We have experimentally demonstrated the feasibility of a scale, rotati
on, and translation invariant all-optical processor for automatic targ
et recognition. This simple processor consists of a single Fourier len
s and uses a phase-coded input image of the target obtained by the rec
ording of the original image onto a phase-only material through a Ronc
hi-type grating. A logarithmic distance measure is introduced to separ
ate two classes of targets under the experiment. A real-time implement
ation of the processor is suggested utilizing a specially designed spa
tial light modulator. (C) 1996 Society of Photo-Optical Instrumentatio
n Engineers.