Stretching Schemes for Coding Frames of Panoramic Videos in Craster Parabolic Projection

Panoramic videos are spherical in nature, which further brings great challenges to deal with them. Usually they are projected to planar domain and processed as planar perspective videos. Craster parabolic projection (CPP), as a sphere-to-plane projection format, achieves approximately uniform sampling on the sphere. Without redundant pixels, it can store and represent panoramic videos effectively. However, frames in CPP format are no longer rectangular, which further violates the off-the-shelf video coding standards. In this paper, four stretching schemes are proposed for coding frames of panoramic videos in CPP. For introducing as few pixels as possible, strips are regard as the basic units. Strips in frames in different areas are stretched into rectangles in different sizes for coding. Spherical continuity, planar continuity, nearest-neighbour interpolation and Lanczos interpolation are considered in stretching respectively. Experimental results demonstrate that, compared with strips in Equi-rectangular projection (ERP) format, the proposed schemes can achieve BD-rate reductions up to 30.68% for Y, 32.68% for U and 34.13% for V, and that different schemes are well adapted for different strips.