CN119545003A

CN119545003A - Method for restoring chrominance blocks and device for decoding images

Info

Publication number: CN119545003A
Application number: CN202411691143.1A
Authority: CN
Inventors: 沈东圭; 朴时奈; 朴俊泽; 林和平
Original assignee: Hyundai Motor Co; Research Institute for Industry Cooperation of Kwangwoon University; Kia Corp
Current assignee: Hyundai Motor Co; Research Institute for Industry Cooperation of Kwangwoon University; Kia Corp
Priority date: 2019-05-15
Filing date: 2020-05-15
Publication date: 2025-02-28
Also published as: CN114009031A; CN114009031B; CN119520800A; KR20200132762A; CN119520801A; CN119545004A

Abstract

The present invention relates to a method for restoring a chrominance block and an apparatus for decoding an image. According to an embodiment of the present invention, a method for restoring a chroma block of a target block to be restored includes the steps of decoding information about correlation between a first residual sample, which is a residual sample of a first chroma component, and a second residual sample, which is a residual sample of a second chroma component, from a bitstream, the first residual sample and the prediction information of the chroma block, generating a predicted sample of the first chroma component and a predicted sample of the second chroma component based on the prediction information, deriving the second residual sample by applying the information about correlation to the first residual sample, and restoring the chroma block of the first chroma component by adding the predicted sample of the first chroma component and the first residual sample, and restoring the chroma block of the second chroma component by adding the predicted sample of the second chroma component and the second residual sample.

Description

Method for restoring chroma block and apparatus for decoding image

The application relates to a method for restoring chroma blocks and a device for decoding images, which are divided into PCT patent applications entering China, wherein the application number of the PCT patent application is 202080042779.7, and the application date of the PCT patent application is 5, 15, and the method is used for decoding the images.

Cross Reference to Related Applications

The present application claims priority from korean patent application No.10-2019-0056974 filed on 5-15 of 2019, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to encoding and decoding of video, and more particularly, to a method for reconstructing a chrominance block and a video decoding apparatus, which improve encoding and decoding efficiency by effectively predicting residual samples of a chrominance component.

Background

Since video data has a larger data amount than audio data or still image data, a large amount of hardware resources (including a memory) are required before compression processing is performed, so that the data is stored or transmitted in its original form.

Accordingly, storing or transmitting video data is typically accompanied by compressing it by use of an encoder before the decoder can receive, decompress, and reproduce the compressed video data. Existing Video compression techniques include h.264/AVC and High Efficiency Video Coding (HEVC) that improves the Coding efficiency of h.264/AVC by approximately 40%.

However, the increasing size, resolution and frame rate of video images, and the resulting increase in the amount of data to be encoded, requires a new and superior compression technique that has better coding efficiency improvements and higher image quality improvements than existing compression techniques.

Disclosure of Invention

Technical problem

In view of this need, the present invention is directed to providing an improved video encoding and decoding technique. In particular, one aspect of the present invention relates to a technique for improving encoding and decoding efficiency by deriving one of Cb and Cr chroma components from the other.

Technical proposal

According to one aspect of the present invention, a method for reconstructing a chroma block of a target block to be reconstructed is provided. The method includes decoding, from a bitstream, correlation information between a first residual sample and a second residual sample, the first residual sample being a residual sample of a first chroma component and the second residual sample being a residual sample of a second chroma component, and prediction information of a chroma block. The method further includes generating predicted samples of the first chrominance component and predicted samples of the second chrominance information based on the prediction information, and deriving second residual samples by applying the correlation information to the first residual samples. The method further includes reconstructing a chroma block of the first chroma component by adding the first residual sample and the predicted sample of the first chroma component and reconstructing a chroma block of the second chroma component by adding the second residual sample and the predicted sample of the second chroma component.

According to another aspect of the present invention, there is provided a video decoding apparatus for reconstructing a chroma block of a target block to be reconstructed. The video decoding device comprises a decoding unit configured to decode, from a bitstream, correlation information between a first residual sample and a second residual sample, the first residual sample being a residual sample of a first chrominance component, and prediction information of a chrominance block, the second residual sample being a residual sample of a second chrominance component. The video decoding device further includes a prediction unit configured to generate predicted samples of the first chrominance component and predicted samples of the second chrominance information based on the prediction information, and a chrominance component reconstruction unit configured to derive the second residual sample by applying the correlation information to the first residual sample. The video decoding device further includes an adder configured to reconstruct a chroma block of the first chroma component by adding the first residual samples of the first chroma component and the predicted samples and reconstruct a chroma block of the second chroma component by adding the second residual samples of the second chroma component and the predicted samples.

Advantageous effects

As described above, according to some embodiments of the present invention, since any one of the Cb chrominance component and the Cr chrominance component is derived without signaling, compression performance of encoding and decoding is improved.

Drawings

Fig. 1 is a block diagram illustrating a video encoding apparatus capable of implementing the techniques of the present invention.

Fig. 2 is a schematic diagram for explaining a method of dividing a block by using QTBTTT structures.

Fig. 3a is a schematic diagram illustrating a plurality of intra prediction modes.

Fig. 3b is a schematic diagram illustrating a plurality of intra prediction modes including a wide-angle intra prediction mode.

Fig. 4 is a block diagram illustrating a video decoding apparatus in which the techniques of the present invention may be implemented.

Fig. 5 is an exemplary block diagram of a video encoding apparatus that may implement an example of a residual block reconstruction method for a chroma component.

Fig. 6 is a flowchart illustrating an example of a residual block reconstruction method for a chrominance component implemented in the video encoding apparatus of fig. 5.

Fig. 7 is a block diagram illustrating an example video decoding apparatus that may implement a residual block reconstruction method for a chrominance component.

Fig. 8 is a flowchart showing an example of a residual block reconstruction method for a chrominance component implemented in the video decoding apparatus of fig. 7.

Fig. 9 is an exemplary block diagram of a video encoding apparatus capable of implementing another example of a residual block reconstruction method for a chrominance component.

Fig. 10 is a flowchart showing an example of a residual block reconstruction method for a chrominance component implemented in the video encoding apparatus of fig. 9.

Fig. 11 is a block diagram illustrating a video decoding apparatus that may implement another example of a residual block reconstruction method for a chrominance component.

Fig. 12 is a flowchart illustrating an example of a residual block reconstruction method implemented in the video decoding apparatus of fig. 11.

Fig. 13 and 14 are flowcharts showing other examples of a residual block reconstruction method for a chrominance component.

Fig. 15 is a flowchart showing an example of performance conditions of a residual reconstruction method for a chrominance component.

Detailed Description

Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, like reference numerals preferably denote like elements, although the elements are shown in different drawings. Furthermore, in the following description of some embodiments, when the subject matter of the present invention is considered to be obscured, a detailed description of related known components and functions will be omitted for clarity and conciseness.

Fig. 1 is a block diagram illustrating a video encoding apparatus capable of implementing the techniques of the present invention. Hereinafter, a video encoding apparatus and elements of the apparatus will be described with reference to fig. 1.

The video encoding apparatus includes an image divider 110, a predictor 120, a subtractor 130, a transformer 140, a quantizer 145, a reordering unit 150, an entropy encoder 155, an inverse quantizer 160, an inverse transformer 165, an adder 170, a filtering unit 180, and a memory 190.

Each element of the video encoding apparatus may be implemented in hardware or software or a combination of hardware and software. The functions of the respective elements may be implemented as software, and the microprocessor may be implemented to perform the software functions corresponding to the respective elements.

A video includes a plurality of images. Each image is divided into a plurality of regions, and encoding is performed on each region. For example, an image is segmented into one or more tiles (tiles) or/and slices (slices). Here, one or more tiles may be defined as a tile set. Each tile or slice is partitioned into one or more Coding Tree Units (CTUs). Each CTU is partitioned into one or more Coding Units (CUs) by a tree structure. The information applied to each CU is encoded as a syntax of the CU, and commonly applied to the syntax of the CTU in which the information included in one CTU is encoded. In addition, information commonly applied to all blocks in one slice is encoded as syntax of a slice header, and information applied to all blocks constituting one image is encoded in an image parameter set (Picture PARAMETER SET, PPS) or an image header. In addition, information commonly referred to by a plurality of images is encoded in a Sequence parameter set (Sequence PARAMETER SET, SPS). In addition, information commonly referenced by one or more SPS is encoded in a Video parameter set (Video PARAMETER SET, VPS). Information commonly applied to one tile or group of tiles may be encoded as syntax of a tile header or a tile group header.

The image divider 110 determines the size of a Coding Tree Unit (CTU). Information about 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 image divider 110 divides each image constituting a video into a plurality of CTUs having a predetermined size, and then recursively divides the CTUs using a tree structure. In the tree structure, leaf nodes are used as Coding Units (CUs), which are the basic units of coding.

The tree structure may be a QuadTree (QT), a Binary Tree (BT), a trigeminal tree (TERNARYTREE, TT), or a structure formed of two or more QT structures, BT structures, and TT structures, the QuadTree (QT), i.e., a node (or parent node), being partitioned into four slave nodes (or child nodes) of the same size, the Binary Tree (BT), i.e., a node, being partitioned into two slave nodes, and the Trigeminal Tree (TT), i.e., a node, being partitioned into three slave nodes at a ratio of 1:2:1. For example, a quadtree plus binary tree (QuadTree plus BinaryTree, QTBT) structure may be used, or a quadtree plus binary tree trigeminal tree (QuadTree plus BinaryTree TERNARYTREE, QTBTTT) structure may be used. BTTT may be referred to herein collectively as a multiple-type tree (MTT).

Fig. 2 exemplarily shows QTBTTT a split tree structure. As shown in fig. 2, the CTU may be first partitioned into QT structures. QT segmentation may be repeated until the size of the segment blocks reaches the minimum block size MinQTSize of the leaf nodes allowed in QT. A first flag (qt_split_flag) indicating whether each node of the QT structure is partitioned into four lower-layer nodes is encoded by the entropy encoder 155 and signaled to the video decoding device. When the leaf node of QT is not greater than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further partitioned into one or more BT structures or TT structures. The BT structure and/or the TT structure may have a plurality of division directions. For example, there may be two directions, i.e., a direction of dividing the blocks of the node horizontally and a direction of dividing the blocks vertically. As shown in fig. 2, when MTT segmentation starts, a second flag (MTT _split_flag) indicating whether a node is segmented, a flag indicating a segmentation direction (vertical or horizontal) in the case of segmentation, and/or a flag indicating a segmentation type (binary or trigeminal) are encoded by the entropy encoder 155 and signaled to the video decoding apparatus.

Alternatively, a CU split flag (split_cu_flag) indicating whether a node is split may be encoded before encoding a first flag (qt_split_flag) indicating whether each node is split into 4 nodes of a lower layer. When the value of the CU partition flag (split_cu_flag) indicates that partition is not performed, a block of nodes becomes a leaf node in the partition tree structure and serves as an encoding unit (CU), which is a basic unit of encoding. When the value of the CU partition flag (split_cu_flag) indicates that partition is performed, the video encoding apparatus starts encoding from the first flag in the above-described manner.

When QTBT is utilized as another example of the tree structure, there may be two types of division, i.e., a type of dividing a block horizontally into two blocks of the same size (i.e., symmetrical horizontal division) and a type of dividing a block vertically into two blocks of the same size (i.e., symmetrical vertical division). A partition flag (split_flag) indicating whether each node of the BT structure is partitioned into lower-layer blocks and partition type information indicating that the partition type is encoded are encoded by the entropy encoder 155 and transmitted to the video decoding apparatus. There may be additional types of partitioning the blocks of a node into two asymmetric blocks. The asymmetric division type may include a type of dividing a block into two rectangular blocks at a size ratio of 1:3, or a type of dividing a block of a node diagonally.

The CUs may have various sizes according to QTBT or QTBTTT partitions of the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (i.e., a leaf node of QTBTTT) is referred to as a "current block". When QTBTTT partitions are employed, the shape of the current block may be square or rectangular.

The predictor 120 predicts the current block to generate a predicted block. Predictor 120 includes an intra predictor 122 and an inter predictor 124.

In general, each current block in an image may be predictively encoded, respectively. In general, prediction of a current block is performed using an intra prediction technique (which uses data from an image including the current block) or an inter prediction technique (which uses data of an image encoded before an image including the current block). Inter prediction includes unidirectional prediction and bidirectional prediction.

The intra prediction unit 122 predicts pixels in the current block using pixels (reference pixels) located around the current block in the current image including the current block. Depending on the prediction direction, there are multiple intra prediction modes. For example, as shown in fig. 3a, the plurality of intra prediction modes may include 2 non-directional modes and 65 directional modes, and the 2 non-directional modes include a planar (planar) mode and a DC mode. The neighboring pixels and equations to be used are defined differently for each prediction mode. The following table lists the intra prediction mode numbers and their names.

For efficient direction prediction of the current block of rectangular shape, direction modes (intra prediction modes 67 to 80 and-1 to-14) indicated by dotted arrows in fig. 3b may be additionally used. These modes may be referred to as "wide-angle intra prediction modes". In fig. 3b, the arrows indicate the respective reference samples for prediction, rather than the prediction direction. The prediction direction is opposite to the direction indicated by the arrow. The wide-angle intra prediction mode is a mode in which prediction is performed in a direction opposite to a specific direction mode without additional bit transmission when the current block is rectangular in shape. In this case, in the wide-angle intra prediction mode, some of the wide-angle intra prediction modes available for the current block may be determined based on a ratio of the width to the height of the rectangular current block. For example, when the current block has a rectangular shape having a height smaller than its width, wide-angle intra prediction modes (intra prediction modes 67 to 80) having an angle smaller than 45 degrees may be used. When the current block has a rectangular shape having a width greater than its height, wide-angle intra prediction modes (intra prediction modes-1 to-14) having an angle greater than-135 degrees may be used.

The intra predictor 122 may determine an intra prediction mode to be used when encoding the current block. In some examples, intra predictor 122 may encode the current block with several intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, the intra predictor 122 may calculate a rate distortion value using rate-distortion (rate-distortion) analysis of several tested intra prediction modes, and may select an intra prediction mode having the best rate distortion characteristics among the tested modes.

The intra predictor 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts the current block using the determined neighbor pixels (reference pixels) and equations according to the selected intra prediction mode. Information about the selected intra prediction mode is encoded by the entropy encoder 155 and transmitted to the video decoding device.

The inter predictor 124 generates a prediction block of the current block through motion compensation. The inter predictor 124 searches for a block most similar to the current block in the reference picture, which has been encoded and decoded earlier than the current picture, and generates a prediction block of the current block using the searched block. Then, the inter predictor generates a motion vector (motion vector) corresponding to a displacement (displacement) between a current block in the current image and a predicted block in the reference image. In general, motion estimation is performed on a luminance component, and a motion vector calculated based on the luminance component is used for both the luminance component and the chrominance component. Motion information including information on a reference picture and information on a motion vector for predicting a current block is encoded by the entropy encoder 155 and transmitted to a video decoding device.

The subtractor 130 subtracts the prediction block generated by the intra predictor 122 or the inter predictor 124 from the current block to generate a residual block.

The transformer 140 may partition the residual block into one or more transform blocks, perform transform on the transform blocks, and transform residual values of the transform blocks from the pixel domain to the frequency domain. In the frequency domain, a transform block is referred to as a block of coefficients that contains one or more transform coefficient values. A two-dimensional (2D) transform kernel may be used for the transform, and a one-dimensional (1D) transform kernel may be used for each of the horizontal transform and the vertical transform. The transform kernel may be based on Discrete Cosine Transform (DCT), discrete Sine Transform (DST), or the like.

The transformer 140 may transform a residual signal in the residual block by using the entire size of the residual block as a transform unit. Also, the transformer 140 may partition the residual block into two sub-blocks in the horizontal direction or the vertical direction, and may perform transformation on only one of the two sub-blocks. Accordingly, the size of the transform block may be different from the size of the residual block (and thus the size of the prediction block). Non-zero residual sample values may not exist or be very sparse in the untransformed sub-block. The residual samples of the untransformed sub-block may not be signaled and may all be considered "0" by the video decoding device. Depending on the partition direction and partition ratio, there may be several partition types. The transformer 140 may provide information about the coding mode (or transform mode) of the residual block (e.g., the information about the coding mode includes information indicating whether to transform the residual block or a sub-block of the residual block, information indicating a partition type selected to partition the residual block into the sub-blocks, and information for identifying the sub-block to be transformed, etc.) to the entropy encoder 155. The entropy encoder 155 may encode information about a coding mode (or a transform mode) of the residual block.

The quantizer 145 quantizes the transform coefficient output from the transformer 140, and outputs the quantized transform coefficient to the entropy encoder 155. The quantizer 145 may directly quantize the relevant residual block for a particular block or frame without transformation.

The reordering unit 150 may perform reordering of coefficient values using the quantized transform coefficients. The reordering unit 150 may change the two-dimensional coefficient array to a one-dimensional coefficient sequence using coefficient scanning (coefficient scanning). For example, the rearrangement unit 150 may scan the coefficients from the DC coefficients to the coefficients in the high frequency region by zigzag scanning (zig-zag scan) or diagonal scanning (diagonal scan) to output a one-dimensional coefficient sequence. Depending on the size of the transform unit and the intra prediction mode, the zig-zag scan utilized may be replaced by a vertical scan for scanning the two-dimensional coefficient array in the column direction and a horizontal scan for scanning the two-dimensional block shape coefficients in the row direction. In other words, the scanning method to be used may be determined in zigzag scanning, diagonal scanning, vertical scanning, and horizontal scanning according to the size of the transform unit and the intra prediction mode.

The entropy encoder 155 encodes the sequence of one-dimensional quantized transform coefficients output from the rearrangement unit 150 by encoding the sequence using various encoding methods such as Context-based adaptive binary arithmetic coding (Context-based Adaptive Binary Arithmetic Code, CABAC), exponential golomb (Exponential Golomb), and the like, thereby encoding to generate a bitstream.

The entropy encoder 155 encodes information related to block division (e.g., CTU size, CU division flag, QT division flag, MTT division type, and MTT division direction) so that a video decoding apparatus can divide blocks in the same manner as a video encoding apparatus. In addition, the entropy encoder 155 encodes information on a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and encodes intra prediction information (i.e., information on an intra prediction mode) or inter prediction information (information on a reference picture index and a motion vector) according to the prediction type.

The inverse quantizer 160 inversely quantizes the quantized transform coefficient output from the quantizer 145 to generate a transform coefficient. The inverse transformer 165 transforms the transform coefficients output from the inverse quantizer 160 from the frequency domain to the spatial domain, and reconstructs a residual block.

The adder 170 adds the reconstructed residual block and the prediction block generated by the predictor 120 to reconstruct the current block. The pixels in the reconstructed current block are used as reference pixels when performing intra prediction of the subsequent block.

The filtering unit 180 filters the reconstructed pixels to reduce block artifacts (blocking artifacts), ringing artifacts (RINGING ARTIFACTS), and blurring artifacts (blurring artifacts) due to block-based prediction and transform/quantization. The filtering unit 180 may include a deblocking filter 182 and a Sample Adaptive Offset (SAO) filter 184.

The deblocking filter 180 filters boundaries between reconstructed blocks to remove block artifacts caused by block-wise encoding/decoding, and the SAO filter 184 performs additional filtering on the deblock filtered video. The SAO filter 184 is a filter for compensating for differences between reconstructed pixels and original pixels caused by lossy encoding (lossy coding).

The reconstructed blocks filtered by the deblocking filter 182 and the SAO filter 184 are stored in a memory 190. Once all blocks in one image are reconstructed, the reconstructed image may be used as a reference image for inter prediction of blocks in a subsequent image to be encoded.

Fig. 4 is an exemplary functional block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure. Hereinafter, a video decoding device and its components will be described with reference to fig. 4.

The video decoding apparatus may include an entropy decoder 410, a rearrangement unit 415, an inverse quantizer 420, an inverse transformer 430, a predictor 440, an adder 450, a filtering unit 460, and a memory 470.

Similar to the video encoding apparatus of fig. 1, each element of the video decoding apparatus may be implemented in hardware, software, or a combination of hardware and software. Further, the function of each element may be implemented as software, and the microprocessor may be implemented to execute the software function corresponding to each element.

The entropy decoder 410 determines a current block to be decoded by decoding a bitstream generated by a video encoding apparatus and extracting information related to block division, and extracts prediction information required to reconstruct the current block, information on a residual signal, and the like.

The entropy decoder 410 extracts information about the size of CTUs from a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS), determines the size of CTUs, and partitions a picture into CTUs of the determined size. Then, the decoder determines the CTU as the highest layer (i.e., root node) of the tree structure, and extracts partition information about the CTU to partition the CTU using the tree structure.

For example, when the CTU is segmented using the QTBTTT structure, a first flag (qt_split_flag) related to the segmentation of QT is extracted to segment each node into four nodes of a sub-layer. For a node corresponding to a leaf node of QT, a second flag (mtt_split_flag) related to the division of MTT and information on a division direction (vertical/horizontal) and/or a division type (binary/trigeminal) are extracted to divide the corresponding leaf node in an MTT structure. Thereby, each node below the leaf node of QT is recursively partitioned in the BT or TT structure.

As another example, when the CTU is partitioned using the QTBTTT structure, a CU partition flag (split_cu_flag) indicating whether to partition the CU may be extracted. When the corresponding block is divided, a first flag (qt_split_flag) may be extracted. In a partitioning operation, zero or more recursive MTT partitions may occur per node after zero or more recursive QT partitions. For example, CTUs may undergo MTT segmentation directly without QT segmentation, or only QT segmentation multiple times.

As another example, when CTUs are segmented using the QTBT structure, a first flag (qt_split_flag) related to QT segmentation is extracted, and each node is segmented into four nodes of the lower layer. Then, a split flag (split_flag) indicating whether to further split a node corresponding to a leaf node of QT with BT and split direction information are extracted.

Once the current block to be decoded is determined through tree structure segmentation, the entropy decoder 410 extracts information about a prediction type indicating whether the current block is intra-predicted or inter-predicted. When the prediction type information indicates intra prediction, the entropy decoder 410 extracts syntax elements of intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the entropy decoder 410 extracts syntax elements for the inter prediction information, that is, information indicating a motion vector and a reference picture referenced by the motion vector.

On the other hand, the entropy decoder 410 extracts information about the encoding mode of the residual block (e.g., information about whether the residual block is encoded or only sub-blocks of the residual block, information indicating a partition type selected to partition the residual block into sub-blocks, information for identifying the encoded residual sub-blocks, quantization parameters, etc.) from the bitstream. Also, the entropy decoder 410 extracts information on the quantized transform coefficient of the current block as information on the residual signal.

The reordering unit 415 may change the sequence of quantized 1D transform coefficients entropy-decoded by the entropy decoder 410 into a 2D coefficient array (i.e., block) in the reverse order of coefficient scanning performed by the video encoding device.

The inverse quantizer 420 inversely quantizes the quantized transform coefficients, and the inverse transformer 430 generates a reconstructed residual block of the current block via reconstructing the residual signal by inversely transforming the inversely quantized transform coefficients from the frequency domain to the spatial domain based on information about the coding mode of the residual block.

When the information on the encoding mode of the residual block indicates that the residual block of the current block is encoded in the video encoding apparatus, the inverse transformer 430 generates a reconstructed residual block of the current block by performing inverse transformation on the inverse quantized transform coefficients using the size of the current block (and thus the size of the residual block to be restored) as a transform unit.

Further, when the information on the encoding mode of the residual block indicates that only one sub-block of the residual block is encoded in the video encoding apparatus, the inverse transformer 430 generates a residual block of the reconstructed current block by reconstructing a residual signal of the transformed sub-block via inverse transforming the inverse quantized transform coefficient using the size of the transformed sub-block as a transform unit, and by setting the residual signal of the untransformed sub-block to "0".

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

The intra predictor 442 determines an intra prediction mode of the current block among a plurality of intra prediction modes based on syntax elements of the intra prediction mode extracted from the entropy decoder 410, and predicts the current block using reference pixels around the current block according to the intra prediction mode.

The inter predictor 444 determines a motion vector of the current block and a reference picture referenced by the motion vector using syntax elements of the inter prediction mode extracted by the entropy decoder 410, and predicts the current block based on the motion vector and the reference picture.

The adder 450 reconstructs the current block by adding the residual block output from the inverse transformer 430 to the prediction block output from the inter predictor 444 or the intra predictor 442. In intra prediction of a block to be decoded later, pixels in the reconstructed current block are used as reference pixels.

The filtering unit 460 may include a deblocking filter 462 and an SAO filter 464. Deblocking filter 462 deblocking filters boundaries between reconstructed blocks to remove block artifacts caused by block-by-block decoding. SAO filter 464 performs additional filtering on the reconstructed block after deblocking filtering the corresponding offset to compensate for differences between the reconstructed pixel and the original pixel caused by lossy encoding. The reconstructed block filtered by the deblocking filter 462 and the SAO filter 464 is stored in a memory 470. When all blocks in one image are reconstructed, the reconstructed image is used as a reference image for inter prediction of blocks in a subsequent image to be encoded.

In the conventional video encoding/decoding method, in order to reduce complexity of prediction of a chrominance component, each chrominance component is predicted in the same manner as a prediction process of a luminance component, or in a simplified manner of a prediction process of a luminance component. However, this conventional method has a problem in that color distortion occurs.

The present invention proposes an encoding and decoding method for efficiently predicting a chrominance component in a chrominance block (i.e., a current block) of a target block to be reconstructed.

The method proposed herein is a method in which information about residual samples (or residual signals) of one of Cb and Cr chroma components is encoded and signaled, and information about residual samples of the other chroma component is derived without being encoded and signaled.

Herein, the residual samples of the chroma component to be derived may be referred to as "second residual samples of the second chroma component", while the residual samples of the chroma component to be encoded and signaled to derive the second residual samples may be referred to as "first residual samples of the first chroma component".

The first chrominance component may be one of a Cb chrominance component and a Cr chrominance component, and the second chrominance component may be the other of the Cb chrominance component and the Cr chrominance component. For example, when the residual samples of the Cb chroma component are encoded and signaled, and the residual samples of the Cr chroma component are derived, the residual samples of the Cb chroma component may be referred to as first residual samples, and the residual samples of the Cr chroma component may be referred to as second residual samples. As another example, when the residual samples of the Cr chroma component are encoded and signaled, and the residual samples of the Cb chroma component are derived, the residual samples of the Cr chroma component may be referred to as first residual samples and the residual samples of the Cb chroma component may be referred to as second residual samples.

The method of deriving the second residual sample may be classified into 1) an embodiment using correlation information about the first residual sample and the second residual sample, 2) an embodiment of determining whether to activate or apply the second residual sample derivation scheme, and the like. In addition, the embodiment using the related information may be divided into different embodiments according to whether or not the inter-chromaticity difference is used. Hereinafter, terms used herein will be first defined, and then each embodiment will be described in detail.

Related information

The related information refers to information for deriving the second residual samples from the first residual samples, and may be adaptively determined according to a range of luminance component values of the current block to be encoded. The related information may include multiplication information or may include multiplication information and offset information.

The related information may be defined and signaled at various locations in the bitstream to the video decoding apparatus and may be decoded from the locations in the bitstream. For example, the relevant information may be defined and signaled at one or more locations in high-level syntax (high-level syntaxes, HLS) such as SPS, PPS, and picture level. As another example, the related information may be signaled at a lower level such as tile group level, tile level, CTU level, unit block level (CU, TU, PU), etc. As another example, a difference value (difference related information) having related information signaled via HLS may be signaled at a lower level.

According to the embodiment, the related information may not be directly signaled, but some information of which the related information can be derived in the video decoding apparatus may be signaled. For example, table information including fixed values of the correlation information may be signaled, and an index value indicating the correlation information used to derive the second residual sample among the fixed values in the table information may be signaled. As another example, the table information may not be signaled, but may be predefined between the video encoding device and the video decoding device. Index values may be defined and signaled at one or more of tile group level, tile level, and unit block level.

The correlation information is information for deriving the second residual samples, so that when the derivation of the second residual samples is applied, it can be signaled. Accordingly, when the first syntax element to be described below indicates that the derivation of the second residual samples is allowed, the related information may be decoded from the bitstream, or when the second syntax element to be described below indicates that the derivation of the second residual samples is applied, the related information may be decoded from the bitstream.

Multiplication information

The multiplication information refers to information indicating a multiplication factor between the first residual sample and the second residual sample. When a multiplication factor is applied to (the value of) the first residual sample, a value equal to (the value of) the second residual sample or a value within a range corresponding to the second residual sample may be derived. The multiplication factor may represent a proportional relationship, a weight relationship, a symbol relationship, etc. between the first residual sample and the second residual sample. Accordingly, the multiplication factor may be an integer such as-1 or a fraction such as 1/2 or-1/2.

When multiplication information is signaled in the form of a flag 0 or 1 and the multiplication factor represents a symbol relationship between the first residual sample and the second residual sample, the multiplication information may represent the multiplication factor by a method shown in equation 1.

[ Equation 1]

Multiplication factor=1-2× (multiplication information)

Multiplication information (i.e., flag) equal to 0 indicates that the first residual sample and the second residual sample have the same symbol relationship, and a multiplication factor of "1" may be applied to the first residual sample. Multiplication information (i.e., flag) equal to 1 indicates that the first residual sample and the second residual sample have different symbol relationships, and a multiplication factor "-1" may be applied to the first residual sample.

Offset information

The offset information refers to information indicating an offset factor between the first residual sample (to which the multiplication factor is applied) and the second residual sample. When the offset factor is applied to the first residual sample (to which the multiplication factor is applied), a value equal to or in a range corresponding to the second residual sample may be derived. The offset factor may be an integer such as-1, 0, or 1 or a fraction such as 1/2 or-1/2.

For the case where the offset factor is equal to 0, if only multiplication information is included in the related information, the offset information may not be signaled, and if both the multiplication information and the offset information are included in the related information, the offset information may indicate that the offset factor is equal to 0.

Difference between chromaticities

The inter-chroma difference refers to a difference between the first residual sample and the second residual sample (i.e., refers to a value obtained by a subtraction between the first residual sample and the second residual sample). More specifically, the inter-chroma difference value corresponds to a value derived by a subtraction between the first residual sample (to which the correlation information is applied) and the second residual sample. For example, if the correlation information includes only multiplication information, the inter-chroma difference may be derived by performing a subtraction between the first residual sample (to which the multiplication factor is applied) and the second residual sample. As another example, if the correlation information includes multiplication information and offset information, the inter-chroma difference value may be derived by performing a subtraction between the first residual sample (to which the multiplication factor and the offset factor are applied) and the second residual sample.

Embodiment 1

Embodiment 1 is a method of using both the correlation information and the difference between chromaticities. Embodiment 1 may be divided into the following sub-embodiments according to the step of the encoding step performed by the process of deriving the inter-chroma difference value and the related information and the step of the decoding step performed by the process of deriving the second residual samples.

Embodiment 1-1

In embodiment 1-1, the process of deriving the inter-chroma difference value and the related information is performed before the step of transforming the residual samples, and the process of deriving the second residual samples is performed after the step of inversely quantizing the residual samples.

Exemplary block diagrams and flowcharts for performing the video encoding apparatus of embodiment 1-1 are shown in fig. 5 and 6, respectively, and exemplary block diagrams and flowcharts for performing the video decoding apparatus of embodiment 1-1 are shown in fig. 7 and 8, respectively.

The subtractor 130 may obtain a first residual sample and a second residual sample (S610). Specifically, the first residual sample may be obtained by a subtraction between a prediction block (or predicted sample) of the first chrominance component and a chrominance block of the first chrominance component, and the second residual sample may be obtained by a subtraction between a prediction block of the second chrominance component and a chrominance block of the second chrominance component. The prediction block of the chrominance component may be derived by the prediction of the predictor 120, and information for the prediction, i.e., prediction information, may be derived in this process. The process of generating predicted samples and the process of deriving prediction information may be equally applied to other embodiments of the present description.

The chrominance component predictor 510 may determine whether the second residual sample is derived from the first residual sample (S620).

The chrominance component predictor 510 may determine one of a method of encoding both the first residual sample and the second residual sample (i.e., a general method) and a method of deriving the second residual sample (i.e., a second residual sample derivation method) for the chrominance block. For example, the chrominance component predictor 510 calculates a rate distortion value through a rate distortion analysis of a general method and a derivation method, and may select or determine one method having the best rate distortion characteristics for the chrominance block. The process of determining whether to derive the second residual samples may be equally applicable to other embodiments of the present description.

When the second residual sample deriving method (i.e., the method of deriving the second residual samples) is selected for the chroma block, the chroma component predictor 510 may modify the first residual samples (S630). Modification of the first residual sample may be achieved by applying the correlation information to the first residual sample.

The chrominance component predictor 510 may derive a difference value between the chrominance using the modified first residual sample and the second residual sample (S640). The inter-chroma difference may be derived by subtracting the modified first residual sample and the second residual sample.

Operation S630 and operation S640 may be performed by the following equation 2.

[ Equation 2]

Cro_r=Cro_resi2-(W*Cro_resi1+Offset)

In equation 2, cro_ resi represents a first residual sample, cro_ resi2 represents a second residual sample, cro_r represents an inter-chroma difference value, W represents a multiplication factor, and Offset represents an Offset factor. Referring again to equation 2 focusing on the second residual sample, cro_resi2 may be a primary signal of the second residual sample (i.e., a primary residual signal of the second chrominance component), and cro_r may be a secondary signal of the second residual sample (i.e., a secondary residual signal of the second chrominance component).

The transformer 140 may transform the inter-chroma difference value and the first residual sample, and the quantizer 145 may quantize the transformed inter-chroma difference value and the transformed first residual sample (S650). Here, the inter-chroma difference value may be quantized by "quantization parameter changed with qp_c_offset" according to a quantization parameter of the first residual sample or the luma component. Qp_c_offset may be determined by various methods. For example, qp_c_offset may be adaptively determined according to one or more of a range of luminance component values (a range of luminance values), a size of a chroma block, and a range of quantization parameters of a luminance component. As another example, qp_c_offset may be determined as a value preset in the video encoding apparatus and the video decoding apparatus. As another example, the video encoding apparatus may determine qp_c_offset as an arbitrary value, perform quantization processing, and signal the value of qp_c_offset used in quantization processing to the video decoding apparatus. The quantization method using qp_c_offset can also be applied to other embodiments of the present specification.

The transformed and quantized inter-chroma difference values, the first residual samples, the related information, and the prediction information may be encoded and signaled to the video decoding apparatus (S660). Here, the second residual samples are not signaled.

The entropy decoder 410 may decode the inter-chroma difference value, the first residual sample, the related information, and the prediction information from the bitstream (S810). The inverse quantizer 420 may inversely quantize the inter-chroma difference value and the first residual sample, and the inverse transformer 430 may inversely transform the inversely quantized inter-chroma difference value and the inversely quantized first residual sample (S820).

The predictor 440 may generate (or reconstruct) predicted samples (or predicted blocks) of the first chrominance component and predicted samples of the second chrominance component based on the prediction information (S820).

The chrominance component reconstruction unit 710 may determine whether to derive a second residual sample from the first residual sample (whether to activate (allow) and/or apply a second residual sample derivation method) (S830). The detailed description of operation S830 will be described below by means of separate embodiments.

When it is determined that the second residual sample is to be derived, the chroma component-reconstruction unit 710 may modify the first residual sample with the (inverse-transformed) correlation information (S840). Further, the chroma component-reconstruction unit 710 may derive a second residual sample using the modified difference between the first residual sample and the inverse transformed chroma (S850). The second residual samples may be derived by adding the modified first residual samples and the inverse transformed inter-chroma difference values.

Operation S630 and operation S640 may be performed by the following equation 3.

[ Equation 3]

Cro_resi2=(W*Cro_resi1+Offset)+Cro_r

The adder 450 may reconstruct a chroma block of the first chroma component by adding the first residual sample of the first chroma component and the prediction block, and may reconstruct a chroma block of the second chroma component by adding the second residual sample of the derived second chroma component and the prediction block (S860).

Embodiments 1 to 2

In embodiments 1-2, the process of deriving the inter-chroma difference and the related information is performed after the step of quantizing the residual samples, and the process of deriving the second residual samples is performed before the step of inversely quantizing the residual samples.

Exemplary block diagrams and flowcharts for performing the video encoding apparatus of embodiments 1-2 are shown in fig. 9 and 10, respectively, and exemplary block diagrams and flowcharts for performing the video decoding apparatus of embodiments 1-2 are shown in fig. 11 and 12, respectively.

The subtractor 130 may obtain a first residual sample and a second residual sample (S1010). Residual samples of each chrominance component may be obtained by subtracting a prediction block and a chrominance block of each chrominance component, and the prediction block and the prediction information of each chrominance component may be derived through a prediction process of the predictor 120.

The transformer 140 may transform the first residual sample and the second residual sample, and the quantizer 145 may quantize the transformed first residual sample and the transformed second residual sample (S1020). Here, the second residual sample may be quantized to a value obtained by adding a quantization offset for quantizing the second residual sample to a quantization parameter of the first residual sample. The quantization offset may be determined by various methods. For example, the quantization offset may be adaptively determined according to one or more of a range of luminance component values (a range of luminance values), a size of the first residual sample value, and a bit depth of the second residual sample. As another example, the quantization offset may be determined as a value preset in the video encoding apparatus and the video decoding apparatus. The video decoding apparatus may determine quantization parameters using delta-QP signaled from the video encoding apparatus, add quantization offsets to the quantization parameters to derive quantization parameters for the second residual samples, and then inversely quantize the second residual samples using the derived quantization parameters. Quantization/inverse quantization methods using quantization offset may be applied to other embodiments of the present specification.

According to an embodiment, the quantization coefficient "0" may be derived by a quantization process for the second residual sample (i.e. there may be no residual signal in the quantization process). In this case, information or syntax elements indicating that the quantization coefficient "0" is derived may be signaled from the video encoding apparatus to the video decoding apparatus.

On the other hand, one or more of a quantization parameter value (first value) of the first residual sample (to which the quantization offset is not added), a value (second value) obtained by adding the quantization offset and the quantization parameter of the first residual sample, and an average value of the first value and the second value may be used for in-loop filtering processing of the second residual sample. For example, one or more of the first value, the second value, and the average value may be used as a parameter to determine the in-loop filter strength of the second residual sample, or may be used as a parameter to determine an index in a table used to determine the boundary strength. The method of using one or more of the first value, the second value, and the average value in the loop filtering process may be applied to other embodiments of the present specification.

The chrominance component predictor 510 may determine whether the second residual sample is derived from the first residual sample (S1030). When it is determined that the second residual sample is to be derived, the chrominance component predictor 510 may modify the quantized first residual sample (S1040). The modification of the first residual samples may be performed by applying the correlation information to the quantized first residual samples.

The chrominance component predictor 510 may derive a chrominance difference value using the modified first residual sample and the quantized second residual sample (S1050). The inter-chroma difference may be derived by performing a subtraction between the modified first residual sample and the quantized second residual sample.

Operations S1040 and S1050 may be performed by the following equation 4.

[ Equation 4]

Q(T(Cro_r))=Q(T(Cro_resi2))-(W*Q(T(Cro_resi1))+Offset)

In equation 4, Q (T (cro_ resi)) represents the transformed and quantized first residual samples, Q (T (cro_ resi 2)) represents the transformed and quantized second residual samples, and Q (T (cro_r)) represents the inter-chroma difference value derived from the transformed and quantized first residual samples and the transformed and quantized second residual samples.

The inter-chroma difference value, the first residual sample, the related information, and the prediction information may be encoded and signaled to the video decoding apparatus (S1060). Here, the second residual samples are not signaled.

The entropy decoder 410 may decode the inter-chroma difference value, the first residual sample, the related information, and the prediction information from the bitstream (S1210). The predictor 440 may generate (or reconstruct) a predicted sample (prediction block) of the first chrominance component and a predicted sample of the second chrominance component based on the prediction information (S1220).

The chrominance component reconstruction unit 710 may determine whether to derive a second residual sample from the first residual sample (i.e., whether to activate and/or apply the second residual sample derivation method) (S1230). The detailed description of operation S1230 will be described below by a separate embodiment.

When it is determined that the second residual sample is to be derived, the chrominance component reconstruction unit 710 may modify the first residual sample using the correlation information (S1240). In addition, the chroma component-reconstruction unit 710 may derive a second residual sample using the modified first residual sample and the difference between the chromas (S1250). The second residual sample may be derived by adding the modified first residual sample and the inter-chroma difference value.

Operations S1240 and S1250 may be performed by the following equation 5.

[ Equation 5]

Q(T(Cro_resi2))=(W*Q(T(Cro_resi1))+Offset)+Q(T(Cro_r))

The inverse quantizer 420 may inversely quantize the first residual sample and the derived second residual sample, and may inversely transform the inversely quantized first residual sample and the inversely quantized second residual sample (S1260). The adder 450 may reconstruct a chroma block of the first chroma component by adding a first residual sample of the inverse transformed first chroma component and the prediction block, and may reconstruct a chroma block of the second chroma component by adding a second residual sample of the inverse transformed second chroma component and the prediction block (S1270).

Embodiment 2

Embodiment 2 is a method of predicting and deriving a second residual sample using correlation information without using an inter-chroma difference value.

Embodiment 2 differs from embodiment 1 in that the inter-chromaticity difference value is not used, and the process of deriving the inter-chromaticity difference value is not performed (S640 or S1050).

In addition to this difference, the rest of the processing of embodiment 1 can also be performed in embodiment 2. Accordingly, as in embodiment 1-1, the process of deriving the correlation information in the video encoding apparatus may be performed before the step of transforming the residual samples, and the process of deriving the second residual samples in the video decoding apparatus may be performed after the step of inverse transforming the residual samples. Furthermore, in the embodiments 1-2, the process of deriving the correlation information in the video encoding apparatus may be performed after the step of quantizing the residual samples, and the process of deriving the second residual samples in the video decoding apparatus may be performed before the step of inversely quantizing the residual samples. However, the remaining steps except for the step of transforming/quantizing the residual samples and the step of inverse quantizing/inverse transforming the residual samples will be described below.

Fig. 13 and 14 show flowcharts illustrating an example of embodiment 2.

The subtractor 130 may subtract the prediction block of the first chrominance component and the chrominance block of the first chrominance component to obtain a first residual sample, and may subtract the prediction block of the second chrominance component and the chrominance block of the second chrominance component to obtain a second residual sample (S1310).

The chrominance component predictor 510 may determine whether the second residual sample is derived from the first residual sample (S1320). When it is determined that the second residual sample is to be derived, the chrominance component predictor 510 may derive the correlation information using the first residual sample and the second residual sample (S1330).

On the other hand, according to an embodiment, when only multiplication information is included in the related information, the second residual sample deriving method may include the following three modes.

1) Mode 1 the value of the Cb residual sample is signaled and derived by applying a multiplication factor of-1/2 or +1/2 to the value of the Cb residual sample.

2) Mode 2 the value of the Cb residual sample is signaled and the value of the Cr residual sample is derived by applying a multiplication factor-1 or +1 to the value of the Cb residual sample.

3) Mode 3 the value of the Cr residual sample is signaled and derived by applying a multiplication factor-1/2 or +1/2 to the value of the Cr residual sample.

In addition, the second residual sample deriving method may further include a mode in which an offset factor is applied to each of the first to third modes when offset information is also included in the correlation information.

In this embodiment, the chrominance component predictor 510 may determine the mode having the best rate-distortion characteristic among the above modes as the mode for the chrominance block. The chrominance component predictor 510 may integrally perform a process of determining one of the above-described general method and the second residual sample deriving method and a process of determining one of modes of the second residual sample deriving method. For example, the chrominance component predictor 510 may determine a mode or method having the best rate-distortion characteristics among modes of the general method and the second residual sample deriving method for the chrominance block.

The first residual sample, the related information, and the prediction information may be encoded and signaled to the video decoding apparatus (S1340). Here, the difference between the second residual sample and the chroma is not signaled.

The entropy decoder 410 may decode the first residual sample, the related information, and the prediction information from the bitstream (S1410).

The predictor 440 may generate (or reconstruct) predicted samples of the first chrominance component (prediction block) and predicted samples of the second chrominance component based on the prediction information (S1420).

The chroma component-reconstruction unit 710 may determine whether to derive a second residual sample from the first residual sample (i.e., whether to activate and/or apply a second residual sample-derivation method) (S1430). The detailed description of operation S1430 will be described below by way of separate embodiments.

When it is determined that the second residual sample is to be derived, the chroma component-reconstruction unit 710 may derive the second residual sample by applying the correlation information to the first residual sample (S1440). For example, when the related information includes multiplication information, the second residual sample may be derived by applying a multiplication factor indicated by the multiplication information to the first residual sample. As another example, when the related information includes multiplication information and offset information, the second residual sample may be derived by applying an offset factor indicated by the offset information to the first residual sample to which the multiplication factor is applied.

Operation S1440 may be performed by the following equation 6.

[ Equation 6]

Cro_resi2=W*Cro_resi1+Offset

Comparing equation 6 with equations 2 to 5, it can be seen that in embodiment 2, the inter-chromaticity difference (i.e., cro_r=0) is not used. Accordingly, the transform/inverse transform process, the quantization/inverse quantization process, and the encoding/decoding process are not performed on the inter-chroma difference value.

The adder 450 may reconstruct a chroma block of the first chroma component by adding the first residual sample of the first chroma component and the prediction block, and may reconstruct a chroma block of the second chroma component by adding the second residual sample of the derived second chroma component and the prediction block (S1450).

Embodiment 3

Embodiment 3 is a method of determining whether to derive a second residual sample from a first residual sample (i.e., whether to allow (activate) and/or apply the second residual sample derivation method).

Whether to perform the second residual sample derivation method may be determined by various criteria. The various criteria may include 1) a value of a syntax element (e.g., flag) indicating whether the derivation of the second residual samples is allowed and/or applied (i.e., whether on or off), 2) a prediction mode of the target block, 3) a range of luma component values, and so forth.

Standard 1 syntax element indicating on/off

The first syntax element and/or the second syntax element may be employed to indicate whether the second residual samples are derived.

The first syntax element, which is a syntax element indicating whether the second residual sample deriving method is allowed (or activated) (i.e., whether on or off), may be defined and signaled to the video decoding apparatus at various positions of the bitstream. For example, the first syntax element may be defined and signaled at a CTU or higher level, or may be defined and signaled at one or more levels of a unit block (PU, TU, CU) level, tile group level, and picture level.

The second syntax element, which is a syntax element indicating whether the second residual sample derivation method is applied to the target block (chroma block) (i.e., whether the target block is on or off), may be defined and signaled to the video decoding apparatus at various positions of the bitstream. For example, the second syntax element may be defined and signaled at a CTU or higher level, or may be defined and signaled at one or more levels of a unit block (PU, TU, CU) level, tile group level, and picture level.

According to an embodiment, the first syntax element may be defined and signaled at a relatively higher level in the bitstream and the second syntax element may be defined and signaled at a relatively lower level in the bitstream. In this case, when the second residual sample deriving method is turned off at a higher level, the second syntax element is not signaled at a lower level, and even when the second residual sample deriving method is turned on at a higher level, it can be selectively determined whether to be turned on or off at a lower level. Accordingly, the bit efficiency of the second residual sample deriving method may be improved.

Fig. 13 shows an example of determining whether to turn on or off the second residual sample derivation method.

The video encoding apparatus may determine whether to allow the second residual sample derivation method, and may set a value of the first syntax element based on a result of the determination, and signal the first syntax element to the video decoding apparatus. Further, the video encoding apparatus may determine whether to apply the second residual sample derivation method, and may set a value of the second syntax element as a result of the determination, and signal the second syntax element to the video decoding apparatus.

The video decoding apparatus may decode the first syntax element from the bitstream (S1510), and may determine whether to allow the second residual sample deriving method according to a value of the first syntax element (S1520).

When the second syntax element indicates that the second residual sample derivation method is allowed (i.e., the first syntax element=1; S1520), the video decoding apparatus may decode the second syntax element from the bitstream (S1530). Further, the video decoding apparatus may determine whether to apply the second residual sample derivation method according to the value of the second syntax element (S1540).

When the second syntax element indicates that the second residual sample derivation method is applied to the target block (i.e., the second syntax element=0; S1540), the video decoding apparatus may derive the second residual sample based on the correlation information and the first residual sample (or the correlation information, the first residual sample, and the inter-chroma difference value) for the target block (S1550).

When the first syntax element indicates that the second residual sample derivation method is not allowed in operation S1520 (i.e., the first syntax element=0), or when the second syntax element indicates that the second residual sample derivation method is not applied in operation S1540, the derivation of the second residual sample is not performed on the target block.

Standard 2 prediction mode of target block

Whether to turn on or off the second residual sample derivation method may be considered or adaptively determined according to a prediction mode of a target block (chroma block).

For example, when the chroma block is predicted in one of an intra mode, an inter mode, an IBC mode, and a palette mode, the derivation of the second residual samples may be turned on or off. As another example, when a chroma block is predicted in two or more of an intra mode, an inter mode, an IBC mode, and a palette mode (when a chroma block is predicted in one of the two or more modes), the derivation of the second residual sample may be turned on or off.

As yet another example, the derivation of the second residual samples may be turned on or off when the chroma block is predicted by a cross-component linear model (CCLM) or a Direct Mode (DM) in intra prediction mode. In this case, only when the chroma block is predicted by the CCLM or DM, information indicating the turning on or off of the derivation of the second residual samples may be signaled to the video decoding apparatus.

As yet another example, when a chroma block is predicted by a bi-prediction mode or a merge mode in an inter mode, and when a chroma block is predicted with reference to a zeroth reference picture, derivation of the second residual sample may be turned on or off. The video decoding apparatus may be signaled with information indicating on or off of the derivation of the second residual samples only when the chroma block is predicted by the bi-prediction mode or the merge mode, or only when the chroma block is predicted with reference to the zeroth reference picture.

The example of considering the prediction mode of the chroma block may be combined with the above-described example using the first syntax element and the second syntax element. For example, in operation S1520, when the first syntax element is equal to 1 and the prediction mode of the chroma block corresponds to the derived prediction mode of the second residual sample that is turned on, the second syntax element may be decoded from the bitstream. (S1530). That is, whether to decode the second syntax element may be determined in consideration of a prediction mode of the chroma block.

Standard 3 Range of values of luminance component

The range of values of the luminance component (range of luminance values) may be divided into two or more portions, and depending on which of the divided portions the value of the luminance component of the target block belongs to, it may be determined whether the second residual sample derivation method is applied.

For example, in the case where the range of the values of the luminance component is divided into two parts (a first part and a second part), the second residual sample derivation method is not applied when the value of the luminance component of the target block belongs to the first part, and the second residual sample derivation method may be applied when the value of the luminance component of the target block belongs to the second part, or vice versa.

Of the two or more parts, the part to which the second residual sample derivation method is not applied may correspond to a "visual perception part" where the user's vision may sharply react, while the part to which the second residual sample derivation method is applied may not correspond to the "visual perception part". Accordingly, the second residual sample deriving method may be selectively applied to only a portion other than the visual sense portion, and not to the visual sense portion, so that degradation of subjective image quality may be prevented.

The one or more partial values indicating the range of the first portion and the partial value indicating the range of the second portion may be signaled from the video encoding device to the video decoding device. According to an embodiment, the partial value may be preset between the video encoding apparatus and the video decoding apparatus without signaling.

Standard 4 quantization results

The second residual sample derivation method may be selectively applied when the quantized coefficients of the second residual samples have very small values (i.e., when a small number of quantized coefficients are present or present) due to the accuracy of the prediction of the second chrominance component. Further, in this case, quantization of only a portion, but not all, of the second residual samples may not be omitted (i.e., only some of the second residual samples are signaled).

Other criteria

The second residual sample derivation method may or may not be applied to the target block when a delta-QP (DQP) of the luma component is greater than or equal to a preset value, when a transform skip (transform skip) mode is not applied to the chroma block, or when a modulation (block differential coded modulation, BDPCM) mode of the block differential coding is not applied to the target block.

The second residual sample derivation method may not be applied to the target block when the image including the target block is a progressive random access (gradual random access, GRA) image for random access or an instantaneous decoding record (instantaneous decoding recoding, IDR) image.

Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications and changes are possible without departing from the spirit and scope of the present invention. For brevity and clarity, exemplary embodiments have been described. Accordingly, it should be understood by those of ordinary skill that the scope of the embodiments is not limited by the embodiments explicitly described above, but is included within the claims and their equivalents.

Claims

1. A method for reconstructing a chrominance block of a target block to be reconstructed, the method comprising:

decoding, from a bitstream, correlation information between the first residual sample and the second residual sample, information about the first residual sample, and prediction information of the chroma block,

wherein the first residual sample is a residual sample of a first chroma component, and the second residual sample is a residual sample of a second chroma component,

wherein information about the second residual sample is not decoded from the bitstream;

Wherein, the prediction information includes intra-frame prediction information or inter-frame prediction information;

generating, based on the prediction information, predicted samples of the first chroma component and predicted samples of the second chroma component;

deriving a second residual sample by applying the relevant information to the first residual sample; and

A chroma block of a first chroma component is reconstructed based on the first residual samples and the predicted samples of the first chroma component, and a chroma block of a second chroma component is reconstructed based on the second residual samples and the predicted samples of the second chroma component.

2 . The method of claim 1 , wherein the first chrominance component is one of a Cb chrominance component and a Cr chrominance component, and the second chrominance component is the other of the Cb chrominance component and the Cr chrominance component.

The method of claim 1 , wherein decoding comprises decoding relevant information from a picture level of a bitstream.

4. The method according to claim 1, wherein the relevant information comprises multiplication information for indicating a multiplication factor between the first residual sample and the second residual sample, and

The deriving the second residual sample includes: deriving the second residual sample by applying a multiplication factor indicated by the multiplication information to the first residual sample.

5. The method according to claim 4, wherein the relevant information further comprises offset information, wherein the offset information is used to indicate an offset factor between the first residual sample and the second residual sample,

The deriving the second residual sample comprises: deriving the second residual sample by applying an offset factor indicated by the offset information to the first residual sample to which the multiplication factor is applied.

6. The method according to claim 1, wherein:

Decoding includes:

decoding a first syntax element from a sequence parameter set level of the bitstream, the first syntax element indicating whether derivation of second residual samples is allowed; and

When the first syntax element indicates that derivation of the second residual sample is allowed, decoding a second syntax element from a level below the sequence parameter set level in the bitstream, the second syntax element indicating whether derivation of the second residual sample is applied to the chroma block,

The derivation of the second residual sample includes: when the second syntax element indicates that the derivation of the second residual sample is applied to the chrominance block, deriving the second residual sample.

7 . The method of claim 6 , wherein decoding the second syntax element comprises decoding the second syntax element taking into account a prediction mode of the target block.

8. A method for encoding a chrominance block of a target block, the method comprising:

encoding the correlation information between the first residual sample and the second residual sample, the information about the first residual sample, and the prediction information of the chrominance block into a bitstream,

wherein information about the second residual sample is not encoded into the bitstream;

9. A method for transmitting a bitstream associated with video data, the method comprising:

generating a bitstream by encoding a chrominance block of a target block;

Sending a bitstream to a video decoding device,

The generating of the bitstream includes: