Image filtering device and method

Abstract

A method for filtering an image by a filtering device according to an embodiment may comprise the steps of: determining a current filter applied to a current block within a filter set including a plurality of filters; pre-processing a difference between a current sample and a neighboring sample of the current sample within the current block on the basis of a predefined function; and filtering the current sample on the basis of the current filter and the pre-processed difference.

Description

Video filtering device and method

[0001] The present disclosure relates to the field of image filtering, and more specifically, to a device and method for adaptively filtering an image based on a fixed filter during an image encoding or decoding process.

[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] 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.

[0005] The residual block generated through inter prediction or intra prediction can be transformed and quantized and then passed to the decoder.

[0006] The encoder and decoder can reconstruct the current block by combining the predicted block and the residual block of the current block. The encoder and decoder can apply a deblocking filter and / or an adaptive loop filter to the reconstructed current block to remove artifacts within the current block.

[0007] A method of filtering an image by a filtering device according to one embodiment may include a step of determining a current filter to be applied to a current block within a filter set including a plurality of filters.

[0008] A method for filtering an image by a filtering device according to one embodiment may include a step of preprocessing a difference between a current sample and surrounding samples of a current sample within a current block based on a predefined function.

[0009] In one embodiment, the predefined function can be defined using an exponential function expressed as a power of a natural constant.

[0010] In one embodiment, the output shape of a predefined function can be controlled using at least one parameter.

[0011] A method of filtering an image by a filtering device according to one embodiment may include a step of filtering a current sample based on a current filter and a preprocessed difference.

[0012] A filtering device according to one embodiment may include at least one memory storing at least one instruction, and at least one processor operating according to the at least one instruction.

[0013] A processor according to one embodiment can determine a current filter to be applied to a current block within a filter set including a plurality of filters.

[0014] A processor according to one embodiment may calculate a difference between a current sample and surrounding samples of the current sample within a current block based on a predefined function.

[0015] In one embodiment, the predefined function can be defined using an exponential function expressed as a power of a natural constant.

[0016] In one embodiment, the output shape of a predefined function can be controlled using at least one parameter.

[0017] A processor according to one embodiment may filter a current sample based on a current filter and a preprocessed difference.

[0018] A computer-readable recording medium according to one embodiment may include a bitstream.

[0019] In one embodiment, the bitstream may include filter information used to filter the current image according to a filtering method.

[0020] In one embodiment, the bitstream may include an encoding result generated based on a current image filtered according to a filtering method.

[0021] FIG. 1 is a block diagram of an image decoding device according to one embodiment.

[0022] FIG. 2 is a block diagram of an image encoding device according to one embodiment.

[0023] FIG. 3 illustrates a process of dividing a current encoding unit to determine at least one encoding unit according to one embodiment.

[0024] FIG. 4 illustrates a process of dividing a non-square coding unit to determine at least one coding unit according to one embodiment.

[0025] 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.

[0026] FIG. 6 illustrates a method for determining a predetermined coding unit among an odd number of coding units according to one embodiment.

[0027] 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.

[0028] 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.

[0029] FIG. 9 illustrates a process of dividing a first encoding unit to determine at least one encoding unit according to one embodiment.

[0030] 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.

[0031] 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.

[0032] FIG. 12 illustrates that, according to one embodiment, the processing order between multiple encoding units may vary depending on the process of splitting the encoding units.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] FIG. 19 is a block diagram of an image encoding and decoding system according to one embodiment.

[0040] Fig. 20 is a block diagram illustrating a configuration of a filtering device according to one embodiment.

[0041] Figure 21 is a diagram illustrating a filter according to one embodiment.

[0042] Fig. 22 is a block diagram illustrating the configuration of a classifier according to one embodiment.

[0043] Fig. 23 is a block diagram illustrating a configuration of a filtering device according to one embodiment.

[0044] Fig. 24 is a block diagram illustrating a configuration of a filtering device according to one embodiment.

[0045] Figure 25 is a flowchart for explaining a method of filtering an image according to one embodiment.

[0046] FIG. 26 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0047] FIG. 27 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0048] FIG. 28 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0049] FIG. 29 is a flowchart illustrating a method for filtering an image according to one embodiment of the present disclosure.

[0050] FIG. 30 is a flowchart illustrating a method for filtering an image according to one embodiment of the present disclosure.

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

[0052] 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.

[0053] 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.

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

[0055] In this 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 performed by other components.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] FIG. 1 illustrates a block diagram of an image decoding device (100) according to one embodiment.

[0060] 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.

[0061] 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.

[0062] To describe in detail the operation of the video decoding device (100), the bitstream acquisition unit (110) can receive a bitstream.

[0063] 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 an 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.

[0064] Below, the division of encoding units according to one embodiment of the present disclosure is described in detail.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] A single maximum coding block (CTB) can be divided into MxN coding blocks containing MxN samples (M, N are integers).

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] If the current encoding unit is not quad-split, the information indicating whether it is multi-split may indicate whether the current encoding unit will not be split any further (NO_SPLIT) or whether it will be binary / ternary split.

[0078] 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.

[0079] 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.

[0080] 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).

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The shape and size of the transformation block and the prediction block may be unrelated.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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).

[0100] 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).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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).

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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).

[0115] 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.

[0116] 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.

[0117] 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).

[0118] 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.

[0119] 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).

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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).

[0130] 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.

[0131] 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).

[0132] 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.

[0133] 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).

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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).

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] According to one embodiment, the image decoding device (100) can divide the first encoding unit to determine encoding units of various shapes.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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).

[0152] 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).

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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).

[0169] 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.

[0170] 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.

[0171] 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).

[0172] 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).

[0173] 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.

[0174] 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.

[0175] 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).

[0176] 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.

[0177] 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.

[0178] 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.

[0179] According to one embodiment, the image decoding device (100) may utilize a predetermined data unit from which recursive division of the encoding unit begins.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] Hereinafter, a method for determining a partitioning rule according to one embodiment of the present disclosure will be described in detail.

[0191] 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.

[0192] 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).

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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).

[0212] 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.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] 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.

[0217] 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.

[0218] 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).

[0219] FIG. 19 is a block diagram of an image encoding and decoding system according to one embodiment.

[0220] 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).

[0221] 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).

[0222] 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).

[0223] 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).

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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).

[0228] 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.

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] Fig. 20 is a block diagram illustrating a configuration of a filtering device according to one embodiment.

[0238] Referring to FIG. 20, the filtering device (2000) may include a classifier (2010) and a filter unit (2030).

[0239] The classifier (2010) and filter unit (2030) may be implemented with at least one processor. At least one processor may include processing circuitry.

[0240] The classifier (2010) and the filter unit (2030) can operate according to at least one instruction stored in at least one memory.

[0241] The filtering device (2000) may include at least one memory for storing input / output data of the classifier (2010) and the filter unit (2030). The filtering device (2000) may include a memory control unit for controlling data input / output of at least one memory.

[0242] In one embodiment, the filtering device (2000) may correspond to the loop filtering unit (1940, 1970) illustrated in FIG. 19. In one embodiment, the filtering device (2000) may be included in each of the image decoding device (100) and the image encoding device (200).

[0243] In one embodiment, the filtering device (2000) can generate a filtered image from an input image. The filtering device (2000) can classify samples or blocks included in the image according to their characteristics, and filter the samples included in the image using a filter appropriate for the classification result.

[0244] In one embodiment, the classifier (2010) can determine which of several classes each of the samples or blocks contained in the image belongs to.

[0245] The filter unit (2030) can determine a filter (or filter coefficients) to be used for filtering samples within a block by considering at least one of the classification results or filter information by the classifier (2010). The filter unit (2030) can apply the adaptively determined filter to one sample and its surrounding samples to generate a filtered sample.

[0246] In one embodiment, if the classification process by the classifier (2010) is performed on a block-by-block basis, the same filter may be applied to samples included in the same block. In one embodiment, if the classification process by the classifier (2010) is performed on a sample-by-sample basis, a filter independently determined for each sample in the image may be applied.

[0247] In one embodiment, the image classified by the classifier (2010) may include at least one of a reconstructed image, a Gaussian-filtered image, a before-blocking-filter image, a deblocking filtered reconstructed image, a predicted image, a residual image, a reconstructed image with a fixed filter applied, a predicted image with a fixed filter applied, or a residual image with a fixed filter applied.

[0248] Here, the predicted image may be an image generated through intra-prediction or inter-prediction for blocks, and the residual image may be an image corresponding to the difference between the original image and the predicted image. Furthermore, the restored image may be an image generated by combining the predicted image and the residual image.

[0249] A deblocking filter can be applied to a restored image to remove artifacts between blocks. A fixed filter may represent a filter whose filter coefficients are pre-agreed between the image encoding device (200) and the image decoding device (100). In other words, a fixed filter may represent a filter predefined in the image encoding device (200) and the image decoding device (100).

[0250] In one embodiment, the image filtered by the filter unit (2030) may include at least one of a restored image, a Gaussian filtered image, an image before a blocking filter, a restored image after deblocking filtering, a predicted image, a residual image, a restored image with a fixed filter applied, a predicted image with a fixed filter applied, or a residual image with a fixed filter applied.

[0251] In one embodiment, when multiple images are filtered by the filter unit (2030), the filtered images may be combined (e.g., weighted combined) to obtain a final filtered image.

[0252] In one embodiment, the types of images classified by the classifier (2010) and the types of images filtered by the filter unit (2030) may be different. For example, a deblocking-filtered restored image may be filtered based on the classification result for the residual image. As another example, a restored image, a deblocking-filtered restored image, a restored image with a fixed filter applied, a residual image, and a residual image with a fixed filter applied may be filtered based on the classification result for the deblocking-filtered restored image or the residual image.

[0253] The types of images classified by the classifier (2010) and filtered by the filter unit (2030) are not limited to the examples mentioned and can be determined by various combinations.

[0254] In one embodiment, the types of images classified by the classifier (2010) and images filtered by the filter unit (2030) may be the same.

[0255] In the following, it is described that the current image is input to the classifier (2010) and the filter unit (2030), but the type of image input to the classifier (2010) and the type of image input to the filter unit (2030) may be the same or different from each other.

[0256] When the classification result of the current image is obtained by the classifier (2010), the filter unit (2030) can determine a filter suitable for filtering samples within the current image based on the classification result and / or filter information. Then, the filter unit (2030) can filter samples within the current image using the determined filter.

[0257] In one embodiment, the filter information can be obtained from the bitstream. Alternatively, in one embodiment, the filter information can be derived from the image encoding device (200) and the image decoding device (100) in the same manner without separate signaling.

[0258] In one embodiment, the bitstream may correspond to the encoding result of the image. In one embodiment, the bitstream may be generated by the image encoding device (200) and transmitted to the image decoding device (100).

[0259] In one embodiment, the bitstream may be stored on a storage medium such as an optical media, a hard disk, or the like.

[0260] In one embodiment, the filter information may include at least one of information indicating whether adaptive filtering is applied to the current image or a block within the current image (e.g., a slice, a maximum coding unit, or a group of maximum coding units), information indicating which of several adaptation parameter sets (APS) included in the bitstream is used for the current image or a block within the current image, or information indicating which of several filter sets is used for the current image or a block within the current image.

[0261] In one embodiment, the APS may include information about filter coefficients, and a filter identified from the classification result by the classifier (2010) may be applied to a sample within the current image. In one embodiment, the classification result by the classifier (2010) may be the class (or class index) of the current block. The filter identified from the classification result may be a filter corresponding to the class of the current block within the filter set.

[0262] According to embodiments of the present disclosure, the output of a fixed filter may be output as a final filtered image, or may be used as an intermediate sample to which a signaled filter is applied. As an example, the signaled filter may represent a filter included in a filter set signaled via APS.

[0263] In the present disclosure, filtering using a signaled filter may be referred to as online filtering, and filtering using a fixed filter may be referred to as offline filtering. Furthermore, the signaled filter may be referred to as an online filter, and the fixed filter may be referred to as an offline filter.

[0264] Figure 21 is a diagram illustrating a filter according to one embodiment.

[0265] In one embodiment, when filtering an image, a first filter (2110), a second filter (2120), and a third filter (2130) as illustrated in FIG. 21 may be used. The first sample (2111), the second sample (2131), and the third sample (2131) may represent samples (which may be referred to as current samples) filtered using the first filter (2110), the second filter (2120), and the third filter (2130), respectively.

[0266] In one embodiment, the first filter (2110) may be applied to a luma-restored image, and the second filter (2120) may be applied to a chroma-restored image. The third filter (2130) may be applied to a restored image to which a fixed filter has been applied. Alternatively, the third filter (2130) may be an example of a fixed filter applied to a restored image.

[0267] In one embodiment, the first filter (2110) applied to the luma restored image and the second filter (2120) applied to the chroma restored image may have a size of 9x9 as illustrated in FIG. 21. The third filter (2130) may have a size of 13x13 as illustrated in FIG. 21. However, FIG. 21 is merely an example, and the embodiments of the present disclosure are not limited thereto, and the first to third filters (2110, 2120, 2130) may be defined in various sizes.

[0268] The filter unit (2030) can determine filter coefficients included in at least one of the first filter (2110), the second filter (2120), and the third filter (2130) based on the classification result and / or filter information of the classifier (2010). For example, based on the class of the current block in the current image and the filter set used for filtering the current image, filter coefficients 0 to 9 of the first filter (2110), filter coefficients 0 to 19 of the second filter (2120), and filter coefficients 0 to 17 of the third filter (2130) can be determined.

[0269] In one embodiment, one or more filters may be used to filter an image. The filter configuration illustrated in FIG. 21 is an example, and the present invention is not limited thereto. In addition to the three filters (2110, 2120, and 2130) illustrated in FIG. 21, various other types of filters may be applied to filter an image.

[0270] Additionally, although FIG. 20 illustrates that the filtering device (2000) includes one classifier (2010), it is not limited thereto, and the filtering device (2000) may include multiple classifiers (2010).

[0271] For example, if the filtering device (2000) includes a first classifier, a second classifier, and a third classifier, the first classifier, the second classifier, and the third classifier can classify blocks of the current image in different ways.

[0272] In one embodiment, if the filtering device (2000) includes one classifier, the classifier can classify blocks of the current image based on the directional values ​​and / or activity values ​​described below.

[0273] In one embodiment, when the filtering device (2000) includes a first classifier, a second classifier, and a third classifier, the first classifier may classify a block of the current image based on a directional feature value of the block in the deblocking filtered restored image, the second classifier may classify a block of the current image based on a sample feature value in the deblocking filtered restored image, and the third classifier may classify a block of the current image based on a sample feature value in the residual image.

[0274] In one embodiment, when a filtering device (2000) includes a plurality of classifiers (2010), one of the plurality of classifiers (2010) may be selected, and a classification result by the selected classifier (2010) may be transmitted to the filter unit (2030). When the filtering device (2000) is included in the image decoding device (100), information indicating one of the plurality of classifiers (2010) may be obtained from a bitstream.

[0275] In one embodiment, if the filtering device (2000) includes multiple classifiers (2010), the classification results from the multiple classifiers (2010) may be combined to obtain a final classification result. For example, if the current block is classified by multiple classifiers (2010), values ​​representing the classes to which the current block belongs may be obtained, and a class corresponding to the average value of the obtained values ​​may be determined as the final class of the current block.

[0276] Hereinafter, a classifier (2010) that classifies the current block based on the directionality value and / or the activity value is described with reference to FIG. 22.

[0277] The current block may be a slice, tile, maximum coding unit, encoding unit, prediction unit, or transform unit segmented from the current image. In one embodiment, the size of the current block may be greater than 1x1. For example, the size of the current block may be 2x2 or 4x4.

[0278] Fig. 22 is a block diagram illustrating the configuration of a classifier according to one embodiment.

[0279] Referring to FIG. 22, the classifier (2200) may include a directionality determination unit (2210), an activity determination unit (2230), and a class determination unit (2250).

[0280] The directionality determination unit (2210) can determine the directionality value of the current block to be classified, and the activity determination unit (2230) can determine the activity value of the current block.

[0281] In the present disclosure, a directionality value may be referred to as a directionality index, a directionality parameter, a directionality variable, a direction value, a direction index, a direction parameter, or a direction variable.

[0282] Additionally, the activity value may be referred to as an activity index, an activity parameter, an activity variable, a strength value, a strength index, a strength parameter, or a strength variable.

[0283] The class determination unit (2250) may determine which class among multiple classes the current block belongs to by using at least one of the directionality value and the activity value. For example, the class determination unit (2250) may determine that the current block belongs to a class indicated by a value combining the directionality value and the activity value. For example, the class determination unit (2250) may determine the class index of the current block by using at least one of the directionality value and the activity value.

[0284] As described above, once the class corresponding to the current block is determined, the filter unit (2030) can determine a filter (or filter coefficient) for filtering samples within the current block based on the determined class.

[0285] In one embodiment, the directionality value determined by the directionality determination unit (2210) and the activity value determined by the class determination unit (2250) may be determined based on 2-D Laplacian values. In the present disclosure, the Laplacian values ​​may be referred to as gradient values.

[0286] In one embodiment, the directionality determination unit (2210) can obtain the gradient value of the current block (or samples within the current block) using samples of the current block and / or surrounding samples of the current block.

[0287] In one embodiment, the directionality determination unit (2210) can obtain the gradient value of the current block by applying a window including the current block. In one embodiment, the window size may be larger than the size of the current block. For example, when the size of the current block is 2x2, the size of the window may be 4x4, 8x8, or 12x12. In this case, samples of the current block and surrounding samples (or samples of surrounding blocks) may be used to obtain the gradient value of the current block.

[0288] In one embodiment, the gradient value of the current block may include a gradient value in at least one of a horizontal direction, a vertical direction, a 45 degree diagonal direction, or a 135 degree diagonal direction.

[0289] In one embodiment, the directionality determination unit (2210) may determine the directionality value using a gradient value in at least one direction among a horizontal direction, a vertical direction, a 45 degree diagonal direction, and a 135 degree diagonal direction. For example, the directionality determination unit (2210) may determine the directionality value using gradient values ​​in the horizontal direction, the vertical direction, the 45 degree diagonal direction, and the 135 degree diagonal direction.

[0290] In one embodiment, the activity determination unit (2230) may determine the activity value using a gradient value in at least one direction among a horizontal direction, a vertical direction, a 45-degree diagonal direction, or a 135-degree diagonal direction. For example, the activity determination unit (2230) may determine the activity value using gradient values ​​in the horizontal direction and the vertical direction.

[0291] The class determination unit (2250) may determine the class (or class index) of the current block using at least one of a directionality value and an activity value. In one embodiment, the class determination unit (2250) may select a filter using the class of the current block determined within a set of filters used for filtering the current block.

[0292] In one embodiment, the class determination unit (2250) may determine the class of the current block based on a value that combines a directionality value and an activity value. For example, the class determination unit (2250) may derive a number of directionality values.

[0293] In one embodiment, the class determination unit (2250) may determine a class using the number of derived directionalities. The number of directionalities may represent the total number of directionalities. The number of directionalities may be derived based on predefined parameters. For example, the class determination unit (2250) may calculate a class index by adding the directional value to the product of the number of directionalities and the activity value.

[0294] Below, an example of classifying classes using multiple classifiers is described with reference to FIG. 23.

[0295] Fig. 23 is a block diagram illustrating a configuration of a filtering device according to one embodiment.

[0296] Referring to FIG. 23, the filtering device (2300) may include a first classifier (2310), a second classifier (2320), and a filter unit (2330). The methods described above in FIGS. 20 and 22 may be substantially equally applied to the present embodiment, and any duplicate descriptions thereof will be omitted herein. The filtering device (2300) of FIG. 23 may be an example of the filtering device (2000) of FIG. 20.

[0297] The filtering device (2300) can classify classes for specifying filters within a filter set using multiple classifiers. In FIG. 23, the case where the filtering device (2300) includes two classifiers is mainly described, but the present invention is not limited thereto, and the filtering device (2300) can classify classes for specifying filters within a filter set using two or more classifiers.

[0298] The first classifier (2310), the second classifier (2320), and the filter unit (2330) may be implemented with at least one processor. At least one processor may include a processing circuit.

[0299] The first classifier (2310), the second classifier (2320), and the filter unit (2330) can operate according to at least one instruction stored in at least one memory.

[0300] The filtering device (2300) may include at least one memory that stores input / output data of the first classifier (2310), the second classifier (2320), and the filter unit (2330). The filtering device (2300) may include a memory control unit that controls data input / output of at least one memory.

[0301] In one embodiment, the filtering device (2300) may correspond to the loop filtering unit (1940, 1970) illustrated in FIG. 19. In one embodiment, the filtering device (2300) may be included in each of the image decoding device (100) and the image encoding device (200).

[0302] In one embodiment, the filtering device (2300) can generate a filtered image from an input image. In one embodiment, the filtering device (2300) can generate a filtered image by applying a filter to the input image.

[0303] In one embodiment, the filtering device (2300) can classify samples or blocks included in an image according to characteristics, and filter the samples included in the image using a filter suitable for the classification result.

[0304] In one embodiment, the first classifier (2310) and the second classifier (2320) can determine which class among several classes each of the samples or blocks included in the image belongs to.

[0305] The filter unit (2330) can determine a filter (or filter coefficients) to be used for filtering samples within a block based on the classification results by the first classifier (2310) or the second classifier (2320). The filter unit (2330) can apply the adaptively determined filter to one sample and its surrounding samples to generate a filtered sample.

[0306] In one embodiment, both the first classifier (2310) and the second classifier (2320) can classify classes to specify filters within a filter set. The first classifier (2310) and the second classifier (2320) can classify blocks of the current image in different ways.

[0307] In one embodiment, both the first classifier (2310) and the second classifier (2320) may be Laplacian-based classifiers that determine directionality and activity values ​​based on 2-D Laplacian values. The embodiment described above in FIG. 22 may be applied in the same manner, and any redundant descriptions are omitted herein.

[0308] In one embodiment, the first classifier (2310) and the second classifier (2320) can determine the class of a block in the current image using activity values ​​and directionality values. The first classifier (2310) and the second classifier (2320) can derive the activity values ​​and directionality values ​​based on a gradient in at least one of the vertical, horizontal, or diagonal directions. The diagonal direction can include a 45-degree diagonal direction and / or a 135-degree diagonal direction. A window surrounding the current block can be used to obtain the gradient.

[0309] In one embodiment, at least one of the activity value or the directionality value may be determined in a different manner, and the classification results of the current block in the image by each classifier (2310, 2320) may be determined differently.

[0310] In one embodiment, the first classifier (2310) and the second classifier (2320) may determine the class of a block within the current image by adding the directionality value to the product of the number of directionality and the activity value. In this case, the number of directionality may be determined in different ways, and the classification results of the block within the current image by each classifier (2310, 2320) may be determined differently.

[0311] Meanwhile, if the current block is classified by the classifier described in FIGS. 20 to 23, a filter to be applied to the current block can be determined based on the classification result. The size of the current block may be 1x1 or larger. For example, the size of the current block may be 2x2 or 4x4. The determined filter may be applied to the current block on a sample-by-sample basis. Filter coefficients may be obtained from the determined filter.

[0312] In one embodiment, a filtered sample for a current sample can be obtained by applying filter coefficients of a determined filter to surrounding samples of the current sample. The surrounding samples to which each filter coefficient is applied can be determined based on the size, type, or shape of the filter. The filter coefficients can be applied to the corresponding surrounding samples. As an example, the filter size, type, or shape of the filter can be defined as in the embodiment described above in FIG. 21. In addition, the filter coefficients of the filter can be defined as in the embodiment described above in FIG. 21. As an example, the filtered sample can be obtained using the following mathematical expression 1.

[0313]

[0314] In mathematical expression 1, x cur represents the current sample (or pixel) being filtered, and x out represents the filtered sample. x k ref represents the kth surrounding sample (or reference sample). The kth surrounding sample may refer to a surrounding sample to which a filter coefficient with an index k value is applied within the filter. In other words, the kth surrounding sample may refer to a surrounding sample to which a filter coefficient wk is applied. The kth surrounding sample is a filter coefficient w k can represent the surrounding samples corresponding to c max and c min represent the upper and lower bounds of the clipping function clip(), respectively, and in this disclosure, c max and cmin can also be expressed in terms of maximum and minimum values. w k represents the filter coefficient corresponding to the kth surrounding sample, and in this disclosure, w k can also be expressed as a weight w k can be obtained from the filter applied to the current block.

[0315] According to mathematical expression 1, the filtering device (2000) can multiply the filter coefficient corresponding to the clipped value of the difference between the current sample and the surrounding sample for each surrounding sample and add them up to generate a filtered sample of the current sample. In the present disclosure, the expression of applying the filter coefficient to the surrounding sample may be an expression encompassing the expression of applying or multiplying the filter coefficient to the difference between the surrounding sample and the current sample.

[0316] The filtering device (2000) can apply a filter coefficient to the difference between the current sample and the surrounding samples corresponding to each filter coefficient in the filter. At this time, the difference between the surrounding sample and the current sample can be determined as a value within a predefined upper limit and lower limit according to a clipping function. The filtering device (2000) can obtain a filtered sample by summing the difference values ​​to which the filter coefficients of the filter are applied. As an example, a value obtained by summing all difference values ​​to which the filter coefficients are applied may be determined as the filtered sample value of the current sample, and as another example, a value obtained by adding a sample value of the current sample (e.g., a restored sample value) to a value obtained by summing all difference values ​​to which the filter coefficients are applied may be determined as the filtered sample value of the current sample.

[0317] As discussed, by reflecting the difference between the current sample and the surrounding reference samples into the current sample, image distortion can be reduced and subjective image quality can be improved. To achieve this filtering goal, it is desirable to set surrounding samples with high similarity to the currently filtered sample to contribute significantly to filtering, while setting surrounding samples with low similarity to contribute less to filtering.

[0318] However, as in the example described in Equation 1, differential adjustment by simply setting upper and lower bounds through clipping cannot effectively reflect the filtering contribution based on the aforementioned similarity. For example, if the sample falls within the upper and lower bounds, there is a problem in that even surrounding samples that differ significantly from the current sample relative to the remaining surrounding samples contribute equally to filtering.

[0319] In one embodiment of the present disclosure, a method for preprocessing the difference between a currently filtered sample and surrounding samples is proposed to improve the aforementioned problems. By applying filter coefficients to the difference between the preprocessed current sample and surrounding samples according to one embodiment of the present disclosure, the similarity with the current sample can be effectively reflected in the filtering process, thereby improving filtering performance and enhancing compression efficiency.

[0320] FIG. 24 is a block diagram illustrating a configuration of a filtering device according to one embodiment of the present disclosure.

[0321] Referring to FIG. 24, the filtering device (2400) may include a classifier (2410), a preprocessing unit (2420), and a filter unit (2430). The methods described above in FIGS. 20 to 23 may be substantially identically applied to the present embodiment, and any redundant description thereof will be omitted herein. The filtering device (2400) of FIG. 24 may be an example of the filtering device (2000) of FIG. 20.

[0322] The classifier (2410), preprocessing unit (2420), and filter unit (2430) may be implemented with at least one processor. At least one processor may include a processing circuit.

[0323] The classifier (2410), preprocessing unit (2420), and filter unit (2430) can operate according to at least one instruction stored in at least one memory.

[0324] The filtering device (2400) may include at least one memory that stores input / output data of the classifier (2410), the preprocessing unit (2420), and the filter unit (2430). The filtering device (2400) may include a memory control unit that controls data input / output of at least one memory.

[0325] In one embodiment, the filtering device (2400) may correspond to the loop filtering unit (1940, 1970) illustrated in FIG. 19. In one embodiment, the filtering device (2400) may be included in each of the image decoding device (100) and the image encoding device (200).

[0326] In one embodiment, the filtering device (2400) can generate a filtered image from an input image. The filtering device (2400) can classify samples or blocks included in the image according to their characteristics, and filter the samples included in the image using a filter appropriate for the classification result.

[0327] In one embodiment, the classifier (2410) can determine which of several classes each of the samples or blocks included in the image belongs to.

[0328] The filter unit (2430) may determine a filter (or filter coefficients) to be used for filtering samples within a block by considering at least one of the classification results or filter information by the classifier (2410). The filter unit (2430) may apply the adaptively determined filter to one sample and its surrounding samples to generate a filtered sample. The embodiments described above in FIGS. 20 to 23 may be applied, and any redundant descriptions will be omitted herein.

[0329] In one embodiment of the present disclosure, the preprocessing unit (2420) may perform preprocessing on reference information provided to the filter unit (2430). The preprocessing unit (2420) may preprocess the difference between the current sample and the surrounding sample (or reference sample) based on a predefined function. In the present disclosure, the reference information may represent the difference between the current sample and the surrounding sample.

[0330] The preprocessing unit (2420) may perform preprocessing on reference information using a predetermined function according to an embodiment of the present disclosure instead of a clipping function that simply sets upper and lower limits as in the embodiment described in mathematical expression 1 above.

[0331] Although FIG. 24 illustrates that the preprocessing unit (2420) is a separate configuration independent from the filter unit (2430), it is not limited thereto. For example, the preprocessing unit (2420) may be implemented as a configuration included in the filter unit (2430), and the preprocessing process performed in the preprocessing unit (2420) may also be performed by the filter unit (2430).

[0332] The preprocessing unit (2420) can preprocess the difference between the current sample and the surrounding samples of the current sample in the current block based on a predefined function. In the present disclosure, for the convenience of explanation, the above-described predefined function for preprocessing may be referred to as a parametric function. The name is not limited thereto, and the parametric function may also be referred to as a parameter-based function, an exponential-based function, a preprocessing function, a parameter operation, a parameter-based operation, an exponential operation, an exponential-based operation, a preprocessing operation, a parametric mathematical expression, a parameter-based mathematical expression, an exponential mathematical expression, an exponential-based mathematical expression, a preprocessing mathematical expression, a parametric preprocessing, a parameter-based preprocessing, an exponential-based preprocessing, an exponential function-based preprocessing, etc. As an example, the parametric function may be predefined in each of the image decoding apparatus (100) and the image encoding apparatus (200).

[0333] In one embodiment, the output shape of a parameter function can be adjusted using at least one parameter. For example, the preprocessing unit (2420) can adjust at least one of the slope, peak position, maximum value, minimum value, or convergence value of the function using the parameter.

[0334] Additionally, in one embodiment, the parameter function may be defined using an exponential function expressed as a power of a natural constant. As an example, the exponential function may have a natural constant as its base and an exponent that combines the difference between the surrounding samples and the current sample and at least one parameter. Specific embodiments of the parameter function used by the preprocessing unit (2420) are described in detail in FIGS. 25 to 28 .

[0335] The filter unit (2430) can determine a filter (or filter coefficients) used for filtering samples within a block based on the classification results by the classifier (2410). The filter unit (2430) can apply the determined filter to the samples within the block and their surrounding samples to generate filtered samples.

[0336] The filter unit (2430) can filter samples within the current block using the difference between the current sample and surrounding samples preprocessed by the determined filter and preprocessing unit (2420). The filter unit (2430) can multiply the preprocessed value of the difference between the current sample and surrounding samples for each sample by a filter coefficient and add them up to generate a filtered sample of the current sample.

[0337] The filter unit (2430) can apply filter coefficients to the preprocessed difference between the current sample and surrounding samples corresponding to each filter coefficient within the filter. The filter unit (2430) can obtain filtered samples by summing the difference values ​​to which the filter coefficients of the filter are applied.

[0338] In one embodiment, the filter unit (2430) may obtain filter coefficients from the determined filter. The filter unit (2430) may determine a group of surrounding samples of the current sample, each of which includes surrounding samples corresponding to a plurality of filter coefficients. The group of surrounding samples may include surrounding samples to which the filter coefficients of the determined filter are applied. As an example, the preprocessing performed by the preprocessing unit (2420) may be performed on the difference between each surrounding sample in the group of surrounding samples and the current sample.

[0339] The filter unit (2430) can obtain a filtered sample value of the current sample by adding the value obtained by multiplying the difference between each preprocessed surrounding sample and the current sample by the filter coefficient corresponding to each surrounding sample. As an example, the filter unit (2430) can obtain a filtered sample using the following mathematical expression 2.

[0340]

[0341] In Equation 2, x cur represents the current sample (or pixel) being filtered, and x out represents the filtered sample. x k ref represents the kth surrounding sample (or reference sample). The kth surrounding sample may mean a surrounding sample to which the filter coefficient with the index k value is applied within the filter. In other words, the kth surrounding sample is the filter coefficient w k can represent the surrounding samples to which the filter coefficient w is applied. The k-th surrounding sample is the filter coefficient w k can represent the surrounding samples corresponding to w k represents the filter coefficient corresponding to the kth surrounding sample, and in this disclosure, w k can also be expressed as a weight w k can be obtained from the filter applied to the current block. θ represents the parameter of the parameter function.

[0342] Referring to Equation 2, the filtered sample can be obtained by multiplying the preprocessed difference by the filter coefficient using a parametric function with θ as a parameter for each filter coefficient and adding the values. The difference between the current sample and the surrounding samples can be preprocessed using a parametric function with θ as a parameter.

[0343] As an example, the sum of all difference values ​​to which the filter coefficients are applied may be determined as the filtered sample value of the current sample, and as another example, the sum of all difference values ​​to which the filter coefficients are applied may be determined as the filtered sample value of the current sample, plus the sample value of the current sample (e.g., the restored sample value).

[0344] Below, specific examples of a preprocessing process using a parameter function are described in FIGS. 25 to 28.

[0345] FIG. 25 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0346] In one embodiment of the present disclosure, the parameter function may be defined using an exponential function expressed as a power of a natural constant. As an example, the exponential function may have a natural constant as its base and an exponent that combines the difference between the surrounding samples and the current sample and at least one parameter.

[0347] In one embodiment, the first parameter function may be defined as in the following mathematical expression 3. In the present disclosure, for convenience of explanation, the difference between a surrounding sample and a current sample may be abbreviated as difference.

[0348]

[0349] In Equation 3, the independent variable x of the first parameter function represents the difference between the surrounding samples and the current sample. In one embodiment, the first parameter function may output a value obtained by multiplying the difference by the output of the first exponential function, as in Equation 3.

[0350] In one embodiment, the first exponential function can be defined as a function whose base is a natural constant and whose exponent is the negative of the absolute value of the difference divided by the first parameter (i.e., a in Equation 3).

[0351] The output according to the input of the first parameter function of mathematical expression 3 is illustrated in FIG. 25. That is, in the illustrated graph of FIG. 25, the horizontal coordinate represents the difference as the input of the parameter function, and the vertical coordinate represents the output of the first parameter function according to the input. In addition, FIG. 25 compares cases where the first parameter is 16, 32, and 64 as an example.

[0352] Referring to Figure 25, when the difference is greater than 0, the output of the first parameter function may increase rapidly while increasing by the value of the first parameter. After the absolute value of the difference exceeds the value of the first parameter, the output of the first parameter function may decrease rapidly. As the absolute value of the difference increases, the output of the first parameter function may approach 0.

[0353] When the difference is less than 0, the output of the first parameter function may decrease rapidly while decreasing by the value of the first parameter. After the absolute value of the difference exceeds the value of the first parameter, the output of the first parameter function may rapidly approach 0. As the absolute value of the difference increases, the output of the first parameter function may approach 0.

[0354] In one embodiment, as illustrated in FIG. 25, if the value of the first parameter is adjusted significantly, the peak value of the first parameter function can be increased. If the value of the first parameter is adjusted small, the influence (or contribution) of surrounding samples with relatively large sample values ​​compared to the current sample can be further reduced.

[0355] By applying a filter coefficient to a preprocessed difference using the first parameter function according to the present disclosure, the similarity of surrounding samples with the current sample can be effectively reflected in filtering, thereby improving filtering performance and increasing compression efficiency.

[0356] FIG. 26 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0357] In one embodiment of the present disclosure, the second parameter function may be defined as in the following mathematical expression 4.

[0358]

[0359] In Equation 4, the independent variable x of the second parameter function represents the difference between the surrounding samples and the current sample. In one embodiment, the second parameter function may output a value obtained by multiplying the difference by the output of the second exponential function, as in Equation 4.

[0360] In one embodiment, the second exponential function can be defined as a function whose base is a natural constant and whose exponent is the negative of the absolute value of the difference raised to the power of the third parameter (i.e., b in Equation 4), divided by the third parameter raised to the power of the second parameter (i.e., a in Equation 4).

[0361] The output according to the input of the second parameter function of mathematical expression 4 is shown in Fig. 26. The left graph of Fig. 26 shows an example by comparing the cases where the second parameter is 16, 32, and 64 and the third parameter is 0.5, and the right graph of Fig. 26 shows an example by comparing the cases where the second parameter is 16, 32, and 64 and the third parameter is 2. Meanwhile, the graph shown in Fig. 25 described above may correspond to the output according to the input of the second parameter function. That is, Fig. 25 may be a diagram showing an example by comparing the cases where the second parameter of the second parameter function is 16, 32, and 64 and the third parameter is 1.

[0362] In the illustrated graph of Fig. 26, the horizontal coordinate represents the difference as the input of the parametric function, and the vertical coordinate represents the output of the second parametric function according to the input.

[0363] Referring to Fig. 26, when the difference is greater than 0, the output of the second parameter function may increase rapidly while the absolute value of the difference increases by the value of the second parameter. Thereafter, as the absolute value of the difference increases, the output of the second parameter function may approach 0. At this time, when the third parameter is 0.5, the output of the second parameter function may decrease relatively gradually. When the third parameter is 2, the output of the second parameter function may decrease very rapidly. When the difference is less than 0, as described above in Fig. 25, it may exhibit a symmetrical appearance with respect to the origin.

[0364] In one embodiment, as illustrated in FIG. 26, if the value of the second parameter is adjusted significantly, the peak value of the second parameter function can be increased. If the value of the second parameter is adjusted small, the influence (or contribution) of surrounding samples with relatively large sample values ​​compared to the current sample can be further reduced.

[0365] By applying a filter coefficient to the preprocessed difference using the second parameter function according to the present disclosure, the similarity of surrounding samples with the current sample can be effectively reflected in the filtering, thereby improving the filtering performance and increasing the compression efficiency.

[0366] FIG. 27 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0367] In one embodiment, the third parameter function may be defined as in the following mathematical expression (5).

[0368]

[0369] In Equation 5, the independent variable x of the third parameter function represents the difference between the surrounding samples and the current sample. In one embodiment, the third parameter function may output a value obtained by dividing the fourth parameter (i.e., a in Equation 5) by a predetermined constant, multiplying a value obtained by subtracting the fourth exponential function from the third exponential function, and dividing a value obtained by adding the fourth exponential function to the third exponential function, as in Equation 5. As an example, the predetermined constant may be defined as 2, as in Equation 5. Alternatively, the predetermined constant may be defined as a power of 2.

[0370] In one embodiment, the third exponential function may be defined as a function whose base is a natural constant and whose exponent is the value obtained by multiplying the difference by a fourth parameter. The fourth exponential function may be defined as a function whose base is a natural constant and whose exponent is the negative of the value obtained by multiplying the difference by a fourth parameter.

[0371] The output according to the input of the third parameter function of mathematical expression 5 is illustrated in FIG. 27. In the illustrated graph of FIG. 27, the horizontal coordinate represents the difference as the input of the parameter function, and the vertical coordinate represents the output of the third parameter function according to the input. In addition, FIG. 27 compares the cases where the fourth parameter is 16, 32, and 64 as an example.

[0372] Referring to Figure 27, when the difference is greater than 0, the output of the fourth parameter function can increase linearly while increasing by the value of the fourth parameter. After the difference exceeds the value of the fourth parameter, the output of the third parameter function can converge to a value obtained by dividing the fourth parameter by a predetermined constant.

[0373] In one embodiment, as illustrated in FIG. 27, if the value of the fourth parameter is adjusted significantly, the linear interval of the third parameter function can be increased. The linear interval represents an interval in which the output increases relatively proportionally as the input difference increases. If the value of the fourth parameter is adjusted small, the linear interval of the third parameter function can be decreased. When the difference exceeds the linear interval, the influence (or contribution) of surrounding samples with relatively large sample values ​​compared to the current sample may no longer increase.

[0374] By applying a filter coefficient to the preprocessed difference using the third parameter function according to the present disclosure, the similarity of surrounding samples with the current sample can be effectively reflected in the filtering, thereby improving the filtering performance and increasing the compression efficiency.

[0375] FIG. 28 is a drawing for explaining the output form of a parameter function according to one embodiment of the present disclosure.

[0376] In one embodiment, the fourth parameter function may be defined as in the following mathematical expression (6).

[0377]

[0378] In Equation 6, the independent variable x of the fourth parameter function represents the difference between the surrounding samples and the current sample. In one embodiment, the fourth parameter function may output a value obtained by dividing the fifth parameter (i.e., a in Equation 6) by a predetermined constant, multiplying the value obtained by subtracting the fifth exponential function from 1, and dividing the value obtained by adding the fifth exponential function to 1, as in Equation 6. As an example, the predetermined constant may be defined as 2, as in Equation 6. Alternatively, the predetermined constant may be defined as a power of 2.

[0379] In one embodiment, the fifth exponential function can be defined as a function whose base is a natural constant and whose exponent is the negative of the product of the differences and the fifth parameter.

[0380] The output according to the input of the fourth parameter function of mathematical expression 6 is illustrated in FIG. 28. In the illustrated graph of FIG. 28, the horizontal coordinate represents the difference as the input of the parameter function, and the vertical coordinate represents the output of the fourth parameter function according to the input. In addition, FIG. 27 compares the cases where the fifth parameter is 16, 32, and 64 as an example.

[0381] Referring to Figure 28, when the difference is greater than 0, the output of the fourth parameter function can increase linearly while increasing by the value of the fifth parameter. After the difference exceeds the value of the fifth parameter, the output of the fourth parameter function can converge to a value obtained by dividing the fifth parameter by a predetermined constant.

[0382] In one embodiment, as illustrated in FIG. 28, if the value of the fifth parameter is adjusted significantly, the linear interval of the fourth parameter function can be increased. The linear interval represents an interval in which the output increases relatively proportionally as the input difference increases. If the value of the fifth parameter is adjusted small, the linear interval of the fourth parameter function can be decreased. When the difference exceeds the linear interval, the influence (or contribution) of surrounding samples with relatively large sample values ​​compared to the current sample may no longer increase.

[0383] By applying a filter coefficient to the preprocessed difference using the fourth parameter function according to the present disclosure, the similarity of surrounding samples with the current sample can be effectively reflected in the filtering, thereby improving the filtering performance and increasing the compression efficiency.

[0384] The parametric preprocessing described above with reference to Figures 25 to 28 can be effective based on the following properties. If the difference between the current sample and surrounding samples is sufficiently small, the surrounding samples are likely to contain reliable information related to the current sample. In this case, by outputting the difference between the current sample and surrounding samples so that it is close to the original value, the information in the surrounding samples can be reflected as is.

[0385] If the difference between the current sample and surrounding samples is sufficiently large, it can be interpreted as a high probability that the surrounding sample does not contain information related to the current sample. In this case, by outputting a difference between the current sample and surrounding samples that is significantly smaller than before, the contribution of the surrounding sample's information to the current sample can be reduced.

[0386] FIG. 29 is a flowchart illustrating a method for filtering an image according to one embodiment of the present disclosure.

[0387] Referring to FIG. 29, the filtering device (2000) can determine a current filter to be applied to the current block within a filter set including a plurality of filters (S2910).

[0388] In one embodiment, the filtering device (2000) can determine a class index of the current block based on one or more sample values ​​of the current block. The filtering device (2000) can determine a current filter within a filter set of the current block using the class index of the current block.

[0389] In one embodiment, the filtering device (2400) can classify samples or blocks included in an image according to their characteristics and filter the samples included in the image using a filter appropriate for the classification result. The filtering device (2400) can determine which class among multiple classes each sample or block included in the image belongs to. The embodiments described above in FIGS. 20 to 23 can be applied, and any redundant descriptions will be omitted herein.

[0390] The filtering device (2000) can preprocess the difference between the current sample and surrounding samples within the current block based on a predefined function (S2920). In the present disclosure, the predefined function for preprocessing may be referred to as a parameter function. In one embodiment, the output form of the parameter function may be adjusted using at least one parameter. The embodiments described above in FIGS. 24 to 28 may be applied, and any redundant descriptions will be omitted herein.

[0391] In one embodiment, the parameter function may be defined using an exponential function expressed as a power of a natural constant. In one embodiment, the exponential function may have a natural constant as its base and an exponent that combines the difference between the surrounding samples and the current sample and at least one parameter.

[0392] In one embodiment, as described above in Equation 3, the parameter function may output a value obtained by multiplying the difference between the surrounding sample and the current sample by the output of the first exponential function. The first exponential function may have a natural constant as its base and an exponent obtained by dividing the negative value of the absolute value of the difference between the surrounding sample and the current sample by the first parameter.

[0393] In one embodiment, as described above in Equation 4, the parameter function may output a value obtained by multiplying the difference between the surrounding sample and the current sample by the output of the second exponential function. The second exponential function may have a natural constant as its base and an exponent obtained by dividing the negative value of the third parameter power of the absolute value of the difference between the surrounding sample and the current sample by the third parameter power of the second parameter.

[0394] In one embodiment, as described above in Equation 5, the parameter function may output a value obtained by dividing the fourth parameter by a predetermined constant, multiplying a value obtained by subtracting the fourth exponential function from the third exponential function, and dividing a value obtained by adding the fourth exponential function to the third exponential function. The third exponential function may have a natural constant as a base and an exponent obtained by multiplying the difference between the surrounding samples and the current sample by the fourth parameter. The fourth exponential function may have a natural constant as a base and an exponent obtained by multiplying the difference between the surrounding samples and the current sample by the fourth parameter. As an example, the predetermined constant may be defined as 2 as in Equation 5. Alternatively, the predetermined constant may be defined as a power of 2.

[0395] In one embodiment, as described above in Equation 6, the parameter function may output a value obtained by dividing the fifth parameter by a predetermined constant, multiplying the value obtained by subtracting the fifth exponential function from 1, and dividing the value obtained by adding the fifth exponential function to 1. The fifth exponential function may have a natural constant as a base, and an exponent that is the negative of the value obtained by multiplying the difference between the surrounding samples and the current sample by the fifth parameter. For example, the predetermined constant may be defined as 2, as in Equation 6. Alternatively, the predetermined constant may be defined as a power of 2.

[0396] In one embodiment, the filtering device (2000) can apply filter coefficients of the current filter to the current sample and / or surrounding samples of the current sample within the current block. The filtering device (2000) can obtain a plurality of filter coefficients from the current filter. The filtering device (2000) can determine a group of surrounding samples of the current sample, each of which includes a surrounding sample corresponding to each of the plurality of filter coefficients. The filtering device (2000) can perform preprocessing on the difference between each surrounding sample within the group of surrounding samples and the current sample.

[0397] The filtering device (2000) can filter the current sample based on the current filter and the preprocessed difference (S2930).

[0398] In one embodiment, the filtering device (2000) may apply the filter coefficients of the current filter to the current sample and / or the surrounding samples of the current sample within the current block. In one embodiment, the filtering device (2000) may add the values ​​obtained by multiplying the difference between each preprocessed surrounding sample and the current sample by the filter coefficients corresponding to each surrounding sample. The embodiments described above in FIGS. 23 to 28 may be applied, and any redundant descriptions will be omitted herein.

[0399] Meanwhile, the preprocessing for filtering described in FIGS. 24 to 29 can be implemented directly using mathematical equations such as Equations 2 to 6 described above, or can be implemented based on a predefined table considering the computational cost of the exponential function. In one embodiment, a table may be defined in which output values ​​are determined based on the difference between the surrounding samples and the current sample. As an example, a filtered sample can be obtained using a difference preprocessed based on a table according to the following Equation 7.

[0400]

[0401] In equation 7, x currepresents the current sample (or pixel) being filtered, and x out represents the filtered sample. x k ref represents the kth surrounding sample (or reference sample). w k represents the filter coefficient corresponding to the kth surrounding sample. min represents the minimum value of the difference between the surrounding sample and the current sample.

[0402] Meanwhile, according to one embodiment of the present disclosure, the filtering device (2000) can perform image filtering based on a neural loop filter (or neural post-filter). Based on a neural network, an image with a quality closer to the original image can be obtained. This will be described below with reference to FIG. 30.

[0403] FIG. 30 is a flowchart illustrating a method for filtering an image according to one embodiment of the present disclosure.

[0404] Referring to FIG. 30, the filtering device (2000) can obtain a decoded image (or restored image) of the current image (S3010). The decoded image of the current image can be generated by the image decoding device (100) and the image encoding device (200).

[0405] In one embodiment, instead of traditional filtering methods such as the Adaptive Loop Filter (ALF) described previously in FIGS. 20 to 23, a neural loop filter based on a neural network may be used for filtering to correct image distortion and improve compression efficiency. The neural loop filter can correct distortion in a restored image using a pre-trained neural network model.

[0406] In one embodiment, the neural loop filter may include a neural network trained using the original image and the compressed image (i.e., the reconstructed image). The neural network may learn distortion patterns in the reconstructed image due to compression.

[0407] The filtering device (2000) can preprocess the difference between the current sample and surrounding samples of the current sample in the current image based on a predefined function (S3020).

[0408] Meanwhile, in one embodiment, when preprocessing is not performed, the filtering device (2000) can obtain a filtered sample using the following mathematical expression 8.

[0409]

[0410] In equation 8, x k ref represents the kth surrounding sample (or reference sample), and x out represents the filtered sample. b k represents a bias value. The bias value may be a value determined individually for each current sample, or a value determined individually for each surrounding sample. That is, when using a neural loop filter that utilizes reference information that has not been preprocessed, the filtering device (2000) can obtain a filtered sample value of the current sample by applying a filter coefficient to the surrounding samples and applying a bias value to the sum of the values.

[0411] According to one embodiment of the present disclosure, by filtering the current sample using the difference between the preprocessed current sample and the surrounding samples as input to a neural loop filter, the similarity with the current sample can be effectively reflected in the filtering, thereby improving the filtering performance and increasing the compression efficiency.

[0412] In one embodiment, the filtering device (2000) can obtain a filtered sample using a preprocessed difference according to the following mathematical expression 9.

[0413]

[0414] In equation 9, x cur represents the current sample (or pixel) being filtered, and x out represents the filtered sample. xk ref represents the kth surrounding sample (or reference sample). The kth surrounding sample may mean a surrounding sample to which the filter coefficient with the index k value is applied within the filter. In other words, the kth surrounding sample is the filter coefficient w k can represent the surrounding samples to which the filter coefficient w is applied. The k-th surrounding sample is the filter coefficient w k can represent the surrounding samples corresponding to w k represents the filter coefficient corresponding to the kth surrounding sample, and in this disclosure, w k can also be expressed as a weight w k can be obtained from the filter applied to the current block. b k represents a bias value. The bias value may be a value determined individually for each current sample, or a value determined individually for each surrounding sample.

[0415] In Equation 9, θ represents a parameter of a parameter function. In one embodiment of the present disclosure, the preprocessing process can be parameterized, and the corresponding parameter can be differentiable for learning. Alternatively, the corresponding parameter can be differentiable piecewise for learning. According to Equation 9, all information can be considered to have equal importance, and the importance of individual reference information can be excluded. Alternatively, preprocessing using different parameters can be performed for different surrounding samples (or reference samples), as in Equation 10 below.

[0416]

[0417] In equation 10, x cur represents the current sample (or pixel) being filtered, and x out represents the filtered sample. x k ref represents the kth surrounding sample (or reference sample). w krepresents the filter coefficient corresponding to the kth surrounding sample. b k represents a bias value. The bias value may be a value determined individually for each current sample, or a value determined individually for each surrounding sample.

[0418] In Equation 10, θ k represents the parameter of the parameter function. θ k can be adaptively determined based on surrounding samples. That is, preprocessing using different parameters may be performed for different surrounding samples (or reference samples). In one embodiment, the preprocessing process may be parameterized, and the parameters may be differentiable for learning. Alternatively, the parameters may be differentiable piecewise for learning.

[0419] In one embodiment, the filtering device (2000) may preprocess the difference between the current sample and surrounding samples within the current image based on a predefined function. That is, even when neural loop filter-based filtering is performed, preprocessing of the difference between the surrounding samples and the current sample may be performed, as in the embodiments described in FIGS. 24 to 29 . In the present disclosure, a predefined function for preprocessing may be referred to as a parameter function. In one embodiment, the output form of the parameter function may be adjusted using at least one parameter. The embodiments described in FIGS. 24 to 29 above may be applied, and redundant descriptions thereof will be omitted herein.

[0420] In one embodiment, the parameter function may be defined using an exponential function expressed as a power of a natural constant. In one embodiment, the exponential function may have a natural constant as its base and an exponent that combines the difference between the surrounding samples and the current sample and at least one parameter.

[0421] In one embodiment, as described above in Equation 3, the parameter function may output a value obtained by multiplying the difference between the surrounding sample and the current sample by the output of the first exponential function. The first exponential function may have a natural constant as its base and an exponent obtained by dividing the negative value of the absolute value of the difference between the surrounding sample and the current sample by the first parameter.

[0422] In one embodiment, as described above in Equation 4, the parameter function may output a value obtained by multiplying the difference between the surrounding sample and the current sample by the output of the second exponential function. The second exponential function may have a natural constant as its base and an exponent obtained by dividing the negative value of the third parameter power of the absolute value of the difference between the surrounding sample and the current sample by the third parameter power of the second parameter.

[0423] In one embodiment, as described above in Equation 5, the parameter function may output a value obtained by dividing the fourth parameter by a predetermined constant, multiplying a value obtained by subtracting the fourth exponential function from the third exponential function, and dividing a value obtained by adding the fourth exponential function to the third exponential function. The third exponential function may have a natural constant as a base and an exponent obtained by multiplying the difference between the surrounding samples and the current sample by the fourth parameter. The fourth exponential function may have a natural constant as a base and an exponent obtained by multiplying the difference between the surrounding samples and the current sample by the fourth parameter. As an example, the predetermined constant may be defined as 2 as in Equation 5. Alternatively, the predetermined constant may be defined as a power of 2.

[0424] In one embodiment, as described above in Equation 6, the parameter function may output a value obtained by dividing the fifth parameter by a predetermined constant, multiplying the value obtained by subtracting the fifth exponential function from 1, and dividing the value obtained by adding the fifth exponential function to 1. The fifth exponential function may have a natural constant as a base, and an exponent that is the negative of the value obtained by multiplying the difference between the surrounding samples and the current sample by the fifth parameter. For example, the predetermined constant may be defined as 2, as in Equation 6. Alternatively, the predetermined constant may be defined as a power of 2.

[0425] In one embodiment, the filtering device (2000) can apply filter coefficients of the current filter to the current sample and / or surrounding samples of the current sample within the current block. The filtering device (2000) can obtain a plurality of filter coefficients from the current filter. The filtering device (2000) can determine a group of surrounding samples of the current sample, each of which includes a surrounding sample corresponding to each of the plurality of filter coefficients. The filtering device (2000) can perform preprocessing on the difference between each surrounding sample within the group of surrounding samples and the current sample.

[0426] The filtering device (2000) can output a filtered image by inputting a decoded image and a preprocessed difference (S3030).

[0427] In one embodiment, the filtering device (2000) may apply the filter coefficients of the current filter to the current sample and / or surrounding samples of the current sample within the current block. As an example, the mathematical expressions 8 to 10 described above may be applied.

[0428] In one embodiment, the decoded image and the preprocessed difference may be input to a filtering device (2000). The filtering device (2000) may include a neural network model of a pre-trained neural loop filter. The neural network model of the neural loop filter may learn various distortion patterns of the restored image due to compression using the original image and the compressed image (i.e., the restored image).

[0429] The filtering device (2000) can predict a correction value for correcting distortion of a decoded image based on input data. That is, the filtering device (2000) can recognize distortion (or distortion pattern) contained in the input data based on a learned neural network and calculate a correction value that minimizes the distortion.

[0430] The filtering device (2000) can output a filtered, i.e., corrected, value. The final corrected sample value can be updated on a sample-by-sample basis. The filtering device (2000) can generate an image with filtering applied as the final output.

[0431] Meanwhile, the preprocessing for filtering described above can be implemented directly using mathematical formulas such as Equations 2 to 6 described above, or can be implemented based on a predefined table considering the computational cost of the exponential function. In one embodiment, a table may be defined in which output values ​​are determined based on the difference between the surrounding samples and the current sample. As an example, a filtered sample can be obtained using a difference preprocessed based on a table according to the following Equation 11.

[0432]

[0433] In equation 11, x cur represents the current sample (or pixel) being filtered, and x out represents the filtered sample. x k ref represents the kth surrounding sample (or reference sample). w krepresents the filter coefficient corresponding to the kth surrounding sample. b k represents the bias value. min represents the minimum value of the difference between the surrounding samples and the current sample.

[0434] One embodiment of the present disclosure aims to reduce image distortion and improve subjective image quality by performing preprocessing on reference information used for filtering.

[0435] One embodiment of the present disclosure aims to effectively reflect the similarity between a current sample and surrounding samples in filtering by applying a filter to preprocessed reference information.

[0436] 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.

[0437] A method of filtering an image by a filtering device according to one embodiment may include a step of determining a current filter to be applied to a current block within a filter set including a plurality of filters.

[0438] A method for filtering an image by a filtering device according to one embodiment may include a step of preprocessing a difference between a current sample and surrounding samples of a current sample within a current block based on a predefined function.

[0439] According to one embodiment, the predefined function can be defined using an exponential function expressed as a power of a natural constant.

[0440] According to one embodiment, the output shape of a predefined function can be controlled using at least one parameter.

[0441] A method of filtering an image by a filtering device according to one embodiment may include a step of filtering a current sample based on a current filter and a preprocessed difference.

[0442] A method for filtering an image by a filtering device according to one embodiment may include a step of obtaining a plurality of filter coefficients from a current filter.

[0443] A method for filtering an image by a filtering device according to one embodiment may include a step of determining a group of surrounding samples of a current sample, the group including surrounding samples corresponding to each of a plurality of filter coefficients.

[0444] In one embodiment, preprocessing may be performed on the difference between each surrounding sample and the current sample within the surrounding sample group.

[0445] A method for filtering an image by a filtering device according to one embodiment may include a step of adding a value obtained by multiplying a difference between each preprocessed surrounding sample and a current sample by a filter coefficient corresponding to each surrounding sample.

[0446] A method for filtering an image by a filtering device according to one embodiment may be such that an exponential function has a natural constant as a base and an exponent is a value that combines a difference between a surrounding sample and a current sample and at least one parameter.

[0447] In one embodiment, the predefined function may output a value obtained by multiplying the output of a first exponential function by the difference between the surrounding samples and the current sample.

[0448] According to one embodiment, the first exponential function may have a natural constant as its base and an exponent of the negative value of the absolute value of the difference between the surrounding samples and the current sample divided by the first parameter.

[0449] In one embodiment, the predefined function may output a value obtained by multiplying the difference between the surrounding samples and the current sample by the output of a second exponential function.

[0450] According to one embodiment, the second exponential function may have a natural constant as the base and an exponent of the negative value of the third parameter power of the absolute value of the difference between the surrounding samples and the current sample divided by the third parameter power of the second parameter.

[0451] According to one embodiment, the predefined function can output a value obtained by multiplying a value obtained by dividing the fourth parameter by a predetermined constant, subtracting a fourth exponential function from a third exponential function, and dividing a value obtained by adding the fourth exponential function to the third exponential function.

[0452] In one embodiment, the third exponential function may have a natural constant as the base and an exponent of the difference between the surrounding samples and the current sample multiplied by a fourth parameter.

[0453] In one embodiment, the fourth exponential function may have a natural constant as its base and an exponent of the negative value of the difference between the surrounding samples and the current sample multiplied by the fourth parameter.

[0454] According to one embodiment, the predefined function can output a value obtained by multiplying a value obtained by dividing a fifth parameter by a predetermined constant, a value obtained by subtracting a fifth exponential function from 1, and a value obtained by dividing a value obtained by adding a fifth exponential function to 1.

[0455] In one embodiment, the fifth exponential function may have a natural constant as its base and an exponent of the negative value of the product of the fifth parameter and the difference between the surrounding samples and the current sample.

[0456] A method for filtering an image by a filtering device according to one embodiment may include a step of determining a class index of a current block based on one or more sample values ​​of the current block.

[0457] A method of filtering an image by a filtering device according to one embodiment may include a step of determining a current filter within a filter set using a class index of a current block.

[0458] An image filtering device according to one embodiment may include at least one memory storing at least one instruction, and at least one processor operating according to at least one instruction.

[0459] A processor included in an image filtering device according to one embodiment can determine a current filter to be applied to a current block within a filter set including a plurality of filters.

[0460] A processor included in an image filtering device according to one embodiment can calculate a difference between a current sample and surrounding samples of a current sample within a current block based on a predefined function.

[0461] According to one embodiment, the predefined function can be defined using an exponential function expressed as a power of a natural constant.

[0462] According to one embodiment, the output shape of a predefined function can be controlled using at least one parameter.

[0463] A processor included in an image filtering device according to one embodiment can filter a current sample based on a current filter and a preprocessed difference.

[0464] A computer-readable recording medium according to one embodiment can store a bitstream.

[0465] In one embodiment, the bitstream may include an encoding result generated based on a current image filtered according to a filtering method.

[0466] In one embodiment, the encoding result included in the bitstream can be generated by determining a current filter to be applied to the current block within a filter set including a plurality of filters.

[0467] In one embodiment, the encoding result included in the bitstream can be generated by calculating the difference between the current sample and surrounding samples of the current sample within the current block based on a predefined function.

[0468] According to one embodiment, the predefined function can be defined using an exponential function expressed as a power of a natural constant.

[0469] According to one embodiment, the output shape of a predefined function can be controlled using at least one parameter.

[0470] In one embodiment, the encoding result included in the bitstream can be generated by filtering the current sample based on the current filter and the preprocessed difference.

[0471] According to one embodiment of the present disclosure, by performing preprocessing on reference information used for filtering, image distortion can be reduced and subjective image quality can be improved.

[0472] One embodiment of the present disclosure can effectively reflect the similarity between a current sample and surrounding samples in filtering and improve filtering performance by applying a filter to preprocessed reference information.

[0473] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

[0474] Meanwhile, the embodiments of the present disclosure described above can be written as a program that can be executed on a computer, and the written program can be stored in a storage medium that can be read by a device.

[0475] A device-readable storage medium may be provided in the form of a non-transitory storage medium. Here, the term "non-transitory storage medium" simply means a tangible device that does not contain signals (e.g., electromagnetic waves). This term does not distinguish between cases where data is permanently stored in the storage medium and cases where data is temporarily stored. For example, a "non-transitory storage medium" may include a buffer in which data is temporarily stored.

[0476] According to one embodiment, the method according to various embodiments disclosed in the present document may be provided as included in a computer program product. The computer program product may be traded as a product between a seller and a buyer. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., compact disc read-only memory (CD-ROM)), or may be distributed online (e.g., downloaded or uploaded) through an application store or directly between two user devices (e.g., smartphones). In the case of online distribution, at least a portion of the computer program product (e.g., a downloadable app) may be temporarily stored or temporarily generated in a machine-readable storage medium, such as the memory of a manufacturer's server, an application store's server, or an intermediary server.

Claims

1. In a method of filtering an image using a filtering device (2000), A step (S2910) of determining a current filter to be applied to a current block within a filter set including multiple filters; A step (S2920) of preprocessing the difference between the surrounding samples of the current sample in the current block and the current sample based on a predefined function, wherein the predefined function is defined using an exponential function expressed as a power of a natural constant, and the output form of the predefined function is adjusted using at least one parameter; and A method for filtering an image, comprising a step (S2930) of filtering the current sample based on the current filter and the preprocessed difference.

2. In paragraph 1, A step of obtaining a plurality of filter coefficients from the current filter; and Further comprising the step of determining a group of surrounding samples of the current sample, which includes surrounding samples corresponding to each of the plurality of filter coefficients, A method for filtering an image, wherein the above preprocessing is performed on the difference between each surrounding sample within the surrounding sample group and the current sample.

3. In paragraph 2, The step of filtering the current sample above (S2930) is: A method for filtering an image, comprising the step of adding up the values ​​obtained by multiplying the difference between each of the preprocessed surrounding samples and the current sample by a filter coefficient corresponding to each of the surrounding samples.

4. In paragraph 1, A method for filtering an image, wherein the exponential function has the natural constant as the base and the value obtained by combining the difference between the surrounding sample and the current sample and the at least one parameter as the exponent.

5. In paragraph 4, The above predefined function outputs a value obtained by multiplying the output of the first exponential function by the difference between the surrounding sample and the current sample, A method for filtering an image, wherein the first exponential function has the natural constant as the base and the negative value of the absolute value of the difference between the surrounding sample and the current sample divided by the first parameter as the exponent.

6. In paragraph 4, The above predefined function outputs a value obtained by multiplying the output of the second exponential function by the difference between the surrounding sample and the current sample, A method for filtering an image, wherein the second exponential function has the natural constant as the base and the exponent is the negative value of the third parameter power of the absolute value of the difference between the surrounding sample and the current sample, divided by the third parameter power of the second parameter.

7. In paragraph 4, The above predefined function outputs a value obtained by multiplying a value obtained by dividing the fourth parameter by a predetermined constant, subtracting a fourth exponential function from a third exponential function, and dividing a value obtained by adding the fourth exponential function to the third exponential function. The above third exponential function has the natural constant as the base, and the exponent is the value obtained by multiplying the difference between the surrounding samples and the current sample by the fourth parameter, A method for filtering an image, wherein the fourth exponential function has the natural constant as the base and the negative value of the difference between the surrounding sample and the current sample multiplied by the fourth parameter as the exponent.

8. In paragraph 4, The above predefined function outputs a value obtained by multiplying the value obtained by dividing the fifth parameter by a predetermined constant, subtracting the fifth exponential function from 1, and dividing the value obtained by adding the fifth exponential function to 1. A method for filtering an image, wherein the fifth exponential function has the natural constant as the base and the negative value of the product of the difference between the surrounding sample and the current sample and the fifth parameter as the exponent.

9. In paragraph 1, The step of determining the current filter (S2910) is: determining a class index of the current block based on one or more sample values ​​of the current block; and A method for filtering an image, comprising the step of determining the current filter within the filter set using the class index of the current block.

10. In the video filtering device (2000), At least one memory storing at least one instruction; and comprising at least one processor operating in accordance with at least one instruction; At least one processor, Determines the current filter applied to the current block within a filter set containing multiple filters, Pre-determine the difference between the current sample and the surrounding samples of the current sample in the current block based on a predefined function, wherein the predefined function is defined using an exponential function expressed as a power of a natural constant, and the output form of the predefined function is adjusted using at least one parameter. An image filtering device that filters the current sample based on the current filter and the preprocessed difference.

11. In a computer-readable recording medium that records a bitstream, The above bitstream includes an encoding result generated based on the current image filtered according to a filtering method, The above filtering method is, A step of determining a current filter to be applied to a current block in the current image within a filter set including a plurality of filters; A step of preprocessing the difference between the surrounding samples of the current sample in the current block and the current sample based on a predefined function, wherein the predefined function is defined using an exponential function expressed as a power of a natural constant, and the output form of the predefined function is adjusted using at least one parameter; and A recording medium comprising a step of filtering the current sample based on the current filter and the preprocessed difference.

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