Abstract

Objects of known shape may be readily detected in an essentially slowly varying background by thresholding the cross correlation of the object scene with an aperture mask consisting of two narrow bands, one of positive transmittance and the other of negative transmittance, close to and on opposite sides of the object outline. This result, which has intuitive appeal, is obtained from the two-dimensional matched filter “optimum” for detecting known signals immersed in a typical low-frequency, isotropic, additive background. Truly spatial (i.e., simultaneously in two dimensions) high-pass filtering is achieved for high-contrast object scenes in an experimental correlator in which bipolar transmittance is effectively obtained by using the known quenching characteristics of a fluorescent screen.

A table of bipolar aperture masks is given for approximating various partial derivatives for edge enhancement. This table indicates that some earlier experiments with negative light may be interpreted as essentially optical differentiation, examples of which are given.

© 1964 Optical Society of America

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Equations (43)

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