JVET-R0043 AHG9: On subpicture interaction with other tools [J. Li, K. Abe (Panasonic)]
Discussion began here with AHG Session 1.15 on Monday 13 April at 1300 UTC (chaired by GJS & YKW).
This contribution proposes to disable tool combinations between (1) subpicture and field coding (2) subpicture and Gradual Decoder Refresh (GDR). It is asserted that the concept between subpicture and field coding are mutually exclusive and that subpicture and GDR do not work well together.
Currently, the field coding indication is essentially metadata. It is not coupled with any aspects of coding. It was commented that it seemed undesirable to couple these only to disallow the combination, which could plausibly be used – e.g., splitting the left and right halves of the picture into two subpictures.
A virtual boundary can be used for GDR, and in the current draft, a virtual boundary can only be used with subpictures if the virtual boundary is in the SPS. However, GDR can also be used without a virtual boundary (e.g., with coding as would have been done for prior standards while providing GDR header information).
The proposed restrictions did not seem necessary and would prohibit potential uses, so no action was taken on this.