Nongeometric Distortion Smoothing Approach for Depth Map Preprocessing

Depth image-based rendering (DIBR) is a process that uses one 2-D color image and its associated depth map to render virtual view 3-D images. One of the main problems in DIBR is how to reduce holes that occur on the generated virtual view images. In general, preprocessing the whole depth image by smoothing filter before image warping can reduce the hole occurrence. However, smoothing the whole depth image not only produces some geometric distortions on the generated virtual directional images, but also increases computation time. This paper proposes an adaptive edge-oriented smoothing process to solve the above problem, in which the adaptive smoothing filter for the depth map is determined by the characteristics of the hole region with or without vertical lines in the color image. The adaptive smoothing filter contains two types: the asymmetric smoothing filter is used to reduce the geometric distortions by smoothing the hole regions with vertical lines that belong to the background; and the horizontal smoothing filter is used to reduce hole occurrence and computation time by smoothing the hole regions without vertical lines. The experiment results show that the proposed method turns out to be a good tradeoff between time saving, hole reduction rate, and virtual view quality.