The analogy between electronic filters or networks and optical filters placed in the focal plane of an imaging arrangement has drawn attention to the potentialities of optical arrangements for information processing. This paper develops the theory of the filter in the focal plane whose transmission at each point is proportional to the intensity of the light from the object. This intensity filter—in imaging arrangements using coherent light sources—has the property of forming a “ghost image” of the whole object, when only a small fragment of the original object is shown. This ghost image can be utilized in principle for recognizing and locating a small fragment in the original object.
© 1963 Optical Society of America
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