Advanced 3D Motion Prediction for Video Based Dynamic Point Cloud Compression.

Point cloud-based immersive media representation format has provided many opportunities for extended reality applications and has become widely used in volumetric content capturing scenarios. The high data rate of the point cloud is one of the key problems preventing the adoption of this media format. MPEG Immersive media working group (MPEG-I) aims to create a point cloud compression methodology relying on the existing video coding hardware implementations to solve this problem. However, in the scope of the state-of-the-art video-based dynamic point cloud compression (V-PCC) standard under MPEG-I, the intrinsic 3D object's motion continuity is destroyed by the 2D projections, resulting in a significant loss of inter prediction coding efficiency. In this paper, we first propose a general model utilizing the 3D motion and 3D to 2D correspondence to calculate the 2D motion vector (MV). Then, under the V-PCC, we propose a geometry-based method using the accurate 3D reconstructed geometry from the 2D geometry video to estimate the 2D MV in the 2D attribute video. In addition, we propose an auxiliary-information-based method using the coarse 3D reconstructed geometry provided by the auxiliary information to estimate the 2D MV in both the 2D geometry and attribute videos. Furthermore, we provide the following two ways to use the estimated 2D MV to improve coding efficiency. The first one is normative. We propose adding the estimated MV into the advanced MV candidate list and find a better MV predictor for each prediction unit (PU). The second one is non-normative. We propose applying the estimated MV as an additional candidate of the centers for motion estimation. We implement the proposed algorithms in the V-PCC reference software. Experimental results show that the proposed methods present significant coding gains compared with the current state-of-the-art motion prediction algorithm.