Quad- Tree Split for Intra Sub-Partition Mode

The Intra Sub-Partition (ISP) mode performs intra prediction by subdividing a block into multiple sub-partitions of the same size. ISP can achieve comparable prediction performance without going through further block partitioning that will incur higher computational cost. Nevertheless, due to its signaling cost, sub-partitioning in ISP is limited to only two ways, that is, vertical or horizontal split. In this paper, we investigate diversification of the ISP sub-partitioning in order to increase its coding efficiency. The proposed method is shown to achieve a BDBR gain of 0.01 % in the Y channel, 0.03 % and 0.00% in the Cb and Cr channels under AI configuration.