Estimation of depth from defocus as polynomial system identification

The two-image depth from defocus problem is considered as a system identification problem. The underlying phenomenon of defocusing is modelled as a linear system with an appropriate transfer function. Using a general measure for the spread, a relation between the spread and the system transfer function is obtained. A parametric transfer function is utilised in deriving an analytical expression for the spread. The two images taken with different camera parameters then become the input-output of such a system. An algorithm for estimating the coefficients of the transfer function is derived. The method is tested on synthetic images as well as images obtained from a camera.