Improving focus measurement via variable window shape on surface radiance distribution for 3D shape reconstruction

Shape-from-focus (SFF) is a technique used to estimate the depth or 3D shape of an object from a sequence of images obtained at different focus settings. Most SFF algorithms compute the focus value of a pixel from a fixed square window surrounding the pixel. Choosing an optimum window size is an important issue in SFF; a small window size is vulnerable to pixel noise, whereas a larger widow size unnecessarily includes uncorrelated neighboring pixels. This paper demonstrates that window shape, which has yet to be effectively dealt with, is very important for improving the accuracy of focus measurements. In this paper, window size and shape are determined pixel-by-pixel using a semivariogram in order to maximally include correlated neighboring pixels. Experiments were then conducted on both synthetic and real objects, with the results confirming that the proposed technique improves the quality-of-focus measurement in comparison to previous methods based on a fixed square window. (c) 2012 Elsevier Ltd. All rights reserved.