Weight-based bit allocation scheme for VR videos in HEVC

Abstract

Since VR videos shown on the head-mounted display (HMD) is omnidirectional, the average distortion of VR videos in all directions shall be calculated in spherical domain. Several metrics have been proposed to calculate the coding loss of VR videos in spherical domain, including S-PSNR, WS-PSNR, CPP-PSNR. The above metrics are all improved based on PSNR by creating a weight map. This paper aims to optimize the rate control scheme on HEVC mostly for WS-PSNR. According to the weight map of WS-PSNR, regions with more weights in plain are more important, thus more bits shall be allocated to the important regions. We use weight-based rate control scheme to realize the above thoughts. Weight-based rate control scheme defines bit per weight (bpw) instead of bpp. Large values of bpw indicate that the important regions deserve high bitrates, thus probably achieving better quality. Consequently, the proposed rate control scheme improves the video quality of VR videos, which leads to average gain of 2.1%, 4.3% and 1.5% of S-PSNR, WS-PSNR and CPP-PSNR.