Method and computer program for processing video information

Abstract

To provide a coordinated design between multiple baseline intra prediction, transform partitioning and transform kernels, and a method for processing video information.SOLUTION: A method includes the steps of retrieving a data block of a video frame having adjacent reference lines and one or more non-adjacent reference lines in the video frame, determining whether a non-adjacent reference line of the one or more non-adjacent reference lines is used for intra prediction of the data block, selecting a target transformation kernel from a first set of transformation kernels to transform the data block when the adjacent reference line is used for intra prediction of the data block, and selecting a target transformation kernel from a second set of transformation kernels to transform the data block when the non-adjacent reference line is used for intra prediction of the data block.SELECTED DRAWING: Figure 23

Description

[Technical field]

[0001] Incorporation by Reference This application is based on and claims the benefit of priority to U.S. Nonprovisional Patent Application No. 17 / 571,284, filed January 7, 2022, which claims priority to U.S. Provisional Application No. 63 / 176,049, entitled “Harmonized Design Among Multiple Reference Line Intra Prediction, Transform Partitioning, and Transform Kernels,” filed April 16, 2021. Both applications are incorporated herein by reference in their entireties.

[0002] Technical Field The present disclosure relates generally to a set of advanced video coding / decoding techniques, and more particularly to a harmonized design between multiple reference line intra prediction, transform partitioning, and transform kernels. [Background technology]

[0003] The background discussion provided herein is intended to generally present the context of the present disclosure. The work of the presently named inventors is not admitted explicitly or implicitly as prior art to the present disclosure, to the extent that that work is described in this background, along with aspects of the description that would not ordinarily be considered prior art at the time of filing.

[0004] Video coding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luminance samples and associated full or subsampled chrominance samples. The sequence of pictures can have a fixed or variable picture rate (alternatively called frame rate), for example, 60 pictures per second or 60 frames per second. Uncompressed video has specific bitrate requirements for streaming or data processing. For example, a video with a pixel resolution of 1920x1080, a frame rate of 60 frames / second, and 4:2:0 chroma subsampling with 8 bits per pixel per color channel requires close to 1.5 Gbit / s of bandwidth. One hour of such video requires more than 600 Gbytes of storage.

[0005] One goal of video coding and decoding may be the reduction of redundancy in an uncompressed input video signal through compression. Compression may help reduce the aforementioned bandwidth and / or storage requirements, possibly by more than one order of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be employed. Lossless compression refers to techniques that allow an exact copy of the original signal to be reconstructed from the compressed original signal through a decoding process. Lossy compression refers to a coding / decoding process in which the original video information is not fully preserved during coding and cannot be fully recovered during decoding. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original and reconstructed signals is made small enough to make the reconstructed signal useful for the intended application, despite some information loss. For video, lossy compression is widely used in many applications. The amount of acceptable distortion depends on the application. For example, a user of a particular consumer video streaming application may tolerate higher distortion than a user of a movie or television broadcast application. The compression ratio achievable by a particular coding algorithm can be selected or adjusted to reflect different distortion tolerances: higher tolerable distortion generally allows for coding algorithms that result in higher loss and higher compression ratios.

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

[0007] Video codec techniques can 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, a picture is spatially subdivided into blocks of samples. When all blocks of samples are coded in intra mode, the picture can be called an intra-picture. Intra-pictures and their derivatives, such as independent decoder refresh pictures, can be used to reset the decoder state and thus can be used as the first picture in a coded video bitstream and video session or as a still image. The samples of the block after intra prediction can then be subject to a transform to the frequency domain, and the transform coefficients so generated can be quantized before entropy coding. Intra-prediction refers to a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value and the smaller the AC coefficients after the transform, the fewer bits are needed for a given quantization step size to represent the block after entropy coding.

[0008] Traditional intra-coding, as known for example from MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to code / decode a block based on surrounding sample data and / or metadata, e.g., obtained during the coding and / or decoding of spatial neighbors and preceding in the decoding order in which the block of data is intra-coded or decoded. Such techniques are referred to below as "intra-prediction" techniques. It should be noted that, at least in some cases, intra-prediction uses only reference data from the current picture being reconstructed and not from other reference pictures.

[0009] There may be various forms of intra prediction. When more than one of such techniques is available in a given video coding technique, the technique used may be referred to as an intra prediction mode. One or more intra prediction modes may be provided for 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 intra coding parameters for a block of video may be coded individually or collectively included in mode codewords. Which codewords are used for a given mode, sub-mode and / or parameter combination may affect the coding efficiency gain through intra prediction, as well as the entropy coding technique used to convert the codewords into a bitstream.

[0010] Certain intra prediction modes were introduced in H.264, explored in H.265, and further explored in newer coding techniques such as joint exploration model (JEM), versatile video coding (VVC), and benchmark set (BMS). In general, in intra prediction, a predictor block can be formed using neighboring sample values ​​that become available. For example, the available values ​​of a particular set of neighboring samples along a particular direction and / or line can be copied into the predictor block. A reference to the direction in use can be coded in the bitstream or may itself be predicted.

[0011] Referring to FIG. 1A, shown at the bottom right is a subset of nine predictor directions specified in the 33 possible intra predictor directions of H.265 (corresponding to the 33 angle modes of the 35 modes specified in H.265). The point where the arrows converge (101) represents the sample being predicted. The arrows indicate the direction in which neighboring samples are used to predict the sample at 101. For example, arrow (102) indicates that sample (101) is predicted from a neighboring sample or samples to the upper right, at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from a neighboring sample or samples to the lower left of sample (101), at an angle of 22.5 degrees from the horizontal.

[0012] 1A, at the top left is shown a square block (104) of 4x4 samples (indicated by a dashed bold line). The square block (104) contains 16 samples, each labeled with "S" and its position in the Y dimension (e.g., row index) and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample (from the top) in the Y dimension and the first sample (from the left) in the X dimension. Similarly, sample S44 is the fourth sample of the block (104) in both the Y and X dimensions. Since the size of the block is 4x4 samples, S44 is at the bottom right. Also shown are examples of reference samples that follow a similar numbering scheme. The reference samples are labeled with R, their Y position (e.g., row index) and X position (column index) relative to the block (104). In both H.264 and H.265, neighboring prediction samples close to the block being reconstructed are used.

[0013] Intra-picture prediction of block 104 may start by copying reference sample values ​​from adjacent samples according to a signal prediction direction. For example, assume that the coded video bitstream includes signaling for this block 104 indicating the prediction direction of the arrow (102), i.e., the sample is predicted from the predicted sample or samples to the upper right and at an angle of 45 degrees from the horizontal. In such a case, samples S41, S32, S23, S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

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

[0015] As video coding technology continues to develop, the number of possible directions is increasing. For example, in H.264 (2003), nine different directions are available for intra prediction. This increases to 33 in H.265 (2013), and at the time of this disclosure, JEM / VVC / BMS can support 65 directions. Experimental studies have been conducted to help identify the most appropriate intra prediction directions, and certain techniques in entropy coding may be used to code those most appropriate directions with a small number of bits, accepting a bit penalty for the direction. Furthermore, sometimes the direction itself can be predicted from the neighboring directions used for intra prediction of the decoded neighboring blocks.

[0016] FIG. 1B shows a schematic diagram (180) showing the 65 intra-prediction directions according to the JEM, illustrating the increase in the number of prediction directions in various coding techniques developed over time.

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

[0018] Inter-picture prediction or inter-prediction may be based on motion compensation. In motion compensation, sample data from a previously reconstructed picture or part thereof (reference picture) may be used to predict a newly reconstructed picture or part of a picture (e.g., a 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 a third dimension, where the third dimension is an indication of the reference picture being used (similar to the temporal dimension).

[0019] In some video compression techniques, a current MV applicable to a region of sample data can be predicted from other MVs, e.g., from those other MVs related to other areas of sample data that are spatially adjacent to the area being reconstructed and that precede the current MV in decoding order. Doing so can substantially reduce the overall amount of data required to code the MV by relying on removing redundancy of correlated MVs, thereby increasing compression efficiency. MV prediction can work effectively because, for example, when coding an input video signal derived from a camera (known as natural video), there is a statistical possibility that areas larger than the area to which a single MV is applicable move in a similar direction in the video sequence, and therefore can possibly be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the actual MV of a given area will be similar or identical to the MV predicted from the surrounding MVs. Such MVs can be represented with fewer bits after entropy coding than would be used if the MVs were directly coded instead of predicted from neighboring MVs. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., sample stream). In other cases, the MV prediction itself may be non-lossy, for example due to rounding errors in computing the predictor from some surrounding MVs.

[0020] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H.265, "High Efficiency Video Coding", December 2016). Among the many MV prediction mechanisms specified by H.265, one that will be described later is a technique called "spatial merge".

[0021] Specifically, referring to Figure 2, a current block (201) contains samples that the encoder found during the motion search process to be predictable from a previous block of the same size but spatially shifted. Instead of coding its MV directly, the MV can be derived from metadata associated with one or more reference pictures, for example from the most recent reference picture (in decoding order) using the MV associated with any one of five surrounding samples denoted A0, A1 and B0, B1, B2 (202 to 206, respectively). In H.265, MV prediction can use predictors from the same reference picture as the neighboring blocks use. Summary of the Invention

[0022] Aspects of the present disclosure relate generally to a set of advanced video coding / decoding techniques, and more particularly to harmonized design among multiple baseline intra prediction, transform partitioning, and transform kernels.

[0023] In some example implementations, a method for processing video information is disclosed. The method includes: retrieving a data block of a video frame, the data block having adjacent reference lines and one or more non-adjacent reference lines in the video frame; determining whether a non-adjacent reference line of the one or more non-adjacent reference lines is used for intra-prediction of the data block. When the adjacent reference line is used for intra-prediction of the data block, the method includes selecting a target transformation kernel from a first set of transformation kernels to transform the data block, and when the non-adjacent reference line is used for intra-prediction of the data block, the method includes selecting a target transformation kernel from a second set of transformation kernels to transform the data block.

[0024] In the above implementation, the first set of transform kernels and the second set of transform kernels are primary transform kernels or secondary transform kernels.

[0025] In any one of the above implementations, the first set of transform kernels may include a superset of transform kernels, and the second set of transform kernels may include a subset of the superset of transform kernels. The first set of transform kernels and the second set of transform kernels may be primary transform kernels, and the second set of transform kernels may include one of a combination of DCT type 2 and ADST as a hybrid transform kernel, a combination of DCT type 2, ADST and flipped ADST as a hybrid transform kernel, a combination of DCT type 2 and IDT as a hybrid transform kernel, or a combination of DCT type 2, ADST, flipped ADST and IDT as a hybrid transform kernel.

[0026] In any one of the above implementations, the first set of transform kernels and the second set of transform kernels may be secondary transform kernels, and when the data block further includes two or more transform partition blocks, the second set of transform kernels may constitute a subset of the first set of transform kernels. In some further implementations, the data block may include two or more transform partition blocks, and the second set of transform kernels includes a NULL set. In some other implementations, the data block may include two or more transform partition blocks, and a selection of a transform kernel from the first set of transform kernels or the second set of transform kernels is signaled separately for each of the two or more transform partition blocks.

[0027] In any one of the above implementations, the first set of transform kernels and the second set of transform kernels may be primary transform kernels, and when the data block further includes two or more transform partition blocks, the second set of transform kernels may constitute a subset of the first set of transform kernels. In some implementations, the data block may include two or more transform partition blocks, and a selection of a transform kernel from the first set of transform kernels or the second set of transform kernels is signaled separately for each of the two or more transform partition blocks. In some implementations, the data block may include two or more transform partition blocks, and a selection from the second set of transform kernels is predefined when non-adjacent baselines are specified and is not signaled in a bitstream associated with the video frame.

[0028] In any one of the above implementations, a baseline index associated with a reference line used for intra prediction of the data block, among the adjacent baseline or one or more non-adjacent baselines, is used to derive a context for entropy coding of a kernel index of a primary transform kernel for transforming a secondary transform kernel selected from the first set of transform kernels or the second set of transform kernels.

[0029] In any one of the above implementations, when the data block further includes two or more transform partition blocks, the second set of transform kernels may constitute a subset of the first set of transform kernels for a subset of the two or more transform partition blocks, and the second set of transform kernels and the first set of transform kernels may be the same for the remaining subsets of the two or more transform partition blocks. In some implementations, the subset of the two or more transform partition blocks may include an upper or left transform partition of the data block.

[0030] In any one of the above implementations, the selection of a target transform kernel from the first set of transform kernels or the second set of transform kernels may be performed in response to multiple transform partition types being enabled to partition the data block into enabled transform blocks, and both the primary transform and the secondary transform being enabled for the data block.

[0031] In some implementations, another method for processing video information is disclosed. The method includes: retrieving a data block of a video frame, the data block having adjacent reference lines and one or more non-adjacent reference lines in the video frame; and determining whether a non-adjacent reference line of the one or more non-adjacent reference lines is used for intra-prediction of the data block. When the adjacent reference line is used for intra-prediction of the data block, the method includes selecting from a first set of transform partition types to partition the data block into transform partition blocks, and when the non-adjacent reference line is used for intra-prediction of the data block, the method includes selecting from a second set of transform partition types to partition the data block into transform partition blocks.

[0032] In such implementations, the second set of transform partition types may include only partition-less partition types. In some implementations, the second set of transform partition types may constitute a subset of the first set of transform partition types, each of which is associated with a number of partitions less than a predetermined threshold.

[0033] Another method for processing video information is disclosed, comprising the steps of: retrieving a data block of a video frame, the data block having one or more reference-lines in the video frame for intra-prediction, each reference-line being associated with a reference-line position index; selecting a reference-line from the one or more reference-lines for intra-prediction of the data block; and selecting a primary or secondary transform kernel from a subset of primary or secondary transform kernels for processing the data block, the subset of primary or secondary transform kernels being selected from the complete set of primary or secondary transform kernels based on a reference-line position index of the reference-line selected for intra-prediction.

[0034] In the above implementation, the subset of primary or secondary transform kernels may be the same for all non-adjacent reference lines when selected for intra prediction.

[0035] In some implementations, a video device is disclosed that may include processing circuitry configured to implement each of the above methods.

[0036] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer, cause the computer to perform any one of the implementations of the above methods for video decoding and / or encoding. [Brief description of the drawings]

[0037] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings.

[0038] [Figure 1A] FIG. 1 is a schematic diagram of an example subset of intra-prediction direction modes.

[0039] [Figure 1B] FIG. 2 is a diagram of an example intra-prediction direction.

[0040] [Diagram 2] FIG. 2 is a schematic diagram of a current block and its surrounding spatial merging candidates for motion vector prediction in one example.

[0041] [Diagram 3] FIG. 3 is a schematic diagram of a simplified block diagram of a communication system (300) according to an example embodiment.

[0042] [Figure 4] FIG. 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an example embodiment.

[0043] [Diagram 5] FIG. 2 is a schematic diagram of a simplified block diagram of a video decoder according to an example embodiment.

[0044] [Figure 6] FIG. 2 is a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment.

[0045] [Figure 7] FIG. 2 is a block diagram of a video encoder according to another example embodiment.

[0046] [Figure 8] FIG. 2 is a block diagram of a video decoder according to another example embodiment.

[0047] [Figure 9] FIG. 2 illustrates a coding block partitioning scheme according to an exemplary embodiment of the present disclosure.

[0048] [Figure 10] FIG. 13 illustrates another coding block partitioning scheme according to an exemplary embodiment of the present disclosure.

[0049] [Figure 11] FIG. 13 illustrates another coding block partitioning scheme according to an exemplary embodiment of the present disclosure.

[0050] [Figure 12] FIG. 13 illustrates another coding block partitioning scheme according to an exemplary embodiment of the present disclosure.

[0051] [Figure 13] FIG. 2 illustrates a scheme for partitioning a coding block into multiple transform blocks and the coding order of the transform blocks, according to an exemplary embodiment of the present disclosure.

[0052] [Figure 14] 4A-4C illustrate another scheme for partitioning a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure.

[0053] [Figure 15] FIG. 2 illustrates another scheme for partitioning a coding block into multiple transform blocks, according to an exemplary embodiment of the present disclosure.

[0054] [Figure 16] FIG. 2 illustrates various baseline-based intra-prediction schemes, according to an exemplary embodiment of the present disclosure.

[0055] [Figure 17] FIG. 1 illustrates a planar rotation transformation according to an exemplary embodiment of the present disclosure.

[0056] [Figure 18] FIG. 2 illustrates various DCT-2, DCT-4 partial butterfly lookup tables according to exemplary embodiments of the present disclosure.

[0057] [Figure 19] FIG. 1 illustrates a DST-7 partial butterfly lookup table in accordance with an exemplary embodiment of the present disclosure.

[0058] [Figure 20] FIG. 1 illustrates a line graph transformation according to an exemplary embodiment of the present disclosure.

[0059] [Figure 21] FIG. 1 illustrates a secondary transform set selection according to an exemplary embodiment of the present disclosure.

[0060] [Figure 22] FIG. 2 illustrates a coding block having four transform blocks, according to an exemplary embodiment of the present disclosure.

[0061] [Figure 23] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 24] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Diagram 25] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure.

[0062] [Figure 26] FIG. 1 is a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to an embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may perform unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., a stream of video pictures captured by the terminal device (310)) for transmission to another terminal device (320) via the network (350). The coded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. One-way data transmission may be implemented in media serving applications and the like.

[0064] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data, which may be implemented, for example, during a video conferencing application. For the bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may code video data (e.g., of a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to reconstruct the video pictures, and display the video pictures on an accessible display device according to the reconstructed video data.

[0065] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be implemented as servers, personal computers, and smartphones, although the applicability of the underlying principles of the present disclosure may not be so limited. The embodiments of the present disclosure may be implemented in desktop computers, laptop computers, tablet computers, media players, wearable computers, dedicated video conferencing equipment, and / or the like. The network (350) represents any number or type of network that conveys coded video data between the terminal devices (310), (320), (330), and (340), including, for example, wireline and / or wireless communication networks. The communication network (350) may exchange data in circuit-switched, packet-switched, and / or other types of channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this discussion, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless explicitly described herein.

[0066] 4 shows an arrangement of a video encoder and a video decoder in a video streaming environment as an example of an application of the disclosed subject matter. The disclosed subject matter may be applicable to other video applications as well, including, for example, video conferencing, digital TV broadcasting, gaming, virtual reality, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0067] A video streaming system may include a video source (401), e.g., a video capture subsystem (413), which may include a digital camera, for creating a stream of uncompressed video pictures or images (402). In one example, the stream of video pictures (402), which includes samples recorded by the digital camera of the video source (401), may be processed by an electronic device (420) including a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), shown as thin lines to emphasize its low amount of data compared to the stream of uncompressed video pictures (402), can be stored on the streaming server (405) for future use or directly to a downstream video device (not shown). One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, can access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) can include a video decoder (410), for example within the electronic device (430). The video decoder (410) decodes the input copy of the encoded video data (407) and creates an output stream of video pictures (411), which is uncompressed and can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). The video decoder 410 can be configured to perform some or all of the various functions described in this disclosure.In some streaming systems, the encoded video data 404, 407, and 409 (e.g., video bitstreams) may be encoded according to a particular video coding / compression standard. Examples of these standards include ITU-T Recommendation H.265. In one example, a video coding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC and other video coding standards.

[0068] It should be noted that the electronic devices (420) and (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).

[0069] 5 shows a block diagram of a video decoder (510) according to any of the following embodiments of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0070] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, where the decoding of each coded video sequence is independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or images. The coded video sequences may be received from a channel (501), which may be a storage device that stores the coded video data or a hardware / software link to a streaming source that transmits the coded video data. The receiver (531) may receive the coded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to their respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To eliminate network jitter, a buffer memory (515) may be located between the receiver (531) and the entropy decoder / parser (520) (hereinafter "parser (520)"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, the buffer memory (515) may be external to and separate from the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), for example for the purpose of eliminating network jitter, and there may be another additional buffer memory (515) internal to the video decoder (510), for example for handling playback timing. When the receiver (531) is receiving data from a store / forward device with sufficient bandwidth and controllability or from an isosynchronous network, the buffer memory (515) may not be necessary or may be small.For use in a best effort packet network such as the Internet, a buffer memory (515) of sufficient size may be required, which may be relatively large in size. Such a buffer memory may be implemented with an adaptive size and may be implemented, at least in part, in an operating system or similar element (not shown) outside the video decoder (510).

[0071] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the coded video sequence. These symbol categories include information used to manage the operation of the video decoder (510) and potentially information to control a rendering device such as a display (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The rendering device control information may be in the form of a Supplemental Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (520) may parse / entropy decode the coded video sequence received by the parser (520). The entropy coding of the coded video sequence may follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include Groups of Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs), Prediction Units (PUs), etc. The parser (520) may also extract from the coded video sequence information such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

[0072] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to generate symbols (521).

[0073] The reconstruction of the symbols (521) can involve a number of different processes or functions, depending on the type of coded video picture or portion thereof (e.g., inter and intra picture, inter and intra block) and other factors. The units involved and how they participate can be controlled by subgroup control information parsed by the parser (520) from the coded video sequence. The flow of such subgroup control information between the parser (520) and a number of processing or functional units described below is not shown for the sake of simplicity.

[0074] In addition to the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into a number of functional units, as described below. In a practical implementation operating under commercial constraints, many of these functional units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of clearly describing the various functions of the disclosed subject matter, a conceptual subdivision into functional units is used in the following disclosure.

[0075] The first unit may include a scalar / inverse transform unit (551), which may receive the quantized transform coefficients as well as control information including information indicating the type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, and location (lie) as symbols (521) from the parser (520). The scalar / inverse transform unit (551) may output a block containing sample values ​​that may be input to an aggregator (555).

[0076] In some cases, the output samples of the scaler / inverse transform (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate blocks of the same size and shape of the block being reconstructed using surrounding block information already reconstructed and stored in the current picture buffer (558). The current picture buffer (558) may buffer, for example, a partially reconstructed and / or a fully reconstructed current picture. The aggregator (555) may, in some implementations, add, on a sample-by-sample basis, prediction information generated by the intra-prediction unit (552) to the output sample information, as provided by the scaler / inverse transform unit (551).

[0077] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to a block that is inter-coded and potentially motion compensated. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for inter-picture prediction. After motion compensating the fetched samples according to the symbols (521) associated with the block, these samples may be added by the aggregator (555) to the output of the scalar / inverse transform unit (551) (the output of unit 551 may be referred to as a residual sample or residual signal) to generate output sample information. The address in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction samples may be controlled by a motion vector available to the motion compensated prediction unit (553), e.g., in the form of a symbol (521) that may have X, Y components (shift) and a reference picture component (time). Motion compensation may also include interpolation of sample values ​​fetched from the reference picture memory (557) when sub-sample accurate motion vectors are used, and may be associated with a motion vector prediction mechanism, etc.

[0078] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). Video compression techniques, controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), may include in-loop filter techniques that may be responsive to meta-information obtained during decoding of previous portions (in decoding order) of the coded picture or coded video sequence, as well as to previously reconstructed and loop filtered sample values. As described in more detail below, several types of loop filters may be included as part of the loop filter unit 556, in various orders.

[0079] The output of the loop filter unit (556) may be a sample stream that can be output to a rendering device (512) and can be stored in a reference picture memory (557) for use in future inter-picture prediction.

[0080] Once a coded picture is fully reconstructed, it can be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (520)), the current picture buffer (558) can become part of the reference picture memory (557), and the fresh current picture buffer can be reallocated before starting the reconstruction of a subsequent coded picture.

[0081] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard such as ITU-T Rec. H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard used in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and to a profile documented in the video compression technique or standard. In particular, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool available for use under that profile. To be standard-compliant, the complexity of the coded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference pixel size, etc. The limits set by the level may be further restricted in some cases through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the coded video sequence.

[0082] In some example embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0083] 6 shows a block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure. 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 in place of the video encoder (403) of the example of FIG. 4.

[0084] The video encoder (603) may receive video samples from a video source (601) (not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In another example, the video source (601) may be implemented as part of the electronic device (620).

[0085] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that may be of 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 delivery system, the video source (601) may be a storage device that can store pre-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 number of individual pictures or images that convey motion when viewed in a sequence. The pictures themselves may be organized as a spatial array of pixels, where each pixel may contain one or more samples depending on the sampling structure, color space, etc. used. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0086] According to some example embodiments, the video encoder (603) can code and compress pictures of a source video sequence into a coded video sequence (643) in real-time or under any other time constraint required by the application. Enforcing an appropriate coding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be functionally coupled to and control other functional units, as described below. This coupling is not shown for the sake of simplicity. Parameters set by the controller (650) may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, ...), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) can be configured to have other appropriate functions associated with the video encoder (603) that are optimized for a particular system design.

[0087] In some example embodiments, the video encoder (603) may be configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (630) (responsible for creating symbols, such as a symbol stream, based on, for example, an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The embedded decoder 633 processes the video stream by the source coder 630 without entropy coding, but the decoder (633) reconstructs the symbols to create sample data in a similar manner as the (remote) decoder does (since any compression between the symbols in entropy coding and the coded video bitstream may be lossless with the video compression techniques considered in the disclosed subject matter). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream yields bit-exact results independent of the decoder location (local or remote), the contents in the reference picture memory (634) are also bit-exact between the local and remote encoders. In other words, the prediction part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchronicity (and the resulting drift when synchronicity cannot be maintained, e.g., due to channel errors) can be used to improve coding quality.

[0088] The operation of the "local" decoder (633) may be the same as a "remote" decoder, such as the video decoder (510), already described above in connection with Figure 5. However, with brief reference also to Figure 5, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) may be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633) within the encoder.

[0089] An observation that may be made at this point is that any decoder technique other than analysis / entropy decoding, which may only be present in the decoder, may necessarily also need to be present in a corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter may sometimes focus on the decoder operations associated with the decoding portion of the encoder. Thus, a description of the encoder techniques may be omitted, as opposed to the decoder techniques being exhaustively described. Only in certain areas or aspects is a more detailed description of the encoder provided below.

[0090] During operation in some example implementations, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with respect to one or more previously coded pictures from a video sequence designated as "reference pictures." In this manner, the coding engine (632) codes differences (or residuals) in color channels between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references for the input picture. The term "residue" and its adjective "residual" may be used interchangeably.

[0091] The local video decoder (633) may decode coded video data of pictures that may be designated as reference pictures based on symbols created by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may be a replica of the source video sequence, typically with some errors. The local video decoder (633) may replicate the decoding process that may be performed by the video decoder on the reference pictures and store the reconstructed reference pictures in a reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content as reconstructed reference pictures obtained by a far-end (remote) video decoder (without transmission errors).

[0092] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata, such as reference picture motion vectors, block shapes, etc., which may serve as suitable prediction references for the new picture. The predictor (635) may operate on a sample block-by-pixel block basis to find suitable prediction references. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (634).

[0093] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0094] All outputs of the aforementioned functional units may be subject to entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by lossless compression of the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0095] The transmitter (640) may buffer the coded video sequence produced by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0096] The controller (650) may manage the operation of the video encoder (603). During coding, the controller (650) may assign to each coded picture a particular coded picture type, which may affect the coding that may be applied to the respective picture. For example, pictures may often be assigned as one of the following picture types:

[0097] An intra picture (I-picture) may be one that can be coded and decoded without using any other picture in a sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, Independent Decoder Refresh ("IDR") pictures. Those skilled in the art are aware of these variations of I-pictures and their respective uses and characteristics.

[0098] A predictive picture (P picture) may be one that can be coded and decoded using intra- or inter-prediction, using at most one motion vector and reference index to predict the sample values ​​of each block.

[0099] Bidirectionally predictive pictures (B-pictures) may be those that can be coded and decoded using intra- or inter-prediction, using up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple-predictive pictures may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0100] A source picture is usually spatially subdivided into a number of sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8 or 16x16 samples each) and may be coded block by block. Blocks may be predictively coded with respect to other (already coded) blocks, as determined by the coding assignment applied to the respective picture of the block. For example, blocks of an I picture may be non-predictively coded, or they may be predictively coded with respect to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of a P picture may be predictively coded via spatial prediction or via temporal prediction with respect to one previously coded reference picture. Blocks of a B picture may be predictively coded via spatial prediction or via temporal prediction with respect to one or two previously coded reference pictures. Source pictures or intermediate processed pictures may be subdivided into other types of blocks for other purposes. The division of coding blocks and other types of blocks may or may not follow the same method, as described in more detail below.

[0101] The video encoder (603) may perform coding operations according to a given video coding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0102] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include other types of redundant data, such as temporal / spatial / SNR enhancement layers, redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0103] A video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given image, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture being encoded / decoded may be called the current picture and partitioned into blocks. When a block in the current picture resembles a reference block in a previously coded and still buffered reference picture in the video, it may be coded by a vector called a motion vector. A motion vector points to a reference block in a reference picture and may have a third dimension that identifies the reference picture in cases where multiple reference pictures are used.

[0104] In some exemplary embodiments, bi-prediction techniques can be used for inter-picture prediction. According to such bi-prediction techniques, two reference pictures are used, such as a first reference picture and a second reference picture, both of which advance the current image in the video in decoding order (but may be past or future, respectively, in display order). A block in the current picture can be coded by a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. A block can be jointly predicted by a combination of the first and second reference blocks.

[0105] Furthermore, to improve coding efficiency, merge mode techniques may be used in inter-picture prediction.

[0106] According to some example 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 sequence of video pictures is partitioned into coding tree units (CTUs) for compression, and the CTUs in a picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may include three parallel coding tree blocks (CTBs), i.e., one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree split into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be split into one CU of 64×64 pixels or four CUs of 32×32 pixels. Each of one or more of the 32×32 blocks may be further split into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine the prediction type of the CU among various prediction types, such as inter prediction type or intra prediction type. The CU may be split into one or more prediction units (PUs) depending on the temporal and / or spatial predictability. In general, each PU includes a luma prediction block (PB) and two chroma PBs. In one embodiment, the prediction operation in coding (encoding / decoding) is performed in units of a prediction block. The split of the CU into PUs (or PBs of different color channels) may be performed in various spatial patterns. The 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 samples, etc.

[0107] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of this disclosure. The video encoder (703) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. The exemplary video encoder (703) may be used in place of the example video encoder (403) of FIG. 4.

[0108] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8x8 samples. The video encoder (703) then determines whether the processing block is best coded using intra-mode, inter-mode, or bi-prediction mode, for example using rate-distortion optimization (RDO). When the processing block is determined to be coded in intra-mode, the video encoder (703) may encode the processing block into a coded picture using intra-prediction techniques, and when the processing block is determined to be coded in inter-mode or bi-prediction mode, the video encoder (703) may encode the processing block into a coded picture using inter-prediction techniques or bi-prediction techniques, respectively. In some exemplary embodiments, the merge mode may be used as a sub-mode of inter-picture prediction when motion vectors are derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In some other exemplary embodiments, there may be a motion vector component applicable to the current block. Accordingly, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module, to determine the perdition mode of a processing block.

[0109] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725), coupled together as shown in the exemplary arrangement of FIG.

[0110] The inter encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter prediction information (e.g., a description of redundant information according to an inter coding technique, motion vectors, merge mode information), and calculate an inter prediction result (e.g., a prediction block) based on the inter prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that is decoded based on the coded video information using a decoding unit 633 (shown as a residual decoder 728 in FIG. 7, as described in more detail below) embedded in the example encoder 603 of FIG. 6.

[0111] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block to previously coded blocks in the same picture, generate transformed and quantized coefficients, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). The intra encoder (722) may calculate intra prediction results (e.g., a prediction block) based on the intra prediction information and reference blocks in the same picture.

[0112] The general controller (721) may 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 the switch (726) based on the prediction mode. For example, when the prediction mode is an intra mode, the general controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723) and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream, and when the prediction mode of the block is an inter mode, the general controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723) and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0113] The residual calculator (723) may be configured to calculate the difference (residual data) between a received block and a prediction result for a 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 transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients are then subjected to a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are appropriately processed to generate decoded pictures, which can be buffered in a memory circuit (not shown) and used as reference pictures.

[0114] The entropy encoder (725) may be configured to format a bitstream to include the encoded blocks and perform entropy coding. The entropy encoder (725) may be configured to include various information in the bitstream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other suitable information in the bitstream. When coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information may be absent.

[0115] 8 shows a diagram of an example video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (810) may be used in place of the example video decoder (410) of FIG. 4.

[0116] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter-decoder (880), a residual decoder (873), a reconstruction module (874), and an intra-decoder (872), coupled together as shown in the exemplary arrangement of FIG.

[0117] The entropy decoder (871) may be configured to reconstruct from a coded picture certain symbols that represent syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra-mode, inter-mode, bi-predictive mode, merged sub-mode, or another sub-mode) that may identify the mode in which the block is coded, certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information, for example in the form of quantized transform coefficients, etc. In one example, when the prediction mode is an inter-mode or bi-predictive mode, the inter-predictive information is provided to the inter-decoder (880), and when the prediction mode is an intra-predictive mode, the intra-predictive information is provided to the intra-decoder (872). The residual information may be subject to inverse quantization and provided to the residual decoder (873).

[0118] The inter decoder (880) may be configured to receive inter prediction information and generate inter prediction results based on the inter prediction information.

[0119] The intra decoder (872) may be configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

[0120] The residual decoder (873) may be configured to perform inverse quantization to extract de-quantized transform coefficients and process the de-quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (including Quantizer Parameters (QP)) that may be provided by the entropy decoder (871) (data paths not shown as this may be only low volume control information).

[0121] The reconstruction module (874) may be configured to combine, in the spatial domain, the residual as output by the residual decoder (873) and the prediction result (possibly as output by an inter- or intra-prediction module) to form a reconstructed block that forms part of the reconstructed picture as part of the reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may also be performed to improve visual quality.

[0122] It should be noted that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technology. In some exemplary embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0123] Turning to coding block partitioning, in some example implementations, a predefined pattern may be applied. As shown in FIG. 9, an example four-way partitioning tree may be used starting from a first predefined level (e.g., 64×64 block level) down to a second predefined level (e.g., 4×4 level). For example, the base block may be subject to four partitioning options, indicated by 902, 904, 906, and 908, with partitions designated as R allowing recursive partitions in that the same partition tree as shown in FIG. 9 may be repeated at a lower scale down to the lowest level (e.g., 4×4 level). In some implementations, additional restrictions may be applied to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitions (e.g., 1:2 / 2:1 rectangular partitions) may be allowed, but these partitions may not be allowed to be recursive, whereas square partitions are allowed to be recursive. Partitioning with recursion according to FIG. 9 produces a final set of coding blocks, if necessary. Such a scheme may be applied to one or more color channels.

[0124] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows for recursive partitioning to form a partitioning tree. As shown in FIG. 10, an exemplary 10-way partitioning structure or pattern may be predefined. A root block may start at a predefined level (e.g., 128×128 level or 64×64 level). The exemplary partitioning structure of FIG. 10 includes various 2:1 / 1:2 and 4:1 / 1:4 rectangular partitions. The three sub-partition partition types shown as 1002, 1004, 1006, and 1008 in the second row of FIG. 10 may be referred to as "T-shaped" partitions. The "T-shaped" partitions 1002, 1004, 1006, and 1008 may be referred to as left T-shaped, upper T-shaped, right T-shaped, and lower T-shaped. In some implementations, no further subdivision of any of the rectangular partitions in FIG. 10 is allowed. The depth of the coding tree may be further defined to indicate the depth of the split from the root node or root block. For example, the coding tree depth for a root node or root block, e.g., a 128x128 block, may be set to 0, and after the root block is split once more according to Fig. 10, the coding tree depth is increased by 1. In some implementations, only the all-square partitions in 1010 may be allowed for recursive partitioning to the next level of the partitioning tree according to the pattern of Fig. 10. In other words, recursive partitioning may not be allowed for the square partitions of patterns 1002, 1004, 1006, and 1006. Partitioning with recursion according to Fig. 10 produces a final set of coding blocks, if necessary. Such a scheme may be applied to one or more color channels.

[0125] After splitting or partitioning the base block according to any of the above partitioning procedures or other procedures, again a final set of partitions or coding blocks may be obtained. Each of these partitions may be one of various partitioning levels. Each of the partitions may be called a coding block (CB). In the various exemplary partitioning implementations above, each resulting CB may be of any of the allowed sizes and partitioning levels. They are called coding blocks because they may form a unit where some basic coding / decoding decisions are made and coding / decoding parameters may be optimized, determined, and signaled in the encoded video bitstream. The highest level in the final partition represents the depth of the coding block partitioning tree. The coding block may be a luma coding block or a chroma coding block.

[0126] In some other example implementations, a quadtree structure may be used to recursively split the base luma and chroma blocks into coding units. Such a split structure may be called a coding tree unit (CTU), and the coding tree unit (CTU) is split into coding units (CUs) by adapting the partitioning to various local characteristics of the base CTU using the quadtree structure. In such implementations, an implicit quadtree split may be performed at the picture boundary, so that a block will remain quadtree split until its size fits the picture boundary. The term CU is used to collectively refer to the units of luma coding blocks and chroma coding blocks (CBs).

[0127] In some implementations, the CB may be further partitioned. For example, the CB may be further partitioned into multiple prediction blocks (PBs) for the purpose of intra- or inter-frame prediction during the coding and decoding process. In other words, the CB may be further divided into different sub-partitions, where individual prediction decisions / configurations may be made. In parallel, the CB may be further partitioned into multiple transform blocks (TBs) to delineate the levels at which a transform or inverse transform of video data is performed. The partitioning scheme of the CB into PBs and TBs may be the same or different. For example, the partitioning scheme may be performed using its own procedure, for example, based on various characteristics of the video data. The partitioning scheme of the PB and TB may be independent in some exemplary implementations. The partitioning scheme and boundaries of the PB and TB may be correlated in some other exemplary implementations. In some implementations, for example, the TB may be partitioned after the PB partition, and in particular, each PB may be further partitioned into one or more TBs after being determined following the partitioning of the coding block. For example, in some implementations, the PB may be split into one, two, four, or some other number of TBs.

[0128] In some implementations, the luma and chroma channels may be treated differently for partitioning base blocks into coding blocks and further partitioning into predictive and / or transform blocks. For example, in some implementations, partitioning of coding blocks into predictive and / or transform blocks may be allowed for luma channels, but such partitioning of coding blocks into predictive and / or transform blocks may not be allowed for chroma channels. In such implementations, transformation and / or prediction of luma blocks may be performed only at the coding block level. In another example, the minimum transform block size of luma and chroma channels may be different, e.g., coding blocks of luma channels may be allowed to be partitioned into smaller transform and / or predictive blocks than chroma channels. In yet another example, the maximum depth of partitioning of coding blocks into transform and / or predictive blocks may be different between luma and chroma channels, e.g., coding blocks of luma channels may be allowed to be partitioned into deeper transform and / or predictive blocks than chroma channels. In a specific example, a luma coding block may be partitioned into transform blocks of multiple sizes that can be represented by a recursive partitioning down to a maximum of two levels, and transform block shapes such as square, 2:1 / 1:2, and 4:1 / 1:4, and transform block sizes from 4×4 to 64×64 may be allowed. However, for a chroma block, only the largest possible transform block specified for the luma block may be allowed.

[0129] In some example implementations for partitioning a coding block into PBs, the depth, shape, and / or other characteristics of the PB partitioning may depend on whether the PB is intra-coded or inter-coded.

[0130] The partitioning of coding blocks (or prediction blocks) into transform blocks may be implemented in various exemplary schemes, including but not limited to, quadtree splitting and predefined pattern splitting, recursively or non-recursively, with additional consideration of transform blocks at coding or prediction block boundaries. In general, the resulting transform blocks may be at different levels of splitting, may not be the same size, and may not need to be square in shape (e.g., they may be rectangular with any allowed size and aspect ratio).

[0131] In some implementations, a coding partition tree scheme or structure may be used. The coding partition tree scheme used for the luma channel and the chroma channel need not be the same. In other words, the luma channel and the chroma channel may have separate coding tree structures. Furthermore, whether the luma channel and the chroma channel use the same coding partition tree structure or different coding partition tree structures, and the actual coding partition tree structure used may depend on whether the slice being coded is a P, B, or I slice. For example, in an I slice, the chroma channel and the luma channel may have separate coding partition tree structures or coding partition tree structure modes, while in a P or B slice, the luma channel and the chroma channel may share the same coding partition tree scheme. When separate coding partition tree structures or modes are applied, the luma channel may be partitioned into CBs by one coding partition tree structure, and the chrominance channel may be partitioned into chrominance CBs by another coding partition tree structure.

[0132] A specific exemplary implementation of coding block and transform block partitioning is described below. In such an exemplary implementation, a base coding block may be split into coding blocks using the recursive quadtree division described above. At each level, whether to continue further quadtree division of a particular partition may be determined by local video data characteristics. The resulting CB may be various quadtree division levels with various sizes. The decision of whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction may be made at the CB level (or at the CU level for all three color channels). Each CB may be further split into one, two, four or other number of PBs depending on the PB division type. Inside a PB, the same prediction process is applied and related information is transmitted to the decoder on a PB basis. After obtaining the residual block by applying the prediction process based on the type of PB division, the CB may be partitioned into TBs according to another quadtree structure similar to the coding tree of the CB. In this specific implementation, the CB or TB is square shaped, but is not necessarily limited to it. Furthermore, in this particular example, the PB may be square or rectangular in shape for inter prediction, and only square for intra prediction. The coding block may be further divided into, for example, four square-shaped TBs. Each TB may be further divided recursively (using quad-tree division) into smaller TBs called residual quad-trees (RQTs).

[0133] Another specific example for partitioning a base coding block into a CB and other PBs and / or TBs is described below. For example, instead of using multiple partition unit types as shown in FIG. 10, a quadtree with nested multiple types of trees using binary and ternary split segmentation structures can be used. The separation of the concepts of CB, PB and TB (i.e., partitioning of CB into PBs and / or TBs and partitioning of PBs into TBs) can be abandoned except when CBs of a size too large for the maximum transform length are required, and such CBs may require further splitting. This exemplary partitioning scheme can be designed to support more flexibility on the CB partitioning shape, so that both prediction and transformation can be performed at the CB level without further partitioning. In such a coding tree structure, the CB may have either a square or a rectangular shape. Specifically, a coding tree block (CTB) can be partitioned first by a quadtree structure. Then, the quadtree leaf nodes can be further partitioned by a multi-type tree structure. An example of a multi-type tree structure is shown in FIG. 11. Specifically, the exemplary multi-type tree structure of FIG. 11 includes four split types called binary splitting (SPLIT_BT_VER) (1102), horizontal binary splitting (SPLIT_BT_HOR) (1104), ternary splitting (SPLIT_TT_VER) (1106), and horizontal trisection (SPLIT_TT_HOR) (1108). And the CBs correspond to the leaves of the multi-type tree. In this exemplary implementation, as long as the CB is not too large for the maximum transform length, this segmentation is used for both prediction and transform processes without any further splitting. This means that in most cases, the CB, PB, and TB have the same block size in the quadtree with nested multi-type tree coding block structure. An exception occurs when the maximum supported transform length is smaller than the width or height of the color components of the CB.

[0134] An example of a quadtree with nested multi-type tree coding block structure of block partitions for one CTB is shown in FIG. 12. More specifically, FIG. 12 shows that a CTB 1200 is a quadtree split into four square partitions 1202, 1204, 1206 and 1208. A decision to further use the multi-type tree structure of FIG. 11 for splitting is made for each of the quadtree split partitions. In the example of FIG. 12, partition 1204 is not further split. Partitions 1202 and 1208 each adopt another quadtree split. In partition 1202, the upper left partition, upper right partition, lower left partition and lower right partition of the second level quadtree split adopt the third level quadtree split, 1104 of FIG. 11, no split and 1108 of FIG. 11, respectively. Partition 1208 adopts another quadtree split, and the top-left, top-right, bottom-left and bottom-right partitions of the second-level quadtree split adopt the third-level split, non-split, non-split of 1106 in Fig. 11, and 1104 in Fig. 11, respectively. Two of the subpartitions of the top-left partition of the third level of 1208 are further split according to 1104 and 1108. Partition 1206 adopts the second-level split pattern according to 1102 in Fig. 11 into two partitions, and the two partitions are further split to the third level according to 1108 and 1102 in Fig. 11. A fourth-level split is applied to one of them according to 1104 in Fig. 11.

[0135] In the above specific example, the maximum luma transform size may be 64 x 64, and the maximum supported chroma transform size may be different from the luma, e.g., 32 x 32. When the width or height of a luma coding block or a chroma coding block is larger than the maximum transform width or height, the luma coding block or the chroma coding block may be automatically split in the horizontal and / or vertical direction to meet the transform size limitation in that direction.

[0136] In the above specific example of partitioning base coding blocks into CBs, the coding tree scheme can support the ability for luma and chroma to have separate block tree structures. For example, in P and B slices, the luma and chroma CTBs in one CTU may share the same coding tree structure. For example, in an I slice, luma and chroma may have separate coding block tree structures. When the separate block tree mode is applied, the luma CTB may be partitioned into luma CBs by one coding tree structure, and the chroma CTBs are partitioned into chroma CBs by another coding tree structure. This means that a CU in an I slice may consist of coding blocks of a luma component or coding blocks of two chroma components, and a CU in a P or B slice is always composed of coding blocks of all three color components, unless the video is monochrome.

[0137] Exemplary implementations for partitioning coding or predictive blocks into transform blocks and the coding order of transform blocks are described in further detail below. In some exemplary implementations, the transform partitioning can support multiple shapes of transform blocks, such as 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1, with transform block sizes ranging from, for example, 4×4 to 64×64. In some implementations, if the coding block is 64×64 or smaller, the transform block partitioning may only be applied to the luma component, so that for chroma blocks, the size of the transform block is the same as the size of the coding block. Otherwise, if the width or height of the coding block is greater than 64, the luma and chroma coding blocks may be implicitly split into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32) transform blocks, respectively.

[0138] In some example implementations, for both intra-coded and inter-coded blocks, the coding blocks may be further partitioned into multiple transform blocks with a partitioning depth up to a predetermined number of levels (e.g., two levels). The depth and size of the transform block partitioning may be related. An example mapping from the transform size of the current depth to the transform size of the next depth is shown in Table 1 below. [Table 1]

[0139] Based on the example mapping of Table 1, for a 1:1 square block, the next level transform split may create four 1:1 square sub-transform blocks. The transform partition may stop at, for example, 4×4. Thus, a transform size of the current depth of 4×4 corresponds to the same size of 4×4 at the next depth. In the example of Table 1, for a 1:2 / 2:1 non-square block, the next level transform split will create two 1:1 square sub-transform blocks, while for a 1:4 / 4:1 non-square block, the next level transform split will create two 1:2 / 2:1 sub-transform blocks.

[0140] In some example implementations, additional restrictions may be applied to the luma components of intra-coded blocks. For example, for each level of transform partitioning, all sub-transform blocks may be restricted to have equal size. For example, for a 32×16 coding block, level 1 transform partitioning creates two 16×16 sub-transform blocks, and level 2 transform partitioning creates eight 8×8 sub-transform blocks. In other words, the second level partitioning must be applied to all first level sub-blocks to keep the transform units equal in size. An example of transform block partitioning of an intra-coded square block according to Table 1 is shown in FIG. 13 with the coding order indicated by the arrows. Specifically, 1302 shows a square coding block. The first level partitioning according to Table 1 into four equal-sized transform blocks is shown at 1304 with the coding order indicated by the arrows. The second level partitioning of all first level equal-sized blocks according to Table 1 into 16 equal-sized transform blocks is shown at 1306 with the coding order indicated by the arrows.

[0141] In some example implementations, the above restrictions on intra-coding may not apply to the luma components of an inter-coded block. For example, after the first level transform split, any one of the sub-transform blocks may be further split independently of the other level. Thus, the resulting transform blocks may or may not be of the same size. An example split of an inter-coded block into transform blocks is shown in FIG. 14 together with their coding order. In the example of FIG. 14, an inter-coded block 1402 is split into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is split into four transform blocks of equal size. Then, as shown at 1404, only one of the four transform blocks (but not all of them) is further split into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes. An example coding order of these seven transform blocks is shown by the arrows at 1404 in FIG. 14.

[0142] In some example implementations, for chroma components, some additional restrictions on transform blocks may be applied, such as for chroma components, the transform block size may be as large as the coding block size, but not smaller than a certain size, e.g., 8×8.

[0143] In some other example implementations, for coding blocks whose either width (W) or height (H) is greater than 64, both the luma and chroma coding blocks may be implicitly split into multiples of min(W, 64) x min(H, 64) and min(W, 32) x min(H, 32) transform units, respectively.

[0144] Figure 15 further illustrates another alternative exemplary scheme for partitioning a coding block or a predictive block into transform blocks. As illustrated in Figure 15, instead of using recursive transform partitioning, a predefined set of partitioning types may be applied to a coding block according to its transform type. In the particular example illustrated in Figure 15, one of six exemplary partitioning types may be applied to split the coding block into various numbers of transform blocks. Such a scheme may be applied to either a coding block or a predictive block.

[0145] More specifically, the partitioning scheme of FIG. 15 provides up to six partition types for any given transform type, as shown in FIG. 15. In this scheme, every coding block or predictive block may be assigned a transform type based on, for example, a rate-distortion cost. In one example, the partition type assigned to a coding block or predictive block may be determined based on the transform partition type of the coding block or predictive block. A particular partition type may correspond to a size and pattern (or partition type) of transform block division, as shown by the four partition types illustrated in FIG. 15. The correspondence between various transform types and various partition types may be predefined. Exemplary correspondences are shown below with capitalized labels indicating transform types that may be assigned to coding blocks or predictive blocks based on rate-distortion cost:

[0146] ·PARTITION_NONE: Allocate the transformation size equal to the block size.

[0147] ·PARTITION_SPLIT: Allocates a transformation size of 1 / 2 the width of the block size and 1 / 2 the height of the block size.

[0148] ·PARTITION_HORZ: Allocates a transformation size with the same width as the block size and 1 / 2 the height of the block size.

[0149] ·PARTITION_VERT: Allocates a transformation size that is 1 / 2 the width of the block size and the same height as the block size.

[0150] ·PARTITION_HORZ4: Allocates a transformation size with the same width as the block size and 1 / 4 of the block size in height.

[0151] ·PARTITION_VERT4: Allocates a transformation size that is 1 / 4 the width of the block size and the same height as the block size.

[0152] In the above example, all partition types as shown in Figure 15 include uniform transform sizes for the partitioned transform blocks. This is not a limitation, but merely an example. In some other implementations, mixed transform block sizes may be used for the partitioned transform blocks in a particular partition type (or pattern).

[0153] Returning to intra prediction, some exemplary implementations may base prediction of samples in a coding block or a prediction block on one or a set of reference lines. In other words, instead of always using the nearest neighboring line (e.g., the neighboring line immediately above or immediately to the left of the prediction block as shown in FIG. 1), multiple reference lines may be provided as an option for intra prediction selection. Such intra prediction implementations may be called Multiple Reference Line Selection (MRLS). In these implementations, the encoder determines and signals which reference line among the multiple reference lines is used to generate an intra predictor. At the decoder side, after analyzing the reference line index, the decoder can generate an intra prediction of the current intra prediction block by identifying the reconstructed reference line sample by looking up the designated reference line according to the intra prediction mode (directional, omnidirectional, and other intra prediction modes). In some implementations, the reference line index may be signaled at the coding block level, and only one of the multiple reference lines may be selected and used for intra prediction of one coding block. In some examples, two or more reference lines may be selected together for intra prediction. For example, two or more reference lines may be combined, averaged, interpolated, with or without weighting, or in any other manner to generate a prediction. In some example implementations, MRLS may be applied only to the luma component and not to the chroma components.

[0154] In FIG. 16, an example of four reference lines MRLS is shown. As shown in the example of FIG. 16, an intra-coding block 1602 may be predicted based on one of four horizontal reference lines 1604, 1606, 1608, and 1610 and four vertical reference lines 1612, 1614, 1616, and 1618. Of these reference lines, 1610 and 1618 are directly adjacent reference lines. The reference lines may be indexed according to their distance from the coding block. For example, the reference lines 1610 and 1618 may be referred to as zero reference lines, while the other reference lines may be referred to as non-zero reference lines. Specifically, the reference lines 1608 and 1616 may be referred to as a first reference line, the reference lines 1606 and 1614 may be referred to as a second reference line, and the reference lines 1604 and 1612 may be referred to as a third reference line.

[0155] Returning to the linear transform, an exemplary 2-D transform process may involve the use of a hybrid transform kernel (which may be composed of a different 1-D transform for each dimension of the coded residual block, for example). Exemplary linear 1-D transform kernels may include, but are not limited to, a) 4-point (4p), 8-point (8p), 16-point (16p), 32-point (32p) & 64-point (64p) DCT-2; b) 4-point, 8-point, 16-point asymmetric DST and their flipped versions; c) 4-point, 8-point, 16-point or 32-point identity transform. Thus, the 2-D transform process may involve the use of a hybrid transform (a different transform for each dimension of the coded residual block), where the selection of the transform used for each dimension may be based on a rate-distortion (RD) criterion. For example, basis functions for 1D DCT-2, DST-4 and DST-7, which may be implemented as hybrids of 2-D transforms, are listed in Table 2. [Table 2]

[0156] For example, DCT-2 (4p-64p), DST-4 (8p, 16p) and DST-7 (4p) transforms exhibit symmetric / antisymmetric properties, and therefore a "partial butterfly" implementation may be supported in some exemplary implementations to reduce the operation count (multiplications, additions / subtractions, shifts). A partial butterfly implementation may include plane rotations using trigonometric cosine and sine functions at various angles, as described in FIG. 17. Exemplary 12-bit lookup tables are shown in FIG. 18 and FIG. 19 and are utilized to generate the trigonometric function values.

[0157] In some example implementations, line graph transforms (LGT) may be used instead of the 1-D DST described above. Essentially and as shown in FIG. 20, a graph is a general mathematical structure consisting of a set of vertices and edges, which can be used to model affinity relations between objects of interest. In practice, weighted graphs (where a set of weights are assigned to edges and potentially to vertices) provide sparse representations for robust modeling of signals / data. LGT can improve coding efficiency by providing better adaptation to diverse block statistics. A separable LGT may be designed and optimized by learning a line graph (characterized by self-loop weights vc1, vc2 and edge weights wc, as shown in the example of FIG. 20) from training data to model the underlying row- and column-wise statistics of the block residual signal, where the associated generalized graph Laplacian (GGL) matrix is ​​used to derive the LGT.

[0158] Given a weighted graph G(W,V), the GGL matrix is ​​defined as follows: L c =D-W+V (1) where W is the non-negative edge weight w c where D is the diagonal degree matrix, and V is the weighted self-loop v c1 , v c2 The matrix L is a diagonal matrix that indicates c can be expressed as:

number

[0159] LGT can be derived by eigendecomposition of GGL Lc. L c = UΦU T (3) where the columns of the orthogonal matrix U are the basis vectors of the LGT, and Φ is the diagonal eigenvalue matrix. In fact, the DCTs and DSTs, including DCT-2, DCT-8 and DST-7, are LGTs derived from a particular form of the GGL: DCT-2 is v c1 = 0. (4) DST-7 is v c1 =w c It is derived by setting (5) DCT-8 is v c2 =w c It is derived by setting (6) DST-4 is v c1 =2w c It is derived by setting (7) DCT-4 is v c2 =2w c It is derived by setting (8)

[0160] In some example implementations, LGT can be implemented as a matrix multiplication. c In v c1 =2w cThis means that it is a DST-4. The 8p LGT core is c In v c1 =1.5w c and the 16p and 32p LGT cores can be derived by setting L c In v c1 =w c This means that it is DST-7.

[0161] In some implementations, a secondary transform may be performed on the primary transform coefficients. The secondary transform may be applied between the forward primary transform and the quantization (at the encoder) and between the dequantization and the inverse primary transform (at the decoder). In some specific example implementations, a predefined set (e.g., 12 sets) of secondary transforms has a predefined number (e.g., 3) of kernels in each set.

[0162] In some example implementations, the secondary transform kernel set may correspond to a particular intra prediction mode. As an example, FIG. 21 lists the index used for secondary transform kernel set selection based on intra prediction mode. In FIG. 21, the first row indicates intra prediction modes for which secondary transform is allowed and thus corresponds to some available transform kernels, and the second row indicates the set index of the corresponding secondary transform set. In the encoder, for each intra prediction mode, the best kernel from multiple (e.g., three) transform kernels from the set can be selected based on RDO (Rate Distortion Optimization) and the selection can be signaled (e.g., four symbols not including IST (intra secondary transform)). In the decoder, the bitstream can be parsed to obtain the kernel used for inverse transform for decoding based on the intra prediction mode and the signaled index in the kernel set corresponding to the intra prediction mode.

[0163] In some example implementations, as a result of the observation that DCT type 2 (DCT-2) and ADST are the most frequently selected primary transform types for intra-coding, in order to achieve higher coding efficiency, an intra-secondary transform (IST) may be selectively enabled when either DCT-2 or ADST is used as the horizontal and vertical primary transform, and may not be enabled under the use of other primary transforms.

[0164] In some example implementations, IST may be enabled only for luma intra blocks and disabled for chroma intra blocks. In one embodiment, either a 4×4 non-separable transform or an 8×8 non-separable transform may be selected based on the block size. In one example, if min(tx_width,tx_height)<8, a 4×4 IST non-separable may be selected. For large blocks where both Tx_width and tx_height are 8 or greater, an 8×8 non-separable IST may be used, where tx_width and tx_height correspond to the width and height of the transform block, respectively.

[0165] In some example implementations, the input to the IST may be a linearized vector of low-frequency primary transform coefficients in zig-zag scan order, which helps achieve more efficient decorrelation of adjacent low-frequency coefficients in the secondary transform.

[0166] In some example implementations, both intra-coded and inter-coded blocks may be further partitioned into multiple transform blocks with a partitioning depth up to a predetermined number of levels (e.g., 2 levels), as described above, thereby forming a transform partitioning tree structure, as described above. In some specific implementations, application of the IST may be limited to the root (depth 0) of the transform partitioning tree structure, or to levels lower than the maximum applicable transform unit partitioning level. By applying this restriction, a reduction in overall encoding time complexity (e.g., ∼50%) with minimal impact on compression efficiency (e.g., ∼0.25% loss) may be achieved.

[0167] In some example implementations, a square transform block size may be utilized to derive the context information, and therefore the context, used to entropy code the kernel index. For rectangular transform blocks, the following smallest square size may be utilized to derive the context information:

[0168] As mentioned above, the determination of coding parameters and configuration for intra prediction and transform of residuals of intra predicted blocks is a complex, resource-intensive, and time-consuming process. When MRLS, multiple transform partition types, multiple transform types, and multiple intra quadratic transforms (different sets, each including multiple quadratic transform kernels) can all be enabled in an intra coded block to improve coding efficiency and quality, the encoder needs to search a large parameter space and all possible combinations of the above factors to find the best coding configuration, transform kernel, and other parameters for each prediction block or coding block, which significantly increases the computational complexity, memory requirements, and encoding time. Moreover, the large parameter space may also result in significant signal overhead.

[0169] In various exemplary implementations below, such parameter space and possible combinations can be conditionally reduced while keeping coding efficiency and coding quality degradation to a minimum. Thus, on average (across various coding blocks), the encoder explores a smaller parameter space and a smaller number of various potential combinations of the various factors above to identify a near-optimal coding scheme for an input coding block or predictive block. In particular, the shrinkage of the parameter space can be adjusted based on whether a zero or non-zero baseline is used for intra prediction for a particular coding block or predictive block. The optimization search space can be significantly reduced when a non-zero baseline is used. The coding configurations and parameters to be optimized can include, but are not limited to, the selection of optimal primary and / or secondary transform kernels. The reduction in parameter space can also lead to a corresponding reduction in the amount of information that needs to be signaled, thereby reducing the signaling overhead in the coded bitstream.

[0170] These example implementations may be used separately or in any order or combination in any manner. In the above and following description, terms such as "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 luma coding block or a chroma coding block. In some circumstances, a coded block / coding block may refer to a prediction block. The term "block size" is used to refer to either the width or height of a coding block, or the maximum width and height, or the minimum width and height, or the area size (width*height), or the aspect ratio (width:height or height:width). In the following disclosure, for purposes of intra prediction, an adjacent (or nearest or zero) reference line refers to a reference line with an index equal to 0, and a non-adjacent or non-zero reference line refers to a reference line with an index greater than 0.

[0171] In the following disclosure, signaling of transform block size may also refer to signaling of transform block splitting structure, scheme, pattern, etc., when this term is used. In this disclosure, an extended set of hybrid transform kernels for the linear transform may be referred to as transform set A. Set A may exhaustively include the collection of all combinations, for example, 1-D DCT types 1-8, DST types 1-8 (ADST), IDT (identity in any direction), LGT, KLT, etc. These 1-D transforms may be applied in any combination along two directions of the 2-D transform as hybrid transforms.

[0172] In a typical exemplary implementation, when a non-zero baseline is applied to an intra-coded block, a reduced set may be used instead of the complete set of primary and / or secondary transform kernels. Thus, when an encoder needs to determine which primary or secondary transform kernel to use for a particular coding block or part of a coding block, during an optimization process (e.g., a rate-distortion optimization process), it only needs to search the reduced set instead of the complete set. The decision of whether to use the zero baseline or the non-zero baseline for a particular coding block may be made in any manner, e.g., it may be made separately by the encoder based on the characteristics of the current coding block and its neighboring blocks.

[0173] In some exemplary implementations, when a non-zero baseline is applied within a block to be coded, only a subset of the primary transform kernels from the complete primary transform kernel set A can be used as candidate primary kernels during the search and optimization process. The subset of primary transform kernels can be predefined based on an offline statistical study that indicates some specific subset of primary transform kernels that are most likely to be optimal in general when a non-zero baseline is used for intra prediction. For example, it can be observed that in most practical cases, when a non-zero baseline is used, DCT type 2 and ADST hybrid kernel types are likely to be optimal primary kernel types.

[0174] The above general implementations may be applied to the reduction of candidate primary transform kernels for intra prediction when a non-zero baseline is used. In some specific example implementations, when a non-zero baseline is used, the subset of primary transform kernels allowed for intra prediction may be limited to a combination of 1-D DCT type 2 and 1-D ADST as a hybrid 2-D transform kernel.

[0175] In some other particular example implementations, when a non-zero baseline is used, the subset of primary transform kernels allowed for intra prediction may be limited to a combination of 1-D DCT type 2, 1-D ADST, and 1-D inverse ADST as hybrid 2-D transform kernels.

[0176] In some other particular example implementations, when a non-zero baseline is used, the subset of primary transform kernels allowed for intra prediction may be limited to a combination of a 1-D DCT type 2 and a 1-D IDT as a hybrid 2-D transform kernel.

[0177] In yet some other specific example implementations, when a non-zero baseline is used, the subset of primary transform kernels allowed for intra prediction may be limited to a combination of 1-D DCT type 2, 1-D ADST, 1-D inverse ADST, and 1-D IDT as hybrid 2-D transform kernels.

[0178] In some example implementations, when a non-zero baseline is used, whether the reduction of the candidate primary or secondary transform kernels can be applied to intra prediction may further depend on whether the prediction block or coding block should be split into multiple transform blocks. The underlying idea is that if the current prediction block or coding block is split into multiple transform blocks, the selection of the primary and / or secondary transform kernels may need to be optimized separately for each of the transform blocks, rather than for the entire prediction block or coding block as a whole, and reducing the number of candidate primary and / or secondary kernels for intra prediction involving non-zero baseline from that for intra prediction involving zero baseline will reduce the optimization burden while minimizing the degradation of the coding efficiency and quality of the encoder.

[0179] Such a reduction may be applied to the selection of the secondary transform kernel. Thus, in some specific examples, when multiple transform blocks exist or exist within a coding block or a predictive block, the allowed secondary transform set for a transform block when a non-zero baseline is applied may be reduced to a subset of the allowed secondary transform set when a zero baseline is applied. In one embodiment, such an implementation may be applied specifically when secondary transform kernel selection is performed and the selection information is signaled for each transform block (rather than at the level of the entire predictive block or coding block).

[0180] In some exemplary implementations, the reduction of the candidate secondary transform kernel set may be hierarchical by using non-zero lines and dividing into transform blocks. For example, when non-zero lines are used for intra prediction and the coding block or predictive block is not further divided into two or more transform units, a first reduced set of secondary transform kernels from the complete secondary transform kernel set for zero-baseline intra prediction may be used as an optimization candidate. However, when non-zero lines are used for intra prediction and the coding block or predictive block is further divided into two or more transform blocks, a second reduced set of secondary transform kernels from the complete secondary transform kernel set for zero-baseline intra prediction may be used as an optimization candidate. The second reduced set of secondary transform kernels may be, for example, a subset of the first reduced set of secondary transform kernels. In other words, when non-zero lines are used for intra prediction, the candidate secondary transform kernel set is reduced from the complete set of secondary transform kernels, and if the coding block or predictive block is further subdivided into two or more transform blocks, then the reduced set of secondary transform kernels may be further reduced.

[0181] In some example implementations, when there are multiple transform blocks inside a coding or predictive block, no secondary transform may be allowed for the transform block when a non-zero baseline is used for intra prediction of the current block. In other words, the encoder may go to the extreme of reducing the set of secondary transform kernels to a null set when a non-zero baseline is used for intra prediction and the coding or predictive block is further subdivided into two or more transform blocks.

[0182] In some other example implementations, a reduction of the candidate transform kernels for intra prediction may be applied to the primary transform depending on whether the prediction block or coding block is split into multiple transform blocks when a non-zero baseline is used. For example, when there are multiple transform blocks inside a coding block or prediction block, the allowed primary transform type set for the transform block when a non-zero baseline is applied may be a subset of the allowed primary transform set (e.g., hybrid transform set) when a zero baseline is applied. In one embodiment, such an implementation may be applied specifically when a primary transform selection is performed and the selection information is signaled for each transform block or transform unit (rather than at the level of the entire prediction block or coding block).

[0183] In some exemplary implementations, the reduction of the candidate primary transform kernel set may be hierarchical. For example, when a non-zero line is used for intra prediction and the coding block or the predictive block is not further divided into two or more transform blocks, a first reduced set of primary transform kernels from the complete primary transform kernel set for intra prediction of zero-baseline (set A above) may be used as an optimization candidate. However, when a non-zero line is used for intra prediction and the coding block or the predictive block is further divided into two or more transform blocks, a second reduced set of secondary transform kernels from the complete primary transform set for intra prediction of zero-baseline (set A above) may be used as an optimization candidate. The second reduced set of primary transform kernels may be, for example, a subset of the first reduced set of primary transform kernels. In other words, when a non-zero line is used for intra prediction, the candidate primary transform kernel set is reduced from the complete set (set A above), and if the coding block or the predictive block is further subdivided into two or more transform blocks, the reduced set of primary transform kernels may be further reduced.

[0184] In another embodiment, when there are multiple transform blocks inside a coding block or a predictive block, the primary transform selection may not be signaled for the transform block when a non-zero baseline is used for intra prediction of the current block. In other words, the subset of primary transform kernels in that situation may be reduced to the extent that the selection of the primary transform kernel is predefined and does not need to be signaled.

[0185] In some example implementations, when multiple reference lines may be used in intra prediction, a reference line index selected for intra-coding of a coding block or other coding unit may be used to derive a context (or CDF) for entropy coding of the primary or secondary transform indexes. Because the reference line index may be correlated with the primary or secondary transform indexes, such implementations may help achieve higher entropy coding efficiency of these indexes in the coded bitstream.

[0186] In some further implementations, when the current coding block has multiple transform blocks and the baseline index indicates that a non-zero baseline is used for the current coding block or the predictive block, the reduced set of primary and secondary transform kernels may be applied to only some, but not all, of the transform blocks. For example, when the current coding block has multiple transform blocks and the baseline index indicates that a non-zero baseline is used, a reduced subset of the primary and / or secondary transform kernels may be used only for the transform blocks toward the top or left boundary of the current coding block or predictive block, while all the primary and secondary transforms can be used as candidates for the transform blocks to be placed in the remaining parts of the current coding block or predictive block.

[0187] This is shown in Figure 22. In the example of Figure 22, there are four transform blocks within one coding block, labeled as TB1-TB4 and represented by 2202-2208 in Figure 22. TB1, TB2 and TB3 are located at the top or left boundary of the current coding block. TB1-TB3 may be processed by selecting from a reduced set of candidate primary and / or secondary transform kernels, and TB4 may be processed by selecting from the full set of candidate primary and / or secondary transform kernels.

[0188] Independently, separately, or in combination or with the various exemplary implementations above, in some further exemplary implementations, when a non-zero baseline is applied to an intra-coded block, a selected subset of transform partition types may be used instead of the complete set of candidate transform partition types. As described above in connection with the example of FIG. 15, a coding block or a predictive block may be assigned to a transform partition type among a set of predefined transform partition types based on the transform type of the coding block or predictive block determined based on, for example, a rate-distortion cost. Such transform partition types correspond to various different predefined transform block partition patterns. These exemplary implementations further reduce the candidate partitioning patterns to select for an intra-coding block or a predictive block when a non-zero baseline is used. Thus, the optimization search space for the optimal partition pattern to be the transform block for the encoder may be reduced. Furthermore, the reduced set of transform partition types may correspond to a pattern with a smaller number of transform block partitions, which can help reduce the amount of optimization when coding or transform configurations and parameters need to be optimized separately for each transform unit.

[0189] For example, in one embodiment, the subset of transform partition types may include only PARTITION_NONE in Figure 15, which indicates that the transform block size is the same as the prediction / coding block size, in other words, no partitioning into transform blocks is performed.

[0190] In another example, in one embodiment, the subset of transform partition types may include only transform partition types that have a number of transform subpartitions below a given threshold. Exemplary thresholds may include, but are not limited to, 1, 2, 3, 4, 5, 6, ..., 16. For example, the threshold may be 2 with respect to FIG. 15, and at such a threshold, the subset of transform partition types may include only PARTITION_NONE, PARTITION_HORZ, and PARTITION_VERT.

[0191] In some further example implementations, the index of the baseline used in the above example implementations may be considered in terms of a reduced set of candidate primary and / or secondary transform kernels and / or a subset of transform partitioning types. In other words, the items included in the various subsets may depend on how far the non-zero baseline is from the current coding block or the prediction block. For example, for the zero baseline, the complete set may be used, while for non-zero baselines, a subset may be used (as described in the above implementations), and the subset may be further reduced as the non-zero baseline index increases.

[0192] For example, in general, different primary and / or secondary transform kernel sets may be applied and / or signaled for a transform block when a different baseline is applied.

[0193] In a further embodiment, for different non-zero baselines, the primary and / or secondary transformation kernel candidates and / or transformation partition candidate types are the same set, in other words, no differentiation may be made between non-zero baselines of different line indices.

[0194] In another further embodiment, for different non-zero baselines, the primary and / or secondary transform kernel candidates and / or transform partition candidate types are different sets.

[0195] Various subsets of primary transform kernels, secondary transform kernels and transform partition types may be predefined for various baseline configurations for intra prediction. Thus, these subsets may not need to be signaled. Indices for these subsets, as determined and selected by the encoder, may be signaled. Such indices may be correlated and thus may be jointly signaled and used to derive a context for entropy coding.

[0196] FIG. 23 shows a flowchart 2300 of an exemplary method according to the principles underlying the implementation above. The exemplary method flow 2300 starts at 2301. At S2310, a data block of a video frame is retrieved. The data block may include adjacent reference lines and one or more non-adjacent reference lines in the video frame. At S2320, it is determined whether one of the one or more non-adjacent reference lines is used for intra-prediction of the data block. At S2330, when adjacent reference lines are used for intra-prediction of the data block, a target transformation kernel may be selected from a first set of transformation kernels to transform the data block. At S2340, when non-adjacent reference lines are used for intra-prediction of the data block, a target transformation kernel may be selected from a second set of transformation kernels to transform the data block. The exemplary method flow 2300 ends at S2399.

[0197] FIG. 24 shows a flowchart 2400 of another exemplary method according to the principles underlying the above embodiment. The exemplary method flow 2400 starts at 2401. At S2410, a data block of a video frame is retrieved. The data block may include adjacent reference lines and one or more non-adjacent reference lines in the video frame. At S2420, it is determined whether one of the one or more non-adjacent reference lines is used for intra-prediction of the data block. At S2430, when adjacent reference lines are used for intra-prediction of the data block, a first set of transform partition types may be selected to partition the data block into transform partition blocks. At S2440, when non-adjacent reference lines are used for intra-prediction of the data block, a second set of transform partition types may be selected to partition the data block into transform partition blocks. The exemplary method flow 2400 ends at S2499.

[0198] FIG. 25 shows a flowchart 2500 of yet another exemplary method according to the principles underlying the above embodiment. The exemplary method flow 2500 starts at 2501. At S2510, a data block of a video frame is retrieved. The data block may include one or more reference lines in the video frame for intra prediction, each reference line being associated with a reference line position index. At S2520, a reference line from the one or more reference lines is selected for intra prediction of the data block. At S2530, a primary or secondary transformation kernel may be selected from a subset of primary or secondary transformation kernels to process the data block, the subset of primary or secondary transformation kernels being selected from the complete set of primary or secondary transformation kernels based on the reference line position index of the selected reference line for intra prediction. The exemplary method flow 2500 ends at S2599.

[0199] The embodiments of the present disclosure may be used separately or in combination in any order. Furthermore, each of the methods (or embodiments), the encoder and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to luma blocks or chroma blocks.

[0200] The techniques described above can be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 26 illustrates a computer system (2600) suitable for implementing certain embodiments of the disclosed subject matter.

[0201] Computer software may be coded using any suitable machine code or computer language that may be subject to assembly, compilation, linking, or similar mechanisms to create code that includes instructions that may be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., either directly or through interpretation, microcode execution, etc.

[0202] The instructions may be executed in various types of computers or components thereof, including, for example, a personal computer, a tablet computer, a server, a smart phone, a gaming device, an Internet of Things device, and the like.

[0203] 26 for the computer system (2600) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure, nor should the arrangement of components be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of the computer system (2600).

[0204] The computer system (2600) may include certain human interface input devices. Such human interface input devices may respond to input by one or more human users, for example, through tactile input (keystrokes, swipes, data glove movements, etc.), audio input (voice, clapping, etc.), visual input (gestures, etc.), and olfactory input (not shown). Human interface input devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (voice, music, ambient sounds, etc.), images (scanned images, photographic images obtained from still image cameras, etc.), and video (2D video, 3D video including stereoscopic vision, etc.).

[0205] The human input interface devices may include one or more of a keyboard (2601), a mouse (2602), a trackpad (2603), a touch screen (2610), a data glove (not shown), a joystick (2605), a microphone (2606), a scanner (2607), and a camera (2608) (only one of each is shown).

[0206] The computer system (2600) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the senses of a human user, for example, through haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (2610), data gloves (not shown), or joystick (2605), although there may be haptic feedback devices that do not function as input devices), audio output devices (speakers (2609), headphones (not shown), etc.), visual output devices (such as screens (2610), including CRT, LCD, plasma, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which may output two-dimensional visual output or greater than three-dimensional output via such means as stereoscopic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0207] The computer system (2600) may also include human-accessible storage devices and their associated media, such as optical media or similar media (2621), including CD / DVD ROM / RW (2620) with CDs / DVDs, thumb drives (2622), removable hard drives or solid state drives (2623), legacy magnetic media such as tapes and floppy disks (not shown), and special ROM / ASIC / PLD based devices such as security dongles (not shown).

[0208] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.

[0209] The computer system (2600) may also include interfaces (2654) to one or more communication networks (2655). The networks may be, for example, wireless, wired, or optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, and the like. Examples of networks include local area networks such as Ethernet, WLAN, and the like, cellular networks including GSM, 3G, 4G, 5G, LTE, and the like, TV wired or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial networks including CANbus, and the like. Certain networks typically require an external network interface adapter that connects to a particular general-purpose data port or peripheral bus (2649) (such as a USB port on the computer system (2600)), while others are typically integrated into the core of the computer system (2600) by attachment to a system bus, as described below (such as an Ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (2600) can communicate with other entities. Such communications may be one-way receive-only (e.g., broadcast TV), one-way transmit-only (e.g., from a particular CANbus to a particular CANbus device), or bidirectional to other computer systems, for example, using local or wide area digital networks. As noted above, specific protocols and protocol stacks may be used in each of these networks and network interfaces.

[0210] The aforementioned human interface devices, human accessible storage devices and network interfaces may be attached to the core (2640) of the computer system (2600).

[0211] The cores (2640) may include one or more central processing units (CPUs) (2641), graphics processing units (GPUs) (2642), dedicated programmable processing units in the form of field programmable gate arrays (FPGAs) (2643), hardware accelerators for specific tasks (2644), graphics adapters (2650), etc. These devices may be connected through a system bus (2648), along with read only memory (ROM) (2645), random access memory (RAM) (2646), and internal mass storage (2647), such as an internal non-user accessible hard drive, SSD, etc. In some computer systems, the system bus (2648) is accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (2648) or through a peripheral bus (2649). In one example, a screen (2610) may be connected to the graphics adapter (2650). Peripheral bus architectures include PCI, USB, and the like.

[0212] The CPU (2641), GPU (2642), FPGA (2643) and accelerator (2644) can execute certain instructions, which in combination can constitute the above-mentioned computer code. The computer code can be stored in ROM (2645) or RAM (2646). Also, temporary data can be stored in RAM (2646), while permanent data can be stored, for example, in internal mass storage (2647). Rapid storage and retrieval from any of the memory devices can be enabled through the use of cache memory, which can be closely associated with one or more of the CPU (2641), GPU (2642), mass storage (2647), ROM (2645), RAM (2646), etc.

[0213] The computer-readable medium can have computer code thereon for performing various computer-implemented operations. The medium and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those skilled in the computer software arts.

[0214] As a non-limiting example, a computer system having the architecture (2600) and in particular the cores (2640) can provide functionality as a result of processors (including CPUs, GPUs, FPGAs, accelerators, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be user-accessible mass storage as introduced above, as well as media associated with specific storage of the cores (2640) of a non-transitory nature, such as the core internal mass storage (2647) or ROM (2645). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the cores (2640). The computer-readable media can include one or more memory devices or chips according to specific needs. The software can cause the cores (2640) and in particular the processors therein (including CPUs, GPUs, FPGAs, etc.) to perform certain processes or certain parts of certain processes described herein, including defining data structures stored in RAM (2646) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (2644)) that may operate in place of or in conjunction with software to perform particular processes, or particular portions of particular processes, described herein. References to software include logic, and vice versa, where appropriate. References to computer-readable media may encompass circuitry (such as integrated circuits (ICs)) that store software for execution, circuitry embodying logic for execution, or both, as appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0215] Although the present disclosure describes some exemplary embodiments, there are modifications, permutations, and various substitute equivalents that are within the scope of the present disclosure. In the above-described implementations and embodiments, any operations of the processes may be combined or arranged in any quantity or order as desired. Furthermore, two or more of the operations of the above-described processes may be performed in parallel. Thus, it will be understood that those skilled in the art can devise various systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and thus are within the spirit and scope of the present disclosure. Appendix A: Acronyms JEM: joint exploration model VVC: versatile video coding BMS: Benchmark set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplementary Enhancement Information VUI: Video Usability Information GOPs: Groups of Pictures TUs: Transform Units PUs: Prediction Units CTUs: Coding Tree Units CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: Hypothetical Reference Decoder SNR: Signal Noise Ratio CPUs: Central Processing Units GPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD: Liquid Crystal Display OLED: Organic Light-Emitting Diode CD: Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application-Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile communications LTE:Long-Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Array SSD: Solid-state drive IC: Integrated Circuit HDR: High Dynamic Range SDR: standard dynamic range JVET:Joint Video Exploration Team MPM: Most probable mode WAIP: Wide-Angle Intra Prediction CU: Coding Unit PU: Prediction Unit TU: Transform Unit CTU: Coding Tree Unit PDPC: Position Dependent Prediction Combination ISP: Intra Sub-Partitions SPS: Sequence Parameter Setting PPS: Picture Parameter Set APS: Adaptation Parameter Set VPS: Video Parameter Set DPS: Decoding Parameter Set ALF: Adaptive Loop Filter SAO: Sample Adaptive Offset CC-ALF: Cross-Component Adaptive Loop Filter CDEF: Constrained Directional Enhancement Filter CCSO: Cross-Component Sample Offset LSO: Local Sample Offset LR: Loop Restoration Filter AV1:AOMedia Video 1 AV2: AOMedia Video 2

Claims

1. 1. A processor-implemented method for video decoding, comprising: extracting a block of data of a video frame from the video bitstream; determining whether at least one non-adjacent reference line is used for intra prediction of said data block; selecting a target transformation kernel from a first set of transformation kernels to transform the data block according to a determination that no non-adjacent reference lines are used for the intra prediction of the data block, the first set of transformation kernels having a first size; selecting the target transformation kernel from a second set of transformation kernels to transform the data block according to a determination that at least one non-adjacent reference line is used for the intra prediction of the data block, the second set of transformation kernels having a second size smaller than the first size; A method comprising:

2. The first set of transformation kernels and the second set of transformation kernels are linear transformation kernels or quadratic transformation kernels. The method of claim 1.

3. The second set of transformation kernels is a subset of the first set of transformation kernels. The method of claim 1.

4. the first set of transformation kernels and the second set of transformation kernels are linear transformation kernels; The second set of transformation kernels comprises: A combination of DCT type 2 and ADST as a hybrid transform kernel; The hybrid transform kernel is a combination of DCT type 2, ADST and inverse ADST; A combination of DCT type 2 and IDT as the hybrid transform kernel; or The hybrid transform kernel is a combination of DCT type 2, ADST, inverse ADST and IDT; The method of claim 3 , comprising one of: When the data block includes two or more transformation partition blocks, the second set of transformation kernels is a subset of the first set of transformation kernels.

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

6. The data block includes two or more transformation partition blocks, the second set of transformation kernels is a NULL set; The method according to claim 5.

7. The data block includes two or more transformation partition blocks, a selection of the target transformation kernel from the first set of transformation kernels or the second set of transformation kernels is signaled separately for each of the two or more transformation partition blocks. The method according to claim 5.

8. The data block includes two or more transformation partition blocks, when non-adjacent baselines are indicated for the data block in the video bitstream, the selection from the second set of transformation kernels is predefined and is not signaled in the video bitstream. The method according to claim 5.

9. The method of claim 8, wherein a baseline index used for intra prediction of the data block is used to derive a context for entropy coding of a kernel index of a primary transformation kernel for transforming a secondary transformation kernel selected from the first set of transformation kernels or the second set of transformation kernels.

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

10. When the data block further includes two or more transformation partition blocks, the second set of transform kernels being a subset of the first set of transform kernels for a subset of the two or more transform partition blocks; the second set of transform kernels and the first set of transform kernels are the same for a remainder of the two or more transform partition blocks.

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

11. The subset of the two or more transform partition blocks includes an upper and / or left transform partition of the data block. The method of claim 10.

12. The selection of the target transformation kernel from the first set of transformation kernels or the second set of transformation kernels is performed when a multiple transformation partition type is enabled for partitioning the data block into transformation blocks and both a primary transformation kernel and a secondary transformation kernel are enabled for the data block.

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

13. A method for partitioning a data block into transform partition blocks according to a determination that no non-adjacent reference lines are used for the intra prediction of the data block, the method comprising: selecting a target transform partition from a first set of transform partitions for partitioning the data block into transform partition blocks, the first set of transform partitions having a first size; selecting the target transform partition from a second set of transform partitions according to a determination that at least one non-adjacent reference line is used for the intra prediction of the data block, the second set of transform partitions having a second size smaller than the first size; The method of claim 1 further comprising:

14. A method for video encoding, executed by a processor, comprising: receiving video data comprising a plurality of video frames including a data block of a current video frame; determining whether at least one non-adjacent reference line is used for intra prediction of said data block; selecting a target transformation kernel from a first set of transformation kernels for the data block according to a determination that no non-adjacent reference lines are used for the intra prediction of the data block, the first set of transformation kernels having a first size; selecting the target transformation kernel from a second set of transformation kernels according to a determination that at least one non-adjacent reference line is used for the intra prediction of the data block, the second set of transformation kernels having a second size smaller than the first size; A method comprising:

15. The method of claim 1, wherein the second set of transformation kernels is a subset of the first set of transformation kernels. The method of claim 14.

16. The selection of the target transformation kernel from the first set of transformation kernels or the second set of transformation kernels is performed when a multiple transformation partition type is enabled for partitioning the data block and both a primary transformation and a secondary transformation are enabled for the data block.

16. The method according to claim 14 or 15.

17. A method for processing visual media data, comprising: obtaining a source video sequence; performing a conversion between the source video sequence and a bitstream of visual media data, the bitstream comprising: a plurality of encoded data blocks, including a current data block; a reference line indicator indicating whether at least one non-adjacent reference line is used for intra prediction of the current data block; a first indicator for a first set of transformation kernels having a first size; a second indicator for a second set of transformation kernels having a second size smaller than the first size; Equipped with when the reference line indicator indicates that at least one non-adjacent reference line is used for intra prediction of the current data block, a transform selected from the first set of transform kernels is used to decode the current data block; when the reference line indicator indicates that no non-adjacent reference lines are used for intra prediction of the current data block, a transform selected from the second set of transform kernels is used to decode the current data block. method.

18. The second set of transformation kernels is a subset of the first set of transformation kernels.

20. The method of claim 17.

19. A device comprising processing circuitry configured to implement a method according to any one of claims 1 to 18.

20. A computer program which, when executed by a processor, causes the processor to perform any one of claims 1 to 18.

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