JVET-P0488 Non-CE7: On updating a variable for context model selection [S. Yoo, J. Choi, J. Lim, S. Kim (LGE)]
In the residual coding part in VVC, a syntax element indicating absolute level in the first pass (i.e., AbsLevelPass1) is referenced when deriving the context model index of sig_coeff_flag, par_flag, and gtx_flag. This contribution points out a mismatch between spec text and software regarding AbsLevelPass1 update process, and introduces two alternative methods to fix the issue as follows:
- Method 1: Change spec text to align with software.
- Method 2: Remove updates process of AbsLevelPass1
For Method 2, the existing update of AbsLevelPass1 is suggested to be removed because the update process is not essentially required. The experiment shows that the BD-rate impact of the Method 2 is 0.00% (AI) / 0.00% (RA) / 0.01% (LDB) for CTC QPs, and 0.00% (AI) / X.XX% (RA) / 0.00% (LDB), for the low QPs, respectively. Note: X.XX% = value not provided in contribution.
Decision (ed./cleanup): It is agreed that the sentence (7-176) can be removed from the text. It is not needed any more after some change adopted in last meeting.
The processing applied to AbsLevelPass1 is otherwise as described as described in the syntax part of the spec – there is no need to change the software.