Method and device for video coding using intra template matching prediction

Abstract

The present embodiment provides a method and device for video coding using intra template matching prediction. In the present embodiment, an image decoding device constructs block vector candidates of a current block on the basis of a template cost indicating a difference between a current template of the current block and a reference template within a predefined reference region. Here, the block vector candidate indicates a reference block corresponding to the reference template, the current template includes pre-reconstructed neighboring pixels of the current block, and the reference template includes neighboring pixels of the reference block. The image decoding device constructs a candidate list for applying a fusion mode, on the basis of the block vector candidates or template costs of the block vector candidates. Here, the candidate list includes new block vector candidates for applying the fusion mode. The image decoding device calculates weights for the new block vector candidates, and predicts the current block on the basis of the weights and the new block vector candidates.

Description

Method and apparatus for video coding using intra-template matching prediction

[0001] The present disclosure relates to an image encoding / decoding method, an apparatus, and a recording medium for storing a bitstream, and more specifically, to an improved method for Intra Template Matching Prediction (IntraTMP).

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

[0003] Because video data contains a large amount of data compared to audio or still image data, storing or transmitting it as is without compression processing requires significant hardware resources, including memory.

[0004] Therefore, typically when storing or transmitting video data, the encoder compresses the video data for storage or transmission, and the decoder receives the compressed video data, decompresses it, and plays it. Such video compression technologies include H.264 / AVC, HEVC (High Efficiency Video Coding), and VVC (Versatile Video Coding), which improves coding efficiency by more than 30% compared to HEVC.

[0005] However, as video size, resolution, and frame rates are gradually increasing, and the amount of data that needs to be encoded is also growing accordingly, a new compression technology is required that offers better encoding efficiency and higher image quality improvement effects than existing compression technologies.

[0006] The present disclosure aims to provide an image encoding / decoding method and apparatus for configuring candidates for Intra Template Matching Prediction (IntraTMP) and predicting a current block based on the configured candidates, and a recording medium for storing a bitstream generated by said image encoding method / apparatus.

[0007] According to an embodiment of the present disclosure, a method for restoring a current block performed by an image decoding device comprises the steps of: constructing block vector candidates of the current block based on a template cost representing the difference between a current template of the current block and a reference template within a predefined reference region, wherein the block vector candidates indicate a reference block corresponding to the reference template, the current template includes surrounding pre-restored pixels of the current block, and the reference template includes surrounding pixels of the reference block; constructing a candidate list for the application of a fusion mode based on the block vector candidates or the template costs of the block vector candidates, wherein the candidate list includes new block vector candidates for the application of the fusion mode; calculating weights for the new block vector candidates; and predicting the current block based on the weights and the new block vector candidates.

[0008] According to another embodiment of the present disclosure, a method for encoding a current block performed by an image encoding device comprises the steps of: configuring block vector candidates of the current block based on a template cost representing the difference between a current template of the current block and a reference template within a predefined reference region, wherein the block vector candidates indicate a reference block corresponding to the reference template, the current template includes surrounding pre-recovered pixels of the current block, and the reference template includes surrounding pixels of the reference block; configuring a candidate list for the application of a fusion mode based on the block vector candidates or the template costs of the block vector candidates, wherein the candidate list includes new block vector candidates for the application of the fusion mode; calculating weights for the new block vector candidates; and predicting the current block based on the weights and the new block vector candidates.

[0009] According to another embodiment of the present disclosure, a method for providing video data to an image decoder comprises: encoding the video data into a bitstream; and delivering the bitstream to the image decoder, wherein the step of encoding the video data comprises: configuring block vector candidates of the current block based on a template cost representing the difference between a current template of the current block and a reference template within a predefined reference region, wherein the block vector candidates indicate a reference block corresponding to the reference template, the current template includes surrounding pre-recovered pixels of the current block, and the reference template includes surrounding pixels of the reference block; configuring a candidate list for the application of a fusion mode based on the block vector candidates or the template costs of the block vector candidates, wherein the candidate list includes new block vector candidates for the application of the fusion mode; calculating weights for the new block vector candidates; and predicting the current block based on the weights and the new block vector candidates.

[0010] As described above, by providing a video encoding / decoding method, an apparatus, and a recording medium storing a bitstream generated by the video encoding method / apparatus according to the present embodiment, it is possible to improve video encoding efficiency and video quality.

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

[0012] Figure 2 is a diagram illustrating a method for dividing blocks using a QTBTTT (QuadTree plus BinaryTree TernaryTree) structure.

[0013] FIGS. 3a and 3b are diagrams showing a plurality of 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 technologies of the present disclosure.

[0016] Figure 6 is an example diagram showing the template of the current block.

[0017] FIG. 7 is an exemplary diagram illustrating the clustering of block vector candidates according to one embodiment of the present disclosure.

[0018] FIG. 8 is an exemplary diagram illustrating a Gaussian elimination method according to one embodiment of the present disclosure.

[0019] FIG. 9 is a flowchart illustrating a method for predicting a current block according to one embodiment of the present disclosure.

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the exemplary drawings. It should be noted that in assigning reference numerals to the components of each drawing, the same components are given the same reference numeral whenever possible, even if they are shown in different drawings. Furthermore, in describing these embodiments, if it is determined that a detailed description of related known components or functions could obscure the essence of these embodiments, such detailed description is omitted.

[0021] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the technologies of the present disclosure. Hereinafter, the image encoding device and its sub-components will be described with reference to FIG. 1.

[0022] The video encoding device may be configured to include a picture splitting unit (110), a prediction unit (120), a subtractor (130), a conversion unit (140), a quantization unit (145), a reordering unit (150), an entropy encoding unit (155), an inverse quantization unit (160), an inverse conversion unit (165), an adder (170), a loop filter unit (180), and a memory (190).

[0023] Each component of the video encoding device may be implemented in hardware or software, or as a combination of hardware and software. Additionally, the function of each component may be implemented in software, and a microprocessor may be implemented to execute the software function corresponding to each component.

[0024] A single image (video) consists 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). And each CTU is divided into one or more Coding Units (CUs) by a tree structure. Information applicable to each CU is encoded as the syntax of the CU, and information applicable to all CUs included in a single CTU is encoded as the syntax of the CTU. Additionally, information applicable to all blocks within a single slice is encoded as the syntax of the slice header, and information applicable 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). Also, information commonly referenced by one or more SPSs is encoded in a Video Parameter Set (VPS). Additionally, information commonly applicable to a single tile or tile group may be encoded as the syntax of a tile or tile group header. The syntax included in the SPS, PPS, slice header, and tile or tile group header may be referred to as high-level syntax.

[0025] The picture splitting unit (110) determines the size of the CTU. Information regarding the size of the CTU (CTU size) is encoded as a syntax of SPS or PPS and transmitted to an image decoding device.

[0026] The picture division unit (110) divides each picture constituting the image into multiple CTUs having a predetermined size, and then recursively divides the CTUs using a tree structure. The leaf nodes in the tree structure become the CUs, which are the basic units of encoding.

[0027] 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 equal size, a BinaryTree (BT) in which an upper node is divided into two lower nodes, a TernaryTree (TT) in which an upper node is divided into three lower nodes in a 1:2:1 ratio, or a structure that combines two or more of these QT, BT, 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 combined may be referred to as an MTT (Multiple-Type Tree).

[0028] Figure 2 is a diagram illustrating a method for dividing blocks using a QTBTTT structure.

[0029] As illustrated in FIG. 2, the CTU can first be split into a QT structure. Quadtree splitting can be repeated until the size of the splitting block reaches the minimum block size of the leaf node allowed in QT (MinQTSize). 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 encoder (155) and signaled to the image decoder. If the leaf node of the QT is not larger than the maximum block size of the root node allowed in BT (MaxBTSize), it can be further split into one or more of the BT structure or TT structure. In the BT structure and / or TT structure, multiple splitting directions may exist. For example, there may be two directions in which the block of the corresponding node is split horizontally and vertically. As shown in Figure 2, when MTT splitting begins, a second flag (mtt_split_flag) indicating whether the nodes have been split, and if splitting has occurred, a flag indicating the splitting direction (vertical or horizontal) and / or the splitting type (binary or ternary) are encoded by the entropy encoding unit (155) and signaled to the image decoding device.

[0030] Alternatively, prior to encoding the first flag (QT_split_flag) indicating whether each node is split into four nodes of the lower layer, the CU split flag (split_cu_flag) indicating whether the node is split may be encoded. If the value of the CU split flag (split_cu_flag) indicates that it is not split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a coding unit (CU), which is the basic unit of encoding. If the value of the CU split flag (split_cu_flag) indicates that it is split, the video encoding device starts encoding from the first flag in the manner described above.

[0031] When QTBT is used as another example of a tree structure, there may be two types: a type that divides the block of the corresponding node horizontally into two blocks of the same size (i.e., symmetric horizontal splitting) and a type that divides it vertically (i.e., symmetric vertical splitting). A splitting flag (split_flag) indicating whether each node of the BT structure is split into a block of a lower layer and splitting type information indicating the type of splitting are encoded by the entropy encoding unit (155) and transmitted to the image decoding device. Meanwhile, there may also be an additional type that divides the block of the corresponding node into two blocks of an asymmetric shape. The asymmetric shape may include a shape that divides the block of the corresponding node into two rectangular blocks with a size ratio of 1:3, or a shape that divides the block of the corresponding node diagonally.

[0032] A CU can have various sizes depending on the QTBT or QTBTTT partitioning from a CTU. Hereinafter, the block corresponding to the CU to be encoded or decoded (i.e., the leaf node of QTBTTT) is referred to as the 'current block'. Depending on the adoption of QTBTTT partitioning, the shape of the current block may be not only square but also rectangular.

[0033] 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).

[0034] Generally, current blocks within a picture can each be predictively coded. Typically, the prediction of a current block can be performed using an intra-prediction technique (using data from the picture containing the current block) or an inter-prediction technique (using data from a picture coded prior to the picture containing the current block). Inter-prediction includes both unidirectional and bidirectional prediction.

[0035] The intra prediction unit (122) predicts pixels within the current block using pixels (reference pixels) located around the current block within the current picture containing the current block. Multiple intra prediction modes exist depending on the prediction direction. For example, as shown in FIG. 3a, multiple intra prediction modes may include two non-directional modes, including Planar mode and DC mode, and 65 directional modes. The surrounding pixels to be used and the calculation formula are defined differently for each prediction mode.

[0036] For efficient directional prediction for a rectangular current block, directional modes (intra-prediction modes 67 through 80 and -1 through -14) illustrated by dashed arrows in FIG. 3b may be additionally used. These may be referred to as "wide angle intra-prediction modes." In FIG. 3b, the arrows indicate 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. Among the wide angle intra-prediction modes, some wide angle intra-prediction modes available for the current block may be determined by the ratio of the width to the height of the rectangular current block. For example, wide-angle intra prediction modes with an angle less than 45 degrees (intra prediction modes 67 to 80) are available when the current block is a rectangular shape with a height less than the width, and wide-angle intra prediction modes with an angle greater than -135 degrees (intra prediction modes -1 to -14) are available when the current block is a rectangular shape with a width less than the height.

[0037] The intra prediction unit (122) can determine the intra prediction mode to use for encoding the current block. In some examples, the intra prediction unit (122) may encode the current block using several intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, the intra prediction unit (122) may calculate the rate-distortion values ​​using a rate-distortion analysis of several tested intra prediction modes and select the intra prediction mode having the best rate-distortion features among the tested modes.

[0038] The intra prediction unit (122) selects one intra prediction mode among a plurality of intra prediction modes and predicts the current block using a calculation formula and surrounding pixels (reference pixels) determined according to the selected intra prediction mode. Information regarding the selected intra prediction mode is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0039] 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 the block most similar to the current block within a reference picture that is encoded and decoded before the current picture, and generates a prediction block for the current block using the searched block. Then, it generates a motion vector (MV) corresponding to the displacement between the current block in the current picture and the prediction block in the reference picture. Generally, motion estimation is performed on the lumina component, and the motion vector calculated based on the lumina component is used for both the lumina component and the chroma component. Motion information including information about the reference picture used to predict the current block and information about the motion vector is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0040] The inter prediction unit (124) may perform interpolation on a reference picture or reference block to increase the accuracy of the prediction. That is, subsamples between two consecutive integer samples are interpolated by applying filter coefficients to a plurality of consecutive integer samples including those two integer samples. When the process of searching for the block most similar to the current block is performed for the interpolated reference picture, the motion vector can be expressed with precision in fractional units rather than precision in integer sample units. The precision or resolution of the motion vector can be set differently for each unit of the target area to be encoded, such as slice, tile, CTU, CU, etc. When such Adaptive Motion Vector Resolution (AMVR) is applied, information regarding the motion vector resolution to be applied to each target area must be signaled for each target area. For example, if the target area is a CU, information regarding the motion vector resolution applied to each CU is signaled. The information regarding the motion vector resolution may be information indicating the precision of the difference motion vector described later.

[0041] 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 representing the block location 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 the reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1), respectively, and generates a first reference block and a second reference block by searching for a block similar to the current block within each reference picture. Then, it generates a prediction block for the current block by averaging or weighting the first reference block and the second reference block. Then, it transmits motion information containing information about the two reference pictures used to predict the current block and information about the two motion vectors to the entropy encoding unit (155). Here, reference picture list 0 consists of restored pictures that are prior to the current picture in the display order, and reference picture list 1 may consist of restored pictures that are prior to the current picture in the display order. However, this is not necessarily limited to this, and restored pictures prior to the current picture in the display order may be additionally included in reference picture list 0, and conversely, restored pictures prior to the current picture may be additionally included in reference picture list 1.

[0042] Various methods can be used to minimize the amount of bits required to encode motion information.

[0043] For example, if the reference picture and motion vector of the current block are identical to the reference picture and motion vector of a neighboring block, the motion information of the current block can be transmitted to an image decoder by encoding information that can identify the neighboring block. This method is called 'merge mode'.

[0044] 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.

[0045] As for the surrounding blocks for deriving merge candidates, as shown in FIG. 4, all or part of the left block (A0), bottom-left block (A1), top block (B0), top-right block (B1), and top-left block (B2) adjacent to the current block within the current picture may be used. Additionally, a block located within a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current picture where the current block is located may be used as a merge candidate. For example, a block located at the same position as the current block within the reference picture (co-located block) or a block adjacent to that same position 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.

[0046] The inter prediction unit (124) constructs a merge list containing a predetermined number of merge candidates using these surrounding blocks. Among the merge candidates included in the merge list, it selects a merge candidate to be used as movement information for the current block and generates merge index information to identify the selected candidate. The generated merge index information is encoded by the entropy encoding unit (155) and transmitted to the image decoding device.

[0047] Merge skip mode is a special case of merge mode; after quantization, when all transform coefficients for entropy coding are close to zero, only neighbor block selection information is transmitted without transmitting residual signals. By utilizing merge skip mode, relatively high coding efficiency can be achieved in images with minimal motion, still images, and screen content images.

[0048] Hereinafter, merge mode and merge skip mode will be collectively referred to as merge / skip mode.

[0049] Another method for encoding motion information is the AMVP (Advanced Motion Vector Prediction) mode.

[0050] In AMVP mode, the inter-prediction unit (124) derives predicted motion vector candidates for the motion vector of the current block using the surrounding blocks of the current block. As surrounding blocks used to derive predicted motion vector candidates, all or part of the left block (A0), bottom-left block (A1), top block (B0), top-right block (B1), and top-left block (B2) adjacent to the current block within the current picture shown in FIG. 4 may be used. Additionally, blocks located within a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current picture where the current block is located may be used as surrounding blocks to derive predicted motion vector candidates. For example, blocks located at the same position as the current block within the reference picture (co-located blocks) or blocks adjacent to the blocks at the same position 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.

[0051] The inter prediction unit (124) derives predicted motion vector candidates using the motion vectors of the surrounding blocks and determines a predicted motion vector for the current block's motion vector using the predicted motion vector candidates. Then, it calculates a difference motion vector by subtracting the predicted motion vector from the current block's motion vector.

[0052] Predicted motion vectors can be obtained by applying a predefined function (e.g., median, mean operation, etc.) to the predicted motion vector candidates. In this case, the image decoder is also aware of the predefined function. Furthermore, since the surrounding blocks used to derive the predicted motion vector candidates have already been encoded and decoded, the image decoder is also aware of the motion vectors of those surrounding blocks. Therefore, the image decoder does not need to encode information to identify the predicted motion vector candidates. Consequently, in this case, information regarding the difference motion vector and the reference picture used to predict the current block is encoded.

[0053] Meanwhile, the predicted motion vector may 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 difference motion vector and information about the reference picture used to predict the current block.

[0054] The subtractor (130) generates a residual block by subtracting the prediction block generated by the intra prediction unit (122) or the inter prediction unit (124) from the current block.

[0055] The conversion unit (140) converts residual signals within a residual block having pixel values ​​in a spatial domain into conversion coefficients in the frequency domain. The conversion unit (140) can convert the residual signals within the residual block using the entire size of the residual block as the conversion unit, or it can divide the residual block into multiple sub-blocks and use the sub-blocks as the conversion unit to perform the conversion. Alternatively, it can divide the residual signals into two sub-blocks, a conversion area and a non-conversion area, and use only the conversion area sub-block as the conversion unit to convert the residual signals. Here, the conversion area 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 the sub-block has been converted, direction (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. Additionally, the size of the converted 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.

[0056] Meanwhile, the transformation unit (140) can perform transformations on the residual block individually in the horizontal and vertical directions. For the transformation, various types of transformation functions or transformation matrices may 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 pair of transformation functions with the best transformation efficiency among the MTS and transform the residual block in the horizontal and vertical directions, respectively. Information (mts_idx) regarding the selected pair of transformation functions among the MTS is encoded by the entropy encoding unit (155) and signaled to the image decoder.

[0057] The quantization unit (145) quantizes the transformation coefficients output from the transformation unit (140) using quantization parameters and outputs the quantized transformation coefficients to the entropy encoding unit (155). The quantization unit (145) may quantize the associated residual block directly without transformation for any block or frame. The quantization unit (145) may apply different quantization coefficients (scaling values) depending on the position of the transformation coefficients within the transformation block. The quantization matrix applied to the quantized transformation coefficients arranged in two dimensions can be encoded and signaled to an image decoder.

[0058] The reordering unit (150) can perform reordering of coefficient values ​​for quantized residual values.

[0059] The reordering unit (150) can convert a two-dimensional coefficient array into a one-dimensional coefficient sequence using coefficient scanning. For example, the reordering unit (150) can output a one-dimensional coefficient sequence by scanning from DC coefficients to coefficients in the high-frequency range using a zig-zag scan or a diagonal scan. Depending on the size of the conversion unit and the intra-prediction mode, a vertical scan that scans the two-dimensional coefficient array in the column direction and a horizontal scan that scans the two-dimensional block-shaped coefficients in the row direction may be used instead of a zig-zag scan. That is, depending on the size of the conversion unit and the intra-prediction mode, the scanning method to be used among a zig-zag scan, a diagonal scan, a vertical scan, and a horizontal scan may be determined.

[0060] The entropy encoding unit (155) generates a bitstream by encoding a sequence of one-dimensional quantized transformation coefficients output from the reordering unit (150) using various encoding methods such as CABAC (Context-based Adaptive Binary Arithmetic Code) and Exponential Golomb.

[0061] Additionally, 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 video decoder can divide the block in the same way as the video encoding unit. Additionally, the entropy encoding unit (155) encodes information regarding a prediction type indicating whether the current block is encoded by intra prediction or by inter prediction, and encodes intra prediction information (i.e., information regarding the intra prediction mode) or inter prediction information (information regarding the encoding mode of motion information (merge mode or AMVP mode), the merge index in the case of merge mode, and the reference picture index and difference motion vector in the case of AMVP mode) according to the prediction type. Additionally, the entropy encoding unit (155) encodes information related to quantization, i.e., information regarding quantization parameters and information regarding the quantization matrix.

[0062] The inverse quantization unit (160) inversely quantizes the quantized transformation coefficients output from the quantization unit (145) to generate transformation coefficients. The inverse transformation unit (165) converts the transformation coefficients output from the inverse quantization unit (160) from the frequency domain to the spatial domain to restore the residual block.

[0063] The adder (170) restores the current block by adding the restored residual block and the prediction block generated by the prediction unit (120). The pixels within the restored current block are used as reference pixels when intra-predicting the next block in sequence.

[0064] The loop filter section (180) performs filtering on the restored pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. caused by block-based prediction and transformation / quantization. The loop filter section (180) may include all or part of a deblocking filter (182), a SAO (Sample Adaptive Offset) filter (184), and an ALF (Adaptive Loop Filter, 186) as an in-loop filter.

[0065] The deblocking filter (182) filters the boundaries between restored blocks to remove blocking artifacts caused by block-unit encoding / decoding, and the SAO filter (184) and ALF (186) perform additional filtering on the deblocking filtered image. The SAO filter (184) and ALF (186) are filters used to compensate for the difference 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 CTU units. In contrast, the ALF (186) performs block-unit filtering, and compensates for distortion by applying different filters by distinguishing the degree of edge and change of the corresponding block. Information regarding the filter coefficients to be used in the ALF can be encoded and signaled to an image decoder.

[0066] The restored blocks filtered through the deblocking filter (182), SAO filter (184), and ALF (186) are stored in memory (190). Once 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.

[0067] The video encoding device can store the bitstream of encoded video data on a non-transient recording medium or transmit it to a video decoding device using a communication network.

[0068] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the technologies of the present disclosure. Hereinafter, the image decoding device and its sub-components will be described with reference to FIG. 5.

[0069] The image decoding device may be configured to include an entropy decoding unit (510), a reordering 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).

[0070] Similar to the image encoding device of FIG. 1, each component of the image decoding device may be implemented in hardware or software, or in combination of hardware and software. Additionally, the function of each component may be implemented in software, and a microprocessor may be implemented to execute the function of the software corresponding to each component.

[0071] The entropy decoding unit (510) determines the current block to be decoded by decoding the bitstream generated by the video encoding device and extracting information related to block division, and extracts prediction information, information on residual signals, etc., necessary to restore the current block.

[0072] The entropy decoding unit (510) extracts information about the CTU size from the SPS (Sequence Parameter Set) or PPS (Picture Parameter Set) to determine 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 divides the CTU using the tree structure by extracting division information for the CTU.

[0073] For example, when splitting a CTU using a QTBTTT structure, first, a first flag (QT_split_flag) related to QT splitting is extracted to split each node into four nodes of the lower layer. Then, for the nodes corresponding to the leaf nodes of QT, a second flag (mtt_split_flag) related to MTT splitting and splitting direction (vertical / horizontal) and / or splitting type (binary / ternary) information are extracted to split the corresponding leaf nodes into an MTT structure. Accordingly, each node below the leaf nodes of QT is recursively split into a BT or TT structure.

[0074] As another example, when splitting a CTU using the QTBTTT structure, a CU splitting flag (split_cu_flag) indicating whether to split the CU is first extracted, and if the block is split, a first flag (QT_split_flag) is extracted. During the splitting process, each node may undergo zero or more iterative MTT splittings after zero or more iterative QT splittings. For example, the CTU may undergo MTT splitting immediately, or conversely, only multiple QT splittings may occur.

[0075] As another example, when splitting a CTU using a QTBT structure, a first flag (QT_split_flag) related to the splitting of QT is extracted to split each node into four nodes of the lower layer. Then, for the nodes corresponding to the leaf nodes of QT, a split flag (split_flag) indicating whether to further split into BTs and split direction information are extracted.

[0076] Meanwhile, when the entropy decoding unit (510) determines the current block to be decoded using the division of the tree structure, it extracts information regarding the prediction type indicating whether the current block is intra-predicted or inter-predicted. If the prediction type information indicates intra-predicted, the entropy decoding unit (510) extracts syntax elements for the intra-predicted information (intra-predicted mode) of the current block. If the prediction type information indicates inter-predicted, the entropy decoding unit (510) extracts syntax elements for the inter-predicted information, namely information indicating the motion vector and the reference picture that the motion vector refers to.

[0077] Additionally, the entropy decoding unit (510) extracts information regarding quantization-related information and information regarding residual signals, as well as information regarding the quantized transformation coefficients of the current block.

[0078] The reordering unit (515) can change the sequence of one-dimensional quantized transformation 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 order performed by the image encoding device.

[0079] The inverse quantization unit (520) inversely quantizes the quantized transformation coefficients and inversely quantizes the quantized transformation coefficients using quantization parameters. The inverse quantization unit (520) may apply different quantization coefficients (scaling values) to the quantized transformation coefficients arranged in two dimensions. The inverse quantization unit (520) may perform inverse quantization by applying a matrix of quantization coefficients (scaling values) from an image encoding device to a two-dimensional array of quantized transformation coefficients.

[0080] The inverse transformation unit (530) generates a residual block for the current block by inversely transforming the inversely quantized transformation coefficients from the frequency domain to the spatial domain and restoring the residual signals.

[0081] Additionally, when the inverse transformation unit (530) inversely transforms only a part of the transformation block (sub-block), it extracts a flag (cu_sbt_flag) indicating that only the sub-block of the transformation block has been transformed, information on the directionality (vertical / horizontal) of the sub-block (cu_sbt_horizontal_flag) and / or information on the position of the sub-block (cu_sbt_pos_flag), restores residual signals by inversely transforming the transformation coefficients of the corresponding sub-block from the frequency domain to the spatial domain, and creates a final residual block for the current block by filling the areas that have not been inversely transformed with "0" values ​​of residual signals.

[0082] Additionally, when MTS is applied, the inverse transformation unit (530) determines a transformation function or transformation matrix to be applied in the horizontal and vertical directions, respectively, using MTS information (mts_idx) signaled from the video encoding device, and performs an inverse transformation on the transformation coefficients within the transformation block in the horizontal and vertical directions using the determined transformation function.

[0083] 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 an intra prediction, and the inter prediction unit (544) is activated when the prediction type of the current block is an inter prediction.

[0084] 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.

[0085] The inter prediction unit (544) determines the motion vector of the current block and the reference picture that the motion vector refers to using the syntax elements for the inter prediction mode extracted from the entropy decoding unit (510), and predicts the current block using the motion vector and the reference picture.

[0086] The adder (550) restores the current block by adding the residual block output from the inverse transformation unit (530) and the prediction block output from the inter prediction unit (544) or the intra prediction unit (542). The pixels within the restored current block are used as reference pixels when intra-predicting the block to be decoded later.

[0087] The loop filter section (560) may include a deblocking filter (562), an SAO filter (564), and an ALF (566) as an in-loop filter. The deblocking filter (562) deblocks the boundaries between restored blocks to remove blocking artifacts caused by block-unit decoding. The SAO filter (564) and the ALF (566) perform additional filtering on the restored blocks after deblocking filtering to compensate for the difference between the restored pixels and the original pixels caused by lossy coding. The filter coefficients of the ALF are determined using information about the filter coefficients decoded from the bitstream.

[0088] The restored blocks filtered through the deblocking filter (562), SAO filter (564), and ALF (566) are stored in memory (570). When all blocks within a picture are restored, the restored picture is used as a reference picture to inter-predict blocks within the picture to be encoded later.

[0089] The present embodiment relates to the encoding and decoding of an image (video) as described above. More specifically, the present invention provides an image encoding / decoding method and apparatus for configuring candidates for intra-template matching and predicting a current block based on the configured candidates, and a recording medium for storing a bitstream generated by the image encoding method / apparatus.

[0090] 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.

[0091] The video encoding device can generate signaling information related to the present embodiment in terms of rate distortion optimization during the encoding of 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 decoder. The video decoder can decode the signaling information related to the decoding of the current block from the bitstream using the entropy decoder (510).

[0092] In the following description, the term 'target block' may be used interchangeably with 'current block' or 'Coding Unit (CU).' Alternatively, 'target block' may refer to a specific area of ​​a Coding Unit.

[0093] Also, a value of one flag being true indicates that the flag is set to 1. Also, a value of one flag being false indicates that the flag is set to 0.

[0094] The decoder-side includes all or part of an inverse quantizer (160), an inverse transform (165), a prediction unit (120), an adder (170), a loop filter (180), and a memory (190) in the image encoding device illustrated in FIG. 1. Alternatively, the decoder-side includes all or part of an inverse quantizer (520), an inverse transform (530), a prediction unit (540), an adder (550), a loop filter (560), and a memory (570) in the image decoding device illustrated in FIG. 5. In relation to a series of decoding processes, the decoder-side of the image encoding device and the decoder-side of the image decoding device perform the same operation. The image encoding device determines information related to the operation of the decoder-side and signals the determined information to the image decoding device. The image decoding device can decode the signaled information and operate the decoder-side based on the decoded information.

[0095] I. IntraTMP(Intra Template Matching Prediction)

[0096] The existing Intra Template Matching Prediction (IntraTMP) technology uses the reconstructed surrounding area of ​​the current block as a template to construct a list of candidates—that is, a candidate list—based on the magnitude of the error cost within a predefined reference area. This constructed candidate list is used for the prediction of the current block in conjunction with the detailed IntraTMP technology.

[0097] The template of the current block may include M (where M is an integer greater than or equal to 1) restored lines, as shown in the example of FIG. 6.

[0098] The number of the aforementioned candidates can be N (where N is an integer greater than or equal to 1).

[0099] Each candidate is indicated by movement in the x-axis direction and movement in the y-axis direction. In this case, a pair of movement in the x-axis direction and movement in the y-axis direction can be defined as a block vector or a block vector candidate.

[0100] By calculating the difference between a predefined reference area and the template of the current block, and sorting the block vector candidates according to the ascending or descending order of the calculated difference, sorted block vector candidates, i.e., a list of candidates to be sorted, can be constructed.

[0101] The difference between a predefined reference region and a template is defined as the error cost or template cost. For example, 19 block vector candidates can be constructed in ascending order of template costs.

[0102] As a method for calculating the aforementioned error cost, one or more of SAD (Sum of Absolute Difference), MR-SAD (Mean-Removal Sum of Absolute Difference), and SATD (Sum of Absolute Transformed Difference) may be used. Here, if two or more methods are used, a candidate list may be constructed for each error cost. That is, two or more candidate lists may be constructed.

[0103] The detailed technologies of IntraTMP may include a fusion mode, a sub-pixel precision mode, a linear filter model, a Local Illuminance Compensation (LIC) mode, etc. The aforementioned detailed technologies may be applied independently, or one or more prediction modes may be applied simultaneously.

[0104] The fusion mode can generate a prediction block by weightedly fusing the reference blocks pointed to by N (where N is an integer greater than or equal to 2) block vector candidates. In this case, the weights used for weighted fusion can be set based on the template cost. Alternatively, the weights for the reference blocks can be derived by utilizing Gaussian elimination on the templates.

[0105] Block vector candidates used in the fusion mode can be sequentially constructed from template candidates sorted in ascending order. For example, if 19 block vector candidates are constructed, 5 candidates corresponding to numbers 1 through 5, or 5 candidates corresponding to numbers 6 through 10, can be constructed as candidates for the fusion mode.

[0106] Final candidates for the application of a fusion mode can be configured based on the aforementioned weight configuration method and block vector candidate configuration method. At this time, the candidates configured for the fusion mode in combination with the weight configuration method are defined as candidate groups. Thus, if 19 block vector candidates are configured, 3 candidate groups can be configured. Additionally, a final candidate group for the application of the fusion mode can be selected from among the 3 candidate groups. At this time, an index for indicating the final candidate group can be signaled to the image decoder.

[0107] Additionally, the number of candidates used for generating prediction blocks within a final candidate group may be determined based on the cost of block vector candidates within that candidate group. For example, the number of candidates may be determined based on a threshold value. In this case, the threshold value may be the value obtained by multiplying the template cost of any block vector candidate by a non-zero integer or a rational number greater than zero. For example, based on block vector candidate 1 of candidate group 1, a value corresponding to "template cost of block vector candidate 1 × 2" may be used as the threshold value. Block vector candidates within the candidate group that have a template cost smaller than the threshold value may be used in the fusion mode.

[0108] The aforementioned threshold value may be explicitly transmitted to a video decoder. The threshold value may be transmitted while being included in one or more levels of the sequence parameter set (SPS), picture parameter set (PPS), video parameter set (VPS), slice header (SH), and coding unit (CU).

[0109] The subpixel accuracy mode can be used for one or more block vector candidates and can be used with additional indicators. When the subpixel accuracy mode is used, the optimal template can be searched using 1 / N (where 1 / N is a non-negative rational number) pixel accuracy. For example, the optimal template can be searched using 1 / 4 pixel accuracy. Or, the optimal template can be searched using 1 / 2 pixel accuracy.

[0110] A linear filter model can be used for one or more block vector candidates, and can be used with additional indicators. A linear filter is constructed between the template of the current block and the template of the reference block, and the constructed linear filter can be used to generate a predicted block of the current block.

[0111] The LIC mode can be used for one or more block vector candidates, and can be used with additional indicators.

[0112] In the prior art, the process of constructing candidates according to the aforementioned detailed prediction mode is a method based on a fixed order. Therefore, the process of constructing the aforementioned candidates may limit the improvement of encoding / decoding efficiency. The present disclosure provides a method for constructing a block vector candidate list for intra-template matching prediction to improve encoding efficiency or reduce complexity. In particular, the present disclosure provides a method for constructing a candidate list for a fusion mode, which is one of the detailed technologies of IntraTMP, and a method for generating a prediction block to improve encoding efficiency.

[0113] The following embodiments are described with reference to an image decoding device, but may be implemented identically or similarly in an image encoding device. Alternatively, the following embodiments are described with reference to the decoder side of the image decoding device, but may be implemented identically or similarly in the decoder side of an image encoding device.

[0114] II. Embodiments according to the present disclosure

[0115] In the present disclosure, the candidate list for the fusion mode of IntraTMP can be adaptively configured based on the distance between block vector candidates or the template cost between block vector candidates.

[0116] After completing the configuration of block vector candidates for the current block, the video decoder can configure a candidate list for the fusion mode based on the distance between block vector candidates or the template cost between block vector candidates.

[0117] Depending on the method of configuring the candidate list for the aforementioned fusion mode, the diversity of candidates used in the fusion mode can be increased.

[0118] Candidates for the fusion mode can be constructed based on a number of block vector candidates combined with a weight determination method. Candidates constructed based on such combinations can be defined as a candidate group. For example, a candidate group can be composed of N block vector candidates combined with weights based on template costs, as shown in Table 1.

[0119]

[0120] In Table 1, block vector candidates, i.e., block vectors, can be composed of movements in the x-axis direction and movements in the y-axis direction. The template cost may be the error cost between the template of the current block and the template within the reference area. Hereinafter, the template within the reference area is defined as the reference template.

[0121] The image decoder can derive new candidates for a fusion mode based on the distance between block vector candidates and / or the template cost between block vector candidates. The derived new candidates may replace existing candidates or be used as additional candidates. If the derived new candidates are used as additional candidates, an indicator regarding whether or not the new candidate configuration process is applied may be signaled to the image decoder. In this case, the candidate list for the fusion mode may include the new candidates for the fusion mode.

[0122] As an example, an image decoder may construct a new candidate based on the distance between block vector candidates. In this case, the distance may be the distance between the block vector candidate and the current block or the distance between the block vector candidates.

[0123] To construct a new candidate for a fusion mode, the image decoding device may use block vector candidates configured for the current block or use an already configured candidate group. As described above, the candidate group may include five sequential candidates among the block vector candidates configured for the current block.

[0124] The image decoding device can construct new candidates for a fusion mode by considering the distance of the block vector candidates in relation to the block vector candidates configured for the current block. Here, the number of block vector candidates configured for the current block may be N (where N is an integer greater than or equal to 1). At this time, the distance of the block vector candidates may be the distance between the reference block corresponding to the block vector candidate and the current block, or the distance between the block vector candidates.

[0125] For example, new candidates for fusion modes can be constructed based on the ascending order of the distance between the reference block and the current block. The distance can be based on movement in the x-direction and movement in the y-direction, or on one of the movement in the x-direction and movement in the y-direction. The distance can be a Euclidean distance or a Manhattan distance. For two points (x1, y1) and (x2, y2), the Manhattan distance is calculated as |x1-x2|+|y1-y2|.

[0126] Alternatively, new candidates for the fusion mode may be configured based on the distance between block vector candidates. The distance between block vector candidates may be defined based on a threshold value. The threshold value may be determined as a positive rational number or a positive integer. Based on the threshold value, the distance may be defined as a circular, cross, or square shape. For example, the threshold value may be set to 1, and if the distance between block vector candidates is smaller than the threshold value, candidates for the fusion mode may be configured while excluding that candidate. Alternatively, the threshold value may be set to 0.5, and if the distance between block vector candidates is closer than the threshold value, candidates for the fusion mode may be configured while excluding that candidate. In this case, the candidate to be removed may be the block vector candidate with the larger template cost.

[0127] For example, block vector candidates can be clustered based on the distance between them, and a representative block vector for each cluster can be calculated. The radius or distance used for clustering can be defined as L (where L is an integer greater than or equal to 1). Alternatively, the distance can be set as a circle or a square, etc. As shown in the example of Fig. 7, block vector candidates within a horizontal and vertical distance of 3 relative to block vector candidate index 0 can be clustered. At this time, the representative block vector within the cluster can be selected from the block vector candidates within the cluster based on the template cost of the block vector candidates or the proximity to the average of the block vectors within the cluster. Subsequently, the representative block vector can be used as an additional new candidate.

[0128] As another example, the video decoder can construct a new candidate based on the difference between the template costs of the block vector candidates. By excluding similar block vectors based on the construction of the new candidate according to the aforementioned method, an increase in encoding efficiency can be expected.

[0129] In the method described above, the difference between the template costs represents the difference in template costs between the candidate indices of the block vector candidates. In this case, the difference in template costs between specific candidate indices can be defined as a threshold. For example, in the block vector candidates configured as shown in Table 1, the difference in template costs between candidate indices 0 and 1 can be set as a threshold.

[0130] The image decoder can construct new candidates for a fusion mode by calculating the template cost difference between one candidate index and a subsequent candidate index based on the threshold value exemplified as described above. For example, the image decoder can set the template cost difference between indices 0 and 1 as a threshold value, and calculate the template cost difference between indices 1 and 2, and the template cost difference between indices 2 and 3.

[0131] If the calculated template cost difference is smaller than the threshold, the image decoder may exclude candidates for the corresponding index or include previous candidates for the corresponding index as new candidates for the fusion mode. For example, if the template cost difference between indices 2 and 3 is smaller than the threshold, the image decoder may configure block vector candidates for indices 0 through 2 as new candidates for the fusion mode. That is, candidates for indices 3 and 4 with larger template costs may be excluded. Alternatively, if the template cost difference between indices 2 and 3 is smaller than the threshold, the image decoder may exclude block vector candidates for index 3 with larger template costs. That is, block vector candidates for indices 0, 1, 2, and 4 may be configured as new candidates for the fusion mode.

[0132] A threshold for configuring new candidates for fusion modes can be explicitly signaled to the image decoder. In this case, the threshold can be signaled while being included in one or more levels of the sequence parameter set (SPS), picture parameter set (PPS), video parameter set (VPS), slice header (SH), and coding unit (CU).

[0133] When generating prediction blocks in the fusion mode of IntraTMP technology, weights for fusion can be derived based on various methods. In this case, one or more of the derivation methods, such as using template costs, utilizing Gaussian elimination between templates, or using regression models between templates, may be applied to derive the weights for fusion.

[0134] As an example, weights derived by Gaussian elimination may represent weights for a single reference block. The weight derivation method may use multiple reference templates and templates of the region surrounding the current block as inputs. Here, the reference templates consist of pixels surrounding the reference block and correspond to the template of the current block.

[0135] N (where N is an integer greater than or equal to 0) pixel values ​​of reference templates may be used as input values. An image decoder may generate linear data using the pixel values ​​of the reference templates and construct a (N+1)×(N+1) matrix based on the linear data. Hereinafter, the constructed matrix is ​​defined as A. Additionally, the pixel values ​​of the current template are defined as C. For a number of reference templates N, matrix A may additionally include one dimension related to the bias.

[0136] For example, if five reference blocks are used, the image decoder can construct a 6×6 matrix. A correlation matrix can be calculated based on the constituent values ​​of matrix A and the pixel values ​​of the current template. The auto-correlation matrix of matrix A is A T It is calculated as A, and the cross-correlation matrix of matrices A and C is A T It can be calculated as C. In this case, if the weights applied to the reference templates are defined as W, then A T A·W=A T A linear relationship like C can be satisfied.

[0137] The image decoder may apply Gaussian elimination to the calculated autocorrelation matrix and cross-correlation matrix to derive W. As shown in the example of FIG. 8, the image decoder A T A, A TA row echelon form matrix is ​​constructed using C, and the row echelon form matrix is ​​transformed into an upper-triangular matrix using forward elimination. The image decoder can calculate the values ​​of the result vector according to Gaussian elimination by applying backward substitution to the upper-triangular matrix. N filter coefficients can be obtained from the values ​​of the result vector, and the obtained filter coefficients can be used as weights for the fusion mode. A normalization process can be applied to the weights for the fusion mode so that the sum of the weights remains 1.

[0138] As another example, when using a regression model, the weights can be derived differently depending on the x and y coordinates inside the reference block used for fusion. The weights derived based on the regression model can represent a model between the templates of candidates for the fusion mode.

[0139] The regression model may be the equation of a straight line or the equation of a plane that minimizes the Mean Square Error (MSE) between reference templates indicated by each block vector. For example, the equation of a straight line means w(x,y)=ax+b or w(x,y)=ay+b, and the variables of the regression model may consist of a and b. The equation of a plane means w(x,y)=ax+by+c, and the variables of the regression model may consist of a, b, and c. w represents the weight. Here, x and y may be the coordinate values ​​of the internal pixels of the current block.

[0140] Alternatively, when deriving weights based on a regression model, Gaussian elimination between N (where N is an integer greater than or equal to 2) reference block templates may be used. For example, when two reference blocks related to candidates 0 and 1 are used, the image decoder may construct a regression model by utilizing Gaussian elimination between reference template 0 and reference template 1.

[0141] When multiple templates are used to calculate a regression model, a first template with the smallest template cost and a second template constructed based on the average of the pixel values ​​of the remaining templates may be used. Alternatively, a second template constructed based on the first template with the smallest template cost and the weighted average of the pixel values ​​of the remaining templates may be used. To apply weights based on the regression model, a second reference block calculated by averaging the pixel values ​​of a first reference block corresponding to the first template and reference blocks corresponding to the remaining templates may be used. Alternatively, a second reference block calculated by weighted averaging the pixel values ​​of a first reference block and reference blocks corresponding to the remaining templates may be used. In this case, weights calculated based on the template costs may be used. Alternatively, predefined weights may be used.

[0142] Here, if two or more weight derivation methods are applied, an indicator indicating one of the derivation methods may be used. For example, the indicator may be transmitted to an image decoder. Alternatively, the image decoder may derive the indicator by utilizing, for example, surrounding information.

[0143] In relation to the aforementioned derivation methods, the image decoder may derive weights based on an indicator indicating one of the derivation methods. Alternatively, the weights may be used while stored in a buffer.

[0144] The image decoder can increase encoding efficiency by improving the accuracy of the prediction block based on the improvement of the aforementioned fusion mode. The image decoder can generate multiple groups by combining a candidate configuration method and a weight derivation method for the fusion mode.

[0145] For example, a candidate group can be generated from a combination of two or more block vectors and weights derived based on template costs. In this case, based on the sum of defined weights, the weight of each reference block can be determined according to the ratio of the costs of each reference template. The sum of defined weights can be 1.

[0146] For example, candidate groups can be generated from a combination of weights derived using two or more block vectors and Gaussian elimination.

[0147] For example, a candidate group can be generated from a combination of weights derived based on two or more block vectors and a regression model.

[0148] The block vector used in the candidate group may be a consecutive candidate among the block vector candidates configured in relation to the current block, or a consecutive candidate among the new candidates mentioned above. For example, among the configured block vector candidates, candidates with indices 0 to 3 may be used. Or, among the candidates configured according to the method of configuring the new candidate, candidates with indices 0 to 3 may be used.

[0149] The image decoding device can generate a prediction block of the current block using a candidate list of fusion modes configured based on the method described above.

[0150] Hereinafter, a method for predicting the current block using an IntraTMP frame is described using the illustration of FIG. 9. The illustration of FIG. 9 can be performed by an image encoding device and an image decoding device. FIG. 9 is described based on the image encoding device, and if necessary, the operation by the image decoding device is additionally described.

[0151] FIG. 9 is a flowchart illustrating a method for predicting a current block according to one embodiment of the present disclosure.

[0152] The video encoding device constructs block vector candidates for the current block based on a template cost representing the difference between the current template of the current block and a reference template within a predefined reference region (S800).

[0153] Here, block vector candidates indicate a reference block corresponding to a reference template. The current template includes surrounding restored pixels of the current block, and the reference template may include surrounding pixels of the reference block.

[0154] The video encoding device constructs a candidate list for the application of a fusion mode based on block vector candidates or template costs of block vector candidates (S802). Here, the candidate list may include new block vector candidates for the application of a fusion mode.

[0155] The video encoding device can construct a candidate list for the application of a fusion mode from block vector candidates or a candidate group of the current block. Here, the candidate group may be pre-configured based on the block vector candidates of the current block. For example, the candidate group may include five sequential candidates among the block vector candidates configured for the current block.

[0156] As an example, the video encoding device can calculate the distance of a block vector candidate based on the distance between a reference block corresponding to the block vector candidate and the current block. The video encoding device can derive new block vector candidates based on the distance of the block vector candidate.

[0157] As another example, if the distance between block vector candidates is smaller than a preset threshold, the video encoding device may not include the candidate with the larger template cost among the block vector candidates in the candidate list.

[0158] The video encoding device can generate clusters of block vector candidates based on the distance between block vector candidates and calculate a representative block vector of the block vector candidates within each cluster. The video encoding device can include the representative block vector in the new block vector candidates for the application of the fusion mode.

[0159] As another example, the video encoding device may not include a candidate with a larger template cost among the block vector candidates in the candidate list if the difference between the template costs of the block vector candidates is smaller than a threshold. Here, the threshold may represent the difference between the template costs of specific block vector candidates in a continuous order.

[0160] The video encoding device calculates weights for new block vector candidates using one of the weight calculation methods (S804).

[0161] The video encoding device obtains an index indicating one of the methods for calculating weights. For example, the video encoding device may obtain the aforementioned index from a higher level. Alternatively, the video encoding device may determine the aforementioned index in terms of rate distortion optimization. The video encoding device may signal the index indicating one of the methods for calculating weights to the video decoder. The video decoder may decode the aforementioned index from the bitstream.

[0162] The video encoding device can calculate weights based on the method indicated by the aforementioned index.

[0163] As an example, the video encoding device can calculate weights based on the template cost corresponding to each new block vector candidate.

[0164] As another example, the image encoding device may calculate an autocorrelation matrix based on the pixel values ​​of reference templates and calculate a cross-correlation matrix based on the pixel values ​​of the reference templates and the pixel values ​​of the current template. The image encoding device may calculate weights by applying Gaussian elimination to the autocorrelation matrix and the cross-correlation matrix.

[0165] As another example, the video encoding device can calculate a regression model between reference templates. The video encoding device can use the regression model to calculate pixel-wise weights of reference blocks corresponding to the reference templates.

[0166] As another example, the video encoding device may select a first reference template with the smallest template cost among the reference templates and calculate a second reference template based on the average or weighted average of the pixel values ​​of the remaining reference templates. The video encoding device may calculate a regression model between the first reference template and the second reference template. Using the regression model, the video encoding device may calculate the pixel-wise weight of the reference block corresponding to the first reference template and the pixel-wise weight of the reference block corresponding to the second reference template.

[0167] The video encoding device generates a predicted block of the current block based on new block vector candidates with weights (S806). The video encoding device can predict the current block by applying weights to reference blocks indicated by the new block vector candidates.

[0168] Subsequently, the video encoding device can generate a residual block by subtracting the prediction block from the current block. The video encoding device can generate transformation coefficients by applying transformation / quantization to the residual block and encode the generated transformation coefficients.

[0169] The image decoder can decode the quantized transform coefficients of the current block from the bitstream and generate a residual block by applying inverse quantization / inverse transform to the quantized transform coefficients. The image decoder can restore the current block by adding the prediction block and the residual block.

[0170] Although the flowcharts and timing diagrams in this specification describe each process as being executed sequentially, this is merely an illustrative explanation of the technical concept of one embodiment of the present disclosure. In other words, a person skilled in the art to which one embodiment of the present disclosure belongs may modify and adapt the flowcharts and timing diagrams in various ways, such as changing the order described in the flowcharts and timing diagrams or executing one or more of the processes in parallel, without departing from the essential characteristics of one embodiment of the present disclosure; therefore, the flowcharts and timing diagrams are not limited to a chronological order.

[0171] It should be understood that the exemplary embodiments described above may be implemented in many different ways. The functions or methods described in one or more examples may be implemented in hardware, software, firmware, or any combination thereof. It should be understood that the functional components described herein are labeled as "...unit" to particularly emphasize their implementation independence.

[0172] Meanwhile, the various functions or methods described in the present embodiment may be implemented as instructions stored in a non-transient recording medium that can be read and executed by one or more processors. A non-transient recording medium includes, for example, any type of recording device in which data is stored in a form readable by a computer system. For example, a non-transient recording medium includes storage media such as an EPROM (erasable programmable read-only memory), a flash drive, an optical drive, a magnetic hard drive, and a solid-state drive (SSD).

[0173] The above description is merely an illustrative explanation of the technical concept of the present embodiment, and a person skilled in the art to which the present embodiment belongs would be able to make various modifications and variations within the scope of the essential characteristics of the present embodiment. Accordingly, the present embodiments are intended to explain, not limit, the technical concept of the present embodiment, and the scope of the technical concept of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present embodiment.

[0174]

[0175] CROSS-REFERENCE TO RELATED APPLICATION

[0176] This patent application claims priority to Korean patent application No. 10-2024-0174499 filed on November 29, 2024, the entire contents of which are incorporated into this patent application by reference.

Claims

1. A method for restoring a current block performed by an image decoding device, A step of constructing block vector candidates of the current block based on a template cost representing the difference between the current template of the current block and a reference template within a predefined reference region, wherein the block vector candidate indicates a reference block corresponding to the reference template, the current template includes surrounding restored pixels of the current block, and the reference template includes surrounding pixels of the reference block; A step of constructing a candidate list for the application of a fusion mode based on the above block vector candidates or the template costs of the above block vector candidates, wherein the candidate list includes new block vector candidates for the application of the fusion mode; A step of calculating weights for the above new block vector candidates; and A step of predicting the current block based on the above weights and the above new block vector candidates A method including 2. In Paragraph 1, The step of constructing the above candidate list is, A candidate list for the application of the fusion mode is constructed from the block vector candidates or candidate groups of the above current block, A method in which the above candidate group is pre-configured based on the block vector candidates of the above current block.

3. In Paragraph 1, The step of constructing the above candidate list is, A step of calculating the distance of the block vector candidate based on the distance between the reference block corresponding to the block vector candidate and the current block; and Step of deriving the new block vector candidates based on the distance of the above block vector candidates A method including 4. In Paragraph 1, The step of constructing the above candidate list is, A method for not including a candidate with a larger template cost among the block vector candidates in the candidate list when the distance between the block vector candidates is smaller than a preset threshold.

5. In Paragraph 1, The step of constructing the above candidate list is, A step of generating clusters of block vector candidates based on the distance between the block vector candidates; A step of calculating representative block vectors of block vector candidates within each cluster; and Step of including the above representative block vector in the above new block vector candidates A method including 6. In Paragraph 1, The step of constructing the above candidate list is, If the difference between the template costs of the above block vector candidates is smaller than a threshold, the candidate with the larger template cost among the above block vector candidates is not included in the candidate list, but, A method in which the above threshold is the difference between the template costs of specific block vector candidates having a continuous order.

7. In Paragraph 1, The step of calculating the above weights is, A method for calculating the weights based on the template costs corresponding to each of the new block vector candidates.

8. In Paragraph 1, The step of calculating the above weights is, A step of calculating an autocorrelation matrix based on the pixel values ​​of the reference templates and calculating a cross-correlation matrix based on the pixel values ​​of the reference templates and the pixel values ​​of the current template; and A step of calculating the weights by applying Gaussian elimination to the autocorrelation matrix and the cross-correlation matrix. A method including 9. In Paragraph 1, The step of calculating the above weights is, A step of calculating a regression model between the above reference templates; and A step of calculating pixel-wise weights of reference blocks corresponding to the reference templates using the above regression model. A method including 10. In Paragraph 9, The step of calculating the above weights is, A step of selecting a first reference template among the above reference templates that has the smallest template cost; A step of calculating a second reference template based on the average or weighted average of the pixel values ​​of the remaining reference templates; A step of calculating a regression model between the first reference template and the second reference template; and A step of calculating the pixel-wise weights of the reference block corresponding to the first reference template and the pixel-wise weights of the reference block corresponding to the second reference template using the regression model. A method including 11. In Paragraph 1, It further includes the step of decoding an index indicating one of the methods for calculating the above weights, and The step of calculating the above weights is, A method for calculating the weights using a method indicated by the index above.

12. A method for encoding a current block performed by an image encoding device, A step of constructing block vector candidates of the current block based on a template cost representing the difference between the current template of the current block and a reference template within a predefined reference region, wherein the block vector candidate indicates a reference block corresponding to the reference template, the current template includes surrounding restored pixels of the current block, and the reference template includes surrounding pixels of the reference block; A step of constructing a candidate list for the application of a fusion mode based on the above block vector candidates or the template costs of the above block vector candidates, wherein the candidate list includes new block vector candidates for the application of the fusion mode; A step of calculating weights for the above new block vector candidates; and A step of predicting the current block based on the above weights and the above new block vector candidates A method including 13. In Paragraph 12, It further includes the step of obtaining an index indicating one of the methods for calculating the above weights, and The step of calculating the above weights is, A method for calculating the weights using a method indicated by the index above.

14. A method for providing video data to a video decoder, A step of encoding the above video data into a bitstream; and Step of transmitting the above bitstream to the above video decoder Includes, The step of encoding the above video data is, A step of constructing block vector candidates of the current block based on a template cost representing the difference between the current template of the current block and a reference template within a predefined reference region, wherein the block vector candidate indicates a reference block corresponding to the reference template, the current template includes surrounding restored pixels of the current block, and the reference template includes surrounding pixels of the reference block; A step of constructing a candidate list for the application of a fusion mode based on the above block vector candidates or the template costs of the above block vector candidates, wherein the candidate list includes new block vector candidates for the application of the fusion mode; A step of calculating weights for the above new block vector candidates; and A step of predicting the current block based on the above weights and the above new block vector candidates A method including

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