Nested polygonal chain mapping of omnidirectional video

Conventionally, the equirectangular projection (ERP) has been used for representing 360-degree panorama videos. However, ERP suffers from over stretching in polar regions and thus increases the bitrate and the encoding/decoding complexity. This paper presents the nested polygonal chain packing method where the top and bottom stripes of an ERP picture are resampled sample-row-wise. The sampling ratio is a linear function of the sample row being processed. The height of the top or bottom stripe can be for example a quarter of the height of the ERP picture. The resampled sample rows are arranged in nested polygonal chains. According to the presented experimental results, the proposed nested polygonal chain packing provides on average 6.1% bitrate reduction compared to ERP.