Method for history-based block partitioning prediction

Abstract

The present embodiment discloses a method for history-based block partitioning prediction. In the present embodiment, an image decoding device acquires a partitioning structure of a current block, predicts the current block on the basis of the partitioning structure of the current block, utilizes the partitioning structure of the current block so as to update a candidate table including candidates for history-based block partitioning prediction, decodes an index indicating one from among candidates in the candidate table, acquires a predictor of the current block from the candidate table on the basis of the decoded index, and sets the partitioning structure of the current block as a partitioning structure corresponding to the acquired predictor.

Description

Method for history-based block splitting 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 a method for History-based Block Partitioning Prediction (HBPP).

[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 using History-based Block Partitioning Prediction (HBPP), and a recording medium 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: a step of obtaining a partition structure of the current block; a step of predicting the current block based on the partition structure of the current block; and a step of updating a candidate table including candidates for history-based block partition prediction using the partition structure of the current block, wherein each candidate is used as a predictor for predicting the partition structure of the current block.

[0008] According to another embodiment of the present disclosure, a method for encoding a current block performed by an image encoding device comprises: a step of obtaining a partition structure of the current block; a step of predicting the current block based on the partition structure of the current block; and a step of updating a candidate table including candidates for history-based block partition prediction using the partition structure of the current block, wherein each candidate is used as a predictor for predicting the partition structure of the current block.

[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 transmitting the bitstream to the image decoder, wherein the step of encoding the video data comprises: obtaining a partition structure of the current block; predicting the current block based on the partition structure of the current block; and updating a candidate table including candidates for history-based block partition prediction using the partition structure of the current block, wherein each candidate is used as a predictor for predicting the partition structure of the current block.

[0010] According to another embodiment of the present disclosure, a method is provided comprising further a step of obtaining an index indicating one of the candidates in the candidate table, wherein the step of obtaining the partition structure comprises: obtaining a predictor of the current block from the candidate table based on the index; and setting the partition structure of the current block to a partition structure corresponding to the predictor.

[0011] 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.

[0012] In addition, by providing a video encoding / decoding method according to the present embodiment, it is possible to reduce the burden on the network based on bit rate reduction in various content such as UHD (Ultra High Definition) video, game broadcasting, 360-degree video streaming, VR / AR (Virtual Reality / Augmented Reality) video, online lectures, etc., and to reduce energy consumption for video playback devices.

[0013] FIG. 1 is an exemplary block diagram of an image encoding device capable of implementing the technologies of the present disclosure.

[0014] Figure 2 is a diagram illustrating a method for dividing blocks using a QTBTTT (QuadTree plus BinaryTree TernaryTree) structure.

[0015] FIGS. 3a and 3b are diagrams showing a plurality of intra prediction modes including wide-angle intra prediction modes.

[0016] Figure 4 is an example diagram of the surrounding blocks of the current block.

[0017] FIG. 5 is an exemplary block diagram of an image decoding device capable of implementing the technologies of the present disclosure.

[0018] Figures 6a to 6c are example diagrams showing a tree structure.

[0019] Figure 7 is an example diagram showing a method of signaling a tree structure.

[0020] Figure 8 is an example diagram showing a single tree structure.

[0021] FIG. 9 is an exemplary diagram illustrating a method for History-based Block Partitioning Prediction (HBPP) according to one embodiment of the present disclosure.

[0022] FIG. 10 is an exemplary diagram illustrating the decoding of a current block based on an HBPP table according to one embodiment of the present disclosure.

[0023] FIG. 11 is an exemplary diagram showing an update of an HBPP table according to one embodiment of the present disclosure.

[0024] FIG. 12 is an exemplary diagram showing HBPP group-by-group management according to one embodiment of the present disclosure.

[0025] FIG. 13 is an exemplary diagram showing the selection of a partition structure of a current block according to one embodiment of the present disclosure.

[0026] FIG. 14 is a flowchart illustrating a method for predicting a current block using HBPP according to one embodiment of the present disclosure.

[0027] 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.

[0028] 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.

[0029] 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).

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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).

[0035] Figure 2 is a diagram illustrating a method for dividing blocks using a QTBTTT structure.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 a 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.

[0048] 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.

[0049] Various methods can be used to minimize the amount of bits required to encode motion information.

[0050] 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'.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Hereinafter, merge mode and merge skip mode will be collectively referred to as merge / skip mode.

[0056] Another method for encoding motion information is the AMVP (Advanced Motion Vector Prediction) mode.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The reordering unit (150) can perform reordering of coefficient values ​​for quantized residual values.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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).

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 utilizing history-based block partitioning prediction (HBPP), and a recording medium storing a bitstream generated by the image encoding method / apparatus.

[0097] The following embodiments may be performed by components within a video encoding apparatus. Additionally, the following embodiments may be performed by components within a video decoding apparatus.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] I. VVC Split Tree

[0103] The image segmentation process of VVC generates various coding units (CUs) based on the recursive segmentation of coding tree units (CTUs). The image is first divided into CTUs of uniform size. The CTU becomes the top node in the segmentation tree structure for dividing into CUs. Therefore, the maximum size of a CU is equal to the size of a CTU. The image is first divided into 128×128 CTUs, and each CTU can be continuously divided into CUs. Within a CTU, CUs can be configured in various sizes and shapes, ranging from a minimum of 4×4 to the maximum allowable CU size.

[0104] In HEVC, CU sizes up to 64×64 are allowed, but in VVC, CUs of size 128×128 may be allowed. Compared to HEVC, VVC can use CUs with a wider range of allowed sizes (e.g., 128×128 CUs). Additionally, compared to HEVC, VVC can use CUs of various partition shapes.

[0105] The size of the CTU is determined for the luminance and chroma components as follows. CtbSizeY, a variable representing the CTU size of the luminance component, is determined based on parameters passed using higher-level syntax such as VPS, SPS, and PPS. Using CtbSizeY and SubWidthC and SubHeightC from Table 1, CtbWidthC and CtbHeightC, variables representing the CTU size of the chroma component, can be determined. If chroma_format_idc is 0 or separate_colour_plane_flag is 1, CtbWidthC and CtbHeightC are 0. In other cases, CtbWidthC and CtbHeightC are determined as in Equation 1.

[0106]

[0107] As mentioned above, VVC uses BT (Binary Tree), TT (Ternary Tree), and QT (Quad Tree) as tree structures for CU partitioning. The BT and TT structures are collectively referred to as MTT (multi-type tree) structures.

[0108] QT is a tree structure that has four child nodes under one node, as in HEVC. When the QT structure is applied to the current block, as exemplified in FIG. 6a, the current block is divided into four child blocks of the same size, and each child block corresponds to a child node. BT is a tree structure that generates two child nodes from one node, and as exemplified in FIG. 6b, the parent block can be divided into two child blocks of the same size in a horizontal or vertical direction. TT is a tree structure that generates three child nodes from one node in a horizontal or vertical direction. As exemplified in FIG. 6c, child blocks can be generated by dividing the width or height of the parent block in a length ratio of 1:2:1 depending on the division direction.

[0109] CUs can have various sizes and shapes ranging from a minimum of 4×4 to a maximum of 128×128. QTs are recursively partitioned within the allowable size. If a partitioned block satisfies the conditions of the MTT configuration (block size, depth, etc.), BT or TT partitioning can be applied to the partitioned block. If BT or TT partitioning is applied to the current node, QT partitioning can no longer be applied to the child nodes.

[0110] In the example of Fig. 7, the root node represents the CTU. The root node is recursively partitioned by QT. When the minimum size block is reached through continuous partitioning that can no longer be partitioned by QT, the block is partitioned into smaller blocks using BT and TT. For example, if the partitioned block becomes smaller than the size of MinQTSize signaled to the SPS, QT is no longer used.

[0111] As previously mentioned, blocks to which BT and TT have been applied are no longer divided according to QT. When the depth of the block's MTT reaches MaxMttDepth, the block is no longer divided. When the width or height of the block becomes equal to MinCbsize, the block is no longer divided.

[0112] In the example of Fig. 7, the flags related to the splitting of the CTU are as follows. split_cu_flag indicates whether to further split the corresponding node, i.e., the corresponding block. split_qt_flag indicates whether to use QT or MTT to split the corresponding block. mtt_split_cu_vertical_flag indicates whether the splitting direction for the MTT splitting of the corresponding block is horizontal or vertical. Additionally, mtt_split_cu_binary_flag indicates whether the MTT splitting of the corresponding block is BT or TT.

[0113] In the case of YUV images, the image consists of a luminance component Y and two chroma components U and V. In VVC, when the characteristics of the luminance component and the chroma component are different, different tree structures may be used so that the images of the luminance component and the chroma component can be segmented differently.

[0114] The single tree structure utilizes the same tree structure in the lumens and chroma components. The single tree structure is used in the I, P, or B slices. The single tree structure can be implemented as shown in the example of Fig. 8. In the example of Fig. 8, the depth of the root node is set to 0.

[0115] The dual tree structure utilizes different tree structures for block splitting in the luminance and chroma components. The dual tree structure can be used only for I slices. The video encoder can specify one of the dual tree or single tree methods by signaling a flag indicating whether to use the dual tree to the video decoder. When the dual tree is used, the size of the smallest luminance block is 4×4, and the size of the chroma block is 4×4 or 8×2.

[0116] 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.

[0117] In this specification, the term 'and / or' includes a combination of a plurality of described items or any of a plurality of described items.

[0118] II. Embodiments according to the present disclosure

[0119] The present disclosure proposes a method for History-based Block Partitioning Prediction (HBPP) to be used in a video compression process. In the proposed method, an image decoder maintains and updates a table containing HBPP candidates in real time. The image decoder decodes a block and updates the table by adding a block partitioning structure used for compressing the corresponding block as a new HBPP candidate according to a pre-set rule in the table.

[0120] Hereinafter, the HBPP candidate table, HBPP table, candidate table, and table may be used interchangeably. Additionally, the HBPP candidate and candidate may be used interchangeably. Each candidate within the candidate table represents a block and can be utilized as a predictor representing the partition structure of the block. The block partition structure, block partition, and partition structure may be used interchangeably.

[0121] FIG. 9 is an illustrative diagram showing a method for HBPP according to one embodiment of the present disclosure.

[0122] In FIG. 9, the block may be a CTU. Alternatively, the block may refer to a block smaller than a CTU. Alternatively, the block may be a CU or a TU (transform unit). As shown in FIG. 9, the image decoder may use HBPP candidates within a candidate table as additional predictors during the process of predicting the current block. Additionally, after completing the prediction of the current block, the image decoder may newly include the partition structure of the current block in the table. At this time, the image decoder may check whether the partition structure of the current block is a redundant candidate within the table, and create an updated table by sorting the candidates within the table based on whether it is a redundant candidate.

[0123] The video decoder can use HBPP candidates as additional predictors in the process of determining the partition structure of the current block. As HBPP candidates, blocks existing at the same location in different channels, in addition to blocks spatially and temporally adjacent to the current block, may be used. Therefore, HBPP candidates can be utilized even when a fourth channel is added in addition to the three YUV channels. Additionally, prediction efficiency can be improved by utilizing the partition structure of previously encoded non-adjacent blocks based on the proposed method.

[0124] For history-based block partitioning prediction, the video decoder stores the partitioning structures of spatially, temporally, and inter-channel adjacent blocks in a table according to preset rules, and uses the table to predict the partitioning structure of the current block. The video decoder stores partitioning structures allowed in video coding, such as the partitioning of CTUs into CUs or the partitioning of CUs exemplified in FIGS. 6a to 6c, in an HBPP table, and manages the candidates stored in the table using an index. Although the video decoder may separately construct a new block structure for the current block, it may decode index n of HBPP_n, which is the partitioning structure of the previous block stored in the table, and construct the block structure of the current block based on the decoded index. An example in FIG. 10 illustrates the decoding process of the current block based on the HBPP table. As shown in FIG. 10, when the size of the table is N (where N is an integer greater than or equal to 1), index n has values ​​from 0 to N-1.

[0125] The block partitioning structures included in the HBPP candidates can be grouped as follows according to the characteristics of the blocks.

[0126] Spatially adjacent blocks represent blocks that have previously been decoded and are located within the same video frame. As shown in FIG. 4, blocks located to the left and above the current block may be used as candidates associated with spatially adjacent blocks. In this disclosure, such a group is defined as HBPP-S.

[0127] Temporarily adjacent blocks represent blocks contained in a video frame that has previously been decoded and has a different time index from the current block. In this disclosure, such group is defined as HBPP-T. For example, a block co-located with the current block in another frame may be included in HBPP-T. A block located at a position shifted by a motion vector in another frame may be included in HBPP-T. Alternatively, a block adjacent to a block co-located with the current block in another frame may be included in HBPP-T.

[0128] Blocks adjacent to each other between channels represent blocks that have previously been decoded and are contained in a channel different from the current channel. In this disclosure, such a group is defined as HBPP-C. For example, for channels U and V, blocks contained in channel Y may be included in the HBPP-C group. Alternatively, if a new channel, channel A, is additionally compressed in addition to channels Y, U, and V, blocks contained in channels Y, U, and V may be included in the HBPP-C group for channel A.

[0129] The process of configuring and managing the HBPP table is described below.

[0130] It is assumed that an HBPP table of size N includes existing block partition structure predictors HBPP_0 to HBPP_N-1. After completing the decoding of the current block, the image decoder may include the block partition structure of the current block in the table as a new predictor. The image decoder may manage the table according to one of the following methods.

[0131] A First-In First-Out (FIFO) method can be utilized. The image decoding device manages existing indexes by assigning the last index N-1 of the table to the current block that has completed decoding, and decreasing the indexes of existing candidates by one. A candidate with an existing index of 0 is deleted from the table.

[0132] A Last-in First-Out (LIFO) method can be utilized. The image decoding device manages existing indexes by assigning the first index 0 of the table to the current block that has completed decoding, and incrementing the indexes of existing candidates one by one. A candidate with an existing index N-1 is deleted from the table.

[0133] The video decoding device may change the management method according to the group of HBPPs in relation to the aforementioned table management method. For example, different management methods may be applied to HBPP-S, HBPP-T, and HBPP-C according to one or more combinations of the following methods.

[0134] The video decoding device manages some groups of HBPP-S, HBPP-T, and HBPP-C using the aforementioned FIFO or LIFO method, but can manage the remaining groups separately.

[0135] For example, the video decoder manages the HBPP-S group using the aforementioned FIFO or LIFO method, but can manage HBPP-T separately. A fixed index m can be assigned to HBPP-T in the table. Additionally, the video decoder manages the HBPP-S group using the aforementioned FIFO or LIFO method, but can manage HBPP-C separately. A fixed index l can be assigned to HBPP-C in the table.

[0136] When a candidate from the same group is newly included in the table for an HBPP candidate of a specific group during the process of updating the table, the image decoding device may delete the candidate and assign a new candidate to the corresponding index, as shown in FIG. 11. When the decoding of the current block is completed in the current frame T, a block that exists at the same location as the current block but is included in a different frame in time is included in the table as a new candidate. At this time, with respect to the left block, which is the previous block of the current block, a block that exists at the same location as the left block and is included in the previous frame is deleted from the table.

[0137] In addition to the method of managing different HBPP groups together within a single table, as shown in FIG. 12, the image decoder may configure and manage different tables for each group. Each table may contain different HBPP groups and may contain a different number of candidates.

[0138] The process of removing duplicate candidates from the HBPP table is described below.

[0139] As described above, it is assumed that an HBPP table of size N includes existing block partition structure predictors HBPP_0 to HBPP_N-1. After completing the decoding of the current block, the image decoder may include the block partition structure of the current block in the table as a new predictor. At this time, if a duplicate candidate exists when compared with the existing table, the image decoder deletes the corresponding candidate from the table. Regarding the processing of duplicate candidates, the image decoder may use one of the following methods.

[0140] If a newly added candidate overlaps with an existing candidate, the image decoding device can delete the existing candidate and assign the corresponding index to the new candidate.

[0141] If a newly added candidate overlaps with an existing candidate, the video decoder may not add a new candidate.

[0142] The following describes the process of reordering indexes in the HBPP candidate table.

[0143] In the process of managing the index of a candidate table by the aforementioned FIFO or LIFO method, the image decoding device may reorganize the order of the index. For example, the order of the index may be reorganized according to one or more of the following methods.

[0144] The video decoder changes the order by reflecting the maximum depth used for block partitioning. For example, if the depth used for block partitioning is greater than that of the previous block, the order may be changed so that the index of the corresponding block becomes smaller or larger.

[0145] The video decoder changes the order based on the group of blocks. For example, if the group of blocks is HBPP-S, the order may be changed so that the corresponding index becomes smaller or larger compared to other groups.

[0146] The video decoder changes the order based on whether MTT is used in relation to block partitioning. For example, if a block is partitioned only by QT, the order may be changed so that the corresponding index becomes smaller or larger.

[0147] The following describes the process of selecting the partition structure of the current block based on candidates within the HBPP table.

[0148] The image decoding device may use a block partitioning structure corresponding to a final predictor selected from among several candidates shown in FIG. 9 as a partitioning structure of the current block. At this time, the partitioning structure of the current block may be selected according to one or more of the following methods.

[0149] The video decoder can use the division structure of the final predictor as is as the division structure of the current block.

[0150] The image decoder may utilize only the partitioning structure up to a certain depth in relation to the partitioning structure of the final predictor. For example, as shown in FIG. 13, only the partitioning structure up to depth 1 may be utilized and the remaining partitioning structure may not be used.

[0151] The image decoder can utilize only the QT partitioning structure from the final predictor's partitioning structure.

[0152] A video decoder can be configured such that, in relation to the partitioning structure of a block included in a UV channel or an A channel, the depth of the partitioning structure is equal to or smaller than that of the Y channel. That is, the characteristics of the partitioning structure (depth, BT, TT, etc.) can be determined based on the characteristics of the partitioning structure of the Y channel (depth, BT, TT, etc.).

[0153] The video decoding device can resolve delay issues that may occur during the decoding process by not using spatially adjacent partition structures that completed decoding immediately prior to the current block.

[0154] The update cycle of the HBPP candidate table is described below.

[0155] The update cycle of the HBPP candidate table can be set according to one or more of the following.

[0156] The video decoder updates the HBPP table within a frame group consisting of multiple video frames. The HBPP table may be reset when decoding of a new video frame group begins.

[0157] The video decoder can reset the table in an I(Intra) frame.

[0158] The video decoder updates the HBPP table within a video frame. The HBPP table can be reset when decoding of a new video frame begins.

[0159] The video decoder updates the HBPP table within a video slice or tile. The HBPP table may be reset when decoding of a new video slice or tile begins.

[0160] The video decoder updates the HBPP table within a group consisting of rows of the CTU. The HBPP table may be reset when decoding for a new row of the CTU begins.

[0161] The video decoder updates the HBPP table within groups consisting of CTU rows within a slice or tile. The HBPP table may be reset when decoding for a new row of CTUs begins.

[0162] The video decoder updates the HBPP table within the CTU. When decoding of a new CTU begins, the video decoder resets the previous table, creates a new table composed of partition information of the block immediately adjacent to the block currently being decoded in the spatial, temporal, and / or channel region, and can use the created table.

[0163] The video decoder can reset the HBPP table when decoding of a new CU begins.

[0164] The following describes the signaling related to the use of HBPP.

[0165] A flag indicating whether to use HBPP within a video sequence can be transmitted via the SPS (sequence parameter set).

[0166] A flag determining whether to use HBPP within a video frame can be transmitted via the PPS (picture parameter set).

[0167] At the slice, tile, or video block (e.g., CTU) level, a flag determining whether to use HBPP may be transmitted.

[0168] Hereinafter, a method for predicting the current block using history-based block partitioning prediction is described using the illustration of FIG. 14. The illustration of FIG. 14 can be performed by an image encoding device and an image decoding device. FIG. 14 is described based on the image encoding device, and if necessary, the operation by the image decoding device is additionally described.

[0169] FIG. 14 is a flowchart illustrating a method for predicting a current block using HBPP according to one embodiment of the present disclosure.

[0170] The video encoding device obtains the division structure of the current block (S1400).

[0171] The video encoding device generates a prediction block of the current block based on the division structure of the current block (S1402).

[0172] The video encoding device obtains a flag indicating whether to use history-based block partitioning prediction. The video encoding device may obtain the flag from, for example, a high level. As another example, the video encoding device may determine the flag in terms of rate distortion optimization. The video encoding device may encode the flag. The video decoder may decode the flag from the bitstream.

[0173] When the use of history-based block partitioning prediction is indicated, the video encoding device utilizes the partitioning structure of the current block to update a candidate table containing candidates for history-based block partitioning prediction (S1404).

[0174] Here, the candidate table includes candidates for history-based block partitioning prediction. Each candidate is used to represent the partitioning structure of each candidate and can be used as a predictor to predict the partitioning structure of the current block. Additionally, the candidates may be composed of a plurality of candidate groups, including a first candidate group containing blocks spatially adjacent to the current block, a second candidate group containing blocks temporally adjacent to the current block, and a third candidate group containing blocks adjacent between channels. Here, temporally adjacent blocks may be blocks included in a pre-coded video frame having a time index different from that of the current block, and may be blocks co-located with the current block or blocks adjacent to blocks in the same location. Blocks adjacent between channels may be blocks included in a pre-coded channel different from the channel being decoded of the current block.

[0175] The video encoding device can update some candidate groups according to a first-in, first-out or last-in, first-out method and assign fixed indices to the remaining candidate groups.

[0176] The video encoding device compares the partition structure of the current block with the partition structures of candidates in the candidate table to determine whether the current block is a duplicate candidate. Depending on whether the current block is a duplicate candidate, the video encoding device may include the current block as a new candidate in the candidate table.

[0177] If the current block is not a duplicate candidate, the video encoding device may, according to the first-in, first-out method, include the new candidate in the candidate table with the last index assigned to it and delete the candidate with the first index from the candidate table. Alternatively, according to the last-in, first-out method, the video encoding device may include the new candidate in the candidate table with the first index assigned to it and delete the candidate with the last index from the candidate table.

[0178] If the current block is a duplicate candidate, the video encoding device may delete the existing candidate that duplicates the current block from the candidate table, include the current block as a new candidate in the candidate table, and assign an index corresponding to the deleted candidate to the new candidate.

[0179] The video encoding device can reorder the indexes corresponding to the candidates to update the candidate table. For example, the order of the indexes can be reordered based on the maximum depth used for partitioning each candidate.

[0180] Regarding the update cycle of the candidate table, the HBPP table may be updated within a frame group composed of multiple video frames. For example, when encoding of a new frame group begins, the video encoding device may reset the candidate table. Alternatively, when encoding of a new CTU or a new CU begins, the candidate table may be reset. The video encoding device may construct a new candidate table using blocks temporally adjacent to the current block and blocks adjacent between channels. The video encoding device may set the partitioning structure of the current block based on the new candidate table. At this time, with respect to the chroma channel of the current block, the depth of the partitioning structure of the chroma channel may be set to be equal to or smaller than the depth of the partitioning structure of the luma channel of the current block.

[0181] As another example, the video encoding device can obtain an index that indicates one of the candidates in a candidate table. The video encoding device can obtain the index, for example, from a high level. As another example, the video encoding device can determine the index in terms of rate distortion optimization. The video encoding device can encode the index. The video decoder can decode the index from a bitstream.

[0182] The video encoding device can obtain a predictor of the current block from a candidate table based on an index and set the partitioning structure of the current block to a partitioning structure corresponding to the predictor of the current block. For example, among the partitioning structures corresponding to the predictor of the current block, a partitioning structure up to a preset depth can be utilized.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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).

[0188] 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.

[0189]

[0190] CROSS-REFERENCE TO RELATED APPLICATION

[0191] This patent application claims priority to Korean patent application No. 10-2024-0173326 filed on November 28, 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 obtaining a candidate table containing candidates for history-based block partitioning prediction; A step of obtaining the partition structure of the current block above; and A step of predicting the current block based on the partition structure of the current block. Includes, A method used to express the partition structure of each candidate.

2. In Paragraph 1, It further includes the step of decoding a flag indicating whether to use the above history-based block partitioning prediction, and If the above flag indicates the use of history-based block splitting prediction, The above candidate table is obtained, and A method comprising the step of updating the candidate table by utilizing the partition structure of the current block.

3. In Paragraph 1, The above candidates are, A method comprising a block spatially adjacent to the current block, a block temporally adjacent to the current block, and a block adjacent between channels.

4. In Paragraph 3, The aforementioned temporally adjacent blocks are, A method comprising a modified video frame having a time index different from the current block, wherein the block is co-located with the current block or is adjacent to the block co-located with the current block.

5. In Paragraph 3, A method in which a block adjacent to the above channels is a block included in a previously decoded channel different from the channel currently being decoded of the above block.

6. In Paragraph 2, The step of updating the above candidate table is, A step of determining whether the current block is a duplicate candidate by comparing the partition structure of the current block with the partition structures of the candidates; and A step of including the current block as a new candidate in the candidate table depending on whether the current block is a duplicate candidate. A method including 7. In Paragraph 6, The step of including the partition structure of the current block in the candidate table is, A method in which, if the current block is not a duplicate candidate, the new candidate is included in the candidate table with the last index assigned to the new candidate according to the first-in, first-out method, and the candidate with the first index is deleted from the candidate table.

8. In Paragraph 6, The step of including the partition structure of the current block in the candidate table is, A method for, when the current block is a duplicate candidate, deleting the existing candidate that is duplicated with the current block from the candidate table, including the current block as a new candidate in the candidate table, and assigning an index corresponding to the deleted candidate to the new candidate.

9. In Paragraph 6, The step of updating the above candidate table is, It further includes the step of reorganizing the order of indices corresponding to the above candidates, and The step of reorganizing the order of the above indices is, A method for reconstructing the order of the above indices based on the maximum depth used in the splitting of each candidate.

10. In Paragraph 1, When decoding of a new CTU (Coding Tree Unit) or a new CU (Coding Unit) begins, Step of resetting the above candidate table; and A step of constructing a new candidate table using blocks temporally adjacent to the current block and blocks adjacent between channels. Includes more, The step of obtaining the above-mentioned segmented structure is, A method for setting the partition structure of the current block based on the above new candidate table.

11. In Paragraph 10, The step of setting the division structure of the current block above is, A method for setting the depth of the segmentation structure of the chroma channel of the current block to be equal to or smaller than the depth of the segmentation structure of the luminance channel of the current block in relation to the chroma channel of the current block.

12. In Paragraph 1, Step of decrypting an index indicating one of the candidates in the above candidate table Includes more, The step of obtaining the above-mentioned segmented structure is, A step of obtaining a predictor of the current block from the candidate table based on the above index; and Step of setting the partition structure of the current block to a partition structure corresponding to the predictor of the current block A method including 13. A method for encoding a current block performed by an image encoding device, A step of obtaining a candidate table containing candidates for history-based block partitioning prediction; A step of obtaining the partition structure of the current block above; and A step of predicting the current block based on the partition structure of the current block. Includes, A method used to express the partition structure of each candidate.

14. In Paragraph 13, A step of obtaining a flag indicating whether to use the history-based block partitioning prediction above; and Step of encoding the above flag Includes more, If the above flag indicates the use of history-based block splitting prediction, The above candidate table is obtained, and A method comprising the step of updating the candidate table by utilizing the partition structure of the current block.

15. In Paragraph 14, The step of updating the above candidate table is, A step of determining whether the current block is a duplicate candidate by comparing it with the partition structure of candidates in the candidate table; and A step of including the partition structure of the current block as a new candidate in the candidate table, depending on whether the current block is a duplicate candidate. A method including 16. In Paragraph 13, A step of obtaining an index that indicates one of the candidates in the above candidate table. Includes more, The step of obtaining the above-mentioned segmented structure is, A step of obtaining a predictor of the current block from the candidate table based on the above index; and Step of setting the partition structure of the current block above to the partition structure corresponding to the predictor above A method including 17. 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 obtaining a candidate table containing candidates for history-based block partitioning prediction; A step of obtaining the partition structure of the current block; and A step of predicting the current block based on the partition structure of the current block. Includes, A method used to express the partition structure of each candidate.

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