JVET-O0665 Non-CE5: Syntax redundancy removal in adaptive loop filter [X. W. Meng (PKU), X. Zheng (DJI), S. S. Wang, S. W. Ma (PKU)]

This contribution proposes to remove syntax redundancy for adaptive loop in VTM-5.0. The proposed method removes the alf_luma_coeff_delta_idx when the number of alf filters equals to NumAlfFilters-1 and remove the alf_luma_coeff_delta_flag when the number of ALF filters equals to 1.

In test1, alf_luma_coeff_delta_idx is removed when the number of alf filters equals to NumAlfFilters-1. In this test, there is no BD-rate change in AI and LDB and minor bitrate reduction in some cases. For LDB, there is minor coding gain in Class E, 0.00%, 0.01%, 0.04% coding gain for Y, Cb and Cr, respectively.

In test 3, alf_luma_min_eg_order_minus1, alf_luma_eg_order_increase_flag, alf_luma_coeff_flag, alf_luma_coeff_delta_abs, alf_luma_coeff_delta_sign, alf_luma_clip_min_eg_order_minus1, alf_luma_clip_eg_order_increase_flag and alf_luma_clip_idx are all removed when the number of ALF filters and alf_luma_coeff_delta_flag both equal to 1. In this test, there is no BD-rate change and minor bitrate reduction in some cases for AI, RA and LDB, respectively.

Test2 is the combination of Test1 and Test3. In this test, there is no BD-rate change in AI and LDB and minor bitrate reduction. For LDB, there is minor coding gain in Class E, 0.00%, 0.01%, 0.04% coding gain for Y, Cb and Cr.

Test3 irrelevant due to adoption of O0669.

Test1: The benefit in bit rate is very small, and the syntax becomes less clear.

No action.