Image encoding / decoding method and device

Abstract

The present invention relates to an image encoding / decoding method and device. The image decoding method according to an embodiment of the present invention may comprise the steps of: independently partitioning a luminance coding tree block and a chrominance coding tree block of the current coding tree unit; setting a luminance region corresponding to the current chrominance block partitioned from the chrominance coding tree block; setting a candidate group on the basis of information about at least one block in the luminance region; determining one corresponding luminance block from the candidate group; and generating a prediction block of the current chrominance block on the basis of prediction information about the corresponding luminance block.

Description

Video encoding / decoding method and device

[0001] The present invention relates to a video encoding / decoding method and device, and more particularly, to a video encoding / decoding method and device for improving the efficiency of intra prediction of a chrominance component using intra prediction information of a luminance component.

[0002] Recently, the demand for multimedia data, such as video, has been rapidly increasing. In particular, the demand for high-resolution, high-quality video, such as HD (High Definition) and UHD (Ultra High Definition) video, is growing across a wide range of applications. High-resolution, high-quality video data typically requires significantly more data volume than conventional video data. Consequently, the transmission and storage costs for storing and / or transmitting high-resolution, high-quality video data increase compared to conventional video data.

[0003] To solve these problems, high-efficiency image encoding / decoding technology for images with higher resolution and quality is required.

[0004] In order to encode an image, various techniques are used, such as an intra prediction technique that predicts the pixel values ​​included in the current picture using pixel information in the current picture, an intra prediction technique that predicts the pixel values ​​included in the current picture from the pictures before or after the current picture, a transform and quantization technique for compressing the energy of the residual signal, which is the difference between the predicted signal and the original signal, and an entropy coding technique that assigns short codes to values ​​with high appearance frequencies and long codes to values ​​with low appearance frequencies. In addition, various tools are being developed to implement each technique in order to improve the efficiency of image coding. In addition, in order to decode an encoded image, the image can be restored and reproduced through an image decoding technique that uses a technique and tools corresponding to the image coding technique.

[0005] Using these video encoding and decoding technologies, video data can be effectively compressed, transmitted, stored, and played back.

[0006] The present disclosure aims to provide an image encoding / decoding method and device that improve the inefficiency of an intra prediction method of a chrominance block based on intra prediction information of a corresponding luminance block and enhance the compression efficiency of image data.

[0007] The technical challenges to be achieved through this disclosure are not limited to the technical challenges mentioned above. Furthermore, other technical challenges not mentioned in this disclosure will be readily apparent to those skilled in the art from this disclosure.

[0008] A video decoding method according to one embodiment of the present invention may include the steps of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit, setting a luminance region corresponding to a current chrominance block divided from the chrominance coding tree block, setting a candidate group based on information about at least one block in the luminance region, determining one corresponding luminance block from among the candidate group, and generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

[0009] In the above image decoding method, the current slice including the current coding tree unit may be characterized as being one of an I slice, a B slice, and a P slice.

[0010] In the above image decoding method, the at least one block may be characterized by including a block including a center sample of the luminance region, a block including a sample at the upper left of the luminance region, a block including a sample at the lower left of the luminance region, a block including a sample at the upper right of the luminance region, and a block including a sample at the lower right of the luminance region.

[0011] In the above image decoding method, the candidate group may be characterized by including available blocks within the luminance range based on the availability of at least one block.

[0012] In the above image decoding method, the availability of the at least one block may be determined based on a prediction mode of each of the at least one block and a prediction mode of the current chrominance block.

[0013] In the above image decoding method, the one corresponding luminance block may be characterized as being a block determined as a result of a search according to a preset order in the candidate group.

[0014] In the above image decoding method, the one corresponding luminance block may be characterized as being a block determined based on information indicating one candidate from the candidate group.

[0015] In the above image decoding method, the prediction information of the corresponding luminance block may be characterized as intra prediction mode information derived based on DIMD, TIMD, and OBIC.

[0016] In the above image decoding method, the prediction information of the corresponding luminance block may be characterized as being intra prediction mode information of a matching luminance block indicated by a block vector of the corresponding luminance block.

[0017] In the above image decoding method, the prediction information of the corresponding luminance block may be characterized as being intra prediction mode information of a reference luminance block indicated by a motion vector of the corresponding luminance block.

[0018] In the above image decoding method, the prediction information of the corresponding luminance block may be a block vector of the corresponding luminance block, and the prediction block of the current chrominance block may be generated based on a reference chrominance block corresponding to a matching luminance block indicated by the block vector of the corresponding luminance block.

[0019] In the above image decoding method, the prediction information of the corresponding luminance block may be a motion vector of the corresponding luminance block, and the prediction block of the current chrominance block may be generated based on a reference chrominance block corresponding to a reference luminance block indicated by the motion vector of the corresponding luminance block.

[0020] In the above image decoding method, the prediction information of the corresponding luminance block may be a block vector of the corresponding luminance block, and the prediction block of the current chrominance block may be generated based on filter coefficients derived based on samples adjacent to a matching luminance block indicated by the block vector of the corresponding luminance block and samples adjacent to a matching chrominance block corresponding to the matching luminance block.

[0021] In the above image decoding method, the prediction information of the corresponding luminance block may be a motion vector of the corresponding luminance block, and the prediction block of the current chrominance block may be generated based on filter coefficients derived based on samples adjacent to a reference luminance block indicated by the motion vector of the corresponding luminance block and samples adjacent to a reference chrominance block corresponding to the reference luminance block.

[0022] A video encoding method according to one embodiment of the present invention may include the steps of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit, setting a luminance region corresponding to a current chrominance block divided from the chrominance coding tree block, setting a candidate group based on information about at least one block in the luminance region, determining one corresponding luminance block from among the candidate groups, and generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

[0023] A non-transitory computer-readable recording medium storing a bitstream generated by an image encoding method according to one embodiment of the present invention can store a bitstream generated by an image encoding method, the bitstream including the steps of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit, setting a luminance area corresponding to a current chrominance block divided from the chrominance coding tree block, setting a candidate group based on information about at least one block in the luminance area, determining one corresponding luminance block from among the candidate groups, and generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

[0024] A method for transmitting a bitstream generated by a video encoding method according to one embodiment of the present invention comprises the steps of transmitting the bitstream, independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit, setting a luminance region corresponding to a current chrominance block divided from the chrominance coding tree block, setting a candidate group based on information about at least one block in the luminance region, determining one corresponding luminance block from among the candidate groups, and generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

[0025] The present disclosure aims to provide an image encoding / decoding method and device that improve the inefficiency of an intra prediction method of a chrominance block based on intra prediction information of a corresponding luminance block and enhance the compression efficiency of image data.

[0026] In addition, according to the present disclosure, a recording medium storing a bitstream generated by the image encoding method or device of the present invention can be provided.

[0027] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the description below.

[0028] FIG. 1 is a block diagram showing an image encoding device according to one embodiment of the present invention.

[0029] FIG. 2 is a block diagram showing an image decoding device according to one embodiment of the present invention.

[0030] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0031] FIG. 4 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

[0032] FIG. 5 is a diagram illustrating a chrominance intra prediction method of direct block vector mode according to one embodiment of the present invention.

[0033] FIG. 6 is a diagram illustrating a color difference intra prediction method of BVG-CCCM mode according to one embodiment of the present invention.

[0034] FIG. 7 is a diagram illustrating a method for predicting a color difference block based on a motion vector according to one embodiment of the present invention.

[0035] FIG. 8 is a diagram illustrating an example of a structure of partitioned blocks based on a dual tree according to an embodiment of the present invention.

[0036] FIG. 9 is a flowchart illustrating an image decoding method for predicting a chrominance block based on information of a luminance block according to an embodiment of the present disclosure.

[0037] The present invention is susceptible to various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0038] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a "second component," and similarly, a second component may also be referred to as a "first component." The term "and / or" includes a combination of multiple related items described herein or any of multiple related items described herein.

[0039] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0040] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Hereinafter, identical components in the drawings will be designated by the same reference numerals, and redundant descriptions of identical components will be omitted.

[0042] FIG. 1 is a block diagram showing an image encoding device according to one embodiment of the present invention.

[0043] Referring to FIG. 1, an image encoding device (100) may include an image segmentation unit (101), an intra prediction unit (102), an inter prediction unit (103), a subtraction unit (104), a transformation unit (105), a quantization unit (106), an entropy encoding unit (107), an inverse quantization unit (108), an inverse transformation unit (109), an addition unit (110), a filter unit (111), and a memory (112).

[0044] Each component shown in Fig. 1 is independently depicted to indicate different characteristic functions in the video encoding device, and does not mean that each component is composed of separate hardware or a single software component. That is, each component is listed and included as a separate component for convenience of explanation, and at least two components among each component may be combined to form a single component, or one component may be divided into multiple components to perform a function, and such integrated and separate embodiments of each component are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

[0045] Additionally, some components may not be essential components that perform essential functions of the present invention, but may be optional components merely used to enhance performance. The present invention may be implemented by including only components essential to implementing the essence of the present invention, excluding components used solely for performance enhancement. A structure that includes only essential components, excluding optional components used solely for performance enhancement, is also within the scope of the present invention.

[0046] The image segmentation unit (101) can segment an input image into at least one block. At this time, the input image can have various shapes and sizes such as a sequence, a picture, a slice, a tile, a segment, a tile group, a coding tree unit, etc. According to another embodiment, the image segmentation unit (101) can segment one input picture into a plurality of sub-pictures defined as a group of rectangular slices, segment each sub-picture into the tiles / slices, and segment the tiles / slices into coding tree units.

[0047] In addition, the image segmentation unit (101) can recursively segment the segmented coding tree unit. The terminal node segmented from the coding tree unit may be referred to as a coding unit (CU). The block may mean a coding unit (CU), or a prediction unit (PU) or a transformation unit (TU) segmented from the coding unit (CU). The segmentation may be performed based on at least one of a quadtree, a binary tree, and a ternary tree. The quadtree is a method of segmenting an upper block into lower blocks whose width and height are half of those of the upper block. The binary tree is a method of segmenting an upper block into lower blocks whose width or height is half of that of the upper block. The ternary tree is a method of segmenting an upper block into three lower blocks. For example, the three lower blocks may be obtained by segmenting the width or height of the upper block at a ratio of 1:2:1. Through the binary tree-based partitioning described above, blocks can have not only square but also non-square shapes. Blocks can first be partitioned into a quad tree. Blocks corresponding to leaf nodes of the quad tree can be left unpartitioned, or can be partitioned into a binary tree or a ternary tree. Leaf nodes of the binary tree or ternary tree can be units of encoding, prediction, and / or transformation.

[0048] The image segmentation unit (101) can recursively segment the CTU into not only a quad tree (QT) but also a multi-type tree (MTT). Here, the MTT can be composed of a binary tree (BT) and a triple tree (TT). For example, the MTT structure can be divided into a vertical binary tree segmentation mode (SPLIT_BT_VER), a horizontal binary tree segmentation mode (SPLIT_BT_HOR), a vertical ternary tree segmentation mode (SPLIT_TT_VER), and a horizontal ternary tree segmentation mode (SPLIT_TT_HOR).

[0049] In addition, the image segmentation unit (101) can segment a CTU by applying a dual tree that uses different CTU segmentation structures for luminance and chrominance components, or by applying a single tree in which luminance and chrominance CTBs (Coding Tree Blocks) within a CTU share a coding tree structure.

[0050] The prediction unit (102, 103) may include an intra-prediction unit (102) that performs intra-prediction and an inter-prediction unit (103) that performs inter-prediction. The prediction unit (102, 103) may determine whether to use intra-prediction or inter-prediction for a prediction unit. In addition, the prediction unit (102, 103) may determine specific information (e.g., intra-prediction mode, inter-prediction mode, motion vector, reference picture, etc.) according to the determined prediction method. At this time, the processing unit where the prediction is performed and the processing unit where the prediction method and specific contents are determined may be different. For example, the prediction unit (102, 103) may determine the prediction method and prediction mode for each prediction unit, and perform prediction according to the transformation unit.

[0051] In another embodiment, the prediction unit may encode the input image using a third mode (e.g., IBC mode, Palette mode, etc.) other than the intra mode and the inter mode. However, if the third mode has functional characteristics similar to the intra mode or the inter mode, the third mode may be classified as the intra mode or the inter mode. In this disclosure, the third mode will be described only when a specific description thereof is required.

[0052] The intra prediction unit (102) can generate a prediction block of the current block based on the intra prediction mode of the current block and reference pixel information around the current block, which is pixel information within the current picture. If a neighboring block of the current block is predicted by inter prediction, the reference pixels included in the inter-predicted neighboring block can be replaced with reference pixels within another neighboring block that has been intra-predicted. That is, if a reference pixel is not available, the intra prediction unit (102) can perform intra prediction of the current block by replacing the unavailable reference pixel with at least one reference pixel among the available reference pixels.

[0053] The intra prediction unit (102) can use multiple reference pixel lines for intra prediction of the current block. When multiple reference pixel lines are available, information indicating a reference pixel line used for intra prediction among the multiple reference pixel lines can be signaled.

[0054] Intra prediction modes used for intra prediction may include a directional prediction mode that uses reference pixel information according to the prediction direction, and a non-directional mode that does not use directional information. Additionally, the mode for predicting luminance information and the mode for predicting chrominance information may be different, and the intra prediction mode information of the luminance component block or the predicted luminance signal information may be utilized to predict chrominance information.

[0055] Alternatively, the intra prediction unit (102) may perform intra prediction on the current block by applying at least one mode among decoder-side intra mode derivation (DIMD), Occurrence-based intra coding (OBIC), extrapolation filter based intra prediction mode (EIP), template based intra mode derivation (TIMD), spatial geometric partitioning mode (SGPM) mode, intra template matching prediction (IntraTMP), and intra block copy. When the intra prediction mode of the block is a predetermined mode, the intra prediction unit (102) may perform intra prediction on the current block by using a block vector indicating a block other than the current block.

[0056] The intra prediction unit (102) may include a reference sample filter, an interpolation filter, and a DC filter. The reference sample filter is a filter that performs filtering on the reference pixels of the current block and may be adaptively applied depending on the prediction mode, size, shape, and / or whether the reference pixel of the current prediction unit is included in a reference pixel line immediately adjacent to the current block. If the prediction mode of the current block is a mode that does not perform reference pixel filtering, the reference pixel filter may not be applied.

[0057] An interpolation filter is a filter that interpolates and filters prediction samples of the current block, and can be adaptively applied depending on the prediction mode, size, shape, and / or whether the reference pixel of the current prediction unit is included in the reference pixel line immediately adjacent to the current block.

[0058] If the prediction mode of the current block is DC mode, a prediction block can be generated by applying a DC filter.

[0059] In one embodiment, the intra prediction unit (102) may perform intra prediction using a pre-trained neural network (NN) model. For example, the intra prediction unit (102) may derive an intra prediction mode of a block to which the DIMD mode is applied and use a pre-trained neural network model to perform intra prediction.

[0060] The inter prediction unit (103) generates a prediction block using the previously restored reference image stored in the memory (112) and the inter prediction mode and motion information. Here, inter prediction may mean motion prediction or motion compensation.

[0061] The inter prediction unit (103) can set the inter mode of a prediction unit included in an encoding unit to one of the Skip Mode, Merge Mode, and Advanced Motion Vector Prediction (AMVP) mode in order to perform motion prediction and / or motion compensation. Then, the inter prediction unit (103) can perform motion prediction and / or motion compensation for the prediction unit according to the set mode.

[0062] In addition, the inter prediction unit (103) can perform motion prediction and / or motion compensation for a prediction unit by applying the AFFINE mode of sub-PU based prediction, the SbTMVP (Subblock-based Temporal Motion Vector Prediction) mode, and the MMVD (Merge with MVD) mode and the GPM (Geometric Partitioning Mode) mode of PU based prediction based on the inter prediction mode. In addition, the inter prediction unit (103) can perform motion prediction and / or motion compensation for the prediction unit by applying HMVP (History based MVP), PAMVP (Pairwise Average MVP), CIIP (Combined Intra / Inter Prediction), AMVR (Adaptive Motion Vector Resolution), DMVR (Decoder side Motion Vector Refinement), BDOF (Bi-Directional Optical-Flow), PROF (Prediction Refinement With Optical Flow), BCW (Bi-predictive with CU Weights), LIC (Local Illumination Compensation), TM (Template Matching), OBMC (Overlapped Block Motion Compensation), etc. to improve the performance of each mode.

[0063] Here, AFFINE mode can be used in both AMVP and MERGE modes. It is a technique with high encoding efficiency. AFFINE mode can be a prediction mode that uses a 4-parameter affine motion model using two control point motion vectors (CPMV) or a 6-parameter affine motion model using three control point motion vectors. Here, CPMV can be a vector representing an affine motion model of any one of the top left, top right, and bottom left of the current block.

[0064] The motion information may include, for example, a motion vector, a reference picture index, a list 1 prediction flag, a list 0 prediction flag, a half-sample interpolation filter index, a bidirectional prediction weight index, etc.

[0065] According to one embodiment, the inter prediction unit (103) may perform inter prediction using a pre-trained neural network model. For example, the inter prediction unit (103) may synthesize a reference frame using a pre-trained neural network model and perform inter prediction based on the synthesized reference frame.

[0066] A residual block containing residual value information, which is the difference value between the prediction unit generated in the prediction unit (102, 103) and the original block of the prediction unit, can be generated. The generated residual block can be input to the transformation unit (130) and transformed.

[0067] The subtraction unit (104) subtracts the block to be encoded from the prediction block generated by the intra prediction unit (102) or inter prediction unit (103) to generate a residual block of the current block. The residual value (residual block) between the generated prediction block and the original block can be input to the transformation unit (105).

[0068] Additionally, the prediction mode information, motion vector information, etc. used for prediction can be encoded together with the residual value in the entropy encoding unit (107) and transmitted to the decoder. When using a specific encoding mode, it is also possible to encode the original block as is and transmit it to the decoding unit without generating a prediction block through the prediction unit (102, 103).

[0069] The transformation unit (105) can perform a transformation on a residual block including residual data to generate and output a transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing a transformation on the residual block. When the transform skip mode is applied, the transformation unit (105) may also skip the transformation on the residual block.

[0070] The conversion unit (105) can determine a conversion type and a conversion kernel based on at least one of encoding parameters such as the size, color component, and prediction mode of the conversion block, and perform conversion on the conversion block using the determined conversion type and conversion kernel.

[0071] According to one embodiment, the transformation unit (105) may perform transformation on a 4x4 luminance residual block generated as an intra prediction result using a transformation type and transformation kernel according to DST (Discrete Sine Transform), and may perform transformation on the remaining residual blocks using a transformation type and transformation kernel according to DCT (Discrete Cosine Transform).

[0072] According to another embodiment, the transform unit (105) may apply the Multiple Transform Selection (MTS) technology that performs the transform by selectively using several transform types and transform kernels. That is, the transform unit (105) may perform the transform in units of sub-blocks using the Sub-block Transform (SBT) technology. Specifically, the SBT may be applied only to inter-prediction blocks, and the current block may be divided into ½ or ¼ sizes in the vertical or horizontal direction, and the transform may be performed on only one of the blocks. For example, the transform unit (105) may perform the transform on the leftmost or rightmost block among the vertically divided current blocks, and may perform the transform on the topmost or bottommost block among the horizontally divided current blocks.

[0073] According to another embodiment, the transform unit (105) may apply a non-separable primary transform (NSPT) technique that performs the transform by selectively using multiple transform kernels based on the intra prediction mode or the size and / or shape of the block.

[0074] According to another embodiment, the transform unit (105) may apply LFNST (Low Frequency Non-Separable Transform), which is a technology that applies a secondary transform to a residual signal that has been transformed into a frequency domain through DCT or DST. LFNST additionally performs a transform on a 4x4 or 8x8 low-frequency region in the upper left, thereby concentrating the residual coefficients in the upper left.

[0075] The quantization unit (106) can quantize the transform coefficients or residual signals converted to the frequency domain by the transform unit (105) according to a quantization parameter (QP). The quantization parameter can vary depending on the block or the importance of the image. The value produced by the quantization unit (106) can be provided to the dequantization unit (108) and the entropy encoding unit (107).

[0076] The above transformation unit (105) and / or quantization unit (106) may be optionally included in the image encoding device (100). That is, the image encoding device (100) may encode the residual block by performing at least one of transformation or quantization on the residual data of the residual block, or by skipping both transformation and quantization. Even if neither transformation nor quantization is performed in the image encoding device (100), or neither transformation nor quantization is performed, a block that is input to the entropy encoding unit (107) is typically referred to as a transformation block.

[0077] The entropy encoding unit (107) can generate and output a bitstream by performing entropy encoding according to a probability distribution on values ​​output by the quantization unit (106), coding parameter values ​​output during the encoding process, information for decoding an image, etc. Here, the information for decoding an image may include syntax elements, etc.

[0078] Coding parameters may include not only information (flags, indexes, etc.) encoded in an encoding device (100) and signaled to a decoding device (200), such as syntax elements, but also information derived during an encoding process or a decoding process, and may mean information necessary when encoding or decoding an image.

[0079] The entropy encoding unit (107) can encode various information such as coefficient information of a transform block, block type information, prediction mode information, division unit information, prediction unit information, transmission unit information, motion vector information, reference frame information, block interpolation information, and filtering information. The coefficients of a transform block can be encoded in units of sub-blocks within the transform block.

[0080] For encoding the coefficients of a transform block, various syntax elements can be encoded, such as Last_sig, a syntax element indicating the position of the first non-zero coefficient in reverse scan order, Coded_sub_blk_flag, a flag indicating whether there is at least one non-zero coefficient in the subblock, Sig_coeff_flag, a flag indicating whether the coefficient is non-zero, Abs_greater1_flag, a flag indicating whether the absolute value of the coefficient is greater than 1, Abs_greater2_flag, a flag indicating whether the absolute value of the coefficient is greater than 2, and Sign_flag, a flag indicating the sign of the coefficient. The residual value of the coefficient that is not encoded by the above syntax elements alone can be encoded through the syntax element remaining_coeff.

[0081] When entropy coding is applied, a small number of bits are allocated to symbols with a high occurrence probability, and a large number of bits are allocated to symbols with a low occurrence probability, thereby representing the symbols, thereby reducing the size of the bit string for the symbols to be encoded. The input data is entropy encoded. For example, entropy coding can use various coding methods such as Exponential Golomb and CABAC (Context-Adaptive Binary Arithmetic Coding).

[0082] The inverse quantization unit (108) and the inverse transformation unit (109) can inverse quantize the values ​​quantized in the quantization unit (106) and inversely transform the values ​​transformed in the transformation unit (105). The residual values ​​generated in the inverse quantization unit (108) and the inverse transformation unit (109) can be combined with the prediction units predicted through the motion estimation unit, motion compensation unit, and intra prediction unit (102) included in the prediction unit (102, 103) to generate a reconstructed block. The addition unit (110) adds the prediction blocks generated in the prediction units (102, 103) and the residual blocks generated through the inverse transformation unit (109) to generate a reconstructed block.

[0083] The filter unit (111) can apply a deblocking filter, a sample adaptive offset (SAO), an adaptive loop filter (ALF), a bilateral filter (BIF), and a LMCS (Luma Mapping with Chroma Scaling) as a filtering technique, in whole or in part, to a restored sample, restored block, or restored image.

[0084] A deblocking filter can remove block distortion caused by boundaries between blocks in a reconstructed picture. To determine whether to perform deblocking, a deblocking filter can be applied to the current block based on the pixels contained in several columns or rows within the block. When applying a deblocking filter to a block, a strong filter or a weak filter can be applied depending on the required deblocking filtering strength. Furthermore, when applying a deblocking filter, horizontal and vertical filtering can be processed in parallel when performing vertical and horizontal filtering.

[0085] Sample adaptive offset may be a method of correcting the offset from the original image on a sample basis for an image on which deblocking has been performed. The filter unit (111) may use a method of dividing the samples included in the image into a certain number of regions, determining the regions on which the offset is to be performed, and applying the offset to the regions, or a method of applying the offset by considering edge information of each sample. Here, the sample adaptive offset may be at least one of a general sample adaptive offset, a bilateral filter, and a cross-component sample adaptive offset (CCSAO).

[0086] Adaptive Loop Filtering (ALF) can be performed based on the comparison of the filtered restored image with the original image. After dividing the pixels included in the image into predetermined groups, a filter to be applied to each group can be determined, and filtering can be performed differentially for each group. Information regarding whether to apply ALF can be transmitted by luminance signal for each coding unit (CU), and the shape and filter coefficients of the ALF filter to be applied can vary depending on each block. Furthermore, an ALF filter of the same form (fixed form) can be applied regardless of the characteristics of the target block.

[0087] An adaptive loop filter can perform filtering based on a comparison between a reconstructed image and the original image. By dividing the samples contained in the image into predetermined groups and determining the filter to be applied to each group, filtering can be performed differentially for each group. Information regarding whether to apply an adaptive loop filter can be signaled for each coding unit (CU), and the shape and filter coefficients of the adaptive loop filter applied to each block can vary.

[0088] According to one embodiment, the filter unit (111) may filter all or part of a restored sample, restored block, or restored image using a pre-trained neural network model. Specifically, the filter unit (111) may apply an adaptive loop filter to all or part of a restored sample, restored block, or restored image using a pre-trained neural network model.

[0089] The memory (112) can store a restored block or picture produced through the filter unit (111). The memory (112) can include a reference picture buffer. In addition, the restored block or picture stored in the memory (112) can be provided to the prediction unit (102, 103) when performing inter prediction.

[0090] Next, an image decoding device according to one embodiment of the present invention will be described with reference to the drawings.

[0091] FIG. 2 is a block diagram showing an image decoding device (200) according to one embodiment of the present invention.

[0092] Referring to FIG. 2, the image decoding device (200) may include an entropy decoding unit (201), an inverse quantization unit (202), an inverse transformation unit (203), a prediction unit (204, 205), an addition unit (206), a filter unit (207), and a memory (208).

[0093] The image decoding device (200) can receive a bitstream output by the image encoding device (100). The image decoding device (200) can receive a bitstream stored in a computer-readable recording medium, or can receive a bitstream streamed through a wired / wireless transmission medium. The image decoding device (200) can decode the bitstream to generate a restored image or a decoded image, and can output the restored image or the decoded image.

[0094] The entropy decoding unit (201) can generate symbols by performing entropy decoding according to a probability distribution for the bitstream. The generated symbols may include symbols in the form of quantized levels. Here, the entropy decoding method may be the reverse process of the entropy encoding method described above.

[0095] The entropy decoding unit (201) can change a one-dimensional vector-shaped coefficient into a two-dimensional block-shaped coefficient through a transform coefficient scanning method to decode a transform coefficient level (quantized level).

[0096] The entropy decoding unit (201) can perform entropy decoding in a procedure opposite to that of the entropy encoding unit (107) of the video encoding device (100). For example, various methods such as Exponential Golomb and CABAC (Context-Adaptive Binary Arithmetic Coding) can be applied in response to the method performed in the video encoder.

[0097] The entropy decoding unit (201) can decode and obtain various information such as coefficient information of the transform block as described above, block type information, prediction mode information, division unit information, prediction unit information, transmission unit information, motion vector information, reference frame information, block interpolation information, and filtering information.

[0098] The inverse quantization unit (202) performs inverse quantization on a quantized transform block to generate a transform block. It operates substantially the same as the inverse quantization unit (108) of Fig. 1.

[0099] The inverse transform unit (203) performs an inverse transform on the transform block to generate a residual block. At this time, the transform method can be determined based on information regarding the prediction method (inter or intra prediction), the size and / or shape of the block, the intra prediction mode, etc. It operates substantially the same as the inverse transform unit (109) of FIG. 1.

[0100] According to one embodiment, the inverse transform unit (203) may perform inverse transform using a transform type and transform kernel according to DST (Discrete Sine Transform) on the transform coefficient levels of the 4x4 luminance component generated as an intra prediction result, and may perform inverse transform using a transform type and transform kernel according to DCT (Discrete Cosine Transform) on the remaining transform coefficient levels.

[0101] According to another embodiment, the inverse transform unit (203) may apply MTS (Multiple Transform Selection) technology to perform transformation by selectively using multiple transformation kernels.

[0102] According to another embodiment, the inverse transform unit (203) may apply LFNST (Low Frequency Non-Separable Transform), which is a technology that applies a secondary inverse transform to a transform coefficient level inversely transformed through a DCT or DST-based transform type and transform kernel.

[0103] According to another embodiment, the inverse transform unit (203) may apply a non separable primary transform (NSPT) technique that performs inverse transform by selectively using a transform kernel based on the intra prediction mode or the size and / or shape of the block.

[0104] The prediction unit (204, 205) can generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit (201) and the previously decoded block or picture information provided by the memory (208).

[0105] The prediction unit (204, 205) may include an intra prediction unit (204) and an inter prediction unit (205). The prediction unit (204, 205) may receive various information such as prediction unit information input from the entropy decoding unit (201), prediction mode information of the intra prediction method, and motion prediction-related information of the inter prediction method, and may distinguish a prediction unit from a current encoding unit and determine a prediction mode of the prediction unit.

[0106] The intra prediction unit (204) can generate a prediction block of the current block based on the intra prediction mode of the current block and reference pixel information around the current block, which is pixel information within the current picture.

[0107] The intra prediction unit (204) can generate a prediction block based on reference pixel information surrounding the current block, which is pixel information within the current picture. The intra prediction unit (204) can use multiple reference pixel lines for intra prediction. When multiple reference pixel lines are available, the intra prediction unit (204) can obtain information indicating a reference pixel line used for intra prediction from among the multiple reference pixel lines.

[0108] The intra prediction mode used for intra prediction may be a directional prediction mode or a non-directional mode. Furthermore, the mode for predicting luminance information may be different from the mode for predicting chrominance information, and the intra prediction mode information of the luminance component block or the predicted luminance signal information may be utilized to predict chrominance information.

[0109] According to one embodiment, the intra prediction unit (204) can perform intra prediction using a pre-trained neural network model. The intra prediction unit (204) can perform intra prediction using the same neural network model as the intra prediction unit (102) of FIG. 1.

[0110] The intra prediction unit (204) operates substantially the same as the intra prediction unit (102) of FIG. 1.

[0111] The inter prediction unit (205) may perform inter prediction on the current prediction unit based on information included in at least one picture among the previous picture or the subsequent picture of the current picture including the current prediction unit, using information necessary for inter prediction of the current prediction unit provided by the image encoding device (100). Alternatively, inter prediction may be performed based on information of some pre-restored area within the current picture including the current prediction unit.

[0112] The inter prediction unit (205) can set the inter mode of a prediction unit included in an encoding unit to one of the skip mode, merge mode, and advanced motion vector prediction (AMVP) mode in order to perform motion prediction and / or motion compensation. In addition, the inter prediction unit (205) can perform motion compensation on the prediction unit according to the set mode.

[0113] In addition, the inter prediction unit (205) can perform motion compensation for the prediction unit by applying the AFFINE mode of sub-PU based prediction, the SbTMVP (Subblock-based Temporal Motion Vector Prediction) mode, and the MMVD (Merge with MVD) mode and the GPM (Geometric Partitioning Mode) mode of PU based prediction based on the inter prediction mode. In addition, the inter prediction unit (205) can perform motion compensation for the prediction unit by applying the HMVP (History based MVP), the PAMVP (Pairwise Average MVP), the CIIP (Combined Intra / Inter Prediction), the AMVR (Adaptive Motion Vector Resolution), the BDOF (Bi-Directional Optical-Flow), the BCW (Bi-predictive with CU Weights), the LIC (Local Illumination Compensation), the TM (Template Matching), the OBMC (Overlapped Block Motion Compensation), etc. to improve the performance of each mode.

[0114] The motion information may include, for example, a motion vector, a reference picture index, a list 1 prediction flag, a list 0 prediction flag, a half-sample interpolation filter index, a bidirectional prediction weight index, etc.

[0115] According to one embodiment, the inter prediction unit (205) can perform inter prediction using a pre-trained neural network model. The inter prediction unit (205) can perform inter prediction using the same neural network model as the inter prediction unit (103) of FIG. 1.

[0116] The inter prediction unit (205) can operate substantially the same as the inter prediction unit (103) of FIG. 1.

[0117] The addition unit (206) adds the prediction block generated by the intra prediction unit (204) or inter prediction unit (205) and the residual block generated by the inverse transformation unit (203) to generate a restored block. It operates substantially the same as the addition unit (110) of Fig. 1.

[0118] The filter unit (207) can reduce various types of noise occurring in restored blocks. The filter unit (207) can include a deblocking filter, a sample adaptive offset, an adaptive loop filter, a bilateral filter, and an LMCS.

[0119] The filter unit (207) can receive information on whether each filter is applied, information on the strength of the filter, etc. from the image encoding device (100). The filter unit (207) of the image decoding device (200) can receive filter-related information provided from the image encoding device (100) and perform filtering on the corresponding block in the image decoding device (200).

[0120] According to one embodiment, the filter unit (207) may filter all or part of a restored sample, restored block, or restored image using a pre-trained neural network model. Specifically, the filter unit (207) may apply an adaptive loop filter to all or part of a restored sample, restored block, or restored image using a pre-trained neural network model.

[0121] The filter unit (207) can operate substantially the same as the filter unit (111) of FIG. 1.

[0122] The memory (208) can store the restoration block generated by the addition unit (206). For example, the memory (208) can include a reference picture buffer. The memory (208) can operate substantially the same as the memory (112) of FIG. 1.

[0123]

[0124] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0125] A video coding system according to one embodiment may include an encoding device (10) and a decoding device (20). The encoding device (10) may transmit encoded video and / or image information or data to the decoding device (20) in the form of a file or streaming through a digital storage medium or a network.

[0126] An encoding device (10) according to one embodiment may include an image generating unit (11), an encoding unit (12), and a transmission unit (13). A decoding device (20) according to one embodiment may include a receiving unit (21), a decoding unit (22), and an image reproducing unit (23). The encoding unit (12) may be referred to as a video / image encoding unit, and the decoding unit (22) may be referred to as a video / image decoding unit. The transmission unit (13) may be included in the encoding unit (12). The receiving unit (21) may be included in the decoding unit (22). The image reproducing unit (23) may include a display unit, and the display unit may be configured as a separate device or an external component.

[0127] The image generation unit (11) can obtain a video / image through a process of capturing, synthesizing, or generating a video / image. The image generation unit (11) can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, a video / image archive including previously captured video / images, etc. The video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate a video / image. For example, a virtual video / image can be generated through a computer, etc., in which case the video / image capture process can be replaced with a process of generating related data.

[0128] The encoding unit (12) can encode the input video / image. The encoding unit (12) can perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency. The encoding unit (12) can output encoded data (encoded video / image information) in the form of a bitstream. The detailed configuration of the encoding unit (12) can be configured in the same manner as the encoding device (100) of FIG. 1 described above.

[0129] The transmission unit (13) can transmit encoded video / image information or data output in the form of a bitstream to the reception unit (21) of the decoding device (20) via a digital storage medium or a network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit (13) can include an element for generating a media file through a predetermined file format and can include an element for transmission via a broadcasting / communication network. The reception unit (21) can extract / receive the bitstream from the storage medium or network and transmit it to the decoding unit (22).

[0130] The decoding unit (22) can decode video / image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding unit (12). The detailed configuration of the decoding unit (22) can be configured identically to the decoding device (200) of FIG. 2 described above.

[0131] The image playback unit (23) can render decrypted video / images. The rendered video / images can be displayed through the display unit.

[0132]

[0133] FIG. 4 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

[0134] As illustrated in FIG. 4, a content streaming system to which an embodiment of the present invention is applied may largely include a multimedia input device, a media storage, an encoding server, a streaming server, a web server, and a user device.

[0135] The encoding server compresses content input from multimedia input devices such as smartphones, cameras, CCTVs, etc. into digital data, creates a bitstream, and transmits it to the streaming server. Alternatively, the encoding server compresses content already stored in a media storage into digital data, creates a bitstream, and transmits it to the streaming server.

[0136] As another example, if multimedia input devices such as smartphones, cameras, CCTVs, etc. directly generate bitstreams, the encoding server may be omitted.

[0137] The above bitstream can be generated by a video encoding method and / or a video encoding device to which an embodiment of the present invention is applied, and the streaming server can temporarily or non-temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0138] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server can act as an intermediary to inform the user of available services. When the user device requests a desired service from the web server, the web server transmits the request to the streaming server, and the streaming server can transmit multimedia data to the user device. At this time, the content streaming system may include a separate control server, and in this case, the control server may play a role in controlling commands / responses between each device within the content streaming system.

[0139] The streaming server can receive content from a media repository and / or encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a certain period of time.

[0140] Examples of the user devices may include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, HMDs), digital TVs, desktop computers, digital signage, etc.

[0141] Each server within the above content streaming system can be operated as a distributed server, in which case data received from each server can be processed in a distributed manner.

[0142]

[0143] According to the existing VVC / H.266 standard, block segmentation can be applied differently depending on the slice type. For example, in the case of inter-slice, a single tree is applied to segment slices and coding units, and the same segmentation method can be applied to both luminance and chrominance components. On the other hand, in the case of intra-slice, a dual tree is applied to segment slices and coding units, so the decision process for segmenting luminance and chrominance components is different, and separate syntax related to segmentation information may exist.

[0144] Furthermore, to improve coding efficiency, techniques for predicting chrominance blocks by referencing information from corresponding luminance blocks can be utilized. However, most techniques for predicting chrominance blocks by referencing information from luminance blocks were developed under the assumption of a single-tree implementation. Therefore, applying techniques for predicting chrominance blocks by referencing information from luminance blocks in a dual-tree implementation may result in reduced coding efficiency.

[0145] Therefore, in a situation where a dual tree is applied, a technique may be required to apply techniques for predicting a chrominance block by referring to information of a luminance block.

[0146]

[0147] When a dual tree is applied to an intra-slice or an inter-slice, the intra prediction mode of the chrominance block referencing luminance information can be as follows.

[0148] For example, the intra prediction mode of the chrominance block may be the DM mode. The DM mode may be a prediction method that uses the intra prediction mode of the chrominance block as the intra prediction mode of the luminance block corresponding to the chrominance block when performing intra prediction of the chrominance block based on the similarity between the luminance component and the chrominance component.

[0149]

[0150] Alternatively, the intra prediction mode of the chrominance block may be a chrominance DBV (direct block vector) mode. When a luminance block corresponding to a chrominance block is intra-predicted using a block vector, the chrominance DBV mode may be a method of deriving a block vector of a chrominance block based on a block vector of a luminance block and performing intra prediction based on the derived block vector of the chrominance block.

[0151] The chrominance intra prediction method in DBV mode can be as described below.

[0152]

[0153] FIG. 5 is a diagram illustrating a chrominance intra prediction method of direct block vector mode according to one embodiment of the present invention.

[0154] Referring to FIG. 5, a current chrominance block may be defined in a chrominance picture. Furthermore, a corresponding luminance block, which is a block corresponding to the current chrominance block, may be defined within a luminance picture corresponding to the chrominance picture. The position of the corresponding luminance block within the luminance picture may correspond to the position of the current chrominance block within the chrominance picture.

[0155] The direct block mode of chrominance intra prediction may be a mode that derives a prediction block of the current chrominance block based on the block vector of the current chrominance block. The block vector of the current chrominance block may be derived based on the block vector of the corresponding luminance block. Specifically, a block vector BV of the corresponding luminance block may be defined. The block vector BV may indicate a matching luminance block.

[0156] In addition, the block vector for chrominance intra prediction of the current chrominance block can be derived based on the block vector of the corresponding luminance block. For example, the block vector for chrominance intra prediction of the current chrominance block can be derived by scaling the block vector BV.

[0157] The prediction block of the current chrominance block can be derived based on a matching chrominance block, which is a block indicated by a block vector for chrominance intra prediction.

[0158]

[0159] Alternatively, the intra prediction mode of the chrominance block may be a block vector guided convolutional cross-component model (BVG-CCCM). When a luminance block corresponding to a chrominance block is intra-predicted using a block vector, the BVG-CCCM mode may be a method of deriving CCCM parameters using samples adjacent to a matching luminance block indicated by a block vector of the corresponding luminance block and samples adjacent to a matching chrominance block corresponding to the matching luminance block, and performing intra prediction based on the CCCM parameters and the prediction value of the corresponding luminance block.

[0160] The chrominance intra prediction method in BVG-CCCM mode can be as described below.

[0161]

[0162] FIG. 6 is a diagram illustrating a color difference intra prediction method of BVG-CCCM mode according to one embodiment of the present invention.

[0163] Referring to FIG. 6, a current chrominance block and a luminance block corresponding to the current chrominance block can be defined. If a block vector is defined for the corresponding luminance block, a matching luminance block indicated by the block vector can be defined. Based on the block vector of the corresponding luminance block, a block vector of the current chrominance block can be derived. Then, a matching chrominance block indicated by the block vector of the current chrominance block can be defined.

[0164] A luminance reference region including samples adjacent to a matching luminance block and a chrominance reference region including samples adjacent to a matching chrominance block can be defined. Then, parameters of CCCM can be derived based on the samples of the luminance reference region and the samples of the chrominance reference region.

[0165] And, the prediction block of the current chrominance block can be derived as in mathematical expression 1 below based on the parameters of CCCM and the sample values ​​of the luminance block corresponding to the current chrominance block.

[0166]

[0167] Here, c0 to c 10 can be a parameter of CCCM. And, C is a sample of a luminance block corresponding to a sample of a current chrominance block, N is a luminance sample located on the top of C, S is a luminance sample located on the bottom of C, E is a luminance sample located on the right of C, and W can be a sample located on the left of C. And, P(-) is a nonlinear term obtained by squaring a luminance sample, and B can be a bias term.

[0168]

[0169] If the chrominance prediction mode is a prediction mode that uses information of a luminance block at a location corresponding to a chrominance block, the embodiment proposed in the present disclosure can also be applied to prediction modes other than the prediction modes described above.

[0170] For example, prediction of a chrominance block can be performed based on the motion vector of a luminance block corresponding to the chrominance block. A method for performing prediction of a chrominance block based on the motion vector of a luminance block corresponding to the chrominance block can be as described below.

[0171]

[0172] FIG. 7 is a diagram illustrating a method for predicting a color difference block based on a motion vector according to one embodiment of the present invention.

[0173] Referring to FIG. 7, a current chrominance block may be defined in a chrominance picture. Furthermore, a corresponding luminance block, which is a block corresponding to the current chrominance block, may be defined within a luminance picture corresponding to the chrominance picture. The position of the corresponding luminance block within the luminance picture may correspond to the position of the current chrominance block within the chrominance picture.

[0174] As illustrated in Fig. 7, the current chrominance block can be predicted based on the motion vector of the corresponding luminance block. If the corresponding luminance block is inter-predicted, the motion vector MV of the corresponding luminance block can be defined. The motion vector MV can point to a reference luminance block.

[0175] And, the motion vector for prediction of the current chrominance block can be derived based on the motion vector of the corresponding luminance block. For example, the motion vector for prediction of the current chrominance block can be derived by scaling the motion vector BV.

[0176] The prediction block of the current chrominance block can be derived based on a reference chrominance block, which is a block indicated by a motion vector for chrominance prediction.

[0177]

[0178] When referring to luminance information to predict a color difference block, the reference sample area for referring to luminance information can be set as follows.

[0179] When a dual tree is applied to an intra-slice or inter-slice, block partitioning of luminance blocks and chrominance blocks can be performed independently. Therefore, the partitioned luminance blocks and chrominance blocks may not overlap each other equally.

[0180]

[0181] FIG. 8 is a diagram illustrating an example of a structure of partitioned blocks based on a dual tree according to an embodiment of the present invention.

[0182] Referring to Fig. 8, a luminance coding tree block and a chrominance coding tree block can be defined. As illustrated in Fig. 8, the chrominance coding tree block can be vertically partitioned based on a binary tree. As a result, a current chrominance unit can be derived from the chrominance coding tree block.

[0183] On the other hand, a luminance coding tree block corresponding to a chrominance coding tree block can be partitioned based on a quad tree. Each of the quad tree-split blocks can be partitioned vertically based on a binary tree or horizontally based on a binary tree. Alternatively, the luminance coding tree block and its sub-blocks can be partitioned based on a ternary tree.

[0184] That is, as illustrated in FIG. 8, when the tree type of the coding tree unit is a dual tree, the block division structures of the luminance coding tree block and the chrominance coding tree block may be different from each other. As a result, the luminance coding tree block corresponding to the current chrominance block may include a plurality of luminance blocks. For example, the luminance coding tree block corresponding to the current chrominance block may include a plurality of blocks in addition to a luminance block including a C sample, a luminance block including a TL sample, a luminance block including a TR sample, a luminance block including a BL sample, and a luminance block including a BR sample. Accordingly, the chrominance blocks and luminance blocks divided into the coding tree blocks may not overlap each other equally.

[0185]

[0186] In such cases, techniques that refer to luminance information for color difference coding are mostly efficient when a single tree is applied, but may be inefficient when a dual tree is applied.

[0187] When the block division structures of the luminance block and the chrominance block are different as a result of applying the dual tree, a luminance area corresponding to the chrominance block can be set using the method below, and chrominance prediction can be performed using information of the set luminance area.

[0188] According to one embodiment, a luminance region corresponding to a chrominance block may be set based on a color format of a coding unit. For example, when the color format is 4:4:4, the sizes of the luminance block and the chrominance block may be the same. Accordingly, a luminance block at the same position as the chrominance block may be set as a luminance region corresponding to the chrominance block. On the other hand, when the color format is 4:2:0, the height and width of the luminance block may be twice the height and width of the chrominance block. Accordingly, the position of the luminance region corresponding to the chrominance block may be set by considering subsampling. In addition, the height and width of the luminance region corresponding to the chrominance block may be scaled by a factor of two.

[0189] In this way, depending on the color format, when sub-sampling is applied to the chrominance component, the luminance area corresponding to the chrominance block can be set to have the position and size of the luminance component corresponding to the sub-sampling of the chrominance component.

[0190]

[0191] When a reference sample area is set for referring to luminance information to predict a chrominance block, information of a luminance block corresponding to a chrominance block may be as described below.

[0192] When a luminance region corresponding to a chrominance block is set according to a color format, a method for obtaining information used to predict the luminance block may be required. However, in a dual-tree application, the luminance region corresponding to the chrominance block may include more than one block. Therefore, a method may be required for determining which luminance block's intra-prediction information to utilize among one or more blocks in the luminance region.

[0193] For example, if the luminance region corresponding to the chrominance block contains one block, the blocks of the chrominance region and the luminance region match, so prediction of the chrominance block can be performed by utilizing the block information of the corresponding luminance region.

[0194] On the other hand, if the luminance region corresponding to the chrominance block includes multiple blocks, the luminance block corresponding to the chrominance block can be determined as follows.

[0195] A luminance block corresponding to a chrominance block can be determined as a luminance block including a sample (C in Fig. 8) located at the center of the luminance region corresponding to the chrominance block. That is, information of a luminance block including the center pixel of the luminance region corresponding to the chrominance block can be utilized to predict the current chrominance block.

[0196] A luminance block corresponding to a chrominance block can be determined as a luminance block including a sample (TL in Fig. 8) located at the upper left of the luminance region corresponding to the chrominance block. That is, information of a luminance block including a sample at the upper left of the luminance region corresponding to the chrominance block can be utilized to predict the current chrominance block.

[0197] A luminance block corresponding to a chrominance block can be determined as a luminance block including a sample located at the lower left (BL in Fig. 8) of a luminance region corresponding to the chrominance block. That is, information of a luminance block including a sample located at the lower left of a luminance region corresponding to the chrominance block can be utilized to predict the current chrominance block.

[0198] A luminance block corresponding to a chrominance block can be determined as a luminance block including a sample (TR in Fig. 8) located at the upper right of the luminance region corresponding to the chrominance block. That is, information of a luminance block including a sample at the upper right of the luminance region corresponding to the chrominance block can be utilized to predict the current chrominance block.

[0199] A luminance block corresponding to a chrominance block can be determined as a luminance block including a sample (BR in Fig. 8) located at the lower right of the luminance region corresponding to the chrominance block. That is, information of a luminance block including a sample at the lower right of the luminance region corresponding to the chrominance block can be utilized to predict the current chrominance block.

[0200]

[0201] When the luminance region corresponding to the chrominance block includes multiple blocks, the luminance block corresponding to the chrominance block can be implicitly determined as one block among the multiple blocks as described below.

[0202] According to one embodiment, a luminance block corresponding to a chrominance block may be determined as a luminance block at a predetermined position among a plurality of blocks included in a luminance area corresponding to the chrominance block. For example, a luminance block corresponding to a chrominance block may be determined as a block including a sample located at the center of a luminance area corresponding to the chrominance block.

[0203] According to another embodiment, the luminance block corresponding to the chrominance block may be a block searched for among a plurality of blocks included in the luminance area according to a preset order. However, at least some blocks among the plurality of blocks included in the luminance area may not include information for intra prediction of the current chrominance block. Accordingly, the searched block may be a block among the plurality of blocks included in the luminance area corresponding to the chrominance block that has prediction information for predicting the chrominance block.

[0204] For example, if the intra prediction mode of the current chrominance block is DM mode, and among the plurality of blocks included in the luminance area corresponding to the current chrominance block, the corresponding luminance block is determined to be a block including a sample located at the center of the luminance area corresponding to the chrominance block, but the corresponding luminance block may be an inter-predicted block. In this case, the corresponding luminance block may not include intra prediction information of the luminance block. Therefore, in order to predict the current chrominance block based on the intra prediction information of the luminance block, a separate luminance block may be required.

[0205] As another example, if the intra prediction mode of the current chrominance block is the DBV mode, and among a plurality of blocks included in a luminance area corresponding to the current chrominance block, the corresponding luminance block is determined to be a block including a sample located at the center of the luminance area corresponding to the chrominance block, but the corresponding luminance block may be a block intra-predicted based on an intra prediction mode that does not use a block vector. Therefore, in order to predict the current chrominance block based on the intra prediction information of the luminance block, a separate luminance block predicted using a block vector may be required.

[0206] That is, in order to determine a luminance block corresponding to a chrominance block, a luminance block having information for intra prediction of the current chrominance block is searched for among a plurality of blocks included in the luminance area according to a preset order, and the intra prediction information of the searched luminance block can be utilized to predict the current chrominance block.

[0207] The luminance block search order can be predefined by considering the correlation between the luminance blocks and the chrominance blocks. For example, the luminance blocks can be searched in the following order: a luminance block including a sample located at the center of the luminance region, a luminance block including a sample located at the upper left of the luminance region, a luminance block including a sample located at the lower left of the luminance region, a luminance block including a sample located at the upper right of the luminance region, and a luminance block including a sample located at the lower right of the luminance region. However, the order is not limited to the above, and the search order of the luminance blocks can be determined in one of all possible orders based on the luminance blocks.

[0208] In a luminance domain corresponding to a chrominance block, if intra prediction information of a plurality of luminance blocks can be used, the intra prediction information of the plurality of luminance blocks can be implicitly weighted and combined for prediction of the current chrominance block. For example, in order to predict the current chrominance block, different prediction blocks for the current chrominance block can be generated using intra prediction information (e.g., intra prediction modes) of each of the plurality of luminance blocks. Then, the final prediction block for the current chrominance block can be generated by weighting and combining the different prediction blocks for the current chrominance block. Alternatively, a block vector for the current chrominance block can be derived by weighting and combining the block vectors of each of the plurality of luminance blocks. Then, intra prediction for the current chrominance block can be performed based on the derived block vector.

[0209]

[0210] Alternatively, if the luminance region corresponding to the chrominance block includes multiple blocks, the luminance block corresponding to the chrominance block can be explicitly determined as one block among the multiple blocks as described below.

[0211] When a luminance region corresponding to a chrominance block includes multiple blocks, the encoder may determine one of the multiple blocks as a luminance block corresponding to the chrominance block, and explicitly signal information about the determined block to the decoder. For example, the encoder may generate a candidate list including a block at the center of the luminance region corresponding to the corresponding chrominance block, a block located at the upper left, a block located at the lower left, a block located at the upper right, and a block located at the lower right as candidates. Then, the encoder may signal information indicating one candidate from the candidate list to the decoder.

[0212] When generating a candidate list, a block among a plurality of blocks in the corresponding luminance region that does not include intra prediction information for predicting the current chrominance block may be excluded from the candidate list. For example, if the intra prediction mode of the current chrominance block is the DM mode and there is no intra prediction mode information of a block located at the center of the luminance region corresponding to the corresponding chrominance block, intra prediction of the current chrominance block cannot be performed based on the information of the block located at the center of the luminance region, and therefore the block located at the center of the luminance region may be excluded from the candidate list. In addition, if intra prediction mode information of a block located at the upper left, a block located at the lower left, a block located at the upper right, and a block located at the lower right exists, the candidate list may include the block located at the upper left, the block located at the lower left, the block located at the upper right, and the blocks located at the lower right.

[0213] That is, if multiple blocks included in the luminance domain are predicted using information necessary for intra prediction of the current chrominance block (e.g., intra prediction mode, block vector), the multiple blocks may be determined to be available in the candidate list derivation process. On the other hand, if multiple blocks included in the luminance domain are predicted without using information necessary for intra prediction of the current chrominance block, the multiple blocks may be determined to be unavailable in the candidate list derivation process.

[0214] And, the order of candidate blocks in the candidate list can be determined according to a preset order. Alternatively, the order of candidate blocks in the candidate list can be changed. Specifically, the order of candidate blocks can be changed based on the correlation between the current chrominance block and the current luminance block, the correlation between the current chrominance block and the corresponding luminance block, the correlation between the current chrominance block and the reference chrominance block, the correlation between the current chrominance block and the current template, the ratio of multiple luminance blocks in the corresponding luminance region, the prediction mode of the luminance region, and the prediction mode of the current chrominance block. Here, the correlation can be derived using a method such as SAD, SATD, MRSAD, MR-SATD, SSE, or MR-SSE.

[0215] In this case, the encoder and decoder can change the order of the candidates in the candidate list in the same manner. Furthermore, the encoder can transmit an index indicating a block in the changed candidate list to the decoder.

[0216]

[0217] When a coding tree unit is split by applying a dual tree, and a plurality of blocks of a luminance region corresponding to a current chrominance block include information regarding intra prediction, one of the plurality of blocks can be explicitly or implicitly determined, and the current chrominance block can be predicted based on the intra prediction information of the determined block.

[0218] On the other hand, if multiple blocks in the luminance domain corresponding to the current chrominance block do not contain information regarding intra prediction, information for intra prediction of the current chrominance block can be derived through the method described below.

[0219] For example, if the intra prediction mode of the current chrominance block is the DM mode and a plurality of blocks in the luminance area corresponding to the current chrominance block are predicted using information other than the intra prediction mode, the intra prediction mode information for the DM mode of the current chrominance block can be derived as follows.

[0220] According to one embodiment, intra prediction mode information for the DM mode of the current chrominance block can be derived using the DIMD method. For example, an edge detection filter, such as a Sobel filter, a Roberts cross filter, a Prewitt filter, a Scharr filter, or a Laplacian filter, can be applied to pixels adjacent to a luminance block corresponding to the current chrominance block. As a result of applying the edge detection filter to a pixel in the corresponding luminance block, a gradient of the corresponding pixel can be calculated. Then, a histogram of gradients (HoG) can be generated based on the calculated gradients. As a result, an intra prediction mode of a luminance component for predicting the DM mode of the current chrominance block can be determined based on the histogram of gradients.

[0221] According to another embodiment, intra prediction mode information for a DM mode of a current chrominance block can be derived using a TIMD method. A luminance template can be determined based on pixels adjacent to a luminance block corresponding to the current chrominance block. Then, a prediction sample for the luminance template can be generated based on samples adjacent to the luminance template and a plurality of intra prediction modes. Among the prediction samples for the luminance template derived based on the plurality of intra prediction modes, one intra prediction mode used to derive a prediction sample having a lowest cost value can be determined. As a result, an intra prediction mode of a luminance component for DM mode prediction of the current chrominance block can be determined based on the cost value of the predicted luminance template.

[0222] According to another embodiment, intra prediction mode information for the DM mode of the current chrominance block can be derived using the OBIC method. A histogram of occurrences (HOC) can be generated based on the intra prediction mode information (sample-wise occurrences of the intra mode) that occurred for each pixel adjacent to the luminance block corresponding to the current chrominance block. As a result, the intra prediction mode of the luminance component for DM mode prediction of the current chrominance block can be determined based on the occurrence histogram.

[0223] According to another embodiment, intra prediction mode information for the DM mode of the current chrominance block can be derived through neural network-based intra prediction. For example, by applying a preprocessing step, a neural network-based parameter determination step, and a postprocessing step using pixels adjacent to a luminance block corresponding to the current chrominance block, the intra prediction mode of the luminance block corresponding to the current chrominance block can be derived. As a result, the intra prediction mode of the luminance component for DM mode prediction of the current chrominance block can be determined as the intra prediction mode output by the neural network.

[0224] Meanwhile, if, among a plurality of blocks in the luminance region corresponding to the current chrominance block, there exists a block predicted using a block vector, intra prediction mode information for the DM mode of the current chrominance block can be derived based on the block vector of the corresponding luminance block. For example, if a block indicated by the block vector of the corresponding luminance block has intra prediction mode information, the intra prediction mode for the DM mode of the current chrominance block can be derived based on the intra prediction mode of the block indicated by the block vector.

[0225] Meanwhile, if, among a plurality of blocks in the luminance region corresponding to the current chrominance block, there exists a block predicted using a block vector, intra prediction mode information for the DM mode of the current chrominance block can be derived based on the block vector of the corresponding luminance block. For example, if a block indicated by the block vector of the corresponding luminance block has intra prediction mode information, the intra prediction mode for the DM mode of the current chrominance block can be derived based on the intra prediction mode of the block indicated by the block vector.

[0226] Meanwhile, if, among a plurality of blocks in the luminance region corresponding to the current chrominance block, there exists a block predicted using a motion vector, intra prediction mode information for the DM mode of the current chrominance block can be derived based on the motion vector of the corresponding luminance block. For example, if a block indicated by the motion vector of the corresponding luminance block has intra prediction mode information, the intra prediction mode for the DM mode of the current chrominance block can be derived based on the intra prediction mode of the block indicated by the motion vector.

[0227] Alternatively, if a plurality of blocks in the luminance region corresponding to the current chrominance block do not contain information regarding intra prediction, intra prediction of the current chrominance block based on intra prediction information of the luminance block may not be performed.

[0228]

[0229] If the intra prediction mode of the current chrominance block is the DBV mode and multiple blocks of the luminance area corresponding to the current chrominance block are predicted using information other than the block vector, intra prediction mode information for the DBV mode of the current chrominance block can be derived as follows.

[0230] According to one embodiment, intra prediction mode information for the DBV mode of the current chrominance block can be derived using the intra block copy (IBC) method. For example, if a luminance block corresponding to the current chrominance block is predicted using the intra block copy method, the prediction block of the corresponding luminance block can be derived as a matching luminance block indicated by the block vector. In addition, the prediction block of the current chrominance block can be derived based on the matching chrominance block corresponding to the matching luminance block.

[0231] Here, if only one luminance block among multiple blocks in the corresponding luminance region is predicted using the intra block copy method, intra prediction of the current chrominance block can be performed based on information of the one luminance block. On the other hand, if multiple blocks in the corresponding luminance region are predicted using the intra block copy method, one block among the multiple blocks can be explicitly or implicitly determined, and intra prediction of the current chrominance block can be performed based on information of the one luminance block.

[0232] According to one embodiment, intra prediction mode information for the DBV mode of the current chrominance block can be derived using the intra template matching (IntraTMP) method. For example, when a luminance block corresponding to the current chrominance block is predicted using the intra template matching method, a prediction block of the corresponding luminance block can be derived based on a matching luminance block, which is a luminance block adjacent to a template most similar to the template of the corresponding luminance block. In addition, a prediction block of the current chrominance block can be derived based on a matching chrominance block corresponding to the matching luminance block.

[0233] Here, if only one luminance block among multiple blocks in the corresponding luminance region is predicted by the intra template matching method, intra prediction of the current chrominance block can be performed based on information of the one luminance block. On the other hand, if multiple blocks in the corresponding luminance region are predicted by the intra template matching method, one block among the multiple blocks can be explicitly or implicitly determined, and intra prediction of the current chrominance block can be performed based on information of the one luminance block.

[0234] According to one embodiment, intra prediction mode information for the DBV mode of the current chrominance block can be derived using a motion vector. For example, if a luminance block corresponding to the current chrominance block is predicted using a motion vector, a prediction block of the corresponding luminance block can be derived based on a reference luminance block indicated by the motion vector. In addition, a prediction block of the current chrominance block can be derived based on a matching chrominance block corresponding to the matching luminance block.

[0235] Here, if only one luminance block among multiple blocks in the corresponding luminance region is predicted using a block vector, intra prediction of the current chrominance block can be performed based on information of the single luminance block. On the other hand, if multiple blocks in the corresponding luminance region are predicted using a block vector, one block among the multiple blocks can be explicitly or implicitly determined, and intra prediction of the current chrominance block can be performed based on information of the single luminance block.

[0236] When there are multiple blocks predicted based on an intra block copy method, an intra template matching method, and a motion vector among multiple blocks of a corresponding luminance area, one block is explicitly or implicitly determined, and intra prediction of a current chrominance block can be performed based on information of one luminance block.

[0237]

[0238] If the intra prediction mode of the current chrominance block is the BVG-CCCM mode and multiple blocks of the luminance area corresponding to the current chrominance block are predicted using information other than the block vector, intra prediction mode information for the BVG-CCCM mode of the current chrominance block can be derived as follows.

[0239] According to one embodiment, intra prediction mode information for the BVG-CCCM mode of the current chrominance block can be derived using an intra block copy (IBC) method. For example, when a luminance block corresponding to the current chrominance block is predicted using the intra block copy method, a prediction block of the corresponding luminance block can be derived based on a matching luminance block indicated by a block vector. In addition, the prediction block of the current chrominance block can be generated based on the matching luminance block, samples adjacent to the matching luminance block, the matching chrominance block, and samples adjacent to the matching chrominance block.

[0240] Here, if only one luminance block among multiple blocks in the corresponding luminance region is predicted using the intra block copy method, intra prediction of the current chrominance block can be performed based on information of the one luminance block. On the other hand, if multiple blocks in the corresponding luminance region are predicted using the intra block copy method, one block among the multiple blocks can be explicitly or implicitly determined, and intra prediction of the current chrominance block can be performed based on information of the one luminance block.

[0241] According to one embodiment, intra prediction mode information for the BVG-CCCM mode of the current chrominance block can be derived using the intra template matching (IntraTMP) method. For example, when a luminance block corresponding to the current chrominance block is predicted using the intra template matching method, a prediction block of the corresponding luminance block can be derived based on a matching luminance block, which is a luminance block adjacent to a template most similar to the template of the corresponding luminance block. In addition, the prediction block of the current chrominance block can be generated based on the matching luminance block, samples adjacent to the matching luminance block, the matching chrominance block, and samples adjacent to the matching chrominance block.

[0242] Here, if only one luminance block among multiple blocks in the corresponding luminance region is predicted by the intra template matching method, intra prediction of the current chrominance block can be performed based on information of the one luminance block. On the other hand, if multiple blocks in the corresponding luminance region are predicted by the intra template matching method, one block among the multiple blocks can be explicitly or implicitly determined, and intra prediction of the current chrominance block can be performed based on information of the one luminance block.

[0243] According to one embodiment, intra prediction mode information for the BVG-CCCM mode of the current chrominance block can be derived using a motion vector. For example, if a luminance block corresponding to the current chrominance block is predicted using a motion vector, a prediction block of the corresponding luminance block can be derived from a reference luminance block indicated by the motion vector. In addition, the prediction block of the current chrominance block can be generated based on a reference luminance block, samples adjacent to the reference luminance block, a reference chrominance block, and samples adjacent to the reference chrominance block.

[0244] Here, if only one luminance block among multiple blocks in the corresponding luminance region is predicted using a block vector, intra prediction of the current chrominance block can be performed based on information of the single luminance block. On the other hand, if multiple blocks in the corresponding luminance region are predicted using a block vector, one block among the multiple blocks can be explicitly or implicitly determined, and intra prediction of the current chrominance block can be performed based on information of the single luminance block.

[0245] When there are multiple blocks predicted based on an intra block copy method, an intra template matching method, and a motion vector among multiple blocks of a corresponding luminance area, one block is explicitly or implicitly determined, and intra prediction of a current chrominance block can be performed based on information of one luminance block.

[0246]

[0247] An image decoding method and an image encoding method for a method of predicting a chrominance block based on information of a luminance block according to an embodiment of the present disclosure may be as described below.

[0248]

[0249] FIG. 9 is a flowchart illustrating an image decoding method for predicting a chrominance block based on information of a luminance block according to an embodiment of the present disclosure. The image decoding method of FIG. 9 can be performed by an image decoding device.

[0250] Referring to FIG. 9, the image decoding device can independently divide the luminance coding tree block and the chrominance coding tree block of the current coding tree unit (S910).

[0251] Here, the current slice containing the current coding tree unit can be one of an I slice, a B slice, and a P slice.

[0252] The image decoding device can set a luminance area corresponding to the current chrominance block divided from the chrominance coding tree block (S920).

[0253] The image decoding device can set a candidate group based on information about at least one block within the luminance range (S930).

[0254] Here, at least one of the blocks may include a block including a center sample of the luminance region, a block including a sample at the upper left of the luminance region, a block including a sample at the lower left of the luminance region, a block including a sample at the upper right of the luminance region, and a block including a sample at the lower right of the luminance region.

[0255] Here, the candidate set may include available blocks within the luminance range based on the availability of at least one block. The availability of at least one block may be determined based on the prediction mode of each of at least one block and the prediction mode of the current chrominance block.

[0256] The image decoding device can determine one corresponding luminance block from among the candidates (S940).

[0257] For example, one corresponding luminance block may be a block determined as a result of a search in a pre-determined order among the candidate blocks.

[0258] Alternatively, a corresponding luminance block may be a block determined based on information indicating one candidate from a pool of candidates.

[0259] The image decoding device can generate a prediction block of the current chrominance block based on prediction information of the corresponding luminance block (S950).

[0260] Here, the prediction information of the corresponding luminance block may be intra prediction mode information derived based on DIMD, TIMD, and OBIC.

[0261] Here, the prediction information of the corresponding luminance block may be intra prediction mode information of the matching luminance block indicated by the block vector of the corresponding luminance block.

[0262] Here, the prediction information of the corresponding luminance block may be intra prediction mode information of the reference luminance block indicated by the motion vector of the corresponding luminance block.

[0263] Here, the prediction information of the corresponding luminance block is a block vector of the corresponding luminance block, and the prediction block of the current chrominance block can be generated based on a reference chrominance block corresponding to the matching luminance block indicated by the block vector of the corresponding luminance block.

[0264] Here, the prediction information of the corresponding luminance block is a motion vector of the corresponding luminance block, and the prediction block of the current chrominance block can be generated based on a reference chrominance block corresponding to a reference luminance block indicated by the motion vector of the corresponding luminance block.

[0265] Here, the prediction information of the corresponding luminance block is a block vector of the corresponding luminance block, and the prediction block of the current chrominance block can be generated based on filter coefficients derived based on samples adjacent to the matching luminance block indicated by the block vector of the corresponding luminance block and samples adjacent to the reference chrominance block corresponding to the reference luminance block.

[0266] Here, the prediction information of the corresponding luminance block is a motion vector of the corresponding luminance block, and the prediction block of the current chrominance block can be generated based on filter coefficients derived based on samples adjacent to a reference luminance block indicated by the motion vector of the corresponding luminance block and samples adjacent to a reference chrominance block corresponding to the reference luminance block.

[0267]

[0268] Meanwhile, the steps described in FIG. 9 can be performed in the same manner in an image encoding method. Furthermore, a bitstream can be generated by an image encoding method including the steps described in FIG. 9. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0269]

[0270] While the exemplary methods of this disclosure are presented as a series of operations for clarity of description, this is not intended to limit the order in which the steps are performed, and individual steps may be performed simultaneously or in different orders, if desired. To implement a method according to this disclosure, additional steps may be included in addition to the steps illustrated, some steps may be excluded and the remaining steps included, or some steps may be excluded and additional steps included.

[0271] The various embodiments of the present disclosure are not intended to list all possible combinations but rather to illustrate representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combinations of two or more.

[0272] Various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, the embodiments may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general processors, controllers, microcontrollers, microprocessors, etc.

[0273] Alternatively, various embodiments of the present disclosure may be implemented in the form of program commands that can be executed by various computer components and recorded on a computer-readable recording medium. Furthermore, a bitstream generated by the encoding method according to the above embodiment may be stored on a non-transitory computer-readable recording medium.

[0274] The computer-readable recording medium may include program commands, data files, data structures, etc., either singly or in combination. The program commands recorded on the computer-readable recording medium may be those specifically designed and configured for the present disclosure or may be known and available to those skilled in the art of computer software.

[0275] As described above, the present disclosure has been described based on specific details, such as specific components, and limited embodiments and drawings. However, the embodiments of the present disclosure are provided merely to facilitate a general understanding of the present disclosure and are not intended to limit the present disclosure to these embodiments. Accordingly, those skilled in the art will appreciate that various modifications and variations can be made based on the description.

[0276] Therefore, the idea of ​​the present invention should not be limited to the embodiments described above, and all things that are modified equally or equivalently to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

[0277] The present invention can be used in a device for encoding an image, a device for decoding an image, and a recording medium for storing a bitstream.

Claims

1. In the video decryption method, A step of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit; A step of setting a luminance area corresponding to a current chrominance block divided from the above chrominance coding tree block; A step of setting a candidate group based on information about at least one block within the luminance region; a step of determining one corresponding luminance block from among the above candidates; and An image decoding method, comprising a step of generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

2. In paragraph 1, The current slice containing the current coding tree unit is A method for decoding an image, characterized in that the image is one of an I slice, a B slice, and a P slice.

3. In paragraph 1, At least one of the above blocks, An image decoding method, characterized in that it comprises a block including a center sample of the luminance region, a block including a sample of the upper left of the luminance region, a block including a sample of the lower left of the luminance region, a block including a sample of the upper right of the luminance region, and a block including a sample of the lower right of the luminance region.

4. In paragraph 1, The above candidates are: An image decoding method, characterized in that it includes available blocks within the luminance range based on the availability of at least one block.

5. In paragraph 4, The availability of at least one of the above blocks is A method for decoding an image, characterized in that the prediction mode is determined based on the prediction mode of each of the at least one block and the prediction mode of the current chrominance block.

6. In paragraph 1, The above one corresponding luminance block is, A video decoding method characterized in that the block is determined as a result of a search in a preset order from the above candidate group.

7. In paragraph 1, The above one corresponding luminance block is, A video decoding method, characterized in that the block is determined based on information indicating one candidate from the above candidate group.

8. In paragraph 1, The prediction information of the corresponding luminance block above is, An image decoding method characterized in that the intra prediction mode information is derived based on DIMD, TIMD, and OBIC.

9. In paragraph 1, The prediction information of the corresponding luminance block above is, An image decoding method, characterized in that the intra prediction mode information of the matching luminance block is indicated by the block vector of the corresponding luminance block.

10. In paragraph 1, The prediction information of the corresponding luminance block above is, An image decoding method, characterized in that the intra prediction mode information of the reference luminance block is indicated by the motion vector of the corresponding luminance block.

11. In paragraph 1, The prediction information of the corresponding luminance block above is, is the block vector of the corresponding luminance block, An image decoding method, characterized in that the prediction block of the current chrominance block is generated based on a matching chrominance block corresponding to a matching luminance block indicated by a block vector of the corresponding luminance block.

12. In paragraph 1, The prediction information of the corresponding luminance block above is, is the motion vector of the corresponding luminance block, An image decoding method, characterized in that the prediction block of the current chrominance block is generated based on a reference chrominance block corresponding to a reference luminance block indicated by a motion vector of the corresponding luminance block.

13. In paragraph 1, The prediction information of the corresponding luminance block above is, is the block vector of the corresponding luminance block, An image decoding method, characterized in that the prediction block of the current chrominance block is generated based on filter coefficients derived based on samples adjacent to a matching luminance block indicated by a block vector of the corresponding luminance block and samples adjacent to a matching chrominance block corresponding to the matching luminance block.

14. In paragraph 1, The prediction information of the corresponding luminance block above is, is the motion vector of the corresponding luminance block, An image decoding method, characterized in that the prediction block of the current chrominance block is generated based on filter coefficients derived based on samples adjacent to a reference luminance block indicated by a motion vector of the corresponding luminance block and samples adjacent to a reference chrominance block corresponding to the reference luminance block.

15. In the video encoding method, A step of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit; A step of setting a luminance area corresponding to a current chrominance block divided from the above chrominance coding tree block; A step of setting a candidate group based on information about at least one block within the luminance region; a step of determining one corresponding luminance block from among the above candidates; and An image encoding method, comprising a step of generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

16. In a non-transitory computer-readable recording medium storing a bitstream generated by an image encoding method, The above image encoding method is, A step of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit; A step of setting a luminance area corresponding to a current chrominance block divided from the above chrominance coding tree block; A step of setting a candidate group based on information about at least one block within the luminance region; a step of determining one corresponding luminance block from among the above candidates; and A non-transitory computer-readable recording medium comprising a step of generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

17. In a method for transmitting a bitstream generated by a video encoding method, The above transmission method includes a step of transmitting the bitstream, The above image encoding method is, A step of independently dividing a luminance coding tree block and a chrominance coding tree block of a current coding tree unit; A step of setting a luminance area corresponding to a current chrominance block divided from the above chrominance coding tree block; A step of setting a candidate group based on information about at least one block within the luminance region; a step of determining one corresponding luminance block from among the above candidates; and A transmission method comprising a step of generating a prediction block of the current chrominance block based on prediction information of the corresponding luminance block.

Images