Geodesic Disparity Compensation for Inter-View Prediction in VR180

The VR180 format is gaining considerable traction among the various promising immersive multimedia formats that will arguably dominate future multimedia consumption applications. VR180 enables stereo viewing of a hemisphere about the user. The increased field of view and the stereo setting result in extensive volumes of data that strongly motivate the pursuit of novel efficient compression tools tailored to this format. This paper’s focus is on the critical inter-view prediction module that exploits correlations between camera views. Existing approaches mainly consist of projection to a plane where traditional multi-view coders are applied, and disparity compensation employs simple block translation in the plane. However, warping due to the projection renders such compensation highly suboptimal. The proposed approach circumvents this shortcoming by performing geodesic disparity compensation on the sphere. It leverages the observation that, as an observer moves from one view point to the other, all points on surrounding objects are perceived to move along respective geodesics on the sphere, which all intersect at the two points where the axis connecting the two view points pierces the sphere. Thus, the proposed method performs inter-view prediction on the sphere by moving pixels along their predefined respective geodesics, and accurately captures the perceived deformations. Experimental results show significant bitrate savings and evidence the efficacy of the proposed approach.