Research On Fast Multi-type Tree Partition Algorithm Based On Sub Block Complexity For VVC

H.266/VVC(Versatile Video Coding)is a new generation of video coding standard,mainly for ultra-high resolution,high dynamic range of ultra-high definition video.In order to make the partition of CU(Coding Units)more flexible,VVC introduces a partition structure of Quad-tree nested in Multi-Type tree,but the coding time increases significantly.Virtual reality 360 degree video is one of the important application scenarios of H.266/VVC,which has different statistical characteristics from traditional video and presents different characteristics in Multi-Type tree partition.At present,there are few researches on the optimization of VVC Multi-Type tree partition for virtual reality 360 degree video.In this paper,a fast algorithm for Multi-Type tree partition decision is designed based on the characteristics of virtual reality 360 degree video in ERP(Equi-Rectangular Projection)projection format.The main contents and innovations of this paper are as follows:(1)In this paper,the relationship between tree selection and texture complexity of CU is studied,and an algorithm of early termination of Quad-tree partition is proposed.In the process of standard Multi-Type tree partition,the encoder will try five partition methods at the same time,and choose the one with the least cost.Through statistical analysis of the characteristics of CU partition structure in different latitude regions of virtual reality 360 degree video in ERP projection format,it is found that for complex texture regions,the encoder is more inclined to choose Quad-tree structure continuously among the five candidate partition methods from the first partition,and once the Binary tree or Ternary tree partition method is selected,the Quad-tree partition mode is no longer attempted.Based on this,this paper calculates the texture complexity of CU,distinguishes simple CU from complex CU,and makes simple CU terminate Quad-tree partition in advance;for complex CU,a sub block complexity difference index is designed to help judge whether the current CU terminates Quad-tree partition and save coding time.Experimental results show that in All Intra mode,compared with the existing VTM 8.0,the coding time is saved by 24%,the WS-PSNR is reduced by 0.02 d B,and the BD-rate is only increased by 0.49%.(2)Furthermore,this paper studies the relationship between the division of Binary and Ternary tree and the characteristics of CU structure after the termination of Quadtree partition,and proposes a fast decision algorithm for the partition of Binary and Ternary tree.In view of the above terminated Quad-tree partition of CU,this paper analyzes the law between the texture direction and the partition direction of CU,and uses the direction measure to judge the partition direction of Binary and Ternary tree;in the selected partition direction,this paper analyzes the characteristics of the partition structure of Binary and Ternary tree,and studies whether the adjacent sub blocks are segmented or merged by calculating the complexity of the four sub blocks of CU,and finally proposes some suggestions According to the characteristics,the final partition method is selected.This part of the algorithm is combined with the previous Quad-tree partition early termination algorithm to get a fast algorithm of VVC Multi-Type tree partition based on sub block complexity.Experimental results show that in All Intra mode,compared with the existing VTM 8.0,the coding time is saved by 42%,the WSPSNR is reduced by 0.05 d B,and the BD-rate is only increased by 1.11%.