KR20200132762A - Method and apparatus for reconstructing chroma block - Google Patents

Abstract

The present invention relates to a chroma block reconstruction method and a video decoding device. The method according to one embodiment of the present invention is to reconstruct the chroma block of a reconstruction target block, and includes: a step of decoding, from a bitstream, information on the correlation between a first residual sample as the residual samples of a first chroma component and a second residual sample as the residual samples of a second chroma component, prediction information on the chroma block, and the first residual sample; a step of generating prediction samples of the first chroma component and prediction samples of the second chroma component based on the prediction information; a step of deriving the second residual sample by applying the correlation information to the first residual sample; and a step of reconstructing the chroma block of the first chroma component by adding the prediction samples of the first chroma component and the first residual sample and reconstructing the chroma block of the second chroma component by adding the prediction samples of the second chroma component and the second residual sample.

Description

Method for restoring color difference blocks and image decoding apparatus {METHOD AND APPARATUS FOR RECONSTRUCTING CHROMA BLOCK}

The present invention relates to encoding and decoding of an image, and more particularly, to a method and an image decoding apparatus for reconstructing a color difference block having improved encoding and decoding efficiency by efficiently predicting residual samples of a color difference component.

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

Accordingly, when moving or transmitting moving picture data, the moving picture data is compressed and stored or transmitted using an encoder, and the decoder receives the compressed moving picture data, decompresses and reproduces the compressed moving picture data. As such video compression technologies, there are H.264/AVC and HEVC (High Efficiency Video Coding), which improves coding efficiency by about 40% compared to H.264/AVC.

However, the size, resolution, and frame rate of an image are gradually increasing, and accordingly, the amount of data to be encoded is also increasing. Accordingly, a new compression technique with higher encoding efficiency and higher quality improvement effect than the existing compression technique is required.

In order to meet these needs, the present invention aims to provide an improved video encoding and decoding technology, and in particular, an aspect of the present invention is to derive the other from one of the Cb color difference component and the Cr color difference component, And a technique for improving the efficiency of decryption.

An aspect of the present invention is a method of restoring a color difference block of a target block to be restored, comprising: a correlation between a first residual sample, which is residual samples of a first color difference component, and a second residual sample, which is residual samples of a second color difference component. Decoding information, the first residual sample, and prediction information of the color difference block from a bitstream; Generating prediction samples of the first color difference component and prediction samples of the second color difference component based on the prediction information; Applying the correlation information to the first residual sample to derive the second residual sample; And reconstructing a color difference block of the first color difference component by adding the prediction samples of the first color difference component and the first residual sample, and adding the prediction samples of the second color difference component and the second residual sample, It provides a color difference block restoration method comprising the step of restoring a color difference block of a second color difference component.

Another aspect of the present invention is an image decoding apparatus for reconstructing a color difference block of a target block to be reconstructed, between a first residual sample, which is residual samples of a first color difference component, and a second residual sample, which is residual samples of a second color difference component. A decoding unit that decodes the correlation information, the first residual sample, and prediction information of the color difference block from a bitstream; A prediction unit that generates prediction samples of the first color difference component and prediction samples of the second color difference component based on the prediction information; A color difference component restoration unit for inducing the second residual sample by applying the correlation information to the first residual sample; And reconstructing a color difference block of the first color difference component by adding the prediction samples of the first color difference component and the first residual sample, and adding the prediction samples of the second color difference component and the second residual sample, It provides an image decoding apparatus comprising an adder for reconstructing a color difference block of a second color difference component.

As described above, according to an embodiment of the present invention, since either one of the Cb color difference component and the Cr color difference component is derived without being signaled, compression performance of encoding and decoding may be improved.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of the present disclosure.
2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.
3A is a diagram illustrating a plurality of intra prediction modes.
3B is a diagram illustrating a plurality of intra prediction modes including wide-angle intra prediction modes.
4 is an exemplary block diagram of an image decoding apparatus capable of implementing the techniques of the present disclosure.
5 is an exemplary block diagram of an image encoding apparatus capable of implementing an example of a method of reconstructing a residual block.
FIG. 6 is a flowchart illustrating an example of a method of reconstructing a residual block implemented in the image encoding apparatus illustrated in FIG. 5.
7 is an exemplary block diagram of an image decoding apparatus capable of implementing an example of a method of reconstructing a residual block.
FIG. 8 is a flowchart illustrating an example of a method of reconstructing a residual block implemented in the image decoding apparatus illustrated in FIG. 7.
9 is an exemplary block diagram of an image encoding apparatus capable of implementing another example of a residual block reconstruction method.
10 is a flowchart illustrating an example of a method of reconstructing a residual block implemented in the image encoding apparatus illustrated in FIG. 9.
11 is an exemplary block diagram of an image decoding apparatus capable of implementing another example of a method of reconstructing a residual block.
12 is a flowchart illustrating an example of a method of reconstructing a residual block implemented in the image decoding apparatus shown in FIG. 11.
13 and 14 are flow charts illustrating still other examples of a method of reconstructing a residual block.
15 is a flowchart illustrating an example of execution conditions of a residual block restoration method.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding identification codes to elements of each drawing, it should be noted that the same elements have the same symbols as possible even if 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 subject matter of the present invention, a detailed description thereof will be omitted.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of the present disclosure. Hereinafter, an image encoding apparatus and subordinate components of the apparatus will be described with reference to FIG. 1.

The image encoding apparatus includes a picture segmentation unit 110, a prediction unit 120, a subtractor 130, a transform unit 140, a quantization unit 145, a rearrangement unit 150, an entropy encoding unit 155, an inverse quantization unit. (160), an inverse transform unit 165, an adder 170, a filter unit 180, and a memory 190 may be included.

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

One image (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 or/and 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 the syntax of the CU, and information commonly applied to CUs included in one CTU is encoded as the syntax of the CTU. In addition, information commonly applied to all blocks in one slice is encoded as the syntax of the slice header, and information applied to all blocks constituting one picture is a picture parameter set (PPS) or picture. It is coded in the header. Further, information commonly referred to by a plurality of pictures is encoded in a sequence parameter set (SPS). In addition, information commonly referred to by one or more SPSs is encoded in a video parameter set (VPS). Also, information commonly applied to one tile or tile group may be encoded as syntax of a tile or tile group header.

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

After dividing each picture constituting an image into a plurality of CTUs (Coding Tree Units) having a predetermined size, the picture dividing unit 110 repetitively divides the CTU using a tree structure. (recursively) split. A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of coding.

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

2 shows a QTBTTT split tree structure. As shown in FIG. 2, the CTU may be first divided into a QT structure. The quadtree division 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 divided into four nodes of a lower layer is encoded by the entropy encoder 155 and signaled to the image decoding apparatus.

If the leaf node of the QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further divided into one or more of a BT structure or a TT structure. In the BT structure and/or the TT structure, a plurality of division directions may exist. For example, there may be two directions in which a block of a corresponding node is divided horizontally and a direction vertically divided. As shown in FIG. 2, when MTT division starts, a second flag (mtt_split_flag) indicating whether or not the nodes are divided, and a flag indicating additional division direction (vertical or horizontal) and/or a division type (Binary or Ternary). A flag indicating) is encoded by the entropy encoder 155 and signaled to the image decoding apparatus. Alternatively, before encoding the first flag (QT_split_flag) indicating whether each node is divided into four nodes of the lower layer, a CU split flag (split_cu_flag) indicating whether the node is divided is encoded. It could be. When it is indicated that the value of the CU split flag (split_cu_flag) 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 encoding. When indicating that the value of the CU split flag (split_cu_flag) is 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, two types of horizontally splitting a block of the corresponding node into two blocks of the same size (i.e., symmetric horizontal splitting) and a type splitting vertically (i.e., symmetric vertical splitting) Branches can exist. A split flag indicating whether each node of the BT structure is divided into blocks of a lower layer and split type information indicating a type to be divided are encoded by the entropy encoder 155 and transmitted to the image decoding apparatus. Meanwhile, a type of dividing the block of the corresponding node into two blocks having an asymmetric shape may further exist. The asymmetric form may include a form of dividing a block of a corresponding node into two rectangular blocks having a size ratio of 1:3, or a form of dividing a block of a corresponding node in a diagonal direction.

The CU can have various sizes according to 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'. According to the adoption of the QTBTTT division, the shape of the current block may be not only square but also rectangular.

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

In general, each of the current blocks in a picture can be predictively coded. In general, prediction of the current block is performed using an intra prediction technique (using data from a picture containing the current block) or an inter prediction technique (using data from a picture coded before a picture containing the current block). Can be done. Inter prediction includes both one-way prediction and two-way prediction.

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. There are a plurality of intra prediction modes according to the 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. Depending on each prediction mode, the surrounding pixels to be used and the equation are defined differently.

For efficient directional prediction for the rectangular-shaped current block, directional modes (67 to 80, intra prediction modes -1 to -14) shown by dotted arrows in FIG. 3B may be additionally used. These may be referred to as "wide angle intra-prediction modes". Arrows in FIG. 3B indicate corresponding reference samples used for prediction, and do not indicate a prediction direction. The prediction direction is opposite to the direction indicated by the arrow. In the wide-angle intra prediction modes, when the current block is a rectangular shape, a specific directional mode is predicted in the opposite direction without additional bit transmission. In this case, among the wide-angle intra prediction modes, some wide-angle intra prediction modes available for the current block may be determined based on a ratio of the width and height of the rectangular current block. For example, wide-angle intra prediction modes with an angle less than 45 degrees (intra prediction modes 67 to 80) can be used when the current block has a rectangular shape with a height smaller than the width, and wide-angle with an angle greater than -135 degrees. The intra prediction modes (intra prediction modes -1 to -14) can be used when the current block has a rectangular shape whose height is greater than the width.

The intra prediction unit 122 may determine an intra prediction mode to be used to encode 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. It is also possible to select an intra prediction mode.

The intra prediction unit 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts the current block 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 image 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 prior to the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector corresponding to a 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 on 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 used to predict the current block and information on a motion vector is encoded by the entropy encoder 155 and transmitted to an image decoding apparatus.

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 divides the residual block into one or more transform blocks, applies the transform to one or more transform blocks, and transforms 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 comprising one or more transform coefficient values. A 2D transformation kernel may be used for transformation, and a 1D transformation kernel may be used for horizontal and vertical transformation respectively. The transform kernel may be based on discrete cosine transform (DCT), discrete sine transform (DST), or the like.

The transform unit 140 may transform residual signals in the residual block by using the entire size of the residual block as a transform unit. In addition, the transform unit 140 may divide the residual block into two sub-blocks in a horizontal or 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 may be very sparse in a subblock on which transformation is not performed. The residual samples of the subblock on which the transformation is not performed are not signaled, and may be regarded as "0" by the image decoding apparatus. There can be several partition types depending on the partitioning direction and the partitioning ratio. The transform unit 140 includes information on the coding mode (or transform mode) of the residual block (e.g., information indicating whether the residual block is transformed or the residual subblock is transformed, and a partition type selected to divide the residual block into subblocks) The entropy encoding unit 155 may be provided with information indicating information and information identifying a subblock on which transformation is performed. The entropy encoder 155 may encode information about a coding mode (or transform mode) of the residual block.

The quantization unit 145 quantizes the transform coefficients output from the transform unit 140 and outputs the quantized transform coefficients to the entropy encoding unit 155. The quantization unit 145 may immediately quantize a related residual block for a certain block or frame without transformation.

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

The entropy encoding unit 155 uses various encoding methods such as Context-based Adaptive Binary Arithmetic Code (CABAC), Exponential Golomb, and the like, and the quantized transform coefficients of 1D output from the reordering unit 150 are A bitstream is generated by encoding the sequence.

In addition, the entropy encoder 155 encodes information such as a CTU size related to block division, a CU division flag, a QT division flag, an MTT division type, and an MTT division direction, so that the video decoding apparatus performs the same block as the video encoding apparatus. Make it possible to divide. 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 intra prediction information (ie, intra prediction) according to the prediction type. Mode information) or inter prediction information (reference picture and motion vector information) is encoded.

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 converts transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain to restore the residual block.

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

The filter unit 180 filters reconstructed pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. that occur due to block-based prediction and transformation/quantization. Perform. The filter unit 180 may include a deblocking filter 182 and a sample adaptive offset (SAO) filter 184.

The deblocking filter 180 filters the boundary between reconstructed blocks to remove blocking artifacts caused by block-based encoding/decoding, and the SAO filter 184 adds additional information to the deblocking-filtered image. Filtering is performed. 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.

The reconstructed block filtered through the deblocking filter 182 and the SAO filter 184 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 a block in a picture to be encoded later.

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

The image decoding apparatus includes an entropy decoding unit 410, a rearrangement unit 415, an inverse quantization unit 420, an inverse transform unit 430, a prediction unit 440, an adder 450, a filter unit 460, and a memory 470. ) Can be included.

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

The entropy decoding unit 410 determines the current block to be decoded by decoding the bitstream generated by the image encoding apparatus and extracting information related to block division, and predicting information and residual signals necessary to restore the current block. Extract information, etc.

The entropy decoding unit 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 partition information for the CTU.

For example, in the case of splitting the CTU using the QTBTTT structure, first, a first flag (QT_split_flag) related to the splitting of the QT is 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 splitting of the MTT and the splitting direction (vertical / horizontal) and/or split type (binary / ternary) information are extracted, and the corresponding leaf node is MTT. Divide into structure. Through this, each node below the leaf node of the QT is recursively divided into a BT or TT structure.

As another example, when splitting the CTU using the QTBTTT structure, first extract the CU split flag (split_cu_flag) indicating whether to split the CU, and if the corresponding block is split, the first flag (QT_split_flag) is extracted. May be. In the segmentation process, each node may have 0 or more repetitive MTT segmentation after 0 or more repetitive QT segmentation. For example, in the CTU, MTT division may occur immediately, or, conversely, only multiple QT divisions may occur.

As another example, when the CTU is divided using the QTBT structure, each node is divided into four nodes of a lower layer by extracting the first flag (QT_split_flag) related to the division of the QT. In addition, a split flag indicating whether or not the node corresponding to the leaf node of the QT is further split into BT and split direction information are extracted.

Meanwhile, when determining the current block to be decoded through the division of the tree structure, the entropy decoder 410 extracts information on a prediction type indicating whether the current block is intra prediction or inter prediction. 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 decoder 410 extracts a syntax element 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 includes information on the coding mode of the residual block (e.g., information on whether the residual block is encoded or only the subblocks of the residual block are encoded, and is selected to divide the residual block into subblocks). Information indicating the partition type, information identifying the encoded residual subblock, quantization parameters, etc.) are extracted from the bitstream. In addition, the entropy decoder 410 extracts information on quantized transform coefficients of the current block as information on the residual signal.

The rearrangement unit 415, in the reverse order of the coefficient scanning order performed by the image encoding apparatus, reconverts the sequence of one-dimensional quantized transform coefficients entropy-decoded by the entropy decoder 410 into a two-dimensional coefficient array (i.e., Block).

The inverse quantization unit 420 inverse quantizes the quantized transform coefficients, and the inverse transform unit 430 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain based on information on the coding mode of the residual block By reconstructing the signals, a reconstructed residual block for the current block is generated.

When the information on the coding mode of the residual block indicates that the residual block of the current block is coded in the image encoding apparatus, the inverse transform unit 430 determines the size of the current block (and thus, to be reconstructed) with respect to the inverse quantized transformation coefficients. A reconstructed residual block for the current block is generated by performing inverse transformation using the residual block size) as a transformation unit.

In addition, when the information on the coding mode of the residual block indicates that only one subblock of the residual block is coded in the image encoding apparatus, the inverse transform unit 430 performs the transformed sub-blocks on the inverse quantized transform coefficients. By using the size of the block as a transformation unit, performing inverse transformation to restore residual signals for the transformed subblock, and filling the residual signals for untransformed subblocks with a value of "0", the reconstructed current block Create a residual block.

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 an intra prediction mode of the current block among a plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the entropy decoding unit 410, and references around 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 using the syntax element for the intra prediction mode extracted from the entropy decoding unit 410, and determines the motion vector and the reference picture. Is used to predict the current block.

The adder 450 adds the residual block output from the inverse transform unit 430 and the prediction block output from the inter prediction unit 444 or the intra prediction unit 442 to restore the current block. The pixels in the reconstructed current block are used as reference pixels for intra prediction of a block to be decoded later.

The filter unit 460 may include a deblocking filter 462 and an SAO filter 464. The deblocking filter 462 performs deblocking filtering on the boundary between reconstructed blocks in order to remove blocking artifacts caused by decoding in units of blocks. The SAO filter 464 performs additional filtering on the reconstructed block after deblocking filtering in order to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding. The reconstructed block filtered through the deblocking filter 462 and the SAO filter 464 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 a block in a picture to be encoded later.

In the conventional video encoding/decoding method, in order to reduce the complexity of prediction for the chrominance component (chroma component), prediction on the chrominance component is performed in the same manner as the prediction process for the luminance component (luma component), or The prediction process was simplified to predict color difference components. However, such a conventional method has a problem in that a color distortion occurs.

In this specification, encoding and decoding methods for effectively predicting a color difference component within a color difference block (chroma block) of a target block (current block) to be reconstructed are proposed.

The methods proposed in the present specification code only information on any one of residual samples (residual signal or difference signal) of Cb color difference component (or Cb chroma component) and residual samples of Cr color difference component (Cr chroma component) and This is a method of signaling and inducing information about the other without coding and signaling.

In the present specification, residual samples of a color difference component (second color difference component) to be derived may be referred to as a second residual sample, and a color difference component (first color difference component) coded and signaled to induce the second residual sample The residual samples of) may be referred to as the first residual sample.

The first color difference component may correspond to any one of the Cb color difference component and the Cr color difference component, and the second color difference component may correspond to the other one of the Cb color difference component and the Cr color difference component. For example, when the residual samples of the Cb color difference component are coded and signaled and the residual samples of the Cr color difference component are derived, the residual samples of the Cb color difference component are referred to as a first residual sample, and the residual samples of the Cr color difference component are second It can be referred to as a residual sample. As another example, when residual samples of the Cr color difference component are coded and signaled and residual samples of the Cb color difference component are derived, the residual samples of the Cr color difference component are referred to as the first residual sample, and the residual samples of the Cb color difference component are referred to as the second residual. It can be referred to as a sample.

The method of deriving the second residual sample is 1) an embodiment using the correlation information between the first residual sample and the second residual sample, and 2) deciding whether to activate or apply (on/off) the second residual sample derivation method. It can be divided into embodiments, etc. Further, embodiments using correlation information may be classified into different embodiments according to whether or not a difference value between color differences is used. Hereinafter, the terms used in the present specification will be first defined, and then each exemplary embodiment will be described in detail.

Correlation information

The correlation information means information for deriving a second residual sample from the first residual sample, and may be adaptively determined according to a range of a luminance component value of a current block to be encoded. The correlation information may include multiplication information or multiplication information and offset information.

The correlation information may be defined at various positions of the bitstream and signaled to the image decoding apparatus, and may be decoded from corresponding positions in the bitstream. For example, the correlation information may be defined and signaled at one or more positions among high level syntaxes (HLS) such as SPS, PPS, and picture level. As another example, the correlation information may be signaled at a lower level such as a tile group level, a tile level, a CTU level, and a unit block level (CU, TU, PU). As another example, a difference value (differential correlation information) with correlation information signaled through HLS may be signaled at a lower level.

Depending on the embodiment, the correlation information may not be signaled directly, but information that can induce or infer the correlation information in the video decoding apparatus may be signaled. For example, table information including fixed values for correlation information may be signaled, and an index value indicating correlation information used for derivation of a second residual sample among fixed values in the table information may be signaled. . As another example, table information may not be signaled, and table information previously determined between the image encoding apparatus and the image decoding apparatus may be used. The index value may be defined and signaled at one or more of a tile group level, a tile level, and a unit block level.

Since the correlation information is information used to induce the second residual sample, it may be signaled when the induction of the second residual sample is turned on. Accordingly, the correlation information is decoded from the bitstream when the first syntax element to be described later indicates that derivation of the second residual sample is allowed, or when the second syntax element indicates that the derivation of the second residual sample is applied. It can be decoded from the bitstream.

Multiplication information

The multiplication information corresponds to information for indicating a multiplication factor between the first residual sample and the second residual sample. When a multiplication factor is applied to the first residual sample (the value of the first residual sample), a value matching the second residual sample (the value of the second residual sample) or a value within the range corresponding to the second residual sample may be derived. have. The multiplication factor may represent a scaling relationship, a weight relationship, a sign relationship, and the like between the first residual sample and the second residual sample. Thus, the multiplication factor may be an integer such as -1 or 1, or a fraction such as 1/2 or -1/2.

When the multiplication information is implemented in the form of a flag (0 or 1) and the multiplication factor indicates a sign relationship between the first residual sample and the second residual sample, the multiplication information may represent the multiplication factor through the same method as in Equation 1. .

Multiplication information = 0 indicates that the first residual sample and the second residual sample have the same sign relationship, and a multiplication factor of 1 may be applied to the first residual sample. Multiplication information = 1 indicates that the first residual sample and the second residual sample have a different sign relationship, and a multiplication factor of -1 may be applied to the first residual sample.

Offset information

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

Regarding the case of offset factor = 0, if only multiplication information is included in the correlation information, offset information is not signaled, and if multiplication information and offset information are included in the correlation information, the offset information may indicate that the offset factor = 0. .

Difference value between color differences

The difference value between the color differences corresponds to a difference value between the first and second residual samples (a value obtained by differentiating the first and second residual samples). Specifically, the color difference value difference value corresponds to a value derived by differentiating the first residual sample and the second residual sample to which the correlation information is applied. For example, when the correlation information includes only multiplication information, a difference value between color differences may be derived by differentiating a first residual sample and a second residual sample to which a multiplication factor is applied. As another example, when the correlation information includes multiplication information and offset information, a difference value between color differences may be derived by differentiating a'first residual sample to which a multiplication factor and an offset factor are applied' and a second residual sample.

Example 1

Example 1 is a method of using both correlation information and a difference value between color differences. Embodiment 1 is based on whether the process of deriving the difference value and correlation information between color differences is performed in which of the encoding steps and the process of deriving the second residual sample is performed in which of the decoding steps. , It can be divided into the following sub-embodiments.

Example 1-1

In Example 1-1, the process of deriving the difference value and correlation information between color differences is performed before the step of converting residual samples, and the process of deriving the second residual sample is performed after the step of inversely transforming the residual samples. .

An exemplary block diagram and a flowchart of an image encoding apparatus for performing Embodiment 1-1 are shown in FIGS. 5 and 6, respectively, and FIG. 7 an exemplary block diagram and a flowchart of an image decoding apparatus for performing Embodiment 1-1. And Fig. 8 respectively.

The subtractor 130 may obtain a first residual sample and a second residual sample (S610). Specifically, the prediction block (prediction samples) of the first color difference component and the color difference block of the first color difference component may be subtracted to obtain a first residual sample, and the color difference between the prediction block of the second color difference component and the second color difference component The block may be subtracted to obtain a second residual sample. The prediction blocks of color difference components may be derived through prediction by the prediction unit 120, and information (prediction information) used for prediction may be derived in this process. The process of generating prediction samples and the process of deriving prediction information may be equally applied to other embodiments of the present specification.

The color difference component predictor 510 may determine whether to derive a second residual sample from the first residual sample (S620).

The chrominance component predictor 510 may determine any one method for a chrominance block among a method of coding both the first residual sample and the second residual sample (a general method) and a method of deriving the second residual sample. For example, the color difference component predictor 510 calculates rate distortion values through rate-distortion analysis of the general method and the method of inducing the second residual sample, and has the best rate distortion characteristics. Can be selected or determined as a method for a color difference block. The method of determining whether to derive the second residual sample may be equally applied to other embodiments of the present specification.

The color difference component predictor 510 may correct the first residual sample when the method for deriving the second residual sample is determined as the method for the color difference block (S630). The correction of the first residual sample may be performed by applying correlation information to the first residual sample.

The color difference component predictor 510 may derive a difference value between color differences using the corrected first and second residual samples (S640). The corrected first residual sample and the second residual sample may be differentiated or subtracted to derive a difference value between color differences.

Process S630 and process S640 may be performed through Equation 2 below.

In Equation 2, Cro_resi1 represents a first residual sample, Cro_resi2 represents a second residual sample, Cro_r represents a difference between color differences, W represents a multiplication factor, and Offset represents an offset factor. Looking at Equation 1 again, focusing on the second residual sample, Cro_resi2 may be the first signal of the second residual sample (the first difference signal of the second color difference component), and Cro_r is the second signal of the second residual sample. It may be a (second difference signal of the second color difference component).

The conversion unit 140 may convert the difference between color differences and the first residual sample, and the quantization unit 145 may quantize the converted difference between the color differences and the converted first residual sample (S650). Here, the difference between color differences may be quantized through'quantization parameter changed using QP_C_offset' in the quantization parameter of the luminance component or the first residual sample. QP_C_offset can be determined through various methods. For example, QP_C_offset may be adaptively determined according to one or more of a range of a luminance component value (a range of a luminance value), a size of a color difference block, and a range of a quantization parameter of a luminance component. As another example, QP_C_offset may be determined as a preset value in the image encoding apparatus and the image decoding apparatus. As another example, the image encoding apparatus may perform a quantization process by determining QP_C_offset as an arbitrary value, and may signal a value of QP_C_offset used in the quantization process to the image decoding apparatus. The quantization method using QP_C_offset may be applied to other embodiments of the present specification.

A difference value between transformed and quantized color differences, a first residual sample, correlation information, and prediction information may be encoded and signaled to the image decoding apparatus (S660). Here, the second residual sample is not signaled.

The entropy decoder 410 may decode a difference value between color differences, a first residual sample, correlation information, and prediction information from the bitstream (S810). The inverse quantization unit 420 may inverse quantize the difference between the color differences and the first residual sample, and the inverse transform unit 430 may inversely transform the difference between the inverse quantized color differences and the inverse quantized first residual sample (S820). .

The prediction unit 440 may generate or restore prediction samples (prediction blocks) of the first color difference component and prediction samples of the second color difference component based on the prediction information (S820).

The color difference component restoration unit 710 may determine whether to derive the second residual sample from the first residual sample (whether to activate (allow) and/or apply the second residual sample derivation method) (S830). Details of the process S830 will be described later through a separate embodiment.

When it is determined to induce the second residual sample, the color difference component restoration unit 710 may correct the (inversely transformed) first residual sample by using the correlation information (S840). In addition, the color difference component restoration unit 710 may derive a second residual sample by using a difference value between the corrected first residual sample and the inversely transformed color difference (S850). A second residual sample may be derived by adding or adding a difference value between the corrected first residual sample and the inversely transformed color difference.

Process S840 and process S850 may be performed through Equation 3 below.

The adder 450 restores the color difference block of the first color difference component by adding the prediction block of the first color difference component and the first residual sample, and adds the prediction block of the second color difference component and the derived second residual sample to obtain a second The color difference block of the color difference component may be restored (S860).

Example 1-2

In Example 1-2, the process of deriving the difference value and correlation information between color differences is performed after the step of quantizing residual samples, and the process of deriving the second residual sample is performed before the step of inverse quantizing the residual samples. do.

An exemplary block diagram and flowchart of an image encoding apparatus for performing Embodiment 1-2 are shown in FIGS. 9 and 10, respectively, and FIG. 11 is an exemplary block diagram and flowchart of an image decoding apparatus for performing Embodiment 1-2. And Fig. 12, respectively.

The subtractor 130 may obtain a first residual sample and a second residual sample (S1010). A prediction block of each of the chrominance components and a chrominance block may be subtracted to obtain residual samples of each of the chrominance components, and prediction blocks and prediction information of each of the chrominance components may be derived through the prediction process of the prediction unit 120. have.

The transform unit 140 may transform the first residual sample and the second residual sample, and the quantization unit 145 may quantize the transformed first residual sample and the transformed second residual sample (S1020). Here, the second residual sample may be quantized by adding a quantization offset for quantization of the second residual sample to a quantization parameter of the first residual sample. The quantization offset can be determined through various methods. For example, the quantization offset may be adaptively determined according to one or more of a range of a luminance component value (a range of a brightness value), a range of a first residual sample value, and a bit-depth of a second residual sample. have. As another example, the quantization offset may be determined as a preset value in the image encoding apparatus and the image decoding apparatus. The image decoding apparatus determines a quantization parameter using delta-QP signaled from the image encoding apparatus, summing the quantization offset to the quantization parameter to derive the quantization parameter of the second residual sample, and then uses the derived quantization parameter to determine the quantization parameter. Inverse quantization of 2 residual samples can be performed. The quantization/dequantization method using the quantization offset may be applied to other embodiments of the present specification.

Depending on the embodiment, quantization coefficients of “0” may be derived through the quantization process of the second residual sample (that is, the difference signal may not exist during the quantization process). In this case, information indicating that quantization coefficients of "0" are derived or a syntax element may be signaled from the image encoding apparatus to the image decoding apparatus.

On the other hand, the quantization parameter value (first value) of the first residual sample (the quantization offset is not added), the value obtained by adding the quantization offset to the quantization parameter of the first residual sample (second value), the first value and the second value One or more of the average values of the values may be used in the in-loop filtering process of the second residual sample. For example, at least one of a first value, a second value, and an average value is used as a parameter for determining the in-loop filtering strength of the second residual sample, or as a parameter for determining an index in the table for determining the boundary strength. It can also be used. A method in which at least one of the first value, the second value, and the average value is used in the in-loop filtering process may be applied to other embodiments of the present specification.

The color difference component predictor 510 may determine whether to derive a second residual sample from the first residual sample (S1030). When it is determined to derive the second residual sample, the color difference component predictor 510 may correct the quantized first residual sample (S1040). The correction of the first residual sample may be performed by applying correlation information to the quantized first residual sample.

The color difference component predictor 510 may derive a difference value between color differences using the corrected first residual sample and the quantized second residual sample (S1050). The corrected first residual sample and the quantized second residual sample may be differentiated or subtracted to derive a difference value between color differences.

Process S1040 and process S1050 may be performed through Equation 4 below.

In Equation 4, Q(T(Cro_resi1)) denotes a transformed and quantized first residual sample, Q(T(Cro_resi2)) denotes a transformed and quantized second residual sample, and Q(T(Cro_r)) Denotes a difference value between a color difference derived from a'transformed and quantized first residual sample' and a'transformed and quantized second residual sample'.

A difference value between color differences, a first residual sample, correlation information, and prediction information may be encoded and signaled to an image decoding apparatus (S1060). Here, the second residual sample is not signaled.

The entropy decoder 410 may decode a difference value between color differences, a first residual sample, correlation information, and prediction information from the bitstream (S1210). The prediction unit 440 may generate or restore prediction samples (prediction blocks) of the first color difference component and prediction samples of the second color difference component based on the prediction information (S1220).

The color difference component restoration unit 710 may determine whether to derive the second residual sample from the first residual sample (ie, whether to activate and/or apply the second residual sample derivation method) (S1230). Details of the S1230 process will be described later through a separate embodiment.

When it is determined to derive the second residual sample, the color difference component restoration unit 710 may correct the first residual sample using the correlation information (S1240). In addition, the color difference component restoration unit 710 may derive a second residual sample by using the corrected first residual sample and a difference value between the color difference (S1250). A second residual sample may be derived by adding or adding a difference value between the corrected first residual sample and the color difference.

Process S1240 and process S1250 may be performed through Equation 5 below.

The inverse quantization unit 420 may inverse quantize the first residual sample and the derived second residual sample, and inversely transform the inverse quantized first residual sample and the inverse quantized second residual sample (S1260). The adder 450 restores the color difference block of the first color difference component by adding the prediction block of the first color difference component and the inversely transformed first residual sample, and adds the prediction block of the second color difference component and the inversely transformed second residual sample. The color difference block of the second color difference component may be restored (S1270).

Example 2

Example 2 is a method of predicting and deriving a second residual sample using correlation information without using a difference value between color differences.

Embodiment 2 is different from Embodiment 1 in that'the difference between color differences is not used' and'the process of deriving the difference between color differences (S640 and S1050) is not performed' of the first embodiment.

Excluding these differences, the rest of the processes of the first embodiment may also be performed in the second embodiment. Therefore, as in Example 1-1, the process of deriving the correlation information in the image encoding apparatus may be performed before the step of converting the residual samples, and the process of deriving the second residual sample in the image decoding apparatus is the residual sample. It can be performed after the step of inverse transforming them. Also, as in Example 1-2, the process of deriving the correlation information in the image encoding apparatus may be performed after the step of quantizing residual samples, and the process of deriving the second residual sample in the image decoding apparatus is a residual sample. Can be performed prior to the step of inverse quantizing the s. However, hereinafter, the remaining steps except for the step of transforming/quantizing residual samples and the step of inverse quantizing/inverse transforming residual samples will be described.

13 and 14 are flowcharts for explaining an example of the second embodiment.

The subtractor 130 obtains a first residual sample by subtracting the prediction block of the first color difference component and the color difference block of the first color difference component, and subtracts the prediction block of the second color difference component and the color difference block of the second color difference component. Two residual samples may be obtained (S1310).

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

Meanwhile, according to an embodiment, the method of deriving the second residual sample may include the following three modes when only multiplication information is included in the correlation information.

1) Mode 1-The values of Cb residual samples are signaled, and the values of Cr residual samples are derived by applying a multiplication factor of -1/2 or +1/2 to the values of the Cb residual samples.

2) Second mode-The values of the Cb residual samples are signaled and the values of the Cr residual samples are derived by applying a multiplication factor of -1 or +1 to the values of the Cb residual samples.

3) Third mode-The values of the Cr residual samples are signaled, and the values of the Cb residual samples are derived by applying a multiplication factor of -1/2 or +1/2 to the values of the Cr residual samples.

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

In this embodiment, the color difference component predictor 510 may determine a mode having the best rate distortion characteristic among the above modes as a mode for a color difference block. The color difference component predictor 510 determines any one of the modes in the'process of determining any one of the general method and the method of deriving the second residual sample' and'the method of deriving the second residual sample' described above. The process can be performed in an integrated manner. For example, the chrominance component predictor 510 may determine a mode or method having the best rate distortion characteristic among'the modes in the method for deriving the second residual sample and the general method' as the method for the color difference block.

The first residual sample, correlation information, and prediction information may be encoded and signaled to an image decoding apparatus (S1340). Here, a difference value between the second residual sample and the color difference is not signaled.

The entropy decoding unit 410 may decode the first residual sample, correlation information, and prediction information from the bitstream (S1410).

The prediction unit 440 may generate or restore prediction samples (prediction blocks) of the first color difference component and prediction samples of the second color difference component based on the prediction information (S1420).

The color difference component restoration unit 710 may determine whether to derive the second residual sample from the first residual sample (ie, whether to activate and/or apply the second residual sample derivation method) (S1430). Details of the S1430 process will be described later through a separate embodiment.

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

The S1440 process may be performed through Equation 6 below.

Comparing Equation 6 with Equations 2 to 5, it can be seen that the difference value between color differences is not used in Example 2 (Cro_r=0). Therefore, a transformation/inverse transformation process, a quantization/inverse quantization process, and an encoding/decoding process for the difference between color differences are not performed.

The adder 450 restores the color difference block of the first color difference component by adding the prediction block of the first color difference component and the first residual sample, and adds the prediction block of the second color difference component and the derived second residual sample to obtain a second The color difference block of the color difference component may be restored (S1450).

Example 3

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

Whether to perform the second residual sample derivation method may be determined according to various criteria. These various criteria include 1) a value of a syntax element (eg, a flag) indicating whether the derivation of the second residual sample is allowed and/or applied (whether on/off), 2) a prediction mode of the target block, 3) A range of luminance component values, etc. may be included.

Criterion 1)-Syntax element indicating whether to on/off

The syntax element indicating whether to derive the second residual sample may include a first syntax element and/or a second syntax element.

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

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

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

An example of determining whether to turn on/off the second residual sample derivation method is shown in FIG. 13.

The image encoding apparatus may determine whether the second residual sample derivation method is allowed, and may signal the result to the image decoding apparatus by setting the result as a value of the first syntax element. In addition, the image encoding apparatus may determine whether or not the second residual sample derivation method is applied, set the result as a value of the second syntax element, and signal the result to the image decoding apparatus.

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

When the second syntax element indicates that the second residual sample derivation method is allowed (first syntax element = 1, S1520), the video decoding apparatus may decode the second syntax element from the bitstream (S1530). In addition, the image decoding apparatus may determine whether a second residual sample derivation method is applied according to the value of the second syntax element (S1540).

In the case where the second syntax element indicates that the second residual sample derivation method is applied (the second syntax element = 0, S1540), the correlation information and the first residual sample (or correlation information, the first A second residual sample may be derived based on the residual sample and a difference value between color differences (S1550).

In step S1520, the first syntax element indicates that the method for deriving the second residual sample is not allowed (the first syntax element = 0), or in step S1540, the second syntax element indicates that the method for deriving the second residual sample is not applied. In this case, the derivation of the second residual sample is not performed.

Criterion 2)-prediction mode of the target block

Whether to turn on/off the second residual sample derivation method may be adaptively determined in consideration of the prediction mode of the target block (color difference block) (according to the prediction mode).

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

As another example, when a color difference block is predicted through a cross-component linear model (CCLM) or a direct mode (DM) among intra prediction modes, the derivation of the second residual sample may be turned on or off. In this case, information indicating on/off for derivation of the second residual sample may be signaled to the image decoding apparatus only when the color difference block is predicted through CCLM or DM.

As another example, when a color difference block is predicted through a bi-prediction mode or a merge mode among inter prediction modes, and when predicted with reference to the 0-th reference image, the second residual sample Induction can be turned on or off. Information indicating on/off for derivation of the second residual sample may be signaled to the image decoding apparatus only when the color difference block is predicted through a bidirectional prediction mode or a merge mode, or predicted with reference to the 0-th reference image.

The example of considering the prediction mode of the color difference block may be combined with the previous example using the first syntax element and the second syntax element. For example, in step S1520, when the first syntax element = 1 and the prediction mode of the color difference block corresponds to the prediction mode in which the derivation of the second residual sample is 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 the prediction mode of the color difference block.

Criterion 3)-Range of luminance component values

The range of the luminance component value (the range of the luminance value) is divided into two or more sections, and whether the second residual sample derivation method is applied or not is determined according to which section the luminance component value of the target block belongs among the divided sections. I can.

For example, when the range of the luminance component value is divided into two sections (the first section and the second section), when the luminance component value of the target block belongs to the first section, the second residual sample derivation method is applied. Instead, a second residual sample derivation method may be applied when the luminance component value of the target block belongs to the second section. It is also possible to apply this in reverse.

Among two or more sections, a section to which the second residual sample derivation method is not applied may correspond to a'visual recognition section' in which the user's vision can react sensitively, and a section to which the second residual sample derivation method is applied May not correspond to the'visual recognition interval'. Accordingly, since the second residual sample derivation method is not applied to the visual recognition section, and the second residual sample derivation method can be selectively applied only to the non-visual recognition section, it is possible to prevent subjective image quality from deteriorating.

One or more (interval values) of a value representing the range of the first section and a value representing the range of the second section may be signaled from the video encoding apparatus to the video decoding apparatus. Depending on the embodiment, the interval value may be preset between the image encoding apparatus and the image decoding apparatus without signaling.

Criterion 4)-Quantization result

When the prediction accuracy for the second color difference component is high and the values of the quantization coefficients for the second residual sample are very small (when there are few quantization coefficients or there are few quantization coefficients), the second residual sample derivation method is Can be applied selectively. Also, in this case, not all of the second residual sample is omitted, but the quantization of a part of the second residual sample may be omitted (ie, only a part of the second residual sample is signaled).

Other standards

When the DQP (delta-QP) of the luminance component is greater than or equal to a preset value, when the transform skip mode is not applied to the color difference block, or when the block differential coded modulation (BDPCM) mode is not applied to the target block In E, the second residual sample derivation method may or may not be applied.

When the picture including the target block is an instantaneous decoding recoding (IDR) picture for random access or a gradual random access (GRA) picture, the second residual sample derivation method may not be applied.

The above description is merely illustrative of the technical idea of the present embodiment, and those of ordinary skill in the technical field to which the present embodiment belongs will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present exemplary embodiments are not intended to limit the technical idea of the present exemplary embodiment, but are illustrative, and the scope of the technical idea of the present exemplary embodiment is not limited by these exemplary embodiments. The scope of protection of this embodiment should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

120, 440: prediction unit 130: subtractor
170, 450: adder 180, 460: filter unit

Claims (14)

As a method of restoring a color difference block of a target block to be restored,
To decode correlation information between the first residual sample, which is the residual samples of the first color difference component and the second residual sample, which is the residual samples of the second color difference component, the first residual sample, and prediction information of the color difference block from a bitstream. step;
Generating prediction samples of the first color difference component and prediction samples of the second color difference component based on the prediction information;
Applying the correlation information to the first residual sample to derive the second residual sample; And
The prediction samples of the first color difference component and the first residual sample are added to restore the color difference block of the first color difference component, and the prediction samples of the second color difference component and the second residual sample are added to the second residual sample. A color difference block restoration method comprising the step of restoring a color difference block of a two color difference component. The method of claim 1,
The first color difference component,
Corresponds to any one of the Cb color difference component and the Cr color difference component,
The second color difference component,
The color difference block restoration method corresponding to the other one of the Cb color difference component and the Cr color difference component. The method of claim 1,
The decoding step,
A color difference block restoration method for decoding the correlation information from a picture level of the bitstream. The method of claim 1,
The correlation information,
Including multiplication information for indicating a multiplication factor between the first residual sample and the second residual sample,
The inducing step,
A method of reconstructing a color difference block by applying a multiplication factor indicated by the multiplication information to the first residual sample to derive the second residual sample. The method of claim 4,
The correlation information,
Further comprising offset information for indicating an offset factor between the first residual sample and the second residual sample,
The inducing step,
A method of reconstructing a color difference block, wherein the second residual sample is derived by applying an offset factor indicated by the offset information to the first residual sample to which the multiplication factor is applied. The method of claim 1,
The decoding step,
Decoding a first syntax element indicating whether derivation of the second residual sample is allowed from a sequence parameter set (SPS) level of the bitstream; And
When the first syntax element indicates that derivation of the second residual sample is allowed, a second syntax element indicating whether derivation of the second residual sample is applied to the color difference block is added to the SPS in the bitstream. Including the step of decoding from the lower level of the level,
The inducing step,
A color difference block reconstruction method for deriving the second residual sample when the second syntax element indicates that the derivation of the second residual sample is applied to the color difference block. The method of claim 6,
The step of decoding the second syntax element,
A method of reconstructing a color difference block, wherein the second syntax element is decoded in consideration of a prediction mode of the target block. An image decoding apparatus that restores a color difference block of a target block to be restored,
To decode correlation information between the first residual sample, which is the residual samples of the first color difference component and the second residual sample, which is the residual samples of the second color difference component, the first residual sample, and prediction information of the color difference block from a bitstream. Decoding unit;
A prediction unit that generates prediction samples of the first color difference component and prediction samples of the second color difference component based on the prediction information;
A color difference component restoration unit for inducing the second residual sample by applying the correlation information to the first residual sample; And
The prediction samples of the first color difference component and the first residual sample are added to restore the color difference block of the first color difference component, and the prediction samples of the second color difference component and the second residual sample are added to the second residual sample. An image decoding apparatus comprising an adder for reconstructing a color difference block of two color difference components. The method of claim 8,
The first color difference component,
Corresponds to any one of the Cb color difference component and the Cr color difference component,
The second color difference component,
The image decoding apparatus corresponding to the other one of the Cb color difference component and the Cr color difference component. The method of claim 8,
The decryption unit,
A video decoding apparatus for decoding the correlation information from a picture level of the bitstream. The method of claim 8,
The correlation information,
Including multiplication information for indicating a multiplication factor between the first residual sample and the second residual sample,
The color difference component restoration unit,
A video decoding apparatus for inducing the second residual sample by applying a multiplication factor indicated by the multiplication information to the first residual sample. The method of claim 11,
The correlation information,
Further comprising offset information for indicating an offset factor between the first residual sample and the second residual sample,
The color difference component restoration unit,
An image decoding apparatus for inducing 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. The method of claim 8,
The decryption unit,
A first syntax element indicating whether derivation of the second residual sample is allowed is decoded from the SPS (sequence parameter set) level of the bitstream, and the first syntax element indicates that derivation of the second residual sample is allowed. In this case, a second syntax element indicating whether the derivation of the second residual sample is applied to the color difference block is decoded from a lower level of the SPS level in the bitstream,
The color difference component restoration unit,
The image decoding apparatus, for inducing the second residual sample when the second syntax element indicates that the derivation of the second residual sample is applied to the color difference block. The method of claim 13,
The decryption unit,
An image decoding apparatus for decoding the second syntax element in consideration of a prediction mode of the target block.

Images