CN116472710A

CN116472710A - Method and apparatus for generating residual signal using reference between components

Info

Publication number: CN116472710A
Application number: CN202180078457.2A
Authority: CN
Inventors: 崔韩率; 朴俊泽; 沈东圭; 朴胜煜
Original assignee: Hyundai Motor Co; Industry Academic Collaboration Foundation of Kwangwoon University; Kia Corp
Current assignee: Hyundai Motor Co; Industry Academic Collaboration Foundation of Kwangwoon University; Kia Corp
Priority date: 2020-11-24
Filing date: 2021-11-24
Publication date: 2023-07-21
Also published as: KR20220071944A

Abstract

The present invention relates to a method and apparatus for generating a residual signal using a reference between components. Embodiments of the present invention provide an image encoding/decoding apparatus and method to derive a residual signal of a chrominance component by deriving the residual signal of the chrominance component of a current block using a residual signal of a pre-stored block without transmitting the residual signal of a partial chrominance component of the current block.

Description

Method and apparatus for generating residual signal using reference between components

Technical Field

In some embodiments, the present invention relates to methods and apparatus for generating a residual signal using a reference between components.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

Since video data has a larger data amount than audio data or still image data, the video data requires a large amount of hardware resources (including a memory) to store or transmit the video data that is not subjected to compression processing.

Accordingly, encoders are commonly used to compress and store or transmit video data; the decoder receives compressed video data, decompresses the received compressed video data, and plays the decompressed video data. Video compression techniques include h.264/AVC, high efficiency video coding (High Efficiency Video Coding, HEVC), and multi-function video coding (Versatile Video Coding, VVC). The coding efficiency of VCC is improved by about 30% or more compared to HEVC.

However, as the image size, resolution, and frame rate gradually increase, the amount of data to be encoded also increases. Accordingly, a new compression technique capable of providing higher coding efficiency and improved image enhancement effect as compared to the existing compression technique is required.

In picture (video) decoding, a residual signal of a Cb signal or a Cr signal may be generated by cross-referencing to generate a residual signal of a chrominance component. The video decoding apparatus derives a residual signal of a Cr signal by multiplying the Cb residual signal by 1 or-1 after receiving the Cb residual signal, or derives a residual signal of the Cb signal by multiplying the Cr residual signal by 1 or-1 after receiving the Cr residual signal, which is called joint coding of chroma residual (joint coding of chroma residual, JCCR). As in JCCR, the residual signal of the chrominance component may still be further utilized to increase the compression ratio. Therefore, a method of efficiently encoding and decoding a residual signal of a chrominance channel in terms of encoding efficiency needs to be considered.

Disclosure of Invention

Technical problem

Embodiments of the present invention provide a video encoding/decoding apparatus and method for deriving a residual signal of a chrominance component of a current block. In deriving the residual signal of the chrominance component, the video encoding/decoding apparatus and method use the residual signal of the previously reconstructed block without transmitting the residual signal of a portion of the chrominance component of the current block.

Solution method

At least one aspect of the present disclosure provides a method performed by a video decoding device for reconstructing a chroma residual block of a current block. The method comprises the following steps: the locations of the first neighboring residual samples of the reference component residual block and the second neighboring residual samples of the chroma residual block are derived based on information representing a reference relationship between the chroma residual block and the decoded reference component residual block within the current block. The method further comprises the steps of: a linear relationship between the first and second adjacent residual samples is generated. The method further comprises the steps of: the chroma residual block is generated by applying a linear relationship to the reference component residual block.

Another aspect of the present invention provides a video decoding apparatus. The video decoding device includes an entropy decoder configured to decode information representative of a reference relationship between a chroma residual block within a current block and a decoded reference component residual block. The video decoding device further comprises a neighboring residual sample deriver configured to derive locations of a first neighboring residual sample of the reference component residual block and a second neighboring residual sample of the chroma residual block based on information representative of the reference relationship. The video decoding device also includes a linear model deriver configured to generate a linear relationship between the first neighboring residual samples and the second neighboring residual samples. The video decoding apparatus further includes a residual signal generator configured to generate a chroma residual block by applying a linear relationship to the reference component residual block.

Yet another aspect of the present invention provides a method performed by a video encoding device for reconstructing a chroma residual block of a current block. The method comprises the following steps: information representing a reference relationship between a chroma residual block and a reference component residual block within the current block is generated. The method further comprises the steps of: the positions of the first neighboring residual samples of the reference component residual block and the second neighboring residual samples of the chroma residual block are derived based on information representing the reference relationship. The method further comprises the steps of: a linear relationship between the first and second adjacent residual samples is generated. The method further comprises the steps of: the chroma residual block is generated by applying a linear relationship to the reference component residual block.

Effects of the invention

As described above, the embodiments of the present invention provide video encoding/decoding apparatuses and methods of deriving a residual signal of a chrominance component of a current block. In deriving the residual signal of the chrominance component, the video encoding/decoding apparatus and method use the residual signal of the previously reconstructed block, thereby improving the encoding efficiency by not transmitting the residual signal of a portion of the chrominance component of the current block.

Drawings

Fig. 1 is a block diagram of a video encoding device in which the techniques of the present invention may be implemented.

Fig. 2 illustrates a method of partitioning a block using a quadtree plus binary tree trigeminal tree (QTBTTT) structure.

Fig. 3a and 3b illustrate a plurality of intra prediction modes including a wide-angle intra prediction mode.

Fig. 4 shows neighboring blocks of the current block.

Fig. 5 is a block diagram of a video decoding apparatus in which the techniques of the present invention may be implemented.

Fig. 6a and 6b show residual blocks of reference components according to an embodiment.

Fig. 7 is a block diagram conceptually illustrating an apparatus for reconstructing a residual signal within a video decoding apparatus according to an embodiment.

Fig. 8a and 8b show the positions of neighboring residual samples according to an embodiment.

Fig. 9a and 9b illustrate a linear relationship between neighboring residual samples of a current chroma block and neighboring residual samples of a reference component block according to an embodiment.

Fig. 10a and 10b show the application of the derived linear relation to the residual block of the reference component according to an embodiment.

Fig. 11 is a flowchart illustrating a method for reconstructing a chroma residual signal performed by a video decoding device according to an embodiment.

Fig. 12 is a flowchart illustrating a method for reconstructing a chroma residual signal performed by a video encoding device according to an embodiment.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying illustrative drawings. In the accompanying drawings, like reference numerals refer to like elements even though the elements are shown in different drawings. In addition, in the following description, detailed descriptions of related known components and functions may be omitted so as not to obscure the subject matter of the present invention.

Fig. 1 is a block diagram of a video encoding device in which the techniques of the present invention may be implemented. Hereinafter, a video encoding apparatus and sub-components of the apparatus are described with reference to fig. 1.

The encoding apparatus may include: 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 loop filtering unit 180, and a memory 190.

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

A video is made up of one or more sequences comprising 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/and slice is partitioned into one or more Coding Tree Units (CTUs). In addition, each CTU is partitioned into one or more Coding Units (CUs) by a tree structure. Information applied to each CU is encoded as a syntax of the CU, and information commonly applied to CUs included in one CTU is encoded as a syntax of the CTU. 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 or more pictures is encoded as a picture parameter set (Picture Parameter Set, PPS) or a picture header. Information commonly referenced by multiple images is encoded as a sequence parameter set (Sequence Parameter Set, SPS). Information commonly referenced by one or more SPS is encoded as a video parameter set (Video Parameter Set, VPS). Information commonly applied to one tile or group of tiles may also be encoded as syntax of a tile or group of tiles header. The syntax included in the SPS, PPS, slice header, tile, or tile set header may be referred to as a high level syntax.

The image divider 110 determines the size of the 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 recursively divides the CTUs by using a tree structure. Leaf nodes in the tree structure become CUs, which are the basic units of coding.

The tree structure may be a Quadtree (QT) in which a higher node (or parent node) is partitioned into four lower nodes (or child nodes) of the same size. The tree structure may also be a Binary Tree (BT) in which a higher node is split into two lower nodes. The tree structure may also be a Trigeminal Tree (TT), where the higher nodes are split into three lower nodes at a ratio of 1:2:1. The tree structure may also be a structure in which two or more of a QT structure, a BT structure, and a TT structure are mixed. For example, a quadtree plus binary tree (quadtree plus binarytree, QTBT) structure may be utilized, or a quadtree plus binary tree trigeminal tree (quadtree plus binarytree ternarytree, QTBTTT) structure may be utilized. Here, BTTT is added to the tree structure to be called multiple-type tree (MTT).

Fig. 2 is a schematic diagram for describing a method of dividing a block by using the QTBTTT structure.

As shown in fig. 2, the CTU may be first partitioned into QT structures. Quadtree partitioning may be recursive until the size of the partitioned block reaches the minimum block size (MinQTSize) of 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 apparatus. When the leaf node of QT is not greater than the maximum block size (MaxBTSize) of the root node allowed in BT, the leaf node may be further divided into at least one of BT structure or TT structure. There may be multiple directions of segmentation in the BT structure and/or the TT structure. For example, there may be two directions, for example, a direction of dividing the block of the corresponding node horizontally and a direction of dividing the block of the corresponding node vertically. As shown in fig. 2, when the MTT division starts, a second flag (MTT _split_flag) indicating whether a node is divided, and a flag additionally indicating a division direction (vertical or horizontal) and/or a flag indicating a division type (binary or trigeminal) in the case that a node is divided are encoded by the entropy encoder 155 and signaled to the video decoding apparatus.

Alternatively, a CU partition flag (split_cu_flag) indicating whether a node is partitioned may be further encoded before encoding a first flag (qt_split_flag) indicating whether each node is partitioned into four nodes of a lower layer. When the value of the CU partition flag (split_cu_flag) indicates that each node is not partitioned, the block of the corresponding node becomes a leaf node in the partition tree structure and becomes a CU, which is a basic unit of encoding. When the value of the CU partition flag (split_cu_flag) indicates that each node is partitioned, the video encoding apparatus first starts encoding the first flag by the above scheme.

When QTBT is used as another example of the tree structure, there may be two types, for example, a type of horizontally dividing a block of a corresponding node into two blocks having the same size (i.e., symmetrical horizontal division) and a type of vertically dividing a block of a corresponding node into two blocks having 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 a partition type are encoded by the entropy encoder 155 and transmitted to the video decoding apparatus. In one embodiment, there may additionally be a type in which the blocks of the respective nodes are divided into two blocks in an asymmetric form to each other. The asymmetric form may include a form in which a block of a corresponding node is divided into two rectangular blocks having a size ratio of 1:3 and/or a form in which a block of a corresponding node is divided in a diagonal direction.

A CU may have various sizes according to QTBT or QTBTTT divided from CTUs. 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 segmentation is employed, the shape of the current block may also be rectangular or square in shape.

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 one embodiment, each of the current blocks in the image may be predictively encoded. In one embodiment, prediction of the current block may be performed by using an intra prediction technique (which uses data from an image including the current block) or an inter prediction technique (which uses data from an image encoded before an image including the current block). Inter prediction may include unidirectional prediction and/or bidirectional prediction.

The intra predictor 122 predicts pixels in the current block by using pixels (reference pixels) located adjacent to 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 two non-directional modes including a planar (planar) mode and a DC mode, and may include 65 directional modes. The neighboring pixels and algorithm equations to be utilized are defined differently according to each prediction mode.

In order to perform efficient direction prediction on the current block having a rectangular shape, direction modes (# 67 to # 80), intra prediction modes # -1 to # -14) as indicated by dotted arrows in fig. 3b may be additionally utilized. The direction mode may be referred to as a "wide angle intra-prediction mode". In fig. 3b, the arrows indicate the respective reference samples for prediction, rather than representing the prediction direction. The prediction direction is opposite to the direction indicated by the arrow. When the current block has a rectangular shape, 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. 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 by a ratio of a width to a height of the current block having a rectangular shape. For example, when the current block has a rectangular shape having a height smaller than a width, wide-angle intra prediction modes (intra prediction modes #67 to # 80) having angles smaller than 45 degrees are available. When the current block has a rectangular shape with a width greater than a height, a wide-angle intra prediction mode having an angle greater than-135 degrees is available.

The intra predictor 122 may determine intra prediction to be used for encoding the current block. In some examples, intra predictor 122 may encode the current block by utilizing multiple intra prediction modes and/or select an appropriate intra prediction mode to utilize from among the test modes. For example, the intra predictor 122 may calculate a rate distortion value by using rate-distortion (rate-distortion) analysis of a plurality of tested intra prediction modes, and/or select an intra prediction mode having the best rate distortion characteristics among the test modes.

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

The inter predictor 124 generates a prediction block of the current block by using a motion compensation process. The inter predictor 124 searches for a block most similar to the current block in a reference picture that has been encoded and decoded earlier than the current picture, and generates a predicted block of the current block by using the searched block. In addition, a Motion Vector (MV) is generated, which corresponds to a displacement (displacement) between a current block in the current image and a prediction block in the reference image. In one embodiment, motion estimation is performed on a luminance (luma) 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 of the reference picture and information on a motion vector for predicting the current block is encoded by the entropy encoder 155 and transmitted to a video decoding device.

The inter predictor 124 may also perform interpolation of reference pictures or reference blocks to increase the accuracy of prediction. For example, sub-samples may be interpolated between two consecutive integer samples by applying filter coefficients to a plurality of consecutive integer samples including the two integer samples. When the process of searching for a block most similar to the current block is performed on the interpolated reference image, the decimal-unit precision may be represented for the motion vector instead of the integer-sample-unit precision. The precision or resolution of the motion vector may be set differently for each target region to be encoded, e.g., a unit such as a slice, tile, CTU, CU, etc. When such an adaptive motion vector resolution (adaptive motion vector resolution, AMVR) is applied, information about the motion vector resolution to be applied to each target region may be signaled for each target region. For example, when the target area is a CU, information about the resolution of a motion vector applied to each CU is signaled. The information on the resolution of the motion vector may be information representing the accuracy of a motion vector difference to be described below.

On the other hand, the inter predictor 124 may perform inter prediction by using bi-directional prediction. In the case of bi-prediction, two reference pictures and two motion vectors representing block positions most similar to the current block in each reference picture are utilized. The inter predictor 124 selects a first reference picture and a second reference picture from the reference picture list0 (RefPicList 0) and the reference picture list1 (RefPicList 1), respectively. The inter predictor 124 also searches for a block most similar to the current block in the corresponding reference picture to generate a first reference block and a second reference block. A prediction block of the current block is generated by averaging or weighted-averaging the first reference block and the second reference block. Motion information including information on two reference pictures for predicting a current block and information on two motion vectors is transferred to the entropy encoder 155. Here, the reference image list0 may be constituted by an image preceding the current image in display order among the pre-restored images, and the reference image list1 may be constituted by an image following the current image in display order among the pre-restored images. However, although not particularly limited thereto, a pre-restored image subsequent to the current image in display order may be additionally included in the reference image list 0. Conversely, a pre-restored image preceding the current image may be additionally included in the reference image list 1.

In order to minimize the amount of bits consumed for encoding motion information, various methods may be utilized.

For example, when a reference image and a motion vector of a current block are identical to those of a neighboring block, information capable of identifying the neighboring block is encoded to transmit the motion information of the current block to a video decoding apparatus. This method is called merge mode (merge mode).

In the merge mode, the inter predictor 124 selects a predetermined number of merge candidate blocks (hereinafter, referred to as "merge candidates") from neighboring blocks of the current block.

As neighboring blocks used to derive the merge candidates, as shown in fig. 4, all or some of a left block A0, a lower left block A1, an upper block B0, an upper right block B1, and an upper left block B2 adjacent to the current block in the current image may be utilized. In addition, in addition to the current picture in which the current block is located, a block located within a reference picture (which may be the same as or different from the reference picture used to predict the current block) may also be used as a merging candidate. For example, a co-located block (co-located block) of a current block within a reference picture or a block adjacent to the co-located block may additionally be used as a merging candidate. If the number of merging candidates selected by the above method is less than a preset number, a zero vector is added to the merging candidates.

The inter predictor 124 configures a merge list including a predetermined number of merge candidates by using neighboring blocks. A merge candidate to be used as motion information of the current block is selected from among the merge candidates included in the merge list, and merge index information for identifying the selected candidate is generated. The generated merging index information is encoded by the entropy encoder 155 and transmitted to a video decoding apparatus.

The merge skip mode is a special case of the merge mode. After quantization, when all transform coefficients used for entropy coding are near zero, only neighboring block selection information is transmitted without transmitting a residual signal. By using the merge skip mode, relatively high encoding efficiency can be achieved for images with slight motion, still images, screen content images, and the like.

Hereinafter, the merge mode and the merge skip mode are collectively referred to as a merge/skip mode.

Another method for encoding motion information is advanced motion vector prediction (advanced motion vector prediction, AMVP) mode.

In the AMVP mode, the inter predictor 124 derives a motion vector prediction candidate for a motion vector of a current block by using neighboring blocks of the current block. As the neighboring blocks used to derive the motion vector prediction candidates, all or some of the left block A0, the lower left block A1, the upper side block B0, the upper right block B1, and the upper left block B2 adjacent to the current block in the current image shown in fig. 4 may be utilized. In addition, in addition to the current picture in which the current block is located, a block located within a reference picture (which may be the same as or different from a reference picture used to predict the current block) may also be used as a neighboring block used to derive a motion vector prediction candidate. For example, a co-located block of the current block within the reference picture or a block adjacent to the co-located block may be utilized. If the number of motion vector candidates selected by the above method is less than a preset number, a zero vector is added to the motion vector candidates.

The inter predictor 124 derives a motion vector prediction candidate by using the motion vector of the neighboring block, and determines a motion vector prediction of the motion vector of the current block by using the motion vector prediction candidate. The motion vector difference is calculated by subtracting the motion vector prediction from the motion vector of the current block.

Motion vector prediction may be obtained by applying a predefined function (e.g., median and average calculations, etc.) to the motion vector prediction candidates. In this case, the video decoding device is also aware of the predefined function. Further, since the neighboring block used to derive the motion vector prediction candidates is a block for which encoding and decoding have been completed, the video decoding apparatus may also already know the motion vector of the neighboring block. Therefore, the video encoding device does not need to encode information for identifying motion vector prediction candidates. Accordingly, in this case, information on a motion vector difference and information on a reference image for predicting a current block are encoded.

On the other hand, motion vector prediction may also be determined by selecting a scheme of any one of the motion vector prediction candidates. In this case, the information for identifying the selected motion vector prediction candidates is additionally encoded together with the information about the motion vector difference and the information about the reference picture for predicting the current block.

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

The transformer 140 transforms a residual signal in a residual block having pixel values of a spatial domain into transform coefficients of a frequency domain. The transformer 140 may transform a residual signal in a residual block by using the entire size of the residual block as a transform unit, or may divide the residual block into a plurality of sub-blocks and perform the transform by using the sub-blocks as transform units. Alternatively, the residual block is divided into two sub-blocks including a transform region and a non-transform region to transform the residual signal by using only the transform region sub-block as a transform unit. The transform region sub-block may be one of two rectangular blocks with a size ratio of 1:1 based on a horizontal axis (or vertical axis). In this case, a flag (cu_sbt_flag) indicating that only the sub-block is transformed, and direction (vertical/horizontal) information (cu_sbt_horizontal_flag) and/or position information (cu_sbt_pos_flag) are encoded by the entropy encoder 155 and signaled to the video decoding apparatus. In addition, the size of the transform region sub-block may have a size ratio of 1:3 based on the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_quad_flag) dividing the corresponding division is additionally encoded by the entropy encoder 155 and signaled to the video decoding device.

On the other hand, the transformer 140 may perform transformation of the residual block separately in the horizontal direction and the vertical direction. For this transformation, various types of transformation functions or transformation matrices may be utilized. For example, the pair-wise transformation function for horizontal and vertical transformations may be defined as a transformation set (multiple transform set, MTS). The transformer 140 may select one transform function pair having the highest transform efficiency in the MTS and transform the residual block in each of the horizontal and vertical directions. Information (mts_idx) about the transform function pairs in the MTS is encoded by the entropy encoder 155 and signaled to the video decoding means.

The quantizer 145 quantizes the transform coefficient output from the transformer 140 using a quantization parameter, and outputs the quantized transform coefficient to the entropy encoder 155. The quantizer 145 may immediately quantize the relevant residual block without transforming any block or frame. The quantizer 145 may apply different quantization coefficients (scaling values) according to the positions of the transform coefficients in the transform block. A quantization matrix applied to quantized transform coefficients arranged in two dimensions may be encoded and signaled to a video decoding apparatus.

The reordering unit 150 may perform the rearrangement of the coefficient values on the quantized residual values.

The rearrangement unit 150 may change the 2D coefficient array to a 1D coefficient sequence by using coefficient scanning. For example, the rearrangement unit 150 may scan the DC coefficient to the high frequency region coefficient using zigzag scanning (zig-zag scan) or diagonal scanning (diagonal scan) to output a 1D coefficient sequence. Instead of the zig-zag scan, a vertical scan that scans the 2D coefficient array in the column direction and a horizontal scan that scans the 2D block type coefficients in the row direction may also be utilized, depending on the size of the transform unit and the intra prediction mode. In one embodiment, the scanning method to be utilized 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 the 1D quantized transform coefficients output from the rearrangement unit 150 by using various encoding schemes including Context-based adaptive binary arithmetic coding (Context-based Adaptive Binary Arithmetic Code, CABAC), exponential golomb (Exponential Golomb), and the like to generate a bitstream.

The entropy encoder 155 encodes information related to block division (e.g., CTU size, CTU division flag, QT division flag, MTT division type, MTT division direction, etc.) so that a video decoding apparatus can divide blocks equally to a video encoding apparatus. The entropy encoder 155 encodes information on a prediction type indicating whether the current block is encoded by intra prediction or inter prediction. The entropy encoder 155 encodes intra prediction information (i.e., information about an intra prediction mode) or inter prediction information (a merge index in the case of a merge mode, and information about a reference picture index and a motion vector difference in the case of an AMVP mode) according to a prediction type. The entropy encoder 155 encodes information related to quantization, i.e., information about quantization parameters and information about quantization matrices.

The inverse quantizer 160 dequantizes the quantized transform coefficients output from the quantizer 145 to generate transform coefficients. The inverse transformer 165 transforms the transform coefficients output from the inverse quantizer 160 from the frequency domain to the spatial domain to restore a residual block.

The adder 170 adds the restored residual block and the prediction block generated by the predictor 120 to restore the current block. The pixels in the restored current block may be used as reference pixels when intra-predicting the next block.

The loop filtering unit 180 performs filtering on the restored pixels to reduce block artifacts (blocking artifacts), ringing artifacts (ringing artifacts), blurring artifacts (blurring artifacts), etc., which occur due to block-based prediction and transform/quantization. The loop filtering unit 180 as an in-loop filter may include all or some of a deblocking filter 182, a sample adaptive offset (sample adaptive offset, SAO) filter 184, and an adaptive loop filter (adaptive loop filter, ALF) 186.

Deblocking filter 182 filters boundaries between restored blocks to remove block artifacts (blocking artifacts) that occur due to block unit encoding/decoding, and SAO filter 184 and ALF 186 additionally filter the deblock filtered video. The SAO filter 184 and ALF 186 are filters for compensating for differences between restored pixels and original pixels that occur due to lossy coding (loss coding). The SAO filter 184 applies an offset as a CTU unit to enhance subjective image quality and coding efficiency. On the other hand, the ALF 186 performs block unit filtering, and applies different filters to compensate for distortion by dividing boundaries of respective blocks and the degree of variation. Information about filter coefficients to be used for ALF may be encoded and signaled to the video decoding apparatus.

The restored blocks filtered by the deblocking filter 182, the SAO filter 184, and the ALF 186 are stored in the memory 190. When all blocks in one image are restored, the restored image may be used as a reference image for inter-predicting blocks within a picture to be subsequently encoded.

Fig. 5 is a functional block diagram of a video decoding apparatus in which the techniques of the present invention may be implemented. Hereinafter, with reference to fig. 5, a video decoding apparatus and sub-components of the apparatus are described.

The video decoding apparatus may be configured to include an entropy decoder 510, a reordering unit 515, an inverse quantizer 520, an inverse transformer 530, a predictor 540, an adder 550, a loop filtering unit 560, and a memory 570.

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

The entropy decoder 510 extracts information related to block segmentation by decoding a bitstream generated by a video encoding apparatus to determine a current block to be decoded, and extracts prediction information required to restore the current block and information about a residual signal.

The entropy decoder 510 determines the size of CTUs by extracting information about the CTU size from a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS), and partitions a picture into CTUs having the determined size. The CTU is determined as the highest layer (i.e., root node) of the tree structure, and the partition information of the CTU is extracted to partition the CTU by using the tree structure.

For example, when dividing a CTU by using the QTBTTT structure, first a first flag (qt_split_flag) related to the division of QT is extracted to divide each node into four nodes of the lower layer. In addition, a second flag (mtt_split_flag), a split direction (vertical/horizontal), and/or a split type (binary/trigeminal) related to the split of the MTT are extracted with respect to a node corresponding to the leaf node of the QT to split the corresponding leaf node into an MTT structure. As a result, each node below the leaf node of QT is recursively partitioned into BT or TT structures.

As another example, when a CTU is divided by using the QTBTTT structure, a CU division flag (split_cu_flag) indicating whether to divide the CU is extracted. When the corresponding block is partitioned, a first flag (qt_split_flag) may also be extracted. During the segmentation process, recursive MTT segmentation of 0 or more times may occur after recursive QT segmentation of 0 or more times for each node. For example, for CTUs, MTT partitioning may occur immediately, or only multiple QT partitioning may occur.

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

On the other hand, when the entropy decoder 510 determines the current block to be decoded by using the partition of the tree structure, the entropy decoder 510 extracts information on 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 510 extracts syntax elements for intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the entropy decoder 510 extracts information representing syntax elements of the inter prediction information, i.e., a motion vector and a reference picture to which the motion vector refers.

The entropy decoder 510 extracts quantization-related information and extracts information on transform coefficients of the quantized current block as information on a residual signal.

The reordering unit 515 may change the sequence of the 1D quantized transform coefficients entropy-decoded by the entropy decoder 510 into a 2D coefficient array (i.e., block) again in the reverse order of the coefficient scan order performed by the video encoding device.

The inverse quantizer 520 dequantizes the quantized transform coefficients, and dequantizes the quantized transform coefficients by using quantization parameters. The inverse quantizer 520 may apply different quantization coefficients (scaling values) to the quantized transform coefficients arranged in 2D. The inverse quantizer 520 may perform inverse quantization by applying a matrix of quantized coefficients (scaled values) from the video encoding device to a 2D array of quantized transform coefficients.

The inverse transformer 530 restores a residual signal by inversely transforming the inversely quantized transform coefficients from the frequency domain to the spatial domain to generate a residual block of the current block.

When the inverse transformer 530 inversely transforms a partial region (sub-block) of the transform block, the inverse transformer 530 extracts a flag (cu_sbt_flag) transforming only the sub-block of the transform block, direction (vertical/horizontal) information (cu_sbt_horizontal_flag) of the sub-block, and/or position information (cu_sbt_pos_flag) of the sub-block. The inverse transformer 530 also inversely transforms transform coefficients of the corresponding sub-block from the frequency domain to the spatial domain to restore a residual signal, and fills the region that is not inversely transformed with a value of "0" as the residual signal to generate a final residual block of the current block.

When applying the MTS, the inverse transformer 530 determines a transform index or a transform matrix to be applied in each of the horizontal direction and the vertical direction by using MTS information (mts_idx) signaled from the video encoding apparatus. The inverse transformer 530 also performs inverse transformation on the transform coefficients in the transform block in the horizontal direction and the vertical direction by using the determined transform function.

The predictor 540 may include an intra predictor 542 and an inter predictor 544. The intra predictor 542 is activated when the prediction type of the current block is intra prediction, and the inter predictor 544 is activated when the prediction type of the current block is inter prediction.

The intra predictor 542 determines an intra prediction mode of the current block among the plurality of intra prediction modes according to syntax elements of the intra prediction mode extracted from the entropy decoder 510. The intra predictor 542 predicts the current block by using neighboring reference pixels of the current block according to an intra prediction mode.

The inter predictor 544 determines a motion vector of the current block and a reference picture to which the motion vector refers by using syntax elements of the inter prediction mode extracted from the entropy decoder 510.

The adder 550 restores the current block by adding the residual block output from the inverse transformer 530 to the prediction block output from the inter predictor 544 or the intra predictor 542. In intra prediction of a block to be decoded later, pixels within the restored current block are used as reference pixels.

The loop filtering unit 560, which is an in-loop filter, may include a deblocking filter 562, an SAO filter 564, and an ALF 566. Deblocking filter 562 performs deblocking filtering on boundaries between restored blocks to remove block artifacts occurring due to block unit decoding. The SAO filter 564 and ALF 566 perform additional filtering on the restored block after deblocking filtering to compensate for differences between restored pixels and original pixels that occur due to lossy encoding. The filter coefficients of the ALF are determined by using information on the filter coefficients decoded from the bitstream.

The restored blocks filtered by the deblocking filter 562, the SAO filter 564, and the ALF 566 are stored in the memory 570. When all blocks in one image are restored, the restored image may be used as a reference image for inter-predicting blocks within a picture to be subsequently encoded.

Embodiments of the present invention relate to encoding and decoding of images (video) as described above. More particularly, embodiments of the present invention provide a video encoding/decoding apparatus and method for deriving a residual signal of a chrominance component of a current block. In deriving the residual signal of the chrominance component, the video encoding/decoding apparatus and method use the residual signal of the previously reconstructed block without transmitting the residual signal of a portion of the chrominance component of the current block.

The embodiments described below may be performed in the inverse transformer 165 of the video encoding apparatus and the inverse transformer 530 of the video decoding apparatus.

In the following description, a current block includes a luminance component and a chrominance component, and the chrominance component includes Cb signals and Cr signals. Accordingly, the residual signal of the chrominance component includes residual signals of Cb signal and Cr signal.

On the other hand, the current block includes a luminance block and a chrominance block. The chroma blocks include Cb blocks and Cr blocks. Thus, the residual block of the chroma block includes a Cb residual block and a Cr residual block. For a luminance block, there is also a residual block for encoding or decoding.

In the following description, values of samples constituting a residual block are collectively referred to as a residual signal. According to circumstances, the expression of the encoding/decoding residual block may be used interchangeably with the expression of the encoding/decoding residual signal.

I. Joint Coding of Chroma Residual (JCCR)

In VVC technology, the residual signal of Cb signal and the residual signal of Cr signal may be jointly encoded based on JCCR. JCCR may be performed on a Transform Unit (TU) basis and activated by tu_joint_cbcr_residual_flag.

The video decoding apparatus may set a variable tucresfode for restoring the residual signal of the chrominance component according to a tu_joint_cbcr_residual_flag indicating JCCR, a tu_cb_coded_flag indicating whether the residual signal of the Cb signal is transformed, and a tu_cr_coded_flag indicating whether the residual signal of the Cr signal is transformed, as follows.

TuCResMode is set to 0 when tu_joint_cbcr_residual_flag=0, i.e., when JCR is not applied. Here, the video decoding apparatus decodes the residual signal of the Cb signal and the residual signal of the Cr signal, respectively.

When tu_joint_cbcr_residual_flag=1, i.e., when JCCR is applied, tucresfode may be set as follows.

TuCResMode is set to 1 when tu_cb_coded_flag=1 and tu_cr_coded_flag=0. TuCResMode is set to 2 when tu_cb_coded_flag=1 and tu_cr_coded_flag=1. TuCResMode is set to 3 when tu_cb_coded_flag=0 and tu_cr_coded_flag=1.

According to the variable TuCResMode, the video decoding apparatus restores residual signals resCb and resCr of the Cb signal as shown in table 1.

TABLE 1

In table 1, resJointC is a joint chrominance component decoded by a video decoding apparatus, the value of CSign is 1 or-1, which can be transmitted by the video encoding apparatus.

On the other hand, three values of TuCResMode shown in table 1 may be applied to intra frames (I frames). Only the case of tucresfode=2 can be applied to predicted frames (P frames) and bi-predicted frames (B frames).

The video encoding apparatus generates a joint chrominance component resJointC as shown in table 2 according to tucresfode so that the video decoding apparatus decodes a residual signal of the chrominance component as shown in table 1.

TABLE 2

TuCResMode	Generation of resJointC
		1	resJointC＝(4·resCb+2·CSign·resCr)/5
2	resJointC＝(resCb+CSign·resCr)/2
		3	resJointC＝(4·resCr+2·CSign·resCb)/5

Method for using residual signal of previously reconstructed component

In case of a component corresponding to a first decoding order among the plurality of components of the current block, the video decoding apparatus may generate a residual block of the first component by applying a bitstream transmitted by the video encoding apparatus to the entropy decoder 510, the inverse quantizer 520, and the inverse transformer 530. In one embodiment, the first component is a luminance signal.

In the case of a component corresponding to a second or subsequent decoding order among the plurality of components of the current block, the video decoding apparatus may decode the residual signal derivation method index. In one embodiment, the component following the second component is a chrominance signal.

In case of the derivation method 1, in the same manner as the method of generating the first luminance component, the video decoding apparatus may reconstruct the residual signal of the corresponding chrominance component by applying the bitstream to the entropy decoder 510, the inverse quantizer 520, and the inverse transformer 530.

In the case of the derivation method 2, the video decoding apparatus may derive a residual block of a chroma component of the current block by applying a linear model to the residual block of the reference component. The linear model parameters may include weights for multiplication and offsets for addition.

Fig. 6a and 6b show residual blocks of reference components according to an embodiment of the present invention.

As shown in fig. 6a, a residual block of a Cb component of the current block may use a luminance component as a reference component, and a residual block of a Cr component of the current block may use a Cb component as a reference component. As another example, a residual block of a Cr component of the current block may utilize a luminance component as a reference component, and a residual block of a Cb component of the current block may utilize the Cr component as a reference component.

As shown in fig. 6b, the luminance component may be used as a reference component for both the Cb component of the current block and the residual block of the Cr component.

On the other hand, the video decoding apparatus may decode the weights and the offset values from the bitstream.

As another example of the present invention, the video decoding apparatus may derive weights and offsets. For example, the video decoding apparatus may decode an index including a list of linear models composed of weights and offsets, and then derive the weights and offset values from, for example, a pre-stored lookup table using the decoded index.

As yet another example of the present invention, the video decoding apparatus may derive weights and offsets as specific values.

As still another example of the present invention, the video decoding apparatus may derive the weights and the offsets by calculating a linear relationship between residual values of reference samples adjacent to the reference component block and residual values of reference samples adjacent to the chroma block of the current block.

In the following description with reference to fig. 7, a device for reconstructing a residual signal, which reconstructs a residual block of a chrominance component of a current block from a residual block of a reference component using a derived linear relationship, is described.

On the other hand, the method for reconstructing a chrominance residual signal performed by the apparatus for reconstructing a residual signal according to the present embodiment may be performed by the inverse transformer 530 of the video decoding apparatus.

Fig. 7 is a block diagram conceptually illustrating an apparatus for reconstructing a residual signal within a video decoding apparatus according to an embodiment of the present invention.

The apparatus for reconstructing a residual signal according to the present embodiment includes all or part of the neighboring residual sample deriver 710, the linear model deriver 720, and the residual signal generator 730.

The neighboring residual sample deriver 710 derives the positions of neighboring residual samples of a chroma block (hereinafter, referred to as a "current chroma block") and a decoded reference component block of each current block. The reference relation between the current chroma block and the reference component block may be the same as shown in fig. 6a and 6 b. In other words, both the current chroma block and the decoded reference component block may be components of the current block. The video encoding device may encode information indicating the above-described reference relationship and transmit the encoded information to the video decoding device. The entropy decoder 510 in the video decoding apparatus may decode information indicating the reference relationship.

Since embodiments of the present invention are directed to residual signals, in the following description, a current chroma block and a current chroma residual block may be used interchangeably, and a reference component block and a reference component residual block may also be used interchangeably.

When the size of the current chroma block is the same as the size of the reference component block, as shown in fig. 8a, the neighboring residual sample deriver 710 may designate all or part of neighboring samples neighboring to the top or left of the current chroma block and the reference component block as neighboring residual samples. Examples of the above-described case may include a case in which a residual block of a Cr component of the current block uses a decoded Cb component as a reference component, or a case in which a residual block of a Cb component of the current block uses a decoded Cr component as a reference component, as shown in fig. 6 a.

When the size of the current chroma block is smaller than the size of the reference component block, the neighboring residual sample deriver 710 selects all n (where n is a natural number) neighboring samples adjacent to the top or left side of the current chroma block as neighboring residual samples. Additionally or alternatively, the neighboring residual sample deriver 710 may select neighboring residual samples by sub-sampling n samples of the top or left portion of the reference component block.

When the width of the current chroma residual block is N (where N is a natural number) and the width of the residual block of the reference component is α×n (where α is a natural number), as shown in fig. 8b, for each non-overlapping region of size α×line_num (where line_num is a natural number) in the top portion of the residual block of the reference component, the neighboring residual sample deriver 710 may select neighboring residual samples by sampling specific positions within the non-overlapping region.

When the height of the current chroma residual block is M (where M is a natural number) and the height of the residual block of the reference component is β×m (where β is a natural number), as shown in fig. 8b, for each non-overlapping region of size line_num×β in the left part of the residual block of the reference component, the neighboring residual sample deriver 710 may select neighboring residual samples by sampling a specific position within the non-overlapping region.

As an example described above, in the examples of fig. 6a and 6b, the residual block of the chrominance component of the current block may utilize the decoded luminance component as a reference component.

The neighboring residual sample deriver 710 may select neighboring residual samples of the current chroma block and neighboring residual samples of the reference component block such that the selected neighboring residual samples form a one-to-one correspondence based on the locations of the samples.

Based on the one-to-one correspondence described above, as shown in fig. 9a and 9b, the linear model deriver 720 may derive weights and offsets by estimating a linear relationship between neighboring residual samples of the reference component block and neighboring residual samples of the current chroma block.

The linear model deriver 720 may derive the linear relationship by applying a least square method to each set of L (where L is a natural number) neighboring residual samples taken from the reference component block and the current chroma block, respectively.

In another embodiment of the present invention, the linear model deriver 720 may derive the weights and offsets by selecting a pair of key neighboring residual samples and then calculating a linear relationship between the two key neighboring residual samples. Based on neighboring residual sample values of the reference component block or the current chroma block, a key neighboring residual sample pair may be formed using an average of j (where j is a natural number) values having a minimum value and a maximum k value (where k is a natural number).

The residual signal generator 530 may generate a residual block of the current chroma component by applying the linear relationship derived by the linear model deriver 720 to the residual block of the previously decoded reference component.

When the residual block of the previously decoded reference component has a different size from the current chroma residual block, the residual signal generator 530 may downsample the residual block of the previously decoded reference component so that the two residual blocks have the same size.

For example, as shown in fig. 10a, when the width of the residual block of the reference component is α times the width of the current chroma residual block and the height of the residual block of the reference component is β times the height of the current chroma residual block, the residual signal generator 530 may generate a reference sample by sampling a specific location within each non-overlapping region of each non-overlapping (α×β) region of the reference component residual block.

The residual signal generator 530 may generate a current chroma residual block by applying the derived linear relationship to the residual block of the reference component. As shown in fig. 10b, the residual signal generator 530 may generate a current chroma residual block by multiplying each sample value in the residual block of the reference component by a weight and adding the offset and the weighted sample values.

Fig. 11 is a flowchart illustrating a method for reconstructing a chrominance residual signal performed by a video decoding apparatus according to an embodiment of the present invention.

The entropy decoder 510 within the video decoding device decodes information representing a reference relationship between a chroma residual block and a reference component residual block within the current block (S1100). The reference relationship between the chroma residual block and the reference component residual block of the current block may be as shown in fig. 6a and 6 b. As shown in fig. 6a and 6b, the video decoding apparatus may use the decoded residual block of the luminance component or the chrominance component as a reference component residual block within the current block.

The inverse transformer 530 within the video decoding apparatus derives the positions of the first neighboring residual samples of the decoded reference component residual block and the second neighboring residual samples of the chroma residual block based on the information representing the reference relationship (S1102).

The video decoding device may select the first adjacent residual sample and the second adjacent residual sample to maintain a one-to-one correspondence between the first adjacent residual sample and the second adjacent residual sample.

When the chroma residual block and the reference component residual block are the same in size, the video decoding device selects all or part of neighboring samples adjacent to the top or left side of the chroma residual block as second neighboring residual samples and selects all or part of neighboring samples adjacent to the top or left side of the reference component residual block as first neighboring residual samples.

When the size of the chroma residual block is smaller than the reference component residual block, the video decoding apparatus may select all n neighboring samples adjacent to the top and left sides of the chroma residual block as second neighboring residual samples, and select the first neighboring residual samples by sub-sampling n samples in the upper and left side portions of the reference residual block.

The video decoding apparatus generates a linear relationship between the first neighboring residual samples and the second neighboring residual samples based on a one-to-one correspondence (S1104).

The video decoding device may derive the linear relationship by applying a least squares method to each set of L samples taken from the first and second adjacent residual samples, respectively.

After decoding an index comprising a list of a plurality of preset linear models, the video decoding apparatus may derive a linear relationship between the first neighboring residual samples and the second neighboring residual samples using the decoded index.

The video decoding apparatus generates a chroma residual block by applying the derived linear relationship to the residual block of the reference component (S1106).

When the size of the residual block of the reference component is different from the size of the chroma residual block, the video decoding apparatus may downsample the residual block of the reference component such that the residual block of the reference component and the chroma residual block have the same size.

The above-described method for reconstructing a chrominance residual signal may also be performed by the inverse transformer 165 of the video decoding apparatus.

The video encoding device searches for the best decoded reference component residual block in terms of reconstruction of the chroma residual block within the current block using rate-distortion analysis. During the search process, the video encoding device generates information representative of a reference relationship between a chroma residual block within the current block and a reference component residual block. An inverse transformer 165 in the video encoding device may reconstruct the chroma residual block of the current block using information representing the reference relationship.

The video encoding apparatus may encode information representing the optimal reference relationship generated during the search and transmit the encoded information to the video decoding apparatus.

Fig. 12 is a flowchart illustrating a method for reconstructing a chrominance residual signal performed by a video encoding apparatus according to an embodiment of the present invention.

The video encoding apparatus generates information representing a reference relationship between a chroma residual block within a current block and a decoded reference component residual block for bit rate distortion analysis (S1200). The reference relationship between the chroma residual block and the reference component residual block of the current block may be as shown in fig. 6a and 6 b. As shown in fig. 6a and 6b, the video encoding apparatus may use a residual block of a luminance component or a chrominance component as a residual block of a reference component within a current block.

The inverse transformer 165 in the video encoding device derives the positions of the first neighboring residual samples of the reference component residual block and the second neighboring residual samples of the chroma residual block based on the information representing the reference relationship (S1202).

The video encoding device may select the first adjacent residual sample and the second adjacent residual sample to maintain a one-to-one correspondence between the first adjacent residual sample and the second adjacent residual sample.

The video encoding device generates a linear relationship between the first neighboring residual samples and the second neighboring residual samples based on a one-to-one correspondence (S1204).

The video encoding apparatus generates a chroma residual block by applying the derived linear relationship to the residual block of the reference component (S1206).

Although the steps in the respective flowcharts are described as being sequentially performed, these steps merely exemplify the technical ideas of some embodiments of the present invention. Accordingly, one of ordinary skill in the art to which the invention pertains may perform the steps by changing the order depicted in the various figures or by performing two or more steps in parallel. Accordingly, the steps in the various flowcharts are not limited to the order shown in chronological order.

It should be understood that the foregoing description presents illustrative embodiments that may be implemented in various other ways. The functions described in some embodiments may be implemented by hardware, software, firmware, and/or combinations thereof. It should also be understood that the functional components described in this specification are labeled as "..units" to highlight the possibility of their independent implementation.

In some embodiments, the various methods or functions described herein may be implemented as instructions stored in a non-volatile recording medium, which may be read and executed by one or more processors. The nonvolatile recording medium may include various types of recording devices that store data in a form readable by a computer system, for example. For example, the nonvolatile recording medium may include a storage medium such as an erasable programmable read-only memory (EPROM), a flash memory drive, an optical disk drive, a magnetic hard disk drive, a Solid State Drive (SSD), and the like.

Although embodiments of the present invention have been described for illustrative purposes, those skilled in the art to which the invention pertains will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. Thus, for the sake of brevity and clarity, embodiments of the invention have been described. The scope of the technical idea of the embodiment of the invention is not limited by the illustration. Accordingly, it will be understood by those of ordinary skill in the art that the scope of the present invention is not limited by the embodiments explicitly described above, but is limited by the claims and their equivalents.

(description of the reference numerals)

510: entropy decoder

530: inverse transformer

710: adjacent residual sample deriver

720: linear model deducer

730: and a residual signal generator.

Cross Reference to Related Applications

The present application claims priority from korean patent application No.10-2020-0158993, filed on 11 months 24 in 2020, and korean patent application No.10-2021-0163120, filed on 11 months 24 in 2021, the entire contents of which are incorporated herein by reference.

Claims

1. A method performed by a video decoding device for reconstructing a chroma residual block of a current block, the method comprising:

deriving the positions of first neighboring residual samples of the reference component residual block and second neighboring residual samples of the chroma residual block based on information representing a reference relationship between the chroma residual block and the decoded reference component residual block within the current block;

generating a linear relationship between the first adjacent residual samples and the second adjacent residual samples; and

the chroma residual block is generated by applying a linear relationship to the reference component residual block.

2. The method of claim 1, further comprising decoding information representative of the reference relationship.

3. The method of claim 1, wherein deriving a location comprises: a residual block of a luminance component or a chrominance component is utilized as a reference component residual block within the current block.

4. The method of claim 1, wherein deriving a location comprises: the first and second adjacent residual samples are selected to maintain a one-to-one correspondence between the first and second adjacent residual samples.

5. The method of claim 1, wherein deriving the position when the chroma residual block and the reference component residual block have the same size comprises:

selecting all or part of adjacent samples adjacent to the top or left side of the chroma residual block as second adjacent residual samples, and

all or part of the neighboring samples adjacent to the top or left side of the reference component residual block are selected as the first neighboring residual samples.

6. The method of claim 1, wherein deriving the position when the size of the chroma residual block is smaller than the size of the reference component residual block comprises:

selecting all n samples adjacent to the top and left of the chroma residual block as second adjacent residual samples, where n is a natural number, and

n samples obtained by sub-sampling the top and left portions of the reference component residual block are selected as first neighboring residual samples.

7. The method of claim 1, wherein when the width of the reference component residual block is a multiple of the width of the chroma residual block, where a is a natural number, deriving the position comprises: for each non-overlapping region of size α×line num in the top portion of the reference component residual block, a first neighboring residual sample obtained by sampling a specific location within each non-overlapping region is selected, where line_num is a natural number.

8. The method of claim 1, wherein when the height of the reference component residual block is β times the height of the chroma residual block, where β is a natural number, deriving the position comprises: for each non-overlapping region of size β×line_num in the left part of the reference component residual block, a first neighboring residual sample obtained by sampling a specific position within each non-overlapping region is selected.

9. The method of claim 1, wherein generating a linear relationship comprises: the linear relationship is derived by applying a least squares method to each set of L adjacent residual samples taken from the first and second adjacent residual samples, respectively, where L is a natural number.

10. The method of claim 1, wherein generating a linear relationship comprises: an index of a list containing a plurality of preset linear models is decoded and the index is used to derive a linear relationship.

11. The method of claim 1, wherein generating the chroma residual block when the size of the reference component residual block is different from the size of the chroma residual block comprises: the reference component residual block is downsampled such that the reference component residual block and the chroma residual block have the same size.

12. A video decoding device, comprising:

an entropy decoder configured to decode information representing a reference relationship between a chroma residual block within a current block and a decoded reference component residual block;

an adjacent residual sample deriver configured to derive locations of a first adjacent residual sample of the reference component residual block and a second adjacent residual sample of the chroma residual block based on information representing a reference relationship;

a linear model deriver configured to generate a linear relationship between the first neighboring residual samples and the second neighboring residual samples; and

a residual signal generator configured to generate a chroma residual block by applying a linear relation to a reference component residual block.

13. A method performed by a video encoding device for reconstructing a chroma residual block of a current block, the method comprising:

generating information representing a reference relationship between a chroma residual block and a reference component residual block within the current block;

deriving locations of first neighboring residual samples of the reference component residual block and second neighboring residual samples of the chroma residual block based on information representing the reference relationship;

14. The method of claim 13, wherein deriving a location comprises: a residual block of a luminance component or a chrominance component is utilized as a reference component residual block within the current block.

15. The method of claim 13, wherein deriving a location comprises: the first and second adjacent residual samples are selected to maintain a one-to-one correspondence between the first and second adjacent residual samples.