KR20230105647A - Method and Apparatus for Video Coding Using Improved Merge with Motion Vector Difference - Google Patents

Abstract

Disclosed are a video coding method and apparatus using improved merge with motion vector difference. The present embodiment provides a video coding method and device, wherein a bidirectional differential motion vector is adaptively generated for bidirectional motion information prediction using a unidirectional differential motion vector derived according to a merge with motion vector difference (MMVD) mode, and the generated bidirectional differential motion vector is adaptively applied to an arbitrary unidirectional reference picture or bidirectional reference picture. The method includes the steps of: generating a bidirectional motion vector predictor of a current block; generating a unidirectional differential motion vector; and generating a bidirectional motion vector of the current block.

Description

Method and Apparatus for Video Coding Using Improved Merge with Motion Vector Difference

The present disclosure relates to a video coding method and apparatus using improved differential motion vector merge.

The contents described below merely provide background information related to the present embodiment and do not constitute prior art.

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

Therefore, when video data is stored or transmitted, an encoder is used to compress and store or transmit the video data, and a decoder receives, decompresses, and reproduces the compressed video data. Examples of such video compression technologies include H.264/AVC, High Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC), which has improved coding efficiency by about 30% or more compared to HEVC.

However, since the size, resolution, and frame rate of video are gradually increasing, and the amount of data to be encoded accordingly increases, a new compression technology with higher encoding efficiency and higher picture quality improvement effect than existing compression technologies is required.

In inter prediction, merge mode uses motion information of a merge candidate list as it is as motion information of a current block (as a coding unit block, also called CU), and does not transmit other additional motion information. This merge mode has an advantage of minimizing the amount of transmitted bits, but has limitations in expressing optimal motion information. In order to compensate for this disadvantage, a Merge with Motion Vector Difference (MMVD) mode corrects motion information by adding a Motion Vector Difference (MVD) to a motion vector derived by the merge mode.

The MMVD mode can generate differential motion vectors for both directions using derived unidirectional differential motion vector information and scaling. For example, when the POC (Picture Order Count) difference between the current picture and the L0/L1 reference pictures is the same, the value of the derived differential motion vector is applied to the L0 and L1 directions as it is. Alternatively, when the absolute value of the POC difference between the current picture and the L0 reference picture is greater than the absolute value of the POC difference between the current picture and the L1 picture, the derived differential motion vector is applied in the L0 direction, and the derived differential motion vector is scaled. Then, the scaled differential motion vector is applied in the L1 direction. On the other hand, if the absolute value of the POC difference between the current picture and the L1 reference picture is greater than the absolute value of the POC difference between the current picture and the L0 reference picture, the derived differential motion vector is applied in the L1 direction, and the derived differential motion vector is used for scaling. After that, the scaled differential motion vector is applied in the L0 direction.

As described above, the existing MMVD mode has a disadvantage in that the value of the derived differential motion vector is always applied to both reference pictures in both directions. Therefore, in order to improve video coding efficiency and video quality, improvement of the MMVD mode needs to be considered.

The present disclosure, in order to improve video quality and improve video encoding efficiency, uses a unidirectional differential motion vector derived according to a Merge with Motion Vector Difference (MMVD) mode to bidirectional predictive motion information (motion information). It is an object of the present invention to provide a video coding method and apparatus for adaptively generating a bidirectional differential motion vector for prediction) and adaptively applying the generated bidirectional differential motion vector to an arbitrary unidirectional reference picture or bidirectional reference picture. .

According to an embodiment of the present disclosure, in the method of generating motion vectors of a current block performed by a video decoding apparatus, a bi-directional motion vector predictor of the current block using a merge mode , where the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor; generating a unidirectional differential motion vector for the current block using a merge with motion vector difference mode; obtaining application direction indication information, wherein the application direction indication information indicates an L0 direction, an L1 direction, or both directions; The differential motion vector is transmitted to the L0-direction motion vector predictor, the L1-direction motion vector predictor, or the bi-directional motion vector predictors according to the application direction indication information. By applying, generating bi-directional motion vectors of the current block.

According to another embodiment of the present disclosure, in a method of generating motion vectors of a current block performed by an image encoding apparatus, bidirectional motion vector predictors of the current block using a merge mode ), wherein the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor; generating a unidirectional differential motion vector for the current block using a merge with motion vector difference mode; An optimal direction is selected by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors, and based on the optimal direction, the current block generating bi-directional motion vectors; Generating application direction indication information based on the optimal direction, wherein the application direction indication information indicates an L0 direction, an L1 direction, or both directions.

According to another embodiment of the present disclosure, a computer readable recording medium storing a bitstream generated by an image encoding method, wherein the image encoding method predicts a bi-directional motion vector of a current block using a merge mode. generating motion vector predictors, wherein the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor; generating a unidirectional differential motion vector for the current block using a merge with motion vector difference mode; An optimal direction is selected by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors, and based on the optimal direction, the current block generating bi-directional motion vectors; and generating application direction indication information based on the optimal direction, wherein the application direction indication information indicates an L0 direction, an L1 direction, or both directions.

As described above, according to the present embodiment, a bi-directional differential motion vector is adaptively generated for bi-directional predictive motion information using the uni-directional differential motion vector derived according to the MMVD mode, and the generated bi-directional differential motion vector is By providing a video coding method and apparatus adaptively applied to any unidirectional reference picture or bidirectional reference picture, it is possible to improve video coding efficiency and video quality.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of this disclosure.
2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.
3A and 3B are diagrams illustrating a plurality of intra prediction modes including wide-angle intra prediction modes.
4 is an exemplary diagram of neighboring blocks of a current block.
5 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure.
6 is an exemplary diagram illustrating generation of bi-directional motion information according to an implicit method according to an embodiment of the present disclosure.
7 is an exemplary diagram illustrating generation of bi-directional motion information according to an explicit method according to an embodiment of the present disclosure.
8 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image encoding apparatus according to an embodiment of the present disclosure.
9 is a flowchart illustrating a method of generating bi-directional motion vectors of a current block by an image encoding apparatus according to another embodiment of the present disclosure.
10 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image decoding apparatus according to an embodiment of the present disclosure.
11 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image encoding apparatus according to another embodiment of the present disclosure.
12 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image decoding apparatus according to another embodiment of the present disclosure.

DETAILED DESCRIPTION Some embodiments of the present disclosure are described in detail below with reference to exemplary drawings. In adding reference numerals to components of each drawing, it should be noted that the same components have the same numerals as much as possible even if they are displayed on different drawings. In addition, in describing the present embodiments, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present embodiments, the detailed description will be omitted.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of this disclosure. Hereinafter, with reference to the illustration of FIG. 1, an image encoding device and sub-components of the device will be described.

The image encoding apparatus includes a picture division unit 110, a prediction unit 120, a subtractor 130, a transform unit 140, a quantization unit 145, a rearrangement unit 150, an entropy encoding unit 155, and an inverse quantization unit. 160, an inverse transform unit 165, an adder 170, a loop filter unit 180, and a memory 190.

Each component of the image encoding device may be implemented as hardware or software, or as a combination of hardware and software. Also, the function of each component may be implemented as software, and the microprocessor may be implemented to execute the software function corresponding to each component.

One image (video) is composed of one or more sequences including a plurality of pictures. Each picture is divided into a plurality of areas and encoding is performed for each area. For example, one picture is divided into one or more tiles and/or slices. Here, one or more tiles may 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 CUs (Coding Units) by a tree structure. Information applied to each CU is coded as a CU syntax, and information commonly applied to CUs included in one CTU is coded as a CTU syntax. In addition, information commonly applied to all blocks in one slice is coded as syntax of a slice header, and information applied to all blocks constituting one or more pictures is a picture parameter set (PPS) or picture coded in the header. Furthermore, information commonly referred to by a plurality of pictures is coded into a Sequence Parameter Set (SPS). Also, information commonly referred to by one or more SPSs is coded into a video parameter set (VPS). Also, information commonly applied to one tile or tile group may be encoded as syntax of a tile or tile group header. Syntax included in the SPS, PPS, slice header, tile or tile group header may be referred to as high level syntax.

The picture divider 110 determines the size of a coding tree unit (CTU). Information on the size of the CTU (CTU size) is encoded as SPS or PPS syntax and transmitted to the video decoding apparatus.

The picture division unit 110 divides each picture constituting an image into a plurality of Coding Tree Units (CTUs) having a predetermined size, and then iteratively divides the CTUs using a tree structure. Divide (recursively). A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of encoding.

As a tree structure, a quad tree (QT) in which a parent node (or parent node) is divided into four subnodes (or child nodes) of the same size, or a binary tree (BinaryTree) in which a parent node is divided into two subnodes , BT), or a TernaryTree (TT) in which a parent node is split into three subnodes at a ratio of 1:2:1, or a structure in which two or more of these QT structures, BT structures, and TT structures are mixed. there is. For example, a QuadTree plus BinaryTree (QTBT) structure may be used, or a QuadTree plus BinaryTree TernaryTree (QTBTTT) structure may be used. Here, BTTT may be combined to be referred to as MTT (Multiple-Type Tree).

2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.

As shown in FIG. 2, the CTU may first be divided into QT structures. Quadtree splitting can be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of leaf nodes allowed by QT. A first flag (QT_split_flag) indicating whether each node of the QT structure is split into four nodes of a lower layer is encoded by the entropy encoder 155 and signaled to the video decoding device. If the leaf node of QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further divided into either a BT structure or a TT structure. A plurality of division directions may exist in the BT structure and/or the TT structure. For example, there may be two directions in which blocks of the corresponding node are divided horizontally and vertically. As shown in FIG. 2, when MTT splitting starts, a second flag (mtt_split_flag) indicating whether nodes are split, and if split, a flag indicating additional split direction (vertical or horizontal) and/or split type (Binary or Ternary) is encoded by the entropy encoding unit 155 and signaled to the video decoding apparatus.

Alternatively, prior to coding the first flag (QT_split_flag) indicating whether each node is split into four nodes of a lower layer, a CU split flag (split_cu_flag) indicating whether the node is split is coded. It could be. When 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 a basic unit of encoding. When the value of the CU split flag (split_cu_flag) indicates splitting, the video encoding apparatus starts encoding from the first flag in the above-described manner.

As another example of a tree structure, when QTBT is used, the block of the corresponding node is divided into two blocks of the same size horizontally (i.e., symmetric horizontal splitting) and the type that splits vertically (i.e., symmetric vertical splitting). Branches may exist. A split flag (split_flag) indicating whether each node of the BT structure is split into blocks of a lower layer and split type information indicating a split type are encoded by the entropy encoder 155 and transmitted to the video decoding device. Meanwhile, a type in which a block of a corresponding node is divided into two blocks having an asymmetric shape may additionally exist. The asymmetric form may include a form in which the block of the corresponding node is divided into two rectangular blocks having a size ratio of 1:3, or a form in which the block of the corresponding node is divided in a diagonal direction may be included.

A CU can have various sizes depending on the QTBT or QTBTTT split from the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (ie, a leaf node of QTBTTT) is referred to as a 'current block'. Depending on the adoption of the QTBTTT division, the shape of the current block may be rectangular as well as square.

The prediction unit 120 predicts a current block and generates a prediction block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124 .

In general, each current block in a picture can be coded predictively. In general, prediction of a current block uses an intra-prediction technique (using data from a picture containing the current block) or an inter-prediction technique (using data from a picture coded before the picture containing the current block). can be performed Inter prediction includes both uni-prediction and bi-prediction.

The intra predictor 122 predicts pixels in the current block using pixels (reference pixels) located around the current block in the current picture including the current block. A plurality of intra prediction modes exist according to the prediction direction. For example, as shown in FIG. 3A, the plurality of intra prediction modes may include two non-directional modes including a planar mode and a DC mode and 65 directional modes. Depending on each prediction mode, the neighboring pixels to be used and the arithmetic expression are defined differently.

For efficient directional prediction of the rectangular current block, directional modes (numbers 67 to 80 and -1 to -14 intra prediction modes) indicated by dotted arrows in FIG. 3B may be additionally used. These may be referred to as “wide angle intra-prediction modes”. In FIG. 3B , arrows indicate corresponding reference samples used for prediction and do not indicate prediction directions. The prediction direction is opposite to the direction the arrow is pointing. Wide-angle intra prediction modes are modes that perform prediction in the opposite direction of a specific directional mode without additional bit transmission when the current block is rectangular. At this time, among the wide-angle intra prediction modes, some wide-angle intra prediction modes usable for the current block may be determined by the ratio of the width and height of the rectangular current block. For example, wide-angle intra prediction modes (67 to 80 intra prediction modes) having an angle smaller than 45 degrees are usable when the current block has a rectangular shape with a height smaller than a width, and a wide angle having an angle greater than -135 degrees. Intra prediction modes (-1 to -14 intra prediction modes) are available when the current block has a rectangular shape where the width is greater than the height.

The intra prediction unit 122 may determine an intra prediction mode to be used 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 be used from the tested modes. For example, the intra predictor 122 calculates rate-distortion values using rate-distortion analysis for several tested intra-prediction modes, and has the best rate-distortion characteristics among the tested modes. Intra prediction mode can also be selected.

The intra prediction unit 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts a current block using neighboring pixels (reference pixels) determined according to the selected intra prediction mode and an arithmetic expression. Information on the selected intra prediction mode is encoded by the entropy encoder 155 and transmitted to the video decoding apparatus.

The inter prediction unit 124 generates a prediction block for a current block using a motion compensation process. The inter-prediction unit 124 searches for a block most similar to the current block in the encoded and decoded reference picture prior to the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector (MV) corresponding to displacement between the current block in the current picture and the prediction block in the reference picture is generated. In general, motion estimation is performed on a luma component, and a motion vector calculated based on the luma component is used for both the luma component and the chroma component. Motion information including reference picture information and motion vector information used to predict the current block is encoded by the entropy encoding unit 155 and transmitted to the video decoding apparatus.

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

Meanwhile, the inter prediction unit 124 may perform inter prediction using bi-prediction. In the case of bi-directional prediction, two reference pictures and two motion vectors representing positions of blocks most similar to the current block within each reference picture are used. The inter prediction unit 124 selects a first reference picture and a second reference picture from reference picture list 0 (RefPicList0) and reference picture list 1 (RefPicList1), respectively, and searches for a block similar to the current block within each reference picture. A first reference block and a second reference block are generated. Then, a prediction block for the current block is generated by averaging or weighted averaging the first reference block and the second reference block. Further, motion information including information on two reference pictures used to predict the current block and information on two motion vectors is delivered to the encoder 150. Here, reference picture list 0 may include pictures prior to the current picture in display order among restored pictures, and reference picture list 1 may include pictures after the current picture in display order among restored pictures. there is. However, it is not necessarily limited to this, and in order of display, ups and downs pictures subsequent to the current picture may be additionally included in reference picture list 0, and conversely, ups and downs pictures prior to the current picture may be additionally included in reference picture list 1. may also be included.

Various methods may be used to minimize the amount of bits required to encode motion information.

For example, when the reference picture and motion vector of the current block are the same as those of the neighboring block, the motion information of the current block can be delivered to the video decoding apparatus by encoding information capable of identifying the neighboring block. This method is called 'merge mode'.

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

Neighboring blocks for deriving merge candidates include a left block (A0), a lower left block (A1), an upper block (B0), and an upper right block (B1) adjacent to the current block in the current picture, as shown in FIG. ), and all or part of the upper left block A2 may be used. Also, a block located in a reference picture (which may be the same as or different from a reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be additionally used as a merge candidate. If the number of merge candidates selected by the method described above is less than the preset number, a 0 vector is added to the merge candidates.

The inter prediction unit 124 constructs a merge list including a predetermined number of merge candidates using these neighboring blocks. Among the merge candidates included in the merge list, a merge candidate to be used as motion information of the current block is selected, and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the encoder 150 and transmitted to the video decoding apparatus.

Merge skip mode is a special case of merge mode. After performing quantization, when all transform coefficients for entropy encoding are close to zero, only neighboring block selection information is transmitted without transmitting residual signals. By using the merge skip mode, it is possible to achieve a relatively high encoding efficiency in low-motion images, still images, screen content images, and the like.

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

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

In the AMVP mode, the inter prediction unit 124 derives predictive motion vector candidates for the motion vector of the current block using neighboring blocks of the current block. Neighboring blocks used to derive predictive motion vector candidates include a left block A0, a lower left block A1, an upper block B0, and an upper right block adjacent to the current block in the current picture shown in FIG. B1), and all or part of the upper left block (A2) may be used. In addition, a block located in 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 will be used as a neighboring block used to derive motion vector candidates. may be For example, a collocated block co-located with the current block within the reference picture or blocks adjacent to the collocated block may be used. If the number of motion vector candidates is smaller than the preset number according to the method described above, a 0 vector is added to the motion vector candidates.

The inter-prediction unit 124 derives predicted motion vector candidates using the motion vectors of the neighboring blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, a differential motion vector is calculated by subtracting the predicted motion vector from the motion vector of the current block.

The predicted motion vector may be obtained by applying a predefined function (eg, median value, average value operation, etc.) to predicted motion vector candidates. In this case, the video decoding apparatus also knows the predefined function. In addition, since a neighboring block used to derive a predicted motion vector candidate is a block that has already been encoded and decoded, the video decoding apparatus also knows the motion vector of the neighboring block. Therefore, the video encoding apparatus does not need to encode information for identifying a predictive motion vector candidate. Therefore, in this case, information on differential motion vectors and information on reference pictures used to predict the current block are encoded.

Meanwhile, the predicted motion vector may be determined by selecting one of the predicted motion vector candidates. In this case, along with information on differential motion vectors and information on reference pictures used to predict the current block, information for identifying the selected predictive motion vector candidate is additionally encoded.

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

The transform unit 140 transforms the residual signal in the residual block having pixel values in the spatial domain into transform coefficients in the frequency domain. The transform unit 140 may transform residual signals in the residual block by using the entire size of the residual block as a transform unit, or divide the residual block into a plurality of subblocks and use the subblocks as a transform unit to perform transformation. You may. Alternatively, the residual signals may be divided into two subblocks, a transform region and a non-transform region, and transform the residual signals using only the transform region subblock as a transform unit. Here, the transformation region subblock may be one of two rectangular blocks having a size ratio of 1:1 based on a horizontal axis (or a vertical axis). In this case, a flag (cu_sbt_flag) indicating that only subblocks have been transformed, directional (vertical/horizontal) information (cu_sbt_horizontal_flag), and/or location information (cu_sbt_pos_flag) are encoded by the entropy encoding unit 155 and signaled to the video decoding device. do. In addition, the size of the transform region subblock may have a size ratio of 1:3 based on the horizontal axis (or vertical axis), and in this case, a flag (cu_sbt_quad_flag) for distinguishing the corresponding division is additionally encoded by the entropy encoder 155 to obtain an image It is signaled to the decryption device.

Meanwhile, the transform unit 140 may individually transform the residual block in the horizontal direction and the vertical direction. 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 may be defined as a multiple transform set (MTS). The transform unit 140 may select one transform function pair having the highest transform efficiency among the MTS and transform the residual blocks in the horizontal and vertical directions, respectively. Information (mts_idx) on a pair of transform functions selected from the MTS is encoded by the entropy encoding unit 155 and signaled to the video decoding device.

The quantization unit 145 quantizes transform coefficients output from the transform unit 140 using a quantization parameter, and outputs the quantized transform coefficients to the entropy encoding unit 155 . The quantization unit 145 may directly quantize a related residual block without transformation for a certain block or frame. The quantization unit 145 may apply different quantization coefficients (scaling values) according to positions of transform coefficients in the transform block. A quantization matrix applied to the two-dimensionally arranged quantized transform coefficients may be coded and signaled to the video decoding apparatus.

The rearrangement unit 150 may rearrange the coefficient values of the quantized residual values.

The reordering unit 150 may change a 2D coefficient array into a 1D coefficient sequence using coefficient scanning. For example, the reordering unit 150 may output a one-dimensional coefficient sequence by scanning DC coefficients to coefficients in a high frequency region using a zig-zag scan or a diagonal scan. . Depending on the size of the transformation unit and intra prediction mode, instead of zig-zag scan, vertical scan that scans a 2D coefficient array in a column direction and horizontal scan that scans 2D block-shaped coefficients in a row direction may be used. That is, a scan method to be used among zig-zag scan, diagonal scan, vertical scan, and horizontal scan may be determined according to the size of the transform unit and the intra prediction mode.

The entropy encoding unit 155 uses various encoding schemes such as CABAC (Context-based Adaptive Binary Arithmetic Code) and Exponential Golomb to convert the one-dimensional quantized transform coefficients output from the reordering unit 150 to each other. A bitstream is created by encoding the sequence.

In addition, the entropy encoding unit 155 encodes information such as CTU size, CU splitting flag, QT splitting flag, MTT splitting type, and MTT splitting direction related to block splitting so that the video decoding apparatus can divide the block in the same way as the video encoding apparatus. make it possible to divide In addition, the entropy encoding unit 155 encodes information about a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and encodes intra prediction information (ie, intra prediction) according to the prediction type. mode) or inter prediction information (motion information encoding mode (merge mode or AMVP mode), merge index in case of merge mode, reference picture index and differential motion vector information in case of AMVP mode) are encoded. Also, the entropy encoding unit 155 encodes information related to quantization, that is, information about quantization parameters and information about quantization matrices.

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

The adder 170 restores the current block by adding the restored residual block and the predicted block generated by the predictor 120. Pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The loop filter unit 180 reconstructs pixels in order to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. caused by block-based prediction and transformation/quantization. perform filtering on The filter unit 180 is an in-loop filter and may include all or part of a deblocking filter 182, a sample adaptive offset (SAO) filter 184, and an adaptive loop filter (ALF) 186. .

The deblocking filter 182 filters the boundary between reconstructed blocks to remove blocking artifacts caused by block-by-block encoding/decoding, and the SAO filter 184 and alf 186 perform deblocking filtering. Additional filtering is performed on the image. The SAO filter 184 and the alf 186 are filters used to compensate for a difference between a reconstructed pixel and an original pixel caused by lossy coding. The SAO filter 184 improves not only subjective picture quality but also coding efficiency by applying an offset in units of CTUs. In contrast, the ALF 186 performs block-by-block filtering. Distortion is compensated for by applying different filters by distinguishing the edge of the corresponding block and the degree of change. Information on filter coefficients to be used for ALF may be coded and signaled to the video decoding apparatus.

The reconstruction block filtered through the deblocking filter 182, the SAO filter 184, and the ALF 186 is stored in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture can be used as a reference picture for inter-prediction of blocks in the picture to be encoded later.

5 is an exemplary block diagram of a video decoding apparatus capable of implementing the techniques of this disclosure. Hereinafter, referring to FIG. 5, a video decoding device and sub-elements of the device will be described.

The image decoding apparatus includes an entropy decoding unit 510, a rearrangement unit 515, an inverse quantization unit 520, an inverse transform unit 530, a prediction unit 540, an adder 550, a loop filter unit 560, and a memory ( 570) may be configured.

Like the image encoding device of FIG. 1 , each component of the image decoding device may be implemented as hardware or software, or a combination of hardware and software. Also, the function of each component may be implemented as software, and the microprocessor may be implemented to execute the software function corresponding to each component.

The entropy decoding unit 510 determines a current block to be decoded by extracting information related to block division by decoding the bitstream generated by the video encoding apparatus, and provides prediction information and residual signals necessary for restoring the current block. extract information, etc.

The entropy decoding unit 510 determines the size of the CTU by extracting information about the CTU size from a sequence parameter set (SPS) or a picture parameter set (PPS), and divides the picture into CTUs of the determined size. Then, the CTU is divided using the tree structure by determining the CTU as the top layer of the tree structure, that is, the root node, and extracting division information for the CTU.

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

As another example, when a CTU is split using the QTBTTT structure, a CU split flag (split_cu_flag) indicating whether the CU is split is first extracted, and when the corresponding block is split, a first flag (QT_split_flag) is extracted. may be During the splitting process, each node may have zero or more iterative MTT splits after zero or more repetitive QT splits. For example, the CTU may immediately undergo MTT splitting, or conversely, only QT splitting may occur multiple times.

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

Meanwhile, when the entropy decoding unit 510 determines a current block to be decoded by using tree structure partitioning, it extracts information about a prediction type indicating whether the current block is intra-predicted or inter-predicted. When the prediction type information indicates intra prediction, the entropy decoding unit 510 extracts syntax elements for intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the entropy decoding unit 510 extracts syntax elements for the inter prediction information, that is, information indicating a motion vector and a reference picture to which the motion vector refers.

In addition, the entropy decoding unit 510 extracts quantization-related information and information about quantized transform coefficients of the current block as information about the residual signal.

The reordering unit 515 converts the sequence of 1-dimensional quantized transform coefficients entropy-decoded in the entropy decoding unit 510 into a 2-dimensional coefficient array (ie, in the reverse order of the coefficient scanning performed by the image encoding apparatus). block) can be changed.

The inverse quantization unit 520 inverse quantizes the quantized transform coefficients and inverse quantizes the quantized transform coefficients using a quantization parameter. The inverse quantization unit 520 may apply different quantization coefficients (scaling values) to the two-dimensionally arranged quantized transform coefficients. The inverse quantization unit 520 may perform inverse quantization by applying a matrix of quantization coefficients (scaling values) from the image encoding device to a 2D array of quantized transformation coefficients.

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

In addition, when the inverse transform unit 530 inverse transforms only a partial region (subblock) of a transform block, a flag (cu_sbt_flag) indicating that only a subblock of the transform block has been transformed, and direction information (vertical/horizontal) information (cu_sbt_horizontal_flag) of the transform block ) and/or the location information (cu_sbt_pos_flag) of the subblock, and inversely transforms the transform coefficients of the corresponding subblock from the frequency domain to the spatial domain to restore the residual signals. By filling , the final residual block for the current block is created.

In addition, when the MTS is applied, the inverse transform unit 530 determines transform functions or transform matrices to be applied in the horizontal and vertical directions, respectively, using MTS information (mts_idx) signaled from the video encoding device, and uses the determined transform functions. Inverse transform is performed on the transform coefficients in the transform block in the horizontal and vertical directions.

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

The intra prediction unit 542 determines the intra prediction mode of the current block among a plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the entropy decoding unit 510, and references the current block according to the intra prediction mode. The current block is predicted using pixels.

The inter prediction unit 544 determines the motion vector of the current block and the reference picture referred to by the motion vector by using the syntax element for the inter prediction mode extracted from the entropy decoding unit 510, and converts the motion vector and the reference picture. to predict the current block.

The adder 550 restores the current block by adding the residual block output from the inverse transform unit and the prediction block output from the inter prediction unit or intra prediction unit. Pixels in the reconstructed current block are used as reference pixels when intra-predicting a block to be decoded later.

The loop filter unit 560 may include a deblocking filter 562, an SAO filter 564, and an ALF 566 as in-loop filters. The deblocking filter 562 performs deblocking filtering on boundaries between reconstructed blocks in order to remove blocking artifacts generated by block-by-block decoding. The SAO filter 564 and the ALF 566 perform additional filtering on the reconstructed block after deblocking filtering to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding. ALF filter coefficients are determined using information on filter coefficients decoded from the non-stream.

The reconstruction block filtered through the deblocking filter 562, the SAO filter 564, and the ALF 566 is stored in the memory 570. When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter-prediction of blocks in the picture to be encoded later.

This embodiment relates to encoding and decoding of images (video) as described above. More specifically, a bi-directional differential motion vector is adaptively generated for bi-directional motion information prediction using a unidirectional differential motion vector derived according to a Merge with Motion Vector Difference (MMVD) mode. and a video coding method and apparatus for adaptively applying the generated bidirectional differential motion vector to an arbitrary unidirectional reference picture or bidirectional reference picture.

The following embodiments may be performed by the inter prediction unit 124 in a video encoding device. In addition, it may be performed by the inter prediction unit 544 in the video decoding device.

The video encoding apparatus may generate signaling information related to the present embodiment in terms of bit rate distortion optimization in encoding of the current block. The image encoding device may encode the image using the entropy encoding unit 155 and transmit it to the image decoding device. The video decoding apparatus may decode signaling information related to decoding of the current block from the bitstream using the entropy decoding unit 510 .

In the following description, the term 'target block' may be used in the same meaning as a current block or a coding unit (CU), or may mean a partial region of a coding unit.

Also, a value of one flag being true indicates a case in which the flag is set to 1. In addition, a false value of one flag indicates a case in which the flag is set to 0.

Hereinafter, predicted motion information is used interchangeably with a Motion Vector Predictor (MVP).

I. Merge/Skip Mode and MMVD

The merge/skip mode includes a regular merge mode, a Merge mode with Motion Vector Difference (MMVD) mode, a Combined Inter and Intra Prediction (CIIP) mode, a Geometric Partitioning Mode (GPM) mode, and a subblock merge mode. (subblock merge) mode. At this time, the subblock merge mode is divided into a subblock-based temporal motion vector prediction (SbTMVP) and an affine merge mode.

Meanwhile, the advanced motion vector prediction (AMVP) mode includes a regular AMVP (regular AMVP) mode, a symmetric MVD (SMVD) mode, and an affine AMVP mode.

Hereinafter, a method of constructing a merge candidate list of motion information in a normal merge/skip mode will be described. In order to support the merge/skip mode, the inter prediction unit 124 in the video encoding apparatus may configure a merge candidate list by selecting a preset number (eg, 6) of merge candidates.

The inter prediction unit 124 searches for spatial merge candidates. The inter prediction unit 124 searches for spatial merge candidates from neighboring blocks as illustrated in FIG. 4 . Up to four spatial merge candidates can be selected. Spatial merge candidates are also referred to as Spatial MVPs (SMVPs).

The inter prediction unit 124 searches for a temporal merge candidate. The inter-prediction unit 124 includes a block (co-located at the same position as the current block) in 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 target block is located. located block) can be added as a temporal merge candidate. One temporal merge candidate may be selected. The temporal merge candidate is also referred to as Temporal MVP (TMVP).

The inter predictor 124 searches for a history-based motion vector predictor (HMVP) candidate. The inter predictor 124 may store the motion vectors of the previous h (here, h is a natural number) number of CUs in a table and then use them as merge candidates. The size of the table is 6, and the motion vector of the previous CU is stored according to the first-in-first-out (FIFO) method. This indicates that up to 6 HMVP candidates are stored in the table. The inter prediction unit 124 may set recent motion vectors among HMVP candidates stored in the table as merge candidates.

The inter prediction unit 124 searches for a Pairwise Average MVP (PAMVP) candidate. The inter prediction unit 124 may set an average of motion vectors of a first candidate and a second candidate in the merge candidate list as a merge candidate.

When the merge candidate list cannot be filled even after performing all of the above search processes (ie, when the preset number cannot be filled), the inter prediction unit 124 adds a zero motion vector as a merge candidate.

In terms of encoding efficiency optimization, the inter predictor 124 may determine a merge index indicating one candidate in the merge candidate list. The inter predictor 124 may derive a Motion Vector Predictor (MVP) from the merge candidate list using the merge index, and then determine the MVP as the motion vector of the current block. Also, the video encoding apparatus may signal the merge index to the video decoding apparatus.

In the case of the skip mode, the video encoding apparatus uses the same motion vector transmission method as the merge mode, but does not transmit a residual block corresponding to a difference between the current block and the prediction block.

The above-described method of constructing the merge candidate list may be equally performed by the inter prediction unit 544 in the video decoding apparatus. The video decoding apparatus may decode the merge index. The inter prediction unit 544 may derive the MVP from the merge candidate list using the merge index, and then determine the MVP as the motion vector of the current block.

Meanwhile, in the case of using the MMVD mode, the inter predictor 124 may derive the MVP from the merge candidate list using the merge index. For example, the first or second candidate of the merge candidate list may be used as MVP. In addition, in terms of encoding efficiency optimization, the inter predictor 124 determines differential motion vector information. The differential motion vector information includes a magnitude index as magnitude information and a distance index as direction information. The inter-prediction unit 124 may derive a motion vector difference (MVD) using the magnitude index and the direction index, and then restore the motion vector of the current block by summing the MVD and MVP. Also, the video encoding apparatus may signal merge index and differential motion vector information to the video decoding apparatus.

Correction in the vertical or horizontal direction is possible according to the direction information, and as shown in Table 1, one of the four directions is determined as the direction information according to the direction index.

The size of the differential motion vector is determined in the range of 1/4 pixel to 32 pixels according to the size information, and the size information is determined according to the size index as shown in Table 2.

The aforementioned MMVD mode may be equally performed by the inter prediction unit 544 in the video decoding apparatus. The image decoding apparatus may decode merge index and differential motion vector information. After constructing the merge candidate list, the inter predictor 544 may derive the MVP from the merge candidate list using the merge index. The inter predictor 544 may derive the MVD using the differential motion vector information and then restore the motion vector of the current block by summing the MVD and the MVP.

Meanwhile, the MMVD mode may generate a differential motion vector for bi-directional predictive motion information using the derived unidirectional differential motion vector and scaling. For example, when the POC (Picture Order Count) difference between the current picture and the L0/L1 reference pictures is the same, the value of the derived differential motion vector is applied to the L0 and L1 directions as it is. Here, L0 represents reference picture list 0, and L1 represents reference picture list 1. If the absolute value of the POC difference between the current picture and the L0 reference picture is greater than the absolute value of the POC difference between the current picture and the L1 picture, the derived differential motion vector is applied in the L0 direction, and the derived differential motion vector is scaled, The scaled differential motion vector is applied in the L1 direction. On the other hand, if the absolute value of the POC difference between the current picture and the L1 reference picture is greater than the absolute value of the POC difference between the current picture and the L0 reference picture, the derived differential motion vector is applied in the L1 direction, and the derived differential motion vector is used for scaling. After that, the scaled differential motion vector is applied in the L0 direction.

As described above, the existing MMVD mode has a disadvantage in that the value of the derived differential motion vector is always applied to both reference pictures in both directions. Hereinafter, a method of adaptively applying differential motion vector information to an arbitrary unidirectional reference picture or bidirectional reference picture will be considered in order to solve this disadvantage.

Hereinafter, embodiments according to the present invention will be described focusing on an image encoding device, but may be similarly applied to an image decoding device.

II. Embodiments According to the Invention

<Embodiment 1> Adaptively generating a bidirectional differential motion vector from a unidirectional differential motion vector

In this embodiment, the video encoding apparatus generates a bidirectional differential motion vector for bidirectional predictive motion information by using a unidirectional differential motion vector and scaling derived according to the MMVD mode. Here, bi-directional predictive motion information, that is, bi-directional motion vector predictors may be generated according to the existing merge mode. Thereafter, the video encoding apparatus generates a final bi-directional motion vector by applying the differential motion vector to the motion vector predictors of L0 and L1. An image encoding apparatus generates bidirectional differential motion vectors using an implicit method or an explicit method.

<Example 1-1> Generation of bi-directional differential motion vectors according to an implicit method

In this embodiment, the video encoding apparatus generates bi-directional differential motion vectors for bi-directional predictive motion information according to an implicit method. Also in this embodiment, similar to the existing MMVD mode, the video encoding apparatus determines a bi-directional differential motion vector in consideration of a POC difference between a current picture and a reference picture as follows.

When the POC difference between the current picture and the L0/L1 reference picture is the same, the video encoding apparatus applies the value of the derived differential motion vector to the L0 and L1 directions as it is. That is, the video encoding apparatus generates bi-directional differential motion vectors in the same way as in the existing MMVD mode.

If the POC difference between the current picture and the L0/L1 reference picture is different, the video encoding apparatus applies the derived differential motion vector as it is to the motion vector predictor in the direction of the reference picture having the smaller absolute value of the POC difference, and the absolute value of the POC difference Scaling is applied to the motion vector predictor in the direction of this large reference picture. Compared to the existing methods, this embodiment has different conditions when scaling is applied to the derived differential motion vectors. In the conventional MMVD mode, scaling is applied to differential motion vectors derived in a direction with a small POC difference, but in this embodiment, scaling is applied to differential motion vectors derived in a direction with a large POC difference. In this embodiment, since applied method indication information indicating one of these different methods can be set in advance according to an agreement between the video encoding device and the video decoding device, the applied method indication information It does not need to be transmitted/parsed.

<Example 1-2> Generating bi-directional differential motion vectors according to an explicit method

In this embodiment, the video encoding apparatus generates bi-directional differential motion vectors for bi-directional predictive motion information according to an explicit method. Also in this embodiment, similar to the existing MMVD mode, the video encoding apparatus determines a bi-directional differential motion vector in consideration of a POC difference between a current picture and a reference picture as follows.

When the POC difference between the current picture and the L0/L1 reference picture is the same, the video encoding apparatus applies the value of the derived differential motion vector to the L0 and L1 directions as it is. That is, the video encoding apparatus generates bi-directional differential motion vectors in the same way as in the existing MMVD mode.

When the POC difference between the current picture and the L0/L1 reference picture is different, in the conventional MMVD mode, the video encoding apparatus scales the derived differential motion vector value to a motion vector predictor in the direction of the reference picture having a small absolute value of the POC difference value, On the other hand, it is applied to the motion vector predictor in the reference picture direction having a large absolute value of the POC difference value. Meanwhile, in the implicit method according to embodiment 1-1, the video encoding apparatus additionally scales and applies differential motion vector values derived according to the MMVD mode to a motion vector predictor in a reference picture direction having a large absolute value of a POC difference value, and , It is applied as it is to the motion vector predictor in the reference picture direction where the absolute value of the POC difference value is small. In addition, since the application method indication information indicating one of these different methods may be set in advance according to an agreement between the video encoding device and the video decoding device, the application method indication information does not need to be transmitted/parsed.

In the explicit method according to the present embodiment, the video encoding device determines one of the existing MMVD mode and the method according to the embodiment 1-1 as application method indication information, and then transmits the application method indication information to the video decoding device. . That is, the existing method and the method according to the embodiment 1-1 are combined with Rate Distortion Optimization (RDO), Sum of Absolute Difference (SAD), Sum of Square Difference (SSE), and the like. After comparing based on the same various measurement methods, the video encoding device selects an appropriate application method. Thereafter, the video encoding apparatus transmits a 1-bit flag indicating an application method as application method indication information to the video decoding apparatus in units of blocks.

<Example 2> Adaptively applying the derived differential motion vector to any unidirectional reference picture or bidirectional reference picture

In this embodiment, instead of generating bidirectional motion vectors by reflecting all derived unidirectional differential motion vectors in bidirectional predictive motion information, the video encoding apparatus adaptively applies ① only motion information in the L0 direction and ② motion in the L1 direction. information only, or ③ both motion information in the L0 and L1 directions. Here, bi-directional predictive motion information, that is, bi-directional motion vector predictors may be generated according to the existing merge mode. An image encoding apparatus applies a differential motion vector to a bi-directional motion vector predictor using an implicit method or an explicit method as follows.

<Example 2-1> Applied to bi-directional predictive motion information according to an implicit method

In this embodiment, the video encoding apparatus adaptively applies a unidirectional differential motion vector derived according to the MMVD mode to bidirectional predictive motion information using an implicit method.

6 is an exemplary diagram illustrating generation of bi-directional motion information according to an implicit method according to an embodiment of the present disclosure.

As shown in the example of FIG. 6 , the video encoding apparatus applies the unidirectional differential motion vector information derived according to the MMVD mode to ① only motion information in the L0 direction, ② applies only motion information in the L1 direction, or ③ motions in the L0 and L1 directions. By applying all of the information, a reference block corresponding to the current block is searched. Thereafter, the image encoding apparatus uses samples of neighboring templates (current templates in the example of FIG. 6) of the current block and neighboring reference templates (L0 reference templates or L1 reference templates in the example of FIG. 6) of the searched reference block. By calculating a cost value between samples of , a direction having a minimum cost value and a corresponding motion vector are determined. Since the process of determining the application direction indication information is identically performed in the video encoding apparatus and the video decoding apparatus, there is no need to transmit/parse information on the determined motion vector. Table 3 shows motion vectors corresponding to the application direction indication information of ①, ②, and ③ described in the example of FIG. 6 .

At this time, the cost value between the samples of the neighboring neighboring template of the current block and the neighboring neighboring template samples of the corresponding reference block is bit rate distortion, Sum of Absolute Transformed Differences (SATD), SAD, SSE, etc. It can be calculated based on various measurement methods such as Here, SATD is a method of calculating SAD after converting samples to be compared into samples in the frequency domain.

<Example 2-2> Explicit Applied to bi-directional predictive motion information according to the method

In this embodiment, the video encoding apparatus adaptively applies unidirectional differential motion vector information derived according to the MMVD mode to bidirectional predictive motion information using an explicit method.

7 is an exemplary diagram illustrating generation of bi-directional motion information according to an explicit method according to an embodiment of the present disclosure.

As in the example of FIG. 7 , the video encoding apparatus applies unidirectional differential motion vector information derived according to the MMVD mode to ① only L0-direction motion information, ② only L1-direction motion information, or ③ L0 and L1-direction motion information. By applying all of the information, a reference block corresponding to the current block is searched. Thereafter, the video encoding apparatus calculates a cost value between the current block (current block in the example of FIG. 7) and the searched reference block (L0 reference block or L1 reference block in the example of FIG. 7), and determines the direction having the minimum cost value and the corresponding Determine the motion vector for Unlike the implicit method according to Example 2-1, the motion vector determination process of the explicit method according to Example 2-2 determines the motion vector using the information of the current block, so the application direction indication information is transmitted to the video decoding device. Should be. This is because the video decoding apparatus cannot use the information of the current block. Motion vectors corresponding to the application direction indication information of ①, ②, and ③ illustrated in FIG. 7 are the same as those in Table 3.

The explicit method illustrated in FIG. 7 is the same as the implicit method of FIG. 6 . Comparison of the cost values of the current block and the corresponding reference block can be calculated according to various measurement methods such as bit rate distortion, SATD, SAD, SSE, etc. .

<Example 3> Combination of Example 1 and Example 2

In this embodiment, the video encoding apparatus uses the method according to Embodiment 1 and the method according to Embodiment 2 in combination. As described above, in the first embodiment, the video encoding apparatus adaptively generates bi-directional differential motion vectors for bi-directional predictive motion information using the derived uni-directional differential motion vectors. In Example 2, the video encoding apparatus adaptively applies the derived differential motion vector to any unidirectional reference picture or bidirectional reference picture.

As an example, according to the first embodiment, the apparatus for encoding an image adaptively generates a bi-directional differential motion vector for bi-directional predictive motion information using the derived uni-directional differential motion vector. Thereafter, the video encoding apparatus corrects the bi-directional predicted motion information using the bi-directional differential motion vector, and then, according to the second embodiment, corrected bi-directional motion information It is adaptively applied to any unidirectional reference picture or both reference pictures. In this case, the video encoding apparatus may select an arbitrary method from among the implicit method and the explicit method proposed in each of the first and second embodiments, and then use the selected method.

As another example, the video encoding apparatus adaptively applies the derived unidirectional differential motion vector to an arbitrary unidirectional reference picture or both reference pictures according to the second embodiment. In this case, when applied to an arbitrary unidirectional reference picture, the video encoding apparatus applies the induced unidirectional differential motion vector as it is. On the other hand, when applied to both reference pictures, the video encoding apparatus adaptively generates bi-directional differential motion vectors for bi-directional predictive motion information using the derived uni-directional differential motion vectors according to the first embodiment, and then converts them to apply

Hereinafter, a method of generating bi-directional motion vectors of a current block based on Realization Example 1 will be described using the drawings of FIGS. 8 to 10 .

8 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image encoding apparatus according to an embodiment of the present disclosure.

The video encoding apparatus generates bi-directional motion vector predictors of the current block using merge mode (S800). Here, the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor.

The video encoding apparatus generates a unidirectional differential motion vector for the current block using the MMVD mode (S802).

The video encoding device acquires application method indication information (S804).

Here, the application method indication information indicates a first application method or a second application method, and the first application method and the second application method convert a differential motion vector to a bi-directional motion vector based on a POC difference between a current picture and bi-directional reference pictures. applied to predictors. Bi-directional reference pictures include an L0 reference picture and an L1 reference picture.

The first application method is a method according to the existing MMVD mode. That is, when the POC difference between the current picture and the L0 reference picture/L1 reference picture is different, the video encoding apparatus applies the difference motion vector as it is to the motion vector predictor in the direction of the reference picture having a large absolute value of the POC difference, and the POC difference Scaling is applied to the motion vector predictor in the reference picture direction having a small absolute value.

The second application method is a method newly proposed in Example 1-1. That is, when the POC difference between the current picture and the L0 reference picture/L1 reference picture is different, the video encoding apparatus applies the difference motion vector as it is to the motion vector predictor in the direction of the reference picture having the small absolute value of the POC difference, and the POC difference Scaling is applied to the motion vector predictor in the reference picture direction having a large absolute value.

Application method indication information may be set in advance according to an agreement between the video encoding device and the video decoding device.

The video encoding apparatus generates bi-directional differential motion vectors using differential motion vectors and scaling according to application method indication information (S806).

The video encoding apparatus generates bidirectional motion vectors of the current block by applying bidirectional differential motion vectors to bidirectional motion vector predictors (S808).

9 is a flowchart illustrating a method of generating bi-directional motion vectors of a current block by an image encoding apparatus according to another embodiment of the present disclosure.

The video encoding apparatus generates bi-directional motion vector predictors of the current block using merge mode (S900). Here, the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor.

The video encoding apparatus generates a unidirectional differential motion vector for the current block using the MMVD mode (S902).

The video encoding apparatus selects an optimal application method by applying a differential motion vector to bi-directional motion vector predictors based on a POC difference between a current picture and bi-directional reference pictures according to the first application method and the second application method; Based on the optimal application method, bi-directional motion vectors of the current block are generated (S904).

The video encoding device applies an application method based on an optimal application method. Instruction information is determined (S906). Here, the application method indication information indicates the first application method or the second application method.

The video encoding device encodes application method indication information (S908). The video encoding apparatus may encode a flag indicating the first application method or the second application method as application method indication information.

10 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image decoding apparatus according to an embodiment of the present disclosure.

The video decoding apparatus generates bi-directional motion vector predictors of the current block using merge mode (S1000). Here, the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor.

The video decoding apparatus generates a unidirectional differential motion vector for the current block using the MMVD mode (S1002).

The video decoding apparatus acquires application method indication information (S1004).

Here, the application method indication information indicates a first application method or a second application method, and the first application method and the second application method convert a differential motion vector to a bi-directional motion vector based on a POC difference between a current picture and bi-directional reference pictures. applied to predictors. The first application method is a method according to the existing MMVD mode, and the second application method is a method newly proposed in Example 1-1.

According to the embodiment 1-1, the application method indication information may be set in advance according to an agreement between the video encoding device and the video decoding device.

According to the embodiment 1-2, the video decoding apparatus may decode a flag indicating the first application method or the second application method from the bitstream as application method indication information.

The video decoding apparatus generates bi-directional differential motion vectors using differential motion vectors and scaling according to application method indication information (S1006).

The video decoding apparatus generates bidirectional motion vectors of the current block by applying bidirectional differential motion vectors to bidirectional motion vector predictors (S1008).

Hereinafter, a method of generating bi-directional motion vectors of the current block based on the second embodiment will be described using the illustrations of FIGS. 11 and 12 .

11 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image encoding apparatus according to another embodiment of the present disclosure.

The video encoding apparatus generates bi-directional motion vector predictors of the current block using merge mode (S1100). Here, the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor.

The video encoding apparatus generates a unidirectional differential motion vector for the current block using the MMVD mode (S1102).

The video encoding apparatus selects an optimal direction by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors, and moves the current block in both directions based on the optimal direction. Vectors are created (S1104).

The video encoding apparatus generates application direction indication information based on the optimal direction (S1106). Here, the application direction indication information indicates an L0-direction motion vector predictor, an L1-direction motion vector predictor, or bidirectional motion vector predictors.

According to Example 2-1, the video encoding apparatus selects an optimal direction based on a cost between a template of a current block and templates of reference blocks of the current block, and then derives application direction indication information based on the selected optimal direction. can do. In this case, the video encoding apparatus may generate reference blocks by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors.

According to Example 2-2, the video encoding apparatus may select an optimal direction based on a cost between a current block and reference blocks of the current block, and then determine application direction indication information based on the selected optimal direction. After that, the video encoding apparatus may encode application direction indication information.

12 is a flowchart illustrating a method for generating bi-directional motion vectors of a current block by an image decoding apparatus according to another embodiment of the present disclosure.

The video decoding apparatus generates bi-directional motion vector predictors of the current block using the merge mode (S1200). Here, the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor.

The video decoding apparatus generates a unidirectional differential motion vector for the current block using the MMVD mode (S1202).

The video decoding apparatus obtains application direction indication information (S1204). Here, the application direction indication information indicates an L0-direction motion vector predictor, an L1-direction motion vector predictor, or bidirectional motion vector predictors.

According to Example 2-1, the apparatus for decoding an image selects an optimal direction based on a cost between a template of a current block and templates of reference blocks of the current block, and then derives application direction indication information based on the selected optimal direction. can do. In this case, the video decoding apparatus may generate reference blocks by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bidirectional motion vector predictors.

According to Example 2-2, the video decoding apparatus may decode application direction indication information from a bitstream.

The video decoding apparatus generates bi-directional motion vectors of the current block by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, or the bi-directional motion vector predictors according to the application direction indication information (S1206). ).

In the flow chart/timing diagram of the present specification, it is described that each process is sequentially executed, but this is merely an example of the technical idea of one embodiment of the present disclosure. In other words, those skilled in the art to which an embodiment of the present disclosure belongs may change and execute the order described in the flowchart/timing diagram within the range that does not deviate from the essential characteristics of the embodiment of the present disclosure, or one of each process Since the above process can be applied by performing various modifications and variations in parallel, the flow chart/timing chart is not limited to a time-series sequence.

In the above description, it should be understood that the exemplary embodiments may be implemented in many different ways. 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 in this specification have been labeled "...unit" to particularly emphasize their implementation independence.

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

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

124: inter predictor
155: entropy encoding unit
510: entropy decoding unit
544 Inter prediction unit

Claims (12)

A method of generating motion vectors of a current block, performed by an image decoding apparatus, comprising:
Generating bi-directional motion vector predictors of the current block using a merge mode, wherein the bi-directional motion vector predictors are an L0-direction motion vector predictor and an L1-direction motion vector predictor. including characters;
generating a unidirectional differential motion vector for the current block using a merge with motion vector difference mode;
obtaining application direction indication information, wherein the application direction indication information indicates an L0 direction, an L1 direction, or both directions;
The differential motion vector is transmitted to the L0-direction motion vector predictor, the L1-direction motion vector predictor, or the bi-directional motion vector predictors according to the application direction indication information. generating bi-directional motion vectors of the current block by applying
Characterized in that, the method comprising a. According to claim 1,
The step of obtaining the application direction indication information,
characterized in that decoding the application direction indication information from a bitstream. According to claim 1,
The step of obtaining the application direction indication information,
characterized in that the application direction indication information is derived based on a cost between a template of the current block and templates of reference blocks of the current block. According to claim 3,
The step of obtaining the application direction indication information,
and generating the reference blocks by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors. According to claim 1,
The generating of the bi-directional motion vectors includes:
When the differential motion vector is applied to the bi-directional motion vector predictors, the differential motion vector is equally applied to the bi-directional motion vector predictors. A method of generating motion vectors of a current block, performed by an image encoding apparatus, comprising:
Generating bi-directional motion vector predictors of the current block using a merge mode, wherein the bi-directional motion vector predictors are an L0-direction motion vector predictor and an L1-direction motion vector predictor. including characters;
generating a unidirectional differential motion vector for the current block using a merge with motion vector difference mode;
An optimal direction is selected by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors, and based on the optimal direction, the current block generating bi-directional motion vectors;
Generating application direction indication information based on the optimal direction
Including,
The application direction indication information may indicate an L0 direction, an L1 direction, or both directions. According to claim 6,
The generating of the bi-directional motion vectors includes:
and selecting the optimal direction based on a cost between a template of the current block and templates of reference blocks of the current block. According to claim 7,
The generating of the bi-directional motion vectors includes:
and generating the reference blocks by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors. According to claim 6,
The generating of the bi-directional motion vectors includes:
and selecting the optimal direction based on a cost between the current block and reference blocks of the current block. According to claim 9,
The method characterized in that it further comprises the step of encoding the application direction indication information. According to claim 6,
The generating of the bi-directional motion vectors includes:
When the differential motion vector is applied to the bi-directional motion vector predictors, the differential motion vector is equally applied to the bi-directional motion vector predictors. A computer-readable recording medium storing a bitstream generated by an image encoding method, the image encoding method comprising:
Generating bi-directional motion vector predictors of a current block using a merge mode, wherein the bi-directional motion vector predictors include an L0-direction motion vector predictor and an L1-direction motion vector predictor. contains;
generating a unidirectional differential motion vector for the current block using a merge with motion vector difference mode;
An optimal direction is selected by applying the differential motion vector to the L0-direction motion vector predictor, the L1-direction motion vector predictor, and the bi-directional motion vector predictors, and based on the optimal direction, the current block generating bi-directional motion vectors;
Generating application direction indication information based on the optimal direction
Including,
Characterized in that, the application direction indication information indicates an L0 direction, an L1 direction, or both directions.

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