Spherical Lanczos Interpolation in Planar Projection or Format Conversions of Panoramic Videos

Panoramic videos provide users with an amazing experience with immersive and interactive viewing, and are now gaining global popularity. Since panoramic videos are spherical in nature while effectively processed in planar projection formats in applications, it is crucial to implement sphere-to-plane projection, where a good interpolation algorithm is of great importance regarding generating high quality planar perspective videos. Moreover, different planar projection formats adapt to different applications according to their own characteristics. It is common to convert one projection format to another, where interpolation algorithms also make a difference on performance. In this paper, an interpolation algorithm named spherical Lanczos (SLAN) is proposed to achieve advanced performance in sphere-to-plane projection or planar projection format conversions of panoramic videos. In SLAN, we fully consider panoramic videos are naturally spherical. Reference pixels are selected carefully, and the weights are calculated correctly. Experimental results demonstrate that the SLAN interpolation algorithm is beneficial for the whole processing chain of panoramic videos both with lossless compression coding and with loss compression coding in terms of the increase in various end-to-end PSNR and the decrease in BD_rate. The cubic projection (CBP) and adjusted cubemap projection (ACP) are also evaluated to illustrate that the proposed algorithm is applicable for all kinds of planar projection format due to their inevitable deformation.