A partially coherent Koehler-illumination imaging system equipped with complementary masks in source and pupil planes can be used to perform image enhancement operations such as directional or non-directional edge enhancement and emphasis of spatial bandpass features. With many objects the use of complementary masks results in high-contrast images. Underlying principles are explained and preliminary experimental results presented.
William T. Rhodes,
"Image Enhancement By Partially Coherent Imaging", Proc. SPIE 0422, 10th Intl Optical Computing Conf, (15 April 1983); doi: 10.1117/12.936121; https://doi.org/10.1117/12.936121