Encoding method, encoding device, decoding method, and decoding device for image

Abstract

Provided are an image decoding method, an image decoding device, an image encoding method and an image encoding device, the image decoding method comprising the steps of: acquiring a reference block in a reference image; determining an intra mode for the reference block on the basis of at least one of a plurality of neighboring samples of the reference block and a plurality of internal samples of the reference block; determining a transform kernel of the current block from among one or more transform kernels by using the intra mode for the reference block; and performing an inverse transform on the current block by using the transform kernel.

Description

Image encoding method, encoding device, decoding method and decoding device

[0001] The present disclosure relates to the field of image encoding and decoding. More specifically, it relates to an encoding and decoding method and device for predicting image samples.

[0002] In image encoding and decoding, the image is divided into blocks, and each block is predicted and decoded through inter prediction or intra prediction.

[0003] Inter prediction is a technique for compressing images by removing temporal redundancy between images. Inter prediction uses a reference image to predict blocks in the current image. The reference block most similar to the current block can be searched within a predetermined search range within the reference image. The current block is predicted based on the reference block, and the predicted block generated as a result of the prediction is subtracted from the current block to generate a residual block.

[0004] Intra prediction is a technique for compressing images by removing spatial redundancy within the image. Intra prediction generates a predicted block based on the surrounding pixels of the current block, depending on the prediction mode. The predicted block is then subtracted from the current block to create a residual block.

[0005] The residual block generated through inter-prediction or intra-prediction undergoes transformation and quantization and is then passed to the decoder. The decoder dequantizes and inversely transforms the residual block, and combines the predicted block of the current block with the residual block to reconstruct the current block. The decoder can filter the reconstructed current block to remove artifacts within it.

[0006] In one embodiment of the present disclosure, a method for decoding an image is provided. The method for decoding an image may include a step of obtaining a reference block in a reference image. The method for decoding an image may include a step of determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of interior samples of the reference block. The method for decoding an image may include a step of determining a transform kernel for a current block from among one or more transform kernels using the intra mode for the reference block. The method for decoding an image may include a step of performing an inverse transform on the current block using the transform kernel.

[0007] In one embodiment of the present disclosure, an image decoding device is provided. The image decoding device may include a memory storing one or more instructions and at least one processor. The at least one processor may obtain a reference block in a reference image by executing one or more instructions. The at least one processor may determine an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block by executing one or more instructions. The at least one processor may determine a transform kernel for a current block from among one or more transform kernels using the intra mode for the reference block by executing one or more instructions. The at least one processor may perform an inverse transform for the current block using the transform kernel by executing one or more instructions.

[0008] In one embodiment of the present disclosure, a video encoding method is provided. The video encoding method may include a step of obtaining a reference block in a reference image. The video encoding method may include a step of determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block. The video encoding method may include a step of determining a transform kernel for a current block from among one or more transform kernels using the intra mode for the reference block. The video encoding method may include a step of performing a transform on the current block using the transform kernel.

[0009] In one embodiment of the present disclosure, an image encoding device is provided. The image encoding device may include a memory storing one or more instructions and at least one processor. The at least one processor may obtain a reference block in a reference image by executing one or more instructions. The at least one processor may determine an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block by executing one or more instructions. The at least one processor may determine a transform kernel for a current block from among one or more transform kernels using the intra mode for the reference block by executing one or more instructions. The at least one processor may perform a transform on the current block using the transform kernel by executing one or more instructions.

[0010] In one embodiment of the present disclosure, a computer-readable storage medium is provided for storing a bitstream encoded by an image encoding method.

[0011] FIG. 1 is a block diagram of an image decoding device according to one embodiment of the present disclosure.

[0012] FIG. 2 is a block diagram of an image encoding device according to one embodiment of the present disclosure.

[0013] FIG. 3 illustrates a process of dividing a current encoding unit to determine at least one encoding unit according to one embodiment of the present disclosure.

[0014] FIG. 4 illustrates a process of dividing a non-square coding unit to determine at least one coding unit according to one embodiment of the present disclosure.

[0015] FIG. 5 illustrates a process of dividing an encoding unit based on at least one of block shape information and segmentation shape mode information according to one embodiment of the present disclosure.

[0016] FIG. 6 illustrates a method for determining a predetermined coding unit among an odd number of coding units according to one embodiment of the present disclosure.

[0017] FIG. 7 illustrates the order in which multiple encoding units are processed when a current encoding unit is divided to determine multiple encoding units according to one embodiment of the present disclosure.

[0018] FIG. 8 illustrates a process for determining that a current encoding unit is split into an odd number of encoding units when encoding units cannot be processed in a predetermined order according to one embodiment of the present disclosure.

[0019] FIG. 9 illustrates a process of dividing a first encoding unit to determine at least one encoding unit according to one embodiment of the present disclosure.

[0020] FIG. 10 illustrates that the shapes into which a second encoding unit of a non-square shape determined by splitting a first encoding unit is split are limited when a predetermined condition is satisfied, according to one embodiment of the present disclosure.

[0021] FIG. 11 illustrates a process of splitting a square-shaped encoding unit when the split shape mode information cannot represent splitting into four square-shaped encoding units according to one embodiment of the present disclosure.

[0022] FIG. 12 illustrates that the processing order between a plurality of encoding units may vary depending on the process of splitting the encoding units according to one embodiment of the present disclosure.

[0023] FIG. 13 illustrates a process in which the depth of an encoding unit is determined as the shape and size of the encoding unit change when the encoding unit is recursively divided to determine a plurality of encoding units according to one embodiment of the present disclosure.

[0024] FIG. 14 illustrates an index (part index, hereinafter referred to as PID) for depth and encoding unit distinction that can be determined according to the shape and size of encoding units according to one embodiment of the present disclosure.

[0025] FIG. 15 illustrates that a plurality of coding units are determined according to a plurality of predetermined data units included in a picture according to one embodiment of the present disclosure.

[0026] FIG. 16 illustrates encoding units that can be determined for each picture when the combination of forms into which encoding units can be divided is different for each picture according to one embodiment of the present disclosure.

[0027] FIG. 17 illustrates various forms of encoding units that can be determined based on segmentation mode information expressed in binary code according to one embodiment of the present disclosure.

[0028] FIG. 18 illustrates another form of a coding unit that can be determined based on segmentation mode information expressed in binary code according to one embodiment of the present disclosure.

[0029] FIG. 19 is a block diagram of an image encoding and decoding system that performs loop filtering according to one embodiment of the present disclosure.

[0030] FIG. 20 is a block diagram showing the configuration of an image decoding device according to one embodiment of the present disclosure.

[0031] FIG. 21 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0032] FIG. 22 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0033] FIG. 23 is a diagram illustrating a process for determining an intra mode for a reference block using surrounding blocks of the reference block in one embodiment of the present disclosure.

[0034] FIG. 24 is a diagram illustrating a process of determining an intra mode for a reference block using surrounding samples of the reference block in one embodiment of the present disclosure.

[0035] FIG. 25 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0036] FIG. 26 is a diagram illustrating a process for determining an intra mode for a reference block using a reference block in one embodiment of the present disclosure.

[0037] FIG. 27 is a diagram illustrating a process of determining an intra mode for a reference block using reference blocks in one embodiment of the present disclosure.

[0038] FIG. 28 is a diagram illustrating a process of determining an intra mode for a reference block using reference blocks in one embodiment of the present disclosure.

[0039] FIG. 29 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0040] FIG. 30 is a diagram illustrating a process of determining an intra mode for a reference block using surrounding samples of the reference block in one embodiment of the present disclosure.

[0041] FIG. 31 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0042] FIG. 32 is a diagram illustrating a process for determining an intra mode for a reference block using surrounding samples of a current block in one embodiment of the present disclosure.

[0043] FIG. 33 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0044] FIG. 34 is a diagram illustrating a process for determining an intra mode for a reference block using a reference block in one embodiment of the present disclosure.

[0045] FIG. 35 is a drawing for explaining the form of a template according to one embodiment of the present disclosure.

[0046] FIG. 36 is a block diagram showing the configuration of an image encoding device according to one embodiment of the present disclosure.

[0047] FIG. 37 is a flowchart of an image encoding method according to one embodiment of the present disclosure.

[0048] FIG. 38 is a flowchart of an image encoding method according to one embodiment of the present disclosure.

[0049] In this disclosure, the expression “at least one of a, b or c” may refer to “a”, “b”, “c”, “a and b”, “a and c”, “b and c”, “all of a, b and c”, or variations thereof.

[0050] In the present disclosure, the expression "a, b and / or c" can be replaced with "at least one of a, b or c." That is, the expression "a, b and / or c" can refer to "a," "b," "c," "a and b," "a and c," "b and c," "all of a, b and c," or variations thereof.

[0051] The present disclosure may be subject to various modifications and various embodiments. Examples are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the embodiments of the present disclosure, and the present disclosure may include all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the various embodiments.

[0052] The terms used in this disclosure are selected from widely used, common terms, taking into account the functions of the disclosure. However, these terms may vary depending on the intentions of those skilled in the art, precedents, the emergence of new technologies, etc. Furthermore, in certain cases, terms may be arbitrarily selected by the applicant, and in such cases, their meanings can be understood through the relevant description. Therefore, the terms used in this disclosure should not be defined simply as names of terms, but rather based on the meanings of the terms and the overall content of the disclosure.

[0053] In this disclosure, singular expressions may include plural expressions unless the context clearly dictates otherwise. In describing embodiments, detailed descriptions of related known technologies will be omitted if they are deemed to unnecessarily obscure the gist of the present disclosure. Furthermore, numbers (e.g., "first," "second," etc.) used in the description of embodiments serve as identifiers to distinguish one component from another.

[0054] In the present disclosure, when a component is referred to as being “connected” or “connected” to another component, the component may be directly connected or connected to the other component, but unless there is a specific description to the contrary, the component may also be connected or connected via another component in between.

[0055] When a part in this disclosure is said to "include" a certain component, this does not mean that other components are excluded, but rather that other components may be further included, unless otherwise specifically stated. Components expressed as "unit", "module", etc. in this disclosure may be two or more components combined into one component, or one component may be divided into two or more more detailed components. In addition, each component described below may additionally perform some or all of the functions performed by other components in addition to its own main function, and some of the main functions performed by each component may be exclusively performed by other components.

[0056] The expression "configured to" as used herein can be used interchangeably with, for example, "suitable for", "having the capacity to", "designed to", "adapted to", "made to", or "capable of", depending on the context. The term "configured to" does not necessarily mean something is "specifically designed to" in terms of hardware. Alternatively, in some contexts, the expression "a system configured to" can include that the system is "capable of" in conjunction with other devices or components. For example, the phrase "a processor configured to perform A, B, and C" can include a dedicated processor for performing the operations (e.g., an embedded processor), or a general-purpose processor (e.g., a CPU or an application processor) that can perform the operations by executing one or more software programs stored in a memory.

[0057] At least one processor according to embodiments of the present disclosure may include various processing circuits and / or multiple processors. For example, the term "processor" as used herein, including in the claims, may include various processing circuits including at least one processor, one or more of which are configured to individually and / or collectively perform the various functions described herein in a distributed manner. As used herein, when "processor," "at least one processor," and "one or more processors" are described as being configured to perform various functions, these terms may include, for example, without limitation, a single processor performing some of the recited functions, other processor(s) performing other of the recited functions, and still other situations where a single processor can perform all of the recited functions. Additionally, the at least one processor may include a combination of processors that perform the various functions enumerated / disclosed, for example, in a distributed manner. The at least one processor may execute program instructions to achieve or perform the various functions.

[0058] In the present disclosure, an 'image' may include a picture, a still image, a frame, a moving image composed of a plurality of consecutive still images, or a video.

[0059] In the present disclosure, a "sample" may include data assigned to a sampling location in an image and may include data to be processed. For example, a sample may include pixels within a frame in a spatial domain. A block may refer to a unit including multiple samples.

[0060] Hereinafter, with reference to FIGS. 1 to 19, an image encoding method and device based on a tree-structured encoding unit and a transformation unit according to an embodiment of the present disclosure, and an image decoding method and device are disclosed.

[0061] FIG. 1 illustrates a block diagram of an image decoding device (100) according to one embodiment of the present disclosure.

[0062] The video decoding device (100) may include a bitstream acquisition unit (110) and a decoding unit (120). The bitstream acquisition unit (110) and the decoding unit (120) may include at least one processor. In addition, the bitstream acquisition unit (110) and the decoding unit (120) may include a memory that stores commands to be executed by at least one processor.

[0063] The bitstream acquisition unit (110) can receive a bitstream. The bitstream includes information obtained by encoding an image by an image encoding device (200) described below. In addition, the bitstream can be transmitted from the image encoding device (200). The image encoding device (200) and the image decoding device (100) can be connected by wire or wirelessly, and the bitstream acquisition unit (110) can receive the bitstream by wire or wirelessly. The bitstream acquisition unit (110) can receive the bitstream from a storage medium such as an optical medium, a hard disk, etc. The decoding unit (120) can restore the image based on information obtained from the received bitstream. The decoding unit (120) can obtain syntax elements for restoring the image from the bitstream. The decoding unit (120) can restore the image based on the syntax elements.

[0064] To describe in detail the operation of the video decoding device (100), the bitstream acquisition unit (110) can receive a bitstream.

[0065] The image decoding device (100) may perform an operation of obtaining a binstring corresponding to a splitting shape mode of an encoding unit from a bitstream. In addition, the image decoding device (100) may perform an operation of determining a splitting rule of the encoding unit. In addition, the image decoding device (100) may perform an operation of splitting the encoding unit into a plurality of encoding units based on at least one of the binstring corresponding to the splitting shape mode and the splitting rule. In order to determine the splitting rule, the image decoding device (100) may determine a first allowable range of the size of the encoding unit according to a ratio of the width and height of the encoding unit. In order to determine the splitting rule, the image decoding device (100) may determine a second allowable range of the size of the encoding unit according to the splitting shape mode of the encoding unit.

[0066] Below, the division of encoding units according to one embodiment of the present disclosure is described in detail.

[0067] First, a picture can be divided into one or more slices or one or more tiles. A slice or a tile can be a sequence of one or more maximum coding tree units (CTUs). Depending on the implementation, a slice may include one or more tiles, and a slice may include one or more maximum coding units. A slice including one or more tiles can be determined within a picture.

[0068] The maximum coding block (Coding Tree Block; CTB) is a concept that contrasts with the maximum coding unit (CTU). A CTB is an NxN block containing NxN samples (N is an integer). Each color component can be divided into one or more CTBs.

[0069] When a picture has three sample arrays (sample arrays for Y, Cr, and Cb components), a maximum coding unit (CTU) is a unit that includes a maximum coding block of luma samples, two maximum coding blocks of corresponding chroma samples, and syntax structures used to encode the luma samples and chroma samples. When a picture is a monochrome picture, a maximum coding unit is a unit that includes a maximum coding block of monochrome samples and syntax structures used to encode the monochrome samples. When a picture is a picture that is encoded with a color plane that is separated by color components, a maximum coding unit is a unit that includes syntax structures used to encode samples of the picture and the image.

[0070] A single maximum coding block (CTB) can be divided into MxN coding blocks containing MxN samples (M, N are integers).

[0071] When a picture has a sample array for each Y, Cr, and Cb component, a coding unit (CU) is a unit that includes a coding block for a luma sample and two coding blocks for corresponding chroma samples, and syntax structures used to encode the luma sample and the chroma samples. When the picture is a monochrome picture, a coding unit is a unit that includes a coding block for a monochrome sample and syntax structures used to encode the monochrome samples. When the picture is a picture that is encoded with a color plane that is separated by color component, a coding unit is a unit that includes syntax structures used to encode samples of the picture and the image.

[0072] As explained above, the maximum coding block and the maximum coding unit are distinct concepts, and the coding block and the coding unit are distinct concepts. That is, the (maximum) coding unit refers to a data structure including a (maximum) coding block including the corresponding sample and a syntax structure corresponding to it. However, since a person skilled in the art can understand that the (maximum) coding unit or the (maximum) coding block refers to a block of a predetermined size including a predetermined number of samples, the following specification will refer to the maximum coding block and the maximum coding unit, or the coding block and the coding unit, without distinction unless there are special circumstances.

[0073] An image can be divided into Coding Tree Units (CTUs). The size of the CTUs can be determined based on information obtained from the bitstream. The shape of the CTUs can be a square of equal size, but is not limited thereto.

[0074] For example, information about the maximum size of a luma coding block can be obtained from the bitstream. For example, the maximum size of the luma coding block indicated by the information about the maximum size of the luma coding block can be one of 4x4, 8x8, 16x16, 32x32, 64x64, 128x128, and 256x256.

[0075] For example, information about the maximum size of a luma coding block that can be split into two and the luma block size difference can be obtained from the bitstream. The information about the luma block size difference can indicate the size difference between a luma maximum coding unit and a maximum luma coding block that can be split into two. Therefore, by combining the information about the maximum size of a luma coding block that can be split into two obtained from the bitstream and the information about the luma block size difference, the size of the luma maximum coding unit can be determined. Using the size of the luma maximum coding unit, the size of the chroma maximum coding unit can also be determined. For example, if the Y: Cb: Cr ratio is 4:2:0 according to the color format, the size of the chroma block can be half the size of the luma block, and similarly, the size of the chroma maximum coding unit can be half the size of the luma maximum coding unit.

[0076] According to one embodiment, since information about the maximum size of a luma coding block capable of binary splitting is obtained from a bitstream, the maximum size of the luma coding block capable of binary splitting can be determined variably. Alternatively, the maximum size of the luma coding block capable of ternary splitting can be fixed. For example, the maximum size of a luma coding block capable of ternary splitting in an I picture may be 32x32, and the maximum size of a luma coding block capable of ternary splitting in a P picture or a B picture may be 64x64.

[0077] Additionally, the maximum coding unit can be hierarchically divided into coding units based on the division shape mode information obtained from the bitstream. As the division shape mode information, at least one of information indicating whether quad division is performed, information indicating whether multi-division is performed, division direction information, and division type information can be obtained from the bitstream.

[0078] For example, information indicating whether a quad split is present may indicate whether the current encoding unit is to be quad split (QUAD_SPLIT) or not to be quad split.

[0079] If the current encoding unit is not quad-split, the information indicating whether it is multi-split may indicate whether the current encoding unit will not be split any further (NO_SPLIT) or whether it will be binary / ternary split.

[0080] When the current encoding unit is binary or ternary split, the split direction information indicates that the current encoding unit is split in either the horizontal or vertical direction.

[0081] When the current encoding unit is split in the horizontal or vertical direction, the split type information indicates that the current encoding unit is split into binary split or ternary split.

[0082] Depending on the split direction information and the split type information, the split mode of the current encoding unit can be determined. The split mode when the current encoding unit is split into binaries in the horizontal direction can be determined as binary horizontal split (SPLIT_BT_HOR), the split mode when the current encoding unit is split into ternary horizontal split (SPLIT_TT_HOR), the split mode when the current encoding unit is split into binaries in the vertical direction can be determined as binary vertical split (SPLIT_BT_VER), and the split mode when the current encoding unit is split into ternary vertical split (SPLIT_TT_VER).

[0083] The image decoding device (100) can obtain segmentation shape mode information from a bitstream from a single binstring. The format of the bitstream received by the image decoding device (100) can include a fixed length binary code, a unary code, a truncated unary code, a predetermined binary code, etc. The binstring represents information as a series of binary numbers. The binstring can be composed of at least one bit. The image decoding device (100) can obtain segmentation shape mode information corresponding to the binstring based on a segmentation rule. The image decoding device (100) can determine whether to quad-segment an encoding unit, whether not to quad-segment, or the segmentation direction and segmentation type based on a single binstring.

[0084] The coding unit may be smaller than or equal to the maximum coding unit. For example, the maximum coding unit is also a coding unit with the maximum size, so it is a coding unit. If the split shape mode information for the maximum coding unit indicates that it is not split, the coding unit determined from the maximum coding unit has the same size as the maximum coding unit. If the split shape mode information for the maximum coding unit indicates that it is split, the maximum coding unit may be split into coding units. In addition, if the split shape mode information for the coding unit indicates splitting, the coding units may be split into coding units of smaller sizes. However, the splitting of the image is not limited thereto, and the maximum coding unit and the coding units may not be distinguished. The splitting of the coding unit is described in more detail with reference to FIGS. 3 to 16.

[0085] Additionally, one or more prediction blocks for prediction may be determined from the coding unit. The prediction blocks may be equal to or smaller than the coding unit. Additionally, one or more transformation blocks for transformation may be determined from the coding unit. The transformation blocks may be equal to or smaller than the coding unit.

[0086] The shape and size of the transformation block and the prediction block may be unrelated.

[0087] In another embodiment, prediction may be performed using the encoding unit as a prediction block. Transformation may also be performed using the encoding unit as a transform block.

[0088] The division of a coding unit is described in more detail with reference to FIGS. 3 to 16. The current block and neighboring blocks of the present disclosure may represent one of a maximum coding unit, a coding unit, a prediction block, and a transform block. In addition, the current block or the current coding unit is a block currently being decoded or encoded, or a block currently being divided. The neighboring block may be a block reconstructed before the current block. The neighboring block may be spatially or temporally adjacent to the current block. The neighboring block may be located on one of the lower left, left, upper left, upper right, upper right, right, and lower right sides of the current block.

[0089] The above-described embodiment describes operations related to an image decoding method performed by an image decoding device (100). Hereinafter, the operations of an image encoding device (200) that performs an image encoding method corresponding to the reverse process of the image decoding method will be described through one embodiment of the present disclosure.

[0090] FIG. 2 illustrates a block diagram of an image encoding device (200) capable of encoding an image based on at least one of block shape information and segmentation shape mode information according to one embodiment of the present disclosure.

[0091] The video encoding device (200) may include an encoding unit (220) and a bitstream generation unit (210). The encoding unit (220) may receive an input image and encode the input image. The encoding unit (220) may encode the input image to obtain at least one syntax element. The syntax element may include at least one of a skip flag, a prediction mode, a motion vector difference, a motion vector prediction method (or index), a transform quantized coefficient, a coded block pattern, a coded block flag, an intra prediction mode, a direct flag, a merge flag, a delta QP, a reference index, a prediction direction, and a transform index. The encoding unit (220) may determine a context model based on block shape information including at least one of a shape, a direction, a ratio of width and height, or a size of an encoding unit.

[0092] The bitstream generation unit (210) can generate a bitstream based on an encoded input image. For example, the bitstream generation unit (210) can generate a bitstream by entropy encoding syntax elements based on a context model. In addition, the image encoding device (200) can transmit the bitstream to the image decoding device (100).

[0093] According to one embodiment of the present disclosure, the encoding unit (220) of the image encoding device (200) can determine the shape of an encoding unit. For example, the encoding unit may be square or have a non-square shape, and information indicating such shape may be included in the block shape information.

[0094] According to one embodiment of the present disclosure, the encoding unit (220) can determine the shape into which the encoding unit is to be split. The encoding unit (220) can determine the shape of at least one encoding unit included in the encoding unit, and the bitstream generation unit (210) can generate a bitstream including split shape mode information including information about the shape of such encoding unit.

[0095] According to one embodiment of the present disclosure, the encoder (220) can determine whether the encoding unit is split or not. If the encoder (220) determines that the encoding unit includes only one encoding unit or that the encoding unit is not split, the bitstream generation unit (210) can generate a bitstream including split shape mode information indicating that the encoding unit is not split. In addition, the encoder (220) can split the encoding unit into a plurality of encoding units, and the bitstream generation unit (210) can generate a bitstream including split shape mode information indicating that the encoding unit is split into a plurality of encoding units.

[0096] According to one embodiment of the present disclosure, information indicating the number of coding units to be split into or the direction in which the coding unit is split may be included in the splitting mode information. For example, the splitting mode information may indicate splitting in at least one of the vertical and horizontal directions, or may indicate no splitting.

[0097] The video encoding device (200) determines information about the segmentation shape mode based on the segmentation shape mode of the encoding unit. The video encoding device (200) determines a context model based on at least one of the shape, direction, width, and height ratio or size of the encoding unit. Then, the video encoding device (200) generates information about the segmentation shape mode for segmenting the encoding unit based on the context model as a bitstream.

[0098] In order to determine a context model, the video encoding device (200) may obtain an array for matching at least one of the shape, direction, width and height ratio or size of the encoding unit with an index for the context model. The video encoding device (200) may obtain an index for the context model based on at least one of the shape, direction, width and height ratio or size of the encoding unit in the array. The video encoding device (200) may determine the context model based on the index for the context model.

[0099] The video encoding device (200) may further determine the context model based on block shape information including at least one of the shape, direction, width, and height ratio or size of a neighboring encoding unit adjacent to the encoding unit, in order to determine the context model. In addition, the neighboring encoding unit may include at least one of encoding units located on the lower left, left, upper left, upper right, right, or lower right of the encoding unit.

[0100] In addition, the video encoding device (200) may compare the length of the width of the upper peripheral encoding unit with the length of the width of the encoding unit to determine the context model. In addition, the video encoding device (200) may compare the length of the height of the left and right peripheral encoding units with the length of the height of the encoding unit. In addition, the video encoding device (200) may determine the context model based on the comparison results.

[0101] Since the operation of the video encoding device (200) includes similar contents to the operation of the video decoding device (100) described in FIGS. 3 to 19, a detailed description is omitted.

[0102] FIG. 3 illustrates a process in which an image decoding device (100) divides a current encoding unit to determine at least one encoding unit according to one embodiment of the present disclosure.

[0103] The block shape may include 4Nx4N, 4Nx2N, 2Nx4N, 4NxN, Nx4N, 32NxN, Nx32N, 16NxN, Nx16N, 8NxN or Nx8N, where N may be a positive integer. The block shape information is information indicating at least one of the shape, direction, width and height ratio or size of the encoding unit.

[0104] The shape of the encoding unit may include square and non-square. When the width and height of the encoding unit are equal (i.e., when the block shape of the encoding unit is 4Nx4N), the image decoding device (100) may determine the block shape information of the encoding unit as square. The image decoding device (100) may determine the shape of the encoding unit as non-square.

[0105] When the width and height of the encoding unit are different (i.e., when the block shape of the encoding unit is 4Nx2N, 2Nx4N, 4NxN, Nx4N, 32NxN, Nx32N, 16NxN, Nx16N, 8NxN, or Nx8N), the image decoding device (100) may determine the block shape information of the encoding unit to be non-square. When the shape of the encoding unit is non-square, the image decoding device (100) may determine the ratio of the width and height among the block shape information of the encoding unit to be at least one of 1:2, 2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1, 1:32, and 32:1. Additionally, based on the width length and height length of the encoding unit, the image decoding device (100) can determine whether the encoding unit is in the horizontal or vertical direction. Additionally, based on at least one of the width length, height length, or area of ​​the encoding unit, the image decoding device (100) can determine the size of the encoding unit.

[0106] According to one embodiment of the present disclosure, the image decoding device (100) can determine the shape of an encoding unit using block shape information, and can determine the shape into which the encoding unit is divided using segmentation shape mode information. That is, the splitting method of the encoding unit indicated by the segmentation shape mode information can be determined depending on which block shape the block shape information used by the image decoding device (100) indicates.

[0107] The image decoding device (100) can obtain the segmentation shape mode information from the bitstream. However, the present invention is not limited thereto, and the image decoding device (100) and the image encoding device (200) can determine the pre-agreed segmentation shape mode information based on the block shape information. The image decoding device (100) can determine the pre-agreed segmentation shape mode information for the maximum coding unit or the minimum coding unit. For example, the image decoding device (100) can determine the segmentation shape mode information for the maximum coding unit as quad split. In addition, the image decoding device (100) can determine the segmentation shape mode information for the minimum coding unit as “not split.” Specifically, the image decoding device (100) can determine the size of the maximum coding unit as 256x256. The image decoding device (100) can determine the pre-agreed segmentation shape mode information as quad split. Quad splitting is a splitting mode that divides both the width and height of an encoding unit in half. The image decoding device (100) can obtain a coding unit of size 128x128 from a maximum coding unit of size 256x256 based on the splitting mode information. In addition, the image decoding device (100) can determine the size of the minimum coding unit as 4x4. The image decoding device (100) can obtain splitting mode information indicating "not splitting" for the minimum coding unit.

[0108] According to one embodiment of the present disclosure, the image decoding device (100) may use block shape information indicating that the current encoding unit is a square shape. For example, the image decoding device (100) may determine whether to not split a square encoding unit, to split it vertically, to split it horizontally, to split it into four encoding units, etc., according to the split shape mode information. Referring to FIG. 3, when the block shape information of the current encoding unit (300) indicates a square shape, the decoding unit (120) may not split an encoding unit (310a) having the same size as the current encoding unit (300) according to the split shape mode information indicating that it is not split, or may determine a split encoding unit (310b, 310c, 310d, 310e, 310f, etc.) based on the split shape mode information indicating a predetermined splitting method.

[0109] Referring to FIG. 3, the image decoding device (100) may determine two encoding units (310b) by vertically dividing the current encoding unit (300) based on the split shape mode information indicating that the current encoding unit (300) is split in the vertical direction according to one embodiment of the present disclosure. The image decoding device (100) may determine two encoding units (310c) by horizontally dividing the current encoding unit (300) based on the split shape mode information indicating that the current encoding unit (300) is split in the horizontal direction. The image decoding device (100) may determine four encoding units (310d) by vertically dividing the current encoding unit (300) and the horizontal direction based on the split shape mode information indicating that the current encoding unit (300) is split in the vertical direction and the horizontal direction. The image decoding device (100) may determine three coding units (310e) into which the current coding unit (300) is vertically divided based on the partition shape mode information indicating that the current coding unit (300) is ternary divided in the vertical direction according to one embodiment of the present disclosure. The image decoding device (100) may determine three coding units (310f) into which the current coding unit (300) is horizontally divided based on the partition shape mode information indicating that the current coding unit (300) is ternary divided in the horizontal direction. However, the partition shapes into which a square coding unit may be divided should not be interpreted as being limited to the above-described shapes, and may include various shapes that the partition shape mode information may indicate. Specified partition shapes into which a square coding unit is divided will be specifically described below through one embodiment of the present disclosure.

[0110] FIG. 4 illustrates a process in which an image decoding device (100) divides a non-square coding unit to determine at least one coding unit according to one embodiment of the present disclosure.

[0111] According to one embodiment of the present disclosure, an image decoding device (100) may utilize block shape information indicating that a current encoding unit is non-square in shape. The image decoding device (100) may determine whether to not split a non-square current encoding unit or to split it using a predetermined method based on the split shape mode information. Referring to FIG. 4, when the block shape information of the current encoding unit (400 or 450) indicates a non-square shape, the image decoding device (100) may determine an encoding unit (410 or 460) having the same size as the current encoding unit (400 or 450) according to the split shape mode information indicating that it is not split, or may determine a split encoding unit (420a, 420b, 430a, 430b, 430c, 470a, 470b, 480a, 480b, 480c) based on the split shape mode information indicating a predetermined splitting method. A predetermined splitting method by which a non-square encoding unit is split will be described in detail below through an embodiment of the present disclosure.

[0112] According to one embodiment of the present disclosure, the image decoding device (100) can determine a form in which an encoding unit is split using split shape mode information, and in this case, the split shape mode information can indicate the number of at least one encoding unit generated by splitting the encoding unit. Referring to FIG. 4, when the split shape mode information indicates that the current encoding unit (400 or 450) is split into two encoding units, the image decoding device (100) can split the current encoding unit (400 or 450) based on the split shape mode information to determine two encoding units (420a, 420b, or 470a, 470b) included in the current encoding unit.

[0113] According to one embodiment of the present disclosure, when the image decoding device (100) splits a current encoding unit (400 or 450) having a non-square shape based on split shape mode information, the image decoding device (100) may split the current encoding unit by considering the position of the long side of the non-square current encoding unit (400 or 450). For example, the image decoding device (100) may split the current encoding unit (400 or 450) in a direction that splits the long side of the current encoding unit (400 or 450) by considering the shape of the current encoding unit (400 or 450) to determine a plurality of encoding units.

[0114] According to one embodiment of the present disclosure, if the splitting shape mode information indicates that the encoding unit is split into an odd number of blocks (ternary splitting), the image decoding device (100) may determine an odd number of encoding units included in the current encoding unit (400 or 450). For example, if the splitting shape mode information indicates that the current encoding unit (400 or 450) is split into three encoding units, the image decoding device (100) may split the current encoding unit (400 or 450) into three encoding units (430a, 430b, 430c, 480a, 480b, 480c).

[0115] According to one embodiment of the present disclosure, the ratio of the width and height of the current encoding unit (400 or 450) may be 4:1 or 1:4. When the ratio of the width and height is 4:1, the length of the width is longer than the length of the height, so the block shape information may be in the horizontal direction. When the ratio of the width and height is 1:4, the length of the width is shorter than the length of the height, so the block shape information may be in the vertical direction. The image decoding device (100) may determine to split the current encoding unit into an odd number of blocks based on the split shape mode information. In addition, the image decoding device (100) may determine the splitting direction of the current encoding unit (400 or 450) based on the block shape information of the current encoding unit (400 or 450). For example, if the current encoding unit (400) is in the vertical direction, the image decoding device (100) can divide the current encoding unit (400) in the horizontal direction to determine encoding units (430a, 430b, 430c). Also, if the current encoding unit (450) is in the horizontal direction, the image decoding device (100) can divide the current encoding unit (450) in the vertical direction to determine encoding units (480a, 480b, 480c).

[0116] According to one embodiment of the present disclosure, the image decoding device (100) may determine an odd number of coding units included in the current coding unit (400 or 450), and the sizes of the determined coding units may not all be the same. For example, among the determined odd number of coding units (430a, 430b, 430c, 480a, 480b, 480c), the size of a given coding unit (430b or 480b) may have a different size from the other coding units (430a, 430c, 480a, 480c). That is, the encoding units into which the current encoding unit (400 or 450) can be divided and determined can have multiple types of sizes, and in some cases, an odd number of encoding units (430a, 430b, 430c, 480a, 480b, 480c) can each have different sizes.

[0117] According to one embodiment of the present disclosure, when the split shape mode information indicates that the coding unit is split into an odd number of blocks, the image decoding device (100) can determine an odd number of coding units included in the current coding unit (400 or 450), and further, the image decoding device (100) can place a predetermined restriction on at least one coding unit among the odd number of coding units generated by splitting. Referring to FIG. 4, the image decoding device (100) can perform a decoding process for a coding unit (430b, 480b) located in the center among three coding units (430a, 430b, 430c, 480a, 480b, 480c) generated by splitting the current coding unit (400 or 450) differently from the decoding process for other coding units (430a, 430c, 480a, 480c). For example, the image decoding device (100) can restrict the encoding unit (430b, 480b) located in the center from being split any further, unlike other encoding units (430a, 430c, 480a, 480c), or can restrict it to be split only a predetermined number of times.

[0118] FIG. 5 illustrates a process in which an image decoding device (100) divides an encoding unit based on at least one of block shape information and division shape mode information according to one embodiment of the present disclosure.

[0119] According to one embodiment of the present disclosure, the image decoding device (100) may determine whether to split or not to split a first coding unit (500) having a square shape into coding units based on at least one of block shape information and split shape mode information. If the split shape mode information indicates that the first coding unit (500) is split in the horizontal direction according to one embodiment of the present disclosure, the image decoding device (100) may split the first coding unit (500) in the horizontal direction to determine a second coding unit (510). The first coding unit, the second coding unit, and the third coding unit used according to one embodiment of the present disclosure are terms used to understand the relationship before and after splitting between coding units. For example, when the first coding unit is split, the second coding unit may be determined, and when the second coding unit is split, the third coding unit may be determined. In the following, the relationship between the first encoding unit, the second encoding unit, and the third encoding unit used can be understood as following the above-described characteristics.

[0120] According to one embodiment of the present disclosure, the image decoding device (100) may determine to split or not split the determined second encoding unit (510) into encoding units based on the splitting shape mode information. Referring to FIG. 5, the image decoding device (100) may split the first encoding unit (500) based on the splitting shape mode information to split the determined second encoding unit (510) of a non-square shape into at least one third encoding unit (520a, 520b, 520c, 520d, etc.) or may not split the second encoding unit (510). The image decoding device (100) can obtain split shape mode information, and the image decoding device (100) can split the first encoding unit (500) based on the obtained split shape mode information to split a plurality of second encoding units (e.g., 510) of various shapes, and the second encoding unit (510) can be split according to the way in which the first encoding unit (500) is split based on the split shape mode information. According to one embodiment of the present disclosure, when the first encoding unit (500) is split into the second encoding unit (510) based on the split shape mode information for the first encoding unit (500), the second encoding unit (510) can also be split into the third encoding unit (e.g., 520a, 520b, 520c, 520d, etc.) based on the split shape mode information for the second encoding unit (510). That is, the coding unit can be recursively split based on the split shape mode information associated with each coding unit. Accordingly, a square coding unit can be determined from a non-square coding unit, and such a square coding unit can be recursively split to determine a non-square coding unit.

[0121] Referring to FIG. 5, among the odd number of third coding units (520b, 520c, 520d) into which the non-square second coding unit (510) is split, a predetermined coding unit (e.g., a coding unit located in the middle or a square coding unit) may be split recursively. According to one embodiment of the present disclosure, the non-square third coding unit (520b), which is one of the odd number of third coding units (520b, 520c, 520d), may be split horizontally into a plurality of fourth coding units. The non-square fourth coding unit (530b or 530d), which is one of the plurality of fourth coding units (530a, 530b, 530c, 530d), may be split again into a plurality of coding units. For example, the fourth coding unit (530b or 530d) having a non-square shape may be further divided into an odd number of coding units. A method that can be used for recursive division of coding units will be described later through an embodiment of the present disclosure.

[0122] According to one embodiment of the present disclosure, the image decoding device (100) may split each of the third encoding units (520a, 520b, 520c, 520d, etc.) into encoding units based on the splitting shape mode information. In addition, the image decoding device (100) may determine not to split the second encoding unit (510) based on the splitting shape mode information. According to one embodiment of the present disclosure, the image decoding device (100) may split the second encoding unit (510) having a non-square shape into an odd number of third encoding units (520b, 520c, 520d). The image decoding device (100) may place a predetermined restriction on a predetermined third encoding unit among the odd number of third encoding units (520b, 520c, 520d). For example, the image decoding device (100) can limit the encoding unit (520c) located in the middle among an odd number of third encoding units (520b, 520c, 520d) to not be divided any further or to be divided a settable number of times.

[0123] Referring to FIG. 5, the image decoding device (100) may limit the coding unit (520c) located in the middle among the odd number of third coding units (520b, 520c, 520d) included in the second coding unit (510) having a non-square shape to not be split any further, or to be split in a predetermined split form (for example, to be split only into four coding units or to be split in a form corresponding to the split form of the second coding unit (510), or to be split only a predetermined number of times (for example, to be split only n times, where n>0). However, the above limitations on the coding unit (520c) located in the middle are merely simple embodiments and should not be interpreted as being limited to the above-described embodiments, but should be interpreted as including various limitations in which the coding unit (520c) located in the middle can be decoded differently from the other coding units (520b, 520d).

[0124] According to one embodiment of the present disclosure, the image decoding device (100) can obtain the segmentation shape mode information used to segment the current encoding unit from a predetermined location within the current encoding unit.

[0125] FIG. 6 illustrates a method for an image decoding device (100) to determine a predetermined encoding unit among an odd number of encoding units according to one embodiment of the present disclosure.

[0126] Referring to FIG. 6, the split shape mode information of the current encoding unit (600, 650) can be obtained from a sample at a predetermined position among a plurality of samples included in the current encoding unit (600, 650) (for example, a sample (640, 690) located in the center). However, the predetermined position within the current encoding unit (600) from which at least one of the split shape mode information can be obtained should not be interpreted as being limited to the center position illustrated in FIG. 6, but should be interpreted as including various positions (for example, top, bottom, left, right, upper left, lower left, upper right, or lower right, etc.) that can be included within the current encoding unit (600). The image decoding device (100) can obtain the split shape mode information obtained from the predetermined position and determine whether or not to split the current encoding unit into encoding units of various shapes and sizes.

[0127] According to one embodiment of the present disclosure, the image decoding device (100) may select one of the coding units when the current coding unit is divided into a predetermined number of coding units. Various methods may be used to select one of the multiple coding units, and a description of such methods will be provided later through one embodiment of the present disclosure.

[0128] According to one embodiment of the present disclosure, an image decoding device (100) can divide a current encoding unit into a plurality of encoding units and determine an encoding unit at a predetermined position.

[0129] According to one embodiment of the present disclosure, the image decoding device (100) may use information indicating the positions of each of the odd-numbered coding units to determine an coding unit located in the middle of the odd-numbered coding units. Referring to FIG. 6, the image decoding device (100) may split the current coding unit (600) or the current coding unit (650) to determine odd-numbered coding units (620a, 620b, 620c) or odd-numbered coding units (660a, 660b, 660c). The image decoding device (100) may use information about the positions of the odd-numbered coding units (620a, 620b, 620c) or odd-numbered coding units (660a, 660b, 660c) to determine the middle coding unit (620b) or the middle coding unit (660b). For example, the image decoding device (100) can determine the coding unit (620b) located in the center by determining the positions of the coding units (620a, 620b, 620c) based on information indicating the positions of predetermined samples included in the coding units (620a, 620b, 620c). Specifically, the image decoding device (100) can determine the coding unit (620b) located in the center by determining the positions of the coding units (620a, 620b, 620c) based on information indicating the positions of samples (630a, 630b, 630c) at the upper left of the coding units (620a, 620b, 620c).

[0130] According to one embodiment of the present disclosure, information indicating the positions of the upper left samples (630a, 630b, 630c) included in each of the coding units (620a, 620b, 620c) may include information on the positions or coordinates of the coding units (620a, 620b, 620c) within the picture. According to one embodiment of the present disclosure, information indicating the positions of the upper left samples (630a, 630b, 630c) included in each of the coding units (620a, 620b, 620c) may include information indicating the width or height of the coding units (620a, 620b, 620c) included in the current coding unit (600), and this width or height may correspond to information indicating the difference between the coordinates of the coding units (620a, 620b, 620c) within the picture. That is, the image decoding device (100) can determine the encoding unit (620b) located in the center by directly using information about the positions or coordinates of the encoding units (620a, 620b, 620c) within the picture or by using information about the width or height of the encoding unit corresponding to the difference between the coordinates.

[0131] According to one embodiment of the present disclosure, information indicating the position of the sample (630a) at the upper left of the upper encoding unit (620a) may represent coordinates (xa, ya), information indicating the position of the sample (530b) at the upper left of the middle encoding unit (620b) may represent coordinates (xb, yb), and information indicating the position of the sample (630c) at the upper left of the lower encoding unit (620c) may represent coordinates (xc, yc). The image decoding apparatus (100) may determine the middle encoding unit (620b) using the coordinates of the upper left samples (630a, 630b, 630c) included in the encoding units (620a, 620b, 620c), respectively. For example, when the coordinates of the samples (630a, 630b, 630c) on the upper left are sorted in ascending or descending order, the encoding unit (620b) including the coordinates (xb, yb) of the sample (630b) located in the center can be determined as the encoding unit located in the center among the encoding units (620a, 620b, 620c) determined by dividing the current encoding unit (600). However, the coordinates indicating the positions of the upper left samples (630a, 630b, 630c) may indicate coordinates indicating the absolute positions within the picture, and further, based on the position of the upper left sample (630a) of the upper left coding unit (620a), the (dxb, dyb) coordinates, which are information indicating the relative position of the sample (630b) of the upper left of the middle coding unit (620b), and the (dxc, dyc) coordinates, which are information indicating the relative position of the sample (630c) of the upper left of the lower coding unit (620c), may be used. In addition, the method of determining the coding unit of a given position by using the coordinates of the corresponding sample as information indicating the position of the sample included in the coding unit should not be interpreted as being limited to the above-described method, but should be interpreted as various arithmetic methods that can utilize the coordinates of the sample.

[0132] According to one embodiment of the present disclosure, the image decoding device (100) can divide the current encoding unit (600) into a plurality of encoding units (620a, 620b, 620c), and select an encoding unit from among the encoding units (620a, 620b, 620c) according to a predetermined criterion. For example, the image decoding device (100) can select an encoding unit (620b) having a different size from among the encoding units (620a, 620b, 620c).

[0133] According to one embodiment of the present disclosure, the image decoding device (100) can determine the width or height of each of the encoding units (620a, 620b, 620c) by using the (xa, ya) coordinate, which is information indicating the position of the sample (630a) at the upper left of the upper encoding unit (620a), the (xb, yb) coordinate, which is information indicating the position of the sample (630b) at the upper left of the middle encoding unit (620b), and the (xc, yc) coordinate, which is information indicating the position of the sample (630c) at the upper left of the lower encoding unit (620c). The image decoding device (100) can determine the size of each of the encoding units (620a, 620b, 620c) using coordinates (xa, ya), (xb, yb), (xc, yc) indicating the positions of the encoding units (620a, 620b, 620c). According to one embodiment of the present disclosure, the image decoding device (100) can determine the width of the upper encoding unit (620a) as the width of the current encoding unit (600). The image decoding device (100) can determine the height of the upper encoding unit (620a) as yb-ya. According to one embodiment of the present disclosure, the image decoding device (100) can determine the width of the middle encoding unit (620b) as the width of the current encoding unit (600). The image decoding device (100) may determine the height of the middle encoding unit (620b) as yc-yb. According to one embodiment of the present disclosure, the image decoding device (100) may determine the width or height of the lower encoding unit using the width or height of the current encoding unit and the width and height of the upper encoding unit (620a) and the middle encoding unit (620b). The image decoding device (100) may determine an encoding unit having a different size from other encoding units based on the width and height of the determined encoding units (620a, 620b, 620c).Referring to FIG. 6, the image decoding device (100) can determine the middle encoding unit (620b) having a different size from the sizes of the upper encoding unit (620a) and the lower encoding unit (620c) as the encoding unit of a predetermined position. However, the process by which the image decoding device (100) described above determines the encoding unit having a different size from other encoding units is merely an embodiment of determining the encoding unit of a predetermined position using the size of the encoding unit determined based on sample coordinates, and therefore, various processes of determining the encoding unit of a predetermined position by comparing the sizes of the encoding units determined according to predetermined sample coordinates can be used.

[0134] The image decoding device (100) can determine the width or height of each of the encoding units (660a, 660b, 660c) by using the (xd, yd) coordinate, which is information indicating the position of the sample (670a) at the upper left of the left encoding unit (660a), the (xe, ye) coordinate, which is information indicating the position of the sample (670b) at the upper left of the middle encoding unit (660b), and the (xf, yf) coordinate, which is information indicating the position of the sample (670c) at the upper left of the right encoding unit (660c). The image decoding device (100) can determine the size of each of the encoding units (660a, 660b, 660c) by using the (xd, yd), (xe, ye), (xf, yf), which are coordinates indicating the positions of the encoding units (660a, 660b, 660c).

[0135] According to one embodiment of the present disclosure, the image decoding device (100) may determine the width of the left coding unit (660a) as xe-xd. The image decoding device (100) may determine the height of the left coding unit (660a) as the height of the current coding unit (650). According to one embodiment of the present disclosure, the image decoding device (100) may determine the width of the middle coding unit (660b) as xf-xe. The image decoding device (100) may determine the height of the middle coding unit (660b) as the height of the current coding unit (600). According to one embodiment of the present disclosure, the image decoding device (100) may determine the width or height of the right coding unit (660c) using the width or height of the current coding unit (650) and the widths and heights of the left coding unit (660a) and the middle coding unit (660b). The image decoding device (100) can determine an encoding unit having a different size from other encoding units based on the width and height of the determined encoding units (660a, 660b, 660c). Referring to FIG. 6, the image decoding device (100) can determine a middle encoding unit (660b) having a different size from the sizes of the left encoding unit (660a) and the right encoding unit (660c) as an encoding unit at a predetermined position. However, the process of the image decoding device (100) described above determining an encoding unit having a different size from other encoding units is merely an embodiment of determining an encoding unit at a predetermined position using the size of an encoding unit determined based on sample coordinates, and therefore, various processes of determining an encoding unit at a predetermined position by comparing the sizes of encoding units determined according to predetermined sample coordinates can be used.

[0136] However, the location of the sample considered for determining the location of the encoding unit should not be interpreted as being limited to the upper left corner described above, and it can be interpreted that information on the location of any sample included in the encoding unit can be used.

[0137] According to one embodiment of the present disclosure, the image decoding device (100) may select an coding unit at a predetermined position from among an odd number of coding units determined by splitting the current coding unit, taking into consideration the shape of the current coding unit. For example, if the current coding unit has a non-square shape in which the width is longer than the height, the image decoding device (100) may determine an coding unit at a predetermined position in the horizontal direction. That is, the image decoding device (100) may determine one of the coding units whose positions vary in the horizontal direction and place a restriction on the corresponding coding unit. If the current coding unit has a non-square shape in which the height is longer than the width, the image decoding device (100) may determine an coding unit at a predetermined position in the vertical direction. That is, the image decoding device (100) may determine one of the coding units whose positions vary in the vertical direction and place a restriction on the corresponding coding unit.

[0138] According to one embodiment of the present disclosure, the image decoding device (100) may use information indicating the positions of each of the even-numbered coding units to determine an coding unit at a predetermined position among an even-numbered coding unit. The image decoding device (100) may determine an even-numbered coding unit by dividing the current coding unit (binary dividing) and may determine an coding unit at a predetermined position using information about the positions of the even-numbered coding units. A specific process for this may correspond to a process of determining an coding unit at a predetermined position (e.g., a center position) among an odd-numbered coding unit described above in FIG. 6, and thus will be omitted.

[0139] According to one embodiment of the present disclosure, when a current encoding unit having a non-square shape is split into a plurality of encoding units, predetermined information about the encoding unit at a predetermined position may be used during the splitting process to determine an encoding unit at a predetermined position among the plurality of encoding units. For example, the image decoding device (100) may use at least one of block shape information and split shape mode information stored in a sample included in a middle encoding unit during the splitting process to determine an encoding unit located in the middle among the encoding units into which the current encoding unit is split.

[0140] Referring to FIG. 6, the image decoding device (100) can split the current encoding unit (600) into a plurality of encoding units (620a, 620b, 620c) based on the split shape mode information, and can determine the encoding unit (620b) located in the middle among the plurality of encoding units (620a, 620b, 620c). Furthermore, the image decoding device (100) can determine the encoding unit (620b) located in the middle by considering the position where the split shape mode information is acquired. That is, the split shape mode information of the current encoding unit (600) can be obtained from a sample (640) located in the center of the current encoding unit (600), and when the current encoding unit (600) is split into a plurality of encoding units (620a, 620b, 620c) based on the split shape mode information, the encoding unit (620b) including the sample (640) can be determined as the encoding unit located in the center. However, the information used to determine the encoding unit located in the center should not be interpreted as being limited to the split shape mode information, and various types of information can be used in the process of determining the encoding unit located in the center.

[0141] According to one embodiment of the present disclosure, predetermined information for identifying a coding unit at a predetermined position may be obtained from a predetermined sample included in the coding unit to be determined. Referring to FIG. 6, the image decoding apparatus (100) may use split shape mode information obtained from a sample at a predetermined position within the current coding unit (600) (e.g., a sample located at the center of the current coding unit (600)) to determine a coding unit at a predetermined position among a plurality of coding units (620a, 620b, 620c) determined by splitting the current coding unit (600) (e.g., a coding unit located at the center of the coding units split into multiple units). That is, the image decoding device (100) can determine the sample at the predetermined position by considering the block shape of the current encoding unit (600), and the image decoding device (100) can determine an encoding unit (620b) that includes a sample from which predetermined information (e.g., division shape mode information) can be obtained among a plurality of encoding units (620a, 620b, 620c) determined by dividing the current encoding unit (600), and can set a predetermined restriction. Referring to FIG. 6, according to an embodiment of the present disclosure, the image decoding device (100) can determine a sample (640) located at the center of the current encoding unit (600) as a sample from which predetermined information can be obtained, and the image decoding device (100) can set a predetermined restriction on the encoding unit (620b) that includes this sample (640) during the decoding process. However, the location of the sample from which certain information can be obtained should not be interpreted as being limited to the above-described location, but may be interpreted as samples at any location included in the encoding unit (620b) to be determined in order to set a limitation.

[0142] According to one embodiment of the present disclosure, the position of a sample from which predetermined information can be obtained may be determined according to the shape of the current encoding unit (600). According to one embodiment of the present disclosure, block shape information may determine whether the shape of the current encoding unit is square or non-square, and may determine the position of a sample from which predetermined information can be obtained according to the shape. For example, the image decoding apparatus (100) may determine a sample located on a boundary that divides at least one of the width and height of the current encoding unit in half as a sample from which predetermined information can be obtained, using at least one of information about the width and information about the height of the current encoding unit. As another example, when the block shape information related to the current encoding unit indicates that the shape is non-square, the image decoding apparatus (100) may determine one of the samples adjacent to the boundary that divides the long side of the current encoding unit in half as a sample from which predetermined information can be obtained.

[0143] According to one embodiment of the present disclosure, when the image decoding device (100) divides a current encoding unit into a plurality of encoding units, the image decoding device (100) may use the split shape mode information to determine an encoding unit at a predetermined position among the plurality of encoding units. According to one embodiment of the present disclosure, the image decoding device (100) may obtain the split shape mode information from a sample at a predetermined position included in the encoding unit, and the image decoding device (100) may divide the plurality of encoding units generated by splitting the current encoding unit using the split shape mode information obtained from a sample at a predetermined position included in each of the plurality of encoding units. That is, the encoding unit may be recursively divided using the split shape mode information obtained from a sample at a predetermined position included in each of the encoding units. Since the recursive division process of the encoding unit has been described above with reference to FIG. 5, a detailed description thereof will be omitted.

[0144] According to one embodiment of the present disclosure, the image decoding device (100) can divide a current encoding unit to determine at least one encoding unit, and can determine the order in which the at least one encoding unit is decoded according to a predetermined block (e.g., the current encoding unit).

[0145] FIG. 7 illustrates the order in which multiple encoding units are processed when an image decoding device (100) determines multiple encoding units by dividing a current encoding unit according to one embodiment of the present disclosure.

[0146] According to one embodiment of the present disclosure, the image decoding device (100) may determine second encoding units (710a, 710b) by vertically splitting the first encoding unit (700) according to the splitting shape mode information, determine second encoding units (730a, 730b) by horizontally splitting the first encoding unit (700), or determine second encoding units (750a, 750b, 750c, 750d) by vertically and horizontally splitting the first encoding unit (700).

[0147] Referring to FIG. 7, the image decoding device (100) can determine the order in which the second encoding units (710a, 710b) determined by vertically dividing the first encoding unit (700) are processed in the horizontal direction (710c). The image decoding device (100) can determine the order in which the second encoding units (730a, 730b) determined by horizontally dividing the first encoding unit (700) are processed in the vertical direction (730c). The image decoding device (100) can determine the second encoding units (750a, 750b, 750c, 750d) determined by dividing the first encoding unit (700) in the vertical and horizontal directions according to a predetermined order (e.g., raster scan order (750e) or z scan order (z scan order)) in which encoding units located in one row are processed and then encoding units located in the next row are processed.

[0148] According to one embodiment of the present disclosure, the image decoding device (100) can recursively split encoding units. Referring to FIG. 7, the image decoding device (100) can split a first encoding unit (700) to determine a plurality of encoding units (710a, 710b, 730a, 730b, 750a, 750b, 750c, 750d), and can recursively split each of the determined plurality of encoding units (710a, 710b, 730a, 730b, 750a, 750b, 750c, 750d). A method for splitting a plurality of coding units (710a, 710b, 730a, 730b, 750a, 750b, 750c, 750d) may be a method corresponding to a method for splitting the first coding unit (700). Accordingly, the plurality of coding units (710a, 710b, 730a, 730b, 750a, 750b, 750c, 750d) may each be independently split into a plurality of coding units. Referring to FIG. 7, the image decoding device (100) may split the first coding unit (700) in the vertical direction to determine the second coding units (710a, 710b), and further may determine to independently split or not split each of the second coding units (710a, 710b).

[0149] According to one embodiment of the present disclosure, the image decoding device (100) may horizontally divide the second encoding unit (710a) on the left into third encoding units (720a, 720b), and may not divide the second encoding unit (710b) on the right.

[0150] According to one embodiment of the present disclosure, the processing order of coding units may be determined based on the splitting process of the coding units. In other words, the processing order of the split coding units may be determined based on the processing order of the coding units immediately before splitting. The image decoding apparatus (100) may determine the processing order of the third coding units (720a, 720b) ​​determined by splitting the second coding unit (710a) on the left, independently from the second coding unit (710b) on the right. Since the second coding unit (710a) on the left is split horizontally and the third coding units (720a, 720b) ​​are determined, the third coding units (720a, 720b) ​​may be processed in the vertical direction (720c). In addition, since the order in which the second encoding unit (710a) on the left and the second encoding unit (710b) on the right are processed corresponds to the horizontal direction (710c), the right encoding unit (710b) can be processed after the third encoding units (720a, 720b) ​​included in the second encoding unit (710a) on the left are processed in the vertical direction (720c). Since the above-described content is intended to explain the process in which the processing order of the encoding units is determined according to the encoding units before splitting, it should not be interpreted as being limited to the above-described embodiment, but should be interpreted as being used in various ways in which encoding units that are split and determined in various forms can be independently processed according to a predetermined order.

[0151] FIG. 8 illustrates a process of determining that a current encoding unit is divided into an odd number of encoding units when the encoding units cannot be processed in a predetermined order, according to one embodiment of the present disclosure, by an image decoding device (100).

[0152] According to one embodiment of the present disclosure, the image decoding device (100) may determine that the current encoding unit is split into an odd number of encoding units based on the acquired split shape mode information. Referring to FIG. 8, a first encoding unit (800) having a square shape may be split into second encoding units (810a, 810b) having a non-square shape, and the second encoding units (810a, 810b) may each be independently split into third encoding units (820a, 820b, 820c, 820d, 820e). According to one embodiment of the present disclosure, the image decoding device (100) can determine a plurality of third encoding units (820a, 820b) by horizontally dividing the left encoding unit (810a) among the second encoding units, and can divide the right encoding unit (810b) into an odd number of third encoding units (820c, 820d, 820e).

[0153] According to one embodiment of the present disclosure, the image decoding device (100) can determine whether there is an odd number of split coding units by determining whether the third coding units (820a, 820b, 820c, 820d, 820e) can be processed in a predetermined order. Referring to FIG. 8, the image decoding device (100) can determine the third coding units (820a, 820b, 820c, 820d, 820e) by recursively splitting the first coding unit (800). The image decoding device (100) can determine whether the first encoding unit (800), the second encoding unit (810a, 810b), or the third encoding unit (820a, 820b, 820c, 820d, 820e) is divided into an odd number of encoding units based on at least one of the block shape information and the split shape mode information. For example, the encoding unit located on the right side of the second encoding unit (810a, 810b) can be divided into an odd number of third encoding units (820c, 820d, 820e). The order in which the plurality of encoding units included in the first encoding unit (800) are processed can be a predetermined order (e.g., z-scan order (830)), and the image decoding device (100) can determine whether the third encoding unit (820c, 820d, 820e) determined by dividing the second encoding unit (810b) on the right into odd numbers satisfies the condition that it can be processed according to the predetermined order.

[0154] According to one embodiment of the present disclosure, the image decoding device (100) can determine whether the third encoding units (820a, 820b, 820c, 820d, 820e) included in the first encoding unit (800) satisfy a condition that they can be processed in a predetermined order, and the condition is related to whether at least one of the width and height of the second encoding unit (810a, 810b) is split in half according to the boundary of the third encoding unit (820a, 820b, 820c, 820d, 820e). For example, the third encoding unit (820a, 820b) determined by splitting the height of the left second encoding unit (810a) of a non-square shape in half can satisfy the condition. Since the boundaries of the third encoding units (820c, 820d, 820e) determined by dividing the right second encoding unit (810b) into three encoding units do not divide the width or height of the right second encoding unit (810b) in half, it may be determined that the third encoding units (820c, 820d, 820e) do not satisfy the condition. In the case where this condition is not satisfied, the image decoding device (100) may determine that there is a disconnection in the scanning order, and may determine that the right second encoding unit (810b) is divided into an odd number of encoding units based on the determination result. According to one embodiment of the present disclosure, when the image decoding device (100) is divided into an odd number of encoding units, a predetermined restriction may be placed on an encoding unit at a predetermined position among the divided encoding units. Since the contents of such restrictions or predetermined positions, etc. have been described above through one embodiment of the present disclosure, a detailed description thereof will be omitted.

[0155] FIG. 9 illustrates a process in which an image decoding device (100) divides a first encoding unit (900) to determine at least one encoding unit according to one embodiment of the present disclosure.

[0156] According to one embodiment of the present disclosure, the image decoding device (100) can split the first coding unit (900) based on the split shape mode information acquired through the bitstream acquisition unit (110). The first coding unit (900) having a square shape can be split into four coding units having a square shape or can be split into a plurality of coding units having a non-square shape. For example, referring to FIG. 9, when the first coding unit (900) is square and the split shape mode information indicates that it is split into coding units having a non-square shape, the image decoding device (100) can split the first coding unit (900) into a plurality of coding units having a non-square shape. Specifically, when the split shape mode information indicates that the first encoding unit (900) is split in the horizontal direction or the vertical direction to determine an odd number of encoding units, the image decoding device (100) can split the first encoding unit (900) having a square shape into second encoding units (910a, 910b, 910c) determined by splitting them in the vertical direction into an odd number of encoding units or second encoding units (920a, 920b, 920c) determined by splitting them in the horizontal direction.

[0157] According to one embodiment of the present disclosure, the image decoding device (100) can determine whether the second encoding units (910a, 910b, 910c, 920a, 920b, 920c) included in the first encoding unit (900) satisfy a condition that they can be processed in a predetermined order, and the condition is related to whether at least one of the width and height of the first encoding unit (900) is split in half according to the boundary of the second encoding unit (910a, 910b, 910c, 920a, 920b, 920c). Referring to FIG. 9, since the boundaries of the second coding units (910a, 910b, 910c) determined by vertically dividing the first coding unit (900) in a square shape do not divide the width of the first coding unit (900) in half, it may be determined that the first coding unit (900) does not satisfy the condition that it can be processed in a predetermined order. In addition, since the boundaries of the second coding units (920a, 920b, 920c) determined by horizontally dividing the first coding unit (900) in a square shape do not divide the height of the first coding unit (900) in half, it may be determined that the first coding unit (900) does not satisfy the condition that it can be processed in a predetermined order. If such a condition is not satisfied, the image decoding device (100) may determine that the scan order is disconnected, and based on the determination result, may determine that the first encoding unit (900) is divided into an odd number of encoding units. According to one embodiment of the present disclosure, when the image decoding device (100) is divided into an odd number of encoding units, a predetermined restriction may be placed on an encoding unit at a predetermined position among the divided encoding units. Since the contents of such restriction or the predetermined position, etc. have been described above through one embodiment of the present disclosure, a detailed description thereof will be omitted.

[0158] According to one embodiment of the present disclosure, the image decoding device (100) can divide the first encoding unit to determine encoding units of various shapes.

[0159] Referring to FIG. 9, the image decoding device (100) can divide the first encoding unit (900) having a square shape and the first encoding unit (930 or 950) having a non-square shape into encoding units of various shapes.

[0160] FIG. 10 illustrates that, according to one embodiment of the present disclosure, a video decoding device (100) limits the shapes into which a second encoding unit can be divided when a non-square shape of a second encoding unit determined by dividing a first encoding unit (1000) satisfies a predetermined condition.

[0161] According to one embodiment of the present disclosure, the image decoding device (100) may determine to split a first coding unit (1000) having a square shape into second coding units (1010a, 1010b, 1020a, 1020b) having a non-square shape based on the split shape mode information acquired through the bitstream acquisition unit (110). The second coding units (1010a, 1010b, 1020a, 1020b) may be independently split. Accordingly, the image decoding device (100) may determine to split or not split into a plurality of coding units based on the split shape mode information related to each of the second coding units (1010a, 1010b, 1020a, 1020b). According to one embodiment of the present disclosure, the image decoding device (100) may determine third coding units (1012a, 1012b) by horizontally dividing the left second coding unit (1010a) having a non-square shape determined by vertically dividing the first coding unit (1000). However, when the image decoding device (100) horizontally divides the left second coding unit (1010a), the right second coding unit (1010b) may be restricted from being horizontally divided in the same direction as the direction in which the left second coding unit (1010a) is divided. If the second encoding unit on the right (1010b) is split in the same direction to determine the third encoding unit (1014a, 1014b), the second encoding unit on the left (1010a) and the second encoding unit on the right (1010b) may be independently split in the horizontal direction to determine the third encoding unit (1012a, 1012b, 1014a, 1014b). However, this is the same result as the image decoding device (100) splitting the first encoding unit (1000) into four square-shaped second encoding units (1030a, 1030b, 1030c, 1030d) based on the split shape mode information, which may be inefficient in terms of image decoding.

[0162] According to one embodiment of the present disclosure, the image decoding device (100) may determine third coding units (1022a, 1022b, 1024a, 1024b) by vertically dividing a second coding unit (1020a or 1020b) having a non-square shape determined by dividing a first coding unit (1000) in a horizontal direction. However, when the image decoding device (100) vertically divides one of the second coding units (e.g., the upper second coding unit (1020a)), the other second coding units (e.g., the lower coding unit (1020b)) may be restricted from being vertically divided in the same direction as the direction in which the upper second coding unit (1020a) is divided, for the reasons described above.

[0163] FIG. 11 illustrates a process in which an image decoding device (100) divides a square-shaped encoding unit when the split shape mode information cannot indicate that the encoding unit is divided into four square-shaped encoding units according to one embodiment of the present disclosure.

[0164] According to one embodiment of the present disclosure, the image decoding device (100) may split the first encoding unit (1100) based on the split shape mode information to determine the second encoding units (1110a, 1110b, 1120a, 1120b, etc.). The split shape mode information may include information about various shapes into which the encoding unit may be split, but the information about various shapes may not include information for splitting the encoding unit into four encoding units having a square shape. According to this split shape mode information, the image decoding device (100) cannot split the first encoding unit (1100) having a square shape into four second encoding units having a square shape (1130a, 1130b, 1130c, 1130d). Based on the segmentation shape mode information, the image decoding device (100) can determine a second encoding unit (1110a, 1110b, 1120a, 1120b, etc.) of a non-square shape.

[0165] According to one embodiment of the present disclosure, the image decoding device (100) can independently split each of the second encoding units (1110a, 1110b, 1120a, 1120b, etc.) having a non-square shape. Each of the second encoding units (1110a, 1110b, 1120a, 1120b, etc.) can be split in a predetermined order using a recursive method, which may be a splitting method corresponding to a method in which the first encoding unit (1100) is split based on splitting shape mode information.

[0166] For example, the image decoding device (100) can determine third coding units (1112a, 1112b) having a square shape by splitting the left second coding unit (1110a) in the horizontal direction, and can determine third coding units (1114a, 1114b) having a square shape by splitting the right second coding unit (1110b) in the horizontal direction. Furthermore, the image decoding device (100) can also determine third coding units (1116a, 1116b, 1116c, 1116d) having a square shape by splitting both the left second coding unit (1110a) and the right second coding unit (1110b) in the horizontal direction. In this case, the encoding unit can be determined in the same form as the first encoding unit (1100) being divided into four square-shaped second encoding units (1130a, 1130b, 1130c, 1130d).

[0167] As another example, the image decoding device (100) may determine third coding units (1122a, 1122b) having a square shape by vertically splitting the upper second coding unit (1120a), and may determine third coding units (1124a, 1124b) having a square shape by vertically splitting the lower second coding unit (1120b). Furthermore, the image decoding device (100) may determine third coding units (1126a, 1126b, 1126a, 1126b) having a square shape by vertically splitting both the upper second coding unit (1120a) and the lower second coding unit (1120b). In this case, the encoding unit can be determined in the same form as the first encoding unit (1100) being divided into four square-shaped second encoding units (1130a, 1130b, 1130c, 1130d).

[0168] FIG. 12 illustrates that the processing order between a plurality of encoding units may vary depending on the process of splitting the encoding units according to one embodiment of the present disclosure.

[0169] According to one embodiment of the present disclosure, the image decoding device (100) can split the first encoding unit (1200) based on the split shape mode information. If the block shape is square and the split shape mode information indicates that the first encoding unit (1200) is split in at least one of the horizontal direction and the vertical direction, the image decoding device (100) can split the first encoding unit (1200) to determine second encoding units (e.g., 1210a, 1210b, 1220a, 1220b, etc.). Referring to FIG. 12, the second encoding units (1210a, 1210b, 1220a, 1220b) having a non-square shape determined by splitting the first encoding unit (1200) only in the horizontal direction or the vertical direction can be independently split based on the split shape mode information for each. For example, the image decoding device (100) can determine third encoding units (1216a, 1216b, 1216c, 1216d) by horizontally dividing second encoding units (1210a, 1210b) generated by vertically dividing the first encoding unit (1200), and can determine third encoding units (1226a, 1226b, 1226c, 1226d) by vertically dividing second encoding units (1220a, 1220b) generated by horizontally dividing the first encoding unit (1200). Since the process of dividing the second encoding units (1210a, 1210b, 1220a, 1220b) has been described above with reference to FIG. 11, a detailed description thereof will be omitted.

[0170] According to one embodiment of the present disclosure, the image decoding device (100) can process encoding units according to a predetermined order. Since the characteristics of processing encoding units according to a predetermined order have been described above with reference to FIG. 7, a detailed description thereof will be omitted. Referring to FIG. 12, the image decoding device (100) can divide a first encoding unit (1200) having a square shape and determine four third encoding units (1216a, 1216b, 1216c, 1216d, 1226a, 1226b, 1226c, 1226d) having a square shape. According to one embodiment of the present disclosure, the image decoding device (100) can determine the processing order of the third encoding units (1216a, 1216b, 1216c, 1216d, 1226a, 1226b, 1226c, 1226d) depending on the form in which the first encoding unit (1200) is divided.

[0171] According to one embodiment of the present disclosure, the image decoding device (100) can determine third encoding units (1216a, 1216b, 1216c, 1216d) by horizontally dividing the second encoding units (1210a, 1210b) generated by vertically dividing them, and the image decoding device (100) can process the third encoding units (1216a, 1216b, 1216c, 1216d) according to an order (1217) of first processing the third encoding units (1216a, 1216c) included in the left second encoding unit (1210a) in the vertical direction and then processing the third encoding units (1216b, 1216d) included in the right second encoding unit (1210b) in the vertical direction.

[0172] According to one embodiment of the present disclosure, the image decoding device (100) can determine third encoding units (1226a, 1226b, 1226c, 1226d) by vertically dividing the second encoding units (1220a, 1220b) generated by being divided in the horizontal direction, and the image decoding device (100) can process the third encoding units (1226a, 1226b, 1226c, 1226d) according to an order (1227) of first processing the third encoding units (1226a, 1226b) included in the upper second encoding unit (1220a) in the horizontal direction and then processing the third encoding units (1226c, 1226d) included in the lower second encoding unit (1220b) in the horizontal direction.

[0173] Referring to FIG. 12, the second encoding units (1210a, 1210b, 1220a, 1220b) can be divided into third encoding units (1216a, 1216b, 1216c, 1216d, 1226a, 1226b, 1226c, 1226d) having a square shape. The second encoding units (1210a, 1210b) determined by being split in the vertical direction and the second encoding units (1220a, 1220b) determined by being split in the horizontal direction are split into different shapes, but according to the third encoding units (1216a, 1216b, 1216c, 1216d, 1226a, 1226b, 1226c, 1226d) determined later, the first encoding unit (1200) is ultimately split into encoding units of the same shape. Accordingly, even if the image decoding device (100) determines encoding units of the same shape as a result by recursively splitting the encoding units through different processes based on the split shape mode information, it can process a plurality of encoding units determined in the same shape in different orders.

[0174] FIG. 13 illustrates a process in which the depth of an encoding unit is determined as the shape and size of the encoding unit change when the encoding unit is recursively divided to determine a plurality of encoding units according to one embodiment of the present disclosure.

[0175] According to one embodiment of the present disclosure, the image decoding device (100) may determine the depth of an encoding unit according to a predetermined criterion. For example, the predetermined criterion may be the length of a long side of the encoding unit. If the length of the long side of the current encoding unit is split to be 2n (n>0) times the length of the long side of the encoding unit before splitting, the image decoding device (100) may determine that the depth of the current encoding unit is increased by n compared to the depth of the encoding unit before splitting. Hereinafter, the encoding unit with increased depth will be expressed as an encoding unit of a lower depth.

[0176] Referring to FIG. 13, according to one embodiment of the present disclosure, based on block shape information indicating a square shape (for example, the block shape information may indicate '0: SQUARE'), the image decoding device (100) may divide a first coding unit (1300) having a square shape to determine a second coding unit (1302), a third coding unit (1304), etc. of a lower depth. If the size of the first coding unit (1300) having a square shape is 2Nx2N, the second coding unit (1302) determined by dividing the width and height of the first coding unit (1300) by half may have a size of NxN. Furthermore, the third coding unit (1304) determined by dividing the width and height of the second coding unit (1302) by half may have a size of N / 2xN / 2. In this case, the width and height of the third encoding unit (1304) correspond to 1 / 4 of the width and height of the first encoding unit (1300). When the depth of the first encoding unit (1300) is D, the depth of the second encoding unit (1302), which is 1 / 2 of the width and height of the first encoding unit (1300), may be D+1, and the depth of the third encoding unit (1304), which is 1 / 4 of the width and height of the first encoding unit (1300), may be D+2.

[0177] According to one embodiment of the present disclosure, based on block shape information indicating a non-square shape (for example, the block shape information may indicate '1: NS_VER' indicating a non-square shape in which the height is longer than the width or '2: NS_HOR' indicating a non-square shape in which the width is longer than the height), the image decoding device (100) may split a first coding unit (1310 or 1320) having a non-square shape to determine a second coding unit (1312 or 1322), a third coding unit (1314 or 1324) of a lower depth, etc.

[0178] The image decoding device (100) can determine a second encoding unit (e.g., 1302, 1312, 1322, etc.) by splitting at least one of the width and height of the first encoding unit (1310) having a size of Nx2N. That is, the image decoding device (100) can split the first encoding unit (1310) in the horizontal direction to determine a second encoding unit (1302) having a size of NxN or a second encoding unit (1322) having a size of NxN / 2, and can also split the first encoding unit (1310) in the horizontal direction and the vertical direction to determine a second encoding unit (1312) having a size of N / 2xN.

[0179] According to one embodiment of the present disclosure, the image decoding device (100) may determine a second coding unit (e.g., 1302, 1312, 1322, etc.) by splitting at least one of the width and the height of the first coding unit (1320) having a size of 2NxN. That is, the image decoding device (100) may split the first coding unit (1320) in the vertical direction to determine a second coding unit (1302) having a size of NxN or a second coding unit (1312) having a size of N / 2xN, and may also split the first coding unit (1320) in the horizontal direction and the vertical direction to determine a second coding unit (1322) having a size of NxN / 2.

[0180] According to one embodiment of the present disclosure, the image decoding device (100) may determine a third encoding unit (e.g., 1304, 1314, 1324, etc.) by splitting at least one of the width and the height of the second encoding unit (1302) having a size of NxN. That is, the image decoding device (100) may split the second encoding unit (1302) in the vertical direction and the horizontal direction to determine a third encoding unit (1304) having a size of N / 2xN / 2, a third encoding unit (1314) having a size of N / 4xN / 2, or a third encoding unit (1324) having a size of N / 2xN / 4.

[0181] According to one embodiment of the present disclosure, the image decoding device (100) may determine a third coding unit (e.g., 1304, 1314, 1324, etc.) by splitting at least one of the width and the height of the second coding unit (1312) having a size of N / 2xN. That is, the image decoding device (100) may split the second coding unit (1312) in the horizontal direction to determine a third coding unit (1304) having a size of N / 2xN / 2 or a third coding unit (1324) having a size of N / 2xN / 4, or split the second coding unit (1312) in the vertical direction and the horizontal direction to determine a third coding unit (1314) having a size of N / 4xN / 2.

[0182] According to one embodiment of the present disclosure, the image decoding device (100) may determine a third coding unit (e.g., 1304, 1314, 1324, etc.) by splitting at least one of the width and the height of the second coding unit (1322) having a size of NxN / 2. That is, the image decoding device (100) may split the second coding unit (1322) in the vertical direction to determine a third coding unit (1304) having a size of N / 2xN / 2 or a third coding unit (1314) having a size of N / 4xN / 2, or split the second coding unit (1322) in the vertical direction and the horizontal direction to determine a third coding unit (1324) having a size of N / 2xN / 4.

[0183] According to one embodiment of the present disclosure, the image decoding device (100) can split a square-shaped encoding unit (e.g., 1300, 1302, 1304) in a horizontal direction or a vertical direction. For example, a first encoding unit (1300) having a size of 2Nx2N can be split in the vertical direction to determine a first encoding unit (1310) having a size of Nx2N, or can be split in the horizontal direction to determine a first encoding unit (1320) having a size of 2NxN. When the depth is determined based on the length of the longest side of the encoding unit according to one embodiment of the present disclosure, the depth of the encoding unit determined by splitting the first encoding unit (1300) having a size of 2Nx2N in the horizontal direction or the vertical direction can be the same as the depth of the first encoding unit (1300).

[0184] According to one embodiment of the present disclosure, the width and height of the third coding unit (1314 or 1324) may be 1 / 4 times that of the first coding unit (1310 or 1320). When the depth of the first coding unit (1310 or 1320) is D, the depth of the second coding unit (1312 or 1322), which is 1 / 2 times the width and height of the first coding unit (1310 or 1320), may be D+1, and the depth of the third coding unit (1314 or 1324), which is 1 / 4 times the width and height of the first coding unit (1310 or 1320), may be D+2.

[0185] FIG. 14 illustrates an index (part index, hereinafter referred to as PID) for depth and encoding unit distinction that can be determined according to the shape and size of encoding units according to one embodiment of the present disclosure.

[0186] According to one embodiment of the present disclosure, the image decoding device (100) can split a first encoding unit (1400) having a square shape to determine second encoding units of various shapes. Referring to FIG. 14, the image decoding device (100) can split the first encoding unit (1400) in at least one of a vertical direction and a horizontal direction according to the split shape mode information to determine second encoding units (1402a, 1402b, 1404a, 1404b, 1406a, 1406b, 1406c, 1406d). That is, the image decoding device (100) can determine the second encoding unit (1402a, 1402b, 1404a, 1404b, 1406a, 1406b, 1406c, 1406d) based on the split shape mode information for the first encoding unit (1400).

[0187] According to one embodiment of the present disclosure, the depth of the second coding units (1402a, 1402b, 1404a, 1404b, 1406a, 1406b, 1406c, 1406d) determined according to the split shape mode information for the first coding unit (1400) having a square shape may be determined based on the length of the long side. For example, since the length of one side of the first coding unit (1400) having a square shape and the length of the long side of the second coding unit (1402a, 1402b, 1404a, 1404b) having a non-square shape are the same, the depth of the first coding unit (1400) and the second coding units (1402a, 1402b, 1404a, 1404b) having a non-square shape may be considered to be the same as D. In contrast, when the image decoding device (100) divides the first encoding unit (1400) into four square-shaped second encoding units (1406a, 1406b, 1406c, 1406d) based on the split shape mode information, the length of one side of the square-shaped second encoding units (1406a, 1406b, 1406c, 1406d) is half the length of one side of the first encoding unit (1400), so the depth of the second encoding units (1406a, 1406b, 1406c, 1406d) may be a depth of D+1, which is one depth lower than D, the depth of the first encoding unit (1400).

[0188] According to one embodiment of the present disclosure, the image decoding device (100) can horizontally split a first encoding unit (1410) having a height longer than width according to split shape mode information into a plurality of second encoding units (1412a, 1412b, 1414a, 1414b, 1414c). According to one embodiment of the present disclosure, the image decoding device (100) can vertically split a first encoding unit (1420) having a width longer than height according to split shape mode information into a plurality of second encoding units (1422a, 1422b, 1424a, 1424b, 1424c).

[0189] According to one embodiment of the present disclosure, the second coding units (1412a, 1412b, 1414a, 1414b, 1414c. 1422a, 1422b, 1424a, 1424b, 1424c) determined according to the split shape mode information for the first coding unit (1410 or 1420) of a non-square shape may have their depths determined based on the length of their long sides. For example, since the length of one side of the second encoding unit (1412a, 1412b) in the shape of a square is half the length of one side of the first encoding unit (1410) in the shape of a non-square having a height longer than a width, the depth of the second encoding unit (1412a, 1412b) in the shape of a square is D+1, which is one depth lower than the depth D of the first encoding unit (1410) in the shape of a non-square.

[0190] Furthermore, the image decoding device (100) can split a non-square first encoding unit (1410) into an odd number of second encoding units (1414a, 1414b, 1414c) based on the split shape mode information. The odd number of second encoding units (1414a, 1414b, 1414c) can include non-square second encoding units (1414a, 1414c) and square second encoding units (1414b). In this case, since the length of the long side of the second encoding unit (1414a, 1414c) of a non-square shape and the length of one side of the second encoding unit (1414b) of a square shape are half the length of one side of the first encoding unit (1410), the depth of the second encoding unit (1414a, 1414b, 1414c) may be a depth of D+1, which is one depth lower than D, which is the depth of the first encoding unit (1410). The image decoding device (100) may determine the depth of the encoding units associated with the first encoding unit (1420) of a non-square shape, in which the width is longer than the height, in a manner corresponding to the above method of determining the depth of the encoding units associated with the first encoding unit (1410).

[0191] According to one embodiment of the present disclosure, when determining an index (PID) for distinguishing split coding units, the image decoding device (100) may determine the index based on a size ratio between the coding units when the coding units split into an odd number of units do not have the same size. Referring to FIG. 14, among the coding units (1414a, 1414b, 1414c) split into an odd number of units, the coding unit (1414b) located in the middle may have the same width as the other coding units (1414a, 1414c) but may have a height that is twice the height of the coding units (1414a, 1414c) that are different in height. That is, in this case, the coding unit (1414b) located in the middle may include two of the other coding units (1414a, 1414c). Accordingly, if the index (PID) of the encoding unit (1414b) located in the middle according to the scanning order is 1, the index of the encoding unit (1414c) located in the next order may be 3, which is an increase of 2. In other words, there may be a discontinuity in the value of the index. According to one embodiment of the present disclosure, the image decoding device (100) may determine whether the encoding units divided into an odd number are not of the same size based on the presence or absence of discontinuity in the index for distinguishing between the divided encoding units.

[0192] According to one embodiment of the present disclosure, the image decoding device (100) may determine whether the current encoding unit is divided into a specific split shape based on the value of an index for distinguishing a plurality of encoding units determined by division. Referring to FIG. 14, the image decoding device (100) may divide a first encoding unit (1410) having a rectangular shape in which a height is longer than a width, to determine an even number of encoding units (1412a, 1412b) or an odd number of encoding units (1414a, 1414b, 1414c). The image decoding device (100) may use an index (PID) indicating each encoding unit to distinguish each of the plurality of encoding units. According to one embodiment of the present disclosure, the PID may be obtained from a sample (e.g., an upper left sample) at a predetermined position of each encoding unit.

[0193] According to one embodiment of the present disclosure, the image decoding device (100) can determine an coding unit at a predetermined position among the coding units that are divided and determined using an index for distinguishing the coding units. According to one embodiment of the present disclosure, when the split shape mode information for the first coding unit (1410) having a rectangular shape with a height longer than the width indicates that the first coding unit (1410) is divided into three coding units, the image decoding device (100) can divide the first coding unit (1410) into three coding units (1414a, 1414b, 1414c). The image decoding device (100) can assign an index to each of the three coding units (1414a, 1414b, 1414c). The image decoding device (100) can compare the indexes for each coding unit to determine the middle coding unit among the coding units divided into an odd number of coding units. The image decoding device (100) may determine a coding unit (1414b) having an index corresponding to a middle value among the indices of the coding units as a coding unit at a middle position among the coding units determined by splitting the first coding unit (1410). According to an embodiment of the present disclosure, when determining an index for distinguishing the split coding units, the image decoding device (100) may determine the index based on a size ratio between the coding units when the coding units do not have the same size. Referring to FIG. 14, the coding unit (1414b) generated by splitting the first coding unit (1410) may have the same width as other coding units (1414a, 1414c) but may be twice the height of the coding units (1414a, 1414c) that are different in height. In this case, if the index (PID) of the encoding unit (1414b) located in the middle is 1, the index of the encoding unit (1414c) located in the next order may be 3, which is an increase of 2.In cases like this where the index increases uniformly and then the increase amount changes, the image decoding device (100) may determine that the current encoding unit is divided into a plurality of encoding units including encoding units having different sizes from other encoding units. According to one embodiment of the present disclosure, when the split shape mode information indicates that the current encoding unit is divided into an odd number of encoding units, the image decoding device (100) may divide the current encoding unit into a form in which an encoding unit at a predetermined position among the odd number of encoding units (for example, a middle encoding unit) has a different size from the other encoding units. In this case, the image decoding device (100) may determine a middle encoding unit having a different size using an index (PID) for the encoding unit. However, the above-described index, the size or position of the encoding unit at the predetermined position to be determined are specific for explaining one embodiment and should not be interpreted as being limited thereto, and it should be interpreted that various indexes, positions and sizes of encoding units can be used.

[0194] According to one embodiment of the present disclosure, an image decoding device (100) can use a predetermined data unit from which recursive division of an encoding unit begins.

[0195] FIG. 15 illustrates that a plurality of coding units are determined according to a plurality of predetermined data units included in a picture according to one embodiment of the present disclosure.

[0196] According to one embodiment of the present disclosure, a predetermined data unit may be defined as a data unit from which a coding unit begins to be recursively split using split shape mode information. That is, it may correspond to a coding unit of the highest depth used in the process of determining multiple coding units for splitting the current picture. For convenience of explanation, this predetermined data unit will be referred to as a reference data unit hereinafter.

[0197] According to one embodiment of the present disclosure, a reference data unit may have a predetermined size and shape. According to one embodiment of the present disclosure, the reference data unit may include MxN samples, where M and N may be the same and may be integers expressed as powers of 2. That is, the reference data unit may have a square or non-square shape, and may be subsequently divided into an integer number of coding units.

[0198] According to one embodiment of the present disclosure, an image decoding device (100) may divide a current picture into a plurality of reference data units. According to one embodiment of the present disclosure, an image decoding device (100) may divide a plurality of reference data units into which a current picture is divided using division shape mode information for each reference data unit. This division process of the reference data units may correspond to a division process using a quad-tree structure.

[0199] According to one embodiment of the present disclosure, the image decoding device (100) can determine in advance the minimum size that a reference data unit included in a current picture can have. Accordingly, the image decoding device (100) can determine reference data units of various sizes having a size greater than or equal to the minimum size, and can determine at least one encoding unit using segmentation mode information based on the determined reference data unit.

[0200] Referring to FIG. 15, the image decoding device (100) may use a reference coding unit (1500) having a square shape, or may use a reference coding unit (1502) having a non-square shape. According to one embodiment of the present disclosure, the shape and size of the reference coding unit may be determined according to various data units (e.g., sequence, picture, slice, slice segment, tile, tile group, maximum coding unit, etc.) that may include at least one reference coding unit.

[0201] According to one embodiment of the present disclosure, the bitstream acquisition unit (110) of the image decoding device (100) can acquire at least one of information on the shape of the reference coding unit and information on the size of the reference coding unit from the bitstream for each of the various data units. The process of determining at least one coding unit included in the square-shaped reference coding unit (1500) has been described above through the process of splitting the current coding unit (300) of FIG. 3, and the process of determining at least one coding unit included in the non-square-shaped reference coding unit (1502) has been described above through the process of splitting the current coding unit (400 or 450) of FIG. 4, so a detailed description thereof will be omitted.

[0202] According to one embodiment of the present disclosure, the image decoding device (100) may use an index for identifying the size and shape of the reference coding unit in order to determine the size and shape of the reference coding unit according to some data units that are predetermined based on a predetermined condition. That is, the bitstream acquisition unit (110) may acquire only an index for identifying the size and shape of the reference coding unit for each slice, slice segment, tile, tile group, maximum coding unit, etc., among the various data units (e.g., sequences, pictures, slices, slice segments, tiles, tile groups, maximum coding units, etc.) that satisfy a predetermined condition (e.g., data units having a size smaller than a slice) from the bitstream. The image decoding device (100) may determine the size and shape of the reference data unit for each data unit that satisfies the predetermined condition by using the index. When information about the shape of the reference coding unit and information about the size of the reference coding unit are obtained from the bitstream for each relatively small-sized data unit and used, the efficiency of the bitstream may not be good. Therefore, instead of directly obtaining information about the shape of the reference coding unit and information about the size of the reference coding unit, only the index may be obtained and used. In this case, at least one of the size and shape of the reference coding unit corresponding to the index indicating the size and shape of the reference coding unit may be determined in advance. That is, the image decoding device (100) can determine at least one of the size and shape of the reference coding unit included in the data unit that serves as the basis for obtaining the index by selecting at least one of the sizes and shapes of the predetermined reference coding units according to the index.

[0203] According to one embodiment of the present disclosure, the image decoding device (100) may use at least one reference coding unit included in one maximum coding unit (1510). That is, the maximum coding unit (1510) for dividing an image may include at least one reference coding unit, and the coding unit may be determined through a recursive splitting process of each reference coding unit. According to one embodiment of the present disclosure, at least one of the width and the height of the maximum coding unit (1510) may correspond to an integer multiple of at least one of the width and the height of the reference coding unit. According to one embodiment of the present disclosure, the size of the reference coding unit may be a size obtained by splitting the maximum coding unit (1510) n times according to a quad tree structure. That is, the image decoding device (100) may determine the reference coding unit by splitting the maximum coding unit (1510) n times according to the quad tree structure, and may split the reference coding unit based on at least one of block shape information and split shape mode information according to one embodiment of the present disclosure.

[0204] According to one embodiment of the present disclosure, the video decoding device (100) can obtain and use block shape information indicating the shape of a current encoding unit or split shape mode information indicating a method of splitting the current encoding unit from a bitstream. The split shape mode information may be included in a bitstream related to various data units. For example, the video decoding device (100) can use split shape mode information included in a sequence parameter set, a picture parameter set, a video parameter set, a slice header, a slice segment header, a tile header, and a tile group header. Furthermore, the video decoding device (100) can obtain and use a syntax element corresponding to block shape information or split shape mode information from the bitstream for each maximum encoding unit and each reference encoding unit.

[0205] Hereinafter, a method for determining a partitioning rule according to one embodiment of the present disclosure will be described in detail.

[0206] The video decoding device (100) can determine a segmentation rule of the video. The segmentation rule may be predetermined between the video decoding device (100) and the video encoding device (200). The video decoding device (100) can determine the segmentation rule of the video based on information obtained from a bitstream. The video decoding device (100) can determine the segmentation rule based on information obtained from at least one of a sequence parameter set, a picture parameter set, a video parameter set, a slice header, a slice segment header, a tile header, and a tile group header. The video decoding device (100) can determine the segmentation rule differently according to a frame, a slice, a tile, a temporal layer, a maximum coding unit, or an coding unit.

[0207] The image decoding device (100) can determine a segmentation rule based on the block shape of the encoding unit. The block shape can include the size, shape, width and height ratio, and direction of the encoding unit. The image encoding device (200) and the image decoding device (100) can determine in advance that the segmentation rule will be determined based on the block shape of the encoding unit. However, the present invention is not limited thereto. The image decoding device (100) can determine the segmentation rule based on information obtained from the bitstream received from the image encoding device (200).

[0208] The shape of the encoding unit may include a square and a non-square shape. If the width and height of the encoding unit are equal, the image decoding device (100) may determine the shape of the encoding unit as a square. In addition, if the width and height of the encoding unit are not equal, the image decoding device (100) may determine the shape of the encoding unit as a non-square shape.

[0209] The size of the coding unit may include various sizes such as 4x4, 8x4, 4x8, 8x8, 16x4, 16x8, ..., 256x256. The size of the coding unit may be classified according to the length of the long side, the length of the short side, or the area of ​​the coding unit. The image decoding device (100) may apply the same splitting rule to the coding units classified into the same group. For example, the image decoding device (100) may classify the coding units having the same long side length into the same size. In addition, the image decoding device (100) may apply the same splitting rule to the coding units having the same long side length.

[0210] The ratio of the width to the height of the coding unit may include 1:2, 2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1, 32:1, or 1:32, etc. In addition, the direction of the coding unit may include a horizontal direction and a vertical direction. The horizontal direction may indicate a case where the length of the width of the coding unit is longer than the length of the height. The vertical direction may indicate a case where the length of the width of the coding unit is shorter than the length of the height.

[0211] The image decoding device (100) can adaptively determine a splitting rule based on the size of the encoding unit. The image decoding device (100) can determine a different allowable splitting mode based on the size of the encoding unit. For example, the image decoding device (100) can determine whether splitting is allowed based on the size of the encoding unit. The image decoding device (100) can determine a splitting direction based on the size of the encoding unit. The image decoding device (100) can determine an allowable splitting type based on the size of the encoding unit.

[0212] Determining the splitting rule based on the size of the encoding unit may be a splitting rule predetermined between the image encoding device (200) and the image decoding device (100). In addition, the image decoding device (100) may determine the splitting rule based on information obtained from the bitstream.

[0213] The image decoding device (100) can adaptively determine a segmentation rule based on the position of the encoding unit. The image decoding device (100) can adaptively determine a segmentation rule based on the position that the encoding unit occupies in the image.

[0214] Additionally, the image decoding device (100) can determine a splitting rule so that encoding units generated through different splitting paths do not have the same block shape. However, this is not limited thereto, and encoding units generated through different splitting paths may have the same block shape. Encoding units generated through different splitting paths may have different decoding processing orders. Since the decoding processing order has been described together with FIG. 12, a detailed description thereof will be omitted.

[0215] FIG. 16 illustrates encoding units that can be determined for each picture when the combination of forms into which encoding units can be divided is different for each picture according to one embodiment of the present disclosure.

[0216] Referring to FIG. 16, the image decoding device (100) can determine a different combination of partitioning shapes into which encoding units can be partitioned for each picture. For example, the image decoding device (100) can decode an image using a picture (1600) that can be partitioned into four encoding units, a picture (1610) that can be partitioned into two or four encoding units, and a picture (1620) that can be partitioned into two, three, or four encoding units, among at least one picture included in the image. The image decoding device (100) can only use partitioning shape information indicating that the picture (1600) is partitioned into four square encoding units to partition the picture (1600) into a plurality of encoding units. The image decoding device (100) can only use partitioning shape information indicating that the picture (1610) is partitioned into two or four encoding units to partition the picture. The video decoding device (100) can only use the segmentation type information indicating that the picture (1620) is segmented into two, three, or four encoding units. The above-described combination of segmentation types is merely an example for explaining the operation of the video decoding device (100), and therefore the above-described combination of segmentation types should not be interpreted as being limited to the above-described example, but should be interpreted as being capable of using various combinations of segmentation types for each predetermined data unit.

[0217] According to one embodiment of the present disclosure, the bitstream acquisition unit (110) of the image decoding device (100) can acquire a bitstream including an index indicating a combination of segmentation type information for each predetermined data unit (e.g., a sequence, a picture, a slice, a slice segment, a tile, a tile group, etc.). For example, the bitstream acquisition unit (110) can acquire an index indicating a combination of segmentation type information from a sequence parameter set, a picture parameter set, a slice header, a tile header, or a tile group header. The image decoding device (100) can determine a combination of segmentation types by which an encoding unit can be divided for each predetermined data unit using the acquired index, and thus can use different combinations of segmentation types for each predetermined data unit.

[0218] FIG. 17 illustrates various forms of encoding units that can be determined based on segmentation mode information that can be expressed in binary code according to one embodiment of the present disclosure.

[0219] According to one embodiment of the present disclosure, the image decoding device (100) can split an encoding unit into various shapes using block shape information and split shape mode information acquired through the bitstream acquisition unit (110). The shapes of the encoding unit that can be split may correspond to various shapes including the shapes described through the above-described embodiments.

[0220] Referring to FIG. 17, the image decoding device (100) can split a square-shaped encoding unit in at least one of the horizontal direction and the vertical direction based on the split shape mode information, and can split a non-square-shaped encoding unit in the horizontal direction or the vertical direction.

[0221] According to one embodiment of the present disclosure, when the image decoding device (100) can divide a square-shaped encoding unit into four square encoding units by horizontally and vertically dividing the square-shaped encoding unit, there may be four types of division forms that the division shape mode information for the square encoding unit can indicate. According to one embodiment of the present disclosure, the division shape mode information may be expressed as a two-digit binary code, and a binary code may be assigned to each division form. For example, when the encoding unit is not divided, the division shape mode information may be expressed as (00)b, when the encoding unit is divided in the horizontal direction and the vertical direction, the division shape mode information may be expressed as (01)b, when the encoding unit is divided in the horizontal direction, the division shape mode information may be expressed as (10)b, and when the encoding unit is divided in the vertical direction, the division shape mode information may be expressed as (11)b.

[0222] According to one embodiment of the present disclosure, when the image decoding device (100) splits a non-square coding unit in a horizontal direction or a vertical direction, the type of split shape that the split shape mode information can indicate may be determined depending on the number of coding units into which the coding unit is split. Referring to FIG. 17, the image decoding device (100) may split a non-square coding unit into up to three according to one embodiment of the present disclosure. The image decoding device (100) may split the coding unit into two coding units, in which case the split shape mode information may be expressed as (10)b. The image decoding device (100) may split the coding unit into three coding units, in which case the split shape mode information may be expressed as (11)b. The image decoding device (100) may determine not to split the coding unit, in which case the split shape mode information may be expressed as (0)b. That is, the image decoding device (100) can use variable length coding (VLC) rather than fixed length coding (FLC) to use a binary code representing segmentation mode information.

[0223] According to one embodiment of the present disclosure, referring to FIG. 17, the binary code of the partition shape mode information indicating that the coding unit is not split may be expressed as (0)b. If the binary code of the partition shape mode information indicating that the coding unit is not split is set to (00)b, all binary codes of the 2-bit partition shape mode information must be used even if there is no partition shape mode information set to (01)b. However, as illustrated in FIG. 17, if three partition shapes for a non-square coding unit are used, the image decoding device (100) can determine that the coding unit is not split even if it uses a 1-bit binary code (0)b as the partition shape mode information, and thus can efficiently use the bitstream. However, the division form of the non-square-shaped encoding unit indicated by the division form mode information should not be interpreted as being limited to only the three forms illustrated in FIG. 17, but should be interpreted as various forms including the embodiments described above.

[0224] FIG. 18 illustrates another form of a coding unit that can be determined based on segmentation mode information that can be expressed in binary code according to one embodiment of the present disclosure.

[0225] Referring to FIG. 18, the image decoding device (100) can split a square-shaped encoding unit in the horizontal direction or the vertical direction based on the split shape mode information, and can split a non-square-shaped encoding unit in the horizontal direction or the vertical direction. That is, the split shape mode information can indicate that a square-shaped encoding unit is split in one direction. In this case, the binary code of the split shape mode information indicating that a square-shaped encoding unit is not split can be expressed as (0)b. If the binary code of the split shape mode information indicating that the encoding unit is not split is set to (00)b, all binary codes of the 2-bit split shape mode information must be used even though there is no split shape mode information set to (01)b. However, as illustrated in FIG. 18, if three types of division forms for a square-shaped encoding unit are used, the image decoding device (100) can determine that the encoding unit is not divided even if it uses a 1-bit binary code (0)b as the division form mode information, and thus can efficiently use the bitstream. However, the division forms of the square-shaped encoding unit indicated by the division form mode information should not be interpreted as being limited to only the three types illustrated in FIG. 18, but should be interpreted as various types including the embodiments described above.

[0226] According to one embodiment of the present disclosure, block shape information or segmentation shape mode information can be expressed using binary code, and such information can be directly generated as a bitstream. In addition, block shape information or segmentation shape mode information that can be expressed using binary code may not be directly generated as a bitstream, but may be used as a binary code input in CABAC (context adaptive binary arithmetic coding).

[0227] According to one embodiment of the present disclosure, a video decoding device (100) describes a process of obtaining syntax for block shape information or segmentation shape mode information through CABAC. A bitstream including a binary code for the syntax can be obtained through a bitstream obtaining unit (110). The video decoding device (100) can detect a syntax element indicating block shape information or segmentation shape mode information by de-binarizing a bin string included in the obtained bitstream. According to one embodiment of the present disclosure, the video decoding device (100) can obtain a set of binary bin strings corresponding to syntax elements to be decoded, and decode each bin using probability information, and the video decoding device (100) can repeat the process until a bin string composed of the decoded bins becomes equal to one of the previously obtained bin strings. The image decoding device (100) can determine syntax elements by performing inverse binarization of an empty string.

[0228] According to one embodiment of the present disclosure, the image decoding device (100) may perform a decoding process of adaptive binary arithmetic coding to determine a syntax for a bin string, and the image decoding device (100) may update a probability model for bins acquired through the bitstream acquisition unit (110). Referring to FIG. 17, the bitstream acquisition unit (110) of the image decoding device (100) may acquire a bitstream representing a binary code representing segmentation mode information according to one embodiment of the present disclosure. Using the acquired binary code having a size of 1 or 2 bits, the image decoding device (100) may determine a syntax for the segmentation mode information. In order to determine the syntax for the segmentation mode information, the image decoding device (100) may update a probability for each bit of the 2-bit binary code. That is, the image decoding device (100) can update the probability of having a value of 0 or 1 when decoding the next bin, depending on whether the value of the first bin among the 2-bit binary codes is 0 or 1.

[0229] According to one embodiment of the present disclosure, the image decoding device (100) can, in the process of determining a syntax, update the probability for bins used in the process of decoding bins of an empty string for the syntax, and the image decoding device (100) can determine that certain bits among the empty strings have the same probability without updating the probability.

[0230] Referring to FIG. 17, in the process of determining a syntax using an empty string indicating split shape mode information for a non-square coding unit, the image decoding device (100) may determine the syntax for the split shape mode information using one bin having a value of 0 when the non-square coding unit is not split. That is, when the block shape information indicates that the current coding unit is a non-square shape, the first bin of the empty string for the split shape mode information may be 0 when the non-square coding unit is not split, and may be 1 when it is split into 2 or 3 coding units. Accordingly, the probability that the first bin of the empty string of the split shape mode information for the non-square coding unit is 0 may be 1 / 3, and the probability that it is 1 may be 2 / 3. As described above, the image decoding device (100) can only express a 1-bit empty string having a value of 0 for the partition shape mode information indicating that a non-square-shaped encoding unit is not partitioned, so the image decoding device (100) can determine the syntax for the partition shape mode information by determining whether the second bin is 0 or 1 only when the first bin of the partition shape mode information is 1. According to one embodiment of the present disclosure, when the first bin for the partition shape mode information is 1, the image decoding device (100) can decode the bin by considering that the probability that the second bin is 0 or 1 is the same probability.

[0231] According to one embodiment of the present disclosure, the image decoding device (100) may utilize various probabilities for each bin in the process of determining a bin of a bin string for the partition shape mode information. According to one embodiment of the present disclosure, the image decoding device (100) may determine the probability of a bin for the partition shape mode information differently depending on the direction of a non-square block. According to one embodiment of the present disclosure, the image decoding device (100) may determine the probability of a bin for the partition shape mode information differently depending on the area or the length of the long side of the current encoding unit. According to one embodiment of the present disclosure, the image decoding device (100) may determine the probability of a bin for the partition shape mode information differently depending on at least one of the shape and the length of the long side of the current encoding unit.

[0232] According to one embodiment of the present disclosure, the image decoding device (100) may determine that the bin probability for the partition shape mode information is the same for encoding units of a predetermined size or larger. For example, the bin probability for the partition shape mode information may be determined to be the same for encoding units of a size of 64 samples or larger based on the length of the long side of the encoding unit.

[0233] According to one embodiment of the present disclosure, the image decoding device (100) may determine the initial probability for bins constituting the empty string of the segmentation shape mode information based on the slice type (e.g., I slice, P slice, or B slice).

[0234] Figure 19 is a block diagram of an image encoding and decoding system that performs loop filtering.

[0235] The encoding unit (1910) of the image encoding and decoding system (1900) transmits an encoded bitstream of an image, and the decoding unit (1950) receives the bitstream and decodes it to output a restored image. Here, the encoding unit (1910) may have a configuration similar to that of the image encoding device (200) described below, and the decoding unit (1950) may have a configuration similar to that of the image decoding device (100).

[0236] In the encoding unit (1910), the prediction encoding unit (1915) outputs prediction data through inter prediction and intra prediction, and the transform and quantization unit (1920) outputs quantized transform coefficients of residual data between the prediction data and the current input image. For example, the transform coefficients may be generated using a transform kernel including at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), or a wavelet transform. The residual data may have information compressed by performing the transform. For example, the residual data may be expressed using a small number of frequencies as the transform is performed. The entropy encoding unit (1925) encodes and transforms the quantized transform coefficients and outputs them as a bitstream. The quantized transform coefficients may be restored to data in the spatial domain through the inverse quantization and inverse transform unit (1930). The inverse quantization and inverse transformation unit (1930) can perform inverse quantization on the quantized transform coefficients and determine residual data by applying a transform kernel. The data in the restored spatial domain passes through the deblocking filtering unit (1935) and the loop filtering unit (1940) and is output as a restored image. The restored image can be used as a reference image for the next input image through the predictive encoding unit (1915).

[0237] The encoded image data among the bitstreams received by the decoding unit (1950) is restored to residual data in the spatial domain through the entropy decoding unit (1955) and the inverse quantization and inverse transformation unit (1960). The prediction data and residual data output from the prediction decoding unit (1975) are combined to form image data in the spatial domain, and the deblocking filtering unit (1965) and the loop filtering unit (1970) can perform filtering on the image data in the spatial domain to output a restored image for the current original image. The restored image can be used as a reference image for the next original image by the prediction decoding unit (1975).

[0238] The loop filtering unit (1940) of the encoding unit (1910) performs loop filtering using filter information input according to user input or system settings. The filter information used by the loop filtering unit (1940) is output to the entropy encoding unit (1925) and transmitted to the decoding unit (1950) together with the encoded image data. The loop filtering unit (1970) of the decoding unit (1950) can perform loop filtering based on the filter information input from the decoding unit (1950).

[0239] FIG. 20 is a block diagram showing the configuration of an image decoding device according to one embodiment of the present disclosure.

[0240] Referring to FIG. 20, the image decoding device (2000) may include an acquisition unit (2010) and a prediction decoding unit (2020).

[0241] In one embodiment of the present disclosure, the acquisition unit (2010) and the prediction decoding unit (2020) may be implemented with at least one processor. In one embodiment of the present disclosure, the image decoding device (2000) may include a memory that stores at least one of input / output data or instructions of the acquisition unit (2010) and the prediction decoding unit (2020). The acquisition unit (2010) and the prediction decoding unit (2020) may operate according to the instructions stored in the memory. In one embodiment of the present disclosure, the image decoding device (2000) may include a memory control unit that controls data input / output of the memory.

[0242] In one embodiment of the present disclosure, the acquisition unit (2010) may correspond to the entropy decoding unit (1955) illustrated in FIG. 19. In one embodiment of the present disclosure, the prediction decoding unit (2020) may correspond to the prediction decoding unit (1975) illustrated in FIG. 19.

[0243] The acquisition unit (2010) can acquire a bitstream generated as a result of encoding an image. The bitstream can include an encoding result for a current block. In one embodiment of the present disclosure, the acquisition unit (2010) can receive the bitstream from an image encoding device via a network. In one embodiment of the present disclosure, the acquisition unit (2010) can acquire the bitstream from a data storage medium including at least one of a magnetic medium such as a hard disk, a floppy disk, and a magnetic tape, an optical recording medium such as a CD-ROM and a DVD, or a magneto-optical medium such as a floptical disk.

[0244] The acquisition unit (2010) can acquire syntax elements for decoding an image from a bitstream. The values ​​corresponding to the syntax elements can be included in the bitstream according to the hierarchical structure of the image. In one embodiment of the present disclosure, the acquisition unit (2010) can acquire the syntax elements by entropy decoding bins included in the bitstream.

[0245] In one embodiment of the present disclosure, a bitstream may include information about a prediction mode of a current block in a current image. The current block may include at least one of a maximum coding unit, an encoding unit, a transformation unit, or a prediction unit segmented from a current image to be decoded. In one embodiment of the present disclosure, the prediction mode of the current block may include at least one of an intra mode, an inter mode, a combined mode, a geometric partitioning mode, a block copy mode, or a template matching prediction mode.

[0246] In one embodiment of the present disclosure, the intra mode may include an intra planar mode of 0 (Intra_Planar) that is non-directional, an intra DC mode of 1 (Intra_DC), intra directional modes of 2 to 66 (Intra_Angular2.. Intra_Angular66) that are directional, and intra wide directional modes of -14 to -1 and 67 to 80 (Intra_Wide_Angular). In one embodiment of the present disclosure, the intra planar mode may refer to a mode that determines a prediction sample based on a weighted average value according to a distance of a left reference sample, an upper reference sample, a lower-left sample of a current block, and an upper-right sample. In one embodiment of the present disclosure, the intra DC mode may refer to a mode that determines an average value of reference samples as a prediction sample. In one embodiment of the present disclosure, in intra directional modes, the positions of reference samples for generating prediction samples of samples within a current block can be identified by considering the direction indicated by the intra directional modes. For example, in mode 34, reference samples located at a 45 degree upper left direction with respect to samples within the current block can be identified. Intra wide directional modes can be used to identify reference samples of samples within a non-square current block. In one embodiment of the present disclosure, the prediction decoding unit (2020) can determine one of the intra wide directional modes as an intra prediction mode of a non-square current block. The number and types of intra prediction modes that can be used in the intra mode by the prediction decoding unit (2020) according to one embodiment of the present disclosure can be set in various ways.

[0247] In one embodiment of the present disclosure, the prediction decoding unit (2020) can determine an intra prediction mode using MPM (most probable modes). The prediction decoding unit (2020) can determine whether to use MPM. The acquisition unit (2010) can obtain information related to whether to use MPM from a bitstream. The prediction decoding unit (2020) can determine a candidate mode list. The prediction decoding unit (2020) can determine the candidate mode list based on the intra mode of the upper block of the current block and the intra mode of the left block. The prediction decoding unit (2020) can determine one of the candidate mode lists as the intra prediction mode of the current block. The prediction decoding unit (2020) can obtain information indicating the intra prediction mode of the current block from the bitstream from the candidate mode list.

[0248] In one embodiment of the present disclosure, the prediction decoding unit (2020) may determine an intra prediction mode using a template. The prediction decoding unit (2020) may determine a template of a current block. The template of the current block may include a left sample, an upper left sample, and / or an upper sample of the current block. The prediction decoding unit (2020) may determine surrounding samples of the template of the current block. The surrounding samples of the template may include a left sample, an upper left sample, and / or an upper sample of the template. The prediction decoding unit (2020) may perform prediction on the template using the surrounding samples of the template as reference samples. The prediction decoding unit (2020) may compare the predicted template with the template of the reconstructed current block to determine an intra mode for the reference block. In one embodiment of the present disclosure, the intra mode for the reference block may include a virtual intra mode or an intra mode of the reference block. The virtual intra mode of the reference block may be an intra mode determined based on at least one of a sample (or an internal sample) of the reference block or a surrounding sample of the reference block. The prediction decoding unit (2020) may determine an intra mode with the smallest error between the predicted template and the template of the reconstructed current block as the intra mode for the reference block. In one embodiment of the present disclosure, the process of the prediction decoding unit (2020) determining the intra prediction mode by performing prediction on the template may be referred to as template-based intra mode derivation (TIMD).

[0249] In one embodiment of the present disclosure, the prediction decoding unit (2020) can infer an intra prediction mode of the current block using surrounding samples of the current block. The prediction decoding unit (2020) can determine a slope using the surrounding samples of the current block. The prediction decoding unit (2020) can determine a plurality of 3 x 3 blocks adjacent to the current block. The prediction decoding unit (2020) can obtain horizontal variations and vertical variations of samples included in each of the determined 3 x 3 blocks. The prediction decoding unit (2020) can determine a slope based on the horizontal variations and vertical variations. The prediction decoding unit (2020) can determine the horizontal variations and vertical variations using a Sobel filter. The prediction decoding unit (2020) can determine an intra prediction mode corresponding to the slope. The prediction decoding unit (2020) may determine the intra prediction mode of the current block based on a plurality of intra prediction modes determined for a plurality of 3 x 3 blocks. In one embodiment of the present disclosure, the prediction decoding unit (2020) may determine the intra prediction mode that is determined most frequently as the intra prediction mode of the current block. In one embodiment of the present disclosure, the prediction decoding unit (2020) may determine an amplitude based on horizontal variation and vertical variation. The prediction decoding unit (2020) may determine the intra prediction mode of the current block based on the amplitude. The prediction decoding unit (2020) may determine a weight of the intra prediction mode corresponding to the slope as the amplitude. For example, the prediction decoding unit (2020) may increase the weight of the intra prediction mode determined based on the slope as the horizontal variation and vertical variation increase. The prediction decoding unit (2020) can determine the intra prediction mode of the current block based on the result reflecting the weight determined according to the size.In one embodiment of the present disclosure, the process by which the prediction decoding unit (2020) determines an intra prediction mode based on a slope may be referred to as decoder side intra mode derivation (DIMD).

[0250] In one embodiment of the present disclosure, the block copy mode may include an intra block copy mode. In one embodiment, the block copy mode may include an intra block copy mode. In one embodiment, the intra block copy mode may be a sub-mode of the intra mode, but is not limited thereto, and may represent a mode separate from the intra mode. In one embodiment, the template matching prediction mode may include a template matching intra prediction mode. The combined mode may include a Combined Inter-Intra Prediction (CIIP) mode that performs prediction by combining prediction according to the intra mode and prediction according to the inter mode. The geometric partitioning mode may include a mode that partitions to include directionality within a block. The geometric partitioning mode may perform prediction using inter prediction or intra prediction for each of the divided regions that are blocked.

[0251] The prediction decoding unit (2020) can restore the current block by performing prediction according to the prediction mode for the current block according to the prediction mode of the current block.

[0252] In one embodiment of the present disclosure, the acquisition unit (2010) can acquire information regarding the prediction mode of the current block from the bitstream. For example, the acquisition unit (2010) can acquire index information indicating the prediction mode of the current block from the bitstream.

[0253] In one embodiment of the present disclosure, when the prediction mode of the current block is the CIIP mode, the prediction decoding unit (2020) can reconstruct the current block by combining inter prediction and intra prediction. For example, the prediction decoding unit (2020) can perform intra prediction according to the planar mode. For example, the prediction decoding unit (2020) can perform inter prediction using a motion vector (MV). The prediction decoding unit (2020) can reconstruct the current block using a weighted sum of a prediction block according to inter prediction and a prediction block according to intra prediction. The weight can be determined based on whether a block adjacent to the current block was intra predicted.

[0254] In one embodiment of the present disclosure, when the prediction mode of the current block is a geometric segmentation mode, the prediction decoding unit (2020) can perform prediction by segmenting the current block. The prediction decoding unit (2020) can obtain a segmentation angle and a segmentation distance for a boundary at which segmentation is performed within the current block. The prediction decoding unit (2020) can segment the current block based on the segmentation angle and the segmentation distance. The prediction decoding unit (2020) can perform inter-prediction or intra-prediction on each of the segmented regions within the current block to reconstruct the current block. The prediction decoding unit (2020) can (i) perform intra-prediction on both segmented regions, (ii) perform inter-prediction on one region and intra-prediction on the other region, or (iii) perform inter-prediction on both segmented regions.

[0255] In one embodiment of the present disclosure, when the prediction mode of the current block is block copy mode, the prediction decoding unit (2020) can reconstruct the current block based on a reference block included in the current image. In one embodiment of the present disclosure, when the prediction mode of the current block is block copy mode, the prediction decoding unit (2020) can determine information about a block vector (BV) representing the reference block. In one embodiment of the present disclosure, the prediction decoding unit (2020) can determine the prediction block based on the reference block. For example, the prediction decoding unit (2020) can determine the prediction block by being identical to the reference block or by performing filtering on the reference block.

[0256] In one embodiment of the present disclosure, when the prediction mode of the current block is the template matching prediction mode, the prediction decoding unit (2020) can reconstruct the current block using a reference block. The acquisition unit (2010) can acquire information related to whether the template matching prediction mode is used. The prediction decoding unit (2020) can determine whether the template matching prediction mode is used based on the acquired information. The reference block can be determined based on at least one of a region included in the current image or a region included in a previously decoded image. In one embodiment of the present disclosure, the prediction decoding unit (2020) can determine the reference block using a cost function. The cost function can include at least one of a sum of absolute difference (SAD), a sum of squared difference (SSD), a sum of absolute transformed difference (SATD), a sum of squared error (SSE), or a mean removed SAD (MR-SAD). For example, the prediction decoding unit (2020) can determine the error between templates using at least one cost function among SAD, SATD, SSE, and MR-SAD. When the cost function is SAD, the prediction decoding unit (2020) can determine the error based on the sum of the absolute values ​​of the differences between each sample of the template of the current block and each sample of the template of the candidate block. When the cost function is SSD, the prediction decoding unit (2020) can determine the error based on the sum of the squares of the differences between each sample of the template of the current block and each sample of the template of the candidate block. The cost function may include a function representing the number of identical samples. The prediction decoding unit (2020) can determine a block with a small error among the candidate blocks as a reference block. The prediction decoding unit (2020) can determine a prediction block by performing template matching intra prediction on the current image.In the present disclosure, the process of determining a reference block for a current block using a template may be referred to as template matching (TM). In the present disclosure, performing a prediction for a current block based on template matching may be referred to as template matching prediction (TMP) or intra-template matching prediction (ITEM).

[0257] The prediction decoding unit (2020) can generate a reconstructed current block using the prediction block. In one embodiment of the present disclosure, the prediction decoding unit (2020) can determine the prediction block as the reconstructed current block. In one embodiment, the prediction decoding unit (2020) can generate a reconstructed current block by combining the prediction block with residual data acquired from the bitstream by the acquisition unit (2010). The reconstructed current block can be used as a reference block for the next block.

[0258] In a prediction mode (e.g., intra mode) that uses reference samples included in a current image, a prediction block of the current block can be generated based on the surrounding samples of the current block according to the prediction mode, assuming that there will be continuity between the surrounding samples of the current block and the samples within the current block. The prediction decoding unit (2020) according to an embodiment of the present disclosure can use not only the surrounding samples of the current block included in the current image but also the spatial reference samples included in the current image for intra prediction. When using samples reconstructed before the current block, the size of the residual data can be reduced by predicting the samples of the current block using not only the samples immediately adjacent to the current block but also samples far from the current block. In an embodiment of the present disclosure, the image decoding apparatus (2000) performs intra prediction using a reference block including unreconstructed samples, thereby increasing the range of an area that can be determined as a reference block. The image decoding apparatus (2000) according to an embodiment of the present disclosure can improve compression efficiency by increasing the efficiency of intra prediction.

[0259] In a prediction mode (e.g., inter mode) that utilizes reference samples included in a reference image rather than the current image, a prediction block of the current block can be generated based on a reference block (or reference sample) of the reference image according to the prediction mode, under the assumption that there will be continuity between the current image and the reference image. An image decoding apparatus (2000) according to an embodiment of the present disclosure can improve compression efficiency by increasing the efficiency of intra prediction.

[0260] The image decoding device (2000) can improve prediction accuracy by considering both a reference block (or reference sample) included in the current image and a reference block (or reference sample) included in an image other than the current image. The image decoding device (2000) according to one embodiment of the present disclosure can improve prediction accuracy by considering both the current image and an image other than the current image.

[0261] The prediction decoding unit (2020) can perform deblocking filtering. The deblocking filter can improve image quality by smoothing the edges between blocks.

[0262] The prediction decoding unit (2020) may perform filtering on samples of the current block on which deblocking filtering has been performed using a sample adaptive offset (SAO) filter and / or a bilateral filter (BIF). The SAO filter and BIF may improve image quality by reducing the error between the restored image and the original image. The SAO filter and BIF may perform filtering on a sample-by-sample basis.

[0263] The predictive decoding unit (2020) can perform filtering using an adaptive loop filter (ALF). ALF can improve image quality by reducing the error between the reconstructed image and the original image. ALF filtering can be performed on a block-by-block basis.

[0264] FIG. 21 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0265] In one embodiment of the present disclosure, the image decoding method may be performed by the image decoding device (2000). For example, the image decoding device (2000) may perform each step of the image decoding method by having the processor of the image decoding device (2000) execute at least one instruction contained in a memory.

[0266] In step S2110, the image decoding device (2000) can perform prediction on the current block according to inter prediction. The image decoding device (2000) can obtain a reference block included in a reference image. The image decoding device (2000) can obtain the reference block based on the motion vector of the current block. The image decoding device (2000) can perform inter prediction based on the reference block to obtain a prediction sample of the current block.

[0267] The video decoding device (2000) can obtain one or more reference blocks corresponding to one or more motion vectors of a current block. In one embodiment of the present disclosure, the current block may be a block included in a bi-predictive (B) picture (or B slice). Inter prediction may be performed on a block included in a B picture (or B slice) according to at most two motion vectors and a reference index. When the current block is included in a B picture or a B slice, the video decoding device (2000) can obtain two reference blocks corresponding to two motion vectors of the current block. In one embodiment of the present disclosure, the current block may be a block included in a predictive (P) picture (or P slice). Inter prediction may be performed on a block included in a P picture (or P slice) according to at most one motion vector and a reference index. If the current block is included in a P picture or P slice, the image decoding device (2000) can obtain one reference block corresponding to one motion vector of the current block.

[0268] In step S2120, the image decoding device (2000) may determine an intra mode for the reference block based on at least one of a peripheral sample of the reference block, an internal sample of the reference block, or a peripheral sample of the current block. In one embodiment of the present disclosure, the intra mode for the reference block may include a virtual intra mode or an intra mode of the reference block. The virtual intra mode of the reference block may be an intra mode determined based on at least one of a sample (or an internal sample) of the reference block or a peripheral sample of the reference block. The image decoding device (2000) may determine the intra mode for the reference block based on temporal information or spatial information of the current block. The temporal information may include information about an image different from the current image including the current block. The spatial information may include information about the current image including the current block.

[0269] In one embodiment of the present disclosure, a reference block may include a block used for inter prediction of a current block. In one embodiment, the surrounding samples of the reference block (or current block) may include adjacent samples and / or non-adjacent samples of the reference block (or current block). The surrounding samples of the reference block may include a left sample, an upper-left sample, and an upper sample of the reference block.

[0270] In one embodiment of the present disclosure, an image decoding device (2000) can determine an intra mode for a reference block based on surrounding samples of the reference block and internal samples of the reference block. The image decoding device (2000) can determine an intra mode for a reference block based on a result of predicting an internal sample of the reference block using the surrounding samples of the reference block. A process of determining an intra mode for a reference block based on surrounding samples of the reference block and internal samples of the reference block by the image decoding device (2000) according to one embodiment of the present disclosure is described in detail with reference to FIGS. 22 to 24 and FIGS. 29 to 30.

[0271] In one embodiment of the present disclosure, an image decoding device (2000) can determine an intra mode for a reference block based on internal samples of the reference block. The image decoding device (2000) can determine an intra mode for the reference block based on a plurality of slopes determined for internal samples of the reference block. A process by which the image decoding device (2000) determines an intra mode for a reference block based on internal samples of the reference block according to one embodiment of the present disclosure is described in detail with reference to FIGS. 25 to 28 and FIGS. 33 to 34.

[0272] In one embodiment of the present disclosure, the image decoding device (2000) can determine an intra mode for a reference block using surrounding samples of the current block. The surrounding samples of the current block may be samples included in a template area of ​​the current block. The process of determining an intra mode for a reference block based on surrounding samples of the current block by the image decoding device (2000) according to one embodiment of the present disclosure is described in detail with reference to FIGS. 33 and 34.

[0273] *236 In one embodiment of the present disclosure, the image decoding device (2000) may determine one of two intra modes obtained from two reference blocks as an intra mode for the reference block. The image decoding device (2000) may determine two intra modes from each of the two reference blocks, and determine one of the two determined intra modes as an intra mode for the reference block. Alternatively, the image decoding device (2000) may determine a virtual intra mode by referring to both reference blocks.

[0274] In step S2130, the image decoding device (2000) may determine a transform kernel using the intra mode for the reference block. The image decoding device (2000) may determine a transform kernel set including a plurality of transform kernels corresponding to the intra mode for the reference block. The image decoding device (2000) may determine the type of the transform kernel set according to the intra mode for the reference block. For example, it may correspond to one of the plurality of transform kernel sets according to the range of the directional index of the intra mode for the reference block. The transform kernel set may include a plurality of transform kernels. For example, a first transform kernel set may include a first transform kernel and a second transform kernel, and a second transform kernel set may include a third transform kernel and a fourth transform kernel. In one embodiment, one or more (e.g., N, where N is 1 or more) transform kernel sets exist according to the type of transform, and each transform kernel set may include one or more (e.g., M, where M is 1 or more) transform kernels.

[0275] In one embodiment of the present disclosure, the number of transform kernels included in each transform kernel set may be determined based on the sum of transform coefficients. For example, when the sum of transform coefficients is less than a predetermined first value, the number of transform kernels may be N1 (e.g., N1 = 1), when the sum of transform coefficients is greater than the predetermined first value and less than a predetermined second value, the number of transform kernels may be N2 (e.g., N1 = 4), and when the sum of transform coefficients is greater than the predetermined second value, the number of transform kernels may be N3 (e.g., N1 = 6).

[0276] In one embodiment of the present disclosure, the image decoding device (2000) may determine a set of transform kernels based on the size of the current block and the intra mode for the reference block. The set of transform kernels may be predetermined based on the size of the current block. For example, the set of transform kernels may be predetermined, M in number, for each size of the current block.

[0277] The image decoding device (2000) can select one of a plurality of transformation kernels as the transformation kernel of the current block. The image decoding device (2000) can determine one of a plurality of transformation kernels included in a transformation kernel set. In one embodiment of the present disclosure, the image decoding device (2000) can obtain index information indicating the transformation kernel of the current block from among the plurality of transformation kernels from the bitstream.

[0278] In one embodiment of the present disclosure, the transform kernel may be at least one of a kernel for a first transform, a kernel for a second transform, or a non-separable first transform kernel combining a first transform and a second transform.

[0279] In one embodiment of the present disclosure, the image decoding device (2000) may determine a transform kernel for a primary transform using an intra mode for a reference block. The transform kernel for the primary transform may include a Discrete Cosine Transform (DCT) kernel and / or a Discrete Sine Transform (DST) kernel. The primary transform may be applied to a vertical direction and / or a horizontal direction of a block. The image decoding device (2000) may obtain information indicating whether the primary transform is a vertical transform or a horizontal transform from a bitstream. The primary transform may be referred to as a Multi Transform Selection (MTS). The transform kernel for the primary transform may be referred to as a core transform kernel.

[0280] In one embodiment of the present disclosure, the image decoding device (2000) may determine a transform kernel for a secondary transform using an intra mode for a reference block. The secondary transform may be applied only to a portion of a residual signal. For example, the secondary transform may be performed only on a left area or an upper left area of ​​a block. The image decoding device (2000) may determine whether to perform the secondary transform for each block. The secondary transform is not performed separately in the vertical and horizontal directions. The secondary transform may be referred to as a low frequency non-separable transform (LFNST).

[0281] In one embodiment of the present disclosure, the image decoding device (2000) can determine a transform kernel for a non-separable primary transform using an intra mode for a reference block. The non-separable primary transform may be a combination of a primary transform and a secondary transform. For example, the transform kernel for the non-separable primary transform may be a combination of a transform kernel for the primary transform and a transform kernel for the secondary transform. The non-separable primary transform is not performed separately in the vertical and horizontal directions.

[0282] In step S2140, the image decoding device (2000) can perform an inverse transformation on the current block using a transformation kernel. The image decoding device (2000) can perform an inverse transformation by applying the selected transformation kernel to the current block. The image decoding device (2000) can obtain a residual signal (or residual data) by performing an inverse transformation using the transformation kernel. The image decoding device (2000) can obtain a residual signal by applying a transformation kernel to a transformation coefficient.

[0283] The image decoding device (2000) can perform an inverse transformation with respect to the first transformation on the residual signal (or residual data). The image decoding device (2000) can apply a transformation kernel for the second transformation to the residual signal to generate a transformation coefficient.

[0284] The image decoding device (2000) can perform an inverse transform for a secondary transform on a residual signal. The image decoding device (2000) can apply a transform kernel for a secondary transform to the residual signal to generate transform coefficients. The image decoding device (2000) can perform an inverse transform for the secondary transform and an inverse transform for the primary transform. The inverse transform for the primary transform has been described above and is therefore omitted.

[0285] The image decoding device (2000) can generate a residual signal by applying a transform kernel for a non-separable first-order transform to the transform coefficients. The image decoding device (2000) may not perform a separate first-order transform and / or second-order transform on a block on which a non-separable first-order transform has been performed.

[0286] The image decoding device (2000) can determine a set of transform kernels for the current block by determining an intra mode for a reference block when the prediction mode of the current block is the inter mode. The image decoding device (2000) can improve encoding efficiency (or transform efficiency) even when the current block is the inter mode by deriving an intra mode for the reference block indicating internal directionality using an already reconstructed reference block and applying the intra mode for the derived reference block to the current block. That is, the image decoding device (2000) can select an appropriate transform kernel for the current block from among various types of transform kernels, like the intra mode, even when the current block is the inter mode by determining the intra mode for the reference block, thereby increasing the compression efficiency of the image. According to one embodiment of the present disclosure, even when the prediction mode of the current block is the inter mode, a secondary transform and a non-separable primary transform can be applied, and various transform kernels for the primary transform can be applied. By applying a direction-dependent transform kernel, such as a second-order transform, the residuals at the boundary between blocks can be efficiently compressed. However, this effect is merely an example of the invention, and the effects and purposes of the present disclosure are not limited by the disclosed content.

[0287] FIG. 22 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0288] In one embodiment of the present disclosure, the image decoding method may be performed by the image decoding device (2000). For example, the image decoding device (2000) may perform each step of the image decoding method by having the processor of the image decoding device (2000) execute at least one instruction contained in a memory.

[0289] In step S2210, the image decoding device (2000) may obtain a reference block of a reference image. In one embodiment of the present disclosure, the reference block may be determined based on a motion vector of the current block. The reference block may include a block used for inter prediction of the current block.

[0290] In step S2220, the image decoding device (2000) can determine an intra mode for the reference block based on at least one of a plurality of surrounding samples and a plurality of internal samples of the reference block.

[0291] In one embodiment of the present disclosure, the surrounding samples of a reference block may include samples located within a predetermined distance from the reference block. The surrounding samples of the reference block may include at least one of adjacent samples and non-adjacent samples of the reference block. The surrounding samples of the reference block may include samples located above, to the left of, and / or to the upper left of the reference block.

[0292] In one embodiment of the present disclosure, the image decoding device (2000) can predict internal samples of a reference block using a plurality of surrounding samples. For example, the image decoding device (2000) can determine prediction samples according to a plurality of intra modes (e.g., intra directional prediction modes 2 to 66, or all possible intra prediction modes) using the surrounding samples of the reference block as reference samples. The image decoding device (2000) can compare the prediction samples with the internal samples of the reference block to determine an error. The image decoding device (2000) can determine an intra mode for the reference block based on the error. For example, the image decoding device (2000) can determine one intra mode with the smallest error among the plurality of intra modes as the intra mode for the reference block.

[0293] In step S2230, the image decoding device (2000) may determine a transform kernel of the current block from among one or more transform kernels using an intra mode for a reference block. In one embodiment of the present disclosure, step S2230 may correspond to step S2130.

[0294] In step S2240, the image decoding device (2000) may perform inverse transformation on the current block using a transformation kernel. In one embodiment of the present disclosure, step S2240 may correspond to step S2140.

[0295] FIG. 23 is a diagram illustrating a process for determining an intra mode for a reference block using surrounding blocks of the reference block in one embodiment of the present disclosure.

[0296] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block of a current block (2310) based on temporal information. The image decoding device (2000) may determine an intra mode for a reference block using surrounding samples (2330) of the reference block (2320) and internal samples of the reference block (2320).

[0297] The video decoding device (2000) references the current block (C) (2310) to the reference block (C). pred )(2320) can be determined. In one embodiment of the present disclosure, the current block (2310) may include a block included in a P picture (or a P slice). The reference block (2320) is a block used for inter prediction of the current block (2310) and may be a block included in a reference picture different from the current picture. The image decoding apparatus (2000) may determine the reference block (2320) included in the reference picture (or reference slice) using the motion vector of the current block (2310). In one embodiment of the present disclosure, the neighboring sample (2330) of the reference block (2320) may be referred to as a temporal neighboring sample.

[0298] The image decoding device (2000) can perform intra prediction according to one or more intra prediction modes using a plurality of surrounding samples. The image decoding device (2000) performs prediction on an internal sample of the reference block (2320) using surrounding samples (2330) of the reference block (2320), thereby generating a predicted sample (R pred) can be obtained. The image decoding device (2000) can obtain a prediction sample of the reference block (2320) by using the surrounding samples (2330) of the reference block (2320) as reference samples according to each of a plurality of intra prediction modes. For example, the image decoding device (2000) can perform prediction for all intra prediction modes, but is not limited thereto, and can perform prediction for a predetermined intra prediction mode set among the intra prediction modes.

[0299] The image decoding device (2000) can determine an error by comparing the predicted sample of the reference block (2320) with the surrounding samples (2330). In one embodiment of the present disclosure, the image decoding device (2000) can determine the error using a cost function. For example, the image decoding device (2000) can determine the error using at least one cost function among SAD, SATD, SSE, and MR-SAD. When the cost function is SAD, the image decoding device (2000) can determine the error based on the sum of the absolute values ​​of the differences between the predicted sample of the reference block (2320) and the surrounding samples (2330). The error can be replaced with the term “cost,” for example. For example, the image decoding device (2000) can determine the error between the predicted sample of the reference block (2320) and the surrounding sample (2330) using the Sum of Absolute Differences (SAD).

[0300] The video decoding device (2000) can determine an intra mode for a reference block based on an error. The video decoding device (2000) can determine an intra mode for a reference block based on an error between intra-predicted samples and internal samples of the reference block. The video decoding device (2000) can determine an intra prediction mode with the smallest error as the intra mode for the reference block.

[0301] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0302] FIG. 24 is a diagram illustrating a process of determining an intra mode for a reference block using surrounding samples of the reference block in one embodiment of the present disclosure.

[0303] Referring to FIG. 24, a current block may have multiple reference blocks. In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for the reference block of the current block (2410) based on temporal information. The image decoding device (2000) may determine an intra mode for the reference block using surrounding samples (2430, 2450) of the reference blocks (2420, 2440) and internal samples of the reference blocks (2420, 2440).

[0304] The video decoding device (2000) provides a first reference block (C) for the current block (C) (2410). pred0 )(2420) and the second reference block (C pred1)(2440) can be determined. In one embodiment of the present disclosure, the current block (2410) may include a block included in a B picture (or a B slice). The reference blocks (2420, 2440) are blocks used for inter prediction of the current block (2410) and may be blocks included in reference images different from the current image. The image decoding apparatus (2000) may determine the reference blocks (2420, 2440) included in the reference image (or reference slice) using the motion vector of the current block (2410). In one embodiment of the present disclosure, the surrounding samples (2430) of the reference blocks (2420, 2440) may be referred to as temporal surrounding samples.

[0305] The image decoding device (2000) performs prediction on the internal sample of the reference block (2420) using the surrounding samples (2430, 2450) of the reference block (2420, 2440), thereby generating a prediction sample (R pred0 , R pred1 ) can be obtained. The image decoding device (2000) can obtain a prediction sample of the reference block (2420, 2440) using the surrounding samples (2430, 2450) of the reference block (2420, 2440) as reference samples according to each of the plurality of intra prediction modes.

[0306] The image decoding device (2000) can determine an error by comparing the predicted sample of the reference block (2420, 2440) with the surrounding samples (2430, 2450). The image decoding device (2000) can determine the error using a cost function. For example, the image decoding device (2000) can determine the error using at least one cost function among SAD, SATD, SSE, and MR-SAD.

[0307] In one embodiment of the present disclosure, the image decoding device (2000) may determine a first candidate intra mode based on at least one of a plurality of surrounding samples (2430) of a first reference block (2420) and a plurality of internal samples included in the reference block (2420). The image decoding device (2000) may determine a second candidate intra mode based on at least one of a plurality of surrounding samples (2450) of a second reference block (2440) of a current block (2410) and a plurality of internal samples of the second reference block (2440). The image decoding device (2000) may determine a first candidate intra mode and a second candidate intra mode having a smallest error from each of the first reference block (2420) and the second reference block (2440). The image decoding device (2000) may select one of the first candidate intra mode and the second candidate intra mode as an intra mode for the reference block. For example, in a case where there is one reference block as in FIG. 23, the image decoding device (2000) can determine the intra mode for the reference block without a process of determining a candidate intra mode.

[0308] In one embodiment of the present disclosure, the image decoding device (2000) can determine an intra mode for a reference block based on an error. The image decoding device (2000) can determine a first error by performing prediction on a plurality of internal samples of a first reference block (2420) using a plurality of surrounding samples (2430) of the first reference block (2420) according to a first candidate intra mode. The image decoding device (2000) can determine a second error by performing prediction on a plurality of internal samples of a second reference block (2440) using a plurality of surrounding samples (2450) of the second reference block (2440) according to a second candidate intra mode. The image decoding device (2000) can determine an intra mode for the reference block from among the first candidate intra mode and the second candidate intra mode based on the first error and the second error. The video decoding device (2000) can determine one of the first candidate intra mode and the second candidate intra mode with a smaller error as the intra mode for the reference block.

[0309] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block based on a quantization parameter (QP) of a slice including the reference block. In one embodiment, the quantization parameter may refer to a variable used in a decoding procedure for a transform coefficient. The image decoding device (2000) may perform inverse quantization based on the quantization parameter. The image decoding device (2000) may obtain a first quantization parameter of a first reference block (2420) and a second quantization parameter of a second reference block (2440). The image decoding device (2000) may determine a candidate intra mode of a reference block with a small quantization parameter as an intra mode for the reference block. When the first quantization parameter is greater than or equal to the second quantization parameter, the image decoding device (2000) may select the second candidate intra mode as the intra mode for the reference block. The image decoding device (2000) can select the first candidate intra mode as the intra mode for the reference block when the first quantization parameter is smaller than the second quantization parameter.

[0310] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block based on a POC (Picture Order Count) value of the reference image. In one embodiment, the POC value may mean a variable related to the display order of the image. The image decoding device (2000) may obtain a first POC value of a first reference block (2420) and a second POC value of a second reference block (2440). The image decoding device (2000) may determine a candidate intra mode of a reference image having a small difference between the POC values ​​of the current image and the reference image as an intra mode for the reference block. The image decoding device (2000) may select the first candidate intra mode as an intra mode for the reference block when the difference between the POC value of the current image (2410) and the first POC value is smaller than the difference between the POC value of the current image (2410) and the second POC value. The image decoding device (2000) may select the second candidate intra mode as the intra mode for the reference block when the difference between the POC value of the current image (2410) and the first POC value is greater than or equal to the difference between the POC value of the current image (2410) and the second POC value.

[0311] In one embodiment of the present disclosure, the video decoding device (2000) can determine an intra mode for a reference block based on bi-prediction weights. The video decoding device (2000) can obtain a prediction sample of a current block based on a weighted sum between a plurality of reference blocks. The video decoding device (2000) can obtain bi-prediction weights for a first reference block (2420) and a second reference block (2440). If the weight for the first reference block (2420) is greater than or equal to the weight for the second reference block (2440), the video decoding device (2000) can select the first candidate intra mode as the intra mode for the reference block. If the weight for the first reference block (2420) is less than the weight for the second reference block, the video decoding device (2000) can select the second candidate intra mode as the intra mode for the reference block.

[0312] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for the reference block based on the slice type of the reference block. If the slice type including the reference block is an Intra (I) slice, the image decoding device (2000) may determine a candidate intra mode of the reference block as the intra mode for the reference block. If the type of the slice including the first reference block (2420) is an I slice, the image decoding device (2000) may select the first candidate intra mode as the intra mode for the reference block. If the type of the slice including the second reference block (2440) is an I slice, the image decoding device (2000) may select the second candidate intra mode as the intra mode for the reference block.

[0313] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0314] FIG. 25 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0315] In one embodiment of the present disclosure, the image decoding method may be performed by the image decoding device (2000). For example, the image decoding device (2000) may perform each step of the image decoding method by having the processor of the image decoding device (2000) execute at least one instruction contained in a memory.

[0316] In step S2510, the image decoding device (2000) may determine a plurality of slopes using a plurality of internal samples of the reference block. The image decoding device (2000) may determine a horizontal change amount and a vertical change amount using a plurality of internal samples of the reference block. For example, the image decoding device (2000) may determine a horizontal change amount and a vertical change amount using a Sobel filter. The image decoding device (2000) may determine an N x N block (or area) (e.g., a 3 x 3 block) included in the reference block. The N x N blocks (or areas) may be determined at predetermined intervals within the reference block. For example, when the interval is 1, the upper left coordinate of the first N x N block may be (x1, y1), and the upper left coordinate of the second N x N block may be (x1 + 1, y1 + 1). Depending on the interval, at least some of the N x N blocks within the reference block may be the same sample. The image decoding device (2000) can obtain the horizontal variation and the vertical variation of the samples included in the determined N x N block. The image decoding device (2000) can determine the slope based on the horizontal variation and the vertical variation. The slope can be determined as a ratio between the horizontal variation and the vertical variation.

[0317] In step S2520, the image decoding device (2000) may determine a plurality of directional intra modes corresponding to a plurality of slopes. The image decoding device (2000) may determine an intra prediction mode corresponding to the slope. For example, when the slope is 0 (i.e., in the horizontal direction), the image decoding device (2000) may determine a horizontal mode (e.g., intra prediction mode 18) as the directional intra mode corresponding to the slope.

[0318] The video decoding device (2000) can generate a histogram of gradients (HOG) using a plurality of gradients. The video decoding device (2000) can determine the HOG based on a plurality of intra prediction modes determined for a plurality of N x N blocks. The HOG may be referred to as gradient statistical information or gradient information. In one embodiment of the present disclosure, the HOG may include information indicating a frequency (or amplitude) of a directional intra mode determined based on the gradients. In one embodiment of the present disclosure, a weight may be applied to the frequency of the directional intra mode of the HOG. The video decoding device (2000) can determine a weight of an intra prediction mode corresponding to a gradient. The video decoding device (2000) can increase the weight of the intra prediction mode determined based on the gradient as the horizontal variation and the vertical variation increase. For example, the weights may be determined based on the sum of the absolute values ​​of the horizontal and vertical changes.

[0319] In step S2530, the image decoding device (2000) may select an intra mode for the reference block from among the determined plurality of directional intra modes. The image decoding device (2000) may determine the intra prediction mode with the highest number of determinations as the intra mode for the reference block of the current block. In one embodiment of the present disclosure, the image decoding device (2000) may determine the intra mode for the reference block based on HOG. The image decoding device (2000) may determine the directional intra mode with the highest frequency (or size) as the intra mode for the reference block.

[0320] In one embodiment of the present disclosure, step S2120 and / or step S2220 may determine an intra mode for a reference block according to steps S2510 to S2530.

[0321] FIG. 26 is a diagram illustrating a process for determining an intra mode for a reference block using a reference block in one embodiment of the present disclosure.

[0322] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block of a current block (2610) based on temporal information. The image decoding device (2000) may determine an intra mode for the reference block using an internal sample of the reference block (2620).

[0323] The video decoding device (2000) references the current block (C) (2610) to the reference block (C). pred )(2620) can be determined. In one embodiment of the present disclosure, the current block (2610) may include a block included in a P picture (or a P slice). The reference block (2620) is a block used for inter prediction of the current block (2610) and may be a block included in a reference picture different from the current picture. The image decoding apparatus (2000) may determine the reference block (2620) included in the reference picture (or reference slice) using the motion vector of the current block (2610).

[0324] The image decoding device (2000) can determine a slope using an internal sample of the reference block (2620). The image decoding device (2000) can determine a horizontal change amount and / or a vertical change amount using an internal sample of the reference block (2620). For example, the image decoding device (2000) can determine a horizontal change amount and a vertical change amount of the reference block (2620) using a Sobel filter. The Sobel filter includes a filter for obtaining a horizontal or vertical change amount within input data. The image decoding device (2000) can determine N x N blocks (e.g., 3 x 3 blocks) included within the reference block (2620). The image decoding device (2000) can determine N x N blocks within the reference block (2620) at predetermined intervals (e.g., 1) in the direction and / or vertical direction.

[0325] The image decoding device (2000) can determine a slope based on horizontal and vertical changes. The image decoding device (2000) can determine the ratio between the horizontal and vertical changes as the slope.

[0326] The video decoding device (2000) can determine an intra prediction mode corresponding to a slope. The video decoding device (2000) can generate an HOG (2630) using slopes of a plurality of N x N blocks within a reference block (2620). The HOG (2630) can include information indicating a frequency (or amplitude) of an intra prediction mode corresponding to the slopes of a plurality of blocks within the reference block (2620). For example, the HOG (2630) can be information including a frequency (or amplitude) corresponding to an intra prediction mode, as illustrated in FIG. 26.

[0327] In one embodiment of the present disclosure, the size (or frequency) of the intra prediction mode of HOG (2630) may be determined based on the horizontal variation and vertical variation. For example, the larger the horizontal variation and vertical variation, the larger the size of the intra prediction mode. For example, the size may be determined based on the sum of the absolute values ​​of the horizontal variation and vertical variation.

[0328] The video decoding device (2000) may select an intra mode for a reference block from among a plurality of determined intra prediction modes. In one embodiment of the present disclosure, the video decoding device (2000) may determine an intra mode for a reference block based on the HOG (2630). The video decoding device (2000) may determine an intra prediction mode with the largest size (or frequency) as the intra mode for the reference block of the current block (2610).

[0329] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0330] FIG. 27 is a diagram illustrating a process of determining an intra mode for a reference block using reference blocks in one embodiment of the present disclosure.

[0331] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block of a current block (2710) based on temporal information. The image decoding device (2000) may determine an intra mode for the reference block using internal samples of the reference blocks (2720, 2740).

[0332] The video decoding device (2000) provides a first reference block (C) for the current block (C) (2710). pred0 )(2720) and the second reference block (C pred1 )(2740) can be determined. In one embodiment of the present disclosure, the current block (2710) may include a block included in a B picture (or a B slice). The first reference block (2720) and the second reference block (2740) are blocks used for inter prediction of the current block (2710) and may be blocks included in a reference picture different from the current picture. The image decoding apparatus (2000) may determine the reference blocks (2720, 2740) included in the reference picture (or the reference slice) using the motion vector of the current block (2710).

[0333] The image decoding device (2000) can determine a slope using internal samples of the reference blocks (2720, 2740). The image decoding device (2000) can determine a horizontal change amount and / or a vertical change amount using internal samples of the reference blocks (2720, 2740). For example, the image decoding device (2000) can determine a horizontal change amount and a vertical change amount of the reference blocks (2720, 2740) using a Sobel filter. The Sobel filter includes a filter for obtaining a horizontal or vertical change amount within the input data. The image decoding device (2000) can determine an N x N block (e.g., a 3 x 3 block) included within the reference blocks (2720, 2740). The video decoding device (2000) can determine N x N blocks inside the reference block (2720, 2740) at predetermined intervals (e.g., 1) in the direction and / or vertical direction.

[0334] The image decoding device (2000) can determine a slope based on horizontal and vertical changes. The image decoding device (2000) can determine the ratio between the horizontal and vertical changes as the slope.

[0335] The video decoding device (2000) can determine an intra prediction mode corresponding to a slope. The video decoding device (2000) can generate HOGs (2730, 2750) using slopes of a plurality of N x N blocks within reference blocks (2720, 2740). The size of a block within the first reference block (2720) may be different from the size of a block within the second reference block (2740). The HOGs (2730, 2750) may include information indicating a frequency (or amplitude) of an intra prediction mode corresponding to the slopes of the plurality of blocks within the reference blocks (2720, 2740). For example, the HOGs (2730, 2750) may be information including a frequency (or amplitude) corresponding to an intra prediction mode, as illustrated in FIG. 27.

[0336] In one embodiment of the present disclosure, the size (or frequency) of the intra prediction mode of HOG (2730, 2750) may be determined based on the horizontal variation and the vertical variation. For example, the larger the horizontal variation and the vertical variation, the larger the size of the intra prediction mode may be determined. For example, the size may be determined based on the sum of the absolute values ​​of the horizontal variation and the vertical variation.

[0337] The video decoding device (2000) can select an intra mode for a reference block from among a plurality of determined intra prediction modes. In one embodiment of the present disclosure, the video decoding device (2000) can determine an intra mode for a reference block based on HOG (2730, 2750).

[0338] In one embodiment of the present disclosure, the image decoding device (2000) may determine a first candidate intra mode based on a plurality of slopes of the first reference block (2720). The image decoding device (2000) may determine the first candidate intra mode based on the first HOG (2730).

[0339] The image decoding device (2000) can determine the second candidate intra mode based on multiple slopes of the second reference block (2740). The image decoding device (2000) can determine the first candidate intra mode based on the second HOG (2750).

[0340] The video decoding device (2000) can determine the first candidate intra mode and the second candidate intra mode having the largest size (or frequency) from each of the first reference block (2720) and the second reference block (2740). The video decoding device (2000) can select one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block. For example, in the case where there is only one reference block as shown in FIG. 26, the video decoding device (2000) can determine the intra mode for the reference block without going through the process of determining the candidate intra mode.

[0341] In one embodiment of the present disclosure, the image decoding device (2000) can determine an intra mode for a reference block based on an error. The image decoding device (2000) can determine a first error by performing prediction on a plurality of internal samples of a first reference block (2720) using a plurality of surrounding samples (2730) of the first reference block (2720) according to a first candidate intra mode. The image decoding device (2000) can determine a second error by performing prediction on a plurality of internal samples of a second reference block (2740) using a plurality of surrounding samples (2750) of the second reference block (2740) according to a second candidate intra mode. The image decoding device (2000) can determine an intra mode for the reference block from among the first candidate intra mode and the second candidate intra mode based on the first error and the second error. The video decoding device (2000) can determine one of the first candidate intra mode and the second candidate intra mode with a smaller error as the intra mode for the reference block.

[0342] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block based on a quantization parameter (QP) of a slice including the reference block. In one embodiment, the quantization parameter may refer to a variable used in a decoding procedure for a transform coefficient. The image decoding device (2000) may perform inverse quantization based on the quantization parameter. The image decoding device (2000) may obtain a first quantization parameter of a first reference block (2720) and a second quantization parameter of a second reference block (2740). The image decoding device (2000) may determine a candidate intra mode of a reference block with a small quantization parameter as an intra mode for the reference block. When the first quantization parameter is greater than or equal to the second quantization parameter, the image decoding device (2000) may select the second candidate intra mode as the intra mode for the reference block. The image decoding device (2000) can select the first candidate intra mode as the intra mode for the reference block when the first quantization parameter is smaller than the second quantization parameter.

[0343] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block based on a POC (Picture Order Count) value of the reference image. In one embodiment, the POC value may mean a variable related to the display order of the image. The image decoding device (2000) may obtain a first POC value of a first reference block (2720) and a second POC value of a second reference block (2740). The image decoding device (2000) may determine a candidate intra mode of a reference image having a small difference between the POC values ​​of the current image and the reference image as an intra mode for the reference block. The image decoding device (2000) may select the first candidate intra mode as an intra mode for the reference block when the difference between the POC value of the current image (2710) and the first POC value is smaller than the difference between the POC value of the current image (2710) and the second POC value. The image decoding device (2000) may select the second candidate intra mode as the intra mode for the reference block when the difference between the POC value of the current image (2710) and the first POC value is greater than or equal to the difference between the POC value of the current image (2710) and the second POC value.

[0344] In one embodiment of the present disclosure, the video decoding device (2000) can determine an intra mode for a reference block based on bi-prediction weights. The video decoding device (2000) can obtain a prediction sample of a current block based on a weighted sum between a plurality of reference blocks. The video decoding device (2000) can obtain bi-prediction weights for a first reference block (2720) and a second reference block (2740). If the weight for the first reference block (2720) is greater than or equal to the weight for the second reference block (2740), the video decoding device (2000) can select the first candidate intra mode as the intra mode for the reference block. If the weight for the first reference block (2720) is less than the weight for the second reference block, the video decoding device (2000) can select the second candidate intra mode as the intra mode for the reference block.

[0345] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for the reference block based on the slice type of the reference block. If the slice type including the reference block is an Intra (I) slice, the image decoding device (2000) may determine a candidate intra mode of the reference block as the intra mode for the reference block. If the type of the slice including the first reference block (2720) is an I slice, the image decoding device (2000) may select the first candidate intra mode as the intra mode for the reference block. If the type of the slice including the second reference block (2740) is an I slice, the image decoding device (2000) may select the second candidate intra mode as the intra mode for the reference block.

[0346] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0347] FIG. 28 is a diagram illustrating a process of determining an intra mode for a reference block using reference blocks in one embodiment of the present disclosure.

[0348] In one embodiment of the present disclosure, the image decoding device (2000) may determine an intra mode for a reference block of a current block (2810) based on temporal information. The image decoding device (2000) may determine an intra mode for the reference block using internal samples of the reference blocks (2820, 2830).

[0349] The video decoding device (2000) provides a first reference block (C) for the current block (C) (2810). pred0 )(2820) and the second reference block (C pred1 )(2830) can be determined. In one embodiment of the present disclosure, the current block (2810) may include a block included in a B picture (or a B slice). The first reference block (2820) and the second reference block (2830) are blocks used for inter prediction of the current block (2810) and may be blocks included in a reference picture different from the current picture. The image decoding apparatus (2000) may determine the reference blocks (2820, 2830) included in the reference picture (or the reference slice) using the motion vector of the current block (2810).

[0350] The image decoding device (2000) can determine a slope using internal samples of the reference blocks (2820, 2830). The image decoding device (2000) can determine a horizontal change amount and / or a vertical change amount using internal samples of the reference blocks (2820, 2830). For example, the image decoding device (2000) can determine a horizontal change amount and a vertical change amount of the reference blocks (2820, 2830) using a Sobel filter. The Sobel filter includes a filter for obtaining a horizontal or vertical change amount within the input data. The image decoding device (2000) can determine an N x N block (e.g., a 3 x 3 block) included within the reference blocks (2820, 2830). The video decoding device (2000) can determine N x N blocks inside the reference block (2820, 2830) at predetermined intervals (e.g., 1) in the direction and / or vertical direction.

[0351] The image decoding device (2000) can determine a slope based on horizontal and vertical changes. The image decoding device (2000) can determine the ratio between the horizontal and vertical changes as the slope.

[0352] The image decoding device (2000) can determine an intra prediction mode corresponding to the slope. The image decoding device (2000) can generate an HOG (2840) using the slopes of a plurality of N x N blocks within the reference blocks (2820, 2830). The size of a block within the first reference block (2820) may be different from the size of a block within the second reference block (2830). The size of a block within the reference blocks (2820, 2830) may be determined based on the size of the reference images. For example, when the size of reference image 0 is twice as large as the size of reference image 1, the slope of the first reference block may be determined based on a 2N x 2N block, and the slope of the second reference block may be determined based on an N x N block. HOG (2840) may include information indicating the frequency (or amplitude) of an intra prediction mode corresponding to the slope of multiple blocks within the reference blocks (2820, 2830). For example, HOG (2840) may be information including the frequency (or amplitude) corresponding to an intra prediction mode as illustrated in FIG. 28. HOG (2840) may include the amplitude (or frequency) for both the intra prediction modes of the first reference block (2820) and the second reference block (2830). In one embodiment, HOG (2840) may be a combined form of HOG (2730) and HOG (2750) of FIG. 27.

[0353] In one embodiment of the present disclosure, the size (or frequency) of the intra prediction mode of HOG (2840) may be determined based on the horizontal variation and vertical variation. For example, the larger the horizontal variation and vertical variation, the larger the size of the intra prediction mode. For example, the size may be determined based on the sum of the absolute values ​​of the horizontal variation and vertical variation.

[0354] The video decoding device (2000) may select an intra mode for a reference block from among a plurality of determined intra prediction modes. In one embodiment of the present disclosure, the video decoding device (2000) may determine an intra mode for a reference block based on the HOG (2840). The video decoding device (2000) may determine an intra prediction mode with the largest size (or frequency) as the intra mode for the reference block of the current block (2810).

[0355] FIG. 29 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0356] In one embodiment of the present disclosure, the image decoding method may be performed by the image decoding device (2000). For example, the image decoding device (2000) may perform each step of the image decoding method by having the processor of the image decoding device (2000) execute at least one instruction contained in a memory.

[0357] In step S2910, the image decoding device (2000) may determine a reference block using template matching. In one embodiment of the present disclosure, the reference block may be included in the same image as the current block.

[0358] The image decoding device (2000) can identify a template of the current block. The template of the current block may include neighboring samples of the current block. The neighboring samples of the current block may include adjacent samples and / or non-adjacent samples of the current block. The form of the template according to one embodiment of the present disclosure is described in detail with reference to FIG. 35.

[0359] The image decoding device (2000) can determine a template similar to the template of the current block from the current image. The image decoding device (2000) can determine a block having a template similar to the current template as a reference block of the current block. The image decoding device (2000) can determine the reference block from among the blocks included in the search area.

[0360] In one embodiment of the present disclosure, the image decoding device (2000) can determine a reference block using a cost function. The image decoding device (2000) can determine a template error between a template of a current block and a candidate template using at least one cost function among SAD, SATD, SSE, and MR-SAD. The image decoding device (2000) can determine a template error based on each sample of the template of the current block and each sample of the candidate template. The image decoding device (2000) can determine a block having a candidate template with a small template error as a reference block.

[0361] In step S2920, the image decoding device (2000) can obtain errors according to multiple intra prediction modes based on surrounding samples of the reference block and internal samples of the reference block.

[0362] In one embodiment of the present disclosure, the image decoding device (2000) can predict internal samples of a reference block using surrounding samples of the reference block. For example, the image decoding device (2000) can determine prediction samples according to a plurality of intra prediction modes (e.g., intra directional prediction modes 2 to 66, or all possible intra prediction modes) using surrounding samples of the reference block as reference samples. The image decoding device (2000) can compare the prediction samples with internal samples of the decoded reference block to determine an error.

[0363] In one embodiment of the present disclosure, the image decoding device (2000) can independently determine a reference sample for determining an error according to an intra prediction mode from a template. For example, when the width and height of the template are the same as those of the current block, the width and height of the reference sample for determining an error according to the intra prediction mode may be twice those of the current block. In addition, the reference sample may include multiple reference lines. For example, the image decoding device (2000) can perform prediction using reference pixels of multiple lines, similar to multi-line reference intra prediction.

[0364] In step S2930, the image decoding device (2000) may determine an intra mode for the reference block based on the error. The image decoding device (2000) may determine one intra mode with the smallest error among a plurality of intra modes as the intra mode for the reference block.

[0365] In one embodiment of the present disclosure, step S2120 and / or step S2220 may determine an intra mode for a reference block according to steps S2910 to S2930.

[0366] FIG. 30 is a diagram illustrating a process of determining an intra mode for a reference block using surrounding samples of the reference block in one embodiment of the present disclosure.

[0367] In one embodiment of the present disclosure, the image decoding device (2000) can determine an intra mode for a reference block of a current block (3010) based on spatial information. The image decoding device (2000) can determine a surrounding sample (or template (T)) of the reference block (3040). R)(3050)) and the inner samples of the reference block (3040) can be used to determine the intra mode for the reference block. In one embodiment of the present disclosure, the neighboring samples (or templates (3050)) of the reference block (3040) may be referred to as spatial neighboring samples.

[0368] The video decoding device (2000) generates a template (T) for the current block (C) (3010). C )(3020) can be determined. In one embodiment of the present disclosure, the reference block (3040) is a block determined using template matching and is different from the reference block (3030) used for inter prediction of the current block (3010). The image decoding device (2000) can determine the reference block (3040) according to template matching using the template (3020) of the current block (3010). The image decoding device (2000) can determine the template error between the template (3020) of the current block (3010) and templates included in the current image. The image decoding device (2000) can determine the block having the template (3050) with the smallest template error as the reference block (3040).

[0369] The image decoding device (2000) can perform intra prediction according to one or more intra prediction modes by using the surrounding samples of the reference block (3040). In one embodiment, the surrounding samples of the reference block (3040) used for intra prediction may be identical to the template (3050) of the reference block (3040). The image decoding device (2000) performs prediction on the internal samples of the reference block (3040) by using the surrounding samples (3050) of the reference block (3040), thereby generating a prediction sample (R pred) can be obtained. The image decoding device (2000) can obtain a prediction sample of the reference block (3040) by using the surrounding samples (3050) of the reference block (3040) as reference samples according to each of a plurality of intra prediction modes. For example, the image decoding device (2000) can perform prediction for all intra prediction modes, but is not limited thereto, and can perform prediction for a predetermined set of intra prediction modes among the intra prediction modes.

[0370] The image decoding device (2000) can determine an error by comparing the predicted sample of the reference block (3040) with the surrounding sample (3050). When the cost function is SAD, the image decoding device (2000) can determine the error based on the sum of the absolute values ​​of the differences between the predicted sample of the reference block (3040) and the surrounding sample (3050).

[0371] The image decoding device (2000) can determine the intra mode for the reference block based on the error. The image decoding device (2000) can determine the intra mode for the reference block based on the error between the intra-predicted samples and the internal samples of the reference block. The image decoding device (2000) can determine the intra prediction mode with the smallest error as the intra mode for the reference block. The image decoding device (2000) can determine the intra mode for the reference block through the reference block of the current image even when the prediction mode of the current image (3010) is the inter mode.

[0372] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0373] FIG. 31 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0374] In one embodiment of the present disclosure, the image decoding method may be performed by the image decoding device (2000). For example, the image decoding device (2000) may perform each step of the image decoding method by having the processor of the image decoding device (2000) execute at least one instruction contained in a memory.

[0375] In step S3110, the image decoding device (2000) may acquire surrounding samples of the current block. In one embodiment of the present disclosure, the surrounding samples of the current block may include adjacent samples and non-adjacent samples of the current block. The surrounding samples of the current block may include left samples, upper-left samples, and / or upper samples of the current block. In one embodiment of the present disclosure, the surrounding samples of the current block may be identical to a template of the current block. The form of the template according to one embodiment of the present disclosure is described in detail with reference to FIG. 35.

[0376] In step S3120, the image decoding device (2000) can obtain errors according to multiple intra prediction modes based on surrounding samples of the current block. The image decoding device (2000) can determine at least some of the surrounding samples of the current block as reference samples, and determine the remaining samples as restored samples.

[0377] In one embodiment of the present disclosure, the image decoding device (2000) can predict the remaining samples of the surrounding samples by using reference samples among the surrounding samples of the current block. For example, the image decoding device (2000) can determine prediction samples according to intra prediction modes (e.g., intra directional prediction modes 2 to 66, or all possible intra prediction modes) by using reference samples of the surrounding samples of the current block. The image decoding device (2000) can compare the prediction sample with the reconstructed sample to determine an error.

[0378] In one embodiment of the present disclosure, the image decoding device (2000) can independently determine a reference sample for determining an error according to an intra prediction mode from a template. For example, when the width and height of the template are the same as those of the current block, the width and height of the reference sample for determining an error according to the intra prediction mode may be twice those of the current block. In addition, the reference sample may include multiple reference lines. For example, the image decoding device (2000) can perform prediction using reference pixels of multiple lines, similar to multi-line reference intra prediction.

[0379] In step S3130, the image decoding device (2000) may determine an intra mode for the reference block based on the error. The image decoding device (2000) may determine one intra mode with the smallest error among multiple intra modes as the intra mode for the reference block.

[0380] In one embodiment of the present disclosure, step S2120 and / or step S2220 may determine an intra mode for a reference block according to steps S3110 to S3130.

[0381] FIG. 32 is a diagram illustrating a process for determining an intra mode for a reference block using surrounding samples of a current block in one embodiment of the present disclosure.

[0382] In one embodiment of the present disclosure, the image decoding device (2000) can determine an intra mode for a reference block of the current block (3210) based on spatial information. The image decoding device (2000) can determine a surrounding sample (or template (T)) of the current block (3210). C )) can be used to determine the intra mode for the reference block. In one embodiment of the present disclosure, the neighboring sample (or template) of the current block (3210) may be referred to as a spatial neighboring sample.

[0383] The image decoding device (2000) can determine a surrounding sample (or template) for the current block (C) (3210). The surrounding samples of the current block (3210) can include adjacent samples and non-adjacent samples of the current block (3210). The image decoding device (2000) can determine a part of the surrounding samples of the current block (3210) as a reference sample (R). ref )(3220) and the rest of the surrounding samples can be determined as restored samples (3230).

[0384] The image decoding device (2000) can perform intra prediction according to one or more intra prediction modes using the reference sample (3220). The image decoding device (2000) performs prediction on the remaining surrounding samples excluding the reference sample (3220) using the reference sample (3220) of the surrounding samples of the current block (3210), thereby obtaining a predicted sample (R pred ) can be obtained. The image decoding device (2000) can obtain a prediction sample from the reference sample (3220) according to each of a plurality of intra prediction modes. For example, the image decoding device (2000) can perform prediction for all intra prediction modes, but is not limited thereto, and can perform prediction for a predetermined set of intra prediction modes among the intra prediction modes.

[0385] The video decoding device (2000) generates a prediction sample (R pred ) and the restored sample (3230) to determine the error. The image decoding device (2000) can determine the error using a cost function. When the cost function is SAD, the image decoding device (2000) can determine the error based on the sum of the absolute values ​​of the differences between the predicted sample and the restored sample (3230).

[0386] The image decoding device (2000) can determine the intra mode for the reference block based on the error. The image decoding device (2000) can determine the intra mode for the reference block based on the error between the prediction sample and the reconstructed sample (3230). The image decoding device (2000) can determine the intra prediction mode with the smallest error as the intra mode for the reference block. The image decoding device (2000) can determine the intra mode for the reference block through the reference block of the current image even when the prediction mode of the current image (3210) is the inter mode.

[0387] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0388] FIG. 33 is a flowchart of an image decoding method according to one embodiment of the present disclosure.

[0389] In one embodiment of the present disclosure, the image decoding method may be performed by the image decoding device (2000). For example, the image decoding device (2000) may perform each step of the image decoding method by having the processor of the image decoding device (2000) execute at least one instruction contained in a memory.

[0390] In step S3310, the image decoding device (2000) may determine a reference block using template matching. In one embodiment of the present disclosure, the reference block may be included in the same image as the current block.

[0391] The image decoding device (2000) can identify a template of the current block. The template of the current block may include neighboring samples of the current block. The neighboring samples of the current block may include adjacent samples and / or non-adjacent samples of the current block. The form of the template according to one embodiment of the present disclosure is described in detail with reference to FIG. 35.

[0392] The image decoding device (2000) can determine a template similar to the template of the current block from the current image. The image decoding device (2000) can determine a block having a template similar to the current template as a reference block of the current block. The image decoding device (2000) can determine the reference block from among the blocks included in the search area.

[0393] In one embodiment of the present disclosure, the image decoding device (2000) can determine a reference block using a cost function. The image decoding device (2000) can determine a template error between a template of a current block and a candidate template using at least one cost function among SAD, SATD, SSE, and MR-SAD. The image decoding device (2000) can determine a template error based on each sample of the template of the current block and each sample of the candidate template. The image decoding device (2000) can determine a block having a candidate template with a small template error as a reference block.

[0394] In step S3320, the image decoding device (2000) may determine a plurality of slopes using a plurality of internal samples of the reference block. The image decoding device (2000) may determine a horizontal variation and a vertical variation using a plurality of internal samples of the reference block. For example, the image decoding device (2000) may determine a horizontal variation and a vertical variation using a Sobel filter. The image decoding device (2000) may determine an N x N block (e.g., a 3 x 3 block) included in the reference block. The image decoding device (2000) may obtain a horizontal variation and a vertical variation of samples included in the determined N x N block. The image decoding device (2000) may determine a slope based on the horizontal variation and the vertical variation. The slope may be determined as a ratio between the horizontal variation and the vertical variation. In one embodiment of the present disclosure, step S3320 may correspond to step S2510 of FIG. 25.

[0395] In step S3330, the image decoding device (2000) can determine a plurality of directional intra modes corresponding to a plurality of slopes. The image decoding device (2000) can determine an intra prediction mode corresponding to a slope.

[0396] The video decoding device (2000) can generate a histogram of gradients (HOG) using a plurality of gradients. The video decoding device (2000) can determine the HOG based on a plurality of intra prediction modes determined for a plurality of N x N blocks. The HOG may be referred to as gradient statistical information or gradient information. In one embodiment of the present disclosure, the HOG may include information indicating a frequency (or amplitude) of a directional intra mode determined based on the gradients. In one embodiment of the present disclosure, a weight may be applied to the frequency of the directional intra mode of the HOG. The video decoding device (2000) may determine a weight of an intra prediction mode corresponding to a gradient. The video decoding device (2000) may increase the weight of the intra prediction mode determined based on the gradient as the horizontal variation and the vertical variation increase. For example, the weight may be determined based on the sum of the absolute values ​​of the horizontal variation and the vertical variation. In one embodiment of the present disclosure, step S3330 may correspond to step S2520 of FIG. 25.

[0397] In step S3340, the image decoding device (2000) may select an intra mode for the reference block from among the determined plurality of directional intra modes. The image decoding device (2000) may determine the intra prediction mode with the highest number of determinations as the intra mode for the reference block of the current block. In one embodiment of the present disclosure, the image decoding device (2000) may determine the intra mode for the reference block based on HOG. The image decoding device (2000) may determine the directional intra mode with the highest frequency (or size) as the intra mode for the reference block. In one embodiment of the present disclosure, step S3340 may correspond to step S2530 of FIG. 25.

[0398] In one embodiment of the present disclosure, step S2120 and / or step S2220 may determine an intra mode for a reference block according to steps S3310 to S3340.

[0399] FIG. 34 is a diagram illustrating a process for determining an intra mode for a reference block using a reference block in one embodiment of the present disclosure.

[0400] In one embodiment of the present disclosure, the image decoding device (2000) can determine an intra mode for a reference block of a current block (3410) based on spatial information. The image decoding device (2000) can determine an intra mode for the reference block using a sample of the reference block (3430).

[0401] The video decoding device (2000) generates a template (T) for the current block (C) (3410). C )(3420) can be determined. In one embodiment of the present disclosure, the reference block (3430) is a block determined using template matching and is different from the reference block used for inter prediction of the current block (3410). The image decoding device (2000) can determine the reference block (3430) according to template matching using the template (3420) of the current block (3410). The image decoding device (2000) can determine the template error between the template (3420) of the current block (3410) and templates included in the current image. The image decoding device (2000) can determine the block having the template (3440) with the smallest template error as the reference block (3430).

[0402] The image decoding device (2000) can determine a slope using an internal sample of the reference block (3430). The image decoding device (2000) can determine a horizontal change amount and / or a vertical change amount using an internal sample of the reference block (3430). For example, the image decoding device (2000) can determine a horizontal change amount and a vertical change amount of the reference block (3430) using a Sobel filter. The Sobel filter includes a filter for obtaining a horizontal or vertical change amount within the input data. The image decoding device (2000) can determine N x N blocks (e.g., 3 x 3 blocks) included within the reference block (3430). The image decoding device (2000) can determine N x N blocks within the reference block (3430) at predetermined intervals (e.g., 1) in the direction and / or vertical direction.

[0403] The image decoding device (2000) can determine a slope based on horizontal and vertical changes. The image decoding device (2000) can determine the ratio between the horizontal and vertical changes as the slope.

[0404] The video decoding device (2000) can determine an intra prediction mode corresponding to a slope. The video decoding device (2000) can generate an HOG (3450) using slopes of a plurality of N x N blocks within a reference block (3430). The HOG (3450) can include information indicating a frequency (or amplitude) of an intra prediction mode corresponding to the slopes of a plurality of blocks within the reference block (3430). For example, the HOG (3450) can be information including a frequency (or amplitude) corresponding to an intra prediction mode, as illustrated in FIG. 34.

[0405] In one embodiment of the present disclosure, the size (or frequency) of the intra prediction mode of HOG (3450) may be determined based on the horizontal variation and vertical variation. For example, the larger the horizontal variation and vertical variation, the larger the size of the intra prediction mode. For example, the size may be determined based on the sum of the absolute values ​​of the horizontal variation and vertical variation.

[0406] The video decoding device (2000) may select an intra mode for a reference block from among a plurality of determined intra prediction modes. In one embodiment of the present disclosure, the video decoding device (2000) may determine an intra mode for a reference block based on the HOG (3450). The video decoding device (2000) may determine an intra prediction mode with the largest size (or frequency) as the intra mode for the reference block of the current block (3410).

[0407] The image decoding device (2000) may determine a transform kernel using the intra mode for the determined reference block. Here, the transform kernel may mean a kernel applied to a residual block to perform an inverse transform for at least one of a first transform, a second transform, or a non-separable first transform. The image decoding device (2000) may determine a transform kernel for at least one of a first transform, a second transform, or a non-separable first transform using the intra mode for the determined reference block.

[0408] FIG. 35 is a drawing for explaining the form of a template according to one embodiment of the present disclosure.

[0409] Referring to FIG. 35, the templates (3510, 3520, 3530, 3540, 3550) of the current block (3500) may have multiple shapes. In one embodiment of the present disclosure, the shape of the template to be compared in the restored area may also be determined based on the template of the current block (3500). In one embodiment of the present disclosure, a template having a shape similar to that of the templates (3510, 3530) may be referred to as an L-shape.

[0410] In one embodiment of the present disclosure, the image decoding device (2000) may determine a template of the current block (3500) to include at least one of a first template located on the left side of the current block (3500), a second template located on the upper side of the current block (3500), and a third template located on the upper left side of the current block (3500). For example, the template (3510) may include the first template located on the left side of the current block (3500), the second template located on the upper side of the current block (3500), and the third template located on the upper left side of the current block (3500), and the template (3520) may include the first template and the second template excluding the third template. Alternatively, the template may include only the second template located on the upper side of the current block (3500) or only the third template located on the left side of the current block (3500). However, without limitation thereto, the template may include a template located to the right of the current block (3500).

[0411] In one embodiment of the present disclosure, the image decoding device (2000) can perform template matching prediction using a template (3530) including at least some of a right reference sample, an upper reference sample, and an upper-right reference sample. The image decoding device (2000) can determine the template based on the coding order (or coding direction) of the block. In one embodiment, when coding of the block is performed from right to left, the image decoding device (2000) can determine a reference block of the current block (3500) or perform template matching prediction using the template (3530).

[0412] In one embodiment of the present disclosure, the image decoding device (2000) can determine a reference block of the current block (3500) or perform template matching prediction using a template (3540) including at least some of a right reference sample, an upper reference sample, a left reference sample, an upper-left reference sample, and an upper-right reference sample. In one embodiment of the present disclosure, the image decoding device (2000) can determine a reference block of the current block (3500) or perform template matching prediction using a template (3540) including referenceable samples when the coding order (or coding direction) of the block changes.

[0413] In one embodiment of the present disclosure, the height of the first template located on the left side of the current block (3500) or the width of the second template located on the upper side of the current block (3500) may be determined based on the height or width of the current block (3500). For example, the template (3550) may include a first template having twice the height of the current block (3500) and a second template having twice the width of the current block (3500). By way of example, the template (3550) is a modified form of the height of the first template of the template (3520) and the width of the second template, but is not limited thereto, and the templates (3510, 3530, 3540) may also have modified forms.

[0414] The template of the current block (3500) may include one or more reference lines. The first template may include m reference lines (where m is an integer greater than or equal to 1), and the second template may include n reference lines (where n is an integer greater than or equal to 1).

[0415] In one embodiment of the present disclosure, the number of reference lines may be a predetermined value. For example, the first template and the second template may each include four reference lines (i.e., m = 4 and n = 4). In one embodiment of the present disclosure, the number of reference lines may be determined according to the size of the current block (3500). For example, the first template and the second template may each include reference lines equal to half the width and half the height of the current block (3500) (i.e., m = W / 2 and n = H / 2).

[0416] In one embodiment of the present disclosure, the form of the template may be signaled. The image decoding device (2000) may obtain information about the form of the template from the bitstream. In one embodiment of the present disclosure, the form of the template may be determined based on the size of the current block (3500).

[0417] FIG. 35 is a drawing for explaining a template according to one embodiment of the present disclosure, and is not limited thereto, and various forms of templates may be determined. In addition, although the present disclosure describes that the image decoding device (2000) performs template matching using a template (3510) including all of a left reference sample, an upper reference sample, and an upper-left reference sample, the present disclosure is not limited thereto, and template matching prediction may be performed using templates of various shapes as described in FIG. 35.

[0418] FIG. 36 is a block diagram showing the configuration of an image encoding device according to one embodiment of the present disclosure.

[0419] Referring to FIG. 36, the image encoding device (3600) may include a prediction encoding unit (3610) and a generation unit (3620).

[0420] In one embodiment of the present disclosure, the prediction encoding unit (3610) and the generation unit (3620) may be implemented with at least one processor. In one embodiment of the present disclosure, the video encoding device (3600) may include a memory that stores input and output data of the prediction encoding unit (3610) and the generation unit (3620). The prediction encoding unit (3610) and the generation unit (3620) may operate according to instructions stored in the memory. In one embodiment of the present disclosure, the video encoding device (3600) may include a memory control unit that controls data input and output of the memory.

[0421] In one embodiment of the present disclosure, the prediction encoding unit (3610) may correspond to the prediction encoding unit (1915) illustrated in FIG. 19. In one embodiment of the present disclosure, the generation unit (3620) may correspond to the entropy encoding unit (1925) illustrated in FIG. 19.

[0422] The prediction encoding unit (3610) can determine the prediction mode of the current block. The current block can include at least one of a maximum coding unit, an encoding unit, a transformation unit, or a prediction unit segmented from the current image to be encoded. In one embodiment of the present disclosure, the prediction mode of the current block can include at least one of an intra mode, an inter mode, a combined mode, a geometric segmentation mode, a block copy mode, or a template matching prediction mode.

[0423] In one embodiment of the present disclosure, the intra mode may include a planar mode (Intra_Planar), a DC mode (Intra_DC), directional modes (Intra_Angular2.. Intra_Angular66), and wide directional modes (Intra_Wide_Angular) of numbers -14 to -1 and numbers 67 to 80. In one embodiment of the present disclosure, the planar mode may refer to a mode that determines a prediction sample based on a weighted average value according to the distance of a left reference sample, an upper reference sample, a lower-left sample, and an upper-right sample of a current block. In one embodiment of the present disclosure, the DC mode may refer to a mode that determines an average value of reference samples as a prediction sample. In one embodiment of the present disclosure, in the directional modes, the positions of reference samples for generating prediction samples of samples within a current block may be identified by considering the direction indicated by the intra directional modes. The wide directional modes may be used to identify reference samples of samples within a non-square current block. In one embodiment of the present disclosure, the prediction encoding unit (3610) may determine one of the wide directional modes as the intra prediction mode of the current non-square block. The number and types of intra prediction modes available to the prediction encoding unit (3610) in the intra mode according to one embodiment of the present disclosure may be set in various ways.

[0424] In one embodiment of the present disclosure, the prediction encoding unit (3610) may determine an intra prediction mode using MPM (most probable modes). The prediction encoding unit (3610) may determine whether to use MPM. The generation unit (3620) may generate a bitstream including information related to whether to use MPM. The prediction encoding unit (3610) may determine a candidate mode list. The prediction encoding unit (3610) may determine the candidate mode list based on the intra mode of the upper block of the current block and the intra mode of the left block. The prediction encoding unit (3610) may determine one of the candidate mode lists as the intra prediction mode of the current block. The prediction encoding unit (3610) may generate a bitstream including information indicating the intra prediction mode of the current block from the candidate mode list.

[0425] In one embodiment of the present disclosure, the prediction encoding unit (3610) may determine an intra prediction mode using a template. The prediction encoding unit (3610) may determine a template of a current block. The template of the current block may include a left sample, an upper left sample, and / or an upper sample of the current block. The prediction encoding unit (3610) may determine surrounding samples of the template of the current block. The surrounding samples of the template may include a left sample, an upper left sample, and / or an upper sample of the template. The prediction encoding unit (3610) may perform prediction on the template using the surrounding samples of the template as reference samples. The prediction encoding unit (3610) may compare the predicted template with the template of the reconstructed current block to determine an intra mode for the reference block. The prediction encoding unit (3610) may determine an intra mode with the smallest error between the predicted template and the template of the reconstructed current block as the intra mode for the reference block. In one embodiment of the present disclosure, the process of determining an intra prediction mode by the prediction encoding unit (3610) performing prediction on a template may be referred to as template-based intra mode derivation (TIMD).

[0426] In one embodiment of the present disclosure, the prediction encoding unit (3610) can infer an intra prediction mode of the current block using surrounding samples of the current block. The prediction encoding unit (3610) can determine a slope using the surrounding samples of the current block. The prediction encoding unit (3610) can determine a plurality of 3 x 3 blocks adjacent to the current block. The prediction encoding unit (3610) can obtain horizontal variations and vertical variations of samples included in each of the determined 3 x 3 blocks. The prediction encoding unit (3610) can determine a slope based on the horizontal variations and vertical variations. The prediction encoding unit (3610) can determine the horizontal variations and vertical variations using a Sobel filter. The prediction encoding unit (3610) can determine an intra prediction mode corresponding to the slope. The prediction encoding unit (3610) can determine the intra prediction mode of the current block based on a plurality of intra prediction modes determined for the plurality of 3 x 3 blocks. In one embodiment of the present disclosure, the prediction encoding unit (3610) may determine the intra prediction mode that is most frequently determined as the intra prediction mode of the current block. In one embodiment of the present disclosure, the prediction encoding unit (3610) may determine the size based on the horizontal variation and the vertical variation. The prediction encoding unit (3610) may determine the intra prediction mode of the current block based on the size. The prediction encoding unit (3610) may determine the weight of the intra prediction mode corresponding to the slope as the size. For example, the prediction encoding unit (3610) may increase the weight of the intra prediction mode determined based on the slope as the horizontal variation and the vertical variation increase. The prediction encoding unit (3610) may determine the intra prediction mode of the current block based on the result in which the weight determined according to the size is reflected.In one embodiment of the present disclosure, the process by which the prediction encoding unit (3610) determines an intra prediction mode based on a slope may be referred to as decoder side intra mode derivation (DIMD).

[0427] In one embodiment of the present disclosure, the block copy mode may include an intra block copy mode. In one embodiment, the block copy mode may include an intra block copy mode. In one embodiment, the intra block copy mode may be a sub-mode of the intra mode, but is not limited thereto, and may represent a mode separate from the intra mode. In one embodiment, the template matching prediction mode may include a template matching intra prediction mode. The combined mode may include a Combined Inter-Intra Prediction (CIIP) mode that performs prediction by combining prediction according to the intra mode and prediction according to the inter mode. The geometric partitioning mode may include a mode that partitions to include directionality within a block. The geometric partitioning mode may perform prediction using inter prediction or intra prediction for each of the divided regions that are blocked.

[0428] In one embodiment of the present disclosure, when the prediction mode of the current block is the CIIP mode, the prediction encoding unit (3610) can perform prediction on the current block by combining inter prediction and intra prediction. For example, the prediction encoding unit (3610) can perform intra prediction according to the Planar mode. For example, the prediction encoding unit (3610) can determine a motion vector of a reference block for the current block. The prediction encoding unit (3610) can perform inter prediction using the motion vector. The prediction encoding unit (3610) can predict the current block using a weighted sum of a prediction block according to inter prediction and a prediction block according to intra prediction. The weight can be determined based on whether a block adjacent to the current block was intra-predicted (or inter-predicted).

[0429] In one embodiment of the present disclosure, when the prediction mode of the current block is a geometric segmentation mode, the prediction encoding unit (3610) can perform prediction by segmenting the current block. The prediction encoding unit (3610) can determine a segmentation angle and a segmentation distance for a boundary at which segmentation is performed within the current block. The prediction encoding unit (3610) can segment the current block based on the segmentation angle and the segmentation distance. The prediction encoding unit (3610) can predict the current block by performing inter prediction or intra prediction on each of the segmented regions within the current block. The prediction encoding unit (3610) can (i) perform intra prediction on both segmented regions, (ii) perform inter prediction on one region and intra prediction on the other region, or (iii) perform inter prediction on both segmented regions.

[0430] In one embodiment of the present disclosure, when the prediction mode of the current block is the template matching prediction mode, the prediction encoding unit (3610) can reconstruct the current block using a reference block. The generation unit (3620) can generate information related to whether the template matching prediction mode is used. The prediction encoding unit (3610) can determine whether the template matching prediction mode is used based on the acquired information. The reference block can be determined based on at least one of a region included in the current image or a region included in a previously decoded image. In one embodiment of the present disclosure, the prediction encoding unit (3610) can determine the reference block using a cost function. The cost function can include at least one of a sum of absolute difference (SAD), a sum of squared difference (SSD), a sum of absolute transformed difference (SATD), a sum of squared error (SSE), or a mean removed SAD (MR-SAD). For example, the prediction encoding unit (3610) can determine the error between templates using at least one cost function among SAD, SATD, SSE, and MR-SAD. When the cost function is SAD, the prediction encoding unit (3610) can determine the error based on the sum of the absolute values ​​of the differences between each sample of the template of the current block and each sample of the template of the candidate block. When the cost function is SSD, the prediction encoding unit (3610) can determine the error based on the sum of the squares of the differences between each sample of the template of the current block and each sample of the template of the candidate block. The cost function may include a function representing the number of identical samples. The prediction encoding unit (3610) can determine a block with a small error among the candidate blocks as a reference block. The prediction encoding unit (3610) can determine a prediction block by performing template matching intra prediction on the current image.In the present disclosure, the process of determining a reference block for a current block using a template may be referred to as template matching (TM). In the present disclosure, performing a prediction for a current block based on template matching may be referred to as template matching prediction (TMP) or intra-template matching prediction (ITEM).

[0431] In one embodiment of the present disclosure, the prediction encoding unit (3610) can determine the intra prediction mode of the current block when the prediction mode of the current block is the intra mode.

[0432] In one embodiment of the present disclosure, the prediction encoding unit (3610) can determine information about a block vector representing a reference block when the prediction mode of the current block is a block copy mode.

[0433] In one embodiment of the present disclosure, the prediction encoding unit (3610) may perform intra prediction or inter prediction on the current block according to the prediction mode of the current block, and may encode the current block using a prediction block generated as a result of performing intra prediction or inter prediction.

[0434] In one embodiment of the present disclosure, when the prediction mode of the current block is block copy mode, the prediction encoding unit (3610) can determine a prediction block from a reference block. For example, the prediction encoding unit (3610) can determine a prediction block that is identical to the reference block or by performing filtering on the reference block. The reference block can be determined based on at least one of a region included in the current image or a region included in a previously decoded image.

[0435] In one embodiment of the present disclosure, when the prediction mode of the current block is a template matching prediction mode, the prediction encoding unit (3610) can reconstruct the current block using a reference block. The prediction encoding unit (3610) can determine a prediction block using the reference block.

[0436] The predictive encoding unit (3610) can perform deblocking filtering. The deblocking filter can improve image quality by smoothing edges between blocks.

[0437] The prediction encoding unit (3610) may perform filtering on samples of the current block on which deblocking filtering has been performed using a Sample Adaptive Offset (SAO) filter and / or a Bilateral Filter (BIF). The SAO filter and BIF may improve image quality by reducing the error between the restored image and the original image. The SAO filter and BIF may perform filtering on a sample-by-sample basis.

[0438] The predictive encoding unit (3610) can perform filtering using an adaptive loop filter (ALF). ALF can improve image quality by reducing the error between the restored image and the original image. ALF can perform filtering on a block-by-block basis.

[0439] In one embodiment of the present disclosure, encoding of a current block may refer to a process of generating information that enables an image decoding device (2000) to restore the current block. The information generated through encoding may be included in a bitstream.

[0440] In one embodiment of the present disclosure, the prediction encoding unit (3610) may generate residual data corresponding to the difference between the predicted block and the current block. If the predicted block is determined to be the current block, residual data may not be generated.

[0441] The generation unit (3620) can generate a bitstream including the encoding result of the image. The bitstream can include the encoding result for the current block.

[0442] In one embodiment of the present disclosure, the generation unit (3620) can generate a bitstream including information about a block vector representing a reference block when the prediction mode of the current block is a block copy mode.

[0443] In one embodiment of the present disclosure, the generation unit (3620) can transmit the bitstream to the image decoding device (2000) via a network.

[0444] In one embodiment of the present disclosure, the generation unit (3620) may store the bitstream in a data storage medium including at least one of a magnetic medium such as a hard disk, a floppy disk, and a magnetic tape, an optical recording medium such as a CD-ROM and a DVD, or a magneto-optical medium such as a floptical disk.

[0445] The generation unit (3620) can generate a bitstream including syntax elements generated through encoding of an image. Values ​​corresponding to the syntax elements can be included in the bitstream according to the hierarchical structure of the image.

[0446] The generation unit (3620) can obtain bins included in the bitstream by entropy encoding syntax elements.

[0447] In one embodiment of the present disclosure, the bitstream may include information about a prediction mode of a current block within a current image.

[0448] In one embodiment of the present disclosure, when the prediction mode of the current block is an intra mode, the bitstream may include information indicating the intra prediction mode of the current block.

[0449] In a prediction mode (e.g., intra mode) that uses reference samples included in a current image, a prediction block of the current block can be generated based on the surrounding samples of the current block according to the intra prediction mode, assuming that there will be continuity between the surrounding samples of the current block and the samples within the current block. The prediction encoding unit (3610) according to an embodiment of the present disclosure can use not only the surrounding samples of the current block included in the current image but also the spatial reference samples included in the current image for intra prediction. When using samples reconstructed before the current block, the size of the residual data can be reduced by predicting the samples of the current block using not only the samples immediately adjacent to the current block but also samples far from the current block. In an embodiment of the present disclosure, the image encoding apparatus (3600) performs intra prediction using a reference block including unreconstructed samples, thereby increasing the range of an area that can be determined as a reference block. The image encoding apparatus (3600) according to an embodiment of the present disclosure can improve compression efficiency by increasing the efficiency of intra prediction.

[0450] In a prediction mode (e.g., inter mode) that utilizes reference samples included in a reference image rather than the current image, a prediction block of the current block can be generated based on a reference block (or reference sample) of the reference image according to the prediction mode, under the assumption that there will be continuity between the current image and the reference image. An image encoding device (3600) according to an embodiment of the present disclosure can improve compression efficiency by increasing the efficiency of intra prediction.

[0451] The video encoding device (3600) can improve prediction accuracy by considering both reference blocks (or reference samples) included in the current image and reference blocks (or reference samples) included in images other than the current image. The video encoding device (3600) according to one embodiment of the present disclosure can improve prediction accuracy by considering both the current image and images other than the current image.

[0452] FIG. 37 is a flowchart of an image encoding method according to one embodiment of the present disclosure.

[0453] In one embodiment of the present disclosure, the image encoding method may be performed by the image encoding device (3600). For example, the image encoding device (3600) may perform each step of the image encoding method by having the processor of the image encoding device (3600) execute at least one instruction contained in a memory.

[0454] In step S3710, the video encoding device (3600) can perform prediction on the current block according to inter prediction. The video encoding device (3600) can obtain a reference block included in a reference image. The video encoding device (3600) can obtain the reference block based on a motion vector of the current block. The video encoding device (3600) can perform inter prediction based on the reference block to obtain a prediction sample of the current block.

[0455] The video encoding device (3600) can obtain one or more reference blocks corresponding to one or more motion vectors of a current block. In one embodiment of the present disclosure, the current block may be a block included in a bi-predictive (B) picture (or B slice). Inter prediction may be performed on a block included in a B picture (or B slice) according to at most two motion vectors and a reference index. When the current block is included in a B picture or a B slice, the video encoding device (3600) can obtain two reference blocks corresponding to two motion vectors of the current block. In one embodiment of the present disclosure, the current block may be a block included in a predictive (P) picture (or P slice). Inter prediction may be performed on a block included in a P picture (or P slice) according to at most one motion vector and a reference index. If the current block is included in a P picture or P slice, the video encoding device (3600) can obtain one reference block corresponding to one motion vector of the current block.

[0456] In step S3720, the image encoding device (3600) may determine an intra mode for the reference block based on at least one of a peripheral sample of the reference block, an internal sample of the reference block, or a peripheral sample of the current block. The image encoding device (3600) may determine the intra mode for the reference block based on temporal information or spatial information of the current block. The temporal information may include information about an image other than the current image including the current block. The spatial information may include information about the current image including the current block.

[0457] In one embodiment of the present disclosure, a reference block may include a block used for inter prediction of a current block. In one embodiment, the surrounding samples of the reference block (or current block) may include adjacent samples and / or non-adjacent samples of the reference block (or current block). The surrounding samples of the reference block may include a left sample, an upper-left sample, and an upper sample of the reference block.

[0458] In one embodiment of the present disclosure, the image encoding device (3600) can determine an intra mode for a reference block based on surrounding samples of the reference block and internal samples of the reference block. The image encoding device (3600) can determine an intra mode for the reference block based on a result of predicting an internal sample of the reference block using the surrounding samples of the reference block. According to one embodiment of the present disclosure, the process of the image encoding device (3600) determining an intra mode for the reference block based on the surrounding samples of the reference block and the internal samples of the reference block corresponds to the process of determining an intra mode for the reference block of the image decoding device (2000) described with reference to FIGS. 22 to 24 and FIGS. 29 to 30.

[0459] In one embodiment of the present disclosure, the image encoding device (3600) can determine an intra mode for a reference block based on internal samples of the reference block. The image encoding device (3600) can determine an intra mode for the reference block based on a plurality of slopes determined for the internal samples of the reference block. According to one embodiment of the present disclosure, the process of the image encoding device (3600) determining an intra mode for the reference block based on the internal samples of the reference block corresponds to the process of determining an intra mode for the reference block of the image decoding device (2000) described with reference to FIGS. 25 to 28 and FIGS. 33 to 34.

[0460] In one embodiment of the present disclosure, the video encoding device (3600) can determine an intra mode for a reference block using surrounding samples of the current block. The surrounding samples of the current block may be samples included in a template area of ​​the current block. According to one embodiment of the present disclosure, the process of the video encoding device (3600) determining an intra mode for a reference block based on surrounding samples of the current block corresponds to the process of determining an intra mode for a reference block of the video decoding device (2000) described with reference to FIGS. 33 and 34.

[0461] In one embodiment of the present disclosure, the image encoding device (3600) may determine one of two intra modes obtained from two reference blocks as an intra mode for the reference block. The image encoding device (3600) may determine two intra modes from each of the two reference blocks, and determine one of the two determined intra modes as an intra mode for the reference block. Alternatively, the image encoding device (3600) may determine a virtual intra mode by referring to both reference blocks.

[0462] In step S3730, the video encoding device (3600) may determine a transform kernel using the intra mode for the reference block. The video encoding device (3600) may determine a transform kernel set including a plurality of transform kernels corresponding to the intra mode for the reference block. The video encoding device (3600) may determine the type of the transform kernel set according to the intra mode for the reference block. For example, it may correspond to one of the plurality of transform kernel sets according to the range of the directional index of the intra mode for the reference block. The transform kernel set may include a plurality of transform kernels. For example, a first transform kernel set may include a first transform kernel and a second transform kernel, and a second transform kernel set may include a third transform kernel and a fourth transform kernel. In one embodiment, one or more (e.g., N, where N is 1 or more) transform kernel sets exist depending on the type of transform, and each transform kernel set may include one or more (e.g., M, where M is 1 or more) transform kernels.

[0463] In one embodiment of the present disclosure, the number of transform kernels included in each transform kernel set may be determined based on the sum of transform coefficients. For example, when the sum of transform coefficients is less than a predetermined first value, the number of transform kernels may be N1 (e.g., N1 = 1), when the sum of transform coefficients is greater than the predetermined first value and less than a predetermined second value, the number of transform kernels may be N2 (e.g., N1 = 4), and when the sum of transform coefficients is greater than the predetermined second value, the number of transform kernels may be N3 (e.g., N1 = 6).

[0464] In one embodiment of the present disclosure, the video encoding device (3600) may determine a set of transform kernels based on the size of the current block and the intra mode for the reference block. The set of transform kernels may be predetermined based on the size of the current block. For example, the set of transform kernels may be predetermined, M in number, for each size of the current block.

[0465] The video encoding device (3600) may select one of a plurality of transform kernels as the transform kernel of the current block. The video encoding device (3600) may determine one of a plurality of transform kernels included in a transform kernel set. In one embodiment of the present disclosure, the video encoding device (3600) may generate a bitstream including index information indicating the transform kernel of the current block among the plurality of transform kernels.

[0466] In one embodiment of the present disclosure, the transform kernel may be at least one of a kernel for a first transform, a kernel for a second transform, or a non-separable first transform kernel combining a first transform and a second transform.

[0467] In one embodiment of the present disclosure, the video encoding device (3600) may determine a transform kernel for a primary transform using an intra mode for a reference block. The transform kernel for the primary transform may include a Discrete Cosine Transform (DCT) kernel and / or a Discrete Sine Transform (DST) kernel. The primary transform may be applied to a vertical direction and / or a horizontal direction of a block. The video encoding device (3600) may generate a bitstream including information indicating whether the primary transform is a vertical transform or a horizontal transform. The primary transform may be referred to as a Multi Transform Selection (MTS). The transform kernel for the primary transform may be referred to as a core transform kernel.

[0468] In one embodiment of the present disclosure, the image encoding device (3600) may determine a transform kernel for a secondary transform using an intra mode for a reference block. The secondary transform may be applied only to a portion of the residual signal on which the primary transform has been performed. For example, the secondary transform may be performed only on a left area or an upper left area of ​​the block. The secondary transform is not performed separately in the vertical and horizontal directions. The secondary transform may be referred to as a low frequency non-separable transform (LFNST).

[0469] In one embodiment of the present disclosure, the video encoding device (3600) may determine a transform kernel for a non-separable primary transform by using an intra mode for a reference block. The video encoding device (3600) may not perform a separate secondary transform on a block on which the non-separable primary transform has been performed. The non-separable primary transform may be a form in which the primary transform and the secondary transform are combined. For example, the transform kernel for the non-separable primary transform may be a combination of a transform kernel for the primary transform and a transform kernel for the secondary transform. The non-separable primary transform is not performed separately in the vertical and horizontal directions.

[0470] In step S3740, the image encoding device (3600) can perform transformation on the current block using a transformation kernel. The image encoding device (3600) can perform transformation by applying the selected transformation kernel to the current block. The image encoding device (3600) can obtain transformation coefficients by performing transformation using the transformation kernel.

[0471] The image encoding device (3600) can generate transform coefficients by applying a transform kernel for a primary transform determined on a residual signal (or residual data).

[0472] The image encoding device (3600) can generate transform coefficients by applying a transform kernel for secondary transform to a residual signal on which primary transform has been performed. The image encoding device (3600) can determine whether to perform secondary transform for each block.

[0473] The image encoding device (3600) can generate transform coefficients by applying a transform kernel for a non-separable first-order transform to a residual signal.

[0474] The video encoding device (3600) can determine a set of transform kernels for the current block by determining an intra mode for a reference block when the prediction mode of the current block is the inter mode. The video encoding device (3600) can improve encoding efficiency (or transform efficiency) even when the current block is the inter mode by deriving an intra mode for the reference block indicating internal directionality using an already reconstructed reference block and applying the intra mode for the derived reference block to the current block. That is, the video encoding device (3600) can select an appropriate transform kernel for the current block from among various types of transform kernels, like the intra mode, even when the current block is the inter mode by determining the intra mode for the reference block, thereby increasing the compression efficiency of the image. According to one embodiment of the present disclosure, even when the prediction mode of the current block is the inter mode, a secondary transform and a non-separable primary transform can be applied, and various transform kernels for the primary transform can be applied. By applying a direction-dependent transform kernel, such as a second-order transform, the residuals at the boundary between blocks can be efficiently compressed. However, this effect is merely an example of the invention, and the effects and purposes of the present disclosure are not limited by the disclosed content.

[0475] FIG. 38 is a flowchart of an image encoding method according to one embodiment of the present disclosure.

[0476] In one embodiment of the present disclosure, the image encoding method may be performed by the image encoding device (3600). For example, the image encoding device (3600) may perform each step of the image encoding method by having the processor of the image encoding device (3600) execute at least one instruction contained in a memory.

[0477] In step S3810, the image encoding device (3600) may obtain a reference block of a reference image. In one embodiment of the present disclosure, the reference block may be determined based on a motion vector of the current block. The reference block may include a block used for inter prediction of the current block.

[0478] In step S3820, the image encoding device (3600) can determine an intra mode for the reference block based on at least one of a plurality of surrounding samples and a plurality of internal samples of the reference block.

[0479] In one embodiment of the present disclosure, the surrounding samples of a reference block may include samples located within a predetermined distance from the reference block. The surrounding samples of the reference block may include at least one of adjacent samples and non-adjacent samples of the reference block. The surrounding samples of the reference block may include samples located above, to the left of, and / or to the upper left of the reference block.

[0480] In one embodiment of the present disclosure, the video encoding device (3600) can predict internal samples of a reference block using a plurality of surrounding samples. For example, the video encoding device (3600) can determine prediction samples according to a plurality of intra modes (e.g., intra directional prediction modes 2 to 66, or all possible intra prediction modes) using the surrounding samples of the reference block as reference samples. The video encoding device (3600) can compare the prediction samples with the internal samples of the reference block to determine an error. The video encoding device (3600) can determine an intra mode for the reference block based on the error. For example, the video encoding device (3600) can determine one intra mode with the smallest error among the plurality of intra modes as the intra mode for the reference block.

[0481] In step S3830, the image encoding device (3600) may determine a transform kernel of the current block from among one or more transform kernels using an intra mode for a reference block. In one embodiment of the present disclosure, step S3830 may correspond to step S3730.

[0482] In step S3840, the image encoding device (3600) may perform transformation on the current block using a transformation kernel. In one embodiment of the present disclosure, step S2240 may correspond to step S3740.

[0483] The methods and embodiments proposed in this disclosure may be used individually or in combination in any order. Furthermore, each of the methods (or embodiments), encoders, and decoders may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In one embodiment, one or more processors execute a program stored on a non-transitory computer-readable medium.

[0484] An image encoding device according to an embodiment of the present disclosure can improve encoding efficiency (or transformation efficiency) even when the current block is an inter mode by deriving an intra mode for a reference block indicating internal directionality using an already reconstructed reference block and applying the intra mode for the derived reference block to the current block. That is, by determining the intra mode for the reference block, the image encoding device can select an appropriate transformation kernel for the current block from among various types of transformation kernels, like the intra mode, even when the current block is an inter mode, thereby improving the compression efficiency of the image. Even when the prediction mode of the current block is an inter mode, a secondary transformation and a non-separable primary transformation can be applied, and various transformation kernels for the primary transformation can be applied. By applying a direction-dependent transformation kernel such as a secondary transformation, residual data at the boundary between blocks can be efficiently compressed. However, the technical effects of the image decoding method according to an embodiment of the present disclosure are not limited to the contents described above, and may include technical features generated according to the present disclosure.

[0485] In one embodiment of the present disclosure, a method for decoding an image is provided. The method for decoding an image may include a step of obtaining a reference block in a reference image. The method for decoding an image may include a step of determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of interior samples of the reference block. The method for decoding an image may include a step of determining a transform kernel for a current block from among one or more transform kernels using the intra mode for the reference block. The method for decoding an image may include a step of performing an inverse transform on the current block using the transform kernel.

[0486] In one embodiment of the present disclosure, the one or more transform kernels may include at least one of a first transform kernel associated with Multi Transform Selection (MTS), a second transform kernel associated with a Low Frequency Non-Separable Transform (LFNST), or a third transform kernel associated with a Non-separable primary transform (NSPT).

[0487] In one embodiment of the present disclosure, the step of determining an intra mode for a reference block may include performing intra prediction according to one or more intra prediction modes using a plurality of surrounding samples. The step of determining the intra mode for the reference block may include determining the intra mode for the reference block based on an error between intra-predicted samples and internal samples of the reference block.

[0488] In one embodiment of the present disclosure, the step of determining an intra mode for a reference block may include the step of determining a plurality of gradients using a plurality of internal samples of the reference block. The step of determining an intra mode for the reference block may include the step of determining a plurality of directional intra modes corresponding to the plurality of gradients. The step of determining an intra mode for the reference block may include the step of selecting an intra mode for the reference block from among the determined plurality of directional intra modes.

[0489] In one embodiment of the present disclosure, the step of determining an intra mode for a reference block may include the step of determining a first candidate intra mode based on at least one of a plurality of surrounding samples of the reference block and a plurality of interior samples of the reference block. The step of determining the intra mode for the reference block may include the step of determining a second candidate intra mode based on at least one of a plurality of surrounding samples of a second reference block of the current block and a plurality of interior samples of the second reference block. The step of determining the intra mode for the reference block may include the step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block.

[0490] In one embodiment of the present disclosure, the step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include determining a first error by performing prediction on a plurality of internal samples of the reference block using a plurality of peripheral samples of the reference block according to the first candidate intra mode. The step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include determining a second error by performing prediction on a plurality of internal samples of the second reference block using a plurality of peripheral samples of the second reference block according to the second candidate intra mode. The step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include determining an intra mode for the reference block from among the first candidate intra mode and the second candidate intra mode based on the first error and the second error.

[0491] In one embodiment of the present disclosure, the step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include the step of obtaining a first quantization parameter of the reference block and a second quantization parameter of the second reference block. The step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include the step of selecting the second candidate intra mode as the intra mode for the reference block when the first quantization parameter is greater than or equal to the second quantization parameter. The step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include the step of selecting the first candidate intra mode as the intra mode for the reference block when the first quantization parameter is less than the second quantization parameter.

[0492] In one embodiment of the present disclosure, the step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include the step of obtaining a first POC value of the reference image and a second POC value of the second reference image. The step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include the step of selecting the first candidate intra mode as the intra mode for the reference block when a difference between the POC value of the current image and the first POC value is less than a difference between the POC value of the current image and the second POC value. The step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the reference block may include the step of selecting the second candidate intra mode as the intra mode for the reference block when a difference between the POC value of the current image and the first POC value is greater than or equal to a difference between the POC value of the current image and the second POC value.

[0493] In one embodiment of the present disclosure, the step of selecting one of the first candidate intra mode and the second candidate intra mode as the intra mode for the refere...

Claims

1. In the video decryption method, A step of obtaining a reference block in a reference image; A step of determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block; A step of determining a transformation kernel of a current block among one or more transformation kernels using an intra mode for the above reference block; and A method comprising the step of performing an inverse transformation on a current block using the above transformation kernel.

2. In paragraph 1, A method wherein the one or more transform kernels include at least one of a first transform kernel associated with Multi Transform Selection (MTS), a second transform kernel associated with a Low Frequency Non-Separable Transform (LFNST), or a third transform kernel associated with a Non-separable primary transform (NSPT).

3. In any one of paragraphs 1 and 2, The step of determining the intra mode for the above reference block is: A step of performing intra prediction according to one or more intra prediction modes using the plurality of surrounding samples; and A method comprising the step of determining an intra mode for the reference block based on an error between the intra predicted samples and internal samples of the reference block.

4. In any one of paragraphs 1 to 3, The step of determining the intra mode for the above reference block is: A step of determining a plurality of slopes using a plurality of internal samples of the above reference block; a step of determining a plurality of directional intra modes corresponding to the plurality of slopes; and A method comprising the step of selecting an intra mode for the reference block from among the determined plurality of directional intra modes.

5. In any one of paragraphs 1 to 4, The step of determining the intra mode for the above reference block is: A step of determining a first candidate intra mode based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block; determining a second candidate intra mode based on at least one of a plurality of surrounding samples of a second reference block of the current block and a plurality of internal samples of the second reference block; and A method comprising the step of selecting one of the first candidate intra mode and the second candidate intra mode as an intra mode for a reference block.

6. In paragraph 5, The step of selecting one of the first candidate intra mode and the second candidate intra mode as an intra mode for a reference block is: A step of determining a first error by performing a prediction on a plurality of internal samples of the reference block using a plurality of surrounding samples of the reference block according to the first candidate intra mode; A step of determining a second error by performing a prediction on a plurality of internal samples of the second reference block using a plurality of surrounding samples of the second reference block according to the second candidate intra mode; and A method comprising the step of determining an intra mode for the reference block among the first candidate intra mode and the second candidate intra mode based on the first error and the second error.

7. In any one of paragraphs 5 to 6, The step of selecting one of the first candidate intra mode and the second candidate intra mode as an intra mode for a reference block is: A step of obtaining a first quantization parameter of the above reference block and a second quantization parameter of the above second reference block; a step of selecting the second candidate intra mode as the intra mode for the reference block when the first quantization parameter is greater than or equal to the second quantization parameter; and A method comprising the step of selecting the first candidate intra mode as the intra mode for the reference block when the first quantization parameter is smaller than the second quantization parameter.

8. In any one of paragraphs 5 to 7, The step of selecting one of the first candidate intra mode and the second candidate intra mode as an intra mode for a reference block is: A step of obtaining a first POC value of the above reference image and a second POC value of the second reference image; a step of selecting the first candidate intra mode as the intra mode for the reference block when the difference between the POC value of the current image and the first POC value is smaller than the difference between the POC value of the current image and the second POC value; and A method comprising the step of selecting the second candidate intra mode as the intra mode for the reference block if the difference between the POC value of the current image and the first POC value is greater than or equal to the difference between the POC value of the current image and the second POC value.

9. In any one of paragraphs 5 to 8, The step of selecting one of the first candidate intra mode and the second candidate intra mode as an intra mode for a reference block is: A step of obtaining bi-prediction weights for the above reference block and the second reference block; a step of selecting the first candidate intra mode as the intra mode for the reference block if the weight for the reference block is greater than or equal to the weight for the second reference block; and A method comprising the step of selecting the second candidate intra mode as the intra mode for the reference block if the weight for the reference block is less than the weight for the second reference block.

10. In any one of paragraphs 5 to 9, The step of selecting one of the first candidate intra mode and the second candidate intra mode as an intra mode for a reference block is: If the type of the slice including the reference block is an I slice, selecting the first candidate intra mode as the intra mode for the reference block; and A method comprising the step of selecting the second candidate intra mode as an intra mode for the reference block, when the type of the slice including the second reference block is an I slice.

11. In any one of paragraphs 1 to 10, The step of determining the intra mode for the above reference block is: A step of determining a first plurality of slopes using a plurality of internal samples of the above reference block; A step of determining a second plurality of slopes using a plurality of internal samples of a second reference block of a second reference image different from the above-mentioned reference image; A step of determining a plurality of directional intra modes corresponding to the first plurality of slopes and the second plurality of slopes; and A method comprising the step of determining an intra mode for the reference block from among the determined plurality of directional intra modes.

12. In a video decoding device, Memory that stores one or more instructions; and comprising at least one processor comprising processing circuitry; The at least one processor executes the one or more instructions, thereby causing the device to: Obtain the reference block in the reference image, determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block; Using the intra mode for the above reference block, determine the transformation kernel of the current block among one or more transformation kernels, A device that performs inverse transformation on the current block using the above transformation kernel.

13. In a video encoding method, A step of obtaining a reference block in a reference image; A step of determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block; A step of determining a transformation kernel of a current block among one or more transformation kernels using an intra mode for the above reference block; and A method comprising the step of performing a transformation on a current block using the above transformation kernel.

14. In paragraph 13, A method wherein the one or more transform kernels include at least one of a first transform kernel associated with Multi Transform Selection (MTS), a second transform kernel associated with a Low Frequency Non-Separable Transform (LFNST), or a third transform kernel associated with a Non-separable primary transform (NSPT).

15. Step of obtaining a reference block in a reference image; A step of determining an intra mode for the reference block based on at least one of a plurality of surrounding samples of the reference block and a plurality of internal samples of the reference block; A step of determining a transformation kernel of a current block among one or more transformation kernels using an intra mode for the above reference block; and A computer-readable storage medium storing a bitstream encoded by an image encoding method, the method comprising the step of performing a transformation on a current block using the above transformation kernel.

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