WO2019204672A1

WO2019204672A1 - Interpolation filter for an intra prediction apparatus and method for video coding

Info

Publication number: WO2019204672A1
Application number: PCT/US2019/028217
Authority: WO
Inventors: Jianle Chen; Maxim SYCHEV; Timofey SOLOVYEV; Alexey Filippov; Georgy ZHULIKOV
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2018-04-19
Filing date: 2019-04-19
Publication date: 2019-10-24
Anticipated expiration: 2020-10-19

Abstract

An apparatus for intra prediction of a sample value of a current full-integer pixel of a current block of a current image frame is disclosed. And the intra prediction having a prediction direction, wherein the apparatus comprises a processing circuitry configured to: determine a sample value of a corresponding sub-integer pixel in a reference block of the current frame, determined on the basis of the prediction direction for the current full-integer pixel, by applying an enhanced bilinear interpolation filter to sample values of neighboring pixels of the corresponding sub-integer pixel in the reference block, wherein the enhanced bilinear interpolation filter is determined on basis of a bilinear interpolation filter and a sharpening filter; and determine the intra predicted sample value of the current full-integer pixel on basis of the sample value of the corresponding sub-integer pixel in the reference block.

Description

INTERPOLATION FILTER FOR AN INTRA PREDICTION APPARATUS AND METHOD FOR VIDEO CODING

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This patent application claims the priority of US provisional application number

62660218, filed on April 19, 2018.

TECHNICAL FIELD

[0002] Embodiments of the present application (disclosure) generally relate to the field of picture processing and more particular to an interpolation filter for intra prediction for video coding as well as an encoding apparatus and a decoding apparatus for implementing the interpolation filter.

BACKGROUND

[0003] Video coding (video encoding and decoding) is used in a wide range of digital video applications, for example broadcast digital TV, video transmission over internet and mobile networks, real-time conversational applications such as video chat, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and camcorders of security applications.

[0004] 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. SUMMARY

[0005] Embodiments of the present application provide apparatuses and methods for encoding and decoding according to the independent claims.

[0006] 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.

[0007] According to a first aspect the invention relates to an apparatus for intra prediction of a sample value of a current full-integer pixel of a current block of a current image frame, the intra prediction having a prediction direction, wherein the apparatus comprises a processing circuitry configured to: determine, for the current full-integer pixel, a corresponding sub-integer pixel in a reference block of the current frame on the basis of the prediction direction; determine a sample value of the corresponding sub-integer pixel by applying an enhanced bilinear interpolation filter to sample values of neighboring pixels of the corresponding sub-integer pixel in the reference block, wherein the enhanced bilinear interpolation filter is determined on basis of a bilinear interpolation filter and a sharpening filter; and determine the intra predicted sample value of the current full-integer pixel on basis of the sample value of the corresponding sub-integer pixel in the reference block.

[0008] Thus, an improved intra prediction apparatus is provided allowing improving the efficiency for image or video coding.

[0009] According to the first aspect, the sample value of the sub-integer pixel is determined by applying an enhanced bilinear interpolation filter determined based on a bilinear interpolation filter and a sharpening filter. With this particular approach, a more appropriate value of the sub-integer pixel may be determined, which results in a more appropriate prediction value of a current pixel.

[0010] In a case of the intra prediction according to the first aspect being performed by an encoding device (encoder), the processing circuitry may be further configured to determine the prediction direction of the current full-integer pixel on the basis of the current block and a reference block of the current frame.

[0011] The reference block may be within the same image frame neighboring to the current block. In particular, the reference block may have been previously processed in the processing of decoding or encoding, that is, in the scan order of a coding/decoding process. [0012] According to the first aspect interpolation with pixel-wise accuracy while keeping the complexity at a low level may be performed. Due to the enhanced bilinear interpolation filter being determined on basis of a bilinear interpolation filter and a sharpening filter, memory bandwidth may be reduced with respect to using separate filters. Further, memory requirements for storing a set of filter coefficients is reduced. As the enhanced bilinear interpolation filter improves the sample value of the sub-integer pixel in the reference block, the invention allows for increasing subjective quality of edges in reconstructed pictures.

[0013] In a further possible implementation from the first aspect, the sharpening filter is a one dimensional high-pass filter. [0014] The one-dimensional filter may be a linear filter with a predetermined or predefined number of taps. The number of taps may be signaled in a bit stream with certain granularity, for instance per video sequence, frame, part of a frame such as a slide or tile, or a coding block. Alternatively, the number of taps may be fixed, for instance, by a standard.

[0015] Accordingly, no additional signaling and may be necessary and, thus, existing interpolation methods can be seamlessly replaced.

[0016] In a further possible implementation from the first aspect, the sharpening filter is a linear 5 -tap or a 3 -tap filter.

[0017] In a further possible implementation from the first aspect, the enhanced bilinear interpolation filter is determined as a convolution of the bilinear interpolation filter and the sharpening filter.

[0018] By determining the enhanced bilinear interpolation filter as a convolution of a bilinear interpolation filter and a sharpening filter, the enhanced bilinear interpolation filter, when applied, functions as a combination filter with the properties of said filters used in the convolution. Thus, instead of applying the filters in a successive manner, the enhanced interpolation may be achieved in a single processing step. Further, the result of applying the enhanced interpolation filter may differ from the result of successive filter application due to intermediate clipping or rounding processes.

[0019] In a further possible implementation from the first aspect, the sharpening filter is a symmetric filter. [0020] A symmetric filter allows for reduced storage requirements in comparison to an asymmetric filter. Further, a data amount to be signaled may be reduced with respect to an asymmetric filter also.

[0021] In a further possible implementation from the first aspect, one or more filter coefficients of the sharpening filter depend on a fractional offset of the corresponding sub-integer pixel in the reference block with respect to a pixel adjacent to the corresponding sub-integer pixel in the reference block.

[0022] When taking the fractional amount of offset of the sub-integer pixel in the reference block into account, the filter may be adjusted in accordance with said fractional amount. For instance, in a case where the sub-integer pixel is close to a pixel in the reference block (i.e., the fractional offset is small), the enhanced bilinear interpolation filter may be determined based on an sharpening filter with a low sharpening effect.

[0023] In a further possible implementation from the first aspect, a set of enhanced bilinear interpolation filters is constructed for respective predetermined fractional positions of the corresponding sub-integer pixel in the reference block with respect to the adjacent pixel in the reference block.

[0024] By providing a set of enhanced bilinear interpolation filters for specific fractional offsets, an enhanced bilinear interpolation filter does not have to be calculated separately when performing intra prediction. [0025] In a further possible implementation from the first aspect, two or more sets of enhanced bilinear interpolation filters are constructed based on the bilinear interpolation filter and variant different enhancement filters.

[0026] For example, the set of filters, from which a specific filter may be selected to be used in intra prediction, may be selected based on a width, a height or an aspect ratio of the current block. [0027] In a further possible implementation from the first aspect, the adjacent pixels of the corresponding sub-integer pixel in the reference block comprise one or more vertically or horizontally neighboring pixels of the corresponding sub-integer pixel in the reference block.

[0028] For example, in a case of the reference block being located on a left side of the current block, the adjacent pixels of the corresponding sub-integer pixel in the reference block may comprise one or more vertically neighboring pixels, whereas, in a case where the reference block is located on a top side of the current block, the adjacent pixels of the corresponding sub-integer pixel in the reference block may comprise one or more horizontally neighboring pixels.

[0029] According to a second aspect, the invention relates to an encoding apparatus for encoding a current image frame, wherein the encoding apparatus comprises an intra prediction apparatus according to the first aspect.

[0030] In a possible implementation, the encoding apparatus may comprise circuitry for further processing, for instance, as described below with reference to Figs. 1 and 2.

[0031] According to a third aspect, the invention relates to a decoding apparatus for decoding a current reconstructed image frame, wherein the decoding apparatus comprises an intra prediction apparatus according to the first aspect.

[0032] In a possible implementation, the decoding apparatus may comprise circuitry for further processing, for instance, as described below with reference to Figs. 1 and 3.

[0033] According to a fourth aspect, the invention relates to a method for intra prediction of a sample value of a current full-integer pixel of a current block of a current image frame, the intra prediction having a prediction direction, wherein the method comprises: determining for the current full-integer pixel a corresponding sub-integer pixel in a reference block of the current frame on the basis of the prediction direction; determining a sample value of the corresponding sub-integer pixel by applying an enhanced bilinear interpolation filter to sample values of neighboring pixels of the corresponding sub-integer pixel in the reference block, wherein the enhanced bilinear interpolation filter is determined on basis of a bilinear interpolation filter and a sharpening filter; and determining the intra predicted sample value of the current pixel in the current block on basis of the sample value of the corresponding sub-integer pixel in the reference block.

[0034] Thus, an improved intra prediction method is provided allowing improving the efficiency for image or video coding.

[0035] According to a fifth aspect, the invention relates to a method for encoding a current image frame, comprising: encoding an image frame applying an intra prediction method for intra prediction of a sample value of a current full-integer pixel of a current block of the image frame according to the fourth aspect. [0036] In a possible implementation, the encoding method may comprise further processing steps, for instance, as described below with reference to Figs. 1 and 2.

[0037] According to a sixth aspect, the invention relates to a method for decoding a current reconstructed image frame, comprising: decoding an image frame applying an intra prediction method for intra prediction of a sample value of a current full-integer pixel of a current block of the image frame according to the fourth aspect.

[0038] In a possible implementation, the decoding method may comprise further processing steps, for instance, as described below with reference to Figs. 1 and 3.

[0039] According to a seventh aspect, the invention relates to a computer program product comprising program code for performing the method of the fourth aspect when executed on a computer or processor.

[0040] In a further possible implementation, the disclosure relates to a non-transitory computer readable storage medium storing a program that, when executed on a computer or processor, performs all method steps according to the fourth aspect of the invention. BRIEF DESCRIPTION OF DRAWINGS

[0041] In the following embodiments of the invention are described in more detail with reference to the attached figures and drawings, in which:

[0042] FIG. 1 A is a block diagram showing an example of a video coding system configured to implement embodiments of the invention; [0043] FIG. 1B is a block diagram showing another example of a video coding system configured to implement embodiments of the invention;

[0044] FIG. 2 is a block diagram showing an example of a video encoder configured to implement embodiments of the invention;

[0045] FIG. 3 is a block diagram showing an example structure of a video decoder configured to implement embodiments of the invention;

[0046] FIG. 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus; [0047] FIG. 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus;

[0048] FIG. 6 shows exemplary angular intra prediction directions and the associated intra prediction modes; [0049] FIG. 7 is a schematic diagram illustrating the intra prediction having a prediction direction;

[0050] FIG. 8A is an exemplary illustration of a filter characteristic of a high-pass filter;

[0051] FIG. 8B is an exemplary illustration of filter characteristics of various filters;

[0052] FIG. 9 shows the steps of method for intra prediction of a sample value of a current full- integer pixel of a current block of a current image frame.

[0053] In the following identical reference signs refer to identical or at least functionally equivalent features if not explicitly specified otherwise.

DETAILED DESCRIPTION

[0054] 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.

[0055] 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.

[0056] 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).

[0057] In case of lossless video coding, the original video pictures can be reconstructed, i.e. 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, i.e. the quality of the reconstructed video pictures is lower or worse compared to the quality of the original video pictures.

[0058] Several video coding standards 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 (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, i.e. coding, the subsequent blocks.

[0059] In the following embodiments of a video coding system 10, a video encoder 100 and a video decoder 200 are described based on Figs. 1 to 3.

[0060] 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 100 (or short encoder 100) and video decoder 200 (or short decoder 200) 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.

[0061] As shown in FIG. 1A, 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.

[0062] The source device 12 comprises an encoder 100, and may additionally, i.e. 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] The video encoder 100 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). [0067] 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.

[0068] The destination device 14 comprises a decoder 200 (e.g. a video decoder 200), and may additionally, i.e. optionally, comprise a communication interface or communication unit 28, apost- processor 32 (or post-processing unit 32) and a display device 34.

[0069] 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 200.

[0070] 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.

[0071] 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. [0072] 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. [0073] 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. 1A 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.

[0074] The decoder 200 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).

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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. [0079] The encoder 100 (e.g. a video encoder 100) or the decoder 200 (e.g. a video decoder 200) or both encoder 100 and decoder 200 may be implemented via processing 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, video coding dedicated or any combinations thereof. The encoder 100 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to encoder 100 of FIG. 2 and/or any other encoder system or subsystem described herein. The decoder 200 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to decoder 200 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. As shown in fig. 5, 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. Either of video encoder 100 and video decoder 200 may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown in Fig. 1B.

[0080] 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.

[0081] 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.

[0082] 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

[0083] Fig. 2 shows a schematic block diagram of an example video encoder 100 that is configured to implement the techniques of the present application. In the example of Fig. 2, the video encoder 100 comprises an input (or input interface), a residual calculation unit 104, a transform processing unit 105, a quantization unit 108, an inverse quantization unit 110, and inverse transform processing unit 112, a reconstruction unit 114, a loop filter unit 120, a decoded picture buffer (DPB) 130, a mode selection unit 160, an entropy encoding unit 170 and an output (or output interface). The mode selection unit 160 may include an inter prediction unit 144, an intra prediction unit 154 and a partitioning unit (not shown). Inter prediction unit 144 may include a motion estimation unit and a motion compensation unit (not shown). A video encoder 100 as shown in Fig. 2 may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec.

[0084] The residual calculation unit 104, the transform processing unit 105, the quantization unit 108, the mode selection unit 160 may be referred to as forming a forward signal path of the encoder 100, whereas the inverse quantization unit 110, the inverse transform processing unit 112, the reconstruction unit 114, the buffer 116, the loop filter 120, the decoded picture buffer (DPB) 130, the inter prediction unit 144 and the intra-prediction unit 154 may be referred to as forming a backward signal path of the video encoder 100, wherein the backward signal path of the video encoder 100 corresponds to the signal path of the decoder (see video decoder 200 in Fig. 3). The inverse quantization unit 110, the inverse transform processing unit 112, the reconstruction unit 114, the loop filter 120, the decoded picture buffer (DPB) 130, the inter prediction unit 144 and the intra-prediction unit 154 are also referred to forming the“built-in decoder” of video encoder 100. Pictures & Picture Partitioning (Pictures & Blocks)

[0085] The encoder 100 may be configured to receive, e.g. via input, 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).

[0086] 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.

[0087] Embodiments of the video encoder 100 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. 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.

[0088] In further embodiments, the video encoder may be configured to receive directly a block of the picture 17, e.g. one, several or all blocks forming the picture 17. The picture block may also be referred to as current picture block or picture block to be coded.

[0089] Like the picture 17, the picture block 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 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. Accordingly, a block may, for example, an MxN (M-column by N-row) array of samples, or an MxN array of transform coefficients.

[0090] Embodiments of the video encoder 100 as shown in Fig. 2 may be configured to encode the picture 17 block by block, e.g. the encoding and prediction is performed per block.

[0091] Embodiments of the video encoder 100 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. CTUs).

[0092] Embodiments of the video encoder 100 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using 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 tile groups (typically non-overlapping), and each 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

[0093] The residual calculation unit 104 may be configured to calculate a residual block (also referred to as residual) based on the picture block and a prediction block (further details about the prediction block are provided later), e.g. by subtracting sample values of the prediction block from sample values of the picture block, sample by sample (pixel by pixel) to obtain the residual block in the sample domain.

Transform [0094] The transform processing unit 105 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 to obtain transform coefficients in a transform domain. The transform coefficients may also be referred to as transform residual coefficients and represent the residual block in the transform domain. [0095] The transform processing unit 105 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 112 (and the corresponding inverse transform, e.g. by inverse transform processing unit 212 at video decoder 30) and corresponding scaling factors for the forward transform, e.g. by transform processing unit 105, at an encoder 100 may be specified accordingly.

[0096] Embodiments of the video encoder 100 (respectively transform processing unit 105) 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 170, so that, e.g., the video decoder 200 may receive and use the transform parameters for decoding. Quantization

[0097] The quantization unit 108 may be configured to quantize the transform coefficients to obtain quantized coefficients, e.g. by applying scalar quantization or vector quantization. The quantized coefficients may also be referred to as quantized transform coefficients or quantized residual coefficients. [0098] The quantization process may reduce the bit depth associated with some or all of the transform coefficients. 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 110, 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.

[0099] Embodiments of the video encoder 100 (respectively quantization unit 108) may be configured to output quantization parameters (QP), e.g. directly or encoded via the entropy encoding unit 170, so that, e.g., the video decoder 200 may receive and apply the quantization parameters for decoding.

Inverse Quantization

[00100] The inverse quantization unit 110 is configured to apply the inverse quantization of the quantization unit 108 on the quantized coefficients to obtain dequantized coefficients, e.g. by applying the inverse of the quantization scheme applied by the quantization unit 108 based on or using the same quantization step size as the quantization unit 108. The dequantized coefficients may also be referred to as dequantized residual coefficients and correspond - although typically not identical to the transform coefficients due to the loss by quantization - to the transform coefficients.

Inverse Transform [00101] The inverse transform processing unit 112 is configured to apply the inverse transform of the transform applied by the transform processing unit 105, e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block (or corresponding dequantized coefficients) in the sample domain. The reconstructed residual block may also be referred to as transform block. Reconstruction

[00102] The reconstruction unit 114 (e.g. adder or summer 114) is configured to add the transform block (i.e. reconstructed residual block) to the prediction block to obtain a reconstructed block in the sample domain, e.g. by adding - sample by sample - the sample values of the reconstructed residual block and the sample values of the prediction block. Filtering

[00103] The loop filter unit 120 (or short “loop filter” 120), is configured to filter the reconstructed block to obtain a filtered block, 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 120 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 sharpening, a smoothing filters or a collaborative filters, or any combination thereof. Although the loop filter unit 120 is shown in FIG. 2 as being an in loop filter, in other configurations, the loop filter unit 120 may be implemented as a post loop filter. The filtered block may also be referred to as filtered reconstructed block. [00104] Embodiments of the video encoder 100 (respectively loop filter unit 120) may be configured to output loop filter parameters (such as sample adaptive offset information), e.g. directly or encoded via the entropy encoding unit 170, so that, e.g., a decoder 200 may receive and apply the same loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer [00105] The decoded picture buffer (DPB) 130 may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder 100. The DPB 130 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) 130 may be configured to store one or more filtered blocks. The decoded picture buffer 130 may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks, 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) 130 may be also configured to store one or more unfiltered reconstructed blocks, or in general unfiltered reconstructed samples, e.g. if the reconstructed block is not filtered by loop filter unit 120, or any other further processed version of the reconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

[00106] The mode selection unit 160 comprises partitioning unit, inter-prediction unit 144 and intra-prediction unit 154, and is configured to receive or obtain original picture data, e.g. an original block (current block of the current picturel7), 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 130 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 or predictor.

[00107] Mode selection unit 160 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, which is used for the calculation of the residual block and for the reconstruction of the reconstructed block.

[00108] Embodiments of the mode selection unitl260 may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit 160), 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 160 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.

[00109] In other words, the partitioning unit may be configured to partition the block 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.

[00110] In the following the partitioning (e.g. by partitioning unit) and prediction processing (by inter-prediction unit 144 and intra-prediction unit 154) performed by an example video encoder 100 will be explained in more detail.

Partitioning

[00111] The partitioning unit may partition (or split) a current block into smaller partitions, e.g. smaller blocks of square or rectangular size. 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). [00112] 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 VVC, 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).

[00113] 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 colour 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.

[00114] 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.

[00115] In embodiments, e.g., according to the latest video coding standard currently in development, which is referred to as Versatile Video Coding (VVC), a combined Quad-tree and binary tree (QTBT) partitioning is for example 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 may be used together with the QTBT block structure.

[00116] In one example, the mode selection unit 160 of video encoder 100 may be configured to perform any combination of the partitioning techniques described herein. [00117] As described above, the video encoder 100 is configured to determine or select the best or an optimum prediction mode from a set of (e.g. pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

[00118] 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.

[00119] The intra-prediction unit 154 is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an intra-prediction block according to an intra- prediction mode of the set of intra-prediction modes.

[00120] The intra prediction unit 154 (or in general the mode selection unit 160) 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 170 in form of syntax elements for inclusion into the encoded picture data, so that, e.g., the video decoder 200 may receive and use the prediction parameters for decoding. The prediction parameters may indicate, for instance, direction of interpolation to be used for a prediction unit (a block for which the intra prediction is to be performed).

Inter-Prediction

[00121] 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 130) 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. [00122] Additional to the above prediction modes, skip mode and/or direct mode may be applied.

[00123] The inter prediction unit 144 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 (current picture block of the current picturel7) and a decoded picture, 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, for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures, or in other words, the current picture and the previously decoded pictures may be part of or form a sequence of pictures forming a video sequence. [00124] The encoder 100 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). [00125] 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. 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. Upon receiving the motion vector for the PU 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. [00126] The motion compensation unit may also generate syntax elements associated with the blocks and video slices for use by video decoder 200 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 [00127] The entropy encoding unit 170 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 (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients, inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data2l which can be output via the output, e.g. in the form of an encoded bitstream 21, so that, e.g., the video decoder 200 may receive and use the parameters for decoding, . The encoded bitstream 21 may be transmitted to video decoder 200, or stored in a memory for later transmission or retrieval by video decoder 200.

[00128] Other structural variations of the video encoder 100 can be used to encode the video stream. For example, a non-transform based encoder 100 can quantize the residual signal directly without the transform processing unit 105 for certain blocks or frames. In another implementation, an encoder 100 can have the quantization unit 108 and the inverse quantization unit 110 combined into a single unit.

Decoder and Decoding Method

[00129] Fig. 3 shows an exemple of a video decoder 200 that is configured to implement the techniques of this present application. The video decoder 200 is configured to receive encoded picture data 21 (e.g. encoded bitstream 21), e.g. encoded by encoder 100, to obtain a decoded picture. 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/or tile groups or tiles) and associated syntax elements.

[00130] In the example of Fig. 3, the decoder 200 comprises an entropy decoding unit 204, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214 (e.g. a summer 214), a loop filter 220, a decoded picture buffer (DBP) 230, a mode application unit 260, an inter prediction unit 244 and an intra prediction unit 254. Inter prediction unit 244 may be or include a motion compensation unit. Video decoder 200 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 100 from FIG. 2. [00131] As explained with regard to the encoder 100, the inverse quantization unit 110, the inverse transform processing unit 112, the reconstruction unit 114 the loop filter 120, the decoded picture buffer (DPB) 130, the inter prediction unit 244 and the intra prediction unit 254 are also referred to as forming the“built-in decoder” of video encoder 100. Accordingly, the inverse quantization unit 210 may be identical in function to the inverse quantization unit 110, the inverse transform processing unit 212 may be identical in function to the inverse transform processing unit 112, the reconstruction unit 214 may be identical in function to reconstruction unit 114, the loop filter 220 may be identical in function to the loop filter 120, and the decoded picture buffer 230 may be identical in function to the decoded picture buffer 130. Therefore, the explanations provided for the respective units and functions of the video 100 encoder apply correspondingly to the respective units and functions of the video decoder 200.

Entropy Decoding

[00132] The entropy decoding unit 204 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 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 04 maybe configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit 170 of the encoder 100. Entropy decoding unit 204 may be further configured to provide inter prediction parameters, intra prediction parameter and/or other syntax elements to the mode application unit 260 and other parameters to other units of the decoder 200. Video decoder 200 may receive the syntax elements at the video slice level and/or the video block level. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be received and/or used.

Inverse Quantization

[00133] The inverse quantization unit 210 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 204) and to apply based on the quantization parameters an inverse quantization on the decoded quantized coefficients to obtain dequantized coefficients, which may also be referred to as transform coefficients. The inverse quantization process may include use of a quantization parameter determined by video encoder 100 for each video block in the video slice (or tile or tile group) to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse Transform

[00134] Inverse transform processing unit 212 may be configured to receive dequantized coefficients, also referred to as transform coefficients, and to apply a transform to the dequantized coefficients in order to obtain reconstructed residual blocks in the sample domain. The reconstructed residual blocks may also be referred to as transform blocks. 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 212 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 204) to determine the transform to be applied to the dequantized coefficients.

Reconstruction

[00135] The reconstruction unit 214 (e.g. adder or summer 214) may be configured to add the reconstructed residual block, to the prediction block to obtain a reconstructed block in the sample domain, e.g. by adding the sample values of the reconstructed residual block and the sample values of the prediction block.

Filtering

[00136] The loop filter unit 220 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block to obtain a filtered block, e.g. 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 sharpening, a smoothing filters or a collaborative filters, or any combination thereof. Although the loop filter unit 220 is shown in FIG. 3 as being an in loop filter, in other configurations, the loop filter unit 220 may be implemented as a post loop filter.

Decoded Picture Buffer [00137] The decoded video blocks of a picture are then stored in decoded picture buffer 230, which stores the decoded pictures as reference pictures for subsequent motion compensation for other pictures and/or for output respectively display.

[00138] The decoder 200 is configured to output the decoded picture, e.g. via output, for presentation or viewing to a user.

Prediction

[00139] The inter prediction unit 244 may be identical to the inter prediction unit 144 (in particular to the motion compensation unit) and the intra prediction unit 254 may be identical to the inter prediction unit 154 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 204). Mode application unit 260 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.

[00140] When the video slice is coded as an intra coded (I) slice, intra prediction unit 254 of mode application unit 260 is configured to generate prediction block 265 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 244 (e.g. motion compensation unit) of mode application unit 260 is configured to produce prediction blocks for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 204. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 200 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB 230. 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.

[00141] Mode application unit 260 is configured to determine the prediction information for a video block of the current video slice by parsing the motion vectors or related information 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 application unit 260 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.

[00142] Embodiments of the video decoder 200 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).

[00143] Embodiments of the video decoder 200 as shown in Fig. 3 may be configured to partition and/or decode the picture by using 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 tile groups (typically non-overlapping), and each 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.

[00144] Other variations of the video decoder 200 can be used to decode the encoded picture data 21. For example, the decoder 200 can produce the output video stream without the loop filtering unit 220. For example, a non-transform based decoder 200 can inverse-quantize the residual signal directly without the inverse-transform processing unit 212 for certain blocks or frames. In another implementation, the video decoder 200 can have the inverse-quantization unit 210 and the inverse- transform processing unit 212 combined into a single unit.

[00145] It should be understood that, in the encoder 100 and the decoder 200, 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.

[00146] It should be noted that further operations may be applied to the derived motion vectors of current block (including but not limit to control point motion vectors of affine mode, sub-block motion vectors in affine, planar, ATMVP modes, temporal motion vectors, and so on). For example, the value of motion vector is constrained to a predefined range according to its representing bit. If the representing bit of motion vector is bitDepth, then the range is -2^A(bitDepth- 1) ~ 2^A(bitDepth-l)-l, where“^A” means exponentiation. For example, if bitDepth is set equal to 16, the range is -32768 ~ 32767; if bitDepth is set equal to 18, the range is -131072-131071. For example, the value of the derived motion vector (e.g. the MVs of four 4x4 sub-blocks within one 8x8 block) is constrained such that the max difference between integer parts of the four 4x4 sub block MVs is no more than N pixels, such as no more than 1 pixel. Here provides two methods for constraining the motion vector according to the bitDepth.

[00147] Method 1 : remove the overflow MSB (most significant bit) by following operations ux= ^bi®epth (1)

mvx ? (ux - 2^bi®epth ) : ux (2)

uy= ^bl®epth (3)

mvy

? (uy - 2^bl®epth ) : uy (4)

where mvx is a horizontal component of a motion vector of an image block or a sub-block, mvy is a vertical component of a motion vector of an image block or a sub-block, and ux and uy indicates an intermediate value;

For example, if the value of mvx is -32769, after applying formula (1) and (2), the resulting value is 32767. In computer system, decimal numbers are stored as two’s complement. The two’s complement of -32769 is 1,0111,1111,1111,1111 (17 bits), then the MSB is discarded, so the resulting two’s complement is 0111,1111,1111,1111 (decimal number is 32767), which is same as the output by applying formula (1) and (2).

Ux= ( mvpx + mvdx +2^bl®epth ) % 2^bl®epth (5)

mvx = ( ux >= 2^{bi®epth 1} ) ? (ux - 2^bi®epth ) : ux (6)

uy= ( mvpy + mvdy +2^bl®epth ) % 2^bl®epth (7)

mvy = ( uy >= 2^bl®eptM ) ? (uy - 2^bl®epth ) : uy (8)

The operations may be applied during the sum of mvp and mvd, as shown in formula (5) to (8).

[00148] Method 2: remove the overflow MSB by clipping the value

, vx)

, vy)

where vx is a horizontal component of a motion vector of an image block or a sub-block, vy is a vertical component of a motion vector of an image block or a sub-block; x, y and z respectively correspond to three input value of the MV clipping process, and the definition of function Clip3 is as follow: (x ; z < x

Clip3( x, y, z ) = jy ; z > y

\z ; otherwise

[00149] 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 200 ofFIG. 1A or an encoder such as video encoder 100 ofFIG. 1A.

[00150] 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.

[00151] 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.

[00152] 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). [00153] 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. 1 according to an exemplary embodiment.

[00154] 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.

[00155] [00156] 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.

[00157] 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.

[00158]

[00159] 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.

[00160] [00161] Fig. 6 gives an example of directional intra prediction modes. The arrows in the figure indicate selectable intra prediction directions. In particular, in Fig. 6, the horizontal intra prediction mode is denoted as mode 18, and vertical intra prediction mode is denoted as mode 50. Such mode, determined at the encoder for a prediction unit may be signaled to the decoder and used there to perform the prediction in the same manner. The determination at the encoder may be performed based on gradient calculation in the (parts of) the blocks neighbors to the prediction unit or based on prediction direction of the neighboring blocks. At the decoder, the prediction direction may be determined from the signaled indication (e.g. signaled prediction direction which may be one of those exemplarily shown in Figure 6). However, the present invention is not limited thereto, and, in general, the determination of the prediction mode may be also performed at the decoder (implicitly, in the same way as at the encoder). This may be performed by gradient computation for the blocks already processed and neighboring to the prediction unit or by deriving the direction based on the prediction direction of the neighboring blocks, or as a combination of both. The present disclosure is not limited to any particular way of deriving the prediction direction at the encoder and/or the decoder.

[00162] While for horizontal and vertical prediction directions, the selection of samples (pixels) to be used for prediction is straightforward, this task requires more effort in case of angular prediction.

[00163] The prediction may be performed in 1/32 pel accuracy. Depending on the angular direction, the prediction may not fall exactly on a full integer sample location among the possible reference samples. Thus, a weighting between two neighboring sample locations may be performed to arrive at the value of the reference sample, as illustrated in Fig. 7.

[00164] Fig. 7 illustrates samples (pixels) to be predicted P0,0, Pl,0 as well as reference samples Rij of adjacent blocks. A prediction directions for P0,0 is illustrated as an arrow. In this specific example, the reference sample for P0,0 to be predicted is positioned between full-integer pixel reference samples R0,0 and Rl,0, such that interpolation is necessary in order to determine the reference sample value of RD,0. Commonly, a bilinear interpolation filter is used to determine the reference samples.

[00165] In particular, Fig. 7 illustrates the fractional offset of the corresponding sub-pixel sample with respect to adjacent full-pixel samples, which is expressed as fractional amounts f and/or l-f. [00166] According to an embodiment, intra prediction of a sample value of a current full-integer pixel of a current block of a current image frame is performed, wherein the intra prediction has a prediction direction as illustrated, for instance, in Figs. 6 and 7. For the current full-integer pixel, a corresponding sub-integer pixel in a reference block of the current frame is determined on the basis of the prediction direction. That is, based on the prediction direction, a sub-integer position of a reference sample within the reference block is determined. The prediction direction may be determined by the encoder 100 and signaled to the decoder, for instance. Alternatively, the prediction direction may be predetermined or signaled to the decoder in any other way.

[00167] The sub-pixel position of the reference sample and, thus, the fractional offset of the sub integer sample with respect to the neighboring pixels may be determined based on the position of the current full-integer pixel and the prediction direction.

[00168] Further, the sample value of said reference sample at sub-integer pixel position is determined by applying an enhanced bilinear interpolation filter to the sample values of neighboring pixels, which are adjacent to the sub-integer reference sample in the reference block.

[00169] The enhanced bilinear interpolation filter is determined on a basis of a bilinear interpolation filter and a sharpening filter or corresponds to a bilinear interpolation filter and a sharpening filter. For instance, the enhanced bilinear interpolation filter may be a convolution of a bilinear interpolation filter and a sharpening filter like a high-pass filter. The sample value of the sub-integer reference sample is determined by applying said enhanced bilinear interpolation filter to the values of neighboring samples. Subsequently, the intra predicted sample value of the current pixel is determined on basis of the determined sample value of the sub-integer reference sample. This is achieved by an intra prediction procedure described in detail above.

[00170] By utilizing an enhanced bilinear interpolation filter determined on basis of a bilinear interpolation filter and a sharpening filter like a high-pass filter, the determination of the sample value of the sub-integer reference sample is reduced to a single processing step in comparison to application of two separate filters (bilinear filter and sharpening filter) successively. Further, the results of successive application of multiple filters differ from the results of a single combined filter, which has, for instance, been determined as a convolution of a bilinear interpolation filter and an enhancement filter, due to clipping or rounding, which could be applied at any step of processing. [00171] Fig. 8A shows an exemplary filter characteristic of a sharpening filter. In the transfer characteristic of the exemplary sharpening filter, the normalized output above a certain cut-off frequency is larger than the normalized output below said cut-off frequency. In other words, the amplitude of high frequencies are amplified with respect to the low frequencies or, the other way round, low frequency amplitudes are damped with respect to high frequency amplitudes.

[00172] In a case where the reference block is positioned above of the current block, the enhanced bilinear interpolation filter is applied to sample values adjacent to the corresponding sub-integer sample in a horizontal direction. In a case where the reference block is positioned on a left side of the current block, the enhanced bilinear interpolation filter is applied to sample values adjacent to the corresponding sub-integer sample in a vertical direction.

[00173] Fig. 8B shows an exemplary 3-tap filter 810, an exemplary 5-tap filter 820, an exemplary bilinear filter 830, and an exemplary combined bilinear and 5-tap filter 840.

[00174] According to an embodiment, for intra-prediction interpolation, the disclosed filter combines bilinear interpolation with a sharpening filter as an enhancement filter.

[00175] The enhancement filter may be a fractional dependent symmetrical filter and/or a high- pass filter.

[00176] Further, the enhancement filter may be a shelving filter, for instance, a low-shelf filter. A shelving filter has a filter characteristic of reducing or increasing signals above or below a set frequency. In particular, a low shelf increases the amplitude of a frequency above a certain threshold frequency and/or reduces the amplitude of a frequency below said certain threshold frequency. A low shelf is thus a particular example of a sharpening filter.

[00177] The sharpening filter enhances details in the reference samples in the reference block. In particular, in a case where the difference of the sample values of reference pixels is large or a variation of sample values in the reference block is large, applying a sharpening filter in combination with bilinear interpolation filter improves the determined sample value of the sub integer reference sample (pixel), such that, in consequence, the prediction of the value of a current pixel in a current block is improved.

[00178] To generate a prediction sample from reference samples, the combination of two interpolation filters is used namely a bilinear interpolation filter combined with an enhancement filter or vice versa. [00179] In a further possible implementation, a selection of an enhancement filter is made based on block width or block height. For example, if a block’s width is larger than a threshold value, a 4-tap Gaussian filter from Joint Exploration Model (JEM) is used. Otherwise, a 4-tap enhanced bilinear interpolation filter is used.

[00180] Although a 4-tap Gaussian filter and a 4-tap enhanced bilinear interpolation filter is used in this example, the present invention is not limited to this, and other enhancement bilinear interpolation filters may be used, according to an embodiment. Further, the selection of an enhancement filter may be based on a block’s height rather than the block’s width.

[00181] As mentioned above, the current and/or reference block may have different sizes. For instance, said blocks may have sizes of 4x4 pixels, 8x8 pixels or any other sized. A block may be a rectangular square or non-square, that is, comprising different dimensions in the width and height direction.

[00182] Further, multiple threshold values may be set defining a plurality of width or height sections, wherein different enhancement filters may be applied.

[00183] In a further possible implementation, the enhancement filter may be a high-pass filter.

[00184] The filter coefficients of an enhanced bilinear interpolation filter may be derived based on a bilinear transform coupled with a high-pass filter. For example, the enhancement filter may be a 5-tap filter or a 3-tap filer as spatial one-dimensional high pass-filters. For example, the 5- tap filter or the 3-tap filter may be a symmetric filter, e.g., a filter where the first and the fifth filter coefficients (or, in the case of the 3-tap filter, the first and the third filter coefficients) are identical and the second and the fourth filter coefficients are identical. In an implementation form, the first and the fifth filter coefficients are negative, while the other filter coefficients of the 5-tap filter are positive.

[00185] Although a symmetrical 5-tap high-pass filter and a symmetrical 3-tap high-pass filter are given as examples above, the present invention is not limited to said sharpening filters. In particular, the enhancement filter may be a symmetrical sharpening filter including another number of taps. Further, the enhancement filter is not limited to a symmetrical filter, and may be a substantially symmetrical filter or an asymmetric filter.

[00186] The use of a symmetric filter allows for reduction of required memory for storage of filter coefficients and/or reduced data amount to be signaled. [00187] A set of filters may be constructed by convolving a bilinear interpolation filter with a subsequent enhancement filter. For instance, a set of separable 4-tap filters may be constructed by convolving the bilinear interpolation filter and the subsequent high-pass filter, for example, as follows:

[f, l-f]*[c0,cl,c0] = [ (l-f)*(c0), f*(c0)+(l-f)*cl_> f (cl)+(l-f)*c0, f (c0) ], where f is a fractional offset in the horizontal or vertical direction of the reference sample (pixel) with respect to adjacent full-integer reference samples (pixels), and [c0,cl,c0] are coefficients of a 3-tap high-pass filter.

[00188] Alternatively, a set of separable 4-tap filters may be constructed by convolving the bilinear interpolation filter and the subsequent high-pass filter, for example, as follows:

[f, l-f]*[c0,cl,c2,cl,c0] = [ (l-f)*c0 + (l-(f+l/2))*cl, f*c0+(f+l/2)*cl + (l-f)*c2 + (1- (f+l/2))*cl, f*c2+(f+l/2)*cl + (l-f)*c0, f*(c0) ], where f is a fractional offset in the horizontal or vertical direction, and [c0,cl,c2,cl,c0] are coefficients of the 5 -tap high-pass fdter in half-pixel resolution.

[00189] The fractional position in these cases may be discrete with a certain precision to obtain a finite size of a table of enhanced bilinear interpolation filters. The final values of the coefficients of enhanced bilinear interpolation filters may be multiplied by a norm factor and rounded so that the sum of coefficients for each offset equals the norm factor. For example, when a normalization factor equals 64 and a fractional offset precision is 1/32, the set of filter coefficients is shown in Table 1 for a case where a 3-tap high-pass filter is used as the enhancement filter.

[00190] In Table 1, filter coefficients are presented for the fractional offsets in the range [0..1/2] since the second part of table can be obtained by symmetrically mirroring of the corresponding coefficients of the shown part.

Table 1. Enhanced bi-linear interpolation filter coefficients (if 3 -tap high-pass fdter is used)

[00191] For example, when a normalization factor equals 64 and a fractional offset precision is 1/32, the set of filter coefficients is shown in Table 2 for a case where a 5-tap high pass filter case is used as the enhancement filter.

Table 2. Enhanced bi-linear interpolation filter coefficients (if 5-tap high-pass filter is used)

[00192] Although in the Tables 1 and 2 filter coefficients of an enhanced bilinear interpolation filter are given for 3-tap and 5-tap high-pass filters, coefficients for an enhanced bilinear interpolation filter may be determined for another filter used as an enhancement filter.

[00193] Further, although the fractional offset precision is 1/32 in the examples given in the tables above coefficients of enhanced bilinear interpolation filters may be determined for other factual offset position like 1/16, 1/64, 1/128 or any other offset precision.

[00194] Based on the position of the corresponding sub-integer pixel, a specific filter may be selected from among a set of filters as illustrated, for example, in Tables 1 or 2, wherein a filter with a phase closest to the fractional offset of the corresponding sub-integer pixel in the reference block may be selected, for example.

[00195] In an embodiment, the spatial high-pass filter is a 5-tap filter. In an embodiment, the 5- tap filter is a symmetric filter, i.e. a filter where the first and the fifth filter coefficients are identical and the second and the fourth filter coefficients are identical. In an embodiment, the first and the fifth filter coefficients are negative, while the other filter coefficients of the 5 -tap filter are positive. In an embodiment, the spatial high-pass filter can be applied separately in the vertical and the horizontal direction. [00196] In an embodiment, the predefined set of filter support pixels in the current frame comprises five neighboring full-integer pixels and half-integer pixels of the current full-integer pixel and the 5-tap filter has the following filter coefficients (-6, 9, 26, 9, -6) within a given numerical precision, which can be normalized by the factor 1/32. [00197] In a further embodiment, the predefined set of filter support pixels in the current frame comprises five neighboring full-integer pixels and half-integer pixels of the current full-integer pixel and the 5-tap filter has the following filter coefficients (-1, 0, 10, 0, -1) within a given numerical precision, which can be normalized by the factor 1/8.

[00198] As can be taken from the enlarged view in figure7, in an embodiment the sample value of the corresponding sub-integer pixel of the current full-integer pixel in the reference block can be determined by the processing unit as follows. The corresponding sub-integer pixel of the current full-integer pixel has the fractional position (f) in a corresponding cell of the sample grid of the reference block.. On the basis of the fractional position, bilinear interpolation can be expressed using a 2-tap filter having the following horizontal coefficients (f,l-f). On the basis of these weighting factors the sample value of the corresponding sub-integer pixel of the current full- integer pixel in the reference frame can be determined

[00199] The disclosed intra-prediction interpolation filter can be applied to luma and chroma, only to luma, or only to chroma at both the encoder and the decoder sides.

[00200] In another example, the enhancement filter coefficients may be fractional dependent. For example, when the first coefficient of 3-tap filter equal to A then the filter is (A, Norm-2* A, A). Moreover, the value of the first coefficient could be smoothly increased or decreased from a 0 fractional offset to half-pixel fractional offset. For example, A = 0 for zero fractional offset and - 1 for half pixel fractional offset with Norm=8 or A = 0 for zero fractional offset and -18 for half pixel fractional offset with Norm=l28 or A = 11 for zero fractional offset and -12 for half pixel fractional offset with Norm=l28.

[00201] Although a smooth increase or decrease of A of a 3-tap filter is described above, such an increase or decrease may be applied to a 5- tap filter or any other enhancements filter as well.

[00202] Further, the increase or decrease of A is not limited to a smooth increase or decrease, but may be a stepwise increase or decrease. Further, the dependency of the coefficients of the enhancement filter on the fractural offset may be of any other kind, like a polynomial dependency on the fractural offset.

[00203] In general, two or more sets of enhanced bilinear filters can be derived based on the bilinear filter and variant additional filters (3 tap or 5 tap filter, with different frequency response). The filter selection among the two or more sets of enhanced bilinear filters as an interpolation filter in intra prediction may be dependent on intra mode and/or block size and /or block aspect ratio.

[00204] In other words, a certain set of filters may be utilized during intra prediction depending on a determined intra prediction mode. Further, the set of filters to be used may be selected based on the size of the current block, for instance, based on the width or the height of the current block. That is, in a case where the width or height of the current block is below a certain threshold, a first set of filters may be user, whereas, in a case where the width or height of the current block is above said certain threshold, a different set of filters may be applied. Still further, the selection of the set of filters to be used in intra prediction processing may be based on the aspect ratio of the current block in the, for example, if the ratio of width to height is above a certain threshold value, a first set of filters may be used and, if the ratio of width to height is below said certain threshold value, a second set of filters different from the first set of filters may be used.

[00205] The main difference between the disclosed intra interpolation filter and other video coding filters is that the disclosed intra interpolation filter combines a bilinear interpolation filter with an enhancement filter like a high-pass filter. Also disclosed is a combination of a bilinear interpolation filter with asymmetrical enhancement filter where coefficients of the enhancement filter depends on fractional offset.

[00206] This filter can be used in a mode-dependent manner for blocks of some sizes and subject to the content of reference samples used for intra-prediction.

[00207] Fig. 9 shows the steps of method for intra prediction of a sample value of a current full- integer pixel of a current block of a current image frame.

[00208] In step S100, a sub-integer pixel in the reference block corresponding to a current full- integer pixel of the current clock is determined on the basis of the prediction direction of the intra prediction and the reference block.

[00209] Further, in step S200, a sample value of the corresponding sub-integer pixel in the reference block is determined by applying an enhanced bilinear interpolation filter to sample values of neighboring full-integer pixels of the corresponding sub-integer pixel in the reference block, wherein the enhanced bilinear interpolation filter is determined on basis of a bilinear interpolation filter and a sharpening filter, for instance, a high pass filter.

[00210] In step S300, the intra predicted sample value of the current full-integer pixel is determined on basis of the sample value of the corresponding sub-integer pixel in the reference block.

[00211] The following documents are incorporated by reference as if reproduced in their entirety: JVET-Fl00l-v3 Algorithm Description of Joint Exploration Test Model 6 (JEM 6) 7 April 20l7“”.

Mathematical Operators [00212] The mathematical operators used in this application are similar to those used in the C programming language. However, the results of integer division and arithmetic shift operations are defined more precisely, and additional operations are defined, such as exponentiation and real valued division. Numbering and counting conventions generally begin from 0, e.g.,“the first” is equivalent to the 0-th,“the second” is equivalent to the l-th, etc. Arithmetic operators

[00213] The following arithmetic operators are defined as follows:

0+ OAddition

Subtraction (as a two-argument operator) or negation (as a unary prefix operator)

* Multiplication, including matrix multiplication

Exponentiation. Specifies x to the power of y. In other contexts, such notation is used x^y

for superscripting not intended for interpretation as exponentiation.

Integer division with truncation of the result toward zero. For example, 7 / 4 and -7 / -4 are truncated to 1 and -7 / 4 and 7 / -4 are truncated to -1.

Used to denote division in mathematical equations where no truncation or rounding is intended.

x Used to denote division in mathematical equations where no truncation or rounding y is intended.

y

f( i ) The summation of f( i ) with i taking all integer values from x up to and including y. i = x

Modulus. Remainder of x divided by y, defined only for integers x and y with x >= 0 x % y

and y > 0. Logical operators

[00214] The following logical operators are defined as follows:

x && y Boolean logical“and” of x and y

x | | y Boolean logical“or” of x and y

! Boolean logical“not”

x ? y : z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates to the value of z.

Relational operators

[00215] The following relational operators are defined as follows:

> Greater than

>= Greater than or equal to

< Less than

<= Less than or equal to

= = Equal to

!= Not equal to

[00216] When a relational operator is applied to a syntax element or variable that has been assigned the value“na” (not applicable), the value“na” is treated as a distinct value for the syntax element or variable. The value“na” is considered not to be equal to any other value.

Bit-wise operators

[00217] The following bit-wise operators are defined as follows:

& Bit-wise “and”. When operating on integer arguments, operates on a two’s complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

| Bit-wise “or”. When operating on integer arguments, operates on a two’s complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0. ^L Bit-wise“exclusive or”. When operating on integer arguments, operates on a two’s complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

X » y Arithmetic right shift of a two’ s complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x prior to the shift operation.

X « y Arithmetic left shift of a two’s complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the least significant bits (LSBs) as a result of the left shift have a value equal to 0.

Assignment operators

[00218] The following arithmetic operators are defined as follows:

= Assignment operator

+ + Increment, i.e., x+ + is equivalent to x = x + 1; when used in an array index, evaluates to the value of the variable prior to the increment operation.

— Decrement, i.e., x— is equivalent to x = x - 1; when used in an array index, evaluates to the value of the variable prior to the decrement operation.

+= Increment by amount specified, i.e., x += 3 is equivalent to x = x + 3, and x += (-3) is equivalent to x = x + (-3).

-= Decrement by amount specified, i.e., x -= 3 is equivalent to x = x - 3, and x -= (-3) is equivalent to x = x - (-3).

Range notation

[00219] The following notation is used to specify a range of values:

x = y..zx takes on integer values starting from y to z, inclusive, with x, y, and z being integer numbers and z being greater than y.

Mathematical functions

[00220] The following mathematical functions are defined:

x >= 0

Abs(

x < 0 Asin( x ) the trigonometric inverse sine function, operating on an argument x that is in the range of -1.0 to 1.0, inclusive, with an output value in the range of -%÷2 to p÷2, inclusive, in units of radians

Atan( x ) the trigonometric inverse tangent function, operating on an argument x, with an output value in the range of -p÷2 to p÷2, inclusive, in units of radians

Ml) x > 0

Atan ^ + p x < 0 && y >= 0

x < 0 && y < 0

Atan ( ^ )^{— p}

⁺ I x = = 0 && y >= 0

p

otherwise

2

Ceil( x ) the smallest integer greater than or equal to x.

Clip 1_Y( x ) = Clip3( 0, ( 1 « BitDepthy ) -

)

Clip l_c( x ) = Clip3( 0, ( 1 « BitDepthc ) -

)

x ; z < x

Clip3( x, y, z ) = j y ; Z > y

(. z ; otherwise

Cos( x ) the trigonometric cosine function operating on an argument x in units of radians.

Floor( x )the largest integer less than or equal to x.

( c + d ; b— a >= d / 2

GetCurrMsb( a, b, c, d ) = j c— d ; a— b > d / 2

(. c ; otherwise

Ln( x ) the natural logarithm of x (the base-e logarithm, where e is the natural logarithm base constant 2.718 281 828...).

Log2( x )the base-2 logarithm of x.

Logl0( x ) the base- 10 logarithm of x.

r x ; x <= y

^Mm( x, y ) = { _y ; _{x >} ;

r x ; x >= y

Max( x, y ) = { y ; x < y

Roimd( x ) = Sign( x ) * Floor( Abs( x ) + 0.5 )

Sign( 0

Sin( x ) the trigonometric sine function operating on an argument x in units of radians

Sqrt( x ) = Vx Swap( x, y ) = ( y, x )

Tan( x ) the trigonometric tangent function operating on an argument x in units of radians Order of operation precedence

[00221] When an order of precedence in an expression is not indicated explicitly by use of parentheses, the following rules apply:

- Operations of a higher precedence are evaluated before any operation of a lower precedence.

- Operations of the same precedence are evaluated sequentially from left to right.

[00222] The table below specifies the precedence of operations from highest to lowest; a higher position in the table indicates a higher precedence. [00223] For those operators that are also used in the C programming language, the order of precedence used in this Specification is the same as used in the C programming language.

Table: Operation precedence from highest (at top of table) to lowest (at bottom of table)

Text description of logical operations

[00224] In the text, a statement of logical operations as would be described mathematically in the following form:

if( condition 0 )

statement 0

else if( condition 1 ) statement 1 else /* informative remark on remaining condition */

statement n

may be described in the following manner:

... as follows I . . . the following applies:

- If condition 0, statement 0

- Otherwise, if condition 1, statement 1

Otherwise (informative remark on remaining condition), statement n

[00225] Each“If ... Otherwise, if ... Otherwise, ...” statement in the text is introduced with“... as follows” or“... the following applies” immediately followed by“If ...“. The last condition of the“If ... Otherwise, if ... Otherwise, ...” is always an“Otherwise, ...”. Interleaved“If ... Otherwise, if ... Otherwise, ...” statements can be identified by matching“... as follows” or“... the following applies” with the ending“Otherwise,

[00226] In the text, a statement of logical operations as would be described mathematically in the following form:

if( condition 0a && condition Ob )

statement 0

else if( condition la | | condition lb )

statement 1

else

statement n

may be described in the following manner:

... as follows I . . . the following applies:

- If all of the following conditions are true, statement 0:

- condition 0a

- condition Ob

- Otherwise, if one or more of the following conditions are true, statement 1 :

- condition la

- condition lb

- Otherwise, statement n

In the text, a statement of logical operations as would be described mathematically in the following form: if( condition 0 )

statement 0

if( condition 1 )

statement 1

may be described in the following manner: When condition 0, statement 0

When condition 1, statement 1

[00227] 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 100 and decoder 200 (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 144 (encoder) and 244 (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 100 and video decoder 200 may equally be used for still picture processing, e.g. residual calculation 104/204, transform 105, quantization 108, inverse quantization 110/210, (inverse) transform 112/212, partitioning 162/262, intra-prediction 154/254, and/or loop filtering 120, 220, and entropy coding 170 and entropy decoding 204.

[00228] Embodiments, e.g. of the encoder 100 and the decoder 200, and functions described herein, e.g. with reference to the encoder 100 and the decoder 200, 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.

[00229] 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. Also, 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.

[00230] 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. [00231] 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.

Claims

1. An apparatus (154, 254) for intra prediction of a sample value of a current full-integer pixel of a current block of a current image frame, the intra prediction having a prediction direction, wherein the apparatus (154, 254) comprises a processing circuitry configured to: determine a sample value of a corresponding sub-integer pixel in a reference block of the current frame, determined on the basis of the prediction direction for the current full -integer pixel, by applying an enhanced bilinear interpolation filter to sample values of neighboring pixels of the corresponding sub-integer pixel in the reference block, wherein the enhanced bilinear interpolation filter is determined on basis of a bilinear interpolation filter and a sharpening filter; and

determine the intra predicted sample value of the current full-integer pixel on basis of the sample value of the corresponding sub-integer pixel in the reference block.

2. The apparatus (154, 254) according to claim 1, wherein the sharpening filter is a one dimensional high-pass filter.

3. The apparatus (154, 254) according to claim 1 or 2, wherein the sharpening filter is a linear 5 -tap or a 3 -tap filter.

4. The apparatus (154, 254) according to any one of claims 1 to 3, wherein the enhanced bilinear interpolation filter is determined as a convolution of the bilinear interpolation filter and the sharpening filter.

5. The apparatus (154, 254) according to any one of claims 1 to 4, wherein the sharpening filter is a symmetric filter.

6. The apparatus (154, 254) according to any one of claims 1 to 5, wherein one or more filter coefficients of the sharpening filter depend on a fractional offset of the corresponding sub-integer pixel in the reference block with respect to a pixel adjacent to the corresponding sub-integer pixel in the reference block.

7. The apparatus (154, 254) according to claim 6, wherein a set of enhanced bilinear interpolation filter coefficients is constructed for respective predetermined fractional positions of the corresponding sub-integer pixel in the reference block with respect to the adjacent pixel in the reference block.

8. The apparatus (154, 254) according to claim 7, wherein two or more sets of enhanced bilinear interpolation filters are constructed based on the bilinear interpolation filter and variants of different enhancement filters.

9. The apparatus (154, 254) according to any one of claims 1 to 8, wherein the adjacent pixels of the corresponding sub-integer pixel in the reference block comprise one or more vertically or horizontally neighboring full-integer pixels of the corresponding sub-integer pixel in the reference block.

10. An encoding apparatus (100) for encoding a current image frame, wherein the encoding apparatus comprises an intra prediction apparatus (154) according to any one of claims 1 to 9.

11. A decoding apparatus (200) for decoding a current reconstructed image frame, wherein the decoding apparatus comprises an intra prediction apparatus (254) according to any one of claims 1 to 9.

12. A method for intra prediction of a sample value of a current full-integer pixel of a current block of a current image frame, the intra prediction having a prediction direction, wherein the method comprises:

13. determining (S200) a sample value of a corresponding sub-integer pixel in a reference block of the current frame, determined o the basis of the prediction direction for the current full- integer pixel, by applying an enhanced bilinear interpolation filter to sample values of neighboring pixels of the corresponding sub-integer pixel in the reference block, wherein the enhanced bilinear interpolation filter is determined on basis of a bilinear interpolation filter and a sharpening filter; and

14. determining (S300) the intra predicted sample value of the current pixel in the current block on basis of the sample value of the corresponding sub-integer pixel in the reference block.

15. A method for encoding a current image frame, comprising: encoding an image frame applying an intra prediction method for intra prediction of a sample value of a current full-integer pixel of a current block of the image frame according to claim 12.

16. A method for decoding a current reconstructed image frame, comprising: decoding an image frame applying an intra prediction method for intra prediction of a sample value of a current full-integer pixel of a current block of the image frame according to claim 12.

17. A computer program product comprising program code for performing the method of any one of claims 12 to 14 when executed on a computer or processor.