JVET-AF0094 [AHG9] On activation of an NNPFGC that contains another NNPFGC [Hendry, J. Nam, S. Kim, J. Lim (LGE)]

It was asserted that the current text for neural-network post-filter group activation (NNPFGA) SEI message has problem such that NNPFGA SEI message cannot activate an NNPFGC that has another NNPFGC as its member. This contribution proposes the following modification to overcome the asserted problem. The proposed modifications are as follows:

1. Remove the constraint that the value of nnpfga_num_filters_minus2 shall be equal to the value of nnpfgc_num_members_minus2 in an NNPFGC SEI message with nnpfgc_id equal to nnpfga_target_id.
2. Specify that the value of nnpfga_num_filters_minus2 shall be equal to or greater than the value of nnpfgc_num_members_minus2 in an NNPFGC SEI message with nnpfgc_id equal to nnpfga_target_id.
3. Specify that nnpfga_num_filters_minus2 plus 2 specifies the number of direct or indirect NNPF members of an NNPFGC SEI message with nnpfgc_id equal to nnpfga_target_id.
4. The list of NNPFs activated by an NNPFGA is the list consisting the direct and indirect NNPF members of the target NNPFGC in the order based on depth-first-search traversal of the NNPFGC’s members.

It was commented that the constraint was introduced for the purpose of hierarchical grouping, and associated activation level by level. No need to change, but some text clarification of the intent could be useful.