WO2021202556A1 - Modes de codage sans perte de codage vidéo - Google Patents

Modes de codage sans perte de codage vidéo Download PDF

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Publication number
WO2021202556A1
WO2021202556A1 PCT/US2021/024921 US2021024921W WO2021202556A1 WO 2021202556 A1 WO2021202556 A1 WO 2021202556A1 US 2021024921 W US2021024921 W US 2021024921W WO 2021202556 A1 WO2021202556 A1 WO 2021202556A1
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WIPO (PCT)
Prior art keywords
transform
current picture
video
syntax element
coding
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PCT/US2021/024921
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English (en)
Inventor
Xianglin Wang
Tsung-Chuan MA
Xiaoyu XIU
Yi-Wen Chen
Hong-Jheng Jhu
Bing Yu
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Beijing Dajia Internet Information Technology Co., Ltd.
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Priority to CN202180025006.2A priority Critical patent/CN115362685A/zh
Publication of WO2021202556A1 publication Critical patent/WO2021202556A1/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
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/12—Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
    • 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
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/124—Quantisation
    • 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
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/157—Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
    • 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
    • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards

Definitions

  • the present application generally relates to video data coding and compression, and in particular, to method and system of improvement and simplification of the lossless coding for 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 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.
  • 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 system and method of improvement and simplification of the lossless coding for video coding.
  • a method of decoding video data includes: receiving, from a video bitstream, a first syntax element of a current picture; in accordance with a determination that the first syntax element indicates that dependent quantization is disabled for the current picture, receiving, from the video bitstream, a second syntax element of the current picture, wherein the second syntax element indicates whether transform skip residual coding under transform-skip mode is disabled for the current picture or not; in accordance with a determination that the first syntax element indicates that dependent quantization is enabled for the current picture, setting the second syntax element to be a default value enabling transform skip residual coding under transform- skip mode for the current picture; and performing transform skip residual decoding and dependent dequantization to the current picture in accordance with the first syntax element and the second syntax element.
  • 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 decoding video data 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 decoding video data 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 through 5B are block diagrams illustrating examples of transform efficient coding using context coding and bypass coding in accordance with some implementations of the present disclosure.
  • FIG. 6 is a block diagram illustrating an exemplary process of dependent scalar quantization in accordance with some implementations of the present disclosure.
  • FIG. 7 is a block diagram illustrating an exemplary state machine for switching between two different scalar quantizers in accordance with some implementations of the present disclosure.
  • FIGS. 8A through 8D are flowcharts illustrating an exemplary process by which a video decoder decodes a current picture of a video bitstream in accordance with some implementations of the present disclosure.
  • FIG. 9 is a block diagram illustrating an example Context-adaptive binary arithmetic coding (CABAC) engine in accordance with some implementations of the present disclosure.
  • CABAC Context-adaptive binary arithmetic coding
  • 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.
  • 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 (CAB AC), 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
  • CAB AC 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.
  • 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 128x128, 64x64, 32x32, and 16x16. But it should be noted that 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 partitioning types, 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 each PU 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 corresponding sample in the CU's original Cb coding block and 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.
  • video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, video encoder 20 may perform Context-Adaptive Binary Arithmetic Coding (CAB AC) on the syntax elements indicating the quantized transform coefficients.
  • CAB AC Context-Adaptive Binary Arithmetic Coding
  • 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.
  • 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.
  • palette-based coding is another coding scheme that has been adopted by many video coding standards.
  • a video coder e.g., video encoder 20 or video decoder 30
  • the palette table includes the most dominant (e.g., frequently used) pixel values in the given block. Pixel values that are not frequently represented in the video data of the given block are either not included in the palette table or included in the palette table as escape colors.
  • Each entry in the palette table includes an index for a corresponding pixel value that in the palette table.
  • the palette indices for samples in the block may be coded to indicate which entry from the palette table is to be used to predict or reconstruct which sample.
  • This palette mode starts with the process of generating a palette predictor for a first block of a picture, slice, tile, or other such grouping of video blocks.
  • the palette predictor for subsequent video blocks is typically generated by updating a previously used palette predictor.
  • the palette predictor is defined at a picture level. In other words, a picture may include multiple coding blocks, each having its own palette table, but there is one palette predictor for the entire picture.
  • a video decoder may utilize a palette predictor for determining new palette entries in the palette table used for reconstructing a video block.
  • the palette predictor may include palette entries from a previously used palette table or even be initialized with a most recently used palette table by including all entries of the most recently used palette table.
  • the palette predictor may include fewer than all the entries from the most recently used palette table and then incorporate some entries from other previously used palette tables.
  • the palette predictor may have the same size as the palette tables used for coding different blocks or may be larger or smaller than the palette tables used for coding different blocks.
  • the palette predictor is implemented as a first-in-first-out (FIFO) table including 64 palette entries.
  • a video decoder may receive, from the encoded video bitstream, a one-bit flag for each entry of the palette predictor.
  • the one-bit flag may have a first value (e.g., a binary one) indicating that the associated entry of the palette predictor is to be included in the palette table or a second value (e.g., a binary zero) indicating that the associated entry of the palette predictor is not to be included in the palette table. If the size of palette predictor is larger than the palette table used for a block of video data, then the video decoder may stop receiving more flags once a maximum size for the palette table is reached.
  • some entries in a palette table may be directly signaled in the encoded video bitstream instead of being determined using the palette predictor.
  • the video decoder may receive, from the encoded video bitstream, three separate m-bit values indicating the pixel values for the luma and two chroma components associated with the entry, where m represents the bit depth of the video data.
  • those palette entries derived from the palette predictor only require a one-bit flag. Therefore, signaling some or all palette entries using the palette predictor can significantly reduce the number of bits needed to signal the entries of a new palette table, thereby improving the overall coding efficiency of palette mode coding.
  • the palette predictor for one block is determined based on the palette table used to code one or more previously coded blocks. But when coding the first coding tree unit in a picture, a slice or a tile, the palette table of a previously coded block may not be available. Therefore a palette predictor cannot be generated using entries of the previously used palette tables. In such case, a sequence of palette predictor initializers may be signaled in a sequence parameter set (SPS) and/or a picture parameter set (PPS), which are values used to generate a palette predictor when a previously used palette table is not available.
  • SPS sequence parameter set
  • PPS picture parameter set
  • An SPS generally refers to a syntax structure of syntax elements that apply to a series of consecutive coded video pictures called a coded video sequence (CVS) as determined by the content of a syntax element found in the PPS referred to by a syntax element found in each slice segment header.
  • a PPS generally refers to a syntax structure of syntax elements that apply to one or more individual pictures within a CVS as determined by a syntax element found in each slice segment header.
  • an SPS is generally considered to be a higher level syntax structure than a PPS, meaning the syntax elements included in the SPS generally change less frequently and apply to a larger portion of video data compared to the syntax elements included in the PPS.
  • FIGS. 5A through 5B are block diagrams illustrating examples of transform efficient coding using context coding and bypass coding in accordance with some implementations of the present disclosure.
  • Transform coefficient coding in VVC is similar to that in HEVC because they both use non-overlapped coefficient groups (also called CGs or subblocks). However, there are also some differences between the two schemes.
  • each CG of coefficients has a fixed size of 4x4.
  • the CG size becomes dependent on the TB size.
  • various CG sizes (1x16, 2x8, 8x2, 2x4, 4x2 and 16x1) are available in VVC.
  • the CGs inside a coding block, and the transform coefficients within a CG are coded according to pre-defmed scan orders.
  • the area of a TB and the type of video component i.e., luma component vs. chroma component
  • the maximum number of context-coded bins is equal to TB zosize*1.15.
  • TB zosize represents the number of samples within a TB after coefficient zero-out.
  • the coded sub block flag which is a flag indicating if a CG contains non-zero coefficient or not, is not considered for CCB count.
  • Coefficient zero-out is an operation performed on a transform block to force coefficients located in a certain region of the transform block to be set to zero.
  • a 64x64 TB has an associated zero-out operation.
  • transform coefficients located outside the top-left 32x32 region of the 64x64 TB are all forced to be zero.
  • coefficient zero-out operation is performed along that dimension to force coefficients located beyond the top-left 32x32 region to be zero.
  • a variable, remBinsPassl is first set to the maximum number of context-coded bins (MCCB) allowed. During the coding process, the variable is decreased by one each time when a context-coded bin is signaled. While the remBinsPassl is larger than or equal to four, a coefficient is signaled with syntax elements including sig coeff flag, abs level gtl flag, par level flag, and abs level gt3 flag, all using context-coded bins in the first pass. The rest part of level information of the coefficient is coded with syntax element of abs remainder using Golomb-Rice code and bypass-coded bins in the second pass.
  • MCCB context-coded bins
  • VVC Unlike in HEVC where a single residual coding scheme is designed for coding both transform coefficients and transform skip coefficients, in VVC two separate residual coding schemes are employed for transform coefficients and transform skip coefficients (i.e., residuals), respectively.
  • the statistical characteristics of residuals in transform skip mode are different from those of transform coefficients and there is no energy compaction around low-frequency components.
  • the residual coding is modified to account for the different signal characteristics of the (spatial) transform skip residual which includes:
  • context modeling for the sign flag is determined based on left and above neighboring coefficient values and sign flag is parsed after sig coeff flag to keep all context coded bins together; [0091] As shown in FIG. 5B, syntax elements sig coeff flag, coeff sign Jlag, abs level gtl Jlag, par level Jlag , are coded in an interleaved manner residual sample by residual sample in the first pass, followed by abs level gtX Jag bitplanes in the second pass, and abs remainder coding in the third pass.
  • FIG. 6 is a block diagram illustrating an exemplary process of dependent scalar quantization in accordance with some implementations of the present disclosure.
  • the maximum QP value is extended from 51 to 63, and the signaling of the initial QP is changed accordingly.
  • the initial value of SliceQpY can be modified at the slice segment layer when a non-zero value of slice qp delta is coded.
  • minimum allowed QP is defined as four because quantization step size becomes one when QP is equal to one.
  • Dependent scalar quantization refers to an approach in which a set of admissible reconstruction values for a transform coefficient depends on the values of the transform coefficient levels that precede the current transform coefficient level in reconstruction order.
  • the admissible reconstruction vectors are packed denser in the N-dimensional vector space (N represents the number of transform coefficients in a transform block). That is, for a given average number of admissible reconstruction vectors per N-dimensional unit volume, the average distortion between an input vector and the closest reconstruction vector is reduced.
  • the approach of dependent scalar quantization is realized by: (a) defining two scalar quantizers with different reconstruction levels and (b) defining a process for switching between the two scalar quantizers. [0098]
  • the two scalar quantizers used, denoted by Q0 and Q1, are illustrated in FIG.
  • the location of the available reconstruction levels is uniquely specified by a quantization step size D.
  • the scalar quantizer used (Q0 or Q1) is not explicitly signaled in the bitstream. Instead, the quantizer used for a current transform coefficient is determined by the parities of the transform coefficient levels that precede the current transform coefficient in coding or reconstruction order.
  • FIG. 7 is a block diagram illustrating an exemplary state machine for switching between two different scalar quantizers in accordance with some implementations of the present disclosure.
  • the switching between the two scalar quantizers is realized via a state machine with four quantizer states (QState).
  • the QState can take four different values: 0, 1, 2, 3. It is uniquely determined by the parities of the transform coefficient levels preceding the current transform coefficient in coding/reconstruction order.
  • the state is set equal to 0.
  • the transform coefficients are reconstructed in scanning order (i.e., in the same order they are entropy decoded).
  • the state is updated as shown in FIG. 7, where k denotes the value of the transform coefficient level.
  • MatrixType : 30 2 (2 for intra&IBC/inter) x 3 (Y/Cb/Cr components) x 5
  • the DC values are separately coded for following scaling matrices: 16x16, 32x32, and 64x64. For TBs of size smaller than 8x8, all elements in one scaling matrix are signalled. If the TBs have size greater than or equal to 8x8, only 64 elements in one 8x8 scaling matrix are signalled as a base scaling matrix.
  • the 8x8 base scaling matrix is up-sampled (by duplication of elements) to the corresponding square size (i.e. 16x16, 32x32, 64x64).
  • corresponding high frequencies of the scaling matrices are also zeroed out. That is, if the width or height of the TB is greater than or equal to 32, only left or top half of the coefficients is kept, and the remaining coefficients are assigned to zero.
  • the number of elements signalled for the 64x64 scaling matrix is also reduced from 8x8 to three 4x4 submatrices, since the bottom-right 4x4 elements are never used.
  • the selected probability models depend on the sum of the absolute levels (or partially reconstructed absolute levels) in a local neighbourhood and the number of absolute levels greater than 0 (given by the number of sig coeff flags equal to 1) in the local neighbourhood.
  • the context modelling and binarization depends on the following measures for the local neighbourhood:
  • reduced 32-point MTS (also called RMTS32) is based on skipping high frequency coefficients and used to reduce computational complexity of 32- point DST-7/DCT-8. And, it accompanies coefficient coding changes including all types of zero-out (i.e., RMTS32 and the existing zero out for high frequency components in DCT2).
  • binarization of last non-zero coefficient position coding is coded based on reduced TU size, and the context model selection for the last non-zero coefficient position coding is determined by the original TU size.
  • 60 context models are used to code the sig _ coeff _flag of transform coefficients.
  • the selection of context model index is based on a sum of a maximum of five previously partially reconstructed absolute level called locSumAbsPassl and the state of dependent quantization QState as follows:
  • “slice ts residual coding disabled flag” is adopted to indicate if residual coding for transform-skip is disabled at the slice level even if the current TU is in transform-skip mode. For example, if slice ts residual coding disabled flag is equal to 1, residual coding for transform-skip is disabled while residual coding for non-transform-skip mode is invoked for the current TU. Moreover, transform coefficient in residual coding for non-transform-skip mode depends on the quantizer state (QState). But since dependent scalar quantization is exclusively applied with transform-skip mode, dependent scalar quantization should be disabled if residual coding for non-transform-skip mode is applied for the current TU with transform-skip mode.
  • QState quantizer state
  • a syntax element “ph dep quant enabled flag” is adopted to condition the presence of another syntax element “slice ts residual coding disabled flag”. Specifically, when the flag “ph dep quant enabled flag” is equal to one (i.e., the dependent quantization is enabled at the current picture), the flag “slice ts residual coding disabled flag” is not signalled but inferred to be 0. When the flag “ph dep quant enabled flag” is equal to zero, the flag “slice ts residual coding disabled flag” is signalled in the bitstream as follows:
  • a picture header syntax element [00115]
  • “ph ts residual coding disabled flag” is adopted to indicate at the picture level if residual coding for transform-skip mode is disabled. If ph ts residual coding disabled flag is equal to 1, residual coding for transform-skip is disabled for the current picture and all slices of the current picture associated with the picture header.
  • the syntax element slice ts residual coding disabled flag may still be signaled to indicate whether the residual coding for transform-skip is enabled in the current slice or not.
  • dependent scalar quantization (including the usage of dependent quantization state to derive context modeling and rice parameter used for parsing residual samples as mentioned in introduction section) is disabled if residual coding for transform-skip mode is disabled.
  • ph ts residual coding disabled flag is set to 1
  • ph dep quant enabled flag is set to be 0.
  • ph ts residual coding disabled flag is set to be 0.
  • slice ts residual coding disabled flag is set to be 0.
  • both ph dep quant enabled flag and slice ts residual coding disabled flag can be equal to 1; but the application of dependent quantization and state-dependent context model and rice parameter derivation is ignored for transform skip, e.g., checking whether the current TU is transform skip mode or not, i.e., !transform_skip_flag[ x0 ][ y0 ][ cldx ].
  • the syntax element ph ts residual coding disabled flag indicates that residual coding for transform- skip is disabled and only residual coding for non-transform-skip is invoked for the current picture and the syntax element ph ts residual coding disabled flag equal to 0 indicates that residual coding for transform-skip is applied for the current picture. If the syntax element ph ts residual coding disabled flag is not present, it is inferred to be 0.
  • the syntax element ph dep quant enabled flag equal to 0 indicates that dependent quantization is disabled for the current picture and the syntax element ph dep quant enabled flag equal to 1 indicates that dependent quantization is enabled for the current picture.
  • syntax element ph dep quant enabled flag When the syntax element ph dep quant enabled flag is not present, it is inferred to be 0.
  • the table below shows one example syntax design where the syntax element ph ts residual coding disabled flag is used to determine the presence of the syntax element ph dep quant enabled flag.
  • the dequantization method (including both dependent quantization and state-dependent context modeling and state-dependent rice-parameter derivation) is enabled for the transform skip mode.
  • the following combinations are supported by changing the values of ph dep quant enabled flag and sli ce ts re si dual coding di sabl ed fl ag : • Case One: when both two flags are equal to one, then dependent quantization is applied to transform skip mode. Meanwhile, residual coding of non-transform-skip mode is applied to transform skip TUs together with state-dependent context modeling and state-dependent rice-parameter derivation
  • variable ZeroPos[ n ] is determined by the dependent scalar quantizer state (QState) and the selected Rice parameter (cRiceParam) associated with the current coefficient at scanning position n as follows:
  • QState is switched among 4 states (state 0, state 1, state 2, and state 3) after coding each transform coefficients according to the scalar quantizer selection (Q0 and Q1) and the parity bit of k, which is the previous quantization level in the reconstruction order.
  • the dependent quantization state (Qstate) is set equal to a constant value if transform coefficient coding is invoked with transform-skip TUs in order to control variable ZeroPos[ n ] as follows:
  • the constant value of the dependent quantization (Qstate) is set equal to 0.
  • variable ZeroPos[ n ] is dependent upon transform-skip flag, Qstate, and cRiceParam as follows:
  • ZeroPos[ n ] ( QState ⁇ 2
  • variable ZeroPos[ n ] is dependent upon with Qstate, cRiceParam, and transform-skip residual coding disabled flag, ts residual coding disabled flag, which may be signaled in the sequence parameter set (SPS), picture level (e.g., parameter set (PPS), picture header), slice header, tiles group header, tile, or at CTU, CU, or TU level.
  • SPS sequence parameter set
  • PPS parameter set
  • picture header e.g., parameter set (PPS)
  • slice header e.g., tiles group header, tile, or at CTU, CU, or TU level.
  • the variable ZeroPos[ n ] is determined as follows:
  • ZeroPos[ n ] ( QState ⁇ 2
  • slice ts residual coding disabled flag can set equal to 1 if ph dep quant enabled flag is equal to 1. Therefore, in transform coefficient coding, the transform coefficient level variable TransCoeffLevel is modified with dependent quantization Qstate as follows if ph dep quant enabled flag and slice ts redisual coding disabled flag are both equal to 1.
  • the derivation of TransCoeffLevel[ x0 ][ y0 ][ cldx ][ xC ][ yC ] may be dependent from the transform-skip flag.
  • the changes to the derivation of TransCoeffLevel[ x0 ][ y0 ][ cldx ][ xC ][ yC ] is as follows:
  • the derivation of TransCoeffLevel[ x0 ][ y0 ][ cldx ][ xC ][ yC ] is dependent from the transform-skip residual coding disabled flag, ts residual coding disabled flag, which may be signaled in sequence parameter set (SPS), picture level (e.g., parameter set (PPS), picture header), slice header, tiles group header, tile, or at CTU, CU, or TU level.
  • SPS sequence parameter set
  • PPS parameter set
  • picture header e.g., parameter set (PPS), picture header
  • slice header e.g., tiles group header, tile, or at CTU, CU, or TU level.
  • TransCoeffLevel[ x0 ][ y0 ][ cldx ][ xC ][ yC ] is as follows:
  • FIGS. 8A through 8D are flowcharts illustrating exemplary processes 800 and 900, respectively, by which a video decoder decodes a current picture of a video bitstream in accordance with some implementations of the present disclosure.
  • dependent scalar quantization is exclusively applied with transform-skip mode, it should be disabled if residual coding for non-transform-skip mode is applied for the current picture with transform-skip mode.
  • the video decoder receives, from a video bitstream, a first syntax element (e.g., ph dep quant enabled flag) of a current picture (810).
  • the video decoder checks whether dependent quantization is disabled for the current picture or not according to the first syntax element (820). In accordance with a determination that dependent quantization is disabled for the current picture (820-Yes), the video decoder then receives, from the video bitstream, a second syntax element (e.g., slice ts residual coding disabled flag) of the current picture (830).
  • a first syntax element e.g., ph dep quant enabled flag
  • the video decoder sets the second syntax element to be a default value enabling transform skip residual coding under transform-skip mode for the current picture (840).
  • the video decoder then performs residual decoding and dependent dequantization to the current picture in accordance with the first syntax element and the second syntax element (850). In some embodiments, when the first syntax element is 0, the second syntax element is 1; and when the second syntax element is 1, the first syntax element is 0.
  • the video decoder when the first syntax element indicates that dependent quantization is disabled for the current picture, the video decoder disables dependent quantization for the current picture (860); when the first syntax element indicates that dependent quantization is enabled for the current picture, the video decoder enables dependent quantization for the current picture (870).
  • the video decoder when the second syntax element indicates that transform skip residual coding is enabled for the current picture under transform-skip mode, the video decoder performs transform skip residual coding under transform-skip mode to the current picture (880); and when the second syntax element indicates that transform skip residual coding is disabled for the current picture under transform-skip mode, the video decoder performs regular residual coding under transform-skip mode to the current picture (890).
  • the video decoder when the transform skip residual coding under transform-skip mode is not disabled for the current picture, receives, from the video bitstream, a third syntax element (e.g., slice ts residual coding disabled flag) indicating whether the transform skip residual coding under transform-skip mode is enabled for a current slice associated with the current picture (892); when the transform skip residual coding under transform-skip mode is disabled for the current picture, the video decoder sets the third syntax element to be a default value disabling the transform skip residual coding under transform-skip for all slices associated with the current picture (894).
  • a third syntax element e.g., slice ts residual coding disabled flag
  • the video decoder when the transform skip residual coding under transform-skip mode is disabled for the current picture, the video decoder derives context modeling and rice parameter used for parsing residual samples of the current picture independent from dependent quantization states of the residual samples of the current picture (896).
  • the video decoder derives context modeling and rice parameter used for parsing residual samples of the current picture independent from dependent quantization states of the residual samples of the current picture. In other words, there is no dependence between the derivation of context modeling and rice parameter and the usage of the dependent quantization states.
  • the video decoder receives, from a video bitstream, a control flag of a current picture (910).
  • the video decoder sets a constant value to a dependent quantization state of the transform skip coding unit (930).
  • the video decoder determines a corresponding zero-position according to the dependent quantization state and a rice parameter (950) and then decodes the coefficient according to the corresponding zero- position and the rice parameter (960).
  • FIG. 9 is a block diagram illustrating an example Context-adaptive binary arithmetic coding (CABAC) engine in accordance with some implementations of the present disclosure.
  • Context-adaptive binary arithmetic coding (CABAC) is a form of entropy coding used in many video coding standards, e.g. H.264/MPEG-4 AVC, High Efficiency Video Coding (HEVC) and VVC.
  • CABAC is based on arithmetic coding, with a few innovations and changes to adapt it to the needs of video coding standards. For example, CABAC codes binary symbols, which keeps the complexity low and allows probability modelling for more frequently used bits of any symbol. Probability models are selected adaptively based on local context, allowing better modelling of probabilities, because coding modes are usually locally well correlated.
  • CABAC uses a multiplication-free range division by the use of quantized probability ranges and probability states.
  • CABAC has multiple probability modes for different contexts. It first converts all non-binary symbols to binary. Then, for each bin (or termed bit), the coder selects which probability model to use, then uses information from nearby elements to optimize the probability estimate. Arithmetic coding is finally applied to compress the data.
  • the context modeling provides estimates of conditional probabilities of the coding symbols. Utilizing suitable context models, a given inter-symbol redundancy can be exploited by switching between different probability models according to already-coded symbols in the neighborhood of the current symbol to encode. Coding a data symbol involves the following stages.
  • Binanzation CABAC uses Binary Arithmetic Coding which means that only binary ⁇ ' decisions (I or 0) are encoded.
  • a non-binary-valued symbol e.g. a transform coefficient or motion vector
  • This process is similar to the process of converting a data symbol into a variable length code but the binary code is further encoded (by the arithmetic coder) prior to transmission. Stages are repeated for each bin (or “bit”) of the binarized symbol.
  • Context mode/ selection ⁇ A "context model” is a probability model for one or more bins of the binarized symbol. This model may be chosen from a selection of available models depending on the statistics of recently coded data symbols. The context model stores the probability of each bin being "1" or "0".
  • Arithmetic encoding An arithmetic coder encodes each bin according to the selected probability model. Note that there are just two sub-ranges for each bin (corresponding to “0” and "1").
  • Probability update The selected context model is updated based on the actual coded value (e g, if the bin value was “1", the frequency count of "1"s is increased).
  • each non-binary syntax element value By decomposing each non-binary syntax element value into a sequence of bins, further processing of each bin value in CAB AC depends on the associated coding-mode decision, which can be either chosen as the regular or the bypass mode. The latter is chosen for bins, which are assumed to be uniformly distributed and for which, consequently, the whole regular binary arithmetic encoding (and decoding) process is simply bypassed.
  • each bin value is encoded by using the regular binary arithmetic coding engine, where the associated probability model is either determined by a fixed choice, based on the type of syntax element and the bin position or bin index (binldx) in the binarized representation of the syntax element, or adaptively chosen from two or more probability models depending on the related side information (e.g. spatial neighbors, component, depth or size of CU/PU/TU, or position within TU). Selection of the probability model is referred to as context modeling. As an important design decision, the latter case is generally applied to the most frequently observed bins only, whereas the other, usually less frequently observed bins, will be treated using a joint, typically zero-order probability model. In this way,
  • CABAC enables selective adaptive probability modeling on a sub-symbol level, and hence, provides an efficient instrument for exploiting inter-symbol redundancies at significantly reduced overall modeling or learning costs. Note that for both the fixed and the adaptive case, in principle, a switch from one probability model to another can occur between any two consecutive regular coded bins.
  • the design of context models in CABAC reflects the aim to find a good compromise between the conflicting objectives of avoiding unnecessary modeling-cost overhead and exploiting the statistical dependencies to a large extent.
  • each probability model in CABAC can take one out of 126 different states with associated model probability values p ranging in the interval [0:01875;0:98125] .
  • the two parameters of each probability model are stored as 7-bit entries in a context memory: 6 bits for each of the 63 probability states representing the model probability pLPS of the least probable symbol (LPS) and 1 bit for nMPS, the value of the most probable symbol (MPS).
  • 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 communication medium such as a signal or carrier wave.
  • 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.

Abstract

L'invention concerne un appareil électronique mettant en œuvre un procédé de codage et de décodage de données vidéo. Le procédé consiste à : recevoir, en provenance d'un flux binaire vidéo, un premier élément de syntaxe d'une image courante ; conformément à une détermination selon laquelle le premier élément de syntaxe indique qu'une quantification dépendante est désactivée pour l'image courante, recevoir, en provenance du flux binaire vidéo, un second élément de syntaxe de l'image courante, le second élément de syntaxe indiquant que le codage résiduel de saut de transformée sous le mode de saut de transformée est, ou non, désactivé pour l'image courante ; conformément à une détermination selon laquelle le premier élément de syntaxe indique qu'une quantification dépendante est activée pour l'image courante, fixer le second élément de syntaxe à une valeur par défaut permettant un codage résiduel de saut de transformée sous le mode de saut de transformée pour l'image courante ; et appliquer un décodage résiduel de saut de transformée et une déquantification dépendante à l'image courante conformément au premier élément de syntaxe et au second élément de syntaxe.
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