Device and method for encoding and decoding image by using intra prediction

Abstract

An image decoding method according to one embodiment may comprise the steps of: deriving an intra prediction mode of an adjacent block on the basis of a plurality of reference sample sets neighboring the adjacent block, if the adjacent block of the current block is a block decoded in a predefined non-regular intra mode; generating an MPM list of the current block by using the derived intra prediction mode of the adjacent block; determining the intra prediction mode of the current block from among intra prediction modes included in the MPM list; and generating a prediction sample of the current block by using the intra prediction mode of the current block.

Description

Device and method for encoding and decoding images using intra prediction

[0001] The present disclosure relates to the field of image encoding and decoding, and more particularly, to a device and method for encoding and decoding an image using intra prediction.

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

[0003] Inter prediction can be a technique for compressing images by removing temporal redundancy between images. Inter prediction can predict blocks in the current image using a reference 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 can be predicted based on the reference block, and the predicted block generated as a result of the prediction can be subtracted from the current block to generate a residual block.

[0004] Standards such as H.264 AVC (Advanced Video Coding) and HEVC (High Efficiency Video Coding) can use the motion vectors of previously encoded blocks adjacent to the current block or blocks included in a previously encoded image as motion vector predictors of the current block to predict the motion vector of the current block. The motion vector difference, which is the difference between the motion vector of the current block and the motion vector predictor, can be signaled to the decoder side through a predetermined method.

[0005] Intra prediction can be a technique for compressing images by removing spatial redundancy within the image. Intra prediction can generate a predicted block based on the surrounding pixels of the current block, depending on the intra prediction mode. Then, the predicted block can be subtracted from the current block to generate a residual block. The intra prediction mode used to generate the predicted block can be signaled to the decoder through a predetermined method.

[0006] The residual block generated through inter-prediction or intra-prediction can be transformed and quantized and then passed to a decoder. The decoder can dequantize and inversely transform the residual block, and combine the predicted block of the current block with the residual block to reconstruct the current block. In certain cases, the decoder can filter the reconstructed current block to remove artifacts within it.

[0007] A method for decoding an image according to one embodiment may include, when a neighboring block of a current block is a block decoded with a predefined non-regular intra mode, deriving an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block.

[0008] A method of decoding an image according to one embodiment may include a step of generating an MPM list of a current block using derived intra prediction modes of surrounding blocks.

[0009] A method for decoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0010] A method of decoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0011] A method of encoding an image according to one embodiment may include, when a neighboring block of a current block is a block encoded in a predefined non-regular intra mode, deriving an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block.

[0012] A method of encoding an image according to one embodiment may include a step of generating an MPM list of a current block using derived intra prediction modes of surrounding blocks.

[0013] A method of encoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block.

[0014] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list.

[0015] A method of encoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0016] A computer-readable recording medium according to one embodiment can record a bitstream including an encoding result of a current block.

[0017] In one embodiment, the encoding result of the current block can be generated by deriving an intra prediction mode of the neighboring block based on a plurality of sets of reference samples neighboring the neighboring block, if the neighboring block of the current block is a block encoded with a predefined non-regular intra mode.

[0018] In one embodiment, the encoding result of the current block can be generated by generating an MPM list of the current block using the derived intra prediction modes of the surrounding blocks.

[0019] In one embodiment, the encoding result of the current block can be generated by determining an intra prediction mode of the current block.

[0020] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list.

[0021] In one embodiment, the encoding result of the current block can be generated by generating a prediction sample of the current block using an intra prediction mode of the current block.

[0022] An image decoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0023] In one embodiment, at least one processor can derive an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block, if the neighboring block of the current block is a block decoded with a predefined non-regular intra mode.

[0024] In one embodiment, at least one processor may generate an MPM list for a current block using derived intra prediction modes of surrounding blocks.

[0025] In one embodiment, at least one processor can determine an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0026] In one embodiment, at least one processor can generate a prediction sample of the current block using an intra prediction mode of the current block.

[0027] An image encoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0028] In one embodiment, at least one processor can derive an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block, if the neighboring block of the current block is a block encoded with a predefined non-regular intra mode.

[0029] In one embodiment, at least one processor may generate an MPM list for a current block using derived intra prediction modes of surrounding blocks.

[0030] In one embodiment, at least one processor can determine an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0031] In one embodiment, at least one processor can generate a prediction sample of the current block using an intra prediction mode of the current block.

[0032] A method of decoding an image according to one embodiment may include a step of deriving an intra prediction mode of a current block based on a plurality of sets of reference samples neighboring the current block, when the mode of the current block is a predefined non-regular intra mode.

[0033] A method of decoding an image according to one embodiment may include a step of determining a set of transform kernels of a current block based on an induced intra prediction mode of the current block.

[0034] A method of decoding an image according to one embodiment may include a step of determining a transform kernel of a current block within a set of transform kernels.

[0035] A method of decoding an image according to one embodiment may include a step of generating a residual sample of a current block by applying a transform kernel of the current block to transform coefficients of the current block.

[0036] A method of encoding an image according to one embodiment may include a step of deriving an intra prediction mode of a current block based on a plurality of sets of reference samples neighboring the current block, when the mode of the current block is a predefined non-regular intra mode.

[0037] A method of encoding an image according to one embodiment may include a step of determining a set of transform kernels of a current block based on an derived intra prediction mode of the current block.

[0038] A method of encoding an image according to one embodiment may include a step of determining a transform kernel of a current block within a set of transform kernels.

[0039] A method of encoding an image according to one embodiment may include a step of generating a transform coefficient of a current block by applying a transform kernel of the current block to residual samples of the current block.

[0040] A computer-readable recording medium according to one embodiment can record a bitstream including an encoding result of a current block.

[0041] In one embodiment, the encoding result of the current block can be generated by deriving an intra prediction mode of the current block based on a plurality of sets of reference samples neighboring the current block, when the mode of the current block is a predefined non-regular intra mode.

[0042] In one embodiment, the encoding result of the current block can be generated by determining a set of transform kernels of the current block based on the derived intra prediction mode of the current block.

[0043] In one embodiment, the encoding result of the current block can be generated by determining a transform kernel of the current block within a set of transform kernels.

[0044] In one embodiment, the encoding result of the current block can be generated by applying the transform kernel of the current block to residual samples of the current block to generate transform coefficients of the current block.

[0045] An image decoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0046] In one embodiment, at least one processor can derive an intra prediction mode of the current block based on a plurality of sets of reference samples neighboring the current block, when the mode of the current block is a predefined non-regular intra mode.

[0047] In one embodiment, at least one processor may determine a set of transform kernels for the current block based on the derived intra prediction mode of the current block.

[0048] In one embodiment, at least one processor may determine a transformation kernel of a current block within a set of transformation kernels.

[0049] In one embodiment, at least one processor can generate a residual sample of the current block by applying a transform kernel of the current block to transform coefficients of the current block.

[0050] A method of decoding an image according to one embodiment may include a step of generating an MPM list of a current block using an intra prediction mode of a surrounding block.

[0051] A method for decoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0052] A method of decoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0053] A method of decoding an image according to one embodiment may include a step of adding an intra prediction mode candidate derived based on a plurality of reference sample sets neighboring a current block to an MPM list.

[0054] A method of encoding an image according to one embodiment may include a step of generating an MPM list of a current block using an intra prediction mode of a surrounding block.

[0055] A method of encoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block.

[0056] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list.

[0057] A method of encoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0058] A method of encoding an image according to one embodiment may include adding an intra prediction mode candidate derived based on a plurality of reference sample sets neighboring a current block to an MPM list.

[0059] A computer-readable recording medium according to one embodiment can record a bitstream including an encoding result of a current block.

[0060] In one embodiment, the encoding result of the current block can be generated by generating an MPM list of the current block using the intra prediction mode of the surrounding blocks.

[0061] In one embodiment, the encoding result of the current block can be generated by determining an intra prediction mode of the current block.

[0062] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list.

[0063] In one embodiment, the encoding result of the current block can be generated by generating a prediction sample of the current block using an intra prediction mode of the current block.

[0064] In one embodiment, the MPM list may include intra prediction mode candidates derived based on a plurality of reference sample sets neighboring the current block.

[0065] An image decoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0066] In one embodiment, at least one processor may generate an MPM list for a current block using intra prediction modes of surrounding blocks.

[0067] In one embodiment, at least one processor can determine an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0068] In one embodiment, at least one processor can generate a prediction sample of the current block using an intra prediction mode of the current block.

[0069] In one embodiment, at least one processor can add an intra prediction mode candidate derived based on a plurality of sets of reference samples neighboring the current block to the MPM list.

[0070] A method of decoding an image according to one embodiment may include a step of generating an MPM list of a current block using an intra prediction mode of a surrounding block.

[0071] A method of decoding an image according to one embodiment may include a step of reordering an MPM list based on a cost value for each intra prediction mode included in the MPM list.

[0072] In one embodiment, the cost value may be calculated based on multiple sets of reference samples neighboring the current block.

[0073] A method of decoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block from among intra prediction modes included in a rearranged MPM list.

[0074] A method of decoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0075] A method of encoding an image according to one embodiment may include a step of generating an MPM list of a current block using an intra prediction mode of a surrounding block.

[0076] A method of encoding an image according to one embodiment may include a step of reordering an MPM list based on a cost value for each of the intra prediction modes included in the MPM list.

[0077] In one embodiment, the cost value may be calculated based on a plurality of sets of reference samples neighboring the current block.

[0078] A method of encoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block.

[0079] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the reordered MPM list.

[0080] A method of encoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0081] A computer-readable recording medium according to one embodiment can record a bitstream including an encoding result of a current block.

[0082] In one embodiment, the encoding result of the current block can be generated by generating an MPM list of the current block using the intra prediction mode of the surrounding blocks.

[0083] In one embodiment, the encoding result of the current block can be generated by reordering the MPM list based on a cost value for each of the intra prediction modes included in the MPM list.

[0084] In one embodiment, the cost value may be calculated based on a plurality of sets of reference samples neighboring the current block.

[0085] In one embodiment, the encoding result of the current block can be generated by determining an intra prediction mode of the current block.

[0086] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the reordered MPM list.

[0087] In one embodiment, the encoding result of the current block can be generated by generating a prediction sample of the current block using an intra prediction mode of the current block.

[0088] An image decoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0089] In one embodiment, at least one processor may generate an MPM list for a current block using intra prediction modes of surrounding blocks.

[0090] In one embodiment, at least one processor can reorder the MPM list based on a cost value for each of the intra prediction modes included in the MPM list.

[0091] In one embodiment, the cost value may be calculated based on multiple sets of reference samples neighboring the current block.

[0092] In one embodiment, at least one processor can determine an intra prediction mode of a current block from among intra prediction modes included in the reordered MPM list.

[0093] In one embodiment, at least one processor can generate a prediction sample of the current block using an intra prediction mode of the current block.

[0094] FIG. 1 is a block diagram of an image decoding device according to one embodiment.

[0095] FIG. 2 is a block diagram of an image encoding device according to one embodiment.

[0096] FIG. 3 illustrates a process of dividing a current encoding unit to determine at least one encoding unit according to one embodiment.

[0097] FIG. 4 illustrates a process of dividing a non-square coding unit to determine at least one coding unit according to one embodiment.

[0098] 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.

[0099] FIG. 6 illustrates a method for determining a predetermined coding unit among an odd number of coding units according to one embodiment.

[0100] 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.

[0101] 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.

[0102] FIG. 9 illustrates a process of dividing a first encoding unit to determine at least one encoding unit according to one embodiment.

[0103] FIG. 10 illustrates that, according to one embodiment, the shapes into which a first encoding unit can be divided are limited when a second encoding unit of a non-square shape determined by splitting the first encoding unit satisfies a predetermined condition.

[0104] 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.

[0105] FIG. 12 illustrates that, according to one embodiment, the processing order between multiple encoding units may vary depending on the division process of the encoding units.

[0106] 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 split to determine a plurality of encoding units according to one embodiment.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] FIG. 17 illustrates various forms of encoding units that can be determined based on segmentation form mode information expressed in binary code according to one embodiment.

[0111] 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.

[0112] FIG. 19 is a block diagram of an image encoding and decoding system that performs loop filtering according to one embodiment.

[0113] FIG. 20 is a block diagram illustrating the configuration of an image decoding device (2000) according to one embodiment.

[0114] FIG. 21 is a diagram illustrating an intra prediction mode according to one embodiment.

[0115] FIG. 22 is a diagram illustrating a method for deriving an intra prediction mode based on a gradient according to one embodiment.

[0116] FIG. 23 is a diagram illustrating a method for generating gradient information according to one embodiment.

[0117] FIG. 24 is a diagram illustrating sample sets required to derive an intra prediction mode according to one embodiment.

[0118] FIGS. 25A and 25B are diagrams illustrating a method for calculating a cost value corresponding to a directional mode of a first group according to one embodiment.

[0119] FIGS. 26A and 26B are diagrams for explaining a method for calculating a cost value corresponding to a directional mode of a second group according to one embodiment.

[0120] FIGS. 27a and 27b are diagrams for explaining a method for calculating a cost value corresponding to a directional mode of a third group according to one embodiment.

[0121] FIG. 28 is a diagram for explaining a method for calculating a cost value corresponding to a horizontal mode according to one embodiment.

[0122] FIG. 29 is a diagram for explaining a method for calculating a cost value corresponding to a vertical mode according to one embodiment.

[0123] FIG. 30 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0124] FIG. 31 is a diagram illustrating peripheral blocks used to generate an MPM list according to one embodiment of the present disclosure.

[0125] FIG. 32 is a diagram illustrating peripheral blocks used to generate an MPM list according to one embodiment of the present disclosure.

[0126] FIG. 33 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0127] FIG. 34 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0128] FIG. 35 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0129] Fig. 36 is a block diagram illustrating a configuration of an image encoding device according to one embodiment.

[0130] Figure 37 is a flowchart of an image encoding method according to one embodiment.

[0131] 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.

[0132] When describing embodiments, detailed descriptions of related known technologies may 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 may correspond to identification symbols used to distinguish one component from another.

[0133] 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.

[0134] 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.

[0135] In the present disclosure, components expressed as "units", "modules", etc. may be two or more components combined into a single component, or a single 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.

[0136] In the present disclosure, 'image' may refer to a picture, a still image, a frame, a moving image composed of a plurality of consecutive still images, or a video.

[0137] In this disclosure, "sample" may refer to data assigned to a sampling location in an image and thus to be processed. For example, a pixel within a frame in a spatial domain may correspond to a sample. A unit containing multiple samples may be defined as a block.

[0138] 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 one embodiment, and an image decoding method and device are disclosed.

[0139] FIG. 1 illustrates a block diagram of an image decoding device (100) according to one embodiment.

[0140] 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.

[0141] 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.

[0142] To describe in detail the operation of the video decoding device (100), the bitstream acquisition unit (110) can receive a bitstream.

[0143] 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.

[0144] Below, the division of encoding units according to one embodiment of the present disclosure is described in detail.

[0145] 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.

[0146] 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.

[0147] 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 the picture and samples of the picture.

[0148] A single maximum coding block (CTB) can be divided into MxN coding blocks containing MxN samples (M, N are integers).

[0149] 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 a 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 a 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 the picture and samples of the picture.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] For example, information about the maximum size of a luma coding block capable of being 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 capable of being split into two. Therefore, by combining the information about the maximum size of a luma coding block capable of being 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.

[0154] 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. In contrast, the maximum size of a 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.

[0155] 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.

[0156] 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.

[0157] 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 will be binary / ternary split.

[0158] 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.

[0159] 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.

[0160] 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).

[0161] 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.

[0162] 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.

[0163] 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.

[0164] The shape and size of the transformation block and the prediction block may be unrelated.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] According to one embodiment, 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.

[0172] 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.

[0173] According to one embodiment, 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.

[0174] Referring to FIG. 3, the image decoding device (100) may determine two coding units (310b) by vertically dividing the current coding unit (300) based on the split shape mode information indicating that the current coding unit (300) is vertically divided, according to an embodiment. The image decoding device (100) may determine two coding units (310c) by horizontally dividing the current coding unit (300) based on the split shape mode information indicating that the current coding unit (300) is horizontally divided, according to an embodiment. The image decoding device (100) may determine four coding units (310d) by vertically and horizontally dividing the current coding unit (300) based on the split shape mode information indicating that the current coding unit (300) is vertically and horizontally divided, according to an embodiment. The image decoding device (100) may determine three coding units (310e) by vertically dividing the current coding unit (300) based on the split shape mode information indicating that the current coding unit (300) is ternary divided, according to an embodiment. The image decoding device (100) can determine three coding units (310f) into which the current coding unit (300) is horizontally divided based on the division shape mode information indicating that the ternary division is horizontally divided. However, the division shapes into which a square coding unit can be divided should not be interpreted as being limited to the above-described shapes, and may include various shapes that can be indicated by the division shape mode information. Specified division shapes into which a square coding unit is divided will be specifically described below through various embodiments.

[0175] 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.

[0176] According to one embodiment, the image decoding device (100) may utilize block shape information indicating that the current encoding unit is non-square. The image decoding device (100) may determine whether to not split the current non-square 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. The predetermined splitting method by which a non-square encoding unit is split will be described in detail through various embodiments below.

[0177] According to one embodiment, the image decoding device (100) may determine a form in which an encoding unit is split using split form mode information, and in this case, the split form mode information may indicate the number of at least one encoding unit generated by splitting the encoding unit. Referring to FIG. 4, when the split form mode information indicates that the current encoding unit (400 or 450) is split into two encoding units, the image decoding device (100) may split the current encoding unit (400 or 450) based on the split form mode information to determine two encoding units (420a, 420b, or 470a, 470b) included in the current encoding unit.

[0178] According to one embodiment, 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.

[0179] According to one embodiment, if the split shape mode information indicates that the coding unit is split into an odd number of blocks (ternary splitting), the image decoding device (100) may determine an odd number of coding units included in the current coding unit (400 or 450). For example, if the split shape mode information indicates that the current coding unit (400 or 450) is split into three coding units, the image decoding device (100) may split the current coding unit (400 or 450) into three coding units (430a, 430b, 430c, 480a, 480b, 480c).

[0180] According to one embodiment, 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 block shape information may be in the horizontal direction because the length of the width is longer than the length of the height. When the ratio of the width and height is 1:4, the block shape information may be in the vertical direction because the length of the width is shorter than the length of the height. 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).

[0181] According to one embodiment, 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.

[0182] According to one embodiment, 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.

[0183] 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.

[0184] According to one embodiment, 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. According to one embodiment, when the split shape mode information indicates splitting the first coding unit (500) in the horizontal direction, 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 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. Hereinafter, the relationship between the first coding unit, the second coding unit, and the third coding unit used may be understood to follow the above-described characteristics.

[0185] According to one embodiment, the image decoding device (100) may determine to split or not split the determined second encoding unit (510) into encoding units based on the split shape mode information. Referring to FIG. 5, the image decoding device (100) may split the first encoding unit (500) based on the split 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 obtain 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, 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.

[0186] Referring to FIG. 5, among the odd number of third coding units (520b, 520c, 520d) determined by splitting the second coding unit (510) having a non-square shape, a predetermined coding unit (e.g., a coding unit located in the middle or a coding unit having a square shape) may be split recursively. According to an embodiment, 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. Methods that can be used for recursive division of coding units will be described later through various embodiments.

[0187] According to one embodiment, the image decoding device (100) may split each of the third encoding units (520a, 520b, 520c, 520d, etc.) into encoding units based on the split shape mode information. In addition, the image decoding device (100) may determine not to split the second encoding unit (510) based on the split shape mode information. According to one embodiment, 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.

[0188] 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).

[0189] According to one embodiment, 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.

[0190] 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.

[0191] 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.

[0192] According to one embodiment, 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 descriptions of such methods will be provided later through various embodiments.

[0193] According to one embodiment, the image decoding device (100) can divide the current encoding unit into a plurality of encoding units and determine an encoding unit at a predetermined position.

[0194] According to one embodiment, 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 divide 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).

[0195] According to one embodiment, 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, 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.

[0196] According to one embodiment, information indicating the position of the sample (630a) at the upper left of the upper encoding unit (620a) may represent (xa, ya) coordinates, information indicating the position of the sample (530b) at the upper left of the middle encoding unit (620b) may represent (xb, yb) coordinates, and information indicating the position of the sample (630c) at the upper left of the lower encoding unit (620c) may represent (xc, yc) coordinates. The image decoding device (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.

[0197] According to one embodiment, the image decoding device (100) may 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) may select an encoding unit (620b) having a different size from among the encoding units (620a, 620b, 620c).

[0198] According to one embodiment, the image decoding device (100) may 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, 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, 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, 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.

[0199] 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).

[0200] According to one embodiment, the image decoding device (100) may determine the width of the left encoding unit (660a) as xe-xd. The image decoding device (100) may determine the height of the left encoding unit (660a) as the height of the current encoding unit (650). According to one embodiment, the image decoding device (100) may determine the width of the middle encoding unit (660b) as xf-xe. The image decoding device (100) may determine the height of the middle encoding unit (660b) as the height of the current encoding unit (600). According to one embodiment, the image decoding device (100) may determine the width or height of the right encoding unit (660c) using the width or height of the current encoding unit (650) and the widths and heights of the left encoding unit (660a) and the middle encoding 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 the 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 the encoding units determined according to predetermined sample coordinates can be used.

[0201] 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.

[0202] According to one embodiment, the image decoding device (100) may select an encoding unit at a predetermined position from among an odd number of encoding units determined by splitting the current encoding unit, taking into consideration the shape of the current encoding unit. For example, if the current encoding unit has a non-square shape in which the width is longer than the height, the image decoding device (100) may determine an encoding unit at a predetermined position in the horizontal direction. That is, the image decoding device (100) may determine one of the encoding units whose positions vary in the horizontal direction and place a restriction on the corresponding encoding unit. If the current encoding unit has a non-square shape in which the height is longer than the width, the image decoding device (100) may determine an encoding unit at a predetermined position in the vertical direction. That is, the image decoding device (100) may determine one of the encoding units whose positions vary in the vertical direction and place a restriction on the corresponding encoding unit.

[0203] According to one embodiment, the image decoding device (100) may use information indicating the positions of each of the even-numbered coding units to determine the coding unit at a predetermined position among the even-numbered coding units. The image decoding device (100) may determine the even-numbered coding units by dividing the current coding unit (binary dividing) and may determine the coding unit at a predetermined position using information about the positions of the even-numbered coding units. A specific process for this may be a process corresponding to the process of determining the coding unit at a predetermined position (e.g., the center position) among the odd-numbered coding units described above in FIG. 6, and thus will be omitted.

[0204] According to one embodiment, 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.

[0205] 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.

[0206] According to one embodiment, 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 device (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 one embodiment, 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 such a 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.

[0207] According to one embodiment, 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, the 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.

[0208] According to one embodiment, when the image decoding device (100) divides the current encoding unit into a plurality of encoding units, the image decoding device (100) may use the split shape mode information to determine the encoding unit at a predetermined position among the plurality of encoding units. According to one embodiment, 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 the 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 the 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.

[0209] According to one embodiment, 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).

[0210] FIG. 7 illustrates the order in which multiple encoding units are processed when an image decoding device (100) divides a current encoding unit to determine multiple encoding units according to one embodiment.

[0211] According to one embodiment, 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).

[0212] 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.

[0213] According to one embodiment, the image decoding device (100) can recursively split the encoding units. Referring to FIG. 7, the image decoding device (100) can split the 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).

[0214] According to one embodiment, 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.

[0215] According to one embodiment, the processing order of the 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 device (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.

[0216] FIG. 8 illustrates a process for 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 invention.

[0217] According to one embodiment, 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, 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).

[0218] According to one embodiment, the image decoding device (100) can determine whether there is an odd number of split encoding units by determining whether the third encoding 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 encoding units (820a, 820b, 820c, 820d, 820e) by recursively splitting the first encoding 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.

[0219] According to one embodiment, the image decoding device (100) may 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 may 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 an embodiment, the image decoding device (100) may place a predetermined restriction on an encoding unit at a predetermined position among the divided encoding units when the encoding unit is divided into an odd number of encoding units. Since the contents of such restrictions or predetermined positions have been described above through various embodiments, a detailed description thereof will be omitted.

[0220] 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.

[0221] According to one embodiment, the image decoding device (100) may 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 may be split into four coding units having a square shape or may 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 non-square coding units, the image decoding device (100) may split the first coding unit (900) into a plurality of non-square coding units. 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.

[0222] According to one embodiment, 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 allows them to 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 units (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, the image decoding device (100) may place a predetermined restriction on an encoding unit at a predetermined position among the divided encoding units when the encoding unit is divided into an odd number of encoding units. Since the contents of such restrictions or predetermined positions, etc. have been described above through various embodiments, a detailed description thereof will be omitted.

[0223] According to one embodiment, the image decoding device (100) can divide the first encoding unit to determine encoding units of various shapes.

[0224] 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.

[0225] FIG. 10 illustrates that, according to one embodiment, 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 splitting a first encoding unit (1000) satisfies a predetermined condition.

[0226] According to one embodiment, 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 split independently. 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, the image decoding device (100) may determine third encoding units (1012a, 1012b) by horizontally dividing the left second encoding unit (1010a) having a non-square shape determined by vertically dividing the first encoding unit (1000). However, when the image decoding device (100) divides the left second encoding unit (1010a) in the horizontal direction, the right second encoding unit (1010b) may be restricted from being horizontally divided in the same direction as the direction in which the left second encoding 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.

[0227] According to one embodiment, 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.

[0228] 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.

[0229] According to one embodiment, 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.

[0230] According to one embodiment, 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.

[0231] 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).

[0232] 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).

[0233] FIG. 12 illustrates that, according to one embodiment, the processing order between multiple encoding units may vary depending on the process of dividing the encoding units.

[0234] According to one embodiment, the image decoding device (100) may 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) may 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 may 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.

[0235] According to one embodiment, 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, 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.

[0236] According to one embodiment, the image decoding device (100) may 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) may 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.

[0237] According to one embodiment, the image decoding device (100) may 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) may 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.

[0238] 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.

[0239] 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.

[0240] According to one embodiment, 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, an encoding unit with an increased depth is expressed as an encoding unit of a lower depth.

[0241] Referring to FIG. 13, according to one embodiment, 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.

[0242] In one embodiment, 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.

[0243] 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.

[0244] According to one embodiment, 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.

[0245] According to one embodiment, 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.

[0246] According to one embodiment, 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 (1312) having a size of N / 2xN. That is, the image decoding device (100) may split the second encoding unit (1312) in the horizontal direction to determine a third encoding unit (1304) having a size of N / 2xN / 2 or a third encoding unit (1324) having a size of N / 2xN / 4, or split the second encoding unit (1312) in the vertical direction and the horizontal direction to determine a third encoding unit (1314) having a size of N / 4xN / 2.

[0247] According to one embodiment, 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 (1322) having a size of NxN / 2. That is, the image decoding device (100) may split the second encoding unit (1322) in the vertical direction to determine a third encoding unit (1304) having a size of N / 2xN / 2 or a third encoding unit (1314) having a size of N / 4xN / 2, or split the second encoding unit (1322) in the vertical direction and the horizontal direction to determine a third encoding unit (1324) having a size of N / 2xN / 4.

[0248] According to one embodiment, the image decoding device (100) may 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 may be split in the vertical direction to determine a first encoding unit (1310) having a size of Nx2N, or may be split in the horizontal direction to determine a first encoding unit (1320) having a size of 2NxN. According to one embodiment, when the depth is determined based on the length of the longest side of the encoding unit, 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 may be the same as the depth of the first encoding unit (1300).

[0249] According to one embodiment, 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.

[0250] 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.

[0251] According to one embodiment, the image decoding device (100) may 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) may 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).

[0252] According to one embodiment, 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).

[0253] According to one embodiment, the image decoding device (100) may split a first encoding unit (1410) having a height greater than its width into a plurality of second encoding units (1412a, 1412b, 1414a, 1414b, 1414c) in a horizontal direction according to the splitting shape mode information. According to one embodiment, the image decoding device (100) may split a first encoding unit (1420) having a width greater than its height into a plurality of second encoding units (1422a, 1422b, 1424a, 1424b, 1424c) in a vertical direction according to the splitting shape mode information.

[0254] According to one embodiment, the depth of the second coding unit (1412a, 1412b, 1414a, 1414b, 1414c. 1422a, 1422b, 1424a, 1424b, 1424c) determined based on the split shape mode information for the first coding unit (1410 or 1420) of a non-square shape may be determined based on the length of the long side. 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.

[0255] 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).

[0256] According to one embodiment, when determining an index (PID) for distinguishing divided coding units, the image decoding device (100) may determine the index based on a size ratio between the coding units when the coding units divided into an odd number are not of the same size. Referring to FIG. 14, among the coding units (1414a, 1414b, 1414c) divided into an odd number, 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 index value. According to one embodiment, 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.

[0257] According to one embodiment, the image decoding device (100) may determine whether the image is divided into a specific split shape based on the value of an index for distinguishing a plurality of coding units that are divided from the current coding unit. Referring to FIG. 14, the image decoding device (100) may divide a first coding unit (1410) having a rectangular shape in which the height is longer than the width, to determine an even number of coding units (1412a, 1412b) or an odd number of coding units (1414a, 1414b, 1414c). The image decoding device (100) may use an index (PID) indicating each coding unit to distinguish each of the plurality of coding units. According to one embodiment, the PID may be obtained from a sample (for example, an upper left sample) at a predetermined position of each coding unit.

[0258] According to one embodiment, the image decoding device (100) may 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, 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) may divide the first coding unit (1410) into three coding units (1414a, 1414b, 1414c). The image decoding device (100) may assign an index to each of the three coding units (1414a, 1414b, 1414c). The image decoding device (100) may 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, 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, 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.

[0259] According to one embodiment, the image decoding device (100) may utilize a predetermined data unit from which recursive division of the encoding unit begins.

[0260] FIG. 15 illustrates that a plurality of encoding units are determined according to a plurality of predetermined data units included in a picture according to one embodiment.

[0261] According to one embodiment, 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.

[0262] In one embodiment, the reference data unit may exhibit a predetermined size and shape. In one embodiment, 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 exhibit a square or non-square shape, and may be subsequently divided into an integer number of coding units.

[0263] According to one embodiment, the video decoding device (100) can divide the current picture into a plurality of reference data units. According to one embodiment, the video decoding device (100) can divide the plurality of reference data units into which the current picture is divided using division type mode information for each reference data unit. This division process of the reference data units can correspond to a division process using a quad-tree structure.

[0264] According to one embodiment, the image decoding device (100) may predetermine the minimum size that a reference data unit included in the current picture may have. Accordingly, the image decoding device (100) may determine reference data units of various sizes having a size greater than or equal to the minimum size, and may determine at least one encoding unit using segmentation mode information based on the determined reference data unit.

[0265] 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, 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.

[0266] According to one embodiment, 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.

[0267] According to one embodiment, the image decoding device (100) may use an index for identifying the size and shape of the reference coding unit 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.

[0268] According to one embodiment, the image decoding device (100) may use at least one reference coding unit included in one maximum coding unit. That is, a maximum coding unit for dividing an image may include at least one reference coding unit, and a coding unit may be determined through a recursive splitting process of each reference coding unit. According to one embodiment, at least one of the width and the height of the maximum coding unit 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, the size of the reference coding unit may be a size obtained by splitting the maximum coding unit n times according to a quad tree structure. That is, the image decoding device (100) may split the maximum coding unit n times according to the quad tree structure to determine the reference coding unit, and may split the reference coding unit based on at least one of block shape information and split shape mode information according to various embodiments.

[0269] According to one embodiment, the video decoding device (100) may obtain and use block shape information indicating the shape of the current encoding unit or split shape mode information indicating a method of splitting the current encoding unit from the bitstream. The split shape mode information may be included in a bitstream related to various data units. For example, the video decoding device (100) may 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) may 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.

[0270] Hereinafter, a method for determining a partitioning rule according to one embodiment of the present disclosure will be described in detail.

[0271] 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.

[0272] 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).

[0273] The shape of the encoding unit may include a square and a non-square. 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.

[0274] 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.

[0275] 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.

[0276] 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.

[0277] 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.

[0278] 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.

[0279] 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.

[0280] 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.

[0281] 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.

[0282] According to one embodiment, 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., sequence, picture, slice, slice segment, tile, 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) of 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.

[0283] 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.

[0284] According to one embodiment, 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.

[0285] 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.

[0286] According to one embodiment, when the image decoding device (100) can divide a square-shaped encoding unit into four square encoding units by horizontally and vertically splitting the encoding unit, there may be four types of splitting modes that the splitting mode information for the square encoding unit can indicate. According to one embodiment, the splitting mode information may be expressed as a two-digit binary code, and a binary code may be assigned to each splitting mode. For example, when the encoding unit is not split, the splitting mode information may be expressed as (00)b, when the encoding unit is split in the horizontal direction and the vertical direction, the splitting mode information may be expressed as (01)b, when the encoding unit is split in the horizontal direction, the splitting mode information may be expressed as (10)b, and when the encoding unit is split in the vertical direction, the splitting mode information may be expressed as (11)b.

[0287] According to one embodiment, 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. 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.

[0288] According to one embodiment, 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 partition shapes of the non-square coding unit indicated by the partition shape mode information should not be interpreted as being limited to only the three shapes illustrated in FIG. 17, but should be interpreted as various shapes including the above-described embodiments.

[0289] 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.

[0290] 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.

[0291] In one embodiment, block shape information or segmentation shape mode information may be expressed using binary code, and such information may be directly generated as a bitstream. Furthermore, block shape information or segmentation shape mode information that may be expressed using binary code may not be directly generated as a bitstream, but may instead be used as a binary code input into CABAC (context adaptive binary arithmetic coding).

[0292] According to one embodiment, the image 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 image 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, the image 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 image 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.

[0293] According to one embodiment, 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. 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.

[0294] According to one embodiment, the image decoding device (100) may, in the process of determining the syntax, update the probability for the bins used in the process of decoding the bins of the empty string for the syntax, and the image decoding device (100) may determine that certain bits among the empty strings have the same probability without updating the probability.

[0295] 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, the image decoding device (100) can decode the bin by considering that the probability that the second bin is 0 or 1 when the first bin for the partition shape mode information is 1 is the same probability.

[0296] According to one embodiment, the image decoding device (100) may use 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, 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, 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, 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.

[0297] According to one embodiment, the image decoding device (100) may determine that the bin probability for the segmentation shape mode information is the same for encoding units of a predetermined size or larger. For example, the bin probability for the segmentation 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.

[0298] According to one embodiment, 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).

[0299] Figure 19 is a block diagram of an image encoding and decoding system that performs loop filtering.

[0300] 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).

[0301] In the encoding unit (1910), the prediction encoding unit (1915) outputs prediction data through inter prediction and intra prediction, and the transformation and quantization unit (1920) outputs quantized transformation coefficients of residual data between the prediction data and the current input image. The entropy encoding unit (1925) encodes and transforms the quantized transformation coefficients and outputs them as a bitstream. The quantized transformation coefficients are restored to spatial domain data through the inverse quantization and inverse transformation unit (1930), and the restored spatial domain data are output as a restored image through the deblocking filtering unit (1935) and the loop filtering unit (1940). The restored image can be used as a reference image of the next input image through the prediction encoding unit (1915).

[0302] 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).

[0303] 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).

[0304] The various embodiments described above describe operations related to the image decoding method performed by the image decoding device (100). Hereinafter, the operations of the image encoding device (200), which performs the image encoding method corresponding to the reverse process of the image decoding method, will be described through various embodiments.

[0305] 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.

[0306] 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.

[0307] 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).

[0308] According to one embodiment, 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.

[0309] According to one embodiment, 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.

[0310] According to one embodiment, the encoder (220) may 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) may generate a bitstream including split shape mode information indicating that the encoding unit is not split. In addition, the encoder (220) may split the encoding unit into a plurality of encoding units, and the bitstream generation unit (210) may generate a bitstream including split shape mode information indicating that the encoding unit is split into a plurality of encoding units.

[0311] According to one embodiment, information indicating the number of encoding units to be split into or the direction in which the encoding unit is to be 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.

[0312] 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.

[0313] 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.

[0314] 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.

[0315] 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.

[0316] 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.

[0317] FIG. 20 is a block diagram illustrating the configuration of an image decoding device (2000) according to one embodiment.

[0318] Referring to FIG. 20, the image decoding device (2000) may include an acquisition unit (2010) and a prediction decoding unit (2030).

[0319] The acquisition unit (2010) and the prediction decoding unit (2030) may be implemented with at least one processor. The at least one processor may include various processing circuitry.

[0320] The acquisition unit (2010) and the prediction decoding unit (2030) can operate according to at least one instruction stored in at least one memory.

[0321] In one embodiment, the image decoding device (2000) may include at least one memory for storing input / output data of the acquisition unit (2010) and the prediction decoding unit (2030). The image decoding device (2000) may include a memory control unit for controlling data input / output of the at least one memory.

[0322] In one embodiment, the acquisition unit (2010) may correspond to the entropy decoding unit (1955) illustrated in FIG. 19, and the prediction decoding unit (2030) may correspond to the prediction decoding unit (1975) illustrated in FIG. 19.

[0323] The acquisition unit (2010) can acquire a bitstream generated as a result of encoding a picture. The bitstream can include an encoding result for the current block.

[0324] The current block may be a maximum coding unit, encoding unit, transformation unit, or prediction unit split from the current picture to be decoded. In one embodiment, the current block may be a sub-block split from a maximum coding unit, encoding unit, transformation unit, or prediction unit. In this case, a maximum coding unit, encoding unit, transformation unit, or prediction unit that includes multiple sub-blocks may be referred to as an upper block.

[0325] In one embodiment, the acquisition unit (2010) can receive a bitstream from an image encoding device over a network.

[0326] In one embodiment, the acquisition unit (2010) may acquire a bitstream from a data storage medium including a magnetic medium (e.g., a hard disk, a floppy disk, or a magnetic tape), an optical recording medium (e.g., a CD-ROM or DVD), and a magneto-optical medium (e.g., a floptical disk).

[0327] The acquisition unit (2010) can acquire syntax elements for decoding a picture from a bitstream. Values ​​corresponding to the syntax elements can be included in the bitstream according to the syntax structure.

[0328] The acquisition unit (2010) can obtain syntax elements by entropy decoding the bins constituting the bitstream.

[0329] The bitstream may include information about the prediction mode of the current block within the current picture. The prediction mode of the current block may be any one of a plurality of prediction modes, including an intra mode and an inter mode.

[0330] The prediction decoding unit (2030) can perform intra prediction or inter prediction on the current block according to the prediction mode of the current block to generate a prediction block of the current block, and can restore the current block using the prediction block.

[0331] The acquisition unit (2010) can acquire information about the intra prediction mode of the current block from the bitstream when the prediction mode of the current block is the intra mode.

[0332] Information about the intra prediction mode of the current block may include information indicating how the intra prediction mode is determined. The method for determining the intra prediction mode may include a method for deriving the intra prediction mode on the decoder side and a method for determining the intra prediction mode indicated by information included in the bitstream.

[0333] In one embodiment, information indicating how to determine the intra prediction mode may not be included in the bitstream, and the prediction decoding unit (2030) may determine the intra prediction mode of the current block according to a predetermined method.

[0334] In one embodiment, if information indicating an intra prediction mode is included in the bitstream, the prediction decoding unit (2030) may determine an intra prediction mode indicated by information obtained from the bitstream among a plurality of intra prediction modes as the intra prediction mode of the current block. The information indicating the intra prediction mode of the current block may include a flag or index indicating any one of the plurality of intra prediction modes.

[0335] In one embodiment, the prediction decoding unit (2030) can determine the intra prediction mode of the current block using samples restored before the current block, if the method of determining the intra prediction mode is a method of deriving the intra prediction mode on the decoder side.

[0336] The prediction decoding unit (2030) can determine which intra prediction mode among several intra prediction modes applicable to the current block is appropriate for the current block using samples restored before the current block. The prediction decoding unit (2030) can determine the intra prediction mode appropriate for the current block as the intra prediction mode of the current block.

[0337] The process of determining the intra prediction mode of the current block using samples restored before the current block is described later.

[0338] When a prediction block is generated through intra prediction or inter prediction for the current block, the prediction decoding unit (2030) can obtain a restored current block using the prediction block.

[0339] In one embodiment, the prediction decoding unit (2030) can determine the prediction block as the restored current block.

[0340] In one embodiment, the prediction decoding unit (2030) can generate a reconstructed current block by combining the residual data obtained from the bitstream by the acquisition unit (2010) with the prediction block. The reconstructed current block can be used to decode the next block.

[0341] FIG. 21 is a diagram illustrating an intra prediction mode according to one embodiment.

[0342] Referring to FIG. 21, intra prediction modes may be predefined in the video encoding device and video decoding device (2000). In the present disclosure, it is assumed that 67 intra prediction modes are defined. However, this is merely an example, and fewer intra prediction modes may be defined, or more intra prediction modes may be defined.

[0343] The predefined intra prediction modes can consist of two non-directional modes and 65 directional modes. The non-directional modes can include the planar mode and the DC mode. The directional modes can include modes 2 to 66 having predetermined angles.

[0344] In particular, mode 2, mode 34, and mode 66 can be defined as diagonal modes, and the intra prediction mode between mode 2 and mode 34 can be defined as a mode with horizontal directionality, and the intra prediction mode between mode 34 and mode 66 can be defined as a mode with vertical directionality, respectively. In addition, depending on the shape of the block, a mode smaller than mode 2 or a mode larger than mode 66 can be used for intra prediction. For example, depending on the ratio of the width and height of the block, a directional prediction mode smaller than mode 2 or larger than mode 66 can be used for intra prediction.

[0345] The more detailed the directional mode, i.e., the more prediction directions corresponding to the directional mode are added, the more diverse the predictor can be generated, resulting in more accurate predictions. However, this also increases the amount of information that must be transmitted. Therefore, from a rate-distortion performance perspective, there may be limitations to continuously adding intra-prediction modes. That is, the amount of information transmitted for intra-prediction modes may exceed the gains gained from reducing prediction error, reducing compression efficiency.

[0346] In recent video compression technology, methods for increasing the size of the accessible area of ​​reconstructed samples are being discussed. As the accessible area of ​​reconstructed samples increases, the video decoding device (2000) can effectively derive an intra-prediction mode based on information derived from the already reconstructed area. By generating a predictor by independently deriving the intra-prediction mode without signaling intra-prediction mode information in the video encoding device, the overhead associated with signaling can be reduced and compression efficiency can be improved.

[0347] In the embodiment of the present disclosure, a method for deriving an intra prediction mode on the image decoding device (2000) side is described to overcome the aforementioned limitations and reduce overhead for intra mode information transmission.

[0348] According to one embodiment of the present disclosure, the image decoding device (2000) can derive an intra prediction mode based on the amount of change in pixel values ​​of a surrounding restored area. Furthermore, according to one embodiment of the present disclosure, the image decoding device (2000) can derive an intra prediction mode based on the difference between predetermined sample sets within the surrounding restored area.

[0349] Hereinafter, a method for deriving an intra prediction mode based on the amount of change in pixel values ​​of a surrounding restored area will be described with reference to FIGS. 22 and 23. In the present disclosure, the amount of change in pixel values ​​may be referred to as a gradient. The gradient may also be referred to as a slope, amount of change, directionality, prediction directionality, etc. In addition, in the present disclosure, a method for deriving an intra prediction mode based on the gradient of a surrounding restored area may be abbreviated as DIMD (Decoder-side intra mode derivation).

[0350] FIG. 22 is a diagram illustrating a method for deriving an intra prediction mode based on a gradient according to one embodiment.

[0351] Referring to FIG. 22, the image decoding device (2000) can derive an intra prediction mode of the current block (2200) based on a gradient between at least two samples belonging to a surrounding area (2210) of the current block (2200).

[0352] In one embodiment, the image decoding device (2000) may calculate a gradient using at least two samples belonging to a surrounding area (2210) of the current block (2200). The image decoding device (2000) may accumulate the calculated gradients to generate gradient information. As an example, the intra prediction mode of the current block (2200) may be selected from among the intra prediction modes described above in FIG. 21.

[0353] DIMD is a technology for directly deriving an intra prediction mode in an image decoding device (2000) based on a gradient. When the DIMD mode is applied to a current block, the image decoding device (2000) can derive a directional intra prediction mode in a reconstructed area (2210) around the current block (2200). The directional intra prediction mode can be derived using gradient information constructed by collecting gradients of a reconstructed area (2210) at a predefined location around the current block (2200).

[0354] In the present disclosure, a gradient may represent a variable calculated using at least two samples belonging to a surrounding area (2210) of a current block (2200). As an example, the gradient may include at least one of a horizontal gradient and a vertical gradient. In the present disclosure, a gradient may also refer to gradient information obtained by accumulating calculated gradients.

[0355] The gradient information may include information about an intra prediction mode mapped to the calculated gradient and / or information about the amplitude (or intensity) of the intra prediction mode. In the present disclosure, the gradient information may be referred to as gradient intensity, gradient size, gradient amplitude, histogram of gradient (HoG), histogram, histogram intensity, histogram size, histogram amplitude, etc.

[0356] In one embodiment, the gradient between at least two samples within a surrounding region (2210) of a current block (2200) may be obtained using a predefined filter. Additionally, gradient information of the current block (2210) may be generated based on the obtained gradient.

[0357] A gradient can be derived using pixels belonging to a surrounding area (2210) of the current block (2200). In one embodiment, a template (2210) for generating gradient information can be defined within a restored area surrounding the current block (2200).

[0358] The template (2210) may include the left, upper left, and upper regions of the current block (2200). As an example, the template (2210) may be defined as an L-shaped region of three pixel lines adjacent to the current block (2200), as illustrated in FIG. 22. A gradient may be calculated using pixels belonging to the template (2210) in the surrounding region of the current block (2200). In one embodiment, the number of pixel lines that may be used as the template (2210) may be defined in various ways.

[0359] In one embodiment, a gradient may be derived by filtering pixels belonging to a template (2210). In one embodiment, filtering may be performed on pixels within a 3x3 pixel area (2220) belonging to the template (2210). The pixel area (2220) to which filtering is applied may be referred to as a window.

[0360] As an example, a 3x3 Sobel filter may be applied to a window (2220). In the present disclosure, the case where the window (2220) is 3x3 is mainly described, but this is only an example and is not limited thereto. For example, the window (2220) may be defined in a size such as 2x2, 4x4, or 5x5.

[0361] In one embodiment, a window (2220) may be determined centered on pixels belonging to a central pixel line within a template (2210) of three pixel lines, and a gradient may be produced by applying filtering to the window (2220).

[0362] The gradient may include at least one of a horizontal gradient and a vertical gradient. An intra prediction mode may be determined based on the calculated gradient. An angle (or prediction direction) may be calculated based on the gradient, and the calculated angle may be mapped to the intra prediction mode having the closest or most similar angle. In other words, an intra prediction mode may be calculated from the gradient. Gradient information may be constructed using the intra prediction mode calculated from the gradient.

[0363] In one embodiment, the image decoding device (2000) may utilize a Sobel filter to obtain a gradient. The Sobel filter may include at least one of a horizontal Sobel filter and a vertical Sobel filter. The Sobel filter may be applied to a 3x3 window (2220) centered on a pixel belonging to the central pixel line of the template (2210). As an example, the horizontal Sobel filter and the vertical Sobel filter may be defined as illustrated in FIG. 22.

[0364] In one embodiment, when a vertical Sobel filter is applied to the template (2210), a horizontal gradient may be output. When a horizontal Sobel filter is applied to the template (2210), a vertical gradient may be output.

[0365] In one embodiment, a vertical Sobel filter may be applied to windows (2220) within a template (2210), thereby outputting horizontal gradients corresponding to each of the windows (2220). Additionally, a horizontal Sobel filter may be applied to windows (2220) within a template (2210), thereby outputting vertical gradients corresponding to each of the windows (2220).

[0366] FIG. 23 is a diagram illustrating a method for generating gradient information according to one embodiment.

[0367] Referring to FIG. 23, the angle (or prediction direction) derived through filtering for the window (2220) can be mapped (or converted) to one of the predefined intra prediction modes. The angle derived from the gradient can be a texture angle or prediction direction of the window (2220). As an example, the intra prediction mode as described above in FIG. 21 can be derived from the gradient. That is, the angle derived through filtering for the window (2220) can be mapped to one of the 65 directional intra prediction modes.

[0368] In one embodiment, the intra prediction mode corresponding to the current window (2220) can be derived according to the description in the following mathematical expression 1.

[0369]

[0370] In mathematical expression 1, G hor represents the horizontal gradient of the current window (2220), and G ver represents the vertical gradient of the current window (2220). According to mathematical expression 1, the angle of the current window (2220) can be calculated using the horizontal gradient and the vertical gradient.

[0371] In one embodiment, an intra prediction mode corresponding to an angle adjacent to an angle calculated using Equation 1 may be derived (or mapped) to an intra prediction mode of the current window (2220).

[0372] In one embodiment, the intensity (or amplitude) for the intra prediction mode corresponding to the current window (2220) can be calculated based on the following mathematical expression 2.

[0373]

[0374] Referring to mathematical expression 2, the strength of the intra prediction mode can be calculated as the sum of the absolute values ​​for the horizontal gradient of the current window (2220) and the vertical gradient of the current window (2220).

[0375] In one embodiment, gradient information (2300) may be generated (or updated) based on an intra prediction mode and the intensity of the intra prediction mode. The gradient information (2300) may be generated by accumulating the intra prediction mode derived from the gradient and the amplitude (or intensity) corresponding to the intra prediction mode. In other words, the gradient information (2300) may be generated by summing the amplitudes for each intra prediction mode collected from the template (2310) based on the intra prediction mode.

[0376] In one embodiment, the gradient information may include at least one intra prediction mode and an amplitude corresponding to the at least one intra prediction mode.

[0377] Fig. 23 shows the gradient in the horizontal direction (G hor ) and vertical gradient (G ver ) induced by the angle (θ) (or predicted direction) and intensity (I θ ) is shown as an example, and the angle (θ) and intensity (I θ ) is an example of accumulated gradient information (2300).

[0378] In one embodiment, the x-axis of the gradient information (2300) may represent an angle (θ) or an intra prediction mode. Here, the angle may be a prediction angle, a prediction direction, a texture angle, or a texture direction. The intra prediction mode may be mapped to the calculated angle (θ). As an example, the angle (θ) may be calculated using the mathematical expression 1 described above. The y-axis of the gradient information (2300) represents the amplitude of the corresponding angle (θ) or the corresponding intra prediction mode. FIG. 23 I θ can be a variable representing amplitude, intensity, or size.

[0379] In one embodiment, angles (or intra prediction modes) at all pixel locations (pixel locations belonging to the central pixel line) within the template (2310) are derived, and the intensity values ​​of the derived angles are summed to obtain angle-specific amplitudes of the current block (2200).

[0380] In one embodiment, the image decoding device (2000) can determine a corresponding intra prediction mode for the entire window (2220) centered on pixels belonging to a central pixel line within a template (2210), and generate / update gradient information (2300) by accumulating the strength of the corresponding intra prediction mode.

[0381] In one embodiment, the image decoding device (2000) can derive an intra prediction mode based on the generated gradient information (2300). As an example, the image decoding device (2000) can derive a plurality of intra prediction modes based on the gradient information (2300). The maximum number of derived intra prediction modes can be defined in advance. For example, the maximum number can be defined as 2, 3, 4, 5, etc. For example, among the intra prediction modes included in the generated gradient information (2300), a predetermined number of intra prediction modes in order of increasing amplitude can be derived as the intra prediction mode of the current block.

[0382] The video decoding device (2000) can generate a prediction block of the current block by performing intra prediction on the current block using the intra prediction mode.

[0383] The video decoding device (2000) can generate a predictor using the derived intra prediction mode. In the present disclosure, the predictor generated using the derived intra prediction mode in the video decoding device (2000) may be referred to as a prediction sample, a prediction block, a temporary prediction sample, a temporary prediction block, an initial prediction sample, or an initial prediction block.

[0384] The video decoding device (2000) can generate a final prediction block by weighting the predictors generated by the derived intra prediction mode. For example, the video decoding device (2000) can generate a final prediction block by weighting the predictors generated by the derived intra prediction mode and the predictors generated by a predetermined intra prediction mode (e.g., planar mode).

[0385] The video decoding device (2000) can reconstruct the current block using the predicted block. For example, the video decoding device (2000) can determine the predicted block as the reconstructed current block. Alternatively, as an example, the video decoding device (2000) can generate the reconstructed current block by combining the predicted block with residual data obtained from the bitstream.

[0386] Hereinafter, a method for deriving an intra prediction mode based on the difference between a given set of samples within a restored surrounding area is described with reference to FIGS. 24 to 29.

[0387] FIG. 24 is a diagram illustrating sample sets required to derive an intra prediction mode according to one embodiment.

[0388] The prediction decoding unit (2030) can identify sample sets restored before the current block (2490) to determine the intra prediction mode of the current block (2490).

[0389] Referring to FIG. 24, the sample sets may include at least one of a first sample set (2420) located below the upper left sample (2410) restored before the current block (2490) in the current image (2400), a second sample set (2440) located to the right of the upper left sample (2410), a third sample set (2460) located above the upper left sample (2410), or a fourth sample set (2480) located to the left of the upper left sample (2410).

[0390] In one embodiment, samples included in a first sample set (2420) may be referred to as first samples, samples included in a second sample set (2440) may be referred to as second samples, and samples included in a third sample set (2460) may be referred to as third samples. Additionally, samples included in a fourth sample set (2480) may be referred to as fourth samples.

[0391] When the coordinates of the upper left sample inside the current block (2490) are (x, y), the coordinates of the upper left sample (2410) restored before the current block (2490) may be (x-1, y-1).

[0392] In one embodiment, when the coordinates of the upper left sample (2410) are (x-1, y-1), the coordinates of the samples included in the first sample set (2420) may be (x-1, y) to (x-1, y+a) (a+1 is the number of samples included in the first sample set (2420)). In addition, the coordinates of the samples included in the second sample set (2440) may be (x, y-1) to (x+b, y-1) (b+1 is the number of samples included in the second sample set (2440)). In addition, the coordinates of the samples included in the third sample set (2460) may be (x-1, yc) to (x-1, y-2) (c-1 is the number of samples included in the third sample set (2460)). Additionally, the coordinates of the samples included in the fourth sample set (2480) may be (xd, y-1) to (x-2, y-1) (d-1 is the number of samples included in the fourth sample set (2480)).

[0393] In one embodiment, the prediction decoding unit (2030) can derive the intra prediction mode of the current block (2490) using two or more of the four sample sets illustrated in FIG. 24.

[0394] The number of samples included in the first sample set (2420), the second sample set (2440), the third sample set (2460), and the fourth sample set (2480) can be determined in various ways.

[0395] In one embodiment, the number of samples included in the first sample set (2420) may be greater than or equal to the number of samples in the vertical direction of the current block (2490) (or the height of the current block (2490)). For example, the number of samples included in the first sample set (2420) may be twice the number of samples in the vertical direction of the current block (2490).

[0396] In one embodiment, the number of samples included in the second sample set (2440) may be greater than or equal to the number of samples in the horizontal direction of the current block (2490) (or the width of the current block (2490)). For example, the number of samples included in the second sample set (2440) may be twice the number of samples in the horizontal direction of the current block (2490).

[0397] In one embodiment, the number of samples included in the third sample set (2460) may be less than the number of samples included in the first sample set (2420), and the number of samples included in the fourth sample set (2480) may be less than the number of samples included in the second sample set (2440).

[0398] The reason why the number of samples included in the third sample set (2460) and the fourth sample set (2480) is set to be smaller than that of the first sample set (2420) and the second sample set (2440) is to ensure stable memory management. If the number of samples included in the third sample set (2460) and the fourth sample set (2480) increases, samples that have already been restored must be stored in the memory for a long time, and the load due to memory access increases. Therefore, a relatively small number of samples are stored in the third sample set (2460) and the fourth sample set (2480).

[0399] The prediction decoding unit (2030) may perform intra prediction using one sample set as a reference sample set according to each of the plurality of directional modes to test multiple directional modes, thereby generating a prediction sample set corresponding to another sample set. This may be understood as intra-predicting one sample set from another sample set according to each of the plurality of directional modes.

[0400] The prediction decoding unit (2030) can determine which sample set should be used as a reference sample set and which sample set's prediction sample set should be generated by considering the prediction direction indicated by the plurality of directional modes.

[0401] The prediction decoding unit (2030) can determine which directional mode is appropriate for the current block (2490) by considering the prediction sample sets generated for each of the plurality of directional modes. Cost values ​​corresponding to the prediction sample sets can be calculated to select the directional mode appropriate for the current block (2490).

[0402] The cost value can represent the accuracy of intra prediction. Higher intra prediction accuracy leads to lower cost values, while lower intra prediction accuracy leads to higher cost values.

[0403] In one embodiment, the prediction decoding unit (2030) can identify directional modes applicable to the current block (2490) before testing multiple directional modes, and determine an intra prediction mode of the current block (2490) from among the identified directional modes.

[0404] The prediction decoding unit (2030) can identify directional modes applicable to the current block (2490) based on the size of the current block (2490). For example, if the size of the current block (2490) is a size to which wide-angle intra prediction can be applied (e.g., 8x4), the prediction decoding unit (2030) can identify that directional modes 8 to 72 are applicable to the current block (2490). In this case, the prediction decoding unit (2030) can determine the intra prediction mode of the current block (2490) by testing directional modes 8 to 72. Additionally, for example, if the size of the current block (2490) is such that wide-angle intra prediction cannot be applied, the prediction decoding unit (2030) can identify that directional modes 2 to 66 are applicable to the current block (2490). In this case, the prediction decoding unit (2030) can determine the intra prediction mode of the current block (2490) by testing directional modes 2 to 66.

[0405] In one embodiment, the predictive decoding unit (2030) can identify directional modes applicable to the current block (2490) based on the directional mode of a previous block reconstructed before the current block (2490). Since blocks within the current image may have similar directional modes, a directional mode suitable for the current block (2490) can be quickly determined by referring to the directional mode of the previous block.

[0406] A previous block restored before the current block (2490) may include at least one of a block located to the left of the current block (2490), a block located above the current block (2490), or a block located to the upper left of the current block (2490).

[0407] The prediction decoding unit (2030) can identify directional modes that can be applied to the current block (2490) based on the directional mode of the previous block, if the previous block restored before the current block (2490) was restored through intra prediction.

[0408] The prediction decoding unit (2030) may determine that directional modes adjacent to the directional mode of the previous block can be applied to the current block (2490). The directional modes adjacent to the directional mode of the previous block may mean directional modes having mode numbers that are identical / similar to the mode numbers of the directional mode of the previous block.

[0409] For example, if the intra prediction mode of the previous block is a directional mode of k (where k is an integer), the prediction decoding unit (2030) may determine that a directional mode of k (where a is an integer) or a directional mode of k+a can be applied to the current block (2490).

[0410] Once the directional modes applicable to the current block (2490) are identified, the prediction decoding unit (2030) can test which of the identified directional modes is suitable for the current block (2490).

[0411] In one embodiment, the prediction decoding unit (2030) may group a plurality of directional modes (e.g., a plurality of directional modes determined to be applicable to the current block (2490)) according to a prediction direction for testing the plurality of directional modes.

[0412] For example, the prediction decoding unit (2030) can classify directional modes in which the prediction direction points to the lower left into a first group, directional modes in which the prediction direction points to the upper left into a second group, and directional modes in which the prediction direction points to the upper right into a third group.

[0413] Referring to FIG. 23, the directional modes -14 to 17 pointing to the lower left can be classified into the first group, the directional modes 19 to 49 pointing to the upper left can be classified into the second group, and the directional modes 51 to 80 pointing to the upper right can be classified into the third group.

[0414] There may be 18 horizontal modes between the directional modes of the first group and the directional modes of the second group, and 50 vertical modes between the directional modes of the second group and the directional modes of the third group. The horizontal modes may be referred to as the directional modes of the fourth group, and the vertical modes may be referred to as the directional modes of the fifth group.

[0415] The reason multiple directional modes are grouped into multiple groups is because the sample set used as the reference sample set and the sample set used as the target of prediction may differ depending on the prediction direction. For directional modes belonging to the same group, the same sample set may be used as the reference sample set and the same sample set used as the target of prediction.

[0416] The fact that directional modes are grouped according to prediction direction is for convenience of explanation, and the grouping operation may or may not be performed by the prediction decoding unit (2030). In other words, in one embodiment, the prediction decoding unit (2030) can determine which group a specific directional mode belongs to, determine which sample sets are required for the directional mode belonging to the group, and test the specific directional mode using the determined sample sets. Alternatively, the prediction decoding unit (2030) can test the specific directional mode using predetermined sample sets without a separate grouping operation.

[0417] Referring to FIGS. 25a to 29, a method for calculating a cost value for each of a plurality of directional modes to determine an intra prediction mode of a current block (2490) is described.

[0418] FIGS. 25A and 25B are diagrams illustrating a method for calculating a cost value corresponding to a directional mode of a first group according to one embodiment.

[0419] As illustrated in FIG. 25A, a first sample set (2420) and a second sample set (2440) may be used for the first group of directional modes pointing in the lower left direction (d1). The first sample set (2420) may be positioned below the upper left sample (2410) restored before the current block (2490), and the second sample set (2440) may be positioned to the right of the upper left sample (2410) restored before the current block (2490).

[0420] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the second sample set (2440) by using the first sample set (2420) indicated by the prediction direction (d1) of the directional mode of the first group as a reference sample set.

[0421] The number of samples included in the prediction sample set may be the same as the number of samples included in the second sample set (2440).

[0422] To generate a prediction sample of one sample in the second sample set (2440), one or more samples in the first sample set (2420) located along the prediction direction (d1) relative to the corresponding sample may be used.

[0423] In one embodiment, an n-tap filter may be applied to a plurality of samples in the first sample set (2420) to consider fractional positions in generating a prediction sample of any one sample in the second sample set (2440). Here, n may be an integer greater than or equal to 1. In one embodiment, n may be adaptively determined based on at least one of the area, aspect ratio, width, and height of the current block (2490), the edge strength of the first sample set (2420), or the edge strength of the second sample set (2440). A method for calculating the edge strength will be described later.

[0424] In one embodiment, the prediction decoding unit (2030) may interpolate integer samples included in the second sample set (2440) to generate sub-samples, and generate prediction samples corresponding to the integer samples and sub-samples based on the first sample set (2420).

[0425] The prediction decoding unit (2030) can compare the prediction sample set with the second sample set (2440) to calculate a cost value corresponding to the directional mode of the first group. The cost value corresponding to the directional mode of the first group can be based on difference values ​​between sample values ​​in the prediction sample set and sample values ​​in the second sample set (2440).

[0426] In one embodiment, the more similar the predicted sample set is to the second sample set (2440), the smaller the cost value can be calculated.

[0427] In one embodiment, the cost value corresponding to the comparison result of the predicted sample set and the second sample set (2440) may include a sum of absolute difference (SAD), a sum of squared error (SSE), a mean removed SAD (MR-SAD), or a mean of absolute difference (MAD) between sample values ​​in the predicted sample set and sample values ​​in the second sample set (2440).

[0428] Next, as illustrated in FIG. 25b, a third sample set (2460) and a fourth sample set (2480) may be used to test the directional mode of the first group. The third sample set (2460) may be positioned above the upper left sample (2410) restored before the current block (2490), and the fourth sample set (2480) may be positioned to the left of the upper left sample (2410) restored before the current block (2490).

[0429] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the third sample set (2460) by using the fourth sample set (2480) indicated by the prediction direction (d1) of the directional mode of the first group as a reference sample set.

[0430] The number of samples included in the prediction sample set may be the same as the number of samples included in the third sample set (2460).

[0431] To generate a prediction sample of one sample in the third sample set (2460), one or more samples in the fourth sample set (2480) located in the prediction direction (d1) relative to that sample may be used.

[0432] In one embodiment, an n-tap filter may be applied to a plurality of samples in a fourth sample set (2480) to consider fractional positions in generating a prediction sample of any one sample in a third sample set (2460), wherein n may be an integer greater than or equal to 1. In one embodiment, n may be adaptively determined based on at least one of the area, aspect ratio, width, height of the current block (2490), the edge strength of the third sample set (2460), or the edge strength of the fourth sample set (2480).

[0433] In one embodiment, the prediction decoding unit (2030) can interpolate integer samples included in the third sample set (2460) to generate sub-samples, and generate prediction samples corresponding to the integer samples and sub-samples based on the fourth sample set (2480).

[0434] The cost value corresponding to the comparison result of the predicted sample set and the third sample set (2460) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the third sample set (2460).

[0435] In one embodiment, the cost values ​​calculated based on the first sample set (2420) and the second sample set (2440) illustrated in FIG. 25a may be referred to as the first preliminary cost values, and the cost values ​​calculated based on the third sample set (2460) and the fourth sample set (2480) illustrated in FIG. 25b may be referred to as the second preliminary cost values.

[0436] The prediction decoding unit (2030) can determine the cost value of the directional mode of the first group using at least one of the first preliminary cost value of the directional mode of the first group or the second preliminary cost value of the directional mode of the first group. The cost value of the directional mode of the first group can be used for comparison with the cost values ​​of other directional modes.

[0437] In one embodiment, the first preliminary cost value may be determined as the cost value of the directional mode of the first group.

[0438] Additionally, in one embodiment, the second preliminary cost value may be determined as the cost value of the directional mode of the first group.

[0439] Additionally, in one embodiment, a smaller value between the first preliminary cost value and the second preliminary cost value may be determined as the cost value of the directional mode of the first group.

[0440] Additionally, in one embodiment, an average of the first preliminary cost value and the second preliminary cost value may be determined as the cost value of the directional mode of the first group.

[0441] The prediction decoding unit (2030) can calculate cost values ​​for each of the plurality of directional modes when there are multiple directional modes classified into the first group.

[0442] FIGS. 26A and 26B are diagrams for explaining a method for calculating a cost value corresponding to a directional mode of a second group according to one embodiment.

[0443] As illustrated in FIG. 26a, a first sample set (2420) and a fourth sample set (2480) can be used for testing the directional mode of the second group pointing in the upper left direction (d2).

[0444] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the first sample set (2420) by using the fourth sample set (2480) indicated by the prediction direction (d2) of the directional mode of the second group as a reference sample set.

[0445] The number of prediction samples included in the prediction sample set may be the same as the number of samples included in the first sample set (2420).

[0446] To generate a prediction sample of one sample in the first sample set (2420), one or more samples in the fourth sample set (2480) located in the prediction direction (d2) relative to that sample may be used.

[0447] In one embodiment, an n-tap filter may be applied to a plurality of samples in a fourth sample set (2480) to generate a prediction sample of one sample in a first sample set (2420), wherein n may be an integer greater than or equal to 1. In one embodiment, n may be adaptively determined based on at least one of the width, aspect ratio, width, height of the current block (2490), the edge strength of the first sample set (2420), or the edge strength of the fourth sample set (2480).

[0448] In one embodiment, the prediction decoding unit (2030) can interpolate integer samples included in the first sample set (2420) to generate sub-samples, and generate prediction samples corresponding to the integer samples and sub-samples based on the fourth sample set (2480).

[0449] The cost value corresponding to the comparison result of the predicted sample set and the first sample set (2420) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the first sample set (2420).

[0450] Next, as illustrated in FIG. 26b, a second sample set (2440) and a third sample set (2460) may be used for testing the directional mode of the second group.

[0451] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the second sample set (2440) by using the third sample set (2460) indicated by the prediction direction (d2) of the directional mode of the second group as a reference sample set.

[0452] The number of prediction samples included in the prediction sample set may be the same as the number of samples included in the second sample set (2440).

[0453] To generate a prediction sample of one sample in the second sample set (2440), one or more samples in the third sample set (2460) located in the prediction direction (d2) relative to that sample may be used.

[0454] In one embodiment, an n-tap filter may be applied to a plurality of samples in a third sample set (2460) to generate a prediction sample of one sample in a second sample set (2440), wherein n may be an integer greater than or equal to 1. In one embodiment, n may be adaptively determined based on at least one of the width, aspect ratio, width, height of the current block (2490), the edge strength of the second sample set (2440), or the edge strength of the third sample set (2460).

[0455] In one embodiment, the prediction decoding unit (2030) can interpolate integer samples included in the second sample set (2440) to generate sub-samples, and generate prediction samples corresponding to the integer samples and sub-samples based on the third sample set (2460).

[0456] The cost value corresponding to the comparison result of the predicted sample set and the second sample set (2440) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the second sample set (2440).

[0457] The cost values ​​calculated based on the first sample set (2420) and the fourth sample set (2480) illustrated in FIG. 26a may be referred to as the first preliminary cost values, and the cost values ​​calculated based on the second sample set (2440) and the third sample set (2460) illustrated in FIG. 26b may be referred to as the second preliminary cost values.

[0458] The prediction decoding unit (2030) can determine the cost value of the directional mode of the second group using at least one of the first preliminary cost value of the directional mode of the second group calculated based on the first sample set (2420) and the fourth sample set (2480), or the second preliminary cost value of the directional mode of the second group calculated based on the second sample set (2440) and the third sample set (2460). The cost value of the directional mode of the second group can be used for comparison with the cost values ​​of other directional modes.

[0459] In one embodiment, the first preliminary cost value of the directional mode of the second group may be determined as the cost value of the directional mode of the second group.

[0460] Additionally, in one embodiment, the second preliminary cost value of the directional mode of the second group may be determined as the cost value of the directional mode of the second group.

[0461] Additionally, in one embodiment, a smaller value between the first preliminary cost value of the directional mode of the second group and the second preliminary cost value of the directional mode of the second group may be determined as the cost value of the directional mode of the second group.

[0462] Additionally, in one embodiment, an average of the first preliminary cost value of the directional mode of the second group and the second preliminary cost value of the directional mode of the second group may be determined as the cost value of the directional mode of the second group.

[0463] The prediction decoding unit (2030) can calculate cost values ​​for each of the plurality of directional modes when there are multiple directional modes classified into the second group.

[0464] FIGS. 27a and 27b are diagrams for explaining a method for calculating a cost value corresponding to a directional mode of a third group according to one embodiment.

[0465] As illustrated in FIG. 27a, a first sample set (2420) and a second sample set (2440) can be used for the directional mode of the third group pointing in the upper right direction.

[0466] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the first sample set (2420) by using the second sample set (2440) indicated by the prediction direction (d3) of the directional mode of the third group as a reference sample set.

[0467] The number of prediction samples included in the prediction sample set may be the same as the number of samples included in the first sample set (2420).

[0468] To generate a prediction sample of one sample in the first sample set (2420), one or more samples in the second sample set (2440) located in the prediction direction (d3) relative to that sample may be used.

[0469] In one embodiment, an n-tap filter may be applied to a plurality of samples in a second sample set (2440) to generate a prediction sample of one sample in a first sample set (2420), wherein n may be an integer greater than or equal to 1. In one embodiment, n may be adaptively determined based on at least one of the width, aspect ratio, width, height of the current block (2490), the edge strength of the first sample set (2420), or the edge strength of the second sample set (2440).

[0470] In one embodiment, the prediction decoding unit (2030) can interpolate integer samples included in the first sample set (2420) to generate sub-samples, and generate prediction samples corresponding to the integer samples and sub-samples based on the second sample set (2440).

[0471] The cost value corresponding to the comparison result of the predicted sample set and the first sample set (2420) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the first sample set (2420).

[0472] Next, as illustrated in FIG. 27b, a third sample set (2460) and a fourth sample set (2480) can be used for testing the directional mode of the third group.

[0473] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the fourth sample set (2480) by using the third sample set (2460) indicated by the prediction direction (d3) of the directional mode of the third group as a reference sample set.

[0474] The number of prediction samples included in the prediction sample set may be the same as the number of samples included in the fourth sample set (2480).

[0475] To generate a prediction sample of one sample in the fourth sample set (2480), one or more samples in the third sample set (2460) located in the prediction direction (d3) relative to that sample may be used.

[0476] In one embodiment, an n-tap filter may be applied to a plurality of samples in a third sample set (2460) to generate a prediction sample of any one sample in a fourth sample set (2480), wherein n may be an integer greater than or equal to 1. In one embodiment, n may be adaptively determined based on at least one of the width, aspect ratio, width, height of the current block (2490), the edge strength of the third sample set (2460), or the edge strength of the fourth sample set (2480).

[0477] In one embodiment, the prediction decoding unit (2030) can interpolate integer samples included in the fourth sample set (2480) to generate sub-samples, and generate prediction samples corresponding to the integer samples and sub-samples based on the third sample set (2460).

[0478] The cost value corresponding to the comparison result of the predicted sample set and the fourth sample set (2480) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the fourth sample set (2480).

[0479] The cost values ​​calculated based on the first sample set (2420) and the second sample set (2440) illustrated in FIG. 27a may be referred to as the first preliminary cost values, and the cost values ​​calculated based on the third sample set (2460) and the fourth sample set (2480) illustrated in FIG. 27b may be referred to as the second preliminary cost values.

[0480] The prediction decoding unit (2030) can determine the cost value of the directional mode of the third group using at least one of the first preliminary cost value of the directional mode of the third group or the second preliminary cost value of the directional mode of the third group. The cost value of the directional mode of the third group can be used for comparison with the cost values ​​of other directional modes.

[0481] In one embodiment, the first preliminary cost value of the directional mode of the third group may be determined as the cost value of the directional mode of the third group.

[0482] Additionally, in one embodiment, the second preliminary cost value of the directional mode of the third group may be determined as the cost value of the directional mode of the third group.

[0483] Additionally, in one embodiment, a smaller value between the first preliminary cost value of the directional mode of the third group and the second preliminary cost value of the directional mode of the third group may be determined as the cost value of the directional mode of the third group.

[0484] Additionally, in one embodiment, an average of the first preliminary cost value of the directional mode of the third group and the second preliminary cost value of the directional mode of the third group may be determined as the cost value of the directional mode of the third group.

[0485] The prediction decoding unit (2030) can calculate cost values ​​for each of the plurality of directional modes when there are multiple directional modes classified into the third group.

[0486] FIG. 28 is a diagram for explaining a method for calculating a cost value corresponding to a horizontal mode according to one embodiment.

[0487] For calculating the cost value corresponding to the horizontal mode, the upper left sample (2410) and the second sample set (2440) restored before the current block (2490) can be used.

[0488] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the second sample set (2440) by using the upper left sample (2410) indicated by the prediction direction (d4) of the horizontal mode as a reference sample. In one embodiment, the sample values ​​of the prediction samples can be determined to be identical to the sample values ​​of the upper left sample (2410).

[0489] The number of prediction samples included in the prediction sample set may be the same as the number of samples included in the second sample set (2440).

[0490] The cost value corresponding to the comparison result of the predicted sample set and the second sample set (2440) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the second sample set (2440).

[0491] In one embodiment, for calculating the cost value corresponding to the horizontal mode, the upper left sample (2410) and the fourth sample set (2480) restored before the current block (2490) may be used.

[0492] The prediction decoding unit (2030) can generate a prediction sample corresponding to the upper left sample (2410) by using the fourth sample set (2480) indicated by the prediction direction (d4) of the horizontal mode as a reference sample set. In one embodiment, the sample value of the prediction sample can be determined by applying the sample values ​​of the samples included in the fourth sample set (2480) to a predetermined formula.

[0493] The cost value corresponding to the comparison result of the predicted sample and the upper left sample (2410) may include SAD, SSE, MR-SAD or MAD between the sample value of the predicted sample and the sample value of the upper left sample (2410).

[0494] For horizontal mode, the cost value calculated based on the second sample set (2440) and the upper left sample (2410) can be referred to as the first preliminary cost value, and the cost value calculated based on the upper left sample (2410) and the fourth sample set (2480) can be referred to as the second preliminary cost value.

[0495] The prediction decoding unit (2030) can determine the cost value of the horizontal mode using at least one of the first preliminary cost value of the horizontal mode or the second preliminary cost value of the horizontal mode. The cost value of the horizontal mode can be used for comparison with the cost values ​​of other directional modes.

[0496] In one embodiment, the first preliminary cost value of the horizontal mode may be determined as the cost value of the horizontal mode.

[0497] Additionally, in one embodiment, the second preliminary cost value of the horizontal mode may be determined as the cost value of the horizontal mode.

[0498] Additionally, in one embodiment, a smaller value between the first preliminary cost value of the horizontal mode and the second preliminary cost value of the horizontal mode may be determined as the cost value of the horizontal mode.

[0499] Additionally, in one embodiment, an average of the first preliminary cost value of the horizontal mode and the second preliminary cost value of the horizontal mode may be determined as the cost value of the horizontal mode.

[0500] FIG. 29 is a diagram for explaining a method for calculating a cost value corresponding to a vertical mode according to one embodiment.

[0501] For calculating the cost value corresponding to the vertical mode, the upper left sample (2410) and the first sample set (2420) restored before the current block (2490) can be used.

[0502] The prediction decoding unit (2030) can generate a prediction sample set corresponding to the first sample set (2420) by using the upper left sample (2410) indicated by the prediction direction (d5) of the vertical mode as a reference sample. In one embodiment, the sample values ​​of the prediction samples can be determined to be identical to the sample values ​​of the upper left sample (2410).

[0503] The number of prediction samples included in the prediction sample set may be the same as the number of samples included in the first sample set (2420).

[0504] The cost value corresponding to the comparison result of the predicted sample set and the first sample set (2420) may include SAD, SSE, MR-SAD or MAD between the sample values ​​in the predicted sample set and the sample values ​​in the first sample set (2420).

[0505] In one embodiment, for calculating the cost value corresponding to the vertical mode, the upper left sample (2410) and the third sample set (2460) restored before the current block (2490) may be used.

[0506] The prediction decoding unit (2030) can generate a prediction sample corresponding to the upper left sample (2410) by using the third sample set (2460) indicated by the prediction direction (d5) of the vertical mode as a reference sample set. In one embodiment, the sample value of the prediction sample can be determined by applying the sample values ​​of the samples included in the third sample set (2460) to a predetermined formula.

[0507] The cost value corresponding to the comparison result of the predicted sample and the upper left sample (2410) may include SAD, SSE, MR-SAD or MAD between the sample value of the predicted sample and the sample value of the upper left sample (2410).

[0508] For vertical mode, the cost value calculated based on the first sample set (2420) and the upper left sample (2410) can be referred to as the first preliminary cost value, and the cost value calculated based on the upper left sample (2410) and the third sample set (2460) can be referred to as the second preliminary cost value.

[0509] The prediction decoding unit (2030) can determine the cost value of the vertical mode using at least one of the first preliminary cost value of the vertical mode or the second preliminary cost value of the vertical mode. The cost value of the vertical mode can be used for comparison with the cost values ​​of other directional modes.

[0510] In one embodiment, the first preliminary cost value of the vertical mode may be determined as the cost value of the vertical mode.

[0511] Additionally, in one embodiment, the second preliminary cost value of the vertical mode may be determined as the cost value of the vertical mode.

[0512] Additionally, in one embodiment, a smaller value between the first preliminary cost value of the vertical mode and the second preliminary cost value of the vertical mode may be determined as the cost value of the vertical mode.

[0513] Additionally, in one embodiment, an average of the first preliminary cost value of the vertical mode and the second preliminary cost value of the vertical mode may be determined as the cost value of the vertical mode.

[0514] In one embodiment, when cost values ​​of directional modes of a first group, cost values ​​of directional modes of a second group, cost values ​​of directional modes of a third group, cost value of a horizontal mode, and cost value of a vertical mode are calculated, the prediction decoding unit (2030) can determine a directional mode having a smallest cost value among the calculated cost values ​​as the intra prediction mode of the current block (2490).

[0515] In one embodiment, when a test is performed on directional modes applicable to the current block (2490), cost values ​​of directional modes that are not applicable to the current block (2490) may not be calculated. For example, for a square-shaped current block (2490), cost values ​​corresponding to directional modes -14 to -1 and directional modes 67 to 80 illustrated in FIG. 23 may not be calculated.

[0516] In one embodiment, since the numbers of samples included in each of the first sample set (2420), the second sample set (2440), the third sample set (2460), and the fourth sample set (2480) may be different from each other, the numbers of samples included in their prediction sample sets may also be different from each other. Therefore, in one embodiment, in order to compare the cost values ​​of directional modes belonging to different groups, MADs may be calculated as cost values. For example, MADs of directional modes of the first group, MADs of directional modes of the second group, MADs of directional modes of the third group, MAD of the horizontal mode, and MAD of the vertical mode may be calculated, and the prediction decoding unit (2030) may determine the directional mode with the smallest MAD as the intra prediction mode of the current block (2490).

[0517] MAD can correspond to the average of the absolute values ​​of the differences between the sample values ​​in the sample set and the sample values ​​in the predicted sample set. In other words, since the MAD can be calculated by dividing the sum of the absolute values ​​of the differences between the sample values ​​in the sample set and the sample values ​​in the predicted sample set by the number of samples, accurate cost comparisons can be made even if the number of samples in the predicted sample sets differs.

[0518] In one embodiment, if the number of samples in the prediction sample sets generated according to the multiple directional modes is the same, SAD, SSE or MR-SAD may be produced as cost values ​​for the multiple directional modes.

[0519] In one embodiment, the prediction decoding unit (2030) may select a representative directional mode from among the directional modes belonging to each group, and compare the cost values ​​of the representative directional modes of each group to determine the intra prediction mode of the current block (2490).

[0520] As described above, when the cost values ​​of the directional modes of the first group are calculated through the embodiment described with reference to FIGS. 25a and 25b, the prediction decoding unit (2030) can determine the directional mode with the smallest cost value as the representative directional mode of the first group. Since the number of samples of the prediction sample sets generated based on the directional modes of the first group may be the same, SAD, SSE, or MR-SAD may be used as the cost value in determining the representative directional mode.

[0521] In addition, when the cost values ​​of the directional modes of the second group and the cost values ​​of the directional modes of the third group are calculated, the prediction decoding unit (2030) can determine the directional mode having the smallest cost value among the directional modes of the second group as the representative directional mode of the second group, and can determine the directional mode having the smallest cost value among the directional modes of the third group as the representative directional mode of the third group.

[0522] The prediction decoding unit (2030) may compare the cost values ​​of the representative directional mode of the first group, the representative directional mode of the second group, the representative directional mode of the third group, the horizontal mode, and the vertical mode, and determine the directional mode with the smallest cost value as the intra prediction mode of the current block (2490). As an example, the cost value used to determine the intra prediction mode of the current block (2490) may be MAD. This is because the number of samples of the prediction sample sets generated according to the representative directional modes of different groups may be different from each other.

[0523] In the above, a method for deriving an intra prediction mode in an image decoding device (2000) based on the amount of change in pixel values ​​of a surrounding restored area or the difference between a predetermined set of samples within the surrounding restored area has been described.

[0524] Below, a method for determining an intra prediction mode based on MPM is described. In the present disclosure, the MPM-based intra prediction mode determination method may be a method for determining an intra prediction mode based on information included in a bitstream. In other words, the MPM-based intra prediction mode determination method may be an explicit signaling-based intra prediction mode determination method.

[0525] FIG. 30 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0526] Referring to FIG. 30, the image decoding device (2000) can generate an MPM list of the current block based on the intra prediction modes of the surrounding blocks (S3010). The image decoding device (2000) can determine the intra prediction mode of the current block from among the intra prediction modes included in the MPM list (S3020).

[0527] In the present disclosure, the MPM list may be referred to as an MPM candidate list, an MPM group, an MPM candidate group, a prediction mode candidate list, a prediction mode candidate group, a candidate list, a candidate group, etc. The MPM list may represent a set of modes used by neighboring blocks of the current block, their adjacent modes, and statistically frequently used modes.

[0528] Candidates within the MPM list may be regular intra modes. In the present disclosure, a regular intra mode refers to a mode included in a regular intra mode set. The regular intra mode set may refer to an intra prediction mode set including intra prediction modes predefined in the video encoding device and the video decoding device (2000). The regular intra mode set may be abbreviated as regular intra mode.

[0529] In one embodiment, the regular intra mode set may be an intra prediction mode set including the intra prediction modes described above in FIG. 21. That is, the regular intra mode represents two non-directional modes and 67 intra prediction modes that can be signaled among prediction modes -14 to 80 determined by considering the aspect ratio of the block, and the regular intra prediction mode set represents a set of these 67 modes. In other words, the regular intra mode set may include two non-directional modes and 65 directional modes. The non-directional modes may include a planar mode and a DC mode. The directional modes that can be signaled may include modes 2 to 66 having a predetermined angle.

[0530] Intra prediction modes within the MPM list have a relatively high probability of being used by the current block. By allocating fewer bits to intra prediction modes within the MPM list, signaling overhead can be reduced and compression efficiency improved.

[0531] In one embodiment, when determining the intra prediction mode, the MPM may be used only for the luma component. Alternatively, in one embodiment, when determining the intra prediction mode, the MPM may be used for both the luma and chroma components.

[0532] In one embodiment, the MPM list may contain a predefined number of candidates. That is, the maximum number of candidates in the MPM list may be predefined. For example, the maximum number may be defined as 3, 4, 5, 6, 7, etc.

[0533] As described above, the MPM list can be constructed using the intra prediction modes of surrounding blocks. The locations of the surrounding blocks used to construct the MPM list can be defined in various ways. This will be explained with reference to Figures 31 and 32 below.

[0534] FIG. 31 is a diagram illustrating peripheral blocks used to generate an MPM list according to one embodiment of the present disclosure.

[0535] Referring to FIG. 31, the surrounding blocks used to generate the MPM list may include at least one of the left block (L, Left) (3110) or the upper block (A, Above) (3120) of the current block (3100). That is, the image decoding device (2000) may construct the MPM list using at least one of the intra prediction mode of the left block (3110) or the intra prediction mode of the upper block (3120).

[0536] In one embodiment, the left block (3110) of the current block (3100) may be a block that includes a sample adjacent to the left of the lower left sample of the current block (3100). The upper block (3120) of the current block (3100) may be a block that includes a sample adjacent to the upper right of the current block (3100). Alternatively, in one embodiment, unlike as illustrated in FIG. 31, the left block (3110) of the current block (3100) may be a block that includes a sample adjacent to the left of the upper left sample of the current block (3100), and the upper block (3120) of the current block (3100) may be a block that includes a sample adjacent to the upper left of the upper left sample of the current block (3100).

[0537] In one embodiment, the image decoding device (2000) may generate an MPM list using a mode with a larger or smaller mode number among the intra prediction mode of the left block (3110) and the intra prediction mode of the upper block (3120). In the present disclosure, a surrounding block used for generating the MPM list may be referred to as a reference block or an MPM reference block. The reference block may represent at least one of the left block (3110) or the upper block (3120).

[0538] In one embodiment, when the intra prediction mode of the surrounding blocks (3110, 3120) is not a regular intra mode, i.e., when the intra prediction mode of the surrounding blocks (3110, 3120) is a non-regular intra mode, the mode of the surrounding blocks (3110, 3120) may be replaced with a predetermined intra prediction mode. As an example, the mode of the surrounding blocks (3110, 3120) decoded with a non-regular intra mode may be replaced with a regular intra mode and used to generate the MPM list.

[0539] In the present disclosure, the non-regular intra mode may collectively refer to a mode other than the regular intra mode, and the contents of the present disclosure are not limited to this designation. For example, the non-regular intra mode according to the present disclosure may also be referred to as the irregular intra mode, the non-intra prediction mode, etc.

[0540] In one embodiment, the non-regular intra mode may include at least one of an inter mode, an intra block copy (IBC) mode, a palette mode, an intra template matching prediction (IntraTMP) mode, a geometric partitioning mode (GPM), a spatial geometric partitioning mode (SGPM), a block-based delta pulse code modulation (BDPCM) mode, an extrapolation filter-based intra prediction (EIP) mode, an intra prediction fusion mode, or a matrix-based intra prediction (MIP) mode.

[0541] In one embodiment, the IntraTMP mode may indicate a method for predicting the current block by specifying a true block within a previously reconstructed search region based on template matching. The SGPM may indicate an intra mode similar to the GPM, which generates prediction samples for geometrically divided partitions through intra prediction. The EIP mode is an extrapolation filter-based prediction technique, which may indicate a method for predicting the interior of a block by filtering based on information outside the block. The intra-prediction fusion mode may indicate a prediction method for determining a final predictor by weighting various predictors generated from multiple reference sample lines. The MIP mode may indicate a method for performing prediction based on a pre-trained matrix. As an example, modes exemplified by the non-regular intra mode may be referenced in High Efficiency Video Coding (HEVC), Versatile Video Coding (VVC), and Enhanced Compression Model (ECM).

[0542] In one embodiment, if the mode of a peripheral block (3110, 3120) is a non-regular intra mode, the mode of that peripheral block (3110, 3120) may be replaced with a planar mode.

[0543] In one embodiment, the regular intra mode can be divided into multiple groups. For example, the regular intra mode can be divided into two, three, four, or any integer number of groups. For convenience of explanation, it is assumed that the regular intra modes are divided into three groups, and these three groups are referred to as groups 1 through 3.

[0544] In one embodiment, the first group may include one or more non-directional modes. The non-directional modes may mean at least one of a planar mode or a DC mode.

[0545] The second group may be referred to as an MPM list, which may include multiple MPMs (most probable modes). The multiple MPMs may include at least one of an intra prediction mode, an adjacent mode, or a default mode of the surrounding blocks (3110, 3120).

[0546] The adjacent mode can be derived by adding or subtracting an offset to the intra prediction mode of the neighboring blocks (3110, 3120). Alternatively, the adjacent mode can be derived by adding or subtracting an offset to the default mode. Here, the offset can be an integer of 1, 2, 3, 4, or more. The adjacent mode can be derived based on a neighboring block (3110, 3120) with a higher priority among the neighboring blocks (3110, 3120) described above. For example, if the intra prediction mode of the neighboring blocks (3110, 3120) corresponds to a non-directional mode, the adjacent mode may not be derived based on the intra prediction mode of the neighboring blocks (3110, 3120).

[0547] The default mode may refer to a mode predefined in the decoding device for constructing the MPM list. For example, the default mode may include at least one of a planar mode, a DC mode, a horizontal mode, a vertical mode, or a diagonal mode. Here, the diagonal mode may refer to one or more of a lower-left diagonal mode, an upper-left diagonal mode, or an upper-right diagonal mode. The default mode may be predefined as modes with a statistically high selection probability.

[0548] The third group may include the remaining modes among the regular intra modes that do not belong to the first and second groups.

[0549] In the above-described embodiment, the first group is defined as a separate group distinct from the second group, but this is not limited thereto. For example, the first group and the second group may be defined as a single group, in which case the non-directional mode of the first group may be any one of the MPMs included in the MPM list of the second group.

[0550] One or more syntax elements may be signaled to specify a group to which a mode identical to the intra prediction mode of the current block (3100) belongs. The syntax elements may be flags or indices. As an example, the syntax elements may include at least one of a first syntax element indicating whether the mode identical to the intra prediction mode of the current block (3100) belongs to a first group, and a second syntax element indicating whether the mode identical to the intra prediction mode of the current block (3100) belongs to a second group (i.e., an MPM list).

[0551] When a second group is specified, an index specifying one of a plurality of MPMs belonging to the second group may be signaled. Based on the MPM specified by the index, the intra prediction mode of the current block (3100) may be derived. Similarly, when a first group (or a third group) is specified, an index specifying one of a plurality of intra prediction modes belonging to the first group (or the third group) may be separately signaled, and based on the signaled index, the intra prediction mode of the current block (3100) may be derived. However, when the first group (or the third group) is configured with one intra prediction mode, the signaling may be omitted.

[0552] In one embodiment, the intra prediction modes of the surrounding blocks (3110, 3120) may be sequentially added to the MPM list according to the priority among the surrounding blocks (3110, 3120). Here, the priority may be defined in the order of the left block (3110) and the upper block (3120), or may be defined in the order of the upper block (3120) and the left block (3110).

[0553] In one embodiment, priorities may be adaptively determined based on the size and / or shape of the current block (3100). For example, if the height of the current block (3100) is greater than its width, the priorities of the upper block (3120) and the left block (3110) may be utilized. Conversely, if the width of the current block (3100) is greater than its height, the priorities of the upper block (3120) and the left block (3110) may be utilized.

[0554] In one embodiment, the video decoding device (2000) can compare the intra prediction modes of the surrounding blocks (3110, 3120) to construct the MPM list as follows. In the following, for convenience of explanation, the intra prediction mode of the left block (3110) is referred to as L mode, and the intra prediction mode of the upper block (3120) is referred to as A mode. In addition, among the L mode and the A mode, the mode with a larger mode number is referred to as Max, and the mode with a smaller mode number is referred to as Min.

[0555] 1) If L mode and A mode are directional modes and are identical to each other.

[0556] The MPM list can be composed of {planner mode, L mode, L mode -1, L mode +1, L mode -2, L mode +2}.

[0557] 2) If L mode and A mode are directional modes and are different from each other.

[0558] 2-1) When Max-Min = 1, the MPM list can be composed of {Planner mode, L mode, A mode, Min-1, Max+1, Min-2}.

[0559] 2-2) If Max-Min >= 61, the MPM list can be composed of {Planner mode, L mode, A mode, Min+1, Max-1, Min+2}.

[0560] 2-1) When Max-Min = 2, the MPM list can be composed of {Planner mode, L mode, A mode, Min+1, Min-1, Max+1}.

[0561] 2-1) If 2 < Max-Min < 61, the MPM list can be composed of {Planner mode, L mode, A mode, Min-1, Min+1, Max-1}.

[0562] 3) If only one of the LA modes is a directional mode

[0563] The MPM list can be composed of {planner mode, Max, Max-1, Max+1, Max-2, Max+2}.

[0564] 4) If neither L mode nor A mode is directional mode

[0565] The MPM list can consist of {Planner Mode, 1(DC), 50(Ver), 18(Hor), 46, 54}.

[0566] In one embodiment, the planner mode may be included in the MPM list, or may be grouped into a different group than the MPM list as one of the default modes, as described above.

[0567] FIG. 32 is a diagram illustrating peripheral blocks used to generate an MPM list according to one embodiment of the present disclosure.

[0568] Referring to FIG. 32, the surrounding blocks used to construct the MPM list may include at least one of a left block (L, Left) (3210), a bottom-left block (BL, Bottom-Left) (3220), an upper block (A, Above) (3230), an upper-right block (AR, Above-Right) (3240), or an upper-left block (AL, Above-Left) (3250) of the current block (3200). That is, the image decoding device (2000) may generate the MPM list using an intra prediction mode of at least one of the left block (3210), the bottom-left block (3220), the upper block (3230), the upper-right block (3240), or the upper-left block (3250).

[0569] In one embodiment, the left block (3210) of the current block (3200) may be a block that includes a sample adjacent to the left of the bottom left sample of the current block (3200). The lower left block (3220) of the current block (3200) may be a block that includes a sample adjacent to the lower left of the bottom left sample of the current block (3200). The upper block (3230) of the current block (3200) may be a block that includes a sample adjacent to the upper right of the top right sample of the current block (3200). The upper right block (3240) of the current block (3200) may be a block that includes a sample adjacent to the upper right of the top right sample of the current block (3200). The upper left block (3250) of the current block (3200) may be a block that includes a sample adjacent to the upper right of the top right sample of the current block (3200).

[0570] Alternatively, in one embodiment, unlike as illustrated in FIG. 32, the left block (3210) of the current block (3200) may be a block that includes a sample adjacent to the left of the upper left sample of the current block (3200), and the upper block (3230) of the current block (3200) may be a block that includes a sample adjacent to the upper left of the upper left sample of the current block (3200).

[0571] In one embodiment, the second group described above may be divided into two sub-groups. In the present disclosure, the first sub-group distinguished from the second group may be referred to as a first MPM list (primary MPM list), and the second sub-group distinguished from the second group may be referred to as a second MPM list (secondary MPM list). For example, if an MPM list is composed of N MPMs, the upper M MPMs belonging to the MPM list may be included in the first MPM list, and the remaining (NM) MPMs may be included in the second MPM list. That is, the first MPM list may include MPMs having indices from 0 to (M-1) belonging to the MPM list. Here, N may denote the maximum number of MPMs that can be included in the MPM list. M may denote the maximum number of MPMs that can be included in the first MPM list. For example, M may be an integer of 3, 4, 5, 6, or higher.

[0572] In one embodiment, the first MPM list may be composed of 6 MPMs, and the second MPM list may be composed of 16 MPMs. In this case, the non-directional mode (or default mode) of the first group may be configured as included in the first MPM list, or may be configured as a separate group. As an example, a reserve MPM list composed of 22 MPMs may be generated, and the first 6 MPMs in the reserve MPM list may be included in the first MPM list, and the remaining MPMs may be included in the second MPM list. In the present disclosure, the reserve MPM list is a candidate list corresponding to the second group described above, and may also be referred to as a general MPM list.

[0573] In one embodiment, the image decoding device (2000) may insert a planar mode as a first candidate into the preliminary MPM list. Thereafter, the image decoding device (2000) may add an intra prediction mode of at least one of the left block (3210), the upper block (3230), the lower left block (3220), the upper right block (3240), or the upper left block (3250) to the preliminary MPM list.

[0574] The video decoding device (2000) can add the intra prediction mode derived based on DIMD to the preliminary MPM list. At this time, the method described above in FIGS. 22 and 23 can be applied. As an example, the intra prediction modes derived based on DIMD can be sorted based on the SAD cost, and a predetermined number of intra prediction modes can be added as candidates to the preliminary MPM list. At this time, the predetermined number can be defined as an integer of 1, 2, 3, 4, 5, or more. The SAD cost can be calculated as the difference between the predicted sample and the reconstructed sample of the template.

[0575] Additionally, the image decoding device (2000) can add a directional mode with an added or subtracted offset to the preliminary MPM list. The directional mode with an added or subtracted offset can be referred to as an adjacent mode, and the method described above in FIG. 31 can be applied in the same manner. Here, any duplicate descriptions related thereto are omitted. Thereafter, the image decoding device (2000) can add a default mode to the preliminary MPM list. The default mode can be the same as described above in FIG. 31.

[0576] In one embodiment, one or more syntax elements may be signaled to specify a group and / or sub-group to which the intra prediction mode of the current block (3200) belongs. The syntax elements may be flags or indices. As an example, an index indicating a group to which the intra prediction mode of the current block (3200) belongs may be signaled. Furthermore, as an example, the preliminary MPM list may be grouped into three or more groups, and an index indicating a group to which the intra prediction mode of the current block (3200) belongs among the plurality of groups may be signaled.

[0577] Alternatively, in one embodiment, at least one of a first flag indicating whether the intra prediction mode of the current block (3200) belongs to a first group, a second flag indicating whether the same mode as the intra prediction mode of the current block (3200) belongs to a second group (i.e., an MPM list), a third flag indicating whether the same mode as the intra prediction mode of the current block (3200) belongs to the first MPM list, or a fourth flag indicating whether the same mode as the intra prediction mode of the current block (3200) belongs to the second MPM list may be signaled.

[0578] When a second group is specified, an index for selecting one of a plurality of MPMs belonging to the second group may be signaled. The intra prediction mode of the current block (3200) may be derived based on the MPM selected by the index. Alternatively, when a first MPM list is selected, an index for specifying one of a plurality of MPMs belonging to the first MPM list may be signaled. The intra prediction mode of the current block may be derived based on the MPM specified by the signaled index. Alternatively, when a second MPM list is selected, an index for specifying one of a plurality of MPMs belonging to the second MPM list may be signaled. The intra prediction mode of the current block (3200) may be derived based on the MPM specified by the signaled index.

[0579] Similarly, when the first group (or the third group) is specified, an index specifying any one of the multiple intra prediction modes belonging to the first group (or the third group) can be separately signaled, and the intra prediction mode of the current block (3200) can be derived based on the signaled index. However, when the first group (or the third group) is configured with one intra prediction mode, signaling of the index can be omitted.

[0580] Meanwhile, in one embodiment, the intra prediction modes of the surrounding blocks (3210, 3220, 3230, 3240, 3250) may be sequentially added to the MPM list according to the priorities among the surrounding blocks (3210, 3220, 3230, 3240, 3250). The priorities may be defined in the order of the left block (3210), the upper block (3230), the lower left block (3220), the upper right block (3240), and the upper left block (3250), or may be defined in the order of the upper block (3230), the left block (3210), the lower left block (3220), the upper right block (3240), and the upper left block (3250).

[0581] In one embodiment, priorities may be adaptively determined based on the size and / or shape of the current block (3200). For example, if the height of the current block (3200) is greater than the width, the priorities of the upper block (3230), the left block (3210), the lower left block (3220), the upper right block (3240), and the upper left block (3250) may be utilized. Conversely, if the width of the current block (3100) is greater than the height, the priorities of the left block (3210), the upper block (3230), the lower left block (3220), the upper right block (3240), and the upper left block (3250) may be utilized.

[0582] Referring again to FIG. 30, the image decoding device (2000) can generate a prediction sample of the current block using the intra prediction mode of the current block (S3030).

[0583] In one embodiment, the image decoding device (2000) can generate a prediction sample of the current block by performing intra prediction on the current block using an intra prediction mode of the current block and reference samples within a reconstructed area around the current block.

[0584] As described above, MPMs can be utilized for efficient encoding / decoding of intra prediction modes. By grouping a predefined number of intra prediction modes to create an MPM list and allocating relatively few bits to the MPMs included in the MPM list, signaling overhead can be reduced and compression efficiency can be improved. Here, as previously described in Figures 21 and 30, intra prediction modes can be predefined into 67 modes.

[0585] Furthermore, in recent video compression technologies, discussions are ongoing to increase prediction accuracy while reducing the number of bits required for prediction mode signaling by considering a larger number of MPMs compared to the existing 6 MPMs. For example, as described above with reference to FIGS. 30 and 32, when determining an intra prediction mode, a first MPM list and a second MPM list, each consisting of 6 and 16 MPMs, respectively, are configured, so that a total of 22 MPMs can be used for intra prediction mode signaling.

[0586] Considering a larger number of MPMs compared to the previous model, signaling overhead for signaling group selection information (e.g., index signaling or hierarchical structure signaling) and mode-specific information within the selected group may increase. Therefore, increasing the probability that the intra-prediction mode of the current block will be selected within the MPM may be particularly important.

[0587] In one embodiment of the present disclosure, taking these points into account, we propose a method for utilizing an intra prediction mode derived based on differences between predetermined sample sets within a surrounding restored region as an MPM. In the present disclosure, the intra prediction mode derived based on differences between predetermined sample sets within a surrounding restored region is referred to as a Cross Line Prediction (CLP) mode, but it should be understood that the contents of the present disclosure are not limited to this designation.

[0588] Since the CLP mode is derived by using sample sets within the restored region close to the current block, the selection probability may be as high as the intra prediction mode of the surrounding blocks of the current block described above (3110, 3120 in FIG. 31, 3210, 3220, 3230, 3240, 3250 in FIG. 32). In addition, since the default modes described above in FIGS. 30 to 32 are modes that consider statistical selection probability rather than relevance to the current block, the selection probability of the CLP mode may be relatively high or similar to that of the default mode.

[0589] By using CLP mode as the MPM, the MPM list can be structured with greater precision in terms of prediction accuracy. This improves the previously described problem of using the increased number of MPMs to determine the intra prediction mode, and improves compression performance by increasing the probability of MPM selection.

[0590] According to one embodiment of the present disclosure, the image decoding device (2000) can generate an MPM list using the CLP mode of the current block. In other words, the image decoding device (2000) can insert the CLP mode of the current block into the MPM list. The CLP mode of the current block can be derived based on multiple reference sample sets neighboring the current block. In this case, the method described above with reference to FIGS. 24 to 29 can be applied. Any duplicate description in this regard may be omitted.

[0591] Specifically, the image decoding device (2000) can calculate a cost value for each of a plurality of predefined directional modes and derive a CLP mode by comparing the calculated cost values. The cost value for the directional mode can correspond to a difference between a reference sample set and a prediction sample set. The image decoding device (2000) can obtain differences between reference samples included in the reference sample set and prediction samples included in the prediction sample set, and calculate a cost value for the directional mode based on the obtained differences.

[0592] In one embodiment, the cost value can be calculated based on SAD, SSE, MR-SAD, and MAD. As described above in FIGS. 24 to 29, the directional modes can be grouped into multiple groups. For example, within each group, a representative directional mode with the lowest cost value calculated based on SAD can be determined, and among the representative directional modes of each group, a directional mode with the lowest cost value calculated based on MAD can be determined. The finally determined directional mode can be induced as a CLP mode.

[0593] In one embodiment, the image decoding device (2000) may generate a prediction sample set corresponding to another reference sample set by using one of a plurality of reference sample sets according to a plurality of directional modes. That is, the image decoding device (2000) may perform intra prediction using one of the sample sets as a reference sample set for each of a plurality of predefined directional modes to generate a prediction sample set corresponding to another sample set. This may be understood as intra-predicting one sample set from one of the sample sets according to each of the plurality of directional modes.

[0594] Additionally, in one embodiment, the image decoding device (2000) can generate an MPM list using the CLP mode of the surrounding block. In other words, the image decoding device (2000) can insert the CLP mode of the surrounding block into the MPM list. The CLP mode of the surrounding block can be derived based on a plurality of reference sample sets neighboring the surrounding block in a method substantially the same as the method for deriving the CLP mode of the current block described above.

[0595] At this time, the surrounding block may include at least one of the left block (3110) or the upper block (3120) described above in FIG. 31. In addition, the surrounding block may include at least one of the left block (3210), the lower left block (3220), the upper block (3230), the upper right block (3240), or the upper left block (3250) described above in FIG. 32.

[0596] In one embodiment, at least one of the CLP mode of the current block or the CLP mode of the surrounding blocks may be included in the MPM list described in FIGS. 30 to 32. As an example, at least one of the CLP mode of the current block or the CLP mode of the surrounding blocks may be included in the MPM list. Alternatively, at least one of the CLP mode of the current block or the CLP mode of the surrounding blocks may be included in at least one of the preliminary MPM list, the first MPM list, or the second MPM list.

[0597] In addition, in one embodiment, the insertion order of the MPM list of the CLP mode may be predefined. For example, the image decoding device (2000) may insert MPM candidates into the MPM list in the following order: peripheral mode, adjacent mode, guided mode, and default mode. As described above with reference to FIGS. 30 and 31, the peripheral mode indicates an intra prediction mode of a peripheral block, the adjacent mode indicates a mode having a prediction direction adjacent to the prediction direction of an intra prediction mode pre-inserted into the MPM list, and the default mode may mean a pre-defined mode for constructing the MPM list. The guided mode may include at least one of the CLP mode of the current block, the CLP mode of the peripheral block, or the DIMD mode described above with reference to FIGS. 22 and 23.

[0598] Alternatively, in one embodiment, the image decoding device (2000) may insert MPM candidates into the MPM list in the following order: peripheral mode, adjacent mode, default mode, and guided mode. Alternatively, the image decoding device (2000) may insert MPM candidates into the MPM list in the following order: peripheral mode, guided mode, adjacent mode, and default mode.

[0599] By utilizing the CLP modes of surrounding blocks as well as the current block's CLP mode as MPMs, the MPM list can be effectively constructed and prediction accuracy can be improved. Furthermore, the aforementioned issues associated with using an increased number of MPMs can be addressed, and compression performance can be enhanced by increasing the MPM selection probability.

[0600] FIG. 33 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0601] Referring to FIG. 33, the image decoding device (2000) can derive the intra prediction mode of a neighboring block decoded in a non-regular intra mode (S3310). In other words, the image decoding device (2000) can derive the intra prediction mode of a neighboring block when the mode of the neighboring block of the current block is a non-regular intra mode.

[0602] In conventional image compression techniques, if the mode of a neighboring block used to generate an MPM list is a non-regular intra mode, it is simply replaced with one of the fixed regular intra modes. For example, if a neighboring block is a block decoded with a non-regular intra mode, the intra prediction mode of the neighboring block can be replaced with a predefined mode, the planar mode, and used to generate the MPM list.

[0603] In this way, simply replacing a fixed mode without considering the characteristics of surrounding blocks can result in an inefficient MPM list, which can lead to a reduced MPM selection probability. In other words, compression efficiency can deteriorate as modes within the MPM list may not satisfy the assumption that the current block is likely to use them.

[0604] In order to improve the above-described problem, in the present disclosure, a method is proposed to generate an efficient MPM list for each block by adaptively changing the mode of the surrounding blocks to the regular intra mode when the mode of the surrounding blocks used for generating the MPM list is the non-regular intra mode.

[0605] In one embodiment, the video decoding device (2000) can replace the mode of a neighboring block decoded with a non-regular intra mode with the CLP mode of the neighboring block. The non-regular intra mode can be predefined. For example, the predefined non-regular intra mode can include at least one of an IBC mode, a palette mode, an intra template matching prediction mode, a GPM, a BDPCM, an SGPM, an EIP mode, an intra prediction fusion mode, or a MIP mode.

[0606] The video decoding device (2000) may first specify the surrounding blocks of the current block to generate an MPM list. For example, the surrounding blocks may be specified as at least one of the left block (3110) or the upper block (3120) described above in FIG. 31. In addition, the surrounding blocks may be specified as at least one of the left block (3210), the lower left block (3220), the upper block (3230), the upper right block (3240), or the upper left block (3250) described above in FIG. 32.

[0607] The video decoding device (2000) can determine whether a neighboring block is a block decoded in a non-regular intra mode. If the neighboring block is a block decoded in a regular intra mode, the video decoding device (2000) can generate an MPM list based on the regular intra mode. If the neighboring block is a block decoded in a non-regular intra mode, the video decoding device (2000) can generate an MPM list based on the CLP mode of the neighboring block. That is, the video decoding device (2000) can derive an intra prediction mode of the neighboring block based on a plurality of reference sample sets neighboring the neighboring block.

[0608] In one embodiment, the image decoding device (2000) may calculate a cost value for each of a plurality of predefined directional modes, and compare the calculated cost values ​​to derive the CLP mode of a surrounding block. The cost value for the directional mode may correspond to a difference between a reference sample set and a prediction sample set. The image decoding device (2000) may obtain differences between reference samples included in the reference sample set and prediction samples included in the prediction sample set, and may calculate a cost value for the directional mode based on the obtained differences.

[0609] In one embodiment, the cost value can be calculated based on SAD, SSE, MR-SAD, and MAD. As described above in FIGS. 24 to 29, the directional modes can be grouped into multiple groups. For example, within each group, a representative directional mode with the lowest cost value calculated based on SAD can be determined, and among the representative directional modes of each group, a directional mode with the lowest cost value calculated based on MAD can be determined. The finally determined directional mode can be induced as a CLP mode.

[0610] In one embodiment, the image decoding device (2000) may generate a prediction sample set corresponding to another reference sample set by using one of a plurality of reference sample sets neighboring neighboring blocks according to a plurality of directional modes. That is, the image decoding device (2000) may perform intra prediction using one of the sample sets as a reference sample set for each of a plurality of predefined directional modes, thereby generating a prediction sample set corresponding to another sample set.

[0611] In one embodiment, the image decoding device (2000) may determine a first reference sample set and a second reference sample set among a plurality of reference sample sets of surrounding blocks for a first directional mode among a plurality of predefined directional modes. The image decoding device (2000) may generate a prediction sample for each reference sample included in the first reference sample set by using the prediction direction of the corresponding directional mode and the reference sample included in the second reference sample set. In other words, the prediction sample set corresponding to the first reference sample set may be generated by using the prediction direction of the first directional mode and the second reference sample set.

[0612] In one embodiment, the prediction sample may be obtained by performing interpolation on reference samples included in the second reference sample set according to the prediction direction of the first directional mode. In one embodiment, the interpolation on the reference samples may also be applied to reference samples included in the first reference sample set.

[0613] In one embodiment, the image decoding device (2000) may calculate a cost value for each of a plurality of predefined directional modes, compare the calculated cost values, and derive the directional mode with the lowest cost value as the CLP mode of the surrounding block. The cost value for the directional mode may correspond to a difference between a reference sample set and a prediction sample set. The image decoding device (2000) may obtain differences between reference samples included in a first reference sample set and prediction samples included in a generated prediction sample set, and may calculate a cost value for the directional mode based on the obtained differences.

[0614] In one embodiment, the cost value may be calculated based on the SAD, in which case the image decoding device (2000) may sum the absolute values ​​of the obtained differences. The image decoding device (2000) may induce the directional mode that minimizes the absolute value of the summed difference among a plurality of predefined directional modes as the CLP mode of the surrounding block.

[0615] In one embodiment, directional modes can be grouped according to the method described above, and among the representative directional modes calculated based on SAD within each group, the directional mode with the lowest cost value calculated based on MAD can be finally derived as the CLP mode of the surrounding block. The image decoding device (2000) can obtain an average difference by dividing the absolute value of the summed difference by the number of reference samples included in a reference sample set determined according to the directional mode. The image decoding device (2000) can derive the directional mode that minimizes the obtained average difference among a plurality of predefined directional modes as the CLP mode of the surrounding block.

[0616] In one embodiment, the plurality of reference sample sets neighboring the surrounding block may include at least one of an upper-left reference sample set including an upper-left reference sample of the surrounding block, a lower reference sample set located below the upper-left reference sample, a right reference sample set located to the right of the upper-left reference sample, a left reference sample set located to the left of the upper-left reference sample, or an upper reference sample set located above the upper-left reference sample. The methods described above in FIGS. 24 to 29 may be applied, and any redundant descriptions thereof will be omitted herein.

[0617] In one embodiment, whether to substitute CLP mode for a neighboring block according to the above-described embodiment may be signaled via syntax. The syntax may be signaled at the sequence, picture, slice, Coding Tree Unit (CTU), Coding Unit (CU), Transform Unit (TU), or Prediction Unit (PU) level. Alternatively, whether to substitute CLP mode for a neighboring block may be adaptively determined based on encoding information of the current block.

[0618] The video decoding device (2000) can generate an MPM list based on the intra prediction mode of the surrounding blocks of the current block (S3320). The video decoding device (2000) can generate an MPM list by setting the mode of the surrounding blocks decoded in a non-regular intra mode to the CLP mode of the corresponding surrounding blocks and using the intra prediction mode of the replaced surrounding blocks. To generate the MPM list, the embodiments described above in FIGS. 30 to 32 can be equally applied, and redundant descriptions are omitted here.

[0619] As described above, considering a larger number of MPMs compared to the conventional one, the signaling overhead for signaling group selection information (e.g., index signaling or hierarchical structure signaling) and signaling mode-specific information within the selected group may increase. Therefore, it may be particularly important to increase the probability that the intra prediction mode of the current block is selected within the MPM. To this end, as in the embodiments described above with reference to FIGS. 30 to 32, the video decoding device (2000) may insert the CLP mode of the current block into the MPM list.

[0620] The video decoding device (2000) can add intra prediction mode candidates derived based on multiple sets of reference samples neighboring the current block to the MPM list. Any descriptions that overlap with the embodiments described above in FIGS. 30 to 32 will be omitted.

[0621] In one embodiment, the image decoding device (2000) may calculate a cost value for each of a plurality of predefined directional modes and compare the calculated cost values ​​to derive a CLP mode. As an example, the image decoding device (2000) may determine a third reference sample set and a fourth reference sample set among a plurality of reference sample sets neighboring the current block for a second directional mode among the plurality of predefined directional modes.

[0622] In one embodiment, the image decoding device (2000) may generate a prediction sample for each reference sample included in the third reference sample set by using the prediction direction of the second directional mode and the reference samples included in the fourth reference sample set. The image decoding device (2000) may obtain a difference between the prediction sample for each reference sample included in the third reference sample set and each reference sample included in the fourth reference sample set. The image decoding device (2000) may derive a directional mode that minimizes the obtained difference for each of a plurality of predefined directional modes as the CLP mode. A cost value for the directional mode may correspond to the difference between the reference sample set and the prediction sample set.

[0623] According to an embodiment of the present disclosure, by adaptively replacing the mode of a decoded neighboring block with a non-regular intra mode in consideration of the characteristics of the neighboring block, a more accurate intra prediction mode can be assigned to the neighboring block, and an MPM list can be effectively generated in terms of prediction accuracy.

[0624] The video decoding device (2000) can determine the intra prediction mode of the current block from among the intra prediction modes included in the MPM list (S3330). As an example, an MPM index specifying the intra prediction mode of the current block may be signaled within the MPM list. In addition, as an example, when an MPM group is divided into multiple subgroups, group selection information specifying the subgroup to which the intra prediction mode of the current block belongs may be signaled. Index information specifying the intra prediction mode of the current block within the selected group may be signaled.

[0625] The video decoding device (2000) can generate a prediction sample of the current block using the intra prediction mode of the current block (S3340). The video decoding device (2000) can generate a prediction sample of the current block by performing intra prediction using reference samples within the decoded area surrounding the current block and the intra prediction mode of the current block.

[0626] The image decoding device (2000) can restore the current block using the prediction sample of the current block. The image decoding device (2000) can generate a restoration sample of the current block by adding a residual sample to the prediction sample of the current block.

[0627] FIG. 34 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0628] Referring to FIG. 34, the image decoding device (2000) can generate an MPM list of the current block based on the intra prediction mode of the surrounding blocks (S3410). In this case, the embodiments described above in FIGS. 30 to 33 can be applied equally, and any redundant descriptions related thereto will be omitted.

[0629] The video decoding device (2000) can rearrange the MPM list (S3420). In one embodiment, the video decoding device (2000) can rearrange the MPM list based on the cost calculation method of the CLP mode derivation process. In the present disclosure, the cost calculation method of the CLP mode derivation process may be referred to as the CLP cost metric.

[0630] In one embodiment, the image decoding device (2000) may calculate a CLP cost value for each intra prediction mode included in the MPM list generated in step S3410 based on the CLP cost metric. In this case, the embodiments described above in FIGS. 24 to 29 may be equally applied, and any redundant descriptions related thereto will be omitted.

[0631] The video decoding device (2000) can rearrange the MPM list by calculating a cost value for each intra prediction mode included in the MPM list generated in step S3410, comparing the calculated cost values, and assigning a lower index in order of the smaller cost value. The cost value for the intra prediction mode included in the MPM list can correspond to a difference between a reference sample set and a prediction sample set obtained based on the prediction direction of the corresponding intra prediction mode. As an example, the video decoding device (2000) can rearrange the MPM list by ordering the calculated cost values ​​in ascending order.

[0632] In one embodiment, the cost value may be calculated based on SAD, SSE, MR-SAD, and MAD. As described above in FIGS. 24 to 29, the directional modes may be grouped into multiple groups. If the intra prediction modes included in the MPM list generated in step S3410 belong to the same group, the MPM list may be sorted based on the cost value calculated based on SAD. If the intra prediction modes included in the MPM list generated in step S3410 belong to different groups, the MPM list may be sorted based on the cost value calculated based on SAD and / or the cost value calculated based on MAD.

[0633] The video decoding device (2000) can determine the intra prediction mode of the current block among the intra prediction modes included in the MPM list (S3430).

[0634] In one embodiment, an MPM index specifying the intra prediction mode of the current block may be signaled within the MPM list. Furthermore, as an example, if an MPM group is divided into multiple subgroups, group selection information specifying the subgroup to which the intra prediction mode of the current block belongs may be signaled. Within the selected group, index information specifying the intra prediction mode of the current block may be signaled.

[0635] The video decoding device (2000) can generate a prediction sample of the current block using the intra prediction mode of the current block (S3440). The video decoding device (2000) can generate a prediction sample of the current block by performing intra prediction using reference samples within the decoded area surrounding the current block and the intra prediction mode of the current block.

[0636] The image decoding device (2000) can restore the current block using the prediction sample of the current block. The image decoding device (2000) can generate a restoration sample of the current block by adding a residual sample to the prediction sample of the current block.

[0637] In one embodiment, the CLP cost metric of the present disclosure may be utilized to determine the DIMD mode described above with reference to FIGS. 22 and 23. For example, CLP cost values ​​may be calculated for intra prediction modes whose accumulated intensities within gradient information exceed a predefined threshold, and the intra prediction mode with the smallest CLP cost value may be determined as the DIMD mode.

[0638] FIG. 35 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0639] According to one embodiment of the present disclosure, a CLP mode can be used as a Virtual Intra Prediction Mode (VIPM) to determine a transform kernel for a block of a non-regular intra mode.

[0640] Referring to FIG. 35, the image decoding device (2000) can derive the intra prediction mode of the current block based on a plurality of reference sample sets neighboring the current block when the mode of the current block is a predefined non-regular intra mode (S3510). That is, when determining the transformation kernel, when the mode of the current block is a predefined non-regular intra mode, the image decoding device (2000) can use the CLP mode of the current block as the intra prediction mode of the current block.

[0641] The CLP mode of the current block can be derived based on multiple sets of reference samples neighboring the current block. In this case, the methods described previously in Figures 24 to 29 can be applied. Any further explanations may be omitted.

[0642] Specifically, the image decoding device (2000) can calculate a cost value for each of a plurality of predefined directional modes and derive a CLP mode by comparing the calculated cost values. The cost value for the directional mode can correspond to a difference between a reference sample set and a prediction sample set. The image decoding device (2000) can obtain differences between reference samples included in the reference sample set and prediction samples included in the prediction sample set, and calculate a cost value for the directional mode based on the obtained differences.

[0643] In one embodiment, the cost value can be calculated based on SAD, SSE, MR-SAD, and MAD. As described above in FIGS. 24 to 29, the directional modes can be grouped into multiple groups. For example, within each group, a representative directional mode with the lowest cost value calculated based on SAD can be determined, and among the representative directional modes of each group, a directional mode with the lowest cost value calculated based on MAD can be determined. The finally determined directional mode can be induced as a CLP mode.

[0644] In one embodiment, the image decoding device (2000) may generate a prediction sample set corresponding to another reference sample set by using one of a plurality of reference sample sets according to a plurality of directional modes. That is, the image decoding device (2000) may perform intra prediction using one of the sample sets as a reference sample set for each of a plurality of predefined directional modes to generate a prediction sample set corresponding to another sample set. This may be understood as intra-predicting one sample set from one of the sample sets according to each of the plurality of directional modes.

[0645] The image decoding device (2000) can determine a set of transform kernels of the current block based on the derived intra prediction mode of the current block (S3520).

[0646] The set of transform kernels used for the inverse transformation of the current block can be determined according to the intra prediction mode of the current block. If the mode of the current block is a predefined non-regular intra mode, the image decoding device (2000) can set the intra prediction mode of the current block to the CLP mode derived in step S3510. The image decoding device (2000) can determine the set of transform kernels of the current block using the set CLP mode.

[0647] The video decoding device (2000) may determine the transform kernel of the current block within the transform kernel set (S3530). In one embodiment, an index indicating the transform kernel applied to the current block within the transform kernel set may be signaled. In one embodiment, the transform kernel of the current block determined in step S3530 may include two transform kernels applied in the horizontal direction and the vertical direction, respectively. Alternatively, in one embodiment, the transform kernel of the current block may be a non-separable transform kernel.

[0648] The image decoding device (2000) can generate a residual sample of the current block by applying the transform kernel of the current block to the transform coefficients of the current block (S3540). That is, the image decoding device (2000) can perform an inverse transform on the current block using the transform kernel of the current block. In one embodiment, the transform coefficients of the current block can be signaled through a bitstream. Prior to step S3510, inverse quantization can be performed on the transform coefficients signaled through the bitstream. That is, the transform coefficients to which the transform kernel of the current block is applied can be inverse quantized transform coefficients.

[0649] Fig. 36 is a block diagram illustrating a configuration of an image encoding device according to one embodiment.

[0650] Referring to FIG. 36, the image encoding device (3600) may include a prediction encoding unit (3610) and a generation unit (3630).

[0651] According to one embodiment, the prediction encoding unit (3610) and the generation unit (3630) may be implemented with at least one processor. The at least one processor may include various processing circuitry.

[0652] In one embodiment, the prediction encoder (3610) and the generator (3630) may operate according to at least one instruction stored in at least one memory.

[0653] The video encoding device (3600) may include at least one memory that stores input / output data of the prediction encoding unit (3610) and the generation unit (3630). In addition, the video encoding device (3600) may include a memory control unit that controls data input / output of the memory.

[0654] In one embodiment, the prediction encoding unit (3610) may correspond to the prediction encoding unit (1915) illustrated in FIG. 19, and the generation unit (3630) may correspond to the entropy encoding unit (1925) illustrated in FIG. 19.

[0655] The prediction encoding unit (3610) can determine the prediction mode of the current block. The current block may be a maximum coding unit, coding unit, transformation unit, or prediction unit divided from the current picture to be encoded.

[0656] In one embodiment, the current block may be a sub-block split from a maximum coding unit, encoding unit, transformation unit, or prediction unit. In this case, a maximum coding unit, encoding unit, transformation unit, or prediction unit that includes multiple sub-blocks may be referred to as a higher-order block.

[0657] In one embodiment, the prediction mode of the current block may be determined as one of a plurality of prediction modes including an intra mode and an inter mode.

[0658] In one embodiment, the prediction encoder (3610) can determine the intra prediction mode of the current block when the prediction mode of the current block is intra mode.

[0659] The intra prediction mode of the current block can be selected from among multiple intra prediction modes. As described with reference to FIG. 21, the multiple intra prediction modes can include a non-directional intra prediction mode and a directional intra prediction mode.

[0660] In one embodiment, 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.

[0661] In one embodiment, encoding of the current block may refer to a process in which the image decoding device (2000) generates information (or syntax elements) necessary to restore the current block. The information generated through encoding may be included in the bitstream. The operations performed by the image encoding device (3600) may substantially correspond to the operations performed by the image decoding device (2000).

[0662] In one embodiment, 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. Information regarding the residual data may be transmitted to the image decoding device (2000) via a bitstream.

[0663] According to one embodiment, the prediction encoding unit (3610) may determine a determination method for the intra prediction mode when the prediction mode of the current block is the intra mode. Information indicating the determination method for the intra mode may be included in the bitstream.

[0664] In one embodiment, the method for determining the intra prediction mode may include a method for deriving the intra prediction mode using samples encoded before the current block or a method for selecting the intra prediction mode from among a plurality of intra prediction modes based on cost.

[0665] A method of selecting an intra prediction mode based on cost may mean a method of selecting an intra prediction mode that causes the smallest cost when performing intra prediction on a current block according to multiple intra prediction modes.

[0666] In one embodiment, information indicating how to determine the intra prediction mode may be included in a sequence parameter set, a picture parameter set, a slice header, or slice data of the bitstream.

[0667] In one embodiment, the prediction encoding unit (3610) may determine the intra prediction mode of the current block according to a method predetermined between the image decoding device (2000) and the image encoding device (3600).

[0668] In one embodiment, the prediction encoding unit (3610) may select an intra prediction mode that causes the smallest cost for encoding the current block among the plurality of intra prediction modes, if the method for determining the intra prediction mode is a method for selecting one of the plurality of intra prediction modes based on cost. Information indicating the selected intra prediction mode may be included in the bitstream. For example, the information indicating the intra prediction mode of the current block may include a flag or index indicating one of the plurality of intra prediction modes.

[0669] In one embodiment, the prediction encoding unit (3610) can derive the intra prediction mode in the same manner as the prediction decoding unit (2030) according to the embodiment described with reference to FIGS. 22 and 23, if the method of determining the intra prediction mode is a method of deriving the intra prediction mode based on the amount of change in pixel values ​​of the restored area around the current block.

[0670] In one embodiment, the prediction encoding unit (3610) can derive the intra prediction mode in the same manner as the prediction decoding unit (2030) according to the embodiment described with reference to FIGS. 24 to 34, if the method of determining the intra prediction mode is a method of deriving the intra prediction mode by using the difference between predetermined sample sets within the surrounding restored area.

[0671] The process of deriving an intra prediction mode by using the difference between a given set of samples within the surrounding restored area has been described above, so a detailed description is omitted here.

[0672] When a prediction block is generated through intra prediction for the current block, the prediction encoding unit (3610) can encode the current block using the prediction block.

[0673] The generation unit (3630) can generate a bitstream including the encoding result of the picture. The bitstream can include the encoding result for the current block.

[0674] In one embodiment, the generation unit (3630) can transmit the bitstream to the image decoding device (2000) over a network.

[0675] In one embodiment, the generation unit (3630) may store the bitstream on a data storage medium including a magnetic medium (e.g., a hard disk, a floppy disk, or a magnetic tape), an optical recording medium (e.g., a CD-ROM or DVD), and a magneto-optical medium (e.g., a floptical disk).

[0676] The generation unit (3630) can generate a bitstream including syntax elements generated through encoding of a picture. Values ​​corresponding to the syntax elements can be included in the bitstream according to the syntax structure.

[0677] The generation unit (3630) can obtain bins included in the bitstream by entropy encoding syntax elements.

[0678] In one embodiment, the bitstream may include information about the prediction mode of the current block within the current picture.

[0679] In one embodiment, if the prediction mode of the current block is intra mode, the bitstream may include information indicating the intra prediction mode of the current block.

[0680] Figure 37 is a flowchart of an image encoding method according to one embodiment.

[0681] Referring to FIG. 37, the image encoding device (3600) can generate an MPM list of the current block using the intra prediction mode of the surrounding blocks (S3710).

[0682] In one embodiment, the video encoding device (3600) may replace the mode of a surrounding block decoded in a non-regular intra mode with the CLP mode of the surrounding block. In this case, the method described above in FIG. 33 may be applied. Here, redundant descriptions are omitted.

[0683] In one embodiment, the video encoding device (3600) can generate an MPM list using the CLP mode of the current block. In other words, the video encoding device (3600) can insert the CLP mode of the current block into the MPM list. The CLP mode of the current block can be derived based on multiple reference sample sets neighboring the current block. In this case, the method described above in FIGS. 24 to 29 can be applied. Here, redundant descriptions are omitted.

[0684] In one embodiment, the video encoding device (3600) may insert the CLP mode of a surrounding block into the MPM list. The surrounding blocks may be subject to the method described above in FIGS. 31 and 32 . Here, redundant descriptions are omitted.

[0685] In one embodiment, the video encoding device (3600) may calculate a CLP cost value for each intra prediction mode included in the MPM list generated in step S3710 based on the CLP cost metric described above in FIG. 34. In this case, the embodiments described above in FIGS. 24 to 29 may be equally applied, and any redundant descriptions will be omitted herein.

[0686] The video encoding device (3600) can rearrange the MPM list by calculating a cost value for each intra prediction mode included in the MPM list generated in step S3710, comparing the calculated cost values, and assigning a lower index in order of the lowest cost value. The cost value for the intra prediction mode included in the MPM list can correspond to a difference between a reference sample set and a prediction sample set obtained based on the prediction direction of the corresponding intra prediction mode. As an example, the video encoding device (3600) can rearrange the MPM list by ordering the calculated cost values ​​in ascending order.

[0687] The video encoding device (3600) can determine the intra prediction mode of the current block (S3720).

[0688] In one embodiment, the video encoding device (3600) can determine the intra prediction mode based on the RD (Rate Distortion) cost for the intra prediction mode. As an example, the video encoding device (3600) can determine the intra prediction mode using a metric of SAD, SATD, or a combination of the two. The video encoding device (3600) can determine the intra prediction mode having the lowest cost value based on a metric that defines the difference between the predictor generated according to the prediction direction of the intra prediction mode and the original block.

[0689] In one embodiment, the video encoding device (3600) can utilize the CLP cost metric described previously in FIG. 34 as an additional metric combination. The cost can be calculated based on the difference between the predicted value and the restored value on a cross line corresponding to a given prediction direction. The content described previously in FIG. 34 can be applied, and any redundant description will be omitted herein.

[0690] In one embodiment, the video encoding device (3600) can determine the intra prediction mode having the lowest cost value based on the combined metrics of the following mathematical expression 3.

[0691]

[0692] In Equation 3, λ1, λ2, and λ3 represent weights applied to each metric. As an example, all three metrics may be considered, or some combination thereof may be considered.

[0693] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list. The video encoding device (3600) may signal an MPM index specifying the intra prediction mode of the current block within the MPM list to the video decoding device (2000).

[0694] The video encoding device (3600) can generate a prediction sample of the current block using the intra prediction mode of the current block (S3730).

[0695] An image encoding device (3600) can encode a current block by performing intra prediction on the current block based on the prediction direction of the intra prediction mode of the current block and the reference sample of the current block. A bitstream resulting from the encoding of the current block can be generated.

[0696] In one embodiment, the video encoding device (3600) may generate residual data using the current block and the predicted block. Information about the residual data may be included in the bitstream.

[0697] In one embodiment, it may be determined that the predicted block corresponds to the current block. In this case, residual data may not be generated.

[0698] In one embodiment of the present disclosure, we propose a method for deriving an intra prediction mode based on a set of surrounding samples.

[0699] In one embodiment of the present disclosure, a method for effectively constructing a Most Probable Mode (MPM) list is proposed.

[0700] In one embodiment of the present disclosure, we propose a method for performing transformation using an intra prediction mode derived based on a set of surrounding samples.

[0701] The technical problems to be achieved through the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present disclosure pertains from the description below.

[0702] A method for decoding an image according to one embodiment may include, when a neighboring block of a current block is a block decoded with a predefined non-regular intra mode, deriving an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block.

[0703] A method of decoding an image according to one embodiment may include a step of generating an MPM list of a current block using derived intra prediction modes of surrounding blocks.

[0704] A method for decoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0705] A method of decoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0706] A method for decoding an image according to one embodiment may include a step of determining a first reference sample set and a second reference sample set among a plurality of reference sample sets for a first directional mode among a plurality of predefined directional modes.

[0707] A method for decoding an image according to one embodiment may include a step of generating a prediction sample for each reference sample included in the first reference sample set by using a prediction direction of a first directional mode and a reference sample included in the second reference sample set.

[0708] In one embodiment, a prediction sample for each reference sample included in the first reference sample set can be obtained by performing interpolation on a reference sample included in the second reference sample set according to a prediction direction of the first directional mode.

[0709] A method for decoding an image according to one embodiment may include a step of obtaining a difference between each reference sample included in the first reference sample set and a prediction sample for each reference sample included in the first reference sample set.

[0710] A method for decoding an image according to one embodiment may include a step of adding the absolute values ​​of the obtained differences.

[0711] A method for decoding an image according to one embodiment may include a step of deriving a directional mode that minimizes the absolute value of the summed difference among the plurality of predefined directional modes as an intra prediction mode of the surrounding block.

[0712] A method for decoding an image according to one embodiment may include a step of obtaining an average difference by dividing the absolute value of the summed difference by the number of reference samples included in a reference sample set determined according to a directional mode.

[0713] A method for decoding an image according to one embodiment may include a step of deriving a directional mode that minimizes the average difference among the plurality of predefined directional modes as an intra prediction mode of the surrounding block.

[0714] In one embodiment, the predefined non-regular intra mode may include at least one of an inter mode, an IBC mode, a palette mode, an IntraTMP mode, a GPM, an SGPM, a BDPCM mode, an EIP mode, an intra prediction fusion mode, or a MIP mode.

[0715] In one embodiment, the plurality of reference sample sets neighboring the peripheral block may include at least one of an upper left reference sample set including an upper left reference sample of the peripheral block, a lower reference sample set located below the upper left reference sample, a right reference sample set located to the right of the upper left reference sample, a left reference sample set located to the left of the upper left reference sample, or an upper reference sample set located above the upper left reference sample.

[0716] A method for decoding an image according to one embodiment may include adding an intra prediction mode candidate derived based on a plurality of reference sample sets neighboring the current block to the MPM list.

[0717] A method for decoding an image according to one embodiment may include a step of determining a third reference sample set and a fourth reference sample set among a plurality of reference sample sets neighboring the current block for a second directional mode among a plurality of predefined directional modes.

[0718] A method for decoding an image according to one embodiment may include a step of generating a prediction sample for each reference sample included in the third reference sample set using the prediction direction of the second directional mode and reference samples included in the fourth reference sample set.

[0719] A method for decoding an image according to one embodiment may include a step of obtaining a difference between prediction samples for each reference sample included in the third reference sample set and each reference sample included in the fourth reference sample set.

[0720] A method for decoding an image according to one embodiment may include a step of deriving a directional mode that minimizes the obtained difference among the plurality of predefined directional modes as the intra prediction mode candidate.

[0721] In one embodiment, the surrounding block may include at least one of a left block, a lower left block, an upper block, an upper right block, or an upper left block of the current block.

[0722] A method of encoding an image according to one embodiment may include, when a neighboring block of a current block is a block encoded in a predefined non-regular intra mode, deriving an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block.

[0723] A method of encoding an image according to one embodiment may include a step of generating an MPM list of a current block using derived intra prediction modes of surrounding blocks.

[0724] A method of encoding an image according to one embodiment may include a step of determining an intra prediction mode of a current block.

[0725] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list.

[0726] A method of encoding an image according to one embodiment may include a step of generating a prediction sample of a current block using an intra prediction mode of the current block.

[0727] A computer-readable recording medium according to one embodiment can record a bitstream including an encoding result of a current block.

[0728] In one embodiment, the encoding result of the current block can be generated by deriving an intra prediction mode of the neighboring block based on a plurality of sets of reference samples neighboring the neighboring block, if the neighboring block of the current block is a block encoded with a predefined non-regular intra mode.

[0729] In one embodiment, the encoding result of the current block can be generated by generating an MPM list of the current block using the derived intra prediction modes of the surrounding blocks.

[0730] In one embodiment, the encoding result of the current block can be generated by determining an intra prediction mode of the current block.

[0731] In one embodiment, the intra prediction mode of the current block may be one of the intra prediction modes included in the MPM list.

[0732] In one embodiment, the encoding result of the current block can be generated by generating a prediction sample of the current block using an intra prediction mode of the current block.

[0733] An image decoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0734] In one embodiment, at least one processor can derive an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block, if the neighboring block of the current block is a block decoded with a predefined non-regular intra mode.

[0735] In one embodiment, at least one processor may generate an MPM list for a current block using derived intra prediction modes of surrounding blocks.

[0736] In one embodiment, at least one processor can determine an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0737] In one embodiment, at least one processor can generate a prediction sample of the current block using an intra prediction mode of the current block.

[0738] An image encoding device according to one embodiment may include at least one memory storing at least one instruction and at least one processor.

[0739] In one embodiment, at least one processor can derive an intra prediction mode of a neighboring block based on a plurality of sets of reference samples neighboring the neighboring block, if the neighboring block of the current block is a block encoded with a predefined non-regular intra mode.

[0740] In one embodiment, at least one processor may generate an MPM list for a current block using derived intra prediction modes of surrounding blocks.

[0741] In one embodiment, at least one processor can determine an intra prediction mode of a current block from among intra prediction modes included in an MPM list.

[0742] In one embodiment, at least one processor can generate a prediction sample of the current block using an intra prediction mode of the current block.

[0743] A method of decoding an image according to one embodiment may include a step of deriving an intra prediction mode of a current block based on a plurality of sets of reference samples neighboring the current block, when the mode of the current block is a predefined non-regular intra mode.

[0744] A method of decoding an image according to one embodiment may include a step of determining a set of transform kernels of a current block based on an induced intra prediction mode of the current block.

[0745] A method of decoding an image according to one embodiment may include a step of determining a transform kernel of a current block within a set of transform kernels.

[0746] A method of decoding an image according to one embodiment may include a step of generating a residual sample of a current block by applying a transform kernel of the current block to transform coefficients of the current block.

[0747] A method for decoding an image according to one embodiment may include a step of determining a first reference sample set and a second reference sample set among a plurality of reference sample sets for a first directional mode among a plurality of predefined directional modes.

[0748] A method for decoding an image according to one embodiment may include a step of generating a prediction sample for each reference sample included in the first reference sample set by using a prediction direction of the first directional mode and a reference sample included in the second reference sample set.

[0749] In one embodiment, a prediction sample for each reference sample included in the first reference sample set can be obtained by performing interpolation on a reference sample included in the second reference sample set according to a prediction direction of the first directional mode.

[0750] A method for decoding an image according to one embodiment may include a step of obtaining a difference between each reference sample included in the first reference sample set and a prediction sample for each reference sample included in the first reference sample set.

[0751] A method for decoding an image according to one embodiment may include a step of adding the absolute values ​​of the obtained differences.

[0752] A method for decoding an image according to one embodiment may include a step of deriving a directional mode that minimizes the absolute value of the summed difference among the plurality of predefined directional modes as an intra prediction mode of the current block.

[0753] A method for decoding an image according to one embodiment may include a step of obtaining an average difference by dividing the absolute value of the summed difference by the number of reference samples included in a reference sample set determined according to a directional mode.

[0754] A method for decoding an image according to one embodiment may include a step of deriving a directional mode that minimizes the average difference among the plurality of predefined directional modes...

Claims

1. When a neighboring block of a current block is a block decoded in a predefined non-regular intra mode, a step of deriving an intra prediction mode of the neighboring block based on a plurality of reference sample sets neighboring the neighboring block; A step of generating an MPM list of the current block using the derived intra prediction mode of the surrounding blocks; A step of determining an intra prediction mode of the current block among the intra prediction modes included in the MPM list; and A method for decoding an image, comprising the step of generating a prediction sample of the current block using an intra prediction mode of the current block.

2. In paragraph 1, The step of deriving the intra prediction mode of the above surrounding blocks is: For a first directional mode among a plurality of predefined directional modes, determining a first reference sample set and a second reference sample set among the plurality of reference sample sets; and A method for decoding an image, comprising the step of generating a prediction sample for each reference sample included in the first reference sample set using the prediction direction of the first directional mode and the reference sample included in the second reference sample set.

3. In paragraph 2, A method for decoding an image, wherein a prediction sample for each reference sample included in the first reference sample set is obtained by performing interpolation on a reference sample included in the second reference sample set according to the prediction direction of the first directional mode.

4. In paragraph 2, The step of deriving the intra prediction mode of the above surrounding blocks is: A step of obtaining a difference between each reference sample included in the first reference sample set and a predicted sample for each reference sample included in the first reference sample set; and A method for decoding an image, further comprising a step of summing the absolute values ​​of the obtained differences.

5. In paragraph 4, The step of deriving the intra prediction mode of the above surrounding blocks is: A method for decoding an image, further comprising a step of deriving a directional mode that minimizes the absolute value of the summed difference among the plurality of predefined directional modes as an intra prediction mode of the surrounding block.

6. In paragraph 4, The step of deriving the intra prediction mode of the above surrounding blocks is: A step of obtaining an average difference by dividing the absolute value of the above-mentioned summed difference by the number of reference samples included in a reference sample set determined according to the directional mode; and A method for decoding an image, further comprising a step of deriving a directional mode that minimizes the average difference among the plurality of predefined directional modes as an intra prediction mode of the surrounding block.

7. In paragraph 1, A method for decoding an image, wherein the above-described predefined non-regular intra mode includes at least one of an inter mode, an IBC (Intra Block Copy) mode, a Palette mode, an IntraTMP (Intra Template Matching Prediction) mode, a GPM (Geometric Partitioning Mode), an SGPM (Spatial Geometric Partitioning Mode), a BDPCM (Block-based Delta Pulse Code Modulation) mode, an EIP (Extrapolation filter-based Intra Prediction) mode, an Intra Prediction Fusion mode, or a MIP (Matrix-based Intra Prediction) mode.

8. In paragraph 1, A method for decoding an image, wherein the plurality of reference sample sets neighboring the peripheral block include at least one of an upper left reference sample set including an upper left reference sample of the peripheral block, a lower reference sample set located below the upper left reference sample, a right reference sample set located to the right of the upper left reference sample, a left reference sample set located to the left of the upper left reference sample, or an upper reference sample set located above the upper left reference sample.

9. In paragraph 1, The step of generating the MPM list of the current block above is: A method for decoding an image, comprising the step of adding an intra prediction mode candidate derived based on a plurality of reference sample sets neighboring the current block to the MPM list.

10. In paragraph 9, The step of adding the intra prediction mode candidate to the MPM list is: For a second directional mode among a plurality of predefined directional modes, a step of determining a third reference sample set and a fourth reference sample set among a plurality of reference sample sets neighboring the current block; A step of generating a prediction sample for each reference sample included in the third reference sample set using the prediction direction of the second directional mode and the reference samples included in the fourth reference sample set; A step of obtaining a difference between predicted samples for each reference sample included in the third reference sample set and each reference sample included in the fourth reference sample set; and A method for decoding an image, further comprising a step of deriving a directional mode that minimizes the obtained difference among the plurality of predefined directional modes as the intra prediction mode candidate.

11. In paragraph 1, A method for decoding an image, wherein the surrounding block includes at least one of a left block, a lower left block, an upper block, an upper right block, or an upper left block of the current block.

12. When a neighboring block of a current block is a block encoded in a predefined non-regular intra mode, a step of deriving an intra prediction mode of the neighboring block based on a plurality of reference sample sets neighboring the neighboring block; A step of generating an MPM list of the current block using the derived intra prediction mode of the surrounding blocks; A step of determining an intra prediction mode of the current block, wherein the intra prediction mode of the current block is one of the intra prediction modes included in the MPM list; and A method for encoding an image, comprising the step of generating a prediction sample of the current block using an intra prediction mode of the current block.

13. In a computer-readable recording medium that records a bitstream, The above bitstream contains the encoding result of the current block, The encoding result of the current block above is, If a neighboring block of the current block is a block encoded in a predefined non-regular intra mode, an intra prediction mode of the neighboring block is derived based on a plurality of reference sample sets neighboring the neighboring block, Generate an MPM list of the current block using the derived intra prediction mode of the surrounding blocks, Determine the intra prediction mode of the current block, wherein the intra prediction mode of the current block is one of the intra prediction modes included in the MPM list, A recording medium generated by generating a prediction sample of the current block using the intra prediction mode of the current block.

Images