JVET-P0436 AHG15: On CU Adaptive Chroma QP Offset Signalling [J. Zhao, S. Paluri, S. Kim (LGE)]
In VVC, there are two issues in terms of CU chroma QP offset signalling. Firstly, chroma QP offset signalling is unnecessary for DUAL_TREE_LUMA case. Secondly, chroma QP offset signalling is inconsistent with the principle of VPDU QP availability as in luma delta QP signalling. Therefore, this document proposes two modifications to the conditions of signalling CU chroma QP offset.
- Modification 1 removes the unnecessary signalling of CU chroma QP offset in the case of DUAL_TREE_LUMA in transform_unit
- Modification 2 makes CU chroma QP offset signalling consistent with the VPDU CU QP delta availability, and for CU larger than 64x64, send the chroma QP offset with the first transform unit regardless of whether it has non-zero CBF or not.
Decision (ed./cleanup): Adopt JVET-P0436 Modification 1 (relation to JVET-P0360 – editor to decide the solution that is best consistent – syntax part should avoid the make existence of syntax elemets dependent on semantics)
It is agreed that modification 2 resolves a problem with VPDU, as the chroma QP offset would currently only be sent with a later TU in a large CU, even though needed earlier.
Decision: Adopt JVET-P0436 Modification 2.