Transform skip coefficient sign prediction

Abstract

Aspects of the present disclosure provide a method and device for video encoding / decoding. In some examples, the device includes a processing circuit, the processing circuit configured to receive a coded video stream including a current block associated with a transform block; and determine whether to use a transform skip in the transform block. In response to determining not to use a transform skip in the transform block, the processing circuit is configured to perform a first transform coefficient sign prediction, in which (i) a first sign of a first plurality of transform coefficients is predicted based on a first plurality of adjacent samples and (ii) a second sign of a second plurality of transform coefficients is predicted based on a second plurality of adjacent samples. The processing circuit is further configured to reconstruct the current block based on the first plurality of transform coefficients and the second plurality of transform coefficients.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Patent Application No. 17 / 984,229, entitled “COEFFICIENT SIGN PREDICTION FOR TRANSFORM SKIP,” filed November 9, 2022, which claims the benefit of priority to U.S. Provisional Application No. 63 / 315,348, entitled “COEFFICIENT SIGN PREDICTION FOR TRANSFORM SKIP,” filed March 1, 2022. The disclosures of these prior applications are incorporated herein by reference in their entireties.

[0002] This disclosure describes embodiments generally relating to video encoding. [Background technology]

[0003] The background discussion provided herein is intended to provide a general overview of the present disclosure, and the work of the named inventors, to the extent that it is described in this background section, is not admitted, expressly or impliedly, as prior art to the present disclosure, as are aspects of the description that may not be admitted as prior art at the time of filing.

[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 with spatial dimensions of, for example, 1920x1080 luma samples and associated chrominance samples. The sequence of pictures can have a fixed or variable picture rate (also informally known as frame rate), for example, 60 pictures per second or 60Hz. Uncompressed video has significant bitrate requirements. For example, a 1080p60 4:2:0 video (1920x1080 luma sample resolution at 60Hz frame rate) with 8 bits per sample requires a bandwidth of nearly 1.5Gbit / s. Playing such a video for one hour requires more than 600GB of storage capacity.

[0005] One of the goals of video encoding and decoding is to reduce redundancy in the input video signal through compression. Compression can help reduce the aforementioned bandwidth or storage capacity requirements, in some cases by more than one order of magnitude. Both lossless and lossy compression, and their combinations, can be used. Lossless compression refers to techniques that can reconstruct an exact copy of the original signal from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original and reconstructed signals is small enough that the reconstructed signal can be used for the intended application. Lossy compression is widely used for video. The amount of distortion that is tolerated varies from application to application. For example, users of a particular consumer streaming application may tolerate more distortion than users of a television distribution application. The achievable compression ratio may reflect that the higher the tolerable distortion, the higher the compression ratio that can be obtained.

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

[0007] Video codec techniques may include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, a picture is spatially subdivided into blocks of samples. A picture may be an intra picture if all blocks of samples are coded in intra mode. 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 initial (first) picture of a coded video bitstream and video session or as a still image. Samples of an intra block may undergo a transform, and the transform coefficients may be quantized before entropy coding. Intra prediction may be a technique that minimizes 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 needed for a given quantization step size to represent the block after entropy coding.

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

[0009] Intra prediction can take many different forms. If more than one such technique is available for a given video coding technique, the technique in use may be coded as an intra prediction mode. In some cases, the mode may include sub-modes and / or parameters that may be coded separately or may be included in a mode codeword. Which codeword is used for a given mode / sub-mode / parameter combination may affect the efficient coding of the gains from intra prediction, as may the entropy coding technique used to convert the codeword into a bitstream.

[0010] Certain modes of intra prediction were introduced in H.264, improved in H.265, and further refined in new coding techniques such as the Joint Search Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). A predictor block can be formed using neighboring sample values ​​belonging to already available samples. The sample values ​​of the neighboring samples are copied to the predictor block according to the direction. The reference to the direction in use can be coded in the bitstream or predicted itself. Summary of the Invention

[0011] Aspects of the present disclosure provide methods and apparatus for video encoding / decoding.

[0012] Some example aspects provide transform coefficient sign prediction when transform skip is applied in one or both dimensions.

[0013] In some examples, an apparatus for video encoding / decoding includes a processing circuit. The processing circuit is configured to receive a coded video stream including a current block associated with a transform block and determine whether to use a transform skip in the transform block. In response to determining not to use a transform skip in the transform block, the processing circuit is configured to perform a first transform coefficient sign prediction, in which (i) a first sign of a first plurality of transform coefficients is predicted based on a first plurality of adjacent samples and (ii) a second sign of a second plurality of transform coefficients is predicted based on a second plurality of adjacent samples. The processing circuit is further configured to reconstruct the current block based on the first plurality of transform coefficients and the second plurality of transform coefficients.

[0014] In some aspects, the processing circuit is configured to perform a second transform coefficient sign prediction for the transform block in response to determining that a transform skip is used for the transform block, the second transform coefficient sign prediction being different from the first transform coefficient sign prediction.

[0015] In some aspects, the first transform coefficient sign prediction is disabled in response to using a transform skip in the transform block.

[0016] In some aspects, the processing circuitry is configured to determine whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip. In response to using the one-dimensional horizontal transform skip in the transform block, signs of coefficients in different columns of the transform block are independently predicted by a second transform coefficient sign prediction. The processing circuitry is configured to predict the coefficient signs of the column using only reconstructed samples adjacent to the column.

[0017] In some aspects, the processing circuit is configured to determine whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip. In response to using one-dimensional horizontal transform skip in the transform block, signs of coefficients in a first column of the transform block are predicted by a second transform coefficient sign prediction based on one or more reconstructed columns to the left of the transform block and one or more reconstructed pixels above the first column of the transform block.

[0018] In some aspects, the processing circuit is configured to determine whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip. In response to using the one-dimensional horizontal transform skip in the transform block, signs of coefficients in columns other than the first column of the transform block are predicted by a second transform coefficient sign prediction using one or more reconstructed pixels in one or more rows above the transform block.

[0019] In some aspects, the processing circuitry is configured to determine whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip. In response to using the one-dimensional vertical transform skip in the transform block, signs of coefficients in different rows of the transform block are independently predicted by a second transform coefficient sign prediction. The processing circuitry is configured to predict coefficient signs of a row using only reconstructed samples adjacent to the row.

[0020] In some aspects, the processing circuit is configured to determine whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip. In response to using the one-dimensional vertical transform skip in the transform block, signs of coefficients in a first row of the transform block are predicted by a second transform coefficient sign prediction based on one or more reconstructed rows above the transform block and one or more reconstructed pixels to the left of the transform block.

[0021] In some aspects, the processing circuit is configured to determine whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip. In response to using the one-dimensional vertical transform skip in the transform block, signs of coefficients in rows other than the first row of the transform block are predicted by a second transform coefficient sign prediction using one or more reconstructed pixels in one or more columns to the left of the transform block.

[0022] In some aspects, the first transform coefficient sign prediction is disabled in response to using a one-dimensional transform skip in the transform block.

[0023] In some aspects, a first total number of symbols predicted by the second transform coefficient sign prediction when a one-dimensional transform skip is applied to the transform block is different from a second total number of symbols predicted by the first transform coefficient sign prediction when no transform skip is applied in any direction to the transform block.

[0024] In some aspects, the processing circuitry is configured to determine whether to use a two-dimensional transform skip. In response to using the two-dimensional transform skip in the transform block, the processing circuitry is configured to predict coefficient signs for only pixels in a first row or a first column of the transform block using one or more reconstructed pixels in one or more rows or columns adjacent to the transform block.

[0025] In some aspects, the processing circuit is configured to determine whether to use forward skip coding (FSC) and, in response to using FSC on the transform block, the processing circuit is configured to predict coefficient signs for only pixels in a first row or a first column of the transform block using one or more reconstructed pixels in one or more rows or columns adjacent to the transform block.

[0026] In some aspects, the processing circuit is configured to determine whether to use a two-dimensional transform skip. In response to using the two-dimensional transform skip in the transform block, a sign of a coefficient in a top-left pixel of the transform block is predicted by a second transform coefficient sign prediction based on one or more reconstructed pixels above the top-left pixel in one or more rows above the transform block and one or more reconstructed pixels to the left of the top-left pixel in one or more columns to the left of the transform block.

[0027] In some aspects, the processing circuit is configured to determine whether to use a two-dimensional transform skip. In response to using the two-dimensional transform skip in the transform block, signs of coefficients of pixels in a first row of the transform block are predicted by a second transform coefficient sign prediction based on the transform block and one or more first reconstructed pixels in one or more rows above the pixel; and one or more second reconstructed pixels to the left or right of the one or more first reconstructed pixels in the one or more rows.

[0028] In some aspects, the processing circuit is configured to determine whether to use a two-dimensional transform skip. In response to using the two-dimensional transform skip in the transform block, signs of coefficients of pixels in a first column of the transform block are predicted by a second transform coefficient sign prediction based on the transform block and one or more first reconstructed pixels in one or more columns to the left of the pixel; and one or more second reconstructed pixels above or below the one or more first reconstructed pixels in the one or more columns.

[0029] In some aspects, the first transform coefficient sign prediction is not enabled in response to using two-dimensional transform skip in the transform block.

[0030] In some aspects, the first transform coefficient code prediction is not enabled for intra coded blocks that use a forward skip coding (FSC) mode.

[0031] In some aspects, a first transform coefficient code prediction is enabled for an inter-coding block based on whether a forward skip coding (FSC) mode is used for the inter-coding block.

[0032] In some examples, an apparatus for video encoding / decoding includes a processing circuit. The processing circuit is configured to determine whether a transform skip is used in a transform block. The processing circuit is further configured to perform a transform coefficient sign prediction based on whether it is determined that the transform skip is used in the transform block. The processing circuit is further configured to determine a transform coefficient based on whether it is determined that the transform skip is used in the transform block. The processing circuit is further configured to reconstruct a current block based on the determined transform coefficient. The transform coefficient sign prediction is a first transform coefficient sign prediction performed on the transform block in response to determining that the transform skip is not used in the transform block.

[0033] In some aspects, the transform coefficient sign prediction is a second transform coefficient sign prediction performed on the transform block in response to determining to use a transform skip in the transform block, the second transform coefficient sign prediction being different from the first transform coefficient sign prediction.

[0034] In some aspects, the first transform coefficient sign prediction is disabled in response to using a transform skip in the transform block.

[0035] In some aspects, in response to using one-dimensional horizontal transform skip in the transform block, signs of coefficients in different columns of the transform block are independently predicted by a second transform coefficient sign prediction, where performing the second transform coefficient sign prediction includes predicting coefficient signs of the column using only reconstructed samples adjacent to the column.

[0036] In some aspects, in response to using one-dimensional horizontal transform skip in the transform block, the signs of coefficients in a first column of the transform block are predicted by a second transform coefficient sign prediction based on one or more reconstructed columns to the left of the transform block; and one or more reconstructed pixels above the first column of the transform block.

[0037] In some aspects, in response to using one-dimensional horizontal transform skip in the transform block, signs of coefficients in columns other than the first column of the transform block are predicted by a second transform coefficient sign prediction using one or more reconstructed pixels in one or more rows above the transform block.

[0038] In some aspects, in response to using one-dimensional vertical transform skip in the transform block, signs of coefficients in different rows of the transform block are independently predicted by a second transform coefficient sign prediction, where performing the second transform coefficient sign prediction includes predicting coefficient signs of the row using only reconstructed samples adjacent to the row.

[0039] In some aspects, in response to using a one-dimensional vertical transform skip in the transform block, the signs of coefficients in a first row of the transform block are predicted by a second transform coefficient sign prediction based on one or more reconstructed pixels above the transform block; and one or more reconstructed pixels to the left of the transform block.

[0040] In some aspects, in response to using a one-dimensional vertical transform skip in the transform block, signs of coefficients in rows other than the first row of the transform block are predicted by a second transform coefficient sign prediction using one or more reconstructed pixel transform coefficients in one or more columns to the left of the transform block.

[0041] In some aspects, transform coefficient sign prediction is disabled in response to using one-dimensional transform skip in the transform block.

[0042] In some aspects, a first total number of symbols predicted by the second transform coefficient sign prediction when a one-dimensional transform skip is applied to the transform block is different from a second total number of symbols predicted by the first transform coefficient sign prediction when no transform skip is applied in any direction to the transform block.

[0043] In some aspects, in response to using two-dimensional transform skip or forward skip coding (FSC) in the transform block, performing a second transform coefficient sign prediction includes predicting coefficient signs for only pixels in a first row or a first column of the transform block using one or more reconstructed pixels in one or more rows or columns adjacent to the transform block.

[0044] In some aspects, in response to using a two-dimensional transform skip in the transform block, the sign of a coefficient in a top-left pixel of the transform block is predicted by a second transform coefficient sign prediction based on reconstructed pixels above the top-left pixel in one or more rows on the transform block; and one or more reconstructed pixels to the left of the top-left pixel in one or more columns to the left of the transform block.

[0045] In some aspects, in response to using a two-dimensional transform skip in the transform block, signs of coefficients of pixels in a first row of the transform block are predicted by a second transform coefficient sign prediction based on one or more first reconstructed pixels in one or more rows above the transform block and the pixels; and one or more second reconstructed pixels to the left or right of the one or more first reconstructed pixels in the one or more rows.

[0046] In some aspects, in response to using a two-dimensional transform skip in the transform block, the sign of a coefficient of a pixel in a first column of the transform block is predicted by a second transform coefficient sign prediction based on the transform block and one or more first reconstructed pixels in one or more columns to the left of the pixel; and one or more second reconstructed pixels above or below the one or more first reconstructed pixels in the one or more columns.

[0047] In some aspects, transform coefficient sign prediction is not enabled in response to using two-dimensional transform skip in the transform block.

[0048] In some aspects, transform coefficient code prediction is not enabled for intra-coded blocks using a forward skip coding (FSC) mode.

[0049] In some aspects, transform coefficient code prediction is not enabled for inter-coding blocks using a forward skip coding (FSC) mode.

[0050] In some aspects, transform coefficient code prediction is enabled for inter-coding blocks that do not use a forward skip coding (FSC) mode.

[0051] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer, cause the computer to perform any of the methods for video encoding / decoding. [Brief description of the drawings]

[0052] 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 1] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Diagram 3] FIG. 2 is a schematic diagram of a simplified block diagram of a decoder according to one embodiment. [Figure 4] FIG. 2 is a schematic diagram of a simplified block diagram of an encoder according to one embodiment. [Diagram 5] FIG. 4 is a block diagram of an encoder according to another embodiment. [Figure 6] FIG. 4 is a block diagram of a decoder according to another embodiment. [Figure 7A] FIG. 2 illustrates an exemplary coding tree structure according to one embodiment of the present disclosure. [Figure 7B] FIG. 2 illustrates an exemplary coding tree structure according to one embodiment of the present disclosure. [Figure 7C] FIG. 2 illustrates an exemplary multi-type tree splitting mode, according to one embodiment of the present disclosure. [Figure 7D] FIG. 2 illustrates an example quadtree with nested multi-type tree coding block structure in accordance with one embodiment of the present disclosure. [Figure 8] FIG. 1 illustrates an example of a line graph transformation (LGF), according to one embodiment. [Figure 9] FIG. 2 illustrates an example of pixel locations within a transform block and adjacent top two rows and left two columns according to one embodiment. [Figure 10A]1 is a flowchart outlining an example process according to some embodiments of the present disclosure. [Figure 10B] 1 is a flowchart outlining an example process according to some embodiments of the present disclosure. [Figure 11] FIG. 1 is a schematic diagram of a computer system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] FIG. 1 illustrates a simplified block diagram of a communication system (100) according to an embodiment of the present disclosure. The communication system (100) includes a plurality of terminal devices capable of communicating with each other, for example, via a network (150). For example, the communication system (100) includes a first pair of terminal devices (110) and (120) interconnected via the network (150). In the example of FIG. 1, the first pair of terminal devices (110) and (120) perform a unidirectional transmission of data. For example, the terminal device (110) may code video data (e.g., a stream of video pictures captured by the terminal device (110)) for transmission to the other terminal device (120) via the network (150). The coded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (120) may receive the coded video data from the network (150), decode the coded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. One-way data transmission may be common, such as in media serving applications.

[0054] In another example, the communication system (100) includes a second pair of terminal devices (130) and (140) for bidirectional transmission of coded video data, such as may occur during a video conference. In the case of bidirectional transmission of data, in one example, each of the terminal devices (130) and (140) can code video data (e.g., a stream of video pictures captured by the terminal device) for transmission to the other of the terminal devices (130) and (140) over the network (150). Each of the terminal devices (130) and (140) can also receive coded video data transmitted by the other of the terminal devices (130) and (140), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device in accordance with the recovered video data.

[0055] In the example of FIG. 1, the terminal devices (110), (120), (130), and (140) may be depicted as a server, a personal computer, and a smartphone, although the principles of the present invention are not so limited. The embodiments of the present disclosure find application in laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. The network (150) represents any number of networks that convey coded video data between the terminal devices (110), (120), (130), and (140), including, for example, wired and / or wireless communication networks. The communication network (150) may exchange data over circuit-switched and / or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this description, the architecture and topology of the network (150) may not be important to the operation of the present disclosure, unless otherwise described below.

[0056] 2 illustrates an arrangement of a video encoder and a video decoder in a streaming environment as an example of an application of the disclosed subject matter. The disclosed subject matter is equally applicable to other video-enabled applications including, for example, video conferencing, digital TV, and storage of compressed video on digital media including compact discs (CDs), digital video discs (DVDs), memory sticks, and the like.

[0057] The streaming system includes a video source (201), e.g., a digital camera, and a capture subsystem (213) that can create, e.g., a stream of uncompressed video pictures (202). In one example, the stream of video pictures (202) includes samples taken by the digital camera. The stream of video pictures (202) is shown in bold to emphasize its large amount of data compared to the encoded video data (204) (or coded video bitstream) and can be processed by an electronic device (220) that includes an encoder (203) coupled to the video source (201). The video encoder (203) can include hardware, software, or a combination thereof to enable or achieve aspects of the disclosed subject matter, as described in more detail below. The encoded video data (204) (or coded video bitstream (204)) is shown in thin to emphasize its small amount of data compared to the stream of video pictures (202) and can be stored on a streaming server (205) for future use. One or more streaming client subsystems, such as the client subsystems (206) and (208) of FIG. 2, can access the streaming server (205) to obtain copies (207) and (209) of the encoded video data (204). The client subsystem (206) can include a video decoder (210), for example, in an electronic device (230). The video decoder (210) decodes the incoming copy (207) of the encoded video data and creates an output stream (211) of video pictures that can be rendered on a display (212) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (204), (207), and (209) (e.g., a video bitstream) can be encoded according to a particular video coding / compression standard. Examples of these standards include ITU-T Recommendation H.265.As an example, a video coding standard under development is informally known as Versatile Video Coding (VVC), and the disclosed subject matter may be used in the context of VVC.

[0058] It should be noted that electronic devices 220 and 230 may include other components (not shown). For example, electronic device 220 may include a video decoder (not shown), and electronic device 230 may also include a video encoder (not shown).

[0059] 3 shows a block diagram of a video decoder (310) according to one embodiment of the present disclosure. The video decoder (310) can be included in an electronic device (330). The electronic device (330) can include a receiver (331) (e.g., a receiving circuit). The video decoder (310) can be used in place of the example video decoder (210) of FIG. 2.

[0060] The receiver (331) may receive one or more coded video sequences that are decoded by the video decoder (310). In the same or another embodiment, one coded video sequence is decoded at a time, and the decoding of each coded video sequence is independent of the other coded video sequences. The coded video sequences may be received from a channel (301), which may be a hardware / software link to a storage device that stores the coded video data. The receiver (331) may receive the coded video data together with other data, such as coded audio data and / or auxiliary data streams, that may be forwarded to a respective usage entity (not shown). The receiver (331) may separate the coded video sequences from the other data. To address network jitter, a buffer memory (315) may be coupled between the receiver (331) and the entropy decoder / parser (320) (hereinafter "parser (320)"). In certain applications, the buffer memory (315) is part of the video decoder (310). In other cases, the buffer memory may be external to the video decoder (310) (not shown). In yet other cases, there may be a buffer memory (not shown) external to the video decoder (310), e.g., to handle network jitter, and another buffer memory internal to the video decoder (310), e.g., to handle playout timing. If the receiver (331) is receiving data from a store / forward device with sufficient bandwidth and controllability, or from an equally synchronous network, the buffer memory (315) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (315) may be needed and may be relatively large, advantageously of an adaptable size, and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (310).

[0061] The video decoder (310) may include a parser (320) for reconstructing symbols (321) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (310) and potential information for controlling a rendering device, such as a rendering device (312) (e.g., a display screen) that is not an integral part of the electronic device (330) but may also be coupled to the electronic device (330) as shown in FIG. 3. The rendering device control information may be in the form of a Supplemental Enhancement Information (SEI message) or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (320) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence may be performed according to a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, and arithmetic coding with or without context dependency, etc. The parser (320) can extract a set of subgroup parameters for at least one subgroup of pixels in the video decoder from the coded video sequence based on at least one parameter corresponding to the group, including groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), and prediction units (PUs), etc. The parser (320) can also extract information from the coded video sequence, such as transform coefficients, quantization parameter values, and motion vectors.

[0062] The parser (320) can perform an entropy decoding / parsing operation on the video sequence received from the buffer memory (315) to produce symbols (321).

[0063] The reconstruction of the symbols (321) may involve several different units, depending on the type of coded video picture or part thereof (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. Which units are involved and how can be controlled by subgroup control information parsed by the parser (320) from the coded video sequence. The flow of such subgroup control information between the parser (320) and the following units is not shown for clarity.

[0064] Beyond the functional blocks already mentioned, the video decoder (310) may be conceptually subdivided into a number of functional units, as described below. In an actual implementation operating under commercial constraints, many of these units will be closely coupled to each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is appropriate:

[0065] The first unit is a scalar / inverse transform unit (351), which receives quantized transform coefficients and control information including the transform used, block size, quantization factor, quantization scaling row / column, etc. as symbols (321) from the parser (320). The scalar / inverse transform unit (351) can output blocks containing sample values ​​that can be input to an aggregator (355).

[0066] In some cases, the output samples of the scalar / inverse transform (351) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed part of the current picture. Such prediction information may be provided by an intra-picture prediction unit (352). In some cases, the intra-picture prediction unit (352) generates a block of the same size and shape as the block being reconstructed using already reconstructed surrounding information fetched from a current picture buffer (358). The current picture buffer (358) may, for example, buffer a partially reconstructed and / or a fully reconstructed current picture. The aggregator (355) adds, possibly on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (352) to the output sample information provided by the scalar / inverse transform unit (351).

[0067] In other cases, the output samples of the scaler / inverse transform unit (351) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensated prediction unit (353) may access the reference picture memory (357) to fetch samples to use for prediction. After motion compensating the fetched samples according to the symbols (321) related to the block, these samples may be added by the aggregator (355) to the output of the scaler / inverse transform unit (351) (called residual samples or residual signals in this case) to generate output sample information. The addresses in the reference picture memory (357) from which the motion compensated prediction unit (353) fetches prediction samples may be controlled by motion vectors available to the motion compensated prediction unit (353) in the form of symbols (321), which may have, for example, X, Y, and reference picture components. Motion compensation may also include interpolation of sample values ​​fetched from the reference picture memory (357) when using sub-sample accurate motion vectors, motion vector prediction mechanisms, etc.

[0068] The output samples of the aggregator (355) may be subjected to various loop filtering techniques in the loop filter unit (356). The video compression techniques may include in-loop filtering techniques controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (356) as symbols (321) from the parser (320), but may also be responsive to meta-information obtained during decoding of previous (in decoding order) parts of the coded picture or coded video sequence, and may also be responsive to previously reconstructed loop filtered sample values.

[0069] The output of the loop filter unit (356) may be a sample stream that can be output to a rendering device (312) and also stored in a reference picture memory (357) for use in future inter-picture prediction.

[0070] Once a particular coded picture is fully reconstructed, it can be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (320)), the current picture buffer (358) can become part of the reference picture memory (357), and a new current picture buffer can be reallocated before beginning reconstruction of the next coded picture.

[0071] The video decoder (310) may perform decoding operations according to a given video compression technique, such as ITU-T Rec. H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard being used, in the sense that the coded video sequence conforms to both the syntax of the video compression technique or standard and to a profile documented in the video compression technique or standard. In particular, a profile may select a particular tool as the only tool that may be used in the profile, among all tools available in the video compression technique or standard. Compliance also requires that the complexity of the coded video sequence falls within a range defined by the level of the video compression technique or standard. In some cases, the level imposes limitations on the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limitations set by the level may be further restricted in some cases through a hypothetical reference decoder (HRD) specification and HRD buffer management metadata signaled in the coded video sequence.

[0072] In one embodiment, the receiver (331) can receive additional (redundant) data along with the encoded video. The additional data can be included as part of the coded video sequence. The additional data can be used by the video decoder (310) to properly decode the data and / or more accurately reconstruct the original video data. The additional data can 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.

[0073] 4 shows a block diagram of a video encoder (403) according to one embodiment of the present disclosure. The video encoder (403) is included in an electronic device (420). The electronic device (420) includes a transmitter (440) (e.g., a transmission circuit). The video encoder (403) can be used in place of the example video encoder (203) of FIG. 2.

[0074] The video encoder (403) can receive video samples from a video source (401) (which in the example of FIG. 4 is not part of the electronic device (420)) that can capture video images to be coded by the video encoder (403). In another example, the video source (401) is part of the electronic device (420).

[0075] The video source (401) may provide a source video sequence to be coded by the video encoder (403) in the form of a digital video sample stream, which may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.), any color space (e.g., BT.601 Y CrCB, RGB, etc.), and any suitable sampling structure (e.g., Y CrCB 4:2:0, Y CrCB 4:4:4). In a media service provision system, the video source (401) may be a storage device that stores pre-prepared video. In a video conferencing system, the video source (401) may be a camera that captures local image information as a video sequence. The video data may be provided as a number of individual pictures that, when viewed in sequence, give motion. The pictures themselves may be organized as a spatial array of pixels, each pixel may contain one or more samples, depending on the sampling structure, color space, etc., in use. Those skilled in the art will readily appreciate the relationship between pixels and samples. The following description focuses on samples.

[0076] According to one embodiment, the video encoder (403) can code and compress pictures of a source video sequence into a coded video sequence (443) in real-time or under any other time constraint required by the application. Enforcing an appropriate coding rate is one of the functions of the controller (450). In some embodiments, the controller (450) controls and is operatively coupled to other functional units as described below. For clarity, coupling is not shown. Parameters set by the controller (450) may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, etc.), picture size, group of pictures (GOP) layout, and maximum motion vector search range, etc. The controller (450) can be configured to have other appropriate functions associated with the video encoder (403) optimized for a particular system design.

[0077] In some embodiments, the video encoder (403) is configured to operate within a coding loop. As an oversimplified explanation, in one example, the coding loop can include a source coder (430) (e.g., responsible for creating symbols, such as a symbol stream, and reference pictures based on an input picture to be coded) and a (local) decoder (433) embedded in the video encoder (403). The decoder (433) reconstructs the symbols to create sample data in a similar manner as the (remote) decoder would (since in the video compression techniques contemplated by the disclosed subject matter, any compression between the symbols and the coded video bitstream is lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (434). Since the decoding of the symbol stream results in a bit-exact result regardless of the location of the decoder (local or remote), the contents in the reference picture memory (434) are also bit-exact between the local and remote encoders. In other words, the prediction part of the encoder will "see" exactly the same sample values ​​as the reference picture samples that the decoder will "see" when using the prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift if synchrony cannot be maintained, e.g., due to channel errors) is used in several related technologies as well.

[0078] The operation of the "local" decoder (433) may be the same as that of a "remote" decoder, such as the video decoder (310) already described in detail above in connection with Figure 3. However, with brief reference also to Figure 3, because symbols are available and the encoding / decoding of the symbols into a coded video sequence by the entropy coder (445) and parser (320) may be lossless, the entropy decoding portion of the video decoder (310), including the buffer memory (315) and parser (320), may not be fully implemented in the local decoder (433).

[0079] The insight gained at this point is that any decoder technique, other than analysis / entropy decoding, present in the decoder must necessarily be present in the corresponding encoder, in substantially the same functional form. For this reason, the disclosed subject matter focuses on the operation of the decoder. A description of the encoder techniques may be omitted, since they are the inverse of the decoder techniques described generically. Only in certain areas is more detailed explanation required, and so will be described below.

[0080] During operation, in some examples, the source coder (430) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from the video sequence designated as “reference pictures.” In this manner, the coding engine (432) codes differences between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references for the input picture.

[0081] The local video decoder (433) can decode the coded video data of pictures that may be designated as reference pictures based on the symbols created by the source coder (430). The operation of the coding engine (432) can advantageously be a lossy process. When the coded video data is decoded by a video decoder (not shown in FIG. 4), the reconstructed video sequence will typically be a replica of the source video sequence that contains some errors. The local video decoder (433) replicates the decoding process that the video decoder may perform on the reference pictures and cause the reconstructed reference pictures to be stored in the reference picture cache (434). In this way, the video encoder (403) can locally store copies of reconstructed reference pictures that have common content as reconstructed reference pictures (without transmission errors) that the far-end video decoder will obtain.

[0082] The predictor (435) can perform the prediction search for the coding engine (432). That is, for a new picture to be coded, the predictor (435) can search the reference picture memory (434) for sample data (as candidate reference pixel blocks) or specific metadata, such as reference picture motion vectors and block shapes, that can serve as suitable prediction references for the new picture. The predictor (435) can 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 (435), the input picture can have prediction references drawn from multiple reference pictures stored in the reference picture memory (434).

[0083] The controller (450) can manage the coding operations of the source coder (430), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0084] The output of all the aforementioned functional units may undergo entropy coding in an entropy coder (445), 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, and arithmetic coding.

[0085] The transmitter (440) may buffer the coded video sequence produced by the entropy coder (445) in preparation for transmission over a communication channel (460), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (440) may merge the coded video data from the video coder (403) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0086] The controller (450) can manage the operation of the video encoder (403). During coding, the controller (450) can assign a particular coded picture type to each coded picture, which can affect the coding technique that can be applied to each picture. For example, in many cases, pictures can be assigned as any of the following picture types:

[0087] An intra picture (I-picture) may be a picture that can be coded and decoded without using any other picture in a sequence as a prediction source. Some video codecs allow various types of intra pictures, including, for example, Independent Decoder Refresh (IDR) pictures. Those skilled in the art are aware of these variations of I-pictures and their respective uses and characteristics.

[0088] A predictive picture (P picture) may be a picture 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.

[0089] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction that uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-predicted picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0090] A source picture is generally spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and may be coded block by block. Blocks may be predictively coded with 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 or temporal prediction with reference to one previously coded reference picture. Blocks of a B-picture may be predictively coded via spatial or temporal prediction with reference to one or two previously coded reference pictures.

[0091] The video encoder (403) may perform coding operations in accordance with a given video coding technique or standard, such as ITU-T Rec. H.265. In its operations, the video encoder (403) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0092] In one embodiment, the transmitter (440) can transmit additional data along with the encoded video. The source coder (430) can include such data as part of the coded video sequence. The additional data can include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures or slices, SEI messages, and VUI parameter set fragments.

[0093] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlations in a given intra-picture, while inter-picture prediction exploits correlations (temporal or otherwise) between pictures. In one example, a particular picture being coded / decoded (called the current picture) is partitioned into blocks. If a block of the current picture is similar to a reference block of a previously coded and still buffered reference picture in the video, the block of the current picture may be coded by a vector called a motion vector. A motion vector points to a reference block of a reference picture, and may have three dimensions that identify the reference picture if multiple reference pictures are used.

[0094] In some embodiments, bidirectional prediction techniques may be used in inter-picture prediction. According to the bidirectional prediction techniques, two reference pictures, such as a first reference picture and a second reference picture, are used that are earlier in decoding order than the current picture in the video (but may be earlier and later, respectively, in display order). A block of the current picture may be coded by a first motion vector that points to a first reference block of the first reference intra picture and a second motion vector that points to a second reference block of the second reference intra picture. A block may be predicted by a combination of the first reference block and the second reference block.

[0095] Furthermore, merge mode techniques can be used for inter-picture prediction to improve coding efficiency.

[0096] According to some 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, according to the High Efficiency Video Coding (HEVC) standard, pictures in a sequence of video pictures are partitioned into coding tree units (CTUs) for compression, and the CTUs of a picture are of the same size (such as 64×64 pixels, 32×32 pixels, or 16×16 pixels). In general, a CTU includes three coding tree blocks (CTBs): one luma CTB and two chroma CTBs. Each CTU may be recursively 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, four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In one example, each CU is analyzed to determine the prediction type of the CU, such as an inter prediction type or an intra prediction type. A CU is divided into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In one embodiment, prediction operations in coding (encoding / decoding) are performed on a prediction block basis. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values ​​(e.g., luma values) of 8×8 pixels, 16×16 pixels, 8×16 pixels, and 16×8 pixels, etc.

[0097] 5 shows a diagram of a video encoder (503) according to another embodiment of the present disclosure. The video encoder (503) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. In one example, the video encoder (503) is used in place of the example video encoder (203) of FIG. 2.

[0098] In an HEVC example, the video encoder (503) receives a matrix of sample values ​​for a processing block, such as a predictive block of 8x8 samples. The video encoder (503) determines whether the processing block is best coded using intra mode, inter mode, or bi-predictive mode, e.g., using rate-distortion optimization. If the processing block is coded in intra mode, the video encoder (503) can use intra prediction techniques to code the processing block into a coding picture. If the processing block is coded in inter mode or bi-predictive mode, the video encoder (503) can use inter prediction or bi-predictive techniques, respectively, to code the processing block into a coding picture. In certain video coding techniques, the merge mode can be an inter-picture prediction sub-mode in which motion vectors are derived from one or more motion vector predictors without the benefit of any coded motion vector components outside the predictors. In other certain video coding techniques, there may be motion vector components applicable to a subject block. In one example, the video encoder (503) includes other components, such as a mode decision module (not shown) for determining the mode of the processing block.

[0099] In the example of FIG. 5, the video encoder (503) includes an inter-encoder (530), an intra-encoder (522), a residual calculator (523), a switch (526), ​​a remainder encoder (524), a general controller (521), and an entropy encoder (525) coupled together as shown in FIG. 5.

[0100] The inter-encoder (530) is configured to receive samples of a current block (e.g., a processing block), compare the block with one or more reference blocks of a reference picture (e.g., blocks of a previous picture and a subsequent intra picture), generate inter-prediction information (e.g., a description of redundant information due to an inter-coding technique, motion vectors, merge mode information), and calculate an inter-prediction result (e.g., a prediction block) using any suitable technique based on the inter-prediction information. In some examples, the reference picture is a decoded reference picture that is decoded based on the encoded video information.

[0101] The intra encoder (522) is configured to receive samples of a current block (e.g., a processing block), possibly compare the block with previously coded blocks in the same intra picture, generate quantized coefficients after transformation, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In one example, the intra encoder (522) also calculates intra prediction results (e.g., predicted blocks) based on the intra prediction information and reference blocks of the same intra picture.

[0102] The general controller (521) is configured to determine general control data and control other components of the video encoder (503) based on the general control data. In one example, the general controller (521) determines the mode of the block and provides a control signal to the switch (526) based on the mode. For example, if the mode is an intra mode, the general controller (521) controls the switch (526) to select an intra mode result to be used by the residual calculator (523) and controls the entropy encoder (525) to select intra prediction information and include the intra prediction information in the bitstream. If the mode is an inter mode, the general controller (521) controls the switch (526) to select an inter prediction result to be used by the residual calculator (523) and controls the entropy encoder (525) to select inter prediction information and include the inter prediction information in the bitstream.

[0103] The residual calculator (523) is configured to calculate the difference (residual data) between the received block and a prediction result selected from the intra-encoder (522) or the inter-encoder (530). The residual encoder (524) is configured to operate on the residual data to encode the residual data and generate transform coefficients. In one example, the residual encoder (524) is configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. A quantization process is then performed on the transform coefficients to obtain quantized transform coefficients. In various embodiments, the video encoder (503) also includes a residual decoder (528). The residual decoder (528) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (522) and the inter-encoder (530) as appropriate. For example, the inter-encoder (530) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (522) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are suitably processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

[0104] The entropy encoder (525) is configured to format a bitstream to include the encoded block. The entropy encoder (525) is configured to include various information in accordance with an appropriate standard, such as the HEVC standard. In one example, the entropy encoder (525) is configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other appropriate information in the bitstream. It should be noted that, in accordance with the disclosed subject matter, when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information is not present.

[0105] 6 shows a diagram of a video decoder (610) according to another embodiment of the present disclosure. The video decoder (610) is configured to receive coded pictures that are part of a coded video sequence and to decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (610) is used in place of the video decoder (210) of the example of FIG. 2.

[0106] In the example of FIG. 6, the video decoder (610) includes an entropy decoder (671), an inter-decoder (680), a residual decoder (673), a reconstruction module (674), and an intra-decoder (672) coupled together as shown in FIG. 6.

[0107] The entropy decoder (671) may be configured to reconstruct from the coded picture certain symbols that represent syntax elements that make up the coded picture. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that can identify the mode in which the block is coded (e.g., intra- or inter-prediction mode, merged submode or the latter two in another submode, etc.), certain samples or metadata used for prediction by the intra- or inter-decoder (672) or inter-decoder (680), respectively, residual information, e.g., in the form of quantized transform coefficients, etc. In one example, the inter-prediction information is provided to the inter-decoder (680) when the prediction mode is an inter- or bi-prediction mode. The intra-prediction information is provided to the intra-decoder (672) when the prediction type is an intra-prediction type. The residual information may undergo inverse quantization and is provided to the residual decoder (673).

[0108] The inter decoder (680) is configured to receive the inter prediction information and to generate inter prediction results based on the inter prediction information.

[0109] The intra decoder (672) is configured to receive the intra prediction information and to generate a prediction result based on the intra prediction information.

[0110] The residual decoder (673) is configured to perform inverse quantization to extract inverse quantized transform coefficients and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (673) may also require certain control information (to include quantization parameters (QP)), which may be provided by the entropy decoder (671) (a data path is not shown as this may only be a small amount of control information).

[0111] The reconstruction module (674) is configured to combine, in the spatial domain, the residual output by the residual decoder (673) and a prediction result (possibly output by an inter- or intra-prediction module) to form a reconstructed block, which may be part of a reconstructed picture and may also be part of a reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0112] It should be noted that the video encoders (203), (403), and (503) and the video decoders (210), (310), and (610) may be implemented using any suitable technology. In one embodiment, the video encoders (203), (403), and (503) and the video decoders (210), (310), and (610) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (203), (403), and (403) and the video decoders (210), (310), and (610) may be implemented using one or more processors executing software instructions.

[0113] This disclosure includes video encoding techniques that may be applied to various video coding technologies and / or standards, including, but not limited to, HEVC, VVC, and AV1. AV1 stands for AOMedia Video 1 (AV1). AOMedia stands for Alliance for Open Media (AOMedia).

[0114] As shown in the first coding tree structure (700) of Figure 7A, VP9 uses a 4-way partition tree that starts at the 64x64 level and goes down to the 4x4 level, with some additional restrictions on blocks 8x8. In Figure 7A, the partitions designated as R can be called recursive in that the same partition tree is repeated at lower scales until the lowest 4x4 level is reached.

[0115] As shown in the second coding tree structure (702) of FIG. 7B, AV1 not only extends the partition tree to a 10-way structure, but also increases the maximum size (called superblock in VP9 / AV1 terminology) to start at 128×128. Note that this includes the 4:1 / 1:4 rectangular partition, which did not exist in VP9. The partition type with three subpartitions in the second row of FIG. 7B is called a "T-shaped" partition. Note that rectangular partitions cannot be further subdivided. In addition to the size of the coding block, a coding tree depth is specified, which indicates the division depth from the root node. Specifically, the coding tree depth of the root node, e.g., 128×128, is set to 0, and after one further division of the tree block, the coding tree depth is increased by 1.

[0116] Instead of enforcing a fixed transform unit size as in VP9, ​​AV1 allows partitioning of luma coding blocks into transform units of multiple sizes that can be represented by recursive partitioning going down up to two levels. To incorporate AV1's extended coding block partitioning, transform sizes from 4x4 to 64x64 square, 2:1 / 1:2, and 4:1 / 1:4 are supported. In the case of chroma blocks, only the largest possible transform units are allowed.

[0117] In order to adapt to various local characteristics in HEVC, etc., CTUs can be divided into CUs by using a quadtree structure, denoted as a coding tree. The decision on whether to code a picture region using inter-picture (temporal) prediction or intra-picture (spatial) prediction is made at the CU level. Each CU can be further divided into one, two, or four PUs depending on the PU partition type. Within one PU, the same prediction process is applied, and related information is sent to the decoder for each PU. After applying the prediction process based on the PU partition type to obtain the residual block, the CU can be partitioned into TUs according to another quadtree structure, similar to the coding tree of the CU. One of the important features of the HEVC structure is that there are multiple partition concepts, including CU, PU, ​​and TU. In HEVC, a CU or TU is only square, but in the case of inter-prediction blocks, a PU can be square or rectangular. In HEVC, one coding block can be further divided into four square sub-blocks, and a transformation is performed on each sub-block, i.e., TU. Each TU can be further recursively divided (using quadtree decomposition) into smaller TUs, which are called residual quadtrees (RQTs).

[0118] At picture boundaries such as HEVC, implicit quadtree partitioning may be used so that a block continues to be quadtree partitioned until its size fits into the picture boundary.

[0119] A quaternary tree with nested multi-type trees using binary split and ternary split segmentation structures such as VVC can replace the concept of multiple partition unit types, i.e., eliminate the separation of CU, PU, ​​and TU concepts except as required for CUs with sizes that are too large for the maximum transform length, and support flexibility in CU partition shapes. In the coding tree structure, CUs can have either square or rectangular shapes. ACTUs are first partitioned by a quaternary tree (also called a quad-tree) structure. The leaf nodes of the quaternary tree can be further partitioned by a multi-type tree structure. As shown in the third coding tree structure (704) of FIG. 7C, the multi-type tree structure includes four split types. For example, the multi-type tree structure includes vertical bisection (SPLIT_BT_VER), horizontal bisection (SPLIT_BT_HOR), vertical trisection (SPLIT_TT_VER), and horizontal trisection (SPLIT_TT_HOR). The leaf nodes of the multi-type tree are called CUs, and this segmentation is used for prediction and transformation processes without further partitioning, unless the CU is too large for the maximum transform length. This means that in most cases, the block sizes of CUs, PUs, and TUs are the same in a quad-tree with a nested multi-type tree coding block structure. An exception occurs when the maximum supported transform length is smaller than the width or height of a color component of a CU. An example of block partitions for one CTU is shown in Figure 7D, which shows an example quad-tree with a nested multi-type tree coding block structure.

[0120] In VVC, etc., the maximum supported luma transform size may be 64 x 64 and the maximum supported chroma transform size may be 32 x 32. If the width or height of the CB is larger than the maximum transform width or height, the CB is automatically split in the horizontal and / or vertical direction to fit the transform size limitation in that direction.

[0121] In VTM7 and other coding tree schemes, the ability for luma and chroma to have separate block tree structures is supported. In some cases, for P and B slices, the luma CTB and chroma CTB in one CTU need to share the same coding tree structure. However, for I slices, luma and chroma can have separate block tree structures. When the separate block tree mode is applied, the luma CTB is partitioned into CUs by one coding tree structure, and the chroma CTB is partitioned into chroma CUs by another coding tree structure. This means that a CU in an I slice may contain or consist of a coding block of a luma component or a coding block of two chroma components, and a CU in a P or B slice may always contain or consist of coding blocks of all three color components, unless the video is monochrome.

[0122] To support extended coding block partitions, multiple transform sizes (e.g., ranging from 4 points to 64 points in each dimension) and transform shapes (e.g., square, rectangular with width / height ratios of 2:1 / 1:2, and 4:1 / 1:4) may be used in AV1, etc.

[0123] The 2D transformation process may include the use of hybrid transform kernels (e.g., composed of a different 1D transform for each dimension of the coded residual block). The first-order 1D transforms may include a) 4-, 8-, 16-, 32-, 64-point DCT-2, b) 4-, 8-, 16-point asymmetric DST (DST-4, DST-7) and their inverse versions, or c) 4-, 8-, 16-, 32-point identity transforms. The basis functions for the DCT-2 and asymmetric DST as used in AV1 are shown in Table 1, where "→" and "↓" indicate the horizontal and vertical dimensions,

number

number

[0124] The availability of hybrid transform kernels may be based on the transform block size and prediction mode. An example of the dependency is shown in Table 2. [Table 2] JPEG2025507466000006.jpg44166

[0125] For chroma components, the selection of the transform type is done in an implicit manner. For intra-prediction residuals, the transform type is selected according to the intra-prediction mode, e.g., as specified in Table 3. For inter-prediction residuals, the transform type may be selected according to the selection of the transform type of the co-located luma block. Thus, for chroma components, no signaling of the transform type in the bitstream is required. [Table 3]

[0126] Line graph transformations (LGTs) such as AV2 have been introduced with the aim of replacing and extending the 1D DST mentioned above (by introducing 32-point and 64-point).

[0127] A graph is a general mathematical structure that includes or consists of a set of vertices and edges, which are used to model affinity relationships between objects of interest. In practice, weighted graphs (where a set of weights are assigned to edges and possibly vertices) provide a sparse representation for robust modeling of signals / data. LGTs can improve coding efficiency by better adapting to various block statistics. A separable LGT is designed and optimized by learning a line graph from the data to model the row- and column-wise statistics underlying the blocks in the residual signal, where the associated Generalized Graph Laplacian (GGL) matrix is ​​used to derive the LGT. Figure 8 shows the weights of the self-loop v c1 , v c2 , and edge weight w c An example of LGT(800) characterized by:

[0128] Given a weighted graph G(W,V), the GGL matrix may be defined as follows: L c =D-W+V where W is the non-negative edge weight w c where D is a diagonal order matrix, and V is a weighted self-loop v c1 , v c2 The matrix L is a diagonal matrix that represents c can be expressed as follows:

number

[0129] Next, LGT is GGL L c It can be derived by eigendecomposition of L c =UΦU T 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 DST-7, are LGTs derived from a particular form of the GGL as follows:

[0130] DCT-2 is v c1 = 0.

[0131] DST-7 is a c1 =w c It can be derived by setting

[0132] DCT-8 is v c2 =w c It can be derived by setting

[0133] DST-4 is v c1 =2w c It can be derived by setting

[0134] DCT-4 is v c2 =2w c It can be derived by setting

[0135] LGT such as AV2 can be implemented as a matrix multiplication. 4p LGT cores are c . c1 =2w c This means that the core is a DST-4. The 8p LGT core is c . c1 =1.5w c The 16p, 32p, and 64p LGT cores can be derived by setting L c . c1 =w c which means that the core is DST-7.

[0136] In an example of residual coding in AV1, for each transform unit, AV1 coefficient coding starts with signaling of a skip sign, followed by the transform kernel type and the end of block (eob) position when the skip sign becomes zero. Then, each coefficient value is mapped to multiple level maps and signs.

[0137] After coding the eob position, the lower level map and the mid level map are coded in reverse scan order, with the former (low level map) indicating whether the magnitude of the coefficient is between 0 and 2, and the latter (mid level map) indicating whether the range is between 3 and 14. The next step, in forward scan order, is to code the signs of the coefficients and the residual values ​​of the coefficients greater than 14 by Exp-Golomb code.

[0138] Regarding the use of context modeling, the low-level map coding incorporates the transform size and direction as well as up to five neighboring coefficient information, while the mid-level map coding follows a similar approach to the low-level map coding, except that the number of neighboring coefficients drops to two. The Exp-Golomb code of the residual level and the signs of the AC coefficients are coded without a context model, while the signs of the DC coefficients are coded using the DC codes of the neighboring transform units.

[0139] In one example of residual coding for transform skip, such as VVC, a CU coded in transform skip mode (TSM) can use a modified transform coding process. The modifications can be summarized as follows: (a) all sub-blocks and positions within the sub-blocks are scanned in forward scan order; (b) the last significant coefficient position is not signaled; (c) the syntax element coded_sub_block_flag is not coded for the last sub-block; (d) changes are made to the context modeling of the syntax sig_coeff_flag, abs_level_gt1, and par_level_flag; (e) the sign flag is context coded based on the left and top neighboring values.

[0140] During the development of AV2, a new mode called forward skip coding (FSC) was introduced to modify the transform coding process of IDTX (2-dimensional transform skip). The modifications introduced by FSC are functionally similar to the above changes introduced in the VVC transform skip mode, but can be summarized as follows: (a) all coding blocks and positions within coding blocks are scanned in forward scan order; (b) the EOB syntax is skipped; (c) a reduced context is used for the coefficient levels; (d) the sign flags are context coded based on left, bottom, and bottom-left.

[0141] For intra blocks, when FSC mode is selected, no transform type is signaled for the transform block. Rather, the signaling of the transform type is packed into the FSC mode at the coding block level. Inter blocks do not signal the FSC mode, but if the transform type is IDTX and the screen content flag is enabled, the FSC scheme is implicitly selected.

[0142] In the case of entropy coding of transform coefficients, the coefficient signs are typically coded separately from the magnitude / level (absolute value of the coefficient values) using a bypass mode. Separate coding means that coding each coefficient sign costs one bit, which can be expensive. To improve the entropy coding efficiency of the coefficient signs, JVET-D0031 (JVET stands for Joint The Joint Video Expert Team (Video Exploration Team) and others have proposed code prediction methods. In one example, instead of signaling the code value, a flag indicating whether the predicted code is the same as the actual code is entropy coded using a context. The context value depends on the level of the coefficient (the absolute value of the coefficient value). This is because the higher the level value, the more accurate the predicted code value.

[0143] First, a group of transform coefficients are identified such that their associated signs need to be predicted. Then, a set of hypotheses for the predicted sign values ​​of these coefficients is created. For example, for three coefficients, the number of hypotheses can be up to 8 (2^3). To predict the sign values, each hypothesis has a cost value associated with it, and the hypothesis with the smallest cost is used to specify the predicted sign values ​​of the coefficients covered by the hypothesis.

[0144] Figure 9 shows an example of pixel locations in a transformed block (900) and its neighbors in the top two rows (902) and left two columns (904). The cost of each hypothesis is calculated as follows: A reconstructed block associated with a given hypothesis (hypothetical reconstruction) is generated according to the usual reconstruction process (inverse quantization, inverse transformation) and the boundary samples of the reconstructed block, i.e. p 0,y and p x,0 The reconstructed pixel p on the left boundary of the reconstructed block is derived. 0,y For each pixel, we perform a simple linear prediction using the two previously reconstructed neighboring pixels to the left and calculate the prediction, pre 0,y =(2p -1,y -p -2,y) and the prediction and the reconstructed pixel p 0,y The absolute difference between is added to the cost of the hypothesis. A similar process is performed for the pixels in the upper row of the reconstructed block, and each prediction pred x,0 =(2p x,-1 -p x,-2 ) and the reconstructed pixel p x,0 The absolute values ​​of the differences between and are summed. Thus, the cost of each coefficient sign prediction hypothesis is calculated as follows:

number

[0145] In some embodiments, when a transform skip (identity transform) is applied to one or both dimensions of a block, or when an FSC mode is used for a coding block, the reconstructed neighboring pixels and pixels in the current block may not be correlated. Thus, the method of coefficient sign prediction may need to be modified to improve coding efficiency.

[0146] The embodiments of the present disclosure include transform coefficient sign prediction, such as when transform skip is applied in one or both dimensions. The methods of the present invention may be used individually or in combination in any order. Furthermore, each of the methods (or embodiments), encoders, and decoders may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits (ICs)). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium.

[0147] In this disclosure, the term block may refer to coefficients in a transform block, the term row may refer to a row of coefficients in a transform block, and the term column may refer to a column of coefficients in a transform block. Aspects of this disclosure may also be applied to other embodiments, for example, by replacing IDTX with transform skip or vice versa.

[0148] The set of transform types with horizontal transform skips may be referred to as Set A. In one example, Set A exhaustively includes, and possibly includes all combinations of, 1-D transforms, where the transform kernel is a matrix. Examples of 1-D transforms include, but are not limited to, DCT, ADST, FLIPADST, LGT, FLIPLGT, KLT, all trigonometric transform types (DCT types 1-8, DST types 1-8), and their vertical derivatives and horizontal transform skips.

[0149] The set of transform types with vertical transform skips may be referred to as Set B. In one example, Set B exhaustively includes, and possibly includes all combinations of, 1-D transforms, where the transform kernel is a matrix. Examples of 1-D transforms include, but are not limited to, DCT, ADST, FLIPADST, LGT, FLIPLGT, KLT, all trigonometric transform types (DCT types 1-8, DST types 1-8), and their horizontal derivatives and vertical transform skips.

[0150] The method can be applied to luma blocks and / or chroma blocks. The sign coefficients can be predicted differently based on whether an identity transform / transform skip is used in the transform block. In some examples, when a one-dimensional identity transform / transform skip is used in the transform block, the signs of N coefficients in different columns (e.g., in the case of a horizontal transform skip) or different rows (e.g., in the case of a vertical transform skip) are predicted differently compared to the sign prediction process when the identity transform / transform skip is not applied.

[0151] In some example embodiments, when a one-dimensional identity transform / transform skip is used in a transform block, the signs of N coefficients in different columns (e.g., in the case of horizontal transform skip) or different rows (e.g., in the case of horizontal transform skip) are predicted independently using adjacent reconstructed samples.

[0152] In one embodiment, when applying the one-dimensional identity transform, sign prediction is disabled.

[0153] In one embodiment, when transform skip is applied only horizontally, the signs of the N coefficients in the first column are predicted using reconstructed pixels in one or more columns to the left of the first column and reconstructed pixels in one or more rows above the first column, for example, K pixels in A column to the left of the first column and B rows above of the transform block. Example values ​​of A include, but are not limited to, values ​​of 2 or greater. Example values ​​of K include, but are not limited to, values ​​of 1 or greater. Example values ​​of B include, but are not limited to, values ​​of 2 or greater.

[0154] For example, referring to FIG. 9, when transform skip is applied only horizontally, the coefficient p 0,1 To predict the sign of, we use the reconstructed pixels in the two columns to the left of the first column of the transformation block (pixel p -1,0 ~p -1,3 and p -2,0 ~p -2,3 ) and p 0,1 The two pixels p in the top two rows immediately above 0,-1 and p 0,-2 and are used.

[0155] In one embodiment, when transform skip is applied only vertically, the signs of the N coefficients in the first row are predicted using reconstructed pixels in one or more rows above the top row of the transform block and reconstructed pixels in one or more first columns to the left of the first row, for example, K pixels in the A row above the top row and the B column to the left of the transform block. Example values ​​of A include, but are not limited to, values ​​of 2 or greater. Example values ​​of K include, but are not limited to, values ​​of 1 or greater. Example values ​​of B include, but are not limited to, values ​​of 2 or greater.

[0156] For example, referring to FIG. 9, the coefficient p 1,0 To predict the sign of , we use the reconstructed pixels in the top two rows of the first row (pixel p 0,-1 ~p 3,-1 , and p0,-2 ~p 3,-2 ) and the two adjacent pixels p -2,0 and p -1,0 is used.

[0157] In one embodiment, when transform skip is applied horizontally, the signs of the N coefficients in each column except the first column are predicted using reconstructed pixels in M ​​rows above the top row of the transform block, where example values ​​of M include, but are not limited to, values ​​of 2 or greater.

[0158] In one embodiment, when applying transform skip vertically, the signs of the N coefficients in each row except the first row are predicted using the reconstructed pixels in M ​​columns to the left of the first column of the transform block. Exemplary values ​​of M include, but are not limited to, values ​​of 2 or greater.

[0159] In one embodiment, the number of coefficient signs predicted when applying a one-dimensional transform skip is different from the number of coefficient signs predicted when no transform skip is applied in any direction. In one example, the number of coefficient signs predicted when applying a one-dimensional transform skip is less than the number of coefficient signs predicted when no transform skip is applied in any direction. In another example, the number of coefficient signs predicted when applying a one-dimensional transform skip may be greater than the number of coefficient signs predicted when no transform skip is applied in any direction.

[0160] In some embodiments, only coefficient signs of N pixels in the first row / column of the transform block are predicted. The coefficient signs may be predicted based on reconstructed pixels in one or more columns to the left of the transform block and / or one or more rows above the transform block. In one example, in certain modes, such as when using 2-dimensional transform skip or when using FSC mode for the coding block, only coefficient signs of N pixels in the first row / column of the transform block are predicted. For example, coefficient signs of N pixels only in the first row / column of the transform block are predicted using K neighboring pixels in the top A rows or left B columns adjacent to the transform block. Example values ​​of K include, but are not limited to, values ​​of 1 or greater. Example values ​​of A include, but are not limited to, values ​​of 2 or greater. Example values ​​of B include, but are not limited to, values ​​of 2 or greater.

[0161] In one embodiment, when transform skip is applied in both directions, the coefficient sign of the top-left pixel may be predicted based on pixels in one or more rows above the top row of the transform block and / or one or more columns to the left of the first column of the transform block. In one example, the coefficient sign of the top-left pixel may be predicted using K adjacent pixels in M ​​rows above the top row and L adjacent pixels in N columns to the left of the first column. Example values ​​of K include, but are not limited to, values ​​of 1 or greater. Example values ​​of M include, but are not limited to, values ​​of 2 or greater. Example values ​​of L include, but are not limited to, values ​​of 1 or greater. Example values ​​of N include, but are not limited to, values ​​of 2 or greater.

[0162] For example, referring to the transform block (900) of FIG. 0,0 The coefficient sign of is two pixels from each of the top two rows, namely p 0,-1 , p 0,-2 and two pixels from each of the left two columns, namely p -1,0 , p -2,0 and are predicted using

[0163] In one embodiment, when applying transform skip in both directions, the coefficient signs of the N pixels in the first row are predicted based on pixels in one or more rows above the top row of the transform block and / or one or more columns to the left of the first column of the transform block. In one example, the coefficient signs of the N pixels in the first row are predicted using adjacent K pixels in M ​​rows above the top row of the transform block. Example values ​​of K include, but are not limited to, values ​​of 1 or greater. Example values ​​of M include, but are not limited to, values ​​of 2 or greater.

[0164] For example, referring to the transform block (900) of FIG. 1,0 The coefficient signs of are two pixels from each of the top two rows, namely p 1,-1 , p 1,-2 , p 0,-1 , p 0,-2 The pixel p 2,0 The coefficient signs of are two pixels from each of the top two rows, namely p 2,-1 , p 2,-2 , p 3,-1 , p 3,-2 Alternatively, for example, pixel p 1,0 The coefficient sign of p 1,-1 , p 1,-2 , p 3,-1 , p 3,-2 Alternatively, for example, pixel p 2,0 The coefficient sign of p 2,-1 , p 2,-2 , p 1,-1 , p 1,-2 may be used to make predictions.

[0165] In one embodiment, when transform skip is applied in both directions, the coefficient signs of the N pixels in the first column are predicted based on pixels in one or more rows above the top row of the transform block and / or one or more columns to the left of the first column of the transform block. In one example, the coefficient signs of the N pixels in the first column are predicted using K neighboring pixels in M ​​columns to the left of the first column of the transform block. Example values ​​of K include, but are not limited to, values ​​of 1 or greater. Example values ​​of M include, but are not limited to, values ​​of 2 or greater. For example, pixel p 0,1 The coefficient signs of are expressed as two pixels from each of the left two columns, namely p -1,1 , p -2,1 , p -1,0 , p -2,0 and the pixel p 0,2 The coefficient signs of are expressed as two pixels from each of the left two columns, namely p -1,2 , p -2,2 , p -1,3 , p -2,3 may be used to make predictions.

[0166] In one embodiment, when using 2-D transform skip, coefficient sign prediction is not applied at all.

[0167] In one embodiment, for intra-coded blocks using FSC mode, coefficient sign prediction is not enabled.

[0168] In one embodiment, for inter-coded blocks using FSC mode, coefficient sign prediction is not enabled.

[0169] In one embodiment, for inter-coded blocks that do not use the FSC mode, coefficient sign prediction is enabled.

[0170] Some aspects include an apparatus having a memory that stores instructions and a processor in communication with the memory, where the processor is configured to cause the apparatus to perform some or all of the steps described in this disclosure when the processor executes the instructions.

[0171] Some aspects include a non-transitory computer-readable storage medium storing computer-readable instructions that, when executed by one or more processors, are configured to cause the one or more processors to perform some or all of the steps described in this disclosure.

[0172] FIG. 10A shows a flow chart outlining a process (1000) according to one embodiment of the present disclosure. The process (1000) can be used to reconstruct a block to generate a prediction block for the block being reconstructed. In various embodiments, the process (1000) is performed by a processing circuit, such as the processing circuit in the terminal devices (110), (120), (130), and (140), where the processing circuit performs the function of a video encoder (203), the processing circuit performs the function of a video decoder (210), the processing circuit performs the function of a video decoder (310), the processing circuit performs the function of a video encoder (403), etc. In some embodiments, the process (1000) is implemented with software instructions, such that the processing circuit performs the process (1000) as the processing circuit executes the software instructions. Processing begins at (S1001) and proceeds to (S1010).

[0173] At (S1010), the method (1000) includes receiving a coded video stream including a current block associated with a transform block.

[0174] At (S1020), the method (1000) includes a step of determining whether to use a transform skip in the transform block.

[0175] In (S1030), the method (1000) includes a step of performing a first transform coefficient sign prediction in response to a determination that a transform skip is not used in the transform block. The first transform coefficient sign prediction includes a step of predicting a first sign of the first plurality of transform coefficients based on the first plurality of adjacent samples, and a step of predicting a second sign of the second plurality of transform coefficients based on the second plurality of adjacent samples. The prediction of the first sign of the first plurality of transform coefficients is independent from the prediction of the second sign of the second plurality of transform coefficients. In (S1040), the method (1000) includes a step of reconstructing the current block based on the first plurality of transform coefficients and the second plurality of transform coefficients.

[0176] FIG. 10B shows a flow chart outlining the process (1050) according to one embodiment of the disclosure. The process (1050) can be used to reconstruct a block to generate a prediction block for the block being reconstructed. In various embodiments, the process (1050) is performed by a processing circuit, such as the processing circuit in the terminal devices (110), (120), (130), and (140), where the processing circuit performs the function of a video encoder (203), the processing circuit performs the function of a video decoder (210), the processing circuit performs the function of a video decoder (310), the processing circuit performs the function of a video encoder (403), etc. In some embodiments, the process (1050) is implemented with software instructions, such that the processing circuit performs the process (1050) as the processing circuit executes the software instructions. Processing begins at (S1051) and proceeds to (S1060).

[0177] At (S1060), the method (1050) includes a step of determining whether a transform skip is used in the transform block. For example, the method (1050) can determine whether a 1-D horizontal transform skip, a 1-D vertical transform skip, a 2-D transform skip, or an FSC is used in the transform block.

[0178] At (S1070), the method (1050) includes performing a transform coefficient sign prediction based on whether it is determined that a transform skip is to be used in the transform block. At (S1080), the method (1050) includes determining a transform coefficient based on whether it is determined that a transform skip is to be used in the transform block. At (S1090), the method (1050) includes reconstructing the current block based on the determined transform coefficients, the transform coefficient sign prediction being a first transform coefficient sign prediction performed for the transform block in response to determining that a transform skip is not to be used in the transform block.

[0179] For example, if 1D horizontal transform skip, 1D vertical transform skip, 2D transform skip, or FSC is not used in the transform block, the method (1050) can perform a first coefficient sign prediction as follows: First, a group of transform coefficients is identified such that the associated sign needs to be predicted. Then, a set of hypotheses for the predicted sign values ​​of these coefficients is created. For example, for three coefficients, the number of hypotheses can be up to 8 (2^3). To predict the sign values, there is a cost value associated with each hypothesis, and the least cost hypothesis is used to specify the predicted sign value of the coefficient covered by the hypothesis. Figure 9 shows an example of pixel locations in a transform block (900) and its neighbors in the top two rows (902) and left two columns (904). The cost of each hypothesis is calculated as follows: A reconstructed block (hypothetical reconstruction) associated with a given hypothesis is generated according to the usual reconstruction process (inverse quantization, inverse transform) and the boundary samples of the reconstructed block, i.e., p 0,y and p x,0 The reconstructed pixel p on the left boundary of the reconstructed block is derived. 0,y For each pixel, a simple linear prediction is performed using the two previously reconstructed neighboring pixels on the left, and the prediction, pred 0,y =(2p -1,y -p -2,y ) and the prediction and the reconstructed pixel p 0,yThe absolute difference between X,0 =(2p x,-1 -p x,-2 ) and the reconstructed pixel p x,0 The absolute values ​​of the differences between and are summed. Thus, the cost calculation for each code prediction hypothesis is:

number

[0180] In some optional aspects, the transform coefficient sign prediction is a second transform coefficient sign prediction performed on the transform block in response to determining to use a transform skip in the transform block, the second transform coefficient sign prediction being different from the first transform coefficient sign prediction. In some other optional aspects, the first transform coefficient sign prediction is disabled in response to using a transform skip in the transform block.

[0181] For example, when one-dimensional horizontal transform skip, one-dimensional vertical transform skip, two-dimensional transform skip, or FSC is used in the transform block, the method (1050) may either skip the above-mentioned first coefficient sign prediction for a row or column of the transform block, or perform a second coefficient sign prediction different from the above-mentioned first coefficient sign prediction. This is because when the transform skip (identity transform) is applied in one or both dimensions of the block, or when the FSC mode is used in the coding block, the reconstructed neighboring pixels may not correlate with the pixels in the current block. Thus, the method of coefficient sign prediction may be modified to improve coding efficiency. For example, when one-dimensional identity transform / transform skip is used in the transform block, the signs of N coefficients in different columns (in the case of horizontal transform skip) or different rows (in the case of vertical transform skip) are predicted in a different way compared to the sign prediction process when the identity transform / transform skip is not applied. In one embodiment, the sign prediction is disabled when the one-dimensional identity transform is applied.

[0182] In one embodiment, for example, in response to using one-dimensional horizontal transform skip in the transform block, signs of coefficients in different columns of the transform block are independently predicted by a second transform coefficient sign prediction, where performing the second transform coefficient sign prediction includes predicting coefficient signs of the column using only reconstructed samples adjacent to the column.

[0183] In one embodiment, for example, in response to using one-dimensional horizontal transform skip in the transform block, the signs of coefficients in the first column of the transform block are predicted by a second transform coefficient sign prediction based on one or more reconstructed columns to the left of the transform block and one or more reconstructed pixels above the first column of the transform block. For example, when applying transform skip only in the horizontal direction, the signs of N coefficients in the first column are predicted using reconstructed pixels in A columns (example values ​​of A include, but are not limited to, 2, 3, . . .) to the left of the first column of the transform block, and K pixels (example values ​​of K include, but are not limited to, 1, 2, 3, . . .) in the top B row (example values ​​of B include, but are not limited to, 2, 3, . . .). For example, referring to FIG. 9, when applying transform skip only in the horizontal direction, the signs of coefficients p 0,1 To predict the sign of , we use the reconstructed pixels in the two columns to the left of the first column of the transformation block (pixel p -1,0 ~p -1,3 , and p -2,0 ~p -2,3 ) and p 0,1 The two pixels p in the top two rows immediately above 0,-1 and p 0,-2 is used.

[0184] In one embodiment, for example, in response to using one-dimensional horizontal transform skip in the transform block, signs of coefficients in columns other than the first column of the transform block are predicted by a second transform coefficient sign prediction using one or more reconstructed pixels in one or more rows above the transform block. For example, when applying transform skip horizontally, signs of N coefficients in each column except the first column are predicted using reconstructed pixels in M ​​rows above the top row of the transform block (example values ​​of M include, but are not limited to, 2, 3, ...).

[0185] In one embodiment, for example, in response to using a one-dimensional vertical transform skip in the transform block, signs of coefficients in different rows of the transform block are independently predicted by a second transform coefficient sign prediction, where performing the second transform coefficient sign prediction includes predicting coefficient signs of the row using only reconstructed samples adjacent to the row.

[0186] In one embodiment, for example, in response to using one-dimensional vertical transform skip in the transform block, the sign of the coefficient in the first row of the transform block is predicted by the second transform coefficient sign prediction based on one or more reconstructed rows above the transform block and one or more reconstructed pixels to the left of the transform block. For example, when applying transform skip only vertically, the sign of N coefficients in the first row is predicted using reconstructed pixels in A rows above the top row of the transform block (example values ​​of A include, but are not limited to, 2, 3, . . .) and K pixels (example values ​​of K include, but are not limited to, 1, 2, 3, . . .) in B columns to the left (example values ​​of B include, but are not limited to, 2, 3, . . .). For example, referring to FIG. 9, coefficient p in the first row of the transform block (900) is predicted using the reconstructed pixels in A rows above the top row of the transform block (example values ​​of B include, but are not limited to, 2, 3, . . .) and K pixels in B columns to the left (example values ​​of B include, but are not limited to, 2, 3, . . .). 1,0 To predict the sign of , we use the reconstructed pixels in the top two rows of the first row (pixel p 0,-1 ~p 3,-1 , and p 0,-2 ~p 3,-2 ) and the two adjacent pixels p -2,0and p -1,0 is used.

[0187] In one embodiment, for example, in response to using one-dimensional vertical transform skip in the transform block, signs of coefficients in rows other than the first row of the transform block are predicted by a second transform coefficient sign prediction using one or more reconstructed pixels in one or more columns to the left of the transform block. For example, when applying transform skip vertically, signs of N coefficients in each row except the first row are predicted using reconstructed pixels in M ​​columns to the left of the first column of the transform block (example values ​​of M include, but are not limited to, 2, 3, etc.).

[0188] In one embodiment, for example, transform coefficient sign prediction is disabled in response to using one-dimensional transform skip in the transform block.

[0189] In one embodiment, for example, a first total number of symbols predicted by the second transform coefficient sign prediction when a one-dimensional transform skip is applied to the transform block is different from a second total number of symbols predicted by the first transform coefficient sign prediction when no transform skip is applied in any direction to the transform block.

[0190] In one embodiment, for example, in response to using a two-dimensional transform skip or forward skip coding (FSC) on the transform block, performing the second transform coefficient sign prediction includes predicting coefficient signs for only pixels in the first row or first column of the transform block using one or more reconstructed pixels in one or more rows or columns adjacent to the transform block. For example, when using a two-dimensional transform skip or when using an FSC mode for the coding block, signs of only N pixels in the first row / column of the transform block are predicted using K neighboring pixels (example values ​​of K include, but are not limited to, 1, 2, 3, ) in the top A rows (example values ​​of A include, but are not limited to, 2, 3, ) or left B columns (example values ​​of B include, but are not limited to, 2, 3, ) adjacent to the transform block.

[0191] In one embodiment, for example, in response to using two-dimensional transform skip in the transform block, the sign of a coefficient in a top-left pixel of the transform block is predicted by a second transform coefficient sign prediction based on one or more reconstructed pixels above the top-left pixel in one or more rows above the transform block and one or more reconstructed pixels to the left of the top-left pixel in one or more columns to the left of the transform block. For example, when applying transform skip in both directions, the coefficient sign of the top-left pixel may be predicted using K neighboring pixels (example values ​​of K include, but are not limited to, 1, 2, 3, . . .) in M ​​rows above the top row (example values ​​of M include, but are not limited to, 2, 3, . . .) and L neighboring pixels (example values ​​of L include, but are not limited to, 1, 2, 3, . . .) in N columns to the left of the first column (example values ​​of N include, but are not limited to, 2, 3, . . .). For example, referring to the transform block (900) of FIG. 9, a pixel p 0,0 The coefficient sign of is two pixels from each of the top two rows, namely p 0,-1 , p 0,-2 and two pixels from each of the left two columns, i.e., p -1,0 , p-2,0 is predicted using

[0192] In one embodiment, for example, in response to using two-dimensional transform skip in the transform block, the sign of a coefficient of a pixel in a first row of the transform block is predicted by a second transform coefficient sign prediction based on one or more first reconstructed pixels in the transform block and one or more rows above the pixel, and one or more second reconstructed pixels to the left or right of the one or more first reconstructed pixels in the one or more rows. For example, when applying transform skip in both directions, the coefficient signs of N pixels in the first row are predicted using K neighboring pixels (example values ​​of K include, but are not limited to, 1, 2, 3, . . .) in M ​​rows (example values ​​of M include, but are not limited to, 2, 3, . . . ) above the top row of the transform block. For example, referring to the transform block (900) of FIG. 9, a pixel p 1,0 The coefficient sign of is two pixels from each of the top two rows, namely p 1,-1 , p 1,-2 , p 0,-1 , p 0,-2 and pixel p 2,0 The coefficient sign of is two pixels from each of the top two rows, namely p 2,-1 , p 2,-2 , p 3,-1 , p 3,-2 is predicted using

[0193] In one embodiment, for example, in response to using two-dimensional transform skip in the transform block, the sign of a coefficient of a pixel in a first column of the transform block is predicted by a second transform coefficient sign prediction based on one or more first reconstructed pixels in the transform block and one or more columns to the left of the pixel, and one or more second reconstructed pixels above or below the one or more first reconstructed pixels in the one or more columns. For example, when applying transform skip in both directions, the coefficient sign of N pixels in the first column is predicted using K neighboring pixels (example values ​​of K include, but are not limited to, 1, 2, 3, . . .) in M ​​rows (example values ​​of M include, but are not limited to, 2, 3, . . .) to the left of the first column of the transform block.

[0194] In one embodiment, for example, transform coefficient sign prediction is not enabled in response to using two-dimensional transform skip in the transform block.

[0195] In one embodiment, for example, transform coefficient code prediction is not enabled for intra-coded blocks using forward skip coding (FSC) mode.

[0196] In one embodiment, for example, transform coefficient code prediction is not enabled for inter-coded blocks using forward skip coding (FSC) mode.

[0197] In one embodiment, for example, coefficient sign prediction is enabled for inter-coding blocks that do not use forward skip coding (FSC) mode.

[0198] The process ends at (S1099).

[0199] 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 11 illustrates a computer system (1100) suitable for implementing certain embodiments of the disclosed subject matter.

[0200] Computer software may be coded using any suitable machine code or computer language and may be assembled, compiled, linked, or similar mechanisms to produce code containing instructions that may be executed directly, or through interpretation, by microcode, such as by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc.

[0201] 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.

[0202] The components of the computer system (1100) illustrated in Figure 11 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 relating to any one or combination of components illustrated in the exemplary embodiment of the computer system (1100).

[0203] The computer system (1100) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users via, for example, tactile input (keystrokes, swipes, data glove movements, etc.), audio input (voice, clapping, etc.), visual input (gestures, etc.), olfactory input (not shown), etc. The human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (voice, music, environmental sounds, etc.), images (scanned images, photographic images obtained from a still camera, etc.), video (2D video, 3D video including stereoscopic video, etc.), etc.

[0204] The human interface input devices may include one or more of a keyboard (1101), a mouse (1102), a trackpad (1103), a touch screen (1110), a data glove (not shown), a joystick (1105), a microphone (1106), a scanner (1107), and a camera (1108) (only one of each is shown).

[0205] The computer system (1100) may also include certain human interface output devices that may stimulate one or more of the senses of a human user through, for example, tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touchscreen (1110), data gloves (not shown), or joystick (1105), although some haptic feedback devices may not function as input devices), audio output devices (speakers (1109), headphones (not shown), etc.), visual output devices (screens (1110), including cathode ray tube (CRT) screens, liquid crystal display (LCD) screens, plasma screens, organic light emitting diode (OLED) screens, etc., each with or without touchscreen input capability, each with or without haptic feedback capability, some of which may be capable of outputting two-dimensional visual output or three or more dimensional visual output via means such as stereoscopic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0206] The computer system (1100) may also include human accessible storage devices and their associated media such as optical media including CD / DVD ROM / RW (1120) with CD / DVD or similar media (1121), thumb drives (1122), removable hard drives or solid state drives (1123), legacy magnetic media such as tapes and floppy disks (not shown), specialized ROM / ASIC / PLD based devices such as security dongles (not shown). ASIC stands for Application Specific Integrated Circuit. PLD stands for Programmable Logic Device.

[0207] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the subject matter disclosed herein does not encompass transmission media, carrier waves, or other transitory signals.

[0208] The computer system (1100) may also include interfaces to one or more communication networks. The networks may be, for example, wireless, wired, optical, etc. Furthermore, the networks may be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless local area networks (LANs), cellular networks such as Global System for Mobile Communications (GSM), 3G, 4G, 5G, and Long Term Evolution (LTE), TV wired or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial networks including controller area network buses (CANbuses), etc. A particular network typically requires an external network interface adapter to be connected to a particular general-purpose data port or peripheral bus (1149) (e.g., a universal serial bus (USB) port of the computer system (1100)). Others are typically integrated into the core of the computer system (1100) by connecting 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 (1100) can communicate with other entities. Such communications can be one-way, receive-only (e.g., television broadcasts), one-way transmit-only (e.g., a CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks can be used with each of these networks and network interfaces, as described above.

[0209] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1140) of the computer system (1100).

[0210] The cores (1140) may include one or more central processing units (CPUs) (1141), graphics processing units (GPUs) (1142), specialized programmable processing units (1143) in the form of field programmable gate areas (FPGAs), hardware accelerators (1144) for specific tasks, etc. These devices may be connected via a system bus (1148), along with read only memory (ROM) (1145), random access memory (1146), internal mass storage such as an internal hard drive that is not accessible to the user, a solid state drive (SSD), etc. (1147). In some computer systems, the system bus (1148) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be connected directly to the core's system bus (1148) or through a peripheral bus (1149). Peripheral bus architectures include Peripheral Component Interconnect (PCI), USB, etc.

[0211] The CPU (1141), GPU (1142), FPGA (1143), and accelerator (1144) may execute certain instructions that may combine to constitute the aforementioned computer code. The computer code may be stored in a ROM (1145) or a random access memory (RAM) (1146). Transient data may also be stored in the RAM (1146), while persistent data may be stored, for example, in internal mass storage (1147). Rapid storage and retrieval from any memory device may be enabled by the use of cache memories that may be closely associated with one or more of the CPU (1141), GPU (1142), mass storage (1147), ROM (1145), and RAM (1146), etc.

[0212] 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 skilled in the computer software arts.

[0213] By way of example and not limitation, the architecture (1100), and in particular the computer system having the cores (1140), may provide functionality as a result of processors (CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be media associated with a user-accessible mass storage device as introduced above, or may be specific storage of the cores (1140) that is non-transitory in nature, such as the core internal mass storage device (1147) or ROM (1145). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the cores (1140). The computer-readable media may include one or more memory devices or chips, depending on the particular needs. The software may cause the cores (1140), and in particular the processors therein (including CPU, GPU, FPGA, etc.) to perform certain processes or certain parts of certain processes described herein, including the definition of data structures stored in RAM (1146) and the modification of such data structures according to the processes defined by the software. Additionally, or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embedded in circuitry (e.g., accelerator (1144)), which may operate in place of or together with software to execute a particular process or a particular portion of a particular process described herein. References to software may include logic, where appropriate, and vice versa. References to computer-readable media may encompass circuitry (such as an integrated circuit (IC)) that stores software for execution, circuitry embodying logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0214] While this disclosure has described several exemplary embodiments, there are modifications, permutations, and various substitute equivalents that fall within the scope of this disclosure. Thus, it will be appreciated that those skilled in the art can conceive of many systems and methods that, while not explicitly shown or described herein, embody the principles of the present disclosure and are therefore within the spirit and scope of the present disclosure.

Claims

1. 1. A method of video decoding in a video decoder, the method comprising: receiving a coded video stream including a current block associated with a transform block; determining whether to use a transform skip in the transform block; performing a first transform coefficient sign prediction in response to determining that the transform skip is not to be used for the transform block, the first transform coefficient sign prediction including: predicting a first sign of the first plurality of transform coefficients based on the first plurality of adjacent samples; predicting a second sign of a second plurality of transform coefficients based on a second plurality of adjacent samples, the prediction of the first sign of the first plurality of transform coefficients being independent from the prediction of the second sign of the second plurality of transform coefficients; reconstructing the current block based on the first plurality of transform coefficients and the second plurality of transform coefficients. method.

2. 2. The method of claim 1, further comprising: in response to determining to use the transform skip for the transform block, performing a second transform coefficient sign prediction for the transform block, the second transform coefficient sign prediction being different from the first transform coefficient sign prediction.

3. The method of claim 1 , wherein the first transform coefficient sign prediction is disabled in response to using the transform skip in the transform block.

4. determining whether to use a transform skip includes determining whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip; in response to using the one-dimensional horizontal transform skip in the transform block, signs of coefficients in different columns of the transform block are independently predicted by the second transform coefficient sign prediction; The method of claim 2 , wherein performing the second transform coefficient sign prediction step comprises predicting the coefficient sign of a column using only reconstructed samples adjacent to the column.

5. determining whether to use a transform skip includes determining whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip; In response to using the one-dimensional horizontal transform skip in the transform block, signs of coefficients in a first column of the transform block are one or more reconstructed columns to the left of the transformation block; and The method of claim 2 , wherein the second transform coefficient sign prediction is predicted based on one or more reconstructed pixels on the first column of the transform block.

6. determining whether to use a transform skip includes determining whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip; 3. The method of claim 2, wherein in response to using the one-dimensional horizontal transform skip in the transform block, signs of coefficients in columns other than a first column of the transform block are predicted by the second transform coefficient sign prediction using one or more reconstructed pixels in one or more rows above the transform block.

7. determining whether to use a transform skip includes determining whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip; in response to using the one-dimensional vertical transform skip in the transform block, signs of coefficients in different rows of the transform block are independently predicted by the second transform coefficient sign prediction; The method of claim 2 , wherein performing the second transform coefficient sign prediction comprises predicting a coefficient sign of a row using only reconstructed samples adjacent to the row.

8. determining whether to use a transform skip includes determining whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip; In response to using the one-dimensional vertical transform skip in the transform block, signs of coefficients in a first row of the transform block are one or more reconstructed rows above the transformation block; and The method of claim 2 , wherein the second transform coefficient sign prediction is predicted based on one or more reconstructed pixels to the left of the transform block.

9. determining whether to use a transform skip includes determining whether to use one of a one-dimensional horizontal transform skip and a one-dimensional vertical transform skip; 3. The method of claim 2, wherein in response to using the one-dimensional vertical transform skip in the transform block, signs of coefficients in rows other than a first row of the transform block are predicted by the second transform coefficient sign prediction using one or more reconstructed pixels in one or more columns to the left of the transform block.

10. The method of claim 1 , wherein the first transform coefficient sign prediction is disabled in response to using a one-dimensional transform skip in the transform block.

11. 3. The method of claim 2, wherein a first total number of symbols predicted by the second transform coefficient sign prediction when a one-dimensional transform skip is applied to the transform block is different from a second total number of symbols predicted by the first transform coefficient sign prediction when the transform skip is not applied in any direction to the transform block.

12. determining whether to use a transform skip includes determining whether to use a two-dimensional transform skip; 3. The method of claim 2, wherein in response to using the two-dimensional transform skip in the transform block, performing the second transform coefficient sign prediction comprises predicting coefficient signs for only pixels in a first row or a first column of the transform block using one or more reconstructed pixels in one or more rows or columns adjacent to the transform block.

13. The step of determining whether to use transform skip includes determining whether to use forward skip coding (FSC); 3. The method of claim 2, wherein in response to using the FSC on the transform block, performing the second transform coefficient sign prediction comprises predicting coefficient signs for only pixels in a first row or a first column of the transform block using one or more reconstructed pixels in one or more rows or columns adjacent to the transform block.

14. determining whether to use a transform skip includes determining whether to use a two-dimensional transform skip; In response to the two-dimensional transform skip being used in the transform block, a sign of a coefficient of a top left pixel of the transform block is one or more reconstructed pixels above the top-left pixel in one or more rows above the transformed block; and 3. The method of claim 2, wherein the second transform coefficient sign prediction is based on one or more reconstructed pixels to the left of the top-left pixel in one or more columns to the left of the transform block.

15. determining whether to use a transform skip includes determining whether to use a two-dimensional transform skip; In response to using the two-dimensional transform skip in the transform block, signs of coefficients of pixels in a first row of the transform block are one or more first reconstructed pixels in one or more rows above the transformation block and the pixel; and 3. The method of claim 2, wherein the second transform coefficient sign prediction is based on one or more second reconstructed pixels to the left or right of the one or more first reconstructed pixels in the one or more rows.

16. determining whether to use a transform skip includes determining whether to use a two-dimensional transform skip; In response to using the two-dimensional transform skip in the transform block, signs of coefficients of pixels in a first column of the transform block are one or more first reconstructed pixels in one or more columns to the left of the transformation block and the pixel; and 3. The method of claim 2, wherein the second transform coefficient sign prediction is predicted based on one or more second reconstructed pixels above or below the one or more first reconstructed pixels in the one or more columns.

17. The method of claim 1 , wherein the first transform coefficient sign prediction is not enabled in response to using two-dimensional transform skip in the transform block.

18. The method of claim 1 , wherein the first transform coefficient sign prediction is not enabled for intra-coded blocks using a forward skip coding (FSC) mode.

19. The method of claim 1 , wherein the first transform coefficient code prediction is enabled for an inter-coding block based on whether a forward skip coding (FSC) mode is used for the inter-coding block.

20. 1. An apparatus including a processing circuit, The processing circuitry is configured to perform a method according to any one of claims 1 to 19. device.

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