Li Li, Li Zhu, Liu Shan, Li Houqiang
IEEE Trans Image Process. 2020 Apr 28. doi: 10.1109/TIP.2020.2989576.
Rate control is a necessary tool for video-based point cloud compression (V-PCC). However, there is no solution specified on this topic yet. In this paper, we propose the first rate control algorithm for V-PCC. Generally, a rate control algorithm is divided into two processes: bit allocation and bitrate control. In V-PCC, the total bits are composed of three parts: the header information including the auxiliary information and occupancy map, the geometry video, and the attribute video. The bit allocation aims to assign the total bits to these three parts. Since the auxiliary information and occupancy map are encoded losslessly, the bit cost of the header information is fixed. Therefore, we only need to assign bits between the geometry and attribute videos. Our first key contribution is the proposed video-level bit allocation algorithm between the geometry and attribute videos to optimize the overall reconstructed point cloud quality. Then we assign geometry and attribute video bits to each group of pictures (GOP), each frame, and each basic unit (BU). Our second key contribution is that we assign zero bits to the BUs with only unoccupied pixels. The unoccupied pixels are useless for the reconstructed quality of the point cloud and therefore should be assigned zero bits. In the bitrate control process, the encoding parameters are determined, and the model parameters are updated for each frame and BU to achieve the target bits. Our third key contribution is that we propose a BU-level model updating scheme to handle the case where various patches may be placed in different positions in neighboring frames. We use the auxiliary information to find the corresponding BU in the previous frame and apply its model parameters to the current BU. The proposed algorithms are implemented in the V-PCC and High Efficiency Video Coding (HEVC) reference software. The experimental results show that the proposed rate control algorithm can achieve significant bitrate savings compared with the state-of-the-art method.
码率控制是基于视频的点云压缩（V-PCC）的一项必要工具。然而，目前尚未有针对该主题的具体解决方案。在本文中，我们提出了首个用于V-PCC的码率控制算法。一般来说，码率控制算法分为两个过程：比特分配和比特率控制。在V-PCC中，总比特数由三部分组成：包括辅助信息和占用图的头部信息、几何视频以及属性视频。比特分配旨在将总比特数分配到这三个部分。由于辅助信息和占用图是无损编码的，所以头部信息的比特成本是固定的。因此，我们只需要在几何视频和属性视频之间分配比特。我们的第一个关键贡献是提出了几何视频和属性视频之间的视频级比特分配算法，以优化整体重建点云质量。然后，我们将几何视频和属性视频的比特分配到每组图片（GOP）、每一帧以及每个基本单元（BU）。我们的第二个关键贡献是，对于仅包含未占用像素的基本单元，我们分配零比特。未占用像素对于点云的重建质量没有用处，因此应分配零比特。在比特率控制过程中，确定编码参数，并针对每一帧和基本单元更新模型参数以达到目标比特数。我们的第三个关键贡献是，我们提出了一种基本单元级模型更新方案，以处理不同补丁可能在相邻帧中处于不同位置的情况。我们使用辅助信息在前一帧中找到对应的基本单元，并将其模型参数应用于当前基本单元。所提出的算法在V-PCC和高效视频编码（HEVC）参考软件中实现。实验结果表明，与现有方法相比，所提出的码率控制算法能够显著节省比特率。
