WO2020085955A1

WO2020085955A1 - Method and apparatus for reference sample filtering

Info

Publication number: WO2020085955A1
Application number: PCT/RU2019/050198
Authority: WO
Inventors: Alexey Konstantinovich FILIPPOV; Vasily Alexeevich RUFITSKIY; Jianle Chen
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2018-10-26
Filing date: 2019-10-25
Publication date: 2020-04-30

Abstract

The present disclosure provides methods and devices for encoding or decoding of video or image data. The method comprises: obtaining a set of reference samples for the current block, wherein the set of reference samples comprises a first reference sample and a second reference sample, and the second reference sample is not adjacent to any other reference sample in the set of reference samples; and filtering the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

Description

METHOD AND APPARATUS FOR REFERENCE SAMPLE FILTERING

TECHNICAL FIELD

The present disclosure relates to the technical field of image and/or video coding and decoding, and in particular to method and apparatus of reference sample filtering for directional intra prediction.

BACKGROUND

Digital video has been widely used since the introduction of DVD-discs. Before transmission the video is encoded and is transmitted using a transmission medium. The viewer receives the video and uses a viewing device to decode and display the video. Over the years the quality of video has improved, for example, because of higher resolutions, color depths and frame rates. This has lead into larger data streams that are nowadays commonly transported over internet and mobile communication networks.

The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modem day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in picture quality are desirable. Higher resolution videos, however, typically require more bandwidth as they have more information. In order to reduce bandwidth requirements video coding standards involving compression of the video have been introduced. When the video is encoded the bandwidth requirements (or corresponding memory requirements in case of storage) are reduced. Often this reduction comes at the cost of quality. Thus, the video coding standards try to find a balance between bandwidth requirements and quality.

The High Efficiency Video Coding (HEVC) is an example of a video coding standard that is commonly known to persons skilled in the art. In HEVC, to split a coding unit (CU) into prediction units (PET) or transform units (TETs). The Versatile Video Coding (VVC) next generation standard is the most recent joint video project of the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG) standardization organizations, working together in a partnership known as the Joint Video Exploration Team (JVET). VVC is also referred to as ITU-T H.266/Next Generation Video Coding (NGVC) standard. In VVC, the concepts of multiple partition types shall be removed, i.e. the separation of the CU, PU and TU concepts except as needed for CUs that have a size too large for the maximum transform length, and supports more flexibility for CU partition shapes.

Processing of these coding units (CUs) (also referred to as blocks) depend on their size, spatial position and a coding mode specified by an encoder. Coding modes can be classified into two groups according to the type of prediction: intra-prediction and inter-prediction modes. Intra prediction modes use samples of the same picture (also referred to as frame or image) to generate reference samples to calculate the prediction values for the samples of the block being reconstructed. Intra prediction is also referred to as spatial prediction. Inter-prediction modes are designed for temporal prediction and uses reference samples of previous or next pictures to predict samples of the block of the current picture.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC l/SC 29/WG 11) are studying the potential need for standardization of future video coding technology with a compression capability that significantly exceeds that of the current HEVC standard (including its current extensions and near-term extensions for screen content coding and high-dynamic-range coding). The groups are working together on this exploration activity in a joint collaboration effort known as the Joint Video Exploration Team (JVET) to evaluate compression technology designs proposed by their experts in this area.

The VTM (Versatile Test Model) standard uses 35 Intra modes whereas the BMS (Benchmark Set) uses 67 Intra modes. The intra mode coding scheme currently described in BMS is considered complex and a disadvantage of non-selected mode set is that the index list is always constant and not adaptive based on the current block properties (for e.g. its neighboring blocks INTRA modes).

SUMMARY Embodiments of the present application provide apparatuses and methods for intra prediction are disclosed. An idea is to apply filters to reference sample non-successively, with an offset between reference samples involved into filtering process. The scope of protection is defined by the claims.

The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to an aspect, the present invention relates to a method of intra-prediction of a current block for encoding or decoding of video or image data, wherein the method comprises: obtaining a set of reference samples for the current block, wherein the set of reference samples comprises a first reference sample and a second reference sample, and the second reference sample is not adjacent to any other reference sample in the set of reference samples; and filtering the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

In an embodiment, a filtering coefficient corresponding to the first reference sample is different from a filtering coefficient corresponding to the second reference sample.

In an embodiment, the first reference sample and the second reference sample are not adjacent in spatial position.

In an embodiment, the first reference sample and the second reference sample are spaced apart from each other by an offset, wherein a position of the first reference sample differs from a position so the second reference sample by a value of the offset.

In an embodiment, the value of the offset is a positive integer greater than one. In an embodiment, the method further comprises: obtaining the value of the offset according to a size of a side of the current block, wherein the second reference sample is determined according to the first reference sample and the value of the offset.

In an embodiment, the method further comprises: obtaining the value of the offset according to an intra prediction mode of the current block, the second reference sample is determined according to the first reference sample and the value of the offset.

In an embodiment, the filtering the first reference sample and the second reference sample to obtain a value of a filtered sample or a predicted sample of the current block comprises: interpolation filtering the first reference sample and the second reference sample to obtain a value of a subpixel filtered sample or subpixel predicted sample of the current block, wherein an interpolation filtering coefficient is calculated according to the value of the offset.

In an embodiment, the method further comprises: interpolation filtering a part of the set of the reference samples to obtain a value of a subpixel filtered sample or subpixel predicted sample, wherein an interpolation filtering coefficient is calculated according to the value of the offset.

In an embodiment, the part of the set of the reference samples is determined according to a sample pattern.

In an embodiment, the sample pattern is selected from a set of predefined sample patterns, according to a subpixel offset, wherein the subpixel offset is determined according to the intra prediction mode of the current block.

In an embodiment, the sample pattern is selected from a set of predefined sample patterns, according to a position of reference sample.

According to an aspect, the present invention relates to an encoder comprising processing circuitry for carrying out any one of the above methods.

According to an aspect, the present invention relates to a decoder comprising processing circuitry for carrying out any one of the above methods.

According to an aspect, the present invention relates to a computer program product comprising a program code for performing any one of above methods. According to an aspect, the present invention relates to an encoder device configured to encode video or image data, wherein the encoder device comprises: an obtaining unit configured to obtain a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample and a second reference sample, and the second reference sample is not adjacent to any other reference sample in the set of reference samples; and a filter unit configured to filter the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

According to an aspect, the present invention relates to a decoder device configured to decode video or image data, wherein the decoder device comprises: an obtaining unit configured to obtain a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample and a second reference sample, and the second reference sample is not adjacent to any other reference sample in the set of reference samples; and a filter unit configured to filter the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are described in more detail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding system configured to implement embodiments of the invention;

FIG. IB is a block diagram showing another example of a video coding system configured to implement embodiments of the invention;

FIG. 2 is a block diagram showing an example of a video encoder configured to implement embodiments of the invention; FIG. 3 is a block diagram showing an example structure of a video decoder configured to implement embodiments of the invention;

FIG. 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus; FIG. 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus;

FIG. 6 illustrates an example of angular intra prediction directions and modes and the associated value of Pang for vertical prediction directions;

FIG. 7 illustrates an example of Transformation of P_ref to Pi, ref for a 4 ^c 4 block;

FIG. 8 illustrates an example of Construction of Pi_{, ref} for horizontal angular prediction;

FIG. 9 illustrates an example of Construction of Pi_{, ref} for vertical angular prediction;

FIG. 10 illustrates an example of Angular intra prediction directions and modes and the associated value of p_ang of a set of intra-prediction modes in JEM and BMS-l;

FIG. 11 illustrates an example of intra-prediction modes in HEVC [1];

FIG. 12 illustrates an example of interpolation filter selection;

FIG. 13 illustrates an example of QTBT explained;

FIG. 14 illustrates an example of Orientation of rectangular blocks;

FIG. 15 illustrates an example of intra-predicting of a block from reference samples of the main reference side; FIG. 16 illustrates another example of intra-predicting of a block from reference samples of the main reference side;

FIG. 17 illustrates another example of intra-predicting of a block from reference samples of the main reference side;

FIG. 18 illustrates an example of a flowchart for setting a value of an offset; FIG. 19 illustrates an example of Interpolation filters used in intra prediction;

FIG. 20 illustrates another example of Interpolation filters used in intra prediction;

FIG. 21 illustrating some examples of sampling patterns;

FIG. 22 illustrates an example of a flowchart for setting a sampling pattern;

FIG. 23 illustrates another example of setting a sampling pattern;

FIG. 24 illustrates an example of an implementation of a filter;

FIG. 25 illustrates another example of an implementation of a filter;

FIG. 26 illustrates an example of filters used in intra reference sample interpolation for intra prediction;

FIG. 27 illustrates another example of filters used in intra reference sample interpolation for intra prediction;

FIG. 28 illustrates another example of filters used in intra reference sample interpolation for intra prediction;

FIG. 29 illustrates another example of filters used in intra reference sample interpolation for intra prediction;

FIG. 30 illustrates another example of filters used in intra reference sample interpolation for intra prediction;

FIG. 31 illustrates an example of reference samples;

FIG. 32 illustrates a flow of a method according to an embodiment.

FIG. 33 illustrates an encoder and a decoder device according to an embodiment.

In the following identical reference signs refer to identical or at least functionally equivalent features if not explicitly specified otherwise. DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Video coding typically refers to the processing of a sequence of pictures, which form the video or video sequence. Instead of the term“picture”, the term“frame” or“image” may be used as synonyms in the field of video coding. Video coding (or coding in general) comprises two parts, video encoding and video decoding. Video encoding is performed at the source side, typically comprising processing (e.g. by compression) the original video pictures to reduce the amount of data required for representing the video pictures (for more efficient storage and/or transmission). Video decoding is performed at the destination side and typically comprises the inverse processing compared to the encoder to reconstruct the video pictures. Embodiments referring to“coding” of video pictures (or pictures in general) shall be understood to relate to “encoding” or“decoding” of video pictures or respective video sequences. The combination of the encoding part and the decoding part is also referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can be reconstructed, the reconstructed video pictures have the same quality as the original video pictures (assuming no transmission loss or other data loss during storage or transmission). In case of lossy video coding, further compression, e.g. by quantization, is performed, to reduce the amount of data representing the video pictures, which cannot be completely reconstructed at the decoder, the quality of the reconstructed video pictures is lower or worse compared to the quality of the original video pictures.

Several video coding standards belong to the group of “lossy hybrid video codecs” (e.g. combine spatial and temporal prediction in the sample domain and 2D transform coding for applying quantization in the transform domain). Each picture of a video sequence is typically partitioned into a set of non-overlapping blocks, and the coding is typically performed on a block level. In other words, at the encoder the video is typically processed, i.e. encoded, on a block (video block) level, e.g. by using spatial (intra picture) prediction and/or temporal (inter picture) prediction to generate a prediction block, subtracting the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), whereas at the decoder the inverse processing compared to the encoder is applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder processing loop such that both will generate identical predictions (e.g. intra- and inter predictions) and/or re-constructions for processing, e.g. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a video encoder 20 and a video decoder 30 are described based on Figs. 1 to 3.

Fig. 1A is a schematic block diagram illustrating an example coding system 10, e.g. a video coding system 10 (or short coding system 10) that may utilize techniques of this present application. Video encoder 20 (or short encoder 20) and video decoder 30 (or short decoder 30) of video coding system 10 represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present application. As shown in FIG. 1 A, the coding system 10 comprises a source device 12 configured to provide encoded picture data 21 e.g. to a destination device 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, optionally, comprise a picture source 16, a pre-processor (or pre-processing unit) 18, e.g. a picture pre-processor 18, and a communication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturing device, for example a camera for capturing a real-world picture, and/or any kind of a picture generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of other device for obtaining and/or providing a real-world picture, a computer generated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture). The picture source may be any kind of memory or storage storing any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed by the pre-processing unit 18, the picture or picture data 17 may also be referred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 and to perform pre- processing on the picture data 17 to obtain a pre-processed picture 19 or pre-processed picture data 19. Pre-processing performed by the pre-processor 18 may, e.g., comprise trimming, color format conversion (e.g. from RGB to YCbCr), color correction, or de-noising. It can be understood that the pre-processing unit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picture data 19 and provide encoded picture data 21 (further details will be described below, e.g., based on Fig. 2).

Communication interface 22 of the source device 12 may be configured to receive the encoded picture data 21 and to transmit the encoded picture data 21 (or any further processed version thereof) over communication channel 13 to another device, e.g. the destination device 14 or any other device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder 30), and may additionally, i.e. optionally, comprise a communication interface or communication unit 28, a post-processor 32 (or post-processing unit 32) and a display device 34. The communication interface 28 of the destination device 14 is configured receive the encoded picture data 21 (or any further processed version thereof), e.g. directly from the source device 12 or from any other source, e.g. a storage device, e.g. an encoded picture data storage device, and provide the encoded picture data 21 to the decoder 30.

The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded picture data 21 or encoded data 13 via a direct communication link between the source device 12 and the destination device 14, e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof.

The communication interface 22 may be, e.g., configured to package the encoded picture data 21 into an appropriate format, e.g. packets, and/or process the encoded picture data using any kind of transmission encoding or processing for transmission over a communication link or communication network.

The communication interface 28, forming the counterpart of the communication interface 22, may be, e.g., configured to receive the transmitted data and process the transmission data using any kind of corresponding transmission decoding or processing and/or de-packaging to obtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces as indicated by the arrow for the communication channel 13 in Fig. 1 A pointing from the source device 12 to the destination device 14, or bi- directional communication interfaces, and may be configured, e.g. to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 and provide decoded picture data 31 or a decoded picture 31 (further details will be described below, e.g., based on Fig. 3 or Fig. 5).

The post-processor 32 of destination device 14 is configured to post-process the decoded picture data 31 (also called reconstructed picture data), e.g. the decoded picture 31, to obtain post-processed picture data 33, e.g. a post-processed picture 33. The post-processing performed by the post-processing unit 32 may comprise, e.g. color format conversion (e.g. from YCbCr to RGB), color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured to receive the post-processed picture data 33 for displaying the picture, e.g. to a user or viewer. The display device 34 may be or comprise any kind of display for representing the reconstructed picture, e.g. an integrated or external display or monitor. The displays may, e.g. comprise liquid crystal displays (LCD), organic light emitting diodes (OLED) displays, plasma displays, projectors , micro LED displays, liquid crystal on silicon (LCoS), digital light processor (DLP) or any kind of other display.

Although Fig. 1A depicts the source device 12 and the destination device 14 as separate devices, embodiments of devices may also comprise both or both functionalities, the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality. In such embodiments the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device 12 and/or destination device 14 as shown in Fig. 1A may vary depending on the actual device and application.

The encoder 20 (e.g. a video encoder 20) and the decoder 30 (e.g. a video decoder 30) each may be implemented as any of a variety of suitable circuitry as shown in Fig. 1B, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, or any combinations thereof. The encoder 20 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to encoder 20 of Fig. 2 and/or any other encoder system or subsystem described herein. The decoder 30 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to decoder 30 of Fig. 3 and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as discussed later. If the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the foregoing (including hardware, software, a combination of hardware and software, etc.) may be considered to be one or more processors. Each of video encoder 20 and 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.

Source device 12 and destination device 14 may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices (such as content services servers or content delivery servers), broadcast receiver device, broadcast transmitter device, or the like and may use no or any kind of operating system. In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in Fig. 1A is merely an example and the techniques of the present application may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.

Fig. 1B is an illustrative diagram of another example video coding system 40 including encoder 20 of Fig. 2 and/or decoder 30 of Fig. 3 according to an exemplary embodiment. The system 40 can implement techniques in accordance with various examples described in the present application. In the illustrated implementation, video coding system 40 may include imaging device(s) 41, video encoder 100, video decoder 30 (and/or a video coder implemented via logic circuitry 47 of processing unit(s) 46), an antenna 42, one or more processor(s) 43, one or more memory store(s) 44, and/or a display device 45. As illustrated, imaging device(s) 41, antenna 42, processing unit(s) 46, logic circuitry 47, video encoder 20, video decoder 30, processor(s) 43, memory store(s) 44, and/or display device 45 may be capable of communication with one another. As discussed, although illustrated with both video encoder 20 and video decoder 30, video coding system 40 may include only video encoder 20 or only video decoder 30 in various examples.

As shown, in some examples, video coding system 40 may include antenna 42. Antenna 42 may be configured to transmit or receive an encoded bitstream of video data, for example. Further, in some examples, video coding system 40 may include display device 45. Display device 45 may be configured to present video data. As shown, in some examples, logic circuitry 47 may be implemented via processing unit(s) 46. Processing unit(s) 46 may include application-specific integrated circuit (ASIC) logic, graphics processor(s), general purpose processor(s), or the like. Video coding system 40 also may include optional processor(s) 43, which may similarly include application-specific integrated circuit (ASIC) logic, graphics processor(s), general purpose processor(s), or the like. In some examples, logic circuitry 47 may be implemented via hardware, video coding dedicated hardware, or the like, and processor(s) 43 may implemented general purpose software, operating systems, or the like. In addition, memory store(s) 44 may be any type of memory such as volatile memory (e.g., Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), etc.) or non volatile memory (e.g., flash memory, etc.), and so forth. In a non-limiting example, memory store(s) 44 may be implemented by cache memory. In some examples, logic circuitry 47 may access memory store(s) 44 (for implementation of an image buffer for example). In other examples, logic circuitry 47 and/or processing unit(s) 46 may include memory stores (e.g., cache or the like) for the implementation of an image buffer or the like.

In some examples, video encoder 20 implemented via logic circuitry may include an image buffer (e.g., via either processing unit(s) 46 or memory store(s) 44)) and a graphics processing unit (e.g., via processing unit(s) 46). The graphics processing unit may be communicatively coupled to the image buffer. The graphics processing unit may include video encoder 20 as implemented via logic circuitry 47 to embody the various modules as discussed with respect to FIG. 2 and/or any other encoder system or subsystem described herein. The logic circuitry may be configured to perform the various operations as discussed herein.

Video decoder 30 may be implemented in a similar manner as implemented via logic circuitry 47 to embody the various modules as discussed with respect to decoder 30 of FIG. 3 and/or any other decoder system or subsystem described herein. In some examples, video decoder 30 may be implemented via logic circuitry may include an image buffer (e.g., via either processing unit(s) 420 or memory store(s) 44)) and a graphics processing unit (e.g., via processing unit(s) 46). The graphics processing unit may be communicatively coupled to the image buffer. The graphics processing unit may include video decoder 30 as implemented via logic circuitry 47 to embody the various modules as discussed with respect to FIG. 3 and/or any other decoder system or subsystem described herein.

In some examples, antenna 42 of video coding system 40 may be configured to receive an encoded bitstream of video data. As discussed, the encoded bitstream may include data, indicators, index values, mode selection data, or the like associated with encoding a video frame as discussed herein, such as data associated with the coding partition (e.g., transform coefficients or quantized transform coefficients, optional indicators (as discussed), and/or data defining the coding partition). Video coding system 40 may also include video decoder 30 coupled to antenna 42 and configured to decode the encoded bitstream. The display device 45 configured to present video frames.

For convenience of description, embodiments of the invention are described herein, for example, by reference to High-Efficiency Video Coding (HEVC) or to the reference software of Versatile Video coding (VVC), the next generation video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). One of ordinary skill in the art will understand that embodiments of the invention are not limited to HEVC or VVC.

Encoder and Encoding Method

Fig. 2 shows a schematic block diagram of an example video encoder 20 that is configured to implement the techniques of the present application. In the example of Fig. 2, the video encoder 20 comprises an input 201 (or input interface 201), a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, and inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy encoding unit 270 and an output 272 (or output interface 272). The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254 and a partitioning unit 262. Inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown). A video encoder 20 as shown in Fig. 2 may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, whereas the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra-prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20, wherein the backward signal path of the video encoder 20 corresponds to the signal path of the decoder (see video decoder 30 in Fig. 3). The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra-prediction unit 254 are also referred to forming the“built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, a picture 17 (or picture data 17), e.g. picture of a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture 19 (or pre-processed picture data 19). For sake of simplicity the following description refers to the picture 17. The picture 17 may also be referred to as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array or matrix of samples with intensity values. A sample in the array may also be referred to as pixel (short form of picture element) or a pel. The number of samples in horizontal and vertical direction (or axis) of the array or picture define the size and/or resolution of the picture. For representation of color, typically three color components are employed, i.e. the picture may be represented or include three sample arrays. In RBG format or color space a picture comprises a corresponding red, green and blue sample array. However, in video coding each pixel is typically represented in a luminance and chrominance format or color space, e.g. YCbCr, which comprises a luminance component indicated by Y (sometimes also L is used instead) and two chrominance components indicated by Cb and Cr. The luminance (or short luma) component Y represents the brightness or grey level intensity (e.g. like in a grey-scale picture), while the two chrominance (or short chroma) components Cb and Cr represent the chromaticity or color information components. Accordingly, a picture in YCbCr format comprises a luminance sample array of luminance sample values (Y), and two chrominance sample arrays of chrominance values (Cb and Cr). Pictures in RGB format may be converted or transformed into YCbCr format and vice versa, the process is also known as color transformation or conversion. If a picture is monochrome, the picture may comprise only a luminance sample array. Accordingly, a picture may be, for example, an array of luma samples in monochrome format or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioning unit (not depicted in Fig. 2) configured to partition the picture 17 into a plurality of (typically non-overlapping) picture blocks 203. These blocks may also be referred to as root blocks, macro blocks (H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU) (H.265/HEVC and VVC). The picture partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receive directly a block 203 of the picture 17, e.g. one, several or all blocks forming the picture 17. The picture block 203 may also be referred to as current picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values), although of smaller dimension than the picture 17. In other words, the block 203 may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture 17, or a luma or chroma array in case of a color picture) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture 17) or any other number and/or kind of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of the block 203 define the size of block 203. Accordingly, a block may, for example, an MxN (M-column by N-row) array of samples, or an MxN array of transform coefficients.

Embodiments of the video encoder 20 as shown in Fig. 2 may be configured encode the picture 17 block by block, e.g. the encoding and prediction is performed per block 203. Embodiments of the video encoder 20 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or encoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTETs) or one or more groups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video encoder 20 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or encoded using one or more slices/tile groups (typically non-overlapping), and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Residual Calculation The residual calculation unit 204 may be configured to calculate a residual block 205 (also referred to as residual 205) based on the picture block 203 and a prediction block 265 (further details about the prediction block 265 are provided later), e.g. by subtracting sample values of the prediction block 265 from sample values of the picture block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

The transform processing unit 206 may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H.265/HEVC. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operations, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit 212 (and the corresponding inverse transform, e.g. by inverse transform processing unit 312 at video decoder 30) and corresponding scaling factors for the forward transform, e.g. by transform processing unit 206, at an encoder 20 may be specified accordingly.

Embodiments of the video encoder 20 (respectively transform processing unit 206) may be configured to output transform parameters, e.g. a type of transform or transforms, e.g. directly or encoded or compressed via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transform coefficients 207 to obtain quantized coefficients 209, e.g. by applying scalar quantization or vector quantization. The quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded down to an m- bit Transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and a corresponding and/or the inverse dequantization, e.g. by inverse quantization unit 210, may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In one example implementation, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208) may be configured to output quantization parameters (QP), e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and apply the quantization parameters for decoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 211, e.g. by applying the inverse of the quantization scheme applied by the quantization unit 208 based on or using the same quantization step size as the quantization unit 208. The dequantized coefficients 211 may also be referred to as dequantized residual coefficients 211 and correspond - although typically not identical to the transform coefficients due to the loss by quantization - to the transform coefficients 207.

Inverse Transform The inverse transform processing unit 212 is configured to apply the inverse transform of the transform applied by the transform processing unit 206, e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block 213 (or corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured to add the transform block 213 (i.e. reconstructed residual block 213) to the prediction block 265 to obtain a reconstructed block 215 in the sample domain, e.g. by adding - sample by sample - the sample values of the reconstructed residual block 213 and the sample values of the prediction block 265.

Filtering The loop filter unit 220 (or short“loop filter” 220), is configured to filter the reconstructed block 215 to obtain a filtered block 221, or in general, to filter reconstructed samples to obtain filtered samples. The loop filter unit is, e.g., configured to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 220 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. a bilateral filter, an adaptive loop filter (ALF), a noise suppression filter (NSF), a sharpening, a smoothing filters or a collaborative filters, or any combination thereof. In an example, the loop filter unit 220 may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit 220 is shown in FIG. 2 as being an in loop filter, in other configurations, the loop filter unit 220 may be implemented as a post loop filter. The filtered block 221 may also be referred to as filtered reconstructed block 221. Decoded picture buffer 230 may store the reconstructed coding blocks after the loop filter unit 220 performs the filtering operations on the reconstructed coding blocks.

Embodiments of the video encoder 20 (respectively loop filter unit 220) may be configured to output loop filter parameters (such as sample adaptive offset information), e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., a decoder 30 may receive and apply the same loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder 20. The DPB 230 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. The decoded picture buffer (DPB) 230 may be configured to store one or more filtered blocks 221. The decoded picture buffer 230 may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks 221, of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. The decoded picture buffer (DPB) 230 may be also configured to store one or more unfiltered reconstructed blocks 215, or in general unfiltered reconstructed samples, e.g. if the reconstructed block 215 is not filtered by loop filter unit 220, or any other further processed version of the reconstructed blocks or samples. Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262, inter-prediction unit 244 and intra-prediction unit 254, and is configured to receive or obtain original picture data, e.g. an original block 203 (current block 203 of the current picture 17), and reconstructed picture data, e.g. filtered and/or unfiltered reconstructed samples or blocks of the same (current) picture and/or from one or a plurality of previously decoded pictures, e.g. from decoded picture buffer 230 or other buffers (e.g. line buffer, not shown).. The reconstructed picture data is used as reference picture data for prediction, e.g. inter-prediction or intra-prediction, to obtain a prediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select a partitioning for a current block prediction mode (including no partitioning) and a prediction mode (e.g. an intra or inter prediction mode) and generate a corresponding prediction block 265, which is used for the calculation of the residual block 205 and for the reconstruction of the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit 260), which provide the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e. select the prediction mode which provides a minimum rate distortion. Terms like“best”,“minimum”, “optimum” etc. in this context do not necessarily refer to an overall“best”,“minimum”, “optimum”, etc. but may also refer to the fulfillment of a termination or selection criterion like a value exceeding or falling below a threshold or other constraints leading potentially to a“sub optimum selection” but reducing complexity and processing time.

In other words, the partitioning unit 262 may be configured to partition the block 203 into smaller block partitions or sub-blocks (which form again blocks), e.g. iteratively using quad- tree-partitioning (QT), binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g., the prediction for each of the block partitions or sub blocks, wherein the mode selection comprises the selection of the tree- structure of the partitioned block 203 and the prediction modes are applied to each of the block partitions or sub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) and prediction processing (by inter-prediction unit 244 and intra-prediction unit 254) performed by an example video encoder 20 will be explained in more detail.

Partitioning

The partitioning unit 262 may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs), and the partitioning unit 262 may partition (or split) a current block 203 into smaller partitions, e.g. smaller blocks of square or rectangular size. For a picture that has three sample arrays, a CTU consists of an N><N block of luma samples together with two corresponding blocks of chroma samples. The maximum allowed size of the luma block in a CTU is specified to be 128^ 128 in the developing versatile video coding (VVC), but it can be specified to be value rather than 128x128 in the future, for example, 256x256. The sequence of CTUs of a picture may be clustered/grouped as slices/tile groups, tiles or bricks in a tile. A tile covers a rectangular region of a picture, and a tile can be divided into one or more bricks. A brick consists of a number of CTU rows within a tile. A tile that is not partitioned into multiple bricks can be referred to as a brick. However, a brick is a true subset of a tile and is not referred to as a tile; and a number of tiles form a tile group. There a re two modes of tile groups are supported in VVC, namely the raster-scan slice/tile group mode and the rectangular slicetile group mode. In the raster-scan tile group mode, a slice/tile grouptile group contains a sequence of tiles in tile raster scan of a picture. In the rectangular slicetile group mode, a slicetile group contains a number of bricks of a picture that collectively form a rectangular region of the picture. The bricks within a rectangular slice are in the order of brick raster scan of the slice. These smaller blocks (which may also be referred to as sub-blocks) may be further partitioned into even smaller partitions. This is also referred to tree-partitioning or hierarchical tree-partitioning, wherein a root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0), may be recursively partitioned, e.g. partitioned into two or more blocks of a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level 1, depth 1), wherein these blocks may be again partitioned into two or more blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2, depth 2), etc. until the partitioning is terminated, e.g. because a termination criterion is fulfilled, e.g. a maximum tree depth or minimum block size is reached. Blocks which are not further partitioned are also referred to as leaf-blocks or leaf nodes of the tree. A tree using partitioning into two partitions is referred to as binary-tree (BT), a tree using partitioning into three partitions is referred to as ternary-tree (TT), and a tree using partitioning into four partitions is referred to as quad-tree (QT).

As mentioned before, the term“block” as used herein may be a portion, in particular a square or rectangular portion, of a picture. With reference, for example, to HEVC and WC, the block may be or correspond to a coding tree unit (CTU), a coding unit (CU), prediction unit (PU), and transform unit (TU) and/or to the corresponding blocks, e.g. a coding tree block (CTB), a coding block (CB), a transform block (TB) or prediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate colour planes and syntax structures used to code the samples. Correspondingly, a coding tree block (CTB) may be an NxN block of samples for some value of N such that the division of a component into CTBs is a partitioning. A coding unit (CU) may be or comprise a coding block of luma samples, two corresponding coding blocks of chroma samples of a picture that has three sample arrays, or a coding block of samples of a monochrome picture or a picture that is coded using three separate color planes and syntax structures used to code the samples. Correspondingly a coding block (CB) may be an MxN block of samples for some values of M and N such that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may be split into CUs by using a quad-tree structure denoted as coding tree. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU.

In embodiments, e.g., according to the latest video coding standard currently in development, which is referred to as Versatile Video Coding (VVC), Quad-tree and binary tree (QTBT) partitioning is used to partition a coding block. In the QTBT block structure, a CU can have either a square or rectangular shape. For example, a coding tree unit (CTU) is first partitioned by a quadtree structure. The quadtree leaf nodes are further partitioned by a binary tree or ternary (or triple) tree structure. The partitioning tree leaf nodes are called coding units (CUs), and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, multiple partition, for example, triple tree partition was also proposed to be used together with the QTBT block structure.

VVC develops a unique signaling mechanism of the partition splitting information in quadtree with nested multi-type tree coding tree structure. In the signalling mechanism, a coding tree unit (CTU) is treated as the root of a quaternary tree and is first partitioned by a quaternary tree structure. Each quaternary tree leaf node (when sufficiently large to allow it) is then further partitioned by a multi-type tree structure. In the multi-type tree structure, a first flag (mtt split cu flag) is signalled to indicate whether the node is further partitioned; when a node is further partitioned, a second flag (mtt split cu vertical flag) is signalled to indicate the splitting direction, and then a third flag (mtt split cu binary flag) is signalled to indicate whether the split is a binary split or a ternary split. Based on the values of mtt split cu vertical flag and mtt split cu binary flag, the multi-type tree slitting mode (MttSplitMode) of a CU can be derived by a decoder based on a predefined rule or a table. It should be noted, for a certain design, for example, 64x64 Luma block and 32x32 Chroma pipelining design in VVC hardware decoders, TT split is forbidden when either width or height of a luma coding block is larger than 64. TT split is also forbidden when either width or height of a chroma coding block is larger than 32. The pipelining design will divide a picture into Virtual pipeline data units s(VPDUs) which are defined as non-overlapping units in a picture. In hardware decoders, successive VPDUs are processed by multiple pipeline stages simultaneously. The VPDU size is roughly proportional to the buffer size in most pipeline stages, so it is important to keep the VPDU size small. In most hardware decoders, the VPDU size can be set to maximum transform block (TB) size. However, in VVC, ternary tree (TT) and binary tree (BT) partition may lead to the increasing of VPDUs size.

In addition, it should be noted that, when a portion of a tree node block exceeds the bottom or right picture boundary, the tree node block is forced to be split until the all samples of every coded CU are located inside the picture boundaries. As an example, the Intra Sub-Partitions (ISP) tool may divide luma intra-predicted blocks vertically or horizontally into 2 or 4 sub-partitions depending on the block size.

In one example, the mode selection unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described herein. As described above, the video encoder 20 is configured to determine or select the best or an optimum prediction mode from a set of (pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction The set of intra-prediction modes may comprise 35 different intra-prediction modes, e.g. non- directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in HEVC, or may comprise 67 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined for VVC. As an example, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for the non-square blocks, e.g. as defined in VVC. As another example, to avoid division operations for DC prediction, only the longer side is used to compute the average for non-square blocks. And, the results of intra prediction of planar mode may be further modified by a position dependent intra prediction combination (PDPC) method. The intra-prediction unit 254 is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an intra-prediction block 265 according to an intra prediction mode of the set of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit 260) is further configured to output intra-prediction parameters (or in general information indicative of the selected intra prediction mode for the block) to the entropy encoding unit 270 in form of syntax elements 266 for inclusion into the encoded picture data 21, so that, e.g., the video decoder 30 may receive and use the prediction parameters for decoding. Inter-Prediction

The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e. previous at least partially decoded pictures, e.g. stored in DBP 230) and other inter-prediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, e.g. half/semi-pel and/or quarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct mode may be applied.

For example, Extended merge prediction, the merge candidate list of such mode is constructed by including the following five types of candidates in order: Spatial MVP from spatial neighbor CUs, Temporal MVP from collocated CUs, History-based MVP from an FIFO table, Pairwise average MVP and Zero MVs. And a bilateral-matching based decoder side motion vector refinement (DMVR) may be applied to increase the accuracy of the MVs of the merge mode. Merge mode with MVD (MMVD), which comes from merge mode with motion vector differences. A MMVD flag is signaled right after sending a skip flag and merge flag to specify whether MMVD mode is used for a CU. And a CU-level adaptive motion vector resolution (AMVR) scheme may be applied. AMVR allows MVD of the CU to be coded in different precision. Dependent on the prediction mode for the current CU, the MVDs of the current CU can be adaptively selected when When a CU is coded in merge mode, the combined inter/intra prediction (CUP) mode may be applied to the current CU. Weighted averaging of the inter and intra prediction signals is performed to obtain the CUP prediction. Affine motion compensated prediction, the affine motion field of the block is described by motion information of two control point (4-parameter) or three control point motion vectors (6-parameter). Subblock- based temporal motion vector prediction (SbTMVP), which is similar to the temporal motion vector prediction (TMVP) in HEVC, but predicts the motion vectors of the sub-CUs within the current CU. Bi-directional optical flow (BDOF), previously referred to as BIO, is a simpler version that requires much less computation, especially in terms of number of multiplications and the size of the multiplier. Triangle partition mode, in such a mode, a CU is split evenly into two triangle- shaped partitions, using either the diagonal split or the anti-diagonal split. Besides, the bi-prediction mode is extended beyond simple averaging to allow weighted averaging of the two prediction signals. The inter prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in Fig. 2). The motion estimation unit may be configured to receive or obtain the picture block 203 (current picture block 203 of the current picture 17) and a decoded picture 231, or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures 231, for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures 231, or in other words, the current picture and the previously decoded pictures 231 may be part of or form a sequence of pictures forming a video sequence. The encoder 20 may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit. This offset is also called motion vector (MV). The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block 265. Motion compensation, performed by the motion compensation unit, may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. ETpon receiving the motion vector for the PET of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists. Motion compensation unit may also generate syntax elements associated with the blocks and the video slice for use by video decoder 30 in decoding the picture blocks of the video slice. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be generated or used. Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CAB AC), syntax-based context-adaptive binary arithmetic coding (SB AC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients 209, inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data 21 which can be output via the output 272, e.g. in the form of an encoded bitstream 21, so that, e.g., the video decoder 30 may receive and use the parameters for decoding. The encoded bitstream 21 may be transmitted to video decoder 30, or stored in a memory for later transmission or retrieval by video decoder 30.

Other structural variations of the video encoder 20 can be used to encode the video stream. For example, a non-transform based encoder 20 can quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another implementation, an encoder 20 can have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

Fig. 3 shows an example of a video decoder 30 that is configured to implement the techniques of this present application. The video decoder 30 is configured to receive encoded picture data 21 (e.g. encoded bitstream 21), e.g. encoded by encoder 20, to obtain a decoded picture 331. The encoded picture data or bitstream comprises information for decoding the encoded picture data, e.g. data that represents picture blocks of an encoded video slice and associated syntax elements.

In the example of Fig. 3, the decoder 30 comprises an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g. a summer 314), a loop filter 320, a decoded picture buffer (DBP) 330, an inter prediction unit 344 and an intra prediction unit 354. Inter prediction unit 344 may be or include a motion compensation unit. Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 100 from Fig. 2

As explained with regard to the encoder 20, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214 the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 344 and the intra prediction unit 354 are also referred to as forming the“built-in decoder” of video encoder 20. Accordingly, the inverse quantization unit 310 may be identical in function to the inverse quantization unit 110, the inverse transform processing unit 312 may be identical in function to the inverse transform processing unit 212, the reconstruction unit 314 may be identical in function to reconstruction unit 214, the loop filter 320 may be identical in function to the loop filter 220, and the decoded picture buffer 330 may be identical in function to the decoded picture buffer 230. Therefore, the explanations provided for the respective units and functions of the video 20 encoder apply correspondingly to the respective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21 (or in general encoded picture data 21) and perform, for example, entropy decoding to the encoded picture data 21 to obtain, e.g., quantized coefficients 309 and/or decoded coding parameters (not shown in Fig. 3), e.g. any or all of inter prediction parameters (e.g. reference picture index and motion vector), intra prediction parameter (e.g. intra prediction mode or index), transform parameters, quantization parameters, loop filter parameters, and/or other syntax elements. Entropy decoding unit 304 maybe configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit 270 of the encoder 20. Entropy decoding unit 304 may be further configured to provide inter prediction parameters, intra prediction parameter and/or other syntax elements to the mode selection unit 360 and other parameters to other units of the decoder 30. Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level. Inverse Quantization

The inverse quantization unit 310 may be configured to receive quantization parameters (QP) (or in general information related to the inverse quantization) and quantized coefficients from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) and to apply based on the quantization parameters an inverse quantization on the decoded quantized coefficients 309 to obtain dequantized coefficients 311, which may also be referred to as transform coefficients 311. The inverse quantization process may include use of a quantization parameter determined by video encoder 20 for each video block in the video slice to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receive dequantized coefficients 311, also referred to as transform coefficients 311, and to apply a transform to the dequantized coefficients 311 in order to obtain reconstructed residual blocks 213 in the sample domain. The reconstructed residual blocks 213 may also be referred to as transform blocks 313. The transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may be further configured to receive transform parameters or corresponding information from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) to determine the transform to be applied to the dequantized coefficients 311.

Reconstruction The reconstruction unit 314 (e.g. adder or summer 314) may be configured to add the reconstructed residual block 313, to the prediction block 365 to obtain a reconstructed block 315 in the sample domain, e.g. by adding the sample values of the reconstructed residual block 313 and the sample values of the prediction block 365. Filtering

The loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321, e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 320 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. a bilateral filter, an adaptive loop filter (ALF), a noise suppression filter (NSF), a sharpening, a smoothing filters or a collaborative filters, or any combination thereof. In an example, the loop filter unit 220 may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit 320 is shown in Fig. 3 as being an in loop filter, in other configurations, the loop filter unit 320 may be implemented as a post loop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decoded picture buffer 330, which stores the decoded pictures 331 as reference pictures for subsequent motion compensation for other pictures and/or for output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. via output 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter prediction unit 244 (in particular to the motion compensation unit) and the intra prediction unit 354 may be identical to the inter prediction unit 254 in function, and performs split or partitioning decisions and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304). Mode selection unit 360 may be configured to perform the prediction (intra or inter prediction) per block based on reconstructed pictures, blocks or respective samples (filtered or unfiltered) to obtain the prediction block 365.

When the video slice is coded as an intra coded (I) slice, intra prediction unit 354 of mode selection unit 360 is configured to generate prediction block 365 for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current picture. When the video picture is coded as an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g. motion compensation unit) of mode selection unit 360 is configured to produce prediction blocks 365 for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 304. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB 330. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Mode selection unit 360 is configured to determine the prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the mode selection unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Embodiments of the video decoder 30 as shown in Fig. 3 may be configured to partition and/or decode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or decoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video decoder 30 as shown in Fig. 3 may be configured to partition and/or decode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or decoded using one or more slices/tile groups (typically non-overlapping), and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder 30 can be used to decode the encoded picture data 21. For example, the decoder 30 can produce the output video stream without the loop filtering unit 320. For example, a non-transform based decoder 30 can inverse-quantize the residual signal directly without the inverse-transform processing unit 312 for certain blocks or frames. In another implementation, the video decoder 30 can have the inverse-quantization unit 310 and the inverse-transform processing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, a processing result of a current step may be further processed and then output to the next step. For example, after interpolation filtering, motion vector derivation or loop filtering, a further operation, such as Clip or shift, may be performed on the processing result of the interpolation filtering, motion vector derivation or loop filtering.

Fig. 4 is a schematic diagram of a video coding device 400 according to an embodiment of the disclosure. The video coding device 400 is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the video coding device 400 may be a decoder such as video decoder 30 of Fig. 1A or an encoder such as video encoder 20 of Fig. 1 A.

The video coding device 400 comprises ingress ports 410 (or input ports 410) and receiver units (Rx) 420 for receiving data; a processor, logic unit, or central processing unit (CPU) 430 to process the data; transmitter units (Tx) 440 and egress ports 450 (or output ports 450) for transmitting the data; and a memory 460 for storing the data. The video coding device 400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports 410, the receiver units 420, the transmitter units 440, and the egress ports 450 for egress or ingress of optical or electrical signals.

The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGAs, ASICs, and DSPs. The processor 430 is in communication with the ingress ports 410, receiver units 420, transmitter units 440, egress ports 450, and memory 460. The processor 430 comprises a coding module 470. The coding module 470 implements the disclosed embodiments described above. For instance, the coding module 470 implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module 470 therefore provides a substantial improvement to the functionality of the video coding device 400 and effects a transformation of the video coding device 400 to a different state. Alternatively, the coding module 470 is implemented as instructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 460 may be, for example, volatile and/or non-volatile and may be a read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM).

Fig. 5 is a simplified block diagram of an apparatus 500 that may be used as either or both of the source device 12 and the destination device 14 from Fig. 1A according to an exemplary embodiment. The apparatus 500 can implement techniques of this present application described above. The apparatus 500 can be in the form of a computing system including multiple computing devices, or in the form of a single computing device, for example, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like.

A processor 502 in the apparatus 500 can be a central processing unit. Alternatively, the processor 502 can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the processor 502, advantages in speed and efficiency can be achieved using more than one processor. A memory 504 in the apparatus 500 can be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. Any other suitable type of storage device can be used as the memory 504. The memory 504 can include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 can further include an operating system 508 and application programs 510, the application programs 510 including at least one program that permits the processor 502 to perform the methods described here. For example, the application programs 510 can include applications 1 through N, which further include a video coding application that performs the methods described here. The apparatus 500 can also include additional memory in the form of a secondary storage 514, which can, for example, be a memory card used with a mobile computing device. Because the video communication sessions may contain a significant amount of information, they can be stored in whole or in part in the secondary storage 514 and loaded into the memory 504 as needed for processing.

The apparatus 500 can also include one or more output devices, such as a display 518. The display 518 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 518 can be coupled to the processor 502 via the bus 512. Other output devices that permit a user to program or otherwise use the apparatus 500 can be provided in addition to or as an alternative to the display 518. When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD), a cathode-ray tube (CRT) display, a plasma display or light emitting diode (LED) display, such as an organic LED (OLED) display.

Although depicted here as a single bus, the bus 512 of the apparatus 500 can be composed of multiple buses. Further, the secondary storage 514 can be directly coupled to the other components of the apparatus 500 or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus 500 can thus be implemented in a wide variety of configurations.

The apparatus 500 can also include or be in communication with an image-sensing device 520, for example a camera, or any other image-sensing device 520 now existing or hereafter developed that can sense an image such as the image of a user operating the apparatus 500. The image-sensing device 520 can be positioned such that it is directed toward the user operating the apparatus 500. In an example, the position and optical axis of the image-sensing device 520 can be configured such that the field of vision includes an area that is directly adjacent to the display 518 and from which the display 518 is visible. The apparatus 500 can also include or be in communication with a sound-sensing device 522, for example a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds near the apparatus 500. The sound-sensing device 522 can be positioned such that it is directed toward the user operating the apparatus 500 and can be configured to receive sounds, for example, speech or other utterances, made by the user while the user operates the apparatus 500.

Although Fig. 5 depicts the processor 502 and the memory 504 of the apparatus 500 as being integrated into a single unit, other configurations can be utilized. The operations of the processor 502 can be distributed across multiple machines (each machine having one or more of processors) that can be coupled directly or across a local area or other network. The memory 504 can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the apparatus 500. Although depicted here as a single bus, the bus 5 l2of the apparatus 500 can be composed of multiple buses. Further, the secondary storage 514 can be directly coupled to the other components of the apparatus 500 or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus 500 can thus be implemented in a wide variety of configurations.

Video coding schemes such as H.264/AVC and HEVC are designed along the successful principle of block-based hybrid video coding. Using this principle a picture is first partitioned into blocks and then each block is predicted by using intra-picture or inter-picture prediction.

Several video coding standards since H.261 belong to the group of“lossy hybrid video codecs” (i.e. combine spatial and temporal prediction in the sample domain and 2D transform coding for applying quantization in the transform domain). Each picture of a video sequence is typically partitioned into a set of non-overlapping blocks and the coding is typically performed on a block level. In other words, at the encoder the video is typically processed, i.e. encoded, on a block (picture block) level, e.g. by using spatial (intra picture) prediction and temporal (inter picture) prediction to generate a prediction block, subtracting the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), whereas at the decoder the inverse processing compared to the encoder is partially applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder processing loop such that both will generate identical predictions (e.g. intra- and inter predictions) and/or re-constructions for processing, i.e. coding, the subsequent blocks.

As used herein, the term“block” may a portion of a picture or a frame. For convenience of description, embodiments of the invention are described herein in reference to High-Efficiency Video Coding (HEVC) or the reference software of Versatile video coding (VVC), developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). One of ordinary skill in the art will understand that embodiments of the invention are not limited to HEVC or VVC. It may refer to a CU, PU, and TU. In HEVC, a CTU is split into CUs by using a quad-tree structure denoted as coding tree. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU. In the newest development of the video compression technical, Quad-tree and binary tree (QTBT) partitioning is used to partition a coding block. In the QTBT block structure, a CU can have either a square or rectangular shape. For example, a coding tree unit (CTU) is first partitioned by a quadtree structure. The quadtree leaf nodes are further partitioned by a binary tree structure. The binary tree leaf nodes are called coding units (CUs), and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, multiple partition, for example, triple tree partition was also proposed to be used together with the QTBT block structure.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC l/SC 29/WG 11) are studying the potential need for standardization of future video coding technology with a compression capability that significantly exceeds that of the current HEVC standard (including its current extensions and near-term extensions for screen content coding and high-dynamic-range coding). The groups are working together on this exploration activity in a joint collaboration effort known as the Joint Video Exploration Team (JVET) to evaluate compression technology designs proposed by their experts in this area. In an example, for directional intra prediction, intra prediction modes are available representing different prediction angles from diagonal-up to diagonal-down. For definition of the prediction angles, an offset value /¾n_g on a 32-sample grid is defined. The association of /¾n_g to the corresponding intra prediction mode is visualized in Fig. 6 for the vertical prediction modes. For the horizontal prediction modes the scheme is flipped to vertical direction and the p_{a ng} values are assigned accordingly. As stated above, angular prediction modes are available for applicable intra prediction block sizes. They may use the same 32-sample grid for the definition of the prediction angles. The distribution of the

values over the 32-sample grid in Fig. 6 reveals an increased resolution of the prediction angles around the vertical direction and a coarser resolution of the prediction angles towards the diagonal directions. The same applies to the horizontal directions. This design stems from the observation that in lots of video content, approximately horizontal and vertical structures play an important role compared to diagonal structures.

In an example, while for the horizontal and vertical prediction directions, the selection of samples to be used for prediction is straightforward, this task requires more effort in case of angular prediction. For modes 11-25, when predicting the current block Be from the set of prediction samples p_ref (also known as main reference side ) in an angular direction, samples of both, the vertical and the horizontal part of p_ref can be involved. Since the determination of the location of the respective samples on either of the branches of p_ref requires some computational effort, a unified one-dimensional prediction reference has been designed for HEVC intra prediction. The scheme is visualized in Fig. 7. Before performing the actual prediction operation, the set of reference samples p_ref is mapped to a 1 -dimensional vector pi,_ref. The projection which is used for the mapping depends on the direction indicated by the intra prediction angle of the respective intra prediction mode. Only reference samples from the part of pref which is to be used for prediction are mapped to pi, ref. The actual mapping of the reference samples to pi,_ref for each angular prediction mode is depicted in Figs. 8 and 9 for horizontal and vertical angular prediction directions, respectively. The reference samples set pi, ref is constructed once for the predicted block. The prediction is then derived from two neighboring reference samples in the set as detailed below. As can be seen from Figs. 8 and 9 the l-dimensional reference sample set is not completely filled for all intra prediction modes. Only the locations which are in the projection range for the corresponding intra prediction direction are included in the set. The prediction for both, horizontal and vertical prediction modes is performed in the same manner with only swapping the x and y coordinates of the block. The prediction from pi,_ref is performed in l/32-pel accuracy. Depending on the value of the angle parameter / _¾, a sample offset zi_dx in pi,_ref and a weighting factor /_fact for a sample at position (x, y) are determined. Here, the derivation for the vertical modes is provided. The derivation for the horizontal modes follows accordingly, swapping x and y.

: mod:

If / fact is not equal to 0, i.e. the prediction does not fall exactly on a full sample location in pi_.,-_cr, a linear weighting between the two neighboring sample locations in pi,_ref is performed as

with 0 < x, y < Nc. It should be noted that the values of i_dx and _fact only depend on y, and therefore only need to be calculated once per row (for vertical prediction modes).

The VTM-1.0 (Versatile Test Model) uses 35 Intra modes whereas the BMS (Benchmark Set) uses 67 Intra modes. Intra-prediction is a mechanism used in many video coding frameworks to increase compression efficiency in the cases where only a given frame can be involved.

Fig. 10 shows an example of 67 intra prediction modes, e.g., as proposed for WC, the plurality of intra prediction modes of 67 intra prediction modes comprising: planar mode (index 0), dc mode (index 1), and angular modes with indices 2 to 66, wherein the left bottom angular mode in Fig 10 refers to index 2 and the numbering of the indices being incremented until index 66 being the top right most angular mode of Fig. 10.

As shown in Fig. 10, the latest version of JEM has some modes corresponding to skew intra prediction directions. For any of these modes, to predict samples within a block interpolation of a set of neighboring reference samples should be performed, if a corresponding position within a block side is fractional. HEVC and VVC uses linear interpolation between two adjacent reference samples. JEM uses more sophisticated 4-tap interpolation filters. Filter coefficients are selected to be either Gaussian or Cubic ones depending on the width or on the height value. Decision on whether to use width or height is harmonized with the decision on main reference side selection: when intra prediction mode is greater or equal to diagonal mode, top side of reference samples is selected to be the main reference side and width value is selected to determine interpolation filter in use. Otherwise, main side reference is selected from the left side of the block and height controls the filter selection process. Specifically, if selected side length is smaller than or equal to 8 samples, Cubic interpolation 4 tap is applied. Otherwise, interpolation filter is a 4-tap Gaussian one.

Specific filter coefficient used in JEM are given in Table 1. Predicted sample is calculated by convoluting with coefficients selected from Table 1 according to subpixel offset and filter type as follows:

In this equation,

indicates a bitwise shift-right operation.

If the Cubic filter is selected, the predicted sample is further clipped to the allowed range of values, that is either defined in a sequence parameter set (SPS) or derived from the bit depth of the selected component.

Table 1. Intra prediction interpolation filters used in JEM

Another set of interpolation filters that have 6-bit precision is presented in Table 2.

Table 2: A set of interpolation filters with 6-bit precision

An intra-predicted sample is calculated by convoluting with coefficients selected from Table 1 according to the subpixel offset and the filter type as follows:

In this equation,“ ^¾>” indicates a bitwise shift-right operation.

Another set of interpolation filters that have 6-bit precision is presented in Table 3.

Table 3: A set of interpolation filters with 6-bit precision

Fig. 11 illustrates a schematic diagram of a plurality of intra prediction modes used in the HEVC UIP scheme. For luminance blocks, the intra prediction modes may comprise up to 36 intra prediction modes, which may include three non-directional modes and 33 directional modes. The non-directional modes may comprise a planar prediction mode, a mean (DC) prediction mode, and a chroma from luma (LM) prediction mode. The planar prediction mode may perform predictions by assuming a block amplitude surface with a horizontal and vertical slope derived from the boundary of the block. The DC prediction mode may perform predictions by assuming a flat block surface with a value matching the mean value of the block boundary. The LM prediction mode may perform predictions by assuming a chroma value for the block matches the luma value for the block. The directional modes may perform predictions based on adjacent blocks as shown in Fig. 11.

H.264/AVC and HEVC specifies that a low-pass filter could be applied to reference samples prior the reference samples being used in intra prediction process. A decision on whether to use reference sample filter or not, is determined by intra prediction mode and block size. This mechanisms may be referred to as Mode Dependent Intra Smoothing (MDIS). There also exists a plurality of methods related to MDIS. For example, the Adaptive Reference Sample Smoothing (ARSS) method may explicitly (i.e. a flag is included into a bitstream) or implicitly (for example, data hiding is used to avoid putting a flag into a bitstream to reduce signaling overhead) signal whether the prediction samples are filtered. In this case, the encoder may make the decision on smoothing by testing the Rate-Distortion (RD) cost for all potential intra prediction modes.

As shown in Fig. 10, the latest version of JEM (JEM-7.2) has some modes corresponding to skew intra prediction directions. For any of these modes, to predict samples within a block interpolation of a set of neighboring reference samples should be performed, if a corresponding position within a block side is fractional. HEVC and VVC use linear interpolation between two adjacent reference samples. JEM uses more sophisticated 4-tap interpolation filters. Filter coefficients are selected to be either Gaussian or Cubic ones depending on the width or on the height value. A decision on whether to use width or height is harmonized with the decision on main reference side selection: when intra prediction mode is greater or equal to diagonal mode, top side of reference samples is selected to be the main reference side and width value is selected to determine interpolation filter in use. Otherwise, main side reference is selected from the left side of the block and height controls the filter selection process. Specifically, if selected side length is smaller than or equal to 8 samples, Cubic interpolation 4 tap is applied. Otherwise, interpolation filter is a 4-tap Gaussian one. This is illustrated in Fig. 12. In the illustrated example, in a case where the intra-prediction mode is greater or equal to diagonal mode, the top side is selected as main reference side. As the top side includes 32 samples, a Gaussian interpolation filter is selected. However, in a case where the intra-prediction modes is less than diagonal mode, the left side is selected as main reference side. As, in the illustrated example, the left side includes 4 samples, the Cubic interpolation filter is used.

In VVC, a partitioning mechanism based on both quad-tree and binary tree and known as QTBT is used. As depicted in Fig. 13, QTBT partitioning can provide not just square but rectangular blocks as well. Of course, some signaling overhead and increased computational complexity at the encoder side are the price of the QTBT partitioning as compared to conventional quad- tree based partitioning used in the HEVC/H.265 standard. Nevertheless, the QTBT-based partitioning is endowed with better segmentation properties and, hence, demonstrates significantly higher coding efficiency than the conventional quad-tree.

Leaves of the trees used for partitioning are being processed in a Z-scan order, so that the current block corresponding to the current leaf will have left and above neighbor blocks that are already reconstructed during encoding or decoding processes, unless the current block is located on the boundary of the slice. This is also illustrated in Fig. 13. Left-to-right scan of the leaves of the tree shown in the right part of Fig. 13 corresponds to the spatial Z-scan order of the blocks shown in the right part of this figure. The same scan is applied in case of quad-tree or multi-type trees.

In this document, the terms“vertically oriented block” (“vertical orientation of a block”) and “horizontally oriented block” (“horizontal orientation of a block”) are applied to rectangular blocks generated by the QTBT framework. These terms have the same meaning as shown in Fig. 14. For directional intra prediction, reference samples are obtained from the samples of the previously reconstructed neighboring blocks. Depending on the size of the block and intra prediction mode, a filter could be applied to the reference samples prior they are used to obtain values of predicted samples. According to a first aspect of the disclosure, a method of intra-prediction processing for video or image (or picture) data is provided. The method may be performed by an encoding or decoding apparatus (for example, an encoder or decoder), wherein the method comprises: obtaining a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample and a second reference sample (in an example, the second reference sample is not adjacent to any other reference samples in the set of reference sample), the first reference sample and the second reference sample are not adjacent in spatial position (in an example, the first and second sample are spaced apart from each other by an offset or in other words a position of the first reference sample differs from a position of the second sample by an offset or offset value, e.g. in one direction); and filtering the first reference sample and the second reference sample to obtain a value of a filtered reference sample (or a predicted sample) for intra prediction of the current block.

In an example, for directional intra prediction (for example, angular prediction mode), a set of reference samples is obtained from the samples of the previously reconstructed neighboring blocks, or a set of reference samples is obtained from the samples of the neighboring blocks. Fig. 15 illustrates processing of reconstructed samples of the above neighboring blocks (refUnflt) in order to obtain above row of filtered reference samples (p) according to an embodiment. From Fig. 15 it could be noticed that unfiltered reference samples selected to be further filtered are not adjacent to each other. In this specific example, the distance between two neighbor samples is equal to samplingOffset variable, which is defined to be equal to 2 samples.

In other words, from the unfiltered reference samples of the above neighboring block, reference samples not adjacent to each other are selected into a set of reference samples, which form the input reference sample to the filter F for determining a filtered reference sample. Although in Fig. 15 the distance between reference samples selected for the set of reference samples (e.g. the samplingOffset) is two, the present disclosure is not limited thereto. In particular, the samplingOffset may be an integer larger than two. For example, the offset between the reference samples, which are obtained for the set of reference samples to be input to the filter F may be three or four.

In one implementation form of the present application, the first reference sample may be any reference sample in the set of reference samples. In an example, in one of Figs. 15 to 17, the first reference sample may be the sample refUnflt[x][y].

In one implementation form of the present application, the second reference sample may be a reference sample, which is obtained according the first reference sample and an offset. For example, the position of the second reference sample may be obtained according to the position of the first reference sample plus a value of the offset, or according to the position of the first reference sample minus a value of the offset.

In an example, the first and second sample are spaced apart from each other by an offset or, in other words, a position of the first reference sample differs from a position of the second sample by an offset or offset value, e.g. in one direction.

In an example, it could be noticed that reference samples selected to be further filtered are not adjacent to each other. For example, in one of Figs. 15 to 17, the second reference sample may be the sample refUnflt[x-2][y], or may be the sample refUnflt[x+2][y]. In this example, the distance between two neighbor samples is equal to samplingOffset variable, which is defined to be equal to 2 samples in this example. That is, a value of the offset is 2.

However, the present disclosure is not limited to the value of the offset being 2. The value of the offset may be any positive integer. For example the value of the offset may be 3, 4 or 5.

In one implementation form of the present application, the method further comprises: obtaining a value of an offset according to a size of the current block, the second reference sample is determined according to the first reference sample and the value of the offset.

In one implementation form of the present application, the method further comprises: obtaining a value of an offset according to a size of a side of the current block, the second reference sample is determined according to the first reference sample and the value of the offset. In an example, the size of the side of the current block is equal to the width of the current block.

In an example, when a direction of the set of reference samples (for example, a direction of the main reference side) is horizontal direction, the size of the side of the current block is equal to the width of the current block. In an example, the size of the side of the current block is equal to the height of the current block.

In an example, when a direction of the set of reference samples (for example, a direction of the main reference side) is vertical direction, the size of the side of the current block is equal to the height of the current block. In an example, the offset could be represented by a syntax element samplingOffset or sub sampling offset.

In one implementation form, samplingOffset is set to 2 if the predicted block comprises 256 predicted samples or greater. When processing reconstructed samples of the above neighboring blocks, refUnflt[x-samplingOffset][y], refUnflt[x+ samplingOffset] [y] are used. Generally, more than three samples could be selected for filtering. In this case they could be sampled as refUnflt[x-A:· samplingOffset] [y], refUnflt[x+ wsamplingOffset][y], where k=l ..N, m=l ..N, and the filter that is applied to the selected samples has an order of 2N.

However, the present disclosure is not limited to setting the samplingOffset to two if the predicted block comprises 256 predicted samples or greater, and the samplingOffset may be set to a predetermined offset value in accordance with the number of predicted samples in the predicted block. For example, in a case where the number of predicted samples is equal to or larger than a predetermined threshold value, the samplingOffset may be set to two; in a case where the number of predicted samples is below said first threshold value, no samplingOffset may be applied (i.e. the samplingOffset is set to 1). Further, for example, in a case where the number of predicted samples is equal to or larger than a second threshold, the samplingOffset may be set to 3.

However, the samplingOffset is not limited to being set to 2 or 3, as described in the following.

In another implementation form, samplingOffset value depends on the size of the side of the block, along which reference samples are being processed. For a row (horizontal direction) of reference samples, the block width is used, and for a column (vertical direction) of reference samples, the block height is used. Particular example of this dependency is shown in Table 4.

Table 4. Dependency of sub sampling offset on the size of corresponding side of the predicted block

As illustrated in Table 4, in a case where the block side size is equal to 4, the offset (e.g. the subsampling offset) is set to 1. In a case where the block side size is equal to 8, the subsampling offset is set to 1 as well. In a case where the block side size is equal to 16, the subsampling offset is set to 2. In a case where the block side size is equal to 32, the subsampling offset is set to 2 as well. Further, in a case where the block side size is equal to or larger than 64, the subsampling offset is set to 3.

However, the present disclosure is not limited to the correspondence of block side size and subsampling offset illustrated in Table 4, and other correspondence may be defined. Processing of reconstructed samples of the left neighboring blocks is performed similarly, however sampling offset is applied to another dimension, e.g. refUnflt[x][y-samplingOffset], refUnflt[x][y+ samplingOffset] are used.

In other words, in a case where processing of the samples of the left neighboring block is performed, the sampling offset is applied to a vertical direction coordinate y of the reference samples.

In one implementation form of the present disclosure, a filtering coefficient corresponding to the first reference sample is different from a filtering coefficient corresponding to the second reference sample. In an example, a filtering coefficient corresponding to the first reference sample or a filtering coefficient corresponding to the second reference sample may be zero (for example, bypass or sample skip).

In one implementation form of the present disclosure, the filtering of the first reference sample and the second reference comprises: weighting the first reference sample and the second reference sample, wherein a weighting coefficient corresponding to the first reference sample is different from a weighting coefficient corresponding to the second reference sample.

In an example, the weighting coefficients correspond to the filtering coefficients.

In an example, a weighting coefficient corresponding to the first reference sample or a weighting coefficient corresponding to the second reference sample may be zero (for example, bypass or sample skip).

In an example, as shown in Fig. 15, filter“F” is applied to the reconstructed samples. For any implementation form, this filter could be a linear or a non-linear filter. For example, filter“F” could be an FIR (finite impulse response) filter (e.g., [1 2 1], [2 3 6 3 2] or [1 1 4 1 1] filter), median filter or bilateral filter.

A case when filter“F” is a [1 2 1] FIR filter is shown in Figs. 16 and 17. In these figures, the value of D is a rounding offset equal to the half of the filter norm, e.g. to 2 for the example of F being the [1 2 1] FIR filter. In the illustrated example, the sample refUnfilt[x][y] is bitwise left-shifted (“<<”) by 1. The result of this operation, the sample reUnfilt[x-2][y], the sample refUnfilt[x+2][y] and the rounding offset D are summed up. Subsequently, the result of the summation is bitwise right-shifted by 2, resulting in the filtered reference sample or predicted sample p[x][y].

Fig. 17 shows an implementation of this filter using summation and shift operations only. In this implementation, the summation is performed in two steps. First, the left-shifted (by 1) reUnfilt[x][y] is added to the rounding offset D and the samples refUnfilt[x-2][y] and refUnfilt[x+2][y] are added. Second, the results of said summations are added to obtain the filtered reference sample or predicted sample p[x][y]. From this figure, it is clear that the filtering has a delay of two consecutive summation operations. In one implementation form of the present disclosure, the method further comprises: obtaining a value of an offset according to an intra prediction mode of the current block, the second reference sample is determined according to the first reference sample and the value of the offset. For example, in an implementation form, the sampling offset is set dependent on the intra prediction mode of a block. A flowchart to derive sampling offset is shown in Fig. 18. A condition on intra prediction mode“c(predModelntra)” may comprise one or a combination of the following:

- predModelntra is an even integer value; - predModelntra is an odd integer value;

- subpixel offset corresponding to predModelntra is greater than a given threshold T_s.

Specifically, according to the method illustrated in Fig. 18 for determining a sampling offset, it is determined whether the intra-prediction mode predModelntra of the current block satisfies a condition“c(prefModelntra)” and whether a filterFlag is set. In a case where the filterFlag is set and the intra prediction mode predModelntra satisfies the condition“c(predModelntra)” an increased samplingOffset is set. For instance, the sampling offset is set to a value of two. On the other hand, in a case where the filterFlag is not set or the condition“c(predMdelntra)” is not satisfied, the sampling offset is set to 1, i.e. no subsampling is applied.

As indicated above, the condition“c(predModelntra)” may comprise that a subpixel offset corresponding to predModelntra is greater than a given threshold. An exemplary correspondence of predModelntra to subpixel offset could be found in Table 5 and Table 6 (predModelntra is denoted as“M” in these tables). Values of the threshold T_s is a positive integer value. For example, T_s could be either 24, 32, 34, 48 or 64.

In one implementation form of the present application, wherein the second reference sample is determined according to the first reference sample and a predefined value of an offset.

In an example, the step“set increased samplingOffset” in Fig. 18 could be performed in one of the following ways: apply values from Table 4 depending on the size of the corresponding block side; set samplingOffset to 2; set samplingOffset to a positive integer value greater than 1

Intra prediction mode Mo in Table 5 and Table 6 is a horizontal mode (mode 18 shown in Fig. 10), if intra prediction mode M (predModelntra) is less than a diagonal mode (mode 34 shown in Fig. 10). Otherwise, if prediction mode M (predModelntra) is not less than a diagonal mode (mode 34 shown in Fig. 10), intra prediction mode M₀ is set to vertical intra prediction mode (mode 50 shown in Fig. 10).

In an embodiment, the method further comprises: interpolation filtering a part of the set of the reference samples to obtain a value of a subpixel filtered sample (or subpixel predicted sample), wherein an interpolation filtering coefficient is calculated according to the value of the offset.

In one implementation form of the present disclosure, the part of the set of the reference samples is determined according to a sample pattern.

In one implementation form of the present disclosure, the sample pattern is selected from a set of predefined sample patterns, according to a subpixel offset, wherein the subpixel offset is determined according to the intra prediction mode of the current block.

In one implementation form of the present disclosure, the sample pattern is selected from a set of predefined sample patterns, according to a position of reference sample.

As illustrated in Figs. 19 and 20, different values of samplingOffset are used at the stage of interpolation filtering, e.g. when a predicted sample predSamples[x’][y’] is calculated using subpixel interpolation on a set of reference samples.

The difference between the two figures is in the pattern used to get the set of reference samples. Fig. 21 gives an example of different sampling patterns that could be used in case of four-tap interpolation filtering. In the figure, the shaded samples refer to reference samples used to calculate a predicted sample. In the patterns illustrated in the figure, at least one selected reference sample is not adjacent to any one of the other reference samples in the set of reference sample.

A flowchart to derive a sampling pattern depending on the subpixel offset“deltaPos” assigned for a row of predicted samples is shown in Fig. 22. In this figure,“filterFlag” denotes a result of mode-dependent intra smoothing (MDIS) check. In particular implementations, this flag is coupled with selection of the type of interpolation filter. When“filterFlag” is 0, a stronger interpolation filter is selected, and when“filterFlag” is 1, a weaker interpolation filter is selected. A stronger filter could be a Cubic filter (Table 1) or a unified inter/intra filter (Tables 2,3). A weaker filter is typically a Gaussian filter (Tables 1-3). The terms“weaker” and

“stronger” indicate the flatness of transfer function, e.g. a“weaker” filter has a more flat transfer function and thus provides lower suppression in the high frequencies range.

Tables 5 and 6 represents the possible values of a subpixel offset for the first row of predicted samples depending on the modes difference. Subpixel offsets for the other rows of predicted samples is obtained by multiplying the subpixel offset for difference between the position of a row the predicted samples and the first row.

Table 5. Dependency of subpixel offset on the modes difference for the first row of predicted samples

Table 6. Dependency of subpixel offset on the modes difference for the first row of predicted samples (another example)

In Fig. 22“idx” denotes the fractional part of the subpixel offset“deltaPos”. The condition on idx, indicated as“c(idx)”, may comprise one of or a combination of the following: idx is greater than or equal to a predetermined threshold T_Smin, exemplary values of T_Smin are 2,4, 6, 8 or 10; idx is lower than or equal to a predetermined threshold T_Smax, exemplary values of T_Smin are 22,24,26,28 or 30; idx is odd; idx is even.

As illustrated in Fig. 22, using the input parameters deltaPos, which indicates the subpixel offset, the fractional subpixel offset idx is determined using the relation idx=deltaPos%32. Further, it is determined whether the filterFlag is set and the condition“c(idx)” is satisfied. In a case where the condition“c(idx)” is satisfied and the filterFlag is set, a modified sampling pattern is set as described further below. On the other hand, in a case where the condition“c(idx)” is not satisfied ot eh filterFlag is not set, a default sampling pattern is set.

In Fig. 22, the step“Set modified sampling pattern” consists of selection of one of the sampling patterns shown in Fig. 21. According to the selected pattern, a set of reference samples is prepared to be further processed by interpolation filter in order to calculate a value of a predicted sample.

In another embodiment shown in Fig. 23, the sampling pattern could be set different depending on the position of the predicted sample predSample[x’][y’] within a row. For example, if intraPredMode is greater than or equal to DIA IDX, pattern“A” is selected if the horizontal position x’ of the sample predSample[x’][y’] is lesser than a predefined threshold Tv. Otherwise, pattern“B” is selected. The value of T is a positive integer, which is a multiple of 4 (that is beneficial for SIMD implementations).

Similarly, if intraPredMode is less than DIA IDX, pattern“A” is selected if the vertical position y’ of the sample predSample[x’][y’] is lesser than a predefined threshold T_y . Otherwise, pattern “B” is selected. The value of T_y is a positive integer which is a multiple of 4 (that is beneficial for SIMD implementations).

Exemplary assignment of patterns“A” and“B” could be as follows:“A” is an unmodified pattern, and“B” is one of the patterns shown in Fig. 21. Although in the described example, the predefined threshold Tx or Ty are multiples of 4, the present disclosure is not limited thereto, and he predefined threshold Tx or Ty may be any other integer.

In one implementation form of the present disclosure, the filtering of the first reference sample and the second reference sample to obtain value of a filtered sample (or subpixel predicted sample) of the current block, comprises: interpolation filtering the first reference sample and the second reference sample to obtain a value of a subpixel filtered sample (or subpixel predicted sample) of the current block, wherein an interpolation filtering coefficient is calculated according to the value of the offset. An embodiment includes convolving reference sample filter with increased sampling offset (i.e., [1 0 2 0 1]) and Gaussian interpolation filter. Coefficients of this 8-tap filter is given in Table 7.

In this example, the increased sampling offset is implemented by using a reference sample filter comprising values equal to zero at certain positions. In particular, at least one non-zero element in the reference sample filter is neighbored by zeros. Further, the reference sample filter is convolved with an interpolation filter, which is not necessarily a Gaussian filter. Subsequently, the resulting convolved filter is applied to the reference samples.

Table 7: A set of normalized 8-tap interpolation filters with obtained by convolving

[1 0 2 0 1] and Gauss filter (Tablet)

In this example, no reference filtering is performed, but this filter is used during interpolation. Exemplary hardware implementations of 4-tap filter and the 8-tap filters are given in Fig. 24. From Table 7 it could be noticed that first and last coefficients of the filter are numbers that are power of two. Hence, it is possible to perform several shift-and-add operations in parallel with multiplication and thus to provide similar processing time for both 4-tap and 8-tap filtering.

For instance, as illustrated in Fig. 24, multiplications with a filter value that is a power of two is implemented as a bitwise shift operation, which is typically faster than a multiplication operation. Thus, in the same time required for performing a multiplication operation, multiple shift operations may be performed in addiction to an addition operation. This allows the application of the 8-tap filter illustrated in the left part of Fig. 24 to be performed in a time duration similar to a time duration necessary for applying a 4-tap filter, as illustrated in the right part of Fig. 24. Input to the illustrated shift registers and the multipliers are the filter coefficient and respective reference sample values. From Table 7 it could be noticed that coefficients ci and c₆ are greater than 2 and less than 11. For these values multiplication could be implemented with just two shift operations and one addition (or one subtraction) operation.

In another embodiment, the first two and the last two coefficients are set to be a power of two (Table 8). Table 8: A set of normalized 8-tap interpolation filters with cO, cl, c6 and c7 set to power of two

In an example, all the filters given in Table 8 could be implemented in hardware using just 4 multipliers (as shown in Fig. 25) or less. It could be noticed, that in both implementations that use Table 7 and Table 8 coefficients ci,c₂, c₅ and c₆ are specified to fall within a range of [4, 10] Besides, in many cases coefficients of different subpixel offsets have the same value.

Hence, it is possible to implement interpolation filtering with these coefficients using just two multipliers for c₃ and c_4. The rest of multiplications could be performed using addition and shift operations. Addition and subtraction operations have the same number operations since one subtraction could be implemented as addition by negation of an argument and raising the carry-flag of the least significant l-bit full-adder. In the same manner, increment or decrement could be performed when summing up results of multiplication. Specifically, for a coefficient C_k, k E { 1,2, 5, 6}, operations are listed in Table 9.

Table 9: Add and shift operations to implement multiplication within a range of [4, 10]

In an example, bilateral filtering could be applied for reference samples. This could be done in a form of preprocessing, i.e. the set of reference samples from that are passed to a bilateral filter are selected to be non-adjacent to each other (see Fig.15).

In an example, filtered samples are obtained by applying a bilateral filter to reference samples: R[^cL = J årefUnflt[x,] · /_r(|refUnflt[x,] - refUnflt[x₀]||) · g,(||x, - x₀||) , where

• the normalization term W_p = ^ ./ (||refUnflt[x, ] - refUnflt[x₀ ]||) · g_s (||x, - x₀1|) ,

• W is a set of reference samples, • f_r is the range kernel for smoothing differences in intensities, which could be implemented in a form of a LUT fetch,

• S_s is the spatial kernel for smoothing differences in coordinates, which could be also implemented in a form of a LUT fetch,

• · is a coordinate of a calculated filtered reference sample,

• refUnflt are unfiltered reference samples.

• p are filtered reference samples.

The preprocessing consists in either

• constructing W in a way that some of reference samples are skipped;

• setting ^~xu ) to zero for the specific values of differences

^— ¾), e.g. when

(X_— ¾) is odd, when

^— ¾) is even or when

^— ¾) is less than a threshold (e.g. equal to 2).

Fig. 26 schematically illustrates the interpolation filters as used in JEM. As can be seen from the figure, for intra reference sample interpolation in intra prediction, a Gaussian 4-tap interpolation filter with 8-bit coefficients or a Cubic 4-tap interpolation filter with 8-bit coefficients is used.

Fig. 27 schematically illustrates interpolation filters, wherein for intra reference sample interpolation in intra prediction, a Gaussian 6-tap interpolation filter with 8-bit coefficients or a Cubic 4-tap interpolation filter with 8-bit coefficients is used.

Fig. 28 schematically illustrates interpolation filters, wherein for intra reference sample interpolation in intra prediction, a Gaussian 6-tap interpolation filter with 8-bit coefficients or a Cubic 6-tap interpolation filter with 8-bit coefficients is used.

In an embodiment shown in Fig. 29, a filtering module is being implemented in predicting luminance and chrominance samples when performing intra-prediction. In this implementation, a 4-tap filter is being used in intra-prediction processes. Another embodiment shows implementation when LUTs (look-up tables) of filter coefficients are used, as illustrated in Fig. 30. In this embodiment, a filtering module loads coefficients from LUTs. A switch shown in intra prediction process determines the filter type being used.

Fig. 31 illustrates an example of reference samples. In the example, the reference samples are within multiple reference lines of the above and the left block.

Fig. 32 illustrates the steps of a method according to an embodiment. The method is a method of intra-prediction of a current block for encoding or decoding of video or image data, wherein, in step S100, a set of reference samples for the current block is obtained. The set of reference samples comprises a first reference sample and a second reference sample. In particular, the second reference sample is not adjacent to any other reference sample in the set of reference samples. In a second step Sl 10, the first reference sample and the second reference sample are filtered to obtain a value of a filtered reference sample or a predicted reference sample for intra prediction of the current block.

Fig. 33 illustrates an encoder and a decoder according to an embodiment.

The encoder 1000 is configured to encode video or image data and comprises an obtaining unit 1100 configured to obtain a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample and a second reference sample. The second reference sample is not adjacent to any other reference sample in the set of reference samples. The encoder 1000 further comprises a filter unit 1200 configured to filter the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

The decoder 2000 is configured to decode video or image data and comprises an obtaining unit 2100 configured to obtain a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample and a second reference sample. The second reference sample is not adjacent to any other reference sample in the set of reference samples. The decoder 2000 further comprises a filter unit 2200 configured to filter the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

Although the encoder 1000 and the decoder 2000 illustrated in Fig. 33 each comprise an obtaining unit and a filter unit, the present disclosure is not limited thereto. In particular, the encoder and the decoder may comprise further units configured to perform processes of an encoding or decoding process described further above.

According to a second aspect of the disclosure a method of video coding is provided, wherein the method comprises: performing intra-prediction process of a block, wherein a predicted sample of the block is calculated from a set of reference samples by applying a filter to the reference samples belonging to the set; and wherein applying a filter comprises weighting of at least a pair of reference samples belonging to the set of reference samples using a pair of weighting coefficients, the weighting comprises: a first weighting coefficient applied to a first reference sample belonging to the set of reference samples; and a second weighting coefficient applied to a second reference sample belonging to the set of reference samples; wherein a first weighting coefficient is greater than the second weighting coefficient, and the distance from the second reference sample to the middle of the set of reference samples is smaller than the distance from the first reference sample to the middle of the set of reference samples (in an example, Reference samples belonging to the set of reference samples are selected from the main reference side. Main reference side is a one-dimensional array of samples, so that a spatial position of the sample is the index of an element of this array. The set of reference samples is a subset of the main reference side. The middle of the set of reference samples could be defined using the spatial positions of the samples belonging to the set, e.g.:

- Half of the sum of the minimum and the maximum values of the spatial positions; - Median of the spatial positions;

Average of all the spatial positions).

In one implementation form, a second weighting coefficient is zero.

In one implementation form, the set of reference samples is composed of the samples of neighboring previously reconstructed blocks. In one implementation form, the filtering is applied in two stages:

• the first stage filter is the same for all of the positions of the predicted sample within a block;

• the second stage filter depends on the position of the predicted samples within a block. In one implementation form, the second stage filter is the same for the same column positions of the predicted samples.

In one implementation form, the second stage filter is the same for the same row positions of the predicted samples.

In one implementation form, the first stage filter is a reference sample filter.

In one implementation form, the second stage filter is a subpixel interpolation filter.

In one implementation form, the subpixel interpolation filter is selected from a set of filters used for intra-prediction process for a given subpixel offset.

In one implementation form, the set of filters comprises a Gauss filter and a Cubic filter.

In one implementation form, reference samples being used to obtain values of predicted pixels are not adjacent to the block of the predicted pixels.

Further features and implementation forms of the method according to the second aspect of the disclosure correspond to the features and implementation forms of the method according to the first aspect or any possible embodiment of the first aspect of the disclosure.

According to a third aspect of the disclosure, a method of intra-prediction for coding video or image data is provided, wherein the method comprises:

• obtaining a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample,

• filtering the first reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block, wherein there is a positive correlation between a filtering coefficient corresponding to the first reference sample and a distance from the first reference sample (for example, spatial position of the first reference sample) to the middle of the set of reference samples (in an example, Reference samples belonging to the set of reference samples are selected from the main reference side. Main reference side is a one-dimensional array of samples, so that a spatial position of the sample is the index of an element of this array. The set of reference samples is a subset of the main reference side. The middle of the set of reference samples could be defined using the spatial positions of the samples belonging to the set, e.g.: Half of the sum of the minimum and the maximum values of the spatial positions;

- Median of the spatial positions;

Average of all the spatial positions).

In one implementation form, the set of reference samples comprises a second reference sample, wherein the filtering the first reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block comprises: filtering the first reference sample and the second reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block; wherein there is a positive correlation between a filtering coefficient corresponding to the first reference sample and a distance from the first reference sample to the middle of the set of reference samples means that the filtering coefficient corresponding to the first reference sample is greater than a filtering coefficient corresponding to the second reference sample, when the distance from the first reference sample to the middle of the set of reference samples is greater than the distance from the second reference sample to the middle of the set of reference samples; or the filtering coefficient corresponding to the first reference sample is less than the filtering coefficient corresponding to the second reference sample, when the distance from the first reference sample to the middle of the set of reference samples is less than the distance from the second reference sample to the middle of the set of reference samples.

In one implementation form, the filtering coefficient is a weighting coefficient. In one implementation form, the weighting coefficient corresponding to the first reference sample is zero (0), or the weighting coefficient corresponding to the second reference sample is zero (0).

In one implementation form, the set of reference samples for the current block is obtained according to samples of the neighboring block of the current block. In one implementation form, the first reference sample and the second reference sample are not adjacent in spatial position.

For instance, the second reference sample may be not adjacent to any other reference sample within the set of reference samples. In one implementation form, the filtering the first reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block, comprises: filtering the first reference sample using a Gauss filter (for example, Table 4 or Table 5 includes coefficients of the Gauss filter).

Further features and implementation forms of the method according to the third aspect of the disclosure correspond to the features and implementation forms of the method according to the first aspect or any possible embodiment of the first aspect of the disclosure, or correspond to the features and implementation forms of the method according to the second aspect or any possible embodiment of the second aspect of the disclosure.

According to a fourth aspect, an encoder is provided, the encoder comprising processing circuitry for carrying out the method according to the first aspect or any possible embodiment of the first aspect of the disclosure, or according to the second aspect or any possible embodiment of the second aspect of the disclosure, or according to the third aspect or any possible embodiment of the third aspect of the disclosure.

According to a fifth aspect, a decoder is provided, the decoder comprising processing circuitry for carrying out the method according to the first aspect or any possible embodiment of the first aspect of the disclosure, or according to the second aspect or any possible embodiment of the second aspect of the disclosure, or according to the third aspect or any possible embodiment of the third aspect of the disclosure.

The method according to the first aspect or second aspect or third aspect of the disclosure can be performed by the apparatus according to the fourth or fifth aspect of the disclosure. Further features and implementation forms of the apparatus according to the fourth or fifth aspect of the disclosure correspond to the features and implementation forms of the method according to the first aspect or any possible embodiment of the first aspect of the disclosure, or according to the second aspect or any possible embodiment of the second aspect of the disclosure, or according to the third aspect or any possible embodiment of the third aspect of the disclosure.

According to a sixth aspect, an apparatus for decoding a video stream is provided, the apparatus including a processor and a memory. The memory is storing instructions that cause the processor to perform the method according to the first aspect or any possible embodiment of the first aspect, or according to the second aspect or any possible embodiment of the second aspect of the disclosure, or according to the third aspect or any possible embodiment of the third aspect of the disclosure.

According to a seventh aspect, a computer-readable storage medium having stored thereon instructions that when executed causes one or more processors configured to code video data is provided. The instructions cause the one or more processors to perform a method according to the first aspect or any possible embodiment of the first aspect, or according to the second aspect or any possible embodiment of the second aspect of the disclosure, or according to the third aspect or any possible embodiment of the third aspect of the disclosure.

According to an eighth aspect, a computer program is provided, the computer program comprising program code for performing the method according to the first aspect or any possible embodiment of the first aspect, or according to the second aspect or any possible embodiment of the second aspect of the disclosure, or according to the third aspect or any possible embodiment of the third aspect of the disclosure when executed on a computer.

In another aspect, a decoder comprising processing circuitry is provided configured for carrying out the above methods.

In another aspect, a computer program product is provided which comprising a program code for performing the above methods.

In another aspect of the present application, a decoder for decoding video data is provided, the decoder comprising: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the above methods.

The processing circuitry can be implemented in hardware, or in a combination of hardware and software, for example by a software programmable processor or the like. Further aspects of the present disclosure are summarized in the following:

The present disclosure provides a method of intra-prediction for coding video or image data, the method comprises: obtaining a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample and a second reference sample (in an example, the second reference sample not adjacent to any other reference samples in the set of reference sample), the first reference sample and the second reference sample are not adjacent in spatial position (in an example, the first and second sample are spaced apart from each other by an offset or in other words a position of the first reference sample differs from a position of the second sample by an offset or offset value, e.g. in one direction); and filtering the first reference sample and the second reference sample to obtain a value of a filtered reference sample (or a predicted sample) for intra prediction of the current block. .In an embodiment,, a filtering coefficient corresponding to the first reference sample is different from a filtering coefficient corresponding to the second reference sample (for example, there is a positive correlation between a filtering coefficient corresponding to the first reference sample and a distance from the first reference sample, the filtering coefficient corresponding to the first reference sample is greater than a filtering coefficient corresponding to the second reference sample, when the distance from the first reference sample to the middle of the set of reference samples is greater than the distance from the second reference sample to the middle of the set of reference samples; or the filtering coefficient corresponding to the first reference sample is less than the filtering coefficient corresponding to the second reference sample, when the distance from the first reference sample to the middle of the set of reference samples is less than the distance from the second reference sample to the middle of the set of reference samples).

In an embodiment, the filtering the first reference sample and the second reference, comprises: weighting the first reference sample and the second reference sample, wherein a weighting coefficient corresponding to the first reference sample is different from a weighting coefficient corresponding to the second reference sample (the weighting coefficient correspond to the filtering coefficient in the claim 1 or 2).

In an embodiment the method further comprises: obtaining a value of an offset according to a size of a side of the current block, wherein the second reference sample is determined according to the first reference sample and the value of the offset. For example, the size of the side of the current block is equal to the width of the current block (in an example, when a direction of the set of reference samples is horizontal direction, the size of the side of the current block is equal to the width of the current block).

For example the size of the side of the current block is equal to the height of the current block (in an example, when a direction of the set of reference samples is vertical direction, the size of the side of the current block is equal to the height of the current block).

In an embodiment the method further comprises: obtaining a value of an offset according to an intra prediction mode of the current block, the second reference sample is determined according to the first reference sample and the value of the offset.

In an embodiment, the second reference sample is determined according to the first reference sample and a predefined value of an offset.

In an embodiment, the predefined value of the offset is positive integer, and the predefined value is greater than 1. In an embodiment, the method further comprises: interpolation filtering a part of the set of the reference samples to obtain a value of a subpixel filtered sample (or subpixel predicted sample), wherein an interpolation filtering coefficient is calculated according to the value of the offset.

In an embodiment, the filtering the first reference sample and the second reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block, comprises: interpolation filtering the first reference sample and the second reference sample to obtain a value of a subpixel filtered sample (or subpixel predicted sample) of the current block, wherein an interpolation filtering coefficient is calculated according to the value of the offset.

For example, the part of the set of the reference samples is determined according to a sample pattern. For example, the sample pattern is selected from a set of predefined sample patterns, according to a subpixel offset, wherein the subpixel offset is determined according to the intra prediction mode of the current block.

For example, the sample pattern is selected from a set of predefined sample patterns, according to a position of reference sample.

Further provided is a method of video coding, the method comprises: performing intra-prediction process of a block, wherein a predicted sample of the block is calculated from a set of reference samples by applying a filter to the reference samples belonging to the set; and wherein applying a filter comprises weighting of at least a pair of reference samples belonging to the set of reference samples using a pair of weighting coefficients, the weighting comprises: a first weighting coefficient applied to a first reference sample belonging to the set of reference samples; and a second weighting coefficient applied to a second reference sample belonging to the set of reference samples; wherein a first weighting coefficient is greater than the second weighting coefficient and the distance from the second reference sample to the middle of the set of reference samples is smaller than the distance from the first reference sample to the middle of the set of reference samples (in an example, Reference samples belonging to the set of reference samples are selected from the main reference side. Main reference side is a one-dimensional array of samples, so that a spatial position of the sample is the index of an element of this array. The set of reference samples is a subset of the main reference side. The middle of the set of reference samples could be defined using the spatial positions of the samples belonging to the set, e.g.: Half of the sum of the minimum and the maximum values of the spatial positions; Median of the spatial positions; Average of all the spatial positions).

In an embodiment, a second weighting coefficient is zero.

In an embodiment, the set of reference samples is composed of the samples of neighboring previously reconstructed blocks. In an embodiment, the filtering is applied in two stages: the first stage filter is the same for all of the positions of the predicted sample within a block; the second stage filter depends on the position of the predicted samples within a block. For example, the second stage filter is the same for the same column positions of the predicted samples.

For example, the second stage filter is the same for the same row positions of the predicted samples.

For example, the first stage filter is a reference sample filter. For example the second stage filter is a subpixel interpolation filter.

In an embodiment, the subpixel interpolation filter is selected from a set of filters used for intra- prediction process for a given subpixel offset.

For example, the set of filters comprises a Gauss filter and a Cubic filter.

In an embodiment, reference samples being used to obtain values of predicted pixels are not adj acent to the block of the predicted pixels.

Further provided is a method of intra-prediction for coding video or image data, the method comprises: obtaining a set of reference samples for a current block, wherein the set of reference samples comprises a first reference sample, filtering the first reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block, wherein there is a positive correlation between a filtering coefficient corresponding to the first reference sample and a distance from the first reference sample (for example, spatial position of the first reference sample) to the middle of the set of reference samples (in an example, Reference samples belonging to the set of reference samples are selected from the main reference side. Main reference side is a one-dimensional array of samples, so that a spatial position of the sample is the index of an element of this array. The set of reference samples is a subset of the main reference side. The middle of the set of reference samples could be defined using the spatial positions of the samples belonging to the set, e.g.: Half of the sum of the minimum and the maximum values of the spatial positions; Median of the spatial positions ; Average of all the spatial positions).

In an embodiment, the set of reference samples comprises a second reference sample, wherein the filtering the first reference sample to obtain a value of a filtered sample(or a predicted sample) of the current block, comprises: filtering the first reference sample and the second reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block; wherein there is a positive correlation between a filtering coefficient corresponding to the first reference sample and a distance from the first reference sample to the middle of the set of reference samples means that, the filtering coefficient corresponding to the first reference sample is greater than a filtering coefficient corresponding to the second reference sample, when the distance from the first reference sample to the middle of the set of reference samples is greater than the distance from the second reference sample to the middle of the set of reference samples; or the filtering coefficient corresponding to the first reference sample is less than the filtering coefficient corresponding to the second reference sample, when the distance from the first reference sample to the middle of the set of reference samples is less than the distance from the second reference sample to the middle of the set of reference samples.

In an embodiment, the filtering coefficient is a weighting coefficient.

In an embodiment, the weighting coefficient corresponding to the first reference sample is zero (0), or the weighting coefficient corresponding to the second reference sample is zero (0). In an embodiment, the set of reference samples for the current block is obtained according to samples of the neighboring block of the current block.

In an embodiment, the first reference sample and the second reference sample are not adjacent in spatial position. In an embodiment, the filtering the first reference sample to obtain a value of a filtered sample (or a predicted sample) of the current block, comprises: filtering the first reference sample using a Gauss filter (for example, Table 10 or Table 11 discloses coefficients of the Gauss filter). Further provided is An encoder comprising processing circuitry for carrying out any one of above methods.

Further provided is a decoder comprising processing circuitry for carrying out any one of the above methods.

Further provided is a computer program product comprising a program code for performing any one of the above methods.

Further provided is a decoder, comprises: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out any one of the above methods.

Further provided is an encoder, comprising: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out any one of the above methods.

Although embodiments of the invention have been primarily described based on video coding, it should be noted that embodiments of the coding system 10, encoder 20 and decoder 30 (and correspondingly the system 10) and the other embodiments described herein may also be configured for still picture processing or coding, i.e. the processing or coding of an individual picture independent of any preceding or consecutive picture as in video coding. In general only inter-prediction units 244 (encoder) and 344 (decoder) may not be available in case the picture processing coding is limited to a single picture 17. All other functionalities (also referred to as tools or technologies) of the video encoder 20 and video decoder 30 may equally be used for still picture processing, e.g. residual calculation 204/304, transform 206, quantization 208, inverse quantization 210/310, (inverse) transform 212/312, partitioning 262/362, intra- prediction 254/354, and/or loop filtering 220, 320, and entropy coding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functions described herein, e.g. with reference to the encoder 20 and the decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted over communication media as one or more instructions or code and executed by a hardware-based processing unit. Computer- readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limiting, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Aso, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term“processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Definitions of Acronyms & Glossary

JEM Joint Exploration Model (the software codebase for future video coding exploration)

JVET Joint Video Experts Team

LUT Look-Up Table

QT QuadTree QTBT QuadTree plus Binary Tree

RDO Rate-distortion Optimization

ROM Read-Only Memory

VTM VVC Test Model

VVC Versatile Video Coding, the standardization project developed by JVET.

CTU / CTB Coding Tree Unit / Coding Tree Block

CU / CB Coding Unit / Coding Block

PU / PB Prediction Unit / Prediction Block

TU/TB Transform Unit / Transform Block

HE VC High Efficiency Video Coding

Claims

1. A method of intra-prediction of a current block for encoding or decoding of video or image data, wherein the method comprises: obtaining a set of reference samples for the current block, wherein the set of reference samples comprises a first reference sample and a second reference sample, and the second reference sample is not adjacent to any other reference sample in the set of reference samples; and filtering the first reference sample and the second reference sample to obtain a value of a filtered reference sample or a predicted sample for intra prediction of the current block.

2. The method of claim 1, wherein a filtering coefficient corresponding to the first reference sample is different from a filtering coefficient corresponding to the second reference sample.

3. The method of claim 1 or 2, wherein the first reference sample and the second reference sample are not adjacent in spatial position.

4. The method of any one of claims 1 to 3, wherein the first reference sample and the second reference sample are spaced apart from each other by an offset, wherein a position of the first reference sample differs from a position of the second reference sample by a value of the offset.

5. The method of claim 4, wherein the value of the offset is a positive integer greater than one.

6 The method of claim 4 or 5, wherein the method further comprises: obtaining the value of the offset according to a size of a side of the current block, wherein the second reference sample is determined according to the first reference sample and the value of the offset.

7. The method of any one of claims 4 to 6, wherein the method further comprises: obtaining the value of the offset according to an intra prediction mode of the current block, the second reference sample is determined according to the first reference sample and the value of the offset.

8. The method of any one of claims 4 to 7, wherein the filtering the first reference sample and the second reference sample to obtain a value of a filtered sample or a predicted sample of the current block comprises: interpolation filtering the first reference sample and the second reference sample to obtain a value of a subpixel filtered sample or subpixel predicted sample of the current block, wherein an interpolation filtering coefficient is calculated according to the value of the offset.

9. The method of any one of claims 4 to 8, wherein the method further comprises: interpolation filtering a part of the set of the reference samples to obtain a value of a subpixel filtered sample or subpixel predicted sample, wherein an interpolation filtering coefficient is calculated according to the value of the offset.

10. The method of claim 9, wherein the part of the set of the reference samples is determined according to a sample pattern.

11. The method of claim 10, wherein the sample pattern is selected from a set of predefined sample patterns, according to a subpixel offset, wherein the subpixel offset is determined according to the intra prediction mode of the current block.

12. The method of claim 10, wherein the sample pattern is selected from a set of predefined sample patterns, according to a position of reference sample.

13. An encoder comprising processing circuitry for carrying out the method according to any one of claims 1 to 12.

14. A decoder comprising processing circuitry for carrying out the method according to any one of claims 1 to 12.

15. A computer program product comprising a program code for performing the method according to any one of claims 1 to 12.