Evaluation of motion compensation and coding strategies for compression of depth map sequences

Current investigations in the area of 3D video systems are based on depth map sequences. They are used to obtain the compatibility to conventional 2D video systems. Instead of transmitting or storing two video sequences for each eye, 2D video and the appropriate depth information is delivered. If the viewer owns a standard TV set only the 2D video is displayed. In the case of using a stereoscopic display or shutter glasses a second virtual view is synthesized based on depth information. Because of limited storage and bandwidth, data compression has to be used. In this paper several approaches for compression of depth sequences, applicable for 3D video systems, are investigated and evaluated. For temporal prediction established video compression standards perform a block based motion compensation and encode the prediction residuals for every block separately. Alternatively, motion compensation methods using control grid interpolation and coding algorithms based on wavelet transform are applicable. Another possible approach is given by a mesh-based interpolation of the depth scene content. In that case the temporal prediction can be obtained by node tracking. We demonstrate the coding performance of these alternative methods for compressing depth map sequences in comparison with the video compression standards MPEG-2, MPEG-4 and H.264.