WO2024081291A1 - Procédé et appareil de prédiction inter-composantes pour un codage vidéo - Google Patents

Procédé et appareil de prédiction inter-composantes pour un codage vidéo Download PDF

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Publication number
WO2024081291A1
WO2024081291A1 PCT/US2023/034899 US2023034899W WO2024081291A1 WO 2024081291 A1 WO2024081291 A1 WO 2024081291A1 US 2023034899 W US2023034899 W US 2023034899W WO 2024081291 A1 WO2024081291 A1 WO 2024081291A1
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Prior art keywords
luma sample
luma
chroma
video
samples
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PCT/US2023/034899
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English (en)
Inventor
Hong-Jheng Jhu
Che-Wei Kuo
Xiaoyu XIU
Ning Yan
Wei Chen
Changyue MA
Xianglin Wang
Bing Yu
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Beijing Dajia Internet Information Technology Co., Ltd
Xianglin Wang
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Application filed by Beijing Dajia Internet Information Technology Co., Ltd, Xianglin Wang filed Critical Beijing Dajia Internet Information Technology Co., Ltd
Publication of WO2024081291A1 publication Critical patent/WO2024081291A1/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
    • 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
    • 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

Definitions

  • This application is related to video coding and compression. More specifically, this application relates to methods and apparatus on improving the coding efficiency of the image/video blocks which applies cross-component prediction technology.
  • 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 (WC), 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.
  • 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.
  • Embodiments of the present disclosure provide methods and apparatus on improving the coding efficiency of the image/video blocks which applies cross-component prediction technology.
  • the method comprises: receiving an encoded block of luma samples for a block of the video data; decoding the encoded block of luma samples to obtain reconstructed luma samples for the block; classifying a luma sample for the block into one of a plurality of sample groups based on edge information of the luma sample, wherein the luma sample is obtained from one or more of the reconstructed luma samples to correspond to a chroma sample for the block; and predicting the chroma sample by applying one of a plurality of linear prediction models corresponding to the classified sample group to the luma sample.
  • a computer system comprising one or more processors and one or more storage devices storing computerexecutable instructions that, when executed, cause the one or more processors to perform the operations including: receiving an encoded block of luma samples for a block of the video data; decoding the encoded block of luma samples to obtain reconstructed luma samples for the block; classifying a luma sample for the block into one of a plurality of sample groups based on edge information of the luma sample, wherein the luma sample is obtained from one or more of the reconstructed luma samples to correspond to a chroma sample for the block; and predicting the chroma sample by applying one of a plurality of linear prediction models corresponding to the classified sample group to the luma sample.
  • a method for video decoding with an Edge-classified linear model may include: receiving an encoded block of luma samples for a first block of video signal; decoding the encoded block of luma samples to obtain reconstructed luma samples; classifying the reconstructed luma samples into plural sample groups based on direction and strength of edge information; applying different linear prediction models to the reconstructed luma samples in different sample groups; predicting chroma samples for the first block of video signal based on the applied linear prediction models.
  • a method for video decoding with a Filter-based linear model may include: receiving an encoded block of luma samples for a first block of video signal; decoding the encoded block of luma samples to obtain reconstructed luma samples; determining a luma sample region and a chroma sample region to derive a multiple linear regression (MLR) model; deriving the MLR model by pseudo inverse matrix calculation; applying the MLR model to the reconstructed luma samples; predicting chroma samples for the first block of video signal based on the applied MLR model.
  • MLR multiple linear regression
  • a method for video decoding with a Gradient linear model may include: receiving an encoded block of luma samples for a first block of video signal, decoding the encoded block of luma samples to obtain reconstructed luma samples; utilizing the sample gradients to exploit the correlation between luma AC information and chroma intensities, determining a luma sample region and a chroma sample region to derive a multiple linear regression (MLR) model; deriving the MLR model by pseudo inverse matrix calculation; applying the MLR model to the reconstructed luma samples; predicting chroma samples for the first block of video signal based on the applied MLR model.
  • MLR multiple linear regression
  • a method for video coding without down-sampled process in convolutional cross-component model may include: receiving an encoded block of luma samples for a first block of video signal; decoding the encoded block of luma samples to obtain reconstructed luma samples; utilizing non-down-sampled luma reference values and/or different selection of non-down- sampled luma reference; determining a luma sample region and a chroma sample region to derive a convolutional cross-component model (CCCM); deriving the CCCM parameters by LDL decomposition; applying the CCCM to the reconstructed luma samples; predicting chroma samples for the first block of video signal based on the applied CCCM.
  • CCCM convolutional cross-component model
  • a method for video coding with a LDL decomposition in a cross-component linear model (CCLM)/Multi -model LM (MMLM) may include: receiving an encoded block of luma samples for a first block of video signal; decoding the encoded block of luma samples to obtain reconstructed luma samples; determining a luma sample region and a chroma sample region to derive a crosscomponent linear model (CCLM)ZMulti-model LM (MMLM); deriving the CCLM/MMLM parameters by LDL decomposition; applying the CCLM/MMLM to the reconstructed luma samples; predicting chroma samples for the first block of video signal based on the applied CCLM/MMLM
  • a method for video coding with a minimal samples restriction in FLM/GLM/ELM/CCCM may include: determining, whether a FLM/GLM/ELM/CCCM scheme is applied in the intra prediction, wherein the number of samples larger than or equal to predefined number in the coded block.
  • a method for video coding with a non-down-sampled and down-sampled luma reference values in CCCM is provided.
  • a method for video coding with a combined multiple modes of FLM/GLM/ELM/CCCM/CCLM is provided.
  • a method for decoding video data comprising: obtaining a video block from a bitstream; obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region; determining, based on the external luma sample values and the external chroma sample values, a set of weighting coefficients corresponding to a filter shape, wherein the filter shape and the set of weighting coefficients are configured for predicting each of the internal chroma sample values based on a plurality of corresponding luma sample values, wherein the plurality of corresponding luma sample values comprise: one or more non-down-sampled luma sample values associated with the filter shape, and one or more non-linear luma sample values; predicting, with the filter shape and the set of weighting coefficients, the internal chroma sample values based on the internal luma sample values; and obtaining predicted video block using
  • a method for encoding video data comprising: obtaining a video block; obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region; determining, based on the external luma sample values and the external chroma sample values, a set of weighting coefficients corresponding to a filter shape, wherein the filter shape and the set of weighting coefficients are configured for predicting each of the internal chroma sample values based on a plurality of corresponding luma sample values, wherein the plurality of corresponding luma sample values comprise: one or more non-down-sampled luma sample values associated with the filter shape, and one or more non-linear luma sample values; predicting, with the filter shape and the set of weighting coefficients, the internal chroma sample values based on the internal luma sample values; and generating a bitstream comprising an encode
  • a computer system comprising: one or more processors; and one or more storage devices storing computer-executable instructions that, when executed, cause the one or more processors to perform the operations of the method of the present disclosure.
  • a computer program product storing computer-executable instructions that, when executed, cause one or more processors to perform the operations of the method of the present disclosure.
  • a computer readable storage medium storing instructions which when executed by a computing device having one or more processors, cause the one or more processors to perform the decoding method of the present disclosure and storing a bitstream to be decoded by the decoding method of the present disclosure.
  • a computer readable storage medium storing instructions which when executed by a computing device having one or more processors, cause the one or more processors to perform the encoding method of the present disclosure and storing a bitstream generated by the encoding method of the present disclosure.
  • a computer readable medium storing a bitstream, wherein the bitstream is to be decoded by performing the operations of the method of the present disclosure.
  • a computer readable medium storing a bitstream, wherein the bitstream is obtained by performing the operations of the method of the present disclosure.
  • Figure 1 is a block diagram illustrating an exemplary system for encoding and decoding video blocks in accordance with some implementations of the present disclosure.
  • Figure 2 is a block diagram illustrating an exemplary video encoder in accordance with some implementations of the present disclosure.
  • Figure 3 is a block diagram illustrating an exemplary video decoder in accordance with some implementations of the present disclosure.
  • Figure 4A to 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.
  • Figure 5 illustrates a general diagram of block-based video encoder for the VVC.
  • Figures 6A to 6E are diagrams illustrating block partitions in the VVC.
  • Figure 7 illustrates a general diagram of video decoder for the VVC.
  • Figure 8 is a diagram illustrating locations of the samples used for the derivation of a and 0.
  • Figures 9A to 9C are diagrams illustrating examples of MDLM, MDLM L and MDLM_T.
  • Figure 10 is a diagram illustrating an example of classifying the neighboring samples into two groups.
  • Figure 11 is a diagram illustrating a knee point T.
  • Figures 12A to 12B are diagrams illustrating an effect of the slope adjustment parameter “u”.
  • Figure 13 is a diagram illustrating used collocated reconstructed luma samples.
  • Figure 14 is a diagram illustrating used neighboring reconstructed samples.
  • Figures 15 A to 15D are diagrams illustrating a process of decoder side intra mode derivation.
  • Figure 16 is a diagram illustrating an example of four reference lines neighboring to a prediction block.
  • Figure 17 is a diagram illustrating a spatial part of the convolutional filter.
  • Figure 18 is a diagram illustrating a reference area (with its paddings) used to derive the filter coefficients.
  • Figures 19A to 19B are diagrams illustrating a chroma sample may simultaneously correlate to multiple luma samples.
  • Figure 20 is a diagram illustrating coefficients/offset of multiple (e.g., 6) luma samples with respect to 1 chroma sample are trained to linear predict the chroma sample inside the CU.
  • Figure 21 is a diagram illustrating different chroma types/color formats can have different predefined filter shapes/taps.
  • Figure 22 is a diagram illustrating a FLM can only use top or left luma/ chroma samples (extended) for parameter derivation.
  • Figure 23 is a diagram illustrating a FLM can use different lines for parameter derivation.
  • Figures 24A to 24D are diagrams illustrating pre-operations before applying the MLR model (GLM l-tap/2-tap).
  • Figure 25 is a diagram illustrating examples of different shape/number of filter taps.
  • Figure 26 is a diagram illustrating examples of different shape/number of filter taps.
  • Figures 27A to 27B are diagrams illustrating examples of different shape/number of filter taps.
  • Figures 28A to 28G are diagrams illustrating examples of different set of filter taps.
  • Figures 29A to 29B are diagrams illustrating 2-fold training for implicitly filter shape derivation.
  • Figure 30 illustrates a workflow of a method for decoding video data according to one or more aspects of the present disclosure.
  • Figure 31 illustrates a workflow of a method for encoding video data according to one or more aspects of the present disclosure.
  • Figure 32 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 cloud servers, server computers, desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital mediaplayers, 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
  • At least a part of components of the source device 12 may operate in a cloud computing service network which may provide software, platforms, and/or infrastructure, such as Software as a Service (SaaS), Platform as a Service (PaaS), or Infrastructure as a Service (laaS).
  • SaaS Software as a Service
  • PaaS Platform as a Service
  • laaS Infrastructure as a Service
  • one or more components in the source device 12 and/or the destination device 14 which are not included in the cloud computing service network may be provided in one or more client devices, and the one or more client devices may communicate with server computers in the cloud computing service network through a wireless communication network (for example, a cellular communication network, a short-range wireless communication network, or a global navigation satellite system (GNSS) communication network) or a wired communication network (e.g., a local area network (LAN) communication network or a power line communication (PLC) network).
  • a wireless communication network for example, a cellular communication network, a short-range wireless communication network, or a global navigation satellite system (GNSS) communication network
  • GNSS global navigation satellite system
  • wired communication network e.g., a local area network (LAN) communication network or a power line communication (PLC) network.
  • LAN local area network
  • PLC power line communication
  • At least a part of operations described herein may be implemented as cloud-based services provided by one or more server computers which are implemented by the at least a part of the components of the source device 12 and/or the at least a part of the components of the destination device 14 in the cloud computing service network; and one or more other operations described herein may be implemented by the one or more client devices.
  • the cloud computing service network may be a private cloud, a public cloud, or a hybrid cloud.
  • the terms such as “cloud,” “cloud computing,” “cloud-based” etc. herein may be used interchangeably as appropriate without departing from the scope of the present disclosure. It should be understood that the present disclosure is not limited to being implemented in the cloud computing service network described above. Instead, the present disclosure may also be implemented in any other type of computing environments currently known or developed in the future.
  • 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 blockiness artifacts from reconstructed video.
  • Another in-loop filter such as Sample Adaptive Offset (SAO) filter, Cross Component Sample Adaptive Offset (CCSAO) 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.
  • SAO Sample Adaptive Offset
  • CCSAO Cross Component Sample Adaptive Offset
  • ALF Adaptive in-Loop Filter
  • the present application is not limited to the embodiments described herein, and instead, the application may be applied to a situation where an offset is selected for any of a luma component, a Cb chroma component and a Cr chroma component according to any other of the luma component, the Cb chroma component and the Cr chroma component to modify said any component based on the selected offset.
  • a first component mentioned herein may be any of the luma component, the Cb chroma component and the Cr chroma component
  • a second component mentioned herein may be any other of the luma component, the Cb chroma component and the Cr chroma component
  • a third component mentioned herein may be a remaining one of the luma component, the Cb chroma component and the Cr chroma component.
  • 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 Figure 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 component differences 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 intraprediction 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 ratedistortion characteristics among the tested modes as the appropriate intra-prediction mode to use.
  • Rate -distort! on 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 subinteger 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 (SBAC), Probability Interval Partitioning Entropy (PIPE) coding or another entropy encoding methodology or technique.
  • CAVLC Context Adaptive Variable Length Coding
  • CABAC Context Adaptive Binary Arithmetic Coding
  • SBAC Syntax-based context-adaptive Binary Arithmetic Coding
  • PIPE Probability Interval Partitioning Entropy
  • the encoded bitstream may then be transmitted to the video decoder 30 as shown in Figure 1, or archived in the storage device 32 as shown in Figure 1 for later transmission to or retrieval by the video decoder 30.
  • the entropy encoding unit 56 may also entropy encode
  • 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 Figure 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 Figure 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, SAG filter, CCS AO 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 Figure 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 128x 128, 64x64, 32x32, and 16x16.
  • 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.
  • 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.
  • FIG. 4D depicts a quad-tree data structure illustrating the end result of the partition process of the CTU 400 as depicted in Figure 4C, 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. It should be noted that the quad-tree partitioning depicted in FIGS.
  • FIG. 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/bi nary -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.
  • Figure 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.
  • a PU may comprise a single PB and syntax structures used to predict the PB.
  • the video encoder 20 may generate predictive luma, 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 CAB AC 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
  • 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”
  • Video coding is performed according to one or more video coding standards.
  • video coding standards include versatile video coding (VVC), high-efficiency video coding (H.265/HEVC), advanced video coding (H.264/AVC), moving picture expert group (MPEG) coding, or the like.
  • Video coding generally utilizes prediction methods (e g., inter-prediction, intra-prediction, or the like) that take advantage of redundancy present in video images or sequences.
  • An important goal of video coding techniques is to compress video data into a form that uses a lower bit rate, while avoiding or minimizing degradations to video quality.
  • the first version of the VVC standard was finalized in July, 2020, which offers approximately 50% bit-rate saving or equivalent perceptual quality compared to the prior generation video coding standard HEVC.
  • the VVC standard provides significant coding improvements than its predecessor, there is evidence that superior coding efficiency can be achieved with additional coding tools.
  • Joint Video Exploration Team JVET
  • ISO/IEC MPEG started the exploration of advanced technologies that can enable substantial enhancement of coding efficiency over VVC.
  • Tn April 2021 one software codebase, called Enhanced Compression Model (ECM) was established for future video coding exploration work.
  • ECM Enhanced Compression Model
  • VTM VVC Test Model
  • CTCs JVET common test conditions
  • FIG. 5 illustrates a block diagram of a generic block-based hybrid video encoding system.
  • the input video signal is processed block by block (called coding units (CUs)).
  • CUs coding units
  • one coding tree unit (CTU) is split into CUs to adapt to varying local characteristics based on quad/binary/ternary-tree.
  • Tn the multi-type tree structure one CTU is firstly partitioned by a quad-tree structure.
  • each quad-tree leaf node can be further partitioned by a binary and ternary tree structure.
  • a binary and ternary tree structure As shown in Figures 6A, 6B, 6C, 6D, and 6E, there are five splitting types, quaternary partitioning, vertical binary partitioning, horizontal binary partitioning, vertical extended quaternary partitioning, and horizontal extended quaternary partitioning.
  • spatial prediction and/or temporal prediction may be performed.
  • Spatial prediction (or “intra prediction”) uses pixels from the samples of already coded neighboring blocks (which are called reference samples) in the same video picture/slice to predict the current video block. Spatial prediction reduces spatial redundancy inherent in the video signal.
  • Temporal prediction (also referred to as “inter prediction” or “motion compensated prediction”) uses reconstructed pixels from the already coded video pictures to predict the current video block. Temporal prediction reduces temporal redundancy inherent in the video signal.
  • Temporal prediction signal for a given CU is usually signaled by one or more motion vectors (MVs) which indicate the amount and the direction of motion between the current CU and its temporal reference.
  • MVs motion vectors
  • one reference picture index is additionally sent, which is used to identify from which reference picture in the reference picture store the temporal prediction signal comes.
  • the mode decision block in the encoder chooses the best prediction mode, for example based on the rate-distortion optimization method.
  • the prediction block is then subtracted from the current video block; and the prediction residual is de-correlated using transform and quantized.
  • the quantized residual coefficients are inverse quantized and inverse transformed to form the reconstructed residual, which is then added back to the prediction block to form the reconstructed signal of the CU.
  • in-loop filtering such as deblocking filter, sample adaptive offset (SAO) and adaptive in-loop filter (AUF) may be applied on the reconstructed CU before it is put in the reference picture store and used to code future video blocks.
  • coding mode inter or intra
  • prediction mode information motion information
  • quantized residual coefficients are all sent to the entropy coding unit to be further compressed and packed to form the bit-stream.
  • block or “video block” as used herein 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 Block
  • 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
  • Figure 7 illustrates a general block diagram of a block-based video decoder.
  • the video bit-stream is first entropy decoded at entropy decoding unit.
  • the coding mode and prediction information are sent to either the spatial prediction unit (if intra coded) or the temporal prediction unit (if inter coded) to form the prediction block.
  • the residual transform coefficients are sent to inverse quantization unit and inverse transform unit to reconstruct the residual block.
  • the prediction block and the residual block are then added together.
  • the reconstructed block may further go through in-loop filtering before it is stored in reference picture store.
  • the reconstructed video in reference picture store is then sent out to drive a display device, as well as used to predict future video blocks.
  • the main focus of this disclosure is to further enhance the coding efficiency of the coding tool of cross-component prediction, cross-component linear model (CCLM), that is applied in the ECM.
  • CCLM cross-component linear model
  • some related coding tools in the ECM are briefly reviewed. After that, some deficiencies in the existing design of CCLM are discussed. Finally, the solutions are provided to improve the existing CCLM prediction design.
  • a cross-component linear model (CCLM) prediction mode is used in the VVC, for which the chroma samples are predicted based on the reconstructed luma samples of the same CU by using a linear model as follows: where pred c (i, j) represents the predicted chroma samples in a CU, and rec L '(i,j) represents the down-sampled reconstructed luma samples of the same CU which are obtained by performing down-sampling on the reconstructed luma samples rec L (i, j).
  • pred c (i, j) represents the predicted chroma samples in a CU
  • rec L '(i,j) represents the down-sampled reconstructed luma samples of the same CU which are obtained by performing down-sampling on the reconstructed luma samples rec L (i, j).
  • - H’ H + W when LM-L mode is applied; where in the LM mode, above samples and left samples of the CU are used together to calculate the linear model coefficients; in the LM_A mode, only the above samples of the CU are used to calculate the linear model coefficients; and in the LM L mode, only the left samples of the CU are used to calculate the linear model coefficients.
  • positions of four neighboring chroma samples are selected as follows:
  • the four neighboring luma samples corresponding to the selected locations are obtained by a down-sampling operation and the obtained four neighboring luma samples are compared four times to find two larger values: X°A and X 1 A, and two smaller values: x% and x 1 ⁇ . Chroma sample values corresponding to the two larger values and the two smaller values are denoted as respectively. Then X a , Xb, Y a and Yb are derived as:
  • Figure 8 illustrates an example of the locations of the left and above samples and the sample of the current block involved in the CCLM mode, including locations of left and above samples of an NxN chroma block in the CU and locations of left and above samples of an 2Nx 2N luma block in the CU.
  • LM_T mode only the above template is used to calculate the linear model coefficients. To get more samples, the above template is extended to (W+H) samples.
  • LM_L mode only left template is used to calculate the linear model coefficients. To get more samples, the left template is extended to (H+W) samples.
  • LM LT mode left and above templates are used to calculate the linear model coefficients.
  • This parameter computation is performed as part of the decoding process, and is not just as an encoder search operation. As a result, no syntax is used to convey the a and P values to the decoder.
  • Chroma mode signalling and derivation process are shown in Table 1.
  • Chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since 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 Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.
  • the first bin indicates whether it is regular (0) or LM modes (1). If it is LM mode, then the next bin indicates whether it is LM CHROMA (0) or not. If it is not LM CHROMA, next 1 bin indicates whether it is LM_L (0) or LM_A (1). For this case, when sps cclm enabled flag is 0, the first bin of the binarization table for the corresponding intra_chroma_pred_mode can be discarded prior to the entropy coding. Or, in other words, the first bin is inferred to be 0 and hence not coded. This single binarization table is used for both sps cclm enabled flag equal to 0 and 1 cases. The first two bins in Table 2 are context coded with its own context model, and the rest bins are bypass coded.
  • the chroma CUs in 32x32 / 32x16 chroma coding tree node are allowed to use CCLM in the following way:
  • all chroma CUs in the 32x32 node can use CCLM
  • all chroma CUs in the 32x16 chroma node can use CCLM.
  • CCLM is not allowed for chroma CU.
  • the LM_A, LM_L modes are also called Multi -Directional Linear Model (MDLM).
  • Figure 9A illustrates an example that MDLM works when the block content cannot be predicted from the L-shape reconstructed region.
  • Figure 9B illustrates MDLM L which only uses left reconstructed samples to derive CCLM parameters.
  • Figure 9C illustrates MDLM T which only uses top reconstructed samples to derive CCLM parameters.
  • JCTVC-C206 Integerization
  • the integerization design utilizes the linear relationship to modelize the correlation of luma signal and chroma signal.
  • the chroma values are predicted from reconstructed luma values of collocated block.
  • Luma and chroma components have different sampling ratios in YUV420 sampling.
  • the sampling ratio of chroma components is half of that of luma component and has 0.5 pixel phase difference in vertical direction.
  • Reconstructed luma needs down-sampling in vertical direction and subsample in horizontal direction to match size of chroma signal.
  • the down-sampling may be implemented by:
  • Equation (1) Float point operation is necessary in equation (8) to calculate linear model parameters a to keep high data accuracy.
  • float point multiplication is involved in equation (1) when a is represented by float point value.
  • the integer implementation of this algorithm is designed. Specifically, fractional part of parameter a is quantized with n personallybits data accuracy. Parameter a value is represented by an up-scaled and rounded integer value a ' and a ' - tzx (l « n a ) . Then the linear model of equation (1) is changed to:
  • table size can be further reduced to 32 by up-scaling when
  • parametera is calculated as follows:
  • JCTVC-I0166 Simplified Parameter Calculation
  • an intra prediction mode called LM is applied to predict chroma PU based on a linear model using the reconstruction of the collocated luma PU.
  • the parameters of the linear model consist of slope (a»k) and y-intercept (b), which are derived from the neighboring luma and chroma pixels using the least mean square solution.
  • Py’ is the reconstructed pixel from the co- located luma PU.
  • PY is the reconstructed neighboring pixel of the co-located luma PU.
  • L, C, LL, LC, k2 and k3 are derived as:
  • variables a, b and k can be derived as: where ImDiv is specified in a 63-entry look-up table, i.e. Table 3, which is online generated by:
  • Equation (19-6) als is a 16-bit signed integer and ImDiv is a 16-bit unsigned integer. Therefore, 16-bit multiplier and 16-bit storage are needed. It is proposed to reduce the bit depth of multipliers to the internal bit depth, as well as the size of the look-up table, as detailed below.
  • Table 4 shows the example of internal bit depth 10.
  • Multi-model LM Multi-model LM (MMLM) prediction mode
  • the chroma samples are predicted based on the reconstructed luma samples of the same CU by using two linear models as follows: where pred c (i,j) represents the predicted chroma samples in a CU and rec L ' (i, j) represents the down-sampled reconstructed luma samples of the same CU.
  • Threshold is calculated as the average value of the neighboring reconstructed luma samples.
  • Figure 10 illustrates an example of classifying the neighboring samples into two groups based on the value Threshold.
  • parameter a For each group, parameter a ; and [T, with i equal to 1 and 2 respectively, 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 group.
  • XA, YA are the x-coordinate (i.e., luma value) and y-coordinate (i.e., chroma value) value for sample A
  • XB, YB are the x-coordinate and y-coordinate value for sample B.
  • the linear model parameters a and (3 are obtained according to the following equations. [00169] Such a method is also called min-max method. The division in the equation above could be avoided and replaced by a multiplication and a shift.
  • the two templates also can be used alternatively in the other two MMLM modes, called MMLM_A, and MMLM L modes.
  • MMLM 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). In MMLM_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)
  • Chroma mode coding For chroma intra mode coding, a total of 11 intra modes are allowed for 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 A and MMLM L). Chroma mode signaling and derivation process are shown in Table 6. Chroma mode coding directly depends on the intra prediction mode of the corresponding luma block. Since 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 Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.
  • MMLM and LM modes may also be used together in an adaptive manner.
  • two linear models are as follows: where pred c (i, j) represents the predicted chroma samples in a CU and rec L ' (i, j) represents the down-sampled reconstructed luma samples of the same CU. Threshold can be simply determined based on the luma and chroma average values together with their minimum and maximum values.
  • Figure 11 shows an example of classifying the neighboring samples into two groups based on the knee point, T, indicated by an arrow.
  • Linear model parameter a 1 and ff 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 the Threshold (XT, YT).
  • Linear model parameter a 2 and /? 2 are derived from the straight-line relationship between luma values and chroma values from two samples, which are maximum luma sample B (XB, YB) and the Threshold (XT, YT).
  • XA, YA are the x-coordinate (i.e., luma value) and y- coordinate (i.e., chroma value) value for sample A
  • XB, YB are the x-coordinate and y- coordinate value for sample B.
  • the linear model parameters a, and pi for each group, with i equal to 1 and 2 respectively, are obtained according to the following equations.
  • the two templates also can be used alternatively in the other two MMLM modes, called MMLM A, and MMLM L modes respectively.
  • MMLM 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).
  • MMLM 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)
  • 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 multi-model LM modes
  • BlkSizeThres LM represents the smallest block size of LM modes and BlkSizeThres MM represents the smallest block size of MMLM 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 mode signaling and derivation process are shown in Table 1. It is worth noting that for a given CU, if it is coded under 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 6, there are no separate MMLM modes to be signaled. 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 Chroma DM mode, the intra prediction mode of the corresponding luma block covering the center position of the current chroma block is directly inherited.
  • CCLM uses a model with 2 parameters to map luma values to chroma values.
  • the scale parameter “a” and the bias parameter “b” define the mapping as follows: (30)
  • mapping function is tilted or rotated around the point with luminance value y r . It is proposed to use the average of the reference luma samples used in the model creation as y r in order to provide a meaningful modification to the model.
  • Figures 12 A to 12B illustrate the effect of the scale adjustment parameter “u”, wherein Figure 12A illustrates the model created without the scale adjustment parameter “u”, and Figure 12B illustrates the model created with the scale adjustment parameter “u”.
  • the scale adjustment parameter is provided as an integer between - 4 and 4, inclusive, and signaled in the bitstream.
  • the unit of the scale adjustment parameter is l/8th of a chroma sample value per one luma sample value (for 10-bit content).
  • adjustment is available for the CCLM models that are using reference samples both above and left of the block (“LM CHROMA IDX” and “MMLM CHROMA IDX”), but not for the “single side” modes. This selection is based on coding efficiency vs. complexity trade-off considerations.
  • the encoder may perform an SATD based search for the best value of the scale update for Cr and a similar SATD based search for Cb. If either one results as a non-zero scale adjustment parameter, the combined scale adjustment pair (SATD based update for Cr, SATD based update for Cb) is included in the list of RD checks for the TU.
  • JVET-Y0092/Z0051 proposed fusion of chroma intra modes.
  • the intra prediction modes enabled for the chroma components in ECM -4.0 are six cross-component linear model (LM) modes including CCLM LT, CCLM L, CCLM T, MMLM LT, MMLM L and MMLM T modes, the direct mode (DM), and four default chroma intra prediction modes.
  • the four default modes are given by the list ⁇ 0, 50, 18, 1 ⁇ and if the DM mode already belongs to that list, the mode in the list will be replaced with mode 66.
  • a decoder-side intra mode derivation (DIMD) method for luma intra prediction is included in ECM-4.0.
  • a horizontal gradient and a vertical gradient are calculated for each reconstructed luma sample of the L-shaped template of the second neighboring row and column of the current block to build a Histogram of Gradients (HoG).
  • HoG Histogram of Gradients
  • the two intra prediction modes with the largest and the second largest histogram amplitude values are blended with the Planar mode to generate the final predictor of the current luma block.
  • DIMD chroma decoder-side derived chroma intra prediction mode
  • a fusion of a non-LM mode and the MMLM LT mode DIMD chroma
  • a DIMD chroma mode uses the DIMD derivation method to derive the chroma intra prediction mode of the current block based on the collocated reconstructed luma samples. Specifically, a horizontal gradient and a vertical gradient are calculated for each collocated reconstructed luma sample of the current chroma block to build a HoG, as shown in Figure 13. Then the intra prediction mode with the largest histogram amplitude values is used for performing chroma intra prediction of the current chroma block.
  • the intra prediction mode derived from the DIMD chroma mode is the same as the intra prediction mode derived from the DM mode, the intra prediction mode with the second largest histogram amplitude value is used as the DIMD chroma mode.
  • a CU level flag is signaled to indicate whether the proposed DIMD chroma mode is applied as shown in Table 7.
  • the two weights, wO and wl are determined by the intra prediction mode of adjacent chroma blocks and shift is set equal to 2.
  • the DIMD chroma mode and the fusion of chroma intra prediction modes are combined. Specifically, the DIMD chroma mode described in the first embodiment is applied, and for I slices, the DM mode, the four default modes and the DIMD chroma mode can be fused with the MMLM LT mode using the weights described in the second embodiment, while for non-I slices, only the DIMD chroma mode can be fused with the MMLM_LT mode using equal weights.
  • DIMD chroma mode with reduced processing and Fusion of chroma intra prediction modes are combined. Specifically, the DIMD chroma mode with reduced processing derives the intra mode based on the neighboring reconstructed Y, Cb and Cr samples in the second neighboring row and column as shown in Figure 14. Other parts are the same as the third embodiment.
  • DivSigTable[16] ⁇ 0, 7, 6, 5 ,5, 4, 4, 3, 3, 2, 2, 1, 1, 1, 1, 1, 0 ⁇ .
  • Derived intra modes are included into the primary list of intra most probable modes (MPM), so the DIMD process is performed before the MPM list is constructed.
  • the primary derived intra mode of a DIMD block is stored with a block and is used for MPM list construction of the neighboring blocks.
  • Figures 15A to 15D illustrate the steps of decoder-side intra mode derivation, wherein intra prediction direction is estimated without intra mode signaling.
  • the first step as shown in Figure 15A includes estimating gradient per sample (for light-grey samples as illustrated in Figure 15 A).
  • the second step as shown in Figure 15B includes mapping gradient values to closest prediction direction within [2,66],
  • the third step as shown in Figure 15C includes selecting 2 prediction directions, wherein for each prediction direction, all absolute gradients Gx and Gy of neighboring pixels with that direction are summed up, and top 2 directions are selected.
  • the fourth step as shown in Figure 15D includes enabling weighted intra prediction with the selected directions.
  • MRL Multiple reference line
  • Multiple reference line (MRL) intra prediction uses more reference lines for intra prediction.
  • FIG 16 an example of 4 reference lines is depicted, where the samples of segments A and F are not fetched from reconstructed neighboring samples but padded with the closest samples from Segment B and E, respectively.
  • HEVC intra-picture prediction uses the nearest reference line (i.e., reference line 0).
  • reference line 0 the nearest reference line
  • 2 additional lines reference line 1 and reference line 3 are used.
  • the index of selected reference line (mrl idx) is signaled and used to generate intra predictor.
  • reference line idx which is greater than 0, only include additional reference line modes in MPM list and only signal mpm index without remaining mode.
  • the reference line index is signaled before intra prediction modes, and Planar mode is excluded from intra prediction modes in case a nonzero reference line index is signaled.
  • MRL is disabled for the first line of blocks inside a CTU to prevent using extended reference samples outside the current CTU line. Also, PDPC is disabled when additional line is used.
  • MRL mode the derivation of DC value in DC intra prediction mode for non-zero reference line indices is aligned with that of reference line index 0.
  • MRL requires the storage of 3 neighboring luma reference lines with a CTU to generate predictions.
  • the CrossComponent Linear Model (CCLM) tool also requires 3 neighboring luma reference lines for its down-sampling filters. The definition of MRL to use the same 3 lines is aligned as CCLM to reduce the storage requirements for decoders.
  • CCCM Convolutional cross-component model
  • CCCM convolutional cross-component model
  • CCCM convolutional cross-component model
  • Multi-model CCCM mode can be selected for PUs which have at least 128 reference samples available.
  • the proposed convolutional 7-tap filter consists of a 5-tap plus sign shape spatial component, a non-linear term and a bias term.
  • the input to the spatial 5-tap component of the filter consists of a center (C) luma sample which is collocated with the chroma sample to be predicted and its above/north (N), below/ south (S), left/west (W) and right/ east (E) neighbors as illustrated in Figure 17.
  • the non-linear term P is represented as power of two of the center luma sample C and scaled to the sample value range of the content:
  • the bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the fdter is calculated as a convolution between the fdter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • predChromaVal coC + ciN + C2S + C3E + C4W + C5P + ceB
  • the filter coefficients c are calculated by minimising MSE between predicted and reconstructed chroma samples in the reference area.
  • Figure 18 illustrates the reference area which consists of 6 lines of chroma samples above and left of the PU. Reference area extends one PU width to the right and one PU height below the PU boundaries. Area is adjusted to include only available samples. The extensions to the area shown in blue are needed to support the “side samples” of the plus shaped spatial filter and are padded when in unavailable areas.
  • the MSE minimization is performed by calculating autocorrelation matrix for the luma input and a cross-correlation vector between the luma input and chroma output.
  • Autocorrelation matrix is LDL decomposed and the final filter coefficients are calculated using back- substitution.
  • the process follows roughly the calculation of the ALF filter coefficients in ECM, however LDL decomposition was chosen instead of Cholesky decomposition to avoid using square root operations.
  • the proposed approach uses only integer arithmetic.
  • CCCM Usage of the mode is signalled with a CABAC coded PU level flag.
  • CABAC context was included to support this.
  • CCCM is considered a sub-mode of CCLM. That is, the CCCM flag is only signalled if intra prediction mode is LM CHROMA IDX (to enable single mode CCCM) or MMLM CHROMA IDX (to enable multi-model CCCM).
  • the encoder performs two new RD checks in the chroma prediction mode loop, one for checking single model CCCM mode and one for checking multi-model CCCM mode.
  • the neighboring reconstructed lumachroma sample pairs are classified into one or more sample groups based on the value Threshold, which only considers the luma DC values. That is, a luma-chroma sample pair is classified by only considering the intensity of the luma sample.
  • Threshold which only considers the intensity of the luma sample.
  • luma component usually preserves abundant textures, and the current luma sample may be highly correlated with neighboring luma samples, such inter-sample correlation (AC correlation) may benefit the classification of luma-chroma sample pairs and can bring additional coding efficiency.
  • the CCLM assumes a given chroma sample only correlates to a corresponding luma sample (L0.5, which can be taken as the fractional luma sample position), and a simple linear regression (SLR) with ordinary least squares (OLS) estimation is used to predict the given chroma sample.
  • SLR simple linear regression
  • OLS ordinary least squares
  • one chroma sample may simultaneously correlate to multiple luma samples (AC or DC correlation), so a multiple linear regression (MLR) model may further improve the prediction accuracy.
  • the CCCM mode can enhance the intra prediction efficiency, there is room to further improve its performance. Meanwhile, some parts of the existing CCCM mode also need to be simplified for efficient codec hardware implementations or improved for better coding efficiency. Furthermore, the tradeoff between its implementation complexity and its coding efficiency benefit needs to be further improved.
  • classifiers considering luma edge or AC information is introduced, in contrast to the above implementations wherein only luma DC values are considered.
  • the present disclosure provides exemplary classifiers.
  • the process of generating linear prediction models for different sample groups may be similar as CCLM or MMLM (e.g., via a least square method, or a simplified min-max method, etc.), but with different metrices for classification.
  • Different classifiers may be used to classify the neighboring luma samples (e.g., of the neighboring luma-chroma sample pairs) and/or the luma samples corresponding to chroma samples to be predicted.
  • the luma samples corresponding to the chroma samples may be obtained by a down-sampling operation to match the locations of the corresponding chroma samples for 4:2:0 video sequences.
  • a luma sample corresponding to a chroma sample may be obtained by performing a down-sampling operation on more than one (e.g., 4) reconstructed luma samples corresponding to the chroma sample (e.g., located around the chroma sample).
  • the luma samples may obtained directly from the reconstructed luma samples in a case of 4:4:4 video sequences, for example.
  • the luma samples may be obtained from respective ones of the reconstructed luma samples that are at respective collocated positions for the corresponding chroma samples.
  • a luma sample to be classified may be obtained from one of four reconstructed luma samples corresponding to the chroma sample that is at a left-top position of the four reconstructed luma samples, which may be considered as a collocated position for the chroma sample.
  • a first classifier may classify luma samples according to their edge strengths. For example, one direction (e.g., 0-degree, 45-degree, or 90-degree, etc.) may be selected to calculate the edge strength.
  • a direction may be formed by a current sample and a neighboring sample along the direction (e g., a neighboring sample located at the right-top of the current sample for 45-degree).
  • An edge strength may be calculated by subtracting the neighbor sample from the current sample.
  • the edge strength may be quantized into one of M segments by M-l thresholds, and the first classifier may use M classes to classify the current sample.
  • N directions may be formed by a current sample and N neighboring samples along the N directions.
  • N edge strengths may be calculated by subtracting N neighboring samples from the current sample, respectively. Similarly, if each of the N edge strengths may be quantized into one of M segments by M-l thresholds, then the first classifier may use MN classes to classify the current sample.
  • a second classifier may be used to classify according to a local pattern. For example, a current luma sample Y0 may be compared with its neighboring N luma samples Yi. A score may be added by one if the value of Y0 is greater than that of Yi, otherwise, the score may be reduced by one. The score may be quantized to form K classes. The second classifier may classify a current sample into one of the K classes. For example, the neighboring luma samples may be obtained from four neighbors that are located above, left, right and below the current luma samples, i.e., without diagonal neighbors.
  • first classifier may be combined with the existing MMLM threshold-based classifier.
  • instance A of the first classifier may be combined with another instance B of the first classifier, where the instance A and B employ different directions (e.g., employing vertical and horizontal directions, respectively).
  • the proposed cross-component method described in the disclosure can also be applied to other prediction coding tools with similar design spirits.
  • the proposed method can also be applied by dividing luma-chroma sample pairs into multiple sample groups.
  • Y/Cb/Cr also can be denoted as Y/U/V in video coding area. If video data is of RGB format, the proposed method can also be applied by simply mapping YUV notation to GBR, for example.
  • a filter-based linear model which utilizes the MLR model is introduced as follows, to take into account the possibilities that one chroma sample may simultaneously correlate to multiple luma samples.
  • the reconstructed collocated and neighboring luma samples can be used to predict the chroma sample, to capture the inter-sample correlation among the collocated luma sample, neighboring luma samples, and the chroma sample.
  • the reconstructed luma samples are linear weighted and combined with one “offset” to generate the predicted chroma sample (C: predicted chroma sample, Lt : Lth reconstructed collocated or neighboring luma samples, cq : filter coefficients, /? : offset, N : filter taps), as shown in the following equation (32-1).
  • the linear weighted plus offset value directly forms the predicted chroma sample (can be low pass, high pass adaptively according to video content), and it is then added by the residual to form the reconstructed chroma sample.
  • the offset term can also be implemented as middle chroma value B (512 for 10-bit content) multiplied by another coefficient, as shown in the following equation (32-2).
  • the top and left reconstructed luma and chroma samples can be used to derive or train the FLM parameters
  • the top and left training samples are collected, and one pseudo inverse matrix is calculated at both encoder and decoder sides to derive the parameters, which are then used to predict the chroma samples in the given CU.
  • N denotes the number of filter taps applied on luma samples
  • M denotes the total top and left reconstructed luma-chroma sample pairs used for training parameters
  • Figure 20 shows an example that N is 6 (6-tap), M is 8, top 2 rows and left 3 columns luma samples and top 1 row and left 1 column chroma samples are used to derive or train the parameters.
  • ELM/FLM/GLM (as discussed below) can be extended straightforwardly to the CfL design in the AVI standard, which transmits model parameters (a, P) explicitly. For example, (1-tap case) deriving a and/or p at encoder at SPS/DPS/VPS/SEFAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels, and signaled to decoder for the CfL mode.
  • FIG. 20 To further improve the coding performance, additional designs may be used in the FLM prediction. As shown in Figure 20 and discussed above, a 6-tap luma filter is used for the FLM prediction. However, though a multiple tap filter can fit well on training data (e g., top and left neighboring reconstructed luma and chroma samples), in some cases that training data do not capture full characteristics of testing data, it may result in overfitting and may not predict well on testing data (i.e., the to-be-predicted chroma block samples). Also, different filter shapes may adapt well to different video block content, leading to more accurate prediction.
  • training data e g., top and left neighboring reconstructed luma and chroma samples
  • different filter shapes may adapt well to different video block content, leading to more accurate prediction.
  • the filter shape and number of filter taps can be predefined or signaled or switched in Sequence Parameter Set (SPS), Adaptation Parameter Set (APS), Picture Parameter Set (PPS), Picture Header (PH), Slice Header (SH), Region, CTU, CU, Subblock, or Sample level.
  • SPS Sequence Parameter Set
  • APS Adaptation Parameter Set
  • PPS Picture Parameter Set
  • PH Picture Header
  • SH Slice Header
  • Region CTU
  • CU Subblock
  • Sample level Sample level
  • a set of filter shape candidates can be predefined, and a selection on the set of filter shape candidates may be signaled or switched in SPS, APS, PPS, PH, SH, Region, CTU, CU, Subblock, or Sample level.
  • Different components e.g., U and V
  • a set of filter shape candidates may be predefined, and a filter shape (1, 2) may denote a 2-tap luma filter, a filter shape (1, 2, 4) may denote a 3 -tap luma filter and the like, as shown in Figure 20.
  • the filter shape selection of U and V components can be switched in PH or in CU or CTU level.
  • N-tap can represent N-tap with or without the offset P as described herein.
  • the FLM or the CCCM filter shape may include a non-linear term.
  • C6 for a center (C) luma sample value which is collocated with the chroma sample to be predicted, its above/north (N), below/south (S), right/east (E) and left/west (W) neighbors, a non-linear term P and a bias term B.
  • the values used to derive the non-linear term P can be a combination of current and neighboring luma samples, but not limited to C*C.
  • P can be derived as following:
  • Q and R can be linear combination of current and neighboring luma samples either in a down-sampled domain (for example, the Q and R being pre-operated luma samples obtained by weighted-average operation) or without any down-sampling process.
  • Different values (Q and R) used to derive the non-linear term are considered as different filter shapes and can be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • a set of filter shape candidates can be predefined or signaled/switched in SPS/DPS/VPS/SEVAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • Different chroma types and/or color formats can have different predefined filter shapes and/or taps.
  • a predefined filter shape (1, 2, 4, 5) may be used for 4:2:0 type-0
  • a predefined filter shape (0, 1, 2, 4, 7) may be used for 4:2:0 type-2
  • a predefined filter shape (1, 4) may be used for 4:2:2
  • a predefined filter shape (0, 1, 2, 3, 4, 5) may be used for 4:4:4, as shown in Figure 21.
  • unavailable luma and chroma samples for deriving the MLR model can be padded from available reconstructed samples.
  • the padding process may be applied in both training data (top and left neighboring reconstructed luma and chroma samples) and testing data (the luma and chroma samples in the CU(s)).
  • One or more shape/number of filter taps may be used for FLM prediction, examples being shown in Figure 25, Figure 26, and Figures 27A to 27B.
  • One or more sets of filter taps may be used for FLM prediction, examples being shown in Figures 28A to 28G.
  • the filter shape candidates can be implicitly derived without explicitly signaling bits.
  • the filter shape candidates can be the filter shape candidates for FLM or GLM (as discussed below).
  • the filter shape candidates can be the cross shape filter for CCCM, any of the filters shown in Figure 25, Figure 26, Figure 27A, Figure 27B, and Figures 28 A to 28G, or other filters mentioned in this disclosure.
  • the well- known “N-fold cross-validation” technique in machine learning area can be used for training filter coefficients. The technique divides the available training data into N sets, and use partial sets for training, others for validation.
  • Step 1 determining M filter shape candidates for predicting the chroma sample values of the current CU
  • Step 2 dividing the available L-shaped template area external to the CU into N regions, denoted as Ro, Ri, ... RN-I , i.e., dividing the training data into N sets for N-fold training, wherein the luma sample values and the chroma sample values of the available template area are known values;
  • Step 3 applying each of the M filter shape candidates respectively to a part of the available template area, i.e., one or more regions among all the N regions Ro, Ri, ... RN-I ;
  • Step 4 deriving M filter coefficient sets corresponding to the M filter shape candidates, denoted as Fo, Fi, ... FM-I;
  • Step 5 applying the derived Fo, Fi, ... FM-1 filter coefficient sets to another part of the available template area to predict the chroma sample values based on corresponding luma sample values, wherein the another part of the available template area is different from the part of the available template area mentioned in Step 3;
  • Step 6 accumulating, for each of the M filter shapes respectively, the errors between the predicted chroma sample values and the known chroma sample values in the another part of the available template area by Sum of Absolute Difference (SAD), Sum of Squared Difference (SSD), or Sum of Absolute Transformed Difference (SATD), denoted as Eo, Ei, ... EM-I;
  • SAD Sum of Absolute Difference
  • SSD Sum of Squared Difference
  • SATD Sum of Absolute Transformed Difference
  • Step 7 sorting and selecting K smallest errors, denoted as E’o, E’i, ... E’K-I, which correspond to K filter shapes and K filter coefficient sets, and
  • Step 8 selecting one filter shape candidate from the K filter shape candidates, to apply to the current CU for chroma prediction. If K is more than 1, then the decoder may still receive signal from the encoder indicating the applied filter. However, if K is 1, then the signaling can be omitted and the filter with the smallest accumulated error is determined to be the applied filter.
  • Figure 29A and Figure 29B illustrate examples of 2-fold training for implicitly filter shape derivation.
  • Figure 29 A shows that in template area, even-row region Ro (yellow) is used for training/ deriving 4 filter coefficient sets, and odd-row region Ri (red) is used for validation/comparing and sorting costs of 4 filter coefficient sets;
  • Figure 29B shows that in template area, Ro (yellow) and Ri (red) are interleaved. It should be understood that Ro and Ri can be exchanged in these examples.
  • one of 4 filter shape candidates is to be selected as the applied filter, while the L-shaped template area is divided into even-numbered and odd-numbered rows or columns.
  • the steps include: predefining 4 filter shape candidates for the current CU (for example, 4 filter shape candidates from Figure 25); dividing the available L-shaped template area (for example, 6 chroma rows and columns for CCCM, note that in CCCM design, each chroma sample involves 6 luma samples for down-sampling) into 2 regions denoted as Ro, Ri, wherein, for example, Ro is composed of the even rows or columns, and Ri is composed of the odd rows or columns (Figure 29 A shows the example that in template area, even-row region Ro is used for training/deriving 4 filter coefficient sets, and odd-row region Ri is used for validation/comparing and sorting costs of 4 filter coefficient sets); applying 4 filter shape candidates independently to a part of the available template area (for example, region Ro); deriving 4 filter coefficient sets for the 4 filter shapes respectively, denoted as Fo
  • the steps include: determining 4 filter shape candidates for the current CU; dividing the available L-shaped template area (for example, 6 chroma rows or columns for CCCM) into 2 regions denoted as Ro, Ri, wherein the luma samples in Ro and Ri are for example interleaved as shown in the following tables: or and Figure 29B shows the example that in template area, Ro and Ri are interleaved; applying 4 filter shape candidates independently to a part of the available template area (for example, region Ro); deriving 4 filter coefficient sets for the 4 filter shapes respectively, denoted as Fo, Fi, ... F 3 ; applying the derived Fo, Fi, ...
  • F3 filter coefficient sets to the other part of the available template area (for example, region Ri) respectively, to predict the corresponding chroma sample values; accumulating, for each of the 4 filter shapes respectively, the errors between the predicted chroma sample values and the known chroma sample values in the other part of the available template area (for example, region Ri) by SAD, SSD, or SATD, denoted as Eo, Ei, ... E3; sorting and selecting 2 smallest accumulated errors in Eo, Ei, ... E3, denoted as E’o, E’i, which correspond to 2 filter shapes and 2 filter coefficient sets; and based on the received signal from the encoder, selecting one filter shape candidate in the 2 filter shape candidates, to apply to the current CU for chroma prediction.
  • non-linear term P may also be included in FLM filters (e g., a 3*2 filter as shown in Figure 20) and derived in a similar way as discussed above.
  • the steps of dividing the available L-shaped template area may be omitted.
  • the M filter coefficient sets may be derived based on the sample values from the available template area and then applied back to the available template area respectively, to predict the corresponding chroma sample values for accumulating the errors.
  • an MLR model (linear equations) must be derived at both the encoder and the decoder.
  • several methods are proposed to derive the pseudo inverse matrix A + , or to directly solve the linear equations.
  • Other known methods like Newton's method, Cayley-Hamilton method, and Eigendecomposition as mentioned in https://en.wikipedia.org/wiki/Invertible_matrix can also be applied.
  • a + can be denoted as A -1 for simplification.
  • the linear equations may be solved as follows
  • linear equations can be solved using Gauss-Jordan elimination, by an augmented matrix and a series of elementary row operation to obtain the reduced row echelon form
  • Gauss-Jordan elimination by an augmented matrix and a series of elementary row operation to obtain the reduced row echelon form
  • A can be firstly decomposed by Cholesky-Crout algorithm, leading to one upper triangular and one lower triangular matrices, and one forward substitution plus one backward substitution can be applied in serial to obtain the solution.
  • Cholesky-Crout algorithm leading to one upper triangular and one lower triangular matrices, and one forward substitution plus one backward substitution can be applied in serial to obtain the solution.
  • 3x3 example shows a 3x3 example.
  • DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels for example, when predefined l «(bitDepth-l), meanC, meanL, or meanC-meanL (mean current chroma or other chroma, luma values from available, or subset of FLM reconstructed neighboring region).
  • bitDepth-l meanC
  • meanL meanL
  • meanC-meanL mean current chroma or other chroma, luma values from available, or subset of FLM reconstructed neighboring region.
  • REG_SQR can be predefined or signaled or switched in SPS/ DPS/VPS/SEFAPS/PPS/PH/SH/Region/CTU/CU/Subblocl ⁇ /Sample levels.
  • Figure 20 shows a typical case that the FLM parameters are derived using top 2 and/or left 3 luma lines and top 1 and/or left 1 chroma lines.
  • using different region for parameter derivation may bring coding benefit because of different block content and the reconstructive quality of different neighboring samples, as mentioned above.
  • Several ways to choose the applied region for parameter derivation are proposed below:
  • the FLM derivation can only use top or left luma and/or chroma samples to derive the parameters. Whether to use FLM, FLM_L, or FLM_T can be predefined or signaled or switched in
  • the number of extended luma/chroma samples can be predefined, or signaled or switched in SPS/ DPS/VPS/SELAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • Figure 22 shows an illustration of FLM L and FLM T (e g., under 4 tap).
  • FLM L or FLM_T When FLM L or FLM_T is applied, only H’ or W’ luma/chroma samples are used for parameter derivation, respectively.
  • different line index can be predefined, or signaled or switched in SPS/DPS/VPS/SEFAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels, to indicate the selected luma-chroma sample pair line. This may benefit from different reconstructive quality of different line samples.
  • FIG 23 shows that similar to MRL, FLM can use different lines for parameter derivation (e.g., under 4 tap).
  • FLM can use light blue/yellow luma and/or chroma samples in index 1
  • the luma sample values of an external region of the video block to be decoded may be referred to as “the external luma sample values”, and the chroma sample values of the external region may be referred to as “the external chroma sample values” throughout the disclosure.
  • Corresponding syntax may be defined as below in Table 9 for the FLM prediction.
  • FLC represents fixed length code
  • TU represents truncated unary code
  • EGk represents exponent! al -golomb code with order k, where k can be fixed or sign al ed/s witched in SPS/ DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels
  • SVLC represents signed EGO
  • UVLC represents unsigned EGO.
  • a new method for cross-component prediction is proposed on the basis of the existing linear model designs, in order to further improve coding accuracy and efficiency. Main aspects of the proposed method are detailed as follows.
  • reference samples/training template/reconstructed neighboring region usually refers to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • pre-operations e.g., pre-linear weighted, sign, scale/abs, thresholding, ReLU
  • the pre-operations may comprise calculating sample differences based on the luma sample values.
  • the sample differences may be characterized as gradients, and thus this new method is also referred to as gradient linear model (GLM) in certain embodiments.
  • FIGS 24 A to 24D show some examples for l-tap/2-tap (with offset) pre-operations, where 2-tap coefficients are denoted as (a, b).
  • each circle as illustrated in Figures 24A to 24D represent an illustrative chroma position in the YUV 4:2:0 format.
  • a luma sample corresponding to a chroma sample may be obtained by performing a down-sampling operation on more than one (e.g., 4) reconstructed luma samples corresponding to the chroma sample (e.g., located around the chroma sample).
  • the chroma position may correspond to one or more luma samples comprising a collocated luma sample.
  • the different 1-tap patterns are designed for different gradient directions and using different “interpolated” luma samples (weighting to different luma location) for gradient calculation. For example, one typical filter [1, 0, -1; 1, 0, -1] is shown in Figures 24A, 24C and 24D, which represents the following operations:
  • Rec L represents the reconstructed luma sample values
  • Rec L ' ' (i,j) represents the pre-operated luma sample values.
  • the 1-tap filters as shown in Figures 24A, 24C and 24D may be understood as alternatives for the downsampling filters as used in CCLM (please refer to equations (6)-(7)), with changed filter coefficients.
  • Pre-operations can be according to gradients, edge direction (detection), pixel intensity, pixel variation, pixel variance, Roberts/Prewitt/compass/Sobel/Laplacian operator, high-pass filter (by calculating gradients or other relevant operators), low-pass filter (by performing weighted-average operations)... etc.
  • the edge direction detectors listed in the examples can be extended to different edge directions. For example, 1-tap (1, -1) or 2-tap (a, b) applied along different directions to detect different edge gradients.
  • the filter shape/coeff can be symmetric with respect to the chroma position, as the Figures 24A to 24D examples (420 type-0 case).
  • the pre-operation parameters can be fixed or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels. Note in the examples, if multiple coefficients apply on one sample (e.g., -1, 4), then they can be merged (e.g., 3) to reduce operations.
  • the pre-operations may relate to calculating sample differences of the luma sample values.
  • the pre-operations may comprise performing downsampling by weighted-average operations.
  • the pre-operations can be applied repeatedly. For example, one may apply one template filtering to template to remove outliers using the low-pass smoothing FIR filter [1, 2, l]/4, or [1, 2, 1; 1, 2, 1 ]/8 (i.e., down-sampling) and then apply 1-tap GLM filter to calculate the sample differences to derive the linear model. It may be contemplated that one may also calculate the sample differences and then enabling down-sampling.
  • the pre-operation coefficients (finally applied (e.g., 3), or middle applied (e.g., -1, 4) to per luma sample) can be limited to power -of-2 values to save multipliers.
  • the proposed new method may be reused for/combined with the above discussed CCLM, which utilizing a simple linear regression (SLR) model and using one corresponding luma sample value to predict the chroma sample value. This is also referred to as a 1 -tap case.
  • SLR simple linear regression
  • deriving the linear model further comprises deriving a scale parameter a and an offset parameter [3 by using the pre-operated neighboring luma sample values and the neighboring chroma sample values.
  • the linear model may be re-writen as: ft (35)
  • L here represents “p re-o P erate d” luma samples.
  • the parameter derivation of 1-tap GLM can reuse CCLM design, but taking directional gradient into consideration (may be with high-pass filter).
  • the scale parameter a may be derived by utilizing a division look-up table, as detailed below, to enable simplification.
  • the scale parameter a and the offset paremeter [3 may be derived by utilizing the above-discussed min-max method.
  • the scale parameter a and the offset paremeter (3 may be derived by: comparing the pre-operated neighboring luma sample values to determine a minimum luma sarnie value YA and a maximum luma sample value YB; determining corresponding choma samples values XA and XB for the minimum luma sarnie value YAand the maximum luma sample value YB, respectively; and deriving the scale parameter a and the offset paremeter /3 based on the minimum luma sarnie value YA, the maximum luma sample value YB, and the corresponding choma samples values XAandXB according to the following equations:
  • the encoder may determine a scale adjustment value (for example, “u”) to be signaled in the bitstream and add the scale adjustment value to the derived scale parameter a.
  • the decoder may dertermine the scale adjustment value (for example, “u”) from the bitstream and add the scale adjustment value to the derived scale parameter a. The added value are finally used to predict the internal chroma sample values.
  • the proposed new method may be reused for/combined with FLM, which utilizing a multiple linear regression (MLR) model and using multiple luma sample values to predict the chroma sample value.
  • FLM which utilizing a multiple linear regression (MLR) model and using multiple luma sample values to predict the chroma sample value.
  • MLR multiple linear regression
  • the linear model may be re-writen as:
  • multiple scale parameters a and an offset parameter p may be derived by using the pre-operated neighboring luma sample values and the neighboring chroma sample values.
  • the offset parameter p is optional.
  • at least one of the multiple scale parameters a may be derived by utilizing the sample differences.
  • another of the multiple scale parameters a may be derived by utilizing the down- sampled luma sample value.
  • at least one of the multiple scale parameters a may be derived by utilizing horizontal or vertical sample differences calculated on the basis of down-sampled neighboring luma sample values.
  • the linear model may combine multiple scale parameters a asscosicated with different pre-opertaions.
  • the used direction oriented filter shape can be derived at decoder to save bit overhead. For example, at the decoder, a number of directional gradient filters may be applied for each reconstructed luma sample of the L-shaped template of the i-th neighboring row and column of the current block. Then the filtered values (gradients) may be accumulated for each direction of the number of directional gradient filters respectively. In an example, the accumulated value is an accumulated value of absolute values of corresponding filtered values. After the accumulation, the direction of the directional gradient filter for which the accumulated value is the largest may be determined as the derived (luma) gradient direction. For example, a Histogram of Gradients (HoG) may be built to determine the largest value. The derived direction can be further applied as the direction for predicting chroma samples in the current block.
  • HoG Histogram of Gradients
  • DIMD decoder-side intra mode derivation
  • Step 1 applying 2 kinds of directional gradient filters (3x3 hor/ver Sobel) for each reconstructed luma sample of the L-shaped template of the 2 nd neighboring row and column of the current block;
  • Step 2 accumulating filtered values (gradients) by SAD (sum of absolute differences) for each of the directional gradient filters;
  • Step 3 Build a Histogram of Gradients (HoG) based on the accumulating filtered values
  • Step 4 The largest value in HoG is determined to be the derived (luma) gradient direction, based on which the GLM filter may be determined.
  • shape candidates are [-1, 0, 1; -1, 0, 1] (horizontal) and [1, 2, 1; -1, -2, -1] (vertical)
  • shape [-1, 0, 1; -1, 0, 1] for GLM based chroma prediction.
  • the gradient filter used for deriving the gradient direction can be the same or different with the GLM filter in shape.
  • both of the filters may be horizontal [-1, 0, 1 ; -1 , 0, 1], or the two filters may have different shapes, while the GLM filter may be determined based on the gradient filter.
  • the proposed GLM can be combined with above discussed MMLM or ELM.
  • each group can share or have its own filter shape, with syntaxes indicating shape for each group.
  • horiontal grandients grad hor may be classified into a first group, which correspond to a first linear model
  • vertical grandients grad_ver may be classified into a second group, which correspond to a second linear model.
  • the horiontal luma patterns may be generated only once.
  • Further possible classifiers are also provided as follows. With the classifers, the neighboring and internal luma-chroma sample pairs of the current video block may be classified into muitple groups based on one or more thresholds.
  • each neighboring/internal chroma sample and its corresponding luma sample may be referred to as a luma-chroma sample pair.
  • the one or more thresholds are associated with intensities of neighboring/ internal luma samples.
  • each of the multiple groups corresponds to a respective one of the plurality of linear models.
  • the following operations may be performed: classifying neighboring reconstructed luma-chroma sample pairs of the current video block into 2 groups based on Threshold,' deriving different linear models for different groups, wherein the deriving process may be GLM simplified, i.e., with the above preoperations to reduce the number of taps; classifying luma-chroma sample pairs inside the CU (internal luma-chroma sample pairs, wherein each of the internal luma-chroma sample pairs comprises an internal chroma sample value to be predicted with the derived linear model) into 2 groups similarly based on Threshold,' applying different linear models to the reconstructed luma samples in different groups; and predicting chroma samples in the CU based on different classified linear models.
  • rec L ' CL j may be down-sampled reconstructed luma samples
  • rec c (i, j) may be reconstructed chroma samples (note only neighbours are available)
  • Threshold may be average value of the neighboring reconstructed luma samples.
  • the number of classes (2) can be extended to multiple classes by increasing the number of Threshold (e.g., equally divided based on min/max of neighboring reconstructed (down-sampled) luma samples, fixed or signaled/switched in
  • the filtered values of FLM/GLM apply on neighboring luma samples are used for classification. For example, if 1 - tap (1, -1) GLM is applied, average AC values are used (physical meaning).
  • the processing can be: classifying neighboring reconstructed luma-chroma sample pairs into K groups based on one or more filter shapes, one or more filtered values, and K-l Threshold Ti; deriving different MLR models for different groups, wherein the deriving process may be GLM simplified, i.e., with the above pre-operations to reduce the number of taps; classifying lumachroma sample pairs inside the CU (internal luma-chroma sample pairs, wherein each of the internal luma-chroma sample pairs comprises an internal chroma sample value to be predicted with the derived linear model) into K groups similarly based on one or more filter shapes, one or more filtered values, and K-l Threshold Ti; applying different linear models to the reconstructed luma samples in different groups; predicting chroma samples in the CU based on different classified linear models.
  • Threshold can be predefined (e.g., 0, or can be a table) or signaled/switched
  • Threshold can be the average AC value (filtered value) (2 groups), or equally divided based on min/max AC (K groups), of neighboring reconstructed (can be down-sampled) luma samples.
  • one filter shape (e.g., 1-tap) may be selected to calculate edge strengths.
  • the direction is determined as a direction along which a sample difference between samples of the current and N neighboring samples (e.g., all 6 luma samples) is calculated.
  • the filter shape [1, 0, -1; 1, 0, -1]
  • the filter at the upper middle in Figure 24A indicates a horizontal direction since a sample difference may be calculated between samples in the horizontal direction
  • the filter below it shape [1, 2, 1; -1, -2, -1] indicates a vertical direction since a sample difference may be calculated between samples in the vertical direction.
  • the positive and negative coefficients in each of the filters enable the calculation of the sample differences.
  • the filter shape used for classification can be the same or different with the filter shape used for MLR prediction.
  • Both and the number of thresholds M-l, the thresholds values Ti can be fixed or signal ed/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • other classifiers/combined-classifiers as discussed in ELM can also be used for FLM and/or GLM.
  • the matrix/parameter derivation in FLM requires floating-point operation (e.g., division in closed-form), which is expensive for decoder hardware, so a fixed-point design is required.
  • floating-point operation e.g., division in closed-form
  • CCLM modified luma reconstructed sample generation of CCLM
  • the original CCLM process can be reused for GLM, including fixed-point operation, MDLM downsampling, division table, applied size restriction, min-max approximation, and scale adjustment.
  • 1-tap GLM can have its own configurations or share the same design as CCLM.
  • each group can apply the same or different simplification operation. For example, samples for each group are padded respectively to the target sample number before applying right shift, and then apply the same derivation process, same division table.
  • the method of implicit filter shape derivation can also be used to determine whether to disable down-sampled process in CCCM filter coefficients (treat with/without down-sampled process as different filter shapes).
  • the 1-tap case can reuse the CCLM design, dividing by n may be implemented by right shift, dividing by A 2 may be implemented by by a LUT.
  • the integerization parameters including n a , n Ai , n Az , r Ai , r Az n table invloved in the integerization design of LMS CCLM and intermediate parameters for deriving the linear model (equations (19)-(20)) can be the same as CCLM or have different values, to have more precision.
  • the integerization parameters can be predefined or signaled/ switched in
  • SPS/DPS/VPS/SEVAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels can be conditioned on sequence bitdepth.
  • bitdepth bitdepth+4.
  • the padding method for GLM can be the same or different with that of CCLM.
  • Division LUT proposed for CCLM/LIC Long Illumination Compensation
  • AVC/HEVC/AV1/WC/AVS can be used for GLM division.
  • reusing the LUT in JCTVC-I0166 for bitdepth 10 case (Table 4).
  • the division LUT can be different from CCLM.
  • CCLM uses min-max with DivTable as in equation 5, but GLM uses 32-entries LMS division LUT as in Table 5.
  • the meanL values may not always be positive (e.g., using filtered/gradient values to classify groups), so sgn(meanL) needs to be extracted, and use abs(meanL) to look-up the division LUT.
  • division LUT used for MMLM classification and parameter derivation can be different. For example, using lower precision LUT (as the LUT in min-max) for mean classification, and using higher precision LUT (as in the LMS) for parameter derivation.
  • ELM/FLM/GLM Similar to the CCLM design, some size restrictions can be applied for ELM/FLM/GLM. For example, same constraint for luma-chroma latency in dual tree may be applied.
  • the size restriction can be according to the CU area/width/height/depth.
  • the threshold can be predefined or signaled in SPS/DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • the predefined threshold may be 128 for chroma CU area.
  • the at least one pre-operation is performed in response to determining that the video block meets an enabling threshold, wherein the enabling threshold is associated with area, width, height or partition depth of the video block. Spesifically, the enabling threshold may define a minium or maximum area, width, height or partition depth of the video block.
  • the video block may comprise a current chroma block and its collocated luma block. It is also proposed to apply the above enabling threshold for the current chroma block and its collocated luma block jointly.
  • the at least one pre-operation is performed in response to determining the enabling threshold is met for both the current chroma block and its collocated luma block. [00335] Line buffer reduction
  • the top template samples generation can be limited to 1 row, to reduce CTU row line buffer storage. Note that only one luma line (general line buffer in intra prediction) is used to make the down-sampled luma samples when the upper reference line is at the CTU boundary.
  • top template can be limited to only use 1 row (but not 2) for parameter derivation (other CUs can still use 2 rows). This saves luma sample line buffer storage when processing CTU row by row at decoder hardware.
  • Several methods can be used to achieve the line buffer reduction. Note the example of limited “1” row can be extended to N rows with similar operations. Similarly, 2-tap or multi-tap can also apply such operations. When applying multi-tap, chroma samples may also need to apply operations.
  • T ake an example where N 4, that is, the video block is at a top boundary of a current CTU, while top 4 rows of neighboring luma sample values and corresponding chroma sample values are used for deriving the linear model.
  • the corresponding chroma sample values may refer to corresponding top 4 rows of neighboring chroma sample values (for example, for the YUV 4:4:4 format).
  • the corresponding chroma sample values may refer to corresponding top 2 rows of neighboring chroma sample values (for example, for the YUV 4:2:0 format).
  • the top 4 rows of neighboring luma sample values and corresponding chroma sample values may be divided into two regions - a first region comprising valid sample values (for example, the one nearest row of luma sample values and corresponding chroma sample values) and a second region comprising invalid sample values (for example, the other three rows of luma sample values and corresponding chroma sample values). Then coefficients of the filter corresponding to sample positions not belonging to the first region may be set as zeros, such that only sample values from the first region are used for calculating the sample differences.
  • the filter [1, 0, -1; 1, 0, -1] can be reduced to [0, 0, 0; 1, 0, -1],
  • the nearest sample values in the first region may be padded to the second region, such that the padded sample values may be used to calculate the sample differences.
  • pred (w0 * pred0 + wl * predl + (1 « (shift — 1))) » shift
  • predO is the predictor based on non-LM mode
  • predl is the predictor based on GLM
  • pred0 is the predictor based on one of CCLM (including all MDLM/MMLM)
  • predl is the predictor based on GLM
  • predl is the predictor based on GLM.
  • Different I/P/B slices can have different designs for weights, w0 and wl , depending on if neighboring blocks is coded with CCLM/GLM/other coding mode or the block size/width/height.
  • the 1-tap GLM has good gain complexity trade-off since it can reuse the existing CCLM module without introducing additional derivation.
  • Such 1-tap design can be extended or generalized further according to one or more aspects of the present disclosure.
  • one single corresponding luma sample L may be generated by combining collocated luma sample and neighboring luma samples.
  • the combination may be a combination of different linear filters, e.g., a combination of a high-pass gradient filter (GLM) and a low-pass smoothing filter (e.g., [1, 2, I; 1, 2, l]/8 FIR down-sampling filter that may be generally used in CCLM), and/or a combination of a linear filter and a non-linear filter (e.g., with power of n, e.g., L n , n can be positive, negative, or +-fractional number (e.g., +1/2, square root or +3, cube, which can rounding and rescale to bitdepth dynamic range)).
  • LLM high-pass gradient filter
  • a low-pass smoothing filter e.g., [1, 2, I; 1, 2, l]/8 FIR down-sampling filter that may be generally used in CCLM
  • n
  • the combination may be repeatedly applied.
  • a combination of GLM and [1 , 2, 1 ; 1 , 2, 1 ]/8 FIR may be applied on the reconstructed luma samples, and then a non-linear power of 1/2 may be applied.
  • the non-linear filter may provide options when linear filter cannot handle the luma-chroma relationship efficiently.
  • non-linear term can be predefined or signaled/ switched in SP S/DP S/VP S/ SEI/AP S/PP S/PH/SH/Regi on/CTU/CU/ Subblock/Sample levels.
  • the GLM may refer to Generalized Linear Model (may be used to generate one single luma sample linearly or non- linearly, and the generated one single luma sample may be fed into the CCLM linear model to derive parameters of the CCLM linear model), linear/non-linear generation may be called general patterns. Different gradient or general patterns can be combined to form another pattern.
  • a gradient pattern may be combined with a CCLM down-sampled value; a gradient pattern may be combined with a non-linear L 2 value; a gradient pattern may be combined with another gradient pattern, the two gradient patterns to be combined may have different directions or the same direction, e.g., [1, 1, 1; -1, -1, -1] and [1, 2, 1; -1, -2, -1], which both have a vertical direction, may be combined, also [1, 1, 1; -1, -1, -1] and [1, 0, -1; 1, 0, -1], which have a vertical and horizontal directions, may be combined, as shown in Figures 24A to 24D.
  • the combination may comprise plus, minus, or linear weighted.
  • pre-operations can be applied repeatedly and GLM can be applied on pre linear weighted/pre-operated samples.
  • CCLM one template filtering can be applied to luma samples, in order to remove outliers using the low-pass smoothing FIR filter [1 , 2, 1 ; 1 , 2, 1 ]/8 (i.e., CCLM down-sampling smoothing filter) and to generate down-sampled luma samples (one down-sampled luma sample corresponding to one chroma sample).
  • 1-tap GLM can be applied on smoothed down-sampled luma samples to derive the MLR model.
  • Some gradient filter patterns such as 3x3 Sobel or Prewitt operators, can be applied on down-sampled luma samples.
  • the following table shows some of the gradient filter patterns.
  • the gradient filter patterns can be combined with other gradient/general filter patterns in the down-sampled luma domain.
  • a combined filter pattern may be applied on down-sampled luma samples.
  • the combined filter pattern may be derived by performing addition or subtraction operations to respective coefficients of the gradient filter pattern and a DC/low-pass based filter pattern, such as filter pattern [0, 0, 0; 0,
  • the combined filter pattern is derived by performing addition or subtraction operations to a coefficient of the gradient filter pattern and a non-linear value such as L 2 .
  • the combined filter pattern is derived by performing addition or subtraction operations to respective coefficients of the gradient filter pattern and another gradient filter pattern having a different or the same direction.
  • the combined filter pattern is derived by performing linear weighted operations to the coefficients of the gradient filter pattern.
  • GLM applied on down-sampled domain can fit in CCCM framework but may sacrifice high frequency accuracy since low-pass smoothing is applied before applying GLM.
  • GLM serves as input of CCCM
  • CCCM applies luma down-sampling before convolution as with CCLM.
  • the reconstructed luma samples are down-sampled to match the lower resolution chroma grid when chroma sub-sampling is used.
  • 1-tap GLM can also be taken as changing CCLM down-sample filter coefficients (e.g., from [1 , 2, 1 ; 1, 2, 1 ]/ 8 to [1 , 2, 1 , -1 , -
  • the GLM can serve as the input of CCCM.
  • the gradient filter of GLM replaces luma down-sampling filter ([1, 2, 1; 1, 2, 1]/ 8) with gradient-based coefficients (e.g., [1, 2, 1, -1, -2, -1).
  • CCCM operation becomes “linear/non-linear combination of gradients”, as shown by the following equation:
  • predChromaVal coC + ciN + C2S + C3E + C4W + C5P + ceB
  • C, N, S, E, W, P are gradients of current or neighboring samples (compared to original down-sample values for CCCM).
  • Related GLM methods described in this disclosure can be applied in the same way before entering CCCM convolution, e.g., classification, separate Cb/Cr control, syntax, pattern combining, PU size restriction etc.
  • the gradient-based coefficients replacement can apply to specific CCCM taps. Also, not only high-pass but low-pass/band-pass/all-pass coefficients replacement can be used.
  • the replacement can be combined with FLM/CCCM shape switch discussed above (leading to different number of taps).
  • gradient patterns in Figures 24A to 24D can be used for replacement.
  • the operations for applying GLM as input of CCCM includes: predefining one or more coefficients candidates for CCCM/FLM down-sampling; determining CCCM/FLM filter shape and number of filter taps for this CU; applying different CCLM downsample coefficients to different filter taps, wherein the coefficients can be high-pass filters (GLM), or low-pass/band-pass/all-pass filters; generating the down-sampled luma samples (using the applied coefficients) for CCCM input samples; and feeding the generated down- sampled luma samples into CCCM process.
  • GLM high-pass filters
  • Which CCCM/FLM taps to apply the coefficients replacement can be predefined (as above examples) or signaled/switched in SPS/DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • the coefficients candidate for CCCM/FLM downsampling can be predefined or signaled/switched in SPS/DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • one or more syntaxes may be introduced to indicate information on the GLM.
  • GLM syntaxes is illustrated in the following Table 10.
  • EGk exponent! al -golomb code with order k, where k can be fixed or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • the GLM on/off control for Cb/Cr components may be jointly or separately.
  • 1 flag may be used to indicate if GLM is active for this CU. If active, 1 flag may be used to indicate if Cb/Cr are both active. If not both active, 1 flag to indicate either Cb or Cr is active.
  • Filter index/gradient (general) pattern may be signaled separately when Cb and/or Cr is active. All flags may have its own context model or be bypass coded.
  • whether to signal GLM on/off flags may depend on luma/chroma coding modes, and/or CU size.
  • GLM may be inferred off when MMLM or MMLM_L or MMLM_T is applied; when CU area ⁇ A, where A can be predefined or signal ed/switched in SPS/DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels; If combined with CCCM, GLM may be inferred off when CCCM is on.
  • CU level GLM enabling flag can be inferred off if current CU is enabled as CCCM/FLM. hasGlmFlag &- 1 pu . cccmFlag;
  • CCCM requires to process down-sampled luma reference values before the calculation of model parameters and applying the CCCM model, which burden decoder processing cycles.
  • CCCM without down-sampling process is proposed, including utilizing non-down-sampled luma reference values and/or different selection of nondown-sampled luma reference.
  • One or more filter shapes may be used for the purpose as described below.
  • the convolutional 7-tap filter may include a 5 -tap plus sign shape spatial component, a non-linear term and a bias term.
  • the input to the spatial 5-tap component of the filter includes a center (C) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and its non-down-sampled above or north (N), below or south (S), left or west (W) and right or east (E) neighbors as illustrated in Figure 17.
  • the non-linear term P is represented as power of two of the center luma sample C and scaled to the sample value range of the content:
  • the bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • predChromaVal coC + ciN + C2S + C3E + C4W + C5P + ceB
  • the convolutional 7-tap filter may include a 6-tap rectangle shape spatial component and a bias term.
  • the input to the spatial 6-tap component of the filter includes a center (b) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and its non-down-sampled below-left or south-west (d), below-right or south-east (f), below or south (e), left or west (a) and right or east (c) neighbors as illustrated Shape 1 in Figure 25.
  • the bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • predChromaVal coa + cib + C2C + cid + C4e + csf + ceB
  • the convolutional 8-tap filter may consist of a 6-tap rectangle shape spatial component, a non-linear term and a bias term.
  • the input to the spatial 6-tap component of the filter consists of a center (b) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and its non-down-sampled below-left or south-west (d), below-right or south-east (f), below or south (e), left or west (a) and right or east (c) neighbors as illustrated Shape 1 in Figure 25.
  • the non-linear term P is represented as power of two of the center luma sample (b) and scaled to the sample value range of the content:
  • the bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • predChromaVal coa + cib + C2C + cad + C4e + csf + ceP+ C7B
  • the convolutional 9-tap filter may consist of a 6-tap rectangle shape spatial component, two non-linear terms and a bias term.
  • the input to the spatial 6-tap component of the filter consists of a center (b) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and which is located substantially at the center of the filter shape, and its non-down-sampled below-left/south-west (d), below- right /south-east (f), below/south (e), left/west (a) and right/east (c) neighbors as illustrated Shape 1 in Figure 25.
  • the non-linear terms P and Q are two non-linear luma sample values, which are represented respectively as power of the luma sample value of the center (b) luma sample and the below/south (e) luma sample then scaled to the sample value range of the content:
  • the bias term B is a bias value which represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • predChromaVal coa + mb + C2C + csd + C4e + csf + C6P+ c?Q+ cxB
  • non-linear terms P and Q can be represented as power of any luma sample values of the non-down-sampled luma sample of the filter.
  • the two non-linear terms P and Q are only exemplary, and the corresponding chroma sample value can be calculated based on one or more non-linear values.
  • reference samples/training templates/reconstructed neighboring regions usually refer to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • the reference samples/training tempi ate/reconstructed neighboring region may be predefined or signaled/ switched in SP S/DP S/VP S/ SEI/AP S/PP S/PH/SH/Regi on/CTU/CU/ Subblock/Sample levels.
  • Figure 9A shows an example that L-shape reconstructed region, left/top reconstructed region to derive parameters.
  • One or more shape/number of filter taps may be used for CCCM prediction, as shown in Figure 25, Figure 26, and Figures 27A to 27B.
  • One or more sets of filter taps may be used for FLM prediction, examples being shown in Figures 28A to 28G.
  • the selected luma reference values are non-down-sampled.
  • One or more predefined shape/number of filter taps may be used for CCCM prediction based on previous decoded information on TB/CB/sl i ce/picture/s equ ence 1 evel .
  • a multiple tap filter can fit well on training data (i.e., top/left neighboring reconstructed luma/chroma samples), in some cases, that training data do not capture full characteristics of the testing data, and it may result in overfitting and may not predict well on the testing data (i.e., the to-be-predicted chroma block samples).
  • different filter shapes may adapt well to different video block content, leading to more accurate prediction.
  • the filter shape/number of filter taps can be predefined or signaled/switched in SPS/DPS/VPS/SEVAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • a set of filter shape candidates can be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • the filter shape selection of U/V components can be switched in PH or in CU/CTU levels. Note that N-tap can represent N-tap with or without the offset /? as described above.
  • Different chroma types/color formats can have different predefined filter shapes/taps. For example, using predefined filter shape for 420 type-0: (1, 2, 4, 5), 420 type-2: (0, 1, 2, 4, 7), 422: (1, 4), 444: (0, 1, 2, 3, 4, 5) as shown in Figure 21.
  • the unavailable luma/chroma samples for deriving the MLR model can be padded from available reconstructed samples. For example, if using a 6-tap (0, 1, 2, 3, 4, 5) filter as in Figure 21, for a CU located at the left picture boundary, the left columns including (0, 3) are not available (out of picture boundary), so (0, 3) are repetitive padding from (1, 4) to apply the 6-tap filter. Note the padding process applied in both training data (top/left neighboring reconstructed luma/chroma samples) and testing data (the luma/chroma samples in the CU).
  • the unavailable luma/chroma samples for deriving the MLR model can be skipped and not used. Then the padding process is not needed for the unavailable luma/chroma samples.
  • CCCM requires to process LDL decomposition to calculate the model parameters of CCCM model, avoiding using square root operations and only integer arithmetic is required.
  • CCLM/MMLM with LDL decomposition are proposed.
  • LDL decomposition may also be used in ELM/FLM/GLM, as described above.
  • reference samples/training templates/reconstructed neighboring regions usually refer to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • One or more reference samples may be used for CCLM/MMLM prediction, i.e., as shown in Figure 18, the reference area may be the same as the reference area in CCCM. Different reference areas may be used for CCLM/MMLM prediction based on previous decoded information on TB/CB/slice/picture/sequence level.
  • training data with multiple reference areas can fit well on the calculation of model parameters, in some cases that training data do not capture full characteristics of testing data, it may result in overfitting and may not predict well on testing data (i.e., the to-be- predicted chroma block samples). Also, different reference areas may adapt well to different video block content, leading to more accurate prediction. To address this issue, the reference shape/number of reference areas can be predefined or signaled/switched in SPS/DPS/VPS/SET/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • a set of reference area candidates can be predefined or signaled/switched in SPS/DPS/VPS/SEEAPS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • Different components U/V may have different reference area switch control.
  • the reference area selection of U/V components can be switched in PH or in CU/CTU levels.
  • Different chroma types/color formats can have different predefined reference areas.
  • the unavailable luma/chroma samples for deriving the MLR model can be padded from available reconstructed samples, the padding process being applied in both training data (top/left neighboring reconstructed luma/chroma samples) and testing data (the luma/chroma samples in the CU).
  • the unavailable luma/chroma samples for deriving the MLR model can be skipped and not used. Then the padding process is not needed for the unavailable luma/chroma samples.
  • FLM requires to process down-sampled luma reference values and calculate model parameters, which burden decoder processing cycles, especially for small blocks.
  • FLM with minimal samples restriction is proposed, for example, FLM is only used for samples larger than predefined number, such as 64, 128.
  • predefined number such as 64, 128.
  • FLM is only used in single model for samples larger than a predefined number, such as 256, and FLM is only used in multi model for samples larger than a predefined number, such as 128.
  • the number of predefined minimal samples for single model may be larger than or equal to the number of predefined minimal samples for multi model.
  • FLM/GLM/ELM/CCCM is only used in single model for samples larger than or equal to a predefined number, such as 128, and FLM/GLM/ELM/CCCM is only used in multi model for samples larger than or equal to a predefined number, such as 256.
  • the number of predefined minimal samples for FLM/GLM7ELM may be larger than or equal to the number of predefined minimal samples for CCCM.
  • CCCM is only used in single model for samples larger than or equal to a predefined number, such as 0, and CCCM is only used in multi model for samples larger than or equal to a predefined number, such as 128.
  • FLM is only used in single model for samples larger than or equal to a predefined number, such as 128, and FLM is only used in multi model for samples larger than or equal to a predefined number, such as 256.
  • two models of multiple modes of FLM/GLM/ELM/CCCM/CCLM may be further combined to bring additional coding efficiency. For example, first the parameters of CCCM(ci) and GLM(a, b) are derived separately, then the weights (wi) between CCCM and GLM are derived by linear regression, finally the weighted CCCM and GLM are used to predict chroma samples from reconstructed luma samples.
  • GLMpredChromaVal a*lumaVal + b
  • CCCMpredChromaVal co*C + ci*N + C2*S + C3*E + C4*W + cs*P + ce*B
  • FinalpredChromaVal wo* GLMpredChromaVal + wi*CCCMpredChromaVal
  • the mode flag can be derived at decoder to save bit overhead.
  • Figure 29A shows the example that in template area, even-row area Ro is used for training/deriving 3 filter coefficient sets, and odd-row area Ri is used for validation/comparing and sorting costs of 3 filter coefficient sets.
  • the convolutional 8-tap filter may include a 6-tap rectangle shape spatial component, a down-sampled luma sample and a bias term.
  • the input to the spatial 6- tap component of the filter includes a center (b) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and its non-down-sampled below-left or south-west (d), below-right or south-east (f), below or south (e), left or west (a) and right or east (c) neighbors as illustrated Shape 1 in Figure 25 and a center (C) down-sampled luma sample which is collocated with the chroma sample to be predicted.
  • the bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • the convolutional 9-tap filter may consist of a 6-tap rectangle shape spatial component, two non-linear terms and a bias term.
  • the input to the spatial 6-tap component of the filter consists of a center (b) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and which is located substantially at the center of the filter shape, and its non-down-sampled below-left/south-west (d), below-right /south-east (f), below/south (e), left/west (a) and right/east (c) neighbors as illustrated Shape 1 in Figure 25 and a center (C) down-sampled luma sample which is collocated with the chroma sample to be predicted (for example, the center (C) down-sampled luma sample value is determined by a weighted-average operation).
  • the non-linear terms P and Q are two non-linear luma sample values, which are represented respectively as power of the luma sample value of the center (b) non-down- sampled luma sample and center (C) down-sampled luma sample then scaled to the sample value range of the content:
  • the bias term B is a bias value which represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • non-linear terms P and Q can be represented as power of any luma sample values of down-sampled/non-down-sampled luma samples for predicting the corresponding chroma sample value.
  • the two non-linear terms P and Q are only exemplary, and the corresponding chroma sample value can be calculated based on one or more non-linear values.
  • the non-linear term Q can also be represented as power of a non-down-sampled luma sample of the filter.
  • the convolutional 9-tap filter may consist of a 6-tap rectangle shape spatial component, two non-linear terms and a bias term.
  • the input to the spatial 6-tap component of the filter consists of a center (b) non-down-sampled luma sample which is collocated with the chroma sample to be predicted and which is located substantially at the center of the filter shape, and its non-down-sampled below-left/south-west (d), below-right /south-east (f), below/south (e), left/west (a) and right/east (c) neighbors as illustrated Shape 1 in Figure 25.
  • the non-linear terms P and Q are two non-linear luma sample values, which are represented respectively as power of the luma sample value of the center (b) luma sample and the below/south (e) luma sample then scaled to the sample value range of the content:
  • the bias term B is a bias value which represents a scalar offset between the input and output (similarly to the offset term in CCLM) and is set to middle chroma value (512 for 10-bit content).
  • Output of the filter is calculated as a convolution between the filter coefficients Ci and the input values and clipped to the range of valid chroma samples:
  • predChromaVal coa + cib + C2C + c.id + C4e + csf + ceP+ c?Q+ csB
  • reference samples/training template/reconstructed neighboring region usually refers to the luma samples used for deriving the MLR model parameters, which are then applied to the inner luma samples in one CU, to predict the chroma samples in the CU.
  • CCCM without down- sampled process and CCCM with down-sampled process may be used by different taps or shapes.
  • the filter shape/number of filter taps with down-sampled values and without down-sampled values may be predefined or signaled/switched in SPS/DPS/VPS/SEI/APS/PPS/PH/SH/Region/CTU/CU/Subblock/Sample levels.
  • the reference samples/training template/reconstructed neighboring region may be predefined or signaled/ switched in SP S/DP S/VP SZ SEI/AP S/PP S/PH/SH/Regi on/CTU/CU/ Subblock/Sample levels.
  • Figure 9A shows an example that L-shape reconstructed region, left/top reconstructed region to derive parameters.
  • Figure 30 illustrates a workflow of a method 3000 for encoding video data according to one or more aspects of the present disclosure.
  • the method 3000 comprises obtaining a video block from a bitstream.
  • the method 3000 comprises obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region.
  • the method 3000 comprises determining, based on the external luma sample values and the external chroma sample values, a set of weighting coefficients corresponding to a filter shape, wherein the filter shape and the set of weighting coefficients are configured for predicting each of the internal chroma sample values based on a plurality of corresponding luma sample values, wherein the plurality of corresponding luma sample values comprise: one or more non-down-sampled luma sample values associated with the filter shape, and one or more non-linear luma sample values.
  • the method 3000 comprises predicting, with the filter shape and the set of weighting coefficients, the internal chroma sample values based on the internal luma sample values.
  • the method 3000 comprises obtaining predicted video block using the predicted internal chroma sample values.
  • the one or more non-linear luma sample values comprise: a first non-linear luma sample value derived by scaling a square of a first luma sample value to a luma sample value range of the video block, wherein the first luma sample value is a non-down- sampled luma sample value associated with the filter shape.
  • the first luma sample value is the non-down-sampled luma sample value of a first luma sample located at the center of the filter shape.
  • the one or more non-linear luma sample values further comprise: a second non-linear luma sample value derived by scaling a square of a second luma sample value to the luma sample value range of the video block.
  • the second luma sample value is a non-down-sampled luma sample value of a second luma sample below the first luma sample.
  • the second luma sample value is a down-sampled luma sample value determined based on luma sample values of the collocated luma samples correspoding to the chroma sample to be predicted.
  • the down-sampled luma sample value is determined by a weighted- average operation.
  • the filter shape is determined according to six luma samples including: a first luma sample located at the center of the filter shape, a second luma sample below the first luma sample; a third luma sample to the left of the first luma sample; a fourth luma sample to the right of the first luma sample; a fifth luma sample below and to the left of the first luma sample; and a sixth luma sample below and to the right of the first luma sample.
  • the set of weighting coefficients further includes a weighting coefficient for a bias value.
  • whether the second luma sample value is a down-sampled luma sample value or a non-down-sampled luma sample value is predefined or signaled at SPS, DPS, VPS, SEI, APS, PPS, PH, SH, Region, CTU, CU, subblock, or sample level.
  • Figure 31 illustrates a workflow of a method 3100 for encoding video data according to one or more aspects of the present disclosure.
  • the method 3100 comprises obtaining a video block.
  • the method 3100 comprises obtaining internal luma sample values of the video block, external luma sample values of an external region of the video block and external chroma sample values of the external region.
  • the method 3100 comprises determining, based on the external luma sample values and the external chroma sample values, a set of weighting coefficients corresponding to a filter shape, wherein the filter shape and the set of weighting coefficients are configured for predicting each of the internal chroma sample values based on a plurality of corresponding luma sample values, wherein the plurality of corresponding luma sample values comprise: one or more non-down-sampled luma sample values associated with the filter shape, and one or more non-linear luma sample values.
  • the method 3100 comprises predicting, with the filter shape and the set of weighting coefficients, the internal chroma sample values based on the internal luma sample values.
  • the method 3100 comprises generating a bitstream comprising an encoded video block by using the predicted internal chroma sample values.
  • the one or more non-linear luma sample values comprise: a first non-linear luma sample value derived by scaling a square of a first luma sample value to a luma sample value range of the video block, wherein the first luma sample value is a non-down- sampled luma sample value associated with the filter shape.
  • the first luma sample value is the non-down-sampled luma sample value of a first luma sample located at the center of the filter shape.
  • the one or more non-linear luma sample values further comprise: a second non-linear luma sample value derived by scaling a square of a second luma sample value to the luma sample value range of the video block.
  • the second luma sample value is a non-down-sampled luma sample value of a second luma sample below the first luma sample.
  • the second luma sample value is a down-sampled luma sample value determined based on luma sample values of the collocated luma samples correspoding to the chroma sample to be predicted.
  • the down-sampled luma sample value is determined by a weighted- average operation.
  • the filter shape is determined according to six luma samples including: a first luma sample located at the center of the filter shape; a second luma sample below the first luma sample; a third luma sample to the left of the first luma sample; a fourth luma sample to the right of the first luma sample; a fifth luma sample below and to the left of the first luma sample; and a sixth luma sample below and to the right of the first luma sample.
  • the set of weighting coefficients further includes a weighting coefficient for a bias value.
  • whether the second luma sample value is a down-sampled luma sample value or a non-down-sampled luma sample value is predefined or signaled at SPS, DPS, VPS, SEI, APS, PPS, PH, SH, Region, CTU, CU, subblock, or sample level.
  • Figure 32 shows a computing environment 3210 coupled with a user interface 3250.
  • the computing environment 3210 can be part of a data processing server.
  • the computing environment 3210 includes a processor 3220, a memory 3230, and an Input/Output (TO) interface 3240.
  • TO Input/Output
  • the processor 3220 typically controls overall operations of the computing environment 3210, such as the operations associated with display, data acquisition, data communications, and image processing.
  • the processor 3220 may include one or more processors to execute instructions to perform all or some of the steps in the above-described methods.
  • the processor 3220 may include one or more modules that facilitate the interaction between the processor 3220 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 3230 is configured to store various types of data to support the operation of the computing environment 3210.
  • the memory 3230 may include predetermined software 3232. Examples of such data includes instructions for any applications or methods operated on the computing environment 3210, video datasets, image data, etc.
  • the memory 3230 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 3240 provides an interface between the processor 3220 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 3240 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 3230, executable by the processor 3220 in the computing environment 3210, for performing the above-described methods and/or storing a bitstream generated by the encoding method described above or a bitstream to be decoded by the decoding method described above.
  • the plurality of programs may be executed by the processor 3220 in the computing environment 3210 to receive (for example, from the video encoder 20 in Figure 2) a bitstream or data stream including encoded video information (for example, video blocks representing encoded video frames, and/or associated one or more syntax elements, etc.), and may also be executed by the processor 3220 in the computing environment 3210 to perform the decoding method described above according to the received bitstream or data stream.
  • a bitstream or data stream including encoded video information (for example, video blocks representing encoded video frames, and/or associated one or more syntax elements, etc.)
  • encoded video information for example, video blocks representing encoded video frames, and/or associated one or more syntax elements, etc.
  • the plurality of programs may be executed by the processor 3220 in the computing environment 3210 to perform the encoding method described above to encode video information (for example, video blocks representing video frames, and/or associated one or more syntax elements, etc.) into a bitstream or data stream, and may also be executed by the processor 3220 in the computing environment 3210 to transmit the bitstream or data stream (for example, to the video decoder 30 in Figure 3).
  • video information for example, video blocks representing video frames, and/or associated one or more syntax elements, etc.
  • the non-transitory computer-readable storage medium may have stored therein a bitstream or a data stream comprising encoded video information (for example, video blocks representing encoded video frames, and/or associated one or more syntax elements etc.) generated by an encoder (for example, the video encoder 20 in Figure 2) using, for example, the encoding method described above for use by a decoder (for example, the video decoder 30 in Figure 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.
  • bitstream generated by the encoding method described above or a bitstream to be decoded by the decoding method described above.
  • a bitstream comprising encoded video information generated by the encoding method described above or encoded video information to be decoded by the decoding method described above.
  • the is also provided a computing device comprising one or more processors (for example, the processor 3220); and the non-transitory computer-readable storage medium or the memory 3230 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 3220
  • non-transitory computer-readable storage medium or the memory 3230 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 having instructions for storage or transmission of a bitstream comprising encoded video information generated by the encoding method described above or encoded video information to be decoded by the decoding method described above.
  • a computer program product comprising a plurality of programs, for example, in the memory 3230, executable by the processor 3220 in the computing environment 3210, for performing the above-described methods.
  • the computer program product may include the non-transitory computer-readable storage medium.
  • the computing environment 3210 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.
  • bitstream comprising storing the bitstream on a digital storage medium, wherein the bitstream comprises encoded video information generated by the encoding method described above or encoded video information to be decoded by the decoding method described above.

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

Abstract

La présente divulgation concerne un procédé de décodage de données vidéo, comprenant les étapes suivantes : obtention d'un bloc vidéo à partir d'un flux binaire ; obtention de valeurs d'échantillon de luminance interne du bloc vidéo, de valeurs d'échantillon de luminance externe d'une région externe du bloc vidéo et de valeurs d'échantillon de chrominance externe de la région externe ; détermination, sur la base des valeurs d'échantillon de luminance externe et des valeurs d'échantillon de chrominance externe, d'un ensemble de coefficients de pondération correspondant à une forme de filtre, la forme de filtre et l'ensemble de coefficients de pondération étant configurés pour prédire chacune des valeurs d'échantillon de chrominance interne sur la base d'une pluralité de valeurs d'échantillon de luminance correspondantes, la pluralité de valeurs d'échantillon de luminance correspondantes comprenant : une ou plusieurs valeurs d'échantillon de luminance non sous-échantillonné associées à la forme de filtre, et une ou plusieurs valeurs d'échantillon de luminance non linéaire ; prédiction, avec la forme de filtre et l'ensemble de coefficients de pondération, des valeurs d'échantillon de chrominance interne sur la base des valeurs d'échantillon de luminance interne ; et obtention d'un bloc vidéo prédit au moyen des valeurs d'échantillon de chrominance interne prédites.
PCT/US2023/034899 2022-10-12 2023-10-11 Procédé et appareil de prédiction inter-composantes pour un codage vidéo WO2024081291A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20210297694A1 (en) * 2018-12-07 2021-09-23 Beijing Bytedance Network Technology Co., Ltd. Context-based intra prediction
US20220038714A1 (en) * 2018-11-05 2022-02-03 Beijing Bytedance Network Technology Co., Ltd. Prediction precision improvements in video coding
US20220053192A1 (en) * 2018-09-12 2022-02-17 Beijing Bytedance Network Technology Co., Ltd. Single-line cross component linear model prediction mode

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Publication number Priority date Publication date Assignee Title
US20220053192A1 (en) * 2018-09-12 2022-02-17 Beijing Bytedance Network Technology Co., Ltd. Single-line cross component linear model prediction mode
US20220038714A1 (en) * 2018-11-05 2022-02-03 Beijing Bytedance Network Technology Co., Ltd. Prediction precision improvements in video coding
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