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Unified primary transform kernel for ISP mode
Abstract
In VVC Draft, for CUs coded as ISP mode, when lfnst_idx is equal to 1 or 2, the primary transform kernels are DCT-2, while when lfnst_idx is 0, an implicit transform scheme is applied and DST-7 or DCT-2 may be applied as the primary transform kernels. It is proposed to use a unified primary transform kernel, DCT-2, for ISP mode when sps_lfnst_enabled_flag is equal to 1. It is asserted that the proposed scheme can reduce the complexity in both encoder and decoder with little loss.
JVET-R0345 Unified primary transform kernel for ISP mode [J.-Y. Huo, W.-H. Qiao, H.-X. Wang, Y.-Z. Ma, F.-Z. Yang (Xidian Univ.), S. Wan (NPU), Y.-F. Yu, Y. Liu (OPPO)]
In VVC Draft, for CUs coded as ISP mode, when lfnst_idx is equal to 1 or 2, the primary transform kernels are DCT-2, while when lfnst_idx is 0, an implicit transform scheme is applied and DST-7 or DCT-2 may be applied as the primary transform kernels. It is proposed to use a unified primary transform kernel, DCT-2, for ISP mode when sps_lfnst_enabled_flag is equal to 1. It is asserted that the proposed scheme can reduce the complexity in both encoder and decoder with little loss.
The experimental results are as below:
- For AI configuration: 0.06%, 0.13%, and 0.12%, with 99% EncT, 100% DecT;
- For RA configuration: 0.02 %, 0.02%, and 0.08%, with 99% EncT, 99% DecT.
It is commented that this is not clearly simplifying, as the transforms are available anyway, and the additional implicit check is minor. There is also some small compression loss.
No action was taken on this.
References:
Cited:
PATENTS:
WO/2024/104476
0.34
20250280133
0.33
20220377335
0.32
2024200814
0.31
2020349369
0.30
4024870
0.28
WO/2024/083090
0.27
WO/2025/157235
0.26
Decisions
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