JVET-R0290 AHG16: LMCS constraint cleanup [F. Bossen (Sharp)]

It is asserted that the expression of constraints on LMCS parameters is needlessly convoluted. An alternative definition of constraints is proposed. While the proposed constraints are not strictly equivalent to the ones in VVC draft 8, no impact on coding efficiency is observed under common test conditions. It is asserted that the proposed constraint is much more straightforward.

The proposal would simplify the expression of the encoder restriction, but give up some flexibility of LMCS. No need to change a decoder implementation, though perhaps a decoder could be simplified by knowing the range is more restricted. There are however divergent opinions on this.

No urgent need of doing this change, nothing is broken, and it gives up some flexibility.

No action on this proposal

It is noted that conformance bitstreams should be made available which exercise the entire range of the current spec.