Source of light with spatially periodic coherence and its uses in image addition or subtraction

We describe image-synthesis processing (i.e., image addition or subtraction) using novel illumination obtained from mutually incoherent point sources. The illumination exhibits periodic coherence whose degree of coherence can take the limiting values of 1 and −1 necessary for processing. By using two point sources satisfying the coherence condition Δa = λf/2b (Δa and 2b are, respectively, the separations between the sources and between the inputs), image subtraction is demonstrated experimentally in an imaging system that uses a diffraction grating. The coherence conditions for performing image synthesis are also given in the case of multiple point sources.