WO2020243100A1 - Procédés et appareil d'amélioration d'estimation du mouvement dans un codage vidéo - Google Patents

Procédés et appareil d'amélioration d'estimation du mouvement dans un codage vidéo Download PDF

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Publication number
WO2020243100A1
WO2020243100A1 PCT/US2020/034568 US2020034568W WO2020243100A1 WO 2020243100 A1 WO2020243100 A1 WO 2020243100A1 US 2020034568 W US2020034568 W US 2020034568W WO 2020243100 A1 WO2020243100 A1 WO 2020243100A1
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WIPO (PCT)
Prior art keywords
motion vector
block
coding block
video
control point
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PCT/US2020/034568
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English (en)
Inventor
Xianglin Wang
Xiaoyu XIU
Yi-Wen Chen
Tsung-Chuan MA
Hong-Jheng Jhu
Shuiming Ye
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Beijing Dajia Internet Information Technology Co., Ltd.
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Application filed by Beijing Dajia Internet Information Technology Co., Ltd. filed Critical Beijing Dajia Internet Information Technology Co., Ltd.
Priority to CN202080038497.XA priority Critical patent/CN114175658A/zh
Publication of WO2020243100A1 publication Critical patent/WO2020243100A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/56—Motion estimation with initialisation of the vector search, e.g. estimating a good candidate to initiate a search
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/513—Processing of motion vectors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/537—Motion estimation other than block-based
    • H04N19/54—Motion estimation other than block-based using feature points or meshes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/567—Motion estimation based on rate distortion criteria

Definitions

  • the present application generally relates to video data encoding and decoding, and in particular, to methods and apparatus for improving motion estimation in video coding.
  • 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 standards as defined by MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), High Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC) standard.
  • 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.
  • 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
  • Each CU contains one or multiple transform units (TUs) and each CU also contains one or multiple prediction units (PUs).
  • Each CU can be coded in either 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 neighboring 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 neighboring blocks within the same video frame or temporal prediction with respect to reference samples in other previous and/or future reference video frames.
  • 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.
  • 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.
  • the encoded video bitstream is then saved in a computer-readable storage medium (e.g., flash memory) to be accessedby 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.
  • video decompression which is an opposite process to the video compression described above
  • the present application describes implementations related to video data encoding and decoding and, more particularly, to methods and apparatus for improving motion estimation in video coding.
  • a method of encoding a coding block of a current picture includes the following operations: selecting, among a plurality of motion vector candidates, an initial motion vector for the coding block, wherein the plurality of motion vector candidates include a motion vector library associated with the coding block; searching, within a predefined range of the initial motion vector, an optimal motion vector for the coding block; identifying, within a reference picture, a previously coded coding block corresponding to the optimal motion vector; and encoding the coding block using the previously coded coding block in the reference picture.
  • an electronic apparatus includes one or more processing units, memory and a plurality of programs stored in the memory.
  • the programs when executed by the one or more processing units, cause the electronic apparatus to perform the method of encoding a coding block of a current picture as described above.
  • a non-transitory computer readable storage medium stores a plurality of programs for execution by an electronic apparatus having one or more processing units.
  • the programs when executed by the one or more processing units, cause the electronic apparatus to perform the method of encoding a coding block of a current picture as described above.
  • a method of encoding a coding block of a current picture under an affine mode includes the following operations: determining multiple initial control point motion vectors for the coding block under an affine mode; for each of the initial control point motion vectors, searching, within a predefined range of the initial control point motion vector, an optimal control point motion vector for the coding block, wherein the optimal motion vector has a lowest rate-distortion cost within the predefined range of the initial control point motion vector; identifying, within a reference picture, a previously coded coding block corresponding to the optimal control point motion vector; and encoding the coding block using the previously coded coding block in the reference picture according to the affine mode.
  • an electronic apparatus includes one or more processing units, memory and a plurality of programs stored in the memory.
  • the programs when executed by the one or more processing units, cause the electronic apparatus to perform the method of encoding a coding block of a current picture under an affine mode as described above.
  • a non-transitory computer readable storage medium stores a plurality of programs for execution by an electronic apparatus having one or more processing units.
  • the programs when executed by the one or more processing units, cause the electronic apparatus to perform the method of encoding a coding block of a current picture under an affine mode as described above.
  • FIG. 1 is a block diagram illustrating an exemplary video encoding and decoding system in accordance with some implementations of the present disclosure.
  • FIG. 2 is a block diagram illustrating an exemplary video encoder in accordance with some implementations of the present disclosure.
  • FIG. 3 is a block diagram illustrating an exemplary video decoder in accordance with some implementations of the present disclosure.
  • FIGS. 4A through 4E are block diagrams illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes in accordance with some implementations of the present disclosure.
  • FIGS. 5A and 5B are block diagrams illustrating a 4-parameter block-based affine motion model and a 6-parameter block-based affine motion model, respectively, in accordance with some implementations of the present disclosure.
  • FIG. 5C is a flowchart illustrating a process of refining control point motion vectors of a coding block under an affine mode in accordance with some implementations of the present disclosure.
  • FIGS. 5D and 5E are block diagrams illustrating search patterns used for refining a control point motion vector in accordance with some implementations of the present disclosure.
  • FIG. 5F is a flowchart illustrating a process of encoding a coding block of a current picture under an affine mode in accordance with some implementations of the present disclosure.
  • FIG. 6A is a flowchart illustrating a process of refining an initial motion vector using a motion vector library for encoding a coding block in accordance with some implementations of the present disclosure.
  • FIG. 6B is a block diagram illustrating how a motion vector library is constructed and updated for a coding block in accordance with some implementations of the present disclosure.
  • FIG. 6C is a flowchart illustrating a process of encoding a coding block of a current picture in accordance with some implementations of the present disclosure.
  • FIG. 1 is a block diagram illustrating an exemplary system 10 for encoding and decoding video blocks in parallel in accordance with some implementations of the present disclosure.
  • system 10 includes a source device 12 that generates and encodes video data to be decoded at a later time by a destination device 14.
  • Source device 12 and destination device 14 may comprise any of a wide variety of electronic devices, including desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like.
  • source device 12 and destination device 14 are equipped with wireless communication capabilities.
  • destination device 14 may receive the encoded video data to be decoded via a link 16.
  • Link 16 may comprise any type of communication medium or device capable of moving the encoded video data from source device 12 to destination device 14.
  • link 16 may comprise a communication medium to enable source device 12 to transmit the encoded video data directly to destination device 14 in real-time.
  • the encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14.
  • the communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines.
  • the communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet.
  • the communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 12 to destination device 14.
  • the encoded video data may be transmitted from output interface 22 to a storage device 32. Subsequently, the encoded video data in storage device 32 may be accessed by destination device 14 via input interface 28.
  • Storage device 32 may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.
  • storage device 32 may correspond to a file server or another intermediate storage device that may hold the encoded video data generated by source device 12.
  • Destination device 14 may access the stored video data from storage device 32 via streaming or downloading.
  • the file server may be any type of computer capable of storing encoded video data and transmitting the encoded video data to destination device 14.
  • Exemplary file servers include a web server (e.g., for a website), an FTP server, network attached storage (NAS) devices, or a local disk drive.
  • Destination device 14 may access the encoded video data through any standard data connection, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server.
  • the transmission of encoded video data from storage device 32 may be a streaming transmission, a download transmission, or a combination of both.
  • source device 12 includes a video source 18, a video encoder 20 and an output interface 22.
  • Video source 18 may include a source such as a video capture device, e.g., a video camera, a video archive containing previously captured video, a video feed interface to receive video from a video content provider, and/or a computer graphics system for generating computer graphics data as the source video, or a combination of such sources.
  • a video capture device e.g., a video camera, a video archive containing previously captured video, a video feed interface to receive video from a video content provider, and/or a computer graphics system for generating computer graphics data as the source video, or a combination of such sources.
  • source device 12 and destination device 14 may form camera phones or video phones.
  • the implementations described in the present application may be applicable to video coding in general, and may be applied to wireless and/or wired applications.
  • the captured, pre-captured, or computer-generated video may be encoded by video encoder 20.
  • the encoded video data may be transmitted directly to destination device 14 via output interface 22 of source device 12.
  • the encoded video data may also (or alternatively) be stored onto storage device 32 for later access by destination device 14 or other devices, for decoding and/or playback.
  • Output interface 22 may further include a modem and/or a transmitter.
  • Destination device 14 includes an input interface 28, a video decoder 30, and a display device 34.
  • Input interface 28 may include a receiver and/or a modem and receive the encoded video data over link 16.
  • the encoded video data communicated over link 16, or provided on storage device 32 may include a variety of syntax elements generated by video encoder 20 for use by video decoder 30 in decoding the video data. Such syntax elements may be included within the encoded video data transmitted on a communication medium, stored on a storage medium, or stored a file server.
  • destination device 14 may include a display device
  • Display device 34 which can be an integrated display device and an external display device that is configured to communicate with destination device 14.
  • Display device 34 displays the decoded video data to a user, and may comprise any of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.
  • LCD liquid crystal display
  • OLED organic light emitting diode
  • Video encoder 20 and video decoder 30 may operate according to proprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions of such standards. It should be understood that the present application is not limited to a specific video coding/decoding standard and may be applicable to other video coding/decoding standards. It is generally contemplated that video encoder 20 of source device 12 may be configured to encode video data according to any of these current or future standards. Similarly, it is also generally contemplated that video decoder 30 of destination device 14 may be configured to decode video data according to any of these current or future standards.
  • Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof.
  • DSPs digital signal processors
  • ASICs application specific integrated circuits
  • FPGAs field programmable gate arrays
  • an electronic device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the video coding/decoding operations disclosed in the present disclosure.
  • Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.
  • CDEC combined encoder/decoder
  • FIG. 2 is a block diagram illustrating an exemplary video encoder 20 in accordance with some implementations described in the present application.
  • Video encoder 20 may perform intra and inter predictive coding of video blocks within video frames. Intra predictive coding relies on spatial prediction to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter predictive coding relies on temporal prediction to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence.
  • video encoder 20 includes video data memory 40, prediction processing unit 41, decoded picture buffer (DPB) 64, summer 50, transform processing unit 52, quantization unit 54, and entropy encoding unit 56.
  • Prediction processing unit 41 further includes motion estimation unit 42, motion compensation unit 44, partition unit 45, intra prediction processing unit 46, and intra block copy (BC) unit 48.
  • video encoder 20 also includes inverse quantization unit 58, inverse transform processing unit 60, and summer 62 for video block reconstruction.
  • a deblocking filter (not shown) may be positioned between summer 62 and DPB 64 to filter block boundaries to remove blockiness artifacts from reconstructed video.
  • Video encoder 20 may take the form of a fixed or programmable hardware unit or may be divided among one or more of the illustrated fixed or programmable hardware units.
  • Video data memory 40 may store video data to be encoded by the components of video encoder 20.
  • the video data in video data memory 40 may be obtained, for example, from video source 18.
  • DPB 64 is a buffer that stores reference video data for use in encoding video data by video encoder 20 (e.g., in intra or inter predictive coding modes).
  • Video data memory 40 and DPB 64 may be formed by any of a variety of memory devices.
  • video data memory 40 may be on-chip with other components of video encoder 20, or off-chip relative to those components.
  • partition unit 45 within prediction processing unit 41 partitions the video data into video blocks.
  • This partitioning may also include partitioning a video frame into slices, tiles, or other larger coding units (CUs) according to a predefined splitting structures such as quad-tree structure associated with the video data.
  • the video frame may be divided into multiple video blocks (or sets of video blocks referred to as tiles).
  • Prediction processing unit 41 may select one of a plurality of possible predictive coding modes, such as one of a plurality of intra predictive coding modes or one of a plurality of inter predictive coding modes, for the current video block based on error results (e.g., coding rate and the level of distortion).
  • Prediction processing unit 41 may provide the resulting intra or inter prediction coded block to summer 50 to generate a residual block and to summer 62 to reconstruct the encoded block for use as part of a reference frame subsequently. Prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy encoding unit 56.
  • intra prediction processing unit 46 within prediction processing unit 41 may perform intra predictive coding of the current video block relative to one or more neighboring blocks in the same frame as the current block to be coded to provide spatial prediction.
  • Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter predictive coding of the current video block relative to one or more predictive blocks in one or more reference frames to provide temporal prediction.
  • Video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.
  • motion estimation unit 42 determines the inter prediction mode for a current video frame by generating a motion vector, which indicates the displacement of a prediction unit (PU) of a video block within the current video frame relative to a predictive block within a reference video frame, according to a predetermined pattern within a sequence of video frames.
  • Motion estimation performed by motion estimation unit 42, is the process of generating motion vectors, which estimate motion for video blocks.
  • a motion vector may indicate the displacement of a PU of a video block within a current video frame or picture relative to a predictive block within a reference frame (or other coded unit) relative to the current block being coded within the current frame (or other coded unit).
  • Intra BC unit 48 may determine vectors, e.g., block vectors, for intra BC coding in a manner similar to the determination of motion vectors by motion estimation unit 42 for inter prediction, or may utilize motion estimation unit 42 to determine the block vector.
  • a predictive block is a block of a reference frame that is deemed as closely matching the PU of the video block to be coded in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics.
  • video encoder 20 may calculate values for sub integer pixel positions of reference frames stored in DPB 64. For example, video encoder 20 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference frame. Therefore, motion estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.
  • Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter prediction coded frame by comparing the position of the PU to the position of a predictive block of a reference frame selected from a first reference frame list (List 0) or a second reference frame list (List 1), each of which identifies one or more reference frames stored in DPB 64. Motion estimation unit 42 sends the calculated motion vector to motion compensation unit 44 and then to entropy encoding unit 56.
  • Motion compensation performed by motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation unit 42.
  • motion compensation unit 44 may locate a predictive block to which the motion vector points in one of the reference frame lists, retrieve the predictive block from DPB 64, and forward the predictive block to summer 50.
  • Summer 50 then forms a residual video block of pixel difference values by subtracting pixel values of the predictive block provided by motion compensation unit 44 from the pixel values of the current video block being coded.
  • the pixel difference values forming the residual vide block may include luma or chroma difference components or both.
  • Motion compensation unit 44 may also generate syntax elements associated with the video blocks of a video frame for use by video decoder 30 in decoding the video blocks of the video frame.
  • the syntax elements may include, for example, syntax elements defining the motion vector used to identify the predictive block, any flags indicating the prediction mode, or any other syntax information described herein. Note that motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.
  • intra BC unit 48 may generate vectors and fetch predictive blocks in a manner similar to that described above in connection with motion estimation unit 42 and motion compensation unit 44, but with the predictive blocks being in the same frame as the current block being coded and with the vectors being referred to as block vectors as opposed to motion vectors.
  • intra BC unit 48 may determine an intra-prediction mode to use to encode a current block.
  • intra BC unit 48 may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and test their performance through rate-distortion analysis. Next, intra BC unit 48 may select, among the various tested intra-prediction modes, an appropriate intra prediction mode to use and generate an intra-mode indicator accordingly.
  • intra BC unit 48 may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and select the intra-prediction mode having the best rate- distortion characteristics among the tested modes as the appropriate intra-prediction mode to use.
  • Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bitrate (i.e., a number of bits) used to produce the encoded block.
  • Intra BC unit 48 may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra -prediction mode exhibits the best rate-distortion value for the block.
  • intra BC unit 48 may use motion estimation unit 42 and motion compensation unit 44, in whole or in part, to perform such functions for Intra BC prediction according to the implementations described herein.
  • a predictive block may be a block that is deemed as closely matching the block to be coded, in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of squared difference (SSD), or other difference metrics, and identification of the predictive block may include calculation of values for sub-integer pixel positions.
  • video encoder 20 may form a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values.
  • the pixel difference values forming the residual video block may include both luma and chroma component differences.
  • Intra prediction processing unit 46 may intra-predict a current video block, as an alternative to the inter-prediction performed by motion estimation unit 42 and motion compensation unit 44, or the intra block copy prediction performed by intra BC unit 48, as described above.
  • intra prediction processing unit 46 may determine an intra prediction mode to use to encode a current block. To do so, intra prediction processing unit 46 may encode a current block using various intra prediction modes, e.g., during separate encoding passes, and intra prediction processing unit 46 (or a mode select unit, in some examples) may select an appropriate intra prediction mode to use from the tested intra prediction modes.
  • Intra prediction processing unit 46 may provide information indicative of the selected intra-prediction mode for the block to entropy encoding unit 56. Entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode in the bitstream.
  • summer 50 forms a residual video block by subtracting the predictive block from the current video block.
  • the residual video data in the residual block may be included in one or more transform units (TUs) and is provided to transform processing unit 52.
  • Transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform.
  • DCT discrete cosine transform
  • Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54.
  • Quantization unit 54 quantizes the transform coefficients to further reduce bit rate. The quantization process may also reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter.
  • quantization unit 54 may then perform a scan of a matrix including the quantized transform coefficients.
  • entropy encoding unit 56 may perform the scan.
  • entropy encoding unit 56 entropy encodes the quantized transform coefficients into a video bitstream using, e.g., context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique.
  • CAVLC context adaptive variable length coding
  • CABAC context adaptive binary arithmetic coding
  • SBAC syntax-based context-adaptive binary arithmetic coding
  • PIPE probability interval partitioning entropy
  • the encoded bitstream may then be transmitted to video decoder 30, or archived in storage device 32 for later transmission to or retrieval by video decoder 30.
  • Entropy encoding unit 56 may also entropy encode the motion vectors and the other syntax elements for the current video frame being coded.
  • Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual video block in the pixel domain for generating a reference block for prediction of other video blocks.
  • motion compensation unit 44 may generate a motion compensated predictive block from one or more reference blocks of the frames stored in DPB 64. Motion compensation unit 44 may also apply one or more interpolation filters to the predictive block to calculate sub-integer pixel values for use in motion estimation.
  • Summer 62 adds the reconstructed residual block to the motion compensated predictive block produced by motion compensation unit 44 to produce a reference block for storage in DPB 64.
  • the reference block may then be used by intra BC unit 48, motion estimation unit 42 and motion compensation unit 44 as a predictive block to inter predict another video block in a subsequent video frame.
  • FIG. 3 is a block diagram illustrating an exemplary video decoder 30 in accordance with some implementations of the present application.
  • Video decoder 30 includes video data memory 79, entropy decoding unit 80, prediction processing unit 81, inverse quantization unit 86, inverse transform processing unit 88, summer 90, and DPB 92.
  • Prediction processing unit 81 further includes motion compensation unit 82, intra prediction processing unit 84, and intra BC unit 85.
  • Video decoder 30 may perform a decoding process generally reciprocal to the encoding process described above with respect to video encoder 20 in connection with FIG. 2.
  • motion compensation unit 82 may generate prediction data based on motion vectors received from entropy decoding unit 80
  • intra prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 80.
  • a unit of video decoder 30 may be tasked to perform the implementations of the present application. Also, in some examples, the implementations of the present disclosure may be divided among one or more of the units of video decoder 30.
  • intra BC unit 85 may perform the implementations of the present application, alone, or in combination with other units of video decoder 30, such as motion compensation unit 82, intra prediction processing unit 84, and entropy decoding unit 80.
  • video decoder 30 may not include intra BC unit 85 and the functionality of intra BC unit 85 may be performed by other components of prediction processing unit 81, such as motion compensation unit 82.
  • Video data memory 79 may store video data, such as an encoded video bitstream, to be decoded by the other components of video decoder 30.
  • the video data stored in video data memory 79 may be obtained, for example, from storage device 32, from a local video source, such as a camera, via wired or wireless network communication of video data, or by accessing physical data storage media (e.g., a flash drive or hard disk).
  • Video data memory 79 may include a coded picture buffer (CPB) that stores encoded video data from an encoded video bitstream.
  • Decoded picture buffer (DPB) 92 of video decoder 30 stores reference video data for use in decoding video data by video decoder 30 (e.g., in intra or inter predictive coding modes).
  • Video data memory 79 and DPB 92 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magneto-resistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices.
  • DRAM dynamic random access memory
  • SDRAM synchronous DRAM
  • MRAM magneto-resistive RAM
  • RRAM resistive RAM
  • video data memory 79 and DPB 92 are depicted as two distinct components of video decoder 30 in FIG. 3. But it will be apparent to one skilled in the art that video data memory 79 and DPB 92 may be provided by the same memory device or separate memory devices.
  • video data memory 79 may be on-chip with other components of video decoder 30, or off-chip relative to those components.
  • video decoder 30 receives an encoded video bitstream that represents video blocks of an encoded video frame and associated syntax elements.
  • Video decoder 30 may receive the syntax elements at the video frame level and/or the video block level.
  • Entropy decoding unit 80 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit 80 then forwards the motion vectors and other syntax elements to prediction processing unit 81.
  • intra prediction processing unit 84 of prediction processing unit 81 may generate prediction data for a video block of the current video frame based on a signaled intra prediction mode and reference data from previously decoded blocks of the current frame.
  • motion compensation unit 82 of prediction processing unit 81 produces one or more predictive blocks for a video block of the current video frame based on the motion vectors and other syntax elements received from entropy decoding unit 80.
  • Each of the predictive blocks may be produced from a reference frame within one of the reference frame lists.
  • Video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference frames stored in DPB 92.
  • intra BC unit 85 of prediction processing unit 81 produces predictive blocks for the current video block based on block vectors and other syntax elements received from entropy decoding unit 80.
  • the predictive blocks may be within a reconstructed region of the same picture as the current video block defined by video encoder 20.
  • Motion compensation unit 82 and/or intra BC unit 85 determines prediction information for a video block of the current video frame by parsing the motion vectors and other syntax elements, and then uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, motion compensation unit 82 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code video blocks of the video frame, an inter prediction frame type (e.g., B or P), construction information for one or more of the reference frame lists for the frame, motion vectors for each inter predictive encoded video block of the frame, inter prediction status for each inter predictive coded video block of the frame, and other information to decode the video blocks in the current video frame.
  • a prediction mode e.g., intra or inter prediction
  • an inter prediction frame type e.g., B or P
  • intra BC unit 85 may use some of the received syntax elements, e.g., a flag, to determine that the current video block was predicted using the intra BC mode, construction information of which video blocks of the frame are within the reconstructed region and should be stored in DPB 92, block vectors for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information to decode the video blocks in the current video frame.
  • a flag e.g., a flag
  • Motion compensation unit 82 may also perform interpolation using the interpolation filters as used by video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 82 may determine the interpolation filters used by video encoder 20 from the received syntax elements and use the interpolation filters to produce predictive blocks.
  • Inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by entropy decoding unit 80 using the same quantization parameter calculated by video encoder 20 for each video block in the video frame to determine a degree of quantization.
  • Inverse transform processing unit 88 applies an inverse transform, e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to reconstruct the residual blocks in the pixel domain.
  • an inverse transform e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process
  • summer 90 reconstructs decoded video block for the current video block by summing the residual block from inverse transform processing unit 88 and a corresponding predictive block generated by motion compensation unit 82 and intra BC unit 85.
  • An in-loop filter (not pictured) may be positioned between summer 90 and DPB 92 to further process the decoded video block.
  • the decoded video blocks in a given frame are then stored in DPB 92, which stores reference frames used for subsequent motion compensation of next video blocks.
  • DPB 92 or a memory device separate from DPB 92, may also store decoded video for later presentation on a display device, such as display device 34 of FIG. 1.
  • a video sequence typically includes an ordered set of frames or pictures.
  • Each frame may include three sample arrays, denoted SL, SCb, and SCr.
  • SL is a two-dimensional array of luma samples.
  • SCb is a two-dimensional array of Cb chroma samples.
  • SCr is a two-dimensional array of Cr chroma samples.
  • a frame may be monochrome and therefore includes only one two-dimensional array of luma samples.
  • video encoder 20 (or more specifically partition unit 45) generates an encoded representation of a frame by first partitioning the frame into a set of coding tree units (CTUs).
  • a video frame may include an integer number of CTUs ordered consecutively in a raster scan order from left to right and from top to bottom.
  • Each CTU is a largest logical coding unit and the width and height of the CTU are signaled by the video encoder 20 in a sequence parameter set, such that all the CTUs in a video sequence have the same size being one of 128x 128, 64x64, 32x32, and 16x 16.
  • the present application is not necessarily limited to a particular size. As shown in FIG.
  • each CTU may comprise one coding tree block (CTB) of luma samples, two corresponding coding tree blocks of chroma samples, and syntax elements used to code the samples of the coding tree blocks.
  • the syntax elements describe properties of different types of units of a coded block of pixels and how the video sequence can be reconstructed at the video decoder 30, including inter or intra prediction, intra prediction mode, motion vectors, and other parameters.
  • a CTU may comprise a single coding tree block and syntax elements used to code the samples of the coding tree block.
  • a coding tree block may be an NxN block of samples.
  • video encoder 20 may recursively perform tree partitioning such as binary-tree partitioning, ternary-tree partitioning, quad-tree partitioning or a combination of both on the coding tree blocks of the CTU and divide the CTU into smaller coding units (CUs).
  • tree partitioning such as binary-tree partitioning, ternary-tree partitioning, quad-tree partitioning or a combination of both on the coding tree blocks of the CTU and divide the CTU into smaller coding units (CUs).
  • the 64x64 CTU 400 is first divided into four smaller CU, each having a block size of 32x32.
  • CU 410 and CU 420 are each divided into four CUs of 16x16 by block size.
  • the two 16x16 CUs 430 and 440 are each further divided into four CUs of 8x8 by block size.
  • each leaf node of the quad-tree corresponding to one CU of a respective size ranging from 32x32 to 8x8.
  • each CU may comprise a coding block (CB) of luma samples and two corresponding coding blocks of chroma samples of a frame of the same size, and syntax elements used to code the samples of the coding blocks.
  • CB coding block
  • a CU may comprise a single coding block and syntax structures used to code the samples of the coding block.
  • quad-tree partitioning depicted in FIGS. 4C and 4D is only for illustrative purposes and one CTU can be split into CUs to adapt to varying local characteristics based on quad/ternary/binary-tree partitions.
  • one CTU is partitioned by a quad-tree structure and each quad-tree leaf CU can be further partitioned by a binary and ternary tree structure.
  • FIG. 4E there are five possible partitioning types of a coding block having a width W and a height H, i.e., quaternary partitioning, horizontal binary partitioning, vertical binary partitioning, horizontal ternary partitioning, and vertical ternary partitioning.
  • video encoder 20 may further partition a coding block of a CU into one or more MxN prediction blocks (PB).
  • a prediction block is a rectangular (square or non-square) block of samples on which the same prediction, inter or intra, is applied.
  • a prediction unit (PU) of a CU may comprise a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and syntax elements used to predict the prediction blocks.
  • a PU may comprise a single prediction block and syntax structures used to predict the prediction block.
  • Video encoder 20 may generate predictive luma, Cb, and Cr blocks for luma, Cb, and Cr prediction blocks of eachPU of the CU.
  • Video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If video encoder 20 uses intra prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the frame associated with the PU. If video encoder 20 uses inter prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more frames other than the frame associated with the PU.
  • video encoder 20 may generate a luma residual block for the CU by subtracting the CU’s predictive luma blocks from its original luma coding block such that each sample in the CU’s luma residual block indicates a difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block.
  • video encoder 20 may generate a Cb residual block and a Cr residual block for the CU, respectively, such that each sample in the CU's Cb residual block indicates a difference between a Cb sample in one of the CU's predictive Cb blocks and a
  • each sample in the CU's Cr residual block may indicate a difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.
  • video encoder 20 may use quad-tree partitioning to decompose the luma, Cb, and Cr residual blocks of a CU into one or more luma, Cb, and Cr transform blocks.
  • a transform block is a rectangular (square or non-square) block of samples on which the same transform is applied.
  • a transform unit (TU) of a CU may comprise a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax elements used to transform the transform block samples.
  • each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block.
  • the luma transform block associated with the TU may be a sub-block of the CU's luma residual block.
  • the Cb transform block may be a sub-block of the CU's Cb residual block.
  • the Cr transform block may be a sub-block of the CU's Cr residual block.
  • a TU may comprise a single transform block and syntax structures used to transform the samples of the transform block.
  • Video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU.
  • a coefficient block may be a two-dimensional array of transform coefficients.
  • a transform coefficient may be a scalar quantity.
  • Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU.
  • Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.
  • video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. After video encoder 20 quantizes a coefficient block, video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, video encoder 20 may perform Context-Adaptive Binary
  • video encoder 20 may output a bitstream that includes a sequence of bits that forms a representation of coded frames and associated data, which is either saved in storage device 32 or transmitted to destination device 14.
  • CABAC Arithmetic Coding
  • video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. Video decoder 30 may reconstruct the frames of the video data based at least in part on the syntax elements obtained from the bitstream. The process of reconstructing the video data is generally reciprocal to the encoding process performed by video encoder 20. For example, video decoder 30 may perform inverse transforms on the coefficient blocks associated with TUs of a current CU to reconstruct residual blocks associated with the TUs of the current CU. Video decoder 30 also reconstructs the coding blocks of the current CU by adding the samples of the predictive blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. After reconstructing the coding blocks for each CU of a frame, video decoder 30 may reconstruct the frame.
  • FIGS. 5 A and 5B are block diagrams illustrating a 4-parameter block-based affine motion model and a 6-parameter block-based affine motion model, respectively, in accordance with some implementations of the present disclosure.
  • a current block 510 is related to a reference block in a reference picture (not shown in the figure) by two motion vectors, MV 0 (mvo x , mvo y ) at the top-left comer control point of the current block 510 and MVi(mvi x , mvi ) at the top-right corner control point of the current block 510.
  • the width of the current block 510 is W (as depicted in FIG. 4E)
  • the motion vector MV(mv x , mv y ) at any location (x, y) within the current block 510 is defined by a linear affine motion model as follows:
  • another current block 520 is related to a reference block (not shown in the figure) by three motion vectors, MV 0 (mvo x , mvo y ) at the top-left comer control point of the current block 520, MVi(mvi x , mvi y ) at the top-right comer control point of the current block 520, and MV 2 (mv2 X , mv2 y ) at the bottom-left corner control point of the current block 520.
  • the motion vector MV(mv x , mv y ) at any location (x, y) within the current block 520 is defined by a linear affine motion model as follows:
  • control point motion vectors (CPMVs). Their accuracy has a significant impact on the coding efficiency. For example, if these control point motion vectors are accurate, the prediction error between the current block and the predicted block based on the reference block can be minimized. But if these control point motion vectors are less accurate, the prediction error between the current block and the predicted block based on the reference block will increase.
  • a process of estimating the CPMVs of a current block includes four steps: (1) generating the predicted samples according to an initial affine motion compensation model; (2) calculating the spatial gradient of the predicted samples in two directions with Sobel filter based on an optical flow model; (3) calculating the correlation matrix based on the predicted samples’ gradient and its coordinates; and (4) updating the affine model compensation parameters based on least mean square estimation (LMSE). The above process is repeated until the affine CPMVs converge when the update after one iteration is less than a predefined threshold.
  • LMSE least mean square estimation
  • R-D rate -distortion
  • the lambda is the weighting factor between the distortion and the bit cost.
  • Video encoder 20 first checks the R-D cost of the translation motion model. If both the width and the height of the current block is greater than 8, then affine motion estimation with 4-parameter affine model is performed. If the R-D cost of the 4-parameter affine model is not too larger than that of the translational motion model, video encoder 20 further checks the R-D cost with 6-parameter affine model. After that, video encoder 20 selects an optimized affine motion compensation model with minimal R-D cost for the current block.
  • the spatial gradients derived from the prediction block are not reliable because they are sensitive to noise present in the block, e.g., the noise captured in original video data and/or the coding noise that are generated during the coding process. Therefore, it is very difficult to derive accurate affine CP MYs based on such inaccurate gradients.
  • the affine motion estimation is a high-dimensional optimization problem. For example, four or six LMSE parameters are to be estimated for the 4-parameter and 6-parameter affine models, respectively. Like other high-dimensional optimization problems, the solution to this optimization problem is highly dependent on the accuracy of the initial CPMVs. If the initial CPMVs are close to a local minimum of the R-D cost, the CP MV search path is likely to be trapped to the local minimum, which severely affects the accuracy of the estimated affine CPMVs.
  • FIG. 5C depicts one enhanced affine motion estimation method in accordance with some implementations of the present disclosure.
  • the proposed method starts with estimating the affine CPMVs using the optical-flow-based affine motion estimation method (532) as described above, i.e., iteratively adjusting the affine CPMVs based on the gradients of prediction block and the difference between the prediction block and the current block measured by the R-D cost. After such affine motion estimation is performed, the proposed method further refines each CP MV based on a pattern-based local motion search.
  • FIG. 5D and 5E are block diagrams illustrating two search patterns used for refining the CPMV in accordance with some implementations of the present disclosure.
  • FIG. 5D depicts a diamond search pattern with the CPMV estimated from the optical-flow-based affine motion estimation method at the center of the diamond pattern (e.g., dot 550)
  • FIG. 5E depicts a rectangle search pattern with the CPMV estimated from the optical-flow-based affine motion estimation method at the center of the rectangle pattern (e.g., dot 560).
  • Each search pattern includes multiple candidate CPMVs (e.g., squares 550-1 and 550-2 in FIG. 5D or squares 560-1 and 560-2 in FIG. 5E).
  • the CPMV at the center of the search pattern is at an integer position of samples and there is a predefined offset between a candidate CPMV and the CPMV and two candidates CPMVs (e.g., the two CPMVs corresponding to the squares 550-1 and 550-2).
  • the offset is one sample or a fraction of one sample in the picture.
  • FIG. 5C depicts an exemplary interactive process of refining the CP MV by searching for a candidate CP MV within the search pattern that has a lower R-D cost than the CP MV.
  • the iterative process includes two loops, the outer loop between the step 534 and the step 542 and the inner loop between the step 536 and the step 540.
  • the inner loop iterates through the candidate CP MVs within a search pattern by refining the k-th candidate CPMV (e.g., calculating its R-D cost and comparing it with the other CPMVs) until the last one in the search patter is examined. By doing so, a CPMV having the lowest R-D cost is identified as a refined CPMV.
  • the refined CPMV is different from the CPMV at the center of the search pattern. For example, the CPMV 550-2 may be identified as the refined CPMV if its associated R-D cost is the lowest within the diamond pattern.
  • a new search pattern centering at the refined CPMV is defined and the inner loop is repeated for the new search pattern.
  • the refined CPMV is the same as the CPMV at the center of the search pattern (e.g., the dot 550).
  • the CPMV at the center of the search pattern is deemed to be the optimal value for the current CPMV of the affine model.
  • the outer loop terminates if one of the two conditions is met. First, when there is no CPMV change, i.e., the refined CPMV is the same as the CPMV at the center of the search pattern as described above, the outer loop should terminate.
  • ⁇ M AC e.g. 3
  • the outer loop terminates to reduce the computational complexity.
  • ⁇ M AC e.g. 3
  • the proposed affine CPMV refinement method above is not limited to any specific search patterns. The method can be applied to many search patterns (e.g., diamond pattern, raster pattern and hexagon pattern).
  • FIG. 5F is a flowchart illustrating a process 570 of encoding a coding block of a current picture under an affine mode performed by an electronic apparatus in accordance with some implementations of the present disclosure.
  • the electronic apparatus determines (575) multiple initial control point motion vectors for the coding block (e.g., two CPMVs in block 510 in FIG. 5A and three CPMVs in block 520 in FIG. 5B) under an affine mode.
  • the multiple initial control point motion vectors are determined by minimizing a difference between pixels predicted from the reference picture by the multiple initial control point motion vectors and actual pixels in the coding block. In one example, the difference is minimized based on an optical flow based affine motion estimation scheme.
  • the electronic apparatus searches (580), within a predefined range of the initial control point motion vector, an optimal control point motion vector for the coding block.
  • the predefined range of the initial control point motion vector includes a pattern of control point motion vector candidates surrounding the initial control point motion vector, the pattern selected from a group consisting of a square pattern, a diamond pattern, a raster pattern and a hexagon pattern such as those patterns depicted in FIGS. 5D and 5E.
  • the optimal motion vector is the one that has a lowest rate -distortion cost within the predefined range of the initial control point motion vector.
  • the electronic apparatus if another control point motion vector within the predefined range of the initial control point motion vector has a rate- distortion cost lower than that of the initial control point motion vector, the electronic apparatus then replaces the initial control point motion vector with the another control point motion vector and continues the search within a newly-predefined range of the another control point motion vector until the optimal control point motion vector is found, i.e., when there is no control point motion vector within the predefined range of the another control point motion vector having a rate-distortion cost lower than that of the another control point motion vector.
  • an upper limit e.g., 3 is also chosen such that the search for the optimal control point motion vector is terminated after the upper limit of iterations with the last one as the optimal control point motion vector.
  • the electronic apparatus then identifies (585), within a reference picture corresponding to the current block, a previously coded coding block corresponding to the optimal control point motion vector.
  • the electronic apparatus encodes (590) the coding block using the previously coded coding block in the reference picture according to the affine mode.
  • the non-affine motion estimation (e.g., regular inter mode) is also treated as an optimization problem mathematically by defining an optimization function based on a motion vector (e.g., a rate-distortion cost) and calculating the rate-distortion cost repeatedly starting with an initial motion vector estimation until an optimal motion vector is found with a lowest R-D cost.
  • a motion vector e.g., a rate-distortion cost
  • different motion vectors are used as candidates for the initial motion vector estimation, including the motion vector prediction of a neighboring block of the current block (assuming that the two blocks share the same reference picture) and the zero MY corresponding to the collocated reference block in the reference picture.
  • These MVP candidates are assumed to have a strong correlation with the MVs of the current block due to the fact that their corresponding blocks are spatial/temporal neighbors of the current block.
  • the new video coding standard allows a block to be further partitioned by multiple tree partitions, i.e. quad-tree binary-tree and ternary-tree.
  • tree partitions i.e. quad-tree binary-tree and ternary-tree.
  • the ternary tree partition is applied, one coding block is split into three sub-partitions with ratio of 1:2:1 in either horizontal or vertical direction.
  • a motion vector (MY) library is constructed and maintained as another possible source of the initial motion vector used by the motion estimation process.
  • the MV library contains the optimal MVs that are selected by the inter blocks that are previously coded in the same picture.
  • the MV candidates in the MV library are rounded to the integer precision for efficiency before being used as the candidates to select the initial MV.
  • FIG. 6A depicts a process of refining an initial motion vector using such a motion vector library for encoding a coding block in accordance with some implementations of the present disclosure.
  • video encoder 20 tests (604) a neighboring block’s motion vector prediction by calculating its R-D cost and tests (606) the zero motion vector by calculating its R-D cost. Between these two candidates, one with a lower R-D cost is kept for further comparison with MV candidates in the MV library. As depicted in FIG. 6A, video encoder 20 tests (608) a MV candidate in the MV library by calculating its R-D cost and comparing it with the winner of the steps 604 and 606. Video encoder 20 repeats the process until the last MV candidate in the MV library is examined (610-Yes) and one MV candidate with the lowest R-D cost is identified as the initial motion vector estimation for the optimization process.
  • This optimization process includes a further refinement of the initial MV (612).
  • the refinement of the motion vector is at a higher resolution, e.g., starting with a half-pel motion search process to a quarter-pel motion process, until an optimal motion vector is found.
  • video encoder 20 encodes (614) the current block using the optimal motion vector and its corresponding block in the reference picture.
  • all the MV candidates stored in the MV library are the optimal MVs selected by the previous coding blocks.
  • each entry in the MV library contains two types of information: 1) the position, the width and the height of a coding block associated with the MY and 2) the optimal MV corresponding to a reference picture of the coding block.
  • the MV library may be set to be empty or initialized with some representative MV values, e.g. zero MVs.
  • the MV library may be updated by merging the MVs of the current block with the old MV candidates in the MV library.
  • the MV library may be updated in one of the two ways: (i) if there is an existing entry in the MV library and the entry has the same block position, block width and block height as the current block, then the MV of the entry in the MV library is updated with the optimal MV of the current block determined above in accordance with FIG. 6A; and (ii) if there is no duplicated entry in the MV library, the current block is added as one new MV candidate to the MV library based on a first-in-first-out (FIFO) rule.
  • FIFO first-in-first-out
  • the MV library has a limit on the maximum number of entries. In this case, the addition of a new entry may cause the removal of the oldest entry from the library based on the FIFO rule.
  • the MV from a parent block level is always kept in the MV library as illustrated in FIG. 6B.
  • a MV library 630 has a maximum of four entries and it is constructed for the coding block 620 when the coding block 620 is subject to different types of partitions as described in FIG. 6B above.
  • an optimal motion vector MV(B0) is determined by video encoder 20 based on the R-D cost analysis.
  • MV(Bl) and MV(B2) are added to the MV library.
  • the entry MV(B0) When the coding block 620 is subject to a vertical BT split, the first entry MV(BO) has to be pushed out of the MV library according to the FIFO rule. However, because the entry MV(B0) is a parent level entry corresponding to the entire block 620, the entry MV(B0) needs to be added back to the end of the MV library 630. To do so, the second oldest entry MY(B1) needs to be removed from the MV library 630. As a result, the entry MV(B0) remains in the MV library 630 for each possible partition of the coding block, including the horizontal ternary tree (TT) split, vertical TT split and quadtree (QT) split.
  • TT horizontal ternary tree
  • QT quadtree
  • FIG. 6C is a flowchart illustrating a process 640 of encoding a coding block of a current picture using a MV library in accordance with some implementations of the present disclosure.
  • the electronic apparatus first selects (650), among a plurality of motion vector candidates, an initial motion vector for the coding block, wherein the plurality of motion vector candidates include a motion vector library associated with the coding block.
  • the electronic device determines (650-1) a rate-distortion cost for each of the plurality of motion vector candidates and then chooses (650-3) a motion vector candidate having a lowest rate -distortion cost as the initial motion vector.
  • the selecting of an initial motion vector for the coding block is performed at an integer resolution and the selecting of the optimal motion vector for the coding block is performed at a sub-integer resolution.
  • the plurality of motion vector candidates also include a zero motion vector corresponding to a collocated coding block in the reference picture and one or more motion vectors, each motion vector associated with a neighboring block of the current block in the current picture.
  • the MV library includes one or more motion vectors, each motion vector associated with a previously coded coding block in the current picture, including, e.g., at least one of a motion vector associated with a previously coded parent coding block in the current picture that covers a region of the coding block or a motion vector associated with a coding block that is not spatially adjacent to the coding block.
  • each coding block corresponds to a motion vector in the motion vector library has unique position and size information in the current picture.
  • the apparatus searches (660), within a predefined range of the initial motion vector, an optimal motion vector for the coding block. For example, the apparatus first identifies (660-1), within the predefined range of the initial motion vector, a plurality of motion vector refinement candidates, each motion vector refinement candidate has a predefined difference from the initial motion vector. The apparatus then determines (660-3) a rate -distortion cost for each of the plurality of motion vector refinement candidates and chooses (660-5) a motion vector refinement candidate having a lowest rate-distortion cost as the optimal motion vector. Finally, the apparatus identifies (670), within a reference picture, a previously coded coding block corresponding to the optimal motion vector, and encodes (680) the coding block using the previously coded coding block in the reference picture.
  • the apparatus may update (690) the motion vector library with the optimal motion vector and its associated position and size information of the current coding block.
  • the apparatus replaces the existing motion vector with the optimal motion vector when there is an existing motion vector in the motion vector library having the same position and size information as the optimal motion vector.
  • the apparatus adds the optimal motion vector and its associated position and size information to the motion vector library and removes an oldest motion vector and its associated position and size information from the motion vector library based on the first-in-first-out rule if the motion vector library exceeds a predefined size of motion vectors and there is no existing motion vector in the motion vector library having the same position and size information as the optimal motion vector.
  • the best mode refers to the winner of all the inter-prediction modes without using AMVR
  • thres is a threshold value, e.g.
  • the costs associated with a regular inter mode with and/or without AMVR can be used to determine if the R-D cost checking for the affine AMVR mode needs to be performed. For example, if the cost of the regular inter mode with AMVR is smaller than the cost of the regular inter mode without AMVR multiplied with a certain threshold, video encoder 20 may test the R-D cost of affine AMVR mode. Otherwise, the R-D cost of affine AMVR mode can be omitted for the current block at encoder side.
  • Computer- readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol.
  • computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a
  • Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the implementations described in the present application.
  • a computer program product may include a computer- readable medium.
  • first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.
  • a first electrode could be termed a second electrode, and, similarly, a second electrode could be termed a first electrode, without departing from the scope of the implementations.
  • the first electrode and the second electrode are both electrodes, but they are not the same electrode.

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Abstract

Un appareil électronique réalise un procédé de codage d'un bloc de codage d'une image actuelle. L'appareil électronique sélectionne, parmi une pluralité de candidats de vecteurs de mouvement, un vecteur de mouvement initial pour le bloc de codage, la pluralité de candidats de vecteurs de mouvement comprenant une bibliothèque de vecteurs de mouvement associée au bloc de codage. L'appareil électronique recherche, dans une plage prédéfinie du vecteur de mouvement initial, un vecteur de mouvement optimal pour le bloc de codage. L'appareil électronique identifie, dans une image de référence, un bloc de codage codé précédemment correspondant au vecteur de mouvement optimal ; et code le bloc de codage à l'aide du bloc de codage précédemment codé dans l'image de référence.
PCT/US2020/034568 2019-05-26 2020-05-26 Procédés et appareil d'amélioration d'estimation du mouvement dans un codage vidéo WO2020243100A1 (fr)

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