WO2025148982A1

WO2025148982A1 - Method, apparatus, and medium for video processing

Info

Publication number: WO2025148982A1
Application number: PCT/CN2025/071535
Authority: WO
Inventors: Wenbin YIN; Kai Zhang; Yang Wang; Lei Zhao; Zhipin DENG; Na Zhang; Li Zhang
Original assignee: Douyin Vision Co Ltd; ByteDance Inc
Current assignee: Douyin Vision Co Ltd; ByteDance Inc
Priority date: 2024-01-09
Filing date: 2025-01-09
Publication date: 2025-07-17
Anticipated expiration: 2026-07-09

Abstract

Embodiments of the present disclosure provide a solution for video processing. In a method for video processing, for a conversion between a current video unit of a video and a bitstream of the video, a plurality of samples of the current video unit are determined. At least a partial of the plurality of samples is determined based on at least one inter prediction. A filtering process is applied to the plurality of samples to obtain a plurality of refined samples. The conversion is performed based on the plurality of refined samples.

Description

METHOD, APPARATUS, AND MEDIUM FOR VIDEO PROCESSING

FIELDS

Embodiments of the present disclosure relates generally to video processing techniques, and more particularly, to a filtering process on inter prediction samples.

BACKGROUND

In nowadays, digital video capabilities are being applied in various aspects of peoples’ lives. Multiple types of video compression technologies, such as MPEG-2, MPEG-4, ITU-TH. 263, ITU-TH.264/MPEG-4 Part 10 Advanced Video Coding (AVC) , ITU-TH. 265 high efficiency video coding (HEVC) standard, versatile video coding (VVC) standard, have been proposed for video encoding/decoding. However, coding efficiency of video coding techniques is generally expected to be further improved.

SUMMARY

Embodiments of the present disclosure provide a solution for video processing.

In a first aspect, a method for video processing is proposed. The method comprises: determining, for a conversion between a current video unit of a video and a bitstream of the video, a plurality of samples of the current video unit, at least a partial of the plurality of samples being determined based on at least one inter prediction; applying a filtering process to the plurality of samples to obtain a plurality of refined samples; and performing the conversion based on the plurality of refined samples. The method in accordance with the first aspect of the present disclosure applies the filtering process to inter prediction samples, and thus the coding performance can be improved.

In a second aspect, an apparatus for video processing is proposed. The apparatus comprises a processor and a non-transitory memory with instructions thereon. The instructions upon execution by the processor, cause the processor to perform a method in accordance with the first aspect of the present disclosure.

In a third aspect, a non-transitory computer-readable storage medium is proposed. The non-transitory computer-readable storage medium stores instructions that cause a processor to perform a method in accordance with the first aspect of the present disclosure.

In a fourth aspect, another non-transitory computer-readable recording medium is proposed. The non-transitory computer-readable recording medium stores a bitstream of a video which is generated by a method performed by an apparatus for video processing. The method comprises: determining a plurality of samples of a current video unit of the video, at least a partial of the plurality of samples being determined based on at least one inter prediction; applying a filtering process to the plurality of samples to obtain a plurality of refined samples; and generating the bitstream based on based on the plurality of refined samples.

In a fifth aspect, a method for storing a bitstream of a video is proposed. The method comprises: determining a plurality of samples of a current video unit of the video, at least a partial of the plurality of samples being determined based on at least one inter prediction; applying a filtering process to the plurality of samples to obtain a plurality of refined samples; generating the bitstream based on based on the plurality of refined samples; and storing the bitstream in a non-transitory computer-readable recording medium.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the following detailed description with reference to the accompanying drawings, the above and other objectives, features, and advantages of example embodiments of the present disclosure will become more apparent. In the example embodiments of the present disclosure, the same reference numerals usually refer to the same components.

Fig. 1 illustrates a block diagram that illustrates an example video coding system, in accordance with some embodiments of the present disclosure;

Fig. 2 illustrates a block diagram that illustrates a first example video encoder, in accordance with some embodiments of the present disclosure;

Fig. 3 illustrates a block diagram that illustrates an example video decoder, in accordance with some embodiments of the present disclosure;

Fig. 4 illustrates nominal vertical and horizontal locations of 4: 2: 2 luma and chroma samples in a picture;

Fig. 5 illustrates an example of encoder block diagram;

Fig. 6 illustrates a picture with 18 by 12 luma CTUs that is partitioned into 12 tiles and 3 raster-scan slices;

Fig. 7 illustrates a picture with 18 by 12 luma CTUs that is partitioned into 24 tiles and 9 rectangular slices;

Fig. 8 illustrates a picture is partitioned int o4 tiles, 11 bricks, and 4 rectangular slices;

Fig. 9A-Fig. 9C illustrate examples of CTBs crossing picture borders, respectively;

Fig. 10 illustrates 67 intra prediction modes;

Fig. 11 illustrates an illustration of picture samples and horizontal and vertical block boundaries on the 8×8 grid, and the nonoverlapping blocks of the 8×8 samples, which can be deblocked in parallel;

Fig. 12 illustrates pixels involved in filter on/off decision and strong/weak filter switch;

Fig. 13A-Fig. 13C illustrate filter shapes for ALF, respectively;

Fig. 14A-Fig. 14C illustrate relative coordinator for the 5×5 diamond filter support, respectively;

Fig. 15 illustrates examples of relative coordinates for the 5×5 diamond filter support;

Fig. 16 illustrates a flowchart of a method for video processing in accordance with embodiments of the present disclosure; and

Fig. 17 illustrates a block diagram of a computing device in which various embodiments of the present disclosure can be implemented.

Throughout the drawings, the same or similar reference numerals usually refer to the same or similar elements.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an example embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.
Example Environment

Fig. 1 is a block diagram that illustrates an example video coding system 100 that may utilize the techniques of this disclosure. As shown, the video coding system 100 may include a source device 110 and a destination device 120. The source device 110 can be also referred to as a video encoding device, and the destination device 120 can be also referred to as a video decoding device. In operation, the source device 110 can be configured to generate encoded video data and the destination device 120 can be configured to decode the encoded video data generated by the source device 110. The source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.

The video source 112 may include a source such as a video capture device. Examples of the video capture device include, but are not limited to, an interface to receive video data from a video content provider, a computer graphics system for generating video data, and/or a combination thereof.

The video data may comprise one or more pictures. The video encoder 114 encodes the video data from the video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. The I/O interface 116 may include a modulator/demodulator and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via the I/O interface 116 through the network 130A. The encoded video data may also be stored onto a storage medium/server 130B for access by destination device 120.

The destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122. The I/O interface 126 may include a receiver and/or a modem. The I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130B. The video decoder 124 may decode the encoded video data. The display device 122 may display the decoded video data to a user. The display device 122 may be integrated with the destination device 120, or may be external to the destination device 120 which is configured to interface with an external display device.

The video encoder 114 and the video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVC) standard and other current and/or further standards.

Fig. 2 is a block diagram illustrating an example of a video encoder 200, which may be an example of the video encoder 114 in the system 100 illustrated in Fig. 1, in accordance with some embodiments of the present disclosure.

The video encoder 200 may be configured to implement any or all of the techniques of this disclosure. In the example of Fig. 2, the video encoder 200 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video encoder 200. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

In some embodiments, the video encoder 200 may include a partition unit 201, a prediction unit 202 which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205 and an intra-prediction unit 206, a residual generation unit 207, a transform unit 208, a quantization unit 209, an inverse quantization unit 210, an inverse transform unit 211, a reconstruction unit 212, a buffer 213, and an entropy encoding unit 214.

In other examples, the video encoder 200 may include more, fewer, or different functional components. In an example, the prediction unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform prediction in an IBC mode in which at least one reference picture is a picture where the current video block is located.

Furthermore, although some components, such as the motion estimation unit 204 and the motion compensation unit 205, may be integrated, but are represented in the example of Fig. 2 separately for purposes of explanation.

The partition unit 201 may partition a picture into one or more video blocks. The video encoder 200 and the video decoder 300 may support various video block sizes.

The mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra-coded or inter-coded block to a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some examples, the mode select unit 203 may select a combination of intra and inter prediction (CIIP) mode in which the prediction is based on an inter prediction signal and an intra prediction signal. The mode select unit 203 may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter-prediction.

To perform inter prediction on a current video block, the motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. The motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from the buffer 213 other than the picture associated with the current video block.

The motion estimation unit 204 and the motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I-slice, a P-slice, or a B-slice. As used herein, an “I-slice” may refer to a portion of a picture composed of macroblocks, all of which are based upon macroblocks within the same picture. Further, as used herein, in some aspects, “P-slices” and “B-slices” may refer to portions of a picture composed of macroblocks that are not dependent on macroblocks in the same picture.

In some examples, the motion estimation unit 204 may perform uni-directional prediction for the current video block, and the motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. The motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. The motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. The motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video block indicated by the motion information of the current video block.

Alternatively, in other examples, the motion estimation unit 204 may perform bi-directional prediction for the current video block. The motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. The motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. The motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. The motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.

In some examples, the motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder. Alternatively, in some embodiments, the motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, the motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

In one example, the motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as the another video block.

In another example, the motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD) . The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signaling techniques that may be implemented by video encoder 200 include advanced motion vector prediction (AMVP) and merge mode signaling.

The intra prediction unit 206 may perform intra prediction on the current video block. When the intra prediction unit 206 performs intra prediction on the current video block, the intra prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements.

The residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block (s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.

In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and the residual generation unit 207 may not perform the subtracting operation.

The transform processing unit 208 may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.

After the transform processing unit 208 generates a transform coefficient video block associated with the current video block, the quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

The inverse quantization unit 210 and the inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. The reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the prediction unit 202 to produce a reconstructed video block associated with the current video block for storage in the buffer 213.

After the reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed to reduce video blocking artifacts in the video block.

The entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When the entropy encoding unit 214 receives the data, the entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.

Fig. 3 is a block diagram illustrating an example of a video decoder 300, which may be an example of the video decoder 124 in the system 100 illustrated in Fig. 1, in accordance with some embodiments of the present disclosure.

The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of Fig. 3, the video decoder 300 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video decoder 300. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

In the example of Fig. 3, the video decoder 300 includes an entropy decoding unit 301, a motion compensation unit 302, an intra prediction unit 303, an inverse quantization unit 304, an inverse transformation unit 305, and a reconstruction unit 306 and a buffer 307. The video decoder 300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200.

The entropy decoding unit 301 may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data) . The entropy decoding unit 301 may decode the entropy coded video data, and from the entropy decoded video data, the motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. The motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode. AMVP is used, including derivation of several most probable candidates based on data from adjacent PBs and the reference picture. Motion information typically includes the horizontal and vertical motion vector displacement values, one or two reference picture indices, and, in the case of prediction regions in B slices, an identification of which reference picture list is associated with each index. As used herein, in some aspects, a “merge mode” may refer to deriving the motion information from spatially or temporally neighboring blocks.

The motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements.

The motion compensation unit 302 may use the interpolation filters as used by the video encoder 200 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. The motion compensation unit 302 may determine the interpolation filters used by the video encoder 200 according to the received syntax information and use the interpolation filters to produce predictive blocks.

The motion compensation unit 302 may use at least part of the syntax information to determine sizes of blocks used to encode frame (s) and/or slice (s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence. As used herein, in some aspects, a “slice” may refer to a data structure that can be decoded independently from other slices of the same picture, in terms of entropy coding, signal prediction, and residual signal reconstruction. A slice can either be an entire picture or a region of a picture.

The intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. The inverse quantization unit 304 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. The inverse transform unit 305 applies an inverse transform.

The reconstruction unit 306 may obtain the decoded blocks, e.g., by summing the residual blocks with the corresponding prediction blocks generated by the motion compensation unit 302 or intra-prediction unit 303. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in the buffer 307, which provides reference blocks for subsequent motion compensation/intra prediction and also produces decoded video for presentation on a display device.

Some exemplary embodiments of the present disclosure will be described in detailed hereinafter. It should be understood that section headings are used in the present document to facilitate ease of understanding and do not limit the embodiments disclosed in a section to only that section. Furthermore, while certain embodiments are described with reference to Versatile Video Coding or other specific video codecs, the disclosed techniques are applicable to other video coding technologies also. Furthermore, while some embodiments describe video coding steps in detail, it will be understood that corresponding steps decoding that undo the coding will be implemented by a decoder. Furthermore, the term video processing encompasses video coding or compression, video decoding or decompression and video transcoding in which video pixels are represented from one compressed format into another compressed format or at a different compressed bitrate.
1. Brief Summary

This disclosure is related to video coding technologies. Specifically, it is related to in-loop filter and other coding tools in image/video coding. The ideas may be applied individually or in various combination, to any existing video coding standard or non-standard video codec like High Efficiency Video Coding (HEVC) and Versatile Video Coding (VVC) . The proposed ideas may be also applicable to future video coding standards or video codec.
2. Abbreviations
AVC Advanced Video Coding
CPB Coded Picture Buffer
CRA Clean Random Access
CTU Coding Tree Unit
CVS Coded Video Sequence
DPB Decoded Picture Buffer
DPS Decoding Parameter Set
GCI General Constraints Information
HEVC High Efficiency Video Coding
JEM Joint Exploration Model
MCTS Motion-Constrained Tile Sets
NAL Network Abstraction Layer
OLS Output Layer Set
PH Picture Header
PPS Picture Parameter Set
PTL Profile, Tier and Level
PU Picture Unit
RRP Reference Picture Resampling
RBSP Raw Byte Sequence Payload
SEI Supplemental Enhancement Information
SH Slice Header
SPS Sequence Parameter Set
VCL Video Coding Layer
VPS Video Parameter Set
VTM VVC Test Model
VUI Video Usability Information
VVC Versatile Video Coding
TU Transform Unit
CU Coding Unit
DF Deblocking Filter
SAO Sample Adaptive Offset
ALF Adaptive Loop Filter
CBF Coding Block Flag
QP Quantization Parameter
RDO Rate Distortion Optimization
BF Bilateral Filter
GDR Gradual Decoding Refresh.
3. Introduction

Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards. The ITU-T produced H. 261 and H. 263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H. 262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H. 265/HEVC standards. Since H. 262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. To explore the future video coding technologies beyond HEVC, the Joint Video Exploration Team (JVET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM) . The JVET meeting is concurrently held once every quarter, and the new coding standard is targeting at 50%bitrate reduction as compared to HEVC. The new video coding standard was officially named as Versatile Video Coding (VVC) in the April 2018 JVET meeting, and the first version of VVC test model (VTM) was released at that time. As there are continuous effort contributing to VVC standardization, new coding techniques are being adopted to the VVC standard in every JVET meeting. The VVC working draft and test model VTM are then updated after every meeting.

The latest version of VVC draft, i.e., Versatile Video Coding (Draft 10) may be found at: https: //jvet-experts. org/doc_end_user/documents/19_Teleconference/wg11/JVET-S2001-v17. zip.

The latest reference software of VVC, named as VTM, could be found at: https: //vcgit. hhi. fraunhofer. de/jvet-u-ee2/VVCSoftware_VTM/-/tree/VTM-11.2.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are studying the potential need for standardization of future video coding technology with a compression capability that significantly exceeds that of the current VVC standard. Such future standardization action could either take the form of extended extension (s) of VVC or an entirely new standard. The groups are working together on this exploration activity in a joint-collaboration effort known as the Joint Video Exploration Team (JVET) to evaluate compression technology designs proposed by their experts in this area. The first Exploration Experiments (EE) were established in JVET meeting during 6–15 January 2021 and the reference software named as Enhanced Compression Model (ECM) . The test model ECM is updated after every JVET meeting.
3.1. Color space and chroma subsampling

Color space, also known as the color model (or color system) , is an abstract mathematical model which simply describes the range of colors as tuples of numbers, typically as 3 or 4 values or color components (e.g. RGB) . Basically speaking, color space is an elaboration of the coordinate system and sub-space.

For video compression, the most frequently used color spaces are YCbCr and RGB.

YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y'CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-difference and red-difference chroma components. Y′ (with prime) is distinguished from Y, which is luminance, meaning that light intensity is nonlinearly encoded based on gamma corrected RGB primaries.

Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.
· 4: 4: 4

Each of the three Y'CbCr components have the same sample rate, thus there is no chroma subsampling. This scheme is sometimes used in high-end film scanners and cinematic postproduction.
· 4: 2: 2

The two chroma components are sampled at half the sample rate of luma: the horizontal chroma resolution is halved while the vertical chroma resolution is unchanged. This reduces the bandwidth of an uncompressed video signal by one-third with little to no visual difference. An example of nominal vertical and horizontal locations of 4: 2: 2 color format is depicted in Fig. 4 in VVC working draft. Fig. 4 illustrates nominal vertical and horizontal locations of 4: 2: 2 luma and chroma samples in a picture.
· 4: 2: 0

In 4: 2: 0, the horizontal sampling is doubled compared to 4: 1: 1, but as the Cb and Cr channels are only sampled on each alternate line in this scheme, the vertical resolution is halved. The data rate is thus the same. Cb and Cr are each subsampled at a factor of 2 both horizontally and vertically. There are three variants of 4: 2: 0 schemes, having different horizontal and vertical siting.
· In MPEG-2, Cb and Cr are cosited horizontally. Cb and Cr are sited between pixels in the vertical direction
(sited interstitially) .
· In JPEG/JFIF, H. 261, and MPEG-1, Cb and Cr are sited interstitially, halfway between alternate luma sam-
ples.
· In 4: 2: 0 DV, Cb and Cr are co-sited in the horizontal direction. In the vertical direction, they are co-sited
on alternating lines.
Table. 3-1 SubWidthC and SubHeightC values derived from chroma_format_idc and
separate_colour_plane_flag

3.2. Coding Flow of a Typical Video Codec

Fig. 5 shows an example of encoder block diagram of VVC, which contains three in-loop filtering blocks: deblocking filter (DF) , sample adaptive offset (SAO) and ALF. Unlike DF, which uses predefined filters, SAO and ALF utilize the original samples of the current picture to reduce the mean square errors between the original samples and the reconstructed samples by adding an offset and by applying a finite impulse response (FIR) filter, respectively, with coded side information signalling the offsets and filter coefficients. ALF is located at the last processing stage of each picture and can be regarded as a tool trying to catch and fix artifacts created by the previous stages.
3.3. Definitions of Video/Coding Units

A picture is divided into one or more tile rows and one or more tile columns. A tile is a sequence of CTUs that covers a rectangular region of a picture.

A tile is divided into one or more bricks, each of which consisting of a number of CTU rows within the tile.

A tile that is not partitioned into multiple bricks is also referred to as a brick. However, a brick that is a true subset of a tile is not referred to as a tile.

A slice either contains several tiles of a picture or several bricks of a tile.

Two modes of slices are supported, namely the raster-scan slice mode and the rectangular slice mode. In the raster-scan slice mode, a slice contains a sequence of tiles in a tile raster scan of a picture. In the rectangular slice mode, a slice contains a number of bricks of a picture that collectively form a rectangular region of the picture. The bricks within a rectangular slice are in the order of brick raster scan of the slice.

Fig. 6 shows an example of raster-scan slice partitioning of a picture, where the picture is divided into 12 tiles and 3 raster-scan slices. Fig. 6 shows a picture with 18 by 12 luma CTUs that is partitioned into 12 tiles and 3 raster-scan slices.

Fig. 7 in the VVC specification shows an example of rectangular slice partitioning of a picture, where the picture is divided into 24 tiles (6 tile columns and 4 tile rows) and 9 rectangular slices. Fig. 7 shows a picture with 18 by 12 luma CTUs that is partitioned into 24 tiles and 9 rectangular slices.

Fig. 8 in the VVC specification shows an example of a picture partitioned into tiles, bricks, and rectangular slices, where the picture is divided into 4 tiles (2 tile columns and 2 tile rows) , 11 bricks (the top-left tile contains 1 brick, the top-right tile contains 5 bricks, the bottom-left tile contains 2 bricks, and the bottom-right tile contain 3 bricks) , and 4 rectangular slices.

Fig. 8 shows a picture is partitioned int o4 tiles, 11 bricks, and 4 rectangular slices.
· CTU/CTB Sizes

In VVC, the CTU size, signaled in SPS by the syntax element log2_ctu_size_minus2, could be as small as 4x4.
Sequence parameter set RBSP syntax

log2_ctu_size_minus2 plus 2 specifies the luma coding tree block size of each CTU.

log2_min_luma_coding_block_size_minus2 plus 2 specifies the minimum luma coding block size.

The variables CtbLog2SizeY, CtbSizeY, MinCbLog2SizeY, MinCbSizeY, MinTbLog2SizeY, MaxTbLog2SizeY, MinTbSizeY, MaxTbSizeY, PicWidthInCtbsY, PicHeightInCtbsY, PicSizeInCtbsY, PicWidthInMinCbsY, PicHeightInMinCbsY, PicSizeInMinCbsY, PicSizeInSamplesY, PicWidthInSamplesC and PicHeightInSamplesC are derived as follows:
CtbLog2SizeY = log2_ctu_size_minus2 + 2                          (7-9)
CtbSizeY = 1 << CtbLog2SizeY                                     (7-10)
MinCbLog2SizeY = log2_min_luma_coding_block_size_minus2 + 2      (7-11)
MinCbSizeY = 1 << MinCbLog2SizeY                                 (7-12)
MinTbLog2SizeY = 2                                               (7-13)
MaxTbLog2SizeY = 6                                               (7-14)
MinTbSizeY = 1 << MinTbLog2SizeY                                 (7-15)
MaxTbSizeY = 1 << MaxTbLog2SizeY                                 (7-16)
PicWidthInCtbsY = Ceil (pic_width_in_luma_samples ÷ CtbSizeY)   (7-17)
PicHeightInCtbsY = Ceil (pic_height_in_luma_samples ÷ CtbSizeY)  (7-18)
PicSizeInCtbsY = PicWidthInCtbsY *PicHeightInCtbsY                (7-19)
PicWidthInMinCbsY = pic_width_in_luma_samples /MinCbSizeY        (7-20)
PicHeightInMinCbsY = pic_height_in_luma_samples /MinCbSizeY       (7-21)
PicSizeInMinCbsY = PicWidthInMinCbsY *PicHeightInMinCbsY                    (7-22)
PicSizeInSamplesY = pic_width_in_luma_samples *pic_height_in_luma_samples   (7-23)
PicWidthInSamplesC = pic_width_in_luma_samples /SubWidthC                   (7-24)
PicHeightInSamplesC = pic_height_in_luma_samples /SubHeightC                (7-25) .
· CTUs in One Picture

Fig. 9A-Fig. 9C illustrate examples of CTBs crossing picture borders, respectively. Fig. 9A illustrates CTSs crossing the bottom picture border. Fig. 9B illustrates CTSs crossing the right picture border. Fig. 9C illustrates CTBs crossing the right bottom picture border.

Suppose the CTB/LCU size indicated by M x N (typically M is equal to N, as defined in HEVC/VVC) , and for a CTB located at picture (or tile or slice or other kinds of types, picture border is taken as an example) border, K x L samples are within picture border wherein either K<M or L<N. For those CTBs as depicted in Fig. 9A to Fig. 9C, the CTB size is still equal to MxN, however, the bottom boundary/right boundary of the CTB is outside the picture.
3.4. Intra Prediction

To capture the arbitrary edge directions presented in natural video, the number of directional intra modes is extended from 33, as used in HEVC, to 65. The extended directional modes are depicted as dotted arrows , and the planar and DC modes remain the same. These denser directional intra prediction modes apply for all block sizes and for both luma and chroma intra predictions.

Conventional angular intra prediction directions are defined from 45 degrees to -135 degrees in clockwise direction as shown in Fig. 10. Fig. 10 shows 67 intra prediction modes. In VTM, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for the non-square blocks. The replaced modes are signalled using the original method and remapped to the indexes of wide angular modes after parsing. The total number of intra prediction modes is unchanged, i.e., 67, and the intra mode coding is unchanged.

In the HEVC, every intra-coded block has a square shape and the length of each of its side is a power of 2. Thus, no division operations are required to generate an intra-predictor using DC mode. In VVC, blocks can have a rectangular shape that necessitates the use of a division operation per block in the general case. To avoid division operations for DC prediction, only the longer side is used to compute the average for non-square blocks.
3.5. Inter Prediction

For each inter-predicted CU, motion parameters consisting of motion vectors, reference picture indices and reference picture list usage index, and extended information needed for the new coding feature of VVC to be used for inter-predicted sample generation. The motion parameter can be signalled in an explicit or implicit manner. When a CU is coded with skip mode, the CU is associated with one PU and has no significant residual coefficients, no coded motion vector delta or reference picture index. A merge mode is specified whereby the motion parameters for the current CU are obtained from neighbouring CUs, including spatial and temporal candidates, and extended schedules introduced in VVC. The merge mode can be applied to any inter-predicted CU, not only for skip mode. The alternative to merge mode is the explicit transmission of motion parameters, where motion vector, corresponding reference picture index for each reference picture list and reference picture list usage flag and other needed information are signalled explicitly per each CU.
3.6. Deblocking Filter

Deblocking filtering typical in-loop filter in video codec. In VVC, the deblocking filtering process is applied on CU boundaries, transform subblock boundaries and prediction subblock boundaries. The prediction subblock boundaries include the prediction unit boundaries introduced by the SbTMVP (Subblock based Temporal Motion Vector prediction) and affine modes, and the transform subblock boundaries include the transform unit boundaries introduced by SBT (Subblock transform) and ISP (Intra Sub-Partitions) modes and transforms due to implicit split of large CUs. As done in HEVC, the processing order of the deblocking filter is defined as horizontal filtering for vertical edges for the entire picture first, followed by vertical filtering for horizontal edges. This specific order enables either multiple horizontal filtering or vertical filtering processes to be applied in parallel threads or can still be implemented on a CTB-by-CTB basis with only a small processing latency.

The vertical edges in a picture are filtered first. Then the horizontal edges in a picture are filtered with samples modified by the vertical edge filtering process as input. The vertical and horizontal edges in the CTBs of each CTU are processed separately on a coding unit basis. The vertical edges of the coding blocks in a coding unit are filtered starting with the edge on the left-hand side of the coding blocks proceeding through the edges towards the right-hand side of the coding blocks in their geometrical order. The horizontal edges of the coding blocks in a coding unit are filtered starting with the edge on the top of the coding blocks proceeding through the edges towards the bottom of the coding blocks in their geometrical order.

Fig. 11 illustrates an illustration of picture samples and horizontal and vertical block boundaries on the 8×8 grid, and the nonoverlapping blocks of the 8×8 samples, which can be deblocked in parallel.
· Boundary Decision

Filtering is applied to 8x8 block boundaries. In addition, it must be a transform block boundary or a coding subblock boundary (e.g., due to usage of Affine motion prediction, ATMVP) . For those which are not such boundaries, filter is disabled.
· Boundary Strength Calculation

For a transform block boundary/coding subblock boundary, if it is located in the 8x8 grid, it may be filterd and the setting of bS [xDi] [yDj] (wherein [xDi] [yDj] denotes the coordinate) for this edge is defined as below.
Table. 3-2 Boundary strength (when SPS IBC is disabled)

Table. 3-3 Boundary strength (when SPS IBC is enabled)

· Deblocking Decision for Luma Component

Wider-stronger luma filter is filters are used only if all the Condition1, Condition2 and Condition 3 are TRUE.

Fig. 12 illustrates pixels involved in filter on/off decision and strong/weak filter switch.

The condition 1 is the “large block condition” . This condition detects whether the samples at P-side and Q-side belong to large blocks, which are represented by the variable bSidePisLargeBlk and bSideQisLargeBlk respectively. The bSidePisLargeBlk and bSideQisLargeBlk are defined as follows.
bSidePisLargeBlk = ( (edge type is vertical and p₀ belongs to CU with width >= 32) | | (edge type is horizontal
and p₀ belongs to CU with height >= 32) ) ? TRUE: FALSE
bSideQisLargeBlk = ( (edge type is vertical and q₀ belongs to CU with width >= 32) | | (edge type is
horizontal and q₀ belongs to CU with height >= 32) ) ? TRUE: FALSE.

Based on bSidePisLargeBlk and bSideQisLargeBlk, the condition 1 is defined as follows.
Condition1 = (bSidePisLargeBlk || bSidePisLargeBlk) ? TRUE: FALSE
Next, if Condition 1 is true, the condition 2 will be further checked. First, the following variables are derived:
– dp0, dp3, dq0, dq3 are first derived as in HEVC
– if (p side is greater than or equal to 32)
dp0 = (dp0 + Abs (p5₀ -2 *p4₀ + p3₀) + 1) >> 1
dp3 = (dp3 + Abs (p5₃ -2 *p4₃ + p3₃) + 1) >> 1
– if (q side is greater than or equal to 32)
dq0 = (dq0 + Abs (q5₀ -2 *q4₀ + q3₀) + 1) >> 1
dq3 = (dq3 + Abs (q5₃ -2 *q4₃ + q3₃) + 1) >> 1
Condition2 = (d < β) ? TRUE: FALSE
where d= dp0 + dq0 + dp3 + dq3.
If Condition1 and Condition2 are valid, whether any of the blocks uses sub-blocks is further checked:

Finally, if both the Condition 1 and Condition 2 are valid, the proposed deblocking method will check the
condition 3 (the large block strong filter condition) , which is defined as follows.
In the Condition3 StrongFilterCondition, the following variables are derived:

As in HEVC, StrongFilterCondition = (dpq is less than (β >> 2) , sp₃ + sq₃ is less than (3*β >> 5) , and
Abs(p₀ -q₀) is less than (5 *t_C + 1) >> 1) ? TRUE : FALSE.
· Stronger Deblocking Filter for Luma

Bilinear filter is used when samples at either one side of a boundary belong to a large block. A sample belonging to a large block is defined as when the width >= 32 for a vertical edge, and when height >= 32 for a horizontal edge.

The bilinear filter is listed below.

Block boundary samples pi for i=0 to Sp-1 and qi for j=0 to Sq-1 (pi and qi are the i-th sample within a row for filtering vertical edge, or the i-th sample within a column for filtering horizontal edge) in HEVC deblocking described above) are then replaced by linear interpolation as follows:
- p_i′= (f_i*Middle_s, t+ (64-f_i) *P_s+32) ＞＞6) , clipped to p_i±tcPD_i
- q_j′= (g_j*Middle_s, t+ (64-g_j) *Q_s+32) ＞＞6) , clipped to q_j±tcPD_j
where tcPD_i and tcPD_j term is a position dependent clipping described in Section 3.6.2 and g_j, f_i, Middle_s, t,
P_s and Q_s are given.
· Deblocking Decison for Chroma

The chroma strong filters are used on both sides of the block boundary. Here, the chroma filter is selected when both sides of the chroma edge are greater than or equal to 8 (chroma position) , and the following decision with three conditions are satisfied: the first one is for decision of boundary strength as well as large block. The proposed filter can be applied when the block width or height which orthogonally crosses the block edge is equal to or larger than 8 in chroma sample domain. The second and third one is basically the same as for HEVC luma deblocking decision, which are on/off decision and strong filter decision, respectively.

In the first decision, boundary strength (bS) is modified for chroma filtering and the conditions are checked sequentially. If a condition is satisfied, then the remaining conditions with lower priorities are skipped.

Chroma deblocking is performed when bS is equal to 2, or bS is equal to 1 when a large block boundary is detected.

The second and third condition is basically the same as HEVC luma strong filter decision as follows.

In the second condition:
d is then derived as in HEVC luma deblocking.
The second condition will be TRUE when d is less than β.
In the third condition StrongFilterCondition is derived as follows:
dpq is derived as in HEVC.
sp₃ = Abs (p₃ -p₀) , derived as in HEVC,
sq₃ = Abs (q₀ -q₃) , derived as in HEVC.
As in HEVC design, StrongFilterCondition = (dpq is less than (β >> 2) , sp₃ + sq₃ is less than (β >> 3) , and
Abs (p₀ -q₀) is less than (5 *t_C + 1) >> 1) .
· Strong Deblocking Filter for Chroma

The following strong deblocking filter for chroma is defined:
p₂′= (3*p₃+2*p₂+p₁+p₀+q₀+4) >> 3
p₁′= (2*p₃+p₂+2*p₁+p₀+q₀+q₁+4) >> 3
p₀′= (p₃+p₂+p₁+2*p₀+q₀+q₁+q₂+4) >> 3.

The proposed chroma filter performs deblocking on a 4x4 chroma sample grid.
· Position Dependent Clipping

The position dependent clipping tcPD is applied to the output samples of the luma filtering process involving strong and long filters that are modifying 7, 5 and 3 samples at the boundary. Assuming quantization error distribution, it is proposed to increase clipping value for samples which are expected to have higher quantization noise, thus expected to have higher deviation of the reconstructed sample value from the true sample value.

For each P or Q boundary filtered with asymmetrical filter, depending on the result of decision-making, position dependent threshold table is selected from two tables (i.e., Tc7 and Tc3 tabulated below) that are provided to decoder as a side information:
Tc7 = {6, 5, 4, 3, 2, 1, 1} ; Tc3 = {6, 4, 2 } ;
tcPD = (Sp == 3) ? Tc3 : Tc7;
tcQD = (Sq == 3) ? Tc3 : Tc7.

For the P or Q boundaries being filtered with a short symmetrical filter, position dependent threshold of lower magnitude is applied:
Tc3 = {3, 2, 1 } .

Following defining the threshold, filtered p’i and q’i sample values are clipped according to tcP and tcQ clipping values:
p”_i = Clip3 (p’_i + tcP_i, p’_i - tcP_i, p’_i) ;
q”_j = Clip3 (q’_j + tcQ_j, q’_j - tcQ _j, q’_j) ;
where p’_i and q’_i are filtered sample values, p”_i and q”_j are output sample value after the clipping and tcP_i tcP_i
are clipping thresholds that are derived from the VVC tc parameter and tcPD and tcQD. The function Clip3 is a clipping function as it is specified in VVC.
· Sub-block Deblocking Adjustment

To enable parallel friendly deblocking using both long filters and sub-block deblocking the long filters is restricted to modify at most 5 samples on a side that uses sub-block deblocking (AFFINE or ATMVP or DMVR) as shown in the luma control for long filters. Extendedly, the sub-block deblocking is adjusted such that that sub-block boundaries on an 8x8 grid that are close to a CU or an implicit TU boundary is restricted to modify at most two samples on each side.

Following applies to sub-block boundaries that not are aligned with the CU boundary.

Where edge equal to 0 corresponds to CU boundary, edge equal to 2 or equal to orthogonalLength-2 corresponds
to sub-block boundary 8 samples from a CU boundary etc. Where implicit TU is true if implicit split of TU is used.
3.7. Sample Adaptive Offset

Sample adaptive offset (SAO) is applied to the reconstructed signal after the deblocking filter by using offsets specified for each CTB by the encoder. The video encoder first makes the decision on whether or not the SAO process is to be applied for current slice. If SAO is applied for the slice, each CTB is classified as one of five SAO types as shown in Table 3-1. The concept of SAO is to classify pixels into categories and reduces the distortion by adding an offset to pixels of each category. SAO operation includes edge offset (EO) which uses edge properties for pixel classification in SAO type 1 to 4 and band offset (BO) which uses pixel intensity for pixel classification in SAO type 5. Each applicable CTB has SAO parameters including sao_merge_left_flag, sao_merge_up_flag, SAO type and four offsets. If sao_merge_left_flag is equal to 1, the current CTB will reuse the SAO type and offsets of the CTB to the left. If sao_merge_up_flag is equal to 1, the current CTB will reuse SAO type and offsets of the CTB above.
Table. 3-4 Specification of SAO type

3.8. Adaptive Loop Filter

Adaptive loop filtering for video coding is to minimize the mean square error between original samples and decoded samples by using Wiener-based adaptive filter. The ALF is located at the last processing stage for each picture and can be regarded as a tool to catch and fix artifacts from previous stages. The suitable filter coefficients are determined by the encoder and explicitly signalled to the decoder. To achieve better coding efficiency, especially for high resolution videos, local adaptation is used for luma signals by applying different filters to different regions or blocks in a picture. In addition to filter adaptation, filter on/off control at coding tree unit (CTU) level is also helpful for improving coding efficiency. Syntax-wise, filter coefficients are sent in a picture level header called adaptation parameter set, and filter on/off flags of CTUs are interleaved at CTU level in the slice data. This syntax design not only supports picture level optimization but also achieves a low encoding latency.
· Signaling of Parameters

According to ALF design in VTM, filter coefficients and clipping indices are carried in ALF APSs. An ALF APS can include up to 8 chroma filters and one luma filter set with up to 25 filters. An index is also included for each of the 25 luma classes. Classes having the same index share the same filter. By merging different classes, the num of bits required to represent the filter coefficients is reduced. The absolute value of a filter coefficient is represented using a 0th order Exp-Golomb code followed by a sign bit for a non-zero coefficient. When clipping is enabled, a clipping index is also signalled for each filter coefficient using a two-bit fixed-length code. Up to 8 ALF APSs can be used by the decoder at the same time.

Filter control syntax elements of ALF in VTM include two types of information. First, ALF on/off flags are signalled at sequence, picture, slice and CTB levels. Chroma ALF can be enabled at picture and slice level only if luma ALF is enabled at the corresponding level. Second, filter usage information is signalled at picture, slice and CTB level, if ALF is enabled at that level. Referenced ALF APSs IDs are coded at a slice level or at a picture level if all the slices within the picture use the same APSs. Luma component can reference up to 7 ALF APSs and chroma components can reference 1 ALF APS. For a luma CTB, an index is signalled indicating which ALF APS or offline trained luma filter set is used. For a chroma CTB, the index indicates which filter in the referenced APS is used.

The data syntax elements of ALF associated to LUMA component in VTM are listed as follows.

alf_luma_filter_signal_flag equal to 1 specifies that a luma filter set is signalled. alf_luma_filter_signal_flag
equal to 0 specifies that a luma filter set is not signalled.
alf_luma_clip_flag equal to 0 specifies that linear adaptive loop filtering is applied to the luma component.
alf_luma_clip_flag equal to 1 specifies that non-linear adaptive loop filtering could be applied to the luma
component.
alf_luma_num_filters_signalled_minus1 plus 1 specifies the number of adpative loop filter classes for which
luma coefficients can be signalled. The value of alf_luma_num_filters_signalled_minus1 shall be in the range of 0 to NumAlfFilters -1, inclusive.
alf_luma_coeff_delta_idx [filtIdx] specifies the indices of the signalled adaptive loop filter luma coefficient
deltas for the filter class indicated by filtIdx ranging from 0 to NumAlfFilters -1. When alf_luma_coeff_delta_idx [filtIdx] is not present, it is inferred to be equal to 0. The length of alf_luma_coeff_delta_idx [filtIdx] is Ceil (Log2 (alf_luma_num_filters_signalled_minus1 + 1) ) bits. The value of alf_luma_coeff_delta_idx [filtIdx] shall be in the range of 0 to alf_luma_num_filters_signalled_minus1, inclusive.
alf_luma_coeff_abs [sfIdx] [j] specifies the absolute value of the j-th coefficient of the signalled luma filter
indicated by sfIdx. When alf_luma_coeff_abs [sfIdx] [j] is not present, it is inferred to be equal 0. The value of alf_luma_coeff_abs [sfIdx] [j] shall be in the range of 0 to 128, inclusive.
alf_luma_coeff_sign [sfIdx] [j] specifies the sign of the j-th luma coefficient of the filter indicated by sfIdx
as follows:
– If alf_luma_coeff_sign [sfIdx] [j] is equal to 0, the corresponding luma filter coefficient has a positive
value.
– Otherwise (alf_luma_coeff_sign [sfIdx] [j] is equal to 1) , the corresponding luma filter coefficient has a
negative value.
When alf_luma_coeff_sign [sfIdx] [j] is not present, it is inferred to be equal to 0.
alf_luma_clip_idx [sfIdx] [j] specifies the clipping index of the clipping value to use before multiplying by
the j-th coefficient of the signalled luma filter indicated by sfIdx. When alf_luma_clip_idx [sfIdx] [j] is not present, it is inferred to be equal to 0.

The coding tree unit syntax elements of ALF associated to LUMA component in VTM are listed as follows.

alf_ctb_flag [cIdx] [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] equal to 1 specifies that the adaptive
loop filter is applied to the coding tree block of the colour component indicated by cIdx of the coding tree unit at luma location (xCtb, yCtb) . alf_ctb_flag [cIdx] [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] equal to 0 specifies that the adaptive loop filter is not applied to the coding tree block of the colour component indicated by cIdx of the coding tree unit at luma location (xCtb, yCtb) .
When alf_ctb_flag [cIdx] [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] is not present, it is inferred to
be equal to 0.
alf_use_aps_flag equal to 0 specifies that one of the fixed filter sets is applied to the luma CTB.
alf_use_aps_flag equal to 1 specifies that a filter set from an APS is applied to the luma CTB. When
alf_use_aps_flag is not present, it is inferred to be equal to 0.
alf_luma_prev_filter_idx specifies the previous filter that is applied to the luma CTB. The value of
alf_luma_prev_filter_idx shall be in a range of 0 to sh_num_alf_aps_ids_luma -1, inclusive. When alf_luma_prev_filter_idx is not present, it is inferred to be equal to 0.
The variable AlfCtbFiltSetIdxY [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] specifying the filter set
index for the luma CTB at location (xCtb, yCtb) is derived as follows:
– If alf_use_aps_flag is equal to 0, AlfCtbFiltSetIdxY [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY]
is set equal to alf_luma_fixed_filter_idx.
– Otherwise, AlfCtbFiltSetIdxY [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] is set equal to
16 + alf_luma_prev_filter_idx.
alf_luma_fixed_filter_idx specifies the fixed filter that is applied to the luma CTB. The value of
alf_luma_fixed_filter_idx shall be in a range of 0 to 15, inclusive.

Based on the ALF design of VTM, the ALF design of ECM further introduces the concept of alternative filter sets into luma filters. The luma filters are be trained multiple alternatives/rounds based on the updated luma CTU ALF on/off decisions of each alternative/rounds. In such way, there will be multiple filter sets that associated to each training alternative and the class merging results of each filter set may be different. Each CTU could select the best filter set by RDO and the related alternative information will be signaled.

The data syntax elements of ALF associated to LUMA component in ECM are listed as follows.

alf_luma_num_alts_minus1 plus 1 specifies the number of alternative filter sets for luma component. The value
of alf_luma_num_alts_minus1 shall be in the range of 0 to 3, inclusive.
alf_luma_clip_flag [altIdx] equal to 0 specifies that linear adaptive loop filtering is applied to the alternative
luma filter set with index altIdxalf_luma_clip_flag [altIdx] equal to 1 specifies that non-linear adaptive loop filtering could be applied to the alternative luma filter set with index altIdx
alf_luma_num_filters_signalled_minus1 [altIdx] plus 1 specifies the number of adpative loop filter classes
for which luma coefficients can be signalled of the alternative luma filter set with index altIdx. The value of alf_luma_num_filters_signalled_minus1 [altIdx] shall be in the range of 0 to NumAlfFilters -1, inclusive.
alf_luma_coeff_delta_idx [altIdx] [filtIdx] specifies the indices of the signalled adaptive loop filter luma
coefficient deltas for the filter class indicated by filtIdx ranging from 0 to NumAlfFilters –1 for the alternative luma filter set with index altIdx. When alf_luma_coeff_delta_idx [filtIdx] [altIdx] is not present, it is inferred to be equal to 0. The length of alf_luma_coeff_delta_idx [altIdx] [filtIdx] is Ceil (Log2 (alf_luma_num_filters_signalled_minus1 [altIdx] + 1) ) bits. The value of alf_luma_coeff_delta_idx [altIdx] [filtIdx] shall be in the range of 0 to alf_luma_num_filters_signalled_minus1 [altIdx] , inclusive.
alf_luma_coeff_abs [altIdx] [sfIdx] [j] specifies the absolute value of the j-th coefficient of the signalled luma
filter indicated by sfIdx of the alternative luma filter set with index altIdx. When alf_luma_coeff_abs [altIdx] [sfIdx] [j] is not present, it is inferred to be equal 0. The value of alf_luma_coeff_abs [altIdx] [sfIdx] [j] shall be in the range of 0 to 128, inclusive.
alf_luma_coeff_sign [altIdx] [sfIdx] [j] specifies the sign of the j-th luma coefficient of the filter indicated by
sfIdx of the alternative luma filter set with index altIdx as follows:
– If alf_luma_coeff_sign [altIdx] [sfIdx] [j] is equal to 0, the corresponding luma filter coefficient has a
positive value.
– Otherwise (alf_luma_coeff_sign [altIdx] [sfIdx] [j] is equal to 1) , the corresponding luma filter coefficient
has a negative value.
When alf_luma_coeff_sign [altIdx] [sfIdx] [j] is not present, it is inferred to be equal to 0.
alf_luma_clip_idx [altIdx] [sfIdx] [j] specifies the clipping index of the clipping value to use before
multiplying by the j-th coefficient of the signalled luma filter indicated by sfIdx of the alternative luma filter set with index altIdx. When alf_luma_clip_idx [altIdx] [sfIdx] [j] is not present, it is inferred to be equal to 0. The coding tree unit syntax elements of ALF associated to LUMA component in ECM are listed as follows.

alf_ctb_luma_filter_alt_idx [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] specifies the index of the
alternative luma filters applied to the coding tree block of the luma component, of the coding tree unit at luma location (xCtb, yCtb) . When
alf_ctb_luma_filter_alt_idx [xCtb >> CtbLog2SizeY] [yCtb >> CtbLog2SizeY] is not present, it is inferred to
be equal to zero.
· Filter Shapes

Fig. 13A-Fig. 13C illustrate filter shapes for ALF, respectively.

In the JEM, up to three diamond filter shapes (as shown in Fig. 13A-Fig. 13C) can be selected for the luma component. An index is signalled at the picture level to indicate the filter shape used for the luma component. Each square represents a sample, and Ci (i being 0～6 (left) , 0～12 (middle) , 0～20 (right) ) denotes the coefficient to be applied to the sample. For chroma components in a picture, the 5×5 diamond shape is always used. In VVC, the 7×7 diamond shape is always used for Luma while the 5×5 diamond shape is always used for Chroma.
· Classification for ALF

Each 2×2 (or 4×4) block is categorized into one out of 25 classes. The classification index C is derived based on its directionality D and a quantized value of activityas follows:

To calculate D andgradients of the horizontal, vertical and two diagonal direction are first calculated using 1-D Laplacian:

Indices i and j refer to the coordinates of the upper left sample in the 2×2 block and R (i, j) indicates a reconstructed sample at coordinate (i, j) .

Then D maximum and minimum values of the gradients of horizontal and vertical directions are set as:

and the maximum and minimum values of the gradient of two diagonal directions are set as:

To derive the value of the directionality D, these values are compared against each other and with two thresholds t₁ and t₂:
Step 1. If bothandare true, D is set to 0.
Step 2. Ifcontinue from Step 3; otherwise continue from Step 4.
Step 3. IfD is set to 2; otherwise D is set to 1.
Step 4. IfD is set to 4; otherwise D is set to 3.

The activity value A is calculated as:

A is further quantized to the range of 0 to 4, inclusively, and the quantized value is denoted as

For both chroma components in a picture, no classification method is applied, i.e. a single set of ALF coefficients is applied for each chroma component.
· Geometric Transformations of Filter Coefficients

Before filtering each 2×2 block, geometric transformations such as rotation or diagonal and vertical flipping are applied to the filter coefficients f (k, l) , which is associated with the coordinate (k, l) , depending on gradient values calculated for that block. This is equivalent to applying these transformations to the samples in the filter support region. The idea is to make different blocks to which ALF is applied more similar by aligning their directionality.

Fig. 14A-Fig. 14C illustrate relative coordinator for the 5×5 diamond filter support, respectively.

Three geometric transformations, including diagonal, vertical flip and rotation are introduced:
Diagonal: f_D (k, l) =f (l, k) ,
Vertical flip: f_V (k, l) =f (k, K-l-1) ,
Rotation: f_R (k, l) =f (K-l-1, k) .
where K is the size of the filter and 0≤k, l≤K-1 are coefficients coordinates, such that location (0, 0) is at
the upper left corner and location (K-1, K-1) is at the lower right corner. The transformations are applied to the filter coefficients f (k, l) depending on gradient values calculated for that block. The relationship between the transformation and the four gradients of the four directions are summarized in Table 3-5. Fig. 14A-Fig. 14C shows the transformed coefficients for each position based on the 5x5 diamond.
Table. 3-5 Mapping of the gradient calculated for one block and the transformations.

· Filtering Process

At decoder side, when ALF is enabled for a block, each sample R (i, j) within the block is filtered, resulting in sample value R′ (i, j) as shown below, where L denotes filter length, f_m, n represents filter coefficient, and f (k, l) denotes the decoded filter coefficients.

Fig. 15 shows an example of relative coordinates used for 5x5 diamond filter support supposing the current sample’s coordinate (i, j) to be (0, 0) . Samples in different coordinates filled with the same color are multiplied with the same filter coefficients. Fig. 15 shows examples of relative coordinates for the 5×5 diamond filter support.
· Non-Linear Filtering Reformulation

Linear filtering can be reformulated, without coding efficiency impact, in the following expression:
O(x, y) =I (x, y) +∑ _(i, j) _≠ _(0, 0) w (i, j) . (I (x+i, y+j) -I (x, y) ) ,
where w (i, j) are the same filter coefficients.

VVC introduces the non-linearity to make ALF more efficient by using a simple clipping function to reduce the impact of neighbor sample values (I (x+i, y+j) ) when they are too different with the current sample value (I (x, y) ) being filtered.

More specifically, the ALF filter is modified as follows:
O′ (x, y) =I (x, y) +∑ _(i, j) _≠ _(0, 0) w (i, j) . K (I (x+i, y+j) -I (x, y) , k (i, j) ) ,
where K (d, b) =min (b, max (-b, d) ) is the clipping function, and k (i, j) are clipping parameters, which
depends on the (i, j) filter coefficient. The encoder performs the optimization to find the best k (i, j) .

The clipping parameters k (i, j) are specified for each ALF filter, one clipping value is signaled per filter coefficient. It means that up to 12 clipping values can be signalled in the bitstream per Luma filter and up to 6 clipping values for the Chroma filter.

In order to limit the signaling cost and the encoder complexity, only 4 fixed values which are the same for INTER and INTRA slices are used.

Because the variance of the local differences is often higher for Luma than for Chroma, two different sets for the Luma and Chroma filters are applied. The maximum sample value (here 1024 for 10 bits bit-depth) in each set is also introduced, so that clipping can be disabled if it is not necessary.

The 4 values have been selected by roughly equally splitting, in the logarithmic domain, the full range of the sample values (coded on 10 bits) for Luma, and the range from 4 to 1024 for Chroma.

More precisely, the Luma table of clipping values have been obtained by the following formula:
with M=2¹⁰ and N=4.

Similarly, the Chroma tables of clipping values is obtained according to the following formula:
with M=2¹⁰, N=4 and A=4.
3.9. Bilateral In-loop Filter
· Bilateral Image Filter

Bilateral image filter is a nonlinear filter that smooths the noise while preserving edge structures. The bilateral filtering is a technique to make the filter weights decrease not only with the distance between the samples but also with increasing difference in intensity. This way, over-smoothing of edges can be ameliorated. A weight is defined as

where Δxand Δy is the distance in the vertical and horizontal and ΔI is the difference in intensity between the
samples.

The edge-preserving de-noising bilateral filter adopts a low-pass Gaussian filter for both the domain filter and the range filter. The domain low-pass Gaussian filter gives higher weight to pixels that are spatially close to the center pixel. The range low-pass Gaussian filter gives higher weight to pixels that are similar to the center pixel. Combining the range filter and the domain filter, a bilateral filter at an edge pixel becomes an elongated Gaussian filter that is oriented along the edge and is greatly reduced in gradient direction. This is the reason why the bilateral filter can smooth the noise while preserving edge structures.
· Bilateral Filter in Video Coding

The bilateral filter in video coding is proposed as a coding tool for the VVC. The filter acts as a loop filter in parallel with the sample adaptive offset (SAO) filter. Both the bilateral filter and SAO act on the same input samples, each filter produces an offset, and these offsets are then added to the input sample to produce an output sample that, after clipping, goes to the next stage. The spatial filtering strength σ_d is determined by the block size, with smaller blocks filtered more strongly, and the intensity filtering strength σ_r is determined by the quantization parameter, with stronger filtering being used for higher QPs. Only the four closest samples are used, so the filtered sample intensity I_F can be calculated as

where I_C denotes the intensity of the center sample, ΔI_A=I_A-I_C the intensity difference between the center
sample and the sample above. ΔI_B, ΔI_L and ΔI_R denote the intensity difference between the center sample and that of the sample below, to the left and to the right respectively.
4. Problems

The existing designs of inter prediction sample derivation in video coding have the following problems:
1. In current inter prediction sample derivation, the compression noise inside prediction sample is not well
considered, which may be suboptimal for video compression.
2. In current inter prediction sample derivation, no filter is used to denoise, which may be suboptimal for
video compression.
5. Detailed solutions

To solve the above problems and some other problems not mentioned, methods as summarized below are disclosed. The embodiments should be considered as examples to explain the general concepts and should not be interpreted in a narrow way. Furthermore, these embodiments can be applied individually or combined in any manner.

In this disclosure, a video unit may refer to a sequence, a picture, a sub-picture, a slice, a CTU, a TU, a block, or a region. The video unit may comprise one color component or it may comprise multiple color components.
1) In one example, a filtering method may be applied to refine the samples of a video unit, where the partial or
all the samples are generated using at least one inter prediction method.
a. In one example, the filtering method may be bilateral filtering (BF) .
b. In one example, the filtering method may be deblocking filtering.
c. In one example, at least one parameter may be signaled to determine the filtering method.
i. In one example, the filtering method may be SAO.
ii. In one example, the filtering method may be CCSAO.
iii. In one example, the filtering method may be ALF.
iv. In one example, the filtering method may be CCALF.
d. In one example, the refined samples of the current inter block may be used for future block’s coding.
i. For example, an intra block succeeding the current inter block in decoding order (within
the same picture) may be applied based on the refined samples.
a) For example, the refined samples may be used as neighboring/reference samples.
b) For example, the refined samples may be used as template samples.
ii. For example, an IBC block succeeding the current inter block in decoding order (within
the same picture) may be applied based on the refined samples.
a) For example, the refined samples may be used as reference samples.
iii. For example, an inter block succeeding the current inter block in decoding order (within
the same picture) may be applied based on the refined samples.
a) For example, the refined samples may be used as template samples.
e. In one example, the neighbouring samples of the current video unit may be used in the filtering
method.
i. In one example, the neighbouring samples may refer to the prediction/reconstruction sam-
ples.
ii. In one example, the neighbouring samples may be adjacent and/or non-adjacent.
iii. In one example, the filtering method may refer to PDPC or gradient PDPC.
f. In one example, the parameters of the filtering method may be pre-defined, or signalled, or derived
on-the-fly.
i. In one example, the derivation of the parameters may be same as a coding tool.
a) In one example, the coding tool may refer to CCLM, or MMLM, or CCCM, or
LIC, or their variants.
g. In one example, when one or more coding tools are used to refine the samples, the filtering method
may be used before or after the coding tools.
i. In one example, the coding tool may refer to OBMC, or LIC.
h. In one example, the inter prediction samples may belong to a video unit.
i. In one example, the inter prediction samples may belong to a CU/PU/subPU/TU.
j. In one example, the inter prediction samples may belong to a picture/slice/tile.
k. In one example, the inter prediction samples may belong to a block/region.
l. In one example, a inter prediction sample may be filtered/modified by the proposed BF with utili-
zation of coded/statistical information.
i. In one example, the filtering result of the proposed BF may be generated by following
formulation:

where I_filtered stands for the updated/modified luma or chroma
sample/pixel and I_C stands for the unmodified luma or chroma sample/pixel that locates at central of the filtering shape. The Δ (delta) denotes the difference between corresponding reference sample and unmodified central sample and the Ω (omega) denotes the sum of vertical and horizontal distance between reference sample and central sample. The n stands for the total number of samples inside the filtering shape and e stands for the strength factor. The μ (Δ, Ω) is a function for computing the filtering weight of each position in the filtering shape.
a) In one example, the function μ (Δ, Ω) may be formulated as:

where σ_d and σ_r are two parameters for filtering.
b) In one example, the function μ (Δ, Ω) may be baked into the look-up-table.
c) In one example, different samples or different positions inside inter prediction
samples may use uniform parameters or look-up-table.
d) Alternatively, different samples or different positions inside inter prediction sam-
ples may use different parameters or look-up-tables.
e) In one example, the parameter such as σ_d and σ_r may be pre-defined, searched,
determined on-the-fly or signalled in the bitstream.
a. In one example, the parameters mentioned above may be set based on
coding mode, size or other coded information of current video unit.
3) In one example, the coded information of current video may
be variance of samples.
4) In one example, the coded information of current video may
be MAD (Mean Absolute Difference) of samples.
b. In one example, the parameters mentioned above may be signaled from
the encoder to the decoder.
f) In one example, the parameter e may be pre-defined, searched, determined on-
the-fly or signalled in the bitstream.
a. In one example, the parameter e may be set based on coding mode, size
or other coded information of current video unit.
3) In one example, the parameter e may be set based on the luma
size of current video unit.
1. In one example, the parameter e may be set based on the
max (width_luma, height_luma) or min (width_luma, height_luma) .
2. In one example, the parameter e may be set based on the
width_luma×height_luma.
4) Alternatively, the parameter e may be set based on the chroma
size of current video unit.
1. In one example, the parameter e may be set based on the
max (width_chroma, height_chroma) or min (width_chroma, height_chroma) .
2. In one example, the parameter e may be set based on the
width_chroma×height_chroma.
b. In one example, the parameter e may be signaled from the encoder to the
decoder.
ii. In one example, the filtering process as described in above bullets may be implemented by
operations on integers.
a) For example, variables may be left-shifted and/or right-shifted before/in/after the
process in keep a suitable calculation precision.
2) It is proposed to apply the filtering method to the Template samples before they are used to perform template
matching.
a. In one example, the proposed method may be applied to template used in TM AMVP mode.
b. In one example, the proposed method may be applied to template used in TM Merge mode.
c. In one example, the proposed method may be applied to template used in TM ARMC method.
d. In one example, the proposed method may be applied to template used in GPM Split Mode Reor-
dering method.
e. In one example, the proposed method may be applied to template used in TM OBMC method.
f. In one example, the proposed method may be applied to template used in TM GPM MMVD method.
g. In one example, the proposed method may be applied to template used in TM SubBlock Refinement
method.
h. In one example, the proposed method may be applied to template used in TM Reordering for
MMVD method.
i. In one example, the proposed method may be applied to template used in TM Reordering for Affine
MMVD method.
j. In one example, the proposed method may be applied to template used in TM Block Level Refer-
ence Picture Reordering method.
k. In one example, the proposed method may be applied to template used in TM BCW Index Deriva-
tion method.
l. In one example, the proposed method may be applied to template used in TM LIC Flag Derivation
method.
m. In one example, the proposed method may be applied to template used in other template matching
based tools.
3) It is proposed to apply the filtering method to the inter prediction samples before they are used to generate
inter reconstruction.
a. In one example, the proposed method may be applied to Luma related inter mode.
b. In one example, the proposed method may be applied to Chroma related inter mode.
c. In one example, the proposed method may be applied to uni-predictive inter mode.
d. In one example, the proposed method may be applied to bi-predictive inter mode.
e. In one example, the proposed method may be applied to inter MERGE mode.
f. In one example, the proposed method may be applied to inter AMVP mode.
g. In one example, the proposed method may be applied to AMVP-MERGE mode.
h. In one example, the proposed method may be applied to CIIP mode.
i. In one example, the proposed method may be applied to LIC mode.
j. In one example, the proposed method may be applied to BDOF mode.
k. In one example, the proposed method may be applied to AFFINE mode.
l. In one example, the proposed method may be applied to DMVR mode.
m. In one example, the proposed method may be applied to MHP mode.
n. In one example, the proposed method may be applied to OBMC mode.
o. In one example, the proposed method may be applied to GPM mode.
p. In one example, the proposed method may be applied to Inter-CCCM mode.
q. In one example, the proposed method may be applied to BCW mode.
r. In one example, the proposed method may be applied to Inter CCP Merge mode.
s. In one example, the proposed method may be applied to template matching based inter mode.
t. In one example, the proposed method may be applied to any other inter related mode.
4) It is proposed to apply a filtering method to LMCS enabled prediction samples before they are used to
generate inter reconstruction.
a. In one example, the original domain may refer to domain that LMCS mapping is NOT performed.
b. In one example, the mapped domain may refer to domain that LMCS mapping is performed.
c. In one example, the proposed method may be applied to prediction samples inside original domain.
d. In one example, the proposed method may be applied to prediction samples inside mapped domain.
e. In one example, the inter prediction samples may be inverse mapped to original domain before they
are filtered by the proposed method.
f. In one example, the inter prediction samples may be mapped to LMCS domain after they are filtered
by the proposed method.
g. In one example, the inter prediction samples may be filtered by the proposed method without for-
ward or inverse mapping of LMCS.
h. In one example, the inter prediction samples may be filtered by the proposed method before they
are mapped into LMCS domain.
i. In one example, the inter prediction sample may be filtered by the proposed method after they are
mapped into LMCS domain.
5) It is proposed to apply a filtering method to different color components of prediction samples, in different
ways or in the same way.
a. The same filtering methods may be applied to different color components.
b. Different filtering methods may be applied to different color components.
c. In one example, the proposed method may be applied to only Luma component.
d. In one example, the proposed method may be applied to only Chroma component.
e. In one example, the proposed method may be applied to a Luma related inter mode.
f. In one example, the proposed method may be applied to a Chroma related inter mode.
g. In one example, the proposed method may be applied to a Cross-Component related inter mode.
h. In one example, the proposed method may be jointly applied to Luma and Chroma related inter
mode.
i. In one example, the proposed method may be applied to a fusion based inter mode.
j. In one example, the proposed method may be applied to a RGB related inter mode.
6) It is proposed to apply the filtering method to different coding areas of prediction.
a. In one example, the proposed method may be applied to a CU.
b. In one example, the proposed method may be applied to a PU.
c. In one example, the proposed method may be applied to a sub PU.
d. In one example, the proposed method may be applied to a TU.
e. In one example, the proposed method may be applied to a CTU.
f. In one example, the proposed method may be applied to a CTU row.
g. In one example, the proposed method may be applied to a slice.
h. In one example, the proposed method may be applied to a tile.
i. In one example, the proposed method may be applied to a picture.
j. In one example, the proposed method may be applied to any other coding unit/area/block.
7) It is proposed to apply the filtering method to different coding type of prediction.
a. In one example, the proposed method may be applied to prediction with QP greater than a threshold.
b. In one example, the proposed method may be applied to prediction with QP lower than a threshold.
c. In one example, the proposed method may be applied to prediction with TID greater than a threshold.
d. In one example, the proposed method may be applied to prediction with TID lower than a threshold.
e. In one example, the proposed method may be applied to prediction in P slice/tile/picture/sub-picture.
f. In one example, the proposed method may be applied to prediction in B slice/tile/picture/sub-picture.
g. In one example, the proposed method may be applied to prediction in low-delay picture.
h. In one example, the proposed method may be applied to prediction with a specific coding mode.
i. The specific coding mode may be affine mode.
ii. The specific coding mode may be subblock-based TMVP.
iii. The specific coding mode may be DMVR.
iv. The specific coding mode may be BDOF.
v. The specific coding mode may be GPM.
vi. The specific coding mode may be CIIP.
8) Whether to and/or how to apply the filtering method to inter prediction samples may depend on a condition.
a. In one example, the condition may be block size.
i. In one example, the filtering method may be applied when width or height of current block
is greater than a threshold.
ii. In one example, the proposed method may be applied when width or height of current block
is less than a threshold.
iii. In one example, the proposed method may be applied when total sample number of current
block is greater than a threshold.
iv. In one example, the proposed method may be applied when total sample number of current
block is less than a threshold.
b. In one example, the condition may be block shape.
i. In one example, the proposed method may be applied when width is greater than or equal
to height.
a) In one example, the proposed method may be applied when the ratio of
width/height is high than or equal to a threshold.
b) In one example, the proposed method may be applied when the ratio of
width/height is lower than or equal to a threshold.
ii. In one example, the proposed method may be applied when height is greater than or equal
to width.
a) In one example, the proposed method may be applied when the ratio of
height/width is high than or equal to a threshold.
b) In one example, the proposed method may be applied when the ratio of
height/width is lower than or equal to a threshold.
c. In one example, the condition may be prediction sample number of current block.
i. In one example, the proposed method may be applied when prediction sample number of
current block is greater than a threshold.
ii. In one example, the proposed method may be applied when prediction sample number of
current block is less than a threshold.
d. In one example, the condition may be picture/slice/tile size.
i. In one example, the proposed method may be applied when width/height of current pic-
ture/slice/tile is greater than a threshold.
ii. In one example, the proposed method may be applied when width/height of current pic-
ture/slice/tile is less than a threshold.
iii. In one example, the proposed method may be applied when total sample number of current
picture/slice/tile is greater than a threshold.
iv. In one example, the proposed method may be applied when total sample number of current
picture/slice/tile is less than a threshold.
e. In one example, the condition may be texture strength related info.
i. In one example, the proposed method may be applied when variance of prediction samples
is greater than a threshold.
ii. In one example, the proposed method may be applied when variance of prediction samples
is less than a threshold.
iii. In one example, the proposed method may be applied when gradient of prediction samples
is greater than a threshold.
iv. In one example, the proposed method may be applied when gradient of prediction samples
is less than a threshold.
v. In one example, the proposed method may be applied when valid band number of predic-
tion samples is greater than a threshold.
vi. In one example, the proposed method may be applied when valid band number of predic-
tion samples is less than a threshold.
vii. In one example, the proposed method may be applied when other texture related info of
prediction samples is greater than a threshold.
viii. In one example, the proposed method may be applied when other texture related info of
prediction samples is less than a threshold.
f. In one example, the condition may be template info.
i. In one example, the proposed method may be applied when template cost of current block
is greater than a threshold.
ii. In one example, the proposed method may be applied when template cost of current block
is less than a threshold.
g. In one example, the condition may be a/some coding tool (s) .
i. In one example, the proposed method may be applied when a/some coding tool (s) is/are
used.
ii. In one example, the proposed method may be applied when a/some coding tool (s) is/are
not used.
iii. In one example, the proposed method may be applied differently for different coding tool
sets.
h. In one example, the condition may be different picture types.
i. In one example, the picture types may be low delay and non-low delay pictures.
ii. In one example, the picture types may depend on whether backward inter-prediction is
applied for a picture.
a) In one example, the backward inter-prediction may refer to one current picture
has a reference picture whose POC is larger than POC of the current picture.
b) In one example, a picture with backward inter-prediction may be defined as a
non-low delay picture.
c) In one example, a picture without backward inter-prediction may be defined as a
low delay picture.
i. In one example, the above mentioned conditions may be used independently.
j. In one example, the above mentioned conditions may be used jointly.
9) It is proposed that the padding method may be applied to inter prediction samples before doing filtering.
a. In one example, the mirrored padding may be applied.
b. In one example, the duplicated padding may be applied.
c. In one example, the reconstructed sample from neighbor blocks may be used for filtering boundary
prediction samples of current block.
d. In one example, the reconstructed sample from neighbor blocks may be used for padding.
e.In one example, the prediction sample from current block may be used for padding.
10) For Bi-prediction, the filtering process may be applied to at least one prediction before it is used to generate
the bi-prediction.
a. Alternatively, the filtering process may be applied to the bi-prediction.
11) For a combined prediction, such as CIIP or GPM, the filtering process may be applied to at least one pre-
diction before it is used to generate the combined prediction.
a. Alternatively, the filtering process may be applied to the final combined prediction.
12) Multiple filtering process may be applied to inter-prediction.
a. For example, a second filtering process may be applied to the results of the first filtering process.
13) At least one inter prediction sample may perform filtering before generating inter reconstruction.
a. In one example, all the inter prediction samples may perform filtering before generating inter re-
construction.
b. In one example, only partial inter prediction samples may perform filtering before generating inter
reconstruction.
c. In one example, whether an inter prediction sample need to perform filtering may depend on certain
metrics.
i. In one example, the metric may be boundary strength/gradient.
ii. In one example, the metric may be the difference between the sample value of a prediction
sample and another sample.
a) In one example, alternatively, the metric may be the difference between the sample
value of a prediction sample and the average/max/min value of multiple samples.
14) Whether and/or how the filtering is performed may depend on the coding information of at least one predic-
tion sample.
a. In one example, the coding information may be whether at least one prediction sample is coded
with deblocking/SAO/CCSAO/BF/ALF/CCALF/LIC/OBMC/subblock OBMC/Intra mode/Inter mode/bi-prediction.
b. In one example, if at least one prediction sample has already performed deblock-
ing/SAO/CCSAO/BF/ALF/CCALF/LIC/OBMC/subblock OBMC/Intra mode/Inter mode/bi-pre-diction when it is coded, the current prediction sample or all the prediction samples will not perform filtering before generating inter reconstruction.
15) In one example, whether to and/how to apply the proposed method may be determined conditionally or
signalled.
16) In one example, a first syntax element (SE) may be signaled to indicate whether the proposed method is
applied or not.
a. For example, the SE may be a flag.
b. For example, the SE may be coded with at least one context model.
c. For example, the SE may be bypass coded.
d. For example, the SE is coded only if the current block is coded with a specific mode.
17) In one example, the disclosed methods may be used in post-processing and/or pre-processing.
18) In one example, the above-mentioned methods may be used jointly.
19) Alternatively, the above-mentioned methods may be used individually.
20) In one example, the proposed/described model parameter inheritance method may be applied to any in-loop
filtering tools, prediction tools, pre-processing, or post-processing filtering method in video coding.
21) In above examples, the video unit may refer to sequence/picture/sub-picture/slice/tile/coding tree unit
(CTU) /CTU row/groups of CTU/coding unit (CU) /prediction unit (PU) /transform unit (TU) /coding tree block (CTB) /coding block (CB) /prediction block (PB) /transform block (TB) /any other region that con-tains more than one luma or chroma sample/pixel.
22) Whether to and/or how to apply the disclosed methods above may be signalled in a bitstream.
a. In one example, they may be signalled at sequence level/group of pictures level/picture level/slice
level/tile group level, such as in sequence header/picture header/SPS/VPS/DPS/DCI/PPS/APS/slice header/tile group header.
b. In one example, they may be signalled at PB/TB/CB/PU/TU/CU/VPDU/CTU/CTU
row/slice/tile/sub-picture/other kinds of region contain more than one sample or pixel.
23) Whether to and/or how to apply the disclosed methods above may be dependent on coded information, such
as block size, colour format, single/dual tree partitioning, colour component, slice/picture type.

Fig. 16 illustrates a flowchart of a method 1600 for video processing in accordance with embodiments of the present disclosure. The method 1600 is implemented during a conversion between a video unit of a video and a bitstream of the video.

At block 1610, for a conversion between a current video unit of a video and a bitstream of the video, a plurality of samples of the current video unit are determined. At least a partial of the plurality of samples is determined based on at least one inter prediction.

At block 1620, a filtering process is applied to the plurality of samples to obtain a plurality of refined samples.

At block 1630, the conversion is performed based on the plurality of refined samples.

The method 1600 enables applying the filtering process to inter prediction samples. In this manner, the coding performance and coding effectiveness can be improved.

In some embodiments, the filtering process comprises at least one of: a bilateral filtering (BF) , or a deblocking filtering.

In some embodiments, at least one parameter is included in the bitstream to determine the filtering process. For example, the filtering process may include at least one of: a sample adaptive offset (SAO) , a cross-component SAO (CCSAO) , an adaptive loop filter (ALF) , or a cross-component ALF (CCALF) .

In some embodiments, the plurality of refined samples of the current video unit is used for coding at least one succeeding video unit in a same picture of the current video unit such as a current inter block.

In some embodiments, the at least one succeeding video unit comprises an intra block succeeding the current inter block in a coding order. The plurality of refined samples may be used as at least one of: neighboring samples, reference samples or template samples for the intra block.

In some embodiments, the at least one succeeding video unit comprises an intra block copy (IBC) block succeeding the current inter block in a coding order. The plurality of refined samples amay be used as reference samples for the IBC block.

In some embodiments, the at least one succeeding video unit comprises an inter block succeeding the current inter block in a coding order. The plurality of refined samples may be used as template samples for the inter block.

In some embodiments, the filtering process is based on neighboring samples of the current video unit, the neighboring samples comprising predicted neighboring samples or reconstructed neighboring samples.

In some embodiments, the neighboring samples comprises adjacent neighboring samples and/or non-adjacent neighboring samples.

In some embodiments, the filtering process comprises at least one of: a Position Dependent Intra Prediction Combination (PDPC) , or a gradient PDPC.

In some embodiments, at least one parameter of the filtering process is predefined, or indicated in the bitstream, or determined during the conversion.

In some embodiments, an approach for determining the at least one parameter is same with that of a coding tool. For example, the coding tool may include at least one of: a Cross-Component Linear Model (CCLM) , a Multi-Model Linear Model (MMLM) , a Cross-Component Chroma Mapping (CCCM) , or a local illumination compensation (LIC) .

In some embodiments, the plurality of samples are refined by the filtering process and a coding tool, the filtering process being applied before the coding tool or after the coding tool. The coding tool comprises at least one of: an overlapped block motion compensation (OBMC) or a local illumination compensation (LIC) .

In some embodiments, the plurality of samples comprises a plurality of inter prediction samples. The plurality of inter prediction samples belong to one of: a video unit, a coding unit, a prediction unit, a sub prediction unit, a transform unit, a picture, a slice, a tile, a block, or a region of the video.

In some embodiments, the plurality of inter prediction samples are filtered by a bilateral filtering based on at least one of: coded information, or statistic information.

In some embodiments, a filtering result of the bilateral filtering is determined by: where I_filtered denotes a filtered luma or chroma sample and I_C denotes an unmodified luma or chroma sample that locates at a central of a filtering shape, Δ denotes a difference between corresponding reference sample and unmodified central sample, Ω denotes a sum of vertical and horizontal distance between reference sample and central sample, n denotes a total number of samples inside the filtering shape, e denotes a strength factor, and μ (Δ, Ω) denotes a function for determining a filtering weight of each position in the filtering shape.

In some embodiments, the function comprises: where σ_d and σ_r are two parameters for filtering.

In some embodiments, the function μ (Δ, Ω) is baked into a look-up table.

In some embodiments, different samples or positions of the plurality of inter prediction samples use uniform parameters or look-up table. Alternatively, in some embodiments, different samples or positions of the plurality of inter prediction samples use different parameters or look-up tables.

In some embodiments, at least one parameter for the bilateral filtering is predefined, or searched, or determined on-the-fly, or indicated in the bitstream, the at least one parameter comprises σ_d and σ_r.

In some embodiments, the at least one parameter is determined based on at least one of: a coding mode, a size or coded information of the current video unit. The coded information comprises at least one of: a variance of samples, or a mean absolute difference of samples.

In some embodiments, the at least one parameter is indicated from an encoder to a decoder. In some embodiments, the strength factor is predefined, or searched, or determined on-the-fly, or indicated in the bitstream.

In some embodiments, the strength factor is determined based on at least one of: a coding mode, a size or coding information of the current video unit. In some embodiments, the strength factor is determined based on a luma size of the current video unit, or a chroma size of the current video unit.

In some embodiments, the strength factor is determined by one of: max (width_luma, height_luma) , min (width_luma, height_luma) , width_luma×height_luma , max (width_chroma, height_chroma) , min (width_chroma, height_chroma) , or width_chroma×height_chroma, where width_luma denotes a luma width, height_luma denotes a luma height, width_chroma denotes a chroma width, and height_chroma denotes a chroma height.

In some embodiments, the strength factor is indicated from an encoder to a decoder.

In some embodiments, the filtering process is implemented by operations on integers. In some embodiments, variables is left-shifted and/or right-shifted before the filtering process, or in the filtering process, or after the filtering process.

In some embodiments, the filtering process is applied to inter prediction samples before generating an inter reconstruction based on the inter prediction samples.

In some embodiments, the filtering process is applied to at least one of: a luma related inter mode, a chroma related inter mode, a uni-predictive inter mode, a bi-predictive inter mode, an inter merge mode, an inter advanced motion vector prediction (AMVP) mode, an AMVP merge mode, a combined inter and intra prediction (CIIP) mode, a local illumination compensation (LIC) mode, a bi-directional optical flow (BDOF) mode, an affine mode, a (DMVR) mode, a multiple hypothesis prediction (MHP) mode, an Overlapped Block Motion Compensation (OBMC) mode, a Geometric Partitioning Mode (GPM) mode, an inter-Cross-Component Chroma Mapping (CCCM) mode, a Bi-prediction with coding unit-level weight (BCW) mode, an inter cross-component prediction (CCP) merge mode, a template matching based inter mode, or a further inter related mode.

In some embodiments, the filtering process is applied to a Luma Mapping with Chroma Scaling (LMCS) enabled prediction samples before generating an inter reconstruction based on the prediction samples. In an original domain, a LMCS mapping is not performed, and in a mapped domain, the LMCS mapping is performed.

In some embodiments, the filtering process is applied to prediction samples inside the original domain, and/or prediction samples inside the mapped domain.

In some embodiments, inter prediction samples are inversed mapped to the original domain before being filtered.

In some embodiments, inter prediction samples are mapped to LMCS domain after being filtered.

In some embodiments, inter prediction samples are filtered by the filtering process without forward or inverse mapping of LMCS.

In some embodiments, inter prediction samples are filtered by the filtering process before being mapped into LMCS domain. Alternatively, in some embodiments, inter prediction samples are filtered by the filtering process after being mapped into LMCS domain.

In some embodiments, the filtering process is applied to a plurality of color components of the prediction samples in different manners or in a same manner.

In some embodiments, a same filtering process is applied to the plurality of color components.

In some embodiments, different filtering processes are applied to the plurality of color components.

In some embodiments, the filtering process is applied to only luma component, or only chroma component. In some embodiments, the filtering process is applied to a luma related inter mode, or a chroma related inter mode.

In some embodiments, the filtering process is applied to a cross-component related inter mode, or jointly applied to luma and chroma related inter mode. In some embodiments, the filtering process is applied to a fusion based inter mode, and/or a RGB related inter mode.

In some embodiments, the filtering process is applied to different coding areas of prediction, wherein the coding areas comprises at least one of: a coding unit, a prediction unit, a sub prediction unit, a transform unit, a coding tree unit, a coding tree unit row, a slice, a tile, a picture, or other coding unit.

In some embodiments, the filtering process is applied to a plurality of coding types of prediction, wherein the plurality of coding types comprise at least one of: a prediction with a quantization parameter greater than a threshold, a prediction with a quantization parameter lower than a threshold, a prediction with a temporal identifier greater than a threshold, a prediction with a temporal identifier lower than a threshold, a prediction in P slice or tile or picture or sub-picture, a prediction in B slice or tile or picture or sub-picture, a prediction in low-delay picture, or prediction with a first coding mode.

In some embodiments, the first coding mode comprises at least one of: an affine mode, a subblock-based Temporal Motion Vector Prediction (TMVP) , a DMVR, a BDOF, a GPM, or a CIIP.

In some embodiments, whether to and/or how to apply the filtering process to inter prediction samples is based on at least one condition. The at least one condition is based on at least one of: a block size, a block shape, a prediction sample number of a current block, a picture size, a slice size, a tile size, texture strength related information, template information, a coding tool, or a picture type.

In some embodiments, the at least one condition comprises one of: a width or height of the current block being greater than a threshold, or the width or height of the current block being less than a threshold.

In some embodiments, the at least one condition comprises one of: a total sample number of the current block being greater than a threshold, or the total sample number of the current block being less than a threshold.

In some embodiments, the at least one condition comprises one of: a width being greater than or equal to a height, a ratio of the width to the height being high than or equal to a threshold, a ratio of the width to the height being lower than or equal to a threshold, the height is greater than or equal to the width, a ratio of the height to the width being high than or equal to a threshold, or a ratio of the height to the width being lower than or equal to a threshold.

In some embodiments, the at least one condition comprises one of: the prediction sample number of current block being greater than a threshold, or the prediction sample number of current block being less than a threshold.

In some embodiments, the at least one condition comprises one of: a width or a height of a current picture or a current slice or a current tile being greater than a threshold, or a width or a height of a current picture or a current slice or a current tile being less than a threshold, a total sample number of a current picture or a current slice or a current tile being greater than a threshold, or a total sample number of a current picture or a current slice or a current tile being less than a threshold.

In some embodiments, the at least one condition comprises one of: a variance of prediction samples being greater than a threshold, a variance of prediction samples being less than a threshold, a gradient of prediction samples being greater than a threshold, a gradient of prediction samples being less than a threshold, a valid band number of prediction samples being greater than a threshold, a valid band number of prediction samples being less than a threshold, other texture related information of prediction samples being greater than a threshold, or other texture related information of prediction samples being less than a threshold.

In some embodiments, the at least one condition comprises one of: a template cost of the current block being greater than a threshold, or a template cost of the current block being less than a threshold.

In some embodiments, the at least one condition comprises one of: the coding tool being used, or the coding tool being not used.

In some embodiments, the filtering process is applied differently for different coding tool sets.

In some embodiments, the at least one condition comprises the picture type being a low delay or non-low delay picture.

In some embodiments, the picture type is based on whether backward inter prediction is applied for a picture, wherein the backward inter prediction refers to a current picture comprising a reference picture whose picture order count being larger than a picture order count of the current picture.

In some embodiments, a picture with backward inter-prediction comprises a non-low delay picture, and a picture without backward inter-prediction comprises a low delay picture.

In some embodiments, a padding process is applied to inter prediction sampled before being filtered. For example, the padding process may include at least one of: a mirrored padding, or a duplicated padding.

In some embodiments, reconstructed samples from at least one neighbor block is used for filtering boundary prediction samples of the current video unit.

In some embodiments, reconstructed samples from at least one neighbor block is used for padding. In some embodiments, prediction samples from the current video unit are used for padding.

In some embodiments, for a bi-prediction, the filtering process is applied to at least one prediction before the at least one prediction being used to generate the bi-prediction. Alternatively, in some embodiments, the filtering process is applied to a bi-prediction generated based on at least one prediction.

In some embodiments, for a combined prediction, the filtering process is applied to at least one prediction before the at least one prediction being used to generate the combined prediction.

In some embodiments, the filtering process is applied to a combined prediction generated based on at least one prediction. In some embodiments, the combined prediction comprises a CIIP or GPM.

In some embodiments, a plurality of filtering processes are applied to an inter prediction of the current video unit.

In some embodiments, a first filtering process is applied to the inter prediction to obtain a first filtering result, and a second filtering process is applied to the first filtering result.

In some embodiments, the filtering process is applied to at least one inter prediction sample before determining an inter reconstruction.

In some embodiments, the filtering process is applied to all inter prediction samples before determining the inter reconstruction.

In some embodiments, the filtering process is applied to a partial of the inter prediction samples before determining the inter reconstruction.

In some embodiments, whether the filtering process is applied to an inter prediction sample is based on at least one metric. The at least one metric comprises at least one of: a boundary strength, a boundary gradient, a difference between a sample value of a prediction sample and another sample, or a difference between a sample value of a prediction sample and an average or maximum or minimum value of a plurality of samples.

In some embodiments, whether to and/or how to apply the filtering process is based on coding information of at least one prediction sample, wherein the coding information comprises whether at least one prediction sample is coded with a first coding mode.

In some embodiments, the first coding mode comprises at least one of: a deblocking, a SAO, a CCSAO, a bilateral filtering, an ALF, a CCAFL, a LIC, an OBMC, a subblock OBMC, an intra mode, an inter mode, or a bi-prediction.

In some embodiments, the first coding mode is applied to the at least one prediction sample, the filtering process is not applied to a current prediction sample or all prediction samples before generating the inter reconstruction.

In some embodiments, the filtering process is applied to template samples before performing a template matching based on the template samples.

In some embodiments, the template samples are used in at least one of: a template matching (TM) AMVP mode, a TM merge mode, an Adaptive Reordering of Merge Candidates with Template Matching (TM ARMC) , a GPM split mode reordering, a TM OBMC, a TM GPM Merge Mode with Motion Vector Difference (MMVD) , a TM subblock refinement mode, a TM Reordering for MMVD mode, a TM reordering for Affine MMVD, a TM block level reference picture reordering, a TM BCW index derivation, a TM LIC flag derivation, or a template used in a further template matching based tool.

In some embodiments, whether to and/or how to apply the method is determined conditionally, or indicated in the bitstream. In some embodiments, a first syntax element (SE) is indicated in the bitstream to indicate whether the method is applied. In some embodiments, the first SE comprises a flag.

In some embodiments, the first SE is coded with at least one context model, or is bypass coded. In some embodiments, the first SE is coded if the current video unit is coded with a coding mode.

In some embodiments, the method 1600 is used in at least one of: a post-processing, or a pre-processing. The method 1600 may be used individually or jointly.

In some embodiments, a determination of parameter of the filtering process is applied to at least one of: an in-loop filtering tool, a prediction tool, a pre-processing filtering, or a post-processing filtering.

In some embodiments, the current video unit comprises one of: a sequence, a picture, a sub-picture, a slice, a tile, a coding tree unit (CTU) , a CTU row, groups of CTU, a coding unit, a prediction unit, a transform unit, a coding tree block (CTB) , a coding block, a prediction block, a transform block, or a region containing more than one luma or chroma sample or pixel.

In some embodiments, information regarding whether to and/or how to apply the method is indicated in the bitstream. In some embodiments, the information is indicated at one of: a sequence level, a group of pictures level, a picture level, a slice level, a tile group level, a sequence header, a picture header, a sequence parameter set (SPS) , a video parameter set (VPS) , a dependency parameter set (DPS) , decoding capability information (DCI) , a picture parameter set (PPS) , an adaptation parameter sets (APS) , a slice header, or a tile group header.

In some embodiments, the information is indicated at one of: a prediction block (PB) , a transform block (TB) , a coding block (CB) , a prediction unit (PU) , a transform unit (TU) , a coding unit (CU) , a virtual pipeline data unit (VPDU) , a coding tree unit (CTU) , a CTU row, a slice, a tile, a sub-picture, or a region containing more than one sample or pixel.

In some embodiments, information regarding whether to and/or how to apply the method 1600 is based on coded information. The coded information comprises at least one of: a block size, a color format, a single and/or dual tree partitioning, a color component, a slice type, or a picture type.

In some embodiments, the conversion comprises encoding the current video unit into the bitstream.

In some embodiments, the conversion comprises decoding the current video unit from the bitstream.

According to further embodiments of the present disclosure, a non-transitory computer-readable recording medium is provided. The non-transitory computer-readable recording medium stores a bitstream of a video which is generated by a method performed by an apparatus for video processing. In the method, a plurality of samples of a current video unit of the video are determined. At least a partial of the plurality of samples is determined based on at least one inter prediction. A filtering process is applied to the plurality of samples to obtain a plurality of refined samples. The bitstream is generated based on based on the plurality of refined samples.

According to still further embodiments of the present disclosure, a method for storing bitstream of a video is provided. In the method, a plurality of samples of a current video unit of the video are determined. At least a partial of the plurality of samples is determined based on at least one inter prediction. A filtering process is applied to the plurality of samples to obtain a plurality of refined samples. The bitstream is generated based on based on the plurality of refined samples. The bitstream is stored in a non-transitory computer-readable recording medium.

Implementations of the present disclosure can be described in view of the following clauses, the features of which can be combined in any reasonable manner.

Clause 1. A method for video processing, comprising: determining, for a conversion between a current video unit of a video and a bitstream of the video, a plurality of samples of the current video unit, at least a partial of the plurality of samples being determined based on at least one inter prediction; applying a filtering process to the plurality of samples to obtain a plurality of refined sample; and performing the conversion based on the plurality of refined samples.

Clause 2. The method of clause 1, wherein the filtering process comprises at least one of: a bilateral filtering (BF) , or a deblocking filtering.

Clause 3. The method of clause 1 or 2, wherein at least one parameter is included in the bitstream to determine the filtering process, and the filtering process comprises at least one of: a sample adaptive offset (SAO) , a cross-component SAO (CCSAO) , an adaptive loop filter (ALF) , or a cross-component ALF (CCALF) .

Clause 4. The method of any of clauses 1-3, wherein the plurality of refined samples of the current video unit is used for coding at least one succeeding video unit in a same picture of the current video unit, the current video unit comprising a current inter block.

Clause 5. The method of clause 4, wherein the at least one succeeding video unit comprises an intra block succeeding the current inter block in a coding order, and the plurality of refined samples are used as at least one of: neighboring samples, reference samples or template samples for the intra block.

Clause 6. The method of clause 4, wherein the at least one succeeding video unit comprises an intra block copy (IBC) block succeeding the current inter block in a coding order, and the plurality of refined samples are used as reference samples for the IBC block.

Clause 7. The method of clause 4, wherein the at least one succeeding video unit comprises an inter block succeeding the current inter block in a coding order, and the plurality of refined samples are used as template samples for the inter block.

Clause 8. The method of any of clauses 1-7, wherein the filtering process is based on neighboring samples of the current video unit, the neighboring samples comprising predicted neighboring samples or reconstructed neighboring samples.

Clause 9. The method of clause 8, wherein the neighboring samples comprises adjacent neighboring samples and/or non-adjacent neighboring samples.

Clause 10. The method of clause 8 or 9, wherein the filtering process comprises at least one of: a Position Dependent Intra Prediction Combination (PDPC) , or a gradient PDPC.

Clause 11. The method of any of clauses 1-10, wherein at least one parameter of the filtering process is predefined, or indicated in the bitstream, or determined during the conversion.

Clause 12. The method of clause 11, wherein an approach for determining the at least one parameter is same with that of a coding tool, the coding tool comprising at least one of: a Cross-Component Linear Model (CCLM) , a Multi-Model Linear Model (MMLM) , a Cross-Component Chroma Mapping (CCCM) , or a local illumination compensation (LIC) .

Clause 13. The method of any of clauses 1-12, wherein the plurality of samples are refined by the filtering process and a coding tool, the filtering process being applied before the coding tool or after the coding tool, wherein the coding tool comprises at least one of: an overlapped block motion compensation (OBMC) or a local illumination compensation (LIC) .

Clause 14. The method of any of clauses 1-13, wherein the plurality of samples comprises a plurality of inter prediction samples, and the plurality of inter prediction samples belong to one of: a video unit, a coding unit, a prediction unit, a sub prediction unit, a transform unit, a picture, a slice, a tile, a block, or a region of the video.

Clause 15. The method of clause 14, wherein the plurality of inter prediction samples are filtered by a bilateral filtering based on at least one of: coded information, or statistic information.

Clause 16. The method of clause 15, wherein a filtering result of the bilateral filtering is determined by: where I_filtered denotes a filtered luma or chroma sample and I_C denotes an unmodified luma or chroma sample that locates at a central of a filtering shape, Δ denotes a difference between corresponding reference sample and unmodified central sample, Ωdenotes a sum of vertical and horizontal distance between reference sample and central sample, n denotes a total number of samples inside the filtering shape, e denotes a strength factor, and μ (Δ, Ω) denotes a function for determining a filtering weight of each position in the filtering shape.

Clause 17. The method of clause 16, wherein the function comprises: wherein σ_d and σ_r are two parameters for filtering.

Clause 18. The method of clause 16, wherein the function μ (Δ, Ω) is baked into a look-up table.

Clause 19. The method of clause 16, wherein different samples or positions of the plurality of inter prediction samples use uniform parameters or look-up table.

Clause 20. The method of clause 16, wherein different samples or positions of the plurality of inter prediction samples use different parameters or look-up tables.

Clause 21. The method of clause 17, wherein at least one parameter for the bilateral filtering is predefined, or searched, or determined on-the-fly, or indicated in the bitstream, the at least one parameter comprises σ_d and σ_r.

Clause 22. The method of clause 21, wherein the at least one parameter is determined based on at least one of: a coding mode, a size or coded information of the current video unit, wherein the coded information comprises at least one of: a variance of samples, or a mean absolute difference of samples.

Clause 23. The method of clause 21, wherein the at least one parameter is indicated from an encoder to a decoder.

Clause 24. The method of clause 16, wherein the strength factor is predefined, or searched, or determined on-the-fly, or indicated in the bitstream.

Clause 25. The method of clause 24, wherein the strength factor is determined based on at least one of: a coding mode, a size or coding information of the current video unit.

Clause 26. The method of clause 25, wherein the strength factor is determined based on a luma size of the current video unit, or a chroma size of the current video unit.

Clause 27. The method of clause 26, wherein the strength factor is determined by one of: max (width_luma, height_luma) , min (width_luma, height_luma) , width_luma×height_luma , max (width_chroma, height_chroma) , min (width_chroma, height_chroma) , or width_chroma×height_chroma, wherein width_luma denotes a luma width, height_luma denotes a luma height, width_chroma denotes a chroma width, and height_chroma denotes a chroma height.

Clause 28. The method of clause 25, wherein the strength factor is indicated from an encoder to a decoder.

Clause 29. The method of any of clauses 1-28, wherein the filtering process is implemented by operations on integers.

Clause 30. The method of clause 29, wherein variables is left-shifted and/or right-shifted before the filtering process, or in the filtering process, or after the filtering process.

Clause 31. The method of any of clauses 1-30, wherein the filtering process is applied to inter prediction samples before generating an inter reconstruction based on the inter prediction samples.

Clause 32. The method of clause 31, wherein the filtering process is applied to at least one of: a luma related inter mode, a chroma related inter mode, a uni-predictive inter mode, a bi-predictive inter mode, an inter merge mode, an inter advanced motion vector prediction (AMVP) mode, an AMVP merge mode, a combined inter and intra prediction (CIIP) mode, a local illumination compensation (LIC) mode, a bi-directional optical flow (BDOF) mode, an affine mode, a (DMVR) mode, a multiple hypothesis prediction (MHP) mode, an Overlapped Block Motion Compensation (OBMC) mode, a Geometric Partitioning Mode (GPM) mode, an inter-Cross-Component Chroma Mapping (CCCM) mode, a Bi-prediction with coding unit-level weight (BCW) mode, an inter cross-component prediction (CCP) merge mode, a template matching based inter mode, or a further inter related mode.

Clause 33. The method of any of clauses 1-32, wherein the filtering process is applied to a Luma Mapping with Chroma Scaling (LMCS) enabled prediction samples before generating an inter reconstruction based on the prediction samples, wherein in an original domain, a LMCS mapping is not performed, and in a mapped domain, the LMCS mapping is performed.

Clause 34. The method of clause 33, wherein the filtering process is applied to prediction samples inside the original domain, and/or prediction samples inside the mapped domain.

Clause 35. The method of clause 33 or 34, wherein inter prediction samples are inversed mapped to the original domain before being filtered.

Clause 36. The method of clause 33 or 34, wherein inter prediction samples are mapped to LMCS domain after being filtered.

Clause 37. The method of clause 33 or 34, wherein inter prediction samples are filtered by the filtering process without forward or inverse mapping of LMCS.

Clause 38. The method of clause 33 or 34, wherein inter prediction samples are filtered by the filtering process before being mapped into LMCS domain.

Clause 39. The method of clause 33 or 34, wherein inter prediction samples are filtered by the filtering process after being mapped into LMCS domain.

Clause 40. The method of any of clauses 1-39, wherein the filtering process is applied to a plurality of color components of the prediction samples in different manners or in a same manner.

Clause 41. The method of clause 40, wherein a same filtering process is applied to the plurality of color components.

Clause 42. The method of clause 40, wherein different filtering processes are applied to the plurality of color components.

Clause 43. The method of any of clauses 1-42, wherein the filtering process is applied to only luma component, or only chroma component.

Clause 44. The method of any of clauses 1-43, wherein the filtering process is applied to a luma related inter mode, or a chroma related inter mode.

Clause 45. The method of any of clauses 1-43, wherein the filtering process is applied to a cross-component related inter mode, or jointly applied to luma and chroma related inter mode.

Clause 46. The method of any of clauses 1-43, wherein the filtering process is applied to a fusion based inter mode, and/or a RGB related inter mode.

Clause 47. The method of any of clauses 1-46, wherein the filtering process is applied to different coding areas of prediction, wherein the coding areas comprises at least one of: a coding unit, a prediction unit, a sub prediction unit, a transform unit, a coding tree unit, a coding tree unit row, a slice, a tile, a picture, or other coding unit.

Clause 48. The method of any of clauses 1-47, wherein the filtering process is applied to a plurality of coding types of prediction, wherein the plurality of coding types comprise at least one of: a prediction with a quantization parameter greater than a threshold, a prediction with a quantization parameter lower than a threshold, a prediction with a temporal identifier greater than a threshold, a prediction with a temporal identifier lower than a threshold, a prediction in P slice or tile or picture or sub-picture, a prediction in B slice or tile or picture or sub-picture, a prediction in low-delay picture, or prediction with a first coding mode.

Clause 49. The method of clause 48, wherein the first coding mode comprises at least one of: an affine mode, a subblock-based Temporal Motion Vector Prediction (TMVP) , a DMVR, a BDOF, a GPM, or a CIIP.

Clause 50. The method of any of clauses 1-49, wherein whether to and/or how to apply the filtering process to inter prediction samples is based on at least one condition, wherein the at least one condition is based on at least one of: a block size, a block shape, a prediction sample number of a current block, a picture size, a slice size, a tile size, texture strength related information, template information, a coding tool, or a picture type.

Clause 51. The method of clause 50, wherein the at least one condition comprises one of: a width or height of the current block being greater than a threshold, or the width or height of the current block being less than a threshold.

Clause 52. The method of clause 50, wherein the at least one condition comprises one of: a total sample number of the current block being greater than a threshold, or the total sample number of the current block being less than a threshold.

Clause 53. The method of clause 50, wherein the at least one condition comprises one of: a width being greater than or equal to a height, a ratio of the width to the height being high than or equal to a threshold, a ratio of the width to the height being lower than or equal to a threshold, the height is greater than or equal to the width, a ratio of the height to the width being high than or equal to a threshold, or a ratio of the height to the width being lower than or equal to a threshold.

Clause 54. The method of clause 50, wherein the at least one condition comprises one of: the prediction sample number of current block being greater than a threshold, or the prediction sample number of current block being less than a threshold.

Clause 55. The method of clause 50, wherein the at least one condition comprises one of: a width or a height of a current picture or a current slice or a current tile being greater than a threshold, or a width or a height of a current picture or a current slice or a current tile being less than a threshold, a total sample number of a current picture or a current slice or a current tile being greater than a threshold, or a total sample number of a current picture or a current slice or a current tile being less than a threshold.

Clause 56. The method of clause 50, wherein the at least one condition comprises one of: a variance of prediction samples being greater than a threshold, a variance of prediction samples being less than a threshold, a gradient of prediction samples being greater than a threshold, a gradient of prediction samples being less than a threshold, a valid band number of prediction samples being greater than a threshold, a valid band number of prediction samples being less than a threshold, other texture related information of prediction samples being greater than a threshold, or other texture related information of prediction samples being less than a threshold.

Clause 57. The method of clause 50, wherein the at least one condition comprises one of: a template cost of the current block being greater than a threshold, or a template cost of the current block being less than a threshold.

Clause 58. The method of clause 50, wherein the at least one condition comprises one of: the coding tool being used, or the coding tool being not used.

Clause 59. The method of clause 50, wherein the filtering process is applied differently for different coding tool sets.

Clause 60. The method of clause 50, wherein the at least one condition comprises the picture type being a low delay or non-low delay picture.

Clause 61. The method of clause 50, wherein the picture type is based on whether backward inter prediction is applied for a picture, wherein the backward inter prediction refers to a current picture comprising a reference picture whose picture order count being larger than a picture order count of the current picture.

Clause 62. The method of clause 61, wherein a picture with backward inter-prediction comprises a non-low delay picture, and a picture without backward inter-prediction comprises a low delay picture.

Clause 63. The method of any of clauses 1-62, wherein a padding process is applied to inter prediction sampled before being filtered.

Clause 64. The method of clause 63, wherein the padding process comprises at least one of: a mirrored padding, or a duplicated padding.

Clause 65. The method of clause 63, wherein reconstructed samples from at least one neighbor block is used for filtering boundary prediction samples of the current video unit.

Clause 66. The method of clause 63, wherein reconstructed samples from at least one neighbor block is used for padding.

Clause 67. The method of clause 63, wherein prediction samples from the current video unit are used for padding.

Clause 68. The method of any of clauses 1-67, wherein for a bi-prediction, the filtering process is applied to at least one prediction before the at least one prediction being used to generate the bi-prediction.

Clause 69. The method of any of clauses 1-67, wherein the filtering process is applied to a bi-prediction generated based on at least one prediction.

Clause 70. The method of any of clauses 1-69, wherein for a combined prediction, the filtering process is applied to at least one prediction before the at least one prediction being used to generate the combined prediction.

Clause 71. The method of any of clauses 1-67, wherein the filtering process is applied to a combined prediction generated based on at least one prediction.

Clause 72. The method of clause 70 or 71, wherein the combined prediction comprises a CIIP or GPM.

Clause 73. The method of any of clauses 1-72, wherein a plurality of filtering processes are applied to an inter prediction of the current video unit.

Clause 74. The method of clause 73, wherein a first filtering process is applied to the inter prediction to obtain a first filtering result, and a second filtering process is applied to the first filtering result.

Clause 75. The method of any of clauses 1-72, wherein the filtering process is applied to at least one inter prediction sample before determining an inter reconstruction.

Clause 76. The method of clause 75, wherein the filtering process is applied to all inter prediction samples before determining the inter reconstruction.

Clause 77. The method of clause 75, wherein the filtering process is applied to a partial of the inter prediction samples before determining the inter reconstruction.

Clause 78. The method of clause 75, wherein whether the filtering process is applied to an inter prediction sample is based on at least one metric, wherein the at least one metric comprises at least one of:a boundary strength, a boundary gradient, a difference between a sample value of a prediction sample and another sample, or a difference between a sample value of a prediction sample and an average or maximum or minimum value of a plurality of samples.

Clause 79. The method of any of clauses 1-78, wherein whether to and/or how to apply the filtering process is based on coding information of at least one prediction sample, wherein the coding information comprises whether at least one prediction sample is coded with a first coding mode.

Clause 80. The method of clause 79, wherein the first coding mode comprises at least one of: a deblocking, a SAO, a CCSAO, a bilateral filtering, an ALF, a CCAFL, a LIC, an OBMC, a subblock OBMC, an intra mode, an inter mode, or a bi-prediction.

Clause 81. The method of clause 79 or 80, wherein the first coding mode is applied to the at least one prediction sample, the filtering process is not applied to a current prediction sample or all prediction samples before generating the inter reconstruction.

Clause 82. The method of any of clauses 1-81, wherein the filtering process is applied to template samples before performing a template matching based on the template samples.

Clause 83. The method of clause 82, wherein the template samples are used in at least one of: a template matching (TM) AMVP mode, a TM merge mode, an Adaptive Reordering of Merge Candidates with Template Matching (TM ARMC) , a GPM split mode reordering, a TM OBMC, a TM GPM Merge Mode with Motion Vector Difference (MMVD) , a TM subblock refinement mode, a TM Reordering for MMVD mode, a TM reordering for Affine MMVD, a TM block level reference picture reordering, a TM BCW index derivation, a TM LIC flag derivation, or a template used in a further template matching based tool.

Clause 84. The method of any of clauses 1-83, wherein whether to and/or how to apply the method is determined conditionally, or indicated in the bitstream.

Clause 85. The method of any of clauses 1-84, wherein a first syntax element (SE) is indicated in the bitstream to indicate whether the method is applied.

Clause 86. The method of clause 85, wherein the first SE comprises a flag.

Clause 87. The method of clause 85, wherein the first SE is coded with at least one context model, or is bypass coded.

Clause 88. The method of clause 85, wherein the first SE is coded if the current video unit is coded with a coding mode.

Clause 89. The method of any of clauses 1-88, wherein the method is used in at least one of: a post-processing, or a pre-processing.

Clause 90. The method of any of clauses 1-89, wherein a determination of parameter of the filtering process is applied to at least one of: an in-loop filtering tool, a prediction tool, a pre-processing filtering, or a post-processing filtering.

Clause 91. The method of any of clauses 1-90, wherein the current video unit comprises one of: a sequence, a picture, a sub-picture, a slice, a tile, a coding tree unit (CTU) , a CTU row, groups of CTU, a coding unit, a prediction unit, a transform unit, a coding tree block (CTB) , a coding block, a prediction block, a transform block, or a region containing more than one luma or chroma sample or pixel.

Clause 92. The method of any of clauses 1-91, wherein information regarding whether to and/or how to apply the method is indicated in the bitstream.

Clause 93. The method of clause 92, wherein the information is indicated at one of: a sequence level, a group of pictures level, a picture level, a slice level, a tile group level, a sequence header, a picture header, a sequence parameter set (SPS) , a video parameter set (VPS) , a dependency parameter set (DPS) , decoding capability information (DCI) , a picture parameter set (PPS) , an adaptation parameter sets (APS) , a slice header, or a tile group header.

Clause 94. The method of clause 92, wherein the information is indicated at one of: a prediction block (PB) , a transform block (TB) , a coding block (CB) , a prediction unit (PU) , a transform unit (TU) , a coding unit (CU) , a virtual pipeline data unit (VPDU) , a coding tree unit (CTU) , a CTU row, a slice, a tile, a sub-picture, or a region containing more than one sample or pixel.

Clause 95. The method of any of clauses 1-91, wherein information regarding whether to and/or how to apply the method is based on coded information, the coded information comprising at least one of:a block size, a color format, a single and/or dual tree partitioning, a color component, a slice type, or a picture type.

Clause 96. The method of any of clauses 1-95, wherein the conversion comprises encoding the current video unit into the bitstream.

Clause 97. The method of any of clauses 1-95, wherein the conversion comprises decoding the current video unit from the bitstream.

Clause 98. An apparatus for video processing comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to perform a method in accordance with any of clauses 1-97.

Clause 99. A non-transitory computer-readable storage medium storing instructions that cause a processor to perform a method in accordance with any of clauses 1-97.

Clause 100. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by an apparatus for video processing, wherein the method comprises: determining a plurality of samples of a current video unit of the video, at least a partial of the plurality of samples being determined based on at least one inter prediction; applying a filtering process to the plurality of samples to obtain a plurality of refined samples; and generating the bitstream based on based on the plurality of refined samples.

Clause 101. A method for storing a bitstream of a video, comprising: determining a plurality of samples of a current video unit of the video, at least a partial of the plurality of samples being determined based on at least one inter prediction; applying a filtering process to the plurality of samples to obtain a plurality of refined samples; generating the bitstream based on based on the plurality of refined samples; and storing the bitstream in a non-transitory computer-readable recording medium.
Example Device

Fig. 17 illustrates a block diagram of a computing device 1700 in which various embodiments of the present disclosure can be implemented. The computing device 1700 may be implemented as or included in the source device 110 (or the video encoder 114 or 200) or the destination device 120 (or the video decoder 124 or 300) .

It would be appreciated that the computing device 1700 shown in Fig. 17 is merely for purpose of illustration, without suggesting any limitation to the functions and scopes of the embodiments of the present disclosure in any manner.

As shown in Fig. 17, the computing device 1700 includes a general-purpose computing device 1700. The computing device 1700 may at least comprise one or more processors or processing units 1710, a memory 1720, a storage unit 1730, one or more communication units 1740, one or more input devices 1750, and one or more output devices 1760.

In some embodiments, the computing device 1700 may be implemented as any user terminal or server terminal having the computing capability. The server terminal may be a server, a large-scale computing device or the like that is provided by a service provider. The user terminal may for example be any type of mobile terminal, fixed terminal, or portable terminal, including a mobile phone, station, unit, device, multimedia computer, multimedia tablet, Internet node, communicator, desktop computer, laptop computer, notebook computer, netbook computer, tablet computer, personal communication system (PCS) device, personal navigation device, personal digital assistant (PDA) , audio/video player, digital camera/video camera, positioning device, television receiver, radio broadcast receiver, E-book device, gaming device, or any combination thereof, including the accessories and peripherals of these devices, or any combination thereof. It would be contemplated that the computing device 1700 can support any type of interface to a user (such as “wearable” circuitry and the like) .

The processing unit 1710 may be a physical or virtual processor and can implement various processes based on programs stored in the memory 1720. In a multi-processor system, multiple processing units execute computer executable instructions in parallel so as to improve the parallel processing capability of the computing device 1700. The processing unit 1710 may also be referred to as a central processing unit (CPU) , a microprocessor, a controller or a microcontroller.

The computing device 1700 typically includes various computer storage medium. Such medium can be any medium accessible by the computing device 1700, including, but not limited to, volatile and non-volatile medium, or detachable and non-detachable medium. The memory 1720 can be a volatile memory (for example, a register, cache, Random Access Memory (RAM) ) , a non-volatile memory (such as a Read-Only Memory (ROM) , Electrically Erasable Programmable Read-Only Memory (EEPROM) , or a flash memory) , or any combination thereof. The storage unit 1730 may be any detachable or non-detachable medium and may include a machine-readable medium such as a memory, flash memory drive, magnetic disk or another other media, which can be used for storing information and/or data and can be accessed in the computing device 1700.

The computing device 1700 may further include additional detachable/non-detachable, volatile/non-volatile memory medium. Although not shown in Fig. 17, it is possible to provide a magnetic disk drive for reading from and/or writing into a detachable and non-volatile magnetic disk and an optical disk drive for reading from and/or writing into a detachable non-volatile optical disk. In such cases, each drive may be connected to a bus (not shown) via one or more data medium interfaces.

The communication unit 1740 communicates with a further computing device via the communication medium. In addition, the functions of the components in the computing device 1700 can be implemented by a single computing cluster or multiple computing machines that can communicate via communication connections. Therefore, the computing device 1700 can operate in a networked environment using a logical connection with one or more other servers, networked personal computers (PCs) or further general network nodes.

The input device 1750 may be one or more of a variety of input devices, such as a mouse, keyboard, tracking ball, voice-input device, and the like. The output device 1760 may be one or more of a variety of output devices, such as a display, loudspeaker, printer, and the like. By means of the communication unit 1740, the computing device 1700 can further communicate with one or more external devices (not shown) such as the storage devices and display device, with one or more devices enabling the user to interact with the computing device 1700, or any devices (such as a network card, a modem and the like) enabling the computing device 1700 to communicate with one or more other computing devices, if required. Such communication can be performed via input/output (I/O) interfaces (not shown) .

In some embodiments, instead of being integrated in a single device, some or all components of the computing device 1700 may also be arranged in cloud computing architecture. In the cloud computing architecture, the components may be provided remotely and work together to implement the functionalities described in the present disclosure. In some embodiments, cloud computing provides computing, software, data access and storage service, which will not require end users to be aware of the physical locations or configurations of the systems or hardware providing these services. In various embodiments, the cloud computing provides the services via a wide area network (such as Internet) using suitable protocols. For example, a cloud computing provider provides applications over the wide area network, which can be accessed through a web browser or any other computing components. The software or components of the cloud computing architecture and corresponding data may be stored on a server at a remote position. The computing resources in the cloud computing environment may be merged or distributed at locations in a remote data center. Cloud computing infrastructures may provide the services through a shared data center, though they behave as a single access point for the users. Therefore, the cloud computing architectures may be used to provide the components and functionalities described herein from a service provider at a remote location. Alternatively, they may be provided from a conventional server or installed directly or otherwise on a client device.

The computing device 1700 may be used to implement video encoding/decoding in embodiments of the present disclosure. The memory 1720 may include one or more video coding modules 1725 having one or more program instructions. These modules are accessible and executable by the processing unit 1710 to perform the functionalities of the various embodiments described herein.

In the example embodiments of performing video encoding, the input device 1750 may receive video data as an input 1770 to be encoded. The video data may be processed, for example, by the video coding module 1725, to generate an encoded bitstream. The encoded bitstream may be provided via the output device 1760 as an output 1780.

In the example embodiments of performing video decoding, the input device 1750 may receive an encoded bitstream as the input 1770. The encoded bitstream may be processed, for example, by the video coding module 1725, to generate decoded video data. The decoded video data may be provided via the output device 1760 as the output 1780.

While this disclosure has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present application as defined by the appended claims. Such variations are intended to be covered by the scope of this present application. As such, the foregoing description of embodiments of the present application is not intended to be limiting.

Claims

A method for video processing, comprising:

determining, for a conversion between a current video unit of a video and a bitstream of the video, a plurality of samples of the current video unit, at least a partial of the plurality of samples being determined based on at least one inter prediction;

applying a filtering process to the plurality of samples to obtain a plurality of refined samples; and

performing the conversion based on the plurality of refined samples.
The method of claim 1, wherein the filtering process comprises at least one of: a bilateral filtering (BF) , or a deblocking filtering.
The method of claim 1 or 2, wherein at least one parameter is included in the bitstream to determine the filtering process, and the filtering process comprises at least one of: a sample adaptive offset (SAO) , a cross-component SAO (CCSAO) , an adaptive loop filter (ALF) , or a cross-component ALF (CCALF) .
The method of any of claims 1-3, wherein the plurality of refined samples of the current video unit is used for coding at least one succeeding video unit in a same picture of the current video unit, the current video unit comprising a current inter block.
The method of claim 4, wherein the at least one succeeding video unit comprises an intra block succeeding the current inter block in a coding order, and the plurality of refined samples are used as at least one of: neighboring samples, reference samples or template samples for the intra block.
The method of claim 4, wherein the at least one succeeding video unit comprises an intra block copy (IBC) block succeeding the current inter block in a coding order, and the plurality of refined samples are used as reference samples for the IBC block.
The method of claim 4, wherein the at least one succeeding video unit comprises an inter block succeeding the current inter block in a coding order, and the plurality of refined samples are used as template samples for the inter block.
The method of any of claims 1-7, wherein the filtering process is based on neighboring samples of the current video unit, the neighboring samples comprising predicted neighboring samples or reconstructed neighboring samples.
The method of claim 8, wherein the neighboring samples comprises adjacent neighboring samples and/or non-adjacent neighboring samples.
The method of claim 8 or 9, wherein the filtering process comprises at least one of: a Position Dependent Intra Prediction Combination (PDPC) , or a gradient PDPC.
The method of any of claims 1-10, wherein at least one parameter of the filtering process is predefined, or indicated in the bitstream, or determined during the conversion.
The method of claim 11, wherein an approach for determining the at least one parameter is same with that of a coding tool, the coding tool comprising at least one of: a Cross-Component Linear Model (CCLM) , a Multi-Model Linear Model (MMLM) , a Cross-Component Chroma Mapping (CCCM) , or a local illumination compensation (LIC) .
The method of any of claims 1-12, wherein the plurality of samples are refined by the filtering process and a coding tool, the filtering process being applied before the coding tool or after the coding tool, wherein the coding tool comprises at least one of: an overlapped block motion compensation (OBMC) or a local illumination compensation (LIC) .
The method of any of claims 1-13, wherein the plurality of samples comprises a plurality of inter prediction samples, and the plurality of inter prediction samples belong to one of: a video unit, a coding unit, a prediction unit, a sub prediction unit, a transform unit, a picture, a slice, a tile, a block, or a region of the video.
The method of claim 14, wherein the plurality of inter prediction samples are filtered by a bilateral filtering based on at least one of: coded information, or statistic information.
The method of claim 15, wherein a filtering result of the bilateral filtering is determined by:

where I_filtered denotes a filtered luma or chroma sample and I_C denotes an unmodified luma or chroma sample that locates at a central of a filtering shape, Δ denotes a difference between corresponding reference sample and unmodified central sample, Ω denotes a sum of vertical and horizontal distance between reference sample and central sample, n denotes a total number of samples inside the filtering shape, e denotes a strength factor, and μ (Δ, Ω) denotes a function for determining a filtering weight of each position in the filtering shape.
The method of claim 16, wherein the function μ (Δ, Ω) comprises:

wherein σ_d and σ_r are two parameters for filtering.
The method of claim 16, wherein the function μ (Δ, Ω) is baked into a look-up table.
The method of claim 16, wherein different samples or positions of the plurality of inter prediction samples use uniform parameters or look-up table.
The method of claim 16, wherein different samples or positions of the plurality of inter prediction samples use different parameters or look-up tables.
The method of claim 17, wherein at least one parameter for the bilateral filtering is predefined, or searched, or determined on-the-fly, or indicated in the bitstream, the at least one parameter comprises σ_d and σ_r.
The method of claim 21, wherein the at least one parameter is determined based on at least one of: a coding mode, a size or coded information of the current video unit, wherein the coded information comprises at least one of: a variance of samples, or a mean absolute difference of samples.
The method of claim 21, wherein the at least one parameter is indicated from an encoder to a decoder.
The method of claim 16, wherein the strength factor is predefined, or searched, or determined on-the-fly, or indicated in the bitstream.
The method of claim 24, wherein the strength factor is determined based on at least one of: a coding mode, a size or coding information of the current video unit.
The method of claim 25, wherein the strength factor is determined based on a luma size of the current video unit, or a chroma size of the current video unit.
The method of claim 26, wherein the strength factor is determined by one of:
max (width_luma, height_luma) ,
min (width_luma, height_luma) ,
width_luma×height_luma,
max (width_chroma, height_chroma) ,
min (width_chroma, height_chroma) ,
width_chroma×height_chroma,

wherein width_luma denotes a luma width, height_luma denotes a luma height, width_chroma denotes a chroma width, and height_chroma denotes a chroma height.
The method of claim 25, wherein the strength factor is indicated from an encoder to a decoder.
The method of any of claims 1-28, wherein the filtering process is implemented by operations on integers.
The method of claim 29, wherein variables is left-shifted and/or right-shifted before the filtering process, or in the filtering process, or after the filtering process.
The method of any of claims 1-30, wherein the filtering process is applied to inter prediction samples before generating an inter reconstruction based on the inter prediction samples.
The method of claim 31, wherein the filtering process is applied to at least one of:

a luma related inter mode, a chroma related inter mode, a uni-predictive inter mode, a bi-predictive inter mode, an inter merge mode, an inter advanced motion vector prediction (AMVP) mode, an AMVP merge mode, a combined inter and intra prediction (CIIP) mode, a local illumination compensation (LIC) mode, a bi-directional optical flow (BDOF) mode, an affine mode, a (DMVR) mode, a multiple hypothesis prediction (MHP) mode, an Overlapped Block Motion Compensation (OBMC) mode, a Geometric Partitioning Mode (GPM) mode, an inter-Cross-Component Chroma Mapping (CCCM) mode, a Bi-prediction with coding unit-level weight (BCW) mode, an inter cross-component prediction (CCP) merge mode, a template matching based inter mode, or a further inter related mode.
The method of any of claims 1-32, wherein the filtering process is applied to a Luma Mapping with Chroma Scaling (LMCS) enabled prediction samples before generating an inter reconstruction based on the prediction samples,

wherein in an original domain, a LMCS mapping is not performed, and in a mapped domain, the LMCS mapping is performed.
The method of claim 33, wherein the filtering process is applied to prediction samples inside the original domain, and/or prediction samples inside the mapped domain.
The method of claim 33 or 34, wherein inter prediction samples are inversed mapped to the original domain before being filtered.
The method of claim 33 or 34, wherein inter prediction samples are mapped to LMCS domain after being filtered.
The method of claim 33 or 34, wherein inter prediction samples are filtered by the filtering process without forward or inverse mapping of LMCS.
The method of claim 33 or 34, wherein inter prediction samples are filtered by the filtering process before being mapped into LMCS domain.
The method of claim 33 or 34, wherein inter prediction samples are filtered by the filtering process after being mapped into LMCS domain.
The method of any of claims 1-39, wherein the filtering process is applied to a plurality of color components of the prediction samples in different manners or in a same manner.
The method of claim 40, wherein a same filtering process is applied to the plurality of color components.
The method of claim 40, wherein different filtering processes are applied to the plurality of color components.
The method of any of claims 1-42, wherein the filtering process is applied to only luma component, or only chroma component.
The method of any of claims 1-43, wherein the filtering process is applied to a luma related inter mode, or a chroma related inter mode.
The method of any of claims 1-43, wherein the filtering process is applied to a cross-component related inter mode, or jointly applied to luma and chroma related inter mode.
The method of any of claims 1-43, wherein the filtering process is applied to a fusion based inter mode, and/or a RGB related inter mode.
The method of any of claims 1-46, wherein the filtering process is applied to different coding areas of prediction,

wherein the coding areas comprises at least one of: a coding unit, a prediction unit, a sub prediction unit, a transform unit, a coding tree unit, a coding tree unit row, a slice, a tile, a picture, or other coding unit.
The method of any of claims 1-47, wherein the filtering process is applied to a plurality of coding types of prediction,

wherein the plurality of coding types comprise at least one of: a prediction with a quantization parameter greater than a threshold, a prediction with a quantization parameter lower than a threshold, a prediction with a temporal identifier greater than a threshold, a prediction with a temporal identifier lower than a threshold, a prediction in P slice or tile or picture or sub-picture, a prediction in B slice or tile or picture or sub-picture, a prediction in low-delay picture, or prediction with a first coding mode.
The method of claim 48, wherein the first coding mode comprises at least one of: an affine mode, a subblock-based Temporal Motion Vector Prediction (TMVP) , a DMVR, a BDOF, a GPM, or a CIIP.
The method of any of claims 1-49, wherein whether to and/or how to apply the filtering process to inter prediction samples is based on at least one condition,

wherein the at least one condition is based on at least one of: a block size, a block shape, a prediction sample number of a current block, a picture size, a slice size, a tile size, texture strength related information, template information, a coding tool, or a picture type.
The method of claim 50, wherein the at least one condition comprises one of: a width or height of the current block being greater than a threshold, or the width or height of the current block being less than a threshold.
The method of claim 50, wherein the at least one condition comprises one of: a total sample number of the current block being greater than a threshold, or the total sample number of the current block being less than a threshold.
The method of claim 50, wherein the at least one condition comprises one of:

a width being greater than or equal to a height,

a ratio of the width to the height being high than or equal to a threshold,

a ratio of the width to the height being lower than or equal to a threshold,

the height is greater than or equal to the width,

a ratio of the height to the width being high than or equal to a threshold, or

a ratio of the height to the width being lower than or equal to a threshold.
The method of claim 50, wherein the at least one condition comprises one of:

the prediction sample number of current block being greater than a threshold, or

the prediction sample number of current block being less than a threshold.
The method of claim 50, wherein the at least one condition comprises one of:

a width or a height of a current picture or a current slice or a current tile being greater than a threshold,

a width or a height of a current picture or a current slice or a current tile being less than a threshold,

a total sample number of a current picture or a current slice or a current tile being greater than a threshold, or

a total sample number of a current picture or a current slice or a current tile being less than a threshold.
The method of claim 50, wherein the at least one condition comprises one of:

a variance of prediction samples being greater than a threshold,

a variance of prediction samples being less than a threshold,

a gradient of prediction samples being greater than a threshold,

a gradient of prediction samples being less than a threshold,

a valid band number of prediction samples being greater than a threshold,

a valid band number of prediction samples being less than a threshold,

other texture related information of prediction samples being greater than a threshold, or

other texture related information of prediction samples being less than a threshold.
The method of claim 50, wherein the at least one condition comprises one of:

a template cost of the current block being greater than a threshold, or

a template cost of the current block being less than a threshold.
The method of claim 50, wherein the at least one condition comprises one of:

the coding tool being used, or

the coding tool being not used.
The method of claim 50, wherein the filtering process is applied differently for different coding tool sets.
The method of claim 50, wherein the at least one condition comprises the picture type being a low delay or non-low delay picture.
The method of claim 50, wherein the picture type is based on whether backward inter prediction is applied for a picture, wherein the backward inter prediction refers to a current picture comprising a reference picture whose picture order count being larger than a picture order count of the current picture.
The method of claim 61, wherein a picture with backward inter-prediction comprises a non-low delay picture, and a picture without backward inter-prediction comprises a low delay picture.
The method of any of claims 1-62, wherein a padding process is applied to inter prediction sampled before being filtered.
The method of claim 63, wherein the padding process comprises at least one of: a mirrored padding, or a duplicated padding.
The method of claim 63, wherein reconstructed samples from at least one neighbor block is used for filtering boundary prediction samples of the current video unit.
The method of claim 63, wherein reconstructed samples from at least one neighbor block is used for padding.
The method of claim 63, wherein prediction samples from the current video unit are used for padding.
The method of any of claims 1-67, wherein for a bi-prediction, the filtering process is applied to at least one prediction before the at least one prediction being used to generate the bi-prediction.
The method of any of claims 1-67, wherein the filtering process is applied to a bi-prediction generated based on at least one prediction.
The method of any of claims 1-69, wherein for a combined prediction, the filtering process is applied to at least one prediction before the at least one prediction being used to generate the combined prediction.
The method of any of claims 1-67, wherein the filtering process is applied to a combined prediction generated based on at least one prediction.
The method of claim 70 or 71, wherein the combined prediction comprises a CIIP or GPM.
The method of any of claims 1-72, wherein a plurality of filtering processes are applied to an inter prediction of the current video unit.
The method of claim 73, wherein a first filtering process is applied to the inter prediction to obtain a first filtering result, and a second filtering process is applied to the first filtering result.
The method of any of claims 1-72, wherein the filtering process is applied to at least one inter prediction sample before determining an inter reconstruction.
The method of claim 75, wherein the filtering process is applied to all inter prediction samples before determining the inter reconstruction.
The method of claim 75, wherein the filtering process is applied to a partial of the inter prediction samples before determining the inter reconstruction.
The method of claim 75, wherein whether the filtering process is applied to an inter prediction sample is based on at least one metric,

wherein the at least one metric comprises at least one of:

a boundary strength,

a boundary gradient,

a difference between a sample value of a prediction sample and another sample, or

a difference between a sample value of a prediction sample and an average or maximum or minimum value of a plurality of samples.
The method of any of claims 1-78, wherein whether to and/or how to apply the filtering process is based on coding information of at least one prediction sample,

wherein the coding information comprises whether at least one prediction sample is coded with a first coding mode.
The method of claim 79, wherein the first coding mode comprises at least one of: a deblocking, a SAO, a CCSAO, a bilateral filtering, an ALF, a CCAFL, a LIC, an OBMC, a subblock OBMC, an intra mode, an inter mode, or a bi-prediction.
The method of claim 79 or 80, wherein the first coding mode is applied to the at least one prediction sample, the filtering process is not applied to a current prediction sample or all prediction samples before generating the inter reconstruction.
The method of any of claims 1-81, wherein the filtering process is applied to template samples before performing a template matching based on the template samples.
The method of claim 82, wherein the template samples are used in at least one of: a template matching (TM) AMVP mode, a TM merge mode, an Adaptive Reordering of Merge Candidates with Template Matching (TM ARMC) , a GPM split mode reordering, a TM OBMC, a TM GPM Merge Mode with Motion Vector Difference (MMVD) , a TM subblock refinement mode, a TM Reordering for MMVD mode, a TM reordering for Affine MMVD, a TM block level reference picture reordering, a TM BCW index derivation, a TM LIC flag derivation, or a template used in a further template matching based tool.
The method of any of claims 1-83, wherein whether to and/or how to apply the method is determined conditionally, or indicated in the bitstream.
The method of any of claims 1-84, wherein a first syntax element (SE) is indicated in the bitstream to indicate whether the method is applied.
The method of claim 85, wherein the first SE comprises a flag.
The method of claim 85, wherein the first SE is coded with at least one context model, or is bypass coded.
The method of claim 85, wherein the first SE is coded if the current video unit is coded with a coding mode.
The method of any of claims 1-88, wherein the method is used in at least one of: a post-processing, or a pre-processing.
The method of any of claims 1-89, wherein a determination of parameter of the filtering process is applied to at least one of: an in-loop filtering tool, a prediction tool, a pre-processing filtering, or a post-processing filtering.
The method of any of claims 1-90, wherein the current video unit comprises one of: a sequence, a picture, a sub-picture, a slice, a tile, a coding tree unit (CTU) , a CTU row, groups of CTU, a coding unit, a prediction unit, a transform unit, a coding tree block (CTB) , a coding block, a prediction block, a transform block, or a region containing more than one luma or chroma sample or pixel.
The method of any of claims 1-91, wherein information regarding whether to and/or how to apply the method is indicated in the bitstream.
The method of claim 92, wherein the information is indicated at one of: a sequence level, a group of pictures level, a picture level, a slice level, a tile group level, a sequence header, a picture header, a sequence parameter set (SPS) , a video parameter set (VPS) , a dependency parameter set (DPS) , decoding capability information (DCI) , a picture parameter set (PPS) , an adaptation parameter sets (APS) , a slice header, or a tile group header.
The method of claim 92, wherein the information is indicated at one of: a prediction block (PB) , a transform block (TB) , a coding block (CB) , a prediction unit (PU) , a transform unit (TU) , a coding unit (CU) , a virtual pipeline data unit (VPDU) , a coding tree unit (CTU) , a CTU row, a slice, a tile, a sub-picture, or a region containing more than one sample or pixel.
The method of any of claims 1-91, wherein information regarding whether to and/or how to apply the method is based on coded information, the coded information comprising at least one of: a block size, a color format, a single and/or dual tree partitioning, a color component, a slice type, or a picture type.
The method of any of claims 1-95, wherein the conversion comprises encoding the current video unit into the bitstream.
The method of any of claims 1-95, wherein the conversion comprises decoding the current video unit from the bitstream.
An apparatus for video processing comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to perform a method in accordance with any of claims 1-97.
A non-transitory computer-readable storage medium storing instructions that cause a processor to perform a method in accordance with any of claims 1-97.
A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by an apparatus for video processing, wherein the method comprises:

determining a plurality of samples of a current video unit of the video, at least a partial of the plurality of samples being determined based on at least one inter prediction;

applying a filtering process to the plurality of samples to obtain a plurality of refined samples; and

generating the bitstream based on based on the plurality of refined samples.
A method for storing a bitstream of a video, comprising:

determining a plurality of samples of a current video unit of the video, at least a partial of the plurality of samples being determined based on at least one inter prediction;

applying a filtering process to the plurality of samples to obtain a plurality of refined samples;

generating the bitstream based on based on the plurality of refined samples; and

storing the bitstream in a non-transitory computer-readable recording medium.