JVET-AN0069 AHG9/AHG13: Updates for the film grain regions SEI message [E. François, F. Urban, P. de Lagrange, D. Doyen (InterDigital), G. Teniou (Tencent)]

This contribution proposes updates for the film grain regions (FGR) SEI message (included in the technologies under consideration for future extensions of VSEI).

Issue 1 – blending equations of synthesized grain with alpha channel

It is questioned why there is a division by 255, etc. rather than by 256. It is noted that the existing film grain characteristics SEI has this design.

Issue 2 simplifies indication of one vs. two models.

Issue 3 proposes reordering the syntax elements and avoids signalling unnecessary syntax elements for region based parameters when operating in frame based mode.

Agreed for issues 1, 2, 3.

JVET-AN0069 AHG9/AHG13: Updates for the film grain regions SEI message