Abstract

Rhodes and Koizumi¹ introduced the complementary source-pupil filtering system, which performed contrast and edge enhancement and exhibited good immunity to coherent artifact noise. In addition, some simple spatial filtering was demonstrated. Their system is partially coherent, and the nonlinear equations describing its behavior do not provide much insight. We introduce two useful classes of masks for use in complementary source-pupil filtering systems that have simple analytical models. The first class of pupil masks is a random array of dark spots on a clear background. Low-contrast objects illuminated by the complementary source yield high-contrast images with no sign of speckle noise. The system can be approximated as a high-pass coherent spatial filter followed by an incoherent system in which the optical transfer function is determined by the pupil mask. The width of the individual dark spots determines the width of the stop band of the high-pass coherent system. The second class of pupil masks is a regular array of dark spots on a clear background. The complementary source produces images with reduced contrast and removes square-wave terms with a spatial frequency determined by the spacing of the dark spots. The system can be modeled as a coherent system designed to notch a particular spatial frequency followed by a clear-aperture incoherent system.

© 1990 Optical Society of America