We present a novel formulation of the range recovery problem based on computation of the differential variation in image intensities with respect to changes in camera position (or aperture size). This method uses a single stationary camera and a pair of calibrated optical masks to directly measure this differential quantity.

More specifically, we show that the spatial derivative of the image formed under an optical attenuation mask, M, is related by a scale factor to a second image formed under the derivative mask M'.