Video decoding method, device, and program executed by a decoder, and video coding method executed by an encoder

Abstract

To provide a method and an apparatus including processing circuitry for video decoding.SOLUTION: The processing circuitry can decode coding information for a block from a coded video bitstream. The coding information can indicate an intra prediction mode for the block and one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block. The processing circuitry can determine whether a secondary transform is disabled for the block based on the one or the combination of the transform partitioning information for the block, the size of the block, and the shape of the block. The processing circuitry can reconstruct the block based on the determination of whether the secondary transform is disabled for the block.SELECTED DRAWING: Figure 19

Description

[Technical field]

[0001] [Incorporated by reference] This patent application claims the benefit of priority to U.S. Provisional Application No. 63 / 112,533, filed November 11, 2020, entitled "METHODS FOR EFFICIENT APPLICATION OF SECONDARY TRANSFORMS," which in turn claims the benefit of priority to U.S. Provisional Application No. 17 / 361,239, filed June 28, 2021, entitled "Method and Apparatus for Video Coding," the entire disclosures of which are hereby incorporated by reference in their entirety.

[0002] [Technical field] This disclosure describes embodiments generally relating to video coding. [Background technology]

[0003] The background description provided herein is intended to generally present the context of the disclosure. The work of the currently named inventors is not admitted expressly or impliedly as prior art to the present disclosure to the extent that that work is described in this Background section, and any aspects of the description that may not otherwise qualify as 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 sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luminance samples and associated chrominance samples. The sequence of pictures can have a fixed or variable picture rate (commonly known as frame rate) of, for example, 60 pictures per second, i.e., 60 Hz. Uncompressed video has certain bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) at 8 bits per sample requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires more than 600 Gbytes of storage space.

[0005] One goal of video coding and decoding can be the reduction of redundancy in the input video signal by compression. Compression can help reduce the above bandwidth or storage space requirements by more than two orders of magnitude in some cases. Both lossless and lossy compression as well as their combinations can be used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be the same as the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely used. The amount of distortion that is tolerated depends on the application, for example, a user of a particular consumer streaming application may tolerate higher distortion than a user of a television distribution application. The achievable compression ratio can reflect that a higher tolerable / acceptable distortion may result in a higher compression ratio.

[0006] Video encoders and decoders can utilize techniques from a number of broad categories, including, for example, motion compensation, transformation, quantization, and entropy coding.

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

[0008] Conventional intra-coding, for example as known from MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to do so from surrounding sample data and / or metadata obtained during encoding / decoding of spatially adjacent and preceding blocks of data in decoding order. Such techniques are hereafter referred to as "intra-prediction" techniques. It should be noted that at least in some cases, intra-prediction uses only reference data from the current picture being reconstructed, and not from the reference picture.

[0009] There may be many different forms of intra-prediction. If more than one such technique is available for a given video coding technique, the technique in use may be coded in an intra-prediction mode. In certain cases, a mode may have sub-modes and / or parameters, which may be coded independently or may be included in a mode codeword. Since which codeword to use for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gain through intra-prediction, entropy coding techniques may be used to convert the codeword into a bitstream.

[0010] A specific mode of intra prediction was introduced by H.264, refined in H.265, and further refined in newer coding techniques such as Joint Exploration Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). A predictor block may be formed using neighboring sample values ​​belonging to already available samples. The sample values ​​of the neighboring samples are copied into the predictor block according to the direction. The reference of the direction in use may be coded into the bitstream or may itself be predicted.

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

[0012] Still referring to FIG. 1A, at the top left is depicted a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, with each sample labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (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 in the block (104) in both the Y and X dimensions. Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown are reference samples that follow a similar numbering scheme. The reference samples are labeled with "R", their Y position (e.g., row index), and their X position (column index) relative to the block (104). In both H.264 and H.265, the predicted samples are adjacent to the block being reconstructed, and therefore negative values ​​do not need to be used.

[0013] Intra-picture prediction can work by copying reference sample values ​​from neighboring samples as necessary depending on the signaled prediction direction. For example, suppose the coded video bitstream includes signaling for this block indicating a prediction direction consistent with arrow (102), i.e., the sample is predicted from one or more prediction samples in the upper right corner at an angle of 45 degrees from the horizontal. In that case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

[0014] In certain cases, values ​​of multiple reference samples may be combined, for example through interpolation, to calculate a reference sample, particularly when the orientation is not equally divisible by 45 degrees.

[0015] The number of possible directions has increased as video coding techniques have developed. In H.264 (2003), nine different directions could be represented. That increased to 33 in H.265 (2013), and JEM / VVC / BMS can support up to 65 directions at the time of this disclosure. Experiments have been performed to identify the most likely directions, and certain techniques in entropy coding are used to represent those likely directions with a small number of bits, while accepting some penalty for less likely directions. Furthermore, the direction itself can sometimes be predicted from neighboring directions used in neighboring, already decoded blocks.

[0016] FIG. 1B shows a schematic diagram (180) representing 65 intra prediction directions according to JEM to illustrate the growing number of prediction directions over time.

[0017] The mapping of intra-prediction direction bits in a coded video bitstream representing directions can vary from one video coding technique to another, and can range, for example, from a simple direct mapping of prediction directions to intra-prediction modes to codewords, to complex adaptation schemes including most-probable modes, and similar techniques. In all cases, however, there may be certain directions that are statistically less likely to occur in the video content than certain other directions. Since the goal of video compression is to reduce redundancy, these less likely directions will be represented by more bits than more likely directions in a video coding technique that works well.

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

[0019] In some video compression techniques, the MV applicable to a particular area of ​​sample data can be predicted from other MVs, e.g., from those related to other areas of sample data that are spatially adjacent to the area being reconstructed and that precede that MV in the decoding order. Doing so can significantly reduce the amount of data required to code the MV, thereby removing redundancy and increasing compression. For example, when coding an input video signal obtained from a camera (known as natural video), MV prediction can work because there is a statistical possibility that areas larger than the area to which a single MV is applicable move in a similar direction, and therefore, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the MV determined for a given area is similar or the same as the MV predicted from the surrounding MVs, and after entropy coding, can be represented with fewer bits than would be used if coding the MV directly. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., a sample stream). In other cases, the MV prediction itself can be lossy, e.g., due to rounding errors when calculating a predictor from several surrounding MVs.

[0020] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H265, “High Efficiency Video Coding”, December 2016). Among the many MV prediction mechanisms proposed by H.265, a technique hereafter called “spatial merge” is described in this specification.

[0021] Referring to Figure 2, a current block (201) has samples that are found by the encoder during the motion search process to be predictable from a previous block of the same size that is spatially shifted. Instead of coding its MV directly, 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 denoted as A0, A1 and B0, B1, B2 (202 to 206, respectively). In H.265, MV prediction can use predictors from the same reference picture that neighboring blocks use. Summary of the Invention

[0022] Aspects of the disclosure provide a method and apparatus for video encoding / decoding. In some examples, the apparatus for video decoding includes a processing circuit. The processing circuit can decode coding information of a block from a coded video bitstream. The coding information can indicate an intra-prediction mode for the block and one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block. The processing circuit can determine whether a secondary transform is disabled for the block based on one or a combination of the transform partitioning information for the block, a size of the block, and a shape of the block. The processing circuit can reconstruct the block based on a determination of whether a secondary transform is disabled for the block.

[0023] In an embodiment, one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes transform partitioning information for the block signaled in the coded video bitstream. The transform partitioning information for the block may indicate a partitioning depth for the block. The processing circuit may partition the block into a plurality of transform blocks. The processing circuit may determine whether a secondary transform is disabled for the block based on the partitioning depth. In an example, the processing circuit determines that the secondary transform is disabled for the block and a secondary transform index is not signaled in response to the partitioning depth being greater than a threshold, where the threshold is 0 or a positive integer. The secondary transform index may indicate a secondary transform kernel to be applied to the block. In an example, the threshold is 0.

[0024] In an embodiment, the one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes the transform partitioning information for the block and the shape of the block signaled in the coded video bitstream. The transform partitioning information may indicate a partitioning depth for the block, and the shape of the block may be a non-square rectangle. The processing circuit may partition the block into a plurality of transform blocks. The processing circuit may determine whether a secondary transform is disabled for the block based on the partitioning depth. In an example, the processing circuit determines that the secondary transform is disabled for the block in response to the partitioning depth being greater than a threshold, the threshold being 0 or a positive integer.

[0025] In an embodiment, the one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes a shape of the block indicated by an aspect ratio of the block. The processing circuitry may determine whether the secondary transform is disabled for the block based on the aspect ratio of the block. In an example, the aspect ratio of the block is a ratio of a first dimension of the block to a second dimension of the block, where the first dimension of the block is greater than or equal to the second dimension. The processing circuitry may determine that the secondary transform is disabled for the block in response to the aspect ratio of the block being greater than a threshold value.

[0026] In an embodiment, the one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes the transform partitioning information and the shape of the block, and the transform partitioning information may indicate a partitioning depth, and the shape of the block is a square. The processing circuit may partition the block into a plurality of transform blocks. The processing circuit may determine whether a secondary transform is disabled for the block based on the partitioning depth. In an example, the processing circuit determines that the secondary transform is disabled for the block in response to the partitioning depth being greater than a threshold value. Here, the threshold value may be 0 or a positive integer.

[0027] In an embodiment, the one or combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes the transform partitioning information for the block and the size of the block. The transform partitioning information may indicate a partitioning depth for the block, and the size of the block may indicate a block width and a block height that are greater than a threshold size. The processing circuit may partition the block into a plurality of transform blocks. The processing circuit may determine whether a secondary transform is disabled for the block based on the partitioning depth for the block. In an example, the processing circuit determines that the secondary transform is disabled for the block in response to the partitioning depth being greater than a threshold. The threshold may be 0 or a positive integer.

[0028] In an embodiment, one of the width W' of the other block and the height H' of the other block is greater than the maximum transform size T. The processing circuitry may divide the other block into a plurality of sub-blocks including the block. The width W of the block may be the minimum of W' and T, and the height H of the block may be the minimum of H' and T. The one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include the transform partitioning information for the block. The transform partitioning information may indicate a partitioning depth for the block. The processing circuitry may determine that the secondary transform is disabled for the block in response to the partitioning depth for the block being greater than a threshold.

[0029] In an embodiment, one of the width W' of the other block and the height H' of the other block is greater than a predefined constant K. The processing circuitry may divide the other block into a plurality of sub-blocks including the block. The width W of the block may be the minimum of W' and K, and the height H of the block may be the minimum of H' and K. The one or combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes a size of the block having W and H. The processing circuitry may determine that a secondary transform is enabled for the block in response to the size of the block being W and H.

[0030] Aspects of the disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer for video decoding, cause the computer to perform a method of video decoding and / or encoding.

[0031] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0032] [Figure 1A] FIG. 2 is a schematic diagram of an example subset of intra-prediction modes. [Figure 1B] FIG. 2 is an illustration of an exemplary intra-prediction direction. [Diagram 2] FIG. 2 is a schematic diagram of a current block and its surrounding spatial merging candidates in one example. [Diagram 3] 1 is a schematic block diagram of a communication system (300) according to an embodiment. [Figure 4] FIG. 4 is a schematic block diagram of a communication system (400) according to an embodiment. [Diagram 5] FIG. 2 is a schematic block diagram of a decoder according to an embodiment; [Figure 6] FIG. 2 is a schematic block diagram of an encoder according to an embodiment; [Figure 7] 4 shows a block diagram of an encoder according to another embodiment. [Figure 8] 4 shows a block diagram of a decoder according to another embodiment; [Figure 9] 1 illustrates an example of a nominal mode for a coding block, according to an embodiment of the disclosure. [Figure 10] 1 illustrates an example of non-directional smooth intra prediction according to aspects of the present disclosure. [Figure 11] 1 illustrates an example of an intra predictor based on recursive filtering in accordance with an embodiment of the disclosure. [Figure 12] 1 illustrates an example of multiple reference lines for a coding block, according to an embodiment of the disclosure. [Figure 13] 4 illustrates an example of a transform block partition for a block according to an embodiment of the disclosure. [Figure 14] 4 illustrates an example of a transform block partition for a block according to an embodiment of the disclosure. [Figure 15] 4 illustrates an example of a linear transformation basis function according to an embodiment of the disclosure. [Figure 16A] 1 illustrates an example dependency of availability of various transform kernels based on transform block size and prediction mode, consistent with a disclosed embodiment. [Figure 16B] 1 illustrates an example transform type selection based on intra-prediction mode, consistent with an embodiment of the disclosure. [Figure 16C] 1 illustrates an example of a general line graph transformation (LGT) characterized by self-loop weights and edge weights, in accordance with a disclosed embodiment. [Figure 16D] 1 illustrates an example Generalized Graph Laplacian (GGL) matrix in accordance with an embodiment of the disclosure. [Figure 17] 17 illustrates an example of a transform coding process (1700) using a 16x64 transform, according to an embodiment of the disclosure. [Figure 18] 18 illustrates an example of a transform coding process (1800) using a 16x48 transform, according to an embodiment of the disclosure. [Figure 19]19 shows a flow chart illustrating a process (1900) according to an embodiment of the disclosure. [Figure 20] FIG. 1 is a schematic diagram of a computer system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to an embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) that are interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) perform a one-way transmission of data. For example, the terminal device (310) may code video data (e.g., a stream of video data captured by the terminal device (310)) for transmission to another terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to recover video pictures, and display the video pictures according to the recovered video data. One-way data transmission may be common, such as in media serving applications.

[0034] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data that may occur, for example, during a video conference. For the bidirectional transmission of data, in the example, each of the terminal devices (330) and (340) may code video data (e.g., a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device in accordance with the recovered video data.

[0035] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be represented as a server, a personal computer, and a smartphone, although the principles of the present disclosure may not be so limited. The embodiments of the present disclosure find use with laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. The network (350) represents any number of networks that convey coded video data between the terminal devices (310), (320), (330), and (340), including, for example, wireline and / or wireless communication networks. The communication network (350) may exchange data in circuit-switched and / or packet-switched channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For the purposes of this discussion, the architecture and topology of the network (350) may be irrelevant to the operation of the present disclosure, unless otherwise described hereinafter.

[0036] 4 illustrates the placement of a video encoder and a video decoder in a streaming environment as an example application of the disclosed subject matter. The disclosed subject matter can be similarly applicable to other video-enabled applications including, for example, video conferencing, digital TV, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0037] The streaming system may include a capture subsystem (413) that may include, for example, a video source (401), e.g., a digital camera, that generates a stream of uncompressed video pictures (402). In an example, the stream of video pictures (402) includes samples taken by the digital camera. The stream of video pictures (402) is represented by a bold line to emphasize its high data volume compared to the encoded video data (404) (or coded video bitstream), which may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), is represented by a thin line to emphasize its lower data volume compared to the stream of video pictures (402), which may be stored in a streaming server (405) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, can access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) can include a video decoder (410), for example in an electronic device (430). The video decoder (410) decodes an incoming copy of the encoded video data (407) and generates an outgoing stream (411) of video pictures that can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (404), (407), and (409) (e.g., a video bitstream) can be encoded according to a particular video coding / compression standard.An example of such a standard is ITU-T Recommendation H.265. In an example, the developing video coding standard is colloquially known as Versatile Video Coding (VVC). The disclosed subject matter may be used in conjunction with VVC.

[0038] It should be noted that electronics 420 and 430 may include other components (not shown). For example, electronics 420 may include a video decoder (not shown), and electronics 430 may similarly include a video encoder (not shown).

[0039] 5 shows a block diagram of a video decoder (510) according to an embodiment of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0040] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510), one coded video sequence at a time, in the same or other embodiments, with the decoding of each coded video sequence being independent of the other coded video sequences. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data. The receiver (531) may receive the encoded video data together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to their respective use entities (not shown). The receiver (531) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (515) may be coupled between the receiver (531) and the entropy decoder / parser (520) (hereafter "parser (520)"). In certain applications, the buffer memory (515) is part of the video decoder (510). In others, it can be external to the video decoder (510) (not shown). In still others, there can be a buffer memory (not shown) external to the video decoder (510), e.g., to combat network jitter, plus another buffer memory (515) within the video decoder (510), e.g., to manipulate playback timing. When the receiver (531) is receiving data from a storage / forwarding device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (515) may be needed, but can be relatively large and advantageously adaptively sized, and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0041] The video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a render device (512) (e.g., a display screen) that is not an essential part of the electronics (530) but may be coupled to the electronics (530) as shown in FIG. 5. The control information for the rendering device may take the form of a Supplemental Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (520) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence may follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, context-dependent or non-context-dependent arithmetic coding, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the group. The subgroups may include a Group of Pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (520) may also extract information from the coded video sequence, such as transform coefficients, quantization parameter values, motion vectors, etc.

[0042] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to generate symbols (521).

[0043] The reconstruction of the symbols (521) can have many different units depending on the type of coded video picture or portion thereof (e.g., inter and intra pictures, inter and intra blocks) and other factors. Which units are included and how may be controlled by subgroup control information parsed by the parser (520) from the coded video sequence. The flow of such subgroup control information between the parser (520) and the following units is not shown for clarity.

[0044] Beyond the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into a number of functional units, which are described below. In an actual implementation operating under commercial constraints, many of these units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is adequate.

[0045] The first unit is a scalar / inverse transform unit (551), which receives the quantized transform coefficients as symbols (521) from the parser (520) along with control information including which transform to use, block size, quantization factor, quantization scaling matrix, etc. The scalar / inverse transform unit (551) can output blocks containing sample values ​​that can be input to an aggregator (555).

[0046] In some cases, the output samples of the scaler / inverse transformer (551) may relate to intra-coded blocks, i.e., blocks that do 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 may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) generates a block of the same size and shape as the block being reconstructed using surrounding already reconstructed information fetched from a current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. The aggregator (555) adds, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transformer unit (551).

[0047] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded and potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, the samples may be added by the aggregator (555) to the output of the scalar / inverse transform unit (551) (in this case referred to as residual samples or residual signals) to generate output sample information. The addresses in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches prediction samples may be controlled by motion vectors available to the motion compensated prediction unit (553), for example in the form of symbols (521), which may have X, Y, and reference picture components. Motion compensation can also include interpolation of sample values ​​fetched from the reference picture memory (557) when sub-sample accurate motion vectors are used, as well as motion vector prediction mechanisms.

[0048] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in a loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to meta-information obtained during decoding of previous portions (in decoding order) of the coded picture or coded video sequence, or even to previously constructed loop filtered sample values.

[0049] The output of the loop filter unit (556) can be a sample stream that can be output to a render device (512) and further stored in a reference picture memory (557) for use in future inter-picture prediction.

[0050] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (520)), the current picture buffer (558) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of a subsequent coded picture.

[0051] The video decoder (510) may perform decoding operations according to a given video compression technique in a standard, such as ITU-T Recommendation H.265. A coded video sequence may conform to a syntax prescribed by the video compression technique or standard in use, in the sense that the coded video sequence conforms to both the syntax of the video compression technique or standard and a profile documented in the video compression technique or standard. In particular, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool available for use under that profile. Also, for compliance, the complexity of the coded video sequence must be within the bounds defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples / second), maximum reference picture size, etc. The limits set by the level may in some cases be further limited through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the coded video sequence.

[0052] In an embodiment, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may take the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0053] 6 shows a block diagram of a video encoder (603) according to an embodiment of the present disclosure. The video encoder (603) is included in an electronic device (620). The electronic device (620) includes a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the example video encoder (403) of FIG.

[0054] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (560) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In other examples, the video source (601) is part of the electronic device (620).

[0055] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that can be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.), any color space (e.g., BT.601 YCrCB, RGB, etc.), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as multiple individual pictures that, when viewed in sequence, impart motion. The picture itself may be organized as a spatial array of pixels, each of which may have one or more samples depending on the sampling structure, color space, etc., in use. Those skilled in the art can easily understand the relationship between pixels and samples. The remainder of this specification focuses on samples.

[0056] According to an embodiment, the video encoder (603) may code and compress pictures of a source video sequence into a coded video sequence (643) in real-time or under any other time constraints required by the application. Imposing an appropriate coding rate is one function of the controller (650). In some embodiments, the controller (650) controls and is operatively coupled to other functional units as described below. Couplings are not shown for clarity. Parameters set by the controller (650) may include parameters related to rate control (picture skip, quantizer, lambda value for rate-distortion optimization techniques, etc.), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured with other appropriate functions related to the video encoder (603) optimized for a particular system design.

[0057] In some embodiments, the video encoder (603) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to generate sample data in a similar manner that a (remote) decoder would also generate (given that any compression between the symbols and the coded video stream is lossless in the video compression techniques contemplated in the disclosed subject matter). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces bit-exact results independent of the location of the decoder (local or remote), the content in the reference picture memory (634) is also bit-perfect between the local and remote encoders. That is, the prediction part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder will "see" when using the prediction during decoding. This basic principle of reference picture synchronicity (and the resulting drift when synchronicity cannot be maintained, e.g., due to channel errors) is also used in several related technologies.

[0058] The operation of the "local" decoder (633) can be the same as a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also momentarily to Figure 5, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) can be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633).

[0059] An observation that can be made at this point is that any decoder technique, except for parsing / entropy decoding, that is present in the decoder must necessarily be present, in substantially the same functional form, in the corresponding encoder. For this reason, the disclosed subject matter focuses on the operation of the decoder. A description of the encoder techniques may be omitted, in that they are the inverse of the decoder techniques that are described generically. Only to certain extents are more detailed descriptions required, and are given below.

[0060] In operation, in some examples, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from the video sequence designated as "reference pictures." In this manner, the coding engine (632) codes differences between pixel blocks of the reference pictures and pixel blocks of the input picture that may be selected as predictive references for the input picture.

[0061] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols generated by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may usually be a copy of the source video sequence with some errors. The local video decoder (633) may reproduce the decoding process that may be performed by the video decoder on the reference pictures, causing the reconstructed reference pictures to be stored in the reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with the reconstructed reference pictures that would be obtained by the far-end video decoder (without transmission errors).

[0062] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may look for certain metadata, such as reference picture motion vectors, block shapes, or sample data (as candidate reference pixel blocks) from the reference picture memory (634) that may be suitable prediction references for the new picture. The predictor (635) may operate on a sample block-by-pixel block basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have prediction references derived from multiple reference pictures stored in the reference picture memory (634).

[0063] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0064] The output of all the above functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced 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.

[0065] The transmitter (640) may buffer the coded video sequence produced by the entropy coder (645) to prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0066] A controller (650) may manage the operation of the video encoder (603). During coding, the controller (650) may assign a particular coded picture type to each coded picture, which may affect the coding technique that may be applied to each picture. For example, pictures may often be assigned as one of the following picture types:

[0067] An Intra Picture (I-picture) may be a picture that can be coded and decoded without using any other picture in a sequence as a source of prediction. Some video codecs allow various types of Intra pictures, including, for example, Independent Decoder Refresh (IDR) pictures. Those skilled in the art are aware of such variations of I-pictures and their respective applications and characteristics.

[0068] A Predictive Picture (P-picture) may be a picture that can be coded and decoded by intra-prediction or inter-prediction using at most one motion vector and reference index to predict sample values ​​of each block.

[0069] A Bi-directionally Predictive Picture (B-picture) may be a picture that can be coded and decoded by intra- or inter-prediction using at most two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple-predictive picture(s) can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0070] A source picture may generally be spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples, respectively) and coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to each picture of the block. For example, blocks of I pictures may be non-predictively coded or they may be predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of P pictures may be predictively coded by spatial prediction with reference to one previously coded reference picture or by temporal prediction. Blocks of B pictures may be predictively coded by spatial prediction with reference to one or two previously coded reference pictures or by temporal prediction.

[0071] The video encoder (603) may perform coding operations according to a given video coding technique or standard, such as ITU-T Recommendation H.265. During its operation, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax defined by the video coding technique or standard being used.

[0072] In an embodiment, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other types of redundant data such as redundant pictures and slices, SEI messages or VUI parameter set fragments, etc.

[0073] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits correlation (temporal or other) between pictures. In an example, a particular picture being encoded / decoded, called the current picture, is partitioned into blocks. If a block in the current picture is similar to a reference block in a reference picture that was previously coded in the video and is still buffered, then that block in the current picture may be coded by a vector called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0074] In some embodiments, bi-prediction techniques may be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, e.g., a first reference picture and a second reference picture, both preceding in decoding order (but may be past and future, respectively, in display order) the current picture in the video. A block in the current picture may be coded with a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. The block is predictable by a combination of the first and second reference blocks.

[0075] Furthermore, merge mode techniques can be used in inter-picture prediction to improve coding efficiency.

[0076] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed in units of blocks. For example, according to the HEVC standard, pictures in a sequence of video pictures are partitioned into coding tree units (CTUs) for compression, and the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), one luma CTB and two chroma CTBs. Each CTU may be recursively quad-tree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels can be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for the CU, such as an inter prediction type or an intra prediction type. A CU is divided into one or more Prediction Units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In an embodiment, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values ​​(e.g., luma values), such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0077] 7 shows a diagram of a video encoder (703) according to another embodiment of the disclosure. The video encoder (703) is configured to receive a processed block of sample values ​​(e.g., a predictive block) in a current video picture included in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. In an example, the video encoder (703) is used in place of the video encoder (403) of the example of FIG. 4.

[0078] In an HEVC example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8x8 samples. The video encoder (703) determines whether the processing block is best coded in intra-mode, inter-mode, or bi-predictive mode, for example using rate-distortion optimization. If the processing block is to be coded in intra-mode, the video encoder (703) may use intra-prediction techniques to encode the processing block into a coded picture, and if the processing block is to be coded in inter-mode or bi-predictive mode, the video encoder (703) may use inter-prediction or bi-prediction techniques, respectively, to encode the processing block into a coded picture. In certain video coding techniques, the merge mode can be an inter-picture prediction sub-mode in which motion vectors are derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In certain other video coding techniques, there may be motion vector components applicable to the current block. In examples, the video encoder (703) includes other components, such as a mode decision module (not shown) that determines the mode of the processing blocks.

[0079] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725), coupled as shown in FIG.

[0080] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture), generate inter-prediction information (e.g., a description of redundant information according to an inter-encoding technique, motion vectors, 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 that has been decoded based on the encoded video information.

[0081] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), in some cases compare the block to previously coded blocks in the same picture, and generate transformed quantized coefficients and, in some cases, intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (722) also calculates an intra prediction result (e.g., a prediction block) based on the intra prediction information and a reference block in the same picture.

[0082] The generic controller (721) is configured to determine generic control data and control other components of the video encoder (703) based on the generic control data. In an example, the generic controller (721) determines the mode of the block and provides a control signal to the switch (726) based on the mode. For example, if the mode is an intra mode, the generic controller (721) controls the switch (726) to select the intra mode result for use by the residual calculator (723), and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream. If the mode is an inter mode, the generic controller (721) controls the switch (726) to select the inter prediction result for use by the residual calculator (723), and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0083] The residual calculator (723) is configured to calculate a difference (residual data) between the received block and a prediction result selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) is configured to operate on the residual data to encode the residual data to generate transform coefficients. In an example, the residual encoder (724) is configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are suitably processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

[0084] The entropy encoder (725) is configured to format a bitstream to include the encoded block. The entropy encoder (725) is configured to include various information in accordance with an appropriate standard, such as the HEVC standard. In an example, the entropy encoder (725) is configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other appropriate information in the bitstream. It should be noted that when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode in accordance with the disclosed subject matter, the residual information is not present.

[0085] 8 shows a diagram of a video decoder (810) according to another embodiment of the disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In an example, the video decoder (810) is used in place of the video decoder (410) of the example of FIG. 4.

[0086] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter decoder (880), a residual decoder (873), a reconstruction module (874), and an intra decoder (872), coupled as shown in FIG.

[0087] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols representing syntax elements from which the coded picture is constructed. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra- or bi-prediction mode in merge or other submodes), the specific samples or metadata used for prediction by the intra decoder (872) or the inter decoder (880), respectively, residual information in the form of, for example, quantized transform coefficients, etc. In an example, if the prediction mode is an inter or bi-prediction mode, the inter prediction information is provided to the inter decoder (880), and if the prediction type is an intra prediction type, the intra prediction information is provided to the intra decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0088] The inter decoder (880) is configured to receive the inter prediction information and to generate inter prediction results based on the inter prediction information.

[0089] The intra decoder (872) is configured to receive the intra prediction information and to generate a prediction result based on the intra prediction information.

[0090] The residual decoder (873) is configured to perform inverse quantization to retrieve inverse quantized transform coefficients, and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also require certain control information (to include quantization parameters (QPs)), which may be provided by the entropy decoder (871) (datapath not shown since this is only low volume control information).

[0091] The reconstruction module (874) is configured to combine the residual output by the residual decoder (873) and the prediction result (possibly output by an inter- or intra-prediction module) in the spatial domain to form a reconstructed block. The reconstructed block may be part of a reconstructed picture, which in turn may be part of a reconstructed video. Note that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0092] It should be noted that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technology. In some embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In other embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0093] Video coding techniques related to efficient application of secondary transforms, such as efficient application of a set of secondary transforms, are disclosed. The efficient application of secondary transforms can be applicable in any suitable video coding format or standard. The video coding format can include an open video coding format designed for video transmission over the Internet, such as AOMedia Video 1 (AV1) or a next-generation AOMedia Video format beyond AV1. The video coding standard can include the High Efficiency Video Coding (HEVC) standard, next-generation video coding beyond HEVC (e.g., Versatile Video Coding (VVC)), and the like.

[0094] Various intra prediction modes may be used in intra prediction, e.g., in AV1, VVC, and / or others. In an embodiment, as in AV1, directional intra prediction is used. In an example, as in the open video coding format VP9, ​​eight directional modes are used, each corresponding to eight angles from 45° to 207°. To exploit more spatial redundancy in the directional texture, for example, in AV1, the directional modes (also called directional intra modes, directional intra prediction modes, angle modes) may be extended to a set of angles with finer granularity, as shown in FIG. 9.

[0095] FIG. 9 illustrates an example of nominal modes for a coding block (CB) (910) according to an embodiment of the disclosure. A particular angle (called a nominal angle) may correspond to a nominal mode. In the example, eight nominal angles (or nominal intra angles) (901)-(908) correspond to eight nominal modes (e.g., V_RED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED), respectively. The eight nominal angles (901)-(908) and the eight nominal modes may be referred to as V_RED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED, respectively. Further, since each nominal angle can correspond to multiple finer angles, 56 angles (or predicted angles) or 56 directional modes (or angular modes, directional intra prediction modes) may be used, for example, in AV1. Each predicted angle may be indicated by a nominal angle and an angular offset (or angular delta). The angular offset may be obtained by multiplying an offset integer I (e.g., −3, −2, −1, 0, 1, 2, or 3) by a step size (e.g., 3°). In an example, the predicted angle is equal to the sum of the nominal angle and the angular offset. In an example, as in AV1, the nominal modes (e.g., eight nominal modes (901)-(908)) may be signaled along with certain non-angular smooth modes (e.g., five non-angular smooth modes, such as DC mode, PAETH mode, SMOOTH mode, vertical SMOOTH mode, and horizontal SMOOTH mode, described below). Then, if the current prediction mode is a directional mode (or an angular mode), an index may be further signaled to indicate the angle offset (eg, offset integer I) corresponding to the nominal angle.In an example, to implement directional prediction modes in a generic way, the 56 directional modes, such as those used in AV1, are implemented with a unified directional predictor that can project each pixel to a reference sub-pixel location and interpolate the reference pixels by a 2-tap bilinear filter.

[0096] A non-directional smooth intra predictor (also referred to as a non-directional smooth intra prediction mode, a non-directional smooth mode, or a non-angular smooth mode) may be used in intra prediction for blocks such as CB. In some examples (e.g., in AV1), the five non-directional smooth intra prediction modes include DC mode or DC predictor (e.g., DC), PAETH mode or PAETH predictor (e.g., PAETH), SMOOTH mode or SMOOTH predictor (e.g., SMOOTH), vertical SMOOTH mode (referred to as SMOOTH_V mode, SMOOTH_V predictor, or SMOOTH_V), and horizontal SMOOTH mode (referred to as SMOOTH_H mode, SMOOTH_H predictor, or SMOOTH_H).

[0097] 10 illustrates examples of non-directional smooth intra-prediction modes (e.g., DC mode, PAETH mode, SMOOTH mode, SMOOTH_V mode, and SMOOTH_H mode) according to an embodiment of the disclosure. To predict a sample (1001) in CB (1000) based on a DC predictor, an average of a first value of a left neighboring sample (1012) and a second value of an above neighboring sample (or top neighboring sample) (1011) may be used as a predictor.

[0098] To predict sample (1001) based on the PAETH predictor, a first value of the left adjacent sample (1012), a second value of the above adjacent sample (1011), and a third value of the above-left adjacent sample (1013) may be obtained. Then, using Equation 1, a reference value is found: Reference value = 1st value + 2nd value - 3rd value (Formula 1)

[0099] One of the first value, the second value, and the third value that is closest to the reference value may be set as a predictor for the sample (1001).

[0100] The SMOOTH_V, SMOOTH_H, and SMOOTH modes can predict CB (1000) using quadratic interpolation in the vertical direction, horizontal direction, and average of the vertical and horizontal directions, respectively. To predict sample (1001) based on the SMOOTH predictor, an average (e.g., a weighted combination) of the first value, the second value, the value of the right sample (1014), and the value of the bottom sample (1016) can be used. In various examples, the right sample (1014) and the bottom sample (1016) are not reconstructed, and thus the value of the top right neighboring sample (1015) and the value of the bottom left neighboring sample (1017) can replace the values ​​of the right sample (1014) and the bottom sample (1016), respectively. Thus, an average (e.g., a weighted combination) of the first value, the second value, the value of the upper right neighboring sample (1015), and the value of the lower left neighboring sample (1017) may be used as the SMOOTH predictor. To predict sample (1001) based on the SMOOTH_V predictor, an average (e.g., a weighted combination) of the second value of the upper right neighboring sample (1011) and the value of the lower left neighboring sample (1017) may be used. To predict sample (1001) based on the SMOOTH_H predictor, an average (e.g., a weighted combination) of the first value of the left neighboring sample (1012) and the value of the upper right neighboring sample (1015) may be used.

[0101] FIG. 11 illustrates an example of an intra predictor based on recursive filtering (also referred to as a filter intra mode or recursive filtering mode) according to an embodiment of the disclosure. To capture the decaying spatial correlation with the reference on the edge, the filter intra mode may be used for a block such as CB(1100). In the example, CB(1100) is a luma block. The luma block (1100) may be divided into multiple patches (e.g., eight 4×2 patches B0-B7). Each of the patches B0-B7 may have multiple neighboring samples. For example, patch B0 has seven neighboring samples (or seven neighbors) R00-R06, including four top neighboring samples R01-R04, two left neighboring samples R05-R06, and a top-left neighboring sample R00. Similarly, patch B7 has four above adjacent samples R71 to R74, two left adjacent samples R75 to R76, and seven adjacent samples R70 to R76, including the above-left adjacent sample R70.

[0102] In some examples, multiple (e.g., five) filter intra modes (or multiple recursive filtering modes) are predefined, for example, for AV1. Each filter intra mode may be represented by a set of eight 7-tap filters that reflect the correlation between a sample (or pixel) in a corresponding 4×2 patch (e.g., B0) and seven neighbors (e.g., R00-R06) adjacent to the 4×2 patch B0. The weighting coefficients of the 7-tap filters may be position-dependent. For each of the patches B0-B7, the seven neighbors (e.g., R00-R06 for B0 and R70-R76 for B7) may be used to predict samples in the corresponding patch. In an example, the neighbors R00-R06 are used to predict samples in patch B0. In an example, the neighbors R70-R76 are used to predict samples in patch B7. For a particular patch in CB (1100), such as patch B0, all seven neighbors (e.g., R00-R06) have already been reconstructed. For other patches in CB (1100), at least one of the seven neighbors has not been reconstructed, and therefore the predicted value of the neighbor (or the predicted sample of the neighbor) may be used as a reference. For example, the seven neighbors R70-R76 of patch B7 have not been reconstructed, and therefore the predicted sample of the neighbor may be used.

[0103] Chroma samples may be predicted from luma samples. In an embodiment, a Chroma from Luma mode (e.g., CfL mode, CfL predictor) may model a chroma sample (or pixel) as a linear function of the concurrent reconstructed luma sample (or pixel). For example, the CfL prediction may be expressed using Equation 2 as follows: CfL(α)=αL A +D (Formula 2) Here, L Arepresents the AC contribution of the luma component, α represents a scaling parameter of the linear model, and D represents the DC contribution of the chroma components. In the example, the reconstructed luma pixels are subsampled based on the chroma resolution and the average is calculated based on the AC contribution (e.g., L A ) are subtracted to form α. Instead of requiring the decoder to calculate the scaling parameter α to approximate the chroma AC components from the AC contributions, in some examples, as in AV1, the CfL mode determines the scaling parameter α based on the original chroma pixels and signals the scaling parameter α in the bitstream, thus reducing decoder complexity and resulting in more accurate prediction. The DC contributions of the chroma components may be calculated using an intra DC mode, which is sufficient for most chroma content and may have a mature and fast implementation.

[0104] Multi-line intra prediction can use more reference lines for intra prediction. A reference line can include multiple samples in a picture. In an example, a reference line includes samples in a row and samples in a column. In an example, an encoder can determine and signal a reference line used to generate an intra predictor. An index indicating a reference line (also called a reference line index) can be signaled before an intra prediction mode. In an example, only MPM is allowed if a non-zero reference line index is signaled. FIG. 12 shows an example of four reference lines for CB (1210). Referring to FIG. 12, a reference line can include up to six segments, e.g., segments A-F and a top-left reference sample. For example, reference line 0 includes segments B and E and a top-left reference sample. For example, reference line 3 includes segments A-F and a top-left reference sample. Segments A and F can be padded with the nearest samples from segments B and E, respectively. In some examples, as in HEVC, only one reference line (e.g., reference line 0 adjacent to CB(120)) is used for intra prediction. In some examples, as in VVC, multiple reference lines (e.g., reference lines 0, 1, and 3) are used for intra prediction.

[0105] In general, a block may be predicted using one or any suitable combination of a variety of intra-prediction modes, such as those described above with reference to FIGS.

[0106] Transform block partitions (also called transform partitions, transform unit partitions) may be implemented to partition blocks into multiple transform units. Figures 13-14 show example transform block partitions according to disclosed embodiments. In some examples, such as in AV1, both intra-coded and inter-coded blocks may be further partitioned into multiple transform units with a partitioning depth of up to multiple levels (e.g., two levels).

[0107] For intra-coded blocks, transform partitioning may be performed such that transform blocks associated with the intra-coded block have the same size, and the transform blocks may be coded in raster scan order. With reference to FIG. 13, transform block partitioning may be performed on a block (e.g., an intra-coded block) (1300). The block (1300) may be partitioned into transform units, such as four transform units (e.g., TBs) (1301)-(1304), with a partitioning depth of 1. The four transform units (e.g., TBs) (1301)-(1304) may have the same size, and may be coded in raster scan order (1310) from transform unit (1301) to transform unit (1304). In an example, the four transform units (TBs) (1301)-(1304) are transformed separately, for example, using different transform kernels. In some examples, each of the four transform units (e.g., TBs) (1301)-(1304) is further partitioned into four transform units. For example, transform unit (1301) is partitioned into transform units (1321), (1322), (1325), and (1326), transform unit (1302) is partitioned into transform units (1323), (1324), (1327), and (1328), transform unit (1303) is partitioned into transform units (1329), (1330), (1333), and (1334), and transform unit (1304) is partitioned into transform units (1331), (1332), (1335), and (1336). The partitioning depth is 2. The transform units (eg, TBs) (1321) to (1336) may have the same size and may be coded in raster scan order (1320) from transform unit (1321) to transform unit (1336).

[0108] For inter-coded blocks, transform partitions may be recursively partitioned with a partitioning depth of up to multiple levels (e.g., two levels). Transform partitions may support any suitable transform unit size and shape. Transform unit shapes may include squares and non-squares (e.g., non-square rectangles) having any suitable aspect ratio. Transform unit sizes may range from 4×4 to 64×64. Transform unit aspect ratios (e.g., ratio of transform unit width to transform unit height) may be 1:1 (square), 1:2, 2:1, 1:4, 4:1, etc. Transform partitions may support 1:1 (square), 1:2, 2:1, 1:4, and / or 4:1 transform unit sizes ranging from 4×4 to 64×64. Referring to FIG. 14, transform block partitions may be performed recursively for blocks (e.g., inter-coded blocks). For example, a block 1400 is partitioned into transform units 1401 through 1407. The transform units (e.g., TBs) 1401 through 1407 may have different sizes and may be coded in a raster scan order 1410 from transform unit 1401 through transform unit 1407. In the example, the partitioning depth of transform units 1401, 1406, and 1407 is 1, and the partitioning depth of transform units 1402 through 1405 is 2.

[0109] In an example, if a coding block is smaller than or equal to 64×64, the transform partition may only be applied to the luma component. In an example, a coding block refers to a CTB.

[0110] If the coding block width W or the coding block height H is greater than 64, the coding block may be implicitly divided into multiple TBs. In this case, the coding block is a luma coding block. The width of one of the multiple TBs may be the minimum of W and 64, and the height of one of the multiple TBs may be the minimum of H and 64.

[0111] If the coding block width W or the coding block height H is greater than 64, the coding block may be implicitly divided into multiple TBs. In this case, the coding block is a chroma coding block. The width of one of the multiple TBs may be the minimum of W and 32, and the height of one of the multiple TBs may be the minimum of H and 32.

[0112] Embodiments of primary transforms, such as those used in AOMedia Video 1 (AV1), are described below. To support extended coding block partitions as described in the disclosure, multiple transform sizes (e.g., ranging from 4-point to 64-point per dimension) and transform shapes (e.g., square, rectangle with width to height ratio of 2:1, 1:2, 4:1, or 1:4) can be used, as in AV1.

[0113] The 2D transform process may use a hybrid transform kernel that may include different 1D transforms for each dimension of the coded residual block. The primary 1D transform may include (a) 4-point, 8-point, 16-point, 32-point, 64-point DCT-2, (b) 4-point, 8-point, 16-point Asymmetric DST (ADST) (e.g., DST-4, DST-7) and corresponding flipped versions (e.g., a flipped version of ADST, i.e., FlipADST, may apply ADST in reverse order), and / or (c) 4-point, 8-point, 16-point, 32-point identity transform (IDTX). Figure 15 illustrates examples of primary transform basis functions according to disclosed embodiments. The primary transform basis functions in the example of Figure 15 include basis functions of DCT-2 and asymmetric DST (DST-4 and DST-7) with N-point input. The linear transformation basis functions shown in FIG. 15 may be used in AV1.

[0114] The availability of hybrid transform kernels may depend on transform block size and prediction mode. Figure 16A shows an example dependency of the availability of various transform kernels (e.g., transform types shown in the first column and described in the second column) based on transform block size (e.g., sizes shown in the third column) and prediction mode (e.g., intra prediction and inter prediction shown in the third column). Exemplary hybrid transform kernels and their availability based on prediction mode and transform block size may be used in AV1. With reference to Figure 16, the symbols "→" and "↓" represent the horizontal dimension (also called horizontal direction) and the vertical dimension (also called vertical direction), respectively. The check mark and the symbol "x" represent the availability of the transform kernel for the corresponding block size and prediction mode. For example, the check mark represents that the transform kernel is available, and the symbol "x" represents that the transform kernel is not available.

[0115] In the example, the transform type (1610) is represented by ADST_DCT, as shown in the first column of Figure 16A. The transform type (1610) includes ADST in the vertical direction and DST in the horizontal direction, as shown in the second column of Figure 16A. According to the third column of Figure 16A, the transform type (1610) is available for intra prediction and inter prediction when the block size is less than or equal to 16x16 (e.g., 16x16 samples, 16x16 luma samples).

[0116] In the example, the transform type (1620) is represented by V_ADST, as shown in the first column of FIG. 16A. The transform type (1620) includes ADST in the vertical direction and IDTX (i.e., identity matrix) in the horizontal direction, as shown in the second column of FIG. 16A. Thus, the transform type (1620) (e.g., V_ADST) is performed in the vertical direction and not in the horizontal direction. According to the third column of FIG. 16A, the transform type (1620) is not available for intra prediction regardless of the block size. The transform type (16220) is available for inter prediction when the block size is smaller than 16×16 (e.g., 16×16 samples, 16×16 luma samples).

[0117] In an example, Figure 16A is applicable to the luma component. For the chroma components, the transform type (or transform kernel) selection may be performed implicitly. In an example, for intra-prediction residuals, the transform type may be selected according to the intra-prediction mode, as shown in Figure 16B. In an example, the transform type selection shown in Figure 16B is applicable to the chroma components. For inter-prediction residuals, the transform type may be selected according to the transform type selection of the co-located luma block. Thus, in an example, the transform type for the chroma components is not signaled in the bitstream.

[0118] Line Graph Transforms (LGT) may be used in transforms such as linear transforms, for example in AOMedia Video 2 (AV2). An 8-bit / 10-bit transform core may be used in AV2. In examples, LGT includes various DCTs, Discrete Sine Transforms (DSTs), as described below. LGTs may include 32-point and 64-point one-dimensional (1D) DSTs.

[0119] A graph is a general mathematical structure that contains a set of vertices and edges that can be used to model affinity relationships between objects of interest. A weighted graph, in which a set of weights is assigned to the edges and, optionally, to the vertices, can provide a sparse representation for robust modeling of signals / data. LGT can improve coding efficiency by providing better adaptation for diverse block statistics. A separable LGT can be designed and optimized by learning a line graph from the data to model the row- and column-wise statistics underlying the block residual signal, and the associated Generalized Graph Laplacian (GGL) matrix can be used to derive the LGT.

[0120] FIG. 16C illustrates a self-loop weight (e.g., v c1 , v c2 ) and edge weight w c Given a weighted graph G(W,V), the GGL matrix can be defined as follows: L c =D-W+V (Formula 3) where W is the non-negative edge weight w c , D can be a diagonal order matrix, and V can be the self-loop weights v c1 and v c2 FIG. 16D shows the matrix L c Here is an example:

[0121] LGT is the GGL matrix L as follows: c can be derived by eigenvalue decomposition of: L c =UΦU T (Formula 4) Here, the columns of the orthogonal matrix U may be basis vectors of the LGT, and Φ may be a diagonal eigenvalue matrix.

[0122] In various examples, a particular DCT and DST (e.g., DCT-2, DCT-8, and DST-7) is a subset of the set of LGTs obtained from a particular form of GGL. c1 Set to 0 (e.g., v c1 =0). DST-7 can be derived by c1 W c (e.g., v c1 =w c ) DCT-8 can be derived by v c2 W c (e.g., v c2 =w c ) DST-4 can be derived by v c1 2w c (e.g., v c1 =2w c ) DCT-4 can be derived by v c2 2w c (e.g., v c2 =2w c ) can be derived by

[0123] In some examples, as in AV2, LGT may be implemented as a matrix multiplication. A 4-point (4p) LGT core c In v c1 2w c The 4p LGT core is a DST-4 since it can be derived by setting c In v c1 1.5w cIn the example, an LGT core, such as a 16-point (16p) LGT core, a 32-point (32p) LGT core, or a 64-point (64p) LGT core, can be derived by setting v c1 W c It seems to be and v c2 can be derived by setting to be 0, allowing the LGT core to become a DST-7w.

[0124] A transform, such as a linear transform, a quadratic transform, may be applied to a block, such as CB. In an example, the transform includes a combination of a linear transform and a quadratic transform. The transform includes a non-separable transform, a separable transform, or a combination of a non-separable transform and a separable transform.

[0125] A secondary transform is performed, as in VVC. In some examples, as in VVC, a Low-Frequency Non-Separable Transform (LFNST), also known as a Reduced Secondary Transform (RST), may be applied between the forward primary transform and quantization at the encoder side, and between the inverse quantization and the inverse primary transform at the decoder side, as shown in Figures 17 and 18, to further decorrelate the primary transform coefficients.

[0126] The application of a non-separable transform that may be used in LFNST is described below (shown in Equation 5) using a 4×4 input block (or input matrix) as an example. To apply a 4×4 non-separable transform (e.g., LFNST), a 4×4 input block X is divided into two parts, X=1, X=1, X=2, X=3, X=4 ... (outside 1) This can be represented by JPEG0007670799000001.jpg119:

number

[0127] The non-separable transform can be computed as follows:

number

[0128] A non-separable quadratic transform may be applied to a block (e.g., CB). In some examples, as in VVC, LFNST is applied between the forward linear transform and quantization (e.g., at the encoder side) and between the inverse quantization and the inverse linear transform, as shown in Figures 17 and 8.

[0129] 17 and 18 show examples of two transform coding processes (1700) and (1800) using a 16×64 transform (or a 64×16 transform, depending on whether the transform is a forward or inverse quadratic transform) and a 16×48 transform (or a 48×16 transform, depending on whether the transform is a forward or inverse quadratic transform), respectively. With reference to FIG. 17, in the process (1700), on the encoder side, a forward linear transform (1710) may first be performed on a block (e.g., a residual block) to obtain a coefficient block (1713). Then, a forward quadratic transform (or forward LFNST) (1712) may be applied to the coefficient block (1713). In the forward quadratic transform (1712), the 64 coefficients of the 4×4 sub-block A through D in the top left corner of the coefficient block (1713) may be represented by a 64-length vector, which may be multiplied by a 64×16 (i.e., 64 width and 16 height) transform matrix, resulting in a 16-length vector. The elements of the 16-length vector are backfilled into the top left 4×4 sub-block of the coefficient block (1713). The coefficients of sub-blocks B through D may be zero. The coefficients obtained after the forward quadratic transform (1712) are then quantized in a quantization step (1714) and entropy coded to generate coded bits in the bitstream (1716).

[0130] The coded bits are received at the decoder side and entropy decoded, possibly followed by an inverse quantization step (1724), to generate a coefficient block (1723). An inverse quadratic transform (or inverse LFNST) (1722), such as an inverse RST8×8, may be performed, for example, to obtain 64 coefficients from the 16 coefficients in the top-left 4×4 sub-block E. The 64 coefficients may be backfilled into 4×4 sub-blocks E-H. The coefficients in the coefficient block (1723) after the inverse quadratic transform may then be processed by an inverse linear transform (1720) to obtain a restored residual block.

[0131] The process (1800) of the example in FIG. 18 is similar to the process (1700), except for the fewer number of coefficients (i.e., 48) processed during the forward second-order transform (1712). Specifically, the 48 coefficients within sub-blocks A to C are processed by a smaller transform matrix of size 48×16. Using a smaller 48×16 transform matrix can reduce the memory size for storing the transform matrix and the number of calculations (e.g., multiplications, additions, subtractions, and / or similar calculations), thus reducing the computational complexity.

[0132] In an example, a 4×4 non-separable transform (e.g., 4×4 LFNST) or an 8×8 non-separable transform (e.g., 8×8 LFNST) is applied according to the block size of a block (e.g., CB). The block size of the block can include the width, height, etc. For example, the 4×4 LFNST is applied to a block where the minimum of the width and height is less than a threshold, e.g., less than 8 (e.g., min(width, height) < 8). For example, the 8×8 LFNST is applied to a block where the minimum of the width and height is greater than a threshold, e.g., greater than 4 (e.g., min(width, height) > 4).

[0133] Since the non-separable transform (e.g., LFNST) can be based on a direct matrix multiplication approach, it can be implemented in a single pass without repetition. To reduce the non-separable transform matrix dimension and minimize the memory space for storing the computational complexity and transform coefficients, a reduced non-separable transform method (or RST) can be used in the LFNST. Thus, in the reduced non-separable transform, an N (e.g., N is 64 for an 8×8 non-separable second-order transform (Non-Separable Secondary Transform, NSST)) -dimensional vector can be mapped to an R -dimensional vector in a different space. Here, N / R (R < N) is the reduction coefficient. Thus, instead of an N×N matrix, the RST matrix is an R×N matrix as shown in Equation 7:

Equation

[0134] In Equation 7, the R rows of the R×N transformation matrix are the R bases of the N-dimensional space. The inverse transformation matrix is ​​the R-th transformation matrix used in the forward transformation (e.g., T R×N ) for the 8×8 LFNST. For the 8×8 LFNST, a reduction factor of 4 may be applied and the 64×64 direct matrix used in the 8×8 non-separable transform may be reduced to a 16×64 direct matrix, as shown in FIG. 17. Alternatively, a reduction factor greater than 4 may be applied and the 64×64 direct matrix used in the 8×8 non-separable transform may be reduced to a 16×48 direct matrix, as shown in FIG. 18. Thus, a 48×16 inverse RST matrix may be used at the decoder side to generate the core (first order) transform coefficients in the 8×8 top-left region.

[0135] 18, if a 16×48 matrix is ​​applied in place of the 16×64 matrix in the same transform set configuration, the input to the 16×48 matrix includes 48 input data from three 4×4 blocks A, B, and C in the upper left 8×8 block, excluding the lower right 4×4 block D. Due to the dimensionality reduction, the memory usage for storing the LFNST matrix can be reduced, for example, from 10 KB to 8 KB, with minimal performance degradation.

[0136] To reduce complexity, LFNST may be restricted to be applicable when coefficients outside the first coefficient subgroup are not significant. In an example, LFNST may be restricted to be applicable only when all coefficients outside the first coefficient subgroup are not significant. With reference to Figures 17 and 18, the first coefficient subgroup corresponds to the top-left block E, so the coefficients outside block E are not significant.

[0137] In an example, primary-only transform coefficients are not significant (e.g., zero) when LFNST is applied. In an example, all primary-only transform coefficients are zero when LFNST is applied. Primary-only transform coefficients can refer to transform coefficients obtained from a primary transform without a secondary transform. Thus, the signaling of the LFNST index can be conditional on the last significant position, so that extra coefficient scans in LFNST are avoided. In some examples, extra coefficient scans are used to check for significant transform coefficients at specific positions. In an example, for example, for pixel-by-pixel multiplication, the worst-case processing of LFNST limits non-separable transforms of 4×4 and 8×8 blocks to 8×16 and 8×47 transforms, respectively. In the above cases, the last significant scan position is less than 8 when LFNST is applied. For other sizes, the last significant scan position is less than 16 when LFNST is applied. For 4×N and N×4 CBs, where N is greater than 8, the restriction can imply that LFNST is applied to the top-left 4×4 region of the CB. In an example, the restriction implies that LFNST is applied only once to the top-left 4×4 region of the CB. In an example, all first-order only coefficients are insignificant (e.g., zero) when LFNST is applied, and the number of operations for the first-order transform is reduced. From an encoder's perspective, quantization of transform coefficients can be significantly simplified if the LFNST transform is tested. Rate-distortion optimized quantization can be performed on at most the first 16 coefficients, e.g., in scan order, and the remaining coefficients can be set to zero.

[0138] The LFNST transforms (e.g., transform kernels, transform cores, or transform matrices) may be selected as described below. In embodiments, multiple transform sets may be available, and one or more non-separable transform matrices (or kernels) may be included in each of the multiple transform sets in the LFNST. In accordance with aspects of the disclosure, a transform set may be selected from multiple transform sets, and a non-separable transform matrix may be selected from one or more non-separable transform matrices in a transform set.

[0139] Table 1 shows an example mapping from intra-prediction modes to multiple transform sets according to an embodiment of the disclosure. The mapping indicates the relationship between the intra-prediction modes and the multiple transform sets. The relationship as shown in Table 1 may be predefined and stored in the encoder and the decoder: [Table 1]

[0140] Referring to Table 1, the plurality of transform sets includes four transform sets, for example, transform sets 0 to 3, which are represented by transform set indexes (e.g., Tr.set index) from 0 to 3, respectively. The index (e.g., IntraPredMode) can indicate an intra prediction mode, and a transform set index can be obtained based on the index and Table 1. Thus, the transform set can be determined based on the intra prediction mode. In an example, when one of three Cross Component Linear Model (CCLM) modes (e.g., INTRA_LT_CCLM, INTRA_T_CCLM, or INTRA_L_CCLM) is used for a CB (e.g., 81<=IntraPredMode<=83), transform set 0 is selected for that CB.

[0141] As described above, each transform set may include one or more non-separable transform matrices. One of the one or more non-separable transform matrices may be selected, for example, by an explicitly signaled LFNST index. The LFNST index may be signaled in the bitstream, for example, once per intra-coded CU (e.g., CB) after the signaling of the transform coefficients. In an embodiment, each transform set includes two non-separable transform matrices (kernels), and the selected non-separable secondary transform candidate may be one of the two non-separable transform matrices. In some examples, LFNST is not applied to a CB (e.g., a CB coded in transform skip mode, or a CB with a number of non-zero coefficients below a threshold). In an example, an LFNST index is not signaled for a CB if LFNST should not be applied to that CB. The default value of the LFNST index is zero and may not be signaled, indicating that LFNST is not applied to the CB.

[0142] In an embodiment, LFNST is restricted to be applicable only when all coefficients outside the first coefficient subgroup are insignificant, and the coding of the LFNST index can depend on the position of the last significant coefficient. The LFNST index may be context coded. In an example, the context coding of the LFNST index does not depend on the intra prediction mode, and only the first bin is context coded. LFNST may be applied to intra-coded CUs in intra slices or inter slices for both luma and chroma components. When dual tree is enabled, the LFNST indexes for luma and chroma components may be signaled separately. For inter slices (e.g., dual tree is disabled), a single LFNST index may be signaled and used for both luma and chroma components.

[0143] An Intra Sub-Partition (ISP) coding mode may be used. In the ISP coding mode, a luma intra predicted block may be divided into two or four sub-partitions in the vertical or horizontal direction depending on the block size. In some examples, the performance improvement is small when RST is applied to all possible sub-partitions. Thus, in some examples, when an ISP mode is selected, LSNST is disabled and an LFNST index (or an RST index) is not signaled. Disabling RST or LFNST for ISP predicted residuals can reduce coding complexity. In some examples, when a Matrix-based Intra Prediction mode (MIP) is selected, LFNST is disabled and an LFNST index is not signaled.

[0144] In some examples, CUs larger than 64x64 are implicitly partitioned (TU tiling) by the maximum transform size limit (e.g., 64x64), and the LFNST index search can make data buffering four times larger for a certain number of decode pipeline stages. Thus, the maximum size allowed for LFNST may be limited to 64x64. In examples, LFNST is enabled only for discrete cosine transform (DCT) type 2 (DCT-2) transforms.

[0145] In some examples, a separable transform scheme may not be efficient for capturing directional texture patterns (e.g., edges along 45° or 135° directions). A non-separable transform scheme may improve coding efficiency, for example, in the above scenario. To reduce computational complexity and memory usage, a non-separable transform scheme may be used as a secondary transform applied to low-frequency transform coefficients obtained from the primary transform. The secondary transform may be applied to a block, and information indicating the secondary transform may be signaled for that block based on prediction mode information, the primary transform type, neighboring reconstructed samples, and / or the like. Furthermore, transform block partition information (also referred to as transform block partitioning information, transform partitioning information, or transform partition information), the size of the coded block, and the shape of the coded block may provide additional information for efficient application and / or signaling of the secondary transform.

[0146] In accordance with aspects of the disclosure, coding information for a block may be decoded from a coded video bitstream. The coding information may indicate an intra-prediction mode for the block and one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block.

[0147] The transform partitioning information may indicate whether and / or how a block may be further partitioned into multiple TBs or TUs. A block may be partitioned into multiple TUs or TBs based on the transform partitioning information for the block, e.g., as described with reference to Figures 13 and 14. In an example, the transform partitioning information is signaled in a coded video bitstream. The transform partitioning information for a block may indicate a partitioning depth for the block.

[0148] In this disclosure, the term block may refer to a prediction block (PB), a coding block (CB), a coded block, a coding unit (CU), a transform block (TB), a transform unit (TU), a luma block (e.g., luma CB), a chroma block (e.g., chroma CB), etc.

[0149] The size of a block may refer to a block width, a block height, a block aspect ratio (e.g., a ratio of a block width to a block height or a ratio of a block height to a block width), a block area size or block area (e.g., a block width x a block height), a minimum of a block width and a block height, a maximum of a block width and a block height, and / or the like. The shape of a block may refer to any suitable shape of a block. The shape of a block may refer to, but is not limited to, a non-square shape, such as a rectangular shape, a square shape, etc. The shape of a block may refer to an aspect ratio of a block.

[0150] In an example, one or a combination of the transform partitioning information for a block, the size of the block, and the shape of the block are signaled in the coded video bitstream. In an example, one or a combination of the transform partitioning information for a block, the size of the block, and the shape of the block are determined based on other information in the coded video bitstream.

[0151] Whether the secondary transform is disabled for a block may be determined based on one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block. In an example, whether information related to the secondary transform (e.g., a secondary transform index) should be signaled, for example, in a coded video bitstream, is determined based on one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block.

[0152] Furthermore, the block may be reconstructed based on a determination of whether the secondary transform is disabled for the block. If it is determined that the secondary transform is disabled for the block, the block may be reconstructed only with a primary transform (e.g., an inverse primary transform) without the secondary transform. In an example, it is determined that information related to the secondary transform (e.g., a secondary transform index) is not signaled in the coded video bitstream. If it is determined that the secondary transform is not disabled for the block (e.g., the secondary transform is enabled for the block), the block may be reconstructed with a primary transform (e.g., an inverse primary transform) and a secondary transform (e.g., an inverse secondary transform). For example, if it is determined that the secondary transform is not disabled for the block and is further determined to be applied to the block, the block is reconstructed with a primary transform and a secondary transform.

[0153] The information associated with the secondary transform (e.g., a secondary transform index) may indicate a secondary transform (e.g., a secondary transform kernel, a secondary transform core, or a secondary transform matrix) that should be applied to the block. In examples, the secondary transform is LFNST, RST, etc. As described above, in embodiments, multiple transform sets may be available and one or more secondary transform matrices (or kernels) may be included in each of the multiple transform sets. In accordance with aspects of the disclosure, a transform set may be selected from the multiple transform sets using any suitable method, including but not limited to those described with reference to Table 1, and a secondary transform (e.g., a secondary transform matrix) that should be applied to the block may be selected from one or more secondary transform matrices in the transform set by the information associated with the secondary transform (e.g., a secondary transform index).

[0154] The information (e.g., secondary transform index) may be implicitly signaled, for example, in the coded video bitstream. In an example, the secondary transform index refers to the LFNST index described above. In some examples, a secondary transform is not applied to a block (e.g., a CB coded in transform skip mode or a CB that does not meet a number threshold of non-zero coefficients). In an example, a secondary transform index (e.g., an LFNST index) is not signaled for a block if a secondary transform should not be applied to the block. The default value of the secondary transform index is zero and may not be signaled, indicating that a secondary transform is not applied to the block.

[0155] In an embodiment, one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include the transform partitioning information for the block. The transform partitioning information may be signaled in the coded video bitstream. The transform partitioning information for the block may indicate a partitioning depth for the block. The block may be partitioned into multiple TUs or TBs based on the transform partitioning information for the block, for example, as described with reference to FIG. 13. Thus, whether the secondary transform is disabled for the block may be determined based on the partitioning depth. In an example, if the partitioning depth is greater than a threshold n, it is determined that the secondary transform is disabled for the block, and the secondary transform index is not signaled. The threshold n may be any suitable integer. The threshold n may be 0 or a positive integer. Exemplary values ​​of the threshold n include, but are not limited to, 0, 1, 2, etc. In an example, the threshold n is 0. The secondary transform index (e.g., an LFNST index) may indicate a secondary transform kernel to be applied to the block.

[0156] According to an aspect of the disclosure, one or a combination of transform partitioning information for a block (e.g., CB), a size of the block, and a shape of the block may be used for application and / or signaling of a secondary transform to the block. In an example, one or a combination of transform partitioning information for a block, a size of the block, and a shape of the block may be used for application and / or signaling of multiple secondary transforms to the block. Whether to disable or enable a secondary transform for a block may be determined based on one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block. Whether to apply a secondary transform to a block may be determined based on one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block. Whether to signal application of a secondary transform to a block may be determined based on one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block.

[0157] In an embodiment, transform partitioning information for a block may be signaled, and the block may be partitioned into multiple TUs or TBs. Whether to disable the secondary transform for a block may depend on the transform partitioning information for the block. The transform partitioning information for the block may indicate a partitioning depth for the block. In an example, whether to disable the secondary transform for a block depends on the partitioning depth for the block. In some examples, whether to signal information related to the secondary transform (e.g., a secondary transform index) depends on the transform partitioning information for the block (e.g., a partitioning depth for the block). In some examples, whether to signal information related to the secondary transform (e.g., a secondary transform index) depends on the transform partitioning information for the block (e.g., a partitioning depth for the block). In an example, the secondary transform index is denoted as stIdx. In an example, based on the partitioning depth and a threshold, for example, if the partitioning depth is greater than a threshold n, it is determined that the secondary transform is disabled and the secondary transform index is not signaled. The threshold n can be any suitable integer. In an example, the threshold n is 0. In an example, the threshold n is a positive integer. Example values ​​of the threshold n include, but are not limited to, 0, 1, 2, etc. In an example, when a block is partitioned into multiple TUs or TBs, whether the secondary transform is disabled for the block and / or whether the secondary transform index is not signaled may depend on the partitioning depth and / or the threshold n.

[0158] In an embodiment, one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include the transform partitioning information for the block and the shape of the block. The transform partitioning information may be signaled in the coded video bitstream. The transform partitioning information may indicate a partitioning depth for the block. The shape of the block may be a non-square rectangle. The block may be partitioned into multiple TUs or TBs. Whether the secondary transform is disabled for the block may be determined based on the partitioning depth. In an example, if the partitioning depth is greater than a threshold, which may be 0 or a positive integer, the secondary transform is determined to be disabled for the block.

[0159] In an embodiment, transform partitioning information for a block may be signaled, the block may have a non-square rectangular shape (i.e., the shape of the block is a non-square rectangle), and the block is further partitioned into multiple TUs or TBs. Whether to disable the secondary transform for a block may depend on the transform partitioning information for the block. The transform partitioning information for the block may indicate a partitioning depth for the block. In an example, whether to disable the secondary transform for a block depends on the partitioning depth for the block. In some examples, whether to signal information related to the secondary transform (e.g., the secondary transform index stIdx) depends on the transform partitioning information for the block (e.g., the partitioning depth for the block). In an example, based on a threshold, such as if the partitioning depth is greater than a threshold n, it is determined that the secondary transform is disabled and the secondary transform index is not signaled. As described above, the threshold n may be any suitable integer, such as 0 or a positive integer. Example values ​​for threshold n include, but are not limited to, 0, 1, 2, etc. In an example, when a block is partitioned into multiple TUs, whether the secondary transform is disabled for the block and / or whether the secondary transform index is not signaled may depend on the partitioning depth and threshold n.

[0160] In an embodiment, one or a combination of the transform partitioning information for a block, the size of the block, and the shape of the block may include the shape of the block as indicated by the aspect ratio of the block. Thus, whether the secondary transform is disabled for a block may be determined based on the aspect ratio of the block.

[0161] In an embodiment, whether to disable a secondary transform for a block may depend on the shape of the block (e.g., the aspect ratio of the block). Whether to apply a secondary transform to a block may depend on the shape of the block (e.g., the aspect ratio of the block). In some examples, whether to signal information related to a secondary transform (e.g., a secondary transform index stIdx) depends on the shape of the block (e.g., the aspect ratio of the block). The aspect ratio of a block may be a ratio of a first dimension of the block to a second dimension of the block, the first dimension of the block being greater than or equal to the second dimension. It may be determined that the secondary transform is disabled for a block if the aspect ratio of the block is greater than a threshold L (e.g., 1, 2, 4, 8, etc.). In an example, the threshold L may be 2 m and m is 0 or a positive integer.

[0162] In an example, if the aspect ratio of a block (e.g., the ratio of the block width to the block height) is greater than a threshold L (e.g., 1, 2, 4, 8, etc.), then the secondary transform index is not signaled and / or the secondary transform is not applied.

[0163] In an example, if the aspect ratio of a block (e.g., the ratio of the block width to the block height) is less than a threshold J (e.g., 1, 1 / 2, 1 / 4, 1 / 8, etc.), then the secondary transform index is not signaled and / or the secondary transform is not applied. In an example, the threshold J is 2 -m and m is 0 or a positive integer.

[0164] In an embodiment, one or a combination of the transform partitioning information for a block, the size of the block, and the shape of the block may include the transform partitioning information and the shape of the block. The transform partitioning information may indicate a partitioning depth for the block. The shape of the block may be square. The block may be partitioned into multiple TUs or TBs. Whether the secondary transform is disabled for the block may be determined based on the partitioning depth. In an example, if the partitioning depth is greater than a threshold, which may be 0 or a positive integer, it is determined that the secondary transform is disabled for the block.

[0165] In an embodiment, a block may be partitioned into multiple TUs or TBs. Furthermore, the shape of the block may be square (e.g., the aspect ratio of the block is 1). Therefore, whether the secondary transform is disabled for a block may depend on the transform partitioning information for the block (e.g., the partitioning depth for the block). In an example, the transform partitioning information for the block is signaled. In some examples, whether information related to the secondary transform (e.g., the secondary transform index stIdx) should be signaled depends on the transform partitioning information for the block (e.g., the partitioning depth for the block).

[0166] In an example, based on the partitioning depth, such as when the partitioning depth is greater than a threshold n, the secondary transform is determined to be disabled and the secondary transform index is determined not to be signaled. The threshold n can be any suitable integer, such as 0 or a positive integer (1, 2, etc.). In an example, when a block is divided into multiple TUs, whether the secondary transform is disabled for the block and / or whether the secondary transform index is not signaled can depend on the partitioning depth and the threshold n.

[0167] In an embodiment, one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include the transform partitioning information for the block and the size of the block. The transform partitioning information may indicate a partitioning depth for the block. The size of the block may indicate a block width (or block width) and a block height (or block height) that are greater than a threshold size. For example, the block width and the block height are greater than the threshold size. The block may be partitioned into multiple TUs or TBs. Whether the secondary transform is disabled for the block may be determined based on the transform partitioning information for the block (e.g., the partitioning depth). In an example, it is determined that the secondary transform is disabled for the block if the partitioning depth is greater than a threshold value, which may be 0 or a positive integer.

[0168] In an embodiment, the size of the block (e.g., the minimum of the block width and the block height) may exceed a threshold size. The threshold size may be any suitable size. In an example, the size of the block refers to the minimum of the block width and the block height, and the threshold size is 64, 128, 256, etc. The block may be partitioned into multiple TUs or TBs. In an example, transform partitioning information for the block is also signaled. Thus, whether to disable a secondary transform for a block may depend on the transform partitioning information for the block (e.g., the partitioning depth for the block). In some examples, information related to the secondary transform (e.g., the secondary transform index) depends on the transform partitioning information for the block (e.g., the partitioning depth for the block).

[0169] In an example, based on the partitioning depth, such as when the partitioning depth is greater than a threshold n, the secondary transform is determined to be disabled and / or information related to the secondary transform (e.g., secondary transform index) is determined not to be signaled. The threshold n can be any suitable integer, such as 0 or a positive integer (1, 2, etc.). In an example, when a block is divided into multiple TUs or TBs, whether the secondary transform is disabled for the block and / or whether the secondary transform index is not signaled can depend on the partitioning depth and the threshold n.

[0170] In examples, exemplary values ​​for the threshold size include, but are not limited to, 256x256, 256x128, 128x256, 128x128, 128x64, 64x128, 64x64, and / or the like.

[0171] In an embodiment, the width W' of the other block and the height H' of the other block may be greater than the maximum transform size T, and the other block may be implicitly divided into multiple sub-blocks that include the block. The maximum transform size T may be, for example, a predefined parameter available to the decoder and / or encoder. In an example, the maximum transform size T is not signaled. The width W of the block (e.g., one of the multiple sub-blocks) may be the minimum of W' and T, and the height H of the block may be the minimum of H' and T. If the partitioning depth for the block (e.g., one of the multiple sub-blocks) is greater than a threshold, it is determined that the secondary transform is not applied and / or information related to the secondary transform (e.g., secondary transform index) is not signaled. The partitioning depth may be signaled. Exemplary values ​​of the threshold include, but are not limited to, 0, 1, 2, and 3. The multiple sub-blocks may further include another sub-block having a size of W×H.

[0172] In an embodiment, one of the width W' of the other block and the height H' of the other block is greater than the maximum transform size T, and the other block may be divided into a plurality of sub-blocks including the block. The width W of the block may be the minimum of W' and T, and the height H of the block may be the minimum of H' and T. One or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include the transform partitioning information for the block indicating the partitioning depth for the block. If the partitioning depth for the block is greater than a threshold, it may be determined that the secondary transform is disabled for the block. Exemplary values ​​of the threshold include, but are not limited to, 0, 1, 2, and 3.

[0173] In an embodiment, the width W' and / or height H' of the other block are greater than a predefined constant K, the other block may be implicitly divided into multiple sub-blocks. Exemplary values ​​of K may include, but are not limited to, 16, 32, 64, 128, and 256. If one or more of the multiple sub-blocks have a width W that is the minimum of W' and K and a height H that is the minimum of H' and K, the secondary transform is applied only to those one or more of the multiple sub-blocks, and / or information related to the secondary transform (e.g., one or more secondary transform indexes) is signaled only for those one or more of the multiple sub-blocks. The one or more of the multiple sub-blocks include the blocks described above.

[0174] In an embodiment, one of the width W' of the other block and the height H' of the other block is greater than a predefined constant K. The other block may be divided into a plurality of sub-blocks including the block. The width W of the block may be the minimum of W' and K, and the height H of the block may be the minimum of H' and K. The one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include a size of the block having W and H. It may be determined that a secondary transform is enabled for the block with a size of W and H. In an example, it is determined that a secondary transform is applied to the block with a size of W and H.

[0175] FIG. 19 shows a flow chart illustrating a process (1900) according to an embodiment of the disclosure. The process (1900) may be used in the reconstruction of blocks such as CB, TB, luma CB, luma TB, chroma CB, chroma TB, etc. In various embodiments, the process (1900) is performed by a processing circuit such as a processing circuit in the terminal devices (310), (320), (330), and (340), a processing circuit performing the function of a video encoder (403), a processing circuit performing the function of a video decoder (410), a processing circuit performing the function of a video decoder (510), a processing circuit performing the function of a video encoder (603), etc. In some examples, the process (1900) is implemented with software instructions, such that the processing circuit performs the process (1900) when the processing circuit executes the software instructions. The process starts at (S1901) and proceeds to (S1910).

[0176] At (S1910), coding information for a block (e.g., CB, luma CB, chroma CB, intra-coded CB, TB, etc.) may be decoded from the coded video bitstream. The coding information may indicate an intra-prediction mode for the block and one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block. The transform partitioning information for the block may include a partitioning depth for the block.

[0177] At (1920), it may be determined whether the secondary transform is disabled for the block based on one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block. In some examples, whether to signal information related to the secondary transform (e.g., a secondary transform index) depends on one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block.

[0178] In an example, whether to disable the secondary transform for a block depends on the transform partitioning information for the block (e.g., the partitioning depth for the block). In an example, if the partitioning depth is greater than a threshold n (e.g., 0 or a positive integer), it is determined that the secondary transform is disabled and the secondary transform index is not signaled. In an example, the threshold n is 0.

[0179] In an example, transform partitioning information for a block may be signaled, the block may have a square rectangular shape, and the block may be further partitioned into multiple TUs or TBs. Thus, whether to disable secondary transforms for a block may depend on the transform partitioning information for the block (e.g., the partitioning depth for the block).

[0180] Whether or not to apply a secondary transform to a block may depend on the shape of the block (e.g., the aspect ratio of the block). In some examples, whether or not to signal information related to a secondary transform (e.g., a secondary transform index stIdx) depends on the shape of the block (e.g., the aspect ratio of the block).

[0181] In an embodiment, a block may be partitioned into multiple TUs or TBs. The shape of a block may be square. Therefore, whether to disable a secondary transform for a block may depend on the transform partitioning information for the block (e.g., the partitioning depth for the block). In an example, the transform partitioning information for the block is signaled. In some examples, whether to signal information related to a secondary transform (e.g., a secondary transform index) depends on the transform partitioning information for the block (e.g., the partitioning depth for the block).

[0182] In an embodiment, the size of a block (e.g., the minimum of a block width and a block height) may exceed a threshold size (e.g., 64, 128, 256, etc.). A block may be partitioned into multiple TUs or TBs. In an example, transform partitioning information for a block is also signaled. Thus, whether a secondary transform should be disabled for a block may depend on the transform partitioning information for the block (e.g., the partitioning depth for the block). In some examples, whether information related to a secondary transform (e.g., a secondary transform index) should be signaled depends on the transform partitioning information for the block (e.g., the partitioning depth for the block).

[0183] At (S1930), the block may be reconstructed based on a determination of whether the secondary transform is disabled for the block. In an example, the secondary transform is determined to be disabled for the block at (S1920), so the block may be reconstructed with only the primary transform, without the secondary transform.

[0184] In an example, since the secondary transform is determined to be enabled for the block in (S1920), the block may be reconstructed by the primary transform and the secondary transform if it is determined that the secondary transform is applied to the block. If the partitioning depth for the block is greater than a threshold n (n is 0 or a positive integer) and the block is partitioned into multiple TUs (or TBs), a different secondary transform may be applied to each of the multiple TUs (or TBs). Which secondary transform (e.g., which secondary transform kernel) should be applied to each TU (or TB) may further be indicated (e.g., signaled in the coded video bitstream) using a corresponding secondary transform index. The process (1900) proceeds to (S1999) and ends.

[0185] The process (1900) may be adapted as appropriate. Steps of the process (1900) may be modified and / or removed. Additional steps may be added. Any order of execution may be used. In an embodiment, the width W' of the other block and the height H' of the other block are greater than the maximum transform size T, and the other block may be implicitly divided into multiple sub-blocks that include the block. The width W of the block may be the minimum of W' and T, and the height H of the block may be the minimum of H' and T. One or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include transform partitioning information for the block indicating a partitioning depth for the block. If the partitioning depth for the block is greater than a threshold, it may be determined that the secondary transform is disabled for the block. The partitioning depth may be signaled. Exemplary values ​​of the threshold include, but are not limited to, 0, 1, 2, and 3.

[0186] In an embodiment, the width W' of the other block and the height H' of the other block are greater than a predefined constant K. The other block may be divided into a plurality of sub-blocks including the block. The width W of the block may be the minimum of W' and K, and the height H of the block may be the minimum of H' and K. The one or a combination of the transform partitioning information for the block, the size of the block, and the shape of the block may include the size of the block having W and H. It is determined that the secondary transform is applied only to the block whose size is W and H.

[0187] The above description regarding the determination of whether a secondary transform is disabled for a block and / or whether information related to a secondary transform (e.g., a secondary transform index) is signaled may be appropriately adapted to the case where multiple transforms are to be applied to a block. In an example, a block is partitioned into multiple TBs, and the multiple TBs may be respectively transformed by using multiple transforms. The multiple transforms may include multiple primary transforms. The multiple transforms may include multiple secondary transforms. The information related to the multiple secondary transforms may include multiple secondary transform indexes respectively indicating the multiple secondary transforms. Whether multiple secondary transforms are disabled for a block and / or whether information related to the multiple secondary transforms (e.g., multiple secondary transform indexes) is signaled may be determined based on one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block, as described above.

[0188] In an example, whether multiple secondary transforms are disabled for a block and / or whether multiple secondary transform indexes associated with the multiple secondary transforms are signaled may be determined based on transform partitioning information (e.g., partitioning depth) for the block. For example, if the partitioning depth is greater than a threshold n (e.g., 0 or a positive integer), the multiple secondary transforms are determined to be disabled for the block and the multiple secondary transform indexes are not signaled. In an example, whether multiple secondary transforms are disabled for a block and / or whether multiple secondary transform indexes associated with the multiple secondary transforms are signaled may be determined based on a shape (e.g., aspect ratio) of the block.

[0189] The disclosed embodiments may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium. The disclosed embodiments may be applied to luma blocks or chroma blocks.

[0190] The above techniques may be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, Figure 20 illustrates a computer system (2000) suitable for implementing certain embodiments of the disclosed subject matter.

[0191] The computer software may be coded in any suitable machine code or computer language that may be subject to mechanisms such as assembly, compilation, linking, etc. to generate code including instructions that may be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., directly, or through interpretation, microcode execution, etc.

[0192] The instructions may be executable by various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smart phones, gaming consoles, Internet of Things devices, and the like.

[0193] The components illustrated in Figure 20 for the computer system (2000) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components described in the exemplary embodiment of the computer system (2000).

[0194] The computer system (2000) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more users through, for example, tactile input (e.g., keyboard, swipes, dataglove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), and olfactory input (not shown). The human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from a still camera), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0195] The input human interface devices may include one or more of a keyboard (2001), a mouse (2002), a trackpad (2003), a touch screen (2010), a data glove (not shown), a joystick (2005), a microphone (2006), a scanner (2007), and a camera (2008) (only one of each is shown).

[0196] The computer system (2000) may also include certain human interface output devices that may stimulate one or more of the user's senses through, for example, tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touchscreen (2010), data gloves (not shown), or joystick (2005), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (2009), headphones (not shown)), visual output devices (e.g., screens (2010) including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touchscreen input capability, each with or without haptic feedback capability, some of which are capable of outputting two-dimensional visual output or output in more than three dimensions by means of stereoscopic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0197] The computer system (2000) may also include human accessible storage devices and their associated media, such as CD / DVD ROM / RW (2020) with CD / DVD or similar media (2021), thumb drives (2022), removable hard disks or solid state drives (2023), legacy magnetic media, such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD based devices, such as security dongles (not shown), and the like.

[0198] Those skilled in the art will also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not include transmission media, carrier waves, or other transitory signals.

[0199] The computer system (2000) may also include an interface (2054) to one or more communication networks (2055). The networks may be, for example, wireless, wireline, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wireline or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and factory networks including CAN bus, etc. Certain networks generally require an external network interface adapter attached to a particular general purpose digital port or peripheral bus (2049) (e.g., a USB port of the computer system (2000)). Others are generally built into the core of the computer system (2000) by attachment to a system bus as described below (e.g., an Ethernet network to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (2000) can communicate with other entities. Such communications can be one-way receive-only (e.g., broadcast TV) or one-way transmit-only (e.g., a CAN bus to a specific CAN bus device), or can be bidirectional to other computer systems, for example, using local or wide area digital networks. Specific protocols or protocol stacks can be used with each of the networks and network interfaces as described above.

[0200] The above human interface devices, human accessible storage devices, and network interfaces may be attached to a core (2040) of the computer system (2000).

[0201] The cores (2040) may include one or more central processing units (CPUs) (2041), graphics processing units (GPUs) (2042), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (2043), hardware accelerators (2044) for specific tasks, graphics adapters (2050), etc. These devices may be connected through a system bus (2048), along with read only memory (ROM) (2045), random access memory (RAM) (2046), internal mass storage devices such as internal non-user accessible hard drives, SSDs, etc. (2047). In some computer systems, the system bus (2048) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripherals may be attached directly to the core's system bus (2048) or through a peripheral bus (2049). In an example, a display 2010 may be connected to a graphics adapter 2050. Architectures for peripheral buses include PCI, USB, and the like.

[0202] The CPU (2041), GPU (2042), FPGA (2043), and accelerator (2044) can execute certain instructions that can be combined to constitute the above computer code. The computer code can be stored in ROM (2045) or RAM (2046). Temporary data can also be stored in RAM (2046), while persistent data can be stored, for example, in an internal mass storage device (2047). Rapid storage and retrieval from any of the memory devices can be made possible by the use of cache memory. The cache memory can be closely associated with one or more of the CPU (2041), GPU (2042), mass storage device (2047), ROM (2045), RAM (2046), etc.

[0203] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those of ordinary skill in the computer software arts.

[0204] By way of example, and not by way of limitation, a computer system having the architecture (2000), and in particular the core (2040), 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 media associated with the user-accessible mass storage devices introduced above, in addition to specific storage of the core (2040) that is non-transitory in nature, such as the core's internal mass storage device (2047) or ROM (2045). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (2040). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (2040), and in particular the processors therein (including CPUs, GPUs, FPGAs, etc.), to execute certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (2046) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system can provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerators (2044)) that can operate in place of or in conjunction with software to execute certain processes or certain portions of certain processes described herein. References to software can encompass logic, where appropriate, and vice versa. References to computer-readable media can encompass circuitry (e.g., integrated circuits (ICs)) storing software for execution, circuitry embodying logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0205] Appendix A: Acronyms JEM: Joint Exploration Model VVC:Versatile Video Coding BMS:Benchmark Set MV:Motion Vector HEVC:High Efficiency Video Coding SEI:Supplementary Enhancement Information VUI:Video Usability Information GOP:Group of Picture(s) TU:Transform Unit(s) PU:Prediction Unit(s) CTU:Coding Tree Unit(s) CTB:Coding Tree Block(s) PB:Prediction Block(s) HRD:Hypothetical Reference Decoder SNR:Signal Noise Ratio CPU:Central Processing Unit(s) GPU:Graphics Processing Unit(s) CRT:Cathode Ray Tube LCD:Liquid-Crystal Display OLED:Organic Light-Emitting Diode CD:Compact Disc DVD:Digital Video Disc ROM:Read-Only Memory RAM:Random Access Memory ASIC:Application-Specific Integrated Circuit PLD:Programmable Logic Device LAN:Local Area Network GSM: Global System for Mobile communications LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI:Peripheral Component Interconnect FPGA:Field Programmable Gate Area(s) SSD: Solid-State Drive IC: Integrated Circuit CU: Coding Unit

[0206] While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents that are within the scope of this disclosure. Thus, it will be apparent to those skilled in the art that numerous systems and methods will be contemplated that embody the principles of the present disclosure and are therefore within its spirit and scope, even if not explicitly shown or described herein.

Claims

1. 1. A method of video decoding performed by a decoder, comprising: decoding coding information of a block from a coded video bitstream, the coding information indicating an intra-prediction mode for the block, and one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block; determining whether a secondary transform is disabled for the block based on the one or the combination of the transform partitioning information for the block, the size of the block, and the shape of the block; reconstructing the block based on a determination of whether the secondary transformation is disabled for the block; having the one or the combination of the transform partitioning information for the block, the size of the block, and the shape of the block comprises the transform partitioning information for the block signaled in the coded video bitstream; the transformation partitioning information for the block indicates a partitioning depth for the block; The method further comprises partitioning the block into a plurality of transformation blocks; determining whether the secondary transformation is disabled for the block comprises determining whether the secondary transformation is disabled for the block based on the partitioning depth. method.

2. determining whether the secondary transform is disabled for the block comprises determining that the secondary transform is disabled for the block in response to the partitioning depth being greater than a threshold; The threshold is 0 or a positive integer. The method of claim 1.

3. The threshold is 0. The method of claim 2.

4. determining that if the secondary transform is determined to be disabled for the block, a secondary transform index indicating a secondary transform kernel to be applied to the block is not signaled. The method according to claim 2 or 3.

5. the one or the combination of the transformation partitioning information for the block, the size of the block, and the shape of the block further includes the shape of the block, and the shape of the block is a non-square rectangle.

5. The method according to any one of claims 1 to 4.

6. the one or the combination of the transformation partitioning information for the block, the size of the block, and the shape of the block further comprises the shape of the block as indicated by an aspect ratio of the block; determining whether the secondary transform is disabled for the block includes determining whether the secondary transform is disabled for the block based on the aspect ratio of the block.

5. The method according to any one of claims 1 to 4.

7. the aspect ratio of the block is a ratio of a first dimension of the block to a second dimension of the block, the first dimension of the block being greater than or equal to the second dimension of the block; determining whether the secondary transform is disabled for the block includes determining that the secondary transform is disabled for the block in response to the aspect ratio of the block being greater than a threshold. The method according to claim 6.

8. the one or the combination of the transformation partitioning information for the block, the size of the block, and the shape of the block further includes the shape of the block, and the shape of the block is a square.

5. The method according to any one of claims 1 to 4.

9. the one or the combination of the transformation partitioning information for the block, the size of the block, and the shape of the block further includes the size of the block, the size of the block indicating a width of the block and a height of the block that are greater than a threshold size; 5. The method according to any one of claims 1 to 4.

10. one of the width W′ of the other block and the height H′ of the other block is greater than the maximum transform size T; The method further includes dividing the other block into a plurality of sub-blocks including the block, wherein a width W of the block is the minimum of W′ and T, and a height H of the block is the minimum of H′ and T; determining whether the secondary transform is disabled for the block comprises determining that the secondary transform is disabled for the block in response to the partitioning depth for the block being greater than a threshold. The method of claim 1.

11. one of the width W′ of the other block and the height H′ of the other block is greater than a predefined constant K; The method further includes dividing the other block into a plurality of sub-blocks including the block, wherein a width W of the block is the minimum of W′ and K, and a height H of the block is the minimum of H′ and K; the one or the combination of the transformation partitioning information for the block, the size of the block, and the shape of the block further comprises the size of the block having W and H; determining whether the secondary transform is disabled for the block includes determining that the secondary transform is enabled for the block in response to the sizes of the block being W and H. The method of claim 1.

12. 1. An apparatus for video decoding, comprising: A non-transitory computer readable medium storing a program; a processing circuit configured to execute the program; having The program, when executed by the processing circuit, causes the processing circuit to carry out a method according to any one of claims 1 to 11. Device.

13. A program which, when executed by a processor, causes the processor to carry out a method according to any one of claims 1 to 11.

14. 1. A method of video coding performed by an encoder, comprising: coding the video bitstream to generate a coded video bitstream; decoding coding information of a block from a coded video bitstream, the coding information indicating an intra-prediction mode for the block, and one or a combination of transform partitioning information for the block, a size of the block, and a shape of the block; determining whether a secondary transform is disabled for the block based on the one or the combination of the transform partitioning information for the block, the size of the block, and the shape of the block; reconstructing the block based on a determination of whether the secondary transformation is disabled for the block; having the one or the combination of the transform partitioning information for the block, the size of the block, and the shape of the block comprises the transform partitioning information for the block signaled in the coded video bitstream; the transformation partitioning information for the block indicates a partitioning depth for the block; The method further comprises partitioning the block into a plurality of transformation blocks; determining whether the secondary transformation is disabled for the block comprises determining whether the secondary transformation is disabled for the block based on the partitioning depth. method.

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