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

Abstract

To provide a method for video decoding and an apparatus including processing circuit therefor.SOLUTION: A processing circuit decodes coding information of a block from a coded video bitstream. The coding information indicates an intra-prediction mode for the block and one or a combination of transform partitioning information for the block, a block size, and a block shape. The processing circuit also determines whether a secondary transform is disabled for the block on the basis of the one or a combination of the transform partitioning information for the block, the block size, and the block shape, and reconstructs the block on the basis of the determination of whether the secondary transform is disabled for the block.SELECTED DRAWING: Figure 19

Description

Technical Field

[0001] [Incorporation by Reference] This patent application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 112,533, filed on November 11, 2020, under the title "METHODS FOR EFFICIENT APPLICATION OF SECONDARY TRANSFORMS", and claims the benefit of priority to U.S. Patent Application No. 17 / 361,239, filed on June 28, 2021, under the title "Method and apparatus for video coding". The entire disclosure of the prior applications is hereby incorporated by reference in its entirety.

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

Background Art

[0003] The description of the background provided herein is for the purpose of generally presenting the background of the disclosure. The research of the presently named inventors, to the extent that the research is described in this background section and aspects of the description that might otherwise be eligible as prior art at the time of filing, are not admitted as prior art to this disclosure, either expressly or implicitly.

[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 picture having, for example, a spatial dimension of 1920×1080 luminance samples and associated chrominance samples. The sequence of pictures can have, for example, a fixed or variable picture rate of 60 pictures per second, i.e., 60 Hz (commonly also known as the frame rate). Uncompressed video has specific bitrate requirements. For example, 1080p60 4:2:0 video at 8 bits per sample (1920×1080 luminance sample resolution at a frame rate of 60 Hz) requires a bandwidth close to 1.5 Gbit / s. One hour of such video requires more than 600 Gbytes of storage space.

[0005] One purpose 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 an order of magnitude in some cases. Both reversible and irreversible compression and combinations thereof can be used. Reversible compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using irreversible 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, irreversible compression is widely used. The amount of acceptable distortion depends on the application. For example, a user for a specific consumer streaming application may tolerate higher distortion than a user for a television distribution application. The achievable compression ratio can reflect that higher acceptable / tolerable distortion can result in a higher compression ratio.

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

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

[0008] For example, conventional intra coding, such as that known from MPEG-2 generation coding techniques, does not use intra prediction. However, some newer video compression techniques include techniques that attempt, for example, from surrounding sample data and / or metadata obtained during the encoding / decoding of spatially adjacent and previously in the decoding order blocks of data. Such techniques are hereinafter referred to as "intra prediction" techniques. Note that in at least some cases, intra prediction uses only reference data from the currently reconstructed picture and not from reference pictures.

[0009] Multiple forms of intra prediction may exist. 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, the mode can have sub - modes and / or parameters, which can be coded independently or can be included in the mode codeword. Which codeword should be used for a given mode, sub - mode, and / or parameter combination can affect the coding efficiency gain through intra prediction, so entropy coding techniques can be used to convert the codeword into a bitstream.

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

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

[0012] Still referring to FIG. 1A, in the upper left, a square block (104) of 4×4 samples (indicated by the thick dashed line) is represented. The square block (104) contains 16 samples, and each sample is labeled using "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 within the block (104) in both the Y and X dimensions. Since the block is 4×4 samples in size, S44 is in the lower right. Further, reference samples following a similar numbering scheme are shown. The reference samples are labeled using "R", its Y position (e.g., row index) and X position (column index) with respect to the block (104). In both H.264 and H.265, the predicted samples are adjacent to the block being reconstructed, and thus negative values need not be used.

[0013] Intra-picture prediction can work by copying the reference sample value from adjacent samples as needed according to the signaled prediction direction. For example, assume that the coded video bitstream contains signaling indicating that for this block, the prediction direction coincides with arrow (102), i.e., the sample is predicted from one or more predicted samples at a 45-degree angle from the horizontal and in the upper right. 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, the values of multiple reference samples may be combined, particularly when the direction is not evenly divisible by 45 degrees, for example, through interpolation, to calculate the reference sample.

[0015] The number of possible directions has been increasing as video coding technology develops. In H.264 (2003), nine different directions could be represented. This 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 conducted to identify the most likely directions, and certain techniques in entropy coding are used to represent those likely directions with fewer bits while accepting some penalty for less likely directions. Further, the direction itself can sometimes be predicted from adjacent directions used in adjacent, already decoded blocks.

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

[0017] The mapping of intra prediction direction bits within the coded video bitstream representing the direction can vary for each video coding technology, ranging from a simple direct mapping of the prediction direction to complex adaptive schemes including the intra prediction mode, codewords, the most probable mode, and similar techniques. In all cases, however, there can be certain directions that occur less statistically likely in video content than certain other directions. Given that the goal of video compression is redundancy reduction, those less likely directions will be represented with more bits than the more likely directions in a well - functioning video coding technology.

[0018] Motion compensation can be an irreversible compression technique, and is related to a technique in which blocks of sample data from a previously reconstructed picture or a portion thereof (reference picture) are spatially shifted in the direction indicated by a motion vector (hereinafter MV) and then used for prediction of a newly reconstructed picture or picture portion. In some cases, the reference picture 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 the temporal dimension).

[0019] In some video compression techniques, the MV applicable to a particular area of sample data can be predicted from other MVs, for example, from other areas of sample data that are spatially adjacent to the area being reconstructed and from those that precede that MV in the decoding order. By doing so, the amount of data required to code the MV can be significantly reduced, thereby removing redundancy and increasing compression. For example, when coding an input video signal obtained from a camera (known as natural video), there is a statistical likelihood that areas larger than the area to which a single MV is applicable move in a similar direction, and thus, in some cases, MV prediction can work effectively by being predictable using a similar motion vector derived from the MVs of adjacent areas. As a result, the MV required for a given area can be similar or the same as the MV predicted from surrounding MVs and can be represented in fewer bits than the number of bits that would be used if the MV were directly coded after entropy coding. In some cases, MV prediction can be an example of reversible compression of a signal (i.e., the MV) derived from the original signal (i.e., the sample stream). In other cases, the MV prediction itself can be irreversible, for example, due to rounding errors when calculating predictors from some 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, in this specification, a technique hereinafter referred to as “spatial merge” is described.

[0021] Referring to FIG. 2, the current block (201) has samples recognized by the encoder during the motion search process as being predictable from a previous block of the same size that has been spatially shifted. Instead of directly coding the MV, the MV can be derived from metadata associated with one or more reference pictures, for example, from the most recent reference picture (in decoding order) using an MV associated with any one of five surrounding samples represented as A0, A1 and B0, B1, B2 (202 to 206 respectively). In H.265, MV prediction can use predictors from the same reference pictures that adjacent blocks are using. SUMMARY OF THE INVENTION

[0022] The disclosed aspects provide methods and apparatuses for video encoding / decoding. In some examples, an 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, block size, and block shape. The processing circuit can determine whether secondary transform is disabled for the block based on one or a combination of transform partitioning information for the block, block size, and block shape. The processing circuit can reconstruct the block based on the determination of whether secondary transform is disabled for the block.

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

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

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

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

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

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

[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 circuit 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 a combination of the transform partitioning information for the block, the size of the block, and the shape of the block includes the size of the block having W and H. The processing circuit may determine that a secondary transform is to be enabled for the block in response to the sizes 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 accompanying drawings. [Brief explanation of the drawings]

[0032]

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Best Mode for Carrying Out the Invention

[0033] FIG. 3 represents a schematic block diagram of a communication system (300) according to an embodiment of the present disclosure. The communication system (300) includes, for example, a plurality of terminal devices that can communicate with each other via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via a network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) perform unidirectional data transmission. 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 coded video data can 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 a video picture, and display the video picture according to the recovered video data. Unidirectional data transmission may be common in media serving applications and the like.

[0034] In another example, the communication system (300) includes, for example, a second pair of terminal devices (330) and (340) that perform bidirectional transmission of coded video data that may appear 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) via the network (350). Each of the terminal devices (330) and (340) may also receive the coded video data transmitted by the other of the terminal devices (330) and (340), may decode the coded video data to recover the video pictures, and may display the video pictures on an accessible display device according to 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, but the principles of the present disclosure need not be so limited. Embodiments of the present disclosure find use in laptop computers, tablet computers, media players, and / or dedicated video conferencing devices. The network (350) corresponds to any number of networks that transfer coded video data among the terminal devices (310), (320), (330) and (340), including, for example, wireline (wired) and / or wireless communication networks. The communication network (350) may exchange data in circuit-switched and / or packet-switched channels. Representative 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 in this specification.

[0036] FIG. 4 shows the arrangement of video encoders and video decoders in a streaming environment as an application example of the disclosed subject matter. The disclosed subject matter can be similarly applicable to other video-related applications including, for example, video conferencing, digital TV, and storage of compressed video on digital media such as CDs, DVDs, memory sticks, etc.

[0037] A streaming system may include a capture subsystem (413) that includes, for example, a video source (401), such as a digital camera, that generates a stream (402) of uncompressed video pictures. In the example, the stream (402) of video pictures includes samples taken by the digital camera. The stream (402) of video pictures is represented in bold lines to emphasize the high data volume compared to the encoded video data (404) (or coded video bitstream) and 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 the disclosed aspects, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)) is represented in thin lines to emphasize the lower data volume compared to the stream (402) of video pictures and 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 read copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) in an electronic device (430). The video decoder (410) decodes an incoming copy (407) of the encoded video data and generates an output stream (411) of video pictures that can be rendered on a display (412), such as a display screen, or other rendering device (not shown). In some streaming systems, the encoded video data (404), (407), and (409) (e.g., video bitstream) may be encoded according to a particular video coding / compression standard.Examples of such standards include ITU-T Recommendation H.265. In an example, the video coding standard under development is commonly known as Versatile Video Coding (VVC). The subject matter disclosed may be used in relation to VVC.

[0038] Note that the electronic devices (420) and (430) can include other components (not shown). For example, the electronic device (420) can include a video decoder (not shown), and the electronic device (430) can similarly include a video encoder (not shown).

[0039] FIG. 5 shows a block diagram of a video decoder (510) according to an embodiment of the present disclosure. The video decoder (510) can be included in an electronic device (530). The electronic device (530) can include a receiver (531) (e.g., a receiving circuit). The video decoder (510) can be used in place of the video decoder (410) in 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. At this time, the decoding of each coded video sequence is independent of other coded video sequences. The coded video sequence may be received from the channel (501), which may be a hardware / software link to a storage device storing 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 transferred to their respective using entities (not shown). The receiver (531) may separate the coded video sequence from other data. To counter network jitter, a buffer memory (515) may be coupled between the receiver (531) and the entropy decoder / parser (520) (hereinafter "parser (520)"). In certain applications, the buffer memory (515) is part of the video decoder (510). Otherwise, it can be outside the video decoder (510) (not shown). Still otherwise, for example, there can be a buffer memory outside the video decoder (not shown) for countering network jitter, and in addition, another buffer memory (515) within the video decoder (510) for operating the playback timing, for example. When the receiver (531) is receiving data from a storage / transfer device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may not be required or may be small. For use in a best-effort packet network such as the Internet, the buffer memory (515) may be required, may be relatively large, and advantageously may be of an adaptable size and may be at least partially implemented in an operating system or similar element outside the video decoder (510) (not shown).

[0041] Video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. The categories of those symbols include information used to manage the operation of the video decoder (510) and, potentially, information for controlling a rendering device, such as a rendering device (512) (e.g., a display screen) that may be coupled to the electronic device (530) but is not an essential part of the electronic device (530) as shown in FIG. 5. The control information for the rendering device may be in 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 can follow video coding techniques or standards and can follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context dependence, etc. The parser (520) may extract a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder from the coded video sequence based on at least one parameter corresponding to that group. The subgroups can include Group of Picture (GOP), picture, tile, slice, macroblock, Coding Unit (CU), block, Transform Unit (TU), Prediction Unit (PU), etc. The parser (520) may also extract information such as transform coefficients, quantization parameter values, motion vectors, etc. from the coded video sequence.

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

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

[0044] Beyond the function blocks already described, the video decoder (510) can conceptually be subdivided into a number of functional units described below. In an actual implementation operating under commercial constraints, many of those units interact closely with each other and can be at least partially incorporated into each other. However, for the purpose of explaining the disclosed subject matter, the conceptual subdivision into functional units below is appropriate.

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

[0046] In some cases, the output samples of the scaler / inverse converter (551) can relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture and can use prediction information from a previously reconstructed part of the current picture. Such prediction information can be supplied by the 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 the 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, in some cases, for each sample, the prediction information generated by the intra prediction unit (552) to the output sample information supplied by the scaler / inverse transform unit (551).

[0047] In other cases, the output samples of the scaler / inverse transform unit (551) can relate to inter-coded and potentially motion-compensated blocks. In such cases, the motion compensation prediction unit (553) can access the reference picture memory (557) to fetch the samples used for prediction. According to the symbols (521) related to the block, after motion-compensating the fetched samples, those samples can be added by the aggregator (555) to the output of the scaler / inverse transform unit (551) (in this case, referred to as residual samples or a residual signal) to generate output sample information. The address in the reference picture memory (557) where the motion compensation prediction unit (553) fetches the prediction samples can be controlled by, for example, the motion vector that the motion compensation prediction unit (553) can utilize in the form of symbols (521) that can have X, Y, and reference picture components. Motion compensation can also include interpolation of the sample values fetched from the reference picture memory (557) when an exact sub-sample motion vector is used, a motion vector prediction mechanism, and the like.

[0048] The output samples of the aggregator (555) can undergo various loop filtering techniques in the loop filter unit (556). Video compression techniques can include in-loop filter techniques. This technique is included in the coded video sequence (also referred to as a coded video bitstream) and is controlled by the parameters made available to the loop filter unit (556) as symbols (521) from the parser (520), but can also respond to the meta information obtained during the decoding of the previous part of the coded picture or coded video sequence (in decoding order), and further, can also respond to the previously configured loop filter processed sample values.

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

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

[0051] The video decoder (510) may perform a decoding operation according to a predetermined video compression technique in a standard such as ITU-T Recommendation H.265. The coded video sequence may conform to the syntax defined 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 the profile documented in the video compression technique or standard. Specifically, the profile can select specific tools from all the tools available in the video compression technique or standard as the only tools available for use under that profile. Also, the complexity of the coded video sequence needs to be within the bounds defined by the level of the video compression technique or standard for compliance. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may, in some cases, be further restricted through the Hypothetical Reference Decoder (HRD) specification and the 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 can take forms such as, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0053] FIG. 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 video encoder (403) of the example of FIG. 4.

[0054] The video encoder (603) may receive video samples from a video source (601) (not part of the electronic device (560) in the example of FIG. 6) that can capture a video image 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 supply 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 bits, 10 bits, 12 bits, 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 storing 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 supplied as a plurality of individual pictures that impart motion when viewed in sequence. The pictures themselves may be organized as a spatial array of pixels, and each pixel may have one or more samples depending on the sampling structure, color space, etc. in use. One of ordinary skill in the art can easily understand the relationship between pixels and samples. This specification will hereinafter focus 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. Enforcing an appropriate coding speed is a function of the controller (650). In some embodiments, the controller (650) controls other functional units as described below and is functionally coupled to the other functional units. The couplings are not shown for clarity. Parameters set by the controller (650) may include parameters related to rate control (picture skip, quantizer, lambda value of rate distortion optimization techniques, etc.), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured to have 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 overly simplified description, by way of example, the coding loop may involve a source coder (630) (e.g., 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 the same way that a (remote) decoder would also generate, (since any compression between the symbols and the coded video stream is reversible in the video compression techniques contemplated by the disclosed subject matter), sample data. The reconstructed sample stream (sample data) is input into the reference picture memory (634). Since the decoding of the symbol stream results in a bit-exact result independent of the location of the decoder (local or remote), the content in the reference picture memory (634) is also bit-exact between the local encoder and the remote encoder. That is, the prediction part of the encoder "sees" 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 synchronization (and the resulting drift if synchronization cannot be maintained, e.g., due to channel errors) is also used in some related arts.

[0058] The operation of the "local" decoder (633) can be the same as that of a "remote" decoder such as the video decoder (510), which has already been described in detail previously with reference to FIG. 5. However, referring temporarily to FIG. 5 as well, since symbols are available and the encoding / decoding of symbols to / from the coded video sequence by the entropy encoder (645) and the parser (520) can be reversible, the entropy decoding part of the video decoder (510) including the buffer memory (515) and the parser (520) may not be fully implemented in the local decoder (633).

[0059] The observation that can be made at this point is that any decoder technology other than the parsing / entropy decoding present in the decoder must necessarily exist in a substantially identical functional form in the corresponding encoder. For this reason, the disclosed subject matter focuses on the operation of the decoder. The description of encoder technology can be omitted since they are the reverse of the decoder technology described comprehensively. A more detailed description is required only within a specific scope and is provided below.

[0060] During operation, in some examples, the source coder (630) may perform motion-compensated predictive coding. This predictively codes the input picture by referring to one or more previously coded pictures from the video sequence designated as "reference pictures". In this way, the coding engine (632) codes the difference between the pixel block of the reference picture that can be selected as a prediction reference for the input picture and the pixel block of the input picture.

[0061] The local video decoder (633) may decode the coded video data of a picture that can be specified as a reference picture based on the symbols generated by the source coder (630). The operation of the coding engine (632) may advantageously be an irreversible process. When the coded video data can be decoded by a video decoder (not shown in FIG. 6), the reconstructed video sequence may typically be a reproduction of the source video sequence with some errors. The local video decoder (633) may reproduce the decoding process that can be executed by the video decoder for the reference picture and store the reconstructed reference picture in the reference picture cache (634). In this way, the video encoder (603) may locally store a copy of the reconstructed reference picture that has the same content as the reconstructed reference picture that would be obtained by a remote video decoder (without transmission errors).

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

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

[0064] The outputs of all the above functional units may undergo entropy coding in an entropy encoder (645). The entropy encoder (645) converts the symbols generated by various functional units into a coded video sequence by reversibly 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 generated by the entropy encoder (645) for transmission via the communication channel (660). The communication channel (660) 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 an auxiliary data stream (source not shown).

[0066] The 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 that may affect the coding technique applicable to each picture. For example, a picture 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 the sequence as a prediction source. Some video codecs, for example, allow various types of Intra Pictures, including Independent Decoder Refresh (IDR) pictures. Those skilled in the art know such variations of I Pictures and their respective applications and features.

[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 a reference index to predict the 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 prediction 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 related metadata for the reconstruction of a single block.

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

[0071] The video encoder (603) may perform coding operations according to a predetermined video coding technology or standard specification such as ITU-T Recommendation H.265. During the operations, the video encoder (603) may perform various compression operations including predictive coding operations that utilize temporal and spatial redundancies in the input video sequence. Thus, the coded video data may conform to the syntax defined by the video coding technology or standard specification 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 have other forms of redundant data such as temporal / spatial / SNR enhancement layers, redundant pictures and slices, SEI messages or VUI parameter set fragments, etc.

[0073] Video may be captured as a plurality of source pictures (video pictures) in a time sequence. Intra picture prediction (often abbreviated as intra prediction) utilizes the spatial correlation in a given picture, and inter picture prediction utilizes the correlation (temporal or otherwise) between pictures. In an example, a particular picture during encoding / decoding, referred to as the current picture, is partitioned into blocks. If a block within the current picture is similar to a reference block within a reference picture that was encoded earlier in the video and is still buffered, that block within the current picture can be encoded by a vector called a motion vector. The motion vector points to the reference block within the reference picture and can have a third dimension identifying the reference picture if multiple reference pictures are being used.

[0074] In some embodiments, dual prediction techniques may be used in inter picture prediction. According to the dual prediction technique, two reference pictures, e.g., a first reference picture and a second reference picture that both precede the current picture in decoding order within the video (however, in display order, they may be in the past and future respectively), are used. A block within the current picture can be encoded by a first motion vector pointing to a first reference block within the first reference picture and a second motion vector pointing to a second reference block within the second reference picture. The block is predictable by a combination of the first reference block and the second reference block.

[0075] Furthermore, merge mode techniques may 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 within a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. Generally, a CTU includes three Coding Tree Blocks (CTBs), which are one luma CTB and two chroma CTBs. Each CTU can be recursively quad-tree divided into one or more Coding Units (CUs). For example, a 64×64 pixel CTU can be divided into one 64×64 pixel CU, or four 32×32 pixel CUs, or sixteen 16×16 pixel CUs. In the example, each CU is analyzed to determine a prediction type for the CU, such as an inter-prediction type or an intra-prediction type. The CU is divided into one or more Prediction Units (PUs) according to its temporal and / or spatial predictability. Generally, each PU includes one luma Prediction Block (PB) and two chroma PBs. In an embodiment, the prediction operation in coding (encoding / decoding) is performed in units of prediction blocks. Using 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] FIG. 7 shows a diagram of a video encoder (703) according to another embodiment of the disclosure. The video encoder (703) receives a processing block (e.g., a prediction block) of sample values within a current video picture included in a sequence of video pictures, and is configured to encode the processing 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 example of HEVC, the video encoder (703) receives a matrix of sample values of a processing block, such as a prediction block of 8×8 samples. The video encoder (703) determines, for example, using rate distortion optimization, whether the processing block is best coded in an intra mode, an inter mode, or a bi-prediction mode. If the processing block is to be coded in the intra mode, the video encoder (703) may use intra prediction techniques to encode the processing block into the coded picture, and if the processing block is to be coded in the inter mode or the bi-prediction mode, the video encoder (703) may use inter prediction or bi-prediction techniques, respectively, to encode the processing block into the coded picture. In certain video coding techniques, the merge mode can be an inter-picture prediction sub-mode in which a motion vector is derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictor. In certain other video coding techniques, there may be coded motion vector components applicable to the target block. In an example, the video encoder (703) includes other components, such as a mode decision module (not shown) that determines the mode of the processing block.

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

[0080] The inter-encoder (730) receives samples of the current block (e.g., a processing block), compares the block with one or more reference blocks (e.g., blocks in the previous and subsequent pictures) in a reference picture, generates inter-prediction information (e.g., a description of redundant information according to inter-encoding techniques, motion vectors, merge mode information), and is configured to calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using some 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) receives samples of the current block (e.g., a processing block), and in some cases, compares the block with blocks that have already been coded within the same picture, generates the quantized coefficients after transformation, and in some cases, also generates 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 predicted block) based on the intra-prediction information and reference blocks within the same picture.

[0082] The general-purpose controller (721) is configured to determine general-purpose control data and control other components of the video encoder (703) based on the general-purpose control data. In an example, the general-purpose controller (721) determines the mode of a block and supplies a control signal to the switch (726) based on the mode. For example, when the mode is the intra mode, the general-purpose controller (721) controls the switch (726) to select the intra mode result for use by the residual calculation unit (723), and selects the intra prediction information and controls the entropy encoder (725) to include the intra prediction information in the bitstream. When the mode is the inter mode, the general-purpose controller (721) controls the switch (726) to select the inter prediction result for use by the residual calculation unit (723), and selects the inter prediction information and controls the entropy encoder (725) to include the inter prediction information in the bitstream.

[0083] The residual calculation unit (723) is configured to calculate the difference (residual data) between the received block and the prediction result selected from the intra encoder (722) or the inter encoder (730). The residual encoder (724) is configured to operate based on the residual data to encode the residual data and generate a transformation coefficient. In the example, the residual encoder (724) is configured to convert the residual data from the spatial domain to the frequency domain and generate a transformation coefficient. Next, the transformation coefficient undergoes quantization processing to obtain the quantized transformation coefficient. In various embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform inverse transformation and generate the decoded residual data. The decoded residual data can be appropriately used by the intra encoder (722) and the inter encoder (730). For example, the inter encoder (730) can generate the decoded block based on the decoded residual data and the inter prediction information, and the intra encoder (722) can generate the decoded block based on the decoded residual data and the intra prediction information. The decoded block is appropriately processed to generate the decoded picture, and the decoded picture is buffered in a memory circuit (not shown.) and can be used as a reference picture in some examples.

[0084] The entropy encoder (725) is configured to format the bitstream to include the encoded block. The entropy encoder (725) is configured to include various information according to 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. Note that there is no residual information when coding a block in either the merge submode of the inter mode or the bi-prediction mode according to the disclosed subject matter.

[0085] FIG. 8 shows a diagram of a video decoder (810) according to another embodiment of the disclosure. The video decoder (810) is configured to receive a coded picture that is part of a coded video sequence and decode the coded picture to generate a reconstructed picture. In 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) that are coupled as shown in FIG. 8.

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

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

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

[0090] The residual decoder (873) is configured to perform inverse quantization to extract the inverse quantized transform coefficients, and process the inverse quantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residual decoder (873) may also request specific control information (for including quantization parameter (QP)), and that information may be supplied by the entropy decoder (871) (this is only low-capacity control information and the data path is not shown).

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

[0092] Note that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) can be implemented by any appropriate technology. In an embodiment, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) can 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) can be implemented using one or more processors that execute software instructions.

[0093] Video coding techniques related to the efficient application of secondary transforms, such as the efficient application of a set of secondary transforms, are disclosed. The efficient application of secondary transforms can be applicable to any appropriate video coding format or standard. The video coding format can include open video coding formats 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 can be used in intra prediction, for example, in AV1, VVC, and / or others. In an embodiment, directional intra prediction is used, such as in AV1. In an example, eight directional modes corresponding to each of eight from 45° to 207° are used, such as in the open video coding format VP9. To utilize more spatial redundancy with directional texture, for example, in AV1, the directional mode (also called the directional intra mode, the directional intra prediction mode, or the angular mode) can be extended to an angle set with finer granularity, as shown in FIG. 9.

[0095] FIG. 9 shows an example of a nominal mode for a coding block (CB) (910) according to an embodiment of the disclosure. A specific angle (referred to as the nominal angle) can correspond to the nominal mode. In the example, eight nominal angles (or nominal intra-angles) (901)-(908) respectively correspond to eight nominal modes (e.g., V_RED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED). The eight nominal angles (901)-(908) and the eight nominal modes can be respectively referred to as V_RED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED. Further, since each nominal angle can correspond to a plurality of finer angles, 56 angles (or prediction angles) or 56 directional modes (or angle modes, directional intra-prediction modes) can be used, for example, in AV1. Each prediction angle can be indicated by a nominal angle and an angle offset (or angle delta). The angle offset can 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 the example, the prediction angle is equal to the sum of the nominal angle and the angle offset. In the example, as in AV1, the nominal modes (e.g., eight nominal modes (901)-(908)) can be notified together with specific non-angular smooth modes (e.g., five non-angular smooth modes such as the DC mode, PAETH mode, SMOOTH mode, vertical SMOOTH mode, and horizontal SMOOTH mode described later). Thereafter, if the current prediction mode is a directional mode (or angle mode), an index can be further notified to indicate the angle offset (e.g., offset integer I) corresponding to the nominal angle.In an example, to implement a directional prediction mode by a general method, 56 directional modes such as those used in AV1 are implemented by a unified direction predictor that projects each pixel to a reference sub-pixel position and interpolates the reference pixels by a 2-tap bilinear filter.

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

[0097] FIG. 10 shows 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 the disclosed embodiments. To predict the sample (1001) within CB (1000) based on the DC predictor, the average of the first value of the left adjacent sample (1012) and the second value of the upper adjacent sample (or the upper adjacent sample) (1011) can be used as the predictor.

[0098] To predict the sample (1001) based on the PAETH predictor, the first value of the left adjacent sample (1012), the second value of the upper adjacent sample (1011), and the third value of the upper left adjacent sample (1013) can be obtained. Then, using Equation 1, the reference value is determined: Reference value = First value + Second value - Third value (Equation 1)

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

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

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

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

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

[0104] Multi-line intra prediction can use more reference lines for intra prediction. The reference lines can include multiple samples within a picture. In an example, the reference lines include samples in a row and samples in a column. In an example, the encoder can determine and notify the reference lines used to generate an intra predictor. An index indicating the reference line (also called a reference line index) can be signaled before the intra prediction mode. In an example, when a non-zero reference line index is signaled, only MPM is permitted. FIG. 12 shows an example of four reference lines for CB (1210). Referring to FIG. 12, the reference lines can include up to six segments, for example, segments A to F, and a top-left reference sample. For example, reference line 0 includes segments B and E and the top-left reference sample. For example, reference line 3 includes segments A to F and the top-left reference sample. Segments A and F can be padded with the closest 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] Generally, a block can be predicted using one or an appropriate combination of various intra prediction modes, such as those described above with reference to FIGS. 9 to 12.

[0106] A transform block partition (also referred to as a transform partition or a transform unit partition) may be implemented to partition a block into a plurality of transform units. FIGS. 13-14 show exemplary transform block partitions according to the disclosed embodiments. In some examples, as in AV1, both intra-coded blocks and inter-coded blocks may be further partitioned into a plurality of transform units with a partitioning depth of up to a plurality of levels (e.g., two levels).

[0107] For an intra-coded block, the transform partitioning can be performed such that the transform blocks associated with the intra-coded block have the same size, and the transform blocks can be coded in raster scan order. Referring to FIG. 13, a transform block partitioning can be performed on a block (e.g., an intra-coded block) (1300). The block (1300) can be partitioned into transform units (e.g., TBs) such as four transform units (1301)-(1304), and the partitioning depth is 1. The four transform units (e.g., TBs) (1301)-(1304) can have the same size and can be coded in raster scan order (1310) from transform unit (1301) to transform unit (1304). In the example, the four transform units (TBs) (1301)-(1304) are separately transformed, 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 (e.g., TBs) (1321)-(1336) can have the same size and can be coded in raster scan order (1320) from transform unit (1321) to transform unit (1336).

[0108] For an inter-coded block, the transform partition can be recursively partitioned with a partitioning depth of up to a plurality of levels (e.g., two levels). The transform partition can support any suitable transform unit size and shape. The transform unit shape can include a square and a non-square (e.g., a non-square rectangle) having any suitable aspect ratio. The transform unit size can range from 4×4 to 64×64. The aspect ratio of the transform unit (e.g., the ratio of the width of the transform unit to the height of the transform unit) can be 1:1 (square), 1:2, 2:1, 1:4, 4:1, etc. The transform partition can 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, the transform block partition can be performed recursively on a block (e.g., an inter-coded block). For example, a block (1400) is partitioned into transform units (1401) to (1407). The transform units (e.g., TUs) (1401) to (1407) can have different sizes and can be coded in raster scan order (1410) from transform unit (1401) to 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) to (1405) is 2.

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

[0110] When the coding block width W or the coding block height H is greater than 64, the coding block can be implicitly divided into a plurality of TUs. At this time, the coding block is a luma coding block. The width of one of the plurality of TUs can be the minimum of W and 64, and the height of one of the plurality of TUs can be the minimum of H and 64.

[0111] When the coding block width W or the coding block height H is greater than 64, the coding block can be implicitly divided into a plurality of TUs. At this time, the coding block is a chroma coding block. The width of one of the plurality of TUs can be the minimum of W and 32, and the height of one of the plurality of TUs can 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 partitioning, 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 a 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 can use a hybrid transform kernel that can include different 1D transforms for each dimension of the coded residual block. The first 1D transform can include (a) 4-point, 8-point, 16-point, 32-point, 64-point DCT-2, (b) 4-point, 8-point, 16-point asymmetric (Asymmetric) DST (ADST) (e.g., DST-4, DST-7) and the corresponding flipped versions (e.g., the flipped version of ADST, i.e., FlipADST can apply ADST in the reverse order.), and / or (c) 4-point, 8-point, 16-point, 32-point identity transform (IDTX). FIG. 15 shows an example of primary transform basis functions according to the disclosed embodiments. The primary transform basis functions in the example of FIG. 15 include the basis functions of DCT-2 and asymmetric DST (DST-4 and DST-7) with N-point inputs. The primary transform basis functions shown in FIG. 15 can be used in AV1.

[0114] The availability of the hybrid transform kernel can depend on the transform block size and the prediction mode. FIG. 16A shows an exemplary dependency of the availability of various transform kernels (e.g., the transform types shown in the first column and explained in the second column) based on the transform block size (e.g., the sizes shown in the third column) and the prediction mode (e.g., the intra prediction and inter prediction shown in the third column). The exemplary hybrid transform kernel and the availability based on the prediction mode and transform block size can be used in AV1. Referring to FIG. 1, the signs of "→" and "↓" represent the horizontal dimension (also called the horizontal method) and the vertical dimension (also called the vertical direction), respectively. The checkmark and "x" signs represent the availability of the transform kernel for the corresponding block size and prediction mode. For example, the checkmark represents that the transform kernel is available, and the symbol "x" sign represents that the transform kernel is not available.

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

[0116] In an example, the conversion type (1620) is represented by V_ADST as shown in the first column of FIG. 16A. The conversion type (1620) includes ADST in the vertical direction and IDTX (i.e., the identity matrix) in the horizontal direction as shown in the second column of FIG. 16A. Thus, the conversion type (1620) (e.g., V_ADST) is executed in the vertical direction and not in the horizontal direction. According to the third column of FIG. 16A, the conversion type (1620) is not available for intra prediction regardless of the block size. The conversion 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, FIG. 16A is applicable to the luma component. For the chroma component, the conversion type (or conversion kernel) selection may be performed implicitly. In an example, for the intra prediction residual, the conversion type may be selected according to the intra prediction mode as shown in FIG. 16B. In an example, the conversion type selection shown in FIG. 16B is applicable to the chroma component. For the inter prediction residual, the conversion type may be selected according to the conversion type selection of the co-located luma block. Thus, in an example, the conversion type for the chroma component is not signaled in the bitstream.

[0118] The Line Graph Transform (LGT) can be used, for example, in AOMedia Video 2 (AV2) in a transform such as a first-order transform. An 8-bit / 10-bit transform core can be used in AV2. In the example, LGT includes various discrete cosine transforms (DCTs), discrete sine transforms (DSTs), as described below. LGT can include 32-point and 64-point one-dimensional (1D) DSTs.

[0119] A graph is a general mathematical structure that can include a set of vertices and edges used to model affinity relationships between objects of interest. A weighted graph, where 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 various block statistics. A separable LGT can be designed and optimized by learning a line graph from the data to model the statistics for each row and column underlying the residual signal of the block, and the associated Generalized Graph Laplacian (GGL) matrix can be used to derive the LGT.

[0120] FIG. 16C shows an example of a general LGT characterized by self-loop weights (e.g., v c1 , v c2 ) and edge weights w c . Considering the weighted graph G(W,V), the GGL matrix can be defined as follows: L c = D - W + V (Equation 3) Here, W can be an adjacency matrix that includes non-negative edge weights w c , D can be a diagonal degree matrix, and V can be a diagonal matrix representing the self-loop weights v c1 and v c2 . FIG. 16D shows an example of the matrix L c .

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

[0122] In various examples, certain DCTs and DSTs (e.g., DCT-2, DCT-8, and DST-7) are subsets of sets of LGTs obtained from specific forms of GGL. DCT-2 can be derived by setting v c1 to 0 (e.g., v c1 = 0). DST-7 can be derived by setting v c1 to w c (e.g., v c1 = w c ). DCT-8 can be derived by setting v c2 to w c (e.g., v c2 = w c ). DST-4 can be derived by setting v c1 to 2w c (e.g., v c1 = 2w c ). DCT-4 can be derived by setting v c2 to 2w c (e.g., v c2 = 2w c ).

[0123] In some examples, like in AV2, the LGT can be implemented as a matrix multiplication. The 4-point (4p) LGT core is DST-4 since it can be derived by setting v c to 2w c1 in L c . The 8-point (8p) LGT core is derived by setting v c to 1.5w c1 in L cCan be derived by setting to. In the example, an LGT core such as a 16 - point (16p) LGT core, 32 - point (32p) LGT core, or 64 - point (64p) LGT core, v c1 to w c is such that v c2 is set to 0, and the LGT core can be DST - 7w.

[0124] Transformations such as primary transformation and secondary transformation can be applied to blocks such as CB. In the example, the transformation includes a combination of primary transformation and secondary transformation. The transformation includes non - separable transformation, separable transformation, or a combination of non - separable transformation and separable transformation.

[0125] The secondary transformation is performed as in VVC. In some examples, as in VVC, the Low - Frequency Non - Separable Transform (LFNST), also known as the Reduced Secondary Transform (RST), can be applied between the forward primary transformation and quantization on the encoder side and between the inverse quantization and inverse - direction primary transformation on the decoder side, as shown in FIGS. 17 and 18, to further decorrelate the primary transformation coefficients.

[0126] The application of the non - separable transformation that can be used in LFNST is described as follows (shown in Equation 5) using a 4×4 input block (or input matrix) as an example. To apply the 4×4 non - separable transformation (e.g., LFNST), the 4×4 input block X is, as shown in Equations 5 and 6, (Outer 1) Can be represented by JPEG2025111550000002.jpg119: [Number]

[0127] The non - separable transformation can be calculated as follows: [Number] Here, (External 2) JPEG2025111550000005.jpg109 indicates a conversion coefficient vector, and T is a 16×16 conversion matrix. (External 3) JPEG2025111550000006.jpg838 can then be rearranged into 4×4 output blocks (or output matrices, coefficient blocks) using the scanning order of the 4×4 input blocks (e.g., horizontal scanning order, vertical scanning order, zigzag scanning order, or diagonal scanning order). Conversion coefficients with smaller indices can be replaced with smaller scanning indices in the 4×4 coefficient blocks.

[0128] Non-separable second-order conversion can be applied to blocks (e.g., CB). In some examples, like in VVC, LFNST is applied between the forward first-order conversion and quantization (e.g., on the encoder side) and between inverse quantization and inverse first-order conversion, as shown in FIGS. 17 and 8.

[0129] Figures 17 and 18 show examples of two transform coding processes (1700) and (1800) that use 16×64 transform (or 64×16 transform depending on whether the transform is a forward or reverse secondary transform) and 16×48 transform (or 48×16 transform depending on whether the transform is a forward or reverse secondary transform), respectively. Referring to FIG. 17, in process (1700), on the encoder side, a forward primary transform (1710) can first be performed on a block (e.g., a residual block), and a coefficient block (1713) is obtained. Thereafter, a forward secondary transform (or forward LFNST) (1712) can be applied to the coefficient block (1713). In the forward secondary transform (1712), 64 coefficients of 4×4 sub-blocks A to D at the upper left corner of the coefficient block (1713) can be represented by a 64-length vector, and the 64-length vector can be multiplied by a transform matrix of 64×16 (i.e., a width of 64 and a height of 16), and as a result, a 16-length vector is obtained. The elements of the 16-length vector are filled back into the upper left 4×4 sub-block of the coefficient block (1713). The coefficients of sub-blocks B to D can be zero. The coefficients obtained after the forward secondary transform (1712) are then quantized in a quantization step (1714) and then entropy-coded to generate coded bits in a bit stream (1716).

[0130] The coded bits are received on the decoder side, entropy-decoded, followed by an inverse quantization step (1724), and a coefficient block (1723) is generated. An inverse secondary transform (or inverse LFNST) (1722), such as an inverse RST8×8, can be performed to obtain 64 coefficients from 16 coefficients in, for example, 4×4 sub-block E at the upper left. The 64 coefficients can be filled back into 4×4 sub-blocks E to H. Further, the coefficients in the coefficient block (1723) after the inverse secondary transform can be processed by an inverse primary transform (1720) to obtain the recovered 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 - C are processed by a smaller transformation matrix of size 48×16. Using a smaller transformation matrix of 48×16 can reduce the memory size for storing the transformation 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 width, height, etc. For example, 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, 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 transformation coefficients, a reduced non-separable transform method (or RST) can be used in 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 factor. 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 R bases in the N-dimensional space. The inverse transformation matrix can be the transpose of the transformation matrix (e.g., T R×N ) used in the forward transformation. For the 8×8 LFNST, a reduction factor of 4 can be applied, and the 64×64 direct matrix used in the 8×8 non-separable transformation can be reduced to a 16×64 direct matrix as shown in FIG. 17. Alternatively, a reduction factor greater than 4 can be applied, and the 64×64 direct matrix used in the 8×8 non-separable transformation can be reduced to a 16×48 direct matrix as shown in FIG. 18. Therefore, a 48×16 inverse RST matrix can be used on the decoder side to generate the core (primary) transformation coefficients within the 8×8 upper left region.

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

[0136] To reduce complexity, LFNST can be restricted to be applicable when the coefficients outside the first coefficient subgroup are not significant. In an example, LFNST can be restricted to be applicable only when all the coefficients outside the first coefficient subgroup are not significant. Referring to FIGS. 17 and 18, since the first coefficient subgroup corresponds to the upper left block E, the coefficients outside block E are not significant.

[0137] In an example, when LFNST is applied, the primary-only conversion coefficients are not significant (e.g., zero). In an example, when LFNST is applied, all primary-only conversion coefficients are zero. The primary-only conversion coefficients can refer to the conversion coefficients obtained from the primary conversion without depending on the secondary conversion. Thus, since the signaling of the LFNST index can be conditioned on the last-significant position, the extra coefficient scanning in LFNST is avoided. In some examples, the extra coefficient scanning is used to check for significant conversion coefficients at specific positions. In an example, for instance, for per-pixel multiplication, the worst-case processing of LFNST limits the non-separable conversions of 4×4 blocks and 8×8 blocks to 8×16 conversions and 8×47 conversions, respectively. In the above case, the last-significant scanning position is less than 8 when LFNST is applied. For other sizes, the last-significant scanning position is less than 16 when LFNST is applied. For 4×N and N×4 CBs where N is greater than 8, the limitation can imply that LFNST is applied to the upper-left 4×4 region of the CB. In an example, the limitation implies that LFNST is applied only once to the upper-left 4×4 region of the CB. In an example, all primary-only coefficients are not significant (e.g., zero) when LFNST is applied, and the number of operations for the primary conversion is reduced. From the perspective of the encoder, the quantization of the conversion coefficients can be significantly simplified when the LFNST conversion is tested. The rate-distortion optimized quantization can be performed, at most, for the first 16 coefficients, for example, in the scanning order, and the remaining coefficients can be set to zero.

[0138] The LFNST transform (e.g., transform kernel, transform core, or transform matrix) can be selected as described below. In an embodiment, multiple transform sets are available, and one or more non-separable transform matrices (or kernels) can be included in each of the multiple transform sets in the LFNST. According to an aspect of the disclosure, the transform set can be selected from a plurality of transform sets, and the non-separable transform matrix can be selected from one or more non-separable transform matrices within the transform set.

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

Table 1

[0140] Referring to Table 1, the multiple transform sets include four transform sets, e.g., transform sets 0 to 3, each represented by a transform set index (e.g., Tr.set index) from 0 to 3. The index (e.g., IntraPredMode) can indicate the intra prediction mode, and based on that index and Table 1, the transform set index can be obtained. 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 CB (e.g., 81 <= IntraPredMode <= 83), transform set 0 is selected for that CB.

[0141] As described above, each transformation set can include one or more non-separable transformation matrices. One of the one or more non-separable transformation matrices can be selected, for example, by an explicitly signaled LFNST index. The LFNST index can be signaled in the bitstream, for example, once per intracoded CU (e.g., CB) after signaling of the transform coefficients. In an embodiment, each transformation set includes two non-separable transformation matrices (kernels), and the selected non-separable second-order transform candidate can be one of the two non-separable transformation matrices. In some examples, LFNST is not applied to a CB (e.g., a CB coded in transform skip mode or a CB with the number of non-zero coefficients less than a threshold). In an example, the 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, which indicates 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 not significant, and the coding of the LFNST index can depend on the position of the last significant coefficient. The LFNST index can 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 can be applied to intracoded CUs within an intra slice or an inter slice for both luma and chroma components. When a dual tree is enabled, the LFNST indices for the luma and chroma components can be signaled separately. For an inter slice (e.g., the dual tree is disabled.), a single LFNST index can be signaled and used for both luma and chroma components.

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

[0144] In some examples, a CU larger than 64×64 is implicitly divided (TU tiling) by a maximum transform size limit (e.g., 64×64), and the LFNST index search may quadruple the data buffering for a specific number of decode pipeline stages. Thus, the maximum size allowed for LFNST can be limited to 64×64. In the example, LFNST is enabled only for the Discrete Cosine Transform (DCT) type 2 (DCT-2) transform.

[0145] In some examples, a separable transform scheme may not be efficient in 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, the non-separable transform scheme can be used as a secondary transform applied to low-frequency transform coefficients obtained from a primary transform. The secondary transform is applicable to blocks, and information indicating the secondary transform can be signaled for the block based on prediction mode information, primary transform type, adjacent reconstructed samples, and / or the like. Further, transform block partitioning information (also referred to as transform block partitioning information, transform partitioning information, or transform partitioning information), the size of the coded block, and the shape of the coded block can provide additional information for efficient application and / or signaling of the secondary transform.

[0146] According to an aspect of the disclosure, coding information of a block can be decoded 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, block size, and block shape for the block.

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

[0148] In the 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), and the like.

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

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

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

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

[0153] Information related to the secondary transformation (e.g., the secondary transformation index) can indicate the secondary transformation (e.g., the secondary transformation kernel, the secondary transformation core, or the secondary transformation matrix) to be applied to the block. In an example, the secondary transformation is LFNST, RST, etc. As described above, in an embodiment, multiple sets of transformations are available, and one or more secondary transformation matrices (or kernels) can be included in each of the multiple sets of transformations. According to the disclosed aspect, the set of transformations can be selected from the multiple sets of transformations using any suitable method including but not limited to those described with reference to Table 1, and the secondary transformation (e.g., the secondary transformation matrix) to be applied to the block can be selected from one or more secondary transformation matrices in the transformation set set by the information related to the secondary transformation (e.g., the secondary transformation index).

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

[0155] In an embodiment, one or a combination of transformation partitioning information about a block, the size of the block, and the shape of the block can include the transformation partitioning information about the block. The transformation partitioning information can be signaled in a coded video bitstream. The transformation partitioning information about the block can indicate the partitioning depth for the block. The block can be partitioned into a plurality of TUs or TBs based on the transformation partitioning information about the block, as described with reference to FIG. 13, for example. Thus, whether the secondary transformation is disabled for the block can be determined based on the partitioning depth. In an example, when the partitioning depth is greater than a threshold n, it is determined that the secondary transformation is disabled for the block and it is determined that the secondary transformation index is not signaled. The threshold n can be any suitable integer. The threshold n can 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 transformation index (e.g., the LFNST index) can indicate the secondary transformation kernel applied to the block.

[0156] According to the disclosed aspect, one or a combination of conversion partitioning information about a block (e.g., CB), the size of the block, and the shape of the block can be used for the application and / or signaling of a secondary conversion for the block. In an example, one or a combination of conversion partitioning information about a block, the size of the block, and the shape of the block can be used for the application and / or signaling of a plurality of secondary conversions for the block. Whether to invalidate or enable a secondary conversion for a block can be determined based on one or a combination of conversion partitioning information about the block, the size of the block, and the shape of the block. Whether to apply a secondary conversion to a block can be determined based on one or a combination of conversion partitioning information about the block, the size of the block, and the shape of the block. Whether to signal the application of a secondary conversion for a block can be determined based on one or a combination of conversion partitioning information about the block, the size of the block, and the shape of the block.

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

[0158] In an embodiment, one or a combination of transformation partitioning information about a block, the size of the block, and the shape of the block can include the transformation partitioning information about the block and the shape of the block. The transformation partitioning information can be signaled in a coded video bitstream. The transformation partitioning information can indicate a partitioning depth for the block. The shape of the block can be a non-square rectangle. The block can be partitioned into a plurality of TUs or TBs. Whether secondary transformation is disabled for the block can be determined based on the partitioning depth. In an example, when the partitioning depth is greater than a threshold that can be 0 or a positive integer, secondary transformation is determined to be disabled for the block. [[ID=!]]

[0159] In an embodiment, the transform partitioning information about a block can be signaled, the block can 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 a plurality of TUs or TBs. Whether the secondary transform should be disabled for a block can depend on the transform partitioning information about the block. The transform partitioning information about the block can indicate the partitioning depth for the block. In an example, whether the secondary transform should be disabled for a block depends on the partitioning depth for the block. In some examples, whether information related to the secondary transform (e.g., the secondary transform index stIdx) should be signaled can depend on the transform partitioning information about the block (e.g., the partitioning depth for the block). In an example, like when the partitioning depth is greater than a threshold n, based on the threshold, the secondary transform is determined to be disabled and the secondary transform index is determined not to be signaled. As described above, the threshold n can be any suitable integer such as 0 or a positive integer. Exemplary values of the threshold n include, but are not limited to, 0, 1, 2, etc. In an example, when a block is divided into a plurality of 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.

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

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

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

[0163] In an example, when the aspect ratio of the block (e.g., the ratio of the width of the block to the height of the block) is less than a threshold J (e.g., 1, 1 / 2, 1 / 4, 1 / 8, etc.), the second-order transformation index is not signaled and / or the second-order transformation 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 transformation partitioning information, block size, and block shape for a block can include the transformation partitioning information and the block shape. The transformation partitioning information can indicate the partitioning depth for the block. The block shape can be square. The block can be partitioned into a plurality of TUs or TBs. Whether the second transformation is disabled for the block can be determined based on the partitioning depth. In an example, when the partitioning depth is greater than a threshold value that can be 0 or a positive integer, the second transformation is determined to be disabled for the block.

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

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

[0167] In an embodiment, one or a combination of transformation partitioning information about a block, the size of the block, and the shape of the block can include the transformation partitioning information about the block and the size of the block. The transformation partitioning information can indicate the partitioning depth for the block. The size of the block can indicate the width of the block (or block width) and the height of the block (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 can be partitioned into a plurality of TUs or TBs. Whether the secondary transformation is disabled for the block can be determined based on the transformation partitioning information about the block (e.g., the partitioning depth). In an example, when the partitioning depth is greater than a threshold that can be 0 or a positive integer, the secondary transformation is determined to be disabled for the block.

[0168] In an embodiment, the size of the block (e.g., the minimum of the block width and the block height) can exceed the threshold size. The threshold size can 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 can be partitioned into a plurality of TUs or TBs. In an example, the transformation partitioning information about the block is also signaled. Therefore, whether the secondary transformation should be disabled for the block can depend on the transformation partitioning information about the block (e.g., the partitioning depth for the block). In some examples, the information related to the secondary transformation (e.g., the secondary transformation index) depends on the transformation partitioning information about the block (e.g., the partitioning depth for the block).

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

[0170] In an example, exemplary values of the threshold size include, but are not limited to, 256×256, 256×128, 128×256, 128×128, 128×64, 64×128, 64×64, and / or the like.

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

[0172] In an embodiment, one of the width W' of another block and the height H' of another block is larger than the maximum conversion size T, and the other block can be divided into a plurality of sub-blocks including the block. The width W of the block can be the minimum of W' and T, and the height H of the block can be the minimum of H' and T. One or a combination of the conversion partitioning information about the block, the size of the block, and the shape of the block can include the conversion partitioning information about the block indicating the partitioning depth for the block. When the partitioning depth for the block is larger than a threshold, the secondary conversion can be determined to be invalid 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 the height H' of another block is larger than a predefined constant K, and the other block can be implicitly divided into a plurality of sub-blocks. Exemplary values of K can include, but are not limited to, 16, 32, 64, 128, and 256. When one or more of the plurality of 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 conversion is applied only to those one or more of the plurality of sub-blocks, and / or information related to the secondary conversion (e.g., one or more secondary conversion indices) is signaled only for those one or more of the plurality of sub-blocks. Those one or more of the plurality of sub-blocks include the above-mentioned block.

[0174] In an embodiment, one of the width W' of another block and the height H' of another 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 can be the minimum of W' and K, and the height H of the block can be the minimum of H' and K. One or a combination of the conversion partitioning information, the size, and the shape of the block for the block can include the size of the block having W and H. The secondary conversion may be determined to be effective for a block whose block size is W and H. In an example, the secondary conversion is determined to be applied to a block whose block size is W and H.

[0175] FIG. 19 shows a flowchart illustrating a process (1900) according to an embodiment of the disclosure. The process (1900) can 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 executed by processing circuits in terminal devices (310), (320), (330) and (340), a processing circuit that executes the function of the video encoder (403), a processing circuit that executes the function of the video decoder (410), a processing circuit that executes the function of the video decoder (510), a processing circuit that executes the function of the video encoder (603), etc. In some examples, since the process (1900) is implemented by software instructions, when the processing circuit executes the software instructions, the processing circuit executes the process (1900). The process starts from (S1901) and proceeds to (S1910).

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

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

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

[0179] In an example, the transformation partitioning information for the block can be signaled, the block can have a square rectangular shape, and the block can be further partitioned into a plurality of TUs or TBs. Thus, whether the secondary transformation should be disabled for the block can depend on the transformation partitioning information for the block (e.g., the partitioning depth for the block).

[0180] Whether a second-order transformation should be applied to a block can depend on the shape of the block (e.g., the aspect ratio of the block). In some examples, whether information related to the second-order transformation (e.g., the second-order transformation index stIdx) should be signaled can depend on the shape of the block (e.g., the aspect ratio of the block).

[0181] In an embodiment, a block can be partitioned into a plurality of TUs or TBs. The shape of the block can be square. Thus, whether the second-order transformation should be disabled for the block can depend on the transformation partitioning information about the block (e.g., the partitioning depth for the block). In an example, the transformation partitioning information about the block is signaled. In some examples, whether information related to the second-order transformation (e.g., the second-order transformation index) should be signaled can depend on the transformation partitioning information about the block (e.g., the partitioning depth for the block).

[0182] In an embodiment, the size of the block (e.g., the minimum of the block width and the block height) can exceed a threshold size (e.g., 64, 128, 256, etc.). The block can be partitioned into a plurality of TUs or TBs. In an example, the transformation partitioning information about the block is also signaled. Thus, whether the second-order transformation should be disabled for the block can depend on the transformation partitioning information about the block (the partitioning depth for the block). In some examples, whether information related to the second-order transformation (e.g., the second-order transformation index) should be signaled can depend on the transformation partitioning information about the block (e.g., the partitioning depth for the block).

[0183] (In S1930), the block can be reconstructed based on a determination of whether the secondary transform is disabled for the block. In the example, since the secondary transform is determined to be disabled for the block in (S1920), the block can be reconstructed only by the primary transform without the secondary transform.

[0184] In the example, since the secondary transform is determined to be enabled for the block in (S1920), the block can be reconstructed by the primary transform and the secondary transform when it is determined that the secondary transform is applied to the block. When 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 a plurality of TUs (or TBs), different secondary transforms can be applied to the plurality of TUs (or TBs) respectively. Which secondary transform (e.g., which secondary transform kernel) should be applied to each TU (or TB) can be further indicated using the corresponding secondary transform index (e.g., signaled in the coded video bitstream). The process (1900) proceeds to (S1999) and ends.

[0185] The process (1900) can be appropriately adapted. The steps of the process (1900) can be changed and / or deleted. Additional steps can be added. Any implementation order can be used. In an embodiment, the width W' of other blocks and the height H' of other blocks are greater than the maximum conversion size T, and the other blocks can be implicitly divided into a plurality of sub-blocks including the block. The width W of the block can be the minimum of W' and T, and the height H of the block can be the minimum of H' and T. One or a combination of the conversion partitioning information about the block, the size of the block, and the shape of the block can include the conversion partitioning information about the block indicating the partitioning depth for the block. When the partitioning depth for the block is greater than a threshold, the secondary conversion can be determined to be invalid for the block. The partitioning depth can 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 other blocks and the height H' of other blocks are greater than a predefined constant K. The other blocks can be divided into a plurality of sub-blocks including the block. The width W of the block can be the minimum of W' and K, and the height H of the block can be the minimum of H' and K. One or a combination of the conversion partitioning information about the block, the size of the block, and the shape of the block can include the size of the block having W and H. The secondary conversion is determined to be applied only to the block whose size of the block is W and H.

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

[0188] In an example, whether the multiple secondary transformations are disabled for a block and / or whether the multiple secondary transformation indexes related to the multiple secondary transformations are signaled can be determined based on the transformation partitioning information (e.g., the partitioning depth) for the block. For example, when the partitioning depth is greater than a threshold n (e.g., 0 or a positive integer), it is determined that the multiple secondary transformations are disabled for the block, and the multiple secondary transformation indexes are not signaled. In an example, whether the multiple secondary transformations are disabled for a block and / or whether the multiple secondary transformation indexes related to the multiple secondary transformations are signaled can be determined based on the shape of the block (e.g., the aspect ratio).

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

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

[0191] The computer software can be coded in any suitable machine code or computer language that can generate code including instructions executable directly by one or more central processing units (CPUs) of a computer, a graphics processing unit (GPU), etc., or through mechanisms such as interpretation and microcode execution according to mechanisms such as assembly, compilation, and linking.

[0192] The instructions are executable on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming machines, Internet of Things devices, etc.

[0193] The components shown in FIG. 20 with respect to the computer system (2000) are illustrative in nature and are not intended to suggest any limitation with respect to the use or functionality of the computer software implementing the embodiments of the present disclosure. The configuration of the components should not be construed as having any dependency or requirement with respect to any one or combination of the components described in the exemplary embodiment of the computer system (2000).

[0194] The computer system (2000) may include a specific human interface input device. Such a human interface input device may respond to input by one or more users through, for example, tactile input (e.g., keyboard, swipe, data glove movement), voice input (e.g., voice, clap), visual input (e.g., gesture), olfactory input (not shown). The human interface device may also be used to capture specific media that is not necessarily directly related to conscious human input, such as voice (e.g., speech, music, ambient sound), images (e.g., scanned images, photographic images obtained from a still camera), video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

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

[0196] The computer system (2000) may also include certain human interface output devices. Such human interface output devices can stimulate the senses of one or more users through, for example, tactile output, sound, light, and smell / taste. Such human interface output devices include tactile output devices (e.g., tactile feedback by a touch screen (2010), a data glove (not shown), or a joystick (2005), although there may also be tactile feedback devices that do not function as input devices), audio output devices (e.g., a speaker (2009), headphones (not shown)), visual output devices (e.g., a CRT screen, an LCD screen, a plasma screen, an OLED screen, regardless of whether they have a touch screen input function or not, and regardless of whether they have a tactile feedback function or not, and some of them can output two-dimensional visual output or output of more than three dimensions by means such as stereoscopic output, virtual reality glasses (not shown), holographic display, and a smoke tank (not shown) (2010)), and a printer (not shown).

[0197] The computer system (2000) can also include human-accessible storage devices and their associated media, such as CD / DVD ROM / RW (2020) by CD / DVD or similar media (2021), a thumb drive (2022), a removable hard disk or solid state drive (2023), legacy magnetic media such as tapes and floppy (registered trademark) disks (not shown), dedicated ROM / ASIC / PLD-based devices such as security dongles (not shown), etc.

[0198] One of ordinary skill in the art should also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not include a transmission medium, a carrier wave, or other transient signals.

[0199] The computer system (2000) can also include an interface (2054) to one or more communication networks (2055). The network can be, for example, wireless, wireline, optical. The network can further be local, wide area, metropolitan, vehicle and industrial, real-time, delay-tolerant, etc. Examples of networks include local area networks such as Ethernet (registered trademark), wireless LAN, 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, vehicle and factory networks including CAN bus, etc. Certain networks generally require an external network interface adapter attached to a specific general-purpose digital port or peripheral bus (2049) (such as a USB port of the computer system (2000)). Others are generally incorporated into the core of the computer system (2000) by attachment to a system bus as described later (such as 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 communication can be unidirectional receive-only (such as broadcast TV) or unidirectional transmit-only (such as CAN bus to a specific CAN bus device), or can be bidirectional to other computer systems using, for example, local or wide area digital networks. A specific protocol or protocol stack can be used with each of the networks and network interfaces as described above.

[0200] The above human interface device, human-accessible storage device, and network interface can be attached to the core (2040) of the computer system (2000).

[0201] The core (2040) can include one or more central processing units (CPUs) (2041), a graphics processing unit (GPU) (2042), a dedicated programmable processing unit in the form of a field programmable gate array (FPGA) (2043), a hardware accelerator for specific tasks (2044), a graphics adapter (2050), and the like. These devices can be connected through a system bus (2048) together with a read-only memory (ROM) (2045), a random access memory (RAM) (2046), a built-in mass storage device such as an internal hard drive not accessible to users, an SSD, etc. (2047). In some computer systems, the system bus (2048) can be accessible in the form of one or more physical plugs to allow for expansion by additional CPUs, GPUs, etc. Peripheral devices can be attached directly to the core's system bus (2048) or through a peripheral bus (2049). In the example, a display (2010) can be connected to the graphics adapter (2050). Architectures for peripheral buses include PCI, USB, and the like.

[0202] The CPU (2041), GPU (2042), FPGA (2043), and accelerator (2044) are capable of executing specific instructions that can together constitute the above computer code. The computer code can be stored in the ROM (2045) or RAM (2046). Temporary data can also be stored in the RAM (2046), while persistent data can be stored, for example, in the built-in mass storage device (2047). Fast storage and retrieval to / from any of the memory devices can be enabled by the use of cache memory. The cache memory can be closely related to one or more CPUs (2041), GPUs (2042), mass storage devices (2047), ROM (2045), RAM (2046), etc.

[0203] A computer-readable medium can have computer code for performing various computer-implemented operations. The medium and the computer code can be specially designed and configured for the purposes of this disclosure, or they can be of the kind well known and available to persons having ordinary skill in the computer software arts.

[0204] As an example, and not by way of limitation, a computer system having an architecture (2000), specifically a core (2040), can provide functionality as a result of software executed by a processor (including a CPU, GPU, FPGA, accelerator, etc.) embodied in one or more tangible computer-readable media. Such computer-readable media can be media associated with the user-accessible mass storage device introduced above, in addition to specific storage devices of the core (2040) that are non-transitory in nature, such as a core-integrated mass storage device (2047) or ROM (2045). The software implementing various embodiments of the present disclosure is stored on such a device and is executable by the core (2040). The computer-readable media can include one or more memory devices or chips, depending on specific needs. The software can cause the core (2040), and specifically the processors (including a CPU, GPU, FPGA, etc.) therein, to define data structures stored in RAM (2046) and to modify such data structures according to processes defined by the software, thereby executing specific processes or specific portions of specific processes described herein. Additionally, or alternatively, the computer system can provide functionality as a result of logic (e.g., an accelerator (2044)) hardwired or otherwise embodied in circuitry that operates instead of or in conjunction with software to execute specific processes or specific portions of specific processes described herein. References to software can, if necessary, include logic, and vice versa. References to computer-readable media can, if necessary, include circuitry (e.g., an integrated circuit (IC)) storing software for execution, circuitry embodying logic for execution, or both. 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] Although the present disclosure has described several exemplary embodiments, there are alternatives, exchanges, and various substitution equivalents within the scope of the present disclosure. Thus, as is apparent, those skilled in the art can embody the principles of the present disclosure, and thus, numerous systems and methods within its spirit and scope can be envisioned, even if not explicitly illustrated or described herein.

Claims

1. A video encoding method performed by an encoder, The step of obtaining coding information for a block of a video sequence, wherein the coding information indicates one or a combination of the intra-prediction mode for the block, the conversion partitioning information for the block, the size of the block, and the shape of the block. A step of determining whether a secondary transformation is disabled for the block based on one or a combination of the transformation partitioning information for the block, the size of the block, and the shape of the block, Based on the determination of whether the aforementioned quadratic transformation is invalid for the block, the steps include encoding the block and It has, The conversion partitioning information for the block, the size of the block, and the shape of the block, one or a combination thereof, include the conversion partitioning information for the block. The conversion partitioning information for the block indicates the partitioning depth for the block. The method further includes the step of partitioning the block into a plurality of transformation blocks, The step of determining whether the quadratic transformation is invalid for the block includes determining whether the quadratic transformation is invalid for the block based on the partitioning depth. method.

2. The step of determining whether the quadratic transformation is disabled for the block includes determining that the quadratic transformation is disabled for the block in response that the partitioning depth is greater than a threshold, The threshold is 0 or a positive integer. The method according to claim 1.

3. The threshold is 0. The method according to claim 2.

4. If it is determined that the quadratic transformation is invalid for the block, it is further determined that the quadratic transformation index indicating the quadratic transformation kernel applied to the block is not signaled to the decoder. The method according to claim 2 or 3.

5. The conversion partitioning information for the block, the size of the block, and the shape of the block, one or a combination thereof, further includes the shape of the block, wherein the shape of the block is a non-square rectangle or a square. The method according to any one of claims 1 to 4.

6. The conversion partitioning information for the block, the size of the block, and the shape of the block, one or a combination thereof, further includes the shape of the block as indicated by the aspect ratio of the block. The step of determining whether the quadratic transformation is invalid for the block includes determining whether the quadratic transformation is invalid for the block based on the aspect ratio of the block. The method according to any one of claims 1 to 4.

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

8. The conversion partitioning information for the block, the size of the block, and the shape of the block, one or a combination thereof, further includes the size of the block, wherein the size of the block indicates the width and height of the block which are greater than the threshold size. The method according to any one of claims 1 to 4.

9. The width W' of the other block and the height H' of the other block are greater than the maximum conversion size T. The method further comprises dividing the other block into a plurality of subblocks including the block, wherein the width W of the block is the minimum of W' and T, and the height H of the block is the minimum of H' and T. The step of determining whether the quadratic transformation is disabled for the block includes determining that the quadratic transformation is disabled for the block in response that the partitioning depth for the block is greater than a threshold. The method according to claim 1.

10. The width W' of the other block and the height H' of the other block are greater than a predetermined constant K. The method further comprises dividing the other block into a plurality of subblocks including the block, wherein the width W of the block is the minimum of W' and K, and the height H of the block is the minimum of H' and K. The conversion partitioning information for the block, the size of the block, and the shape of the block, one or a combination thereof, further includes the size of the block having W and H, The step of determining whether the quadratic transformation is disabled for the block includes determining that the quadratic transformation is enabled for the block in response to the size of the block being W and H. The method according to claim 1.

11. A device for video encoding, A non-temporary computer-readable medium that stores a program, A processing circuit configured to execute the aforementioned program It has, When the program is executed by the processing circuit, it causes the processing circuit to perform the method according to any one of claims 1 to 10. Device.

12. A program that, when executed by a processor, causes the processor to perform the method according to any one of claims 1 to 10.

13. A video encoding method performed by an encoder, The step of obtaining coding information for a block of a video sequence, wherein the coding information indicates one or a combination of the intra-prediction mode for the block, the conversion partitioning information for the block, the size of the block, and the shape of the block. A step of determining whether a secondary transformation is disabled for the block based on one or a combination of the transformation partitioning information for the block, the size of the block, and the shape of the block, A step of encoding the block based on a determination of whether the aforementioned quadratic transformation is invalid for the block, The steps include: encoding the coding information and including it in the video bitstream along with the encoded block to generate an encoded video bitstream; The steps include storing the encoded video bitstream on a non-temporary recording medium and It has, The conversion partitioning information for the block, the size of the block, and the shape of the block, one or a combination thereof, include the conversion partitioning information for the block. The conversion partitioning information for the block indicates the partitioning depth for the block. The method further includes the step of partitioning the block into a plurality of transformation blocks, The step of determining whether the quadratic transformation is invalid for the block includes determining whether the quadratic transformation is invalid for the block based on the partitioning depth. method.

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