WO2022170073A1 - Filtre de boucle adaptatif inter-composants - Google Patents

Filtre de boucle adaptatif inter-composants Download PDF

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Publication number
WO2022170073A1
WO2022170073A1 PCT/US2022/015281 US2022015281W WO2022170073A1 WO 2022170073 A1 WO2022170073 A1 WO 2022170073A1 US 2022015281 W US2022015281 W US 2022015281W WO 2022170073 A1 WO2022170073 A1 WO 2022170073A1
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WIPO (PCT)
Prior art keywords
component
video
filter
samples
block
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PCT/US2022/015281
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English (en)
Inventor
Che-Wei Kuo
Xiaoyu XIU
Yi-Wen Chen
Wei Chen
Hong-Jheng Jhu
Bing Yu
Xianglin Wang
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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 CN202280013936.0A priority Critical patent/CN116830577A/zh
Publication of WO2022170073A1 publication Critical patent/WO2022170073A1/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
    • H04N19/80—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation
    • H04N19/82—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation involving filtering within a prediction loop
    • 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
    • H04N19/117—Filters, e.g. for pre-processing or post-processing
    • 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
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component

Definitions

  • This application is related to video coding and compression, more specifically, to methods and apparatus on improving both the luma and the chroma coding efficiency.
  • 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 and receive or otherwise communicate digital video data across a communication network, and/or store the digital video data on a storage device. Due to a limited bandwidth capacity of the communication network and limited memory resources of the storage device, video coding may be used to compress the video data according to one or more video coding standards before it is communicated or stored.
  • video coding standards include Versatile Video Coding (VVC), Joint Exploration test Model (JEM), High-Efficiency Video Coding (HEVC/H.265), Advanced Video Coding (AVC/H.264), Moving Picture Expert Group (MPEG) coding, or the like.
  • VVC Versatile Video Coding
  • JEM Joint Exploration test Model
  • HEVC/H.265 High-Efficiency Video Coding
  • AVC/H.264 Advanced Video Coding
  • MPEG Moving Picture Expert Group
  • Video coding generally utilizes prediction methods (e.g., inter-prediction, intra-prediction, or the like) that take advantage of redundancy inherent in the video data.
  • Video coding aims to compress video data into a form that uses a lower bit rate, while avoiding or minimizing degradations to video quality.
  • the present application describes implementations related to video data encoding and decoding and, more particularly, to methods and apparatus on improving the coding efficiency of both luma and chroma components, including improving the coding efficiency by exploring cross-component relationship between luma and chroma components.
  • Embodiments of the present disclosure provide a loop filter called a jointcomponent adaptive loop filter (JCALF) implemented to explore the cross-component relationship between the luma and chroma components.
  • JCALF jointcomponent adaptive loop filter
  • a method of decoding video signal comprises: receiving, from the video signal, a picture frame that includes a first component and a second component; determining a first filter for the first component based on a first set of one or more samples of the second component associated with a respective sample of the first component; determining a first filtered sample value for the respective sample of the first component according to the first filter; and modifying a value of the respective sample of the first component based on the determined first filtered sample value.
  • the first component is a luma component and the second component is a first chroma component.
  • the first filter for the first component is additionally based on a second set of one or more samples of the first component associated with the respective sample of the first component.
  • the picture frame further includes a third component, and the first filter for the first component is additionally based on a third set of one or more samples of the third component associated with the respective sample of the first component.
  • the third component is a second chroma component.
  • 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 coding 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 coding video data as described above.
  • a computer readable storage medium stores therein a bitstream comprising encoded video information generated by the method for video encoding as described above.
  • FIG. 1 is a block diagram illustrating an exemplary system for encoding and decoding video blocks 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.
  • FIG. 5 is a block diagram illustrating some exemplary ALF filter shapes in accordance with some implementations of the present disclosure.
  • FIG. 6 is a block diagram illustrating some exemplary subsampled Laplacian calculations in accordance with some implementations of the present disclosure.
  • FIG. 7A is a block diagram illustrating an exemplary placement of cross-component adaptive loop filter (CC-ALF) with respect to other loop filters in accordance with some implementations of the present disclosure.
  • CC-ALF cross-component adaptive loop filter
  • FIG. 7B is a block diagram illustrating an exemplary diamond shaped filter applied by CC-ALF in accordance with some implementations of the present disclosure.
  • FIG. 8 is a block diagram illustrating an exemplary modified block classification at virtual boundaries in accordance with some implementations of the present disclosure.
  • FIGs. 9A-9C are block diagrams illustrating some exemplary modified ALF filterings for luma component at virtual boundaries in accordance with some implementations of the present disclosure.
  • FIGs. 10A-10C are block diagrams illustrating exemplary implementation of jointcomponent adaptive loop filter (JCALF) in accordance with some implementations of the present disclosure.
  • JCALF jointcomponent adaptive loop filter
  • FIG. 11 is a block diagram illustrating that JCALF can use 3 components to filter one target component in accordance with some implementations of the present disclosure.
  • FIG. 12 is a flowchart illustrating an exemplary process of decoding video signal using cross-component correlation in accordance with some implementations of the present disclosure.
  • FIG. 13 is a diagram illustrating a computing environment coupled with a user interface, according to 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.
  • the 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.
  • the source device 12 and the 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.
  • the source device 12 and the destination device 14 are equipped with wireless communication capabilities.
  • the destination device 14 may receive the encoded video data to be decoded via a link 16.
  • the link 16 may comprise any type of communication medium or device capable of moving the encoded video data from the source device 12 to the destination device 14.
  • the link 16 may comprise a communication medium to enable the source device 12 to transmit the encoded video data directly to the 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 the 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.
  • RF Radio Frequency
  • 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 the source device 12 to the destination device 14.
  • the encoded video data may be transmitted from an output interface 22 to a storage device 32. Subsequently, the encoded video data in the storage device 32 may be accessed by the destination device 14 via an input interface 28.
  • the 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, Digital Versatile Disks (DVDs), Compact Disc Read-Only Memories (CD-ROMs), flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing the encoded video data.
  • the storage device 32 may correspond to a file server or another intermediate storage device that may hold the encoded video data generated by the source device 12.
  • the destination device 14 may access the stored video data from the storage device 32 via streaming or downloading.
  • the file server may be any type of computer capable of storing the encoded video data and transmitting the encoded video data to the destination device 14.
  • Exemplary file servers include a web server (e.g., for a website), a File Transfer Protocol (FTP) server, Network Attached Storage (NAS) devices, or a local disk drive.
  • the destination device 14 may access the encoded video data through any standard data connection, including a wireless channel (e.g., a Wireless Fidelity (Wi-Fi) connection), a wired connection (e.g., Digital Subscriber Line (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 the encoded video data from the storage device 32 may be a streaming transmission, a download transmission, or a combination of both.
  • the source device 12 includes a video source 18, a video encoder 20 and the output interface 22.
  • the video source 18 may include a source such as a video capturing device, e.g., a video camera, a video archive containing previously captured video, a video feeding 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 capturing device e.g., a video camera, a video archive containing previously captured video, a video feeding 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.
  • the source device 12 and the 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 the video encoder 20.
  • the encoded video data may be transmitted directly to the destination device 14 via the output interface 22 of the source device 12.
  • the encoded video data may also (or alternatively) be stored onto the storage device 32 for later access by the destination device 14 or other devices, for decoding and/or playback.
  • the output interface 22 may further include a modem and/or a transmitter.
  • the destination device 14 includes the input interface 28, a video decoder 30, and a display device 34.
  • the input interface 28 may include a receiver and/or a modem and receive the encoded video data over the link 16.
  • the encoded video data communicated over the link 16, or provided on the storage device 32 may include a variety of syntax elements generated by the video encoder 20 for use by the 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 on a file server.
  • the destination device 14 may include the display device 34, which can be an integrated display device and an external display device that is configured to communicate with the destination device 14.
  • the 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
  • the video encoder 20 and the video decoder 30 may operate according to proprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10, AVC, or extensions of such standards. It should be understood that the present application is not limited to a specific video encoding/decoding standard and may be applicable to other video encoding/decoding standards. It is generally contemplated that the video encoder 20 of the 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 the video decoder 30 of the destination device 14 may be configured to decode video data according to any of these current or future standards.
  • the video encoder 20 and the video decoder 30 each may be implemented as any of a variety of suitable encoder and/or decoder 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 encoding/decoding operations disclosed in the present disclosure.
  • Each of the video encoder 20 and the 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.
  • CODEC 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.
  • the 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.
  • the term “frame” may be used as synonyms for the term “image” or “picture” in the field of video coding.
  • the video encoder 20 includes a video data memory 40, a prediction processing unit 41, a Decoded Picture Buffer (DPB) 64, a summer 50, a transform processing unit 52, a quantization unit 54, and an entropy encoding unit 56.
  • the prediction processing unit 41 further includes a motion estimation unit 42, a motion compensation unit 44, a partition unit 45, an intra prediction processing unit 46, and an intra Block Copy (BC) unit 48.
  • the video encoder 20 also includes an inverse quantization unit 58, an inverse transform processing unit 60, and a summer 62 for video block reconstruction.
  • An in-loop filter 63 such as a deblocking filter, may be positioned between the summer 62 and the DPB 64 to filter block boundaries to remove blocky artifacts from reconstructed video.
  • Another in-loop filter such as Sample Adaptive Offset (SAO) filter and/or Adaptive in-Loop Filter (ALF), may also be used in addition to the deblocking filter to filter an output of the summer 62.
  • the in-loop filters may be omitted, and the decoded video block may be directly provided by the summer 62 to the DPB 64.
  • the 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.
  • the video data memory 40 may store video data to be encoded by the components of the video encoder 20.
  • the video data in the video data memory 40 may be obtained, for example, from the video source 18 as shown in FIG. 1.
  • the DPB 64 is a buffer that stores reference video data (for example, reference frames or pictures) for use in encoding video data by the video encoder 20 (e.g., in intra or inter predictive coding modes).
  • the video data memory 40 and the DPB 64 may be formed by any of a variety of memory devices.
  • the video data memory 40 may be on-chip with other components of the video encoder 20, or off-chip relative to those components.
  • the partition unit 45 within the prediction processing unit 41 partitions the video data into video blocks.
  • This partitioning may also include partitioning a video frame into slices, tiles (for example, sets of video blocks), or other larger Coding Units (CUs) according to predefined splitting structures such as a Quad- Tree (QT) structure associated with the video data.
  • the video frame is or may be regarded as a two-dimensional array or matrix of samples with sample values.
  • a sample in the array may also be referred to as a pixel or a pel.
  • a number of samples in horizontal and vertical directions (or axes) of the array or picture define a size and/or a resolution of the video frame.
  • the video frame may be divided into multiple video blocks by, for example, using QT partitioning.
  • the video block again is or may be regarded as a two-dimensional array or matrix of samples with sample values, although of smaller dimension than the video frame.
  • a number of samples in horizontal and vertical directions (or axes) of the video block define a size of the video block.
  • the video block may further be partitioned into one or more block partitions or sub-blocks (which may form again blocks) by, for example, iteratively using QT partitioning, Binary-Tree (BT) partitioning or Triple-Tree (TT) partitioning or any combination thereof.
  • BT Binary-Tree
  • TT Triple-Tree
  • block or video block may be a portion, in particular a rectangular (square or non- square) portion, of a frame or a picture.
  • the block or video block may be or correspond to a Coding Tree Unit (CTU), a CU, a Prediction Unit (PU) or a Transform Unit (TU) and/or may be or correspond to a corresponding block, e.g., a Coding Tree Block (CTB), a Coding Block (CB), a Prediction Block (PB) or a Transform Block (TB) and/or to a sub-block.
  • CTU Coding Tree Unit
  • PU Prediction Unit
  • TU Transform Unit
  • a corresponding block e.g., a Coding Tree Block (CTB), a Coding Block (CB), a Prediction Block (PB) or a Transform Block (TB) and/or to a sub-block.
  • CTB Coding Tree Block
  • PB Prediction Block
  • TB Transform Block
  • the 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).
  • the prediction processing unit 41 may provide the resulting intra or inter prediction coded block to the summer 50 to generate a residual block and to the summer 62 to reconstruct the encoded block for use as part of a reference frame subsequently.
  • the prediction processing unit 41 also provides syntax elements, such as motion vectors, intramode indicators, partition information, and other such syntax information, to the entropy encoding unit 56.
  • the intra prediction processing unit 46 within the prediction processing unit 41 may perform intra predictive coding of the current video block relative to one or more neighbor blocks in the same frame as the current block to be coded to provide spatial prediction.
  • the motion estimation unit 42 and the motion compensation unit 44 within the 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.
  • the video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.
  • the 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 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 the motion estimation unit 42, is the process of generating motion vectors, which estimate motion for video blocks.
  • a motion vector for example, may indicate the displacement of a video block within a current video frame or picture relative to a predictive block within a reference frame relative to the current block being coded within the current frame.
  • the predetermined pattern may designate video frames in the sequence as P frames or B frames.
  • the 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 the motion estimation unit 42 for inter prediction, or may utilize the motion estimation unit 42 to determine the block vector.
  • a predictive block for the video block may be or may correspond to a block or a reference block of a reference frame that is deemed as closely matching 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.
  • the video encoder 20 may calculate values for sub-integer pixel positions of reference frames stored in the DPB 64. For example, the 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, the 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.
  • the motion estimation unit 42 calculates a motion vector for a video block in an inter prediction coded frame by comparing the position of the video block 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 the DPB 64.
  • the motion estimation unit 42 sends the calculated motion vector to the motion compensation unit 44 and then to the entropy encoding unit 56.
  • Motion compensation performed by the motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by the motion estimation unit 42.
  • the 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 the DPB 64, and forward the predictive block to the summer 50.
  • the summer 50 then forms a residual video block of pixel difference values by subtracting pixel values of the predictive block provided by the motion compensation unit 44 from the pixel values of the current video block being coded.
  • the pixel difference values forming the residual video block may include luma or chroma difference components or both.
  • the motion compensation unit 44 may also generate syntax elements associated with the video blocks of a video frame for use by the 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 the motion estimation unit 42 and the motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.
  • the intra BC unit 48 may generate vectors and fetch predictive blocks in a manner similar to that described above in connection with the motion estimation unit 42 and the 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.
  • the intra BC unit 48 may determine an intra-prediction mode to use to encode a current block.
  • the 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.
  • the 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. For example, the 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.
  • Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded
  • the intra BC unit 48 may use the motion estimation unit 42 and the 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 SAD, SSD, or other difference metrics, and identification of the predictive block may include calculation of values for sub- integer pixel positions.
  • the 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.
  • the intra prediction processing unit 46 may intra-predict a current video block, as an alternative to the inter-prediction performed by the motion estimation unit 42 and the motion compensation unit 44, or the intra block copy prediction performed by the intra BC unit 48, as described above. In particular, the intra prediction processing unit 46 may determine an intra prediction mode to use to encode a current block.
  • the intra prediction processing unit 46 may encode a current block using various intra prediction modes, e.g., during separate encoding passes, and the intra prediction processing unit 46 (or a mode selection unit, in some examples) may select an appropriate intra prediction mode to use from the tested intra prediction modes.
  • the intra prediction processing unit 46 may provide information indicative of the selected intra-prediction mode for the block to the entropy encoding unit 56.
  • the entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode in the bitstream.
  • the 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 TUs and is provided to the transform processing unit 52.
  • the 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
  • the transform processing unit 52 may send the resulting transform coefficients to the quantization unit 54.
  • the quantization unit 54 quantizes the transform coefficients to further reduce the 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.
  • the quantization unit 54 may then perform a scan of a matrix including the quantized transform coefficients.
  • the entropy encoding unit 56 may perform the scan.
  • the 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 (SB AC), 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
  • SB AC Syntax -based context-adaptive Binary Arithmetic Coding
  • PIPE Probability Interval Partitioning Entropy
  • the encoded bitstream may then be transmitted to the video decoder 30 as shown in FIG. 1, or archived in the storage device 32 as shown in FIG. 1 for later transmission to or retrieval by the video decoder 30.
  • the entropy encoding unit 56 may also
  • the inverse quantization unit 58 and the 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.
  • the motion compensation unit 44 may generate a motion compensated predictive block from one or more reference blocks of the frames stored in the DPB 64.
  • the 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.
  • the summer 62 adds the reconstructed residual block to the motion compensated predictive block produced by the motion compensation unit 44 to produce a reference block for storage in the DPB 64.
  • the reference block may then be used by the intra BC unit 48, the motion estimation unit 42 and the 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.
  • the video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, a summer 90, and a DPB 92.
  • the prediction processing unit 81 further includes a motion compensation unit 82, an intra prediction unit 84, and an intra BC unit 85.
  • the video decoder 30 may perform a decoding process generally reciprocal to the encoding process described above with respect to the video encoder 20 in connection with FIG. 2.
  • the motion compensation unit 82 may generate prediction data based on motion vectors received from the entropy decoding unit 80, while the intra-prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from the entropy decoding unit 80.
  • a unit of the 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 the video decoder 30.
  • the intra BC unit 85 may perform the implementations of the present application, alone, or in combination with other units of the video decoder 30, such as the motion compensation unit 82, the intra prediction unit 84, and the entropy decoding unit 80.
  • the video decoder 30 may not include the intra BC unit 85 and the functionality of intra BC unit 85 may be performed by other components of the prediction processing unit 81, such as the motion compensation unit 82.
  • the video data memory 79 may store video data, such as an encoded video bitstream, to be decoded by the other components of the video decoder 30.
  • the video data stored in the video data memory 79 may be obtained, for example, from the 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).
  • the video data memory 79 may include a Coded Picture Buffer (CPB) that stores encoded video data from an encoded video bitstream.
  • the DPB 92 of the video decoder 30 stores reference video data for use in decoding video data by the video decoder 30 (e.g., in intra or inter predictive coding modes).
  • the video data memory 79 and the 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
  • the video data memory 79 and the DPB 92 are depicted as two distinct components of the video decoder 30 in FIG. 3. But it will be apparent to one skilled in the art that the video data memory 79 and the DPB 92 may be provided by the same memory device or separate memory devices.
  • the video data memory 79 may be on-chip with other components of the video decoder 30, or off-chip relative to those components.
  • the video decoder 30 receives an encoded video bitstream that represents video blocks of an encoded video frame and associated syntax elements.
  • the video decoder 30 may receive the syntax elements at the video frame level and/or the video block level.
  • the entropy decoding unit 80 of the video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements.
  • the entropy decoding unit 80 then forwards the motion vectors or intra-prediction mode indicators and other syntax elements to the prediction processing unit 81.
  • the intra prediction unit 84 of the 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.
  • the motion compensation unit 82 of the 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 the entropy decoding unit 80.
  • Each of the predictive blocks may be produced from a reference frame within one of the reference frame lists.
  • the video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference frames stored in the DPB 92.
  • the intra BC unit 85 of the prediction processing unit 81 produces predictive blocks for the current video block based on block vectors and other syntax elements received from the entropy decoding unit 80.
  • the predictive blocks may be within a reconstructed region of the same picture as the current video block defined by the video encoder 20.
  • the motion compensation unit 82 and/or the 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, the 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
  • the 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 the 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
  • the motion compensation unit 82 may also perform interpolation using the interpolation filters as used by the video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, the motion compensation unit 82 may determine the interpolation filters used by the video encoder 20 from the received syntax elements and use the interpolation filters to produce predictive blocks.
  • the inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by the entropy decoding unit 80 using the same quantization parameter calculated by the video encoder 20 for each video block in the video frame to determine a degree of quantization.
  • the 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.
  • the summer 90 reconstructs decoded video block for the current video block by summing the residual block from the inverse transform processing unit 88 and a corresponding predictive block generated by the motion compensation unit 82 and the intra BC unit 85.
  • An in-loop filter 91 such as deblocking filter, SAO filter and/or ALF may be positioned between the summer 90 and the DPB 92 to further process the decoded video block.
  • the in-loop filter 91 may be omitted, and the decoded video block may be directly provided by the summer 90 to the DPB 92.
  • the decoded video blocks in a given frame are then stored in the DPB 92, which stores reference frames used for subsequent motion compensation of next video blocks.
  • the DPB 92, or a memory device separate from the DPB 92, may also store decoded video for later presentation on a display device, such as the 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.
  • the video encoder 20 (or more specifically the partition unit 45) generates an encoded representation of a frame by first partitioning the frame into a set of 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 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.
  • the video encoder 20 may recursively perform tree partitioning such as binary-tree partitioning, ternary-tree partitioning, quad-tree partitioning or a combination thereof on the coding tree blocks of the CTU and divide the CTU into smaller CUs.
  • tree partitioning such as binary-tree partitioning, ternary-tree partitioning, quad-tree partitioning or a combination thereof on the coding tree blocks of the CTU and divide the CTU into smaller CUs.
  • the 64x64 CTU 400 is first divided into four smaller CUs, 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 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.
  • a CU may comprise a single coding block and syntax structures used to code the samples of the coding block.
  • 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.
  • the video encoder 20 may further partition a coding block of a CU into one or more MxN PBs.
  • a PB is a rectangular (square or non-square) block of samples on which the same prediction, inter or intra, is applied.
  • a PU of a CU may comprise a PB of luma samples, two corresponding PBs of chroma samples, and syntax elements used to predict the PBs. In monochrome pictures or pictures having three separate color planes, a PU may comprise a single PB and syntax structures used to predict the PB.
  • the video encoder 20 may generate predictive luma (Y), Cb, and Cr blocks for luma, Cb, and Cr PBs of each PU of the CU.
  • the video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If the video encoder 20 uses intra prediction to generate the predictive blocks of a PU, the video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the frame associated with the PU. If the video encoder 20 uses inter prediction to generate the predictive blocks of a PU, the 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.
  • the 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.
  • the 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.
  • the 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 respectively.
  • a transform block is a rectangular (square or nonsquare) block of samples on which the same transform is applied.
  • a 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.
  • the 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.
  • the 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.
  • the 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.
  • the 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.
  • the video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, the video encoder 20 may perform CABAC on the syntax elements indicating the quantized transform coefficients.
  • the 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 the storage device 32 or transmitted to the destination device 14.
  • the video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream.
  • the 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 the video encoder 20.
  • the 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.
  • the 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.
  • video coding achieves video compression using primarily two modes, i.e., intra-frame prediction (or intra-prediction) and inter-frame prediction (or interprediction). It is noted that IBC could be regarded as either intra-frame prediction or a third mode. Between the two modes, inter-frame prediction contributes more to the coding efficiency than intra-frame prediction because of the use of motion vectors for predicting a current video block from a reference video block.
  • motion information of spatially neighboring CUs and/or temporally co-located CUs as an approximation of the motion information (e.g., motion vector) of a current CU by exploring their spatial and temporal correlation, which is also referred to as “Motion Vector Predictor (MVP)” of the current CU.
  • MVP Motion Vector Predictor
  • the motion vector predictor of the current CU is subtracted from the actual motion vector of the current CU to produce a Motion Vector Difference (MVD) for the current CU.
  • MVD Motion Vector Difference
  • a set of rules need to be adopted by both the video encoder 20 and the video decoder 30 for constructing a motion vector candidate list (also known as a “merge list”) for a current CU using those potential candidate motion vectors associated with spatially neighboring CUs and/or temporally co-located CUs of the current CU and then selecting one member from the motion vector candidate list as a motion vector predictor for the current CU.
  • a motion vector candidate list also known as a “merge list”
  • an adaptive loop filter with block-based filter adaption is applied.
  • ALF adaptive loop filter
  • FIG. 5 is a block diagram illustrating some exemplary ALF filter shapes in accordance with some implementations of the present disclosure.
  • two diamond filter shapes are used.
  • the 5x5 diamond shape (left) is applied for chroma components and the 7 ⁇ 7 diamond shape (right) is applied for luma component.
  • block classification is implemented.
  • each 4 ⁇ 4 block is categorized into one of 25 classes.
  • the classification index C is derived based on its directionality D and a quantized value of activity ⁇ , as follows:
  • indices i and j refer to the coordinates of the upper left sample within the 4 ⁇ 4 block and R(i,j) indicates a reconstructed sample at coordinate (i,j).
  • FIG. 6 is a block diagram illustrating some exemplary subsampled Laplacian calculations in accordance with some implementations of the present disclosure, (a) shows subsampled positions for vertical gradient, (b) shows subsampled positions for horizontal gradient, (c) shows subsampled positions for diagonal gradient, (d) shows subsampled positions for diagonal gradient.
  • the subsampled 1-D Laplacian calculation is applied. As shown in FIG. 6, the same subsampled positions are used for gradient calculation of all directions. [0091] Then D maximum and minimum values of the gradients of horizontal and vertical directions are set as:
  • Step 1 If both and are true, D is set to 0.
  • Step 2 If , continue from Step 3; otherwise continue from Step 4.
  • Step 3 If , D is set to 2; otherwise D is set to 1. Step 4. If , D is set to 4; otherwise D is set to 3.
  • the activity value A is calculated as:
  • A is further quantized to the range of 0 to 4, inclusively, and the quantized value is denoted as A.
  • Table 1 Exemplary mapping of the gradient calculated for one block and the transformations.
  • each sample R(i,j) within the CU is filtered, resulting in sample value R'(i,j) as shown below, where f(k,l) denotes the decoded filter coefficients, K(x,y) is the clipping function and c(k,l) denotes the decoded clipping parameters.
  • the variable k and 1 vary between and where L denotes the filter length.
  • the clipping function K(x,y') min(y, max(—y,x)) corresponds to the function Clip3 (— y, y, x).
  • the clipping operation introduces nonlinearity to make ALF more efficient by reducing the impact of neighbor sample values that are too different from the current sample value.
  • cross-component adaptive loop filter uses luma- sample values to refine each chroma component by applying an adaptive, linear filter to the luma channel and then using the output of this filtering operation for chroma refinement.
  • FIG. 7A is a block diagram illustrating an exemplary placement of CC-ALF with respect to other loop filters in accordance with some implementations of the present disclosure.
  • FIG. 7A provides a system-level diagram of the CC-ALF process with respect to the SAO, luma ALF and chroma ALF processes.
  • FIG. 7B is a block diagram illustrating an exemplary diamond shaped filter applied by CC-ALF in accordance with some implementations of the present disclosure.
  • Filtering in CC-ALF is accomplished by applying a linear, diamond-shaped filter to the luma channel.
  • One filter is used for each chroma channel, and the operation is expressed as where (x,y) is the chroma component i location being refined, (x Y ,y Y ) is the luma location based on (x,y) , S i is the filter support area in the luma component, and c i (x 0 ,y 0 ) represents the filter coefficients.
  • the luma-filter support is the region collocated with the current chroma sample after accounting for the spatial scaling factor between the luma and chroma planes.
  • CC-ALF filter coefficients are computed by minimizing the mean square error of each chroma channel with respect to the original chroma content.
  • the VTM algorithm uses a coefficient derivation process similar to the one used for chroma ALF. Specifically, a correlation matrix is derived, and the coefficients are computed using a Cholesky decomposition solver in an attempt to minimize a mean-square error metric.
  • a maximum of 8 CC-ALF filters can be designed and transmitted per picture. The resulting filters are then indicated for each of the two chroma channels on a CTU basis.
  • CC-ALF Additional characteristics include:
  • the design uses a 3 ⁇ 4 diamond shape with 8 taps.
  • Each of the transmitted coefficients has a 6-bit dynamic range and is restricted to power- of-2 values.
  • the eighth filter coefficient is derived at the decoder such that the sum of the filter coefficients is equal to 0.
  • An APS may be referenced in the slice header.
  • CC-ALF filter selection is controlled at CTU-level for each chroma component.
  • Boundary padding for the horizontal virtual boundaries uses the same memory access pattern as luma ALF.
  • the reference encoder can be configured to enable some basic subjective tuning through the configuration file.
  • the VTM attenuates the application of CC-ALF in regions that are coded with high Quantization Parameter (QP) and are either near-mid-grey or contain a large amount of luma high frequencies. Algorithmically, this is accomplished by disabling the application of CC-ALF in CTUs where any of the following conditions are true:
  • QP Quantization Parameter
  • the slice QP value minus 1 is less than or equal to the base QP value.
  • ALF filter parameters are signalled in the adaptation parameter set (APS).
  • APS adaptation parameter set
  • up to 25 sets of luma-filter coefficients and clipping-value indexes, and up to 8 sets of chroma-filter coefficients and clipping-value indexes could be signalled.
  • filter coefficients of different classifications for the luma component can be merged.
  • the indices of the APSs used for the current slice are signaled.
  • Clipping-value indexes which are decoded from the APS, allow determining clipping values using a table of clipping values for both luma and chroma components. These clipping values are dependent on the internal bitdepth. More precisely, the clipping values are obtained by the following formula: with B equal to the internal bitdepth, ⁇ is a predefined constant value equal to 2.35, and N equal to 4, which is the number of allowed clipping values in VVC. The AlfClip is then rounded to the nearest value with the format of power of 2.
  • APS indices can be signaled to specify the luma-filter sets that are used for the current slice.
  • the filtering process can be further controlled at the CTB level.
  • a flag is always signalled to indicate whether ALF is applied to a luma CTB.
  • a luma CTB can choose a filter set among 16 fixed filter sets and the filter sets from APSs.
  • a filter-set index is signaled for a luma CTB to indicate which filter set is applied.
  • the 16 fixed filter sets are predefined and hard-coded in both the encoder and the decoder.
  • an APS index is signaled in the slice header to indicate the chroma-filter sets being used for the current slice.
  • a filter index is signaled for each chroma CTB if there is more than one chroma-filter set in the APS.
  • the filter coefficients are quantized with a norm equal to 128.
  • a bitstream conformance is applied so that the coefficient value of the noncentral position is in the range of -2 7 to 2 7 - 1, inclusive.
  • the central position coefficient is not signalled in the bitstream and is considered as equal to 128.
  • FIG. 8 is a block diagram illustrating an exemplary modified block classification at virtual boundaries in accordance with some implementations of the present disclosure.
  • VVC to reduce the line buffer requirement of ALF, modified block classification and filtering are employed for the samples near horizontal CTU boundaries.
  • a virtual boundary is defined as a line by shifting the horizontal CTU boundary with “N” samples as shown in FIG. 8, with N equal to 4 for the Luma component and 2 for the Chroma component.
  • Modified block classification is applied for the luma component as depicted in FIG. 8.
  • the ID Laplacian gradient calculation of the 4x4 block below the virtual boundary only the samples below the virtual boundary are used.
  • the quantization of activity value A is accordingly scaled by taking into account the reduced number of samples used in ID Laplacian gradient calculation.
  • FIGs. 9A-9C are block diagrams illustrating some exemplary modified ALF filterings for luma component at virtual boundaries in accordance with some implementations of the present disclosure. As shown in FIGs. 9A-9C, when the sample being filtered is located below the virtual boundary, the neighboring samples that are located above the virtual boundary are padded. Meanwhile, the corresponding samples at the other sides are also padded, symmetrically.
  • a simple padding process is applied for slice, tile and subpicture boundaries when the filter across the boundaries is disabled.
  • the simple padding process is also applied at the picture boundary.
  • the padded samples are used for both the classification and filtering process. To compensate for the extreme padding when filtering samples just above or below the virtual boundary, the filter strength is reduced for those cases for both luma and chroma by increasing the right shift in equation 1-12 by 3.
  • chroma ALF and CC-ALF design in the VVC standard only one component is used to filter or refine another component.
  • luma ALF uses luma samples to filter luma samples
  • CC-ALF uses luma samples to filter/refine Cb or Cr samples per time.
  • this one-to-one filtering 1) requires many similar functionality control flags or filter coefficients signaling, which introduces signalling overhead, and 2) the information of only one component is taken into account during coefficient derivation, which may lead to suboptimal coefficient results since not only luma components can bring information to chroma components, chroma components can also bring information to luma components.
  • JCALF joint-component adaptive loop filter
  • FIGs. 10 A- 10C are block diagrams illustrating exemplary implementation of JCALF in accordance with some implementations of the present disclosure. Specifically, FIGs. 10A-10C illustrates using at least 1, max 3 components as input to derive at least 1, maximum 3 component filter coefficients. FIGs. 10A and 10B illustrates using JCALF, all or any component can work independently with other modules. FIG. 10C illustrates using JCALF, all or any component can work in parallel with other modules, for example, luma and chroma ALF as in the FIGs 10 A- 10C, or CC-ALF.
  • FIG. 11 is a block diagram illustrating that JCALF can use 3 components to filter one target component in accordance with some implementations of the present disclosure.
  • JCALF can use 3 components’ current/collocated and neighboring samples per time to filter one target component (Y/Cb/Cr).
  • the filter shape can be fixed or signaled/ switched in one or more of Sequence Parameter Set (SPS), Adaptation Parameter Set (APS), Picture Parameter Set (PPS), Picture Header (PH), Slice Header (SH), region, Coding Tree Unit (CTU), Coding Unit (CU), and subblock levels.
  • SPS Sequence Parameter Set
  • PPS Picture Parameter Set
  • PPS Picture Header
  • SH Slice Header
  • region Coding Tree Unit
  • CTU Coding Unit
  • CU Coding Unit
  • subblock levels subblock levels.
  • Each of the different target components can share the same source component shape as shown in FIG. 11, or has its own different shape.
  • Plural filter sets i.e., shape/coefficient
  • Table 2 Exemplary plural filter sets (i.e., shape/coefficient) can be used in the same picture frame.
  • the filtered value in the filtering process, can replace the current component reconstructed value as in FIG. 10A and/or FIG. 10B.
  • the filtered value is derived as: where (x,y) is the current luma or chroma component i location being refined, (x j ,y j ) is the source j component (Y, Cb, Cr) location (current or collocated) based on (x,y), (x 0 ,y 0 ) is the neighboring sample distance, is the filter support area (filter shape) in the source component, and c ji (x 0 ,y 0 ) represents the filter coefficients.
  • the filtered value in the filtering process, can be a delta value added to the current sample as in FIG. 10C.
  • the filtered value is derived as:
  • EGk exponential-golomb code with order k, where k can be fixed
  • FIG. 12 is a flowchart illustrating an exemplary process 1200 of decoding video signal using cross-component correlation in accordance with some implementations of the present disclosure.
  • the video decoder 30 receives, from the video signal, a picture frame that includes a first component and a second component (1210).
  • the video decoder 30 determines a first filter for the first component based on a first set of one or more samples of the second component associated with a respective sample of the first component.
  • the first component is a luma component and the second component is a first chroma component (1220).
  • the video decoder 30 determines a first filtered sample value for the respective sample of the first component according to the first filter (1230).
  • the video decoder 30 additionally modifies a value of the respective sample of the first component based on the determined first filtered sample value (1240).
  • the first filter for the first component is additionally based on a second set of one or more samples of the first component associated with the respective sample of the first component (1250).
  • the picture frame further includes a third component, and wherein the first filter for the first component is additionally based on a third set of one or more samples of the third component associated with the respective sample of the first component, wherein the third component is a second chroma component (1260).
  • the video decoder 30 further determines a second filter for the second component based on a fourth set of one or more samples of the third component associated with a respective sample of the second component, determines a second filtered sample value for the respective sample of the second component according to the second filter, and modifies a value of the respective sample of the second component based on the determined second filtered sample value.
  • modifying the value of the respective sample of the first component based on the determined first filtered sample value (1240) includes replacing the value of the respective sample of the first component by the determined first filtered sample value.
  • the first set of one or more samples of the second component associated with the respective sample of the first component is the output from an in-loop filter, and the respective sample of the first component is the output from the in-loop filter, wherein the in-loop filter is sample adaptive offset (SAO).
  • SAO sample adaptive offset
  • modifying the value of the respective sample of the first component based on the determined first filtered sample value (1240) includes adding the determined first filtered sample value to the value of the respective sample of the first component.
  • the value of the respective sample of the first component is an output from an in-loop filter
  • the in-loop filter is an adaptive in-loop filter (ALF).
  • the first set of one or more samples of the second component associated with the respective sample of the first component is selected from one or more of collocated and neighboring samples of the second component relative to the respective sample of the first component.
  • the third set of one or more samples of the third component associated with the respective sample of the first component is selected from one or more of collocated and neighboring samples of the third component relative to the respective sample of the first component.
  • the second set of one or more samples of the first component associated with the respective sample of the first component is selected from one or more of current and neighboring samples of the first component relative to the respective sample of the first component.
  • the first filter has a joint filter shape comprising a first sub- filter shape based on the first set of one or more samples of the second component, a second sub-filter shape based on the second set of one or more samples of the first component, and a third sub-filter shape based on the third set of one or more samples of the third component
  • the joint filter shape is fixed or signalled in one or more of Sequence Parameter Set (SPS), Adaptation Parameter Set (APS), Picture Parameter Set (PPS), Picture Header (PH), Slice Header (SH), region, Coding Tree Unit (CTU), Coding Unit (CU), and subblock levels.
  • SPS Sequence Parameter Set
  • APS Adaptation Parameter Set
  • PPS Picture Parameter Set
  • PH Picture Header
  • SH Slice Header
  • region Coding Tree Unit
  • CTU Coding Tree Unit
  • CU Coding Unit
  • one or more filter shapes are present in the picture frame.
  • the first filter is an adaptive loop filter.
  • FIG. 13 shows a computing environment 1310 coupled with a user interface 1350.
  • the computing environment 1310 can be part of a data processing server.
  • the computing environment 1310 includes a processor 1320, a memory 1330, and an Input/Output (I/O) interface 1340.
  • I/O Input/Output
  • the processor 1320 typically controls overall operations of the computing environment 1310, such as the operations associated with display, data acquisition, data communications, and image processing.
  • the processor 1320 may include one or more processors to execute instructions to perform all or some of the steps in the above-described methods.
  • the processor 1320 may include one or more modules that facilitate the interaction between the processor 1320 and other components.
  • the processor may be a Central Processing Unit (CPU), a microprocessor, a single chip machine, a Graphical Processing Unit (GPU), or the like.
  • the memory 1330 is configured to store various types of data to support the operation of the computing environment 1310.
  • the memory 1330 may include predetermined software 1332. Examples of such data includes instructions for any applications or methods operated on the computing environment 1310, video datasets, image data, etc.
  • the memory 1330 may be implemented by using any type of volatile or non-volatile memory devices, or a combination thereof, such as a Static Random Access Memory (SRAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), an Erasable Programmable Read- Only Memory (EPROM), a Programmable Read-Only Memory (PROM), a Read-Only Memory (ROM), a magnetic memory, a flash memory, a magnetic or optical disk.
  • SRAM Static Random Access Memory
  • EEPROM Electrically Erasable Programmable Read-Only Memory
  • EPROM Erasable Programmable Read- Only Memory
  • PROM Programmable Read-Only Memory
  • ROM Read-Only Memory
  • magnetic memory a magnetic memory
  • flash memory
  • the I/O interface 1340 provides an interface between the processor 1320 and peripheral interface modules, such as a keyboard, a click wheel, buttons, and the like.
  • the buttons may include but are not limited to, a home button, a start scan button, and a stop scan button.
  • the I/O interface 1340 can be coupled with an encoder and decoder.
  • a non-transitory computer-readable storage medium comprising a plurality of programs, for example, in the memory 1330, executable by the processor 1320 in the computing environment 1310, for performing the above-described methods.
  • the non-transitory computer-readable storage medium may have stored therein a bitstream or a data stream comprising encoded video information (for example, video information comprising one or more syntax elements) generated by an encoder (for example, the video encoder 20 in FIG. 2) using, for example, the encoding method described above for use by a decoder (for example, the video decoder 30 in FIG. 3) in decoding video data.
  • the non-transitory computer-readable storage medium may be, for example, a ROM, a Random Access Memory (RAM), a CD-ROM, a magnetic tape, a floppy disc, an optical data storage device or the like.
  • the is also provided a computing device comprising one or more processors (for example, the processor 1320); and the non-transitory computer-readable storage medium or the memory 1330 having stored therein a plurality of programs executable by the one or more processors, wherein the one or more processors, upon execution of the plurality of programs, are configured to perform the above-described methods.
  • processors for example, the processor 1320
  • non-transitory computer-readable storage medium or the memory 1330 having stored therein a plurality of programs executable by the one or more processors, wherein the one or more processors, upon execution of the plurality of programs, are configured to perform the above-described methods.
  • a computer program product comprising a plurality of programs, for example, in the memory 1330, executable by the processor 1320 in the computing environment 1310, for performing the above-described methods.
  • the computer program product may include the non-transitory computer-readable storage medium.
  • the computing environment 1310 may be implemented with one or more ASICs, DSPs, Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), FPGAs, GPUs, controllers, micro-controllers, microprocessors, or other electronic components, for performing the above methods.
  • ASICs application-specific integrated circuits
  • DSPs Digital Signal Processing Devices
  • PLDs Programmable Logic Devices
  • FPGAs field-programmable Logic Devices
  • GPUs GPUs
  • controllers micro-controllers
  • microprocessors microprocessors, or other electronic components, for performing the above methods.
  • 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.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

Appareil électronique qui réalise un procédé de décodage de données vidéo. Le procédé consiste : à recevoir, à partir du signal vidéo, une trame d'image qui comprend un premier composant et un deuxième composant ; à déterminer un filtre pour le premier composant sur la base d'un premier ensemble d'un ou de plusieurs échantillons du second composant associé à un échantillon respectif du premier composant ; à déterminer une première valeur d'échantillon filtrée pour l'échantillon respectif du premier composant selon le filtre ; et à modifier une valeur de l'échantillon respectif du premier composant sur la base de la première valeur d'échantillon filtrée déterminée. Le premier composant est un composant luma et le second composant est un premier composant chroma. Dans certains modes de réalisation, le filtre pour le premier composant est en outre basé sur un second ensemble d'un ou de plusieurs échantillons du premier composant associé à l'échantillon respectif du premier composant.
PCT/US2022/015281 2021-02-08 2022-02-04 Filtre de boucle adaptatif inter-composants WO2022170073A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170188000A1 (en) * 2015-12-23 2017-06-29 Canon Kabushiki Kaisha Method, apparatus and system for determining a luma value
US10419757B2 (en) * 2016-08-31 2019-09-17 Qualcomm Incorporated Cross-component filter
US20200404341A1 (en) * 2012-09-28 2020-12-24 Interdigital Madison Patent Holdings, Sas Cross-plane filtering for chroma signal enhancement in video coding
WO2020259538A1 (fr) * 2019-06-27 2020-12-30 Mediatek Inc. Procédé et appareil de filtrage à boucle adaptatif inter-composantes de codage vidéo
WO2020262396A1 (fr) * 2019-06-24 2020-12-30 Sharp Kabushiki Kaisha Systèmes et procédés permettant de réduire une erreur de reconstruction dans un codage vidéo sur la base d'une corrélation inter-composantes

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20200404341A1 (en) * 2012-09-28 2020-12-24 Interdigital Madison Patent Holdings, Sas Cross-plane filtering for chroma signal enhancement in video coding
US20170188000A1 (en) * 2015-12-23 2017-06-29 Canon Kabushiki Kaisha Method, apparatus and system for determining a luma value
US10419757B2 (en) * 2016-08-31 2019-09-17 Qualcomm Incorporated Cross-component filter
WO2020262396A1 (fr) * 2019-06-24 2020-12-30 Sharp Kabushiki Kaisha Systèmes et procédés permettant de réduire une erreur de reconstruction dans un codage vidéo sur la base d'une corrélation inter-composantes
WO2020259538A1 (fr) * 2019-06-27 2020-12-30 Mediatek Inc. Procédé et appareil de filtrage à boucle adaptatif inter-composantes de codage vidéo

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