Template-based intra mode derivation with reference line selection

Abstract

A video coder determines, for a current block, a plurality of costs of a plurality of intra prediction modes (IPMs) for predicting a template of the current block and determines a single template-based intra mode derivation (TIMD) mode based on an IPM, from the plurality of IPMs, with the lowest cost of the plurality of costs. The coder further determines a TIMD mode predictor based on the single TIMD mode by combining: a first TIMD mode generated by applying the single TIMD mode to a first reference line of the current block and a second TIMD mode generated by applying the single TIMD mode to a second reference line of the current block that is different from the first reference line. The coder generates, based on the TIMD mode predictor, a prediction block for the current block.

Description

TITLETemplate-based Intra Mode Derivation with Reference Line SelectionCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 615,057, filed December 27, 2023, which is hereby incorporated by reference in its entirety.BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Some features are shown by way of example, and not by limitation, in the accompanying drawings. In the drawings, like numerals reference similar elements.

[0003] FIG. 1 shows an example video coding / decoding system in which embodiments of the present disclosure may be implemented.

[0004] FIG. 2 shows an example encoder in which embodiments of the present disclosure may be implemented.

[0005] FIG. 3 shows an example decoder in which embodiments of the present disclosure may be implemented.

[0006] FIG. 4 shows an example quadtree partitioning of a coding tree block (CTB).

[0007] FIG. 5 shows an example quadtree corresponding to the example quadtree partitioning of the CTB in FIG. 4.

[0008] FIG. 6 show examples of binary tree and ternary tree partitions.

[0009] FIG. 7 shows an example of combined quadtree and multi-type tree partitioning of a CTB.

[0010] FIG. 8 shows an example tree corresponding to the combined quadtree and multi-type tree partitioning of theCTB shown in FIG. 7.

[0011] FIG. 9 shows an example set of reference samples determined for intra prediction of a current block.

[0012] FIGS. 10A and 10B show example intra prediction modes.

[0013] FIG. 11 shows an example of a current block and corresponding reference samples.

[0014] FIG. 12 shows an example of applying an intra prediction mode (e.g, an angular mode) for prediction of a current block.

[0015] FIG. 13A shows an example of inter prediction performed for a current block in a current picture.

[0016] FIG. 13B shows an example motion vector.

[0017] FIG. 14 shows an example of bi-prediction performed for a current block.

[0018] FIG. 15A shows example spatial candidate neighboring blocks relative to a current block being coded.

[0019] FIG. 15B shows example locations of two temporal, co-located blocks relative to a current block.

[0020] FIG. 16 shows an example of intra block copy (IBC).

[0021] FIG. 17 shows an example of template-based intra mode derivation (TIMD) for coding a current block, according to some embodiments.

[0022] FIG. 18 shows an example of signaling TIMD for decoding a current block, according to some embodiments.

[0023] FIG. 19 shows a flowchart of a method for applying a TIMD technique for a current block, according to some embodiments.

[0024] FIG. 20 shows a flowchart of a method for applying a TIMD technique for a current block, according to some embodiments.

[0025] FIG. 21 shows a flowchart of a method for applying a TIMD technique for a current block, according to some embodiments.

[0026] FIG. 22 shows a block diagram of an example computer system in which embodiments of the present disclosure maybe implemented.DETAILED DESCRIPTION

[0027] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be apparent to those skilled in the art that the disclosure, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the disclosure.

[0028] References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0029] Also, it is noted that individual embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in a figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination can correspond to a return of the function to the calling function or the main function.

[0030] The term “computer-readable medium” includes, but is not limited to, portable or non-portable storage devices, optical storage devices, and various other mediums capable of storing, containing, or carrying instruction(s) and / or data. A computer-readable medium may include a non-transitory medium in which data can be stored and that does not include carrier waves and / or transitory electronic signals propagating wirelessly or over wired connections. Examples of a non-transitory medium may include, but are not limited to, a magnetic disk or tape, optical storage media such as compact disk (CD) or digital versatile disk (DVD), flash memory, memory or memory devices. A computer-readable medium may have stored thereon code and / or machine-executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combinationof instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and / or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, or the like.

[0031] Furthermore, embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks (e.g, a computer-program product) may be stored in a computer-readable or machine-readable medium. A processor(s) may perform the necessary tasks.

[0032] A video sequence, comprising multiple pictu res / frames, may be represented in digital form for storage and / or transmission. Representing a video sequence in digital form may require a large quantity of bits. Large data sizes that may be associated with video sequences may require significant resources for storage and / or transmission. Video encoding may be used to compress a size of a video sequence for more efficient storage and / or transmission. Video decoding may be used to decompress a compressed video sequence for display and / or other forms of consumption.

[0033] FIG. 1 shows an example video coding / decoding system 100 in which embodiments of the present disclosure may be implemented. Video coding / decoding system 100 comprises a source device 102, a transmission medium 104, and a destination device 106. Source device 102 encodes a video sequence 108 into a bitstream 110 for more efficient storage and / or transmission. Source device 102 may store and / or send / transmit bitstream 110 to destination device 106 via transmission medium 104. Destination device 106 decodes bitstream 110 to display video sequence 108. Destination device 106 may receive bitstream 110 from source device 102 via transmission medium 104. Source device 102 and / or destination device 106 may be any of a plurality of different devices (e.g., a desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.).

[0034] Source device 102 may comprise (e.g, for encoding video sequence 108 into bitstream 110) one or more of a video source 112, an encoder 114, and / or an output interface 116. Video source 112 may provide and / or generate video sequence 108 based on a capture of a natural scene and / or a synthetically generated scene. A synthetically generated scene may be a scene comprising computer generated graphics and / or screen content. Video source 112 may comprise a video capture device (e.g, a video camera), a video archive comprising previously captured natural scenes and / or synthetically generated scenes, a video feed interface to receive captured natural scenes and / or synthetically generated scenes from a video content provider, and / or a processor to generate synthetic scenes.

[0035] A video sequence, such as video sequence 108, may comprise a series of pictures (also referred to as frames). A video sequence may achieve an impression of motion based on successive presentation of pictures of the video sequence using a constant time interval or variable time intervals between the pictures. A picture may comprise one or more sample arrays of intensity values. The intensity values may be taken (e.g, measured, determined, provided) at a series of regularly spaced locations within a picture. A color picture may comprise (e.g, typically comprises) a luminance sample array and two chrominance sample arrays. The luminance sample array may compriseintensity values representing the brightness (e.g, luma component, Y) of a picture. The chrominance sample arrays may comprise intensity values that respectively represent the blue and red components of a picture (e.g., chroma components, Cb and Cr) separate from the brightness. Other color picture sample arrays may be possible based on different color schemes (e.g., a red, green, blue (RGB) color scheme). A pixel, in a color picture, may refer to / comprise / be associated with all intensity values (e.g., luma component, chroma components), for a given location, in the sample arrays (e.g., three sample arrays are used for one luma component and two chroma components, respectively) used to represent color pictures. A monochrome picture may comprise a single, luminance sample array. A pixel, in a monochrome picture, may refer to / comprise / be associated with the intensity value (e.g, luma component) at a given location in the single, luminance sample array used to represent monochrome pictures.

[0036] Encoder 114 may encode video sequence 108 into bitstream 110. Encoder 114 may apply / use (e.g, to encode video sequence 108) one or more prediction techniques to reduce redundant information in video sequence 108. Redundant information is information that may be predicted at a decoder and need not be transmitted to the decoder for accurate decoding of video sequence 108. For example, encoder 114 may apply spatial prediction (e.g, intra-frame or intra prediction), temporal prediction (e.g, inter-frame prediction or inter prediction), inter-layer prediction, and / or other prediction techniques to reduce redundant information in video sequence 108. Encoder 114 may partition pictures comprising video sequence 108 into rectangular regions referred to as blocks, for example, before applying one or more prediction techniques. Encoder 114 may then encode a block using the one or more of the prediction techniques.

[0037] For temporal prediction, encoder 114 may search for a block similar to the block being encoded in another picture (e.g, referred to as a reference picture) of video sequence 108. The block determined during the search (e.g, referred to as a prediction block) may then be used to predict the block being encoded. For spatial prediction, encoder 114 may form a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 108. A reconstructed sample refers to a sample that was encoded and then decoded. Encoder 114 may determine a prediction error (e.g, also referred to as a residual) based on the difference between a block being encoded and a prediction block. The prediction error may represent non-redundant information that may be sent / transmitted to a decoder for accurate decoding of video sequence 108.

[0038] Encoder 114 may apply a transform to the prediction error (e.g. using a discrete cosine transform (DCT), or any other transform) to generate transform coefficients. Encoder 114 may form bitstream 110 based on the transform coefficients and other information used to determine prediction blocks using / based on prediction types, motion vectors, and / or prediction modes. Encoder 114 may perform one or more of quantization and entropy coding of the transform coefficients and / or the other information used to determine the prediction blocks, for example, before forming bitstream 110. The quantization and / or the entropy coding may further reduce the quantity of bits needed to store and / or transmit video sequence 108.

[0039] Output interface 116 may be configured to write and / or store bitstream 110 onto transmission medium 104 for transmission to destination device 106. In addition or alternatively, output interface 116 may be configured tosend / transmit, upload, and / or stream bitstream 110 to destination device 106 via transmission medium 104. Output interface 116 may comprise a wired and / or a wireless transmitter configured to send / transmit, upload, and / or stream bitstream 110 in accordance with one or more proprietary, open-source, and / or standardized communication protocols (e.g, Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, 3rd Generation Partnership Project (3GPP) standards, Institute of Electrical and Electronics Engineers (IEEE) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and / or any other communication protocol).

[0040] Transmission medium 104 may comprise wireless, wired, and / or computer readable medium. For example, transmission medium 104 may comprise one or more wires, cables, air interfaces, optical discs, flash memory, and / or magnetic memory. In addition or alternatively, transmission medium 104 may comprise one or more networks (e.g, the internet) or file servers configured to store and / or send / transmit encoded video data.

[0041] Destination device 106 may decode bitstream 110 into video sequence 108 for display. Destination device 106 may comprise one or more of an input interface 118, a decoder 120, and / or a video display 122. Input interface 118 may be configured to read bitstream 110 stored on transmission medium 104 by source device 102. In addition or alternatively, input interface 118 may be configured to receive, download, and / or stream bitstream 110 from source device 102 via transmission medium 104. Input interface 118 may comprise a wired and / or a wireless receiver configured to receive, download, and / or stream bitstream 110 in accordance with one or more proprietary, open-source, standardized communication protocols, and / or any other communication protocol (e.g, such as referenced herein).

[0042] Decoder 120 may decode video sequence 108 from encoded bitstream 110. The decoder 120 may generate prediction blocks for pictures of video sequence 108 in a similar manner as encoder 114 and determine the prediction errors for the blocks, for example, to decode video sequence 108. Decoder 120 may generate the prediction blocks using / based on prediction types, prediction modes, and / or motion vectors received in bitstream 110. Decoder 120 may determine the prediction errors using the transform coefficients received in bitstream 110. Decoder 120 may determine the prediction errors by weighting transform basis functions using the transform coefficients. Decoder 120 may combine the prediction blocks and the prediction errors to decode video sequence 108. Video sequence 108 at the destination device 106 may be, or may not necessarily be, the same video sequence sent, such as video sequence 108 as sent by the source device 102. Decoder 120 may decode a video sequence that approximates video sequence 108, for example, because of lossy compression of video sequence 108 by encoder 114 and / or errors introduced into encoded bitstream 110 during transmission to destination device 106.

[0043] Video display 122 may display video sequence 108 to a user. Video display 122 may comprise a cathode rate tube (CRT) display, a liquid crystal display (LCD), a plasma display, a light emitting diode (LED) display, and / or any other display device suitable for displaying video sequence 108.

[0044] Video coding / decoding system 100 is merely an example and video encoding / decoding systems different from the video coding / decoding system 100 and / or modified versions of the video coding / decoding system 100 may similarlyperform the methods and processes as described herein. For example, the video coding / decoding system 100 may comprise other components and / or arrangements. For example, video source 112 may be external to source device 102. Similarly, video display 122 may be external to destination device 106 or omitted altogether (e.g, if video sequence 108 is intended for consumption by a machine and / or storage device). In an example, source device 102 may further comprise a video decoder and destination device 106 may further comprise a video encoder. For example, source device 102 may be configured to further receive an encoded bitstream from destination device 106 to support two-way video transmission between the devices.

[0045] Encoder 114 and / or decoder 120 may operate according to one or more proprietary or industry video coding standards. For example, encoder 114 and / or decoder 120 may operate in accordance with one or more proprietary, open-source, and / or standardized protocols (e.g. International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.263, ITU-T H.264 and Moving Picture Expert Group (M PEG)-4 Visual (also known as Advanced Video Coding (AVC)), ITU-T H.265 and MPEG-H Part 2 (also known as High Efficiency Video Coding (H EVC)), ITU-T H.265 and MPEG-I Part 3 (also known as Versatile Video Coding (WC)), the WebM VP8 and VP9 codecs, and / or AO Media Video 1 (AV1 ), and / or any other video coding protocol).

[0046] FIG. 2 shows an example encoder. Encoder 200 as shown in FIG. 2 may implement one or more processes described herein. Encoder 200 may encode a video sequence 202 into a bitstream 204 for more efficient storage and / or transmission. Encoder 200 may be implemented in video coding / decoding system 100 as shown in FIG. 1 (e.g, as encoder 114) or in any computing, communication, or electronic device (e.g, desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.). Encoder 200 may comprise one or more of an inter prediction unit 206, an intra prediction unit 208, combiners 210 and 212, a transform and quantization unit (TR + Q) 214, an inverse transform and quantization unit (iTR + iQ) 216, an entropy coding unit 218, one or more filters 220, and / or a buffer 222.

[0047] Encoder 200 may partition pictures (e.g, frames) of (e.g, comprising) video sequence 202 into blocks and encode video sequence 202 on a block-by-block basis. Encoder 200 may perform / apply a prediction technique on a block being encoded using either inter prediction unit 206 or intra prediction unit 208. Inter prediction unit 206 may perform inter prediction by searching for a block similar to the block being encoded in another, reconstructed picture (e.g, a reference picture) of video sequence 202. A reconstructed picture refers to a picture that was encoded and then decoded. The block determined during the search (e.g, referred to as a prediction block) may then be used to predict the block being encoded to remove redundant information. Inter prediction unit 206 may exploit temporal redundancy or similarities in scene content from picture to picture in video sequence 202 to determine the prediction block. For example, scene content between pictures of video sequence 202 may be similar except for differences due to motion and / or affine transformation of the screen content over time.

[0048] Intra prediction unit 208 may perform intra prediction by forming a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 202. A reconstructed sample refers to a sample that was encoded and then decoded. Intra prediction unit 208 may exploitspatial redundancy or similarities in scene content within a picture of video sequence 202 to determine the prediction block. For example, the texture of a region of scene content in a picture may be similar to the texture in the immediate surrounding area of the region of the scene content in the same picture.

[0049] Combiner 210 may determine a prediction error (e.g. , referred to as a residual) based on the difference between the block being encoded and the prediction block. The prediction error may represent non-redundant information that may be sent / transmitted to a decoder for accurate decoding of video sequence 202.

[0050] Transform and quantization unit (TR + Q) 214 may transform and quantize the prediction error. Transform and quantization unit 214 may transform the prediction error into transform coefficients by applying, for example, a DCT to reduce correlated information in the prediction error. Transform and quantization unit 214 may quantize the coefficients by mapping data of the transform coefficients to a predefined set of representative values. Transform and quantization unit 214 may quantize the coefficients to reduce irrelevant information in bitstream 204. The irrelevant information refers to information that may be removed from the coefficients without producing visible and / or perceptible distortion in video sequence 202 after decoding (e.g., ata receiving device).

[0051] Entropy coding unit 218 may apply one or more entropy coding methods to the quantized transform coefficients to further reduce the bit rate. For example, entropy coding unit 218 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and / or syntax-based context-based binary arithmetic coding (SBAC). The entropy coded coefficients may be packed to form bitstream 204.

[0052] Inverse transform and quantization unit (iTR + iQ) 216 may inverse quantize and inverse transform the quantized transform coefficients to determine a reconstructed prediction error. Combiner 212 may combine the reconstructed prediction error with the prediction block to form a reconstructed block. Filter(s) 220 may filter the reconstructed block, for example, using a deblocking filter and / or a sample-adaptive offset (SAO) filter. Buffer 222 may store the reconstructed block for prediction of one or more other blocks in the same and / or different picture of video sequence 202.

[0053] Encoder 200 may further comprise an encoder control unit. The encoder control unit may be configured to control one or more units of encoder 200 as shown in FIG. 2. The encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other video cording protocol. For example, the encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AV1 , and / or any other video coding standard / format.

[0054] The encoder control unit may be configured to attempt to minimize (or reduce) the bitrate of bitstream 204 and / or maximize (or increase) the reconstructed video quality (e.g., within the constraints of a proprietary coding protocol, industry video coding standard, and / or any other video cording protocol). For example, the encoder control unit may be configured to attempt to minimize or reduce the bitrate of bitstream 204 such that the reconstructed video quality does not fall below a certain level / th reshold, and / or to maximize or increase the reconstructed video quality suchthat the bitrate of bitstream 204 does not exceed a certain level / th reshold. The encoder control unit may determine / control one or more of: partitioning of the pictures of video sequence 202 into blocks, whether a block is inter predicted by inter prediction unit 206 or intra predicted by intra prediction unit 208, a motion vector for inter prediction of a block, an intra prediction mode among a plurality of intra prediction modes for intra prediction of a block, filtering performed by filter(s) 220, and / or one or more transform types and / or quantization parameters applied by transform and quantization unit 214. The encoder control unit may determine / control one or more of the above based on a ratedistortion measure fora block or picture being encoded. The encoder control unit may determine / control one or more of the above to reduce the rate-distortion measure for a block or picture being encoded.

[0055] The prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and / or transform and / or quantization parameters, may be sent to entropy coding unit 218 to be further compressed (e.g, to reduce the bitrate). For example, entropy coding unit 218 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and / or syntax-based context-based binary arithmetic coding (SBAC) to achieve further compression. The prediction type, prediction information, and / or transform and / or quantization parameters may be packed with the prediction error to form bitstream 204.

[0056] Encoder 200 is merely an example and encoders different from encoder 200 and / or modified versions of encoder 200 may perform the methods and processes as described herein. For example, encoder 200 may comprise other components and / or arrangements. One or more of the components shown in FIG. 2 may be optionally included in encoder 200 (e.g, entropy coding unit 218 and / or filters(s) 220).

[0057] FIG. 3 shows an example decoder. A decoder 300 as shown in FIG. 3 may implement one or more processes described herein. Decoder 300 may decode a bitstream 302 into a decoded video sequence 304 for display and / or some other form of consumption. Decoder 300 may be implemented in video coding / decoding system 100 in FIG. 1 and / or in a computing, communication, or electronic device (e.g, desktop computer, laptop computer, tablet computer, smartphone, wearable device, television, camera, video gaming console, set-top box, and / or video streaming device). Decoder 300 may comprise an entropy decoding unit 306, an inverse transform and quantization (iTR + iQ) unit 308, a combiner 310, one or more filters 312, a buffer 314, an inter prediction unit 316, and / or an intra prediction unit 318.

[0058] Decoder 300 may comprise a decoder control unit configured to control one or more units of decoder 300. The decoder control unit may control the one or more units of decoder 300 such that bitstream 302 is decoded in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other communication protocol. For example, the decoder control unit may control the one or more units of decoder 300 such that the bitstream 302 is decoded in conformance with one or more of ITU-T H.263, AVC, H EVC, WC, VP8, VP9, AV1 , and / or any other video coding standard / format.

[0059] The decoder control unit may determine / control one or more of: whether a block is inter predicted by inter prediction unit 316 or intra predicted by intra prediction unit 318, a motion vector for inter prediction of a block, an intra prediction mode among a plurality of intra prediction modes for intra prediction of a block, filtering performed by filter(s)312, and / or one or more inverse transform types and / or inverse quantization parameters to be applied by inverse transform and quantization unit 308. One or more of the control parameters used by the decoder control unit may be packed in bitstream 302.

[0060] Entropy decoding unit 306 may entropy decode the bitstream 302. For example, entropy decoding unit 306 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and syntax-based context-based binary arithmetic coding (SBAC) to decompress the prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and transform and quantization parameters. Inverse transform and quantization unit 308 may inverse quantize and / or inverse transform the quantized transform coefficients to determine a decoded prediction error. Combiner 310 may combine the decoded prediction error with a prediction block to form a decoded block. The prediction block may be generated by intra prediction unit 318 or inter prediction unit 316 (e.g, as described above with respect to encoder 200 in FIG 2). Filter(s) 312 may filter the decoded block, for example, using a deblocking filter and / or a sample-adaptive offset (SAG) filter. Buffer 314 may store the decoded block for prediction of one or more other blocks in the same and / or different picture of the video sequence in bitstream 302. Decoded video sequence 304 may be output from filters) 312 as shown in FIG. 3.

[0061] Decoder 300 is merely an example and decoders different from decoder 300 and / or modified versions of decoder 300 may perform the methods and processes as described herein. For example, decoder 300 may have other components and / or arrangements. One or more of the components shown in FIG. 3 may be optionally included in decoder 300 (e.g, entropy decoding unit 306 and / or filters(s) 312).

[0062] Although not shown in FIGS. 2 and 3, each of encoder 200 and decoder 300 may further comprise an intra block copy unit in addition to inter prediction and intra prediction units. The intra block copy unit may perform / operate similar to an inter prediction unit but may predict blocks within the same picture. For example, the intra block copy unit may exploit repeated patterns that appear in screen content. The screen content may include computer generated text, graphics, animation, etc.

[0063] Video encoding and / or decoding may be performed on a block-by-block basis. The process of partitioning a picture into blocks may be adaptive based on the content of the picture. For example, larger block partitions may be used in areas of a picture with higher levels of homogeneity to improve coding efficiency.

[0064] A picture (e.g, in HEVC, or any other coding standard / format) may be partitioned into non-overlapping square blocks, which may be referred to as coding tree blocks (CTBs). The CTBs may comprise samples of a sample array. A CTB may have a size of 2nx2n samples, where n may be specified by a parameter of the encoding system. For example, n may be 4, 5, 6, or any other value. A CTB may have any other size. A CTB may be further partitioned by a recursive quadtree partitioning into coding blocks (CBs) of half vertical and half horizontal size. The CTB may form the root of the quadtree. A CB that is not split further as part of the recursive quadtree partitioning may be referred to as a leaf CB of the quadtree, and otherwise may be referred to as a non-leaf CB of the quadtree. A CB may have a minimum size specified by a parameter of the encoding system. For example, a CB may have a minimum size of 4x4,8x8, 16x16, 32x32, 64x64 samples, or any other minimum size. A CB may be further partitioned into one or more prediction blocks (PBs) for performing inter and / or intra prediction. A PB may be a rectangular block of samples on which the same prediction type / mode may be applied. A CB may also be further partitioned into intra sub-partitions (ISP) where the reconstructed samples of each sub-partition are available to generate the prediction of the next subpartition. For example, a CB may be split into 2 to 4 sub-partitions. For transformations, a CB may be partitioned into one or more transform blocks (TBs). A TB may be a rectangular block of samples that may determine / indicate an applied transform size.

[0055] FIG. 4 shows an example quadtree partitioning of a CTB 400. FIG. 5 shows an example quadtree 500 corresponding to the example quadtree partitioning of CTB 400 in FIG. 4. As shown in the examples of FIGS. 4 and 5, CTB 400 may first be partitioned into four CBs of half vertical and half horizontal size. Three of the resulting CBs of the first level partitioning of CTB 400 are leaf CBs. The three leaf CBs of the first level partitioning of CTB 400 are respectively labeled 7, 8, and 9 in FIGS. 4 and 5. The non-leaf CB of the first level partitioning of CTB 400 is partitioned into four sub-CBs of half vertical and half horizontal size. Three of the resulting sub-CBs of the second level partitioning of CTB 400 are leaf CBs. The three leaf CBs of the second level partitioning of CTB 400 are respectively labeled 0, 5, and 6 in FIGS. 4 and 5. Finally, The non-leaf CB of the second level partitioning of CTB 400 is partitioned into four leaf CBs of half vertical and half horizontal size. The four leaf CBs are respectively labeled 1, 2, 3, and 4 in FIGS. 4 and 5.

[0066] The example CTB 400 of FIG. 4 is partitioned into 10 leaf CBs respectively labeled 0-9, but may be partitioned into other quantities of leaf CBs. The 10 leaf CBs may correspond to 10 CB leaf nodes (e.g, 10 CB leaf nodes of quadtree 500 as shown in FIG. 5). In other examples, a CTB may be partitioned into a different number of leaf CBs.The resulting quadtree partitioning of CTB 400 may be scanned using a z-scan (e.g, left-to-right, top-to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label (e.g, indicator, index) of each CB leaf node in FIGS. 4 and 5 may correspond to the sequence order for encoding / decoding. For example, CB leaf node 0 may be encoded / decoded first and CB leaf node 9 may be encoded / decoded last. Although not shown in FIGS. 4 and 5, each CB leaf node may comprise one or more PBs and / or TBs.

[0067] A picture, in WC (or in any other coding standard / format), may be partitioned in a similar manner (such as in HEVC). A picture maybe first partitioned into non-overlapping square CTBs. The CTBs may then be partitioned, using a recursive quadtree partitioning, into CBs of half vertical and half horizontal size. A quadtree leaf node (e.g, in WC) may be further partitioned by a binary tree or ternary tree partitioning (or any other partitioning) into CBs of unequal sizes.

[0068] FIG. 6 shows example binary tree and ternary tree partitions. A binary tree partition may divide a parent block in half in either a vertical direction 602 or a horizontal direction 604. The resulting partitions may be half in size as compared to the parent block. In other examples, the resulting partitions may correspond to sizes that are less than and / or greater than half of the parent block size. A ternary tree partition may divide a parent block into three parts in either a vertical direction 606 ora horizontal direction 608. FIG. 6 shows an example in which the middle partition may be twice as large as the other two end partitions in the ternary tree partitions. In other examples, partitions may be ofother sizes relative to each other and to the parent block. Binary and ternary tree partitions are examples of multi-type tree partitioning. Multi-type tree partitions may comprise partitioning a parent block into other quantities of smaller blocks. The block partitioning strategy (e.g. , in VVC) may be referred to as a combination of quadtree and multi-type tree partitioning (quadtree + multi-type tree partitioning) because of the addition of binary and / or ternary tree partitioning to quadtree partitioning.

[0069] FIG. 7 shows an example of combined quadtree and multi-type tree partitioning of a CTB 700. FIG. 8 shows an example tree 800 corresponding to the combined quadtree and multi-type tree partitioning of CTB 700 shown in FIG. 7. In both FIGS. 7 and 8, quadtree splits are shown in solid lines and multi-type tree splits are shown in dashed lines. For ease of explanation, CTB 700 is shown with the same quadtree partitioning as the CTB 400 described in FIG. 4, and a description of the quadtree partitioning of CTB 700, which is similar to that for CTB 400, is omitted. The quadtree partitioning of the CTB 700 is merely an example and a CTB may be quadtree partitioned in a manner different from the CTB 700. Additional multi-type tree partitions of CTB 700 may be made relative to three leaf CBs shown in FIG. 4. The three leaf CBs in FIG. 4 that are shown in FIG. 7 as being further partitioned may be leaf CBs 5, 8, and 9. The three leaf CBs may be further partitioned using one or more binary and / or ternary tree partitions.

[0070] The leaf CB 5 of FIG. 4 may be partitioned into two CBs based on a vertical binary tree partitioning. The two resulting CBs may be leaf CBs respectively labeled 5 and 6 in FIGS. 7 and 8. The leaf CB 8 of FIG. 4 may be partitioned into three CBs based on a vertical ternary tree partition. Two of the three resulting CBs may be leaf CBs respectively labeled 9 and 14 in FIGS. 7 and 8. The remaining, non-leaf CB may be partitioned first into two CBs based on a horizontal binary tree partition. One of the two CBs may be a leaf CB labeled 10. The other of the two CBs may be further partitioned into three CBs based on a vertical ternary tree partition. The resulting three CBs may be leaf CBs respectively labeled 11, 12, and 13 in FIGS. 7 and 8. The leaf CB 9 of FIG. 4 may be partitioned into three CBs based on a horizontal ternary tree partition. Two of the three CBs may be leaf CBs respectively labeled 15 and 19 in FIGS. 7 and 8. The remaining, non-leaf CB may be partitioned into three CBs based on another horizontal ternary tree partition. The resulting three CBs may all be leaf CBs respectively labeled 16, 17, and 18 in FIGS. 7 and 8.

[0071] Altogether, CTB 700 may be partitioned into 20 leaf CBs respectively labeled 0-19. The 20 leaf CBs may correspond to 20 leaf nodes (e.g., 20 leaf nodes of tree 800 shown in FIG. 8). The resulting combination of quadtree and multi-type tree partitioning of the CTB 700 may be scanned using a z-scan (left-to-right, top-to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label of each CB leaf node in FIGS. 7 and 8 may correspond to the sequence order for encoding / decoding, with CB leaf node 0 encoded / decoded firstand CB leaf node 19 encoded / decoded last. Although not shown in FIGS. 7 and 8, it should be noted that each CB leaf node may comprise one or more PBs and / or TBs.

[0072] A coding standard / format (e.g., HEVC, VVC, or any other coding standard / format) may define various units (e.g., in addition to specifying various blocks (e.g., CTBs, CBs, PBs, TBs)). Blocks may comprise a rectangular area of samples in a sample array. Units may comprise the collocated blocks of samples from the different sample arrays (e.g., luma and chroma sample arrays) that form a picture as well as syntax elements and prediction data of the blocks. Acoding tree unit (CTU) may comprise the collocated CTBs of the different sample arrays and may form a complete entity in an encoded bitstream. A coding unit (CU) may comprise the collocated CBs of the different sample arrays and syntax structures used to code the samples of the CBs. A prediction unit (PU) may comprise the collocated PBs of the different sample arrays and syntax elements used to predict the PBs. A transform unit (TU) may comprise TBs of the different samples arrays and syntax elements used to transform the TBs.

[0073] A block may refer to any of a CTB, CB, PB, TB, CTU, CU, PU, and / or TU (e.g. , in the context of HEVC, WC, or any other coding format / standard). A block may be used to refer to similar data structures in the context of any video coding format / standard / protocol. For example, a block may refer to a macroblock in the AVC standard, a macroblock or a sub-block in the VP8 coding format, a superblock or a sub-block in the VP9 coding format, and / or a superblock or a sub-block in the AV1 coding format.

[0074] In intra prediction, samples of a block to be encoded (e.g, also referred to as a current block) may be predicted from samples in a line of samples immediately adjacent to the current block. For example, the line of samples may include samples of the column immediately adjacent to the left-most column of the current block and samples of the row immediately adjacent to the top-most row of the current block. The samples from the immediately adjacent column and row may be jointly referred to as reference samples. Each sample of the current block may be predicted (e.g, in an intra prediction mode) by projecting the position of the sample in the current block in a given direction to a point along the reference samples. The sample may be predicted by interpolating between the two closest reference samples of the projection point if the projection does not fall directly on a reference sample. A prediction error (e.g, referred to as a residual) may be determined for the current block based on differences between the predicted sample values and the original sample values of the current block.

[0075] Predicting samples and determining a prediction error based on a difference between the predicted samples and original samples may be performed (e.g, at an encoder) for a plurality of different intra prediction modes (e.g, including non-directional intra prediction modes). The encoder may select one of the plurality of intra prediction modes and its corresponding prediction error to encode the current block. The encoder may send an indication of the selected prediction mode and its corresponding prediction error to a decoder for decoding of the current block. The decoder may decode the current block by predicting the samples of the current block, using the intra prediction mode indicated by the encoder, and / or combining the predicted samples with the prediction error.

[0076] FIG. 9 shows an example set of reference samples 902 determined for intra prediction of a current block 904. Current block 904 may correspond to a block being encoded and / or decoded. Current block 904 may correspond to block 3 of partitioned CTB 700 as shown in FIG. 7. As described herein, the numeric labels 0-19 of the blocks of partitioned CTB 700 may correspond to the sequence order for encoding / decoding the blocks and may be used as such in the example of FIG. 9.

[0077] In some embodiments, reference samples 902 may include a line of samples (e.g, reference line #0908) immediately adjacent to current block 904 and include samples from a column and a row immediately adjacent to current block 904. For example, the line of samples may include reference samples to the left and / or above currentblock 904. In some embodiments, reference samples 902 may be obtained (or selected) from a reference line of multiple reference lines (MRL), which may include samples adjacent to current block 904 and also non-adjacent samples. The MRL may include reference lines (e.g. , reference lines 908-912) identified by corresponding reference line indices (e.g., also referred to as reference line numbers and maybe identified by a variable / parameter rljium) that indicate an i-th line of samples (e.g., / being rljium + 1) adjacent to current block 904 such that an rljium of 0 indicates the reference line immediate adjacent (or closest) to current block 904 (i.e, a 1stline of samples) and a higher value of rljium indicates a line of samples further away from current block 904. In other words, the reference line index (which may be equivalently referred to as reference line number) may indicate a specific reference line with a unique abscissa and / or ordinate with respect to current block 904 (e.g, from a top left sample of current block 904). For example, reference samples 902 for predicting current block 904 may be retrieved or determined from reference line #0 908 (i.e, rljium = 0), reference line #1 910 (i.e, rljium = 1), or reference line #2912 (i.e, rljium = 2). An encoder may select a reference line from a set of MRL (for example, including reference lines 908-912) and signal an MLR index (MRLJNDEX) in the bitstream to indicate the selected reference line. For example, the encoder may signal a codeword encoding the MRL index. The decoder may decode the codeword to determine the MRL index that identifies a specific reference line used in intra prediction of current block 904.

[0078] The set of MRL may be from an MRL list storing reference line indices (e.g, refjium) indicating / identifying the corresponding reference lines. In some examples, the MRL list may include non-adjacent reference lines such as reference lines 1, 3, 5, 7, 10, and / or 12. In this example, the MRL list may be an ordered list of reference line indices such as {0, 1, 3, 5, 7, 12), where the index 0 of the MRL list points (i.e, MRLJNDEX = 0) to reference line 0 (i.e, rljium = 0), index 1 of the MRL list (i.e, MRL_ / NDEX = 1) points to reference line 1 (i.e, rljium = 1), index 2 of the MRL list (i.e, MRLJNDEX = 2) points to reference line 3 (i.e, rljium = 3), index 3 of the MRL list (i.e, MRL_ / NDEX = 3) points to reference line 5 (i.e, rljium = 5), index 4 of the MRL list (i.e, MRLJNDEX = 4) points to reference line 7 (i.e, rl_num = 7), and index 5 of the MRL list (i.e, MRL_ / NDEX = 5) points to reference line 12 (i.e, rljium = 12).

[0079] In some embodiments, the MRL list may be a preconfigured list of reference line indices. For example, the same MRL list maybe predetermined and stored at both the encoder and the decoder such that the MRL list does not need to be signaled from the encoder to the decoder. In some embodiments, the MRL list may include a set of reference line indices selected at the encoder and the MRL list may be signaled in the bitstream to the decoder. For example, the MRL list may be signaled per CTU, per picture frame, per sequence of picture frame, or per video, etc.

[0080] In some embodiments, the encoder may signal a specific reference line (e.g, indicated by a reference line number / index) by signaling in the bitstream an index of the MRL list (e.g, MRL_INDEX), which may be identically determined at the decoder. The decoder may decode the MRL index to select a reference line index from the MRL list and use the reference line identified by the reference line index for intra prediction of current block 904.

[0081] For current block 904 that is w x h samples in size, reference samples 902 may comprise: 2w samples (or any other quantity of samples) of an i-th row (e.g, indicated by an MRL index) adjacent to the top-most row of current block 904, 2h samples (or any other quantity of samples) of the i-th column adjacent to the left-most column of current block904, and the top left neighboring corner sample(s) extending from the i-th column and i-th row with respect to current block 904. Current block 904 may be square, such that w = h = s. In other examples, a current block need not be square, such that w h. Available samples from neighboring blocks of current block 904 may be used for constructing the set of reference samples 902. Samples may not be available for constructing the set of reference samples 902, for example, if the samples lie outside the picture of the current block, the samples are part of a different slice of the current block (e.g ., if the concept of slices is used), and / or the samples belong to blocks that have been inter coded and constrained intra prediction is indicated. Intra prediction may not be dependent on inter predicted blocks, for example, if constrained intra prediction is indicated.

[0082] Samples that may not be available for constructing the set of reference samples 902 may comprise samples in blocks that have not already been encoded and reconstructed at an encoder and / or decoded at a decoder based on the sequence order for encoding / decoding. Restriction of such samples from inclusion in the set of reference samples 902 may allow identical prediction results to be determined at both the encoder and decoder. In the example of FIG. 9, samples from neighboring blocks 0, 1, 2, and 8 may be available to construct reference samples 902 given that these blocks are encoded and reconstructed at an encoder and decoded at a decoder prior to coding of current block 904. The samples from neighboring blocks 0, 1, 2, and 8 may be available to construct reference samples 902, for example, if there are no other issues (e.g., as mentioned above) preventing the availability of the samples from the neighboring blocks 0, 1, 2, and 8. The portion of reference samples 902 from neighboring block 6 may not be available due to the sequence order for encoding / decoding (e.g., because the block 6 may not have already been encoded and reconstructed at the encoder and / or decoded at the decoder based on the sequence order for encoding / decoding).

[0083] In some examples, unavailable samples from reference samples 902 may be filled with one or more of the available reference samples 902. For example, an unavailable reference sample may be filled with a nearest available reference sample. The nearest available reference sample may be determined by moving in a clock-wise direction through reference samples 902 from the position of the unavailable reference. The reference samples 902 may be filled with the mid-value of the dynamic range of the picture being coded, for example, if no reference samples are available.

[0084] Reference samples 902 may be filtered based on the size of current block 904 being coded and an applied intra prediction mode. FIG.9 shows an example determination of reference samples from an associated reference line for intra prediction of a block.

[0085] Samples of current block 904 may be intra predicted based on reference samples 902, for example, based on (e.g., after) determination and (optionally) filtering of reference samples 902. At least some (e.g., most) encoders / decoders may support a plurality of intra prediction modes in accordance with one or more video coding standards. For example, HEVC supports 35 intra prediction modes, including a planar mode, a direct current (DC) mode, and 33 angular modes. WC supports 67 intra prediction modes, including a planar mode, a DC mode, and 65 angular modes. Planar and DC modes may be used to predict smooth and gradually changing regions of a picture. Angular modes may be used to predict directional structures in regions of a picture. Any quantity of intra prediction modes may be supported.

[0086] FIGS. 10A and 10B show example intra prediction modes. FIG. 10A shows 35 intra prediction modes, such as supported by HEVC. The 35 intra prediction modes may be indicated / identified by indices 0 to 34. Prediction mode 0 may correspond to planar mode. Prediction mode 1 may correspond to DC mode. Prediction modes 2-34 may correspond to angular modes. Prediction modes 2-18 may be referred to as horizontal prediction modes because the principal source of prediction is in the horizontal direction. Prediction modes 19-34 may be referred to as vertical prediction modes because the principal source of prediction is in the vertical direction.

[0087] FIG. 10B shows 67 intra prediction modes, such as supported by WC. The 67 intra prediction modes may be indicated / identified by indices 0 to 66. Prediction mode 0 may correspond to planar mode. Prediction mode 1 corresponds to DC mode. Prediction modes 2-66 may correspond to angular modes. Prediction modes 2-34 may be referred to as horizontal prediction modes because the principal source of prediction is in the horizontal direction. Prediction modes 35-66 may be referred to as vertical prediction modes because the principal source of prediction is in the vertical direction. Some of the intra prediction modes illustrated in FIG. 10B may be adaptively replaced by wide- angle directions because blocks in WC need not be squares.

[0088] FIG. 11 shows a current block 904 and corresponding reference samples 902 from FIG. 9. To further describe how intra prediction modes are applied to determine a prediction (e.g., a prediction block) of current block 904, FIG. 11 shows current block 904 and reference samples 902, from a reference line among a set of multiple reference lines (MRL) 908-910, in a two-dimensional x, y plane, where a sample may be referenced as p[x] [y] . To simplify the prediction process, reference samples 902 may be placed in two, one-dimensional arrays. The reference samples 902 belonging to a reference line I from the set of MRL 908-912, above the current block 904, may be placed in the onedimensional array re / ) [x]: re / j[x] = pH + x]H], (x > 0). (1)The reference samples 902 belonging to reference line I, to the left of current block 904, may be placed in the onedimensional array ref2[y] ref2\y] = pH]H + y (y > 0). (2)The variable I represents how many lines away the selected reference line is from current block. For example, if reference line #0908 is selected, then I is set to 1 to indicate the reference line adjacent to current block 904. For example, if reference line #1 910 is selected, then I is set to 2. For example, if reference line #2912 is selected, then I is set to 3.

[0089] The prediction process may comprise determination of a predicted sample p [x] [y] (e.g., a predicted value) at a location [x] [y] in current block 904. For planar mode, a sample at the location [x] [y] in current block 904 may be predicted by determining / calculati ng the mean of two interpolated values. The first of the two interpolated values may be based on a horizontal linear interpolation at the location [x] [y] in current block 904. The second of the two interpolated values may be based on a vertical linear interpolation at location [x] [y] in current block 904. The predicted sample p [x] [y] in current block 904 may be determined / calcu lated as:where h[x][y] = (5 - x - 1) ■ ref2y] + (x + 1) ■ re / i[s] (4) may be the horizonal linear interpolation at the location [x] [y] in current block 904 andmay be the vertical linear interpolation at the location [x] [y] in current block 904. s may be equal to a length of a side (e.g., a number of samples on a side) of the current block 904.

[0090] For DC mode, a sample at a location [x] [y] in current block 904 may be predicted by the mean of the reference samples 902. The predicted sample p[x] [y] in current block 904 may be determined / calculated as:

[0091] For angular modes, a sample ata location [x][y] in current block 904 may be predicted by projecting the location [x] [y] in a direction specified by a given angular mode to a point on the horizontal or vertical line of samples comprising reference samples 902. The sample at the location [x] [y] may be predicted by interpolating between the two closest reference samples of the projection point if the projection does not fall directly on a reference sample. The direction specified by the angular mode may be given by an angle <p defined relative to the y-axis for vertical prediction modes (e.g, modes 19-34 in HEVC and modes 35-66 in VVC). The direction specified by the angular mode may be given by an angle cp defined relative to the x-axis for horizontal prediction modes (e.g, modes 2-18 in HEVC and modes 2-34 in WC).

[0092] FIG. 12 shows an example applying an intra prediction mode (e.g, an angular mode such as vertical prediction mode 906) for prediction of a current block 904. FIG. 12 specifically shows prediction of a sample at a location [x] [y] in current block 904 for a vertical prediction mode 906. Vertical prediction mode 906 may be given by an angle cp with respect to the vertical axis. The location [x] [y] in current block 904, in vertical prediction modes, may be projected to a point (e.g. , referred to as a projection point) on the horizontal line of reference samples re fa [x] . The reference samples 902 are only partially shown in FIG. 12 and shown as being from a reference line with reference line index of 0 for ease of illustration. Reference samples 902 may be from another reference line of the set of MRL, as explained in FIG. 9. As shown in FIG. 12, the projection point on the horizontal line of reference samples rej [x] may not be exactly on a reference sample. A predicted sample p [x] [y] in current block 904 may be determined / calculated by linearly interpolating between the two reference samples, for example, if the projection point falls at a fractional sample position between two reference samples. The predicted sample p[x][y] may be determined / calculated as: p[x][y] = (1 - if) ■ refa [x 4- + 1 ] + if■ refa [x + f + 2], (7) if may be the integer part of the horizontal displacement of the projection point relative to the location [x] [y] . f may be determined / calculated as a function of the tangent of the angle (p of the vertical prediction mode 906 as:ii = L(y + 1) - tan ^J. (8) ifmay be the fractional part of the horizontal displacement of the projection point relative to the location [x] [y] and may be determined / calculated as: if= ((y + 1) -tan <p) - L(y + 1) ■ tan ^J, (9) where [ ■ ] is the integer floor function.

[0093] For horizontal prediction modes, a location [x][y] of a sample in current block 904 may be projected onto the vertical line of reference samples ref2[y ] . A predicted sample p [x] [y]for horizontal prediction modes may be determined / calculated as: p[x][y] = (1 - if) ■ re / 2[y + k + 1] + if ref2y + i, + 2], (10) ii may be the integer part of the vertical displacement of the projection point relative to the location [x] [y] . i j may be determined / calculated as a function of the tangent of the angle <p of the horizontal prediction mode as: ii = L(x + 1) ■ tan (joj. (11) if may be the fractional part of the vertical displacement of the projection point relative to the location [x] [y], ifmay be determined / calculated as:where [ ■ ] is the integer floor function.

[0094] The interpolation functions given by Equations (7) and (10) may be implemented by an encoder and / or a decoder (e.g., encoder 200 in FIG. 2 and / or decoder 300 in FIG. 3). The interpolation functions may be implemented by finite impulse response (FIR) filters. For example, the interpolation functions may be implemented as a set of two-tap FIR filters. The coefficients of the two-tap FIR filters may be respectively given by (1 -if) and if. The predicted sample p[x] [y], in angular intra prediction, may be calculated with some predefined level of sample accuracy (e.g., 1 / 32 sample accuracy, or accuracy defined by any other metric). For 1 / 32 sample accuracy, the set of two-tap FIR interpolation filters may comprise up to 32 different two-tap FIR interpolation filters — one for each of the 32 possible values of the fractional part of the projected displacement if. In other examples, different levels of sample accuracy may be used.

[0095] In some examples, the FIR filters may be used for predicting chroma samples and / or luma samples. For example, the two-tap interpolation FIR filter may be used for predicting chroma samples and a same and / or a different interpolation technique / filter may be used for luma samples. For example, a four-tap FIR filter may be used to determine a predicted value of a luma sample. Coefficients of the four tap FIR filter may be determined based on if(e.g., similar to the two-tap FIR filter). For 1 / 32 sample accuracy, a set of 32 different four-tap FIR filters may comprise up to 32 different four-tap Fl R filters — one for each of the 32 possible values of the fractional part of the projected displacement if. In other examples, different levels of sample accuracy may be used. The set of four-tap FIR filters may be stored in a look-up table (LUT) and referenced based on if. A predicted sample p[x] [y] , for vertical prediction modes, may be determined based on the four-tap FIR filter as:3 (13) p[ ][y] = y fT[i] ■ ref][x + ildx + i], i=0 where fT ], 7= 0. . .3, may be the filter coefficients, and Idx is integer displacement. A predicted sample p [x] [y ] , for horizontal prediction modes, may be determined based on the four-tap FIR filter as:

[0096] Supplementary reference samples may be determined / constructed if the location [x] [y] of a sample in current block 904 to be predicted is projected to a negative x coordinate. The location [x] [y] of a sample may be projected to a negative x coordinate, for example, if negative vertical prediction angles cp are used. The supplementary reference samples may be determined / constructed by projecting the reference samples in ref2[y] in the vertical line of reference samples 902 to the horizontal line of reference samples 902 using the negative vertical prediction angle cp. Supplementary reference samples may be similarly determined / constructed, for example, if the location [x] [y] of a sample in current block 904 to be predicted is projected to a negative y coordinate. The location [x] [y] of a sample may be projected to a negative y coordinate, for example, if negative horizontal prediction angles cp are used. The supplementary reference samples maybe determined / constructed by projecting the reference samples in ref^x] on the horizontal line of reference samples 902 to the vertical line of reference samples 902 using the negative horizontal prediction angle cp.

[0097] An encoder may determine / predict samples of a current block being encoded (e.g, current block 904) for a plurality of intra prediction modes (e.g., using one or more of the functions described herein). For example, an encoder may determine / predict samples of a current block for each of 35 intra prediction modes in HEVC and / or 67 intra prediction modes in WC. The encoder may determine, for each intra prediction mode applied, a corresponding prediction error for the current block based on a difference (e.g, sum of squared differences (SSD), sum of absolute differences (SAD), or sum of absolute transformed differences (SATD)) between the prediction samples, generated from reference samples 902 of a reference line from a set of MRL, determined for the intra prediction mode and the original samples of the current block. The encoder may determine / selectone of the intra prediction modes to encode the current block based on the determined prediction errors. For example, the encoder may determine / select one of the intra prediction modes that results in the smallest prediction error for the current block. In some examples, the encoder may determine / select the intra prediction mode and the associated reference line to encode the current block based on a rate-distortion measure (e.g, Lagrangian rate-distortion cost) determined using the prediction errors. The encoder may signal, in the bitstream to a decoder for decoding of the current block, an indication of the determined / selected intra prediction mode and an indication of the associated MRL index (which may indicate a reference line index). The encoder may also signal in the bitstream to the decoder a corresponding prediction error (e.g, residual) of the intra prediction mode.

[0098] A decoder may determine / predict samples of a current block being decoded (e.g. , current block 904) for an intra prediction mode. For example, a decoder may receive an indication of a reference line (e.g., a reference line index or an MRL index associated with the reference line index) and an intra prediction mode (e.g., an angular intra prediction mode) from an encoder for a current block. The decoder may retrieve a set of reference samples and perform intra prediction based on the MRL index and the intra prediction mode indicated by the encoder for the current block in a similar manner (e.g., as described above for the encoder). For example, the decoder may obtain the reference samples from a reference line indicated / identified by the decoded MRL index. The decoder may add predicted values of the samples (e.g, determined based on the intra prediction mode) of the current block to a residual of the current block to reconstruct the current block. In some examples, a decoder need not receive an indication of an angular intra prediction mode from an encoder for a current block. Instead, the decoder may determine an intra prediction mode through other decoder-side means (e.g, by applying template-based intra mode derivation (TIMD) tool / technique).

[0099] While various examples herein correspond to intra prediction modes in HEVC and WC, the methods, devices, and systems as described herein may be applied to / used for other intra prediction modes (e.g, as used in other video coding standards / formats, such as VP8, VP9, AV1, etc.).

[0100] Intra prediction may exploit correlations between spatially neighboring samples in the same picture of a video sequence to perform video compression. Inter prediction is another coding tool that may be used to perform video compression. Inter prediction may exploit correlations in the time domain between blocks of samples in different pictures of a video sequence. For example, an object may be seen across multiple pictures of a video sequence. The object may move (e.g, by some translation and / or affine motion) or remain stationary across the multiple pictures. A current block of samples in a current picture being encoded may have / be associated with a corresponding block of samples in a previously decoded picture. The corresponding block of samples may accurately predict the current block of samples. The corresponding block of samples may be displaced from the current block of samples, for example, due to movement of the object, represented in both blocks, across the respective pictures of the blocks. The previously decoded picture may be a reference picture. The corresponding block of samples in the reference picture may be a reference block for motion compensated prediction. An encoder may use a block matching technique to estimate the displacement (or motion) of the object and / or to determine the reference block in the reference picture.

[0101] Similar to intra prediction, an encoder may determine a difference between a current block and a prediction for a current block. An encoder may determine a difference, for example, based on / after determining / generating a prediction for a current block (e.g, using inter prediction). The difference may be a prediction error (e.g, a residual). The encoder may store and / or send (e.g, signal), in / via a bitstream, the prediction error and / or other related prediction information. The prediction error and / or other related prediction information may be used for decoding and / or other forms of consumption. A decoder may decode the current block by predicting the samples of the current block (e.g, by using the related prediction information) and combining the predicted samples with the prediction error.

[0102] FIG. 13A shows an example of inter prediction. The inter prediction may be performed fora current block 1300 in a current picture 1302 being encoded. An encoder (e.g, encoder 200 as shown in FIG. 2) may perform interprediction to determine and / or generate a reference block 1304 in a reference picture 1306. Reference block 1304 may be used to predict the current block 1300. Reference pictures (e.g, reference picture 1306) may be prior decoded pictures available at the encoder and / or a decoder. Availability of a prior decoded picture may depend / be based on whether the prior decoded picture is available in a decoded picture buffer, at the time, current block 1300 is being encoded and / or decoded. The encoder may search the one or more reference pictures 1306 for a block (e.g., a candidate reference block) that is similar (or substantially similar) to current block 1300. The encoder may determine the best matching block from the blocks (e.g., candidate reference blocks) tested during the searching process. The best matching block may be a reference block 1304. The encoder may determine that reference block 1304 is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a ratedistortion criterion (e.g, Lagrangian rate-distortion cost). The one or more cost criteria may be based on a difference (e.g, SSD, SAD, and / or SATD) between prediction samples of reference block 1304 and original samples of current block 1300.

[0103] The encoder may search for reference block 1304 within a reference region (e.g, a search range 1308). The reference region (e.g, a search range 1308) may be positioned around a collocated block (or position) 1310, of current block 1300, in reference picture 1306. Collocated block 1310 may have a same position in the reference picture 1306 as the current block 1300 in the current picture 1302. The reference region (e.g, search range 1308) may at least partially extend outside of reference picture 1306. Constant boundary extension may be used, for example, if the reference region (e.g, search range 1308) extends outside of reference picture 1306. The constant boundary extension may be used such that values of the samples in a row or a column of reference picture 1306, immediately adjacent to a portion of the reference region (e.g, search range 1308) extending outside of reference picture 1306, may be used for sample locations outside of reference picture 1306. A subset of potential positions, or all potential positions, within the reference region (e.g, search range 1308) may be searched for reference block 1304. The encoder may utilize one or more search implementations to determine and / or generate the reference block 1304. For example, the encoder may determine a set of candidate search positions based on motion information of neighboring blocks (e.g, a motion vector 1312) to the current block 1300.

[0104] One or more reference pictures may be searched by the encoder during inter prediction to determine and / or generate the best matching reference block. The reference pictures searched by the encoder may be included in (e.g, added to) one or more reference picture lists. For example, in HEVC and WC (and / or in one or more other communication protocols), two reference picture lists may be used (e.g, a reference picture list 0 and a reference picture list 1). A reference picture list may include one or more pictures. The reference picture 1306 of reference block 1304 may be indicated by a reference index pointing into a reference picture list comprising reference picture 1306.

[0105] FIG. 13B shows an example motion vector. A displacement between reference block 1304 and current block 1300 may be interpreted as an estimate of the motion between reference block 1304 and current block 1300 across their respective pictures. The displacement may be represented by a motion vector 1312. For example, motion vector 1312 may be indicated by a horizontal component (MVx) and a vertical component (MVy) relative to the position ofcurrent block 1300. A motion vector (e.g, motion vector 1312) may have fractional or integer resolution. A motion vector with fractional resolution may point between two samples in a reference picture to provide a better estimation of the motion of current block 1300. For example, a motion vector may have 1 / 2, 1 / 4, 1 / 8, 1 / 16, 1 / 32, or any other fractional sample resolution. Interpolation between the two samples at integer positions may be used to generate a reference block and its corresponding samples at fractional positions, for example, if a motion vector points to a noninteger sample value in the reference picture. The interpolation may be performed by a filter with two or more taps.

[0106] The encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between reference block 1304 and current block 1300. The encoder may determine the difference between reference block 1304 and current block 1300, for example, based on / after reference block 1304 is determined and / or generated, using inter prediction, for current block 1300. The difference may be a prediction error (e.g, a residual). The encoder may store and / or send (e.g, signal), in / via a bitstream, the prediction error and / or related motion information. The prediction error and / or the related motion information may be used for decoding (e.g, decoding current block 1300) and / or other forms of consumption. The motion information may comprise the motion vector 1312 and a reference indicator / index. The reference indicator may indicate the reference picture 1306 in a reference picture list. In other examples, the motion information may comprise an indication of motion vector 1312 and / or an indication of the reference indicator / index. The reference indicator may indicate reference picture 1306 in the reference picture list comprising reference picture 1306. A decoder may decode current block 1300 by determining and / or generating the reference block 1304, which may correspond to / form (e.g, be considered as) a prediction of the current block 1300. The decoder may determine and / or generate the reference block 1304, for example, based on the related motion information. The decoder may decode current block 1300 based on combining the prediction (e.g, a reference block) with the prediction error (e.g, a residual block).

[0107] Inter prediction, as shown in FIG. 13A, may be performed using one reference picture 1306 as a source of a prediction for current block 1300. Inter prediction based on a prediction of a current block using a single picture may be referred to as uni-prediction.

[0108] Inter prediction of a current block, using bi-prediction, may be based on two pictures (e.g, the source of prediction may be from the two pictures). Bi-prediction may be useful, for example, if a video sequence comprises fast motion, camera panning, zooming, and / or scene changes. Bi-prediction also may be useful to capture fade outs of one scene or fade outs from one scene to another, where two pictures may effectively be displayed simultaneously with different levels of intensity.

[0109] One or both of uni-prediction and bi-prediction may be avai lable / used for performing inter prediction (e.g, at an encoder and / or at a decoder). Performing a specific type of inter prediction (e.g, uni-prediction and / or bi-prediction) may depend on a slice type of current block. For example, for P slices, only uni-prediction may be available / used for performing inter prediction. For B slices, either uni-prediction or bi-prediction may be available / used for performing inter prediction. An encoder may determine and / or generate a reference block, for predicting a current block, from a reference picture list 0, for example, if the encoder is using uni-prediction. An encoder may determine and / or generatea first reference block, for predicting a current block, from a reference picture list 0 and determine and / or generate a second reference block, for predicting the current block, from a reference picture list 1, for example, if the encoder is using bi-prediction.

[0110] FIG. 14 shows an example of bi-prediction. Two reference blocks 1402 and 1404 may be used to predict a current block 1400. Reference block 1402 may be in a reference picture of one of reference picture list 0 or reference picture list 1. Reference block 1404 may be in a reference picture of another one of reference picture list 0 or reference picture list 1. As shown in FIG. 14, reference block 1402 may be in a first picture that precedes (e.g, in time) a current picture of current block 1400, and the reference block 1404 may be in a second picture that succeeds (e.g, in time) the current picture of current block 1400. The first picture may precede the current picture in terms of a picture order count (ROC). The second picture may succeed the current picture in terms of the POC. In other examples, the reference pictures may both precede or both succeed the current picture in terms of POC. A POC may be / indicate an order in which pictures are output (e.g, from a decoded picture buffer). A POC may be / indicate an order in which pictures are generally intended to be displayed. Pictures that are output may not necessarily be displayed but may undergo different processing and / or consumption (e.g, transcoding). The two reference blocks determined and / or generated using / for biprediction may correspond to (e.g, be comprised in) a same reference picture. The reference picture may be included in both the reference picture list 0 and the reference picture list 1 , for example, if the two reference blocks correspond to the same reference picture.

[0111] A configurable weight and / or offset value may be applied to one or more inter prediction reference blocks. An encoder may enable the use of weighted prediction using a flag in a picture parameter set (PPS). The encoder may send / signal the weight and / or offset parameters in a slice segment header for current block 1400. Different weight and / or offset parameters may be sent / signaled for luma and / or chroma components.

[0112] The encoder may determine and / or generate the reference blocks 1402 and 1404 for the current block 1400 using inter prediction. The encoder may determine a difference between current block 1400 and each of reference blocks 1402 and 1404. The differences may be prediction errors or residuals. The encoder may store and / or send / signal, in / via a bitstream, the prediction errors and / or their respective related motion information. The prediction errors and their respective related motion information may be used for decoding and / or other forms of consumption.

[0113] The motion information for reference block 1402 may comprise a motion vector 1406 and / or a reference indicator / index. The reference indicator may indicate a reference picture, of the reference block 1402, in a reference picture list. In some examples, the motion information for reference block 1402 may comprise an indication of motion vector 1406 and / or an indication of the reference index. The reference index may indicate the reference picture, of reference block 1402, in the reference picture list.

[0114] The motion information for reference block 1404 may comprise a motion vector 1408 and / or a reference index / indicator. The reference indicator may indicate a reference picture, of the reference block 1404, in a reference picture list. The motion information for reference block 1404 may comprise an indication of motion vector 1408 and / oran indication of the reference index. The reference index may indicate the reference picture, of the reference block 1404, in the reference picture list.

[0115] A decoder may decode current block 1400 by determining and / or generating the reference blocks 1402 and 1404. The decoder may determine and / or generate the reference blocks 1402 and 1404, for example, based on the respective related motion information for the reference blocks 1402 and 1404. The reference blocks 1402 and 1404 may correspond to / form (e.g, be considered as) the prediction (e.g, used to generate a prediction block) of the current block 1400. The decoder may decode the current block 1400 based on combining the prediction with the prediction errors.

[0116] Motion information may be predictively coded, for example, before being stored and / or sent / signaled in / via a bit stream (e.g, in H EVC, WC, and / or other video coding standards / formats / protocols). The motion information for a current block may be predictively coded based on motion information of one or more blocks neighboring the current block. The motion information of the neighboring block(s) may often correlate with the motion information of the current block because the motion of an object represented in the current block is often the same as (or similar to) the motion of objects in the neighboring block(s). Motion information prediction techniques (such as those in HEVC and WC) may comprise advanced motion vector prediction (AMVP) and / or inter prediction block merging (e.g, merge mode).

[0117] An encoder (e.g, encoder 200 as shown in FIG. 2), may code a motion vector. The encoder may code the motion vector (e.g, using AMVP) as a difference between a motion vector of a current block being coded and a motion vector predictor (MVP). An encoder may determine / select the MVP from a list of candidate MVPs. The candidate MVPs may be / correspond to previously decoded motion vectors of neighboring blocks in the current picture of the current block, and / or blocks at or near the collocated position of the current block in other reference pictures. The encoder and / or a decoder may reciprocally generate and / or determine the list of candidate MVPs.

[0118] The encoder may determine / select an MVP from the list of candidate MVPs. Then, the encoder may send / signal, in / via a bitstream, an indication of the selected MVP and / or a motion vector difference (MVD). The encoder may indicate the selected MVP in the bitstream using an index / indicator. The index may indicate the selected MVP in the list of candidate MVPs. The MVD may be determined / calculated based on a difference between the motion vector of the current block and the selected MVP. For example, for a motion vector (e.g, comprising a horizontal component (MVx) and a vertical component (MVy)) that indicates a position relative to a position of the current block being coded, the MVD may be represented by two components MVD, and MVDy. MVD, and MVDymay be determined / calculated as:MVD, = MV, - MVP„ (15)MVDy= MVy- MVPy(16)MVDx and MVDy may respectively represent horizontal and vertical components of the MVD. MVPx and MVPy may respectively represent horizontal and vertical components of the MVP.

[0119] A decoder (e.g, decoder 300 as shown in FIG. 3) may decode the motion vector by adding the MVD to the MVP indicated in / via the bitstream. The decoder may decode the current block by determining and / or generating thereference block. The decoder may determine and / or generate the reference block, for example, based on the decoded motion vector. The reference block may correspond to / form (e.g, be considered as) the prediction of the current block (e.g, a prediction block). The decoder may decode the current block by combining the prediction with the prediction error.

[0120] The list of candidate MVPs (e.g., in HEVC, WC, and / or one or more other communication protocols), for AMVP, may comprise two or more candidates (e.g., candidates A and B). Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate MVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being coded; one (or any other quantity of) temporal candidate MVP determined / derived from two (or any other quantity of) temporal, co-located blocks (e.g, if both of the two spatial candidate MVPs are not available or are identical); and / or zero motion vector candidate MVPs (e.g, if one or both of the spatial candidate MVPs or temporal candidate MVPs are not available). Other quantities of spatial candidate MVPs, spatial neighboring blocks, temporal candidate MVPs, and / or temporal, co-located blocks may be used for the list of candidate MVPs.

[0121] FIG. 15A shows example spatial candidate neighboring blocks for a current block. For example, five (or any other quantity of) spatial candidate neighboring blocks may be located relative to a current block 1500 being encoded. The five spatial candidate neighboring blocks may be A0, A1, B0, B1 , and B2. FIG. 15B shows temporal, co-located blocks for the current block. For example, two (or any other quantity of) temporal, co-located blocks may be located relative to current block 1500 being coded. The two temporal, co-located blocks may be CO and C1. The two temporal, co-located blocks may be in one or more reference pictures that may be different from the current picture of current block 1500.

[0122] An encoder (e.g, encoder 200 as shown in FIG. 2) may code a motion vector using inter prediction block merging (e.g, a merge mode). For example, the encoder (e.g, using merge mode) may reuse the same motion information of a neighboring block (e.g, one of neighboring blocks A0, A1, B0, B1, and B2) for inter prediction of a current block. For example, the encoder (e.g, using merge mode) may reuse the same motion information of a temporal, co-located block (e.g, one of temporal, co-located blocks CO and C1) for inter prediction of a current block. An MVD need not be sent (e.g, indicated, signaled) for the current block because the same motion information as that of a neighboring block or a temporal, co-located block may be used for the current block (e.g, at the encoder and / or a decoder). A signaling overhead for sending / signaling the motion information of the current block may be reduced because the MVD need not be indicated for the current block. The encoder and / or the decoder may reciprocally generate a candidate list of motion information from neighboring blocks or temporal, co-located blocks of the current block (e.g, in a manner similar to AMVP). The encoder may determine to use (e.g, inherit) motion information, of one neighboring block or one temporal, co-located block in the candidate list, for predicting motion information of the current block being coded. The encoder may signal / send, in / via a bitstream, an indication of the determined motion information from the candidate list. For example, the encoder may signal / send an indicator / index. The index may indicate thedetermined motion information in the list of candidate motion information. The encoder may signal / send the index to indicate the determined motion information.

[0123] A list of candidate motion information for merge mode (e.g. , in H EVC, WC, or any other coding formats / standards / protocols) may comprise: up to four (or any other quantity of) spatial merge candidates derived / determined from five (or any other quantity of) spatial neighboring blocks (e.g., as shown in FIG. 15A); one (or any other quantity of) temporal merge candidate derived from two (or any other quantity of) temporal, co-located blocks (e.g., as shown in FIG. 15B); and / or additional merge candidates comprising bi-predictive candidates and zero motion vector candidates. In some examples, the spatial neighboring blocks and the temporal, co-located blocks used for merge mode may be the same as the spatial neighboring blocks and the temporal, co-located blocks used for AMVP.

[0124] Inter prediction may be performed in other ways and variants than those described herein. For example, motion information prediction techniques other than AMVP and merge mode may be used. While various examples herein correspond to inter prediction modes, such as used in HEVC and WC, the methods, devices, and systems as described herein may be applied to / used for other inter prediction modes (e.g., as used for other video coding standards / formats such as VP8, VP9, AV1, etc.). History based motion vector prediction (HMVP), combined intra / inter prediction mode (CUP), and / or merge mode with motion vector difference (MMVD) (e.g., as described in WC) may be performed / used and are within the scope of the present disclosure.

[0125] A block matching operation (or technique) may be applied / used (e.g., in inter prediction) to determine a reference block in a different picture than that of a current block being coded (e.g., encoded and / or decoded). A block matching operation also may be applied / used to determine a reference block in a same picture as that of a current block being coded. The reference block, in a same picture as that of the current block, as determined using block matching may often not accurately predict the current block (e.g., for camera captured videos). Prediction accuracy for screen content videos may not be similarly impacted, for example, if a reference block in the same picture as that of the current block is used for encoding. Screen content videos may comprise, for example, computer generated text, graphics, animation, etc. Screen content videos may comprise (e.g, may often comprise) repeated patterns (e.g, repeated patterns of text and / or graphics) within the same picture. Using a reference block (e.g, as determined using block matching), in a same picture as that of a current block being encoded, may provide efficient compression for screen content videos.

[0126] A prediction technique may be used (e.g, in HEVC, WC, and / or any other coding standards / formats / protocols) to exploit correlation between blocks of samples within a same picture (e.g, of screen content videos). The prediction technique may be intra block copy (IBC) or current picture referencing (CPR). An encoder may apply / use a block matching technique (e.g, similar to inter prediction) to determine a displacement vector (e.g, a block vector (BV)). The BV may indicate a relative position of a reference block (e.g, in accordance with intra block compensated prediction), that best matches the current block, from a position of the current block. For example, the relative position of the reference block may be a relative position of a top-left corner (or any other point / sample) of the reference block. The BV may indicate a relative displacement from the current block to the reference block that bestmatches the current block. The encoder may determine the best matching reference block from blocks tested during a searching process (e.g. , in a manner similar to that used for inter prediction). The encoder may determine that a reference block is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a rate-distortion criterion (e.g., Lagrangian rate-distortion cost). The one or more cost criteria may be based on, for example, one or more differences (e.g., an SSD, an SAD, an SATD, and / or a difference determined based on a hash function) between the prediction samples of the reference block and the original samples of the current block. A reference block may correspond to / comprise prior decoded blocks of samples (e.g., reconstructed samples) of the current picture. The reference block may comprise decoded blocks of samples of the current picture prior to being processed by in-loop filtering operations (e.g, deblocking and / or SAO filtering).

[0127] FIG. 16 shows an example of IBC (e.g, an IBC mode). The example shown in FIG. 16 may correspond to screen content. The rectangular portions / sections with arrows beginning at their boundaries may be the current blocks being encoded. The rectangular portions / sections that the arrows point to may be the reference blocks for predicting the respective current blocks.

[0128] A reference block may be determined and / or generated, for a current block, using IBC. The encoder may determine a difference (e.g, a corresponding sample-by-sample difference) between the reference block and the current block. The difference may be a prediction error or residual. The encoder may store and / or send / signal, in / via a bitstream the prediction error and / or related prediction information. The prediction error and / or the related prediction information may be used for decoding and / or other forms of consumption. The prediction information may comprise a BV. The prediction information may comprise an indication of the BV. A decoder (e.g, decoder 300 as shown in FIG. 3), may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the current block, for example, based on the prediction information (e.g, the BV). The reference block may correspond to / form (e.g, be considered as) the prediction (e.g, a prediction block) of the current block. The decoder may decode the current block by combining the prediction (e.g, prediction block) with the prediction error (e.g, residual or residual block).

[0129] A BV may be predictively coded (e.g, in HEVC, WC, and / or any other coding standards / formats / protocols) before being stored and / or sent / signaled in / via a bitstream. For example, the BV for a current block may be predictively coded based on a BV of one or more blocks neighboring the current block. For example, an encoder may predictively code a BV using the merge mode (e.g, in a manner similar to as described herein for inter prediction), AMVP (e.g, as described herein for inter prediction), or a technique similar to AMVP. The technique similar to AMVP may be BV prediction and difference coding (or AMVP for IBC).

[0130] An encoder (e.g, encoder 200 as shown in FIG. 2) performing BV prediction and coding may code a BV as a difference between the BV of a current block being coded and a block vector predictor (BVP). An encoder may select / determine the BVP from a list of candidate BVPs. The candidate BVPs may comprise / correspond to previously decoded BVs of neighboring blocks in the current picture of the current block. The encoder and / or a decoder may reciprocally generate or determine the list of candidate BVPs.

[0131] The encoder may send / signal, in / via a bitstream, an indication of the selected BVP and a block vector difference (BVD). The encoder may indicate the selected BVP in the bitstream using an index / i ndicator. The index may indicate (e.g., point to) the selected BVP in the list of candidate BVPs. The BVD may be determined / calculated based on a difference between a BV of the current block and the selected BVP. For example, for a BV (e.g., represented by a horizontal component (BVx) and a vertical component (BVy)) that indicates a position relative to a position of the current block being coded, the BVD may be represented by two components BVDXand BVDy. BVDTand BVDymay be determined / calculated as:BVDX= BVX- BVPX, (17)BVDy= BVy- BVPy. (18)BVDx and BVDy may respectively represent horizontal and vertical components of the BVD. BVPx and BVPy may respectively represent horizontal and vertical components of the BVP. A decoder (e.g., decoder 300 as shown in FIG. 3), may decode the BV by adding the BVD to the BVP indicated in / via the bitstream. The decoder may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the reference block, for example, based on the decoded BV. The reference block may correspond to / form (e.g., be considered as) the prediction (e.g., a prediction block) of the current block. The decoder may decode the current block by combining the prediction (e.g., the prediction block) with the prediction error (e.g., residual or residual block).

[0132] A same BV as that of a neighboring block may be used for the current block and a BVD need not be separately signaled / sent for the current block, such as in the merge mode. A BVP (in the candidate BVPs), which may correspond to a decoded BV of the neighboring block, may itself be used as a BV for the current block. Not sending the BVD may reduce the signaling overhead.

[0133] A list of candidate BVPs (e.g., in HEVC, WC, and / or any other coding standard / format / protocol) may comprise two (or more) candidates. The candidates may comprise candidates A and B. Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate BVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being encoded; and / or one or more of last two (or any other quantity of) coded BVs (e.g., if spatial neighboring candidates are not available). Spatial neighboring candidates may not be available, for example, if neighboring blocks are encoded using intra prediction or inter prediction. Locations of the spatial candidate neighboring blocks, relative to a current block, being encoded using IBC maybe illustrated in a manner similar to spatial candidate neighboring blocks used for coding motion vectors in inter prediction (e.g., as shown in FIG. 15A). For example, five spatial candidate neighboring blocks of a current block being coded using IBC may be respectively denoted A0, A1, B0, B1, and B2as shown in FIG. 15A.

[0134] FIG. 17 shows an example of template-based intra mode derivation (TIMD) for coding a current block, according to some embodiments. TIMD is a type of intra prediction in which an intra prediction mode (IPM) may be reciprocally determined (e.g., independently derived) by an encoder (e.g., encoder 200) and a decoder (e.g., decoder 300) such that the IPM determined (e.g., selected) by the encoder does not need to be signaled to the decoder. Hence signaling bandwidth is reduced and TIMD may be considered as a type of decoder-side intra mode derivation process.

[0135] As shown in FIG. 17, for TIMD, a video coder (e.g, encoder 200 or decoder 300) may determine a template 1704 for current block 1702. Template 1704 may comprise one or more regions of samples in a reconstructed region 1708 of a current picture (or frame) of current block 1702. The one or more regions may include reconstructed samples neighboring (e.g., adjacent to) current block 1702. In some examples, the one or more regions of template 1704 may comprise a template region 1704A to the left of current block 1702 (e.g., a left template) and a template region 1704B above current block 1702 (e.g., an above template). In some examples, template 1704 may include a region that is above and to the left of current block 1702 (e.g., the region enclosed by reference of template 1706 and template regions 1704A-B). Template regions 1704A and 1704B may have a thickness (e.g, width and height respectively) of L1 and L2 samples, respectively. For example, L1 and / or L2 may be 2 samples, 4 samples, 8 samples, etc. Template region 1704A may have a height of N samples, which may be a height of current block 1702. Template region 1704B may have a width of M samples, which may be a width of current block 1702.

[0136] In TIMD, reference of template 1706 is used to derive a template predictor for template 1704. The video coder may determine (e.g, select and obtain) reference of template 1706 as a region of samples (in reconstructed region 1708) neighboring (e.g, adjacent to) template 1704. For example, reference of template 1706 may comprise reconstructed samples left and / or above template 1704. Reference of template 1706 may have a thickness to the left of template region 1704A of R1 samples and a thickness above template region 1704B of R2 samples. For example, R1 and / or R2 may be 1 sample. In some examples, similar to reference samples 902 being selected from a reference line of MRL as explained in FIG. 9, reference of template 1706 may include template reference samples selected from a template reference line of template MRL. Thus, reference of template 1706 may refer to a region of samples greater than 1 sample wide and be, e.g, 2 samples wide indicating two template reference lines, 4 samples indicating four template reference lines, etc. In some examples, reference of template 1706 may include an upper region having a width greater than template region 1704B (e.g, a width that is greater or equal to twice the width of template region 1704B, 2(M+L1) samples, 2(M+L1)+R1 samples, etc.). In some examples, reference of template 1706 may include a left region having a height greater than template region 1704A (e.g, a height that is greater or equal to twice the height of template region 1704A, 2(N+L1) samples, 2(N+L1)+R2 samples, etc.).

[0137] In some examples, a TIMD mode predictor may be determined using a list of candidate intra prediction modes (IPMs). For example, the list may include IPMs from a most probable mode (MPM) list. In some examples, one or more of a DC mode, a planar mode, a horizontal and / or vertical DC mode, or a horizontal and / or vertical planar may be added to the list of candidate IPMs. A cost (e.g, SAD or SATD) for each candidate IPM in the list may be determined based on differences between reconstructed samples in template 1704 and predicted samples of template 1704 generated based on reference of template 1706 and using the candidate IPM. For example, the video coder may determine the predicted samples by applying the candidate IPM to samples of reference of template 1706.

[0138] In some examples, a first IPM and a second IPM, from the list, with the lowest costs of costs (determined for candidate IPMs in the list) are selected to determine (e.g, derive) a first TIMD mode and a second TIMD mode. In an example, the first and second TIMD modes are determined as the first and second IPMs, respectively.

[0139] In some examples, the first and second TIMD modes may be determined by refining the first and second IPMs. For example, an angular mode range may be extended from a first range of the list (e.g ., 67 modes) to a second range (e.g., 131 modes) and costs of the two adjacent modes (i.e, + / -1 mode) of each selected IPM may be determined. For example, the first TIMD mode may be determined as an IPM having the smallest cost among costs of the first IPM and its two adjacent modes in the second range. The second TIMD mode may be determined as an IPM having the smallest cost among costs of the second IPM and its two adjacent modes in the second range.

[0140] In some embodiments, based on the second TIMD mode not being selected for predicting the current block, the TIMD mode predictor may be determined as the first TIMD mode only.

[0141] In some embodiments, a TIMD mode predictor may be determined based on combining (e.g, blending or fusing) the first TIMD mode and the second TIMD mode. For example, the TIMD mode predictor may be a linear combination of the first TIMD mode and the second TIMD mode.

[0142] In some embodiments, the first and second TIMD modes are determined based on reference samples from a same reference line neighboring template 1704 such as a reference line #0 (template reference line #0) that is immediately adjacent to template 1704.. Similarly, template reference line #0 may correspond to template reference line index 0 and may be the closest template reference line (i.e, immediately adjacent) to template 1704.

[0143] In some embodiments, the TIMD mode predictor may be determined based on generating the first TIMD mode and the second TIMD mode. For example, the first TIMD mode may be generated by applying the first TIMD mode to reference samples from a reference line I (for instance I is reference line #0) in the neighborhood of current block 1702 and the second TIMD mode may be generated by applying the second TIMD mode to reference samples from either the same reference line ( / ) or another reference line (for instance 1+1 where 1+1 designates reference line #1) depending on a set of conditions. For example, reference line 1+1 may be selected for generating the second TIMD mode based on the following being satisfied: the current block is not coded as an intra sub-partition (ISP) block, and the second TIMD mode is an angular prediction mode not represented by non-fractional angles. Otherwise, the reference line I is selected for generating the second TIMD mode. Generally, reference samples used to generate the first and second TIMD modes are located in template 1704.

[0144] In some embodiments, each weight of the generated first and second TIMD modes, in the linear combination, may be determined based on costs of the selected first and second TIMD modes, respectively. For example, a weight, for a selected TIMD mode, may be determined as being inversely proportional to a cost of the TIMD mode. The TIMD mode predictor may be applied to template 1704 (e.g, reference line #0 in template 1704) to determine a prediction block for current block 1702. An encoder may generate a residual (e.g, prediction error) based on a difference between the prediction block and current block 1702. A decoder may reconstruct current block 1702 based on the reciprocally generated prediction block and the residual received from the encoder in a bitstream.

[0145] In some embodiments, selection of the second TIMD mode (IPM2) for the fusion process may be further based on comparing a cost (costIPMi) of the first TIMD mode IPM1) against a threshold cost. In an example, the threshold cost may be a fixed value. In some examples, the threshold cost may be based on the first IPM cost. In an example, thethreshold cost comprises scaling a cost of a selected TIMD mode (e.g, the first TIMD mode with the lowest cost) by a scaling factor a greater than 1. For example, the second TIMD mode (IPM2) may be selected for blending in the fusion process if the following condition (21) is fulfilled: costIPM2< a. costIPM] (21) where: a is greater than 1 (e.g., a may be a value in the range of 1 to 2); costIPM? is a cost (e.g., SATD, SSE, SAD, etc.) of the second TIMD mode; and costIPMi is the cost of the first TIMD mode.

[0146] In some examples, the first TIMD mode is determined as the TIMD mode predictor (i.e, the TIMD mode predictor is derived only from the first TIMD mode, without fusion process of one or more additional TIMD modes), for example, based on condition (21) not being fulfilled. In these examples, the first TIMD mode was selected using reference samples from a template reference line with template MRL index #0 (i.e., reference line #0 adjacent to the template), but the TIMD predictor may be generated by applying the first TIMD mode to a different reference line index (e.g., with respect to the example MRL list described in FIG. 9, MRL index #1 would indicate reference line #1 adjacent to the current block and MRL index #2 would indicate reference line #3 adjacent to the current block) signaled in the bitstream. For example, during an encoder side rate-distortion optimization (RDO) check, the TIMD predictor generated with the reference line I from the MRL list providing the lowest RDO cost may be selected and signaled as the MRL index (indicating the reference line I in the MRL list) associated with the selected TIMD predictor.

[0147] FIG. 18 shows an example of TIMD signaling for decoding a current block, according to some embodiments. At block 1802, a decoder (e.g., decoder 300 of FIG. 3) receives (e.g., from a bitstream) an indication of whether TIMD is applied to generate a prediction block for coding a current block. As explained above, TIMD is a type of intra prediction in which a template, of the current block, in the reconstructed region of the picture is used to derive an intra prediction mode for coding the current block. For example, the indication may be a flag that indicates whether TIMD is enabled (e.g, applied).

[0148] At block 1804, the decoder determines whether to apply TIMD based on the indication received at block 1802.

[0149] At block 1810, based on the indication of TIMD being applied (e.g, enabled or being selected), the decoder determines (e.g, derives) a TIMD mode predictor based on a plurality of intra prediction modes (IPMs), e.g, without additional signaling from an encoder indicating a specific intra prediction mode. As described above in FIG. 17, the TIMD mode predictor may be determined based on determining two IPMs, from the plurality of IPMs, having the lowest costs of costs determined for the plurality of IPMs. Because the encoder and decoder reciprocally (e.g, independently and identically) determine the TIMD mode predictor, signaling of any specific intra prediction mode (IPM) may be omitted from the bitstream. At block 1812, the decoder generates a prediction block based on the determined TIMD mode predictor (e.g, as described in FIG. 17).

[0150] At block 1806, based on the indication of TIMD not being applied (e.g, disabled or not being selected), the decoder receives (e.g, parses) an indication of an intra prediction mode (IPM) from the bitstream. The indication may comprise a plurality of bits representing an index specifying the IPM from a list of IPMs (e.g, an MPM list). At block 1808, the decoder generates a prediction block based on the indicated IPM (e.g, as described in FIGS. 9-12).

[0151] At block 1814, the decoder reconstructs the current block based on the prediction block and a residual, e.g, received from the bitstream.

[0152] In existing technologies, TIMD was introduced as a decoder-side technique in which intra prediction of a current block may be performed to determine a prediction block for reconstructing the current block without a need for explicit signaling of any specific intra prediction modes in the bitstream. Further, a TIMD mode predictor may be generated as a linear combination of two or more TI D modes generated using two or more intra prediction modes (IPMs), from a list of IPMs, having the lowest costs (e.g., SATD, SSE, or SAD, etc.) of costs of the IPMs in the list. In some examples, under certain conditions as explained in reference to FIG. 17, a TIMD mode predictor is generated as the IPM (e.g, selected as the first TIMD mode) with the lowest cost of costs of the IPMs in the list. The costs are determined as respective differences between the predicted samples and reconstructed samples in a template for a plurality of different intra prediction modes. Reference samples come from the adjacent reference line to the template in the reference of template. The list of IPMs may include one or more angular IPMs, a DC mode, and / or one or more planar modes (e.g, a vertical planar mode or a horizontal planar mode). The linear combination of multiple IPMs is also referred to as TIMD IPM fusion or TIMD IPM blending. In some examples, the TIMD mode with the lowest template cost (the first TIMD mode) is selected to generate the TIMD mode predictor. This TIMD mode may be selected using the reference line adjacent to the template and having a (template) reference line index 0 (e.g, associated with MRL index 0 or MRLJNDEX = 0); however, another reference line with an index not equal to 0 (e.g, associated with another MRL index other than the MRL index 0) may be selected at the encoder and signaled in the bitstream for generating a TIMD predictor with a lower RD cost.

[0153] Embodiments of the present disclosure are related to an approach for improving prediction of a TIMD predictor generated by a TIMD mode (e.g, when one TIMD mode is selected for generating the TIMD predictor). A video coder (e.g, encoder and / or decoder) may generate a TIMD predictor from the determination of one TIMD mode based on a plurality of intra prediction modes (IPM) candidates. Improvements of prediction of the TIMD predictor may be achieved by generating the selected / determined TIMD mode using (e.g, applying the TIMD mode to) reference samples belonging to at least a non-adjacent reference line to the current block. In some embodiments, the reference line used to generate the TIMD mode may be identified based on a reference line ! signaled by the encoder to the decoder in the bitstream (with I = MRL_LIST[MRL_INDEX]). For example, the reference line used to generate the TIMD mode may be determined based on an MRL index of an MRL list storing reference indices identifying respective reference lines.

[0154] In some examples, the video decoder may increment a reference index of the signaled reference line to determine the reference line for the TIMD mode. For example, the TIMD mode may be generated from non-adjacent reference line 1+1,

[0155] In some examples, the TIMD mode predictor may be generated from a TIMD mode generated from non- adjacent reference line / +1 or a fusion of two TIMD modes generated from different reference lines I (or I +1) and 1+1 (or 1+2) where each of the two TIMD modes are equal to the selected / determined TIMD mode.

[0156] In some examples, the TIMD mode predictor is generated from a non-adjacent reference line indicated by incrementing the MRL index signaled in the bitstream. For example, the reference line determined for the TIMD mode may be indicated / identified by the reference line index at MRLJNDEX + 1 (i.e, MRLJst[MRL_INDEX + 1J] or a fusion of two TIMD modes generated from different reference lines corresponding to, e.g., MRLJst[MRLJNDEX + 1] and MRLJist[MRLJNDEX+ 1J+1.

[0157] The video coder may determine (e.g., derive) weights of a linear combination of the generated TIMD modes based on costs of the TIMD modes in the linear combination. For example, a weight for a TIMD mode may be inversely proportional to the cost for the TIMD mode.

[0158] These and other features of the present disclosure are described further below.

[0159] FIG. 19 shows a flowchart 1900 of a method for applying a TIMD technique for a current block, according to some embodiments. The method of flowchart 1900 may be implemented by a video coder (e.g, encoder 200 in FIG. 2 or decoder 300 in FIG. 3). The method of flowchart may be performed reciprocally by an encoder and a decoder such that an intra prediction mode need not be signaled by the encoder to the decoder to reconstruct current block using intra prediction techniques.

[0160] At block 1902, the video coder determines a plurality of costs of a plurality of intra prediction modes (IPMs) for predicting a template of a current block. In some examples, the video coder may determine the plurality of costs based on TIMD being applied (e.g, enabled) for the current block. Each cost for a respective IPM, of the plurality of IPMs, is based on differences between: predicted samples, of a template, generated from the IPM applied to reference samples of the template; and reconstructed samples of the template. Examples of the template of the current block and the reference of the template are shown and described with respect to FIG. 17.

[0161] In some examples, the video coder may be a decoder that determines the plurality of costs based on receiving (e.g, parsing and decoding), from a bitstream, an indication of the TIMD being applied (e.g, enabled) for the current block. For example, an encoder may determine that TIMD is applied for coding the current block and signal the indication in the bitstream to the decoder. In some examples, the indication may be a syntax element (e.g, a flag such as timdjag) that is activated and signaled in the bitstream at the block level (e.g, per block).

[0162] At block 1903, the video coder determines a TIMD mode predictor based on the plurality of IPMs. Block 1903 may comprise blocks 1904-1913.

[0163] At block 1904, the video coder determines a first TIMD mode and a second TIMD mode, based on a first IPM and a second IPM, from the plurality of IPMs, with the lowest costs of the plurality of costs, e.g, as described with respect to FIG. 17.

[0164] At block 1906, the video coder determines whether to select the second TIMD mode to determine the TIMD mode predictor. As explained above, the encoder and decoder independently and reciprocally determine whether to select the second TIMD mode, which permits no additional signaling to be needed in the bitstream to conditionally select the second TIMD mode. The second TIMD mode may be selected or not selected based on satisfying one ormore conditions, as explained above with respect to FIG. 17. For example, a threshold may be set to compare the first and second TIMD modes costs to select or not select the second TIMD for the generation of the TIMD mode predictor.

[0165] At block 1910, based on the second TIMD mode being selected, the video coder determines the TIMD mode predictor comprising a linear combination of the first TIMD mode and the second TIMD mode. Block 1910 may include blocks 1912 and 1913, which may be performed in either order. At block 1912, the video coder determines, based on costs of the first TIMD mode and second TIMD mode, respective weights of the first TIMD mode and the second TIMD mode in the linear combination.

[0156] In some examples, each weight of a generated TIMD mode may be determined as being inversely proportional to a cost of the TIMD mode such that a smaller cost (e.g, SSE, SSD, or SADT) is associated with a higher weight. In other words, the TIMD mode with the smaller cost will have a higher weight than that of the other TIMD mode with the higher cost. For example, a first weight (weight / ) for the first TIMD mode with a first cost (costModel) and a second weight weight?) for the second TIMD mode with a second cost (costMode?) may be determined as follows: costMode2 weight] - costMode] +costMode2 costModel weight? - 1 - weight] - costMode1+costMode2

[0167] In some embodiments, more generally, weights (e.g, first and second weights) of the TIMD modes (e.g, first and second TIMD modes) selected to determine the TIMD mode predictor may be determined (e.g, computed) based on costs of the TIMD modes. For example, a weight for a TIMD mode may be determined to be inversely proportional to a cost for the TIMD mode and / or proportional to a difference between a sum of the costs and the cost of the TIMD mode. For example, the weights of the TIMD modes may be determined according to the following equation (24):wtis the weight associated to the i-th IPM of the i-th TIMD mode. costlPM, is the cost associated with (e.g, determined for) the i-th IPM of the i-th TIMD mode. For example, w.| represents the first weight of the first TIMD mode, and w2represents the second weight of the second TIMD mode, n (e.g., 3, 4, etc.) represents the number of TIMD modes to be combined (i.e, in a linear combination with the weights) to generate the TIMD mode predictor.

[0168] At block 1913, one or more reference lines are determined from a set of MRL to generate the first TIMD mode and the second TIMD mode, as explained above with respect to FIG. 17.

[0169] As explained above, the TIMD mode predictor comprises a linear combination of a number of selected TIMD modes (e.g., the first and second TIMD modes are selected at block 1910). The linear combination comprises the weights determined for the TIMD modes, as described above with respect to 1912. For example, the TIMD mode predictor IPMPUD) may be determined according to the linear combination (25) below:JPMTIMD = Z i ^ x IPMi (25)Wi may be the weight for an i-th TIMD mode comprising an i-th IPM.

[0170] At block 1908, based on the second TIMD mode not being selected, the video coder determines the TIMD mode predictor based on the first TIMD mode, which may be determined based on the IPM with the lowest templatecost. For example, the TIMD mode predictor may be determined as the first Tl M D mode. As explained above, the first TIMD mode may be selected and determined using reference samples belonging to a (template) reference line adjacent to the template (e.g . , reference line index 0 that is immediately adjacent to the template).

[0171] At block 1909, as part of determining the TIMD mode predictor, the video coder determines a reference line from a set of MRL to generate the first TIMD mode based on (e.g., in response to) the second TIMD mode not being selected at block 1906. In some examples, the reference line may be determined based on a reference line (with a reference index / ) signaled in the bitstream from the encoder to the decoder. For example, the reference line (e.g., reference line / +1) may be determined by incrementing an index of the signaled reference line.

[0172] In some examples, the bitstream may include an MRL index (to an MRL list) that specifies / identifies / indicates a reference line index stored in the MRL list. In some examples, the reference line may be determined by incrementing (e.g, by 1) the MRL index signaled in the bitstream and retrieving the reference index stored at the incremented MRL index. Other examples are described above.

[0173] In some embodiments, the TIMD mode predictor is determined based on the first TIMD mode applied to a plurality of reference lines. For example, the TIMD mode predictor may be generated by a blending / combination / fusion of a first TIMD mode predictor (generated using the first TIMD mode) and a second TIMD mode predictor (generated using the first TIMD mode). In other words, the second TIMD mode (that was not selected at block 1906) may be set equal to the first TIMD mode and the identical first and second TIMD modes may be blended. The first TIMD mode (and corresponding first TIMD mode predictor) may be generated using reference samples from a first reference line / and the second TIMD mode (set equal to the first TIMD mode and corresponds to the second TIMD mode predictor) may be generated using reference samples from a second reference line (e.g, reference line / +1) different from the first reference line.

[0174] In some examples, respective weights of the first TIMD mode and the second TIMD mode (set equal to the first TIMD mode) in the linear combination are determined by the coder. For example, the first and second TIMD modes may be set with the same weight (e.g, wi = w? = 0.5) or the first TIMD mode (generated using a reference line closer to the current block) may be set with a higher weight than the second TIMD mode (e.g, wi = 2 / 3 and W2 = 1 / 3).

[0175] In some embodiments, based on the second TIMD mode not being selected at block 1906, one or more conditions may be checked to determine whether the TIMD mode predictor is determined based on the first TIMD mode generated with one reference line or with a plurality of reference lines. For example, the one or more conditions may include one or more of whether the block size (of the current block) is less than a threshold representative of a block size (e.g, 16x16 or 8x8...), the picture resolution is less than a threshold representative of a picture resolution size (e.g. 1280x720), Quantization Parameter (QP) is less than a threshold representative of a QP (e.g. QP 32), or a combination thereof. In an example, the one or more conditions may include all three conditions. In some examples, based on the one or more conditions being satisfied, the video coder determines to use reference samples from a reference line (e.g, reference line 1+1) that is not immediately adjacent to the current block to generate the TIMD mode predictor. Otherwise (e.g, the block size is greater than the threshold), the TIMD mode predictor is determined as a fusion of thefirst TIMD mode and the second TIMD mode set equal to the first TIMD mode, with respective weights selected by the video coder (e.g, wj = W2 = 0.5

[0176] In some examples, reference samples from reference line I are used to generate the first TIMD mode, reference samples from another reference line (e.g., reference line 1+1) are used to generate the second TIMD mode and the first and second TIMD modes are blended with respective weights to generate the TIMD mode predictor.

[0177] In some embodiments, the reference line is not shifted by one, but the MRL index is shifted by one. Thus, reference samples from the reference line identified / indicated by MRL index MRLJNDEX + 1 is used (rather than reference line 1+1). For example, based on the second TIMD mode not being selected (block 1906) (i.e, only the first TIMD mode is selected), reference samples from reference line MRL_list[MRL_l NDEX + 1] may be used to generate the TIMD mode predictor, where MRLJist is the list of MRL (e.g. MRLJist = {0, 1, 3, 5, 12}), MRLJNDEX is the index of currently selected MRL index (corresponding to reference line I determined above). As an example, if MRLJist[MRL_INDEX + 1] is not available a fallback solution is to select reference line 1+1.

[0178] As illustrated in the examples above, the first TIMD mode may be applied to a plurality of reference lines to generate the TIMD mode predictor, according to some embodiments.

[0179] At block 1914, the video coder generates, based on the TIMD mode predictor, a prediction block for the current block. For example, the video coder may apply the TIMD mode predictor to the template of the current block to generate the prediction block for the current block (e.g., as described above with respect to FIGS. 10-12 and 17). For example, as explained above with respect to blocks 1909 and 1913, the one or more TIMD modes of the TIMD mode predictor may be applied to one or more reference lines neighboring the current block (e.g., within a template of the current block) to generate the prediction block.

[0180] In some examples, when the video coder is a decoder, the decoder may reconstruct the current block based on the prediction block and a residual (e.g, a prediction error or a residual block). For example, the decoder may receive (e.g, decode) the residual from a bitstream.

[0181] In some examples, when the video coder is an encoder, the encoder may determine (e.g, generate) the residual based on a difference between the prediction block and current block. The encoder may encode the determined residual in the bitstream.

[0182] FIG. 20 shows a flowchart 2000 of a method for applying a TIMD technique for a current block, according to some embodiments. The method of flowchart 2000 may be implemented by a video coder (e.g, encoder 200 in FIG. 2 or decoder 300 in FIG. 3). The method of flowchart may be performed reciprocally by an encoder and a decoder such that an intra prediction mode need not be signaled by the encoder to the decoder to reconstruct current block using intra prediction techniques. In some examples, flowchart 2000 shows more detailed operations corresponding to block 1902 and block 1904 of FIG. 19.

[0183] At block 2002, the video coder determines a plurality of costs of a plurality of intra prediction modes (IPMs) for predicting a template of a current block. In some examples, block 2002 corresponds to block 1902 of FIG. 19 and the video coder may perform the same or similar operations. For example, each of the IPMs may be applied to a referenceof the template (e.g, reference samples in a template reference line of reference of template 1706) to generate a prediction of the template (e.g., template 1704) and an associated cost representing a similarity between the prediction of the template and the samples of the template may be determined, as explained above in FIG. 17. Block 2002 may include block 2004.

[0184] In some examples, the video coder may determine the plurality of costs based on TIMD being applied for a current block. For example, the decoder may receive (and decode) from a bitstream an indication of TIMD being applied for coding the current block.

[0185] At block 2004, the video coder generates the plurality of IPMs comprising candidate IPMs from a most probable modes (MPM) list. In some examples, the plurality of IPMs may further comprise a DC mode, a planar mode, a vertical planar mode, a horizontal planar mode, a vertical DC mode, a horizontal DC mode, or IPMs generated from template of the prediction block of neighboring blocks to the current block or a combination thereof. Then, the cost for each IPM in the MPM list is determined and corresponds to each cost of the plurality of costs.

[0186] In some examples, the MPM list may be generated for each block for use in an intra prediction mode. For example, for signaling an intra prediction mode (IPM), the encoder may encode an index, into the MPM list, indicating a selected IPM. Using the MPM list may reduce the number of bits involved in signaling indexes of chosen IPMs. In some examples, the MPM list comprises 22 candidate IPMs. For example, the MPM list comprises a first portion (e.g., 6 IPMs) of candidate IPMs referred to as a primary MPM list. The primary MPMs are planar intra prediction mode, an IPM from a left neighboring block, an IPM from an above neighboring block, an IPM from a below-left neighboring block, an IPM from an above-right neighboring block and an IPM from an above-left neighboring block, as described with respect to FIG. 15A. The MPM list may comprise a second portion (e.g., the next 16 candidate IPMs) of candidate IPMs referred to as a secondary MPM list. The secondary MPM list includes or consists of IPMs derived by offsets from the IPMs in the primary MPM list. In some examples, one or more decoder decoder-side intra mode derivation (DIMD) modes may be added to the MPM list after the primary MPMs and before the secondary MPMs in the final MPM list. In some examples, other IPMs not included in the MPM list are included in a separate, non-MPM list.

[0187] At block 2006, the video coder determines a first TIMD mode and a second TIMD mode, based on a first IPM and a second IPM, from the plurality of IPMs, with the lowest costs of the plurality of costs. In some examples, block 2006 corresponds to block 1904 of FIG. 19 and the video coder may perform the same or similar operations. Block 2006 may include blocks 2008-2010.

[0188] In some examples, a number of available angular IPMs may be extended from a first range (e.g., 67 modes) to a second range (e.g., 131 modes) and each of the first IPM and the second IPM may be refined (e.g., adjusted) to determine the first TIMD mode and the second TIMD mode.

[0189] At block 2008, the video coder determines the first TIMD mode based on one IPM among: the first IPM and one or more IPMs from the second range and adjacent to the first IPM. For example, the one or more IPMs may be determined as the two adjacent IPM modes (e.g, + / - 1 1PM) adjacent to the first IPM.

[0190] At block 2010, the video coder determines the second TIMD mode based on one I PM among: the second IPM and one or more IPMs from the second range and adjacent to the second IPM. Blocks 2008 and 2010 may be performed in any order. For example, the one or more IPMs may be determined as the two adjacent IPM modes (e.g, + / - 1 1PM) adjacent to the second IPM.

[0191] FIG. 21 shows a flowchart 2100 of a method for applying a TIMD technique for a current block, according to some embodiments. The method of flowchart 2100 may be implemented by a video coder (e.g., encoder 200 in FIG. 2 or decoder 300 in FIG. 3). The method of flowchart may be performed reciprocally by an encoder and a decoder such that an intra prediction mode need not be signaled by the encoder to the decoder to reconstruct current block using intra prediction techniques.

[0192] At block 2102, the video coder determines a plurality of costs of a plurality of intra prediction modes (IPMs) for predicting a template of a current block. In some examples, the video coder may determine the plurality of costs based on TIMD being applied (e.g., enabled) for the current block. Each cost for a respective IPM, of the plurality of IPMs, is based on differences between: predicted samples, of a template, generated from the IPM applied to reference samples of the template; and reconstructed samples of the template. For example, the template may include one or more template regions comprising reconstructed samples neighboring or adjacent to the current block, as described above in FIG. 17. For example, the template may comprise a left template region to the left of the current block and / or an above template region above the current block. Block 2102 may correspond to block 1902 of FIG. 19.

[0193] In some examples, the plurality of costs comprise sum of squared differences (SSD), sum of absolute differences (SAD), or sum of absolute transformed differences (SATD).

[0194] In some examples, when the video coder is an encoder, the encoder may signal, in a bitstream, an indication of the TIMD being applied for the current block. In some examples, when the video coder is a decoder, the decoder may receive (e.g, parse and decode), from the bitstream, the indication of the TIMD being applied for the current block.

[0195] At block 2104, the video coder determines a first TIMD mode based on a first IPM, from the plurality of IPMs, with the lowest cost of the plurality of costs. For example, block 2104 may correspond to block 1904 of FIG. 19. In some examples, the video coder determines a plurality of TIMD modes for which each respective cost is below a threshold cost determined based on the first TIMD mode with the lowest cost. For example, more than one TIMD mode may be determined and selected, as explained above with respect to block 1906 of FIG. 19.

[0196] At block 2108, the video coder determines a TIMD mode predictor based on the first TIMD mode applied to at least a reference line that is not adjacent (e.g, not immediately adjacent) to the current block. For example, block 2108 may correspond to block 1908 of FIG. 19.

[0197] In some examples, the reference line is one of multiple reference lines (MRL) in the template. In some examples, the reference line is one reference line in an MRL list of reference line indices identifying corresponding reference lines.

[0198] In some examples, the TIMD mode predictor is determined based on the first TIMD mode applied to a plurality of reference lines, as explained with respect to FIG. 19. For example, the TIMD mode predictor may be determined asa linear combination of a first TIMD mode predictor (corresponding to the first TIMD mode applied to a first reference line) and a second TIMD mode predictor (corresponding to the first TIMD mode applied to a second reference line different from the first reference line). In some examples, the first reference line has reference line index 0 and is immediately adjacent to the current block.

[0199] At block 2110, the video coder generates, based on the TIMD mode predictor, a prediction block for the current block. As explained above, the TIMD mode predictor may be applied to one or more reference lines (e.g., from the template) to generate the prediction block. In some examples, the TIMD mode predictor may be based on one TIMD mode that is applied to a plurality of reference lines. For example, block 2110 may correspond to block 1914 of FIG. 19.

[0200] In some examples, when the video coder is an encoder, the encoder may determine a residual (e.g, a prediction error or a residual block) based on (e.g, a difference) the prediction block and the current block, and encode the residual in the bitstream. In some examples, when the video coder is a decoder, the decoder may decode, from the bitstream, the residual of the current block, and reconstruct the current block based on (e.g, combine or add) the prediction block and the residual.

[0201] Embodiments of the present disclosure may be implemented in hardware using analog and / or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. Consequently, embodiments of the disclosure may be implemented in the environment of a computer system or other processing system. An example of such a computer system 2200 is shown in FIG. 22. Blocks depicted in the figures above, such as the blocks in FIGS. 1 , 2, and 3, may execute on one or more computer systems 2200. Furthermore, each of the steps of the flowcharts depicted in this disclosure may be implemented on one or more computer systems 2200.

[0202] Computer system 2200 includes one or more processors, such as processor 2204. Processor 2204 may be, for example, a special purpose processor, general purpose processor, microprocessor, or digital signal processor. Processor 2204 may be connected to a communication infrastructure 2202 (for example, a bus or network). Computer system 2200 may also include a main memory 2206, such as random access memory (RAM), and may also include a secondary memory 2208.

[0203] Secondary memory 2208 may include, for example, a hard disk drive 2210 and / or a removable storage drive 2212, representing a magnetic tape drive, an optical disk drive, or the like. Removable storage drive 2212 may read from and / or write to a removable storage unit 2216 in a well-known manner. Removable storage unit 2216 represents a magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 2212. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 2216 includes a computer usable storage medium having stored therein computer software and / or data.

[0204] In alternative implementations, secondary memory 2208 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 2200. Such means may include, for example, a removable storage unit 2218 and an interface 2214. Examples of such means may include a programcartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a thumb drive and USB port, and other removable storage units 2218 and interfaces 2214 which allow software and data to be transferred from removable storage unit 2218 to computer system 2200.

[0205] Computer system 2200 may also include a communications interface 2220. Communications interface 2220 allows software and data to be transferred between computer system 2200 and external devices. Examples of communications interface 2220 may include a modem, a network interface (such as an Ethernet card), a communications port, etc. Software and data transferred via communications interface 2220 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 2220. These signals are provided to communications interface 2220 via a communications path 2222. Communications path 2222 carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link, and other communications channels.

[0206] As used herein, the terms "computer program medium” and "computer readable medium” are used to refer to tangible storage media, such as removable storage units 2216 and 2218 or a hard disk installed in hard disk drive 2210. These computer program products are means for providing software to computer system 2200. Computer programs (also called computer control logic) may be stored in main memory 2206 and / or secondary memory 2208. Computer programs may also be received via communications interface 2220. Such computer programs, when executed, enable the computer system 2200 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 2204 to implement the processes of the present disclosure, such as any of the methods described herein. Accordingly, such computer programs represent controllers of the computer system 2200.

[0207] In another embodiment, features of the disclosure may be implemented in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine to perform the functions described herein will also be apparent to persons skilled in the art.

Claims

CLAIMSWhat is claimed is:

1. A method comprising: determining, for a current block, a plurality of costs of a plurality of intra prediction modes (I PMs) for predicting a template of the current block; determining a single template-based intra mode derivation (TIMD) mode based on an IPM, from the plurality of IPMs, with a lowest cost of the plurality of costs; determining a TIMD mode predictor based on the single TIMD mode by combining: a first TIMD mode generated by applying the single TIMD mode to a first reference line of the current block; and a second TIMD mode generated by applying the single TIMD mode to a second reference line of the current block that is different from the first reference line; and generating, based on the TIMD mode predictor, a prediction block for the current block.

2. A method comprising: determining, for a current block, a plurality of costs of a plurality of intra prediction modes (IPMs) for predicting a template of the current block; determining a template-based intra mode derivation (TIMD) mode based on an IPM, from the plurality of IPMs, with a lowest cost of the plurality of costs; determining a TIMD mode predictor based on the TIMD mode applied to a first reference line of the current block and the TIMD mode applied to a second reference line of the current block different from the first reference line; and generating, based on the TIMD mode predictor, a prediction block for the current block.

3. The method according to claim 2, wherein the TIMD mode is a single TIMD mode selected based on the plurality of IPMs based on the plurality of costs.

4. The method according to claim 3, wherein the determining the TIMD mode predictor further comprises combining: a first TIMD mode generated by applying the single TIMD mode to the first reference line of the current block; and a second TIMD mode generated by applying the single TIMD mode to the second reference line of the current block.

5. The method according to any one of claims 1 and 4, wherein the first TIMD mode and the second TIMD mode are combined linearly based on respective weights.

6. The method according to claim 5, wherein the weight of the first TIMD mode is higher than the weight of the second TIMD mode, wherein the second reference line is determined based on the first reference line.

7. The method according to claim 5, wherein the weight of the first TIMD mode is same as the weight of the second TIMD mode.

8. The method according to any one of claims 1 and 2, wherein the determining the TIM D mode predictor based on the TIMD mode is further based on one or more of: a size of the current block being less than a threshold size; or a quantization parameter (QP) being less than a threshold QP.

9. The method according to any one of claims 1 and 2, wherein the determining the plurality of costs is based on the TIMD being applied for the current block.

10. The method according to claim 9, further comprising: receiving, from a bitstream, an indication of TIMD being applied for the current block.

11. The method according to any one of claims 1 and 2, wherein the first and second reference lines are from multiple reference lines (MRLs) of the current block.

12. The method according to claim 11, wherein the MRLs are from the template of the current block.

13. The method according to any one of claims 11 and 12, wherein the first and second reference lines are from a list of reference lines comprising the MRLs.

14. The method according to any one of claims 1 and 2, wherein the first reference line or the second reference includes reference samples that are not adjacent to the current block.

15. The method according to any one of claims 1 and 2, wherein the first reference line or the second reference line is adjacent to a reference line immediately adjacent to the current block.

16. The method according to any one of claims 1 and 2, further comprising: receiving, from a bitstream, a first index, to a list of reference lines, that indicates the first reference line of the current block.

17. The method according to claim 16, wherein the second reference line is identified by a second index determined based on incrementing the first index by an integer.

18. The method according to claim 16, wherein the second reference line is identified as an adjacent reference line to the first reference line of the current block.

19. The method according to any one of claims 1 and 2, further comprising: determining a residual based on a difference between the current block and the prediction block for the current block; and signaling the residual in a bitstream to encode the current block.

20. The method according to any one of claims 1 and 2, further comprising: decoding, from a bitstream, a residual associated with the current block; and decoding the current block based on adding the residual to the current block.

21. A non-transitory computer readable medium storing a bitstream, which, when decoded by a decoder, causes the decoder to perform the method according to any of claims 1-18 and 20.

22. A non-transitory computer-readable recording medium storing a bitstream generated by the method for encoding a video according to any one of claims 1-19.

23. A decoder comprising:one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the decoder to perform the method of any one of claims 1-18 and 20.

24. An encoder comprising: one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the encoder to perform the method of any one of claims 1-19.

25. A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors of an apparatus, cause the apparatus to perform the method of any one of claims 1-20.

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