December 2020 4.Congratulations to Dr. Linwei Zhu on his paper “Circular Intra Prediction for 360 Degree Video Coding” was accepted by Journal of Visual Communication and Image Representation.

 

Fig. 1 Proposed circular intra prediction. O(0, 0) is the center of the to-be predicted block. N(x, y) is one point in the to-be-predicted block. M(x0, y0) is one point in the circle whose center is O(0, 0) and radius is R. N(x, y) and the reference pixel are located at the same circle whose center is M(x0, y0).

Fig. 2 Proposed video codec with CIP

Different from traditional 2D video, the contents of 360 degree video are deformed due to the projection from 3D sphere to 2D plane. As a result, the traditional Angular Intra Prediction (AIP) with a linear pattern may not be always efficient. To further improve the coding performance of 360 degree video, a novel intra prediction method is presented in this paper, i.e., Circular Intra Prediction (CIP), which takes consideration of the spherical characteristics of 360 degree video. In specific, the proposed CIP is performed in a circular pattern, where the center of circle is located around the to be-predicted block, and different centers of circle are able to produce different CIP modes, as illustrated in Fig. 1. The distance between center of this circle and center of the to-be-predicted block is adaptively determined according to the degree of projection deformation, where stronger projection deformation needs shorter distance, and vice versa. As the increase of the distance, the CIP is more and more close to the traditional AIP. In addition, one additional binary flag is utilized to achieve better coding performance from the competition between AIP and CIP with the rate-distortion optimization. The proposed algorithm is implemented on the platform of Versatile video coding Test Model (VTM) 5.0 + 360Lib 9.1, as shown in Fig. 2. Extensive experiments show that the proposed method can achieve bit rate reduction on this platform for 360 degree video coding.