JVET-P0476 Non-CE8: Palette mode and prediction mode signalling [Y.-H. Chao, C.-H. Hung, W.-J Chien, M. Karczewicz (Qualcomm)]
Discussed in BoG JVET-P0999.
In this document, a cleanup of prediction mode signalling, i.e. signalling MODE_INTRA, MODE_INTER, MODE_IBC, and MODE_PLT, is proposed. The proposed signalling unifies the signalling condition of prediction mode for I slice and P/B slice, and IBC enabled and disabled. The results on YUV4:4:4 sequences show minor loss compared to VTM6.0:
IBC ON:
Dual Tree OFF: 0.08 % AI, -0.06 % RA, 0.08 % LB
Dual Tree ON: 0.01 % AI, 0.02 % RA, 0.08% LB
IBC OFF:
Dual Tree OFF: 0.00 % AI, -0.01 % RA, -0.06 % LB
Dual Tree ON: 0.00 % AI, -0.03 % RA, 0.00% LB
The results on YUV4:2:0 sequences compared to VTM6.0 are as follows:
Overall: 0.00 % AI, 0.00 % RA, -0.01 % LB
ClassF: 0.01 % AI, 0.03 % RA, 0.10 % LB
ClassSCC: 0.02 % AI, -0.01 % RA, -0.21 % LB
In this contribution, signalling changes for pred_mode_flag and pred_mode_plt_flag are proposed.
It was commented that whether this kind of change would be desirable should be discussed in Track.
It was commented that since PLT mode is a 4:4:4 mode, it would be desirable to have minimum impact on 4:2:0 syntax.
It was commented by one expert that the proposed changes are reasonable.
It was commented that since the adoptions in this meeting (such as CE8-1.3, and also potentially include JVET-P0526 with non-normative improvement on PLT), it recommended by one expert that knowing the impact of performance on the new anchor would be better. It is also commented by proponents and one expert that this proposal only affect 1-bit flag and should not be an issue for coding performance. The main focus is on mode signalling definition consistency and simplification.
It is better to have a closer look at the syntax changes. An offline discussion with more interested experts involved is recommended.
In JVET-P0516, the 1st aspect (PLT mode signalling) is also proposed.
Options will be 1) no change at all; 2) change only PLT signalling; 3) change both PLT and prediction mode signalling.
BoG recommendation: Further discussion in Track A.