Efficient Projection and Coding Tools for 360° Video

In this paper, an efficient cubemap projection format and 360° specific coding tools are proposed. The proposed hybrid equi-angular cubemap projection applies efficient mapping functions to achieve more uniform sampling and reduce the boundary artifacts across different faces. We propose several 360° specific coding tools that respect the spherical geometry in the 2D coding domain. Our tools appropriately process the reference information across the frame boundary and the discontinuous edge in inter prediction, intra prediction, and in-loop filters. As compared to the padded equirectangular projection integrated in 360Lib-5.0 and HM-16.16, the experimental results indicate that the average BD-rate reduction provided by the proposed algorithm achieves 35.5%/69.5%/71.6% in terms of the end-to-end WS-PSNR-Y/U/V, respectively. For subjective quality comparison, the seam artifacts caused by the discontinuous edge and frame boundary are also noticeably reduced by the proposed 360° specific coding tools.