Methods and devices for intra block copy

Abstract

Methods for video decoding and encoding, apparatuses, and non-transitory computer-readable storage media are provided. In one method, a decoder may at least one block vector (BV) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode. Additionally, the decoder may obtain a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear filter of a local illumination compensation (LIC) mode.

Description

METHODS AND DEVICES FOR INTRA BLOCK COPYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is based upon and claims priority to U.S. Provisional Application No. 63 / 619,717, filed on January 10, 2024, to U.S. Provisional Application No. 63 / 570,742, filed on March 27, 2024, and to U.S. Provisional Application No. 63 / 649,294, filed on May 17, 2024. The disclosures of the previously filed applications mentioned above are incorporated by reference in their entireties for all purposes.TECHNICAL FIELD

[0002] The present disclosure is related to video coding and compression, and in particular but not limited to, methods and apparatus on improving the Intra Block Copy (IBC) method in a video encoding or decoding process.BACKGROUND

[0003] Digital video is supported by a variety of electronic devices, such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video gaming consoles, smart phones, video teleconferencing devices, video streaming devices, etc. The electronic devices transmit and receive or otherwise communicate digital video data across a communication network, and / or store the digital video data on a storage device. Due to a limited bandwidth capacity of the communication network and limited memory resources of the storage device, video coding may be used to compress the video data according to one or more video coding standards before it is communicated or stored. For example, video coding standards include Versatile Video Coding (VVC), Joint Exploration test Model (JEM), High-Efficiency Video Coding (HEVC / H.265), Advanced Video Coding (AVC / H.264), Moving Picture Expert Group (MPEG) coding, or the like. Video coding generally utilizes prediction methods (e.g., inter-prediction, intra-prediction, or the like) that take advantage of redundancy inherent in the video data. Video coding aims to compress video data into a form that uses a lower bit rate, while avoiding or minimizing degradations to video quality.SUMMARY

[0004] The present disclosure provides examples of techniques relating to improving the Intra Block Copy method in a video encoding or decoding process.

[0005] According to a first aspect of the present disclosure, there is provided a method for video decoding. In the method, a decoder may obtain at least one block vector (BV) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode. Furthermore, the decoder may obtain a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear filter of a local illumination compensation (LIC) mode, wherein the at least one BV candidate list comprises at least one of following lists: an integer-pel BV candidate list, a sub-pel BV candidate list, or a composite BV candidate list comprising at least one integer-pel BV and at least one sub-pel BV.

[0006] According to a second aspect of the present disclosure, there is provided a method for video decoding. In the method, a decoder may obtain a prediction block for a current block based on multiple initial predictions of the current block, wherein the multiple initial predictions comprise a BV prediction obtained based on a BV prediction mode.

[0007] According to a third aspect of the present disclosure, there is provided a method for video encoding. In the method, an encoder may obtain at least one block vector (BV) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode. Furthermore, the encoder may obtain a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear filter of a local illumination compensation (LIC) mode, wherein the at least one BV candidate list comprises at least one of following lists: an integer-pel BV candidate list, a sub-pel BV candidate list, or a composite BV candidate list comprising at least one integer-pel BV and at least one sub-pel BV.

[0008] According to a fourth aspect of the present disclosure, there is provided a method for video encoding. In the method, an encoder may obtain a prediction block for a current block based on multiple initial predictions of the current block, wherein the multiple initial predictions comprise a BV prediction obtained based on a BV prediction mode.

[0009] According to a fifth aspect of the present disclosure, there is provided an apparatus for video decoding. The apparatus includes one or more processors; and a memory coupled to the one or more processors and configured to store instructions executable by the one or more processors, where the one or more processors, upon execution of the instructions, are configured to perform the method according to the first aspect.

[0010] According to a sixth aspect of the present disclosure, there is provided an apparatus for video encoding. The apparatus includes one or more processors; and a memory coupled to the oneor more processors and configured to store instructions executable by the one or more processors, where the one or more processors, upon execution of the instructions, are configured to perform the method according to the second aspect.

[0011] According to a seventh aspect of the present disclosure, there is provided a non-transitory computer-readable storage medium for storing computer-executable instructions that, when executed by one or more computer processors, cause the one or more computer processors to perform the method according to the first aspect.

[0012] According to an eighth aspect of the present disclosure, there is provided a non-transitory computer-readable storage medium for storing computer-executable instructions that, when executed by one or more computer processors, cause the one or more computer processors to perform the method according to the second aspect.

[0013] According to a ninth aspect of the present disclosure, there is provided a non-transitory computer-readable storage medium for storing a bitstream to be decoded by the method according to the first aspect.

[0014] According to a tenth aspect of the present disclosure, there is provided a non-transitory computer-readable storage medium for storing a bitstream to be decoded by the method according to the second aspect.

[0015] According to an eleventh aspect of the present disclosure, there is provided a method for receiving a bitstream, where the bitstream comprises encoded video information to be decoded by the method according to the first aspect.

[0016] According to a twelfth aspect of the present disclosure, there is provided a method for transmitting a bitstream, where the bitstream comprises encoded video information to be decoded by the method according to the second aspect.

[0017] It is to be understood that both the foregoing general description and the following detailed description are examples only and are not restrictive of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate examples consistent with the present disclosure and, together with the description, serve to explain the principles of the disclosure.

[0019] FIG. 1 is a block diagram illustrating an exemplary system for encoding and decoding video blocks in accordance with some implementations of the present disclosure.

[0020] FIG. 2 is a block diagram illustrating an exemplary video encoder in accordance with some implementations of the present disclosure.

[0021] FIG. 3 is a block diagram illustrating an exemplary video decoder in accordance with some implementations of the present disclosure.

[0022] FIGS. 4A through 4E are block diagrams illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes in accordance with some implementations of the present disclosure.

[0023] FIGS. 5A-5B show examples of 4-parameter affine model in accordance with some examples of the present disclosure.

[0024] FIG. 5C shows an example of 6-parameter affine model in accordance with some examples of the present disclosure.

[0025] FIG. 6 shows an example of adjacent neighboring blocks for inherited affine merge candidates in accordance with some examples of the present disclosure.

[0026] FIG. 7 shows an example of adjacent neighboring blocks for constructed affine merge candidates in accordance with some examples of the present disclosure.

[0027] FIG. 8 shows a current CTU processing order and its available reference samples in current and left CTU in accordance with some examples of the present disclosure.

[0028] FIG. 9 shows padding candidates for the replacement of the zero-vector in the IBC list in accordance with some examples of the present disclosure.

[0029] FIG. 10 shows reference area for IBC when CTU (m, n) is coded in accordance with some examples of the present disclosure.

[0030] FIG. 11 shows IBC reference area for camera-captured content in accordance with some examples of the present disclosure.

[0031] FIGS. 12A-12B show the division methods for angular modes in accordance with some examples of the present disclosure.

[0032] FIG. 13 A shows spatial neighboring blocks used by ATVMP in accordance with some examples of the present disclosure.

[0033] FIG. 13B shows an example of deriving sub-CU motion field by applying a motion shift from spatial neighbor and scaling the motion information from the corresponding collocated sub- CUs in accordance with some examples of the present disclosure.

[0034] FIG. 14 is a flow chart of decoding a bin in accordance with some examples of the present disclosure.

[0035] FIG. 15 shows intra template matching search area used in some examples of the present disclosure.

[0036] FIG. 16A shows an example of BV adjustment for horizontal flip in accordance with some examples of the present disclosure.

[0037] FIG. 16B shows an example of BV adjustment for vertical flip in accordance with some examples of the present disclosure.

[0038] FIG. 17 shows an example of the five locations in reconstructed luma samples in accordance with some examples of the present disclosure.

[0039] FIG. 18 shows an example of the prediction process of DBV method in accordance with some examples of the present disclosure.

[0040] FIG. 19 shows an example of AM VP IBC candidate clustering based on the L2 distance and the TM cost in accordance with some examples of the present disclosure.

[0041] FIG. 20 shows an updated IntraTMP search area in accordance with some examples of the present disclosure.

[0042] FIG. 21 shows an example of using IntraTMP block vector for an IBC block in accordance with some examples of the present disclosure.

[0043] FIGS. 22A-22D show sub-pel precisions supported in the IntraTMP mode in accordance with some examples of the present disclosure.

[0044] FIG. 23 shows sub-pel positions at 1 / 2-pel precision supported in the IntraTMP mode in accordance with some examples of the present disclosure.

[0045] FIG. 24 shows one example of supported sub-pel precisions and directions in the IntraTMP mode in accordance with some examples of the present disclosure.

[0046] FIG. 25 shows one exemplary definition of the weighted template cost in accordance with some examples of the present disclosure.

[0047] FIG. 26 shows one example of block vectors before and after adding fractional refinements in accordance with some examples of the present disclosure.

[0048] FIG. 27 shows one example of non-adjacent spatial neighboring candidates for OBIC mode in accordance with some examples of the present disclosure.

[0049] FIG. 28 shows one example of the histogram of occurrences (HoC) of IPM modes in the spatial neighborhood of a CU in accordance with some examples of the present disclosure.

[0050] FIG. 29 is a diagram illustrating a computing environment coupled with a user interface in accordance with some examples of the present disclosure.

[0051] FIG. 30 is a flow chart illustrating a method for video decoding in accordance with some examples of the present disclosure.

[0052] FIG. 31 is a flow chart illustrating a method for video decoding in accordance with some examples of the present disclosure.

[0053] FIG. 32 is a flow chart illustrating a method for video encoding corresponding to the method for video decoding as shown in FIG. 30 in accordance with some examples of the present disclosure.

[0054] FIG. 33 is a flow chart illustrating a method for video encoding corresponding to the method for video decoding as shown in FIG. 31 in accordance with some examples of the present disclosure.DETAILED DESCRIPTION

[0055] Reference will now be made in detail to specific implementations, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous nonlimiting specific details are set forth in order to assist in understanding the subject matter presented herein. But various alternatives may be used without departing from the scope of claims and the subject matter may be practiced without these specific details. For example, the subject matter presented herein can be implemented on many types of electronic devices with digital video capabilities.

[0056] It should be illustrated that the terms '‘first,” “second,” and the like used in the description, claims of the present disclosure, and the accompanying drawings are used to distinguish objects, and not used to describe any specific order or sequence. It should be understood that the data used in this way may be interchanged under an appropriate condition, such that the embodiments of the present disclosure described herein may be implemented in orders besides those shown in the accompanying drawings or described in the present disclosure.

[0057] FIG. 1 is a block diagram illustrating an exemplary system 10 for encoding and decoding video blocks in parallel in accordance with some implementations of the present disclosure. As shown in FIG. 1, the system 10 includes a source device 12 that generates and encodes video data to be decoded at a later time by a destination device 14. The source device 12 and the destination device 14 may comprise any of a wide variety of electronic devices, including cloud servers, server computers, desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some implementations, the source device 12 and the destination device 14 are equipped with wireless communication capabilities.

[0058] In some implementations, the destination device 14 may receive the encoded video data to be decoded via a link 16. The link 16 may comprise any type of communication medium or device capable of moving the encoded video data from the source device 12 to the destination device 14. In one example, the link 16 may comprise a communication medium to enable the source device 12 to transmit the encoded video data directly to the destination device 14 in real time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to the destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a Radio Frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from the source device 12 to the destination device 14.

[0059] In some other implementations, the encoded video data may be transmitted from an output interface 22 to a storage device 32. Subsequently, the encoded video data in the storage device 32 may be accessed by the destination device 14 via an input interface 28. The storage device 32 mayinclude any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, Digital Versatile Disks (DVDs), Compact Disc Read-Only Memories (CD-ROMs), flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing the encoded video data. In a further example, the storage device 32 may correspond to a file server or another intermediate storage device that may hold the encoded video data generated by the source device 12. The destination device 14 may access the stored video data from the storage device 32 via streaming or downloading. The file server may be any type of computer capable of storing the encoded video data and transmitting the encoded video data to the destination device 14. Exemplary file servers include a web server (e.g., for a website), a File Transfer Protocol (FTP) server, Network Attached Storage (NAS) devices, or a local disk drive. The destination device 14 may access the encoded video data through any standard data connection, including a wireless channel (e g., a Wireless Fidelity (Wi-Fi) connection), a wired connection (e g., Digital Subscriber Line (DSL), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server. The transmission of the encoded video data from the storage device 32 may be a streaming transmission, a download transmission, or a combination of both.

[0060] As shown in FIG. 1, the source device 12 includes a video source 18, a video encoder 20 and the output interface 22. The video source 18 may include a source such as a video capturing device, e.g., a video camera, a video archive containing previously captured video, a video feeding interface to receive video from a video content provider, and / or a computer graphics system for generating computer graphics data as the source video, or a combination of such sources. As one example, if the video source 18 is a video camera of a security surveillance system, the source device 12 and the destination device 14 may form camera phones or video phones. However, the implementations described in the present application may be applicable to video coding in general, and may be applied to wireless and / or wired applications.

[0061] The captured, pre-captured, or computer-generated video may be encoded by the video encoder 20. The encoded video data may be transmitted directly to the destination device 14 via the output interface 22 of the source device 12. The encoded video data may also (or alternatively) be stored onto the storage device 32 for later access by the destination device 14 or other devices, for decoding and / or playback. The output interface 22 may further include a modem and / or a transmitter. The encoded video data may comprise a sequence of pictures, each of which maycomprise one or more sample arrays, for example, luma (Y) only for monochrome; luma and two chroma in YCbCr orYCgCo domain; or green, blue, and red in GBR (also known as RGB) domain. For convenience of notation and terminology in this application, in some embodiments, variables and terms associated with each set of three sample arrays may be referred to as luma and chroma, where the two chroma arrays may be referred to as Cb and Cr, regardless of the actual color representation method in use. The video data may be in a chroma format of 4:0:0, 4:2:0, 4:2:2, or 4:4:4, but the present application is not limited thereto.

[0062] The destination device 14 includes the input interface 28, a video decoder 30, and a display device 34. The input interface 28 may include a receiver and / or a modem and receive the encoded video data over the link 16. The encoded video data communicated over the link 16, or provided on the storage device 32, may include a variety of syntax elements generated by the video encoder 20 for use by the video decoder 30 in decoding the video data. Such syntax elements may be included within the encoded video data transmitted on a communication medium, stored on a storage medium, or stored on a file server.

[0063] In some implementations, the destination device 14 may include the display device 34, which can be an integrated display device and an external display device that is configured to communicate with the destination device 14. The display device 34 displays the decoded video data to a user, and may comprise any of a variety of display devices such as a Liquid Crystal Display (LCD), a plasma display, an Organic Light Emitting Diode (OLED) display, or another type of display device.

[0064] The video encoder 20 and the video decoder 30 may operate according to proprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10, AVC, or extensions of such standards. It should be understood that the present application is not limited to a specific video encoding / decoding standard and may be applicable to other video encoding / decoding standards. It is generally contemplated that the video encoder 20 of the source device 12 may be configured to encode video data according to any of these current or future standards. Similarly, it is also generally contemplated that the video decoder 30 of the destination device 14 may be configured to decode video data according to any of these current or future standards.

[0065] The video encoder 20 and the video decoder 30 each may be implemented as any of a variety of suitable encoder and / or decoder circuitry, such as one or more microprocessors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field ProgrammableGate Arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When implemented partially in software, an electronic device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the video encoding / decoding operations disclosed in the present disclosure. Each of the video encoder 20 and the video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder / decoder (CODEC) in a respective device.

[0066] In some implementations, at least a part of components of the source device 12 (for example, the video source 18, the video encoder 20 or components included in the video encoder 20 as described below with reference to Fig. 2, and the output interface 22) and / or at least a part of components of the destination device 14 (for example, the input interface 28, the video decoder 30 or components included in the video decoder 30 as described below with reference to Fig. 3, and the display device 34) may operate in a cloud computing service network which may provide software, platforms, and / or infrastructure, such as Software as a Service (SaaS), Platform as a Service (PaaS), or Infrastructure as a Service (laaS). In some implementations, one or more components in the source device 12 and / or the destination device 14 which are not included in the cloud computing service network may be provided in one or more client devices, and the one or more client devices may communicate with server computers in the cloud computing service network through a wireless communication network (for example, a cellular communication network, a short-range wireless communication network, or a global navigation satellite system (GNSS) communication network) or a wired communication network (e.g., a local area network (LAN) communication network or a power line communication (PLC) network). In an embodiment, at least a part of operations described herein may be implemented as cloud-based services provided by one or more server computers which are implemented by the at least a part of the components of the source device 12 and / or the at least a part of the components of the destination device 14 in the cloud computing service network; and one or more other operations described herein may be implemented by the one or more client devices. In some implementations, the cloud computing service network may be a private cloud, a public cloud, or a hybrid cloud. The terms such as “cloud,” “cloud computing,” “cloud-based” etc. herein may be used interchangeably as appropriate without departing from the scope of the present disclosure. It should be understood that the present disclosure is not limited to being implemented in the cloudcomputing service network described above. Instead, the present disclosure may also be implemented in any other type of computing environments currently known or developed in the future.

[0067] FIG. 2 is a block diagram illustrating an exemplary video encoder 20 in accordance with some implementations described in the present application. The video encoder 20 may perform intra and inter predictive coding of video blocks within video frames. Intra predictive coding relies on spatial prediction to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter predictive coding relies on temporal prediction to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence. It should be noted that the term “frame” may be used as synonyms for the term “image” or “picture” in the field of video coding.

[0068] As shown in FIG. 2, the video encoder 20 includes a video data memory 40, a prediction processing unit 41, a Decoded Picture Buffer (DPB) 64, a summer 50, a transform processing unit 52, a quantization unit 54, and an entropy encoding unit 56. The prediction processing unit 41 further includes a motion estimation unit 42, a motion compensation unit 44, a partition unit 45, an intra prediction processing unit 46, and an intra Block Copy (BC) unit 48. In some implementations, the video encoder 20 also includes an inverse quantization unit 58, an inverse transform processing unit 60, and a summer 62 for video block reconstruction. An in-loop filter 63, such as a deblocking filter, may be positioned between the summer 62 and the DPB 64 to filter block boundaries to remove blockiness artifacts from reconstructed video. Another in-loop filter, such as Sample Adaptive Offset (SAO) filter, Cross Component Sample Adaptive Offset (CCSAO) filter and / or Adaptive in-Loop Filter (ALF), may also be used in addition to the deblocking filter to filter an output of the summer 62. It should be illustrated that for the CCSAO technique, the present application is not limited to the embodiments described herein, and instead, the application may be applied to a situation where an offset is selected for any of a luma component and two chroma components (which may represent Y, Cb and Cr in Y CbCr domain; Y, Cg and Co in Y CgCo domain; or G, B and R in RGB domain for convenience of notation and terminology in this application as described above) according to any other of the luma component and the two chroma components to modify said any component based on the selected offset. Further, it should also be illustrated that a first component mentioned herein may be any of the luma component and the two chroma components, a second component mentioned herein may be any other of the lumacomponent and the two chroma components, and a third component mentioned herein may be a remaining one of the luma component and the two chroma components. In some examples, the inloop filters may be omitted, and the decoded video block may be directly provided by the summer 62 to the DPB 64. The video encoder 20 may take the form of a fixed or programmable hardware unit or may be divided among one or more of the illustrated fixed or programmable hardware units.

[0069] The video data memory 40 may store video data to be encoded by the components of the video encoder 20. The video data in the video data memory 40 may be obtained, for example, from the video source 18 as shown in FIG. 1. The DPB 64 is a buffer that stores reference video data (for example, reference frames or pictures) for use in encoding video data by the video encoder 20 (e.g., in intra or inter predictive coding modes). The video data memory 40 and the DPB 64 may be formed by any of a variety of memory devices. In various examples, the video data memory 40 may be on-chip with other components of the video encoder 20, or off-chip relative to those components.

[0070] As shown in FIG. 2, after receiving the video data, the partition unit 45 within the prediction processing unit 41 partitions the video data into video blocks. This partitioning may also include partitioning a video frame into slices, tiles (for example, sets of video blocks), or other larger Coding Units (CUs) according to predefined splitting structures such as a Quad-Tree (QT) structure associated with the video data. The video frame is or may be regarded as a two- dimensional array or matrix of samples with sample values. A sample in the array may also be referred to as a pixel or a pel. A number of samples in horizontal and vertical directions (or axes) of the array or picture define a size and / or a resolution of the video frame. The video frame may be divided into multiple video blocks by, for example, using QT partitioning. The video block again is or may be regarded as a two-dimensional array or matrix of samples with sample values, although of smaller dimension than the video frame. A number of samples in horizontal and vertical directions (or axes) of the video block define a size of the video block. The video block may further be partitioned into one or more block partitions or sub-blocks (which may form again blocks) by, for example, iteratively using QT partitioning, Binary-Tree (BT) partitioning or TripleTree (TT) partitioning or any combination thereof. It should be noted that the term “block” or “video block” as used herein may be a portion, in particular a rectangular (square or non- square) portion, of a frame or a picture. With reference, for example, to HEVC and VVC, the block or video block may be or correspond to a Coding Tree Unit (CTU), a CU, a Prediction Unit (PU) ora Transform Unit (TU) and / or may be or correspond to a corresponding block, e.g. a Coding Tree Block (CTB), a Coding Block (CB), a Prediction Block (PB) or a Transform Block (TB) and / or to a sub-block.

[0071] The prediction processing unit 41 may select one of a plurality of possible predictive coding modes, such as one of a plurality of intra predictive coding modes or one of a plurality of inter predictive coding modes, for the current video block based on error results (e.g., coding rate and the level of distortion). The prediction processing unit 41 may provide the resulting intra or inter prediction coded block to the summer 50 to generate a residual block and to the summer 62 to reconstruct the encoded block for use as part of a reference frame subsequently. The prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to the entropy encoding unit 56.

[0072] In order to select an appropriate intra predictive coding mode for the current video block, the intra prediction processing unit 46 within the prediction processing unit 41 may perform intra predictive coding of the current video block relative to one or more neighbor blocks in the same frame as the current block to be coded to provide spatial prediction. The motion estimation unit 42 and the motion compensation unit 44 within the prediction processing unit 41 perform inter predictive coding of the current video block relative to one or more predictive blocks in one or more reference frames to provide temporal prediction. The video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

[0073] In some implementations, the motion estimation unit 42 determines the inter prediction mode for a current video frame by generating a motion vector, which indicates the displacement of a video block within the current video frame relative to a predictive block within a reference video frame, according to a predetermined pattern within a sequence of video frames. Motion estimation, performed by the motion estimation unit 42, is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a video block within a current video frame or picture relative to a predictive block within a reference frame relative to the current block being coded within the current frame. The predetermined pattern may designate video frames in the sequence as P frames or B frames. The intra BC unit 48 may determine vectors, e.g., block vectors, for intra BC coding in a manner similar to the determination of motion vectors by the motion estimation unit 42 for inter prediction, or may utilize the motion estimation unit 42 to determine the block vector.

[0074] A predictive block for the video block may be or may correspond to a block or a reference block of a reference frame that is deemed as closely matching the video block to be coded in terms of pixel difference, which may be determined by Sum of Absolute Difference (SAD), Sum of Square Difference (SSD), or other difference metrics. In some implementations, the video encoder 20 may calculate values for sub-integer pixel positions of reference frames stored in the DPB 64. For example, the video encoder 20 may interpolate values of one-quarter pixel positions, one- eighth pixel positions, or other fractional pixel positions of the reference frame. Therefore, the motion estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.

[0075] The motion estimation unit 42 calculates a motion vector for a video block in an inter prediction coded frame by comparing the position of the video block to the position of a predictive block of a reference frame selected from a first reference frame list (List 0) or a second reference frame list (List 1), each of which identifies one or more reference frames stored in the DPB 64. The motion estimation unit 42 sends the calculated motion vector to the motion compensation unit 44 and then to the entropy encoding unit 56.

[0076] Motion compensation, performed by the motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by the motion estimation unit 42. Upon receiving the motion vector for the current video block, the motion compensation unit 44 may locate a predictive block to which the motion vector points in one of the reference frame lists, retrieve the predictive block from the DPB 64, and forward the predictive block to the summer 50. The summer 50 then forms a residual video block of pixel difference values by subtracting pixel values of the predictive block provided by the motion compensation unit 44 from the pixel values of the current video block being coded. The pixel difference values forming the residual video block may include luma or chroma component differences or both. The motion compensation unit 44 may also generate syntax elements associated with the video blocks of a video frame for use by the video decoder 30 in decoding the video blocks of the video frame. The syntax elements may include, for example, syntax elements defining the motion vector used to identify the predictive block, any flags indicating the prediction mode, or any other syntax information described herein. Note that the motion estimation unit 42 and the motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.

[0077] In some implementations, the intra BC unit 48 may generate vectors and fetch predictive blocks in a manner similar to that described above in connection with the motion estimation unit 42 and the motion compensation unit 44, but with the predictive blocks being in the same frame as the current block being coded and with the vectors being referred to as block vectors as opposed to motion vectors. In particular, the intra BC unit 48 may determine an intra-prediction mode to use to encode a current block. In some examples, the intra BC unit 48 may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and test their performance through rate-distortion analysis. Next, the intra BC unit 48 may select, among the various tested intra-prediction modes, an appropriate intra-prediction mode to use and generate an intra-mode indicator accordingly. For example, the intra BC unit 48 may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and select the intra-prediction mode having the best rate-distortion characteristics among the tested modes as the appropriate intra-prediction mode to use. Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bitrate (i.e., a number of bits) used to produce the encoded block. Intra BC unit 48 may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

[0078] In other examples, the intra BC unit 48 may use the motion estimation unit 42 and the motion compensation unit 44, in whole or in part, to perform such functions for Intra BC prediction according to the implementations described herein. In either case, for Intra block copy, a predictive block may be a block that is deemed as closely matching the block to be coded, in terms of pixel difference, which may be determined by SAD, SSD, or other difference metrics, and identification of the predictive block may include calculation of values for sub-integer pixel positions.

[0079] Whether the predictive block is from the same frame according to intra prediction, or a different frame according to inter prediction, the video encoder 20 may form a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values. The pixel difference values forming the residual video block may include both luma and chroma component differences.

[0080] The intra prediction processing unit 46 may intra-predict a current video block, as an alternative to the inter-prediction performed by the motion estimation unit 42 and the motioncompensation unit 44, or the intra block copy prediction performed by the intra BC unit 48, as described above. In particular, the intra prediction processing unit 46 may determine an intra prediction mode to use to encode a current block. To do so, the intra prediction processing unit 46 may encode a current block using various intra prediction modes, e.g., during separate encoding passes, and the intra prediction processing unit 46 (or a mode selection unit, in some examples) may select an appropriate intra prediction mode to use from the tested intra prediction modes. The intra prediction processing unit 46 may provide information indicative of the selected intraprediction mode for the block to the entropy encoding unit 56. The entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode in the bitstream.

[0081] After the prediction processing unit 41 determines the predictive block for the current video block via either inter prediction or intra prediction, the summer 50 forms a residual video block by subtracting the predictive block from the current video block. The residual video data in the residual block may be included in one or more TUs and is provided to the transform processing unit 52. The transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform, such as a Discrete Cosine Transform (DCT) or a conceptually similar transform.

[0082] The transform processing unit 52 may send the resulting transform coefficients to the quantization unit 54. The quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process may also reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, the quantization unit 54 may then perform a scan of a matrix including the quantized transform coefficients. Alternatively, the entropy encoding unit 56 may perform the scan.

[0083] Following quantization, the entropy encoding unit 56 entropy encodes the quantized transform coefficients into a video bitstream using, e.g., Context Adaptive Variable Length Coding (CAVLC), Context Adaptive Binary Arithmetic Coding (CAB AC), Syntax-based context-adaptive Binary Arithmetic Coding (SBAC), Probability Interval Partitioning Entropy (PIPE) coding or another entropy encoding methodology or technique. The encoded bitstream may then be transmitted to the video decoder 30 as shown in FIG. 1, or archived in the storage device 32 as shown in FIG. 1 for later transmission to or retrieval by the video decoder 30. The entropy encoding unit 56 may also entropy encode the motion vectors and the other syntax elements for the current video frame being coded.

[0084] The inverse quantization unit 58 and the inverse transform processing unit 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual video block in the pixel domain for generating a reference block for prediction of other video blocks. As noted above, the motion compensation unit 44 may generate a motion compensated predictive block from one or more reference blocks of the frames stored in the DPB 64. The motion compensation unit 44 may also apply one or more interpolation fdters to the predictive block to calculate sub-integer pixel values for use in motion estimation.

[0085] The summer 62 adds the reconstructed residual block to the motion compensated predictive block produced by the motion compensation unit 44 to produce a reference block for storage in the DPB 64. The reference block may then be used by the intra BC unit 48, the motion estimation unit 42 and the motion compensation unit 44 as a predictive block to inter predict another video block in a subsequent video frame.

[0086] FIG. 3 is a block diagram illustrating an exemplary video decoder 30 in accordance with some implementations of the present application. The video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, a summer 90, and a DPB 92. The prediction processing unit 81 further includes a motion compensation unit 82, an intra prediction unit 84, and an intra BC unit 85. The video decoder 30 may perform a decoding process generally reciprocal to the encoding process described above with respect to the video encoder 20 in connection with FIG. 2. For example, the motion compensation unit 82 may generate prediction data based on motion vectors received from the entropy decoding unit 80, while the intra-prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from the entropy decoding unit 80.

[0087] In some examples, a unit of the video decoder 30 may be tasked to perform the implementations of the present application. Also, in some examples, the implementations of the present disclosure may be divided among one or more of the units of the video decoder 30. For example, the intra BC unit 85 may perform the implementations of the present application, alone, or in combination with other units of the video decoder 30, such as the motion compensation unit 82, the intra prediction unit 84, and the entropy decoding unit 80. In some examples, the video decoder 30 may not include the intra BC unit 85 and the functionality of intra BC unit 85 may be performed by other components of the prediction processing unit 81, such as the motioncompensation unit 82.

[0088] The video data memory 79 may store video data, such as an encoded video bitstream, to be decoded by the other components of the video decoder 30. The video data stored in the video data memory 79 may be obtained, for example, from the storage device 32, from a local video source, such as a camera, via wired or wireless network communication of video data, or by accessing physical data storage media (e.g., a flash drive or hard disk). The video data memory 79 may include a Coded Picture Buffer (CPB) that stores encoded video data from an encoded video bitstream. The DPB 92 of the video decoder 30 stores reference video data for use in decoding video data by the video decoder 30 (e.g., in intra or inter predictive coding modes). The video data memory 79 and the DPB 92 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including Synchronous DRAM (SDRAM), Magnetoresistive RAM (MRAM), Resistive RAM (RRAM), or other types of memory devices. For illustrative purpose, the video data memory 79 and the DPB 92 are depicted as two distinct components of the video decoder 30 in FIG. 3. But it will be apparent to one skilled in the art that the video data memory 79 and the DPB 92 may be provided by the same memory device or separate memory devices. In some examples, the video data memory 79 may be on-chip with other components of the video decoder 30, or off-chip relative to those components.

[0089] During the decoding process, the video decoder 30 receives an encoded video bitstream that represents video blocks of an encoded video frame and associated syntax elements. The video decoder 30 may receive the syntax elements at the video frame level and / or the video block level. The entropy decoding unit 80 of the video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. The entropy decoding unit 80 then forwards the motion vectors or intra-prediction mode indicators and other syntax elements to the prediction processing unit 81.

[0090] When the video frame is coded as an intra predictive coded (I) frame or for intra coded predictive blocks in other types of frames, the intra prediction unit 84 of the prediction processing unit 81 may generate prediction data for a video block of the current video frame based on a signaled intra prediction mode and reference data from previously decoded blocks of the current frame.

[0091] When the video frame is coded as an inter-predictive coded (i.e., B or P) frame, the motion compensation unit 82 of the prediction processing unit 81 produces one or more predictive blocksfor a video block of the current video frame based on the motion vectors and other syntax elements received from the entropy decoding unit 80. Each of the predictive blocks may be produced from a reference frame within one of the reference frame lists. The video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference frames stored in the DPB 92.

[0092] In some examples, when the video block is coded according to the intra BC mode described herein, the intra BC unit 85 of the prediction processing unit 81 produces predictive blocks for the current video block based on block vectors and other syntax elements received from the entropy decoding unit 80. The predictive blocks may be within a reconstructed region of the same picture as the current video block defined by the video encoder 20.

[0093] The motion compensation unit 82 and / or the intra BC unit 85 determines prediction information for a video block of the current video frame by parsing the motion vectors and other syntax elements, and then uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, the motion compensation unit 82 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code video blocks of the video frame, an inter prediction frame type (e.g., B or P), construction information for one or more of the reference frame lists for the frame, motion vectors for each inter predictive encoded video block of the frame, inter prediction status for each inter predictive coded video block of the frame, and other information to decode the video blocks in the current video frame.

[0094] Similarly, the intra BC unit 85 may use some of the received syntax elements, e.g., a flag, to determine that the current video block was predicted using the intra BC mode, construction information of which video blocks of the frame are within the reconstructed region and should be stored in the DPB 92, block vectors for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information to decode the video blocks in the current video frame.

[0095] The motion compensation unit 82 may also perform interpolation using the interpolation filters as used by the video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, the motion compensation unit 82 may determine the interpolation filters used by the video encoder 20 from the received syntax elements and use the interpolation filters to produce predictive blocks.

[0096] The inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by the entropy decoding unit 80 using the same quantization parameter calculated by the video encoder 20 for each video block in the video frame to determine a degree of quantization. The inverse transform processing unit 88 applies an inverse transform, e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to reconstruct the residual blocks in the pixel domain.

[0097] After the motion compensation unit 82 or the intra BC unit 85 generates the predictive block for the current video block based on the vectors and other syntax elements, the summer 90 reconstructs decoded video block for the current video block by summing the residual block from the inverse transform processing unit 88 and a corresponding predictive block generated by the motion compensation unit 82 and the intra BC unit 85. An in-loop filter 91 such as deblocking filter, SAO filter, CCSAO filter and / or ALF may be positioned between the summer 90 and the DPB 92 to further process the decoded video block. In some examples, the in-loop filter 91 may be omitted, and the decoded video block may be directly provided by the summer 90 to the DPB 92. The decoded video blocks in a given frame are then stored in the DPB 92, which stores reference frames used for subsequent motion compensation of next video blocks. The DPB 92, or a memory device separate from the DPB 92, may also store decoded video for later presentation on a display device, such as the display device 34 of FIG. 1.

[0098] In a typical video coding process, a video sequence typically includes an ordered set of frames or pictures. Each frame may include three sample arrays, denoted SL, SCb, and SCr. SL is a two-dimensional array of luma samples. SCb is a two-dimensional array of Cb chroma samples. SCr is a two-dimensional array of Cr chroma samples. In other instances, a frame may be monochrome and therefore includes only one two-dimensional array of luma samples.

[0099] As shown in FIG. 4A, the video encoder 20 (or more specifically the partition unit 45) generates an encoded representation of a frame by first partitioning the frame into a set of CTUs. A video frame may include an integer number of CTUs ordered consecutively in a raster scan order from left to right and from top to bottom. Each CTU is a largest logical coding unit and the width and height of the CTU are signaled by the video encoder 20 in a sequence parameter set, such that all the CTUs in a video sequence have the same size being one of 128x 128, 64x64, 32x32, and 16x 16. But it should be noted that the present application is not necessarily limited to a particularsize. As shown in FIG. 4B, each CTU may comprise one CTB of luma samples, two corresponding coding tree blocks of chroma samples, and syntax elements used to code the samples of the coding tree blocks. The syntax elements describe properties of different types of units of a coded block of pixels and how the video sequence can be reconstructed at the video decoder 30, including inter or intra prediction, intra prediction mode, motion vectors, and other parameters. In monochrome pictures or pictures having three separate color planes, a CTU may comprise a single coding tree block and syntax elements used to code the samples of the coding tree block. A coding tree block may be an NxN block of samples.

[0100] To achieve a better performance, the video encoder 20 may recursively perform tree partitioning such as binary-tree partitioning, ternary-tree partitioning, quad-tree partitioning or a combination thereof on the coding tree blocks of the CTU and divide the CTU into smaller CUs. As depicted in FIG. 4C, the 64x64 CTU 400 is first divided into four smaller CUs, each having a block size of 32x32. Among the four smaller CUs, CU 410 and CU 420 are each divided into four CUs of 16x16 by block size. The two 16x16 CUs 430 and 440 are each further divided into four CUs of 8x8 by block size. FIG. 4D depicts a quad-tree data structure illustrating the end result of the partition process of the CTU 400 as depicted in FIG. 4C, each leaf node of the quad-tree corresponding to one CU of a respective size ranging from 32x32 to 8x8. Like the CTU depicted in FIG. 4B, each CU may comprise a CB of luma samples and two corresponding coding blocks of chroma samples of a frame of the same size, and syntax elements used to code the samples of the coding blocks. In monochrome pictures or pictures having three separate color planes, a CU may comprise a single coding block and syntax structures used to code the samples of the coding block. It should be noted that the quad-tree partitioning depicted in FIGS. 4C and 4D is only for illustrative purposes and one CTU can be split into CUs to adapt to varying local characteristics based on quad / ternary / binary-tree partitions. In the multi-type tree structure, one CTU is partitioned by a quad-tree structure and each quad-tree leaf CU can be further partitioned by a binary and ternary tree structure. As shown in FIG. 4E, there are five possible partitioning types of a coding block having a width W and a height H, i.e., quaternary partitioning, horizontal binary partitioning, vertical binary partitioning, horizontal ternary partitioning, and vertical ternary partitioning.

[0101] In some implementations, the video encoder 20 may further partition a coding block of a CU into one or more MxN PBs. APB is a rectangular (square or non-square) block of samples onwhich the same prediction, inter or intra, is applied. A PU of a CU may comprise a PB of luma samples, two corresponding PBs of chroma samples, and syntax elements used to predict the PBs. In monochrome pictures or pictures having three separate color planes, a PU may comprise a single PB and syntax structures used to predict the PB. The video encoder 20 may generate predictive luma, Cb, and Cr blocks for luma, Cb, and Cr PBs of each PU of the CU.

[0102] The video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If the video encoder 20 uses intra prediction to generate the predictive blocks of a PU, the video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the frame associated with the PU. If the video encoder 20 uses inter prediction to generate the predictive blocks of a PU, the video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more frames other than the frame associated with the PU.

[0103] After the video encoder 20 generates predictive luma, Cb, and Cr blocks for one or more PUs of a CU, the video encoder 20 may generate a luma residual block for the CU by subtracting the CU’s predictive luma blocks from its original luma coding block such that each sample in the CU’s luma residual block indicates a difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block. Similarly, the video encoder 20 may generate a Cb residual block and a Cr residual block for the CU, respectively, such that each sample in the CU's Cb residual block indicates a difference between a Cb sample in one of the CU's predictive Cb blocks and a corresponding sample in the CU's original Cb coding block and each sample in the CU's Cr residual block may indicate a difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.

[0104] Furthermore, as illustrated in FIG. 4C, the video encoder 20 may use quad-tree partitioning to decompose the luma, Cb, and Cr residual blocks of a CU into one or more luma, Cb, and Cr transform blocks respectively. Atransform block is a rectangular (square or non-square) block of samples on which the same transform is applied. A TU of a CU may comprise a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax elements used to transform the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. In some examples, the luma transform block associated with the TU may be a sub-block of the CU's luma residualblock. The Cb transform block may be a sub-block of the CU's Cb residual block. The Cr transform block may be a sub-block of the CU's Cr residual block. In monochrome pictures or pictures having three separate color planes, a TU may comprise a single transform block and syntax structures used to transform the samples of the transform block.

[0105] The video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. A coefficient block may be a two-dimensional array of transform coefficients. A transform coefficient may be a scalar quantity. The video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU. The video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.

[0106] After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block or a Cr coefficient block), the video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. After the video encoder 20 quantizes a coefficient block, the video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, the video encoder 20 may perform CABAC on the syntax elements indicating the quantized transform coefficients. Finally, the video encoder 20 may output a bitstream that includes a sequence of bits that forms a representation of coded frames and associated data, which is either saved in the storage device 32 or transmitted to the destination device 14.

[0107] After receiving a bitstream generated by the video encoder 20, the video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. The video decoder 30 may reconstruct the frames of the video data based at least in part on the syntax elements obtained from the bitstream. The process of reconstructing the video data is generally reciprocal to the encoding process performed by the video encoder 20. For example, the video decoder 30 may perform inverse transforms on the coefficient blocks associated with TUs of a current CU to reconstruct residual blocks associated with the TUs of the current CU. The video decoder 30 also reconstructs the coding blocks of the current CU by adding the samples of the predictive blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. After reconstructing the coding blocks for each CU of a frame, video decoder 30 may reconstruct the frame.

[0108] As noted above, video coding achieves video compression using primarily two modes, i.e., intra-frame prediction (or intra-prediction) and inter-frame prediction (or inter-prediction). It is noted that IBC could be regarded as either intra-frame prediction or a third mode. Between the two modes, inter-frame prediction contributes more to the coding efficiency than intra-frame prediction because of the use of motion vectors for predicting a current video block from a reference video block.

[0109] But with the ever improving video data capturing technology and more refined video block size for preserving details in the video data, the amount of data required for representing motion vectors for a current frame also increases substantially. One way of overcoming this challenge is to benefit from the fact that not only a group of neighboring CUs in both the spatial and temporal domains have similar video data for predicting purpose but the motion vectors between these neighboring CUs are also similar. Therefore, it is possible to use the motion information of spatially neighboring CUs and / or temporally co-located CUs as an approximation of the motion information (e.g., motion vector) of a current CU by exploring their spatial and temporal correlation, which is also referred to as “Motion Vector Predictor (MVP)” of the current CU.

[0110] Instead of encoding, into the video bitstream, an actual motion vector of the current CU determined by the motion estimation unit 42 as described above in connection with FIG. 2, the motion vector predictor of the current CU is subtracted from the actual motion vector of the current CU to produce a Motion Vector Difference (MVD) for the current CU. By doing so, there is no need to encode the motion vector determined by the motion estimation unit 42 for each CU of a frame into the video bitstream and the amount of data used for representing motion information in the video bitstream can be significantly decreased.

[0111] Like the process of choosing a predictive block in a reference frame during inter-frame prediction of a code block, a set of rules need to be adopted by both the video encoder 20 and the video decoder 30 for constructing a motion vector candidate list (also known as a “merge list”) for a current CU using those potential candidate motion vectors associated with spatially neighboring CUs and / or temporally co-located CUs of the current CU and then selecting one member from the motion vector candidate list as a motion vector predictor for the current CU. By doing so, there is no need to transmit the motion vector candidate list itself from the video encoder 20 to the video decoder 30 and an index of the selected motion vector predictor within the motion vector candidatelist is sufficient for the video encoder 20 and the video decoder 30 to use the same motion vector predictor within the motion vector candidate list for encoding and decoding the current CU.

[0112] The main focus of this disclosure is to further enhance the Intra Block Copy method by either improving the coding efficiency and / or reducing its coding complexities.

[0113] Affine model

[0114] In HEVC, only translation motion model is applied for motion compensated prediction. While in the real world, there are many kinds of motion, e.g. zoom in / out, rotation, perspective motions and other irregular motions. In the WC, affine motion compensated prediction is applied by signaling one flag for each inter coding block to indicate whether the translation motion model or the affine motion model is applied for inter prediction. In the current WC, two affine modes, including 4-paramter affine mode and 6-parameter affine mode, are supported for one affine coding block.

[0115] The 4-parameter affine model has the following parameters: two parameters for translation movement in horizontal and vertical directions respectively, one parameter for zoom motion and one parameter for rotational motion for both directions. In this model, horizontal zoom parameter is equal to vertical zoom parameter, and horizontal rotation parameter is equal to vertical rotation parameter. To achieve a better accommodation of the motion vectors and affine parameter, those affine parameters are to be derived from two MVs (which are also called control point motion vector (CPMV)) located at the top-left corner and top-right corner of a current block. As shown in FIG. 4, the affine motion field of the block is described by two CPMVs (Vo, Vi). Based on the control point motion, the motion field (w, vy) of one affine coded block is described as

[0116] The 6-parameter affine mode has the following parameters: two parameters for translation movement in horizontal and vertical directions respectively, two parameters for zoom motion and rotation motion respectively in horizontal direction, another two parametersfor zoom motion and rotation motion respectively in vertical direction. The 6-parameter affine motion model is coded with three CPMVs. As shown in FIG. 5, the three control points of one 6-paramter affine block are located at the top-left, top-right and bottom left corner of the block. The motion at top-left control point is related to translation motion, and the motion at topright control point is related to rotation and zoom motion in horizontal direction, and the motion at bottom-left control point is related to rotation and zoom motion in vertical direction. Compared to the 4-parameter affine motion model, the rotation and zoom motion in horizontal direction of the 6-parameter may not be same as those motion in vertical direction. Assuming (Vo, Vi, V2) are the MVs of the top-left, top-right and bottom-left corners of the current block in FIG. 5, the motion vector of each sub-block (v y7) is derived using the three MVs at control points as:

[0117] Affine merge mode

[0118] In affine merge mode, the CPMVs for the current block are not explicitly signaled but derived from neighboring blocks. Specifically, in this mode, motion information of spatial neighbor blocks is used to generate CPMVs for the current block. The affine merge mode candidate list has a limited size. For example, in the current WC design, there may be up to five candidates. The encoder may evaluate and choose the best candidate index based on ratedistortion optimization algorithms. The chosen candidate index is then signaled to the decoder side. The affine merge candidates can be decided in three ways:

[0119] Inherited from neighboring affine coded blocks

[0120] Constructed from translational MVs from neighboring blocks

[0121] Zero MVs

[0122] For the inherited method, there may be up to two candidates. The candidates are obtained from the neighboring blocks located at the bottom-left of the current block (e.g., scanning order is from A0 to Al as shown in FIG. 6) and from the neighboring blocks locatedat the top-right of the current block (e.g., scanning order is from BO to B2 as shown in FIG. 6), if available.

[0123] For the constructed method, the candidates are the combinations of neighbor’s translational MVs, which are generated by two steps.

[0124] Step 1: obtain four translational MVs from available neighbors.

[0125] MV1: MV from the one of the three neighboring blocks close to the top-left corner of the current block. As shown in the FIG. 7, the scanning order is B2, B3 and A2.

[0126] MV2: MV from the one of the one from the two neighboring blocks close to the topright corner of the current block. As shown in the FIG. 7, the scanning order is Bland B0.

[0127] MV3: MV from the one of the one from the two neighboring blocks close to the bottom-left corner of the current block. As shown in the FIG. 7, the scanning order is Aland A0.

[0128] MV4: MV from the temporally collocated block of the neighboring block close to the bottom-right corner of current block. As shown in the Fig, the neighboring block is T.

[0129] Step 2: derive combinations based on the four translational MVs from step 1.

[0130] Combination 1: MV1, MV2, MV3

[0131] Combination 2: MV1, MV2, MV4

[0132] Combination 3: MV1, MV3, MV4

[0133] Combination 4: MV2, MV3, MV4

[0134] Combination 5: MV1, MV2

[0135] Combination 6: MV1, MV3

[0136] When the merge candidate list is not full after filling with inherited and constructed candidates, zero MVs are inserted at the end of the list.

[0137] Affine AMVP mode

[0138] Affine AMVP (advanced motion vector prediction) mode may be applied for CUs with both width and height larger than or equal to 16. An affine flag in CU level is signalled in the bitstream to indicate whether affine AMVP mode is used and then another flag is signalled toindicate whether 4-parameter affine or 6-parameter affine. In this mode, the difference of the CPMVs of current CU and their predictors CPMVPs is signalled in the bitstream. The affine AMVP candidate list size is 2 and the affine AMVP candidate list is generated by using the following four types of CPMV candidate in order:

[0139] Inherited affine AMVP candidates that extrapolated from the CPMVs of the neighbour CUs

[0140] Constructed affine AMVP candidates CPMVPs that are derived using the translational MVs of the neighbour CUs

[0141] Translational MVs from neighboring CUs

[0142] Temporal MVs from collocated CUs

[0143] Zero MVs

[0144] The checking order of inherited affine AMVP candidates is the same to the checking order of inherited affine merge candidates. The only difference is that, for AMVP candidate, only the affine CU that has the same reference picture as in current block is considered. No pruning process is applied when inserting an inherited affine motion predictor into the candidate list.

[0145] Constructed AMVP candidate is derived from the same spatial neighbors as affine merge mode. The same checking order is used as done in affine merge candidate construction. In addition, reference picture index of the neighboring block is also checked. The first block in the checking order that is inter coded and has the same reference picture as in current CUs is used. When the current CU is coded with 4-parameter affine mode, and mvo and m are both available, mvo and mware added as one candidate in the affine AMVP candidate list. When the current CU is coded with 6-parameter affine mode, and all three CPMVs are available, they are added as one candidate in the affine AMVP candidate list. Otherwise, constructed AMVP candidate is set as unavailable.

[0146] If the number of affine AMVP list candidates is still less than 2 after valid inherited affine AMVP candidates and constructed AMVP candidate are inserted, mvo, inv / and / ni^willbe added, in order, as the translational MVs to predict all control point MVs of the current CU, when available. Finally, zero MVs are used to fill the affine AMVP list if it is still not full.

[0147] Intra block copy in Versatile Video Coding (VVC)

[0148] Intra block copy (IBC) is a tool adopted in HEVC extensions on SCC. It is well known that it significantly improves the coding efficiency of screen content materials. Since IBC mode is implemented as a block level coding mode, block matching (BM) is performed at the encoder to find the optimal block vector (or motion vector) for each CU. Here, a block vector is used to indicate the displacement from the current block to a reference block, which is already reconstructed inside the current picture. The luma block vector of an IBC-coded CU is in integer precision. The chroma block vector rounds to integer precision as well. When combined with AMVR, the IBC mode can switch between 1-pel and 4-pel motion vector precisions. An IBC- coded CU is treated as the third prediction mode other than intra or inter prediction modes. The IBC mode is applicable to the CUs with both width and height smaller than or equal to 64 luma samples.

[0149] At the encoder side, hash-based motion estimation is performed for IBC. The encoder performs RD check for blocks with either width or height no larger than 16 luma samples. For non-merge mode, the block vector search is performed using hash-based search first. If hash search does not return valid candidate, block matching based local search will be performed.

[0150] In the hash-based search, hash key matching (32-bit CRC) between the current block and a reference block is extended to all allowed block sizes. The hash key calculation for every position in the current picture is based on 4x4 subblocks. For the current block of a larger size, a hash key is determined to match that of the reference block when all the hash keys of all 4*4 subblocks match the hash keys in the corresponding reference locations. If hash keys of multiple reference blocks are found to match that of the current block, the block vector costs of each matched reference are calculated and the one with the minimum cost is selected.

[0151] In block matching search, the search range is set to cover both the previous and current CTUs.

[0152] At CU level, IBC mode is signalled with a flag and it can be signaled as IBC AMVP mode or IBC skip / merge mode as follows:- IBC skip / merge mode: a merge candidate index is used to indicate which of the block vectors in the list from neighboring candidate IBC coded blocks is used to predict the current block. The merge list consists of spatial, HMVP, and pairwise candidates.- IBC AMVP mode: block vector difference is coded in the same way as a motion vector difference. The block vector prediction method uses two candidates as predictors, one from left neighbor and one from above neighbor (if IBC coded). When either neighbor is not available, a default block vector will be used as a predictor. A flag is signaled to indicate the block vector predictor index.

[0153] IBC reference region

[0154] To reduce memory consumption and decoder complexity, the IBC in VVC allows only the reconstructed portion of the predefined area including the region of current CTU and some region of the left CTU. FIG. 8 illustrates the reference region of IBC Mode, where each block represents 64x64 luma sample unit.

[0155] Intra block copy in Enhanced Compression Model (ECM)

[0156] In ECM, IBC is improved from aspects below.

[0157] IBC merge / AMVP list construction

[0158] The IBC merge / AMVP list construction is modified as follows:• Only if an IBC merge / AMVP candidate is valid, it can be inserted into the IBC merge / AMVP candidate list.• Above-right, bottom-left, and above-left spatial candidates and one pairwise average candidate can be added into the IBC merge / AMVP candidate list.• Template based adaptive reordering (ARMC-TM) is applied to IBC merge list.

[0159] Three candidates are located on the nearest corners of the reference region, and three additional candidates are determined in the middle of the three sub-regions (A, B, and C), whose coordinates are determined by the width, and height of the current block and the AX and AY parameters, as is depicted in FIG. 9.

[0160] IBC with Template Matching

[0161] Template Matching is used in IBC for both IBC merge mode and IBC AMVP mode.

[0162] The IBC-TM merge list is modified compared to the one used by regular IBC merge mode such that the candidates are selected according to a pruning method with a motion distance between the candidates as in the regular TM merge mode. The ending zero motion fulfillment is replacedby motion vectors to the left (-W, 0), top (0, -H) and top-left (-W, -H), where W is the width and H the height of the current CU.

[0163] In the IBC-TM merge mode, the selected candidates are refined with the Template Matching method prior to the RDO or decoding process. The IBC-TM merge mode has been put in competition with the regular IBC merge mode and a TM-merge flag is signaled.

[0164] In the IBC-TM AMVP mode, up to 3 candidates are selected from the IBC-TM merge list. Each of those 3 selected candidates are refined using the Template Matching method and sorted according to their resulting Template Matching cost. Only the 2 first ones are then considered in the motion estimation process as usual.

[0165] The Template Matching refinement for both IBC-TM merge and AMVP modes is quite simple since IBC motion vectors are constrained (i) to be integer and (ii) within a reference region as shown in FIG. 8. So, in IBC-TM merge mode, all refinements are performed at integer precision, and in IBC-TM AMVP mode, they are performed either at integer or 4-pel precision depending on the AMVR value. Such a refinement accesses only to samples without interpolation. In both cases, the refined motion vectors and the used template in each refinement step must respect the constraint of the reference region.

[0166] IBC reference area

[0167] The reference area for IBC is extended to two CTU rows above. FIG. 10 illustrates the reference area for coding CTU (m,n).

[0168] IBC adaptation for camera-captured content

[0169] When adapt IBC for camera-captured content, IBC reference range is reduced from 2 CTU rows to 2x128 rows as shown in FIG. 11. At encoder side to reduce the complexity, the local search range is set to [-8,8] horizontally and [-8,8] vertically centered at the first block vector predictor of the current CU. This encoder modification is not applied to SCC sequences.

[0170] Subblock-based temporal motion vector prediction (SbTMVP)

[0171] The SbTMVP process is illustrated in FIGS. 13A-13B. SbTMVP predicts the motion vectors of the sub-CUs within the current CU in two steps. In the first step, the spatial neighbor Al in FIG. 13A is examined. In the second step, the motion shift identified in Step 1 is applied (i.e., added to the current block’s coordinates) to obtain sub-CU-level motion information (motion vectors and reference indices) from the collocated picture as shown in FIG. 13B.

[0172] Intra template matching

[0173] Intra template matching prediction (Intra TMP) is a special intra prediction mode that copies the best prediction block from the reconstructed part of the current frame, whose L-shaped template matches the current template. For a predefined search range, the encoder searches for the most similar template to the current template in a reconstructed part of the current frame and uses the corresponding block as a prediction block. The encoder then signals the usage of this mode, and the same prediction operation is performed at the decoder side.

[0174] The prediction signal is generated by matching the L-shaped causal neighbor of the current block with another block in a predefined search area in FIG. 15 consisting of:R1 : current CTUR2: top-left CTUR3 : above CTUR4: left CTU

[0175] Sum of absolute differences (SAD) is used as a cost function.

[0176] Within each region, the decoder searches for the template that has the minimum SAD with respect to the current one and uses its corresponding block as a prediction block.

[0177] Within each region, the decoder constructs a candidate list of up to 19 template matching block vectors that are ranked in ascending order according to the template cost (SAD). The following modes are supported:

[0178] First is single predictor: a single predictor is selected from the candidate list.

[0179] Second is fusion of multiple predictors: multiple predictors are blended multiple to derive the final prediction block. The blending weights are either computed from the template matching cost of each predictor, or with Wiener-filter based weight derivation method.

[0180] Third is sub-pel precision: when single predictor is used, sub-pel precision can be used with 1 / 2-pel precision, 1 / 4-pel precision, or 3 / 4-pel precision, each with 8 possible directions.

[0181] Fourth is linear filter model: a linear filter can be learned between the reference template and current template and apply the linear model to reference block. This mode can be used for single predictor when sub-pel precision is not used.

[0182] The dimensions of all regions (SearchRange w, SearchRange h) are set proportional to the block dimension (BlkW, BlkH) to have a fixed number of SAD comparisons per pixel. That is:SearchRange w = a * BlkWSearchRange h = a * BlkH where ‘a’ is a constant that controls the gain / complexity trade-off. In practice, ‘a’is equal to 5.

[0183] To speed-up the template matching process, the search range of all search regions is subsampled by a factor of 3. After finding the best match, a refinement process is performed. The refinement is done via a second template matching search around the best match with a reduced range.

[0184] The Intra template matching tool is enabled for CUs with size less than or equal to 64 in width and height. This maximum CU size for Intra template matching is configurable.

[0185] The Intra template matching prediction mode is signaled at CU level through a dedicated flag when DIME) is not used for current CU.

[0186] IBC with local illumination compensation (IBC-LIC)

[0187] Intra block copy with local illumination compensation (IBC-LIC) is a coding tool which compensates the local illumination variation within a picture between the CU coded with IBC and its prediction block with a linear equation. The parameters of the linear equation are derived same as LIC for inter prediction except that the reference template is generated using block vector in IBC-LIC. IBC-LIC can be applied to IBC AMVP mode and IBC merge mode. For IBC AMVP mode, an IBC-LIC flag is signalled to indicate the use of IBC-LIC. For IBC merge mode, the IBC- LIC flag is inferred from the merge candidate.

[0188] IntraTMP derived block vector candidates for IBC

[0189] In this method block vector (BV) derived from the intra template matching prediction (IntraTMP) is used for intra block copy (IBC). The stored IntraTMP BV of the neighbouring blocks along with IBC BV are used as spatial BV candidates in IBC candidate list construction.

[0190] IntraTMP block vector is stored in the IBC block vector buffer, and the current IBC block can use both IBC BV and IntraTMP BV of neighbouring blocks as BV candidate for IBC BV candidate list as shown in FIG. 21. IntraTMP block vectors are added to IBC block vector candidate list as spatial candidates.

[0191] Spatial Geometric partitioning mode (SGPM)

[0192] SGPM is an intra mode that resembles the inter coding tool of GPM, where the two prediction parts are generated from intra predicted process. In this mode, a candidate list is built with each entry containing one partition split and two intra prediction modes. 26 partition modesand 3 of intra prediction modes are used to form the combinations, the length of the candidate list is set equal to 16. The selected candidate index is signalled.

[0193] Decoder side intra mode derivation (DIMD)

[0194] When DIMD is applied, up to five intra modes are derived from the reconstructed neighbor samples, and those five predictors are combined with the planar mode predictor with the weights derived from the histogram of gradients.

[0195] SGPM with IntraTMP and IBC

[0196] In this mode, SGPM mode tests block vectors of neighboring CU’s in addition to regular prediction modes. Specifically, the following steps are performed sequentially:

[0197] Obtain block vectors of all merge candidates (e.g., from the spatial neighboring blocks coded either with IBC mode or IntraTMP mode).

[0198] Select the best block vector according to SATD template cost

[0199] Test up to 6 best block vectors (if available) inside SGPM candidate list construction.

[0200] IntraTMP extension to DIMD

[0201] In the DIMD mode, up to five intra modes may be derived from the reconstructed neighbor samples. The final prediction is generated by blending up to five predictors and the planar mode predictor with the weights derived from the histogram of gradients. In this extension mode, it adaptively selects between planar or block-vector based prediction obtained from IntraTMP or IBC mode of neighboring blocks for the blending with an angular intra prediction.

[0202] IntraTMP extension to LIC

[0203] This mode extends the usage of Local Illumination Compensation to Intra- TMP prediction mode, in addition to the IBC and Inter coding modes. A CU-level flag is signaled to indicate the use of LIC at luma block level. For screen content coding, the Intra- TMP LIC mode is extended to support top-only, left-only for computing single linear model parameters. MMLM is also supported for Intra TMP -LIC mode in screen content coding. Specifically:

[0204] The LIC usage for an IntraTMP mode is signaled through a CU-level flag;

[0205] Usages of LIC and FLM (CCCM-like filtering) are mutually exclusive for a given CU;

[0206] Usages of LIC together with fusion in intra TMP is allowed;

[0207] Top-only and Left-only template usage for LIC model determination is allowed for screen content coding. For camera-captured coding, only the top-left template is employed;

[0208] Multi Mode Linear Model (MMLM) is suppored similarly to IBC-LIC, for screen content coding;

[0209] When LIC is used for a given CU, the Intra TMP search process employs MRSAD rather than SAD distortion function to search for block vector.

[0210] Fusion for template-based intra mode derivation (TIMD)

[0211] For each intra prediction mode in MPMs, as well as the wide-angle modes if the aboveright and / or bottom-left reference samples are available, SATD between the prediction and reconstruction samples of the template is calculated. First two intra prediction modes with the minimum SATD and one non-angular intra prediction mode (i.e. DC or Planar) with the lowest SATD cost are selected as the TIMD modes. These three TIMD modes are fused with the weights after applying PDPC process, and such weighted intra prediction is used to code the current CU. Position dependent intra prediction combination (PDPC) is included in the derivation of the TIMD modes.

[0212] The conditions below are checked to determine whether the non-angular intra prediction mode is used in fusion:

[0213] the non-angular intra prediction mode is different from the two selected intra prediction modes.

[0214] costMode3 < 1.5*costModel, where the costMode3 is the SATD cost of the non-angular intra prediction mode and costModel is the SATD cost of the first intra prediction mode.

[0215] If both of the conditions are true, three intra prediction modes are used to generate the prediction. And the weights of each intra prediction mode are computed from SATD cost:

[0217] Otherwise, the non-angular intra prediction mode is not used in prediction. And the costs of the two selected modes are compared with a threshold, in the test the cost factor of 2 is applied as follows:

[0218] costMode2 < 2*costModel .

[0219] If this condition is true, the fusion is applied, otherwise only model is used.

[0220] Weights of the modes are computed from their SATD costs as follows:

[0221] weight 1 = costMode2 / (costModel + costMode2)

[0222] weight2 = 1 - weight 1

[0223] The division operations are conducted using the same lookup table (LUT) based integerization scheme used by the CCLM.

[0224] Besides, location-dependent sample-based fusion used in DIMD fusion process is used for the TIMD fusion but the location-dependent criterion applying to amplitudes of the selected predictors is replaced by a SATD cost-based criteria. The location-dependent criterion is determined from a ratio of the normalized SATD of the selected TIMD predictors computed in above and left template area.

[0225] Occurrence-based intra coding (OBIC)

[0226] The occurrence-based intra coding (OBIC) mode derives the intra prediction modes of the current block based on the sample-wise occurrence of the intra modes in the spatial neighborhood of the block. For this, adjacent and non-adjacent spatial neighboring blocks are checked and the intra prediction modes of the blocks are collected into an occurrence histogram. Instead of Histogram of Gradient (HoG) as in DIMD, the OBIC method uses the Histogram of occurrence (HoC), which consists of the intra modes and their sample-wise occurrences. The occurrence values are calculated based on the number of samples that are coded in a certain intra prediction mode in that neighborhood. For example, if a uiWidth x uiHeight block is coded with an IPM mode, the occurrence of the mode in that particular block is calculated as:

[0227] HoC [IPM] += uiWidth * uiHeight;

[0228] Where uiWidth and uiHeight are the width and height of a spatial neighboring block.

[0229] The occurrences of the existing modes from the spatial neighborhood blocks are accumulated into the histogram.

[0230] FIG. 27 shows the non-adjacent spatial neighboring blocks that are used in OBIC mode’s HoC generation.

[0231] Up to five angular modes with the highest occurrence along with the planar mode orblock vector-based prediction (same as in DIMD) are selected from the HoC and used for final prediction by blending the prediction of the selected modes.

[0232] Some blocks, mentioned below, use more than one intra mode for prediction. In such cases, all the intra modes of such blocks are selected and used when creating the OBIC histogram:

[0233] DIMD: up to 5 angular modes

[0234] TIMD: up to 2 modes

[0235] SGPM: 2 modes

[0236] OBTC: up to 5 angular modes

[0237] Moreover, the virtual intra prediction modes (VIPMs) of following blocks are considered only in inter slices when creating the histogram of OBIC mode:

[0238] MIP block

[0239] IntraTMP block

[0240] IBC block

[0241] EIP block

[0242] The blending weights are calculated similarly to the DIMD mode, but instead of using gradient values from the template, the occurrence values are used for OBIC. Moreover, the planar mode’s weight is also decided similarly to DIMD mode.

[0243] The OBIC mode is applied to only luma blocks. Moreover, the mode is disabled forblocks that have less than 64 samples. Usage of the mode is signaled with a CABAC coded PU level flag. The OBIC mode is used as a sub-mode of DIMD and its flag is signaled after DIMD flag.

[0244] In video coding, intra block copy is well known to accurately predict screen content and artificially generated content where patterns and edges may repeat within the frame. Intra block copy may also be beneficial for natural content predictions where the current frame has repeated textures. For the coding scenarios without too much repeated content, the mode of intra block copy may not be selected while its minimum signaling bits are still transmitted. In this case, to further enhance the coding efficiency of intra block copy, it is desired, therefore, to provide more flexible on / off control mechanisms at different granularities.

[0245] In the inter-predicted coding modes, fractional motion vectors are used to improve the prediction accuracy. However, in the current intra block copy mode, only integer motion vectors are used. It is desirable to explore the coding benefits of fractional motion vectors for intra block copy. When fractional motion is used in intra block copy, several subsequent problems need to be resolved: fractional motion derivation, signaling, interpolation padding, interpolation filtering selection, interactions with other coding tools, etc.

[0246] When fractional block / motion vectors are supported in the IBC mode and / or IntraTMP modes, these fractional block / motion vectors may be available to be reused in other coding modes (IBC submodes or / and SGPM, DIMD, TIMD, OBIC, etc.) to improve the coding efficiency of these coding modes.

[0247] In this disclosure, the coding tool of intra block copy is improved from aspects below:• Interpolation based fractional intra block copyo Fractional motion search o Fractional motion refinement o Conditional sample / pixel padding for fractional interpolation o Interpolation filter switch o Multi-hypothesis fractional intra block copy• Signaling of motion information• IBC merge / AMVP motion candidate list construction• Combination with intra template matching• Improvements for IntraTMP mode

[0248] Flexible on / off control mechanisms

[0249] In this section, several methods are proposed to do on / off control for the application of the IBC mode. The on / off control indicates whether the IBC mode is allowed to be possibly enabled for the current sequence, frame, slice, CTU, or block which is at different granularities. If IBC mode is on, further flags (e.g., whether IBC mode is enabled or disabled for a specific block) or / and information (e.g., block vectors) may be signaled. If IBC mode is off, no more flags or information is signaled.

[0250] In some embodiments, the on / off control of intra block copy may be based on explicit signaling methods:

[0251] In one embodiment, the on / off control is based on one or more, sequence level, or frame level, or slice level or Coding tree unit (CTU) level, or block level flag, or any combination of different levels of flags. When any combination of different levels of flags are used, the transmission of lower level of flags are dependent on the on / off of higher level of flags. In one example, if the frame level flag indicates the turned off of IBC mode, no more flags are transmitted at slice or block level. Otherwise, lower level flag(s) is / are further transmitted.

[0252] In another embodiment, the on / off control is based on different regions. The purpose of the region concept is to provide a more flexible granularity for IBC on / off control.

[0253] In one embodiment, the region here may be defined as non-overlapping areas within a frame or a slice or a CTU. For all the blocks located within a specific region, a single on / off control flag may be signed to indicate whether IBC mode is turned off for all these blocks are not. The size of the regions may be predefined as a set of fixed values such as M x N, or a group of signaled values.

[0254] In some other embodiments, the on / off control of intra block copy may be based on local information, and no explicit signaling is required:

[0255] In some embodiments, the on / off control is based on the prediction information.

[0256] In one embodiment, the IBC mode is always turned off for inter predicted blocks.

[0257] In another embodiment, the IBC mode is always turned off for uni-predicted or / and bipredicted inter blocks.

[0258] Yet in another embodiment, the IBC mode is always turned off for blocks which are coded at sub-block modes. The sub-block mode is the mode which divides current block into sub-blocks and each sub-block may have its own motion information. For example, affine mode, SbTMVP mode.

[0259] In another embodiment, the IBC mode is always turned off for blocks which are not coded at sub-block modes.

[0260] In some other embodiments, the on / off control is based on the other coding information

[0261] In one embodiment, the IBC model is always turned off when one or more other coding mode(s) is / are applied for the current block. For example, the IBC mode is always turned off when affine mode is enabled.

[0262] In some other embodiments, the on / off control is based on the frame type.

[0263] In one embodiment, the IBC mode are always turned off for B frame or / and P frame.

[0264] In some other embodiments, the on / off control is based on the block information.

[0265] In one embodiment, the IBC mode is always turned off for coding blocks smaller than a specific size (e.g., 8x8 blocks) or larger than a specific size (e.g., 64x64).

[0266] In one embodiment, the IBC mode is always turned off for wide blocks (e.g., a block with its width is M times longer than its height) or long blocks (e.g., a block with its height is N times longer than its width), while the value of M and N may be fixed values (e.g., M =2, N =3) or signaled at sequence or frame level.

[0267] CABAC context window

[0268] In the current IBC design, there may be one or more IBC mode related flags which are CABAC context coded. For example, the IBC enabling flag at block level is context coded. Since statistics may be different with different slice or frame types, it is desirable to have a context’s probability state updated at a rate that may provide more accurate probability estimation (e.g., tomore accurately predict the likelihood of one bin having the value of 1 or 0) under the given slice / frame type.

[0269] In some embodiments, for each context model related to IBC mode, three windows may be predefined for three different slices, including I, B and P slices, respectively.

[0270] In some embodiments, for each context model related to IBC mode, two windows may be predefined for different slices with two different prediction modes, including intra-predicted (I slice) and inter-predicted slices (B and P slices), respectively.

[0271] Based on the multiple context windows updated under the given slice / frame type, one or more IBC mode related flags (e.g., motion precision, interpolation filter selection for motion compensated block prediction or / and template prediction, etc) may be further signaled by using different context bins.

[0272] In one example, the motion information precision flag may be signaled separately or jointly for different slice / frame type. The signaled motion precision flag may depend on the current supported precision types (e.g., 1 -pel, 4-pel, or fractional -pel such as 1 / 2, or / and 1 / 4, or / and 1 / 8- pel, or / and 1 / 16-pel) under a given slice / frame type.

[0273] In another example, the interpolation filter selection (e.g., 12-tap, 6-tap, 4-tap, 2-tap or / and O-tap filters) may be further signaled separately or jointly for different slice / frame type.

[0274] In some embodiments, one or more IBC mode related flags (e.g., motion precision, interpolation filter selection for motion compensated block prediction or / and template prediction, etc.) may be further signaled separately or jointly for different video components type.

[0275] In one example, the motion precision flags may be supported and then signaled differently for luma and chroma components. In one embodiment, 4-pel, 1-pel, 1 / 2-pel and 1 / -4 pel may be supported and signaled for luma components, while only 4-pel, 1-pel and 1 / 2-pel precision are supported for chroma components.

[0276] In another example, the motion precision flags may be supported and then signaled jointly for luma and chroma components, which indicates that a set of motion precision flags are signaled for all video components (luma and chroma components). In one example, 4-pel, 1-pel, 1 / 2-pel and 1 / -4 pel may be supported and signaled for all three components. In another example, 4-pel, 1-pel, 1 / 2-pel may be supported and signaled for all three components. Yet in another example, 4- pel, 1-pel, 1 / 4-pel may be supported and signaled for all three components, while in this case 1 / 2- pel is always converted to 1 / 4-pel precision first before signaling.

[0277] When different motion precisions are supported and signaled for different video components, corresponding interpolation fdter for each motion precision may be similarly or differently defined for different video components. For example, the 2-tap filter for luma and chroma components may be the same or different. For another example, the interpolation filter used at each motion precision may be the same or different, and the application of the interpolation filter at each motion precision and each video components may be defined separately or jointly.

[0278] In some embodiments, one or more IBC mode related flags (e.g., motion precision, interpolation filter selection for motion compensated block prediction or / and template prediction, etc.) may be further signaled separately or jointly by considering different slice / frame type, different video components, and / or different video resolutions.

[0279] When multiple windows are defined for different slices or frames, the context window sizes and initialization parameters may also be retrained separately or jointly.

[0280] Interpolation based fractional intra block copy

[0281] Fractional motion search

[0282] In one embodiment, the fractional motion search may be performed at encoder side, and the final motion may be signaled to the decoder side. The signaled motion may be in the format of motion difference after subtracting the motion predictors which are already known to both the encoder and the decoder. The motion search may be performed in three steps:• In step 1, the best N integer motion vectors with minimum distortion cost (e.g., Sum of Absolute Difference (SAD)) may be searched first.• In step 2, half-pel refinement is applied around each of the N integer motion vectors. In this step 2, there may be M best half-pel positions (the best M positions may indicate M half-pel motion differences which have the lowest rate distortion cost) that can be obtained. For example, the encoder or decoder may obtain M best half-pel positions having the lowest rate distortion cost. If K of the N integer motion vectors are selected, the output may be K*M half-pel positions in total.• In step 3, quarter-pel refinement is applied around the best half-pel position of each N integer motion vectors. In this step 3, a set of Q quarter-pel positions may be obtained for each of the K*M half-pel positions obtained in step 2. And the best R quarter-pel positions of all K*M*Q candidate positions may be generated. The best (e.g., the position with minimum rate-distortion) of the R positions may be determined by full rate-distortioncalculations and signaled to the decoder. For example, the encoder may generate the best R quarter-pel positions and then select the best one with the minimum rate-distortion of the R positions and signal the best one of the R positions to the decoder. The values of N, M, K, Q, and R are position integer numbers.

[0283] After the three-steps, the best refined motion vectors (after half-pel or / and quarter-pel refinement) is signaled (e.g., in the format of motion vector differences). In this disclosure, motion vector is used to be interchangeable with block vector that identifies a reference / prediction block in the same picture / frame in this section and following sections.

[0284] In some examples, if the actual highest precision after quarter-pel refinement is only at half-pel (e.g., the highest precision bit or the last bit of the quarter-pel motion vector is zero), the signaling of these refined motion vectors may be performed in two different methods.

[0285] In one method, the refined motion vectors are still signaled at quarter-pel or 1 / 4-pel. In this case, half-pel or / l / 2-pel precision is never signaled.

[0286] In another method, the refined motion vectors are signaled at actual precision, which is only half-pel or 1 / 2-pel. In this case, signaling of half-pel or / 1 / 2-pel precision is supported.

[0287] In another embodiment, the fractional motion search can be performed at both encoder and decoder side, such that the final fractional motion does not need to be signaled. In this method, template matching based method may be used to find the best fractional motion.

[0288] In one or more embodiments, an inverse-L shape sample / pixel area adjacent to the coding block may be used as the matching template, the pixel / sample width may be prefixed, or configurable or signaled at sequence or / and picture, or / and slice, or / and CTU level.

[0289] Within a constrained search area (defined by a prefixed, or configurable or signaled number of CTUs, or CTU lines, or samples from above, left, or / and above-left spatial areas), the template similarity between any adj acent / non-adj acent reference blocks and the current coding block are calculated, and the best N reference blocks with closest similarity are selected as the candidates in a template list.

[0290] An extra flag indicates whether to use the template matching method is signaled. If the flag is true, another index value indicates which candidate in the template list is used shall be further signaled.

[0291] In another embodiment, both encoder search method and the template matching method are jointly used. For example, integer motion and fractional refinement method are first employedat the encoder, and then another template refinement are further applied at both the encoder and the decoder side. Since the encoder search method is already accurate enough, the template refinement may be performed at a higher precision and in a small area. For example, encode side motion refinement is performed up to half-pel or quarter-pel precision, while the template refinement may be further performed at quarter-pel or eighth-pel sixteenth-pel.

[0292] In order to constrain the complexity during the fractional motion search, several methods may be provided as below.

[0293] The best SAD (sum of absolute differences) or SATD (sum of absolute transformed differences) cost of using other coding modes (e.g., other intra coding modes such as angular modes, planar mode) for the current coding block is used as a threshold for early termination of the current fractional motion search. In one example, given that the current best SAD or SATD cost from other coding modes is X, a predefined threshold factor is f (e g., an example value could be 1.1, 1.2, 1.21, etc ), and the best SAD or SATD cost from current integer motion search of IBC mode is Y, if Y >= f * X, the subsequent fractional motion search may be simplified (e.g., the N best integer motion vectors for further fractional refinement may be reduced to N’, and N’ < N) or skipped (e.g., the N best integer motion vectors for further fractional refinement may be reduced to 0). Note that the value of N, N’ and f, may be predefined or signaled or adaptively determined (e.g., based on the texture richness of the current coding block).

[0294] The fractional search may be simplified or skipped based on the combination of the other coding modes. For example, if the current coding block is enabled for IBC-CIIP or / and IBC-LIC, the fractional search for IBC may be simplified (e.g., the N best integer motion vectors for further fractional refinement may be reduced to N’, and N’ < N) or skipped (e.g., the N best integer motion vectors for further fractional refinement may be reduced to 0). Note that the value of N, N’ and f, may be predefined or signaled or adaptively determined (e g., based on the texture richness of the current coding block).

[0295] When the fractional search is simplified, several different simplification methods may be provided as below.

[0296] In one example, the N best integer motion vectors selected for further fractional refinement may be reduced to N’, where N’ < N.

[0297] The N best integer motion vectors selected for further fractional refinement may not be from only the current integer search process, but also come from the previous integer or / andfractional search process (history search process) of the same current coding block or different coding blocks. For example, for the current block, the encoder side may perform several rounds of motion search process, where different modes (e.g., IBC-CIIP, IBC-LIC) may be enabled or disabled for the current block at each round. The later rounds of motion search process may be based on the best output of the previously performed / early rounds of motion search process. For example, when IBC-CIIP or / and IBC-LIC is / are enabled for the current motion search process, the best outputs (e.g., the best M integer / fractional motion vectors, M >= 1) of the previous rounds of motion search process, where IBC-CIIP or / and IBC-LIC is / are disabled, may be put into the candidate list and further refined by the current integer / fractional search process.

[0298] Fractional motion refinement

[0299] With or without fractional motion search process, a start motion vector (MV) may be identified. The start Mv may be adjusted from two reasons:• For smaller signaling overhead, the start Mv may be rounded to a specific precision or value so that the mv difference between the start Mv and a selected mv predictor is minimized.• For smaller signaling overhead, a few least important bits of the start MV may be discarded.

[0300] With or without the aforementioned adjustment, the start Mv may need to be refined at the decoder side.

[0301] In one or more embodiments, a template matching based on method may be used. In one example, an inverse-L shape sample / pixel area adjacent to the coding block may be used as the matching template. The start Mv may be refined at integer-pel or / and fractional -pel level. The potential refinement set may be { 1 / 4-pel, 2 / 4-pel, 3 / 4-pel} or / and { 1 / 8-pel, 3 / 8-pel, 5 / 8-pel, 7 / 8- pel}, and the refinement directions are two horizontal and two vertical directions (positive and negative values). The refined Mv that generated a prediction block with most similar template is selected as the final Mv. Note that the selected refinement may be implicitly derived by the decoder if the most similar template is selected, or may be explicitly derived by the encoder if multiple refinement Mvs which have N most similar templates are derived.

[0302] In one or more embodiments, an extra flag may be signaled to indicate whether this fractional motion refinement is applied or not. The extra flag may be transmitted at sequence, picture, slice or CTU level.

[0303] Conditional sample / pixel padding for fractional interpolation

[0304] When fractional based Mv is used, interpolation operation may require a larger number of pixels / samples than the current block. The actual number difference depends on the interpolation filter tap length. In case some pixels / samples are not available, a pixel / sample padding process may be needed. Different padding schemes may be used.

[0305] In one or more embodiments, one type of repeating padding may be used. The unavailable pixel / sample position may be padded with the same value of the nearest pixels / sample which are available on the same row or column. This repeating padding may be performed at horizontal direction first (left and right boundary padding), and then followed by vertical direction (top and bottom boundary padding). Alternatively, this repeating padding may be performed at vertical direction (top and bottom boundary padding) first, and then followed by horizontal direction (left and right boundary padding).

[0306] In one or more embodiments, one type of symmetric padding may be used. The unavailable pixel / sample position may be padded with the pixel at a position symmetric to the padding boundary. This padding may be performed at horizontal direction first (left or right boundary padding), and then followed by vertical direction (top or bottom boundary padding). Alternatively, this repeating padding may be performed at vertical direction (top or bottom boundary padding) first, and then followed by horizontal direction (left or right boundary padding).

[0307] In one or more embodiments, the padding process may be conditionally skipped or simplified.

[0308] In one embodiment, depending on the value of the fractional part of the motion vector, the padding process may be partially skipped or fully skipped. In one example, if the horizontal or vertical part of the motion vector is equal to zero, the corresponding vertical or horizontal padding may be or may not be skipped. In case both directions of the motion vector are equal to zero, the whole padding process may be fully skipped or may be still performed.

[0309] In another embodiment, even if the horizontal or / and vertical part of the motion vector is not equal to zero, the corresponding padding process at horizontal or / and vertical direction may be still skipped in order to reduce computation or / and bandwidth access cost. One example in this case is that the number of unavailable samples needed for interpolation process is less than a threshold value N, N may be predefined value such as 1, or signaled. For example, given a 12-tap interpolation filter, the number of the top and left samples needed for interpolation is 5, while the number of the bottom and right samples needed for interpolation is 6. If the number of unavailablesamples needed for interpolation process at horizontal direction (left and right side) or vertical direction (top and bottom side) is less than 2, then the padding process at one direction may be skipped.

[0310] In another embodiment, if all the required samples involved in an interpolation process related to a specific motion vector are checked to be valid (e.g., all samples involved in an interpolation process are located inside of the valid reference area, as shown in FIGS. 8, 10, 11), the whole padding process may be fully skipped or may be still performed.

[0311] In another embodiment, as for an interpolation process, the number of the required left or the top samples located outside of the reference block pointed by an integer MV or the integer part of the MV is 1 less than the number of the required right or the bottom samples, the padding size for the left and top samples may be reduced by 1. For example, if a 12-tap interpolation fdter is used for an IBC coding block with non-zero fractional parts for both horizontal and vertical direction of the motion vector, the padding size for top and left samples are both 5, while the padding size for bottom and right samples are both 6.

[0312] In another embodiment, under certain circumstances, the interpolation process is only for motion search (e.g., encoder fractional motion estimation) or motion reordering (e.g., ARMC), motion refinement (e.g., IBC-DBV, IBC template matching), parameter generation for prediction refinement (e.g., template prediction generation for IBC-LIC parameter derivation), but not for final prediction generation of the current coding block, the padding process may be skipped, for example, by forcefully setting the fractional part as zero.

[0313] Interpolation filter switch

[0314] For different reasons, the interpolation filter may need to be switched. For example, longer tap length of filter may be preferred if the image / video content has rich noises and a smoothing filter effect is desired. While a shorter tap length of filter may be preferred if padding complexity needs to be reduced or the image / video content has rich texture edges.

[0315] In one or more embodiments, the filter switch may be decided at the decoder side by analyzing the image / video content (such as histogram of gradients), which requires no signaling bits.

[0316] In one or more other embodiments, the filter switch may be evaluated at the encoder side and signaled at different granularities (sequence, picture, slice, CTU level, or region based).

[0317] In one or more other embodiments, the filter switch may be evaluated at the encoder side and signaled for different frame / slice types (e.g., I, B and P slices).

[0318] In one or more other embodiments, the filter switch may be evaluated at the encoder side and signaled for different video components (e.g., luma and Chroma components, or Y, Cb, and Cr components).

[0319] In one or more other embodiments, the filter switch may be evaluated at the encoder side and signaled for motion precisions (e.g., 1-pel, 4-pel, or fractional-pel such as 1 / 2, or / and 1 / 4, or / and 1 / 8-pel, or / and 1 / 16-pel).

[0320] In one or more other embodiments, the filter switch may be evaluated at the encoder side and signaled for different interpolation scenarios (e.g., regular compensated prediction for current block, or compensated prediction for the templates, such as the top or / and left templates, of the current block).

[0321] In another embodiment, the filter switch provided above at any combination of above specified scenarios may be predefined and no signaling is needed. For example, 2-tap interpolation filter may be always used if three conditions are satisfied: chroma components, template prediction generation and natural content.

[0322] Another example for predefined filter switch without signaling is dependent on the block size.

[0323] In one embodiment, for small blocks, shorter interpolation filter length or even no interpolation is applied. In case where luma and chroma components have different ratio, such as YUV420 video format, the sizes of small blocks may be defined different for different components. For example, for chroma blocks with size 2x2, or / and 2x4, or / and 4x2, shorter interpolation filter such as 2-tap filtering process, or even no interpolation is performed. In the case no interpolation process is performed, the non-zero fractional parts of the chroma motion vectors may be clipped or rounded to an integer value. For luma blocks with 4x4, or / and 4x8, or / and 8x4, shorter interpolation filter such as 4-tap or 2-tap filtering process, or even no interpolation is performed. In the case no interpolation process is performed, the non-zero fractional parts of the luma motion vectors may be clipped or rounded to an integer value.

[0324] In another embodiment, the filter switch provided above may be dependent on other flags and no signaling is needed as well. For example, if a video block is flagged to be coded at a specificmode (intra TMP mode), or coded at a specific motion precision, the filter switch may be determined accordingly.

[0325] In one embodiment, the filter switch is predefined according to a specific mode. For example, when ARMC, IBC template matching mode, IBC-BVDP and IBC-BVPC modes are used, the reference template generation for template matching cost calculation may use an interpolation filter with smaller length (e.g., 2-tap, 4-tap, 6-tap) than the default filter (e.g., default 12-tap or 8-tap filter for luma, while default 6-tap filter for chroma). While for IBC-LIC and processing an IBC chroma sample, the default luma (e.g., 12-tap filter) or / and chroma interpolation filter (e.g., 6-tap filter) may be used, respectively. In another example, for template matching related tools such as ARMC, IBC template matching mode, IBC-BVDP and IBC-BVPC modes, the reference template may be generated by ignoring the fractional parts (e.g., clipped or round to an integer value) and the interpolation process and padding process may be fully skipped.

[0326] The above provided filter switch methods may be applied in any combination.

[0327] Multi-hypothesis fractional intra block copy

[0328] When multiple motion vectors (either from motion search or / and motion refinement) are available, multiple prediction blocks may be generated. In case that the average of multiple similar blocks can generate a better block prediction, multi -hypothesis intra block copy may be used.

[0329] In one or more embodiments, the number of multi-hypotheses may be predefined, configured or signaled. In addition, the weight to average the multiple predicted hypothesis may be also predefined, configured or signaled.

[0330] In one example, the number of multi-hypothesis may be equal to 2. In this case, the currently uni-predicted IBC mode may be extended to bi-predicted IBC mode. The weights used for combining the two predictions may be inherited from spatial neighbor neighbors, signaled, or derived at the encoder and decoder side without signaling, or reuse the same weights used for interpredicted blocks, or adaptively selected from a predefined weight set at the encoder side and signaled to the decoder side.

[0331] In one or more other embodiments, the number of multi-hypotheses may be implicitly determined at the decoder side. For example, if N prediction blocks may be generated, and the signaled value is N, which out of the range of a valid single prediction block (0 through N-l), it indicates that multi-hypothesis is enabled, and the average of all N prediction blocks may be used.

[0332] The multiple hypothesis may be generated from N motion / block vectors, where each motion / block vector may generate one specific motion compensated prediction block, where N is a positive integer number. The N motion motion / block vectors may be obtained from the same candidate list or different candidate lists. In one example, the N motion / block vectors may be obtained from the same IBC merge candidate list or AMVP list, or partially obtained from the IBC merge candidate list and partially from IBC AMVP candidate list. In another example, the N motion / block vectors may be all or partially obtained from the intra template matching method.

[0333] In the case of bi-predicted IBC mode (e.g., a special case of multi-hypothesis, where the number of multi-hypotheses is reduced to 2), there may be several sub-modes as follows.

[0334] One sub-mode may be AMVP -AMVP mode. In this sub-mode, the motion from both directions may be derived at the encoder side and then explicitly signaled to the decoder. For the MV predictors, two indexes (for two directions) or one index (one of the two directions) may be signaled. In case only one index is signaled, the other index may be derived at the decoder side (e.g., bilateral matching or template matching methods (use the signaled index as the matching target) may be used to find the closest candidate by minimizing the prediction differences between the two directions). For the MV differences, two MV differences (for two directions) or one MV difference (one of the two directions) may be signaled.

[0335] Another sub-mode may be merge-merge mode. In this sub-mode, the motion from both directions may be selected by the encoder from one or more constructed merge lists, and then the selected indexes may be signaled to the decoder. In this sub-mode, since the indexes, not the real motion, are signaled, it may be called as implicit signaling.

[0336] Another sub-mode may be AMVP-merge mode. In this sub-mode, the motion from one direction may be derived and explicitly signaled to the decoder, while the motion from the other direction may be implicitly signaled and then derived at the decoder side.

[0337] In the case of bi-predicted IBC mode, the switching between different sub-modes, if more than two sub-modes are supported, may be signaled to the decoder (e.g., a flag to select a specific sub-mode) or dynamically decided by the decoder (e.g., based on the sub-mode selections from top or left neighboring blocks, or based on the size or shape of the current coding block, or texture analysis of the current coding block, or other modes’ statistics such as histogram of gradients, etc.) without signaling.

[0338] The application of bi-predicted TBC mode may be further combined with multi -hypothesis mode. In this case, the generated prediction from bi-predicted IBC mode is used as the base prediction, and then weighted averaged with additional multi-hypothesis predictions (e.g., one or multiple additional multi-hypothesis predictions). If multiple additional multi -hypothesis predictions are supported, the number may be predefined (e.g., fixed as 3) or further signaled (e.g., a flag to indicate the value of number).

[0339] Interpolation process for template matching

[0340] In case template based adaptive reordering (ARMC-TM) is applied to IBC merge or / and AMVP mode, or / and template matching based motion refinement is applied to IBC merge or / and AMVP mode, the fractional motion / block vector may need to be adaptively used.

[0341] For template based adaptive reordering (ARMC-TM), template-based distortion cost may need to be calculated for each motion / block vector candidate. As this template-based distortion cost is for candidate reordering only, not for the final compensated prediction, the fractional part of each motion / block vector candidate, if there are non-zero fractional parts, may need or not need to be considered for the template-based distortion calculation. Specifically, in one or more examples, a fractional motion-based interpolation process may be or may not be performed for each motion / block vector candidate without non-zero fractional part.

[0342] Similarly, when the template distortion cost is calculated for each motion refinement position, the fractional part of each position may need or not need to be considered.

[0343] Signaling of motion information

[0344] When multiple precisions are supported for the motion vectors in intra block copy, the allowable signaling methods may be defined accordingly.

[0345] In one or more embodiments, only one precision is allowed to have zero motion vector difference. This one precision may be predefined, or configurable or signaled. For example, this precision may be predefined as the highest precision supported by the motion vector, such as 1 / 4- pel or 1 / 8-pel.

[0346] In one or more embodiments, multiple precisions are allowed to have zero motion vector difference. These multiple precisions may be predefined, or configurable or signaled. For example, this precision may be predefined as the highest precision or the second-highest precision supported by the motion vector, such as 1 / 4-pel and 1-pel. In case multiple precisions are allowed to have zero motion vector difference, after the signaled indication (1 flag or 1 bit bin) of zero motionvector difference, another one or more flags are additionally transmitted to indicate which precision is used.

[0347] In case multiple precisions are supported, the current precision flag may be signed in different ways. In one example, the flag indicating whether the current precision is greater than 0 is signaled first. If yes, then another flag indicating whether the current precision is greater than 1 is further signaled. Alternatively, the second flag indicating whether the current precision is greater than 1 may be implicitly derived at the decoder without explicit signaling. In one example, the values of the motion / block vector difference may be used to achieve this purpose (e.g., even or odd motion / block vector difference may indicate a specific motion precision value). Herein the values of 0, 1 or other values greater than 1 may be predefined or configured for representing different motion vector (or motion vector difference) precisions (e.g., 0 represents 1 -pel precision, 1 represents 1 / 2-pel precision, 2 represents 1 / 4-pel precision, 3 represents 1 / 8-pel precision).

[0348] In one or more embodiments, multiple MV candidates in the IBC merge / AMVP motion candidate list are separated into different groups. In one example, the group criteria may be the MV precision, where the MV candidates in the same group have the same actual MV precision. The actual MV precision is defined as the MV precision after right shifting all least important zero bits of a Mv.

[0349] IBC merge / AMVP motion candidate list construction

[0350] In one or more embodiments, multiple MV candidates in the IBC merge / AMVP motion candidate list are separated into different groups. In one example, the group criteria may be the Mv precision, where the Mv candidates in the same group have the same actual MV precision. The actual MV precision is defined as the Mv precision after right shifting all least important zero bits of an MV.

[0351] In one or more other embodiments, multiple IBC merge / AMVP motion candidate lists other than the exiting lists are created. For each list, only the Mv candidate with the same actual Mv precision are added. Similarly, the actual Mv precision is defined as the Mv precision after right shifting all least important zero bits of a Mv.

[0352] In case multiple groups of candidate lists or / and multiple candidate lists are generated, the group index or / and candidate list index needs to be determined first before the actual Mv candidate index can be decided. In one or more other examples, the group index or / and candidate list index may be evaluated at the encoder side and then signaled to the decoder. In other one or more otherexamples, the group index or / and candidate list index may be inherited from a specific neighbor block, without explicit signaling.

[0353] Combination with intra template matching

[0354] When a motion vector is determined for an intra block copy, a prediction block may be generated based on this motion vector. When combined with intra template matching, the prediction block generated by the intra block copy is further refined by the intra template matching. Specifically, for a predefined search range around the generated prediction block by the intra block copy, the encoder searches for the most similar template to the current template in a reconstructed part of the current frame and uses the corresponding block as a prediction block. In this method, the prediction block generated by intra block copy is considered as a starting block position, which is used to guide the subsequent block search process in intra template matching method.

[0355] The combination of intra block copy and intra template matching prediction mode may be signaled at CU level through a dedicated flag. Alternatively, the original intra block copy flag on top of the original intra template matching mode flag may be used to indicate the combination of intra block copy and intra template matching prediction mode. Alternatively, the original intra template matching mode flag on top of the original intra block copy mode flag may be used to indicate the combination of intra block copy and intra template matching prediction mode.

[0356] In one or more other examples, the combination of intra block copy and intra template matching prediction may generate an improved motion vector.

[0357] In one example, the intra block copy (IBC) mode provides an initial motion vector, where this initial motion vector may be further refined by the intra template matching method. In this case, IBC mode is used to signal a coarse motion vector as a starting point, which may be used to guide the subsequent intraTMP process.

[0358] In one embodiment, the initial / coarse motion vector may be signal as IBC AMVP mode, which is realized by signaling a MV predictor and MV difference. In another embodiment, the initial / coarse motion vector may be signal as IBC merge mode, which is realized by signaling an index in a constructed merge list. Note that in this IBC guided intraTMP mode, the signaled MV, either in the form of IBC AMVP mode or merge mode, the corresponding AMVP list or merge list may be constructed as the same process or a different process as in the default IBC AMVP or merge mode.

[0359] Once an initial MV is signaled, the normal intraTMP process may be performed to further refine this initial MV. In one embodiment, the intraTMP process may be performed similarly as the default intraTMP process. In another embodiment, the intraTMP process may be performed in a modified version. In one example, the search area as in the default intraTMP process may be reduced to a smaller area. Additionally, the search granularity as in the default intraTMP process may be changed as well (e.g., the sampling grid is changed from 3 x 3 to 1 x 1).

[0360] In another example, the motion / block vector obtained from the intra template matching method may be reused to generate IBC merge candidate list or IBC AMVP candidate list. In this case, the motion / block vector generated for the spatial adj acent or non-adj acent neighboring blocks may be cached or saved. In one example, the motion / block vector for neighboring blocks which are coded in intra template matching method may be saved in a history motion vector table. In addition, or alternatively, the motion / block vector for neighboring blocks which are coded in intra template matching method may be saved in a local cache of the encoder, and then reused by the encoder during the motion search process.

[0361] In other examples, the combination of intra block copy and intra template matching prediction may generate an improved prediction block. In one example, two prediction blocks may be separately generated by the intra block copy and intra template matching prediction methods, and a weighted average of these two prediction blocks may be generated to represent the final prediction block of the current coding block. In another example, multiple prediction blocks (e.g., N > 1) may be separately generated, wherein M (e.g., M is smaller or equal to N) of the N prediction blocks may be generated by the intra block copy, and S (e.g., S is smaller or equal to N) of the N prediction blocks may be generated by intra template matching prediction. When combining the N prediction blocks (e.g., N > 1), the values of the weight may be derived by using the matching cost values (e.g., one example of matching cost calculation may be based on the L- shape template, and a higher matching cost value may indicate a lower weight value, while a lower matching cost value may indicate a higher weight value) or least square flavor methods.

[0362] In another example, more than two prediction blocks may be separately generated by the intra block copy and intra template matching prediction methods. In this case, a multi -hypothesis based prediction mode may be defined. Note that the multiple hypothesis (e.g., multiple prediction blocks) may be from only IBC mode or IntraTMP mode, or may be from both IBC mode and IntraTMP mode.

[0363] In the case of multi -hypothesis mode, the IBC encoder may generate multiple prediction blocks based on searching multiple block vectors. For IBC-AMVP mode, the corresponding multiple block vectors may be signaled to the decoder side by a combination of block vector predictor indexes and block vector differences. For IBC-merge mode, the corresponding multiple block vectors may be signaled to the decoder side by a group of candidate indexes from a constructed merge candidate list.

[0364] In another example, the intraTMP mode may be unified with or replaced by the IBC mode.

[0365] In one embodiment, the existing IBC-TM mode may be extended by reusing the similar searching pattern and searching area in the intraTMP mode, as shown in the FIG. 16.

[0366] In another embodiment, a zero block vector, which has both zero horizontal component and zero vertical component, may be added to the IBC-AMVP and IBC-merge list. In this case, when the zero block vector is selected from IBC-AMVP and IBC-merge list, it indicates that the same or similar searching pattern and searching area as used in intraTMP mode may be used in the IBC mode with template matching.

[0367] Improvements for IntraTMP mode

[0368] In the current IntraTMP mode (Intra template matching prediction mode), sub-pel precision is supported. Several methods are proposed to further improve the IntraTMP mode.

[0369] In some examples, a new candidate list may be constructed for IntraTMP block vector derivation. The new candidate list may include only sub-pel block vectors or both integer and sub- pel block vectors. Alternatively, the existing candidate list of integer-pel block vectors may be updated by adding sub-pel block vectors. A template matching based reordering process may be applied to the new or the updated existing candidate list.

[0370] In one or more examples, one or more block vectors, at integer or sub-pel or both integer and sub-pel precisions, in the candidate list may be selected by the encoder and signaled to the decoder side. When the selected candidate index is signaled, the integer precision and the sub-pel precision may be jointly or separately signaled. For the joint signaling, the integer precisions and the sub-pel precisions may be included in the same candidate list, with or without template based reordering. For the separate signaling, the integer precisions and the sub-pel precisions may be included in a different candidate list, and the signaled integer precision and sub-pel precision may be separately determined at the encoder side.

[0371] In one or more examples, for separate signaling, the selected integer block vector from the existing integer block vector candidate list may be signaled first, and afterward another index value from a new candidate list may be also signaled. This new candidate list may be constructed by including only sub-pel precisions and associated positions / directions at a specific sub-pel precision. Alternatively, this new candidate list may also include the integer precision of the signaled integer block vector (e.g., output from the integer block vector search). A reordering process (e.g., template matching based reordering method) may or may not be applied to the new candidate list.

[0372] In one or more examples, the signaled index value of the new candidate list may cover the full range (all candidates in the new candidate list) or partial range (only a few candidates located in the front of the new candidate list) of the new candidate list. In one example, only one of the top two candidate indexes may be selected and signaled (e.g., the first two candidates are allowed to be selected with one single flag being signaled from encoder to decoder). In another example, only one of the top four candidate indexes may be selected and signaled. When a reordering process is applied to the new candidate list, the list may be sorted based on the SAD cost or / and SATD cost between the template samples of the current CU and their corresponding prediction samples.

[0373] In one example, predefined constant indexes, e.g., the index value 0, in the candidate list, may be selected by both the encoder and decoder. Note that in the case of predefined constant indexes, no signaling is needed to indicate the selected index at the decoder side.

[0374] In one or more examples, the signaling based index selection and the predefined constant index selection (no signaling) may be dynamically switched under certain conditions.

[0375] In one embodiment, the switching may be based on the block size or shape of the current block. In one condition, for block size smaller or bigger than a predefined threshold, e.g., the number of samples / pixels of a coding block smaller or bigger than a value such as 128 (e.g., 8x16 or 4x32 blocks), constant index value (e.g., value 0) may be always selected without further signaling.

[0376] In another condition, for block size smaller or bigger than a predefined threshold (similarly defined as before), the construction of candidate list may be simplified by only including specific sub-pel block vector(s) (e.g., only 1 sub-pel block vector at a predefined precision / position) or integer block vector(s) (e.g., only 1 integer-pel block vector which is alreadyselected in a separate process), where only index value 0 is available such that no need to do index selection and template matching based reordering process may not be needed. Alternatively, the switching may be dependent on the block shape, e.g., if the width or the height of the block is twice the height or the width of the block, constant index value or simplified candidate list may be applied.

[0377] In another embodiment, the switching may be based on specifically signaled flags (e.g. sps (sequence parameter set) or pps (picture parameter set) level flags). In one example, a sps flag may be explicitly signaled to the decoder to indicate whether a predefined constant index selection method (e.g., always choose the index value 0) is applied or not. If the flag is true, a predefined constant index value is selected at the decoder and no further signaling is needed. If the flag is false, a specific index value is further signaled.

[0378] In another embodiment, the switching may be based on the current sub-mode under the IntraTMP mode. For example, if the current candidate list is constructed for the intraTMP LIC mode, the constant index selection method may be inferred to be always enabled without checking other conditions or explicit flags. Alternatively, the constant index selection method may be inferred to be always disabled without checking other conditions or explicit flags.

[0379] In another embodiment, the switching may be based on the availability of the template for the current block. In one example, when only one side of the template (e.g., top-only or left-only) is available, the constant index selection method may be inferred to be always enabled without checking other conditions or explicit flags. In another example, when only one side of the template (e.g., top-only or left-only) is available, the construction of candidate list may be simplified by only including specific sub-pel block vector(s) (e.g., only 1 sub-pel block vector at a predefined precision / position) or integer block vector(s) (e.g., only 1 integer-pel block vector which is already selected in a separate process), where only index value 0 is available such that no need to do index selection and template matching based reordering process may not be needed.

[0380] In some examples, the currently supported sub-pel precisions include 1 / 2-pel precision, 1 / 4-pel precision, and 3 / 4-pel precision, as shown in the FIG. 22A. To minimize the system complexity or / and overhead, a subset of sub-pel precisions may be supported. In one embodiment, only 1 / 4-pel precision may be supported, as shown in the FIG. 22B. In another embodiment, only 1 / 4-pel and 1 / 2-pel precisions may be supported.

[0381] In some examples, for each supported sub-pel precision, 8 possible directions are further supported, as shown in FIG. 22A. To minimize the system complexity or / and overhead, a subset of directions may be supported. In one embodiment, only the top, top right, and right directions are supported. One example is shown in FIG. 22C, where three directions are supported for each of the three supported precisions. Another example is shown in FIG. 22D, where three directions are supported for each of the two supported precisions. In an alternative example, only 1 / 2-pel and 1 / 4-pel precisions may be supported, and 8 directions are supported for each of the two precisions, as shown in FIG. 24. FIG. 24 shows pixels at supported 1 / 4-pel positions and pixels at supported 1 / 2-pel positions in different shapes (i.e., circle and triangle) for the purpose of distinguishing that they are at different fractional posisitions, the supported 1 / 2-pel positions in FIG. 24 include eight 1 / 2-pel positions at the specific direction as indicated in FIG. 24, i.e., top, top right, right, bottom right, bottom, bottom left, left, and top left.

[0382] In some examples, more sub-pel positions may be supported at specific precisions. As shown in the FIG. 23, more sub-pel positions at the 1 / 2-pel precision are supported than FIG. 22A.

[0383] In one or more examples, two different candidate lists may be constructed for the block vector derivation in intraTMP. One candidate list may be the same as the existing candidate list, which includes candidate block vectors at the integer precisions. The other candidate list may include sub-pel precisions and directions surrounding a selected block vector at the integer precision, and the included sub-pel precisions and directions may be defined as the example shown in the FIG. 24. A template matching based reordering process may be applied to the second list. Different signaling methods may be provided as follows.

[0384] In one method, the selected candidate index from the first candidate list, which includes block vectors at the integer precisions, may be signaled first. An on / off flag is further signaled to indicate whether sub-pel precisions / directions are applied. If the flag is false, no sub-pel precisions / directions are supported. If the flag is true, the second candidate list, which includes sub-pel precisions / directions surrounding the selected and signaled integer block vector, is constructed. A selected candidate index may be further signaled for the second candidate list. Alternatively, a predefined candidate index, such as the index value 0, may be selected, and no signaling is needed.

[0385] If a candidate index is signaled for the second candidate list, the signaled candidate index may be selected from a subset of the second candidate list. For example, only one of the indexvalues from 0 to N may be signaled, where the value N is less or equal to the size of the second candidate list, and the value of N may be predefined, configured, or signaled at different granularities (e.g., sequence, picture or slices level). In one example, the value of N is predefined at 1.

[0386] In another method, the selected candidate index from the first candidate list, which includes block vectors at the integer precisions, may be signaled first. A candidate index from the second candidate list may or may not be further signaled immediately without signaling an on / off flag. In this method, a specific value combination (e.g., both sub-pel precision value and direction value are equal to 0) for sub-pel precision and direction may be used to represent that no sub-pel precision is supported for the signaled integer block vector. And this specific value combination may be also included in the second candidate list. With or without template matching based reordering process applied on the second candidate list, a candidate index, which represents a selected combination of supported sub-pel precisions and directions, may or may not be further signaled, depending on whether predefined candidate index is selected at the decoder side.

[0387] If a candidate index is signaled for the second candidate list, the signaled candidate index may be selected from a subset of the second candidate list. For example, only one of the index values from 0 to N may be signaled, where the value N is less or equal to the size of the second candidate list, and the value of N may be predefined, configured, or signaled at different granularities (e.g., sequence, picture or slices level). In one example, the value of N is predefined at 1 .

[0388] With or without further signaling for selecting the candidate from the second candidate list, the selected candidate may indicate that only integer precision is supported or indicate that a specific combination of sub-pel precisions and directions is supported.

[0389] If the value combination representing the integer-precision (e.g., no sub-pel precision is supported) is included in the candidate list, the associated template matching cost may be scaled, if template matching based reordering process is applied. The scaling factor (e.g., 0.85, or 0.9) may be predefined, or configured, or signaled at different granularities (e.g., sequence, picture or slices level).

[0390] In some examples, multi-model template selection may be supported for sub-pel precisions. In the current IntraTMP mode, the integer-pel block vector candidate list may be constructed by adding block vectors from three different templates: top template only, left templateonly or L shape template (including both left and top templates, if both available). For sub-pel precision block vectors, the candidate derivation may be selected by considering multiple templates as well.

[0391] In one embodiment, the multi-template based selection for sub-pel precisions may be performed separately from the integer-pel precisions. And a similar process may be applied.

[0392] In another embodiment, the multi-template based selection for integer-pel precisions may be inherited or reused for the sub-pel precisions. For example, if the candidate derivation for the inter-pel precision may be constructed by one type of template (e.g., top template only), the candidate derivation for the sub-pel precision may use the same type of template. If template based reordering is applied for the candidates at the sub-pel precisions, the template cost may reuse / inherit the template type used for the corresponding integer-pel candidate.

[0393] In another embodiment, the multi-template based selection for integer-pel block vector derivation may be used as early terminations for sub-pel block vector derivation. If an integer block vector is derived / selected / signaled by using a specific template type (e.g., top template, left template or L-shape (includes both top and left directions) template), it indicates that sub-pel precisions are not supported for this integer block vector, and further signaling for selecting sub- pel precisions / directions is not applied. In one example, if an integer block vector is derived / selected / signaled by using only top or left template, it indicates that sub-pel precisions are not supported, and further template matching based reordering process or / and signaling is not applied, if otherwise needed.

[0394] Note that an integer block vector is derived from only a specific template type (e.g., top or left template only), either because other templates are not available (e.g., the current block is located on the picture boundary or CTU boundary), or a specific template type is intentionally used, even if L shape template is available.

[0395] For block vectors at the sub-pel precision, interpolation process is applied to generate the prediction block. The applied interpolation filter may be predefined or dynamically switched. In one embodiment, a fixed 8-tap or 12-tap interpolation filter may be applied for the prediction block generation or / and the template based reordering process. In another embodiment, the interpolation filter may be dynamically switched. In one example, the interpolation filter may be determined based on the sub-pel precision, e.g., 4-tap interpolation filter is applied for 1 / 2-pel precision, while 8-tap interpolation filter is applied for 1 / 4-pel precision or 3 / 4-pel precision. In another example,the interpolation filter may be determined based on size of the current block. For small blocks, such as the block with the number of pixels below 8x8, shorter tap of interpolation filter (e.g., 4- tap filter) is used, while for other large blocks, longer tap of interpolation filters (e.g., 12-tap filter) is used. In another example, the interpolation filter may be differently applied for prediction block generation and the template generation process, if the template based reordering process is applied for the candidate list which includes the sub-pel precisions and directions. For example, an 8-tap or 12-tap interpolation filter may be applied for generating the prediction block, while a shorter tap interpolation filter such as 2-tap, 4-tap or 6 tap interpolation filter is applied for generating template samples for template based reordering process. In another example, the interpolation filter may be differently applied for generating luma and chroma prediction blocks, if intraTMP mode is also applied for chroma block predictions.

[0396] Given a specific number of taps (e g., 8-tap, or 4 -tap), the applied interpolation filter coefficients may be specifically designed to achieve better high-pass filter characteristics or low- pass filter characteristics for the current image or video content. In one example, a 4-tap Gaussian or Cubic interpolation filter (e.g., low-pass filters for better denoising effect) is selected to calculate the motion compensated prediction blocks for the current coding block or / and the motion compensated template predictions for the current template, where the template may be used for searching or / and reordering block vectors at the sub-pel positions.

[0397] Padding process may be needed for searching sub-pel block vectors, if some samples used for the interpolation process are not available (e g., out of the boundary of a picture / CTU / reconstructed area). The padding process may be either performed for the interpolation process of generating prediction blocks of the current block or generating template predictions of the current template.

[0398] In one embodiment, the two padding processes may be performed individually. In another embodiment, the two padding processes may be performed jointly. In the latter case, a larger padding buffer may be constructed to include both template samples and prediction samples.

[0399] For either individual padding or joint padding process, the padding order may be horizontal directions first (e.g., left and right padding directions) and then followed by vertical directions (e.g., top and bottom padding directions). Alternatively, the padding order may be vertical directions first (e.g., top and bottom padding directions) and then followed by horizontal directions (e.g., left and right padding directions).

[0400] Different template size may be supported for IntraTMP. In the current IntraTMP mode, a fixed template size (e.g., 4 rows or 4 columns of template pixels for top and left template) is used. A smaller template size may be supported in IntraTMP for small blocks. For example, a fixed template size at 2*width or 2*height may be used for blocks with the number of pixels below 8x8 (e g., L-shape template with size at 2*width may be used for the 4x8 blocks, where the left template is 4 columns, which is equal to the width of the current block, and the above template is 2 rows). This different template size may be applied to sub-pel precision reordering process or / and integer- pel block vector candidate derivation.

[0401] In the current IntraTMP mode (Intra template matching prediction mode), candidate block vectors at different precisions may be searched at both the encoder and the decoded side. The encoder may select one or multiple block vectors from all the candidate block vectors and then signal the selected block vectors (one or multiple, at integer or / and sub-pel precisions) to the decoder side in the form of candidate indexes. A single candidate list containing both integer-pel and sub-pel block vectors may be constructed. Alternatively, different candidate lists may be constructed separately (e.g., one for integer-pel precisions and another one for sub-pel precisions). The candidate lists (either one or multiple lists) may be constructed by including up to a specific number (predefined or signaled value) of block vectors that are ranked in ascending order according to a specific type of template cost (e.g., SAD (sum of absolute differences) or SATD (sum of absolute transformed differences) based cost function).

[0402] When block vectors are searched for constructing the candidate lists, multiple rounds may be used. In the first round, block vectors may be searched at lower granularity (e.g., one block vector for each 3x3 or 2x2 sample / pixel grid), while in the subsequent round (e.g., the second round or the third round, if needed) block vectors may be searched at higher granularity (e.g., one block vector for each 2x2 or 1x1 sample / pixel grid) or / and higher precisions (e.g., integerprecisions or / and sub-pel precisions such as 1 / 2-pel, 1 / 4-pel, 1 / 8-pel, etc.) around the candidates from the previous round (e.g., the first round). At each searching round, the selected template cost function may be the same or different.

[0403] In one specific example, the integer block search may be performed in two rounds. In the FIRST search, the intraTMP search regions is subsampled by a factor of 3. Note that the subsampling factor determines the searching granularity. For the subsampling factor 3x3, it indicates that one block vector is searched for every three samples in the horizontal direction andthree samples in the vertical direction. After finding the best match, a refinement process is further applied by refining the BV around the best match within a reduced range. For the first search, SAD cost function may be used. For the second search (e.g., the refinement process), SATD cost function may be used.

[0404] In another example, when SATD based cost function is used, the refinement process (e.g., the second round or subsequence round of searching process) may be reduced to a smaller area (e.g., from a 5x5 or 4x4 local area to a smaller area such as 3x3). In the case that a smaller local area is applied for the refinement process, the subsampling factor of the initial search (e.g., the first search) may be reduced as well to compensate for the loss of the smaller local area for the refinement process. For example, the subsampling factor of the initial search may be reduced to 3x3 from 4x4 or 5x5, if the subsampling factor is initially set with a higher value than 3.

[0405] In one example, in the first round, an SAD based cost function may be used for the template cost calculation, while in the second round, an SATD based cost function may be used for the template cost calculation. For the third round (e.g., searching block vectors at higher precisions such as sub-pel precisions from a subset of the candidates generated after the second round) (e g.,) or subsequent rounds (e.g., from lower sub-pel precisions such as 1 / 2-pel precision to higher sub-pel precisions such as 1 / 4-pel or / and 1 / 8-pel precisions), if needed, an SAD based cost function may be used.

[0406] In another example, in the first round and second round, an SAD based cost function may be used. While in the third round, an SATD based cost function may be used to reorder a subset of the output candidates of the second round.

[0407] In another example, if a mean-removed SAD based cost function is used in the first round, a mean-removed SATD or non-mean-removed SATD based cost function may be used in the subsequence round (e.g., the second round, or the third round, if there is a third round).

[0408] Given a specific type of template cost (e.g.., SAD, SATD, mean-removed SAD or mean- removed SATD), weighted template cost may be applied. In one example, the weights of the template cost may be defined according to the spatial distance to the current block. As shown in the FIG. 25, an exemplary definition of the weighted template cost is provided. In the FIG. 25, given a current coding block with block size at 8x8 and template size at 4x4 (4 lines of samples to the above and 4 columns of samples to the left of the current block), a group of weights {wl, w2, w3, w4] is defined for each line / column of template samples, which are decided by the spatialdistance to the above and left edge of the current block. Tn one example, the group of weights may be defined as {8, 1, 1, 1 }, which means that the closest line / column of template samples has weight value 8 and other line / column of template samples has the same weight value 1 (e.g., near template samples have higher significance than far template samples in terms of the calculation of the template cost).

[0409] In FIG. 25, both top and left templates are available for the exemplary coding block. For coding blocks with only top or left template available, similar weights may be defined according to the spatial distance between the template samples and the corresponding edge of the current coding block. This definition of the weighted template cost may be provided as prioritized template cost, where the samples with higher cost weight values have higher priorities than the samples with lower cost weight values.

[0410] In the current IntraTMP mode (Intra template matching prediction mode), fusion of multiple predictors may be supported. Several methods are provided to further improve the IntraTMP fusion mode:

[0411] In the IntraTMP fusion mode, multiple predictors may be averaged or blended to derive the final prediction block. The averaging or blending weights may be computed from the template costs of each predictor.

[0412] In one embodiment, each one of the multiple predictors may be generated either by a selected integer block vector (signaled or a predefined position from an existing candidate list) or a selected sub-pel block vector (signaled or a predefined position from an existing candidate list). If a sub-pel block vector is selected to generate a predictor for the IntraTMP fusion mode, the methods provided above may be similarly applied (e.g., a new candidate list containing sub-pel block vectors may be constructed, a template based reordering method may be further applied to the new candidate list).

[0413] In another embodiment, when the averaging or blending weights are computed from the template costs of each predictor, the template costs may be calculated or adjusted based on sdifferent ways:

[0414] In one embodiment, the template cost may be calculated based on SAD or SATD cost functions. In case the multiple predictors to be averaged or blended are searched by using different template types (e.g., some predictors are searched by using only top template, while other predictors are searched by using L shape template), the template cost associated with eachpredictor needs to be scaled to match different template types. In one example, the cost needs to be scaled based on the number of the involved template samples / pixels. Specifically, the predictors searched by using only top template samples needs to be scaled up to match the number of all L shape template samples. While the predictors searched by using only left template samples need all to be scaled up to match the number of all L shape template samples, if the L shape template is available for the current coding unit.

[0415] In another embodiment, a fixed scale factor may be predefined or signaled to scale the template cost for some predictors before calculating the average or blending costs.

[0416] In another embodiment, the number of predictors selected for the fusion mode may be predefined or / and adaptively determined. In one example, the predictors may be selected based on the magnitude of the template cost. For example, the predictors with template costs less than a predefined or signaled threshold value are selected. The predefined threshold value may be dynamically determined based on the minimum template cost value within a specific group of candidate predictors.

[0417] For the current IntraTMP LIC mode, LIC model parameters are derived after the blockvector based prediction signals, where the block-vector predictions may be generated by only using motion vectors / block vectors at integer precisions. Methods that using block vectors / motion vectors at fractional precisions for predictions generations are provided as below:

[0418] Given a list of selected block vectors / motion vectors at integer precisions, sub-pel refinement process may be further applied. The refinement process may be performed similarly as the previously provided methods for IntraTMP non-LIC mode, which uses the template matching based process to select the best fractional positions for each tested integer BV. Compared to the non-LIC mode, the refinement process for LIC mode may utilize different methods for calculating the template cost for reordering purpose.

[0419] In one method, the mean-removed SAD or SATD cost metric may be used for template cost calculations.

[0420] In another method, the SAD or SATD cost metric may be used, but LIC based linear transform process may be further applied on top of the interpolated template predictions before the template cost calculation.

[0421] The interpolation filter type may be similarly or differently selected for the template generation (for interpolations during the reordering process) and final prediction generation (forinterpolations after the reordering process). For example, 4-tap bilinear interpolation filter may be used for the reordering of the obtained block / motion vectors, while the same filter or a different interpolation filter such as 8-tap filter may be used for prediction generation.

[0422] In IntraTMP mode, after the process for searching integer block vectors, a refinement process for searching fractional block vectors may be or not be performed. If fractional searching is performed, the best fractional refinements may be added on top of the previously searched integer block vectors, making the refined block vectors pointing to a new reference block at another integer position, and this new reference block may contain some samples spatially covered by the reference block but not available (out of picture boundary or decoding buffer or not decoded yet). In this case, the padding process may be needed. As shown in the FIG. 26, the reference block pointed by the block vector 1 (before adding the fractional refinements) is checked to be valid after integer searching process, while the reference block pointed by the block vector 2 (after adding the fractional refinements) may not be valid, where some samples may not be available (out of picture boundary or decoding buffer or not decoded yet). In this case, padding process is needed and the padding process should start from the reference block pointed by the block vector before adding the fractional refinements. For the specific example shown in the FIG. 26, the anchor of the padding process should be the reference blocked pointed by the block vector 1.

[0423] Improvements for SGPM mode

[0424] In the current SGPM mode, the two partitions may be coded with regular intra prediction modes or block-vector prediction modes (e.g., IBC or IntraTMP). However, the block-vector predictions are generated by only using motion vectors / block vectors at integer precisions. Methods that using block vectors / motion vectors at fractional precisions for predictions generations are provided as below:

[0425] Construct a candidate list by adding block / motion vectors from adjacent or / and nonadj acent neighboring blocks which are coded with IBC or / and IntraTMP modes. This construction process may be skipped in some conditions. In one example, an existing candidate list (e.g., an existing list of block / motion vectors already constructed in other modes such as TIMD, DIMD modes), if available, may be reused.

[0426] Obtain block / motion vectors with full fractional precisions (without rounding or clipping operations) or partial fractional precisions (with certain level of rounding or clipping operations at a middle fractional precision) from adjacent or non-adjacent neighboring blocks coded at IBC orIntraTMP modes. For example, if the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block is 1 / 4-pel, or 1 / 8-pel or 1 / 16-pel, the obtained block / motion vectors for the neighboring blocks may be partially rounded or clipped (e.g., from 1 / 16-pel precision or 1 / 8-pel precision or 1 / 4-pel to 1 / 2-pel precision, or from 1 / 16-pel precision or 1 / 8-pel precision to 1 / 4-pel precision) before used for the current coding block. Alternatively, the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block may be fully kept (without any rounding or clipping) before used for the current coding block.

[0427] Switching between integer only block / motion vectors or fractional block / motion vectors. This switching may be implicitly or explicitly performed. In one example, the implicit switching may be based on distance between the neighboring blocks where the block / motion vectors are obtained and the current coding block. For the block / motion vectors coming from non-adjacent neighboring blocks with distance larger than a specific distance (e.g., N pixel / samples away), the integer only block / motion vectors (with rounding or clipping operations to change the fractional precision to integer precision) may be used. For block / motion vectors coming from neighboring blocks with distance smaller than or equal to a specific distance (e.g., within N pixel / samples), the fractional block / motion vectors may be used. In another example, the explicit switching may be based on explicit signaling (e.g., a switching flag may be explicitly signaled from the encoder to the decoder). In another example, fractional block / motion vectors or integer only block / motion vectors may be always used for SGPM mode, without further implicit or explicit switching.

[0428] Check the validity of the obtained block / motion vectors by removing redundant vectors.

[0429] Check the validity of the obtained block / motion vectors by removing vectors pointing to a reference block with unavailable samples inside the reference block and inside the template areas of the reference block, where the template areas are defined according to the template size used for the template matching based reordering process of the obtained block / motion vectors. The template size may be similarly or differently defined for the template-based reordering in different modes. For SGPM mode, the template size may be defined as 1 (e g., 1 row on the top and 1 column to the left of the current coding unit) or 4 or adaptively switching between 4 or 2 according to the width and height of the current coding unit.

[0430] Select the best block / motion vectors (up to a predefined number such as 6, if available) according to the template cost (SAD or SATD or mean-removed SAD or mean-removed SATDcost metric / functions). The necessary padding process may be needed when a selected block / motion vector has a valid fractional component and some or all adjacent samples of the template area are unavailable.

[0431] Test all the selected block / motion vectors inside the SGPM candidate list construction or an existing candidate list, if a candidate list is used, by blending with one or multiple selected angular intra predictions to decide whether use block / motion vector-based prediction or other non- angular prediction such as planar or DC mode. The necessary padding processing may be still needed if a selected block / motion vector has a valid fractional component and some or all adjacent samples of the reference block area unavailable.

[0432] The interpolation fdter type may be similarly or differently selected for the template generation (for interpolations during the reordering process) and final prediction generation (for interpolations after the reordering process). For example, 4-tap bilinear interpolation filter may be used for the reordering of the obtained block / motion vectors, while the same filter or a different interpolation filter such as 8-tap filter may be used for prediction generation.

[0433] Improvements for TIMD mode

[0434] In the TIMD mode, several intra prediction modes may be fused with a number of weights, and such weighted intra prediction is used to code the current CU. Those intra prediction modes may include angular modes or / and non-angular modes (e.g., include Planar mode, DC mode). It is proposed to add block-vector based predictions from adjacent or non-adjacent neighboring blocks which are coded with IBC or / and IntraTMP modes to extend the non-angular modes for TIMD.

[0435] Construct a candidate list by adding block / motion vectors from adjacent or / and non- adjacent neighboring blocks which are coded with IBC or / and IntraTMP modes. This construction process may be skipped in some conditions. In one example, an existing candidate list (e.g., an existing list of block / motion vectors already constructed in other modes such as SGPM, DIMD modes), if available, may be reused.

[0436] Obtain block / motion vectors with full fractional precisions (without rounding or clipping operations) or partial fractional precisions (with certain level of rounding or clipping operations at a middle fractional precision) from adjacent or non-adjacent neighboring blocks coded at IBC or IntraTMP modes. For example, if the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block is 1 / 4-pel, or 1 / 8-pel or 1 / 16-pel, the obtained block / motion vectors for the neighboring blocks may be partially rounded or clipped (e.g.,from 1 / 16-pel precision or 1 / 8-pel precision or 1 / 4-pel to 1 / 2-pel precision, or from 1 / 16-pel precision or 1 / 8-pel precision to 1 / 4-pel precision) before used for the current coding block. Alternatively, the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block may be fully kept (without any rounding or clipping) before used for the current coding block.

[0437] Switching between integer only block / motion vectors or fractional block / motion vectors. This switching may be implicitly or explicitly performed. In one example, the implicit switching may be based on distance between the neighboring blocks where the block / motion vectors are obtained and the current coding block. For the block / motion vectors coming from non-adjacent neighboring blocks with distance larger than a specific distance (e.g., N pixel / samples away), the integer only block / motion vectors (with rounding or clipping operations to change the fractional precision to integer precision) may be used. For block / motion vectors coming from neighboring blocks with distance smaller than or equal to a specific distance (e.g., within N pixel / samples), the fractional block / motion vectors may be used. In another example, the explicit switching may be based on explicit signaling (e.g., a switching flag may be explicitly signaled from the encoder to the decoder). In another example, fractional block / motion vectors or integer only block / motion vectors may be always used for TIMD mode, without further implicit or explicit switching.

[0438] Check the validity of the obtained block / motion vectors by removing redundant vectors.

[0439] Check the validity of the obtained block / motion vectors by removing vectors pointing to a reference block with unavailable samples inside the reference block and inside the template areas of the reference block, where the template areas are defined according to the template size used for the template matching based reordering process of the obtained block / motion vectors. The template size may be similarly or differently defined for the template-based reordering in different modes. For TIMD mode, the template size may be defined as 1 (e.g., 1 row on the top and 1 column to the left of the current coding unit) or 4 or adaptively switching between 4 or 2 according to the width and height of the current coding unit.

[0440] Select the best block / motion vectors (up to a predefined number such as 6, if available) according to the template cost (SAD or SATD or mean-removed SAD or mean-removed SATD cost metric / functions). The necessary padding process may be needed when a selected block / motion vector has a valid fractional component and some or all adjacent samples of the template area are unavailable.

[0441] Test all the selected block / motion vectors inside a candidate list, if a candidate list is used, by blending with one or multiple selected angular intra predictions to decide whether use block / motion vector-based prediction or other non-angular prediction such as planar or DC mode. The necessary padding processing may be still needed if a selected block / motion vector has a valid fractional component and some or all adjacent samples of the reference block area unavailable.

[0442] The interpolation filter type may be similarly or differently selected for the template generation (for interpolations during the reordering process) and final prediction generation (for interpolations after the reordering process). For example, 4-tap bilinear interpolation filter may be used for the reordering of the obtained block / motion vectors, while the same filter or a different interpolation filter such as 8-tap filter may be used for prediction generation.

[0443] Improvements for DIMD mode

[0444] In DIMD mode, it may adaptively select between planar or block-vector based prediction obtained from IntraTMP or IBC mode of neighboring blocks for the blending with an angular intra prediction. However, similar to the current SGPM mode, the block-vector predictions are generated by only using motion vectors / block vectors at integer precisions. Methods that using block vectors / motion vectors at fractional precisions for predictions generations are provided as below:

[0445] Construct a candidate list by adding block / motion vectors from adjacent or / and nonadj acent neighboring blocks which are coded with IBC or / and IntraTMP modes. This construction process may be skipped in some conditions. In one example, an existing candidate list (e g., an existing list of block / motion vectors already constructed in other modes such as TIMD, SGPM modes), if available, may be reused.

[0446] Obtain block / motion vectors with full fractional precisions (without rounding or clipping operations) or partial fractional precisions (with certain level of rounding or clipping operations at a middle fractional precision) from adjacent or non-adjacent neighboring blocks coded at IBC or IntraTMP modes. For example, if the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block is 1 / 4-pel, or 1 / 8-pel or 1 / 16-pel, the obtained block / motion vectors for the neighboring blocks may be partially rounded or clipped (e.g., from 1 / 16-pel precision or 1 / 8-pel precision or 1 / 4-pel to 1 / 2-pel precision, or from 1 / 16-pel precision or 1 / 8-pel precision to 1 / 4-pel precision) before used for the current coding block. Alternatively, the highest fractional precision of the block / motion vectors supported by an adjacentor non-adjacent neighboring block may be fully kept (without any rounding or clipping) before used for the current coding block.

[0447] Switching between integer only block / motion vectors or fractional block / motion vectors. This switching may be implicitly or explicitly performed. In one example, the implicit switching may be based on distance between the neighboring blocks where the block / motion vectors are obtained and the current coding block. For the block / motion vectors coming from non-adjacent neighboring blocks with distance larger than a specific distance (e.g., N pixel / samples away), the integer only block / motion vectors (with rounding or clipping operations to change the fractional precision to integer precision) may be used. For block / motion vectors coming from neighboring blocks with distance smaller than or equal to a specific distance (e.g., within N pixel / samples), the fractional block / motion vectors may be used. In another example, the explicit switching may be based on explicit signaling (e.g., a switching flag may be explicitly signaled from the encoder to the decoder). In another example, fractional block / motion vectors or integer only block / motion vectors may be always used for DIMD mode, without further implicit or explicit switching.

[0448] Check the validity of the obtained block / motion vectors by removing redundant vectors.

[0449] Check the validity of the obtained block / motion vectors by removing vectors pointing to a reference block with unavailable samples inside the reference block and inside the template areas of the reference block, where the template areas are defined according to the template size used for the template matching based reordering process of the obtained block / motion vectors. The template size may be similarly or differently defined for the template-based reordering in different modes. For DIMD mode, the template size may be defined as 1 (e.g., 1 row on the top and 1 column to the left of the current coding unit) or 4 or adaptively switching between 4 or 2 according to the width and height of the current coding unit.

[0450] Select the best block / motion vectors (up to a predefined number such as 6, if available) according to the template cost (SAD or SATD or mean-removed SAD or mean-removed SATD cost metric / functions). The necessary padding process may be needed when a selected block / motion vector has a valid fractional component and some or all adj cent samples of the template area are unavailable.

[0451] Test all the selected block / motion vectors inside a candidate list, if a candidate list is used, by blending with one or multiple selected angular intra predictions to decide whether use block / motion vector-based prediction or other non-angular prediction such as planar or DC mode.The necessary padding processing may be still needed if a selected block / motion vector has a valid fractional component and some or all adjacent samples of the reference block area unavailable.

[0452] The interpolation filter type may be similarly or differently selected for the template generation (for interpolations during the reordering process) and final prediction generation (for interpolations after the reordering process). For example, 4-tap bilinear interpolation filter may be used for the reordering of the obtained block / motion vectors, while the same filter or a different interpolation filter such as 8-tap filter may be used for prediction generation.

[0453] Improvements for OBIC mode

[0454] In the OBIC mode, several intra prediction modes may be fused with a number of weights, and such weighted intra prediction is used to code the current CU. Those intra prediction modes may include angular modes or / and non-angular modes (e.g., include Planar mode, DC mode). It is proposed to add block-vector based predictions from adjacent or non-adjacent neighboring blocks which are coded with IBC or / and IntraTMP modes to extend the non-angular modes for OBIC.

[0455] Construct a candidate list by adding block / motion vectors from adjacent or / and non- adjacent neighboring blocks which are coded with IBC or / and IntraTMP modes. This construction process may be skipped in some conditions. In one example, an existing candidate list (e g., an existing list of block / motion vectors already constructed in other modes such as SGPM, DIMD modes), if available, may be reused.

[0456] Obtain block / motion vectors with full fractional precisions (without rounding or clipping operations) or partial fractional precisions (with certain level of rounding or clipping operations at a middle fractional precision) from adjacent or non-adjacent neighboring blocks coded at IBC or IntraTMP modes. For example, if the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block is 1 / 4-pel, or 1 / 8-pel or 1 / 16-pel, the obtained block / motion vectors for the neighboring blocks may be partially rounded or clipped (e g., from 1 / 16-pel precision or 1 / 8-pel precision or 1 / 4-pel to 1 / 2-pel precision, or from 1 / 16-pel precision or 1 / 8-pel precision to 1 / 4-pel precision) before used for the current coding block. Alternatively, the highest fractional precision of the block / motion vectors supported by an adjacent or non-adjacent neighboring block may be fully kept (without any rounding or clipping) before used for the current coding block.

[0457] Switching between integer only block / motion vectors or fractional block / motion vectors. This switching may be implicitly or explicitly performed. In one example, the implicit switchingmay be based on distance between the neighboring blocks where the block / motion vectors are obtained and the current coding block. For the block / motion vectors coming from non-adjacent neighboring blocks with distance larger than a specific distance (e.g., N pixel / samples away), the integer only block / motion vectors (with rounding or clipping operations to change the fractional precision to integer precision) may be used. For block / motion vectors coming from neighboring blocks with distance smaller than or equal to a specific distance (e.g., within N pixel / samples), the fractional block / motion vectors may be used. In another example, the explicit switching may be based on explicit signaling (e.g., a switching flag may be explicitly signaled from the encoder to the decoder). In another example, fractional block / motion vectors or integer only block / motion vectors may be always used for OBIC mode, without further implicit or explicit switching.

[0458] Check the validity of the obtained block / motion vectors by removing redundant vectors.

[0459] Check the validity of the obtained block / motion vectors by removing vectors pointing to a reference block with unavailable samples inside the reference block and inside the template areas of the reference block, where the template areas are defined according to the template size used for the template matching based reordering process of the obtained block / motion vectors. The template size may be similarly or differently defined for the template-based reordering in different modes. For OBIC mode, the template size may be defined as 1 (e.g., 1 row on the top and 1 column to the left of the current coding unit) or 4 or adaptively switching between 4 or 2 according to the width and height of the current coding unit.

[0460] Select the best block / motion vectors (up to a predefined number such as 6, if available) according to the template cost (SAD or SATD or mean-removed SAD or mean-removed SATD cost metric / functions). The necessary padding process may be needed when a selected block / motion vector has a valid fractional component and some or all adjacent samples of the template area are unavailable.

[0461] Test all the selected block / motion vectors inside a candidate list, if a candidate list is used, by blending with one or multiple selected angular intra predictions to decide whether use block / motion vector-based prediction or other non-angular prediction such as planar or DC mode. The necessary padding processing may be still needed if a selected block / motion vector has a valid fractional component and some or all adjacent samples of the reference block area unavailable.

[0462] The interpolation filter type may be similarly or differently selected for the template generation (for interpolations during the reordering process) and final prediction generation (forinterpolations after the reordering process). For example, 4-tap bilinear interpolation filter may be used for the reordering of the obtained block / motion vectors, while the same filter or a different interpolation filter such as 8-tap filter may be used for prediction generation.

[0463] FIG. 29 shows a computing environment 2910 coupled with a user interface 2950. The computing environment 2910 can be part of a data processing server. The computing environment 2910 includes a processor 2920, a memory 2930, and an Input / Output (I / O) interface 2940.

[0464] The processor 2920 typically controls overall operations of the computing environment 2910, such as the operations associated with display, data acquisition, data communications, and image processing. The processor 2920 may include one or more processors to execute instructions to perform all or some of the steps in the above-described methods. Moreover, the processor 2920 may include one or more modules that facilitate the interaction between the processor 2920 and other components. The processor may be a Central Processing Unit (CPU), a microprocessor, a single chip machine, a Graphical Processing Unit (GPU), or the like.

[0465] The memory 2930 is configured to store various types of data to support the operation of the computing environment 2910. The memory 2930 may include predetermined software 2932. Examples of such data includes instructions for any applications or methods operated on the computing environment 2910, video datasets, image data, etc. The memory 2930 may be implemented by using any type of volatile or non-volatile memory devices, or a combination thereof, such as a Static Random Access Memory (SRAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), an Erasable Programmable Read-Only Memory (EPROM), a Programmable Read-Only Memory (PROM), a Read-Only Memory (ROM), a magnetic memory, a flash memory, a magnetic or optical disk.

[0466] The I / O interface 2940 provides an interface between the processor 2920 and peripheral interface modules, such as a keyboard, a click wheel, buttons, and the like. The buttons may include but are not limited to, a home button, a start scan button, and a stop scan button. The I / O interface 2940 can be coupled with an encoder and decoder.

[0467] FIG. 30 is a flowchart illustrating a method for video decoding according to an example of the present disclosure.

[0468] In Step 3001, the processor 2920, at the side of a decoder, may obtain at least one block vector (BV) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode. Intra TMP mode is a special intra prediction mode that copies the best predictionblock from a reference block of the current frame, whose L-shaped template matches the current template. The BV refers to a vector points from the current block to the reference block. The BV candidate list is a collection of potential BVs that might be suitable for predicting the current block.

[0469] In Step 3002, the processor 2920, at the side of the decoder, may obtain a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear fdter of a local illumination compensation (LIC) mode, where the at least one BV candidate list includes at least one of following lists: an integer-pel BV candidate list, a sub-pel BV candidate list, or a composite BV candidate list including at least one integer-pel BV and at least one sub-pel BV. In some embodiments, the prediction block for the current block is obtained based on the at least one BV. In some other embodiments, the prediction block for the current block is obtained based on the at least one BV and the linear filter of the LIC mode. However, whether the linear filter of the LIC mode is used for obtaining the prediction block is not limited. In some embodiments, the at least one BV obtained for prediction may be at least one integer-pel BV, which may be obtained from an integer-pel BV candidate list, or from a composite BV candidate list including at least one integer-pel BV and at least one sub-pel BV. In some other embodiments, the at least one BV obtained for prediction may be at least one BV including a fractional component, which may be obtained from a sub-pel BV candidate list, or a composite BV candidate list including at least one integer-pel BV and at least one sub-pel BV. However, the specific type of the candidate lists selected for obtaining the at least one BV is not limited to the embodiments of the present disclosure.

[0470] In some examples, the processor 2920, at the side of the decoder, may perform one of followings steps to obtain the at least one BV: in response to receiving a first candidate index, determining an integer-pel BV based on an integer-pel BV candidate list and the first candidate index, or based on a composite BV candidate list and the first candidate index; or in response to receiving a second candidate index, determining a sub-pel BV based on a sub-pel BV candidate list and the second candidate index, or based on a composite BV candidate list and the first candidate index.

[0471] In some examples, the processor 2920, at the side of the decoder, may further obtain a reordered BV candidate list by reordering all BVs in a first BV candidate list of the at least one block BV candidate list based on template matching.

[0472] In some examples, the processor 2920, at the side of the decoder, may perform the followings step to obtain the at least one BV: in response to receiving a third candidate index, determining a first BV based on the first BV candidate list based on the third candidate index, where the third candidate index is configured to indicate one of all BV candidates in the first candidate list, or one of a top number of BV candidates in the reordered BV candidate list.

[0473] In some examples, reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching includes: reordering all BVs in the first BV candidate list based on a sum of absolute differences (SAD) costs or a sum of absolute transformed differences (SATD) costs between template samples of the current block and corresponding prediction samples of the template samples.

[0474] In some examples, the processor 2920, at the side of the decoder, may perform the followings step to obtain the prediction block for the current block based on the at least one BV: obtaining the prediction block for the current block based on the at least one BV by applying a first interpolation filter; wherein obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching includes: obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching by using a second interpolation filter.

[0475] In some examples, the first interpolation filter is identical to the second interpolation filter, and the processor 2920, at the side of the decoder, may further perform one padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter, and a second interpolation process of generating prediction samples of template samples of the current block for template matching.

[0476] In some examples, performing the one padding process for the first interpolation process and the second interpolation process includes one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

[0477] In some examples, the first interpolation filter is different from the second interpolation filter, and the processor 2920, at the side of the decoder, may further perform a first padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter; and perform a second padding process for a secondinterpolation process of generating prediction samples of template samples of the current block for template matching.

[0478] In some examples, at least one of the first padding process or the second padding process includes one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

[0479] In some examples, the processor 2920, at the side of the decoder, may further construct the at least one BV candidate list by multiple searching rounds, wherein the multiple searching rounds include a first searching round and a second searching round after the first searching round, the second searching round is performed in a region around a searching result of the first searching round, and a granularity or a precision of the second searching round is higher than a granularity or a precision of the first searching round.

[0480] In some examples, the first searching round and the second searching round are for searching integer-pel BVs, a searching region of the first searching round is subsampled by a factor of 3, and a searching region of the second searching round is subsampled by a factor less than 3.

[0481] In some examples, the processor 2920, at the side of the decoder, may further reorder searching results of at least one searching round of the multiple searching rounds based on template matching.

[0482] In some examples, reordering the searching results of the at least one searching round of the multiple searching rounds based on template matching includes one of followings: reordering searching results of the first searching round based on a SAD based cost function, reordering searching results of the second searching round based on a SATD based cost function, and reordering searching results of a third searching round after the second searching round based on a SAD based cost function; reordering the searching results of the first searching round based on a SAD based cost function, reordering the searching results of the second searching round based on a SAD based cost function, and reordering the searching results of a third searching round after the second searching round based on a SATD based cost function; or reordering the searching results of the first searching round based on a mean-removed SAD based cost function, and reordering the searching results of the second searching round based on a mean-removed SATD or non-mean-removed SATD based cost function.

[0483] In some embodiments, the processor 2920, at the side of the decoder, may obtain multiple BV candidates based on the at least one BV candidate list; obtain multiple initial prediction blocks based on the multiple BV candidates; and obtain the prediction block for the current block based on the multiple initial prediction blocks.

[0484] In some embodiments, obtaining the prediction block for the current block based on the multiple initial prediction blocks includes: determining weights of the multiple initial prediction blocks based on template matching; and obtaining the prediction block for the current block based on the multiple initial prediction blocks and the weights of the multiple initial prediction blocks.

[0485] In some embodiments, determining the weight of the initial prediction block based on template matching includes: calculating a template matching cost of the initial prediction block based on a template type of the initial prediction block.

[0486] In some embodiments, the processor 2920, at the side of the decoder, may further select the multiple BV candidates from the at least one BV candidate list based on template matching costs of the multiple BV candidates.

[0487] In some embodiments, the processor 2920, at the side of the decoder, may perform one of following steps to obtain the at least one BV : obtaining the at least one B V based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; in response to meeting a constant index selection condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; or in response to meeting a dynamic switching condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one candidate index signaled by an encoder.

[0488] In some examples, the constant index selection or the dynamic switching condition includes one of followings: a block size of the current block is smaller or bigger than a first predefined threshold; a block shape of the current block meets a predefined shape; a flag signaled by an encoder is true or false, wherein the flag is at a sequence parameter set (SPS) level or a picture parameter set (PPS) level; a specific sub-mode of the IntraTMP mode is or is not applied; or whether a specific part of template samples of the current block is available for template matching.

[0489] In some examples, the processor 2920, at the side of the decoder, may further, in response to determining that a block size of the current block is smaller or greater than a second predefinedthreshold, construct the at least one BV candidate list including at least one specific integer-pel BV or at least one specific sub-pel BV, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode includes: obtaining the at least one BV based on at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index.

[0490] In some examples, the processor 2920, at the side of the decoder, may further determine a width or a height of a template size of the current block as less than 4; or determine a width and a height of a template size of the current block as being different.

[0491] In some examples, obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching includes: determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block; obtaining a weighted sum cost between the template samples of the current block and corresponding prediction samples of the template samples for each BV in the first BV candidate list; and reordering all BVs in the first BV candidate list based on the weighted sum cost for each BV in the first BV candidate list.

[0492] In some examples, the current block is a 8x8 block, and a template size of the current block includes 4 lines of template samples above the current block and 4 columns of template samples on the left of the current block; wherein determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block includes: determining that a closest line of template samples and a closest column of template samples have a same weight of 8; and determining other three lines of template samples and other three columns of template samples have a same weight of 1.

[0493] In some examples, the template samples of the current block include only top template samples above the current block, or only left template samples on the left of the current block.

[0494] In some examples, reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching includes: reordering all BVs in the first BV candidate list based on a sum of mean-removed SAD costs or SATD costs between template samples of the current block and corresponding prediction samples of the template samples; or reordering all BVs in the first BV candidate list based on a sum of costs between template samples of the current block and corresponding prediction samples of the template samples, wherein the corresponding prediction samples are filtered based on the linear filter.

[0495] In some examples, the processor 2920, at the side of the decoder, may apply a same interpolation fdter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for an interpolation process for obtaining the prediction block.

[0496] In some examples, the processor 2920, at the side of the decoder, may obtain an integer- pel BV and a sub-pel BV based on the at least one BV candidate list; obtain a BV by adding fractional refinement of the sub-pel BV to the integer-pel BV; and in response to determining that a sample in a first reference block pointed to by the BV is not available, perform a padding process in an area starting from a boundary of a second reference block pointed to by the integer-pel BV.

[0497] FIG. 31 is a flowchart illustrating a method for video decoding according to an example of the present disclosure.

[0498] In Step 3101, the processor 2920, at the side of a decoder, may obtain a prediction block for a current block based on multiple initial predictions of the current block, where the multiple initial predictions include a BV prediction obtained based on a BV prediction mode. The multiple initial predictions are used for obtain the prediction block of the current block, and at least one initial prediction is a BV prediction, which is a block-vector based prediction from adjacent or non-adjacent neighboring blocks obtained based on a BV prediction mode, for example, an intrTMP mode or an IBC mode.

[0499] In some examples, the processor 2920, at the side of the decoder, may perform one of following steps: constructing a BV candidate list by adding at least one BV of at least one neighboring block coded in the BV prediction mode; skipping a constructing process for a BV candidate list by using an existing BV candidate list; in response to meeting a switching condition, switching to obtain an integer BV or a factional BV in the BV prediction mode; determining at least one BV for the BV prediction mode by selecting a predefined number of BVs from a BV candidate list; determining, by the decoder and based on a first cost testing result, whether to use the BV prediction for obtaining the prediction block, where the multiple initial predictions further include at least one angular intra prediction, and the first cost testing result is obtained by blending the BV prediction with the at least one angular intra prediction; determining, by the decoder and based on a second cost testing result, whether to use a non-angular intra prediction for obtaining the prediction block, wherein the multiple initial predictions further include the non-angular intra prediction and at least one angular intra predictions, and the second cost testing result is obtainedby blending the BV prediction with the at least one angular intra predictions; determining at least one BV based on a fractional precision of the sub-pel BV with or without a rounding operation; determining at least one BV based on a fractional precision of the sub-pel BV with or without a clipping operation; removing a redundant BV candidate obtained from at least one BV candidate list; removing a BV candidate pointing to a reference block with unavailable samples inside the reference block or a template area of the reference block; in response to determining that the BV has a valid fractional component, and at least one sample in a template area of a reference block pointed to by the BV is unavailable, performing a padding process for the at least one sample; or applying a same interpolation filter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for obtaining an initial prediction block of the multiple initial prediction blocks.

[0500] In some examples, the switching condition includes: a distance between a neighboring block, from which a BV of the BV prediction mode is obtained, and the current block is larger or smaller than a specific distance; or receiving a switching flag.

[0501] In some examples, the processor 2920, at the side of the decoder, may obtain the prediction block for the current block based on the multiple initial predictions of the current block based on a spatial Geometric partitioning (SGPM) mode, a decoder side intra mode derivation (DIMD) mode, a template-based intra mode derivation (TIMD) mode, or an occurrence-based intra coding (OBIC) mode.

[0502] In some examples, the BV prediction mode includes an IntraTMP mode, or an intra block copy (IBC) mode.

[0503] FIG. 32 is a flowchart illustrating a method for video encoding corresponding to the method of video decoding as shown in FIG. 30, according to an example of the present disclosure.

[0504] In Step 3201, the processor 2920, at the side of an encoder, may obtain at least one block vector (BV) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode. Intra TMP mode is a special intra prediction mode that copies the best prediction block from a reference block of the current frame, whose L-shaped template matches the current template. The BV refers to a vector points from the current block to the reference block. The BV candidate list is a collection of potential BVs that might be suitable for predicting the current block.

[0505] In Step 3202, the processor 2920, at the side of the encoder, may obtain a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear filterof a local illumination compensation (LIC) mode, wherein the at least one BV candidate list includes at least one of following lists: an integer-pel BV candidate list, a sub-pel BV candidate list, or a composite BV candidate list including at least one integer-pel BV and at least one sub- pel BV. In some embodiments, the prediction block for the current block is obtained based on the at least one BV. In some other embodiments, the prediction block for the current block is obtained based on the at least one BV and the linear filter of the LIC mode. However, whether the linear filter of the LIC mode is used for obtaining the prediction block is not limited. In some embodiments, the at least one BV obtained for prediction may be at least one integer-pel BV, which may be obtained from an integer-pel BV candidate list, or from a composite BV candidate list including at least one integer-pel BV and at least one sub-pel BV. In some other embodiments, the at least one BV obtained for prediction may be at least one BV including a fractional component, which may be obtained from a sub-pel BV candidate list, or a composite BV candidate list including at least one integer-pel BV and at least one sub-pel BV. However, the specific type of the candidate lists selected for obtaining the at least one BV is not limited to the embodiments of the present disclosure.

[0506] In some examples, the processor 2920, at the side of the encoder, may further perform one of followings steps : signaling a first candidate index to a decoder for the decoder to determine an integer-pel BV based on an integer-pel BV candidate list and the first candidate index, or based on a composite BV candidate list and the first candidate index; or signaling a second candidate index to a decoder for the decoder to determine a sub-pel BV based on a sub-pel BV candidate list and the second candidate index, or based on a composite BV candidate list and the first candidate index. In some embodiments, the processor 2920, at the side of the encoder, may determine the integer-pel BV based on the integer-pel BV candidate list and the first candidate index, or based on a composite BV candidate list and the first candidate index; or the processor 2920, at the side of the encoder, may determine the sub-pel BV based on the sub-pel BV candidate list and the second candidate index, or based on a composite BV candidate list and the first candidate index.

[0507] In some examples, the processor 2920, at the side of the encoder, may further obtain a reordered BV candidate list by reordering all BVs in a first BV candidate list of the at least one block BV candidate list based on template matching.

[0508] In some examples, the processor 2920, at the side of the encoder, may further perform the followings step : signaling a third candidate index to a decoder for the decoder to determine a firstBV based on the first BV candidate list and the third candidate index, wherein the third candidate index is configured to indicate one of all BV candidates in the first candidate list, or one of a top number of BV candidates in the reordered BV candidate list. In some embodiments, the processor may determine the first BV based on the first BV candidate list and the third candidate index.

[0509] In some examples, reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching includes: reordering all BVs in the first BV candidate list based on a sum of absolute differences (SAD) costs or a sum of absolute transformed differences (SATD) costs between template samples of the current block and corresponding prediction samples of the template samples.

[0510] In some examples, the processor 2920, at the side of the encoder, may perform the followings step to obtain the prediction block for the current block based on the at least one BV: obtaining the prediction block for the current block based on the at least one BV by applying a first interpolation filter; wherein obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching includes: obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching by using a second interpolation filter.

[0511] In some examples, the first interpolation filter is identical to the second interpolation filter, and the processor 2920, at the side of the encoder, may further perform one padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter, and a second interpolation process of generating prediction samples of template samples of the current block for template matching.

[0512] In some examples, performing the one padding process for the first interpolation process and the second interpolation process includes one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

[0513] In some examples, the first interpolation filter is different from the second interpolation filter, and the processor 2920, at the side of the encoder, may further perform a first padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter; and perform a second padding process for a second interpolation process of generating prediction samples of template samples of the current block for template matching.

[0514] In some examples, at least one of the first padding process or the second padding process includes one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

[0515] In some examples, the processor 2920, at the side of the encoder, may further construct the at least one BV candidate list by multiple searching rounds, wherein the multiple searching rounds include a first searching round and a second searching round after the first searching round, the second searching round is performed in a region around a searching result of the first searching round, and a granularity or a precision of the second searching round is higher than a granularity or a precision of the first searching round.

[0516] In some examples, the first searching round and the second searching round are for searching integer-pel BVs, a searching region of the first searching round is subsampled by a factor of 3, and a searching region of the second searching round is subsampled by a factor less than 3.

[0517] In some examples, the processor 2920, at the side of the encoder, may further reorder searching results of at least one searching round of the multiple searching rounds based on template matching.

[0518] In some examples, reordering the searching results of the at least one searching round of the multiple searching rounds based on template matching includes one of followings: reordering searching results of the first searching round based on a SAD based cost function, reordering searching results of the second searching round based on a SATD based cost function, and reordering searching results of a third searching round after the second searching round based on a SAD based cost function; reordering the searching results of the first searching round based on a SAD based cost function, reordering the searching results of the second searching round based on a SAD based cost function, and reordering the searching results of a third searching round after the second searching round based on a SATD based cost function; or reordering the searching results of the first searching round based on a mean-removed SAD based cost function, and reordering the searching results of the second searching round based on a mean-removed SATD or non-mean-removed SATD based cost function.

[0519] In some embodiments, the processor 2920, at the side of the encoder, may obtain multiple BV candidates based on the at least one BV candidate list; obtain multiple initial prediction blocksbased on the multiple BV candidates; and obtain the prediction block for the current block based on the multiple initial prediction blocks.

[0520] In some embodiments, obtaining the prediction block for the current block based on the multiple initial prediction blocks includes: determining weights of the multiple initial prediction blocks based on template matching; and obtaining the prediction block for the current block based on the multiple initial prediction blocks and the weights of the multiple initial prediction blocks.

[0521] In some embodiments, determining the weight of the initial prediction block based on template matching includes: calculating a template matching cost of the initial prediction block based on a template type of the initial prediction block.

[0522] In some embodiments, the processor 2920, at the side of the encoder, may further select the multiple BV candidates from the at least one BV candidate list based on template matching costs of the multiple BV candidates.

[0523] In some embodiments, the processor 2920, at the side of the encoder, may perform one of following steps to obtain the at least one BV: obtaining the at least one BV based on at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; in response to meeting a constant index selection condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; or in response to meeting a dynamic switching condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one candidate index signaled by an encoder.

[0524] In some examples, the constant index selection or the dynamic switching condition includes one of followings: a block size of the current block is smaller or greater than a first predefined threshold; a block shape of the current block meets a predefined shape; a flag signaled by an encoder is true or false, wherein the flag is at a sequence parameter set (SPS) level or a picture parameter set (PPS) level; a specific sub-mode of the IntraTMP mode is or is not applied; or whether a specific part of template samples of the current block is available for template matching.

[0525] In some examples, the processor 2920, at the side of the encoder, may further, in response to determining that a block size of the current block is smaller or greater than a second predefined threshold, construct the at least one BV candidate list including at least one specific integer-pel BV or at least one specific sub-pel BV, wherein obtaining the at least one BV based on the at leastone BV candidate list for the IntraTMP mode includes: obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index.

[0526] In some examples, the processor 2920, at the side of the encoder, may further determine a width or a height of a template size of the current block as less than 4; or determine a width and a height of a template size of the current block as being different.

[0527] In some examples, obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching includes: determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block; obtaining a weighted sum cost between the template samples of the current block and corresponding prediction samples of the template samples for each BV in the first BV candidate list; and reordering all BVs in the first BV candidate list based on the weighted sum cost for each BV in the first BV candidate list.

[0528] In some examples, the current block is a 8x8 block, and a template size of the current block includes 4 lines of template samples above the current block and 4 columns of template samples on the left of the current block; wherein determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block includes: determining that a closest line of template samples and a closest column of template samples have a same weight of 8; and determining other three lines of template samples and other three columns of template samples have a same weight of 1 .

[0529] In some examples, the template samples of the current block include only top template samples above the current block, or only left template samples on the left of the current block.

[0530] In some examples, reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching includes: reordering all BVs in the first BV candidate list based on a sum of mean-removed SAD costs or SATD costs between template samples of the current block and corresponding prediction samples of the template samples; or reordering all BVs in the first BV candidate list based on a sum of costs between template samples of the current block and corresponding prediction samples of the template samples, wherein the corresponding prediction samples are filtered based on the linear filter.

[0531] In some examples, the processor 2920, at the side of the encoder, may apply a same interpolation filter or different interpolation filters for a template generation process duringreordering BV candidates in a BV candidate list and for an interpolation process for obtaining the prediction block.

[0532] In some examples, the processor 2920, at the side of the encoder, may obtain an integer- pel BV and a sub-pel BV based on at least one BV candidate list; obtain a BV by adding fractional refinement of the sub-pel BV to the integer-pel BV; and in response to determining that a sample in a first reference block pointed to by the BV is not available, perform a padding process in an area starting from a boundary of a second reference block pointed to by the integer-pel BV.

[0533] FIG. 33 is a flowchart illustrating a method for video encoding corresponding to the method of video decoding shown in FIG. 31, according to an example of the present disclosure.

[0534] In Step 3301, the processor 2920, at the side of an encoder, may obtain a prediction block for a current block based on multiple initial predictions of the current block, wherein the multiple initial predictions include a BV prediction obtained based on a BV prediction mode. The multiple initial predictions are used for obtain the prediction block of the current block, and at least one initial prediction is a BV prediction, which is a block-vector based prediction from adjacent or non-adjacent neighboring blocks obtained based on a BV prediction mode, for example, an intrTMP mode or an IBC mode.

[0535] In some examples, the processor 2920, at the side of the encoder, may perform one of following steps: constructing a BV candidate list by adding at least one BV of at least one neighboring block coded in the BV prediction mode; skipping a constructing process for a BV candidate list by using an existing BV candidate list; in response to meeting a switching condition, switching to obtain an integer BV or a factional BV in the BV prediction mode; signaling a switching flag to a decoder for the decoder to switch to obtain an integer BV or a factional BV for applying the BV prediction mode; determining at least one BV for the BV prediction mode by selecting a predefined number of BVs from a BV candidate list; determining, by the encoder and based on a first cost testing result, whether to use the BV prediction for obtaining the prediction block, wherein the multiple initial predictions further include at least one angular intra prediction, and the first cost testing result is obtained by blending the BV prediction with the at least one angular intra prediction; determining, by the encoder and based on a second cost testing result, whether to use a non-angular intra prediction for obtaining the prediction block, wherein the multiple initial predictions further include the non-angular intra prediction and at least one angular intra predictions, and the second cost testing result is obtained by blending the BV prediction withthe at least one angular intra predictions; determining at least one BV based on a fractional precision of the sub-pel BV with or without a rounding operation; determining at least one BV based on a fractional precision of the sub-pel BV with or without a clipping operation; removing a redundant BV candidate obtained from at least one BV candidate list; removing a BV candidate pointing to a reference block with unavailable samples inside the reference block or a template area of the reference block; in response to determining that the BV has a valid fractional component, and at least one sample in a template area of a reference block pointed to by the BV is unavailable, performing a padding process for the at least one sample; or applying a same interpolation fdter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for obtaining an initial prediction block of the multiple initial prediction blocks.

[0536] In some examples, the switching condition includes: a distance between a neighboring block, from which a BV of the BV prediction mode is obtained, and the current block is larger or smaller than a specific distance.

[0537] In some examples, the processor 2920, at the side of the encoder, may obtain the prediction block for the current block based on the multiple initial predictions of the current block based on a spatial Geometric partitioning (SGPM) mode, a decoder side intra mode derivation (DIMD) mode, a template-based intra mode derivation (TIMD) mode, or an occurrence-based intra coding (OBIC) mode.

[0538] In some examples, the BV prediction mode includes an IntraTMP mode, or an intra block copy (IBC) mode.

[0539] In an embodiment, there is also provided a method of storing a bitstream, comprising storing the bitstream on a digital storage medium, wherein the bitstream comprises encoded video information generated by the encoding method described above or encoded video information to be decoded by the decoding method described above.

[0540] In an embodiment, there is also provided a method for transmitting a bitstream generated by the encoder described above. In an embodiment, there is also provided a method for receiving a bitstream to be decoded by the decoder described above.

[0541] In an embodiment, there is also provided a non-transitory computer-readable storage medium comprising a plurality of programs, for example, in the memory 2930, executable by the processor 2920 in the computing environment 2910, for performing the above-described methodsand / or storing a bitstream generated by the encoding method described above or a bitstream to be decoded by the decoding method described above. In an embodiment, the plurality of programs may be executed by the processor 2920 in the computing environment 2910 to receive (for example, from the video encoder 20 in FIG. 2) a bitstream or data stream including encoded video information (for example, video blocks representing encoded video frames, and / or associated one or more syntax elements, etc.), and may also be executed by the processor 2920 in the computing environment 2910 to perform the decoding method described above according to the received bitstream or data stream. In another example, the plurality of programs may be executed by the processor 2920 in the computing environment 2910 to perform the encoding method described above to encode video information (for example, video blocks representing video frames, and / or associated one or more syntax elements, etc.) into a bitstream or data stream, and may also be executed by the processor 2920 in the computing environment 2910 to transmit the bitstream or data stream (for example, to the video decoder 30 in FIG. 3). Alternatively, the non-transitory computer-readable storage medium may have stored therein a bitstream or a data stream comprising encoded video information (for example, video blocks representing encoded video frames, and / or associated one or more syntax elements etc.) generated by an encoder (for example, the video encoder 20 in FIG. 2) using, for example, the encoding method described above for use by a decoder (for example, the video decoder 30 in FIG. 3) in decoding video data. The non- transitory computer-readable storage medium may be, for example, a ROM, a Random Access Memory (RAM), a CD-ROM, a magnetic tape, a floppy disc, an optical data storage device or the like.

[0542] In an embodiment, there is provided a bitstream generated by the encoding method described above or a bitstream to be decoded by the decoding method described above. In an embodiment, there is provided a bitstream comprising encoded video information generated by the encoding method described above or encoded video information to be decoded by the decoding method described above.

[0543] In an embodiment, the is also provided a computing device comprising one or more processors (for example, the processor 2920); and the non-transitory computer-readable storage medium or the memory 2930 having stored therein a plurality of programs executable by the one or more processors, wherein the one or more processors, upon execution of the plurality of programs, are configured to perform the above-described methods.

[0544] In an embodiment, there is also provided a computer program product having instructions for storage or transmission of a bitstream comprising encoded video information generated by the encoding method described above or encoded video information to be decoded by the decoding method described above. In an embodiment, there is also provided a computer program product comprising a plurality of programs, for example, in the memory 2930, executable by the processor 2920 in the computing environment 2910, for performing the above-described methods. For example, the computer program product may include the non-transitory computer-readable storage medium.

[0545] In an embodiment, the computing environment 2910 may be implemented with one or more ASICs, DSPs, Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), FPGAs, GPUs, controllers, micro-controllers, microprocessors, or other electronic components, for performing the above methods.

[0546] The description of the present disclosure has been presented for purposes of illustration and is not intended to be exhaustive or limited to the present disclosure. Many modifications, variations, and alternative implementations will be apparent to those of ordinary skill in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Unless specifically stated otherwise, an order of steps of the method according to the present disclosure is only intended to be illustrative, and the steps of the method according to the present disclosure are not limited to the order specifically described above, but may be changed according to practical conditions. In addition, at least one of the steps of the method according to the present disclosure may be adjusted, combined or deleted according to practical requirements.

[0547] The examples were chosen and described in order to explain the principles of the disclosure and to enable others skilled in the art to understand the disclosure for various implementations and to best utilize the underlying principles and various implementations with various modifications as are suited to the particular use contemplated. Therefore, it is to be understood that the scope of the disclosure is not to be limited to the specific examples of the implementations disclosed and that modifications and other implementations are intended to be included within the scope of the present disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method for video decoding, comprising: obtaining, by a decoder, at least one block vector (BV) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode; and obtaining, by the decoder, a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear filter of a local illumination compensation (LIC) mode, wherein the at least one BV candidate list comprises at least one of following lists: an integer-pel BV candidate list, a sub-pel BV candidate list, or a composite BV candidate list comprising at least one integer-pel BV and at least one sub-pel BV.

2. The method of claim 1, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises one of followings: in response to receiving a first candidate index, determining an integer-pel BV based on an integer-pel BV candidate list and the first candidate index, or based on the composite BV candidate list and the first candidate index; or in response to receiving a second candidate index, determining a sub-pel BV based on a sub-pel BV candidate list and the second candidate index, or based on a composite BV candidate list and the first candidate index.

3. The method of claim 1, further comprising: obtaining, by the decoder, a reordered BV candidate list by reordering all BVs in a first BV candidate list of the at least one block BV candidate list based on template matching.

4. The method of claim 3, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises: in response to receiving a third candidate index, determining a first BV based on the first BV candidate list based on the third candidate index, wherein the third candidate index is configured to indicate one of all BV candidates in the first candidate list, or one of a top number of BV candidates in the reordered BV candidate list.

5. The method of claim 3, wherein reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching comprises: reordering all BVs in the first BV candidate list based on a sum of absolute differences (SAD) costs or a sum of absolute transformed differences (SATD) costs between template samples of the current block and corresponding prediction samples of the template samples.

6. The method of claim 3, wherein obtaining the prediction block for the current block based on the at least one BV comprises: obtaining the prediction block for the current block based on the at least one BV by applying a first interpolation filter; and wherein obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching comprises: obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching by using a second interpolation filter.

7. The method of claim 6, wherein the first interpolation filter is identical to the second interpolation filter, and the method further comprises: performing, by the decoder, one padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter, and a second interpolation process of generating prediction samples of template samples of the current block for template matching.

8. The method of claim 6, wherein performing the one padding process for the first interpolation process and the second interpolation process comprises one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

9. The method of claim 6, wherein the first interpolation filter is different from the second interpolation filter, and the method further comprises: performing, by the decoder, a first padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter; and performing, by the decoder, a second padding process for a second interpolation process of generating prediction samples of template samples of the current block for template matching.

10. The method of claim 9, wherein at least one of the first padding process or the second padding process comprises one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

11. The method of claim 1, further comprising: constructing, by the decoder, the at least one BV candidate list by multiple searching rounds, wherein the multiple searching rounds comprise a first searching round and a second searching round after the first searching round, the second searching round is performed in a region around a searching result of the first searching round, and a granularity or a precision of the second searching round is higher than a granularity or a precision of the first searching round.

12. The method of claim 11, wherein the first searching round and the second searching round are for searching integer-pel BVs, a searching region of the first searching round is subsampled by a factor of 3, and a searching region of the second searching round is subsampled by a factor less than 3.

13. The method of claim 1, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises one of followings: obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index;in response to meeting a constant index selection condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; or in response to meeting a dynamic switching condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one candidate index signaled by an encoder.

14. The method of claim 13, wherein the constant index selection or the dynamic switching condition comprises one of followings: a block size of the current block is smaller or greater than a first predefined threshold; a block shape of the current block meets a predefined shape; a flag signaled by an encoder is true or false, wherein the flag is at a sequence parameter set (SPS) level or a picture parameter set (PPS) level; a specific sub-mode of the IntraTMP mode is or is not applied; or whether a specific part of template samples of the current block is available for template matching.

15. The method of claim 1, further comprising: in response to determining that a block size of the current block is smaller or greater than a second predefined threshold, constructing, by the decoder, the at least one BV candidate list comprising at least one specific integer-pel BV or at least one specific sub-pel BV, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises: obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index.

16. The method of claim 3, further comprising: determining a width or a height of a template size of the current block as less than 4; or determining a width and a height of a template size of the current block as being different.

17. The method of claim 3, wherein obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching comprises: determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block; obtaining a weighted sum cost between the template samples of the current block and corresponding prediction samples of the template samples for each BV in the first BV candidate list; and reordering all BVs in the first BV candidate list based on the weighted sum cost for each BV in the first BV candidate list.

18. The method of claim 17, wherein the current block is a 8x8 block, and a template size of the current block comprises 4 lines of template samples above the current block and 4 columns of template samples on the left of the current block; wherein determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block comprises: determining that a closest line of template samples and a closest column of template samples have a same weight of 8; and determining other three lines of template samples and other three columns of template samples have a same weight of 1 .

19. The method of claim 17, wherein the template samples of the current block comprise only top template samples above the current block, or only left template samples on the left of the current block.

20. The method of claim 3, wherein reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching comprises: reordering all BVs in the first BV candidate list based on a sum of mean-removed SAD costs or SATD costs between template samples of the current block and corresponding prediction samples of the template samples; orreordering all BVs in the first BV candidate list based on a sum of costs between template samples of the current block and corresponding prediction samples of the template samples, wherein the corresponding prediction samples are filtered based on the linear filter.

21. The method of claim 1, further comprising: applying a same interpolation filter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for an interpolation process for obtaining the prediction block.

22. The method of claim 1, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises: obtaining an integer-pel BV and a sub-pel BV based on the at least one BV candidate list; wherein the method further comprises: obtaining, by the decoder, a BV by adding fractional refinement of the sub-pel BV to the integer-pel BV; and in response to determining that a sample in a first reference block pointed to by the BV is not available, performing, by the decoder, a padding process in an area starting from a boundary of a second reference block pointed to by the integer-pel BV.

23. A method for video decoding, comprising: obtaining, by a decoder, a prediction block for a current block based on multiple initial predictions of the current block, wherein the multiple initial predictions comprise a BV prediction obtained based on a BV prediction mode.

24. The method of claim 23, further comprising one of following steps: constructing, by the decoder, a BV candidate list by adding at least one BV of at least one neighboring block coded in the BV prediction mode; skipping, by the decoder, a constructing process for a BV candidate list by using an existing BV candidate list;in response to meeting a switching condition, switching, by the decoder, to obtain an integer BV or a factional BV in the BV prediction mode; determining, by the decoder, at least one BV for the BV prediction mode by selecting a predefined number of BVs from a BV candidate list; determining, by the decoder and based on a first cost testing result, whether to use the BV prediction for obtaining the prediction block, wherein the multiple initial predictions further comprise at least one angular intra prediction, and the first cost testing result is obtained by blending the BV prediction with the at least one angular intra prediction; determining, by the decoder and based on a second cost testing result, whether to use a non-angular intra prediction for obtaining the prediction block, wherein the multiple initial predictions further comprise the non-angular intra prediction and at least one angular intra predictions, and the second cost testing result is obtained by blending the BV prediction with the at least one angular intra predictions; determining, by the decoder, at least one BV based on a fractional precision of the sub-pel BV with or without a rounding operation; determining, by the decoder, at least one BV based on a fractional precision of the sub-pel BV with or without a clipping operation; removing, by the decoder, a redundant BV candidate obtained from at least one BV candidate list; removing, by the decoder, a BV candidate pointing to a reference block with unavailable samples inside the reference block or a template area of the reference block; in response to determining, by the decoder, that the BV has a valid fractional component, and at least one sample in a template area of a reference block pointed to by the BV is unavailable, performing, by the decoder, a padding process for the at least one sample; or applying, by the decoder, a same interpolation filter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for obtaining an initial prediction block of the multiple initial prediction blocks.

25. The method of claim 24, wherein the switching condition comprises: a distance between a neighboring block, from which a BV of the BV prediction mode is obtained, and the current block is larger or smaller than a specific distance; orreceiving a switching flag.

26. The method of claim 23, wherein obtaining the prediction block for the current block based on the multiple initial predictions of the current block comprises: obtaining the prediction block based on a spatial Geometric partitioning (SGPM) mode, a decoder side intra mode derivation (DIMD) mode, a template-based intra mode derivation (TIMD) mode, or an occurrence-based intra coding (OBIC) mode.

27. The method of claim 23, wherein the BV prediction mode comprises an IntraTMP mode, or an intra block copy (IBC) mode.

28. A method for video encoding, comprising: obtaining, by an encoder, at least one block vector (B V) based on at least one BV candidate list for an intra template matching prediction (IntraTMP) mode; and obtaining, by the encoder, a prediction block for a current block based on the at least one BV, or based on the at least one BV and a linear filter of a local illumination compensation (LIC) mode, wherein the at least one BV candidate list comprises at least one of following lists: an integer-pel BV candidate list, a sub-pel BV candidate list, or a composite BV candidate list comprising at least one integer-pel BV and at least one sub-pel BV.

29. The method of claim 28, further comprising: signaling a first candidate index to a decoder for the decoder to determine an integer-pel BV based on an integer-pel BV candidate list and the first candidate index, or based on the composite BV candidate list and the first candidate index; or signaling a second candidate index to a decoder for the decoder to determine a sub-pel BV based on a sub-pel BV candidate list and the second candidate index, or based on a composite BV candidate list and the first candidate index.

30. The method of claim 28, further comprising:obtaining, by the encoder, a reordered BV candidate list by reordering all BVs in a first B V candidate list of the at least one block BV candidate list based on template matching.

31. The method of claim 30, further comprising: signaling a third candidate index to a decoder for the decoder to determine a first B V based on the first BV candidate list based on the third candidate index, wherein the third candidate index is configured to indicate one of all BV candidates in the first candidate list, or one of a top number of BV candidates in the reordered BV candidate list.

32. The method of claim 30, wherein reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching comprises: reordering all BVs in the first BV candidate list based on a sum of absolute differences (SAD) costs or a sum of absolute transformed differences (SATD) costs between template samples of the current block and corresponding prediction samples of the template samples.

33. The method of claim 30, wherein obtaining the prediction block for the current block based on the at least one BV comprises: obtaining the prediction block for the current block based on the at least one BV by applying a first interpolation filter; and wherein obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching comprises: obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching by using a second interpolation filter.

34. The method of claim 33, wherein the first interpolation filter is identical to the second interpolation filter, and the method further comprises: performing, by the encoder, one padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter, and a second interpolation process of generating prediction samples of template samples of the current block for template matching.

35. The method of claim 33 wherein performing the one padding process for the first interpolation process and the second interpolation process comprises one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

36. The method of claim 33, wherein the first interpolation filter is different from the second interpolation filter, and the method further comprises: performing, by the encoder, a first padding process for a first interpolation process of generating the prediction block of the current block based on the first interpolation filter; and performing, by the encoder, a second padding process for a second interpolation process of generating prediction samples of template samples of the current block for template matching.

37. The method of claim 36, wherein at least one of the first padding process or the second padding process comprises one of followings: performing padding along a horizontal direction, and then performing padding along a vertical direction; or performing padding along a vertical direction, and then performing padding along a horizontal direction.

38. The method of claim 28, further comprising: constructing, by the encoder, the at least one BV candidate list by multiple searching rounds, wherein the multiple searching rounds comprise a first searching round and a second searching round after the first searching round, the second searching round is performed in a region around a searching result of the first searching round, and a granularity or a precision of the second searching round is higher than a granularity or a precision of the first searching round.

39. The method of claim 38, wherein the first searching round and the second searching round are for searching integer-pel BVs, a searching region of the first searching round issubsampled by a factor of 3, and a searching region of the second searching round is subsampled by a factor less than 3.

40. The method of claim 28, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises one of followings: obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; in response to meeting a constant index selection condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index; or in response to meeting a dynamic switching condition, obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode according to at least one candidate index signaled by an encoder.

41. The method of claim 40, wherein the constant index selection or the dynamic switching condition comprises one of followings: a block size of the current block is smaller or greater than a first predefined threshold; a block shape of the current block meets a predefined shape; a flag signaled by an encoder is true or false, wherein the flag is at a sequence parameter set (SPS) level or a picture parameter set (PPS) level; a specific sub-mode of the IntraTMP mode is or is not applied; or whether a specific part of template samples of the current block is available for template matching.

42. The method of claim 28, further comprising: in response to determining that a block size of the current block is smaller or greater than a second predefined threshold, constructing, by the encoder, the at least one BV candidate list comprising at least one specific integer-pel BV or at least one specific sub-pel BV, wherein obtaining the at least one BV based on the at least one BV candidate list for the IntraTMP mode comprises:obtaining the at least one BV based on at least one BV candidate list for the IntraTMP mode according to at least one predefined constant candidate index.

43. The method of claim 30, further comprising: determining a width or a height of a template size of the current block as less than 4; or determining a width and a height of a template size of the current block as being different.

44. The method of claim 30, wherein obtaining the reordered BV candidate list by reordering all BVs in the first BV candidate list based on template matching comprises: determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block; obtaining a weighted sum cost between the template samples of the current block and corresponding prediction samples of the template samples for each BV in the first BV candidate list; and reordering all BVs in the first BV candidate list based on the weighted sum cost for each BV in the first BV candidate list.

45. The method of claim 44, wherein the current block is a 8x8 block, and a template size of the current block comprises 4 lines of template samples above the current block and 4 columns of template samples on the left of the current block; wherein determining a plurality of weights for template samples of the current block according to a plurality of spatial distances from the template samples to the current block comprises: determining that a closest line of template samples and a closest column of template samples have a same weight of 8; and determining other three lines of template samples and other three columns of template samples have a same weight of 1.

46. The method of claim 44, wherein the template samples of the current block comprise only top template samples above the current block, or only left template samples on the left of the current block.

47. The method of claim 30, wherein reordering all BVs in the first BV candidate list of the at least one block BV candidate list based on template matching comprises: reordering all BVs in the first BV candidate list based on a sum of mean-removed SAD costs or SATD costs between template samples of the current block and corresponding prediction samples of the template samples; or reordering all BVs in the first BV candidate list based on a sum of costs between template samples of the current block and corresponding prediction samples of the template samples, wherein the corresponding prediction samples are filtered based on the linear filter.

48. The method of claim 30, further comprises: applying a same interpolation filter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for an interpolation process for obtaining the prediction block.

49. The method of claim 30, wherein obtaining the at least one BV based on at least one BV candidate list for the IntraTMP mode comprises: obtaining an integer-pel BV and a sub-pel BV based on at least one BV candidate list; wherein the method further comprises: obtaining, by the encoder, a BV by adding fractional refinement of the sub-pel BV to the integer-pel BV; and in response to determining that a sample in a first reference block pointed to by the BV is not available, performing, by the encoder, a padding process in an area starting from a boundary of a second reference block pointed to by the integer-pel BV.

50. A method for video encoding, comprising: obtaining, by an encoder, a prediction block for a current block based on multiple initial predictions of the current block, wherein the multiple initial predictions comprise a BV prediction obtained based on a BV prediction mode.51 . The method of claim 50, further comprising one of following steps: constructing, by the encoder, a BV candidate list by adding at least one BV of at least one neighboring block coded in the BV prediction mode; skipping, by the encoder, a constructing process for a BV candidate list by using an existing BV candidate list; in response to meeting a switching condition, switching, by the encoder, to obtain an integer BV or a factional BV in the BV prediction mode; signaling a switching flag to a decoder for the decoder to switch to obtain an integer BV or a factional BV for applying the BV prediction mode; determining, by the encoder, at least one BV for the BV prediction mode by selecting a predefined number of BVs from a BV candidate list; determining, by the encoder and based on a first cost testing result, whether to use the BV prediction for obtaining the prediction block, wherein the multiple initial predictions further comprise at least one angular intra prediction, and the first cost testing result is obtained by blending the BV prediction with the at least one angular intra prediction; determining, by the encoder and based on a second cost testing result, whether to use a non-angular intra prediction for obtaining the prediction block, wherein the multiple initial predictions further comprise the non-angular intra prediction and at least one angular intra predictions, and the second cost testing result is obtained by blending the BV prediction with the at least one angular intra predictions; determining, by the encoder, at least one BV based on a fractional precision of the sub-pel BV with or without a rounding operation; determining, by the encoder, at least one BV based on a fractional precision of the sub-pel BV with or without a clipping operation; removing, by the encoder, a redundant BV candidate obtained from at least one BV candidate list; removing, by the encoder, a BV candidate pointing to a reference block with unavailable samples inside the reference block or a template area of the reference block; in response to determining, by the encoder, that the BV has a valid fractional component, and at least one sample in a template area of a reference block pointed to by the BV is unavailable, performing, by the encoder, a padding process for the at least one sample; orapplying, by the encoder, a same interpolation filter or different interpolation filters for a template generation process during reordering BV candidates in a BV candidate list and for obtaining an initial prediction block of the multiple initial prediction blocks.

52. The method of claim 51, wherein the switching condition comprises: a distance between a neighboring block, from which a BV of the BV prediction mode is obtained, and the current block is larger or smaller than a specific distance.

53. The method of claim 50, wherein obtaining the prediction block for the current block based on the multiple initial predictions of the current block comprises: obtaining the prediction block based on a spatial Geometric partitioning (SGPM) mode, a decoder side intra mode derivation (DIMD) mode, a template-based intra mode derivation (TIMD) mode, or an occurrence-based intra coding (OBIC) mode.

54. The method of claim 50, wherein the BV prediction mode comprises an IntraTMP mode, or an intra block copy (IBC) mode.

55. An apparatus for video coding, comprising: one or more processors; and a memory coupled to the one or more processors and configured to store instructions executable by the one or more processors, wherein the one or more processors, upon execution of the instructions, are configured to perform the method in any one of claims 1-54.

56. A non-transitory computer-readable storage medium for storing computer-executable instructions that, when executed by one or more computer processors, cause the one or more computer processors to perform the method in any of claims 1-54.

57. A non-transitory computer-readable storage medium for storing a bitstream to be decoded by the method in any of claims 1-27.

58. A method for transmitting a bitstream, comprising: generating a bitstream by performing the encoding method according to any of claims 28-; and transmitting the bitstream to a decoding device.

59. A method for storing a bitstream, comprising: generating a bitstream by performing the encoding method according to any of claims 28-; and storing the bitstream on a non-transitory computer-readable storage medium.

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