Method and device for geometric partitioning mode by motion vector refinement

Abstract

A method and device for video decoding are provided. The method includes receiving a control variable associated with a video block, the control variable enabling an adaptive switch between a set of multiple motion vector refinement (MVR) offsets, partitioning the video block into a first geometric partition and a second geometric partition, receiving one or more syntax elements to determine first and second MVR offsets to be applied to the first and second geometric partitions from a selected set of MVR offsets, obtaining a first motion vector (MV) and a second MV from a candidate list for the first and second geometric partitions, calculating a first refined MV and a second refined MV based on the first and second MVs and the first and second MVR offsets, and obtaining a prediction sample for the video block based on the first and second refined MV.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 195,179, filed May 31, 2021, the disclosure of which is hereby incorporated by reference in its entirety for all purposes.

[0002] The present disclosure relates to the coding and compression of video. More particularly, the present disclosure relates to methods and apparatus for improving the coding efficiency of a Geometric Partitioning Mode (GPM), also known as an Angular Weight Prediction (AWP) mode.

Background Art

[0003] To compress video data, various video coding techniques can be used. Video coding is performed according to one or more video coding standards. For example, some well-known video coding standards include Versatile Video Coding (VVC), High Efficiency Video Coding (also known as HEVC, H.265, or MPEG-H Part 2), and Advanced Video Coding (also known as AVC, H.264, or MPEG-4 Part 10), which were jointly developed by ISO / IEC MPEG and ITU-T VECG. AOMedia Video 1 (AV1) was developed by the Alliance for Open Media (AOM) as a successor to the previous standard VP9. Audio Video Coding (AVS) refers to digital audio and digital video compression standards and is another series of video compression standards developed by the Audio and Video Coding Standard Workgroup of China. Most of the existing video coding standards are based on well-known hybrid video coding frameworks, that is, using block-based prediction methods (e.g., inter prediction, intra prediction) to reduce the redundancy present in video images or sequences, and using transform coding to compress the energy of the prediction error. An important goal of video coding techniques is to compress video data into a form that uses a lower bitrate while avoiding or minimizing the degradation of video quality.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides a method and apparatus for video coding, as well as a non-transitory computer-readable storage medium.

Means for Solving the Problems

[0005] According to a first aspect of the present disclosure, a method for decoding a video block with GPM is provided. The method can include receiving a control variable associated with the video block, the control variable enabling an adaptive switch between sets of a plurality of motion vector refinement (MVR) offsets, and the control variable being applied at a coding level. The method can include partitioning the video block into a first geometric partition and a second geometric partition. The method can include receiving one or more syntax elements to determine a first MVR offset and a second MVR offset applied to the first and second geometric partitions from a selected set of MVR offsets. The method can include obtaining a first motion vector (MV) and a second MV from a candidate list for the first geometric partition and the second geometric partition. The method can include calculating a first refined MV and a second refined MV based on the first and second MVs and the first and second MVR offsets. Further, the method can include obtaining a prediction sample for the video block based on the first and second refined MVs.

[0006] According to a second aspect of the present disclosure, an apparatus for video decoding is provided. The apparatus can include one or more processors and a non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium is configured to store instructions executable by the one or more processors. The one or more processors are configured to implement the method of the first aspect when executing the instructions.

[0007] According to a third aspect of the present disclosure, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium can store computer-executable instructions that, when executed by one or more computer processors, cause the one or more computer processors to implement the method of the first aspect.

[0008] The accompanying drawings are incorporated herein and form a part of this specification, showing examples consistent with the present disclosure and serving to explain the principles of the present disclosure together with the description.

Brief Description of the Drawings

[0009]

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Best Mode for Carrying Out the Invention

[0010] The embodiments illustrated by way of example in the accompanying drawings are now referred to in detail. The following description refers to the accompanying drawings, and the same numerals in different drawings represent the same or similar elements unless otherwise indicated. The implementation examples described in the following description of the embodiments do not represent all implementation examples consistent with the present disclosure. Instead, these implementation examples are merely examples of apparatuses and methods consistent with aspects of the present disclosure as recited in the appended claims.

[0011] The terms used in the present disclosure are for the sole purpose of describing particular embodiments and are not intended to limit the present disclosure. When used in the present disclosure and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will also be understood that the term “and / or” as used herein means any and all possible combinations of one or more of the associated listed items and is intended to encompass them.

[0012] For the purpose of describing various information, terms such as “first,” “second,” “third,” etc. may be used in this specification, but it will be understood that the information should not be limited by these terms. These terms are used only to distinguish one category of information from another. For example, without departing from the scope of the present disclosure, the first information may be referred to as the second information, and similarly, the second information may be referred to as the first information. It will be understood that the term “if” as used herein means, depending on the context, “when” or “upon,” or “in response to a judgment.”

[0013] The first-generation AVS standard includes the national standard of the Republic of China, "Information Technology, Advanced Audio Video Coding, Part 2: Video" (also known as AVS1), and "Information Technology, Advanced Audio Video Coding Part 16: Radio Television Video" (also known as AVS+). It can provide about 50% bitrate savings at the same perceptual quality compared to the MPEG-2 standard. The video part of the AVS1 standard was published as a national standard of the Republic of China in February 2006. The second-generation AVS standard includes a series of national standards of the Republic of China, "Information Technology, Efficient Multimedia Coding" (also known as AVS2), mainly targeting the transmission of additional HD TV programs. The coding efficiency of AVS2 is twice that of AVS+. In May 2016, AVS2 was issued as a national standard of the Republic of China. On the other hand, the video part of the AVS2 standard was submitted by the Institute of Electrical and Electronics Engineers (IEEE) as an international standard for application. The AVS3 standard is a new-generation video coding standard for the application of UHD video aiming to exceed the coding efficiency of the latest international standard HEVC. In March 2019, at the 68th AVS meeting, the AVS3-P2 baseline was completed, which provides about 30% bitrate savings compared to the HEVC standard. Currently, a reference software called High Performance Model (HPM) is maintained by the AVS group to demonstrate the reference implementation of the AVS3 standard.

[0014] Similar to HEVC, the AVS3 standard is constructed based on a block-based hybrid video coding framework.

[0015] FIG. 1 shows a schematic diagram of a block-based video encoder for VVC. Specifically, FIG. 1 shows a typical encoder 100. The encoder 100 includes a video input 110, motion compensation 112, motion estimation 114, intra / inter mode decision 116, block predictor 140, adder 128, transform 130, quantization 132, prediction related information 142, intra prediction 118, picture buffer 120, inverse quantization 134, inverse transform 136, adder 126, memory 124, in-loop filter 122, entropy encoding 138, and bitstream 144.

[0016] Within the encoder 100, a video frame is partitioned into a plurality of video blocks for processing. For each given video block, a prediction is formed based on an inter prediction method or an intra prediction method.

[0017] A prediction residual representing the difference between the current video block, a part of the video input 110 and its prediction part, and a part of the block predictor 140 is sent from the adder 128 to the transform 130. Then the transform coefficients are sent from the transform 130 to the quantization 132 for entropy reduction. Then the quantized coefficients are sent to the entropy encoding 138 to generate a compressed video bitstream. As shown in FIG. 1, prediction related information 142 from the intra / inter mode decision 116, such as video block partitioning information, motion vector (MV), reference picture index, and intra prediction mode, is also sent by the entropy encoding 138 and stored in the compressed bitstream 144. The compressed bitstream 144 includes the video bitstream.

[0018] Within the encoder 100, decoder related circuits are also required to reconstruct pixels for prediction purposes. First, the prediction residual is reconstructed by the inverse quantization 134 and the inverse transform 136. This reconstructed prediction residual is combined with the block predictor 140 to generate the unfiltered reconstructed pixels for the current video block.

[0019] Spatial prediction (or "intra prediction") predicts the current video block by using pixels from samples of already-coded adjacent blocks (referred to as reference samples) within the same video frame as the current video block.

[0020] Temporal prediction (also called "inter prediction") predicts the current video block by using reconstructed pixels from already-coded video pictures. Temporal prediction reduces the temporal redundancy inherent in the video signal. Usually, the temporal prediction signal for a given coding unit (CU) or coding block is signaled by one or more MVs that indicate the amount and direction of motion between the current CU and its temporal reference. Further, when multiple reference pictures are involved, one reference picture index is additionally transmitted and used to identify from which reference picture in the reference picture store the temporal prediction signal originated.

[0021] Motion estimator 114 takes in signals from video input 110 and picture buffer 120 and outputs a motion estimation signal to motion compensator 112. Motion compensator 112 takes in signals from video input 110, picture buffer 120, and the motion estimation signal from motion estimator 114 and outputs a motion compensation signal to intra / inter mode decision 116.

[0022] After spatial and / or temporal prediction is performed, the intra / inter mode decision 116 within the encoder 100 selects the best prediction mode, for example, based on a rate distortion optimization method. Next, the block predictor 140 is derived from the current video block, and the resulting prediction residual is decorrelated using the transform 130 and quantization 132. The resulting quantized residual coefficients are inverse quantized by the inverse quantization 134 and inverse transformed by the inverse transform 136 to form a reconstructed residual, and then the reconstructed residual is added back to the prediction block to form the reconstructed signal of the CU. Further, in-loop filtering 122 such as a deblocking filter, sample adaptive offset (SAO), and / or adaptive loop filter (ALF) may be applied to the reconstructed CU, and then placed in the reference picture store of the picture buffer 120 and used to code future video blocks. To form the output video bitstream 144, the coding mode (inter or intra), prediction mode information, motion information, and quantized residual coefficients are all sent to the entropy coding unit 138, further compressed, and packed to form a bitstream.

[0023] FIG. 1 gives a block diagram of a general-purpose block-based hybrid video coding system. The input video signal is processed block by block (referred to as a coding unit (CU)). Different from HEVC which partitions blocks based only on quadtree, in AVS3, one coding tree unit (CTU) is divided into CUs so as to adapt to local characteristics that vary based on quadtree / binary tree / extended quadtree. In addition, the concept of multiple partition unit types in HEVC is removed, that is, in AVS3, there is no separation of CUs, prediction units (PUs), and transform units (TUs). Instead, each CU is always used as the basic unit for both prediction and transform without further partitioning. In the tree partitioning structure of AVS3, one CTU is first partitioned based on a quadtree structure. Then each quadtree leaf node may be further partitioned based on a binary tree and extended quadtree structures.

[0024] As shown in FIGS. 2A, 2B, 2C, 2D, and 2E, there are five partitioning types, namely, four-division, horizontal two-division, vertical two-division, horizontally extended quadtree division, and vertically extended quadtree division.

[0025] FIG. 2A shows a diagram depicting a block four-division in a multi-type tree structure according to the present disclosure.

[0026] FIG. 2B shows a diagram depicting a block vertical two-division in a multi-type tree structure according to the present disclosure.

[0027] FIG. 2C shows a diagram depicting a block horizontal two-division in a multi-type tree structure according to the present disclosure.

[0028] FIG. 2D shows a diagram depicting a block vertical three-division in a multi-type tree structure according to the present disclosure.

[0029] FIG. 2E shows a diagram depicting a block horizontal three-division in a multi-type tree structure according to the present disclosure.

[0030] In FIG. 1, spatial prediction and / or temporal prediction can be performed. Spatial prediction (or "intra prediction") uses pixels from samples of already-coded adjacent blocks (referred to as reference samples) within the same video picture / slice to predict the current video block. Spatial prediction reduces the spatial redundancy inherent in the video signal. Temporal prediction (also called "inter prediction" or "motion-compensated prediction") uses reconstructed pixels from already-coded video pictures to predict the current video block. Temporal prediction reduces the temporal redundancy inherent in the video signal. Usually, the temporal prediction signal for a given CU is signaled by one or more motion vectors (MVs) indicating the amount and direction of motion between the current CU and its temporal reference. Also, when multiple reference pictures are involved, one reference picture index is further transmitted and used to identify from which reference picture in the reference picture store the temporal prediction signal originated. After spatial and / or temporal prediction, a mode decision block in the encoder selects the best prediction mode, for example based on a rate-distortion optimization method. Then the prediction block is subtracted from the current video block, and the prediction residual is decorrelated using a transform and then quantized. The quantized residual coefficients are inverse quantized and inverse transformed to form a reconstructed residual, and then the reconstructed residual is added back to the prediction block to form the reconstructed signal of the CU. Further, in-loop filtering such as a deblocking filter, sample adaptive offset (SAO), and adaptive loop filter (ALF) may be applied to the reconstructed CU, after which it is placed in the reference picture store and used as a reference for coding future video blocks. To form the output video bitstream, the coding mode (inter or intra), prediction mode information, motion information, and quantized residual coefficients are all sent to an entropy coding unit and further compressed and packed.

[0031] FIG. 3 is a block diagram showing a block-based video decoder according to some implementation examples of the present disclosure. First, a video bitstream is entropy decoded by an entropy decoding unit (e.g., entropy decoder 301). Coding mode and prediction information are sent to a spatial prediction unit (when intra-coded) (e.g., intra prediction 308) or a temporal prediction unit (when inter-coded) (e.g., motion compensation 307) to form a prediction block. Residual transform coefficients are sent to an inverse quantization unit (e.g., inverse quantization 302) and an inverse transform unit (e.g., inverse transform 303) to reconstruct a residual block. Then, the prediction block and the residual block are added together (e.g., passed through intra / inter mode selection 309 and / or stored in memory 304). The reconstructed block can further pass through in-loop filtering and then be stored in a reference picture store (e.g., picture buffer 306). Next, the reconstructed video in the reference picture store is sent to drive a display device and is also used to predict future video blocks.

[0032] The focus of the present disclosure is to improve the coding performance of the Geometric Partitioning Mode (GPM) used in both the VVC standard and the AVS3 standard. In AVS3, the tool is also known as Angle Weight Prediction (AWP), which follows the same design concept as GPM but has some minor differences in specific design details. To facilitate the description of the present disclosure, hereinafter, the existing GPM design in the VVC standard is used as an example to explain the main aspects of the GPM / AWP tool. On the other hand, another existing inter-prediction technique called Merge Mode with Motion Vector Difference (MMVD) applied in both the VVC standard and the AVS3 standard is also briefly considered, provided that it is closely related to the technology proposed in the present disclosure. Then, some drawbacks of the current GPM / AWP design are identified. Finally, the proposed method is provided in detail. Throughout the present disclosure, the existing GPM design in the VVC standard is used as an example, but it should be noted that those skilled in the art of modern video coding technology will recognize that the proposed technology can also be applied to other GPM / AWP designs or other coding tools having the same or similar design concept.

[0033] Geometric Partitioning Mode (GPM) In VVC, the geometric partitioning mode is supported for inter prediction. The geometric partitioning mode is signaled as a special merge mode by one CU-level flag. In the current GPM design, a total of 64 partitions are supported by the GPM mode for each possible CU size where both the width and height are 8 or more and 64 or less, except for 8×64 and 64×8.

[0034] When this mode is used, the CU is divided into two parts by a geometrically positioned line as shown in FIG. 4 (description will be given later). The location of the dividing line is mathematically derived from the angles of the specific partitions and the offset parameters. Each part of the geometric partition within the CU is inter-predicted using its own motion, and only uni-directional prediction is allowed for each partition, i.e., each part has one motion vector and one reference index. Similar to the conventional bi-directional prediction, motion constraints by uni-directional prediction are applied to ensure that only two motion compensation predictions are required for each CU. When the geometric partitioning mode is used for the current CU, a geometric partition index indicating the partition mode (angle and offset) of the geometric partition, and two merge indices (one for each partition) are further signaled. The number of maximum GPM candidate sizes is explicitly signaled at the sequence level.

[0035] FIG. 4 shows the permitted GPM partitions, and the division within each picture has one identical division direction.

[0036] Uni-directional prediction candidate list structure To derive the uni-directional prediction motion vector for one geometric partition, first, one uni-directional prediction candidate list is directly derived from the normal merge candidate list generation process. Let n denote the index of the uni-directional prediction motion within the geometric uni-directional prediction candidate list. The LX motion vector of the n-th merge candidate is used as the uni-directional prediction motion vector for the geometric partitioning mode, where X is equal to the parity of n.

[0037] These motion vectors are indicated by "x" in FIG. 5 (described later). If the corresponding LX motion vector of the n-th extended merge candidate does not exist, the L(1 - X) motion vector of the same candidate is used instead as the uni-directional prediction motion vector for the geometric partitioning mode.

[0038] FIG. 5 shows the selection of the uni-directional prediction motion vector from the motion vectors of the merge candidate list for GPM.

[0039] Mixing along geometric partition edges After each geometric partition is obtained using its own motion, mixing is applied to two unidirectional prediction signals to derive samples around the geometric partition edges. The mixing weights for each position of the CU are derived based on the distance from each individual sample position to the corresponding partition edge.

[0040] GPM Signaling Design According to the current GPM design, the use of GPM is indicated by signaling one flag at the CU level. This flag is signaled only when the current CU is coded in merge mode or skip mode. Specifically, when this flag is equal to 1, it indicates that the current CU is predicted by GPM. Otherwise (when the flag is equal to 0), the CU is coded by another merge mode such as normal merge mode, merge mode with motion vector difference, combination of inter and intra prediction, etc. When GPM is enabled for the current CU, one syntax element, namely merge_gpm_partition_idx, is further signaled to indicate the applied geometric partition mode (specifying the direction and offset of the straight line from the CU center that divides the CU into two partitions, as shown in Figure 4). Then, two syntax elements, merge_gpm_idx0 and merge_gpm_idx1, are signaled to indicate the indexes of the uni-directional prediction merge candidates used for the first and second GPM partitions. More specifically, these two syntax elements are used to determine the uni-directional MVs of the two GPM partitions from the uni-directional prediction merge list described in the chapter "Uni-directional Prediction Merge List Structure". According to the current GPM design, in order to make the two uni-directional MVs more different, the two indexes cannot be the same. Based on such prior knowledge, first, the uni-directional prediction merge index of the first GPM partition is signaled and used as a prediction unit to reduce the signaling overhead of the uni-directional prediction merge index of the second GPM partition. Specifically, if the second uni-directional prediction merge index is smaller than the first uni-directional prediction merge index, its original value is directly signaled. Otherwise (when the second uni-directional prediction merge index is larger than the first uni-directional prediction merge index), after subtracting 1 from its value, it is signaled to the bitstream. On the decoder side, first, the first uni-directional prediction merge index is decodedThen, for decoding the second unidirectional prediction merge index, if the parsed value is smaller than the first unidirectional prediction merge index, the second unidirectional prediction merge index is set equal to the parsed value; otherwise (if the parsed value is equal to or greater than the first unidirectional prediction merge index), the second unidirectional prediction merge index is set equal to the value obtained by adding 1 to the parsed value. Table 1 shows the existing syntax elements used in the GPM mode in the current VVC specification.

[0041]

Table 1

[0042] On the other hand, in the current GPM design, for binarization of two unidirectional prediction merge indexes, i.e., merge_gpm_idx0 and merge_gpm_idx1, a truncated unary code is used. In addition, since the two unidirectional prediction merge indexes cannot be made the same, different maximum values are used to shorten the codewords of the two unidirectional prediction merge indexes, and the two unidirectional prediction merge indexes are set equal to MaxGPMMergeCand - 1 and MaxGPMMergeCand - 2 for merge_gpm_idx0 and merge_gpm_idx1, respectively. MaxGPMMergeCand is the number of candidates in the unidirectional prediction merge list.

[0043] When the GPM / AWP mode is applied, two different binarization methods are applied to translate the syntax merge_gpm_partition_idx into a 2-bit string. Specifically, syntax elements are binarized by fixed-length codes and shortened binary codes in the VVC standard and the AVS3 standard, respectively. On the other hand, in the case of the AWP mode in AVS3, different maximum values are used for the binarization of the values of syntax elements. Specifically, in AVS3, the number of permitted GPM / AWP partition modes is 56 (i.e., the maximum value of merge_gpm_partition_idx is 55), and in VVC, the number is increased to 64 (i.e., the maximum value of merge_gpm_partition_idx is 63).

[0044] Merge mode with motion vector difference (MMVD) In addition to the conventional merge mode that derives the motion information of one current block from its spatial / temporal neighbors, the MMVD / UMVE mode is introduced as one special merge mode in both the VVC standard and the AVS standard. Specifically, in both VVC and AVS3, the mode is signaled by one MMVD flag at the coded block level. In the MMVD mode, the first two candidates in the merge list for the normal merge mode are selected as the two basic merge candidates for MMVD. After one basic merge candidate is selected and signaled, additional syntax elements are signaled to indicate the motion vector difference (MVD) added to the motion of the selected merge candidate. The MMVD syntax elements include a merge candidate flag for selecting the basic merge candidate, a distance index for specifying the magnitude of the MVD, and a direction index for indicating the direction of the MVD.

[0045] In the existing MMVD design, the distance index specifies the magnitude of the MVD defined based on a set of predefined offsets from the starting point. As shown in FIGS. 6A and 6B, the offsets are added to the horizontal or vertical component of the starting MV (i.e., the MV of the selected basic merge candidate).

[0046] FIG. 6A shows the MMVD mode with respect to the L0 reference. FIG. 6B shows the MMVD mode with respect to the L1 reference.

[0047] Table 2 shows the MVD offsets applied in AVS3 respectively.

[0048]

Table 2

[0049] As shown in Table 3, the direction index is used to specify the sign of the signaled MVD. Note that the meaning of the MVD sign can vary according to the starting MV. When the starting MV is a uni - directional prediction MV or a bi - directional prediction MV, the MV points to two reference pictures, and the POCs of both are greater than the POC of the current picture or both are less than the POC of the current picture, the signaled sign is the sign of the MVD added to the starting MV. When the starting MV is a bi - directional prediction MV pointing to two reference pictures, the POC of one picture is greater than the current picture and the POC of the other picture is less than the current picture, the signaled sign is applied to the L0 MVD, and the inverse value of the signaled sign is applied to the L1 MVD.

[0050]

Table 3

[0051] Motion Signaling for Normal Intra - Mode Similar to the HEVC standard, in addition to the merge / skip mode, in both VVC and AVS3, it is permitted that one inter CU explicitly specifies its motion information in the bitstream. Overall, the signaling of motion information in both VVC and AVS3 remains the same as that of the HEVC standard. Specifically, first, one inter prediction syntax, i.e., inter_pred_idc, is signaled to indicate whether the prediction signal is from list L0, L1, or both. For each reference list used, the corresponding reference picture is identified by signaling one reference picture index ref_idx_lx (x = 0, 1) for the corresponding reference list, and the corresponding MV is represented by one MVP index mvp_lx_flag (x = 0, 1) used to select the MV predictor (MVP) and then the motion vector difference (MVD) between the target MV and the selected MVP. In addition, in the VVC standard, one control flag mvd_l1_zero_flag is signaled at the slice level. When mvd_l1_zero_flag is equal to 0, the L1 MVD is signaled in the bitstream; otherwise (when the mvd_l1_zero_flag flag is equal to 1), the L1 MVD is not signaled and its value is always inferred as 0 at the encoder and decoder.

[0052] Bidirectional prediction by CU-level weighting In standards prior to VVC and AVS3, when weighted prediction (WP) is not applied, the bidirectional prediction signal is generated by averaging the unidirectional prediction signals obtained from two reference pictures. In VVC, to improve the efficiency of bidirectional prediction, one tool coding, i.e., bidirectional prediction by CU-level weighting (BCW), is introduced. Specifically, instead of simple averaging, the BCW bidirectional prediction is extended as shown below by allowing the weighted average of two prediction signals. P’(i,j)=((8 - w)·P0(i,j)+w·P1(i,j)+4)≫3

[0053] In VVC, when the current picture is a single low-delay picture, the weight of one BCW coding block is permitted to be selected from a set of predefined weight values \(w\in\{-2,3,4,5,10\}\), and weight 4 represents the conventional bi-directional prediction case where two uni-directional prediction signals are equally weighted. In the case of low delay, only three weights \(w\in\{3,4,5\}\) are permitted. Generally, there are some design similarities between WP and BCW, but the two coding tools target solving the problem of illumination change at different granularities. However, the interaction between WP and BCW may complicate the VVC design in some cases, so it is not allowed for the two tools to be enabled simultaneously. Specifically, when WP is enabled for a slice, the BCW weights for all bi-directional prediction CUs within the slice are not signaled and are inferred to be 4 (i.e., equal weights are applied).

[0054] Template matching Template matching (TM) is a decoder-side MV derivation method for refining the motion information of the current CU by finding the best match between a template consisting of the reconstructed samples above and to the left of the current CU and a reference block (i.e., the same size as the template) in the reference picture. As shown in Figure 7, within a search range of \([-8,+8]\) pels, one MV is searched around the initial motion vector of the current CU. The best match can be defined as the MV that achieves the lowest match cost, such as sum of absolute differences (SAD), sum of absolute transformed differences (SATD), etc., between the current template and the reference template. There are two different methods for applying the TM mode to inter-coding.

[0055] In the AMVP mode, based on the template matching difference, the MVP candidate is determined to select the one that reaches the minimum difference between the template of the current block and the template of the reference block. Then, TM is only performed on this specific MVP candidate for MV refinement. By using iterative diamond search, TM refines this MVP candidate from 1-pel MVD accuracy (or 4-pel in the case of 4-pel AMVR mode) within the [-8, +8] search range. The AMVP candidate can be further refined by using a cross search of 1-pel MVD accuracy (or 4-pel in the case of 4-pel AMVR mode) according to the AMVR mode specified in Table 14 below, followed by sequentially using 1 / 2-pel and 1 / 4-pel ones. This search process ensures that the MVP candidate still maintains the same MV accuracy as that indicated by the AMVR mode after the TM process.

[0056]

Table 4

[0057] In the merge mode, a similar search method is applied to the merge candidate indicated by the merge index. As shown in the above table, TM can perform all up to 1 / 8-pel MVD accuracy depending on whether an alternative interpolation filter (used when AMVR is in 1 / 2-pel mode) is used according to the merged motion information, or can skip the part behind 1 / 2-pel MVD accuracy.

[0058] As described above, the unidirectional motion used to generate the predicted samples of two GPM partitions is directly obtained from the normal merge candidates. If there is no strong correlation between the MVs of the spatial / temporal adjacent blocks, the derived unidirectional MVs from the merge candidates may not be accurate enough to capture the true motion of each GPM partition. Motion estimation can provide more accurate motion, but at the cost of signaling overhead that cannot be ignored by any motion refinement that can be applied on top of the existing unidirectional MVs. On the other hand, the MVMD mode is used in both the VVC standard and the AVS3 standard and has been proven to be an efficient signaling mechanism for reducing the MVD signaling overhead. Therefore, it may also be beneficial to combine GPM with the MMVD mode. Such a combination can, in some cases, improve the overall coding efficiency of the GPM tool by providing more accurate MVs to capture the individual motions of each GPM partition.

[0059] As discussed earlier, in both the VVC standard and the AVS3 standard, the GPM mode is only applied to the merge / skip modes. Such a design may not be optimal in terms of coding efficiency considering that not all non-merge inter CUs can benefit from the flexible non-square partitions of GPM. On the other hand, for the same reasons as described above, the unidirectional prediction motion candidates derived from the normal merge / skip modes are not always accurate enough to capture the true motion of the two geometric partitions. Based on such an analysis, a proper extension of the GPM mode to non-merge inter modes (i.e., CUs that explicitly signal motion information in the bitstream) may expect additional coding gains. However, the improvement in MV accuracy comes at the cost of increased signaling overhead. Therefore, it should be important to identify an effective signaling method that can minimize the signaling cost while providing more accurate MVs for the two geometric partitions in order to efficiently apply the GPM mode to the explicit inter modes.

[0060] Proposed method In the present disclosure, a method is proposed to further improve the coding efficiency of GPM by applying further motion refinement on top of the existing unidirectional MVs applied to each GPM partition. The proposed method is referred to as Geometric Partition Mode with Motion Vector Refinement (GPM-MVR). In addition, in the proposed scheme, motion refinement is signaled in a similar way to one of the existing MMVD designs, i.e., based on a set of pre-defined sizes and directions of MVDs for motion refinement.

[0061] In another aspect of the present disclosure, a solution is provided for extending the GPM mode to an explicit inter-mode. For ease of explanation, these schemes are referred to as Geometric Partition Mode with Explicit Motion Signaling (GPM-EMS). Specifically, in the proposed GPM-EMS scheme, the existing motion signaling mechanisms, i.e., MVP and MVD, are utilized to specify the corresponding unidirectional MVs of two geometric partitions in order to achieve better harmony with the regular inter-mode.

[0062] Geometric partition mode with separate motion vector refinement To improve the coding efficiency of GPM, in this chapter, one improved geometric partitioning mode with separate motion vector refinement is proposed. Specifically, considering the GPM partition, the proposed method first uses the existing syntax merge_gpm_idx0 and merge_gpm_idx1 to identify the uni-directional MVs for two GPM partitions from the existing uni-directional prediction merge candidate list and uses these as the base MVs. After the two base MVs are determined, two new sets of syntax elements are introduced to separately specify the values of the motion refinement applied on the base MVs of the two GPM partitions. Specifically, first, two flags, namely gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag, are signaled to indicate whether GPM-MVR is applied to the first and second GPM partitions, respectively. When the flag of one GPM partition is equal to 1, the corresponding value of the MVR applied to the base MV of that partition is signaled in MMVD format, i.e., one distance index (indicated by the syntax elements gpm_mvr_partIdx0_distance_idx and gpm_mvr_partIdx1_distance_idx) specifies the magnitude of the MVR, and one direction index (indicated by the syntax elements gpm_mvr_partIdx0_direction_idx and gpm_mvr_partIdx1_distance_idx) specifies the direction of the MVR. Table 4 shows the syntax elements introduced by the proposed GPM-MVR method.

[0063]

Table 5

[0064] Based on the proposed syntax elements shown in Table 4, in the decoder, the last MV used to generate the uni - directional prediction samples for each GPM segment is equal to the sum of the signaled motion vector refinement and the corresponding base MV. In practice, different sets of MVR sizes and directions may be pre - defined and applied to the proposed GPM - MVR scheme, which can provide various trade - offs between motion vector accuracy and signaling overhead. In one particular example, it is proposed to reuse the eight MVD offsets (i.e., 1 / 4, 1 / 2, 1, 2, 4, 8, 16, and 32 pels) and four MVD directions (i.e., ±x and y axes) used in the VVC standard for the proposed GPM - MVR scheme. In another example, the existing five MVD offsets {1 / 4, 1 / 2, 1, 2, and 4 pels} and four MVD directions (i.e., ±x and y axes) used in the AVS3 standard are applied in the proposed GPM - MVR scheme.

[0065] As discussed in the "GPM Signaling Design" chapter, since the uni - directional MVs used for two GPM segments cannot be the same, in the existing GPM design, one constraint is applied to make the two uni - directional prediction merge indexes different. However, in the proposed GPM - MVR scheme, further motion refinement is applied on top of the existing GPM uni - directional MVs. Therefore, even when the base MVs of two GPM segments are the same, the last uni - directional MVs used to predict the two segments will still be different unless the values of the two motion vector refinements are the same. Based on the above considerations, this constraint (limiting the two uni - directional prediction merge indexes to be different) is removed when the proposed GPM - MVR scheme is applied. In addition, since the two uni - directional prediction merge indexes are allowed to be the same, the same maximum value MaxGPMMergeCand - 1 is used for the binarization of both merg_gpm_idx0 and merge_gpm_idx1, where MaxGPMMergeCand is the number of candidates in the uni - directional prediction merge list.

[0066] As analyzed above, when the unidirectional prediction merge indexes of two GPM partitions (i.e., merge_gpm_idx0 and merge_gpm_idx1) are the same, in order to ensure that the last MVs used for the two partitions are different, the values of the two motion vector refinements cannot be made the same. Based on such conditions, in one embodiment of the present disclosure, when the unidirectional prediction merge indexes of two GPM partitions are the same (i.e., merge_gpm_idx0 is equal to merge_gpm_idx1), one signaling redundancy removal method is proposed to reduce the signaling overhead of the MVR of the second GPM partition by using the MVR of the first GPM partition. In one example, the following signaling conditions are applied:

[0067] First, when the flag gpm_mvr_partIdx0_enable_flag is equal to 0 (i.e., GPM-MVR is not applied to the first GPM partition), the flag of gpm_mvr_partIdx1_enable_flag is not signaled but is inferred to be 1 (i.e., GPM-MVR is applied to the second GPM partition).

[0068] Second, when both flags gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 1 (i.e., GPM-MVR is applied to two GPM partitions), and gpm_mvr_partIdx0_direction_idx is equal to gpm_mvr_partIdx1_direction_idx (i.e., the MVRs of the two GPM partitions have the same direction), the magnitude of the MVR of the first GPM partition (i.e., gpm_mvr_partIdx0_distance_idx) is used to predict the magnitude of the MVR of the second GPM partition (i.e., gpm_mvr_partIdx1_distance_idx). Specifically, if gpm_mvr_partIdx1_distance_idx is smaller than gpm_mvr_partIdx0_distance_idx, its original value is directly signaled. Otherwise (gpm_mvr_partIdx1_distance_idx is greater than gpm_mvr_partIdx0_distance_idx), 1 is subtracted from the value and signaled to the bitstream. On the decoder side, to decode the value of gpm_mvr_partIdx1_distance_idx, if the parsed value is smaller than gpm_mvr_partIdx0_distance_idx, gpm_mvr_partIdx1_distance_idx is set equal to the parsed value, and otherwise (the parsed value is equal to or greater than gpm_mvr_partIdx0_distance_idx), gpm_mvr_partIdx1_distance_idx is set equal to the parsed value plus 1. In such cases, to further reduce overhead, different maximum values MaxGPMMVRDistance - 1 and MaxGPMMVRDistance - 2 may be used for the binarization of gpm_mvr_partIdx0_distance_idx and gpm_mvr_partIdx1_distance_idx, where MaxGPMMVRDistance is the number of allowed magnitudes for motion vector refinement.

[0069] In another embodiment, the signaling order is switched to gpm_mvr_partIdx0_direction_idx / gpm_mvr_partIdx1_direction_idx and gpm_mvr_partIdx0_distance_idx / gpm_mvr_partIdx1_distance_idx so that the MVR of direction is signaled before the size of the MVR. Accordingly, following the same logic as above, the encoder / decoder can adjust the signaling of the MVR direction of the second GPM section using the MVR direction of the first GPM section. In another embodiment, it is proposed to first signal the size and direction of the MVR of the second GPM section and use these to adjust the signaling of the size and direction of the MVR of the 1 th GPM section.

[0070] In another embodiment, it is proposed to signal the syntax elements related to GPM-MVR before signaling the existing GPM syntax elements. Specifically, in such a design, first, two flags, gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag, are signaled to indicate whether GPM-MVR is applied to the first and second GPM sections, respectively. When the flag of one GPM section is equal to 1, the distance index (indicated by the syntax elements gpm_mvr_partIdx0_distance_idx and gpm_mvr_partIdx1_distance_idx) and the direction index (indicated by the syntax elements gpm_mvr_partIdx0_direction_idx and gpm_mvr_partIdx1_ direction _idx) are used to specify the magnitude and direction of the MVR. signaled . Thereafter, the existing syntax merge_gpm_idx0 and merge_gpm_idx1 are signaled to identify the unidirectional MV, i.e., the base MV, for the two GPM sections. Table 5 shows the proposed GPM-MVR signaling method.

[0071]

Table 6

[0072] Similar to the signaling method in Table 4, when the GPM-MVR signaling method in Table 5 is applied, specific conditions may be applied to ensure that the resulting MVs used for predicting two GPM sections are not the same. Specifically, depending on the values of MVR applied to the first and second GPM sections, the following conditions for suppressing the signaling of the unidirectional prediction merge indices merge_gpm_idx0 and merge_gpm_idx1 are proposed.

[0073] First, when the values of both gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 0 (i.e., GPM-MVR is disabled for both of the two GPM sections), the values of merge_gpm_idx0 and merge_gpm_idx1 cannot be made the same.

[0074] Second, when gpm_mvr_partIdx0_enable_flag is equal to 1 (i.e., GPM-MVR is enabled for the first GPM section) and gpm_mvr_partIdx1_enable_flag is equal to 0 (i.e., GPM-MVR is disabled for the second GPM section), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same.

[0075] Third, when gpm_mvr_partIdx0_enable_flag is equal to 0 (i.e., GPM-MVR is disabled for the first GPM section) and gpm_mvr_partIdx1_enable_flag is equal to 1 (i.e., GPM-MVR is enabled for the second GPM section), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same.

[0076] Fourth, when the values of both gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 1 (i.e., GPM-MVR is enabled for both of the two GPM sections), the determination of whether the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same depends on the values of MVR applied to the two GPM sections (indicated by gpm_mvr_partIdx0_direction_idx and gpm_mvr_partIdx0_distance_idx, and gpm_mvr_partIdx1_direction_idx and gpm_mvr_partIdx1_distance_idx). If the values of the two MVRs are equal, it is not permitted for merge_gpm_idx0 and merge_gpm_idx1 to be the same. Otherwise (when the values of the two MVRs are not equal), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same.

[0077] In the above four cases, when the values of merge_gpm_idx0 and merge_gpm_idx1 are not allowed to be the same, the index value of one section can be used as a predictor of the index value of another section. In one method, it is proposed to first signal merge_gpm_idx0 and use its value to predict merge_gpm_idx1. Specifically, in the encoder, when merge_gpm_idx1 is greater than merge_gpm_idx0, the value of merge_gpm_idx1 transmitted to the decoder is reduced by 1. In the decoder, when the received value of merge_gpm_idx1 is equal to or greater than the received value of merge_gpm_idx0, the value of merge_gpm_idx1 is increased by 1. In another method, it is proposed to first signal merge_gpm_idx1 and use its value to predict merge_gpm_idx0. Therefore, in such a case, in the encoder, when merge_gpm_idx0 is greater than merge_gpm_idx1, the value of merge_gpm_idx0 transmitted to the decoder is reduced by 1. In the decoder, when the received value of merge_gpm_idx0 is equal to or greater than the received value of merge_gpm_idx1, the value of merge_gpm_idx0 is increased by 1. In addition, similar to the existing GPM signaling design, different maximum values MaxGPMMergeCand-1 and MaxGPMMergeCand-2 can be used for the binarization of the first and second index values, respectively, according to the signaling order. On the other hand, since there is no correlation between the two index values, when the values of merge_gpm_idx0 and merge_gpm_idx1 are allowed to be the same, the same maximum value MaxGPMMergeCand-1 is used for the binarization of both of the two index values.

[0078] In the above method, in order to reduce the signaling cost, different maximum values can be applied to the binarization of merge_gpm_idx0 and merge_gpm_idx1. The selection of the corresponding maximum value depends on the decoded values of MVR (indicated by gpm_mvr_partIdx0_enable, gpm_mvr_partIdx1_enable, gpm_mvr_partIdx0_direction_idx, gpm_mvr_partIdx1_direction_idx, gpm_mvr_partIdx0_distance_idx, and gpm_mvr_partIdx1_distance_idx). Such a design brings unwanted parsing dependencies between different GPM syntax elements and may affect the overall parsing. To solve such problems, in one embodiment, always the same maximum value (e.g., MaxGPMMergeCand - 1) is proposed for the parsed values of merge_gpm_idx0 and merge_gpm_idx1. When such a method is used, one bitstream conformity constraint can be used to prevent the two decoded MVs of the two GPM segments from being the same. In another method, such non - conformity constraints can also be removed so that the decoded MVs of the two GPM segments are allowed to be the same. On the other hand, when such a method is applied (i.e., using the same maximum value for merge_gpm_idx0 and merge_gpm_idx1), there is no parsing dependency between merge_gpm_idx0 / merge_gpm_idx1 and other GPM - MVR syntax elements. Therefore, the signaling order of these syntax elements is no longer a problem. In one example, it is proposed to move the signaling of merge_gpm_idx0 / merge_gpm_idx1 before the signaling of gpm_mvr_partIdx0_enable, gpm_mvr_partIdx1_enable, gpm_mvr_partIdx0_direction_idx, gpm_mvr_partIdx1_direction_idx, gpm_mvr_partIdx0_distance_idx, and gpm_mvr_partIdx1_distance_idx.

[0079] Geometric partitioning mode with symmetric motion vector refinement In the case of the GPM-MVR method discussed above, two separate MVR values are signaled, and one is applied to improve the base MV of only one GPM partition. Such a method can be efficient in terms of improving prediction accuracy by allowing independent motion refinement for each GPM partition. However, such flexible motion refinement comes at the cost of increasing the signaling overhead, on the condition that two different sets of GMP-MVR syntax elements need to be sent from the encoder to the decoder. To reduce the signaling overhead, in this chapter, one geometric partitioning mode with symmetric motion vector refinement is proposed. Specifically, in this method, according to the symmetric relationship between the picture order count (POC) values of the current picture and the reference picture associated with two GPM partitions, one single MVR value is signaled for one GPM CU and used for both of the two GPM partitions. Table 6 shows the syntax elements when the proposed method is applied.

[0080]

Table 7

[0081] As shown in Table 6, after the base MVs of the two GPM partitions are selected (based on merge_gpm_idx0 and merge_gpm_idx1), one flag, gpm_mvr_enable_flag, is signaled to indicate whether the GPM-MVR mode is applied to the current GPM CU. When this flag is equal to 1, this indicates that motion refinement is applied to enhance the base MVs of the two GPM partitions. Otherwise (when the flag is equal to 0), this indicates that motion refinement is not applied to either of the two partitions. When the GPM-MVR mode is enabled, additional syntax elements are further signaled by the direction index gpm_mvr_direction_idx and the magnitude index gpm_mvr_distance_idx to specify the value of the applied MVR. In addition, similar to the MMVD mode, the meaning of the MVR sign can vary according to the relationship between the current picture of the GPM partition and the POCs of the two reference pictures. Specifically, when both POCs of the two reference pictures are greater than or less than the POC of the current picture, the signaled sign is the sign of the MVR added to both of the two base MVs. Otherwise (when the POC of one reference picture is greater than the POC of the current picture and the POC of the other reference picture is less than the POC of the current picture), the signaled sign is applied to the MVR of the first GPM partition, and the opposite sign is applied to the second GPM partition. In Table 6, it is permitted that the values of merge_gpm_idx0 and merge_gpm_idx1 are the same.

[0082] In another embodiment, it is proposed to signal two different flags to separately control the enabling / disabling of the GPM-MVR mode for two separate GPM partitions. However, when the GPM-MVR mode is enabled, only one MVR is signaled based on the syntax elements gpm_mvr_direction_idx and gpm_mvr_distance_idx. The corresponding syntax table for such a signaling method is shown in Table 7.

[0083] [Table 8]

[0084] When the signaling method of Table 7 is applied, the values ​​of merge_gpm_idx0 and merge_gpm_idx1 are allowed to be identical. However, to ensure that the resulting MVs applied to the two GPM partitions are not redundant, when the flag gpm_mvr_partIdx0_enable_flag is equal to 0 (i.e., GPM-MVR is not applied to the first GPM partition), the flag gpm_mvr_partIdx1_enable_flag is not signaled but is inferred to be 1 (i.e., GPM-MVR is applied to the second GPM partition).

[0085] Adaptation of the Permitted MVR to the GPM-MVR In the GPM-MVR method discussed above, a set of fixed MVR values ​​is used for GPM CUs at both the encoder and the decoder in one video sequence. Such a design is suboptimal for video content with high resolution or intense motion. In those cases, the MV tends to be much larger, so that the fixed MVR values ​​may not be optimal for capturing the true motion of those blocks. To further improve the coding performance of the GPM-MVR mode, this disclosure proposes to support the adaptation of the MVR values ​​allowed to be selected by the GPM-MVR mode at various coding levels, such as sequence level, picture / slice picture, coding block group level, etc. For example, multiple MVR sets as well as corresponding codewords may be derived offline according to the specific motion characteristics of different video sequences. The encoder can select the best MVR set and signal the corresponding index of the selected set to the decoder.

[0086] In some embodiments of the present disclosure, in addition to the default MVR offsets including the magnitudes of eight offsets (i.e., 1 / 4, 1 / 2, 1, 2, 4, 8, 16, and 32 pels) and four MVR directions (i.e., the ±x and y axes), another MVR offset defined in the following table is proposed for the GPM - MVR mode. Table 15 shows the proposed offset magnitudes within the set of the second MVR offsets. Table 16 shows the proposed MVR directions within the set of the second MVR offsets.

[0087]

Table 9

[0088]

Table 10

[0089] In Tables 15 and 16 above, the values +1 / 2 and -1 / 2 on the x - axis and y - axis indicate the diagonal directions in the horizontal and vertical directions (+45° and -45°). As shown in Tables 15 and 16, compared with the existing set of MVR offsets, the set of the second MVR offsets introduces two new offset magnitudes (i.e., 3 pels and 6 pels) and four offset directions (45°, 135°, 225°, and 315°). The newly added MVR offsets make the set of the second MVR offsets more suitable for coding video blocks with high - motion. In addition, to enable an adaptive switch between the two sets of MVR offsets, one control flag is proposed to be signaled at one specific coding level (e.g., sequence, picture, slice, CTU, and coding block, etc.) to indicate which set of MVR offsets is selected for the GPM - MVR mode applied at the coding level. Assuming that the proposed adaptation is implemented at the picture level, Table 17 below shows the corresponding syntax elements signaled in the picture header.

[0090]

Table 11

[0091] In Table 17 above, a new flag ph_gpm_mvr_offset_set_flag is used to indicate the selection of the corresponding GPM MVR offset used for that picture. When this flag is equal to 0, this means that the default MVR offsets (i.e., sizes of 1 / 4, 1 / 2, 1, 2, 4, 8, 16, and 32 pels, and the 4 MVR directions of ±x and y axes) are applied in the GPM-MVR mode within this picture. Otherwise, when this flag is equal to 1, this means that the second MVR offset (i.e., sizes of 1 / 4, 1 / 2, 1, 2, 3, 4, 6, 8, 16 pels, and the 8 MVR directions of ±x, y axes, and 45°, 135°, 225°, and 315°) is applied in the GPM-MVR mode within this picture.

[0092] Different methods may be applied to signal the MVR offset. First, it is proposed to binarize the MVR direction using a fixed-length codeword, provided that the MVR directions are usually statistically uniformly distributed. Taking the default MVR offset as an example, there are a total of 4 directions, and the codewords 00, 01, 10, and 11 can be used to represent these 4 directions. On the other hand, since the size of the MVR offset can have a varying distribution adapted to the specific motion characteristics of the video content, it is proposed to binarize the MVR size using a variable-length codeword. The following Table 18 shows one specific codeword table that can be used for the binarization of the MVR sizes of the set of default MVD offsets and the set of second MVD offsets.

[0093]

Table 12

[0094] In other embodiments, variable codewords of different fixed lengths may be applied to binarize the magnitudes of the MVR offsets of the set of default and second MVR offsets. For example, the bins "0" and "1" in the above codeword table may be swapped to match various 0 / 1 statistical information of the CABAC engine. In other ways, one statistical-based binarization method may be applied to adaptively design the optimal codeword for the magnitude of the MVR offset on-the-fly rather than signaling it. The statistical information used to determine the optimal codeword can be, but is not limited to, the probability distribution of the magnitudes of the MVR offsets collected over a plurality of previously coded pictures, slices, and / or coding blocks. The codewords may be re-determined / updated at various frequency levels. For example, the update may be performed each time a CU is coded in the GPM-MVR mode. In another example, the update may be re-determined and / or updated each time a plurality, e.g., 8 or 16, of CUs are coded in the GPM-MVR mode. In other ways, instead of re-designing a new set of codewords, the proposed statistical-based method may also be used to re-order the MVR magnitude values based on the same set of codewords by assigning shorter codewords to more used magnitudes and longer codewords to less used magnitudes. Taking the following table as an example, assuming that the statistical information is collected at the picture level, the "usage" row shows the corresponding percentages of the different MVR offset magnitudes used by the GPM-MVR coding blocks within the previously coded picture.According to the values within the "usage" row (i.e., the shortened single-term codewords) that use the same binarization method, the encoder / decoder can order the MVR magnitude values based on their usage. Then, the encoder / decoder assigns the shortest codeword (i.e., "1") to the most frequently used MVR magnitude (i.e., 1 pel), the next shortest codeword (i.e., "01") to the next most frequently used MVR magnitude (i.e., 1 / 2 pel), and the longest codewords (i.e., "0000001" and "0000000") to the two least used MVR magnitudes (i.e., 16 pel and 32 pel). As can be understood, with such a reordering method, the same set of codewords can be freely reordered again to correspond to the dynamic changes in the statistical distribution of MVR magnitudes.

[0095]

Table 13

[0096] Encoder Acceleration Logic for GPM-MVR Rate-Distortion Optimization In the case of the proposed GPM-MVR method, in order to determine the optimal MVR for each GPM section, the encoder may need to test the rate-distortion cost of each GPM section multiple times, varying the MVR values being applied each time. This can significantly increase the complexity of encoding in the GPM mode. To address the issue of encoding complexity, the following high-speed encoding logic is proposed in this chapter.

[0097] First, due to the quadtree / binary tree / trinary tree block partitioning structure applied in VVC and AVS3, during the rate-distortion optimization (RDO) process, the same coding block can be identified and divided by different partitioning paths respectively. In the current VTM / HPM encoder implementation example, the GPM and GPM-MVR modes are always tested whenever the same CU is obtained by different combinations of block partitioning together with other inter and intra coding modes. Generally, for different partitioning paths, only the adjacent blocks of one CU can be different, and should have a relatively minor impact on the optimal coding mode selected by one CU. Based on such considerations, in order to reduce the total number of GPM RDOs applied, it is proposed to remember the decision of whether the GPM mode is selected when the RD cost of one CU is first identified. Thereafter, when the same CU is re-identified by the RDO process (by a different partitioning path), the RD cost of GPM (including GPM-MVR) is only confirmed if GPM was selected for that CU for the first time. If GPM is not selected for the initial RD confirmation of one CU, when the same CU is realized by a different partitioning path, only GPM (without GPM-MVR) is tested. In another way, when GPM is not selected for the initial RD confirmation of one CU and the same CU is realized by a different partitioning path, neither GPM nor GPM-MVR is tested.

[0098] Second, in order to reduce the number of GPM partitions for the GPM-MVR mode, it is proposed to maintain the first M GPM partition modes without the minimum RD cost when the RD cost of one CU is first identified. Thereafter, when the same CU is re-identified by the RDO process (by a different partitioning path), only those M GPM partition modes are tested for the GPM-MVR mode.

[0099] Thirdly, in order to reduce the number of GPM partitions to be tested for each initial RDO process, it is proposed that first, the sum of absolute difference (SAD) values when using different unidirectional prediction merge candidates for two GPM partitions be calculated. Then, for each GPM partition under one specific partition mode, the best unidirectional prediction merge candidate having the minimum SAD value is selected, and the corresponding SAD value of the partition mode equal to the sum of the SAD values of the best unidirectional prediction merge candidates for two GPM partitions is calculated. Then, for the subsequent RD process, only the first N partition modes having the best SAD values for the previous step are tested for the GPM-MVR mode.

[0100] Geometric partitions with explicit motion signaling In this chapter, a plurality of methods for extending the GPM mode to the normal inter-mode bidirectional prediction in which two unidirectional MVs of the GPM mode are explicitly signaled from the encoder to the decoder are proposed.

[0101] In the first solution (Solution 1), it is proposed to completely reuse the existing motion signaling for bidirectional prediction to signal the two unidirectional MVs in the GPM mode. Table 8 shows the modified syntax table of the proposed method, and the newly added syntax elements are shown in italic bold. As shown in Table 8, in this solution, all existing syntax elements that signal L0 and L1 motion information are completely reused to indicate the unidirectional MVs of the two GPM partitions respectively. In addition, it is assumed that the L0 MV is always associated with the first GPM partition and the L1 MV is always associated with the second GPM partition. On the other hand, in Table 8, the inter-prediction syntax, i.e., inter_pred_idc, is signaled before the GPM flag (i.e., gpm_flag), and thus the value of inter_pred_idc can be used to condition the presence of the gpm_flag. Specifically, the flag gpm_flag needs to be signaled only when inter_pred_idc is equal to PRED_BI (i.e., bidirectional prediction) and both inter_affine_flag and sym_mvd_flag are equal to 0 (i.e., the CU is not coded by either affine mode or SMVD mode). When the flag gpm_flag is not signaled, its value is always inferred to be 0 (i.e., the GPM mode is disabled). When gpm_flag is 1, another syntax element gpm_partition_idx is further signaled to indicate the GPM mode selected for the current CU (from a total of 64 GPM partitions).

[0102]

Table 14

[0103] In another way, it is proposed to place the signaling of the flag gpm_flag before other inter-signaling syntax elements so that the value of gpm_flag can be used to determine whether other inter-syntax elements need to exist. Table 9 shows the corresponding syntax table when such a method is applied, and the newly added syntax elements are shown in italic bold. As can be seen, in Table 9, first gpm_flag is signaled. When gpm_flag is equal to 1, the corresponding signaling of inter_pred_idc, inter_affine_flag, and sym_mvd_flag can be bypassed. Instead, the corresponding values of the three syntax elements can be inferred as PRED_BI, 0, and 0 respectively.

[0104]

Table 15

[0105] In both Table 8 and Table 9, the SMVD mode cannot be combined with the GPM mode. In another example, it is proposed to permit the SMVD mode when the current CU is coded by the GPM mode. When such a combination is permitted, by following the same design of SMVD, it is assumed that the MVDs of two GPM partitions are symmetric, and therefore only the MVD of the first GPM partition needs to be signaled, and the MVD of the second GPM partition is always symmetric to the first MVD. When such a method is applied, the corresponding signaling condition of sym_mvd_flag for gpm_flag can be removed.

[0106] As shown above, in the first solution, it is always assumed that L0 MV is used for the first GPM partition and L1 MV is used for the second GPM partition. Such a design may not be optimal in the sense that it prohibits the MV of the two GPM partitions from coming from the same prediction list (L0 or L1). To solve such a problem, a signaling design shown in Table 10 proposes an alternative GPM-EMS method, Solution 2. In Table 10, the newly added syntax elements are shown in italic bold. As shown in Table 10, first, the flag gpm_flag is signaled. When this flag is equal to 1 (i.e., GPM is enabled), the syntax gpm_partition_idx is signaled to specify the selected GPM mode. Then, an additional flag gpm_pred_dir_flag0 is signaled to indicate the corresponding prediction list from which the MV of the first GPM partition comes. When the flag gpm_pred_dir_flag0 is equal to 1, this indicates that the MV of the first GPM partition comes from L1, and otherwise (when the flag is equal to 0), this indicates that the MV of the first GPM partition comes from L0. Subsequently, the existing syntax elements ref_idx_l0, mvp_l0_flag, and mvd_coding() are utilized to signal the reference picture index, mvp index, and the value of the MVD of the first GPM partition. On the other hand, similar to the first partition, another syntax element gpm_pred_dir_flag1 is introduced to select the corresponding prediction list of the second GPM partition, followed by the existing syntax elements ref_idx_l1, mvp_l1_flag, and mvd_coding() being used to derive the MV of the second GPM partition.

[0107]

Table 16

[0108] Finally, it should be noted that some existing coding tools in VVC and AVS3, which are specifically designed for bidirectional prediction, such as bidirectional optical flow, decoder-side motion vector refinement (DMVR), and bidirectional prediction by CU weight (BCW), can be automatically bypassed when the proposed GPM-EMS method is enabled for one inter-CU, on the condition that the GPM mode consists of two unidirectional prediction segments (excluding the mixed samples on the split edge). For example, on the condition that BCW cannot be applied to the GPM mode, in order to reduce the signaling overhead, when one of the proposed GPM-EMSs is enabled for one CU, the corresponding BCW weight does not need to be signaled to the CU any further.

[0109] Combination of GPM-MVR and GPM-EMS In this chapter, it is proposed to combine GPM-MVR and GPM-EMS for one CU having geometric shape partitions. Specifically, unlike GPM-MVR or GPM-EMS where only one of merge-based motion signaling or explicit signaling is applicable to signal the unidirectional prediction MVs of two GPM partitions, in the proposed method, 1) one partition uses GPM-MVR-based motion signaling and the other uses GPM-EMS-based motion signaling, or 2) both partitions use GPM-MVR-based motion signaling, or 3) both partitions use GPM-EMS-based motion signaling are permitted. Using the GPM-MVR signaling in Table 4 and the GPM-EMS in Table 10, Table 11 shows the corresponding syntax table after the proposed GPM-MVR and GPM-EMS are combined. In Table 11, the newly added syntax elements are shown in italic bold. As shown in Table 11, two additional syntax elements gpm_merge_flag0 and gpm_merge_flag1 are introduced into Partition #1 and #2 that specify the corresponding partitions using GPM-MVR-based merge signaling or GPM-EMS-based explicit signaling, respectively. When this flag is 1, it means that GPM-MVR-based signaling is enabled for the partition where the GPM unidirectional prediction motion is signaled by merge_gpm_idxX, gpm_mvr_partIdxX_enabled_flag, gpm_mvr_partIdxX_direction_idx, and gpm_mvr_partIdxX_distance_idx, where X = 0, 1. Otherwise, when this flag is 0, it means that the unidirectional prediction motion of this partition is explicitly signaled by the GPM-EMS method using the syntax elements gpm_pred_dir_flagX, ref_idx_lX, mvp_lX_flag, and mvd_lX, where X = 0, 1.

[0110]

Table 17

[0111] Combination of GPM-MVR and template matching In this chapter, different solutions for combining GPM-MVR with template matching are provided.

[0112] In Method 1, when one CU is coded in GPM mode, it is proposed to signal two separate flags for two GPM segments, where each flag indicates whether the unidirectional motion of the corresponding segment is further refined by template matching. When this flag is enabled, a template is generated using the reconstructed samples adjacent to the top-left of the current CU, and then the unidirectional motion of the segment is refined by minimizing the difference between the template and its reference samples according to the same procedure introduced in the "Template Matching" chapter. Otherwise (when the flag is disabled), template matching is not applied to this segment and GPM-MVR can be further applied. Using the GPM-MVR signaling method in Table 5 as an example, Table 12 shows the corresponding syntax table when GPM-MVR is combined with template matching. In Table 12, the newly added syntax elements are shown in italic bold.

[0113]

Table 18

[0114] As shown in Table 12, in the proposed method, two additional flags, gpm_tm_enable_flag0 and gpm_tm_enable_flag1, are first signaled to indicate whether the movement is refined for each of the two GPM partitions. When this flag is 1, this indicates that TM is applied to refine the one-way MV of one partition. When this flag is 0, one flag (gpm_mvr_partIdx0_enable_flag or gpm_mvr_partIdx0_enable_flag) is further signaled to indicate whether GPM-MVR is applied to the GPM partition. When the flag of one GPM partition is equal to 1, the distance index (indicated by the syntax elements gpm_mvr_partIdx0_distance_idx and gpm_mvr_partIdx1_distance_idx) and the direction index (indicated by the syntax elements gpm_mvr_partIdx0_direction_idx and gpm_mvr_partIdx1_ direction _idx) are signaled to specify the magnitude and direction of the MVR. Then, the existing syntax merge_gpm_idx0 and merge_gpm_idx1 are signaled to identify the one-way MV for the two GPM partitions. On the other hand, similar to the signaling conditions applied to Table 5, the following conditions may be applied to ensure that the resulting MVs used for prediction of the two GPM partitions are not the same.

[0115] First, when both values of gpm_tm_enable_flag0 and gpm_tm_enable_flag1 are equal to 1 (i.e., TM is enabled for both of the two GPM partitions), the values of merge_gpm_idx0 and merge_gpm_idx1 cannot be the same.

[0116] Second, when one of gpm_tm_enable_flag0 and gpm_tm_enable_flag1 is 1 and the other is 0, the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same.

[0117] Otherwise, that is, when both gpm_tm_enable_flag0 and gpm_tm_enable_flag1 are equal to 1, and first, when both the values of gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 0 (i.e., GPM-MVR is disabled for both of the two GPM partitions), the values of merge_gpm_idx0 and merge_gpm_idx1 cannot be made the same. Second, when gpm_mvr_partIdx0_enable_flag is equal to 1 (i.e., GPM-MVR is enabled for the first GPM partition) and gpm_mvr_partIdx1_enable_flag is equal to 0 (i.e., GPM-MVR is disabled for the second GPM partition), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same. Third, when gpm_mvr_partIdx0_enable_flag is equal to 0 (i.e., GPM-MVR is disabled for the first GPM partition) and gpm_mvr_partIdx1_enable_flag is equal to 1 (i.e., GPM-MVR is enabled for the second GPM partition), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same. Fourth, when both the values of gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 1 (i.e., GPM-MVR is enabled for both of the two GPM partitions), the determination of whether the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same depends on the values of MVR applied to the two GPM partitions (indicated by gpm_mvr_partIdx0_direction_idx and gpm_mvr_partIdx0_distance_idx, as well as gpm_mvr_partIdx1_direction_idx and gpm_mvr_partIdx1_distance_idx).When the values of two MVRs are equal, merge_gpm_idx0 and merge_gpm_idx1 are not allowed to be the same. Otherwise (when the values of the two MVRs are not equal), the values of merge_gpm_idx0 and merge_gpm_idx1 are allowed to be the same.

[0118] In the above method 1, TM and MVR are exclusively applied to GPM. In such a way, it is prohibited to further apply MVR on the refined MV in TM mode. Therefore, in order to further provide more MV candidates for GPM, a method 2 is proposed to enable the application of the MVR offset on the TM refined MV. Table 13 shows the corresponding syntax table when GPM-MVR is combined with template matching. In Table 13, the newly added syntax elements are shown in italic bold.

[0119]

Table 19

[0120] As shown in Table 13, different from Table 12, the signaling conditions of gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag for gpm_tm_enable_flag0 and gpm_tm_enable_flag1 are removed. Therefore, regardless of whether TM is applied to refine the unidirectional movement of one GPM section, MV refinement is always allowed to be applied to the MV of the GPM section. Similarly to the above, in order to ensure that the resulting MVs of the two GPM sections are not the same, the following conditions should be applied.

[0121] First, when one of gpm_tm_enable_flag0 and gpm_tm_enable_flag1 is 1 and the other is 0, the values of merge_gpm_idx0 and merge_gpm_idx1 are allowed to be the same.

[0122] Otherwise, that is, when both gpm_tm_enable_flag0 and gpm_tm_enable_flag1 are equal to 1, or both of these flags are equal to 0, first, when both values of gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 0 (that is, GPM-MVR is disabled for both of the two GPM sections), the values of merge_gpm_idx0 and merge_gpm_idx1 cannot be made the same. Second, when gpm_mvr_partIdx0_enable_flag is equal to 1 (that is, GPM-MVR is enabled for the first GPM section), and gpm_mvr_partIdx1_enable_flag is equal to 0 (that is, GPM-MVR is disabled for the second GPM section), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same. Third, when gpm_mvr_partIdx0_enable_flag is equal to 0 (that is, GPM-MVR is disabled for the first GPM section), and gpm_mvr_partIdx1_enable_flag is equal to 1 (that is, GPM-MVR is enabled for the second GPM section), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same. Fourth, when both values of gpm_mvr_partIdx0_enable_flag and gpm_mvr_partIdx1_enable_flag are equal to 1 (that is, GPM-MVR is enabled for both of the two GPM sections), the determination of whether the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be the same depends on the values of MVR applied to the two GPM sections (indicated by gpm_mvr_partIdx0_direction_idx and gpm_mvr_partIdx0_distance_idx, as well as gpm_mvr_partIdx1_direction_idx and gpm_mvr_partIdx1_distance_idx).When the values of two MVRs are equal, merge_gpm_idx0 and merge_gpm_idx1 are not permitted to be identical. Otherwise (when the values of the two MVRs are not equal), the values of merge_gpm_idx0 and merge_gpm_idx1 are permitted to be identical.

[0123] In the above two methods, it is necessary to signal two separate flags to indicate whether TM is applied to each GPM section. The additional signaling may reduce the overall coding efficiency due to the additional overhead, especially at a particularly low bit rate. To reduce the signaling overhead, instead of introducing additional signaling, Method 3 is proposed for inserting TM-based unidirectional MVs into the unidirectional MV candidate list in GPM mode. The TM-based unidirectional MV is generated according to the same TM process described in the "Template Matching" chapter that uses the original unidirectional MV of GPM as the initial MV. In such a way, there is no need to further signal an extra control flag from the encoder to the decoder. Instead, the decoder can identify whether one MV is refined by TM based on the corresponding merge index received from the bitstream (i.e., merge_gpm_idx0 and merge_gpm_idx1). Different methods may exist for arranging the regular GPM MV candidates (i.e., non-TM) and the TM-based MV candidates. In one method, it is proposed to arrange the TM-based MV candidates at the beginning of the MV candidate list, followed by arranging the non-TM-based MV candidates. In another method, it is proposed to first arrange the non-TM-based MV candidates at the beginning, followed by arranging the TM-based candidates. In another method, it is proposed to arrange the TM-based MV candidates and the non-TM-based MV candidates alternately. For example, this can be done by arranging the first N non-TM-based candidates, then all the TM-based candidates, and finally the remaining non-TM-based candidates. In another example, this can be done by arranging the first N TM-based candidates, then all the non-TM-based candidates, and finally the remaining TM-based candidates. In another example, it is proposed to arrange the non-TM-based candidates and the TM-based candidates continuously, i.e., one non-TM-based candidate, one TM-based candidate, etc.

[0124] The above method may be implemented using a device that includes one or more circuits, where the one or more circuits include application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components. The device can use the circuits in combination with other hardware or software components for performing the aforementioned method. Each module, sub-module, unit, or sub-unit disclosed above can be at least partially implemented using one or more circuits.

[0125] FIG. 9 shows a computing environment (or computing device) 910 coupled to a user interface 960. The computing environment 910 can be part of a data processing server. In some embodiments, the computing device 910 can execute any of the various methods or processes (such as encoding / decoding methods or processes) described herein according to the various examples of the present disclosure. The computing environment 910 can include a processor 920, a memory 940, and an I / O interface 950.

[0126] The processor 920 typically controls the overall operation of the computing environment 910, such as operations related to display, data acquisition, data communication, and image processing. The processor 920 can include one or more processors for executing instructions to perform all or some of the steps in the aforementioned method. Further, the processor 920 can include one or more modules that facilitate interaction between the processor 920 and other components. The processor can be a central processing unit (CPU), a microprocessor, a single-chip machine, a GPU, etc.

[0127] Memory 940 is configured to store various types of data to support the operation of computing environment 910. Memory 940 can include a predetermined software 942. Examples of such data include instructions for any application or method operating on computing environment 910, video data sets, image data, and the like. Memory 940 can be implemented by using any type of volatile or non-volatile memory device, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic or optical disks, or combinations thereof.

[0128] I / O interface 950 provides an interface between processor 920 and peripheral interface modules such as a keyboard, click wheel, buttons, and the like. The buttons can include, but are not limited to, a home button, a scan start button, and a scan stop button. I / O interface 950 can be coupled to an encoder and a decoder.

[0129] In some embodiments, a non-transitory computer-readable storage medium including a plurality of programs, such as those included within memory 940, is also provided, and the plurality of programs are executable by processor 920 within computing environment 910 to implement the methods described above. For example, the non-transitory computer-readable storage medium can be a ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device, and the like.

[0130] The non-transitory computer-readable storage medium stores a plurality of programs for execution by a computing device having one or more processors, and when the plurality of programs are executed by the one or more processors, cause the computing device to implement the foregoing method for motion prediction.

[0131] In some embodiments, the computing environment 910 may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), graphics processing units (GPUs), controllers, microcontrollers, microprocessors, or other electronic components to implement the above method.

[0132] FIG. 8 is a flowchart illustrating a method for decoding a video block in a GPM according to an example of the present disclosure.

[0133] In step 801, the processor 1020 can receive a control flag associated with the video block. The control flag can be a control variable including one or more flags, such as a binary flag, a non-binary flag, or any other variable. In one or more examples, the control variable can be the flag "ph_gpm_mvr_offset_set_flag" shown in Table 17.

[0134] In some examples, the control variable enables an adaptive switch between sets of multiple MVR offsets, and the control variable is applied at the coding level.

[0135] In some examples, the coding level can be a sequence level, a picture / slice level, a CTU level, or a coded block level. For example, when a control variable is signaled at the picture level on the encoder side, the decoder side receives a control variable for indicating which set of MVR offsets to select for the purpose of selecting a corresponding MVR offset associated with the current video block at the picture level in response thereto.

[0136] In step 802, the processor 1020 can partition the video block into a first geometric partition and a second geometric partition.

[0137] In step 803, the processor 1020 can receive one or more syntax elements and determine a first MVR offset and a second MVR offset applied to the first and second geometric partitions from the selected set of MVR offsets. The selected MVR offset can be one MVR offset selected by the control variable.

[0138] In some examples, a set of multiple MVR offsets can include a first set of MVR offsets and a second set of MVR offsets. In some examples, the first set of MVR offsets can include a plurality of default MVR offsets including a plurality of default offset magnitudes and a plurality of default MVR directions. In some examples, the second set of MVR offsets can include a plurality of alternative MVR offsets including a plurality of alternative offset magnitudes and a plurality of alternative MVR directions. In some examples, the second set of MVR offsets can include more offset magnitudes and more MVR directions than the first set of MVR offsets. For example, the plurality of default offset magnitudes and the plurality of default MVR directions can include eight offset magnitudes (i.e., 1 / 4, 1 / 2, 1, 2, 4, 8, 16, and 32 pels) and four MVR directions (i.e., the ±x and y axes). The plurality of alternative offset magnitudes and the plurality of alternative MVR directions can include the offsets and directions shown in Tables 15 and 16.

[0139] As shown in Tables 15 and 16, the set of alternative MVR offsets can include more offset magnitudes in addition to the plurality of default offset magnitudes, and the set of alternative MVR offsets can include more MVR directions in addition to the plurality of default MVR directions.

[0140] In some examples, in response to determining that the control variable is equal to 0, the processor 1020 can determine that the first set of MVR offsets is to be applied, and in response to determining that the control variable is equal to 1, the processor 1020 can determine that the second set of MVR offsets is to be applied.

[0141] In some examples, the plurality of default offset magnitudes and the plurality of alternative offset magnitudes can each be binarized using variable length codewords.

[0142] As shown in Table 18, the first default offset size (i.e., 1 / 4 pel) indicates a distance of 1 / 4 pixel from the video block, is binarized as 001, the second default offset size (i.e., 1 / 2 pel) indicates a distance of 1 / 2 pixel from the video block, is binarized as 1, the third default offset size (i.e., 1 pel) indicates a distance of 1 pixel from the video block, is binarized as 01, the fourth default offset size (i.e., 2 pels) indicates a distance of 2 pixels from the video block, is binarized as 0001, the fifth default offset size (i.e., 4 pels) indicates a distance of 4 pixels from the video block, is binarized as 00001, the sixth default offset size (i.e., 8 pels) indicates a distance of 8 pixels from the video block, is binarized as 000001, the seventh default offset size (i.e., 16 pels) indicates a distance of 16 pixels from the video block, is binarized as 0000001, and the eighth default offset size (i.e., 32 pels) indicates a distance of 32 pixels from the video block, is binarized as 0000000.

[0143] Furthermore, as shown in Table 18, the magnitude of the first alternative offset (i.e., 1 / 4 pel) indicates a distance of 1 / 4 pixel from the video block and is binarized as 001, the magnitude of the second alternative offset (i.e., 1 / 2 pel) indicates a distance of 1 / 2 pixel from the video block and is binarized as 1, the magnitude of the third alternative offset (i.e., 1 pel) indicates a distance of 1 pixel from the video block and is binarized as 01, the magnitude of the fourth alternative offset (i.e., 2 pels) indicates a distance of 2 pixels from the video block and is binarized as 0001, the magnitude of the fifth alternative offset (i.e., 3 pels) indicates a distance of 3 pixels from the video block and is binarized as 00001, the magnitude of the sixth alternative offset (i.e., 4 pels) indicates a distance of 4 pixels from the video block and is binarized as 000001, the magnitude of the seventh alternative offset (i.e., 6 pels) indicates a distance of 6 pixels from the video block and is binarized as 0000001, the magnitude of the eighth alternative offset (i.e., 8 pels) indicates a distance of 8 pixels from the video block and is binarized as 00000001, and the magnitude of the ninth alternative offset (i.e., 16 pels) indicates a distance of 16 pixels from the video block and is binarized as 00000000.

[0144] In some examples, the processor 1020 further receives a first geometric section enabling syntax element (e.g., gpm_mvr_partIdx0_enable_flag) indicating whether the MVR is applied to the first geometric section, and in response to determining that this geometric section enabling syntax element is equal to 1, a first direction syntax element (e.g., gpm_mvr_partIdx0_direction_idx) and a first size syntax element (e.g., gpm_mvr_partIdx0_distance_idx) indicating the direction and magnitude of the first MVR offset of the first geometric section determined based on the selected set of MVR offsets are received, a second geometric section enabling syntax element (e.g., gpm_mvr_partIdx1_enable_flag) indicating whether the MVR is applied to the second geometric section is received, and in response to determining that the second geometric section enabling syntax element is equal to 1, a second direction syntax element (e.g., gpm_mvr_partIdx1_direction_idx) and a second size syntax element (e.g., gpm_mvr_partIdx1_distance_idx) indicating the direction and magnitude of the second MVR offset of the second geometric section determined based on the selected set of MVR offsets can be received.

[0145] In step 804, the processor 1020 can obtain the first MV and the second MV from the candidate lists for the first geometric section and the second geometric section.

[0146] In step 805, the processor 1020 can calculate the first refined MV and the second refined MV based on the first and second MVs and the first and second MVR offsets.

[0147] In step 806, the processor 1020 can obtain prediction samples for the video block based on the first and second refined MVs.

[0148] In some examples, an apparatus for decrypting video blocks with GPM is provided. The apparatus includes a processor 1020 and a memory 1040 configured to store instructions executable by the processor. When executing the instructions, the processor is configured to perform the method shown in FIG. 8.

[0149] In some other examples, a non-transitory computer-readable storage medium storing instructions is provided. When the instructions are executed by a processor 1020, the instructions cause the processor to perform the method shown in FIG. 8.

[0150] Other examples of the present disclosure will be apparent to those skilled in the art in view of the present specification and by practicing the present disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure, including departures from the present disclosure within the scope of well-known or customary practice in the art, in accordance with the general principles of the present disclosure. The specification and examples are intended to be considered only as exemplary.

[0151] It will be understood that the present disclosure is not limited to the exact examples described above and illustrated in the accompanying drawings, and various modifications and changes can be made without departing from the scope of the present disclosure.

Claims

1. A method for decoding a video block in a geometric partitioning mode (GPM), comprising: receiving a control variable associated with the video block, the control variable enabling an adaptive switch between sets of a plurality of motion vector refinement (MVR) offsets, the control variable being applied at a coding level, the video block including a first geometric partition and a second geometric partition; receiving one or more syntax elements to determine a first MVR offset of the first geometric partition and a second MVR offset of the second geometric partition from a selected set of MVR offsets; obtaining a first motion vector (MV) and a second MV from a candidate list for the first geometric partition and the second geometric partition; calculating a first refined MV and a second refined MV based on the first and second MVs and the first and second MVR offsets; obtaining a prediction sample for the video block based on the first and second refined MVs; including: the sets of the plurality of MVR offsets include a set of first MVR offsets and a set of second MVR offsets; the set of the second MVR offsets includes magnitudes of offsets of the set of the first MVR offsets and MVR directions, the method.

2. The method according to claim 1, wherein the coding level includes a sequence level, a picture level, a coding tree unit level, or a coded block level.

3. The set of the first MVR offsets includes a plurality of default MVR offsets including magnitudes of a plurality of default offsets and a plurality of default MVR directions, The method according to claim 1, wherein the set of the second MVR offsets includes a plurality of alternative MVR offsets including magnitudes of a plurality of alternative offsets and a plurality of alternative MVR directions.

4. In response to determining that the control variable is equal to 0, determining that the set of the first MVR offset is to be applied; In response to determining that the control variable is equal to 1, determining that the set of the second MVR offset is to be applied The method according to claim 1, further comprising.

5. The method according to claim 3, wherein the magnitudes of the plurality of default offsets and the magnitudes of the plurality of alternative offsets are each binarized using variable length codewords.

6. The set of the second MVR offset includes magnitudes of more offsets in addition to the magnitudes of the plurality of default offsets, The method according to claim 5, wherein the set of the second MVR offset includes more MVR directions in addition to the plurality of default MVR directions.

7. The magnitudes of the plurality of default offsets are The magnitude of the first default offset, which indicates a distance of 1 / 4 pixel from the video block and is binarized as 001, and The magnitude of the second default offset, which indicates a distance of 1 / 2 pixel from the video block and is binarized as 1, and The magnitude of the third default offset, which indicates a distance of 1 pixel from the video block and is binarized as 01, and The magnitude of the fourth default offset, which indicates a distance of 2 pixels from the video block and is binarized as 0001, and The magnitude of the fifth default offset, which indicates a distance of 4 pixels from the video block and is binarized as 00001, and The magnitude of the sixth default offset, which indicates a distance of 8 pixels from the video block and is binarized as 000001, The size of the seventh default offset, which indicates a distance of 16 pixels from the video block and is binarized as 0000001, and The size of the eighth default offset, which indicates a distance of 32 pixels from the video block and is binarized as 0000000, and The method according to claim 6, comprising.

8. The sizes of the plurality of alternative offsets are The size of the first alternative offset, which indicates a distance of 1 / 4 pixel from the video block and is binarized as 001, and The size of the second alternative offset, which indicates a distance of 1 / 2 pixel from the video block and is binarized as 1, and The size of the third alternative offset, which indicates a distance of 1 pixel from the video block and is binarized as 01, and The size of the fourth alternative offset, which indicates a distance of 2 pixels from the video block and is binarized as 0001, and The size of the fifth alternative offset, which indicates a distance of 3 pixels from the video block and is binarized as 00001, and The size of the sixth alternative offset, which indicates a distance of 4 pixels from the video block and is binarized as 000001, and The size of the seventh alternative offset, which indicates a distance of 6 pixels from the video block and is binarized as 0000001, and The size of the eighth alternative offset, which indicates a distance of 8 pixels from the video block and is binarized as 00000001, and The size of the ninth alternative offset, which indicates a distance of 16 pixels from the video block and is binarized as 00000000, and The method according to claim 6, comprising.

9. Receiving the one or more syntax elements to determine the first MVR offset of the first geometric section and the second MVR offset of the second geometric section from the set of the selected MVR offsets is Receiving a first geometric section enabling syntax element indicating whether the MVR is applied to the first geometric section; In response to determining that the enabling syntax element of the first geometric section is equal to 1, a syntax element of a first direction indicating a direction of the first MVR offset of the first geometric section determined based on the selected set of MVR offsets, and a syntax element of a first magnitude indicating a magnitude of the first MVR offset of the first geometric section determined based on the selected set of MVR offsets; Receiving a second geometric section enabling syntax element indicating whether the MVR is applied to the second geometric section; In response to determining that the enabling syntax element of the second geometric section is equal to 1, a syntax element of a second direction indicating a direction of the second MVR offset of the second geometric section determined based on the selected set of MVR offsets, and a syntax element of a second magnitude indicating a magnitude of the second MVR offset of the second geometric section determined based on the selected set of MVR offsets, the method according to claim 1.

10. The first geometric section enabling syntax element includes gpm_mvr_partIdx0_enable_flag, The syntax element of the first direction includes gpm_mvr_partIdx0_direction_idx, and the syntax element of the first magnitude includes gpm_mvr_partIdx0_distance_idx, The second geometric section enabling syntax element includes gpm_mvr_partIdx1_enable_flag, The syntax element of the second direction includes gpm_mvr_partIdx1_direction_idx, and the syntax element of the second magnitude includes gpm_mvr_partIdx1_distance_idx, the method according to claim 9.

11. An apparatus for video decoding, comprising: One or more processors; A memory configured to store instructions executable by the one or more processors, An apparatus, wherein when the one or more processors execute the instructions, they are configured to perform the method according to any one of claims 1 to 10. **Claim 12** A non-transitory computer-readable storage medium storing computer-executable instructions, wherein when the computer-executable instructions are executed by one or more computer processors, the one or more computer processors are caused to perform the method according to any one of claims 1 to 10 to decode a video bitstream and store the decoded video bitstream in the non-transitory computer-readable storage medium. **Claim 13** A computer program including instructions that, when executed by one or more computer processors, cause the one or more computer processors to perform the method according to any one of claims 1 to 10.

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