Template preprocessing for reference filtering

Abstract

A video coder determines a range of values of samples in a reference block associated with a current block. Based on the range and in accordance with a priority ordering of samples in a template of the reference block, a plurality of samples from the template of the reference block is selected. The coder derives parameters of a filter based on the selected plurality of samples and corresponding samples from a template of the current block. The coder applies the filter, with the derived parameters, to the reference block to generate a prediction block. The current block is coded based on the prediction block.

Description

TITLETemplate Preprocessing for Reference FilteringCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 550,241, filed February 6, 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 shows an example video coding / decoding system in which embodiments of the present disclosure may be implemented.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0021] FIG. 17A shows a current block and a reference block with corresponding templates used in determining scale and offset parameters for local illumination compensation (LIO).

[0022] FIG. 17B shows a process for calculating a predicted block when LIO is applied.

[0023] FIG. 18A illustrates a process for calculating a predicted block in a random access configuration of bi- predictive inter prediction.

[0024] FIG. 18B illustrates a process for calculating a predicted block in a low delay B configuration of bi-predictive inter prediction.

[0025] FIG. 19A and 19B illustrate luma and chroma sampling examples.

[0026] FIG. 20A illustrates a template of a reference block with a single-tap filter.

[0027] FIG. 20B illustrates a template of a reference block with several multi-tap filter.

[0028] FIG. 200 illustrates example multi-tap filter shapes.

[0029] FIG. 21A and 21 B show example correspondences between samples in the template of the reference block and samples in the template of the current block.

[0030] FIG. 22A and 22B show two example subsampling schemes when the aspect ratio between the short edge and the long edge is 2:1.

[0031] FIG. 23A, 23B, 230, and 23D show example subsampling schemes when the aspect ratio between the short edge and the long edge is 4:1.

[0032] FIG. 24A shows example templates for a current block and a reference block, showing template samples and samples outside of the template that are used in the derivation of filter parameters.

[0033] FIG. 24B shows the example templates shown in FIG. 24A with some samples excluded from consideration in calculating filter parameters.

[0034] FIG. 25 shows a histogram of sample values of the reference block, according to some embodiments.

[0035] FIG. 26 show histograms for an example reference block and for the template of the reference block.

[0036] FIG. 27A and 27B illustrate several different template formats that can be used with multi-tap filters of several shapes.

[0037] FIG. 28 shows a flowchart of a process for encoding a current block using template preprocessing for reference filtering, according to some embodiments.

[0038] FIG. 29 shows a flowchart of a process for decoding a current block using template preprocessing for reference filtering, according to some embodiments.

[0039] FIG. 30 shows a flowchart of a process for selecting template samples for calculating filter parameters based on a priority ordering, according to some embodiments.

[0040] FIG. 31 shows a flowchart of a process for selecting template samples using a histogram of the samples of the reference block, according to some embodiments.

[0041] FIG. 32 shows a flowchart of a process for selecting a subset of template samples for calculating filter parameters, according to some embodiments.

[0042] FIG. 33 shows a flowchart of a process for selecting a multi-tap filter and applying the selected multi-tap filter to generate the prediction block, according to some embodiments.

[0043] FIG. 34 shows a reference block and a current block with corresponding probe templates that can be used to evaluate a plurality of multi-tap filters, according to some embodiments.

[0044] FIG. 35 shows a flowchart of a method for an encoder to classify template samples into groups, and to select a filter that is most suited for each group, according to some embodiments.

[0045] FIG. 36 shows a flowchart of a method for a decoder to classify template samples into groups, and to select a filter that is most suited for each group, according to some embodiments.

[0046] FIG. 37 shows a flowchart of a process for encoding a current block using template preprocessing for reference filtering, according to some embodiments.

[0047] FIG. 38 shows a flowchart of another process for decoding a current block using template preprocessing for reference filtering, according to some embodiments.

[0048] FIG. 39 shows a flowchart of a process for selecting a subset of template samples for calculating filter parameters, according to some embodiments.

[0049] FIG. 40 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented.DETAILED DESCRIPTION

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 / ordata. A computer-readable medium may include a non-transitory medium in which data can be stored and that does not include carrier waves and / or transitory electronic signals propagating wirelessly or over wired connections. Examples of a non-transitory medium may include, but are not limited to, a magnetic disk or tape, optical storage media such as compact disk (CD) or digital versatile disk (DVD), flash memory, memory or memory devices. A computer-readable medium may have stored thereon code and / or machine-executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any 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.

[0054] 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.

[0055] 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.

[0056] 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.).

[0057] Source device 102 may comprise (e.g., for encoding video sequence 108 into bitstream 110) one or more of a video source 112, an encoder 114, and / or an output interface 116. Video source 112 may provide and / or generate video sequence 108 based on a capture of a natural scene and / or a synthetically generated scene. A synthetically generated scene may be a scene comprising computer generated graphics and / or screen content. Video source 112 may comprise a video capture device (e.g., a video camera), a video archive comprising previously captured natural scenes and / or synthetically generated scenes, a video feed interface to receive captured natural scenes and / or synthetically generated scenes from a video content provider, and / or a processor to generate synthetic scenes.

[0058] 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 Or) 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.

[0059] 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.

[0060] For temporal prediction, encoder 114 may search for a block similar to the block being encoded in another picture (e.g., referred to as a reference picture) of video sequence 108. The block determined during the search (e.g., referred to as a prediction block) may then be used to predict the block being encoded. For spatial prediction, encoder 114 may form a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 108. A reconstructed sample refers to a sample that was encoded and then decoded. Encoder 114 may determine a prediction error (e.g., also referred to as a residual) based on the difference between a block being encoded and a prediction block. The prediction error may represent non-redundant information that may be sen t / tran sm itted to a decoder for accurate decoding of video sequence 108.

[0061] Encoder 114 may apply a transform to the prediction error (e.g. using a discrete cosine transform (DOT), 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.

[0062] 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 (ATSO) 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).

[0063] 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.

[0064] 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).

[0065] 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, forexample, 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.

[0066] 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.

[0067] 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.

[0068] 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 (WO)), the WebM VP8 and VP9 codecs, and / or AOMedia Video 1 (AV1), and / or any other video coding protocol).

[0069] FIG. 2 shows an example encoder. Encoder 200 as shown in FIG. 2 may implement one or more processes described herein. Encoder 200 may encode a video sequence 202 into a bitstream 204 for more efficient storage and / or transmission. Encoder 200 may be implemented in video coding / decoding system 100 as shown in FIG. 1 (e.g., as encoder 114) or in any computing, communication, or electronic device (e.g., desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.). Encoder 200 may comprise one or more of an inter prediction unit 206, an intra prediction unit 208, combiners 210 and 212, a transform and quantization unit (TR + Q) 214, an inverse transform and quantization unit (iTR + iQ) 216, an entropy coding unit 218, one or more filters 220, and / or a buffer 222.

[0070] 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 predictthe 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.

[0071] 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.

[0072] 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.

[0073] 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 DOT to reduce correlated information in the prediction error. Transform and quantization unit 214 may quantize the coefficients by mapping data of the transform coefficients to a predefined set of representative values. Transform and quantization unit 214 may quantize the coefficients to reduce irrelevant information in bitstream 204. The irrelevant information refers to information that may be removed from the coefficients without producing visible and / or perceptible distortion in video sequence 202 after decoding (e.g., at a receiving device).

[0074] 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.

[0075] 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 (SAC) 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.

[0076] 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 inconformance with one or more of ITU-T H.263, AVO, HEVO, WO, VP8, VP9, AV1 , and / or any other video coding standard / format.

[0077] The encoder control unit may be configured to attempt to minimize (or reduce) the bitrate of bitstream 204 and / or maximize (or increase) the reconstructed video quality (e.g., within the constraints of a proprietary coding protocol, industry video coding standard, and / or any other video cording protocol). For example, the encoder control unit may be configured to attempt to minimize or reduce the bitrate of bitstream 204 such that the reconstructed video quality does not fall below a certain level / th reshold , and / or to maximize or increase the reconstructed video quality such that the bitrate of bitstream 204 does not exceed a certain level / th reshold. The encoder control unit may determine / control one or more of: partitioning of the pictures of video sequence 202 into blocks, whether a block is inter predicted by inter prediction unit 206 or intra predicted by intra prediction unit 208, a motion vector for inter prediction of a block, an intra prediction mode among a plurality of intra prediction modes for intra prediction of a block, filtering performed by filter(s) 220, and / or one or more transform types and / or quantization parameters applied by transform and quantization unit 214. The encoder control unit may determine / control one or more of the above based on a ratedistortion measure 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.

[0078] 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.

[0079] 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).

[0080] 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.

[0081] 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 inconformance 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, AVO, HEVO, WO, VP8, VP9, AV1, and / or any other video coding standard / format.

[0082] 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.

[0083] Entropy decoding unit 306 may entropy decode the bitstream 302. For example, entropy decoding unit 306 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and syntax-based context-based binary arithmetic coding (SBAC) to decompress the prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and transform and quantization parameters. Inverse transform and quantization unit 308 may inverse quantize and / or inverse transform the quantized transform coefficients to determine a decoded prediction error. Combiner 310 may combine the decoded prediction error with a prediction block to form a decoded block. The prediction block may be generated by intra prediction unit 318 or inter prediction unit 316 (e.g., as described above with respect to encoder 200 in FIG 2). Filter(s) 312 may filter the decoded block, for example, using a deblocking filter and / or a sample-adaptive offset (SAC) 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.

[0084] 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).

[0085] 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.

[0086] 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.

[0087] A picture (e.g., in HEVC, or any other coding standard / format) may be partitioned into non-overlapping square blocks, which may be referred to as coding tree blocks (CTBs). The CTBs may comprise samples of a sample array. A CTB may have a size of 2nx2n samples, where n may be specified by a parameter of the encoding system. For example, n may be 4, 5, 6, or any other value. A CTB may have any other size. A CTB may be further partitioned by a recursive quadtree partitioning into coding blocks (CBs) of half vertical and half horizontal size. The CTB may form the root of the quadtree. A CB that is not split further as part of the recursive quadtree partitioning may be referred to as a leaf CB of the quadtree, and otherwise may be referred to as a non-leaf CB of the quadtree. A CB may have a minimum size specified by a parameter of the encoding system. For example, a CB may have a minimum size of 4x4, 8x8, 16x16, 32x32, 64x64 samples, or any other minimum size. A CB may be further partitioned into one or more prediction blocks (PBs) for performing inter and / or intra prediction. A PB may be a rectangular block of samples on which the same prediction type / mode may be applied. 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.

[0088] 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.

[0089] 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.

[0090] A picture, in VVC (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 VVC) may be further partitioned by a binary tree or ternary tree partitioning (or any other partitioning) into CBs of unequal sizes.

[0091] 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 horizontal direction 608. FIG. 6 shows an example in which the middle partition may be twice as large as the other two end partitions in the ternary tree partitions. In other examples, partitions may be 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 WO) 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.

[0092] 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.

[0093] The leaf CB 5 of FIG. 4 may be partitioned into two CBs based on a vertical binary tree partitioning. The two resulting CBs may be leaf CBs respectively labeled 5 and 6 in FIGS. 7 and 8. The leaf CB 8 of FIG. 4 may be partitioned into three CBs based on a vertical ternary tree partition. Two of the three resulting CBs may be leaf CBs respectively labeled 9 and 14 in FIGS. 7 and 8. The remaining, non-leaf CB may be partitioned first into two CBs based on a horizontal binary tree partition. One of the two CBs may be a leaf CB labeled 10. The other of the two CBs may be further partitioned into three CBs based on a vertical ternary tree partition. The resulting three CBs may be leaf CBs respectively labeled 11, 12, and 13 in FIGS. 7 and 8. The leaf CB 9 of FIG. 4 may be partitioned into three CBs based on a horizontal ternary tree partition. Two of the three CBs may be leaf CBs respectively labeled 15 and 19 in FIGS. 7 and 8. The remaining, non-leaf CB may be partitioned into three CBs based on another horizontal ternary tree partition. The resulting three CBs may all be leaf CBs respectively labeled 16, 17, and 18 in FIGS. 7 and 8.

[0094] Altogether, CTB 700 may be partitioned into 20 leaf CBs respectively labeled 0-19. The 20 leaf CBs may correspond to 20 leaf nodes (e.g., 20 leaf nodes of tree 800 shown in FIG. 8). The resulting combination of quadtree and multi-type tree partitioning of the CTB 700 may be scanned using a z-scan (left-to-right, top-to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label of each CB leaf node in FIGS. 7 and 8 may correspond to the sequence order for encoding / decoding, with CB leaf node 0 encoded / decoded first and CB leaf node19 encoded / decoded last. Although not shown in FIGS. 7 and 8, it should be noted that each OB leaf node may comprise one or more PBs and / or TBs.

[0095] A coding standard / format (e.g., HEVC, WO, or any other coding standard / format) may define various units (e.g., in addition to specifying various blocks (e.g., CTBs, QBs, 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.

[0096] 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, VVC, 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 A 1 coding format.

[0097] In intra prediction, samples of a block to be encoded (e.g., also referred to as a current block) may be predicted from 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.

[0098] Predicting samples and determining a prediction error based on a difference between the predicted samples and original samples may be performed (e.g., at an encoder) for a plurality of different intra prediction modes (e.g., including non-directional intra prediction modes). The encoder may select one of the plurality of intra prediction modes and its corresponding prediction error to encode the current block. The encoder may send an indication of the selected prediction mode and its corresponding prediction error to a decoder for decoding of the current block. The decoder may decode the current block by predicting the samples of the current block, using the intra prediction mode indicated by the encoder, and / or combining the predicted samples with the prediction error.

[0099] 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 ofpartitioned 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.

[0100] 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 the row immediately adjacent to the top-most row of current block 904, 2h samples (or any other quantity of samples) of the column immediately adjacent to the left-most column of current block 904, and the top left neighboring corner sample 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.

[0101] Samples that may not be available for constructing the set of reference samples 902 may comprise samples in blocks that have not already been encoded and reconstructed at an encoder and / or decoded at a decoder based on the sequence order for encoding / decoding. Restriction of such samples from inclusion in the set of reference samples 902 may allow identical prediction results to be determined at both the encoder and decoder. In the example of FIG. 9, samples from neighboring blocks 0, 1, and 2 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 , and 2 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, and 2.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).

[0102] 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.

[0103] Reference samples 902 may be filtered based on the size of current block 904 being coded and an applied intra prediction mode. FIG. 9 shows an example determination of reference samples for intra prediction of a block. Reference samples may be determined in a different manner than described above. For example, multiple reference lines may be used in other instances (e.g., in WO).

[0104] Samples of current block 904 may be intra predicted based on reference samples 902, for example, based on (e.g., after) determination and (optionally) filtering of reference samples 902. At least some (e.g., most) encoders / decoders may support a plurality of intra prediction modes in accordance with one or more video codingstandards. For example, HEVC supports 35 intra prediction modes, including a planar mode, a direct current (DC) mode, and 33 angular modes. WC supports 67 intra prediction modes, including a planar mode, a DC mode, and 65 angular modes. Planar and DC modes may be used to predict smooth and gradually changing regions of a picture. Angular modes may be used to predict directional structures in regions of a picture. Any quantity of intra prediction modes may be supported.

[0105] FIGS. 10A and 10B show example intra prediction modes. FIG. 10A shows 35 intra prediction modes, such as supported by HEVC. The 35 intra prediction modes may be indicated / identified by indices 0 to 34. Prediction mode 0 may correspond to planar mode. Prediction mode 1 may correspond to DC mode. Prediction modes 2-34 may correspond to angular modes. Prediction modes 2-18 may be referred to as horizontal prediction modes because the principal source of prediction is in the horizontal direction. Prediction modes 19-34 may be referred to as vertical prediction modes because the principal source of prediction is in the vertical direction.

[0106] FIG. 10B shows 67 intra prediction modes, such as supported by VVC. 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.

[0107] 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 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, onedimensional arrays. The reference samples 902, above the current block 904, may be placed in the one-dimensional array re / ) [x]: re | [x] = p[-1 + x][— 1], (x > 0). (1)The reference samples 902 to the left of current block 904 may be placed in the one-dimensional array re / 2[y]: re / 2[y] = p[-1] [-1 + y], (y > 0). (2)

[0108] 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 determin ing / calcu I atin g 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:1P [x] [y] = z — (h [x] [y] + v [x] [y] + s), (3)2 ■ swhere / i[x][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 / i [x] + (y + 1) ■ ref2[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.

[0109] 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:

[0110] 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 HEVO and modes 35-66 in WO). The direction specified by the angular mode may be given by an angle cp defined relative to the x-axis for horizontal prediction modes (e.g., modes 2-18 in HEVO and modes 2-34 in WO).

[0111] FIG. 12 shows an example applying an intra prediction mode (e.g., an angular mode such as vertical prediction mode 906) for prediction of a current block 904. FIG. 12 specifically shows prediction of a sample at a location [x][y] in current block 904 for a vertical prediction mode 906. Vertical prediction mode 906 may be given by an angle cp with respect to the vertical axis. The location [x] [y] in current block 904, in vertical prediction modes, may be projected to a point (e.g., referred to as a projection point) on the horizontal line of reference samples re / i [ ]■ The reference samples 902 are only partially shown in FIG. 12 for ease of illustration. As shown in FIG. 12, the projection point on the horizontal line of reference samples re / j [x] may not be exactly on a reference sample. A predicted sample p[x][y] in current block 904 may be determined / calculated by linearly interpolating between the two reference samples, for example, if the projection point falls at a fractional sample position between two reference samples. The predicted sample p[x][y] may be determined / calculated as: p[x][y] = (1 - if) ■ re / j [x + if + 1] + if■ re / i + + 2]. (7) if may be the integer part of the horizontal displacement of the projection point relative to the location [x][y], if may be determined / calculated as a function of the tangent of the angle cp of the vertical prediction mode 906 as: ii = L(y + 1) ’ tan <pj. (8) if may 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 = (0 + 1) ■ tan <p) - L(y + 1) ■ tan <p], (9) where [ ■ ] is the integer floor function.

[0112] 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:PMM = (1 - if) ■ ref2[y + i;+ 1] + if■ ref2[y + i; + 2], (10) if may be the integer part of the vertical displacement of the projection point relative to the location [x][y], i^may be determined / calculated as a function of the tangent of the angle cp of the horizontal prediction mode as: it = [(x + 1) ■ tan <pj. (11) if may be the fractional part of the vertical displacement of the projection point relative to the location [x] [y] . ifmay be determined / calculated as: if = ((x + 1 ) ■ tan <p) - [(x + 1) ■ tan <p], (12) where [ ■ ] is the integer floor function.

[0113] 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.

[0114] In some examples, the FIR filters may be used for predicting chroma samples and / or luma samples. For example, the two-tap interpolation FIR filter may be used for predicting chroma samples and a same and / or a different interpolation technique / filter may be used for luma samples. For example, a four-tap FIR filter may be used to determine a predicted value of a luma sample. Coefficients of the four tap FIR filter may be determined based on if(e.g., similar to the two-tap FIR filter). For 1 / 32 sample accuracy, a set of 32 different four-tap FIR filters may comprise up to 32 different four-tap 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 / T[ / ], = 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:

[0115] Supplementary reference samples may be determined / constructed if the location [x][y] of a sample in current block 904 to be predicted is projected to a negative x coordinate. The location [x][y] of a sample may be projected to a negative x coordinate, for example, if negative vertical prediction angles cp are used. The supplementary reference samples may be determined / constructed by projecting the reference samples in ref2y] 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 re / )[x] on the horizontal line of reference samples 902 to the vertical line of reference samples 902 using the negative horizontal prediction angle cp.

[0116] 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 WO. 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 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 based on the determined prediction errors. For example, the encoder may determine / select one of the intra prediction modes that results in the smallest prediction error for the current block. In some examples, the encoder may determine / select the intra prediction mode 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 send an indication of the determined / selected intra prediction mode and its corresponding prediction error (e.g., residual) to a decoder for decoding of the current block.

[0117] 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 an intra prediction mode (e.g., an angular intra prediction mode) from an encoder for a current block. The decoder may construct a set of reference samples and perform intra prediction based on the intra prediction mode indicated by the encoder for the current block in a similar manner (e.g., as described above for the encoder). 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 anencoder for a current block. Instead, the decoder may determine an intra prediction mode through other, decoder-side means.

[0118] While various examples herein correspond to intra prediction modes in HEVC and WO, 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.).

[0119] Intra prediction may exploit correlations between spatially neighboring samples in the same picture of a video sequence to perform video compression. Inter prediction is another coding tool that may be used to perform video compression. Inter prediction may exploit correlations in the time domain between blocks of samples in different pictures of a video sequence. For example, an object may be seen across multiple pictures of a video sequence. The object may move (e.g., by some translation and / or affine motion) or remain stationary across the multiple pictures. A current block of samples in a current picture being encoded may have / be associated with a corresponding block of samples in a previously decoded picture. The corresponding block of samples may accurately predict the current block of samples. The corresponding block of samples may be displaced from the current block of samples, for example, due to movement of the object, represented in both blocks, across the respective pictures of the blocks. The previously decoded picture may be a reference picture. The corresponding block of samples in the reference picture may be a reference block for motion compensated prediction. An encoder may use a block matching technique to estimate the displacement (or motion) of the object and / or to determine the reference block in the reference picture.

[0120] 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.

[0121] 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.

[0122] The encoder may search for reference block 1304 within a reference region (e.g., a search range 1308). The reference region (e.g., a search range 1308) may be positioned around a collocated block (or position) 1310, of current block 1300, in reference picture 1306. Collocated block 1310 may have a same position in the reference picture 1306 as the current block 1300 in the current picture 1302. The reference region (e.g., search range 1308) may at least partially extend outside of reference picture 1306. Constant boundary extension may be used, for example, if the reference region (e.g., search range 1308) extends outside of reference picture 1306. The constant boundary extension may be used such that values of the samples in a row or a column of reference picture 1306, immediately adjacent to a portion of the reference region (e.g., search range 1308) extending outside of reference picture 1306, may be used for sample locations outside of reference picture 1306. A subset of potential positions, or all potential positions, within the reference region (e.g., search range 1308) may be searched for reference block 1304. The encoder may utilize one or more search implementations to determine and / or generate the reference block 1304. For example, the encoder may determine a set of candidate search positions based on motion information of neighboring blocks (e.g., a motion vector 1312) to the current block 1300.

[0123] 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 HEVO and WO (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.

[0124] 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 noninteger sample value in the reference picture. The interpolation may be performed by a filter with two or more taps.

[0125] 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 interprediction, 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).

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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 / indicate an order in which pictures are output (e.g., from a decoded picture buffer). A POC may be / indicate an order in which pictures are generally intended to be displayed. Pictures that are output may not necessarily be displayed but may undergo different processing and / or consumption (e.g., transcoding). The two reference blocks determined and / or generated using / for biprediction may correspond to (e.g., be comprised in) a same reference picture. The reference picture may be included in both the reference picture list 0 and the reference picture list 1, for example, if the two reference blocks correspond to the same reference picture.

[0130] 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 / sign aled for luma and / or chroma components.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] Motion information may be predictively coded, for example, before being stored and / or sen t / sign aled in / via a bit stream (e.g., in HEVO, WO, and / or other video coding standards / formats / protocols). The motion information for acurrent 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 VVC) may comprise advanced motion vector prediction (AMVP) and / or inter prediction block merging (e.g., merge mode).

[0136] An encoder (e.g., encoder 200 as shown in FIG. 2), may code a motion vector. The encoder may code the motion vector (e.g., using AMVP) as a difference between a motion vector of a current block being coded and a motion vector predictor (MVP). An encoder may determine / select the MVP from a list of candidate MVPs. The candidate MVPs may be / correspond to previously decoded motion vectors of neighboring blocks in the current picture of the current block, and / or blocks at or near the collocated position of the current block in other reference pictures. The encoder and / or a decoder may reciprocally generate and / or determine the list of candidate MVPs.

[0137] The encoder may determine / select an MVP from the list of candidate MVPs. Then, the encoder may send / signal, in / via a bitstream, an indication of the selected MVP and / or a motion vector difference (MVD). The encoder may indicate the selected MVP in the bitstream using an index / indicator. The index may indicate the selected MVP in the list of candidate MVPs. The MVD may be determ ined / calcu lated 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 MVDZand MVDy. MVDZand MVDymay be determined / calculated as:MVDZ= MVZ- MVPZ, (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.

[0138] 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.

[0139] 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 determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being coded; one (or any other quantity of) temporal candidate MVP determined / derived from two (or any other quantity of) temporal, co-located blocks (e.g., if both of the two spatial candidate MVPs are not available or are identical); and / or zero motion vector candidate MVPs (e.g., if one or both ofthe 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.

[0140] 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.

[0141] An encoder (e.g., encoder 200 as shown in FIG. 2) may code a motion vector using inter prediction block merging (e.g., a merge mode). For example, the encoder (e.g., using merge mode) may reuse the same motion information of a neighboring block (e.g., one of neighboring blocks A0, A1 , B0, B1 , and B2) for inter prediction of a current block. For example, the encoder (e.g., using merge mode) may reuse the same motion information of a temporal, co-located block (e.g., one of temporal, co-located blocks CO and C1) for inter prediction of a current block. An MVD need not be sent (e.g., indicated, signaled) for the current block because the same motion information as that of a neighboring block or a temporal, co-located block may be used for the current block (e.g., at the encoder and / or a decoder). A signaling overhead for sending / signaling the motion information of the current block may be reduced because the MVD need not be indicated for the current block. The encoder and / or the decoder may reciprocally generate a candidate list of motion information from neighboring blocks or temporal, co-located blocks of the current block (e.g., in a manner similar to AMVP). The encoder may determine to use (e.g., inherit) motion information, of one neighboring block or one temporal, co-located block in the candidate list, for predicting motion information of the current block being coded. The encoder may signal / send, in / via a bitstream, an indication of the determined motion information from the candidate list. For example, the encoder may signal / send an indicator / index. The index may indicate the determined motion information in the list of candidate motion information. The encoder may signal / send the index to indicate the determined motion information.

[0142] A list of candidate motion information for merge mode (e.g., in HEVO, WO, or any other coding formats / standards / protocols) may comprise: up to four (or any other quantity of) spatial merge candidates derived / d etermined 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.

[0143] 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 examplesherein correspond to inter prediction modes, such as used in HEVC and VVC, the methods, devices, and systems as described herein may be applied to / used for other inter prediction modes (e.g., as used for other video coding standards / formats such as VP8, VP9, AV1, etc.). History based motion vector prediction (HMVP), combined intra / inter prediction mode (OHP), and / or merge mode with motion vector difference (MMVD) (e.g., as described in WO) may be performed / used and are within the scope of the present disclosure.

[0144] 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.

[0145] 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 the reference block may be a relative position of a top-left corner (or any other poin t / 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 rate-distortion cost). The one or more cost criteria may be based on, for example, one or more differences (e.g., an SSD, an SAD, an SATD, and / or a difference determined based on a hash function) between the prediction samples of the reference block and the original samples of the current block. A reference block may correspond to / comprise prior decoded blocks of samples (e.g., reconstructed samples) of the current picture. The reference block may comprise decoded blocks of samples of the current picture prior to being processed by in-loop filtering operations (e.g., deblocking and / or SAO filtering).

[0146] 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 blocksbeing encoded. The rectangular portions / sections that the arrows point to may be the reference blocks for predicting the respective current blocks.

[0147] 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).

[0148] A BV may be predictively coded (e.g., in HEVO, WO, 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).

[0149] 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 / determ ine 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.

[0150] 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 BVDZand BVDy. BVDZand BVDymay be determined / calculated as:BVDZ= BVZ- BVPZ, (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).

[0151] 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.

[0152] A list of candidate BVPs (e.g., in HEVO, WO, and / or any other coding stand ard / format / protocol) may comprise two (or more) candidates. The candidates may comprise candidates A and B. Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate BVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being encoded; and / or one or more of last two (or any other quantity of) coded BVs (e.g., if spatial neighboring candidates are not available). Spatial neighboring candidates may not be available, for example, if neighboring blocks are encoded using intra prediction or inter prediction. Locations of the spatial candidate neighboring blocks, relative to a current block, being encoded using IBC 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.

[0153] Local illumination compensation (LIC) is a prediction technique proposed for improving motion compensation in VVC. LIC models illumination variation between a current block and its reference block as a function of that between a current block template and a reference block template. The parameters of the LIC function are denoted by a scale a and an offset (bias) , to form the linear equation (19) (shown below) that is used to compensate illumination variations in the reference block. Pref is a sample (e.g., a reference sample) in the reference block pointed to by a motion vector (MV) in inter prediction (or a displacement vector in intra prediction).Ppred—CT * Pref ~ ft

[0154] The parameters a and are derived based on a template associated with the current block (referred to as current block template or current template) and a corresponding template associated with the reference block (referred to as reference block template or reference template). Consequently, LIC incurs no additional signaling overhead, other than for an LIC flag that may be signaled to indicate the use of LIC.

[0155] The application of LIC to the reference block associated with a current block comprises adjusting reference samples by multiplying the reference samples (respectively the values of the samples) with a (respectively with a value of a) and adding (respectively a value of ) in accordance with the above-described linear equation for compensating for local illumination differences. The parameters a and are derived from samples in the templates of the currentblock and the reference block using, for example, a least mean squares method. The parameters a and can be derived using all, a subset, or subsets of samples in the templates.

[0156] FIG. 17A shows a current block and a reference block with their corresponding templates that are used in determining a and for LIO for inter prediction. A current block 1704 is shown in a current picture 1702 and a reference block 1708 is shown in a reference picture 1706. In an example sequence of pictures, the current block 1704 may correspond to the current block 1400 shown in FIG. 14 and the reference block 1708 may correspond to either reference block 1402 or reference block 1404. Corresponding templates 1714 and 1716 are shown in relation to the current block 1704 and reference block 1708, respectively. The current template 1714 comprises neighboring samples adjacent to the current block boundary (current block border) 1710 at the left edge and the top edge of the current block 1704. The length of the current template 1714 is the sum of the lengths of the left column and the top row of samples in the current block 1704. The reference template 1716 comprises neighboring samples adjacent to the reference block boundary (reference block border) 1712 at the left edge and the top edge of the reference block 1708. The length of the reference template 1716 is the sum of the lengths of the left column and the top row of samples in the reference block 1708. In the illustrated example, the templates 1714 and 1716 have a height of 1 sample (i.e., the left portion of each template 1714 and 1716 is a singe column of samples, and the top portion of each template 1714 and 1716 is a single row of samples).

[0157] The scale parameter, a, can be determined by:

[0158] The offset parameter, , can be determined by

[0159] In the above two equations (20) and (21), n is the number of samples, Trec(i) is the ithsample of the current template (as noted above, the current template is the template of the current block), and Tref(i) is the ithsample of the reference template (as noted above, the reference template is the template of the reference block). The current block may also be referred to as the predicted block, the reconstructed block, or the block to be predicted. It will be noted that when the current block 1704 is yet to be reconstructed, the neighboring blocks (to which the samples of the current template 1714 belong) adjacent to the left edge and the top edge of the current block 1704 have been reconstructed.

[0160] FIG. 17B shows a process 1720 to calculate a predicted block when performing inter prediction using LIO.

[0161] At block 1722, template samples for the current block and the reference block are obtained. LIO uses a one- tap filter 1718 to sample templates 1714 and 1716. The one-tap filter 1718 is used to obtain each respective template sample from the same relative position in the two templates 1714 and 1716.

[0162] At block 1724, the template samples (e.g., neighbor samples of the reference block and the current block) are used in the equation (20) to calculate the scale parameter. In some implementations, as shown above, the offset parameter is calculated using the calculated scale parameter.

[0163] After scale a and offset parameters are determined by applying the one-tap filter 1718 to the current template 1714 and the reference template 1716, at block 1726, they (i.e., scale a and offset ) are applied to respective reference samples Pref to obtain prediction samples Ppred (samples of the prediction block) in accordance with the equation (19) shown above.

[0164] The thus determined predicted block may be subtracted from the current block to obtain the prediction errors (residuals) that are subsequently encoded in a bitstream. The predicted block determined based on LIC may have improved illumination variation relative to the reference block, and may consequently yield smaller prediction errors that need to be encoded.

[0165] LIC is described for inter prediction in the Enhanced Compression Model (ECM) software algorithm that is currently under coordinated exploration study by the Joint Video Exploration Team (JVET) of ITU-T Video Coding Experts Group (VCEG) and ISO / IEC MPEG as potential enhanced video coding technology beyond the capabilities of VVC.

[0166] Bidirectional prediction, sometimes referred to as “bi-prediction,” has been in use for inter prediction for some time and is described above in relation to FIG. 14 among others. As one of the primary methods in the conventional inter prediction of video coding, bi-prediction can improve the coding efficiency when compared with uni-prediction. In general, it can generate a better predicted block from both forward and backward prediction blocks than a uni-prediction block, except for scene change or illumination change. Conventional bi-prediction assigns equal weights to each of the reference blocks when predicting the current block.

[0167] VVC adopted bi-prediction with coding unit (CU)-level weight (BCW) as one of the tools which enhanced the coding efficiency of conventional bi-prediction by assigning different weights to the two prediction blocks in the process of inter prediction. BCW (also known as generalized bi-prediction (GBi)) is thus a weighted bi-prediction technique for predicting a block by weighted-averaging two motion-compensated blocks. BCW extends the notion of weighted biprediction to the CU level allowing bi-prediction weights to be determined per CU. The determined bi-prediction weights are applied to bi-prediction PUs, across all color components, to bi-predict the CU.

[0168] In conventional BCW, a list of pre-defined candidate weights is used. At the encoder, one of the pre-defined candidate weights is selected as a BCW weight for a bi-predicted CU. For a non-merge coded CU (a CU for which merge mode is not used to code the motion vector), a BCW index associated with the selected BCW weight is signaled to the decoder. The BCW index points to the entry of the selected BCW weight in the list of pre-defined candidate weights. For a merge coded CU, the BCW index is inherited from neighboring blocks based on a signaled merge candidate index. The merge candidate index points to a merge candidate of the merge coded CU.

[0169] Generally, for non-low delay pictures (e.g., where reference picture list 0 corresponds to pictures that precede the current picture and reference picture list 1 corresponds to pictures that follow the current picture in terms of POC, see FIG. 18A), the list of pre-defined candidate weights may include {-2 / 8, 3 / 8, 4 / 8, 5 / 8, and 10 / 8}. For low delay pictures (e.g., where both reference picture list 0 and reference picture list 1 correspond to pictures that precede the current picture, see FIG. 18B), the list may be reduced to {3 / 8, 4 / 8, and 5 / 8}. The different weights between the two uni-prediction blocks are used to adaptively highlight either the forward or backward predicted block. In ECM-9.0, BOW is applied to a bi-predicted CU.

[0170] An index, referred to as the “BOW index,” is used to identify the weights for the current block. The BOW index is signaled for non-merge coded CUs, whereas for merge coded CUs, the BOW index is inherited from neighboring blocks according to the signaled merge candidate index. Note that BOW weights are applied to each color plane belonging to a given CU, i.e., to luma and both chroma blocks.

[0171] The current block can be calculated in accordance with the AMVP mode or merge mode. As described above, in AMVP mode, the reference block is determined at the encoder and is signaled to the decoder whereas in the merge mode the reference block (from which the BOW index is inherited) is selected from among neighbors of the current block, in accordance with an index signaled from the encoder.

[0172] In some implementations, BOW may be improved for the merge mode by applying a template matching technique. For example, the BOW index for merge coded CUs may be derived based on template matching cost. More particularly, the technique proposes to derive the BOW weight, for merge coded CUs, based on the list of pre-defined candidate weights using template matching (TM) cost. Given an inherited BCW weight, the technique proposes adjusting the BCW weight based on the list of pre-defined candidate weights. Specifically, the technique compares the BCW weight with one or more neighboring weights in the list of pre-defined candidate weights, based on TM cost. For example, if the BCW weight corresponds to the value 4 / 8 from the list {3 / 8, 4 / 8, and 5 / 8}, the technique proposes comparing the weight 3 / 8 with the weights 4 / 8 and 5 / 8 based on TM cost. Since the inherited BCW index is likely to have higher accuracy than another BCW index, the TM cost of the inherited BCW index is multiplied with 0.90625, that is, the cost is reduced by 3 / 32. Besides, the TM cost of the equal weight is multiplied with 0.90625 since bi-predicted samples are beneficial for bi-directional optical flow (BDOF) and BDOF is only applied to CU with equal weight. The TM cost for a BCW weight is calculated based on templates (neighboring reconstructed samples) of the current block and the reference blocks obtained respectively from reference picture list 0 and reference picture list 1. The weight with the minimum TM cost is selected as the BCW weight for the BCW prediction.

[0173] In some implementations, the conventional LIC design may be extended to bi-predicted CUs. Specifically, for one bi-predicted current block, two different linear models may be derived to compensate the illumination changes that exist between the current block and its two prediction blocks. Then, the final bi-prediction of the current block is calculated as the combination of two uni-prediction blocks after the LIC adjustment, i.e., as shown in equation (22) below:P7x,y]=n-w)p07x,y]+wPl7x,y] (22) and pd [x,y]=ao-Po [x,y]+(3o pi' [x,y]=arPi [x,y]+ i

[0174] where oo and [3o, and oi and represent the scales and the offsets in reference picture list 0 (L0) and reference picture list 1 (L1), respectively; w indicates the weight (as indicated by the CU-level BCW index) that isapplied when combining the two uni-prediction blocks. Similar to the conventional LIO design, one control flag is signaled for AMVP bi-predicted CUs to indicate the enabling / disabling of the LIO, while the control flag is inherited from one neighboring block for merge inter CUs (including AMVP-Merge mode). Additionally, LIC is disabled when decoderside motion vector refinement (DMVR) (including multi-pass DMVR, adaptive DMVR and affine DMVR) and bidirectional optical flow (BDOF) is applied.

[0175] To reuse the linear model derivation of the conventional LIC, one iterative approach is applied to alternately derive the L0 and L1 linear models. Specifically, given the two MVs of the current block, the iterative approach assumes To (e.g., template of block 0 in Figures 18A-B) and Ti (e.g., template of block 1 in Figures 18A-B) are the two predictions of the current block’s template T. The method first derives the L0 linear model (oo and o) that results in the minimum difference between To and T; Then, the L1 linear model (oi and i) can be calculated that minimizes the difference between Ti, and the updated template. Finally, the L0 linear model is refined again in the same manner.

[0176] In some implementations, the following two changes are applied to better handle the interaction between the LIC and the overlapped block motion compensation (OBMC): it is proposed to enable the OBMC to the inter blocks where the LIC is applied. Additionally, to achieve a better complexity / performance trade-off, the OBMC is only applied for refining the prediction samples on the top and left boundaries of one LIC CU while the OBMC on the internal subblock boundaries are always disabled. Besides the MVs, it is proposed to also take the LIC parameters of one neighboring block (when it is coded by the LIC) into consideration when generating its corresponding prediction samples for the OBMC of the current CU.

[0177] FIG. 19A and 19B illustrate luma and chroma sampling examples. The convolutional cross-component model (CCCM) is applied to predict chroma samples from reconstructed luma samples in a similar spirit as done by the crosscomponent linear model (CCLM) modes. As with CCLM, the reconstructed luma samples are down sampled to match the lower resolution chroma grid when chroma subsampling is used, as shown to FIG. 19B. Similar to CCLM top, left or top and left reference samples are used as templates for model derivation.

[0178] Also, similarly to CCLM, there is an option of using a single model or multi-model variant of CCCM. The multimodel variant uses two models, one model derived for samples above the average luma reference value and another model for the rest of the samples (following the spirit of the CCLM design). Multi-model CCCM mode can be selected for PUs which have at least 128 reference samples available.

[0179] A convolutional 7 -tap filter may be used in CCCM. The convolutional filter consists of a 5-tap plus sign shape spatial component, a nonlinear term and a bias term. The input to the spatial 5-tap component of the filter consists of a center (C) luma sample which is collocated with the chroma sample to be predicted and its above / north (N), below / south (S), left / west (W) and right / east (E) neighbors as illustrated below. The nonlinear term is represented as power of two of the center luma sample C and scaled to the sample value range of the content. The bias term B represents a scalar offset between the input and output (similarly to the offset term in CCLM).

[0180] The output of the filter is calculated as a convolution between the filter coefficients c(and the input values and clipped to the range of valid chroma samples:predChromaVal = coC + c-?N + c S + C3E + C4W + C5P + c@B (23)

[0181] The filter coefficients c(are calculated by minimizing MSE between predicted and reconstructed chroma samples in a reference area. The reference area consists of 2 or 6 lines of chroma samples above and left of the PU. Whether to use 6 lines or 2 lines of neighboring samples to derive the CCCM model parameters in the single model CCCM is determined by a template cost. Similarly, for the multi-model CCCM mode, the two candidates use 6 lines neighboring luma samples or luma samples collocated to the current chroma block to derive mean values which separate samples into two groups. The cost is derived by applying the candidate CCP (either 2 or 6 lines) on a template, calculating the sum of absolute difference (SAD) between CCP predicted samples and reconstructed samples in the template.

[0182] Reference sample values just outside of the top-left corner of the PU are used as the offsets (offsetLuma, offsetCb and offsetCr) for simplicity. The samples values used in both model creation and final prediction (i.e., luma and chroma in the reference area, and luma in the current PU) are reduced by these fixed values, as follows: O' = C - offsetLuma; N' = N - offsetLuma; S' = S - offsetLuma; E' = E - offsetLuma; W' = W - offsetLuma; P' = non Linear(C'); and B = midValue = 1 « (bitDepth - 1). The chroma value is then predicted using the following equation, where offsetChroma is equal to offsetCr and offsetCb for Cr and Cb components, respectively: predChromaVal = coC + c-jN' + C2S' + C3E' + cWV' + C5P' + c@B + offsetChroma. (24).

[0183] Illumination variations in reference blocks sometimes cause large prediction errors. In addition to illumination variations, other types of artefacts and / or differences between a reference block and a current block (e.g., quantization or camera noise, a reference block being smoother than a current block) might further increase prediction errors. Local illumination compensation (LIC) and various multiparametric filtering techniques have been proposed to reduce the impact of such variation in generating the prediction block for the current block.

[0184] LIC and multiparametric filtering techniques include two stages: a stage of filter parameter derivation from the templates of predicted and reference blocks, and a stage of application of the derived parameters to the reference block(s) in order to obtain a predictor of the predicted block (as noted above, the predictor of the prediction block may be referred to as the prediction block).

[0185] Large differences between the prediction block and the current block can lower compression performance. One of the issues that reduces the similarity of the prediction block to the current block and thus can cause large differences is that the reference templates may contain samples that are not representative for the reference block. The use of such template samples that are not representative for the reference block can lead to deriving suboptimal model parameters.

[0186] Embodiments of the present disclosure are related to preprocessing the reference templates in order to select samples that are most representative of the reference block and then using the selected samples for deriving model parameters for LIC or multiparametric filtering techniques. In some embodiments, improved model parameters provide for improved illumination compensation and reduction of other types of artifacts and / or differences of the referenceblocks, and thus may yield better compression performance. These and other features of the present disclosure are described further below.

[0187] As noted above, the prediction block’s similarity to the current block may be improved by preprocessing the reference template. Since both the reference templates and the reference blocks are available on both encoder and decoder sides, it is possible to preprocess the reference template in such a way that minimizes the number of unrepresentative (i.e., unrepresentative of the reference block) samples in the reference templates.

[0188] In example embodiments of the present disclosure, such reference template preprocessing may be performed to improve model parameter determination for single-tap filters and multiparametric (also referred to as “multi-tap”) filters. FIG. 20A illustrates an example reference block 2002 with a reference template 2006 that is adjacent to the left edge and top edge of the reference block boundary 2004, and an example single-tap filter 2008. The single-tap filter 2008 may be used in LIO, to derive the LIO parameters. FIG. 20B and FIG. 200 illustrate some non-limiting example multiparametric filters that may be used in embodiments: a plus-sign shaped 5-tap filter 2014, an x-shaped 5-tap filter 2016, and a square-shaped 9-tap filter 2018. FIG. 20B illustrates a reference template 2010 that is 3 samples high and extends adjacent to the left and top edges of the reference block 2002, for use with multiparametric filters such as filters 2014-2018. FIG. 200 illustrates the use of “N”, “S”, “E”, “W”, “NE”, “NW”, “SE” and “SW” (North, South, East, West, North East, North West, South East, and South West, respectively) directions to identify respective positions in the various filter shapes.

[0189] As shown in FIG. 20B, in addition to samples in the 3-sample high template 2010, multiparametric filters may overlap samples in a 1 -sample high layer of outer samples 2012 surrounding the template 2010. For example, when filter 2018 is positioned as shown in FIG. 20B with its center (“C”) within the template 2010 area, its NE, E, SE, S and SW sample positions are overlapping the layer / area of outer samples 2012. It should be noted that the layer of outer samples 2012 may include some samples from the reference block 2002. FIG. 21 A and 21 B illustrate that whereas with a single-tap filter only samples (e.g., sample 2106) of the template of the reference block 2104 are compared to samples (e.g., sample 2108) of the template of the current block 2102, with a multi-tap filter, additionally, samples (e.g., sample 2110) of the reference block 2104 may also be compared to samples of the template of the current block 2102.

[0190] A key idea underpinning embodiments of the present disclosure is to select such samples for a reference template that are the most representative for its reference block. For example, when the reference template is to be subsampled before being used for model parameter derivation, embodiments of the present disclosure can be used to select a subset of samples of the reference template that are most representative of the reference block.

[0191] In some implementations of the ECM, all template samples adjacent to the left edge of the reference block and a subsampling of template samples along the long edge of the reference block are used to derive model parameters for LIC. FIG. 22A illustrates the subsampling of template samples along the top edge of the reference block that is currently used in the ECM (i.e., ECM-11.0). As shown in FIG. 22A, the subsampling of the top portion of the template selects every second sample, starting at the zero-offset relative to the top-left corner of the block, along the top edge.

[0192] In some embodiments of the present disclosure, in addition to the subsampling shown in FIG. 22A, the subsampling shown in FIG. 22B may also be evaluated during a preprocessing of the template. Whereas the subsampling of FIG. 22A starts at the zero-offset relative to the top-left of the reference block, the subsampling of FIG. 22B starts at the one-offset relative to the top-left of the reference block. The evaluation can be used to select, from the two subsampling options shown in FIG. 22A and 22B, the option that yields the subset of template samples that is most representative of the reference block. In this manner, the process of selecting template samples for deriving LIO parameters can select a subsampling that is the most representative of the reference block.

[0193] In order to perform the selection, an embodiment calculates the range of values of the samples (i.e., range of sample values) in the reference block. The range, for example, may be determined by determining a minimum sample value (Vmin) and a maximum sample value (\ / max] within the reference block. Thereafter, for each sample belonging to a particular candidate option, a difference D is computed as shown in equation (25):0, otherwise

[0194] D may be considered as a difference between a template sample being considered and the range of samples values of the reference block. It may also be considered as a distance from the template sample being considered to the range of samples values.

[0195] In the two options shown in FIGs. 22A and 22B, for each option where denotes the offset from the top-left corner of the reference block, the integral value Dzimay be calculated as follows:

[0196] Eventually, the option with the minimal value of value Dziis selected for deriving the filter parameters. In general, the formula can be written as follows: ibest = argmin Dsi= argmin (E^“o Ds(i + A • $)) (27) i i

[0197] where N is the number of template samples available for given option , A is the step size between template samples, and s denotes a template sample index, ibest may be considered the subset of template samples that is most representative of the reference block.

[0198] In accordance with the two options of selecting subsets of the reference template shown in FIGs. 22A-22B, each option can be defined by a starting offset and a step size for selected samples in the reference template. When options are determined in accordance with the starting offset and step size, if the aspect ratio of the reference block is 2:1 as in, for example, FIGs. 22A and 22B, two options for selecting a subset of template samples can be considered.

[0199] FIGs. 23A-23D show another embodiment for a reference block with the aspect ratio of 4:1 where 4 options of selecting template reference samples are available along the longer side. In this embodiment, formulas (25)-(27) are applicable without any changes. FIGs. 23A, 23B, 230 and 23D, show subsets of reference template samples starting at offsets 0, 1, 2 and 3, respectively, and a step size of 3 (i.e., 3 unused samples between each pair of used samples).

[0200] A similar problem of selecting subsets of reference template samples that poorly represent the reference block also exists for multi-parametric reference filter for inter prediction (MP-RFIP). FIG. 24A shows an example of the template samples used to derive filter parameters for MP-RFIP. A 2-sample high template 2406 may be used for the reference block 2402, and an outer sample layer 2410 (which may include some samples 2412 within the reference block) may be included in samples used for deriving model parameters. A corresponding template 2408 is used for the current block 2404. In MP-RFIP as originally proposed, all available template samples may be involved in the parameter derivation process, and that can result in inaccurate model parameters (also referred to as “filter coefficients”).

[0201] FIG. 24B illustrates an embodiment where some template samples 2414 are excluded from the consideration due to their irrelevance to the reference block to which the derived filter parameters are applied to. For example, these template samples 2414 may have sample values that are very different from (e.g., outside the range of) samples in the reference block. Excluding the reference template samples 2414 from consideration also results in excluding the colocated current template samples 2416. Skipping these template samples may increase the reliability of the MP-RFIP parameter derivation process and the accuracy of derived filter coefficients.

[0202] FIG. 25 illustrates a histogram 2500 of sample values generated for a reference block, according to some embodiments. The x-axis represents samples values, and the y-axis represents the frequency of occurrence of respective sample values. Based on the histogram 2500, a minimum sample value 2502 and a maximum sample value 2504 can be determined thereby yielding the range 2506 of sample values for samples within the reference block. Each column along the x-axis may represent a single value or a subrange of values.

[0203] FIG. 26 illustrates a mechanism for selecting samples based on histograms generated for both template samples and block samples, according to some embodiments. Histogram 2600 is generated for the samples in the reference block and histogram 2602 is generated for the samples in the reference template. Based on histogram 2600, it can be determined that the sample values in the reference block range from a minimum sample value 2502 to a maximum sample value 2504. Based on the histogram 2602, it can be determined that the sample values of the reference template range from a minimum sample value 2604 to a maximum sample value 2606. Accordingly, by selecting template samples in the overlapped sample range 2608, a subset of template samples that is more representative of the reference block can be selected for use in model parameter derivation. Note that when the range 2608 is selected, template samples that have values between the template minimum sample value 2604 and the block minimum sample value 2502 may not be selected when the template minimum is outside the overlapped range.

[0204] Histograms such as 2600 and 2602 provide information on how frequently samples belonging to the overlapped range appear in the reference templates and the reference block. In some embodiments, this property of the histograms enables selection of the most frequently appearing samples that may additionally have a denoising effect on the template due to removing less frequent sample values from different parts of the histogram. These sample values can often correspond to outlier samples. For example, in some embodiments, instead of selecting all reference template samples that are within the sample value range in the reference block, only samples having valuescorresponding to the bins of reference block histogram with the highest magnitudes may be selected. In some embodiments, only reference template samples with values corresponding to the bins with highest magnitudes in the template histogram (e.g., 2602) and the bins with highest magnitudes in the reference block histogram (e.g., 2500) may be selected. For example, the bins with highest magnitudes may be those corresponding to a predetermined number of the bins, or bins having or associated with a magnitude above a predetermined threshold. The magnitude of each bin represents an accumulated count of occurrences of sample values within a range of values indicated by that bin. For ease of illustration, the count or frequency of occurrence of values associated with each bin is shown graphically as a height of the bin where a taller column / bin represents a higher magnitude of the bin.

[0205] In some embodiments, for multiparametric filters, different template formats can be considered in selecting the most representative subset of reference template samples for a particular reference block. FIG. 27A shows three example template formats along the top of the reference block 2702. Template 2704 extends across only the length of the top edge of the reference block 2702. Template 2706 extends further to the right of the reference block 2702. Template 2708 extends further on both sides of the reference block 2702. Similarly, FIG. 27B shows three example template formats along the left of the reference block 2702. Template 2710 extends across only the length of the left edge of the reference block 2702. Template 2714 extends further to down of the reference block 2702. Template 2712 extends further lower and higher than the reference block 2702.

[0206] Example embodiments are described primarily in relation to LIO and MP-RFIP. However, it should be noted that embodiments are not limited thereto, and may be incorporated in any video encoding or decoding process that utilizes template-based model parameter derivation for models / fi Iters used in generating a predictor of a current block. Moreover, embodiments may be applicable to luma and / or chroma samples.

[0207] FIG. 28 illustrates a flowchart 2800 of a method for encoding a bitstream where the process includes template preprocessing for reference filtering, according to some embodiments of the present disclosure. The reference filtering may be performed in order to select a subset of reference template samples that are most representative of the reference block. As noted above, the use of reference template samples that are representative of the reference block in model parameter derivation may improve the compression performance. The method of flowchart 2800 may be implemented by an encoder, such as encoder 200 in FIG. 2.

[0208] The method of flowchart 2800 begins at 2802. At 2802, the encoder obtains reference template samples (samples within a template of a reference block), and reference block samples (samples within the reference block). The encoder may also obtain current template samples (samples within a template of the current block).

[0209] The encoder calculates a range for the sample values for the obtained reference block samples. The range may be identified by a minimum sample value and a maximum sample value determined for the reference block samples. Some embodiments may consider all samples of the reference block in determining the range. However, embodiments are not limited to considering all reference block samples, and may consider only a subset of the reference block samples.

[0210] The current template is adjacent to the current block in the current picture and the reference template is adjacent to the reference block. The reference block is in a picture different than the current picture (e.g. , in inter prediction). According to some embodiments, the current template comprises one or more columns of neighbor samples nearest a left edge of the current block and one or more rows of neighbor samples nearest a top edge of the current block, and the reference template comprises one or more columns of neighbor samples nearest a left edge of the reference block and one or more rows of neighbor samples nearest a top edge of the reference block. The reference template and the current template have identical size, shape and relative placement relative to its block. FIGs. 20A-20B illustrate example non-limiting templates that extend adjacent to the left edge and adjacent to the top edge.

[0211] In some embodiments, the templates (e.g., reference template and corresponding current template) may comprise only neighbor samples from above the block or only neighbor samples to the left of the block. Moreover, in some embodiments, the templates may extend to the left and / or right of the top edge of the block, or above and / or below the left edge of the block. A non-limiting set of different template formats that may be used in embodiments is illustrated in FIGs. 27A-27B.

[0212] Templates of height 1 or more may be used for deriving parameters for single-tap filters (e.g., 1 -tap filter 2008 in FIG. 20A), and templates of height 2 or more may be used for deriving parameters for multi-tap filters (e.g., filters 2016, 2018, and 2020 in FIG. 20B). In some embodiments, when deriving parameters for multi-tap parameters, one or more outer samples from an area immediately adjacent to the reference template may be considered in addition to samples in the template. For example, a 1 -sample high layer surrounding the template may be considered as providing the outer samples. Embodiments are not limited to a particular height or format for the templates.

[0213] At 2804, based on the range determined at 2802 and in accordance with a priority ordering of samples in a template of the reference block, a plurality of reference template samples are selected. A process determining the plurality of reference template samples if described in relation to FIG. 30, according to some embodiments. The process shown in FIG. 30 determines the range of sample values for the reference block and, based on the filter type, a required number of reference template samples to derive the filter parameters. A plurality groups of reference template samples are determined according to the determined range, and the selection of the plurality of template samples is performed by selecting the required number of reference template samples from the determined groups according to a priority ordering.

[0214] In some embodiments, the selecting at 2804 includes identifying at least one sample in the template of the reference block that is not in the determined range, and selecting, as the plurality of samples, samples in the reference template excluding the identified at least one sample. FIG. 24B shows an example template with excluded samples.

[0215] In some embodiments, the selecting the plurality of samples from the reference template comprises generating a first histogram of samples in the reference block; identifying a minimum for the range and a maximum for the range from the first histogram; generating a second histogram of reference template samples, and identifying theplurality of samples based on an overlapping range of the first histogram and the second histogram. FIG. 32 illustrates an example histogram-based approach to select the plurality of reference template samples.

[0216] At 2806, parameters of a filter are derived based on the selected plurality of reference template samples and corresponding samples from a template of the current block. In some embodiments, this operation comprises deriving the parameters for a single-tap filter. The deriving of parameters for the single-tap filter may comprise calculating LIO parameters based on the selected plurality of samples (selected at 2804) and corresponding samples from the template of the current block.

[0217] In some embodiments, the filter is a multi-tap filter. Example non-limiting multi-tap filters are shown in FIG. 200. Example multi-tap filters are described above in relation to MP-RFIP. In some embodiments the filter is a FIR filter. The filter parameters may be derived using the multi-tap filter shape and a known technique such as a technique used in MP-RFIP, or another known technique.

[0218] At 2808, the filter is applied, with the derived parameters, to the reference block to generate a prediction block.

[0219] The generating of the prediction block may include processing the reference block with the filter in accordance with the calculated filter coefficients to obtain the prediction block.

[0220] In some embodiments, the processing of the reference block with the filter in accordance with the calculated filter coefficients to obtain the prediction block may include calculating an adjusted reference block, and using the adjusted reference block to obtain the prediction block.

[0221] At 2810, a prediction error based on the prediction block and the current block is encoded a bitstream.

[0222] For example, the prediction error (residual) is calculated based on the difference between the prediction block and the current block. The encoder encodes, in the bitstream, the prediction error based on the prediction block and the current block. The encoded prediction error values, when illumination compensation has been applied to the reference block or other artifact / difference reduction has been performed by applying filters with filter parameters calculated using reference template preprocessing as in embodiments of this disclosure, may be smaller compared to when such reference template preprocessing is not applied, and thus may be more efficiently encoded.

[0223] FIG. 29 illustrates a flowchart 2900 of a method for decoding a bit stream, including template preprocessing for reference filtering, in accordance with embodiments of the present disclosure. As noted above in relation to flowchart 2800, the reference filtering may be performed in order to select a subset of reference template samples that are most representative of the reference block. As noted above, the use of reference template samples that are representative of the reference block in model parameter derivation may improve the compression performance. The method of flowchart 2900 may be implemented by a decoder, such as decoder 300 in FIG. 3.

[0224] The method of flowchart 2900 begins at 2902. At 2902, the decoder obtains reference template samples and reference block samples. The decoder may also obtain current block samples. The decoder also determines the range of sample values in the reference template. The obtaining of samples and the determination of the range of sample values of reference template samples may be performed in the same manner as described in relation to block 2802 of flowchart 2800.

[0225] At 2904, based on the range determined at 2902 and in accordance with a priority ordering of samples in a template of the reference block, a plurality of reference template samples are selected. The selection of the plurality of reference template samples may be performed in the same manner as described in relation to block 2804 of flowchart 2800.

[0226] At 2906, parameters of a filter are derived based on the selected plurality of samples and corresponding samples from a template of the current block. The deriving of the filter parameters may be performed in a manner that is the same or similar to that described in relation to block 2806 of flowchart 2800.

[0227] At 2908, the filter is applied, with the derived parameters, to the reference block to generate a prediction block. The applying of the filter may be performed in a manner that is the same or similar to that described in relation to block 2808 of flowchart 2800.

[0228] At 2910, the current block is reconstructed based on the prediction error received in the bitstream, and the prediction block. For example, the reconstructed current block may be determined based on the sum of the prediction error and the prediction block.

[0229] FIG. 30 shows a flowchart 3000 of a process for selecting template samples for calculating filter parameters based on a priority ordering, according to some embodiments. The process of flowchart 3000 may be used, for example, at 2804 of flowchart 2800 or at 2904 of flowchart 2900, to select template samples.

[0230] The process of flowchart 3000 may begin at 3002. At 3002, the overlapping range between sample values of the reference template and the reference block is determined. The range of sample values of the reference template may be determined as described in relation to 2802 or 2902 of flowcharts 2800 or 2900, respectively. An example histogram-based method for determining the overlapping range of sample values of the reference template and the reference block is described in relation to flowchart 3200.

[0231] At 3004, the reference template samples that have the same values as samples in the reference block are determined as a first group (referred also as category A) of reference template samples. Thus, the sample value of each reference template sample in the first group is the same as the sample value of at least one sample of the reference block. The number of samples in category A is determined as NA.

[0232] At 3006, the reference template samples that are in the overlapped range with the reference block (e.g., determined at 3002) and are not already in category A are collected to a second group (also referred to as category B). That is, the sample value of each reference template sample in category B is within the range of sample values of the reference block. The number of samples in category B is determined as NB.

[0233] At 3008, reference template from outside the overlapped range is determined as a third group (referred to as category 0). Category C, thus, includes all reference template samples that are not in category A or category B. For example, these reference template samples may be selected in order of increasing absolute distance between respective values of selected reference template samples and the range. In some embodiments, some outlier samples may be removed from category C, for example, as described in relation to FIG. 24B.

[0234] At 3010, a required number of reference template samples is determined. The required number of reference template samples may be determined in accordance with the filter. For example, the encoder / decoder may have respective predefined required number of samples for each of a plurality of filters of different shapes and sizes of filters. For example, FIG. 20B and FIG. 200 show some example filters of different shapes and sizes.

[0235] At 3012, a bin width is determined for a reference block histogram. The bin width can be calculated by a known method such as, for example, using the methods described in Mark Jenkinson, “Histogram Bin Size”, https: / / www.fmrib.ox.ac.uk / datasets / techrep / tr00mj2 / tr00mj2 / node24.html.

[0236] At 3014, the reference block histogram is generated in accordance with the bin width determined at 3012.

[0237] At 3016 a set L of selected reference samples is initialized (e.g., empty set), and a number N is initialized to the required number of reference template samples determined at 3010.

[0238] Thereafter, at 3016 and 3018, respective samples from category A are added to set L. For each sample added to set L from category A, N is decremented by 1 and NA is decremented by 1 (i.e., N = N-1, A = A - 1). The adding of respective samples proceeds until N and NA remains greater than 0 (i.e., N > 0 && NA > 0).

[0239] After adding samples from category A to set L at 3016-3018, if set L does not have the required number of samples, then further samples may be considered for addition from lower priority categories of B and C. If set L has the required number of samples (i.e., N == 0), then the selection the reference template samples is complete.

[0240] At 3020-3022, respective samples from category B are added to set L. For each sample added to set L from category B, N is decremented by 1 and NB is decremented by 1 (i.e., N = N-1, NB = NB- 1). The adding of respective samples proceeds until N and NB remains greater than 0 (i.e., N > 0 && NB > 0).

[0241] After adding samples from category B to set L at 3020-3022, if set L does not have the required number of samples, then further samples may be considered for addition from lower priority category C. If set L has the required number of samples (i.e., N==0), then the selection the reference template samples is complete.

[0242] At 3024-3026, respective samples from category C are added to set L. For each sample added to set L from category C, N is decremented by 1 and Nc is decremented by 1 (i.e., N = N-1, Nc = Nc - 1). The adding of respective samples proceeds until N and Nc remains greater than 0 (i.e., N > 0 && Nc > 0).

[0243] The set L provides the plurality of reference template samples that are to be used for deriving filter parameters.

[0244] FIG. 31 shows a flowchart 3100 of a process for selecting template samples using a histogram of the samples of the reference block, according to some embodiments. The process of flowchart 3100 may be used during one or both 3018 (adding samples from category A to L) and 3022 (adding samples from category B to L) in flowchart 3000 to select samples from within the selected category. The histogram may be generated with each bin of a plurality of bins of the histogram corresponding to samples that have sample values in a respectively different range of values indicated by that bin. In particular, a data structure may be used to store a frequency of occurrences of sample values, from the reference block, in each respective range of values corresponding to each bin. The frequency of occurrencesassociated with each bin is graphically represented as a height of the bin in FIG. 25 and FIG. 26, but may be stored in association with each bin as an accumulated count.

[0245] The process of flowchart 3100 may begin at 3102. At 3102, the histogram bin that contains the largest number of reference block samples and, within the bin range (i.e., range defined by the maximum value and the minimum value defined for the bin) of which, the sample value of at least one reference template is present, is selected. That is, reference template samples from the category are selected in the order of the magnitudes (e.g., an accumulated frequency of occurrences represented graphically as heights of bins) of the reference block sample histogram bins in which their respective sample values fit. In considering the respective bins, any bin for which there are no reference template samples that have sample values within its range (i.e., maximum and minimum defined for the bin) is skipped. The histogram of reference block samples may be built at 3012-3012 of the process of flowchart 3000.

[0246] At 3104, among the reference template samples that have sample values within the selected bin, a reference template sample is selected based on the value of a metric M. The metric M may be defined, for example, as the sum of absolute difference (SAD) of the reference template sample and the reference block samples within this histogram bin. Embodiments, however, are not limited to using SAD as metric M.

[0247] FIG. 32 shows a flowchart 3200 of a method for use in selecting a subset of template samples for calculating filter parameters, according to some embodiments of the present disclosure. The method of flowchart 3200 may be performed during the method of flowchart 2800 or during the method of flowchart 2900. For example, when selecting the plurality of reference template samples (e.g., block 2804 in flowchart 2800 and / or block 2904 in flowchart 2900), ranges of the sample values in the reference template and the reference block may be determined using the method of flowchart 3200. Further the frequency of occurrences of particular sample values and / or sub ranges of sample values may also be determined in accordance with the histograms resulting from flowchart 3200. The method of flowchart 3200 may also be used in the processes described in relation to FIG. 37 and FIG. 38 below. For example, the subset of reference template samples at blocks 3704 and 3804 may be determined based on differences between values of respective reference template samples and the range of reference block sample values. FIGs. 25 and 26 illustrate example histograms.

[0248] At 3202, a first histogram of reference block samples is generated. Any known technique for calculating a histogram may be used.

[0249] At 3204, a minimum and a maximum for the range of sample values are determined from the first histogram.

[0250] At 3206, a second histogram is generated from reference template samples. Any known technique for calculating a histogram may be used.

[0251] At 3208, a subset of the reference template samples is identified based on the overlapping range of the first histogram and the second histogram. The identified subset may correspond to the subset of reference template samples for calculating filter parameters.

[0252] The identified plurality of samples each may have a respective value that is within the overlapping range.

[0253] In some embodiments, the identifying the plurality of samples based on the overlapping range of the first histogram and the second histogram may further comprise identifying the plurality of samples based further on a frequency of occurrence, in the first histogram, of values of respective samples of said plurality of samples. In some embodiments, the identified plurality of samples each may have a respective value that is within the overlapping range and may have at least the frequency of occurrence in the first histogram higher than a predefined threshold value.

[0254] FIG. 33 shows a flowchart 3300 of a method for selecting an optimal multi-tap filter and applying the selected multi-tap filter to generate the prediction block, according to some embodiments of the present disclosure. For example, after having selected a subset of reference template samples according to the method of flowchart 3200, the method of flowchart 2800 or the method of flowchart 2900, may perform the method of flowchart 3300 at 2806 or 2906 to select a multi-tap filter and to derive model parameters for that filter.

[0255] At 3302, a respective set of parameters for each multi-tap filter of a plurality of multi-tap filters is calculated. For example, in some embodiments, a plurality of multi-tap filters (different multi-tap filter shapes), as shown, for example, in FIGs. 20B-20C are selected forevaluation and the corresponding parameters (filter coefficients) are calculated. Filter coefficient calculation for the multi-tap filters can be performed using known methods.

[0256] At 3304, based on a portion of the template of the reference block and a portion the template of the current block, one of the plurality of multi-tap filters is selected as the filter. For example, each multi-tap filter may be applied, using the determined filter coefficients, to a probe template in the reference template and the current template. Probe templates are described in relation to FIG. 34. The multi-tap filter that has the lowest cost, based on its application to the probe templates of the reference block and the current block, may be the selected multi-tap filter.

[0257] At 3306, the selected multi-tap filter using the corresponding derived parameters is applied to the reference block to generate a prediction block.

[0258] FIG. 34 shows a reference block 3402 and a current block 3404 with the corresponding probe templates 3410 and 3414, respectively. As noted above, the probe templates can be used to evaluate a plurality of multi-tap filters to select a filter that is to be applied to the reference block to generate the prediction block. Parameter such as filter coefficients of the multi-tap filters (e.g., with shapes 3416, 3418, and 3420) may be derived using corresponding samples (e.g., samples 3417, 3419, and 3421 for filter shapes 3416, 3418, and 3420, respectively) from current block template 3412.

[0259] The one row and one column of neighbors that are immediately adjacent to the reference block 3402 is used as the reference probe template 3410. The reference probe template 3410 is part of the illustrated 3-sample high reference template 3406. As noted before, a 1 -sample high outer layer of samples 3408 of the reference template may also be considered for filter parameter derivation. Similarly, one row and one column of neighbors that are immediately adjacent to the current block 3404 is used as the current probe template 3414. The current probe template 3414 is part of the illustrated 3-sample high current template 3412.

[0260] FIG. 35 shows a flowchart 3500 of a method for an encoder to classify reference template samples and / or current template samples to groups, and to select a filter that is most suited for each group, according to some embodiments of the present disclosure. The method of flowchart 3500 may be performed by an encoder 200.

[0261] At 3502, samples are classified. Classification of samples can be performed using a classification filter (e.g., Laplace classifier) using known techniques. In some embodiments, the classification may be performed on current template samples, and in some other embodiments the classification is performed on reference template samples. The classification results in the reference template samples being grouped into a plurality of groups. Samples may be classified into different groups according to their properties. For example, template samples may belong to edges, smooth regions, or transition areas between samples of edges and smooth regions.

[0262] At 3504, a model type is defined for each group of samples. In some embodiments, a particular multi-tap format may be configured as being preferred for a particular group. For example, in some embodiments, different ones of the multi-tap filter formats shown in FIG. 200 may be used for respective groups of samples.

[0263] At 3506, model parameters are derived for each group of samples. The model parameter derivation may be performed using known methods.

[0264] At 3508, models are derived using the derived parameters for each group of samples. For example, a respective model is derived for each group based on the model type defined at 3504 and the parameters determined at 3506. With this process, different types of filters are applied to different groups to derive filter coefficients that are more optimal for each group of samples.

[0265] At 3510, a prediction block is generated using the plurality of models comprising the respective model derived for each group of samples. For example, respective samples of the prediction block are generated by applying the respective filter derived at 3508 for the group to which each sample belongs.

[0266] At 3512, a current block is encoded using the prediction block. For example, the prediction error resulting from subtracting the prediction block from the current block is encoded in the bitstream.

[0267] FIG. 36 shows a flowchart 3600 of a method for a decoder to classify reference template samples and / or current template samples to groups, and to select a filter that is most suited for each group, according to some embodiments of the present disclosure. The method of flowchart 3600 may be performed by a decoder 300.

[0268] Blocks 3602-3610 of the method of flowchart 3600 may be identical to blocks 3502-3510 of the method of flowchart 3500, and are thus not described again.

[0269] At 3612, a current block is decoded using the prediction block. For example, the current block may be reconstructed based on the prediction error received from the bitstream and the prediction block calculated at block 3612.

[0270] Preforming the template preprocessing can result the number of reference template samples belonging to the groups obtained after classification being greater than the number of reference template samples belonging to the same groups and remaining after the template preprocessing stage. This remaining number of reference template samples belonging to one of the groups can be insufficient for reliably deriving filter parameters (e.g., the filtercoefficients) for this group. In some embodiments, to generate enough reference template samples, this group may be be merged with one of the other groups to obtain a large enough number of template samples. For example, one or more adjacent groups of samples may be merged. In the case when just two groups are available, the classification stage may be skipped for this block.

[0271] In some embodiments, the mechanism of adding the nearest reference template samples belonging to a given group may include adding samples outside the reference block range until the number of added / selected reference template samples within this given group reaches the threshold value, which is sufficient to reliably derive (determine) filter parameters (coefficients). For example, this threshold value may be determined as k*N, where N is the number of filter parameters. Practical values of k may be equal to 1, 2, 3, 4, etc. In general, k may include non-integer values. For example, for a filter with 7 parameters, and k being 2, the threshold value may be determined as 2 *7 = 14 samples.

[0272] FIG. 37 illustrates a flowchart 3700 of a method for encoding a bitstream where the process includes template preprocessing for reference filtering, according to some embodiments of the present disclosure. The reference filtering may be performed in order to select a subset of reference template samples that are most representative of the reference block. As noted above, the use of reference template samples that are representative of the reference block in model parameter derivation may improve the compression performance. The method of flowchart 3700 may be implemented by an encoder, such as encoder 200 in FIG. 2.

[0273] The method of flowchart 3700 begins at 3702. At 3702, the encoder obtains reference template samples (samples within a template of a reference block), and reference block samples (samples within the reference block). The encoder may also obtain current template samples (samples within a template of the current block).

[0274] The encoder calculates a range for the sample values for the obtained reference block samples. The range may be identified by a minimum sample value and a maximum sample value determined for the reference block samples. Some embodiments may consider all samples of the reference block in determining the range. However, embodiments are not limited to considering all reference block samples and may consider a subset of the reference block samples.

[0275] The current template is adjacent to the current block in the current picture and the reference template is adjacent to the reference block. The reference block may be in the same picture as the current block (e.g., when using intra prediction) or in a picture different than the current picture (e.g., when using inter prediction). According to some embodiments, the current template comprises one or more columns of neighbor samples nearest a left edge of the current block and one or more rows of neighbor samples nearest a top edge of the current block, and the reference template comprises one or more columns of neighbor samples nearest a left edge of the reference block and one or more rows of neighbor samples nearest a top edge of the reference block. The reference template and the current template have identical size, shape and relative placement relative to its block. FIGs. 20A-20B illustrate example nonlimiting templates that extend adjacent to the left edge and adjacent to the top edge.

[0276] In some embodiments, the templates (e.g., reference template and corresponding current template) may comprise only neighbor samples from above the block or only neighbor samples to the left of the block. Moreover, insome embodiments, the templates may extend to the left and / or right of the top edge of the block, or above and / or below the left edge of the block. A non-limiting set of different template formats that may be used in embodiments is illustrated in FIGs. 27A-27B.

[0277] Templates of height 1 or more may be used for deriving parameters for single-tap filters, and templates of height 2 or more may be used for deriving parameters for multi-tap filters. In some embodiments, when deriving parameters for multi-tap parameters, one or more outer samples from an area immediately adjacent to the reference template may be considered in addition to samples in the template. For example, a 1 -sample high layer surrounding the template may be considered as providing the outer samples. Embodiments are not limited to a particular height or format for the templates.

[0278] At 3704, selecting, based on differences between values of respective samples in the template of the reference block and the range, a subset from a plurality of subsets of samples in the reference template as a plurality of reference template samples to be used in the deriving of filter parameters.

[0279] In some embodiments, the selecting of the plurality of reference template samples may be performed by determining, based on differences between values of respective reference template samples and the range, a subset from a plurality of subsets of reference template samples as the plurality of samples. Subset determination, according to some embodiments, is further described in relation to FIG. 39.

[0280] Each of the subsets of the plurality of subsets may comprise a respectively different subset of samples from a portion of the template of the reference block. The portion may comprise samples along a longer edge of the reference block. The longer edge may be one of the above edge or the left edge.

[0281] Wherein when an aspect ratio of a longer edge of the reference block and a shorter edge of the reference block is y:1, the plurality of subsets may comprise at least y subsets, where a leftmost sample that is above the reference block in each of the y subsets is offset from a top left edge of the reference block or a bottom-most sample that is left of the reference block in each of the y subsets is offset from a bottom left edge of the reference block by a respectively different number of samples. Each of the y subsets may comprise a same set of neighboring samples left of the reference block.

[0282] In some embodiments, the selecting at 2804 includes identifying at least one sample in the template of the reference block that is not in the determined range, and selecting, as the plurality of samples, samples in the reference template excluding the identified at least one sample. FIG. 24B shows an example template with excluded samples.

[0283] In some embodiments, the selecting, based on the determined range, the plurality of samples from the reference template comprises generating a first histogram of samples in the reference block; identifying a minimum for the range and a maximum for the range from the first histogram; generating a second histogram of reference template samples, and identifying the plurality of samples based on an overlapping range of the first histogram and the second histogram. FIG. 32 further illustrates the histogram-based approach to select the plurality of reference template samples.

[0284] At 3706, parameters of a filter are derived based on the selected plurality of samples and corresponding samples from a template of the current block. This operation comprises deriving the parameters for a single-tap filter. The deriving of parameters for the single-tap filter may comprise calculating LIC parameters based on the selected plurality of samples (selected at 3704) and corresponding samples from the template of the current block. Known techniques may be used to derive the parameters using the selected plurality of samples.

[0285] At 3708, the filter is applied, with the derived parameters, to the reference block to generate a prediction block.

[0286] The generating of the prediction block may include processing the reference block with the filter in accordance with the calculated filter coefficients to obtain the prediction block.

[0287] In some embodiments, the processing of the reference block with the filter in accordance with the calculated filter coefficients to obtain the prediction block may include calculating an adjusted reference block, and using the adjusted reference block to obtain the prediction block.

[0288] At 3710, a prediction error based on the prediction block and the current block is encoded a bitstream.

[0289] For example, the prediction error (residual) is calculated based on the difference between the prediction block and the current block. The encoder encodes, in the bitstream, the prediction error based on the prediction block and the current block. The encoded prediction error values, when illumination compensation has been applied to the reference block or other artifact / difference reduction has been performed by applying filters with filter parameters calculated as in embodiments of this disclosure, may be smaller compared to when such filtering is not applied, and thus may be more efficiently encoded.

[0290] FIG. 38 illustrates a flowchart 3800 of a method for decoding a bit stream, including template preprocessing for reference filtering, in accordance with embodiments of the present disclosure. As noted above in relation to flowchart 3700, the reference filtering may be performed in order to select a subset of reference template samples that are most representative of the reference block. As noted above, the use of reference template samples that are representative of the reference block in model parameter derivation may improve the compression performance. The method of flowchart 3800 may be implemented by a decoder, such as decoder 300 in FIG. 3.

[0291] The method of flowchart 3800 begins at 3802. At 3802, the decoder obtains reference template samples, and reference block samples. The decoder may also obtain current block samples. The samples may be obtained in the same manner as described in relation to block 3702 of flowchart 3700.

[0292] At 3804, selecting, based on differences between values of respective samples in the template of the reference block and the range, a subset from a plurality of subsets of samples in the reference template as a plurality of samples in the template of the reference block. The subset may be selected in the same manner as described in relation to block 3704 of flowchart 3700.

[0293] At 3806, parameters of a filter are derived based on the selected plurality of samples and corresponding samples from a template of the current block. The deriving of the filter parameters may be performed in a manner that is the same or similar to that described in relation to block 3706 of flowchart 3700.

[0294] At 3808, the filter is applied, with the derived parameters, to the reference block to generate a prediction block. The applying of the filter may be performed in a manner that is the same or similar to that described in relation to block 3708 of flowchart 3700.

[0295] At 3810, the current block is reconstructed based on the prediction error received in the bitstream, and the prediction block. For example, the reconstructed current block may be determined based on the sum of the prediction error and the prediction block.

[0296] FIG. 39 shows a flowchart 3900 of a method for selecting a subset of template samples for calculating filter parameters, according to some embodiments of the present disclosure. The method of flowchart 3900 may be performed during the method of flowchart 3700 or during the method of flowchart 3800. For example, when selecting the plurality of reference template samples (e.g., as described with respect to block 3704 in flowchart 3700 and / or block 3804 in flowchart 3800), a subset can be determined from a plurality of subsets of reference template samples as the plurality of reference template samples, in accordance with the method of flowchart 3900. The subset may be determined based on differences between values of respective reference template samples and the range of reference block sample values.

[0297] The method of flowchart 3900 may begin at 3902. At 3902, for each sample in the subset, a respective difference is determined (1) as an absolute value between each sample and the range when the value of that sample is outside the range and (2) as a predetermined constant value when the value of that sample is within the range. In some embodiments, the differences can be determined in accordance with equation 25.

[0298] At 3904, the sum of the respective differences of samples in the subset is determined. In some embodiments, this sum may be determined in accordance with equation 26.

[0299] At 3906, the sum of the respective differences of samples in the subset and corresponding sums in others of the subsets of the plurality of subsets are compared. The subset that is selected as the plurality of samples may be determined as the subset that has the minimum sum of differences. In some embodiments, this selection may be performed in accordance with equation 27.

[0300] In some embodiments, the method of flowchart 3900 may further include identifying, based on the comparing at 3906, the sum of the respective differences of samples in the subset as a minimum among all the sum of the respective differences of samples in the subset and corresponding sums in others of the subsets of the plurality of subsets.

[0301] 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.

[0302] 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 (for example, 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.

[0303] 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.

[0304] 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.

[0305] 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.

[0306] 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.

[0307] In another embodiment, features of the disclosure may be implemented in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine to perform the functions described herein will also be apparent to persons skilled in the art.

Claims

CLAIMSWhat is claimed is:

1. A method, comprising: determining a range of values of samples in a reference block associated with a current block; selecting, based on the range and in accordance with a priority ordering of samples in a template of the reference block, a plurality of samples from the template of the reference block; deriving parameters of a filter based on the selected plurality of samples and corresponding samples from a template of the current block; applying the filter, with the derived parameters, to the reference block to generate a prediction block; and coding the current block based on the prediction block.

2. The method of claim 1 , wherein the selecting the plurality of samples from the template of the reference block, comprises: identifying at least one sample in the template of the reference block that has a value that is not in the range; and selecting, as the plurality of samples, samples in the reference template in accordance with the priority ordering and excluding the identified at least one sample.

3. The method of any one of claims 1 -2, wherein the selecting the plurality of samples from the template of the reference block comprises: determining a required number of samples; and adding, to a selection set, a first number of samples from a first set of samples from the template of the reference block, wherein each sample in the first set has a sample value that is same as a sample value of at least one sample in the reference block.

4. The method of claim 3, wherein the first number is the lesser of the required number and a total number of samples in the first set.

5. The method of any one of claims 3-4, wherein the selecting the plurality of samples from the template of the reference block further comprises: adding, to the selection set of samples and based on the number of samples in the selection set after the adding the first number of samples being less than the required number of samples, a second number of samples from a second set of samples from the template of the reference block, wherein each sample in the second set has a sample value that is in the range and is not in the first set.

6. The method of claim 5, wherein the selecting the plurality of samples in the template of the reference block further comprises: adding, to the selection set of samples and based on a number of samples in the selection set after the adding the first set and the adding the second set being less than the required number of samples, a third number of samples from the template of the reference block that have sample values that are outside the determined range.

7. The method of claim 6, wherein the adding, to the selection set of samples, the third number of samples from the template of the reference block that have sample values that are outside the determined range comprises adding to the selection set respective samples with values from outside the range in order of distances to the range.

8. The method of any one of claims 6-7, wherein the third number of samples are selected in order of increasing absolute distance between respective values of the third number of samples and the range.

9. The method of any one of claims 5-8, wherein the adding, to the selection set of samples, the second number of samples from the first set of samples comprises adding to the selection set respective samples from the second set in order of, for each sample from the second set, a frequency of occurrence of corresponding sample values in the reference block.

10. The method of claim 9, wherein the selecting the plurality of samples in the template of the reference block comprises: generating a histogram of samples from the reference block, each bin of a plurality of bins in the histogram corresponding to samples that have sample values in a respectively different range, wherein the frequency of occurrence of corresponding sample values in the reference block is determined in accordance with a bin, of the plurality of bins, corresponding to the sample value of the each sample in the second set.

11. The method of claim 10, wherein the adding to the selection set respective samples from the second set in order of, for each sample from the second set, a frequency of occurrence of corresponding sample values in the reference block comprises selecting the each sample from the second set in order of a value of a metric comparing the each sample from the second set to samples of the reference block in the bin corresponding to the sample value of the each sample.

12. The method of any one of claims 3-11 , wherein the adding, to the selection set of samples, the first number of samples from the first set of samples comprises adding to the selection set respective samples from the first set of samples in order of, for each sample from the first set, a frequency of occurrence of corresponding sample values in the reference block.

13. The method according to claim 12, wherein the selecting the plurality of samples in the template of the reference block comprises: generating a histogram of samples from the reference block, each bin of a plurality of bins in the histogram corresponding to samples that have sample values in a respectively different range, wherein the frequency of occurrence of corresponding sample values in the reference block is determined in accordance with a bin, of the plurality of bins, corresponding to the sample value of the each sample in the first set.

14. The method of any one of claims 1-13, wherein the determining the range of values of samples in the reference block associated with the current block comprises: generating a first histogram of the samples in the reference block; and identifying a minimum for the range and a maximum for the range from the first histogram.

15. The method of claim 14, wherein the selecting, based on the determined range, the plurality of samples from a template of the reference block comprises: generating a second histogram of samples from the template of the reference block; and identifying the plurality of samples based on an overlapping range of the first histogram and the second histogram and the priority ordering.

16. The method of claim 15, wherein the identified plurality of samples each has a respective value that is within the overlapping range.

17. The method of any one of claims 15-16, wherein the identifying the plurality of samples based on the overlapping range of the first histogram and the second histogram further comprises identifying the plurality of samples further based on a frequency of occurrence, in the first histogram, of values of respective samples of said plurality of samples.

18. The method of claim 17, wherein the identified plurality of samples each has a respective value that is within the overlapping range and has at least the frequency of occurrence in the first histogram higher than a threshold.

19. The method of any one of claims 15-18, wherein the deriving parameters of the filter based on the selected plurality of samples and corresponding samples from the template of the current block comprises deriving the parameters for a single-tap filter, and wherein the applying the filter to the reference block to generate the prediction block comprises applying the single-tap filter, using the derived parameters, to the reference block to generate the prediction block.

20. The method of claim 19 wherein the deriving the parameters for the single-tap filter comprises calculating local illumination control (LIC) parameters based on the selected plurality of samples and corresponding samples from a template of the current block.

21. The method of any one of claims 15-20, wherein the deriving parameters of the filter based on the selected plurality of samples and corresponding samples from the template of the current block comprises deriving the parameters for a multi-tap filter, and wherein the applying the filter to at least one of the reference block or the current block comprises applying the multi-tap filter using the derived parameters, to the reference block to generate the prediction block.

22. The method of claim 21 , wherein the deriving parameters of the filter based on the selected plurality of samples and corresponding samples from the template of the current block comprises: calculating a respective set of parameters for each multi-tap filter of a plurality of multi-tap filters; and selecting one of the plurality of multi-tap filters as the filter, based on a portion of the template of the reference block and a portion of the template of the current block, from the plurality of multi-tap filters, and wherein the applying the filter to at least one of the reference block or the current block comprises applying the multi-tap filter, using the corresponding derived parameters, to the reference block to generate the prediction block.

23. The method of claim 22, wherein the portions correspond to each other with respect to a relative position in the reference template and the current template.

24. The method of any one of claims 1 -23, wherein the determining the range of values of samples in the reference block associated with the current block comprises determining a minimum for the range and a maximum for the range from the values of samples in the reference block.

25. The method of any one of claims 1 -24, wherein the selecting the plurality of samples from the template of the reference block comprises determining, based on comparing values of respective samples in the template of the reference block with the range, a subset from a plurality of subsets of samples in the reference template as the plurality of samples.

26. The method of any one of claims 1 -25, wherein the deriving the parameters of the filter based on the selected plurality of samples and corresponding samples from the template of the current block comprises classifying the selected plurality of samples into two or more groups and determining a respective filter for each group, and wherein the applying the filter to at least one of the reference block or the current block comprises applying, for each of the two or more groups, the corresponding filter to samples in the group to generate the prediction block.

27. A method, comprising: determining a range of values of samples in a reference block associated with a current block; selecting, based on differences between values of respective samples in a template of the reference block and the range, a subset from a plurality of subsets of samples in the reference template as a plurality of samples in the template of the reference block; deriving parameters of a filter based on the selected plurality of samples and corresponding samples from a template of the current block; applying the filter, with the derived parameters, to the reference block to generate a prediction block; and coding the current block based on the prediction block.

28. The method of claim 27, wherein the filter is a single-tap filter.

29. The method of any one of claims 27-28, wherein the selecting the plurality of samples from the template of the reference block comprises: determining, based on differences between values of respective samples in the template of the reference block and the range, a subset from a plurality of subsets of samples in the reference template as the plurality of samples.

30. The method of claim 29, wherein the determining the subset from the plurality of subsets of samples in the reference template as the plurality of samples, comprises: for each sample in the subset, determining a respective difference as: an absolute value between the each sample and the range when the value of the each sample is outside the range; and a predetermined value when the value of the each sample is within the range; and determining a sum of the respective differences of samples in the subset; and comparing the sum of the respective differences of samples in the subset and corresponding sums in others of the subsets of the plurality of subsets.

31. The method of claim 30, wherein the determining the subset from the plurality of subsets of samples in the reference template as the plurality of samples further comprises: determining, based on the comparing, the sum of the respective differences of samples in the subset as a minimum among the sum of the respective differences of samples in the subset and sums of the others of the subsets of the plurality of subsets.

32. The method of any one of claims 29-31 , wherein each of the subsets of the plurality of subsets comprises a respectively different subset of samples from a portion of the template of the reference block.

33. The method of claim 32, wherein the portion comprises samples along a longer edge of the reference block.

34. The method of claim 33, wherein the longer edge is one of the above edge or the left edge.

35. The method of any one of claims 33-34, wherein based on an aspect ratio of a longer edge of the reference block to a shorter edge of the reference block being y: 1 , the plurality of subsets comprises at least y subsets, wherein a leftmost sample that is above the reference block in each of the y subsets is offset from a top left edge of the reference block or a bottom-most sample that is left of the reference block in each of the y subsets is offset from a bottom left edge of the reference block by a respectively different number of samples.

36. The method of claim 35, wherein said each of the y subsets comprises a same set of neighboring samples left of the reference block.

37. The method of any one of claims 29-36, wherein the derived parameters are for a single-tap filter.

38. The method of claim 37, wherein the deriving the parameters for the single-tap filter comprises calculating local illumination control (LIC) parameters based on the selected plurality of samples and corresponding samples from the template of the current block.

39. The method of any one of claims 27-38, wherein the selecting a plurality of samples in the template of the reference block, comprises: identifying at least one sample in the template of the reference block that has a value that is not in the range; and selecting, as the plurality of samples, samples in the reference template excluding the identified at least one sample.

40. The method of any one of claims 27-39, wherein the determining the range of values of samples in the reference block associated with the current block comprises: generating a first histogram of the samples in the reference block; and identifying a minimum for the range and a maximum for the range from the first histogram.

41. The method of claim 40, wherein the selecting, based on the determined range, the plurality of samples from the template of the reference block comprises: generating a second histogram of samples from the template of the reference block; and identifying the plurality of samples based on an overlapping range of the first histogram and the second histogram.

42. The method of claim 41 , wherein the identified plurality of samples each has a respective value that is within the overlapping range.

43. The method of any one of claims 41-42, wherein the identifying the plurality of samples based on the overlapping range of the first histogram and the second histogram further comprises identifying the plurality of samples further based on a frequency of occurrence, in the first histogram, of values of respective samples of the plurality of samples.

44. The method of claim 43, wherein the identified plurality of samples each has a respective value that is within the overlapping range and has at least the frequency of occurrence in the first histogram higher than a threshold.

45. The method of any one of claims 41-44, wherein the derived parameters are for a single-tap filter, and wherein the applying the filter to the reference block to generate the prediction block comprises applying the single-tap filter, using the derived parameters, to the reference block to generate the prediction block.

46. The method of claim 45, wherein the deriving the parameters for the single-tap filter comprises calculating local illumination control (LIC) parameters based on the selected plurality of samples and corresponding samples from a template of the current block.

47. The method of any one of claims 27-46, wherein the determining the range of values of samples in the reference block associated with the current block comprises determining a minimum for the range and a maximum for the range from the values of samples in the reference block.

48. The method of any one of claims 27-47, wherein the selecting the plurality of samples from the template of the reference block comprises determining, based on comparing values of respective samples in the template of the reference block with the range, the subset from the plurality of subsets of samples in the reference template as the plurality of samples.

49. The method of any one of claims 27-48, wherein the deriving the parameters of the filter based on the selected plurality of samples and corresponding samples from the template of the current block comprises classifying the selected plurality of samples into two or more groups and determining a respective filter for each group, and wherein the applying the filter to at least one of the reference block or the current block comprises applying, for each of the two or more groups, the corresponding filter to samples in the group to generate the prediction block.

50. The method of any one of claims 1 -49, wherein the coding the current block comprises reconstructing the current block based on a prediction error received in a bitstream and the prediction block.

51. The method of any one of claims 1-49, wherein the coding the current block comprises encoding, in a bitstream, a prediction error based on the prediction block and the current block.

52. 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 1-51.

53. An encoder comprising: one or more processors; andmemory storing instructions that, when executed by the one or more processors, cause the encoder to perform the method of any one of claims 1 -49 or 51.

54. 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 -49 or 51.

55. 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 1-50.

56. 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 1-50.

57. A bitstream generated according to any one of claims 1 -51.

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