Method, apparatus and program for improved intra-mode encoding

Abstract

In a method of video decoding performed in a video decoder, coded information of a current block and neighboring blocks of the current block are received from a coded video bitstream. A Most Probable Mode (MPM) list is generated from the current block. The MPM list includes an intra mode determined based on the intra modes of the neighboring blocks of the current block. One of a gradient value and a cost value of the neighboring blocks is calculated based on the intra modes of the MPM list. The intra modes of the MPM list are sorted based on the one of the gradient value and the cost value of the neighboring blocks, and each intra mode in the MPM list is associated with a respective one of the gradient value and the cost value. Furthermore, the current block is reconstructed based on the MPM list.

Description

[Technical field]

[0001] INCORPORATION BY REFERENCE This application claims the benefit of priority to U.S. Patent Application No. 17 / 888,558, entitled "METHOD AND APPARATUS FOR IMPROVED INTRA-MODE ENCODING," filed on August 16, 2022, which claims the benefit of priority to U.S. Provisional Application No. 63 / 286,979, entitled "IMPROVED INTRA-MODE ENCODING," filed on December 7, 2021. The disclosures of the prior applications are hereby incorporated by reference in their entireties.

[0002] Technical Field This disclosure describes embodiments generally relating to video coding. [Background technology]

[0003] The 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 filing, 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 chrominance samples. The sequence of pictures can have a fixed or variable picture rate (also informally known as frame rate), for example, 60 pictures per second or 60 Hz. Uncompressed video has specific bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) with 8 bits per sample 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 the input video signal through compression. Compression may help reduce the aforementioned bandwidth and / or storage space requirements, in some cases by more than one order of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When lossy compression is used, the reconstructed signal may not be identical to the original signal, but the distortion between the original and reconstructed signals is small enough to make the reconstructed signal useful for the intended application. For video, lossy compression is widely used. The amount of acceptable distortion depends on the application, e.g., users of certain consumer streaming applications may tolerate higher distortion than users of television distribution applications. The achievable compression ratio may reflect that a higher tolerable / acceptable distortion can result in a higher compression ratio.

[0006] Video encoders and decoders may utilize techniques from several broad categories, including motion compensation, 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 a previously reconstructed reference picture. 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 may be an intra picture. Intra pictures and their derivatives, such as independent decoder refresh pictures, can be used to reset the decoder state and thus can be used as the first picture in a coded video bitstream and video session or as a still image. Samples of an intra block may be subjected to a transform, and the transform coefficients may be quantized before entropy coding. Intra prediction may be a technique that minimizes 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 coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to do so from surrounding sample data and / or metadata obtained during the encoding and / or decoding of blocks of data that are spatially neighbors and that precede them in decoding order. 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 reference pictures.

[0009] There may be various forms of intra prediction. If more than one such technique is available for a given video coding technique, the technique used may be coded in an intra prediction mode. In some cases, a mode may have sub-modes and / or parameters, which may be coded separately or may be included 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). A predictor block can be formed using neighboring sample values ​​belonging to already available samples. The sample values ​​of the neighboring samples are copied to the predictor block according to a certain direction. The reference to the direction used can be coded in the bitstream or may itself be predicted.

[0011] Referring to FIG. 1, at the bottom right, a subset of 9 known predictor directions from the 33 possible predictor directions (corresponding to the 33 angle modes of the 35 intra modes) of H.265 is depicted. The point (101) where the arrows converge represents the sample to be predicted. The arrows represent the direction from which the sample is predicted. For example, arrow (102) indicates that sample (101) is predicted from the sample(s) to the top right and at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from the sample(s) to the bottom left of sample (101), at an angle of 22.5 degrees from the horizontal.

[0012] Continuing to refer to FIG. 1, at the top left, a square block (104) of 4×4 samples is depicted (indicated by a thick dashed line). 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. Additionally, reference samples are shown that follow a similar numbering scheme. The reference samples are labeled with R and their Y position (e.g., row index) and X position (column index) relative to the block (104). In both H.264 and H.265, the predicted samples are neighbors of the block being reconstructed, so there is no need to use negative values.

[0013] Intra-picture prediction can work by copying reference sample values ​​from neighboring samples that are filled by the signaled prediction direction. For example, assume that the coded video bitstream includes signaling for this block that indicates a prediction direction that is aligned with the arrow (102). That is, the sample is predicted from the top right sample or prediction sample at an angle of 45 degrees from the horizontal. In that 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 some cases, particularly when the orientation 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 develops, the number of possible directions has increased. In H.264 (2003), nine different directions could be represented. This increased to 33 in H.265 (2013), and JEM / VVC / BMS at the time of this disclosure can support up to 65 directions. Experiments are performed to identify the most likely directions, and certain techniques in entropy coding are used to represent those likely directions with a small number of bits while accepting some penalty for the less likely directions. Furthermore, the direction itself may be predictable from nearby directions used in nearby already decoded blocks.

[0016] FIG. 2 shows a schematic diagram (201) depicting 65 intra prediction directions with JEM to illustrate the increasing number of prediction directions over time.

[0017] The mapping of intra-prediction direction bits to directions in the coded video bitstream can vary from one video coding technique to another, 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. In all cases, however, there will be some directions that are statistically less likely to occur in the video content than certain other directions. Because the goal of video compression is to reduce redundancy, in a well-performing video coding technique, these less likely ways are represented by more bits than the more likely directions. Summary of the Invention [Problem to be solved by the invention]

[0018] Aspects of the present disclosure provide a method and apparatus for video encoding / decoding. In some examples, the apparatus for video decoding includes a receiving circuit and a processing circuit. [Means for solving the problem]

[0019] According to an aspect of the present disclosure, a method of video decoding performed in a video decoder is provided. In the method, coded information of a current block and neighboring blocks of the current block may be received from a coded video bitstream. A most probable mode (MPM) list may be generated from the current block. The MPM list may include an intra mode determined based on the intra modes of neighboring blocks of the current block. One of a gradient value and a cost value of the neighboring blocks may be calculated based on the intra modes of the MPM list. The intra modes of the MPM list may be sorted based on the one of the gradient values ​​and the cost values ​​of the neighboring blocks, and each intra mode in the MPM list may be associated with a respective one of the gradient value and the cost value. Furthermore, the current block may be reconstructed based on the MPM list.

[0020] In some embodiments, the gradient values ​​may correspond to a histogram of gradients (HoG). Thus, sorting the intra modes of the MPM list may further include sorting the intra modes of the MPM list in descending order based on the HoG of the neighboring blocks. The intra mode of the MPM list associated with the highest HoG may be the first item of the MPM list.

[0021] In some embodiments, to sort the intra modes of the MPM list, the intra modes of the MPM list may be sorted in ascending order based on the cost values ​​of the neighboring blocks, and the intra mode of the MPM list associated with the smallest cost value may be the first item of the MPM list.

[0022] In some embodiments, to sort the intra modes of the MPM list, a first intra mode of the intra modes associated with the highest HoG and a second intra mode of the intra modes associated with the second highest HoG may be determined. Further, a determination may be made to determine whether (i) the first intra mode is different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, and (ii) whether the second intra mode is different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks. In response to the first intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, the first intra mode may be added to the MPM list after other intra modes of the MPM list are sorted. In response to the second intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, the second intra mode may be added as the last item in the MPM list.

[0023] In some embodiments, to sort the intra modes of the MPM list, a first intra mode of the intra modes associated with a minimum cost value and a second intra mode of the intra modes associated with a second minimum cost value may be determined. A determination may be made to determine whether (i) the first intra mode is different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, and (ii) whether the second intra mode is different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks. In response to the first intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, the first intra mode may be added after the other intra modes of the MPM list are sorted. In response to the second intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, the second intra mode may be added as the last item in the MPM list.

[0024] In the method, an MPM index may be further encoded from the encoded information. An intra mode of a current block may be determined based on the MPM index and the MPM list, where the MPM index may indicate which intra mode in the MPM list is applied to intra code the current block.

[0025] In some embodiments, the intra modes of the non-MPM list may be sorted based on one of a HoG and a cost value of the neighboring blocks calculated based on the intra modes of the non-MPM list, where each of the intra modes in the non-MPM list may be associated with a respective one of the HoG and the cost value.

[0026] In one example, to sort the intra modes of the non-MPM list, the intra modes of the non-MPM list can be sorted in descending order based on the HoG of the neighboring blocks, where the intra mode of the non-MPM list associated with the highest HoG can be the first item of the non-MPM list.

[0027] In another example, to sort the intra modes of the non-MPM list, the intra modes of the non-MPM list can be sorted in ascending order based on the cost values ​​of the neighboring blocks, where the intra mode of the non-MPM list associated with the smallest cost value can be the first item of the non-MPM list.

[0028] According to another aspect of the present disclosure, there is provided an apparatus, the apparatus having a processing circuit, the processing circuit being configured to perform any of the above methods for video encoding.

[0029] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer for video decoding, cause the computer to perform any of the above methods for video decoding. [Brief description of the drawings]

[0030] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings.

[0031] [Figure 1] FIG. 2 is a schematic diagram of an example subset of intra-prediction modes.

[0032] [Diagram 2] FIG. 2 is an illustration of an exemplary intra-prediction direction.

[0033] [Diagram 3]FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to an embodiment.

[0034] [Figure 4] FIG. 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an embodiment.

[0035] [Diagram 5] FIG. 2 is a schematic diagram of a simplified block diagram of a decoder according to an embodiment.

[0036] [Figure 6] FIG. 2 is a schematic diagram of a simplified block diagram of an encoder according to an embodiment.

[0037] [Figure 7] 4 shows a block diagram of an encoder according to another embodiment;

[0038] [Figure 8] 4 shows a block diagram of a decoder according to another embodiment;

[0039] [Figure 9] FIG. 1 is a schematic diagram of template-based intra-mode derivation (TIMD) according to one embodiment.

[0040] [Figure 10] 1 illustrates neighboring coding units of a current coding unit in intra mode coding, according to some embodiments of the present disclosure.

[0041] [Figure 11] 1 is a flowchart outlining an exemplary decoding process according to some embodiments of the present disclosure.

[0042] [Figure 12] 1 is a flowchart outlining an exemplary encoding process according to some embodiments of the present disclosure.

[0043] [Figure 13] 1 is a schematic diagram of a computer system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to an 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) perform a 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 can 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 recover a video picture, and display the video picture according to the recovered video data. One-way data transmission may be common in media service applications, etc.

[0045] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of encoded video data, such as may occur during a video conference. 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 recover the video pictures, and display the video pictures on an accessible display device in accordance with the recovered video data.

[0046] In the example of FIG. 3, terminal devices (310), (320), (330), and (340) may be depicted as a server, a personal computer, and a smartphone, although the principles of the present disclosure may not be so limited. Embodiments of the present disclosure find application in laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. Network (350) represents any number of networks that convey encoded video data between terminal devices (310), (320), (330), and (340), including, for example, wired and / or wireless communication networks. Communication network (350) may exchange data in circuit-switched and / or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of the present discussion, the architecture and topology of network (350) may not be important to the operation of the present disclosure, unless otherwise described below.

[0047] 4 illustrates an arrangement of a video encoder and a video decoder in a streaming environment as an example of an application for the disclosed subject matter. The disclosed subject matter may be equally applicable to other video-enabled applications including, for example, video conferencing, digital TV, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0048] The streaming system may include a video source (401), e.g., a digital camera, and may include a capture subsystem (413) that generates, e.g., a stream of uncompressed video pictures (402). In one example, the stream of video pictures (402) includes samples captured by a digital camera. The stream of video pictures (402), depicted as a thick line to emphasize its higher data volume when 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 achieve aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream), depicted as a thin line to emphasize its lower data volume when compared to the stream of video pictures (402), may be stored in a streaming server (405) for future use. 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 an electronic device (430). The video decoder (410) decodes the incoming copy of the encoded video data (407) and generates an outgoing stream of video pictures (411) that can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (404), (407), and (409) (e.g., a video bitstream) can be encoded according to some video encoding / compression standard.Examples of these standards include ITU-T Recommendation H.265. In one example, a video coding standard under development is informally known as VVC. The disclosed subject matter may be used in the context of Versatile Video Coding (VVC).

[0049] 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).

[0050] 5 shows a block diagram of a video decoder (510) according to an embodiment 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.

[0051] 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 at a time, and the decoding of each coded video sequence is independent of the other coded video sequences. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data. The receiver (531) may receive the encoded video data together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to respective usage entities (not shown). The receiver (531) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (515) may be coupled between the receiver (531) and the entropy decoder / parser (520) (hereinafter the "parser"). In some applications, the buffer memory (515) is 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 yet another buffer memory (515) internal to the video decoder (510), e.g. to handle playback timing. If the receiver (531) is receiving data from a storage / forwarding device of sufficient bandwidth and controllability, or from an isochronous network, the buffer memory (515) may not be required or may be small. For use in best-effort packet networks such as the Internet, the buffer memory (515) may be required and may be relatively large, advantageously of adaptive size, and may be implemented, at least in part, in an operating system or similar element (not shown) external to the video decoder (510).

[0052] 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 render device (512) (e.g., a display screen). The render device may not be an integral part of the electronic device (530) as shown in FIG. 5, but may be coupled to the electronic device (530). The control information for the rendering device(s) may be in the form of a Supplementary Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (520) may parse / entropy decode the received coded video sequence. The 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) can 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 group. The subgroups can 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) can also extract information from the coded video sequence, such as transform coefficients, quantizer parameter values, motion vectors, etc.

[0053] The parser (520) performs an entropy decoding / parsing operation on the video sequence received from the buffer memory (515), thereby generating symbols (521).

[0054] The reconstruction of symbols (521) can involve several different units, depending on the type of coded video picture or its parts (e.g., inter and intra pictures, inter and intra blocks) and other factors. Which units are involved and how can 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 the following units is not depicted for clarity.

[0055] In addition to the functional blocks already mentioned, the video decoder (510) may be conceptually divided into a number of functional units, as described below. In a practical implementation working within commercial constraints, many of these units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is appropriate.

[0056] The first unit is a scaler / inverse transform unit (551). The scaler / inverse transform unit (551) receives quantized transform coefficients and control information as symbol(s) (521) from the parser (520). The control information includes which transform to use, block size, quantization factor, quantization scaling matrix, etc. The scaler / inverse transform unit (551) can output a block containing sample values ​​that can be input to an aggregator (555).

[0057] 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 part 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) generates a block of the same size and shape as the block being reconstructed using surrounding already reconstructed information taken from 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. The aggregator (555) may add, sample by sample, the prediction information generated by the intra prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0058] In other cases, the output samples of the scaler / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensation prediction unit (553) may access a reference picture memory (557) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (521) for the block, these samples may be added by an aggregator (555) to the output of the scaler / inverse transform unit (in this case referred to as residual samples or residual signals) to generate output sample information. The addresses in the reference picture memory (557) from which the motion compensation unit (553) fetches 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, X, Y, and reference picture components. Motion compensation may include interpolation of sample values ​​fetched from the reference picture memory (557) when subsample accurate motion vectors are used, motion vector prediction mechanisms, etc.

[0059] The output samples of the aggregator (555) can be subjected to various loop filtering techniques in a loop filter unit (556). Video compression techniques can include in-loop filter techniques that are controlled by parameters contained in the coded video sequence (also called coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but can also be responsive to meta-information obtained during decoding of a previous part (in decoding order) of the coded picture or coded video sequence, as well as to previously reconstructed loop filtered sample values.

[0060] The output of the loop filter unit (556) can be a sample stream, which can be output to a render device (512) or can be stored in a reference picture memory (557) for use in future inter-picture prediction.

[0061] Once an encoded picture is fully reconstructed, it can be used as a reference picture for future predictions. For example, once an encoded picture corresponding to a current picture is fully reconstructed and the encoded picture is identified (e.g., by the parser (520)) as a reference picture, the current picture buffer (558) can become part of the reference picture memory (557) and a fresh current picture buffer can be reallocated before starting the reconstruction of a subsequent encoded picture.

[0062] The video decoder (510) may perform decoding operations according to a given video compression technique in a standard, such as ITU-T Recommendation H.265. The coded video sequence may conform to the syntax prescribed by the video compression technique or standard being used, in the sense that the coded 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 certain tools from all tools available in the video compression technique or standard as the only tools available for use under that profile. Compliance may also require that the complexity of the coded video sequence be within a range defined by the 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 coded video sequence.

[0063] In some 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) improvement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0064] 6 shows a block diagram of a video encoder (603) according to an embodiment of the present disclosure. The video encoder (603) is included in an electronic device (620). The electronic device (620) includes a transmitter (640) (e.g., a transmission circuit). The video encoder (603) can be used in place of the video encoder (403) in the example of FIG. 4.

[0065] 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) is part of the electronic device (620).

[0066] 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, ...) 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 that stores 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 that impart motion when viewed in sequence. The pictures themselves 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.

[0067] According to an embodiment, 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 is one function of the controller (650). In some embodiments, the controller (650) controls and is operatively coupled to other functional units, such as those described below. Such couplings are not depicted for clarity. Parameters set by the controller (650) can 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 with other suitable functions for the video encoder (603) optimized for a certain system design.

[0068] In some embodiments, the video encoder (603) is configured to operate in an encoding loop. As a simplistic description, in one example, the encoding loop can 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). The decoder (633) reconstructs the symbols to generate sample data in a similar manner that a (remote) decoder would also generate (since in the video compression techniques contemplated in the disclosed subject matter, any compression between the symbols and the encoded video bitstream is lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces 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 also used in several related technologies.

[0069] 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, since 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 the parser (420), may not be fully implemented in the local decoder (633).

[0070] One observation that can be made at this point is that any decoder technique, other than parsing / entropy decoding, that exists in a decoder must necessarily exist in substantially the same functional form in the corresponding encoder. For this reason, the disclosed subject matter focuses on the decoder operation. The description of the encoder techniques can be abbreviated since they are the inverse of the decoder techniques, which are described generically. Only in certain areas is more detailed explanation required and is provided below.

[0071] During operation, in some examples, 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 between pixel blocks of the input picture and pixel blocks of the reference picture(s) that may be selected as predictive references for the input picture.

[0072] The local video decoder (633) can decode the coded 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 coding engine (632) can advantageously be a lossy process. When the coded video data can be decoded by a video decoder (not shown in FIG. 6), the reconstructed video sequence can typically be a copy of the source video sequence 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 the reconstructed reference pictures that would be obtained by the far-end video decoder.

[0073] 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 certain 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 derived from multiple reference pictures stored in the reference picture memory (634).

[0074] 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.

[0075] The output of all the above functional units can be subjected to 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.

[0076] The transmitter (640) can buffer the coded video sequence produced by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) can merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0077] A controller (650) may manage the operation of the video encoder (603). During encoding, the controller (650) may assign a 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:

[0078] 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, as well as their respective uses and characteristics.

[0079] 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.

[0080] A bidirectionally predictive picture (B picture) may be one that can be encoded and decoded using intra- or inter-prediction that uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-predictive picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0081] A source picture is usually spatially divided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and may be coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks, as determined by the coding assignment applied to the respective picture of the block. For example, blocks of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of a P picture may be predictively coded via spatial 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.

[0082] 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.

[0083] In some embodiments, the sender (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 forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0084] Video may be captured as multiple source pictures (video pictures) in a temporal sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlations in a given picture, while inter-picture prediction exploits correlations (temporal or otherwise) between pictures. In one example, a particular picture to be encoded / decoded, called the current picture, is divided into blocks. If a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, that block in the current picture can be coded by a vector called a motion vector. The motion vector points to a reference block in the reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0085] In some embodiments, bi-prediction techniques can be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, such as a first reference picture and a second reference picture, both of which precede the current picture in decode order (but may be past and future, respectively, in display order) in the video. A block in the current picture can be coded with 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 predicted by a combination of the first and second reference blocks.

[0086] Furthermore, to improve coding efficiency, merge mode techniques can be used in inter-picture prediction.

[0087] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, according to the HEVC standard, pictures in a sequence of video pictures are divided into coding tree units (CTUs) for compression, and the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), one luma CTB and two chroma CTBs. Each CTU can be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels can be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In one example, each CU is analyzed to determine a prediction type for that CU, such as an inter prediction type or an intra prediction type. A CU is divided into one or more prediction units (PUs) depending on temporal and / or spatial predictability. Generally, each PU includes a luma prediction block (PB) and two chroma PBs. In an embodiment, the prediction operation in encoding / decoding is performed in units of a prediction block. Taking a luma prediction block as an example of a prediction block, the prediction block includes 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.

[0088] 7 shows a diagram of a video encoder (703) according to another embodiment of the present disclosure. The video encoder (703) is configured to receive a processed block of sample values ​​(e.g., a predictive block) in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. In one example, the video encoder (703) is used in place of the video encoder (403) in the example of FIG. 4.

[0089] In an HEVC 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) determines whether the processing block is best coded using intra mode, inter mode, or bi-predictive mode, e.g., using rate-distortion optimization. If the processing block is coded in intra mode, the video encoder (703) may use intra prediction techniques to encode the processing block into a coded picture; if the processing block is coded in inter mode or bi-predictive mode, the video encoder (703) may use inter prediction techniques or bi-predictive techniques, respectively, to encode the processing block into a coded picture. In certain video coding techniques, a merge mode may be an inter-picture prediction submode 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 certain other video coding techniques, there may be motion vector components applicable to the current block. In one example, the video encoder (703) includes other components, such as a mode decision module (not shown) for determining a mode of a processing block.

[0090] In the example of FIG. 7, the video encoder (703) includes the inter-encoder (730), the intra-encoder (722), the residual calculator (723), the switch (726), the residual encoder (724), the general controller (721), and the entropy coder (725), coupled together as shown in FIG.

[0091] 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), generate inter prediction information (e.g., a description of redundant information due to inter encoding 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 encoded video information.

[0092] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), optionally compare the block to blocks already encoded in the same picture, generate transformed and quantized coefficients, and optionally generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In one example, the intra encoder (722) also calculates an intra prediction result (e.g., a predicted block) based on the intra prediction information and a reference block in the same picture.

[0093] The general controller (721) is 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 the mode of the block and provides a control signal to the switch (726) based on the mode. For example, if the mode is intra mode, the general controller (721) controls the switch (726) to select the 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 mode is inter mode, the general controller (721) controls the switch (726) to select the 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.

[0094] The residual calculator (723) is configured to calculate a difference (residual data) between the received block and a prediction result selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) is configured to encode the residual data to generate transform coefficients based on the residual data. In one example, the residual encoder (724) is configured to transform the residual data from a spatial domain to a frequency domain to generate transform coefficients. The transform coefficients are then subjected to a quantization process to obtain quantized transform coefficients. In various 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) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) may generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are suitably processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and, in some examples, used as reference pictures.

[0095] The entropy encoder (725) is configured to format a bitstream to include the encoded block. The entropy encoder (725) is configured to include various information in accordance with a suitable standard, such as the HEVC standard. In one example, the entropy encoder (725) is 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. It is noted that, in accordance with the disclosed subject matter, when encoding a block in a merged sub-mode of either the inter mode or the bi-prediction mode, the residual information is not present.

[0096] 8 shows a diagram of a video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (810) is used in place of the video decoder (410) in the example of FIG. 4.

[0097] 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 FIG. 8.

[0098] 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- or inter-prediction information, etc.) that may identify the mode in which the block is coded (e.g., intra- or inter-prediction mode, merged submode or the latter two in another submode), certain samples or metadata used for prediction by the intra-decoder (872) or the inter-decoder (880), respectively, residual information, e.g., in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter- or bi-prediction 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).

[0099] The inter decoder (880) is configured to receive inter prediction information and generate inter prediction results based on the inter prediction information.

[0100] The intra decoder (872) is configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

[0101] The residual decoder (873) is configured to perform inverse quantization to extract dequantized transform coefficients, and to process the dequantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also require certain control information (including quantizer parameters (QP)), which may be provided by the entropy decoder (871) (data path not depicted since this is only low volume control information).

[0102] The reconstruction module (874) is 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 a reconstructed block, which may be part of a reconstructed picture, which may be part of a reconstructed video. It is noted that other suitable operations, such as deblocking operations, may be performed to improve visual quality.

[0103] It should be noted that the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using any suitable techniques. In one embodiment, the video encoders (403), (603), (703) and the video decoders (410), (510), (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (403), (603), (603) and the video decoders (410), (510), (810) may be implemented using one or more processors executing software instructions.

[0104] The present disclosure includes improvements to intra-mode coding.

[0105] ITU-T VCEG (Q6 / 16) and ISO / IEC MPEG (JTC 1 / SC29 / WG11) published the H.265 / HEVC (High Efficiency Video Coding) standard in 2013 (version 1), 2014 (version 2), 2015 (version 3), and 2016 (version 4). In 2015, the two standards organizations jointly formed the Joint Video Exploration Team (JVET) to explore the possibility of developing the next video coding standard beyond HEVC. In April 2018, JVET officially launched the standardization process for the next generation video coding beyond HEVC. This new standard was named Versatile Video Coding (VVC), and JVET was renamed the Joint Video Experts Team. In July 2020, H.266 / VVC version 1 was finalized. In January 2021, an ad-hoc group was established to investigate improved compression beyond VVC capabilities.

[0106] In decoder side intra mode derivation (DIMD), the intra modes can be derived using associated syntax elements signaled in the bitstream, or the intra modes can be derived at the decoder side without using associated syntax elements signaled in the bitstream. Numerous methods can be used to derive the intra modes at the decoder side, and decoder side intra mode derivation is not limited to the methods described in the disclosure.

[0107] In DIMD, two intra modes from a plurality of candidate intra modes for a current CU / PU can be derived from reconstructed neighboring samples of the current CU / PU. In DIMD, texture gradient analysis can be performed at both the encoder side and the decoder side to generate the plurality of candidate intra modes based on the reconstructed neighboring samples. Each of the plurality of candidate intra modes can be associated with a respective gradient history (or a respective gradient). Two intra modes (e.g., intraMode1 and intraMode2) with the highest gradient history (or highest gradients in a histogram diagram) can be selected. The intra mode predictors of the two selected intra modes (e.g., intraMode1 and intraMode2) can be combined with a planar mode predictor using a weighted sum. A final intra mode predictor for the current CU / PU can be formed based on a combination of intraMode1, intraMode2, and planar.

[0108] Table 1 shows an exemplary DIMD signaling process. As shown in Table 1, the DIMD flag (e.g., DIMD_flag) can be signaled before the ISP flag (e.g., ISP_flag). If the DIMD flag is 1 (or true), it can indicate that the current CU / PU uses DIMD, and the ISP flag can be further parsed to verify whether ISP is applied for the current CU / PU. If the DIMD flag is not 1 (or false), it can indicate that the current CU / PU does not use DIMD. Thus, syntax elements related to other intra-coding tools (e.g., MIP, MRL, MPM, etc.) can be parsed at the decoder.

[0109] The context modeling of the DIMD flag can depend on the neighboring CU / PU. For example, the context modeling of the DIMD flag can depend on (i) the availability of the left neighboring CU / PU or the top neighboring CU / PU, and (ii) whether the left neighboring CU / PU or the top neighboring CU / PU also uses DIMD. If either the left neighboring CU / PU or the top neighboring CU / PU exists and uses DIMD, the context index (e.g., ctxIdx) can be 1. If both the left neighboring CU / PU and the top neighboring CU / PU exist and use DIMD, ctxIdx can be 2. Otherwise, ctxIdx can be 0. [Table 1]

[0110] The template-based intra mode derivation (TIMD) can use a reference sample of the current CU as a template to select an intra mode from among a set of candidate intra prediction modes associated with the TIMD. The selected intra mode can be determined as the best intra mode, for example, based on a cost function. As shown in FIG. 9, a reconstructed sample in a neighborhood of the current CU (902) can be used as a template (904). The reconstructed sample in the template (904) can be compared with a predicted sample of the template (904). The predicted sample can be generated using a reference sample (906) of the template (904). The reference sample (906) can be a reconstructed sample in a neighborhood around the template (904). The cost function can be used to calculate a cost (or distortion) between the predicted sample and the reconstructed sample in the template (904) based on each candidate intra prediction mode of the set of candidate intra prediction modes. The intra-prediction mode with the least cost (or distortion) may be selected as the intra-prediction mode (eg, the best intra-prediction mode) for intra-predicting the current CU (902).

[0111] Table 2 shows an example encoding process related to TIMD. As shown in Table 2, the TIMD flag (e.g., TIMD_flag) can be signaled if the DIMD flag (e.g., DIMD_flag) is not 1 (or not true). If the DIMD flag is 1, the current CU / PU can use DIMD and parse the ISP flag (e.g., ISP_flag) to determine whether ISP is used for the current CU / PU. If the DIMD flag is not 1, the TIMD flag is parsed. If the TIMD flag is 1, the TIMD can be applied to the current CU / PU without applying other intra-coding tools (e.g., ISP is not allowed if TIMD is used). If the TIMD flag is not 1 (or false), syntax elements related to other intra-coding tools (e.g., MIP, MRL, MPM, etc.) can be parsed at the decoder. [Table 2]

[0112] In a related example, explicitly signaled intra modes and decoder-side derived intra modes can be applied to perform intra prediction at the decoder side, e.g., the decoder can use DIMD to derive intra modes and use the derived intra modes for intra prediction.

[0113] In some embodiments, a general MPM list with 22 items may be constructed first, then the first 6 items of the general MPM list may be included in a Primary MPM (PMPM) list, and the remaining items may form a Secondary MPM (SMPM) list. The first item in the general MPM list may be a planar mode. The remaining items in the general MPM list may include (i) intra modes of the left (L), top (A), bottom left (BL), top right (AR), and top left (AL) neighboring blocks, (ii) directional modes with offsets from the first two available directional modes of the neighboring blocks, and (iii) a default mode. Exemplary locations of the L, A, BL, AR, and AL neighboring blocks are shown in FIG. 10.

[0114] If the height of a CU block (e.g., 1002 in Figure 10) is not less than the width of the CU block, the order of the neighboring blocks may be A, L, BL, AR, AL; otherwise, the order of the neighboring blocks may be L, A, BL, AR, AL. The order of MPM items can be important because item indices can be encoded in truncated binary and later in the truncated binary may require more bits to encode.

[0115] If the neighboring blocks AL, A, and AR are in a different CTU than the CTU of the current CU (e.g., 1002), the neighboring blocks AL, A, and AR may be considered unavailable due to line buffer limitations, and thus the intra-mode of the unavailable neighboring CU may not be inserted into the MPM list.

[0116] The remaining intra modes can be considered as non-MPM modes. For example, in ECM 2.0, the total available intra modes for a luma CU are 67, and the number of non-MPM modes is 45.

[0117] In VVC, if a neighboring CU is an inter-coded CU, the intra mode of the neighboring CU may be considered as a planar mode, and the planar mode may be inserted into the MPM list.

[0118] The intra-modes of the intra-coded CUs may be stored in memory in units of 4x4 pixel samples. For intra-coded CUs to which DIMD is applied, the decoder-side derived intra-mode with the highest histogram of gradient (HoG) may be stored. For intra-coded CUs to which TIMD is applied, the decoder-side derived intra-mode with the lowest sum of absolute transform difference (SATD) cost may be stored. For intra-coded CUs to which block-based delta pulse code modulation (BDPCM) is applied, the signaled BDPCM direction may be stored. For intra-coded CUs to which matrix-based intra prediction (MIP) or template matching prediction (TMP) is applied, the planar mode may be stored. For other intra-coded CUs, the intra-modes derived from the MPM list or non-MPM list may be stored.

[0119] To improve the accuracy of the MPM list, if the neighboring blocks are inter-coded, the propagated intra prediction mode can be derived using the motion vectors and reference pictures associated with the inter-coded neighboring blocks. For inter-coded CUs, the intra mode can be propagated from the referenced area to the inter-coded CU.

[0120] In some embodiments, such as ECM 2.0, the General MPM List may include one or more of the following items: The order of the General MPM List may be shown as follows: For each item numbered (or ordered) below, if any condition is not met, then no intra mode is inserted into the General MPM List for that item. Before inserting each item, a pruning check may be performed to remove redundancy. 1. Planar 2. If the current CU's height is greater than or equal to its width, and A exists, and A is intra, then A. L if the current CU's height is less than its width, and L is present and L is intra. 3. If the height of the current CU is greater than or equal to the width, and L exists, L is intra, and L is in the same CTU, then L. If the height of the current CU is less than the width, A exists, A is intra, and A is in the same CTU, then A. 4. If the current CU's height is greater than or equal to the width, and A is present and A is inter, then the propagated intra mode of A. If the current CU's height is less than the width, and L is present and L is inter, then the propagated intra mode of L. 5. If the current CU's height is greater than or equal to the width, L exists, and L is inter, then the propagated intra mode of L. If the current CU's height is less than the width, A exists, and A is inter, then the propagated intra mode of A. 6. BL, if present and BL is intra. 7. If AR exists, AR is intra and AR is in the same CTU, then AR. 8. AL, if AL exists and AL is intra and AL is in the same CTU. 9.If BL is present and BL is inter, the propagated intra mode of BL. 10.If AR is present and AR is inter, the propagated intra mode of AR. 11.If AL is present and AL is inter, the propagated intra mode of AL.

[0121] In this disclosure, various metrics can be used to sort all or a subset of the MPM list. Sorting can be performed based on a template, which is a reconstructed sample of the current block's neighborhood. An example template for the current block is shown in FIG.

[0122] In an embodiment, a gradient analysis, such as a texture gradient analysis, may be performed on the template of the current block to generate gradient values. The texture gradient analysis may be configured to evaluate the distortion in size (e.g., density, intensity, resolution or detail) between closer and more distant objects (or pixels). In the disclosed gradient analysis, horizontal and vertical Sobel filters may be applied to multiple small regions (or window positions) of the template to generate multiple gradient values. Each gradient value may be calculated based on a respective horizontal component (G h ) and their respective vertical components (G v ). The horizontal component may indicate the intensity of a small region in the horizontal direction, and the vertical component may indicate the intensity of said small region in the vertical direction. The amplitude of the gradient value may be equal to the sum of (i) the absolute value of the horizontal component of the gradient value and (ii) the absolute value of the vertical component of the gradient value. The order of the items in the MPM list may be based on the gradient values. For example, a history of gradients (HoG) (or histogram of gradients) for a template may be generated based on the amplitude of the gradient values. In the histogram of gradients, each HoG (or amplitude) may be associated with a respective angle intra-mode in the MPM list. For example, arctan(G v / G h) may indicate the angular intra modes in the MPM list. The MPM list may be sorted based on HoG. In one example, the MPM list may be sorted in descending order of HoG. The intra mode associated with the highest HoG (or maximum amplitude) may be placed in the first entry of the MPM list. Both the encoder and the decoder may perform the sorting process.

[0123] In an embodiment, a cost function may be used to calculate a respective cost (or distortion) value, or rate-distortion cost, between a predicted sample and a reconstructed sample of a template based on each MPM item (or intra prediction mode) in the MPM list, where the predicted sample of the template may be generated based on each one of the MPM items in the MPM list. The cost function may be configured to evaluate a difference between the predicted sample and the reconstructed sample of the template. Exemplary cost functions may include sum of absolute differences (SAD), sum of absolute difference transform (SATD), mean square error (MSE), mean absolute difference (MAD), number of matching pixels (MPC), and the like. Thus, based on the cost function, each of the MPM items may correspond to a respective cost value, such as a SAD value or a SATD value. The order of the items in the MPM list may be based on the cost values. The MPM list may be sorted in ascending order of the cost values ​​(e.g., SATD) associated with the MPM items. The intra mode in the MPM list with the smallest SATD may be placed in the first item of the MPM list. Both the encoder and the decoder may perform the sorting process.

[0124] In some embodiments, certain intra modes may be excluded from sorting the MPM list, and the certain intra modes may be added to the MPM list after sorting, for example, to the end of the sorted MPM list.

[0125] In one example, the intra modes associated with the highest and second highest HoGs may be recorded as intraModeHog1 and intraModeHog2, respectively. If intraModeHog1 differs from the intra modes of one or more positions, such as positions L or A shown in FIG. 10, intraModeHog1 may be removed from the sorting and may be added to the MPM list after the other intra modes have been sorted. If intraModeHog2 differs from the intra modes of one or more positions, such as positions L or A, intraModeHog2 may be removed from the sorting and may be added to the end of the MPM list as the last item after the other intra modes have been sorted.

[0126] In one example, the intra modes with the smallest and second smallest SATD can be recorded as intraModeSatd1 and intraModeSatd2, respectively. If intramodeSatd1 differs from the intra modes at one or more positions, such as positions L or A, intramodeSatd1 can be removed from the sorting and can be added to the MPM list after the other intra modes have been sorted. If intramodeSatd2 differs from the intra modes at one or more positions, such as positions L or A, intramodeSatd2 can be removed from the sorting and can be added to the end of the MPM list as the last item after the other intra modes have been sorted.

[0127] In this disclosure, the non-MPM list can also be sorted. The non-MPM list can include intra modes that are not included in the MPM list. For example, in ECM 2.0, the total intra modes for a luma CU is 67. The MPM list can include 22 intra modes, and the non-MPM list can include the remaining 45 intra modes. The non-MPM list can be sorted based on a template, which is a reconstructed sample of the neighborhood of the current block.

[0128] In one embodiment, a history of gradients (HoG) of the template can be calculated for each or a subset of the non-MPM items. The intra modes in the non-MPM list can be ordered based on the HoG. In one example, the non-MPM list is ordered in descending order of HoG. Thus, the intra mode in the non-MPM list associated with the highest HoG can be placed in the first item of the non-MPM list. Both the encoder and the decoder can perform this sorting process.

[0129] In one embodiment, a cost value (e.g., SATD or SAD) of the template can be calculated for each or a subset of the non-MPM items in the non-MPM list. The non-MPM list can be ordered based on the cost value. In one example, the non-MPM list is ordered in ascending order of cost value (e.g., SATD). Thus, the item with the smallest SATD can be placed as the first item in the non-MPM list. Both the encoder and the decoder perform this sorting process.

[0130] FIG. 11 shows a flowchart outlining an exemplary decoding process (1100) according to some embodiments of the present disclosure. FIG. 12 shows a flowchart outlining an exemplary encoding process (1200) according to some embodiments of the present disclosure. The proposed processes can be used separately or in combination in any order. Furthermore, each process (or embodiment), 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.

[0131] In embodiments, any of the operations of the processes (e.g., 1100 and 1200) may be combined or arranged in any quantity or order as desired. In various embodiments, two or more operations of the processes (e.g., 1100 and 1200) may be performed in parallel.

[0132] The processes (e.g., (1100) and (1200)) can be used in the reconstruction and / or encoding of blocks to generate a prediction block for a block being reconstructed. In various embodiments, the processes (e.g., (1100) and (1200)) are performed by processing circuitry, such as processing circuitry in terminal devices (310), (320), (330) and (340), processing circuitry performing the functions of a video encoder (303), processing circuitry performing the functions of a video decoder (410), processing circuitry performing the functions of a video decoder (510), processing circuitry performing the functions of a video encoder (603), etc. In some embodiments, the processes (e.g., (1100) and (1200)) are implemented in software instructions, such that the processing circuitry performs the processes (e.g., (1100) and (1200)) when the processing circuitry executes the software instructions.

[0133] As shown in Figure 11, the process (1100) may start at (S1101) and proceed to (S1110), where coded information for a current block and neighboring blocks of the current block may be received from a coded video bitstream.

[0134] In (S1120), a most probable mode (MPM) list may be generated for the current block. The MPM list may include an intra mode determined based on the intra modes of neighboring blocks of the current block.

[0135] In (S1130), a metric, such as one of a gradient value and a cost value, of the neighboring blocks can be calculated based on the intra mode of the MPM list.

[0136] At (S1140), the intra modes in the MPM list may be sorted based on the one of the gradient values ​​and cost values ​​of the neighboring blocks, where each intra mode in the MPM list may be associated with a respective one of the gradient value and cost value.

[0137] In (S1150), the current block can be reconstructed based on the MPM list.

[0138] In some embodiments, the gradient value may correspond to a Histogram of Gradients (HoG). Thus, sorting the intra modes of the MPM list may further include sorting the intra modes of the MPM list in descending order based on the HoG of the neighboring blocks. The intra mode of the MPM list associated with the highest HoG may be the first item of the MPM list.

[0139] In some embodiments, to sort the intra modes of the MPM list, the intra modes of the MPM list may be sorted in ascending order based on the cost values ​​of the neighboring blocks, and the intra mode of the MPM list associated with the smallest cost value may be the first item of the MPM list.

[0140] In some embodiments, to sort the intra modes of an MPM list, a first intra mode of the intra modes associated with a highest HoG and a second intra mode of the intra modes associated with a second highest HoG may be determined. Also, a determination may be made to determine whether (i) the first intra mode is different from the intra mode of a left neighboring block of the neighboring blocks and an intra mode of an upper neighboring block of the neighboring blocks, and (ii) whether the second intra mode is different from the intra mode of the left neighboring block of the neighboring blocks and an intra mode of the upper neighboring block of the neighboring blocks. In response to the first intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, the first intra mode may be added to the MPM list after other intra modes of the MPM list have been sorted. In response to the second intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the above neighboring block of the neighboring blocks, the second intra mode may be added as the last item in the MPM list.

[0141] In some embodiments, to sort the intra modes of an MPM list, a first intra mode of the intra modes associated with a smallest cost value and a second intra mode of the intra modes associated with a second smallest cost value may be determined. A determination may be made to determine whether (i) the first intra mode is different from the intra mode of a left neighboring block of the neighboring blocks and an intra mode of an upper neighboring block of the neighboring blocks, and (ii) whether the second intra mode is different from the intra mode of the left neighboring block of the neighboring blocks and an intra mode of the upper neighboring block of the neighboring blocks. In response to the first intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the upper neighboring block of the neighboring blocks, the first intra mode may be added after other intra modes of the MPM list have been sorted. In response to the second intra mode being different from the intra mode of the left neighboring block of the neighboring blocks and the intra mode of the above neighboring block of the neighboring blocks, the second intra mode may be added as the last item in the MPM list.

[0142] In the process (1100), an MPM index may be further encoded from the encoded information. An intra mode of the current block may be determined based on the MPM index and the MPM list, and the MPM index may indicate which intra mode in the MPM list is applied to intra code the current block.

[0143] In some embodiments, the intra modes of the non-MPM list can be sorted based on one of the HoG and cost values ​​of neighboring blocks calculated based on the intra modes of the non-MPM list, and each intra mode in the non-MPM list can be associated with a respective one of the HoG and cost values.

[0144] In one example, to sort the intra modes of the non-MPM list, the intra modes of the non-MPM list can be sorted in descending order based on the HoG of the neighboring blocks, where the intra mode of the non-MPM list associated with the highest HoG can be the first item of the non-MPM list.

[0145] In another example, to sort the intra modes of the non-MPM list, the intra modes of the non-MPM list can be sorted in ascending order based on the cost values ​​of the neighboring blocks, where the intra mode of the non-MPM list associated with the smallest cost value can be the first item of the non-MPM list.

[0146] As shown in Figure 12, the process (1200) can start at (S1201) and proceed to (S1210). At (S1210), a most probable mode (MPM) list can be generated for a current block in a picture of a video. The MPM list can include an intra mode that is formed based on the intra modes of neighboring blocks of the current block and indicates a most probable intra mode for the current block.

[0147] In (S1220), one of a gradient value and a cost value of the neighboring block may be calculated based on the intra mode of the MPM list.

[0148] In (S1230), the intra modes in the MPM list can be sorted based on one of the gradient values ​​and cost values ​​of the neighboring blocks, and each intra mode in the MPM list can be associated with a respective one of the gradient values ​​and cost values.

[0149] At (S1240), the current block may be encoded based on the MPM list.

[0150] The techniques described above can be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 13 illustrates a computer system (1300) suitable for implementing certain embodiments of the disclosed subject matter.

[0151] Computer software may be coded using any suitable machine code or computer language and may be subject to assembly, compilation, linking, or similar mechanisms to produce code containing instructions that are executable by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., either directly, or through interpretation, microcode execution, etc.

[0152] 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, and the like.

[0153] 13 for computer system (1300) 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 (1300).

[0154] The computer system (1300) 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).

[0155] The input human interface devices may include one or more (only one of each is shown) of a keyboard (1301), a mouse (1302), a trackpad (1303), a touch screen (1310), a data glove (not shown), a joystick (1305), a microphone (1306), a scanner (1307), and a camera (1308).

[0156] The computer system (1300) may also include some type of human interface output device. 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 (1310), data gloves (not shown), or joystick (1305); although there may be haptic feedback devices that do not act as input devices), audio output devices (e.g., speakers (1309), headphones (not shown)), visual output devices (e.g., screens (1310) 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 means such as stereoscopic output; virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0157] The computer system (1300) may also include human accessible storage and associated media, such as optical media including CD / DVD ROM / RW (1320) along with CD / DVD or similar media (1321), thumb drives (1322), removable hard drives or solid state drives (1323), legacy magnetic media such as tapes and floppy disks (not shown), specialized ROM / ASIC / PLD based devices such as security dongles (not shown), etc.

[0158] 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.

[0159] The computer system (1300) may also include an interface (1354) to one or more communication networks (1355). 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, WLAN, 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 CANBus, etc. Some networks typically require an external network interface adapter that is attached to some kind of general-purpose data port or peripheral bus (1349) (e.g., a USB port of the computer system (1300)). Others are typically integrated into the core of the computer system (1300) 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 (1300) can communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast television), unidirectional transmit only (e.g., CANbus to certain CANbus devices), or bidirectional, for example, to other computer systems using local or wide area digital networks. With each of these networks and network interfaces as described above, certain protocols and protocol stacks may be used.

[0160] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1340) of the computer system (1300).

[0161] The core (1340) may include one or more central processing units (CPUs) (1341), graphics processing units (GPUs) (1342), specialized programmable processing units in the form of field programmable gate arrays (FPGAs) (1343), hardware accelerators for certain tasks (1344), graphics adapters (1350), and the like. These devices may be connected through a system bus (1348), along with read-only memory (ROM) (1345), random access memory (1346), and internal mass storage devices (1347), such as internal non-user-accessible hard drives, solid-state drives (SSDs), and the like. In some computer systems, the system bus (1348) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, and the like. Peripheral devices may be attached directly to the core's system bus (1348) or through a peripheral bus (1349). In one example, a screen 1310 may be connected to a graphics adapter 1350. Architectures for peripheral buses include PCI, USB, and the like.

[0162] The CPU (1341), GPU (1342), FPGA (1343), and accelerator (1344) can execute certain instructions that, in combination, may constitute the computer code described above. The computer code may be stored in a ROM (1345) or a RAM (1346). Temporary data may also be stored in the RAM (1346), while persistent data may be stored, for example, in an internal mass storage device (1347). 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 (1341), GPU (1342), mass storage device (1347), ROM (1345), RAM (1346), etc.

[0163] 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.

[0164] By way of example and not limitation, a computer system having the architecture (1300), and in particular the core (1340), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, 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 some type of storage of the core (1340) of a non-transitory nature such as mass storage (1347) internal to the core or ROM (1345). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (1340). The computer readable media can include one or more memory devices or chips depending on the particular needs. The software can cause the core (1340) and in particular the processors therein (including a CPU, GPU, FPGA, etc.) to execute certain processes or certain specific portions thereof described herein, including defining data structures stored in RAM (1346) 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 (1344)), 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.

[0165] Appendix A: Acronyms JEM: joint exploration model VVC: versatile video coding BMS: benchmark set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplementary Enhancement Information VUI: Video Usability Information GOP: Group of Pictures TU: Transform Unit PU: Prediction Unit CTU: Coding Tree Unit CTB: Coding Tree Block PB: Prediction Block HRD: Hypothetical Reference Decoder SNR: Signal Noise Ratio CPU: Central Processing Unit GPU: Graphics Processing Unit CRT: Cathode Ray Tube LCD: Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application-Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile communications LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Areas SSD: solid-state drive IC: Integrated Circuit CU: Coding Unit While this disclosure has described several exemplary embodiments, there are alterations, substitutions, and various substitute equivalents, which fall within the scope of this disclosure. Thus, it will be appreciated that those skilled in the art will be able to devise many systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are thus within the spirit and scope of the present disclosure.

Claims

1. 1. A method of video decoding performed by a video decoder, the method comprising: receiving coded information of a current block and neighboring blocks of the current block from a coded video bitstream; generating a Most Probable Mode (MPM) list for a current block, the MPM list including intra modes determined based on intra modes of neighboring blocks of the current block; Calculating gradient values ​​of the neighboring blocks based on intra modes of the MPM list, the gradient values ​​corresponding to a Histogram of Gradients (HoG); sorting the intra modes of the MPM list in descending order based on HoG of the neighboring blocks, where each intra mode in the MPM list is associated with a corresponding gradient value, and the intra mode of the MPM list associated with the highest HoG is the first entry of the MPM list; and reconstructing the current block based on the MPM list; Sorting the intra modes of the MPM list may further include: determining a first intra mode among the intra modes associated with a highest HoG and a second intra mode among the intra modes associated with a second highest HoG; (i) determining whether the first intra mode is different from an intra mode of a left neighboring one of the neighboring blocks and an intra mode of an upper neighboring one of the neighboring blocks, and (ii) determining whether the second intra mode is different from an intra mode of the left neighboring one of the neighboring blocks and an intra mode of the upper neighboring one of the neighboring blocks; in response to the first intra mode being different from an intra mode of the left neighboring one of the neighboring blocks and an intra mode of the above neighboring one of the neighboring blocks, adding the first intra mode to the MPM list after other intra modes in the MPM list have been sorted; and in response to the second intra mode being different from an intra mode of the left neighboring one of the neighboring blocks and an intra mode of the above neighboring one of the neighboring blocks, adding the second intra mode as a last item in the MPM list. method.

2. 1. A method of video decoding performed by a video decoder, the method comprising: receiving coded information of a current block and neighboring blocks of the current block from a coded video bitstream; generating a Most Probable Mode (MPM) list for a current block, the MPM list including intra modes determined based on intra modes of neighboring blocks of the current block; calculating cost values ​​of the neighboring blocks based on intra modes of the MPM list; sorting the intra modes of the MPM list in ascending order based on the cost values ​​of the neighboring blocks, where each intra mode in the MPM list is associated with a corresponding cost value, and the intra mode of the MPM list associated with the smallest cost value is the first entry of the MPM list; and reconstructing the current block based on the MPM list; Sorting the intra modes of the MPM list may further include: determining a first intra-mode of the intra-modes associated with a smallest cost value and a second intra-mode of the intra-modes associated with a second smallest cost value; (i) determining whether the first intra mode is different from an intra mode of a left neighboring one of the neighboring blocks and an intra mode of an upper neighboring one of the neighboring blocks, and (ii) determining whether the second intra mode is different from an intra mode of the left neighboring one of the neighboring blocks and an intra mode of the upper neighboring one of the neighboring blocks; in response to the first intra mode being different from an intra mode of the left neighboring one of the neighboring blocks and an intra mode of the above neighboring one of the neighboring blocks, adding the first intra mode to the MPM list after other intra modes have been sorted; and in response to the second intra mode being different from an intra mode of the left neighboring one of the neighboring blocks and an intra mode of the above neighboring one of the neighboring blocks, adding the second intra mode as a last item in the MPM list. method.

3. decoding an MPM index from the encoded information; determining an intra mode of a current block based on the MPM index and the MPM list, the MPM index indicating which intra mode in the MPM list is applied to intra-code the current block; The method of claim 1.

4. 2. The method of claim 1, further comprising: sorting the intra modes of the non-MPM list based on one of an HoG and a cost value of the neighboring blocks calculated based on the intra modes of the non-MPM list, wherein each of the intra modes in the non-MPM list is associated with a respective one of an HoG and a cost value.

5. Sorting the intra modes of the non-MPM list comprises: sorting the intra modes of the non-MPM list in descending order based on HoG of the neighboring blocks, the intra mode of the non-MPM list associated with the highest HoG being the first entry of the non-MPM list; The method according to claim 4.

6. Sorting the intra modes of the non-MPM list comprises: sorting the intra modes of the non-MPM list in ascending order based on cost values ​​of the neighboring blocks, the intra mode of the non-MPM list associated with the smallest cost value being the first entry of the non-MPM list; The method according to claim 4.

7. Apparatus comprising processing circuitry configured to carry out the method of any one of claims 1 to 6.

8. A computer program product for causing at least one processor to carry out the method according to any one of claims 1 to 6.

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