Signaling EOB for 1-D transform skipping

Abstract

A method, apparatus, and computer-readable storage medium for implementing EOC / EOR signaling, the method includes receiving a video bitstream including a transform block having two dimensions, the transform block being entropy coded, determining whether a one-dimensional transform skip is applied to the transform block based on a syntax element in the video bitstream, obtaining an end position value associated with the transform block from the video bitstream in response to the one-dimensional transform skip being applied to the transform block, the end position value indicating only one of a horizontal coordinate end position within the transform block and a vertical coordinate end position within the transform block, and extracting the transform block from the video bitstream according to the end position value.

Description

[Technical field]

[0001] [Incorporated by reference] This application is based on and claims the benefit of priority to U.S. Non-Provisional Application No. 17 / 991,206, entitled "Signalling of EOB for One Dimensional Transform Skip," filed November 21, 2022. This U.S. Non-Provisional Application is based on and claims the benefit of priority to U.S. Provisional Application No. 63 / 300,427, entitled "Signalling of EOB for One Dimensional Transform Skip," filed January 18, 2022, the entire contents of which are incorporated by reference.

[0002] [Technical field] This disclosure describes a set of advanced video coding techniques for efficient compression and / or signaling of video data. More specifically, the disclosed techniques involve signaling and / or derivation of End of Block (EOB) when one-dimensional transform skip mode is applied. [Background technology]

[0003] This background discussion provided herein is intended to generally present the context of the present disclosure. Work of the inventors named in this application, to the extent that their work is described in this background section, and aspects of this description that may not otherwise qualify as prior art at the time of the filing of this application, are not admitted, either explicitly or implicitly, as prior art to the present disclosure.

[0004] Video encoding 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 (also called frame rate), for example, a picture rate of 60 pictures per second or 60 frames per second. Uncompressed video has specific bit rate requirements for streaming or data processing. For example, a video with a pixel resolution of 1920x1080, a frame rate of 60 frames per second, and 4:2:0 chroma subsampling with 8 bits per color channel per pixel requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires more than 600 Gbytes of storage space.

[0005] One goal of video encoding and decoding may be the reduction of redundancy in an uncompressed input video signal through compression. Compression may help reduce the above bandwidth and / or storage space requirements, possibly by more than one order of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal through a decoding process. Lossy compression refers to an encoding / decoding process where the original video information is not fully preserved during encoding 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 will be small enough to render 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 encoding algorithm can be selected or adjusted to reflect different distortion tolerances; generally, higher tolerable distortion permits encoding 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 divided into blocks of samples. If 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 therefore 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 subjected 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 the 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 required for a given quantization step size to represent the block after entropy coding.

[0008] Traditional intra-coding, e.g. as known from MPEG-2 generation encoding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to encode / decode a block based on surrounding sample data and / or metadata that are obtained during the encoding and / or decoding of its spatial neighbors and that precede in decoding order the block of data being 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. If more than one such technique 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 in a particular codec. In certain 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 of a block of video may be coded separately or may be included jointly in a mode codeword. Which codeword to use 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 codeword into a bitstream.

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

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

[0012] 1A, a square block (104) of 4×4 samples is depicted at the top left (shown in bold dashed lines). The square block (104) contains 16 samples, each labeled with an “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 in the block (104) in both the Y and X dimensions. Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown is an exemplary reference sample that follows a similar numbering scheme. The reference sample is labeled R and its 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 in the vicinity of the block being reconstructed are used.

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

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

[0015] As video coding technology continues to develop, the number of possible directions has increased. In H.264 (2003), for example, nine different directions are available for table intra prediction. This increases to 33 in H.265 (2013), and JEM / VVC / BMS at the time of this disclosure can support up to 65 directions. Experiments are performed to help identify the most suitable intra prediction directions, and certain techniques may be used in entropy coding to code these most suitable directions with a small number of bits while accepting a certain bit penalty for the direction. Furthermore, in some cases, the direction itself can be predicted from the neighboring directions used in the intra prediction of the decoded neighboring blocks.

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

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

[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 for prediction of a newly reconstructed picture or part thereof (e.g., block) after being spatially shifted in a direction indicated by a motion vector (hereinafter, MV). In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions, X and Y, or three dimensions, with the third dimension being an indication of the reference picture to be used (similar to the temporal dimension).

[0019] In some video compression techniques, the current MV applicable to a particular region of sample data can be predicted from other MVs, e.g., other MVs associated with other regions of sample data that are spatially adjacent to the region being reconstructed and that precede the current MV in decoding order. Doing so can substantially reduce the overall amount of data required to encode the MV by relying on reducing redundancy in the associated MVs, thereby increasing compression efficiency. MV prediction can work effectively because, for example, when encoding an input video signal derived from a camera (known as natural video), there is a statistical probability that regions larger than the region to which a single MV is applicable in a video sequence move in similar directions and therefore can potentially be predicted using similar motion vectors derived from MVs of neighboring regions. The result is that the actual MV for a given region is similar or identical to the MV predicted from the surrounding MVs. Such MVs may then be represented with fewer bits after entropy encoding than would be used if the MVs were directly encoded 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 the original signal (i.e., sample stream). In other cases, the MV prediction itself may be lossy, for example due to rounding errors in computing the predictor from several surrounding MVs.

[0020] H.265 / HEVC (ITU-T Rec. H.265, "High Efficiency Video Coding", December 2016) describes various MV prediction mechanisms. Among the many MV prediction mechanisms specified by H.265, a technique hereafter referred to as "spatial merge" is described herein.

[0021] Specifically, referring to FIG. 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 directly encoding its MV, the MV can be derived from metadata associated with one or more reference pictures, e.g., from the most recent reference picture (in decoding order), using MVs associated with any of the five surrounding samples, denoted A0, A1, and B0, B1, B2 (202-206, 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 provide methods and apparatus for video encoding and decoding, and more specifically, for signaling and / or deriving an end of block (EOB) when a one-dimensional transform skip mode is applied. In some example implementations, a method for video processing is disclosed. The method may include receiving a video bitstream including a transform block having two dimensions, the transform block being entropy coded, determining whether a one-dimensional transform skip is applied to the transform block based on a syntax element in the video bitstream, obtaining an end position value associated with the transform block from the video bitstream in response to the one-dimensional transform skip being applied to the transform block, the end position value indicating only one of a horizontal coordinate end position within the transform block and a vertical coordinate end position within the transform block, and extracting the transform block from the video bitstream according to the end position value.

[0023] Aspects of the present disclosure also provide a video encoding or decoding device or apparatus including circuitry configured to perform any of the implementations of the above methods.

[0024] 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 a method for video decoding and / or encoding. [Brief description of the drawings]

[0025] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Figure 1A] 1 shows a schematic diagram of an example subset of intra-prediction direction modes. [Figure 1B] 1 shows an illustrative diagram of an exemplary intra-prediction direction. [Diagram 2] 1 illustrates a schematic diagram of a current block and its surrounding spatial merging candidates for motion vector prediction in one example. [Diagram 3] 1 illustrates a simplified block diagram of a communication system in accordance with an exemplary embodiment; [Figure 4] 4 shows a simplified block diagram schematic of a communication system (400) in accordance with an example embodiment. [Diagram 5] 1 shows a schematic diagram of a simplified block diagram of a video decoder according to an exemplary embodiment; [Figure 6] 1 shows a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7] 1 shows a block diagram of a video encoder according to an example embodiment. [Figure 8] 2 shows a block diagram of a video decoder according to an exemplary embodiment; [Figure 9] 1 illustrates directional intra-prediction modes according to an exemplary embodiment of the present disclosure. [Figure 10] 1 illustrates a non-directional intra-prediction mode according to an exemplary embodiment of the present disclosure. [Figure 11] 1 illustrates a recursive intra-prediction mode according to an exemplary embodiment of the present disclosure. [Figure 12]4 illustrates transform block partitioning and scanning of an intra-prediction block according to an exemplary embodiment of the present disclosure. [Figure 13] 4 illustrates transform block partitioning and scanning of an inter-prediction block according to an exemplary embodiment of this disclosure. [Figure 14] 1 illustrates an example 1D transform skip and associated transform coefficient blocks in the horizontal direction. [Figure 15] 1 illustrates an exemplary 1D transform skip and associated transform coefficient blocks in the vertical direction. [Figure 16] 1 illustrates an exemplary Line Graph Transform (LGT) according to an exemplary embodiment of the present disclosure. [Figure 17] 1 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 18] 1 shows a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to one 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 encode video data (e.g., a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more encoded video bitstreams. The terminal device (320) may receive the encoded video data from the network (350), decode the encoded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. The one-way data transmission may be implemented in a media service application or the like.

[0027] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of encoded 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 encode video data (e.g., a stream of video pictures captured by the 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 receive the encoded video data transmitted by the other of the terminal devices (330) and (340), decode the encoded video data to reconstruct the video pictures, and display the video pictures on an accessible display device in accordance with the reconstructed video data.

[0028] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be implemented as servers, personal computers, and smartphones, although applicability of the underlying principles of the present disclosure may not be limited thereto. The embodiments of the present disclosure may be implemented in desktop computers, laptop computers, tablet computers, media players, wearable computers, and / or dedicated video conferencing equipment. The network (350) represents any number or type of network that conveys encoded video data between the terminal devices (310), (320), (330), and (340), including, for example, wired (wired) 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 discussion herein, the architecture and topology of the network (350) may not be important to the operation of the present disclosure, unless explicitly described below.

[0029] 4 shows an arrangement of video encoders and video decoders in a video streaming environment as an example of an application for the disclosed subject matter. The disclosed subject matter may be equally applicable to other video applications including, for example, video conferencing, digital TV broadcasting, gaming, virtual reality, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0030] The video streaming system may include a video source (401), e.g., a digital camera, and may include a video capture subsystem (413) that generates, e.g., a stream of uncompressed video pictures or images (402). In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), depicted as a bold line to emphasize its high data volume compared to the encoded video data (404) (or encoded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), depicted as a thin line to emphasize its lower data volume compared to the uncompressed video picture stream (402), can be stored on the streaming server (405) for future use or directly on 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) can decode an input copy of the encoded video data (407) and generate an output stream of uncompressed video pictures (411) that can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). Video decoder 410 may 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 encoding / compression standard. Examples of these standards include ITU-T Recommendation H.265. In one example, a video encoding 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 encoding standards.

[0031] It is noted that electronic devices 420 and 430 may include other components (not shown). For example, electronic device 420 may include a video decoder (not shown), and electronic device 430 may also include a video encoder (not shown).

[0032] 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) can be included in an electronic device (530). The electronic device (530) can include a receiver (531) (e.g., a receiving circuit). The video decoder (510) can be used in place of the video decoder (310) in the example of FIG. 4.

[0033] 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, and 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 together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded through respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To combat network jitter, a buffer memory (515) may be located between the receiver (531) and the entropy decoder / parser (520) (hereinafter the "parser"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, it may be external to the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), e.g., to combat network jitter, and there may be an additional buffer memory (515) internal to the video decoder (510), e.g., to handle playback timing. If the receiver (531) is receiving data from a store / forward device of sufficient bandwidth and controllability, or from an isochronous network, the buffer memory (515) may not be needed or may be small. For use with best-effort packet networks such as the Internet, a sufficient size of the buffer memory (515) may be required, and the size may be relatively large.Such a buffer memory may be implemented with an adaptive size and may be implemented, at least in part, outside the video decoder (510) in an operating system or similar element (not shown).

[0034] The video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a display (512) (e.g., a display screen). The display may or may not be an integral part of the electronic device (530) as shown in FIG. 5 and may be coupled to the electronic device (530). The control information for the rendering device(s) may be in the form of Supplementary Enhancement Information (SEI) messages or Video Usability Information (VUI) parameter set fragments (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 a Group of Pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (520) may also extract information from the coded video sequence such as transform coefficients (e.g., Fourier transform coefficients), quantizer parameter values, motion vectors, etc.

[0035] The parser (520) can perform an entropy decoding / parsing operation on the video sequence received from the buffer memory (515) to generate symbols (521).

[0036] The reconstruction of the symbols (521) may involve several different processing or functional units, 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 are involved may be controlled by subgroup control information parsed by the parser (520) from the coded video sequence. The flow of such subgroup control information between the parser (520) and several of the processing or functional units described below is not depicted for the sake of simplicity.

[0037] In addition to the functional blocks already mentioned, the video decoder (510) can be conceptually divided into several functional units, as described below. In a practical implementation working under commercial constraints, many of these functional units will 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 adopted in the following disclosure.

[0038] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients and control information as symbol(s) (521) from the parser (520). The control information may include information indicating what type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output a block containing sample values ​​that can be input to an aggregator (555).

[0039] 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 may use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using surrounding block information already reconstructed and stored in a current picture buffer (558). The current picture buffer (558) may, for example, buffer a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0040] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such a case, the motion compensation prediction unit (553) may access the reference picture memory (557) to retrieve samples used for inter-picture prediction. After motion compensating the retrieved samples according to the symbols (521) for the block, these samples may be added by an aggregator (555) to the output of the scalar / inverse transform unit (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 compensation unit (553) retrieves the prediction samples may be controlled by a motion vector available to the motion compensation unit (553) in the form of a symbol (521). The symbol may have, for example, an X, a Y component (shift), and a reference picture component (time). Motion compensation may involve the interpolation of sample values ​​taken from a reference picture memory (557) when sub-sample accurate motion vectors are used, and may also involve motion vector prediction mechanisms, etc.

[0041] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in a loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to meta-information obtained during decoding of previous portions (in decoding order) of the coded picture or coded video sequence, as well as to previously reconstructed loop filtered sample values. As will be described in more detail below, several types of loop filters may be included as part of the loop filter unit 556, in various orders.

[0042] The output of the loop filter unit (556) can be a sample stream, which can be output to a rendering device (512) or can be stored in a reference picture memory (557) for use in future inter-picture prediction.

[0043] Once a particular 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 a fresh current picture buffer can be reallocated before beginning reconstruction of a subsequent coded picture.

[0044] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard such as ITU-T Recommendation H.265. The encoded video sequence may conform to the syntax prescribed by the video compression technique or standard being used, in the sense that the encoded video sequence conforms to the syntax of the video compression technique or standard and the profile documented in the video compression technique or standard. Specifically, the 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 conform to a standard, the complexity of the encoded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level constrains the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in units of megasamples per second), maximum reference picture size, etc. The limits set by the level may be further constrained through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management, possibly signaled in the encoded video sequence.

[0045] In some exemplary embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the encoded video sequence(s). 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.

[0046] 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 transmitting circuit). The video encoder (603) may be used in place of the video encoder (403) in the example of FIG. 4.

[0047] The video encoder (603) can receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that can capture video images to be encoded by the video encoder (603). In another example, the video source (601) can be implemented as part of the electronic device (620).

[0048] The video source (601) may provide a source video sequence to be encoded 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 service system, the video source (601) may be a storage device capable of storing pre-prepared video. In a video conferencing system, the video source (601) may be a camera that captures image information locally as a video sequence. The video data may be provided as a number of individual pictures or images that impart motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each of which may contain one or more samples, depending on the sampling structure, color space, etc., in use. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0049] According to some example embodiments, the video encoder (603) can encode and compress pictures of a source video sequence into an encoded video sequence (643) in real-time or under any other time constraint required by an application. Enforcing an appropriate encoding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be operatively coupled to and control other functional units, such as those described below. Such couplings are not depicted for the sake of brevity. Parameters set by the controller (650) may include parameters related to rate control (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 suitable functions for the video encoder (603) optimized for a particular system design.

[0050] In some example embodiments, the video encoder (603) may be configured to operate in an encoding loop. As a simplistic explanation, in one example, the encoding loop may include a source encoder (630) (e.g., responsible for generating symbols such as a symbol stream based on an input picture to be encoded and a reference picture(s)) and a (local) decoder (633) embedded in the video encoder (603). Even if the embedded decoder 633 processes the encoded video stream without entropy coding by the source decoder 630, the decoder (633) reconstructs the symbols to generate sample data in a similar manner as a (remote) decoder would also generate them (in the video compression techniques considered in the disclosed subject matter, any compression between the symbols in the entropy coding and the encoded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream yields bit-accurate results regardless of the decoder location (local or remote), the contents of the reference picture memory (634) are also bit-accurate 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 the prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0051] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, e.g., the video decoder (410), already described in detail above in connection with Figure 5. However, referring also briefly 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 (420) may be lossless, the entropy decoding portion of the video decoder (410), including the buffer memory (415) and parser (420), may not be fully implemented in the encoder's local decoder (633).

[0052] An observation that can be made at this point is that any decoder technique, except for parsing / entropy decoding, which may only exist in the decoder, may need to exist in substantially the same functional form in the corresponding encoder. For this reason, the disclosed subject matter may sometimes focus on the decoder operation, which is similar to the decoding portion of the encoder. Thus, a description of the encoder technique may be omitted, since it is the inverse of the decoder technique, which is described generically. Only in certain areas or aspects of the encoder is a more detailed description provided below.

[0053] In operation, in some example implementations, the source encoder (630) may perform motion-compensated predictive encoding, which predictively encodes an input picture with reference to one or more previously encoded pictures from a video sequence, designated as "reference pictures." In this manner, the encoding engine (632) encodes differences (or residuals) in color channels between pixel blocks of the input picture and pixel blocks of a reference picture(s) that may be selected as a predictive reference for the input picture. The terms "residual" and its derivative "residual" may be used interchangeably.

[0054] The local video decoder (633) can decode the encoded video data of pictures that may be designated as reference pictures based on the symbols generated by the source encoder (630). The operation of the encoding engine (632) can advantageously be a lossy process. When the encoded video data can be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence can be a copy of the source video sequence, typically with some errors. The local video decoder (633) can replicate the decoding process that may be performed on the reference pictures by the video decoder and store the reconstructed reference pictures in a reference picture cache (634). In this way, the video encoder (603) can locally store copies of reconstructed reference pictures that have common content (in the absence of transmission errors) as reconstructed reference pictures that would be obtained by a far-end (remote) video decoder.

[0055] 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., that 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).

[0056] The controller (650) may manage the encoding operations of the source encoder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0057] The output of all of the above functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0058] The transmitter (640) can buffer the encoded video sequence generated by the entropy encoder (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) can merge the encoded video data from the video encoder (630) with other data to be transmitted, such as encoded audio data and / or auxiliary data streams (sources not shown).

[0059] The controller (650) may manage the operation of the video encoder (603). During encoding, the controller (650) may assign a certain coding picture type to each coded picture. The coding picture type may affect the coding technique that may be applied to each picture. For example, pictures may often be assigned as one of the following picture types:

[0060] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures 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 will recognize these variations of I-pictures and their respective uses and characteristics.

[0061] A predictive picture (P-picture) may be one that can be encoded and decoded using intra- or inter-prediction, which uses at most one motion vector and reference index to predict the sample values ​​of each block.

[0062] Bidirectionally predicted pictures (B-pictures) may be those that can be coded and decoded using intra- or inter-prediction, which uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multi-predictive pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0063] A source picture may typically be spatially divided into multiple sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks, as determined by the coding assignment applied to the respective picture of the block. For example, blocks of an I picture may be non-predictively coded or predictively coded with reference 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 reference to one previously coded reference picture. Blocks of a B picture may be predictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures. Source pictures or intermediate processing pictures may be subdivided into other types of blocks for other purposes. As will be explained in more detail below, the division of coding blocks and other types of blocks may or may not follow the same scheme.

[0064] The video encoder (603) may perform encoding operations according to a given video encoding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive encoding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the encoded video data may conform to a syntax specified by the video encoding technique or standard used.

[0065] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source encoder (630) may include such data as part of the encoded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other types of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0066] A video may be captured as multiple source pictures (video pictures) in a temporal sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture to be coded / decoded, called a current picture, may be divided into blocks. If 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 if multiple reference pictures are used.

[0067] In some exemplary embodiments, bidirectional prediction techniques can be used in inter-picture prediction. Such bidirectional prediction techniques use two reference pictures, such as a first reference picture and a second reference picture, both of which precede the current picture in decoding order (but may be past or future, respectively, in display order) in the video. 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.

[0068] Furthermore, to improve coding efficiency, merge mode techniques may be used in inter-picture prediction.

[0069] According to some example embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, a picture in a sequence of video pictures is divided 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), one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels or four CUs of 32×32 pixels. Each of the one or more 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for that CU among various prediction types, such as an inter prediction type or an intra prediction type. The CU may be divided into one or more prediction units (PUs) depending on temporal and / or spatial predictability. In general, each PU includes a luma prediction block (PB) and two chroma PBs. In some embodiments, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. The division of a CU into PUs (or PBs of different color channels) may be performed in various division patterns. For example, a luma or chroma PB may include a matrix of values ​​(e.g., luma values) for pixels, such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0070] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of the present 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 an encoded picture that is part of an encoded video sequence. The exemplary video encoder (703) may be used in place of the video encoder (403) in the example of FIG. 4.

[0071] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive block, such as 8×8 samples. The video encoder (703) then determines whether the processing block is best coded using an intra mode, an inter mode, or a bi-directional predictive mode, for example using rate-distortion optimization (RDO). If it is determined that the processing block is coded in an intra mode, the video encoder (703) may use intra prediction techniques to code the processing block into a coded picture. If it is determined that the processing block is coded in an inter mode or a bi-directional predictive mode, the video encoder (703) may use inter prediction techniques or bi-directional prediction techniques, respectively, to code the processing block into a coded picture. In some exemplary embodiments, a merge mode may be used as a sub-mode of inter-picture prediction, in which a motion vector is derived from one or more motion vector predictors, but without the benefit of coded motion vector components outside the predictors. In some exemplary embodiments, there may be motion vector components applicable to the current block. Thus, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module (not shown) for determining a prediction mode for a processing block.

[0072] 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 coder (725) coupled together as shown in the exemplary arrangement of FIG.

[0073] The inter encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block with one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter prediction information (e.g., a description of redundant information due to inter coding techniques, motion vectors, merge mode information), and calculate an inter prediction result (e.g., a predicted block) based on the inter prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the 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 620 of FIG. 6.

[0074] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block to blocks already encoded 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 also calculate intra prediction results (e.g., predicted blocks) based on the intra prediction information and reference blocks in the same picture.

[0075] 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 for a block and provides a control signal to the switch (726) based on the prediction mode. For example, if the prediction mode is an intra mode, the general controller (721) controls the switch (726) to select a result of the intra mode for use by the residual calculator (723), and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream. If the prediction mode for the block is an inter mode, the general controller (721) controls the switch (726) to select a result of inter prediction 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.

[0076] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for that 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 exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform to generate decoded residual data. The decoded residual data can be suitably used by the intra-encoder (722) and the inter-encoder (730). For example, the inter-encoder (730) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are suitably processed to generate decoded pictures, which can be buffered in a memory circuit (not shown) and used as reference pictures.

[0077] The entropy encoder (725) is configured to format a bitstream to include the encoded block and to perform entropy encoding. The entropy encoder (725) is 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 encoding a block in a merged sub-mode of either the inter mode or the bi-prediction mode, the residual information may not be present.

[0078] 8 shows a diagram of an exemplary video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive encoded pictures that are part of an encoded video sequence and decode the encoded pictures to generate reconstructed pictures. In one example, the video decoder (810) may be used in place of the video decoder (410) in the example of FIG. 4.

[0079] 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 configuration of FIG. 8.

[0080] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent the 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, if the prediction mode is an inter- or bi-predictive mode, the inter-prediction information is provided to the inter-decoder (880). If the prediction type is an intra-prediction type, the intra-prediction information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0081] An inter decoder (880) may be configured to receive inter prediction information and generate inter prediction results based on the inter prediction information.

[0082] The intra decoder (872) may be configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

[0083] The residual decoder (873) may be configured to perform inverse quantization to extract dequantized transform coefficients and process the dequantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (including quantizer parameters (QP)), which may be provided by the entropy decoder (871) (data path not depicted since this is only control information for low data volume).

[0084] A reconstruction module (874) may be configured to combine, in the spatial domain, the residual output by the residual decoder (873) and the prediction result (output by the intra- or inter-prediction module, as the case may be) to form reconstructed blocks that form part of the reconstructed picture as part of the reconstructed video. Note that other suitable operations, such as deblocking operations, may also be performed to improve visual quality.

[0085] It should be noted that the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using any suitable technology. In some exemplary embodiments, the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using one or more integrated circuits. In other embodiments, the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using one or more processors executing software instructions.

[0086] Returning to the intra prediction process, samples in a block (e.g., luma or chroma prediction block, or coding block if not further divided into prediction blocks) are predicted by samples of one or more adjacent lines, next adjacent lines, or other lines, or a combination thereof. The residual between the actual block being coded and the prediction block may then be processed through a transform followed by quantization. Various intra prediction modes may be made available, and parameters related to intra mode selection and other parameters may be signaled in the bitstream. The various intra prediction modes may relate, for example, to one or more line positions for predicting samples, the direction in which prediction samples are selected from one or more prediction lines, and other special intra prediction modes.

[0087] For example, the set of intra-prediction modes (interchangeably referred to as "intra modes") may include a predetermined number of directional intra-prediction modes. As described above with respect to the example implementation of FIG. 1, these intra-prediction modes may correspond to a predetermined number of directions in which an out-of-block sample is selected as a prediction for a sample being predicted within a particular block. In another particular example implementation, eight main directional modes may be supported and predefined, corresponding to angles from 45 degrees to 207 degrees relative to the horizontal axis.

[0088] In some other implementations of intra prediction, the directional intra modes may be further extended to an angle set with finer granularity to further exploit more kinds of spatial redundancy in the directional texture. For example, the above eight angle implementation may be configured to provide eight nominal angles called V_PRED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED and D67_PRED as shown in FIG. 9, and for each nominal angle, a predetermined number (e.g., seven) of finer angles may be added. With such extension, a larger total number (e.g., 56 in this example) of directional angles may become available for intra prediction, corresponding to the same number of predetermined directional intra modes. The prediction angle may be represented by the nominal intra angle + angle delta. In the above specific example with seven finer angle directions per nominal angle, the angle delta may be -3 to 3 times a step size of 3 degrees.

[0089] In some implementations, instead of or in addition to the above directional intra modes, a certain number of non-directional intra prediction modes may also be predefined and available. For example, five non-directional intra modes called smooth intra prediction modes may be specified. These non-directional intra mode prediction modes may be specifically called DC, PAETH, SMOOTH, SMOOTH_V and SMOOTH_H intra modes. Prediction of samples of a particular block under these exemplary non-directional modes is shown in FIG. 10. As an example, FIG. 10 shows that a 4×4 block 1002 is predicted by samples from an upper neighboring line and / or a left neighboring line. A particular sample 1010 in the block 1002 may correspond to a directly above sample 1004 of the sample 1010 in the upper neighboring line of the block 1002, a left above sample 1006 of the sample 1010 as an intersection of the upper neighboring line and the left neighboring line, and a directly left sample 1008 of the sample 1010 in the left neighboring line of the block 1002. For the exemplary DC intra prediction mode, the average of the left and above neighboring samples 1008 and 1004 may be used as a predictor for sample 1010. For the exemplary PAETH intra prediction mode, the above, left and above left reference samples 1004, 1008 and 1006 may be fetched, and then the value of any of these three reference samples that is closest to (above+left-topleft) may be set as a predictor for sample 1010. For the exemplary SMOOTH_V intra prediction mode, sample 1010 may be predicted by quadratic interpolation in the vertical direction of the above-left neighboring sample 1006 and the left neighboring sample 1008. For the exemplary SMOOTH_H intra prediction mode, sample 1010 may be predicted by quadratic interpolation in the horizontal direction of the above-left neighboring sample 1006 and the above neighboring sample 1004. For the exemplary SMOOTH intra prediction mode, sample 1010 may be predicted by an average of quadratic interpolation in the vertical and horizontal directions. The above non-directional intra mode implementations are given merely as non-limiting examples.Other non-directional selections of adjacent lines and samples are also contemplated, as well as schemes for combining prediction samples to predict a particular sample within a prediction block.

[0090] The selection of a particular intra-prediction mode by the encoder from the above directional or non-directional modes at various coding levels (picture, slice, block, unit, etc.) may be signaled in the bitstream. In some exemplary implementations, the exemplary eight nominal directional modes (total of 13 choices) along with the five non-angle smooth modes may be signaled first. Then, if the signaled mode is one of the eight nominal angle intra modes, an index is further signaled to indicate the selected angle delta relative to the corresponding signaled nominal angle. In some other exemplary implementations, all intra-prediction modes may be indexed together for signaling (e.g., 56 directional modes plus 5 non-directional modes resulting in 61 intra-prediction modes).

[0091] In some example implementations, the example 56 or other number of directional intra-prediction modes may be implemented using a joint directional predictor that projects each sample of a block to a reference subsample position and interpolates the reference sample using a 2-tap bilinear filter.

[0092] In some implementations, further filter modes, called FILTER INTRA modes, may be designed to capture the decaying spatial correlation with the references on the edges. For these modes, prediction samples within the block in addition to out-of-block samples may be used as intra prediction reference samples for some patches within the block. These modes may, for example, be predefined and made available for intra prediction at least for the luma block (or only the luma block). A certain number (e.g., 5) of filter intra modes may be predesigned, each of which is represented by a set of n-tap filters (e.g., 7-tap filters) that reflects the correlation between a sample in a 4×2 patch and its n neighbors. In other words, the weight coefficients of the n-tap filters may depend on the position. Taking an 8×8 block, a 4×2 patch, and 7-tap filtering as examples, an 8×8 block 1102 may be divided into eight 4×2 patches as shown in FIG. 11. These patches are indicated by B0, B1, B1, B3, B4, B5, B6, and B7 in FIG. 11. For each patch, its seven neighbors, indicated by R0-R7 in FIG. 11, may be used to predict samples in the current patch. For patch B0, all neighbors may already be reconstructed. However, for other patches, some of the neighbors may be in the current block and therefore not reconstructed, in which case the predicted values ​​of the nearest neighbors are used as reference. For example, all neighbors of patch B7 as shown in FIG. 11 are not reconstructed, so the predicted samples of the neighbors are used instead.

[0093] In some implementations of intra prediction, one color component may be predicted using one or more other color components. The color components may be any one of the components in YCrCb, RGB, XYZ color space, etc. For example, prediction of a chroma component (e.g., a chroma block) from a luma component (e.g., a luma reference sample), called Chroma from Luma (or CfL), may be implemented. In some example implementations, cross-color prediction may be allowed only from luma to chroma. For example, a chroma sample in a chroma block may be modeled as a linear function of the corresponding reconstructed luma sample. CfL prediction may be implemented as follows: CfL(α)=α×L AC +DC (1)

[0094] Here, L AC denotes the AC contribution of the luma component, α denotes a parameter of the linear model, and DC denotes the DC contribution of the chroma component. For example, the AC components are obtained for each sample of the block, and the DC component is obtained for the entire block. Specifically, the reconstructed luma samples may be subsampled to the chroma resolution, and then the average luma value (DC of luma) may be subtracted from each luma value to form the AC contribution in luma. The luma AC contribution is then used in the linear mode of equation (1) to predict the AC value of the chroma component. Instead of requiring the decoder to calculate the scaling parameters to approximate or predict the chroma AC components from the luma AC contribution, an exemplary CfL implementation may determine the parameter α based on the original chroma samples and signal these in the bitstream. This reduces the complexity of the decoder and results in a more accurate prediction. As for the DC contribution of the chroma component, in some exemplary implementations, it may be calculated using an intra DC mode within the chroma component.

[0095] A transform of the residual of either the intra-predicted block or the inter-predicted block may then be performed, followed by quantization of the transform coefficients. For the purpose of performing the transform, both the intra-coded block and the inter-coded block may be further partitioned into multiple transform blocks (sometimes used interchangeably as "transform units", although the term "unit" is usually used to represent a collection of three color channels, e.g., a "coding unit" includes a luma coding block and a chroma coding block) before the transform. In some implementations, a maximum partition depth of the coded block (or predictive block) may be specified (the term "coded block" may be used interchangeably with "coding block"). For example, such partitioning may not be performed beyond two levels. The partitioning of the predictive block into transform blocks may be handled differently between intra-predicted blocks and inter-predicted blocks. However, in some implementations, such partitioning may be similar between intra-predicted blocks and inter-predicted blocks.

[0096] In some example implementations, for intra-coded blocks, transform partitioning may be performed such that all transform blocks have the same size and the transform blocks are coded in raster scan order. An example of such transform block partitioning of an intra-coded block is shown in Figure 12. Specifically, Figure 12 shows that a coded block 1202 is partitioned into 16 transform blocks of the same block size via mid-level quadtree partitioning 1204, as indicated by 1206. An example raster scan order for coding is indicated by the ordered arrows in Figure 12.

[0097] In some example implementations, for inter-coded blocks, transform unit partitioning may be done recursively with a partition depth up to a predetermined number of levels (e.g., two levels). The partitioning may stop or continue recursively at any level for any sub-partition, as shown in FIG. 13. In particular, FIG. 13 illustrates an example where a block 1302 is partitioned into four quadtree sub-blocks 1304, one of which is further partitioned into four second-level transform blocks, while the partitioning of the other sub-block stops after the first level, resulting in a total of seven transform blocks of two different sizes. An example raster scan order for coding is further illustrated by the ordered arrows in FIG. 13. Although FIG. 13 illustrates an example implementation of up to two levels of quadtree partitioning of square transform blocks, in some production implementations, the transform partitioning may support 1:1 (square), 1:2 / 2:1 and 1:4 / 4:1 transform block shapes and sizes ranging from 4×4 to 64×64. In some example implementations, if the coding block is 64x64 or smaller, transform block partitioning may only be applied to the luma component (in other words, the chroma transform blocks will be the same as the coding block under that condition). Otherwise, if the coding block width or height is greater than 64, both the luma coding block and the chroma coding block may be implicitly divided into multiples of min(W,64)xmin(H,64) and min(W,32)xmin(H,32) transform blocks, respectively.

[0098] Each of the above transform blocks may then undergo a linear transform, which essentially moves the residuals in the transform block from the spatial domain to the frequency domain. In some implementations of the actual linear transform, multiple transform sizes (ranging from 4 points to 64 points for each of the two dimensions) and transform shapes (square, rectangular with width / height ratios of 2:1 / 1:2 and 4:1 / 1:4) may be allowed to support the above exemplary extended coding block partitioning.

[0099] Turning to the actual linear transform, in some exemplary implementations, the 2D transform process may involve the use of hybrid transform kernels (which may, for example, be composed of a different 1D transform for each dimension of the coded residual transform block). Exemplary 1D transform kernels may include, but are not limited to, a) 4-point, 8-point, 16-point, 32-point, 64-point DCT-2, b) 4-point, 8-point, 16-point asymmetric DST (DST-4, DST-7) and their inverted versions, c) 4-point, 8-point, 16-point, 32-point identity transform. The selection of the transform kernel to be used for each dimension may be based on a rate-distortion (RD) criterion. For example, the basis functions of the DCT-2 and asymmetric DST that may be implemented are listed in Table 1. [Table 1]

[0100] In some example implementations, the availability of hybrid transform kernels for a particular primary transform implementation may be based on the transform block size and prediction mode. Example dependencies are listed in Table 2. For chroma components, the selection of the transform type may be performed in an implicit manner. For example, for intra-prediction residuals, the transform type may be selected according to the intra-prediction mode, as specified in Table 3. For inter-prediction residuals, the transform type for a chroma block may be selected according to the selection of the transform type of the co-located luma block. Thus, for chroma components, there is no signaling of the transform type in the bitstream. IDTX in Table 1 represents the identity transform. [Table 2] [Table 3]

[0101] In some example implementations, when performing the transform, a transform skip mode may be applied. The transform skip mode may include multiple variants.

[0102] In one implementation, when the residuals within a residual block are highly uncorrelated, the above 2D transform may not be very efficient and may be skipped (ie, no transform is needed).

[0103] In one implementation, as shown in FIG. 14, 1D transform is applied only in the vertical direction, and the horizontal 1D transform is skipped. This mode is called horizontal transform skip. A 4×4 block is an exemplary resultant transform coefficient block (or simply transform block) after vertical 1D transform, and each cell indicates a corresponding transform coefficient. As can be seen, the low frequency components of the transform coefficients obtained after 1D transform are concentrated in the upper row of the block, and the high frequency components are in the lower row of the block. Specifically, in this exemplary block, all transform coefficients in the fourth row are all zero.

[0104] In one implementation, as shown in FIG. 15, the 1D transform is applied only in the horizontal direction, and the 1D transform in the vertical direction is skipped. This mode is called vertical transform skip. A 4×4 block is an exemplary resultant transform coefficient block after the horizontal 1D transform, and each cell indicates a corresponding transform coefficient. As can be seen, the low frequency components of the transform coefficients obtained after the 1D transform are concentrated in the left column of the block, and the high frequency components are in the right column of the block. Specifically, in this exemplary block, all transform coefficients in the fourth column are all zero.

[0105] In some example implementations, an identity transform (IDTX) may be used to skip transform coding in certain directions (e.g., horizontal or vertical), and IDTX can be particularly beneficial for coding sharp edges.

[0106] In some example implementations, a secondary transform may be performed on the primary transform coefficients. For example, a low-frequency non-separable transform (LFNST), also known as a reduced secondary transform, may be applied between the forward primary transform and quantization (at the encoder) and between the inverse quantization and inverse primary transform (at the decoder side) to further decorrelate the primary transform coefficients.

[0107] In some example implementations, the transformation may include a Line Graph Transform (LGT), as shown in FIG. 16. A graph may be a general mathematical structure composed of a set of vertices and edges, which is used to model similarity relationships between objects of interest. In practice, a weighted graph (where a set of weights is assigned to edges and potentially vertices) may provide a sparse representation for robust modeling of signals / data. LGT may improve coding efficiency by providing better adaptation for diverse block statistics. A separable LGT may be designed and optimized by learning a line graph from the data to model the statistics on the underlying rows and columns of the block residual signal, and the associated generated graph Laplacian (GGL) matrix is ​​used to derive the LGT.

[0108] In one implementation, given a weighted graph G(W,V), the GGL matrix may be defined as LE=D-W+V, where W may be an adjacency matrix composed of non-negative edge weights Wc, D may be a diagonal matrix, and V may be a diagonal matrix representing weighted self-loops Vc1, Vc2. e may be expressed as follows:

number

[0109] LGT can then be derived by eigendecomposition of GGL Lc.

number

[0110] where the columns of the orthogonal matrix U are the basis vectors of the LGT, and Φ is the diagonal eigenvalue matrix. In fact, DCTs and DSTs, including DCT-2, DCT-8, and DST7, are LGTs derived from a particular form of GGL. DCT-2 is derived by setting Vc1 = 0, DST-7 is derived by setting Vc = Wc, DCT-8 is derived by setting Vc2 = Wc, and DST-4 is derived by setting Vc1 = 2w c and DCT-4 is derived by setting Vc2=2 w c It is derived by setting

[0111] LGT may be implemented as a matrix multiplication. A 4p LGT core has vc1=2w c This means that the DST-4 core is a DST-4 core. The 8p LGT core has a vc1 = 1.5w c and the 16p, 32p and 64p LGT cores may be derived by setting vc1=wc in Lc, which means DST-7.

[0112] In some implementations, a level map scheme may be used for coefficient coding, compared to a coding scheme that processes each 2D transform coefficient sequentially. For each transform unit (or transform block), coefficient coding begins with coding a skip code, followed by a primary transform kernel type and end-of-block (EOB) position signaling if transform coding is not skipped. The coefficient values ​​are then coded in a multi-level map scheme plus a code value. The level map is coded as three level planes, namely a low level plane, a mid level plane, and a high level plane, and the code is coded as another separate plane. The low level plane, the mid level plane, and the high level plane correspond to different ranges of coefficient magnitude. The low level plane corresponds to an exemplary range of 0 to 2, the mid level plane corresponds to an exemplary range of 3 to 14, and the high level plane covers a range of, for example, 15 and above. The three level planes may be coded as follows: (a) The EOB position is coded first. (b) the low-level plane and the mid-level plane are coded together in a backward scan order, where the scan order may include a zigzag scan applied on a whole transform unit basis; (c) the code plane and the high-level plane are coded together in a forward scan order; (d) the residual (coefficient level minus 14) is entropy coded using an Exp-Golomb code. The context model applied to the low-level plane depends on the primary transform direction (bidirectional, horizontal and vertical) and the transform size, and up to a predefined number (e.g., 5) of neighboring coefficients (in the frequency domain) are used to derive the context. The mid-level plane may use a similar context model, but the number of neighboring coefficients of the context may be reduced, e.g., from 5 to 2. The high-level plane may be coded by an Exp-Golomb code without using a context model.The DC code is coded using a context modeling approach, where a weighted average of the above and left adjacent block DC code values ​​may be used to derive context information, as described in equation (4) below.

number

[0113] The weighting depends on the length of the intersection of the neighboring transform block with the current transform block. The derived context information is used as an index to access three different contexts for coding the DC code, as shown in Equation 5 below. The code values ​​of other coefficients may be coded directly without using a context model.

number

[0114] In this disclosure, various embodiments are disclosed for improving video encoding / decoding techniques under 1D transform skip mode. As mentioned above, under 1D transform skip mode, the energy concentration pattern is different compared to 2D transform mode where the transform is performed in two dimensions. For example, the energy is concentrated in the top row or left column of the transform block under 1D transform skip mode. On the other hand, under 2D transform, the energy is concentrated in, for example, the top left corner. By utilizing the different energy concentration pattern under 1D transform skip mode, these improvements may include higher video data compression rate, higher coding efficiency, and lower signaling overhead.

[0115] In this disclosure, the term block may refer to a transform block, a coded block, a predictive block, and so on.

[0116] In this disclosure, the term chroma block may refer to a block in any of the chrominance (color) channels.

[0117] In this disclosure, the term transform block may also refer to a coefficient within a transform block, the term row may also refer to a row of coefficients within a transform block, and the term column may also refer to a column of coefficients within a transform block.

[0118] Conversion skip by EOR and / or EOC signaling

[0119] In this disclosure, the set of transform types with horizontal transform skip is hereinafter referred to as Set A. Set A may include all combinations of 1D transforms whose transform kernels are matrices. Examples of 1D transforms include, but are not limited to, DCT, ADST, FLIPADST, LGT, FLIPLGT, KLT, KLT, all trigonometric transform types (DCT types 1-8, DST types 1-8) and their derivatives in the vertical direction and transform skips in the horizontal direction.

[0120] In this disclosure, the set of transform types with transform skip in the vertical direction is hereinafter referred to as Set B. Set B may include all combinations of 1D transforms whose transform kernels are matrices. Examples of 1D transforms include, but are not limited to, DCT, ADST, FLIPADST, LGT, FLIPLGT, KLT, KLT, all trigonometric transform types (DCT types 1-8, DST types 1-8) and their derivatives in the horizontal direction and transform skip in the vertical direction.

[0121] The embodiments in this disclosure may be applied to luma blocks and / or chroma blocks.

[0122] In some example implementations, when a one-dimensional (1D) transform skip is applied, instead of signaling an End of Block (EOB) value indicating both the vertical and horizontal position (i.e., the x-axis and y-axis position) within a 2D block, an End of Row (EOR) or End of Column (EOC) value is signaled indicating only the horizontal or vertical coordinate of a position within a 2D block.

[0123] In one implementation, as shown in FIG. 14, when transform skip is applied only in the horizontal direction (in this case, the 1D transform is performed vertically), an EOR value is signaled to indicate the row index of the last row of the transform block (or transform coefficient block) that has at least one nonzero coefficient value. In the example shown in FIG. 14, the third row is the last row that has at least one nonzero coefficient value. In this case, an EOR value of 2 is signaled. Note that the example shown in FIG. 14 uses row index 0 as the first row index. Other row index numbers, such as 1, may be selected as the first row index, in which case the EOR value would be 3 instead.

[0124] In one implementation, as shown in FIG. 15, when transform skip is applied only vertically (in this case, the 1D transform is performed horizontally), an EOC value is signaled to indicate the column index of the last column of the transform block that has at least one nonzero coefficient value. In the example shown in FIG. 15, the third column is the last column that has at least one nonzero coefficient value. In this case, an EOC value of 2 is signaled. Note that the example shown in FIG. 15 uses column index 0 as the first column index. Other column index numbers, such as 1, may be selected as the first column index, in which case the EOC value would be 3 instead.

[0125] In some example implementations, when an EOR value is signaled, the EOB value may be derived as one of EOR*stride, EOR*stride-1, (EOR+1)*stride, or (EOR+1)*stride-1, where stride is the transform block width. Note that variations in these formulas depend, for example, on whether the row index starts at 0 or 1 and whether the EOB starts at 0 or 1.

[0126] In some example implementations, when the transform block width is 64 or greater, the stride may be capped to a value less than 64, such as 32. In this case, the encoder may consider the capped stride value when coding the transform coefficients.

[0127] In some example implementations, when an EOC value is signaled, the EOC value may be derived as one of EOC*stride, EOC*stride-1, (EOC+1)*stride, or (EOC+1)*stride-1, where stride is the transform block height. Note that variations in these formulas depend, for example, on whether the column index starts at 0 or 1 and whether EOC starts at 0 or 1.

[0128] In some example implementations, when the transform block height is equal to or greater than 64, the stride may be capped to a value less than 64, such as 32. In this case, the encoder may consider the capped stride value when coding the transform coefficients.

[0129] In some example implementations, when a one-dimensional transform skip is applied only in the horizontal direction, all coefficients located in rows with indices less than or equal to EOR need to be coded, regardless of whether they are 0 or not. When a one-dimensional transform skip is applied only in the vertical direction, all coefficients located in columns with indices less than or equal to EOC need to be coded, regardless of whether they are 0 or not.

[0130] In some example implementations, when performing entropy coding on the EOR and / or EOC, the context used to entropy code the values ​​of the EOR and / or EOC is different from the context used to entropy code the values ​​of the EOB because the probability model associated with the EOR and / or EOC is different from the probability model associated with the EOB.

[0131] In some example implementations, when transform skip is applied only in the horizontal direction, the EOR value is signaled to indicate the row index of the last row of the transform coefficient block having at least one non-zero coefficient value. The context used to entropy code the EOR value may depend on factors including the transform block height, or may depend only on the transform block height.

[0132] In some example implementations, when transform skip is applied only in the vertical direction, the EOC value is signaled to indicate the column index of the last column of the transform coefficient block having at least one non-zero coefficient value. The context used to entropy code the EOC value may depend on factors including the transform block width, or may depend only on the transform block width.

[0133] In some exemplary implementations, when coding of transform coefficients and transform skipping are applied only in the horizontal direction, if i) the current transform coefficient is the last transform coefficient to be coded in the row indexed by EOR, and ii) all previous transform coefficients in the same row are coded as 0, the current transform coefficient may be derived as non-zero. This is particularly useful on the decoder side, since the decoder only needs to derive this current transform coefficient as non-zero without having to decode this information from the raw video bitstream. With reference to FIG. 14, row 2 is the row indexed by EOR. When the currently processed transform coefficient is the last one in this row, the decoder may directly derive the current transform coefficient as non-zero, since the first three transform coefficients in this row are all 0. Additionally or alternatively, in this case, the flag indicating whether the level of the current transform coefficient is 1 or more is not signaled, but is derived by the decoder as true (meaning that the level of the current transform coefficient is 1 or more).

[0134] In some example implementations, when coding of transform coefficients and transform skipping are applied only in the vertical direction, a current transform coefficient may be derived as non-zero if i) the current transform coefficient is the last transform coefficient to be coded in a column indexed by EOC, and ii) all previous transform coefficients in the same column are coded as zero. The decoder only needs to derive this current transform coefficient as non-zero without needing to decode this information from the raw video bitstream. With reference to FIG. 15, column 2 is the column indexed by EOC. When the current transform coefficient to be processed is the last one in this column, the decoder may directly derive the transform coefficient as non-zero, since the first three transform coefficients in this column are all zero. Additionally or alternatively, a flag indicating whether the level of the current transform coefficient is equal to or greater than 1 is not signaled, but is derived as true by the decoder.

[0135] In some example implementations, when transform skip is applied only horizontally, the context used to entropy code the magnitude of the current transform coefficient may depend on factors including previously coded coefficients. In one implementation, the previously coded coefficients considered include only previously coded coefficients in the same row. For example, referring to FIG. 14, the context used to entropy code the magnitude of the last transform coefficient in row 1 may depend on the previous three coded coefficients in the same row. Alternatively, in another implementation, the previously coded coefficients considered may include only previously coded coefficients in the same row that are in the immediate vicinity of the current coefficient.

[0136] In some example implementations, when transform skip is applied only horizontally, the context used to entropy code the magnitude of the current transform coefficient may depend on factors including previously coded coefficients. In one implementation, the previously coded coefficients considered include only previously coded coefficients in the same column. For example, referring to FIG. 15, the context used to entropy code the magnitude of the last transform coefficient in column 1 may depend on the previous three coded coefficients in the same column. Alternatively, in another implementation, the previously coded coefficients considered may include only previously coded coefficients in the same column that are in the immediate vicinity of the current coefficient.

[0137] The various embodiments described above generally apply to 1D transform skip scenarios where there is only a 1D transform applied in one direction and the 1D transform in the other direction is skipped. These various embodiments may also be applied to the identity transform (IDTX).

[0138] In various exemplary implementations above, transform coefficients in a transform block, such as the transform blocks shown in Figures 14 and 15, may or may not need to undergo an additional quantization process. For example, the transform coefficients may be obtained immediately after the 1D transform on the residual block. Alternatively, the transform coefficients may be further subjected to a quantization process to be converted into quantized transform coefficients. The embodiments in this disclosure may be applied to both unquantized transform coefficients or quantized transform coefficients. Furthermore, in this disclosure, transform coefficients may generally refer to unquantized transform coefficients or quantized transform coefficients.

[0139] 17 shows an example method 1700 for decoding video data. The method 1700 may include some or all of the following steps: receiving a video bitstream including a transform block having two dimensions, where the transform block is entropy coded, determining based on a syntax element in the video bitstream whether a one-dimensional transform skip is applied to the transform block, obtaining an end position value associated with the transform block from the video bitstream in response to the one-dimensional transform skip being applied to the transform block, where the end position value indicates only one of an end position in a horizontal coordinate of the transform block and an end position in a vertical coordinate of the transform block, and extracting the transform block from the video bitstream according to the end position value.

[0140] An end position value, such as EOR or EOC, may be signaled in the bitstream. In one implementation, the indication may also be a signal to indicate whether EOR or EOC is signaled.

[0141] At the decoder side, once EOR or EOC is obtained, the decoder may derive a position range in the bitstream assigned to the transform coefficients of the transform block. The decoder may then perform entropy decoding based on the position range to obtain the transform coefficients of the transform block. Note that the transform coefficients may be in a quantized format, followed by an inverse quantization process to convert the quantized transform coefficients to an unquantized format, or alternatively, the transform coefficients may be in an unquantized format. Retrieving the transform block may include deriving and / or decoding the transform coefficients of the transform block from the bitstream. The retrieved transform block may then undergo an inverse transform to obtain the corresponding residual block.

[0142] The embodiments of the present disclosure may be used individually or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to luma blocks or chroma blocks.

[0143] The techniques described above can be implemented as computer software using computer readable instructions and can be physically stored on one or more computer readable media. For example, Figure 18 illustrates a computer system (1800) suitable for implementing certain embodiments of the disclosed subject matter.

[0144] Computer software can be coded using any suitable machine code or computer language and can be subject to assembly, compilation, linking, or similar mechanisms to produce code containing instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., either directly, or through interpretation, microcode execution, etc.

[0145] The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smart phones, gaming devices, Internet of Things devices, etc.

[0146] 18 for computer system (1800) 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 computer system (1800).

[0147] The computer system (1800) may include certain human interface input devices that may be responsive to input by one or more human users through, for example, tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), and olfactory input (not shown). Human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from still image cameras), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0148] The input human interface devices may include one or more (only one of each is shown) of a keyboard (1801), a mouse (1802), a trackpad (1803), a touch screen (1810), a data glove (not shown), a joystick (1805), a microphone (1806), a scanner (1807), and a camera (1808).

[0149] The computer system (1800) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, 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 (1810), data gloves (not shown), or joystick (1805); although there may be haptic feedback devices that do not act as input devices), audio output devices (e.g., speakers (1809), headphones (not shown)), visual output devices (e.g., screens (1810) including CRT screens, LCD screens, plasma screens, OLED screens; each may or may not have touch screen input capability, each may or may not have haptic feedback capability, some of which may output two-dimensional visual output or higher than three-dimensional output through such means as stereoscopic output; virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0150] The computer system (1800) may also include human accessible storage devices and associated media, such as optical media including CD / DVD ROM / RW (1820) along with CD / DVD or similar media (1821), thumb drives (1822), removable hard drives or solid state drives (1823), legacy magnetic media such as tapes and floppy disks (not shown), specialized ROM / ASIC / PLD based devices (not shown) such as security dongles, etc.

[0151] 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.

[0152] The computer system (1800) may also include an interface (1854) to one or more communication networks (1855). The networks may be, for example, wireless, wired, optical. The networks may further be local, wide area, metropolitan, in-vehicle and industrial, real-time, delay tolerant, etc. Examples of networks include Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wired or wireless wide area digital networks including cable television, satellite television, terrestrial broadcast television, in-vehicle and industrial including CAN Bus, etc. Certain networks usually require an external network interface adapter that is attached to a specific general-purpose data port or peripheral bus (1849) (e.g., a USB port of the computer system (1800)). Others are usually integrated into the core of the computer system (1800) by attachment to a system bus as described below (e.g., 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 (1800) can communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast television), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Each of these networks and network interfaces as described above may use specific protocols and protocol stacks.

[0153] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1840) of the computer system (1800).

[0154] The cores (1840) may include one or more central processing units (CPUs) (1841), graphics processing units (GPUs) (1842), specialized programmable processing units in the form of field programmable gate arrays (FPGAs) (1843), hardware accelerators for specific tasks (1844), graphics adapters (1850), etc. These devices may be connected through a system bus (1848), along with read only memory (ROM) (1845), random access memory (1846), internal mass storage devices (1847), such as internal non-user accessible hard drives, solid state drives (SSDs), etc. In some computer systems, the system bus (1848) may be 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 (1848) or through a peripheral bus (1849). In one example, a screen (1810) may be connected to the graphics adapter (1850). Architectures for peripheral buses include PCI, USB, and the like.

[0155] The CPU (1841), GPU (1842), FPGA (1843), and accelerator (1844) can execute certain instructions that, in combination, may constitute the above-mentioned computer code. The computer code may be stored in a ROM (1845) or a RAM (1846). Temporary data may also be stored in the RAM (1846), while persistent data may be stored, for example, in an internal mass storage device (1847). Rapid storage and retrieval from any of the memory devices may be enabled through the use of a cache memory that may be closely associated with one or more of the CPU (1841), GPU (1842), mass storage device (1847), ROM (1845), RAM (1846), etc.

[0156] The computer-readable medium can have computer code thereon for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the kind well known and available to those having skill in the computer software arts.

[0157] As a non-limiting example, a computer system having the architecture (1800), and specifically the cores (1840), can provide functionality as a result of the 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 the specific storage of the cores (1840) of a non-transitory nature, such as the mass storage device (1847) internal to the core or ROM (1845). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the cores (1840). The computer-readable media can include one or more memory devices or chips according to specific needs. The software can cause the cores (1840) and specifically the processors therein (including CPUs, GPUs, FPGAs, etc.) to perform certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (1846) and modifying such data structures according to processes defined by the software. Additionally or alternatively, a computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (1844)) that may operate in place of or in conjunction with software to perform particular processes or portions of particular processes described herein. References to software may include logic, and vice versa, where appropriate. References to computer-readable media may include, where appropriate, circuitry (such as an integrated circuit (IC)) that stores software for execution, circuitry that embodies logic for execution, or both. The present disclosure encompasses any appropriate combination of hardware and software.

[0158] While this disclosure describes several exemplary embodiments, modifications, permutations, and various substitute equivalents exist and fall within the scope of this disclosure. It will thus be recognized that those skilled in the art will be able to devise numerous systems and methods that, although not explicitly shown or described herein, embody the principles of this disclosure and are therefore within its spirit and scope.

[0159] Appendix A: Abbreviations 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 to 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 Areas 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 method for video processing, comprising: receiving a video bitstream including a transform block having two dimensions, the transform block being entropy coded; determining whether a one-dimensional transform skip is applied to the transform block based on a syntax element in the video bitstream; responsive to the one-dimensional transform skip being applied to the transform block, obtaining from the video bitstream an end position value associated with the transform block, the end position value indicating only one of a horizontal coordinate end position within the transform block and a vertical coordinate end position within the transform block; extracting the transformation block from the video bitstream according to the end position value; The method includes:

2. The end position value is an end of row (EOR) value indicating the horizontal coordinate end location within the transform block, the end of row value including an end row index of a last row having at least one non-zero transform coefficient within the transform block; an end of column (EOC) value indicating the vertical coordinate end location within the transform block, the end of column (EOC) value including an end column index of a last column having at least one non-zero transform coefficient within the transform block; The method of claim 1 , comprising one of:

3. the EOR value is signaled in the video bitstream as the end position value when transform skip is applied only in the horizontal direction of the transform block; The method of claim 2 , wherein the EOC value is signaled in the video bitstream as the end position value when transform skip is applied only in a vertical direction of the transform block.

4. The method of claim 2 , wherein the context used for entropy coding the EOR value is determined based on a height of the transform block.

5. The method of claim 2 , wherein a context used for entropy coding the EOC value is determined based on a width of the transform block.

6. The EOR value is signaled, the method comprising: In response to the current transform coefficient being the last transform coefficient in a row indexed by said EOR value and all preceding transform coefficients in this same row being zero, Deriving the current transform coefficient as non-zero; deriving a level flag indicating that the level of the current transform coefficient is equal to or greater than 1 as true; The method of claim 2 , further comprising obtaining the transform coefficients in the transform block by:

7. The EOC value is signaled, the method comprising: In response to the current transform coefficient being the last transform coefficient in a sequence indexed by said EOC value and all preceding transform coefficients in this same sequence being zero, Deriving the current transform coefficient as non-zero; deriving a level flag indicating that the level of the current transform coefficient is equal to or greater than 1 as true; The method of claim 2 , further comprising obtaining the transform coefficients in the transform block by:

8. The EOR value is signaled; The context used to entropy code the magnitude of the current transform coefficient in the transform block is a preceding transform coefficient in the same row as the current transform coefficient, or The immediately preceding transform coefficient in the same row, without any other preceding transform coefficients in the same row The method of claim 2, wherein the determination is based on one of:

9. The EOC value is signaled; The context used to entropy code the magnitude of the current transform coefficient in the transform block is a preceding transform coefficient in the same column as the current transform coefficient, or The immediately preceding transform coefficient in the same column that has no other preceding transform coefficients in the same column The method of claim 2, wherein the determination is based on only one of:

10. deriving an end of block (EOB) value indicating an end location of a last non-zero transform coefficient in the transform block based on the EOR value or the EOC value; The method of claim 2 , wherein fetching the transform block from the video bitstream according to the end position value comprises fetching the transform block from the video bitstream according to the EOB value.

11. The step of deriving the EOB value comprises: In response to the end position value being the EOR value, the EOB value is EOR value * stride value EOR value * stride value - 1 (EOR value + 1) * stride value, or (EOR value + 1) * stride value - 1 deriving The method of claim 10 , wherein the stride value is equal to or related to a width of the transform block.

12. the stride value is the width of the transform block in response to the width being less than 64; The method of claim 11 , wherein the stride value is 32 in response to the width of the transform block being 64 or greater.

13. The step of deriving the EOB value comprises: In response to the end position value being the EOC value, the EOB value is EOC value * stride value EOC value * stride value - 1 (EOC value + 1) * stride value, or (EOC value + 1) * stride value - 1 deriving The method of claim 10 , wherein the stride value is equal to or related to a height of the transform block.

14. the stride value is the height of the transform block in response to the height of the transform block being less than 64; The method of claim 13 , wherein the stride value is 32 in response to the height of the transform block being 64 or greater.

15. In accordance with the transform skip being applied only in a horizontal direction of the transform block, each transform coefficient in a row having a row index less than or equal to a last row index is coded and transmitted in the video bitstream, regardless of whether each transform coefficient is zero; The method of claim 2, wherein, in accordance with the transform skip being applied only in the vertical direction of the transform block, each transform coefficient in a column having a column index less than or equal to a last column index is coded and transmitted in the video bitstream, regardless of whether the each transform coefficient is zero or not.

16. The method of claim 2 , wherein a context used to entropy code the EOR or EOC value is different from a context used to entropy code an EOB value in the video bitstream.

17. 1. A device for video processing, comprising: a memory for storing computer instructions; a processor in communication with the memory; 17. A device comprising: a processor configured to, when the processor executes the computer instructions, cause the device to perform a method according to any one of claims 1 to 16.

18. A computer program which, when executed by a processor, causes the processor to carry out a method according to any one of claims 1 to 16.

19. 1. A method for video processing, comprising: obtaining a video bitstream including a transform block having two dimensions, the transform block being entropy coded; setting a syntax element in the video bitstream indicating whether a one-dimensional transform skip is applied to the transform block; setting, in response to the one-dimensional transform skip being applied to the transform block, an end position value associated with the transform block in the video bitstream, the end position value indicating only one of a horizontal coordinate end position within the transform block and a vertical coordinate end position within the transform block; The method includes:

Images