WO2024081722A1 - Techniques de sous-échantillonnage pour une prédiction inter-composantes dans un codage vidéo - Google Patents

Techniques de sous-échantillonnage pour une prédiction inter-composantes dans un codage vidéo Download PDF

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Publication number
WO2024081722A1
WO2024081722A1 PCT/US2023/076580 US2023076580W WO2024081722A1 WO 2024081722 A1 WO2024081722 A1 WO 2024081722A1 US 2023076580 W US2023076580 W US 2023076580W WO 2024081722 A1 WO2024081722 A1 WO 2024081722A1
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Prior art keywords
block
video data
luma samples
subsampling
cross
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PCT/US2023/076580
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English (en)
Inventor
Yao-Jen Chang
Vadim Seregin
Bappaditya Ray
Marta Karczewicz
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Qualcomm Incorporated
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Priority claimed from US18/483,891 external-priority patent/US20240129458A1/en
Application filed by Qualcomm Incorporated filed Critical Qualcomm Incorporated
Publication of WO2024081722A1 publication Critical patent/WO2024081722A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—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
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/59—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/593—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial prediction techniques
    • 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

Definitions

  • This disclosure relates to video encoding and video decoding.
  • Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, so-called “smart phones,” video teleconferencing devices, video streaming devices, and the like.
  • PDAs personal digital assistants
  • laptop or desktop computers tablet computers
  • e-book readers digital cameras
  • digital recording devices digital media players
  • video gaming devices video game consoles
  • cellular or satellite radio telephones so-called “smart phones”
  • video teleconferencing devices video streaming devices, and the like.
  • Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), ITU-T H.266/Versatile Video Coding (VVC), and extensions of such standards, as well as proprietary video codecs/formats such as AOMedia Video 1 (AVI) that was developed by the Alliance for Open Media.
  • the video devices may transmit, receive, encode, decode, and/or store digital video information more efficiently by implementing such video coding techniques.
  • Video coding techniques include spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences.
  • a video slice e.g., a video picture or a portion of a video picture
  • video blocks which may also be referred to as coding tree units (CTUs), coding units (CUs) and/or coding nodes.
  • Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture.
  • Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures.
  • Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.
  • a video coder may be configured to predict chroma samples from one or more reconstructed luma samples when coding a block of video data using a cross-component prediction mode.
  • the luma and chroma samples of the video data may a chroma sub sampling format where two or more pixel locations share the same chroma sample value. However, each pixel has a single luma sample value. As such, there are more luma samples than chroma samples for some pictures of video data.
  • This disclosure describes techniques for determining a subsampling technique to use for luma samples of the block of video data when coding the block according to a cross-component prediction mode.
  • the subsampling technique is to not apply subsampling to the luma samples.
  • a prediction model for a crosscomponent prediction mode may be configured to use multiple luma samples to predict a single chroma sample value.
  • a video coder may be configured to code a block of video data using a cross-component prediction mode by applying a combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples.
  • the video coder may predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • the downsampling filters used may be based on the prediction model shape. In this way, coding efficiency may be increased and/or distortion may be decreased.
  • this disclosure describes a method of decoding video data, the method comprising receiving a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determining a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode, and decoding the block of video data using the sub sampling technique and the crosscomponent prediction mode.
  • this disclosure describes an apparatus configured to decode video data, the apparatus comprising a memory, and one or more processors coupled to the memory, the one or more processors configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determine a subsampling technique, from a plurality of sub sampling techniques, for the luma samples of the block of video data for a crosscomponent prediction mode, and decode the block of video data using the subsampling technique and the cross-component prediction mode.
  • this disclosure describes an apparatus configured to decode video data, the apparatus comprising means for receiving a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, means for determining a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode, and means for decoding the block of video data using the subsampling technique and the cross-component prediction mode.
  • this disclosure describes a non-transitory computer-readable storage medium storing instructions that, when executed, case one or more processors of a device configured to decode video data to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determine a subsampling technique, from a plurality of sub sampling techniques, for the luma samples of the block of video data for a crosscomponent prediction mode, and decode the block of video data using the subsampling technique and the cross-component prediction mode.
  • this disclosure describes a method of encoding video data, the method comprising receiving a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determining a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode, and encoding the block of video data using the subsampling technique and the crosscomponent prediction mode.
  • this disclosure describes an apparatus configured to encode video data, the apparatus comprising a memory, and one or more processors coupled to the memory, the one or more processors configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determine a subsampling technique, from a plurality of sub sampling techniques, for the luma samples of the block of video data for a crosscomponent prediction mode, and encode the block of video data using the subsampling technique and the cross-component prediction mode.
  • this disclosure describes an apparatus configured to encode video data, the apparatus comprising means for receiving a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, means for determining a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode, and means for encoding the block of video data using the subsampling technique and the cross-component prediction mode.
  • this disclosure describes a non-transitory computer-readable storage medium storing instructions that, when executed, case one or more processors of a device configured to encode video data to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determine a subsampling technique, from a plurality of sub sampling techniques, for the luma samples of the block of video data for a crosscomponent prediction mode, and encode the block of video data using the subsampling technique and the cross-component prediction mode.
  • FIG. 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.
  • FIG. 2 illustrates a reconstructed neighbor area for luma and chroma samples relative to a current block.
  • FIG. 3 illustrates an example diamond 3x3 model shape for subsampling.
  • FIG. 4 illustrates an example of classifying neighbor samples int two groups for multi-model linear mode prediction mode.
  • FIG. 5 illustrates an example effect of a slope adjustment parameter for a crosscomponent linear model.
  • FIG. 6 illustrates an example 4x2 subsampling filter.
  • FIG. 7 illustrates example elongated prediction model shapes.
  • FIG. 8 illustrates an example 5x4 prediction model shape.
  • FIG. 9 illustrates example one-directional prediction model shapes.
  • FIG. 10 illustrates example gradient downsampling filters.
  • FIG. 11 illustrates example samples and their locations for a 3x3 filter shape.
  • FIG. 12 illustrates example samples and their locations used for non-linear derivation in a 3x2 prediction model shape.
  • FIG. 13 illustrates example samples and their locations used for non-linear derivation in a 3x3 prediction model shape.
  • FIG. 14 is illustrates example non-adjacent neighbor samples for deriving crosscomponent prediction models.
  • FIG. 15 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.
  • FIG. 16 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.
  • FIG. 17 is a flowchart illustrating an example method for encoding a current block in accordance with the techniques of this disclosure.
  • FIG. 18 is a flowchart illustrating an example method for decoding a current block in accordance with the techniques of this disclosure.
  • FIG. 19 is a flowchart illustrating another example method for encoding a current block in accordance with the techniques of this disclosure.
  • FIG. 20 is a flowchart illustrating another example method for decoding a current block in accordance with the techniques of this disclosure.
  • a video coder may be configured to predict chroma samples from one or more reconstructed luma samples when coding a block of video data using a cross-component prediction mode.
  • the luma and chroma samples of the video data may a chroma subsampling format where two or more pixel locations share the same chroma sample value. However, each pixel has a single luma sample value. As such, there are more luma samples than chroma samples for some pictures of video data.
  • a video coder may be configured to use a filter surrounding the position for which the subsampling is applied. For example, a video coder may use 4x2 filter to derive subsampled luma samples in 4:2:0 format.
  • Such subsampling may smooth the signal, which may be beneficial for some video content, but may not be optimal for other video content (e.g., video content that has sharp detail, such as graphics or screen content). For sharper detailed video content, such as graphics or screen content, smoothing may eliminate or reduce certain patterns and the derived prediction models from such smoothing may be less efficient.
  • This disclosure describes techniques for determining a subsampling technique to use for luma samples of the block of video data when coding the block according to a cross-component prediction mode.
  • the subsampling technique is to not apply subsampling to the luma samples.
  • a prediction model for a crosscomponent prediction mode may be configured to use multiple luma samples to predict a single chroma sample value.
  • a video coder may be configured to code a block of video data using a cross-component prediction mode by applying a combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples.
  • the video coder may predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • the downsampling filters used may be based on the prediction model shape. In this way, coding efficiency may be increased and/or distortion may be decreased.
  • FIG. 1 is a block diagram illustrating an example video encoding and decoding system 100 that may perform the techniques of this disclosure for cross-component chroma prediction.
  • the techniques of this disclosure are generally directed to coding (encoding and/or decoding) video data.
  • video data includes any data for processing a video.
  • video data may include raw, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.
  • system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116, in this example.
  • source device 102 provides the video data to destination device 116 via a computer-readable medium 110.
  • Source device 102 and destination device 116 may be or include any of a wide range of devices, such as desktop computers, notebook (i.e., laptop) computers, mobile devices, tablet computers, set-top boxes, telephone handsets such as smartphones, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, broadcast receiver devices, or the like.
  • source device 102 and destination device 116 may be equipped for wireless communication, and thus may be referred to as wireless communication devices.
  • source device 102 includes video source 104, memory 106, video encoder 200, and output interface 108.
  • Destination device 116 includes input interface 122, video decoder 300, memory 120, and display device 118.
  • video encoder 200 of source device 102 and video decoder 300 of destination device 116 may be configured to apply the techniques for subsampling video data for cross-component chroma prediction.
  • source device 102 represents an example of a video encoding device
  • destination device 116 represents an example of a video decoding device.
  • a source device and a destination device may include other components or arrangements.
  • source device 102 may receive video data from an external video source, such as an external camera.
  • destination device 116 may interface with an external display device, rather than include an integrated display device.
  • System 100 as shown in FIG. 1 is merely one example.
  • any digital video encoding and/or decoding device may perform techniques for subsampling video data for cross-component chroma prediction.
  • Source device 102 and destination device 116 are merely examples of such coding devices in which source device 102 generates coded video data for transmission to destination device 116.
  • This disclosure refers to a “coding” device as a device that performs coding (encoding and/or decoding) of data.
  • video encoder 200 and video decoder 300 represent examples of coding devices, in particular, a video encoder and a video decoder, respectively.
  • source device 102 and destination device 116 may operate in a substantially symmetrical manner such that each of source device 102 and destination device 116 includes video encoding and decoding components.
  • system 100 may support one-way or two-way video transmission between source device 102 and destination device 116, e.g., for video streaming, video playback, video broadcasting, or video telephony.
  • video source 104 represents a source of video data (i.e., raw, unencoded video data) and provides a sequential series of pictures (also referred to as “frames”) of the video data to video encoder 200, which encodes data for the pictures.
  • Video source 104 of source device 102 may include a video capture device, such as a video camera, a video archive containing previously captured raw video, and/or a video feed interface to receive video from a video content provider.
  • video source 104 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video.
  • video encoder 200 encodes the captured, pre-captured, or computer-generated video data.
  • Video encoder 200 may rearrange the pictures from the received order (sometimes referred to as “display order”) into a coding order for coding. Video encoder 200 may generate a bitstream including encoded video data. Source device 102 may then output the encoded video data via output interface 108 onto computer-readable medium 110 for reception and/or retrieval by, e.g., input interface 122 of destination device 116.
  • Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memories.
  • memories 106, 120 may store raw video data, e.g., raw video from video source 104 and raw, decoded video data from video decoder 300. Additionally or alternatively, memories 106, 120 may store software instructions executable by, e.g., video encoder 200 and video decoder 300, respectively.
  • memory 106 and memory 120 are shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 may also include internal memories for functionally similar or equivalent purposes.
  • memories 106, 120 may store encoded video data, e.g., output from video encoder 200 and input to video decoder 300.
  • portions of memories 106, 120 may be allocated as one or more video buffers, e.g., to store raw, decoded, and/or encoded video data.
  • Computer-readable medium 110 may represent any type of medium or device capable of transporting the encoded video data from source device 102 to destination device 116.
  • computer-readable medium 110 represents a communication medium to enable source device 102 to transmit encoded video data directly to destination device 116 in real-time, e.g., via a radio frequency network or computer-based network.
  • Output interface 108 may modulate a transmission signal including the encoded video data, and input interface 122 may demodulate the received transmission signal, according to a communication standard, such as a wireless communication protocol.
  • the communication medium may include 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 packetbased network, such as a local area network, a wide-area network, or a global network such as the Internet.
  • the communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 102 to destination device 116.
  • source device 102 may output encoded data from output interface 108 to storage device 112.
  • destination device 116 may access encoded data from storage device 112 via input interface 122.
  • Storage device 112 may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.
  • source device 102 may output encoded video data to file server 114 or another intermediate storage device that may store the encoded video data generated by source device 102. Destination device 116 may access stored video data from file server 114 via streaming or download.
  • File server 114 may be any type of server device capable of storing encoded video data and transmitting that encoded video data to the destination device 116.
  • File server 114 may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS) server, and/or a network attached storage (NAS) device.
  • a file transfer protocol service such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol
  • CDN content delivery network
  • HTTP hypertext transfer protocol
  • MBMS Multimedia Broadcast Multicast Service
  • eMBMS Enhanced MBMS
  • NAS network attached storage
  • File server 114 may, additionally or alternatively, implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, or the like.
  • HTTP streaming protocols such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, or the like.
  • Destination device 116 may access encoded video data from file server 114 through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a 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 file server 114.
  • Input interface 122 may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server 114, or other such protocols for retrieving media data.
  • Output interface 108 and input interface 122 may represent wireless transmitters/receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of IEEE 802.11 standards, or other physical components.
  • output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to a cellular communication standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like.
  • output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to other wireless standards, such as an IEEE 802.11 specification, an IEEE 802.15 specification (e.g., ZigBeeTM), a BluetoothTM standard, or the like.
  • source device 102 and/or destination device 116 may include respective system-on-a-chip (SoC) devices.
  • SoC system-on-a-chip
  • source device 102 may include an SoC device to perform the functionality attributed to video encoder 200 and/or output interface 108
  • destination device 116 may include an SoC device to perform the functionality attributed to video decoder 300 and/or input interface 122.
  • the techniques of this disclosure may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.
  • multimedia applications such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.
  • DASH dynamic adaptive streaming over HTTP
  • Input interface 122 of destination device 116 receives an encoded video bitstream from computer-readable medium 110 (e.g., a communication medium, storage device 112, file server 114, or the like).
  • the encoded video bitstream may include signaling information defined by video encoder 200, which is also used by video decoder 300, such as syntax elements having values that describe characteristics and/or processing of video blocks or other coded units (e.g., slices, pictures, groups of pictures, sequences, or the like).
  • Display device 118 displays decoded pictures of the decoded video data to a user.
  • Display device 118 may represent any of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.
  • LCD liquid crystal display
  • OLED organic light emitting diode
  • video encoder 200 and video decoder 300 may each be integrated with an audio encoder and/or audio decoder, and may include appropriate MUX-DEMUX units, or other hardware and/or software, to handle multiplexed streams including both audio and video in a common data stream.
  • Video encoder 200 and video decoder 300 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
  • a 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 techniques of this disclosure.
  • Each of video encoder 200 and video decoder 300 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.
  • a device including video encoder 200 and/or video decoder 300 may implement video encoder 200 and/or video decoder 300 in processing circuitry such as an integrated circuit and/or a microprocessor.
  • Such a device may be a wireless communication device, such as a cellular telephone, or any other type of device described herein.
  • Video encoder 200 and video decoder 300 may operate according to a video coding standard, such as ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC) or extensions thereto, such as the multi-view and/or scalable video coding extensions.
  • video encoder 200 and video decoder 300 may operate according to other proprietary or industry standards, such as ITU-T H.266, also referred to as Versatile Video Coding (VVC).
  • video encoder 200 and video decoder 300 may operate according to a proprietary video codec/format, such as AOMedia Video 1 (AVI), extensions of AVI, and/or successor versions of AVI (e.g., AV2).
  • a proprietary video codec/format such as AOMedia Video 1 (AVI), extensions of AVI, and/or successor versions of AVI (e.g., AV2).
  • video encoder 200 and video decoder 300 may operate according to other proprietary formats or industry standards. The techniques of this disclosure, however, are not limited to any particular coding standard or format. In general, video encoder 200 and video decoder 300 may be configured to perform the techniques of this disclosure in conjunction with any video coding techniques that use subsampling.
  • video encoder 200 and video decoder 300 may perform block-based coding of pictures.
  • the term “block” generally refers to a structure including data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and/or decoding process).
  • a block may include a two-dimensional matrix of samples of luminance and/or chrominance data.
  • video encoder 200 and video decoder 300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.
  • YUV e.g., Y, Cb, Cr
  • video encoder 200 and video decoder 300 may code luminance and chrominance components, where the chrominance components may include both red hue and blue hue chrominance components.
  • video encoder 200 converts received RGB formatted data to a YUV representation prior to encoding
  • video decoder 300 converts the YUV representation to the RGB format.
  • pre- and post-processing units may perform these conversions.
  • This disclosure may generally refer to coding (e.g., encoding and decoding) of pictures to include the process of encoding or decoding data of the picture.
  • this disclosure may refer to coding of blocks of a picture to include the process of encoding or decoding data for the blocks, e.g., prediction and/or residual coding.
  • An encoded video bitstream generally includes a series of values for syntax elements representative of coding decisions (e.g., coding modes) and partitioning of pictures into blocks.
  • references to coding a picture or a block should generally be understood as coding values for syntax elements forming the picture or block.
  • HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs).
  • a video coder such as video encoder 200 partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video coder partitions CTUs and CUs into four equal, nonoverlapping squares, and each node of the quadtree has either zero or four child nodes. Nodes without child nodes may be referred to as “leaf nodes,” and CUs of such leaf nodes may include one or more PUs and/or one or more TUs.
  • the video coder may further partition PUs and TUs.
  • a residual quadtree represents partitioning of TUs.
  • PUs represent inter-prediction data
  • TUs represent residual data.
  • CUs that are intra-predicted include intra-prediction information, such as an intra-mode indication.
  • video encoder 200 and video decoder 300 may be configured to operate according to VVC.
  • a video coder such as video encoder 200 partitions a picture into a plurality of CTUs.
  • Video encoder 200 may partition a CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or Multi-Type Tree (MTT) structure.
  • QTBT quadtree-binary tree
  • MTT Multi-Type Tree
  • the QTBT structure removes the concepts of multiple partition types, such as the separation between CUs, PUs, and TUs of HEVC.
  • a QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning.
  • a root node of the QTBT structure corresponds to a CTU.
  • Leaf nodes of the binary trees correspond to CUs.
  • blocks may be partitioned using a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of triple tree (TT) (also called ternary tree (TT)) partitions.
  • QT quadtree
  • BT binary tree
  • TT triple tree
  • a triple or ternary tree partition is a partition where a block is split into three sub-blocks.
  • a triple or ternary tree partition divides a block into three sub-blocks without dividing the original block through the center.
  • the partitioning types in MTT e.g., QT, BT, and TT), may be symmetrical or asymmetrical.
  • video encoder 200 and video decoder 300 may be configured to code video data in blocks.
  • a superblock can be either 128x128 luma samples or 64x64 luma samples.
  • a superblock may be defined by different (e.g., larger) luma sample sizes.
  • a superblock is the top level of a block quadtree.
  • Video encoder 200 may further partition a superblock into smaller coding blocks.
  • Video encoder 200 may partition a superblock and other coding blocks into smaller blocks using square or non-square partitioning.
  • Non-square blocks may include N/2xN, NxN/2, N/4xN, and NxN/4 blocks.
  • Video encoder 200 and video decoder 300 may perform separate prediction and transform processes on each of the coding blocks.
  • AVI also defines a tile of video data.
  • a tile is a rectangular array of superblocks that may be coded independently of other tiles. That is, video encoder 200 and video decoder 300 may encode and decode, respectively, coding blocks within a tile without using video data from other tiles. However, video encoder 200 and video decoder 300 may perform filtering across tile boundaries. Tiles may be uniform or non-uniform in size. Tile-based coding may enable parallel processing and/or multi -threading for encoder and decoder implementations.
  • video encoder 200 and video decoder 300 may use a single QTBT or MTT structure to represent each of the luminance and chrominance components, while in other examples, video encoder 200 and video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT/MTT structure for the luminance component and another QTBT/MTT structure for both chrominance components (or two QTBT/MTT structures for respective chrominance components).
  • Video encoder 200 and video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, superblock partitioning, or other partitioning structures.
  • a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate color planes and syntax structures used to code the samples.
  • a CTB may be an NxN block of samples for some value of N such that the division of a component into CTBs is a partitioning.
  • a component is an array or single sample from one of the three arrays (luma and two chroma) that compose a picture in 4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample of the array that compose a picture in monochrome format.
  • a coding block is an MxN block of samples for some values of M and N such that a division of a CTB into coding blocks is a partitioning.
  • the blocks may be grouped in various ways in a picture.
  • a brick may refer to a rectangular region of CTU rows within a particular tile in a picture.
  • a tile may be a rectangular region of CTUs within a particular tile column and a particular tile row in a picture.
  • a tile column refers to a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements (e.g., such as in a picture parameter set).
  • a tile row refers to a rectangular region of CTUs having a height specified by syntax elements (e.g., such as in a picture parameter set) and a width equal to the width of the picture.
  • a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile.
  • a tile that is not partitioned into multiple bricks may also be referred to as a brick.
  • a brick that is a true subset of a tile may not be referred to as a tile.
  • the bricks in a picture may also be arranged in a slice.
  • a slice may be an integer number of bricks of a picture that may be exclusively contained in a single network abstraction layer (NAL) unit.
  • NAL network abstraction layer
  • a slice includes either a number of complete tiles or only a consecutive sequence of complete bricks of one tile.
  • NxN and N by N interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, e.g., 16x16 samples or 16 by 16 samples.
  • an NxN CU generally has N samples in a vertical direction and N samples in a horizontal direction, where N represents a nonnegative integer value.
  • the samples in a CU may be arranged in rows and columns.
  • CUs need not necessarily have the same number of samples in the horizontal direction as in the vertical direction.
  • CUs may include NxM samples, where M is not necessarily equal to N.
  • Video encoder 200 encodes video data for CUs representing prediction and/or residual information, and other information.
  • the prediction information indicates how the CU is to be predicted in order to form a prediction block for the CU.
  • the residual information generally represents sample-by-sample differences between samples of the CU prior to encoding and the prediction block.
  • video encoder 200 may generally form a prediction block for the CU through inter-prediction or intra-prediction. Inter-prediction generally refers to predicting the CU from data of a previously coded picture, whereas intra-prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter-prediction, video encoder 200 may generate the prediction block using one or more motion vectors.
  • Video encoder 200 may generally perform a motion search to identify a reference block that closely matches the CU, e.g., in terms of differences between the CU and the reference block. Video encoder 200 may calculate a difference metric using a sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or other such difference calculations to determine whether a reference block closely matches the current CU. In some examples, video encoder 200 may predict the current CU using uni-directional prediction or bi-directional prediction.
  • SAD sum of absolute difference
  • SSD sum of squared differences
  • MAD mean absolute difference
  • MSD mean squared differences
  • VVC also provide an affine motion compensation mode, which may be considered an inter-prediction mode.
  • affine motion compensation mode video encoder 200 may determine two or more motion vectors that represent non- translational motion, such as zoom in or out, rotation, perspective motion, or other irregular motion types.
  • video encoder 200 may select an intra-prediction mode to generate the prediction block.
  • VVC provides sixty-seven intra-prediction modes, including various directional modes, as well as planar mode and DC mode.
  • video encoder 200 selects an intra-prediction mode that describes neighboring samples to a current block (e.g., a block of a CU) from which to predict samples of the current block. Such samples may generally be above, above and to the left, or to the left of the current block in the same picture as the current block, assuming video encoder 200 codes CTUs and CUs in raster scan order (left to right, top to bottom).
  • Video encoder 200 encodes data representing the prediction mode for a current block. For example, for inter-prediction modes, video encoder 200 may encode data representing which of the various available inter-prediction modes is used, as well as motion information for the corresponding mode. For uni -directional or bi-directional inter-prediction, for example, video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. Video encoder 200 may use similar modes to encode motion vectors for affine motion compensation mode.
  • AVI includes two general techniques for encoding and decoding a coding block of video data. The two general techniques are intra prediction (e.g., intra frame prediction or spatial prediction) and inter prediction (e.g., inter frame prediction or temporal prediction).
  • video encoder 200 and video decoder 300 do not use video data from other frames of video data.
  • video encoder 200 encodes blocks of a current frame based on the difference between sample values in the current block and predicted values generated from reference samples in the same frame.
  • Video encoder 200 determines predicted values generated from the reference samples based on the intra prediction mode.
  • video encoder 200 may calculate residual data for the block.
  • the residual data such as a residual block, represents sample by sample differences between the block and a prediction block for the block, formed using the corresponding prediction mode.
  • Video encoder 200 may apply one or more transforms to the residual block, to produce transformed data in a transform domain instead of the sample domain.
  • video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to residual video data.
  • DCT discrete cosine transform
  • an integer transform an integer transform
  • wavelet transform or a conceptually similar transform
  • video encoder 200 may apply a secondary transform following the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal dependent transform, a Karhunen-Loeve transform (KLT), or the like.
  • Video encoder 200 produces transform coefficients following application of the one or more transforms.
  • video encoder 200 may perform quantization of the transform coefficients.
  • Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression.
  • video encoder 200 may reduce the bit depth associated with some or all of the transform coefficients. For example, video encoder 200 may round an zz-bit value down to an m-bit value during quantization, where n is greater than m.
  • video encoder 200 may perform a bitwise right-shift of the value to be quantized.
  • video encoder 200 may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients.
  • the scan may be designed to place higher energy (and therefore lower frequency) transform coefficients at the front of the vector and to place lower energy (and therefore higher frequency) transform coefficients at the back of the vector.
  • video encoder 200 may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector.
  • video encoder 200 may perform an adaptive scan.
  • video encoder 200 may entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CAB AC).
  • Video encoder 200 may also entropy encode values for syntax elements describing metadata associated with the encoded video data for use by video decoder 300 in decoding the video data.
  • video encoder 200 may assign a context within a context model to a symbol to be transmitted.
  • the context may relate to, for example, whether neighboring values of the symbol are zero-valued or not.
  • the probability determination may be based on a context assigned to the symbol.
  • Video encoder 200 may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to video decoder 300, e.g., in a picture header, a block header, a slice header, or other syntax data, such as a sequence parameter set (SPS), picture parameter set (PPS), or video parameter set (VPS).
  • Video decoder 300 may likewise decode such syntax data to determine how to decode corresponding video data.
  • video encoder 200 may generate a bitstream including encoded video data, e.g., syntax elements describing partitioning of a picture into blocks (e.g., CUs) and prediction and/or residual information for the blocks.
  • video decoder 300 may receive the bitstream and decode the encoded video data.
  • video decoder 300 performs a reciprocal process to that performed by video encoder 200 to decode the encoded video data of the bitstream.
  • video decoder 300 may decode values for syntax elements of the bitstream using CAB AC in a manner substantially similar to, albeit reciprocal to, the CABAC encoding process of video encoder 200.
  • the syntax elements may define partitioning information for partitioning of a picture into CTUs, and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU.
  • the syntax elements may further define prediction and residual information for blocks (e.g., CUs) of video data.
  • the residual information may be represented by, for example, quantized transform coefficients.
  • Video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of a block to reproduce a residual block for the block.
  • Video decoder 300 uses a signaled prediction mode (intra- or inter-prediction) and related prediction information (e.g., motion information for inter-prediction) to form a prediction block for the block.
  • Video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block.
  • Video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along boundaries of the block.
  • This disclosure may generally refer to “signaling” certain information, such as syntax elements.
  • the term “signaling” may generally refer to the communication of values for syntax elements and/or other data used to decode encoded video data. That is, video encoder 200 may signal values for syntax elements in the bitstream. In general, signaling refers to generating a value in the bitstream.
  • source device 102 may transport the bitstream to destination device 116 substantially in real time, or not in real time, such as might occur when storing syntax elements to storage device 112 for later retrieval by destination device 116.
  • video encoder 200 and video decoder 300 may be configured to perform one or more techniques for determining subsampling techniques and/or prediction models for a cross-component prediction mode.
  • video encoder 200 and video decoder 300 may be configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data, determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode, and code the block of video data using the subsampling technique and the cross-component prediction mode.
  • Chroma subsampling is a method used in image and video compression to reduce the amount of data used to represent a signal. In general, chroma subsampling is based on the principle that the human visual system is less sensitive to variations in color (chroma) than it is to variations in brightness (luma).
  • the luma samples may be subsampled to match the chroma block size when cross-component prediction is used.
  • cross-component prediction involves predicting the value of a chroma sample from a corresponding luma sample.
  • Examples of cross-component prediction modes which use such subsampling of luma components may include local illumination compensation (LIC), chroma linear mode, cross-component linear mode (CCLM or LM), multi-model LM (MMLM) mode, convolutional cross-component chroma inter prediction (CCCM), gradient linear model (GLM), among others.
  • LIC local illumination compensation
  • CCLM or LM cross-component linear mode
  • MMLM multi-model LM
  • CCCM convolutional cross-component chroma inter prediction
  • GLM gradient linear model
  • prediction model parameters are derived from the reconstructed neighbor samples between luma and chroma component.
  • video encoder 200 and video decoder 300 may be configured to derive model parameters for coding current block 400 from reconstructed samples in neighbor reconstructed area 402 of a picture. Then, video encoder 200 and video decoder 300 apply the derived model to the reconstructed luma samples of current block 400 to derive the prediction of chroma samples for current block 400.
  • a linear prediction model may be in the form:
  • Chroma prediction a * Recontructed luma + b, where a and b are prediction model parameters, Reconstructed luma is a corresponding reconstructed luma sample, and Chroma prediction is the corresponding predicted chroma sample.
  • a linear prediction model may be represented as:
  • Chroma_pr ediction i a i * Reconstructed Jumat + b, where i represents the model shape or filter support, e.g., model shape 401 shown in FIG. 3, of the luma neighborhood, a, and b are the model parameters.
  • neighbor luma reconstructed samples are subsampled to derive a prediction model.
  • Reconstructed luma samples of the current block are subsampled as well, in order to apply the subsampled reconstructed luma samples as inputs to the prediction model for chroma prediction derivation.
  • Multi-model LM (MMLM) mode is an example coding mode where two linear models between the luma neighboring reconstructed samples and chroma neighboring reconstructed samples are derived by classifying the sample pairs into two groups using a threshold luma value.
  • the threshold luma value is the average of the luma neighboring reconstructed samples.
  • chromaVal is the predicted chroma value and lumaVal is the corresponding luma value.
  • FIG. 5 illustrates an example adjustment of linear model 430 to produce an adjusted linear model 440.
  • the slope of the line 432 of linear model 430 is adjusted to line 442.
  • Delta values, u may be an integer between -4 and 4, inclusive, and may be signaled in the bitstream.
  • a slope adjustment flag may be signaled to indicate whether to apply the delta value to the slope if one of LM mode and MMLM mode is used.
  • cross-component chroma inter prediction uses a 7-tap filter to predict chroma samples from reconstructed luma samples in a similar manner as done by the current CCLM modes.
  • the reconstructed luma samples are downsampled (or subsampled) to match the lower resolution chroma grid when chroma subsampling is used.
  • the inputs to the 7-tap filter are listed below:
  • a center (C, aO) luma sample which is collocated with the chroma sample to be predicted • Above/north (N, al), below/south (S, a4), left/west (W, a2) and right/east (E, a3) neighbors of the center luma sample as illustrated in FIG. 3.
  • 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).
  • a video coder may be configured to use a filter surrounding the position for which the subsampling is applied.
  • a video coder may use 4x2 filter 450, shown in FIG. 6, to derive subsampled luma samples in 4:2:0 format (e.g., as in VVC).
  • Such subsampling may smooth the signal, which may be beneficial for some video content, but may not be optimal for other video content (e.g., video content that has sharp detail, such as graphics or screen content). For sharper detailed video content, such as graphics or screen content, smoothing may eliminate or reduce certain patterns and the derived prediction models from such smoothing may be less efficient.
  • the techniques of this disclosure may be applied to any cross-component prediction mode where, in one example, reconstructed luma samples are used to derive a chroma prediction in a non 4:4:4 format (e.g., any format that includes chroma subsampling relative to luma).
  • the techniques of this disclosure may be applied to LIC, chroma linear mode, CCLM, LM, , MMLM, CCCM, GLM, and other similar coding modes.
  • video encoder 200 and video decoder 300 may be configured to determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode. For example, relative to the luma subsampling filters discussed above, video encoder 200 and video decoder 300 may be configured to use a weaker luma filter which takes the neighbor samples with less weights than the center samples when subsampling or smoothing luma samples for a cross-component prediction mode.
  • video encoder 200 and video decoder 300 may be configured to not apply luma subsampling to the reconstructed luma samples when coding video data using a cross-component prediction mode. That is, one of the plurality of possible subsampling techniques that video encoder 200 and video decoder 300 may use is to not apply subsampling to the luma samples of the block of video data.
  • video encoder 200 and video decoder 300 may be configured to derive a prediction model for predicting chroma samples using a larger amount of luma samples compared to the amount of chroma samples.
  • video encoder 200 and video decoder 300 apply the prediction model to derive the chroma prediction
  • the prediction model is also applied to nonsubsampled reconstructed luma samples of the current block.
  • video encoder 200 and video decoder 300 may be configured to not apply luma subsampling when coding screen and graphics content coding using a cross-component prediction mode. In this way, the detail of luma samples is not lost, resulting in better coding efficiency and less distortion in the screen and graphics content.
  • a cross-component prediction mode where no luma subsampling is applied is one of a plurality of cross-component prediction modes.
  • video encoder 200 may be configured to encode a flag or index indicating the that the a cross-component prediction mode uses no luma subsampling.
  • Video decoder 300 may receive and decode the flag or index to determine the particular cross-component prediction mode to use.
  • video encoder 200 and video decoder 300 are configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data.
  • Video encoder 200 and video decoder may determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode.
  • video encoder 200 and video decoder 300 may determine to not apply subsampling to the luma samples of the block of video data. That is, not applying subsampling is one of the possible subsampling techniques.
  • video encoder 200 and video decoder 300 may determine to not apply subsampling to the luma samples of the block of video data based on the video data being graphics content or screen content.
  • Video encoder 200 and video decoder 300 may then code (e.g., encode and decode, respectively), the block of video data using the subsampling technique (e.g., no subsampling) and the cross-component prediction mode.
  • video encoder 200 and video decoder 300 predicts the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples
  • the prediction model uses a 3x2 filter shape
  • video encoder 200 and video decoder 300 may predict one chroma sample of the block using the prediction model using the 3x2 filter shape and six luma samples.
  • video encoder 200 and video decoder 300 may be configured to use different prediction model shapes for, compared to the techniques described above, when coding video data using a cross-component prediction mode.
  • the prediction mode is in the form of a filter.
  • the downsampled, or not downsampled, luma samples, depending on the subsampling technique determine, are used as inputs to the prediction model.
  • Example prediction model shapes may include diamond 3x3, diamond 5x5, diamond 7x5, square shapes, and others.
  • video encoder 200 and video decoder 300 may be configured to use a prediction model shape that is more elongated in the horizontal direction relative to the vertical direction.
  • the prediction model is represented as a filter
  • the filter shape for the prediction model may have more taps horizontally than vertically.
  • FIG. 7 shows examples of an elongated horizontal prediction model shape 460 and 462, where (x,y) are the luma positions and ‘a are the model parameters.
  • the prediction model shape may be nonsymmetrical in some examples.
  • An example of a 5x4 prediction model shape 464 is shown in FIG. 8.
  • Examples of one-directional prediction model shapes are shown in FIG. 9.
  • FIG. 9 shows a horizontal 1x3 prediction model shape 466, a vertical 3x1 prediction model shape 468, a top-left to bottom-right diagonal prediction model shape 470, and a topright to bottom-left diagonal prediction model shape 472.
  • the order in which neighboring samples are included in the prediction model may not be important (e.g., may be arbitrary) as long as video encoder 200 and video decoder 300 include those samples in the same order.
  • the inputs of the filter e.g., the prediction model
  • the inputs of filter are luma samples (or chroma samples) without downsampling.
  • Various filters e.g., subsampling or downsampling filters
  • the combination of filters may be a linear combination of those various filters (e.g., downsampling filters) with the coefficients implicitly derived or signaled.
  • video encoder 200 and video decoder 300 may perform implicit coefficient derivation using already reconstructed luma and chroma neighboring samples.
  • video encoder 200 and video decoder 300 may minimize the difference between the reconstructed chroma samples and the prediction neighbor chroma samples using the prediction model with one or more (downsampling) filters applied to the reconstructed luma samples.
  • the linear combination of the one or more (downsampling) filters can be applied to luma samples corresponding to the specific chroma shape of the prediction model used for the cross-component prediction mode.
  • the prediction model shape can be a one-directional shape, as shown in FIG. 9, and the luma samples corresponding to aO, al, and a2 are applied with the linear combination of the one or more (downsampling) filters.
  • the downsampling filters can be one or more of the 3x2 downsampling filters 480, e.g., H, Gl, G2, G3, and G4, as shown in FIG. 10.
  • the filter sample location relative to the currently filtered sample (C) and the filter coefficients is illustrated.
  • Gl, G2, G3 and G4 are the gradient filters along one of the horizontal, vertical, and diagonal directions.
  • video encoder 200 and video decoder 300 may be configured to use a combination of filters (e.g., corresponding to a combination of prediction shapes) that are applied to the luma samples.
  • video encoder 200 and video decoder 300 may use downsampled luma samples corresponding to multiple chroma positions as the inputs of a prediction model, and video encoder 200 and video decoder 300 may apply multiple downsampling filters to luma samples for each chroma sample position.
  • Example prediction models may include one or more of the one-directional prediction models shown in FIG. 9.
  • the two downsampling filters in the above example may be downsampling filter H (see FIG. 10), and a gradient filter (e.g., Gl, G2, G3, or G4) which has the same direction as the one-directional prediction model used.
  • gradient filter Gl may be applied for a horizontal prediction model (e.g. prediction model shape 466 of FIG. 9)
  • gradient filter G2 may be applied for a vertical prediction model (e.g., prediction model shape 468 of FIG.
  • gradient filter G3 may be applied for a top-left to bottom-right prediction model (e.g., prediction model shape 470 of FIG. 9), and gradient filter G4 may be applied for a top-right to bottom-left prediction model (e.g., prediction model shape 472 of FIG. 9).
  • video encoder 200 and video decoder 300 may operate according to a constraint that specifies that multiple subsampling filters for luma samples may be only applied to the inputs corresponding to a certain group of chroma positions.
  • Example groups of chroma positions may include a center position only, or center and north (e.g., above) positions, etc.
  • Video encoder 200 and video decoder 300 may use the same downsampling filter for the remaining chroma positions.
  • video encoder 200 and video decoder 300 are configured to use downsampled luma samples corresponding to the same chroma position as the inputs of the prediction model.
  • each input may be generated with a different downsampling filter.
  • the same position e.g., (x, y)
  • has different downsampling luma samples applied e.g., H, Gl, G2, G3 and G4 as follows: cO * H (x, y) + cl * Gl (x, y) + c2 * G2 (x, y) + c3 * G3 (x, y) + c4 * G4 (x, y), where cO, cl, c2, c3, c4 are weighting factors for each term.
  • the inputs of a prediction model are downsampled luma samples corresponding to different gradient predictors, and each gradient predictor is applied with different downsampling luma samples.
  • a gradient predictor could be any predictor difference.
  • NW, N, NE, W, E, SW, S, and SE are luma samples.
  • no downsampling filter can be applied to some or all chroma predictors or predictor gradients, and the other downsampling filters can be applied to the same (or some other) chroma predictors or the same (or some other) predictor gradients.
  • video encoder 200 and video decoder 300 may be configured to code video data using a cross-component prediction mode that uses multiple crosscomponent prediction models that apply one or more of the different alternatives described above for combining a prediction model shape with different downsampling filters for luma components, including no downsampling (e.g., no subsampling of luma to match the size of chroma).
  • a cross-component prediction mode that uses multiple crosscomponent prediction models that apply one or more of the different alternatives described above for combining a prediction model shape with different downsampling filters for luma components, including no downsampling (e.g., no subsampling of luma to match the size of chroma).
  • the filter shapes for the prediction model may include a nonlinear term(s) and/or a shift term(s) to calculate a final predictor, where the inputs of nonlinear term could be one sample at current position (x, y) or a plurality of samples around the position (x, y).
  • video encoder 200 and video decoder 300 may be configured to apply the nonlinear terms to the downsampled luma samples in the same direction, and add the non-linear term to the prediction model.
  • the prediction model shapes for the prediction model may include a horizontal location (x_c) and a vertical location (y_c) w of the center luma sample (or the center chroma sample), which are calculated with respect to the top-left coordinates of the block. If a prediction model shape is along a specific direction, as shown in FIG. 9, video encoder 200 and video decoder 300 may be constrained such that only one of x_c and y_c is added to the cross-component prediction model.
  • the prediction model has horizontal shape, as shown in prediction model shape 466 of FIG. 9, which is applied with gradient filter G1 of FIG. 10, x_c is added to the model. If the model is vertical prediction shape, as shown in prediction model shape 468 of FIG. 9, applied with gradient filter G2 of FIG. 10, y_c is added to the model. If the model is a diagonal prediction shape, as shown in prediction model shapes 470 or 472 of FIG. 9, applied with gradient filters G3 or G4 of FIG. 10, y_c is added to the model. This example can be used with any of the previous methods described above.
  • the one-dimensional location is applied with directional nonlinear terms as follows: cO * H (x, y) + cl * H (x - 1, y) + c2 * H (x + 1, y) + c3 * G1 (x, y) + c4 * G1 (x - 1, y) + c5 * G1 (x + 1, y) + c6 * P(H (x, y)) + c7 * P(H (x - 1, y)) + c8 * P(H (x + 1, y)) + c9 * x_c.
  • ci are weighting factors for each term
  • P( a ) is a nonlinear term with ‘a’ as input.
  • Video encoder 200 may be configured to signal a syntax element that indicates the particular component models (e.g., ModeO, Model, etc.) to use for a particular cross-component prediction mode.
  • video encoder 200 and video decoder 300 may be configured to determine a cross-component model for the cross-component prediction mode, and then determine the subsampling technique from the cross-component model for the cross-component prediction mode.
  • ModeO filter shape shown in FIG. 2: CCCM
  • Model (filters shown in FIG. 10): cO * H (x, y) + cl * G1 (x, y) + c2 * G2 (x, y) + c3 * G3 (x, y) + c4 * G4 (x, y), where (x,y) is the position of the luma sample being filtered, and c0-c4 are weighting factors for each term.
  • Mode4 (prediction model shape 468 in FIG. 9): cO * H (x, y) + cl * H (x, y-1) + c2 * H (x, y+1) + c3 * G1 (x, y) + c4 * G1 (x, y-1) + c5 * G1 (x, y+1) + c6 * P(H (x, y)) + c7 * P(H (x - 1, y)) + c8 * P(H (x + 1, y)) + c9 * y_c
  • video encoder 200 and video decoder 300 may be configured to determine the subsampling technique to include the application of a combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data.
  • video encoder 200 and video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions in the block of video data.
  • video encoder 200 and video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data at particular chroma sample positions in the block of video data according to a constraint.
  • video encoder 200 and video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples, and predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • the prediction model includes non-linear terms.
  • Applying the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples may include applying the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions to produce downsampled luma samples.
  • applying the combination of downsampling filters to the luma samples of the block of video data to produce the downsampled luma samples may include applying the combination of downsampling filters to the luma samples of the block of video data based on the prediction model shape to produce the downsampled luma samples.
  • the combination of downsampling filters includes a plurality of 3x2 downsampling filters.
  • the prediction model shape may be one or more of a one- directional shape, a diamond 3x3 shape, a diamond 5x5 shape, a diamond 7x5 shape, or a shape that is larger in a horizontal direction than a vertical direction.
  • Video encoder 200 may be configured to signal the choice of subsampling filter (or no subsampling filter) using a block level flag or syntax element (e.g., an index), a slice level syntax element (e.g., in a slice header), a picture level syntax element (e.g., in a picture header or PPS), or in a sequence level syntax element (e.g., in an SPS or VPS).
  • a block level flag or syntax element e.g., an index
  • a slice level syntax element e.g., in a slice header
  • a picture level syntax element e.g., in a picture header or PPS
  • a sequence level syntax element e.g., in an SPS or VPS
  • Multiple variants of a cross-component prediction mode using different subsampling techniques, including no subsampling, may be applied to already reconstructed neighbor luma samples to derive chroma prediction in the reconstructed neighbor area. Since reconstructed neighbor chroma samples are available, the comparison may be performed based on how close the chroma prediction is to the reconstructed neighbor chroma samples, and the cross-component prediction mode variant which has the closest match is chosen and is applied to obtain the chroma prediction for the current block.
  • the choices of cross-component prediction mode variants may be ordered according to the cost of how close the match is. Instead of signaling a mode flag or index, a flag or index is signaled to that ordered list of cross-component prediction mode choices. In another way, that ordered list may be treated as a mode flag or mode index predictor. For example, a syntax element is signaled that indicates whether a mode flag is equal to the predictor.
  • Multiple prediction model shapes may be used in the prediction model.
  • the choice of the shape can be signaled at a block, slice, picture, sequence levels.
  • the signaling is dependent on the choice of subsampling filter or no subsampling.
  • the choice of the shape is signaled if no subsampling is chosen.
  • the choice of the shape is implicitly derived using the reconstructed samples in a similar manner as described above for mode signaling using the closest match, where multiple prediction model shapes are evaluated for the reconstructed area and the one with the closest match (or the smallest cost in terms of the difference) is selected.
  • the choices of the prediction model shapes may be ordered according to the cost of how close the match is, and instead of signaling a mode shape flag or index, a flag or index is signaled to that ordered list of the shapes.
  • that ordered list may be treated as a shape flag or shape index predictor.
  • the choice of subsampling, prediction model shapes, or other cross-component prediction mode variants may be signaled for all cross-component prediction modes, or they can be signaled only for certain cross-component prediction mode variants.
  • CCCM mode may have 3 options: using top and left samples to derive the model, use only top samples to derive the mode, or only using left samples to derive the mode.
  • the subsampling choice, prediction model shapes or other crosscomponent prediction mode options may be signaled only for CCCM using top and left samples for mode derivation and are not signaled for other cases. This may provide enough diversity and at the same time save overhead.
  • other cross-component prediction modes mentioned above, such as LIC, LM, GLM, etc. may use the same technique.
  • the prediction model may use non-linear terms.
  • An example of a non-linear term may be a square of reconstructed luma sample divided by a bitdepth.
  • a reconstructed luma sample is one and is located in the center of the prediction model shape.
  • non-liner term may not be the optimal choice for all video content.
  • the choice of non-linear terms may depend on subsampling techniques determined, the prediction model shape, and/or other cross-component prediction mode parameters.
  • all samples used in the prediction model shape or model filtering may be used to derive the non-linear terms.
  • only certain samples may be used for determining non-linear terms, e.g., a center sample, diagonal samples, anti-diagonal samples, samples in one line, samples in one row or column, and other combinations of samples.
  • the choice of the samples to derive the non-linear terms may represent a certain directional property.
  • the 3x2 filter shown in FIG. 6 may be used as the prediction model shape.
  • FIG. 12 and FIG. 13 show other examples of samples used to derive the non-linear terms.
  • the samples used to derive the non-linear terms are the shaded samples.
  • a weighted average of multiple samples may be used to derive a non-linear term.
  • The3x2 prediction model shape 3x2 was used as an example. However, similar multiple nonlinear terms techniques including a directionality bias may be used in combination with other prediction model shapes.
  • video encoder 200 and video decoder 300 may be configured to add one delta value to a first weight parameter in a prediction model.
  • CCCM prediction model Take CCCM prediction model as an example.
  • video encoder 200 and video decoder 300 may update a second weight parameter in a prediction model by the derivation with the assumption that predChromaVal is the same when the center (C) luma sample is equal to the average of luma samples in the template (denoted as Cave).
  • a delta u value is added to the value of weight parameter C5 of nonlinear term P, and co is updated accordingly as follows:
  • Explicit signaling may be used to determine whether to enable the slope adjustment for the prediction model, and determine the delta value u. Note that other fixed values may be applied to Cave to update the second weight parameter in prediction model.
  • template-based slope adjustment is proposed. One flag is signaled to determine if the template-based slope adjustment is used for this CU. If it is true, then the template-based SAD costs for each delta index d are calculated, where a delta index d corresponds to a delta value u. Then the best delta index d with the lowest SAD cost is selected for this CU.
  • Video encoder 200 and video decoder 300 may use template-based MMLM to determine how many linear models are used in MMLM. One flag may be signaled to determine if the template-based MMLM is used for this CU. If it is true, then the template-based SAD cost for each multi-model index m are calculated, where a multi- model index m corresponds to a value for the number of linear models in MMLM. Then, the best multi-model index m with the lowest SAD cost is selected for this CU.
  • video encoder 200 and video decoder 300 may derive the cross-component prediction models (CCMs) disclose herein from non- adjacent neighboring samples, as shown in FIG. 14, where the cross-hatched regions around the current block 496 are potential candidate regions which may be used to derive the weighting factors of CCMs. Note that the locations of the regions could be any locations in the picture, and the shape of the regions is not limited to be square.
  • a candidate region list is constructed using the available regions in order. A flag is signaled to indicate whether non-adjacent CCP (e.g., crosscomponent prediction) is applied to the current chroma block. If non-adjacent CCP is applied, an index is signaled to indicate which candidate in the candidate region list is used to derive the prediction model.
  • CCMs cross-component prediction models
  • a candidate list is constructed to add the CCMs using the adjacent neighboring samples first, and then add the CCMs using the non-adjacent neighboring regions later. If a CCM flag is enabled, an index is signaled to indicate which candidate in the list is used to derive the prediction model.
  • FIG. 15 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure.
  • FIG. 15 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure.
  • this disclosure describes video encoder 200 according to the techniques of VVC and HEVC.
  • the techniques of this disclosure may be performed by video encoding devices that are configured to other video coding standards and video coding formats, such as AVI and successors to the AVI video coding format.
  • video encoder 200 includes video data memory 230, mode selection unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, decoded picture buffer (DPB) 218, and entropy encoding unit 220.
  • Any or all of video data memory 230, mode selection unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, DPB 218, and entropy encoding unit 220 may be implemented in one or more processors or in processing circuitry.
  • video encoder 200 may be implemented as one or more circuits or logic elements as part of hardware circuitry, or as part of a processor, ASIC, or FPGA.
  • video encoder 200 may include additional or alternative processors or processing circuitry to perform these and other functions.
  • Video data memory 230 may store video data to be encoded by the components of video encoder 200.
  • Video encoder 200 may receive the video data stored in video data memory 230 from, for example, video source 104 (FIG. 1).
  • DPB 218 may act as a reference picture memory that stores reference video data for use in prediction of subsequent video data by video encoder 200.
  • Video data memory 230 and DPB 218 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices.
  • Video data memory 230 and DPB 218 may be provided by the same memory device or separate memory devices.
  • video data memory 230 may be on-chip with other components of video encoder 200, as illustrated, or off-chip relative to those components.
  • reference to video data memory 230 should not be interpreted as being limited to memory internal to video encoder 200, unless specifically described as such, or memory external to video encoder 200, unless specifically described as such. Rather, reference to video data memory 230 should be understood as reference memory that stores video data that video encoder 200 receives for encoding (e.g., video data for a current block that is to be encoded). Memory 106 of FIG. 1 may also provide temporary storage of outputs from the various units of video encoder 200.
  • the various units of FIG. 15 are illustrated to assist with understanding the operations performed by video encoder 200.
  • the units may be implemented as fixed- function circuits, programmable circuits, or a combination thereof.
  • Fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed.
  • Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed.
  • programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware.
  • Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable.
  • one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.
  • Video encoder 200 may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and/or programmable cores, formed from programmable circuits.
  • ALUs arithmetic logic units
  • EFUs elementary function units
  • digital circuits analog circuits
  • programmable cores formed from programmable circuits.
  • memory 106 FIG. 1 may store the instructions (e.g., object code) of the software that video encoder 200 receives and executes, or another memory within video encoder 200 (not shown) may store such instructions.
  • Video data memory 230 is configured to store received video data.
  • Video encoder 200 may retrieve a picture of the video data from video data memory 230 and provide the video data to residual generation unit 204 and mode selection unit 202.
  • Video data in video data memory 230 may be raw video data that is to be encoded.
  • Mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra-prediction unit 226.
  • Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes.
  • mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of motion estimation unit 222 and/or motion compensation unit 224), an affine unit, a linear model (LM) unit, or the like.
  • LM linear model
  • Mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations.
  • the encoding parameters may include partitioning of CTUs into CUs, prediction modes for the CUs, transform types for residual data of the CUs, quantization parameters for residual data of the CUs, and so on.
  • Mode selection unit 202 may ultimately select the combination of encoding parameters having rate-distortion values that are better than the other tested combinations.
  • Video encoder 200 may partition a picture retrieved from video data memory 230 into a series of CTUs, and encapsulate one or more CTUs within a slice.
  • Mode selection unit 202 may partition a CTU of the picture in accordance with a tree structure, such as the MTT structure, QTBT structure, superblock structure, or the quadtree structure described above.
  • video encoder 200 may form one or more CUs from partitioning a CTU according to the tree structure.
  • Such a CU may also be referred to generally as a “video block” or “block.”
  • mode selection unit 202 also controls the components thereof (e.g., motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226) to generate a prediction block for a current block (e.g., a current CU, or in HEVC, the overlapping portion of a PU and a TU).
  • motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in DPB 218).
  • motion estimation unit 222 may calculate a value representative of how similar a potential reference block is to the current block, e.g., according to sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or the like. Motion estimation unit 222 may generally perform these calculations using sample-by-sample differences between the current block and the reference block being considered. Motion estimation unit 222 may identify a reference block having a lowest value resulting from these calculations, indicating a reference block that most closely matches the current block.
  • SAD sum of absolute difference
  • SSD sum of squared differences
  • MAD mean absolute difference
  • MSD mean squared differences
  • Motion estimation unit 222 may form one or more motion vectors (MVs) that defines the positions of the reference blocks in the reference pictures relative to the position of the current block in a current picture. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for unidirectional inter-prediction, motion estimation unit 222 may provide a single motion vector, whereas for bi-directional inter-prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then generate a prediction block using the motion vectors. For example, motion compensation unit 224 may retrieve data of the reference block using the motion vector. As another example, if the motion vector has fractional sample precision, motion compensation unit 224 may interpolate values for the prediction block according to one or more interpolation filters. Moreover, for bi-directional inter-prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by respective motion vectors and combine the retrieved data, e.g., through sample-by-sample averaging or weighted averaging.
  • MVs
  • motion estimation unit 222 and motion compensation unit 224 may be configured to encode coding blocks of video data (e.g., both luma and chroma coding blocks) using translational motion compensation, affine motion compensation, overlapped block motion compensation (OBMC), and/or compound inter-intra prediction.
  • coding blocks of video data e.g., both luma and chroma coding blocks
  • OBMC overlapped block motion compensation
  • intraprediction unit 226 may generate the prediction block from samples neighboring the current block. For example, for directional modes, intra-prediction unit 226 may generally mathematically combine values of neighboring samples and populate these calculated values in the defined direction across the current block to produce the prediction block. As another example, for DC mode, intra-prediction unit 226 may calculate an average of the neighboring samples to the current block and generate the prediction block to include this resulting average for each sample of the prediction block.
  • intra-prediction unit 226 may be configured to encode coding blocks of video data (e.g., both luma and chroma coding blocks) using directional intra prediction, non-directi onal intra prediction, recursive filter intra prediction, chroma-from-luma (CFL) prediction, intra block copy (IBC), and/or color palette mode.
  • Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes.
  • Intra-prediction unit 226 may also configured to encode video data using a cross-component prediction mode, such as LIC, chroma linear mode, CCLM, LM, , MMLM, CCCM, GLM, and other similar coding modes, using one or more of the techniques of this disclosure described above.
  • a cross-component prediction mode such as LIC, chroma linear mode, CCLM, LM, , MMLM, CCCM, GLM, and other similar coding modes, using one or more of the techniques of this disclosure described above.
  • intra-prediction unit 226 is configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data.
  • Intra-prediction unit 226 may determine a sub sampling technique, from a plurality of sub sampling techniques, for the luma samples of the block of video data for a cross-component prediction mode.
  • intra-prediction unit 226 may determine to not apply subsampling to the luma samples of the block of video data. That is, not applying subsampling is one of the possible subsampling techniques.
  • intraprediction unit 226 may determine to not apply subsampling to the luma samples of the block of video data based on the video data being graphics content or screen content. [0174] Intra-prediction unit 226 may then encode the block of video data using the subsampling technique (e.g., no subsampling) and the cross-component prediction mode. In this example, intra-prediction unit 226 may predicts the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • the subsampling technique e.g., no subsampling
  • intra-prediction unit 226 may predicts the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • intra-prediction unit 226 may be configured to determine the subsampling technique to include the application of a combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data.
  • intra-prediction unit 226 may apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples, and predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • Mode selection unit 202 provides the prediction block to residual generation unit 204.
  • Residual generation unit 204 receives a raw, unencoded version of the current block from video data memory 230 and the prediction block from mode selection unit 202.
  • Residual generation unit 204 calculates sample-by-sample differences between the current block and the prediction block. The resulting sample-by-sample differences define a residual block for the current block.
  • residual generation unit 204 may also determine differences between sample values in the residual block to generate a residual block using residual differential pulse code modulation (RDPCM).
  • RPCM residual differential pulse code modulation
  • residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.
  • each PU may be associated with a luma prediction unit and corresponding chroma prediction units.
  • Video encoder 200 and video decoder 300 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction unit of the PU.
  • video encoder 200 may support PU sizes of 2Nx2N or NxN for intra prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN, or similar for inter prediction.
  • Video encoder 200 and video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.
  • each CU may be associated with a luma coding block and corresponding chroma coding blocks.
  • the size of a CU may refer to the size of the luma coding block of the CU.
  • the video encoder 200 and video decoder 300 may support CU sizes of 2Nx2N, 2NxN, or Nx2N.
  • mode selection unit 202 For other video coding techniques such as an intra-block copy mode coding, an affine-mode coding, and linear model (LM) mode coding, as some examples, mode selection unit 202, via respective units associated with the coding techniques, generates a prediction block for the current block being encoded. In some examples, such as palette mode coding, mode selection unit 202 may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based on a selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 to be encoded.
  • mode selection unit 202 via respective units associated with the coding techniques, generates a prediction block for the current block being encoded.
  • mode selection unit 202 may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based on a selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 to be encoded.
  • residual generation unit 204 receives the video data for the current block and the corresponding prediction block. Residual generation unit 204 then generates a residual block for the current block. To generate the residual block, residual generation unit 204 calculates sample-by-sample differences between the prediction block and the current block.
  • Transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”).
  • Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block.
  • transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to a residual block.
  • transform processing unit 206 may perform multiple transforms to a residual block, e.g., a primary transform and a secondary transform, such as a rotational transform.
  • transform processing unit 206 does not apply transforms to a residual block.
  • transform processing unit 206 may apply one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”).
  • Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block.
  • transform processing unit 206 may apply a horizontal/vertical transform combination that may include a discrete cosine transform (DCT), an asymmetric discrete sine transform (ADST), a flipped ADST (e.g., an ADST in reverse order), and an identity transform (IDTX).
  • DCT discrete cosine transform
  • ADST asymmetric discrete sine transform
  • IDDTX identity transform
  • the transform is skipped in one of the vertical or horizontal directions. In some examples, transform processing may be skipped.
  • Quantization unit 208 may quantize the transform coefficients in a transform coefficient block, to produce a quantized transform coefficient block. Quantization unit 208 may quantize transform coefficients of a transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder 200 (e.g., via mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce loss of information, and thus, quantized transform coefficients may have lower precision than the original transform coefficients produced by transform processing unit 206.
  • QP quantization parameter
  • Inverse quantization unit 210 and inverse transform processing unit 212 may apply inverse quantization and inverse transforms to a quantized transform coefficient block, respectively, to reconstruct a residual block from the transform coefficient block.
  • Reconstruction unit 214 may produce a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and a prediction block generated by mode selection unit 202. For example, reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by mode selection unit 202 to produce the reconstructed block.
  • Filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. Operations of filter unit 216 may be skipped, in some examples.
  • filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. In other examples, filter unit 216 may apply a constrained directional enhancement filter (CDEF), which may be applied after deblocking, and may include the application of non-separable, non-linear, low-pass directional filters based on estimated edge directions. Filter unit 216 may also include a loop restoration filter, which is applied after CDEF, and may include a separable symmetric normalized Wiener filter or a dual self-guided filter.
  • CDEF constrained directional enhancement filter
  • Video encoder 200 stores reconstructed blocks in DPB 218. For instance, in examples where operations of filter unit 216 are not performed, reconstruction unit 214 may store reconstructed blocks to DPB 218. In examples where operations of filter unit 216 are performed, filter unit 216 may store the filtered reconstructed blocks to DPB 218.
  • Motion estimation unit 222 and motion compensation unit 224 may retrieve a reference picture from DPB 218, formed from the reconstructed (and potentially filtered) blocks, to inter-predict blocks of subsequently encoded pictures.
  • intra-prediction unit 226 may use reconstructed blocks in DPB 218 of a current picture to intra-predict other blocks in the current picture.
  • entropy encoding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy encoding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy encoding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intra-mode information for intra-prediction) from mode selection unit 202. Entropy encoding unit 220 may perform one or more entropy encoding operations on the syntax elements, which are another example of video data, to generate entropy-encoded data.
  • prediction syntax elements e.g., motion information for inter-prediction or intra-mode information for intra-prediction
  • entropy encoding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CAB AC operation, a variable-to-variable (V2V) length coding operation, a syntax -based context-adaptive binary arithmetic coding (SB AC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential -Golomb encoding operation, or another type of entropy encoding operation on the data.
  • entropy encoding unit 220 may operate in bypass mode where syntax elements are not entropy encoded.
  • Video encoder 200 may output a bitstream that includes the entropy encoded syntax elements needed to reconstruct blocks of a slice or picture.
  • entropy encoding unit 220 may output the bitstream.
  • entropy encoding unit 220 may be configured as a symbol -to- symbol adaptive multi-symbol arithmetic coder.
  • a syntax element in AVI includes an alphabet of N elements, and a context (e.g., probability model) includes a set of N probabilities.
  • Entropy encoding unit 220 may store the probabilities as n-bit (e.g., 15-bit) cumulative distribution functions (CDFs).
  • CDFs cumulative distribution functions
  • Entropy encoding unit 220 may perform recursive scaling, with an update factor based on the alphabet size, to update the contexts.
  • the operations described above are described with respect to a block. Such description should be understood as being operations for a luma coding block and/or chroma coding blocks.
  • the luma coding block and chroma coding blocks are luma and chroma components of a CU.
  • the luma coding block and the chroma coding blocks are luma and chroma components of a PU.
  • operations performed with respect to a luma coding block need not be repeated for the chroma coding blocks.
  • operations to identify a motion vector (MV) and reference picture for a luma coding block need not be repeated for identifying a MV and reference picture for the chroma blocks. Rather, the MV for the luma coding block may be scaled to determine the MV for the chroma blocks, and the reference picture may be the same.
  • the intraprediction process may be the same for the luma coding block and the chroma coding blocks.
  • Video encoder 200 represents an example of a device configured to encode video data including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to perform one or more techniques of this disclosure.
  • FIG. 16 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure.
  • FIG. 16 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure.
  • this disclosure describes video decoder 300 according to the techniques of VVC and HEVC.
  • the techniques of this disclosure may be performed by video coding devices that are configured to other video coding standards.
  • video decoder 300 includes coded picture buffer (CPB) memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314.
  • CPB memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314 may be implemented in one or more processors or in processing circuitry.
  • the units of video decoder 300 may be implemented as one or more circuits or logic elements as part of hardware circuitry, or as part of a processor, ASIC, or FPGA.
  • video decoder 300 may include additional or alternative processors or processing circuitry to perform these and other functions.
  • Prediction processing unit 304 includes motion compensation unit 316 and intraprediction unit 318. Prediction processing unit 304 may include additional units to perform prediction in accordance with other prediction modes. As examples, prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of motion compensation unit 316), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder 300 may include more, fewer, or different functional components.
  • motion compensation unit 316 may be configured to decode coding blocks of video data (e.g., both luma and chroma coding blocks) using translational motion compensation, affine motion compensation, OBMC, and/or compound inter-intra prediction, as described above.
  • Intra-prediction unit 318 may be configured to decode coding blocks of video data (e.g., both luma and chroma coding blocks) using directional intra prediction, non-directi onal intra prediction, recursive filter intra prediction, CFL, IBC, and/or color palette mode, as described above.
  • Intra-prediction unit 318 may also configured to decode video data using a cross-component prediction mode, such as LIC, chroma linear mode, CCLM, LM, , MMLM, CCCM, GLM, and other similar coding modes, using one or more of the techniques of this disclosure described above.
  • a cross-component prediction mode such as LIC, chroma linear mode, CCLM, LM, , MMLM, CCCM, GLM, and other similar coding modes, using one or more of the techniques of this disclosure described above.
  • intra-prediction unit 318 is configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data.
  • Intra-prediction unit 318 may determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode.
  • intra-prediction unit 318 may determine to not apply subsampling to the luma samples of the block of video data. That is, not applying subsampling is one of the possible subsampling techniques.
  • intraprediction unit 318 may determine to not apply subsampling to the luma samples of the block of video data based on the video data being graphics content or screen content. [0200] Intra-prediction unit 318 may then decode the block of video data using the subsampling technique (e.g., no subsampling) and the cross-component prediction mode. In this example, intra-prediction unit 318 may predicts the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • the subsampling technique e.g., no subsampling
  • intra-prediction unit 318 may predicts the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • intra-prediction unit 318 may be configured to determine the subsampling technique to include the application of a combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data.
  • intra-prediction unit 318 may apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples, and predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder 300.
  • the video data stored in CPB memory 320 may be obtained, for example, from computer-readable medium 110 (FIG. 1).
  • CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream.
  • CPB memory 320 may store video data other than syntax elements of a coded picture, such as temporary data representing outputs from the various units of video decoder 300.
  • DPB 314 generally stores decoded pictures, which video decoder 300 may output and/or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream.
  • CPB memory 320 and DPB 314 may be formed by any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM, or other types of memory devices.
  • CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices.
  • CPB memory 320 may be on-chip with other components of video decoder 300, or off-chip relative to those components.
  • video decoder 300 may retrieve coded video data from memory 120 (FIG. 1). That is, memory 120 may store data as discussed above with CPB memory 320. Likewise, memory 120 may store instructions to be executed by video decoder 300, when some or all of the functionality of video decoder 300 is implemented in software to be executed by processing circuitry of video decoder 300.
  • the various units shown in FIG. 16 are illustrated to assist with understanding the operations performed by video decoder 300.
  • the units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to FIG. 15, fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed.
  • Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware.
  • Fixed- function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable.
  • one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.
  • Video decoder 300 may include ALUs, EFUs, digital circuits, analog circuits, and/or programmable cores formed from programmable circuits.
  • on-chip or off-chip memory may store instructions (e.g., object code) of the software that video decoder 300 receives and executes.
  • Entropy decoding unit 302 may receive encoded video data from the CPB and entropy decode the video data to reproduce syntax elements.
  • Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.
  • video decoder 300 reconstructs a picture on a block-by-block basis.
  • Video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed, i.e., decoded, may be referred to as a “current block”).
  • Entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of a quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and/or transform mode indication(s).
  • Inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 306 to apply.
  • Inverse quantization unit 306 may, for example, perform a bitwise left-shift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit 306 may thereby form a transform coefficient block including transform coefficients.
  • inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block.
  • inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.
  • KLT Karhunen-Loeve transform
  • prediction processing unit 304 generates a prediction block according to prediction information syntax elements that were entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 may generate the prediction block. In this case, the prediction information syntax elements may indicate a reference picture in DPB 314 from which to retrieve a reference block, as well as a motion vector identifying a location of the reference block in the reference picture relative to the location of the current block in the current picture. Motion compensation unit 316 may generally perform the inter-prediction process in a manner that is substantially similar to that described with respect to motion compensation unit 224 (FIG. 15).
  • intra-prediction unit 318 may generate the prediction block according to an intra-prediction mode indicated by the prediction information syntax elements. Again, intra-prediction unit 318 may generally perform the intra-prediction process in a manner that is substantially similar to that described with respect to intra-prediction unit 226 (FIG. 15). Intra-prediction unit 318 may retrieve data of neighboring samples to the current block from DPB 314.
  • Reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.
  • Filter unit 312 may perform one or more filter operations on reconstructed blocks. For example, filter unit 312 may perform deblocking operations to reduce blockiness artifacts along edges of the reconstructed blocks. Operations of filter unit 312 are not necessarily performed in all examples.
  • Video decoder 300 may store the reconstructed blocks in DPB 314. For instance, in examples where operations of filter unit 312 are not performed, reconstruction unit 310 may store reconstructed blocks to DPB 314. In examples where operations of filter unit 312 are performed, filter unit 312 may store the filtered reconstructed blocks to DPB 314. As discussed above, DPB 314 may provide reference information, such as samples of a current picture for intra-prediction and previously decoded pictures for subsequent motion compensation, to prediction processing unit 304. Moreover, video decoder 300 may output decoded pictures (e.g., decoded video) from DPB 314 for subsequent presentation on a display device, such as display device 118 of FIG. 1.
  • decoded pictures e.g., decoded video
  • video decoder 300 represents an example of a video decoding device including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to perform one or more techniques of this disclosure.
  • FIG. 17 is a flowchart illustrating an example method for encoding a current block in accordance with the techniques of this disclosure.
  • the current block may be or include a current CU.
  • video encoder 200 FIGGS. 1 and 15
  • other devices may be configured to perform a method similar to that of FIG. 17.
  • video encoder 200 initially predicts the current block (350). For example, video encoder 200 may form a prediction block for the current block. Video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, video encoder 200 may calculate a difference between the original, unencoded block and the prediction block for the current block. Video encoder 200 may then transform the residual block and quantize transform coefficients of the residual block (354). Next, video encoder 200 may scan the quantized transform coefficients of the residual block (356). During the scan, or following the scan, video encoder 200 may entropy encode the transform coefficients (358). For example, video encoder 200 may encode the transform coefficients using CAVLC or CAB AC.
  • Video encoder 200 may then output the entropy encoded data of the block (360).
  • FIG. 18 is a flowchart illustrating an example method for decoding a current block of video data in accordance with the techniques of this disclosure.
  • the current block may be or include a current CU.
  • video decoder 300 FIGGS. 1 and 16
  • other devices may be configured to perform a method similar to that of FIG. 18.
  • Video decoder 300 may receive entropy encoded data for the current block, such as entropy encoded prediction information and entropy encoded data for transform coefficients of a residual block corresponding to the current block (370). Video decoder 300 may entropy decode the entropy encoded data to determine prediction information for the current block and to reproduce transform coefficients of the residual block (372). Video decoder 300 may predict the current block (374), e.g., using an intra- or interprediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. Video decoder 300 may then inverse scan the reproduced transform coefficients (376), to create a block of quantized transform coefficients. Video decoder 300 may then inverse quantize the transform coefficients and apply an inverse transform to the transform coefficients to produce a residual block (378). Video decoder 300 may ultimately decode the current block by combining the prediction block and the residual block (380).
  • entropy encoded data for the current block such as en
  • FIG. 19 is a flowchart illustrating another example method for encoding a current block in accordance with the techniques of this disclosure.
  • the techniques of FIG. 19 may be performed by one or more structural units of video encoder 200, including intra-prediction unit 226.
  • video encoder 200 may be configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data (550), determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode (552), and encode the block of video data using the subsampling technique and the crosscomponent prediction mode (554).
  • the cross-component prediction mode may be one of local illumination compensation (LIC), chroma linear mode, cross-component linear mode (CCLM), multi -model LM (MMLM) mode, cross-component chroma inter prediction (CCCM), or gradient linear model (GLM).
  • LIC local illumination compensation
  • CCLM cross-component linear mode
  • MMLM multi -model LM
  • CCCM cross-component chroma inter prediction
  • GLM gradient linear model
  • video encoder 200 is configured to determine to not apply subsampling to the luma samples of the block of video data.
  • video encoder 200 may be configured to predict the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • the prediction model includes non-linear terms.
  • the prediction model uses a 3x2 filter shape, and to encode ode the block of video data using the sub sampling technique and the cross-component prediction mode, video encoder 200 is configured to predict one chroma sample of the block using the prediction model using the 3x2 filter shape and six luma samples.
  • video encoder 200 is configured to determine to not apply sub sampling to the luma samples of the block of video data based on the video data being graphics content or screen content.
  • video encoder 200 is configured to determine to apply a combination of downsampling filters to the luma samples of the block of video data.
  • Video encoder 200 may apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions in the block of video data.
  • video encoder 200 may apply the combination of downsampling filters to the luma samples of the block of video data at particular chroma sample positions in the block of video data according to a constraint.
  • video encoder 200 may determine to apply the combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data.
  • video encoder 200 may apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples, and predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • video encoder 200 may apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions to produce downsampled luma samples.
  • video encoder 200 may apply the combination of downsampling filters to the luma samples of the block of video data based on the prediction model shape to produce the downsampled luma samples.
  • the combination of downsampling filters includes a plurality of 3x2 downsampling filters.
  • the prediction model shape is a one-directional shape, a diamond 3x3 shape, a diamond 5x5 shape, a diamond 7x5 shape, or a shape that is larger in a horizontal direction than a vertical direction.
  • the prediction model includes non-linear terms.
  • video encoder 200 may be configured to determine a cross-component model for the cross-component prediction mode, and determine the subsampling technique from the cross-component model for the crosscomponent prediction mode.
  • video encoder 200 may determine the cross-component model for the cross-component prediction mode from non-adjacent neighbor blocks of the block of video data.
  • video encoder 200 may receive a syntax element that indicates the subsampling technique, wherein a first subsampling technique of the plurality of subsampling techniques includes not applying sub sampling to the luma samples of the block of video data, and a second sub sampling technique of the plurality of sub sampling techniques includes a combination of downsampling filters to be applied to the luma samples of the block.
  • FIG. 20 is a flowchart illustrating another example method for decoding a current block in accordance with the techniques of this disclosure.
  • the techniques of FIG. 20 may be performed by one or more structural units of video decoder 300, including intra-prediction unit 318.
  • video decoder 300 may be configured to receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data (550), determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode (552), and decode the block of video data using the subsampling technique and the cross- component prediction mode (554).
  • the cross-component prediction mode may be one of local illumination compensation (LIC), chroma linear mode, cross-component linear mode (CCLM), multi -model LM (MMLM) mode, cross-component chroma inter prediction (CCCM), or gradient linear model (GLM).
  • LIC local illumination compensation
  • CCLM cross-component linear mode
  • MMLM multi -model LM
  • CCCM cross-component chroma inter prediction
  • GLM gradient linear model
  • video decoder 300 is configured to determine to not apply subsampling to the luma samples of the block of video data.
  • video decoder 300 may be configured to predict the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • the prediction model includes non-linear terms.
  • the prediction model uses a 3x2 filter shape
  • video decoder 300 is configured to predict one chroma sample of the block using the prediction model using the 3x2 filter shape and six luma samples.
  • video decoder 300 is configured to determine to not apply sub sampling to the luma samples of the block of video data based on the video data being graphics content or screen content.
  • video decoder 300 is configured to determine to apply a combination of downsampling filters to the luma samples of the block of video data.
  • Video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions in the block of video data.
  • video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data at particular chroma sample positions in the block of video data according to a constraint.
  • video decoder 300 may determine to apply the combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data. [0236] In other examples, to decode the block of video data using the subsampling technique and the cross-component prediction mode, video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples, and predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions to produce downsampled luma samples.
  • video decoder 300 may apply the combination of downsampling filters to the luma samples of the block of video data based on the prediction model shape to produce the downsampled luma samples.
  • the combination of downsampling filters includes a plurality of 3x2 downsampling filters.
  • the prediction model shape is a one-directional shape, a diamond 3x3 shape, a diamond 5x5 shape, a diamond 7x5 shape, or a shape that is larger in a horizontal direction than a vertical direction.
  • the prediction model includes non-linear terms.
  • video decoder 300 may be configured to determine a cross-component model for the cross-component prediction mode, and determine the subsampling technique from the cross-component model for the crosscomponent prediction mode.
  • video decoder 300 may determine the cross-component model for the cross-component prediction mode from non-adjacent neighbor blocks of the block of video data.
  • video decoder 300 may receive a syntax element that indicates the subsampling technique, wherein a first subsampling technique of the plurality of subsampling techniques includes not applying sub sampling to the luma samples of the block of video data, and a second sub sampling technique of the plurality of sub sampling techniques includes a combination of downsampling filters to be applied to the luma samples of the block.
  • Aspect 1 A - A method of coding video data comprising: determining a subsampling filter for luma components of video data for a prediction mode; and coding the video data using the subsampling filter.
  • Aspect 2A The method of Aspect 1 A, wherein the prediction mode is one of local illumination compensation (LIC), chroma linear mode, cross-component linear mode (CCLM or LM), cross-component chroma inter prediction (CCCM), or gradient linear model (GLM).
  • LIC local illumination compensation
  • CCLM or LM cross-component linear mode
  • CCCM cross-component chroma inter prediction
  • GLM gradient linear model
  • Aspect 3A The method of Aspect 1 A, wherein the subsampling filter is no subsampling based on the video data being graphics or screen content.
  • Aspect 4A The method of Aspect 1 A, wherein the subsampling filter is larger in a horizontal direction than a vertical direction.
  • Aspect 5A The method of Aspect 1 A, further comprising coding a flag that indicates the subsampling filter.
  • Aspect 6A The method of any of Aspects 1 A-5A, wherein coding comprises decoding.
  • Aspect 7A The method of any of Aspects 1 A-5A, wherein coding comprises encoding.
  • Aspect 8A - A device for coding video data, the device comprising one or more means for performing the method of any of Aspects 1 A-7A.
  • Aspect 9A The device of Aspect 8A, wherein the one or more means comprise one or more processors implemented in circuitry.
  • Aspect 10A The device of any of Aspects 8 A and 9A, further comprising a memory to store the video data.
  • Aspect 11 A The device of any of Aspects 8A-10A, further comprising a display configured to display decoded video data.
  • Aspect 12A The device of any of Aspects 8A-11 A, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.
  • Aspect 13A The device of any of Aspects 8A-12A, wherein the device comprises a video decoder.
  • Aspect 14A The device of any of Aspects 8A-13A, wherein the device comprises a video encoder.
  • Aspect 15A - A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform the method of any of Aspects 1 A-7A.
  • Aspect IB - A method of decoding video data, the method comprising: receiving a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data; determining a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode; and decoding the block of video data using the sub sampling technique and the crosscomponent prediction mode.
  • Aspect 2B - The method of Aspect IB, wherein determining the sub sampling technique comprises: determining to not apply subsampling to the luma samples of the block of video data.
  • Aspect 3B The method of Aspect 2B, wherein decoding the block of video data using the subsampling technique and the cross-component prediction mode comprises: predicting the chroma samples of the block using a prediction model for the crosscomponent prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • Aspect 4B The method of Aspect 3B, wherein the prediction model includes non-linear terms.
  • Aspect 5B The method of Aspect 3B, wherein the prediction model uses a 3x2 filter shape, and wherein decoding the block of video data using the sub sampling technique and the cross-component prediction mode comprises: predicting one chroma sample of the block using the prediction model using the 3x2 filter shape and six luma samples.
  • Aspect 6B The method of Aspect 2B, wherein determining to not apply subsampling to the luma samples of the block of video data comprises: determining to not apply subsampling to the luma samples of the block of video data based on the video data being graphics content or screen content.
  • Aspect 7B The method of Aspect IB, wherein determining the sub sampling technique comprises: determining to apply a combination of downsampling filters to the luma samples of the block of video data.
  • Aspect 8B The method of Aspect 7B, further comprising: applying the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions in the block of video data.
  • Aspect 9B The method of Aspect 7B, further comprising: applying the combination of downsampling filters to the luma samples of the block of video data at particular chroma sample positions in the block of video data according to a constraint.
  • Aspect 10B The method of Aspect 7B, wherein determining to apply the combination of downsampling filters to the luma samples of the block of video data comprises: determining to apply the combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data.
  • Aspect 1 IB The method of Aspect 7B, wherein decoding the block of video data using the subsampling technique and the cross-component prediction mode comprises: applying the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples; and predicting the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • Aspect 12B - The method of Aspect 1 IB, wherein applying the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples comprises: applying the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions to produce downsampled luma samples.
  • Aspect 13B - The method of Aspect 1 IB, wherein applying the combination of downsampling filters to the luma samples of the block of video data to produce the downsampled luma samples comprises: applying the combination of downsampling filters to the luma samples of the block of video data based on the prediction model shape to produce the downsampled luma samples.
  • Aspect 14B The method of Aspect 13B, wherein the combination of downsampling filters includes a plurality of 3x2 downsampling filters.
  • Aspect 15B - The method of Aspect 13B, wherein the prediction model shape is a one-directional shape, a diamond 3x3 shape, a diamond 5x5 shape, a diamond 7x5 shape, or a shape that is larger in a horizontal direction than a vertical direction.
  • Aspect 16B The method of Aspect 1 IB, wherein the prediction model includes non-linear terms.
  • Aspect 17B The method of Aspect IB, wherein determining the subsampling technique, from the plurality of subsampling techniques, for the luma samples of the block of video data for the cross-component prediction mode comprises: determining a cross-component model for the cross-component prediction mode; and determining the subsampling technique from the cross-component model for the cross-component prediction mode.
  • Aspect 18B The method of Aspect 17B, wherein determining the crosscomponent model for the cross-component prediction mode comprises: determining the cross-component model for the cross-component prediction mode from non-adjacent neighbor blocks of the block of video data.
  • Aspect 19B The method of any of Aspects 1B-18B, wherein determining the subsampling technique comprises: receiving a syntax element that indicates the subsampling technique, wherein a first subsampling technique of the plurality of subsampling techniques includes not applying subsampling to the luma samples of the block of video data, and a second sub sampling technique of the plurality of sub sampling techniques includes a combination of downsampling filters to be applied to the luma samples of the block.
  • Aspect 20B The method of any of Aspects 1B-19B, wherein the crosscomponent prediction mode is one of local illumination compensation (LIC), chroma linear mode, cross-component linear mode (CCLM), multi-model LM (MMLM) mode, cross-component chroma inter prediction (CCCM), or gradient linear model (GLM).
  • LIC local illumination compensation
  • CCLM cross-component linear mode
  • MMLM multi-model LM
  • CCCM cross-component chroma inter prediction
  • GLM gradient linear model
  • Aspect 2 IB - An apparatus configured to decode video data comprising: a memory; and one or more processors coupled to the memory, the one or more processors configured to: receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data; determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode; and decode the block of video data using the subsampling technique and the crosscomponent prediction mode.
  • Aspect 22B The apparatus of Aspect 2 IB, wherein to determine the subsampling technique, the one or more processors are further configured to: determine to not apply subsampling to the luma samples of the block of video data.
  • Aspect 23B The apparatus of Aspect 22B, wherein to decode the block of video data using the subsampling technique and the cross-component prediction mode, the one or more processors are further configured to: predict the chroma samples of the block using a prediction model for the cross-component prediction mode that uses a larger number of the luma samples relative to the chroma samples.
  • Aspect 24B The apparatus of Aspect 23B, wherein the prediction model includes non-linear terms.
  • Aspect 25B The apparatus of Aspect 23B, wherein the prediction model uses a 3x2 filter shape, and wherein to decode the block of video data using the subsampling technique and the cross-component prediction mode, the one or more processors are further configured to: predict one chroma sample of the block using the prediction model using the 3x2 filter shape and six luma samples.
  • Aspect 26B The apparatus of Aspect 22B, wherein to determine to not apply sub sampling to the luma samples of the block of video data, the one or more processors are further configured to: determine to not apply subsampling to the luma samples of the block of video data based on the video data being graphics content or screen content.
  • Aspect 27B The apparatus of Aspect 2 IB, wherein to determine the subsampling technique, the one or more processors are further configured to: determine to apply a combination of downsampling filters to the luma samples of the block of video data.
  • Aspect 28B The apparatus of Aspect 27B, wherein the one or more processors are further configured to: apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions in the block of video data.
  • Aspect 29B The apparatus of Aspect 27B, wherein the one or more processors are further configured to: apply the combination of downsampling filters to the luma samples of the block of video data at particular chroma sample positions in the block of video data according to a constraint.
  • Aspect 30B The apparatus of Aspect 27B, wherein to determine to apply the combination of downsampling filters to the luma samples of the block of video data, the one or more processors are further configured to: determine to apply the combination of downsampling filters, from among a plurality of combinations of downsampling filters, to the luma samples of the block of video data.
  • Aspect 3 IB The apparatus of Aspect 27B, wherein to decode the block of video data using the subsampling technique and the cross-component prediction mode, the one or more processors are further configured to: apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples; and predict the chroma samples of the block using the downsampled luma samples as inputs to a prediction model having a prediction model shape.
  • Aspect 32B The apparatus of Aspect 3 IB, wherein to apply the combination of downsampling filters to the luma samples of the block of video data to produce downsampled luma samples, the one or more processors are further configured to: apply the combination of downsampling filters to the luma samples of the block of video data at multiple chroma sample positions to produce downsampled luma samples.
  • Aspect 33B The apparatus of Aspect 3 IB, wherein to apply the combination of downsampling filters to the luma samples of the block of video data to produce the downsampled luma samples, the one or more processors are further configured to: apply the combination of downsampling filters to the luma samples of the block of video data based on the prediction model shape to produce the downsampled luma samples.
  • Aspect 34B The apparatus of Aspect 33B, wherein the combination of downsampling filters includes a plurality of 3x2 downsampling filters.
  • Aspect 35B The apparatus of Aspect 33B, wherein the prediction model shape is a one-directional shape, a diamond 3x3 shape, a diamond 5x5 shape, a diamond 7x5 shape, or a shape that is larger in a horizontal direction than a vertical direction.
  • Aspect 36B The apparatus of Aspect 3 IB, wherein the prediction model includes non-linear terms.
  • Aspect 37B The apparatus of Aspect 21B, wherein to determine the subsampling technique, from the plurality of subsampling techniques, for the luma samples of the block of video data for the cross-component prediction mode, the one or more processors are further configured to: determine a cross-component model for the cross-component prediction mode; and determine the subsampling technique from the cross-component model for the cross-component prediction mode.
  • Aspect 38B The apparatus of Aspect 37B, wherein to determine the crosscomponent model for the cross-component prediction mode, the one or more processors are further configured to: determine the cross-component model for the crosscomponent prediction mode from non-adjacent neighbor blocks of the block of video data.
  • Aspect 39B The apparatus of any of Aspects 21B-28B, wherein to determine the subsampling technique, the one or more processors are further configured to: receive a syntax element that indicates the subsampling technique, wherein a first subsampling technique of the plurality of sub sampling techniques includes not applying sub sampling to the luma samples of the block of video data, and a second subsampling technique of the plurality of subsampling techniques includes a combination of downsampling filters to be applied to the luma samples of the block.
  • Aspect 40B The apparatus of any of Aspects 21B-29B, wherein the crosscomponent prediction mode is one of local illumination compensation (LIC), chroma linear mode, cross-component linear mode (CCLM), multi-model LM (MMLM) mode, cross-component chroma inter prediction (CCCM), or gradient linear model (GLM).
  • LIC local illumination compensation
  • CCLM cross-component linear mode
  • MMLM multi-model LM
  • CCCM cross-component chroma inter prediction
  • GLM gradient linear model
  • a method of encoding video data comprising: receiving a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data; determining a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode; and encoding the block of video data using the subsampling technique and the crosscomponent prediction mode.
  • Aspect 42B - An apparatus configured to encode video data comprising: a memory; and one or more processors coupled to the memory, the one or more processors configured to: receive a block of video data, wherein chroma samples of the block of video data are subsampled relative to luma samples of the block of video data; determine a subsampling technique, from a plurality of subsampling techniques, for the luma samples of the block of video data for a cross-component prediction mode; and encode the block of video data using the subsampling technique and the crosscomponent prediction mode.
  • Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol.
  • computer- readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave.
  • Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure.
  • a computer program product may include a computer-readable medium.
  • such computer-readable storage media may include one or more of RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium.
  • coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave are included in the definition of medium.
  • DSL digital subscriber line
  • computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media.
  • Disk and disc includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer- readable media.
  • processors such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry.
  • processors such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry.
  • processors such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry.
  • processors such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry.
  • the terms “processor” and “processing circuitry,” as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein.
  • the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec.
  • the techniques could be fully implemented in one or more circuits or logic elements.
  • the techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set).
  • IC integrated circuit
  • a set of ICs e.g., a chip set.
  • Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

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Abstract

Un procédé de codage de données vidéo consiste à recevoir un bloc de données vidéo, des échantillons de chrominance du bloc de données vidéo étant sous-échantillonnés par rapport à des échantillons de luminance du bloc de données vidéo (par exemple, un contenu vidéo de 4:2:0 ou 4:2:2). Un codeur vidéo peut déterminer une technique de sous-échantillonnage, parmi une pluralité de techniques de sous-échantillonnage, pour les échantillons de luminance du bloc de données vidéo pour un mode de prédiction inter-composantes, et peut coder le bloc de données vidéo à l'aide de la technique de sous-échantillonnage et du mode de prédiction inter-composantes. Une première technique de sous-échantillonnage de la pluralité de techniques de sous-échantillonnage consiste à ne pas appliquer un sous-échantillonnage aux échantillons de luminance du bloc de données vidéo, et une seconde technique de sous-échantillonnage de la pluralité de techniques de sous-échantillonnage comprend une combinaison de filtres de sous-échantillonnage à appliquer aux échantillons de luminance du bloc.
PCT/US2023/076580 2022-10-13 2023-10-11 Techniques de sous-échantillonnage pour une prédiction inter-composantes dans un codage vidéo WO2024081722A1 (fr)

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US202263379419P 2022-10-13 2022-10-13
US63/379,419 2022-10-13
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US202363478318P 2023-01-03 2023-01-03
US63/478,318 2023-01-03
US202363488000P 2023-03-02 2023-03-02
US63/488,000 2023-03-02
US18/483,891 2023-10-10
US18/483,891 US20240129458A1 (en) 2022-10-13 2023-10-10 Techniques for subsampling for cross component prediction in video coding

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