JVET-Q0629 CE2-related: Palette mode excluding small blocks [H.-J. Jhu, X. Xiu, Y.-W. Chen, T.-C. Ma, X. Wang (Kwai Inc.)] [late]
It is observed that applying palette mode on small CUs introduces insignificant coding gain and brings extra complexity on the small blocks. This contribution proposes to disable palette mode for CU that are smaller or equal to 16 pixels. The proposed method reports negligible BD-rate changes compared to VTM7 and reduces complexity.
The worst case complexity (in terms of palette table construction) is reduced by factor of 2, and the loss is close to zero.
The text change is simple, one additional condition on block size for sending the PLT flag.
Decision: Adopt JVET-Q0629, disable palette mode for 4x4 blocks.
Proponents were asked to clarify with the proponents of JVET-Q0504 if the restriction is properly expressed for dual tree chroma in 4:2:0 and 4:2:2 cases. It was later confirmed that v4 of JVET-Q0629 includes text is properly considering this.