Hardware-Friendly Design for Intra-Mode Encoding

Abstract

A method, apparatus, and computer-readable storage medium for intra-prediction mode encoding in video decoding include receiving an encoded video bitstream, constructing a list of intra-modes for blocks in the encoded video bitstream according to a predetermined rule based on a size of the blocks, partitioning the list of intra-modes into a plurality of intra-mode sets for the blocks, extracting from the encoded video bitstream a set index indicating an intra-mode set from the plurality of intra-mode sets, extracting from the encoded video bitstream a mode index indicating an intra-prediction mode from the intra-mode set, determining an intra-prediction mode for the block based on the set index and the mode index, and decoding the encoded video bitstream based on the intra-prediction mode.

Description

[Technical field]

[0001] [Related Applications] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 236,542, filed August 24, 2021, and U.S. Nonprovisional Application No. 17 / 573,856, filed January 12, 2022, the entire contents of both applications being incorporated by reference.

[0002] [Technical field] The present disclosure relates to video encoding and / or decoding techniques, and in particular to improved design and signaling of intra-prediction mode coding. [Background technology]

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

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

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

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

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

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

[0009] There may be various forms of intra prediction. If more than one such technique is available in a given video coding technique, the technique used may be referred to as an intra prediction mode. One or more intra prediction modes may be provided in a particular codec. In certain cases, a mode may have sub-modes and / or may be associated with various parameters, and the mode / sub-mode information and intra coding parameters of a block of video may be coded separately or may be included jointly in a mode codeword. Which codeword to use for a given mode, sub-mode and / or parameter combination may affect the coding efficiency gain through intra prediction, as well as the entropy coding technique used to convert the codeword into a bitstream.

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

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

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

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

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

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

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

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

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

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

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

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

[0022] This disclosure describes various embodiments of methods, apparatus, and computer-readable storage media for video encoding and / or decoding.

[0023] According to one aspect, an embodiment of the present disclosure provides a method for intra-prediction mode encoding in video decoding. The method includes receiving, by a device, an encoded video bitstream. The device includes a memory storing instructions and a processor in communication with the memory. The method also includes building, by the device, a list of intra-modes for blocks in the encoded video bitstream according to a predetermined rule based on a size of the block, partitioning, by the device, the list of intra-modes into a plurality of intra-mode sets for the block, extracting, by the device, from the encoded video bitstream, a set index indicating an intra-mode set from the plurality of intra-mode sets, extracting, by the device, from the encoded video bitstream, a mode index indicating an intra-prediction mode from the intra-mode set, determining, by the device, an intra-prediction mode for the block based on the set index and the mode index, and decoding, by the device, the encoded video bitstream based on the intra-prediction mode.

[0024] According to another aspect, an embodiment of the present disclosure provides an apparatus for video encoding and / or decoding, the apparatus including a memory storing instructions and a processor in communication with the memory, the processor being configured, when executing the instructions, to cause the apparatus to perform the above-described method for video decoding and / or encoding.

[0025] In another aspect, an embodiment of the present disclosure provides a non-transitory computer-readable medium having stored thereon instructions that, when executed by a computer for video decoding and / or encoding, cause the computer to perform the above-described method for video decoding and / or encoding.

[0026] These and other aspects and their implementations are described in more detail in the drawings, detailed description, and claims. [Brief description of the drawings]

[0027] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Figure 1A] 1 shows a schematic diagram of an example subset of intra-prediction direction modes. [Figure 1B] 1 shows an illustrative diagram of an exemplary intra-prediction direction. [Diagram 2] 1 illustrates a schematic diagram of a current block and its surrounding spatial merging candidates for motion vector prediction in one example. [Diagram 3] 1 illustrates a simplified block diagram of a communication system in accordance with an exemplary embodiment; [Figure 4] 4 shows a simplified block diagram schematic of a communication system (400) in accordance with an example embodiment. [Diagram 5] 1 shows a schematic diagram of a simplified block diagram of a video decoder according to an exemplary embodiment; [Figure 6] 1 shows a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7]1 shows a block diagram of a video encoder according to an example embodiment. [Figure 8] 2 shows a block diagram of a video decoder according to an exemplary embodiment; [Figure 9] 1 illustrates directional intra-prediction modes according to an exemplary embodiment of the present disclosure. [Figure 10] 1 illustrates a non-directional intra-prediction mode according to an exemplary embodiment of the present disclosure. [Figure 11] 1 illustrates a recursive intra-prediction mode according to an exemplary embodiment of the present disclosure. [Figure 12] 4 illustrates various reference line based intra prediction schemes according to an exemplary embodiment of the present disclosure. [Figure 13] 1 illustrates offset-based refinement for intra prediction according to an exemplary embodiment of the present disclosure. [Figure 14A] 13 shows another diagram of offset-based refinement for intra prediction according to an exemplary embodiment of the present disclosure. [Figure 14B] 13 shows another diagram of offset-based refinement for intra prediction according to an exemplary embodiment of the present disclosure. [Figure 15] 1 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 16] 1 shows a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which show, by way of example, specific embodiments. It should be noted, however, that the present invention may be embodied in a variety of different forms. Accordingly, it is not intended that the subject matter as directed or claimed be construed as being limited to any of the embodiments set forth below. It should also be noted that the present invention may be embodied as a method, device, component, or system. Accordingly, embodiments of the present invention may take the form of, for example, hardware, software, firmware, or any combination thereof.

[0029] Throughout the specification and claims, terms may have a nuanced meaning that is suggested or implied in the context beyond the explicitly stated meaning. 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 subject matter of the claims is intended to include combinations of example embodiments / implementations in whole or in part.

[0030] Generally, 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, and A, B, or C, which are used herein in an exclusive sense. Furthermore, 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, singular terms (such as "a," "an," or "the") may be understood as conveying singular or plural usage, depending at least in part on the context. Additionally, the terms "based on" or "determined by" may be understood as not necessarily intended to convey an exclusive set of factors, but may instead permit the existence of additional factors not necessarily explicitly recited, again depending at least in part on the context.

[0031] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to one embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may perform unidirectional transmission of data. For example, the terminal device (310) may encode video data (e.g., a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more encoded video bitstreams. The terminal device (320) may receive the encoded video data from the network (350), decode the encoded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. The one-way data transmission may be implemented in a media service application or the like.

[0032] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of encoded video data, which may be implemented, for example, during a video conferencing application. For the bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may encode video data (e.g., a stream of video pictures captured by the terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may receive the encoded video data transmitted by the other of the terminal devices (330) and (340), decode the encoded video data to reconstruct the video pictures, and display the video pictures on an accessible display device in accordance with the reconstructed video data.

[0033] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be implemented as servers, personal computers, and smartphones, although applicability of the underlying principles of the present disclosure may not be limited thereto. The embodiments of the present disclosure may be implemented in desktop computers, laptop computers, tablet computers, media players, wearable computers, and / or dedicated video conferencing equipment. The network (350) represents any number or type of network that conveys encoded video data between the terminal devices (310), (320), (330), and (340), including, for example, wired (wired) and / or wireless communication networks. The communication network (350) may exchange data in circuit-switched, packet-switched, and / or other types of channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of discussion herein, the architecture and topology of the network (350) may not be important to the operation of the present disclosure, unless explicitly described below.

[0034] 4 shows an arrangement of video encoders and video decoders in a video streaming environment as an example of an application for the disclosed subject matter. The disclosed subject matter may be equally applicable to other video applications including, for example, video conferencing, digital TV broadcasting, gaming, virtual reality, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0035] The video streaming system may include a video source (401), e.g., a digital camera, and may include a video capture subsystem (413) that generates, e.g., a stream of uncompressed video pictures or images (402). In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), depicted as a bold line to emphasize its high data volume compared to the encoded video data (404) (or encoded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), depicted as a thin line to emphasize its lower data volume compared to the uncompressed video picture stream (402), can be stored on the streaming server (405) for future use or directly on a downstream video device (not shown). One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, can access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) can include a video decoder (410), for example within the electronic device (430). The video decoder (410) can decode an input copy of the encoded video data (407) and generate an output stream of uncompressed video pictures (411) that can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). Video decoder 410 may be configured to perform some or all of the various functions described in this disclosure.In some streaming systems, the encoded video data (404), (407), and (409) (e.g., video bitstreams) may be encoded according to a particular video encoding / compression standard. Examples of these standards include ITU-T Recommendation H.265. In one example, a video encoding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC and other video encoding standards.

[0036] It is noted that electronic devices 420 and 430 may include other components (not shown). For example, electronic device 420 may include a video decoder (not shown), and electronic device 430 may also include a video encoder (not shown).

[0037] 5 shows a block diagram of a video decoder (510) according to any of the following embodiments of the present disclosure. The video decoder (510) can be included in an electronic device (530). The electronic device (530) can include a receiver (531) (e.g., a receiving circuit). The video decoder (510) can be used in place of the video decoder (310) in the example of FIG. 4.

[0038] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, and the decoding of each coded video sequence is independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or images. The coded video sequences may be received from a channel (501), which may be a storage device that stores the coded video data or a hardware / software link to a streaming source that transmits the coded video data. The receiver (531) may receive the coded video data together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded through respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To combat network jitter, a buffer memory (515) may be located between the receiver (531) and the entropy decoder / parser (520) (hereinafter the "parser"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, it may be external to the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), e.g., to combat network jitter, and there may be an additional buffer memory (515) internal to the video decoder (510), e.g., to handle playback timing. If the receiver (531) is receiving data from a store / forward device of sufficient bandwidth and controllability, or from an isochronous network, the buffer memory (515) may not be needed or may be small. For use with best-effort packet networks such as the Internet, a sufficient size of the buffer memory (515) may be required, and the size may be relatively large.Such a buffer memory may be implemented with an adaptive size and may be implemented, at least in part, outside the video decoder (510) in an operating system or similar element (not shown).

[0039] The video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a display (512) (e.g., a display screen). The display may or may not be an integral part of the electronic device (530) as shown in FIG. 5 and may be coupled to the electronic device (530). The control information for the rendering device(s) may be in the form of Supplementary Enhancement Information (SEI) messages or Video Usability Information (VUI) parameter set fragments (not shown). The parser (520) may parse / entropy decode the coded video sequence received by the parser (520). The entropy coding of the coded video sequence may follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include a Group of Pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (520) may also extract information from the coded video sequence such as transform coefficients (e.g., Fourier transform coefficients), quantizer parameter values, motion vectors, etc.

[0040] The parser (520) can perform an entropy decoding / parsing operation on the video sequence received from the buffer memory (515) to generate symbols (521).

[0041] The reconstruction of the symbols (521) may involve several different processing or functional units, depending on the type of coded video picture or portion thereof (e.g., inter and intra picture, inter and intra block) and other factors. The units involved and how they are involved may be controlled by subgroup control information parsed by the parser (520) from the coded video sequence. The flow of such subgroup control information between the parser (520) and several of the processing or functional units described below is not depicted for the sake of simplicity.

[0042] In addition to the functional blocks already mentioned, the video decoder (510) can be conceptually divided into several functional units, as described below. In a practical implementation working under commercial constraints, many of these functional units will interact closely with each other and may be at least partially integrated with each other. However, for purposes of clearly describing the various functions of the disclosed subject matter, a conceptual subdivision into functional units is adopted in the following disclosure.

[0043] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients and control information as symbol(s) (521) from the parser (520). The control information may include information indicating what type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output a block containing sample values ​​that can be input to an aggregator (555).

[0044] In some cases, the output samples of the scaler / inverse transform (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but may use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using surrounding block information already reconstructed and stored in a current picture buffer (558). The current picture buffer (558) may, for example, buffer a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0045] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such a case, the motion compensation prediction unit (553) may access the reference picture memory (557) to retrieve samples used for inter-picture prediction. After motion compensating the retrieved samples according to the symbols (521) for the block, these samples may be added by an aggregator (555) to the output of the scalar / inverse transform unit (the output of unit 551 may be referred to as a residual sample or residual signal) to generate output sample information. The address in the reference picture memory (557) from which the motion compensation unit (553) retrieves the prediction samples may be controlled by a motion vector available to the motion compensation unit (553) in the form of a symbol (521). The symbol may have, for example, an X, a Y component (shift), and a reference picture component (time). Motion compensation may involve the interpolation of sample values ​​taken from a reference picture memory (557) when sub-sample accurate motion vectors are used, and may also involve motion vector prediction mechanisms, etc.

[0046] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in a loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to meta-information obtained during decoding of previous portions (in decoding order) of the coded picture or coded video sequence, as well as to previously reconstructed loop filtered sample values. As will be described in more detail below, several types of loop filters may be included as part of the loop filter unit 556, in various orders.

[0047] The output of the loop filter unit (556) can be a sample stream, which can be output to a rendering device (512) or can be stored in a reference picture memory (557) for use in future inter-picture prediction.

[0048] Once a particular coded picture is fully reconstructed, it can be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (520)), the current picture buffer (558) can become part of the reference picture memory (557), and a fresh current picture buffer can be reallocated before beginning reconstruction of a subsequent coded picture.

[0049] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard such as ITU-T Recommendation H.265. The encoded video sequence may conform to the syntax prescribed by the video compression technique or standard being used, in the sense that the encoded video sequence conforms to the syntax of the video compression technique or standard and the profile documented in the video compression technique or standard. Specifically, the profile may select a particular tool from all tools available in the video compression technique or standard as the only tool available for use under that profile. To conform to a standard, the complexity of the encoded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level constrains the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in units of megasamples per second), maximum reference picture size, etc. The limits set by the level may be further constrained through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management, possibly signaled in the encoded video sequence.

[0050] In some exemplary embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the encoded video sequence(s). The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0051] 6 shows a block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure. The video encoder (603) may be included in an electronic device (620). The electronic device (620) may further include a transmitter (640) (e.g., a transmitting circuit). The video encoder (603) may be used in place of the video encoder (403) in the example of FIG. 4.

[0052] The video encoder (603) can receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that can capture video images to be encoded by the video encoder (603). In another example, the video source (601) can be implemented as part of the electronic device (620).

[0053] The video source (601) may provide a source video sequence to be encoded by the video encoder (603) in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 YCrCB, RGB, XYZ, ...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media service system, the video source (601) may be a storage device capable of storing pre-prepared video. In a video conferencing system, the video source (601) may be a camera that captures image information locally as a video sequence. The video data may be provided as a number of individual pictures or images that impart motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each of which may contain one or more samples, depending on the sampling structure, color space, etc., in use. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0054] According to some example embodiments, the video encoder (603) can encode and compress pictures of a source video sequence into an encoded video sequence (643) in real-time or under any other time constraint required by an application. Enforcing an appropriate encoding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be operatively coupled to and control other functional units, as described below. Such couplings are not depicted for the sake of brevity. Parameters set by the controller (650) may include parameters related to rate control (picture skip, quantizer, lambda value for rate-distortion optimization techniques, ...), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) can be configured to have other suitable functions for the video encoder (603) optimized for a particular system design.

[0055] In some example embodiments, the video encoder (603) may be configured to operate in an encoding loop. As a simplistic explanation, in one example, the encoding loop may include a source encoder (630) (e.g., responsible for generating symbols such as a symbol stream based on an input picture to be encoded and a reference picture(s)) and a (local) decoder (633) embedded in the video encoder (603). Even if the embedded decoder 633 processes the encoded video stream without entropy coding by the source decoder 630, the decoder (633) reconstructs the symbols to generate sample data in a similar manner as a (remote) decoder would also generate them (in the video compression techniques considered in the disclosed subject matter, any compression between the symbols in the entropy coding and the encoded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream yields bit-accurate results regardless of the decoder location (local or remote), the contents of the reference picture memory (634) are also bit-accurate between the local and remote encoders. In other words, the prediction part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder "sees" when using the prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0056] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, e.g., the video decoder (410), already described in detail above in connection with Figure 5. However, referring also briefly to Figure 5, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (420) may be lossless, the entropy decoding portion of the video decoder (410), including the buffer memory (415) and parser (420), may not be fully implemented in the encoder's local decoder (633).

[0057] An observation that can be made at this point is that any decoder technique, except for parsing / entropy decoding, which may only exist in the decoder, may need to exist in substantially the same functional form in the corresponding encoder. For this reason, the disclosed subject matter may sometimes focus on the decoder operation, which is similar to the decoding portion of the encoder. Thus, a description of the encoder technique may be omitted, since it is the inverse of the decoder technique, which is described generically. Only in certain areas or aspects of the encoder is a more detailed description provided below.

[0058] In operation, in some example implementations, the source encoder (630) may perform motion-compensated predictive encoding, which predictively encodes an input picture with reference to one or more previously encoded pictures from a video sequence, designated as “reference pictures.” In this manner, the encoding engine (632) encodes differences (or residuals) in color channels between pixel blocks of the input picture and pixel blocks of a reference picture(s) that may be selected as predictive references for the input picture.

[0059] The local video decoder (633) can decode the encoded video data of pictures that may be designated as reference pictures based on the symbols generated by the source encoder (630). The operation of the encoding engine (632) can advantageously be a lossy process. When the encoded video data can be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence can be a copy of the source video sequence, typically with some errors. The local video decoder (633) can replicate the decoding process that may be performed on the reference pictures by the video decoder and store the reconstructed reference pictures in a reference picture cache (634). In this way, the video encoder (603) can locally store copies of reconstructed reference pictures that have common content (in the absence of transmission errors) as reconstructed reference pictures that would be obtained by a far-end (remote) video decoder.

[0060] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata, such as reference picture motion vectors, block shapes, etc., that may serve as suitable prediction references for the new picture. The predictor (635) may operate on a sample block-by-pixel block basis to find suitable prediction references. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (634).

[0061] The controller (650) may manage the encoding operations of the source encoder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0062] The output of all of the above functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0063] The transmitter (640) can buffer the encoded video sequence generated by the entropy encoder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) can merge the encoded video data from the video encoder (630) with other data to be transmitted, such as encoded audio data and / or auxiliary data streams (sources not shown).

[0064] The controller (650) may manage the operation of the video encoder (603). During encoding, the controller (650) may assign a certain coding picture type to each coded picture. The coding picture type may affect the coding technique that may be applied to each picture. For example, pictures may often be assigned as one of the following picture types:

[0065] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures in a sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, Independent Decoder Refresh ("IDR") pictures. Those skilled in the art will recognize these variations of I-pictures and their respective uses and characteristics.

[0066] A predictive picture (P-picture) may be one that can be encoded and decoded using intra- or inter-prediction, which uses at most one motion vector and reference index to predict the sample values ​​of each block.

[0067] Bidirectionally predicted pictures (B-pictures) may be those that can be coded and decoded using intra- or inter-prediction, which uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multi-predictive pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0068] A source picture may typically be spatially divided into multiple sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks, as determined by the coding assignment applied to the respective picture of the block. For example, blocks of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of a P picture may be predictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. Blocks of a B picture may be predictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures. Source pictures or intermediate processing pictures may be subdivided into other types of blocks for other purposes. As will be explained in more detail below, the division of coding blocks and other types of blocks may or may not follow the same scheme.

[0069] The video encoder (603) may perform encoding operations according to a given video encoding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive encoding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the encoded video data may conform to a syntax specified by the video encoding technique or standard used.

[0070] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source encoder (630) may include such data as part of the encoded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other types of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0071] A video may be captured as multiple source pictures (video pictures) in a temporal sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture to be coded / decoded, called a current picture, may be divided into blocks. If a block in the current picture resembles a reference block in a previously coded and still buffered reference picture in the video, it may be coded by a vector called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0072] In some exemplary embodiments, bidirectional prediction techniques can be used in inter-picture prediction. Such bidirectional prediction techniques use two reference pictures, such as a first reference picture and a second reference picture, both of which precede the current picture in decoding order (but may be past or future, respectively, in display order) in the video. A block in the current picture can be coded by a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. A block can be jointly predicted by a combination of the first and second reference blocks.

[0073] Furthermore, to improve coding efficiency, merge mode techniques may be used in inter-picture prediction.

[0074] According to some example embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may include three parallel coding tree blocks (CTBs), one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels or four CUs of 32×32 pixels. Each of the one or more 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for that CU among various prediction types, such as an inter prediction type or an intra prediction type. The CU may be divided into one or more prediction units (PUs) depending on temporal and / or spatial predictability. In general, each PU includes a luma prediction block (PB) and two chroma PBs. In some embodiments, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. The division of a CU into PUs (or PBs of different color channels) may be performed in various division patterns. For example, a luma or chroma PB may include a matrix of values ​​(e.g., luma values) for pixels, such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0075] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of the present disclosure. The video encoder (703) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into an encoded picture that is part of an encoded video sequence. The exemplary video encoder (703) may be used in place of the video encoder (403) in the example of FIG. 4.

[0076] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive block, such as 8×8 samples. The video encoder (703) then determines whether the processing block is best coded using an intra mode, an inter mode, or a bi-directional predictive mode, for example using rate-distortion optimization (RDO). If it is determined that the processing block is coded in an intra mode, the video encoder (703) may use intra prediction techniques to code the processing block into a coded picture. If it is determined that the processing block is coded in an inter mode or a bi-directional predictive mode, the video encoder (703) may use inter prediction techniques or bi-directional prediction techniques, respectively, to code the processing block into a coded picture. In some exemplary embodiments, a merge mode may be used as a sub-mode of inter-picture prediction, in which a motion vector is derived from one or more motion vector predictors, but without the benefit of coded motion vector components outside the predictors. In some exemplary embodiments, there may be motion vector components applicable to the current block. Thus, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module (not shown) for determining a prediction mode for a processing block.

[0077] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy coder (725) coupled together as shown in the exemplary arrangement of FIG.

[0078] The inter encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block with one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter prediction information (e.g., a description of redundant information due to inter coding techniques, motion vectors, merge mode information), and calculate an inter prediction result (e.g., a predicted block) based on the inter prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the coded video information using a decoding unit 633 (shown as a residual decoder 728 in FIG. 7, as described in more detail below) embedded in the example encoder 620 of FIG. 6.

[0079] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block to blocks already encoded in the same picture, generate transformed and quantized coefficients, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). The intra encoder (722) may also calculate intra prediction results (e.g., predicted blocks) based on the intra prediction information and reference blocks in the same picture.

[0080] The general controller (721) may be configured to determine general control data and control other components of the video encoder (703) based on the general control data. In one example, the general controller (721) determines a prediction mode for a block and provides a control signal to the switch (726) based on the prediction mode. For example, if the prediction mode is an intra mode, the general controller (721) controls the switch (726) to select a result of the intra mode for use by the residual calculator (723), and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream. If the prediction mode for the block is an inter mode, the general controller (721) controls the switch (726) to select a result of inter prediction for use by the residual calculator (723), and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0081] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for that block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients are then subjected to a quantization process to obtain quantized transform coefficients. In various exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform to generate decoded residual data. The decoded residual data can be suitably used by the intra-encoder (722) and the inter-encoder (730). For example, the inter-encoder (730) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are suitably processed to generate decoded pictures, which can be buffered in a memory circuit (not shown) and used as reference pictures.

[0082] The entropy encoder (725) is configured to format a bitstream to include the encoded block and to perform entropy encoding. The entropy encoder (725) is configured to include various information in the bitstream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other suitable information in the bitstream. When encoding a block in a merged sub-mode of either the inter mode or the bi-prediction mode, the residual information may not be present.

[0083] 8 shows a diagram of an exemplary video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive encoded pictures that are part of an encoded video sequence and decode the encoded pictures to generate reconstructed pictures. In one example, the video decoder (810) may be used in place of the video decoder (410) in the example of FIG. 4.

[0084] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter decoder (880), a residual decoder (873), a reconstruction module (874), and an intra decoder (872) coupled together as shown in the exemplary configuration of FIG. 8.

[0085] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent the syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra-mode, inter-mode, bi-predictive mode, merged sub-mode, or another sub-mode) that may identify the mode in which the block is coded, certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information, for example in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter- or bi-predictive mode, the inter-prediction information is provided to the inter-decoder (880). If the prediction type is an intra-prediction type, the intra-prediction information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0086] An inter decoder (880) may be configured to receive inter prediction information and generate inter prediction results based on the inter prediction information.

[0087] The intra decoder (872) may be configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

[0088] The residual decoder (873) may be configured to perform inverse quantization to extract dequantized transform coefficients and process the dequantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (including quantizer parameters (QP)), which may be provided by the entropy decoder (871) (data path not depicted since this is only control information for low data volume).

[0089] A reconstruction module (874) may be configured to combine, in the spatial domain, the residual output by the residual decoder (873) and the prediction result (output by the intra- or inter-prediction module, as the case may be) to form reconstructed blocks that form part of the reconstructed picture as part of the reconstructed video. Note that other suitable operations, such as deblocking operations, may also be performed to improve visual quality.

[0090] It should be noted that the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using any suitable technology. In some exemplary embodiments, the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using one or more integrated circuits. In other embodiments, the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using one or more processors executing software instructions.

[0091] Returning to the intra prediction process, samples within a block (e.g., luma or chroma prediction block, or coding block if not further divided into prediction blocks) are predicted by adjacent, next adjacent, or other line or lines, or a combination thereof, to generate a prediction block. The residual between the actual block being coded and the prediction block may then be processed via a transform and subsequent quantization. Various intra prediction modes may be made available, and parameters related to intra mode selection and other parameters may be signaled in the bitstream. For example, various intra prediction modes may be associated with the line position or positions for predicting samples, the direction in which the prediction sample is selected from the prediction line or lines, and other special intra prediction modes.

[0092] For example, the set of intra-prediction modes (also referred to as "intra modes") may include a predetermined number of directional intra-prediction modes. As described above in connection with the example implementation of FIG. 1, these intra-prediction modes may correspond to a predetermined number of directions in which a sample outside a block is selected as a prediction for a sample predicted within a particular block. In another particular example implementation, eight main directional modes may be supported and predefined, corresponding to angles from 45° to 207° relative to the horizontal axis.

[0093] In some other implementations of intra prediction, the directional intra modes may be further extended to angles set with finer granularity to further exploit more diverse spatial redundancy in the directional texture. For example, the above eight angle implementation may be configured to provide eight nominal angles called V_PRED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED as shown in FIG. 9. For each nominal angle, a predetermined number (e.g., seven) finer angles may be added. Such extensions may result in a larger total number of directional angles (e.g., 56 in this example) available for intra prediction, corresponding to the same number of predetermined directional intra modes. The prediction angle may be represented as the nominal intra angle plus an angle delta. In the above specific example with seven finer angle directions for each nominal angle, the angle delta may be -3 to 3 multiplied by a step size of 3°.

[0094] The above directional intra-prediction may also be referred to as unidirectional intra-prediction, and is distinct from bidirectional intra-prediction (also referred to as intra-bidirectional prediction) described later in this disclosure.

[0095] In some implementations, instead of or in addition to the above directional intra modes, a certain number of non-directional intra prediction modes may also be predefined and made available. For example, five non-directional intra modes called smooth intra prediction modes may be specified. These non-directional intra mode prediction modes may be specifically called DC, PAETH, SMOOTH, SMOOTH_V and SMOOTH_H intra modes. Prediction of samples of a particular block in these exemplary non-directional modes is shown in FIG. 10. As an example, FIG. 10 shows that a 4×4 block 1002 is predicted by samples from an upper neighboring line and / or a left neighboring line. A particular sample 1010 in the block 1002 may correspond to a directly above sample 1004 of the sample 1010 in the upper neighboring line of the block 1002, a left above sample 1006 of the sample 1010 as the intersection of the above and left neighboring lines, and a directly left sample 1008 of the sample 1010 in the left neighboring line of the block 1002. In the exemplary DC intra prediction mode, the average of the left and top neighboring samples 1008 and 1004 may be used as the predictor of sample 1010. In the exemplary PAETH intra prediction mode, the top, left and top left reference samples 1004, 1008 and 1006 may be taken, and then the closest value of these three reference samples to (top+left-top left) may be set as the predictor of sample 1010. In the exemplary SMOOTH_V intra prediction mode, sample 1010 may be predicted by quadratic interpolation in the vertical direction of the top left neighboring sample 1006 and the left neighboring sample 1008. In the exemplary SMOOTH_H intra prediction mode, sample 1010 may be predicted by quadratic interpolation in the horizontal direction of the top left neighboring sample 1006 and the top neighboring sample 1004. In the exemplary SMOOTH intra prediction mode, sample 1010 may be predicted by the average of quadratic interpolation in the vertical and horizontal directions. The implementation of the non-directional intra modes above is shown merely as a non-limiting example. Non-directional selection of other adjacent lines and other samples, as well as combination schemes of prediction samples to predict a particular sample within a prediction block, are also considered.

[0096] At various coding levels (picture, slice, block, unit, etc.), the encoder's selection of a particular intra-prediction mode from the above directional or non-directional modes may be signaled in the bitstream. In some exemplary implementations, the eight exemplary nominal directional modes (total of 13 choices) may be signaled first along with the five non-angle smooth modes. Then, if the signaled mode is one of the eight nominal angle intra modes, an index is further signaled to indicate the selected angle delta relative to the corresponding signaled nominal angle. In some other exemplary implementations, all intra-prediction modes may be indexed together for signaling (e.g., 56 directional modes plus 5 non-directional modes to generate 61 intra-prediction modes).

[0097] In some example implementations, the example 56 directional intra-prediction modes or any other number of directional intra-prediction modes may be implemented using a joint directional predictor that projects each sample of a block to a reference sub-sample position and interpolates the reference sample with a 2-tap bilinear filter.

[0098] In some implementations, further filter modes, called FILTER INTRA modes, may be designed to capture the decaying spatial correlation with the references on the edges. In these modes, prediction samples within the block in addition to out-of-block samples may be used as intra prediction reference samples for some patches within the block. For example, these modes may be predefined and enabled for intra prediction for at least the luma block (or only the luma block). A certain number (e.g., 5) of filter intra modes may be predesigned, each represented by a set of n-tap filters (e.g., 7-tap filters) that reflect the correlation between a sample within a 4×2 patch and its n adjacent neighbors. In other words, the weight coefficients of the n-tap filters may depend on the position. Taking an 8×8 block, a 4×2 patch, and 7-tap filtering as examples, an 8×8 block 1102 may be divided into eight 4×2 patches, as shown in FIG. 11. These patches are indicated by B0, B1, B1, B3, B4, B5, B6, and B7 in FIG. 11. For each patch, its seven neighbors, indicated by R0-R7 in FIG. 11, may be used to predict samples in the current patch. For patch B0, all neighbors may already be reconstructed. However, for other patches, some of the neighbors may be in the current block and not reconstructed. In that case, the predicted values ​​of the nearest neighbors are used as a reference. For example, as shown in FIG. 11, not all neighbors of patch B7 are reconstructed, so the predicted samples of some neighbors, e.g., B4, B5 and / or B6, are used instead.

[0099] In some implementations of intra prediction, one color component may be predicted using one or more other color components. The color components may be any one of the color components in YCrCb, RGB, XYZ color space, etc. For example, prediction of a chroma component (e.g., a chroma block) from a luma component (e.g., a luma reference sample), called CfL (Chroma from Luma), may be implemented. In some example implementations, cross-color (inter-color) prediction may be allowed only from luma to chroma. For example, a chroma sample in a chroma block may be modeled as a linear function of the corresponding reconstructed luma sample. CfL prediction may be implemented as follows: CfL(α)=α×L AC +DC (1)

[0100] Here, L AC where α denotes the AC contribution of the luma component, α denotes a parameter of the linear model, and DC denotes the DC contribution of the chroma component. For example, the AC components are obtained for each sample of the block, while the DC components are obtained for the entire block. Specifically, the reconstructed luma samples may be subsampled to the chroma resolution, and then the average luma value (DC of luma) may be subtracted from each luma value to form the AC contribution in luma. The luma AC contribution is then used in the linear mode of equation (1) to predict the AC value of the chroma component. Instead of requiring the decoder to calculate a scaling parameter to approximate or predict the chroma AC component from the luma AC contribution, an exemplary CfL implementation may determine the parameter α based on the original chroma samples and signal it in the bitstream. This reduces the decoder complexity and results in a more accurate prediction. As for the DC contribution of the chroma component, in some exemplary implementations, it may be calculated using an intra DC mode within the chroma component.

[0101] Returning to intra prediction, in some example implementations, prediction of samples in a coding block or a predictive block may be based on one of a set of reference lines. In other words, multiple reference lines may be provided as options for intra prediction selection, rather than always using the nearest neighboring line (e.g., the nearest upper neighboring line or the nearest left neighboring line of the predictive block shown in FIG. 1 above). Such an implementation of intra prediction may be called Multiple Reference Line Selection (MRLS). In these implementations, the encoder determines and signals which of the multiple reference lines is used to generate an intra predictor. At the decoder side, after parsing the reference line index, the intra prediction of the current intra prediction block can be generated by identifying the reconstructed reference sample by searching the designated reference line according to the intra prediction mode (e.g., directional, non-directional and other intra prediction modes). In some implementations, the reference line index may be signaled at the coding block level, and only one of the multiple reference lines may be selected and used for intra prediction of one coding block. In some examples, more than one reference line may be selected simultaneously for intra prediction. For example, more than one reference line may be combined, with or without weighting, averaged, interpolated, or otherwise combined to generate a prediction. In some example implementations, MRLS may be applied only to the luma component, and not to the chroma components.

[0102] An example of four reference lines MRLS is shown in Figure 12. As shown in the example of Figure 12, an intra-coded block 1202 may be predicted based on any one of four horizontal reference lines 1204, 1206, 1208, and 1210 and four vertical reference lines 1212, 1214, 1216, and 1218. Among these reference lines, 1210 and 1218 are nearest neighboring reference lines. The reference lines may be indexed according to their distance from the coding block. For example, the reference lines 1210 and 1218 may be referred to as zero reference lines, and the other reference lines may be referred to as non-zero reference lines. Specifically, the reference lines 1208 and 1216 may be referred to as first reference lines, the reference lines 1206 and 1214 may be referred to as second reference lines, and the reference lines 1204 and 1212 may be referred to as third reference lines.

[0103] In some embodiments, for a particular coding block, coding unit, prediction block or prediction unit that is intra-coded, its intra mode needs to be signaled by one or more syntax elements in the bitstream. As mentioned above, the number of possible intra prediction modes can be huge, and 62 intra prediction modes may be available: 56 directional intra prediction modes, 5 non-directional modes and one Chroma from Luma mode (e.g., chroma components only). To signal these intra prediction modes, a first syntax may be signaled to indicate which nominal angle or non-directional mode is equal to the nominal mode of the current block. Then, if the mode of the current block is a directional mode, a second syntax may be signaled to indicate which delta angle is equal to the delta angle of the current block. In some situations during video encoding and / or decoding, there may be a strong correlation between the intra prediction mode of the current block and its neighboring blocks.

[0104] In various embodiments, this correlation may be exploited to design a more efficient syntax for intra-mode coding. In some implementations, the available intra-prediction modes of a current block may be divided into multiple intra-prediction mode sets according to the intra-prediction modes of its neighboring blocks. To obtain the intra-prediction mode of the current block, first, a mode set index may be signaled to indicate the mode set index of the intra-prediction mode of the current block, and then a mode index may be signaled to indicate the index of the intra-prediction mode in the mode set.

[0105] Here, in various embodiments of the present disclosure, "XYZ is signaled" may indicate that XYZ is encoded into the encoded bitstream during the encoding process, and / or after the encoded bitstream is transmitted from one device to another, "XYZ is signaled" may indicate that XYZ is decoded / extracted from the encoded bitstream during the decoding process.

[0106] For example, in some of the above implementations, the number of available intra-prediction modes may include 62 different modes, including, for example, 56 directional intra-prediction modes (e.g., 8 nominal directions with 7 fine angles in each nominal direction), 5 non-directional modes, and one chroma-from-luma mode (chroma components only). Once an intra-mode is selected during the encoding process for a particular coding block, coding unit, prediction block, or prediction, signaling corresponding to the selected intra-mode must be included in the bitstream. The syntax signaling must be able to distinguish all these 62 modes in some manner. For example, these 62 modes may be signaled using a single syntax for 62 indexes, each corresponding to one mode. In some other example implementations, one syntax may be signaled to indicate which nominal angle or non-directional mode is used as the nominal mode in the current block, and then another syntax may be further signaled to indicate which delta angle is selected for the current block if the nominal mode of the current block is a directional mode.

[0107] Since various syntaxes for intra coding typically occupy a large part of the bitstream and intra mode selection must be signaled frequently, e.g., at various coding levels, reducing the number of bits used for intra mode signaling becomes important in improving video coding efficiency. In practice, the use of various intra prediction modes may follow certain statistical patterns, and such usage patterns may be exploited to design the intra mode indexing and syntax signaling so that signaling efficiency can be enhanced. Furthermore, there may be some correlation on average between intra mode selections from block to block. Such correlations may be obtained statistically offline and taken into account in the design of the syntax for intra mode selection signaling. The goal is to reduce the number of bits of signaling syntax elements in the coded bitstream on average. For example, some general statistics may indicate that there may be a strong correlation between the optimal intra prediction modes of a current block and its neighboring blocks. Such correlations may be exploited in designing the syntax for intra mode coding.

[0108] In some embodiments, offset-based refinement for intra prediction (ORIP) may be used after generating intra prediction samples to improve video encoding / decoding performance. When ORIP is applied, the prediction samples are refined by adding offset values.

[0109] As shown in FIG. 13, intra prediction (1330) is performed based on reference samples. The reference samples may include samples from one or more left reference lines (1312) and / or one or more top reference lines (1310). An offset-based refinement for intra prediction (ORIP) (1350) may generate offset values ​​using neighboring reference samples. In some implementations, the neighboring reference samples for ORIP may be the same set as the reference samples for intra prediction. In some other implementations, the neighboring reference samples for ORIP may be a different set than the reference samples for intra prediction.

[0110] In some implementations referring to Figures 14A and 14B, ORIP may be performed at the 4x4 sub-block level. For each 4x4 sub-block (1471, 1472, 1473, and / or 1474), an offset is generated from its neighboring samples. For example, for the first sub-block (1471), an offset is generated from its upper neighboring samples (P1, P2, P3, and P4 in 1420), left neighboring samples (P5, P6, P7, and P8 in 1410), and / or upper left neighboring sample (P0) (1401). In some implementations, the upper neighboring samples may include both the upper neighboring samples (P1, P2, P3, and P4 in 1420) and the upper left neighboring sample (P0) (1401). In other implementations, the left neighboring samples may include both the left neighboring samples (P5, P6, P7, and P8 in 1410) and the upper left neighboring sample (P0) (1401).

[0111] The first sub-block (1471) includes 4x4 pixels, where each pixel of the 4x4 pixels corresponds to predN, which is the Nth adjacent prediction sample before refinement, for example pred0, pred1, pred2, ..., pred16.

[0112] In various embodiments, the offset value for each pixel of a given sub-block may be calculated based on neighboring samples according to a formula, which may be a predefined formula or may be indicated by parameters coded in the coded bitstream.

[0113] In some implementations, referring to FIG. 14B, the offset value for the kth position of a given sub-block (offset(k)) may be generated as follows:

number

[0114] W kn is the predefined weight for offset calculation. P n are the values ​​of the adjacent samples (e.g., P0, P1, P2, ..., P8). k is the predicted value of the pixel after application of intra prediction or other prediction (e.g., inter prediction). k is the refinement value of a pixel after applying ORIP. clip3() is the mathematical function of clip3. n is an integer between 0 and 8 inclusive. k is an integer between 0 and 15 inclusive.

[0115] In some implementations, W kn may be predefined or may be obtained according to Table 1. [Table 1]

[0116] In some other implementations, the sub-block-based ORIP may only apply to a given set of intra prediction modes and / or may be different for luma and chroma depending on the intra prediction mode. Table 2 shows one implementation of sub-block-based ORIP with various intra prediction modes and either luma or chroma channels. Taking the luma channel as an example, when the prediction mode is either DC or SMOOTH, ORIP is always ON and no further signaling is required, when the prediction mode is HOR / VER and angle_delta is equal to 0, block level signaling is required to enable / disable ORIP, and / or when the intra prediction mode is other modes, ORIP is always OFF and no further signaling is required. [Table 2]

[0117] With reference to the second 4x4 subblock (1473), because of its relative position with the first 4x4 subblock (1471), the top neighboring sample of the second subblock may be some pixels of the first subblock. P1 of the second subblock may be pred12 of the first subblock, P2 of the second subblock may be pred13 of the first subblock, P3 of the second subblock may be pred14 of the first subblock, and P4 of the second subblock may be pred15 of the first subblock. The top left neighboring sample of the second subblock (P0) may be the left neighboring sample of the first subblock (P8).

[0118] In various embodiments, the intra-prediction modes or mode options available for a current block being coded may be divided into multiple intra-prediction mode sets. A mode set index may be assigned to each set. Each set may include multiple intra-mode prediction modes. The manner in which the available intra-prediction modes are divided and ordered and the intra-prediction modes are ordered in each of the mode sets may be determined at least in part according to the intra-prediction modes used by its neighboring blocks based on the correlation between the intra-prediction modes between blocks. The intra-prediction modes used by the neighboring blocks may be referred to as "reference intra-prediction modes" or "reference modes." An intra-prediction mode for a particular unit may be determined and selected. The selection of the intra-prediction mode may be signaled. First, a mode set index may be signaled to indicate the mode set index of the intra-prediction mode set that includes the selected intra-prediction mode. Second, a mode index (also referred to as a mode position index within the set) may be signaled to indicate the index of the selected intra-prediction mode within the mode set.

[0119] The general implementation of intra-prediction mode partitioning and ordering above and the specific examples below exploit statistical effects and neighbor correlations to dynamically index these modes, and thus the design of syntax for signaling the selection in the coded video bitstream can be optimized to improve coding efficiency. For example, these implementations can help reduce the number of syntaxes for signaling and can help more efficient context generation for entropy coding.

[0120] The various embodiments and / or implementations described in this disclosure may be used separately or in combination in any order. Furthermore, some, all, or any partial or complete combination of these embodiments and / or implementations may be implemented as part of an encoder and / or decoder, and may be implemented in hardware and / or software, for example, hard-coded into dedicated processing circuitry (e.g., one or more integrated circuits). In another example, they may be implemented by one or more processors executing a program stored on a non-transitory computer-readable medium.

[0121] There may be some issues / challenges associated with intra-mode encoding: For example, the hardware implementation of intra-mode encoding, especially the process of building the intra-mode list for small blocks, may be very difficult.

[0122] This disclosure describes various embodiments of intra-prediction mode encoding in video encoding and / or decoding, addressing at least one of the above-mentioned problems / challenges and achieving efficient software / hardware implementation for improved intra-mode encoding. In some embodiments, to simplify the syntax for efficient software / hardware implementation, the signaling and / or encoding for intra-prediction modes for small blocks may be implemented according to predetermined rules.

[0123] In various embodiments, referring to FIG. 15, a method 1500 for intra-prediction mode encoding in video decoding may include some or all of steps 1510, by a device including a memory for storing instructions and a processor in communication with the memory, receiving an encoded video bitstream; step 1520, by the device, constructing a list of intra-modes for blocks in the encoded video bitstream according to a predetermined rule based on a size of the blocks; step 1530, by the device, dividing the list of intra-modes into a plurality of intra-mode sets for the blocks; step 1540, by the device, extracting from the encoded video bitstream a set index indicating an intra-mode set from the plurality of intra-mode sets; step 1550, by the device, extracting from the encoded video bitstream a mode index indicating an intra-prediction mode from the intra-mode set; step 1560, by the device, determining an intra-prediction mode for the block based on the set index and the mode index; and step 1570, by the device, decoding the encoded video bitstream based on the intra-prediction mode.

[0124] In various embodiments of the present disclosure, the size of a block (for example, but not limited to, a coding block, a prediction block, or a transformation block) may refer to a width or height of the block. The width or height of the block may be an integer value in units of pixels. In various embodiments of the present disclosure, the size of a block may refer to an area size of the block. The area size of the block may be an integer value calculated by multiplying the width of the block by the height of the block in units of pixels. In some various embodiments of the present disclosure, the size of a block may refer to a maximum value of the width or height of the block, a minimum value of the width or height of the block, or an aspect ratio of the block. The aspect ratio of the block may be calculated as the width divided by the height of the block, or may be calculated as the height divided by the width of the block.

[0125] In some implementations, the mode type of the intra mode may include at least one of a directional mode, a non-directional mode, a smooth mode (e.g., smooth, smooth_v, smooth_h), a DC mode, a PAETH mode, and / or a mode that generates a prediction sample according to a given prediction direction. In some other implementations, in a loose classification, the directional mode may broadly include any mode that is not a smooth (smooth, smooth_v, smooth_h), DC, or PAETH mode, and a mode that generates a prediction sample according to a given direction. In some other implementations, the non-directional mode may include a smooth mode (e.g., smooth, smooth_v, smooth_h), a DC mode, a PAETH mode, and a luma-for-chroma mode. In some other implementations, in a loose classification, the non-directional mode may broadly include any mode that is not a directional mode.

[0126] In some implementations, the available intra-prediction modes for the current block may be split / separated into multiple intra-prediction mode sets. To obtain the intra-prediction mode of the current block, first, a mode set index may be signaled to indicate the mode set index of the intra-prediction mode of the current block, and then a mode index may be signaled to indicate the index of the intra-prediction mode within the mode set.

[0127] Here, in various embodiments of the present disclosure, a "first" mode set not only indicates "one" mode set, but also indicates the "first" mode set with the smallest mode set index, a "second" mode set not only indicates "another" mode set, but also indicates the "second" mode set with the second smallest mode set index, and so on. For example, the number of intra-prediction mode sets may be indicated by M, and the mode set index may range, for example, from 1 to M or from 0 to M-1. If the mode set index is in the range from 1 to M, the "first" mode set is the "first" mode set whose mode set index is 1, the "second" mode set is the "second" mode set whose mode set index is 2, and so on. If the mode set index is in the range from 0 to M-1, the "first" mode set is the "first" mode set whose mode set index is 0, the "second" mode set is the "second" mode set whose mode set index is 1, and so on.

[0128] Here, in various embodiments of the present disclosure, "XYZ is signaled" may indicate that XYZ is encoded into the encoded bitstream during the encoding process, and / or after the encoded bitstream is transmitted from one device to another, "XYZ is signaled" may indicate that XYZ is decoded / extracted from the encoded bitstream during the decoding process.

[0129] Here, in various embodiments of the present disclosure, a "block" may refer to a prediction block, a coding block, a transform block, or a coding unit (CU).

[0130] Referring to step 1510, the device may be the electronic device (530) of Figure 5 or the video decoder (810) of Figure 8. In some implementations, the device may be a decoder (633) in the encoder (620) of Figure 6. In other implementations, the device may be part of the electronic device (530) of Figure 5, part of the video decoder (810) of Figure 8, or part of the decoder (633) in the encoder (620) of Figure 6. The encoded video bitstream may be the encoded video sequence of Figure 8, or the intermediate encoded data of Figure 6 or Figure 7. The blocks may represent blocks being encoded or blocks that have already been encoded.

[0131] Referring to step 1520, the device may build a list of intra modes for the block according to a predetermined rule based on the size of the block. Referring to step 1530, the device may divide the list of intra modes into multiple intra mode sets for the block. The predetermined rule may be one of a set of predetermined rules or may be selected from the set of predetermined rules based on the size of the block.

[0132] In some implementations, the intra mode list is constructed based on a predetermined rule for the current block. After constructing the intra mode list, the intra prediction modes are divided into multiple intra prediction mode sets according to corresponding indexes in the intra mode list. To signal the intra prediction mode of the current block, first, a mode set index may be signaled to indicate the mode set index of the intra prediction mode of the current block, and then a mode index may be signaled to indicate the index of the intra prediction mode in the mode set. The predetermined rule may be different for different block sizes, which may be indicated by the number of samples in the block.

[0133] In various embodiments, in response to the size of the block being equal to or greater than the first threshold, the list of intra modes includes a first sub-list at the top of the list, the first sub-list including all non-directional intra-prediction modes. For example, if the list of intra modes is divided into multiple intra-mode sets, the non-directional intra-prediction modes may be divided into the first intra-mode set because they are at the top of the list. In some implementations, the non-directional modes may include smooth modes (e.g., smooth, smooth_v, smooth_h), DC modes, PAETH modes, and luma-for-chroma modes. In some other implementations, in a loose classification, the non-directional modes may broadly include any modes that are not directional modes.

[0134] In some implementations, for blocks whose block size is equal to or greater than a first threshold (TH1), first, all non-directional modes are added to the mode list. Then, an offset is added to the directional intra-prediction modes of neighboring blocks to derive an intra-prediction mode, and the derived intra-prediction mode is added to the intra-mode list. Finally, after adding all the derived intra-prediction modes, if the intra-prediction mode set is still not full, a default mode is used to fill the remaining positions of the intra-mode list. For example, the first threshold is 8×8. In another example, the first threshold is 32 in number of samples.

[0135] In some other implementations, depending on the neighboring block using a directional intra-prediction mode, the list of intra modes includes a second sub-list next to the first sub-list in the list, the second sub-list includes a plurality of derived intra-prediction modes based on the directional intra-prediction modes of the neighboring block. For example, when the list of intra modes is divided into a plurality of intra-mode sets, the plurality of derived intra-prediction modes based on the directional intra-prediction modes of the neighboring block are likely to be divided into either the first intra-mode set or the second intra-mode set, since the plurality of derived intra-prediction modes are immediately next to the non-directional intra-prediction modes from the beginning of the list. In some implementations, the neighboring blocks of the current block may include the block above (top) the current block, the block to the left of the current block, or both the block above (top) and the block to the left of the current block.

[0136] In some other implementations, the multiple derived intra prediction modes include nine directional intra prediction modes by adding an offset of [0, -1, +1, -2, +2, -3, +3, -4, +4] to the directional intra prediction mode of the neighboring block. For example, if the directional intra prediction mode of the neighboring block has a particular directional angle (x°) and the directional angle step size is 3°, the multiple derived intra prediction modes may include nine directional intra prediction modes with directional angles of x, x±3, x±6, x±9, and x±12°.

[0137] In another example, the available intra-prediction modes for the current block are 61, including 5 non-directional modes and 56 directional modes. If the neighboring blocks of the current block are coded with one or more directional intra-prediction modes, first, the 5 non-directional modes are added to the mode list, and then 9 directional intra-prediction modes are derived by adding an offset of [0, -1, +1, -2, +2, -3, +3, -4, +4] to each of the directional modes of the neighboring blocks. If no directional modes exist in the neighboring blocks, the second step may be skipped. For example, if only one neighboring box is coded with one directional intra-prediction mode, 9 directional intra-prediction modes may be derived, resulting in 14 (= 9 + 5) modes being added to the mode list, and then the default mode is added to the mode list. In another example, if two adjacent blocks are coded with two directional intra prediction modes, 18 (=9*2) directional intra prediction modes may be derived, resulting in 23 (=18+5) modes being added to the mode list, and then a default mode is added to the mode list. In some situations, if two adjacent blocks are coded with two directional intra prediction modes, less than 18 directional intra prediction modes may be derived after removing any overlap between the two sets of nine derived directional intra prediction modes. In extreme situations, if two adjacent blocks are coded with two of the same directional intra prediction modes, only nine directional intra prediction modes may be derived after removing any overlap between the same two sets of nine derived directional intra prediction modes.

[0138] In some other implementations, the list of intra modes includes a third sublist next to the second sublist in the list, the third sublist including a default intra prediction mode. In some other implementations, the default intra prediction mode includes at least one nominal directional intra prediction mode with a delta angle of zero. For example, the default intra prediction mode may include all other nominal directional intra prediction modes with a delta angle of zero that are not already included in the derived intra prediction modes above based on the directional intra prediction modes of neighboring blocks.

[0139] In various embodiments, in response to the size of the block being smaller than the first threshold, the list of intra modes includes a first sublist at the beginning of the list, the first sublist including all non-directional intra-prediction modes. In some implementations, in response to the neighboring block using a directional intra-prediction mode, the list of intra modes includes a second sublist following the first sublist in the list, the second sublist including all directional intra-prediction modes of the neighboring block. In some other implementations, the list of intra modes includes a third sublist following the second sublist in the list, the third sublist including a default intra-prediction mode. In some other implementations, in response to the number of all directional intra-prediction modes of the neighboring block being greater than one, the directional intra-prediction modes of the neighboring blocks in the list of intra modes have an angle order from smallest to largest.

[0140] In some implementations, for blocks whose block size is smaller than a first threshold TH1, first, all non-directional modes are added to the mode list, then the directional intra-prediction modes of the neighboring blocks are added to the intra-mode list, and then a default mode is used to fill the remaining positions of the intra-mode list. In one example, the first threshold (TH1) is set to a block size of 8×8. In another example, if there are two directional intra-prediction modes in the neighboring blocks, the directional mode with a smaller angle is added to the mode list first. For example, the vertical mode is 90° and the horizontal mode is 180°, and the angle of the vertical mode is smaller than that of the horizontal mode, so the vertical mode is added to the mode list first.

[0141] In various embodiments, in response to the size of the block being smaller than the first threshold, the list of intra modes includes a predefined default intra prediction mode. In some implementations, the predefined default intra prediction modes in the list of intra modes have the following order: first, all non-directional intra prediction modes; second, directional intra prediction modes with a delta angle of zero; third, directional intra prediction modes with a delta angle of +2 or 2 times the step size; fourth, directional intra prediction modes with a delta angle of +1 or 1 times the step size; and / or fifth, directional intra prediction modes with a delta angle of +3 or 3 times the step size. In some implementations, the step size may be a default value of 3°.

[0142] In some implementations, for blocks whose block size is less than a threshold (TH1), a predefined default mode is used to fill all positions in the intra mode list. For example, the predefined default mode may be as follows: first, all non-directional modes are added to the mode list, second, directional modes with delta angles equal to 0 are added to the mode list, third, directional modes with delta angles equal to 2 and -2 are added to the mode list, fourth, directional modes with delta angles equal to 1 and -1 are added to the mode list, and / or fifth, directional modes with delta angles equal to 3 and -3 are added to the mode list.

[0143] In various embodiments, in response to the size of the block being smaller than a first threshold, the intra mode set indicated by the set index belongs to N intra mode sets, the N intra mode set being at the beginning of the multiple intra mode sets, where N is a positive integer.

[0144] In some implementations, for blocks smaller than a threshold (TH1), only the first N intra mode sets are allowed and signaled for the current block, where N is a positive integer. In one example, N is set to 1, indicating that only the first intra mode set is allowed and signaled for the current block. In another example, N is set to 2, indicating that only the first and second intra mode sets are allowed and signaled for the current block.

[0145] The embodiments of the present disclosure may be used individually or combined in any order. Furthermore, each of the methods (or embodiments), the encoder and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to a luma block or a chroma block, and in a chroma block, the embodiments may be applied to more than one color component individually or to more than one color component together.

[0146] It is to be understood that in the present disclosure, any of the steps or actions in the various embodiments may be combined in any amount or order as desired. It is to be understood that in the present disclosure, two or more steps or actions in the various embodiments may be performed in parallel.

[0147] The techniques described above can be implemented as computer software using computer readable instructions and can be physically stored on one or more computer readable media. For example, Figure 17 illustrates a computer system (2600) suitable for implementing certain embodiments of the disclosed subject matter.

[0148] Computer software can be coded using any suitable machine code or computer language and can be subject to assembly, compilation, linking, or similar mechanisms to produce code containing instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., either directly, or through interpretation, microcode execution, etc.

[0149] The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smart phones, gaming devices, Internet of Things devices, etc.

[0150] 17 for computer system (2600) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure, nor should the arrangement of components be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of computer system (2600).

[0151] The computer system (2600) may include certain human interface input devices that may be responsive to input by one or more human users through, for example, tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), and olfactory input (not shown). Human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from still image cameras), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0152] The input human interface devices may include one or more (only one of each is shown) of a keyboard (2601), a mouse (2602), a trackpad (2603), a touch screen (2610), a data glove (not shown), a joystick (2605), a microphone (2606), a scanner (2607), and a camera (2608).

[0153] The computer system (2600) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, through tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (2610), data gloves (not shown), or joystick (2605); although there may be haptic feedback devices that do not act as input devices), audio output devices (e.g., speakers (2609), headphones (not shown)), visual output devices (e.g., screens (2610) including CRT screens, LCD screens, plasma screens, OLED screens; each may or may not have touch screen input capability, each may or may not have haptic feedback capability, some of which may output two-dimensional visual output or higher than three-dimensional output through such means as stereoscopic output; virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0154] The computer system (2600) may also include human accessible storage devices and associated media, such as optical media including CD / DVD ROM / RW (2620) along with CD / DVD or similar media (2621), thumb drives (2622), removable hard drives or solid state drives (2623), legacy magnetic media such as tapes and floppy disks (not shown), specialized ROM / ASIC / PLD based devices (not shown) such as security dongles, etc.

[0155] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.

[0156] The computer system (2600) may also include an interface (2654) to one or more communication networks (2655). The networks may be, for example, wireless, wired, optical. The networks may further be local, wide area, metropolitan, in-vehicle and industrial, real-time, delay tolerant, etc. Examples of networks include Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wired or wireless wide area digital networks including cable television, satellite television, terrestrial broadcast television, in-vehicle and industrial including CAN Bus, etc. Certain networks usually require an external network interface adapter that is attached to a specific general-purpose data port or peripheral bus (2649) (e.g., a USB port of the computer system (2600)). Others are usually integrated into the core of the computer system (2600) by attachment to a system bus as described below (e.g., an Ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (2600) can communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast television), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Each of these networks and network interfaces as described above may use specific protocols and protocol stacks.

[0157] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (2640) of the computer system (2600).

[0158] The cores (2640) may include one or more central processing units (CPUs) (2641), graphics processing units (GPUs) (2642), specialized programmable processing units in the form of field programmable gate arrays (FPGAs) (2643), hardware accelerators for specific tasks (2644), graphics adapters (2650), etc. These devices may be connected through a system bus (2648), along with read only memory (ROM) (2645), random access memory (2646), internal mass storage devices (2647), such as internal non-user accessible hard drives, solid state drives (SSDs), etc. In some computer systems, the system bus (2648) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (2648) or through a peripheral bus (2649). In one example, a screen (2610) may be connected to the graphics adapter (2650). Architectures for peripheral buses include PCI, USB, and the like.

[0159] The CPU (2641), GPU (2642), FPGA (2643), and accelerator (2644) may execute certain instructions that may combine to constitute the above-mentioned computer code. The computer code may be stored in a ROM (2645) or a RAM (2646). Temporary data may also be stored in the RAM (2646), while persistent data may be stored, for example, in an internal mass storage device (2647). Rapid storage and retrieval from any of the memory devices may be enabled through the use of a cache memory that may be closely associated with one or more of the CPU (2641), GPU (2642), mass storage device (2647), ROM (2645), RAM (2646), etc.

[0160] The computer-readable medium can have computer code thereon for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the kind well known and available to those having skill in the computer software arts.

[0161] As a non-limiting example, a computer system having the architecture (2600), and in particular the cores (2640), can provide functionality as a result of the processors (including CPUs, GPUs, FPGAs, accelerators, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be user-accessible mass storage as introduced above as well as media associated with the cores' (2640) specific storage of a non-transitory nature, such as the cores' internal mass storage devices (2647) or ROM (2645). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the cores (2640). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the cores (2640) and in particular the processors therein (including CPUs, GPUs, FPGAs, etc.) to perform certain processes or certain specific portions thereof described herein, including defining data structures stored in RAM (2646) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (2644)), which may operate in place of or in conjunction with software to perform particular processes or portions of particular processes described herein. Reference to software includes logic, and vice versa, as appropriate. Reference to a computer-readable medium may include circuitry (e.g., an integrated circuit (IC)) that stores software for execution, circuitry that embodies logic for execution, or both, as appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0162] While the particular invention has been described with reference to exemplary embodiments, this description is not intended to be limiting. Various modifications of the exemplary and further embodiments of the present invention will become apparent to those skilled in the art from this description. Those skilled in the art will readily recognize that the above and various other modifications may be made to the exemplary embodiments illustrated and described herein without departing from the spirit and scope of the present invention. It is therefore contemplated that the appended claims will cover any such modifications and alternative embodiments. Certain proportions in the drawings may be exaggerated and other proportions may be minimized. Accordingly, the disclosure and drawings are to be regarded as illustrative and not restrictive.

Claims

1. 1. A method for intra-prediction mode encoding in video decoding, comprising: receiving, by a device including a memory storing instructions and a processor in communication with the memory, an encoded video bitstream; constructing, by the device, a list of intra modes for the blocks in the encoded video bitstream according to predetermined rules based on a size of the blocks; partitioning, by the device, the list of intra-modes into a plurality of intra-mode sets for the block; extracting, by the device, from the encoded video bitstream a set index indicating an intra-mode set from the plurality of intra-mode sets; extracting, by the device, from the encoded video bitstream a mode index indicating an intra-prediction mode from the intra mode set; determining, by the device, the intra-prediction mode for the block based on the set index and the mode index; decoding, by the device, the encoded video bitstream based on the intra-prediction mode; Including, The predetermined rule is: If the size of the block is greater than or equal to a first threshold, the list of intra modes includes a first sublist at the beginning of the list; The first sub-list includes all non-directional intra-prediction modes. The method includes:

2. the first threshold is 8×8; or The method of claim 1 , wherein the first threshold is 32 samples.

3. The predetermined rule is: If a neighboring block uses a directional intra-prediction mode and the size of the block is equal to or greater than the first threshold, the list of intra modes includes a second sublist that is next to the first sublist in the list; the second sub-list includes a plurality of derived intra-prediction modes based on the directional intra-prediction modes of the neighboring blocks. The method of claim 1 or 2, comprising:

4. 4. The method of claim 3, wherein the derived intra prediction modes include nine directional intra prediction modes by adding an offset of [0, -1, +1, -2, +2, -3, +3, -4, +4] to the directional intra prediction modes of the neighboring blocks.

5. The predetermined rule is: the list of intra modes includes a third sublist that is next to the second sublist in the list; The third sub-list includes a default intra-prediction mode. The method according to claim 3 or 4, comprising:

6. The method of claim 5 , wherein the default intra-prediction modes include at least one nominally directional intra-prediction mode having a delta angle of zero.

7. The predetermined rule is: If the size of the block is less than the first threshold, the list of intra modes includes the first sublist at the beginning of the list; The first sub-list includes all non-directional intra-prediction modes. The method of claim 1 , comprising:

8. The predetermined rule is: the list of intra modes includes a second sublist that is next to the first sublist in the list; The second sub-list includes a default intra-prediction mode. The method of claim 7, comprising:

9. 1. An apparatus for intra-prediction mode encoding in video decoding, comprising: A memory for storing instructions; a processor in communication with the memory; 9. An apparatus comprising: a processor configured to execute the instructions, the processor being configured to cause the apparatus to perform a method according to any one of claims 1 to 8.

10. A computer program product causing a processor to carry out a method according to any one of claims 1 to 8.

11. 1. A method for intra-prediction mode encoding performed by a video encoder, comprising: constructing, by the video encoder, a list of intra modes for the blocks in the encoded video bitstream according to predetermined rules based on a size of the blocks; partitioning, by the video encoder, the list of intra modes into a plurality of intra mode sets for the block; including, by the video encoder, a set index in the encoded video bitstream indicating an intra mode set from the plurality of intra mode sets; including, by the video encoder, a mode index in the encoded video bitstream indicating an intra-prediction mode from the intra mode set; Including, the intra prediction mode for the block is determined based on the set index and the mode index; The predetermined rule is: If the size of the block is greater than or equal to a first threshold, the list of intra modes includes a first sublist at the beginning of the list; The first sub-list includes all non-directional intra-prediction modes. The method includes:

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