No abstract

A white-light processing technique for optical image subtraction using a liquid crystal television (LCTV) spatial light modulator is described. Real-world scenes are fed into the LCTV through a TV camera. The input image is then processed by a dual-channel white-light optical processor. A pair of double-grating interferometers is inserted into the Fourier plane of the optical processor such that the output image is modulated by two sets of complementary achromatic fringe patterns, each possessing the same spatial frequency but shifted by a half-period. Two sequential exposures are needed for coding the difference between the two input scenes onto one photographic film. Each of the exposures is taken through one of the grating interferometers. The coded difference image can be obtained by bandpass filtering of the coded photographic transparency.