Palette predictor generation and signaling

Abstract

This disclosure relates generally to video coding, and more particularly to methods and systems for generating and signaling a palette prediction block for a video block in an intra-prediction mode based on a palette of pixel values. In some example implementations, at least a portion of a palette for predicting a current video block is inherited from at least one neighboring block predicted under a palette intra-prediction mode. The size of the inherited portion of the palette of the current video block is determined before performing any merging of the palette corresponding to the at least one neighboring block.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. non-provisional patent application Ser. No. 17 / 869,268, filed July 20, 2022, which claims the benefit of priority to U.S. provisional patent application Ser. No. 63 / 299,665, entitled "Palette Predictor Generation and Signaling," filed January 14, 2022, each of which is incorporated by reference in its entirety herein.

[0002] FIELD This disclosure relates generally to video coding, and more particularly, to methods and systems related to generation and signaling of palette prediction blocks for video blocks in intra-prediction modes that are based on a palette of pixel values. [Background technology]

[0003] The discussion of the background art provided herein is intended to generally present the context of the present disclosure. The inventors' work is not admitted, expressly or impliedly, as prior art to the present disclosure to the extent that that work is described in this background section, together with aspects of the description that may not otherwise be admitted as prior art at the time of filing of this application.

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

[0005] One objective of video coding and decoding may be the reduction of redundancy in an uncompressed input video signal through compression. Compression may help reduce the aforementioned bandwidth and / or storage space requirements, in some cases by more than one order of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be employed. Lossless compression refers to techniques where an exact copy of the original signal may be reconstructed from the compressed original signal through a decoding process. Lossy compression refers to a coding / decoding process where the original video information is not fully preserved when coding and cannot be fully restored when decoding. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for its intended application, even with some information loss. For video, lossy compression is widely adopted in many applications. The amount of distortion that can be tolerated depends on the application. For example, a user of a particular consumer video streaming application may tolerate higher distortion than a user of a movie or television broadcast application. The compression ratio achievable by a particular coding algorithm may be selected or adjusted to reflect different distortion tolerances. That is, in general, higher distortion tolerance allows for coding algorithms that result in higher losses and higher compression ratios.

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

[0007] Video codec technology may include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, pictures are spatially subdivided into blocks of samples. If all blocks of samples are coded in intra mode, the picture may be called an intra picture. Intra pictures and their derived pictures, such as independent decoder refresh pictures, are used to reset the decoder state and may therefore be used as the first picture in a coded video bitstream and video session or as a still image. Samples of the block after intra prediction may then be transformed to the frequency domain, and the transform coefficients so generated may be quantized before entropy coding. Intra prediction refers to a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value after transformation and the smaller the AC coefficients, the fewer bits are needed at a given quantization step size to represent the block after entropy coding.

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

[0009] Intra prediction may take many different forms. When two or more of such techniques are available in a given video coding technique, the technique used may be referred to as an intra prediction mode. One or more intra prediction modes may be provided in a particular codec. In certain cases, a mode may have sub-modes and / or may be associated with various parameters, and the mode / sub-mode information and intra coding parameters of a block of video may be coded individually or collectively included in the codeword of the mode. Which codeword is used for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gains via intra prediction, and thus may also affect 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 novel coding techniques such as the Joint Search Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). In general, in intra prediction, the predictor block may be formed using neighboring sample values ​​that become available. For example, the available values ​​of a particular set of neighboring samples along a particular direction and / or line may be copied to the predictor block. The reference to the direction in use may be coded in the bitstream or may itself be predicted.

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

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

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

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

[0015] The number of possible directions has increased as video coding technology continues to develop. In H.264 (2003), for example, nine different directions are available for intra prediction. This increases to 33 in H.265 (2013), and JEM / VVC / BMS may support up to 65 directions at the time of this disclosure. Experimental studies have been conducted to help identify the most suitable intra prediction directions, and those most suitable directions may be encoded with a small number of bits using certain techniques of entropy coding, accepting certain bit penalties for the directions. Furthermore, the direction itself may be predicted from neighboring directions used in intra prediction of the decoded neighboring blocks.

[0016] FIG. 1B shows a schematic diagram (180) showing 65 intra prediction directions according to JEM to illustrate the increasing number of prediction directions in various encoding techniques that have evolved over time.

[0017] Methods for mapping bits representing intra-prediction directions in a coded video bitstream to prediction directions can vary across video coding techniques, and can range, for example, from simple direct mappings of prediction directions to intra-prediction modes to complex adaptation schemes including codewords, most probable modes, and similar techniques. In all cases, however, there may be certain directions of intra-prediction that are statistically less likely to occur in the video content than certain other directions. Because the goal of video compression is to reduce redundancy, in a well-designed video coding technique, those less likely directions may be represented with more bits than the more likely directions.

[0018] Inter-picture prediction, or inter-prediction, may be based on motion compensation. In motion compensation, sample data from a previously reconstructed picture or part thereof (reference picture) may be used to predict a newly reconstructed picture or picture part (e.g., block) after being spatially shifted in a direction indicated by a motion vector (hereinafter, MV). In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions X and Y, or three dimensions, with the third dimension being an indication of the reference picture in use (similar to the temporal dimension).

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

[0020] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Recommendation H.265, "High Efficiency Video Coding", December 2016). Among the many MV prediction mechanisms specified by H.265, the one described below is a technique hereafter referred to as "spatial merging".

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

[0022] FIELD This disclosure relates generally to video coding, and more particularly, to methods and systems related to generation and signaling of palette prediction blocks for video blocks in intra-prediction modes that are based on a palette of pixel values.

[0023] In an exemplary implementation, a method for generating an intra-predictor block of a current video block in a video stream is disclosed. The current video block may be intra-coded in palette mode. The method includes: determining from the video stream that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; and generating a predictor block of the current video block based on at least the palette index and the current palette.

[0024] In the above implementation, determining cacheN may include determining a size of the inherited portion of the current palette based on at least one palette size corresponding to the at least one reference palette.

[0025] In any one of the above implementations, determining cacheN may include determining a first palette size of a first neighboring video block of the current video block, determining a second palette size of a second neighboring video block of the current video block, and determining cacheN based on the first palette size and the second palette size.

[0026] In any one of the above implementations, the first neighboring video block and the second neighboring video block may include the immediately upper and left video blocks of the current video block, respectively. Determining cacheN based on the first palette size and the second palette size includes determining a size of the inherited portion of the current palette as: increasing N to the larger of the first palette size and the second palette size; increasing N to the smaller of the first palette size and the second palette size; or determining a size of the inherited portion of the current palette as the smaller of: a predetermined maximum inherited palette size and increasing N to the larger of the first palette size and the second palette size; or determining a size of the inherited portion of the current palette as the smaller of: a predetermined maximum inherited palette size and increasing N to the smaller of the first palette size and the second palette size. The symbol N indicates a predetermined palette size increment, where N is an integer greater than or equal to 0 and less than or equal to 8.

[0027] In any one of the above implementations, determining cacheN may include allocating a palette size of the inherited portion of the current palette independent of at least one reference palette, where the palette size is an integer greater than or equal to 0 and less than or equal to 8.

[0028] In any one of the above implementations, the palette size may be predetermined or signaled in a syntax element within the video stream.

[0029] In any one of the above implementations, the syntax element may include one component of a video parameter set, a sequence parameter set, a picture parameter set, an adaptation parameter set, a frame header, a slice header, a picture header, a tile header, or a coding tree unit header associated with the current video block.

[0030] In any one of the above implementations, cacheN may be derived from a coding information item of the current video block or at least one neighboring video block.

[0031] In any one of the above implementations, the coded information item may include at least one of a block size or a prediction mode associated with the current video block or at least one neighboring video block.

[0032] In any one of the above implementations, cacheN may be derived as the number of repeated palette entries in at least one reference palette associated with at least one neighboring video block.

[0033] In any one of the above implementations, the at least one neighboring video block may include M neighboring video blocks, and a number of common palette entries I of at least K of the M neighboring video blocks is determined as cacheN, where M is an integer greater than or equal to 2, and K is an integer less than or equal to M.

[0034] In any one of the above implementations, the at least one neighboring video block corresponding to the at least one reference palette may be selected from three or more neighboring video blocks of the current video block.

[0035] In any one of the above implementations, the three or more neighboring video blocks may include at least one block that is not adjacent to the current video block.

[0036] In any one of the above implementations, at least one neighboring video block may be selected from three or more neighboring video blocks by scanning the three or more neighboring video blocks in a predetermined scanning order to determine a first set of neighboring video blocks intra-coded in palette mode, and a set of cached palettes of the first set of neighboring video blocks may be used to determine or derive at least one reference palette.

[0037] In any one of the above implementations, the method may further include merging at least one reference palette into a cached palette having S unique palette entries.

[0038] In any one of the above implementations, when S>cacheN, the method may further include one of: selecting first cacheN palette entries from the cached palette in accordance with a predetermined scanning order to generate the inherited portion of the current palette having cacheN palette entries; selecting last cacheN palette entries from the cached palette in accordance with a predetermined scanning order to generate the inherited portion of the current palette having cacheN palette entries; selecting duplicate palette entries from at least one reference palette in accordance with a predetermined scanning order and, if necessary, further selecting a first non-duplicate palette entry from the cached palette in accordance with a predetermined scanning order to generate the inherited portion of the current palette having cacheN palette entries; or selecting duplicate palette entries from at least one reference palette in accordance with a predetermined scanning order and, if necessary, further selecting a last non-duplicate palette entry from the cached palette in accordance with a predetermined scanning order to generate the inherited portion of the current palette having cacheN palette entries.

[0039] In any one of the above implementations, when S<(cacheN), the method may further include filling the first S palette entries of the inherited portion of the current palette using the cached palette, determining (cacheN-S) target palette entries from the cached palette, offsetting each of the (cacheN-S) target palette entries to generate a modified target palette entry, and including the modified target palette entry in the last (cacheN-S) entries of the inherited portion of the current palette.

[0040] In any one of the above implementation forms, when S < cacheN, the method further includes filling the first S palette entries of the inherited part of the current palette using the cached palette, and filling the last (cacheN - S) palette entries of the inherited part of the current palette with the first (cacheN - S) palette entries from the palette entry list.

[0041] In any one of the above implementation forms, the palette entry list may be signaled in the video stream by one of a sequence parameter set, a picture parameter set, an adaptive parameter set, a frame header, a slice header, a picture header, a tile header, or a coding tree unit header.

[0042] Aspects of the present disclosure also provide a video encoding or decoding device or apparatus including a circuit configured to execute any of the implementation forms of the above method.

[0043] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that cause a computer to perform a method for video decoding and / or encoding when executed by the computer for video decoding and / or encoding.

[0044] Further features, properties, and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings.

Brief Description of the Drawings

[0045] [Figure 1A] It is a schematic diagram of an exemplary subset of intra prediction directivity modes. [Figure 1B] It is a diagram showing an exemplary intra prediction direction. [Diagram 2] It is a schematic diagram showing the current block and its surrounding spatial merge candidates for motion vector prediction in an example. [Diagram 3] 1 is a schematic diagram of a simplified block diagram of a communication system (300) according to an exemplary embodiment. [Figure 4] 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an exemplary embodiment. [Diagram 5] 2 is a schematic diagram of a simplified block diagram of a video decoder according to an example embodiment; [Figure 6] 1 is a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7] 4 is a block diagram of a video encoder according to another example embodiment. [Figure 8] 4 is a block diagram of a video decoder according to another exemplary embodiment. [Figure 9] FIG. 2 illustrates a coding block partitioning scheme according to an exemplary embodiment of the present disclosure. [Figure 10] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 11] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 12] FIG. 2 illustrates an exemplary partitioning of a base block into coding blocks according to an exemplary partitioning scheme. [Figure 13] FIG. 2 illustrates an exemplary division-of-thirds scheme. [Figure 14] FIG. 2 illustrates an exemplary quadtree / binary tree coding block partitioning scheme. [Figure 15] 4A-4C are diagrams illustrating a scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 16] 4A-4C are diagrams illustrating another scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 17]FIG. 13 illustrates another scheme for splitting a coding block into multiple transform blocks, according to an exemplary embodiment of the present disclosure. [Figure 18] A diagram showing an example of a scanning order of coding palette entries for a coding block predicted under palette intra prediction mode. [Figure 19] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 20] 1 is a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Throughout this specification and the claims, terms may have subtle meanings that are suggested or implied in the context beyond the meaning explicitly stated. The phrases "in one embodiment" or "in some embodiments" used herein do not necessarily refer to the same embodiment, and the phrases "in another embodiment" or "in other embodiments" used herein do not necessarily refer to different embodiments. Similarly, the phrases "in one implementation" or "in some implementations" used herein do not necessarily refer to the same implementation, and the phrases "in another implementation" or "in other implementations" used herein do not necessarily refer to different implementations. For example, the claimed subject matter is intended to include all or part of the exemplary embodiments / implementations.

[0047] Generally, technical terms may be understood at least in part from their usage in context. For example, terms such as "and", "or", or "and / or" as used herein may include various meanings that may depend at least in part on the context in which such terms are used. Typically, "or" when used to relate a list such as A, B, or C is intended to mean A, B, and C, which are used herein in an inclusive sense, as well as A, B, or C, which are used herein in an exclusive sense. In addition, the terms "one or more" or "at least one" as used herein may be used to describe any feature, structure, or characteristic in a singular sense, or may be used to describe a combination of features, structures, or characteristics in a plural sense, depending at least in part on the context. Similarly, terms such as "a", "an", or "the" may also be understood to convey a singular usage or a plural usage, depending at least in part on the context. In addition, the terms "based on" or "determined by" may be understood not to be intended to convey an exclusive set of factors, but may instead allow for the existence of additional factors not necessarily explicitly described, again depending at least in part on the context. FIG. 3 illustrates a simplified block diagram of a communication system (300) according to one embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that may communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may implement unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., of a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams.The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to recover the video picture, and display the video picture according to the recovered video data. The one-way data transmission may be implemented in media serving applications, etc.

[0048] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) implementing bidirectional transmission of coded video data, which may be implemented, for example, during video conferencing applications. For the bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may code video data (e.g., of a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device according to the recovered video data.

[0049] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be implemented as a server, a personal computer, and a smartphone, although application of the principles underlying the present disclosure may not be so limited. The embodiments of the present disclosure may be implemented in desktop computers, laptop computers, tablet computers, media players, wearable computers, dedicated video conferencing equipment, and the like. The network (350) represents any number or type of network that conveys coded video data between the terminal devices (310), (320), (330), and (340), including, for example, wired (wired connection) and / or wireless communication networks. The communication network (350) 9 may exchange data over circuit-switched channels, packet-switched channels, and / or other types of 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 (350) may not be important to the operation of the present disclosure unless expressly described herein.

[0050] 4 shows an arrangement of video encoders and video decoders in a video streaming environment as one example for an application of the disclosed subject matter. The disclosed subject matter may be equally applicable to other video applications including, for example, video conferencing, digital television broadcasting, gaming, virtual reality, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0051] A video streaming system may include a video source (401) for creating a stream of uncompressed video pictures or images (402), e.g., a video capture subsystem (413) that may include a digital camera. In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), shown as a thick line to emphasize the large amount of data when compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), shown with thin lines to emphasize its low amount of data compared to the stream of uncompressed video pictures (402), may be stored directly on the streaming server (405) or on a downstream video device (not shown) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, may access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) within the electronic device (430). The video decoder (410) decodes the input copy of the encoded video data (407) and creates an output stream of video pictures (411), which is uncompressed and may be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). The video decoder 410 may be configured to perform some or all of the various functions described in this disclosure.In some streaming systems, the encoded video data (404), (407), and (409) (e.g., video bitstreams) may be encoded according to a particular video coding / compression standard. Examples of such standards include ITU-T Recommendation H.265. In one example, a video coding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC, as well as other video coding standards.

[0052] It should be noted that the electronic devices (420) and (430) may include other components (not shown). For example, the electronic device (420) may include a video decoder (not shown) and the electronic device (430) may also include a video encoder (not shown).

[0053] 5 shows a block diagram of a video decoder (510) according to any of the following embodiments of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0054] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, with the decoding of each coded video sequence being independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or video images. The coded video sequences are received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data, or a streaming source that transmits the encoded video data. The receiver (531) may receive the encoded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To combat network jitter, a buffer memory (515) may be disposed between the receiver (531) and the entropy decoder / parser (520) (hereinafter, "parser (520)"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, the buffer memory (515) may be separate and external to the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), for example to combat network jitter, and there may be another additional buffer memory (515) internal to the video decoder (510), for example to handle playback timing. When the receiver (531) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may be unnecessary or may be small.For use with best-effort packet networks such as the Internet, a buffer memory (515) of sufficient size may be required, which may be relatively large in size. Such a buffer memory may be implemented with an adaptive size and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0055] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and information for controlling a rendering device such as a display (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may be in the form of a supplemental enhancement information (SEI message) or a parameter set fragment (not shown) of video usability information (VUI). The parser (520) may parse / entropy decode the coded video sequence received by the parser (520). The entropy coding of the coded video sequence may be according to a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), prediction units (PUs), etc. The parser (520) may also extract information from the coded video sequence, such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

[0056] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to create symbols (521).

[0057] The reconstruction of the symbols (521) may involve a number of different processing or functional units, depending on the type of video picture or portion thereof that has been coded (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. The units that are included and how they are included may be controlled by subgroup control information parsed from the coded video sequence by the parser (520). The flow of such subgroup control information between the parser (520) and the following processing or functional units is not shown for the sake of simplicity.

[0058] Besides the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these functional units may closely interact with each other and may be, at least in part, integrated with each other. However, for the purpose of clearly describing the various functions of the disclosed subject matter, a conceptual subdivision into functional units is adopted in the following disclosure.

[0059] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients as well as control information from the parser (520) including information indicating which type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output blocks including sample values ​​that may be input to an aggregator (555).

[0060] In some cases, scaler / inverse transform unitThe output samples of (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using information of surrounding blocks that have already been reconstructed and stored in the current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0061] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for inter-picture prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, these samples may be added to the output of the scalar / inverse transform unit (551) by the aggregator (555) to generate output sample information (the output of unit 551 may be referred to as a residual sample or residual signal). The address in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction sample may be controlled by a motion vector, available to the motion compensated prediction unit (553) in the form of a symbol (521), which may have, for example, an X component, a Y component (shift), and a reference picture component (time). Motion compensation may also include interpolation of sample values ​​fetched from a reference picture memory (557) when sub-sample accurate motion vectors are used, and may be associated with a motion vector prediction mechanism, etc.

[0062] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to previously reconstructed and loop filtered sample values ​​as well as meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence. As described in more detail below, several types of loop filters may be included as part of the loop filter unit 556 in various orders.

[0063] The output of the loop filter unit (556) may be a sample stream that can be stored in a reference picture memory (557) for use in future inter-picture prediction as well as output to a rendering device (512).

[0064] Once a particular coded picture has been fully reconstructed, it may be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture has been fully reconstructed and the coded picture has been identified as a reference picture (e.g., by the parser (520)), the current picture buffer (558) may become part of the reference picture memory (557) and a new current picture buffer may be relocated before beginning reconstruction of a subsequent coded picture.

[0065] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard, such as ITU-T Recommendation H.265. The coded video sequence may comply with the syntax specified by the video compression technique or standard being used in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and the profile documented in the video compression technique or standard. Specifically, the profile may select a particular tool from all tools available in the video compression technique or standard as the only tool that can be used under that profile. To comply with a standard, the complexity of the coded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may be further limited in some cases by the specification of a hypothetical reference decoder (HRD) and metadata for HRD buffer management signaled within the coded video sequence.

[0066] In some example embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0067] 6 shows a block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure. The video encoder (603) may be included in an electronic device (620). The electronic device (620) may further include a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the video encoder (403) of the example of FIG. 4.

[0068] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In another example, the video source (601) may be implemented as part of the electronic device (620).

[0069] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 YCrCb, RGB, XYZ ...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device capable of storing previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as a number of individual pictures or images that give motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each of which may contain one or more samples depending on the sampling structure, color space, etc. being used. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0070] According to some example embodiments, the video encoder (603) may code and compress pictures of a source video sequence into a coded video sequence (643) in real time or under any other time constraint required by the application. Enforcing an appropriate coding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be operatively coupled to and control other functional units as described below. For simplicity, couplings are not shown. Parameters set by the controller (650) may include rate control related parameters (picture skip, quantizer, lambda value of rate distortion optimization techniques, etc.), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured with other appropriate functions for the video encoder (603) optimized for a particular system design.

[0071] In some example embodiments, the video encoder (603) may be configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a similar manner as a (remote) decoder would create them, even if the embedded decoder 633 processes the video stream coded by the source coder 630 without entropy coding (because in the video compression techniques contemplated in the disclosed subject matter, any compression between the symbols and the coded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream produces bit-exact results regardless of the location of the decoder (local or remote), the contents of the reference picture memory (634) are also bit-exact between the local and remote encoders. In other words, the predictive part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0072] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also briefly to Figure 5, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) may be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633) within the encoder.

[0073] At this point, it can be said that any decoder technology, except for parsing / entropy decoding, which may only exist in the decoder, may necessarily also need to exist in the corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter may focus on the decoder operation, which is similar to the decoding part of the encoder. Thus, the description of the encoder technology may be omitted, since it is the reverse of the decoder technology described in general. Only in certain areas or aspects, a more detailed description of the encoder is provided below.

[0074] In operation, in some example implementations, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from a video sequence designated as "reference pictures." In this manner, the coding engine (632) codes color channel differences (or residuals) between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references to the input picture. The terms "residual" and its adjective form "residual" may be used interchangeably.

[0075] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols created by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may usually be a replica of the source video sequence with some errors. The local video decoder (633) may replicate the decoding process that may be performed by the video decoder on the reference pictures, such that the reconstructed reference pictures are stored in a reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with reconstructed reference pictures obtained by a far-end (remote) video decoder (without transmission errors).

[0076] The predictor (635) may perform a predictive search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata such as reference picture motion vectors, block shapes, etc., that may serve as suitable predictive references for the new picture. The predictor (635) may operate on sample blocks, pixel block by pixel block, to find a suitable predictive reference. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have predictive references drawn from multiple reference pictures stored in the reference picture memory (634).

[0077] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0078] The output of all the aforementioned functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by lossless compression of the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0079] The transmitter (640) may buffer the coded video sequence created by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0080] The controller (650) may manage the operation of the video encoder (603). During coding, the controller (650) may assign a particular coded picture type to each coded picture, which may affect the coding techniques that may be applied to the respective picture. For example, pictures may often be assigned as one of the following picture types:

[0081] 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 source of prediction. Some video codecs allow different types of intra pictures, including, for example, independent decoder refresh ("IDR") pictures. Those skilled in the art are aware of these variations of I-pictures, as well as their respective uses and characteristics.

[0082] A predictive picture (P picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which uses at most one motion vector and reference index to predict sample values ​​for each block.

[0083] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction that uses at most two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-prediction picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0084] A source picture may generally be spatially subdivided into multiple sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and coded block by block. A block 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, a block of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial prediction or intra prediction). A pixel block of a P picture may be predictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. A block of a B picture may be predictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures. A source picture or an intermediate processed picture may be subdivided into other types of blocks for other purposes. The division of coding blocks and other types of blocks may or may not follow the same method, as described in more detail below.

[0085] The video encoder (603) 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 (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0086] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0087] Video may be captured in a time sequence as multiple source pictures (video pictures). Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture being encoded / decoded, called the current picture, may be divided into blocks. When a block in the current picture is similar to a reference block in a previously coded yet buffered reference picture in the video, it may be coded by a vector, called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0088] In some exemplary embodiments, bi-prediction techniques may be used for inter-picture prediction. According to such bi-prediction techniques, two reference pictures, such as a first reference picture and a second reference picture, are used, both of which advance the current picture in the video in decoding order (but may be in the past or future, respectively, in display order). A block in the current picture may be coded by a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. A block may be jointly predicted by a combination of the first reference block and the second reference block.

[0089] Furthermore, merge mode techniques may be used to improve coding efficiency in inter-picture prediction.

[0090] According to some exemplary embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may include three parallel coding tree blocks (CTBs), i.e., one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels. Each of one or more of the 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for that CU from among various prediction types, such as an inter prediction type and an intra prediction type. A CU may be 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 in units of prediction blocks. The division of a CU into PUs (or PBs of different color channels) may be performed in various spatial patterns. A luma PB or a chroma PB may include a matrix of sample values ​​(e.g., luma values), such as, for example, 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0091] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of the present disclosure. The video encoder (703) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. The exemplary video encoder (703) may be used in place of the example video encoder (403) of FIG. 4.

[0092] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive block of 8×8 samples. The video encoder (703) then determines, for example, using rate-distortion optimization (RDO), whether the processing block is best coded using intra-mode, inter-mode, or bi-predictive mode. If it is determined that the processing block is coded in intra-mode, the video encoder (703) may encode the processing block into a coded picture using intra-prediction techniques, and when it is determined that the processing block is coded in inter-mode or bi-predictive mode, the video encoder (703) may encode the processing block into a coded picture using inter-prediction techniques or bi-prediction techniques, respectively. In some exemplary embodiments, a merge mode may be used as a sub-mode of inter-picture prediction, in which a motion vector is derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In some other exemplary embodiments, there may be motion vector components applicable to the current block. Thus, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module, to determine the prediction mode of a processing block.

[0093] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725) coupled to each other as shown in the exemplary arrangement of FIG.

[0094] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter-prediction information (e.g., a description of redundancy information, motion vectors, merge mode information according to inter-encoding techniques), and calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the encoded video information using a decoding unit 633 incorporated in the example encoder 620 of FIG. 6 (shown as residual decoder 728 of FIG. 7, as described in more detail below).

[0095] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block with already coded blocks in the same picture, generate transformed quantized coefficients, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). The intra encoder (722) may calculate intra prediction results (e.g., prediction blocks) based on the intra prediction information and reference blocks in the same picture.

[0096] The generic controller (721) may be configured to determine generic control data and control other components of the video encoder (703) based on the generic control data. In one example, the generic controller (721) determines a prediction mode of the block and provides a control signal to the switch (726) based on the prediction mode. For example, when the prediction mode is an intra mode, the generic controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723) and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream, and when the prediction mode of the block is an inter mode, the generic controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723) and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0097] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for a block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) may generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks may be appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures.

[0098] The entropy encoder (725) may be configured to format a bitstream to include the encoded block and to perform entropy coding. The entropy encoder (725) may be configured to include various information in the bitstream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other suitable information in the bitstream. When coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information may not be present.

[0099] 8 shows a diagram of an example video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (810) may be used in place of the example video decoder (410) of FIG. 4.

[0100] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter-decoder (880), a residual decoder (873), a reconstruction module (874), and an intra-decoder (872), all coupled together as shown in the exemplary arrangement of FIG. 8.

[0101] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent the syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra-mode, inter-mode, bi-predictive mode, merged submode, or another submode) that may identify the mode in which the block is coded, certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information, for example in the form of quantized transform coefficients, etc. In one example, when the prediction mode is an inter-predictive mode or a bi-predictive mode, the inter-predictive information is provided to the inter-decoder (880), and when the prediction type is an intra-predictive type, the intra-predictive information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0102] The inter decoder (880) may be configured to receive the inter prediction information and generate inter prediction results based on the inter prediction information.

[0103] The intra decoder (872) may be configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0104] The residual decoder (873) may be 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 (873) may also utilize certain control information (to include quantizer parameters (QP)), which may be provided by the entropy decoder (871) (a data path is not shown, as this may be only a small amount of control information).

[0105] The reconstruction module (874) may be configured to combine, in the spatial domain, the residual as output by the residual decoder (873) and the prediction result (possibly as output by an inter prediction module or an intra prediction module) to form a reconstructed block that forms part of a reconstructed picture as part of the reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may also be performed to improve visual quality.

[0106] It should be noted that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technique. In some exemplary embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (403), (603), and (603) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0107] Turning to block partitioning for coding and decoding, a general partitioning may start from a base block and may follow a predefined set of rules, a specific pattern, a partitioning tree, or any partitioning structure or scheme. The partitioning may be hierarchical and recursive. After isolating or partitioning the base block according to any of the exemplary partitioning procedures described below or other procedures, or combinations thereof, a final set of partitions or coding blocks may be obtained. Each of these partitions may be at one of various partitioning levels in the partitioning hierarchy and may be partitions of various shapes. Each of the partitions may be referred to as a coding block (CB). In various exemplary partitioning implementations described further below, each resulting CB may be a CB of any of the allowed sizes and partitioning levels. Such partitions are referred to as coding blocks because they may form a unit for which some basic coding / decoding decisions may be made and coding / decoding parameters may be optimized, determined, and signaled in the encoded video bitstream. The highest or deepest level in the final partitioning represents the depth of the coding block partitioning tree structure. The coding block may be a luma coding block or a chroma coding block. The CB tree structure for each color is sometimes called a coding block tree (CBT).

[0108] The coding blocks of all color channels may be collectively referred to as a coding unit (CU). The hierarchical structure of all color channels may be collectively referred to as a coding tree unit (CTU). The partitioning pattern or partitioning structure of various color channels within a CTU may or may not be the same.

[0109] In some implementations, the split tree scheme or structure used for the luma channel and the chroma channel may not need to be the same. In other words, the luma channel and the chroma channel may have separate coding tree structures or patterns. Furthermore, whether the luma channel and the chroma channel use the same coding partition tree structure or different coding partition tree structures, and the actual coding partition tree structure to be used may depend on whether the slice being coded is a P slice, a B slice, or an I slice. For example, for an I slice, the chroma channel and the luma channel may have separate coding partition tree structures or coding partition tree structure modes, while for a P slice or a B slice, the luma channel and the chroma channel may share the same coding partition tree scheme. When separate coding partition tree structures or modes are applied, the luma channel may be split into CBs by one coding partition tree structure, and the chroma channel may be split into chroma CBs by another coding partition tree structure.

[0110] In some exemplary implementations, a predefined partitioning pattern may be applied to the base block. As shown in FIG. 9, an exemplary four-way partitioning tree may start at a first predefined level (e.g., 64×64 block level or other size as the base block size), and the base block may be partitioned hierarchically down to a predefined lowest level (e.g., 4×4 level). For example, the base block may follow four predefined partitioning options or patterns illustrated by 902, 904, 906, and 908, and the partitioning designated as R allows for recursive partitioning in that the same partitioning option illustrated in FIG. 9 may be repeated at a lower scale down to the lowest level (e.g., 4×4 level). In some implementations, additional restrictions may be added to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitioning (e.g., 1:2 / 2:1 rectangular partitioning) may be allowed but not recursive, while square partitioning is allowed to be recursive. Subsequent partitioning of FIG. 9 by recursion, if necessary, generates a final set of coding blocks. A coding tree depth may be further defined to indicate the division depth from a root node or root block. For example, the coding tree depth for a root node or root block of a 64×64 block may be set to 0, and after the root block is further divided one time according to FIG. 9, the coding tree depth increases by 1. The maximum or deepest level from a 64×64 base block to a 4×4 minimum division is 4 (starting from level 0) in the above scheme. Such a division scheme may be applied to one or more of the color channels. Each color channel may be independently divided according to the scheme of FIG. 9 (e.g., for each of the color channels at each hierarchical level, a division pattern or option in the predefined pattern may be determined independently). Alternatively, two or more color channels may share the same hierarchical pattern tree of FIG. 9 (e.g., for two or more color channels at each hierarchical level, the same division pattern or option in the predefined pattern may be selected).

[0111] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows the recursive partitioning to form a partitioning tree. As illustrated in FIG. 10, an exemplary ten-way partitioning structure or pattern may be predefined. The root block may start from a predefined level (e.g., from a base block at a 128×128 level or a 64×64 level). The exemplary partitioning structure in FIG. 10 includes various 2:1 / 1:2 and 4:1 / 1:4 rectangular partitions. A partitioning type with three sub-partitions, shown at 1002, 1004, 1006, and 1008 in the second column of FIG. 10, may be referred to as a “T-shaped” partition. The “T-shaped” partitions 1002, 1004, 1006, and 1008 may be referred to as a left T-shaped, an upper T-shaped, a right T-shaped, and a lower T-shaped. In some exemplary implementations, none of the rectangular partitions in FIG. 10 may be further subdivided. A coding tree depth may be further defined to indicate the partitioning depth from the root node or root block. For example, the coding tree depth for a root node or root block of a 128x128 block may be set to 0, and after the root block is further split one time according to FIG. 10, the coding tree depth increases by 1. In some implementations, only the all-square split of 1010 may allow recursive splitting to the next level of the split tree following the pattern of FIG. 10. In other words, recursive splitting may not be possible for the square splits in the T-shaped patterns 1002, 1004, 1006, and 1008. If necessary, the splitting procedure following FIG. 10 by recursion generates a final set of coding blocks. Such a scheme may be applied to one or more of the color channels. In some implementations, more flexibility may be added to the use of splits less than 8x8 levels. For example, in some cases, 2x2 chroma inter prediction may be used.

[0112] In some other example implementations of coding block partitioning, a quadtree structure may be used to partition a base block or an intermediate block into quadtree partitions. Such quadtree partitioning may be applied hierarchically and recursively to any square partition. Whether a base block or intermediate block or partition is further quadtree partitioned may be adapted to various local characteristics of the base block or intermediate block / partition. The quadtree partitioning at the picture boundary may be further adapted. For example, an implicit quadtree partitioning may be implemented at the picture boundary such that a block continues to be quadtree partitioned until its size fits into the picture boundary.

[0113] In some other example implementations, a hierarchical bisection from the base block may be used. For such a scheme, the base block or mid-level block may be divided into two divisions. The bisection may be either horizontal or vertical. For example, a horizontal bisection may divide the base block or mid-block into equal left and right divisions. Similarly, a vertical bisection may divide the base block or mid-block into equal top and bottom divisions. Such bisections may be hierarchical and recursive. It may be determined at each of the base block or mid-block whether the bisection scheme should continue and, if the scheme continues further, whether a horizontal or vertical bisection should be used. In some implementations, further divisions may stop at a predefined minimum division size (in one or both dimensions). Alternatively, further divisions may stop when a predefined division level or depth from the base block is reached. In some implementations, the aspect ratio of the division may be limited. For example, the aspect ratio of the division may not be smaller than 1:4 (or larger than 4:1). Thus, a vertical strip division, having a vertical to horizontal aspect ratio of 4:1, can only be further divided vertically into an upper and lower division, each having a vertical to horizontal aspect ratio of 2:1.

[0114] In yet some other examples, a third division scheme may be used to divide the base block or any intermediate blocks, as shown in FIG. 13. The ternary pattern may be implemented vertically, as shown at 1302 in FIG. 13, or horizontally, as shown at 1304 in FIG. 13. The exemplary division ratio in FIG. 13 is shown as 1:2:1 either vertically or horizontally, but other ratios may be predefined. In some implementations, two or more different ratios may be predefined. Such a third division scheme may be used to complement a quadtree or bipartite structure, in that while such a third division scheme may capture an object located at a block center in one continuous division, the quadtree and bipartite always divide along the block center, thus dividing the object into separate divisions. In some implementations, the width and height of the divisions of the exemplary third tree are always powers of two to avoid further transformations.

[0115] The above partitioning schemes may be combined in any manner at different partitioning levels. As an example, the quadtree and bipartitioning schemes described above may be combined to partition the base block into a quadtree-bipartition (QTBT) structure. In such a scheme, the base block or intermediate blocks / partitions may be either quadtree partitioned or bipartitioned, if specified, subject to a set of predefined conditions. A particular example is shown in FIG. 14. In the example of FIG. 14, the base block is first quadtree partitioned into four partitions, as shown by 1402, 1404, 1406, and 1408. Each of the resulting partitions is then either quadtree partitioned into four further partitions (such as 1408) or biparted into two further partitions at the next level (e.g., either horizontally or vertically, such as 1402 or 1406, both of which are symmetric), or not partitioned (such as 1404). Bisection or quadtree division may be recursively enabled for square division, as shown by the overall exemplary division pattern in 1410 and the corresponding tree structure / representation in 1420, where solid lines represent quadtree division and dashed lines represent bisection. A flag may be used for each bisection node (non-leaf binary division) to indicate whether the bisection is horizontal or vertical. For example, flag "0" may represent horizontal bisection and flag "1" may represent vertical bisection, as shown in 1420, which matches the division structure in 1410. In the case of a quadtree division, there is no need to indicate the division type, since a quadtree division always divides a block or division both horizontally and vertically to generate four sub-blocks / divisions of equal size. In some implementations, flag "1" may represent horizontal bisection and flag "0" may represent vertical bisection.

[0116] In some example implementations of QTBT, the quadtree and bisection rule sets may be represented by the following predefined parameters and corresponding functions associated with them: -CTU size: quadtree root node size (base block size) -MinQTSize: The minimum allowable quadtree leaf node size. -MaxBTSize: Maximum allowed binary tree root node size -MaxBTDepth: Maximum allowed binary tree depth -MinBTSize: The minimum allowable binary tree leaf node size. In some exemplary implementations of the QTBT partitioning structure, the CTU size may be set as 128×128 luma samples with two corresponding 64×64 blocks of chroma samples (when the exemplary chroma subsampling is considered and used), the MinQTSize may be set as 16×16, the MaxBTSize may be set as 64×64, the MinBTSize may be set as 4×4 (for both width and height), and the MaxBTDepth may be set as 4. A quadtree partition may be applied to the CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may have a size from its minimum allowable size of 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If a node is 128×128, it will not be split by the binary tree first because its size exceeds MaxBTSize (i.e., 64×64). Otherwise, any node that does not exceed MaxBTSize may be split by the binary tree. In the example of FIG. 14, the base block is 128×128. The base block is only capable of quadtree partitioning according to a predefined set of rules. The base block has a partition depth of 0. Each of the four resulting partitions is 64×64, not exceeding MaxBTSize, and may be further quadtree or bintree partitioned at level 1. The process continues. When the bintree depth reaches MaxBTDepth (i.e., 4), no further partitions may be considered. When the width of a bintree node is equal to MinBTSize (i.e., 4), no further horizontal partitions may be considered. Similarly, when the height of a bintree node is equal to MinBTSize, no further vertical partitions may be considered.

[0117] In some example implementations, the above QTBT scheme may be configured to support flexibility for luma and chroma to have the same QTBT structure or separate QTBT structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU may share the same QTBT structure. However, for I slices, the luma CTB may be divided into CBs by a QTBT structure, and the chroma CTB may be divided into chroma CBs by another QTBT structure. This means that CUs may be used to refer to different color channels in an I slice, for example, an I slice may consist of a coding block of a luma component or a coding block of two chroma components, and a CU in a P slice or B slice may consist of coding blocks of all three color components.

[0118] In some other implementations, the QTBT scheme may be complemented with the ternary scheme described above. Such implementations may be referred to as a multi-type tree (MTT) structure. For example, in addition to the bisection of the node, one of the trisection patterns of FIG. 13 may be selected. In some implementations, only square nodes may undergo trisection. An additional flag may be used to indicate whether the trisection is horizontal or vertical.

[0119] The design of two-level or multi-level trees, such as the QTBT implementation and the QTBT implementation complemented by trisection, may be motivated primarily by reduced complexity. In theory, the complexity of traversing a tree is T D where T represents the number of split types and D is the depth of the tree. Trade-offs may be made by using multitypes (T) while reducing the depth (D).

[0120] In some implementations, the CB may be further divided. For example, the CB may be further divided into multiple prediction blocks (PBs) for the purpose of intra-frame or inter-frame prediction during the coding and decoding processes. In other words, the CB may be further divided into different sub-divisions, where individual prediction decisions / configurations may be made. In parallel, the CB may be further divided into multiple transform blocks (TBs) for the purpose of describing the level at which the transformation or inverse transformation of the video data is performed. The division scheme of the CB into PBs and TBs may be the same or different. For example, each division scheme may be implemented using a unique procedure based on, for example, various characteristics of the video data. The division schemes of the PBs and TBs may be independent in some exemplary implementations. The division schemes and boundaries of the PBs and TBs may be correlated in some other exemplary implementations. In some implementations, for example, the TBs may be divided after the PB division, and in particular, each PB may be determined following the division of the coding block, and then further divided into one or more TBs. For example, in some implementations, the PB may be divided into one, two, four, or other number of TBs.

[0121] In some implementations, the luma and chroma channels may be processed differently to split the base blocks into coding blocks and further into predictive and / or transform blocks. For example, in some implementations, splitting of coding blocks into predictive and / or transform blocks may be allowed for the luma channel, but such splitting of coding blocks into predictive and / or transform blocks may not be allowed for the chroma channels. In such implementations, therefore, the transform and / or prediction of luma blocks may be performed only at the coding block level. In another example, the minimum transform block size of the luma and chroma channels may be different, e.g., the coding blocks of the luma channel may be allowed to be split into smaller transform and / or predictive blocks than the chroma channels. In yet another example, the maximum depth of the splitting of coding blocks into transform and / or predictive blocks may be different between the luma and chroma channels, e.g., the coding blocks of the luma channel may be allowed to be split into deeper transform and / or predictive blocks than the chroma channels. As a specific example, a luma coding block may be divided into transform blocks of multiple sizes that can be represented by a recursive partitioning down by up to two levels, and transform block shapes such as square, 2:1 / 1:2, and 4:1 / 1:4, as well as transform block sizes from 4×4 to 64×64 may be allowed. However, for chroma blocks, only the largest possible transform block designated for the luma block may be allowed.

[0122] In some example implementations for partitioning a coding block into PBs, the depth, shape, and / or other characteristics of the PB partition may depend on whether the PB is intra-coded or inter-coded.

[0123] The division of the coding block (or prediction block) into transform blocks may be performed in various exemplary manners, including but not limited to quadtree division and predefined pattern division, recursively or non-recursively, further considering transform blocks at the boundaries of the coding block or prediction block. In general, the resulting transform blocks may be at different division levels, may not be the same size, and may not need to be square in shape (e.g., they may be rectangular with some allowed size and aspect ratio). Further examples are described in more detail below in connection with Figures 15, 16, and 17.

[0124] However, in some other implementations, the CB obtained via any of the above partitioning schemes may be used as a basic or minimum coding block for prediction and / or transformation. In other words, no further partitioning is performed for the purpose of performing inter-prediction / intra-prediction and / or for the purpose of transformation. For example, the CB obtained from the above QTBT scheme may be used as a unit for performing prediction as it is. Specifically, such a QTBT structure removes the concept of multiple partition types, i.e., removes the separation of CU, PU, ​​and TU, and supports more flexibility on CU / CB partition shapes as described above. In such a QTBT block structure, the CU / CB can have either a square or rectangular shape. The leaf nodes of such a QTBT are used as units for prediction and transformation processing without further partitioning. This means that the CU, PU, ​​and TU have the same block size in such an exemplary QTBT coding block structure.

[0125] The various CB division schemes described above, as well as further division of the CB into PB and / or TB (including no PB / TB division), may be combined in any manner. The following specific implementations are provided as non-limiting examples.

[0126] Specific exemplary implementations of the division of coding blocks and transform blocks are described below. In such exemplary implementations, base blocks may be divided into coding blocks using recursive quadtree division or predefined division patterns described above (such as the division patterns of Figures 9 and 10). At each level, whether further quadtree division of a particular division should be continued may be determined by local video data characteristics. The resulting CBs may be at various quadtree division levels and of various sizes. The decision of whether to code a picture area using inter-picture (temporal) prediction or intra-picture (spatial) prediction may be made at the CB level (or at the CU level for all three color channels). Each CB may be further divided into one, two, four, or other number of PBs according to a predefined PB division type. Within one PB, the same prediction process may be applied, and related information may be transmitted to the decoder on a PB basis. After obtaining the residual blocks by applying the prediction process based on the PB division type, the CBs may be divided into TBs according to another quadtree structure similar to the coding tree for CBs. In this particular implementation, the CB or TB may not be limited to a square. Furthermore, in this particular example, the PB may be square or rectangular in inter prediction, and only square in intra prediction. The coding block may be divided, for example, into four square TBs. Each TB may be further divided recursively (using quadtree partitioning) into smaller TBs called residual quadtrees (RQTs).

[0127] Another exemplary implementation for splitting a base block into CB, PB, and / or TB is further described below. For example, rather than using multiple split unit types such as the types shown in FIG. 9 or FIG. 10, a quadtree with nested multi-type trees using bipartite and tripartite segmentation structures (e.g., QTBT or QTBT with tripartites described above) may be used. Separation of CB, PB, and TB (i.e., splitting CB into PB and / or TB, and splitting PB into TB) may be abandoned except when necessary for CBs with sizes too large for the maximum transform length, when such CBs require further splitting. This exemplary splitting scheme may be designed to support further flexibility on CB splitting shapes, such that prediction and transformation can both be performed at the CB level without further splitting. In such coding tree structures, CBs can have either square or rectangular shapes. Specifically, a coding tree block (CTB) may first be split by a quadtree structure. Then, the quadtree leaf nodes may be further split by a nested multi-type tree structure. An example of a nested multi-type tree structure using bisection or trisection is shown in Figure 11. Specifically, the example multi-type tree structure of Figure 11 includes four split types called vertical bisection (SPLIT_BT_VER) (1102), horizontal bisection (SPLIT_BT_HOR) (1104), vertical trisection (SPLIT_TT_VER) (1106), and horizontal trisection (SPLIT_TT_HOR) (1108). Then, CB corresponds to a leaf of the multi-type tree. In this example implementation, as long as CB is not too large for the maximum transform length, this segmentation is used for both prediction and transform processing without further splitting. This means that in most cases, CB, PB, and TB have the same block size in a quadtree 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 the color components of CB.In some implementations, in addition to bisection or trisection, the nested pattern of FIG. 11 may further include a quadtree division.

[0128] One specific example of a quadtree with nested multi-type tree coding block structure of block partitions (including quadtree partition, bipartition, and tripartition options) for one base block is shown in FIG. 12. More specifically, FIG. 12 shows that a base block 1200 is quadtree partitioned into four square partitions 1202, 1204, 1206, and 1208. A decision to further use the multi-type tree structure and quadtree of FIG. 11 for further partitioning is made for each of the quadtree partitioned partitions. In the example of FIG. 12, partition 1204 is not further partitioned. Partition 1202 and partition 1208 each adopt another quadtree partition. In partition 1202, the second level quadtree partitioned top left, top right, bottom left, and bottom right partitions adopt third level partitions of quadtree, horizontal bipartition 1104 of FIG. 11, non-partition, and horizontal tripartition 1108 of FIG. 11, respectively. Partition 1208 adopts another quadtree partitioning, and the second level quadtree partitioned top-left, top-right, bottom-left, and bottom-right partitions adopt the third level partitioning of vertical third partition 1106, unpartitioned, unpartitioned, and horizontal bisection 1104 of FIG. 11, respectively. Two of the subpartitions of the third level top-left partition of 1208 are further partitioned according to horizontal bisection 1104 and horizontal third partition 1108 of FIG. 11, respectively. Partition 1206 adopts the second level partitioning pattern into two partitions following vertical bisection 1102 of FIG. 11, and the two partitions are further partitioned at the third level according to horizontal third partition 1108 and vertical bisection 1102 of FIG. 11. A fourth level partitioning is further applied to one of them according to horizontal bisection 1104 of FIG. 11.

[0129] In the above specific example, the maximum luma transform size may be 64×64, and the maximum supported chroma transform size may be different from the luma, e.g., 32×32. Even if the above example CB of FIG. 12 is not generally further divided into smaller PBs and / or TBs, when the width or height of a luma coding block or a chroma coding block is larger than the maximum transform width or maximum transform height, the luma coding block or the chroma coding block may be automatically divided in the horizontal and / or vertical directions to satisfy the transform size constraints in that direction.

[0130] In the specific example of the division of the base block into CBs above, as described above, the coding tree scheme may support the ability for luma and chroma to have separate block tree structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU may share the same coding tree structure. For I slices, for example, luma and chroma may have separate coding block tree structures. When separate block tree structures are applied, the luma CTB may be divided into luma CBs by one coding tree structure, and the chroma CTB is divided into chroma CBs by another coding tree structure. This means that a CU in an I slice may be composed of a coding block of a luma component or a coding block of two chroma components, and a CU in a P slice or B slice is always composed of coding blocks of all three color components, unless the video is monochrome.

[0131] When a coding block is further divided into multiple transform blocks, the transform blocks therein may be ordered in the bitstream according to various orders or scanning methods. Exemplary implementations for dividing a coding block or a predictive block into transform blocks and the coding order of the transform blocks are described in further detail below. In some exemplary implementations, as described above, the transform division may support transform blocks of multiple shapes, e.g., 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1, with transform block sizes ranging from, e.g., 4×4 to 64×64. In some implementations, if the coding block is smaller than or equal to 64×64, the transform block division may be applied only to the luma component, such that for chroma blocks, the transform block size is identical to the coding block size. Otherwise, if the width or height of the coding block is greater than 64, both the luma coding block and the chroma coding block may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively, of transform blocks.

[0132] In some example implementations of transform block partitioning, for both intra-coded and inter-coded blocks, a coding block may be further partitioned into multiple transform blocks with a partition depth up to a predefined number of levels (e.g., two levels). The partition depth and size of the transform block may be related. For some example implementations, the mapping from the transform size of the current depth to the transform size of the next depth is shown below in Table 1. [Table 1]

[0133] Based on the example mapping of Table 1, for a 1:1 square block, the next level transform split may create four 1:1 square sub-transform blocks. The transform split may stop at, for example, 4×4. Thus, a transform size of the current depth of 4×4 corresponds to the same size of 4×4 of the next depth. In the example of Table 1, for a 1:2 / 2:1 non-square block, the next level transform split may create two 1:1 square sub-transform blocks, while for a 1:4 / 4:1 non-square block, the next level transform split may create two 1:2 / 2:1 sub-transform blocks.

[0134] In some example implementations, further restrictions may be applied on transform block partitioning for the luma components of intra-coded blocks. For example, for each level of transform partitioning, all sub-transform blocks may be restricted to have equal size. For example, for a 32×16 coding block, level 1 transform partitioning creates two 16×16 sub-transform blocks, and level 2 transform partitioning creates eight 8×8 sub-transform blocks. In other words, to keep the transform units equal in size, a second level partitioning must be applied to all first level sub-blocks. An example of transform block partitioning for an intra-coded square block according to Table 1 is shown in FIG. 15 with the coding order indicated by the arrows. Specifically, 1502 shows a square coding block. The first level partitioning according to Table 1 into four equal-sized transform blocks is shown in 1504 with the coding order indicated by the arrows. The second level partitioning of all first level equal-sized blocks according to Table 1 into 16 equal-sized transform blocks is shown in 1506 with the coding order indicated by the arrows.

[0135] In some example implementations, the above restrictions on intra-coding may not apply to the luma components of an inter-coded block. For example, after the first level of transform splitting, any one of the sub-transform blocks may be further split independently at another level. Thus, the resulting transform blocks may or may not be blocks of the same size. An example splitting of an inter-coded block into transform blocks according to their coding order is shown in FIG. 16. In the example of FIG. 16, an inter-coded block 1602 is split into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is split into four transform blocks of equal size. Then, only one of the four transform blocks (but not all of them) is further split into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes, as shown by 1604. An example coding order of these seven transform blocks is shown by arrows at 1604 in FIG. 16.

[0136] In some example implementations, for chroma components, some further restrictions on the transform blocks may be applied: for example, for chroma components, the transform block size may be as large as the coding block size, but cannot be smaller than a predefined size, e.g., 8×8.

[0137] In some other example implementations, for coding blocks with either width (W) or height (H) greater than 64, both luma coding blocks and chroma coding blocks may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32) transform units, respectively, where in this disclosure, “min(a,b)” can return the smaller value between a and b.

[0138] FIG. 17 further illustrates another alternative exemplary scheme for splitting a coding block or a predictive block into transform blocks. As illustrated in FIG. 17, instead of using recursive transform partitioning, a set of predefined partition types may be applied to a coding block according to the transform type of the coding block. In the particular example illustrated in FIG. 17, one of six exemplary partition types may be applied to split the coding block into various numbers of transform blocks. Such a scheme for generating transform block partitions may be applied to either a coding block or a predictive block.

[0139] More specifically, the partitioning scheme of FIG. 17 provides up to six exemplary partitioning types for any given transform type (transform type refers to the type of primary transform, such as, for example, ADST). In this scheme, every coding block or predictive block may be assigned a transform partitioning type, for example, based on a rate-distortion cost. In one example, the transform partitioning type assigned to a coding block or predictive block may be determined based on the transform type of the coding block or predictive block. As shown by the six transform partitioning types illustrated in FIG. 17, a particular transform partitioning type may correspond to the partitioning size and pattern of the transform block. The correspondence between various transform types and various transform partitioning types may be predefined. An example is shown below, where the capitalized labels indicate transform partitioning types that may be assigned to a coding block or predictive block based on a rate-distortion cost.

[0140] ·PARTITION_NONE: Allocate the transformation size equal to the block size.

[0141] ·PARTITION_SPLIT: Allocates a transformation size of 1 / 2 the block size in width and 1 / 2 the block size in height.

[0142] ·PARTITION_HORZ: Allocates a transformation size with width equal to the block size and height equal to 1 / 2 the block size.

[0143] ·PARTITION_VERT: Allocates a transformation size with a width half the block size and a height equal to the block size.

[0144] ·PARTITION_HORZ4: Allocates a transformation size with width equal to the block size and height equal to 1 / 4 of the block size.

[0145] ·PARTITION_VERT4: Allocates a transformation size with a width of 1 / 4 of the block size and a height equal to the block size.

[0146] In the above example, the transform split types shown in Figure 17 include all uniform transform sizes for the split transform blocks. This is not a limitation but merely an example. In some other implementations, mixed transform block sizes may be used for the split transform blocks in a particular split type (or pattern).

[0147] The PB (or CB, also called PB, when not further divided into predictive blocks) obtained from any of the above partitioning schemes in pixel format can become individual blocks coded via either intra prediction or inter prediction. For inter prediction of the current PB, the predictor block can be generated from a reconstructed block in one or more reference frames associated with the corresponding motion vector. For intra prediction of the current PB, the pixel values ​​of the predictor block can be generated instead based on a reconstructed version of the neighboring video samples of the current PB. In either inter prediction or intra prediction situations, the residual between the current PB and the predictor block is obtained and coded during the encoding process. The residual block may then be transformed as is or transformed into frequency space in small TB units during the encoding process. The transform coefficients may then be quantized and entropy coded. The coded transform coefficients may then be included in the coded bitstream. The reconstruction of the current block in the decoder or encoder is based on decoding the residual and combining the decoded residual and the reconstructed predictor block, correspondingly. For the reconstruction process in the encoder, as described above, the quantized residual of the current block is directed to be reconstructed without having to go through entropy coding and decoding.

[0148] For intra prediction, various exemplary modes may be supported in a particular implementation. For example, intra prediction based on neighboring samples may be directional or non-directional. Examples of directional intra prediction modes have been described in connection with FIG. 1A and FIG. 1B above. For example, each pixel of the current PB may be predicted by a reconstructed sample of either the immediately upper row or the immediately left row of the current PB along the previous cell direction. In some other implementations, the directional intra prediction mode may also include neighboring samples beyond the immediately upper sample and the immediately left sample of the current PB. In a particular example, samples from one or more of the second or third upper or left neighboring lines of the current block along a particular direction may be used to predict each pixel of the current coding block and form a corresponding intra predictor block.

[0149] Omnidirectional intra prediction may be implemented in various exemplary forms, taking into account gradients, spatial correction of samples, and coherence of luma and / or chroma planes. For example, omnidirectional intra prediction modes may include, but are not limited to, DC, Paeth, Smooth, Smooth Vertical, Smooth Horizontal, Recursive-based-filtering (modes 0-4), and Chroma-from-luma (CfL) prediction modes. In some exemplary implementations, omnidirectional intra prediction may be specifically invoked for certain types of images and may further include particularly efficient modes. For example, for screen content (rather than general motion content), Intra Block Copy (IBC) mode and Palette mode may be invoked. BC mode specifically exploits coding gains that may be achieved for repeating patterns (such as text patterns) within the current frame. BC mode may implement intra prediction using a mechanism similar to, for example, motion vector-based inter prediction. On the other hand, paletted intra prediction mode (also referred to as "palette mode" for simplicity) takes advantage of the coding gain that can be achieved as a result of relatively small pixel values ​​in some coding blocks of screen content.

[0150] Therefore, in particular, the palette intra prediction mode may be called to generate a predictor block of the current PB using a limited number of pixel values ​​(or color values). For example, each pixel in the PB may be predicted by one of a set of entries in the palette. The palette may include a limited number of pixel values. These values ​​may be indexed in the palette, and each pixel of the PB may refer to an index in the palette as the prediction of the pixel. Since the number of values ​​or entries in the palette, or the size of the palette, is limited, the index is represented by a small number of bits. Therefore, the prediction of each pixel in the palette mode requires fewer bits to code than the full range pixel value.

[0151] For example, the size of the palette may be limited to 8. Thus, the index into the palette may be coded with 3 bits. Thus, the pixel-by-pixel prediction of the current PB takes 3 bits instead of the full color depth (e.g., 8 bits). The expense or cost in bits of the palette intra prediction mode includes both the predictor block and the overhead of transmitting the palette in the bitstream. As long as the palette size is limited to a certain size, the cost decreases for larger block sizes. Thus, the palette mode may provide significant coding gains for large PBs with large block sizes, but its benefits in terms of coding efficiency may decrease for PBs with small block sizes. Thus, in some example implementations, the palette mode may not be allowed for PBs with sizes smaller than a threshold block size. For example, the palette mode may only be allowed for PBs with block sizes equal to or greater than a threshold block size of 8×8.

[0152] In some exemplary implementations of palette mode, PBs that are intra-coded under palette prediction mode may not be allowed to be further divided into small transform blocks. In other words, intra prediction in palette mode may only be performed on transform blocks (which are also predictive blocks because they should not be further divided into transform blocks). Therefore, in order to avoid large transform blocks, an upper limit on PB size may also be specified in some exemplary implementations. For example, palette mode may only be applied when both the width and height of a coding block are equal to or less than a threshold, e.g., 64.

[0153] The palette mode may be applied separately to the luma and chroma of a coding block. In some example implementations, whether to apply the palette mode may be determined independently between luma and chroma. Thus, for a prediction unit consisting of both a luma prediction block and a chroma prediction block, the decision to apply the palette mode may be made independently for the luma prediction block and the chroma prediction block. For example, for a luma channel, each entry in the palette may be a scalar value, while for a chroma channel, each entry in the palette may be a two-dimensional tuple. In some other example implementations, whether to apply the palette mode to the luma plane and the chroma plane is tied, with either they all being predicted under the palette mode or none of them being predicted. The palette used in the palette mode may alternatively be referred to as a color palette. The term color may represent one of the luma, or chroma.

[0154] As mentioned above, the use of a color palette predictor is beneficial when a block may be approximated with a small number of unique colors (or color values), which may allow for the construction of a small-sized color palette to provide efficient prediction. As mentioned or implied above, in a palette mode for predicting a current intra-coding block, the bitstream structure generated by the encoder may include an array and structure map representing the color palette, for example, in the form of a 2D array filled with indexes of colors in the color palette as the prediction block of the current coding block. In some implementations, the size of the color palette may be limited to 2-8 (corresponding to 1-3 bit color indexes). The encoder may explore different sizes of palettes, and different color values ​​in the palette, to optimize the resulting rate-distortion cost and maximize the coding gain.

[0155] In some example implementations, such a palette mode may be available for coding the current PB when the current PB should be intra-coded under the DC prediction mode. In other words, from a signaling perspective, the palette intra prediction mode may be considered as a submode under the DC intra prediction mode. Therefore, whether the current block is potentially predicted under the palette mode may be first indicated by a bitstream syntax element for DC intra prediction (e.g., DC intra prediction flag). A DC intra prediction flag of "0" (or "1") indicates that the current coding block is neither DC predicted nor predicted based on a color palette, and a DC intra prediction flag of "1" (or "0") may indicate that the current coding block is either DC predicted or predicted based on a color palette. In the latter situation, an additional syntax element or flag may be included in the bitstream to indicate whether the current block is DC predicted or predicted by a color palette. Such an additional syntax element or flag may not be present in the latter situation. In some other alternative implementations, a flat independent of and / or parallel to the DC prediction mode flag may be used to signal whether the current block is predicted under palette mode or not.

[0156] When the current block is predicted under palette mode, additional information associated with the color palette used (e.g., palette size and palette entries) may be included explicitly or may be derivable from the bitstream. In some situations, the color palette used for the current coding block may be self-contained and independent of other previous coding blocks in the bitstream. In some other situations, the palette used for the current coding block may depend on other previous coding blocks, especially in situations where the current coding block is highly correlated with previous coding blocks predicted under palette intra-coding mode, since the current coding block and these neighboring blocks may have the same color pixel value distribution and therefore may share one or more entries in their color palettes. In such situations, some or all of the color palette of the current coding block may include palette entries of entries of the neighboring block palette. The neighboring block palette may be referred to as a reference palette. The neighboring block palette may also be referred to as a cache / cached palette, or a single collective cache / cached palette, since it is available during the encoding and decoding process for the reconstruction of the current coding block and may be maintained in a cache. A portion or the entire color palette of the current coding block that is based on a cached palette may be referred to as an inherited part of the current color palette. The coding of this inherited part of the color palette may then be based on neighboring palettes.

[0157] Coding gain may be achieved when coding the inherited portion of the color palette based on neighboring palettes. The remaining palette entries of the current coding block other than the inherited portion, if any, may be explicitly signaled in the bitstream. The size of the inherited portion of the current color palette (i.e., the number of entries in the unique portion of the current color palette) may be derived or explicitly signaled.

[0158] Thus, in some example implementations, to provide the above color palette information in a bitstream when palette mode is enabled, several syntax elements may be signaled, including, but not limited to, (1) a first flag called has_palette_y indicating whether palette mode should be applied to the current coding block (e.g., after the DC mode flag has been signaled and applied, as described above), (2) a syntax element called palette_size_y_minus_2 specifying the palette size, and (3) a second flag called use_palette_color_cache_y indicating whether at least one color index is inherited from a neighboring palette, which may be organized and maintained in a palette cache during the encoding or decoding process. If the number of inherited palette entries is less than the signaled palette size, the remaining color indexes may be explicitly signaled. In some example implementations, two chroma color components may share the has_palette_uv and palette_size_uv_minus_2 syntax elements (meaning that both of the two chroma components either contain inherited palette entries or not, and when using inherited palette entries, they contain the same number of inherited palette entries), but the color indexes in the palette used for prediction of the current chroma block may be signaled separately for the Cb and Cr components. These example syntaxes for signaling palettes of three color components are shown below: [Table 2A] [Table 2B] [Table 2C] [Table 2D] [Table 2E]

[0159] In the above example syntax table, the function get_palette_cache() is called, which returns the size of the palette cache and builds the palette cache from the color palettes of the neighboring blocks. As mentioned above, the palette cache refers to a palette derived or maintained from the palettes used by the neighboring blocks. In order to obtain the size of the palette cache, which represents the number of unique entries of the neighboring color palettes and is related to the size of the part of the inherited palette entries of the current coding block, the palettes of the neighboring blocks need to be retrieved with their entries deduplicated. Thus, this function can be equivalent to, for example, sorting the available palette colors from the upper and left blocks and then removing the duplicate entries. In addition, after the palette entries of the current block are all determined and / or parsed, they need to be sorted in ascending order and cached to facilitate the calculations performed in get_palette_cache() for subsequent blocks, since some calculations are performed assuming that the neighboring palette entries are arranged in ascending order.

[0160] An example of the get_palette_cache() function is detailed below. This example shows that the get_palette_cache() function may involve complex calculations to generate a palette cache that contains all neighboring palette entries in ascending order with no duplicates. This process may be thought of as merging palette entries from neighboring blocks, such as the top and left neighboring blocks. get_palette_cache(plane) {Type aboveN=0 if((MiRow*MI_SIZE)%64){ aboveN=PaletteSizes[plane][MiRow-1][MiCol] } leftN=0 if(AvailL){ leftN=PaletteSizes[plane][MiRow][MiCol-1] } aboveIdx=0 leftIdx=0 n=0 while(aboveIdx<aboveN&&leftIdx<leftN){ aboveC=PaletteColors[plane][MiRow-1][MiCol][aboveIdx] leftC=PaletteColors[plane][MiRow][MiCol-1][leftIdx] if(leftC<aboveC){ if(n==0||leftC!=PaletteCache[n-1]){ PaletteCache[n]=leftC n++ } leftIdx++ }else{ if(n==0||aboveC!=PaletteCache[n-1]){ PaletteCache[n]=aboveC n++ } aboveIdx++ if(leftC==aboveC){ leftIdx++ } } } while(aboveIdx<aboveN){ val=PaletteColors[plane][MiRow-1][MiCol][aboveIdx] aboveIdx++ if(n==0||val!=PaletteCache[n-1]){ PaletteCache[n]=val n++} } while(leftIdx <leftN){ val=PaletteColors[plane][MiRow][MiCol-1][leftIdx] leftIdx++ if(n==0||val!=PaletteCache[n-1]){ PaletteCache[n]=val n++ } } return n }

[0161] Once the color palette of the current coding block is established (including inherited palette entries and explicitly signaled palette entries not used in the neighbor palette), it may be used as a basis for predicting the current coding block. For each pixel in a coding block predicted under palette mode, the selected palette index may be signaled and coded, for example, in a diagonal scan order, as shown in FIG. 18. The different shadings in FIG. 18 correspond to different palette indices (or palette values). The scan may proceed in a diagonal direction starting from the top left and ending at the bottom right. After all palette indices along the diagonal of the coding block have been selected and coded, the scan moves to the top right sample of the next diagonal. In some example implementations, the first index of the current palette coding block may be coded first using a separate syntax element called color_index_map_y, and the remaining indexes may be coded, for example, using their upper, left, and top left neighbor indices as a context for entropy coding. The associated syntax for signaling palette indices of a palette mode predictor block is shown below. [Table 3A] [Table 3B]

[0162] Thus, in the above exemplary implementation, from the decoder's point of view, the get_palett_cache() function or its equivalent may need to be called and executed to determine the size of the palette cache. The size of the palette cache may be referred to as cacheN, which may also represent the size of the inherited part of the color palette for the current coding block. Execution of the get_palett_cache() function in palette mode may involve complex calculations to parse and reconstruct the palette entries of neighboring blocks in the palette cache. Without cacheN, parsing of the palette mode parameters of the current coding block cannot proceed.

[0163] The decoding process of a video block generally includes multiple aspects. In a first aspect, the decoding process must parse the bitstream to extract various syntax element data elements. In a second aspect, the decoding process may extract coded information and reconstruct the encoded video block based on the coded information and various syntax elements extracted from the bitstream. In the process of decoding a current coding block encoded in a palette intra-prediction mode, the parameter cacheN needs to be obtained first to proceed with parsing the bitstream in order to obtain other parameters of the color palette of the current coding block.

[0164] According to the above implementation, since the get_palette_cache() function involves both parsing the bitstream and reconstructing neighboring coding blocks (since it needs to actually determine the palette entries of the neighboring blocks and merge these entries by identifying overlapping palette entries), the parsing of the current coding block not only needs to wait for the parsing process of the neighboring coding blocks, but also needs to wait until at least a part of the reconstruction process of the neighboring coding blocks is completed.

[0165] In some situations, and to improve parallel processing during the decoding process and the reconstruction speed of the current coding block, it may be desirable for the parsing process of the current coding block in the bitstream to begin as soon as the neighboring blocks have been parsed, without waiting for the completion of the reconstruction process of the neighboring blocks (e.g., before processing and merging the neighboring block palette entries).

[0166] For such purposes, and in some other example implementations of the present disclosure, the encoding and decoding schemes in palette mode may be designed such that the complexity associated with determining the size of the cached palette cacheN beyond the parsing step of the neighboring coding blocks may be reduced or avoided. For example, the parameter cacheN may be determined without the need to perform a merging process of palette entries of neighboring blocks. Thus, the decoder may start parsing information related to the palette mode of the current coding block from the bitstream as soon as the neighboring coding block is parsed. Thus, the parsing of the current coding block from the bitstream may be performed in parallel with further reconstruction of the neighboring coding blocks. Once the current coding block information is parsed from the bitstream, other information associated with the neighboring coding blocks that may be required for the reconstruction of the current coding block may be available from the parallel reconstruction process of the neighboring coding blocks.

[0167] In some example implementations, the derivation of cacheN, the size of the inherited portion of the color palette for the current coding block, may be based on the palette sizes of the neighboring blocks of the current coding block, rather than the contents (or palette entry values). For example, two neighboring blocks of the current coding block (such as the immediate upper and left neighboring blocks) may be used to derive the cacheN parameter. The palette sizes of the upper and left neighboring blocks may be represented as paletteA (top) and paletteL (left). Such palette size parameters may be obtained during the parsing process of the neighboring blocks, or may be explicitly signaled within the bitstream of the neighboring blocks (and thus may be extracted by bitstream parsing alone). Then, without knowing the palette entries of both of these neighboring blocks, cacheN may be derived as a function of paletteA and / or palette before parsing the current coding block. In this way, parsing of the palette parameters may begin without having to wait until the neighboring block palette entries have been extracted, merged, and de-duplicated. An example of the functional relationship between cacheN, paletteA, and paletteB is: Max(paletteA, paletteL)+N (where N is an integer, and example values ​​of N include, but are not limited to, 0, 1, 2, 3, 4, 5, 6, 7, 8, ...), Min(paletteA, paletteL)+N (where N is an integer, and examples of values ​​for N include, but are not limited to, 0, 1, 2, 3, 4, 5, 6, 7, 8, ...); Min(Max(paletteA,paletteL)+N,T) (where N is an integer and example values ​​of N include, but are not limited to, 0, 1, 2, 3, 4, 5, 6, 7, 8, ... and T is a given maximum number of palettes allowed in a block), or Min(Min(paletteA,paletteL)+N,T) (N is an integer, example values ​​of N include, but are not limited to, 0, 1, 2, 3, 4, 5, 6, 7, 8, ..., and T is a given maximum number of palettes allowed in a block); may include, but is not limited to:

[0168] The value of T, which represents the maximum allowable size of the color palette, may be applied to the size of the entire color palette, including both inherited and non-inherited portions.

[0169] In some other example implementations, the value of cacheN may be derived as a fixed size. Examples of fixed sizes include, but are not limited to, 0, 1, 2, 3, 4, 5, 6, 7, 8, .... Such a fixed cacheN may be predetermined. Alternatively, the value of cacheN may be signaled in the bitstream. For example, the value of cacheN may be signaled in a high-level syntax, including, but not limited to, being signaled as part of a sequence parameter set (SPS), a video parameter set (VPS), a picture parameter set (PPS), an adaptation parameter set (APS), a frame header, a slice header, a picture header, a tile header, or a coding tree unit (CTU) header.

[0170] In some example implementations, the value of cacheN may be derived by some already coded information, including but not limited to, block size of the current coding block or of neighboring blocks, prediction mode, etc. For example, a large cacheN value may be derived for a large current coding block size and / or a larger block size for neighboring blocks (so that improved coding efficiency can be achieved even with large color palette sizes), and in another example, a small cacheN may be used when the neighboring blocks are coded in intra block copy mode.

[0171] In some example implementations, the size of cacheN may be derived by the number of repeated palette entries in the neighboring blocks. Specifically, the same repeated palette entries in the neighboring blocks may appear frequently in the current coding block, and the highest coding gain may be achieved by only inheriting these entries in the color palette of the current coding block. Thus, cacheN, the size of the inherited patent, may be set as the number of repeated palette entries in the neighboring blocks. The neighboring blocks may include the immediately upper and left blocks. In some example implementations, the neighboring blocks may extend to other non-immediate upper / left blocks. For example, the number of repeated palette entries in the neighboring blocks may be signaled in the bitstream and thus may be obtained only by parsing.

[0172] For example, when two neighboring blocks (e.g., the immediately upper block and the immediately left block) are used to derive the cached palette, the number of palette entries used in both of the two neighboring blocks may be used to derive the value of cacheN. In other words, the number of palette entries used in both of the two neighboring blocks may be used as cacheN.

[0173] In another more general example, when M neighboring blocks are used to derive the cached palette, where M is an integer, the number of palette entries used in at least K neighboring blocks is used to derive the value of cacheN. Example values ​​of K include, but are not limited to, 1, 2, 3, 4, 5, ..., M. For example, as noted above, M may be 2 and K may be 2. In another example, M may be 3 or more and K may be any number from 1 to M.

[0174] In any of the above implementations, three or more neighboring blocks may be used to derive the cachN parameter. Some of the neighboring blocks may include, for example, non-immediate (or non-adjacent) neighboring blocks of the current coding block. When multiple neighboring blocks are to be relied upon to determine the inherited portion of the color palette of the current coding block, the above-mentioned M neighboring blocks may be identified by scanning all neighboring blocks of the current coding block until M neighboring blocks encoded in palette mode are encountered (note that not all neighboring blocks are encoded in palette mode, because they may also be encoded in other intra- or inter-prediction modes). The order of scanning may be predefined.

[0175] Based on the above method, after the palette entries of the color palette from the neighboring blocks are merged and deduplicated, the variable cacheN of the current block is derived without knowing the actual palette size, allowing parsing of the palette and other information of the current coding block without delay. The actual size of the palette cache after such merging and deduplicating of the neighboring block palette entries may differ from the derived cacheN. When this happens, a set of rules may be implemented for the encoder and decoder to select palette entries from the merged and deduplicated palette cache to form cacheN number of palette entries as the inherited part of the color palette for the current coding block.

[0176] In some example implementations, if the size of the merged palette entries in a palette cache, called S, is greater than cacheN, the following rules may be used to select a palette entry from the palette cache:

[0177] For example, the first cacheN entries may be selected from the palette cache. Such selection may be performed according to a predetermined scanning order in a merge list of neighboring palette entries. In such an implementation, in the merge list or palette cache, the palette entries of the neighboring palettes may also be ordered in a predetermined manner.

[0178] In another example, the last cacheN entries may be selected from the palette cache. Such selection may be performed according to a predetermined scanning order in a merge list of neighboring palette entries. In such an implementation, in the merge list or palette cache, the palette entries of the neighboring palettes may also be ordered in a predetermined manner.

[0179] In another example, duplicate palette entries from both neighboring blocks (e.g., the top-left neighboring block, or other neighboring blocks) should be selected from the merged list first. The scanning of the entries may be from left to right, or any other predetermined scanning order from the merged palette entry list to select duplicate palette entries for the inherited portion of the palette for the current coding block. Correspondingly, the duplicate entries may be arranged in the merged entry list from left to right. Such scanning determines which duplicate entries are included in the inherited portion of the palette for the current coding block, especially when the number of duplicate entries is greater than cacheN. Thereafter, if more entries are needed to form cacheN number of entries for the inherited portion of the color palette for the current block, the first few entries in the merged list may be selected, for example, until cacheN number of entries for the inherited portion of the color palette for the current block is filled.

[0180] In yet another example, duplicate entries from neighboring blocks (e.g., the top-left neighboring block, or other neighboring blocks) should be selected from the merge list first. The scanning of the entries may be from left to right, or any other predefined scanning order from the merged palette entry list to select duplicate palette entries for the inheritance portion of the palette for the current coding block. Correspondingly, the duplicate entries may be arranged in the merged entry list from left to right. Such scanning determines which duplicate entries are included in the inheritance portion of the palette for the current coding block, especially when the number of duplicate entries is greater than cacheN. Thereafter, if more entries are needed to form cacheN number of entries for the inheritance portion of the color palette for the current block, the last few entries of the merge list may be selected, for example, until cacheN number of entries for the inheritance portion of the color palette for the current block is filled.

[0181] On the other hand, in some other example implementations, if the size S of the merged palette entries is smaller than cacheN, indicating that the palette entries in the palette cache are not enough to fill cacheN number of entries in the inherited portion of the color palette for the current coding block and additional palette entries are needed, and the following rules may be used to select such additional palette entries:

[0182] For example, for each required additional entry, a color pixel offset value may be determined and added to one of the existing entries in the palette cache (or the inherited portion of the color palette for the current coding block). The offset value may be either positive or negative. The selected existing palette entry may be, for example, (1) the largest entry in the merge list, (2) the smallest entry in the merge list, or (3) the most frequently used entry in the merge list. The offset values ​​of the different added entries may be the same or different. The offset values ​​may be extrapolated or interpolated from the existing palette entries, for example, in the palette cache or in the inherited portion of the color palette for the current coding block.

[0183] In another example, a set of predefined palette entry values ​​may be used as additional palette entries of the color palette for the current coding block. These predefined palette entry values ​​may be signaled in the bitstream as high-level syntax, such as sequence, picture, frame, slice, superblock, and other levels. The values ​​cacheN-S used to fill the inherited portion of the color palette for the current coding block, up to cacheN entries, may be obtained as needed in the order of the set of predefined palette entries starting from the first predefined entry, as signaled or otherwise specified.

[0184] FIG. 19 shows a flowchart 1900 of an exemplary method according to the principles underlying the above implementations for intra prediction in palette mode. The flow of the exemplary decoding method starts at S1901. At S1910, it is determined that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block from the video stream. At S1920, a size cacheN of an inherited portion of the current palette associated with the current video block is determined before performing any merging of the at least one reference palette, where cacheN is an integer. At S1930, the inherited portion of the current palette is derived based on cacheN and the at least one reference palette. At S1940, a palette index into the current palette for an element of the current video block is extracted from the video stream. At S1950, a predictor block of the current video block is generated based on at least the palette index and the current palette. The exemplary method stops at S1999.

[0185] In the embodiments and implementations of the present disclosure, any steps and / or operations may be combined or arranged in any quantity or order, as desired. Two or more of the steps and / or operations may be performed in parallel. The embodiments and implementations of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors, or one or more integrated circuits). In one example, the one or more processors execute a program stored in a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to a luma block or a chroma block. The term block may be interpreted as a prediction block, a coding block, or a coding unit, i.e., a CU. The term block here may also be used to refer to a transform block. In the following items, when referring to a block size, it may refer to either the width or height of the block, or the maximum value of the width and height, or the minimum value of the width and height, or the size of the area (width*height), or the aspect ratio of the block (width:height, or height:width).

[0186] The techniques described above may be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 20 illustrates a computer system (2000) suitable for implementing certain embodiments of the disclosed subject matter.

[0187] The computer software may be coded using any suitable machine code or computer language that may undergo assembly, compilation, linking, or similar mechanisms to produce code containing instructions that may be executed directly by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., or through interpretation, execution of microcode, etc.

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

[0189] The components illustrated in Figure 20 for the computer system (2000) 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. The arrangement of components should not be interpreted as having a dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of the computer system (2000).

[0190] The computer system (2000) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users, for example, via tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), olfactory input (not shown). Human interface devices may be used to capture certain media not necessarily directly associated with conscious human input, such as audio (voice, music, ambient sounds, etc.), images (scanned images, photographic images obtained from still image cameras, etc.), video (two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0191] The input human interface devices may include one or more (only one of each shown) of a keyboard (2001), a mouse (2002), a trackpad (2003), a touch screen (2010), a data glove (not shown), a joystick (2005), a microphone (2006), a scanner (2007), a camera (2008).

[0192] The computer system (2000) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, by haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (2010), data gloves (not shown), or joystick (2005), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (2009), headphones (not shown)), visual output devices (e.g., screens (2010), including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which may be capable of two-dimensional visual output, or four or more dimensions of output by means of stereoscopic image output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown), etc.), and printers (not shown).

[0193] The computer system (2000) may also include human accessible storage devices and their associated media, such as optical media including CD / DVD ROM / RW (2020) with media (2021) such as CDs / DVDs, thumb drives (2022), removable hard drives or solid state drives (2023), legacy magnetic media such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD based devices (not shown) such as security dongles, and the like.

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

[0195] The computer system (2000) may also include an interface (2054) to one or more communication networks (2055). The networks may be, for example, wireless, wired, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, cellular networks including wireless LAN, GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television and terrestrial television, vehicular and industrial including CAN bus, etc. Certain networks typically require an external network interface adapter connected to a particular general purpose data port or peripheral bus (2049) (e.g., a USB port on the computer system (2000)), while others are generally integrated into the core of the computer system (2000) by connecting to a system bus, as described below (e.g., an Ethernet interface for a PC computer system, or a cellular network interface for a smartphone computer system). Using any of these networks, the computer system (2000) can communicate with other entities. Such communications may be one-way receive only (e.g., terrestrial broadcast television), one-way transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks may be used in each of these networks and network interfaces, as described above.

[0196] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to the core (2040) of the computer system (2000).

[0197] The cores (2040) may include one or more central processing units (CPUs) (2041), graphics processing units (GPUs) (2042), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (2043), hardware accelerators for specific tasks (2044), graphics adapters (2050), and the like. These devices may be connected via a system bus (2048), along with read-only memory (ROM) (2045), random access memory (2046), internal mass storage (2047), such as an internal non-user accessible hard drive, SSD, and the like. In some computer systems, the system bus (2048) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, and the like. Peripheral devices may be attached directly to the core's system bus (2048) or via a peripheral bus (2049). In one example, a screen (2010) may be connected to the graphics adapter (2050). Architectures for peripheral buses include PCI, USB, etc.

[0198] The CPU (2041), GPU (2042), FPGA (2043), and accelerator (2044) can execute certain instructions that may combine to constitute the aforementioned computer code. The computer code may be stored in a ROM (2045) or a RAM (2046). Temporary data may also be stored in the RAM (2046), and persistent data may be stored, for example, in an internal mass storage (2047). Rapid storage and retrieval from any of the memory devices may be enabled by the use of a cache memory that may be closely associated with one or more of the CPU (2041), GPU (2042), mass storage (2047), ROM (2045), RAM (2046), and the like.

[0199] The computer-readable medium may bear computer code 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.

[0200] As a non-limiting example, a computer system (2000) having an architecture, and in particular a core (2040), may provide functionality as a result of a processor (or processors) (including CPUs, GPUs, FPGAs, accelerators, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be user-accessible mass storage as described above, as well as media associated with specific storage of the core (2040) that is non-transitory in nature, such as the core internal mass storage (2047) or ROM (2045). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the core (2040). The computer-readable media may include one or more memory devices or chips, depending on the particular needs. The software may cause the core (2040), and in particular the processors (including CPUs, GPUs, FPGAs, etc.) therein, to perform certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (2046) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (2044)), which may operate in place of or in conjunction with software to perform particular processes or portions of particular processes described herein. Where appropriate, references to software may encompass logic, and vice versa. Where appropriate, references to computer-readable media may encompass circuitry (such as integrated circuits (ICs)) that stores software for execution, circuitry that embodies logic for execution, or both. The present disclosure encompasses any suitable combination of hardware and software.

[0201] While this disclosure has described several exemplary embodiments, there are modifications, substitutions, and various alternative equivalents that are within the scope of this disclosure. Thus, it will be appreciated that those skilled in the art can devise numerous systems and methods that, although 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. Appendix A: Acronyms JEM: Joint Exploration Model VVC: Versatile Video Coding BMS: Benchmark Set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplemental Extended Information VUI: Video Usability Information GOP: Group of Pictures TU: conversion unit PU: Prediction unit CTU: Coding Tree Unit CTB: coding tree block PB: Predicted block HRD: Hypothetical Reference Decoder SNR: Signal to Noise Ratio CPU: Central Processing Unit GPU: Graphics Processing Unit CRT: cathode ray tube LCD: Liquid crystal display OLED: Organic Light Emitting Diode CD:Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile Communications LTE: Long Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Area SSD: Solid State Drive IC: Integrated Circuit HDR: High Dynamic Range SDR: Standard Dynamic Range JVET: Joint Video Exploration Team MPM: Most Probable Mode WAIP: Wide-angle Intra Prediction CU: coding unit PU: Prediction unit TU: conversion unit CTU: Coding Tree Unit PDPC: Position-dependent prediction combination ISP: Intra subdivision SPS: Sequence Parameter Set PPS: Picture Parameter Set APS: Adaptive Parameter Set VPS: Video Parameter Set DPS: Decoding Parameter Set ALF: Adaptive Loop Filter SAO: Sample Adaptive Offset CC-ALF: Cross-component adaptive loop filter CDEF: Constrained Directional Enhancement Filter CCSO: Cross component sample offset LSO: Local Sample Offset LR: Loop recovery filter AV1:AOMedia Video 1 AV2:AOMedia Video 2 CfL: Chroma from Luma SDT: Semi-disjoint tree SDP: Semi-separate split SST: Semi-separated tree SB: Super Block IBC (or IntraBC): Intrablock copy CDF: Cumulative density function SCC: Screen Content Coding GBI: Generalized Biprediction BCW: Bi-prediction with CU-level weights CIIP: Combined Intra-Inter Prediction POC: Picture Order Count RPS: Reference Picture Set DPB: Decoded Picture Buffer [Explanation of symbols]

[0202] 101 sample, 102 arrow, 103 arrow, 104 square block, 201 current block, 300 communication system, 310 terminal device, 320 terminal device, 330 terminal device, 340 terminal device, 350 network, 400 communication system, 401 video source, 402 stream of video pictures or images, 403 video encoder, 404 video data, 405 streaming server, 406 client subsystem, 407 copy, 408 client subsystem, 409 copy, 410 video decoder, 411 output stream of video pictures, 412 display, 413 video capture subsystem, 420 electronic device, 430 electronic device, 501 channel, 510 video decoder, 512 display, 515 buffer memory, 520 entropy decoder / parser, 521 symbol, 530 electronic device, 531 receiver, 551 Scaler / inverse transform unit, 552 Intra picture prediction unit, 553 Motion compensation prediction unit, 555 Aggregator, 556 Loop filter unit, 557 Reference picture memory, 558 Current picture buffer, 603 Video encoder, 620 Electronic device, 630 Source coder, 632 Coding engine, 633 Local video decoder, 634 Reference picture memory, 635 Predictor, 640 Transmitter, 643 Coded video sequence, 645 Entropy coder, 650 Controller, 660 Communication channel, 703 Video encoder, 721 Generic controller, 722 Intra encoder, 723 Residual calculator, 724 Residual encoder, 725 Entropy encoder, 726 Switch, 728 Residual decoder, 730 Inter encoder, 810 Video decoder, 871 Entropy decoder, 872 Intra decoder, 873 Residual decoder, 874 Reconstruction module, 880 Interdecoder, 1002 T-partition, 1004 T-partition, 1006 T-partition, 1008 T-partition, 1010 Square partition, 1102 Vertical bisection (SPLIT_BT_VER), 1104split horizontally into two (SPLIT_BT_HOR), 1106 split vertically into three (SPLIT_TT_VER), 1108 split horizontally into three (SPLIT_TT_HOR), 1200 base block, 1202 square partition, 1204 square partition, 1206 square partition, 1208 square partition, 1402 partition, 1404 partition, 1406 partition, 1408 partition, 2000 computer system, 2001 keyboard, 2002 mouse, 2003 trackpad, 2005 joystick, 2006 microphone, 2007 scanner, 2008 camera, 2009 speaker, 2010 touch screen, 2020 CD / DVD ROM / RW, 2021 CD / DVD, 2022 thumb drive, 2023 removable hard drive or solid state drive, 2040 core, 2041 central processing unit (CPU), 2042 graphics processing unit (GPU), 2043 field programmable gate area (FPGA), 2044 hardware accelerator for a particular task, 2045 read only memory (ROM), 2046 random access memory (RAM), 2047 internal mass storage, 2048 system bus, 2049 general purpose data port or peripheral bus, 2050 graphics adapter, 2054 interface, 2055 one or more communication networks, R05 reference sample, R08 reference sample, S14 sample, S21 sample, S23 sample, S32 sample, S44 sample

Claims

1. 16. A processor-implemented method for generating an intra predictor block for a current video block in a video stream, the current video block being intra-coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, prior to performing any merging of the at least one reference palette, where cacheN is an integer indicating a number of non-overlapping palette entries; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; and generating the predictor block for the current video block based on at least the palette index and the current palette.

2. A processor-implemented method for generating an intra predictor block for a current video block in a video stream, the current video block being intra-coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; The method of claim 1, wherein determining cacheN comprises determining the size of the inherited portion of the current palette based on at least one palette size corresponding to the at least one reference palette.

3. determining cacheN, determining a first palette size of a first neighboring video block of the current video block; determining a second palette size of a second neighboring video block of the current video block; determining cacheN based on the first palette size and the second palette size.

4. the first neighboring video block and the second neighboring video block include immediately above and to the left of the current video block, respectively; The step of determining cacheN based on the first palette size and the second palette size comprises determining the size of the inherited portion of the current palette by: increasing N to the larger of the first pallet size and the second pallet size; or increasing N to the smaller of the first pallet size and the second pallet size; or the smaller of a predetermined maximum inherited palette size and the larger of the first palette size and the second palette size, increased by N; or determining the predetermined maximum inherited palette size as the smaller of the predetermined maximum inherited palette size and the smaller of the first palette size and the second palette size increased by N; 4. The method of claim 3, wherein N denotes a predetermined palette size increment, N being an integer greater than or equal to 0 and less than or equal to 8.

5. A processor-implemented method for generating an intra predictor block for a current video block in a video stream, the current video block being intra-coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; The method of claim 1, wherein determining cacheN comprises allocating a palette size of the inherited portion of the current palette independent of the at least one reference palette, the palette size being an integer greater than or equal to 0 and less than or equal to 8.

6. The method of claim 5 , wherein the palette size is predetermined or signaled in a syntax element within the video stream.

7. 7. The method of claim 6, wherein the syntax element comprises a component of one of a video parameter set, a sequence parameter set, a picture parameter set, an adaptation parameter set, a frame header, a slice header, a picture header, a tile header, or a coding tree unit header associated with the current video block.

8. A processor executed method for generating an intra predictor block for a current video block in a video stream, the current video block being intra coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; The method of claim 1, wherein cacheN is derived from a coding information item of the current video block or the at least one neighboring video block.

9. The method of claim 8 , wherein the coded information item includes at least one of a block size or a prediction mode associated with the current video block or the at least one neighboring video block.

10. A processor-implemented method for generating an intra predictor block for a current video block in a video stream, the current video block being intra-coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; The method of claim 1, wherein cacheN is derived as a number of repeated palette entries in the at least one reference palette associated with the at least one neighboring video block.

11. 11. The method of claim 10, wherein the at least one neighboring video block includes M neighboring video blocks, and a number of common palette entries I for at least K of the M neighboring video blocks is determined as cacheN, where M is an integer greater than or equal to 2, and K is an integer less than or equal to M.

12. A processor-implemented method for generating an intra predictor block for a current video block in a video stream, the current video block being intra-coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; The method, wherein the at least one neighboring video block corresponding to the at least one reference palette is selected from three or more neighboring video blocks of the current video block.

13. The method of claim 12 , wherein the three or more neighboring video blocks include at least one block that is not adjacent to the current video block.

14. the at least one neighboring video block is selected from the three or more neighboring video blocks by scanning the three or more neighboring video blocks in a predetermined scan order to determine a first set of neighboring video blocks that are intra-coded in the palette mode; a set of cached palettes of the first set of neighboring video blocks is used to determine or derive the at least one reference palette. The method of claim 12.

15. The method of claim 1 , further comprising merging the at least one reference palette into a cached palette having S unique palette entries.

16. A processor executed method for generating an intra predictor block for a current video block in a video stream, the current video block being intra coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; and merging the at least one reference palette into a cached palette having S unique palette entries; When S>cacheN, the method further comprises: selecting a first cacheN palette entries from the cached palette according to a predetermined scanning order to generate the inherited portion of the current palette having cacheN palette entries; selecting a last cacheN number of palette entries from the cached palette according to a predetermined scanning order to generate the inherited portion of the current palette having cacheN number of palette entries; selecting a duplicate palette entry from the at least one reference palette according to a predetermined scanning order and, if necessary, further selecting a first non-duplicate palette entry from the cached palette to generate the inherited portion of the current palette having cached N palette entries; or selecting duplicate palette entries from the at least one reference palette according to a predetermined scanning order and, if necessary, further selecting a last non-duplicate palette entry from the cached palette to generate the inherited portion of the current palette having N palette entries.

17. A processor executed method for generating an intra predictor block for a current video block in a video stream, the current video block being intra coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; and merging the at least one reference palette into a cached palette having S unique palette entries; When S<(cacheN), the method further comprises: filling the first S palette entries of the inherited portion of the current palette using the cached palette; determining (cacheN-S) target palette entries from the cached palette; offsetting each of the (cacheN-S) target palette entries to generate a modified target palette entry; and including the modified target palette entry in the last (cacheN-S) entries of the inherited portion of the current palette.

18. A processor executed method for generating an intra predictor block for a current video block in a video stream, the current video block being intra coded in palette mode, the method comprising: determining that the current video block is coded based on at least one reference palette corresponding to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, before performing any merging of the at least one reference palette, where cacheN is an integer; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating the predictor block for the current video block based on at least the palette index and the current palette; and merging the at least one reference palette into a cached palette having S unique palette entries; When S<cacheN, the method further comprises: filling the first S palette entries of the inherited portion of the current palette using the cached palette; and filling the last (cacheN-S) palette entries of the inherited portion of the current palette with the first (cacheN-S) palette entries from a palette entry list.

19. 20. The method of claim 18, wherein the palette entry list is signaled within the video stream in one of a sequence parameter set, a picture parameter set, an adaptation parameter set, a frame header, a slice header, a picture header, a tile header, or a coding tree unit header.

20. 1. A video device comprising: a memory for storing computer instructions; and a processor in communication with the memory, the computer instructions causing the processor to: determining that a current video block in the video stream is coded based on at least one reference palette that corresponds to at least one neighboring video block; determining a size of an inherited portion of a current palette associated with the current video block, cacheN, prior to performing any merging of the at least one reference palette, where cacheN is an integer indicating a number of non-overlapping palette entries; deriving the inherited portion of the current palette based on cacheN and the at least one reference palette; extracting from the video stream a palette index for an element of the current video block into the current palette; generating a predictor block for the current video block based on at least the palette index and the current palette.

21. A computer program product for causing a processor to carry out the method of claim 1.

Images