Image encoding / decoding method and apparatus using adaptive size limitation of chroma blocks and bitstream transmission method

Abstract

Provided is an image encoding / decoding method and device. The image decoding method performed by the image decoding device includes: determining a partition structure of a current block composed of chrominance components; determining a partition type of the current block based on the partition structure; obtaining multiple lower-layer blocks by partitioning the current block based on the partition type, and decoding the lower-layer blocks based on the prediction mode of the lower-layer blocks.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly, to a method and apparatus for encoding / decoding an image by limiting the size of a chrominance block, and a method for transmitting a bit stream generated by the image encoding method / apparatus of the present disclosure. Background Art

[0002] Recently, the demand for high-resolution and high-quality images, such as high-definition (HD) images and ultra-high-definition (UHD) images, is increasing in various fields. As the resolution and quality of image data are improved, the amount of information or bits transmitted is relatively increased compared to existing image data. The increase in the amount of information or bits transmitted leads to an increase in transmission cost and storage cost.

[0003] Therefore, efficient image compression technology is needed to effectively transmit, store, and reproduce information about high-resolution and high-quality images. Summary of the invention

[0004] Technical issues

[0005] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0006] Another object of the present disclosure is to provide a method and apparatus for encoding / decoding an image by limiting the size of a chroma block.

[0007] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus that does not signal segmentation information when a chroma block cannot be segmented.

[0008] Another object of the present disclosure is to provide a method for transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0009] Another object of the present disclosure is to provide a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0010] Another object of the present disclosure is to provide a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0011] The technical problems solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not described herein will be apparent to those skilled in the art through the following description.

[0012] Technical Solution

[0013] According to one aspect of the present disclosure, an image decoding method performed by an image decoding device may include: determining a partition structure of a current block composed of chrominance components; based on the partition structure, determining a partition type of the current block; based on the partition type, obtaining multiple lower-layer blocks by partitioning the current block; and decoding the lower-layer block based on a prediction mode of the lower-layer block.

[0014] The partition structure based on the current block is a dual-tree structure determined independently of the partition type of the luminance component block corresponding to the current block, and the partition type of the current block can be determined by determining the partition type of the current block based on an available partition type, wherein the available partition type is determined based on the width or height of the current block.

[0015] The partition structure of the current block may be determined based on partition information obtained from a bitstream based on the available partition types.

[0016] The available partition type may be determined by not allowing a predetermined partition type based on a width or height of the current block being equal to or smaller than a predetermined value, and the predetermined value may be determined based on the number of pixels processed per clock by the image decoding device.

[0017] A vertical trifurcated partition type may not be allowed as a partition type of the current block based on a width of the current block being equal to or smaller than twice the number of pixels processed per clock by the image decoding apparatus.

[0018] Based on the fact that the width of the current block is 8, the vertical trifurcated partition type may not be allowed to be the partition type of the current block.

[0019] A quadtree partition type and a vertical trigeminal partition type may not be allowed as the partition type of the current block based on that a width of the current block is equal to or smaller than the number of pixels processed per clock by the image decoding apparatus.

[0020] Based on the fact that the width of the current block is 4, the quadtree partition type and the vertical binary partition type are not allowed to be used as the partition type of the current block.

[0021] Based on the image decoding apparatus performing an image processing process on a pixel set consisting of a 1×4 matrix per clock and the height of the current block being 8, a horizontal trifurcated partition type is not allowed as a partition type of the current block.

[0022] Based on the image decoding apparatus performing an image processing process on a pixel set consisting of a 1×4 matrix per clock and the height of the current block being 4, a quadtree partition type and a horizontal binary partition type are not allowed as partition types of the current block.

[0023] The width of the current block may be determined based on a width and a color format of a luma block corresponding to the current block.

[0024] The width of the current block may be determined as a value obtained by dividing a width of a luma block corresponding to the current block by a component ratio of chroma samples to luma samples derived based on the color format.

[0025] According to an aspect of the present disclosure, an image decoding device may include a memory and at least one processor. The at least one processor may include: determining a partition structure of a current block composed of chrominance components; determining a partition type of the current block based on the partition structure; obtaining multiple lower-layer blocks by partitioning the current block based on the partition type; and decoding the lower-layer block based on a prediction mode of the lower-layer block. Based on the partition structure of the current block being a dual-tree structure determined independently of a partition type of a luminance component block corresponding to the current block, the partition type of the current block may be determined by determining the partition type of the current block based on available partition types, wherein the available partition types are determined based on the width or height of the current block.

[0026] According to an aspect of the present disclosure, an image encoding method performed by an image encoding device may include: selecting a partition structure of a current block composed of chrominance components; based on the partition structure, selecting an available partition type of the current block; based on the available partition type, obtaining multiple lower layer blocks by partitioning the current block; and encoding prediction mode information of the lower layer block and the partition information of the current block based on a result of encoding the lower layer block.

[0027] Based on the partition structure of the current block being a dual tree structure determined independently of a partition type of a luminance component block corresponding to the current block, an available partition type of the current block may be determined based on a width or a height of the current block.

[0028] The available segmentation type can be determined by limiting the use of a predetermined segmentation type based on the width or height of the current block being equal to or less than a predetermined value, and the predetermined value can be determined according to the predetermined segmentation type depending on whether the value obtained by dividing the width or height of the current block is less than 4.

[0029] In addition, a transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0030] In addition, a computer-readable recording medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0031] The features described above with respect to a brief summary of the present disclosure are merely exemplary aspects of the following detailed description of the present disclosure and do not limit the scope of the present disclosure.

[0032] Beneficial Effects

[0033] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0034] According to the present disclosure, an image encoding / decoding method and apparatus can be provided, which can reduce bit flow by not signaling segmentation information of a chroma block when the size of the chroma block is limited and a predetermined segmentation type is limited accordingly.

[0035] Furthermore, according to the present disclosure, a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure may be provided.

[0036] Furthermore, according to the present disclosure, a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure can be provided.

[0037] Furthermore, according to the present disclosure, there can be provided a recording medium storing a bit stream received and decoded by the image decoding device according to the present disclosure and used to reconstruct an image.

[0038] Those skilled in the art will appreciate that the effects that can be achieved by the present disclosure are not limited to what has been specifically described above, and other advantages of the present disclosure will be more clearly understood from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a view schematically showing a video coding system to which an embodiment of the present disclosure is applicable.

[0040] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0041] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0042] Figure 4 is a diagram of a segmentation structure of an image according to an embodiment.

[0043] Figure 5 is a view showing an embodiment of partition types of blocks according to a multi-type tree structure.

[0044] Figure 6 is a schematic diagram illustrating a signaling mechanism of block partition information in a quadtree with a nested multi-type tree structure according to the present invention.

[0045] Figure 7 is a diagram showing an embodiment in which a CTU is partitioned into a plurality of CUs.

[0046] Figure 8 is a view illustrating an embodiment of a redundant partition pattern.

[0047] Fig. 9 is a flowchart illustrating a video / image encoding method based on inter-frame prediction.

[0048] Fig.10 is a view illustrating a configuration of the inter prediction unit 180 according to the present disclosure.

[0049] Fig.11 is a flowchart illustrating a video / image decoding method based on inter-frame prediction.

[0050] Fig.12 is a view illustrating a configuration of the inter prediction unit 260 according to the present disclosure.

[0051] Fig.13 is a view illustrating neighboring blocks that may be used as spatial merging candidates according to an embodiment.

[0052] Fig.14 is a view schematically illustrating a merge candidate list construction method according to an embodiment.

[0053] Fig.15 is a view schematically illustrating a motion vector predictor candidate list construction method according to an embodiment.

[0054] Fig.16 is a view illustrating a syntax structure for transmitting an MVD from an image encoding device to an image decoding device according to an embodiment.

[0055] Fig.17 is a flowchart illustrating an IBC-based video / image encoding method according to an embodiment.

[0056] Fig.18 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image encoding method according to an embodiment.

[0057] Fig.19 is a flowchart illustrating an IBC-based video / image decoding method according to an embodiment.

[0058] Fig. 20 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image decoding method according to an embodiment.

[0059] Fig.21 is a view illustrating a pipeline delay problem according to an embodiment.

[0060] Fig. 22 is a view illustrating experimental data measured in a case where partitioning of a chroma block into 2xN chroma blocks is restricted when a current block has a dual-tree structure.

[0061] Fig.23 is a view illustrating a method of determining, by a decoding apparatus according to an embodiment, whether vertical trisection splitting (SPLIT_TT_VER) is allowed for a current block.

[0062] Fig.24 is a view illustrating a method of determining, by a decoding apparatus according to an embodiment, whether horizontal three-way splitting (SPLIT_TT_HOR) is allowed for a current block.

[0063] Fig.25 is a view illustrating a method of determining, by a decoding apparatus according to an embodiment, whether horizontal binary splitting (SPLIT_BT_HOR) is allowed for a current block.

[0064] Fig.26 is a view illustrating a method of determining, by a decoding apparatus according to an embodiment, whether vertical binary splitting (SPLIT_BT_VER) is allowed for a current block.

[0065] Fig. 27 2 is a view illustrating a method of determining, by a decoding apparatus according to an embodiment, whether to allow quadtree partitioning for a current block.

[0066] Fig.28 is a view illustrating experimental results obtained in the case where only the first restriction condition is applied.

[0067] Fig.29 is a view illustrating experimental results obtained in the case where all of the first, second, and third restriction conditions are applied.

[0068] Fig.30 is a flowchart illustrating a method of encoding an image by an encoding apparatus according to an embodiment.

[0069] Fig.31 is a view illustrating syntax for bitstream signaling information about partitioning of a current block according to an embodiment.

[0070] Fig.32 is a flowchart illustrating a method of decoding an image by a decoding device according to an embodiment.

[0071] Fig.33 is a view illustrating a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0072] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, the present disclosure can be implemented in various forms and is not limited to the embodiments described herein.

[0073] When describing the present disclosure, if it is determined that the detailed description of related known functions or configurations makes the scope of the present disclosure unnecessarily ambiguous, the detailed description thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

[0074] In the present disclosure, when a component is "connected", "coupled" or "linked" to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component "includes" or "has" other components, unless otherwise specified, it means that other components may also be included, rather than excluding other components.

[0075] In the present disclosure, the terms first, second, etc. are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise specified. Accordingly, within the scope of the present disclosure, the first component in one embodiment may be referred to as the second component in another embodiment, and similarly, the second component in one embodiment may be referred to as the first component in another embodiment.

[0076] In the present disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not mean that the components must be separated. That is, multiple components can be integrated and implemented in one hardware or software unit, or one component can be distributed and implemented in multiple hardware or software units. Therefore, even if not specifically stated, embodiments in which these components are integrated or distributed are also included in the scope of the present disclosure.

[0077] In the present disclosure, the components described in the various embodiments are not necessarily essential components, and some components may be optional components. Therefore, embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, embodiments that include other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0078] The present disclosure relates to encoding and decoding of images. Unless otherwise defined in the present disclosure, terms used in the present disclosure may have general meanings commonly used in the technical field to which the present disclosure belongs.

[0079] In the present disclosure, a "picture" generally refers to a unit representing an image within a specific time period, and a slice / tile is a coding unit that constitutes a part of a picture. A picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0080] In the present disclosure, "pixel" or "pel" may mean the smallest single unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0081] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of ​​a picture and information related to the area. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "area". In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0082] In the present disclosure, "current block" may mean one of "current coding block", "current coding unit", "coding target block", "decoding target block" or "processing target block". When prediction is performed, "current block" may mean "current prediction block" or "prediction target block". When transform (inverse transform) / quantization (dequantization) is performed, "current block" may mean "current transform block" or "transform target block". When filtering is performed, "current block" may mean "filtering target block".

[0083] Furthermore, in the present disclosure, unless explicitly stated as a chroma block, “current block” may mean “luminance block of the current block.” “Chroma block of the current block” may be expressed by including an explicit description of a chroma block such as “chroma block” or “current chroma block.”

[0084] In the present disclosure, the slash " / " or "," may be interpreted as indicating "and / or". For example, "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A / B / C" may mean "at least one of A, B, and / or C".

[0085] In the present disclosure, the term "or" should be interpreted to indicate "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", or 3) both "A and B". In other words, in the present disclosure, "or" should be interpreted to indicate "additionally or alternatively".

[0086] Video compilation system overview

[0087] Figure 1 is a view schematically illustrating a video coding system according to the present disclosure.

[0088] The video coding system according to an embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver encoded video and / or image information or data to the decoding device 20 via a digital storage medium or a network in the form of a file or a stream.

[0089] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be called a video / image encoding unit, and the decoding unit 22 may be called a video / image decoding unit. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display and the display may be configured as a separate device or an external component.

[0090] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may (electronically) generate the video / image. For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0091] The encoding unit 12 may encode the input video / image. For compression and coding efficiency, the encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 may output encoded data (encoded video / image information) in the form of a bitstream.

[0092] The transmitter 13 may transmit the encoded video / image information or the data output in the form of a bit stream to the receiver 21 of the decoding device 20 in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmitting through a broadcast / communication network. The receiver 21 may extract / receive a bit stream from a storage medium or a network and transmit the bit stream to the decoding unit 22.

[0093] The decoding unit 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoding unit 12, such as dequantization, inverse transformation, and prediction.

[0094] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0095] Overview of Image Coding Device

[0096] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0097] like Figure 2 As shown, the image encoding device 100 may include an image partitioner 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame prediction unit 180, an intra-frame prediction unit 185, and an entropy encoder 190. The inter-frame prediction unit 180 and the intra-frame prediction unit 185 may be collectively referred to as a "prediction unit". The transformer 120, the quantizer 130, the dequantizer 140, and the inverse transformer 150 may be included in a residual processor. The residual processor may also include a subtractor 115.

[0098] In some embodiments, all or at least some of the components configuring the image encoding apparatus 100 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium.

[0099] The image partitioner 110 may partition an input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, a processing unit may be referred to as a coding unit (CU). A coding unit may be obtained by recursively partitioning a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QT / BT / TT) structure. For example, a coding unit may be partitioned into multiple coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the partitioning of the coding unit, a quadtree structure may be applied first, and then a binary tree structure and / or a ternary tree structure may be applied. The coding process according to the present disclosure may be performed based on a final coding unit that is no longer partitioned. The maximum coding unit may be used as the final coding unit, and a coding unit of a deeper depth obtained by partitioning the maximum coding unit may also be used as the final coding unit. Here, the coding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the coding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be split or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from a transform coefficient.

[0100] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction based on the current block or CU. The prediction unit may generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. The information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0101] The intra prediction unit 185 can predict the current block by referring to the samples in the current picture. Depending on the intra prediction mode and / or the intra prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used according to the settings. The intra prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0102] The inter prediction unit 180 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter prediction unit 180 may configure a motion information candidate list based on the neighboring blocks and generate information specifying which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter prediction unit 180 may use the motion information of the neighboring block as the motion information of the current block. In the case of skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding the motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0103] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may not only apply intra prediction or inter prediction, but may also apply intra prediction and inter prediction simultaneously to predict the current block. The prediction method of applying both intra prediction and inter prediction simultaneously to predict the current block may be referred to as combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra block copy (IBC) to predict the current block. Intra block copy may be used for content image / video coding of games, etc., such as screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter-frame prediction techniques described in this disclosure.

[0104] The prediction signal generated by the prediction unit can be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal can be transmitted to the transformer 120.

[0105] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size rather than square.

[0106] The quantizer 130 may quantize the transform coefficients and transmit them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients in the block form into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0107] The entropy encoder 190 may perform various encoding methods, such as exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 190 may encode information required for video / image reconstruction (e.g., values ​​of syntax elements, etc.) together or separately in addition to quantized transform coefficients. The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The signaled information, transmitted information, and / or syntax elements described in the present disclosure may be encoded and included in a bitstream through the above-described encoding process.

[0108] The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from the entropy encoder 190 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the image encoding device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0109] The quantized transform coefficients output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150.

[0110] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample array). If there is no residual in the block to be processed, such as when the skip mode is applied, the prediction block can be used as a reconstructed block. The adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0111] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. The filter 160 can generate various information related to filtering and transmit the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bit stream.

[0112] The modified reconstructed picture transferred to the memory 170 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied by the image encoding device 100, prediction mismatch between the image encoding device 100 and the image decoding device may be avoided and encoding efficiency may be improved.

[0113] The DPB of the memory 170 may store the modified reconstructed picture for use as a reference picture in the inter-frame prediction unit 180. The memory 170 may store the motion information of the block from which the motion information in the current picture is derived (or encoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame prediction unit 180 and used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store the reconstructed samples of the reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0114] Overview of image decoding device

[0115] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0116] like Figure 3As shown, the image decoding device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, and an intra-frame prediction unit 265. The inter-frame prediction unit 260 and the intra-frame prediction unit 265 may be collectively referred to as a "prediction unit". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0117] According to an embodiment, all or at least some of the plurality of components configuring the image decoding apparatus 200 may be configured by hardware components (eg, a decoder or a processor). In addition, the memory 250 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0118] The image decoding apparatus 200 having received a bit stream including video / image information may perform the same operation as that performed by Figure 2 The image may be reconstructed by a process corresponding to the process performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using a processing unit applied in the image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The coding unit may be obtained by partitioning the coding tree unit or the maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 may be reproduced by a reproduction device (not shown).

[0119] The image decoding apparatus 200 may receive the image in the form of a bit stream from Figure 2The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The image decoding device may also decode the picture based on the parameter set information and / or the general constraint information. The information and / or syntax elements signaled / received described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring block and the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, and perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. The information related to the prediction in the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value on which entropy decoding is performed in the entropy decoder 210, that is, the quantized transform coefficient and related parameter information can be input to the dequantizer 220. In addition, information about filtering among the information decoded by the entropy decoder 210 can be provided to the filter 240. Meanwhile, a receiver (not shown) for receiving a signal output from the image encoding device may be further configured as an internal / external element of the image decoding device 200 , or the receiver may be a component of the entropy decoder 210 .

[0120] Meanwhile, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or at least one of an intra-frame prediction unit 265.

[0121] The dequantizer 220 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 220 may rearrange the quantized transform coefficient in the form of a two-dimensional block. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may perform dequantization on the quantized transform coefficient by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0122] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0123] The prediction unit may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about the prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0124] The same as described in the prediction unit of the image encoding device 100 , the prediction unit can generate a prediction signal based on various prediction methods (techniques) described later.

[0125] The intra prediction unit 265 may predict the current block by referring to samples in the current picture. The description of the intra prediction unit 185 is also applicable to the intra prediction unit 265.

[0126] The inter prediction unit 260 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter prediction unit 260 may configure a motion information candidate list based on the neighboring blocks, and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and information about the prediction may include information indicating an inter prediction mode of the current block.

[0127] The adder 235 can generate a reconstructed block by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the prediction unit (including the inter-frame prediction unit 260 and / or the intra-prediction unit 265). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 is also applicable to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0128] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0129] The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter-frame prediction unit 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame prediction unit 260 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0130] In the present disclosure, the embodiments described in the filter 160, the inter-frame prediction unit 180 and the intra-frame prediction unit 185 of the image encoding device 100 can be equally or correspondingly applied to the filter 240, the inter-frame prediction unit 260 and the intra-frame prediction unit 265 of the image decoding device 200.

[0131] Overview of Image Partitioning

[0132] The video / image coding method according to the present disclosure can be performed based on the image partition structure as follows. Specifically, the prediction, residual processing ((inverse) transform, (de)quantization, etc.), syntax element coding and filtering processes described later can be performed based on the CTU, CU (and / or TU, PU) derived from the image partition structure. The image can be partitioned in block units and the block partitioning process can be performed in the image partitioner 110 of the encoding device. The partition-related information can be encoded by the entropy encoder 190 and sent to the decoding device in the form of a bitstream. The entropy decoder 210 of the decoding device can derive the block partition structure of the current picture based on the partition-related information obtained from the bitstream, and based on this, a series of processes (e.g., prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) can be performed to perform image decoding.

[0133] A picture may be partitioned into a sequence of coding tree units (CTUs). Figure 4 An example of a picture being partitioned into CTUs is shown. A CTU may correspond to a coding tree block (CTB). Alternatively, a CTU may include a coding tree block of luma samples and two corresponding coding tree blocks of chroma samples. For example, for a picture containing three sample arrays, a CTU may include one N×N block of luma samples and two corresponding blocks of chroma samples.

[0134] Overview of CTU Partitions

[0135] As described above, the coding unit may be obtained by recursively partitioning the coding tree unit (CTU) or the largest coding unit (LCU) according to the quadtree / binary tree / ternary tree (QT / BT / TT) structure. For example, the CTU may be first partitioned into a quadtree structure. Thereafter, the leaf nodes of the quadtree structure may be further partitioned by a multi-type tree structure.

[0136] Partitioning according to the quadtree means that the current CU (or CTU) is equally partitioned into four. By partitioning according to the quadtree, the current CU can be partitioned into four CUs with the same width and the same height. When the current CU is no longer partitioned into a quadtree structure, the current CU corresponds to a leaf node of the quadtree structure. The CU corresponding to the leaf node of the quadtree structure may no longer be partitioned and may be used as the above-mentioned final coding unit. Alternatively, the CU corresponding to the leaf node of the quadtree structure may be further partitioned by a multi-type tree structure.

[0137] Figure 5 is a view showing an embodiment of partition types of a block according to a multi-type tree structure. The partition according to the multi-type tree structure may include two types of partitions according to a binary tree structure and two types of partitions according to a ternary tree structure.

[0138] The two types of splits according to the binary tree structure may include vertical binary split (SPLIT_BT_VER) and horizontal binary split (SPLIT_BT_HOR). Vertical binary split (SPLIT_BT_VER) means that the current CU is equally split into two in the vertical direction. Figure 4 As shown in FIG, by vertical binary splitting, two CUs with the same height as the current CU and half the width of the current CU can be generated. Horizontal binary splitting (SPLIT_BT_HOR) means that the current CU is equally split into two in the horizontal direction. Figure 5 As shown, through horizontal binary splitting, two CUs with a height half of the height of the current CU and the same width as the current CU can be generated.

[0139] The two types of splits according to the triad structure may include vertical triad split (SPLIT_TT_VER) and horizontal triad split (SPLIT_TT_HOR). In vertical triad split (SPLIT_TT_VER), the current CU is split in a vertical direction at a ratio of 1:2:1. Figure 5 As shown, through vertical three-pronged splitting, two CUs with the same height as the current CU and a width of 1 / 4 of the width of the current CU, and a CU with the same height as the current CU and a width of half the width of the current CU can be generated. In horizontal three-pronged splitting (SPLIT_TT_HOR), the current CU is split in the horizontal direction at a ratio of 1:2:1. Figure 5 As shown, through horizontal trifurcated splitting, two CUs whose height is 1 / 4 of the height of the current CU and whose width is the same as the current CU, and a CU whose height is half of the height of the current CU and whose width is the same as the current CU can be generated.

[0140] Figure 6 is a diagram illustrating a signaling mechanism of block partition information in a quadtree having a nested multi-type tree structure according to the present disclosure.

[0141] Here, the CTU is regarded as the root node of the quadtree and is partitioned into a quadtree structure for the first time. Information (e.g., qt_split_flag) specifying whether to perform quadtree segmentation on the current CU (CTU or node (QT_node) of the quadtree) is signaled. For example, when qt_split_flag has a first value (e.g., "1"), the current CU can be partitioned by the quadtree. In addition, when qt_split_flag has a second value (e.g., "0"), the current CU is not quadtree partitioned, but becomes a leaf node (QT_leaf_node) of the quadtree. Each quadtree leaf node can then be further partitioned into a multi-type tree structure. That is, the leaf node of the quadtree can become a node (MTT_node) of a multi-type tree. In the multi-type tree structure, a first flag (e.g., Mtt_split_cu_flag) is signaled to specify whether the current node is additionally partitioned. If the corresponding node is additionally partitioned (e.g., if the first flag is 1), a second flag (e.g., Mtt_split_cu_vertical_flag) may be signaled to specify the partition direction. For example, the partition direction may be a vertical direction when the second flag is 1, and a horizontal direction when the second flag is 0. Then, a third flag (e.g., Mtt_split_cu_binary_flag) may be signaled to specify whether the partition type is a binary partition type or a ternary partition type. For example, the partition type may be a binary partition type when the third flag is 1, and a ternary partition type when the third flag is 0. The nodes of the multi-type tree obtained by binary partitioning or ternary partitioning may be further partitioned into a multi-type tree structure. However, the nodes of the multi-type tree may not be partitioned into a quadtree structure. If the first flag is 0, the corresponding node of the multi-type tree is no longer partitioned, but becomes a leaf node (MTT_leaf_node) of the multi-type tree. The CU corresponding to the leaf node of the multi-type tree may be used as the above-mentioned final coding unit.

[0142] Based on mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, a multi-type tree partition mode (MttSplitMode) of a CU may be derived as shown in the following Table 1. In the following description, a multi-type tree partition mode may be referred to as a multi-tree partition type or a partition type.

[0143] [Table 1]

[0144] MttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flag SPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

[0145] Figure 7 is a view showing an example of partitioning a CTU into a plurality of CUs by applying a multi-type tree after applying a quadtree. Figure 7 , the bold block edges 710 represent quadtree partitioning, while the remaining edges 720 represent multi-type tree partitioning.

[0146] A CU may correspond to a coding block (CB). In an embodiment, a CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples.

[0147] The chroma component (sample) CB or TB size may be derived based on the luma component (sample) CB or TB size based on the component ratio according to the color format (chroma format, e.g., 4:4:4, 4:2:2, 4:2:0, etc.) of the picture / image. In the case of a 4:4:4 color format, the chroma component CB / TB size may be set equal to the luma component CB / TB size. In the case of a 4:2:2 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to the height of the luma component CB / TB. In the case of a 4:2:0 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to half the height of the luma component CB / TB.

[0148] In an embodiment, when the size of the CTU is 128 based on the luma sample unit, the size of the CU may have a size from 128x128 to 4x4, which is the same size as the CTU. In an embodiment, in the case of a 4:2:0 color format (or chroma format), the chroma CB size may have a size from 64x64 to 2x2.

[0149] Meanwhile, in an embodiment, the CU size and the TU size may be the same. Alternatively, there may be multiple TUs in a CU region. The TU size generally indicates the luma component (sample) transform block (TB) size.

[0150] The TU size can be derived based on the maximum allowed TB size maxTbSize as a predetermined value. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) with maxTbSize can be derived from the CU, and transform / inverse transform can be performed in units of TU (TB). For example, the maximum allowed luma TB size can be 64x64 and the maximum allowed chroma TB size can be 32x32. If the width or height of the CB partitioned according to the tree structure is larger than the maximum transform width or height, the CB can be automatically (or implicitly) partitioned until the TB size limits in the horizontal and vertical directions are met.

[0151] In addition, for example, when intra prediction is applied, the intra prediction mode / type may be derived in units of CU (or CB), and the neighboring reference sample derivation and prediction sample generation process may be performed in units of TU (or TB). In this case, there may be one or more TUs (or TBs) in a CU (or CB) region, and in this case, multiple TUs or (TBs) may share the same intra prediction mode / type.

[0152] Meanwhile, for a quadtree coding tree scheme with nested multi-type trees, the following parameters may be signaled from the encoding device to the decoding device as SPS syntax elements. For example, at least one of the CTU size as a parameter indicating the root node size of the quadtree, the MinQTSize as a parameter indicating the minimum allowed quadtree leaf node size, the MaxBtSize as a parameter indicating the maximum allowed binary tree root node size, the MaxTtSize as a parameter indicating the maximum allowed ternary tree root node size, the MaxMttDepth as a parameter indicating the maximum allowed hierarchical depth of multi-type tree partitioning from the quadtree leaf node, the MinBtSize as a parameter indicating the minimum allowed binary tree leaf node size, or the MinTtSize as a parameter indicating the minimum allowed ternary tree leaf node size is signaled.

[0153] As an embodiment using a 4:2:0 chroma format, the CTU size may be set to 128x128 luminance blocks and two 64x64 chrominance blocks corresponding to these luminance blocks. In this case, MinOTSize may be set to 16x16, MaxBtSize may be set to 128x128, MaxTtSzie may be set to 64x64, MinBtSize and MinTtSize may be set to 4x4, and MaxMttDepth may be set to 4. Quadtree partitioning may be applied to a CTU to generate a quadtree leaf node. A quadtree leaf node may be referred to as a leaf QT node. The size of a quadtree leaf node may be from 16x16 size (e.g., MinOTSize) to 128x128 size (e.g., CTU size). If the leaf QT node is 128x128, it may not be additionally partitioned into a binary tree / ternary tree. This is because, in this case, even if partitioned, it exceeds MaxBtsize and MaxTtszie (e.g., 64x64). In other cases, the leaf QT node can be further partitioned into a multi-type tree. Therefore, the leaf QT node is the root node of the multi-type tree, and the leaf QT node can have a multi-type tree depth (mttDepth) value of 0. If the multi-type tree depth reaches MaxMttdepth (for example, 4), further partitioning may not be considered. If the width of the multi-type tree node is equal to MinBtSize and is less than or equal to 2xMinTtSize, further horizontal partitioning may not be considered. If the height of the multi-type tree node is equal to MinBtSize and is less than or equal to 2xMinTtSize, further vertical partitioning may not be considered. When partitioning is not considered, the encoding device may skip the signaling of the partition information. In this case, the decoding device may derive partition information having a predetermined value.

[0154] At the same time, one CTU may include a coding block of luma samples (hereinafter referred to as "luminance block") and two coding blocks of chroma samples corresponding thereto (hereinafter referred to as "chroma blocks"). The above coding tree scheme may be applied equally or individually to the luma block and chroma block of the current CU. Specifically, the luma block and chroma block in one CTU may be partitioned into the same block tree structure, and in this case, the tree structure is represented as SINGLE_TREE. Alternatively, the luma block and chroma block in one CTU may be partitioned into separate block tree structures, and in this case, the tree structure may be represented as DUAL_TREE. That is, when the CTU is partitioned into dual trees, the block tree structure for the luma block and the block tree structure for the chroma block may exist separately. In this case, the block tree structure for the luma block may be referred to as DUAL_TREE_LUMA, and the block tree structure for the chroma component may be referred to as DUAL_TREE_CHROMA. For P and B slices / block groups, the luma block and the chroma block in one CTU may be restricted to have the same coding tree structure. However, for I slices / patch groups, luma blocks and chroma blocks may have separate block tree structures from each other. If a separate block tree structure is applied, luma CTBs may be partitioned into CUs based on a specific coding tree structure, and chroma CTBs may be partitioned into chroma CUs based on another coding tree structure. That is, this means that a CU in an I slice / patch group to which a separate block tree structure is applied may include a coding block of a luma component or a coding block of two chroma components, and a CU of a P or B slice / patch group may include blocks of three color components (one luma component and two chroma components).

[0155] Although a quadtree coding tree structure with nested multi-type trees has been described, the structure for partitioning a CU is not limited thereto. For example, the BT structure and the TT structure may be interpreted as concepts included in a multi-partition tree (MPT) structure, and the CU may be interpreted as being partitioned by the QT structure and the MPT structure. In an example where a CU is partitioned by the QT structure and the MPT structure, a syntax element (e.g., MPT_split_type) including information about how many blocks a leaf node of the QT structure is partitioned into and a syntax element (e.g., MPT_split_mode) including information about which of the vertical and horizontal directions a leaf node of the QT structure is partitioned into may be signaled to determine the partition structure.

[0156] In another example, the CU may be partitioned in a manner different from the QT structure, the BT structure, or the TT structure. That is, instead of partitioning a CU of a lower depth into 1 / 4 of a CU of a higher depth according to the QT structure, partitioning a CU of a lower depth into 1 / 2 of a CU of a higher depth according to the BT structure, or partitioning a CU of a lower depth into 1 / 4 or 1 / 2 of a CU of a higher depth according to the TT structure, in some cases the CU of a lower depth may be partitioned into 1 / 5, 1 / 3, 3 / 8, 3 / 5, 2 / 3, or 5 / 8 of a CU of a higher depth, and the method of partitioning the CU is not limited thereto.

[0157] The quadtree coding block structure with multi-type trees can provide a very flexible block partition structure. Due to the partition types supported in the multi-type trees, different partition patterns can potentially produce the same coding block structure in some cases. In the encoding device and the decoding device, by limiting the occurrence of such redundant partition patterns, the amount of data of the partition information can be reduced.

[0158] For example, Figure 8 The following figure shows the redundant partitioning patterns that may appear in binary tree partitioning and ternary tree partitioning. Figure 8 As shown, the consecutive binary partitions 810 and 820 for one direction of the two-step level have the same coding block structure as the binary partition for the center partition after the ternary partition. In this case, the binary tree partition for the center blocks 830 and 840 of the ternary tree partition can be prohibited. This prohibition applies to CUs of all pictures. When this particular partition is prohibited, the signaling of the corresponding syntax element can be modified by reflecting this prohibition, thereby reducing the number of bits for signaling the partition. For example, as Figure 8 As shown in the example shown in , when binary tree partitioning for the center block of a CU is prohibited, the syntax element mtt_split_cu_binary_flag specifying whether the partitioning is binary partitioning or ternary partitioning is not signaled and its value may be derived as 0 by the decoding device.

[0159] Overview of Inter Prediction

[0160] Hereinafter, inter prediction according to the present disclosure will be described.

[0161] The prediction unit of the image encoding device / image decoding device according to the present disclosure may perform inter-frame prediction in units of blocks to derive prediction samples. Inter-frame prediction may refer to prediction derived in a manner that depends on data elements (e.g., sample values, motion information, etc.) of pictures other than the current picture. When inter-frame prediction is applied to the current block, the prediction block (prediction block or prediction sample array) of the current block may be derived based on the reference block (reference sample array) specified by the motion vector on the reference picture indicated by the reference picture index. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. A temporally neighboring block may be referred to as a collocated reference block, a collocated CU (ColCU), or colBlock, and a reference picture including a temporally neighboring block may be referred to as a collocated picture (colPic) or colPicture. For example, a motion information candidate list may be constructed based on neighboring blocks of a current block, and a flag or index information specifying which candidate is selected (used) may be signaled to derive a motion vector and / or a reference picture index for the current block.

[0162] Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the motion information of the current block can be equal to the motion information of the selected neighboring block. In the case of skip mode, unlike merge mode, a residual signal may not be sent. In the case of motion information prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference. In the present disclosure, MVP mode may have the same meaning as advanced motion vector prediction (AMVP).

[0163] According to the inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. The motion vector in the L0 direction may be referred to as the L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as the L0 prediction, prediction based on the L1 motion vector may be referred to as the L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as the Bi prediction. Here, the L0 motion vector may specify a motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may specify a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include pictures before the current picture in the output order as reference pictures, and the reference picture list L1 may include pictures after the current picture in the output order. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may also include pictures after the current picture in the output order as reference pictures. In this case, within the reference picture list L0, the previous picture may be indexed first, and then the subsequent picture may be indexed. The reference picture list L1 may further include a picture preceding the current picture in the output order as a reference picture. In this case, within the reference picture list L1, the subsequent picture may be indexed first, and then the previous picture may be indexed. Here, the output order may correspond to a picture order count (POC) order.

[0164] Fig. 9 is a flowchart illustrating a video / image encoding method based on inter-frame prediction.

[0165] Fig.10 is a view illustrating a configuration of the inter prediction unit 180 according to the present disclosure.

[0166] Fig. 9 The encoding method can be Figure 2 The image encoding device of the present invention may be performed. Specifically, step S610 may be performed by the inter prediction unit 180, and step S620 may be performed by the residual processor. Specifically, step S620 may be performed by the subtractor 115. Step S630 may be performed by the entropy encoder 190. The prediction information of step S630 may be derived by the inter prediction unit 180, and the residual information of step S630 may be derived by the residual processor. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficient for the residual sample. As described above, the residual sample may be derived as a transform coefficient by the transformer 120 of the image encoding device, and the transform coefficient may be derived as a quantized transform coefficient by the quantizer 130. The information about the quantized transform coefficient may be encoded by the entropy encoder 190 through the residual coding process.

[0167] The image encoding device may perform inter-frame prediction on the current block (S610). The image encoding device may derive the inter-frame prediction mode and motion information of the current block and generate a prediction sample of the current block. Here, the inter-frame prediction mode determination, motion information derivation, and prediction sample generation processes may be performed simultaneously or any one of them may be performed before the other processes. For example, Fig.10 As shown, the inter-frame prediction unit 180 of the image encoding device may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183. The prediction mode determination unit 181 may determine the prediction mode of the current block, the motion information derivation unit 182 may derive the motion information of the current block, and the prediction sample derivation unit 183 may derive the prediction sample of the current block. For example, the inter-frame prediction unit 180 of the image encoding device may search for a block similar to the current block in a predetermined area (search area) of the reference picture through motion estimation, and derive a reference block whose difference with the current block is equal to or less than a predetermined criterion or a minimum value. Based on this, a reference picture index of a reference picture in which the designated reference block is located may be derived, and a motion vector may be derived based on the position difference between the reference block and the current block. The image encoding device may determine a mode applied to the current block among various prediction modes. The image encoding device may compare rate-distortion (RD) costs for various prediction modes, and determine the best prediction mode for the current block. However, the method of determining the prediction mode of the current block by the image encoding device is not limited to the above example, and various methods may be used.

[0168] For example, when the skip mode or merge mode is applicable to the current block, the image encoding device may derive a merge candidate from a neighboring block of the current block, and use the derived merge candidate to construct a merge candidate list. In addition, the image encoding device may derive a reference block whose difference with the current block is equal to or less than a predetermined criterion or a minimum value from the reference blocks specified by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information specifying the selected merge candidate may be generated and signaled to the image decoding device. The motion information of the selected merge candidate may be used to derive the motion information of the current block.

[0169] As another example, when the MVP mode is applied to the current block, the image encoding device may derive a motion vector predictor (MVP) candidate from a neighboring block of the current block, and use the derived MVP candidate to construct an MVP candidate list. In addition, the image encoding device may use the motion vector of the MVP candidate selected from the MVP candidates included in the MVP candidate list as the MVP of the current block. In this case, for example, the motion vector indicating the reference block derived by the above-mentioned motion estimation may be used as the motion vector of the current block, and the current block having the motion vector with the smallest difference from the motion vector of the current block among the MVP candidates may be the selected MVP candidate. A motion vector difference (MVD) as the difference obtained by subtracting MVP from the motion vector of the current block may be derived. In this case, index information specifying the selected MVP candidate and information about MVD may be signaled to the image decoding device. In addition, when the MVP mode is applied, the value of the reference picture index may be constructed as reference picture index information and signaled separately to the image decoding device.

[0170] The image encoding device may derive residual samples based on the predicted samples (S620). The image encoding device may derive residual samples by comparing the original samples of the current block with the predicted samples. For example, the residual samples may be derived by subtracting the corresponding predicted samples from the original samples.

[0171] The image encoding device may encode the image information including the prediction information and the residual information (S630). The image encoding device may output the encoded image information in the form of a bitstream. The prediction information may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and information about motion information as information related to the prediction process. Among the prediction mode information, the skip flag specifies whether the skip mode is applicable to the current block, and the merge flag specifies whether the merge mode is applicable to the current block. Alternatively, the prediction mode information may specify one of a plurality of prediction modes, such as a mode index. When the skip flag and the merge flag are 0, it can be determined that the MVP mode is applicable to the current block. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving a motion vector. Among the candidate selection information, the merge index may be signaled when the merge mode is applicable to the current block and may be information for selecting one of the merge candidates included in the merge candidate list. Among the candidate selection information, the mvp flag or the mvp index may be signaled when the MVP mode is applicable to the current block and may be information for selecting one of the mvp candidates in the mvp candidate list. In addition, the information about the motion information may include information about the above-mentioned MVD and / or reference picture index information. In addition, the information about the motion information may include information specifying whether to apply L0 prediction, L1 prediction or Bi prediction. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients used for the residual sample.

[0172] The output bit stream may be stored in a (digital) storage medium and transmitted to the image decoding device or may be transmitted to the image decoding device via a network.

[0173] As described above, the image encoding device can generate a reconstructed picture (a picture including reconstructed samples and reconstructed blocks) based on the reference sample and the residual sample. This is for the image encoding device to derive the same prediction result as the prediction result performed by the image decoding device, thereby improving the coding efficiency. Therefore, the image encoding device can store the reconstructed picture (or reconstructed sample and reconstructed block) in a memory and use it as a reference picture for inter-frame prediction. As described above, the in-loop filtering process is also applicable to the reconstructed picture.

[0174] Fig.11 is a flowchart illustrating a video / image decoding method based on inter-frame prediction.

[0175] Fig.12 is a view illustrating a configuration of the inter prediction unit 260 according to the present disclosure.

[0176] The image decoding device may perform an operation corresponding to the operation performed by the image encoding device. The image decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0177] Fig.11 The decoding method can be obtained by Figure 3 The image decoding device of the present invention is performed. Steps S810 to S830 may be performed by the inter-prediction unit 260, and the prediction information of step S810 and the residual information of step S840 may be obtained from the bitstream by the entropy decoder 210. The residual processor of the image decoding device may derive the residual samples of the current block based on the residual information (S840). Specifically, the dequantizer 220 of the residual processor may perform dequantization based on the dequantized transform coefficient derived according to the residual information to derive the transform coefficient, and the inverse transformer 230 of the residual processor may perform an inverse transform on the transform coefficient to derive the residual sample of the current block. Step S850 may be performed by the adder 235 or the reconstructor.

[0178] Specifically, the image decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S810). The image decoding apparatus may determine which inter prediction mode is applicable to the current block based on prediction mode information in the prediction information.

[0179] For example, it may be determined whether the skip mode is applicable to the current block based on a skip flag. In addition, it may be determined whether the merge mode or the MVP mode is applicable to the current block based on a merge flag. Alternatively, one of various inter-frame prediction mode candidates may be selected based on a mode index. The inter-frame prediction mode candidate may include a skip mode, a merge mode, and / or an MVP mode or may include various inter-frame prediction modes to be described below.

[0180] The image decoding device may derive motion information of the current block based on the determined inter prediction mode (S820). For example, when the skip mode or merge mode is applicable to the current block, the image decoding device may construct a merge candidate list to be described below, and select one of the merge candidates included in the merge candidate list. The selection may be performed based on the above-mentioned candidate selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. For example, the motion information of the selected merge candidate may be used as the motion information of the current block.

[0181] As another example, when the MVP mode is applicable to the current block, the image decoding device may construct an MVP candidate list, and use the motion vector of the MVP candidate selected from the MVP candidates included in the MVP candidate list as the MVP of the current block. The selection may be performed based on the above-mentioned candidate selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list of the current block may be derived as a reference picture referenced for inter-frame prediction of the current block.

[0182] The image decoding device may generate a prediction sample of the current block based on the motion information of the current block (S830). In this case, a reference picture may be derived based on a reference picture index of the current block, and a sample of the reference block indicated by a motion vector of the current block on the reference picture may be used to derive the prediction sample of the current block. In some cases, a prediction sample filtering process may also be performed on all or some of the prediction samples of the current block.

[0183] For example, Fig.12 As shown, the inter-frame prediction unit 260 of the image decoding device may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263. In the inter-frame prediction unit 260 of the image decoding device, the prediction mode determination unit 261 may determine the prediction mode of the current block based on the received prediction mode information, the motion information derivation unit 262 may derive the motion information (motion vector and / or reference picture index, etc.) of the current block based on the received motion information, and the prediction sample derivation unit 263 may derive the prediction sample of the current block.

[0184] The image decoding device may generate residual samples of the current block based on the received residual information (S840). The image decoding device may generate reconstructed samples of the current block based on the predicted samples and the residual samples and generate a reconstructed picture based thereon (S850). Thereafter, the in-loop filtering process is applied to the reconstructed picture as described above.

[0185] As described above, the inter-frame prediction process may include a step of determining an inter-frame prediction mode, a step of deriving motion information according to the determined prediction mode, and a step of performing prediction (generating prediction samples) based on the derived motion information. As described above, the inter-frame prediction process may be performed by an image encoding device and an image decoding device.

[0186] Hereinafter, the steps of deriving motion information according to the prediction mode will be described in more detail.

[0187] As described above, inter-frame prediction can be performed using the motion information of the current block. The image encoding device can derive the best motion information of the current block through a motion estimation process. For example, the image encoding device can use the original block in the original picture of the current block in fractional pixel units to search for a similar reference block with high correlation within a predetermined search range in the reference picture, and use it to derive motion information. The similarity of the block can be calculated based on the sum of absolute differences (SAD) between the current block and the reference block. In this case, the motion information can be derived based on the reference block with the smallest SAD in the search area. The derived motion information can be signaled to the image decoding device according to various methods based on the inter-frame prediction mode.

[0188] When the merge mode is applicable to the current block, the motion information of the current block is not directly sent, and the motion information of the neighboring blocks is used to derive the motion information of the current block. Therefore, the motion information of the current prediction block can be indicated by sending flag information specifying that the merge mode is used and candidate selection information (e.g., merge index) specifying which neighboring block is used as a merge candidate. In the present disclosure, since the current block is a unit for predicting performance, the current block can be used as the same meaning as the current prediction block, and the neighboring block can be used as the same meaning as the neighboring prediction block.

[0189] The image encoding device may search for a merge candidate block for deriving motion information of the current block to perform a merge mode. For example, up to five merge candidate blocks may be used, but not limited thereto. The maximum number of merge candidate blocks may be sent in a slice header or a tile group header, but not limited thereto. After finding the merge candidate block, the image encoding device may generate a merge candidate list and select the merge candidate block with the minimum RD cost as the final merge candidate block.

[0190] The present disclosure provides various embodiments for configuring a merge candidate block of a merge candidate list. The merge candidate list may use, for example, five merge candidate blocks. For example, four spatial merge candidates and one temporal merge candidate may be used.

[0191] Fig.13 is a view illustrating neighboring blocks that can be used as spatial merging candidates.

[0192] Fig.14 is a view schematically illustrating a method for constructing a merge candidate list according to an example of the present disclosure.

[0193] The image encoding / decoding apparatus may insert a spatial merge candidate derived by searching for spatial neighboring blocks of the current block into the merge candidate list (S1110). Fig.13As shown, the spatial neighboring blocks may include the left bottom corner neighboring block A0, the left neighboring block A1, the right top corner neighboring block B0, the top neighboring block B1, and the left top corner neighboring block B2 of the current block. However, this is an example, and in addition to the above-mentioned spatial neighboring blocks, additional neighboring blocks such as the right neighboring block, the bottom neighboring block, and the right bottom neighboring block may be further used as spatial neighboring blocks. The image encoding / decoding device may detect available blocks by searching the spatial neighboring blocks based on priority, and derive motion information of the detected blocks as spatial merging candidates. For example, the image encoding / decoding device may detect available blocks by searching in the order of A1, B1, B0, A0, and B2. Fig.13 The five blocks shown are used and the available candidates are indexed sequentially to build a merge candidate list.

[0194] The image encoding / decoding device may insert a temporal merge candidate derived by searching for temporal neighboring blocks of the current block into a merge candidate list (S1120). The temporal neighboring block may be located on a reference picture different from the current picture in which the current block is located. The reference picture in which the temporal neighboring block is located may be referred to as a collocated picture or a col picture. The temporal neighboring blocks may be searched in the order of the right bottom corner neighboring block and the right bottom center block of the collocated block of the current block on the col picture. Meanwhile, when motion data compression is applied in order to reduce memory load, specific motion information may be stored as representative motion information of each predetermined storage unit of the col picture. In this case, it is not necessary to store motion information of all blocks in the predetermined storage unit, thereby obtaining a motion data compression effect. In this case, the predetermined storage unit may be predetermined to be, for example, a 16×16 sample unit or an 8×8 sample unit, or the size information of the predetermined storage unit may be signaled from the image encoding device to the image decoding device. When motion data compression is applied, the motion information of the temporal neighboring block may be replaced with the representative motion information of the predetermined storage unit in which the temporal neighboring block is located. That is, in this case, from the perspective of implementation, the temporal merging candidate can be derived based on the motion information of the prediction block covering the arithmetically left shifted position after being arithmetically right shifted by a predetermined value based on the coordinates (left top sample position) of the temporal neighboring block (rather than the prediction block located on the coordinates of the temporal neighboring block). For example, when the predetermined storage unit is 2 n x2 nWhen the coordinates of the sample unit and the temporally neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the modified position ((xTnb >> n) << n), (yTnb >> n) << n)) can be used for temporal merge candidates. Specifically, for example, when the predetermined storage unit is a 16x16 sample unit and the coordinates of the temporally neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the modified position ((xTnb >> 4) << 4), (yTnb >> 4) << 4)) can be used for temporal merge candidates. Alternatively, for example, when the predetermined storage unit is an 8x8 sample unit and the coordinates of the temporally neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the modified position ((xTnb >> 3) << 3), (yTnb >> 3) << 3)) can be used for temporal merge candidates.

[0195] Referring again to Fig.14 , the image encoding / decoding device may check whether the number of current merge candidates is less than the maximum number of merge candidates (S1130). The maximum number of merge candidates may be predefined or signaled from the image encoding device to the image decoding device. For example, the image encoding device may generate and encode information about the maximum number of merge candidates and send the encoded information to the image decoding device in the form of a bitstream. When the maximum number of merge candidates is satisfied, the subsequent candidate addition process S1140 may not be performed.

[0196] When, as a result of the check in step S1130, the number of current merge candidates is less than the maximum number of merge candidates, the image encoding / decoding device may derive additional merge candidates according to a predetermined method and then insert the additional merge candidates into the merge candidate list (S1140).

[0197] When, as a result of the check in step S1130, the number of current merge candidates is not less than the maximum number of merge candidates, the image encoding / decoding device may end the construction of the merge candidate list. In this case, the image encoding device may select the best merge candidate from among the merge candidates configuring the merge candidate list and signal candidate selection information (e.g., merge index) specifying the selected merge candidate to the image decoding device. The image decoding device may select the best merge candidate based on the merge candidate list and the candidate selection information.

[0198] As described above, the motion information of the selected merge candidate may be used as the motion information of the current block, and the prediction sample of the current block may be derived based on the motion information of the current block. The image encoding device may derive the residual sample of the current block based on the prediction sample, and signal the residual information of the residual sample to the image decoding device. As described above, the image decoding device may generate a reconstructed sample based on the residual sample derived from the residual information and the prediction sample, and generate a reconstructed picture based thereon.

[0199] When skip mode is applied to the current block, the motion information of the current block can be derived using the same method as the case where merge mode is applied. However, when skip mode is applied, the residual signal of the corresponding block is omitted, and thus the prediction sample can be directly used as the reconstructed sample.

[0200] When the MVP mode is applied to the current block, the reconstructed spatial neighboring blocks (e.g., Fig.13 The motion vector predictor (MVP) candidate list is generated by reconstructing the motion vector of the spatial neighboring block (as shown) and / or the motion vector corresponding to the temporal neighboring block (or Col block). That is, the motion vector of the reconstructed spatial neighboring block and the motion vector corresponding to the temporal neighboring block can be used as the motion vector predictor candidate of the current block. When bi prediction is applied, the MVP candidate list for L0 motion information derivation and the MVP candidate list for L1 motion information derivation are generated and used separately. The prediction information (or information about the prediction) of the current block may include candidate selection information (e.g., MVP flag or MVP index) specifying the best motion vector predictor candidate selected from the motion vector predictor candidates included in the MVP candidate list. In this case, the prediction unit can use the candidate selection information to select the motion vector predictor of the current block from the motion vector predictor candidates included in the MVP candidate list. The prediction unit of the image encoding device can obtain the motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor and encode it, and output the encoded MVD in the form of a bitstream. That is, the MVD can be obtained by subtracting the motion vector predictor from the motion vector of the current block. The prediction unit of the image decoding device can obtain the motion vector difference included in the information about the prediction and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor. The prediction unit of the image encoding device can obtain or derive the reference picture index of the designated reference picture from the information about the prediction.

[0201] Fig.15 is a view schematically illustrating a method for constructing a motion vector predictor candidate list according to an example of the present disclosure.

[0202] First, the spatial candidate blocks of the current block can be searched and the available candidate blocks can be inserted into the MVP candidate list (S1210). Thereafter, it is determined whether the number of MVP candidates included in the MVP candidate list is less than 2 (S1220), and when the number of MVP candidates is 2, the construction of the MVP candidate list can be completed.

[0203] In step S1220, when the number of available spatial candidate blocks is less than 2, the temporal candidate blocks of the current block can be searched and the available candidate blocks can be inserted into the MVP candidate list (S1230). When the temporal candidate block is not available, a zero motion vector can be inserted into the MVP candidate list, thereby completing the construction of the MVP candidate list.

[0204] Meanwhile, when the MVP mode is applied, the reference picture index may be explicitly signaled. In this case, the reference picture index refidxL0 for L0 prediction and the reference picture index refidxL1 for L1 prediction may be signaled differently. For example, when the MVP mode is applied and Bi prediction is applied, information about refidxL0 and information about refidxL1 may be signaled.

[0205] As described above, when the MVP mode is applied, information about the MVP derived by the image encoding device may be signaled to the image decoding device. For example, the information about the MVD may include information about the x and y components of the specified absolute value (MVD absolute value) and the sign of the MVD. In this case, when the MVD absolute value is greater than 0, information about whether the MVD absolute value is greater than 1 and the specified MVD remainder may be signaled in steps. For example, information about whether the MVD absolute value is greater than 1 may be signaled only when the value of the flag information specifying whether the MVD absolute value is greater than 0 is 1.

[0206] Fig.16 is a view illustrating a syntax structure for transmitting an MVD from an image encoding device to an image decoding device according to an embodiment of the present disclosure.

[0207] exist Fig.16 In the , abs_mvd_greater0_flag[0] specifies whether the absolute value of the x component of the MVD is greater than 0, and abs_mvd_greater0_flag[1] specifies whether the absolute value of the y component of the MVD is greater than 0. Similarly, abs_mvd_greater1_flag[0] specifies whether the absolute value of the x component of the MVD is greater than 1, and abs_mvd_greater1_flag[1] specifies whether the absolute value of the y component of the MVD is greater than 1. Fig.16As shown in the figure, abs_mvd_greater1_flag can be sent only when abs_mvd_greater0_flag is 1. Fig.16 In , abs_mvd_minus2 can specify the value obtained by subtracting 2 from the absolute value of MVD, and mvd_sign_flag specifies whether the sign of MVD is positive or negative. Fig.16 The grammatical structure shown, the MVD can be derived as shown in the following equation 1.

[0208] [Equation 1]

[0209] MVD[compIdx]=abs_mvd_greater0_flag[compIdx]*(abs_mvd_minus2[compIdx]+2)*(1-2*mvd_sign_flag[compIdx])

[0210] Meanwhile, the MVD (MVDL0) for L0 prediction and the MVD (MVDL1) for L1 prediction may be signaled differently, and the information about the MVD may include information about MVDL0 and / or information about MVDL1. For example, when the MVP mode is applied to the current block and the BI prediction is applied, the information about MVDL0 and the information about MVDL1 may be signaled.

[0211] Overview of Intra Block Copy (IBC) Prediction

[0212] Hereinafter, IBC prediction according to the present disclosure will be described.

[0213] IBC prediction can be performed by a prediction unit of an image encoding / decoding device. IBC prediction can be referred to as IBC for short. IBC can be used for content image / motion image coding such as screen content coding (SCC). IBC prediction can basically perform IBC prediction in the current picture, but can be performed similarly to inter-frame prediction because the reference block is derived within the current picture. That is, IBC can use at least one of the inter-frame prediction techniques described in the present disclosure. For example, IBC can use at least one of the above-mentioned motion information (motion vector) derivation methods. It can be considered that IBC prediction partially modifies and uses at least one of the inter-frame prediction techniques. IBC can refer to the current picture and can therefore be called a current picture reference (CPR).

[0214] For IBC, the image encoding device may perform block matching (BM) and derive the best block vector (or motion vector) of the current block (e.g., CU). The derived block vector (or motion vector) may be signaled to the image decoding device through the bitstream using a method similar to the signaling of motion information (motion vector) in the above-mentioned inter-frame prediction. The image decoding device may derive the reference block of the current block in the current picture through the signaled block vector (motion vector), and thereby derive the prediction signal (prediction block or prediction sample) of the current block. Here, the block vector (or motion vector) may specify the displacement from the current block to the reference block located in the reconstructed area in the current picture. Therefore, the block vector (or motion vector) may be referred to as a displacement vector. Hereinafter, in IBC, a motion vector may correspond to a block vector or a displacement vector. The motion vector of the current block may include a motion vector of a luminance component (luminance motion vector) or a motion vector of a chrominance component (chrominance motion vector). For example, the luminance motion vector of a CU encoded by IBC may be an integer sample unit (i.e., integer precision). The chrominance motion vector may be pruned in integer sample units. As described above, IBC may use at least one of the inter-frame prediction techniques, and, for example, may use the above-described merge mode or MVP mode to encode / decode a luma motion vector.

[0215] When applying a merge mode to a luma IBC block, it can be similar to the reference Fig.14 The described merge candidate list in inter mode constructs a merge candidate list for a luma IBC block. However, in the case of a luma IBC block, temporally neighboring blocks may not be used as merge candidates.

[0216] When MVP mode is applied to the brightness IBC block, it can be similar to the reference Fig.15 The MVP candidate list in the inter mode described above constructs the MVP candidate list for the luma IBC block. However, in the case of the luma IBC block, the temporal candidate block may not be used as the MVP candidate.

[0217] In IBC, the reference block is derived from the reconstructed area in the current picture. In this case, in order to reduce the memory consumption and complexity of the image decoding device, a predefined area among the reconstructed areas in the current picture can be referenced. The predefined area can include the current CTU in which the current block is included. By limiting the referenceable reconstruction area to the predefined area, the IBC mode can be implemented in hardware using local on-chip memory.

[0218] An image encoding apparatus for performing IBC may search a predefined area to determine a reference block having a minimum RD cost and derive a motion vector (block vector) based on the positions of the reference block and the current block.

[0219] Whether to apply IBC to the current block can be signaled as IBC performance information at the CU level. Information about the signaling method (IBC MVP mode or IBC skip / merge mode) of the motion vector of the current block can be signaled. The IBC performance information can be used to determine the prediction mode of the current block. Therefore, the IBC performance information can be included in the information about the prediction mode of the current block.

[0220] In the case of IBC skip / merge mode, a merge candidate index may be signaled to specify a block vector to be used for prediction of the current luma block among the block vectors included in the merge candidate list. In this case, the merge candidate list may include neighboring blocks encoded by IBC. The merge candidate list may be configured to include spatial merge candidates but not temporal merge candidates. In addition, the merge candidate list may also include history-based motion vector predictor (HMVP) candidates and / or paired candidates.

[0221] In the case of the IBC MVP mode, the block vector difference can be encoded using the same method as the motion vector difference of the inter-frame mode described above. The block vector prediction method can be constructed similarly to the MVP mode of the inter-frame mode and use an MVP candidate list including two candidates as predictors. One of the two candidates can be derived from the left neighboring block, and the other candidate can be derived from the top neighboring block. In this case, candidates can only be derived from the corresponding neighboring block when the left or top neighboring block is IBC encoded. If the left or top neighboring block is not available, for example, it is not IBC encoded, the default block vector can be included in the MVP candidate list as a predictor. In addition, information (e.g., a flag) specifying one of the two block vector predictors is signaled similarly to the MVP mode of the inter-frame mode and used as candidate selection information. The MVP candidate list may include an HMVP candidate and / or a zero motion vector as a default block vector.

[0222] The HMVP candidate may be referred to as a history-based MVP candidate, and an MVP candidate, a merge candidate, or a block vector candidate used before encoding / decoding of the current block may be stored in the HMVP list as an HMVP candidate. Thereafter, when the merge candidate list or the mvp candidate list of the current block does not include the maximum number of candidates, the candidate stored in the HMVP list may be added as an HMVP candidate to the merge candidate list or the mvp candidate list of the current block.

[0223] The pair of candidates means candidates derived by selecting two candidates from among candidates already included in the merge candidate list of the current block according to a predetermined order and calculating an average of the selected two candidates.

[0224] Fig.17 is a flowchart illustrating a video / image encoding method based on IBC.

[0225] Fig.18 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image encoding method according to the present disclosure.

[0226] Fig.17 The encoding method can be Figure 2 The image encoding device of the present invention may be performed by the image encoding device. Specifically, step S1410 may be performed by the prediction unit and step S1420 may be performed by the residual processor. Specifically, step S1420 may be performed by the subtractor 115. Step S1430 may be performed by the entropy encoder 190. The prediction information of step S1430 may be derived by the prediction unit and the residual information of step S1430 may be derived by the residual processor. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficient for the residual sample. As described above, the residual sample may be derived through the transform coefficient via the transformer 120 of the image encoding device, and the transform coefficient may be derived through the transform coefficient quantized by the quantizer 130. The information about the quantized transform coefficient may be encoded by the entropy encoder 190 through the residual coding process.

[0227] The image encoding device may perform IBC prediction (IBC-based prediction) for the current block (S1410). The image encoding device may derive a prediction mode and a motion vector (block vector) of the current block and generate a prediction sample of the current block. The prediction mode may include at least one of the above-mentioned inter-frame prediction modes. Here, the prediction mode determination, motion vector derivation, and prediction sample generation processes may be performed simultaneously, or any one process may be performed before the other processes. For example, Fig.18 As shown, the prediction unit of the image encoding device for performing the video / image encoding method based on IBC may include a prediction mode determination unit, a motion vector derivation unit, and a prediction sample derivation unit. The prediction mode determination unit may determine the prediction mode of the current block, the motion vector derivation unit may derive the motion vector of the current block, and the prediction sample derivation unit may derive the prediction sample of the current block. For example, the prediction unit of the image encoding device may search for a block similar to the current block in the reconstruction area of ​​the current picture (or a certain area (search area) of the reconstruction area) and derive a reference block whose difference with the current block is equal to or less than a certain criterion or minimum value. The image encoding device may derive a motion vector based on the displacement difference between the reference block and the current block. The image encoding device may determine a mode applied to the current block among various prediction modes. The image encoding device may compare RD costs for various prediction modes and determine the best prediction mode for the current block. However, the method of determining the prediction mode of the current block by the image encoding device is not limited to the above example and various methods may be used.

[0228] For example, when a skip mode or a merge mode is applied to the current block, the image encoding device may derive a merge candidate from a neighboring block of the current block, and use the derived merge candidate to construct a merge candidate list. In addition, the image encoding device may derive a reference block whose difference with the current block is equal to or less than a specific criterion or a minimum value from the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information specifying the selected merge candidate may be generated and signaled to the image decoding device. Using the motion vector of the selected merge candidate, the motion vector of the current block may be derived.

[0229] As another example, when the MVP mode is applied to the current block, the image encoding device may derive a motion vector predictor (MVP) candidate from a neighboring block of the current block, and use the derived MVP candidate to construct an MVP candidate list. In addition, the image encoding device may use the motion vector of an MVP candidate selected from among the MVP candidates included in the MVP candidate list as the MVP of the current block. In this case, for example, the motion vector indicating the reference block derived by the above-mentioned motion estimation may be used as the motion vector of the current block, and the MVP candidate with the smallest difference from the motion vector of the current block among the MVP candidates may become the selected MVP candidate. The motion vector difference (MVD) obtained by subtracting the MVP from the motion vector of the current block may be derived. In this case, index information specifying the selected MVP candidate and information about the MVD may be signaled to the image decoding device.

[0230] The image encoding device may derive residual samples based on the predicted samples (S1420). The image encoding device may derive residual samples by comparing the original samples of the current block with the predicted samples. For example, the residual samples may be derived by subtracting the corresponding predicted samples from the original samples.

[0231] The image encoding device may encode the image information including the prediction information and the residual information (S1430). The image encoding device may output the encoded image information in the form of a bitstream. The prediction information may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index) and information about a motion vector as information related to the prediction process. Among the prediction mode information, the skip flag specifies whether the skip mode is applied to the current block, and the merge flag specifies whether the merge mode is applied to the current block. Alternatively, the prediction mode information may specify one of a plurality of prediction modes, such as a mode index. When the skip flag and the merge flag are 0, it may be determined that the MVP mode is applicable to the current block. The information about the motion vector may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving the motion vector. Among the candidate selection information, the merge index may be signaled when the merge mode is applied to the current block, and may be information for selecting one of the merge candidates included in the merge candidate list. Among the candidate selection information, an MVP flag or an MVP index may be signaled when the MVP mode is applied to the current block, and may be information for selecting one of the MVP candidates included in the MVP candidate list. In addition, the information about the motion vector may include information about the above-mentioned MVD. In addition, the information about the motion vector may include information specifying whether L0 prediction, L1 prediction or bi prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients used for the residual sample.

[0232] The output bit stream may be stored in a (digital) storage medium and transmitted to the image decoding device or may be transmitted to the image decoding device via a network.

[0233] At the same time, as described above, the image encoding device can generate a reconstructed picture (a picture including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This is for the image encoding device to derive the same prediction result as the prediction result performed by the image decoding device, thereby improving the coding efficiency. Therefore, the image encoding device can store the reconstructed picture (or reconstructed samples and reconstructed blocks) in a memory and use it as a reference picture for inter-frame prediction. As described above, the in-loop filtering process is also applicable to the reconstructed picture.

[0234] Fig.19 is a flowchart illustrating a video / image decoding method based on IBC.

[0235] Fig. 20 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image decoding method according to the present disclosure.

[0236] The image decoding device may perform an operation corresponding to the operation performed by the image encoding device. The image decoding device may perform IBC prediction on the current block based on the received prediction information to derive a prediction sample.

[0237] Fig.19 The decoding method can be obtained by Figure 3 The image decoding device of the present invention may perform the above steps. Steps S1610 to S1630 may be performed by a prediction unit, and the prediction information of step S1610 and the residual information of step S1640 may be obtained from the bitstream by the entropy decoder 210. The residual processor of the image decoding device may derive the residual samples of the current block based on the residual information (S1640). Specifically, the dequantizer 220 of the residual processor may perform dequantization based on the quantized transform coefficient derived according to the residual information to derive the transform coefficient, and the inverse transformer 230 of the residual processor may perform an inverse transform on the transform coefficient to derive the residual sample of the current block. Step S1650 may be performed by the adder 235 or the reconstructor.

[0238] Specifically, the image decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S1610). The image decoding apparatus may determine which prediction mode is applicable to the current block based on prediction mode information in the prediction information.

[0239] For example, it can be determined based on a skip flag whether to apply a skip mode to the current block. In addition, it can be determined based on a merge flag whether to apply a merge node or MVP mode to the current block. Alternatively, one of the various prediction mode candidates can be selected based on a mode index. The prediction mode candidate can include a skip mode, a merge mode, and / or an MVP mode or can include the various inter-frame prediction modes described above.

[0240] The image encoding device may derive the motion vector of the current block based on the determined prediction mode (S1620). For example, when the skip mode or the merge mode is applied to the current block, the image decoding device may construct the above-mentioned merge candidate list and select one of the merge modes included in the merge candidate list. The selection may be performed based on the above-mentioned candidate selection information (merge index). The motion vector of the current block may be derived using the motion vector of the selected merge candidate. For example, the motion vector of the selected merge candidate may be used as the motion vector of the current block.

[0241] As another example, when the MVP mode is applied to the current block, the image decoding device may construct an MVP candidate list, and use the motion vector of the MVP candidate selected from the MVP candidates included in the MVP candidate list as the MVP of the current block. The selection may be performed based on the above-mentioned candidate selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block.

[0242] The image decoding device may generate a prediction sample of the current block based on the motion vector of the current block (S1630). The prediction sample of the current block may be derived using a sample of a reference block indicated by the motion vector of the current block on the current picture. In some cases, a prediction sample filtering process may be further performed for all or some of the prediction samples of the current block.

[0243] For example, Fig. 20 As shown, the prediction unit of the image decoding device for performing the IBC-based video / image decoding method may include a prediction mode determination unit, a motion vector deriving unit, and a prediction sample deriving unit. The prediction unit of the image decoding device may determine the prediction mode of the current block based on the received prediction mode information in the prediction mode determination unit, derive the motion vector of the current block based on the received information about the motion vector in the motion vector deriving unit, and derive the prediction sample of the current block in the prediction sample deriving unit.

[0244] The image decoding device may generate residual samples of the current block based on the received residual information (S1640). The image decoding device may generate reconstructed samples of the current block based on the predicted samples and the residual samples, and generate a reconstructed picture based thereon (S1650). Thereafter, as described above, the in-loop filtering process is also applicable to the reconstructed picture.

[0245] As described above, one unit (e.g., coding unit (CU)) may include a luma block (luma coding block (CB)) and a chroma block (chroma CB). In this case, the luma block and the chroma block corresponding thereto may have the same motion information (e.g., motion vector) or different motion information. For example, the motion information of the chroma block may be derived based on the motion information of the luma block, so that the luma block and the chroma block corresponding thereto have the same motion information.

[0246] Intra prediction on chroma blocks

[0247] When intra prediction is performed on the current block, prediction of the luminance component block (luminance block) of the current block and prediction of the chrominance component block (chrominance block) can be performed. In this case, the intra prediction mode of the chrominance block can be set separately from the intra prediction mode of the luminance block.

[0248] For example, an intra prediction mode for a chroma block may be specified based on the intra chroma prediction mode information, and the intra chroma prediction mode information may be signaled in the form of an intra_chroma_pred_mode syntax element. For example, the intra chroma prediction mode information may represent one of a plane mode, a DC mode, a vertical mode, a horizontal mode, a derived mode (DM), and a cross-component linear model (CCLM) mode. Here, the plane mode may specify intra prediction mode #0, the DC mode may specify intra prediction mode #1, the vertical mode may specify intra prediction mode #26, and the horizontal mode may specify intra prediction mode #10. DM may also be referred to as a direct mode. CCLM may also be referred to as a linear model (LM).

[0249] Meanwhile, DM and CCLM are related intra prediction modes for predicting chrominance blocks using information about luma blocks. DM may indicate a mode in which the same intra prediction mode as the intra prediction mode of the luma component is applied as the intra prediction mode for the chroma component. In addition, CCLM may indicate an intra prediction mode in which samples derived by subsampling the reconstructed samples of the luma block and then applying α and β as CCLM parameters to the subsampled samples in generating a prediction block for the chroma block are used as prediction samples for the chroma block.

[0250] [Equation 2]

[0251] pred C (i, j) = α·rec L ′(i, j)+β

[0252] Among them, pred c (i, j) may represent the predicted sample of the (i, j) coordinate of the current chroma block in the current CU. L '(i, j) can represent the reconstructed sample of the (i, j) coordinate of the current luminance block in the CU. For example, rec L '(i, j) may represent the downsampled reconstructed samples of the current luma block. The linear model coefficients α and β may be signaled or derived from neighboring samples.

[0253] Coding efficiency degradation problem of 2×N and N×2 blocks

[0254] In the case of the VVC standard, the encoding target image is a high-resolution image such as UHD or FHD. The hardware configuration for processing such high-resolution images is becoming more and more complex. In an embodiment, TVM, which is the VVC specification and standard software, can use a CTU of size 128×128 during intra prediction. Even in this case, as the size of the minimum CU block, a 4×4 block can be used in the case of a luminance block. In the case of a chrominance block, a 2×2 block can be used when the tree structure of the current block is a single tree, and a 2×8, 8×2, or 4×4 block can be used when the tree structure of the current block is a dual tree.

[0255] Therefore, when a UHD image with a resolution of 3840×2160 is encoded by performing intra-frame prediction via VTM software, all luminance blocks are encoded into 4×4 blocks according to the dual tree, and all chrominance blocks can be encoded into 4×4 blocks. In this case, the UHD image is divided into 518,400 4×4 luminance blocks and chrominance blocks. In the hardware implementation of VTM, the corresponding hardware should be driven even in the data throughput that occurs in the worst case. Therefore, when this happens, in order to prepare for this, the hardware manufacturing cost increases and processing delays occur during encoding and decoding.

[0256] In the case of a technique using association between luminance blocks and chrominance blocks (e.g., CCLM), since the encoding of the chrominance blocks should be performed after the encoding of all luminance blocks is completed, Fig.21 As shown, pipeline delay problems occur in hardware implementation.

[0257] In addition, unlike a single tree, in the case of a dual tree, the encoding of the chroma block should be performed after the encoding of all the luminance blocks is completed. Therefore, by delaying the encoding of the chroma block until the encoding of the luminance block is completed, a pipeline delay problem occurs in the hardware implementation. Specifically, since 2×8, 2×16, and 2×32 structures are generated in the chroma block of the dual tree, the existing hardware structure that performs encoding and decoding in units of 4×1 per clock may not be used. Therefore, a new hardware structure for performing a process in units of 2×2 or 1 / 4 per clock is required.

[0258] The present disclosure proposes a method for adaptively limiting the size of a chroma block or limiting or adjusting the size of an application block of a CCLM prediction block in order to solve the above-mentioned problems in hardware implementation. Therefore, the complexity of hardware implementation can be significantly reduced while minimizing the loss of coding efficiency.

[0259] In the following description, limiting a specific block size may indicate that segmentation into blocks of a specific size is not allowed. In order to not allow segmentation into blocks of a specific size, segmentation under specific conditions may be limited. This may indicate that segmentation under specific conditions is set to be unavailable. In this case, the upper layer block may be segmented into a block size different from the specific block size, and then the segmented block may be used as a current block to perform a series of coding processes (prediction, residual processing, block reconstruction, image / video information encoding / decoding, etc.). The image / video information may include segmentation information, and the segmentation information may include information specifying segmentation into block sizes other than the limited segmentation size.

[0260] Improved performance based on block split limit implementation

[0261] The encoding apparatus and the decoding apparatus according to an embodiment may solve the complexity of hardware implementation by adaptively limiting the size of a block partitioned from a CTU depending on whether the CTU of the current image is partitioned according to a single-tree or dual-tree structure.

[0262] As described above, in the case of a dual tree, after encoding or decoding all luminance blocks of a certain size is completed, encoding of a chrominance block corresponding to the luminance block can be performed. Therefore, it is necessary to use a pipeline method different from the single tree hardware used in H.264 and HEVC.

[0263] In the case of using the VVC standard, when the dual tree is applied, in the case of a 4:2:0 color format, after encoding the 64×64 luminance block, encoding of the 32×32 chrominance block is performed. Therefore, encoding and decoding of the luminance block and the chrominance block are performed sequentially. In the case of the luminance block, the method of processing 4×1 pixels per clock used in the existing hardware can be used without change. However, since a 2x8, 2x16, or 2x32 structure is generated in the chrominance block, the existing hardware structure for encoding and decoding in units of 4x1 may not be used.

[0264] In order to use the existing hardware structure without change, the size of the chroma block can be limited to the existing encoding and decoding units. For example, when the process is performed in units of A×1 per clock as the encoding and decoding unit, the B×N block size of the chroma block can be limited so that the chroma block is encoded / decoded in this structure. Here, A can be an integer greater than 0 and less than or equal to the maximum width of the block, B can be an integer greater than 0 and less than A, and N can be a value represented by a power of 2 greater than 1 (for example, 2, 4, 8, 16, 32, 64, 128, 256...). Here, limiting the block size can mean prohibiting segmentation into corresponding block sizes. Therefore, the chroma block can be segmented into block sizes up to the block size immediately before being segmented into the corresponding block size.

[0265] For example, when the process is performed in units of 4×1 per clock as encoding and decoding units, the 2×N block size of the chroma block may be limited so that the chroma block is encoded / decoded in this structure. Here, N may be a value represented by a power of 2 greater than 1.

[0266] For example, the chroma block may be prohibited from being split into 2xN blocks. In an embodiment, in order to prohibit the chroma block from being split into this size, the quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trinary splitting, or vertical trinary splitting for generating a chroma block having a size of 2×N by splitting the current block may be restricted.

[0267] Limiting this partitioning is applicable only when the current block has a dual-tree structure, only when the current block has a single-tree structure, or when the current block has either a dual-tree structure or a single-tree structure.

[0268] Meanwhile, when the current block is a luminance block, the tree structure of the current block is a single tree, and the color format of the current block is 4:2:2 or 4:2:0, in order to limit the generation of a 2×N chrominance block, splitting the current block to generate a 4×N luminance block may be limited. For example, quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trifurcating splitting, or vertical trifurcating splitting for generating a luminance block having a size of 4×N by splitting the current block may be limited.

[0269] Fig. 22 2 is a diagram illustrating a coding rate measured in a case where a chroma block is restricted from being divided into 2×N chroma blocks when a current block has a dual tree structure. Fig. 22 As shown in the experimental results, coding losses of 0.02% for Y, 0.34% for Cb, and 0.38% for Cr were observed in all intra experiments. By limiting the 2×N blocks, the 4×1 pixel processing of existing hardware can be applied to chroma blocks without change, and the coding loss can also be minimized.

[0270] At the same time, according to the above-described embodiment, it can be applied to the case where the encoding / decoding process is performed in units of 1×A per clock. For example, the N×B block size of the chrominance block can be limited so that the chrominance block is encoded / decoded in the encoding / decoding structure in which the encoding / decoding process is performed in units of 1×A per clock. Here, A can be an integer greater than 0 and less than or equal to the maximum width of the block, B can be an integer greater than 0 and less than A, and N can be a value represented by a power of 2 greater than 1 (for example, 2, 4, 8, 16, 32, 64, 128, 256...). Here, limiting the block size can mean prohibiting segmentation into corresponding block sizes. Therefore, the chrominance block can be segmented into block sizes up to the block size immediately before being segmented into the corresponding block size.

[0271] For example, when the process is performed in units of 1×4 per clock as encoding and decoding units, the N×2 block size of the chroma block may be limited so that the chroma block is encoded / decoded in this structure. Here, N may be a value represented by a power of 2 greater than 1.

[0272] For example, the chroma block may be prohibited from being split into N×2 blocks. In an embodiment, in order to prohibit the chroma block from being split into such a size, quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trifurcating splitting, or vertical trifurcating splitting for generating a chroma block having an N×2 size by splitting the current block may be restricted.

[0273] Limiting this partitioning is applicable only when the current block has a dual-tree structure, only when the current block has a single-tree structure, or when the current block has either a dual-tree structure or a single-tree structure.

[0274] Meanwhile, when the current block is a luminance block, the tree structure of the current block is a single tree and the color format of the current block is 4:2:2 or 4:2:0, in order to limit the generation of N×2 chrominance blocks, the segmentation of the current block to generate an N×4 luminance block may be limited. For example, quadtree segmentation, horizontal binary tree segmentation, vertical binary tree segmentation, horizontal trifurcating segmentation, or vertical trifurcating segmentation for generating a luminance block having an N×4 size by segmenting the current block may be limited.

[0275] Example 1

[0276] As described above, the encoding device and the decoding device may limit the chroma block to be segmented into a size of 2×N. For example, the encoding / decoding device may limit the minimum width of the chroma block to a length of 4 samples. To this end, the encoding / decoding device according to the embodiment may determine whether a predetermined segmentation mode is allowed for the current block based on whether the current block is a chroma block or the width of the current block. Hereinafter, the decoding device will be described, but the following description applies to the encoding device accordingly.

[0277] Fig.23 2310 is a view illustrating a method for determining by a decoding device whether vertical three-pronged splitting (SPLIT_TT_VER) is allowed for a current block. A decoding device according to an embodiment may determine whether a current block is a chroma block (S2310). The decoding device may check the value of a cIdx parameter specifying a color component of the current block to determine whether the current block is a chroma block. When the value of cIdx is 0, the decoding device may determine that the current block is a luminance block. When the value of cIdx is greater than 0, the decoding device may determine that the current block is a chroma block. More specifically, when the value of cIdx is 1 or 2, the decoding device may determine that the current block is a chroma cb block. When the value of cIdx is 2, the decoding device may determine that the current block is a chroma cr block.

[0278] In addition, the decoding device according to the embodiment can further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., DUAL_TREE_CHROMA) for the chroma component, the decoding device can determine that the current block is a chroma block and the tree type is a dual tree type.

[0279] Next, the decoding device may determine whether the width of the current block is equal to or less than the length of 8 samples (S2320). When the value of the parameter specifying the width of the current block is equal to or less than 8, the decoding device may determine that the width of the current block is equal to or less than 8.

[0280] Meanwhile, in the case of a chroma block, the width of the chroma block may be determined based on the width of the corresponding luminance block. In this case, the width of the current chroma block may be determined based on the width of the luminance block and the color format of the current image. For example, when the color format is 4:4:4, the width and height of the chroma block may be set to the width and height of the luminance block, respectively. When the color format is 4:2:2, the width of the chroma block may be set to half the width of the luminance block, and the height of the chroma block may be set to the height of the luminance block. When the color format is 4:2:0, the width of the chroma block may be set to half the width of the luminance block, and the height of the chroma block may be set to half the height of the luminance block.

[0281] Therefore, when the color format of the current block is 4:4:4, the decoding device may perform step S2320 by determining whether the width of the luminance block is equal to or less than 8. Similarly, when the color format of the current block is 4:2:2 or 4:2:0, the decoding device may perform step S2320 by determining whether the width of the luminance block is equal to or less than 16.

[0282] Finally, when all the above conditions are met, the decoding device may determine that the current block does not allow vertical trifurcated splitting (S2330). For example, when the current block is a chroma block and the width is equal to or less than 8, the decoding device may determine that the current block does not allow vertical trifurcated splitting. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual tree type, and the width is equal to or less than 8, the decoding device may determine that the current block does not allow vertical trifurcated splitting.

[0283] Meanwhile, when the above conditions are not met, the decoding device may determine that vertical trifurcated splitting is allowed for the current block. In this case, by determining an additional condition that the current block cannot be split by vertical trifurcated splitting, the decoding device may determine whether vertical trifurcated splitting is allowed for the current block (S2340). For example, when the number of times the current block is split from a quad leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowed hierarchical depth of a multi-type tree split from a quad leaf node, the decoding device may determine that vertical trifurcated splitting is not allowed for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, it may be determined that vertical trifurcated splitting is allowed for the current block.

[0284] Example 2

[0285] As mentioned above, it is necessary to limit the minimum height of the chroma block to a length of four samples. Fig.24 A method of limiting horizontal trifurcated division for a current block by an encoding / decoding apparatus according to an embodiment in order to limit a minimum height of a chroma block is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applicable to an encoding apparatus.

[0286] Fig.24 24 is a view illustrating a method for determining by a decoding device whether horizontal three-way splitting (SPLIT_TT_HOR) is allowed for a current block. The decoding device according to an embodiment may determine whether the current block is a chroma block (S2410). As described above, the decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0287] In addition, the decoding device according to the embodiment can further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., DUAL_TREE_CHROMA) for the chroma component, the decoding device can determine that the current block is a chroma block and the tree type is a dual tree type.

[0288] Next, the decoding device according to the embodiment may determine whether the height of the current block is equal to or less than the length of 8 samples (S2420). When the value of the parameter specifying the height of the current block is equal to or less than 8, the decoding device may determine that the height of the current block is equal to or less than 8. Alternatively, as described above, the decoding device may perform step S2420 based on whether the height of the luminance block is equal to or less than 8 or 16 according to the color format of the current block.

[0289] As described above, in the case of a chroma block, the height of the chroma block may be determined based on the height of the corresponding luminance block. For example, when the color format of the current block is 4:4:4 or 4:2:2, the decoding device may perform step S2420 by determining whether the height of the luminance block is equal to or less than 8. Similarly, when the color format of the current block is 4:2:2, the decoding device may perform step S2420 by determining whether the height of the luminance block is equal to or less than 16.

[0290] Finally, when all the above conditions are met, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block (S2430). For example, when the current block is a chroma block and the height is equal to or less than 8, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual tree type, and the height is equal to or less than 8, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block.

[0291] Meanwhile, when the above-mentioned conditions are not satisfied, the decoding device may determine that horizontal trifurcated splitting is allowed for the current block. In this case, as described above, by determining the additional condition that horizontal trifurcated splitting is not allowed for the current block, the decoding device may determine whether horizontal trifurcated splitting is allowed for the current block (S2440). For example, when the number of times the current block is split from a quad leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowed hierarchical depth of a multi-type tree split from a quad leaf node, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, it may be determined that horizontal trifurcated splitting is allowed for the current block.

[0292] Example 3

[0293] As mentioned above, it is necessary to limit the minimum height of the chroma block to a length of four samples. Fig.25 A method of limiting horizontal binary splitting of a current block by an encoding / decoding apparatus according to an embodiment in order to limit a minimum height of a chroma block is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applicable to an encoding apparatus.

[0294] Fig.25 25 is a view illustrating a method for determining by a decoding device whether horizontal binary splitting (SPLIT_BT_HOR) is allowed for a current block. The decoding device according to an embodiment may determine whether the current block is a chroma block (S2510). As described above, the decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0295] In addition, the decoding device according to the embodiment can further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., DUAL_TREE_CHROMA) of the chroma component, the decoding device can determine that the current block is a chroma block and the tree type is a dual tree type.

[0296] Next, the decoding device according to the embodiment may determine whether the height of the current block is equal to or less than the length of 4 samples (S2520). When the value of the parameter specifying the height of the current block is equal to or less than 4, the decoding device may determine that the height of the current block is equal to or less than 4. Alternatively, as described above, the decoding device may perform step S2520 based on whether the height of the luminance block is equal to or less than 4 or 8 according to the color format of the current block. For example, when the color format of the current block is 4:4:4 or 4:2:2, the decoding device may perform step S2520 by determining whether the height of the luminance block is equal to or less than 4. Similarly, when the color format of the current block is 4:2:2, the decoding device may perform step S2520 by determining whether the height of the luminance block is equal to or less than 8.

[0297] Finally, when all the above conditions are met, the decoding device may determine that horizontal binary splitting is not allowed for the current block (S2530). For example, when the current block is a chroma block and the height is equal to or less than 4, the decoding device may determine that horizontal binary splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual tree type, and the height is equal to or less than 4, the decoding device may determine that horizontal binary splitting is not allowed for the current block.

[0298] Meanwhile, when the above-mentioned conditions are not satisfied, the decoding device may determine that horizontal binary splitting is allowed for the current block. In this case, as described above, by determining the additional condition that horizontal binary splitting is not allowed for the current block, the decoding device may determine whether horizontal binary splitting is allowed for the current block (S2540). For example, when the number of times the current block is split from a quad leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowed hierarchical depth of a multi-type tree split from a quad leaf node, the decoding device may determine that horizontal binary splitting is not allowed for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, it may be determined that horizontal binary splitting is allowed for the current block.

[0299] Example 4

[0300] As mentioned above, it is necessary to limit the minimum width of the chrominance block to a length of four pixels. Fig.26A method of limiting vertical binary division of a current block by an encoding / decoding apparatus according to an embodiment in order to limit a minimum width of a chroma block is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applicable to an encoding apparatus.

[0301] Fig.26 26 is a view illustrating a method for determining by a decoding device whether vertical binary splitting (SPLIT_BT_VER) is allowed for a current block. The decoding device according to an embodiment may determine whether the current block is a chroma block (S2610). As described above, the decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0302] In addition, the decoding device according to the embodiment can further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., DUAL_TREE_CHROMA) of the chroma component, the decoding device can determine that the current block is a chroma block and the tree type is a dual tree type.

[0303] Next, the decoding device according to the embodiment may determine whether the width of the current block is equal to or less than the length of 4 samples (S2620). When the value of the parameter specifying the width of the current block is equal to or less than 4, the decoding device may determine that the width of the current block is equal to or less than 4. Alternatively, as described above, the decoding device may perform step S2620 based on whether the width of the luminance block is equal to or less than 4 or 8 according to the color format of the current block. For example, when the color format of the current block is 4:4:4, the decoding device may perform step S2620 by determining whether the width of the luminance block is equal to or less than 4. Similarly, when the color format of the current block is 4:2:2 or 4:2:0, the decoding device may perform step S2620 by determining whether the width of the luminance block is equal to or less than 8.

[0304] Finally, when all the above conditions are met, the decoding device may determine that vertical binary splitting is not allowed for the current block (S2630). For example, when the current block is a chroma block and the width is equal to or less than 4, the decoding device may determine that vertical binary splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual tree type, and the width is equal to or less than 4, the decoding device may determine that vertical binary splitting is not allowed for the current block.

[0305] Meanwhile, when the above-mentioned conditions are not satisfied, the decoding device may determine that vertical binary splitting is allowed for the current block. In this case, as described above, by determining the additional condition that vertical binary splitting is not allowed for the current block, the decoding device may determine whether vertical binary splitting is allowed for the current block (S2640). For example, when the number of times the current block is split from a quad leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowed hierarchical depth of a multi-type tree split from a quad leaf node, the decoding device may determine that vertical binary splitting is not allowed for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, it may be determined that vertical binary splitting is allowed for the current block.

[0306] Example 5

[0307] As mentioned above, it is necessary to limit the minimum width or height of the chrominance block to 4 pixels. In the following, in order to limit the minimum width and height of the chrominance block, reference will be made to Fig. 27 A method of limiting quadtree partitioning of a current block by an encoding / decoding apparatus according to an embodiment is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applicable to an encoding apparatus.

[0308] Fig. 27 27 is a view illustrating a method for determining whether quadtree partitioning is allowed for a current block by a decoding device according to an embodiment. The decoding device according to an embodiment may determine whether the current block is a chroma block (S2710). The decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0309] In addition, the decoding device according to the embodiment can further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., DUAL_TREE_CHROMA) for the chroma component, the decoding device can determine that the current block is a chroma block and the tree type is a dual tree type.

[0310] Next, the decoding device according to the embodiment may determine whether the width or height of the current block is equal to or less than the length of 4 samples (S2720). When the value of the parameter specifying the width of the current block is equal to or less than 4, the decoding device may determine that the width of the current block is equal to or less than 4. Alternatively, as described above, the decoding device may perform step S2720 based on whether the width of the luminance block is equal to or less than 4 or 8 according to the color format of the current block. For example, when the color format of the current block is 4:4:4, the decoding device may perform step S2720 by determining whether the width of the luminance block is equal to or less than 4. In a similar manner, when the color format is 4:4:2 or 4:2:0, the decoding device may perform step S2720 by determining whether the width of the luminance block is equal to or less than 8.

[0311] Finally, when all the above conditions are met, the decoding device may determine that quadtree splitting is not allowed for the current block (S2730). For example, when the current block is a chroma block and the width or height is equal to or less than 4, the decoding device may determine that quadtree splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual tree type, and the width or height is equal to or less than 4, the decoding device may determine that quadtree splitting is not allowed for the current block.

[0312] Meanwhile, when the above-mentioned conditions are not satisfied, the decoding device may determine that quadtree splitting is allowed for the current block. In this case, as described above, by determining the additional condition that quadtree splitting is not allowed for the current block, the decoding device may determine whether quadtree splitting is allowed for the current block (S2740). For example, when the number of times the current block is split from a quadtree leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowed hierarchical depth of a multi-type tree split from a quadtree leaf node, the decoding device may determine that quadtree splitting is not allowed for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, the decoding device may determine that quadtree splitting is allowed.

[0313] Implementing performance improvements based on CCLM application restrictions

[0314] The encoding device and decoding device according to the embodiment can adaptively perform CCLM prediction according to the size of the chrominance block. As described above, since in CCLM prediction, the sample value of the chrominance block is generated based on the sample value of the luminance block, it is necessary to refer to the corresponding (e.g., co-located) luminance sample. Since CCLM prediction can be performed after encoding / decoding of all luminance samples is completed, delays in the hardware pipeline inevitably occur.

[0315] In addition, unlike a single tree block in which encoding / decoding of a co-located chroma block is performed after encoding / decoding of a luminance block, CCLM prediction in a dual tree in which luminance blocks and chroma blocks having a certain size or larger are independently encoded further deteriorates the hardware pipeline delay problem. In the worst case, in a dual tree CTU, CCLM prediction is performed in 256 CUs, which significantly affects throughput (e.g., data throughput) in hardware implementation.

[0316] Therefore, in order to reduce the data throughput of CCLM prediction, the encoding device and the decoding device according to the embodiment can determine whether to perform CCLM prediction according to the size of the chroma block when performing CCLM prediction. In addition, the encoding device and the decoding device can determine whether to perform CCLM prediction depending on whether the tree structure of the chroma block is a single tree or a double tree and the size of the chroma block.

[0317] More specifically, when the number of pixels (samples) of the chroma block is equal to or less than 16 when CCLM prediction is performed (first restriction condition), the encoding device and the decoding device according to the embodiment may restrict (e.g., prohibit) CCLM prediction. For example, the encoding device and the decoding device may not perform CCLM prediction with respect to chroma blocks of size 2×2, 2×4, 2×8, 4×2, 4×4, or 8×2. It has been experimentally confirmed that by performing CCLM prediction in this manner, the data throughput can be halved compared to the case where CCLM is performed without restricting the size of the chroma block with respect to all chroma blocks.

[0318] Alternatively, when performing CCLM prediction, the encoding device and the decoding device may limit CCLM prediction when the width of the chroma block is 2 samples in length (e.g., 2×N chroma block) (second restriction condition), and limit CCLM prediction when the height of the chroma block is 2 samples in length (e.g., N×2 chroma block) (third restriction condition).

[0319] In an embodiment, the encoding device and the decoding device may use a selective combination of the first restriction, the second restriction, and the third restriction. For example, the encoding device may use a combination of the first restriction and the second restriction, a combination of the first restriction and the third restriction, a combination of the second restriction and the third restriction, or a combination of the first restriction, the second restriction, and the third restriction.

[0320] An example of coding loss rate according to the above combination is Fig.28 and Fig.29 Shown in. Fig.28 is a view illustrating experimental results obtained in the case where only the first restriction condition is applied. Fig.29is a diagram illustrating experimental results obtained when all first, second and third constraints are applied. The experiment was performed on VTM5 software and for all frames based on the dual tree. Fig.28 As shown in the experimental results, coding losses of Y0.03%, Cb 0.53% and Cr 0.60% were observed in all intra-frame experiments applying only the first restriction condition.

[0321] In addition, if Fig.29 As shown in the experimental results, coding losses of Y 0.05%, Cb 0.75%, and Cr 0.83% were observed in all intra-frame experiments applying only the first to third constraints. Fig.29 In the experimental results of , the chroma blocks for which CCLM prediction is not performed are 2xN, Nx2, and 4x4 chroma blocks. Fig.28 and Fig.29 In the experimental example of , by limiting CCLM prediction in chroma blocks with a predetermined size, the data throughput for encoding chroma blocks can be reduced and the coding loss can be minimized.

[0322] Encoding method

[0323] Fig.30 is a flowchart illustrating a method for encoding an image by a decoding device according to an embodiment. The encoding device according to the embodiment may include a memory and at least one processor, and the encoding device may perform the following encoding method using at least one processor. Fig.30 The encoding method for executing the above-mentioned embodiment is described.

[0324] The encoding device according to the embodiment may select a partition structure of a current block composed of chrominance components (S3010). For example, the encoding device may select the partition structure of the current block as any one of a single tree structure determined by a partition type of a luminance component block corresponding to the current block and a dual tree structure determined independently of the partition type of the luminance component block corresponding to the current block.

[0325] In addition, after performing encoding of the current block under the single-tree structure and the dual-tree structure as described below, the encoding apparatus according to an embodiment may select a partition structure having a higher encoding rate as the partition structure of the current block.

[0326] In addition, even when a CTU having a single tree structure is partitioned into lower-layer blocks, the encoding device may change the partition structure of the lower-layer blocks of the CTU to a dual-tree structure according to a predetermined condition. In an embodiment, the encoding device may determine the partition structure of the chroma block to be a dual-tree structure so that in the process of partitioning the luminance block and the chroma block into the same partition type and generating the lower-layer block, when the size of the luminance block reaches the minimum divisible size, the chroma block is further partitioned. Therefore, even when the CTU has a single tree structure, the partition structure of the current block may be selected as a dual-tree structure.

[0327] Next, the encoding device according to the embodiment may select an available partition type of the current block based on the partition structure (S3020). For example, the encoding device may determine the partition type of the current block based on the available partition types determined based on the width or height of the current block.

[0328] In an embodiment, the encoding device may not allow a predetermined partition type in which the width or height of the lower layer block is a predetermined value among multiple partition types as an available partition type that can partition the current block. Therefore, the encoding device may determine the partition type of the current block as an available partition type other than the predetermined partition type among multiple partition types. The predetermined value may be greater than 0 and less than the value of the processing block per clock of the image encoding device. In this case, the encoding device may determine whether to allow the predetermined partition type as an available partition type by further considering whether the partition structure of the current block is a single tree structure or a dual tree structure.

[0329] The width of the current block may be determined based on the color format and width of the luma block corresponding to the current block. For example, the width of the current block may be determined as a value obtained by dividing the width of the luma block corresponding to the current block by a component ratio of chroma samples to luma samples derived based on the color format. The width of the lower layer block may be determined by dividing the width of the current block according to the partition type of the current block.

[0330] For example, when the size of the processing block per clock of the image encoding device is 4×1, when the width of the current block is 4, the encoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block, and when the width of the current block is 8, the vertical trigeminal partition type may not be allowed as the partition type of the current block.

[0331] More specifically, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 4, and the color format of the luminance block is 4:4:4, the encoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block.

[0332] In addition, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 8, and the color format of the luminance block is 4:2:2 or 4:2:0, the encoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block.

[0333] In addition, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 8, and the color format of the luminance block is 4:4:4, the encoding device may not allow the vertical trifurcated partition type as the partition type of the current block.

[0334] In addition, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 16, and the color format of the luminance block is 4:2:2 or 4:2:0, the encoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block.

[0335] In addition, when the partition structure of the current block is a dual tree structure and the width of the current block is equal to or less than 4, the encoding apparatus may not allow a quadtree partition type and a vertical binary partition type as the partition type of the current block.

[0336] In addition, when the partition structure of the current block is a dual-tree structure and the width of the current block is equal to or less than 8, the encoding apparatus may not allow a vertical trifurcated partition type as a partition type of the current block.

[0337] In addition, when the size of the processing block per clock of the image decoding device is 1×4 and the height of the current block is 4, the encoding device may not allow the quadtree partition type and the horizontal binary partition type as the partition type of the current block. In this case, the decoding device can determine whether to allow the partition type by further considering whether the partition structure of the current block is a single tree structure or a dual tree structure.

[0338] In addition, when the size of the processing block per clock of the image decoding device is 1×4 and the height of the current block is 8, the encoding device may not allow the horizontal trifurcated partition type as the partition type of the current block. In this case, the decoding device may determine whether to allow the partition type by further considering whether the partition structure of the current block is a single tree structure or a dual tree structure.

[0339] Next, the encoding device may obtain a plurality of lower-layer blocks by segmenting the current block based on the available segmentation types determined as described above (S3030). The encoding device may encode the current block by applying the allowed segmentation types among the above-mentioned quadtree and multi-tree segmentation types, and calculate the RD cost according to each segmentation type. The encoding device may determine the segmentation mode applied to the current block according to the RD cost determined based on each segmentation mode. For example, when the segmentation of the horizontal trident mode is allowed for the current block, the encoding device may determine to apply the horizontal trident mode as the segmentation mode of the current block, and calculate the optimal RD cost when the current block is segmented and encoded with the corresponding type.

[0340] The encoding device may encode the current block using the lower layer blocks obtained by partitioning the current block into the partition type determined to be applied to the current block. The encoding device may perform the above-mentioned intra-frame, inter-frame or IBC prediction based on the lower layer block to generate prediction information, generate residual information according to the prediction result, and encode the current block by encoding the prediction information and the residual information.

[0341] Next, the encoding device may encode the prediction mode information of the lower layer block and the partition information of the current block based on the result of encoding the lower layer block (S3040). The encoding device may encode the information about the partitioning of the current block and the information about the prediction so as to represent the partition structure and the partition type of the current block. For example, the encoding device may generate a bitstream by encoding information about the partition structure of the CTU constituting the current image (e.g., sps_qtbtt_dual_tree_intra_flag). In an embodiment, when the CTU is partitioned in a single tree structure, the encoding device may encode sps_qtbtt_dual_tree_intra_flag as a first value (e.g., 0) specifying that the CTU is partitioned in a single tree structure. Alternatively, when the CTU is partitioned in a dual tree structure, the encoding device may encode sps_qtbtt_dual_tree_intra_flag as a second value (e.g., 1) specifying that the CTU is partitioned in a dual tree structure.

[0342] In addition, as described above, the encoding device may use qt_split_flag to specify whether the current block is divided into a quadtree structure. When the current block is divided into a quadtree, the encoding device may set qt_split_flag to a first value (e.g., 1) and perform encoding. When the current block is not divided into a quadtree, the encoding device may set qt_split_flag to a second value (e.g., 0) and perform encoding.

[0343] In this embodiment, when the current block is not partitioned into quadtrees but partitioned into multitrees, the encoding apparatus may specify whether the current block is partitioned into multitrees using mtt_split_cu_flag which is multitree partition information.

[0344] When the current block is partitioned into multiple trees, the encoding apparatus may set mtt_split_cu_flag to a first value (eg, 1) and perform encoding. When the current block is not partitioned into multiple trees, the encoding apparatus may set mtt_split_cu_flag to a second value (eg, 0) and perform encoding.

[0345] In addition, the encoding device may encode mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag to specify the multi-tree partition type and multi-tree partition direction of the current block. For example, mtt_split_cu_vertical_flag may be set to a first value (e.g., 0) when the current block is partitioned in the horizontal direction and set to a second value (e.g., 1) when the current block is partitioned in the vertical direction. mtt_split_cu_binary_flag may be set to a first value (e.g., 0) when the current block is partitioned into a ternary tree and may be set to a second value (e.g., 1) when the current block is partitioned into a binary tree.

[0346] At the same time, if Fig.31 As shown, the encoding device can encode information about the partition of the current block by encoding split_cu_flag (3110) as partition information specifying whether the current block is partitioned, split_cu_flag (3120) as quadtree partition information specifying whether to perform quadtree partition of the current block, mtt_split_cu_vertical_flag (3130) as partition direction information specifying the partition direction of the current block in the multi-tree structure, and mtt_split_cu_binary_flag (3140) as partition type information specifying whether the partition type of the current block is a binary partition type or a ternary partition type in the multi-tree structure.

[0347] As described above, split_cu_flag (3110) may be set to a first value (e.g., 0) when the current block is not split, and may be set to a second value (e.g., 1) when the current block is split into lower-layer blocks. split_qt_flag (3120) may be set to a first value (e.g., 0) when the current block is split into a quadtree, and may be set to a second value (e.g., 1) when the current block is not split into a quadtree but is split into a multitree. mtt_split_cu_vertical_flag (3130) may be set to a first value (e.g., 0) when the current block is split in the horizontal direction, and may be set to a second value (e.g., 1) when the current block is split in the vertical direction. mtt_split_cu_binary_flag (3140) may be set to a first value (e.g., 0) when the current block is split into a ternary tree, and may be set to a second value (e.g., 1) when the current block is split into a binary tree.

[0348] The encoding device may encode information about the partition of the current block based on whether the predetermined partition is allowed for the current block. For example, when both quadtree partitioning and multitree partitioning are allowed for the current block, the encoding device may not encode split_cu_flag. In this case, the decoding device may derive split_cu_flag as a predetermined value.

[0349] In addition, when quadtree partitioning is allowed for the current block but multi-tree partitioning is not allowed, the encoding device may not encode qt_split_flag. In this case, the decoding device may derive qt_split_flag as a predetermined value.

[0350] In addition, when qt_split_flag specifies to perform quadtree splitting, horizontal binary splitting and horizontal ternary splitting are not allowed for the current block, or vertical binary splitting and vertical ternary splitting are not allowed, the encoding device may not encode mtt_split_cu_vertical_flag. In this case, the decoding device may derive mtt_split_cu_vertical_flag as a predetermined value.

[0351] In addition, when qt_split_flag specifies that quadtree splitting is performed, or vertical binary splitting or vertical ternary splitting is not allowed for the current block, or mtt_split_cu_vertical_flag specifies horizontal splitting and horizontal binary splitting or horizontal ternary splitting is not allowed for the current block, or mtt_split_cu_vertical_flag specifies vertical splitting, the encoding device may not encode mtt_split_cu_binary_flag. In this case, the decoding device may derive mtt_split_cu_binary_flag as a predetermined value.

[0352] BitTorrent

[0353] Reference Fig.31 The method for generating a bitstream by an encoding device is described in more detail. The encoding device may determine whether to split the current block based on the above embodiment. More specifically, the encoding device may determine the value of a parameter allowSplitTtVer that specifies whether vertical trifurcated splitting is allowed for the current block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0354] In addition, the encoding device can determine the value of the parameter allowSplitTtHor that specifies whether horizontal trisection splitting is allowed for the current block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0355] In addition, the encoding device can determine the value of the parameter allowSplitBtVer that specifies whether vertical binary splitting is allowed for the current block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0356] In addition, the encoding device can determine the value of the parameter allowSplitBtHor that specifies whether horizontal binary splitting is allowed for the current block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0357] According to the determination, the encoding device may determine whether at least one of split_cu_flag (3110), qt_split_flag (3120), mtt_split_cu_vertical_flag (3130), or mtt_split_cu_binary_flag (3140) as the segmentation information of the current block is output as a bitstream, as described above with reference to Fig.31 described.

[0358] Decoding method

[0359] Fig.32 is a flowchart illustrating a method for decoding an image by a decoding device according to an embodiment. Fig.32 The decoding method for executing the above-mentioned embodiment is described. The decoding apparatus according to the embodiment may include a memory and at least one processor, and the decoding apparatus may execute the following decoding method using the at least one processor.

[0360] The decoding device according to the embodiment may determine the partition structure of the current block composed of chrominance components (S3210). For example, the decoding device may determine whether the partition structure of the current block is a single tree structure determined by the partition type of the luminance component block corresponding to the current block or a dual tree structure determined independently of the partition type of the luminance component block corresponding to the current block.

[0361] For example, the decoding device may obtain information about the partition structure of the CTU constituting the current image (e.g., sps_qtbtt_dual_tree_intra_flag). In an embodiment, sps_qtbtt_dual_tree_intra_flag may indicate that the CTU is partitioned in a single tree structure. In this case, the decoding device may determine the partition structure of the current block generated by partitioning the CTU as a single tree structure. Alternatively, sps_qtbtt_dual_tree_intra_flag may indicate that the CTU is partitioned in a dual tree structure. In this case, the decoding device may determine the partition structure of the current block generated by partitioning the CTU as a dual tree structure.

[0362] In addition, even when a CTU having a single tree structure is divided into lower layer blocks, the encoding device may change the partition structure of the lower layer block of the CTU to a dual tree structure according to a predetermined condition. In an embodiment, the decoding device may determine the partition structure of the chroma block to be a dual tree structure so that in the process of partitioning the luminance block and the chroma block into the same partition type and generating the lower layer block, when the size of the luminance block reaches the minimum divisible size, the chroma block is further partitioned.

[0363] Next, the decoding apparatus may determine the partition type of the current block based on the partition structure of the current block (S3220). For example, the decoding apparatus may determine the partition type of the current block based on the available partition types determined based on the width or height of the current block.

[0364] In an embodiment, the decoding device may not allow a predetermined partition type in which the width or height of the lower layer block is a predetermined value among multiple partition types as an available partition type that can partition the current block. Therefore, the decoding device may determine the partition type of the current block as an available partition type other than the predetermined partition type among multiple partition types. The predetermined value may be greater than 0 and less than the value of the processing block per clock of the image decoding device. In this case, the encoding device may determine whether to allow the predetermined partition type as an available partition type by further considering whether the partition structure of the current block is a single tree structure or a dual tree structure.

[0365] The width of the current block may be determined based on the color format and width of the luma block corresponding to the current block. For example, the width of the current block may be determined as a value obtained by dividing the width of the luma block corresponding to the current block by a component ratio of chroma samples to luma samples derived based on the color format. The width of the lower layer block may be determined by dividing the width of the current block according to the partition type of the current block.

[0366] For example, when the size of the processing block per clock of the image decoding device is 4×1, when the width of the current block is 4, the decoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block, and when the width of the current block is 8, the vertical trigeminal partition type may not be allowed as the partition type of the current block.

[0367] More specifically, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 4, and the color format of the luminance block is 4:4:4, the decoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block.

[0368] In addition, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 8, and the color format of the luminance block is 4:2:2 or 4:2:0, the decoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block.

[0369] In addition, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 8, and the color format of the luminance block is 4:4:4, the decoding device may not allow the vertical trifurcated partition type as the partition type of the current block.

[0370] In addition, when the partition structure of the current block is a single tree structure, the width of the luminance block corresponding to the current block is equal to or less than 16, and the color format of the luminance block is 4:2:2 or 4:2:0, the decoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the current block.

[0371] In addition, when the partition structure of the current block is a dual tree structure and the width of the current block is equal to or less than 4, the decoding apparatus may not allow a quadtree partition type and a vertical binary partition type as the partition type of the current block.

[0372] In addition, when the partition structure of the current block is a dual-tree structure and the width of the current block is equal to or less than 8, the decoding apparatus may not allow a vertical trifurcated partition type as a partition type of the current block.

[0373] In addition, when the size of the processing block per clock of the image decoding device is 1×4 and the height of the current block is 4, the decoding device may not allow the quadtree partition type and the horizontal binary partition type as the partition type of the current block. In this case, the decoding device can determine whether to allow the partition type by further considering whether the partition structure of the current block is a single tree structure or a dual tree structure.

[0374] In addition, when the size of the processing block per clock of the image decoding device is 1×4 and the height of the current block is 8, the decoding device may not allow the horizontal trifurcated partition type as the partition type of the current block. In this case, as described above, the decoding device can determine whether to allow the partition type by further considering whether the partition structure of the current block is a single tree structure or a dual tree structure.

[0375] According to the above determination, the decoding device can determine the partition type of the current block by determining an available partition type other than a predetermined partition type among multiple partition types. For example, the decoding device can obtain partition information from the bitstream based on the available partition types, and determine the partition type of the current block based on the obtained partition information.

[0376] More specifically, the decoding device may obtain or derive information about the partitioning of the current block from the bitstream based on whether the predetermined partitioning is allowed. Fig.31 When the predetermined split is allowed, the decoding apparatus may obtain at least one of split_cu_flag (3110), split_qt_flag (3120), mtt_split_cu_vertical_flag (3130), or mtt_split_cu_binary_flag (3140), which is information about the split of the current block, from the bitstream by parsing the bitstream.

[0377] Meanwhile, when the predetermined segmentation is not allowed, the decoding device may determine the information about the segmentation of the current block as a value specifying a segmentation other than the predetermined segmentation. For example, when the predetermined segmentation is not allowed, the information about the segmentation of the current block may be derived as a predetermined value without being obtained from the bitstream. For example, the split_cu_flag specifying whether to perform the segmentation may be derived as 0.

[0378] In an embodiment, when the value of split_cu_flag is 1, and based on the above embodiment, all vertical trisection splitting, horizontal trisection splitting, vertical binary splitting and horizontal binary splitting are not allowed for the current block, split_qt_flag specifying whether to perform quadtree splitting can be exported as 1, otherwise, it can be exported as 0.

[0379] When horizontal trisection splitting or horizontal binary splitting is allowed for the current block, mtt_split_cu_vertical_flag, which is split direction information, may be derived as 0, and otherwise, may be derived as 1.

[0380] When vertical binary splitting and horizontal binary splitting are not allowed for the current block, mtt_split_cu_binary_flag as the splitting type information can be exported as 0, and when vertical trisection splitting and horizontal trisection splitting are not allowed for the current block, it can be exported as 1, when horizontal binary splitting and vertical trisection splitting are allowed for the current block, it can be exported as 1-mtt_split_cu_vertical_flag value, and when vertical binary splitting and horizontal trisection splitting are allowed for the current block, it can be exported as the value of mtt_split_cu_vertical_flag.

[0381] As described above, the decoding apparatus may determine the partition type of the current block as a partition mode corresponding to any one of the quadtree or the multitree based on split_qt_flag (3120), mtt_split_cu_vertical_flag (3130), and mtt_split_cu_binary_flag (3140) and Table 1.

[0382] Next, the decoding device according to the embodiment may obtain a plurality of lower layer blocks by segmenting the current block based on the segmentation type (S3230). The decoding device may decode the lower layer block based on the prediction mode of the lower layer block (S3240). For example, the decoding device may decode the image by performing the above-mentioned intra / inter / IBC prediction based on the lower layer block. In an embodiment, when IBC prediction is performed to perform prediction of a chroma block, the decoding device may derive a motion vector of the chroma block from the luminance block by applying the above-mentioned embodiment.

[0383] Application Examples

[0384] Although for the sake of clarity of description, the exemplary method of the present disclosure described above is represented as a series of operations, it is not intended to limit the order of executing the steps, and these steps can be performed simultaneously or in different orders when necessary. In order to implement the method according to the present invention, the steps described may further include other steps, may include the remaining steps except some steps, or may include other additional steps except some steps.

[0385] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) may perform an operation (step) of confirming an execution condition or situation of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is met, the image encoding device or the image decoding device may perform the predetermined operation after determining whether the predetermined condition is met.

[0386] The various embodiments of the present disclosure are not a list of all possible combinations and are intended to describe representative aspects of the present disclosure, and matters described in the various embodiments may be applied independently or in combination of two or more.

[0387] Various embodiments of the present disclosure may be implemented in hardware, firmware, software or a combination thereof. In the case of implementing the present disclosure in hardware, the present disclosure may be implemented in an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a general purpose processor, a controller, a microcontroller, a microprocessor, etc.

[0388] In addition, the image decoding device and the image encoding device of the embodiment of the present disclosure can be included in multimedia broadcast transmission and reception equipment, mobile communication terminals, home theater video equipment, digital theater video equipment, surveillance cameras, video chat equipment, real-time communication equipment such as video communication, mobile streaming equipment, storage media, cameras, video on demand (VoD) service providing equipment, OTT video (over the top video) equipment, Internet streaming service providing equipment, three-dimensional (3D) video equipment, video phone video equipment, medical video equipment, etc., and can be used to process video signals or data signals. For example, OTT video equipment can include game consoles, Blu-ray players, Internet access TVs, home theater systems, smart phones, tablet PCs, digital video recorders (DVRs), etc.

[0389] Fig.33 is a view showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0390] like Fig.33As shown in , a content streaming transmission system to which an embodiment of the present disclosure is applied may mainly include an encoding server, a streaming transmission server, a network server, a media storage, a user device, and a multimedia input device.

[0391] The encoding server compresses the content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server can be omitted.

[0392] A bitstream may be generated by applying the image encoding method or the image encoding device according to the embodiment of the present disclosure, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0393] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server serves as a medium to notify the user of the service. When the user requests the required service from the network server, the network server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server serves as a command / response between devices in the control content streaming system.

[0394] The streaming server may receive content from a media storage and / or encoding server. For example, when content is received from an encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

[0395] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, tablet PCs, tablet computers, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0396] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0397] The scope of the present disclosure includes software or executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations according to the methods of various embodiments to be performed on a device or computer, and a non-transitory computer-readable medium having such software or commands stored thereon and executable on a device or computer.

[0398] Industrial Applicability

[0399] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising: determining a partitioning structure of a current block composed of chrominance components; Based on the segmentation structure, determining a segmentation type of the current block; Based on the segmentation type, obtaining a plurality of lower-layer blocks by segmenting the current block; as well as Decoding the lower layer block based on the prediction mode of the lower layer block, wherein determining the partition type of the current block is performed by determining the partition type of the current block based on available partition types, the available partition types being determined based on a width or a height of the current block, wherein, based on the fact that the partition structure of the current block is a dual-tree structure and the width of the current block is 8, a vertical trifurcated partition type is not allowed as the partition type of the current block, regardless of the height of the current block, and Wherein, based on the fact that the partition structure of the current block is a dual-tree structure and the height of the current block is 8, a horizontal three-branch partition type is allowed as the partition type of the current block having a width greater than 4.

2. The image decoding method according to claim 1, wherein: The partition type of the current block is determined based on partition information obtained from a bitstream based on the available partition types.

3. The image decoding method according to claim 1, in, determining the available partition type by not allowing a predetermined partition type based on the width or height of the current block being equal to or less than a predetermined value, and The predetermined value is determined based on the number of pixels processed per clock by the image decoding device.

4. The image decoding method according to claim 1, wherein: Based on the width of the current block being 4, a quadtree partition type and a vertical binary partition type are not allowed to be the partition type of the current block.

5. The image decoding method according to claim 1, wherein: Based on the image decoding apparatus performing an image processing process on a pixel set consisting of a 1×4 matrix per clock and the height of the current block being 8, a horizontal trifurcated partition type is not allowed as the partition type of the current block.

6. The image decoding method according to claim 1, wherein: Based on the image decoding apparatus performing an image processing process on a pixel set consisting of a 1×4 matrix per clock and the height of the current block being 4, a quadtree partition type and a horizontal binary partition type are not allowed as the partition type of the current block.

7. The image decoding method according to claim 1, wherein: The width of the current block is determined based on a width and a color format of a luma block corresponding to the current block.

8. The image decoding method according to claim 7, wherein: The width of the current block is determined as a value obtained by dividing a width of the luma block corresponding to the current block by a component ratio of chroma samples to luma samples derived based on the color format.

9. An image encoding method performed by an image encoding device, the image encoding method comprising: Selecting a partitioning structure for a current block consisting of chrominance components; Based on the segmentation structure, selecting an available segmentation type for the current block; Based on the available segmentation types, obtaining a plurality of lower-layer blocks by segmenting the current block; as well as Based on the result of encoding the lower layer block, encoding the prediction mode information of the lower layer block and the partition information of the current block, wherein the available segmentation type of the current block is determined based on the width or height of the current block, wherein, based on the fact that the partition structure of the current block is a dual-tree structure and the width of the current block is 8, a vertical trifurcated partition type is not allowed as the partition type of the current block, regardless of the height of the current block, and Wherein, based on the fact that the partition structure of the current block is a dual-tree structure and the height of the current block is 8, a horizontal three-branch partition type is allowed as the partition type of the current block having a width greater than 4.

10. The image encoding method according to claim 9, in, determining the available partition types by limiting use of predetermined partition types based on the width or height of the current block being equal to or less than a predetermined value, and Wherein, according to the predetermined segmentation type, the predetermined value is determined depending on whether a value obtained by dividing the width or height of the current block is less than 4.

11. A method for transmitting a bit stream, comprising: sending said bit stream generated by the image encoding method, Wherein, the image encoding method comprises: Selecting a partitioning structure for a current block consisting of chrominance components; Based on the segmentation structure, selecting an available segmentation type for the current block; Based on the available partition types, obtaining a plurality of lower-layer blocks by partitioning the current block; and Based on the result of encoding the lower layer block, encoding the prediction mode information of the lower layer block and the partition information of the current block, wherein the available segmentation type of the current block is determined based on the width or height of the current block, wherein, based on the fact that the partition structure of the current block is a dual-tree structure and the width of the current block is 8, a vertical trifurcated partition type is not allowed as the partition type of the current block, regardless of the height of the current block, and Wherein, based on the fact that the partition structure of the current block is a dual-tree structure and the height of the current block is 8, a horizontal three-branch partition type is allowed as the partition type of the current block having a width greater than 4.

Images