Template matching search regions selection based on refinement windows

Abstract

A decoder obtains, using block vector information of reconstructed neighboring blocks, a first set of candidates for predicting a current block. At least one search region, overlapped by a first refine window of first refine windows determined relative to positions of the first set of candidates, is identified from a plurality of search regions defined based on a position of the current block. Based on a first template matching search of the plurality of search regions excluding the at least one search region, the decoder determines a second set of candidates to determine second refine windows. Based on a second template matching search of a plurality of refine windows obtained using one or more of the first refine windows and one or more of the second refine windows, a candidate for predicting the current block is determined. The current block is coded based on the selected candidate.

Description

TITLETemplate Matching Search Regions Selection Based on Refinement Windows CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 663,052, filed June 21 , 2024, 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 illustrates an example video coding / decoding system in which embodiments of the present disclosure may be implemented.

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

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

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

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

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

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

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

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

[0012] FIG. 10A, FIG. 10B illustrate example intra prediction modes.

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

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

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

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

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

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

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

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

[0021] FIG. 17 illustrates, for an example current block, a reference region or search area of reconstructed samples within which, in Intra Template Match Prediction (IntraTMP), a search is performed for a candidate reference block of which the template best matches the template of the current block.

[0022] FIG. 18 illustrates a current block in a current coding tree unit (CTU), and the reference region with the corresponding IntraTMP search regions R1-R6 identified.

[0023] FIG. 19A illustrates the sparse search stage of IntraTMP.

[0024] FIG. 19B illustrates a block vector according to IntraTMP where the block vector’s refinement window is clipped at the boundary of a search region.

[0025] FIG. 20 illustrates an example of the top-template type that can be used in IntraTMP.

[0026] FIG. 21 illustrates an example of the left-template type that can be used in IntraTMP.

[0027] FIG. 22 illustrates an example of the L-shape template type that can be used in IntraTMP.

[0028] FIG. 23A and FIG. 23B illustrate adjacent blocks and non-adjacent blocks for determining block vector candidates, according to IntraTMP with merge candidates.

[0029] FIG. 24 illustrates an example IntraTMP with merge candidates process.

[0030] FIG. 25A shows an example of Auto-Relocated Block Vector Prediction (AR-BVP) applied to Intra Block Copy (IBC).

[0031] FIG. 25B shows examples of refinement windows of AR-BVP candidates derived from different positions associated with a guiding block vector.

[0032] FIG. 25C shows an example of IntraTMP with block vector predictor (BVP) candidates derived using IntraTMP AR-BVP merge.

[0033] FIG. 26A illustrates example refinement windows for sparse block vector candidates, and merge block vector candidates.

[0034] FIG. 26B illustrates some examples of overlap of refinement windows.

[0035] FIGs. 27A-B illustrate examples of enlarged refinement windows and corresponding new block vector predictor candidates, according to some embodiments.

[0036] FIG. 28 illustrates clustering the enlarged window generated in FIGs. 27A-B and another refinement window, according to some embodiments.

[0037] FIG. 29A illustrates an example of the clustering algorithm shown in relation to FIGs. 27A-B and FIG. 28 and is applied to the adjacent and non-adjacent merge candidate lists, according to some embodiments.

[0038] FIG. 29B illustrates examples of storing an enlargement window, according to some embodiments.

[0039] FIGs. 30A-B illustrate examples of overlapping refinement windows of Merge and sparse BVP candidates in the boundary of the regular TMP reference region, according to some embodiments.

[0040] FIGs. 31A-B illustrate examples of overlapping refinement windows of Merge and sparse BVP candidates between the refinement windows of two merge BVP candidates, according to some embodiments.

[0041] FIG. 32A illustrates a flowchart of an example clustering process applied to Sparse candidates and merge BVP candidates at the same stage of the clustering process.

[0042] FIG. 32B illustrates a flowchart of an example clustering process similar to FIG. 32A.

[0043] FIG. 32C shows an example process for applying TMP AR-BVP candidates to the TMP determination of the merge candidates, according to some embodiments.

[0044] FIG. 33A illustrates another example of an enlarged refinement window and its encompassed merge refinement windows with their top left and bottom right parameters identified, according to some embodiments.

[0045] FIG. 33B illustrates further examples of enlarged refinement windows including one encompassing a merge refinement window and a sparse refinement window with their top left and bottom right parameters identified, according to some embodiments.

[0046] FIG. 33C illustrates the relationship between an example current block’s position, height and width and the location and size of search regions R1-R6 in the reference region.

[0047] FIG. 34A depicts one example of the TMP search region arrangement for a current block size of 16x16 samples, located at the absolute coordinates of (404, 276) belonging to the third CTU row and fourth CTU column (CTU size of 128x128).

[0048] FIG. 34B illustrates a clustered refinement window of two merge BVP candidates (BVP-M1 and BVP-M2).

[0049] FIG. 35 illustrates a flowchart of a process for skipping duplicated template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments of the present disclosure.

[0050] FIG. 36 illustrates a flowchart of another process for skipping duplicate template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments of the present disclosure.

[0051] FIG. 37 illustrates a flowchart of a process for skipping duplicate template match cost calculations in search regions that are overlapped by at least one refinement window and to generate a refined list of sparse and merge candidates from which to select a predicted candidate for the current block, according to some embodiments of the present disclosure.

[0052] FIG. 38 illustrates a flowchart of an example method for encoding a bitstream where the process includes reducing the overhead in generating the list of block vector predictor candidates for determining the prediction block by avoiding duplicate template match cost calculations in search regions overlapped by a refinement window, according to some embodiments.

[0053] FIG. 39 illustrates a flowchart of an example method for decoding a bitstream where the process includes reducing the overhead in generating the list of block vector predictor candidates for determining the prediction block by avoiding duplicate template match cost calculations in search regions overlapped by a refinement window, according to some embodiments.

[0054] FIG. 40 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented.DETAILED DESCRIPTION

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 digitalversatile 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 combination of 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.

[0059] 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.

[0060] A video sequence, comprising multiple pictures / 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.

[0061] 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.).

[0062] 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 generatedscenes, 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.

[0063] 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 comprise intensity 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.

[0064] 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.

[0065] 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 maydetermine 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.

[0066] 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.

[0067] 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 to send / 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).

[0068] 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.

[0069] 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).

[0070] 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.

[0071] 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.

[0072] 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 similarly perform 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.

[0073] 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 (MPEG)-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 (HEVC)), ITU-T H.265 and MPEG-I Part 3 (also known as Versatile Video Coding (VVC)), the WebM VP8 and VP9 codecs, and / or AOMedia Video 1 (AV1), and / or any other video coding protocol).

[0074] 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 formore 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.

[0075] 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.

[0076] 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 exploit spatial 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.

[0077] 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.

[0078] 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 toinformation that may be removed from the coefficients without producing visible and / or perceptible distortion in video sequence 202 after decoding (e.g., at a receiving device).

[0079] 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.

[0080] 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 (SAG) 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.

[0081] 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, WC, VP8, VP9, AV1 , and / or any other video coding standard / format.

[0082] 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 / threshold, and / or to maximize or increase the reconstructed video quality such that the bitrate of bitstream 204 does not exceed a certain level / threshold. 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 rate-distortion measure for a 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.

[0083] 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.

[0084] 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).

[0085] 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, smart phone, 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.

[0086] 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, HEVC, VVC, VP8, VP9, AV1 , and / or any other video coding standard / format.

[0087] 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.

[0088] 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 binaryarithmetic 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 filter(s) 312 as shown in FIG. 3.

[0089] 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).

[0090] 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.

[0091] 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.

[0092] A picture (e.g., in HEVC, or any other coding standard / format) may be partitioned into nonoverlapping 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 maybe 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 subpartition are available to generate the prediction of the next sub-partition. 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.

[0093] 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.

[0094] 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.

[0095] A picture, in WC (or in any other coding standard / format), may be partitioned in a similar manner (such as in HEVC). A picture may be 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.

[0096] 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 or a horizontaldirection 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 of other 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.

[0097] 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.

[0098] 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, nonleaf 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.

[0099] 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 forencoding / decoding, with CB leaf node 0 encoded / decoded first and 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.

[0100] A coding standard / format (e.g., HEVC, WC, 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. A coding 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.

[0101] 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.

[0102] 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.

[0103] 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 blockby 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.

[0104] 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.

[0105] In some embodiments, reference samples 902 may include a line of samples 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 current block 904. In some embodiments, reference samples 902 may be obtained (or selected) from a reference line of multiple reference lines (MRL), which may include a line of samples adjacent to current block 904 and also a line of non-adjacent samples. The MRL may include reference lines identified by corresponding reference line indices that indicate an i-th line of samples adjacent to current block 904 such that the O-th line indicates the reference line immediate adjacent (or closest) to current block 904 and a higher numbered i-th line indicates a line of samples further away from current block 904. An encoder may select a reference line from a set of MRL and signal an MLR index 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.

[0106] 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 -th column adjacent to the left-most column of current block 904, and the top left neighboring corner sample(s) extending from the -th column and -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.

[0107] 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 samplesfrom 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).

[0108] 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.

[0109] 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. In some examples, a filtering scheme (e.g., a filtering algorithm) may be applied to reference samples 902 to improve prediction accuracy. The filtering scheme may be one of a plurality of filter types including at least: a smoothing filter (or reference sample smoothing filter) or an interpolation filter. In some examples, if reference samples of a given block are to be filtered, only one of the plurality of filter types is selected (e.g., activated) to be applied to the reference samples. For example, if the smoothing filter is selected (e.g., activated), the interpolation filter is not selected (e.g., disabled) or vice versa.

[0110] Many 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. VVC 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.

[0111] FIGS. 10A-B 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.

[0112] 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 VVC need not be squares.

[0113] 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 one-dimensional array ref^x] refi [x] = p[—l + x] [— Z], (x > 0). (1)The reference samples 902 belonging to reference line / , to the left of current block 904, may be placed in the one-dimensional array ref2[y]: ref2[y] = p [-l] [-l + y], (y > 0). (2)The variable / represents how many lines away the selected reference line is from current block. For example, if reference line #0 908 is selected, then / is set to 1 to indicate the reference line adjacent to current block 904. For example, if reference line #1 910 is selected, then / is set to 2. For example, if reference line #2 912 is selected, then / is set to 3.

[0114] In some examples, if MRL is not activated or selected, then reference samples 902 may be from reference line #0 908 that is immediately adjacent to current block 904. In this example, the variable / in Equations (1) and (2) is set to 1.

[0115] 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 / calculating 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 / calculated as:P [ ] [y] = — (h[x] [y] + v[x] [y] + s), (3) where^[ ] [y] = (s - x - 1) ■ ref2[y] + (x + 1) ■ re / i[s] (4) may be the horizonal linear interpolation at the location [x] [y] in current block 904 and v[x] [y] = (s - y - 1) ■ re Jx] + (y + 1) - re s] (5) may 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.

[0116] 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:

[0117] For angular modes, a sample at a 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 cp 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 ( defined relative to the x-axis for horizontal prediction modes (e.g., modes 2-18 in HEVC and modes 2- 34 in WC).

[0118] FIG. 12 shows an example of 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 ref [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 ref [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[ ] [y] = (1 - if) ■ ref [x + it+ 1] + i{■ ref [x + it+ 2], (7) itmay be the integer part of the horizontal displacement of the projection point relative to the location [x] [y]. itmay be determined / calculated as a function of the tangent of the angle (p of the vertical prediction mode 906 as: if = L(y + 1) ■ tan <pj. (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 <jp) - L(y + 1) ■ tan <pj, (9) where [ ■ J is the integer floor function.

[0119] 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:itmay be the integer part of the vertical displacement of the projection point relative to the location [x] [y] . ifmay be determined / calculated as a function of the tangent of the angle cp of the horizontal prediction mode as: if = [(x + 1) ■ tan cjoj. (11) ifmay be the fractional part of the vertical displacement of the projection point relative to the location [x] [y], if may be determined / calculated as:where [ ■ J is the integer floor function.

[0120] 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.

[0121] 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 fourtap FIR filter may be determined based on i{(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 FIR 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:where fT[ / ], / = 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:

[0122] 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 (p 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 may be 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.

[0123] 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 and / or including extended intra prediction modes from WAIP for rectangular blocks. 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 (e.g., from a set of MRL), determined for the intra prediction mode and the original samples of the current block. The encoder may determine / select one of the intra prediction modes to encode the current block basedon the determined prediction errors. For example, the encoder may determi ne / select one of the intra prediction modes that results in the smallest prediction error for the current block. In some examples, the encoder may determi ne / 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 determi ned / 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.

[0124] 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. In some examples, when MRL is not enabled / activated / selected, the reference line has reference line index 0 and is immediately adjacent to the current block. In these examples, no indication of MRL index is signaled.

[0125] 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).

[0126] 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.).

[0127] 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, forexample, 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.

[0128] 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.

[0129] FIG. 13A shows an example of inter prediction. The inter prediction may be performed for a current block 1300 in a current picture 1302 being encoded. An encoder (e.g., encoder 200 as shown in FIG. 2) may perform inter prediction 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 rate-distortion 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.

[0130] 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 thesamples 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.

[0131] 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 VVC (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.

[0132] 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 of current 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 non-integer sample value in the reference picture. The interpolation may be performed by a filter with two or more taps.

[0133] 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).

[0134] 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.

[0135] 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.

[0136] One or both of uni-prediction and bi-prediction may be available / 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 generate a 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.

[0137] 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 (POC). 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 / indicatean 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 bi-prediction 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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 / or an indication of the reference index. The reference index may indicate the reference picture, of the reference block 1404, in the reference picture list.

[0142] 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.

[0143] Motion information may be predictively coded, for example, before being stored and / or sent / signaled in / via a bit stream (e.g., in HEVC, VVC, 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).

[0144] 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 determi ne / 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.

[0145] The encoder may determi ne / 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 MVDXand MVDy. MVDXand MVDymay be determined / calculated as:MVDX= MVX- MVPX, (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.

[0146] 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 the reference 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.

[0147] The list of candidate MVPs (e.g., in HEVC, VVC, 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 determi ned / 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 determi ned / derived from two (or any other quantity of) temporal, colocated 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.

[0148] 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 AO, A1, BO, 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.

[0149] 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, colocated 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 the determined motion information in the list of candidate motion information. The encoder may signal / send the index to indicate the determined motion information.

[0150] A list of candidate motion information for merge mode (e.g., in HEVC, VVC, 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.

[0151] 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.). Historybased motion vector prediction (HMVP), combined intra / inter prediction mode (CIIP), 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.

[0152] 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.

[0153] A prediction technique may be used (e.g., in HEVC, VVC, 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 thereference 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 best matches 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 ratedistortion 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 SAG filtering).

[0154] 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.

[0155] 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).

[0156] 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).

[0157] 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.

[0158] 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 / indicator. 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. BVDXand 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).

[0159] 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.

[0160] 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 determi ned / 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 may be 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 AO, A1 , BO, B1 , and B2 as shown in FIG. 15A.

[0161] The most probable mode (MPM) refers to the intra prediction mode (IPM) that is most likely to be the best mode for the current block being encoded or decoded. In current intra prediction techniques, the MPM is determined by analyzing the intra prediction modes of the neighboring CUs (e.g., also referred to as blocks) of a current block (or CU) to be coded (e.g., encoded or decoded). For example, WC uses a list of 6 MPMs (referred to as the “MPM list”) for luma intra prediction. The MPM list is derived from the intra prediction modes of the neighboring CUs, and is updated as the encoder progresses through the video frame. When encoding a block, the encoder may determine if the current block is a candidate for any of the MPMs in the MPM list. If it is, the encoder then compares the prediction errors of the respective MPMs to determine which MPM from the MPM list is the best mode for the current block. If the current block is not a candidate for any of the MPMs in the MPM list, the encoder may then evaluate all intra prediction modes (e.g., 67 in VVC) to determine the best mode for the current block.

[0162] The use of MPMs can significantly improve the coding efficiency because the encoder does not need to signal the intra prediction mode for the current block if it is one of the MPMs. Instead, the decoder can infer the intra prediction mode for the current block from the corresponding MPM list reciprocally and identically generated at the decoder. Thus, signaling overhead in the bitstream may be reduced.

[0163] In some examples, three types of intra modes are considered to construct the MPM list: default intra modes; neighboring intra modes; and derived intra modes. A unified 6 MPM list is used for intra blocks irrespective of whether Multiple Reference Lines (MRL) and Intra Sub-Partitions (ISP) coding tools are applied. The MPM list for the current block is constructed based on intra modes of the left neighbor block (e.g., block corresponding to A1 in FIG. 15A) and the above neighbor block (e.g., block corresponding to B1 in FIG. 15A) of the current block. Suppose the mode of the left neighbor block is denoted as Left and the mode of the above neighbor block is denoted as Above, the unified MPM list may be constructed as follows: when a neighboring block is not available, its intra mode is set to planar mode by default; if both modes Left and Above are non-angular modes, then the MPM list is set to include{planar, DC, V, H, V - 4, V + 4}, where “V” and “H” refer to vertical mode and horizontal mode, respectively; if one of modes Left and Above is an angular mode, and the other is non-angular, set a mode Max as the larger mode in Left and Above, and set MPM list to include {planar, Max, Max - 1 , Max + 1 , Max — 2, Max + 2}; if Left and Above are both angular and they are different, set a mode Max and a mode Min as the larger mode in Left and Above and as the smaller mode in Left and Above, respectively, and thereafter, if Max - Min is equal to 1 , then set MPM list to include {planar, Left, Above, Min - 1 , Max + 1 , Min - 2}, if Max - Min is greater than or equal to 62, then set MPM list to include {planar, Left, Above,Min + 1 , Max - 1 , Min + 2}, if Max - Min is equal to 2, set MPM list to include {planar, Left, Above, Min + 1 , Min - 1 , Max + 1 }, or otherwise, set MPM list to include {planar, Left, Above, Min - 1 , -Min + 1 , Max - 1}; and if Left and Above are both angular and they are the same, set MPM list to include {planar, Left, Left - 1 , Left + 1 , Left - 2, Left + 2}.

[0164] The encoder may encode an MPM index in the bitstream to indicate the position of the selected intra prediction mode in the MPM list to the decoder. The encoder may represent the MPM index as a codeword and entropy encode the codeword into the bitstream. The decoder may derive the MPM list in a manner identical to the encoder, and use the MPM index obtained from the codeword decoded from bitstream to obtain the intra prediction mode from the MPM list derived at the decoder. In some instances, the first bin of codeword, representing the MPM index, is context coded using an arithmetic coder (e.g., CABAC) so as to achieve additional coding efficiencies. For example, three contexts may be used, corresponding to whether the current intra block is MRL enabled, ISP enabled, or a normal intra block.

[0165] During the 6 MPM list generation process, pruning may be used to remove duplicated intra modes so that the MPM list includes only unique intra modes. For entropy coding of the 61 non-MPM modes (that is, the 67 modes in VVC minus the 6 MPM), a truncated binary code (TBC) may be used.

[0166] In some implementations, the MPM list is extended to include 16 additional candidates, and is divided into two parts, the primary MPM (PMPM) (e.g., including 6 entries) and the secondary (SMPM) (e.g., including 16 entries). In some implementations, the first entry in the general MPM list is the planar mode. The remaining entries include the intra modes of the adjacent neighboring blocks corresponding to positions left (L), above (A), below-left (BL), above-right (AR), and above-left (AL) (e.g., shown in FIG.15A as A1 , B1, AO, BO, and B2), and decoder-side intra mode derivation (DIMD) modes which are sorted in ascending order of a cost such as, for example, SAD, SSD, SATD, etc. In some examples, up to a preconfigured / predetermined number of modes (e.g., 5) with the smallest costs are added to the MPM list. The cost for a respective MPM (e.g., an IPM corresponding to an entry in the MPM list) may be computed between the prediction of the reconstructed samples of the template of the current block and the reconstructed samples. For example, the prediction may be generated by applying the respective MPM for the template. Sorted directional modes are added into the general MPM list, and then the default modes, until the general MPM list with 22 entries is constructed. In some examples, if a CU block is vertically oriented, the order of neighboring blocks corresponds to A, L, BL, AR, AL; otherwise, it is L, A, AL, AR, BL.

[0167] I ntra-template matching prediction (IntraTMP) is a special intra-prediction mode that selects a prediction block within a pre-determined reference region (RR) or search area from the reconstructed samples within the current frame. IntraTMP uses a pre-defined template of the current block to search for a candidate reference block of which the template best matches the template of the current block. FIG. 17 illustrates, for an example current block 1700, a reference region 1712 or search area from thereconstructed samples 1704 within which a search is performed for a candidate reference block 1706 of which the template 1708 (“candidate reference block template”) best matches the template 1702 (“current block template”) of the current block 1700. In this example the reference region is divided in four rectangular reference regions (R1 , R2, R3, and R4).

[0168] By computing a cost function (e.g., SAD, SATD) between the template 1702 of the current block and the templates of several candidate reference blocks, N candidates with lower template costs, each indicated by a corresponding block vector predictor (BVP) candidate 1710 (BVP candidate may also be referred to herein as block vector (BV) candidate), are stored in an intraTMP list and ranked by lower cost value (ascending cost). This process is performed by both encoder and decoder.

[0169] The residual blocks obtained as the difference between the samples of the current block 1700 and the candidate's reference blocks 1706 in the list are computed, and the reference block with the better rate-distortion performance is selected as the best intraTMP reference block. An index indicating the position of the best BVP or BV candidate within the intraTMP list is signaled to the decoder in order to facilitate the block decoding using the IntraTMP prediction mode.

[0170] Due to the reference region having an irregular (non-rectangular) shape and to facilitate its hardware implementation, the template matching in the reference region 1712 is carried out in a set of rectangular sub-regions (R1 to R4 in the example of FIG. 17), whose dimensions are determined based on the current blocks' size and relative position inside the current CTU.

[0171] The global reference region 1712 dimensions comprising all sub-regions are determined by the SearchRange_w and SearchRange_h parameters, which are set proportional to the current block 1700 dimension (CbWidth, CbHeight) using a multifactor parameter denoted as 'a', which controls the gain / complexity trade-off. In some implementations of IntraTMP, the multifactor parameter 'a' may be uniform and equal to 5 or may be determined by of the current block dimension.Search Range_w = a * CbWidthSearchRange_h = a * CbHeight

[0172] In some implementations of IntraTMP, the global RR for block dimensions 4 and 8 were extended to 64 pixels, according to the following equations:SearchRange_w = max (64, 5* CbWidth) SearchRange_h = max (64, 5* CbHeight)

[0173] In practice, this has the effect of using a variable multifactor parameter 'a' based on the block dimensions, as shown in the following table:

[0174] FIG. 18 illustrates a current block 1800 in a current CTU 1804, and the reference region 1812 with example corresponding TMP search regions R1-R6 identified. An example reference block 1816, and reference block template 1818 and current block template 1808 are also illustrated.

[0175] In order to reduce the high computational burn of the exhaustive template matching searching in the whole RR, the searching process is split into 2 steps: a sparse search step, and a refinement search step.

[0176] The sparse search is illustrated in FIG. 19A. The sparse search in some implementations is carried out in a regular grid using a subsampling interval of 3 in the horizontal and vertical directions. FIG. 19A shows an example candidate reference block 1916 in search region 4 (R4) and the corresponding reference template 1918. The template cost is computed for each reference block position within a search region (e.g., reference block position 1920 of reference block 1916), and the BVP candidates associated with the best (e.g., least cost) reference block are recorded in a sparse list and sorted in ascending order cost. The subsample positions are shown in the form of dark squares in within the RR region, separately determined for each search region. In some implementations of IntraTMP, the size of the sparse list is set to 30.

[0177] The refinement search, the second step, is a refinement of the reference block candidates (correspondingly, BVP candidates) in the sparse list. In some implementations, the refinement is made in a window of 3x3 pixels around the sparse BVP candidates using a sampling interval of 1. If the refinement window (refine window) crosses into another search region, the refinement window is clipped to the region boundary to which the candidate belongs. FIG. 19B illustrates a current block 1906 and template 1908 located in a current CTU 1904 of a current frame 1900 (i.e., current picture), corresponding RR with respective search regions R1-R6, and an example BVP 1910 with its refinement search window 1912 being clipped where R4 (search region in which the BVP 1910 is located) borders R1 and R3. The 19 refined candidates with the lowest template cost(e.g., SAD cost) are selected for a “Refined IntraTMP list”.

[0178] Once the encoder / decoder has constructed the Refined IntraTMP List, the encoder / decoder can select among different intraTMP sub-modes by checking the rate-distortion performance of each submode. The IntraTMP sub-mode is signaled to the decoder in combination with an index to the best candidate in the Refined IntraTMP List or a cluster of candidates (e.g. the Fusion mode). The IntraTMP sub-modes may be the single predictor sub-mode, the fusion sub-mode, the sub-pel precision sub-mode, and the linear filter mode sub-mode. In the single predictor sub-mode, a single BVP candidate is selected from the Refined IntraTMP List and signaled to the decoder. In the fusion sub-mode, multiple BVP candidates are blended to derive the final BV prediction block. The blending weights may be either computed from the template matching cost of each predictor or with a Wiener-filter-based weightderivation method. In the sub-pel precision sub-mode, when a single predictor is used, sub-pel precision can be used with 1 / 2-pel precision, 1 / 4-pel precision, and 3 / 4-pel precision, each with 8 possible directions. In the linear filter model sub-mode, a linear filter can be learned between the reference and current templates and applied to the reference block. This mode can be used for a single predictor when sub-pel precision is not used and a single predictor is used.

[0179] In some implementations of IntraTMP several types of template shapes may be used. Five types of templates have been proposed according to the current block location in the frame: top template, left template, L-shape template, an only top template type, and an only left template type.

[0180] The template type of top template may be used when only the current block’s top samples are available, such as when the current block is located to the left boundary of the picture. Consequently, the TMP cost is computed using the top samples of the current and reference blocks. In some implementations, the top template is four samples in height.

[0181] The template type of left-template may be used when only the left samples of the current block are available, such as when the current block is located at the top boundary of the picture. Consequently, the TMP cost is computed using exclusively the left samples of both the current and the reference block. In some implementations, the left template is four samples in width.

[0182] The L-shape template type is used in the other cases (e.g., the current block is not located at the top or left boundary of the picture) where the samples surrounding the current block included in the L- Shape are available. Consequently, the TMP cost is computed using the L-shape template of both the current and the reference block. In some implementations, the L-shape template is four samples in width and height.

[0183] The L-shape template introduces two more template types: the Only-Top (Only-T) and Only-Left (Only-L) templates. Therefore, in addition to the L-Shape TMP cost, the TMP cost for the Only-T and Only-L templates are also computed, and the best N BV candidates are stored in different Only-T and Only-L lists.

[0184] FIG. 20 depicts an example of the top-template type. Only the top templates (e.g., template 2001 of current block and template 2000 of reference block 1816) are used for the TMP cost computation in 2003. The sparse search 2003 is computed using a sampling interval (SI) 2002 of three, and one sparse list (sparse candidates list) 2004 is built using the best (lower cost) 30 BV candidates in some implementations. Those candidates are refined in 2006 using a 3x3 window 2005 with an SI of 1 , and a Refined Candidates List 2007 is built.

[0185] For the left-template type, the same top-template type logic is applied, but the left templates (2100 and 2101) of reference and current blocks are used instead of the top templates illustrated in FIG. 21 . The TMP cost calculation in search regions 2103, search intervals for sparse search 2102, sparse candidates list 2104, refinement of the sparse list 2106, refinement search windows 2105, and the refinedcandidates list 2107 of the Only-L process shown in FIG. 21 may be identical (except for the use of Only- L template instead of Only-T template) to 2003, 2002, 2004, 2006, 2005, and 2007, respectively, described in relation to FIG. 20.

[0186] FIG. 22 depicts an example of a current block that has available (e.g., reconstructed samples are available for) the L-shape template 2201 , and the L-shape template 2200 of the reference block is used to compute the L-shape TMP cost in all search regions, as it was described for the top-template and lefttemplate type.

[0187] In addition to the L-shape cost, the Only-Top TMP and Only-Left TMP costs may also be computed. In some implementations, the Sparse search builds three sparse lists, one Sparse L-Shape List with a size of 30 BV candidates, and two additional lists, the Only-T sparse list and Only-L sparse list, both with a length of 6 BV candidates.

[0188] These three sparse lists are refined by computing the respective template type cost using a window of 3x3 in some implementations. The best N BV candidates, which have obtained the lower TMP costs, are stored in three new refined lists: the Refined L-Shape List with a size of 19 BV candidates, the Refined Only-T List with a length of 3 BV candidates and Refined Only-L List with a size of 3 BV candidates. In some implementations, the final IntraTMP List has 19 candidates as the L-Shape List, but it is a combination of the BVs candidates in the L-Shape List, and the Refined Only-T and Only-L Lists.

[0189] IntraTMP is described in F. Wang et al, “EE2-1 .20i / j: Combination of IntraTMP tests”, JVET- AD0086, April 2023; L. Zhang et al, “EE2-1 .11 : Intra template matching prediction fusion”, JVET-AD0072, April 2023; J.-Y. Huo et al, “EE2-1.16: A Fusion method of Intra Template Matching Prediction (Intra TMP)”, JVET-AD0116, April 2023; and P. Lin et al, “EE2-1.19: IntraTMP with multiple modes”, JVET- AD0194, April 2023, the content of which are herein incorporated by reference.

[0190] In addition to the sparse BVP candidates obtained by TMP searching within the RR in IntraTMP, another set of merge BVP candidates is proposed in another technique “IntraTMP with merge candidates”. In some implementations, merge BVP candidates are a subset of the IBC merge candidates, comprising only the spatial candidates of the current block. In particular, the TMP merge BVP candidates may use the 5 adjacent BV from the adjacent blocks (e.g., 2300 in FIG. 23A) and the 20 non-adjacent BV candidates (e.g., 2301 in FIG. 23B) from the non-adjacent neighboring blocks encoded using an IBC or TMP mode.

[0191] The IntraTMP with merge candidates process is illustrated in FIG. 24. A maximum of 50 BVP candidates 2405 from the adjacent blocks and BVP candidates 2406 from non-adjacent blocks are ranked in ascending TMP cost at 2407, and the best 10 candidates (candidates with lower TMP costs) comprise the TMP merge list 2408, which is ordered in ascending TMP cost. A sparse list 2404 is generated at 2403 for the current block, as described above in relation to IntraTMP, by calculating TMP costs for reference templates (e.g., L-shape reference templates) 2400 and the current block’s template 2401 insearch regions using a predetermined sampling interval 2402. In some implementations, up to 10 merge BVP candidates are checked in the sparse list 2404 for duplicates, and the redundant BVPs in the TMP merge list are removed from the list 2409 to generate the updated TMP merge list 2410.

[0192] Thereafter, the merge BVPs from the updated TMP merge list 2410 compete with the BVP candidates in the sparse list 2404, and the best 30 candidates from the sparse list 2404 and the updated merge list 2410, based on the TMP cost, are selected for the final or updated sparse list 2411 .

[0193] BVPs in the updated sparse list 2411 are refined using a window whose size depends on the BVP type to generate the refined candidates list 2414. BVPs from the sparse searching in the regular TMP reference region use a 3x3 refinement window 2412 (sampling interval of 1 sample). Otherwise, BVPs included in the updated sparse list 2411 from the updated TMP merge list 2410, whether inside or outside the regular reference region, use a window size of 11x11 samples 2413 (sampling interval of 1 sample).

[0194] IntraTMP with merge candidates is described in K. Naser et al, “EE2-1 .2: IntraTMP with Merge Candidates,” JVET-AG0151 , January 2024, the content of which is herein incorporated by reference.

[0195] Another technique, known as auto-relocated block vector prediction (AR-BVP), may be used in the construction of the AMVP and / or merge IBC list. In some implementations, a guiding BV is selected from the BVP candidates in the AMVP and / or merge IBC list. A BV (referred to herein as a “coding BV”) pointing to a reference block of a block containing a position derived relative to a position pointed to by the guiding BV is identified. An AR-BVP candidate can be determined as the combination of the guiding BV and the identified coding BV. For example, the coding BV may be similar to a block vector displacement (BVD) in AMVP IBC.

[0196] FIG. 25A shows an example of AR-BVP applied to IBC where the guiding BV (BV-1) 2501 is a BVP candidate in the IBC list. The guiding BV may be used to identify a first reference block (e.g., reference PU1), and five positions of the first reference block that are aligned with the five positions of the current block 2506 are also identified. Each of the five positions is checked to determine if a coding block containing the sample at the position is encoded / decoded using the IBC mode or IntraTMP mode. These positions are denoted correspond to the center of block (CT) 2520, left-top (LT) 2521 , right-top (TR) 2522, left-bottom (LB) 2523, and right-bottom (RB) 2524. In the case that AR-BVP is used in IBC and a block containing a sample at a position of at least one of the five positions (CT, LT, RT, LB, and RB) defined relative to the first reference block was encoded / decoded using IntraTMP or IBC mode, the block vector used to indicate the reference block of the first reference block is used as the coding BV to combine with the guiding BV.

[0197] FIG. 25A further shows one example of multiple candidate AR BVPs iteratively derived from the initial guiding BV 2501. Guiding BV 2501 points to the first reference block (PU1). The five positions of the first reference block PU1 , correspond to the guiding BV 2501 applied to the five respective positions (CT,LT, RT, LB, and RB) of current block 1906. Each of the five positions of the first reference block may be checked to determine if a block at any of those positions was coded in an IBC or IntraTMP mode. For example, a block at the position CT of the first reference block may be determined to be coded using BV- CT1 2504. Then, BV-CT1 2504 may be applied to the first reference block to determine a second reference block (reference PU2), from which five positions of the second reference block may be checked to derive one or more AR-BVPs. For example, the first AR-BVP candidate (BVP-AR1) 2505 may be derived as the addition of the guiding BV 2501 and the coding BV(BV-CT1) 2504 used for the encoding / decoding of the block containing / at position CT of the first reference block. The second AR-BVP candidate, BV-AR2 2507, may be derived as the addition of previous AR-BVP (BVP-AR1 2505) and a block vector BV-LT2i 2506 derived from a block at LT position of the second reference block (reference PU2). For example, each of the five positions of the second reference block (reference PU2) may be checked to determine if a block containing the sample at those respective positions was encoded / decoded in an IntraTMP or IBC mode. For example, the block at the LT position may satisfy the condition and was coded using BV-LT2i 2506, which points to a third reference block (reference PU3).

[0198] This cascading process may be iterated multiple times and referred to a number of hops. In some examples, the cascading process may be constrained to one hop. For example, BVP-AR1 2505 may be added as a candidate AR BVP derived from BVP-1 2501 , but BVP-AR2 2507— which corresponds to a second hop— would not be determined and added as a second candidate AR BVP.

[0199] The AR-BVP candidates 2505 (and 2507) may be included in the AMVP and / or merge lists after the spatial adjacent candidates. In some examples, AR-BVP candidates 2505 (and 2507) may be included in the AMVP and / or merge lists after the spatial non-adjacent candidates. In some examples, AR-BVP candidates may be included in the AMVP and / or merge lists after the HMVP candidates.

[0200] In some examples, AR-BVP technique may be implemented for IntraTMP and is referred to as IntraTMP AR-BVP merge. This technique uses the BVPs in the IntraTMP merge list as guiding BVs for the AR-BVP process.

[0201] In some examples, the TMP AR-BVP candidates, 2505 and 2507, may be included in the TMP merge lists after the adjacent and non-adjacent merge candidates. In some examples, TMP AR-BVP candidates 2505 and 2507 and the adjacent and the non-adjacent merge candidates may be sorted in an ascending order of the TMP costs within the TMP merge list. In some embodiments, the merge candidates (adjacent and non-adjacent candidates) and the AR-BVP candidates outside the TMP reference region may be included first within the TMP merge list.

[0202] In some examples, the refinement window for the AR-BVP candidates may have a different window size than that of the TMP merge candidates and the TMP sparse candidates. FIG. 25B shows examples of refinement windows for AR-BVP candidates derived from different positions associated with the initial guiding BV 2501 , according to some embodiments. The first AR-BVP candidate (BVP-AR1)2503 is derived as the addition of the guiding BV 2501 and the coding BV(BV-CT1) 2502 used for the encoding / decoding of a block containing the central position (CT) of the reference block (reference PU). Since the BVs of a block are typically referenced with respect to the upper left Conner of the block, the guiding BV 2501 is illustrated as starting from the upper left Conner of the current block 1906. The BV associated with the block containing the central position CT, BV-CT1 2502, is shifted based on the guiding BV 2501 so that the addition of these two BVs can generate AR-BVP candidate BVP-AR1 2503. Similarly, another AR-BVP candidate, BV-RT 1 2505, is derived based on the BV associated with a block containing the sample at the RT position of the reference block. An AR-BVP candidate may be refined with a refinement window 2514. Specific refinement window 2514 for a given AR-BVP candidate is set according to the AR-BVP candidate. For example, positions 2533 and 2535 pointed to by BVP-AR1 2503 and BVP-AR2 2505, respectively, are used to determine the respective refinement windows.

[0203] The following source code represent an example implementation for obtaining the five positions relative to a guiding BV and determining if a block at each of the five positions is coded based on IBC or IntraTMP mode: const PredictionUnit& pu = *cs.getPU(area.pos(), CHANNEL_TYPE_LUMA); / / pu is the top left corner of the CB / / posCand indicate the 5 offset postions related to the CB. The pu position is equal to the topleftf) not centerQPosition posCand[5] ={pu.Y().center(),pu.Y().topLeft(),pu.Y().topRight(), pu.Y().bottomLeft(),pu.Y().bottomRight() }; / / EXAMPLE pu: {PU: x = 32, y = 24, width = 8, height = 8} posCand = {{x=36 y=28 }, {x=32 y=24 }, {x=39 y=24 }, {x=32 y=31 }, {x=39 y=31 }} / / Loop FOR to test the five positions around a first IBC Merge / AMVP candidate or TMP merge candidate / / bvBasedMergeCandidateslTMP_AR is the list of TMP merge candidates for (int mergeindex = 0; (mergeindex < 25) && (bvBasedMergeCandidateslTMP_AR.size() < totalNum); mergelndex++){ cMv_Sparse = SparseCandidateslTMP[mergelndex]; offsetX = cMv_Sparse.m_pX; offsetY = cMv_Sparse.m_pY; cMv = Mv(offsetX, offsetY); / / This is the merge candidate to use as base for the AR-BVP for (int n = 0; n < 5 && bvBasedMergeCandidateslTMP_AR.size() < totalNum; n++) / / Check the 5 positions around the Merge BV { / / puCascadedid the merge candidate + one of the offset (CT, TL, TR, BL, BR) const PredictionUnit* puCascaded = pu.cs->getPURestricted(posCand[n].offset(offsetX, offsetY), pu, pu.chType); if (IpuCascaded || ((puCascaded->cu->predMode != MODEJBC) && (!puCascaded->cu->tmpFlag))){ continue; / / If the block in that position was not encoded with IBC or TMP, skip it and go to the next among the 5}Mv arbv = cMv + puCascaded->bv; / / Build the AR-BVP candidate / / Check if reference block pointed out for the AR-BVP is already decoded if (PU::validltmpBv(pu, arbv.hor, arbv. ver)){ if (!PU::CheckBvAvailable(bvBasedMergeCandidateslTMP, arbv) && !PU::CheckBvAvailable(bvBasedMergeCandidateslTMP_AR, arbv)){ / / If the AR-BVP is valid and it is not already in the TMP merge list, it is added at the end of the TMP Merge list bvBasedMergeCandidateslTMP_AR.push_back(arbv); if (bvBasedMergeCandidateslTMP_AR.size() >= totalNum){ break; / / If the list is complete, finish the TMP AR-BVP process }}}

[0204] FIG. 25C shows one example of IntraTMP with BVP candidates derived using IntraTMP AR-BVP merge as discussed above with respect to FIGS. 25A and 25B. In FIG. 25C, TMP merge candidate BVP- M1 2531 pointing to a location outside the TMP reference region is used as a guiding BV to derive two AR-BVP candidates, BV-AR1 2533 and BV-AR2 2535. Likewise, TMP merge candidate BVP-M2 2536 is used as guiding BV to derive a new AR-BVP candidate BV-AR3 2538.

[0205] FIG. 26A depicts an example of refinement windows of 5 BVP merge candidates (BVP-M1 to BVP-M5) located outside of the regular TMP reference region, one merge BVP candidate (BVP-M6) located inside of the regular TMP reference region, and one merge BVP candidate (BVP-M7) which is partially overlapping the regular TMP reference region. FIG. 26A also shows an example of refinement windows of three sparse BVP candidates (BVP-S1 to BVP-S3) positions within the regular TMP reference region.

[0206] Because the sparse BVP candidates in IntraTMP are obtained by applying a sampling interval of 3, and the refinement window is ±1 sample around the BVP candidate, the refinement windows of any two sparse BPVs never overlap. The refinement windows of two sparse BVP candidates could overlap only at the boundaries of two search subregions because the sampling interval is applied individually to each subregion (e.g., BVP-S4 and BVP-S5 in FIG. 26B). To avoid such overlap, refinement widows of the sparse BVPs may be constrained to the subregion to which the BVP candidate belongs.

[0207] On the other hand, the BVP merge candidates come from spatial neighbor blocks without any constraint related to their position. Consequently, the refinement windows of the merge candidates may overlap with one another. FIG. 26B shows several examples of refinement windows of merge candidates overlapping:• BVP-M1 and BVP-M2 are two merge BVP candidates outside the TMP reference region, of which the refinement windows overlap with each other;• BVP-M5 and BVP-S2 depict the overlapping of the refinement windows of a merge BVP candidate and a sparse BVP candidate inside the regular TMP reference region; and• BVP-M6 and BVP-S3 show the overlapping of the refinement windows of a merge BVP candidate (BVP-M6) and a sparse BVP candidate (BVP-S3) inside the regular TMP reference region, where the refinement window of the sparse BVP is constrained to the boundaries of the subregion.

[0208] The refinement window overlap presents at least two issues that can affect the performance of encoders and decoders: the TMP cost is computed twice at the overlapping locations, which increases the complexity inefficiently; and two BVP candidates whose refinement windows overlap reduce the diversity of the candidates in the merge list.

[0209] In relation to the first of the two issues, since IntraTMP with merge candidates calculates template costs for each reference block candidate (e.g., with a sampling interval of 1 within the refinement window), duplicate calculations in the overlapped regions can significantly increase the computation load. In relation to the second issue, since the size of the refined list (e.g., 2414 in FIG. 24) is limited, including two BVP candidates that have significant overlap would often necessitate excluding another candidate that is further from the overlapping candidates.

[0210] Some techniques provide for implementing a clustering algorithm to merge the merge BVP candidates that are close to each other whose refinement search windows overlap. As a result, the new refinement search window is extended (enlarged) to cover the refinement search windows of both BVP candidates.

[0211] According to some techniques, a new BVP candidate is determined based on the extended refinement window, and the new BVP candidate replaces the overlapping BVP candidates whose refinement windows were encompassed in the extended refinement window. Having a single refinement window avoids the above identified issue of duplicated computation. Having only a single BVP candidatein the merge list for each group of overlapping refinement windows avoids the above identified issue of reduced diversity of candidates in the merge list.

[0212] FIG. 27A shows one example of two BVP merge candidates, BVP, and BVPk, whose refinement windows 2702 and 2701 partially overlap. The clustering algorithm according to embodiments of the present disclosure determines a new refinement window (Wik) 2700 with dimensions (Whik, Wvik) covering both original refinement windows (W, 2701 and Wk 2702). The new merge BVP candidate (BVPik) is computed as the centroid of the new refinement window (Wik) 2700.

[0213] In another embodiment, FIG. 27B, the clustering algorithm determines a new refinement window (Wik) 2700 with dimensions (Whik, Wvik) covering both original refinement windows (W, 2701 and Wk 2702). However, instead of determining a new merge BVP candidate (BVPik) computed as the centroid of the new refinement window (Wik) 2700, the clustering may select one of the BVP merge candidates, BVPi and BVPk, according to one specific criterion (e.g. the candidate with lower TMP cost). The example of FIG. 27B, the merge BVP candidate BVP, has a cost of 1324 and BVPk has a cost of 2782, so the candidate BVP, is selected to represent the enlarged refinement window 2700.

[0214] The dimensions of the enlarged refinement window (Wik) 2700 may be indicated by its top-left and bottom-right corners, which may be determined by the top-left 2703 and bottom-right 2704 displacement vectors.

[0215] The clustering may be iteratively applied through the BVP candidates in the TMP Merge list. Therefore, a merged BVP candidate (e.g., BVPik in FIG. 27A (or BVP, in FIG. 27B) having refinement window 2700) can be clustered with another BVP candidate in the list (e.g., BVPmhaving refinement window 2801), resulting in a new BVP candidate (BVPikm) and a new refinement window (Wikm 2800), as shown in FIG. 28.

[0216] FIG. 29A illustrates a flowchart of the clustering algorithm shown in relation to FIGs. 27A-B and FIG. 28 being applied to the adjacent merge BVP candidates 2405 and the non-adjacent merge BVP candidates 2406, according to some techniques. The adjacent merge BVP candidates 2405 and non- adjacent merge BVP candidates 2406 may be determined as described above in relation to the IntraTMP with merge candidates technique. In process 2900 according to some examples, at 2901 the clustering algorithm shown in FIGs. 27A-28 is applied to merge adjacent 2405 and non-adjacent 2406 candidates. The clustered merge candidates are stored in the Merge list 2902, which candidates have no overlapped refinement windows (i.e., any overlapped refinement windows were encompassed in enlarged windows determined according to clustering shown in FIGs. 27A-28) and an additional refinement window list 2904 comprising the refinement window dimensions for each BVP candidate in the merge list 2902. The merge list 2902 includes new BVP candidates corresponding to enlarged refinement windows according to the clustering algorithm shown in FIGs. 27A-28 and BVP candidates from lists 2405 and 2406. For example, the result of the clustering may result in the BVP candidates with corresponding refinement windows thatare non-overlapping with each other. In some examples, such as that described in relation to FIG. 27A, the refinement window list 2904 may include, for each BVP candidate in merge list 2902, the height and width of the corresponding refinement window, which may be either an enlarged refinement window, determined according to the clustering shown in FIGs. 27A-28, or a non-enlarged refinement window. It should be noted that in some embodiments, there may be a predetermined maximum size constraint on a refinement window (e.g., based on a threshold of area of refinement window) to, for example, prevent the refinement window from encompassing the entire picture. In such instances, there may be some overlap in the refinement windows in the merge list 2902. In techniques such as that described in relation to FIG. 27A, the BVP candidate stored in merge list 2902 for an enlarged refinement window may be the centroid of the enlarged window. In some techniques such as that described in relation to FIG. 27B, the enlarged refinement windows may be stored in the form of the top-left and bottom-right coordinates of the enlarged refinement window and the BVP candidate stored in merge list 2902 for the enlarged window may be the BVP candidate of one of the overlapping refinement windows that is encompassed by the enlarged refinement window. For example, for a particular enlarged refinement window that encompasses two refinement windows W, and Wk, the BVP candidate BVP, of W, may be selected as the corresponding BVP candidate based on some selection criterion, and the top-left and bottom-right of the enlarged refinement window can be specified as displacement vectors from BVP,.

[0217] FIG. 29B illustrates an example of storing an enlargement window (enlarged refinement window) by its top-left and bottom-right position (e.g., position of sample or pixel) defined in relation to the selected BVP candidate and an example of storing an example enlargement window by its top-left and bottom-right coordinates (or corresponding vectors), according to some examples. In one illustrative example, an enlarged refinement window 2920 encompassing the refinement windows of BVPi and BVP2 may be indicated (and represented) in the merge list 2902 as its selected corresponding BVP candidate (e.g., candidate BVP1) and its top-left TL1* and bottom-right BR1* positions may be specified in the refinement window list 2904 as displacement vectors TL1 and BR1 (as also shown in the table “Ex.1 ”), respectively, from BVP1. In another illustrative example, an enlargement window 2922 encompassing example refinement windows of BVP1 and BVP2 may be indicated (and represented) in the merge list 2902 as its selected corresponding BVP candidate (e.g., candidate BVP1) and its top-left TL1* and bottom-right BR1* positions may be specified in the refinement window list 2904 as vectors TL1* and BR1* (as also shown in the table “Ex.2”), respectively, from the current block. For example, vector TL1* may be equal to a sum of the BVP candidate and TL1 and vector BR1* may be equal to a sum of the BVP candidate and BR1. It should be noted that vector TLr indicates a displacement from the current block (e.g., a top-left corner or sample of the current block) to position TL1*. Similarly, vector BR1* indicates a displacement from the current block e.g., a top-left corner or sample of the current block) to position BR1*.

[0218] More generally, the refinement window may be represented by indications of any pair of diagonally opposite positions / corners of the refinement window. For example, while the example of FIG. 29B shows the refinement window as being represented by indications of the top-left and bottom-right positions of the refinement window, the refinement window may alternatively be represented by indications of the top-right and bottom-left positions of the refinement window.

[0219] Note that in implementations in which a new BVP candidate that is the centroid of the enlarged window is calculated and specified in the merge list, having the width and height of the enlarged window stored in the refinement window list similarly enables calculating the top-left and bottom-right corners of the enlarged refinement window.

[0220] Embodiments are not limited to a particular manner of generating the merge list 2902. For example, merge list 2902 may be generated as a new list by, sequentially selecting each BVP candidate from the list of adjacent and non-adjacent merge BVP candidates, determining whether the selected BVP candidate’s refinement window overlaps the refinement windows of any of the BVP candidates currently in the merge list 2902, adding the selected BVP candidate to the merge list 2902 if no overlap is determined, or replacing the overlapping BVP candidate in the merge list 2902 with the new BVP candidate determined from the enlarged refinement window that encompasses the two overlapping windows. Adding a new BVP candidate to merge list 2902 may include recording information for the BVP candidate and its corresponding refinement window. When a BVP candidate already in the merge list 2902 is replaced with a new BVP candidate having a corresponding enlarged refinement window, the BVP candidate information and the corresponding refinement window information for the list position of the replaced BVP candidate are updated. The corresponding refinement window information may be maintained in merge list 2902 or in a list (e.g., 2904) separate from the merge list 2902. Moreover, when a new BVP candidate corresponding to an enlarged refinement window is added to the merge list 2902, the new BVP candidate is compared to each BVP candidate in the merge list 2902 to merge any BVP candidates in merge list 2902 that overlap with the new refinement window. This process may be iterated until no further overlaps between entries in merge list 2902 occur.

[0221] In an alternative, the merge list 2902 may be formed by updating the list of adjacent and non- adjacent merge BVP candidates in-place. For example, each BVP candidate from the list of adjacent and non-adjacent merge BVP candidates may be sequentially selected, a determination made as to whether the selected BVP candidate’s refinement window overlaps the refinement windows of any of the BVP candidates currently in the merge list 2902 (e.g., in this example of in-place updating, BVP candidates preceding the selected candidate in the list of adjacent and non-adjacent merge BVP candidates), keeping the selected candidate at its current position if no overlap is determined, or, if an overlap is determined, removing the overlapping BVP candidate from the merge list 2902 and replacing the selectedBVP candidate at its position in the merge list 2902 with the new BVP candidate determined from the enlarged refinement window that encompasses the two overlapping windows.

[0222] The new clustered merge BVP candidates in merge list 2902 are checked at 2906 to determine if they are already duplicated in the initial sparse list 2404, and a best predetermined number (e.g., 10) of non-redundant merge BVP candidates (i.e. , BVP candidates in the updated TMP merge list) 2908 compete with the sparse BVP candidates of sparse list 2404 at 2910. A best predetermined number (e.g., 30) of BVP candidates, based on their TMP costs, among both the updated TMP merge and the Sparse list (2908 and 2404 respectively), are selected for the sparse and merge list 2912.

[0223] Because the BVP merge candidates (i.e., those from updated merge list 2908 that are selected to the final sparse list 2912) may be located within the regular TMP reference region, or close to it, their refinement windows may also overlap the refinement windows of the sparse BVPs candidates (i.e., those from sparse list 2404 that are selected to the sparse and merge list 2912). FIG. 26B, for example, illustrates some overlapping refinement windows of sparse BVP candidates and merge BVP candidates. Consequently, according to some embodiments, the clustering algorithm can also be applied to avoid refinement windows overlapping between merge BVP candidates and sparse BVP candidates. For example, at 2913 the sparse and merge list 2912 is processed to merge any overlapping refinement windows including sparse BVP candidates. Then at 2916, the refinement of the processed BVP candidates from the sparse and merge list 2912 as determined at 2913 is performed. Merge candidates are refined using the corresponding refinement window sizes from the refinement window list 2914, and Sparse candidates are refined using the predetermined sparse refinement window size (e.g., 3x3) 2412. The refinement process at 2916 yields a refined list 2918 of sparse BVP candidates and merge BVP candidates. For example, the refined list 2918 may include the best candidate from the respective refinement window corresponding to each of the BVP candidates in the sparse and merge list 2912 after the processing at 2913 and 2916.

[0224] Note that, according to process 2900, the sparse and merge list 3210 may include BVP candidates that have overlapping refinement windows because it includes BVP candidates from the sparse list 2404 and from the updated merge list 2908 and as, for example, shown in FIGs. 30A-31 B, there may be overlaps between the refinement windows of BVP candidates in lists 2404 and 2908. However, because any overlaps between a merge BVP candidate and a sparse candidate are subjected to a clustering process at 2913, no duplicated TMP cost calculations are performed during the refinement search 2916. Moreover, since groups of two or more BVP candidates that are located close to each other have been replaced in the refined list by newly determined BVP candidates based on enlarged refinement windows, the diversity of the refined list 2918 is improved.

[0225] FIG. 30A, FIG. 30B, FIG. 31 A and FIG. 31 B show examples of overlapping of the refinement windows (3002 and 3001) of merge BVP candidates and sparse BVP candidates in the boundary of theregular TMP reference region and between the refinement windows (3101 and 3102) of two merge BVP candidates within the regular TMP reference region, respectively. The corresponding enlarged refinement windows 3000 and 3100 are also shown.

[0226] FIG. 32A shows a flowchart of a clustering process 3200 according to some techniques, applied to the sparse list 2404 and the adjacent merge BVP candidates 2405 and non-adjacent merge BVP candidates 2406 at the same TMP BVP clustering stage 3202 of the clustering process 3200. As described above, the sparse list 2404 may be generated according to the sparse search stage in an IntraTMP process, and the adjacent merge BVP candidates 2405 and non-adjacent merge BVP candidates 2406 may be determined according to FIGs. 23A-23B as in the IntraTMP with merge candidates process. As a result of the clustering, two lists are built: a sparse and merge list 3204 that includes BVP candidates from any of the lists 2404, 2405, 2406 and / or BVP candidates corresponding to enlarged refinement windows for any of the BVP candidates from the lists 2404, 2405, 2406, and a refinement window list 3206 comprising corresponding information (e.g., height and width of the refinement window or the top-left and bottom-right coordinates) of the corresponding refinement windows. It should be note that in some embodiments, the refinement window information may be maintained in the same list as the corresponding BVP candidate information.

[0227] At 3208, the BVP candidates in list 3204 may be reordered in ascending / increasing TM cost of the BVP candidates (non-clustered BVP candidate, a new BVP candidate defined for the centroid of the clustered refinement search regions, or one of the BVP candidates whose refinement windows partially or fully overlap) and pruned to the best 30 candidates forming the updated sparse and merge list 3210. The refinement stage 3212 of BVP candidates of the updated sparse and merge list 3210 uses the refinement window list 3214 to apply the refinement search efficiently to respective BVP candidates in the updated sparse and merge list 3210 and to generate the refined list 3216. During the refinement search, similar to that described above in relation to the refinement stage of IntraTMP, for the respective refinement window of each BVP candidate in the list being considered, the candidate reference block that has the best TMP cost is determined and the BVP candidate corresponding to that candidate reference block is added to the refined list 3216.

[0228] Note that, according to process 3200, the updated sparse and merge list 3210 does not include BVP candidates that have overlapping refinement windows because any overlaps between a merge BVP candidate and another merge BVP candidate, and between a merge BVP candidate and a sparse candidate were already considered at 3202. Thus, no duplicated TMP cost calculations are performed during the refinement search of refinement stage 3212. Moreover, since groups of two or more BVP candidates that are located close to each other have been replaced in the refined list by newly determined BVP candidates based on enlarged refinement windows, the diversity of the refined list 3216 is improved.

[0229] FIG. 32B shows a flowchart 3220 for a process that is identical to that of FIG. 32A except that, before the clustering at 3202, the merge list comprising the adjacent merge candidates and non-adjacent merge candidates is sorted and pruned (e.g., to 10 candidates having the lowest TMP costs), e.g., as shown at 2407.

[0230] FIG. 32C shows a flowchart 3230 for a process that is identical to that of FIG. 32B, except that the clustering at 3202 includes, in addition to candidates on the sparse list 2404 and adjacent and non- adjacent merge candidates, merge ARBV candidates of merge list 2408. A block is added to apply the AR-BVP to the merge list 2408 to generate AR-BVP candidates using the BVPs in the merge list 2408 as guiding BVs. Block 2409 is applied to the merge list 2408 and the generated AR-BVP candidates.

[0231] As described above, the AR-BVP technique may be applied to TMP merge candidates in the initial merge list 2408 to derive additional BVP candidates (referred to as “merge AR-BVP candidates”) to be used in generating an updated merge list 2409. However, the number of TMP merge candidates in the initial merge list 2408 may be small for reasons such as a limited number of the adjacent and non- adjacent blocks being coded (encoded or decoded) using the IBC mode or the IntraTMP mode, the BVs of such adjacent and non-adjacent neighboring blocks being invalid, or the candidates derived from these merge candidates being duplicated in the list. This leads to a small number of merge AR-BVP candidates being generated which significantly reduces the efficiency of the AR-BVP merge technique.

[0232] Some techniques relate to the use of the AR-BVP technique on TMP BVP candidates to derive additional BVP candidates to provide a diversity of candidates. For example, the AR-BVP technique may be applied to the BVP candidates derived in a search process using the TMP such as the sparse list to generate sparse AR-BVP candidates for use in the IntraTMP coding. The number of candidates in the sparse list is typically larger than the number of BV candidates in the initial merge list 2408. Consequently, there can be more derived sparse AR-BVP candidates than the merge AR-BVP candidates, leading to better BVP candidates to be selected for the refinement stage.

[0233] FIG. 32A-B show the TMP Merge clustering algorithm, which is applied between the best (e.g., 30) sparse BVP candidates of sparse list 2404 and the merge BVP candidates, of merge list 2407, obtained from adjacent 2405 and non-adjacent candidates 2406. FIG. 32C shows the TMP Merge clustering algorithm also including the Merge AR-BVPs. In the clustering algorithm shown in FIGS. 32A and 32B, the refinement windows of the sparse BVP candidates (3x3) and the refinement window of the merge BVP candidates (11x11) are compared to verify if they are overlapped (in FIG. 32C, Merge AR- BVP candidates use a refinement window of 5x5).

[0234] A Merge and sparse BVP candidates clustering is illustrated in FIGs. 33A-B (also FIGs. 27A-B), which, in FIG. 33A, shows the refinement window overlapping of two merge BVPs (3320 and 3321).When the refinement windows of two BVP candidates overlap, a new refinement window is determined by the Top-Left (TL) coordinates 3326, which may be the minimum value of the TL coordinates of the BVPcandidates refinement window, and its Bottom-Right (BR) coordinates 3327, which may be the maximum value of the BR coordinates of the BVP candidates refinement window.

[0235] The refinement window of the two clustered BVP candidates is stored in a Refinement Window list 3206 to be used conveniently in the refinement stage.

[0236] The clustering algorithm enlarges the refinement window when two candidates overlap, so the clustered refined windows may have a significantly bigger dimension than the original candidates. In particular, for the small dimension block size, the refinement window of a clustered candidate may fully overlap a sparse reference region.

[0237] FIG. 33B shows some BVP clustering examples, some between merge BVP candidates clustering (BVP-M2 and BVP-M3, and BVP-M4 and BVP-M5) outside of the reference regions (R1 to R6), and others between a merge and a sparse BVP candidate (BVP-M6 and BVP-S4), partially overlapping the TMP search region R1 . The TL and BR coordinates characterize the new clustered refinement windows (3330 to 3335).

[0238] The clustering of two BVP candidates may reduce the TMP cost computation in the refinement stage (e.g., 3212 in FIG.32A-B). However, the clustering between the merge candidates and the sparse candidates does not avoid the TMP cost computation in a search region that will be newly computed in the refinement stage if the refinement window fully overlaps the search region.

[0239] It was noted above that the reference region which is searched for IntraTMP is determined in accordance with the location of the current block, and that the reference region is subdivided into several search regions (e.g., R1-R6). The position and dimensions of each search region R1-R6 are determined according to three parameters: the current block (CB) size, the multifactor parameter “a”, and the position of the CB within the CTU.

[0240] CB width determines the right boundary of regions R6, R3, and R5, as well as the left boundary of region R5. The CB height determines the bottom boundary of the region R5 and the above and bottom boundary of the regions R3, R4, and R6. The multifactor parameter "a" constrains the maximum height and width of the sparse search regions set. The position of the current block inside the CTU determines the right boundaries of regions R3 and R5, as well as the bottom boundaries of regions R4 and R6.

[0241] FIG. 33C shows an example current block 1906 in a current CTU 1904 within a current picture / frame 1900. It also shows the current template 1908, and the reference template 3338 of a reference block 3336. FIG. 33C also shows current block’s width and height (CbWidth and CbHeight) parameters, calculated in accordance with the current block’s position within the CTU 1904. The position and the dimension of each of the search regions R1-R6 determined as a multiple ‘a’ of CbWidth and / or CbHeight is also illustrated.

[0242] According to the CB position and the relative CB position in the current CTU, some of the nearest search regions (R3, R4, R5, and R6) may have smaller dimensions than the merge refinement window,so the TMP cost is computed two times, one at the sparse stage and the other at the refinement stage of the merge candidate. As noted above, template matching costs are calculated for candidate reference blocks at each sample position within a refinement window. Thus, if a search region (R1-R6) is overlapped by a refinement window, template matching cost calculation in that search region in the sparse search stage would be duplicative. This calculation of the same values multiple times results in wasted computation.

[0243] Embodiments of the present disclosure enable checking, for each TMP search region, if the refinement window of any BVP merge candidates fully overlaps the search region. When it is determined that a search region is overlapped by a refinement window, the search region is skipped. By skipping the search region for the sparse search stage and / or the refinement search stage of IntraTMP, embodiments improve the efficiency of encoders / decoders.

[0244] FIG. 34A depicts one example of the TM search region arrangement for a current block size of 16x16 samples, in which the top-left sample is located at the absolute coordinates of (404, 276) belonging to the third CTU row and fourth CTU column (CTU size of 128x128).

[0245] Each search region's top left (TL) and bottom right (BR) coordinated (3407 to 3418) is determined according to the CB size (e.g., 16x16), CB location relative to the current CTU (20,20), and multifactor parameter (a=5). It can be observed that the TL coordinates of the region R4 are R4.TL= (389, 240), and the BR coordinates are R4.BR=(403, 260).

[0246] FIG. 34B illustrates a clustered refinement window as a result of two overlapped refinement windows of two merge BVP candidates (BVP-M1 and BVP-M2), 3423 and 3422. The TL and BR coordinates of the clustered refinement window BVP-M1 M2 are BVP-M1 M2.TL=(378,236) 3524 and BVP-M1 M2.BR=(408,264) 3425 respectively.

[0247] The overlapping condition of an i-th search region R[i] and a clustered (or not) refinement window of a j-th merge (or AR-BVP) candidate BVP-M [j] may be obtained for a comparison of each horizontal and vertical component of the TL and BR coordinates of the respective search region and BVP candidate, as follows (19):( / ? [ / ]. TL. x > BVP-M[j]. TL. x) && (R[i]. TL. y > BVP-M[j]. TL.y) && (R[i]. BR.x <= BVP-M[j]. BR.x) && ( / ? [ / ]. BR. y <= BVP-M[j]. BR. y) (19)The condition of Equation (19) shows: an x (horizontal) component of the TL coordinate of an i-th reference region (R[iJ) being greater than or equal to the x component of the TL coordinate of a y-th BVP candidate (BVP-M [j]),- a y (horizontal) component of the TL coordinate of the i-th reference region (R[iJ) being greater than or equal to the y component of the TL coordinate of a y-th BVP candidate (BVP-M [j]),- an x (horizontal) component of the BR coordinate of the i-th reference region (R[iJ) being less than or equal to the x component of the BR coordinate of the y-th BVP candidate (BVP-M[j]),- and a y(horizontal) component of the BR coordinate of the i-th reference region (R[i]) being less than or equal to the y component of the BR coordinate of the y-th BVP candidate (BVP-M[j]).

[0248] Following the example illustrated in FIG. 34A and FIG. 34B, it can be observed how the simple condition is met:R4.TL = (389,240), R4.BR = (403, 260), BVP-M1 M2.TL = (378,236), BVP-M1 M2.BR = (408,264), and (389 > 378) && (240 > 236) && (403 <= 408) && (260 <= 264).

[0249] FIG. 35 depicts a flowchart 3500 of a process for skipping duplicate template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments of the present disclosure. The flowchart operations represented by blocks with a dotted fill pattern (3512, 3516, 3518, 3522, 3524) represent the algorithm logic that determines the search regions to be skipped. First, the merge list 3506 is built using the adjacent 3502 and non-adjacent candidates 3504, and it may be ranked / sorted according to some criteria such as, for example, the TMP cost. The process of flowchart 3500 may, at 3502 and 3504, determine adjacent merge candidates and non- adjacent merge candidates in a manner similar to operations to obtain adjacent merge BVP candidates 2405 and non-adjacent merge BVP candidates 2406, respectively, of FIGs. 32A-C. The merge list 3506 can be determined by sorting and pruning the determined adjacent merge candidates and non-adjacent merge candidates in a manner similar to 2407 of FIGs. 32B-C. In some embodiments, alternatively or additionally to the TMP costs, another criterion such as, for example, sorting the candidates so that candidates that are outside of the TMP reference regions appear first may be used.

[0250] The merge list 3506 may be clustered 3508 as described in relation to FIGs. 27A-B and / or FIGs. 32A-C to obtain the largest refinement window with potential overlapping with a TMP sparse search region. It should be noted that in some embodiments, the clustering can be skipped in determining whether one or more search regions are overlapped by a refinement window. For instance, if the refinement window is made larger (e.g., from the 11x11 size currently used for IntraTMP with merge candidates etc., to 25x25), the initial refinement window of a merge (or ARBVP) candidate block may itself (without requiring that it is clustered with another refinement window) overlap a search region and thus clustering may not be necessary (e.g., may be optional) to determine at least one search region to be skipped.

[0251] An index j, used for iterating through the clustered merge refinement windows, and an index i, used for iterating through the predetermined search regions (e.g., R1-R6) are initialized at 3510 and 3514 respectively. The TL and BR coordinates are computed for each TMP search region and each merge candidate in the merge list or the clustered merge candidates. The TL and BR of respective clusteredmerge refinement windows are selected at 3512, with the incrementing of j provided at 3521 so that the process can step through respective refinement windows in the clustered or non-clustered refinement windows list 3508. The TL and BR of respective search regions are selected at 3518 by incrementing index i at 3520. The process iterates so that, for each refinement window in the clustered merge refinement windows in the list 3508, each of the search regions can be tested at 3522 to determine whether the refinement window overlaps the search region. Equation (19) above (overlapping condition) can be used for the test for overlap at 3522.

[0252] The search regions that are overlapped by at least one of the refinement windows (enlarged or non-enlarged) are checked at 3522, and upon all search regions having been searched for overlap by each of the merge refinement windows, at 3526 the TMP cost calculations are performed in the nonoverlapped search regions for respective samples (based on sample interval 3528), and the sparse list of candidates is built at 3530.

[0253] FIG. 36 illustrates a flowchart 3600 of another process for skipping duplicate template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments of the present disclosure. The process of flowchart 3600 (blocks 3602-3630) may be identical to the process of flowchart 3500 (blocks 3502-3530) except that flowchart 3600 includes, at3605, merge AR-BVP candidates (e.g., a maximum of 25), in the evaluation for inclusion in the merge list3606.

[0254] FIG. 37 illustrates a flowchart 3700 of a process for skipping duplicate template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments of the present disclosure. Blocks 3702-3730 of the process of flowchart 3700 may be identical to the process of flowchart 3600 (blocks 3602-3630) except that flowchart 3700 includes subsequent use of the sparse list at block 3730 and the merge list at block 3706, in the clustering at 3732. In some embodiments, blocks 3705 and / or 3708 may not be performed.

[0255] The operations from clustering at block 3732 to generation of the refined list at block 3746 may be similar to, or the same as, operations 3202 to 3216 described in relation to FIGs. 32A-C.

[0256] FIG. 38 illustrates a flowchart 3800 of a process for encoding a current block by skipping template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments. For example, in some embodiments, since template matching costs will be calculated during a refinement stage for each sample in each refinement window determined for merge candidates (e.g., candidates determined in accordance with FIGs. 23A-B and 25A-C), skipping one or more search regions that overlap a refinement window when template matching costs are calculated for sparse candidates would avoid duplicated calculating the template matching costs for the same samples. In some examples, the process of flowchart 3800 may be performed by an encoder (e.g., encoder 200 of FIG. 2).

[0257] The process of flowchart 3800 may begin when the encoder is encoding a current block at block3802. At 3802, the encoder obtains, using vector information (e.g., block vector) of reconstructed neighboring blocks (e.g., adjacent, non-adjacent, history-based candidates, etc.), a first set of candidates for predicting a current block. For example, the process of flowchart 3800 may include the process of flowchart 3700. At block 3802, the encoder may determine a set of adjacent merge BVP candidates and a set of non-adjacent merge BVP candidates as described in relation to blocks 3702 and 3704 of flowchart 3700 and which may be examples of the first set of candidates. Further descriptions of determining the sets of adjacent merge BVP candidates and non-adjacent merge BVP candidates are provided in relation to FIGs. 23A-B, 24 and 29A-B, among others. In some implementations, a set of AR-BVP candidates may also be determined as described in relation to block 3706 of flowchart 3700. Further descriptions of AR- BVP candidate determination are provided in relation to FIGs. 25A-C and 32C, among others. The determined merge BVP candidates (the adjacent merge BVP candidates, the non-adjacent merge BVP candidates, and optionally, the AR-BVP candidates) are then ordered (sorted) according to at least a template matching cost metric such as, for example, SAD, SATD, etc., and pruned to include only a predetermined number of the best (e.g., lowest cost) candidates. The selected BVP candidates may be maintained in a list, referred to herein as the merge list. The generation of the merge list is further described in relation to FIGs. 24, 29A and 32A-C, among others. In some embodiments, the merge list is limited to 25 merge BVP candidates.

[0258] At 3804, the encoder determines a plurality of first refinement windows based on positions of the first set of candidates. For example, each position (e.g., location) may be indicated by the position (e.g., location) of the current block (e.g., the top-left sample) displaced by each respective candidate of the first set of candidates. The plurality of first refinement windows may be determined such that each first refinement window of the plurality of first refinement windows encompasses at least one candidate from the first set of candidates. That is, each refinement window encompasses (fully overlaps) the reference block corresponding to at least one merge BVP candidate from the merge list. In some embodiments, each refinement window encompasses only one refinement window. As described in relation to FIGs. 19B, 32C etc., a refinement window of a predetermined size (e.g., 11x11 for adjacent / non-adjacent candidates and 5x5 for AR-BVP candidates) is initially determined for each merge candidate.

[0259] After the initial refinement window for each merge candidate in the merge list is determined, a clustering of refinement windows is performed in some embodiments. The clustering includes identifying groups of two or more candidates whose refinement windows overlap (partially overlap) and deriving an enlarged refinement window that encompasses the overlapping group of two or more refinement windows. The overlapping candidates are replaced in the merge list by the enlarged refinement window. The clustering may iteratively continue to further enlarge any enlarged refinement window that overlaps with other enlarged refinement window or a non-enlarged refinement window. The term non-enlargedrefinement window refers to a refinement window that is initially determined for a reference block corresponding to a merge candidate and that has not overlapped with any other refinement window. Thus at the end of the clustering step, the merge list may include candidates for which the refinement windows are enlarged and candidates for which the refinement windows are not enlarged. In example embodiments, the merge list and / or an associated list of refinement windows is used to keep track of the refinement window (e.g., top left and bottom right coordinates of refinement windows) associated with each candidate. Clustering of refinement windows of merge candidates is described in relation to, for example, FIGs. 27A-B.

[0260] At 3806, the encoder identifies, from a plurality of search regions determined based on at least a position (e.g., a location) of the current block, at least one search region overlapped by a first refinement window of the plurality of first refine windows. For example, the position of the current block may refer to the top-left corner / sample of the current block. As noted above, a reference region is determined for the current block, and a plurality of search regions (e.g., R1-R6) are determined subdividing the reference region. The boundaries of each the plurality of search regions may be defined according to (e.g., relative to) the position and / or location of the current block. In some implementations the boundaries of the search region may also be based on the size of the current block.

[0261] In example embodiments, for each candidate in the merge list after the clustering at 3904, it is determined whether the corresponding refinement window overlaps any of the search regions. In some embodiments, the determination of overlap can be performed by comparing the TL and BR coordinates of the refinement window with the TL and BR coordinates of each of the search regions. Equation (19), specified above, enables efficient calculation of overlap between a refinement window and a search region. In some embodiments, search regions that are determined to be fully overlapped (e.g., fully encompassed, contained within) by at least one of the refinement windows are identified. As noted above, a refinement window that is determined to overlap a search region may not necessarily be an enlarged refinement window. Because the sizes of respective search regions are determined based on the position and size of the current block, a non-enlarged refinement window may be capable of overlapping a search region. In some embodiments, the identified at least one search region may only partially overlap the refinement window. For example, in such embodiments, a search window of which at least a predetermined minimum threshold percentage portion is overlapped by a refinement window may be considered as overlapped and may be elected to be skipped.

[0262] At 3808, the encoder determines, based on a first template matching search of the plurality of search regions excluding the at least one search region, a second set of candidates for predicting the current block. Second candidates of the second set of candidates are located in respective search regions other than the identified at least one search region, of the plurality of search regions.

[0263] In some embodiments, the second candidate determining technique may include determining sparse candidates (e.g., at sampling intervals of 3 or 4 etc.) such as described in relation to FIGs. 18-22, while skipping over overlapped search regions. For example, the sparse search for sparse candidates may be performed only in search regions that are not overlapped by a refinement window of any of the merge BVP candidates in the merge list. In some implementations, a list of non-overlapped search regions may be generated, and the sparse search or the refinement search for sparse candidates is performed only for samples that are in the list of non-overlapped search regions. Alternatively, a list of overlapped search regions may be maintained, and the search regions can calculate template matching costs for sparse candidates and / or template matching costs in the refinement windows of sparse candidates according to a predetermined ordering of the search regions while skipping over any search region that is found in the list of overlapped search regions.

[0264] In some embodiments, the second set of candidates may consist only of sparse candidates that are located in the non-overlapped search regions. The second set of candidate may be stored in a sparse list. An example sparse list and its generation is described in relation to block 3730 in flowchart 3700. In some embodiments, the operations of blocks 3806-3808 may be performed as described in relation to FIGs. 35-36 to determine a sparse list in which all candidates are located in search regions that are not overlapped by any refinement windows determined at the clustering of merge candidates (e.g., blocks 3508 / 3608).

[0265] As described above, when a search region is fully overlapped by an enlarged or non-enlarged refinement window of a merge BVP candidate, each sample in that search region would be subjected to the corresponding template matching cost calculation during the refinement search for that refinement window. Therefore, by skipping the search region entirely for template matching cost calculation associated with sparse candidates, embodiments avoid duplicate template matching cost calculations in that search region.

[0266] At 3810, the encoder determines a plurality of second refinement windows based on the second set of candidates. Each second refinement window of the plurality of second refinement windows encompasses a candidate from the second set of candidates. For example, a refinement window is determined for each of the second set of candidates based on a refinement window of a predetermined size (e.g., 3x3, 4x4) for each sample in the reference block corresponding to a sparse candidate in the sparse list. In some embodiments, the refinement window may depend on the position of each second candidate and also the type, i.e., the second candidates are from TMP search— so the refinement window may have a size of 5x5 if TMP search interval is 3 and is 7x7 if TMP search interval is 4, etc.

[0267] At 3812, the encoder selects, based on a second template matching search of a plurality of refinement windows determined using one or more of the first refinement windows and one or more of the second refinement windows, a candidate for predicting the current block.

[0268] This step may include a second clustering that includes refinement windows of both the merge list candidates and the sparse list candidates, followed by a refinement stage.

[0269] The second clustering may be performed as described in relation to block 3732. The refinement windows of merge candidates of the merge list 3706 after the first clustering at 3708 and the refinement windows of sparse candidates in the sparse list at block 3730 are considered for the second clustering. The second clustering may result in a combined list of sparse and merge candidates and the corresponding refinement windows (e.g., 3734 and 3736 respectively), that is then rearranged according to template matching costs and pruned to identify a predetermined number of the best candidates (e.g., blocks 3738-3740).

[0270] The refinement windows (e.g., 3744) of the candidates in the spare and merge candidates list (e.g., 3740) are then subjected to refinement search. The template matching cost is calculated for each sample in the respective refinement windows, (e.g., 3742) to determine a refined list of candidates (e.g., 3746).

[0271] The candidate for predicting the current block may be selected by considering the template matching cost of the respective candidates in the refined list. In some embodiments, the candidate may be selected by filtering the refined list based on template matching costs and then calculating a rate distortion optimization or the like for respective candidates in the filtered refined list.

[0272] At 3814, the encoder encodes the current block based on the selected candidate. For example, the reference block corresponding to the candidate selected at 3912 may be subtracted from the current block, and the difference may be encoded as in the bitstream that is subsequently output by the encoder.

[0273] FIG. 39 illustrates a flowchart 3900 of a method for decoding a current block by skipping template match cost calculations in search regions that are overlapped by at least one refinement window, according to some embodiments. For example, in some embodiments, since template matching costs will be calculated during a refinement stage for each sample in each refinement window determined for merge candidates (e.g., candidates determined in accordance with FIGs. 23A-B and 25A-C), skipping one or more search regions that overlap a refinement window when template matching costs are calculated for sparse candidates would avoid duplicated calculating the template matching costs for the same samples. In some examples, the process of flowchart 3900 may be performed by a decoder (e.g., decoder 300 of FIG. 3).

[0274] The process of flowchart 3900 may begin when the decoder is decoding a current block at block 3902. At 3902, the decoder obtains, using vector information of reconstructed neighboring blocks, a first set of candidates for predicting a current block. Operations of block 3902 may be the same or similar as the operations described in relation to block 3802 of flowchart 3800.

[0275] At 3904, the decoder determines a plurality of first refinement windows based on positions of the first set of candidates. Each first refinement window of the plurality of first refinement windows mayencompass at least one candidate from the first set of candidates. Operations of block 3904 may be the same or similar as the operations described in relation to block 3804 of flowchart 3800.

[0276] At 3906, the decoder identifies, from a plurality of search regions determined based on at least a location or position of the current block, at least one search region overlapped by a first refinement window of the plurality of first refine windows. Operations of block 3906 may be the same or similar as the operations described in relation to block 3806 of flowchart 3800.

[0277] At 3908, the decoder determines, based on a first template matching search of the plurality of search regions excluding the at least one search region, a second set of candidates for predicting the current block. Second candidates of the second set of candidates are located in respective search regions, other than the identified at least one search region, of the plurality of search regions. Operations of block 3908 may be the same or similar as the operations described in relation to block 3808 of flowchart 3800.

[0278] At 3910, the decoder determines a plurality of second refinement windows based on the second set of candidates. Each second refinement window of the plurality of second refinement windows encompassing a candidate from the second set of candidates. Operations of block 3910 may be the same or similar as the operations described in relation to block 3810 of flowchart 3800.

[0279] At 3912, the decoder selects, based on a second template matching search of a plurality of refinement windows determined (e.g., obtained) using one or more of the first refinement windows and one or more of the second refinement windows, a candidate for predicting the current block. Operations of block 3912 may be the same or similar as the operations described in relation to block 3812 of flowchart 3800.

[0280] At 3914, the decoder reconstructs the current block based on the selected candidate. For example, a residual obtained in relation to the current block from the bitstream is added to the reference block corresponding to the candidate selected at 3912 to determine the current block.

[0281] 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 4000 is shown in FIG. 40. Blocks depicted in the figures above, such as the blocks in FIGS. 1 , 2, and 3, may execute on one or more computer systems 4000. Furthermore, each of the steps of the flowcharts depicted in this disclosure may be implemented on one or more computer systems 4000.

[0282] Computer system 4000 includes one or more processors, such as processor 4004. Processor 4004 may be, for example, a special purpose processor, general purpose processor, microprocessor, or digital signal processor. Processor 4004 may be connected to a communication infrastructure 4002 (forexample, a bus or network). Computer system 4000 may also include a main memory 4006, such as random access memory (RAM), and may also include a secondary memory 4008.

[0283] Secondary memory 4008 may include, for example, a hard disk drive 4010 and / or a removable storage drive 4012, representing a magnetic tape drive, an optical disk drive, or the like. Removable storage drive 4012 may read from and / or write to a removable storage unit 4016 in a well-known manner. Removable storage unit 4016 represents a magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 4012. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 4016 includes a computer usable storage medium having stored therein computer software and / or data.

[0284] In alternative implementations, secondary memory 4008 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 4000. Such means may include, for example, a removable storage unit 4018 and an interface 4014. Examples of such means may include a program cartridge 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 4018 and interfaces 4014 which allow software and data to be transferred from removable storage unit 4018 to computer system 4000.

[0285] Computer system 4000 may also include a communications interface 4020. Communications interface 4020 allows software and data to be transferred between computer system 4000 and external devices. Examples of communications interface 4020 may include a modem, a network interface (such as an Ethernet card), a communications port, etc. Software and data transferred via communications interface 4020 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 4020. These signals are provided to communications interface 4020 via a communications path 4022. Communications path 4022 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.

[0286] 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 4016 and 4018 or a hard disk installed in hard disk drive 4010. These computer program products are means for providing software to computer system 4000. Computer programs (also called computer control logic) may be stored in main memory 4006 and / or secondary memory 4008. Computer programs may also be received via communications interface 4020. Such computer programs, when executed, enable the computer system 4000 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 4004 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 4000.

[0287] 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: obtaining, using block vector (BV) information of reconstructed neighboring blocks, a first set of candidates for predicting a current block; identifying, from a plurality of search regions defined based on a position of the current block, at least one search region overlapped by a first refine window of first refine windows determined relative to positions of the first set of candidates; determining, based on a first template matching search of the plurality of search regions excluding the at least one search region, a second set of candidates for predicting the current block; determining second refine windows based on the second set of candidates; selecting, based on a second template matching search of a plurality of refine windows obtained using one or more of the first refine windows and one or more of the second refine windows, a candidate for predicting the current block; and coding the current block based on the selected candidate.

2. The method of claim 1 , wherein: the first and second set of candidates are BV candidates and the selected candidate is a BV candidate; or the first and second set of candidates are block vector predictor (BVP) candidates and the selected candidate is a BVP candidate.

3. The method of any one of claims 1 -2, wherein the identifying the at least one search region is overlapped by the first refine window comprises: comparing a top-left coordinate and a bottom-right coordinate of the at least one search region with a top-left coordinate and a bottom-right coordinate of the first refine window, respectively.

4. The method of any one of claims 1 -3, wherein the identifying the at least one search region comprises: for each search region of the plurality of search regions, comparing a top-left coordinate and a bottom-right coordinate of the each search region with a top-left coordinate and a bottom-right coordinate of each first refine window from the plurality of first refine windows to determine whether the each search window is overlapped by one of the first refine windows.

5. The method of any one of claims 1 -4, wherein the at least one identified search region is fully overlapped by or is contained within the first refine window.

6. The method of any one of claims 3-5, wherein the at least one search region is identified as overlapping the first refine window based on:a horizontal component of the top-left coordinate of the at least one search region being greater than or equal to a horizontal component of the top-left coordinate of the first refine window; a vertical component of the top-left coordinate of the at least one search region being greater than or equal to a vertical component of the top-left coordinate of the first refine window; a horizontal component of the bottom-right coordinate of the at least one search region being less than or equal to a horizontal component of the bottom-right coordinate of the first refine window; and a vertical component of the bottom-right coordinate of the at least one search region being less than or equal to a vertical component of the bottom-right coordinate of the first refine window.

7. The method of any one of claims 1 -6, wherein the at least one search region is partially overlapped by the first refine window.

8. The method of any one of claims 1-7, wherein the plurality of search regions subdivide a reference region for searching candidates of the current block.

9. The method of any one of claims 1 -8, wherein boundaries of the plurality of search regions are defined relative to the position of the current block.

10. The method of claim 9, wherein the boundaries of the plurality of search regions are determined according to the position of the current block and a size of the current block.11 . The method of any one of claims 1 -10, wherein the determining the first refine windows relative to the positions of the first set of candidates, comprises: determining a refine window, of the first refine windows, centered at a position of a candidate of the first set of candidates.

12. The method of any one of claims 1-11 , wherein the determining the first refine windows relative to the positions of the first set of candidates, comprises detecting two or more of the first refine windows that overlap, wherein each of the two or more overlapping first refine windows encompasses a respective first candidate from the set of first candidates; determining a rectangular area that encompasses the two or more overlapping first refine windows; and adding the rectangular area as a refine window to a list comprising the plurality of first refine windows.

13. The method of claim 12, wherein the adding the rectangular area to the list comprises replacing the two or more overlapping first refine windows in the list with the rectangular area.

14. The method of any one of claims 1 -13, wherein the determining the second set of candidates comprises:applying a sampling interval to the plurality of search regions excluding the at least one search region to determine a set of sparse candidates, wherein the second set of candidates are a subset of the set of sparse candidates.

15. The method of claim 14, wherein each second window of the second refine windows for a respective candidate of the second set of candidates encompasses the respective candidate and is based on a first predetermined window size.

16. The method of any one of claims 1 -15, wherein the first set of candidates comprises BVs of adjacent neighboring blocks or BVs of non-adjacent neighboring blocks.

17. The method of claim 16, further comprising: deriving auto-relocated block vector prediction (AR-BVP) candidates from the first set of candidates; and adding the AR-BVP candidates to the first set of candidates.

18. The method of any one of claims 1 -17, wherein at least one of the plurality of refine windows encompasses two or more candidates from the first set of candidates.

19. The method of any one of claims 1 -18, wherein at least one of the plurality of refine windows encompasses a candidate from the first set of candidates and a candidate from the second set of candidates.

20. The method of any one of claims 1 -19, wherein each first refine window of the first refine windows encompasses at least one candidate from the first set of candidates.21 . The method of any one of claims 1 -20, wherein respective refine windows, each of a first predetermined window size, are determined for the first set of candidates, and wherein the first refine windows are determined based on clustering overlapping windows of the refine windows.

22. The method of claim 21 , wherein the second refine windows are formed based on a second predetermined window size different from the first predetermined window size.

23. The method of any one of claims 1 -22, wherein the coding the current block comprises: reconstructing the current block based on the selected candidate.

24. The method of claim 23, wherein the current block is reconstructed based on a residual of the current block, obtained from a bitstream, and a reference block corresponding to the selected candidate.

25. The method of any one of claims 1 -24, wherein the selecting the candidate comprises: obtaining, from the bitstream, an index to a list of candidates comprising the candidate, wherein the index indicates the selected candidate.

26. The method of any one of claims 1 -22, wherein the coding the current block comprises: encoding the current block based on the selected candidate.

27. The method of claim 26, wherein the current block is encoded based on signaling, in a bitstream, a residual based on a difference between the current block and a reference block corresponding to the selected candidate.

28. 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- 27.

29. 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 1-22 or 26-27.

30. A non-transitory computer-readable recording medium storing a bitstream generated by the method for encoding a video according to any one of claims 1-22 or 26-27.

31. 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 1-25.

32. 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 one of claims 1-25.

33. A bitstream generated according to any one of claims 1-22 or 26-27.

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