Harmonized design for intra bi-prediction and multiple reference line selection

Abstract

To provide a method, an apparatus, and a computer readable storage medium for intra bi-prediction and multiple reference line intra prediction performed by a video decoder.SOLUTION: In a communication system, a method includes the steps of: receiving, by a device including a processor in communication with a memory, a coded video bitstream for a block; determining whether a single directional intra prediction applies to the block based on mode information of the block, the mode information of the block including at least one of a reference line index of the block, an intra prediction mode of the block, and a size of the block; in response to determining that the single directional intra prediction applies to the block, performing the single directional intra prediction to the block; and in response to determining that the intra bi-prediction applies to the block, performing the intra bi-prediction to the block.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] [Related Applications] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 215,888, filed June 28, 2021, and U.S. Nonprovisional Application No. 17 / 570,603, filed January 7, 2022, the entire contents of both applications being incorporated by reference.

[0002] [Technical field] This disclosure relates to video encoding and / or decoding techniques, and in particular to improved design and signaling of intra bi-prediction and multiple reference line selection schemes. [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 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 have been 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 bi-directional prediction and multiple reference line intra prediction in video decoding. The method includes receiving, by a device, an encoded video bitstream for a block. The device includes a memory that stores instructions and a processor in communication with the memory. The method also includes determining, by the device, whether unidirectional intra prediction or intra bi-directional prediction is applied to the block based on mode information of the block, where the mode information of the block includes at least one of a reference line index of the block, an intra prediction mode of the block, and a size of the block; performing, by the device, unidirectional intra prediction on the block in response to determining that unidirectional intra prediction is applied to the block; and performing, by the device, intra bi-directional prediction on the block in response to determining that intra bi-directional prediction is applied to the block.

[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 13A] 1 illustrates intra bi-prediction according to an exemplary embodiment of the present disclosure. [Figure 13B] 1 illustrates another intra bi-prediction scheme according to an exemplary embodiment of the present disclosure. [Figure 14] 1 illustrates a flow diagram of a method according to an exemplary embodiment of the present disclosure. [Figure 15] 1 illustrates intra bi-prediction based on multiple reference lines according to an exemplary embodiment of the present disclosure. [Figure 16] 1 illustrates another intra bi-prediction method based on multiple reference lines according to an exemplary embodiment of the present disclosure. [Figure 17] 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 addition to the unidirectional intra-prediction described in previous parts of this disclosure, two reference pixels along the prediction direction may be used in combination to achieve a directional predictor, which may be referred to as bidirectional intra-prediction or intra bi-prediction (IBP).

[0104] In some implementations, for a current block (e.g., a coding block or a coded block), IBP may be applicable to directional modes when the directional modes have an angle smaller than 90°, such as, but not limited to, D67_PRED and D45_PRED in Figure 9. In some other implementations, IBP may also be applicable to directional modes when the directional modes have an angle larger than 180°, such as, but not limited to, D203_PRED in Figure 9.

[0105] When intra bi-prediction is applied, two reference pixels along the direction of the directional mode are selected. One reference pixel is from the top or top-right of the current block, and the other pixel is from the left or bottom-left of the current block. To achieve the predictor, a weighted average of the two reference pixels may be calculated.

[0106] FIG. 13A shows an example of an IBP for a coding block (1330) in directional mode with prediction direction (1340) from A (1322) to B (1312). A and B are two reference samples / values, also called the first predictor and the second predictor. A is at the intersection of the direction (1340) with the top reference line (1320), and B is at the intersection of the direction (1340) with the left reference line (1310). The prediction of pixel (x, y) (1332), a pixel in the coding block (1330), is denoted as pred(x, y). pred(x, y) may be generated by a weighted combination of the two predictors A and B, as shown in Equation (2). Pred(x,y)=w*A+(1-w)*B (2)

[0107] A and / or B may be derived in a directional prediction process that includes interpolation for fractional pixel references. Figure 13B shows another example of an IBP for a coding block (1330) in different direction modes with different prediction directions (1350) from A (1314) to B (1324).

[0108] In some implementations where IBP is applied, two reference pixels located in the adjacent top reference line and the adjacent left reference line along the direction are weighted to realize a predictor. Both IBP and multiple reference line selection (MRLS) may be applied to a coded block, resulting in some problems / challenges. For example, one problem / challenge may include how to apply IBP to a current block when one or more reference samples in one or more non-adjacent reference lines are selected.

[0109] This disclosure describes various embodiments for signaling and / or determining multiple reference line intra prediction in video encoding and / or decoding, which address at least one of the problems / challenges mentioned above.

[0110] In various embodiments, with reference to Figure 14, a method 1400 for intra bi-directional prediction and multiple reference line intra prediction in video decoding is provided. The method 1400 may include some or all of steps 1410 of receiving, by a device including a memory for storing instructions and a processor in communication with the memory, an encoded video bitstream for a block, a step 1420 of determining, by the device, whether unidirectional intra prediction or intra bi-directional prediction is applied to the block based on mode information of the block, the mode information of the block including at least one of a reference line index of the block, an intra prediction mode of the block, and a size of the block, a step 1430 of performing, by the device, unidirectional intra prediction on the block in response to determining that unidirectional intra prediction is applied to the block, and a step 1440 of performing, by the device, intra bi-directional prediction on the block in response to determining that intra bi-directional prediction is applied to the block. In some implementations, step 1420 may include a step in which the device determines whether unidirectional intra prediction or intra bidirectional prediction is applied to the block based on mode information of the block, where the mode information of the block includes at least one of a reference line index of the block, an intra prediction mode of the block, or a size of the block.

[0111] In some implementations, if an intra-prediction mode does not belong to one of the above smooth modes or if the intra-prediction mode generates one or more prediction samples according to a given prediction direction, the intra-prediction mode may be classified as one of the directional modes and / or may be referred to as a directional intra-prediction mode (or directional mode).

[0112] In various embodiments of the present disclosure, the size of a block (such as, but not limited to, a coding block, a prediction block, or a transform block) may refer to a width or height of the block, which may be an integer value in units of pixels.

[0113] In various embodiments of the present disclosure, the size of a block (such as, but not limited to, a coding block, a prediction block, or a transformation block) may indicate the area size of the block, which may be an integer value calculated by multiplying the width of the block by the height of the block in units of pixels.

[0114] In some various embodiments of the present disclosure, the size of a block (such as, but not limited to, a coding block, a prediction block, or a transform block) may refer to the maximum width or height of the block, the minimum width or height of the block, or the aspect ratio of the block, which may be calculated as the width divided by the height of the block, or alternatively, the height divided by the width of the block.

[0115] In this disclosure, the reference line index indicates a reference line among the multiple reference lines. In various embodiments, a reference line index of 0 for a block may indicate a neighboring reference line for the block, which is also the closest reference line to the block. For example, referring to the block (1202) in FIG. 12, the top reference line (1210) is the top neighboring reference line for the block (1202) and is also the top reference line closest to the block. The left reference line (1218) is the left neighboring reference line for the block (1202) and is also the left reference line closest to the block. A reference line index greater than 0 for a block indicates a non-neighboring reference line for the block, which is also the reference line that is not the closest to the block. For example, referring to block (1202) of FIG. 12, a reference line index of 1 may indicate a top reference line (1208) and / or a left reference line (1216), a reference line index of 2 may indicate a top reference line (1206) and / or a left reference line (1214), and / or a reference line index of 3 may indicate a top reference line (1204) and / or a left reference line (1212).

[0116] Referring to step 1410, 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 block may represent a block being encoded or a block that has already been encoded.

[0117] In some implementations, when a directional intra-prediction mode is selected for a block to generate an intra-predictor from samples of non-adjacent reference lines, it may be determined whether unidirectional intra-prediction or intra-bidirectional prediction is applied to the block, and this determination may depend on the mode information of the block. In some implementations, the mode information of the block may include, but is not limited to, a reference line index (e.g., indicating which reference line is a reference line among multiple reference lines), one or more intra-prediction angles (e.g., indicating which directional intra-prediction mode is a directional intra-prediction mode among multiple directional intra-prediction modes), and / or a size of the block.

[0118] Referring to step 1420, the device may determine whether unidirectional intra prediction or intra bi-prediction is applied to the block based on the mode information of the block. In some implementations, step 1420 may include determining that unidirectional intra prediction is applied to the block in response to a reference line index of the block indicating a non-adjacent reference line. As an example, unidirectional intra prediction may be applied to the non-adjacent reference line regardless of the intra prediction angle of the current block.

[0119] In various embodiments, step 1420 may include determining that intra bi-prediction is applied to the block in response to the reference line index of the block indicating a neighboring reference line. As an example, intra bi-prediction may be applied only to the neighboring reference lines of the current block.

[0120] In various embodiments, step 1420 may include determining that unidirectional intra prediction is applied to the block in response to the reference line index of the block being greater than a predefined threshold, and / or determining that intra bidirectional prediction is applied to the block in response to the reference line index of the block being less than or equal to a predefined threshold. As an example, the decision of whether unidirectional intra prediction or intra bidirectional prediction is applied to the non-adjacent reference lines also depends on whether the value of the reference line index is greater than a predefined value N, where N is a non-negative integer (e.g., 0, 1, 2, 3, or 4).

[0121] In one example, the predetermined value N is 0. If the value of the reference line index of the block is greater than 0, i.e., if any non-adjacent reference line (e.g., any of lines 1212, 1214, 1216, 1204, 1206, and / or 1208 in FIG. 12) is used for the block, unidirectional intra prediction is applied to the block, and / or if the value of the reference line index of the block is less than or equal to 0, i.e., if any adjacent reference line (e.g., any of lines 1218 and / or 1210 in FIG. 12) is used for the block, intra bidirectional prediction is applied to the block.

[0122] In another example, the predetermined value N is 1. If the value of the reference line index of the block is greater than 1, i.e., if any of the first subset of non-adjacent reference lines (e.g., any of lines 1212, 1214, 1204, and / or 1206 in FIG. 12) is used for the block, unidirectional intra prediction is applied to the block, and / or if the value of the reference line index of the block is less than or equal to 1, i.e., if any of the adjacent reference lines (e.g., any of lines 1218 and / or 1210 in FIG. 12) and / or any of the second subset of non-adjacent reference lines (e.g., any of lines 1218 and / or 1210 in FIG. 12) is used for the block, intra bidirectional prediction is applied to the block.

[0123] In various embodiments, step 1420 may include determining that intra bidirectional prediction is applied to the block in response to the intra prediction mode of the block belonging to a first selected set of intra prediction modes and the reference line index indicating a neighboring reference line, determining that unidirectional intra prediction is applied to the block in response to the intra prediction mode of the block belonging to the first selected set of intra prediction modes and the reference line index indicating a non-neighboring reference line, and / or determining that intra bidirectional prediction is applied to the block in response to the intra prediction mode of the block belonging to a second selected set of intra prediction modes. In some implementations, the first selected set of intra prediction modes does not overlap with the second selected set of intra prediction modes. In some other implementations, the second selected set of intra prediction modes may include a diagonal intra prediction mode.

[0124] In some implementations, for a selected set of intra prediction modes, IBP is applied to both adjacent and non-adjacent reference lines, while for the remaining set of intra prediction modes, IBP is applied only to adjacent reference lines. In other implementations, the selected set of intra prediction modes may include some intra prediction modes with some specific direction angles, so that only integer samples are used as reference values ​​for intra prediction. In one example, only integer samples are used as reference values ​​for some intra prediction modes with diagonal directions (i.e., 45° or 225°). In another example, when intra prediction is applied by using only integer samples for diagonal intra prediction modes, IBP may also be applied to non-adjacent reference lines, and the diagonal intra prediction modes are intra prediction modes with diagonal directions (i.e., 45° or 225°).

[0125] In various embodiments, step 1420 may include determining that unidirectional intra prediction is applied to the block in response to the block's reference line index being an odd number and / or the reference line index indicating a non-adjacent reference line, and / or determining that intra bidirectional prediction is applied to the block in response to the block's reference line index being an even number and / or the reference line index indicating a neighboring reference line.

[0126] In some implementations, the decision of whether unidirectional intra prediction or intra bidirectional prediction is applied to the non-adjacent reference lines depends on whether the value of the reference line index is even or odd. In one example, if the value of the reference line index of the block is odd, unidirectional intra prediction is applied to the block, and / or if the value of the reference line index of the block is even, intra bidirectional prediction is applied to the block. As another example, if the value of the reference line index of the block is even, unidirectional intra prediction is applied to the block, and / or if the value of the reference line index of the block is odd, intra bidirectional prediction is applied to the block.

[0127] In various embodiments, there may be only one reference line index for a block. During encoding, the reference line index of the block may be coded into the coded bitstream, and / or during decoding, the reference line index of the block may be decoded / extracted from the coded bitstream. Step 1440 may include determining a first predictor based on the reference line index of the block, determining a second predictor based on the reference line index of the block, and / or determining a final predictor for the block according to a weighted calculation between the first predictor and the second predictor.

[0128] In some implementations, when intra bidirectional prediction is applied and the reference line index of a block indicates the use of a non-adjacent reference line for intra prediction, in order to generate an intra predictor from samples in the non-adjacent reference line, both predictor A and predictor B are generated from samples in the non-adjacent reference line, and then a weighting calculation is performed based on predictor A and predictor B to generate a final IBP predictor.

[0129] In various embodiments, there may be more than one reference line index for a block. A first reference line index may indicate a reference line to use among the plurality of above reference lines and a second reference line index may indicate a reference line to use among the plurality of left reference lines, or vice versa, where the first reference line index indicates a reference line to use among the plurality of left reference lines and the second reference line index indicates a reference line to use among the plurality of above reference lines. During encoding, more than one reference line index for a block may be coded into the coded bitstream, and / or during decoding, more than one reference line index for a block may be decoded / extracted from the coded bitstream.

[0130] In some implementations, step 1440 may include determining a first predictor based on a first reference line index of the block, determining a second predictor based on a second reference line index of the block, and / or determining a final predictor for the block according to a weighted calculation between the first predictor and the second predictor.

[0131] In some other implementations, the first reference line index indicates a non-adjacent reference line and the first predictor is generated from a first sample in the non-adjacent reference line, and / or the second reference line index indicates an adjacent reference line and the second predictor is generated from a second sample in the adjacent reference line.

[0132] In one example referring to FIG. 15, when intra bi-prediction is applied to a coding block (1530), an intra predictor (1532) is generated from samples in two reference lines including one non-adjacent reference line and / or one or more adjacent reference lines. As shown in FIG. 15, the coding block has a left adjacent reference line (1510), an upper adjacent reference line (1520), and at least one upper adjacent reference line (1521 and / or 1522). For example and without limitation, a first reference line index of 2 may indicate an upper non-adjacent reference line (1522), so that the predictor (1528) is generated from samples of the non-adjacent reference line (1522) selected by the MRLS according to the prediction direction (1550). In some implementations, a second reference line index of 0 may indicate a left adjacent reference line (1510). In some other implementations, the left adjacent reference line (1510) may be indicated / implied without the second reference line index. Predictor B (1514) is generated from samples of the adjacent reference line (1510) according to the prediction direction (1550). Predictor A and predictor B are then weighted and combined to generate an intra predictor (1532) according to the IBP scheme, for example, according to the equation in equation (2). In some implementations, the weight (w) may depend on the distance between the intra predictor (1532) and either predictor A or predictor B. In equation (2), the smaller the distance between the intra predictor (1532) and predictor A (1528) (i.e., the closer the predictor (1532) is to predictor A (1528)), the larger the weight (w). Similarly, in equation (2), the greater the distance between the intra predictor (1532) and predictor A (1528) (i.e., the farther the predictor (1532) is from predictor A (1528)), the smaller the weight (w).

[0133] 15 shows an example having a single left reference line and multiple top reference lines. Similarly, in another example, when intra bidirectional prediction is applied to a coding block, a single top reference line and multiple left reference lines may be applied to the coding block.

[0134] In various embodiments, there may be more than one reference line index for a block. A first reference line index may indicate a reference line to use among the plurality of top reference lines and a second reference line index may indicate more than one reference line to use among the plurality of left reference lines, or vice versa, where the first reference line index indicates a reference line to use among the plurality of left reference lines and the second reference line index may indicate more than one reference line to use among the plurality of top reference lines. During encoding, more than one reference line index for a block may be encoded into the encoded bitstream, and / or during decoding, more than one reference line index for a block may be decoded / extracted from the encoded bitstream.

[0135] In some implementations, step 1440 may include the first reference line index indicating a non-adjacent reference line and the first predictor being generated from a first sample at the non-adjacent reference line, and / or the second reference line index indicating a plurality of reference lines and the second predictor being generated as a linear weighted average of samples obtained from each of the plurality of reference lines along a prediction angle.

[0136] In some other implementations, when intra bidirectional prediction is applied to generate intra predictions from samples of non-adjacent reference lines, one or both predictors are generated using samples of multiple (more than one) reference lines.

[0137] In one example, referring to Figure 16, the predictor is generated using a linear weighted sum of more than one sample (a first sample (1626) from a first reference line (1620), a second sample (1627) from a second reference line (1621), and a third sample (1628) from a third reference line (1622)) from multiple reference lines along a prediction angle (1650). The weight of each sample may be predefined according to the relative position of the sample (of the multiple reference lines) involved in the derivation of the predictor.

[0138] In various embodiments, method 1400 may further include determining that intra bidirectional prediction is applied to the block and disabling a reference sample filtering process in response to the reference line index of the block indicating a non-adjacent reference line, using a reference sample for intra bidirectional prediction in response to a reference sample from the non-adjacent reference being available, and / or using an available adjacent reference sample for intra bidirectional prediction in response to a reference sample from the non-adjacent reference being unavailable.

[0139] In some implementations, when bidirectional intra prediction is applied to one or more non-adjacent reference lines, the reference sample filtering process may be disabled. Thus, one or more reference samples from one or more non-adjacent (or non-zero) reference lines may be taken and used directly for intra bidirectional prediction. If one or more reference samples from one or more non-adjacent (or non-zero) reference lines are unavailable, they may be padded from one or more available adjacent reference samples. In some other implementations, padding the unavailable reference samples may include copying from available adjacent reference samples.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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).

[0145] 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).

[0146] 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).

[0147] 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).

[0148] 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.

[0149] 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.

[0150] 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.

[0151] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (2640) of the computer system (2600).

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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. A method of video encoding performed by an encoder, comprising: encoding a video bitstream; transmitting the video bitstream; Including, The step of encoding the video bitstream comprises: determining whether unidirectional intra prediction or intra bi-prediction is applied to the block based on mode information of the block; performing the unidirectional intra prediction on the block if it is determined that the unidirectional intra prediction is applied to the block; performing the intra bidirectional prediction on the block if it is determined that the intra bidirectional prediction is applied to the block; If it is determined that the intra bi-prediction is applied to the block, and the reference line index of the block indicates a non-adjacent reference line, Disabling the reference sample filtering process; if a reference sample from the non-adjacent reference line is available, using the reference sample for intra bi-prediction; if the reference samples from the non-adjacent reference lines are unavailable, using available adjacent reference samples for intra bi-prediction; A method comprising:

2. The step of determining whether the unidirectional intra prediction or the intra bidirectional prediction is applied to the block comprises: The method of claim 1 , comprising determining that the unidirectional intra prediction is applied to the block if the reference line index of the block indicates a non-adjacent reference line.

3. The step of determining whether the unidirectional intra prediction or the intra bidirectional prediction is applied to the block comprises: The method of claim 1 , comprising determining that the intra bi-prediction is applied to the block if the reference line index of the block indicates a neighboring reference line.

4. The step of determining whether the unidirectional intra prediction or the intra bidirectional prediction is applied to the block comprises: determining that the unidirectional intra prediction is applied to the block if the reference line index of the block is greater than a predetermined threshold; determining that the intra bi-prediction is applied to the block if the reference line index of the block is less than or equal to the predetermined threshold; The method of claim 1 , comprising:

5. The method of claim 4, wherein the predetermined threshold is a non-negative integer.

6. The step of determining whether the unidirectional intra prediction or the intra bidirectional prediction is applied to the block comprises: determining that the intra bi-prediction is applied to the block if the intra prediction mode of the block belongs to a first selected set of intra prediction modes and the reference line index indicates a neighboring reference line; determining that the unidirectional intra prediction is applied to the block if the intra prediction mode of the block belongs to the first selected set of intra prediction modes and the reference line index indicates a non-adjacent reference line; determining that intra bi-prediction is applied to the block if the intra prediction mode of the block belongs to a second selected set of intra prediction modes; 2. The method of claim 1 , wherein the first selected set of intra-prediction modes does not overlap with the second selected set of intra-prediction modes.

7. The method of claim 6, wherein the second selected set of intra prediction modes includes a diagonal intra prediction mode.

8. The step of determining whether the unidirectional intra prediction or the intra bidirectional prediction is applied to the block comprises: determining that the unidirectional intra prediction is applied to the block if the reference line index of the block is odd and / or if the reference line index indicates a non-adjacent reference line; determining that the intra bi-prediction is applied to the block if the reference line index of the block is even and / or if the reference line index indicates an adjacent reference line; The method of claim 1 , comprising:

9. The step of performing intra bidirectional prediction on the block, comprising: determining a first predictor based on the reference line index of the block; determining a second predictor based on the reference line index of the block; determining a final predictor for the block according to a weighted calculation between the first predictor and the second predictor; 9. The method of claim 1, comprising:

10. The step of performing the intra bi-directional prediction on the block, comprising: determining a first predictor based on a first reference line index of the block; determining a second predictor based on a second reference line index of the block; determining a final predictor for the block according to a weighted calculation between the first predictor and the second predictor; 9. The method of claim 1, comprising:

11. The method of claim 10, wherein the first reference line index indicates a non-adjacent reference line, and the first predictor is generated from a first sample in the non-adjacent reference line; The method of claim 10 , wherein the second reference line index indicates an adjacent reference line, and the second predictor is generated from a second sample in the adjacent reference line.

12. The step of performing the intra bidirectional prediction on the block, comprising: the first reference line index indicates a non-adjacent reference line, and the first predictor is generated from a first sample in the non-adjacent reference line; the second reference line index indicates a plurality of reference lines, and the second predictor is generated as a linear weighted average of samples taken from each of the plurality of reference lines along a prediction angle; The method of claim 10, comprising:

13. An apparatus for encoding a video bitstream, comprising: a memory for storing instructions; a processor in communication with the memory; 13. An apparatus comprising: a processor configured, when the processor executes the instructions, to cause the apparatus to perform the method of any one of claims 1 to 12.

14. A computer program causing a processor to carry out a method according to any one of claims 1 to 12.

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