JVET-AL0095 AHG 9: On constituent rectangles SEI message [C. Kim, H. Tan, J. Nam, J. Lee, J. Lim, S. Kim (LGE)]

This contribution proposes two changes to the specification of constituent rectangles (CR) SEI message.

• To skip unnecessary syntax elements when a layer contains a single constituent rectangle.
• To improve the presence condition for the size of the guard band

It was suggested that the first proposal would inherently require that all sample locations in the coded picture are in the CR, which is not currently a requirement.

No action on the first proposal.

The current design doesn’t allow signalling a zero size guardband in one direction but not in the other. The contribution doesn’t address this issue. It might make sense to remove the _minus1 from guard band size signalling. suggested to condition the presence of the cr_guardbands_present_flag[ ] on having more than one CR in a row and/or column.

It was suggested that signalling of the guardband might still be useful for the subbitstream extraction use case. However, guardbands are not included on the edges of the picture but just between CRs.

Semantics changes for cr_guardbands_present_flag[ ] are also proposed.

Decision: remove the _minus1 in the cr_guardband_hor_size_minus1 and cr_guardband_verr_size_minus1. Also add semantics change for cr_guardbands_present_flag[ ], with precise language determined by editors.