KR20210091673A - Video Encoding and Decoding Using Adaptive Color Transform - Google Patents

Abstract

This disclosure relates to video encoding and decoding using adaptive color transform on a residual signal. According to an aspect of the present disclosure, depending on a syntax element indicating a maximum transform size allowed for a sequence of pictures, the allowance of color space transform is controlled at a sequence level, or depending on the size of a coding block the application of color space transform is controlled at the block level. Thereby, the maximum amount of memory required by adaptive color transform is limited. A method for decoding video data includes the steps of: obtaining first residual data; determining whether to apply a color space transform to the first residual data; generating second residual data; generating a prediction block; and generating a restored block.

Description

Video Encoding and Decoding Using Adaptive Color Transform

The present invention relates to video encoding and decoding. More specifically, it relates to video encoding and decoding using adaptive color transforms on residual signals.

Since video data has a large amount of data compared to audio data or still image data, it requires a lot of hardware resources including memory to store or transmit itself without compression processing.

Therefore, in general, when storing or transmitting video data, an encoder is used to compress and store or transmit the video data, and a decoder receives, decompresses, and reproduces the compressed video data. As such a video compression technology, H.264/AVC and High Efficiency Video Coding (HEVC), which improves encoding efficiency by about 40% compared to H.264/AVC, exist.

However, as the size, resolution, and frame rate of each picture constituting a video are gradually increasing, and accordingly, the amount of data to be encoded is also increasing. Therefore, a new compression technique with better encoding efficiency and higher picture quality than existing compression techniques. this is required

This disclosure presents several improved ways of efficiently operating adaptive color conversion, including reducing the maximum memory size required by adaptive color conversion.

One aspect of the present disclosure provides a method of decoding video data. The decoding method may include: obtaining first residual data for a current block from a bitstream; determining whether to apply color space conversion to the first residual data based on a color conversion control flag of a higher level and a color conversion control flag of a block level; in response to determining that a color space transform is applied to the first residual data, performing an inverse color transform on the first residual data to generate second residual data; generating a prediction block for the current block; and generating a reconstructed block for the current block based on the prediction block and the second residual data.

Another aspect of the present disclosure provides an apparatus for decoding video data including one or more processors. The one or more processors are configured to: obtain first residual data for a current block from the bitstream; determine whether to apply color space transformation to the first residual data based on a color conversion control flag of a higher level and a color conversion control flag of a block level; in response to determining that a color space transform is applied to the first residual data, perform an inverse color transform on the first residual data to generate second residual data; and generate a prediction block for the current block, and generate a reconstructed block for the current block based on the prediction block and the second residual data.

The upper-level color conversion control flag is signaled in the bitstream depending on a maximum conversion size allowed for a sequence of pictures including the current block, and the block-level color conversion control flag is the upper-level color conversion control flag. Signaled in the bitstream depending on a flag, the upper-level color conversion control flag and the block-level color conversion control flag are inferred to be false when not signaled in the bitstream.

According to another aspect of the present disclosure, a method of decoding video data includes: decoding a syntax element indicating a maximum transform size allowed for a sequence of pictures of video data from a bitstream; decoding a first control flag indicating whether application of a color space transform is permitted to blocks in the sequence from the bitstream when the maximum transform size is smaller than 64 indicated by the syntax element; and a second indicating whether the color space transformation is applied to a current block in the sequence from the bitstream when the first control flag indicates that application of the color space transformation is permitted to the blocks in the sequence. and decoding the control flag. The method reconstructs first residual data for a current block from the bitstream and inverse color transform on the first residual data when the second control flag indicates that the color space transform is applied to the current block. to generate second residual data; generating a prediction block for the current block; and generating a reconstructed block for the current block based on the prediction block and the second residual data.

1 is an exemplary block diagram of a video encoding apparatus that may implement the techniques of this disclosure.
2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.
3 is a diagram illustrating a plurality of intra prediction modes.
4 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of the present disclosure.
5 is a schematic diagram of a video decoder employing adaptive color conversion that may be used in the techniques of this disclosure.
6 is a flowchart illustrating a method of encoding video data according to an aspect of the present disclosure.
7 is a flowchart illustrating a method of decoding video data according to an aspect of the present disclosure.
8 is a flowchart illustrating a method of decoding video data according to another aspect of the present disclosure.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that in adding identification codes to the components of each drawing, the same components are to have the same reference numerals as much as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is an exemplary block diagram of a video encoding apparatus that may implement the techniques of this disclosure. Hereinafter, a video encoding apparatus and sub-components of the apparatus will be described with reference to FIG. 1 .

The video encoding apparatus includes a picture division unit 110 , a prediction unit 120 , a subtractor 130 , a transform unit 140 , a quantization unit 145 , a reordering unit 150 , an entropy encoding unit 155 , and an inverse quantization unit. 160 , an inverse transform unit 165 , an adder 170 , a loop filter unit 180 , and a memory 190 may be included.

Each component of the video encoding apparatus may be implemented as hardware or software, or a combination of hardware and software. In addition, the function of each component may be implemented in software and the microprocessor may be implemented to execute the function of the software corresponding to each component.

One video (video) is composed of a plurality of pictures. Each picture is divided into a plurality of regions, and encoding is performed for each region. For example, one picture is divided into one or more tiles and/or slices. Here, one or more tiles may be defined as a tile group. Each tile or/slice is divided into one or more Coding Tree Units (CTUs). And each CTU is divided into one or more CUs (Coding Units) by a tree structure. Information applied to each CU is encoded as a syntax of the CU, and information commonly applied to CUs included in one CTU is encoded as a syntax of the CTU. In addition, information commonly applied to all blocks in one slice is encoded as a syntax of a slice header, and information applied to all blocks constituting one or more pictures is a picture parameter set (PPS) or a picture. encoded in the header. Furthermore, information commonly referred to in a sequence composed of a plurality of pictures is encoded in a sequence parameter set (SPS). Also, information commonly applied to one tile or tile group may be encoded as a syntax of a tile or tile group header.

The picture divider 110 determines the size of a coding tree unit (CTU). Information on the size of the CTU (CTU size) is encoded as a syntax of the SPS or PPS and transmitted to the video decoding apparatus.

The picture divider 110 divides each picture constituting a video into a plurality of coding tree units (CTUs) having a predetermined size, and then repeatedly divides the CTUs using a tree structure. (recursively) divide. A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of encoding.

As a tree structure, a quadtree (QT) in which a parent node (or parent node) is divided into four child nodes (or child nodes) of the same size, or a binary tree (BinaryTree) in which a parent node is divided into two child nodes , BT), or a ternary tree (TT) in which a parent node is divided into three child nodes in a 1:2:1 ratio, or a structure in which two or more of these QT structures, BT structures, and TT structures are mixed there is. For example, a QuadTree plus BinaryTree (QTBT) structure may be used, or a QuadTree plus BinaryTree TernaryTree (QTBTTT) structure may be used. Here, BTTT may be collectively referred to as a Multiple-Type Tree (MTT).

2 shows the QTBTTT split tree structure. As shown in FIG. 2 , the CTU may be first divided into a QT structure. The quadtree splitting may be repeated until the size of a splitting block reaches the minimum block size (MinQTSize) of a leaf node allowed in QT. A first flag (QT_split_flag) indicating whether each node of the QT structure is split into four nodes of a lower layer is encoded by the entropy encoder 155 and signaled to the video decoding apparatus. If the leaf node of the QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in the BT, it may be further divided into any one or more of the BT structure or the TT structure. A plurality of division directions may exist in the BT structure and/or the TT structure. For example, there may be two directions in which the block of the corresponding node is divided horizontally and vertically. As shown in FIG. 2 , when MTT splitting starts, a second flag (mtt_split_flag) indicating whether or not nodes are split, and a flag indicating additionally split directions (vertical or horizontal) and/or split type (Binary or Ternary) ) is encoded by the entropy encoder 155 and signaled to the video decoding apparatus. Alternatively, before encoding the first flag (QT_split_flag) indicating whether each node is split into four nodes of a lower layer, a CU split flag (split_cu_flag) indicating whether the node is split is encoded could be When the CU split flag (split_cu_flag) value indicates that it is not split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a coding unit (CU), which is a basic unit of coding. When the CU split flag (split_cu_flag) value indicates to be split, the video encoding apparatus starts encoding from the first flag in the above-described manner.

When QTBT is used as another example of the tree structure, there are two types of splitting the block of the corresponding node into two blocks of the same size horizontally (ie, symmetric horizontal splitting) and vertically (ie, symmetric vertical splitting). branches may exist. A split flag (split_flag) indicating whether each node of the BT structure is split into blocks of a lower layer and split type information indicating a split type are encoded by the entropy encoder 155 and transmitted to the video decoding apparatus. On the other hand, there may be additionally a type in which the block of the corresponding node is divided into two blocks having an asymmetric shape. The asymmetric form may include a form in which the block of the corresponding node is divided into two rectangular blocks having a size ratio of 1:3, or a form in which the block of the corresponding node is divided in a diagonal direction.

A CU may have various sizes depending on the QTBT or QTBTTT split from the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (ie, a leaf node of QTBTTT) is referred to as a 'current block'. Depending on the adoption of QTBT or QTBTTT partitioning, the shape of the current block may be rectangular as well as square.

The prediction unit 120 generates a prediction block by predicting the current block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124 .

The intra prediction unit 122 predicts pixels in the current block by using pixels (reference pixels) located around the current block in the current picture including the current block. A plurality of intra prediction modes exist according to a prediction direction. For example, as shown in FIG. 3A , the plurality of intra prediction modes may include two non-directional modes including a planar mode and a DC mode and 65 directional modes. According to each prediction mode, the neighboring pixels to be used and the formula are defined differently.

The intra prediction unit 122 may determine an intra prediction mode to be used for encoding the current block. In some examples, the intra prediction unit 122 may encode the current block using several intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, the intra prediction unit 122 calculates rate-distortion values using rate-distortion analysis for several tested intra prediction modes, and has the best rate-distortion characteristics among the tested modes. An intra prediction mode may be selected.

The intra prediction unit 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts the current block by using a neighboring pixel (reference pixel) determined according to the selected intra prediction mode and an equation. Information on the selected intra prediction mode is encoded by the entropy encoder 155 and transmitted to the video decoding apparatus.

The inter prediction unit 124 generates a prediction block for the current block through a motion compensation process. The inter prediction unit 124 searches for a block most similar to the current block in the coded and decoded reference picture before the current picture, and generates a prediction block for the current block by using the found block. Then, a motion vector corresponding to the displacement between the current block in the current picture and the prediction block in the reference picture is generated. In general, motion estimation is performed for a luma component, and a motion vector calculated based on the luma component is used for both the luma component and the chroma component. Motion information including information on a reference picture and information on a motion vector used to predict the current block is encoded by the entropy encoder 155 and transmitted to the video decoding apparatus. The inter prediction unit 124 may perform interpolation on a reference picture or reference block in order to increase prediction accuracy. That is, sub-pixels between two consecutive integer pixels are interpolated by applying filter coefficients to a plurality of consecutive integer pixels including the two integer pixels. When the process of searching for a block most similar to the current block is performed with respect to the interpolated reference picture, the motion vector may be expressed up to the precision of the decimal unit rather than the precision of the integer pixel unit. The precision or resolution of the motion vector may be set differently for each unit of a target region to be encoded, for example, a slice, a tile, a CTU, or a CU.

The subtractor 130 generates a residual block by subtracting the prediction block generated by the intra prediction unit 122 or the inter prediction unit 124 from the current block.

The transform unit 140 may transform the residual signals in the residual block. The two-dimensional size of the residual block may be used as a transform unit (hereinafter, 'TU'), which is a block size for performing transformation. Alternatively, a residual block may be divided into a plurality of subblocks and residual signals in the corresponding subblock may be transformed by using each subblock as a TU.

The transform unit 140 divides the residual block into one or more subblocks and applies a transform to the one or more subblocks to transform the residual values of the transform blocks from the pixel domain to the frequency domain. In the frequency domain, transformed blocks are referred to as coefficient blocks or transform blocks including one or more transform coefficient values. A two-dimensional transform kernel may be used for the transform, and a one-dimensional transform kernel may be used for each of the horizontal transform and the vertical direction. The transform kernel may be based on a discrete cosine transform (DCT), a discrete sine transform (DST), or the like.

The transform unit 140 may separately transform the residual block or transform unit in a horizontal direction and a vertical direction. For transformation, various types of transformation kernels or transformation matrices may be used. For example, a pair of transform kernels for horizontal transformation and vertical transformation may be defined as a multiple transform set (MTS). The transform unit 140 may select one transform kernel pair having the best transform efficiency among MTSs and transform the residual blocks in horizontal and vertical directions, respectively. The information (mts_idx) on the transform kernel pair selected from the MTS is encoded by the entropy encoder 155 and signaled to the video decoding apparatus.

The quantization unit 145 quantizes the transform coefficients output from the transform unit 140 using a quantization parameter, and outputs the quantized transform coefficients to the entropy encoding unit 155 . The quantization unit 145 may directly quantize a related residual block for a certain block or frame without transformation. The quantization unit 145 may apply different quantization coefficients (scaling values) according to positions of the transform coefficients in the transform block. A matrix of quantization coefficients applied to two-dimensionally arranged quantized transform coefficients may be encoded and signaled to a video decoding apparatus.

The reordering unit 150 may rearrange the coefficient values on the quantized residual values. The reordering unit 150 may change a two-dimensional coefficient array into a one-dimensional coefficient sequence through coefficient scanning. For example, the reordering unit 150 may output a one-dimensional coefficient sequence by scanning from DC coefficients to coefficients in a high frequency region using a zig-zag scan or a diagonal scan. . A vertical scan for scanning a two-dimensional coefficient array in a column direction and a horizontal scan for scanning a two-dimensional block shape coefficient in a row direction may be used instead of the zig-zag scan according to the size of the transform unit and the intra prediction mode. That is, a scanning method to be used among zig-zag scan, diagonal scan, vertical scan, and horizontal scan may be determined according to the size of the transform unit and the intra prediction mode.

The entropy encoding unit 155 uses various encoding methods such as Context-based Adaptive Binary Arithmetic Code (CABAC) and Exponential Golomb to convert the one-dimensional quantized transform coefficients output from the reordering unit 150 . A bitstream is created by encoding the sequence.

In addition, the entropy encoder 155 encodes information such as CTU size, CU split flag, QT split flag, MTT split type, and MTT split direction related to block splitting, so that the video decoding apparatus divides the block in the same way as the video encoding apparatus. to be able to divide. Also, the entropy encoder 155 encodes information on a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and intra prediction information (ie, intra prediction) according to the prediction type. Mode information) or inter prediction information (information about reference pictures and motion vectors) is encoded. Also, the entropy encoder 155 encodes information related to quantization, that is, information about a quantization parameter and information about a quantization matrix.

The inverse quantization unit 160 inverse quantizes the quantized transform coefficients output from the quantization unit 145 to generate transform coefficients. The inverse transform unit 165 reconstructs a residual block by transforming the transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain.

The addition unit 170 reconstructs the current block by adding the reconstructed residual block to the prediction block generated by the prediction unit 120 . Pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The loop filter unit 180 reconstructs pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. generated due to block-based prediction and transformation/quantization. filter on them. The loop filter unit 180 may include at least one of a deblocking filter 182 , a sample adaptive offset (SAO) filter 184 , and an adaptive loop filter (ALF) 186 .

The deblocking filter 182 filters the boundary between the reconstructed blocks in order to remove blocking artifacts caused by block-by-block encoding/decoding, and the SAO filter 184 adds additional information to the deblocking-filtered image. perform filtering. The SAO filter 184 is a filter used to compensate for a difference between a reconstructed pixel and an original pixel caused by lossy coding, and is performed in such a way that an offset corresponding to each reconstructed pixel is added. . The ALF 186 performs filtering on the target pixel by applying filter coefficients to the target pixel to be filtered and neighboring pixels of the target pixel. The ALF 186 divides the pixels included in the image into a predetermined group and then determines one filter to be applied to the corresponding group, thereby differentially filtering each group. Information on filter coefficients to be used for ALF may be encoded and signaled to a video decoding apparatus.

The restored block filtered through the loop filter unit 180 is stored in the memory 190 . When all blocks in one picture are reconstructed, the reconstructed picture may be used as a reference picture for inter prediction of blocks in a picture to be encoded later.

4 is an exemplary functional block diagram of a video decoding apparatus capable of implementing the techniques of the present disclosure. Hereinafter, a video decoding apparatus and sub-components of the apparatus will be described with reference to FIG. 4 .

The video decoding apparatus includes an entropy decoding unit 410, a reordering unit 415, an inverse quantization unit 420, an inverse transform unit 430, a prediction unit 440, an adder 450, a loop filter unit 460, and a memory ( 470) may be included.

Like the video encoding apparatus of FIG. 1 , each component of the video decoding apparatus may be implemented as hardware or software, or a combination of hardware and software. In addition, the function of each component may be implemented in software and the microprocessor may be implemented to execute the function of the software corresponding to each component.

The entropy decoding unit 410 decodes the bitstream generated by the video encoding apparatus and extracts information related to block division to determine a current block to be decoded, and prediction information and residual signal required to reconstruct the current block. extract information, etc.

The entropy decoder 410 determines the size of the CTU by extracting information on the CTU size from a sequence parameter set (SPS) or a picture parameter set (PPS), and divides the picture into CTUs of the determined size. Then, the CTU is determined as the uppermost layer of the tree structure, that is, the root node, and the CTU is divided using the tree structure by extracting division information on the CTU.

For example, when a CTU is split using the QTBTTT structure, a first flag (QT_split_flag) related to QT splitting is first extracted and each node is split into four nodes of a lower layer. And, for the node corresponding to the leaf node of QT, the second flag (MTT_split_flag) related to the split of MTT and the split direction (vertical / horizontal) and / or split type (binary / ternary) information are extracted and the corresponding leaf node is set to MTT split into structures. Through this, each node below the leaf node of QT is recursively divided into a BT or TT structure.

As another example, when a CTU is split using the QTBTTT structure, a CU split flag (split_cu_flag) indicating whether a CU is split is first extracted, and when the block is split, a first flag (QT_split_flag) is extracted. may be In the partitioning process, each node may have zero or more repeated MTT splits after zero or more repeated QT splits. For example, in the CTU, MTT division may occur immediately, or conversely, only multiple QT divisions may occur.

As another example, when a CTU is split using the QTBT structure, a first flag (QT_split_flag) related to QT splitting is extracted and each node is split into four nodes of a lower layer. And, for a node corresponding to a leaf node of QT, a split flag (split_flag) indicating whether or not to be further split into BT and split direction information are extracted.

On the other hand, when the entropy decoding unit 410 determines a current block to be decoded through division of the tree structure, information on a prediction type indicating whether the current block is intra-predicted or inter-predicted is extracted. When the prediction type information indicates intra prediction, the entropy decoder 410 extracts a syntax element for intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the entropy decoding unit 410 extracts a syntax element for the inter prediction information, that is, a motion vector and information indicating a reference picture referenced by the motion vector.

Also, the entropy decoding unit 410 extracts quantization-related information and information on quantized transform coefficients of the current block as information on the residual signal.

The reordering unit 415 re-orders the sequence of one-dimensional quantized transform coefficients entropy-decoded by the entropy decoder 410 in the reverse order of the coefficient scanning order performed by the video encoding apparatus into a two-dimensional coefficient array (that is, block) can be changed.

The inverse quantization unit 420 inverse quantizes the quantized transform coefficients by using the quantization parameter. The inverse quantizer 420 may apply different quantization coefficients (scaling values) to the two-dimensionally arranged quantized transform coefficients. The inverse quantizer 420 may perform inverse quantization by applying a matrix of quantization coefficients (scaling values) from the video encoding apparatus to a two-dimensional array of quantized transform coefficients.

The inverse transform unit 430 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to reconstruct residual signals to generate a reconstructed residual block for the current block. In addition, when MTS is applied, the inverse transform unit 430 determines a transform kernel or transform matrix to be applied in the horizontal and vertical directions, respectively, using the MTS information (mts_idx) signaled from the video encoding apparatus, and uses the determined transform kernel. Inverse transform is performed on transform coefficients in the transform block in the horizontal and vertical directions.

The prediction unit 440 may include an intra prediction unit 442 and an inter prediction unit 444 . The intra prediction unit 442 is activated when the prediction type of the current block is intra prediction, and the inter prediction unit 444 is activated when the prediction type of the current block is inter prediction.

The intra prediction unit 442 determines the intra prediction mode of the current block from among the plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the entropy decoding unit 410, and references the vicinity of the current block according to the intra prediction mode. Predict the current block using pixels.

The inter prediction unit 444 determines a motion vector of the current block and a reference picture referenced by the motion vector by using the syntax element for inter prediction information extracted from the entropy decoding unit 410, and divides the motion vector and the reference picture. to predict the current block.

The adder 450 reconstructs the current block by adding the residual block output from the inverse transform unit and the prediction block output from the inter predictor or intra predictor. Pixels in the reconstructed current block are used as reference pixels when intra-predicting a block to be decoded later.

The loop filter unit 460 may include at least one of a deblocking filter 462 , an SAO filter 464 , and an ALF 466 . The deblocking filter 462 deblocks and filters the boundary between reconstructed blocks in order to remove a blocking artifact caused by block-by-block decoding. The SAO filter 464 performs filtering in such a way that an offset corresponding to the reconstructed block after deblocking filtering is added to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding. do. The ALF 466 performs filtering on the target pixel by applying filter coefficients to the target pixel to be filtered and neighboring pixels of the target pixel. The ALF 466 divides the pixels included in the image into a predetermined group and determines one filter to be applied to the corresponding group, thereby differentially filtering each group. ALF filter coefficients are determined using information on filter coefficients decoded from a bitstream.

The restored block filtered through the loop filter unit 460 is stored in the memory 470 . When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of blocks in a picture to be encoded later.

The techniques of this disclosure generally relate to applying a color space transform to the coding of video data. The following description is mainly focused on a decoding technique, that is, an operation of a video decoder, and a description of the coding techniques is simplified as it is opposite to the comprehensively described decoding technique.

Most screen content is captured in RGB color space instead of YCbCr color space. For each image block in the RGB color space, there is usually a strong correlation between the different color components. If RGB data is directly compressed without color space conversion, coding efficiency may be reduced because redundancies between color channels are not reduced. It can be converted to a different color space to remove redundancy between color components. The terms color space conversion and color conversion are the same and may be used interchangeably herein.

YCbCr is often used to represent the color of compressed video data in that there is little data overlapping between Y, Cb, and Cr components. Therefore, coding video data using the YCbCr color representation (also referred to as color format) provides good compression performance in many cases. Compared to the YCbCr color space, the YCoCg color space is simpler and faster to calculate, and the correlation between color components is lower. However, color conversion may cause color distortion leading to subjective quality degradation.

In HEVC Screen Content Coding (SCC), adaptive color transform (ACT) is used to adaptively transform the residual signal after prediction from the RGB or YUV color space to the YCgCo space. One ACT flag is marked for each transform unit (TU) to adaptively select one of the two color spaces. If the ACT flag is 1, the TU residual is coded in the YCgCo space, otherwise the TU residual is coded in the original color space. In the case of video data in which the sampling ratio of the color format is 4:4:4, the ACT encoding technique can be used in the VVC framework.

5 is a schematic diagram of a video decoder employing adaptive color conversion that may be used in the techniques of this disclosure.

As shown in FIG. 5 , one additional decoding module, the inverse ACT unit 510 , is used to transform the residual of the YCgCo domain back to the original domain after the inverse transformation. That is, color space transformation is performed in the residual signal domain.

The entropy decoding unit 502 decodes the coefficient level of the current block, and the inverse quantization unit 504 and the inverse transform unit 506 inversely quantizes the coefficient level and then inversely transforms it to restore the residual of the current block. The entropy decoding unit 502 parses the block-level ACT flag for the current block when the tree type is single-tree partitioning and the corresponding higher-level ACT flag is true. If the block level ACT flag for the current block is true, the residual of the current block is processed by the inverse ACT unit 510 , otherwise the residual of the current block is passed directly to the adder 512 . Since the color space of the residual is converted from YCbCr (or RGB) to YCoCg in the video encoder, the inverse ACT unit 510 converts it back to YCbCr (or RGB) for reconstruction. A prediction block for the current block is generated by the inter prediction unit 514 or the intra prediction unit 516, and is added to the residual of the current block in the adder 512 to reconstruct the current block. The reconstructed current block is processed by in-loop filters 518 to improve image quality. The filtered picture is stored in a decoded picture block (DPB) 520 to be referenced by the inter prediction module.

In the VVC framework, one CU is also used as a transform processing unit, unless the maximum transform size is less than the width or height of one CU. Accordingly, the block level ACT flag may be signaled as a CU syntax. In addition, since the residual signal is additionally (inverse) transformed, ACT is used only when there is at least one non-zero transform coefficient in the case of a CU that performs inter prediction and IBC (Intra Block Copy) encoding. In the CU, the ACT is activated only when the chroma components select the same prediction mode as the luma component, that is, the DM mode. In addition, a set of QP offsets (-5, -5, -3) is applied to the transform residual to compensate for the change in the dynamic range of the residual signal before and after color conversion.

Adaptive color transformation (ACT) is a forward and backward color transformation such as [Equation 1] using a pair of YCoCg transformation matrices to convert sample values from the YCbCr color space to the YCoCg color space and to the original color space. may be used. Compared to the YCbCr color space, the YCoCg color space is simpler and faster to calculate, and the correlation between color components is lower.

Here, [C0, C1, C2] is [Cb, Cr, Y].

Adaptive color transformation (ACT) is a forward and backward color transformation as in [Equation 2] using a pair of YCoCg transformation matrices to convert sample values from the RGB color space to the YCoCg color space and to the native color space. may be used.

Here, [C0, C1, C2] is [R, G, B].

The high-level ACT flag may be transmitted at a sequence level such as a sequence parameter set (SPS) or a picture level such as a picture parameter set (PPS) to indicate whether the ACT is activated or deactivated for a sequence or picture. For example, if the high-level ACT flag is false (“0”), the ACT is disabled for the entire sequence or picture, whereas if the high-level ACT flag is true (“1”), it is applied to one or more blocks in the sequence or picture. One or more block-level ACT flags are sent to indicate whether the ACT is enabled or disabled for the ACT.

1. ACT memory bandwidth limit

The adaptive color conversion (ACT) uses all three components of the residual signal in the forward and backward color conversion processes. When the three components are unavailable, the use of the ACT is not allowed. For example, when luma and chroma components are divided into separate tree structures and encoded, use of ACT is not allowed. That is, ACT may be allowed to be used only for blocks divided by single tree partitioning.

Thus, if the upper level ACT flag is true (“1”) and single tree block partitioning is used to partition the current CU, the block level ACT flag is signaled for the current CU. When the block level ACT flag for the current CU is true (“1”), the color space of the residuals of the current CU is transformed by color transform. If the block level ACT flag for the current CU is false (“0”) or the block level ACT flag is not signaled for the current CU, the ACT is deactivated for the current CU. Similarly, when Intra sub-partition prediction (ISP) is applied only to the luma component and not to the chroma components, the block level ACT flag is not signaled for the current CU and the ACT is deactivated.

Since the adaptive color transformation (ACT) requires all three color components, a memory for temporarily storing the sample values of each component is required between the inverse transform and the inverse ACT. Therefore, as the maximum transform size allowed in a video codec increases, in a hardware implementation of video encoders/decoders, more memory bandwidth may be required to deliver and store samples of the transformed residual data. For example, the draft VVC standard allows up to 64 point conversion, so that the values of up to 64Х64Х3 color components need to be stored for inverse-ACT.

According to one aspect of the present disclosure, several schemes are introduced to reduce the maximum memory size required by adaptive color conversion (ACT).

The first method is to limit the size of the transform unit in which the ACT is used by controlling whether or not the ACT is allowed or not depending on a higher-level syntax indicating the maximum transform size. As an example, a syntax element (eg, a 1-bit flag) indicating a maximum transform size allowed for luma blocks included in a sequence of pictures in a sequence parameter set (SPS) may be signaled. If the syntax element is “1”, the maximum transform size of the luma sample may be 64, and if the syntax element is “0”, the maximum transform size may be 32. Therefore, the video encoder may signal the high-level ACT flag only when the syntax element is “0” so that activation of the ACT is allowed only when the maximum transform size is 32. Accordingly, ACT requires a memory bandwidth corresponding to the value of a maximum of 32Х32Х3 color components.

The second method is to restrict the application of the ACT to a large block by controlling the activation of the ACT at the block level depending on the size of the CU or TU. That is, the present method controls the signaling of the ACT flag at the block level according to the size of the CU, instead of controlling the signaling of the higher-level ACT flag depending on the maximum transform size. The table below shows example coding unit syntax according to this method. In the illustrated syntax, graying of elements is used to indicate or aid understanding of potential changes in the syntax.

According to the first scheme, when the maximum transform size indicated in the SPS level is 64, ACT is deactivated for all blocks in the sequence (including blocks of 32Х32). On the other hand, in the second method, ACT may be selectively activated for blocks of 32Х32 or less.

The third method is to apply (inverse) transform, (inverse) quantization, and (inverse) ACT for each subblock by dividing the 64Х64 CU into, for example, four 32Х32 subblocks when ACT is activated for a 64Х64 CU. According to this method, the use of ACT is allowed even for a 64Х64 CU, but the ACT still requires a memory bandwidth corresponding to the value of a maximum of 32Х32Х3 color components.

2. Combination of prediction and ACT between color components

In another aspect of the present disclosure, after removing redundancy between components through inter-color component prediction, color space conversion is performed on the residual signal of the color components.

The video encoder may predict at least one of the color components of the current block from the other color component(s) to generate residual blocks of the color components used for the forward color transformation. The video decoder may generate a prediction block by predicting at least one of the color components of the current block from other color component(s), and may add it to a related residual block among the residual blocks of the color components obtained through inverse color transformation. As an example, the video encoder and the video decoder may predict the second chroma component from the first chroma component, and generate a residual value of the second chroma component by differentiating the original sample value and the predicted value. As another example, the video encoder and the video decoder may predict the first and second chroma components from the luma component, respectively, and generate residual values of the first and second chroma components.

Specifically, Cr can be predicted linearly from Cb, and when the predicted value of Cr is "k * Cb", the residual of Cr input to the forward color conversion of [Equation 1] is "Cr - k * Cb". k may be predefined as “1”, and modes using different k may be introduced. For example, k may be set to "+1" or "-1", and k may be signaled at a block level or a slice level. Here, the operation of predicting the Cr component from the Cb component and generating the residual of Cr may be hidden in the forward color conversion operation by replacing “C1” in [Equation 1] with “Cr - k * Cb”. That is, forward color conversion and prediction between color components can be integrated into one process.

By further generalizing the linear relationship between Cb and Cr, when the predicted value of the Cr component is "k1 * Cb + k2", the residual of the Cr component input to the forward color conversion of [Equation 1] is "Cr - k1" * Cb - k2". The operation of predicting the Cr component from the Cb component and generating the residual of Cr can be hidden in the forward color conversion operation by replacing “C1” in [Equation 1] with “Cr - k1 * Cb - k2”.

In some embodiments, the prediction of the chroma components may be predicted by a linear sum between them. As an example, the predicted value of the Cb component may be determined as “(Cb + Cr)/2”, and the predicted value of Cr may be determined as “(Cb - Cr)/2”. As another example, the predicted values of the Cb and Cr components are "(1 + k)Cb + (1-k)Cr" and "(1 + k)Cb - (1 - k) which are generalized expressions of the linear sum between Cb and Cr. )Cr". Here, modes using different k may be introduced, and the mode may be determined using tu_cbf_cb and tu_cbf_cr of a block to which a corresponding pixel belongs. tu_cbf_cb and tu_cbf_cr are flags representing the presence of a non-zero transform coefficient in a transform block for a Cb component and a Cr component.

On the other hand, if there is a linear correlation between the Cb component and the Cr component (eg, Cb = k * Cr), the ACT transformation is a reduced color transformation instead of [Equation 1] using a color transformation matrix of 3Х3. You can also use matrices. As an example, elements for one chroma component (eg, Cr) are removed, so that a color conversion matrix of 3Х2 may be used. As another example, in the color conversion matrix of 3Х3 of [Equation 1], a 2×2 color conversion matrix composed of only the upper left four matrix coefficients may be used. Alternatively, in the color transformation matrix of 3Х3 of [Equation 1], all matrix coefficients of the second row and the second column are replaced with 0, and the forward color transformation of the form [Equation 3] may be performed. After obtaining the Y and Cr residual signals through the inverse color transformation of the form [Equation 3], the video decoder may restore the Cr residual signal according to a linear correlation between the Cb component and the Cr component. Accordingly, it is possible to reduce the calculation and delay required for color conversion.

Although the above examples illustrate the YCbCr color format, it is apparent to those skilled in the art that a similar method may be applied to other color formats such as (R, G, B).

3. Constraints between ACT and cross-component prediction

CCLM (Cross-Component Linear Model) is a technology for improving encoding prediction performance by removing redundancy existing between a luma signal and a chroma signal. CCLM predicts a chroma sample based on the reconstructed luma sample of the same CU, using the following exemplary linear model that calculates the association between the chroma sample and the co-located reconstructed luma sample.

Here, pred _c (i, j) represents a chroma sample predicted in the CU and rec' _L (i, j) is a down-sampled sample of the reconstructed luma component of the same CU. The linear model coefficients α and β are not signaled separately and are derived from the surrounding samples.

In order to prevent interference between the ACT technique and the CCLM technique, which have similar characteristics in that the ACT technique removes redundancy between color components, when one technique is applied, the other technique may not be used. In an embodiment, the video encoder/decoder does not use CCLM when ACT is applied in the current CU. That is, CCLM can be used only when ACT is not applied in the current CU. In another embodiment, when the current CU uses CCLM, the ACT is not applied in the current CU. That is, ACT is available in the current CU only when CCLM is not used in the current CU level. In another embodiment, CCLM and ACT are controlled at the CU level or the TU level so that only one of the two is used. Alternatively, CCLM and ACT may be used together only for blocks obtained by single-tree partitioning.

Joint coding of chroma residuals (JCCR) is a technique for jointly coding the residual signal of Cb and Cr components. More specifically, the video encoder transmits one signal called resJointC[x][y], and the video decoder restores resCb and resCr, which are residual signals of Cb and Cr components, in a previously agreed manner according to the mode. When the TU level flag tu_joint_cbcr_residual_flag is 1, the video encoder/decoder can select the JCCR mode as shown in the table below by using the coded block pattern (CBF) of the Cb/Cr signal and the CSign transmitted at the slice level. Whether or not JCCR is applied is signaled by tu_joint_cbcr_residual_flag, which is a TU level flag.

On the video encoder side, JCCR technology is applied as follows. Modes 1, 2, and 3 used in JCCR technology are applied only to I slices, and only mode 2 is applied to P and B slices.

If the mode is 2, the video encoder generates resJointC as follows.

resJointC[ x ][ y ] = ( resCb[ x ][ y ] + CSign * resCr[ x ][ y ] ) / 2

If the mode is 1, the video encoder generates resJointC as follows.

resJointC[ x ][ y ] = ( 4 * resCb[ x ][ y ] + 2 * CSign * resCr[ x ][ y ] ) / 5

If the mode is 3, the video encoder constructs resJointC as follows.

resJointC[ x ][ y ] = ( 4 * resCr[ x ][ y ] + 2 * CSign * resCb[ x ][ y ] ) / 5

Both ACT and JCCR are residual-based coding tools, and ACT and JCCR may be used together for a block obtained by single tree partitioning. Accordingly, the video decoder decodes the residual signal of the luma component and resJointC[x][y] from the bitstream, and restores the residual signal of the Cb component and the residual signal of the Cr component from resJointC[x][y], and these Inverse color conversion may be performed on the residual signals.

Alternatively, when one technique is applied, the other technique may not be used. For example, ACT and JCCR may be controlled at a CU level or a TU level so that only one of them is used.

6 is a flowchart illustrating a method of encoding video data using one or more techniques described above, according to an aspect of the present disclosure.

The video encoder may encode a higher-level syntax element indicating a maximum transform size allowed for a sequence of pictures of video data into a bitstream (S610). The syntax element may be a 1-bit flag signaled in the SPS syntax. If the syntax element is "1", the maximum transform size is 64, and if "0", the maximum transform size is 32.

When it is indicated by the syntax element that the maximum transform size is less than 64, the video encoder may encode in the bitstream a first control flag indicating whether application of a color space transform is allowed for blocks in the sequence. (S620). The first control flag may be signaled in the SPS syntax. If the first control flag is “1”, it indicates that color space transform is allowed to be applied to blocks in the sequence, and if the first control flag is “0”, color space transform is not allowed to be applied to blocks in the sequence. indicates not.

When the first control flag indicates that application of color space transformation is permitted for blocks in the sequence, the video encoder generates a second control flag indicating whether color space transformation is applied to the current block in the sequence. It can be encoded in the bitstream (S630). The second control flag may be a 1-bit flag included in the CU syntax or the TU syntax.

In order to generate the first residual data for the current block, the video encoder may generate prediction values for the current block, and may generate first residual data by differentiating the prediction values from original samples of the current block ( S640 ). . The first residual data may include residual blocks for color components of the current block. The video encoder may predict at least one of the color components of the current block from other color component(s) of the current block to generate residual blocks of color components used for forward color transformation. The inter-color component prediction may be to linearly predict the second chroma component from the first chroma component.

When the second control flag indicates that color space transformation is applied to the current block, the video encoder performs forward color transformation on the first residual data for the current block to perform a forward color transformation to the second residual data (forward color transformed residual data) may be generated, and the second residual data may be encoded in the bitstream (S650). On the other hand, when the second control flag indicates that color space transformation is not applied to the current block, the video encoder transfers the first residual data to the bitstream without performing forward color transformation on the first residual data for the current block. can be encoded.

7 is a flowchart illustrating a method of decoding video data using one or more techniques described above, according to an aspect of the present disclosure.

The video decoder may decode a syntax element of a higher level indicating a maximum transform size allowed for a sequence of pictures of video data from the bitstream ( S710 ). The syntax element may be a 1-bit flag signaled in the SPS syntax. If the syntax element is “1”, the maximum transform size may be 64, and if “0”, the maximum transform size may be 32.

When it is indicated by the syntax element that the maximum transform size is less than 64, the video decoder may decode a first control flag indicating whether application of the color space transform is allowed to blocks in the sequence from the bitstream. (S720). The first control flag may be a 1-bit flag signaled in the SPS syntax. If the first control flag is true (“1”), it indicates that the application of color space transform is allowed for blocks in the sequence, and if the first control flag is false (“0”), the color space for blocks in the sequence is allowed. Indicates that the application of the transform is not allowed.

When the first control flag indicates that application of color space transform is permitted to blocks in the sequence, the video decoder is configured to use a second control flag indicating whether color space transform is applied to a current block in the sequence from a bitstream. The control flag may be decoded (S730). The second control flag may be a 1-bit flag included in the CU syntax or the TU syntax. If the second control flag is true (“1”), it indicates that color space transformation is applied for the current block, and if the second control flag is false (“0”), it indicates that color space transformation is not applied for the current block.

The video decoder may generate a prediction block for the current block by performing inter prediction or intra prediction, and may reconstruct first residual data (ie, forward color-transformed residual blocks) of the current block from the bitstream (S740). ). The first residual data may include residual blocks for color components of the current block. The video decoder may predict at least one of the color components of the current block from the other color component(s) to reconstruct the residual blocks of the color components.

When the second control flag indicates that color space transformation is applied to the current block, the video decoder performs reverse color transformation on the first residual data to generate second residual data (ie, backward color transformed residual blocks). generated ( S750 ), and second residual data may be added to the prediction block to generate a reconstructed block with respect to the current block ( S760 ). On the other hand, when the second control flag indicates that the color space transform is not applied to the current block, the video decoder may add the first residual data to the prediction block to generate a reconstructed block for the current block.

8 is a flowchart illustrating a method of decoding video data using one or more techniques described above, according to another aspect of the present disclosure.

The video decoder obtains first residual data for the current block from the bitstream (S810). The first residual data includes residual data (residual block) for each of the color components of the current block. The video decoder determines whether to apply the color space transformation to the first residual data based on the upper-level color transformation control flag and the block-level color transformation control flag ( S820 ). The higher-level color conversion control flag is signaled in the bitstream depending on the maximum conversion size allowed for the sequence of pictures including the current block.

For example, the video decoder decodes a syntax element indicating a maximum transform size allowed for a sequence of pictures from the bitstream, and when the syntax element indicates that the maximum transform size is smaller than a preset value, from the bitstream Decodes high-level color conversion control flags. The upper-level color conversion control flag may be a 1-bit flag signaled in the SPS syntax. If the upper-level color conversion control flag is true ("1"), it indicates that color space conversion is allowed for blocks in the sequence, and if the upper-level color conversion control flag is false ("0"), the Indicates that application of color space transform is not allowed for blocks.

The block-level color conversion control flag is signaled in the bitstream depending on the upper-level color conversion control flag. That is, when the upper-level color conversion control flag indicates that the application of color space conversion is permitted to blocks in the sequence, the video decoder decodes the block-level color conversion control flag for the current block from the bitstream. The block-level color conversion control flag may be a 1-bit flag included in the CU syntax or the TU syntax. If the block-level color conversion control flag is true ("1"), it indicates that color space conversion is allowed for the current block; if the block-level color conversion control flag is false ("0"), the color space for the current block is allowed. Indicates that the application of the transform is not allowed.

When the upper-level color conversion control flag and the block-level color conversion control flag are not signaled in the bitstream, it is inferred as false ('0') by the video decoder.

The video decoder generates a prediction block for the current block by performing inter prediction or intra prediction (S830).

In response to determining that a color space transform is to be applied on the first residual data, the video decoder performs an inverse color transform on the first residual data to generate second residual data, and to the prediction block and the second residual data. A reconstructed block for the current block is generated based on the block (S840). On the other hand, in response to determining that the color space transform is not applied to the first residual data, the video decoder generates a reconstructed block for the current block based on the prediction block and the first residual data.

Color space conversion is allowed only if it is partitioned into a single tree. Accordingly, the video decoder infers that the block-level color conversion control flag is false (“0”) when the luma and chroma components of the current block are encoded using the dual split tree (that is, the color space conversion for the current block). determines that it does not apply).

Color space conversion may be allowed only when the chroma sampling format is 4:4:4. Therefore, when the chroma sampling format for video data is a chroma sampling format other than 4:4:4, the video decoder infers that the high-level color conversion control flag is false (“0”) (ie, blocks in the sequence). determines that the application of color space transformations is not allowed for ).

Color space transform may not be allowed to be applied to the coding block together with the cross-component linear mode (CCLM). Accordingly, the video decoder determines that CCLM (cross-component linear mode) is not applied to chroma components of the current block when it is indicated by the block-level color transformation control flag that color space transformation is to be applied to the current block.

In some cases, color space transformation may be used in conjunction with prediction between chroma components. Accordingly, in order to generate prediction blocks of color components for the current block, at least one of the color components of the current block may be predicted from another color component.

It should be understood that the exemplary embodiments in the above description may be implemented in many different ways. The functions described in one or more examples may be implemented in hardware, software, firmware, or any combination thereof. It should be understood that the functional components described herein have been labeled "...unit" to particularly further emphasize their implementation independence.

Meanwhile, various functions or methods described in the present disclosure may be implemented as instructions stored in a non-transitory recording medium that can be read and executed by one or more processors. The non-transitory recording medium includes, for example, any type of recording device in which data is stored in a form readable by a computer system. For example, the non-transitory recording medium includes a storage medium such as an erasable programmable read only memory (EPROM), a flash drive, an optical drive, a magnetic hard drive, and a solid state drive (SSD).

The above description is merely illustrative of the technical idea of this embodiment, and various modifications and variations will be possible by those skilled in the art to which this embodiment belongs without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are for explanation rather than limiting the technical spirit of the present embodiment, and the scope of the technical spirit of the present embodiment is not limited by these embodiments. The protection scope of the present embodiment should be interpreted by the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present embodiment.

Claims (20)

A method of decoding video data, comprising:
obtaining first residual data for a current block from the bitstream;
determining whether to apply color space conversion to the first residual data based on a color conversion control flag of a higher level and a color conversion control flag of a block level;
in response to determining that a color space transform is applied to the first residual data, performing an inverse color transform on the first residual data to generate second residual data;
generating a prediction block for the current block; and
generating a reconstructed block for the current block based on the prediction block and the second residual data;
including,
The upper-level color conversion control flag is signaled in the bitstream depending on a maximum conversion size allowed for a sequence of pictures including the current block, and the block-level color conversion control flag is the upper-level color conversion control flag. Signaled in the bitstream depending on a flag, the upper-level color conversion control flag and the block-level color conversion control flag are inferred to be false when not signaled in the bitstream. The method of claim 1,
decoding a syntax element indicating a maximum transform size allowed for the sequence of pictures from the bitstream; and
decoding the upper-level color conversion control flag from the bitstream when it is indicated by the syntax element that the maximum conversion size is smaller than the preset value;
Further comprising, a decryption method. 3. The method of claim 2,
decoding the block-level color conversion control flag for the current block from the bitstream when the higher-level color conversion control flag indicates that application of color space conversion is permitted to the blocks in the sequence;
Further comprising, a decryption method. The method of claim 1,
When the luma component and the chroma component of the current block are encoded using a dual split tree, determining that color space conversion is not applied to the current block without decoding the block-level color conversion control flag;
Further comprising, a decryption method. The method of claim 1,
When the chroma sampling format for the video data is a chroma sampling format other than 4:4:4, application of color space transformation to blocks in the sequence is not allowed without decoding of the upper-level color transformation control flag. Deciding not to
Further comprising, a decryption method. The method of claim 1,
The step of generating a prediction block for the current block includes:
determining that cross-component linear mode (CCLM) is not applied to chroma components of the current block when the block-level color conversion control flag indicates that the color space conversion is applied to the current block;
Further comprising, a decryption method. The method of claim 1,
The step of generating a prediction block for the current block includes:
predicting at least one of the color components of the current block from another color component;
Including, a decryption method. The method of claim 1,
The first residual data is
and residual data for each of the color components of the current block. An apparatus for decoding video data, comprising:
one or more processors;
The one or more processors,
obtain first residual data for the current block from the bitstream,
determining whether to apply color space transformation to the first residual data based on a color conversion control flag of a higher level and a color conversion control flag of a block level;
in response to determining that a color space transform is applied to the first residual data, performing an inverse color transform on the first residual data to generate second residual data;
generating a prediction block for the current block;
and generate a reconstructed block for the current block based on the prediction block and the second residual data,
The upper-level color conversion control flag is signaled in the bitstream depending on a maximum conversion size allowed for a sequence of pictures including the current block, and the block-level color conversion control flag is the upper-level color conversion control flag. Signaled in the bitstream depending on a flag, the upper-level color conversion control flag and the block-level color conversion control flag are inferred to be false when not signaled in the bitstream. 10. The method of claim 9,
the one or more processors,
Decodes a syntax element indicating a maximum transform size allowed for the sequence of pictures from the bitstream,
and decode the upper-level color conversion control flag from the bitstream when it is indicated by the syntax element that the maximum transform size is smaller than the preset value. 11. The method of claim 10,
the one or more processors,
and decode the block-level color conversion control flag for the current block from the bitstream when it is indicated by the higher-level color conversion control flag that application of color space conversion to blocks in the sequence is permitted. , decryption device. 10. The method of claim 9,
the one or more processors,
and determine that color space transformation is not applied to the current block without decoding the block-level color transformation control flag when the luma component and the chroma component of the current block are encoded using a dual split tree. . 10. The method of claim 9,
the one or more processors,
When the chroma sampling format for the video data is a chroma sampling format other than 4:4:4, application of color space transformation to blocks in the sequence is not allowed without decoding of the upper-level color transformation control flag. A decryption device, configured to determine that no. 10. The method of claim 9,
the one or more processors,
and determine that cross-component linear mode (CCLM) is not applied to chroma components of the current block when it is indicated by the block-level color conversion control flag that the color space transformation is applied to the current block. Device. 10. The method of claim 9,
the one or more processors,
The decoding apparatus, configured to predict at least one of color components of the current block from another color component as part of generating the prediction block for the current block. 10. The method of claim 9,
The first residual data is
and residual data for each of the color components of the current block. A method of decoding video data, comprising:
decoding a syntax element indicating a maximum transform size allowed for a sequence of pictures of video data from a bitstream;
decoding a first control flag indicating whether application of a color space transform is permitted to blocks in the sequence from the bitstream when the maximum transform size is smaller than 64 indicated by the syntax element;
A second control indicating whether the color space transform is applied to the current block in the sequence from the bitstream when the first control flag indicates that application of the color space transform is permitted to the blocks in the sequence decoding the flag;
When it is indicated by the second control flag that the color space transformation is applied to the current block, the first residual data for the current block is restored from the bitstream, and the inverse color transformation is performed on the first residual data. generating second residual data;
generating a prediction block for the current block; and
generating a reconstructed block for the current block based on the prediction block and the second residual data;
Including, a decryption method. 18. The method of claim 17,
When the second control flag indicates that the color space transformation is applied to the current block, determining that cross-component linear mode (CCLM) is not applied to the chroma components of the current block. Decryption method. 18. The method of claim 17,
When the luma component and the chroma component of the current block are encoded using a dual split tree, determining that application of a color space transform is not allowed to the current block without decoding the second control flag , the decryption method. 18. The method of claim 17,
The step of generating a prediction block for the current block includes:
and predicting at least one of the color components of the current block from another color component.

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