JVET-R0197 AHG12: On signalling of loop filter across tiles and slices enabled flags [N. Park, J. Nam, H. Jang, J. Lim, Hendry, S. Kim (LGE)]
In the current VVC draft, the flags loop_filter_across_tiles_enabled_flag and loop_filter_across_slices_enabled_flag are signalled when it is specified that there is picture partitioning, regardless whether tiles and / or slices are present. It is asserted that loop_filter_across_tiles_enabled_flag is not needed when there is only one tile in the picture and, likewise, loop_filter_across_slices_enabled_flag is not needed when there is no tile that is divided into more than one rectangular slice.
This contribution proposed the following:
- Condition the presence of (pps_)loop_filter_across_tiles_enabled_flag to be present only when NumTilesInPic is greater than 1.
- Condition the presence of (pps_)loop_filter_across_slices_enabled_flag to be present only when there is at least one tile that is divided into more than one rectangular slice.
It is remarked that no action needs to be taken if contribution JVET-R0069 is adopted.
The first aspect would not be possible if the flag is moved to the SPS. This aspect relates to other contributions discussed in section 6.2.2.1 under JVET-R0053 (item 3); see notes there.
For the second aspect, it was pointed out that this would not allow disabling filtering across slice boundaries that contain multiple tiles that have filtered tile boundaries (in the raster scan slice and rectangular slice cases).