Abstract

We introduce a partially coherent optical image enhancement system capable of eliminating unwanted sinusoidal signals that are additive in object amplitude transmittance. The spatial distribution of the pupil mask in a Koehler illumination imaging system remains fixed while the source distribution is changed to block sinusoids of different spatial frequencies. The operating principle is a variation of dark field imaging. In dark field imaging, the pupil is chosen to block all bright regions of the source so that no undiffracted light is passed by the pupil. A similar principle can be employed to block sinusoids of different spatial frequencies. For a single sinusoid object, two spatially shifted images of the source are incident on the pupil. The source is chosen so that these shifted versions are completely blocked by the pupil to prevent that particular sinusoid from reaching the output image plane. The choice of a pseudorandom pupil distribution combined with the appropriate source distribution leads to good rejection of unwanted sinusoids while preserving image detail.

© 1989 Optical Society of America