Method for adaptively correcting inter-component prediction signal in inter prediction

Abstract

The present embodiment provides a method for adaptively correcting an inter-component prediction signal in inter prediction. In the present embodiment, an image decoding device determines an inverse transform unit of a current chroma block, and obtains chroma prediction signals of the inverse transform unit and luma prediction signals of a corresponding luma block. The image decoding device obtains filter coefficients indicating a correlation between the luma prediction signals and the chroma prediction signals, and generates chroma correction signals of the inverse transform unit by applying the filter coefficients to luma reconstruction signals of the corresponding luma block. The image decoding device obtains a weight, and generates final chroma prediction signals of the inverse transform unit by performing a weighted summation of the chroma prediction signals and the chroma correction signals on the basis of the weight.

Description

A method for adaptive compensation of inter-component prediction signals in inter prediction

[0001] The present disclosure relates to a video coding method and device for adaptively compensating inter-component prediction signals in inter prediction.

[0002] The content described below merely provides background information related to the present invention and does not constitute prior art.

[0003] Since video data has a large amount of data compared to voice data or still image data, it requires a lot of hardware resources, including memory, to store or transmit it without processing for compression.

[0004] Therefore, when storing or transmitting video data, the encoder compresses the video data and stores or transmits it, and the decoder receives the compressed video data, decompresses it, and plays it back. These video compression technologies include H.264 / AVC, HEVC (High Efficiency Video Coding), and VVC (Versatile Video Coding), which improves encoding efficiency by about 30% compared to HEVC.

[0005] However, as video size, resolution, and frame rate continue to increase, the amount of data to be encoded also increases. Therefore, a new compression technology with better encoding efficiency and improved image quality is needed. In particular, when the current block is predicted using inter prediction, a method for efficiently predicting chroma components is required.

[0006] The present disclosure provides a video coding method and device for generating a restoration block of a current chroma block by correcting prediction signals of a current chroma block based on a relationship between corresponding luma components and chroma components when predicting a current chroma block according to inter prediction, and adding the corrected prediction signals to residual signals.

[0007] According to an embodiment of the present disclosure, a method for restoring a current chroma block, performed by a video decoding device, is provided, comprising: determining an inverse transform unit of the current chroma block; obtaining chroma prediction signals of the inverse transform unit and luma prediction signals of a corresponding luma block, wherein the corresponding luma block is a luma region positionally corresponding to the inverse transform unit of the current chroma block; obtaining filter coefficients indicating a correlation between the luma prediction signals and the chroma prediction signals; applying the filter coefficients to luma restoration signals of the corresponding luma block to generate chroma correction signals of the inverse transform unit; obtaining weights; and generating final chroma prediction signals of the inverse transform unit by weighting the chroma prediction signals and the chroma correction signals based on the weights.

[0008] According to another embodiment of the present disclosure, a method for encoding a current block, performed by a video encoding apparatus, is provided, comprising: determining an inverse transform unit of the current chroma block; obtaining chroma prediction signals of the inverse transform unit and luma prediction signals of a corresponding luma block, wherein the corresponding luma block is a luma region positionally corresponding to the inverse transform unit of the current chroma block; obtaining filter coefficients indicating a correlation between the luma prediction signals and the chroma prediction signals; applying the filter coefficients to luma restoration signals of the corresponding luma block to generate chroma correction signals of the inverse transform unit; obtaining weights; and generating final chroma prediction signals of the inverse transform unit by weighting the chroma prediction signals and the chroma correction signals based on the weights.

[0009] According to another embodiment of the present disclosure, a method for providing video data to a video decoding device is provided, comprising: encoding the video data into a bitstream; and transmitting the bitstream to the video decoding device, wherein the encoding of the video data comprises: determining an inverse transform unit of a current chroma block; obtaining chroma prediction signals of the inverse transform unit and luma prediction signals of a corresponding luma block, wherein the corresponding luma block is a luma region that is positionally corresponding to an inverse transform unit of the current chroma block; obtaining filter coefficients indicating a correlation between the luma prediction signals and the chroma prediction signals; applying the filter coefficients to luma reconstruction signals of the corresponding luma block to generate chroma correction signals of the inverse transform unit; obtaining weights; and generating final chroma prediction signals of the inverse transform unit by weighting the chroma prediction signals and the chroma correction signals based on the weights.

[0010] As described above, according to the present embodiment, when predicting a current chroma block according to inter prediction, the prediction signals of the current chroma block are corrected based on the relationship between the corresponding luma component and the chroma component, and the corrected prediction signals are added to residual signals, thereby providing a video coding method and device for generating a restoration block of the current chroma block, thereby making it possible to improve video encoding efficiency and enhance video quality.

[0011] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the techniques of the present disclosure.

[0012] Figure 2 is a drawing for explaining a method of dividing a block using the QTBTTT (QuadTree plus BinaryTree TernaryTree) structure.

[0013] FIGS. 3A and 3B are diagrams illustrating multiple intra prediction modes, including wide-angle intra prediction modes.

[0014] Figure 4 is an example diagram of the surrounding blocks of the current block.

[0015] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the techniques of the present disclosure.

[0016] FIG. 6 is a block diagram illustrating in detail a portion of an image decoding device according to one embodiment of the present disclosure.

[0017] FIG. 7 is an exemplary diagram showing correction of prediction signals of chroma components according to one embodiment of the present disclosure.

[0018] FIG. 8 is an exemplary diagram showing the positions of samples of chroma components and the positions of corresponding luma samples according to one embodiment of the present disclosure.

[0019] FIG. 9 is an exemplary diagram showing the locations of surrounding blocks according to one embodiment of the present disclosure.

[0020] FIG. 10 is an exemplary diagram illustrating corresponding luma blocks according to one embodiment of the present disclosure.

[0021] FIG. 11 is an exemplary diagram showing a process for determining an inverse transform kernel according to one embodiment of the present disclosure.

[0022] FIG. 12 is an exemplary diagram showing a process for determining an inverse transform kernel according to another embodiment of the present disclosure.

[0023] FIG. 13 is a flowchart illustrating a method by which a video encoding device encodes a current chroma block according to one embodiment of the present disclosure.

[0024] FIG. 14 is a flowchart illustrating a method by which a video decoding device restores a current chroma block according to one embodiment of the present disclosure.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to exemplary drawings. When designating components in each drawing, it should be noted that, where possible, identical components are given the same reference numerals, even if they appear in different drawings. Furthermore, in describing the present embodiments, detailed descriptions of related known structures or functions will be omitted if they are deemed to obscure the gist of the present embodiments.

[0026] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the techniques of the present disclosure. Hereinafter, the image encoding device and its subcomponents will be described with reference to the illustration in FIG. 1.

[0027] The video encoding device may be configured to include a picture segmentation unit (110), a prediction unit (120), a subtractor (130), a transformation unit (140), a quantization unit (145), a reordering unit (150), an entropy encoding unit (155), an inverse quantization unit (160), an inverse transformation unit (165), an adder (170), a loop filter unit (180), and a memory (190).

[0028] Each component of the video encoding device may be implemented in hardware, software, or a combination of hardware and software. Furthermore, the functions of each component may be implemented in software, with a microprocessor executing the software functions corresponding to each component.

[0029] A single image (video) is composed of one or more sequences containing multiple pictures. Each picture is divided into multiple regions, and encoding is performed for each region. For example, a single picture is divided into one or more tiles and / or slices. Here, one or more tiles can be defined as a tile group. Each tile or slice is divided into one or more Coding Tree Units (CTUs). Each CTU is then divided into one or more Coding Units (CUs) by a tree structure. Information applied to each CU is encoded as the syntax of the CU, and information commonly applied to CUs included in a CTU is encoded as the syntax of the CTU. In addition, information commonly applied to all blocks within a single slice is encoded as the syntax of the slice header, and information applied to all blocks constituting one or more pictures is encoded in the Picture Parameter Set (PPS) or the picture header. Furthermore, information commonly referenced by multiple pictures is encoded in a Sequence Parameter Set (SPS). And, information commonly referenced by one or more SPS is encoded in a Video Parameter Set (VPS). In addition, information commonly applied to one tile or tile group may be encoded as syntax of a tile or tile group header. Syntaxes included in an SPS, PPS, slice header, tile or tile group header may be referred to as high level syntax.

[0030] The picture segmentation unit (110) determines the size of the CTU. Information about the size of the CTU (CTU size) is encoded as the syntax of SPS or PPS and transmitted to the image decoding device.

[0031] The picture segmentation unit (110) divides each picture constituting an image into a plurality of CTUs having a predetermined size, and then recursively divides the CTUs using a tree structure. A leaf node in the tree structure becomes a CU, which is a basic unit of encoding.

[0032] The tree structure may be a QuadTree (QT) in which an upper node (or parent node) is divided into four lower nodes (or child nodes) of the same size, a BinaryTree (BT) in which an upper node is divided into two lower nodes, or a TernaryTree (TT) in which an upper node is divided into three lower nodes in a 1:2:1 ratio, or a structure that mixes two or more of the QT structures, BT structures, and TT structures. For example, a QTBT (QuadTree plus BinaryTree) structure may be used, or a QTBTTT (QuadTree plus BinaryTree TernaryTree) structure may be used. Here, BTTT may be combined and referred to as a MTT (Multiple-Type Tree).

[0033] Figure 2 is a drawing for explaining a method of dividing a block using the QTBTTT structure.

[0034] As illustrated in FIG. 2, a CTU may first be split into a QT structure. The quadtree splitting may be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of the leaf node allowed in the QT. A first flag (QT_split_flag) indicating whether each node of the QT structure is split into four nodes of the lower layer is encoded by the entropy encoding unit (155) and signaled to the image decoding device. If the leaf node of the QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in the BT, it may be further split into one or more of the BT structure or the TT structure. There may be multiple splitting directions in the BT structure and / or the TT structure. For example, there may be two directions in which the block of the corresponding node is split horizontally and two directions in which the block is split vertically. As illustrated in FIG. 2, when MTT splitting begins, a second flag (mtt_split_flag) indicating whether nodes have been split, and if splitting has occurred, a flag indicating the splitting direction (vertical or horizontal) and / or a flag indicating the splitting type (Binary or Ternary) are encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0035] Alternatively, before encoding the first flag (QT_split_flag) indicating whether each node is split into four nodes of a lower layer, a CU split flag (split_cu_flag) indicating whether the node is split may be encoded. If the CU split flag (split_cu_flag) value indicates that the node is not split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a CU (coding unit), which is a basic unit of encoding. If the CU split flag (split_cu_flag) value indicates that the node is split, the video encoding device starts encoding from the first flag in the above-described manner.

[0036] As another example of a tree structure, when QTBT is used, there may be two types: a type that horizontally splits the block of the corresponding node into two blocks of the same size (i.e., symmetric horizontal splitting) and a type that vertically splits it (i.e., symmetric vertical splitting). A split flag (split_flag) indicating whether each node of the BT structure is split into blocks of a lower layer and split type information indicating the type of split are encoded by the entropy encoding unit (155) and transmitted to the image decoding device. Meanwhile, there may additionally be a type that splits the block of the corresponding node into two blocks of an asymmetrical shape. The asymmetric shape may include a shape that splits the block of the corresponding node into two rectangular blocks with a size ratio of 1:3, or a shape that splits the block of the corresponding node in a diagonal direction.

[0037] A CU can have various sizes depending on the QTBT or QTBTTT partitioning from the CTU. Hereinafter, the block corresponding to the CU to be encoded or decoded (i.e., the leaf node of the QTBTTT) is referred to as the "current block." Depending on the QTBTTT partitioning employed, the current block may be rectangular as well as square.

[0038] The prediction unit (120) predicts the current block and generates a prediction block. The prediction unit (120) includes an intra prediction unit (122) and an inter prediction unit (124).

[0039] In general, each current block within a picture can be predictively coded. Prediction of the current block can typically be performed using either intra-prediction (using data from the picture containing the current block) or inter-prediction (using data from a picture coded before the picture containing the current block). Inter-prediction encompasses both unidirectional and bidirectional prediction.

[0040] The intra prediction unit (122) predicts pixels within the current block using pixels (reference pixels) located around the current block within the current picture including the current block. There are multiple intra prediction modes depending on the prediction direction. For example, as shown in Fig. 3a, the multiple intra prediction modes may include two non-directional modes including the Planar mode and the DC mode, and 65 directional modes. The surrounding pixels to be used and the calculation formula are defined differently depending on each prediction mode.

[0041] For efficient directional prediction for a rectangular current block, directional modes (intra prediction modes 67 to 80 and -1 to -14) indicated by dotted arrows in Fig. 3b may be additionally used. These may be referred to as "wide-angle intra-prediction modes." In Fig. 3b, the arrows point to corresponding reference samples used for prediction, and do not indicate the prediction direction. The prediction direction is opposite to the direction indicated by the arrows. Wide-angle intra-prediction modes are modes that perform prediction in the opposite direction of a specific directional mode without additional bit transmission when the current block is rectangular. At this time, among the wide-angle intra-prediction modes, some wide-angle intra-prediction modes available for the current block may be determined based on the ratio of the width and height of the rectangular current block. For example, wide-angle intra prediction modes (intra prediction modes 67 to 80) having an angle less than 45 degrees are available when the current block is a rectangular shape whose height is smaller than its width, and wide-angle intra prediction modes (intra prediction modes -1 to -14) having an angle greater than -135 degrees are available when the current block is a rectangular shape whose width is larger than its height.

[0042] The intra prediction unit (122) can determine an intra prediction mode to be used to encode the current block. In some examples, the intra prediction unit (122) can encode the current block using multiple intra prediction modes and select an appropriate intra prediction mode to be used from the tested modes. For example, the intra prediction unit (122) can calculate bit-rate distortion values ​​using rate-distortion analysis for multiple tested intra prediction modes and select an intra prediction mode with the best bit-rate distortion characteristics among the tested modes.

[0043] The intra prediction unit (122) selects one intra prediction mode from among multiple intra prediction modes and predicts the current block using surrounding pixels (reference pixels) and an operation formula determined according to the selected intra prediction mode. Information about the selected intra prediction mode is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0044] The inter prediction unit (124) generates a prediction block for the current block using a motion compensation process. The inter prediction unit (124) searches for a block most similar to the current block within reference pictures that were encoded and decoded before the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector (MV) corresponding to the displacement between the current block within the current picture and the prediction block within the reference picture is generated. Generally, motion estimation is performed on the luma component, and the motion vector calculated based on the luma component is used for both the luma component and the chroma component. The motion information including information on the reference picture used to predict the current block and information on the motion vector is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0045] The inter prediction unit (124) may perform interpolation on a reference picture or a reference block to improve prediction accuracy. That is, subsamples between two consecutive integer samples are interpolated by applying filter coefficients to a plurality of consecutive integer samples including the two integer samples. When a process of searching for a block most similar to the current block is performed on the interpolated reference picture, the motion vector can be expressed up to a precision in decimal units rather than a precision in integer sample units. The precision or resolution of the motion vector can be set differently for each target region to be encoded, such as a slice, tile, CTU, CU, etc. When such adaptive motion vector resolution (AMVR) is applied, information on the motion vector resolution to be applied to each target region must be signaled for each target region. For example, when the target region is a CU, information on the motion vector resolution applied to each CU is signaled. Information on the motion vector resolution may be information indicating the precision of a differential motion vector, which will be described later.

[0046] Meanwhile, the inter prediction unit (124) can perform inter prediction using bi-prediction. In the case of bi-prediction, two reference pictures and two motion vectors indicating the block position most similar to the current block within each reference picture are used. The inter prediction unit (124) selects a first reference picture and a second reference picture from reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1), respectively, and searches for a block similar to the current block within each reference picture to generate a first reference block and a second reference block. Then, the first reference block and the second reference block are averaged or weighted averaged to generate a prediction block for the current block. Then, motion information including information on two reference pictures used to predict the current block and information on two motion vectors is transmitted to the entropy encoding unit (155). Here, reference picture list 0 may be composed of pictures that are before the current picture in display order among the restored pictures, and reference picture list 1 may be composed of pictures that are after the current picture in display order among the restored pictures. However, this is not necessarily limited to this, and restored pictures that are after the current picture in display order may be additionally included in reference picture list 0, and conversely, restored pictures that are before the current picture may be additionally included in reference picture list 1.

[0047] Various methods can be used to minimize the number of bits required to encode motion information.

[0048] For example, if the reference picture and motion vector of the current block are identical to those of a neighboring block, the motion information of the current block can be transmitted to the image decoding device by encoding information that can identify the neighboring block. This method is called 'merge mode'.

[0049] In merge mode, the inter prediction unit (124) selects a predetermined number of merge candidate blocks (hereinafter referred to as 'merge candidates') from the surrounding blocks of the current block.

[0050] As the surrounding blocks for deriving merge candidates, all or part of the left block (A0), the lower left block (A1), the upper block (B0), the upper right block (B1), and the upper left block (B2) adjacent to the current block within the current picture may be used, as illustrated in FIG. 4. In addition, a block located within a reference picture (which may or may not be the same as the reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block within the reference picture or blocks adjacent to the block at the co-located block may be additionally used as a merge candidate. If the number of merge candidates selected by the method described above is less than a preset number, a 0 vector is added to the merge candidates.

[0051] The inter prediction unit (124) uses these surrounding blocks to construct a merge list containing a predetermined number of merge candidates. Among the merge candidates included in the merge list, the merge candidate to be used as motion information of the current block is selected and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the entropy encoding unit (155) and transmitted to the video decoding device.

[0052] Merge Skip mode is a special case of merge mode. After quantization, when all transform coefficients for entropy encoding are close to zero, only neighboring block selection information is transmitted without transmitting residual signals. By utilizing merge skip mode, relatively high encoding efficiency can be achieved for low-motion images, still images, and screen content images.

[0053] Hereinafter, merge mode and merge skip mode are collectively referred to as merge / skip mode.

[0054] Another method for encoding motion information is Advanced Motion Vector Prediction (AMVP) mode.

[0055] In AMVP mode, the inter prediction unit (124) derives predicted motion vector candidates for the motion vector of the current block using neighboring blocks of the current block. As neighboring blocks used to derive predicted motion vector candidates, all or some of the left block (A0), the lower left block (A1), the upper block (B0), the upper right block (B1), and the upper left block (B2) adjacent to the current block in the current picture as shown in FIG. 4 may be used. In addition, a block located in a reference picture (which may or may not be the same as the reference picture used to predict the current block) other than the current picture in which the current block is located may be used as the neighboring block used to derive predicted motion vector candidates. For example, a block co-located with the current block in the reference picture or blocks adjacent to the block in the co-located block may be used. If the number of motion vector candidates is less than a preset number by the method described above, a 0 vector is added to the motion vector candidates.

[0056] The inter prediction unit (124) derives predicted motion vector candidates using the motion vectors of these surrounding blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, the predicted motion vector is subtracted from the motion vector of the current block to produce a differential motion vector.

[0057] The predicted motion vector can be obtained by applying a predefined function (e.g., median, mean, etc.) to the predicted motion vector candidates. In this case, the image decoding device also knows the predefined function. In addition, since the surrounding blocks used to derive the predicted motion vector candidates are blocks that have already been encoded and decoded, the image decoding device also already knows the motion vectors of the surrounding blocks. Therefore, the image encoding device does not need to encode information to identify the predicted motion vector candidates. Therefore, in this case, information about the differential motion vector and information about the reference picture used to predict the current block are encoded.

[0058] Alternatively, the predicted motion vector can be determined by selecting one of the predicted motion vector candidates. In this case, information for identifying the selected predicted motion vector candidate is additionally encoded, along with information about the differential motion vector and the reference picture used to predict the current block.

[0059] The subtractor (130) subtracts the prediction block generated by the intra prediction unit (122) or inter prediction unit (124) from the current block to generate a residual block.

[0060] The transformation unit (140) transforms residual signals within a residual block having pixel values ​​in a spatial domain into transform coefficients in a frequency domain. The transformation unit (140) may transform the residual signals within the residual block using the entire size of the residual block as a transformation unit, or may divide the residual block into a plurality of sub-blocks and use the sub-blocks as transformation units to perform the transformation. Alternatively, the residual signals may be transformed using only the transformation domain sub-block as a transformation unit by dividing the sub-blocks into two sub-blocks, that is, a transformation domain and a non-transform domain. Here, the transformation domain sub-block may be one of two rectangular blocks having a size ratio of 1:1 with respect to the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_flag) indicating that only a sub-block has been converted, directionality (vertical / horizontal) information (cu_sbt_horizontal_flag), and / or position information (cu_sbt_pos_flag) are encoded by the entropy encoding unit (155) and signaled to the image decoding device. In addition, the size of the conversion area sub-block may have a size ratio of 1:3 with respect to the horizontal axis (or vertical axis), and in this case, a flag (cu_sbt_quad_flag) distinguishing the corresponding division is additionally encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0061] Meanwhile, the transformation unit (140) can individually perform transformations on the residual block in the horizontal and vertical directions. For the transformation, various types of transformation functions or transformation matrices can be used. For example, a pair of transformation functions for horizontal transformation and vertical transformation can be defined as a Multiple Transform Set (MTS). The transformation unit (140) can select one transformation function pair with the best transformation efficiency among the MTS and transform the residual block in the horizontal and vertical directions, respectively. Information (mts_idx) on the transformation function pair selected among the MTS is encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0062] The quantization unit (145) quantizes the transform coefficients output from the transform unit (140) using quantization parameters and outputs the quantized transform coefficients to the entropy encoding unit (155). The quantization unit (145) may directly quantize a related residual block without transformation for a certain block or frame. The quantization unit (145) may also apply different quantization coefficients (scaling values) according to the positions of the transform coefficients within the transform block. The quantization matrix applied to the quantized transform coefficients arranged in two dimensions may be encoded and signaled to an image decoding device.

[0063] The rearrangement unit (150) can perform rearrangement of coefficient values ​​for quantized residual values.

[0064] The reordering unit (150) can change a two-dimensional coefficient array into a one-dimensional coefficient sequence by using coefficient scanning. For example, the reordering unit (150) can output a one-dimensional coefficient sequence by scanning from the DC coefficient to the coefficients of the high-frequency region by using a zig-zag scan or a diagonal scan. Depending on the size of the transformation unit and the intra prediction mode, a vertical scan that scans the two-dimensional coefficient array in the column direction or a horizontal scan that scans the two-dimensional block-shaped coefficients in the row direction may be used instead of the zig-zag scan. That is, depending on the size of the transformation unit and the intra prediction mode, the scanning method to be used may be determined among the zig-zag scan, the diagonal scan, the vertical scan, and the horizontal scan.

[0065] The entropy encoding unit (155) generates a bitstream by encoding a sequence of one-dimensional quantized transform coefficients output from the rearrangement unit (150) using various encoding methods such as CABAC (Context-based Adaptive Binary Arithmetic Code) and Exponential Golomb.

[0066] In addition, the entropy encoding unit (155) encodes information related to block division, such as CTU size, CU division flag, QT division flag, MTT division type, and MTT division direction, so that the image decoding device can divide the block in the same manner as the image encoding device. In addition, the entropy encoding unit (155) encodes information about a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and encodes intra prediction information (i.e., information about an intra prediction mode) or inter prediction information (information about an encoding mode of motion information (merge mode or AMVP mode), a merge index in the case of a merge mode, and a reference picture index and a differential motion vector in the case of an AMVP mode) according to the prediction type. In addition, the entropy encoding unit (155) encodes information related to quantization, that is, information about a quantization parameter and information about a quantization matrix.

[0067] The inverse quantization unit (160) inversely quantizes the quantized transform coefficients output from the quantization unit (145) to generate transform coefficients. The inverse transform unit (165) transforms the transform coefficients output from the inverse quantization unit (160) from the frequency domain to the spatial domain to restore the residual block.

[0068] An adder (170) adds the restored residual block and the predicted block generated by the prediction unit (120) to restore the current block. The pixels within the restored current block are used as reference pixels when intra-predicting the next block.

[0069] The loop filter unit (180) performs filtering on restored pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. that occur due to block-based prediction and transformation / quantization. The loop filter unit (180) may include all or part of a deblocking filter (182), a sample adaptive offset (SAO) filter (184), and an adaptive loop filter (ALF, 186) as an in-loop filter.

[0070] The deblocking filter (182) filters the boundaries between restored blocks to remove blocking artifacts caused by block-based encoding / decoding, and the SAO filter (184) and the ALF (186) perform additional filtering on the deblocking-filtered image. The SAO filter (184) and the ALF (186) are filters used to compensate for the differences between restored pixels and original pixels caused by lossy coding. The SAO filter (184) improves not only subjective image quality but also encoding efficiency by applying an offset in units of CTUs. In contrast, the ALF (186) performs block-based filtering, and compensates for distortion by applying different filters by distinguishing the edges and degrees of variation of the corresponding block. Information on filter coefficients to be used in the ALF can be encoded and signaled to an image decoding device.

[0071] The restored blocks filtered through the deblocking filter (182), SAO filter (184), and ALF (186) are stored in the memory (190). When all blocks within a picture are restored, the restored picture can be used as a reference picture for inter-predicting blocks within a picture to be encoded later.

[0072] The video encoding device can store the bitstream of encoded video data on a non-transitory storage medium or transmit it to the video decoding device using a communication network.

[0073] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the techniques of the present disclosure. Hereinafter, the image decoding device and its subcomponents will be described with reference to FIG. 5.

[0074] The video decoding device may be configured to include an entropy decoding unit (510), a rearrangement unit (515), an inverse quantization unit (520), an inverse transformation unit (530), a prediction unit (540), an adder (550), a loop filter unit (560), and a memory (570).

[0075] Similar to the video encoding device of FIG. 1, each component of the video decoding device may be implemented in hardware, software, or a combination of hardware and software. Furthermore, the functions of each component may be implemented in software, with a microprocessor executing the software functions corresponding to each component.

[0076] The entropy decoding unit (510) decodes the bitstream generated by the image encoding device to extract information related to block division, thereby determining the current block to be decoded, and extracts prediction information, information on residual signals, etc. required to restore the current block.

[0077] The entropy decoding unit (510) extracts information about the CTU size from the Sequence Parameter Set (SPS) or the Picture Parameter Set (PPS), determines the size of the CTU, and divides the picture into CTUs of the determined size. Then, the CTU is determined as the top layer of the tree structure, i.e., the root node, and the CTU is divided using the tree structure by extracting division information about the CTU.

[0078] For example, when splitting a CTU using the QTBTTT structure, first, the first flag (QT_split_flag) related to the splitting of QT is extracted, and each node is split into four nodes of the lower layer. Then, for the nodes corresponding to the leaf nodes of QT, the second flag (mtt_split_flag) related to the splitting of MTT and the split direction (vertical / horizontal) and / or split type (binary / ternary) information are extracted, and the corresponding leaf nodes are split into the MTT structure. Accordingly, each node below the leaf nodes of QT are split recursively into the BT or TT structure.

[0079] As another example, when splitting a CTU using the QTBTTT structure, the CU split flag (split_cu_flag) indicating whether the CU is split is first extracted, and if the block is split, the first flag (QT_split_flag) may be extracted. During the splitting process, each node may undergo zero or more repeated QT splits followed by zero or more repeated MTT splits. For example, a CTU may undergo an MTT split right away, or conversely, may undergo only multiple QT splits.

[0080] As another example, when splitting a CTU using the QTBT structure, the first flag (QT_split_flag) related to the splitting of QT is extracted, and each node is split into four nodes of the lower layer. Furthermore, for nodes corresponding to leaf nodes of QT, a split flag (split_flag) indicating whether to further split into BTs and splitting direction information are extracted.

[0081] Meanwhile, when the entropy decoding unit (510) determines the current block to be decoded by using the division of the tree structure, it extracts information on the prediction type indicating whether the current block is intra-predicted or inter-predicted. If the prediction type information indicates intra-prediction, the entropy decoding unit (510) extracts syntax elements for intra-prediction information (intra-prediction mode) of the current block. If the prediction type information indicates inter-prediction, the entropy decoding unit (510) extracts syntax elements for inter-prediction information, i.e., information indicating a motion vector and a reference picture referenced by the motion vector.

[0082] Additionally, the entropy decoding unit (510) extracts information about the quantized transform coefficients of the current block as information related to quantization and information about residual signals.

[0083] The rearrangement unit (515) can change the sequence of one-dimensional quantized transform coefficients entropy-decoded in the entropy decoding unit (510) back into a two-dimensional coefficient array (i.e., block) in the reverse order of the coefficient scanning performed by the image encoding device.

[0084] The inverse quantization unit (520) inversely quantizes the quantized transform coefficients and inversely quantizes the quantized transform coefficients using the quantization parameters. The inverse quantization unit (520) may also apply different quantization coefficients (scaling values) to the quantized transform coefficients arranged in two dimensions. The inverse quantization unit (520) may perform inverse quantization by applying a matrix of quantized coefficients (scaling values) from an image encoding device to a two-dimensional array of quantized transform coefficients.

[0085] The inverse transform unit (530) inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore residual signals, thereby generating a residual block for the current block.

[0086] In addition, when the inverse transform unit (530) inversely transforms only a portion of a transform block (sub-block), it extracts a flag (cu_sbt_flag) indicating that only a sub-block of the transform block has been transformed, directionality (vertical / horizontal) information (cu_sbt_horizontal_flag) of the sub-block, and / or position information (cu_sbt_pos_flag) of the sub-block, and inversely transforms the transform coefficients of the corresponding sub-block from the frequency domain to the spatial domain to restore residual signals, and fills “0” values ​​with residual signals for areas that have not been inversely transformed, thereby generating a final residual block for the current block.

[0087] In addition, when MTS is applied, the inverse transform unit (530) determines a transform function or a transform matrix to be applied in the horizontal and vertical directions using MTS information (mts_idx) signaled from the image encoding device, and performs inverse transform on the transform coefficients within the transform block in the horizontal and vertical directions using the determined transform function.

[0088] The prediction unit (540) may include an intra prediction unit (542) and an inter prediction unit (544). The intra prediction unit (542) is activated when the prediction type of the current block is intra prediction, and the inter prediction unit (544) is activated when the prediction type of the current block is inter prediction.

[0089] The intra prediction unit (542) determines the intra prediction mode of the current block among a plurality of intra prediction modes from the syntax elements for the intra prediction mode extracted from the entropy decoding unit (510), and predicts the current block using reference pixels around the current block according to the intra prediction mode.

[0090] The inter prediction unit (544) uses the syntax elements for the inter prediction mode extracted from the entropy decoding unit (510) to determine the motion vector of the current block and the reference picture referenced by the motion vector, and predicts the current block using the motion vector and the reference picture.

[0091] An adder (550) adds the residual block output from the inverse transform unit (530) and the predicted block output from the inter prediction unit (544) or the intra prediction unit (542) to restore the current block. The pixels within the restored current block are used as reference pixels when intra-predicting a block to be decoded later.

[0092] The loop filter unit (560) may include a deblocking filter (562), an SAO filter (564), and an ALF (566) as in-loop filters. The deblocking filter (562) deblocks the boundaries between restored blocks to remove blocking artifacts caused by block-by-block decoding. The SAO filter (564) and the ALF (566) perform additional filtering on restored blocks after deblocking filtering to compensate for differences between restored pixels and original pixels caused by lossy coding. The filter coefficients of the ALF are determined using information about filter coefficients decoded from the non-stream.

[0093] The restored blocks filtered through the deblocking filter (562), SAO filter (564), and ALF (566) are stored in the memory (570). When all blocks within a picture are restored, the restored picture is used as a reference picture for inter-predicting blocks within a picture to be encoded later.

[0094] The present embodiment relates to encoding and decoding of images (video) as described above. More specifically, when predicting a current chroma block according to inter prediction, a video coding method and device are provided, which generate a reconstructed block of the current chroma block by correcting prediction signals of the current chroma block based on the relationship between the corresponding luma component and the chroma component, and adding the corrected prediction signals to residual signals.

[0095] The following embodiments may be performed by a prediction unit (120) within a video encoding apparatus. Additionally, the following embodiments may be performed by a prediction unit (540) within a video decoding apparatus.

[0096] The video encoding device can generate signaling information related to the present embodiment in terms of rate distortion optimization in encoding the current block. The video encoding device can encode the signaling information using the entropy encoding unit (155) and then transmit it to the video decoding device. The video decoding device can decode the signaling information related to the decoding of the current block from the bitstream using the entropy decoding unit (510).

[0097] In the following description, the term "target block" may be used interchangeably with the current block or coding unit (CU). Alternatively, the term "target block" may also refer to a portion of a coding unit.

[0098] Also, a value of a flag being true indicates that the flag is set to 1. Also, a value of a flag being false indicates that the flag is set to 0.

[0099] The decoder side includes all or part of the inverse quantization unit (160), the inverse transform unit (165), the prediction unit (120), the adder (170), the loop filter unit (180), and the memory (190) in the video encoding device illustrated in FIG. 1. Alternatively, the decoder side includes all or part of the inverse quantization unit (520), the inverse transform unit (530), the prediction unit (540), the adder (550), the loop filter unit (560), and the memory (570) in the video decoding device illustrated in FIG. 5. With respect to a series of decoding processes, the decoder side of the video encoding device and the decoder side of the video decoding device perform the same operation. The video encoding device determines information related to the operation of the decoder side and signals the determined information to the video decoding device. The video decoding device can decode the signaled information and operate the decoder side based on the decoded information.

[0100] I-1. Conversion Technology - Primary Conversion Technology

[0101] As mentioned above, for efficient video compression, quantization or scaling can be additionally applied to residual signals remaining after prediction using various prediction techniques. At this time, a transform technique can be applied based on the importance of perceptual visual information inherent in the residual signals to cluster the residual signals into one group according to frequency components, and then scaling can be performed. However, for non-natural signals, such as screen contents, this frequency-based transform technique can be inefficient. In such cases, the transform technique can be omitted, and only scaling can be performed, or encoding / decoding can be performed without applying scaling.

[0102] When a transform is applied in HEVC, DCT-II is used as a transform kernel (hereinafter, used interchangeably with transform type) to transform residual signals. However, in order to apply a more appropriate transform technique depending on the diversity of residual signal characteristics, Multiple Transform Selection (MTS) can be used. MTS determines the optimal type among multiple transform types, and then transforms the block according to the determined transform type. For example, in VVC, as shown in Table 1, in addition to DCT-II, two other transform types, DCT-VIII and DST-VII, are added so that residual signals can be transformed in various ways.

[0103]

[0104] Here, basis functions form a transformation matrix that defines each transformation type. Hereinafter, DCT-II, DCT-VIII, and DST-VII are used interchangeably with DCT2, DCT8, and DST7, respectively.

[0105] Meanwhile, the flag determining whether MTS is used can be controlled at the block level. Furthermore, MTS use can be controlled using an activation flag at the higher SPS level.

[0106] When MTS is enabled in SPS, a CU level flag may be displayed to indicate whether MTS is applied. Here, MTS may be applied to the luma component. The CU level flag may be expressed when both the width and height of the Transform Block (TB) are less than or equal to 32 pixels, and the Coded Block Flag (CBF), which indicates whether any of the transform coefficient levels have non-zero values, is true.

[0107] When the CU level flag is 0, DCT2 is used as a bidirectional kernel in both the horizontal and vertical directions. On the other hand, when the CU level flag is not 0, MTS is applied. MTS can be used in two ways: explicit MTS and implicit MTS.

[0108] In explicit MTS, the kernel used for the TB is explicitly transmitted. Typically, the index of the transformation kernel can be transmitted. For example, the kernel index, mts_idx, can be defined as shown in Table 2.

[0109]

[0110] Here, trTypeHor and trTypeVer represent the horizontal transformation type and the vertical transformation type, respectively. Additionally, 0 represents DCT2, 1 represents DST7, and 2 represents DCT8.

[0111] Meanwhile, in implicit MTS, for example, the transformation type can be determined implicitly even if MTS is not explicitly signaled in the case of an intra block. In VVC, the horizontal and vertical transformation types can be determined implicitly, as in Equation 1.

[0112]

[0113] Here, nTbW and nTbH represent the horizontal and vertical lengths of the transformation block, respectively.

[0114] Meanwhile, the next-generation technology, ECM (Enhanced Compression Model) software, increases the number and types of MTS kernels, adding DST7, DCT8, DCT5, DST4, DST1, and identity transform.

[0115] I-2. Low-frequency Non-separable Transform (LFNST)

[0116] The LFNST technique applies a secondary transform to the low-frequency region among the transform coefficients generated according to the primary transform of the transform unit (TU) during intra prediction. In terms of encoding, the LFNST technique applies the secondary transform to L low-frequency primary transform coefficients among the W×H primary transform coefficients, thereby generating K (where K ≤ L) secondary transform coefficients. Here, the size of the transform kernel of the LFNST is L×K. That is, the LFNST technique expresses the L low-frequency primary transform coefficients among the W×H primary transform coefficients as a 1×L vector, and then applies the L×K transform kernel to generate a 1×K vector. Thereafter, the LFNST technique expresses the 1×K vector as a two-dimensional array in the low-frequency region for subsequent processes such as quantization.

[0117] Compared to the first-order transformation that applies separate transformation kernels in the horizontal and vertical directions, the LFNST technique performs a non-separable transform that transforms a one-dimensional vector.

[0118] Meanwhile, the type of transformation kernel can be determined based on the intra prediction mode of the current TU, the size of the TU, and the LFNST index (lfnst_idx). For example, in VVC, a set of transformation kernels can be determined based on the intra prediction mode (IntraPredMode) of the current TU, as shown in Table 3.

[0119]

[0120] Here, the intra prediction mode (IntraPredMode) follows the example of Fig. 3b. Additionally, lfnstTrSetIdx is an index indicating a kernel set. In Table 3, IntraPredMode values ​​of 81, 82, and 83 indicate CCLM (Cross-component Linear Model) prediction modes.

[0121] For each kernel set (lfnstTrSetIdx), two types of kernels are defined. Which kernel is selected among the two types of kernels can be indicated by the LFNST index. If the LFNST index is 0, it means that LFNST is not performed, and if the LFNST index is 1 or 2, a different LFNST kernel within the same kernel set is applied. Since there is one more kernel set depending on the size of the TU, there are a total of 4×2×2 = 16 transformation kernels. The kernel sizes of LFNST are defined as 16×16 and 16×48. In addition, the kernel size can be adjusted as shown in Table 4 depending on the size of the TU.

[0122]

[0123] In ECM, a set of transformation kernels can be defined depending on the block shape and intra prediction mode. For example, by utilizing the symmetry property of square blocks, a set of 35 transformation kernels is defined for a square block depending on the intra prediction mode.

[0124] Meanwhile, when MIP (Matrix-weighted Intra Prediction) prediction is performed on the current TU in VVC, the image decoding device maps the intra prediction mode of the current TU to the Planar mode and then determines the transformation kernel according to the mapped prediction mode. The MIP technology includes MIP boundary downsampling, Matrix-Vector multiplication, and MIP prediction upsampling processes. 'MIP boundary downsampling' refers to the process of downsampling a specific number of pixels among the boundary pixels of the current block. 'Matrix-Vector multiplication' refers to the process of generating a reduced prediction block by multiplying the downsampled pixels (i.e., 'vector') by a preset matrix. 'MIP prediction upsampling' refers to the process of generating a final prediction block by upsampling the reduced prediction block.

[0125] In addition, when MIP prediction is performed in the next-generation technology, ECM (Enhanced Compression Model), the video decoding device obtains a directional prediction mode by applying DIMD (Decoder-side Intra Mode Derivation) to the MIP-predicted block, i.e., the output of the 'Matrix-Vector Product'. The video decoding device maps the intra prediction mode of the current TU to the obtained directional prediction mode, and then determines the transformation kernel according to the mapped prediction mode. The DIMD technology calculates the gradient of each sample for adjacent samples of the current block, generates a HoG (Histogram of Gradient) from the calculated gradients, and derives a prediction mode for intra prediction of the current block according to the generated HoG.

[0126] Meanwhile, when the DCT2 / DCT2 transform kernel is applied as a first transform to the intra-predicted TU in VVC, the LFNST technique can be applied as a second transform.

[0127] In ECM, when the block size of the TUs encoded according to intra prediction is small (e.g., 4×4, 4×8, 8×4, 4×16, 16×4, 8×8, 8×16, 16×8), the non-separable first-order transform technique can be applied. In addition, when the block size is large and the DCT2 / DCT2 transform kernel is applied to the block as the first-order transform, the LFNST technique can be applied.

[0128] I-3 Non-separable Primary Transform (NSPT)

[0129] The non-separable first-order transform technique performs a non-separable first-order transform using a pre-learned transform kernel instead of performing vertical and horizontal transforms on the residual signals of blocks predicted in the intra prediction mode.

[0130] NSPT technology uses non-separable primary transformation kernels of different sizes depending on the size of the residual block. For example, if the size of the transformation block is 4×4, a 16×16 kernel is applied to generate 4×4 transformation coefficients. As another example, if the size of the transformation block is 4×8, a 32×20 kernel is applied to generate 20 transformation coefficients. The generated transformation coefficients are arranged in the transformation block according to the promised scanning order. If the number of transformation coefficients generated after the transformation is less than the number of pixels in the transformation block, the remaining area where the transformation coefficients are not arranged is filled with 0.

[0131] For non-separable first-order transformations, transformation kernels can be defined based on the block shape, intra prediction mode, and NSPT index (nspt_idx). For example, by leveraging the symmetry of square blocks, there are 35 sets of transformation kernels for a square block, each with its own intra prediction mode. The NSPT index (i.e., the LFNST index) can be used to indicate one of the candidate kernels within the transformation kernel set.

[0132] A non-separable first-order transform can be applied to the luma component. Furthermore, if a non-separable first-order transform is applied, the second-order transform, i.e., LFNST, may not be performed.

[0133] Hereinafter, “prediction block”, “prediction unit block”, “decoding block”, and “decoding target block” may be used interchangeably.

[0134] Hereinafter, “luma component block” and “luma block” may be used interchangeably.

[0135] Hereinafter, “corresponding luma block”, “corresponding position luma block”, “corresponding luma area”, and “corresponding position luma area” may be used interchangeably.

[0136] Hereinafter, “chroma component block” and “chroma block” may be used interchangeably.

[0137] The following embodiments are described with a focus on a video decoding device, but can be implemented in the same or similar manner in a video encoding device. Alternatively, the following embodiments are described with a focus on the decoder side of a video decoding device, but can also be implemented in the same or similar manner in the decoder side of a video encoding device.

[0138] II. Embodiments according to the present disclosure

[0139] FIG. 6 is a block diagram illustrating in detail a portion of an image decoding device according to one embodiment of the present disclosure.

[0140] The video decoding device according to the present embodiment determines prediction and transformation units, and performs prediction and inverse transformation on the current block corresponding to the determined unit using the determined prediction technique and prediction mode, thereby finally generating a restoration block of the current block. The example illustrated in FIG. 6 may be performed by the inverse transformation unit (530), the prediction unit (540), and the adder (550) of the video decoding device. Meanwhile, the same operations as the example illustrated in FIG. 6 may be performed by the inverse transformation unit (165), the picture division unit (110), the prediction unit (120), and the adder (170) of the video encoding device. At this time, the video decoding device uses encoding information parsed from the bitstream, but the video encoding device may use encoding information set from a higher level in terms of minimizing rate distortion. Hereinafter, for convenience, the present embodiment will be described with reference to the video decoding device.

[0141] As shown in the example of FIG. 5, the prediction unit (540) includes an intra prediction unit (542) and an inter prediction unit (544) depending on the prediction technology, but as shown in FIG. 6, the prediction unit (540) may include all or part of the prediction unit determination unit (602), the prediction technology determination unit (604), the prediction mode determination unit (606), and the prediction execution unit (608).

[0142] The prediction unit determination unit (602) determines a prediction unit (PU). The prediction technique determination unit (604) determines a prediction technique (e.g., intra prediction, inter prediction, IBC (Intra Block Copy) mode, palette mode, a technique that mixes intra and inter prediction, etc.) for the prediction unit. The prediction mode determination unit (606) determines a detailed prediction mode for the prediction technique. The prediction execution unit (608) generates a prediction block of the current block according to the determined prediction mode.

[0143] The inverse transform unit (530) includes all or part of the inverse transform unit determination unit (610), the inverse transform kernel determination unit (612), and the inverse transform execution unit (614). The inverse transform unit determination unit (610) determines a transformation unit for the inverse quantization signals (i.e., inverse quantization transform coefficients) of the current block. The inverse transform kernel determination unit (612) determines an inverse transform kernel, and the inverse transform execution unit (614) inversely transforms the transformation unit expressed by the inverse quantization transform coefficients, thereby generating residual samples.

[0144] Hereinafter, the transform unit (TU) on the encoding side can be used interchangeably with the transform block. The inverse transform unit and inverse transform block on the decoding side correspond to the TU and transform block, respectively. Therefore, the inverse transform unit and inverse transform block can be used interchangeably with the TU and transform block.

[0145] A transform unit is a unit that determines whether to perform an inverse transform with respect to transform coefficients and represents a unit in which information about the inverse transform is transmitted. An image decoding device determines a kernel to be applied to a transform unit and performs an inverse transform of transform coefficients based on the determined kernel. At least one kernel may be determined for one transform unit. According to an embodiment, an inverse transform of N orders may be applied, and the sizes of the transform unit and the inverse transform kernel in each order may not be the same. For example, when an inverse transform of N orders is applied to a current transform unit block (hereinafter, transform block or current transform block), the sizes of the kernels used for the inverse transform of each order may not be the same. That is, the image decoding device may apply an inverse transform to some of the input transform coefficients.

[0146] An adder (550) adds a prediction block and residual samples to generate a restoration block. The restoration block is stored in memory and can be used to predict other blocks.

[0147] If the color format of the input video is a YUV format (such as YUV420, YUV411, YUV422, YUV444), the video decoding device can perform prediction and restoration of the chroma component after performing prediction and restoration of the luma component. That is, the luma component and the chroma component can be sequentially restored by the components illustrated in Fig. 6. Meanwhile, if the color format of the input video is RGB, the video encoding device can perform color format conversion from RGB to YUV and then encode the converted video. Here, in the case of the YUV format, the color format represents the correspondence between the pixels of the luma component and the pixels of the chroma component.

[0148] The prediction unit determination unit (602) determines the size and shape of the prediction target block, and may utilize all direct or indirect information transmitted from the video encoding device. The prediction unit determination unit (602) may utilize direct information related to the size and shape of the current block, and may utilize information that may influence the determination of the size and shape of the current block, such as the number of divisions, depth, shape of division, direction of division, size information related to the minimum division block, and division information / prediction mode of the decoded neighboring blocks.

[0149] The prediction unit determined by the prediction unit determination unit (602) may be a current block, one of the sub-blocks into which the current block is divided, a set of pixels, or a single pixel. The prediction unit may include size information and shape information for performing prediction of chroma components and luma components.

[0150] The prediction unit can be determined dependently or independently for the chroma component and the luma component. Dependent determination means that the prediction unit of the luma component or chroma components is not determined for each component, but rather, when the prediction unit of one component is determined, the units of the other components or components are determined with a corresponding size and shape. In this case, one component may correspond to one or more of the luma component and the chroma component. That is, the luma component may be determined based on information of the chroma components. For example, the prediction unit of the chroma component may have a size corresponding to the prediction unit of the luma component depending on the color format. In the case of dependent determination, information about the prediction unit of the other component corresponding to one component, i.e., the dependently determined component, may be omitted. Independent determination means that the prediction units of the luma component and the chroma component are determined separately. In the case of independent determination, information about the prediction unit of each component may be signaled separately.

[0151] The prediction technique determination unit (604) determines a prediction technique for each prediction unit. As described above, the prediction technique may be one of inter prediction, intra prediction, IBC mode, palette mode, or a technique combining intra and inter prediction. In this case, the prediction technique for the chroma component may be determined in the same manner as the prediction technique for the corresponding luma component, without separate signaling or parsing of information. In some embodiments, a technique combining intra and inter prediction may be included in inter prediction.

[0152] For example, if the prediction technique of the current block is not intra prediction, the video decoding device parses 1-bit flag information. For example, if the parsed flag indicates a skip mode, the video decoding device determines the prediction mode of the current block to be a merge mode of inter prediction or an IBC merge mode. In the skip mode, the video decoding device can use the prediction signals as restoration signals without performing an inverse transformation process (i.e., without parsing the residual signals). Here, skip may be a method of not transmitting motion information (e.g., a motion vector, a reference picture, a reference picture list, etc.) or transmitting motion information using only at least one piece of syntax information. Additionally, skip may be a method of not transmitting a residual signal of the current block.

[0153] On the other hand, if the parsed flag does not indicate a Skip mode for the current block, the prediction technique determination unit (604) can parse a series of 1-bit flags to determine the prediction technique of the current block as one of techniques such as inter prediction, intra prediction, IBC mode, palette mode, etc.

[0154] For example, if Skip is not applied to the current block and the prediction technique is determined to be Inter-Prediction or IBC mode, the video decoding device parses a 1-bit flag. Depending on the parsed flag, the prediction mode of the current block can be determined as either General Merge mode or Advanced Motion Vector Prediction (AMVP) mode.

[0155] The prediction mode determination unit (606) determines the detailed prediction mode of the current prediction unit block (hereinafter, used interchangeably with the current block) in relation to the prediction technology.

[0156] For example, if the prediction technology of the current block is inter prediction, the prediction mode determining unit (606) may determine the general merge mode or AMVP mode as the prediction mode of the current block. In the general merge mode or AMVP mode, the image decoding device generates prediction blocks according to one or more motion compensations based on parsed motion information, and weights and combines the generated multiple prediction blocks to generate final prediction signals of the current block. At this time, one or more of the prediction blocks may include a signal of a decoded area within a frame including the current block.

[0157] As another example, if the prediction technique for the current block is inter-prediction and intra-predicted samples are used for the final prediction block of the current block, the surrounding reconstructed region of the current block can be defined as a template, and an intra-prediction mode can be derived using this template. The template can also include regions not adjacent to the current block. The final prediction block of the current block can then be generated using the derived intra-prediction mode.

[0158] As another example, if the prediction technology of the current block is inter prediction, the prediction mode determining unit (606) may determine a geometric partitioning-based prediction mode (hereinafter, geometric partitioning mode (GPM)) as the prediction mode of the current block. In GPM, the image decoding device divides the current block into two or more sub-regions according to geometric partitioning, generates prediction blocks according to one or more motion compensations based on the motion information and prediction mode information of the parsed current block, and weights and combines the generated plurality of prediction blocks to generate final prediction signals of the current block. According to an embodiment, if inter prediction is used and the geometric partitioning mode is determined, at least one block among the sub-blocks in the current block may be predicted according to inter prediction.

[0159] Meanwhile, if the prediction technique of the current block is intra prediction, the prediction mode of the current block may be a mode that generates a prediction block of the current block based on at least one of a directional prediction mode, a planar mode (Horizontal Planar, Vertical Planar, or Regular Planar), a DC mode, an EIP (Extrapolation intra prediction) prediction mode, a matrix-based prediction mode (for example, MIP), or a prediction mode based on correlation between components (for example, CCLM (Cross Component Linear Model), CCCM (Convolutional Cross Component Model), GLM (Gradient Linear Model), etc.).

[0160] For example, if the prediction technology of the current block is intra prediction, the prediction mode of the current block may be a matrix-based intra prediction mode (for example, MIP (Matrix-based Intra Prediction)). The MIP mode may signal / parse and / or derive an index of a matrix based on a predefined matrix according to an agreement between an image encoding device and an image decoding device, or may signal / parse and / or derive a matrix and generate a prediction block of the current block based on the matrix.

[0161] As another example, if the prediction technique for the current block is intra prediction, the prediction mode for the current block may be intra-template matching prediction (IntraTMP). IntraTMP mode defines a restored area surrounding the current block as a template, and performs template matching on the restored area surrounding the current block to generate a predicted block. The template may also include areas not adjacent to the current block.

[0162] As another example, if the prediction technique of the current block is intra prediction, the prediction mode of the current block may be an intra geometric segmentation-based prediction mode. The intra geometric segmentation-based prediction mode may divide the current block into one or more sub-regions according to geometric segmentation, generate a prediction block of each region using intra prediction modes including different directional prediction modes, Planar mode, DC mode, etc., and generate a prediction block of the current block by weighting each prediction block. According to an embodiment, if the prediction technique is intra prediction and the geometric segmentation-based prediction mode is determined, at least one sub-block among all sub-blocks in the current block may be predicted according to intra prediction.

[0163] As another example, if the current block is a chroma block and the prediction technique of the current block is intra prediction, the current block can be predicted according to DM (Direct Mode). DM mode can perform prediction of the current chroma block based on a prediction method applied to a luma block corresponding to the current chroma block, or a prediction method predefined between a video encoding device and a video decoding device.

[0164] As another example, the relationship between the surrounding restored chroma samples of the current chroma component and the surrounding restored luma samples of the luma region at the location corresponding to the current chroma block may be calculated using a linear and / or nonlinear model, and a prediction block of the current chroma block may be generated based on one or more of the calculated models.

[0165] As another example, there may be various methods for deriving the intra prediction mode of the current block. Among the multiple methods, one or more may be used based on the signaling / parsing of flags and / or indices.

[0166] Meanwhile, if the prediction technology of the current block is IBC prediction, a prediction block can be obtained from a previously restored area within a frame including the current block using one or more block vectors, and a final prediction block can be generated based on the prediction block. The video encoding device can signal information of the block vector, and the video decoding device can parse information of the block vector. For example, the video decoding device can construct a block vector candidate list according to a position and search order defined according to an agreement between the video encoding device and the video decoding device, and parse information such as an index. The video decoding device can obtain final block vector information by correcting the initial block vector information obtained based on the parsed information using a method such as template matching.

[0167] For example, if the prediction technique of the current block is IBC prediction, the prediction mode of the current block may be an IBC geometric partitioning-based prediction mode (hereinafter, IBC geometric partitioning mode). The IBC geometric partitioning mode may divide the current block into one or more sub-regions according to the geometric partitioning, generate a prediction block for each region using a different block vector, and weight and combine the prediction blocks to generate a final prediction block of the current block. According to an embodiment, if the current block is IBC prediction and the geometric partitioning mode is determined, at least one of all sub-blocks within the current block may be predicted according to the IBC prediction.

[0168] As another example, if the current block is a chroma block and the prediction technology of the current block is IBC prediction, and the corresponding luma block is restored during the process of constructing a block vector candidate list or obtaining a block vector, the block vector information of the luma block at the corresponding position can be used. For example, if the block division structures of the luma component and the chroma component are the same, the block vector information of the corresponding luma block can be scaled according to a color format to generate information, and the scaled information can be used as the block vector and / or block vector candidate of the current chroma block. On the other hand, if the block division structures of the luma component and the chroma component are different, one or more block vectors can be acquired according to a predefined position and order within the corresponding luma region. The acquired block vector can be scaled according to a color format to generate information, and the scaled information can be used as the block vector and / or block vector candidate of the current chroma block.

[0169] Meanwhile, if the prediction technology of the current block is a mixed technology of intra prediction and inter prediction, the surrounding restoration area of ​​the current block may be defined as a template, and an intra prediction mode may be derived using information of some or all pixels of the template, or an intra prediction block may be generated based on template matching. The prediction block of the current block may be derived according to the derived intra prediction mode, or the prediction block may be generated based on block vector information signaled from a video encoding device. The final prediction block may be generated by mixing the prediction block / intra prediction block, or inter prediction block generated based on template matching and / or block vector, according to a method such as weighted summation.

[0170] A template may include both adjacent and non-adjacent regions to the current block. The non-adjacent region may be an region within a certain distance of pixel lines from the current block. When a non-adjacent region is used as a template, information on whether it is used and / or the distance may be transmitted from the video encoding device to the video decoding device. For example, the distance information may be defined according to an agreement between the video encoding device and the video decoding device, and the transmission of the information may be omitted. If defined according to an agreement, the value may be fixed to a specific constant or may be variably determined based on the horizontal and vertical pixel lengths of the prediction unit, the block width, the aspect ratio, etc. Thereafter, the final prediction block of the current block may be generated using the derived intra prediction mode.

[0171] The prediction execution unit (608) generates a final prediction block of the current decryption block (hereinafter, used interchangeably with the current block) according to the determined prediction technology and prediction mode.

[0172] As an example, after prediction and restoration of a luma component block, prediction and restoration of a corresponding chroma component block can be performed. Here, a block can be a coding unit (CU), a coding tree unit (CTU), a set of one or more CUs, and / or a set of one or more CTUs.

[0173] As an example, the prediction performing unit (608) performs prediction according to the prediction mode determined as described above to generate a prediction block of the current block, and the adder (550) adds the prediction block of the current block and residual samples (i.e., residual block) to generate a restoration block.

[0174] In relation to the inverse transformation, the entropy decoding unit (510) decodes the transform coefficients. If a secondary transformation is applied, the entropy decoding unit (510) decodes the quantized secondary transform coefficients. If a secondary transformation is not applied, the entropy decoding unit (510) decodes the quantized primary transform coefficients. The entropy decoding unit (510) parses information such as the quantization method and quantization parameter information.

[0175] The inverse quantization unit (520) inversely quantizes the decoded quantized transform coefficients based on information such as the quantization method and quantization parameter information to generate inverse quantized transform coefficients.

[0176] The inverse transform unit (530) generates residual samples by inversely transforming the TU expressed as inverse quantization transform coefficients. As shown in FIG. 6, the inverse transform unit (530) may include an inverse transform unit determination unit (610), an inverse transform kernel determination unit (612), and an inverse transform execution unit (614). Additionally, the inverse transform unit (530) may include a prediction signal correction unit (609).

[0177] As an example, the inverse transformation unit determination unit (610) may determine a single TU or a sub-block obtained by dividing a single TU into multiple sub-blocks as the target of inverse transformation. For example, the TU may be the entire current block that is the target of prediction, or a portion of the current block (e.g., a sub-region or sub-block).

[0178] The prediction signal correction unit (609) can perform correction of prediction signals within the determined inverse transform unit for the determined inverse transform unit. The correction of the prediction signals can be applied only to the inverse transform unit of a specific component (e.g., applied to a luma component, applied to a chroma component, etc.). The correction of the prediction signals can be applied to the predicted inverse transform unit according to a specific prediction technique (e.g., applied to an inter prediction technique, applied to inter prediction and IBC prediction, applied to intra prediction, etc.). For example, when applied to a chroma component block (hereinafter, used interchangeably with a chroma block), correction of the prediction signals can be applied when a non-zero residual value exists with respect to a corresponding position luma block (hereinafter, used interchangeably with a corresponding luma block).

[0179] As an example, whether to compensate for prediction signals may be indicated for the current inverse transform unit based on the signaling / parsing of flag / index information. When compensation of prediction signals is applied to chroma components, a single flag / index may be signaled / parsed to indicate whether compensation is performed for the Cb and Cr components. Alternatively, flags / indexes indicating whether compensation is performed for each of the Cb and Cr components may be signaled / parsed.

[0180] FIG. 7 is an exemplary diagram showing correction of prediction signals of chroma components according to one embodiment of the present disclosure.

[0181] As an example, when correction of prediction signals is applied to the current inverse transform unit, as shown in FIG. 7, the image decoding device can perform correction of prediction signals in the inverse transform unit of the chroma component. As in the example of FIG. 7, in order to correct the prediction signals, prediction signals and residual signals of the luma component at a position corresponding to the current chroma transform block can be used. M and P may represent weights of prediction signals related to the chroma component, respectively, and N and Q may represent weights of corrected prediction signals related to the chroma component, respectively. Depending on the embodiment, some processes may be omitted / added / changed in the block diagram shown in FIG. 7.

[0182] As an example, when prediction signals are corrected with respect to the inverse transform unit of the current chroma component (hereinafter, 'chroma component'), the image decoding device can utilize the correlation between the luma component and the chroma component based on the prediction signals of the corresponding position luma component and the restoration signal. The image decoding device can model the correlation between the prediction signals of the inverse transform unit of the chroma component and the prediction signals of the corresponding position luma component as in Equation 2, and calculate the filter coefficients c0 to c7 that define the correlation, for example, using the Gaussian elimination method.

[0183]

[0184] In Equation 2, L0 to L5 represent luma prediction signals at corresponding positions, C represents a prediction signal of the inverse transform unit of the chroma component, c6 represents a filter coefficient related to a nonlinear term, and c7 represents a filter coefficient related to bias B.

[0185] In some embodiments, depending on the color format of the input video, the positions of each sample among the prediction signals of the inverse transform unit of the chroma component and the positions of the samples within the corresponding luma prediction block may be different. Fig. 8 shows the positions of the samples of the chroma component and the positions of the corresponding luma samples. In the example of Fig. 8, the example of (a) may be applied in the case of the YUV4:2:0 format, the example of (b) may be applied in the case of the YUV4:2:2 format, and the example of (c) may be applied in the case of the YUV4:4:4 format. With respect to the cases illustrated in Fig. 8, filter coefficients may be derived using Equation 2. Depending on the color format of the input video, among L0 to L5 of Equation 2, the sample values ​​within the luma block that do not correspond may be set to 0. For example, in the case of the YUV4:2:2 format, L3 = L4 = L5 = 0 may be applied.

[0186] As an example, after deriving the filter coefficients as described above, the image decoding device can perform correction of the prediction signals by applying the filter coefficients to the restored luma signals at the corresponding positions, as in Equation 3. According to the correction, the image decoding device can generate a correction signal C' with respect to the inverse transform unit of the chroma component.

[0187]

[0188] In Equation 3, c0 to c7 represent filter coefficients derived from Equation 2 based on the correlation between the chroma prediction signal and the luma prediction signal at the corresponding position. With respect to the positions illustrated in FIG. 8 according to the color format of the input image, L0 to L5 represent luma prediction signals at the corresponding positions. After correcting the prediction signal of the inverse transform unit of the current chroma component, the image decoding device can weight-sum the prediction signal after correction and the prediction signal before correction to generate final prediction signals as in Equation 4 with respect to the inverse transform unit of the chroma component. At this time, the weights for the weighted sum may be different for the Cb component and the Cr component.

[0189]

[0190] In mathematical expression 4, n and u can be integers greater than or equal to 1. M and N are M+M = 2. n is an integer greater than or equal to 0, and P and Q are P+Q = 2 u It can be an integer greater than or equal to 0 that satisfies . Hereinafter, with respect to the weights of the prediction signals before correction and the weights of the prediction signals after correction, the case where M and P have the same value and N and Q have the same value is described. If M and P have different values ​​and N and Q have different values, it indicates that the weighted sum can be performed separately for the Cb and Cr components.

[0191] As an example, with respect to weights M and N, information about the values ​​or values ​​may be signaled / parsed. Alternatively, information about a weight table defined according to an agreement between an image encoding device and an image decoding device (e.g., index information indicating a table, index information indicating an element within the table, etc.) may be signaled / parsed.

[0192] For example, if there is no residual signal of the corresponding luma block, the weights may be implicitly determined as N=0, M=1. For example, if cbf (coded block flag, indicating luma cbf or root cbf) is 0 with respect to the residual signal of the corresponding luma block, it may indicate that there is no residual signal. If there is no residual signal, the flag / index indicating whether to adaptively compensate the inter-component prediction signal in inter prediction may not be signaled / parsed.

[0193] As an example, the image decoding device can implicitly determine the weights depending on whether the prediction signals of the surrounding blocks are corrected with respect to the inverse transform unit of the chroma component.

[0194] For example, the positions of the surrounding blocks with respect to the inverse transform unit of the chroma component may be determined as in the example of FIG. 9 according to an agreement between the image encoding device and the image decoding device. In addition to the example of FIG. 9, non-adjacent surrounding blocks may also be utilized. A weight may be implicitly determined according to the number of blocks in which correction of prediction signals is performed among the surrounding blocks with respect to the current inverse transform unit of the chroma component. For example, if the prediction signals are corrected in Y surrounding blocks among T blocks, (M:N)=(1:7) may be implicitly determined. The weight of 1:7 described above is one of various embodiments, and indicates that other weights may be determined. At this time, depending on the information of the residual signal of the corresponding luma block (e.g., whether the residual signal exists, etc.), the weight may be determined differently depending on whether the prediction signals of the surrounding blocks are corrected. Among the T blocks, if there is no block in which correction of the prediction signal has been performed, the weight may be implicitly determined based on information of the residual signal of the corresponding luma block (e.g., whether or not the residual signal exists). The above example indicates that the weight N may be set to a larger value as the number of blocks in the surrounding blocks of the inverse transform unit of the chroma component in which correction of the prediction signal has been applied increases.

[0195] As another example, a merge candidate list may be constructed based on whether prediction signals of surrounding blocks are corrected and the weights used in relation to the inverse transform unit of the chroma component. The merge candidate list may be constructed based on a preset order according to an agreement between an image encoding device and an image decoding device. Information added to the merge candidate list may be as follows. For example, only information of blocks for which prediction signals have been corrected may be added to the list. In addition, at least one of information such as filter coefficients (c0 to c7), weights (M, N), etc. may be added to the list. When information of surrounding blocks is inherited and applied to the current block, a merge index may be signaled / parsed. At this time, both the filter coefficients and weights may be inherited. Alternatively, only the filter coefficients or weights may be inherited. When the filter coefficients are inherited, the weights of the filters of surrounding blocks may be applied as is to the current transform block. The video decoding device can set the inherited weights as initial values, and then correct the initial values ​​based on the correlation between the prediction signals of the inverse transform unit of the chroma component and the prediction signals of the corresponding position luma component, and use the corrected values ​​for the weighted sum.

[0196] As another example, with respect to the inverse transform unit of a chroma component, the weights may be implicitly determined according to the prediction technique / prediction mode of the corresponding luma block. If the block partition structure is a 'single tree', the block partition structure of the chroma component is the same as the block partition structure of the luma component. If the prediction technique of the luma block at the corresponding position is an inter prediction technique, an IBC prediction technique, or an intra prediction technique, the weights may be determined differently. For example, in the case of an intra prediction technique, the weights may be implicitly determined as (M:N)=(3:1), in the case of an inter prediction technique, (M:N)=(1:3), and in the case of an IBC prediction technique, (M:N)=(1:3).

[0197] As another example, when the block partition structure is a 'dual tree', the block partition structure of the chroma component can be determined separately from the block partition structure of the luma component. At this time, the partition structures of the luma block and the chroma block can be the same up to a specific partition depth. Information about the specific partition depth can be a fixed value according to an agreement between the video encoding device and the video decoding device, or can be signaled / parsed by specific units such as CTU, slice, etc. As in the example of Fig. 10, the video decoding device can check the prediction technology and / or prediction mode of blocks A, B, C, D, and E of the corresponding luma blocks, and determine the weights according to the prediction technology / prediction mode of the blocks. For example, among the five locations, if the number of blocks to which intra prediction technology is applied is greater, the weights may be implicitly determined as (M:N)=(3:1), and if the number of blocks to which inter prediction technology and / or IBC prediction technology is applied is greater, the weights may be implicitly determined as (M:N)=(1:3).

[0198] For example, as one of the factors for determining the weight, the quantization parameter (QP) of the corresponding luma block with respect to the inverse transform unit of the chroma component can be utilized. If the residual signal of the corresponding luma block exists and is inversely quantized using a high QP, the value of the weight N can be determined to be larger. Here, the high QP can indicate a case where the QP of the corresponding position luma block is larger than a certain threshold. If the partition structure is a single tree, the QP of the corresponding luma block can be identified. If the partition structure is a dual tree, the high QP can be identified by checking the average QP or the maximum QP of the corresponding position luma block and comparing the QP with a certain threshold. The high QP can indicate a case where the difference value between the QP of the transform unit block of the chroma component and the QP of the corresponding position luma block is larger than a certain threshold. At this time, only the case where the QP of the corresponding position luma block is higher can be considered. The QP of the corresponding position luma block can be determined by one of the examples described above.

[0199] For example, when there is a residual signal of a corresponding luma block with respect to a transform unit of a chroma component, the image decoding device can implicitly determine a weight depending on how the inverse transform is performed. The weight may be determined differently depending on whether a non-separable inverse transform is performed or a separable inverse transform is performed. For example, when a non-separable first inverse transform is performed on the corresponding position luma block, (M:N)=(7:1) may be implicitly determined. When a non-separable second inverse transform is performed, (M:N)=(3:1) may be determined, and when a non-separable inverse transform is not performed, (M:N)=(1:3) may be implicitly determined. In the above examples, each weight is one embodiment, and different weights may be implicitly determined depending on the above-mentioned conditions.

[0200] As an example, with respect to the transform unit of the chroma component, the image decoding device can implicitly determine the weight based on the information of the residual signal of the corresponding luma block.

[0201] For example, the image decoding device can implicitly determine a weight according to the number of residual samples having a value of 0 among the residual samples in the corresponding luma block. If the number of residual samples having a value of 0 is more than half of the samples in the corresponding position luma block, (M:N)=(3:1) can be implicitly determined. With respect to the residual samples in the corresponding position luma block, if the variance value is higher than a certain threshold, (M:N)=(1:3) can be implicitly determined. If the maximum absolute value of the residual samples in the corresponding position luma block is higher than a certain threshold, (M:N)=(1:3) can be implicitly determined.

[0202] In the embodiments related to weight determination described above, the value of M:N represents one embodiment for each condition, and different weights may be implicitly determined based on the conditions described above. The image decoding device may determine the weights using at least one method among the embodiments described above. For example, two or more embodiments may be applied to a single transformation unit.

[0203] In the example of FIG. 6, the prediction signal correction unit (609) is included in the inverse transformation unit (530), but as another example, it may be included in the prediction unit (540) or the adder (550). When included in the prediction unit (540), the prediction signal correction unit (609) may correct the prediction signals based on the TU.

[0204] The inverse transform kernel determination unit (612) can determine a separable vertical and horizontal first-order inverse transform kernel and / or a non-separable second-order inverse transform kernel, or can determine a non-separable first-order inverse transform kernel. The inverse transform performing unit (614) can inverse transform the inverse quantized transform coefficients using the determined inverse transform kernel.

[0205] As an example, whether to perform a non-separable inverse transform can be determined based on the signaling / parsing of a flag or index. Here, whether to perform a non-separable inverse transform indicates whether to perform a non-separable first inverse transform or a non-separable second inverse transform. Alternatively, whether to perform a non-separable inverse transform can be implicitly determined based on the size of a current transform block. The current transform block represents a TU or a sub-block transform unit. The sub-block transform unit can be a transform unit into which a TU is divided or a transform unit corresponding to a sub-region of the current block.

[0206] FIG. 11 is an exemplary diagram showing a process for determining an inverse transform kernel according to one embodiment of the present disclosure.

[0207] The inverse transform kernel decision unit (612) can determine the type of inverse transform kernel of the current transform block according to the example of Fig. 11. The order illustrated in Fig. 11 may be changed, and some orders may be omitted.

[0208] For example, whether to perform a non-separable inverse transformation and whether to perform a non-separable first-order inverse transformation with respect to the current transformation block may be determined based on signaling / parsing of flags and / or indices. Alternatively, whether to perform a non-separable inverse transformation and whether to perform a non-separable first-order inverse transformation may be determined implicitly based on the size of the current inverse transformation unit.

[0209] FIG. 12 is an exemplary diagram showing a process for determining an inverse transform kernel according to another embodiment of the present disclosure.

[0210] As another example, the inverse transform kernel decision unit (612) can determine the type of inverse transform kernel of the current transform block according to the example of Fig. 12. The order illustrated in Fig. 12 may be changed, and some orders may be omitted.

[0211] As an example, whether to perform a non-separable inverse transform with respect to the current transformation block may be determined based on signaling / parsing of flags and / or indices. In some embodiments, when a non-separable inverse transform is performed, whether to perform a non-separable first inverse transform or a non-separable second inverse transform may be determined based on the size of the block. For example, when the size of the block is N×4 or 4×N (16≥N≥4) or 8×N or N×8 (16≥N≥8), a non-separable first inverse transform may be performed on the block, and a non-separable second inverse transform may be performed on blocks of different sizes.

[0212] Below, we describe a method for determining a separable first-order inverse transform kernel.

[0213] For example, if a separable first inverse transform is performed on the current transform block, a table may be defined according to an agreement between an image encoding device and an image decoding device, and by signaling / parsing the index of the table, a vertical kernel and a horizontal kernel may be determined. For example, different tables may be configured according to the prediction combinations of sub-regions (e.g., inter / inter prediction, inter / intra prediction, IBC / intra prediction, intra / IntraTMP prediction, etc.). Here, a combination among inter prediction, intra prediction, IBC prediction, and IntraTMP prediction may be considered as the prediction combination.

[0214] As another example, if a non-separable second-order inverse transform is performed on the current transform block, an implicitly fixed kernel (e.g., DCT2, DCT2 as vertical and horizontal kernels) may be used as the separable first-order inverse transform kernel. The fixed kernel may be adaptively changed depending on the size / aspect ratio of the current transform block.

[0215] Below, we describe a method for determining a non-separable first-order inverse transform kernel.

[0216] As an example, depending on the size of the current transformation block, whether or not to perform an inseparable first-order inverse transformation can be implicitly determined.

[0217] As an example, when a non-separable first-order inverse transform is performed on the current transform block, the non-separable first-order inverse transform kernel can be determined based on the size of the current transform block and the prediction mode of each sub-region.

[0218] As another example, the non-separable first-order inverse transform can only be applied to blocks where all sub-regions are intra-predicted.

[0219] As another example, the video decoding device signals / parses an index and / or flag indicating a non-separable first-order inverse transform kernel with respect to the current transform block. The video decoding device can determine the inverse transform kernel indicated by the parsed index / flag as the non-separable first-order inverse transform kernel of the current transform block based on the size of the current transform block, the prediction mode of each sub-region of the current block, etc.

[0220] At this time, based on the prediction combination of the sub-regions of the current block (e.g., inter / inter prediction, inter / intra prediction, IBC / intra prediction, intra / IntraTMP prediction, etc.), the types of available inverse transform kernels can be configured differently according to the agreement between the video encoding device and the video decoding device. Here, as the prediction combination, a combination among inter prediction, intra prediction, IBC prediction, and IntraTMP prediction can be considered.

[0221] As another example, if the prediction mode of each sub-region of the current block is not included in the intra prediction (such as directional intra prediction), the image decoding device may derive at least one directionality in all or part of a region of a prediction block corresponding to the current transform block, and use an inseparable first-order inverse transform kernel corresponding to one of the at least one derived directionality. Alternatively, if the prediction mode of each sub-region of the current block is included in the intra prediction (such as directional intra prediction), the image decoding device may derive at least one directionality in all or part of a region of a prediction block corresponding to the current transform block, and use an inseparable first-order inverse transform kernel corresponding to one of the at least one derived directionality. For example, a directionality similar to the intra prediction mode of each sub-region of the current block among the derived directionality may be used. The image decoding device applies a Sobel filter to the region corresponding to the current transform block in the prediction block to calculate vertical / horizontal slope and scale values ​​for each preset unit. The image decoding device can construct a Histogram of Gradient (HoG) from vertical / horizontal slope and size values ​​for each preset unit, and derive directionality based on the HoG. Here, the Sobel filter represents an edge detection filter, and the preset unit can be, for example, a pixel or a group of pixels.

[0222] As another example, when there are N kinds of available non-separable first-order inverse kernels, with respect to the transform block in the current block to which the geometric partitioning mode is applied, the kinds of available non-separable first-order inverse kernels are K (K <N) 개일 수 있다. K 개 중, 사용할 커널의 정보(일 예시로, K개 중, 하나의 인덱스 정보)를 시그널링 / 파싱하여 1차 역변환에 사용할 커널이 결정될 수 있다.

[0223] As another example, with respect to the current transformation block, if an inseparable second-order inverse transform is used, the use of an inseparable first-order inverse transform is restricted. In some embodiments, if the inseparable first-order inverse transform index is parsed first, whether or not the inseparable second-order inverse transform is parsed may depend on the index value of the inseparable first-order inverse transform.

[0224] Below, we describe a method for determining a non-separable second-order inverse transform kernel.

[0225] As an example, depending on the size of the current transformation block, whether or not to perform an inseparable second-order inverse transformation can be implicitly determined.

[0226] As an example, when a non-separable second-order inverse transform is performed on the current transform block, the non-separable second-order inverse transform kernel can be determined based on the size of the current transform block and the prediction mode of each sub-region.

[0227] As another example, the non-separable second-order inverse transform can only be applied to blocks where all sub-regions are intra-predicted.

[0228] As another example, the video decoding device signals / parses an index and / or flag indicating a non-separable second-order inverse transform kernel with respect to the current transform block. The video decoding device can determine the inverse transform kernel indicated by the parsed index / flag as the non-separable second-order inverse transform kernel of the current transform block based on the size of the current transform block, the prediction mode of each sub-region of the current block, etc.

[0229] At this time, based on the prediction combination of the sub-regions of the current block (e.g., inter / inter prediction, inter / intra prediction, IBC / intra prediction, intra / IntraTMP prediction, etc.), the types of available inverse transform kernels can be configured differently according to the agreement between the video encoding device and the video decoding device. Here, as the prediction combination, a combination among inter prediction, intra prediction, IBC prediction, and IntraTMP prediction can be considered.

[0230] As another example, if the prediction mode of each sub-region of the current block is not included in the intra prediction (such as directional intra prediction), the video decoding device may derive at least one directionality in all or part of a region of a prediction block corresponding to the current transform block, and use an inseparable second-order inverse transform kernel corresponding to one of the at least one derived directionality. Alternatively, if the prediction mode of each sub-region of the current block is included in the intra prediction (such as directional intra prediction), the video decoding device may derive at least one directionality in all or part of a region of a prediction block corresponding to the current transform block, and use an inseparable second-order inverse transform kernel corresponding to one of the at least one derived directionality. For example, a directionality similar to the intra prediction mode of each sub-region of the current block among the derived directionality may be used. The video decoding device calculates vertical / horizontal slope and scale values ​​for each preset unit by applying a Sobel filter to a region corresponding to the current transform block in the prediction block. The image decoding device can construct an HoG from vertical / horizontal slope and size values ​​for each preset unit, and derive directionality based on the HoG. Here, the Sobel filter represents a boundary detection filter, and the preset unit can be, for example, a pixel or a pixel group.

[0231] As another example, when there are N kinds of available non-separable second-order inverse kernels, with respect to the transform block in the current block to which the geometric partitioning mode is applied, the kinds of available non-separable second-order inverse kernels are K (K <N) 개일 수 있다. K 개 중, 사용할 커널의 정보(일 예시로, K개 중, 하나의 인덱스 정보)를 시그널링 / 파싱하여 2차 역변환에 사용할 커널이 결정될 수 있다.

[0232] As another example, in relation to the current transform block, when a non-separable second inverse transform is performed, the first inverse transform may be performed using separable vertical and horizontal inverse transform kernels. As the kernel used for the first inverse transform, a fixed kernel (e.g., DCT2, DCT2 as a vertical and horizontal kernel) may be used according to an agreement between the image encoding device and the image decoding device based on the type of the second inverse transform kernel.

[0233] Hereinafter, a method for correcting prediction signals of chroma components is described using examples of FIGS. 13 and 14.

[0234] FIG. 13 is a flowchart illustrating a method by which a video encoding device encodes a current chroma block according to one embodiment of the present disclosure.

[0235] The video encoding device determines the inverse transform unit of the current chroma block (S1300).

[0236] The video encoding device obtains chroma prediction signals of an inverse transform unit and luma prediction signals of a corresponding luma block (S1302). The corresponding luma block may represent a luma region that is positionally corresponding to the inverse transform unit of the current chroma block.

[0237] An image encoding device can generate residual signals by subtracting prediction signals of the current block from signals of the current block. The image encoding device can apply transformation / quantization to the residual signals to generate quantized transform coefficients, and encode the quantized transform coefficients to generate a bitstream. At the decoder side, the image encoding device can restore the residual signals by applying inverse quantization / inverse transformation to the quantized transform coefficients.

[0238] A video encoding device can, on the decoder side, obtain chroma residual signals related to the inverse transform unit of the current chroma block and luma residual signals of the corresponding luma block. The video encoding device can generate luma restoration signals by adding the luma residual signals and luma prediction signals.

[0239] The video encoding device acquires a flag indicating correction of chroma prediction signals of the inverse transform unit (S1304). The video encoding device may acquire the aforementioned flag from a higher level. Alternatively, the video encoding device may determine the value of the aforementioned flag from the perspective of optimizing encoding efficiency.

[0240] Additionally, the video encoding device can encode the aforementioned flag.

[0241] The video encoding device checks the flag (S1306).

[0242] If the aforementioned flag indicates correction of chroma prediction signals (Yes in S1306), the video encoding device can perform the following steps.

[0243] The video encoding device obtains filter coefficients representing correlations between luma prediction signals and chroma prediction signals (S1308).

[0244] As an example, the video encoding device can calculate filter coefficients representing correlations based on luma prediction signals and chroma prediction signals.

[0245] As another example, a video encoding apparatus may generate a merge candidate list including candidate blocks for which correction of chroma prediction signals has been performed. The merge candidate list may include filter coefficients used for correction of chroma prediction signals of the candidate blocks as information of the candidate blocks for which correction of chroma prediction signals has been performed. The video encoding apparatus may determine a merge index and encode the merge index, for example, in terms of optimizing encoding efficiency. The video encoding apparatus may extract a candidate block in the merge candidate list using the merge index and inherit the filter coefficients of the candidate block.

[0246] The image encoding device applies filter coefficients to luma restoration signals of a corresponding luma block to generate chroma correction signals of an inverse transform unit (S1310).

[0247] The video encoding device obtains weights for weighting chroma prediction signals and chroma correction signals (S1312).

[0248] As an example, a video encoding device may determine an index indicating an element within a weight table, for example, in terms of optimizing encoding efficiency. The video encoding device may extract a weight from the table based on the index.

[0249] As another example, the merge candidate list may additionally include weights as information on candidate blocks for which correction of chroma prediction signals has been performed. The video encoding device may extract candidate blocks within the merge candidate list using the merge index and inherit the weights of the candidate blocks.

[0250] As another example, the video encoding device can implicitly determine a weight based on the number of blocks among the surrounding blocks associated with the inverse transform unit for which correction of chroma prediction signals has been performed.

[0251] As another example, the video encoding device can implicitly determine weights based on the block division structure of the current chroma block and the prediction technology of the corresponding luma block.

[0252] As another example, the video encoding device can implicitly determine the weights based on the magnitude of the quantization parameters of the corresponding luma block.

[0253] As another example, the video encoding device can implicitly determine the weights based on whether an inseparable first-order inverse transform or an inseparable second-order inverse transform is applied to the corresponding luma block with respect to the inverse transform unit.

[0254] The video encoding device weights and adds chroma prediction signals and chroma correction signals based on weights (S1314).

[0255] By weighting the chroma prediction signals and the chroma correction signals, the video encoding device can generate final chroma prediction signals of the inverse transform unit. The video encoding device can generate restoration signals with respect to the inverse transform unit by adding the chroma residual signals and the final chroma prediction signals.

[0256] If the aforementioned flag does not indicate correction of chroma prediction signals (No in S1306), the video encoding device may omit the process of correcting chroma prediction signals. The video encoding device may generate restoration signals in relation to the inverse transform unit by adding chroma residual signals and chroma prediction signals.

[0257] FIG. 14 is a flowchart illustrating a method by which a video decoding device restores a current chroma block according to one embodiment of the present disclosure.

[0258] The video decoding device determines the inverse transformation unit of the current chroma block (S1400).

[0259] The video decoding device obtains chroma prediction signals of an inverse transform unit and luma prediction signals of a corresponding luma block (S1402). The corresponding luma block may represent a luma region that is positionally corresponding to the inverse transform unit of the current chroma block.

[0260] An image decoding device can decode quantized transform coefficients from a bitstream. The image decoding device can restore residual signals by applying inverse quantization / inverse transformation to the quantized transform coefficients.

[0261] The video decoding device can obtain chroma residual signals and luma residual signals of a corresponding luma block in relation to the inverse transform unit of the current chroma block. The video decoding device can generate luma restoration signals by adding the luma residual signals and luma prediction signals.

[0262] The video decoding device decodes a flag indicating correction of chroma prediction signals of an inverse transform unit (S1404). The video decoding device can decode the aforementioned flag from a bitstream.

[0263] The video decoding device checks the flag (S1406).

[0264] If the aforementioned flag indicates correction of chroma prediction signals (Yes in S1406), the video decoding device may perform the following steps.

[0265] The video decoding device obtains filter coefficients representing correlations between luma prediction signals and chroma prediction signals (S1408).

[0266] As an example, the image decoding device can calculate filter coefficients representing correlations based on luma prediction signals and chroma prediction signals.

[0267] As another example, a video decoding device may generate a merge candidate list including candidate blocks for which correction of chroma prediction signals has been performed. The merge candidate list may include filter coefficients used for correction of chroma prediction signals of the candidate blocks, as information on the candidate blocks for which correction of chroma prediction signals has been performed. The video decoding device may decode a merge index from a bitstream. The video decoding device may extract a candidate block within the merge candidate list using the merge index and inherit the filter coefficients of the candidate block.

[0268] The image decoding device applies filter coefficients to luma restoration signals of a corresponding luma block to generate chroma correction signals of an inverse transform unit (S1410).

[0269] The video decoding device obtains weights for weighting chroma prediction signals and chroma correction signals (S1412).

[0270] As an example, a video decoding device can obtain an index indicating an element in a weight table from a bitstream. The video decoding device can extract a weight from the table based on the index.

[0271] As another example, the merge candidate list may additionally include weights as information about candidate blocks for which correction of chroma prediction signals has been performed. The video decoding device may extract candidate blocks within the merge candidate list using the merge index and inherit the weights of the candidate blocks.

[0272] As another example, the video decoding device can implicitly determine the weights based on the number of blocks among the surrounding blocks associated with the inverse transform unit for which correction of chroma prediction signals has been performed.

[0273] As another example, the video decoding device can implicitly determine weights based on the block division structure of the current chroma block and the prediction technology of the corresponding luma block.

[0274] As another example, the image decoding device can implicitly determine the weights based on the magnitude of the quantization parameters of the corresponding luma block.

[0275] As another example, the video decoding device can implicitly determine the weights based on whether a non-separable first-order inverse transform or a non-separable second-order inverse transform is applied to the corresponding luma block with respect to the inverse transform unit.

[0276] The video decoding device weights and adds chroma prediction signals and chroma correction signals based on weights (S1414).

[0277] By weighting the chroma prediction signals and the chroma correction signals, the video decoding device can generate final chroma prediction signals of the inverse transform unit. The video decoding device can generate restoration signals with respect to the inverse transform unit by adding the chroma residual signals and the final chroma prediction signals.

[0278] If the aforementioned flag does not indicate correction of chroma prediction signals (No in S1406), the video decoding device may omit the process of correcting chroma prediction signals. The video decoding device may generate restoration signals in relation to the inverse transform unit by adding chroma residual signals and chroma prediction signals.

[0279] Although the flowchart / timing diagram of this specification describes each process as being executed sequentially, this is merely an illustrative description of the technical idea of ​​one embodiment of the present disclosure. In other words, a person of ordinary skill in the art to which one embodiment of the present disclosure belongs may modify and apply various modifications and variations by changing the order described in the flowchart / timing diagram without departing from the essential characteristics of one embodiment of the present disclosure, or by executing one or more of the processes in parallel. Therefore, the flowchart / timing diagram is not limited to a chronological order.

[0280] It should be understood that the exemplary embodiments described above can be implemented in many different ways. The functions or methods described in one or more examples can be implemented in hardware, software, firmware, or any combination thereof. It should be understood that the functional components described herein are labeled as "units" to further emphasize their implementation independence.

[0281] Meanwhile, the various functions or methods described in this embodiment may also be implemented as instructions stored on a non-transitory storage medium that can be read and executed by one or more processors. Non-transitory storage media include, for example, all types of storage devices that store data in a form readable by a computer system. For example, non-transitory storage media include storage media such as erasable programmable read-only memory (EPROM), flash drives, optical drives, magnetic hard drives, and solid-state drives (SSDs).

[0282] The above description is merely an example of the technical idea of ​​the present embodiment, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical idea of ​​the present embodiment, but rather to explain it, and the scope of the technical idea of ​​the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be interpreted by the claims below, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of rights of the present embodiment.

[0283]

[0284]

[0285] CROSS-REFERENCE TO RELATED APPLICATION

[0286] This patent application claims priority to Korean patent application No. 10-2024-0053611, filed on April 22, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. In a method for restoring a current chroma block performed by a video decoding device, A step of determining an inverse transformation unit of the current chroma block; A step of obtaining chroma prediction signals of the above inverse transformation unit and luma prediction signals of a corresponding luma block, wherein the corresponding luma block is a luma area positionally corresponding to the inverse transformation unit of the current chroma block; A step of obtaining filter coefficients representing a correlation between the luma prediction signals and the chroma prediction signals; A step of applying the filter coefficients to the luma restoration signals of the corresponding luma block to generate chroma correction signals of the inverse transformation unit; Step of obtaining weights; and A step of generating final chroma prediction signals of the inverse transform unit by weighting the chroma prediction signals and the chroma correction signals based on the weights. A method comprising:

2. In paragraph 1, A step of decoding a flag indicating correction of chroma prediction signals of the above inverse transformation unit; and Steps to check the above flags Including more, A method for performing a step of calculating the filter coefficients when the flag indicates correction of the chroma prediction signals.

3. In paragraph 1, The step of obtaining the above filter coefficients is: A method for calculating filter coefficients representing the correlation based on the luma prediction signals and the chroma prediction signals.

4. In paragraph 1, The step of obtaining the above filter coefficients is: A step of generating a merge candidate list, wherein the merge candidate list includes filter coefficients used for correction of chroma prediction signals of a candidate block as information of the candidate block for which correction of chroma prediction signals has been performed; A step of decrypting the merge index; and A step of extracting a candidate block in the merge candidate list using the merge index and inheriting the filter coefficients of the candidate block. A method comprising:

5. In paragraph 1, The step of obtaining the above weight is: A step of decrypting an index pointing to an element within a table; and A step of extracting the weight from the table based on the index. A method comprising:

6. In paragraph 1, The step of obtaining the above weight is: A method for implicitly determining the weight according to the number of blocks among the surrounding blocks related to the above inverse transformation unit in which correction of chroma prediction signals has been performed.

7. In paragraph 1, The step of obtaining the above weight is: A method for implicitly determining the weights according to the block division structure of the current chroma block and the prediction technology of the corresponding luma block.

8. In paragraph 1, The step of obtaining the above weight is: A method for implicitly determining the weight based on the size of the quantization parameter of the corresponding luma block.

9. In paragraph 1, The step of obtaining the above weight is: A method for implicitly determining the weights based on whether an inseparable inverse transform is applied to the corresponding luma block with respect to the inverse transform unit.

10. In a method for encoding a current block performed by a video encoding device, A step of determining an inverse transformation unit of the current chroma block; A step of obtaining chroma prediction signals of the above inverse transformation unit and luma prediction signals of a corresponding luma block, wherein the corresponding luma block is a luma area positionally corresponding to the inverse transformation unit of the current chroma block; A step of obtaining filter coefficients representing a correlation between the luma prediction signals and the chroma prediction signals; A step of applying the filter coefficients to the luma restoration signals of the corresponding luma block to generate chroma correction signals of the inverse transformation unit; Step of obtaining weights; and A step of generating final chroma prediction signals of the inverse transform unit by weighting the chroma prediction signals and the chroma correction signals based on the weights. How to include.

11. In paragraph 10, A step of obtaining a flag indicating correction of chroma prediction signals of the above inverse transformation unit; a step of encoding the above flag; and Steps to check the above flags Including more, A method for performing a step of calculating the filter coefficients when the flag indicates correction of the chroma prediction signals.

12. In paragraph 10, The step of obtaining the above filter coefficients is: A method for calculating filter coefficients representing the correlation based on the luma prediction signals and the chroma prediction signals.

13. In paragraph 10, The step of obtaining the above filter coefficients is: A step of generating a merge candidate list, wherein the merge candidate list includes filter coefficients used for correction of chroma prediction signals of a candidate block as information of the candidate block for which correction of chroma prediction signals has been performed; Step for determining merge index; a step of encoding the above merge index; and A step of extracting a candidate block in the merge candidate list using the merge index and inheriting the filter coefficients of the candidate block. A method comprising:

14. In paragraph 10, The step of obtaining the above weight is: A step of determining an index indicating an element within a table; and A step of extracting the weight from the table based on the index. A method comprising:

15. In paragraph 10, The step of obtaining the above weight is: A method for implicitly determining the weights based on whether an inseparable inverse transform is applied to the corresponding luma block with respect to the inverse transform unit.

16. In a method for providing video data to a video decoding device, A step of encoding the above video data into a bitstream; and A step of transmitting the above bitstream to the image decoding device Including, The step of encoding the above video data is: A step of determining the inverse transformation unit of the current chroma block; A step of obtaining chroma prediction signals of the above inverse transformation unit and luma prediction signals of a corresponding luma block, wherein the corresponding luma block is a luma area positionally corresponding to the inverse transformation unit of the current chroma block; A step of obtaining filter coefficients representing a correlation between the luma prediction signals and the chroma prediction signals; A step of applying the filter coefficients to the luma restoration signals of the corresponding luma block to generate chroma correction signals of the inverse transformation unit; Step of obtaining weights; and A step of generating final chroma prediction signals of the inverse transform unit by weighting the chroma prediction signals and the chroma correction signals based on the weights. A method comprising:

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