JVET-AQ0129 AHG9: On the Alpha Channel Information SEI message [C.-H. Demarty, A. Ak, E. François, P. de Lagrange, F. Urban, N. Caramelli (InterDigital)]

At the previous meeting, a new value of alpha_channel_use_idc was introduced to distinguish auxiliary alpha layers intended for film grain blending from other usages.

This contribution proposes a complementary update to align this change with the ISO/IEC 23001-11 (green metadata) specification. Since green metadata attenuation maps are conveyed using auxiliary layers of type AUX_ALPHA and ISO/IEC 23001-11 already specifies alpha_channel_use_idc equal to 3 for this purpose, this contribution proposes reserving value 3 for display adaptation and assigning a different value to film grain blending.

The proposed changes remove potential ambiguities when the same auxiliary picture type is referenced by different SEI messages while maintaining consistency between VSEI and the published green metadata specification.

It was questioned if the green metadata specification is a normative reference to VSEI.

A wording change was suggested to use “shall be equal” rather than “is equal to”.

It is noted that the language of the constraint refers to “Green SEI message” which is not the name of the green metadata SEI message.

It was suggested that the constraint be imposed in the ACI SEI message semantics for alpha_channel_use_idc rather than in the SDI SEI message. This is also relevant for the existing language in the SDI SEI regarding FGRC and ACI SEI messages.

Agreed to the -v2 version.

SEI processing order (SPO) SEI message (2)

Contributions in this area were discussed during 1150–1205 on Friday 10 July 2026 (chaired by S. Deshpande).