Warping error analysis and reduction for depth image based rendering in 3DTV

Interactive free-viewpoint selection applied to a 3D multi-view video signal is an attractive feature of the rapidly developing 3DTV media. In recent years, significant research has been done on free-viewpoint rendering algorithms which mostly have similar building blocks. In our previous work, we have analyzed the principal building blocks of most recent rendering algorithms and their contribution to the overall rendering quality. We have discovered that the first step, Warping determines the basic quality level of the complete rendering chain. In this paper, we have analyzed the warping step in more detail since it leads to ways for improvement. We have observed that the accuracy of warping is mainly determined by two factors which are sampling and rounding errors when performing pixel-based warping and quantization errors of depth maps. For each error factor, we have proposed a technique that can reduce the errors and thus increase the warping quality. Pixel-based warping errors are reduced by employing supersampling at the reference and virtual images and we decrease depth map errors by creating depth maps with more quantization levels. The new techniques are evaluated with two series of experiments using real-life and synthetic data. From these experiments, we have observed that reducing warping errors may increases the overall rendering quality and that the impact of errors due to pixel-based warping is much larger than that of errors due to depth quantization.