A general analysis of the image fill-factor influence on Zernike-type phase contrast filtering is presented. We define image fill factor as the ratio of the object support area over the illuminating area. We first consider binary-phase objects and then generalize to arbitrarily quantized and continuous-phase objects. Numerical simulations are presented for binary- and quadratic-phase objects, where the contrast of the output image is evaluated as a function of the image fill factor, image phase variations, and filter phase. The results obtained show that the image fill factor can significantly modify the contrast and irradiance of the contrasted image.
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