Research On Fast Intra Algorithm Based On The Sum Of Region-directional Dispersion For 360-degree Video

With the development of Virtual Reality,VR 360-degree video becomes more and more popular.However,the resolution of VR 360-degree video is ultra-high(typically 4K to 8K),which needs more encoding time than traditional video.Current algorithms lack the optimization of such videos.In order to reduce the computational complexity of Virtual Reality 360-degree video coding,the paper studies the problems of CU(Coding Unit)partitioning and mode selection for 360-degree video under ERP(Equirectangular Projection)format,and designs the fast intra algorithm for CU partitioning and mode selection.The main innovations are as follows:(1)Aiming at the complexity of intra mode selection process for 360-degree video,the paper studies the rules of mode decision and puts forward a new metric named SRD(the Sum of Region-directional Dispersion)to calculate the cost of angular modes.The fast intra mode selection algorithm for 360-degree video is proposed based on the metric.Through counting the optimal mode of each area,each area calculates different diecrtions of SRD and compares them to determine mode interval.Thus the process of RMD(Rough Mode Decision)is greatly simplified and the number of candidate modes in RMD and RDO has decreased.Experimental results show that the designed algorithm can reduce the encoding time by 29%,while BD-rate only increases by 1.0%.(2)Aiming at the complexity of intra CU partition for 360-degree video,the research counts the depth relationship between current CU and its neighbor blocks in different regions.Using the relationship,the algorithm of fast intra CU partitioning based on SRD is proposed.Each area adopts different directions of SRD to calculate and compare them with given threshold,thus the majority of CUs can be terminated in advance.Experimental results show that the designed algorithm can reduce the encoding time by 38%,while BD-rate only increases by 0.4%.(3)The first two algorithms are integrated to form the overall algorithm of the paper.The experimental results show that the overall algorithm can reduce the encoding time by 53%,while BD-rate only increases by 1.6%.