Method, device and storage medium for decoding video data

Abstract

A method, apparatus and computer-readable storage medium for encoding / decoding video data in a decoder. The method includes: receiving an encoded video code stream of a data block; extracting a transform partition type associated with the data block from the encoded video code stream; and in response to the transform partition type belonging to a subset of a predetermined transform partition type set, each transform partition type in the predetermined transform partition type set specifies a splitting mode for splitting the data block into transform blocks: extracting a transform type of a transform associated with a transform block split from the data block, as represented by a signal in the encoded video code stream, wherein the transform type belongs to a first predetermined transform type set; and performing an inverse transform on the transform block according to the transform type.

Description

[0001] Incorporation by reference

[0002] This application is based upon and claims the benefit of priority of U.S. Provisional Application No. 63 / 175,897, filed on April 16, 2021, and U.S. Non-Provisional Application No. 17 / 568,275, filed on January 4, 2022, both of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure describes a set of advanced video coding techniques. More specifically, the disclosed techniques relate to the interaction between transform partitioning schemes and primary / secondary transform type selection in video encoding and decoding. Background Art

[0004] The background description provided herein is for the purpose of presenting the present disclosure in general. The extent to which the work of the presently named inventors described in this background section and in various aspects of this specification is performed does not indicate that it qualifies as prior art at the time of filing this application, and it is never expressly or impliedly admitted that it is prior art to the present disclosure.

[0005] Video encoding and decoding may be performed using inter-picture prediction with motion compensation. An uncompressed digital video may include a series of pictures, each picture having a spatial size of, for example, 1920×1080 luma samples and associated full or subsampled chroma samples. The series of pictures may have a fixed or variable picture rate (alternatively referred to as a frame rate) of, for example, 60 pictures per second or 60 frames per second. For streaming or data processing, uncompressed video has specific bit rate requirements. For example, a video with a pixel resolution of 1920×1080, a frame rate of 60 frames per second, a chroma subsampling of 4:2:0, and 8 bits per pixel / color channel requires a bandwidth of nearly 1.5 Gbit / s. One hour of such video requires more than 600 GB of storage space.

[0006] One purpose of video encoding and decoding can be to reduce redundancy in an uncompressed input video signal by compression. Compression can help reduce the bandwidth and / or storage space requirements mentioned above, in some cases by two orders of magnitude or more. Lossless compression and lossy compression and their combinations can be used. Lossless compression refers to a technique that can reconstruct an exact copy of the original signal from the compressed original signal through a decoding process. Lossy compression refers to the following encoding / decoding process: the original video information is not completely preserved during encoding and cannot be completely restored during decoding. When lossy compression is used, the reconstructed signal may be different from the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal usable for the intended application, despite the loss of some information. In the case of video, lossy compression is widely used in many applications. The amount of distortion that can be tolerated depends on the application. For example, users of some consumer video streaming applications can tolerate higher distortion than users of movie or television broadcast applications. The compression rate that can be achieved by a specific encoding algorithm can be selected or adjusted to reflect various distortion tolerances: higher tolerable distortion generally allows the encoding algorithm to produce higher losses and higher compression rates.

[0007] Video encoders and decoders may utilize techniques and steps from several broad categories including, for example, motion compensation, Fourier transforms, quantization, and entropy coding.

[0008] Video codec techniques may include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, pictures are spatially subdivided into blocks of samples. When all blocks of samples are encoded in intra-mode, the picture may be referred to as an intra-picture. Intra-pictures and their derivatives (e.g., independent decoder refresh pictures) can be used to reset the decoder state and can therefore be used as the first picture in an encoded video stream and video session, or as a still image. The samples of the block after intra-prediction can then be transformed into the frequency domain, and the transform coefficients so generated can be quantized before entropy coding. Intra-prediction represents a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value after the transform and the smaller the AC coefficient, the fewer bits are required to represent the block after entropy coding at a given quantization step size.

[0009] Traditional intra-frame coding, such as known from coding techniques such as MPEG-2, does not use intra-frame prediction. However, some newer video compression techniques include techniques that attempt to encode / decode blocks based on, for example, surrounding sample data and / or metadata that are obtained during spatially adjacent encoding and / or decoding and that precede the data block being intra-coded or decoded in decoding order. Such techniques are hereinafter referred to as "intra-frame prediction" techniques. It should be noted that, at least in some cases, intra-frame prediction uses only reference data from the current picture being reconstructed, and does not use reference data from reference pictures.

[0010] Intra-frame prediction can take many different forms. When more than one such technique can be used in a given video coding technique, the technique in use may be referred to as an intra-frame prediction mode. One or more intra-frame prediction modes may be provided in a particular codec. In some cases, a mode may have sub-modes and / or may be associated with various parameters, and the mode / sub-mode information and the intra-frame coding parameters of a video block may be encoded separately or jointly contained in a mode codeword. Which codeword is used for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gain through intra-frame prediction, and therefore may affect the entropy coding technique used to convert the codeword into a bitstream.

[0011] H.264 introduced an intra prediction mode, which was refined in H.265 and further refined in newer coding techniques such as the Joint Exploration Model (JEM), Next Generation Video Coding (VVC), and Benchmark Set (BMS). Typically, for intra prediction, values ​​belonging to neighboring samples that have become available can be used to form a predictor block. For example, available values ​​for a particular set of neighboring samples can be copied to the prediction block along a certain direction and / or row. Reference to the direction of use can be encoded in the bitstream, or it can be predicted itself.

[0012] refer to Figure 1A , a subset of 9 prediction directions specified in the 33 possible intra-frame prediction directions of H.265 (corresponding to the 33 angular modes of the 35 intra-frame modes specified in H.265) is depicted at the bottom right. The point (101) where the arrows converge represents the sample being predicted. The arrows represent the direction along which the sample at 101 is predicted using neighboring samples. For example, arrow (102) indicates that sample (101) is predicted based on one or more neighboring samples at a 45 degree angle to the horizontal direction at the top right. Similarly, arrow (103) indicates that sample (101) is predicted based on one or more neighboring samples at a 22.5 degree angle to the horizontal direction at the bottom left of sample (101).

[0013] Still reference Figure 1A, a square block (104) of 4×4 samples is depicted in the upper left (indicated by the bold dashed line). The square block (104) includes 16 samples, each of which is labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample in the Y dimension (starting from the top) and the first sample in the X dimension (starting from the left). Similarly, sample S44 is the fourth sample in the block (104) in both the Y and X dimensions. Since the size of the block is 4×4 samples, S44 is located in the lower right corner. An exemplary reference sample is also shown that follows a similar numbering scheme. The reference sample is labeled with R, its Y position (e.g., row index) and X position (column index) relative to the block (104). In H.264 and H.265, prediction samples adjacent to the block being reconstructed are used.

[0014] The intra picture prediction of block 104 may start by copying reference sample values ​​from neighboring samples according to a signaled prediction direction. For example, assume that the encoded video bitstream includes signaling indicating the prediction direction of arrow (102) for this block 104, i.e., predicting samples according to one or more prediction samples at the top right and at a 45 degree angle to the horizontal. In this case, samples S41, S32, S23, and S14 are predicted according to the same reference sample R05. Sample S44 is then predicted according to reference sample R08.

[0015] In some cases, the values ​​of multiple reference samples may be combined, such as by interpolation, to compute the reference sample; in particular, when the direction is not divisible by 45 degrees.

[0016] As video coding technology continues to develop, the number of possible directions increases. In H.264 (2003), for example, nine different directions can be used for intra-frame prediction. In H.265 (2013), this increased to 33 directions, and at the time of this disclosure, JEM / VVC / BMS can support up to 65 directions. Experimental studies have been conducted to help identify the most appropriate intra-frame prediction directions, and some techniques in entropy coding can be used to encode those most appropriate directions with small bits, accepting a certain bit cost for the direction. In addition, the direction itself can sometimes be predicted based on the adjacent directions used in the intra-frame prediction of decoded adjacent blocks.

[0017] Figure 1B A schematic diagram (180) is shown depicting 65 intra prediction directions according to JEM to illustrate the increase in the number of prediction directions in various encoding techniques developed over time.

[0018] The manner in which bits representing intra-prediction directions are mapped to the prediction directions in the coded video bitstream may vary from one video coding technique to another; for example, it may range from a simple direct mapping of prediction directions to intra-prediction modes, to mapping of prediction directions to codewords, to complex adaptive schemes involving most probable modes, and the like. However, in all cases, there may be certain intra-prediction directions that are statistically less likely to occur in the video content than certain other directions. Since the goal of video compression is to reduce redundancy, in a well-designed video coding technique, those less likely directions may be represented by more bits than more likely directions.

[0019] Inter-picture prediction or inter-prediction may be based on motion compensation. In motion compensation, sample data from a previously reconstructed picture or portion thereof (reference picture) may be used to predict a newly reconstructed picture or picture portion (e.g., block) after being spatially shifted in a direction indicated by a motion vector (hereinafter MV). In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions, X and Y, or three dimensions, with the third dimension being an indication of the reference picture being used (similar to the time dimension).

[0020] In some video compression techniques, the current MV applicable to a region of sample data may be predicted based on other MVs, for example, based on other MVs related to another region of sample data that is spatially adjacent to the region being reconstructed and that precede the current MV in decoding order. Doing so can greatly reduce the total amount of data required to encode the MV by eliminating redundancy in the related MVs, thereby increasing compression efficiency. MV prediction can work effectively, for example, because when encoding an input video signal obtained from a camera (called natural video), there is a statistical probability that a larger area than the area for which a single MV applies moves in a similar direction in the video sequence, so in some cases, similar motion vectors derived from MVs of neighboring areas can be used to predict the larger area. This makes the actual MV for a given region similar or identical to the MV predicted from the surrounding MVs. Further, after entropy coding, the MV can be represented using a smaller number of bits than would be used if the MV was encoded directly (rather than predicted from neighboring MVs). In some cases, MV prediction can be an example of losslessly compressing a signal (i.e., MV) derived from an original signal (i.e., a sample stream). In other cases, the MV prediction itself may be lossy, for example due to round-off errors when computing the prediction value from multiple surrounding MVs.

[0021] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Recommendation H.265, "High Efficiency Video Coding", December 2016). Among the multiple MV prediction mechanisms specified by H.265, described below is a technique hereinafter referred to as "spatial merge".

[0022] Specifically, refer to Figure 2 , the current block (201) includes samples that have been found by the encoder during the motion search process, which can be predicted from a previous block of the same size that has been spatially offset. Instead of encoding the MV directly, the MV can be derived from metadata associated with one or more reference pictures, for example using the MV associated with any of the five surrounding samples labeled A0, A1 and B0, B1, B2 (corresponding to 202 to 206), which is derived from the nearest reference picture (in decoding order). In H.265, MV prediction can use prediction values ​​from the same reference picture being used by neighboring blocks. Summary of the invention

[0023] This disclosure describes various embodiments of methods, apparatus, and computer-readable storage media for video encoding and / or decoding.

[0024] According to one aspect, an embodiment of the present disclosure provides a method for encoding / decoding video data in a decoder. The method includes: receiving an encoded video code stream of a data block; extracting a transform partition type associated with the data block from the encoded video code stream; and in response to the transform partition type belonging to a subset of a predetermined transform partition type set, each transform partition type in the predetermined transform partition type set specifies a splitting mode for splitting the data block into transform blocks: extracting a transform type of a transform associated with a transform block split from the data block, the transform type being represented by a signal in the encoded video code stream, wherein the transform type belongs to a first predetermined transform type set; and performing an inverse transform on the transform block according to the transform type.

[0025] According to another aspect, an embodiment of the present disclosure provides a method for encoding / decoding video data. The method includes: receiving an encoded video code stream of a data block; extracting a transform partition type associated with the data block of the video data from the encoded video code stream; in response to the transform partition type belonging to a subset of a predetermined transform partition type set, extracting a transform type associated with the transform block of the data block from the encoded video code stream; and in response to the transform partition type not belonging to the predetermined transform partition type set, identifying the transform type of the data block in a default manner.

[0026] According to another aspect, an embodiment of the present disclosure provides a method for encoding / decoding video data. The method includes: receiving an encoded video code stream of a data block; extracting a transform type of a transform associated with a transform block of the data block from the encoded video code stream; and in response to the transform type belonging to a predetermined transform type set: extracting a transform partition type associated with the data block from the encoded video code stream.

[0027] According to another aspect, an embodiment of the present disclosure provides a device for video encoding and / or decoding. The device includes: a memory storing instructions; and a processor communicating with the memory. When the processor executes the instructions, the processor is configured to cause the device to perform the above-mentioned method for video decoding and / or encoding.

[0028] According to yet another aspect, an embodiment of the present disclosure provides a non-transitory computer-readable medium storing instructions, which, when executed by a computer for video decoding and / or encoding, causes the computer to perform the above-mentioned method for video decoding and / or encoding.

[0029] The above and other aspects and implementations thereof are described in more detail in the drawings, the description and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further features, properties and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings, in which:

[0031] Figure 1A A schematic diagram of an exemplary subset of intra-prediction directional modes is shown.

[0032] Figure 1B A diagram of exemplary intra prediction directions is shown.

[0033] Figure 2 A schematic diagram of a current block and its surrounding spatial merging candidates for motion vector prediction in one example is shown.

[0034] Figure 3 A schematic illustration of a simplified block diagram of a communication system (300) is shown according to an exemplary embodiment.

[0035] Figure 4 A schematic illustration of a simplified block diagram of a communication system (400) is shown according to an exemplary embodiment.

[0036] Figure 5 A schematic illustration of a simplified block diagram of a video decoder according to an exemplary embodiment is shown.

[0037] Figure 6A schematic illustration of a simplified block diagram of a video encoder according to an exemplary embodiment is shown.

[0038] Figure 7 A block diagram of a video encoder according to another exemplary embodiment is shown.

[0039] Figure 8 A block diagram of a video decoder according to another exemplary embodiment is shown.

[0040] Fig. 9 A directional intra prediction mode according to an exemplary embodiment of the present disclosure is shown.

[0041] Fig.10 A non-directional intra prediction mode according to an exemplary embodiment of the present disclosure is shown.

[0042] Fig.11 A recursive intra prediction mode according to an exemplary embodiment of the present disclosure is shown.

[0043] Fig.12 Transform block partitioning and scanning of an intra prediction block according to an exemplary embodiment of the present disclosure are shown.

[0044] Fig.13 Transform block partitioning and scanning of an inter prediction block according to an exemplary embodiment of the present disclosure are shown.

[0045] Fig.14 A low frequency inseparable transformation process according to an exemplary embodiment of the present disclosure is shown.

[0046] Fig.15 An intra prediction scheme based on respective reference lines according to an exemplary embodiment of the present disclosure is shown.

[0047] Fig.16 A non-recursive block partitioning scheme according to an exemplary embodiment of the present disclosure is shown.

[0048] Fig.17 A flow chart according to an exemplary embodiment of the present disclosure is shown.

[0049] Fig.18 A schematic diagram of a computer system according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0050] Figure 3A simplified block diagram of a communication system (300) according to one embodiment of the present disclosure is shown. The communication system (300) includes a plurality of terminal devices that can communicate with each other via, for example, a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). Figure 3 In the example of , the first terminal device pair (310) and (320) can perform unidirectional data transmission. For example, the terminal device (310) can encode video data (for example, video data of a video picture stream collected by the terminal device (310)) for transmission to another terminal device (320) via the network (350). The encoded video data can be transmitted in the form of one or more encoded video code streams. The terminal device (320) can receive the encoded video data from the network (350), decode the encoded video data to restore the video picture, and display the video picture based on the restored video data. The unidirectional data transmission can be implemented in applications such as media services.

[0051] In another example, the communication system (300) includes a second terminal device pair (330) and (340) that performs bidirectional transmission of encoded video data, which can be implemented, for example, during a video conferencing application. For bidirectional data transmission, in one example, each of the terminal devices (330) and (340) can encode video data (e.g., video data of a video picture stream collected by the terminal device) for transmission to the other terminal device (330) and (340) via a network (350). Each of the terminal devices (330) and (340) can also receive the encoded video data transmitted by the other terminal device (330) and (340), and can decode the encoded video data to restore the video picture, and can display the video picture on an accessible display device based on the restored video data.

[0052] exist Figure 3In the example of, terminal device (310), terminal device (320), terminal device (330) and terminal device (340) can be implemented as a server, a personal computer and a smart phone, but the applicability of the underlying principles of the present disclosure may not be limited to this. Embodiments of the present disclosure can be implemented in a desktop computer, a laptop computer, a tablet computer, a media player, a wearable computer, a dedicated video conferencing device, etc. Network (350) represents any number of networks that transmit encoded video data between terminal devices (310), terminal devices (320), terminal devices (330) and terminal devices (340), including, for example, wired (wired) and / or wireless communication networks. Communication network (350) 9 can exchange data in circuit switching channels, packet switching channels and / or other types of channels. Representative networks include telecommunication networks, local area networks, wide area networks and / or the Internet. For the purpose of this discussion, unless explicitly stated herein, the architecture and topology of network (350) may be irrelevant to the operation of the present disclosure.

[0053] As examples of applications for the disclosed subject matter, Figure 4 The placement of the video encoder and video decoder in a video streaming environment is shown. The disclosed subject matter is equally applicable to other video applications, including, for example, video conferencing, digital TV, broadcasting, gaming, virtual reality, storing compressed video on digital media including CDs, DVDs, memory sticks, etc., and the like.

[0054] The video streaming system may include a video acquisition subsystem (413), which may include a video source (401), such as a digital camera, for creating an uncompressed video picture or image stream (402). In one example, the video picture stream (402) includes samples recorded by the digital camera of the video source 401. The video picture stream (402), which is depicted as a thick line to emphasize the high amount of data compared to the encoded video data (404) (or the encoded video bitstream), can be processed by an electronic device (420), which includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination of hardware and software to implement or implement various aspects of the disclosed subject matter as described in more detail below. The encoded video data (404) (or the encoded video bitstream (404)), depicted as thin lines to emphasize the lower data volume compared to the uncompressed video picture stream (402), can be stored on the streaming server (405) for future use, or directly stored in a downstream video device (not shown). One or more streaming client subsystems, such as Figure 4The client subsystem (406) and the client subsystem (408) in the streaming server (405) can access the streaming server (405) to retrieve the copy (407) and the copy (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) in the electronic device (430). The video decoder (410) decodes the incoming copy (407) of the encoded video data and generates an uncompressed output video picture stream (411) that can be presented on a display (412) (e.g., a display screen) or other presentation device (not depicted). The video decoder 410 can be configured to perform some or all of the various functions described in the present disclosure. In some streaming systems, the encoded video data (404), (407) and (409) (e.g., video bitstreams) can be encoded according to certain video encoding / compression standards. Examples of these standards include ITU-T Recommendation H.265. In one example, the video coding standard under development is informally referred to as Next Generation Video Coding (VVC). The disclosed subject matter may be used in the context of VVC and other video coding standards.

[0055] It should be noted that the electronic device (420) and the electronic device (430) may include other components (not shown). For example, the electronic device (420) may include a video decoder (not shown), and the electronic device (430) may also include a video encoder (not shown).

[0056] In the following, Figure 5 A block diagram of a video decoder (510) according to any embodiment of the present disclosure is shown. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used to replace Figure 4 A video decoder (410) in an example of FIG.

[0057] The receiver (531) may receive one or more encoded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one encoded video sequence may be decoded at a time, wherein the decoding of each encoded video sequence is independent of the other encoded video sequences. Each video sequence may be associated with multiple video frames or images. The encoded video sequence may be received from a channel (501), which may be a hardware / software link leading to a storage device storing the encoded video data or a streaming source transmitting the encoded video data. The receiver (531) may receive the encoded video data and other data, such as encoded audio data and / or auxiliary data streams, which may be forwarded to their respective processing circuits (not depicted). The receiver (531) may separate the encoded video sequence from the other data. To prevent network jitter, a buffer memory (515) may be provided between the receiver (531) and the entropy decoder / parser (520) (hereinafter referred to as "parser (520)"). In some applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, the buffer memory (515) may be located outside the video decoder (510) and separate from the video decoder (510) (not depicted). In still other applications, a buffer memory (not depicted) may be provided outside the video decoder (510) for the purpose of, for example, preventing network jitter, and another additional buffer memory (515) may be provided inside the video decoder (510) for, for example, processing playback timing. When the receiver (531) receives data from a storage / forward device with sufficient bandwidth and controllability or from an isochronous network, the buffer memory (515) may not be required, or the buffer memory may be made smaller. For use on a traffic packet network such as the Internet, a buffer memory (515) of sufficient size may be required, and the size of the buffer memory (515) may be relatively large. Such a buffer memory may be implemented to have an adaptive size and may be implemented at least in part in an operating system or similar element (not depicted) external to the video decoder (510).

[0058] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the encoded video sequence. The categories of these symbols include information for managing the operation of the video decoder (510) and potential information for controlling a presentation device such as a display (512) (e.g., a display screen), which may or may not be an integral part of the electronic device (530), but may be coupled to the electronic device (530), such as Figure 5As shown. The control information for the rendering device may be in the form of auxiliary enhancement information (SEI message) or video usability information (VUI) parameter set fragments (not depicted). The parser (520) may parse / entropy decode the encoded video sequence received by the parser (520). The entropy encoding of the encoded video sequence may be performed according to a video coding technique or standard, and may follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract a subgroup parameter set for at least one subgroup of the subgroups of pixels in the video decoder from the encoded video sequence based on at least one parameter corresponding to the subgroup. The subgroup may include a group of pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (520) may also extract information such as transform coefficients (e.g., Fourier transform coefficients), quantizer parameter values, motion vectors, etc. from the encoded video sequence.

[0059] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515), thereby creating symbols (521).

[0060] Depending on the type of coded video picture or portion of coded video picture (e.g., inter-picture and intra-picture, inter-block and intra-block) and other factors, the reconstruction of the symbol (521) may involve a number of different processing or functional units. The units involved and the manner in which the units are involved may be controlled by the parser (520) through subgroup control information parsed from the coded video sequence. For simplicity, such subgroup control information flow between the parser (520) and the various processing or functional units described below is not depicted.

[0061] In addition to the functional blocks already mentioned, the video decoder (510) can be conceptually subdivided into a number of functional units as described below. In actual implementations operating under commercial constraints, many of these functional units interact closely with each other and may be at least partially integrated with each other. However, for the purpose of clearly describing the various functions of the disclosed subject matter, the conceptual subdivision into multiple functions is adopted in the following of this disclosure.

[0062] The first unit may include a sealer / inverse transform unit (551). The sealer / inverse transform unit (551) may receive quantized transform coefficients as symbols (521) and control information from the parser (520), including information indicating which type of inverse transform to use, block size, quantization factors / parameters, quantization scaling matrices, etc. The sealer / inverse transform unit (551) may output a block including sample values, which may be input into an aggregator (555).

[0063] In some cases, the output samples of the scaler / inverse transform (551) may belong to an intra-coded block; that is, a block that does not use prediction information from a previously reconstructed picture, but may use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may use surrounding block information that has been reconstructed and stored in a current picture buffer (558) to generate a block of the same size and shape as the block being reconstructed. For example, the current picture buffer (558) buffers a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551) on a per-sample basis.

[0064] In other cases, the output samples of the scaler / inverse transform unit (551) may belong to a block that is inter-coded and potentially motion compensated. In this case, the motion compensated prediction unit (553) may access the reference picture memory (557) to extract samples for inter-picture prediction. After the extracted samples are motion compensated according to the symbols (521) belonging to the block, these samples may be added to the output of the scaler / inverse transform unit (551) by the aggregator (555) (the output of unit 551 may be referred to as residual samples or residual signals), thereby generating output sample information. The extraction of prediction samples by the motion compensated prediction unit (553) from the address in the reference picture memory (557) may be controlled by a motion vector, which may be provided to the motion compensated prediction unit (553) in the form of symbols (521), which may have, for example, an X component, a Y component (offset), and a reference picture component (time). Motion compensation may also include interpolation of sample values ​​fetched from the reference picture memory (557) when using sub-sample accurate motion vectors, and may also be associated with motion vector prediction mechanisms, etc.

[0065] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in a loop filter unit (556). The video compression techniques may include in-loop filter techniques controlled by parameters included in the coded video sequence (also referred to as a coded video bitstream) and available to the loop filter unit (556) as symbols (521) from the parser (520), however, the video compression techniques may also be responsive to meta information obtained during decoding of a previous (in decoding order) portion of the coded picture or coded video sequence, as well as to previously reconstructed and loop filtered sample values. A variety of types of loop filters may be included as part of the loop filter unit 556 in various orders, as will be described in further detail below.

[0066] The output of the loop filter unit (556) may be a sample stream that may be output to a rendering device (512) and stored in a reference picture memory (557) for future inter-picture prediction.

[0067] Once fully reconstructed, certain coded pictures may be used as reference pictures for future inter-picture prediction. For example, once 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) may become part of the reference picture memory (557), and a new current picture buffer may be reallocated before starting reconstruction of a subsequent coded picture.

[0068] The video decoder (510) may perform decoding operations according to a predetermined video compression technique employed in a standard such as ITU-T Recommendation H.265. The encoded video sequence may conform to the syntax specified by the video compression technique or standard used in the sense that the encoded video sequence follows the syntax of the video compression technique or standard and the profile recorded in the video compression technique or standard. Specifically, the profile may select certain tools from all the tools available in the video compression technique or standard as the only tools available for use under the profile. To conform to the standard, the complexity of the encoded video sequence may be within a range defined by the hierarchy of the video compression technique or standard. In some cases, the hierarchy limits the maximum picture size, the maximum frame rate, the maximum reconstruction sampling rate (measured in, for example, mega samples per second), the maximum reference picture size, etc. In some cases, the limits set by the hierarchy may be further defined by the hypothetical reference decoder (HRD) specification and metadata of the HRD buffer management signaled in the encoded video sequence.

[0069] In some exemplary embodiments, the receiver (531) may receive additional (redundant) data when receiving the encoded video. The additional data may be included as part of the encoded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or more accurately reconstruct the original video data. The additional data may take the form of, for example, temporal, spatial or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0070] Figure 6 A block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure is shown. The video encoder (603) may be included in an electronic device (620). The electronic device (620) may further include a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used to replace Figure 4 A video encoder (403) in an example.

[0071] The video encoder (603) can be used to obtain the video source (601) (not Figure 6 In an example of an electronic device (620) receiving video samples, a video source (601) can capture video images to be encoded by a video encoder (603). In another example, the video source (601) can be implemented as a part of the electronic device (620).

[0072] The video source (601) may provide a source video sequence in the form of a digital video sample stream to be encoded by a video encoder (603), the digital video sample stream may have any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 YCrCb, RGB, XYZ, ...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media service system, the video source (601) may be a storage device capable of storing previously prepared videos. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as a plurality of separate pictures or images that are given motion when viewed sequentially. The picture itself may be constructed as a spatial pixel array, wherein each pixel may include one or more samples depending on the sampling structure, color space, etc. used. A person of ordinary skill in the art may easily understand the relationship between pixels and samples. The following description focuses on the samples.

[0073] According to some exemplary embodiments, the video encoder (603) may encode and compress the pictures of the source video sequence into an encoded video sequence (643) in real time or under any other time constraints required by the application. Implementing an appropriate encoding speed constitutes a function of the controller (650). In some embodiments, the controller (650) may be functionally coupled to and control other functional units as described below. For simplicity, the coupling is not depicted in the figure. The parameters set by the controller (650) may include rate control related parameters (picture skipping, quantizer, lambda value of rate distortion optimization technology...), picture size, picture group (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured to have other suitable functions that are related to the video encoder (603) optimized for a certain system design.

[0074] In some exemplary embodiments, the video encoder (603) may be configured to operate in an encoding loop. As an oversimplified description, in one example, the encoding loop may include a source encoder (630) (e.g., responsible for creating symbols, such as a symbol stream, based on an input picture to be encoded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a manner similar to how a (remote) decoder may create sample data, even though the embedded decoder 633 processes a video stream encoded by the source encoder 630 without entropy encoding (because in the video compression techniques considered in the disclosed subject matter, any compression between the entropy-encoded symbols and the encoded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces a bit-accurate result that is independent of the decoder location (local or remote), the contents of the reference picture memory (634) also correspond bit-accurately between the local encoder and the remote encoder. In other words, the reference picture samples "seen" by the prediction part of the encoder are exactly the same sample values ​​that the decoder will "see" when using the prediction during decoding. This basic principle of reference picture synchronization (and the drift that occurs when synchronization cannot be maintained, e.g. due to channel errors) is used to improve encoding quality.

[0075] The operation of the "local" decoder (633) may be similar to that described above in conjunction with Figure 5 The "remote" decoder of the video decoder (510) described in detail is identical. However, additional brief reference is made to Figure 5 , since the symbols are available and the entropy encoder (645) and the parser (520) are capable of losslessly encoding / decoding the symbols into the encoded video sequence, the entropy decoding portion of the video decoder (510) including the buffer memory (515) and the parser (520) may not be fully implemented in the local decoder (633) in the encoder.

[0076] At this point, it can be observed that any decoder technology other than parsing / entropy decoding, which can only exist in a decoder, must also be present in a corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter can sometimes focus on decoder operations, which are combined with the decoding portion of the encoder. Therefore, the description of encoder technology can be simplified because encoder technology is mutually inverse to the decoder technology described comprehensively. Hereinafter, only in certain areas or aspects, a more detailed description of the encoder is provided.

[0077] During operation, in some exemplary implementations, the source encoder (630) may perform motion compensated predictive coding that predictively encodes an input picture by referencing one or more previously encoded pictures from a video sequence designated as "reference pictures." In this manner, the encoding engine (632) encodes the differences (or residuals) in color channels between pixel blocks of the input picture and pixel blocks of a reference picture that may be selected as a prediction reference for the input picture. The term "residual" and its adjective form "residual" may be used interchangeably.

[0078] The local video decoder (633) may decode the encoded video data of the picture that may be designated as the reference picture based on the symbol created by the source encoder (630). The operation of the encoding engine (632) may advantageously be a lossy process. When the encoded video data may be decoded at the video decoder ( Figure 6 When decoded from a local video decoder (not shown), the reconstructed video sequence may typically be a copy of the source video sequence with some errors. The local video decoder (633) replicates the decoding process that may be performed by the video decoder on the reference picture and may cause the reconstructed reference picture to be stored in the reference picture cache (634). In this way, the video encoder (603) may store a copy of the reconstructed reference picture locally that has common content (absent transmission errors) with the reconstructed reference picture to be obtained by the far-end (remote) video decoder.

[0079] The predictor (635) may perform a prediction search for the encoding engine (632). That is, for a new picture to be encoded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or certain metadata, such as reference picture motion vectors, block shapes, etc., that may be used as appropriate prediction references for the new picture. The predictor (635) may operate on a pixel block by pixel block basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have prediction references taken from multiple reference pictures stored in the reference picture memory (634).

[0080] The controller (650) may manage encoding operations of the source encoder (630), including, for example, setting parameters and subgroup parameters for encoding video data.

[0081] The outputs of all the above functional units may be entropy encoded in an entropy encoder (645). The entropy encoder (645) performs lossless compression on the symbols generated by the various functional units according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc., thereby converting the symbols into a coded video sequence.

[0082] The transmitter (640) can buffer the encoded video sequence created by the entropy encoder (645) in preparation for transmission over a communication channel (660), which can be a hardware / software link to a storage device that can store the encoded video data. The transmitter (640) can combine the encoded video data from the video encoder (603) with other data to be transmitted, such as encoded audio data and / or auxiliary data streams (source not shown).

[0083] The controller (650) may manage the operation of the video encoder (603). During encoding, the controller (650) may assign a certain coded picture type to each coded picture, but this may affect the coding techniques that can be applied to the corresponding picture. For example, a picture may generally be assigned to any of the following picture types:

[0084] An intra picture (I picture) may be a picture that can be encoded and decoded without using any other picture in the sequence as a prediction source. Some video codecs allow for different types of intra pictures, including, for example, independent decoder refresh ("IDR") pictures. Those of ordinary skill in the art are aware of these variations of I pictures and their corresponding applications and features.

[0085] A predictive picture (P picture) may be a picture that can be encoded and decoded using intra prediction or inter prediction, which uses at most one motion vector and a reference index to predict sample values ​​for each block.

[0086] Bidirectional predictive pictures (B pictures), which can be pictures that can be encoded and decoded using intra-frame prediction or inter-frame prediction, which uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple predictive pictures can use more than two reference pictures and associated metadata to reconstruct a single block.

[0087] The source picture may typically be spatially subdivided into a plurality of coding blocks of samples (e.g., blocks of 4×4, 8×8, 4×8, or 16×16 samples), and encoded block by block. These blocks may be predictively encoded with reference to other (already encoded) blocks, which are determined by the coding allocation applied to the corresponding picture of the block. For example, blocks of an I picture may be non-predictively encoded, or blocks of an I picture may be predictively encoded (spatial prediction or intra-frame prediction) with reference to already encoded blocks of the same picture. Blocks of pixels of a P picture may be predictively encoded by spatial prediction with reference to a previously encoded reference picture or by temporal prediction. Blocks of a B picture may be predictively encoded by spatial prediction with reference to one or two previously encoded reference pictures or by temporal prediction. For other purposes, source pictures or intermediately processed pictures may be subdivided into other types of blocks. The division of coding blocks and other types of blocks may or may not follow the same approach, as described in further detail below.

[0088] The video encoder (603) may perform encoding operations according to a predetermined video encoding technique or standard, such as ITU-T H.265 Recommendation. In operation, the video encoder (603) may perform various compression operations, including predictive encoding operations that exploit temporal and spatial redundancy in an input video sequence. Thus, the encoded video data may conform to the syntax specified by the video encoding technique or standard used.

[0089] In some exemplary embodiments, the transmitter (640) may transmit additional data when transmitting the encoded video. The source encoder (630) may include such data as part of the encoded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0090] The captured video may be taken as a plurality of source pictures (video pictures) in a temporal sequence. Intra-picture prediction (often shortened to intra-prediction) exploits spatial correlations in a given picture, while inter-picture prediction exploits temporal or other correlations between pictures. For example, a particular picture being encoded / decoded may be divided into blocks, and the particular picture being encoded / decoded is referred to as the current picture. When a block in the current picture is similar to a reference block in a reference picture that was previously encoded in the video and is still buffered, the block in the current picture may be encoded by a vector called a motion vector. The motion vector points to a reference block in a reference picture, and in the case where multiple reference pictures are used, the motion vector may have a third dimension that identifies the reference picture.

[0091] In some exemplary embodiments, a bidirectional prediction technique may be used for inter-picture prediction. According to this bidirectional prediction technique, two reference pictures are used, such as a first reference picture and a second reference picture that precede the current picture in the video in decoding order (but may be in the past or future, respectively, in display order). A block in the current picture may be encoded by a first motion vector pointing to a first reference block in the first reference picture and a second motion vector pointing to a second reference block in the second reference picture. The block may be jointly predicted by a combination of the first reference block and the second reference block.

[0092] In addition, merge mode technology can be used for inter-picture prediction to improve coding efficiency.

[0093] According to some exemplary embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed in units of blocks. For example, a picture in a video picture sequence is divided into coding tree units (CTUs) for compression, and the CTUs in the picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. Typically, a CTU may include three parallel coding tree blocks (CTBs): a luminance CTB and two chrominance CTBs. Each CTU may be recursively split into one or more coding units (CUs) in a quadtree. For example, a 64×64 pixel CTU may be split into a 64×64 pixel CU, or four 32×32 pixel CUs. Each of the one or more 32×32 blocks may be further split into four 16×16 pixel CUs. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for the CU among a plurality of prediction types, such as an inter-prediction type or an intra-prediction type. A CU may be split into one or more prediction units (PUs) based on temporal and / or spatial predictability. Typically, each PU includes a luma prediction block (PB) and two chroma PBs. In one embodiment, the prediction operation in encoding (encoding / decoding) is performed in units of prediction blocks. Splitting a CU into PUs (or PBs of different color channels) can be performed in various spatial modes. For example, a luma or chroma PB may include a matrix of values ​​(e.g., luma values) for samples, such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0094] Figure 7 A diagram of a video encoder (703) according to another exemplary embodiment of the present disclosure is shown. The video encoder (703) is configured to receive a processed block (e.g., a prediction block) of sample values ​​within a current video picture in a sequence of video pictures and encode the processed block into an encoded picture that is part of an encoded video sequence. In an example, the video encoder (703) may be used instead of Figure 4 A video encoder (403) in an example.

[0095] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8×8 samples, etc. The video encoder (703) then uses, for example, rate-distortion optimization (RDO) to determine whether to use intra mode, inter mode, or bidirectional prediction mode to best encode the processing block. When it is determined that the processing block is encoded in intra mode, the video encoder (703) may use intra prediction techniques to encode the processing block into an encoded picture; and when it is determined that the processing block is encoded in inter mode or bidirectional prediction mode, the video encoder (703) may use inter prediction or bidirectional prediction techniques to encode the processing block into an encoded picture, respectively. In some exemplary embodiments, merge mode may be used as a sub-mode of inter-picture prediction, in which motion vectors are derived from one or more motion vector predictors without the aid of encoded motion vector components external to the predictor. In some other exemplary embodiments, there may be motion vector components applicable to the subject block. Therefore, the video encoder (703) may include a sub-mode that is not in Figure 7 Components explicitly shown in, such as a mode decision module for determining a prediction mode for a processing block.

[0096] exist Figure 7 In the example of FIG. 7 , the video encoder ( 703 ) includes Figure 7 The exemplary arrangement shown in FIG. 1 includes an inter-frame encoder (730), an intra-frame encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725) coupled together.

[0097] The inter-frame encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block with one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture in display order), generate inter-frame prediction information (e.g., redundant information description according to an inter-frame coding technique, motion vectors, merge mode information), and calculate an inter-frame prediction result (e.g., a predicted block) based on the inter-frame prediction information using any suitable technique. In some examples, the reference picture is based on coded video information, using a video code embedded in the video codec. Figure 6 The decoding unit 633 (eg, Figure 7 The decoded reference picture is decoded by the residual decoder 728, as described in further detail below.

[0098] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block with an encoded block in the same picture, and generate quantization coefficients after transformation, and in some cases also generate intra prediction information (e.g., intra prediction direction information according to one or more intra coding techniques). The intra encoder (722) can calculate an intra prediction result (e.g., a predicted block) based on the intra prediction information and a reference block in the same picture.

[0099] The general controller (721) can be configured to determine general control data and control other components of the video encoder (703) based on the general control data. In one example, the general controller (721) determines a prediction mode of a block and provides a control signal to a switch (726) based on the prediction mode. For example, when the prediction mode is an intra-frame mode, the general controller (721) controls the switch (726) to select an intra-frame mode result for use by the residual calculator (723), and controls the entropy encoder (725) to select intra-frame prediction information and include the intra-frame prediction information in the bitstream; and when the prediction mode of the block is an inter-frame mode, the general controller (721) controls the switch (726) to select an inter-frame prediction result for use by the residual calculator (723), and controls the entropy encoder (725) to select inter-frame prediction information and include the inter-frame prediction information in the bitstream.

[0100] The residual calculator (723) may be configured to calculate the difference (residual data) between the received block and the prediction result of the block selected from the intra encoder (722) or the inter encoder (730). The residual encoder (724) may be configured to encode the residual data to generate a transform coefficient. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate the transform coefficient. The transform coefficient is then subjected to quantization to obtain a quantized transform coefficient. In various exemplary embodiments, the video encoder (703) further includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be appropriately used by the intra encoder (722) and the inter encoder (730). For example, the inter encoder (730) may generate a decoded block based on the decoded residual data and the inter prediction information, and the intra encoder (722) may generate a decoded block based on the decoded residual data and the intra prediction information. The decoded blocks are appropriately processed to generate decoded pictures, and the decoded pictures may be buffered in a memory circuit (not shown) and used as reference pictures.

[0101] The entropy encoder (725) may be configured to format the code stream to include the encoded blocks, and to perform entropy encoding. The entropy encoder (725) may be configured to include various information in the code stream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-frame prediction information or inter-frame prediction information), residual information, and other suitable information in the code stream. When the block is encoded in the merge sub-mode of the inter-frame mode or the bidirectional prediction mode, the residual information may not be present.

[0102] Figure 8 A diagram of an exemplary video decoder (810) according to another embodiment of the present disclosure is shown. The video decoder (810) is configured to receive an encoded picture as part of an encoded video sequence and decode the encoded picture to generate a reconstructed picture. In one example, the video decoder (810) may be used instead of Figure 4 A video decoder (410) in an example of FIG.

[0103] exist Figure 8 In the example of FIG. 8 , the video decoder ( 810 ) includes Figure 8 The exemplary arrangement shown in FIG. 8 is an entropy decoder (871), an inter-frame decoder (880), a residual decoder (873), a reconstruction module (874), and an intra-frame decoder (872) coupled together.

[0104] The entropy decoder (871) may be configured to reconstruct certain symbols from the encoded picture, the symbols representing syntax elements constituting the encoded picture. Such symbols may include, for example, a mode for encoding a block (e.g., intra mode, inter mode, bidirectional prediction mode, merge submode, or another submode), prediction information (e.g., intra prediction information or inter prediction information) that may identify certain samples or metadata used by an intra decoder (872) or an inter decoder (880) for prediction, residual information in the form of, for example, quantized transform coefficients, and the like. In one example, when the prediction mode is an inter or bidirectional prediction mode, the inter prediction information is provided to an inter decoder (880); and when the prediction type is an intra prediction type, the intra prediction information is provided to an intra decoder (872). The residual information may be subjected to inverse quantization and provided to a residual decoder (873).

[0105] The inter-frame decoder (880) may be configured to receive the inter-frame prediction information and generate an inter-frame prediction result based on the inter-frame prediction information.

[0106] The intra decoder (872) may be configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

[0107] The residual decoder (873) may be configured to perform inverse quantization to extract dequantized transform coefficients, and process the dequantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (to include quantizer parameters (QP)) that may be provided by the entropy decoder (871) (data path not depicted as this is only low data volume control information).

[0108] The reconstruction module (874) may be configured to combine the residual output by the residual decoder (873) with the prediction result (which may be output by the inter-frame prediction module or the intra-frame prediction module, as appropriate) in the spatial domain to form a reconstructed block, which forms part of a reconstructed picture, and the reconstructed picture is part of the reconstructed video. It should be noted that other suitable operations such as deblocking operations may also be performed to improve visual quality.

[0109] It should be noted that the video encoder (403), video encoder (603) and video encoder (703) and video decoder (410), video decoder (510) and video decoder (810) may be implemented using any suitable technology. In some exemplary embodiments, the video encoder (403), video encoder (603) and video encoder (703) and video decoder (410), video decoder (510) and video decoder (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoder (403), video encoder (603) and video encoder (603) and video decoder (410), video decoder (510) and video decoder (810) may be implemented using one or more processors that execute software instructions.

[0110] Returning to the intra prediction process, in the intra prediction process, samples in a block (e.g., a luma prediction block or a chroma prediction block, or a coding block if not further split into prediction blocks) are predicted by samples of adjacent, next adjacent, or one or more other rows, or a combination thereof, to generate a prediction block. The residual between the actual block being encoded and the prediction block may then be processed by a transform, followed by quantization. Various intra prediction modes may be made available, and parameters related to intra mode selection and other parameters may be signaled in the bitstream. For example, various intra prediction modes may involve one or more row positions for prediction samples, directions along which prediction samples are selected from one or more prediction rows, and other special intra prediction modes.

[0111] For example, a set of intra-prediction modes (interchangeably referred to as "intra-modes") may include a predetermined number of directional intra-prediction modes. As described above in connection with the exemplary implementation of FIG. 1, these intra-prediction modes may correspond to a predetermined number of directions along which out-of-block samples are selected as predictions for samples predicted in a particular block. In another specific exemplary implementation, eight (8) primary directional modes may be supported and predefined, corresponding to angles ranging from 45 degrees to 207 degrees from a horizontal axis.

[0112] In some other implementations of intra prediction, in order to further exploit more types of spatial redundancy in directional textures, the directional intra mode can be further extended to a set of angles with finer granularity. For example, the above 8-angle implementation can be configured to provide 8 nominal angles, such as Fig. 9 As shown, these 8 nominal angles are called V_PRED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED and D67_PRED, and for each nominal angle, a predetermined number (e.g., 7) of finer angles can be added. With this extension, a larger total number (e.g., 56 in this example) of directional angles can be used for intra-frame prediction, corresponding to the same number of predetermined directional intra-frame modes. The predicted angle can be represented by the nominal intra-frame angle plus the angle increment. For the specific example above with 7 finer angle directions for each nominal angle, the angle increment can be -3 to 3 times the step size, which is 3 degrees.

[0113] In some implementations, as an alternative to or in addition to the above-mentioned directional intra-frame mode, a predetermined number of non-directional intra-frame prediction modes may be predefined, and a predetermined number of non-directional intra-frame prediction modes may be made available. For example, 5 non-directional intra-frame modes called smooth intra-frame prediction modes may be specified. These non-directional intra-frame mode prediction modes may be specifically referred to as DC intra-frame mode, PAETH intra-frame mode, SMOOTH intra-frame mode, SMOOTH_V intra-frame mode, and SMOOTH_H intra-frame mode. Fig.10 The prediction of samples for a particular block under these exemplary non-directional modes is shown. As an example, Fig.10A 4×4 block 1002 is shown predicted by samples from a top neighboring row and / or a left neighboring row. A particular sample 1010 in the block 1002 may correspond to a sample 1004 directly above the sample 1010 in the top neighboring row of the block 1002, a sample 1006 to the upper left of the sample 1010 as the intersection of the top neighboring row and the left neighboring row, and a sample 1008 directly to the left of the sample 1010 in the left neighboring row of the block 1002. For the exemplary DC intra prediction mode, an average of the left neighboring sample 1008 and the upper neighboring sample 1004 may be used as a prediction value for the sample 1010. For the exemplary PAETH intra prediction mode, the top reference sample 1004, the left reference sample 1008, and the upper left reference sample 1006 may be extracted, and then the value of the three reference samples closest to (top+left−upper left) may be set as the prediction value for the sample 1010. For the exemplary SMOOTH_V intra prediction mode, sample 1010 can be predicted by performing quadratic interpolation on the top left adjacent sample 1006 and the left adjacent sample 1008 along the vertical direction. For the exemplary SMOOTH_H intra prediction mode, sample 1010 can be predicted by performing quadratic interpolation on the top left adjacent sample 1006 and the top adjacent sample 1004 along the horizontal direction. For the exemplary SMOOTH intra prediction mode, sample 1010 can be predicted by the average value of the quadratic interpolation along the vertical direction and the horizontal direction. The above non-directional intra mode implementation is only described as a non-limiting example. Other adjacent rows, other non-directional selections of samples, and ways to combine prediction samples to predict specific samples in the prediction block are also considered.

[0114] At different coding levels (pictures, slices, blocks, units, etc.), a specific intra-frame prediction mode is selected by the encoder from the above-mentioned directional or non-directional modes, which can be represented by a signal in the code stream. In some exemplary implementations, exemplary 8 nominal directional modes and 5 non-angle smooth modes (a total of 13 options) can first be represented by a signal. Then, if the signaled mode is one of the 8 nominal angle intra-frame modes, an index is further signaled to indicate the selected angle increment to the corresponding nominal angle represented by the signal. In some other exemplary implementations, all intra-frame prediction modes can be indexed together (e.g., 56 directional modes plus 5 non-directional modes to generate 61 intra-frame prediction modes) for signaling.

[0115] In some example implementations, the example 56 or other number of directional intra prediction modes may be implemented using a unified directional predictor that projects each sample of a block to a reference subsample location and interpolates the reference samples via a 2-tap bilinear filter.

[0116] In some implementations, in order to capture the attenuated spatial correlation with references on edges, additional filter modes called FILTER INTRA modes may be designed. For these modes, in addition to samples outside the block, the predicted samples within the block can be used as intra-prediction reference samples for some slices within the block. For example, these modes can be predefined and made available for intra-prediction of at least luminance blocks (or only luminance blocks). A predetermined number (e.g., five) of filter intra modes can be predesigned, each of which is represented by a set of n-tap filters (e.g., 7-tap filters) to reflect the correlation between, for example, samples in a 4×2 slice and n neighbors adjacent to the slice. In other words, the weight factor of the n-tap filter may depend on the position. Taking an 8×8 block, a 4×2 slice, and a 7-tap filter as an example, Fig.11 As shown, the 8×8 block 1102 can be split into 8 4×2 slices. Fig.11 In , these patches are represented by B0, Bl, B2, B3, B4, B5, B6 and B7. For each patch, its 7 nearest neighbors (in Fig.11 In the example, R0 to R7 are used to predict the samples in the current slice. For slice B0, all neighbors may have been reconstructed. However, for other slices, some neighbors are located in the current block and therefore may not be reconstructed. Then the prediction values ​​of the immediate neighbors are used as reference. For example, if Fig.11 All neighbors of the indicated patch B7 are therefore used instead for prediction samples of the neighbors.

[0117] In some implementations of intra prediction, a color component can be predicted using one or more other color components. The color component can be any one of the components in YCrCb, RGB, XYZ color space, etc. For example, it is possible to predict a chroma component (e.g., a chroma block) from a luma component (e.g., a luma reference sample), which is called chroma from luma or CfL. In some exemplary implementations, cross-color prediction may only allow from luma to chroma. For example, the chroma samples in a chroma block may be modeled as a linear function of coincident reconstructed luma samples. CfL prediction may be implemented as follows:

[0118] CfL(α)=α×L AC +DC (1)

[0119] Among them, L ACIndicates the AC contribution of the luma component, α indicates the parameters of the linear model, and DC indicates the DC contribution of the chroma component. For example, the AC component is obtained for each sample of the block, while the DC component is obtained for the entire block. Specifically, the reconstructed luma samples can be subsampled to the chroma resolution, and then the average luma value (the DC of luma) can be subtracted from each luma value to form the AC contribution of the luma. The AC contribution of the luma is then used in the linear model of equation (1) to predict the AC value of the chroma component. In order to estimate or predict the chroma AC component based on the luma AC contribution (rather than requiring the decoder to calculate the scaling parameters), an exemplary CfL implementation may determine the parameter α based on the original chroma samples and signal the parameter α in the bitstream. This reduces the complexity of the decoder and produces more accurate predictions. As for the DC contribution of the chroma component, in some exemplary implementations, the DC contribution of the chroma component can be calculated using the intra-frame DC mode within the chroma component.

[0120] In some exemplary implementations of reference lines, multi-line intra prediction may be used. In these implementations, more than one reference line may be available for selection in intra prediction, and the encoder decides and signals which reference line to use to generate the intra prediction. The reference line index may be signaled before the intra prediction mode, and in the case of a non-zero reference line index signaled, only the most likely prediction mode is allowed. Fig.15 , depicts an example of 4 reference rows and an upper left reference sample (from reference row 0 to reference row 3), wherein each reference row is composed of six segments, namely segments A to F (as indicated by 1502-1512). In addition, segments A and F can be filled by the closest samples from segments B and E, respectively.

[0121] Then, a transformation of the residual of the intra-frame prediction block or the inter-frame prediction block can be implemented, followed by quantization of the transformation coefficients. In order to perform the transformation, before the transformation, the intra-frame coding block and the inter-frame coding block can be further divided into multiple transform blocks (sometimes interchangeably used as "transform units", even if the term "unit" is generally used to represent a set of three color channels, for example, a "coding unit" may include a luminance coding block and a chrominance coding block). In some implementations, the maximum partition depth of the coding block (or prediction block) can be specified (the term "coded block" can be used interchangeably with "coding block"). For example, this division will not exceed 2 levels. The operation of dividing the prediction block into transform blocks can be handled differently between intra-frame prediction blocks and inter-frame prediction blocks. However, in some implementations, this division can be similar between intra-frame prediction blocks and inter-frame prediction blocks.

[0122] In some exemplary implementations, for intra-coded blocks, transform partitioning may be performed in a manner that all transform blocks have the same size, and the transform blocks are encoded in a raster scan order. Fig.12 An example of such a transform block partitioning of an intra-coded block is shown. Specifically, Fig.12 The coding block 1202 is shown to be divided into 16 transform blocks of equal block size, as shown at 1206, by means of a mid-level quadtree split 1204. An exemplary raster scan order for encoding is given by Fig.12 The sequence is shown by arrows.

[0123] In some exemplary implementations, for inter-frame coding blocks, the transform unit division may be performed in a recursive manner, where the division depth may be up to a predetermined number of levels (e.g., 2 levels). Fig.13 As shown, the split can stop or continue recursively for any sub-partition and at any level. Specifically, Fig.13 An example is shown where a block 1302 is split into four quadtree sub-blocks 1304, one of which is further split into four secondary transform blocks, while the division of the other sub-blocks stops after the first level, resulting in a total of 7 transform blocks of two different sizes. The exemplary raster scan order for encoding is further represented by Fig.13 The sequence of arrows is shown in Figure 2. Fig.13 An exemplary implementation of quadtree splitting of up to two levels of square transform blocks is shown, but in some generation implementations, transform partitioning can support 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1 transform block shapes and sizes, ranging from 4×4 to 64×64. In some exemplary implementations, if the coding block is less than or equal to 64×64, the transform block partitioning can only be applied to the luma component (in other words, the chroma transform block can be the same as the coding block under this condition). Otherwise, if the coding block width or height is greater than 64, the luma coding block and chroma coding block can be implicitly split into multiple min(W, 64)×min(H, 64) transform blocks and min(W, 32)×min(H, 32) transform blocks, respectively.

[0124] In some exemplary implementations, Fig.16 As shown in FIG. 1 , another alternative exemplary scheme for dividing a coding block or a prediction block into transform blocks is provided. Fig.16 As shown, instead of using recursive transform partitioning, a predetermined set of partition types may be applied to a coding block according to the transform type of the coding block. Fig.16In the specific example shown, one of six exemplary partition types may be applied to split the coding block into various numbers of transform blocks. This scheme may be applicable to coding blocks or prediction blocks. In the present disclosure, the term "partition type" may generally refer to the way a block (e.g., prediction block or coding block) is partitioned, which may refer to "transform partition type", "prediction block partition type" or "coding block partition type". In addition, for the description under "transform partition type", the same concept may also apply to "coding block partition type" and vice versa.

[0125] In more detail, Fig.16 As shown, Fig.16 The partitioning scheme of provides up to 6 partitioning types for any given transform type. In this scheme, a transform type can be assigned to each coding block or prediction block based on, for example, rate-distortion cost. In one example, the partitioning type assigned to a coding block or prediction block can be determined based on the transform type of the coding block or prediction block. A specific partitioning type can correspond to a transform block split size and mode (or partitioning type), such as Fig.16 The four partition types shown are shown. The correspondence between various transform types and various partition types can be predefined. An exemplary correspondence is shown below, where the capital letter label indicates the transform type that can be assigned to the coding block or prediction block based on the rate-distortion cost:

[0126] PARTITION_NONE: Allocate a transform size equal to the block size.

[0127] PARTITION_SPLIT: Allocates a transform size that is 1 / 2 the width of the block size and 1 / 2 the height of the block size.

[0128] PARTITION_HORZ: Allocates a transform size that has the same width as the block size and is 1 / 2 the height of the block size.

[0129] PARTITION_VERT: Allocates a transform size that is 1 / 2 the width of the block size and has the same height as the block size.

[0130] PARTITION_HORZ4: Allocates a transform size that has the same width as the block size and is 1 / 4 of the height of the block size.

[0131] PARTITION_VERT4: Allocates a transform size that is 1 / 4 the width of the block size and has the same height as the block size.

[0132] In the above example, for the divided transform blocks, such as Fig.16 The partition types shown all include a uniform transform size. This is merely an example and not a limitation. In some other implementations, in a specific partition type (or mode), a mixed transform block size may be used for the transform blocks of the partition.

[0133] Then, a main transform can be performed on each transform block obtained as above. The main transform essentially moves the residual in the transform block from the spatial domain to the frequency domain. In some implementations of the actual main transform, in order to support the above exemplary extended coding block partitioning, multiple transform sizes (ranging from 4 points to 64 points for each of the two dimensions) and transform shapes (square; rectangular with aspect ratios of 2:1 / 1:2 and 4:1 / 1:4) can be allowed.

[0134] Turning to the actual main transform, in some exemplary implementations, the 2-D transform process may involve the use of a hybrid transform kernel (e.g., the hybrid transform kernel may be composed of a different 1-D transform for each dimension of the encoded residual transform block). Exemplary 1-D transform kernels may include, but are not limited to: a) 4-point DCT-2, 8-point DCT-2, 16-point DCT-2, 32-point DCT-2, 64-point DCT-2; b) 4-point asymmetric DST, 8-point asymmetric DST, 16-point asymmetric DST (DST-4, DST-7) and their flipped versions; c) 4-point identity transform, 8-point identity transform, 16-point identity transform, 32-point identity transform. The selection of the transform kernel for each dimension may be based on a rate-distortion (RD) criterion. For example, the basis functions for DCT-2 and asymmetric DST that can be implemented are listed in Table 1.

[0135] Table 1: Exemplary primary transform basis functions (DCT-2, DST-4, and DST-7 for N-point input)

[0136]

[0137] In some exemplary implementations, the availability of a hybrid transform kernel for a particular main transform implementation may be based on the transform block size and the prediction mode. Exemplary dependencies are listed in Table 2. For chroma components, transform type selection may be performed in an implicit manner. For example, for intra-frame prediction residuals, the transform type may be selected based on the intra-frame prediction mode, as specified in Table 3. For inter-frame prediction residuals, the transform type of the chroma block may be selected based on the transform type selection of the co-located luma block. Therefore, for chroma components, there is no transform type signaling in the bitstream.

[0138] Table 2: AV1 hybrid transform kernels and their availability based on prediction mode and block size. Here, → and ↓ indicate the horizontal and vertical dimensions; √ and × indicate the kernel availability for that block size and prediction mode.

[0139]

[0140]

[0141] Table 3: Transform type selection for chroma component intra prediction residual

[0142] Intra-frame prediction Vertical Transformation Horizontal Transform DC_PRED DCT DCT V_PRED ADST DCT H_PRED DCT ADST D45_PRED DCT DCT D135_PRED ADST ADST D113_PRED ADST DCT D157_PRED DCT ADST D203_PRED DCT ADST D67_PRED ADST DCT SMOOTH_PRED ADST ADST SMOOTH_V_PRED ADST DCT SMOOTH_H_PRED DCT ADST PAETH_PRED ADST ADST

[0143] In some implementations, a secondary transform may be performed on the primary transform coefficients. Fig.14 As shown, LFNST (Low Frequency Non-Separable Transform) can be applied between the forward main transform and quantization (at the encoder) and between dequantization and inverse main transform (at the decoder side) to further decorrelate the main transform coefficients, which is called a simplified secondary transform. In essence, LFNST can take a portion of the main transform coefficients, such as the low-frequency portion (thus, "simplified" from the complete set of main transform coefficients of the transform block) for secondary transform. In an exemplary LFNST, depending on the transform block size, a 4×4 non-separable transform or an 8×8 non-separable transform can be applied. For example, 4×4 LFNST can be applied to smaller transform blocks (e.g., min (width, height) <8), while 8×8 LFNST can be applied to larger transform blocks (e.g., min (width, height)>8). For example, if 4×4 LFNST is performed on an 8×8 transform block, only the low-frequency 4×4 portion of the 8×8 main transform coefficients will be further subjected to secondary transform.

[0144] Specifically, Fig.14As shown, the transform block may be 8×8 (or 16×16). Therefore, the forward main transform 1402 of the transform block generates an 8×8 (or 16×16) main transform coefficient matrix 1404, where each square cell represents a 2×2 (or 4×4) portion. For example, the input to the forward LFNST may not be the complete 8×8 (or 16×16) main transform coefficients. For example, a 4×4 (or 8×8) LFNST may be used for the secondary transform. Therefore, only the 4×4 (or 8×8) low-frequency main transform coefficients of the main transform coefficient matrix 1404 may be used as input to the LFNST, as indicated by the shaded portion (upper left corner) 1406. The remaining portion of the main transform coefficient matrix may not be subjected to the secondary transform. Therefore, after the secondary transform, the portion of the main transform coefficient that is subjected to the LFNST becomes the secondary transform coefficient, while the remaining portion that is not subjected to the LFNST (e.g., the unshaded portion of the matrix 1404) remains the corresponding main transform coefficient. In some exemplary implementations, the remaining parts that are not subjected to the secondary transform may all be set to zero coefficients.

[0145] An example of application of the non-separable transform used in LFNST is described below. To apply the exemplary 4×4 LFNST, a 4×4 input block X (e.g., representing a 4×4 low-frequency portion of a main transform coefficient block, e.g. Fig.14 The shaded portion 1406 of the main transformation matrix 1404 can be expressed as:

[0146]

[0147] The 2-D input matrix can first be linearized or scanned into vectors in the exemplary order.

[0148] Then, the non-separable transformation of 4×4 LFNST can be calculated as in indicates the output transform coefficient vector, and T is the 16×16 transform matrix. The resulting 16×1 coefficient vector is then transformed using the scan order of the block (e.g., horizontal, vertical, or diagonal). Scan in reverse into 4×4 blocks. Coefficients with smaller indices can be placed in a 4×4 coefficient block together with smaller scan indices. In this way, redundancy in the main transform coefficients X can be further exploited by the second transform T, thereby providing additional compression enhancement.

[0149] The above exemplary LFNST is based on the direct matrix multiplication method to apply the non-separable transform, enabling the implementation of LFNST in a single pass without the need for multiple iterations. In some further exemplary implementations, the dimension of the non-separable transform matrix (T) of the exemplary 4×4 LFNST can be further reduced to minimize the computational complexity and the memory space requirements for storing the transform coefficients. Such an implementation can be referred to as the Reduced Non-Separable Transform (RST). More specifically, the main idea of RST is to map an N-dimensional vector (in the above example, N is 4×4 = 16, but for an 8×8 block, N can be equal to 64) to an R-dimensional vector in a different space, where N / R (R < N) represents the dimension reduction factor. Therefore, instead of an N×N transform matrix, the RST matrix becomes an R×N matrix, as follows:

[0150]

[0151] Among them, the R rows of the transform matrix are the reduced R bases in the N-dimensional space. Therefore, this transform converts the input vector or N dimensions into an output vector of reduced R dimensions. Thus, as Fig.14 shown, the secondary transform coefficients 1408 transformed from the main coefficient 1406 are reduced in dimension by a factor or N / R. Fig.14 The three squares around 1408 in

[0152] can be filled with zeros. The inverse transform matrix of RTS can be the transpose of its forward transform. For the exemplary 8×8 LFNST (the description here is more diverse compared to the above 4×4 LFNST), an exemplary reduction factor of 4 can be applied, so the 64×64 direct non-separable transform matrix is correspondingly simplified to a 16×64 direct matrix. Additionally, in some implementations, a part (rather than all) of the input main coefficients can be linearized into the input vector of LFNST. For example, only a part of the exemplary 8×8 input main transform coefficients can be linearized into the above X vector. For a specific example, among the four 4×4 quadrants of the 8×8 main transform coefficient matrix, the lower right corner (high-frequency coefficients) can be ignored, and only the other three quadrants are linearized into a 48×1 vector in a predetermined scan order instead of a 64×1 vector. In such an implementation, the non-separable transform matrix can be further simplified from 16×64 to 16×48.

[0153] Therefore, an exemplary simplified 48×16 inverse RST matrix can be used on the decoder side to generate the upper left, upper right, and lower left 4×4 quadrants of the 8×8 core (main) transform coefficients. Specifically, when a further simplified 16×48 RST matrix (instead of 16×64 RST) is applied to the same transform set configuration, the non-separable secondary transform can extract the vectorized 48 matrix elements from the three 4×4 quadrant blocks of the 8×8 main coefficient block (excluding the lower right 4×4 block) as input. In such an implementation, the deleted lower right 4×4 main transform coefficients can be ignored in the secondary transform. This further simplified transform can convert the 48×1 vector into a 16×1 output vector, and the 16×1 output vector is reversely scanned into a 4×4 matrix to fill the Fig.14 1408. The three squares of secondary transform coefficients around 1408 may be filled with zeros.

[0154] With this dimensionality reduction of the RST, the memory usage for storing all LFNST matrices is reduced. For example, in the above example, the memory usage can be reduced from 10KB to 8KB with a fairly small performance degradation compared to an implementation without dimensionality reduction.

[0155] In some implementations, to reduce complexity, the LFNST can be further restricted to be performed only when the coefficients are outside the main transform coefficient portion to be subjected to the LFNST (e.g., Fig.14 LFNST is applied only when all coefficients (except for the portion 1406 of 1404) are insignificant. Therefore, when LFNST is applied, all primary-only transform coefficients (e.g., Fig.14The unshaded portion of the primary coefficient matrix 1404 of the matrix 1404 may be close to zero. This restriction allows the LFNST index signaling to be adjusted at the last significant position, thereby avoiding some additional coefficient scans that might be required to check for significant coefficients at a particular position when the restriction is not applied. In some implementations, the worst-case processing of LFNST (in terms of multiplications per pixel) may restrict the inseparable transforms for 4×4 blocks and 8×8 blocks to 8×16 transforms and 8×48 transforms, respectively. In these cases, when LFNST is applied, the last-significant scan position must be less than 8, while the other dimensions are less than 16. For blocks of shape 4×N and N×4 with N>8, the above restriction means that LFNST is now only applied once to the upper left 4×4 region. Since all primary-only coefficients are zero when LFNST is applied, the number of operations required for the primary transform is reduced in this case. From the encoder's perspective, the quantization of coefficients can be simplified when testing the LFNST transform. For the first 16 coefficients (in scanning order), rate-distortion optimized quantization (RDO) must be maximized, and the remaining coefficients can be forced to zero.

[0156] In some exemplary implementations, the available RST kernels may be specified as multiple transform sets, each of which includes multiple inseparable transform matrices. For example, there may be a total of 4 transform sets, each of which has 2 inseparable transform matrices (kernels) for use by LFNST. These kernels can be pre-trained offline, so they are data-driven. The offline trained transform kernels may be stored in a memory, or may be hard-coded in an encoding or decoding device for use during the encoding / decoding process. The selection of a transform set during the encoding or decoding process may be determined by an intra-frame prediction mode. The mapping from intra-frame prediction mode to a transform set may be pre-defined. An example of such a predetermined mapping is shown in Table 4. For example, as shown in Table 4, if one of the three cross-component linear model (CCLM) modes (INTRA_LT_CCLM, INTRA_T_CCLM, or INTRA_L_CCLM) is used for the current block (ie, 81 <= predModeIntra <= 83), then transform set 0 may be selected for the current chroma block. For each transform set, the selected inseparable secondary transform candidate may be further specified by an explicitly signaled LFNST index. For example, after the transform coefficients, the index may be signaled once for each intra CU in the codestream.

[0157] Table 4: Transformation selection table

[0158] IntraPredMode Transform Set Index IntraPredMode<0 1 0<=IntraPredMode<=1 0 2<=IntraPredMode<=12 1 13<=IntraPredMode<=23 2 24<=IntraPredMode<=44 3 45<=IntraPredMode<=55 2 56<=IntraPredMode<=80 1 81<=IntraPredMode<=83 0

[0159] Because in the above exemplary implementation, LFNST is limited to be applicable only when all coefficients outside the first coefficient subgroup or part are not valid, the LFNST index encoding depends on the position of the last significant coefficient. In addition, the LFNST index can be context-coded, but it does not depend on the intra prediction mode, and only the first bin can be context-coded. In addition, LFNST can be applied to intra CUs in intra slices and inter slices, as well as luma and chroma. If dual tree is enabled, the LFNST indexes for luma and chroma can be signaled separately. For inter slices (dual tree disabled), a single LFNST index can be signaled, and a single LFNST index is used for both luma and chroma.

[0160] In some exemplary implementations, when the intra sub-partitioning (ISP) mode is selected, LFNST may be disabled and the RST index may not be signaled, because even if RST is applied to each feasible partition block, the performance improvement may be negligible. In addition, disabling RST for the residual of ISP prediction may reduce coding complexity. In some further implementations, when the multivariate linear regression intra prediction (MIP) mode is selected, LFNST may also be disabled and the RST index may not be signaled.

[0161] Considering that large CUs larger than 64×64 (or any other predetermined size representing the maximum transform block size) are implicitly split (e.g., TU tiling) due to the existing maximum transform size limit (e.g., 64×64), LFNST index search may increase the data buffer by four times for a certain number of decoding pipeline stages. Therefore, in some implementations, the maximum size allowed for LFNST may be limited to, for example, 64×64. In some implementations, LFNST may be enabled only when DCT2 is used as the primary transform.

[0162] In some other implementations, an intra secondary transform (IST) is provided for the luminance component by defining, for example, 12 secondary transform sets, wherein there are, for example, 3 kernels in each set. An intra mode dependent index can be used to select a transform set. The kernel selection in a set can be based on a syntax element represented by a signal. IST can be enabled when DCT2 or ADST is used as both the horizontal transform and the vertical main transform. In some implementations, depending on the block size, a 4×4 inseparable transform or an 8×8 inseparable transform can be selected. If min(tx_width, tx_height)<8, a 4×4 IST can be selected. For larger blocks, an 8×8 IST can be used. Here, tx_width (tx_width) and tx_height (tx_height) correspond to the width and height of the transform block, respectively. The input of the IST can be a low-frequency main transform coefficient in a zigzag scan order.

[0163] Various transforms in the video encoding or decoding process (e.g., the primary transform of samples in the residual block or the secondary transform of blocks in the primary transform coefficient process) may not be very effective in capturing directional texture patterns (e.g., edges in the 45 degree direction (e.g., directions substantially away from the horizontal or vertical direction)) when only separable transform schemes are used. As described above, in some exemplary implementations, one or more non-separable transform designs may be used for the secondary transform of the primary transform coefficients.

[0164] The transform block partitioning and the transform type applied to the partitioned transform block may be related to each other. For example, certain transform types may be more suitable for specific partition types. For example, with recursive partitioning (such as previously described in Fig.13 Compared with the division described in Fig.16 The transform partitioning scheme shown in and described above provides a non-recursive partitioning type. If for all available partitioning modes (e.g., Fig.16 If all available transform types are allowed for the transform blocks divided under the transform partition type in (transform partition type in), the encoder needs to perform optimization in a large parameter space when determining which transform partition type is used to obtain the transform block and which transform type is used for each divided transform block. In practice, a certain transform type set is usually more suitable for a specific type of transform partition type than other transform types. In the various implementations described below, the interaction between transform partition types and transform types may be considered, and this interaction may be used to obtain a scheme to limit the allowed transform types for a specific partition type, and similarly limit the allowed partition types for a specific transform type. Such an implementation may reduce the optimization space of the encoder when determining the transform partition mode and transform type selection for each divided transform block, especially when non-recursive transform partitioning is used.

[0165] These exemplary implementations may be used individually or in any order or in any combination. In the above and below disclosure, the terms "coded block", "coding block", etc. may be used to refer to a picture unit on which prediction or transformation is performed. A coding block may be a luminance coding block, or may be a chrominance coding block. In some cases, a coded / coding block may refer to a prediction block. The term "block size" is used to refer to the width or height of a coding block, or the maximum value of the width and height, or the minimum value of the width and height, or the area size (width*height), or the aspect ratio (width:height, or height:width).

[0166] Multiple candidate primary transform types

[0167] In one embodiment, there may be multiple candidate primary transform types for a block. The block may include a transform block resulting from a partition. The selection and / or signaling of the primary transform type may be limited to a predetermined set of transform partition types. The predetermined set of transform partition types may be a larger set of available transform partition types (e.g., Fig.16 In other words, the selection of the primary transform is made and signaled only if the transform partition type of the block belongs to the predetermined set of transform partition types. Otherwise, for example, if the transform partition type is something else, a default transform type may be used instead of selecting and signaling the primary transform type.

[0168] In one implementation, the primary transform type may include at least one of: discrete cosine transform (DCT) type 1 to DCT type 8; asymmetric discrete sine transform (ADST); discrete sine transform (DST) type 1 to DST type 8; line graph transform (LGT); or Karhunen-Loeve Transform (KLT).

[0169] In one implementation, the set of predetermined transform partition types only includes, for example Fig.16 PARTITION_NONE among the various transform partition types of , i.e., the transform block size is equal to the prediction block (or coding block) size. Therefore, it is possible to select and / or signal the main transform type only when the transform type belongs to this predetermined set.

[0170] In one implementation, the number of partitions may also be considered to determine the set of predetermined transform partition types. For example, only if the number of partitions of a particular transform partition type is less than or equal to a predetermined threshold, the particular transform partition type may be considered as part of the set of predetermined transform partition types, for which the primary transform type may be selected and / or signaled. In one implementation, the predetermined threshold may be an integer from 1 to 16.

[0171] Multiple candidate secondary transform types

[0172] In one embodiment, there may be multiple candidate secondary transform types for a block. The block may include a transform block resulting from a partition. The selection and / or signaling of the secondary transform type may only be applicable to a predetermined set of transform partition types. The predetermined set of transform partition types may be a larger set of available transform partition types (e.g., Fig.16 In other words, the selection of the secondary transform is made and signaled only when the transform partition type of the block belongs to the predetermined transform partition type set. Otherwise, for example, if the transform partition type is other than the set, a default secondary transform type may be used instead of selecting and signaling the secondary transform type, or the secondary transform may not be performed.

[0173] In one implementation, the secondary transform type may include a KLT. The KLT may be configured with different kernels.

[0174] In one implementation, the set of predetermined transform partition types may only include, for example Fig.16 PARTITION_NONE among the various transform partition types of , i.e., the transform block size is equal to the prediction block (or coding block) size. Therefore, the secondary transform type can be selected and / or signaled only when the transform type belongs to this predetermined set.

[0175] In one implementation, the number of partitions may also be considered to determine the set of predetermined transform partition types. For example, only when the number of partitions of a particular transform partition type is less than or equal to a predetermined threshold, the particular transform partition type may be considered as part of the set of predetermined transform partition types, for which a secondary transform type may be selected and / or signaled. In one implementation, the predetermined threshold may be an integer from 1 to 16.

[0176] In one implementation, the selection and / or signaling of the secondary transform type may be based on a combination of a transform partition type and a primary transform type. The combination may include a transform partition type in a predetermined set of transform partition types and a primary transform type in a predetermined set of transform types. For example, the secondary transform type may need to be selected and / or signaled only when the transform partition type is PARTITION_NONE and the primary transform type used by the block is DCT or ADST. Otherwise, for example, if the transform partition type is other types, a default secondary transform type may be used instead of selecting and signaling the secondary transform type, or the secondary transform may not be performed.

[0177] Transformation related signaling

[0178] In the present disclosure, various signaling mechanisms are disclosed with the aim of improving signaling efficiency and taking into account the order of transform-related syntax elements / parameters.

[0179] In one embodiment, the transform partition type information may be signaled before the primary / secondary transform type selection information. The primary / secondary transform type selection needs to be signaled only when the transform partition belongs to a predetermined transform partition type set (e.g., PARTITION_NONE). Otherwise, if the transform partition does not belong to the predetermined transform partition type set, the primary / secondary transform type selection may not need to be signaled. Instead, the primary / secondary transform type may be derived as a predetermined default transform type.

[0180] In one embodiment, the primary / secondary transform type selection information may be signaled before the transform partition type information. In this case, the selection and / or signaling of the transform partition type may depend on the primary / secondary transform type selection information.

[0181] In one implementation, the transform partition type information may need to be signaled only when the primary transform type belongs to a predetermined transform type set. Otherwise, the transform partition type information may not need to be signaled. For example, the predetermined transform type set may include, but is not limited to, DCT type 1 to DCT type 8, ADST, DST type 1 to DST type 8, LGT, and KLT.

[0182] In one implementation, the transform partition type information may need to be signaled only when the secondary transform type belongs to a predetermined transform type set. As an example, the predetermined transform type set may include, but is not limited to, a specific KLT having a kernel associated with a predetermined KLT index. Otherwise, if the secondary transform type does not belong to the predetermined transform type set, the transform partition type information may not need to be signaled. Instead, the transform partition type information may be derived as a predetermined default transform partition type (e.g., PARTITION_NONE).

[0183] Fig.17 An exemplary method 1700 for decoding video data is shown. The method 1700 may include some or all of the following steps: step 1710, receiving an encoded video stream of a data block; step 1720, extracting a transform partition type associated with the data block from the encoded video stream; step 1730, in response to the transform partition type belonging to a subset of a predetermined transform partition type set, each transform partition type in the predetermined transform partition type set specifying a splitting mode for splitting the data block into transform blocks: extracting a transform type of a transform associated with a transform block split from the data block, the transform type being signaled in the encoded video stream, wherein the transform type belongs to a first predetermined transform type set; and performing an inverse transform on the transform block according to the transform type.

[0184] In the embodiments of the present disclosure, any steps and / or operations may be combined or arranged in any number or order as desired. Two or more steps and / or operations may be performed in parallel.

[0185] The embodiments of the present disclosure may be used alone or in any order. In addition, each 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 embodiments of the present disclosure may be applicable to luminance blocks or chrominance blocks.

[0186] The above techniques may be implemented as computer software using computer-readable instructions and physically stored in one or more computer-readable media. Fig.18 A computer system (1800) suitable for implementing certain embodiments of the disclosed subject matter is shown.

[0187] Computer software may be encoded using any suitable machine code or computer language that may be subjected to assembly, compilation, linking or similar mechanisms to create code comprising instructions that may be executed directly by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., or through interpretation, microcode execution, etc.

[0188] The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smart phones, gaming devices, Internet of Things devices, and the like.

[0189] Fig.18 The components of the computer system (1800) shown are exemplary in nature and are not intended to suggest any limitation on the scope of use or functionality of computer software implementing embodiments of the present disclosure. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components shown in the exemplary embodiment of the computer system (1800).

[0190] The computer system (1800) may include certain human-machine interface input devices. Such human-machine interface input devices may be responsive to input from one or more human users through, for example, tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), olfactory input (not depicted). Human-machine interface devices may also be used to capture certain media that are not necessarily directly related to human conscious input, such as audio (e.g., voice, music, ambient sounds), images (e.g., scanned images, captured images obtained from a still image camera), and videos (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0191] The human-machine interface input device may include one or more of the following (only one of each is shown): keyboard (1801), mouse (1802), touchpad (1803), touch screen (1810), data gloves (not shown), joystick (1805), microphone (1806), scanner (1807), camera (1808).

[0192] The computer system (1800) may also include certain human-computer interface output devices. Such human-computer interface output devices may stimulate one or more human user senses through, for example, tactile output, sound, light, and smell / taste. Such human-computer interface output devices may include tactile output devices (e.g., tactile feedback of a touch screen (1810), a data glove (not shown), or a joystick (1805), but may also be a tactile feedback device that is not an input device), audio output devices (e.g., speakers (1809), headphones (not depicted)), visual output devices (e.g., screens (1810) including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capabilities, each with or without tactile feedback capabilities, some of which are capable of outputting two-dimensional visual outputs or outputs in more than three dimensions through devices such as stereoscopic image output, virtual reality glasses (not depicted), holographic displays and smoke boxes (not depicted), and printers (not depicted).

[0193] The computer system (1800) may also include human-accessible storage devices and their associated media, such as optical media including CD / DVD ROM / RW (1820) with CD / DVD etc. media (1821), thumb drives (1822), removable hard drives or solid-state drives (1823), traditional magnetic media such as tapes and floppy disks (not depicted), dedicated ROM / ASIC / PLD based devices such as security dongles (not depicted), and the like.

[0194] Those skilled in the art should also understand that the term "computer-readable media" used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.

[0195] The computer system (1800) may also include an interface (1854) to one or more communication networks (1855). The network may be, for example, a wireless network, a wired network, an optical network. The network may further be a local network, a wide area network, a metropolitan area network, a vehicle and industrial network, a real-time network, a delay-tolerant network, etc. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television, and terrestrial broadcast television, vehicle and industrial networks including CAN buses, etc. Some networks typically require an external network interface adapter attached to some general data port or peripheral bus (1849) (e.g., a USB port of the computer system (1800)); as described below, other network interfaces are typically integrated into the kernel of the computer system (1800) by attaching to the system bus (e.g., connected to an Ethernet interface in a PC computer system or connected to a cellular network interface in a smartphone computer system). The computer system (1800) can use any of these networks to communicate with other entities. Such communications may be one-way receive only (e.g., broadcast television), one-way send only (e.g., CANBus connected to certain CANBus devices), or bidirectional, for example, using a LAN or WAN digital network to connect to other computer systems. As described above, certain protocols and protocol stacks may be used on each of those networks and network interfaces.

[0196] The above-mentioned human-machine interface device, human-machine accessible storage device and network interface may be attached to the kernel (1840) of the computer system (1800).

[0197] The kernel (1840) may include one or more central processing units (CPUs) (1841), graphics processing units (GPUs) (1842), dedicated programmable processing units in the form of field programmable gate arrays (FPGAs) (1843), hardware accelerators (1844) for certain tasks, graphics adapters (1850), and the like. These devices, as well as read-only memory (ROM) (1845), random access memory (1846), internal mass storage (1847) such as internal non-user accessible hard drives, SSDs, and the like, may be connected via a system bus (1848). In some computer systems, the system bus (1848) may be accessed in the form of one or more physical plugs to enable expansion by additional CPUs, GPUs, and the like. Peripheral devices may be attached directly to the kernel's system bus (1848) or to the kernel's system bus (1848) via a peripheral bus (1849). In one example, a screen (1810) may be connected to a graphics adapter (1850). The architecture of the peripheral bus includes PCI, USB, and the like.

[0198] The CPU (1841), GPU (1842), FPGA (1843) and accelerator (1844) can execute certain instructions, which can be combined to form the above-mentioned computer code. The computer code can be stored in ROM (1845) or RAM (1846). Transition data can also be stored in RAM (1846), while permanent data can be stored, for example, in internal mass storage (1847). Fast storage and retrieval to any storage device can be performed by using a cache, which can be closely associated with the following: one or more CPUs (1841), GPUs (1842), mass storage (1847), ROM (1845), RAM (1846), etc.

[0199] The computer readable medium may have thereon computer codes for performing various computer-implemented operations. The medium and computer codes may be those specially designed and constructed for the purposes of the present disclosure, or the medium and computer codes may be of a type well known and available to those skilled in the art of computer software.

[0200] As a non-limiting example, a computer system having an architecture (1800), particularly a kernel (1840), may provide functionality due to one or more processors (including CPUs, GPUs, FPGAs, accelerators, etc.) executing software contained in one or more tangible computer-readable media. Such computer-readable media may be media associated with user-accessible mass storage as described above, as well as memories of certain non-temporary kernels (1840), such as kernel internal mass storage (1847) or ROM (1845). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the kernel (1840). Depending on specific needs, the computer-readable medium may include one or more storage devices or chips. The software may enable the kernel (1840), particularly the processors therein (including CPUs, GPUs, FPGAs, etc.), to perform specific processes or specific parts of specific processes described herein, including defining data structures stored in RAM (1846) and modifying such data structures according to processes defined by the software. In addition or in the alternative, the computer system may provide functionality due to logic hardwired or otherwise embodied in circuitry (e.g., accelerator (1844)) that may replace software or operate in conjunction with software to perform specific processes or specific portions of specific processes described herein. Where appropriate, references to portions of software may include logic and vice versa. Where appropriate, references to portions of computer-readable media may include circuitry (e.g., integrated circuits (ICs)) storing software for execution, circuitry embodying logic for execution, or both. The present disclosure includes any suitable combination of hardware and software.

[0201] Although the present disclosure has described multiple exemplary embodiments, there are modifications, permutations, and various replacement equivalents that fall within the scope of the present disclosure. Therefore, it should be understood that those skilled in the art will be able to design many systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and therefore fall within the spirit and scope of the present disclosure.

[0202] Appendix A: Acronyms

[0203] JEM: Joint Exploration Model

[0204] VVC: Next Generation Video Coding

[0205] BMS: Benchmark Set

[0206] MV: Motion Vector

[0207] HEVC: High Efficiency Video Coding

[0208] SEI: Supplementary Enhancement Information

[0209] VUI: Video Availability Information

[0210] GOP: Group of Pictures

[0211] TU: Transform Unit

[0212] PU: prediction unit

[0213] CTU: Coding Tree Unit

[0214] CTB: Coding Tree Block

[0215] PB: prediction block

[0216] HRD: Hypothetical Reference Decoder

[0217] SNR: Signal to Noise Ratio

[0218] CPU: Central Processing Unit

[0219] GPU: Graphics Processing Unit

[0220] CRT: cathode ray tube

[0221] LCD: Liquid Crystal Display

[0222] OLED: Organic Light Emitting Diode

[0223] CD: compact disc

[0224] DVD: Digital Video Disc

[0225] ROM: Read Only Memory

[0226] RAM: Random Access Memory

[0227] ASIC: Application-Specific Integrated Circuit

[0228] PLD: Programmable Logic Device

[0229] LAN: Local Area Network

[0230] GSM: Global System for Mobile Communications

[0231] LTE: Long Term Evolution

[0232] CANBus: Controller Area Network Bus

[0233] USB: Universal Serial Bus

[0234] PCI: Peripheral Component Interconnect

[0235] FPGA: Field Programmable Gate Array

[0236] SSD: Solid State Drive

[0237] IC: Integrated Circuit

[0238] HDR: High Dynamic Range

[0239] SDR: Standard Dynamic Range

[0240] JVET: Joint Video Exploration Team

[0241] MPM: Most Probable Mode

[0242] WAIP: Wide Angle Intra Prediction

[0243] CU: Coding Unit

[0244] PU: prediction unit

[0245] TU: Transform Unit

[0246] CTU: Coding Tree Unit

[0247] PDPC: Position Dependent Prediction Combination

[0248] ISP: Intra-frame sub-partitioning

[0249] SPS: Sequence parameter settings

[0250] PPS: Picture Parameter Set

[0251] APS: Adaptive Parameter Set

[0252] VPS: Video Parameter Set

[0253] DPS: Decoding Parameter Set

[0254] ALF: Adaptive Loop Filter

[0255] SAO: Sample Adaptive Offset

[0256] CC-ALF: Cross-Component Adaptive Loop Filter

[0257] CDEF: Constrained Directed Enhancement Filter

[0258] CCSO: Cross-Component Sampling Offset

[0259] LSO: Local Sampling Offset

[0260] LR: Loop Restoration Filter

[0261] AV1: AOMedia Video 1

[0262] AV2: AOMedia Video 2

Claims

1. A method for decoding video data, characterized in that: The method comprises: Receiving an encoded video stream of data blocks; Extracting a transform partition type associated with the data block from the encoded video code stream; and In response to the transform partition type belonging to a subset of a predetermined transform partition type set, the subset of the predetermined transform partition type set only includes PARTITION_NONE for no transform block partitioning, each transform partition type in the predetermined transform partition type set specifies a splitting mode for partitioning the data block into transform blocks: extracting a transform type of a transform associated with a transform block split from the data block, the transform type being signaled in the coded video bitstream, wherein the transform type belongs to a first predetermined transform type set, the transform being a quadratic transform, the first predetermined transform type set including a Karonen-Loewe transform (KLT); and In response to the transform partition type not belonging to a subset of the predetermined set of transform partition types: Determining a transform type associated with the transform block as a predetermined default transform type; According to the transform type, an inverse transform is performed on the transform block.

2. The method according to claim 1, characterized in that When the transform is a main transform, the first predetermined transform type set includes: Discrete cosine transform DCT type 1 to DCT type 8; Asymmetric discrete sine transform ADST; Discrete sine transform DST type 1 to DST type 8; Line graph transform LGT; and Kallenin-Loewy transform KLT.

3. The method according to claim 1, characterized in that: The method further comprises: The number of transform partitions associated with each transform partition type in the subset of the predetermined set of transform partition types is less than or equal to a predetermined threshold.

4. The method according to claim 3, characterized in that The predetermined threshold value includes integers from 1 to 16, inclusive.

5. The method according to claim 1, characterized in that The transform type further indicates that a type of a main transform associated with the transform block belongs to a second predetermined transform type set.

6. The method according to claim 5, wherein: The second predetermined transform type set includes DCT and ADST.

7. An apparatus for decoding video data, comprising a memory and a processor, wherein instructions are stored in the memory, and wherein the instructions enable the processor to execute the method according to any one of claims 1 to 6.

8. A method for encoding video data, characterized in that The method comprises: Get the video code stream of the data block; Extracting a transform partition type associated with the data block from the video code stream; and In response to the transform partition type belonging to a subset of a predetermined transform partition type set, the subset of the predetermined transform partition type set only includes PARTITION_NONE for no transform block partitioning, each transform partition type in the predetermined transform partition type set specifies a splitting mode for partitioning the data block into transform blocks: extracting a transform type of a transform associated with a transform block split from the data block, the transform type being represented by a signal in the video bitstream, wherein the transform type belongs to a first predetermined transform type set, the transform is a quadratic transform, and the first predetermined transform type set includes a Karonen-Loewe transform (KLT); and In response to the transform partition type not belonging to a subset of the predetermined set of transform partition types: Determining a transform type associated with the transform block as a predetermined default transform type; According to the transform type, an inverse transform is performed on the transform block.

9. An apparatus for encoding video data, comprising a memory and a processor, wherein instructions are stored in the memory, and wherein the instructions enable the processor to execute the method according to claim 8.

10. A non-transitory computer-readable medium storing instructions, which, when executed by a computer for video decoding, cause the computer to execute the method according to any one of claims 1 to 6; and, when executed by a computer for video encoding, cause the computer to execute the method according to claim 8.

11. A method for processing a video code stream, characterized in that: The video code stream is decoded based on the method according to any one of claims 1 to 6, or generated according to the method according to claim 8.

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