JVET-P0298 CE7-related: Unification of CCB check method and bypass coding between two residual coding modes [Y. Kato, K. Abe, T. Toma (Panasonic)]
In this contribution, it is proposed to simplify the CCB (Context Coded bins) check method and unify the syntax design after CCB count exceeds the maximum number between transform residual and transform skip (TS) residual. Two items are proposed. In Item1, the CCB check method is changed from per coefficient flag to per coefficient of each pass in VTM6.0. This CCB check method is same as that of CE7-1.3b. In Item2, level mapping is disabled after CCB count on top of CE7-1.3b-alternative method. This Item2 is also same concept of JVET-O0406. As a modified Item2, bypass sign flag is excluded from the pass of bypass-coded coefficients on Item2. In this item, syntaxes of transform residual and TS residual after CCB count exceeds the maximum number are exactly the same.
Simulation results reportedly are shown as follows:
Item1:
ClassF: 0.02% AI, 0.02% RA, -0.01% LB ClassTGM: 0.04% AI, 0.00% RA, -0.01%LB
Item1 (Low QP):
ClassF: 0.08%AI, -0.01%RA, 0.03%LB ClassTGM: 0.10%AI, 0.06%RA, 0.00%LB
Item2
ClassF: 0.01% AI, 0.02% RA, 0.00% LB ClassTGM: 0.05% AI, 0.04% RA, -0.06%LB
Item2 (Low QP):
ClassF: -1.21%AI, -1.55%RA, -0.44%LB ClassTGM: -1.36%AI, -2.01%RA, -0.91%LB
The “level mapping” performs prediction of the abs value. The results show this is not necessary in the remaining coefficient coding after the ctx bin budget is exceeded.
After inspection of the draft text, the additional change on top of CE7-1.3b* is straightforward and simple. Decision: Adopt JVET-P0298 second aspect.