APPARATUSES FOR ENCODING AND DECODING IMAGE, AND METHODS FOR ENCODING AND DECODING IMAGE THEREBY

Provided is an image decoding method including: obtaining, from a sequence parameter set of a bitstream, information indicating a plurality of first reference image lists for an image sequence including a current image; obtaining, from a group header of the bitstream, an indicator for a current block group including a current block in the current image; obtaining a second reference image list based on a first reference image list indicated by the indicator; and prediction-decoding a lower block of the current block based on a reference image included in the second reference image list.

TECHNICAL FIELD

The present disclosure relates to the fields of image encoding and decoding. More particularly, the present disclosure relates to a method and apparatus for encoding an image and a method and apparatus for decoding the image, by using a hierarchical structure of the image.

BACKGROUND ART

In image encoding and decoding, an image may be split into blocks, and each block may be prediction-encoded and prediction-decoded via inter-prediction or intra-prediction.

Inter-prediction is a method of compressing images by removing temporal redundancy between the images, and a representative example of inter-prediction is motion estimation encoding. In motion estimation encoding, blocks of a current image are predicted by using at least one reference image. A reference block most similar to a current block may be searched for in a predetermined search range by using a predetermined evaluation function. The current block is predicted based on the reference block, and a prediction block generated as a result of the prediction is subtracted from the current block to generate and encode a residual block. Here, to more accurately perform prediction, pixels of a sub pel unit that is smaller than an integer pel unit may be generated by performing interpolation on a reference image, and inter-prediction may be performed based on the pixels of the sub pel unit.

In codecs such as H.264 advanced video coding (AVC) and high efficiency video coding (HEVC), in order to predict a motion vector of a current block, a motion vector of previously encoded blocks which are adjacent to the current block or blocks included in a previously encoded picture is used as a prediction motion vector of the current block. A differential motion vector, which is a difference between the motion vector and the prediction motion vector of the current block, is signaled to a decoder by using a predetermined method.

DESCRIPTION OF EMBODIMENTS

Technical Problem

A technical objective of image encoding and decoding apparatuses and image encoding and decoding methods thereby, according to an embodiment, is to encode and decode an image through a low bit rate by using a hierarchical structure of the image.

Solution to Problem

An image decoding method according to an embodiment includes: obtaining, from a sequence parameter set of a bitstream, information indicating a plurality of first reference image lists for an image sequence including a current image; obtaining, from a group header of the bitstream, an indicator for a current block group including a current block in the current image; obtaining a second reference image list based on a first reference image list indicated by the indicator, from among the plurality of first reference image lists; and prediction-decoding a lower block of the current block based on a reference image included in the second reference image list.

ADVANTAGEOUS EFFECTS OF DISCLOSURE

Image encoding and decoding apparatuses and image encoding and decoding methods thereby, according to an embodiment, may encode and decode an image through a low bit rate by using a hierarchical structure of the image.

However, effects achievable by the image encoding and decoding apparatuses and the image encoding and decoding methods thereby, according to an embodiment, are not limited to these mentioned above, and other effects that are not mentioned could be clearly understood by one of ordinary skill in the art from the following descriptions.

BEST MODE

An image decoding method according to an embodiment includes: obtaining, from a sequence parameter set of a bitstream, information indicating a plurality of first reference image lists for an image sequence including a current image; obtaining, from a group header of the bitstream, an indicator for a current block group including a current block in the current image; obtaining a second reference image list based on a first reference image list indicated by the indicator, from among the plurality of first reference image lists; and prediction-decoding a lower block of the current block based on a reference image included in the second reference image list.

According to an embodiment, based on a first reference image list other than the first reference image list indicated by the indicator from among the plurality of first reference image lists, and the second reference image list, lower blocks included in a next block group in the current image may be prediction decoded.

According to an embodiment, the obtaining of the second reference image list may include obtaining the second reference image list by changing an order of one or more of reference images included in the first reference image list indicated by the indicator.

According to an embodiment, the first reference image list indicated by the indicator may include a first type of reference image and a second type of reference image, wherein the obtaining of the second reference image list may include obtaining the second reference image list by excluding the second type of reference image from the first reference image list indicated by the indicator.

According to an embodiment, the first reference image list indicated by the indicator may include a first type of reference image and a second type of reference image, wherein the obtaining of the second reference image list may include obtaining the second reference image list by excluding the second type of reference image from the first reference image list indicated by the indicator and adding, to the first reference image list indicated by the indicator, a second type of reference image indicated by a picture order count (POC)-related value obtained from the group header.

According to an embodiment, the first reference image list indicated by the indicator may include only a first type of reference image, wherein the obtaining of the second reference image list may include obtaining the second reference image list by adding, to the first reference image list indicated by the indicator, a second type of reference image indicated by a picture order count (POC)-related value obtained from the group header.

According to an embodiment, the obtaining of the second reference image list may include obtaining the second reference image list including a first type of reference images included in any one reference image list indicated by the indicator and a second type of reference images included in another reference image list indicated by the indicator.

According to an embodiment, higher indices may be assigned to one of the first type of reference images and the second type of reference images than the other.

According to an embodiment, the image decoding method may further include obtaining, from the group header, order information of the first type of reference images and the second type of reference images, wherein indices according to the order information may be assigned to the first type of reference images and the second type of reference images.

According to an embodiment, the image decoding method may further include obtaining, from the group header, a difference value between a picture order count (POC)-related value of one or more of reference images included in the first reference image list indicated by the indicator and a POC-related value of one or more of reference images to be included in the second reference image list, wherein the obtaining of the second reference image list may include obtaining the second reference image list by replacing, based on the obtained difference value, one or more of the reference images included in the first reference image list indicated by the indicator.

According to an embodiment, the image decoding method may further include: determining a plurality of blocks in the current image; obtaining address information with respect to block groups from the bitstream; and, according to the obtained address information, configuring, in the current image, block groups each including one or more blocks, wherein the current block may be any one of the plurality of blocks, and the current block group may be any one of the block groups.

According to an embodiment, the address information may include identification information of a lower right block from among the blocks included in each of the block groups, wherein the configuring of the block groups may include: configuring a first block group including an upper left block located at an upper left side from among the plurality of blocks and the lower right block indicated by the identification information of the lower right block; identifying an upper left block of a second block group, based on identification information of the blocks included in the first block group; and configuring the second block group including the lower right block indicated by the identification information of the lower right block and the identified upper left block.

According to an embodiment, the image decoding method may further include: obtaining, from the bitstream, at least one post-processing parameter set for luma mapping; obtaining, from the group header or a picture parameter set of the bitstream, identification information indicating a post-processing parameter set applied to luma mapping with respect to a prediction sample of the lower block obtained as a result of the prediction-decoding; and luma mapping the prediction sample according to the post-processing parameter set indicated by the identification information.

An image decoding apparatus according to an embodiment includes: an obtainer configured to obtain, from a sequence parameter set of a bitstream, information indicating a plurality of first reference image lists for an image sequence including a current image and obtain, from a group header of the bitstream, an indicator for a current block group including a current block in the current image; and a prediction decoder configured to obtain a second reference image list based on a first reference image list indicated by the indicator from among the plurality of first reference image lists and prediction-decode a lower block of the current block based on a reference image included in the second reference image list.

An image encoding method according to an embodiment includes: constructing a plurality of first reference image lists for an image sequence including a current image; selecting, from among the plurality of first reference image lists, a first reference image list for a current block group including a current block in the current image; obtaining a second reference image list based on the selected first reference image list; and prediction-encoding a lower block of the current block based on a reference image included in the second reference image list.

MODE OF DISCLOSURE

As the present disclosure allows for various changes and numerous examples, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present disclosure to particular modes of practice, and it will be understood that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of various embodiments are encompassed in the present disclosure.

In the description of embodiments, certain detailed explanations of related art are omitted when it is deemed that they may unnecessarily obscure the essence of the present disclosure. Also, numbers (for example, a first, a second, and the like) used in the description of the specification are merely identifier codes for distinguishing one element from another.

Also, in the present specification, it will be understood that when elements are “connected” or “coupled” to each other, the elements may be directly connected or coupled to each other, but may alternatively be connected or coupled to each other with an intervening element therebetween, unless specified otherwise.

In the present specification, regarding an element represented as a “unit” or a “module”, two or more elements may be combined into one element or one element may be divided into two or more elements according to subdivided functions. In addition, each element described hereinafter may additionally perform some or all of functions performed by another element, in addition to main functions of itself, and some of the main functions of each element may be performed entirely by another component.

Also, in the present specification, an “image” or a “picture” may denote a still image of a video or a moving image, i.e., the video itself.

Also, in the present specification, a “sample” or a “signal” denotes data assigned to a sampling position of an image, i.e., data to be processed. For example, pixel values of an image in a spatial domain and transform coefficients on a transform region may be samples. A unit including at least one such sample may be defined as a block.

Hereinafter, an image encoding method and apparatus and an image decoding method and apparatus based on a coding unit of a tree structure and a transform unit according to an embodiment are described with reference toFIGS.1through19.

FIG.1is a block diagram of an image decoding apparatus100according to an embodiment.

The image decoding apparatus100may include a bitstream obtainer110and a decoder120. The bitstream obtainer110and the decoder120may include at least one processor. Also, the bitstream obtainer110and the decoder120may include a memory storing instructions to be performed by the at least one processor.

The bitstream obtainer110may receive a bitstream. The bitstream includes information about image encoding of an image encoding apparatus200described later. Also, the bitstream may be transmitted from the image encoding apparatus200. The image encoding apparatus200and the image decoding apparatus100may be connected by wire or wirelessly, and the bitstream obtainer110may receive the bitstream by wire or wirelessly. The bitstream obtainer110may receive the bitstream from a storage medium, such as an optical medium or a hard disk. The decoder120may reconstruct an image based on information obtained from the received bitstream. The decoder120may obtain, from the bitstream, a syntax element for reconstructing the image. The decoder120may reconstruct the image based on the syntax element.

To describe, in detail, an operation of the image decoding apparatus100, the bitstream obtainer110may receive the bitstream.

The image decoding apparatus100may perform an operation of obtaining, from the bitstream, a bin string corresponding to a split shape mode of a coding unit. Also, the image decoding apparatus100may perform an operation of determining a split rule of the coding unit. Also, the image decoding apparatus100may perform an operation of splitting the coding unit into a plurality of coding units, based on at least one of the bin string corresponding to the split shape mode and the split rule. In order to determine the split rule, the image decoding apparatus100may determine a first range of a permissible size of the coding unit according to a ratio between a width and a height of the coding unit. In order to determine the split rule, the image decoding apparatus100may determine a second range of the permissible size of the coding unit according to a split shape mode of the coding unit.

Hereinafter, splitting of the coding unit is described in detail according to an embodiment of the present disclosure.

First, one picture may be split into one or more slices or one or more tiles. One slice or one tile may be a sequence of one or more largest coding units (i.e., coding tree units (CTUs)). According to an embodiment, one slice may include one or more tiles, and one slice may include one or more CTUs. The slice including one tile or a plurality of tiles may be determined in the picture.

As a concept compared to the CTU, there is a largest coding block (i.e., a coding tree block (CTB)). The CTB denotes N×N blocks including N×N samples (N is an integer). Each color component may be split into one or more CTBs.

When a picture has three sample arrays (sample arrays for Y, Cr, and Cb components), a CTU includes a CTB of a luma sample, two CTBs of chroma samples corresponding to the luma sample, and syntax structures used to encode the luma sample and the chroma samples. When a picture is a monochrome picture, a CTU includes a CTB of a monochrome sample and syntax structures used to encode the monochrome samples. When a picture is a picture encoded in color planes separated according to color components, a CTU includes syntax structures used to encode the picture and samples of the picture.

One CTB may be split into M×N coding blocks including M×N samples (M and N are integers).

When a picture has sample arrays for Y, Cr, and Cb components, a coding unit includes a coding block of a luma sample, two coding blocks of chroma samples corresponding to the luma sample, and syntax structures used to encode the luma sample and the chroma samples. When a picture is a monochrome picture, a coding unit includes a coding block of a monochrome sample and syntax structures used to encode the monochrome samples. When a picture is a picture encoded in color planes separated according to color components, a coding unit includes syntax structures used to encode the picture and samples of the picture.

As described above, a CTB and a CTU are conceptually distinguished from each other, and a coding block and a coding unit are conceptually distinguished from each other. That is, a coding unit (a CTU) refers to a data structure including a coding block (a CTB) including a corresponding sample and a syntax structure corresponding to the coding block (the CTB). However, because it is understood by one of ordinary skill in the art that a coding unit (a CTU) or a coding block (a CTB) refers to a block of a certain size including a certain number of samples, a CTB and a CTU, or a coding block and a coding unit are mentioned in the following specification without being distinguished unless otherwise described.

An image may be split into CTUs. A size of each CTU may be determined based on information obtained from a bitstream. A shape of each CTU may be a square shape of the same size. However, an embodiment is not limited thereto.

For example, information about a maximum size of a luma coding block may be obtained from a bitstream. For example, the maximum size of the luma coding block indicated by the information about the maximum size of the luma coding block may be one of 4×4, 8×8, 16×16, 32×32, 64×64, 128×128, and 256×256.

For example, information about a luma block size difference and a maximum size of a luma coding block that may be split into two may be obtained from a bitstream. The information about the luma block size difference may refer to a size difference between a luma CTU and a luma CTB that may be split into two. Accordingly, when the information about the maximum size of the luma coding block that may be split into two and the information about the luma block size difference obtained from the bitstream are combined with each other, a size of the luma CTU may be determined. A size of a chroma CTU may be determined by using the size of the luma CTU. For example, when a Y:Cb:Cr ratio is 4:2:0 according to a color format, a size of a chroma block may be half a size of a luma block, and a size of a chroma CTU may be half a size of a luma CTU.

According to an embodiment, because information about a maximum size of a luma coding block that is binary splittable is obtained from a bitstream, the maximum size of the luma coding block that is binary splittable may be variably determined. In contrast, a maximum size of a luma coding block that is ternary splittable may be fixed. For example, the maximum size of the luma coding block that is ternary splittable in an I-picture may be 32×32, and the maximum size of the luma coding block that is ternary splittable in a P-picture or a B-picture may be 64×64.

Also, a CTU may be hierarchically split into coding units based on split shape mode information obtained from a bitstream. At least one of information indicating whether quad splitting is performed, information indicating whether multi-splitting is performed, split direction information, and split type information may be obtained as the split shape mode information from the bitstream.

For example, the information indicating whether quad splitting is performed may indicate whether a current coding unit is quad split (QUAD_SPLIT) or not.

When the current coding unit is not quad split, the information indicating whether multi-splitting is performed may indicate whether the current coding unit is no longer split (NO_SPLIT) or binary/ternary split.

When the current coding unit is binary split or ternary split, the split direction information indicates that the current coding unit is split in one of a horizontal direction and a vertical direction.

When the current coding unit is split in the horizontal direction or the vertical direction, the split type information indicates that the current coding unit is binary split or ternary split.

A split mode of the current coding unit may be determined according to the split direction information and the split type information. A split mode when the current coding unit is binary split in the horizontal direction may be determined to be a binary horizontal split mode (SPLIT_BT_HOR), a split mode when the current coding unit is ternary split in the horizontal direction may be determined to be a ternary horizontal split mode (SPLIT_TT_HOR), a split mode when the current coding unit is binary split in the vertical direction may be determined to be a binary vertical split mode (SPLIT_BT_VER), and a split mode when the current coding unit is ternary split in the vertical direction may be determined to be a ternary vertical split mode SPLIT_TT_VER.

The image decoding apparatus100may obtain, from the bitstream, the split shape mode information from one bin string. A form of the bitstream received by the image decoding apparatus100may include fixed length binary code, unary code, truncated unary code, pre-determined binary code, or the like. The bin string is information in a binary number. The bin string may include at least one bit. The image decoding apparatus100may obtain the split shape mode information corresponding to the bin string, based on the split rule. The image decoding apparatus100may determine whether to quad-split a coding unit, whether not to split a coding unit, a split direction, and a split type, based on one bin string.

The coding unit may be smaller than or same as the CTU. For example, because a CTU is a coding unit having a maximum size, the CTU is one of coding units. When split shape mode information about a CTU indicates that splitting is not performed, a coding unit determined in the CTU has the same size as that of the CTU. When split shape code information about a CTU indicates that splitting is performed, the CTU may be split into coding units. Also, when split shape mode information about a coding unit indicates that splitting is performed, the coding unit may be split into smaller coding units. However, the splitting of the image is not limited thereto, and the CTU and the coding unit may not be distinguished. The splitting of the coding unit will be described in detail with reference toFIGS.3through16.

Also, one or more prediction blocks for prediction may be determined from a coding unit. The prediction block may be the same as or smaller than the coding unit. Also, one or more transform blocks for transform may be determined from a coding unit. The transform block may be the same as or smaller than the coding unit.

The shapes and sizes of the transform block and prediction block may not be related to each other.

In another embodiment, prediction may be performed by using a coding unit as a prediction unit. Also, transform may be performed by using a coding unit as a transform block.

The splitting of the coding unit will be described in detail with reference toFIGS.3through16. A current block and a neighboring block of the present disclosure may indicate one of the CTU, the coding unit, the prediction block, and the transform block. Also, the current block of the current coding unit is a block that is currently being decoded or encoded or a block that is currently being split. The neighboring block may be a block reconstructed before the current block. The neighboring block may be adjacent to the current block spatially or temporally. The neighboring block may be located at one of the lower left, left, upper left, top, upper right, right, and lower right of the current block.

FIG.3illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a current coding unit, according to an embodiment.

A block shape may include 4N×4N, 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N, 16N×N, N×16N, 8N×N, or N×8N. Here, N may be a positive integer. Block shape information is information indicating at least one of a shape, a direction, a ratio of width and height, or a size of a coding unit.

The shape of the coding unit may include a square and a non-square. When the lengths of the width and height of the coding unit are the same (i.e., when the block shape of the coding unit is 4N×4N), the image decoding apparatus100may determine the block shape information of the coding unit to be a square. The image decoding apparatus100may determine the shape of the coding unit to be a non-square.

When the width and the height of the coding unit are different from each other (i.e., when the block shape of the coding unit is 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N, 16N×N, N×16N, 8N×N, or N×8N), the image decoding apparatus100may determine the block shape information of the coding unit to be a non-square shape. When the shape of the coding unit is non-square, the image decoding apparatus100may determine the ratio of the width and height among the block shape information of the coding 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. Also, the image decoding apparatus100may determine whether the coding unit is in a horizontal direction or a vertical direction, based on the length of the width and the length of the height of the coding unit. Also, the image decoding apparatus100may determine the size of the coding unit, based on at least one of the length of the width, the length of the height, or the area of the coding unit.

According to an embodiment, the image decoding apparatus100may determine the shape of the coding unit by using the block shape information, and may determine a splitting method of the coding unit by using the split shape mode information. That is, a coding unit splitting method indicated by the split shape mode information may be determined based on a block shape indicated by the block shape information used by the image decoding apparatus100.

The image decoding apparatus100may obtain the split shape mode information from a bitstream. However, an embodiment is not limited thereto, and the image decoding apparatus100and the image encoding apparatus200may determine pre-agreed split shape mode information, based on the block shape information. The image decoding apparatus100may determine the pre-agreed split shape mode information with respect to a CTU or a smallest coding unit. For example, the image decoding apparatus100may determine split shape mode information with respect to the CTU to be a quad split. Also, the image decoding apparatus100may determine split shape mode information regarding the smallest coding unit to be “not to perform splitting.” In particular, the image decoding apparatus100may determine the size of the CTU to be 256×256. The image decoding apparatus100may determine the pre-agreed split shape mode information to be a quad split. The quad split is a split shape mode in which the width and the height of the coding unit are both bisected. The image decoding apparatus100may obtain a coding unit of a 128×128 size from the CTU of a 256×256 size, based on the split shape mode information. Also, the image decoding apparatus100may determine the size of the smallest coding unit to be 4×4. The image decoding apparatus100may obtain split shape mode information indicating “not to perform splitting” with respect to the smallest coding unit.

According to an embodiment, the image decoding apparatus100may use the block shape information indicating that the current coding unit has a square shape. For example, the image decoding apparatus100may determine whether not to split a square coding unit, whether to vertically split the square coding unit, whether to horizontally split the square coding unit, or whether to split the square coding unit into four coding units, based on the split shape mode information. Referring toFIG.3, when the block shape information of a current coding unit300indicates a square shape, the decoder120may not split a coding unit310ahaving the same size as the current coding unit300, based on the split shape mode information indicating not to perform splitting, or may determine coding units310b,310c,310d,310e, or310fsplit based on the split shape mode information indicating a certain splitting method.

Referring toFIG.3, according to an embodiment, the image decoding apparatus100may determine two coding units310bobtained by splitting the current coding unit300in a vertical direction, based on the split shape mode information indicating to perform splitting in a vertical direction. The image decoding apparatus100may determine two coding units310cobtained by splitting the current coding unit300in a horizontal direction, based on the split shape mode information indicating to perform splitting in a horizontal direction. The image decoding apparatus100may determine four coding units310dobtained by splitting the current coding unit300in vertical and horizontal directions, based on the split shape mode information indicating to perform splitting in vertical and horizontal directions. According to an embodiment, the image decoding apparatus100may determine three coding units310eobtained by splitting the current coding unit300in a vertical direction, based on the split shape mode information indicating to perform ternary-splitting in a vertical direction. The image decoding apparatus100may determine three coding units310fobtained by splitting the current coding unit300in a horizontal direction, based on the split shape mode information indicating to perform ternary-splitting in a horizontal direction. However, splitting methods of the square coding unit are not limited to the above-described methods, and the split shape mode information may indicate various methods. Certain splitting methods of splitting the square coding unit will be described in detail below in relation to various embodiments.

FIG.4illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a non-square coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus100may use block shape information indicating that a current coding unit has a non-square shape. The image decoding apparatus100may determine whether not to split the non-square current coding unit or whether to split the non-square current coding unit by using a certain splitting method, based on split shape mode information. Referring toFIG.4, when the block shape information of a current coding unit400or450indicates a non-square shape, the image decoding apparatus100may determine a coding unit410or460having the same size as the current coding unit400or450, based on the split shape mode information indicating not to perform splitting, or may determine coding units420aand420b,430ato430c,470aand470b, or480ato480csplit based on the split shape mode information indicating a certain splitting method. Certain splitting methods of splitting a non-square coding unit will be described in detail below in relation to various embodiments.

According to an embodiment, the image decoding apparatus100may determine a splitting method of a coding unit by using the split shape mode information and, in this case, the split shape mode information may indicate the number of one or more coding units generated by splitting a coding unit. Referring toFIG.4, when the split shape mode information indicates to split the current coding unit400or450into two coding units, the image decoding apparatus100may determine two coding units420aand420b, or470aand470bincluded in the current coding unit400or450, by splitting the current coding unit400or450based on the split shape mode information.

According to an embodiment, when the image decoding apparatus100splits the non-square current coding unit400or450based on the split shape mode information, the image decoding apparatus100may consider the location of a long side of the non-square current coding unit400or450to split a current coding unit. For example, the image decoding apparatus100may determine a plurality of coding units by splitting a long side of the current coding unit400or450, based on the shape of the current coding unit400or450.

According to an embodiment, when the split shape mode information indicates to split (ternary-split) a coding unit into an odd number of blocks, the image decoding apparatus100may determine an odd number of coding units included in the current coding unit400or450. For example, when the split shape mode information indicates to split the current coding unit400or450into three coding units, the image decoding apparatus100may split the current coding unit400or450into three coding units430a,430b, and430c, or480a,480b, and480c.

According to an embodiment, a ratio of the width and height of the current coding unit400or450may be 4:1 or 1:4. When the ratio of the width and height is 4:1, the block shape information may be a 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 a vertical direction because the length of the width is shorter than the length of the height. The image decoding apparatus100may determine to split a current coding unit into the odd number of blocks, based on the split shape mode information. Also, the image decoding apparatus100may determine a split direction of the current coding unit400or450, based on the block shape information of the current coding unit400or450. For example, when the current coding unit400is in the vertical direction, the image decoding apparatus100may determine the coding units430ato430cby splitting the current coding unit400in the horizontal direction. Also, when the current coding unit450is in the horizontal direction, the image decoding apparatus100may determine the coding units480ato480cby splitting the current coding unit450in the vertical direction.

According to an embodiment, the image decoding apparatus100may determine the odd number of coding units included in the current coding unit400or450, and not all the determined coding units may have the same size. For example, a certain coding unit430bor480bfrom among the determined odd number of coding units430a,430b, and430c, or480a,480b, and480cmay have a size different from the size of the other coding units430aand430c, or480aand480c. That is, coding units which may be determined by splitting the current coding unit400or450may have multiple sizes and, in some cases, all of the odd number of coding units430a,430b, and430c, or480a,480b, and480cmay have different sizes.

According to an embodiment, when the split shape mode information indicates to split a coding unit into the odd number of blocks, the image decoding apparatus100may determine the odd number of coding units included in the current coding unit400or450, and in addition, may put a certain restriction on at least one coding unit from among the odd number of coding units generated by splitting the current coding unit400or450. Referring toFIG.4, the image decoding apparatus100may set a decoding process regarding the coding unit430bor480blocated at the center among the three coding units430a,430b, and430cor480a,480b, and480cgenerated as the current coding unit400or450is split to be different from that of the other coding units430aand430c, or480aor480c. For example, the image decoding apparatus100may restrict the coding unit430bor480bat the center location to be no longer split or to be split only a certain number of times, unlike the other coding units430aand430c, or480aand480c.

FIG.5illustrates a process, performed by the image decoding apparatus100, of splitting a coding unit based on at least one of block shape information and split shape mode information, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine to split or not to split a square first coding unit500into coding units, based on at least one of the block shape information and the split shape mode information. According to an embodiment, when the split shape mode information indicates to split the first coding unit500in a horizontal direction, the image decoding apparatus100may determine a second coding unit510by splitting the first coding unit500in a horizontal direction. A first coding unit, a second coding unit, and a third coding unit used according to an embodiment are terms used to understand a relation before and after splitting a coding unit. For example, a second coding unit may be determined by splitting a first coding unit, and a third coding unit may be determined by splitting the second coding unit. It will be understood that the structure of the first coding unit, the second coding unit, and the third coding unit follows the above descriptions.

According to an embodiment, the image decoding apparatus100may determine to split or not to split the determined second coding unit510into coding units, based on the split shape mode information. Referring toFIG.5, the image decoding apparatus100may or may not split the non-square second coding unit510, which is determined by splitting the first coding unit500, into one or more third coding units520a, or520b,520c, and520dbased on the split shape mode information. The image decoding apparatus100may obtain the split shape mode information, and may obtain a plurality of various-shaped second coding units (e.g.,510) by splitting the first coding unit500, based on the obtained split shape mode information, and the second coding unit510may be split by using a splitting method of the first coding unit500based on the split shape mode information. According to an embodiment, when the first coding unit500is split into the second coding units510based on the split shape mode information of the first coding unit500, the second coding unit510may also be split into the third coding units520a, or520b,520c, and520dbased on the split shape mode information of the second coding unit510. That is, a coding unit may be recursively split based on the split shape mode information of each coding unit. Therefore, a square coding unit may be determined by splitting a non-square coding unit, and a non-square coding unit may be determined by recursively splitting the square coding unit.

Referring toFIG.5, a certain coding unit from among the odd number of third coding units520b,520c, and520ddetermined by splitting the non-square second coding unit510(e.g., a coding unit at a center location or a square coding unit) may be recursively split. According to an embodiment, the square third coding unit520cfrom among the odd number of third coding units520b,520c, and520dmay be split in a horizontal direction into a plurality of fourth coding units. A non-square fourth coding unit530bor530dfrom among a plurality of fourth coding units530a,530b,530c, and530dmay be split into a plurality of coding units again. For example, the non-square fourth coding unit530bor530dmay be split into the odd number of coding units again. A method that may be used to recursively split a coding unit will be described below in relation to various embodiments.

According to an embodiment, the image decoding apparatus100may split each of the third coding units520a, or520b,520c, and520dinto coding units, based on the split shape mode information. Also, the image decoding apparatus100may determine not to split the second coding unit510based on the split shape mode information. According to an embodiment, the image decoding apparatus100may split the non-square second coding unit510into the odd number of third coding units520b,520c, and520d. The image decoding apparatus100may put a certain restriction on a certain third coding unit from among the odd number of third coding units520b,520c, and520d. For example, the image decoding apparatus100may restrict the third coding unit520cat a center location from among the odd number of third coding units520b,520c, and520dto be no longer split or to be split a settable number of times.

Referring toFIG.5, the image decoding apparatus100may restrict the third coding unit520c, which is at the center location from among the odd number of third coding units520b,520c, and520dincluded in the non-square second coding unit510, to be no longer split, to be split by using a certain splitting method (e.g., split into only four coding units or split by using a splitting method of the second coding unit510), or to be split only a certain number of times (e.g., split only n times (where n>0)). However, the restrictions on the third coding unit520cat the center location are not limited to the above-described examples, and may include various restrictions for decoding the third coding unit520cat the center location differently from the other third coding units520band520d.

According to an embodiment, the image decoding apparatus100may obtain the split shape mode information, which is used to split a current coding unit, from a certain location in the current coding unit.

FIG.6illustrates a method, performed by the image decoding apparatus100, of determining a certain coding unit from among an odd number of coding units, according to an embodiment.

Referring toFIG.6, split shape mode information of a current coding unit600or650may be obtained from a sample of a certain location (e.g., a sample640or690of a center location) from among a plurality of samples included in the current coding unit600or650. However, the certain location in the current coding unit600, from which at least one piece of the split shape mode information may be obtained, is not limited to the center location inFIG.6, and may include various locations included in the current coding unit600(e.g., top, bottom, left, right, upper left, lower left, upper right, and lower right locations). The image decoding apparatus100may obtain the split shape mode information from the certain location and may determine to split or not to split the current coding unit into various-shaped and various-sized coding units.

According to an embodiment, when the current coding unit is split into a certain number of coding units, the image decoding apparatus100may select one of the coding units. Various methods may be used to select one of a plurality of coding units, as will be described below in relation to various embodiments.

According to an embodiment, the image decoding apparatus100may split the current coding unit into a plurality of coding units, and may determine a coding unit at a certain location.

According to an embodiment, image decoding apparatus100may use information indicating locations of the odd number of coding units, to determine a coding unit at a center location from among the odd number of coding units. Referring toFIG.6, the image decoding apparatus100may determine the odd number of coding units620a,620b, and620cor the odd number of coding units660a,660b, and660cby splitting the current coding unit600or the current coding unit650. The image decoding apparatus100may determine the middle coding unit620bor the middle coding unit660bby using information about the locations of the odd number of coding units620a,620b, and620cor the odd number of coding units660a,660b, and660c. For example, the image decoding apparatus100may determine the coding unit620bof the center location by determining the locations of the coding units620a,620b, and620cbased on information indicating locations of certain samples included in the coding units620a,620b, and620c. In detail, the image decoding apparatus100may determine the coding unit620bat the center location by determining the locations of the coding units620a,620b, and620cbased on information indicating locations of upper left samples630a,630b, and630cof the coding units620a,620b, and620c.

According to an embodiment, the information indicating the locations of the upper left samples630a,630b, and630c, which are included in the coding units620a,620b, and620c, respectively, may include information about locations or coordinates of the coding units620a,620b, and620cin a picture. According to an embodiment, the information indicating the locations of the upper left samples630a,630b, and630c, which are included in the coding units620a,620b, and620c, respectively, may include information indicating widths or heights of the coding units620a,620b, and620cincluded in the current coding unit600, and the widths or heights may correspond to information indicating differences between the coordinates of the coding units620a,620b, and620cin the picture. That is, the image decoding apparatus100may determine the coding unit620bat the center location by directly using the information about the locations or coordinates of the coding units620a,620b, and620cin the picture, or by using the information about the widths or heights of the coding units, which correspond to the difference values between the coordinates.

According to an embodiment, information indicating the location of the upper left sample630aof the upper coding unit620amay include coordinates (xa, ya), information indicating the location of the upper left sample630bof the middle coding unit620bmay include coordinates (xb, yb), and information indicating the location of the upper left sample630cof the lower coding unit620cmay include coordinates (xc, yc). The image decoding apparatus100may determine the middle coding unit620bby using the coordinates of the upper left samples630a,630b, and630cwhich are included in the coding units620a,620b, and620c, respectively. For example, when the coordinates of the upper left samples630a,630b, and630care sorted in an ascending or descending order, the coding unit620bincluding the coordinates (xb, yb) of the sample630bat a center location may be determined as a coding unit at a center location from among the coding units620a,620b, and620cdetermined by splitting the current coding unit600. However, the coordinates indicating the locations of the upper left samples630a,630b, and630cmay include coordinates indicating absolute locations in the picture, or may use coordinates (dxb, dyb) indicating a relative location of the upper left sample630bof the middle coding unit620band coordinates (dxc, dyc) indicating a relative location of the upper left sample630cof the lower coding unit620cwith reference to the location of the upper left sample630aof the upper coding unit620a. A method of determining a coding unit at a certain location by using coordinates of a sample included in the coding unit, as information indicating a location of the sample, is not limited to the above-described method, and may include various arithmetic methods capable of using the coordinates of the sample.

According to an embodiment, the image decoding apparatus100may split the current coding unit600into a plurality of coding units620a,620b, and620c, and may select one of the coding units620a,620b, and620cbased on a certain criterion. For example, the image decoding apparatus100may select the coding unit620b, which has a size different from that of the others, from among the coding units620a,620b, and620c.

According to an embodiment, the image decoding apparatus100may determine the width or height of each of the coding units620a,620b, and620cby using the coordinates (xa, ya) that is the information indicating the location of the upper left sample630aof the upper coding unit620a, the coordinates (xb, yb) that is the information indicating the location of the upper left sample630bof the middle coding unit620b, and the coordinates (xc, yc) that is the information indicating the location of the upper left sample630cof the lower coding unit620c. The image decoding apparatus100may determine the respective sizes of the coding units620a,620b, and620cby using the coordinates (xa, ya), (xb, yb), and (xc, yc) indicating the locations of the coding units620a,620b, and620c. According to an embodiment, the image decoding apparatus100may determine the width of the upper coding unit620ato be the width of the current coding unit600. The image decoding apparatus100may determine the height of the upper coding unit620ato be yb-ya. According to an embodiment, the image decoding apparatus100may determine the width of the middle coding unit620bto be the width of the current coding unit600. The image decoding apparatus100may determine the height of the middle coding unit620bto be yc-yb. According to an embodiment, the image decoding apparatus100may determine the width or height of the lower coding unit620cby using the width or height of the current coding unit600or the widths or heights of the upper and middle coding units620aand620b. The image decoding apparatus100may determine a coding unit, which has a size different from that of the others, based on the determined widths and heights of the coding units620ato620c. Referring toFIG.6, the image decoding apparatus100may determine the middle coding unit620b, which has a size different from the size of the upper and lower coding units620aand620c, as the coding unit of the certain location. However, the above-described method, performed by the image decoding apparatus100, of determining a coding unit having a size different from the size of the other coding units merely corresponds to an example of determining a coding unit at a certain location by using the sizes of coding units, which are determined based on coordinates of samples, and thus, various methods of determining a coding unit at a certain location by comparing the sizes of coding units, which are determined based on coordinates of certain samples, may be used.

The image decoding apparatus100may determine the width or height of each of the coding units660a,660b, and660cby using the coordinates (xd, yd) that is information indicating the location of an upper left sample670aof the left coding unit660a, the coordinates (xe, ye) that is information indicating the location of an upper left sample670bof the middle coding unit660b, and the coordinates (xf, yf) that is information indicating a location of the upper left sample670cof the right coding unit660c. The image decoding apparatus100may determine the respective sizes of the coding units660a,660b, and660cby using the coordinates (xd, yd), (xe, ye), and (xf, yf) indicating the locations of the coding units660a,660b, and660c.

According to an embodiment, the image decoding apparatus100may determine the width of the left coding unit660ato be xe-xd. The image decoding apparatus100may determine the height of the left coding unit660ato be the height of the current coding unit650. According to an embodiment, the image decoding apparatus100may determine the width of the middle coding unit660bto be xf-xe. The image decoding apparatus100may determine the height of the middle coding unit660bto be the height of the current coding unit600. According to an embodiment, the image decoding apparatus100may determine the width or height of the right coding unit660cby using the width or height of the current coding unit650or the widths or heights of the left and middle coding units660aand660b. The image decoding apparatus100may determine a coding unit, which has a size different from that of the others, based on the determined widths and heights of the coding units660ato660c. Referring toFIG.6, the image decoding apparatus100may determine the middle coding unit660b, which has a size different from the sizes of the left and right coding units660aand660c, as the coding unit of the certain location. However, the above-described method, performed by the image decoding apparatus100, of determining a coding unit having a size different from the size of the other coding units merely corresponds to an example of determining a coding unit at a certain location by using the sizes of coding units, which are determined based on coordinates of samples, and thus, various methods of determining a coding unit at a certain location by comparing the sizes of coding units, which are determined based on coordinates of certain samples, may be used.

However, locations of samples considered to determine locations of coding units are not limited to the above-described upper left locations, and information about arbitrary locations of samples included in the coding units may be used.

According to an embodiment, the image decoding apparatus100may select a coding unit at a certain location from among an odd number of coding units determined by splitting the current coding unit, considering the shape of the current coding unit. For example, when the current coding unit has a non-square shape, a width of which is longer than a height, the image decoding apparatus100may determine the coding unit at the certain location in a horizontal direction. That is, the image decoding apparatus100may determine one of coding units, locations of which are different in the horizontal direction, and put a restriction on the coding unit. When the current coding unit has a non-square shape, a height of which is longer than a width, the image decoding apparatus100may determine the coding unit at the certain location in a vertical direction. That is, the image decoding apparatus100may determine one of coding units, locations of which are different in the vertical direction, and may put a restriction on the coding unit.

According to an embodiment, the image decoding apparatus100may use information indicating respective locations of an even number of coding units, to determine the coding unit at the certain location from among the even number of coding units. The image decoding apparatus100may determine an even number of coding units by splitting (binary-splitting) the current coding unit, and may determine the coding unit at the certain location by using the information about the locations of the even number of coding units. An operation related thereto may correspond to the operation of determining a coding unit at a certain location (e.g., a center location) from among an odd number of coding units, which has been described in detail above in relation toFIG.6, and thus, detailed descriptions thereof are not provided here.

According to an embodiment, when a non-square current coding unit is split into a plurality of coding units, certain information about a coding unit at a certain location may be used in a splitting operation to determine the coding unit at the certain location from among the plurality of coding units. For example, the image decoding apparatus100may use at least one of block shape information and split shape mode information, which is stored in a sample included in a middle coding unit, in a splitting operation to determine a coding unit at a center location from among the plurality of coding units determined by splitting the current coding unit.

Referring toFIG.6, the image decoding apparatus100may split the current coding unit600into the plurality of coding units620a,620b, and620cbased on the split shape mode information, and may determine the coding unit620bat a center location from among the plurality of the coding units620a,620b, and620c. Furthermore, the image decoding apparatus100may determine the coding unit620bat the center location, based on a location from which the split shape mode information is obtained. That is, the split shape mode information of the current coding unit600may be obtained from the sample640at a center location of the current coding unit600and, when the current coding unit600is split into the plurality of coding units620a,620b, and620cbased on the split shape mode information, the coding unit620bincluding the sample640may be determined as the coding unit at the center location. However, information used to determine the coding unit at the center location is not limited to the split shape mode information, and various types of information may be used to determine the coding unit at the center location.

According to an embodiment, certain information for identifying the coding unit at the certain location may be obtained from a certain sample included in a coding unit to be determined. Referring toFIG.6, the image decoding apparatus100may use the split shape mode information, which is obtained from a sample at a certain location in the current coding unit600(e.g., a sample at a center location of the current coding unit600) to determine a coding unit at a certain location from among the plurality of the coding units620a,620b, and620cdetermined by splitting the current coding unit600(e.g., a coding unit at a center location from among a plurality of split coding units). That is, the image decoding apparatus100may determine the sample at the certain location by considering a block shape of the current coding unit600, determine the coding unit620bincluding a sample, from which certain information (e.g., the split shape mode information) may be obtained, from among the plurality of coding units620a,620b, and620cdetermined by splitting the current coding unit600, and may put a certain restriction on the coding unit620b. Referring toFIG.6, according to an embodiment, the image decoding apparatus100may determine the sample640at the center location of the current coding unit600as the sample from which the certain information may be obtained, and may put a certain restriction on the coding unit620bincluding the sample640, in a decoding operation. However, the location of the sample from which the certain information may be obtained is not limited to the above-described location, and may include arbitrary locations of samples included in the coding unit620bto be determined for a restriction.

According to an embodiment, the location of the sample from which the certain information may be obtained may be determined based on the shape of the current coding unit600. According to an embodiment, the block shape information may indicate whether the current coding unit has a square or non-square shape, and the location of the sample from which the certain information may be obtained may be determined based on the shape. For example, the image decoding apparatus100may determine a sample located on a boundary for splitting at least one of a width and height of the current coding unit in half, as the sample from which the certain information may be obtained, by using at least one of information about the width of the current coding unit and information about the height of the current coding unit. As another example, when the block shape information of the current coding unit indicates a non-square shape, the image decoding apparatus100may determine one of samples adjacent to a boundary for splitting a long side of the current coding unit in half, as the sample from which the predetermined information may be obtained.

According to an embodiment, when the current coding unit is split into a plurality of coding units, the image decoding apparatus100may use the split shape mode information to determine a coding unit at a certain location from among the plurality of coding units. According to an embodiment, the image decoding apparatus100may obtain the split shape mode information from a sample at a certain location in a coding unit, and split the plurality of coding units, which are generated by splitting the current coding unit, by using the split shape mode information, which is obtained from the sample of the certain location in each of the plurality of coding units. That is, a coding unit may be recursively split based on the split shape mode information, which is obtained from the sample at the certain location in each coding unit. An operation of recursively splitting a coding unit has been described above in relation toFIG.5, and thus, detailed descriptions thereof will not be provided here.

According to an embodiment, the image decoding apparatus100may determine one or more coding units by splitting the current coding unit, and may determine an order of decoding the one or more coding units, based on a certain block (e.g., the current coding unit).

FIG.7illustrates an order of processing a plurality of coding units when the image decoding apparatus100determines the plurality of coding units by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine second coding units710aand710bby splitting a first coding unit700in a vertical direction, determine second coding units730aand730bby splitting the first coding unit700in a horizontal direction, or determine second coding units750ato750dby splitting the first coding unit700in vertical and horizontal directions, based on split shape mode information.

Referring toFIG.7, the image decoding apparatus100may determine to process the second coding units710aand710b, which are determined by splitting the first coding unit700in a vertical direction, in a horizontal direction order710c. The image decoding apparatus100may determine to process the second coding units730aand730b, which are determined by splitting the first coding unit700in a horizontal direction, in a vertical direction order730c. The image decoding apparatus100may determine to process the second coding units750ato750d, which are determined by splitting the first coding unit700in vertical and horizontal directions, in a certain order for processing coding units in a row and then processing coding units in a next row (e.g., in a raster scan order or Z-scan order750e).

According to an embodiment, the image decoding apparatus100may recursively split coding units. Referring toFIG.7, the image decoding apparatus100may determine the plurality of coding units710aand710b,730aand730b, or750ato750dby splitting the first coding unit700, and recursively split each of the determined plurality of coding units710aand710b,730aand730b, or750ato750d. A splitting method of the plurality of coding units710aand710b,730aand730b, or750ato750dmay correspond to a splitting method of the first coding unit700. As such, each of the plurality of coding units710aand710b,730aand730b, or750ato750dmay be independently split into a plurality of coding units. Referring toFIG.7, the image decoding apparatus100may determine the second coding units710aand710bby splitting the first coding unit700in a vertical direction, and may determine to independently split or not to split each of the second coding units710aand710b.

According to an embodiment, the image decoding apparatus100may determine third coding units720aand720bby splitting the left second coding unit710ain a horizontal direction, and may not split the right second coding unit710b.

According to an embodiment, a processing order of coding units may be determined based on an operation of splitting a coding unit. In other words, a processing order of split coding units may be determined based on a processing order of coding units immediately before being split. The image decoding apparatus100may determine a processing order of the third coding units720aand720bdetermined by splitting the left second coding unit710a, independently of the right second coding unit710b. Because the third coding units720aand720bare determined by splitting the left second coding unit710ain a horizontal direction, the third coding units720aand720bmay be processed in a vertical direction order720c. Because the left and right second coding units710aand710bare processed in the horizontal direction order710c, the right second coding unit710bmay be processed after the third coding units720aand720bincluded in the left second coding unit710aare processed in the vertical direction order720c. An operation of determining a processing order of coding units based on a coding unit before being split is not limited to the above-described example, and various methods may be used to independently process coding units, which are split and determined to have various shapes, in a certain order.

FIG.8illustrates a process in which, when coding units are not processable in a predetermined order, an image decoding apparatus determines that a current coding unit is split into an odd number of coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine that the current coding unit is split into an odd number of coding units, based on obtained split shape mode information. Referring toFIG.8, a square first coding unit800may be split into non-square second coding units810aand810b, and the second coding units810aand810bmay be independently split into third coding units820aand820b, and820cto820e. According to an embodiment, the image decoding apparatus100may determine the plurality of third coding units820aand820bby splitting the left second coding unit810ain a horizontal direction, and may split the right second coding unit810binto the odd number of third coding units820cto820e.

According to an embodiment, the image decoding apparatus100may determine whether any coding unit is split into an odd number of coding units, by determining whether the third coding units820aand820b, and820cto820eare processable in a certain order. Referring toFIG.8, the image decoding apparatus100may determine the third coding units820aand820b, and820cto820eby recursively splitting the first coding unit800. The image decoding apparatus100may determine whether any of the first coding unit800, the second coding units810aand810b, and the third coding units820aand820b, and820cto820eare split into an odd number of coding units, based on at least one of the block shape information and the split shape mode information. For example, the right second coding unit810bamong the second coding units810aand810bmay be split into an odd number of third coding units820c,820d, and820e. A processing order of a plurality of coding units included in the first coding unit800may be a certain order (e.g., a Z-scan order830), and the image decoding apparatus100may determine whether the third coding units820c,820d, and820e, which are determined by splitting the right second coding unit810binto an odd number of coding units, satisfy a condition for processing in the certain order.

According to an embodiment, the image decoding apparatus100may determine whether the third coding units820aand820b, and820cto820eincluded in the first coding unit800satisfy the condition for processing in the certain order, and the condition relates to whether at least one of a width and height of the second coding units810aand810bis split in half along a boundary of the third coding units820aand820b, and820cto820e. For example, the third coding units820aand820bdetermined when the height of the left second coding unit810aof the non-square shape is split in half may satisfy the condition. It may be determined that the third coding units820cto820edo not satisfy the condition because the boundaries of the third coding units820cto820edetermined when the right second coding unit810bis split into three coding units are unable to split the width or height of the right second coding unit810bin half. When the condition is not satisfied as described above, the image decoding apparatus100may determine disconnection of a scan order, and may determine that the right second coding unit810bis split into an odd number of coding units, based on a result of the determination. According to an embodiment, when a coding unit is split into an odd number of coding units, the image decoding apparatus100may put a certain restriction on a coding unit at a certain location from among the split coding units. The restriction or the certain location has been described above in relation to various embodiments, and thus, detailed descriptions thereof will not be provided herein.

FIG.9illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a first coding unit900, according to an embodiment.

According to an embodiment, the image decoding apparatus100may split the first coding unit900, based on split shape mode information, which is obtained through the bitstream obtainer110. The square first coding unit900may be split into four square coding units, or may be split into a plurality of non-square coding units. For example, referring toFIG.9, when the split shape mode information indicates to split the first coding unit900into non-square coding units, the image decoding apparatus100may split the first coding unit900into a plurality of non-square coding units. In detail, when the split shape mode information indicates to determine an odd number of coding units by splitting the first coding unit900in a horizontal direction or a vertical direction, the image decoding apparatus100may split the square first coding unit900into an odd number of coding units, e.g., second coding units910a,910b, and910cdetermined by splitting the square first coding unit900in a vertical direction or second coding units920a,920b, and920cdetermined by splitting the square first coding unit900in a horizontal direction.

According to an embodiment, the image decoding apparatus100may determine whether the second coding units910a,910b,910c,920a,920b, and920cincluded in the first coding unit900satisfy a condition for processing in a certain order, and the condition relates to whether at least one of a width and height of the first coding unit900is split in half along a boundary of the second coding units910a,910b,910c,920a,920b, and920c. Referring toFIG.9, because boundaries of the second coding units910a,910b, and910cdetermined by splitting the square first coding unit900in a vertical direction do not split the width of the first coding unit900in half, it may be determined that the first coding unit900does not satisfy the condition for processing in the certain order. In addition, because boundaries of the second coding units920a,920b, and920cdetermined by splitting the square first coding unit900in a horizontal direction do not split the height of the first coding unit900in half, it may be determined that the first coding unit900does not satisfy the condition for processing in the certain order. When the condition is not satisfied as described above, the image decoding apparatus100may decide disconnection of a scan order, and may determine that the first coding unit900is split into an odd number of coding units, based on a result of the decision. According to an embodiment, when a coding unit is split into an odd number of coding units, the image decoding apparatus100may put a certain restriction on a coding unit at a certain location from among the split coding units. The restriction or the certain location has been described above in relation to various embodiments, and thus, detailed descriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus100may determine various-shaped coding units by splitting a first coding unit.

Referring toFIG.9, the image decoding apparatus100may split the square first coding unit900or a non-square first coding unit930or950into various-shaped coding units.

FIG.10illustrates that a shape into which a second coding unit is splittable is restricted when the second coding unit having a non-square shape, which is determined when the image decoding apparatus100splits a first coding unit1000, satisfies a certain condition, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine to split the square first coding unit1000into non-square second coding units1010aand1010bor1020aand1020b, based on split shape mode information, which is obtained by the bitstream obtainer110. The second coding units1010aand1010bor1020aand1020bmay be independently split. As such, the image decoding apparatus100may determine to split or not to split each of the second coding units1010aand1010bor1020aand1020binto a plurality of coding units, based on the split shape mode information of each of the second coding units1010aand1010bor1020aand1020b. According to an embodiment, the image decoding apparatus100may determine third coding units1012aand1012bby splitting the non-square left second coding unit1010a, which is determined by splitting the first coding unit1000in a vertical direction, in a horizontal direction. However, when the left second coding unit1010ais split in a horizontal direction, the image decoding apparatus100may restrict the right second coding unit1010bnot to be split in a horizontal direction in which the left second coding unit1010ais split. When third coding units1014aand1014bare determined by splitting the right second coding unit1010bin a same direction, because the left and right second coding units1010aand1010bare independently split in a horizontal direction, the third coding units1012aand1012bor1014aand1014bmay be determined. However, this case serves equally as a case in which the image decoding apparatus100splits the first coding unit1000into four square second coding units1030a,1030b,1030c, and1030d, based on the split shape mode information, and may be inefficient in terms of image decoding.

According to an embodiment, the image decoding apparatus100may determine third coding units1022aand1022bor1024aand1024bby splitting the non-square second coding unit1020aor1020b, which is determined by splitting the first coding unit1000in a horizontal direction, in a vertical direction. However, when a second coding unit (e.g., the upper second coding unit1020a) is split in a vertical direction, for the above-described reason, the image decoding apparatus100may restrict the other second coding unit (e.g., the lower second coding unit1020b) not to be split in a vertical direction in which the upper second coding unit1020ais split.

FIG.11illustrates a process, performed by the image decoding apparatus100, of splitting a square coding unit when split shape mode information is unable to indicate that the square coding unit is split into four square coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine second coding units1110aand1110bor1120aand1120b, etc. by splitting a first coding unit1100, based on split shape mode information. The split shape mode information may include information about various methods of splitting a coding unit but, the information about various splitting methods may not include information for splitting a coding unit into four square coding units. According to such split shape mode information, the image decoding apparatus100may not split the square first coding unit1100into four square second coding units1130a,1130b,1130c, and1130d. The image decoding apparatus100may determine the non-square second coding units1110aand1110bor1120aand1120b, etc., based on the split shape mode information.

According to an embodiment, the image decoding apparatus100may independently split the non-square second coding units1110aand1110bor1120aand1120b, etc. Each of the second coding units1110aand1110bor1120aand1120b, etc. may be recursively split in a certain order, and this splitting method may correspond to a method of splitting the first coding unit1100, based on the split shape mode information.

For example, the image decoding apparatus100may determine square third coding units1112aand1112bby splitting the left second coding unit1110ain a horizontal direction, and may determine square third coding units1114aand1114bby splitting the right second coding unit1110bin a horizontal direction. Furthermore, the image decoding apparatus100may determine square third coding units1116a,1116b,1116c, and1116dby splitting both of the left and right second coding units1110aand1110bin a horizontal direction. In this case, coding units having the same shape as the four square second coding units1130a,1130b,1130c, and1130dsplit from the first coding unit1100may be determined.

As another example, the image decoding apparatus100may determine square third coding units1122aand1122bby splitting the upper second coding unit1120ain a vertical direction, and may determine square third coding units1124aand1124bby splitting the lower second coding unit1120bin a vertical direction. Furthermore, the image decoding apparatus100may determine square third coding units1126a,1126b,1126c, and1126dby splitting both of the upper and lower second coding units1120aand1120bin a vertical direction. In this case, coding units having the same shape as the four square second coding units1130a,1130b,1130c, and1130dsplit from the first coding unit1100may be determined.

FIG.12illustrates that a processing order between a plurality of coding units may be changed depending on a process of splitting a coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus100may split a first coding unit1200, based on split shape mode information. When a block shape indicates a square shape and the split shape mode information indicates to split the first coding unit1200in at least one of horizontal and vertical directions, the image decoding apparatus100may determine second coding units1210aand1210bor1220aand1220b, etc. by splitting the first coding unit1200. Referring toFIG.12, the non-square second coding units1210aand1210bor1220aand1220bdetermined by splitting the first coding unit1200in only a horizontal direction or vertical direction may be independently split based on the split shape mode information of each coding unit. For example, the image decoding apparatus100may determine third coding units1216a,1216b,1216c, and1216dby splitting the second coding units1210aand1210b, which are generated by splitting the first coding unit1200in a vertical direction, in a horizontal direction, and may determine third coding units1226a,1226b,1226c, and1226dby splitting the second coding units1220aand1220b, which are generated by splitting the first coding unit1200in a horizontal direction, in a vertical direction. An operation of splitting the second coding units1210aand1210bor1220aand1220bhas been described above in relation toFIG.11, and thus, detailed descriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus100may process coding units in a certain order. An operation of processing coding units in a certain order has been described above in relation toFIG.7, and thus, detailed descriptions thereof will not be provided herein. Referring toFIG.12, the image decoding apparatus100may determine four square third coding units1216a,1216b,1216c, and1216d, and1226a,1226b,1226c, and1226dby splitting the square first coding unit1200. According to an embodiment, the image decoding apparatus100may determine processing orders of the third coding units1216a,1216b,1216c, and1216d, and1226a,1226b,1226c, and1226dbased on a splitting method of the first coding unit1200.

According to an embodiment, the image decoding apparatus100may determine the third coding units1216a,1216b,1216c, and1216dby splitting the second coding units1210aand1210bgenerated by splitting the first coding unit1200in a vertical direction, in a horizontal direction, and may process the third coding units1216a,1216b,1216c, and1216din a processing order1217for initially processing the third coding units1216aand1216c, which are included in the left second coding unit1210a, in a vertical direction and then processing the third coding unit1216band1216d, which are included in the right second coding unit1210b, in a vertical direction.

According to an embodiment, the image decoding apparatus100may determine the third coding units1226a,1226b,1226c, and1226dby splitting the second coding units1220aand1220bgenerated by splitting the first coding unit1200in a horizontal direction, in a vertical direction, and may process the third coding units1226a,1226b,1226c, and1226din a processing order1227for initially processing the third coding units1226aand1226b, which are included in the upper second coding unit1220a, in a horizontal direction and then processing the third coding unit1226cand1226d, which are included in the lower second coding unit1220b, in a horizontal direction.

Referring toFIG.12, the square third coding units1216a,1216b,1216c, and1216d, and1226a,1226b,1226c, and1226dmay be determined by splitting the second coding units1210aand1210b, and1220aand1920b, respectively. Although the second coding units1210aand1210bare determined by splitting the first coding unit1200in a vertical direction differently from the second coding units1220aand1220bwhich are determined by splitting the first coding unit1200in a horizontal direction, the third coding units1216a,1216b,1216c, and1216d, and1226a,1226b,1226c, and1226dsplit therefrom eventually show same-shaped coding units split from the first coding unit1200. As such, by recursively splitting a coding unit in different manners based on the split shape information, the image decoding apparatus100may process a plurality of coding units in different orders even when the coding units are eventually determined to be the same shape.

FIG.13illustrates a process of determining a depth of a coding unit when a shape and size of the coding unit change, when the coding unit is recursively split such that a plurality of coding units are determined, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine the depth of the coding unit, based on a certain criterion. For example, the certain criterion may be the length of a long side of the coding unit. When the length of a long side of a coding unit before being split is 2n times (n>0) the length of a long side of a split current coding unit, the image decoding apparatus100may determine that a depth of the current coding unit is increased from a depth of the coding unit before being split, by n. In the following description, a coding unit having an increased depth is expressed as a coding unit of a lower depth.

Referring toFIG.13, according to an embodiment, the image decoding apparatus100may determine a second coding unit1302and a third coding unit1304of lower depths by splitting a square first coding unit1300based on block shape information indicating a square shape (for example, the block shape information may be expressed as ‘0: SQUARE’). Assuming that the size of the square first coding unit1300is 2N×2N, the second coding unit1302determined by splitting a width and height of the first coding unit1300in ½ may have a size of N×N. Furthermore, the third coding unit1304determined by splitting a width and height of the second coding unit1302in ½ may have a size of N/2×N/2. In this case, a width and height of the third coding unit1304are ¼ times those of the first coding unit1300. When a depth of the first coding unit1300is D, a depth of the second coding unit1302, the width and height of which are ½ times those of the first coding unit1300, may be D+1, and a depth of the third coding unit1304, the width and height of which are ¼ times those of the first coding unit1300, may be D+2.

According to an embodiment, the image decoding apparatus100may determine a second coding unit1312or1322and a third coding unit1314or1324of lower depths by splitting a non-square first coding unit1310or1320based on block shape information indicating a non-square shape (for example, the block shape information may be expressed as ‘1: NS_VER’ indicating a non-square shape, a height of which is longer than a width, or as ‘2: NS_HOR’ indicating a non-square shape, a width of which is longer than a height).

The image decoding apparatus100may determine a second coding unit1302,1312, or1322by splitting at least one of a width and height of the first coding unit1310having a size of N×2N. That is, the image decoding apparatus100may determine the second coding unit1302having a size of N×N or the second coding unit1322having a size of N×N/2 by splitting the first coding unit1310in a horizontal direction, or may determine the second coding unit1312having a size of N/2×N by splitting the first coding unit1310in horizontal and vertical directions.

According to an embodiment, the image decoding apparatus100may determine the second coding unit1302,1312, or1322by splitting at least one of a width and height of the first coding unit1320having a size of 2N×N. That is, the image decoding apparatus100may determine the second coding unit1302having a size of N×N or the second coding unit1312having a size of N/2×N by splitting the first coding unit1320in a vertical direction, or may determine the second coding unit1322having a size of N×N/2 by splitting the first coding unit1320in horizontal and vertical directions.

According to an embodiment, the image decoding apparatus100may determine a third coding unit1304,1314, or1324by splitting at least one of a width and height of the second coding unit1302having a size of N×N. That is, the image decoding apparatus100may determine the third coding unit1304having a size of N/2×N/2, the third coding unit1314having a size of N/4×N/2, or the third coding unit1324having a size of N/2×N/4 by splitting the second coding unit1302in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus100may determine the third coding unit1304,1314, or1324by splitting at least one of a width and height of the second coding unit1312having a size of N/2×N. That is, the image decoding apparatus100may determine the third coding unit1304having a size of N/2×N/2 or the third coding unit1324having a size of N/2×N/4 by splitting the second coding unit1312in a horizontal direction, or may determine the third coding unit1314having a size of N/4×N/2 by splitting the second coding unit1312in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus100may determine the third coding unit1304,1314, or1324by splitting at least one of a width and height of the second coding unit1322having a size of N×N/2. That is, the image decoding apparatus100may determine the third coding unit1304having a size of N/2×N/2 or the third coding unit1314having a size of N/4×N/2 by splitting the second coding unit1322in a vertical direction, or may determine the third coding unit1324having a size of N/2×N/4 by splitting the second coding unit1322in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus100may split the square coding unit1300,1302, or1304in a horizontal or vertical direction. For example, the image decoding apparatus100may determine the first coding unit1310having a size of N×2N by splitting the first coding unit1300having a size of 2N×2N in a vertical direction, or may determine the first coding unit1320having a size of 2N×N by splitting the first coding unit1300in a horizontal direction. According to an embodiment, when a depth is determined based on the length of the longest side of a coding unit, a depth of a coding unit determined by splitting the first coding unit1300having a size of 2N×2N in a horizontal or vertical direction may be the same as the depth of the first coding unit1300.

According to an embodiment, a width and height of the third coding unit1314or1324may be ¼ times those of the first coding unit1310or1320. When a depth of the first coding unit1310or1320is D, a depth of the second coding unit1312or1322, the width and height of which are ½ times those of the first coding unit1310or1320, may be D+1, and a depth of the third coding unit1314or1324, the width and height of which are ¼ times those of the first coding unit1310or1320, may be D+2.

FIG.14illustrates depths that are determinable based on shapes and sizes of coding units, and part indexes (PIDs) that are for distinguishing the coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus100may determine various-shape second coding units by splitting a square first coding unit1400. Referring toFIG.14, the image decoding apparatus100may determine second coding units1402aand1402b,1404aand1404b, and1406a,1406b,1406c, and1406dby splitting the first coding unit1400in at least one of vertical and horizontal directions based on split shape mode information. That is, the image decoding apparatus100may determine the second coding units1402aand1402b,1404aand1404b, and1406a,1406b,1406c, and1406d, based on the split shape mode information of the first coding unit1400.

According to an embodiment, a depth of the second coding units1402aand1402b,1404aand1404b, and1406a,1406b,1406c, and1406d, which are determined based on the split shape mode information of the square first coding unit1400, may be determined based on the length of a long side thereof. For example, because the length of a side of the square first coding unit1400equals the length of a long side of the non-square second coding units1402aand1402b, and1404aand1404b, the first coding unit2100and the non-square second coding units1402aand1402b, and1404aand1404bmay have the same depth, e.g., D. However, when the image decoding apparatus100splits the first coding unit1400into the four square second coding units1406a,1406b,1406c, and1406dbased on the split shape mode information, because the length of a side of the square second coding units1406a,1406b,1406c, and1406dis ½ times the length of a side of the first coding unit1400, a depth of the second coding units1406a,1406b,1406c, and1406dmay be D+1 which is lower than the depth D of the first coding unit1400by 1.

According to an embodiment, the image decoding apparatus100may determine a plurality of second coding units1412aand1412b, and1414a,1414b, and1414cby splitting a first coding unit1410, a height of which is longer than a width, in a horizontal direction based on the split shape mode information. According to an embodiment, the image decoding apparatus100may determine a plurality of second coding units1422aand1422b, and1424a,1424b, and1424cby splitting a first coding unit1420, a width of which is longer than a height, in a vertical direction based on the split shape mode information.

According to an embodiment, a depth of the second coding units1412aand1412b, and1414a,1414b, and1414c, or1422aand1422b, and1424a,1424b, and1424c, which are determined based on the split shape mode information of the non-square first coding unit1410or1420, may be determined based on the length of a long side thereof. For example, because the length of a side of the square second coding units1412aand1412bis ½ times the length of a long side of the first coding unit1410having a non-square shape, a height of which is longer than a width, a depth of the square second coding units1412aand1412bis D+1 which is lower than the depth D of the non-square first coding unit1410by 1.

Furthermore, the image decoding apparatus100may split the non-square first coding unit1410into an odd number of second coding units1414a,1414b, and1414cbased on the split shape mode information. The odd number of second coding units1414a,1414b, and1414cmay include the non-square second coding units1414aand1414cand the square second coding unit1414b. In this case, because the length of a long side of the non-square second coding units1414aand1414cand the length of a side of the square second coding unit1414bare ½ times the length of a long side of the first coding unit1410, a depth of the second coding units1414a,1414b, and1414cmay be D+1 which is lower than the depth D of the non-square first coding unit1410by 1. The image decoding apparatus100may determine depths of coding units split from the first coding unit1420having a non-square shape, a width of which is longer than a height, by using the above-described method of determining depths of coding units split from the first coding unit1410.

According to an embodiment, the image decoding apparatus100may determine PIDs for identifying split coding units, based on a size ratio between the coding units when an odd number of split coding units do not have equal sizes. Referring toFIG.14, a coding unit1414bof a center location among an odd number of split coding units1414a,1414b, and1414cmay have a width equal to that of the other coding units1414aand1414cand a height which is two times that of the other coding units1414aand1414c. That is, in this case, the coding unit1414bat the center location may include two of the other coding unit1414aor1414c. Therefore, when a PID of the coding unit1414bat the center location is 1 based on a scan order, a PID of the coding unit1414clocated next to the coding unit1414bmay be increased by 2 and thus may be 3. That is, discontinuity in PID values may be present. According to an embodiment, the image decoding apparatus100may determine whether an odd number of split coding units do not have equal sizes, based on whether discontinuity is present in PIDs for identifying the split coding units.

According to an embodiment, the image decoding apparatus100may determine whether to use a specific splitting method, based on PID values for identifying a plurality of coding units determined by splitting a current coding unit. Referring toFIG.14, the image decoding apparatus100may determine an even number of coding units1412aand1412bor an odd number of coding units1414a,1414b, and1414cby splitting the first coding unit1410having a rectangular shape, a height of which is longer than a width. The image decoding apparatus100may use PIDs indicating respective coding units so as to identify respective coding units. According to an embodiment, the PID may be obtained from a sample of a certain location of each coding unit (e.g., an upper left sample).

According to an embodiment, the image decoding apparatus100may determine a coding unit at a certain location from among the split coding units, by using the PIDs for distinguishing the coding units. According to an embodiment, when the split shape mode information of the first coding unit1410having a rectangular shape, a height of which is longer than a width, indicates to split a coding unit into three coding units, the image decoding apparatus100may split the first coding unit1410into three coding units1414a,1414b, and1414c. The image decoding apparatus100may assign a PID to each of the three coding units1414a,1414b, and1414c. The image decoding apparatus100may compare PIDs of an odd number of split coding units to determine a coding unit at a center location from among the coding units. The image decoding apparatus100may determine the coding unit1414bhaving a PID corresponding to a middle value among the PIDs of the coding units, as the coding unit at the center location from among the coding units determined by splitting the first coding unit1410. According to an embodiment, the image decoding apparatus100may determine PIDs for distinguishing split coding units, based on a size ratio between the coding units when the split coding units do not have equal sizes. Referring toFIG.14, the coding unit1414bgenerated by splitting the first coding unit1410may have a width equal to that of the other coding units1414aand1414cand a height which is two times that of the other coding units1414aand1414c. In this case, when the PID of the coding unit1414bat the center location is 1, the PID of the coding unit1414clocated next to the coding unit1414bmay be increased by 2 and thus may be 3. When the PID is not uniformly increased as described above, the image decoding apparatus100may determine that a coding unit is split into a plurality of coding units including a coding unit having a size different from that of the other coding units. According to an embodiment, when the split shape mode information indicates to split a coding unit into an odd number of coding units, the image decoding apparatus100may split a current coding unit in such a manner that a coding unit of a certain location among an odd number of coding units (e.g., a coding unit of a center location) has a size different from that of the other coding units. In this case, the image decoding apparatus100may determine the coding unit of the center location, which has a different size, by using PIDs of the coding units. However, the PIDs and the size or location of the coding unit of the certain location are not limited to the above-described examples, and various PIDs and various locations and sizes of coding units may be used.

According to an embodiment, the image decoding apparatus100may use a certain data unit where a coding unit starts to be recursively split.

FIG.15illustrates that a plurality of coding units are determined based on a plurality of certain data units included in a picture, according to an embodiment.

According to an embodiment, a certain data unit may be defined as a data unit where a coding unit starts to be recursively split by using split shape mode information. That is, the certain data unit may correspond to a coding unit of an uppermost depth, which is used to determine a plurality of coding units split from a current picture. In the following descriptions, for convenience of explanation, the certain data unit is referred to as a reference data unit.

According to an embodiment, the reference data unit may have a certain size and a certain size shape. According to an embodiment, the reference data unit may include M×N samples. Herein, M and N may be equal to each other, and may be integers expressed as powers of 2. That is, the reference data unit may have a square or non-square shape, and may be split into an integer number of coding units.

According to an embodiment, the image decoding apparatus100may split the current picture into a plurality of reference data units. According to an embodiment, the image decoding apparatus100may split the plurality of reference data units, which are split from the current picture, by using the split shape mode information of each reference data unit. The operation of splitting the reference data unit may correspond to a splitting operation using a quad-tree structure.

According to an embodiment, the image decoding apparatus100may previously determine the minimum size allowed for the reference data units included in the current picture. Accordingly, the image decoding apparatus100may determine various reference data units having sizes equal to or greater than the minimum size, and may determine one or more coding units by using the split shape mode information with reference to the determined reference data unit.

Referring toFIG.15, the image decoding apparatus100may use a square reference coding unit1500or a non-square reference coding unit1502. According to an embodiment, the shape and size of reference coding units may be determined based on various data units capable of including at least one reference coding unit (e.g., sequences, pictures, slices, slice segments, tiles, tile groups, CTUs, or the like).

According to an embodiment, for each of various data units described above, the bitstream obtainer110of the image decoding apparatus100may obtain, from a bitstream, at least one of information about a shape of the reference coding unit and information about a size of the reference coding unit. An operation of splitting the square reference coding unit1500into one or more coding units has been described above in relation to the operation of splitting the current coding unit300ofFIG.3, and an operation of splitting the non-square reference coding unit1502into one or more coding units has been described above in relation to the operation of splitting the current coding unit400or450ofFIG.4. Thus, detailed descriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus100may use a PID for identifying the size and shape of reference coding units, to determine the size and shape of reference coding units according to some data units previously determined based on a certain condition. That is, the bitstream obtainer110may obtain, from the bitstream, only the PID for identifying the size and shape of reference coding units with respect to each slice, slice segment, tile, tile group, or CTU which is a data unit satisfying a certain condition (e.g., a data unit having a size equal to or smaller than a slice) among the various data units (e.g., sequences, pictures, slices, slice segments, tiles, tile groups, CTUs, or the like). The image decoding apparatus100may determine the size and shape of reference data units with respect to each data unit, which satisfies the certain condition, by using the PID. When the reference coding unit shape information and the reference coding unit size information are obtained and used from the bitstream according to each data unit having a relatively small size, efficiency of using the bitstream may not be high, and therefore, only the PID may be obtained and used instead of directly obtaining the reference coding unit shape information and the reference coding unit size information. In this case, at least one of the size and shape of reference coding units corresponding to the PID for identifying the size and shape of reference coding units may be previously determined. That is, the image decoding apparatus100may determine at least one of the size and shape of reference coding units included in a data unit serving as a unit for obtaining the PID, by selecting the previously determined at least one of the size and shape of reference coding units based on the PID.

According to an embodiment, the image decoding apparatus100may use one or more reference coding units included in a CTU. That is, a CTU split from a picture may include one or more reference coding units, and coding units may be determined by recursively splitting each reference coding unit. According to an embodiment, at least one of a width and height of the CTU may be integer times at least one of the width and height of the reference coding units. According to an embodiment, the size of reference coding units may be obtained by splitting the CTU n times based on a quadtree structure. That is, the image decoding apparatus100may determine the reference coding units by splitting the CTU n times based on a quadtree structure, and may split the reference coding unit based on at least one of the block shape information and the split shape mode information according to various embodiments.

According to an embodiment, the image decoding apparatus100may obtain block shape information indicating the shape of a current coding unit or split shape mode information indicating a splitting method of the current coding unit, from the bitstream, and may use the obtained information. The split shape mode information may be included in the bitstream related to various data units. For example, the image decoding apparatus100may use the 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, or a tile group header. Furthermore, the image decoding apparatus100may obtain, from the bitstream, a syntax element corresponding to the block shape information or the split shape mode information according to each CTU, each reference coding unit, or each processing block, and may use the obtained syntax element.

Hereinafter, a method of determining a split rule, according to an embodiment of the present disclosure will be described in detail.

The image decoding apparatus100may determine a split rule of an image. The split rule may be pre-determined between the image decoding apparatus100and the image encoding apparatus200. The image decoding apparatus100may determine the split rule of the image, based on information obtained from a bitstream. The image decoding apparatus100may determine the split rule based on the 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, or a tile group header. The image decoding apparatus100may determine the split rule differently according to frames, slices, tiles, temporal layers, CTUs, or coding units.

The image decoding apparatus100may determine the split rule based on a block shape of a coding unit. The block shape may include a size, shape, a ratio of width and height, and a direction of the coding unit. The image encoding apparatus200and the image decoding apparatus100may pre-determine to determine the split rule based on the block shape of the coding unit. However, an embodiment is not limited thereto. The image decoding apparatus100may determine the split rule of the image, based on information obtained from a bitstream received from the image encoding apparatus200.

The shape of the coding unit may include a square and a non-square. When the lengths of the width and height of the coding unit are the same, the image decoding apparatus100may determine the shape of the coding unit to be a square. Also, when the lengths of the width and height of the coding unit are not the same, the image decoding apparatus100may determine the shape of the coding unit to be a non-square.

The size of the coding unit may include various sizes, such as 4×4, 8×4, 4×8, 8×8, 16×4, 16×8, and to 256×256. The size of the coding unit may be classified based on the length of a long side of the coding unit, the length of a short side, or the area. The image decoding apparatus100may apply the same split rule to coding units classified as the same group. For example, the image decoding apparatus100may classify coding units having the same lengths of the long sides as having the same size. Also, the image decoding apparatus100may apply the same split rule to coding units having the same lengths of long sides.

The ratio of the width and 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, 1:32, or the like. Also, a direction of the coding unit may include a horizontal direction and a vertical direction. The horizontal direction may indicate a case in which the length of the width of the coding unit is longer than the length of the height thereof. The vertical direction may indicate a case in which the length of the width of the coding unit is shorter than the length of the height thereof.

The image decoding apparatus100may adaptively determine the split rule based on the size of the coding unit. The image decoding apparatus100may differently determine an allowable split shape mode based on the size of the coding unit. For example, the image decoding apparatus100may determine whether splitting is allowed based on the size of the coding unit. The image decoding apparatus100may determine a split direction according to the size of the coding unit. The image decoding apparatus100may determine an allowable split type according to the size of the coding unit.

The split rule determined based on the size of the coding unit may be a split rule pre-determined between the image encoding apparatus200and the image decoding apparatus100. Also, the image decoding apparatus100may determine the split rule based on the information obtained from the bitstream.

The image decoding apparatus100may adaptively determine the split rule based on a location of the coding unit. The image decoding apparatus100may adaptively determine the split rule based on the location of the coding unit in the image.

Also, the image decoding apparatus100may determine the split rule such that coding units generated via different splitting paths do not have the same block shape. However, an embodiment is not limited thereto, and the coding units generated via different splitting paths have the same block shape. The coding units generated via the different splitting paths may have different decoding process orders. Because the decoding process orders have been described above with reference toFIG.12, details thereof are not provided again.

FIG.16illustrates coding units which may be determined for each picture, when a combination of shapes into which a coding unit may be split is different for each picture, according to an embodiment.

Referring toFIG.16, the image decoding apparatus100may, for each picture, differently determine a combination of split shapes into which a coding unit may be split. For example, the image decoding apparatus100may decode an image by using a picture1600which may be split into four coding units, a picture1610which may be split into two or four coding units, and a picture1620which may be split into two, three, or four coding units, from among one or more pictures included in the image. In order to split the picture1600into a plurality of coding units, the image decoding apparatus100may use only split shape information indicating a split into four square coding units. In order to split the picture1610, the image decoding apparatus100may use only split shape information indicating a split into two or four coding units. In order to split the picture1620, the image decoding apparatus100may use only split shape information indicating a split into two, three, or four coding units. The combinations of the split shapes described above are only an embodiment for describing an operation of the image decoding apparatus100. Thus, the combinations of the split shapes described above should not be interpreted to be limited to the embodiment described above, and should be interpreted such that various types of combinations of the split shapes may be used for a predetermined data unit.

According to an embodiment, the bitstream obtainer110of the image decoding apparatus100may obtain a bitstream including an index indicating a combination of split shape information for each predetermined data unit (for example, a sequence, a picture, a slice, a slice segment, a tile, or a tile group). For example, the bitstream obtainer110may obtain the index indicating the combination of the split shape information from a sequence parameter set, a picture parameter set, a slice header, a tile header, or a tile group header. The bitstream obtainer110of the image decoding apparatus100may determine, for each predetermined data unit, a combination of split shapes into which a coding unit may be split by using the obtained index, and thus, for each predetermined data unit, a different combination of the split shapes may be used.

FIG.17illustrates various shapes of a coding unit, which may be determined based on split shape mode information which may be represented as a binary code, according to an embodiment.

According to an embodiment, the image decoding apparatus100may split the coding unit into various shapes by using block shape information and split shape mode information obtained by the bitstream obtainer110. Shapes into which the coding unit may be split may correspond to various shapes including the shapes described according to the embodiments described above.

Referring toFIG.17, the image decoding apparatus100may split a square coding unit in at least one of a horizontal direction and a vertical direction and may split a non-square coding unit in the horizontal direction or the vertical direction, based on the split shape mode information.

According to an embodiment, when the image decoding apparatus100may split a square coding unit in the horizontal direction and the vertical direction into four square coding units, split shapes which may be indicated by the split shape mode information with respect to the square coding unit may correspond to four types. According to an embodiment, the split shape mode information may be represented as a two-digit binary code, and each split shape may be assigned with a binary code. For example, when a coding unit is not split, the split shape mode information may be represented as (00)b, when a coding unit is split in a horizontal direction and a vertical direction, the split shape mode information may be represented as (01)b, when a coding unit is split in the horizontal direction, the split shape mode information may be represented as (10)b, and when a coding unit is split in the vertical direction, the split shape mode information may be represented as (11)b.

According to an embodiment, when the image decoding apparatus100splits a non-square coding unit in a horizontal direction or a vertical direction, split shape types which may be indicated by the split shape mode information may be determined depending on the number of coding units into which the non-square coding unit is split. Referring toFIG.17, the image decoding apparatus100may split up to three coding units from a non-square coding unit, according to an embodiment. The image decoding apparatus100may split a coding unit into two coding units, and in this case, the split shape mode information may be represented as (10)b. The image decoding apparatus100may split a coding unit into three coding units, and in this case, the split shape mode information may be represented as (11)b. The image decoding apparatus100may determine not to split a coding unit, and in this case, the split shape mode information may be represented as (0)b. That is, to use the binary code indicating the split shape mode information, the image decoding apparatus100may use variable length coding (VLC) rather than fixed length coding (FLC).

Referring toFIG.17, according to an embodiment, a binary code of the split shape mode information indicating not to split the coding unit may be represented as (0)b. When the binary code of the split shape mode information indicating not to split the coding unit is configured as (00)b, all of 2-bit binary codes of the split shape mode information may have to be used, even though there is no split shape mode information configured as (01)b. However, when, as illustrated inFIG.17, three split shape types with respect to the non-square coding unit are used, the image decoding apparatus100may determine not to split the coding unit, even by using a 1-bit binary code (0)b as the split shape mode information. Thus, a bitstream may be efficiently used. However, the split shapes of the non-square coding unit indicated by the split shape mode information should not be interpreted as being limited to the three split shape types illustrated inFIG.17and should be interpreted to include various shapes including the embodiments described above.

FIG.18illustrates another shape of a coding unit, which may be determined based on split shape mode information which may be represented as a binary code, according to an embodiment.

Referring toFIG.18, the image decoding apparatus100may split a square coding unit in a horizontal direction or a vertical direction and may split a non-square coding unit in the horizontal direction or the vertical direction, based on the split shape mode information. That is, the split shape mode information may indicate to split the square coding unit in one direction. In this case, a binary code of the split shape mode information indicating not to split the square coding unit may be represented as (0)b. When the binary code of the split shape mode information indicating not to split the coding unit is configured as (00)b, all of 2-bit binary codes of the split shape mode information may have to be used, even though there is no split shape mode information configured as (01)b. However, when, as illustrated inFIG.18, three split shape types with respect to the square coding unit are used, the image decoding apparatus100may determine not to split the coding unit, even by using a 1-bit binary code (0)b as the split shape mode information. Thus, a bitstream may be efficiently used. However, the split shapes of the square coding unit indicated by the split shape mode information should not be interpreted as being limited to the three split shape types illustrated inFIG.18and should be interpreted to include various shapes including the embodiments described above.

According to an embodiment, the block shape information or the split shape mode information may be represented by using a binary code, and the block shape information or the split shape mode information may be directly generated as a bitstream. Also, the block shape information or the split shape mode information which may be represented as a binary code may not be directly generated as a bitstream and may be used as a binary code which is input in context adaptive binary arithmetic coding (CABAC).

According to an embodiment, a process in which the image decoding apparatus100obtains syntax with respect to the block shape information or the split shape mode information through the CABAC, is described. A bitstream including a binary code with respect to the syntax may be obtained by the bitstream obtainer110. The image decoding apparatus100may detect a syntax element indicating the block shape information or the split shape mode information by inverse binarizing a bin string included in the obtained bistream. According to an embodiment, the image decoding apparatus100may obtain a set of binary bin strings corresponding to a syntax element to be decoded and may decode each bin by using probability information. Also, the image decoding apparatus100may repeat this process until a bin string composed of these decoded bins becomes the same as one of previously obtained bin strings. The image decoding apparatus100may determine the syntax element by performing inverse binarization on the bin string.

According to an embodiment, the image decoding apparatus100may determine the syntax with respect to the bin string by performing a decoding process of adaptive binary arithmetic coding, and the image decoding apparatus100may update a probability model with respect to the bins obtained by the bitstream obtainer110. Referring toFIG.17, the bitstream obtainer110of the image decoding apparatus100may obtain a bitstream indicating a binary code representing split shape mode information, according to an embodiment. The image decoding apparatus100may determine the syntax with respect to the split shape mode information by using the obtained 1-bit or 2-bit-sized binary code. In order to determine the syntax with respect to the split shape mode information, the image decoding apparatus100may update a probability with respect to each bit of the 2-bit binary code. That is, according to whether a value of a first bin of the 2-bit binary code is 0 or 1, the image decoding apparatus100may update a probability for a next bin of having the value of 0 or 1 when the next bin is decoded.

According to an embodiment, in the process of determining the syntax, the image decoding apparatus100may update the probability with respect to the bins, in a process of decoding the bins of the bin string with respect to the syntax, and with respect to a predetermined bit from among the bin string, the image decoding apparatus100may not update the probability and may determine that the probability is the same.

Referring toFIG.17, in a process of determining the syntax by using the bin string representing the split shape mode information with respect to the non-square coding unit, the image decoding apparatus100may determine the syntax with respect to the split shape mode information by 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 a current coding unit has a non-square shape, a first bin of the bin string with respect to the split shape mode information may be 0, when the non-square coding unit is not split, and may be 1, when the non-square coding unit is split into two or three coding units. Accordingly, the probability that the first bin of the bin string of the split shape mode information with respect to the non-square coding unit is 0 may be ⅓, and the probability that the first bin of the bin string of the split shape mode information with respect to the non-square coding unit is 1 may be ⅔. As described above, because the split shape mode information indicating that the non-square coding unit is not split may be represented by using only a 1-bit bin string having the value of 0, the image decoding apparatus100may determine the syntax with respect to the split shape mode information by determining whether a second bin is 0 or 1, only when the first bin of the split shape mode information is 1. According to an embodiment, when the first bin with respect to the split shape mode information is 1, the image decoding apparatus100may regard that the probability that the second bin is 0 and the probability that the second bin is 1 are the same as each other and may decode the bin.

According to an embodiment, in the process of determining the bins of the bin string with respect to the split shape mode information, the image decoding apparatus100may use various probabilities with respect to each bin. According to an embodiment, the image decoding apparatus100may differently determine the probabilities of the bins with respect to the split shape mode information, according to a direction of a non-square block. According to an embodiment, the image decoding apparatus100may differently determine the probabilities of the bins with respect to the split shape mode information, according to a width or a length of a longer side of a current coding unit. According to an embodiment, the image decoding apparatus100may differently determine the probabilities of the bins with respect to the split shape mode information, according to at least one of a shape and a length of a longer side of a current coding unit.

According to an embodiment, the image decoding apparatus100may determine that the probabilities of the bins with respect to the split shape mode information are the same for coding units having a size that is equal to or greater than a predetermined size. For example, the image decoding apparatus100may determine that the probabilities of the bins with respect to the split shape mode information are the same as each other with respect to the coding units having a size that is equal to or greater than 64 samples based on a length of a longer side of the coding unit.

According to an embodiment, the image decoding apparatus100may determine initial probabilities of the bins composed in the bin string of the split shape mode information based on a slice type (for example, an I-slice, a P-slice, or a B-slice).

FIG.19illustrates a block diagram of an image encoding and decoding system performing loop filtering.

An encoding end1910of an image encoding and decoding system1900transmits an encoded bitstream of an image and a decoding end1950outputs a reconstructed image by receiving and decoding the bitstream. Here, the encoding end1910may have a similar configuration as the image encoding apparatus200to be described below, and the decoding end1950may have a similar configuration as the image decoding apparatus100.

In the encoding end1910, a prediction encoder1915outputs prediction data via inter-prediction and intra-prediction, and a transformer and quantizer1920outputs a quantized transform coefficient of residual data between the prediction data and a current input image. An entropy encoder1925encodes and transforms the quantized transform coefficient and outputs the quantized transform coefficient as a bitstream. The quantized transform coefficient is reconstructed as data of a spatial domain via an inverse quantizer and inverse transformer1930, and the reconstructed data of the spatial domain is output as a reconstructed image via a deblocking filter1935and a loop filter1940. The reconstructed image may be used as a reference image of a next input image via the prediction encoder1915.

Encoded image data among the bitstream received by the decoding end1950is reconstructed as residual data of the spatial domain via an entropy decoder1955and an inverse quantizer and inverse transformer1960. Prediction data and residual data that are output from a prediction decoder1975may be combined to construct image data of the spatial domain, and a deblocking filter1965and a loop filter1970may perform filtering on the image data of the spatial domain to output a reconstructed image with respect to a current original image. The reconstructed image may be used as a reference image for a next original image via the prediction decoder1975.

The loop filter1940of the encoding end1910performs loop filtering by using filter information input according to a user input or system setting. The filter information used by the loop filter1940is output to the entropy encoder1925and transmitted to the decoding end1950together with the encoded image data. The loop filter1970of the decoding end1950may perform loop filtering based on the filter information input from the decoding end1950.

Various embodiments described above describe an operation related to the image decoding method performed by the image decoding apparatus100. Hereinafter, an operation of the image encoding apparatus200performing an image encoding method, which corresponds to an inverse process of the image decoding method, is described according to various embodiments.

FIG.2is a block diagram of the image encoding apparatus200capable of encoding an image based on at least one of block shape information and split shape mode information, according to an embodiment.

The image encoding apparatus200may include an encoder220and a bitstream generator210. The encoder220may receive an input image and encode the input image. The encoder220may obtain at least one syntax element by encoding the input image. 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 encoder220may determine a context model based on the block shape information including at least one of a shape, a direction, a ratio between a width and a height, or a size of a coding unit.

The bitstream generator210may generate a bitstream based on the encoded input image. For example, the bitstream generator210may generate the bitstream by entropy encoding the syntax element based on the context model. Also, the image encoding apparatus200may transmit the bitstream to the image decoding apparatus100.

According to an embodiment, the encoder220of the image encoding apparatus200may determine a shape of the coding unit. For example, the coding unit may have a square shape or a non-square shape, and information indicating the square shape or the non-square shape may be included in the block shape information.

According to an embodiment, the encoder220may determine into which shape the coding unit is to be split. The encoder220may determine a shape of at least one coding unit included in the coding unit, and the bitstream generator210may generate the bitstream including the split shape mode information including information about the shape of the coding unit.

According to an embodiment, the encoder220may determine whether or not to split the coding unit. When the encoder220determines that only one coding unit is included in the coding unit or the coding unit is not split, the bitstream generator210may generate the bitstream including the split shape mode information indicating that the coding unit is not split. Also, the encoder220may split the coding unit into a plurality of coding units, and the bitstream generator210may generate the bitstream including the split shape mode information indicating that the coding unit is split into the plurality of coding units.

According to an embodiment, information indicating into which number of coding units the coding unit is to be split or in which direction the coding unit is to be split may be included in the split shape mode information. For example, the split shape mode information may indicate to split the coding unit in at least one direction of a vertical direction and a horizontal direction or may indicate not to split the coding unit.

The image encoding apparatus200may determine information with respect to a split shape mode, based on the split shape mode of the coding unit. The image encoding apparatus200may determine a context model based on at least one of a shape, a direction, a ratio between a width and a height, or a size of the coding unit. Also, the image encoding apparatus200may generate the information with respect to the split shape mode for splitting the coding unit as a bitstream based on the context model.

In order to determine the context model, the image encoding apparatus200may obtain an arrangement for making a correspondence between at least one of the shape, the direction, the ratio between the width and the height, or the size of the coding unit, and an index with respect to the context model. The image encoding apparatus200may obtain, from the arrangement, the index with respect to the context model based on at least one of the shape, the direction, the ratio between the width and the height, or the size of the coding unit. The image encoding apparatus200may determine the context model based on the index with respect to the context model.

In order to determine the context model, the image encoding apparatus200may determine the context model further based on block shape information including at least one of a shape, a direction, a ratio between a width and a height, or a size of a neighboring coding unit adjacent to the coding unit. Also, the neighboring coding unit may include at least one of coding units located at a lower left side, a left side, an upper left side, an upper side, an upper right side, a right side, and a lower right side of the coding unit.

Also, the image encoding apparatus200may compare a width of the upper neighboring coding unit with a width of the coding unit, in order to determine the context model. Also, the image encoding apparatus200may compare heights of the left and right neighboring coding units with a height of the coding unit. Also, the image encoding apparatus200may determine the context model based on results of the comparison.

The operation of the image encoding apparatus200include similar aspects as the operation of the image decoding apparatus100described with reference toFIGS.3through19, and thus, is not described in detail.

Hereinafter, embodiments according to the technical concept of the disclosure are sequentially described in detail.

FIG.20is a block diagram of components of an image decoding apparatus2000according to an embodiment.

Referring toFIG.20, the image decoding apparatus2000may include an obtainer2010, a block determiner2030, a prediction decoder2050, and a reconstructor2070. The obtainer2010illustrated inFIG.20may correspond to the bitstream obtainer110illustrated inFIG.1, and the block determiner2030, the prediction decoder2050, and the reconstructor2070may correspond to the decoder120illustrated inFIG.1.

The obtainer2010, the block determiner2030, the prediction decoder2050, and the reconstructor2070according to an embodiment may be realized as at least one processor. The image decoding apparatus2000may include one or more data storages (not shown) storing input and output data of the obtainer2010, the block determiner2030, the prediction decoder2050, and the reconstructor2070. Also, the image decoding apparatus2000may also include a memory controller (not shown) controlling data inputting and outputting of the data storage.

The obtainer2010may receive a bitstream generated as a result of encoding an image. The obtainer2010may obtain, from the bitstream, syntax elements for decoding the image. Binary values corresponding to the syntax elements may be included in the bitstream according to a hierarchical structure of the image. The obtainer2010may obtain the syntax elements by entropy coding the binary values included in the bitstream.

FIG.21is an example diagram of a structure of a bitstream2100generated according to a hierarchical structure of an image.

Referring toFIG.21, the bitstream2100may include a sequence parameter set2110, a picture parameter set2120, a group header2130, and a block parameter set2140.

In detail, the sequence parameter set2110includes information used for an image sequence including one or more images.

The picture parameter set2120includes information used in one image and may refer to the sequence parameter set2110.

The group header2130includes information used in a block group determined in the image and may refer to the picture parameter set2120and the sequence parameter set2110. The group header2130may be a slice header.

Also, the block parameter set2140includes information used in a block determined in the image and may refer to the group header2130, the picture parameter set2120, and the sequence parameter set2110.

According to an embodiment, the block parameter set2140may be identified as at least one of a parameter set of a CTU, a parameter set of a coding unit, a parameter set of a prediction unit, and a parameter set of a transform unit, according to a hierarchical structure of the block determined in the image.

The obtainer2010may obtain, from the bitstream2100, information used for decoding the image, according to the hierarchical structure of the image, and the block determiner2030, the prediction decoder2050, and the reconstructor2070to be described below may perform required operations by using the information obtained by the obtainer2010.

The structure of the bitstream2100illustrated inFIG.21is only an example, and one or more of the parameter sets illustrated inFIG.21may not be included in the bitstream2100, or a parameter set which is not illustrated, for example, a video parameter set, may be included in the bitstream2100.

The block determiner2030may split a current image into blocks and configure, in the current image, block groups including at least one block. Here, the block may correspond to a tile, and the block group may correspond to a slice. The slice may be referred to as a tile group.

The prediction decoder2050may inter-predict or intra-predict lower blocks of the blocks split from the current image to obtain prediction samples corresponding to the lower blocks. Here, the lower block may be at least one of a CTU, a coding unit, and a transform unit.

Hereinafter, descriptions are given by limiting the block as the tile and the block group as the slice. However, it is only an example, and when there is a B block including a set of A blocks, the A block may correspond to a block, and the B block may correspond to a block group. For example, when a set of CTUs corresponds to a tile, the CTU may be the block, and the tile may be the block group.

As described with reference toFIGS.3through16, the block determiner2030may split the current image to determine the transform unit, the coding unit, the CTU, the tile, the slice, etc.

FIG.22illustrates a slice, a tile, and a CTU determined in a current image2200.

The current image2200is split into a plurality of CTUs. Sizes of the CTUs may be determined based on information obtained from a bitstream. The CTUs may have same-sized square shapes.

A tile includes one or more CTUs. The tile may have a square or rectangular shape.

A slice includes one or more tiles. The slice may have a square shape or a non-square shape.

According to an embodiment, the block determiner2030may split the current image2200into a plurality of CTUs according to information obtained from the bitstream, and may configure, in the current image2200, a tile including at least one CTU and a slice including at least one tile.

According to an embodiment, the block determiner2030may split the current image2200into a plurality of tiles according to information obtained from the bitstream, and may split each tile into one or more CTUs. Also, the block determiner2030may configure, in the current image2200, a slice including at least one tile.

According to an embodiment, the block determiner2030may split the current image2200into one or more slices according to information obtained from the bitstream, and may split each slice into one or more tiles. Also, the block determiner2030may split each tile into one or more CTUs.

The block determiner2030may use address information of slices obtained from the bitstream, in order to configure the slices in the current image2200. The block determiner2030may configure, in the current image2200, the slices including one or more tiles, according to the address information of the slices obtained from the bitstream. The address information of the slices may be obtained from a video parameter set, a sequence parameter set, a picture parameter met, or a group header of the bitstream.

A method, performed by the block determiner2030, of configuring the slices in the current image2200is described with reference toFIGS.23and24.

FIGS.23and24are diagrams for describing a method of configuring slices in the current image2200.

When tiles are configured in the current image2200, the block determiner2030may configure, in the current image2200, slices including at least one tile, according to address information of the slices obtained from a bitstream.

To describe with reference toFIG.23, slices2310,2320,2330,2340, and2350may be determined in the current image2200according to a raster scan direction2300, and the slices2310,2320,2330,2340, and2350may be sequentially decoded according to the raster scan direction2300.

According to an embodiment, the address information may include an identification value of a lower right tile located at a lower right end from among tiles included in each of the slices2310,2320,2330,2340, and2350.

In detail, the address information of the slices2310,2320,2330,2340, and2350may include 9, which is an identification value of the lower right tile of the first slice2310, 7, which is an identification value of the lower right tile of the second slice2320, 11, which is an identification value of the lower right tile of the third slice2330,12, which is an identification value of the lower right tile of the fourth slice2340, and15, which is an identification value of the lower right tile of the fifth slice2350. According to an embodiment, when the fourth slice2340is configured in the current image2200, the fifth slice2350, which is the last slice, may be automatically identified, and thus, the address information of the fifth slice2350may not be included in the bitstream.

In order to configure the first slice2310, the block determiner2030may identify an upper left tile from among the tiles of the current image2200, that is, a tile having an identification value of 0. Also, the block determiner2030may determine a region including Tile 0, and Tile 9 identified from the address information, as the first slice2310.

Next, in order to configure the second slice2320, the block determiner2030may determine a tile having a least identification value from among tiles not included in a previous slice, that is, the first slice2310, namely, Tile 2, as an upper left tile of the second slice2320. Also, the block determiner2030may determine a region including Tile 2, and Tile 7 identified from the address information, as the second slice2320.

Likewise, in order to specify the third slice2330, the block determiner2030may determine a tile having a least identification value from among tiles not included in previous slices, that is, the first slice2310and the second lice2320, namely, Tile 10, as an upper left tile of the third slice2330. Also, the block determiner2030may determine a region including Tile 10, and Tile 11 identified from the address information, as the third slice2330.

That is, according to an embodiment, the slices may be configured in the current image2200by using only the identification information of the lower right tiles included in the bitstream.

According to another embodiment, as the address information for determining the slices, the obtainer2010may obtain an identification value of an upper left tile and an identification value of a lower right tile included in each of the slices, and the block determiner2030may configure the slices in the current image2200according to the information obtained by the obtainer2010. Because the upper left tile and the lower right tile included in each of the slices may be identified from the address information, the block determiner2030may configure regions including the upper left tiles and the lower right tiles identified from the address information as the slices.

According to another embodiment, as the address information for configuring the slices, the obtainer2010may obtain an identification value of an upper left tile included in each of the slices, a width of each slice, and a height of each slice, and the block determiner2030may configure the slices in the current image2200according to the information obtained by the obtainer2010.

For example, the address information of the second slice2320inFIG.23may include 2, which is an identification value of the upper left tile, 2, which is a width of the slice, and 2, which is a height of the slice. Here, that the width and the height are 2 denotes that there are two tile rows and two tile columns in a width direction and a height direction of the second slice2320.

According to an embodiment, the upper left tile of the first slice2310is fixed as tile 0, and thus, an identification value of the upper left tile of the first slice2310may not be included in a bitstream.

According to another embodiment, the width and the height of the slice obtained from the bitstream may be values obtained by dividing the number of tile rows and the number of tile columns arranged in the width direction and the height direction of the slice by a predetermined scaling factor. In other words, when the address information of the second slice2320inFIG.23indicates 2, which is the identification value of the upper left tile, 1, which is the width of the slice, and 1, which is the height of the slice, the block determiner2030may multiply 1, which is the width of the slice, and 1, which is the height of the slice, by a predetermined scaling factor, for example, 2, so as to identify that there are two tile rows and two tile columns in the width direction and the height direction of the slice.

The block determiner2030may determine the first through fifth slices2310through2350in the current image2200, according to the address information of the first through fifth slices2310through2350. When up to the fourth slice2340is determined in the current image2200according to the address information, the fifth slice2350may be automatically determined, and thus, the address information of the last slice may not be included in the bitstream.

According to another embodiment, address information of a slice including a tile located at a first row or a tile located at a first column, from among the slices to be determined in the current image2200, may further include a value indicating the number of slices subsequently existing in a right direction or a lower direction of the corresponding slice, in addition to the identification value of the upper left tile of the corresponding slice, the width of the slice, and the height of the slice. The value indicating the number of slices subsequently existing in the right direction or the lower direction of the slice may be replaced by a value indicating the number of slices arranged in a width direction or a height direction of the slice.

The address information of the first slice2310may include information that one slice (that is, the second slice2320) exists in the right direction and one slice (that is, the fourth slice2340) exists in the lower direction. Because the first slice2310includes both of the tile located at the first row and the tile located at the first column in the image2200, the address information of the first slice2310may include the value indicating the number of slices subsequently existing in the right direction of the slice and the value indicating the number of slices subsequently existing in the lower direction of the slice.

Because the second slice2320includes only the tile located at the first row, the address information of the second slice2320may include the value indicating the number of slices subsequently existing in the lower direction of the slice.

Because the value(s) indicating the number of slices subsequently existing in the right direction and/or the lower direction is (are) included in the address information, address information of a last slice in a width direction of the current image2200(the second slice2320and/or the fifth slice2350inFIG.23) may omit the width of the slice, and address information of a last slice in a height direction of the current image2200(the fourth slice2340and/or the fifth slice2350inFIG.23) may omit the height of the slice. For example, that is because, because the block determiner2030may already know that the first slice2310has one subsequent slice existing in the width direction of the current image2200, the block determiner2030may derive the width of the subsequent slice of the first slice2310by considering a width of the current image2200, even when the value indicating the width of the subsequent slice is not included in the bitstream. InFIG.23, because four tiles exist in the width direction of the current image2200and two tiles exist in the width direction of the first slice2310, it may be identified that two tiles exist in the width direction of the second slice2320subsequently existing with respect to the first slice2310. Likewise, because the block determiner2030may know that the first slice2310has one subsequent slice existing in the height direction of the current image2200, the block determiner2030may derive the height of the subsequent slice of the first slice2310, even when the value indicating the height of the subsequent slice is not included in the bitstream.

According to another embodiment, the obtainer2010may obtain, from the bitstream, split information for splitting the current image2200into slices, and the block determiner2030may split the current image2200into slices according to the split information. Here, the split information may indicate, for example, a quad-split, a bi-split of the height, a bi-split of the width, etc.

The block determiner2030may split each of slices obtained when the current image2200is initially split, according to the split information, and may hierarchically obtain smaller slices.

As illustrated inFIG.24, the block determiner2030may determine two regions2410and2420by bi-splitting a width of the current image2200according to the split information and may determine two regions2412and2414by bi-splitting a height of the left region2410according to split information of the left region2410. When split information of the right region2420indicates a non-split, and the regions2412and2414split from the left region2410are not further split, the block determiner2030may configure the upper left region2412as a first slice, the right region2420as a second slice, and the lower left region2414as a third slice.

According to another embodiment, the block determiner2030may configure the slices in the current image2200according to pre-configured map information, and may further split at least one slice in the current image2200or merge two or more slices, according to correction information obtained from the bitstream, to configure final slices. The map information may include address information of slices located in an image. For example, the block determiner2030may initially configure the slices in the image2200according to the map information obtained from a video parameter set or a sequence parameter set of the bitstream, and may finally configure the slices in the image2200according to correction information obtained from a picture parameter set.

When tiles and slices are determined in the current image, the block determiner2030may inter-predict at least one of coding units included in the tiles. Here, a method of configuring a reference image list used for inter-prediction is described.

Referring toFIG.20, the prediction decoder2050prediction-decodes the coding units included in the tiles determined in the current image. The prediction decoder2050may prediction-decode the coding units through inter-prediction or intra-prediction. According to inter-prediction, a prediction sample of the coding unit is obtained based on a reference block in a reference image indicated by a motion vector, and a reconstruction sample of the coding unit is obtained based on residual data obtained from the prediction sample and a bitstream. The residual data may not be included in the bitstream according to a prediction mode, and in this case, the prediction sample may be determined as the reconstruction sample.

For inter-prediction, a reference image list including reference images may have to be constructed. According to an embodiment, the obtainer2010may obtain information indicating a plurality of first reference image lists from a sequence parameter set of the bitstream. The information indicating the plurality of first reference image lists may include a picture order count (POC)-related value of the reference image. The plurality of first reference image lists are used for an image sequence including a current image.

According to an embodiment, the information indicating the plurality of first reference image lists may include the number of first reference image lists. In this case, the prediction decoder2050may construct the first reference image lists corresponding to the number of first reference image lists that is identified from the bitstream. In this case, the prediction decoder2050may construct the first reference image lists according to the same method performed by an image encoding apparatus3300.

When encoding coding units included in a predetermined slice, it may be inappropriate to use the plurality of first reference image lists for an image sequence, depending on the characteristics of an image. Thus, when there is no reference image list which may be used for inter-predicting the coding units in a current slice, from among the plurality of first reference image lists, a new reference image list may be obtained from a group header. However, in this case, because the new reference image list is included in the group header, a bit rate may be increased. Thus, a method for constructing an optimum reference image list to be used for a current slice by using the plurality of first reference image lists signaled through the sequence parameter set, is required.

According to an embodiment, the obtainer2010may obtain, from the group header of the bitstream, an indicator indicating at least one of the plurality of first reference image lists used for an image sequence. Also, the prediction decoder2050may obtain a second reference image list modified and refined from the first reference image list indicated by the indicator.

The second reference image list may be obtained by substituting at least one of reference images included in the first reference image list indicated by the indicator by another reference image, by changing an order of one or more of the reference images, or by adding a new reference image to the first reference image list.

To construct the second reference image list, the obtainer2010may obtain modification and refinement information from the group header of the bitstream. The modification and refinement information may include a POC-related value of a reference image to be removed from the first reference image list indicated by the indicator, a POC-related value of a reference image to be added to the second reference image list, a difference value between the POC-related value of the reference image to be removed from the first reference image list and the POC-related value of the reference image to be added to the second reference image list, information for changing an order of images, etc. According to an embodiment, in addition to the group header of the bitstream, the modification and refinement information may be obtained from a parameter set, for example, a picture parameter set.

When the second reference image list is obtained, the prediction decoder2050may prediction-decode coding units included in a slice based on at least one of reference images included in the second reference image list to obtain prediction samples of the coding units.

The prediction decoder2050may prediction-decode coding units included in a next slice by using a first reference image list other than the first reference image list indicated by the indicator, from among the plurality of first reference image lists used for the image sequence, and the second reference image list. In other words, the second reference image list obtained for the current slice may also be used for the next slice. In detail, an indicator indicating a reference image list used in the next slice between the first reference image list other than the first reference image list indicated by the indicator obtained with respect to the current slice and the second reference image list, may be newly obtained, and according to the reference image list indicated by the indicator or a reference image list modified and refined from the reference image list indicated by the indicator, the coding units included in the next slice may be prediction-decoded. Accordingly, even when a new reference image list is not signaled through the sequence parameter set or the group header, an appropriate reference image list for prediction-decoding the coding units of the slices may be constructed only by updating previous reference image lists.

Hereinafter, a method of obtaining the second reference image list modified and refined from the first reference image list is described with reference toFIGS.25through30.

FIG.25is an example diagram illustrating a plurality of first reference image lists2510,2520, and2530obtained from a sequence parameter set.

FIG.25illustrates three first reference image lists2510,2520, and2530. This is only an example, and the number of first reference image lists obtained from the sequence parameter set may be variously modified.

Referring toFIG.25, the first reference image lists2510,2520, and2530may include short-term type or long-term type reference images. The short-term type reference images indicate images designated as short-term types from among reconstructed images stored in a decoded picture buffer (DPB), and the long-term type reference images indicate images designated as long-term types from among the reconstructed images stored in the DPB.

The reference images included in the first reference image lists2510,2520, and2530may be specified by POC-related values. In detail, the short-term type reference image may be specified by a difference value between a POC of a current image and a POC of the short-term type reference image, that is, a delta value, and the long-term type reference image may be specified by a least significant bit (LSB) of a POC of the long-term type reference image. The long-term type reference image may also be specified by a most significant bit (MSB) of the POC of the long-term type reference image.

According to an embodiment, the first reference image lists2510,2520, and2530may include only the short-term type reference images or only the long-term type reference images. That is, all of the reference images illustrated inFIG.25may be the short-term type reference images or the long-term type reference images. Also, according to an embodiment, some of the first reference image lists2510,2520, and2530may include only the short-term type reference images, and the others may include only the long-term type reference images.

FIG.26is a diagram for describing a method of obtaining the second reference image list.

The prediction decoder2050may obtain a second reference image list2600by changing at least one of reference images included in the first reference image list2510indicated by the indicator to another reference image. Referring toFIG.26, it may be identified that a short-term type reference image having a delta value of −1, a long-term type reference image having an LSB of 10, and a short-term type reference image having a delta value of −3 in the first reference image list2510are respectively replaced by a short-term type reference image having a delta value of −2, a long-term type reference image having an LSB of 8, and a short-term type reference image having a delta value of −5 in the second reference image list2600.FIG.26illustrates that all reference images in the first reference image list2510are replaced by other reference images. However, it is only an example, and only one or more of the reference images in the first reference image list2510may be replaced by other reference images.

According to an embodiment, the prediction decoder2050may replace only a particular type of reference image from among the reference images included in the first reference image list2510, for example, a long-term type reference image, by another long-term type reference image. That is, a short-term type reference image from among the reference images included in the first reference image list2510may be intactly maintained in the second reference image list2600, and only the long-term type reference image may be replaced by another long-term type reference image according to information obtained from a bitstream. Referring toFIG.26, only a particular type of reference image from among the reference images included in the first reference image list2510, that is, the long-term type reference image having the LSB of 10, may be replaced by the long-term reference image having the LSB of 8 in the second reference image list2600. According to an embodiment, the long-term type reference image from among the reference images included in the first reference image list2510may be intactly maintained in the second reference image list2600, and only the short-term type reference image in the first reference image list2510may be replaced by another short-term type reference image.

To replace the reference image, the obtainer2010may obtain a POC-related value of a new reference image from a group header of the bitstream, and the prediction decoder2050may include, in the second reference image list2600, a reference image indicated by the POC-related value obtained by the obtainer2010.

To specify a reference image to be replaced by the new reference image (that is, a reference image to be removed), from among the reference images included in the first reference image list2510, the obtainer2010may further obtain, from the bitstream, an index of the reference image to be removed from the first reference image list2510. When all of the reference images included in the first reference image list2510are to be removed, the index of the reference image to be removed from the first reference image list2510may not be included in the bitstream.

As described above, when a particular type of reference image is predetermined to be removed from the first reference image list2510, the index of the reference image to be removed may not be included in the bitstream, and the prediction decoder2050may remove the predetermined reference image from among the reference images included in the first reference image list2510and may include, in the second reference image list2600, the reference image indicated by the POC-related value obtained from the bitstream.

According to an embodiment, information indicating the new reference image to be included in the second reference image list2600may be a difference value between the POC-related value of the new reference image and a POC-related value of the reference image to be removed from the first reference image list2510. For example, inFIG.26, because the reference image having the LSB of 10 in the first reference image list2510is replaced by the reference image having the LSB of 8 in the second reference image list2600, the information indicating the new reference image may include 2(10−8). The prediction decoder2050may derive the POC-related value of the reference image to be newly included in the second reference image list2600, based on the difference value between the POC-related values, and the POC-related value of the reference image to be removed from the first reference image list2510.

According to an embodiment, the new reference image may be added in the second reference image list2600according to the order of the reference image to be removed from the first reference image list2510indicated by the indicator. As illustrated inFIG.26, when a long-term type reference image assigned with an index of 1 is removed from the first reference image list2510, a new reference image may also be assigned with an index of 1.

FIG.27is a diagram for describing another method of obtaining the second reference image list.

The prediction decoder2050may obtain a second reference image list2700by excluding particular types of reference images from among the reference images in the first reference image list2510indicated by the indicator from among the plurality of first reference image lists for the image sequence. Referring toFIG.27, it may be identified that the long-term type reference image from among the reference images in the first reference image list2510indicated by the indicator is not included in the second reference image list2700.

According to an embodiment, the prediction decoder2050may also obtain the second reference image list2700in which the short-term type reference image from among the reference images in the first reference image list2510is excluded.

FIG.28is a diagram for describing another method of obtaining the second reference image list.

The prediction decoder2050may also obtain a second reference image list2800by changing an order of the reference images in the first reference image list2510indicated by the indicator, according to modification and refinement information obtained from the group header of the bitstream. Here, according to the modification and refinement information, the order of all reference images in the first reference image list2510may be changed, or the order of one or more reference images in the first reference image list2510may be changed.

For example, the modification and refinement information obtained from the group header of the bitstream may include indices of the reference images in the first reference image list2510arranged according to an order in which the reference images are to be changed. In detail, inFIG.28, when a reference picture having an index of 0, a reference picture having an index of 1, and a reference picture having an index of 2 in the first reference image list2510are to be respectively changed to the reference picture having the index of 1, the reference picture having the index of 2, and the reference picture having the index of 0 in the second reference image list2800, the group header of the bitstream may include (2, 0, 1) as the modification and refinement information. The prediction decoder2050may assign the index of 0 to the reference image assigned with the index of 2 in the first reference image list2510, the index of 1 to the reference image assigned with the index of 0, and the index of 2 to the reference image assigned with the index of 1, to construct the second reference image list2800.

As another example, the modification and refinement information obtained from the group header of the bitstream may include indices of reference images, an order of which has to be changed, from among the reference images in the first reference image list2510. In detail, inFIG.28, when the order of the reference picture having the index of 1 and the reference picture having the index of 2 in the first reference image list2510is to be changed, the group header of the bitstream may include (1, 2) as the modification and refinement information. The prediction decoder2050may assign the index of 2 to the reference image assigned with the index of 1 in the first reference image list2510and the index of 1 to the reference image assigned with the index of 2 to construct the second reference image list2800.

FIG.29is a diagram for describing another method of obtaining the second reference image list.

The number of first reference image lists indicated by the indicator from among the plurality of first reference image lists used for the image sequence may be plural. That is, as illustrated inFIG.29, the indicator may indicate a first reference image list2910including only short-term type reference images and a first reference image list2920including only long-term type reference images.

The prediction decoder2050may obtain a second reference image list2930including the short-term type reference images and the long-term type reference images included in the first reference image lists2910and2920indicated by the indicator. Here, in the second reference image list2930, higher indices may be assigned to the long-term type reference images than the short-term type reference images. In contrast, in the second reference image list2930, higher indices may be assigned to the short-term type reference images than the long-term type reference images.

According to an embodiment, the obtainer2010may obtain, from the bitstream, order information of the short-term type reference images and the long-term type reference images, and the prediction decoder2050may, according to the obtained order information, assign the indices to the short-term type reference images and the long-term type reference images included in the second reference image list2930.

According to another embodiment, the first reference image list2910and the first reference image list2920may include at least one reference image, regardless of a type of the reference image. In this case, when a short-term type reference image exists in the first reference image list2910, and a long-term type reference image exists in the first reference image list2920, indicated by the indicator, the prediction decoder2950may obtain the second reference image list2930including the short-term type reference image included in the first reference image list2910and the long-term type reference image included in the first reference image list2920. Alternatively, when a long-term type reference image exists in the first reference image list2910, and a short-term type reference image exists in the first reference image list2920, indicated by the indicator, the prediction decoder2950may obtain the second reference image list2930including the long-term type reference image included in the first reference image list2910and the short-term type reference image included in the first reference image list2920.

FIG.30is a diagram for describing another method of obtaining the second reference image list.

A first reference image list3010indicated by the indicator may include only short-term reference images. According to an embodiment, the first reference image list3010indicated by the indicator may include only long-term type reference images.

When the first reference image list3010includes only short-term type reference images, the obtainer2010may obtain, from the bitstream, POC-related values of long-term type reference images to be included in a second reference image list3030, and may construct the second reference image list3030including the long-term type reference images indicated by the obtained POC-related values and the short-term type reference images included in the first reference image list3010. That is, the first reference image list3010including only the short-term type reference images may be signaled through the sequence parameter set, and the POC-related values of the long-term type reference images may be signaled through the group header.

When the reference image lists are transmitted through the sequence parameter set rather than the group header, the reference image lists may not have to be transmitted for each block group, and thus, a compression rate may be improved due to reduction of an overhead. For example, when a prediction structure is repeated for each group of picture (GOP), the reference list may be repeatedly transmitted for each GOP. When the reference image lists which may be frequently transmitted are transmitted through the sequence parameter set, a bit rate may further be reduced.

Here, according to a type of the reference image, that is, whether the reference image is a long-term type or a short-term type, an availability with respect to the sequence parameter set may be different. While the short-term type reference image is related to a pattern in which the prediction structure is repeated as the example above, the long-term type reference image is highly related to correlation between a current picture and the long-term reference image. For example, when, although the prediction structure is repeated for each GOP, a long-term type reference image is not valid anymore because the content of an image is completely changed due to screen conversion, etc., a reference list with respect to short-term type reference images may be obtained from the sequence parameter set, and the long-term type reference image may be separately transmitted through the group header, so that transmission of the entire reference lists through the group header may be avoided.

According to an embodiment, when only the long-term type reference image is included in the first reference image list, the obtainer2010may obtain, from the bitstream, a POC-related value of the short-term type reference image to be included in the second reference image list, and may construct the second reference image list including the short-term type reference image indicated by the POC-related value and the long-term type reference image included in the first reference image list.

When constructing the second reference image list3030, the reference images indicated by the POC-related value obtained from the group header of the bitstream may be assigned with higher indices or lower indices than the reference images included in the first reference image list3010.

As described above, when the second reference image list is completely constructed, the prediction decoder2050may inter-predict the coding units based on the reference images included in the second reference image list. As a result of the inter-prediction, prediction samples corresponding to the coding units may be obtained.

The reconstructor2070obtains reconstruction samples of the coding units by using the prediction samples. According to an embodiment, the reconstructor2070may obtain the reconstruction samples of the coding units by adding residual data obtained from the bitstream to the prediction samples.

The reconstructor2070may perform luma mapping on the prediction samples of the coding units before obtaining the reconstruction samples.

Luma mapping is to change luma values of the prediction samples according to a parameter obtained from the bitstream, and for example, may correspond to a type of tone mapping.

According to an embodiment, the obtainer2010may obtain parameters for luma mapping from one or more post-processing parameter sets of the bitstream. Each of the one or more post-processing parameter sets may include parameters used for luma mapping or adaptive loop filtering to be described below.

The parameters used for luma mapping may include, for example, a range of luma values to be changed, a delta value to be applied to the luma value of the prediction samples, etc.

FIG.31is a diagram illustrating a bitstream including a plurality of post-processing parameter sets used for luma mapping or adaptive loop filtering.

A bitstream3100may include, in addition to a sequence parameter set (SPS)3110, a picture parameter set (PPS)3120, a group header (GH)3130, and a block parameter set (BPS)3140, described above, a plurality of post-processing parameter sets3150a,3150b, and3150c. The post-processing parameter sets3150a,3150b, and3150cmay be included in the bitstream regardless of a hierarchical structure of an image, unlike the SPS3110, the PPS3120, the GH3130, and the BPS3140.

An identifier may be assigned to each of the post-processing parameter sets3150a,3150b, and3150c, in order to identify the same. According to an embodiment, identifiers 0, 1, and 2 may be assigned to post-processing parameter set A3150a, post-processing parameter set B3150b, and post-processing parameter set C3150c, respectively.

The obtainer2010may obtain, from the PPS3120, the GH3130, or the BPS3140, an identifier indicating a post-processing parameter set from among the plurality of post-processing parameter sets3150a,3150b, and3150c, the post-processing parameter set being used for luma mapping the prediction samples. The reconstructor2070may change the luma value of the prediction samples by using the parameters obtained from the post-processing parameter set indicated by the identifier.

When the obtainer2010obtains the identifier from the PPS3120, the post-processing parameter set indicated by the identifier is used for the prediction samples derived in a current image, and when the obtainer2010obtains the identifier from the GH3130, the post-processing parameter set indicated by the identifier is used for the prediction samples derived in a current slice. Also, when the obtainer2010obtains the identifier from the BPS3140, the post-processing parameter set indicated by the identifier is used for the prediction samples derived in a current block.

According to an embodiment, the obtainer2010may obtain, from the bitstream, the identifier indicating any one of the plurality of post-processing parameter sets3150a,3150b, and3150cand correction information. Here, the correction information may include information for changing the parameters included in the post-processing parameter set indicated by the identifier. For example, the correction information may include a difference value between a value of the parameter included in the post-processing parameter set indicated by the identifier and a value of a parameter to be changed.

The reconstructor2070may correct the parameters of the post-processing parameter set indicated by the identifier according to the correction information and may change the luma value of the prediction samples by using the corrected parameters.

According to another embodiment, the identifier obtained from the bitstream may indicate a plurality of post-processing parameter sets. In this case, the reconstructor2070may construct a new parameter set by combining one or more of the parameters included in each of the post-processing parameter sets indicated by the identifier, and may perform luma mapping on the prediction samples by using the newly constructed parameter set.

The reconstructor2070obtains reconstruction samples corresponding to the current coding unit by using the prediction samples generated as a result of prediction-decoding or the prediction samples on which luma mapping is performed. When the reconstruction samples are obtained, the reconstructor2070may apply adaptive loop filtering to the reconstruction samples.

Adaptive loop filtering denotes one-dimensional filtering performed on sample values of the reconstruction samples by using filter coefficients signaled through the bitstream. Adaptive loop filtering may be separately performed on the luma value and a chroma value. The filter coefficient may include a filter coefficient with respect to a one-dimensional filter. Each filter coefficient of the one-dimensional filter may be represented as a difference value between sequential filter coefficients, and the difference value may be signaled through the bitstream.

As described above, one or more of the post-processing parameter sets include the parameters used for luma mapping, and the others include the parameters (for example, the filter coefficients) used for adaptive loo filtering. For example, post-processing parameter set A3150aand post-processing parameter set B3150bmay include the parameters used for adaptive loop filtering, and post-processing parameter set C3150cmay include the parameters used for luma mapping.

The obtainer2010may obtain, from the PPS3120, the GH3130, or the BPS3140, an identifier indicating a post-processing parameter set from among the plurality of post-processing parameter sets3150a,3150b, and3150c, the post-processing parameter set being used for adaptive loop filtering of the reconstruction samples. The reconstructor2070may filter the reconstruction samples by using the parameters obtained from the post-processing parameter set indicated by the identifier. When the obtainer2010obtains the identifier from the PPS, the post-processing parameter set indicated by the identifier is used for the reconstruction samples derived in the current image, and when the obtainer2010obtains the identifier from the GH, the post-processing parameter set indicated by the identifier is used for the reconstruction samples derived in the current slice. Also, when the obtainer2010obtains the identifier from the BPS, the post-processing parameter set indicated by the identifier is used for the reconstruction samples derived in the current block.

According to an embodiment, the obtainer2010may obtain, from the bitstream, the identifier indicating any one of the plurality of post-processing parameter sets3150a,3150b, and3150cand correction information. Here, the correction information may include information for changing the filter coefficients included in the post-processing parameter set indicated by the identifier. For example, the correction information may include a difference value between a value of the filter coefficient included in the post-processing parameter set indicated by the identifier and a value of a filter coefficient to be changed.

The reconstructor2070may correct the filter coefficients of the post-processing parameter set indicated by the identifier according to the correction information and may filter the reconstruction samples by using the corrected filter coefficients.

According to another embodiment, the identifier obtained from the bitstream may indicate a plurality of post-processing parameter sets. In this case, the reconstructor2070may construct a new filter coefficient set by combining one or more of the filter coefficients included in each of the post-processing parameter sets indicated by the identifier, and may filter the reconstruction samples by using the newly constructed filter coefficient set.

According to another embodiment, when the identifier obtained from the bitstream indicates a plurality of post-processing parameter sets, the reconstruction2070may filter a luma value of the reconstruction samples by using the filter coefficients included in any one post-processing parameter set indicated by the identifier and may filter a chroma value of the reconstruction samples by using the filter coefficients included in another post-processing parameter set indicated by the identifier.

According to another embodiment, the obtainer2010may obtain, from the bitstream, an identifier indicating any one post-processing parameter set, and filter coefficient information. In this case, the reconstructor2070may combine one or more of filter coefficients included in post-processing parameter sets indicated by the identifier with a filter coefficient signaled through the bitstream and may filter the reconstruction samples by using a set of the combined filter coefficients.

According to an embodiment, the reconstructor2070may additionally perform deblocking filtering on the reconstruction samples on which adaptive loop filtering is performed.

As described above, the prediction decoder2050may decode the coding unit included in the current slice via inter-prediction. According to an embodiment, when the coding unit is decoded, a boundary of the current slice may be regarded as a picture boundary.

According to an embodiment, in a decoder-side motion vector refinement (DMVR) mode in which a decoder directly derives a motion vector of a coding unit, the prediction decoder2050, when deriving a motion vector of a current coding unit, may limit a search range to a boundary of a region of a reference image, the region being at the same location as the current slice.

According to an embodiment, when a motion vector of a current coding unit signaled through the bitstream indicates a block outside the boundary of the region of the reference image, the region being at the same location as the current slice, the prediction samples may be obtained by padding the region at the same location as the current slice.

According to an embodiment, the prediction decoder2050may consider a boundary of a slice as a boundary of a picture in a bi-optical flow (BIO) processing mode and may prediction-decode the current coding unit. The BIO processing mode indicates a sample-wise motion vector improvement process performed with respect to block-wise motion compensation for bi-directional prediction.

When the obtainer2010performs entropy-coding on binary values included in the bitstream based on CABAC, the obtainer2010may selectively apply wave front parallel processing (WPP) by considering the number of tiles included in a slice. The WPP indicates processing of a current CTU after completion of processing of a CTU at an upper right side, for parallel encoding/decoding. In detail, the WPP configures a probability model of a first CTU at each row by using probability information obtained by processing a second CTU at an upper row.

When the slice includes only one tile, the obtainer2010may configure probability models with respect to CTUs included in the tile, based on the WPP, and when the slice includes a plurality of tiles, the obtainer2010may not apply the WPP to CTUs included in the tiles.

FIG.32is a diagram for describing an image decoding method according to an embodiment.

In operation S3210, the image decoding apparatus2000obtains, from an SPS of a bitstream, information indicating a plurality of first reference image lists for an image sequence including a current image. The plurality of first reference image lists may include at least one of a short-term type reference image and a long-term type reference image.

In operation S3220, the image decoding apparatus2000configures, in a current image, blocks and a block group including at least one block. The block may be a tile, and the block group may be a slice.

According to an embodiment, the image decoding apparatus2000may split the current image into a plurality of CTUs according to information obtained from the bitstream, and may configure, in the current image, a tile including at least one CTU and a slice including at least one tile.

According to an embodiment, the image decoding apparatus2000may split the current image into a plurality of tiles according to information obtained from the bitstream, and may split each tile into one or more CTUs. Also, the block determiner2030may configure, in the current image, a slice including at least one tile.

According to an embodiment, the image decoding apparatus2000may split the current image into one or more slices according to information obtained from the bitstream, and may split each slice into one or more tiles. Also, the block determiner2030may split each tile into one or more CTUs.

As described above, the image decoding apparatus2000may configure, in the current image, slices, according to address information obtained from the bitstream.

In operation S3230, the image decoding apparatus2000may obtain, from a GH of the bitstream, an indicator for a current block group including a current block in the current image, and may obtain a second reference image list based on a first reference image list obtained by the indicator. The image decoding apparatus2000may further obtain, from the bitstream, modification and refinement information for obtaining the second reference image list, together with the indicator. The modification and refinement information may include at least one of a POC-related value of a reference image to be removed from the first reference image list indicated by the indicator, a POC-related value of a reference image to be added to the second reference image list, a difference value between the POC-related value of the reference image to be removed from the first reference image list and the POC-related value of the reference image to be added to the second reference image list, and information for changing an order of images.

In operation S3240, the image decoding apparatus2000prediction-decodes a lower block of the current block based on a reference image included in the second reference image list.

When prediction samples corresponding to the lower block are obtained as a result of the prediction-decoding, the image decoding apparatus2000may specify a post-processing parameter set for luma mapping the prediction samples, according to an identifier indicating at least one of a plurality of post-processing parameter sets. Also, the image decoding apparatus2000may change a luma value of the prediction samples by using parameters included in the post-processing parameter set indicated by the identifier.

According to an embodiment, the image decoding apparatus2000may obtain reconstruction samples based on the prediction samples obtained as a result of the prediction-decoding or prediction samples on which luma mapping is performed and may perform adaptive loop filtering on the reconstruction samples. To this end, the image decoding apparatus2000may specify a post-processing parameter set for adaptive loop filtering, according to an identifier indicating at least one of the plurality of post-processing parameter sets. Also, the image decoding apparatus2000may filter the reconstruction samples by using the parameters included in the post-processing parameter set indicated by the identifier.

FIG.33is a diagram illustrating components of the image encoding apparatus3300, according to an embodiment.

Referring toFIG.33, the image encoding apparatus3300includes a block determiner3310, a prediction encoder3330, a reconstructor3350, and a generator3370. The generator3370illustrated inFIG.33may correspond to the bitstream generator210illustrated inFIG.2, and the block determiner3310, the prediction decoder3330, and the reconstructor3350may correspond to the encoder220illustrated inFIG.2.

The block determiner3310, the prediction encoder3330, the reconstructor3350, and the generator3370according to an embodiment may be realized as at least one processor. The image encoding apparatus3300may include one or more data storages (not shown) storing input and output data of the block determiner3310, the prediction encoder3330, the reconstructor3350, and the generator3370. Also, the image encoding apparatus3300may include a memory controller (not shown) controlling data inputting and outputting of the data storages.

The block determiner3310may split a current image into blocks and may configure, in the current image, block groups including at least one block. Here, the block may correspond to a tile, and the block group may correspond to a slice. The slice may be referred to as a tile group.

As described with reference toFIGS.3through16, the block determiner3310may determine a transform unit, a coding unit, a CTU, a tile, a slice, etc. by splitting the current image.

According to an embodiment, the block determiner3310may split the current image into a plurality of CTUs and may configure, in the current image, a tile including at least one CTU and a slice including at least one tile.

According to an embodiment, the block determiner3310may split the current image into a plurality of tiles and may split each tile into one or more CTUs. Also, the block determiner3310may configure, in the current image, a slice including at least one tile.

According to an embodiment, the block determiner3310may split the current image into one or more slices and may split each slice into one or more tiles. Also, the block determiner3310may split each tile into one or more CTUs.

The prediction encoder3330inter-predicts or intra-predicts lower blocks of the blocks split from the current image to obtain prediction samples corresponding to the lower blocks. Here, the lower block may be at least one of a CTU, a coding unit, and a transform unit.

The prediction encoder3330may prediction-encode coding units through inter-prediction or intra-prediction. According to inter-prediction, a prediction sample of a current coding unit may be obtained based on a reference block in a reference image indicated by a motion vector, and residual data corresponding to a difference between the prediction sample and the current coding unit may be transmitted to the image decoding apparatus2000through a bitstream. According to a prediction mode, residual data may not be included in the bitstream.

Hereinafter, a method of constructing a reference image list used for inter-prediction is described.

According to an embodiment, the prediction encoder3330may construct a plurality of first reference image lists for an image sequence including a current image. The prediction encoder3330selects at least one of the plurality of first reference image lists used for the image sequence. The prediction encoder3330may select a first reference image list used for a current slice from among the plurality of first reference image lists. Also, the prediction encoder3330obtains a second reference image list modified and refined from the selected first reference image list.

The second reference image list may be obtained by substituting at least one of reference images included in the first reference image list by another reference image, by changing an order of one or more of the reference images, or by adding a new reference image to the first reference image list.

When the second reference image list is obtained, the prediction encoder3330may encode the coding units included in the slice through inter-prediction by using at least one of reference images included in the second reference image list.

The prediction encoder3330may prediction-encode coding units included in a next slice by using a first reference image list other than the first reference image list selected for the current slice from among the plurality of first reference image lists used for the image sequence, and the second reference image list. In other words, the second reference image list obtained for the current slice may also be used for the next slice.

Hereinafter, a method of obtaining the second reference image list modified and refined from the first reference image list is described.

According to an embodiment, the prediction encoder3330may obtain the second reference image list by changing at least one of reference images included in the first reference image list by another reference image.

According to an embodiment, the prediction encoder3330may replace only a particular type of reference image from among the reference images included in the first reference image, for example, a long-term type reference image, by another long-term type reference image. That is, a short-term type reference image from among the reference images included in the first reference image list may be intactly maintained in the second reference image list, and only the long-term type reference image may be replaced by another long-term type reference image.

According to an embodiment, regardless of a type of the reference images included in the first reference image list, at least one of the reference images included in the first reference image list may be replaced by another reference image. According to an embodiment, a new reference image may be added to the second reference image list according to the order of a reference image to be removed from the first reference image list. That is, when a long-term type reference image assigned with an index of 1 is removed from the first reference image list, the new reference image may also be assigned with the index of 1.

According to an embodiment, the prediction encoder3330may obtain the second reference image list by excluding particular types of reference images from among the reference images in the first reference image list selected for the current slice from among the plurality of first reference image lists for the image sequence.

According to an embodiment, the prediction encoder3330may obtain the second reference image list by changing an order of one or more reference images from among the reference images in the first reference image list selected for the current slice from among the plurality of first reference image lists for the image sequence.

According to an embodiment, the prediction encoder3330may obtain the second reference image list by using a first reference image list including only short-term type reference images and a first reference image list including only long-term type reference images. For example, the prediction encoder3330may include, in the second reference image list, the short-term type reference images included in the first reference image list and the long-term type reference images included in the first reference image list.

Also, according to an embodiment, when the first reference image list includes only a short-term type reference image, the prediction encoder3330may obtain the second reference image list including the short-term type reference image included in the first reference image list and a new long-term type reference image. In contrast, when the first reference image list includes only a long-term type reference image, the prediction encoder3330may obtain the second reference image list including the long-term type reference image included in the first reference image list and a new short-term type reference image.

When the construction of the second reference image list is completed, the prediction encoder3330may inter-predict the coding units based on the reference image included in the second reference image list. As a result of the inter-prediction, prediction samples corresponding to the coding units may be obtained.

The reconstructor3350obtains reconstruction samples of the coding units by using the prediction samples. A reconstructed image including the reconstruction samples may be stored in a DPB as a reference image for a subsequent image.

According to an embodiment, the reconstructor3350may perform luma mapping on the prediction samples of the coding units before obtaining the reconstruction samples. The reconstructor3350may obtain parameters for luma mapping from a plurality of post-processing parameter sets.

Each of the plurality of post-processing parameter sets may include parameters used for luma mapping or adaptive loop filtering to be described below. In other words, some of the post-processing parameter sets include the parameters used for luma mapping, and the others include the parameters used for adaptive loop filtering. For example, at least one parameter set may include the parameters used for luma mapping, and the other parameter sets may include the parameters used for adaptive loop filtering. The reconstructor3350may generate the plurality of post-processing parameter sets including the parameters used for luma mapping or the parameters used for adaptive loop filtering. As described above, the plurality of post-processing parameter sets may be signaled to the image decoding apparatus2000through the bitstream.

The reconstructor3350may obtain the parameters from a post-processing parameter set selected from among the plurality of post-processing parameter sets and may change a luma value of the prediction samples by using the obtained parameters.

According to an embodiment, the reconstructor3350may correct the parameters of the post-processing parameter set selected from among the plurality of post-processing parameter sets and may change the luma value of the prediction samples by the corrected parameters.

Also, according to an embodiment, the reconstructor3350may construct a new parameter set by combining one or more of the parameters included in at least two post-processing parameter sets from among the plurality of post-processing parameter sets and may change the luma value of the prediction samples by using the parameters of the newly constructed parameter set.

The reconstructor3350obtains the reconstruction samples corresponding to the current coding unit by using the prediction samples generated as a result of prediction-decoding or the prediction samples on which luma mapping is performed. When the reconstruction samples are obtained, the reconstructor3350may apply adaptive loop filtering to the reconstruction samples.

As described above, some of the post-processing parameter sets may include the parameters used for luma mapping, and the others may include the parameters (for example, filter coefficients) used for adaptive loop filtering. The reconstructor3350may filter the reconstruction samples by using the parameters obtained from at least one of the plurality of post-processing parameter sets.

According to an embodiment, the reconstructor3350may correct the parameters obtained from any one of the plurality of post-processing parameter sets and may filter the reconstruction samples by using the corrected parameters.

Also, according to an embodiment, the reconstructor3350may construct a new parameter set by combining one or more of the parameters included in at least two post-processing parameter sets from among the plurality of post-processing parameter sets and may filter the reconstruction samples by using the parameters of the newly constructed parameter set.

Also, according to an embodiment, the reconstructor3350may filter a luma value of the reconstruction samples by using any one post-processing parameter set from among the plurality of post-processing parameter sets and may filter a chroma value of the reconstruction samples by using another post-processing parameter set.

When the prediction encoder3330inter-predicts the coding unit included in the current slice, the prediction encoder3330may consider a boundary of the current slice as a picture boundary.

When the prediction encoder3330derives a motion vector of the current coding unit, the prediction encoder3330may limit a search range to a boundary of a region of a reference image, the region being at the same location as the current slice.

According to an embodiment, the prediction encoder3330may consider a boundary of a slice as a boundary of a picture in a BIO processing mode and may prediction-encode the current coding unit.

The generator3370generates a bitstream including information used for encoding an image. As described above, the bitstream may include a SPS, a PPS, a GH, a BPS, and at least one post-processing parameter set.

The information included in the bitstream generated by the generator3370is described above with respect to the image decoding apparatus2000, and thus, its detailed description is omitted.

The generator3370may entropy-code binary values corresponding to syntax elements based on CABAC. Here, the generator3370may selectively apply WPP by considering the number of tiles included in the slice. When the slice includes only one tile, the generator3370may configure probability models with respect to CTUs included in the tile, based on the WPP, and when the slice includes a plurality of tiles, the generator3370may not apply the WPP to CTUs included in the tiles.

FIG.34is a diagram for describing an image encoding method according to an embodiment.

In operation S3410, the image encoding apparatus3300constructs a plurality of first reference image lists for an image sequence including a current image. The plurality of first reference image lists may include at least one of a short-term type reference image and a long-term type reference image.

In operation S3420, the image encoding apparatus3300configures, in a current image, blocks and a block group including at least one block. The block may be a tile, and the block group may be a slice.

According to an embodiment, the image encoding apparatus3300may split the current image into a plurality of CTUs and may configure, in the current image, a tile including at least one CTU and a slice including at least one tile.

According to an embodiment, the image encoding apparatus3300may split the current image into a plurality of tiles and may split each tile into one or more CTUs. Also, the image encoding apparatus3300may configure, in the current image, a slice including at least one tile.

According to an embodiment, the image encoding apparatus3300may split the current image into one or more slices and may split each slice into one or more tiles. Also, the image encoding apparatus3300may split each tile into one or more CTUs.

In operation S3230, the image encoding apparatus3300may select a first reference image list for a current block group including a current block in a current image from among a plurality of first reference image lists and may obtain a second reference image list based on the selected first reference image list.

In operation S3240, the image encoding apparatus3300prediction-decodes a lower block included in the current block based on a reference image included in the second reference image list.

When prediction samples corresponding to the lower block are obtained as a result of the prediction-encoding, the image encoding apparatus3300may change a luma value of the prediction samples by using parameters included in at least one of a plurality of post-processing parameter sets.

According to an embodiment, the image encoding apparatus3300may obtain reconstruction samples based on the prediction samples obtained as a result of the prediction-encoding or prediction samples on which luma mapping is performed and may perform adaptive loop filtering on the reconstruction samples. To this end, the image encoding apparatus3300may filter the reconstruction samples by using the parameters included in at least one of the plurality of post-processing parameter sets.

Meanwhile, the embodiments of the present disclosure described above may be written as computer-executable programs that may be stored in a medium.

The medium may continuously store the computer-executable programs, or temporarily store the computer-executable programs or instructions for execution or downloading. Also, the medium may be any one of various recording media or storage media in which a single piece or plurality of pieces of hardware are combined, and the medium is not limited to a medium directly connected to a computer system, but may be distributed on a network. Examples of the medium include magnetic media, such as a hard disk, a floppy disk, and a magnetic tape, optical recording media, such as CD-ROM and DVD, magneto-optical media such as a floptical disk, and ROM, RAM, and a flash memory, which are configured to store program instructions. Other examples of the media include recording media and storage media managed by application stores distributing applications or by websites, servers, and the like supplying or distributing other various types of software.