A fast intra prediction algorithm for 360-degree equirectangular panoramic video

360-degree video has been gaining its popularity as virtual reality (VR) technology develops in recent years. To compress these videos using standard video encoders, most of them are converted to a 2D image planar format with equirectangular projection (ERP). Compared with other encoders, High Efficiency Video Coding (HEVC) achieves significant improvements in coding efficiency. However, exhaustive computational complexity of HEVC makes it too time-consuming to compress 360-degree videos of high resolution and high frame rate for VR application. In this paper, a fast intra prediction algorithm is proposed according to the characteristics of ERP format video. Compared with original reference software HM 16.15, experimental results show that the proposed algorithm can achieve about 24.5% encoder time saving on average in All-Intra configuration with negligible quality loss.

I. Introduction

As interests in virtual reality (VR) application rise, 360-degree videos are gaining its popularity. These videos provide a spherical representation of the scene, which can be viewed freely using head mounted displays (HMDs). To be compressed by standard encoders, these videos are converted to two-dimensions (2D) image planar format by projections such as equirectangular (ERP), equal-area (EAP) and cubemap (CMP). Currently, most 360-degree panoramic videos are provided in ERP format. Similar to Geographic Coordinate System (GCS), a point on a sphere can be located by latitude and longitude. In ERP format video, a point can be mapped to a 2D plane by simply defining longitude as value of horizontal coordinate and latitude as the vertical. To provide more realistic visual experience, most 360-degree videos are high resolution and high frame rate. Thus, efficient video coding tool is vital for virtual reality application.