JVET-Q0044 AHG9/AHG12: Simplification of slice index with subpictures [T. Nishi, V. Drugeon (Panasonic)]
This contribution was discussed Tuesday 7 January 2020 at 1405 (chaired by GJS).
It is suggested to simplify the indexing of slices by aligning the picture level slice index to the subpicture level slice index, thereby removing the need to map the subpicture level slice index to the picture level slice index.
That means, disallow the picture-level slice index values allocated as shown in the first figure below. For the same picture partitioning (into subpictures, slices and tiles), use the picture-level slice index values as in the second figure below.
In other words, picture-level slice index values for slices within a subpicture are required to be continuous. In other words, for any two slices sliceA and sliceB belonging to different subpictures subpicA and subpicB, respectively, when the subpicture index of subpicA is less than that of subpicB, the picture-level slice index value of sliceA shall be less than that sliceB.
Picture divided in 12 tiles, 8 slices and 2 subpictures
Picture divided in 12 tiles, 8 slices and 2 subpictures with slices indexed according to their decoding order
It was commented that it is only an editorial matter what slice numbers are assigned to the slices in the text, and that the proposal does simplify the concept in the text by removing a LUT concept.
The proponent indicated that they intended for the text to also align the slice index values with the slice order, i.e., that the slice index values within each subpicture are consecutive.
This was further discussed Thursday 16 January in Track A at 1310 (chaired by GJS).
A sentence was added in a revision, saying “When rect_slice_flag is equal to 1, the decoding order of VCL NAL units within a subpicture is specified to be in increasing order of their subpicture-level slice index values, i.e., the slice_address values.”
Decision (cleanup): Adopt. Text was made available in a revision of the contribution.