Dually Octagonal Projection for 360 Video with Less-Distortion Introduced

The appearance of virtual and augmented reality has tremendously catalyzed 360 videos that provide immersive visual experience. In order to directly employ the existing compression standards, an efficient projection format is required considering the distortion introduced and compression standards compatibility. The equirectangular projection (ERP) is currently the most prevalent projection scheme, however, it introduces severely high sampling density near the poles. The Craster Parabolic Projection (CPP) is issued for uniform sampling on the sphere, but it does not preserve the shape of objects, especially at two sides of the CPP planes. Therefore, we propose a novel CPP-based projection format, named Dually Octagonal Projection (DOP) that projects the spherical video onto two mirrored octagons, striking a balance between distortion and uniform sampling. Besides, a brief format conversion function helps the improvements of 360 video quality. Our experimental results demonstrate that considerable BD-rate gain can be achieved by the DOP over the ERP particularly on detailed and informative videos. The compact format for the DOP is further verified to be more adaptive to encoders.