JVET-L0353 CE6-related: MTS using DST-4 and transposed DCT-2 [Y. Lin, J. Zheng, Q. Yu, N. Zhang (HiSilicon), C. Zhu (UESTC)]

This contribution was reviewed in the BoG reported in JVET-L0685.

This document presents a MTS (multiple transform selection) approach for VVC. It is proposed to use a DST-4 and transpose of DCT-2 as transform cores for the MTS, due to asserted benefits of reusing a circuit implementation of existing DCT-2 transform, reusing transform coefficients of an existing DCT-2 transform and enabling partial butterfly implementation for the proposed transpose of DCT-2. Test results reportedly show coding performance of 0.06%/0.06%/-0.04%/0.03% on average for AI/RA/LDB/LDP configurations compared to BMS-2.0.1 with VTM configuration. Encoding and decoding time slightly decrease due to partial butterfly implementation of the proposed transpose of DCT-2.

It was noted that a forward DCT-2 is needed at the decoder side. The proposed method enables DCT-2 butterfly for one MTS transform type, and it is one stage calculation, for the other transform type, DST-4 is used, which does not have a fast method currently. The performance loss is relatively higher for Class A, but the average loss is reportedly small (below 0.1%). It was reported by the proponent that the coding performance of the proposed method is slightly better than CE6-1.7a under CTC.

The BoG indicated that the proposed method looks interesting for complexity reduction of MTS transform types. Further study in a CE was recommended.