On secondary transforms for scalable video coding

In this paper, we present a secondary transform scheme for inter-layer prediction residue in scalable video coding (SVC). Efficient prediction of the co-located blocks from the base layer (BL) can significantly improve the enhancement layer (EL) coding in SVC, especially when the temporal information from previous EL frames is less correlated than the co-located BL information. However, Guo et al. showed that because of the peculiar frequency characteristics of EL residuals, the conventional DCT Type-2 transform is suboptimal and is often outperformed by either the DCT Type-3, or DST Type-3 when these transforms are applied to the EL residuals. However, their proposed technique requires upto 8 additional transform cores, two of which are of size 32×32. Here, in this work, we propose a secondary transform scheme, where the proposed transform is applied only to the lower 8x8 frequency coefficients after DCT, for block sizes 8×8 to 32×32. Our proposed transform scheme requires at most only 2 additional cores. We also propose a low-complexity 8x8 Rotational Transform as a special case of secondary transforms in this paper. Simulation results show that the proposed transform scheme provides significant BD-Rate improvement over the conventional DCT-based coding scheme for video sequences in the ongoing scalable extensions of HEVC standardization.