JVET-T0085 AHG12: Rice parameter derivation for high bit-depth coding [T. Hashimoto, T. Ikai (Sharp)]
This contribution was discussed in JVET session 11 at 2240 on Monday 12 October (chaired by GJS & JRO).
This contribution proposes to improve the derivation of rice parameter for regular residual coding (RRC) for high bit-depth coding. VVC derives Rice parameter in RRC with look-up table and its range is restricted from 0 to 3. It is asserted that this restriction causes worse performance of VTM in high bit-depth coding compared to HEVC Format Range extension profile where Rice parameter derivation can be extended when persistent_rice_adaptation_enabled_flag is equal to 1. To resolve this problem, this contribution introduces a Rice parameter derivation method using a predicted remainder value.
It is reported 1.52% and 25.02% in bdrateY in AI-12 qp= −13, −8, −3, 2, 7, and AI-16 −33, −28, −23, 18, 13, and 0.24% and 16.95% in bdrateY in LDB-12 qp= −13, −8, −3, 2, 7, and LDB-16 −33, −28, −23, 18, 13 respectively.
This is conceptually similar with JVET-T0072, but uses a modified version of the current lookup table for Rice parameter derivation. This avoids the latency problem of JVET-T0072 but requires a second table to be used depending on bit depth.
The contributor said this scheme is consistent with the current design in VVC v1.
A difference is that this scheme does not use the current LUT approach and instead uses a formula.
(A previous editorial proposal for VVC v1 had a formula approach that produces the same results as the current LUT approach, so using a formula is possible with VVC v1.)
It was asked whether this has a backward compatibility issue. The proponent suggested having a new flag to select between the two methods.
JVET-T0072 has a history tracking, basically as in HEVC range extensions. This one does not have that.
It was commented that it would be good to study more test cases before selecting one.