Block candidates for intra template match prediction

Abstract

To enable better video compression, an encoder and decoder are based on determining a first block vector prediction (BVP) candidate for predicting a block of pixel lumas of a current block of an image to be decoded, by applying a search using template matching prediction (TMP) for the block, wherein the first block vector prediction (BVP) candidate is a sparse candidate pointing to a spatially sub-sampled position of the image to be decoded; deriving an auto-relocated BVP candidate by using the first block vector prediction (BVP) candidate and determining the auto-relocated BVP candidate as a block vector which is equal to the vector addition of the first block vector prediction (BVP) candidate and a block vector which was used to predict a block at a position pointed to by the first block vector prediction (BVP) candidate, starting from a position of the current block; determining a list of BVP candidates comprising the first BVP candidate and the auto-relocated BVP candidate and determining, based on the list of BVP candidates, a final block vector indicating a reference block for predicting the current block.

Description

[0001] BLOCK CANDIDATES FOR INTRA TEMPLATE MATCH PREDICTION

[0002] FIELD OF THE INVENTION

[0003] Methods and apparatuses for video encoding and decoding.

[0004] BACKGROUND OF THE INVENTION.

[0005] Successive generations of video coders have produced more and more tools to try to make good predictions of the pixel colors (luma and chroma) of a block of the image, based on similarity with information that was already decoded previously. The better the predictions are, the less corrective (residual) bits have to be sent in the compressed bitstream to decoders. Several intra-prediction techniques exist for predicting the current block based on colors present in previously decoded blocks of the same current image. It is desired to have better candidate blocks from which to do the prediction of the current block.

[0006] SUMMARY OF THE INVENTION

[0007] Such a better set (a.k.a. list) of candidate predictor blocks can be obtained by a method of decoding a sequence of images comprising: determining a first block vector prediction (BVP) candidate for predicting a block of pixel lumas of a current block of an image to be decoded, by applying a search using template matching prediction (TMP) for the block, which selects the first block vector prediction candidate based on a match between pixels in a template of the first block vector prediction (BVP) candidate and a template of the current block, wherein the first block vector prediction (BVP) candidate is a sparse candidate pointing to a spatially sub-sampled position of the image to be decoded; deriving an auto-relocated BVP candidate by using the first block vector prediction (BVP) candidate and determining the auto-relocated BVP candidate as a block vector which is equal to the vector addition of the first block vector prediction (BVP) candidate and a block vector which was used to predict a block at a position pointed to by the first block vector prediction (BVP) candidate starting from a position of the current block; determining a list of BVP candidates comprising the first BVP candidate and the autorelocated BVP candidate; determining, based on the list of BVP candidates, a final block vector indicating a reference block for predicting the current block; and decoding the current block based on the reference block. In an embodiment the method has the auto-relocated BVP candidate added in a list of sparse candidates, which list of sparse candidates is used for selecting the final block vector.

[0008] In an embodiment the method has one or more spatially offset candidates, which are located at a position offset from a position of the auto-relocated BVP candidate by a fixed horizontal and / or vertical distance, added to the list of sparse candidates.

[0009] A method of encoding a sequence of images comprising: determining a first block vector prediction (BVP) candidate for predicting a block of pixel lumas of a current block of an image to be decoded, by applying a search using template matching prediction (TMP) for the block, which selects the first block vector prediction candidate based on a match between pixels in a template of the first block vector prediction (BVP) candidate and a template of the current block, wherein the first block vector prediction (BVP) candidate is a sparse candidate pointing to a spatially sub-sampled position of the image to be decoded; deriving an auto-relocated BVP candidate by using the first block vector prediction (BVP) candidate and determining the auto-relocated BVP candidate as a block vector which is equal to the vector addition of the first block vector prediction (BVP) candidate and a block vector which was used to predict a block at a position pointed to by the first block vector prediction (BVP) candidate starting from a position of the current block; determining a list of BVP candidates comprising the first BVP candidate and the autorelocated BVP candidate; determining, based on the list of BVP candidates, a final block vector indicating a reference block for predicting the current block; and encoding the current block based on the reference block.

[0010] An embodiment of the method of encoding, in which the auto-relocated BVP candidate is added in a list of sparse candidates, which list of sparse candidates is used for selecting the final block vector.

[0011] An embodiment of the method of encoding, wherein one or more spatially offset candidates, which are located at a position offset from a position of the auto-relocated BVP candidate by a fixed horizontal and / or vertical distance, are added to the list of sparse candidates.

[0012] A video decoding apparatus comprising a memory and a processor arranged to perform any embodiment of the above mentioned decoding method.

[0013] A video encoding apparatus comprising a memory and a processor arranged to perform any embodiment of the above mentioned encoding method.

[0014] A computer program product comprising computer code to instruct a processor to execute one of the methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Some features are shown by way of example, and not by limitation, in the accompanying drawings. In the drawings, like numerals reference similar elements.

[0016] FIG. 1 illustrates an example video coding / decoding system in which embodiments of the present disclosure may be implemented.

[0017] FIG. 2 illustrates an example encoder in which embodiments of the present disclosure may be implemented.

[0018] FIG. 3 illustrates an example decoder in which embodiments of the present disclosure may be implemented.

[0019] FIG. 4 illustrates an example quadtree partitioning of a coding tree block (CTB).

[0020] FIG. 5 illustrates an example quadtree corresponding to the example quadtree partitioning of the CTB in FIG. 4.

[0021] FIG. 6 illustrates examples of binary tree and ternary tree partitions.

[0022] FIG. 7 illustrates an example of combined quadtree and multi-type tree partitioning of a CTB.

[0023] FIG. 8 illustrates an example tree corresponding to the combined quadtree and multi-type tree partitioning of the CTB shown in FIG. 7.

[0024] FIG. 9 illustrates an example set of reference samples determined for intra prediction of a current block.

[0025] FIG. 10A, FIG. 10B illustrate example intra prediction modes.

[0026] FIG. 11 illustrates an example of a current block and corresponding reference samples.

[0027] FIG. 12 illustrates an example of applying an intra prediction mode (e.g., an angular mode) for prediction of a current block.

[0028] FIG. 13A illustrates an example of inter prediction performed for a current block in a current picture.

[0029] FIG. 13B illustrates an example motion vector.

[0030] FIG. 14 illustrates an example of bi-prediction performed for a current block.

[0031] FIG. 15A illustrates example spatial candidate neighboring blocks relative to a current block being coded.

[0032] FIG. 15B illustrates example locations of two temporal, co-located blocks relative to a current block.

[0033] FIG. 16 illustrates an example of intra block copy (IBC).

[0034] FIG. 17 illustrates, for an example current block, a reference region or search area of reconstructed samples within which in Intra Template Match Prediction (IntraTMP) a search is performed for a candidate reference block of which the template best matches the template of the current block.

[0035] FIG. 18 illustrates a current block in a current CTU, and the reference region with the corresponding IntraTMP search regions R1-R6 identified. FIG. 19A illustrates the sparse search stage of IntraTMP.

[0036] FIG. 19B illustrates a block vector according to IntraTMP where the block vector’s refinement window is clipped at the boundary of a search region.

[0037] FIG. 20 illustrates an example of the top-template type that can be used in IntraTMP.

[0038] FIG. 21 illustrates an example of the left-template type that can be used in IntraTMP.

[0039] FIG. 22 illustrates an example of the L-shape template type that can be used in IntraTMP.

[0040] FIG. 23A and FIG. 23B illustrate adjacent blocks and non-adjacent blocks for determining block vector candidates, according to IntraTMP with Merge Candidates.

[0041] FIG. 24 illustrates an IntraTMP with Merge Candidates process, according to some embodiments.

[0042] FIG. 25 illustrates example refinement windows for sparse block vector candidates and merge block vector candidates, according to some embodiments.

[0043] FIG. 26A shows an example of auto-relocated block vector prediction (AR-BVP) applied to IBC, according to some embodiments.

[0044] FIG. 26B shows examples of refinement windows of AR-BVP candidates derived from different positions associated with a guiding BV, according to some embodiments.

[0045] FIG. 27 shows an example of IntraTMP with BVP candidates derived using IntraTMP AR-BVP merge, according to some embodiments.

[0046] FIG. 28 shows an example of the IntraTMP AR-BVP merge process, according to some embodiments.

[0047] FIG. 29 shows an example of sparse AR-BVP candidates in IntraTMP generated by applying the AR-BVP technique to the TMP BV candidates, according to some embodiments.

[0048] FIG. 30A shows an example process for applying TMP sparse AR-BVP candidates to the TMP, according to some embodiments.

[0049] FIG. 3 OB shows another example process for applying TMP sparse AR-BVP candidates to the TMP, according to some embodiments.

[0050] FIG. 31 shows a flowchart of a method for generating a list of BVP candidates for coding a current block, according to some embodiments.

[0051] FIG. 32 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented.

[0052] DETAILED DESCRIPTION

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The term “computer-readable medium” includes, but is not limited to, portable or nonportable storage devices, optical storage devices, and various other mediums capable of storing, containing, or carrying instruction(s) and / or data. A computer-readable medium may include a non- transitory medium in which data can be stored and that does not include carrier waves and / or transitory electronic signals propagating wirelessly or over wired connections. Examples of a non-transitory medium may include, but are not limited to, a magnetic disk or tape, optical storage media such as compact disk (CD) or digital versatile disk (DVD), flash memory, memory or memory devices. A computer-readable medium may have stored thereon code and / or machine -executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any 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.

[0057] 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. 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.

[0058] 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.).

[0059] 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.

[0060] A video sequence, such as video sequence 108, may comprise a series of pictures (also referred to as frames). A video sequence may achieve an impression of motion based on successive presentation of pictures of the video sequence using a constant time interval or variable time intervals between the pictures. A picture may comprise one or more sample arrays of intensity values. The intensity values may be taken (e.g., measured, determined, provided) at a series of regularly spaced locations within a picture. A color picture may comprise (e.g., typically comprises) a luminance sample array and two chrominance sample arrays. The luminance sample array may comprise intensity values representing the brightness (e.g., luma component, Y) of a picture. The chrominance sample arrays may comprise intensity values that respectively represent the blue and red components of a picture (e.g., chroma components, Cb and Cr) separate from the brightness. Other color picture sample arrays may be possible based on different color schemes (e.g., a red, green, blue (RGB) color scheme). A pixel, in a color picture, may refer to / comprise / be associated with all intensity values (e.g., luma component, chroma components), for a given location, in the sample arrays (e.g., three sample arrays are used for one luma component and two chroma components, respectively) used to represent color pictures. A monochrome picture may comprise a single, luminance sample array. A pixel, in a monochrome picture, may refer to / comprise / be associated with the intensity value (e.g., luma component) at a given location in the single, luminance sample array used to represent monochrome pictures.

[0061] 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.

[0062] For temporal prediction, encoder 114 may search for a block similar to the block being encoded in another picture (e.g., referred to as a reference picture) of video sequence 108. The block determined during the search (e.g., referred to as a prediction block) may then be used to predict the block being encoded. For spatial prediction, encoder 114 may form a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 108. A reconstructed sample refers to a sample that was encoded and then decoded. Encoder 114 may determine a prediction error (e.g., also referred to as a residual) based on the difference between a block being encoded and a prediction block. The prediction error may represent non-redundant information that may be sent / transmitted to a decoder for accurate decoding of video sequence 108.

[0063] Encoder 114 may apply a transform to the prediction error (e.g. using a discrete cosine transform (DCT), or any other transform) to generate transform coefficients. Encoder 114 may form bitstream 110 based on the transform coefficients and other information used to determine prediction blocks using / based on prediction types, motion vectors, and / or prediction modes. Encoder 114 may perform one or more of quantization and entropy coding of the transform coefficients and / or the other information used to determine the prediction blocks, for example, before forming bitstream 110. The quantization and / or the entropy coding may further reduce the quantity of bits needed to store and / or transmit video sequence 108.

[0064] Output interface 116 may be configured to write and / or store bitstream 110 onto transmission medium 104 for transmission to destination device 106. In addition or alternatively, output interface 116 may be configured to send / transmit, upload, and / or stream bitstream 110 to destination device 106 via transmission medium 104. Output interface 116 may comprise a wired and / or a wireless transmitter configured to send / transmit, upload, and / or stream bitstream 110 in accordance with one or more proprietary, open-source, and / or standardized communication protocols (e.g., Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, 3rd Generation Partnership Project (3GPP) standards, Institute of Electrical and Electronics Engineers (IEEE) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and / or any other communication protocol).

[0065] 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.

[0066] 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).

[0067] Decoder 120 may decode video sequence 108 from encoded bitstream 110. The decoder 120 may generate prediction blocks for pictures of video sequence 108 in a similar manner as encoder 114 and determine the prediction errors for the blocks, for example, to decode video sequence 108. Decoder 120 may generate the prediction blocks using / based on prediction types, prediction modes, and / or motion vectors received in bitstream 110. Decoder 120 may determine the prediction errors using the transform coefficients received in bitstream 110. Decoder 120 may determine the prediction errors by weighting transform basis functions using the transform coefficients. Decoder 120 may combine the prediction blocks and the prediction errors to decode video sequence 108. Video sequence 108 at the destination device 106 may be, or may not necessarily be, the same video sequence sent, such as video sequence 108 as sent by the source device 102. Decoder 120 may decode a video sequence that approximates video sequence 108, for example, because of lossy compression of video sequence 108 by encoder 114 and / or errors introduced into encoded bitstream 110 during transmission to destination device 106.

[0068] 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.

[0069] 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.

[0070] Encoder 114 and / or decoder 120 may operate according to one or more proprietary or industry video coding standards. For example, encoder 114 and / or decoder 120 may operate in accordance with one or more proprietary, open-source, and / or standardized protocols (e.g., International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.263, ITU-T H.264 and Moving Picture Expert Group (MPEG)-4 Visual (also known as Advanced Video Coding (AVC)), ITU-T H.265 and MPEG-H Part 2 (also known as High Efficiency Video Coding (HEVC)), ITU-T H.265 and MPEG-I Part 3 (also known as Versatile Video Coding (VVC)), the WebM VP8 and VP9 codecs, and / or AOMedia Video 1 (AVI), and / or any other video coding protocol).

[0071] 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.

[0072] Encoder 200 may partition pictures (e.g., frames) of (e.g., comprising) video sequence 202 into blocks and encode video sequence 202 on a block-by-block basis. Encoder 200 may perform / apply a prediction technique on a block being encoded using either inter prediction unit 206 or intra prediction unit 208. Inter prediction unit 206 may perform inter prediction by searching for a block similar to the block being encoded in another, reconstructed picture (e.g., a reference picture) of video sequence 202. A reconstructed picture refers to a picture that was encoded and then decoded. The block determined during the search (e.g., referred to as a prediction block) may then be used to predict the block being encoded to remove redundant information. Inter prediction unit 206 may exploit temporal redundancy or similarities in scene content from picture to picture in video sequence 202 to determine the prediction block. For example, scene content between pictures of video sequence 202 may be similar except for differences due to motion and / or affine transformation of the screen content over time.

[0073] 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.

[0074] 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.

[0075] Transform and quantization unit (TR + Q) 214 may transform and quantize the prediction error. Transform and quantization unit 214 may transform the prediction error into transform coefficients by applying, for example, a DCT to reduce correlated information in the prediction error. Transform and quantization unit 214 may quantize the coefficients by mapping data of the transform coefficients to a predefined set of representative values. Transform and quantization unit 214 may quantize the coefficients to reduce irrelevant information in bitstream 204. The irrelevant information refers to information that may be removed from the coefficients without producing visible and / or perceptible distortion in video sequence 202 after decoding (e.g., at a receiving device).

[0076] 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.

[0077] Inverse transform and quantization unit (iTR + iQ) 216 may inverse quantize and inverse transform the quantized transform coefficients to determine a reconstructed prediction error. Combiner 212 may combine the reconstructed prediction error with the prediction block to form a reconstructed block. Filter(s) 220 may filter the reconstructed block, for example, using a deblocking filter and / or a sample -adaptive offset (SAG) filter. Buffer 222 may store the reconstructed block for prediction of one or more other blocks in the same and / or different picture of video sequence 202.

[0078] Encoder 200 may further comprise an encoder control unit. The encoder control unit may be configured to control one or more units of encoder 200 as shown in FIG. 2. The encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other video cording protocol. For example, the encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AVI, and / or any other video coding standard / format. The encoder control unit may be configured to attempt to minimize (or reduce) the bitrate of bitstream 204 and / or maximize (or increase) the reconstructed video quality (e.g., within the constraints of a proprietary coding protocol, industry video coding standard, and / or any other video cording protocol). For example, the encoder control unit may be configured to attempt to minimize or reduce the bitrate of bitstream 204 such that the reconstructed video quality does not fall below a certain level / threshold, and / or to maximize or increase the reconstructed video quality such that the bitrate of bitstream 204 does not exceed a certain level / threshold. The encoder control unit may determine / control one or more of: partitioning of the pictures of video sequence 202 into blocks, whether a block is inter predicted by inter prediction unit 206 or intra predicted by intra prediction unit 208, a motion vector for inter prediction of a block, an intra prediction mode among a plurality of intra prediction modes for intra prediction of a block, filtering performed by filter(s) 220, and / or one or more transform types and / or quantization parameters applied by transform and quantization unit 214. The encoder control unit may determine / control one or more of the above based on a rate-distortion measure for a block or picture being encoded. The encoder control unit may determine / control one or more of the above to reduce the ratedistortion measure for a block or picture being encoded.

[0079] 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 contextbased 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.

[0080] 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).

[0081] 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. Decoder 300 may comprise a decoder control unit configured to control one or more units of decoder 300. The decoder control unit may control the one or more units of decoder 300 such that bitstream 302 is decoded in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other communication protocol. For example, the decoder control unit may control the one or more units of decoder 300 such that the bitstream 302 is decoded in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AVI, 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 (SAG) filter. Buffer 314 may store the decoded block for prediction of one or more other blocks in the same and / or different picture of the video sequence in bitstream 302. Decoded video sequence 304 may be output from filter(s) 312 as shown in FIG. 3.

[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. 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.

[0086] A picture (e.g., in HEVC, or any other coding standard / format) may be partitioned into non-overlapping square blocks, which may be referred to as coding tree blocks (CTBs). The CTBs may comprise samples of a sample array. A CTB may have a size of 2nx2n samples, where n may be specified by a parameter of the encoding system. For example, n may be 4, 5, 6, or any other value. A CTB may have any other size. A CTB may be further partitioned by a recursive quadtree partitioning into coding blocks (CBs) of half vertical and half horizontal size. The CTB may form the root of the quadtree. A CB that is not split further as part of the recursive quadtree partitioning may be referred to as a leaf CB of the quadtree, and otherwise may be referred to as a non-leaf CB of the quadtree. A CB may have a minimum size specified by a parameter of the encoding system. For example, a CB may have a minimum size of 4x4, 8x8, 16x16, 32x32, 64x64 samples, or any other minimum size. A CB may be further partitioned into one or more prediction blocks (PBs) for performing inter and / or intra prediction. A PB may be a rectangular block of samples on which the same prediction type / mode may be applied. A CB may also be further partitioned into intra sub-partitions (ISP) where the reconstructed samples of each sub-partition are available to generate the prediction of the next sub-partition. For example, a CB may be split into 2 to 4 sub-partitions. For transformations, a CB may be partitioned into one or more transform blocks (TBs). A TB may be a rectangular block of samples that may determine / indicate an applied transform size.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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 VVC) may be referred to as a combination of quadtree and multi-type tree partitioning (quadtree + multi-type tree partitioning) because of the addition of binary and / or ternary tree partitioning to quadtree partitioning.

[0091] 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.

[0092] 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.

[0093] 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 node 19 encoded / decoded last. Although not shown in FIGS. 7 and 8, it should be noted that each CB leaf node may comprise one or more PBs and / or TBs.

[0094] A coding standard / format (e.g., HEVC, VVC, or any other coding standard / format) may define various units (e.g., in addition to specifying various blocks (e.g., CTBs, CBs, PBs, TBs)). Blocks may comprise a rectangular area of samples in a sample array. Units may comprise the collocated blocks of samples from the different sample arrays (e.g., luma and chroma sample arrays) that form a picture as well as syntax elements and prediction data of the blocks. 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.

[0095] 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 AV 1 coding format.

[0096] In intra prediction, samples of a block to be encoded (e.g., also referred to as a current block) may be predicted from samples in a line of samples immediately adjacent to the current block. For example, the line of samples may include samples of the column immediately adjacent to the left-most column of the current block and samples of the row immediately adjacent to the top-most row of the current block. The samples from the immediately adjacent column and row may be jointly referred to as reference samples. Each sample of the current block may be predicted (e.g., in an intra prediction mode) by projecting the position of the sample in the current block in a given direction to a point along the reference samples. The sample may be predicted by interpolating between the two closest reference samples of the projection point if the projection does not fall directly on a reference sample. A prediction error (e.g., referred to as a residual) may be determined for the current block based on differences between the predicted sample values and the original sample values of the current block.

[0097] 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.

[0098] FIG. 9 shows an example set of reference samples 902 determined for intra prediction of a current block 904. Current block 904 may correspond to a block being encoded and / or decoded. Current block 904 may correspond to block 3 of partitioned CTB 700 as shown in FIG. 7. As described herein, the numeric labels 0-19 of the blocks of partitioned CTB 700 may correspond to the sequence order for encoding / decoding the blocks and may be used as such in the example of FIG. 9.

[0099] In some embodiments, reference samples 902 may include a line of samples immediately adjacent to current block 904 and include samples from a column and a row immediately adjacent to current block 904. For example, the line of samples may include reference samples to the left and / or above current block 904. In some embodiments, reference samples 902 may be obtained (or selected) from a reference line of multiple reference lines (MRL), which may include a line of samples adjacent to current block 904 and also a line of non-adjacent samples. The MRL may include reference lines identified by corresponding reference line indices that indicate an i-th line of samples adjacent to current block 904 such that the Q-th line indicates the reference line immediate adjacent (or closest) to current block 904 and a higher numbered i-th line indicates a line of samples further away from current block 904. An encoder may select a reference line from a set of MRL and signal an MLR index in the bitstream to indicate the selected reference line. For example, the encoder may signal a codeword encoding the MRL index. The decoder may decode the codeword to determine the MRL index that identifies a specific reference line used in intra prediction of current block 904.

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

[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, 2, and 8 may be available to construct reference samples 902 given that these blocks are encoded and reconstructed at an encoder and decoded at a decoder prior to coding of current block 904. The samples from neighboring blocks 0, 1, 2, and 8 may be available to construct reference samples 902, for example, if there are no other issues (e.g., as mentioned above) preventing the availability of the samples from the neighboring blocks 0, 1, 2, and 8. The portion of reference samples 902 from neighboring block 6 may not be available due to the sequence order for encoding / decoding (e.g., because the block 6 may not have already been encoded and reconstructed at the encoder and / or decoded at the decoder based on the sequence order for encoding / decoding).

[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] Samples of current block 904 may be intra predicted based on reference samples 902, for example, based on (e.g., after) determination and (optionally) filtering of reference samples 902. In some examples, a filtering scheme (e.g., a filtering algorithm) may be applied to reference samples 902 to improve prediction accuracy. The filtering scheme may be one of a plurality of filter types including at least: a smoothing filter (or reference sample smoothing filter) or an interpolation filter. In some examples, if reference samples of a given block are to be filtered, only one of the plurality of filter types is selected (e.g., activated) to be applied to the reference samples. For example, if the smoothing filter is selected (e.g., activated), the interpolation filter is not selected (e.g., disabled) or vice versa.

[0104] Many encoders / decoders may support a plurality of intra prediction modes in accordance with one or more video coding standards. For example, HEVC supports 35 intra prediction modes, including a planar mode, a direct current (DC) mode, and 33 angular modes. VVC supports 67 intra prediction modes, including a planar mode, a DC mode, and 65 angular modes. Planar and DC modes may be used to predict smooth and gradually changing regions of a picture. Angular modes may be used to predict directional structures in regions of a picture. Any quantity of intra prediction modes may be supported.

[0105] FIGS. 10A-C 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, from a reference line among a set of multiple reference lines (MRL) 908-910, in a two-dimensional x, y plane, where a sample may be referenced as p [x] [y] . To simplify the prediction process, reference samples 902 may be placed in two, one -dimensional arrays. The reference samples 902 belonging to a reference line I from the set of MRL 908-912, above the current block 904, may be placed in the one -dimensional array ref^x] refi[x] = p[—l + x] [— / ], (x > 0). (1)

[0108] The reference samples 902 belonging to reference line / , to the left of current block 904, may be placed in the one -dimensional array ref2[y] : ref2[y] = p[-!]H + y], (y > 0). (2)

[0109] The variable I represents how many lines away the selected reference line is from current block. For example, if reference line #0 908 is selected, then I is set to 1 to indicate the reference line adjacent to current block 904. For example, if reference line #1 910 is selected, then I is set to 2. For example, if reference line #2 912 is selected, then I is set to 3.

[0110] In some examples, if MRL is not activated or selected, then reference samples 902 may be from reference line #0 908 that is immediately adjacent to current block 904. In this example, the variable I in Equations (1) and (2) is set to 1. The prediction process may comprise determination of a predicted sample p[x] [y] (e.g., a predicted value) at a location [x] [y] in current block 904. For planar mode, a sample at the location [x] [y] in current block 904 may be predicted by determining / calculating the mean of two interpolated values. The first of the two interpolated values may be based on a horizontal linear interpolation at the location [x] [y] in current block 904. The second of the two interpolated values may be based on a vertical linear interpolation at location [x] [y] in current block 904. The predicted sample p [x] [y] in current block 904 may be determined / calculated as:

[0111] 1 p[ ][y] = - — (h[x] [y] + v[x] [y] + s), (3)

[0112] 2 ■ s where [x] [y] = (s — x — 1) ■ ref2[y] + (x + 1) ■ re / Js] (4) may be the horizonal linear interpolation at the location [x] [y] in current block 904 and v[x] [y] = (s - y - 1) - ref^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.

[0113] 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:

[0114] For angular modes, a sample at a location [x] [y] in current block 904 may be predicted by projecting the location [x] [y] in a direction specified by a given angular mode to a point on the horizontal or vertical line of samples comprising reference samples 902. The sample at the location [x] [y] may be predicted by interpolating between the two closest reference samples of the projection point if the projection does not fall directly on a reference sample. The direction specified by the angular mode may be given by an angle cp defined relative to the y-axis for vertical prediction modes (e.g., modes 19-34 in HEVC and modes 35-66 in VVC). The direction specified by the angular mode may be given by an angle cp defined relative to the x-axis for horizontal prediction modes (e.g., modes 2-18 in HEVC and modes 2- 34 in VVC).

[0115] FIG. 12 shows an example of applying an intra prediction mode (e.g., an angular mode such as vertical prediction mode 906) for prediction of a current block 904. FIG. 12 specifically shows prediction of a sample at a location [x] [y] in current block 904 for a vertical prediction mode 906. Vertical prediction mode 906 may be given by an angle cp with respect to the vertical axis. The location [x] [y] in current block 904, in vertical prediction modes, may be projected to a point (e.g., referred to as a projection point) on the horizontal line of reference samples ref [x] . The reference samples 902 are only partially shown in FIG. 12 and shown as being from a reference line with reference line index of 0 for ease of illustration. Reference samples 902 may be from another reference line of the set of MRL, as explained in FIG. 9. As shown in FIG. 12, the projection point on the horizontal line of reference samplesrefi M 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 - jf) ■ re / 1[x + it+ 1] + if■ re / 1[x + it+ 2], (7) it may be the integer part of the horizontal displacement of the projection point relative to the location [x] [y] . it 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 = ((y + 1) - tan <p) - L(y + 1) - tan <pj, (9) where [ ■ J is the integer floor function.

[0116] For horizontal prediction modes, a location [x][y] of a sample in current block 904 may be projected onto the vertical line of reference samples ref2[y] . A predicted sample p [x] [y]for horizontal prediction modes may be determined / calculated as: p[x] [y] = (1 - if) - ref2[y + it+ 1] + if■ ref2[y + it+ 2], (10) it 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: ij = [(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] . if may be determined / calculated as: if = ((x + 1) ■ tan <p) — [(x + 1) ■ tan <pj, (12) where [ ■ J is the integer floor function.

[0117] 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.

[0118] In some examples, the FIR fdters may be used for predicting chroma samples and / or luma samples. For example, the two-tap interpolation FIR fdter may be used for predicting chroma samples and a same and / or a different interpolation technique / fdter 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[z], i = 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:

[0119] Supplementary reference samples may be determined / constructed if the location [x] [y] of a sample in current block 904 to be predicted is projected to a negative x coordinate. The location [x] [y] of a sample may be projected to a negative x coordinate, for example, if negative vertical prediction angles cp are used. The supplementary reference samples may be determined / constructed by projecting the reference samples in ref2[y] in the vertical line of reference samples 902 to the horizontal line of reference samples 902 using the negative vertical prediction angle cp. Supplementary reference samples may be similarly determined / constructed, for example, if the location [x] [y] of a sample in current block 904 to be predicted is projected to a negative y coordinate. The location [x] [y] of a sample may be projected to a negative y coordinate, for example, if negative horizontal prediction angles cp are used. The supplementary reference samples may be determined / constructed by projecting the reference samples inrefiMonthe horizontal line of reference samples 902 to the vertical line of reference samples 902 using the negative horizontal prediction angle cp.

[0120] 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 VVC and / or including extended intra prediction modes from WAIP for rectangular blocks. The encoder may determine, for each intra prediction mode applied, a corresponding prediction error for the current block based on a difference (e.g., sum of squared differences (SSD), sum of absolute differences (SAD), or sum of absolute transformed differences (SATD)) between the prediction samples, generated from reference samples 902 of a reference line (e.g., from a set of MRL), determined for the intra prediction mode and the original samples of the current block. The encoder may determine / select one of the intra prediction modes to encode the current block based on the determined prediction errors. For example, the encoder may determine / select one of the intra prediction modes that results in the smallest prediction error for the current block. In some examples, the encoder may determine / select the intra prediction mode and the associated reference line to encode the current block based on a rate-distortion measure (e.g., Lagrangian rate-distortion cost) determined using the prediction errors. The encoder may signal, in the bitstream to a decoder for decoding of the current block, an indication of the determined / selected intra prediction mode and an indication of the associated MRL index (which may indicate a reference line index). The encoder may also signal in the bitstream to the decoder a corresponding prediction error (e.g., residual) of the intra prediction mode.

[0121] A decoder may determine / predict samples of a current block being decoded (e.g., current block 904) for an intra prediction mode. For example, a decoder may receive an indication of a reference line (e.g., a reference line index or an MRL index associated with the reference line index) and an intra prediction mode (e.g., an angular intra prediction mode) from an encoder for a current block. The decoder may retrieve a set of reference samples and perform intra prediction based on the MRL index and the intra prediction mode indicated by the encoder for the current block in a similar manner (e.g., as described above for the encoder). For example, the decoder may obtain the reference samples from a reference line indicated / identified by the decoded MRL index. In some examples, when MRL is not enabled / activated / selected, the reference line has reference line index 0 and is immediately adjacent to the current block. In these examples, no indication of MRL index is signaled.

[0122] The decoder may add predicted values of the samples (e.g., determined based on the intra prediction mode) of the current block to a residual of the current block to reconstruct the current block. In some examples, a decoder need not receive an indication of an angular intra prediction mode from an encoder for a current block. Instead, the decoder may determine an intra prediction mode through other decoder-side means (e.g., by applying template-based intra mode derivation (TIMD) tool / technique). While various examples herein correspond to intra prediction modes in HEVC and VVC, 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, AVI, etc.).

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] One or more reference pictures may be searched by the encoder during inter prediction to determine and / or generate the best matching reference block. The reference pictures searched by the encoder may be included in (e.g., added to) one or more reference picture lists. For example, in HEVC and VVC (and / or in one or more other communication protocols), two reference picture lists may be used (e.g., a reference picture list 0 and a reference picture list 1). A reference picture list may include one or more pictures. The reference picture 1306 of reference block 1304 may be indicated by a reference index pointing into a reference picture list comprising reference picture 1306.

[0128] FIG. 13B shows an example motion vector. A displacement between reference block 1304 and current block 1300 may be interpreted as an estimate of the motion between reference block 1304 and current block 1300 across their respective pictures. The displacement may be represented by a motion vector 1312. For example, motion vector 1312 may be indicated by a horizontal component (MVx) and a vertical component (MVy) relative to the position of current block 1300. A motion vector (e.g., motion vector 1312) may have fractional or integer resolution. A motion vector with fractional resolution may point between two samples in a reference picture to provide a better estimation of the motion of current block 1300. For example, a motion vector may have 1 / 2, 1 / 4, 1 / 8, 1 / 16, 1 / 32, or any other fractional sample resolution. Interpolation between the two samples at integer positions may be used to generate a reference block and its corresponding samples at fractional positions, for example, if a motion vector points to a non-integer sample value in the reference picture. The interpolation may be performed by a fdter with two or more taps.

[0129] The encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between reference block 1304 and current block 1300. The encoder may determine the difference between reference block 1304 and current block 1300, for example, based on / after reference block 1304 is determined and / or generated, using inter prediction, for current block 1300. The difference may be a prediction error (e.g., a residual). The encoder may store and / or send (e.g., signal), in / via a bitstream, the prediction error and / or related motion information. The prediction error and / or the related motion information may be used for decoding (e.g., decoding current block 1300) and / or other forms of consumption. The motion information may comprise the motion vector 1312 and a reference indicator / index. The reference indicator may indicate the reference picture 1306 in a reference picture list. In other examples, the motion information may comprise an indication of motion vector 1312 and / or an indication of the reference indicator / index. The reference indicator may indicate reference picture 1306 in the reference picture list comprising reference picture 1306. A decoder may decode current block 1300 by determining and / or generating the reference block 1304, which may correspond to / form (e.g., be considered as) a prediction of the current block 1300. The decoder may determine and / or generate the reference block 1304, for example, based on the related motion information. The decoder may decode current block 1300 based on combining the prediction (e.g., a reference block) with the prediction error (e.g., a residual block).

[0130] Inter prediction, as shown in FIG. 13 A, 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.

[0131] 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.

[0132] 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 uniprediction 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.

[0133] 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 (e.g. takes a reference block from an indicated one of pictures stored in list 0). Reference block 1404 may be in a reference picture of another one of reference picture list 0 or reference picture list 1 (e.g. the prediction from the future is done by using a reference block in some picture stored in reference picture list 1, such as the picture for display immediately after the currently being decoded picture at picture order count or presentation time poc+1 (which picture due to reordering of the decoding may have already been decoded prior to the picture for poc)). 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. Modem advanced video compression systems allow the optimal specification of all such prediction aspects, e.g. which pictures should be maintained in the lists for later predictions etc. 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 bi-prediction may correspond to (e.g., be comprised in) a same reference picture. The reference picture may be included in both the reference picture list 0 and the reference picture list 1, for example, if the two reference blocks correspond to the same reference picture.

[0134] 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, or in another data segment. Different weight and / or offset parameters may be sent / signaled for luma and / or chroma components.

[0135] 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 predictions from reference blocks 1402 and 1404. A weighted combination of the pixel lumas of the two blocks (motion-shifted to the currently being predicted block position) may serve as a good predictor of the block, if those reference blocks correspond to a part of an object which has moved to another position overtime, but, there may e.g. be specular illumination differences which cannot easily be predicted by a two-dimensional block shift model, but can be coded as a residual or error of the prediction, which would involve less bits if the prediction is already mostly correct. 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.

[0136] 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 (e.g. the third picture of list 0, which may e.g. maintain for prediction purposes the previous image, the pre-previous image, and some image from long time ago for predicting blocks of a static background, and it may be indicated that the current block is best predicted using a block of that static background).

[0137] 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. 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.

[0138] Since a direct coding of all the required motion vectors as two motion components may involve an unnecessary large amount of bits in the bitstream, motion information may be predictively coded, for example, before being stored and / or sent / signaled in / via a bit stream (e.g., in HEVC, VVC, and / or other video coding standards / formats / protocols). The motion information for a current block may be predictively coded based on motion information of one or more blocks neighboring the current block. If e.g. several blocks lie in a large object that undergoes substantially a two-dimensional (planar) repositioning, the motion vector of the neighboring block horizontally adjacent may be an accurate (perhaps even perfect) predictor for the motion vector of the current block, as both blocks may be undergoing the same motion at the current time of the video. 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).

[0139] 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 (collocated means the same block position, but in a previous picture). E.g., although there may be motion going on around the current block, if the object is larger than the motion-produced displacement, then the block of the same / co-located position in a previous object may still be inside the object, and although being a different part of the object, still undergo that same motion. Hence, using the motion vector previously established for that colocated block in e.g. the image previously decoded for poc-1 may yield the perfect motion vector for the currently being decoded block, i.e. for searching motion-displaced reference blocks for the current block in any reference image. In any case, even if not entirely correct, such candidate motion vectors may form good predictors, i.e. will in general be good candidates in a list of prediction motion vectors from which to select the best one for doing the actual prediction and coding the actual motion vector difference (i.e. the error of the prediction in one or more of the two motion vector components) The encoder and / or a decoder may reciprocally generate and / or determine the list of candidate MVPs, i.e. the will maintain the same list, so the encoder can easily indicate to the decoder which motion vector to select for the prediction of the actual motion vector of the current block.

[0140] 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 (e.g. number three of the maintained list) and / or a motion vector difference (MVD). The encoder may indicate the selected MVP in the bitstream using an index / indicator. The index may indicate the selected MVP in the list of candidate MVPs. The MVD may be determined / calculated based on a difference between the motion vector of the current block and the selected MVP. For example, for a motion vector (e.g., comprising a horizontal component (MVx) and a vertical component (MVy)) that indicates a position relative to a position of the current block being coded, the MVD may be represented by two components MVDXand MVDy. MVDXand MVDymay be determined / calculated as:

[0141] MVDX= MVX- MVPX, (15)

[0142] MVDy= MVy- MVPy (16)

[0143] 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.

[0144] A decoder (e.g., decoder 300 as shown in FIG. 3) may decode the motion vector by adding the MVD (communicated in the bitstream as MVDx and MVDy) 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.

[0145] The list of candidate MVPs (e.g., in HEVC, VVC, and / or one or more other communication protocols), for AMVP, may comprise typically two (or more) candidates (e.g., candidates A and B). Candidates A and B may comprise e.g.: up to two (or any other quantity of) spatial candidate MVPs determined / derived e.g. typically from five (or any other quantity of) spatial neighboring blocks of a current block being coded; one (or any other quantity of) temporal candidate MVP determined / derived from two (or any other quantity of) temporal, co-located blocks (e.g., if both of the two spatial candidate MVPs are not available or are identical); and / or zero motion vector candidate MVPs (e.g., if one or both of the spatial candidate MVPs or temporal candidate MVPs are not available). Other quantities of spatial candidate MVPs, spatial neighboring blocks, temporal candidate MVPs, and / or temporal, co-located blocks may be used for the list of candidate MVPs.

[0146] 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. A typical AMVP would use the 5 candidates as indicated, since they have a strong likelihood of being good predictor candidates. But in actuality some may be better predictors than others, e.g. if there is a boundary of the object at the top, and the B candidates are located in another object (e.g. the background) which may undergo different motion, whereas the A candidates lie in the same object, so well-predicting candidates can be selected from such candidates that could potentially be good predictors motion vectors. The five spatial candidate neighboring blocks may be AO, Al, BO, Bl, 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 Cl. 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 (e.g. poc-2).

[0147] 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, Al, B0, Bl, 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 Cl) for inter prediction of a current block. An MVD need not be sent (e.g., indicated, signaled) for the current block because the same motion information as that of a neighboring block or a temporal, co-located block may be used for the current block (e.g., at the encoder and / or a decoder). A signaling overhead for sending / signaling the motion information of the current block may be reduced because the MVD need not be indicated for the current block. The encoder and / or the decoder may reciprocally generate a candidate list of motion information from neighboring blocks or temporal, colocated blocks of the current block (e.g., in a manner similar to AMVP). The encoder may determine to use (e.g., inherit) motion information, of one neighboring block or one temporal, co-located block in the candidate list, for predicting motion information of the current block being coded. The encoder may signal / send, in / via a bitstream, an indication of the determined motion information from the candidate list. For example, the encoder may signal / send an indicator / index. The index may indicate the determined motion information in the list of candidate motion information. The encoder may signal / send the index to indicate the determined motion information.

[0148] A list of candidate motion information for merge mode (e.g., in HEVC, VVC, or any other coding formats / standards / protocols) may comprise: up to four (or any other quantity of) spatial merge candidates derived / determined from five (or any other quantity of) spatial neighboring blocks (e.g., as shown in FIG. 15 A); 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.

[0149] Inter prediction may be performed in other ways and variants than those described herein. For example, motion information prediction techniques other than AMVP and merge mode may be used. While various examples herein correspond to inter prediction modes, such as used in HEVC and 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, AVI, etc.). Historybased motion vector prediction (HMVP), combined intra / inter prediction mode (CIIP), and / or merge mode with motion vector difference (MMVD) (e.g., as described in VVC) may be performed / used and are within the scope of the present disclosure.

[0150] 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). The encoder determined the best matching block (by comparing the coding quality and cost for all of them), and sent the best coded situation to the encoder, and the encoder merely had to determine which block to take from which reference image using which motion-determined block displacement as indicated by the motion data in the received bitstream.

[0151] 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.

[0152] 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 comer (or any other point / sample) of the reference block. The BV may indicate a relative displacement from the current block to the reference block that best matches the current block. The encoder may determine the best matching reference block from blocks tested during a searching process (e.g., in a manner similar to that used for inter prediction). The encoder may determine that a reference block is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a rate-distortion criterion (e.g., Lagrangian ratedistortion cost). The one or more cost criteria may be based on, for example, one or more differences (e.g., an SSD (sum of squared differences), an SAD (sum of absolute differences), an SATD (sum of transformed differences), 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).

[0153] FIG. 16 shows an example of IBC (e.g., an IBC mode). The example shown in FIG. 16 may correspond to screen content. The rectangular portions / sections with arrows beginning at their boundaries may be the current blocks being encoded. The rectangular portions / sections that the arrows point to may be the reference blocks for predicting the respective current blocks.

[0154] 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).

[0155] A BV may be predictively coded (e.g., in HEVC, VVC, 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).

[0156] An encoder (e.g., encoder 200 as shown in FIG. 2) performing BV prediction and coding may code a BV as a difference between the BV of a current block being coded and a block vector predictor (BVP). An encoder may select / determine the BVP from a list of candidate BVPs. The candidate BVPs may comprise / correspond to previously decoded BVs of neighboring blocks in the current picture of the current block. The encoder and / or a decoder may reciprocally generate or determine the list of candidate BVPs.

[0157] The encoder may send / signal, in / via a bitstream, an indication of the selected BVP and a block vector difference (BVD). The encoder may indicate the selected BVP in the bitstream using an index / indicator. The index may indicate (e.g., point to) the selected BVP in the list of candidate BVPs. The BVD may be determined / calculated based on a difference between a BV of the current block and the selected BVP. For example, for a BV (e.g., represented by a horizontal component (BVx) and a vertical component (BVy)) that indicates a position relative to a position of the current block being coded, the BVD may be represented by two components BVDXand BVDy. BVDXand BVDymay be determined / calculated as:

[0158] BVDX= BVX— BVPX, (17)

[0159] BVDy = BVy - BVPy. (18)

[0160] 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 / viathe 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).

[0161] 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.

[0162] A list of candidate BVPs (e.g., in HEVC, VVC, and / or any other coding standard / format / protocol) may comprise two (or more) candidates. The candidates may comprise candidates A and B. Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate BVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being encoded; and / or one or more of last two (or any other quantity of) coded BVs (e.g., if spatial neighboring candidates are not available). Spatial neighboring candidates may not be available, for example, if neighboring blocks are encoded using intra prediction or inter prediction. Locations of the spatial candidate neighboring blocks, relative to a current block, being encoded using IBC 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, Al, BO, Bl, and B2 as shown in FIG. 15 A.

[0163] The most probable mode (MPM) refers to the intra prediction mode (IPM) that is most likely to be the best mode for the current block being encoded or decoded. In current intra prediction techniques, the MPM is determined by analyzing the intra prediction modes of the neighboring CUs (e.g., also referred to as blocks) of a current block (or CU) to be coded (e.g., encoded or decoded). For example, VVC uses a list of 6 MPMs (referred to as the “MPM list”) for luma intra prediction. The MPM list is derived from the intra prediction modes of the neighboring CUs, and is updated as the encoder progresses through the video frame. When encoding a block, the encoder may determine if the current block is a candidate for any of the MPMs in the MPM list. If it is, the encoder then compares the prediction errors of the respective MPMs to determine which MPM from the MPM list is the best mode for the current block. If the current block is not a candidate for any of the MPMs in the MPM list, the encoder may then evaluate all intra prediction modes (e.g., 67 in VVC) to determine the best mode for the current block.

[0164] The use of MPMs can significantly improve the coding efficiency because the encoder does not need to signal the intra prediction mode for the current block if it is one of the MPMs. Instead, the decoder can infer the intra prediction mode for the current block from the corresponding MPM list reciprocally and identically generated at the decoder. Thus, signaling overhead in the bitstream may be reduced.

[0165] In some examples, three types of intra modes are considered to construct the MPM list: default intra modes; neighboring intra modes; and there may be derived intra modes. A unified 6 MPM list is used for intra blocks irrespective of whether Multiple Reference Lines (MRL) and Intra SubPartitions (ISP) coding tools are applied. The MPM list for the current block is constructed based on intra modes of the left neighbor block (e.g., block corresponding to Al in FIG. 15A) and the above neighbor block (e.g., block corresponding to Bl in FIG. 15A) of the current block. Suppose the mode of the left neighbor block is denoted as Left and the mode of the above neighbor block is denoted as Above, the unified MPM list may be constructed as follows: when a neighboring block is not available, its intra mode is set to planar mode by default; if both modes Left and Above are non-angular modes, then the MPM list is set to include {planar, DC, V, H, V - 4, V + 4}, where “V” and “H” refer to vertical mode and horizontal mode, respectively; if one of modes Left and Above is an angular mode, and the other is non- angular, set a mode Max as the larger mode in Left and Above, and set MPM list to include {planar, Max, Max - 1, Max + 1, Max — 2, Max + 2}; if Left and Above are both angular and they are different, set a mode Max and a mode Min as the larger mode in Left and Above and as the smaller mode in Left and Above, respectively, and thereafter, if Max - Min is equal to 1, then set MPM list to include {planar, Left, Above, Min - 1, Max + 1, Min - 2}, if Max - Min is greater than or equal to 62, then set MPM list to include {planar, Left, Above, Min + 1, Max - 1, Min + 2}, if Max - Min is equal to 2, set MPM list to include {planar, Left, Above, Min + 1, Min - 1, Max + 1}, or otherwise, set MPM list to include {planar, Left, Above, Min - 1, -Min + 1, Max - I}; and if Left and Above are both angular and they are the same, set MPM list to include {planar, Left, Left - 1, Left + 1, Left - 2, Left + 2} .

[0166] The encoder may encode an MPM index in the bitstream to indicate the position of the selected intra prediction mode in the MPM list to the decoder. The encoder may represent the MPM index as a codeword and entropy encode the codeword into the bitstream. The decoder may derive the MPM list in a manner identical to the encoder, and use the MPM index obtained from the codeword decoded from bitstream to obtain the intra prediction mode from the MPM list derived at the decoder. In some instances, the first bin of codeword, representing the MPM index, is context coded using an arithmetic coder (e.g., CABAC) so as to achieve additional coding efficiencies. For example, three contexts may be used, corresponding to whether the current intra block is MRL enabled, ISP enabled, or a normal intra block.

[0167] During the 6 MPM list generation process, pruning may be used to remove duplicated intra modes so that the MPM list includes only unique intra modes. For entropy coding of the 61 non- MPM modes (that is, the 67 modes in VVC minus the 6 MPM), a truncated binary code (TBC) may be used.

[0168] In some implementations, the MPM list is extended to include 16 additional candidates, and is divided into two parts, the primary MPM (PMPM) (e.g., including 6 entries) and the secondary (SMPM) (e.g., including 16 entries). In some implementations, the first entry in the general MPM list is the planar mode. The remaining entries include the intra modes of the adjacent neighboring blocks corresponding to positions left (L), above (A), below-left (BL), above-right (AR), and above-left (AL) (e.g., shown in FIG.15A as Al, Bl, AO, BO, and B2), and decoder-side intra mode derivation (DIMD) modes which are sorted in ascending order of a cost such as, for example, SAD, SSD, SATD, etc. In some examples, up to a preconfigured / predetermined number of modes (e.g., 5) with the smallest costs are added to the MPM list. The cost for a respective MPM (e.g., an IPM corresponding to an entry in the MPM list) may be computed between the prediction of the reconstructed samples of the template of the current block and the reconstructed samples. For example, the prediction may be generated by applying the respective MPM for the template. Sorted directional modes are added into the general MPM list, and then the default modes, until the general MPM list with 22 entries is constructed. In some examples, if a CU block is vertically oriented, the order of neighboring blocks corresponds to A, L, BL, AR, AL; otherwise, it is L, A, AL, AR, BL.

[0169] Intra-template matching prediction (IntraTMP) is a special intra-prediction mode that selects a prediction block within a pre -determined reference region (RR) or search area from the reconstructed samples within the current frame. IntraTMP uses a pre-defined template of the current block to search for a candidate reference block of which the template best matches the template of the current block. FIG. 17 illustrates, for an example current block 1700, a reference region 1712 or search area from the reconstructed samples 1704 within which a search is performed for a candidate reference block 1706 of which the template 1708 (“candidate reference block template”) best matches the template 1702 (“current block template”) of the current block 17OO.In this example the reference region is divided in four rectangular reference regions (Rl, R2, R3, and R4).

[0170] By computing a cost function (e.g., SAD, SATD), by the decoder (and the encoder emulating the decoder), between the template 1702 of the current block and the templates of several candidate reference blocks, N candidates with lower template costs, each indicated by a corresponding block vector predictor (BVP) candidate 1710 (BVP candidate may also be referred to herein as block vector (BV) candidate), are stored in an intraTMP list and ranked by lower cost value (ascending cost). This process is performed by both encoder and decoder, so they maintain the same situation-based data. Limiting to e.g. 4 coding tree units (CTUs) limits the amount of computation that needs to be done in decoders.

[0171] The residual blocks obtained as the difference between the samples of the current block 1700 (i.e. the encoder now verifying which one of the template-based determined candidates does actually the best prediction of the currently to be decoded pixel lumas) and the candidate's reference blocks 1706 in the list are computed, and the reference block with the better rate-distortion performance is selected as the best intraTMP reference block. An index indicating the position of the best BVP or BV candidate within the intraTMP list is signaled to the decoder in order to facilitate the block decoding using the IntraTMP prediction mode.

[0172] Due to the reference region having an irregular (non-rectangular) shape and to facilitate its hardware implementation, the template matching in the reference region 1712 is carried out in a set of rectangular sub-regions (R1 to R4 in the example of FIG. 17), whose dimensions are determined based on the current blocks' size and relative position inside the current CTU.

[0173] The global reference region 1712 dimensions comprising all sub-regions are determined by the SearchRange w and SearchRange _h parameters, which are set proportional to the current block 1700 dimension (CbWidth, CbHeight) using a multifactor parameter denoted as 'a', which controls the gain / complexity trade-off. In some implementations of IntraTMP, the multifactor parameter 'a' may be uniform and equal to 5 or may be determined by of the current block dimension.

[0174] SearchRange w = a * CbWidth

[0175] SearchRange _h = a * CbHeight

[0176] In some implementations of IntraTMP, the global RR for block dimensions 4 and 8 were extended to 64 pixels, according to the following equations:

[0177] SearchRange w = max (64, 5* CbWidth) SearchRange _h = max (64, 5* CbHeight)

[0178] In practice, this has the effect of using a variable multifactor parameter 'a' based on the block dimensions, as shown in the following table:

[0179] FIG. 18 illustrates a current block 1800 in a current CTU 1804, and the reference region

[0180] 1812 with example corresponding TMP search regions R1-R6 identified. An example reference block 1816, and reference block template 1818 and current block template 1808 are also illustrated.

[0181] In order to reduce the high computational burden of the exhaustive template matching searching in the whole RR, the searching process is split into 2 steps: a sparse search step, and a refinement search step. The sparse search is illustrated in FIG. 19A. The sparse search in some implementations is carried out in a regular grid using a subsampling interval (e.g., 4 pixels or 3 pixels) in the horizontal and vertical directions. FIG. 19A shows an example candidate reference block 1916 in search region 4 (R4) and the corresponding reference template 1918. The template cost is computed for each reference block position within a search region (e.g., reference block position 1920 of reference block 1916), and the BVP candidates associated with the best (e.g., least cost) reference blocks are recorded in a sparse list and sorted in an ascending order based on the cost. The subsample positions are shown in the form of dark squares within the RR region, separately determined for each search region. In some implementations of IntraTMP, the size of the sparse list is set to 30. In general, the sparse candidates are a limited set of candidates, which are good candidates based on a similarity of pixels in their template versus the pixels in the template of the currently to be decoded block, the limitation being in the sense that not all pixel positions in an already decoded vicinity of the current block have been checked for adding to the sparse candidates list, because typically candidates are tested on a sub-sampled pixel grid with a subsampling factor e.g. 4x.

[0182] The refinement search, the second step, is a refinement of the reference block candidates (correspondingly, BVP candidates) in the sparse list. In some implementations, the refinement is made in a window of a predetermined size (e.g., 5x5 pixels or 3x3 pixels) around the respective sparse BVP candidates using a sampling interval of 1. In other words, in addition to the sparse BVP, one or more additional BVP candidates can be generated within the refinement search window at the integer pixel positions. If the refinement window crosses into another search region, the refinement window is clipped to the region boundary to which the candidate belongs. FIG. 19B illustrates a current block 1906 and template 1908 located in a current CTU 1904 of a current frame 1900 (i.e., current picture), corresponding RR with respective search regions R1-R6, and an example BVP 1910 with its refinement search window 1912 being clipped where R5 (search region in which the BVP 1910 is located) borders R2 and R3. The 19 candidates with the lowest template costs (e.g., SAD costs) among the generated additional candidates and the sparse BVP candidates are selected to generate a “refined IntraTMP list.” Once the encoder / decoder has constructed the refined IntraTMP list, the encoder / decoder can select among different intraTMP sub-modes by checking the rate-distortion performance of each submode (the wording mode of intra-prediction means here a different manner or method of prediction, e.g. IntraTMP is a different mode than directional prediction which continues the value of an adjacent pixel as luma predictor along a line through the currently predicted block; sub-modes are variants of the mode, which vary according to some detail; sometimes mode can also point to a single predictor, e.g. along a certain angle). The IntraTMP sub-mode is signaled to the decoder in combination with an index to the best candidate in the refined IntraTMP list or a cluster of candidates (e.g. the fusion mode). The IntraTMP sub-modes may be the single predictor sub-mode, the fusion sub-mode, the sub-pel precision sub-mode, and the linear filter mode sub-mode. In the single predictor sub-mode, a single BVP candidate is selected from the refined IntraTMP list and signaled to the decoder. In the fusion sub-mode, multiple BVP candidates are blended to derive the final BV prediction block (like bidirectional inter-prediction). The blending weights may be either computed from the template matching cost of each predictor or with a Wiener-filter-based weight derivation method. In the sub-pel precision sub-mode, when a single predictor is used, sub-pel precision can be used with 1 / 2 -pel precision, 1 / 4-pel precision, and 3 / 4-pel precision, each with 8 possible directions. In the linear filter model sub-mode, a linear filter can be learned between the reference and current templates and applied to the reference block. This mode can be used for a single predictor when sub-pel precision is not used and a single predictor is used.

[0183] In some implementations of IntraTMP, several types of template shapes may be used. Five types of templates have been proposed according to the current block location in the frame: top template, left template, L-shape template, an only top template type, and an only left template type.

[0184] The template type of top template may be used when only the current block’s top samples are available, such as when the current block is located to the left boundary of the picture. Consequently, the TMP cost is computed using the top samples of the current and reference blocks. In some implementations, the top template is four samples in height.

[0185] The template type of left-template may be used when only the left samples of the current block are available, such as when the current block is located at the top boundary of the picture. Consequently, the TMP cost is computed using exclusively the left samples of both the current and the reference block. In some implementations, the left template is four samples in width.

[0186] The L-shape template type is used in the other cases (e.g., the current block is not located at the top or left boundary of the picture) where the samples surrounding the current block included in the L-Shape are available. Consequently, the TMP cost is computed using the L-shape template of both the current and the reference block. In some implementations, the L-shape template is four samples in width and height.

[0187] The L-shape template introduces two more template types: the Only-Top (Only-T) and Only-Left (Only-L) templates. Therefore, in addition to the L-shape TMP cost, the TMP cost for the Only-T and Only-L templates are also computed, and the best N BV candidates are stored in different Only-T and Only-L lists.

[0188] FIG. 20 depicts an example of the top-template type. Only the top templates (e.g., template 2001 of current block and template 2000 of reference block 1816) are used for the TMP cost computation in 2003. The sparse search 2003 is computed using a sampling interval (SI) 2002 of three, and one Sparse List (sparse candidates list) 2004 is built using the best (lower cost) 30 BV candidates in some implementations. Those candidates are refined in 2006 using a 3x3 window 2005 with an SI of 1, and a Refined Candidates List 2007 is built.

[0189] For the left-template type, the same top-template type logic is applied, but the left templates (2100 and 2101) of reference and current blocks are used instead of the top templates illustrated in FIG. 21. The TMP cost calculation in search regions 2103, search intervals for sparse search 2102, sparse candidates list 2104, refinement of the sparse list 2116, refinement search windows 2105, and the refined candidates list 2107 of the Only-L process shown in FIG. 21 may be identical (except for the use of Only-L template instead of Only-T template) to 2003, 2002, 2004, 2006, 2005, and 2007, respectively, described in relation to FIG. 20.

[0190] FIG. 22 depicts an example of a current block that has available (e.g., reconstructed samples are available for) the L-shape template 2201, and the L-shape template 2200 of the reference block is used to compute the L-shape TMP cost in all search regions, as it was described for the toptemplate and left-template type.

[0191] In addition to the L-shape cost, the Only-Top TMP and Only-Left TMP costs may also be computed. In some implementations, the sparse search builds three sparse lists, one sparse L-shape list with a size of 30 BV candidates, and two additional lists, the Only-T sparse list and Only-L sparse list, both with a length of 6 BV candidates.

[0192] These three sparse lists are refined by computing the respective template type cost using a window of 3x3 in some implementations. The best N BV candidates, which have obtained the lower TMP costs, are stored in three new refined lists: the refined L-shape list with a size of 19 BV candidates, the refined Only-T list with a length of 3 BV candidates and refined Only-L list with a size of 3 BV candidates. In some implementations, the final IntraTMP List has 19 candidates as the L-Shape List, but it is a combination of the BVs candidates in the L-Shape List, and the Refined Only-T and Only-L Lists. In addition to the sparse BVP candidates obtained by TMP searching within the RR in IntraTMP, a set of merge BVP candidates may be generated using another technique called “IntraTMP with merge candidates.” In some implementations, merge BVP candidates are a subset of the IBC (intra block copy) merge candidates, including only the spatial candidates of the current block, (merge candidates are (reused) vectors used in blocks in an already decoded vicinity, typically according to some geometric selection scheme which is pre-fixed for encoder and decoder) In particular, the TMP merge BVP candidates may use the 5 adjacent BVs from the adjacent blocks (e.g., 2300 in FIG. 23A) and multiple (e.g., 20) non-adjacent BV candidates (e.g., 2301 in FIG. 23B) from the non-adjacent neighboring blocks encoded using an IBC or TMP mode.

[0193] An example of the IntraTMP with merge candidates process is illustrated in FIG. 24. In this example, a maximum of 50 BVP candidates including BVP candidates 2405 from the adjacent blocks and BVP candidates 2406 from non-adjacent blocks are reordered and pruned in block 2407 to remove duplicate BVP candidates. In some examples, the BVP candidates are ranked in an ascending order based on the associated TMP costs, and the best 10 candidates (candidates with the lowest TMP costs) are selected to generate the TMP merge list 2408. The TMP merge list 2408 can be ordered ascendingly according to the TMP costs of the BVP candidates. The BVP candidates in the TMP merge list 2408 may also be referred to as “merge BVP candidates.” In addition, a sparse list 2404 is generated at block 2403 for the current block, as described above in relation to IntraTMP. For example, the sparse list 2404 can be generated by calculating TMP costs for reference templates (e.g., L-shape reference templates) 2400 and the current block’s template 2401 in search regions using a predetermined sampling interval 2402. In some implementations, up to 10 merge BVP candidates in the TMP merge list 2408 are checked in the sparse list 2404 for duplicates, and the redundant BVPs in the TMP merge list 2408 are removed in block 2409 to generate the updated TMP merge list 2410.

[0194] Thereafter, the merge BVP candidates from the updated TMP merge list 2410 are considered along with the BVP candidates in the sparse list 2404 to select (e.g., based on the TMP costs) the candidates at block 2420 for refinement. In some example, the best 30 candidates (e.g., having the lowest TMP costs) are selected to form the updated sparse list 2411.

[0195] BVP candidates in the updated sparse list 2411 can be refined at block 2424 using a refinement search window (also referred to as a “search window”) to generate a refined candidates list 2414. In some implementations, the size of the search window for a BVP candidate depends on the type of the BVP candidate. For example, BVP candidates generated from the sparse searching in the regular TMP reference region (in the initial sparse list 2404) can use a 5x5 refinement window 2412 (with a sampling interval of 1 sample). BVP candidates from the updated TMP merge list 2410, whether inside or outside the regular reference region, can use a search window size of 11x11 samples 2413 (with a sampling interval of 1 sample) for refinement. In some implementations, the refined candidate list 2414 includes 19 BV candidates.

[0196] FIG. 25 depicts an example of refinement windows of 5 merge BVP candidates (BVP -Ml to BVP-M5) located outside of the regular TMP reference region, one merge BVP candidate (BVP-M6) located inside the regular TMP reference region (i.e. region of doing intra TMP), and one merge BVP candidate (BVP-M7) which is partially overlapping with the regular TMP reference region. FIG. 25 also shows an example of refinement windows of three sparse BVP candidates (BVP-S1 to BVP-S3) positioned within the regular TMP reference region. Better candidates are checked for the various pixel positions in those smaller drawn rectangles, around the original sparse candidate which was selected as a potentially well-predicting candidate, which would typically lie in the middle of that small typically square-shaped rectangle (e.g. check 3x3 or 5x5, or 11x11 etc. extra positions, depending on such aspects as e.g. allowable computational complexity for atypical decoder (the size of the refinement window may be different for different types of candidate, e.g. sparse vs. merge)). After adding sparse and merge candidates in the list, and creating extra candidates by refining them to slightly differing reference block position block vectors, a final shortended intraTMP list may be derived, containing a fixed amount of candidates (e.g. 20). From these final candidates an intraTMP mode can then be selected by the encoder (e.g. single BV prediction, fusion of at least two reference BVs of two selected candidates, etc.), and signaled to the decoder.

[0197] Another technique, which is called Auto-relocated block vector prediction (AR- BVP), may be used in the construction of the AMVP and / or merge IBC list. In some implementations, a guiding BV is selected from the BVP candidates in the AMVP and / or merge IBC list. The guiding block vector is a starting vector for the final displacement. A BV (referred to herein as a “coding BV”) pointing to a reference block of a block containing a position derived relative to a position pointed to by the guiding BV is identified. An AR-BVP candidate can be determined as the combination of the guiding BV and the identified coding BV. For example, the coding BV may be similar to a block vector displacement (BVD) in AMVP IBC.

[0198] FIG. 26A shows an example of AR-BVP applied to IBC where the guiding BV (BV-1) 2601 is a BVP candidate in the IBC list (list of neighboring blocks which were predicted using IBC), according to some embodiments. The guiding BV may be used to identify a first reference block (e.g., reference PU1), and five positions of the first reference block that are aligned with the five positions of the current block 2106 are also identified (i.e. in the position pointed to offset by fixed offsets). Each of the five positions are checked to determine if a coding block containing the sample at the position is encoded / decoded using the IBC mode or IntraTMP mode. These positions are denoted corresponding to the center of block (CT) 2620, left-top (LT) 2621, right-top (TR) 2622, left-bottom (LB) 2623, and rightbottom (RB) 2624. In the case that AR-BVP is used in IBC and a block containing a sample at a position of at least one of the five positions (CT, LT, RT, LB, and RB) defined relative to the first reference block was encoded / decoded using IntraTMP or IBC mode, the block vector used to indicate the reference block of the first reference block is used as the coding BV to combine with the guiding BV.

[0199] FIG. 26A further shows one example of multiple candidate AR BVPs iteratively derived from the initial guiding BV 2601. Guiding BV 2601 points to the first reference block (PU1). The five positions of the first reference block PU1, correspond to the guiding BV 2601 applied to the five respective positions (CT, LT, RT, LB, and RB) of current block 2106. Each of the five positions of the first reference block may be checked to determine if a block at any of those positions was coded in an IBC or IntraTMP mode. For example, a block at the position CT of the first reference block may be determined to be coded using BV-CT1 2604 (e.g. by IBC). Then, BV-CT1 2604 may be applied to the first reference block to determine a second reference block (reference PU2), from which five positions of the second reference block may be checked to derive one or more AR-BVPs. For example, the first AR- BVP candidate (BVP -ARI) 2605 may be derived as the addition of the guiding BV 2601 and the coding BV(BV-CTl) 2604 used for the encoding / decoding of the block containing / at position CT of the first reference block. The second AR-BVP candidate, BV-AR2 2607, may be derived as the addition of previous AR-BVP (BVP -ARI 2605) and a block vector BV-LT21 2606 derived from a block at LT position of the second reference block (reference PU2). For example, each of the five positions of the second reference block (reference PU2) may be checked to determine if a block containing the sample at those respective positions was encoded / decoded in an IntraTMP or IBC mode. For example, the block at the LT position may satisfy the condition and was coded using BV-LT21 2606, which points to a third reference block (reference PU3).

[0200] This cascading process may be iterated multiple times and referred to a number of hops. In some examples, the cascading process may be constrained to one hop. For example, BVP-AR1 2605 may be added as a candidate AR BVP derived from BVP- 1 2601, but BVP-AR2 2607 — which corresponds to a second hop — would not be determined and added as a second candidate AR BVP. In some embodiments, the AR-BVP candidates 2605 (and 2607) may be included in the AMVP and / or merge lists after the spatial adjacent candidates. In some embodiments, AR-BVP candidates 2605 (and 2607) may be included in the AMVP and / or merge lists after the spatial nonadj acent candidates. In some embodiments, AR-BVP candidates 2305 (and 2307) may be included in the AMVP and / or merge lists after the HMVP candidates.

[0201] In some examples, AR-BVP technique may be implemented for IntraTMP and is referred to as IntraTMP AR-BVP merge. This technique uses the BVPs in the IntraTMP merge list as guiding BVs for the AR-BVP process.

[0202] In some examples, the TMP AR-BVP candidates, 2605 and 2607, may be included in the TMP merge lists after the adjacent and non-adj acent merge candidates. In some examples, TMP AR-BVP candidates 2605 and 2607 and the adjacent and the non-adjacent merge candidates may be sorted in an ascending order of the TMP costs within the TMP merge list. In some embodiments, the merge candidates (adjacent and non-adjacent candidates) and the AR-BVP candidates outside the TMP reference region may be included first within the TMP merge list.

[0203] In some examples, the refinement window for the AR-BVP candidates may have a different window size than that of the TMP merge candidates and the TMP sparse candidates. FIG. 26B shows examples of refinement windows for AR-BVP candidates derived from different positions associated with the initial guiding BV 2601, according to some embodiments. The first AR-BVP candidate (BVP-AR1) 2603 is derived as the addition of the guiding BV 2601 and the coding BV(BV- CTI) 2602 used for the encoding / decoding of a block containing the central position (CT) of the reference block (reference PU). Since the BVs of a block are typically referenced with respect to the upper left Conner of the block (but that need not be a limitation of all embodiments), the guiding BV 2601 is illustrated as starting from the upper left Conner of the current block 2106. The BV associated with the block containing the central position CT, BV-CT1 2602, is shifted based on the guiding BV 2601 so that the addition of these two BVs can generate AR-BVP candidate BVP-AR1 2603. Similarly, another AR- BVP candidate, BV-RT1 2605, is derived based on the BV associated with a block containing the sample at the RT position of the reference block. An AR-BVP candidate may be refined with a refinement window 2114. Specific refinement window 2114 for a given AR-BVP candidate is set according to the AR-BVP candidate. For example, positions 2633 and 2635 pointed to by BVP-AR1 2603 and BVP-AR2 2605, respectively, are used to determine the respective refinement windows.

[0204] In some embodiments, the following source code represent an example implementation for obtaining the five positions relative to a guiding BV and determining if a block at each of the five positions is coded based on IBC or IntraTMP mode: const PredictionUnit& pu = *cs.getPU(area.pos(), CHANNEL_TYPE_LUMA); / / pu is the top left comer of the CB

[0205] / / posCand indicate the 5 offset postions related to the CB.The pu position is equal to the topleft() not centerQ Position posCand[5] ={pu.Y().center(),pu.Y().topLeft(),pu.Y().topRight(), pu . Y() .bottomLeftO ,pu . Y () ,bottomRight() } ;

[0206] / / EXAMPLE pu: {PU: x = 32, y = 24, width = 8, height = 8} posCand = {{x=36 y=28 }, {x=32 y=24 }, {x=39 y=24 }, {x=32 y=31 }, {x=39 y=31 }}

[0207] / / Loop FOR to test the five positions around a first IBC Merge / AMVP candidate or TMP merge candidate

[0208] / / bvBasedMergeCandidatesITMP_AR is the list of TMP merge candiates for (int mergeindex = 0; (mergeindex < 25) && (bvBasedMergeCandidatesITMP_AR.size() < totalNum); mergelndex++)

[0209] { cMv_Sparse = SparseCandidatesITMP[mergeIndex]; offsetX = cMv_Sparse.m_pX; offsetY = cMv_Sparse.m_pY; cMv = Mv(offsetX, offsetY); / / This is the Merge candidate to use as base for the AR-BVP for (int n = 0; n < 5 && bvBasedMergeCandidatesITMP_AR.size() < totalNum; n++) / / Check the 5 positions around the Merge BV

[0210] {

[0211] / / puCascadedid the Merge candidate + one of the offset (CT, TL, TR, BL, BR) const PredictionUnit* puCascaded = pu.cs->getPURestricted(posCand[n].offset(offsetX, offsetY), pu, pu.chType); if (! puCascaded || ((puCascaded->cu->predMode != MODE_IBC) && (!puCascaded->cu- >tmpFlag)))

[0212] { continue; / / If the block in that position was not encoded with IBC or TMP, skip it and go to the next among the 5

[0213] }

[0214] Mv arbv = cMv + puCascaded->bv; / / Build the AR-BVP candidate

[0215] / / Check if reference block pointed out for the AR-BVP is already decoded if (PU::validItmpBv(pu, arbv.hor, arbv. ver)) { if (!PU::CheckBvAvailable(bvBasedMergeCandidatesITMP, arbv) && ! PU : : CheckBvAvailable(bvBasedMergeCandidatesITMP_AR, arbv)) {

[0216] / / If the AR-BVP is valid and it is not already in the TMP merge list, it is added at the end of the TMP Merge list bvBasedMergeCandidatesITMP_AR.push_back(arbv); if (bvBasedMergeCandidatesITMP_AR.size() >= totalNum)

[0217] { break; / / If the list is complete, finish the TMP AR-BVP process

[0218] }

[0219] }

[0220] }

[0221] FIG. 27 shows one example of IntraTMP with BVP candidates derived using IntraTMP AR-BVP merge as discussed above with respect to FIGS. 26A and 26B. In FIG. 27, TMP merge candidate BVP -Ml 2701 pointing to a location outside the TMP reference region is used as a guiding BV to derive two AR-BVP candidates, BV-AR1 2703 and BV-AR2 2705. Likewise, TMP Merge candidate BVP-M2 2706 is used as guiding BV to derive a new ARB VP candidate BV-AR3 2708.

[0222] FIG. 28 shows an example of the IntraTMP AR-BVP merge process. The process shown in FIG. 28 is similar to the process shown in FIG. 24 except that a block 2802 is added to apply the AR-BVP to the merge list 2408 to generate AR-BVP candidates using the BVPs in the merge list 2408 as guiding BVs. Block 2409 is applied to the merge list 2408 and the generated AR-BVP candidates.

[0223] As discussed above, the AR-BVP technique may be applied to TMP merge candidates in the initial merge list 2408 to derive additional BVP candidates (referred to as “merge AR-BVP candidates”) to be used in generating an updated merge list 2410. However, the number of TMP merge candidates in the initial merge list 2408 may be small for reasons such as a limited number of the adjacent and non-adjacent blocks being coded (encoded or decoded) using the IBC mode or the IntraTMP mode, the BVs of such adjacent and non-adjacent neighboring blocks being invalid, or the candidates derived from these merge candidates being duplicated in the list. This leads to a small number of merge AR-BVP candidates being generated which significantly reduces the efficiency of the AR-BVP merge technique.

[0224] Embodiments relate to the use of the AR-BVP technique on TMP BVP candidates to derive additional BVP candidates to provide diversity of candidates. For example, the AR-BVP technique may be applied to the BVP candidates derived in a search process using the TMP such as the sparse list to generate sparse AR-BVP candidates for use in the IntraTMP coding. The number of candidates in the sparse list is typically larger than the number of BV candidates in the initial merge list 2408. Consequently, there can be more derived sparse AR-BVP candidates than the merge AR-BVP candidates, leading to better BVP candidates to be selected for the refinement stage. FIG. 29 shows an example of sparse AR-BVP candidates in IntraTMP generated by applying the AR-BVP technique to the TMP BV candidates, according to some embodiments. Compared with FIG. 27, in addition to the BV-AR1 2703 and BV-AR2 2705, which are merge AR-BVP candidates derived from the BVP-M1 merge candidate as explained above, a few sparse AR-BVP candidates are generated. For example, the sparse candidate TMP BVP-S2 may be used as a guiding BV, from which two new sparse ARB VP candidates, BV-AR3 2907 and BV-AR4 2909 can be derived using the AR-BVP technique as discussed above with respect to FIGS. 25-26B.

[0225] In some embodiments, the five positions used to determine the coding BVs for deriving the sparse AR-BVP candidates may be based on the size of current block 2106, as explained in FIGS. 26A-B. In other words, the reference block of the current block may be the same size as the current block and thus the size of the reference block determines the five positions, CT, LT, RT, LB, and RB in the reference block. In other embodiments, the five positions used to determine the coding BVs for deriving the sparse AR-BVP candidates may be based on the size of the refinement window at the position pointed to by the TMP sparse BVP candidate. For example, the positions may include a first position pointed to by the TMP sparse BVP candidate in the sparse list and the four comers of the refinement window centered at the first position.

[0226] In some embodiments, the TMP sparse AR-BVP candidates 2907 and 2909 may be included in the TMP merge lists after the adjacent and non-adjacent merge candidates, e.g., after blocks 2405 and 2406 of FIG. 24 or FIG. 28. In some embodiments, TMP sparse AR-BVP candidates 2907 and 2909, and the adjacent and the non-adjacent merge candidates may be sorted in an ascending order based on the TMP costs within the TMP merge list. In some embodiments, the merge candidates (adjacent and non-adjacent), and the AR-BVP candidates pointing outside of the TMP reference region may be included first within the TMP merge list before other candidates. In another embodiment, the refinement window for the sparse AR-BVP candidates may use a different refinement window size than that of the TMP merge candidates and the TMP sparse candidates as shown in FIG. 29.

[0227] FIG. 30A shows an example process 3000A for applying TMP sparse AR-BVP candidates to the TMP, according to some embodiments. Process 3000A may be performed at the encoder and the decoder to generate the same refined list 2414 at block 2424. Operations of process 3000A that have the same labels as those in FIGS. 24 and 28 are performed in the same or similar way.

[0228] Compared with FIG. 28, process 3000A may include a new processing block 3002 (realized typically as a processing circuit pre-arranged to perform the processing), which may generate one or more sparse AR-BVP candidates from BVP candidates in sparse list 2404. In some examples, the sparse AR BVP candidates may be derived by setting each BVP candidate in sparse list 2404 as a guiding BV, as explained in reference to FIGS. 25-29. For example, for a BVP in the sparse list 2404, the reference block pointed to by the BVP can be identified. Five locations, such as the CT, LT, LB, RT, and RB, of the reference block may be determined. For each of the five locations, the coding block that contains the sample at the location can be identified and the associated coding mode of the coding block can be determined. If the coding block is coded using an intra prediction mode having a BV associated therewith, such as the IntraTMP mode or the IBC mode, the BV of the coding block (coding BV) can be combined with the guiding BV to generate the sparse AR-BVP candidate. The remaining locations can be evaluated similarly. The same process can be repeated for other BVP candidates in the sparse list 2404 to generate additional sparse AR-BVP candidates.

[0229] In some embodiments, operations at block 3002 may be performed after obtaining adjacent and non-adjacent BVP candidates at block 2405 and 2406, respectively. In some embodiments, operations at block 3002 may be performed before operations at blocks 2405 and 2406. In some examples, the various candidates such as adjacent, non-adjacent, and sparse AR-BVP candidates may be reordered and / or pruned at block 3004 to generate the resulting merge list 3006. The merge list 2408 before the sparse AR-BVP candidates and the merge AR-BVP candidates are added is referred to as the initial merge list 2408.

[0230] As shown in FIG. 30A, the refinement search window for AR-BVP candidates (merge AR-BVP candidates and sparse AR-BVP candidates) can be set to be different from other merge candidates. To do so, a determination box 3010 can be added to determine whether a merge BVP candidate is an AR-BVP candidate. If not, the refinement search window can be set to a size 3012 used before the AR-BVP technique is applied, such as 11x11. If the merge BVP candidate is an AR-BVP candidate, the refinement search window can be set to be a smaller size 3014 (e.g., 3x3). In this way, the refinement search window for merge candidates in the initial merge list 2408 has a larger size than that of the AR-BVP candidates.

[0231] FIG. 30B shows another example process 3000B for applying TMP sparse AR-BVP candidates to the TMP, according to some embodiments. Process 3000B may be performed at the encoder and the decoder to generate the same refined list at block 2414. Operations of process 3000B that have the same labels as those in FIGS. 24, 28, and 30A are performed in the same or similar way.

[0232] Compared with FIG. 30A, process 3000B combines the sparse AR-BVP candidates generated at block 3002 with the sparse list 2404 (also referred to as the “initial sparse list 2404”). In some examples, the sparse AR BVP candidates may be derived by setting each BVP candidate in sparse list 2404 as a guiding BV, as explained in reference to FIG. 30A. In some examples, the BVP candidates in the initial sparse list 2404 and the generated AR-BVP are reordered and / or pruned at block 3020 to generate the sparse list 3022. The sparse list 3022 can be used to remove the redundant merge BVP candidates in the merge list 3006 at block 2409. Other blocks of the process 3000B may be performed in a similar way as the corresponding blocks in the process 3000A.

[0233] FIG. 31 illustrates a flowchart 3100 of a method for generating a list of BVP candidates for coding a current block, according to some embodiments. Specifically, the list of BVP candidates may be generated based on applying an AR-BVP technique to a list of TMP candidates (in a sparse list 2404) to generate one or more additional BVP candidates referred to as sparse AR-BVP candidates. In some examples, flowchart 3100 may be performed by an encoder (e.g., encoder 200 of FIG. 2) or a decoder (e.g., decoder 300 of FIG. 3).

[0234] At block 3102, a first block vector prediction (BVP) candidate is determined. In some examples, the first BVP candidate is generated by applying a search using TMP for a current block. In some examples, the search is performed as the sparse search illustrated in FIG. 19A for the current block. The first BVP candidate may be from the list of the search such as the sparse list 2404 as shown in FIGS. 30A-B.

[0235] At block 3104, an AR-BVP candidate is derived based on applying an AR-BVP technique to the first BVP candidate. For example, it can be determined whether the blocks at a set of positions, defined relative to the position indicated by the first BVP candidate, are coded (e.g., encoded / decoded) via an intra prediction model with a coding BV, such as an IBC mode or an IntraTMP mode. For instance, the coder (encoder or decoder) can determine a reference block based on the first BVP candidate. The coder can identify a coding BV associated with a position of the set of positions within the reference block and derive the AR-BVP candidate (sparse AR-BVP candidate) by combining the coding BV with the first BVP candidate.

[0236] The set of positions can include a center position, a left top position, a left bottom position, a right top position, or a right bottom position of the reference block as described above with respect to FIGS. 26A-B and can be determined by applying the first BVP candidate to the respective positions of the current block. In some examples, the set of positions include a center position indicated by the first BVP candidate and the four positions of the four comers of a reference block identified by the first BVP candidate. In some examples, the set of positions include the position indicated by the first BVP candidate and the four positions of the four comers of a refinement window associated with the first BVP candidate. For example, the refinement window may be centered at the position pointed to by the first BVP candidate.

[0237] To identify the coding BV, the coder can determine a coding block containing a sample at the position and determine that the coding block is coded via the intra prediction model with a coding BV (e.g., the IBC mode or the IntraTMP mode). The coding BV of the coding block can be determined as the coding BV associated with the position. The AR-BVP candidate can be derived by adding the coding BV to the first BVP candidate.

[0238] In some embodiments, each position of the first set of positions may be contained by a different coding block. Accordingly, up to the number of the set of positions of new AR-BVP candidates may be added if each of the coding blocks is coded in IBC or IntraTMP mode.

[0239] In some embodiments, the AR-BVP technique may be iteratively applied a number of times (e.g., hops) to derive additional BVP candidates. For example, the coder may further determine a second reference block based on the combination of the coding BV with the first BVP candidate (which can be a first derived AR-BVP candidate) and identifying a second coding BV associated with a second position within the second reference block. A second AR-BVP candidate may be derived by combining the second coding BV with the combination of the coding BV with the first BVP candidate (the first derived AR-BVP candidate).

[0240] In some examples, the AR-BVP technique may be applied to multiple BVP candidates, such as multiple BVP candidates in the sparse list 2404 to generate multiple sparse AR-BVP candidates.

[0241] At block 3106, a list of BVP candidates is determined based on the first BVP candidate and the AR-BVP candidate (e.g., the sparse AR-BVP candidate). In some examples, an initial merge list of BVP candidates (e.g., the initial merge list 2408) corresponding to adjacent and non-adjacent merge BVP candidates may be determined, as shown at blocks 2405 and 2406 of FIGS. 30A-B. In some implementations, the initial merge list of BVP candidates has a pre -determined number of BVP candidates (e.g., 10). The initial merge list can be updated based on the sparse AR-BVP candidate and an initial sparse list (e.g., the sparse list 2404). For example, the sparse AR-BVP candidate (and other AR- BVP candidates, such as other sparse AR-BVP candidates and merge AR-BVP candidates) can be added to the initial merge list. The resulting list of candidates can be reordered, e.g. based on the template matching costs (TMP costs) and pruned to remove duplicates and limit the number of BVP candidates in the merge list to the pre -determined number. In some examples, the initial sparse list (e.g., the sparse list 2404) may be used to further update the merge list. For example, the BVP candidates in the merge list can be evaluated against the initial sparse list to remove any redundant merge BVP candidates in the updated merge list. As a result, the updated merge list may have the same or fewer number of BVP candidates than the initial merge list.

[0242] The updated merge list (e.g., updated merge list 2410) can be used in conjunction with the initial sparse list (e.g., the sparse list 2404) to generate the sparse list of BVP candidates (e.g., the updated sparse list 2411). In some examples, the sparse list of BVP candidates are selected from the initial sparse list and the updated merge list by selecting those BVP candidates having lower TMP costs than remaining candidates. In some implementations, the number of candidates in the sparse list is kept the same as the number of candidates in the initial sparse list.

[0243] In some examples, generating the list of BVP candidates may further include applying a refinement process to the BVP candidates in the sparse list. As discussed above with respect to FIGS. 24, 28, and 30, the refinement process can involve a refinement window within which additional BVP candidates may be evaluated and generated. For example, for a BVP candidate to be refined, the coder (encoder or decoder) may determine a refinement search window associated with the BVP candidate. The refinement search window can be determined to be at the position pointed to by the BVP candidate from the left top sample of the current block. The size of the refinement search window can be determined according to the type of the BVP candidate. For example, the search window for an AR-BVP candidate can have a first size; the search window for a BVP candidate from the initial sparse list can have a second size; and the search window for a BVP candidate from the initial merge list has a third size. In some examples, the first size, the second size, and the third size can be different, and the first size is smaller than the second size which is smaller than the third size. For example, the first size is 3x3, the second size is 5x5, and the third size is 11x11.

[0244] Additional BVP candidates may be generated according to a sampling interval in each search window and the BVP candidates having the lowest TMP costs can be included in the list of BVP candidates (e.g., the refined list 2414). In some implementations, the list of BVP candidates has a fewer number of BVP candidates than the sparse list.

[0245] At block 3108, a BV indicating a reference block for predicting the current block is determined based on the list of BVP candidates. For example, at the encoder, the encoder may compute costs (e.g., RDO cost) for reference blocks indicated by corresponding BVP candidates in the list of BVP candidates to determine a BVP candidate associated with a lowest cost. Then, the encoder may signal an index in the bitstream to indicate that BVP candidate, in the list of BVP candidates, to be used as the BV. At the decoder, the decoder may decode from the bitstream an indication (e.g., index) of the BVP candidate in the list of BVP candidates and then identify the BVP from the list according to the indication. The identified BVP may be used as the BV to obtain a reference block for reconstructing the current block.

[0246] At block 3110, the current block is coded based on the reference block. In some embodiments, at the encoder, the current block may be encoded by subtracting the reference block corresponding to the determined BV from the current block to determine a residual (e.g., residual block). The residual may be encoded and signaled in the bitstream. At the decoder, the decoder may determine a predicted block for the current block by determining the reference block identified by the BV. The current block may be reconstructed (e.g., decoded) based on a residual (e.g., residual block) obtained from a bitstream and the predicted block (e.g., reference block). For example, the current block may be determined by adding the residual to the reference block identified by the BV.

[0247] 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 3200 is shown in FIG. 32. Blocks depicted in the figures above, such as the blocks in FIGS. 1, 2, and 3, may execute on one or more computer systems 3200. Furthermore, each of the steps of the flowcharts depicted in this disclosure may be implemented on one or more computer systems 3200.

[0248] Computer system 3200 includes one or more processors, such as processor 3204. Processor 3204 may be, for example, a special purpose processor, general purpose processor, microprocessor, or digital signal processor. Processor 3204 may be connected to a communication infrastructure 3202 (for example, a bus or network). Computer system 3200 may also include a main memory 3206, such as random access memory (RAM), and may also include a secondary memory 3208. Secondary memory 3208 may include, for example, a hard disk drive 3210 and / or a removable storage drive 3212, representing a magnetic tape drive, an optical disk drive, or the like. Removable storage drive 3212 may read from and / or write to a removable storage unit 3216 in a well- known manner. Removable storage unit 3216 represents a magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 3212. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 3216 includes a computer usable storage medium having stored therein computer software and / or data.

[0249] In alternative implementations, secondary memory 3208 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 3200. Such means may include, for example, a removable storage unit 3218 and an interface 3214. 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 3218 and interfaces 3214 which allow software and data to be transferred from removable storage unit 3218 to computer system 3200.

[0250] Computer system 3200 may also include a communications interface 3220. Communications interface 3220 allows software and data to be transferred between computer system 3200 and external devices. Examples of communications interface 3220 may include a modem, a network interface (such as an Ethernet card), a communications port, etc. Software and data transferred via communications interface 3220 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 3220. These signals are provided to communications interface 3220 via a communications path 3222. Communications path 3222 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.

[0251] 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 3216 and 3218 or a hard disk installed in hard disk drive 3210. These computer program products are means for providing software to computer system 3200. Computer programs (also called computer control logic) may be stored in main memory 3206 and / or secondary memory 3208. Computer programs may also be received via communications interface 3220. Such computer programs, when executed, enable the computer system 3200 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 3204 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 3200.

[0252] 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

CLAIMS:

1. A method of decoding a sequence of images comprising: determining a first block vector prediction (BVP) candidate for predicting a block of pixel lumas of a current block of an image to be decoded, by applying a search using template matching prediction (TMP) for the block, which selects the first block vector prediction candidate based on a match between pixels in a template of the first block vector prediction (BVP) candidate and a template of the current block, wherein the first block vector prediction (BVP) candidate is a sparse candidate pointing to a spatially sub-sampled position of the image to be decoded; deriving an auto-relocated BVP candidate by using the first block vector prediction (BVP) candidate and determining the auto-relocated BVP candidate as a block vector which is equal to the vector addition of the first block vector prediction (BVP) candidate and a block vector which was used to predict a block at a position pointed to by the first block vector prediction (BVP) candidate starting from a position of the current block; determining a list of BVP candidates comprising the first BVP candidate and the autorelocated BVP candidate; determining, based on the list of BVP candidates, a final block vector indicating a reference block for predicting the current block; and decoding the current block based on the reference block.

2. The method as claimed in claim 1, in which the auto-relocated BVP candidate is added in a list of sparse candidates, which list of sparse candidates is used for selecting the final block vector.

3. The method as claimed in claim 1 or 2, wherein one or more spatially offset candidates, which are located at a position offset from a position of the auto-relocated BVP candidate by a fixed horizontal and / or vertical distance, are added to the list of sparse candidates.

4. A method of encoding a sequence of images comprising: determining a first block vector prediction (BVP) candidate for predicting a block of pixel lumas of a current block of an image to be decoded, by applying a search using template matching prediction (TMP) for the block, which selects the first block vector prediction candidate based on a match between pixels in a template of the first block vector prediction (BVP) candidate and a template of the current block, wherein the first block vector prediction (BVP) candidate is a sparse candidate pointing to a spatially sub-sampled position of the image to be decoded;deriving an auto-relocated BVP candidate by using the first block vector prediction (BVP) candidate and determining the auto-relocated BVP candidate as a block vector which is equal to the vector addition of the first block vector prediction (BVP) candidate and a block vector which was used to predict a block at a position pointed to by the first block vector prediction (BVP) candidate starting from a position of the current block; determining a list of BVP candidates comprising the first BVP candidate and the autorelocated BVP candidate; determining, based on the list of BVP candidates, a final block vector indicating a reference block for predicting the current block; and encoding the current block based on the reference block.

5. The method as claimed in claim 4, in which the auto-relocated BVP candidate is added in a list of sparse candidates, which list of sparse candidates is used for selecting the final block vector.

6. The method as claimed in claim 4 or 5, wherein one or more spatially offset candidates, which are located at a position offset from a position of the auto-relocated BVP candidate by a fixed horizontal and / or vertical distance, are added to the list of sparse candidates.

7. A video decoding apparatus comprising a memory and a processor arranged to perform a method as claimed in one of the claims 1 to 3.

8. A video encoding apparatus comprising a memory and a processor arranged to perform a method as claimed in one of the claims 4 to 6.

9. A computer program product comprising computer code to instruct a processor to execute one of the methods as claimed in claim 1 to 6.

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