Optimal Camera Parameters for Depth from Defocus

Pictures taken with finite aperture lenses typically have out-of-focus regions. While such defocus blur is useful for creating photographic effects, it can also be used for depth estimation. In this paper, we look at different camera settings for Depth from Defocus (DFD), the conditions under which depth can be estimated unambiguously for those settings and optimality of different settings in terms of lower bound of error variance. We present results for general camera settings, as well as two of the most widely used camera settings namely, variable aperture and variable focus. We show that for variable focus, the range of depth needs to be larger than twice the focal length to unambiguously estimate depth. We analytically derive the optimal aperture ratio, and also show that there is no single optimal parameter for variable focus. Furthermore we show how to choose focus in order to minimize error variance in a particular region of the scene.