WO2020236991A1

WO2020236991A1 - Methods and apparatuses for video coding using triangle partition

Info

Publication number: WO2020236991A1
Application number: PCT/US2020/033882
Authority: WO
Inventors: Xianglin Wang; Yi-Wen Chen; Xiaoyu XIU; Tsung-Chuan MA; Hong-Jheng Jhu; Shuiming Ye
Original assignee: Beijing Dajia Internet Information Technology Co., Ltd.
Priority date: 2019-05-20
Filing date: 2020-05-20
Publication date: 2020-11-26
Also published as: CN113841406A

Abstract

Methods and apparatuses are provided for video coding. The method includes: partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU; obtaining a first merge list including a plurality of candidates, each including one or more motion vectors; obtaining a uni-prediction motion vector for each PU by selecting the one or more motion vectors from the first merge list; and pruning the uni-prediction motion vector.

Description

METHODS AND APPARATUSES FOR VIDEO CODING USING TRIANGUE

PARTITION

CROSS-REFERENCE TO REUATED APPUICATION

[0001] The present application claims priority to U.S. Provisional Application No. 62/850,534, entitled“Video Coding Using Triangle Partition” filed on May 20, 2019, and U.S. Provisional Application No. 62/851,630, entitled“Video Coding Using Triangle Partition” filed on May 22, 2019, the entirety of both of which are incorporated by reference for all purpose.

FIEUD

[0002] The present application generally relates to video coding and compression, and in particular but not limited to, methods and apparatus for motion compensated prediction using triangular prediction unit (i.e. a special case of geometric partition prediction unit) in video coding.

BACKGROUND

[0003] Digital video is supported by a variety of electronic devices, such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video gaming consoles, smart phones, video teleconferencing devices, video streaming devices, etc. The electronic devices transmit, receive, encode, decode, and/or store digital video data by implementing video compression/decompression. Digital video devices implement video coding techniques, such as those described in the standards defined by Versatile Video Coding (VVC), Joint Exploration Test Model (JEM), MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), and extensions of such standards.

[0004] Video coding generally utilizes prediction methods (e.g., inter-prediction, intra prediction) that take advantage of redundancy present in video images or sequences. An important goal of video coding techniques is to compress video data into a form that uses a lower bit rate, while avoiding or minimizing degradations to video quality. With ever-evolving video services becoming available, encoding techniques with better coding efficiency are needed. Block partitioning schemes in each standard are also evolving.

[0005] Video compression typically includes performing spatial (intra frame) prediction and/or temporal (inter frame) prediction to reduce or remove redundancy inherent in the video data. For block-based video coding, a video frame is partitioned into one or more slices, each slice having multiple video blocks, which may also be referred to as coding tree units (CTUs). Each CTU may contain one coding unit (CU) or recursively split into smaller CUs until the predefined minimum CU size is reached. Each CU (also named leaf CU) contains one or multiple transform units (TUs) and each CU also contains one or multiple prediction units (PUs). Each CU may be coded in intra, inter or IBC modes. Video blocks in an intra coded (I) slice of a video frame are encoded using spatial prediction with respect to reference samples in neighbor blocks within the same video frame. Video blocks in an inter coded (P or B) slice of a video frame may use spatial prediction with respect to reference samples in neighbor blocks within the same video frame or temporal prediction with respect to reference samples in other previous and/or future reference video frames.

[0006] Spatial or temporal prediction based on a reference block that has been previously encoded, e.g., a neighbor block, results in a predictive block for a current video block to be coded. The process of finding the reference block may be accomplished by block matching algorithm. Residual data representing pixel differences between the current block to be coded and the predictive block is referred to as a residual block or prediction errors. An inter-coded block is encoded according to a motion vector that points to a reference block in a reference frame forming the predictive block, and the residual block. The process of determining the motion vector is typically referred to as motion estimation. An intra coded block is encoded according to an intra prediction mode and the residual block. For further compression, the residual block is transformed from the pixel domain to a transform domain, e.g., frequency domain, resulting in residual transform coefficients, which may then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned to produce a one-dimensional vector of transform coefficients, and then entropy encoded into a video bitstream to achieve even more compression.

[0007] The encoded video bitstream is then saved in a computer-readable storage medium (e.g., flash memory) to be accessed by another electronic device with digital video capability or directly transmitted to the electronic device wired or wirelessly. The electronic device then performs video decompression (which is an opposite process to the video compression described above) by, e.g., parsing the encoded video bitstream to obtain syntax elements from the bitstream and reconstructing the digital video data to its original format from the encoded video bitstream based at least in part on the syntax elements obtained from the bitstream, and renders the reconstructed digital video data on a display of the electronic device.

[0008] With digital video quality going from high definition, to 4Kx2K or even 8Kx4K, the amount of vide data to be encoded/decoded grows exponentially. It is a constant challenge in terms of how the video data may be encoded/decoded more efficiently while maintaining the image quality of the decoded video data.

[0009] In a Joint Video Experts Team (JVET) meeting, JVET defined the first draft of Versatile Video Coding (VVC) and the VVC Test Model 1 (VTM1) encoding method. It was decided to include a quadtree with nested multi-type tree using binary and ternary splits coding block structure as the initial new coding feature of VVC. Since then, the reference software VTM to implement the encoding method and the draft VVC decoding process has been developed during the JVET meetings.

SUMMARY

[0010] In general, this disclosure describes examples of techniques relating to motion compensated prediction using geometric shaped prediction unit in video coding.

[0011] According to a first aspect of the present disclosure, there is provided a method for video coding with geometric partition, including: partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU; constructing a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both; locating a first candidate for the first PU according to a first merge candidate index; locating a second candidate for the second PU according to a second merge candidate index; obtaining a first uni-prediction motion vector, MVo, for the first PU by selecting a List Xi motion vector of the first candidate, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1; obtaining a second uni -prediction motion vector, MVi, for the second PU by selecting a List X₂ motion vector of the second candidate, wherein X2 corresponds to the second merge candidate index and takes a value of 0 or 1 ; and in response to determining that the MVo and the MV 1 are same, pruning the first uni prediction motion vector, the MVo, and the second uni-prediction motion vector, the MVi.

[0012] According to a second aspect of the present disclosure, an apparatus for video coding with geometric partition is provided, including: one or more processors; and a memory configured to store instructions executable by the one or more processors; wherein the one or more processors, upon execution of the instructions, are configured to: partition video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU; construct a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both; locate a first candidate for the first PU according to a first merge candidate index; locate a second candidate for the second PU according to a second merge candidate index; obtain a first uni-prediction motion vector, MVo, for the first PU by selecting a List Xi motion vector of the first candidate, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1 ; obtain a second uni prediction motion vector, MVi, for the second PU by selecting a List X₂ motion vector of the second candidate, wherein X2 corresponds to the second merge candidate index and takes a value of 0 or 1; and in response to determining that the MVo and the MV 1 are same, prune the first uni-prediction motion vector, the MVo, and the second uni -prediction motion vector, the

MVi. [0013] According to a third aspect of the present disclosure, there is provided a non-transitory computer-readable storage medium for video coding with geometric partition storing computer-executable instructions that, when executed by one or more computer processors, cause the one or more computer processors to perform acts, including: partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU; constructing a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both; locating a first candidate for the first PU according to a first merge candidate index; locating a second candidate for the second PU according to a second merge candidate index; obtaining a first uni -prediction motion vector, MVo, for the first PU by selecting a List Xi motion vector of the first candidate, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1 ; obtaining a second uni-prediction motion vector, MVi, for the second PU by selecting a List X2 motion vector of the second candidate, wherein X2 corresponds to the second merge candidate index and takes a value of 0 or 1; and in response to determining that the MVo and the MVi are same, pruning the first uni-prediction motion vector, the MVo, and the second uni -prediction motion vector, the MVi.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A more particular description of the examples of the present disclosure will be rendered by reference to specific examples illustrated in the appended drawings. Given that these drawings depict only some examples and are not therefore considered to be limiting in scope, the examples will be described and explained with additional specificity and details through the use of the accompanying drawings.

[0015] FIG. 1 is a block diagram illustrating an exemplary video encoder in accordance with some implementations of the present disclosure.

[0016] FIG. 2 is a block diagram illustrating an exemplary video decoder in accordance with some implementations of the present disclosure. [0017] FIG. 3 is a schematic diagram illustrating a quadtree plus binary tree (QTBT) structure in accordance with some implementations of the present disclosure.

[0018] FIG. 4 is a schematic diagram illustrating an example of a picture divided into CTUs in accordance with some implementations of the present disclosure.

[0019] FIG. 5 is a schematic diagram illustrating multi-type tree splitting modes in accordance with some implementations of the present disclosure.

[0020] FIG. 6 is a schematic diagram illustrating positions of neighboring blocks in accordance with some implementations of the present disclosure.

[0021] FIG. 7 is a schematic diagram illustrating motion vector scaling for a temporal merge candidate in accordance with some implementations of the present disclosure.

[0022] FIG. 8 is a schematic diagram illustrating candidate positions for a temporal merge candidate in accordance with some implementations of the present disclosure.

[0023] FIG. 9 is a schematic diagram illustrating splitting a CU into triangular prediction units in accordance with some implementations of the present disclosure.

[0024] FIG. 10 is a schematic diagram illustrating one example of uni-prediction motion vector (MV) selection for triangle partition mode in accordance with some implementations of the present disclosure.

[0025] FIG. 11 is a schematic diagram illustrating one example of motion vector (MV) population under triangle prediction mode in accordance with some implementations of the present disclosure.

[0026] FIG. 12A is a schematic diagram illustrating one example of simplified motion vector population for triangle prediction mode in accordance with some implementations of the present disclosure.

[0027] FIG. 12B is a schematic diagram illustrating another example of simplified motion vector population for triangle prediction mode in accordance with some implementations of the present disclosure. [0028] FIG. 12C is a schematic diagram illustrating a third example of simplified motion vector population for triangle prediction mode in accordance with some implementations of the present disclosure.

[0029] FIG. 12D is a schematic diagram illustrating a fourth example of simplified motion vector population for triangle prediction mode in accordance with some implementations of the present disclosure.

[0030] FIG. 13A is a schematic diagram illustrating another example of simplified motion vector population for triangle prediction mode in accordance with some implementations of the present disclosure.

[0031] FIG. 13B is a schematic diagram illustrating another example of simplified motion vector population for triangle prediction mode in accordance with some implementations of the present disclosure.

[0032] FIG. 14 is a block diagram illustrating an exemplary apparatus for video coding in accordance with some implementations of the present disclosure.

[0033] FIG. 15 is a flowchart illustrating an exemplary process of video coding for motion compensated prediction using geometric prediction unit in accordance with some implementations of the present disclosure.

DETAILED DESCRIPTION

[0034] Reference will now be made in detail to specific implementations, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous non-limiting specific details are set forth in order to assist in understanding the subject matter presented herein. But it will be apparent to one of ordinary skill in the art that various alternatives may be used. For example, it will be apparent to one of ordinary skill in the art that the subject matter presented herein may be implemented on many types of electronic devices with digital video capabilities.

[0035] Reference throughout this specification to“one embodiment,”“an embodiment,”“an example,”“some embodiments,”“some examples,” or similar language means that a particular feature, structure, or characteristic described is included in at least one embodiment or example. Features, structures, elements, or characteristics described in connection with one or some embodiments are also applicable to other embodiments, unless expressly specified otherwise.

[0036] Throughout the disclosure, the terms“first,”“second,”“third,” etc. are all used as nomenclature only for references to relevant elements, e.g. devices, components, compositions, steps, etc., without implying any spatial or chronological orders, unless expressly specified otherwise. For example, a“first device” and a“second device” may refer to two separately formed devices, or two parts, components or operational states of a same device, and may be named arbitrarily.

[0037] As used herein, the term“if’ or“when” may be understood to mean“upon” or“in response to” depending on the context. These terms, if appear in a claim, may not indicate that the relevant limitations or features are conditional or optional.

[0038] The terms “module,” “sub-module,” “circuit,” “sub-circuit,” “circuitry,” “sub circuitry,”“unit,” or“sub-unit” may include memory (shared, dedicated, or group) that stores code or instructions that may be executed by one or more processors. A module may include one or more circuits with or without stored code or instructions. The module or circuit may include one or more components that are directly or indirectly connected. These components may or may not be physically attached to, or located adjacent to, one another.

[0039] A unit or module may be implemented purely by software, purely by hardware, or by a combination of hardware and software. In a pure software implementation, for example, the unit or module may include functionally related code blocks or software components, that are directly or indirectly linked together, so as to perform a particular function.

[0040] FIG. 1 shows a block diagram illustrating an exemplary block-based hybrid video encoder 100 which may be used in conjunction with many video coding standards using block- based processing. In 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 either an inter prediction approach or an intra prediction approach. In inter prediction, one or more predictors are formed through motion estimation and motion compensation, based on pixels from previously reconstructed frames. In intra prediction, predictors are formed based on reconstructed pixels in a current frame. Through mode decision, a best predictor may be chosen to predict a current block.

[0041] A prediction residual, representing the difference between a current video block and its predictor, is sent to a Transform circuitry 102. Transform coefficients are then sent from the Transform circuitry 102 to a Quantization circuitry 104 for entropy reduction. Quantized coefficients are then fed to an Entropy Coding circuitry 106 to generate a compressed video bitstream. As shown in FIG. 1, prediction-related information 110 from an inter prediction circuitry and/or an Intra Prediction circuitry 112, such as video block partition info, motion vectors, reference picture index, and intra prediction mode, are also fed through the Entropy Coding circuitry 106 and saved into a compressed video bitstream 114.

[0042] In the encoder 100, decoder-related circuitries are also needed in order to reconstruct pixels for the purpose of prediction. First, a prediction residual is reconstructed through an Inverse Quantization 116 and an Inverse Transform circuitry 118. This reconstructed prediction residual is combined with a Block Predictor 120 to generate un-filtered reconstructed pixels for a current video block.

[0043] Spatial prediction (or“intra prediction”) uses pixels from samples of already coded neighboring blocks (which are called reference samples) in the same video frame as the current video block to predict the current video block.

[0044] Temporal prediction (also referred to as“inter prediction”) uses reconstructed pixels from already-coded video pictures to predict the current video block. Temporal prediction reduces temporal redundancy inherent in the video signal. Temporal prediction signal for a given coding unit (CU) or coding block is usually signaled by one or more motion vectors (MVs) which indicate the amount and the direction of motion between the current CU and its temporal reference. Further, if multiple reference pictures are supported, one reference picture index is additionally sent, which is used to identify from which reference picture in the reference picture store the temporal prediction signal comes. [0045] After spatial and/or temporal prediction is performed, an intra/inter mode decision circuitry 121 in the encoder 100 chooses the best prediction mode, for example based on the rate-distortion optimization method. The block predictor 120 is then subtracted from the current video block; and the resulting prediction residual is de-correlated using the transform circuitry 102 and the quantization circuitry 104. The resulting quantized residual coefficients are inverse quantized by the inverse quantization circuitry 116 and inverse transformed by the inverse transform circuitry 118 to form the reconstructed residual, which is then added back to the prediction block to form the reconstructed signal of the CU. Further in-loop filtering 115, such as a deblocking filter, a sample adaptive offset (SAO), and/or an adaptive in-loop filter (ALF) may be applied on the reconstructed CU before it is put in the reference picture store of the picture buffer 117 and used to code future video blocks. To form the output video bitstream 114, coding mode (inter or intra), prediction mode information, motion information, and quantized residual coefficients are all sent to the entropy coding unit 106 to be further compressed and packed to form the bit-stream.

[0046] For example, a deblocking filter is available in AVC, HEVC as well as the now- current version of VVC. In HEVC, an additional in-loop filter called SAO (sample adaptive offset) is defined to further improve coding efficiency. In the now-current version of the VVC standard, yet another in-loop filter called ALF (adaptive loop filter) is being actively investigated, and it has a good chance of being included in the final standard.

[0047] These in-loop filter operations are optional. Performing these operations helps to improve coding efficiency and visual quality. They may also be turned off as a decision rendered by the encoder 100 to save computational complexity.

[0048] It should be noted that intra prediction is usually based on unfiltered reconstructed pixels, while inter prediction is based on filtered reconstructed pixels if these filter options are turned on by the encoder 100.

[0049] FIG. 2 is a block diagram illustrating an exemplary block-based video decoder 200 which may be used in conjunction with many video coding standards. This decoder 200 is similar to the reconstruction-related section residing in the encoder 100 of FIG. 1. In the decoder 200, an incoming video bitstream 201 is first decoded through an Entropy Decoding 202 to derive quantized coefficient levels and prediction-related information. The quantized coefficient levels are then processed through an Inverse Quantization 204 and an Inverse Transform 206 to obtain a reconstructed prediction residual. A block predictor mechanism, implemented in an Intra/inter Mode Selector 212, is configured to perform either an Intra Prediction 208, or a Motion Compensation 210, based on decoded prediction information. A set of unfiltered reconstructed pixels are obtained by summing up the reconstructed prediction residual from the Inverse Transform 206 and a predictive output generated by the block predictor mechanism, using a summer 214.

[0050] The reconstructed block may further go through an In-Loop Filter 209 before it is stored in a Picture Buffer 213 which functions as a reference picture store. The reconstructed video in the Picture Buffer 213 may be sent to drive a display device, as well as used to predict future video blocks. In situations where the In-Loop Filter 209 is turned on, a filtering operation is performed on these reconstructed pixels to derive a final reconstructed Video Output 222.

[0051] Video coding/decoding standards mentioned above, such as VVC, JEM, HEVC, MPEG-4, Part 10, are conceptually similar. For example, they all use block-based processing. Block partitioning schemes in some standards are elaborated below.

High Efficient Video Coding (HEVC)

[0052] HEVC is based on a hybrid block-based motion-compensated transform coding architecture. The basic unit for compression is termed coding tree unit (CTU). The maximum CTU size is defined as up to 64 by 64 luma pixels, and two blocks of 32 by 32 chroma pixels for 4:2:0 chroma format. Each CTU may contain one coding unit (CU) or recursively split into four smaller CUs until the predefined minimum CU size is reached. Each CU (also named leaf CU) contains one or multiple prediction units (PUs) and a tree of transform units (TUs).

[0053] In general, except for monochrome content, a CTU may include one luma coding tree block (CTB) and two corresponding chroma CTBs; a CU may include one luma coding block (CB) and two corresponding chroma CBs; a PU may include one luma prediction block (PB) and two corresponding chroma PBs; and a TU may include one luma transform block (TB) and two corresponding chroma TBs. However, exceptions may occur because the minimum TB size is 4x4 for both luma and chroma (i.e., no 2x2 chroma TB is supported for 4:2:0 color format) and each intra chroma CB always has only one intra chroma PB regardless of the number of intra luma PBs in the corresponding intra luma CB.

[0054] For an intra CU, the luma CB may be predicted by one or four luma PBs, and each of the two chroma CBs is always predicted by one chroma PB, where each luma PB has one intra luma prediction mode and the two chroma PBs share one intra chroma prediction mode. Moreover, for the intra CU, the TB size cannot be larger than the PB size. In each PB, the intra prediction is applied to predict samples of each TB inside the PB from neighboring reconstructed samples of the TB. For each PB, in addition to 33 directional intra prediction modes, DC and planar modes are also supported to predict flat regions and gradually varying regions, respectively.

[0055] For each inter PU, one of three prediction modes including inter, skip, and merge, may be selected. Generally speaking, a motion vector competition (MVC) scheme is introduced to select a motion candidate from a given candidate set that includes spatial and temporal motion candidates. Multiple references to the motion estimation allow finding the best reference in 2 possible reconstructed reference picture lists (namely List 0 and List 1). For the inter mode (termed AMVP mode, where AMVP stands for advanced motion vector prediction), inter prediction indicators (List 0, List 1, or bi-directional prediction), reference indices, motion candidate indices, motion vector differences (MVDs) and prediction residual are transmitted. As for the skip mode and the merge mode, only merge indices are transmitted, and the current PU inherits the inter prediction indicator, reference indices, and motion vectors from a neighboring PU referred by the coded merge index. In the case of a skip coded CU, the residual signal is also omitted.

Joint Exploration Test Model (JEM)

[0056] The Joint Exploration Test Model (JEM) is built up on top of the HEVC test model. The basic encoding and decoding flowchart of HEVC is kept unchanged in the JEM; however, the design elements of most important modules, including the modules of block structure, intra and inter prediction, residue transform, loop filter and entropy coding, are somewhat modified and additional coding tools are added. The following new coding features are included in the JEM.

[0057] In HEVC, a CTU is split into CUs by using a quadtree structure denoted as coding tree to adapt to various local characteristics. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU may be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU may be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU. One of key features of the HEVC structure is that it has the multiple partition conceptions including CU, PU, and TU.

[0058] FIG. 3 is a schematic diagram illustrating a quadtree plus binary tree (QTBT) structure in accordance with some implementations of the present disclosure.

[0059] The QTBT structure removes the concepts of multiple partition types, i.e., it removes the separation of the CU, PU and TU concepts, and supports more flexibility for CU partition shapes. In the QTBT block structure, a CU may have either a square or rectangular shape. As shown in FIG. 3, a coding tree unit (CTU) is first partitioned by a quaternary tree (i.e., quadtree) structure. The quadtree leaf nodes may be further partitioned by a binary tree structure. There are two splitting types in the binary tree splitting: symmetric horizontal splitting and symmetric vertical splitting. The binary tree leaf nodes are called coding units (CUs), and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In the JEM, a CU sometimes consists of coding blocks (CBs) of different colour components, e.g., one CU contains one luma CB and two chroma CBs in the case of P and B slices of the 4:2:0 chroma format, and sometimes consists of a CB of a single component, e.g., one CU contains only one luma CB or just two chroma CBs in the case of I slices.

[0060] The following parameters are defined for the QTBT partitioning scheme. - CTU size: the root node size of a quadtree, the same concept as in the HEVC;

- MinQTSize: the minimum allowed quadtree leaf node size;

- MaxBTSize: the maximum allowed binary tree root node size;

- MaxBTDepth: the maximum allowed binary tree depth;

- MinBTSize: the minimum allowed binary tree leaf node size.

[0061] In one example of the QTBT partitioning structure, the CTU size is set as 128x128 luma samples with two corresponding 64x64 blocks of chroma samples (with a 4:2:0 chroma format), the MinQTSize is set as 16x16, the MaxBTSize is set as 64x64, the MinBTSize (for both width and height) is set as 4x4, and the MaxBTDepth is set as 4. The quadtree partitioning is applied to the CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may have a size from 16x 16 (i.e., the MinQTSize) to 128x128 (i.e., the CTU size). If the quadtree leaf node is 128x 128, it will not be further split by the binary tree since the size exceeds the MaxBTSize (i.e., 64x64). Otherwise, the quadtree leaf node could be further partitioned by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and it has the binary tree depth as 0. When the binary tree depth reaches MaxBTDepth (i.e., 4), no further splitting is considered. When the binary tree node has a width equal to MinBTSize (i.e., 4), no further horizontal splitting is considered. Similarly, when the binary tree node has a height equal to MinBTSize, no further vertical splitting is considered. The leaf nodes of the binary tree are further processed by prediction and transform processing without any further partitioning. In the JEM, the maximum CTU size is 256x256 luma samples.

[0062] An example of block partitioning by using the QTBT scheme, and the corresponding tree representation are illustrated in FIG. 3. The solid lines indicate quadtree splitting and dotted lines indicate binary tree splitting. As shown in FIG. 3, the coding tree unit (CTU) 300 is first partitioned by a quadtree structure, and three of the four quadtree leaf nodes 302, 304, 306, 308 are further partitioned by either a quadtree structure or a binary tree structure. For example, the quadtree leaf node 306 is further partitioned by quadtree splitting; the quadtree leaf node 304 is further partitioned into two leaf nodes 304a, 304b by binary tree splitting; and the quadtree leaf node 302 is also further partitioned by binary tree splitting. In each splitting (i.e., non-leaf) node of the binary tree, one flag is signaled to indicate which splitting type (i.e., horizontal or vertical) is used, where 0 indicates horizontal splitting and 1 indicates vertical splitting. For example, for the quadtree leaf node 304, 0 is signaled to indicate horizontal splitting, and for the quadtree leaf node 302, 1 is signaled to indicate vertical splitting. For quadtree splitting, there is no need to indicate the splitting type since quadtree splitting always splits a block both horizontally and vertically to produce 4 sub-blocks with an equal size.

[0063] In addition, the QTBT scheme supports the ability for the luma and chroma to have a separate QTBT structure. Currently, for P and B slices, the luma and chroma CTBs in one CTU share the same QTBT structure. However, for I slices, the luma CTB is partitioned into CUs by a QTBT structure, and the chroma CTBs are partitioned into chroma CUs by another QTBT structure. This means that a CU in an I slice consists of a coding block of the luma component or coding blocks of two chroma components, and a CU in a P or B slice consists of coding blocks of all three colour components.

Versatile Video Coding (VYC)

[0064] In a Joint Video Experts Team (JVET) meeting, the JVET defined the first draft of the Versatile Video Coding (VVC) and the VVC Test Model 1 (VTM1) encoding method. It was decided to include a quadtree with nested multi-type tree using binary and ternary splits coding block structure as the initial new coding feature of VVC.

[0065] In VVC, the picture partitioning structure divides the input video into blocks called coding tree units (CTUs). A CTU is split using a quadtree with nested multi-type tree structure into coding units (CUs), with a leaf coding unit (CU) defining a region sharing the same prediction mode (e.g. intra or inter). Here, the term“unit” defines a region of an image covering all components; the term“block” is used to define a region covering a particular component (e.g. luma), and may differ in spatial location when considering the chroma sampling format such as 4:2:0.

Partitioning of the picture into CTUs

[0066] FIG. 4 is a schematic diagram illustrating an example of a picture divided into CTUs in accordance with some implementations of the present disclosure. [0067] In VVC, pictures are divided into a sequence of CTUs, and the CTU concept is the same as that of the HEVC. For a picture that has three sample arrays, a CTU consists of an NxN block of luma samples together with two corresponding blocks of chroma samples. FIG. 4 shows the example of a picture 400 divided into CTUs 402.

[0068] The maximum allowed size of the luma block in a CTU is specified to be 128x128 (although the maximum size of the luma transform blocks is 64x64).

Partitioning of the CTUs using a tree structure

[0069] FIG. 5 is a schematic diagram illustrating multi-type tree splitting modes in accordance with some implementations of the present disclosure.

[0070] In HEVC, a CTU is split into CUs by using a quaternary -tree structure denoted as coding tree to adapt to various local characteristics. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the leaf CU level. Each leaf CU may be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied, and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a leaf CU may be partitioned into transform units (TUs) according to another quaternary -tree structure similar to the coding tree for the CU. One of key feature of the HEVC structure is that it has the multiple partition conceptions including CU, PU, and TU.

[0071] In VVC, a quadtree with nested multi -type tree using binary and ternary splits segmentation structure replaces the concepts of multiple partition unit types, i.e. it removes the separation of the CU, PU and TU concepts except as needed for CUs that have a size too large for the maximum transform length, and supports more flexibility for CU partition shapes. In the coding tree structure, a CU may have either a square or rectangular shape. A coding tree unit (CTU) is first partitioned by a quaternary tree (i.e., quadtree) structure. Then the quaternary tree leaf nodes may be further partitioned by a multi-type tree structure. As shown in FIG. 5, there are four splitting types in multi-type tree structure: vertical binary splitting 502 (SPLIT BT VER), horizontal binary splitting 504 (SPLIT BT HOR), vertical ternary splitting 506 (SPLIT TT VER), and horizontal ternary splitting 508 (SPLIT TT HOR). The multi-type tree leaf nodes are called coding units (CUs), and unless the CU is too large for the maximum transform length, this segmentation is used for prediction and transform processing without any further partitioning. This means that, in most cases, the CU, PU and TU have the same block size in the quadtree with nested multi-type tree coding block structure. The exception occurs when the maximum supported transform length is smaller than the width or height of the color component of the CU. In VTM1, a CU consists of coding blocks (CBs) of different color components, e.g., one CU contains one luma CB and two chroma CBs (unless the video is monochrome, i.e., having only one color component).

Partitioning CUs into multiple prediction units

[0072] In VVC, for each CU partitioned based on the structure illustrated above, prediction of the block content may be performed either on the whole CU block or in a sub-block manner explained in the following paragraphs. The operation unit of such prediction is called prediction unit (or PU).

[0073] In the case of intra prediction (or intra-frame prediction), usually the size of the PU is equal to the size of the CU. In other words, the prediction is performed on the whole CU block. For inter prediction (or inter-frame prediction), the size of the PU may be equal or less than the size of the CU. In other words, there are cases where a CU may be split into multiple PUs for prediction.

[0074] Some examples of having the PU size smaller than the CU size include an affine prediction mode, an Advanced Temporal Level Motion Vector Prediction (ATMVP) mode, and a triangle prediction mode, etc.

[0075] Under the affine prediction mode, a CU may be split into multiple 4x4 PUs for prediction. Motion vectors may be derived for each 4x4 PU and motion compensation may be performed accordingly on the 4x4 PU. Under the ATMVP mode, a CU may be split into one or multiple 8x8 PUs for prediction. Motion vectors are derived for each 8x8 PU and motion compensation may be performed accordingly on the 8x8 PU. Under the triangle prediction mode, a CU may be split into two triangular shape prediction units. Motion vectors are derived for each PU and motion compensation is performed accordingly. The triangle prediction mode is supported for inter prediction. More details of the triangle prediction mode are illustrated below.

Regular merge mode motion vector candidate list

[0076] According to the current VVC, under the regular merge mode where a whole CU is predicted without splitting into more than one PU, the motion vector candidate list or the merge candidate list is constructed using a different procedure than that for the triangle prediction mode.

[0077] Firstly, spatial motion vector candidates are selected based on motion vectors from neighboring blocks as indicated in FIG. 6, which is a schematic diagram illustrating positions of spatial merge candidates in accordance with some implementations of the present disclosure. In the derivation of spatial merge candidates of a current block 602, a maximum of four merge candidates are selected among candidates that are located in positions as depicted in FIG. 6. These candidates are selected according to certain order. One exemplar order of derivation is Ai - Bi - Bo - Ao - (B2). The position B2 is considered only when any PU of positions Ai, Bi, Bo, Ao is not available or is intra coded. It should be noted that other different orders may also be used. For example, in later stage of VVC, the order was changed to Bi - Ai - Bo ->

[0078] Next, a temporal merge candidate is derived. In the derivation of the temporal merge candidate, a scaled motion vector is derived based on the co-located PU belonging to the picture which has the smallest Picture Order Count (POC) difference with the current picture within the given reference picture list. The reference picture list to be used for derivation of the co located PU is explicitly signaled in the slice header. The scaled motion vector for the temporal merge candidate is obtained as illustrated by the dotted line in FIG. 7 which illustrates motion vector scaling for the temporal merge candidate in accordance with some implementations of the present disclosure. The scaled motion vector for the temporal merge candidate is scaled from the motion vector of the co-located PU col PU using the POC distances, tb and td, where tb is defined to be the POC difference between the reference picture of the current picture curr ref and the current picture curr_pic and td is defined to be the POC difference between the reference picture of the co-located picture col ref and the co-located picture col_pic. The reference picture index of the temporal merge candidate is set equal to zero. A practical realization of the scaling process is described in the HEVC draft specification. For a B-slice, two motion vectors, one for reference picture List 0 and the other for reference picture List 1, are obtained and combined to make the bi-predictive merge candidate.

[0079] FIG. 8 is a schematic diagram illustrating candidate positions for the temporal merge candidate in accordance with some implementations of the present disclosure.

[0080] The position of co-located PU is selected between two candidate positions, C3 and H, as depicted in FIG. 8. If the PU at position H is not available, or is intra coded, or is outside of the current CTU, position C3 is used for the derivation of the temporal merge candidate. Otherwise, position H is used for the derivation of the temporal merge candidate.

[0081] After inserting both spatial and temporal motion vectors into the merge candidate list as described above, history-based merge candidates are added. The so-called history-based merge candidates include those motion vectors from previously coded CUs, which are maintained in a separate motion vector list, and managed based on certain rules.

[0082] After inserting history-based candidates, if the merge candidate list is not full, pairwise average motion vector candidates are further added into the list. As its name indicates, this type of candidates is constructed by averaging candidates already in the current list. More specifically, based on a certain order or rule, two candidates in the merge candidate list are taken each time and the average motion vector of the two candidates is appended to the current list.

[0083] After inserting pairwise average motion vectors, if the merge candidate list is still not full, zero motion vectors will be added to make the list full.

Triangle prediction mode (or triangular partition model

[0084] FIG. 9 is a schematic diagram illustrating splitting a CU into triangular prediction units in accordance with some implementations of the present disclosure. [0085] The concept of the triangle prediction mode is to introduce triangular partitions for motion compensated prediction. The triangle prediction mode may also be named the triangular prediction unit mode, or triangular partition mode. As shown in FIG. 9, a CU 902 or 904 is split into two triangular prediction units Partition 0 and Partition 1, in either the diagonal or the inverse diagonal direction (i.e., either splitting from top-left comer to bottom-right comer as shown in CU 902 or splitting from top-right comer to bottom-left comer as shown in CU 904). Each triangular prediction unit in the CU is inter-predicted using its own uni-prediction motion vector and reference frame index which are derived directly and/or indirectly from a candidate in the regular merge candidate list. A weighting process is performed to the diagonal edge after predicting the triangular prediction units. Then, the transform and quantization process are applied to the whole CU. It is noted that this mode is only applied to skip and merge modes in the current VVC. Although in FIG. 9, the CU is shown as a square block, the triangle prediction mode may be applied to non-square (i.e. rectangular) shape CUs as well.

Uni-prediction motion vector derivation

[0086] FIG. 10 is a schematic diagram illustrating uni -prediction motion vector selection for triangle partition mode in accordance with some implementations of the present disclosure.

[0087] In some examples, the uni-prediction motion vector for each triangle partition is derived directly from the merge candidate list that is formed for the regular merge mode as illustrated in the previous section of“regular merge mode motion vector candidate list.” Given a merge candidate index, a candidate may be located from the merge candidate list. Then for the candidate, its List X motion vector with X equal to the parity value (p) of the merge candidate index value, is used as the uni-prediction motion vector for triangle partition mode. These motion vectors are marked with“x” in FIG. 10. In case a corresponding List X (or List p) motion vector does not exist, the List (1-X) (or List (1-p)) motion vector of the same candidate is used as the uni-prediction motion vector for triangle partition mode.

[0088] A predictor is derived for each of the triangular PUs based on its motion vector. It is worth noting that the predictor derived covers a larger area than the actual triangular PU so that there is an overlapped area of the two predictors along the shared diagonal edge of the two triangular PUs. A weighting process is applied to the diagonal edge area between the two predictors to derive a final prediction for the CU. The weighting factors currently used for the luminance and the chrominance samples are {7/8, 6/8, 5/8, 4/8, 3/8, 2/8, 1/8} and {6/8, 4/8, 2/8}, respectively.

Triangle prediction mode syntax and signaling

[0089] Here, triangle prediction mode is signaled using a triangle prediction flag. The triangle prediction flag is signaled when a CU is coded in either skip mode or merge mode. For a given CU, if the triangle prediction flag has a value of 1, it means that the corresponding CU is coded using triangle prediction mode. Otherwise, the CU is coded using a prediction mode other than triangle prediction mode.

[0090] For example, the triangle prediction flag is conditionally signaled in either skip mode or merge mode. Firstly, a triangle prediction tool enable/disable flag is signaled in sequence parameter set (or SPS). Only if this triangle prediction tool enable/disable flag is true, the triangle prediction flag is signaled at CU level. Secondly, triangle prediction tool is only allowed in B-slice. So only in a B-slice, the triangle prediction flag is signaled at CU level. Thirdly, triangle prediction mode is signaled only for a CU with a size equal or larger than a certain threshold, e.g. 64. If a CU has a size smaller than that threshold, triangle prediction flag is not signaled. Fourthly, triangle prediction mode may be allowed for a CU only if that CU is not coded in regular merge mode, or MMVD or subblock merge mode or CUP mode. For a CU satisfying these conditions, the triangle partition mode is applied.

[0091] If the triangle prediction mode is used, a triangle partition orientation flag is signaled to indicate if the partition is orientated from the top-left comer to the bottom-right comer or from the top-right comer to the bottom-left comer.

[0092] When triangle prediction flag is signaled, it is signaled using Context-adaptive binary arithmetic coding (CABAC) entropy coder with certain contexts. The contexts are formed based on the triangle prediction flag values of the top and the left block to the current CU.

[0093] To code (i.e. either encoder or decode) a triangle prediction flag for a current block (or a current CU), triangle prediction flag from both the top and the left block (or CU) are derived and their values are summed up. This results in three possible contexts corresponding to the following cases:

1) Both the left block and the top block have a triangle prediction flag of 0;

2) Both the left block and the top block have a triangle prediction flag of 1 ;

3) Otherwise.

[0094] Separate probabilities are maintained for each of the three contexts. Once a context value is determined for a current block, the triangle prediction flag of the current block is coded using the CABAC probability model corresponding to that context value.

[0095] If the triangle prediction flag is true, a triangle partition orientation flag is signaled to indicate if the partition is orientated from the top-left comer to the bottom-right comer or from the top-right comer to the bottom-left comer.

[0096] In case triangle prediction mode is used for a CU, two merge index values are signaled to indicate the merge index values of the first and the second uni-prediction merge candidate respectively for triangle prediction. These two merge index values are used to locate two merge candidates from the uni-prediction motion vector candidate list described above, for the first and second partition, respectively. For triangle prediction, the two merge index values are required to be different so that the two predictors of the two triangular partitions may be different from each other. As a result, the first merge index value is signaled directly. To signal the second merge index value, if it is smaller than the first merge index value, its value is signaled directly. Otherwise, its value is subtracted by 1 before being signaled to decoder. At the decoder side, the first merge index is decoded and used directly. To decode the second merge index value, a value denoted as“idx” is firstly decoded from CABAC engine. The second merge index value would be equal to the value of idx if idx is smaller than the first merge index value. Otherwise, the second merge index value would be equal to (idx+1).

Block motion vector population under triangle prediction mode

[0097] According to the VVC standard draft, if a CU is coded under triangle prediction mode, different motion vectors are used to populate (i.e. be stored in) the motion vector buffer of the 4x4 sub-blocks inside the CU depending on the sub-block locations. Such motion vector population is performed for the purpose of motion vector prediction in coding other CUs that may be spatially or temporally neighboring to the current CU. More specifically, subblocks inside the first triangle partition (i.e. partition 0) are populated with the uni-prediction motion vector of the first triangle partition, denoted as MVo; and subblocks inside the second triangle partition (i.e. partition 1) are populated with the uni-prediction motion vector of the second triangle partition, and those 4x4 sub-blocks sitting on the diagonal partition border are populated with a motion vector formed from both MVo and MVi. The formed motion vector, denoted as MVoi, may be either uni-predicted or bi-predicted, depending on the characteristics of MVo and MVi. If MVo and MV i come from different reference lists, these two uni-prediction motion vectors are directly combined to formed a bi-predicted motion vector. If they refer to the same reference list, the reference picture of MV i is checked to see if it exists in the other reference list. If it does, MVi is converted to refer to the same reference picture but the other reference list, and then it is combined with MVo to form a bi-predicted motion vector. If the reference picture of MVi does not exist in the other reference list, the reference picture of MVo is checked to see if it exists in the other reference list. If it does, MVo is converted to refer to the same reference picture but the other reference list, and then it is combined with MVi to form a bi-predicted motion vector. If the reference picture of MVo does not exist in the other reference list, MVo is used directly as the formed motion vector, and in this case the formed motion vector is a uni-predicted motion vector. An example is shown in FIG. 11. In this example, a 32x32 size CU is coded under triangle prediction mode. In this case, those 4x4 blocks inside partition 0 are populated with the uni-prediction motion vector of partition 0; those 4x4 blocks inside partition 1 are populated with the uni-prediction motion vector of partition 1; and those 4x4 blocks sitting on the diagonal border line (marked as squares with solid borderlines) are populated with the formed motion vector MVoi described above. It is worth noting that in the process described above, a motion vector that is used to populate a 4x4 block may or may not be the same as the motion vector that is used for forming an inter prediction for the 4x4 block. While the disclosed sub-block in this disclosure has a size of 4x4, the sub-block size may be adapted to 2x2, 8x8, or other sizes, where the disclosed methods may be adapted accordingly.

Uni-prediction motion vector derivation with limited motion vector pruning

[0098] In some examples, the uni-prediction motion vector for each triangle partition is derived directly from the merge candidate list that is formed for the regular merge mode as illustrated in the section of“regular merge mode motion vector candidate list.” Such a method is simple. However, as shown in FIG. 10, the number of selectable motion vectors may be limited for triangle partition. For example, when a motion vector marked with“x” in the figure exists, the corresponding uni-prediction motion vector of the same merge candidate but from the other reference list (i.e. those motion vectors not marked with“x” in the figure) would have no chance to be used for triangle prediction. Meanwhile, it often occurs that some of the motion vectors marked with“x” may be the same as each other, which may further limit the motion vector variety and sacrifice coding efficiency.

[0099] Another problem with triangle prediction is associated with its current block motion vector population method as described in the section of“block motion vector population under triangle prediction mode.” The corresponding operations in populating the motion vectors are not so simple. More implementation friendly methods may be preferable.

[0100] According to some examples of the present disclosure, given two merge index values under triangle prediction mode, two uni-prediction motion vectors may be located based on the procedures described in the section of“uni-prediction motion vector derivation”. Additionally, motion vector pruning operations may be performed. In case these two uni-prediction motion vectors derived for partition 0 and partition 1 respectively are the same, their corresponding uni-prediction motion vectors from the other reference list, if exist, may be used instead.

[0101] The disclosed examples mentioned above may be implemented in different ways. Assume the two uni-prediction motion vectors located based on the procedures described in the section of“uni-prediction motion vector derivation” are MVo and MVi respectively for triangle partition 0 and partition 1. In one example, if MVi is the same as MVo, the corresponding motion vector sharing the same merge index as MVi but from the other reference list, if it exists, is used for partition 1 instead. If it does not exist, MV i is still to be used. In another example, if MVI is the same as MVo, the corresponding motion vector sharing the same merge index as MVi but from the other reference list, if it exists, is used instead. If it does not exist or it is the same as MVo, MVi is still to be used. In this case, the corresponding motion vector sharing the same merge index as MVo but from the other reference list, if it exists, is used for partition 0. If it does not exist, MVo is still to be used for partition 0.

[0102] In the description above, the checking and processing order of the partition number 0 and 1, together with their MVo and MVi respectively, are all relative. Therefore, their checking and processing order may be exchanged in the description and the resulted method is still covered under the same spirit of the current disclosure. For example, instead of performing the pruning operation first on MVi with respect to MVo as described in the examples above, the pruning operation may also be performed first on MVo with respect to MVi.

[0103] Based on the disclosed examples, different methods may be used in determining if two uni-prediction motion vectors are the same or not. In one example, two uni-prediction motion vectors are considered the same when a coding device determines that the two vectors have the same X and Y components and the same POC (i.e. picture order count) for their reference picture. The X and Y components of a motion vector represent the relative horizontal and vertical offset values respectively from the current block to their corresponding reference blocks. In another example, two uni-prediction motion vectors are considered the same when the coding device determines that the two vectors have the same X and Y components, the same reference list and the same reference picture index. In yet another example, two uni prediction motion vectors are considered the same when the coding device determines that the two vectors have the same X and Y components, regardless of their reference list or reference picture index. Here, the coding device may be an electronic device having a chip for encoding video data. [0104] With the disclosed methods illustrated above, more motion vectors may be selected and used for triangle prediction with no extra signaling overhead. This improves coding efficiency. The complexity of the associated motion vector pruning operations is limited.

Simplified block motion vector population

[0105] According to some examples of the present disclosure, block motion vector population operation does not have to follow the procedure described in the section of“block motion vector population under triangle prediction mode.” Some simplified schemes may be used instead. In the following description of the disclosure, the motion vectors used for triangle partition 0 and 1 are denoted as MVo and MV i respectively; and the motion vector formed from both MVo and MVi, based on the procedure described in the section of“block motion vector population under triangle prediction mode,” is denoted as MVoi. As explained earlier, MVoi may be either a bi-predicted or a uni-predicted motion vector.

[0106] In an example of the present disclosure, instead of populating the 4x4 blocks with different motion vectors, this formed motion vector MVoi is used to populate every 4x4 block in the current CU.

[0107] In another example of the present disclosure, instead of populating the 4x4 blocks with different motion vectors, the uni-prediction motion vector associated with the triangle partition located at the bottom of the CU is used to populate every 4x4 block in the current CU. One example is shown in FIG. 9, where partition 1 is the triangle partition located at the bottom, and its motion vector MV i is used to populate every 4x4 block in the CU.

[0108] In yet another example of the present disclosure, the uni-prediction motion vector associated with the triangle partition located at the bottom of the CU is used to populate every 4x4 block in the current CU, except the two 4x4 blocks located at the two comers on the diagonal partition border. For the two 4x4 blocks located at the two comers on the diagonal partition border, the formed motion vector MVoi is used to populate them. This is shown in FIG. 12A and FIG. 12B, where only the two 4x4 blocks with solid borderlines are populated with the formed motion vector MVoi. More specifically, as shown in FIG. 12A, the top-left 4x4 block and the bottom-right 4x4 block are populated with the formed motion vector MVoi, when the current CU is split from top-left comer to bottom-right comer. When the current CU is split from top-right comer to bottom-left comer, as shown in FIG. 12B, the top-right 4x4 block and the bottom-left 4x4 block are populated with the formed motion vector MVoi.

[0109] In another example of the present disclosure, block motion vector population operation still follows the procedure described in the section of “block motion vector population under triangle prediction mode,” except those 4x4 blocks sitting on the diagonal border line (marked with solid borderlines in the FIG. 11). For the two 4x4 blocks located at the two comers on the diagonal partition border, the formed motion vector MVoi is used to populate them. For the other 4x4 blocks sitting on the diagonal border line, the uni-prediction motion vector associated with the triangle partition located at the bottom of the CU is used to populate them.

[0110] In another example of the present disclosure, block motion vector population operation still follows the procedure described in the section of “block motion vector population under triangle prediction mode,” except those 4x4 blocks sitting on the diagonal border line (marked with solid borderlines in the FIG. 11). For the two 4x4 blocks located at the two comers on the diagonal partition border, the formed motion vector MVoi is used to populate them. For the other 4x4 blocks sitting on the diagonal border line, the uni-prediction motion vector associated with the triangle partition located at the upper part of the CU is used to populate them.

[0111] In another example of the present disclosure, the current CU is partitioned into four quarter-sized regions. The blocks in each region are populated with a same motion vector, while blocks in different regions may be populated with different motion vectors. More specifically, blocks in the quarter-sized regions sitting on the diagonal border are populated with MVoi, and blocks in the quarter-sized regions inside each triangle partition are populated with the uni-prediction motion vector of that partition. An example is shown in FIG. 13 A. In this figure, 4x4 blocks in the two quarter-sized regions (marked with solid borderlines) that contain the diagonal partition border are populated with MVoi, while 4x4 blocks in other two quarter-sized regions are populated with MVo or MVi depending on which triangle partition they are in. In the case of FIG. 13 A, 4x4 blocks in the top-right quarter-sized region are populated with MVo, and 4x4 blocks in the bottom-left quarter-sized region are populated with MVi. In the case of FIG. 13B, 4x4 blocks in the top-left quarter-sized region are populated with MVo, and 4x4 blocks in the bottom-right quarter-sized region are populated with MV i.

[0112] In another example of the present disclosure, every block in the current CU is populated with the motion vector MVoi, except the two 4x4 comer blocks located at the two comers of partition 0 and partition 1, respectively. These two comer blocks are not sitting on the diagonal partition border. An example is shown in FIG. 12C and FIG. 12D, where these two comer blocks are indicated with solid borderlines. According to this embodiment of the disclosure, these two comer blocks are populated with the corresponding uni-prediction motion vector of their triangle partition. More specifically, as shown in FIG. 12C, the top-right 4x4 block and the bottom-left 4x4 block are respectively populated with MVo and MVi, when the current CU is split from top-left comer to bottom-right comer. When the current CU is split from top-right comer to bottom-left comer, as shown in FIG. 12D, the top-left 4x4 block and the bottom-right 4x4 block are respectively populated with MVo andMVi. While the examples in FIGS. 11-13 use sub-block with a size of 4x4, the method may be adapted for different sub block sizes such as 2x2, 8x8, or other sizes.

[0113] In still another example of the present disclosure, in case that the current CU has a width equal to 4 pixels or has a height equal to 4 pixels, every block in the current CU is populated with MVoi if it is coded with triangle prediction mode. It is worth noting that this example may be used jointly with each of those examples illustrated above.

[0114] In the above processes, although a first merge list containing 5 merge candidates is used in all the examples in this disclosure for illustration, in practice the size of the first merge list may be defined differently, e.g. 6, or 4, or some other values. All the methods described in this disclosure are equally applicable to the cases when the first merge list has a size other than

5. [0115] Although the methods of forming a uni-prediction merge list in this disclosure are described with respect to triangle prediction mode, these methods are applicable to other prediction modes of similar kinds. For example, under the more general geometric partition prediction mode wherein a CU is partitioned into two PUs along a line not exactly diagonal, the two PUs may have a geometric shape such as triangle, wedge, or trapezoid shapes. In such cases, prediction of each PU may be formed in a similar manner as in the triangle prediction mode, the methods described herein are equally applicable.

[0116] FIG. 14 is a block diagram illustrating an apparatus for video coding in accordance with some implementations of the present disclosure. The apparatus 1400 may be a terminal, such as a mobile phone, a tablet computer, a digital broadcast terminal, a tablet device, or a personal digital assistant.

[0117] As shown in FIG. 14, the apparatus 1400 may include one or more of the following components: a processing component 1402, a memory 1404, a power supply component 1406, a multimedia component 1408, an audio component 1410, an input/output (I/O) interface 1412, a sensor component 1414, and a communication component 1416.

[0118] The processing component 1402 usually controls overall operations of the apparatus 1400, such as operations relating to display, a telephone call, data communication, a camera operation and a recording operation. The processing component 1402 may include one or more processors 1420 for executing instructions to complete all or a part of steps of the above method. Further, the processing component 1402 may include one or more modules to facilitate interaction between the processing component 1402 and other components. For example, the processing component 1402 may include a multimedia module to facilitate the interaction between the multimedia component 1408 and the processing component 1402.

[0119] The memory 1404 is configured to store different types of data to support operations of the apparatus 1400. Examples of such data include instructions, contact data, phonebook data, messages, pictures, videos, and so on for any application or method that operates on the apparatus 1400. The memory 1404 may be implemented by any type of volatile or non-volatile storage devices or a combination thereof, and the memory 1404 may be a Static Random Access Memory (SRAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), an Erasable Programmable Read-Only Memory (EPROM), a Programmable Read-Only Memory (PROM), a Read-Only Memory (ROM), a magnetic memory, a flash memory, a magnetic disk or a compact disk.

[0120] The power supply component 1406 supplies power for different components of the apparatus 1400. The power supply component 1406 may include a power supply management system, one or more power supplies, and other components associated with generating, managing and distributing power for the apparatus 1400.

[0121] The multimedia component 1408 includes a screen providing an output interface between the apparatus 1400 and a user. In some examples, the screen may include a Liquid Crystal Display (LCD) and a Touch Panel (TP). If the screen includes a touch panel, the screen may be implemented as a touch screen receiving an input signal from a user. The touch panel may include one or more touch sensors for sensing a touch, a slide and a gesture on the touch panel. The touch sensor may not only sense a boundary of a touching or sliding actions, but also detect duration and pressure related to the touching or sliding operation. In some examples, the multimedia component 1408 may include a front camera and/or a rear camera. When the apparatus 1400 is in an operation mode, such as a shooting mode or a video mode, the front camera and/or the rear camera may receive external multimedia data.

[0122] The audio component 1410 is configured to output and/or input an audio signal. For example, the audio component 1410 includes a microphone (MIC). When the apparatus 1400 is in an operating mode, such as a call mode, a recording mode and a voice recognition mode, the microphone is configured to receive an external audio signal. The received audio signal may be further stored in the memory 1404 or sent via the communication component 1416. In some examples, the audio component 1410 further includes a speaker for outputting an audio signal.

[0123] The I/O interface 1412 provides an interface between the processing component 1402 and a peripheral interface module. The above peripheral interface module may be a keyboard, a click wheel, a button, or the like. These buttons may include but not limited to, a home button, a volume button, a start buton and a lock buton.

[0124] The sensor component 1414 includes one or more sensors for providing a state assessment in different aspects for the apparatus 1400. For example, the sensor component 1414 may detect an on/off state of the apparatus 1400 and relative locations of components. For example, the components are a display and a keypad of the apparatus 1400. The sensor component 1414 may also detect a position change of the apparatus 1400 or a component of the apparatus 1400, presence or absence of a contact of a user on the apparatus 1400, an orientation or acceleration/deceleration of the apparatus 1400, and a temperature change of apparatus 1400. The sensor component 1414 may include a proximity sensor configured to detect presence of a nearby object without any physical touch. The sensor component 1414 may further include an optical sensor, such as a CMOS or CCD image sensor used in an imaging application. In some examples, the sensor component 1414 may further include an acceleration sensor, a gyroscope sensor, a magnetic sensor, a pressure sensor, or a temperature sensor.

[0125] The communication component 1416 is configured to facilitate wired or wireless communication between the apparatus 1400 and other devices. The apparatus 1400 may access a wireless network based on a communication standard, such as WiFi, 4G, or a combination thereof. In an example, the communication component 1416 receives a broadcast signal or broadcast related information from an external broadcast management system via a broadcast channel. In an example, the communication component 1416 may further include a Near Field Communication (NFC) module for promoting short-range communication. For example, the NFC module may be implemented based on Radio Frequency Identification (RFID) technology, infrared data association (IrDA) technology, Ultra-Wide Band (UWB) technology, Bluetooth (BT) technology and other technology.

[0126] In an example, the apparatus 1400 may be implemented by one or more of Application Specific Integrated Circuits (ASIC), Digital Signal Processors (DSP), Digital Signal Processing Devices (DSPD), Programmable Logic Devices (PLD), Field Programmable Gate Arrays (FPGA), controllers, microcontrollers, microprocessors or other electronic elements to perform the above method.

[0127] A non-transitory computer readable storage medium may be, for example, a Hard Disk Drive (HDD), a Solid-State Drive (SSD), Flash memory, a Hybrid Drive or Solid-State Hybrid Drive (SSHD), a Read-Only Memory (ROM), a Compact Disc Read-Only Memory (CD-ROM), a magnetic tape, a floppy disk and etc.

[0128] FIG. 15 is a flowchart illustrating an exemplary process of video coding for motion compensated prediction using geometric partition in accordance with some implementations of the present disclosure.

[0129] In step 1501, the processor 1420 partitions video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs). The two PUs may include at least one geometric shaped PU. For example, the geometric shaped PU may include a pair of triangular shaped PUs, a pair of wedge-shaped PUs, or other geometric shaped PUs.

[0130] In step 1502, the processor 1420 constructs a first merge list including a plurality of candidates, each including one or more motion vector, a List 0 motion vector or a List 1 motion vector. For example, the processor 1420 may construct the first merge list based on a merge list construction process for regular merge prediction. The processor 1420 may obtain the first merge list from other electronic devices or storage as well.

[0131] In step 1503, the processor 1420 locates a first candidate for the first PU according to a first merge candidate index.

[0132] In step 1504, the processor 1420 locates a second candidate for the second PU according to a second merge candidate index.

[0133] In step 1505, the processor 1420 obtains a first uni-prediction motion vector, MVo, for the first PU by selecting a List Xi motion vector of the first candidate, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1. [0134] In step 1506, the processor 1420 obtains a second uni-prediction motion vector, MV i, for the second PU by selecting a List X2 motion vector of the second candidate, wherein X2 corresponds to the second merge candidate index and takes a value of 0 or 1.

[0135] In step 1507, the processor 1420 prunes the first uni-prediction motion vector, the MVo, and the second uni-prediction motion vector, the MV 1 in response to determining that the MVo and the MV 1 are same.

[0136] In some examples, there is provided an apparatus for video coding. The apparatus includes a processor 1420; and a memory 1404 configured to store instructions executable by the processor; where the processor, upon execution of the instructions, is configured to perform a method as illustrated in FIG. 15.

[0137] In some other examples, there is provided a non-transitory computer readable storage medium 1404, having instructions stored therein. When the instructions are executed by a processor 1420, the instructions cause the processor to perform a method as illustrated in FIG. 15.

[0138] The description of the present disclosure has been presented for purposes of illustration, and is not intended to be exhaustive or limited to the present disclosure. Many modifications, variations, and alternative implementations will be apparent to those of ordinary skill in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

[0139] The examples were chosen and described in order to explain the principles of the disclosure, and to enable others skilled in the art to understand the disclosure for various implementations and to best utilize the underlying principles and various implementations with various modifications as are suited to the particular use contemplated. Therefore, it is to be understood that the scope of the disclosure is not to be limited to the specific examples of the implementations disclosed and that modifications and other implementations are intended to be included within the scope of the present disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method for video coding with geometric partition, comprising:

partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs), a first PU and a second PU, including at least one geometric shaped PU;

constructing a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both;

locating a first candidate for the first PU according to a first merge candidate index; locating a second candidate for the second PU according to a second merge candidate index;

obtaining a first uni-prediction motion vector, MVo, for the first PU by selecting a List Xi motion vector of the first candidate, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1;

obtaining a second uni-prediction motion vector, MVi, for the second PU by selecting a List X2 motion vector of the second candidate, wherein X2 corresponds to the second merge candidate index and takes a value of 0 or 1; and

in response to determining that the MVo and the MVi are same, pruning the first uni prediction motion vector, the MVo, and the second uni-prediction motion vector, the MVi.

2. The method for video coding with geometric partition of claim 1, wherein pruning the MVo and the MV 1 further comprises:

in response to determining that a List (1- X2) motion vector of the second candidate exists, obtaining an updated second uni -prediction motion vector by selecting the List (1- X2) motion vector of the second candidate for the second PU.

3. The method for video coding with geometric partition of claim 1, wherein pruning the MVo and the MV ₁ further comprises:

in response to determining that a List (1- X2) motion vector of the second candidate does not exist, and in response to determining that a List (1- Xi) motion vector of the first candidate exists, obtaining an updated first uni-prediction motion vector by selecting the List (1- Xi) motion vector of the first candidate for the first PU.

4. The method for video coding with geometric partition of claim 1, wherein determining that the MVo and the MVi are same further comprises:

determining X and Y components of the MVo and X and Y components of the MV ₁ are same.

5. The method for video coding with geometric partition of claim 4, further comprising: determining a first picture order count (POC) of a first reference picture associated with the MVo and a second POC of a second reference picture associated with the MVi are same.

6. The method for video coding with geometric partition of claim 4, further comprising: determining a first reference list of the MVo and a second reference list of the MVi are same; and

determining a first reference picture index of the MVo and a second reference picture index of the MVi are same.

7. The method for video coding with geometric partition of claim 1, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1, and X2 corresponds to the second merge candidate index and takes a value of 0 or 1, further comprises:

assigning a parity value of the first merge candidate index, pi, to Xi, if List pi motion vector of the first candidate exists; assigning a value of (1 - pi) to Xi, if List pi motion vector of the first candidate does not exist;

assigning a parity value of the second merge candidate index, p2, to X2, if List p2 motion vector of the second candidate exists; and

assigning a value of (1 - P2) to X2, if List p2 motion vector of the second candidate does not exist.

8. An apparatus for video coding with geometric partition, comprising:

one or more processors; and

a memory configured to store instructions executable by the one or more processors; wherein the one or more processors, upon execution of the instructions, are configured to: partition video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs), a first PU and a second PU, including at least one geometric shaped PU;

construct a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both;

locate a first candidate for the first PU according to a first merge candidate index; locate a second candidate for the second PU according to a second merge candidate index;

obtain a first uni-prediction motion vector, MVo, for the first PU by selecting a List Xi motion vector of the first candidate, wherein Xi corresponds to the first merge candidate index and takes a value of 0 or 1;

obtain a second uni-prediction motion vector, MVi, for the second PU by selecting a List X2 motion vector of the second candidate, wherein X2 corresponds to the second merge candidate index and takes a value of 0 or 1; and in response to determining that the MVo and the MVi are same, prune the first uni prediction motion vector, the MVo, and the second uni-prediction motion vector, the MVi.

9. The apparatus for video coding with geometric partition of claim 8, wherein the one or more processors are further configured to:

in response to determining that a List (1- X2) motion vector of the second candidate exists, obtain an updated second uni -prediction motion vector by selecting the List (1- X2) motion vector of the second candidate for the second PU.

10. The apparatus for video coding with geometric partition of claim 8, wherein the one or more processors are further configured to:

in response to determining that a List (1- X2) motion vector of the second candidate does not exist, and in response to determining that a List (1- Xi) motion vector of the first candidate exists, obtain an updated first uni -prediction motion vector by selecting the List (1- Xi) motion vector of the first candidate for the first PU..

11. The apparatus for video coding with geometric partition of claim 8, wherein the one or more processors are further configured to:

determine X and Y components of the MVo and X and Y components of the MVi are same.

12. The apparatus for video coding with geometric partition of claim 11, wherein the one or more processors are further configured to:

determine a first picture order count (POC) of a first reference picture associated with the MVo and a second POC of a second reference picture associated with the MVi are same.

13. The apparatus for video coding with geometric partition of claim 11, wherein the one or more processors are further configured to:

determine a first reference list of the MVo and a second reference list of the MVi are same; and

determine a first reference picture index of the MVo and a second reference picture index of the MVi are same.

14. The apparatus for video coding with geometric partition of claim 8, wherein the one or more processors are further configured to:

assign a parity value of the first merge candidate index, pi, to Xi, if List pi motion vector of the first candidate exists;

assign a value of (1 - pi) to Xi, if List pi motion vector of the first candidate does not exist;

assign a parity value of the second merge candidate index, p2, to X2, if List p2 motion vector of the second candidate exists; and

assign a value of (1 - P2) to X2, if List p2 motion vector of the second candidate does not exist.

15. A non-transitory computer-readable storage medium for video coding with geometric partition storing computer-executable instructions that, when executed by one or more computer processors, cause the one or more computer processors to perform acts comprising:

16. The non-transitory computer-readable storage medium for video coding with geometric partition of claim 15, wherein pruning the MVo and the MVi further causes the one or more computer processors to perform:

17. The non-transitory computer-readable storage medium for video coding with geometric partition of claim 15, wherein pruning the MVo and the MVi further causes the one or more computer processors to perform:

18. The non-transitory computer-readable storage medium for video coding with geometric partition of claim 15, wherein determining that the MVo and the MVi are same further causes the one or more computer processors to perform:

determining X and Y components of the MVo and X and Y components of the MV i are same.

19. The non-transitory computer-readable storage medium for video coding with geometric partition of claim 18, wherein the acts further comprise:

determining a first picture order count (POC) of a first reference picture associated with the MVo and a second POC of a second reference picture associated with the MVi are same.

20. The non-transitory computer-readable storage medium for video coding with geometric partition of claim 18, wherein the acts further comprise:

determining a first reference list of the MVo and a second reference list of the MVi are same; and