Method, apparatus and computer program for video decoding

Abstract

To provide a method, an apparatus, and a non-transitory computer-readable storage medium for video encoding / decoding.SOLUTION: The apparatus includes processing circuitry that determines reconstructed samples of a first color component in a filter support region of a current picture that is a part of a coded video sequence. The processing circuitry performs a filter process on the reconstructed samples of the first color component in the filter support region. A quantization step size of the filter process is separately set for one of a coding block, a video frame, and a video sequence. The processing circuitry reconstructs samples of a second color component different from the first color component in the filter support region, based on an output value of the filter process.SELECTED DRAWING: Figure 20

Description

Technical Field

[0001] [Related Applications] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 113,125, "IMPROVED CROSS-Component Sample Offset using Adaptive Quantization and Offset Scaling", filed on November 12, 2020, and U.S. Patent Application No. 17 / 360,865, "METHOD AND APPARATUS FOR VIDEO CODING", filed on June 28, 2021. The entire disclosure of the foregoing applications is hereby incorporated by reference in its entirety.

[0002] [Technical Field] The present disclosure generally describes embodiments related to video coding.

Background Art

[0003] The background description provided herein is for the purpose of presenting an overview of the context of the present disclosure. The research of the presently named inventors, to the extent that it is described in this background section, is not admitted to be prior art to the present disclosure, either explicitly or implicitly, any more than is the description of aspects that may not constitute prior art at the time of filing.

[0004] Video coding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a series of pictures, each picture having a spatial dimension of, for example, 1920×1080 luminance samples and associated chrominance samples. The series of pictures can have a fixed or variable picture rate, for example, 60 pictures per second or 60 Hz (also known as the frame rate in short). Uncompressed video has significant bitrate requirements. For example, 8-bit / sample 1080p60 4:2:0 video (1920×1080 luminance sample resolution at 60 Hz frame rate) requires a bandwidth close to 1.5 Gbit / s. One hour of such video requires more than 600 GByte of storage space.

[0005] One purpose of video coding and decoding can be to reduce redundancy in the input video signal through compression. Compression can, in some cases, help reduce the bandwidth or storage space requirements by more than two orders of magnitude. Both lossy and lossless compression, as well as combinations thereof, can be utilized. Lossless compression represents techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal is not identical to the original signal, but the distortion between the original signal and the reconstructed signal is small enough to produce a useful reconstructed signal for the intended application. In the case of video, lossy compression is widely used. The amount of tolerable distortion depends on the application, and users of certain consumer streaming applications can tolerate higher distortion than users of television distribution applications. The achievable compression ratio can reflect that the higher the acceptable / tolerable distortion, the higher the compression ratio that can be achieved.

[0006] Video encoders and decoders can utilize techniques from several broad classifications, including, for example, motion compensation, transformation, quantization, and entropy coding.

[0007] Video codec technology can include techniques known as intra coding. In intra coding, sample values are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, a picture is spatially subdivided into blocks of samples. When all blocks of samples are coded in an intra mode, that picture can be an intra picture. Intra pictures, and their derivatives such as independent decoder refresh pictures, can be used to reset the decoder state and thus can be used as the first picture in a coded video bitstream and video session or as a still image. Samples of an intra block can be transformed, and the transform coefficients can be quantized prior to entropy coding. Intra prediction can be a technique that minimizes sample values in the domain before transformation. In some cases, the smaller the DC value after transformation and the smaller the AC coefficients, the fewer bits are required with a given quantization step size to represent the block after entropy coding.

[0008] Traditional intra coding, such as that known from MPEG-2 production coding technology, does not use intra prediction. However, some new video compression techniques attempt, for example, from surrounding sample data and / or metadata obtained during encoding and / or decoding of spatially adjacent data blocks that precede in decoding order. Such techniques are hereinafter referred to as "intra prediction" techniques. In at least some cases, intra prediction uses only reference data from the current picture being reconstructed rather than from a reference picture.

[0009] There can be many different forms of intra prediction. When more than one such technique can be used in a given video coding technique, the technique used can be coded in an intra prediction mode. In certain cases, the mode can have sub - modes and / or parameters, which can be coded individually or included in a mode codeword. Which codeword should be used for a given combination of mode, sub - mode, and / or parameter can affect the improvement of coding efficiency through intra prediction, and thus entropy coding techniques can be used to convert the codeword into a bitstream.

[0010] Certain intra prediction modes were introduced by H.264, improved in H.265, and further improved in newer coding techniques such as the joint exploration model (JEM), versatile video coding (VVC), and benchmark set (BMS). A prediction block can be formed using neighboring sample values belonging to already available samples. The sample values of the neighboring samples are copied into the prediction block according to a direction. The reference to the direction in use can be coded within the bitstream or can itself be predicted.

[0011] Referring to FIG. 1A, in the lower right, a subset of 9 prediction directions can be seen from 33 possible prediction directions of H.265 (corresponding to the angular modes of 33 out of 35 intra modes). The point (101) where the arrows converge represents the sample being predicted. The arrows represent the direction in which the sample is being predicted. For example, arrow (102) indicates that sample (101) is predicted from one or more samples at an angle of 45 degrees from the horizontal and upwards to the right. Similarly, arrow (103) indicates that sample (101) is predicted from one or more samples at an angle of 22.5 degrees from the horizontal and downwards to the left of sample (101).

[0012] Referring further to FIG. 1A, in the upper left, a square block (104) of 4×4 samples (indicated by thick dashed lines) is shown. The square block (104) contains 16 samples, and each sample is labeled with "S", its Y - dimensional position (e.g., row index), and its X - dimensional position (e.g., column index). For example, sample S21 is the second sample from the top in the Y - dimension and the first sample from the left in the X - dimension. Similarly, sample S44 is the fourth sample within the block (104) in both the Y and X dimensions. When the block is of size 4×4 samples, S44 is in the lower right. Further, reference samples following a similar numbering scheme are shown. The reference samples are labeled by R, its Y - position (e.g., row index) and X - position (column index) with respect to the block (104). In both H.264 and H.265, the predicted samples are in the neighborhood of the block being reconstructed, and thus negative values need not be used.

[0013] Intra - picture prediction can operate by copying the reference sample value from neighboring samples when appropriate according to the signaled prediction direction. For example, the coding video bitstream includes signaling indicating the prediction direction that matches the arrow (102) for this block. That is, the samples are predicted from one or more predicted samples at an angle of 45 degrees from horizontal and upwards to the right. In this case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Sample S44 is then predicted from reference sample R08.

[0014] In certain cases, to calculate the reference sample, when the direction cannot be evenly divided by 45 degrees in particular, the values of multiple reference samples may be combined, for example, through interpolation.

[0015] The number of possible directions has been increasing as video coding technology has evolved. In H.264 (2003), nine different directions could be presented. This increased to 33 in H.265 (2013), and JEM / VVC / BMS can support up to 65 directions as of the time of this disclosure. Experiments have been conducted to identify the most likely directions, and specific techniques in entropy coding are used to represent these likely directions with a small number of bits while accepting a penalty for certain less likely directions. Further, the direction itself may be predictable from neighboring directions in neighboring already decoded blocks.

[0016] FIG. 1B shows a diagram (105) showing 65 intra prediction directions according to JEM to illustrate the increasing number of prediction directions over time.

[0017] The mapping of the intra prediction direction bits in the coded video bitstream representing the direction varies by video coding technology and ranges from a simple direct mapping of the prediction direction to the intra prediction mode, to the codeword, to complex adaptive schemes including the most accurate mode, and similar techniques. However, in all cases, there may exist certain directions that statistically occur less often in video content than certain other directions. Since the goal of video compression is redundancy reduction, these less likely directions will be represented by more bits than the more likely directions in well - operating video coding technology.

[0018] Motion compensation is a lossy compression technique that may be related to a technique in which blocks of sample data from a previously reconstructed picture or a portion thereof (reference picture) are spatially shifted in a direction indicated by a motion vector (hereinafter, MV) and then used for prediction of a newly reconstructed picture or picture portion. In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV can have two dimensions X and Y, or three dimensions where the third dimension is an indication of the reference picture in use (the latter may be indirectly the temporal dimension).

[0019] In some video compression techniques, the MV applicable to a particular region of sample data can be predicted from other MVs, for example from an MV associated with another region of sample data spatially adjacent to the region being reconstructed and preceding the said MV in the decoding order. Doing so can, as a result, reduce the amount of data necessary to encode the MV, thereby removing redundancy and improving compression. MV prediction can, for example, be statistically likely when coding an input video signal obtained from a camera (known as natural video), where regions larger than the region to which a single MV is applicable move in a similar direction and thus, in some cases, can be predicted using a similar MV derived from the MVs of neighbouring regions. This results in an MV found for a given region that is similar or identical to the MV predicted from the surrounding MVs. Also, this can be presented with fewer bits than would be used if the MV were directly coded after entropy coding. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., the MV) obtained from the original signal (i.e., the sample stream). In other cases, MV prediction itself can be lossy, for example when rounding errors occur when calculating a predictor from several surrounding MVs.

[0020] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H.265, "High Efficiency Video Coding", December 2016). One of the many MV prediction mechanisms provided by H.265 described herein is a technique hereinafter referred to as "spatial merge".

[0021] Referring to FIG. 1C, the current block (111) can include samples found by the encoder as being predictable from a previous block of the same size that has been spatially shifted during the motion search process. Instead of directly coding the MV, the MV can be derived from metadata associated with one or more reference pictures, for example, from the most recent reference picture (in decoding order), using the MV associated with any one of five surrounding samples A0, A1, and B0, B1, B2 (112-116 respectively). In H.265, the MV prediction can use predictors from the same reference picture used by neighboring blocks. SUMMARY OF THE INVENTION

[0022] Aspects of the disclosure provide an apparatus for video encoding / decoding. The apparatus includes a processing circuit that determines reconstructed samples of a first color component in a filter support region of a current picture that is part of a coded video sequence. The processing circuit performs a filtering process on the reconstructed samples of the first color component in the filter support region. The quantization step size of the filtering process is set individually for one of a coding block, a video frame, and a video sequence. The processing circuit reconstructs samples of a second color component in the filter support region based on the output value of the filtering process. The second color component is different from the first color component.

[0023] In an embodiment, the quantization step size is a predetermined constant for one of the coding block, the video frame, and the video sequence.

[0024] In an embodiment, the quantization step size is an integer that is a power of 2.

[0025] In an embodiment, the quantization step size is one of a plurality of quantization step sizes determined based on an index included in a bitstream corresponding to one of the coding block, the video frame, and the video sequence.

[0026] In an embodiment, the quantization step size is included in a bitstream corresponding to one of the coding block, the video frame, and the video sequence.

[0027] In an embodiment, the processing circuit determines whether the output value of the filtering process is scaled based on the reconstructed sample of the first color component in the filter support region. In response to the output value of the filtering process being scaled, the processing circuit reconstructs samples of the second color component in the filter support region based on the scaled output value of the filtering process.

[0028] In an embodiment, the processing circuit determines whether the output value of the filtering process is scaled based on the reconstructed sample of the first color component in the filter support region and a syntax element indicating whether scaling of the output value of the filtering process is enabled.

[0029] In an embodiment, the processing circuit determines the scaled output value of the filtering process based on the reconstructed sample of the first color component in the filter support region and the quantization step size.

[0030] The disclosed embodiments provide a method for video encoding / decoding. In the method, reconstructed samples of a first color component in a filter support region of a current picture, which is part of a coding video sequence, are determined. Filtering is performed on the reconstructed samples of the first color component in the filter support region. A quantization step size of the filtering is set individually for one of a coding block, a video frame, and a video sequence. Samples of a second color component in the filter support region are reconstructed based on an output value of the filtering. The second color component is different from the first color component.

[0031] The disclosed embodiments also provide a non-transitory computer-readable medium storing instructions that, when executed by at least one processor, cause the at least one processor to execute any one or a combination of methods for video decoding.

Brief Description of the Drawings

[0032] Further features, characteristics, and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0057] <I. Video Decoder and Encoder System>

[0058] FIG. 2 shows a simplified block diagram of a communication system (200) according to an embodiment of the present disclosure. The communication system (200) includes a plurality of terminal devices that can communicate with each other, for example, via a network (250). For example, the communication system (200) includes a first pair of terminal devices (210) and (220) interconnected via a network (250). In the example of FIG. 2, the first pair of terminal devices (210) and (220) perform unidirectional data transmission. For example, the terminal device (210) encodes video data (a stream of video pictures captured by the terminal device (210)) for transmission to another terminal device (220) via the network (250). The encoded video data can be transmitted in the form of one or more coded video bitstreams. The terminal device (220) receives the coded video data from the network (250), decodes the coded video data to restore the video pictures, and may display the video pictures according to the restored video data. Unidirectional data transmission may be common in media serving applications and the like.

[0059] In another example, the communication system (200) includes a second pair of terminal devices (230) and (240) that perform bidirectional transmission of coded video data that may occur, for example, during a video conference. In bidirectional data transmission, the terminal devices (230) and (240) may encode video data (e.g., a stream of video pictures captured by the terminal device) for transmission to the terminal devices (230) and (240) via the network (250). Each of the terminal devices (230) and (240) may receive the coded video data transmitted by the other of the terminal devices (230) and (240), may decode the coded video data to restore the video pictures, and may display the video pictures on an accessible display device according to the restored video data.

[0060] In the example of FIG. 2, the terminal devices (210), (220), (230), and (240) may be shown as a server, a personal computer, and a smartphone, but the principles of the present disclosure are not limited thereto. Embodiments of the present disclosure have applications with laptop computers, tablet computers, media players, and / or dedicated video conferencing facilities. The network (250) represents any number of networks that carry coded video data among the terminal devices (210), (220), (230), and (240), including, for example, wired (wired) and / or wireless communication networks. The communication network (250) may exchange data on circuit-switched and / or packet-switched channels. Representative networks include electronic communication networks, local area networks, wide area networks, and / or the Internet. For the purposes of the discussion of the present invention, the architecture and topology of the network (250) may not be important for the operation of the present disclosure, unless otherwise specifically stated below.

[0061] FIG. 3 shows the arrangement of a video encoder and a video decoder in a streaming environment as an example of the application of the disclosed subject matter. The disclosed subject matter is equally applicable to, for example, video conferencing, digital TV, CD, DVD, memory stick, and other video-capable applications, etc., including storage of compressed video on digital media.

[0062] A streaming system may include, for example, a video source (301) that generates an uncompressed video picture stream (302), and a capture subsystem (313) that may include, for example, a digital video camera. In one example, the video picture stream (302) includes samples captured by a digital camera. The video picture stream (302) is shown in bold lines to emphasize its high data capacity compared to the encoded video data (304) (or coded video bitstream), and may be processed by an electronic device (320) that includes a video encoder (303) coupled to the video source (301). The video encoder (303) includes hardware, software, or a combination thereof, and can enable or implement aspects of the disclosed subject matter as detailed below. The encoded video data (304) (or encoded video bitstream (304)) is shown in thin lines to emphasize its low data capacity compared to the video picture stream (302), and may be stored in a streaming server (305) for future use. One or more streaming client subsystems, such as client subsystems (306) and (308) of FIG. 3, can access the streaming server (305) to read copies (307) and (309) of the encoded video data (304). The client subsystem (306) may include, for example, a video decoder (310) within an electronic device (330). The video decoder (310) decodes an input copy (307) of the encoded video data and generates an output video picture stream (311) that can be rendered on a display (312) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (304), (307), and (309) (e.g., video bitstreams) may be encoded according to a particular video coding / compression standard. Examples of these standards include ITU-T Recommendation H.265. In one example, a video coding standard under development is known informally as VVC (Versatile Video Coding). The disclosed subject matter may be used in the context of VVC.

[0063] Note that the electronic devices (320) and (330) may include other components (not shown). For example, the electronic device (320) can include a video decoder (not shown), and the electronic device (330) can also include a video encoder (not shown).

[0064] FIG. 4 shows a block diagram of a video decoder (410) according to an embodiment of the present disclosure. The video decoder (410) may be included in an electronic device (430). The electronic device (430) may include a receiver (431) (e.g., a receiving circuit). The video decoder (410) can be used in place of the video decoder (310) in the example of FIG. 3.

[0065] The receiver (431) may receive one or more coded video sequences to be decoded by the video decoder (410), one coded video sequence at a time in the same or another embodiment. Here, the decoding of each coded video sequence is independent of other coded video sequences. The coded video sequence may be received from a channel (401) that may be a hardware / software link to a storage device storing the encoded video data. The receiver (431) may receive the encoded video data together with other data, such as coded audio data and / or auxiliary data streams that may be transferred to respective usage entities (not shown). The receiver (431) may separate the coded video sequence from other data. To remove network jitter, a buffer memory (415) may be coupled between the receiver (431) and the entropy decoder / parser (420) (hereinafter, "parser (420)"). In certain applications, the buffer memory (415) is part of the video decoder (410). Alternatively, it may be external to the video decoder (410) (not shown). Still alternatively, for example, to remove network jitter, in addition to another buffer memory (415) that may be external to the video decoder (410) or internal to the video decoder (410) to process the playout timing, a buffer memory (not shown) may exist. When the receiver (431) is receiving data controllably from a storage / transfer device with sufficient bandwidth or from an isosynchronous network, the buffer memory (415) may not be necessary or may be made small. For use in a best-effort packet network such as the Internet, a buffer memory (415) may be required, may be relatively large, advantageously be of an adaptable size, and may be implemented at least partially in an operating system or similar elements (not shown) external to the video decoder (410).

[0066] Video decoder (410) may include a parser (420) to reconstruct symbols (421) from a coded video sequence. The categories of these symbols include information used to manage the operation of video decoder (410) and, in some cases, information for controlling a rendering device (such as a display screen) like rendering device (412) that is not an integrated part of electronic device (430) but can be coupled to electronic device (430) as shown in FIG. 4. The control information for the rendering device may be in the form of SEI (Supplemental Enhancement Information) messages or VUI (Video Usability Information) parameter set fragments (not shown). Parser (420) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence can follow video coding techniques or standards and can follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context dependency, etc. Parser (420) may extract a set of subgroup parameters from the coded video sequence based on at least one parameter corresponding to at least one subgroup of pixels in the video decoder for at least one of the subgroups. Subgroups can include GOP (Groups of Picture), picture, tile, slice, macroblock, coding units (CU), block, transform units (TU), prediction units (PU), etc. Parser (420) may also extract information such as transform coefficients, quantization parameter values, MV, etc. from the coded video sequence.

[0067] Parser (420) may perform an entropy decoding / parsing operation on the video sequence received from buffer memory (415) to generate symbols (421).

[0068] The reconstruction of symbol (421) may include multiple different units depending on the type of the coded video picture or a portion thereof (e.g., inter and intra pictures, inter and intra blocks) and other factors. How the units are included can be controlled by subgroup control information parsed from the coded video sequence by the parser (420). Such a flow of subgroup control information between the parser 420 and the following multiple units is not shown for clarity.

[0069] Beyond the function blocks already mentioned, the video decoder (410) can be conceptually subdivided into a number of functional units, as will be described later. In an actual implementation operating under commercial constraints, many of these units can interact closely with each other and can be at least partially integrated with each other. However, for the purpose of explaining the disclosed subject matter, the following conceptual subdivision into functional units is appropriate.

[0070] The first unit is the scaler / inverse transform unit 451. The scaler / inverse transform unit (451) receives, as symbols (421) from the parser (420), quantized transform coefficients and control information including which transform to use, block size, quantization coefficients, quantization scaling matrix, etc. The scaler / inverse transform unit (451) can output a block including sample values that can be input to the aggregator (455).

[0071] In some examples, the output samples of the scaler / inverse transform unit (451) can belong to an intra-coding block, i.e., a block that does not use prediction information from a previously reconstructed picture but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information can be provided by the intra-picture prediction unit (452). In some cases, the intra-picture prediction unit (452) generates a block of the same size and shape as the block being reconstructed, using the surrounding already-reconstructed information fetched from the current picture buffer (458). The current picture buffer (458) buffers, for example, the partially reconstructed current picture and / or the completely reconstructed current picture. The aggregator (455) adds, in some cases, sample-by-sample, the prediction information generated by the intra prediction unit (452) to the output sample information provided by the scaler / inverse transform unit (451).

[0072] In other cases, the output samples of the scaler / inverse transform unit (451) can be related to inter-coded and possibly motion-compensated blocks. In such cases, the motion compensation prediction unit (453) can access the reference picture memory (457) to fetch the samples used for prediction. After motion-compensating the samples fetched according to the symbol (421) associated with the block, these samples can be added by the aggregator (455) to the output of the scaler / inverse transform unit (451) to generate the output sample information (in this case, called the residual samples or residual signal). The address in the reference picture memory (457) from which the motion compensation prediction unit (453) fetches the prediction samples can be controlled by the available MV of the motion compensation prediction unit (453) in the form of symbols (421) that can have, for example, X, Y, and reference picture components. Motion compensation can include interpolation of the sample values fetched from the reference picture memory (457) when an exact MV of sub-samples is in use, an MV prediction mechanism, etc.

[0073] The output samples of the aggregator (455) can undergo various loop filtering techniques in the loop filter unit (456). The video compression technique is controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (456) as symbols (421) from the parser (420), but also responds to meta information obtained during the decoding of the previous part (in decoding order) of the coded picture or coded video sequence, and can include in-loop filtering techniques that can also respond to previously reconstructed and loop-filtered sample values.

[0074] The output of the loop filter unit (456) can be a sample stream that can be output to the renderer device (412) and stored in the reference picture memory (457) for use in future inter-picture prediction.

[0075] Once a particular coded picture is fully reconstructed, it can be used as a reference picture for future prediction. For example, when the coded picture corresponding to the current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (420)), the current picture buffer (458) can become part of the reference picture memory (457), and a fresh current picture buffer can be reallocated before starting the reconstruction of subsequent coded pictures.

[0076] The video decoder (410) may perform a decoding operation in accordance with a predetermined video compression technique of a standard such as ITU-T Rec. H.265. The coding video sequence may conform to the syntax specified by the video compression technique or standard in use in the sense that the coding video sequence conforms to both the video compression technique or standard and the profile documented in the video compression technique or standard. Specifically, the profile can select specific tools from all the tools available in the video compression technique or standard as tools that can be used only under the profile. Also, what is required for compliance may be that the complexity of the coding video sequence is within the limits defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, the maximum frame rate, the maximum reconstruction sample rate (e.g., measured in megasamples per second), the maximum reference picture size, etc. The limits set by the level may, in some cases, be further restricted through the HRD (Hypothetical Reference Decoder) specification and the metadata for HRD buffer management signaled in the coding video sequence.

[0077] In an embodiment, the receiver (431) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coding video sequence. The additional data may be used by the video decoder 410 to correctly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0078] FIG. 5 shows a block diagram of a video encoder (503) according to an embodiment of the present disclosure. The video encoder (503) is included in an electronic device (520). The electronic device (520) includes a transmitter (540) (e.g., a transmission circuit). The video encoder (503) can be used instead of the video encoder (303) in the example of FIG. 3.

[0079] The video encoder (503) may receive video samples from a video source (501) (not part of the electronic device (520) in the example of FIG. 5) that can capture a video image to be coded by the video encoder (503). In another example, the video source (501) is part of the electronic device (520).

[0080] The video source (501) may provide a source video sequence to be coded by the video encoder (503) in the form of a digital video sample stream of any suitable bit depth (e.g., 8 bits, 10 bits, 12 bits,...), any color space (e.g., BT.601 Y CrCB, RGB,...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media providing system, the video source (501) may be a storage device that stores pre-prepared video. In a video conferencing system, the video source (501) may be a camera that captures local image information as a video sequence. The video data may subsequently be provided as a plurality of individual pictures that give movement when viewed in succession. The pictures themselves may be organized as a spatial array of pixels. Each pixel may contain one or more samples depending on the sampling structure, color space, etc. in use. A person skilled in the art can immediately understand the relationship between a pixel and a sample. The following description focuses on samples.

[0081] According to one embodiment, the video encoder (503) may encode and compress pictures of a source video sequence into a coded video sequence (543) in real time or under any other time constraints required by an application. Implementing an appropriate coding speed is one function of the control unit (550). In some embodiments, the control unit (550) controls other functional units described below and is functionally coupled to the other functional units. The coupling is not shown for clarity. The parameters set by the control unit (550) may include rate control related parameters (picture skip, quantizer, lambda value of rate distortion optimization techniques, ...), picture size, GOP (group of pictures) layout, maximum MV allowable reference region, etc. The control unit (550) may be configured to have other appropriate functions related to the video encoder (503) optimized for a particular system design.

[0082] In some embodiments, the video encoder (503) is configured to operate within a coding loop. As a very simplified explanation, in one example, the coding loop may include a source coder (530) (which is responsible for generating symbols such as a symbol stream based on an input picture and a reference picture to be coded), and a (local) decoder (533) built into the video encoder (503). The decoder (533) reconstructs the symbols in the same way as a (remote) decoder generates when any compression between the symbols and the coding bitstream is lossless in the video compression technology considered in the subject matter of the disclosure, to generate sample data. The reconstructed sample stream (sample data) is input into the reference picture memory (534). When the decoding of the symbol stream results in a bit-exact result independent of the decoder position (local or remote), the content of the reference picture memory (534) is also bit-exact between the local encoder and the remote encoder. In other words, the prediction part of the encoder "sees" exactly the same sample values as the decoder "sees" as reference picture samples when using prediction during decoding. This basic principle of reference picture synchronization (and the resulting drift if synchronization cannot be maintained, for example due to channel errors) is also used similarly in some related technologies.

[0083] The operation of the "local" decoder (533) may be the same as that of a "remote" decoder such as the video decoder (410) detailed above in relation to FIG. 4. Briefly referring to FIG. 4 for a moment, however, since the symbols are available and the encoding / decoding of the symbols into the coded video sequence by the entropy encoder (545) and the parser (420) can be lossless, the entropy decoding part of the video decoder (410) including the buffer memory (415), and the parser (420) need not be fully implemented in the local decoder (533).

[0084] The consideration made in this regard is that any decoder technology, except for the parse / entropy decoding existing in the decoder, needs to exist in substantially the same functional form as in the corresponding encoder. For this reason, the disclosed subject matter focuses on decoder operations. The description of encoder technologies can be omitted because they are the reverse of the decoder technologies that are comprehensively described. More detailed descriptions are necessary only in specific areas and are provided below.

[0085] During operation, in some examples, the source coder (530) may perform motion-compensated predictive coding. This predictively codes the input picture by referring to one or more previously coded pictures from the video sequence designated as the "reference picture". In this method, the coding engine (532) codes the difference between the pixel block of the input picture and the pixel block of the reference picture that may be selected as the prediction reference for the input picture.

[0086] The local video decoder (533) may decode the coded video data of the picture that may be designated as the reference picture based on the symbols generated by the source coder (530). The operation of the coding engine (532) may advantageously be a lossy process. When the coded video data can be decoded in a video decoder (not shown in FIG. 5), the reconstructed video sequence may typically be a replica of the source video sequence with some errors. The local video decoder (533) replicates the decoding process that may be performed by the video decoder for the reference picture, and may produce a reconstructed reference picture to be stored in the reference picture cache (534). In this way, the video encoder (503) may store a copy of the reconstructed reference picture having the same content as the reconstructed reference picture obtained by the remote video decoder (if there are no transmission errors).

[0087] Predictor (535) may perform predictive search for the coding engine (532). That is, for a new picture to be coded, predictor (535) may search the reference picture memory (534) for sample data (such as a candidate reference pixel block) or specific metadata such as reference picture MV, block shape, etc. that can function as an appropriate prediction criterion for the new picture. Predictor (535) may operate on a sample block - pixel block basis to find an appropriate prediction criterion. In some examples, the input picture may have prediction criteria drawn from a plurality of reference pictures stored in the reference picture memory (534) as determined by the search results obtained by predictor (535).

[0088] The control unit (550) may manage the coding operations of the source coder (530), including for example the setting of parameters and subgroup parameters used for the coding of video data.

[0089] The outputs of all the aforementioned functional units may undergo entropy coding in the entropy coder (545). The entropy coder (545) converts the symbols generated by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques such as Huffman coding, variable - length coding, arithmetic coding, etc.

[0090] The transmitter (540) may buffer the coded video sequence generated by the entropy coder (545) for transmission via a communication channel (560) which may be a hardware / software link to a storage device capable of storing the coded video data. The transmitter (540) may merge the coded video data from the video coder (503) with other data to be transmitted, such as coded audio data and / or an auxiliary data stream (source not shown).

[0091] The control unit (550) may manage the operation of the video encoder (503). During coding, the control unit (550) may assign to each coding picture a specific coding picture type that can affect the coding technique applicable to each picture. For example, a picture may often be assigned as one of the following picture types.

[0092] An intra picture (I picture) may be a picture that can be coded and decoded without using any other picture in the sequence as a source of prediction. Some video codecs allow different types of intra pictures, for example, IDR (Independent Decoder Refresh) pictures. Those skilled in the art recognize the variations of I pictures and their individual applications and characteristics.

[0093] A predicted picture (P picture) may typically be a picture that can be coded and decoded using intra prediction or inter prediction with one MV and a reference index to predict the sample values of each block.

[0094] A bi - directional predicted picture (B picture) may typically be a picture that can be coded and decoded using intra prediction or inter prediction with up to two MVs and reference indices to predict the sample values of each block. Similarly, a multi - predicted picture can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0095] Source pictures are generally spatially subdivided into a plurality of sample blocks (e.g., blocks of 4×4, 8×8, 4×8, or 16×16 samples each) and may be coded block by block. The blocks may be coded predictively by reference to other (already coded) blocks determined by the coding assignment applied to each picture of the block. For example, blocks of an I picture may be coded non-predictively, or they may be coded predictively by reference to already coded blocks of the same picture (spatial prediction or intra prediction). Pixel blocks of a P picture may be coded predictively via spatial prediction or via temporal prediction by reference to one previously coded reference picture. Blocks of a B picture may be coded predictively via spatial prediction or via temporal prediction by reference to one or two previously coded reference pictures.

[0096] Video encoder (503) may perform coding operations according to a predetermined video coding technology or standard such as ITU-T Rec.H.265. In that operation, video encoder (503) may perform various compression operations including predictive coding operations that utilize temporal and spatial redundancies in the input video sequence. The coded video data may thus conform to the syntax specified by the video coding technology or standard being used.

[0097] In one embodiment, transmitter (540) may transmit additional data along with the coded video. Source coder (530) may include such data as part of the coded video sequence. The additional data may include other forms of redundant data such as temporal / spatial / SNR enhancement layers, redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0098] Video may be captured as a plurality of source pictures (video pictures) in a time series. Intra picture prediction (sometimes abbreviated as intra prediction) utilizes spatial correlation within a given picture, and inter picture prediction utilizes correlation (temporal or otherwise) between pictures. In one example, a particular picture during encoding / decoding is referred to as the current picture and is partitioned into blocks. When a block in the current picture is similar to a reference block in a reference picture that has been previously coded and is still buffered in the block MV video, the block in the current picture can be coded by a vector called an MV. The MV points to the reference block within the reference picture and can have a third dimension to identify the reference picture when multiple reference pictures are in use.

[0099] In some embodiments, bi - prediction techniques can be used in inter picture prediction. According to the bi - prediction technique, two reference pictures such as a first reference picture and a second reference picture that are both before the current picture in the video in decoding order (but can be in the past and future in display order respectively) are used. A block within the current picture can be coded by a first MV pointing to a first reference block within the first reference picture and a second MV pointing to a second reference block within the second reference picture. The block can be predicted by the combination of the first reference block and the second reference block.

[0100] Furthermore, in order to improve coding efficiency, merge mode techniques can be used in inter picture prediction.

[0101] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed within a unit of blocks. For example, according to the HEVC standard, pictures in a video picture sequence are partitioned into coding tree units (CTUs) for compression. CTUs within a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. Usually, a CTU includes three coding tree blocks (CTBs), that is, one luma CTB and two chroma CTBs. Each CTU can be recursively quad-tree divided into one or more coding units (CUs). For example, a 64×64 pixel CTU can be divided into one 64×64 pixel CU, or four 32×32 pixel CUs, or sixteen 16×16 pixel CUs. In one example, each CU is analyzed to determine a prediction type of the CU, such as an inter prediction type or an intra prediction type. The CU is divided into one or more prediction units (PUs) depending on temporal and / or spatial predictability. Usually, each PU includes a luma prediction block (PB) and two chroma PBs. In one embodiment, a prediction operation in coding (encoding / decoding) is performed within a unit of prediction blocks. Using the luma prediction block as an example of a prediction block, the prediction block includes a matrix of values (e.g., luma values) for pixels such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0102] FIG. 6 shows a diagram of a video encoder (603) according to another embodiment of the present disclosure. The video encoder (603) is configured to receive a processing block (e.g., a prediction block) of sample values in a current video picture in a video picture sequence and encode the processing block into a coding picture that is part of a coded video sequence. In one example, the video encoder (603) is used instead of the video encoder (303) in the example of FIG. 3.

[0103] In an example of HEVC, a video encoder (603) receives a matrix of sample values of a processing block, such as a prediction block of 8×8 samples. The video encoder (603) determines, for example using rate distortion optimization, whether the processing block is optimally coded using an intra mode, an inter mode, or a bi-prediction mode. When the processing block is coded in the intra mode, the video encoder (603) may use intra prediction techniques to encode the processing block into the coding picture. When the processing block is coded in the inter mode or the bi-prediction mode, the video encoder (603) may use inter prediction or bi-prediction techniques, respectively, to encode the processing block into the coding picture. In certain video coding techniques, the merge mode can be an inter-picture prediction sub-mode in which the MV is obtained from one or more MV predictors without the benefit of the coded MV component outside the predictor. In certain other video coding techniques, there may be an MV component applicable to the target block. In one example, the video encoder (603) includes other components, such as a mode decision module (not shown), to determine the mode of the processing block.

[0104] In the example of FIG. 6, the video encoder (603) includes an inter encoder (630), an intra encoder (622), a residual calculator (623), a switch (626), a residual encoder (624), a general control unit (621), and an entropy encoder (625) that are coupled together as shown in FIG. 6.

[0105] The inter-encoder (630) is configured to receive samples of a current block (e.g., a block being processed), compare the block with one or more reference blocks (e.g., blocks in a previous picture and a subsequent picture) in a reference picture, generate inter-prediction information (e.g., an explanation of redundant information by an inter-coding technique, an MV, merge mode information), and calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture decoded based on coded video information.

[0106] The intra-encoder (622) is configured to receive samples of a current block (e.g., a block being processed) and, in some cases, compare the block with already-coded blocks in a sample picture, and also generate quantized coefficients after transformation and, in some cases, intra-prediction information (e.g., intra-prediction direction information by one or more intra-coding techniques). In one example, the intra-encoder (622) also calculates an intra-prediction result (e.g., a predicted block) based on the intra-prediction information and reference blocks within the same picture.

[0107] The general control unit (621) is configured to determine general control data and control other components of the video encoder (603) based on the general control data. In one example, the general control unit (621) determines a mode of a block and provides a control signal to a switch (626) based on the mode. For example, when the mode is an intra mode, the general control unit (621) controls the switch (626) to select an intra-mode result for use by the residual calculator (623), and controls the entropy encoder (625) to select the intra-prediction information and include the intra-prediction information in a bitstream. When the mode is an inter mode, the general control unit (621) controls the switch (626) to select an inter-prediction result for use by the residual calculator (623), and controls the entropy encoder (625) to select the inter-prediction information and include the inter-prediction information in a bitstream.

[0108] The residual calculator (623) is configured to calculate the difference (residual data) between the received block and the selected prediction result from the intra encoder (622) or the inter encoder (630). The residual encoder (624) is configured to operate based on the residual data to encode the residual data and generate transform coefficients. In one example, the residual encoder (624) is configured to convert the residual data from the spatial domain to the frequency domain and generate transform coefficients. The transform coefficients are then subjected to quantization processing to obtain quantized transform coefficients. In various embodiments, the video encoder (603) also includes a residual decoder (628). The residual decoder (628) is configured to perform inverse transformation and generate decoded residual data. The decoded residual data can be appropriately used by the intra encoder (622) and the inter encoder (630). For example, the inter encoder (630) can generate a decoded block based on the decoded residual data and the inter prediction information, and the intra encoder (622) can generate a decoded block based on the decoded residual data and the intra prediction information. The decoded block is appropriately processed to generate a decoded picture, which in some examples is buffered in a memory circuit (not shown) and can be used as a reference picture.

[0109] The entropy encoder (625) is configured to format the bitstream to include the encoded block. The entropy encoder (625) is configured to include various information according to a suitable standard such as HEVC. In one example, the entropy encoder (625) is configured to include general control data, selected prediction information (e.g., intra prediction information or inter prediction information), residual information, and other suitable information in the bitstream. Note that there is no residual information when coding a block in the merge submode of either the inter mode or the bi-prediction mode according to the disclosed subject matter.

[0110] FIG. 7 shows a diagram of a video encoder (710) according to another embodiment of the present disclosure. The video decoder (710) is configured to receive a coded picture that is part of a coded video sequence and decode the coded picture to generate a reconstructed picture. In one example, the video decoder (710) is used in place of the video decoder (310) in the example of FIG. 3.

[0111] In the example of FIG. 7, the video decoder (710) includes an entropy decoder (771), an inter decoder (780), a residual decoder (773), a reconstruction module (774), and an intra decoder (772) that are coupled together as shown in FIG. 7.

[0112] The entropy decoder (771) may be configured to reconstruct from the coded picture specific symbols that represent the generated syntax elements of the coded picture. Such symbols may include, for example, the coded mode of a block (e.g., the latter two of the intra mode, inter mode, bi - directional mode, merge sub - mode, or another sub - mode), prediction information (e.g., intra prediction information or inter prediction information) that can identify specific samples or metadata used for prediction by each of the intra decoder (772) or the inter decoder (780), residual information in the form of, for example, quantized transform coefficients, etc. In one example, when the prediction mode is an inter or bi - directional prediction mode, the inter prediction information is provided to the inter decoder (780), and when the prediction type is an intra prediction type, the intra prediction information is provided to the intra decoder (772). The residual information is inverse - quantized and provided to the residual decoder (773).

[0113] The inter decoder (780) is configured to receive the inter prediction information and generate an inter prediction result based on the inter prediction information.

[0114] The intra decoder (772) is configured to receive the intra prediction information and generate a prediction result based on the intra prediction information.

[0115] The residual decoder (773) is configured to perform inverse quantization to extract the inverse quantized transform coefficients, and process the inverse quantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residual decoder (773) may also require certain control information (for including the Quantizer Parameter: QP). This information may be provided by the entropy decoder (771) (since this is only low-capacity control information, the data path is not shown).

[0116] The reconstruction module (774) is configured to combine, in the spatial domain, the residual as the output by the residual decoder (773) and the prediction result (optionally as the output by the inter or intra prediction module) to form a reconstruction block that can be part of the reconstructed picture and can also be part of the reconstructed video. Other suitable operations such as a deblocking operation can be performed to improve the visual quality.

[0117] Note that the video encoders (303), (503), and (603), and the video decoders (310), (410), and (710) can be implemented using any suitable technology. In one embodiment, the video encoders (303), (503), and (603), and the video decoders (310), (410), and (710) can be implemented using one or more integrated circuits. In another embodiment, the video encoders (303), (503), and (603), and the video decoders (310), (410), and (710) can be implemented using one or more processors that execute software instructions.

[0118] <II. Adaptive Loop Filter>

[0119] In some related examples, such as VVC Draft8, an adaptive loop filter (ALF) can be applied together with block-based filter adaptation. In the luma component, based on the directionality and activity of each 4×4 block, one of 25 filters can be selected for each 4×4 block.

[0120] Figures 8A - 8B show exemplary diamond filter shapes of the ALF according to some embodiments of the present disclosure. Figure 8A shows a 5×5 diamond shape applicable to the chroma component, and Figure 8B shows a 7×7 diamond shape applicable to the luma component.

[0121] In some related examples, for the luma component, each 4×4 block can be classified into one of 25 classes. The classification index C of the 4×4 block can be derived as follows based on the directionality D and the quantized value A^ of the activity of the 4×4 block:

Equation

[0122] To calculate D and A^, first, the gradients in the horizontal, vertical, and two diagonal directions of the 4×4 block can be calculated as follows using a 1D Laplacian:

Equation

[0123] To reduce the complexity of block classification, subsampled 1D Laplacian calculations can be applied. Figures 9A - 9D each show exemplary subsampling positions used for the gradients in the vertical, horizontal, diagonal, and anti-diagonal directions according to some embodiments.

[0124]

Mathematics

[0125] Next, the maximum and minimum values of the gradients in two diagonal directions can be set as follows:

Mathematics

[0126] To derive the directionality value D, these values can be compared with each other and with two threshold values t1 and t2.

[0127] Step 1:

Mathematics

[0128] Step 2:

Mathematics

[0129] Step 3:

Mathematics

[0130] Step 4:

Mathematics

[0131] ]>The activity value A is calculated as follows:

Mathematics

[0132] A is further quantized in the range of 0 to 4 including both ends, and the quantized value is denoted as A^.

[0133] For the chroma components within the picture, the classification method is not applied. For example, a single set of ALF coefficients can be applied to each chroma component.

[0134] Before filtering each 4×4 luma block, geometric transformations such as rotation, diagonal flipping, and vertical flipping are applied to the filter coefficients f(k, l) and the corresponding filter clipping values c(k, l) depending on the gradient values calculated for each block. This is equivalent to applying these transformations to the samples within the filter support region (or filter support area) in order to make the different blocks to which ALF is applied more similar by aligning their orientations.

[0135] The three geometric transformations including diagonal flipping, vertical flipping, and rotation can be described as follows:

Number

Table 1

[0136] In some related examples such as VVC Draft8, the filter parameters of ALF are signaled within an adaptation parameter set (APS). Within one APS, a maximum of 25 sets of luma filter coefficients and clipping value indices, and a maximum of 8 sets of chroma filter coefficients and clipping value indices can be signaled. To reduce bit overhead, the filter coefficients of different classifications of the luma component can be merged. In the slice header, the index of the APS used for the current slice is signaled. The signaling of ALF is CTU-based in VVC Draft8.

[0137] The clipping value index is decoded from the APS and enables the determination of the clipping values using a table of clipping values for the luma and chroma components. These clipping values depend on the internal bit depth. For example, the table of clipping values can be obtained by the following formula:

Equation

Table 2

[0138] In the slice header, up to seven APS indices can be signaled to specify the luma filter set used for the current slice. The filtering process can be further controlled at the CTB level. A flag can be signaled to indicate whether the ALF is applied to the luma CTB. The luma CTB can select a filter set from among 16 fixed filter sets and the filter sets from the APS. A filter set index is signaled for the luma CTB to indicate which filter set is applied. The 16 fixed filter sets are predefined in both the encoder and the decoder and can be hard-coded.

[0139] For the chroma component, the APS index can be signaled in the slice header to indicate the chroma filter set used for the current slice. At the CTB level, if there is more than one chroma filter set in the APS, the filter index can be signaled for each chroma CTB.

[0140] The filter coefficients can be quantized, where the norm is equal to 128. To limit the complexity of multiplication, bit-stream compliance can be applied, and as a result, the coefficient values at non-central positions can be in the range from -27 to 27 - 1 including both ends. The coefficient at the central position is not signaled in the bit stream and is considered to be equal to 128.

[0141] In some related examples such as VVC Draft8, the syntax and semantics of the clipping index, and the corresponding values can be defined as follows:

[0142] alf_luma_clip_idx[sfIdx][j] specifies the clipping index of the clipping value to be used before multiplication by the j-th coefficient of the signalled luma filter indicated by sfIdx. The bitstream compliance requirement is that the value of alf_luma_clip_idx[sfIdx][j] for sfIdx = 0..alf_luma_num_filters_signalled_minus1 and j = 0..11 is in the range 0 to 3, inclusive.

[0143] The luma filter clipping value AlfClipL[adaptation_parameter_set_id][filtIdx] having the element AlfClipL[adaptation_parameter_set_id][filtIdx][j] for filtIdx = 0..NumAlfFilters-1 and j = 0..11 is derived in Table 2, depending on bitDepth set equal to BitDepthY, and clipIdx set equal to alf_luma_clip_idx[alf_luma_coeff_delta_idx[filtIdx]][j].

[0144] alf_chroma_clip_idx[altIdx][j] specifies the clipping index of the clipping value to be used before multiplication by the j-th coefficient of the alternative chroma filter having index altIdx. The bitstream compliance requirement is that the value of alf_chroma_clip_idx[altIdx][j] for altIdx = 0..alf_chroma_num_alt_filters_minus1, j = 0..5 is in the range 0 to 3, inclusive.

[0145] The luma filter clipping value AlfClipC[adaptation_parameter_set_id][altIdx] having the element AlfClipC[adaptation_parameter_set_id][altIdx][j] where altIdx = 0..alf_chroma_num_alt_filters_minus1 and j = 0..5 is derived in Table 2 depending on the bitDepth set equal to BitDepthC and the clipIdx set equal to alf_chroma_clip_idx[altIdx][j].

[0146] On the decoder side, when ALF is effective for a CTB, each sample R(i, j) in the CU is filtered, resulting in a corresponding sample value R'(i, j) as shown below:

Equation

[0147] Figure 10 shows an exemplary modified block classification applied to the luma component according to an embodiment of the present disclosure. The modified block classification and filtering are utilized for samples near the horizontal CTU boundary and can reduce the line buffer requirements of the ALF. As shown in Figure 10, the virtual boundary is defined as a line shifted by "N" samples from the horizontal CTU boundary. Here, N is equal to 4 for the luma component and 2 for the chroma component, respectively.

[0148] In the 1D Laplacian gradient calculation of the 4×4 block above the virtual boundary, only the samples above the virtual boundary are used. Similarly, in the 1D Laplacian gradient calculation of the 4×4 block below the virtual boundary, only the samples below the virtual boundary are used. The quantization of the activity value A is thus scaled considering the reduced number of samples used in the 1D Laplacian gradient calculation.

[0149] Figure 11 shows an exemplary modified ALF for the luma component at the virtual boundary according to some embodiments. In the filtering process, the symmetric padding operation at the virtual boundary can be used for both the luma and chroma components. As shown in Figure 11, when the samples being filtered are located below the virtual boundary, the neighboring samples located above the virtual boundary are padded. On the other hand, the corresponding samples on the other side are also padded symmetrically.

[0150] To improve coding efficiency, a coding unit synchronous picture quadtree-based ALP is used in some related examples. The luma picture can be divided into several multilevel quadtree partitions, and each partition boundary is aligned with the boundary of the largest coding unit (LCU). Each partition has a unique filtering process and can be called a filter unit (FU).

[0151] The two-pass encoding flow is described as follows. In the first pass, the quadtree splitting pattern and the best filter for each FU are determined. The filtering distortion is estimated by fast filtering distortion estimation (FFDE) during the determination process. According to the determined quadtree splitting pattern and the selected filters for all FUs, the reconstructed picture is filtered. In the second pass, CU synchronous ALF on / off control is executed. According to the ALF on / off result, the filtered picture from the first pass is partially restored by the reconstructed picture.

[0152] FIG. 12 shows an exemplary LCU aligned picture quadtree splitting according to an embodiment. A top-down splitting strategy is adopted, and the rate distortion criterion is used to split the picture into multi-level quadtree partitions. Each partition is called a filter unit. The splitting process aligns the quadtree partitions to the LCU boundaries. The encoding order of the FUs follows the z-scan order. For example, as shown in FIG. 12, the picture is split into 10 FUs, and the encoding order is FU0, FU1, FU2, FU3, FU4, FU5, FU6, FU7, FU8, and FU9.

[0153] FIG. 13 shows an exemplary quadtree splitting pattern corresponding to FIG. 12. To show the picture quadtree splitting pattern, the splitting flags are encoded and transmitted in the z-order.

[0154] The filters for each FU can be selected from two filter sets based on the rate distortion criterion. The first set has a 1 / 2 symmetric square and rhombus filter newly derived for the current FU. The second set is derived from a time-delay filter buffer that stores the previously derived filters for the FU of the previous picture. Among these two filters, the filter with the minimum rate distortion cost can be selected for the current FU. Similarly, if the current FU is not the minimum FU and can be further divided into four child FUs, the rate distortion costs of the four child FUs are calculated. By comparing the rate distortion costs for each case of division and non-division, a quadtree division pattern for the picture can be determined.

[0155] In some related examples, the maximum quadtree division level is 2, which means that the maximum number of FUs is 16. During the quadtree division decision, the correlation values for deriving the Wiener coefficients of the 16 FUs (minimum FUs) at the bottom quadtree level can be reused. The remaining FUs can derive their Wiener filters from the correlations of the 16 FUs at the bottom quadtree division level. Therefore, only one frame buffer access is needed to derive the filter coefficients for all FUs.

[0156] After the quadtree division pattern is determined, CU synchronous ALF on / off control can be performed to further reduce the filtering distortion. By comparing the filtering distortion and the distortion without filtering, the leaf CUs can explicitly switch the ALF on / off in their local regions. The coding efficiency can be further improved by redesigning the filter coefficients according to the ALF on / off results. However, the redesign process requires additional frame buffer accesses. In some related examples, there is no redesign process after the CU synchronous ALF on / off decision to minimize the number of frame buffer accesses.

[0157] <III. Adaptive Loop Filter>

[0158] In some related examples, a cross-component adaptive loop filter (CC-ALF) is utilized. The CC-ALF refines each chroma component using luma sample values.

[0159] FIG. 14A shows an exemplary arrangement of a CC-ALF according to an embodiment of the present disclosure. FIG. 14B shows an exemplary linear diamond-shaped filter applied to the luma channel for each chroma component during CC-ALF operation. The filter coefficients can be transmitted within the APS, scaled by a factor of, for example, 210, and rounded for fixed-point representation. The application of the filter is controlled with a variable block size and signaled by the context coding flag received for each block of samples. The block size is received at the slice level for each chroma component, together with the CC-ALF enable flag. In the example, the following block sizes (in chroma samples) are supported: 16×16, 32×32, and 64×64.

[0160] Table 3 shows the syntax elements related to the CC-ALF.

Table 3

[0161] In Table 3, the fact that the syntax element alf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is equal to 0 indicates that the inter-component Cb filter is not applied to the sample block in the Cb color component at the luma position (xCtb, yCtb). The fact that the syntax element aalf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is not equal to 0 indicates that the alf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]-th inter-component Cb filter is applied to the sample block in the Cb color component at the luma position (xCtb, yCtb).

[0162] The fact that the syntax element alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is equal to 0 indicates that the inter-component Cr filter is not applied to the sample block in the Cr color component at the luma position (xCtb, yCtb). The fact that the syntax element alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is not equal to 0 indicates that the alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]-th inter-component Cr filter is applied to the sample block in the Cr color component at the luma position (xCtb, yCtb).

[0163] <IV. Chroma Sampling Format>

[0164] FIG. 15 shows an exemplary relative position of upper-left chroma samples when chroma_format_idc is equal to 1 (4:2:0 chroma format) and chroma_sample_loc_type_top_field or chroma_sample_loc_type_bottom_field is equal to the value of variable ChromaLocType. The area represented by the upper-left 4:2:0 chroma samples is shown relative to the area represented by the upper-left luma samples.

[0165] <V. Constrained Directional Enhancement Filter>

[0166] One goal of the in-loop constrained directional enhancement filter (CDEF) is to filter out coding artifacts while retaining the details of the image. In some related examples such as HEVC, the sample adaptive offset (SAO) algorithm can achieve a similar goal by defining signal offsets for different classes of pixels. Different from SAO, CDEF is a non-linear spatial filter. The filter design is constrained so that it can be easily vectorized, for example, implemented by single instruction multiple data (SIMD) operations. This does not apply to other non-linear filters such as median filters and bilateral filters.

[0167] The CDEF design is derived from the following observations. The amount of ringing artifacts in the coded image tends to be approximately proportional to the quantization step size. The amount of detail is a characteristic of the input image, but the minimum amount of detail retained in the quantized image also tends to be proportional to the quantization step size. For a given quantization step size, the size of the ringing is usually smaller than the size of the detail.

[0168] CDEF identifies the direction of each block and operates by adaptively filtering at a small angle along the identified direction and along a direction rotated 45 degrees from the identified direction. The filter strength is signaled explicitly. This allows for fine control over blurring. Efficient encoder search is designed for the filter strength. CDEF is based on two previously proposed in-loop filters, and the combined filter is adopted for the new AOMedia Video1 (AV1) codec.

[0169] FIG. 16 shows an exemplary direction search for an 8×8 block according to an embodiment of the present disclosure. The direction search operates on the reconstructed pixels immediately following the deblocking filter. Since those pixels are available to the decoder, there is no need to signal the direction. The search operates on an 8×8 block. The 8×8 block is small enough to adequately handle non-linear edges and large enough to immediately estimate the direction when applied to the quantized image. Having a constant direction across the 8×8 region also makes vectorization of the filter easier. For each block, the direction that best matches the pattern within each block is determined by minimizing the sum of squared differences (SSD) between the quantized block and the closest full-direction block. A full-direction block is a block in which all pixels along a line in one direction have the same value.

[0170] One reason for identifying the direction is to align the filter taps along a direction that reduces ringing while preserving directional edges or patterns. However, directional filtering alone may not be sufficient to adequately reduce ringing. It is desirable to use filter taps for pixels not along the main direction. To reduce the risk of blurring, these additional taps are handled more conservatively. For this reason, CDEF defines primary taps and secondary taps. The full 2D CDEF filter is represented as follows:

Equation

[0171] <Loop Restoration in VI.AV1>

[0172] The set of in - loop restoration methods can typically be used in post - deblocking video coding to remove noise and improve edge quality beyond traditional deblocking operations. These methods are switchable within a frame for appropriately sized tiles. The specific methods described are based on a separable symmetric Wiener filter and a dual self - guiding filter with subspace projection. Since the statistics of the content can vary significantly within a frame, these tools are integrated within a switchable framework where different tools can be triggered in different regions of the frame.

[0173] In the Wiener filter, all pixels in the degraded frame can be reconstructed as the non - causal filtered version of each pixel within the w×w window around each pixel. Here, w = 2r+1 is odd for an integer r. The 2D filter taps are in column - vectorized form w 2When indicated by the ×1 element vector F, as a result of simple linear minimum mean square error (LMMSE) optimization, the filter parameter is F = H -1 given by M. Here, H = E[XX T is the autocovariance of x, the column vectorized version of w samples within a w×w window around the pixel, and w 2 samples. M = E[YX T is the cross-correlation with the scalar source sample y of x to be estimated. The encoder can estimate H and M from the realization of the deblocked frame and the source, and transmit the resulting filter F to the decoder. However, this not only incurs a substantial bitrate cost of transmitting w 2 taps, but also results in non-separable filtering that makes decoding extremely complex. Therefore, some additional constraints are imposed on the characteristics of F. First, F is constrained to be separable. As a result, the filtering can be implemented as separable horizontal and vertical w-tap convolutions. Second, each of the horizontal and vertical filters is constrained to be symmetric. Third, the sum of both the horizontal and vertical filter coefficients is assumed to be 1.

[0174] The local linear model of the induced filtering can be expressed as follows.

Equation

[0175] The local linear model is used to calculate the filtered output y from the unfiltered sample x. Here, F and G are determined based on the statistics of the degraded image and the guidance image in the neighborhood of the filtered pixels. When the guidance image is the same as the degraded image, the resulting so-called self-guidance filtering has the effect of smoothing that preserves edges. A specific form of self-guidance filtering depends on two parameters: the radius r and the noise parameter e, and is listed as follows.

[0176] (1) Obtain the mean μ and variance σ of the pixels within the (2r + 1)×(2r + 1) window around all pixels. 2 This can be effectively implemented by box filtering based on integral imaging.

[0177] (2) Calculate the following for all pixels: [Equation]

[0178] (3) Calculate F and G for all pixels as the mean of the values of f and g within the 3×3 window around the pixel for use.

[0179] Filtering is controlled by r and e. Here, the higher r is, the higher the spatial dispersion is, and the higher e is, the higher the range dispersion is.

[0180] Figure 17 shows an exemplary subspace projection according to an embodiment. Neither of the inexpensive restorations X1 and X2 exists close to the source Y, but appropriate multipliers {α,β} can bring them closer to the source as long as they are moving in a somewhat correct direction.

[0181] [VII. Component - to - Component Sample Offset Filter]

[0182] The cross-component sample offset (CCSO) filter is a loop filtering approach for reducing the distortion of reconstructed samples. In the CCSO filter, when the processed input reconstructed sample of the first color component is given, a non-linear mapping can be used to derive the output offset. The output offset can be added to the reconstructed sample of the second color component during the filtering process of the CCSO filter. The input reconstructed sample of the first color component is located within the filter support area (or filter support region).

[0183] FIG. 18 shows an exemplary filter support area according to an embodiment of the present disclosure. The filter support area includes four reconstructed samples: p0, p1, p2, and p3. The four input reconstructed samples are in a cross shape in the vertical and horizontal directions. The central sample of the first color component (denoted by c), and the sample to be filtered of the second color component are at the same position. When processing the input reconstructed samples, the following steps are applied.

[0184] Step 1: First, the delta values between p0 to p3 and c are calculated and shown as m0, m1, m2, and m3.

[0185] Step 2: The delta values m0 to m3 are further quantized. The quantized values are shown as d0, d1, d2, and d3. The quantized values can be -1, 0, and 1 based on the following quantization process. (a) If m < -N, then d = -1; (b) if -N <= m <= N, then d = 0; (c) if m > N, then d =
. Here, N is called the quantization step size, and exemplary values of N include 4, 8, 12, and 16.

[0186] The quantized values d0 to d3 can be used to identify one combination of non-linear mappings. For example, the CCSO filter of FIG. 8 has four filter taps d0 to d3, and each filter tap can have one of three quantized values (e.g., -1, 0, and 1), and thus, a total of 34 There are 81 combinations.

[0187] Figures 19A - 19B show a tabular form of 81 exemplary combinations of non - linear mapping in a CCSO filter according to an embodiment. The last column of the table represents the output offset value for each combination. Examples of offset values are integers, such as 0, 1, - 1, 3, - 3, 5, - 5, and - 7.

[0188] The final filtering process of the CCSO filter can be applied as follows.

Number

[0189] <VIII. Improved Inter - Component Sample Offset Filter>

[0190] In the related CCSO filter, when processing the input reconstruction samples, the quantization step size is a fixed value, which may limit the performance of the CCSO filter. Further, the output offset value for each combination of the processed input reconstruction samples is a fixed value, which may further limit the performance of the CCSO filter.

[0191] In the present disclosure, the CCSO filter can be defined as a filtering process that uses the reconstruction samples of the first color component (e.g., Y, Cb, or Cr) as input and applies the output to the second color component of the block, which is different from the first color component of the block.

[0192] The input to the non-linear mapping of the CCSO filter is one or more processed reconstruction samples within the filter support area (or filter support region) of the first color component of the block. When processing one or more input reconstruction samples, quantization processing can be applied, and the quantization processing can be controlled by the quantization step size N. When the input reconstruction samples are processed, the output offset value can be read from the non-linear mapping of the CCSO filter. The output offset value can be applied to the second color component of the block.

[0193] The present disclosure includes a method for improving the performance of the CCSO filter. In the present disclosure, the filter support area (or region) can be defined as the area where filtering processing such as the CCSO filter is performed. In quantization processing, the range of possible sample values can be decomposed into a finite set of intervals (or steps) called quantization intervals. The difference between two quantization intervals can be called the quantization step size.

[0194] According to an aspect of the present disclosure, an adaptive quantization step size (e.g., N described in Chapter VII (the chapter of the inter-component sample offset filter)) can be used when processing the input reconstruction samples within the filter support area (or region) of the CCSO filter. In some embodiments, the quantization step size can vary based on the characteristics of the coding block, video frame, and / or video sequence. The variation of the quantization step size can improve the overall coding efficiency.

[0195] In one embodiment, the quantization step size N can be a predetermined constant integer. Examples of N include 4, 8, 12, and 16. N can vary for different coding blocks, video frames, or video sequences.

[0196] In one embodiment, the quantization step size N is an integer power of 2 N , for example, 2, 4, 8, or 16.

[0197] In one embodiment, the quantization step size N can be signaled. The quantization step size N can be signaled by a block-level parameter, a slice-level parameter, a tile-level parameter, or a frame-level parameter.

[0198] In one embodiment, when an array of possible quantization step sizes is given, an index can be signaled to indicate which quantization step size is selected. The index can be signaled by a block-level parameter, a slice-level parameter, a tile-level parameter, a CTU-level parameter, a video frame-level parameter, or a sequence-level parameter.

[0199] In one example, the array of possible quantization step sizes can be {4, 8, 12, 16}, and an index within [0, 3] can be signaled to indicate which value within the array is selected.

[0200] In one example, the index can be signaled using a fixed-length codeword, e.g., {00, 01, 10, 11}.

[0201] In one example, the array of possible quantization step sizes can be {4, 8, 16}, and an index within [0, 2] can be signaled to indicate which value within the said array is selected.

[0202] In one example, the index can be signaled using a variable-length codeword, e.g., {0, 10, 11} or {1, 00, 01}.

[0203] In one embodiment, the quantization step size N or the index of N can be signaled in a high-level parameter set, such as a decoding parameter set (DPS), a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), an adaption parameter set (APS), a slice header, or a picture header.

[0204] According to an aspect of the present disclosure, an adaptive offset value can be used based on the characteristics of a filter support region. In some embodiments, an offset value derived from the non-linear mapping of a CCSO filter can be further scaled based on the characteristics of the filter support region.

[0205] In one embodiment, the scaling of the offset value can depend on the delta values (e.g., m0 to m3) and / or the quantization step size N. Here, m0 to m3 are the delta values between the surrounding samples p0 to p3 and the central sample c described in Chapter VII (the chapter on the inter-component sample offset filter). In one embodiment, the scaling of the offset value can depend on the ratio r between the average of the absolute values of m0 to m3 and N.

[0206] In one embodiment, the average of the absolute values of m0 to m3 can be calculated first and denoted as m'. The ratio r can be derived as r = m' / N. Next, the offset value derived from the non-linear mapping can be scaled by the maximum value between 1 and r, e.g., max(1, m' / N).

[0207] In one example, d0 = 1, d1 = -1, d2 = 0, d3 = 0, and m0 = 8, m1 = -8, m2 = 3, m3 = 1. The quantization step size N is 4, and the output offset value s is 3. Thus, m’ = avg(abs(m0)+abs(m1)+abs(m2)+abs(m3)) = avg(8 + 8 + 3 + 1) = 5, where avg and abs represent the average and absolute operations, respectively. The ratio r = m’ / N = 5 / 4 = 1, and the final offset value is s×r = 3×1 = 3.

[0208] In one embodiment, the average m' can be calculated using a subset of the absolute values of m0 to m3. These corresponding quantized values d0 to d3 are not zero (for example, if the quantized value is zero, the corresponding m is excluded from the calculation of m'). The ratio r can be derived as m’ / N. Next, the output offset value derived from the non-linear mapping can be scaled by the maximum value between 1 and r, e.g., max(1, m’ / N).

[0209] In one example, d0 = 1, d1 = -1, d2 = 0, d3 = 0, and m0 = 8, m1 = -8, m2 = 3, m3 = 1. The quantization step size N is 4, and the output offset value s is 3. Thus, m’ = avg(abs(m0)+abs(m1)) = avg(8 + 8) = 8, where avg and abs represent the average and absolute operations, respectively. The ratio r = m’ / N = 8 / 4 = 2, and the final offset value is s×r = 3×2 = 6.

[0210] In one embodiment, the adaptation of the output offset value can always be enabled (or turned on). That is, the scaling of the output offset value can always be used in the CCSO filter.

[0211] In one embodiment, a syntax element indicating whether to enable adaptation of the output offset value can be signaled, for example, as a block-level parameter, a video frame-level parameter, a slice-level parameter, a tile-level parameter, a CTU-level parameter, or a sequence-level parameter. The syntax element can be signaled within a high-level parameter set (e.g., DPS, VPS, SPS, PPS, or APS), a slice header, a picture header, or an SEI message.

[0212] <IX. Flowchart>

[0213] FIG. 20 shows a flowchart illustrating an overview of an exemplary process (2000) according to an embodiment of the present disclosure. In various embodiments, process (2000) is performed by processing circuits such as those within terminal devices (210), (220), (230), and (240), a processing circuit that performs the functions of video encoder (303), a processing circuit that performs the functions of video decoder (310), a processing circuit that performs the functions of video decoder (410), a processing circuit that performs the functions of intra prediction module (452), a processing circuit that performs the functions of video encoder (503), a processing circuit that performs the functions of predictor (535), a processing circuit that performs the functions of intra encoder (622), a processing circuit that performs the functions of intra decoder (772), and the like. In some embodiments, process (2000) is implemented by software instructions, and thus, when the processing circuit executes the software instructions, the processing circuit performs process (2000).

[0214] Process (2000) may typically begin at step (S2010), where process (2000) determines a reconstructed sample of a first color component in a filter support region of a current picture that is part of a coded video sequence. Next, process (2000) proceeds to step (S2020).

[0215] In step (S2020), the process (2000) performs a filtering process on the reconstructed samples of the first color component in the filter support area. The quantization step size of the filtering process is set individually for one of the coding block, video frame, and video sequence. Next, the process (2000) proceeds to step (S2030).

[0216] In step (S2030), the process (2000) reconstructs the samples of the second color component in the filter support area based on the output value of the filtering process. The second color component is different from the first color component. Next, the process (2000) ends.

[0217] In an embodiment, the quantization step size is a predetermined constant for one of the coding block, video frame, and video sequence.

[0218] In an embodiment, the quantization step size is an integer that is a power of 2.

[0219] In an embodiment, the quantization step size is one of a plurality of quantization step sizes determined based on an index included in a bitstream corresponding to one of the coding block, video frame, and video sequence.

[0220] In an embodiment, the quantization step size is included in a bitstream corresponding to one of the coding block, video frame, and video sequence.

[0221] In an embodiment, the process (2000) determines whether the output value of the filtering process is scaled based on the reconstructed samples of the first color component in the filter support area. In response to the output value of the filtering process being scaled, the process (2000) reconstructs the samples of the second color component in the filter support area based on the scaled output value of the filtering process.

[0222] In an embodiment, the process (2000) determines whether the output value of the filtering process is scaled based on a reconstruction sample of a first color component in a filter support region and a syntactic element indicating whether scaling of the output value of the filtering process is enabled.

[0223] In an embodiment, the process (2000) determines a scaled output value of the filtering process based on a reconstruction sample of a first color component in a filter support region and a quantization step size.

[0224] <X. Computer System>

[0225] The above-described technology can be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, FIG. 21 shows a computer system (2100) suitable for implementing a particular embodiment of the subject matter of the present disclosure.

[0226] The computer software can be processed by mechanisms such as assembly, compilation, linking, etc. to generate code including instructions executable directly or through interpretation, microcode execution, etc. by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., and can be coded using any suitable machine code or computer language.

[0227] The instructions can be executed on various computers or components thereof including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, Internet of Things devices, etc.

[0228] The components shown in FIG. 21 of the computer system (2100) are illustrative only and do not imply any limitation as to the use or functionality of the computer software implementing the embodiments of the present disclosure. Further, the component configuration should not be construed as having any dependencies or requirements related to any one or combination of the components shown in the exemplary embodiments of the computer system (2100).

[0229] The computer system (2100) may include a specific human interface input device. Such a human interface input device may respond to input by one or more human users through, for example, sensory input (e.g., keystrokes, swipes, data glove movements), voice input (e.g., voice, clapping), visual input (e.g., gestures), olfactory input (not shown). The human interface device can also be used to capture certain media that are not necessarily directly related to conscious input by humans, such as voice (e.g., conversation, music, ambient sound), images (e.g., scanned images, photographic images obtained from a digital camera), video (e.g., including 2D video, 3D video, stereoscopic video).

[0230] The input human interface device may include one or more of a keyboard (2101), a mouse (2102), a trackpad (2103), a touch screen (2110), a data glove (not shown), a joystick (2105), a microphone (2106), a scanner (2107), and a camera (2108) (only one of which is shown).

[0231] The computer system (2100) may also include certain human interface output devices. Such human interface output devices may stimulate the senses of one or more human users, for example, through sensory output, sound, light, and smell / taste. Such human interface output devices may include sensory output devices (e.g., a touch screen (2110), a data glove (not shown), or a joystick (2105) for sensory feedback, although there may also be sensory feedback devices that do not function as input devices), a sound output device (e.g., a speaker (2109), headphones (not shown)), a visual output device (e.g., a screen (2110), a CRT screen, an LCD screen, a plasma screen, an OLED screen, each with or without touch screen input capabilities, each with or without sensory feedback capabilities, some of which may output two-dimensional visual output or three-dimensional or higher-dimensional output through means such as stereoscopic output, virtual reality glasses (not shown), a holographic display, and a smoke tank (not shown), and a printer (not shown)). These visual output devices (e.g., the screen (2110)) can be connected to the system bus (2148) through a graphics adapter (2150).

[0232] The computer system (2100) may also include a human-accessible memory device and related media such as an optical medium like a CD / DVDROM / RW (2120) with a medium (2121) such as a CD / DVD, a thumb drive (2122), a removable hard drive or a solid-state drive (2123), legacy magnetic media such as tapes and floppy disks (not shown), and devices based on dedicated ROM / ASIC / PLD such as a security dongle (not shown).

[0233] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the subject matter of this disclosure does not include a transmission medium, a carrier wave, or other transient signals.

[0234] The computer system (2100) may also include a network interface (2154) to one or more communication networks (2155). The one or more communication networks (2155) can be, for example, wireless, wired, or optical. The one or more communication networks (2155) can further be local, wide area, metropolitan area, vehicle and industrial, real-time, delay-tolerant, etc. Examples of the one or more communication networks include local area networks such as Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wired or wireless wide area digital networks including cable TV, satellite TV, terrestrial broadcast TV, vehicle and industrial including CANBus, etc. Certain networks generally require an external network interface attached to a specific general-purpose data port or peripheral device bus (2149) (e.g., the USB port of the computer system (2100)). Others are generally integrated into the core of the computer system (2100) by attachment to a system bus as described later (e.g., an Ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system). Using these networks, the computer system (2100) can communicate with other entities. Such communication can be one-way reception only (e.g., broadcast TV), one-way transmission only (e.g., CANbus to a specific CANbus device), or two-way to other computer systems using, for example, local or wide area digital networks. Specific protocols and protocol stacks can be used for each of the networks and network interfaces described above.

[0235] The aforementioned human interface device, human-accessible storage device, and network interface can be attached to the core (2140) of the computer system (2100).

[0236] The core (2140) may include one or more central processing units (CPUs) (2141), a graphics processing unit (GPU) (2142), a dedicated programmable processing unit in the form of an FPGA (2143), a hardware accelerator for specific tasks (2144), a graphics adapter (2150), and the like. These devices may be connected through a system bus (2148) together with a built-in mass storage device (1547) such as a read-only memory (ROM) (2145), a random access memory (2146), an internal hard drive not accessible to users, an SSD, and the like. In some computer systems, the system bus (2148) may be accessible in the form of one or more physical plugs to enable expansion by additional CPUs, GPUs, etc. Peripheral devices may be attachable directly to the core's system bus (2148) or through a peripheral device bus (2149). In the example, a screen (2110) can be connected to the graphics adapter (2150). The architecture of the peripheral device bus includes PCI, USB, and the like.

[0237] The CPU (2141), GPU (2142), FPGA (2143), and accelerator (2144) can execute specific instructions that, when combined, can generate the aforementioned computer code. The computer code can be stored in the ROM (2145) or the RAM (2146). Temporary data can also be stored in the RAM (2146), while permanent data can be stored, for example, in the built-in mass storage device (2147). Fast storage and reading to / from any of the memory devices can be enabled through the use of a cache memory that can be closely associated with one or more of the CPU (2141), GPU (2142), mass storage device (2147), ROM (2145), RAM (2146), and the like.

[0238] A computer-readable medium may have computer code for performing operations implemented by various computers. The medium and the computer code may be specially designed and configured for the purposes of the present disclosure or may be of the kind well known and available to those skilled in the field of computer software.

[0239] By way of example and not limitation, a computer system (2100) having an architecture, and specifically a core (2140), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be associated with a specific storage device of the core (2140) having non-transitory characteristics such as an on-core mass storage device (2147) or ROM (2145), and media associated with a user-accessible mass storage device as described above. The software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (2140). The computer-readable media can include one or more memory devices or chips as required by a particular need. The software can cause the core (2140) and specifically the processor (including a CPU, GPU, FPGA, etc.) therein to perform a specific process or a specific portion of a specific process described herein, including the definition of a data structure stored in a RAM (2146) and changes to the data structure according to the process defined by the software. Additionally or alternatively, the computer system can provide functionality as a result of an implementation in logic hardwired or other circuitry (e.g., an accelerator (2144)) operable with or instead of the software to perform a specific process or a specific portion of a specific process described herein. References to software include logic and, where appropriate, vice versa. References to a computer-readable media can, where appropriate, include circuitry (such as an integrated circuit (IC)) for storing software for execution, circuitry for implementing logic for execution, or both. The present disclosure includes any suitable combination of hardware and software.

[0240] The present disclosure has described several exemplary embodiments, but alternatives, substitutions, and various equivalents exist and are encompassed within the scope of the present disclosure. It will be apparent to those skilled in the art that, although not explicitly shown or described herein, many systems and methods can be devised that implement the principles of the present disclosure and are thus included within the spirit and scope of the present disclosure.

[0241] Appendix A: Abbreviations ALF: Adaptive Loop Filter AMVP: Advanced Motion Vector Prediction APS: Adaptation Parameter Set ASIC: Application-Specific Integrated Circuit ATMVP: Alternative / Advanced Temporal Motion Vector Prediction AV1: AOMedia Video 1 AV2: AOMedia Video 2 BMS: Benchmark Set BV: Block Vector CANBus: Controller Area Network Bus CB: Coding Block CC-ALF: Cross-Component Adaptive Loop Filter CD: Compact Disc CDEF: Constrained Directional Enhancement Filter CPR: Current Picture Referencing CPU: Central Processing Unit CRT: Cathode Ray Tube CTB: Coding Tree Block CTU: Coding Tree Unit CU: Coding Unit DPB: Decoder Picture Buffer DPCM: Differential Pulse-Code Modulation DPS: Decoding Parameter Set DVD: Digital Video Disc FPGA: Field Programmable Gate Area JCCR: Joint CbCr Residual Coding JVET: Joint Video Exploration Team GOP: Groups of Pictures GPU: Graphics Processing Unit GSM: Global System for Mobile communications HDR: High Dynamic Range HEVC: High Efficiency Video Coding HRD: Hypothetical Reference Decoder IBC: Intra Block Copy IC: Integrated Circuit ISP: Intra Sub-Partitions JEM: Joint Exploration Model LAN: Local Area Network LCD: Liquid-Crystal Display LR: Loop Restoration Filter LRU: Loop Restoration Unit LTE: Long-Term Evolution MPM: Most Probable Mode MV: Motion Vector OLED: Organic Light-Emitting Diode PBs: Prediction Blocks PCI: Peripheral Component Interconnect PDPC: Position Dependent Prediction Combination PLD: Programmable Logic Device PPS: Picture Parameter Set PU: Prediction Unit RAM: Random Access Memory ROM: Read-Only Memory SAO: Sample Adaptive Offset SCC: Screen Content Coding SDR: Standard Dynamic Range SEI: Supplementary Enhancement Information SNR: Signal Noise Ratio SPS: Sequence Parameter Set SSD: Solid-state Drive TU: Transform Unit USB: Universal Serial Bus VPS: Video Parameter Set VUI: Video Usability Information VVC: Versatile Video Coding WAIP: Wide-Angle Intra Prediction

Claims

Claim 1 A method for video decoding in a decoder, comprising: determining a reconstructed sample of a first color component in a filter support region of a current picture that is part of a coded video sequence; performing a filtering process on the reconstructed sample of the first color component in the filter support region, wherein a quantization step size of the filtering process is individually set for each one of a coding block, a video frame, and a video sequence; reconstructing samples of a second color component in the filter support region based on an output value of the filtering process, wherein the second color component is different from the first color component; A method comprising the above steps.

Images