Robust depth-from-defocus for autofocusing in the presence of image shifts

A new passive ranging technique named Robust Depth-from-Defocus (RDFD) is presented for autofocusing in digital cameras. It is adapted to work in the presence of image shift and scale change caused by camera/hand/object motion. RDFD is similar to spatial-domain Depth-from-Defocus (DFD) techniques in terms of computational efficiency, but it does not require pixel correspondence between two images captured with different defocus levels. It requires approximate correspondence between image regions in different image frames as in the case of Depth-from-Focus (DFF) techniques. Theory and computational algorithm are presented for two different variations of RDFD. Experimental results are presented to show that RDFD is robust against image shifts and useful in practical applications. RDFD also provides insight into the close relation between DFF and DFD techniques.