JVET-AL0204 AHG9: On picture width and height for the film grain characteristics SEI message [M. M. Hannuksela, J. Boyce (Nokia)]

The following aspects are proposed for the film grain characteristics (FGC) SEI message in this contribution:

1. Addition of fg_pic_width_in_luma_samples and fg_pic_height_in_luma_samples to an extension of the FGC SEI message. When present, they indicate the width and the height of the picture for which the film grain modelling information is indicated in units of luma samples. When fg_pic_width_in_luma_samples and fg_pic_height_in_luma_samples are not present, there is no change to the existing specifications on picture width and height for the FGC SEI message.
2. Clarifications how the input image Î to which the film grain model applies is derived.

Conceptually similar to JVET-AL0086, with some syntax differences.

It was commented that in some previous precedence case, using extension mechanisms was disliked. It might however in the current case resolve the problem for new implementations and avoid possible conflict with existing implementations.

JVET-AL0204 AHG9: On picture width and height for the film grain characteristics SEI message [M. M. Hannuksela, J. Boyce (Nokia)]