$\lambda$-Domain Perceptual Rate Control for 360-Degree Video Compression
$\lambda$-Domain Perceptual Rate Control for 360-Degree Video Compression
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DOI：
10.1109/jstsp.2019.2963154
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发表时间：
2020-01
影响因子：
7.5
通讯作者：
Li Li-Li;Ning Yan;Zhu Li;Shan Liu;Houqiang Li
中科院分区：
文献类型：
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作者：
Li Li-Li;Ning Yan;Zhu Li;Shan Liu;Houqiang Li
使用各种投影方法将 360 度视频投影为 2D 格式，以实现高效压缩。作为通用视频压缩的必要组成部分，码率控制对于投影360度视频压缩也是不可或缺的。然而，目前的码率控制算法尚未针对360度视频压缩进行优化。码率控制算法中的编码树单元(CTU)级比特分配没有考虑到2D格式的不同像素对视觉体验有不同影响的特点。在本文中，我们首先考虑到这一特性提出了一个最佳的 CTU 级别权重。 CTU 级别权重是像素级别权重的近似值，因为码率控制算法的最小粒度通常是 CTU。其次，基于CTU级别权重，提出了加权CTU级别比特分配算法，以实现更好的编码性能。每个CTU的比特被分配为CTU的拉格朗日乘数$\lambda$与其CTU级别权重成反比。这种CTU级比特分配方案适用于所有360度视频投影格式。第三，我们提出了一种用于等矩形投影（ERP）格式的CTU行（CR）级速率控制算法。 ERP格式中同一行的不同CTU组合成一个CR，以提供更稳定的模型参数。所提出的算法在最新的视频编码标准高效视频编码（HEVC）参考软件中实现。实验结果表明，与最先进的码率控制算法相比，该算法能够实现更好的主观和客观质量以及更小的码率误差。
The 360-degree video is projected to 2-D formats using various projection methods for efficient compression. As a necessary part of general-video compression, rate control is also indispensable for the projected 360-degree video compression. However, the current rate control algorithm has not been optimized for the 360-degree video compression yet. The Coding Tree Unit (CTU) level bit allocation in the rate control algorithm has not taken into consideration the characteristic that various pixels in 2-D formats have different influences on the visual experiences. In this article, we first propose an optimal CTU level weight taking this characteristic into consideration. The CTU level weight is an approximation to the pixel level weight since the smallest granularity of a rate control algorithm is usually CTU. Second, based on the CTU level weight, a weighted CTU level bit allocation algorithm is proposed to achieve better coding performance. The bits of each CTU are assigned that the Lagrange multiplier $\lambda$ of a CTU is inversely proportional to its CTU level weight. This CTU level bit allocation scheme is applied to all the 360-degree video projection formats. Third, we propose a CTU row (CR) level rate control algorithm for the Equi-Rectangle Projection (ERP) format. Different CTUs in the same row in the ERP format are combined into a CR to provide more stable model parameters. The proposed algorithms are implemented in the newest video coding standard High Efficiency Video Coding (HEVC) reference software. The experimental results show that the proposed algorithm is able to achieve much better subjective and objective qualities as well as smaller bitrate errors compared with the state-of-the-art rate control algorithm.