WO2021134048A1 - Control of filtering across boundaries in video coding - Google Patents

Abstract

Methods, devices and systems for controlling loop filtering processes across boundaries during video encoding and decoding are described. One example method includes performing a conversion between a video comprising a video region that includes a subpicture and a bitstream of the video, wherein the bitstream conforms to a format rule that specifies whether a first syntax element is signaled in the bitstream is based on whether the subpicture is treated as a picture, and wherein the first syntax element is related to an application of a loop filtering process across a subpicture boundary associated with the video region.

Description

CONTROL OF FILTERING ACROSS BOUNDARIES IN VIDEO CODING

CROSS-REFERENCE TO RELATED APPLICATION [001] Under the applicable patent law and/or rules pursuant to the Paris Convention, this application is made to timely claim the priority to and benefits of U.S. Provisional Patent Application No. US 62/954,393 filed on December 27, 2019. For all purposes under the law, the entire disclosures of the aforementioned applications are incorporated by reference as part of the disclosure of this application.

TECHNICAL FIELD

[002] This patent document relates to image and video coding and decoding.

BACKGROUND

[003] Digital video accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

[004] The present document discloses methods, techniques and systems that can be used by video encoders and decoders to control loop filtering processes across boundaries during video encoding and decoding, respectively.

[005] In one example aspect, a video processing method is disclosed. The method includes determining, for a conversion between a video comprising a video region and a bitstream of the video, whether to apply a loop filtering process across a boundary associated with the video region, and performing, based on the determining, the conversion, wherein the bitstream includes one or more syntax elements indicative of whether the loop filtering process is applicable on a per-video region basis.

[006] In another example aspect, another video processing method is disclosed. The method includes performing a conversion between a video comprising a video region that includes a subpicture and a bitstream of the video, wherein the bitstream conforms to a format rule that specifies whether a first syntax element is signaled in the bitstream is based on whether the subpicture is treated as a picture, and wherein the first syntax element is related to an application of a loop filtering process across a subpicture boundary associated with the video region.

[007] In yet another example aspect, a video encoder apparatus is disclosed. The video encoder comprises a processor configured to implement above-described methods.

[008] In yet another example aspect, a video decoder apparatus is disclosed. The video decoder comprises a processor configured to implement above-described methods.

[009] In yet another example aspect, a computer readable medium having code stored thereon is disclose. The code embodies one of the methods described herein in the form of processor- executable code.

[0010] These, and other, features are described throughout the present document.

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 shows an example of partitioning a picture with luma coding tree units (CTUs). [0012] FIG. 2 shows another example of partitioning a picture with luma CTUs.

[0013] FIG. 3 shows an example partitioning of a picture.

[0014] FIG. 4 shows another example partitioning of a picture.

[0015] FIG. 5 is a block diagram of an example encoder implementation.

[0016] FIG. 6 is an illustration of picture samples and horizontal and vertical block boundaries, which enable deblocking in parallel.

[0017] FIG. 7 shows examples of pixels involved in filter on/off decision and filter selection. [0018] FIG. 8 shows four 1-D directional patterns for EO sample classification: horizontal (EO class = 0), vertical (EO class = 1), 135° diagonal (EO class = 2), and 45° diagonal (EO class = 3). [0019] FIG. 9 shows examples of ALF filter shapes.

[0020] FIG. 10 shows an example of loop filter line buffer requirement for a Luma component. [0021] FIG. 11 shows an example of loop filter line buffer requirement for a Chroma component. [0022] FIG. 12 shows an example of modified block classification at virtual boundaries.

[0023] FIG. 13 shows Modified ALF filtering for Luma component at virtual boundaries.

[0024] FIG. 14A-14C shows examples of modified luma ALF filtering at virtual boundary. [0025] FIG. 15 shows examples of repetitive padding for luma ALF filtering at picture/subpicture/slice/tile boundary. [0026] FIG. 16 illustrates an example of horizontal wrap around motion compensation in VVC. [0027] FIG. 17 shows an image of HEC in 3x2 layout.

[0028] FIG. 18A-18B show placement of CC-ALF with respect to other loop filters.

[0029] FIG. 19 is a block diagram of an example video processing system in which disclosed techniques may be implemented.

[0030] FIG. 20 is a block diagram of an example hardware platform used for video processing. [0031] FIG. 21 is a block diagram that illustrates a video coding system in accordance with some embodiments of the present disclosure.

[0032] FIG.22 is a block diagram that illustrates an encoder in accordance with some embodiments of the present disclosure.

[0033] FIG. 23 is a block diagram that illustrates a decoder in accordance with some embodiments of the present disclosure.

[0034] FIGS. 24-25 show flowcharts for example methods of video processing.

DETAILED DESCRIPTION

[0035] Section headings are used in the present document for ease of understanding and do not limit the applicability of techniques and embodiments disclosed in each section only to that section. Furthermore, H.266 terminology is used in some description only for ease of understanding and not for limiting scope of the disclosed techniques. As such, the techniques described herein are applicable to other video codec protocols and designs also.

1. Summary

[0036] This document is related to video coding technologies. Specifically, it is about controlling of in-loop filtering across picture region boundaries. It may be applied to any video coding standard or non-standard video codec that supports single-layer video coding and multi-layer video coding, e.g., Versatile Video Coding (VVC) that is being developed.

2. Abbreviations

ALF Adaptive Loop Filter

APS Adaptation Parameter Set

AU Access Unit

AUD Access Unit Delimiter

AVC Advanced Video Coding CL VS Coded Layer Video Sequence

CPB Coded Picture Buffer

CRA Clean Random Access

CTU Coding Tree Unit

CVS Coded Video Sequence

DPB Decoded Picture Buffer

DPS Decoding Parameter Set

EOB End Of Bitstream

EOS End Of Sequence

GDR Gradual Decoding Refresh

HEVC High Efficiency Video Coding

IDR Instantaneous Decoding Refresh

JEM Joint Exploration Model

MCTS Motion-Constrained Tile Sets

NAL Network Abstraction Layer

OLS Output Layer Set

PH Picture Header

PPS Picture Parameter Set

PU Picture Unit

RBSP Raw Byte Sequence Payload

SAO Sample Adaptive Offset

SEI Supplemental Enhancement Information

SPS Sequence Parameter Set

VCL Video Coding Layer

VPS Video Parameter Set

VTM VVC Test Model

VUI Video Usability Information

VVC Versatile Video Coding 3. Initial discussion

[0037] 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 VVC project is now aiming for technical completion (FDIS) at the July 2020 meeting.

3.1. Picture partitioning schemes in HEVC

[0038] HEVC includes four different picture partitioning schemes, namely regular slices, dependent slices, tiles, and Wavefront Parallel Processing (WPP), which may be applied for Maximum Transfer Unit (MTU) size matching, parallel processing, and reduced end-to-end delay.

[0039] Regular slices are similar as in H.264/AVC. Each regular slice is encapsulated in its own NAL unit, and in-picture prediction (intra sample prediction, motion information prediction, coding mode prediction) and entropy coding dependency across slice boundaries are disabled. Thus a regular slice can be reconstructed independently from other regular slices within the same picture (though there may still have interdependencies due to loop filtering operations).

[0040] The regular slice is the only tool that can be used for parallelization that is also available, in virtually identical form, in H.264/AVC. Regular slices based parallelization does not require much inter-processor or inter-core communication (except for inter-processor or inter-core data sharing for motion compensation when decoding a predictively coded picture, which is typically much heavier than inter-processor or inter-core data sharing due to in-picture prediction). However, for the same reason, the use of regular slices can incur substantial coding overhead due to the bit cost of the slice header and due to the lack of prediction across the slice boundaries. Further, regular slices (in contrast to the other tools mentioned below) also serve as the key mechanism for bitstream partitioning to match MTU size requirements, due to the in-picture independence of regular slices and that each regular slice is encapsulated in its own NAL unit. In many cases, the goal of parallelization and the goal of MTU size matching place contradicting demands to the slice layout in a picture. The realization of this situation led to the development of the parallelization tools mentioned below.

[0041] Dependent slices have short slice headers and allow partitioning of the bitstream at treeblock boundaries without breaking any in-picture prediction. Basically, dependent slices provide fragmentation of regular slices into multiple NAL units, to provide reduced end-to-end delay by allowing a part of a regular slice to be sent out before the encoding of the entire regular slice is finished.

[0042] In WPP, the picture is partitioned into single rows of coding tree blocks (CTBs). Entropy decoding and prediction are allowed to use data from CTBs in other partitions. Parallel processing is possible through parallel decoding of CTB rows, where the start of the decoding of a CTB row is delayed by two CTBs, so to ensure that data related to a CTB above and to the right of the subject CTB is available before the subject CTB is being decoded. Using this staggered start (which appears like a wavefront when represented graphically), parallelization is possible with up to as many processors/cores as the picture contains CTB rows. Because inpicture prediction between neighboring treeblock rows within a picture is permitted, the required inter-processor/inter-core communication to enable in-picture prediction can be substantial. The WPP partitioning does not result in the production of additional NAL units compared to when it is not applied, thus WPP is not a tool for MTU size matching. However, if MTU size matching is required, regular slices can be used with WPP, with certain coding overhead.

[0043] Tiles define horizontal and vertical boundaries that partition a picture into tile columns and rows. Tile column runs from the top of a picture to the bottom of the picture. Likewise, tile row runs from the left of the picture to the right of the picture. The number of tiles in a picture can be derived simply as number of tile columns multiply by number of tile rows.

[0044] The scan order of CTBs is changed to be local within a tile (in the order of a CTB raster scan of a tile), before decoding the top-left CTB of the next tile in the order of tile raster scan of a picture. Similar to regular slices, tiles break in-picture prediction dependencies as well as entropy decoding dependencies. However, they do not need to be included into individual NAL units (same as WPP in this regard); hence tiles cannot be used for MTU size matching. Each tile can be processed by one processor/core, and the inter-processor/inter-core communication required for in-picture prediction between processing units decoding neighboring tiles is limited to conveying the shared slice header in cases a slice is spanning more than one tile, and loop filtering related sharing of reconstructed samples and metadata. When more than one tile or WPP segment is included in a slice, the entry point byte offset for each tile or WPP segment other than the first one in the slice is signaled in the slice header.

[0045] For simplicity, restrictions on the application of the four different picture partitioning schemes have been specified in HEVC. A given coded video sequence cannot include both tiles and wavefronts for most of the profiles specified in HEVC. For each slice and tile, either or both of the following conditions must be fulfilled: 1) all coded treeblocks in a slice belong to the same tile; 2) all coded treeblocks in a tile belong to the same slice. Finally, a wavefront segment contains exactly one CTB row, and when WPP is in use, if a slice starts within a CTB row, it must end in the same CTB row.

[0046] A recent amendment to HEVC is specified in the JCT-VC output document JCTVC- AC1005, J. Boyce, A. Ramasubramonian, R. Skupin, G. J. Sullivan, A. Tourapis, Y.-K. Wang (editors), "HEVC Additional Supplemental Enhancement Information (Draft 4)," Oct. 24, 2017, publicly available herein: http://phenix.int- evry.fr/jct/doc_end_user/documents/29_Macau/wgl l/JCTVC-AC1005-v2.zip. With this amendment included, HEVC specifies three MCTS-related SEI messages, namely temporal MCTSs SEI message, MCTSs extraction information set SEI message, and MCTSs extraction information nesting SEI message.

[0047] The temporal MCTSs SEI message indicates existence of MCTSs in the bitstream and signals the MCTSs. For each MCTS, motion vectors are restricted to point to full-sample locations inside the MCTS and to fractional-sample locations that require only full-sample locations inside the MCTS for interpolation, and the usage of motion vector candidates for temporal motion vector prediction derived from blocks outside the MCTS is disallowed. This way, each MCTS may be independently decoded without the existence of tiles not included in the MCTS.

[0048] The MCTSs extraction information sets SEI message provides supplemental information that can be used in the MCTS sub-bitstream extraction (specified as part of the semantics of the SEI message) to generate a conforming bitstream for an MCTS set. The information consists of a number of extraction information sets, each defining a number of MCTS sets and containing RBSP bytes of the replacement VPSs, SPSs, and PPSs to be used during the MCTS subbitstream extraction process. When extracting a sub-bitstream according to the MCTS subbitstream extraction process, parameter sets (VPSs, SPSs, and PPSs) need to be rewritten or replaced, slice headers need to be slightly updated because one or all of the slice address related syntax elements (including first_slice segment_in_pic_flag and slice_segment_address) typically would need to have different values.

3.2. Partitioning of pictures in VVC

[0049] In VVC, 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. The CTUs in a tile are scanned in raster scan order within that tile.

[0050] A slice consists of an integer number of complete tiles or an integer number of consecutive complete CTU rows within a tile of a picture.

[0051] 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 complete tiles in a tile raster scan of a picture. In the rectangular slice mode, a slice contains either a number of complete tiles that collectively form a rectangular region of the picture or a number of consecutive complete CTU rows of one tile that collectively form a rectangular region of the picture. Tiles within a rectangular slice are scanned in tile raster scan order within the rectangular region corresponding to that slice.

[0052] A subpicture contains one or more slices that collectively cover a rectangular region of a picture. [0053] FIG. 1 shows an example of raster-scan slice partitioning of a picture, where the picture is divided into 12 tiles and 3 raster-scan slices.

[0054] FIG. 2 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.

[0055] FIG. 3 shows an example of a picture partitioned into tiles and rectangular slices, where the picture is divided into 4 tiles (2 tile columns and 2 tile rows) and 4 rectangular slices.

[0056] FIG. 4 shows an example of subpicture partitioning of a picture, where a picture is partitioned into 18 tiles, 12 on the left-hand side each covering one slice of 4 by 4 CTUs and 6 tiles on the right-hand side each covering 2 vertically-stacked slices of 2 by 2 CTUs, altogether resulting in 24 slices and 24 subpictures of varying dimensions (each slice is a subpicture).

3.3. Signalling of subpictures, slices, and tiles in VVC

[0057] In the latest VVC draft text, information of subpictures, includes subpicgture layout (i.e., the number of subpictures for each picture and the position and size of each picture) and other sequence-level subpicture informaiton, is signalled in the SPS. The order of subpictures signalled in the SPS defines the subpiture index. A list of subpicture IDs, one for each subpicture, may be explicitly signalled, e.g., in the SPS or in the PPS.

[0058] Tiles in VVC are conceptually the same as in HEVC, i.e., each picture is partitioned into tile columns and tile rows, but with different syntax in the PPS for signalling of tiles.

[0059] In VVC, the slice mode is also signalled in the PPS. When the slice mode is the rectangualr slice mode, the sice layout (i.e., the number of slices for each picture and the position and size of each slice) for each picture is signalled in the PPS. The order of the rectangular slices within a pictue signalled in the PPS defines the picture-level slice index. The subpicture-level slice index is defined as the order of the slices within a subpicture in increasing order of the their picture-level slice indices. The positions and sizes of the rectangular slices are signalled/derived based on either the subpicture positions and sizes that are signalled in the SPS (when each subpicure contains only one slice), or based on the tile positions and sizes that are signalled in the PPS (when a subpicure may contain more than one slice). When the slice mode is the raster- scan slice mode, similarly as in HEVC, the layout of slices within a picture is signalled in the slices themselves, with different details. 3.4. In-loop filtering in VVC

[0060] 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. .5. Deblocking filter (DB)

[0061] The input of DB is the reconstructed samples before in-loop filters.

[0062] 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.

[0063] FIG. 6 is an illustration of picture samples and horizontal and vertical block boundaries on the 8x8 grid, and the nonoverlapping blocks of the 8x8 samples, which can be deblocked in parallel.

3.5.1. Boundary decision

[0064] In HEVC, filtering is applied to 8x8 block boundaries, as depicted in FIG. 6. However, in VVC, finer filtering is used, wherein 4x4 block boundaries are filtered. 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. 3.5.2. Boundary strength calculation

[0065] 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 in Table 3-1 and Table 3-2, respectively.

Table 3-1. Boundary strength (when SPS IBC is disabled)

Table 3-2. Boundary strength (when SPS IBC is enabled)

3.5.3. Deblocking decision for luma component

[0066] The deblocking decision process is described in this sub-section.

[0067] FIG. 7 shows examples of pixels involved in filter on/off decision and strong/weak filter selection.

[0068] Wider-stronger luma filter is filters are used only if all the Conditionl, Condition2 and Condition 3 are TRUE.

[0069] 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 qo belongs to CU with width >= 32) | | (edge type is horizontal and qo belongs to CU with height >= 32))? TRUE: FALSE [0070] Based on bSidePisLargeBlk and bSideQisLargeBlk, the condition 1 is defined as follows. Condition 1 = (bSidePisLargeBlk || bSidePisLargeBlk) ? TRUE: FALSE [0071] 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 HE VC

- 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 Conditionl and Condition2 are valid, whether any of the blocks uses sub-blocks is further checked:

If (bSidePisLargeBlk)

{

If (mode block P == SUBBLOCKMODE)

Sp =5 else Sp =7

} else Sp = 3

If (bSideQisLargeBlk)

{

If (mode block Q == SUBBLOCKMODE)

Sq =5 else Sq =7

} else Sq = 3

[0072] 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: dpq is derived as in HEVC. sp3 = Abs( p3 - p0 ), derived as in HEVC if (p side is greater than or equal to 32) if(Sp==5) sp₃ = ( sp₃ + Abs( p₅ - p₃ ) + 1) » 1 else sp₃ = ( sp₃ + Abs( p7 - p3 ) + 1) » 1 sq₃ = Abs( qo - q₃ ), derived as in HEVC if (q side is greater than or equal to 32)

If(Sq==5) sq₃ = ( sq₃ + Abs( qs - q3 ) + 1) » 1 else sq₃ = ( sq₃ + Abs( q7 - q3 ) + 1) » 1

As in HEVC, StrongFilterCondition = (dpq is less than ( b » 2 ), sp₃ + sq₃ is less than ( 3*β » 5 ), and Abs( p₀ - qo ) is less than ( 5 * tc + 1 ) » 1) ? TRUE : FALSE.

3.5.4. Stronger deblocking filter for luma (designed for larger blocks)

[0073] 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.

[0074] The bilinear filter is listed below.

[0075] 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_t * Middle _Sit + (64 — f_t) * P_s + 32) » 6), clipped to p_i ± tcPD_i

— q_i' = ( g_j * Middle_{s t} + (64 — g_j ) * Q_s + 32) » 6), clipped to q_j ± tcPD_j

[0076] where tcPD_t and tcPD_j term is a position dependent clipping described in Section 3.5.7 and g_j , f_i, Middle_{s t} , P_s and Q_s are given below: 3.5.5. Deblocking control for chroma

[0077] 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.

[0078] 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.

[0079] Chroma deblocking is performed when bS is equal to 2, or bS is equal to 1 when a large block boundary is detected.

[0080] The second and third condition is basically the same as HEVC luma strong filter decision as follows.

[0081] In the second condition: d is then derived as in HEVC luma deblocking.

The second condition will be TRUE when d is less than b.

[0082] 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

[0083] As in HEVC design, StrongFilterCondition = (dpq is less than ( b » 2 ), sp₃ + sq₃ is less than ( b » 3 ), and Abs( p₀ - qo ) is less than ( 5 * tc + 1 ) » 1)

3.5.6. Strong deblocking filter for chroma

[0084] The following strong deblocking filter for chroma is defined:

p₀ - (p₃+p₂+p₁+2*p₀+q₀+q₁+q₂+4) » 3

[0085] The proposed chroma filter performs deblocking on a 4x4 chroma sample grid. 3.5.7. Position dependent clipping

[0086] 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.

[0087] For each P or Q boundary filtered with asymmetrical filter, depending on the result of decision-making process in section 3.5.2, 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;

[0088] 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 };

[0089] Following defining the threshold, filtered p ' i and q ' i sample values are clipped according to tcP and tcQ clipping values: p ”i = Clip 3 (p ’i + tcPi, p ’i - tcPi, p 'i); q”_{j =} Clip3(q ’_j + tcQ_j, q ’_{j -} tcQ_j, q 'j);

[0090] where p \ and q \ are filtered sample values, p ’ i and q ’ j are output sample value after the clipping and tcPi tcPi 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.

3.5.8. Sub-block deblocking adjustment

[0091] 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. Additionally, 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.

[0092] Following applies to sub-block boundaries that not are aligned with the CU boundary. If (mode block Q == SUBBLOCKMODE && edge !=0) { if (!(implicitTU && (edge == (64 / 4)))) if (edge == 2 || edge == (orthogonalLength - 2) || edge == (56 / 4) || edge == (72 / 4))

Sp = Sq = 2; else

Sp = Sq = 3; else

Sp = Sq = bSideQisLargeBlk ? 5:3

}

[0093] 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.

3.6. Sample adaptive offset (SAO)

[0094] The input of SAO is the reconstructed samples after DB. The concept of SAO is to reduce mean sample distortion of a region by first classifying the region samples into multiple categories with a selected classifier, obtaining an offset for each category, and then adding the offset to each sample of the category, where the classifier index and the offsets of the region are coded in the bitstream. In HE VC and VVC, the region (the unit for SAO parameters signaling) is defined to be a CTU.

[0095] Two SAO types that can satisfy the requirements of low complexity are adopted in HEVC. Those two types are edge offset (EO) and band offset (BO), which are discussed in further detail below. An index of an SAO type is coded (which is in the range of [0, 2]). For EO, the sample classification is based on comparison between current samples and neighboring samples according to 1-D directional patterns: horizontal, vertical, 135° diagonal, and 45° diagonal.

[0096]

[0097] FIG. 8 shows four 1-D directional patterns for EO sample classification: horizontal (EO class = 0), vertical (EO class = 1), 135° diagonal (EO class = 2), and 45° diagonal (EO class = 3) [0098] For a given EO class, each sample inside the CTB is classified into one of five categories. The current sample value, labeled as “c,” is compared with its two neighbors (labeled as “a” and “b”) along the selected 1-D pattern. The classification rules for each sample are summarized in Table 3-3. Categories 1 and 4 are associated with a local valley and a local peak along the selected 1-D pattern, respectively. Categories 2 and 3 are associated with concave and convex corners along the selected 1-D pattern, respectively. If the current sample does not belong to EO categories 1-4, then it is category 0 and SAO is not applied.

Table 3-3. Sample Classification Rules for Edge Offset

3.7. Adaptive Loop Filter (ALF)

[0099] In VVC, an Adaptive Loop Filter (ALF) with block-based filter adaption is applied. For the luma component, one among 25 filters is selected for each 4x4 block, based on the direction and activity of local gradients.

3.7.1. Filter shape

[00100] Two diamond filter shapes (as shown in FIG. 9) are used. The 7x7 diamond shape is applied for luma component and the 5x5 diamond shape is applied for chroma components.

[00101]

[00102] FIG. 9 shows example ALF filter shapes (chroma: 5x5 diamond, luma: 7x7 diamond).

3.7.2. Block classification

[00103] For luma component, each 4 x 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 activity A , as follows:

C = SD + A (2-1)

[00104] To calculate D and A , gradients of the horizontal, vertical and two diagonal direction are first calculated using 1-D Laplacian:

[00105] Where indices i and j refer to the coordinates of the upper left sample within the 4 x 4 block and R(i,j ) indicates a reconstructed sample at coordinate

[00106] Then D maximum and minimum values of the gradients of horizontal and vertical directions are set as: (2-6)

[00107] The maximum and minimum values of the gradient of two diagonal directions are set as:

[00108] To derive the value of the directionality D, these values are compared against each other and with two thresholds t_x and t₂ :

Step 1. If both

are true, D is set to 0.

Step 2. , continue from Step 3; otherwise continue from Step 4.

Step

set to 2; otherwise D is set to 1.

Step

set to 4; otherwise D is set to 3.

[00109] The activity value A is calculated as:

[00110] A is further quantized to the range of 0 to 4, inclusively, and the quantized value is denoted as A.

[00111] For chroma components in a picture, no classification method is applied, i.e. a single set of ALF coefficients is applied for each chroma component.

3.7.3. Geometric transformations of filter coefficients and clipping values [00112] Before filtering each 4x4 luma block, geometric transformations such as rotation or diagonal and vertical flipping are applied to the filter coefficients f(k, l ) and to the corresponding filter clipping values c(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. Three geometric transformations, including diagonal, vertical flip and rotation are introduced: Diagonal: f_D(k, l ) = f(l,k), c_D(k, l ) = c(Z, /c), (2-9)

Vertical flip: f_v(k, l ) = f(k, K — l — 1), c_K(/c, Z) = c(k, K — l — 1) (2-10)

Rotation: f_R(k, l ) = f(K — l — 1, k ), c_R(/c, Z) = c(Zf — Z — 1, k) (2-11)

[00113] 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 comer and location (K — l, K — 1) is at the lower right corner. The transformations are applied to the filter coefficients / ( k , I) and to the clipping values c(k, Z) depending on gradient values calculated for that block. The relationship between the transformation and the four gradients of the four directions are summarized in the following table.

Table 3-4. Mapping of the gradient calculated for one block and the transformations

3.7.4. Filter parameters signalling

[00114] ALF filter parameters are signalled in Adaptation Parameter Set (APS). In one APS, up to 25 sets of luma filter coefficients and clipping value indexes, and up to eight sets of chroma filter coefficients and clipping value indexes could be signalled. To reduce bits overhead, filter coefficients of different classification for luma component can be merged. In slice header, the indices of the APSs used for the current slice are signaled.

[00115] Clipping value indexes, which are decoded from the APS, allow determining clipping values using a table of clipping values for both luma and Chroma components. These clipping values are dependent of the internal bitdepth. More precisely, the clipping values are obtained by the following formula:

AlfClip= (round

(2-12)

[00116] with B equal to the internal bitdepth, a is a pre-defmed constant value equal to 2.35, and N equal to 4 which is the number of allowed clipping values in VVC. [00117] In slice header, up to 7 APS indices can be signaled to specify the luma filter sets that are used for the current slice. The filtering process can be further controlled at CTB level. A flag is always signalled to indicate whether ALF is applied to a luma CTB. A luma CTB can choose a filter set among 16 fixed filter sets and the filter sets from APSs. A filter set index is signaled for a luma CTB to indicate which filter set is applied. The 16 fixed filter sets are pre-defmed and hard-coded in both the encoder and the decoder.

[00118] For chroma component, an APS index is signaled in slice header to indicate the chroma filter sets being used for the current slice. At CTB level, a filter index is signaled for each chroma CTB if there is more than one chroma filter set in the APS.

[00119] The filter coefficients are quantized with norm equal to 128. In order to restrict the multiplication complexity, a bitstream conformance is applied so that the coefficient value of the non-central position shall be in the range of-2⁷ to 2⁷ - 1, inclusive. The central position coefficient is not signalled in the bitstream and is considered as equal to 128.

3.7.5. Filtering process

[00120] At decoder side, when ALF is enabled for a CTB, each sample R(i,j ) within the CU is filtered, resulting in sample value R'(i,j ) as shown below,

(2-13)

[00121] where f(k, l ) denotes the decoded filter coefficients, K(x,y) is the clipping function and c(k, l ) denotes the decoded clipping parameters. The variable k and 1 varies between —

and j where L denotes the filter length. The clipping function K (x, y) = min(y, max(— y, x)) which corresponds to the function Clip 3 (— y, y, x).

3.7.6. Virtual boundary filtering process for line buffer reduction

[00122] In hardware and embedded software, picture-based processing is practically unacceptable due to its high picture buffer requirement. Using on-chip picture buffers is very expensive and using off-chip picture buffers significantly increases external memory access, power consumption, and data access latency. Therefore, DF, SAO, and ALF will be changed from picture-based to LCU-based decoding in real products. When LCU-based processing is used for DF, SAO, and ALF, the entire decoding process can be done LCU by LCU in a raster scan with an LCU-pipelining fashion for parallel processing of multiple LCUs. In this case, line buffers are required for DF, SAO, and ALF because processing one LCU row requires pixels from the above LCU row. If off-chip line buffers (e.g. DRAM) are used, the external memory bandwidth and power consumption will be increased; if on-chip line buffers (e.g. SRAM) are used, the chip area will be increased. Therefore, although line buffers are already much smaller than picture buffers, it is still desirable to reduce line buffers.

[00123] In VTM-4.0, as shown in FIG. 10, the total number of line buffers required is 11.25 lines for the Luma component. The explanation of the line buffer requirement is as follows: The deblocking of horizontal edge overlapping with CTU edge cannot be performed as the decisions and filtering require lines K, L, M, M from the first CTU and Lines O, P from the bottom CTU. Therefore, the deblocking of the horizontal edges overlapping with the CTU boundary is postponed until the lower CTU comes. Therefore, for the lines K, L, M, N reconstructed luma samples have to be stored in the line buffer (4 lines). Then the SAO filtering can be performed for lines A till J. The line J can be SAO filtered as deblocking does not change the samples in line K. For SAO filtering of line K, the edge offset classification decision is only stored in the line buffer (which is 0.25 Luma lines). The ALF filtering can only be performed for lines A-F.

As shown in FIG. 10, the ALF classification is performed for each 4x4 block. Each 4x4 block classification needs an activity window of size 8x8 which in turn needs a 9x9 window to compute the Id Laplacian to determine the gradient.

[00124] Therefore, for the block classification of the 4x4 block overlapping with lines G, H, I, J needs, SAO filtered samples below the Virtual boundary. In addition, the SAO filtered samples of lines D, E, F are required for ALF classification. Moreover, the ALF filtering of Line G needs three SAO filtered lines D, E, F from above lines. Therefore, the total line buffer requirement is as follows:

- Lines K-N (Horizontal DF pixels): 4 lines

- Lines D-J (SAO filtered pixels): 7 lines

- SAO Edge offset classifier values between line J and line K: 0.25 line [00125] Therefore, the total number of luma lines required is 7 + 4 + 0.25 = 11.25.

[00126] Similarly, the line buffer requirement of the Chroma component is illustrated in FIG. 11. The line buffer requirement for Chroma component is evaluated to be 6.25 lines. [00127] In order to eliminate the line buffer requirements of SAO and ALF, the concept of virtual boundary (VB) is introduced to reduce the line buffer requirement of ALF in the latest VVC. Modified block classification and filtering are employed for the samples near horizontal CTU boundaries. As shown in FIG. 10, VBs are upward shifted horizontal LCU boundaries by N pixels. For each LCU, SAO and ALF can process pixels above the VB before the lower LCU comes but cannot process pixels below the VB until the lower LCU comes, which is caused by DF. With consideration of the hardware implementation cost, the space between the proposed VB and the horizontal LCU boundary is set as four pixels for luma component (i.e. N=4 in FIG. 10 or FIG. 12) and two pixels for chroma component (i.e. N=2).

[00128] FIG. 12 shows a modified block classification at virtual boundaries [00129] Modified block classification is applied for the Luma component as depicted in FIG. 13. For the ID Laplacian gradient calculation of the 4x4 block above the virtual boundary, only the samples above the virtual boundary are used. Similarly, for the ID Laplacian gradient calculation of the 4x4 block below the virtual boundary, only the samples below the virtual boundary are used. The quantization of activity value A is accordingly scaled by taking into account the reduced number of samples used in ID Laplacian gradient calculation.

[00130] For filtering processing, mirrored (symmetric) padding operation at the virtual boundaries are used for both Luma and Chroma components. As shown in FIG. 13, when the sample being filtered is located below the virtual boundary, the neighboring samples that are located above the virtual boundary are padded. Meanwhile, the corresponding samples at the other sides are also padded, symmetrically.

[00131] For another example, if one sample located at (i, j) (e.g., the P0A with dash line in FIG. 14B is padded, then the corresponding sample located at (m, n) (e.g., the P3B with dash line in FIG. 14B which share the same filter coefficient is also padded even the sample is available, as depicted in FIGS. 14A-14C.

[00132] FIG. 14A shows one required line above/below VB need to be padded (per side).

[00133] FIG. 14B shows 2 required lines above/below VB need to be padded (per side)

[00134] FIG. 14C shows 3 required lines above/below VB need to be padded (per side)

[00135] Different to the mirrored (symmetric) padding method used at horizontal CTU boundaries, repetitive (one-side) padding process is applied for slice, tile and subpicture boundaries when filter across the boundaries is disabled. The repetitive (one-side) padding process is also applied at picture boundary. The padded samples are used for both classification and filtering process. FIG. 15 depicts an example of repetitive padding method for luma ALF filtering at picture/subpicture/slice/tile boundary.

[00136] FIG. 15 shows examples of repetitive padding for luma ALF filtering at picture/subpicture/slice/tile boundary.

3.8. 360-degree video coding

[00137] The horizontal wrap around motion compensation in the VTM5 is a 360-specific coding tool designed to improve the visual quality of reconstructed 360-degree video in the equi- rectangular (ERP) projection format. In conventional motion compensation, when a motion vector refers to samples beyond the picture boundaries of the reference picture, repetitive padding is applied to derive the values of the out-of-bounds samples by copying from those nearest neighbors on the corresponding picture boundary. For 360-degree video, this method of repetitive padding is not suitable, and could cause visual artefacts called “seam artefacts” in a reconstructed viewport video. Because a 360-degree video is captured on a sphere and inherently has no “boundary,” the reference samples that are out of the boundaries of a reference picture in the projected domain can always be obtained from neighboring samples in the spherical domain. For a general projection format, it may be difficult to derive the corresponding neighboring samples in the spherical domain, because it involves 2D-to-3D and 3D-to-2D coordinate conversion, as well as sample interpolation for fractional sample positions. This problem is much simpler for the left and right boundaries of the ERP projection format, as the spherical neighbors outside of the left picture boundary can be obtained from samples inside the right picture boundary, and vice versa.

[00138] FIG. 16 shows an example of horizontal wrap around motion compensation in VVC [00139] The horizontal wrap around motion compensation process is as depicted in FIG.

16. When a part of the reference block is outside of the reference picture’s left (or right) boundary in the projected domain, instead of repetitive padding, the “out-of-boundary” part is taken from the corresponding spherical neighbors that are located within the reference picture toward the right (or left) boundary in the projected domain. Repetitive padding is only used for the top and bottom picture boundaries. As depicted in FIG. 16, the horizontal wrap around motion compensation can be combined with the non-normative padding method often used in 360-degree video coding. In VVC, this is achieved by signaling a high-level syntax element to indicate the wrap-around offset, which should be set to the ERP picture width before padding; this syntax is used to adjust the position of horizontal wrap around accordingly. This syntax is not affected by the specific amount of padding on the left and right picture boundaries, and therefore naturally supports asymmetric padding of the ERP picture, i.e., when left and right padding are different. The horizontal wrap around motion compensation provides more meaningful information for motion compensation when the reference samples are outside of the reference picture’s left and right boundaries.

[00140] For projection formats composed of a plurality of faces, no matter what kind of compact frame packing arrangement is used, discontinuities appear between two or more adjacent faces in the frame packed picture. For example, considering the 3x2 frame packing configuration depicted in FIG. 17, the three faces in the top half are continuous in the 3D geometry, the three faces in the bottom half are continuous in the 3D geometry, but the top and bottom halves of the frame packed picture are discontinuous in the 3D geometry. If in-loop filtering operations are performed across this discontinuity, face seam artifacts may become visible in the reconstructed video.

[00141] To alleviate face seam artifacts, in-loop filtering operations may be disabled across discontinuities in the frame-packed picture. A syntax was proposed to signal vertical and/or horizontal virtual boundaries across which the in-loop filtering operations are disabled. Compared to using two tiles, one for each set of continuous faces, and to disable in-loop filtering operations across tiles, the proposed signaling method is more flexible as it does not require the face size to be a multiple of the CTU size.

[00142] FIG. 17 shows an image of HEC in 3x2 layout

3.9. JVET-P0080 on Cross Component Adaptive Loop Filter

[00143] FIG. 18A below illustrates the placement of CC-ALF with respect to the other loop filters. CC-ALF operates by applying a linear, diamond shaped filter. FIG. 18B to the luma channel for each chroma component, which is expressed as

where

(x, y) is chroma component i location being refined (x_c, y_c) is the luma location based on (x, y)

S_i is filter support in luma for chroma component i q(x₀,y₀) represents the filter coefficients

(2-14)

[00144] FIG. 18A shows placement of CC-ALF with respect to other loop filters, (b) Diamond shaped filter.

[00145] The luma location (x_c,y_c), around which the support region is centered, is computed based on the spatial scaling factor between the luma and chroma planes. All filter coefficients are transmitted in the APS and have 8-bit dynamic range. An APS may be referenced in the slice header. CC-ALF coefficients used for each chroma component of a slice are also stored in a buffer corresponding to a temporal sublayer. Reuse of these sets of temporal sublayer filter coefficients is facilitated using slice-level flags. The application of the CC-ALF filters is controlled on a variable block size (i.e. 16x16, 32x32, 64x64, 128x128) and signalled by a context-coded flag received for each block of samples. The block size along with an CC-ALF enabling flag is received at the slice-level for each chroma component. Boundary padding for the horizontal virtual boundaries makes use of repetition. For the remaining boundaries the same type of padding is used as for rengular ALF.

3.10. Control of in-loop filtering across boundaries in VVC

[00146] In the latest VVC draft text, in-loop filtering across region boundaries is controlled by the following syntax elements or variables:

1) loop_filter_across_subpic_enabled_flag[ i ]: for controlling of deblocking, SAO, and ALF across subpicture boundaries, signalled in the SPS, one for each subpicture.

2) loop_filter_across_ tiles enabled_flag: for controlling of deblocking, SAO, and ALF across tile boundaries, signalled in the PPS, just one (thus applicable to all tiles in all pictures referring to the PPS).

3) loop_filter_across_ slices enabled_flag: for controlling of deblocking, SAO, and ALF across slice boundaries, signalled in the PPS, just one (thus applicable to all tiles in all pictures referring to the PPS). 4) VirtualBoundariesDisabledFlag: for controlling of deblocking, SAO, and ALF across specified virtual boundaries, derived based on signalling in the SPS and PH (equal to 1 when either of the SPS flag sps virtual boundaries present flag or the picture header flag ph virtual boundaries present flag is equal to 1).

[00147] In the latest VVC draft text, for any particular boundary, whenever one of the above flags indicates that filtering across the boundary is turned off, regardless of the values of other flags, filtering across the boundary is turned off.

4. Examples of technical problems solved by solutions described herein

[00148] The existing VVC design for controlling of in-loop filtering across region boundaries has the following problems:

1) The different flags for controlling of in-loop filtering across region boundaries can be conflicting with each other. For example, it is possible that the encoder chooses to turn on filtering across the boundaries of some independently coded subpictures as it found that otherwise those subpictures being presented together has very annoying artifacts, way worse than the quality degradations in other extraction scenarios when turned off filtering across the boundaries of those subpictures. However, in this case, if for whatever reason the loop_filter_across_ tiles enabled_flag or loop_filter_across_ slices enabled_flag is equal to 0, then filtering across the subpicture boundaries that are also tile or slice boundaries would be turned off anyway.

2) The subpicture feature introduced to VVC was mainly support of region-of-interest and other extraction based use cases. For AVC, such use cases were supported by using slices or slices groups. For HEVC, these use cases were supported by slices and MCTSs. Therefore, the ability to turn off filtering across slice boundaries was needed in AVC and HEVC. However, in VVC, such need is gone.

3) When subpi c treated as pi c fl ag[ i ] is equal to 0 for a subpicture, motion compensation is constrained for coding of the subpicture across all pictures in the CLVS, therefore it is not independently coded and not extractable. In this case, there is no good reason to have loop_filter_across_subpic_enabled_flag[ i ] equal to 0 (i.e., to turn off loop filtering across the boundaries of the subpicture). However, this is allowed by the current design. 5. Example embodiments and solutions

[00149] To solve the above problems, methods as summarized below are disclosed. The items should be considered as examples to explain the general concepts and should not be interpreted in a narrow way. Furthermore, these items can be applied individually or combined in any manner.

1) To solve the first and second problems, the loop_filter_across_slices enabled_flag is removed and the loop_filter_across_tiles enabled_flag is made subpicture-specific (i.e., signalled once for each subpicture), still signalled in the PPS and only controls whether filtering across tile boundaries within a subpicture (excluding those tile boundaries that are also the boundaries of the subpicture) is on or off. a. Alternatively, the subpicture-specific loop_filter_across_ tiles enabled_flag is signalled in the SPS. The main (if not only) purpose of turning of filtering across tile boundaries is for reducing data exchange between different processing cores in parallel encoding. Such a purpose usually won't change across pictures, thus while it makes sense to signal tile layout in the PPS for load balancing purpose, signalling of the loop_filter_across_ tiles enabled_flag in the SPS makes sense, particularly after the flag is made subpicture specific. i. Alternatively, furthermore, the subpicture-specific loop_filter_across_ tiles enabled_flag signalled in the SPS may be conditioned on “if( subpi cs present fl ag )”. b. Alternatively, the loop_filter_across_ slices enabled_flag is kept, and both loop_filter_across_ tiles enabled_flag and loop_filter_across_ slices enabled_flag are made subpicture-specific. i. In an alternative to item lb, the subpicture-specific loop_filter_across_ tiles enabled_flag and loop_filter_across_ slices enabled_flag are signalled in the SPS instead of in the PPS. c. Alternatively, it is constrained that loop_filter_across_ slices enabled_flag and loop_filter_across_ tiles enabled_flag shall have the same value. i. Alternatively, it is constrained that loop_filter_across_ slices enabled_flag and loop_filter_across_tiles enabled_flag for subpictures in the same tile shall have the same value. d. Alternatively, loop_filter_across_ slices enabled_flag and/or loop_filter_across_ tiles enabled_flag associated with one representative subpicture among multiple subpictures in the same tile may be signaled. i. In one example, the representative subpicture may be the first one to be coded/decoded in coding/decoding order. ii. Alternatively, furthermore, loop_filter_across_ slices enabled_flag and/or loop_filter_across_ tiles enabled_flag associated with other subpictures in the same tile may be inferred to be equal to the signaled values. e. Alternatively, for a boundary that is a not subpicture boundary, but is a slice boundary and also a tile boundary, when loop_filter_across_ slices enabled_flag and loop_filter_across_ tiles enabled_flag have different values, the following applies: If the slice containing the current CTU is the same as or a superset of the tile containing the CTU, the behavior is determined by using the loop_filter_across_ tiles enabled_flag while ignoring the loop_filter_across_ slices enabled_flag. Otherwise, the behavior is determined by using the loop_filter_across_ slices enabled_flag while ignoring the loop_filter_across_ tiles enabled_flag. This means to use only the flag for which the associated entity (slice or tile) containing the current CTU is smaller than the other associated entity. f. Alternatively, for a boundary that is the subpicture boundary, the following applies: i. If loop_filter_across_subpic_enabled_flag[ i ] for the current block is equal to 0, filtering across the boundary is off, regardless of the values of other flags. ii. Otherwise (loop_filter_across_subpic_enabled_flag[ i ] for the current block is equal to 1), the following applies: 1) If loop_filter_across_tiles enabled_flag is equal to 1 or loop_filter_across_ slices enabled_flag is equal to 1, filtering across the boundary is on.

2) Otherwise, filtering across the boundary is off. g. Alternatively, for a boundary that is a subpicture boundary, regardless of whether it is also a tile boundary or virtual boundary, whether filtering across the boundary is on or off is solely determined by the loop_filter_across_subpic_enabled_flag[ i ] associated with the current block, regardless of the values of loop_filter_across_ slices enabled_flag, loop_filter_across_ tiles enabled_flag, and VirtualBoundariesDisabledFlag. h. Alternatively, remove both loop_filter_across_ tiles enabled_flag and loop_filter_across_slices enabled_flag. i. Alternatively, in above examples, those tile boundaries that are also the boundaries of the subpicture are also included that are controlled by the above- mentioned flags. i. Alternatively, furthermore, a conformance bitstream shall satisfy that the controlling flags (e.g., loop_filter_across_ tiles enabled_flag, loop_filter_across_ slices enabled_flag) for subpictures within the same tile shall have the same values. j . In one example, for above bullets (including bullet 1), it may be applied only when the subpi c treated as pi c_fl ag[ i ] is true. ) To solve the third problem, the presence of the syntax element loop_filter_across_subpic_enabled_flag[ i ] is conditioned on "if( subpic_treated_as_pic_flag[ i ] )". a. Alternatively, furthermore, when loop_filter_across_subpic_enabled_flag[ i ] is not present (i.e., when the subpicture is not motion-constrained and hence not extractable) the value of loop_filter_across_subpic_enabled_flag[ i ] is inferred to be equal to 1 (i.e., filtering across the boundaries of the subpicture is allowed). b. In an alternative, the syntax element loop_filter_across_subpic_enabled_flag[ i ] is not conditioned on "if( subpi c treated as pi c fl ag[ i ] )", but it is constrained that the value of loop_filter_across_subpic_enabled_flag[ i ] shall be equal to 1 when subpic_treated_as_pic_flag[ i ] is equal to 0. ) In one example, loop_filter_across_tiles_enabled_flag is made tile-specific (i.e., signalled once for each tile). A loop _filter _across_tiles enabled_flag signaled in a first tile only controls the filtering behavior across the boundaries of the first tile. ) In one example, loop_filter_across_ slices enabled_flag is made slice-specific (i.e., signalled once for each slice). A loop_filter_across_ slices enabled_flag signaled in a first slice only controls the filtering behavior across the boundaries of the first slice. ) In one example, it is signaled (such as in SPS or PPS or picture header or slice header) how to control the filtering behavior across a boundary shared by more than one kind of video units. For example, the boundary may be both a sub-picture boundary and a slice boundary, or it may be both a sub-picture boundary and a tile boundary, or it may be both a slice boundary and a tile boundary. a. In one example, for different kinds of shared boundaries, different controlling messages (e.g. flags) are signaled. For example, a first boundary as both a subpicture boundary and a slice boundary, and a second boundary both as a subpicture boundary and a tile boundary may be controlled by different messages.) In above examples, the filtering process may include but not limited to the processes of the following filtering methods: a. Deblocking filter b. Sample adaptive offset c. Adaptive loop filter d. Cross-component adaptive loop filter e. Bilateral filter f. Transform domain filter (e.g., Hadamard filter) g. Alternatively, furthermore, in one example, all the allowed filtering methods may be controlled with the same syntax element (e.g., loop_filter_across_subp_icenabled_ flag, loop_filter_across_tiles_enabled_flag) for enabling/disabling filtering across a video processing unit (e.g., subpicture, slice/tile/brick). 6. Embodiments

Below are some example embodiments, for some alternatives of implementation aspects 1 and 2 summarized in Section 5, which can be applied to the WC specification. The changed texts are based on the latest WC text in JVET-P2001-vl4. Most relevant parts that have been added or modified are shown in underline , bolded and italicized text, and the most relevant removed parts are highlighted in enclosed in bolded double brackets, e.g., [[a]] indicates that “a” has been removed. There are some other changes that are editorial in nature and thus not highlighted.

6.1. First embodiment

7.3.2.3 Sequence parameter set RBSP syntax

Alternatively, the following may apply:

7.3.2.3 Sequence parameter set RBSP syntax

7.4.3.3 Sequence parameter set RBSP semantics subpics_present_flag equal to 1 specifies that subpicture parameters are present in in the SPS RBSP syntax. subpics_present flag equal to 0 specifies that subpicture parameters are not present in the SPS RBSP syntax.

NOTE 2 - When a bitstream is the result of a sub-bitstream extraction process and contains only a subset of the subpictures of the input bitstream to the sub-bitstream extraction process, it might be required to set the value of subpics_present flag equal to 1 in the RBSP of the SPSs. sps_num_subpics_minusl plus 1 specifies the number of subpictures, sps num subpics minusl shall be in the range of 0 to 254. When not present, the value of sps num subpics minusl is inferred to be equal to 0. subpic_ctu_top_left_x[ i ] specifies horizontal position of top left CTU of i-th subpicture in unit of CtbSizeY. The length of the syntax element is

Ceil( Log2( pic width max in luma samples / CtbSizeY ) ) bits. When not present, the value of subpic_ctu_top_left_x[ i ] is inferred to be equal to 0. subpic_ctu_top_left_y[ i ] specifies vertical position of top left CTU of i-th subpicture in unit of CtbSizeY. The length of the syntax element is

Ceil( Log2( pic height max in luma samples / CtbSizeY ) ) bits. When not present, the value of subpic_ctu_top_left_y[ i ] is inferred to be equal to 0. subpic_width_minusl[ i ] plus 1 specifies the width of the i-th subpicture in units of CtbSizeY. The length of the syntax element is Ceil( Log2( pic width max in luma samples / CtbSizeY ) ) bits. When not present, the value of subpic_width_minusl[ i ] is inferred to be equal to Ceil( pic width max in luma samples / CtbSizeY ) - 1. subpic_height_minusl[ i ] plus 1 specifies the height of the i-th subpicture in units of CtbSizeY. The length of the syntax element is

Ceil( Log2( pic height max in luma samples / CtbSizeY ) ) bits. When not present, the value of subpic_height_minusl[ i ] is inferred to be equal to Ceil( pic height max in luma samples / CtbSizeY ) - 1. subpic_treated_as_pic_flag[ i ] equal to 1 specifies that the i-th subpicture of each coded picture in the CLVS is treated as a picture in the decoding process excluding in-loop filtering operations, subpi c treated as pi c fl ag[ i ] equal to 0 specifies that the i-th subpicture of each coded picture in the CLVS is not treated as a picture in the decoding process excluding in-loop filtering operations. When not present, the value of subpi c treated as pi c fl ag[ i ] is inferred to be equal to 0. loop_filter_across_subpic_enabled_flag[ i ] equal to 1 specifies that in-loop filtering operations may be performed across the boundaries of the i-th subpicture in each coded picture in the CLVS. loop_filter_across_subpic_enabled_flag[ i ] equal to 0 specifies that in-loop filtering operations are not performed across the boundaries of the i-th subpicture in each coded picture in the CLVS. When not present, the value of 1 oop fi 1 ter across_ subpi c _enabled_pic _flag[ i ] is inferred to be equal to 1.

It is a requirement of bitstream conformance that the following constraints apply:

- For any two subpictures subpicA and subpicB, when the subpicture index of subpicA is less than that of subpicB, any coded slice NAL unit of subPicA shall precede any coded slice NAL unit of subPicB in decoding order.

- The shapes of the subpictures shall be such that each subpicture, when decoded, shall have its entire left boundary and entire top boundary consisting of picture boundaries or consisting of boundaries of previously decoded subpictures. sps_subpic_id_present_flag equal to 1 specifies that subpicture ID mapping is present in the SPS. sps subpic_id present flag equal to 0 specifies that subpicture ID mapping is not present in the SPS. sps subpic id signalling present flag equal to 1 specifies that subpicture ID mapping is signalled in the SPS. sps_subpic_id_signalling_present flag equal to 0 specifies that subpicture ID mapping is not signalled in the SPS. When not present, the value of sps subpi c_i d_si gnal 1 i ng present fl ag is inferred to be equal to 0. sps_subpic_id_len_minusl plus 1 specifies the number of bits used to represent the syntax element sps_subpic_id[ i ]. The value of sps_ subpic id len minusl shall be in the range of 0 to 15, inclusive. sps_subpic_id[ i ] specifies that subpicture ID of the i-th subpicture. The length of the sps_subpic_id[ i ] syntax element is sps subpic id len minusl + 1 bits. When not present, and when sps subpi c id present flag equal to 0, the value of sps_subpic_id[ i ] is inferred to be equal to i, for each i in the range of 0 to sps num subpics minusl, inclusive loop filter across tiles enabled flasf i 1 equal to 1 specifies that in-loop filtering operations may be performed across tile boundaries within the i-th subpicture in each coded picture in the CLVS. Herein tile boundaries within a subpicture do not includes tile boundaries that are also the boundaries of the subpicture, loop filter across tiles enabled flasf i J equal to 0 specifies that in-loop filtering operations are not performed across tile boundaries within the i- th subpicture in each coded picture in the CLVS. The in-loop fllterins operations include the deblockins filter , sample adaptive offset filter , and adaptive loop filter operations. When there is no tile boundaries within the i-th subpicture , the value of

7.3.2.4 Picture parameter set RBSP syntax

7.4.3.4 Picture parameter set RBSP semantics pps subpic id signalling present flag equal to 1 specifies that subpicture ID mapping is signalled in the PPS. pps_subpic_id_signalling_present flag equal to 0 specifies that subpicture ID mapping is not signalled in the PPS. When s p s_s ub p i c_i d p re sen t_fl ag is 0 or sps subpi c_i d_si gnal 1 i ng present fl ag is equal to 1, pps subpi c_i d_si gnal 1 i ng present fl ag shall be equal to 0. pps_num_subpics_minusl plus 1 specifies the number of subpictures in the coded pictures referring to the PPS.

It is a requirement of bitstream conformance that the value of pps num subpic minusl shall be equal to sps num subpics minusl. pps_subpic_id_len_minusl plus 1 specifies the number of bits used to represent the syntax element pps_subpic_id[ i ]. The value of pps_ subpic id len minusl shall be in the range of 0 to 15, inclusive.

It is a requirement of bitstream conformance that the value of pps subpic id len minusl shall be the same for all PPSs that are referred to by coded pictures in a CLVS. pps_subpic_id[ i ] specifies the subpicture ID of the i-th subpicture. The length of the pps_subpic_id[ i ] syntax element is pps subpic id len minusl + 1 bits. no_pic_partition_flag equal to 1 specifies that no picture partitioning applied to each picture referring to the PPS. no pi c parti ti on_fl ag equal to 0 specifies each picture referring to the PPS may be partitioned into more than one tile or slice. It is a requirement of bitstream conformance that the value of no pi c parti ti on fl ag shall be the same for all PPSs that are referred to by coded pictures within a CLVS.

It is a requirement of bitstream conformance that the value of no_pic_partition_flag shall not be equal to 1 when the value of sps num subpics minusl + 1 is greater than 1. pps_log2_ctu_size_minus5 plus 5 specifies the luma coding tree block size of each CTU. pps_log2_ctu_size_minus5 shall be equal to sps_log2_ctu_size_minus5. num_exp_tile_columns_minusl plus 1 specifies the number of explicitly provided tile column widths. The value of num exp tile columns minusl shall be in the range of 0 to PicWidthlnCtbsY - 1, inclusive. When no pi c parti ti on fl ag is equal to 1, the value of num exp tile columns minusl is inferred to be equal to 0. num_exp_tile_rows_minusl plus 1 specifies the number of explicitly provided tile row heights. The value of num exp tile rows minusl shall be in the range of 0 to PicHeightlnCtbsY - 1, inclusive. When no_pic_partition_flag is equal to 1, the value of num tile rows minusl is inferred to be equal to 0. tile_column_width_minusl[ i ] plus 1 specifies the width of the i-th tile column in units of CTBs for i in the range of 0 to num exp tile columns minusl - 1, inclusive. tile_column_width_minusl[ num exp tile columns minusl ] is used to derive the width of the tile columns with index greater than or equal to num exp tile columns minusl as specified in clause 6.5.1. When not present, the value of tile_column_width_minusl[ 0 ] is inferred to be equal to PicWidthlnCtbsY - 1. tile_row_height_minusl[ i ] plus 1 specifies the height of the i-th tile row in units of CTBs for i in the range of 0 to num exp tile rows minusl - 1, inclusive. tile_row_height_minusl[ num exp tile rows minusl ] is used to derive the height of the tile rows with index greater than or equal to num exp tile rows minusl as specified in clause 6.5.1. When not present, the value of tile_row_height_minusl[ 0 ] is inferred to be equal to PicHeightlnCtbsY - 1. rect_slice_flag equal to 0 specifies that tiles within each slice are in raster scan order and the slice information is not signalled in PPS. rect slice flag equal to 1 specifies that tiles within each slice cover a rectangular region of the picture and the slice information is signalled in the PPS. When not present, rect slice flag is inferred to be equal to 1. When subpics present flag is equal to 1, the value of rect slice flag shall be equal to 1. single_slice_per_subpic_flag equal to 1 specifies that each subpicture consists of one and only one rectangular slice, si ngl e_sl i ce per subpi c fl ag equal to 0 specifies that each subpicture may consist one or more rectangular slices. When subpics present flag is equal to 0, si ngl e_sl i ce per subpi c fl ag shall be equal to 0. When single_slice per subpic flag is equal to 1, num sl i ces i n_pi c m i nusl is inferred to be equal to sps num subpics minusl. num_slices_in_pic_minusl plus 1 specifies the number of rectangular slices in each picture referring to the PPS. The value of num slices in pic minus l shall be in the range of 0 to MaxSlicesPerPicture - 1, inclusive, where MaxSlicesPerPicture is specified in Annex A. When no pic partition flag is equal to 1, the value of num sl i ces i n_pic minus 1 is inferred to be equal to 0. tile_idx_delta_present_flag equal to 0 specifies that tile idx delta values are not present in the PPS and that all rectangular slices in pictures referring to the PPS are specified in raster order according to the process defined in clause 6.5.1. ti 1 e_i dx del ta present fl ag equal to 1 specifies that tile idx delta values may be present in the PPS and that all rectangular slices in pictures referring to the PPS are specified in the order indicated by the values of tile idx delta. slice_width_in_tiles_minusl[ i ] plus 1 specifies the width of the i-th rectangular slice in units of tile columns. The value of slice_width_in_tiles_minusl[ i ] shall be in the range of 0 to NumTileColumns - 1, inclusive. When not present, the value of slice_width_in_tiles_minusl[ i ] is inferred as specified in clause 6.5.1. slice_height_in_tiles_minusl[ i ] plus 1 specifies the height of the i-th rectangular slice in units of tile rows. The value of slice_height_in_tiles_minusl[i] shall be in the range of 0 to NumTileRows - 1, inclusive. When not present, the value of slice_height_in_tiles_minusl[ i ] is inferred as specified in clause 6.5.1. num_slices_in_tile_minusl[ i ] plus 1 specifies the number of slices in the current tile for the case where the i-th slice contains a subset of CTU rows from a single tile. The value of num_slices_in_tile_minusl[ i ] shall be in the range of 0 to RowHeight[ tileY ] - 1, inclusive, where tileY is the tile row index containing the i-th slice. When not present, the value of num_slices_in_tile_minusl[ i ] is inferred to be equal to 0. slice_height_in_ctu_minusl[ i ] plus 1 specifies the height of the i-th rectangular slice in units of CTU rows for the case where the i-th slice contains a subset of CTU rows from a single tile. The value of slice_height_in_ctu_minusl[ i ] shall be in the range of 0 to RowHeight[ tileY ] - 1, inclusive, where tileY is the tile row index containing the i-th slice. tile_idx_delta[ i ] specifies the difference in tile index between the i-th rectangular slice and the ( i + 1 )-th rectangular slice. The value of tile_idx_delta[ i ] shall be in the range of- NumTilesInPic + 1 to NumTilesInPic - 1, inclusive. When not present, the value of tile_idx_delta[ i ] is inferred to be equal to 0. In all other cases, the value of tile_idx_delta[ i ] shall not be equal to 0.

[[ loop_filter_across_tiles_enabled_flag equal to 1 specifies that in-loop filtering operations may be performed across tile boundaries in pictures referring to the PPS. loop_filter_across_ tiles enabled_flag equal to 0 specifies that in-loop filtering operations are not performed across tile boundaries in pictures referring to the PPS. The in-loop filtering operations include the deblocking filter, sample adaptive offset filter, and adaptive loop filter operations. When not present, the value of loop_filter_across_ tiles enabled_flag is inferred to be equal to 1. loop_filter_across_slices_enabled_flag equal to 1 specifies that in-loop filtering operations may be performed across slice boundaries in pictures referring to the PPS. loop_filter_across_ slice enabled_flag equal to 0 specifies that in-loop filtering operations are not performed across slice boundaries in pictures referring to the PPS. The in-loop filtering operations include the deblocking filter, sample adaptive offset filter, and adaptive loop filter operations. When not present, the value of loop_filter_across_ slices enabled_flag is inferred to be equal to 0.]]

8.8.3 Deblocking filter process 8.8.3.1 General

The deblocking filter process is applied to all coding subblock edges and transform block edges of a picture, except the following types of edges:

- Edges that are at the boundary of the picture, - Edges that coincide with the boundaries of a subpicture for which loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0,

- Edges that coincide with the virtual boundaries of the picture when VirtualBoundariesDisabledFlag is equal to 1,

- Edges that coincide with tile boundaries within a subpicture for which [[when]] loop filter_across_ tiles enabled flag [SubPicIdx / is equal to 0,

- [[Edges that coincide with slice boundaries when loop_filter_across_ slices enabled_flag is equal to 0,]]

- Edges that coincide with upper or left boundaries of slices with slice deblocking filter disabled flag equal to 1,

- Edges within slices with slice deblocking filter disabled flag equal to 1,

- Edges that do not correspond to 4x4 sample grid boundaries of the luma component,

- Edges that do not correspond to 8x8 sample grid boundaries of the chroma component,

- Edges within the luma component for which both sides of the edge have intra bdpcm luma flag equal to 1,

- Edges within the chroma components for which both sides of the edge have intra bdpcm chroma flag equal to 1,

- Edges of chroma subblocks that are not edges of the associated transform unit.

8.8.3.2 Deblocking filter process for one direction

For each coding unit and each coding block per colour component of a coding unit indicated by the colour component index cldx ranging from firstCompIdx to lastCompIdx, inclusive, with coding block width nCbW, coding block height nCbH and location of top-left sample of the coding block ( xCb, yCb ), when cldx is equal to 0, or when cldx is not equal to 0 and edgeType is equal to EDGE VER and xCb % 8 is equal 0, or when cldx is not equal to 0 and edgeType is equal to EDGE HOR and yCb % 8 is equal to 0, the edges are filtered by the following ordered steps:

1. The variable filterEdgeFlag is derived as follows: - If edgeType is equal to EDGE VER and one or more of the following conditions are true, filterEdgeFlag is set equal to 0:

- The left boundary of the current coding block is the left boundary of the picture.

- The left boundary of the current coding block is the left or right boundary of the subpicture and loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0.

- The left boundary of the current coding block is the left boundary of the tile but not a subpicture boundary and loop filter_across_ tiles enabled flag [SubPicIdx / is equal to 0.

- [[The left boundary of the current coding block is the left boundary of the slice and loop_filter_across_ slices enabled_flag is equal to 0.]]

- The left boundary of the current coding block is one of the vertical virtual boundaries of the picture and VirtualBoundariesDisabledFlag is equal to 1.

- Otherwise, if edgeType is equal to EDGE HOR and one or more of the following conditions are true, the variable filterEdgeFlag is set equal to 0:

- The top boundary of the current luma coding block is the top boundary of the picture.

- The top boundary of the current coding block is the top or bottom boundary of the subpicture and loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0.

- The top boundary of the current coding block is the top boundary of the tile but not a subpicture boundary and loop filter_across_ tiles enabled flag [SubPicIdx / is equal to 0.

- [[The top boundary of the current coding block is the top boundary of the slice and loop_filter_across_ slices enabled_flag is equal to 0.]]

- The top boundary of the current coding block is one of the horizontal virtual boundaries of the picture and VirtualBoundariesDisabledFlag is equal to 1.

- Otherwise, filterEdgeFlag is set equal to 1. .. 8.8.4 Sample adaptive offset process 8.8.4.2 CTB modification process

For all sample locations ( xSi, ySj ) and ( xYi, yYj ) with i = 0.mCtbSw - 1 and j = 0.mCtbSh - 1, the following applies:

- If one or more of the following conditions are true, saoPicture[ xSi ][ ySj ] is not modified:

- SaoTypeIdx[ cldx ][ rx ][ ry ] is equal to 0.

- VirtualBoundariesDisabledFlag is equal to 1 and xSj is equal to ( ( VirtualBoundariesPosX[ n ] / scaleWidth ) - 1 ) for any n = 0..VirtualBoundariesNumVer - 1 and SaoTypeIdx[ cldx ][ rx ][ ry ] is equal to 2 and SaoEoClass[ cldx ][ rx ][ ry ] is not equal to 1.

- VirtualBoundariesDisabledFlag is equal to 1 and xSj is equal to ( VirtualBoundariesPosX[ n ] / scaleWidth ) for any n = 0..VirtualBoundariesNumVer - 1 and SaoTypeIdx[ cldx ][ rx ][ ry ] is equal to 2 and SaoEoClass[ cldx ][ rx ][ ry ] is not equal to 1.

- VirtualBoundariesDisabledFlag is equal to 1 and ySj is equal to ( ( VirtualBoundariesPosY[ n ] / scaleHeight ) - 1 ) for any n = 0..VirtualBoundariesNumHor - 1 and SaoTypeIdx[ cldx ][ rx ][ ry ] is equal to 2 and SaoEoClass[ cldx ][ rx ][ ry ] is not equal to 0.

- VirtualBoundariesDisabledFlag is equal to 1 and ySj is equal to ( VirtualBoundariesPosY[ n ] / scaleHeight ) for any n = 0..VirtualBoundariesNumHor - 1 and SaoTypeIdx[ cldx ][ rx ][ ry ] is equal to 2 and SaoEoClass[ cldx ][ rx ][ ry ] is not equal to 0.

- Otherwise, if SaoTypeIdx[ cldx ][ rx ][ ry ] is equal to 2, the following ordered steps apply:

1. The values of hPos[ k ] and vPos[ k ] for k = 0..1 are specified in Table 42 based on SaoEoClass[ cldx ][ rx ][ ry ].

2. The variable edgeldx is derived as follows:

- The modified sample locations ( xSik', ySjk' ) and ( xYik', yYjk' ) are derived as follows:

( xSik', ySjk' ) = ( xSi + hPos[ k ], ySj + vPos[ k ] ) (1404) ( xYik', yYjk' ) = ( cldx = = 0 ) ? ( xSik', yS_jk' ) : ( xSuf * SubWidthC, ySjk' * Sub HeightC ) (1405)

- If one or more of the following conditions for all sample locations ( xSik', ySjk' ) and ( xYik', yYjk' ) with k = 0..1 are true, edgeldx is set equal to 0:

-The sample at location ( xSik', ySjk' ) is outside the picture boundaries.

-The sample at location ( xSik', ySjk' ) belongs to a different subpicture and loop_filter_across_ subpic enabled_flag[ SubPicIdx ] for the subpicture to which the sample recPicture[ xSi ][ ySj ] belongs to is equal to 0.

-[[loop_filter_across_ slices enabled_flag is equal to 0 and the sample at location ( xSik ' , y Sjk ' ) belongs to a different slice.]]

-loop filter_across_ tiles enabled flag [SubPicIdx / is equal to 0 and the sample at location ( xSik', ySjk' ) belongs to a different tile within the same subpicture.

- Otherwise, edgeldx is derived as follows:

-The following applies: edgeldx =

2 + Sign( recPicture[ xSi ][ ySj ] - recPicture[ xSi + hPos[ 0 ] ][ ySj + vPos[ 0 ] ] )

+

Sign( recPicture[ xSi ][ ySj ] - recPicture[ xSi + hPos[ 1 ] ][ ySj + vPos[ 1 ] ] ) (1406)

-When edgeldx is equal to 0, 1, or 2, edgeldx is modified as follows: edgeldx = ( edgeldx = = 2 ) ? 0 : ( edgeldx + 1 ) (1407)

3. The modified picture sample array saoPicture[ xSi ][ ySj ] is derived as follows: saoPicture[ xSi ][ ySj ] = Clip3( 0, ( 1 « BitDepth ) - 1, recPicture[ xSi ][ ySj ] +

SaoOffsetVal[ cldx ][ rx ][ ry ][ edgeldx ] ) (1408)

8.8.5 Adaptive loop filter process

8.8.5.5 ALF boundary position derivation process

The variable clipTopPos is modified as follows: - If y - ( CtbSizeY - 4 ) is greater than or equal to 0, the variable clipTopPos is set equal to yCtb + CtbSizeY - 4.

- Otherwise, if VirtualBoundariesDisabledFlag is equal to 1, and yCtb + y - VirtualBoundariesPosY[ n ] is greater than or equal to 0 and less than 3 for any n = O..VirtualBoundariesNumHor - 1, the following applies: clipTopPos = VirtualBoundariesPosY[ n ]

(1468)

- Otherwise, if y is less than 3 and one or more of the following conditions are true, the variable clipTopPos is set equal to yCtb:

- The top boundary of the current coding tree block is the top boundary of the tile but not a subpicture boundary . and loop filter_across_ tiles enabled fl anf SubPicIdx / is equal to 0.

- [[The top boundary of the current coding tree block is the top boundary of the slice, and loop_filter_across_ slices enabled_flag is equal to 0.]]

- The top boundary of the current coding tree block is the top boundary of the subpicture, and loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0.

The variable clipBottomPos is modified as follows:

- If VirtualBoundariesDisabledFlag is equal to 1, VirtualBoundariesPosY[ n ] is not equal to pic height in luma samples - 1 or 0, and VirtualBoundariesPosY[ n ] - yCtb - y is greater than 0 and less than 5 for any n = O..VirtualBoundariesNumHor - 1, the following applies: clipBottomPos = VirtualBoundariesPosY[ n ]

(1469)

- Otherwise, if CtbSizeY - 4 - y is greater than 0 and is less than 5, the variable clipBottomPos is set equal to yCtb + CtbSizeY - 4.

- Otherwise, if CtbSizeY - y is less than 5, and one or more of the following conditions are true, the variable clipBottomPos is set equal to yCtb + CtbSizeY:

- The bottom boundary of the current coding tree block is the bottom boundary of the tile but not a subpicture boundary . and loop filter_across_ tiles enabled fl au/ SubPicIdx ] is equal to 0. - [[The bottom boundary of the current coding tree block is the bottom boundary of the slice, and loop_filter_across_ slices enabled_flag is equal to 0.]]

- The bottom boundary of the current coding tree block is the bottom boundary of the subpicture, and loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0.

The variable clipLeftPos is modified as follows:

- If VirtualBoundariesDisabledFlag is equal to 1, and xCtb + x - VirtualBoundariesPosX[ n ] is greater than or equal to 0 and less than 3 for any n = O..VirtualBoundariesNumVer - 1, the following applies: clipLeftPos = VirtualBoundariesPosX[ n ]

(1470)

- Otherwise, if x is less than 3, and one or more of the following conditions are true, the variable clipLeftPos is set equal to xCtb:

- The left boundary of the current coding tree block is the left boundary of the tile but not a subpicture boundary . and loop filter_across_ tiles enabled fl au/ SubPicIdx / is equal to 0.

- [[The left boundary of the current coding tree block is the left boundary of the slice, and loop_filter_across_ slices enabled_flag is equal to 0.]]

- The left boundary of the current coding tree block is the left boundary of the subpicture, and loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0.

The variable clipRightPos is modified as follows:

- If VirtualBoundariesDisabledFlag is equal to 1, and VirtualBoundariesPosX[ n ]- xCtb - x is greater than 0 and less than 5 for any n = O..VirtualBoundariesNumVer - 1, the following applies: clipRightPos = VirtualBoundariesPosX[ n ]

(1471)

- Otherwise, if CtbSizeY - x is less than 5, and one or more of the following conditions are true, the variable clipRightPos is set equal to xCtb + CtbSizeY:

- The right boundary of the current coding tree block is the right boundary of the tile but not a subpicture boundary . and loop filter_across_ tiless enabled flag [SubPicIdx / is equal to 0. - [[The right boundary of the current coding tree block is the right boundary of the slice, and loop_filter_across_ slices enabled_flag is equal to 0.]]

- The right boundary of the current coding tree block is the right boundary of the subpicture, and loop_filter_across_subpic_enabled_flag[ SubPicIdx ] is equal to 0.

[[The variable clipTopLeftFlag and clipBotRightFlag are modified as following:

- If the coding tree block covering the luma position ( xCtb, yCtb ) and the coding tree block covering the luma position ( xCtb - CtbSizeY, yCtb - CtbSizeY) belong to different slices, and loop_filter_across_ slices enabled_flag is equal to 0, clipTopLeftFlag is set equal to 1.

- If the coding tree block covering the luma position ( xCtb, yCtb ) and the coding tree block covering the luma position ( xCtb + CtbSizeY, yCtb + CtbSizeY) belong to different slices, and loop_filter_across_ slices enabled_flag is equal to 0, clipBotRightFlag is set equal to 1.]]

[00150] FIG. 19 is a block diagram showing an example video processing system 1900 in which various techniques disclosed herein may be implemented. Various implementations may include some or all of the components of the system 1900. The system 1900 may include input 1902 for receiving video content. The video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format. The input 1902 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON), etc. and wireless interfaces such as Wi-Fi or cellular interfaces.

[00151] The system 1900 may include a coding component 1904 that may implement the various coding or encoding methods described in the present document. The coding component 1904 may reduce the average bitrate of video from the input 1902 to the output of the coding component 1904 to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component 1904 may be either stored, or transmitted via a communication connected, as represented by the component 1906. The stored or communicated bitstream (or coded) representation of the video received at the input 1902 may be used by the component 1908 for generating pixel values or displayable video that is sent to a display interface 1910. The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder.

[00152] Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on. Examples of storage interfaces include SATA (serial advanced technology attachment), PCI, IDE interface, and the like. The techniques described in the present document may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display.

[00153] FIG. 20 is a block diagram of a video processing apparatus 2000. The apparatus 2000 may be used to implement one or more of the methods described herein. The apparatus 2000 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 2000 may include one or more processors 2002, one or more memories 2004 and video processing hardware 2006. The processor(s) 2002 may be configured to implement one or more methods described in the present document. The memory (memories) 2004 may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware 2006 may be used to implement, in hardware circuitry, some techniques described in the present document.

[00154] FIG. 21 is a block diagram that illustrates an example video coding system 100 that may utilize the techniques of this disclosure.

[00155] As shown in FIG. 21, video coding system 100 may include a source device 110 and a destination device 120. Source device 110 generates encoded video data which may be referred to as a video encoding device. Destination device 120 may decode the encoded video data generated by source device 110 which may be referred to as a video decoding device.

[00156] Source device 110 may include a video source 112, a video encoder 114, and an input/output (EO) interface 116.

[00157] Video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder 114 encodes the video data from 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. I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via I/O interface 116 through network 130a. The encoded video data may also be stored onto a storage medium/server 130b for access by destination device 120. [00158] Destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122.

[00159] I/O interface 126 may include a receiver and/or a modem. I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/ server 130b. Video decoder 124 may decode the encoded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with the destination device 120, or may be external to destination device 120 which be configured to interface with an external display device. [00160] Video encoder 114 and video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding(VVM) standard and other current and/or further standards.

[00161] FIG. 22 is a block diagram illustrating an example of video encoder 200, which may be video encoder 114 in the system 100 illustrated in FIG.21.

[00162] Video encoder 200 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 22, video encoder 200 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of video encoder 200. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

[00163] The functional components of video encoder 200 may include a partition unit 201, a predication 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. [00164] In other examples, video encoder 200 may include more, fewer, or different functional components. In an example, predication unit 202 may include an intra block copy(IBC) unit. The IBC unit may perform predication in an IBC mode in which at least one reference picture is a picture where the current video block is located.

[00165] Furthermore, some components, such as motion estimation unit 204 and motion compensation unit 205 may be highly integrated, but are represented in the example of FIG. 22 separately for purposes of explanation.

[00166] Partition unit 201 may partition a picture into one or more video blocks. Video encoder 200 and video decoder 300 may support various video block sizes.

[00167] 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- 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 example, Mode select unit 203 may select a combination of intra and inter predication (CUP) mode in which the predication is based on an inter predication signal and an intra predication signal. 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 interpredication.

[00168] To perform inter prediction on a current video block, 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. 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 buffer 213 other than the picture associated with the current video block. [00169] Motion estimation unit 204 and 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.

[00170] In some examples, motion estimation unit 204 may perform uni-directional prediction for the current video block, and motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. 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. 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. Motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.

[00171] In other examples, motion estimation unit 204 may perform bi-directional prediction for the current video block, 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. 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. 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. 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.

[00172] In some examples, motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.

[00173] In some examples, motion estimation unit 204 may do not output a full set of motion information for the current video. Rather, 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, 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. [00174] In one example, 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.

[00175] In another example, 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.

[00176] 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 predication (AMVP) and merge mode signaling.

[00177] Intra prediction unit 206 may perform intra prediction on the current video block. When intra prediction unit 206 performs intra prediction on the current video block, 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.

[00178] 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.

[00179] 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 residual generation unit 207 may not perform the subtracting operation.

[00180] 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.

[00181] After transform processing unit 208 generates a transform coefficient video block associated with the current video block, 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.

[00182] Inverse quantization unit 210 and 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. Reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the predication unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.

[00183] After reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block.

[00184] Entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, 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.

[00185] FIG. 23 is a block diagram illustrating an example of video decoder 300 which may be video decoder 114 in the system 100 illustrated in FIG. 21.

[00186] The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 23, 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.

[00187] In the example of FIG. 23, 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. Video decoder

300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200 (FIG. 22).

[00188] 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). Entropy decoding unit

301 may decode the entropy coded video data, and from the entropy decoded video data, motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode.

[00189] 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. [00190] Motion compensation unit 302 may use interpolation filters as used by video encoder 20 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.

[00191] Motion compensation unit 302 may uses some 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.

[00192] Intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transform unit 303 applies an inverse transform.

[00193] Reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 202 or intra-prediction unit 303 to form decoded blocks. 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 buffer 307, which provides reference blocks for subsequent motion compensation/intra predication and also produces decoded video for presentation on a display device.

[00194] FIGS. 24-25 show example methods that can implement the technical solution described above in, for example, the embodiments shows in FIGS. 19-23.

[00195] FIG. 24 shows a flowchart for an example method 2400 of video processing. The method 2400 includes, at operation 2410, determining, for a conversion between a video comprising a video region and a bitstream of the video, whether to apply a loop filtering process across a boundary associated with the video region, the bitstream including one or more syntax elements indicative of whether the loop filtering process is applicable on a per-video region basis. [00196] The method 2400 includes, at operation 2420, performing, based on the determining, the conversion.

[00197] FIG. 25 shows a flowchart for an example method 2500 of video processing. The method 2500 includes, at operation 2510, performing a conversion between a video comprising a video region that includes a subpicture and a bitstream of the video, the bitstream conforming to a format rule that specifies whether a first syntax element is signaled in the bitstream is based on whether the subpicture is treated as a picture, and the first syntax element being related to an application of a loop filtering process across a subpicture boundary associated with the video region.

[00198] A listing of solutions preferred by some embodiments is provided next.

[00199] Al. A method of video processing, comprising determining, for a conversion between a video comprising a video region and a bitstream of the video, whether to apply a loop_filtering process across a boundary associated with the video region; and performing, based on the determining, the conversion, wherein the bitstream includes one or more syntax elements indicative of whether the loop filtering process is applicable on a per-video region basis.

[00200] A2. The method of solution Al, wherein the video region is a subpicture.

[00201] A3. The method of solution A2, wherein the one or more syntax elements are signaled in the picture parameter set (PPS).

[00202] A4. The method of solution A2, wherein the one or more syntax elements control whether the loop filtering process across tile boundaries within the subpicture is enabled.

[00203] A5. The method of solution A4, wherein the tile boundaries within the subpicture exclude tile boundaries that are coincident with boundaries of the subpicture.

[00204] A6. The method of solution A2, wherein the one or more syntax elements are signaled in the sequence parameter set (SPS).

[00205] A7. The method of solution A6, wherein the one or more syntax elements are signaled in response to the video comprising the subpicture.

[00206] A8. The method of any of solutions A2 to A7, wherein the one or more syntax elements include a first syntax element and a second syntax element.

[00207] A9. The method of solution A8, wherein the first syntax element and the second syntax element have a same value. [00208] A10. The method of solution A8, wherein the first syntax element and the second syntax element for subpictures in a same tile have a same value.

[00209] Al l. The method of solution A8, wherein the first syntax element and the second syntax element are associated with one representative subpicture among multiple subpictures in a same tile.

[00210] A12. The method of solution Al l, wherein the one representative subpicture is a first subpicture to be coded or decoded in an encoding order or a decoding order, respectively.

[00211] A13. The method of solution A8, wherein the boundary is a slice boundary and a tile boundary, and wherein the first syntax element and the second syntax element have different values.

[00212] A14. The method of solution A13, wherein upon a determination that a slice comprising a current coding tree unit (CTU) is identical to or a superset of a tile comprising the current CTU, the conversion is based on the first syntax element and not based on the second syntax element. [00213] A15. The method of solution A8, wherein the boundary is a subpicture boundary, and wherein the application of the loop filtering process across the boundary is enabled based on either the first syntax element or the second syntax element being equal to one.

[00214] A16. The method of solution A8, wherein the boundary is a subpicture boundary and a tile boundary, and wherein the application of the loop_filtering process across the boundary is enabled based on either the first syntax element or the second syntax element being equal to one. [00215] A17. The method of any of solutions A8 to A16, wherein the first syntax element is used for controlling a deblocking filter (DF), a sample adaptive offset (SAO), and an adaptive loop filter (ALF) across tile boundaries, and wherein the second syntax element is used for controlling a deblocking filter (DF), a sample adaptive offset (SAO), and an adaptive loop filter (ALF) across slice boundaries.

[00216] A18. The method of any of solutions A8 to A17, wherein the first syntax element is loop_filter_across_tiles enabled_flag and the second syntax element is loop_filter_across_slices enabled_flag.

[00217] A19. The method of solution Al, wherein the video region is a tile.

[00218] A20. The method of solution Al, wherein the video region is a slice. [00219] A21. The method of solution Al, wherein the video region comprises at least a first type of video unit and a second type of video unit, and wherein the boundary is a boundary of the first type of video unit and a boundary of the second type of video unit.

[00220] A22. The method of solution A21, wherein the first type of video unit is a subpicture and the second type of video unit is a slice.

[00221] A23. The method of solution A21, wherein the first type of video unit is a subpicture and the second type of video unit is a tile.

[00222] A24. The method of solution A21, wherein the first type of video unit is a slice and the second type of video unit is a tile.

[00223] A25. A method of video processing, comprising performing a conversion between a video comprising a video region that includes a subpicture and a bitstream of the video, wherein the bitstream conforms to a format rule that specifies whether a first syntax element is signaled in the bitstream is based on whether the subpicture is treated as a picture, and wherein the first syntax element is related to an application of a loop_filtering process across a subpicture boundary associated with the video region.

[00224] A26. The method of solution A25, wherein the format rule specifies that the bitstream includes a second syntax element indicating whether the subpicture is treated as the picture. [00225] A27. The method of solution A25, wherein the first syntax element is inferred to indicate that the loop_filtering process across the subpicture boundary is allowed in response to the bitstream excluding the first syntax element.

[00226] A28. The method of any of solutions A25 to A27, wherein the first syntax element is loop_filter_across_ subpic enabled_flag and the second syntax element is subpi c treated as pi c_fl ag .

[00227] A29. The method of solution A28, wherein the first syntax element is inferred to indicate that the loop filtering process across the boundaries of the subpicture is allowed in response to the second syntax element indicating that the subpicture is not treated as the picture.

[00228] A30. The method of any of solutions Al to A29, wherein the loop_filtering process comprises at least one of a deblocking filter, a sample adaptive offset (SAO) filter, an adaptive loop filter (ALF), a cross-component adaptive loop filter, a bilateral filter, and a transform domain filter. [00229] A31. The method of any of solutions A1 to A30, wherein the conversion comprises decoding the video from the bitstream representation.

[00230] A32. The method of any of solutions A1 to A30, wherein the conversion comprises encoding the video into the bitstream representation.

[00231] A33. A method of writing a bitstream representing a video to a computer-readable recording medium, comprising generating a bitstream from a video according to a method described in any one or more of solutions A1 to A32; and writing the bitstream to the computer- readable recording medium.

[00232] A34. A video processing apparatus comprising a processor configured to implement a method recited in any one or more of solutions A1 to A33.

[00233] A35. A computer-readable medium having instructions stored thereon, the instructions, when executed, causing a processor to implement a method recited in one or more of solutions A1 to A33.

[00234] A36. A computer readable medium that stores the bitstream representation generated according to any one or more of solutions A1 to A33.

[00235] A37. A video processing apparatus for storing a bitstream representation, wherein the video processing apparatus is configured to implement a method recited in any one or more of solutions A1 to A33.

[00236] Another listing of solutions preferred by some embodiments is provided next.

[00237] Bl. A method of video processing, comprising determining, for a conversion between a subpicture of a video and a coded representation of the video, whether to apply a loop filter across a boundary within the subpicture; and performing the conversion based on the determining; wherein a format of the coded representation permits individualized signaling of applicability of a loop filter.

[00238] B2. The method of solution Bl, wherein a first field at a picture level indicates whether the independent signaling at subpicture level is used in the coded representation.

[00239] B3. The method of solution Bl, wherein a first field at a video sequence level indicates whether the independent signaling at subpicture level is used in the coded representation. [00240] B4. The method of any of solutions B1 to B4, wherein the individualized signaling of applicability of a loop filter includes a signaling of applicability across tiles within the subpicture and/or a signaling of applicability across slices within the subpicture.

[00241] B5. A method of video processing, comprising determining, based on a condition, whether to parse a field that indicates whether to apply a loop filter across a boundary of a video portion of a video region of a video; performing a conversion of samples within the video portion of the video and a coded representation of the video, based on the determination.

[00242] B6. The method of solution B5, wherein the condition corresponds to whether the video portion in the video region is treated as a picture.

[00243] B7. The method of solution B6, wherein the condition corresponds to whether a subpi c treated as pi c fl ag is true.

[00244] B8. The method of solution B6, further comprising, when the video portion in the video region is not treated as a picture, the field is not parsed for decoding.

[00245] B9. The method of solution B8, further comprising, applying a loop_filter_across a boundary of the video portion of the video region of the video is disabled.

[00246] B10. The method of solution B6, further comprising, when the video portion in the video region is treated as a picture, the field is parsed.

[00247] B11. The method of solution B8, further comprising, whether to apply a loop filter across the boundary of the video portion of the video region of the video is determined by the parsed field. [00248] B 12. A method of video processing, comprising performing a determination, for a conversion between a video portion of a video region of a video and a coded representation of the video, whether to apply a loop filter across a boundary of the video portion based on a condition; and performing the conversion based on the determining.

[00249] B13. The method of solution B 12, wherein the condition corresponds to whether the video portion is treated as a picture.

[00250] B14. The method of solution B12, wherein the condition corresponds to whether the subpi c treated as pi c fl ag is true in the coded representation.

[00251] B15. The method of any of solutions B12 to B13, wherein an indication of applicability of the loop filter across the boundary of the video portion is omitted in the coded representation. [00252] B16. The method of any of above claims, wherein the video portion is a subpicture and the video region is a picture.

[00253] B 17. The method of any of above claims, wherein the video portion is a tile and the video region is a picture.

[00254] B18. The method of solution B 17, wherein a tile-specific field in the coded representation is indicative of whether to apply the loop filter across the boundary of the video portion.

[00255] B19. The method of any of above claims, wherein the video portion is a slice and the video region is a picture.

[00256] B20. The method of solution B19, wherein a slice-specific field in the coded representation is indicative of whether to apply the loop_filter across the boundary of the video portion.

[00257] B21. The method of any of above claims, wherein the loop filter is a deblocking filter. [00258] B22. The method of any of above claims, wherein the loop_filter is a sample adaptive offset (SAO) filter.

[00259] B23. The method of any of above claims, wherein the loop filter is an adaptive loop filter. [00260] B24. The method of any of above claims, wherein the loop_filter is a cross-component adaptive loop filter.

[00261] B25. The method of any of above claims, wherein the loop filter is a bilateral filter. [00262] B26. The method of any of above claims, wherein the loop filter is a transform domain filter.

[00263] B27. The method of any of solutions B1 to B26, wherein the performing the conversion comprising encoding the video to generate the coded representation.

[00264] B28. The method of any of solutions B1 to B26, wherein the performing the conversion comprises parsing and decoding the coded representation to generate the video.

[00265] B29. A video decoding apparatus comprising a processor configured to implement a method recited in one or more of solutions B1 to B28.

[00266] B30. A video encoding apparatus comprising a processor configured to implement a method recited in one or more of solutions B1 to B28. [00267] B31. A computer program product having computer code stored thereon, the code, when executed by a processor, causes the processor to implement a method recited in any of solutions B1 to B28.

[00268] In the present document, the term “video processing” may refer to video encoding, video decoding, video compression or video decompression. For example, video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa. The bitstream representation of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax. For example, a macroblock may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream.

[00269] The disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.

[00270] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[00271] The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). [00272] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[00273] While this patent document contains many specifics, these should not be construed as limitations on the scope of any subject matter or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular techniques. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[00274] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments. [00275] Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.

Claims

WHAT IS CLAIMED IS:

1. A method of video processing, comprising: determining, for a conversion between a video comprising a video region and a bitstream of the video, whether to apply a loop filtering process across a boundary associated with the video region; and performing, based on the determining, the conversion, wherein the bitstream includes one or more syntax elements indicative of whether the loop filtering process is applicable on a per-video region basis.

2. The method of claim 1, wherein the video region is a subpicture.

3. The method of claim 2, wherein the one or more syntax elements are signaled in the picture parameter set (PPS).

4. The method of claim 2, wherein the one or more syntax elements control whether the loop filtering process across tile boundaries within the subpicture is enabled.

5. The method of claim 4, wherein the tile boundaries within the subpicture exclude tile boundaries that are coincident with boundaries of the subpicture.

6. The method of claim 2, wherein the one or more syntax elements are signaled in the sequence parameter set (SPS).

7. The method of claim 6, wherein the one or more syntax elements are signaled in response to the video comprising the subpicture.

8. The method of any of claims 2 to 7, wherein the one or more syntax elements include a first syntax element and a second syntax element.

9. The method of claim 8, wherein the first syntax element and the second syntax element have a same value.

10. The method of claim 8, wherein the first syntax element and the second syntax element for subpictures in a same tile have a same value.

11. The method of claim 8, wherein the first syntax element and the second syntax element are associated with one representative subpicture among multiple subpictures in a same tile.

12. The method of claim 11, wherein the one representative subpicture is a first subpicture to be coded or decoded in an encoding order or a decoding order, respectively.

13. The method of claim 8, wherein the boundary is a slice boundary and a tile boundary, and wherein the first syntax element and the second syntax element have different values.

14. The method of claim 13, wherein upon a determination that a slice comprising a current coding tree unit (CTU) is identical to or a superset of a tile comprising the current CTU, the conversion is based on the first syntax element and not based on the second syntax element.

15. The method of claim 8, wherein the boundary is a subpicture boundary, and wherein the application of the loop filtering process across the boundary is enabled based on either the first syntax element or the second syntax element being equal to one.

16. The method of claim 8, wherein the boundary is a subpicture boundary and a tile boundary, and wherein the application of the loop filtering process across the boundary is enabled based on either the first syntax element or the second syntax element being equal to one.

17. The method of any of claims 8 to 16, wherein the first syntax element is used for controlling a deblocking filter (DF), a sample adaptive offset (SAO), and an adaptive loop filter (ALF) across tile boundaries, and wherein the second syntax element is used for controlling a deblocking filter (DF), a sample adaptive offset (SAO), and an adaptive loop filter (ALF) across slice boundaries.

18. The method of any of claims 8 to 17, wherein the first syntax element is loop_filter_across_ tiles enabled_flag and the second syntax element is loop_filter_across_slices enabled_flag.

19. The method of claim 1, wherein the video region is a tile.

20. The method of claim 1, wherein the video region is a slice.

21. The method of claim 1, wherein the video region comprises at least a first type of video unit and a second type of video unit, and wherein the boundary is a boundary of the first type of video unit and a boundary of the second type of video unit.

22. The method of claim 21, wherein the first type of video unit is a subpicture and the second type of video unit is a slice.

23. The method of claim 21, wherein the first type of video unit is a subpicture and the second type of video unit is a tile.

24. The method of claim 21, wherein the first type of video unit is a slice and the second type of video unit is a tile.

25. A method of video processing, comprising: performing a conversion between a video comprising a video region that includes a subpicture and a bitstream of the video, wherein the bitstream conforms to a format rule that specifies whether a first syntax element is signaled in the bitstream is based on whether the subpicture is treated as a picture, and wherein the first syntax element is related to an application of a loop filtering process across a subpicture boundary associated with the video region.

26. The method of claim 25, wherein the format rule specifies that the bitstream includes a second syntax element indicating whether the subpicture is treated as the picture.

27. The method of claim 25, wherein the first syntax element is inferred to indicate that the loop filtering process across the subpicture boundary is allowed in response to the bitstream excluding the first syntax element.

28. The method of any of claims 25 to 27, wherein the first syntax element is loop_filter_across_ subpic enabled_flag and the second syntax element is subpi c treated as pi c_fl ag .

29. The method of claim 28, wherein the first syntax element is inferred to indicate that the loop filtering process across the boundaries of the subpicture is allowed in response to the second syntax element indicating that the subpicture is not treated as the picture.

30. The method of any of claims 1 to 29, wherein the loop filtering process comprises at least one of a deblocking filter, a sample adaptive offset (SAO) filter, an adaptive loop filter (ALF), a cross-component adaptive loop filter, a bilateral filter, and a transform domain filter.

31. The method of any of claims 1 to 30, wherein the conversion comprises decoding the video from the bitstream representation.

32. The method of any of claims 1 to 30, wherein the conversion comprises encoding the video into the bitstream representation.

33. A method of writing a bitstream representing a video to a computer-readable recording medium, comprising: generating a bitstream from a video according to a method described in any one or more of claims 1 to 32; and writing the bitstream to the computer-readable recording medium.

34. A video processing apparatus comprising a processor configured to implement a method recited in any one or more of claims 1 to 33.

35. A computer-readable medium having instructions stored thereon, the instructions, when executed, causing a processor to implement a method recited in one or more of claims 1 to 33.

36. A computer readable medium that stores the bitstream representation generated according to any one or more of claims 1 to 33.

37. A video processing apparatus for storing a bitstream representation, wherein the video processing apparatus is configured to implement a method recited in any one or more of claims 1 to 33.