WO2022178433A1 - Compensation d'éclairage local améliorée pour prédiction inter-composantes - Google Patents

Compensation d'éclairage local améliorée pour prédiction inter-composantes Download PDF

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Publication number
WO2022178433A1
WO2022178433A1 PCT/US2022/017342 US2022017342W WO2022178433A1 WO 2022178433 A1 WO2022178433 A1 WO 2022178433A1 US 2022017342 W US2022017342 W US 2022017342W WO 2022178433 A1 WO2022178433 A1 WO 2022178433A1
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WIPO (PCT)
Prior art keywords
block
video
sample
luma
sample pairs
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PCT/US2022/017342
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English (en)
Inventor
Xianglin Wang
Hong-Jheng Jhu
Yi-Wen Chen
Xiaoyu Yu
Wei Chen
Che-Wei Kuo
Bing Yu
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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 CN202280016220.6A priority Critical patent/CN116868571A/zh
Publication of WO2022178433A1 publication Critical patent/WO2022178433A1/fr

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    • 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
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
    • 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
    • H04N19/136—Incoming video signal characteristics or properties
    • H04N19/14—Coding unit complexity, e.g. amount of activity or edge presence estimation
    • 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
    • H04N19/17—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 an image region, e.g. an object
    • H04N19/176—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 an image region, e.g. an object the region being a block, e.g. a macroblock

Definitions

  • This application is related to video coding and compression, more specifically, to methods and apparatus on improving the coding efficiency and simplifying the complexity of local illumination compensation (LIC).
  • LIC local illumination compensation
  • 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 and simplifying the complexity of local illumination compensation (LIC).
  • LIC local illumination compensation
  • a method of decoding video signal comprises: determining two or more reference sample pairs, each of the reference sample pairs comprising a neighboring reconstructed luma sample of a current block and a corresponding neighboring reconstructed luma sample of a reference block; classifying the two or more reference sample pairs into one or more groups; deriving one or more linear models based on the classified one or more groups of the sample pairs; and predicting a luma sample value in the current block by applying the one or more linear models to a corresponding reconstructed luma sample in the reference block.
  • the reference block is displaced by a motion vector from the current block.
  • 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 signal 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 signal as described above.
  • a computer readable storage medium stores therein a bitstream comprising video information generated by the method for video decoding 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 an exemplary straight line derivation of parameters (a and b) using the min-max method in accordance with some implementations of the present disclosure.
  • FIG. 6 is a block diagram illustrating exemplary locations of the samples used for the derivation of parameters (a and b) in accordance with some implementations of the present disclosure.
  • FIG. 7 is a block diagram illustrating an exemplary derivation of parameters for the multi-model linear model (MMLM) by classifying the neighboring samples into two groups in accordance with some implementations of the present disclosure.
  • MMLM multi-model linear model
  • FIG. 8 is a block diagram illustrating an exemplary derivation of prediction model parameters by classifying the neighboring samples into two groups based on the knee point in accordance with some implementations of the present disclosure.
  • FIGs. 9A and 9B are block diagrams illustrating exemplary neighboring samples used for deriving Illumination Compensation (IC) parameters in accordance with some implementations of the present disclosure.
  • FIG. 10 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 1 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 11 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 2 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 12 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 3 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 13 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 4 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 14 is a flowchart illustrating an exemplary process of decoding video signal in accordance with some implementations of the present disclosure.
  • FIG. 15 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.
  • 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, intra mode 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.
  • 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.
  • 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/ theoretically 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 disclosure.
  • 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.
  • 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.
  • 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.
  • APU of a CU may comprise a PB of luma samples, two corresponding PBs of chroma samples, and syntax elements used to predict the PBs.
  • 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 non square) 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 inter prediction). 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 an exemplary straight line derivation of parameters (a and b) using the min-max method, in accordance with some implementations of the present disclosure.
  • FIG. 6 is a block diagram illustrating exemplary locations of the samples used for the derivation of parameters (a and b) in accordance with some implementations of the present disclosure.
  • pred c (i, j) a ⁇ rec L '(i,j) + b
  • the linear model parameter a and b are derived from the straight-line relationship between luma values and chroma values from two samples, which are minimum luma sample A (XA, YA) and maximum luma sample B (XB, YB) inside the set of neighboring luma samples, as exemplified in FIG. 5.
  • XA, YA are the x-coordinate value (i.e. a luma value) and y-coordinate value (i.e. a chroma value) for sample A
  • XB, YB are the x-coordinate value and y-coordinate value for sample B.
  • the linear model parameters a and b are obtained according to the following equations. b - T G axA
  • Such a method is also called min-max method as shown in FIG. 5.
  • the division in the equation above could be avoided and replaced by a multiplication and a shift.
  • the neighboring samples of the longer boundary are first subsampled to have the same number of samples as that of the shorter boundary.
  • FIG. 6 shows the locations of the top left samples and the sample of the current block involved in the CCLM mode.
  • the two templates can also be used alternatively in the other two LM modes, called LM_A, and LM_L modes.
  • LM_A mode only the pixel samples in the above template are used to calculate the linear model coefficients. To get more samples, the above template is extended to the size of (W+W).
  • LM_L mode only the pixel samples in the left template are used to calculate the linear model coefficients. To get more samples, the left template is extended to the size of (H+H).
  • chroma intra mode coding For the chroma intra mode coding, a total of 8 intra modes are allowed for the chroma intra mode coding. Those modes include five traditional intra modes and three cross component linear model modes (CCLM, LM_A, and LM_L).
  • the chroma mode signaling and derivation process are shown in Table 1.
  • the chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since a separate block partitioning structure for luma and chroma components is enabled in I slices, one chroma block may correspond to multiple luma blocks. Therefore, for the chroma DM mode, it is directly inherited that the intra prediction mode of the corresponding luma block covers the center position of the current chroma block.
  • FIG. 7 is a block diagram illustrating an exemplary derivation of parameters for the multi-model linear model (MMLM) by classifying the neighboring samples into two groups, in accordance with some implementations of the present disclosure.
  • MMLM multi-model linear model
  • the multi-model linear model (MMLM) prediction mode is implemented.
  • Threshold is calculated as the average value of the neighboring reconstructed luma samples.
  • FIG. 7 shows an example of classifying the neighboring samples into two groups based on the value Threshold.
  • the threshold is 17.
  • parameters a, and b ⁇ are derived from the straight-line relationship between luma values and chroma values from two samples, which are the minimum luma sample A (XA, YA) and the maximum luma sample B (XB, YB) inside the group.
  • XA, YA are the x-coordinate value (i.e. luma value) and y-coordinate value (i.e.
  • Such a method is also called the min-max method.
  • the division in the equation above could be avoided and replaced by a multiplication and a shift.
  • the two templates can also be used alternatively in the other two MMLM modes, called MMLM_A and MMLM_L modes.
  • the above template is extended to the size of (W+W).
  • the MMLM L mode only the pixel samples in the left template are used to calculate the linear model coefficients. To get more samples, the left template is extended to the size of (H+H).
  • chroma intra mode coding For the chroma intra mode coding, a total of 11 intra modes are allowed for the chroma intra mode coding. Those modes include five traditional intra modes and six cross component linear model modes (CCLM, LM_A, LM_L, MMLM, MMLM Aand MMLM L).
  • the chroma mode signaling and derivation process are shown in Table 2.
  • the chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since a separate block partitioning structure for luma and chroma components is enabled in I slices, one chroma block may correspond to multiple luma blocks. Therefore, for the chroma DM mode, it is directly inherited that the intra prediction mode of the corresponding luma block covers the center position of the current chroma block.
  • FIG. 8 is a block diagram illustrating an exemplary derivation of prediction model parameters by classifying the neighboring samples into two groups based on the knee point, in accordance with some implementations of the present disclosure.
  • MMLM and LM modes may also be used together in an adaptive manner.
  • Threshold can be simply determined based on the luma and chroma average values together with their minimum and maximum values.
  • FIG. 8 shows an example of classifying the neighboring samples into two groups based on the knee point, T, indicated by an arrow.
  • Linear model parameters a x and b c are derived from the straight-line relationship between luma values and chroma values from two samples, which are the minimum luma sample A (XA, YA) and the Threshold (Cc, Ut).
  • Linear model parameters a 2 and b 2 are derived from the straight-line relationship between luma values and chroma values from two samples, which are the maximum luma sample B (X B , Y B ) and the Threshold (Cc, Uc).
  • XA, YA are the x-coordinate value (i.e. luma value) and y-coordinate value (i.e. chroma value) for sample A
  • X B , Y B are the x-coordinate value and y-coordinate value for sample B.
  • the linear model parameters a, and b, for each group, with i equal to 1 and 2 respectively, are obtained according to the following equations: bi — YA a iC ⁇
  • the two templates can also be used alternatively in the other two MMLM modes, called the MMLM_A, and MMLM_L modes respectively.
  • MMLM A mode only the pixel samples in the above template are used to calculate the linear model coefficients. To get more samples, the above template is extended to the size of (W+W).
  • MMLM L mode only the pixel samples in the left template are used to calculate the linear model coefficients. To get more samples, the left template is extended to the size of (H+H).
  • condition check used to select LM modes (CCLM, LM_A, and LM_L) or multi-model LM modes (MMLM, MMLM A, and MMLM L).
  • LM modes CCLM, LM_A, and LM_L
  • MMLM, MMLM A, and MMLM L multi-model LM modes
  • the symbol d represents a pre-determined threshold value. In one example, d may take a value of 0. In another example, d may take a value of 8.
  • chroma intra mode coding For the chroma intra mode coding, a total of 8 intra modes are allowed for the chroma intra mode coding. Those modes include five traditional intra modes and three cross component linear model modes.
  • the chroma mode signaling and derivation process are shown in Table 3. It is worth noting that for a given CU, if it is coded under the linear model mode, whether it is a conventional single model LM mode or a MMLM mode is determined based on the condition check above. Unlike the case shown in Table 2, there are no separate MMLM modes to be signaled.
  • the chroma mode coding directly depends on the intra prediction mode of the corresponding luma block.
  • one chroma block may correspond to multiple luma blocks. Therefore, for the chroma DM mode, it is directly inherited that the intra prediction mode of the corresponding luma block covers the center position of the current chroma block.
  • LIC Local Illumination Compensation
  • the parameters of the function can be denoted by a scale a and an offset b, which forms a linear equation, that is a*r[c]+b to compensate illumination changes, where p[x] is a reference sample, to which it is pointed by MV at a location x on the reference picture. Since a and b can be derived based on current block template and the reference block template, no signaling overhead is required for them, except that an LIC flag is signaled for the AMVP mode to indicate the use of LIC.
  • FIGs. 9 A and 9B are block diagrams illustrating exemplary neighboring samples used for deriving Illumination Compensation (IC) parameters, in accordance with some implementations of the present disclosure.
  • a least square error method is employed to derive the parameters a and b by using the neighboring samples of the current CU and their corresponding reference samples. More specifically, as illustrated in FIG. 9A and FIG. 9B, the samples being used are the subsampled (2:1 subsampling) neighboring samples of the CU and the corresponding samples (identified by motion information of the current CU or sub-CU) in the reference picture.
  • the IC parameters are derived and applied for each prediction direction separately.
  • LIC When LIC is enabled for a picture, the additional CU level RD check is needed to determine whether LIC is applied or not for a CU.
  • MR-SAD mean- removed sum of absolute difference
  • MR-SATD mean-removed sum of absolute Hadamard -transformed difference
  • LIC is disabled for the entire picture when there is no obvious illumination change between a current picture and its reference pictures.
  • histograms of a current picture and every reference picture of the current picture are calculated at the encoder. If the histogram difference between the current picture and every reference picture of the current picture is smaller than a given threshold, LIC is disabled for the current picture; otherwise, LIC is enabled for the current picture.
  • the LIC can efficiently model local illumination variations, its performance can be still improved.
  • the LIC design also introduces significant complexity to both encoder and decoder design. The tradeoff between its implementation complexity and its coding efficiency needs to be further optimized.
  • the number of reference samples used for deriving the LIC parameters may be reduced, compared to the currently adopted method in LIC, or limited to a particular value range.
  • the illumination compensation (IC) parameter calculation with more limited number of reference samples is further described below.
  • model parameters are generated for LIC with more limited number of reference samples to reduce the necessary calculation. In one embodiment, only half of those reference sample pairs currently used are applied in determining the LIC parameters according to the present disclosure.
  • a reference sample pair refers to a neighboring luma sample of the current CU and its corresponding reference luma sample, for example, a neighboring reconstructed luma sample of a current block and a corresponding neighboring reconstructed luma sample of a reference block).
  • those reference samples can be selected in a spatially further down-sampled manner by taking one out of every two neighboring reference sample pairs into consideration in deriving the IC model parameters.
  • the maximum number of reference sample pairs that are used in deriving LIC model parameters is limited to a pre-determined value based on the size and shape of corresponding luma blocks.
  • a pre-determined value based on the size and shape of corresponding luma blocks.
  • Method 1, 2, 3, and 4 Four different examples (labelled as Method 1, 2, 3, and 4) are provided in Table 4, where the pre-determined values can be 2, 4 and/or 8 depending on the size and shape of the luma block of the current CU, for example, the size and shape of a luma block of the current block or the reference block..
  • FIG. 10 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 1 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 11 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 2 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 12 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 3 of Table 4, in accordance with some implementations of the present disclosure.
  • FIG. 13 is a block diagram illustrating example location of reference sample(s) (in gray block(s)) in method 4 of Table 4, in accordance with some implementations of the present disclosure.
  • only the blocks with a block size equal to or larger than a certain threshold may be used in forming the inter prediction of the LIC.
  • the minimum block size is limited to 8 or 16. In that case, the maximum number of reference sample pairs may be limited to 8.
  • one adaptive LIC scheme is implemented. Compared to the method where LIC is fixedly applied with one linear model, the algorithm and system disclosed herein adaptively adjusts the number of linear models. [00125] In some embodiments, a Multi-model Local illumination compensation method is further described below.
  • one or more Multi-model LIC (MMLIC) modes are added. In each MMLIC mode, the reconstructed neighboring samples are classified into two classes using a threshold which is the average of the luma reconstructed neighboring samples. The linear model of each class is derived using the Least-Mean-Square (LMS) method.
  • LMS Least-Mean-Square
  • a model in which the samples are predicted based on the reference samples pointed to by MV at a location x on reference picture by using two linear models is as follows:
  • pred (i, j) a 2 ' rec i/ rec '(i,j) > Threshold
  • pred (i,j) represents the predicted samples
  • rec '(i,j) represents the reference sample pointed to by MV at a location x on reference picture.
  • Threshold is calculated as the average value of the neighbouring reconstructed samples.
  • FIG. 7 shows an example of classifying the neighboring samples into two groups based on the value Threshold.
  • parameter a, and b ⁇ are derived from the straight- line relationship between a neighboring luma sample value of the current CU and its corresponding reference luma sample value from two sample pairs, which are the minimum luma sample A (XA, YA) and maximum luma sample B (XB, YB) inside the group.
  • XA, YA are the x-coordinate value (i.e. luma value) and y-coordinate value (i.e. corresponding reference luma value) for sample A
  • XB, YB are the x-coordinate value and y-coordinate value for sample B.
  • the linear model parameters a and b are obtained according to the following equations. a ye ⁇ 3 ⁇ 4 ⁇ — — —
  • the two templates can also be used alternatively in the other two MMLIC modes, called MMLIC A, and MMLIC L modes.
  • MMLIC A mode only pixel samples in the above template are used to calculate the linear model coefficients. To get more samples, the above template is extended to the size of (W+W).
  • MMLIC L mode only pixel samples in the left template are used to calculate the linear model coefficients. To get more samples, the left template is extended to the size of (H+H).
  • the parameter derivation in the LIC may only use MMLIC modes. For example, only one or more MMLIC modes are allowed and the LIC modes are disabled that are based on a single model. In this case, it’s unnecessary to determine whether LIC modes or multi-model LIC modes are applied. For example, the condition check that is used to select LIC modes or multi-model LIC modes is no longer needed. Multi-model LIC modes are always used for the parameter derivation and sample value prediction in the LIC.
  • the block based pixel classification for model selection in the MMLIC mode is described below.
  • the block- based pixel classification is used to select different models in the MMLIC mode.
  • classification is pixel based, i.e. each reconstructed luma sample is checked against a classification threshold and based on the comparison result when a corresponding LIC model is selected for that pixel.
  • classification is done on a block level, with the classification decision applied to all pixels in the block.
  • the block size may be NxM, wherein N and M are positive numbers such as 2 or 4.
  • classification may be performed using different methods, involving all or just partial samples in the block. For example, the average of all samples in each NxM block may be used to decide which linear model to use for the block. In another example, for simplification, a classification may be made by simply checking one sample from each block to determine which linear model to use for the block. The one sample may be the top-left sample of each NxM block.
  • a three-model based local illumination compensation is implemented.
  • three parameter sets are used in the local illumination compensation mode to compensate illumination changes.
  • the parameters of the function can be denoted by a scale a and an offset b, which form a linear equation, that is, the luma samples are predicted based on the reconstructed luma samples of the same CU in the reference picture (or a reference block) by using three linear models as follows: a*p[x]+ ?
  • ⁇ pred (i,j) a 2 rec (i, j) + b 2 if rec (i, j) > Threshold- L and rec L '(i,j) ⁇ Threshold 2
  • Threshold- L and Threshold 2 can be calculated by the maximum and minimum values of the neighboring reconstructed luma samples (denoted as Lmax and Lmin respectively in the following). In one example, Threshold- L and Threshold 2 can be calculated as follows: Lmax Lmin Lmax Lmin
  • Threshold- L and Threshold 2 can be calculated as the average values of the neighboring reconstructed luma samples.
  • all neighboring reconstructed luma samples are separated into two groups based on the average value of the neighbouring reconstructed luma samples.
  • Luma samples with values smaller than the average value belong to one group, and those with values not smaller than the average value belong to another group.
  • Threshold and Threshold 2 can be calculated as the average values of each group. With the values of Threshold and Threshold 2 determined, the neighboring reconstructed luma samples can be separated into three groups depending on the relationship between the luma value and the values of Threshold- ⁇ and Threshold 2.
  • the first group contains the reconstructed luma samples with values ranging from the minimum luma sample value to Threshold .
  • the second group contains the reconstructed luma samples with values ranging from Threshold- L to Threshold 2.
  • the third group contains the remaining reconstructed luma samples.
  • linear model parameters may be derived for each group respectively.
  • parameter a and b are separately derived from the straight-line relationship between a neighboring luma sample value of the current CU and its corresponding reference luma sample value from two sample pairs, which are the minimum value luma sample and the maximum value luma sample inside each of the three groups.
  • linear model parameters a x and b c are derived from the straight- line relationship between a neighboring luma sample value of the current CU and its corresponding reference luma sample value from two sample pairs, which are the minimum value luma sample and Threshold .
  • Linear model parameters a 2 and b 2 are derived from the straight-line relationship between a neighboring luma sample value of the current CU and its corresponding reference luma sample value from two sample pairs, which are Threshold and Threshold 2 .
  • Linear model parameters a 3 and b 3 are derived from the straight-line relationship between a neighboring luma sample value of the current CU and its corresponding reference luma sample value from two sample pairs, which are the maximum luma sample and Threshold 2.
  • the model classification threshold is based on reconstructed luma samples inside the current CU.
  • the reconstructed luma samples inside a current CU are used to calculate the model classification threshold in a cross-component linear model.
  • the threshold is calculated as the average value of the reconstructed luma samples inside a CU.
  • the threshold is calculated as the average value of the reconstructed luma samples inside the CU and the reconstructed luma samples neighboring to the CU.
  • the model classification threshold is based on the minimum and maximum luma samples.
  • the minimum and maximum samples are used to derive the model classification threshold.
  • the threshold is calculated as the (max + min )/N, where max is the sample value of the maximum sample, min is the sample value of the minimum sample and N is any value (e.g. 2).
  • FIG. 14 is a flowchart illustrating an exemplary process 1400 of decoding video signal in accordance with some implementations of the present disclosure.
  • the video decoder 30 determines two or more reference sample pairs, each of the reference sample pairs comprising a neighboring reconstructed luma sample of a current block and a corresponding neighboring reconstructed luma sample of a reference block (1410).
  • the video decoder 30 classifies the two or more reference sample pairs into one or more groups (1420).
  • the video decoder 30 derives one or more linear models based on the classified one or more groups of the sample pairs (1430).
  • the video decoder 30 predicts a luma sample value in the current block by applying the one or more linear models to a corresponding reconstructed luma sample in the reference block (1440).
  • the video decoder 30 adjusts the luma sample value in the current block based on the predicted luma sample value.
  • the reference block is displaced by a motion vector from the current block.
  • determining the two or more reference sample pairs (1410) includes determining a pre-determined number of sample pairs based on size and shape of a luma block of the reference block or the current block.
  • the pre-determined number of sample pairs is 2, 4, or 8.
  • predicting a luma sample value in the current block (1440) includes predicting the luma sample value in the current block by applying the one or more linear models to the corresponding reconstructed luma sample in the reference block having a block size equal or larger than a threshold.
  • deriving one or more linear models based on the classified one or more groups of the sample pairs (1430) includes always deriving two or more linear models based on classified two or more groups of the sample pairs and each linear model is corresponding to each group of the sample pairs.
  • classifying the two or more reference sample pairs into one or more groups (1420) includes classifying the two or more reference sample pairs into one or more groups according to a value associated with all pixels in the reference block.
  • the value associated with all pixels in the reference block is an average value of all pixels in the reference block or one sample value selected from all pixels in the reference block.
  • deriving one or more linear models based on the classified one or more groups of the sample pairs (1430) includes deriving three linear models based on classified three groups of the sample pairs and each linear model is corresponding to each group of the sample pairs.
  • classifying the two or more reference sample pairs into one or more groups (1420) includes classifying the two or more reference sample pairs into one or more groups based one or more threshold values, and the one or more threshold values are based on average value of the reconstructed luma samples inside the reference block and/or the neighboring reconstructed luma sample of a reference block.
  • classifying the two or more reference sample pairs into one or more groups (1420) includes classifying the two or more reference sample pairs into one or more groups based on one or more threshold values, and the one or more threshold values are calculated as (MAX + MIN )/N, wherein MAX is a maximum sample value of the reconstructed luma samples inside the reference block, MIN is a minimum sample value of the reconstructed luma samples inside the reference block, and N is a predetermined value.
  • FIG. 15 shows a computing environment 1510 coupled with a user interface 1550.
  • the computing environment 1510 can be part of a data processing server.
  • the computing environment 1510 includes a processor 1520, a memory 1530, and an Input/Output (I/O) interface 1540.
  • I/O Input/Output
  • the processor 1520 typically controls overall operations of the computing environment 1510, such as the operations associated with display, data acquisition, data communications, and image processing.
  • the processor 1520 may include one or more processors to execute instructions to perform all or some of the steps in the above-described methods.
  • the processor 1520 may include one or more modules that facilitate the interaction between the processor 1520 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 1530 is configured to store various types of data to support the operation of the computing environment 1510.
  • the memory 1530 may include predetermined software 1532. Examples of such data includes instructions for any applications or methods operated on the computing environment 1510, video datasets, image data, etc.
  • the memory 1530 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
  • the EO interface 1540 provides an interface between the processor 1520 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 EO interface 1540 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 1530, executable by the processor 1520 in the computing environment 1510, 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 1520); and the non-transitory computer-readable storage medium or the memory 1530 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 1520
  • non-transitory computer-readable storage medium or the memory 1530 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 1530, executable by the processor 1520 in the computing environment 1510, for performing the above-described methods.
  • the computer program product may include the non-transitory computer-readable storage medium.
  • the computing environment 1510 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.
  • DSPDs Digital Signal Processing Devices
  • PLDs Programmable Logic Devices
  • FPGAs FPGAs
  • GPUs GPUs
  • controllers micro-controllers
  • microprocessors or other electronic components
  • 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.

Abstract

L'invention concerne un appareil électronique qui réalise un procédé de décodage de données vidéo. Le procédé consiste à : déterminer au moins deux paires d'échantillons de référence, chacune des paires d'échantillons de référence comprenant un échantillon de luminance reconstruit voisin d'un bloc courant et un échantillon de luminance reconstruit voisin correspondant d'un bloc de référence ; classer les au moins deux paires d'échantillons de référence dans un ou plusieurs groupes ; dériver un ou plusieurs modèles linéaires sur la base des un ou plusieurs groupes classés des paires d'échantillons ; et prédire une valeur d'échantillon de luminance dans le bloc courant en appliquant les un ou plusieurs modèles linéaires à un échantillon de luminance reconstruit correspondant dans le bloc de référence. Dans certains modes de réalisation, le bloc de référence est déplacé par un vecteur de mouvement à partir du bloc courant.
PCT/US2022/017342 2021-02-22 2022-02-22 Compensation d'éclairage local améliorée pour prédiction inter-composantes WO2022178433A1 (fr)

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