one of a Y coding tree block, a Cb coding tree block, and a Cr coding tree block.

[0078] 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.

[0079] Reconstructed neighboring block: may refer to 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 refer to a reconstructed neighboring unit. The reconstructed spatial neighboring block may be a block that is within the current picture and has been reconstructed by encoding or decoding or both encoding and decoding. The reconstructed temporal neighboring block is a block at a position corresponding to the current block of the current picture within the reference image or a neighboring block of the block.

[0080] Unit depth: can represent the degree of partitioning of a unit. In a tree structure, the highest node (root node) can correspond to the first unit that is not partitioned. In addition, the highest node can have a minimum depth value. In this case, the depth of the highest node can be level 0. A node with a depth of level 1 can represent a unit generated by partitioning the first unit once. A node with a depth of level 2 can represent a unit generated by partitioning the first unit twice. A node with a depth of level n can represent a unit generated by partitioning the first unit n times. A leaf node can be the lowest node and a node that cannot be further partitioned. The depth of a leaf node can be the maximum level. For example, the predefined value of the maximum level can be 3. The depth of the root node can be the lowest, and the depth of the leaf node can be the deepest. In addition, when a unit is represented as a tree structure, the level at which the unit exists can represent the unit depth.

[0081] Bitstream: can represent a stream of bits including coded image information.

[0082] Parameter set: corresponds to header information in the configuration within 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 a tile header information. The term "tile group" may mean a group of tiles and has the same meaning as a slice.

[0083] An adaptation parameter set may refer to a parameter set that can be shared by reference in different pictures, sub-pictures, slices, tile groups, tiles, or partitions. In addition, information in an adaptation parameter set may be used by referencing a different adaptation parameter set for a sub-picture, slice, tile group, tile, or partition within a picture.

[0084] In addition, regarding the 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.

[0085] 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.

[0086] In addition, regarding the adaptation parameter set, different adaptation parameter sets may be referenced by using identifiers of different adaptation parameter sets for tiles or partitions within a slice.

[0087] In addition, regarding the adaptation parameter sets, different adaptation parameter sets may be referenced by using identifiers of different adaptation parameter sets for partitions within a tile.

[0088] Information about the adaptation parameter set identifier may be included in a parameter set or a header of the sub-picture, and an adaptation parameter set corresponding to the adaptation parameter set identifier may be used for the sub-picture.

[0089] 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.

[0090] 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.

[0091] A picture may be partitioned into one or more tile rows and one or more tile columns.

[0092] 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 shape within a picture and may include one or more CTUs. In addition, at least one or more parallel blocks / blocks / strips may be included in a sub-picture.

[0093] A tile may be an area having a rectangular / square shape within a picture and may include one or more CTUs. In addition, a tile may be partitioned into one or more partitions.

[0094] A partition may refer to one or more CTU rows within a tile. A tile may be partitioned into one or more partitions, and each partition may have at least one or more CTU rows. A tile that is not partitioned into two or more may be referred to as a partition.

[0095] A slice may include one or more tiles within a picture, and may include one or more partitions within a tile.

[0096] Parsing: may mean determining the value of a syntax element by performing entropy decoding, or may mean the entropy decoding itself.

[0097] 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.

[0098] Prediction mode: may be information indicating a mode of encoding / decoding using intra-frame prediction or a mode of encoding / decoding using inter-frame prediction.

[0099] Prediction unit: may represent a basic unit when performing prediction (such as inter-frame prediction, intra-frame prediction, inter-frame compensation, intra-frame compensation, and motion compensation). A single prediction unit may be partitioned into multiple partitions of smaller size, or may be partitioned into multiple prediction units of lower levels. Multiple partitions may be basic units when performing prediction or compensation. Partitions generated by splitting a prediction unit may also be prediction units.

[0100] Prediction unit partition: may represent a shape obtained by partitioning a prediction unit.

[0101] A reference picture list may refer to a list including one or more reference pictures used for inter prediction or motion compensation. There are several types of available reference picture lists, including LC (List Combination), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3).

[0102] The inter prediction indicator may refer to the direction of inter prediction (unidirectional prediction, bidirectional prediction, etc.) of the current block. 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.

[0103] 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.

[0104] The reference picture index may refer to an index indicating a specific reference picture in a reference picture list.

[0105] A reference picture may refer to a reference picture that is referenced by a specific block for the purpose of performing inter-frame prediction or motion compensation on the specific block. Alternatively, a reference picture may be a picture including a reference block that is referenced by a current block for inter-frame prediction or motion compensation. Hereinafter, the terms "reference picture" and "reference image" have the same meaning and may be replaced with each other.

[0106] A motion vector may be a two-dimensional vector used for inter-frame prediction or motion compensation. A motion vector may represent an offset between a coding / decoding target block and a reference block. For example, (mvX, mvY) may represent a motion vector. Here, mvX may represent a horizontal component, and mvY may represent a vertical component.

[0107] The search range may be a two-dimensional area 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.

[0108] The motion vector candidate may refer to a prediction candidate block or a motion vector of the prediction candidate block when predicting a motion vector. In addition, the motion vector candidate may be included in a motion vector candidate list.

[0109] The motion vector candidate list may mean a list consisting of one or more motion vector candidates.

[0110] The motion vector candidate index may represent an indicator indicating a motion vector candidate in the motion vector candidate list. Alternatively, the motion vector candidate index may be an index of a motion vector predictor.

[0111] The motion information may represent information including at least one of the following items: 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.

[0112] The merge candidate list may mean a list consisting of one or more merge candidates.

[0113] The merge candidate may represent a spatial merge candidate, a temporal merge candidate, a combined merge candidate, a combined bi-predictive merge candidate, or a zero merge candidate. The merge candidate may include motion information such as a reference picture index for each list, a motion vector, a prediction list utilization flag, and an inter prediction indicator.

[0114] The merge index may represent an indicator indicating a merge candidate in the merge candidate list. Alternatively, the merge index may indicate a block from which the merge candidate is derived in a reconstructed block that is spatially / temporally adjacent to the current block. Alternatively, the merge index may indicate at least one piece of motion information of the merge candidate.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] Delta quantization parameter: may represent the difference between the predicted quantization parameter and the quantization parameter of the encoding / decoding target unit.

[0119] Scan: can refer to a method of ordering coefficients within a cell, block, or matrix. For example, the operation of changing a two-dimensional matrix of coefficients to a one-dimensional matrix can be called a scan, and the operation of changing a one-dimensional matrix of coefficients to a two-dimensional matrix can be called a scan or an inverse scan.

[0120] 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.

[0121] 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 for which dequantization will be performed 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.

[0122] 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.

[0123] 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.

[0124] Quantization matrix coefficients: can represent each element in the quantization matrix. Quantization matrix coefficients can also be called matrix coefficients.

[0125] Default matrix: may represent a predetermined quantization matrix preliminarily defined in an encoder or decoder.

[0126] Non-default matrix: may represent a quantization matrix that is not initially defined in the encoder or decoder but is signaled by the user.

[0127] Statistical value: The statistical value for at least one of the variables, coding parameters, constant values, etc. having calculable specific values ​​can be one or more of the average value, total 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.

[0128] Figure 1 is a block diagram showing a configuration of an encoding device according to an embodiment to which the present invention is applied.

[0129] 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.

[0130] 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.

[0131] The encoding device 100 may perform encoding on the input image by using an intra mode or an inter mode or both the intra mode and the 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 be switched to the intra mode. Alternatively, when the inter mode is used as a prediction mode, the switch 115 may be switched to the inter mode. Here, the intra mode may represent an intra prediction mode, and the inter mode may represent an inter prediction mode. The encoding device 100 may generate a prediction block for an input block of the input image. In addition, the encoding device 100 may encode the residual block using the residual of the input block and the prediction block after generating the prediction block. The input image may be referred to as a current image as a current encoding target. The input block may be referred to as a current block as a current encoding target, or may be referred to as an encoding target block.

[0132] 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.

[0133] 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 image when performing motion prediction, and derive a motion vector by using the retrieved area. In this case, the search area may be used as the area. The reference image may be stored in the reference picture buffer 190. Here, when encoding / decoding of the reference image is performed, the reference image may be stored in the reference picture buffer 190.

[0134] 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.

[0135] 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, the merge mode, the advanced motion vector prediction (AMVP) mode, and the current picture reference mode is used for motion prediction and motion compensation of the prediction unit included in the corresponding coding unit. Then, depending on the determined mode, inter-picture prediction or motion compensation may be performed differently.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] In order to encode the transform coefficient level (quantized level), the entropy encoding unit 150 may change the coefficient in the two-dimensional block form into a one-dimensional vector form by using a transform coefficient scanning method.

[0143] The coding parameters may include information such as syntax elements (flags, indexes, etc.) that are encoded in the encoder and transmitted 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, the direction of multi-type tree partitioning direction (horizontal or vertical), type of multi-type tree partitions (symmetric or asymmetric) and tree (binary tree or ternary tree) structure of multi-type tree partitions, 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, frame 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, residual Information on whether a difference signal exists, coding block pattern, coding block flag (CBF), quantization parameter, quantization parameter residual, quantization matrix, whether to apply an in-loop filter, in-loop filter coefficients, in-loop filter taps, in-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 an adaptive sample point offset, adaptive sample point offset value, adaptive sample point offset category, adaptive sample point 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 value, positive and negative sign information, reconstructed luminance sample, reconstructed chrominance sample, residual luminance sample, residual chrominance sample, luminance transform coefficient, chrominance transform coefficient, quantized luminance level, quantized chrominance level, transform coefficient level scanning method, size of motion vector search area on decoder side , the shape of the motion vector search area at the decoder side, the number of motion vector searches at the decoder side, information about the CTU size, information about the minimum block size, information about the maximum block size, information about the maximum block depth, information about the minimum block depth, image display / output order, slice identification information, slice type, slice partition information, parallel block identification information, parallel block type, parallel block partition information, parallel block group identification information, parallel block group type, parallel block 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. ,

[0144] 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.

[0145] When the encoding apparatus 100 performs encoding by inter-frame prediction, the encoded current image may be used as a reference image for another image that is subsequently processed. Therefore, the encoding apparatus 100 may reconstruct or decode the encoded current image, or store the reconstructed or decoded image as a reference image in the reference picture buffer 190.

[0146] 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. A reconstructed block may be generated by adding the dequantized or inversely transformed coefficient or the dequantized and inversely transformed coefficient to the prediction block. 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.

[0147] 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.

[0148] 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.

[0149] 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 and 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.

[0150] 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 through a coding unit (CU), and the form and coefficient of ALF to be applied to each block may vary.

[0151] The reconstructed block or the reconstructed image that has passed through the filter unit 180 may be stored in the reference picture buffer 190. The reconstructed block processed by the filter unit 180 may be a part of the reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks processed by the filter unit 180. The stored reference image may be used later in inter-frame prediction or motion compensation.

[0152] Figure 2 is a block diagram showing a configuration of a decoding device according to an embodiment to which the present invention is applied.

[0153] The decoding device 200 may be a decoder, a video decoding device, or an image decoding device.

[0154] Reference Figure 2 , the decoding device 200 may include an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra-frame prediction unit 240, a motion compensation unit 250, an adder 225, a filter unit 260 and a reference picture buffer 270.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] In order to decode the transform coefficient levels (quantized levels), the entropy decoding unit 210 may change the coefficients in the form of a one-way vector into a two-dimensional block form by using a transform coefficient scanning method.

[0160] 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.

[0161] 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.

[0162] When the inter mode is used, the motion compensation unit 250 may generate a prediction block by performing motion compensation on the current block, wherein the motion compensation uses a motion vector and a reference image stored in the reference picture buffer 270 .

[0163] 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 the reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks processed by the filter unit 260. The stored reference image can be used later in inter-frame prediction or motion compensation.

[0164] 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 multiple lower-level cells is schematically shown.

[0165] 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 transform coefficient.

[0166] 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.

[0167] The partition structure may indicate 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 partitioning. 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 predefined depth or a predefined size. For example, the depth of the LCU may be 0, and the depth of the smallest coding unit (SCU) may be a predefined maximum depth. Here, as described above, the LCU may be a coding unit having 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 as the horizontal size or vertical size or both the horizontal size and the vertical size of the CU decrease through partitioning, the CU depth increases by 1. For example, for each depth, the size of the non-partitioned CU may be 2N×2N. In addition, in the case of a partitioned CU, a CU of size 2N×2N may be partitioned into four CUs of size N×N. As the depth increases by 1, the size of N may be halved.

[0168] In addition, information on whether a CU is partitioned may be indicated by using 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.

[0169] Reference Figure 3 , an LCU with a depth of 0 may be a 64×64 block. 0 may be the minimum depth. An SCU with a depth of 3 may be an 8×8 block. 3 may be the maximum depth. A CU with a block of 32×32 and a block of 16×16 may be represented as depth 1 and depth 2, respectively.

[0170] 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, the size of each of the four coding units partitioned may be 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.

[0171] For example, when one coding unit is partitioned into two sub-coding units, the horizontal size or vertical size (width or height) of each of the two sub-coding units may be half of the horizontal size or vertical size of the original coding unit. For example, when a coding unit of size 32×32 is partitioned vertically into two sub-coding units, each of the two sub-coding units may have a size of 16×32. For example, when a coding unit of size 8×32 is partitioned horizontally into two sub-coding units, each of the two sub-coding units may have a size of 8×16. When one coding unit is partitioned into two sub-coding units, the coding unit may be said to be binary partitioned, or partitioned according to a binary tree partition structure.

[0172] 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 in 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 vertically divided 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 ternary partitioned or partitioned according to a ternary tree partition structure.

[0173] 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.

[0174] 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 a coding block obtained from a binary tree partition or a ternary tree partition of a coding unit corresponding to a leaf node of a quadtree from being further quadtree partitioned, a block partitioning operation and / or an operation of transmitting partition information with a signal may be effectively performed.

[0175] The fact that the coding unit corresponding to the node of the quadtree is partitioned may be signaled using the quad partition information. The quad 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 quad 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 quad partition information may be a flag having a predetermined length (e.g., one bit).

[0176] 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 be further partitioned by any 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 be further partitioned by the binary tree partitioning or the ternary tree partitioning, or may not be further partitioned.

[0177] 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.

[0178] The multi-type tree partition indication information having a first value (eg, "1") may indicate that the current coding unit will be subjected to 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 be subjected to multi-type tree partitioning.

[0179] 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 according to 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.

[0180] When the coding unit corresponding to the node of the multi-type tree is further partitioned according to the multi-type tree partition structure, the current coding unit may include partition tree information. The partition tree information may indicate a tree partition structure to be used to partition the 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.

[0181] The partition indication information, the partition tree information and the partition direction information may all be flags having a predetermined length (eg, one bit).

[0182] At least any one of the quadtree partition indication information, the multi-type tree partition indication information, the partition direction information, and the partition tree information may be entropy encoded / decoded. In order to entropy encode / decode those types of information, information about neighboring coding units adjacent to the current coding unit may be used. For example, 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 likely to be similar to the partition type of the current coding unit. Therefore, context information for entropy encoding / decoding the information about the current coding unit may be derived from the information about the neighboring coding units. The information about the neighboring coding units may include at least any one of the quadtree partition information, the multi-type tree partition indication information, the partition direction information, and the partition tree information.

[0183] As another example, among binary tree partitioning and ternary tree partitioning, binary tree partitioning may be preferentially performed. That is, the current coding unit may be firstly subjected to binary tree partitioning, and then the coding unit corresponding to the leaf node of the binary tree may be set as the root node for the ternary tree partitioning. In this case, for the coding unit corresponding to the node of the ternary tree, neither quadtree partitioning nor binary tree partitioning may be performed.

[0184] A coding unit that cannot be partitioned according to a quadtree partition structure, a binary tree partition structure, and / or a ternary tree partition structure becomes a basic unit for encoding, prediction, and / or transformation. That is, the coding unit cannot be further partitioned for prediction and / or transformation. Therefore, partition structure information and partition information for partitioning a coding unit into prediction units and / or transformation units may not exist in the bitstream.

[0185] However, when the size of the coding unit (i.e., the basic unit for partitioning) is larger than the size of the maximum transform block, the coding unit may be recursively partitioned until the size of the coding unit is reduced to be equal to or smaller than the size of the maximum transform block. For example, when the size of the coding unit is 64×64 and when the size of the maximum transform block is 32×32, the coding unit may be partitioned into four 32×32 blocks for transforming. For example, when the size of the coding unit is 32×64 and the size of the maximum transform block is 32×32, the coding unit may be partitioned into two 32×32 blocks for transforming. In this case, the partitioning of the coding unit for transforming is not separately signaled, and the partitioning of the coding unit for transforming may be determined by comparison between the horizontal size or vertical size of the coding unit and the horizontal size or vertical size of the maximum transform block. For example, when the horizontal size (width) of the coding unit is larger than the horizontal size (width) of the maximum transform block, the coding unit may be vertically divided into two equal parts. For example, when the vertical size (height) of the coding unit is larger than the vertical size (height) of the maximum transform block, the coding unit may be horizontally divided into two equal parts.

[0186] Information of the maximum and / or minimum size of the coding unit and information of the maximum and / or minimum size of the transform block may be signaled or determined at a higher level of the coding unit. The higher level may be, for example, a sequence level, a picture level, a slice level, a tile group level, a tile block level, etc. For example, the minimum size of the coding unit may be determined as 4×4. For example, the maximum size of the transform block may be determined as 64×64. For example, the minimum size of the transform block may be determined as 4×4.

[0187] Information of a minimum size of a coding unit corresponding to a leaf node of a quadtree (quadtree minimum size) and / or information of a maximum depth of a multi-type tree from a root node to a leaf node (maximum tree depth of a multi-type tree) may be signaled or determined at a higher level of the coding unit. For example, the higher level may be a sequence level, a picture level, a slice level, a tile group level, a tile level, etc. Information of the minimum size of the quadtree and / or information of the maximum depth of the multi-type tree may be signaled or determined for each of an intra-picture slice and an inter-picture slice.

[0188] 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. 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-frame slice, the maximum size of the ternary tree may be 32×32. For example, for an inter-frame 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 as the minimum size of the coding block.

[0189] 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.

[0190] Depending on the size information 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 be included in the bitstream or may not be included in the bitstream.

[0191] 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 derived from the second value.

[0192] 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 binary partitioned or ternary partitioned. Therefore, the multi-type tree partition indication information may not be transmitted by a signal, but may be derived from the second value.

[0193] 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 by binary or ternary partitions. Therefore, the multi-type tree partition indication information may not be transmitted 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 according to the binary tree partition structure and / or the ternary tree partition structure, a coding unit smaller than the minimum size of the binary tree and / or the minimum size of the ternary tree is generated.

[0194] Optionally, the binary tree partition or ternary tree partition may be limited based on the size of the virtual pipeline data unit (hereinafter, the pipeline buffer size). For example, when the coding unit is divided into sub-coding units that do not fit 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 (e.g., 64×64). For example, when the pipeline buffer size is 64×64, the following division may be limited.

[0195] - N×M (N and / or M is 128) ternary tree partitions for coding units

[0196] - 128×N (N<=64) binary tree partitions along the horizontal direction for the coding unit

[0197] - N×128 (N<=64) binary tree partitions along the vertical direction for the coding unit

[0198] 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 binary partitioned and / or ternary partitioned. Therefore, the multi-type tree partition indication information may not be transmitted by a signal, but may be derived from the second value.

[0199] Optionally, the multi-type tree partition indication information can be transmitted by signal only when at least one of the vertical binary tree partition, the horizontal binary tree partition, the vertical ternary tree partition, and the horizontal ternary tree partition is feasible for the coding unit corresponding to the node of the multi-type tree. Otherwise, the coding unit may not be binary partitioned and / or ternary partitioned. Therefore, the multi-type tree partition indication information may not be transmitted by signal, but may be derived from the second value.

[0200] Optionally, only when both vertical binary tree partitioning and horizontal binary tree partitioning or both vertical ternary tree partitioning and horizontal ternary tree partitioning are feasible for the coding unit corresponding to the node of the multi-type tree, the partition direction information can be transmitted by signal. Otherwise, the partition direction information may not be transmitted by signal, but may be derived from the value indicating the possible partition direction.

[0201] 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 feasible for the coding tree corresponding to the node of the multi-type tree. Otherwise, the partition tree information may not be signaled, but may be derived from a value indicating a possible partition tree structure.

[0202] Figure 4 is a diagram illustrating an intra prediction process.

[0203] Figure 4 The arrows from the center to the outside in may represent the prediction direction of the intra prediction mode.

[0204] 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.

[0205] 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.

[0206] 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.

[0207] Regardless of the block size, the number of intra-frame prediction modes can be fixed to N. Optionally, 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.

[0208] 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, and thus the replaced sample value is used as the reference sample of the current block.

[0209] Figure 7 is a diagram showing reference samples that can be used for intra prediction.

[0210] As in Figure 7 As shown in , at least one of the reference sample line 0 to the reference sample line 3 can be used for intra prediction of the current block. Figure 7 In the example, the samples of fragment A and fragment F may be filled with the samples of the closest fragment B and fragment E, respectively, instead of being retrieved from the reconstructed neighboring blocks. Index information indicating the reference sample line to be used for intra prediction of the current block may be transmitted by signal. When the upper boundary of the current block is the boundary of the CTU, only the reference sample line 0 may be available. Therefore, in this case, the index information may not be transmitted by signal. When a reference sample line other than the reference sample line 0 is used, filtering for the prediction block, which will be described later, may not be performed.

[0211] When intra prediction is performed, a filter may be applied to at least one of a reference sample and a prediction sample based on an intra prediction mode and a current block size.

[0212] In the case of the planar mode, when generating the prediction block of the current block, according to the position of the prediction target sample in the prediction block, the sample value of the prediction target sample may be generated by using the weighted sum of the upper reference sample and the left reference sample of the current sample and the upper right reference sample and the lower left reference sample of the current block. In addition, in the case of the DC mode, when generating the prediction block of the current block, the average value of the upper reference sample and the left reference sample of the current block may be used. In addition, in the case of the angular mode, the prediction block may be generated by using the upper reference sample, the left reference sample, the upper right reference sample and / or the lower left reference sample of the current block. In order to generate the prediction sample value, interpolation of real units may be performed.

[0213] In the case of intra prediction between color components, a prediction block of a second color component of a current block may be generated based on a corresponding reconstruction block of a first color component. For example, the first color component may be a luminance component, and the second color component may be a chrominance component. For intra prediction between color components, parameters of a linear model between the first color component and the second color component may be derived based on a template. The template may include upper adjacent samples and / or left adjacent samples of the current block and upper adjacent samples and / or left adjacent samples of a reconstruction block of the first color component corresponding thereto. For example, the sample value of the first color component with the maximum value among the samples in the template and the sample value of the second color component corresponding thereto, and the sample value of the first color component with the minimum value among the samples in the template and the sample value of the second color component corresponding thereto may be used to derive the parameters of the linear model. When the parameters of the linear model are derived, the corresponding reconstruction block may be applied to the linear model to generate a prediction block of the current block. Depending on the video format, subsampling may be performed on the adjacent samples of the reconstruction block of the first color component and the corresponding reconstruction block. For example, when one sample of the second color component corresponds to four samples of the first color component, the four samples of the first color component may be subsampled to calculate one corresponding sample. In this case, parameter derivation of a linear model and intra prediction between color components may be performed based on the corresponding subsampled samples. Whether to perform intra prediction between color components and / or the range of a template may be signaled as an intra prediction mode.

[0214] The current block may be partitioned into two or four sub-blocks in the horizontal direction or the vertical direction. The partitioned sub-blocks may be sequentially reconstructed. 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 transmitted by a signal. Intra prediction based on sub-blocks may be limited to being performed only when reference sample line 0 is used. When subblock-based intra prediction is performed, filtering for a prediction block, which will be described later, may not be performed.

[0215] The final prediction block may be generated by performing filtering on the prediction block of the intra prediction. The filtering may be performed by applying a predetermined weight to the filtering target sample, the left reference sample, the upper reference sample, and / or the upper left reference sample. The weight and / or reference sample (range, position, etc.) used for filtering may be determined based on at least one of the block size, the intra prediction mode, and the position of the filtering target sample in the prediction block. The filtering may be performed only in the case of a predetermined intra prediction mode (e.g., DC, plane, vertical, horizontal, diagonal, and / or adjacent diagonal mode). The adjacent diagonal mode may be a mode in which the diagonal mode is added to k or the diagonal mode is subtracted from k. For example, k may be a positive integer of 8 or less.

[0216] The intra-frame prediction mode of the current block may be entropy encoded / decoded by predicting the intra-frame prediction mode of a block existing adjacent to the current block. When the intra-frame prediction mode of the current block is the same as that of the neighboring block, information that the intra-frame prediction mode of the current block is the same as that of the neighboring block may be transmitted 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 may be transmitted 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 may be entropy encoded / decoded by performing entropy encoding / decoding based on the intra-frame prediction mode of the neighboring block.

[0217] Figure 5 is a diagram illustrating an embodiment of an inter-picture prediction process.

[0218] 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).

[0219] An I picture may be encoded by intra prediction without requiring inter picture prediction. A P picture may be encoded by inter picture prediction using a reference picture existing in one direction (i.e., forward or backward) relative to a current block. A B picture may be encoded by inter picture prediction using a reference picture preset in two directions (i.e., forward and backward) relative to a 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.

[0220] Hereinafter, embodiments of inter-picture prediction will be described in detail.

[0221] Inter-picture prediction or motion compensation may be performed using reference pictures and motion information.

[0222] The motion information of the current block may be derived during inter-picture prediction by each of the encoding apparatus 100 and the decoding apparatus 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 co-located with the current block. The co-located picture may be one of one or more reference pictures included in a reference picture list.

[0223] The derivation method of motion information may differ 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, triangle partition mode, inter-intra combined prediction mode, affine mode, etc. Here, the merge mode may be referred to as motion merge mode.

[0224] 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.

[0225] The encoding device 100 may calculate a motion vector difference (MVD) between a motion vector of a current block and a motion vector candidate, and may perform entropy coding on the motion vector difference (MVD). In addition, the encoding device 100 may perform entropy coding on a motion vector candidate index and generate a bitstream. The motion vector candidate index may indicate the best motion vector candidate among the motion vector candidates included in the motion vector candidate list. The decoding device may perform entropy decoding on the motion vector candidate index included in the bitstream, and may select a motion vector candidate of a decoding target block from the motion vector candidates included in the motion vector candidate list by using the entropy-decoded motion vector candidate index. In addition, the decoding device 200 may add the entropy-decoded MVD to the motion vector candidate extracted by entropy decoding, thereby deriving a motion vector of the decoding target block.

[0226] 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.

[0227] In addition, the encoding device 100 calculates a motion vector difference (MVD) between a motion vector in the current block and a candidate motion vector 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.

[0228] 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.

[0229] Another example of a method of deriving current motion information may be a merge mode. The merge mode may represent a method of merging motions of multiple blocks. The merge mode may represent a mode of deriving motion information of a current block from motion information of neighboring blocks. When the merge mode is applied, the motion information of the reconstructed neighboring blocks and / or the motion information of the co-located blocks may be used to generate a merge candidate list. The motion information may include at least one of a motion vector, a reference picture index, and an inter-picture prediction indicator. The prediction indicator may indicate unidirectional prediction (L0 prediction or L1 prediction) or bidirectional prediction (L0 prediction and L1 prediction).

[0230] 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 block co-located with 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.

[0231] 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 transmit the bitstream to the decoding device 200 using a signal. 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 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.

[0232] In addition, the encoding device 100 performs entropy encoding on the correction information for correcting the motion vector in the motion information of the merge candidate, and transmits it to the decoding device 200 by signal. The decoding device 200 may correct the motion vector of the merge candidate selected by the merge index based on the correction information. Here, the correction information may include at least one of information on whether to perform correction, correction direction information, and correction size information. As described above, the prediction mode that corrects the motion vector of the merge candidate based on the correction information transmitted by the signal may be referred to as a merge mode with a motion vector difference.

[0233] 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.

[0234] The sub-block merge mode may represent a mode for deriving motion information in units of sub-blocks of a coding block (CU). When the sub-block merge mode is applied, the sub-block merge candidate list may be generated using motion information of a sub-block co-located with the current sub-block in a reference image (sub-block based temporal merge candidates) and / or affine control point motion vector merge candidates.

[0235] The triangular partition mode may denote a mode of deriving motion information by partitioning the current block into diagonal directions, deriving each prediction sample using each of the derived motion information, and deriving the prediction sample of the current block by weighting each of the derived prediction samples.

[0236] 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.

[0237] 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.

[0238] The decoding apparatus 200 may use the optical flow to compensate for the prediction samples derived through the inter-frame prediction.

[0239] Figure 6 is a diagram illustrating transform and quantization processing.

[0240] As in 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 residual signal is subjected to a primary transform to generate a transform coefficient, and the transform coefficient is subjected to a secondary transform to generate a secondary transform coefficient.

[0241] At least one scheme selected from various predefined transform schemes is used to perform the primary transform. For example, examples of predefined transform schemes include discrete cosine transform (DCT), discrete sine transform (DST) and Karhunen-Loève transform (KLT). The transform coefficients generated by the primary transform may undergo a secondary transform. The transform scheme for the primary transform and / or the secondary transform may be determined based on the coding parameters of the current block and / or the neighboring blocks of the current block. Optionally, transform information indicating the transform scheme may be transmitted by a signal. DCT-based transforms may include, for example, DCT-2, DCT-8, etc. DST-based transforms may include, for example, DST-7.

[0242] A quantization level signal (quantization 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 or block size / shape of the block, the quantization level signal may be scanned according to at least one of a diagonal upper right scan, a vertical scan, and a horizontal scan. For example, when the coefficients are scanned along a diagonal upper right scan, the coefficients in block form are changed to a one-dimensional vector form. In addition to the diagonal upper right scan, a horizontal scan that scans the coefficients in a two-dimensional block form horizontally or a vertical scan that scans the coefficients in a two-dimensional block form vertically may be used according to the size of the transform block and / or the intra prediction mode. The scanned quantization level coefficients may be entropy encoded for insertion into a bitstream.

[0243] The decoder entropy decodes the bit stream to obtain quantization level coefficients. The quantization level coefficients may be arranged in a two-dimensional block form by inverse scanning. For the inverse scanning, at least one of diagonal upper right scanning, vertical scanning, and horizontal scanning may be used.

[0244] The quantization level coefficients may then be inverse quantized, followed by a secondary inverse transform as required, and finally a primary inverse transform as required to produce a reconstructed residual signal.

[0245] Inverse mapping in the dynamic range can be performed for the luminance component reconstructed by intra-frame prediction or inter-frame prediction before in-loop filtering. The dynamic range can be divided into 16 equal segments, and the mapping function for each segment can be transmitted by a signal. The mapping function can be transmitted by 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 a mapping area via mapping using a 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.

[0246] 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 transmitted by signaling at the slice level or the parallel block group level. Scaling can be applied only when the mapping for the luminance component is available and the division of the luminance component and the division of the chroma component follow the same tree structure. Scaling can be performed based on the average value of the sample value of the luminance prediction block corresponding to the chroma block. In this case, when the current block uses inter-frame prediction, the luminance prediction block can represent the mapped luminance prediction block. The value required for scaling can be derived by referring to the lookup table using the index 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 the 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.

[0247] Information indicating whether mapping / inverse mapping of luma components and chroma components is available may be signaled through a sequence parameter set.

[0248] The prediction block of the current block may be generated based on a block vector indicating the displacement between the current block and the reference block in the current picture. In this way, the prediction mode for generating the prediction block with reference to the current picture is called an intra-block copy (IBC) mode. The IBC mode may be applied to M×N (M<=64, N<=64) coding units. The IBC mode may include a skip mode, a merge mode, an AMVP mode, and the like. In the case of a skip mode or a merge mode, a merge candidate list is constructed, and a merge index is transmitted with a signal so that a merge candidate can be specified. The block vector of the specified merge candidate may be used as the block vector of the current block. The merge candidate list may include at least one of a spatial candidate, a history-based candidate, a candidate based on an average of two candidates, and a zero merge candidate. In the case of the AMVP mode, a difference block vector may be transmitted 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. An index about the neighboring block to be used may be transmitted with a signal. The prediction block in the IBC mode is included in the current CTU or the left CTU and is limited to a block in a reconstructed area. For example, the value of the block vector may be limited so that the prediction block of the current block is located in the region of three 64×64 blocks preceding the 64×64 block to which the current block belongs in the encoding / decoding order. By limiting the value of the block vector in this way, the memory consumption and device complexity of the implementation according to the IBC mode can be reduced.

[0249] In the following, reference is made to Figures 8 to 19 , describes an image encoding / decoding method according to an embodiment of the present invention.

[0250] According to the present invention, entropy encoding / decoding of inter prediction information may be performed by encoding / decoding prediction determination information, encoding / decoding inter prediction mode information, and / or encoding / decoding detailed inter prediction information.

[0251] When entropy encoding / decoding of inter-frame prediction information for a current coding block is performed, a step of encoding / decoding prediction determination information may be performed. For example, the prediction determination information may be information indicating a prediction mode of the current coding block, and may include at least one of a skip indicator and a prediction mode indicator. Here, the prediction mode may be one of an intra-frame prediction mode, an inter-frame prediction mode, an IBC mode, a skip mode, and a palette mode.

[0252] Figure 8 is a flowchart illustrating an encoding / decoding process of a skip indicator according to one embodiment of the present invention.

[0253] The skip indicator may indicate whether the mode of the current coding block is a skip mode.

[0254] In addition, the skip indicator may indicate whether there is a residual signal of the current coding block. For example, when the skip indicator indicates the skip mode, entropy encoding / decoding, inverse quantization, and inverse transformation for the residual signal may not be performed.

[0255] In addition, when determining whether to perform the inter-frame prediction mode of the current coding block, the skip indicator may be used. For example, when the skip indicator indicates the skip mode, the inter-frame prediction information of the current coding block may be obtained.

[0256] The skip indicator may be a single bit having a specific value. For example, the skip indicator may be a single bit having a value of 0 (or "false") or 1 (or "true"). However, this example is not exhaustive.

[0257] As in Figure 8 As shown in , the step of encoding / decoding the skip indicator may be performed in the entropy encoder / decoder (S801). Here, when the encoded / decoded skip indicator is "0", the prediction mode indicator may be encoded / decoded (S802). In addition, when the encoded / decoded skip indicator is "1", the inter-frame prediction information may be encoded / decoded, and entropy decoding, inverse quantization, and inverse transformation may not be performed on the residual signal.

[0258] Optionally, on the contrary, when the skip indicator of encoding / decoding is "0", the inter-frame prediction information may be encoded / decoded, and entropy decoding, inverse quantization, and inverse transformation of the residual signal may not be performed. Optionally, when the skip indicator of encoding / decoding is "1", the prediction mode indicator may be encoded / decoded.

[0259] The skip indicator may be encoded / decoded by using at least one or more of CABAC (Context Adaptive Binary Arithmetic Coding) and bypass coding.

[0260] The skip indicator may be used to encode / decode information about the inter-prediction mode. For example, the skip indicator may be used to encode / decode information about at least one inter-prediction mode among the general merge mode, MMVD (merge mode with motion vector difference), and IBC (intra-block copy) mode. In other words, the encoder may determine whether to encode at least one of the general merge mode information, MMVD mode information, and IBC mode information based on the skip indicator. In addition, the decoder may determine whether to decode at least one of the general merge mode information, MMVD mode information, and IBC mode information based on the skip indicator.

[0261] The skip indicator may indicate the IBC mode. In addition, when the skip indicator indicating the IBC mode is "0", the skip indicator indicating the MMVD mode may be encoded / decoded. In other words, depending on whether the skip indicator is the IBC mode, it may be determined whether the MMVD mode is used.

[0262] For example, the MMVD mode information may be encoded / decoded only when the skip indicator is not the IBC mode.

[0263] The skip indicator may be binarized by encoding such as fixed length encoding, variable length encoding, and truncated unary binarization.

[0264] The skip indicator can be used to obtain information about two prediction modes. In this case, the skip indicator can be binarized by truncated unary binarization. For example, when the binary bit of the skip indicator is "10", information about the general merge mode can be obtained. When the binary bit of the skip indicator is "11", information about the IBC mode can be obtained. In addition, when the binary bit of the skip indicator is "0", information about the remaining prediction modes except the general merge mode and the IBC mode can be obtained. Here, the general merge mode may represent a merge mode that is not a merge mode with motion vector difference (or MMVD), a sub-block merge mode, a triangle partition mode, and a combined inter-intra prediction mode (or CIIP mode). The general merge mode may represent the above Figure 5 The merge mode.

[0265] Fig. 9 is a flowchart illustrating an encoding / decoding process of a prediction mode indicator according to an embodiment of the present invention.

[0266] The prediction mode indicator may indicate one of the inter prediction mode, intra prediction mode, IBC mode, and palette mode. For example, the prediction mode indicator may be a single bit having a value of "0 (or false)" or "1 (true)".

[0267] As in Fig. 9 As shown in , the encoder / decoder may encode / decode the prediction mode indicator (S901). When the prediction mode indicator is a first value (e.g., "1") (S902-true), the inter-frame prediction mode information may be entropy encoded / decoded (S903). In addition, when the encoded / decoded prediction mode indicator is a second value (e.g., "0") (S902-false), the intra-frame prediction mode information may be entropy encoded / decoded (S904).

[0268] When performing the step of entropy encoding / decoding the prediction determination information according to the present invention, entropy encoding / decoding can be adaptively performed by using the prediction information of the spatial neighboring blocks. In other words, based on the prediction information of the spatial neighboring blocks, the step of entropy encoding / decoding the prediction determination information of the current coding block can be performed.

[0269] Here, the prediction information of the spatial neighboring block can be at least one of the following items: a skip indicator of the spatial neighboring block, a prediction mode indicator, information of a single inter-frame prediction mode, information of a multi-frame inter-frame prediction mode, information of a combined inter-frame prediction mode, and a residual signal presence indicator (cbf).

[0270] Specifically, the CABAC context model information for entropy encoding / decoding the prediction mode indicator of the current coding block may be determined based on the prediction mode indicator of at least one spatial neighboring block. Here, the spatial neighboring block may be a block adjacent to the left or top of the current coding block.

[0271] For example, based on whether the prediction mode indicator of the upper spatial neighboring block and the prediction mode indicator of the left spatial neighboring block both indicate the intra prediction mode, the CABAC context model information of the prediction mode indicator of the current coding block may be determined.

[0272] When entropy encoding / decoding of inter prediction information for a current coding block is performed, a step of encoding / decoding inter prediction mode information may be performed. The inter prediction mode information may be information indicating a detailed mode of an inter prediction mode of the current coding block.

[0273] Here, the inter prediction mode may be any one of a single inter prediction mode, a multi-inter prediction mode, and a combined inter prediction mode.

[0274] Here, the single inter prediction mode information may be information indicating one inter prediction mode. In addition, the multi-inter prediction mode information may be information indicating a plurality of inter prediction modes.

[0275] For example, the single inter prediction mode information may include at least one of MMVD_flag, Triangle_flag, DMVR_flag, and MH_flag.

[0276] Here, MMVD_flag may be information showing whether to perform an MMVD inter prediction mode of a current coding block. Here, MMVD_flag may show the same information as mmvd_merge_flag.

[0277] Triangle_flag may be information showing whether a triangle partition inter prediction mode of a current coding block is performed.

[0278] DMVR_flag may be information showing whether a DMVR inter prediction mode of a current coding block is performed.

[0279] MH_flag may be information showing whether to perform an MH (Multiple Hypothesis) inter prediction mode of a current coding block. Here, the MH mode may be used in the same meaning as a CIIP (Combined Inter and Intra Prediction) mode.

[0280] In addition, the inter-frame prediction mode can be any of the following modes: merge mode, AMVP mode, affine merge mode, affine inter-frame mode, ATMVP (optional temporal motion vector prediction) mode, STMVP (sub-block based temporal motion vector prediction) mode, BIO (bidirectional optical flow), FRUC (frame rate up conversion) (= PMMVD, pattern matching motion vector derivation), MMVD, Gbi (generalized dual prediction) (= BCW, dual prediction with CU weights) mode, triangle partitioning mode, MH (multiple hypothesis prediction) mode and DMVR (decoding-side motion vector refinement).

[0281] Fig.10 and Fig.11 is a diagram illustrating an embodiment of an encoding / decoding process for single inter prediction mode information according to multiple inter prediction mode information. Here, the multiple inter prediction mode information may be expressed as a multiple inter prediction mode indicator or a multiple inter prediction mode index.

[0282] The multi-frame inter prediction mode information according to the present invention may represent an indicator indicating a combination of inter prediction modes including a plurality of inter prediction modes. Here, in addition, in order to indicate a specific inter prediction mode within the combination, entropy encoding / decoding may be performed on the single inter prediction mode information.

[0283] In other words, after entropy encoding / decoding multiple inter-frame prediction mode information, entropy encoding / decoding may be performed on single-frame prediction mode information, wherein the single-frame prediction mode information is used to indicate a specific inter-frame prediction mode within an inter-frame prediction mode combination including multiple inter-frame prediction modes.

[0284] For example, the skip indicator may be used as information about multiple inter-frame prediction modes. Here, a combination of inter-frame prediction modes may be indicated by the skip indicator, wherein the combination of inter-frame prediction modes includes at least one or more of a merge mode, an MMVD, an affine merge mode, an ATMVP mode, an MH (multiple hypothesis) mode, and a triangle partition mode.

[0285] Entropy decoding of the multi-frame inter prediction mode indicator may be performed in the decoder. Here, when the decoded multi-frame inter prediction mode indicator is "1", it may indicate a combination of inter prediction modes including at least one of merge mode, MMVD, affine merge mode, ATMVP mode, multi-hypothesis prediction mode, and triangle partition mode. In addition, when the decoded multi-frame inter prediction mode indicator is "0", it may indicate a combination of inter prediction modes including at least one of AMVP mode, affine inter mode, and GBi mode.

[0286] For example, as in Fig.10 As shown in , entropy encoding / decoding of a multi-frame inter prediction mode indicator (S1001) may be performed in the encoder / decoder. Here, when the encoded / decoded multi-frame inter prediction mode indicator is "1", the steps of entropy encoding / decoding MMVD_flag (S1002), entropy encoding / decoding Subblock_merge_flag indicating whether to perform sub-block merge mode (S1003), entropy encoding / decoding MH-flag (S1004), and entropy encoding / decoding Triangle_flag (S1005) may be sequentially performed. In addition, when the encoded / decoded multi-frame inter prediction mode indicator is "0", the step of entropy encoding / decoding Affine_inter_flag indicating affine inter mode (S1006) may be performed.

[0287] Optionally, as in Fig.11As shown in , entropy encoding / decoding of a multi-frame inter prediction mode indicator (S1101) may be performed in the encoder / decoder. Here, when the encoded / decoded multi-frame inter prediction mode indicator is "1", the steps of entropy encoding / decoding Merge_flag indicating whether to perform a merge mode (S1102), entropy encoding / decoding MMVD_flag (S1103), entropy encoding / decoding MH_flag (S1104), and entropy encoding / decoding Subblock_merge_flag (S1105) may be sequentially performed. In addition, when the encoded / decoded multi-frame inter prediction mode indicator is "0", the step of entropy encoding / decoding Affine_inter_flag (S1106) may be performed.

[0288] Optionally, when the skip indicator indicates a skip mode, a combination of at least one or more inter-prediction modes including a merge mode, an MMVD mode, an affine merge mode, an ATMVP mode, a multi-hypothesis prediction mode, and a triangle partition mode may be indicated. In addition, when the skip indicator indicates not a skip mode, a combination of inter-prediction modes including an AMVP mode, an affine inter mode, and a GBi mode may be indicated.

[0289] Fig.12 is a diagram illustrating one embodiment of an inter prediction mode according to multiple inter prediction mode information. Fig.12 (a) shows that according to Fig.10 An embodiment of the inter-frame prediction mode information assigns an inter-frame prediction mode, and Fig.12 (b) can be shown according to Fig.11 An embodiment of allocating an inter-frame prediction mode according to the inter-frame prediction mode information.

[0290] In addition, a predetermined inter prediction mode may be indicated according to a combination of a plurality of single inter prediction mode information.

[0291] For example, as in Fig.12 As shown in (a) of FIG. 1 , when MMVD_flag, Subblock_merge_flag, MH_flag, and Triangle_flag are all “0” (or indicate “false”), a general merge mode may be indicated.

[0292] Optionally, as in Fig.12 As shown in (b) of FIG. 8 , when Merge_flag, MMVD_flag, MH_flag, and Subblock_merge_flag are all “0” (or indicate “false”), a triangle partition mode may be indicated.

[0293] Alternatively, when Subblock_merge_flag, Regular_merge_flag, and MH_flag are all "0" (or indicate "false"), a triangular partition mode may be indicated. Here, MH_flag may be an indicator indicating an MH mode or a CIIP mode.

[0294] The combined inter prediction mode information according to the present invention may represent an indicator indicating a combined inter prediction mode. The combined inter prediction mode may represent combining multiple inter prediction modes into one mode. In other words, one combined inter prediction mode indicator may indicate multiple inter prediction modes.

[0295] For example, the ATMVP mode and the affine merge mode may be combined, and the corresponding combined mode may be indicated by Subblock_merge_flag.

[0296] Optionally, the merge mode and the MMVD mode may be combined, and the corresponding mode may be indicated by Merge_MMVD_flag.

[0297] Fig.13 is a diagram illustrating one embodiment for an inter prediction mode according to inter prediction mode information including combined inter prediction mode information.

[0298] When the multiple inter prediction mode information are all "0 (or false)", a specific combined inter prediction mode may be indicated.

[0299] For example, as in Fig.13 As shown in (a) of FIG. 1 , when both Merge_MMVD_flag and MH_flag are “0” (or indicate “false”), a combined inter prediction mode combining the ATMVP mode and the affine merge mode may be indicated.

[0300] Optionally, as in Fig.13 As shown in (b) of FIG. 1 , when Subblock_merge_flag, MH_flag, and Triangle_flag are all “0” (or indicate “false”), a combined inter prediction mode combining the merge mode and the MMVD mode may be indicated.

[0301] In addition, Fig.12 and Fig.13 In the example, "1", "0" and "X" can represent "true", "false" and "not present", respectively, however, this is not exhaustive.

[0302] According to one embodiment of the present invention, when two or more inter-frame prediction mode information are entropy encoded / decoded, each inter-frame prediction mode information may be entropy encoded / decoded independently or independently.

[0303] Fig.14 1 is a diagram for explaining a process of performing entropy encoding / decoding of inter-frame prediction mode information independently of previously encoded / decoded inter-frame prediction mode information according to an embodiment of the present invention. Here, the previously encoded / decoded inter-frame prediction mode information may refer to information encoded / decoded before the current encoding / decoding target information.

[0304] As in Fig.14 As shown in , the step of entropy encoding / decoding the first inter-frame prediction mode information is performed (S1401), and independently of this, the step of entropy encoding / decoding the second inter-frame prediction mode information can be performed (S1402). Here, Fig.14 The first inter prediction mode information described in may be inter prediction mode information encoded / decoded before encoding / decoding of the current block is performed, and the second inter prediction mode information may be an inter prediction mode to be currently entropy encoded / decoded.

[0305] Fig.15 1 is a diagram for explaining a process of performing entropy encoding / decoding of inter-frame prediction mode information according to previously encoded / decoded inter-frame prediction mode information according to an embodiment of the present invention. Here, the previously encoded / decoded inter-frame prediction mode information may refer to information encoded / decoded before the current encoding / decoding target information.

[0306] As in Fig.15 As shown in , the step of entropy encoding / decoding the first inter-frame prediction mode information is performed (S1501), and the step of entropy encoding / decoding the second inter-frame prediction mode information can be performed depending on the encoded / decoded first inter-frame prediction mode information (S1502). Here, in Fig.15 The first inter prediction mode information described in may be previously encoded / decoded inter prediction mode information, and the second inter prediction mode information may be an inter prediction mode to be currently entropy encoded / decoded.

[0307] When the first inter prediction mode information indicates a specific value, a step of entropy encoding / decoding the second inter prediction mode information may be performed.

[0308] For example, as in Fig.15 As shown in , when the first inter prediction mode information indicates '0', a step of entropy encoding / decoding the second inter prediction mode information may be performed.

[0309] Alternatively, on the contrary, when the first inter prediction mode information indicates "1", the step of entropy encoding / decoding the second inter prediction mode information may be performed. For example, when the general merge mode information (Regular_merge_flag) indicates "1", the step of entropy encoding / decoding the mmvd_merge_flag indicating the MMVD mode may be performed.

[0310] When entropy encoding / decoding of inter prediction information for the current coding block is performed, a step of encoding / decoding detailed inter prediction information may be performed. For example, detailed inter prediction information may indicate information that needs to be transmitted with a signal in addition to information indicating an inter prediction mode for the current coding block.

[0311] The detailed inter prediction information may include at least one of single detailed inter prediction mode information, combined detailed inter prediction mode information, and a residual signal presence indicator. For example, the detailed inter prediction information may include at least one of the following items: motion information index, motion vector difference, reference direction, reference picture index, triangle prediction combination index, affine information index, CPMV difference, intra prediction mode index, motion vector direction index, motion vector size index, and combined mode detailed information index.

[0312] The residual signal presence indicator may indicate whether there is a coefficient other than "0" in the residual signal as a result of performing transformation and quantization on the current coding block. When the residual signal presence indicator indicates "0", inverse quantization and inverse transformation may not be performed. In other words, when the residual signal presence indicator indicates that there is no coefficient but "0" in the residual signal, inverse quantization and inverse transformation may not be performed.

[0313] When entropy encoding and decoding of detailed inter prediction information are performed, entropy encoding / decoding of single detailed inter prediction mode information may be performed.

[0314] For example, when the current coding block performs the merge mode, entropy encoding / decoding for the motion information index may be performed. The motion information index may indicate specific motion information within the merge candidate list.

[0315] Optionally, when the current coding block performs the MMVD mode, entropy encoding / decoding for the motion information index, the motion vector direction index, and the motion vector size index may be performed. The motion information index may indicate specific initial motion information within the MMVD initial motion candidate list, and the motion direction index may indicate the direction of the improved motion vector centered on the specific initial motion information. In addition, the motion vector size index may indicate the size of the improved motion vector.

[0316] When entropy encoding and decoding of detailed inter prediction information are performed, entropy encoding and decoding of combined detailed inter prediction mode information may be performed.

[0317] Here, the combined detailed inter prediction mode information may be detailed information of two or more prediction modes. Here, when detailed information of two prediction modes are combined, one prediction mode may be referred to as a first prediction mode, and the other prediction mode may be referred to as a second prediction mode.

[0318] Fig.16 and Fig.17 is a diagram illustrating one embodiment of combining detailed inter prediction mode information.

[0319] The combined detailed inter prediction mode information may be configured in the order of detailed information of a specific prediction mode. For example, the combined detailed inter prediction mode information may be configured in the order of detailed information of L first prediction modes, detailed information of M second prediction modes, and detailed information of N third prediction modes. Here, L, M, and N may be positive integers.

[0320] For example, as in Fig.16 As described in (a), when the current coding block performs a combined inter prediction mode of the affine merge mode and the ATMVP mode, the combined detailed inter prediction mode information may be configured in the order of detailed information of the ATMVP mode and detailed information of the four affine merge modes.

[0321] For example, Fig.16 As described in (b), when the current coding block performs a combined inter prediction mode of the affine merge mode and the ATMVP mode, the combined detailed inter prediction mode information may be configured in the order of detailed information of one ATMVP mode and detailed information of five affine merge modes. Here, the combined mode detailed information index indicating the affine merge mode may be the same as the affine information index of the single detailed inter prediction mode information for the affine merge mode.

[0322] In addition, as in Fig.17 As described in (a), when the current coding block performs a combined inter prediction mode of the merge mode and the MMVD mode, the combined detailed inter prediction mode information may be configured in the order of two MMVD detailed information and five merge mode detailed information.

[0323] In addition, if Fig.17 As described in (c), when the current coding block performs a combined inter prediction mode of the merge mode and the MMVD mode, the combined detailed inter prediction mode information may be configured in the order of 2 MMVD detailed information and three merge mode detailed information.

[0324] The combined detailed inter-frame prediction mode information may be configured by inserting different prediction information between specific prediction mode detailed information. For example, among the detailed information of the M first prediction modes, N second prediction modes may be inserted starting from the Mxth detailed information. After the detailed information of the second prediction mode is inserted, the detailed information of the remaining first prediction modes may be configured. Here, M and N may be positive integers, and x may be a positive integer less than M.

[0325] For example, as in Fig.17 As described in (b), when the current coding block performs a combined inter-frame prediction mode of a merge mode and an MMVD mode, the combined detailed inter-frame prediction mode information may be configured in the order of detailed information of two merge modes, detailed information of two MMVDs, and detailed information of three merge modes.

[0326] The combined detailed inter prediction mode information indicating the MMVD mode may be the same as the motion information index of the single detailed inter prediction mode information for the MMVD mode. In addition, entropy encoding / decoding for the motion direction index and the motion vector size index information may also be performed.

[0327] The combined detailed inter prediction mode information indicating the merge mode may have the same motion information index as the single detailed inter prediction mode information for the merge mode.

[0328] When encoding / decoding the combined detailed inter-frame prediction mode information index indicating a specific MMVD mode, encoding / decoding for MMVD prediction information may be additionally performed. In this case, the MMVD prediction information may include at least one or more of an MMVD prediction mode indicator, an MMVD direction information index, and an MMVD size information index (or an MMVD distance information index).

[0329] When the first combined prediction mode index information is a specific index, encoding / decoding for the second combined prediction mode information may be performed. For example, when the index of the detailed prediction information for the merge mode is 0 or 1, encoding / decoding for the MMVD prediction information may be performed.

[0330] When entropy encoding and decoding of detailed inter prediction information are performed, a residual signal presence indicator may be encoded / decoded.

[0331] According to certain conditions, encoding / decoding of the residual signal presence indicator (tu_cbf_luma) may be performed. Here, the specific conditions may include the prediction mode of the current coding block, the size of the coding block, the shape of the coding block, the prediction mode of the neighboring coding block, QP, CTU boundary, and parallel block boundary.

[0332] For example, when the current coding block is in a specific prediction mode, the residual signal presence indicator may be encoded / decoded. As an example thereof, when the merge mode indicator in the current coding block is "0" (or "false"), encoding / decoding of the residual signal presence indicator may be performed. As another example, when the CIIP mode indicator in the current coding block is "1" (or "true"), encoding / decoding of the residual signal presence indicator may be performed. Here, the CIIP mode may be a mode in which prediction is performed by combining inter-frame prediction and intra-frame prediction, and in this case, the inter-frame prediction and the intra-frame prediction may be predicted as a merge mode and a plane mode, respectively. As another example, when the skip mode indicator in the current coding block is "0" (or "false"), encoding / decoding of the residual signal presence indicator may be performed. Here, the CIIP mode may be used in the same meaning as the MH mode.

[0333] Optionally, when the size of the current coding block is greater than or less than a specific threshold, encoding / decoding of the residual signal presence indicator may be performed.

[0334] As an example, when the width or height of the block is greater than or less than a certain threshold, encoding / decoding of the residual signal presence indicator may be performed. For example, when the width or height of the current coding block is greater than the maximum size of the transform block, encoding / decoding of the residual signal presence indicator may be performed.

[0335] As another example, if the area of ​​the block is greater than or less than a certain threshold, encoding / decoding of the residual signal presence indicator may be performed. Here, the area of ​​the block may be the product of the width and height of the block.

[0336] Optionally, when the current coding block exists on a tile boundary, encoding / decoding of a residual signal existence indicator may be performed.

[0337] Optionally, when the current coding block is on a tile boundary, encoding / decoding of a residual signal presence indicator may be performed.

[0338] The above conditions may be combined by “and” or “or.” Depending on the conditions, probability models may be used differently in entropy encoding / decoding of the residual signal presence indicator.

[0339] In one embodiment of the present invention, since encoding / decoding of the residual signal existence indicator is performed only when the residual signal existence indicator needs to be encoded / decoded, the bit overhead of the residual signal indicator can be reduced.

[0340] The prediction determination information according to the present invention may include a merge mode indicator (eg, general_merge_flag). Here, the merge mode indicator may indicate whether at least one detailed merge mode is used.

[0341] For example, when the merge mode indicator has a first value (e.g., '1' or true), at least one detailed merge mode information may be obtained. In addition, the detailed merge mode information may include at least one of the following items: a general merge mode indicator (Regular_merge_flag), an MMVD mode indicator (mmvd_merge_flag), a triangle partition mode index (merge_triangle_idx), a subblock merge mode indicator (merge_subblock_flag), and a CIIP mode indicator (ciip_flag). Here, the detailed merge mode information may be included in the above-mentioned inter-frame prediction mode information.

[0342] Fig.18 is a flowchart for explaining an image decoding method according to an embodiment of the present invention.

[0343] Reference Fig.18 , the image decoding apparatus may obtain prediction information and residual signal information for a current block from a bitstream (S1801). Here, the prediction information may be used to determine a prediction mode of the current block.

[0344] In addition, prediction information can be obtained through entropy decoding.

[0345] In addition, a context model for entropy decoding prediction information may be determined based on a prediction mode of a neighboring block of the current block.

[0346] In addition, the neighboring block may be at least one of the blocks located on the left or top of the current block.

[0347] In addition, the context model may be determined based on whether the prediction mode of the neighboring block is an intra prediction mode.

[0348] In addition, the prediction information may include at least one of the following items: general merge mode information, MMVD (merge mode with motion vector difference) mode information, triangle partition mode information, CIIP (combined inter-frame and intra-frame prediction) mode information, IBC (intra-frame block copy) mode information and sub-block merge mode information.

[0349] In addition, the MMVD mode information may be decoded based on the general merge mode information.

[0350] In addition, the MMVD mode information may be decoded based on the IBC mode information.

[0351] In addition, triangle partition mode information may be decoded based on general merge mode information, CIIP mode information, and subblock merge mode information.

[0352] In addition, when the horizontal size or the vertical size of the current block is greater than the predetermined size, step S1801 may obtain residual signal information of the current block. Here, the predetermined size may be determined based on maximum transform block size information obtained from the bitstream.

[0353] In addition, the image decoding apparatus may reconstruct the current block based on prediction information and residual signal information obtained from the bitstream (S1802).

[0354] Fig.19 is a diagram for explaining an image encoding method according to an embodiment of the present invention.

[0355] Reference Fig.19 , the image encoding apparatus may generate prediction information and residual signal information for a current block (S1901).

[0356] In addition, the prediction information may include at least one of the following items: general merge mode information, MMVD (merge mode with motion vector difference) mode information, triangle partition mode information, CIIP (combined inter-frame and intra-frame prediction) mode information, IBC (intra-frame block copy) mode information and sub-block merge mode information.

[0357] In addition, the MMVD mode information may be encoded based on the general merge mode information.

[0358] Additionally, the MMVD mode information may be encoded based on the IBC mode information.

[0359] In addition, triangle partition mode information may be encoded based on general merge mode information, CIIP mode information, and subblock merge mode information.

[0360] In addition, when the horizontal size or the vertical size of the current block is greater than the maximum transform block size, step S1901 may generate residual signal information.

[0361] In addition, the image encoding apparatus may reconstruct the current block based on the prediction information and the residual signal information (S1902).

[0362] A bit stream generated by the image encoding method of the present invention may be temporarily stored in a computer-readable non-transitory recording medium, and may be decoded by the above-mentioned image decoding method.

[0363] Specifically, in a computer-readable non-transitory recording medium including a bitstream decoded by an image decoding device, the bitstream may include prediction information and residual signal information of a current block, and the prediction information may be used to determine a prediction mode of the current block, and the current block may be restored based on the prediction information and the residual signal information. In the image decoding device, the prediction information may be obtained by entropy decoding, and a context mode for entropy decoding the prediction information may be determined based on a prediction mode of a neighboring block of the current block.

[0364] The above-described embodiments may be performed in the same manner in an encoder and a decoder.

[0365] At least one or a combination of the above embodiments may be used to encode / decode a video.

[0366] The order in which the above-described embodiments are applied may be different between the encoder and the decoder, or the order in which the above-described embodiments are applied may be the same in the encoder and the decoder.

[0367] The above-described embodiments may be performed on each of a luminance signal and a chrominance signal, or may be performed identically on the luminance signal and the chrominance signal.

[0368] The block shape to which the above-described embodiment of the present invention is applied may have a square shape or a non-square shape.

[0369] The above-mentioned embodiments of the present invention may be applied according to the size of at least one of a coding block, a prediction block, a transform block, a block, a current block, a coding unit, a prediction unit, a transform unit, a unit, and a current unit. Here, the size may be defined as a minimum size or a maximum size or both a minimum size and a maximum size, so that the above-mentioned embodiments are applied, or may be defined as a fixed size to which the above-mentioned embodiments are applied. In addition, in the above-mentioned embodiments, the first embodiment may be applied to a first size, and the second embodiment may be applied to a second size. In other words, the above-mentioned embodiments may be applied according to size combinations. In addition, the above-mentioned embodiments may be applied when the size is equal to or greater than the minimum size and equal to or less than the maximum size. In other words, the above-mentioned embodiments may be applied when the block size is included in a specific range.

[0370] 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 4×4 or larger, the above embodiment may be applied. For example, when the size of the current block is 16×16 or larger, 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.

[0371] The above-described embodiments of the present invention may be applied according to time layers. In order to identify the time layers to which the above-described embodiments may be applied, a corresponding identifier may be transmitted by a signal, and the above-described 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-described embodiments may be applied, or may be defined as a specific layer indicating that the embodiment is applied. In addition, a fixed time layer to which the embodiment is applied may be defined.

[0372] For example, when the temporal layer of the current image is the lowest layer, the above embodiment may be applied. For example, when the temporal layer identifier of the current image is 1, the above embodiment may be applied. For example, when the temporal layer of the current image is the highest layer, the above embodiment may be applied.

[0373] A slice type or a tile group type to which the above-described embodiments of the present invention are applied may be defined, and the above-described embodiments may be applied according to the corresponding slice type or tile group type.

[0374] In the above embodiments, the method is described based on a flowchart having a series of steps or units, but the present invention is not limited to the order of the steps, but some steps may be performed simultaneously with other steps or in a different order. In addition, it should be understood by those of ordinary skill in the art that the steps in the flowchart are not mutually exclusive, and other steps may be added to the flowchart, or some steps may be deleted from the flowchart without affecting the scope of the present invention.

[0375] The embodiments include various aspects of the examples. All possible combinations of the 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.

[0376] Embodiments of the present invention may be implemented in the form of program instructions, wherein the program instructions may 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 magnetic tapes; optical data storage media, such as CD-ROMs or DVD-ROMs; magnetic optimal media, such as floppy disks; and hardware devices, such as read-only memories (ROMs), random access memories (RAMs), flash memories, etc., which are specifically constructed to store and implement program instructions. Examples of program instructions include not only machine language codes formatted by a compiler, but also high-level language codes that can be implemented by a computer using an interpreter. The hardware device may be configured to be operated by one or more software modules to perform processing according to the present invention, and vice versa.

[0377] Although the present invention has been described according to specific items such as detailed elements and limited embodiments and drawings, they are provided only to help more generally understand the present invention, and the present invention is not limited to the above embodiments. It will be appreciated by those skilled in the art that various modifications and changes can be made from the above description.

[0378] 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.

[0379] Industrial Applicability

[0380] The present invention can be used to encode or decode images.

Claims

1. A method for decoding an image, the method comprising: Obtain prediction information and residual signal information for a current block from a bitstream; generating a prediction block of the current block based on the prediction information and the residual signal information; as well as generating a reconstructed block of the current block based on the predicted block of the current block, Wherein, the prediction information is obtained by entropy decoding, wherein a context model for entropy decoding the prediction information is determined based on a prediction mode of a neighboring block of the current block, wherein the prediction information is used to determine a prediction mode of the current block, and The prediction information includes at least one of the following items: general merge mode information, merge mode with motion vector difference MMVD mode information, partition mode information, combined inter-frame and intra-frame prediction CIIP mode information, intra-frame block copy IBC mode information and sub-block merge mode information.

2. A method for encoding an image, the method comprising: determining a prediction mode for a current block in the image; generating a prediction block of the current block based on the prediction mode of the current block; as well as Encoding information about the prediction mode of the current block and residual signal information of the current block; wherein a context model for encoding information about the prediction mode is determined based on the prediction mode of a neighboring block of the current block, and Among them, the information about the prediction mode includes at least one of the following items: general merge mode information, merge mode with motion vector difference MMVD mode information, partition mode information, combined inter-frame and intra-frame prediction CIIP mode information, intra-frame block copy IBC mode information and sub-block merge mode information.

3. A method for sending a bit stream, comprising: Obtaining a bit stream for an image, wherein the bit stream is generated by an image encoding method; and sending the bit stream, Wherein, the image encoding method comprises: determining a prediction mode for a current block in the image; generating a prediction block of the current block based on the prediction mode of the current block; and Encoding information about the prediction mode of the current block and residual signal information of the current block; wherein a context model for encoding information about the prediction mode is determined based on the prediction mode of a neighboring block of the current block, and Among them, the information about the prediction mode includes at least one of the following items: general merge mode information, merge mode with motion vector difference MMVD mode information, partition mode information, combined inter-frame and intra-frame prediction CIIP mode information, intra-frame block copy IBC mode information and sub-block merge mode information.

Images