JVET-P0666 Non-CE5: Combination of JVET-P0470 and JVET-P0557 on simplification of CC-ALF [X. Li., X. Zhao, L. Zhao, X. Du, S. Liu (Tencent), N. Hu, J. Dong, V. Seregin, M. Karczewicz (Qualcomm)] [late]
This proposal provides a combination of JVET-P0470 and JVET-P0557 on simplification of cross-component ALF.
1. Using shifts instead of multiplications, limiting the coefficients range to [-8, 8].
Another aspect is limiting the input to 12 bits irrespective to the bit depth.
With the proposed method, the dynamic range of filter coefficients are constrained within 4-bit including 1-bit sign and shift instead of multiplication is used in filtering process so that 16-bit operation is kept for up to 12-bit internal bit-depth. Coding performance is reported as follows
- Over VTM-6, BD rate changes are 0.11%, -7.27%, -5.83% for AI, 0.17%, -10.38%, -9.86% for RA, 0.14%，-15.63%，-11.80% for LDB.
- Over CE5-2.1, BD rate changes are -0.02%, 0.35%, 0.21% for AI, 0.01%, 0.36%, 0.23% for RA, -0.03%， 0.04%， -0.05% for LDB.
BoG recommendation: Test the results with limiting the coefficient range to [-8, 8]. The proponents are advised to discuss offline what coefficient bit depth (range) to test in the CE.