  The polyhedron projection for 360-degree video is becoming more and more
popular since it can lead to much less geometry distortion compared with the
equirectangular projection. However, in the polyhedron projection, we can
observe very obvious texture discontinuity in the area near the face boundary.
Such a texture discontinuity may lead to serious quality degradation when
motion compensation crosses the discontinuous face boundary. To solve this
problem, in this paper, we first propose to fill the corresponding neighboring
faces in the suitable positions as the extension of the current face to keep
approximated texture continuity. Then a co-projection-plane based 3-D padding
method is proposed to project the reference pixels in the neighboring face to
the current face to guarantee exact texture continuity. Under the proposed
scheme, the reference pixel is always projected to the same plane with the
current pixel when performing motion compensation so that the texture
discontinuity problem can be solved. The proposed scheme is implemented in the
reference software of High Efficiency Video Coding. Compared with the existing
method, the proposed algorithm can significantly improve the rate-distortion
performance. The experimental results obviously demonstrate that the texture
discontinuity in the face boundary can be well handled by the proposed
algorithm.
