JVET-P0699 Non-CE6 / Non-CE3: On ISP and Maximum Transform Size [K. Naser, T. Poirier, T. Urban, G. Rath (InterDigital)] [late]

Due to the adoption of JVET- O0545, the maximum transform size changes between 64x64 and 32x32 depending on the SPS flag sps_max_luma_transform_size_64_flag. This change impacted the use of ISP, since ISP is allowed up to the maximum transform size. That is, when sps_max_luma_transform_size_64_flag is zero, ISP is allowed up to CU sizes 32x32. Experimental results show 0.00% and, 0.01% and -0.03% AI and, RA and LDB luma loss when ISP maximum size is 32x32 under CTC. It is argued that in general there is no need for ISP beyond 32x32 CU’s, and therefore it is proposed to either limit the maximum size to 32x32, independently from sps_max_luma_transform_size_64_flag, or to add an SPS flag to enable ISP up to 64x64. The second option is inline with the design of the SBT, whose maximum size is controlled by sps_sbt_max_size_64_flag.

There is no reason of a complexity problem to disable ISP for large blocks. Main benefit would be to speed up encoder search. This could also be achieved in a non-normative way. It is undesirable to introduce too many specific settings and additional SPS flags for fast encoder benefits.

Method 4 would become obsolete when the sbt related flag would be removed (see under JVET-P0391).

No need for action was identified on this, as JVET-P0983 was adopted.