JVET-P0576 AHG18: on low level coding for lossless [H. Jang, J. Choi, J. Nam, S. Kim, J. Lim (LGE)]
This contribution suggests to support lossless coding for VVC. In this proposal, in order to adaptively control whether lossless coding or lossy coding, a flag is transmitted to bypass transform and quantization in CU level as HEVC, and several low level coding tools are disabled for lossless block. The mandatory low level coding tool restriction is described as below:
- Disabling transform related coding tools and syntax signalling; MTS, LFNST, SBT and transform skip for lossless coded block.
- Disabling JointCbCr and the syntax signalling for lossless coded block
- Disabling LMCS in slice level and the syntax signalling
- Disabling sign data hiding for transform/quantization bypass block.
In order to support co-existence between the lossless coding and lossy coding at the CU-level, the following additional restrictions are suggested.
- Bypass ALF processing for lossless coded block.
- Support residual coding for Size MxN(M= 64 or N = 64) when MaxTbSize of 64 is signaled in SPS.
- Implicit TU tiling to 32 for lossless block
- Extend coefficient scanning
No need for action was evident. Implicit TU tiling was agreed by discussion in CE3 (JVET-P0352). It is further noted that lossless coding will be possible in VTM7, but existing high level flags together with appropriate signalling at block level are sufficient to disable tools that would be in conflict.