Revisiting transform and partitioning tools for post VVC codec

Transform and partitioning represent core components of the video coding architectures. Compared with HEVC, VVC is characterized by higher number of transform types, additional transform level (LFNST) and more flexible partitioning via the binary tree and ternary tree. This flexibility in transform and partitioning provides about 2% and 10% coding gain. Nevertheless, the current design is not ultimately optimized for the highest coding gain, but rather for the compromise with the design complexity. That is, the potential of combining higher transform and partitioning diversity is higher than the current state in VVC. This can be demonstrated by utilizing some early transform and partitioning proposals in the context of VVC development, which were not adopted due to the complexity concerns. In this paper, we revisit these designs targeting the maximum bitrate saving. This is to establish a new state of the art anchor for the post VVC development.