Fast CU size decision algorithm for VVC intra coding

Recently, an emerging video coding standard called Versatile Video Coding (VVC) is established using quadtree with nested multi-type tree structure to improve the coding efficiency. However, the coding complexity increases dramatically due to the flexible block partition structure. To tackle this issue, a fast CU size decision algorithm is proposed to speed up the intra coding process utilizing the coding information and the texture information, which consists of a fast quadtree decision method (FQD) and a fast multi-type tree decision method (FMD). Firstly, the correlation of the depths of the neighboring CUs is analyzed, which can predict the quadtree depth of the current CU early to skip unnecessary depths. Then, the distribution of the Rate-Distortion (RD) cost of the multi-type tree combined with the texture information is utilized to make an early decision on the splits of the binary-tree (BT) and ternary-tree (TT). Experimental results demonstrate that the proposed algorithm can reduce the coding complexity by 51.89% on average, with negligible loss of coding performance. Compared with state-of-the-art methods, the proposed algorithm can obtain an additional time saving from 6% to 17%, while keeps a better coding performance.