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. 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. Extensive experiments show that the proposed method can achieve bit rate reduction on this platform for 360 degree video coding.

与传统的2D视频不同，由于从3D球体到2D平面的投影，360度视频的内容会变形。结果，具有线性图案的传统角内预测（AIP）可能并不总是有效的。为了进一步提高360度视频的编码性能，本文提出了一种新颖的帧内预测方法，即循环帧内预测（CIP），它考虑了360度视频的球形特征。具体地，所提出的CIP以圆形模式执行，其中，圆心位于要预测的块周围，并且不同的圆心能够产生不同的CIP模式。该圆的中心与待预测块的中心之间的距离是根据投影变形的程度自适应地确定的，在这种情况下，较强的投影变形需要更短的距离，反之亦然。随着距离的增加，CIP越来越接近传统的AIP。另外，利用速率失真优化技术，利用一个附加的二进制标志从AIP和CIP之间的竞争中获得更好的编码性能。所提出的算法是在通用视频编码测试模型（VTM）5.0 + 360Lib 9.1的平台上实现的。大量实验表明，该方法可以在该平台上实现360度视频编码的比特率降低。通过速率失真优化，利用一个附加的二进制标志从AIP和CIP之间的竞争中获得更好的编码性能。所提出的算法是在通用视频编码测试模型（VTM）5.0 + 360Lib 9.1的平台上实现的。大量实验表明，该方法可以在该平台上实现360度视频编码的比特率降低。通过速率失真优化，利用一个附加的二进制标志从AIP和CIP之间的竞争中获得更好的编码性能。所提出的算法是在通用视频编码测试模型（VTM）5.0 + 360Lib 9.1的平台上实现的。大量实验表明，该方法可以在该平台上实现360度视频编码的比特率降低。