Circular Intra Prediction for 360 Degree Video Coding
Circular Intra Prediction for 360 Degree Video Coding
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360 度视频编码的循环帧内预测
DOI：
10.1016/j.jvcir.2020.103000
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发表时间：
2021
影响因子：
2.6
通讯作者：
Shiqi Wang
中科院分区：
文献类型：
--
作者：
Linwei Zhu;Yun Zhang;Na Li;Jinyong Pi;Shiqi Wang
摘要与传统的2D视频不同，360度视频的内容是从3D球体到2D平面的投影，因此会发生变形。因此，具有线性图案的传统角度帧内预测（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，本文提出了一种新的帧内预测方法，循环帧内预测（CIP），其考虑360度视频的球形特性。具体地，所提出的CIP以圆形图案执行，其中圆心位于待预测块周围，并且不同的圆心能够产生不同的CIP模式。该圆的圆心与待预测块的圆心之间的距离根据投影变形的程度自适应地确定，其中投影变形越强需要的距离越短，反之亦然。随着距离的增加，CIP越来越接近传统的AIP。此外，通过率失真优化，利用一个额外的二进制标志来从AIP和CIP之间的竞争中获得更好的编码性能。该算法在通用视频编码测试模型（VTM）5.0+360Lib 9.1平台上实现。大量的实验表明，所提出的方法可以实现在该平台上的360度视频编码的比特率降低。
Abstract 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.