Improved Intra Prediction Angle

Abstract

The processing circuit receives coding information of a current coding block in a current picture from a coded video bitstream. The coding information indicates directional intra-prediction of the current coding block. The processing circuit determines an index to an entry in an angle-offset mapping lookup table according to the coding information of the current coding block. The angle-offset mapping lookup table stores a set of derivative values ​​associated with angles, where the set of derivative values ​​includes two or more integers that are powers of 2. The processing circuit accesses the entry to obtain the derivative value, and for a pixel in the current coding block, determines an offset indicating a reference position in the current picture according to the derivative value and the position of the pixel, and reconstructs the pixel in the current coding block based on the reference position in the current picture.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to U.S. patent application Ser. No. 18 / 215,284, entitled "REFINED INTRA PREDICTION ANGLES," filed Jun. 28, 2023, which claims the benefit of priority to U.S. provisional application Ser. No. 63 / 445,190, entitled "Refined intra prediction angles," filed Feb. 13, 2023. The entire disclosure of the prior application is incorporated by reference.

[0002] [Technical field] This disclosure describes embodiments that relate generally to video coding. [Background technology]

[0003] The background art discussion provided herein is intended to generally present the context for the present disclosure, and the inventors' work, to the extent described in this background art section, as well as aspects of the description that are not admitted as prior art at the time of filing, are not admitted expressly or implicitly as prior art to the present disclosure.

[0004] Image / video compression can help transmit image / video files across different devices, storage, and networks with minimal quality degradation. In some examples, video codec technology can compress video based on spatial and temporal redundancy. In one example, video codecs can use a technique called intra-prediction, which can compress images based on spatial redundancy. For example, intra-prediction can use reference data from the current picture being reconstructed for sample prediction. In another example, video codecs can use a technique called inter-prediction, which can compress images based on temporal redundancy. For example, inter-prediction can predict samples in a current picture from a previously reconstructed picture using motion compensation. Motion compensation is commonly represented by a motion vector (MV). Summary of the Invention

[0005] 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. The processing circuit receives coding information of a current coding block in a current picture from a coded video bitstream. The coding information indicates directional intra-prediction of the current coding block. The processing circuit determines an index to an entry in an angle-offset mapping lookup table according to the coding information of the current coding block. The angle-offset mapping lookup table stores a set of derivative values ​​associated with angles, where the set of derivative values ​​includes two or more integers that are powers of two. The processing circuit accesses the entry in the angle-offset mapping lookup table according to the index to obtain a derivative value of the directional intra-prediction of the current coding block, determines, for a pixel in the current coding block, an offset indicating a reference position in the current picture according to the derivative value and the position of the pixel, and reconstructs the pixel in the current coding block based on the reference position in the current picture.

[0006] In some examples, the set of derived values ​​in the angle-to-offset mapping lookup table includes all integers that are a power of 2 between the minimum value in the set of derived values ​​and the maximum value in the set of derived values. In one example, the set of derived values ​​is limited to N bits, where N is a positive integer, and the set of derived values ​​is a power of 2. i (i∈[1, 2, ..., N]). In one example, the set of derivative values ​​includes 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, and 2048. In some embodiments, to reduce computational complexity, when a derivative value that is a power of 2 is used in a multiplication operation, the multiplication operation is performed using shift operations.

[0007] In some examples, the difference between each two adjacent derived values ​​in the set of derived values ​​is a multiple of two.

[0008] In some examples, the set of derived values ​​is associated with increasing angles, and the difference between adjacent derived values ​​in the set of derived values ​​varies monotonically.

[0009] In some examples, the set of derived values ​​includes a diagonal derived value associated with a 45° angle and a derived pair including a first derived value and a second derived value having the same absolute index difference relative to the diagonal derived value, wherein the product of the first derived value and the second derived value is within a range related to the square of the diagonal derived value. In one example, the square of the diagonal derived value is one of 2048, 4096, and 8192. In one example, the product of the first derived value and the second derived value is within [Td, T+d], where T indicates the square of the diagonal derived value and d indicates a predefined range parameter.

[0010] According to some aspects of the present disclosure, a processing circuit receives coding information for a current coding block in a current picture from a coded video bitstream, the coding information indicating a particular delta angle and a particular nominal angle that collectively correspond to a particular directional intra-prediction angle within a first set of directional intra-prediction angles, the first set of directional intra-prediction angles including a predefined nominal angle and a finer angle, the finer angle being separated from the predefined nominal angle by the delta angle. The processing circuit determines that the current coding block is a non-square rectangle, and, in response to the current coding block being a non-square rectangle, determines a mapped intra-prediction angle that is outside the first set of directional intra-prediction angles and is mapped to the particular directional intra-prediction angle. The processing circuit reconstructs the current coding block based on the mapped intra-prediction angle.

[0011] In some examples, the processing circuit determines a mapped intra-prediction angle from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio or width-to-height ratio being greater than a threshold, and the directional intra-prediction angle of the mapped subset is mapped from a nominal angle of at least 45° using a delta angle.

[0012] In some examples, the processing circuit determines a mapped intra-prediction angle from the directional intra-prediction angle of the mapped subset in response to a height-to-width ratio of the current coding block being greater than 2, and the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a first nominal angle of 45° using a delta angle and a second nominal angle of 67° using a delta angle.

[0013] In some examples, the processing circuit determines a mapped intra-prediction angle from the directional intra-prediction angle of the mapped subset in response to a width-to-height ratio of the current coding block being greater than 2, and the directional intra-prediction angle of the mapped subset being less than 45° and mapped from a nominal angle of 203° using a delta angle.

[0014] In some examples, the processing circuit determines a mapped intra-prediction angle from the directional intra-prediction angle of the mapped subset in response to a height-to-width ratio of the current coding block being equal to 2, and the directional intra-prediction angle of the mapped subset being greater than 203° and mapped from a nominal angle of 45° using a delta angle.

[0015] In some examples, the processing circuit determines a mapped intra-prediction angle from the directional intra-prediction angles of the mapped subset in response to the height-to-width ratio of the current coding block being greater than a threshold, and the directional intra-prediction angle of the mapped subset is mapped from the nominal angle using a subset of delta angles on the side of the nominal angle.

[0016] In some examples, the processing circuit determines a first side and a second side from the top side (top edge) and the left side (left edge), where the first side has more intra-coded neighboring blocks than the second side, and maps one or more directional intra-prediction angles from the second side to the first side.

[0017] In some examples, the processing circuit determines a reference line index and, depending on whether the reference line index is greater than zero and the current coding block is a non-square rectangle, determines a mapped intra-prediction angle that is outside the first set of directional intra-prediction angles and is mapped to a particular directional intra-prediction angle.

[0018] In some examples, the processing circuit determines that the syntax element indicates enabling angle mapping, and determines a mapped intra-prediction angle that is outside the first set of directional intra-prediction angles and is mapped to a particular directional intra-prediction angle in response to the syntax element indicating enabling angle mapping and the current coding block being a non-square rectangle. The syntax element is at least one of a sequence level, a frame level, a slice level, and a superblock level.

[0019] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer, cause the computer to perform a method for video decoding. [Brief explanation of the drawings]

[0020] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of an exemplary block diagram of a communication system (100). [Figure 2] FIG. 2 is a schematic diagram of an exemplary block diagram of a decoder. [Figure 3] FIG. 2 is a schematic diagram of an exemplary block diagram of an encoder. [Figure 4] 1 shows a diagram illustrating eight nominal angles in some examples. [Figure 5] 1 illustrates an example of a lookup table according to some embodiments. [Figure 6] 10 shows a diagram of a current block to illustrate non-directional smooth intra-prediction modes in some examples. [Figure 7] 10 shows a diagram of a current block illustrating recursive filtering-based intra prediction in some examples. [Figure 8] 10 shows a diagram illustrating a modified intra prediction module with offset-based refinement for intra prediction in some examples. [Figure 9]10 shows a diagram illustrating sub-block-based offset-based refinement for intra prediction in some examples. [Figure 10] 10 shows a table of predefined weights for offset calculation in some examples. [Figure 11] 10 shows a table of mode-dependent on / off of sub-block-based offset-based refinement for intra prediction in some examples. [Figure 12] 1 illustrates an example of a lookup table according to some embodiments. [Figure 13] 1 shows a flowchart outlining a process according to some embodiments of the present disclosure. [Figure 14] 1 shows a flowchart outlining a process according to some embodiments of the present disclosure. [Figure 15] 1 shows a flowchart outlining another process according to some embodiments of the present disclosure. [Figure 16] 1 shows a flowchart outlining another process according to some embodiments of the present disclosure. [Figure 17] FIG. 1 is a schematic diagram of a computer system according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] 1 shows a block diagram of a video processing system 100 in some examples. The video processing system 100 is an example of an application of the disclosed subject matter, a video encoder and video decoder in a streaming environment. The disclosed subject matter is equally applicable to other video-enabled applications, including, for example, video conferencing, digital TV, streaming services, storage of compressed video on digital media (including CDs, DVDs, memory sticks, etc.), etc.

[0022] The video processing system (100) includes a video source (101) and a capture subsystem (113) that can include, for example, a digital camera, creating a stream of uncompressed video pictures (102). In one example, the video picture stream (102) includes samples captured by the digital camera. The video picture stream (102), shown with a thick line to emphasize its high data volume compared to the encoded video data (104) (or coded video bitstream), can be processed by an electronic device (120) that includes a video encoder (103) coupled to the video source (101). The video encoder (103) can include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (104) (or coded video bitstream), shown with a thin line to emphasize its low data volume compared to the video picture stream (102), can be stored on a streaming server (105) for future use. One or more streaming client subsystems, such as client subsystems 106 and 108 in FIG. 1, can access the streaming server 105 to retrieve copies 107 and 109 of the encoded video data 104. The client subsystem 106 may include, for example, a video decoder 110 within an electronic device 130. The video decoder 110 decodes an input copy 107 of the encoded video data and creates an output stream 111 of video pictures that can be rendered on a display 112 (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data 104, 107, and 109 (e.g., a video bitstream) can be encoded according to several video coding / compression standards. Examples of these standards include ITU-T Recommendation H.265. In one example, the developing video coding standard is informally known as Versatile Video Coding (VVC).The disclosed subject matter may be used in the context of VVC.

[0023] It is noted that electronic devices 120 and 130 may include other components (not shown). For example, electronic device 120 may include a video decoder (not shown), and electronic device 130 may include a video encoder (not shown).

[0024] 2 shows an exemplary block diagram of a video decoder (210). The video decoder (210) can be included in an electronic device (230). The electronic device (230) can include a receiver (231) (e.g., a receiving circuit). The video decoder (210) can be used in place of the video decoder (110) in the example of FIG. 1.

[0025] The receiver (231) may receive one or more coded video sequences to be decoded by the video decoder (210). In one embodiment, one coded video sequence may be received at a time, with the decoding of each coded video sequence being independent of the decoding of other coded video sequences. The coded video sequences may be received from a channel (201), which may be a hardware / software link to a storage device that stores the coded video data. The receiver (231) may receive the coded video data along with other data (e.g., coded audio data and / or auxiliary data streams), which may be forwarded to respective using entities (not shown). The receiver (231) may separate the coded video sequences from the other data. To prevent network jitter, a buffer memory (215) may be coupled between the receiver (231) and the entropy decoder / parser (220) (hereinafter referred to as "parser" (220)). In certain applications, the buffer memory (215) is part of the video decoder (210). In other cases, it may be external to the video decoder (not shown). In still other cases, there may be a buffer memory (not shown) external to the video decoder (210), for example, to prevent network jitter, and there may be yet another buffer memory (215) within the video decoder (210), for example, to handle playback timing. If the receiver (231) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isochronous network, the buffer memory (215) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (215) may be needed and may be relatively large, advantageously adaptively sized, and may be implemented at least in part in an operating system and similar elements (not shown) external to the video decoder (210).

[0026] The video decoder (210) may include a parser (220) for reconstructing symbols (221) from the coded video sequence. These symbol categories include information used to manage the operation of the video decoder (210) and potentially include information for controlling a rendering device, such as a rendering device (212) (e.g., a display screen) that is not an integral part of the electronic device (230) but can be coupled to the electronic device (230), as shown in FIG. 2. The rendering device control information 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 (220) 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 (220) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the group. The subgroup may include a group of pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (220) may also extract information from the coded video sequence, such as transform coefficients, quantization parameter values, motion vectors, etc.

[0027] The parser (220) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (215) to generate symbols (221).

[0028] The reconstruction of the symbols (221) can involve several different units, depending on the type of video picture or portion thereof being coded (e.g., inter-picture and intra-picture, inter-block and intra-block) and other factors. Which units are involved and how they are involved can be controlled by subgroup control information parsed by the parser (220) from the coded video sequence. The flow of such subgroup control information between the parser (220) and the following units is not shown for clarity.

[0029] In addition to the functional blocks described above, the video decoder (210) can be conceptually subdivided into multiple functional units, as described below. In a practical implementation operating under commercial constraints, many of these units will interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, a conceptual subdivision into the following functional units is appropriate:

[0030] The first unit is a scalar / inverse transform unit (251), which receives quantized transform coefficients as symbols (221) from the parser (220), along with control information (including which transform to use, block size, quantization coefficients, quantization scaling matrix, etc.) The scalar / inverse transform unit (251) can output blocks containing sample values ​​that can be input to an aggregator (255).

[0031] In some cases, the output samples of the scaler / inverse transform unit (251) may relate to intra-coded blocks. Intra-coded blocks are blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by the intra-picture prediction unit (252). In some cases, the intra-picture prediction unit (252) generates blocks of the same size and shape as the block being reconstructed using surrounding, already reconstructed information retrieved from the current picture buffer (258). The current picture buffer (258), for example, buffers a partially reconstructed and / or fully reconstructed current picture. In some cases, the aggregator (255) adds, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (252) to the output sample information provided by the scaler / inverse transform unit (251).

[0032] In other cases, the output samples of the scalar / inverse transform unit (251) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion-compensated prediction unit (253) may access a reference picture memory (257) to retrieve samples used for prediction. After motion-compensating the retrieved samples according to the symbols (221) associated with the block, these samples may be added by the aggregator (255) to the output of the scalar / inverse transform unit (251) (in this case, referred to as residual samples or residual signals) to generate output sample information. The addresses in the reference picture memory (257) from which the motion-compensated prediction unit (253) retrieves prediction samples may be controlled by motion vectors available to the motion-compensated prediction unit (253), for example, in the form of symbols (221) that may have X, Y, and reference picture components. Motion compensation may also include interpolation of sample values ​​retrieved from the reference picture memory (257) when sub-sample accurate motion vectors are used, motion vector prediction mechanisms, and the like.

[0033] The output samples of the aggregator 255 may be subjected to various loop filtering techniques in a loop filter unit 256. The video compression techniques may include in-loop filtering techniques controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit 256 as symbols 221 from the parser 220. The video compression may also be responsive to meta-information obtained during decoding of previous portions (in decoding order) of the coded picture or coded video sequence, as well as to previously reconstructed loop-filtered sample values.

[0034] The output of the loop filter unit (256) can be a sample stream that can be output to a rendering device (212) and stored in a reference picture memory (257) for use in future inter-picture prediction.

[0035] Once a particular coded picture is fully reconstructed, it can be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (220)), the current picture buffer (258) can become part of the reference picture memory (257), and a new current picture buffer can be reallocated before beginning reconstruction of a subsequent coded picture.

[0036] The video decoder (210) may perform decoding operations in accordance with a given video compression technology or standard, such as ITU-T Rec. H.265. The coded video sequence may conform to the syntax specified by the video compression technology or standard being used, in the sense that the coded video sequence conforms to both the syntax and profile of the video compression technology or standard as documented in the video compression technology or standard. Specifically, a profile can select certain tools from all tools available in the video compression technology or standard as the only tools for use under that profile. Compliance may also require the complexity of the coded video sequence to fall within a range defined by the level of the video compression technology or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. In some cases, the limits set by the level can be further constrained through a Hypothetical Reference Decoder (HRD) specification and metadata about HRD buffer management signaled in the coded video sequence.

[0037] In one embodiment, the receiver (231) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (210) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0038] 3 shows an example block diagram of a video encoder (303). The video encoder (303) is included in an electronic device (320). The electronic device (320) includes a transmitter (340) (e.g., a transmission circuit). The video encoder (303) can be used in place of the video encoder (103) in the example of FIG. 1.

[0039] The video encoder (303) may receive video samples from a video source (301) (not part of the electronic device (320) in the example of FIG. 3) that may capture video images to be coded by the video encoder (303). In another example, the video source (301) is part of the electronic device (320).

[0040] The video source (301) may provide a source video sequence to be coded by the video encoder (303) in the form of a digital video sample stream, which may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.), any color space (e.g., BT.601 Y CrCB, RGB, etc.), and any suitable sampling structure (e.g., Y CrCb 4:2:0, Y CrCb 4:4:4). In a media presentation system, the video source (301) may be a storage device that stores pre-prepared video. In a video conferencing system, the video source (301) may be a camera that captures local image information as a video sequence. Video data may be provided as multiple individual pictures that convey 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 will readily understand the relationship between pixels and samples. The following description will focus on samples.

[0041] According to one embodiment, the video encoder (303) may code and compress pictures of a source video sequence into a coded video sequence (343) in real time or under any other required time constraints. Achieving an appropriate coding rate is one function of the controller (350). In some embodiments, the controller (350) can control and is operatively coupled to other functional units, as described below. Coupling is not shown for clarity. Parameters set by the controller (350) can include rate control-related parameters (e.g., picture skip, quantization, lambda values ​​for rate-distortion optimization techniques), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. The controller (350) can be configured to have other appropriate functionality associated with the video encoder (303) optimized for a particular system design.

[0042] In some embodiments, the video encoder (303) is configured to operate in a coding loop. As a very simplified description, in one example, the coding loop can include a source coder (330) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (333) embedded in the video encoder (303). The decoder (333) reconstructs the symbols to generate sample data similar to that generated by the (remote) decoder. The reconstructed sample stream (sample data) is input to a reference picture memory (334). Because decoding of the symbol stream produces bit-for-bit accurate results independent of the location of the decoder (local or remote), the contents in the reference picture memory (334) are also bit-for-bit accurate between the local and remote encoders. In other words, the predictive portion of the encoder "sees" the exact same sample values ​​as the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchronization (including the resulting drift when synchronization cannot be maintained, for example, due to channel errors) is used in several related techniques as well.

[0043] The operation of the "local" decoder (333) can be the same as the "remote" decoder (210), such as the video decoder (210), already described in detail above in connection with Figure 2. However, briefly referring to Figure 2, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (345) and parser (220) can be lossless, the entropy decoding portion of the video decoder (210), including the buffer memory (215) and parser (220), may not be fully implemented in the local decoder (433).

[0044] In one embodiment, decoder technology, excluding analysis / entropy decoding, present in the decoder is present in the corresponding encoder in the same or substantially the same functional form. Therefore, the subject matter of the disclosure focuses on decoder operation. A description of the encoder technology can be omitted, as it is the reverse of the decoder technology, which is described generically. In certain areas, more detailed descriptions are provided below.

[0045] During operation, in some examples, the source coder (330) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from a video sequence designated as “reference pictures.” In this manner, the coding engine (332) codes differences between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references for the input picture.

[0046] The local video decoder (333) may decode coded video data of pictures that may be designated as reference pictures based on symbols created by the source coder (330). The operation of the coding engine (332) may advantageously be a lossy process. When the coded video data is decoded by a video decoder (not shown in FIG. 3), the reconstructed video sequence may typically be a replica of the source video sequence, with some errors. The local video decoder (333) may replicate the decoding process that may be performed by the video decoder on the reference pictures and store the reconstructed reference pictures in the reference picture memory (334). In this way, the video encoder (303) may locally store copies of reconstructed reference pictures that have common content with reconstructed reference pictures (without transmission errors) obtained by the far-end video decoder.

[0047] The predictor (335) may perform a predictive search for the coding engine (332). That is, for a new picture to be coded, the predictor (335) may search the reference picture memory (334) for sample data (as candidate reference pixel blocks) or specific metadata (reference picture motion vectors, block shapes, etc.), which may serve as suitable prediction references for the new picture. The predictor (335) may operate sample block-by-pixel block to find suitable prediction references. In some cases, as determined by the search results obtained by the predictor (335), the input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (334).

[0048] The controller (350) may manage the coding operations of the source coder (330), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0049] The output of all the above functional units may undergo entropy coding in an entropy coder (345), which converts the symbols produced by the various functional units into a coded video sequence by applying lossless compression to the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0050] The transmitter (340) may buffer the coded video sequence produced by the entropy coder (345) and prepare it for transmission over a communication channel (360), which may be a hardware / software link to a storage device that stores the coded video data. The transmitter (340) may merge the coded video data from the video encoder (330) with other data to be transmitted, such as coded audio data and / or an auxiliary data stream (not shown).

[0051] The controller (350) may manage the operation of the video encoder (303). During coding, the controller (350) may assign a particular 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, a picture may be assigned as one of the following picture types:

[0052] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures in the sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, Independent Decoder Refresh (IDR) pictures. Those skilled in the art will recognize these variations of I-pictures and their respective uses and characteristics.

[0053] A predictive picture (P picture) may be coded 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.

[0054] Bidirectionally predicted pictures (B-pictures) may be coded and decoded using intra- or inter-prediction, which uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multi-predicted pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0055] A source picture is typically spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and may be coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks, as determined by the coding assignment applied to the block's respective picture. 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 prediction 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.

[0056] The video encoder (303) may perform coding operations in accordance with a predetermined video coding technique or standard, such as ITU-T Rec. H.265. In doing so, the video encoder (303) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0057] In one embodiment, the transmitter (340) may transmit additional data along with the coded video. The source coder (330) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other types of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0058] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation within a given picture, while inter-picture prediction exploits correlation (temporal or other) between pictures. In one example, a particular picture being encoded / decoded, called the current picture, is partitioned into blocks. When a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, the block in the current picture can be coded by a vector called a motion vector. A motion vector points to a reference block within the reference picture and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0059] In some embodiments, bi-prediction techniques can be used in inter-picture prediction. Bi-prediction techniques use two reference pictures, such as a first reference picture and a second reference picture, both of which precede the current picture in decoding order (but may also be past and future, respectively, in display order) in a 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.

[0060] Furthermore, to improve coding efficiency, merge mode techniques can be used in inter-picture prediction.

[0061] According to some embodiments of the present disclosure, prediction, such as inter-picture prediction and intra-picture prediction, is performed in units of blocks. For example, according to the HEVC standard, pictures in a sequence of video pictures are partitioned into coding tree units (CTUs) for compression, and the CTUs within a picture have the same size, such as 64x64 pixels, 32x32 pixels, or 16x16 pixels. Typically, a CTU includes three coding tree blocks (CTBs), one luma CTB and two chroma CTBs. Each CTU can be recursively quadtree-decomposed into one or more coding units (CUs). For example, a 64x64 pixel CTU can be partitioned into one CU of 64x64 pixels, four CUs of 32x32 pixels, or 16 CUs of 16x16 pixels. In one example, each CU is analyzed to determine the CU's prediction type, 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 one embodiment, the prediction operation of coding (encoding / decoding) is performed on a prediction block basis. Using a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values ​​(e.g., luma values), such as 8x8 pixels, 16x16 pixels, 8x16 pixels, 16x8 pixels, etc.

[0062] It is noted that the video encoders (103) and (303) and the video decoders (110) and (210) may be implemented using any suitable technology. In one embodiment, the video encoders (103) and (303) and the video decoders (110) and (210) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (103) and (303) and the video decoders (110) and (210) may be implemented using one or more processors executing software instructions.

[0063] Aspects of this disclosure provide techniques for improving intra-prediction angles.

[0064] Various video processing standards have been developed for image and / or video processing such as storage, transmission, compression, reconstruction, etc., such as HEVC (High Efficiency Video Coding), VVC (Versatile Video Coding), AV1 (AOMedia Video 1), etc. Additional video coding techniques may be further developed to provide improved coding performance.

[0065] According to one aspect of the present disclosure, AV1 includes techniques for directional intra prediction and non-directional smooth intra prediction. For directional intra prediction, AV1 provides eight nominal angles (also referred to as base angles in some examples) called V_PRED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED.

[0066] 4 shows a diagram illustrating eight nominal angles in AV1. Among the eight nominal angles, D45_PRED represents directional intra prediction with 45° relative to the positive X direction, D67_PRED represents directional intra prediction with 67° relative to the positive X direction, V_PRED represents directional intra prediction with 90° (vertical) relative to the positive X direction, D113_PRED represents directional intra prediction with 113° relative to the positive X direction, D135_PRED represents directional intra prediction with 135° relative to the positive X direction, D157_PRED represents directional intra prediction with 157° relative to the positive X direction, H_PRED represents directional intra prediction with 180° relative to the positive X direction, and D203_PRED represents directional intra prediction with 203° relative to the positive X direction.

[0067] Furthermore, to utilize more diverse spatial redundancy in directional textures, AV1 includes directional intra modes that are expanded to angle sets with finer granularity. In some examples, an angle set of seven angles with finer granularity is used for each nominal angle. Therefore, AV1 has a total of 56 directional angles (also called prediction angles or intra-prediction angles). In one example, a prediction angle is indicated by a combination of a nominal angle and a delta angle, where the delta angle is a multiple of a step size. For example, the step size is 3, and the delta angle can be one of −9°, −6°, −3°, 0°, 3°, 6°, and 9°. For example, for a nominal angle of D45_PRED, the angle set can include prediction angles of 36°, 39°, 42°, 45°, 48°, 51°, and 54°. AV1 includes 56 directional intra-prediction modes corresponding to the 56 directional angles, respectively. In some examples, to implement a directional prediction mode in AV1, for a directional prediction mode (corresponding to a directional angle), a unified directional predictor projects each pixel in the current block to a reference sub-pixel position according to the prediction angle and interpolates the reference pixel by a 2-tap bilinear filter.

[0068] According to one aspect of the present disclosure, a tangent function or a cotangent function (also called a derivative function) can be used to project pixels in the current block to reference positions according to the intra-prediction angle. For example, the horizontal offset between a pixel and a reference position (e.g., a sub-pixel position) can be determined by the cotangent function of the intra-prediction angle and the pixel's vertical position, or the vertical offset between a pixel and a reference position (e.g., a sub-pixel position) can be determined by the tangent function of the intra-prediction angle and the pixel's horizontal position. The tangent function or the cotangent function can be implemented by pre-computation to reduce computation. In some examples, a lookup table can contain pre-computed values ​​of the tangent function or the cotangent function, which is then used to map each intra-prediction angle to the horizontal and vertical offsets between each pixel in the current block and the reference position.

[0069] FIG. 5 shows example pseudocode (500) for a lookup table in some embodiments. In the example of FIG. 5, the lookup table includes multiple values ​​associated with angles within [0, 90°]. For example, the lookup table includes 90 values ​​associated with integer angles from 0° to 89°. A non-zero value associated with an angle corresponds to the integer value of the cotangent of the corresponding angle multiplied by 64. For example, cotangent(45°) multiplied by 64 equals 64, and cotangent(23°) multiplied by 64 is approximately the integer 151. A non-zero value associated with an angle is also referred to as a derived value associated with the angle. In the example of FIG. 5, when the derived value associated with an angle is zero, the angle is not in the angle set for directional intra-prediction. For example, the first row includes three zeros associated with 0°, 1°, and 2°; therefore, 0°, 1°, and 2° are not in the angle set for directional intra-prediction. The second row contains 2048 associated with 3°, 0 associated with 4°, and 0 associated with 5°; therefore, 4° and 5° are not in the set of angles for directional intra prediction.

[0070] 5 can be used to calculate the vertical offset or horizontal offset of each pixel in the current block relative to the reference position. For example, when the intra-prediction angle is 113°, the horizontal offset between the first pixel and the reference position (e.g., the top reference position) can be determined by a derived value associated with 67° and the vertical position of the first pixel, or the vertical offset between the second pixel and the reference position (e.g., the left reference position) can be determined by a derived value associated with 23° and the horizontal position of the second pixel.

[0071] Note that the derived values ​​in Figure 5 are offsets on a per pixel basis. In one example, the derived value associated with 45° is 64, which indicates that, in one example, as the pixel's row number increases by 1, the horizontal offset value between each pixel in the current block and the reference location increases by 1 pixel. In some examples, the lookup table in Figure 5 is also referred to as an angle-offset lookup table or an angle-offset mapping table or an angle-offset mapping lookup table.

[0072] AV1 uses five non-directional smooth intra prediction modes denoted by DC (prediction or mode), PAETH (prediction or mode), SMOOTH (prediction or mode), SMOOTH_V (prediction or mode), and SMOOTH_H (prediction or mode).

[0073] 6 shows a diagram of a current block (610) to illustrate the non-directional smooth intra prediction mode in some examples. For a current pixel (denoted as current pixel in FIG. 6) in the current block (610), the above-neighboring sample (denoted by above) is a pixel in the above reference line (top row) for the current block (610), the left-neighboring sample (denoted by left) is a pixel in the left-reference line (left column) for the current block (610), and the above-left-neighboring sample (denoted by above-left) is a pixel relative to the top-left corner of the current block (610). The above-neighboring sample has the same horizontal position as the current pixel, the left-neighboring sample has the same vertical position as the current pixel, and the above-left-neighboring sample has the same horizontal position as the left-neighboring sample and the same vertical position as the above-neighboring sample.

[0074] For DC prediction, the average of the left and above neighboring samples is used as the predictor of the current block. For PAETH prediction, the above, left, and above-left neighboring samples (also called reference samples) are fetched first, and then the value closest to (above + left - (above-left)) is set as the predictor for the current pixel to be predicted. For SMOOTH_V mode, quadratic interpolation in the vertical direction is used to predict the current block. For SMOOTH_H mode, quadratic interpolation in the horizontal direction is used to predict the current block. For SMOOTH mode, the average of quadratic interpolation in both the vertical and horizontal directions is used to predict the current block.

[0075] According to one aspect of the present disclosure, a technique called a recursive filtering-based intra predictor can be used to capture decaying spatial correlation. In some examples, a mode called a filter intra mode is designed for the luma block to capture decaying spatial correlation with edge references. In some examples, AV1 includes five filter intra modes, each of which is represented by a set of eight 7-tap filters that reflect the correlation between a pixel within a 4x2 patch and its seven neighbors. In other words, the weight coefficients of the 7-tap filters are position-dependent.

[0076] FIG. 7 shows a diagram of a current block (710) illustrating recursive filtering-based intra prediction in some examples. For example, the current block (710) is an 8×8 block and can be divided into eight 4×2 patches, indicated by B0, B1, B2, B3, B4, B5, B6, and B7 in FIG. 7. Each patch can have neighboring samples, such as seven upper and left neighboring samples, indicated by R0 through R6. The neighboring samples of a patch are used to predict pixels within the patch. For example, for patch B0, the upper and left neighboring samples have already been reconstructed, and patch B0 can be predicted based on the upper and left neighboring samples. However, for other patches, not all of the upper and left neighboring samples have been reconstructed. In one example, the predicted values ​​of the nearest neighbors can be used as a reference. For example, the upper and left neighboring samples of patch B7 are not reconstructed, and the predicted values ​​of neighboring samples (e.g., in patches B5 and B6) can be used instead. In one example, the patches are predicted in an order such as B0, B1, B2, B3, B4, B5, B6 and B7.

[0077] In some examples, chroma samples can be predicted from luma samples, and the prediction technique is called chroma from luma (CfL) prediction. CfL prediction is a chroma-only intra predictor that models chroma pixels as a linear function of the corresponding reconstructed luma pixels. For example, CfL prediction is expressed as follows: CfL(α)=α×L AC +DC formula (1) where L AC denotes the AC contribution of the luma component, α denotes a parameter of the linear model, and DC denotes the DC contribution of the chroma component. In some examples, the reconstructed luma pixels are subsampled to the chroma resolution and then the mean is subtracted to form the AC contribution. Instead of requiring the decoder to calculate scaling parameters to approximate the chroma AC components from the AC contributions, in some examples, the parameter α can be determined based on the original chroma pixels on the encoder side, and the parameter α can be signaled in the bitstream. Determining the parameter α on the encoder side can reduce decoder complexity and result in more accurate prediction. In some examples, the DC contribution of the chroma component can be calculated using an intra DC mode, which is sufficient for most chroma content and has a fast implementation.

[0078] In AV1, the total number of available intra-prediction modes is 62, including 56 directional intra-prediction modes, five non-directional modes, and one chroma-from-luma mode (for chroma components only). In some examples, to signal the intra-prediction mode, a first syntax is signaled to indicate the nominal mode of the current block, where the nominal mode can indicate a nominal angle for a directional intra-prediction mode or can be a non-directional mode. Then, a second syntax is signaled to indicate which delta angle is used for the current block when the intra-prediction mode of the current block is a directional intra-prediction mode. In some examples, the correlation between the intra-prediction mode of the current block and its neighboring blocks can be used to improve coding efficiency. For example, the intra-prediction modes available to the current block can be divided into multiple intra-prediction mode sets according to the intra-prediction modes of the neighboring blocks. To obtain the intra-prediction mode of the current block, a mode set index is first signaled to indicate the mode set index of the intra-prediction mode for the current block, and then a mode index is next signaled to indicate the index of the intra-prediction mode within the mode set.

[0079] In some examples, an intra-prediction technique called offset-based refinement for intra prediction (ORIP) can be used.

[0080] 8 shows a diagram illustrating a modified intra prediction module (800) using offset-based refinement for intra prediction in some examples. The modified intra prediction module (800) includes an intra prediction sub-module (820) and an offset-based refinement for intra prediction (ORIP) sub-module (830). The intra prediction sub-module (820) can perform any suitable intra prediction for the current block based on neighboring reference samples (810) of the current block to generate intra prediction samples. After generating the intra prediction samples, the ORIP sub-module (830) can generate offset values ​​based on the neighboring reference samples (810) and add the offset values ​​to the intra prediction samples for refinement.

[0081] In some examples, the refinement is performed at the 4x4 sub-block level: for each 4x4 sub-block, an offset is generated from the above and left neighboring samples of that sub-block.

[0082] Figure 9 shows a diagram illustrating sub-block-based ORIP in some examples. In the example of Figure 9, the current coding block (910) is an 8x8 block and is divided into four 4x4 sub-blocks, as indicated by the vertical and horizontal dashed lines. For the 4x4 sub-blocks, the upper and left neighboring samples of the 4x4 sub-blocks are indicated by P0 to P8. Note that the upper and left neighboring samples of the 4x4 sub-blocks can be reconstructed samples of other coding blocks or can be predicted samples of other sub-blocks within the current coding block (910) before refinement.

[0083] In some examples, for each of the 16 pixels in the 4x4 sub-block, the offset value is calculated based on a combination of upper and left neighboring samples with different weights. In one example, the offset value for the kth position of the 4x4 sub-block is generated according to Equation (2) and is used to calculate the refined intra-predicted sample value pred_refined. k can be calculated according to equation (3). offset(k)=(Σ 8 n=0 W kn *{P n -pred k}+32)>>6 Formula (2) pred_refined k =clip3(pred k +offset(k)) Equation (3) where pred k denotes the intra-predicted sample value of the pixel at the kth position before refinement, and P n denotes the nth adjacent sample such as P0 to P8, and W kn denotes the weight for the nth neighboring sample for calculating the offset value of the kth position.

[0084] FIG. 10 shows a table of predefined weights for offset calculation in some examples.

[0085] In some examples, sub-block-based ORIP is applied only to a predefined set of intra-prediction modes and is applied differently for luma and chroma depending on the mode.

[0086] 11 shows a table of mode-dependent on / off of sub-block-based ORIP in some examples. In one example, when the intra-prediction mode is either DC or SMOOTH, ORIP is always on and no further signaling is required. However, when the intra-prediction mode is H_PRED / V_PRED with angle_delta equal to 0, block-level signaling is required to enable / disable ORIP.

[0087] According to one aspect of the present disclosure, in a related example, the intra-prediction angles are approximately evenly distributed within a range determined based on two nominal angles (e.g., 45° to 203°) and a delta angle, such as from 36° to 212°, which may not be optimal.

[0088] According to another aspect of the present disclosure, in a related example, the same range of intra-prediction angles is applied to blocks having different shapes, such as square blocks and non-square rectangular blocks, which may not be optimal.

[0089] According to some aspects of the present disclosure, the difference between adjacent non-zero derived values ​​monotonically decreases as the intra-prediction angle increases in an angle-offset lookup table (also referred to as an angle-offset mapping table).

[0090] According to one aspect of the present disclosure, the derived values ​​in the angle-offset lookup table may affect the computational complexity. The derived values ​​in the angle-offset lookup table may be appropriately adjusted to reduce the computational complexity.

[0091] In some embodiments, when the minimum difference between adjacent non-zero derived values ​​is denoted as min_diff, all differences between any adjacent non-zero derived values ​​are restricted to be multiples of min_diff. For example, when min_diff is equal to 2, any adjacent non-zero derived values ​​are restricted to be multiples of min_diff. The difference between the winning values ​​must be a multiple of 2, such as 2, 4, 6, 8, 10, 12, etc.

[0092] In some embodiments, the derived values in the angle-offset look-up table are from M to N (M < N), where both M and N are positive integers, M represents the minimum value of the derived values in the angle-offset look-up table, and N represents the maximum value of the derived values. When all the powers of 2 between M and N are included in the angle-offset look-up table, then when a power of 2 derived value is used to calculate the offset, the multiplication operation for calculating the offset by multiplying the derived value with the pixel position parameter can be performed by a shift operation. Therefore, when the set of derived values includes two or more values that are powers of 2, the computational complexity is reduced. Note that the angle associated with the derived value can be appropriately determined based on the arctangent function or the arccotangent function.

[0093] FIG. 12 shows an example of pseudo-code (1200) for a look-up table (angle-offset look-up table) in some embodiments. In the example of FIG. 12, the look-up table includes a plurality of values associated with angles within [0, 90°]. For example, the look-up table includes 90 derived values associated with 90 angles in ascending order. Note that the non-zero derived values are in descending order and may not correspond to integer angles. The exact value of the angle of the non-zero derived value can be calculated by the arctangent function or the arccosine function. Comparing FIG. 12 with FIG. 5, the look-up table in FIG. 12 includes all values that are powers of 2, such as 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048 between 0 and 2048. Using FIG. 12 can reduce the computational complexity compared to the look-up table in FIG. 5.

[0094] In some embodiments, the product of a pair of derived values ​​in a lookup table (also called an angle-offset mapping table) associated with a prediction mode index equal to an angle of 45° falls within a small range specified by a fixed value [Td, T+d]. In one example, T is 2048, 4096, 8192, and d is 0, 1, 2, 3, 4, 5, ..., 32, ..., 64, .... For example, a derived value associated with 45°, also called a diagonal derived value, has a value of 64 at index 45 in the lookup table of FIG. 12, and the value of T is the square of 64, which is equal to 4096. For a derived pair including a first derived value at a first index and a second derived value at a second index in the lookup table of FIG. 12, the sum of the first index and the second index is 90. The first derived value and the second derived value can be appropriately adjusted so that the product of the first derived value and the second derived value is constrained to be within the range [Td, T+d]. Adjusting the derived values ​​of the lookup table can reduce the computational complexity and keep the resolution within a certain range.

[0095] According to some aspects of the present disclosure, when the shape of a block is not square, one (or both) sides of the delta angle of one (or more) nominal angles and / or the nominal angle itself may be mapped to another angle to perform intra prediction.

[0096] In some embodiments, when the width / height ratio or height / width ratio is greater than a threshold, one or more nominal angles, along with all of their delta angles, are mapped to another angle for intra prediction.

[0097] In some examples, when the height / width ratio is greater than 2, the nominal angles D45_PRED and D67_PRED, along with their delta angles (e.g., 45°, 45°±3°, 45°±6°, 45°±9°, 67°, 67°-3°, 67°-6°, 67°-9°), are mapped to other angles for intra prediction. For example, the mapped angles are greater than 203°, e.g., greater than 212°.

[0098] In some examples, when the width / width ratio is greater than 2, the nominal angle D203_PRED is mapped to other angles for intra prediction, along with delta angles (e.g., 203°, 203°+3°, 203°+6°, 203°+9°). For example, the mapped angle is less than 45°, e.g., less than 36°.

[0099] In some examples, when the height / width ratio is 2, the nominal angle D45_PRED, along with its delta angles (e.g., 45°, 45°±3°, 45°±6°, 45°±9°), is mapped to other angles for intra prediction. For example, the mapped angle is greater than 203°, e.g., greater than 212°.

[0100] In some embodiments, when the shape of a block is not square, one side of the delta angle of one nominal angle and / or the nominal angle itself can be mapped to another angle to perform intra prediction.

[0101] In some examples, when the width / height ratio is greater than 2, such as 4, all positive delta angles of the nominal angle of D203_PRED (e.g., 203°+3°, 203°+6°, 203°+9°) are mapped to other angles less than 45°, such as less than 36°.

[0102] In some embodiments, one side of the delta angle of one nominal angle and / or the nominal angle itself can be mapped to another angle on the other side of the current block to perform intra prediction if there are more neighboring intra blocks on that side. In some examples, angles less than 135°, such as nominal angles D113_PRED, V_PRED, D67_PRED, and D45_PRED, and related finer angles based on the delta angle, may be referred to as upward directional angles, and angles greater than 135°, such as nominal angles D157_PRED, H_PRED, and D203_PRED, and related finer angles based on the delta angle, may be referred to as left directional angles.

[0103] In some examples, when the upper neighboring block of the current block has more intra-coded blocks than the left neighboring block of the current block, some of the left directional angles are mapped to upward directional angles. In some examples, when the left neighboring block of the current block has more intra-coded blocks than the upper neighboring block of the current block, some of the upward directional angles are mapped to left directional angles.

[0104] In some examples, when the upper neighboring block of the current block has more directional (angle) intra-coded blocks than the left neighboring block of the current block, some of the left directional angles are mapped to upward directional angles. In some examples, when the left neighboring block of the current block has more directional (angle) intra-coded blocks than the upper neighboring block of the current block, some of the upward directional angles are mapped to left directional angles.

[0105] In some embodiments, when the shape of the block is not square and the reference line index for intra prediction is greater than zero (e.g., a non-zero reference line), one or more nominal angles, along with its / their delta angle, may be mapped to other angles to perform intra prediction.

[0106] In some embodiments, one high-level syntax is signaled at the sequence / frame / slice / superblock / level to indicate whether angle mapping is applicable for non-square blocks.

[0107] 13 shows a flowchart outlining a process (1300) according to one embodiment of the present disclosure. The process (1300) can be used in a video encoder. In various embodiments, the process (1300) is performed by a processing circuit, such as a processing circuit performing the functions of a video encoder (103), a processing circuit performing the functions of a video encoder (303), etc. In some embodiments, the process (1300) is implemented with software instructions, and thus, the processing circuit performs the process (1300) when it executes the software instructions. The process begins at (S1301) and proceeds to (S1310).

[0108] At (S1310), the use of directional intra prediction for coding a current coding block in a current picture is determined.

[0109] In (S1320), an index to an entry in a lookup table (e.g., an angle-offset mapping lookup table) is determined, the lookup table storing a set of derived values ​​associated with the angle, the set of derived values ​​including two or more integers that are powers of two.

[0110] At (S1330), an entry in the lookup table is accessed according to the index to obtain a derived value of the directional intra prediction of the current coding block.

[0111] In (S1340), for a pixel in the current coding block, an offset indicating a reference position in the current picture is determined according to the derived value and the position of the pixel. The reference position in the current picture is used for directional intra prediction of the pixel.

[0112] At (S1350), coding information of the current coding block is generated, which indicates directional intra prediction of the current coding block.

[0113] In some examples, the set of derived values ​​in the lookup table includes all integers that are a power of 2 between the minimum value in the set of derived values ​​and the maximum value in the set of derived values. In one example, the set of derived values ​​is limited to N bits, where N is a positive integer, and the set of derived values ​​is a power of 2. i (i∈[1,2,...,N]).

[0114] In some examples, the difference between each two adjacent derived values ​​in the set of derived values ​​is a multiple of two.

[0115] In some examples, the set of derived values ​​is associated with increasing angles, and the difference between adjacent derived values ​​in the set of derived values ​​varies monotonically, such as monotonically decreasing.

[0116] In some examples, the set of derived values ​​includes a diagonal derived value associated with a 45° angle and a derived pair including a first derived value and a second derived value on different sides of the 45° angle and having the same absolute index difference relative to the diagonal derived value, wherein the product of the first derived value and the second derived value is within a range related to the square of the diagonal derived value. In one example, the square of the diagonal derived value is one of 2048, 4096, and 8192. In some examples, the product of the first derived value and the second derived value is within [Td, T+d], where T indicates the square of the diagonal derived value and d indicates a predefined range parameter.

[0117] The process then proceeds to (S1399) and ends.

[0118] The process 1300 may be adapted as appropriate. Steps in the process 1300 may be modified and / or omitted. Additional steps may be added. Any suitable order of performance may be used.

[0119] 14 shows a flowchart outlining a process (1400) according to one embodiment of the present disclosure. The process (1400) can be used in a video encoder. In various embodiments, the process (1400) is performed by a processing circuit, such as a processing circuit performing the functions of a video encoder (103), a processing circuit performing the functions of a video encoder (303), etc. In some embodiments, the process (1400) is implemented with software instructions, and thus, the processing circuit performs the process (1400) when it executes the software instructions. The process begins at (S1401) and proceeds to (S1410).

[0120] At (S1410), the use of directional intra prediction for coding a current coding block in a current picture is determined.

[0121] At (S1420), it is determined that the current coding block is a non-square rectangle.

[0122] At (S1430), a mapped intra-prediction angle is determined according to whether the current coding block is a non-square rectangle, and the mapped intra-prediction angle is outside a first set of directional intra-prediction angles and is mapped to a specific directional intra-prediction angle within the first set of directional intra-prediction angles, and the first set of directional intra-prediction angles includes a predefined nominal angle and a finer angle, and the finer angle is away from the predefined nominal angle by a delta angle.

[0123] In some examples, the mapped intra-prediction angle is used for directional intra-prediction of the current coding block. In one example, a lookup table is accessed according to the mapped intra-prediction angle to obtain a derived value for directional intra-prediction of the current coding block. For a pixel in the current coding block, an offset indicating a reference position in the current picture is determined according to the derived value and the position of the pixel. The reference position in the current picture is used for directional intra-prediction of the pixel.

[0124] At (S1440), coding information for the current coding block is determined, where the coding information indicates a particular delta angle and a particular nominal angle that collectively correspond to a particular directional intra-prediction angle within the first set of directional intra-prediction angles.

[0125] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio or width-to-height ratio being greater than a threshold, and the directional intra-prediction angle of the mapped subset is mapped from a nominal angle of at least 45° using a delta angle.

[0126] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio of the current coding block being greater than 2, and the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a first nominal angle of 45° using a delta angle and a second nominal angle of 67° using a delta angle.

[0127] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the width-to-height ratio of the current coding block being greater than 2, and the directional intra-prediction angle of the mapped subset being less than 45° and mapped from a nominal angle of 203° using a delta angle.

[0128] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio of the current coding block being equal to 2, and the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a nominal angle of 45° using a delta angle.

[0129] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio of the current coding block being greater than a threshold, and the directional intra-prediction angle of the mapped subset is mapped from the nominal angle using a subset of delta angles on the side of the nominal angle.

[0130] In some examples, a first side and a second side are determined from the top side (top edge) and the left side (left edge). The first side has more intra-coded neighboring blocks than the second side. Then, one or more directional intra-prediction angles are mapped from the second side to the first side.

[0131] In some examples, a first side and a second side are determined from the top side (upper edge) and the left side (left edge). The first side has more directional (angle) intra-coded neighboring blocks than the second side. Then, one or more directional intra-prediction angles are mapped from the second side to the first side.

[0132] In some examples, a reference line index is determined. If the reference line index is greater than zero and the current coding block is a non-square rectangle, a mapped intra-prediction angle is determined, and the mapped intra-prediction angle is outside the first set of directional intra-prediction angles and is mapped to a specific directional intra-prediction angle.

[0133] In some examples, a syntax element is generated in the encoding information indicating the enabling of angle mapping. Note that the syntax element may be any suitable high-level syntax element, such as a sequence level, frame level, slice level, superblock level, etc.

[0134] The process then proceeds to (S1499) and ends.

[0135] The process 1400 may be adapted as appropriate. Steps in the process 1400 may be modified and / or omitted. Additional steps may be added. Any suitable order of performance may be used.

[0136] 15 shows a flowchart outlining a process (1500) according to one embodiment of the present disclosure. The process (1500) can be used in a video decoder. In various embodiments, the process (1500) is performed by a processing circuit, such as a processing circuit that performs the functions of the video decoder (110), a processing circuit that performs the functions of the video decoder (210), etc. In some embodiments, the process (1500) is implemented with software instructions, and thus, the processing circuit performs the process (1500) when it executes the software instructions. The process begins at (S1501) and proceeds to (S1510).

[0137] At (S1510), coding information for a current coding block in a current picture is received from a coded video bitstream, the coding information indicating directional intra prediction of the current coding block.

[0138] At (S1520), an index to an entry in a lookup table (e.g., an angle-offset mapping lookup table) is determined according to the coding information of the current coding block, and the lookup table stores a set of derived values ​​associated with the angle, the set of derived values ​​including two or more integers that are powers of two.

[0139] At (S1530), an entry in the lookup table is accessed according to the index to obtain a derived value of the directional intra prediction of the current coding block.

[0140] At (S1540), for a pixel in the current coding block, an offset indicating a reference position in the current picture is determined according to the derived value and the position of the pixel.

[0141] At (S1550), pixels in the current coding block are reconstructed based on reference positions in the current picture.

[0142] In some examples, the set of derived values ​​in the lookup table includes all integers that are a power of 2 between the minimum value in the set of derived values ​​and the maximum value in the set of derived values. In one example, the set of derived values ​​is limited to N bits, where N is a positive integer, and the set of derived values ​​is a power of 2. i (i∈[1,2,...,N]).

[0143] In some examples, the difference between each two adjacent derived values ​​in the set of derived values ​​is a multiple of two.

[0144] In some examples, the set of derived values ​​is associated with increasing angles, and the difference between adjacent derived values ​​in the set of derived values ​​varies monotonically, such as monotonically decreasing.

[0145] In some examples, the set of derived values ​​includes a diagonal derived value associated with a 45° angle and a derived pair including a first derived value and a second derived value on different sides of the 45° angle and having the same absolute index difference relative to the diagonal derived value, wherein the product of the first derived value and the second derived value is within a range related to the square of the diagonal derived value. In one example, the square of the diagonal derived value is one of 2048, 4096, and 8192. In some examples, the product of the first derived value and the second derived value is within [Td, T+d], where T indicates the square of the diagonal derived value and d indicates a predefined range parameter.

[0146] The process then proceeds to (S1599) and ends.

[0147] The process 1500 may be adapted as appropriate. Steps in the process 1500 may be modified and / or omitted. Additional steps may be added. Any suitable order of performance may be used.

[0148] 16 shows a flowchart outlining a process (1600) according to one embodiment of the present disclosure. The process (1600) can be used in a video decoder. In various embodiments, the process (1600) is performed by a processing circuit, such as a processing circuit that performs the functions of the video decoder (110), a processing circuit that performs the functions of the video decoder (210), etc. In some embodiments, the process (1600) is implemented with software instructions, and thus, the processing circuit performs the process (1600) when it executes the software instructions. The process begins at (S1601) and proceeds to (S1610).

[0149] At (S1610), coding information for a current coding block in a current picture is received from a coded video bitstream, the coding information indicating a particular delta angle and a particular nominal angle that collectively correspond to a particular directional intra-prediction angle within a first set of directional intra-prediction angles, the first set of directional intra-prediction angles including a predefined nominal angle and finer angles, the finer angles being separated from the predefined nominal angle by the delta angle.

[0150] At (S1620), it is determined that the current coding block is a non-square rectangle.

[0151] At (S1630), a mapped intra-prediction angle is determined according to the current coding block being a non-square rectangle, and the mapped intra-prediction angle is outside the first set of directional intra-prediction angles and is mapped to a specific directional intra-prediction angle.

[0152] At (S1640), the current coding block is reconstructed based on the mapped intra-prediction angles.

[0153] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio or width-to-height ratio being greater than a threshold, and the directional intra-prediction angle of the mapped subset is mapped from a nominal angle of at least 45° using a delta angle.

[0154] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio of the current coding block being greater than 2, and the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a first nominal angle of 45° using a delta angle and a second nominal angle of 67° using a delta angle.

[0155] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the width-to-height ratio of the current coding block being greater than 2, and the directional intra-prediction angle of the mapped subset being less than 45° and mapped from a nominal angle of 203° using a delta angle.

[0156] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio of the current coding block being equal to 2, and the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a nominal angle of 45° using a delta angle.

[0157] In some examples, a mapped intra-prediction angle is determined from the directional intra-prediction angle of the mapped subset in response to the height-to-width ratio of the current coding block being greater than a threshold, and the directional intra-prediction angle of the mapped subset is mapped from the nominal angle using a subset of delta angles on the side of the nominal angle.

[0158] In some examples, a first side and a second side are determined from the top side (top edge) and the left side (left edge). The first side has more intra-coded neighboring blocks than the second side. Then, one or more directional intra-prediction angles are mapped from the second side to the first side.

[0159] In some examples, a first side and a second side are determined from the top side (upper edge) and the left side (left edge). The first side has more directional (angle) intra-coded neighboring blocks than the second side. Then, one or more directional intra-prediction angles are mapped from the second side to the first side.

[0160] In some examples, a reference line index is determined. If the reference line index is greater than zero and the current coding block is a non-square rectangle, a mapped intra-prediction angle is determined, and the mapped intra-prediction angle is outside the first set of directional intra-prediction angles and is mapped to a specific directional intra-prediction angle.

[0161] In some examples, a syntax element indicating enabling angle mapping is determined. A mapped intra-prediction angle is determined in response to the syntax element indicating enabling angle mapping and the current coding block being a non-square rectangle. The mapped intra-prediction angle is outside the first set of directional intra-prediction angles and is mapped to a specific directional intra-prediction angle. It should be noted that the syntax element may be any appropriate high-level syntax element, such as a sequence level, frame level, slice level, superblock level, etc.

[0162] The process then proceeds to (S1699) and ends.

[0163] The process 1600 may be adapted as appropriate. Steps in the process 1600 may be modified and / or omitted. Additional steps may be added. Any suitable order of performance may be used.

[0164] The techniques described above may be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, Figure 17 illustrates a computer system (1700) suitable for implementing certain embodiments of the disclosed subject matter.

[0165] Computer software may be coded using any suitable machine code or computer language that may be subject to assembly, compilation, linking, or similar mechanisms to create code that includes instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., directly or through interpretation, microcode execution, etc.

[0166] The instructions may be executed in various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, Internet of Things devices, etc.

[0167] 17 for computer system (1700) are exemplary in nature and are not intended to suggest any limitation regarding the scope of use or functionality of the computer software implementing 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 shown in the exemplary embodiment of computer system (1700).

[0168] The computer system 1700 may include certain human interface input devices. Such human interface input devices may respond to input by one or more human users, for example, through tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), or olfactory input (not shown). The human interface input devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., voice, music, ambient sounds), images (e.g., scanned images, photographic images obtained from a still image camera), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic vision).

[0169] The human interface input devices may include one or more of a keyboard (1701), a mouse (1702), a trackpad (1703), a touch screen (1710), a data glove (not shown), a joystick (1705), a microphone (1706), a scanner (1707), and a camera (1708) (only one of each is shown).

[0170] The computer system (1700) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, through tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touchscreen (1710), data gloves (not shown), or joystick (1705), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (1709), headphones (not shown), etc.), visual output devices (e.g., screens (1710), including CRT, LCD, plasma, and OLED screens, each with or without touchscreen input capability and each with or without haptic feedback capability, some of which may provide two-dimensional visual output or greater 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).

[0171] The computer system (1700) may also include human-accessible storage devices and their associated media, such as optical media or similar media (1721), including CD / DVD ROM / RW (1720) with CDs / DVDs, thumb drives (1722), removable hard drives or solid-state drives (1723), legacy magnetic media such as tape and floppy disks (not shown), and special ROM / ASIC / PLD-based devices such as security dongles (not shown).

[0172] 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.

[0173] The computer system 1700 may also include interfaces 1754 to one or more communications networks 1755. Networks may be, for example, wireless, wired, or optical. Networks may further be local, wide-area, metropolitan, vehicular, industrial, real-time, delay-tolerant, etc. Examples of networks include local area networks such as Ethernet and WLAN; cellular networks including GSM, 3G, 4G, 5G, LTE, etc.; TV wired or wireless wide-area digital networks including cable TV, satellite TV, and terrestrial TV; and vehicular and industrial networks including CANbus, etc. Certain networks typically require an external network interface adapter (e.g., a USB port on the computer system 1700) attached to a particular general-purpose data port or peripheral bus 1749; others are typically integrated into the core of the computer system 1700 by attachment to a system bus (e.g., an Ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system), as described below. Using any of these networks, the computer system (1700) can communicate with other entities. Such communications can be one-way receive-only (e.g., broadcast TV), one-way transmit-only (e.g., from a particular CANbus to a particular CANbus device), or bidirectional to other computer systems, using, for example, local or wide-area digital networks. As noted above, specific protocols and protocol stacks can be used in each of these networks and network interfaces.

[0174] The above-mentioned human interface devices, human-accessible storage devices, and network interfaces can be attached to the core (1740) of the computer system (1700).

[0175] The core (1740) may include one or more central processing units (CPUs) (1741), graphics processing units (GPUs) (1742), dedicated programmable processing units in the form of field programmable gate arrays (FPGAs) (1743), task-specific hardware accelerators (1744), graphics adapters (1750), etc. These devices may be connected through a system bus (1748), along with read-only memory (ROM) (1745), random access memory (RAM) (1746), and internal mass storage (1747), such as an internal non-user-accessible hard drive or SSD. In some computer systems, the system bus (1748) is accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (1748) or through a peripheral bus (1749). In one example, a screen (1710) may be connected to the graphics adapter (1750). Peripheral bus architectures include PCI, USB, and the like.

[0176] The CPU (1741), GPU (1742), FPGA (1743), and accelerator (1744) can execute specific instructions, which, in combination, can constitute the computer code described above. The computer code can be stored in ROM (1745) or RAM (1746). Temporary data can be stored in RAM (1746), while permanent data can be stored, for example, in internal mass storage (1747). High-speed storage and retrieval from any of the memory devices can be enabled through the use of cache memory, which can be closely associated with one or more of the CPU (1741), GPU (1742), mass storage (1747), ROM (1745), RAM (1746), etc.

[0177] The computer-readable medium may have computer code thereon for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the kind well known and available to those skilled in the computer software arts.

[0178] By way of example and not limitation, a computer system having the architecture (1700) and particularly the core (1740) can provide functionality as a result of the 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 the core's (1740) specific storage of a non-transitory nature, such as the core's internal mass storage (1747) or ROM (1745). Software implementing various embodiments of the present disclosure can be stored on such devices and executed by the core (1740). The computer-readable media can include one or more memory devices or chips according to particular needs. The software can cause the core (1740) and particularly the processor therein (including a CPU, GPU, FPGA, etc.) to perform particular processes or particular portions of particular processes described herein, including defining data structures stored in RAM (1746) 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 (1744)), which may operate in place of or in conjunction with software to perform particular processes or portions of particular processes described herein. References to software include logic, and vice versa, where appropriate. References to computer-readable media may encompass circuitry (such as an integrated circuit (IC)) that stores software for execution, circuitry embodying logic for execution, or both, as appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0179] The use of "at least one" in this disclosure is intended to include any one or combination of the listed elements. For example, reference to at least one of A, B, or C; at least one of A, B, and C; at least one of A, B, and / or C; and at least one of A through C is intended to include A only, B only, C only, or any combination thereof.

[0180] While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents that fall within the scope of this disclosure. It will thus be appreciated that those skilled in the art will be able to devise various systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are therefore within the spirit and scope of the present disclosure.

Claims

1. 1. A method of video decoding, comprising: receiving coding information for a current coding block in a current picture from a coded video bitstream, the coding information indicating directional intra prediction of the current coding block; determining an index to an entry in an angle-offset mapping lookup table according to the coded information of a current coding block, the angle-offset mapping lookup table storing a set of derived values ​​associated with angles, the set of derived values ​​including two or more integers that are powers of two; accessing the entry in the angle-offset mapping lookup table according to the index to obtain a derived value of the directional intra prediction for the current coding block; determining, for a pixel in the current coding block, an offset indicating a reference position in the current picture according to the derived value and a position of the pixel; reconstructing the pixels in the current coding block based on the reference locations in the current picture; A method comprising:

2. 2. The method of claim 1 , wherein the set of derived values ​​in the angle-to-offset mapping lookup table includes all integers that are powers of two between a minimum value in the set of derived values ​​and a maximum value in the set of derived values.

3. The set of derived values ​​is limited to N bits, where N is a positive integer, and the set of derived values ​​is 2 i The method of claim 2 , wherein i∈[1, 2, ..., N].

4. 3. The method of claim 2, wherein the set of derived values ​​includes 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, and 2048.

5. 2. The method of claim 1, further comprising the step of using a shift operation to perform a multiplication operation when a derived value of a power of two is used in the multiplication operation.

6. The method of claim 1 , wherein the difference between each two adjacent derived values ​​in the set of derived values ​​is a multiple of two.

7. The method of claim 1 , wherein the set of derived values ​​is associated with increasing angles, and the difference between adjacent derived values ​​in the set of derived values ​​varies monotonically.

8. 2. The method of claim 1, wherein the set of derived values ​​includes a diagonal derived value associated with a 45° angle and a derived pair including a first derived value and a second derived value having the same absolute index difference relative to the diagonal derived value, and a product of the first derived value and the second derived value is within a range related to the square of the diagonal derived value.

9. 9. The method of claim 8, wherein the square of the diagonal derivative is one of 2048, 4096, and 8192.

10. 9. The method of claim 8, wherein the product of the first derivative and the second derivative is in [Td, T+d], where T denotes the square of the diagonal derivative and d denotes a predefined range parameter.

11. 1. A method of video decoding, comprising: receiving coding information for a current coding block in a current picture from a coded video bitstream, the coding information indicating a particular delta angle and a particular nominal angle that collectively correspond to a particular directional intra-prediction angle within a first set of directional intra-prediction angles, the first set of directional intra-prediction angles including a predefined nominal angle and finer angles, the finer angles being separated from the predefined nominal angle by a delta angle; determining that the current coding block is a non-square rectangle; determining a mapped intra-prediction angle that is outside the first set of directional intra-prediction angles and that is mapped to the specific directional intra-prediction angle according to the current coding block being the non-square rectangle; reconstructing the current coding block based on the mapped intra-prediction angle; A method comprising:

12. The step of determining the mapped intra-prediction angle comprises:

12. The method of claim 11, further comprising: determining a mapped intra-prediction angle from a mapped subset of directional intra-prediction angles in response to a height-to-width ratio or a width-to-height ratio being greater than a threshold, wherein the mapped subset of directional intra-prediction angles are mapped from a nominal angle of at least 45° using the delta angle.

13. The step of determining the mapped intra-prediction angle comprises:

12. The method of claim 11, further comprising: determining the mapped intra-prediction angle from directional intra-prediction angles of a mapped subset in response to a height-to-width ratio of the current coding block being greater than 2, wherein the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a first nominal angle of 45° using the delta angle and a second nominal angle of 67° using the delta angle.

14. The step of determining the mapped intra-prediction angle comprises:

12. The method of claim 11, further comprising: determining the mapped intra-prediction angle from a directional intra-prediction angle of a mapped subset in response to a width-to-height ratio of the current coding block being greater than 2, wherein the directional intra-prediction angle of the mapped subset is less than 45° and is mapped from a nominal angle of 203° using the delta angle.

15. The step of determining the mapped intra-prediction angle comprises:

12. The method of claim 11, further comprising: determining the mapped intra-prediction angle from a directional intra-prediction angle of a mapped subset in response to a height-to-width ratio of the current coding block being equal to 2, wherein the directional intra-prediction angle of the mapped subset is greater than 203° and is mapped from a nominal angle of 45° using the delta angle.

16. The step of determining the mapped intra-prediction angle comprises:

12. The method of claim 11, further comprising: determining the mapped intra-prediction angle from a mapped subset of directional intra-prediction angles in response to a height-to-width ratio of the current coding block being greater than a threshold, wherein the directional intra-prediction angle of the mapped subset is mapped from the nominal angle using a subset of the delta angles on one side of the nominal angle.

17. The step of determining the mapped intra-prediction angle comprises: determining a first side and a second side from the top and left sides, the first side having more intra-coded neighboring blocks than the second side; mapping one or more directional intra-prediction angles from the second side to the first side; The method of claim 11 further comprising:

18. The step of determining the mapped intra-prediction angle comprises: determining a reference line index; determining the mapped intra-prediction angle that is outside the first set of directional intra-prediction angles and that is mapped to the specific directional intra-prediction angle according to the reference line index being greater than zero and the current coding block being the non-square rectangle; The method of claim 11 further comprising:

19. The step of determining the mapped intra-prediction angle comprises: determining that a syntax element indicates enabling angle mapping; determining, in response to the syntax element indicating enabling of the angle mapping and the current coding block being the non-square rectangle, the mapped intra-prediction angle that is outside the first set of directional intra-prediction angles and that is mapped to the particular directional intra-prediction angle; The method of claim 11 further comprising:

20. 20. The method of claim 19, wherein the syntax elements are at least one of a sequence level, a frame level, a slice level, and a superblock level.

21. 1. An apparatus including a processing circuit, Apparatus, wherein the processing circuitry is configured to perform the method of any one of claims 1 to 10.

22. 1. An apparatus including a processing circuit, 21. Apparatus, wherein the processing circuitry is configured to perform a method according to any one of claims 11 to 20.

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

24. A computer program causing a computer to carry out the method according to any one of claims 11 to 20.

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