Noise and coherence in optical image processing I The Callier effect and its influence on image contrast

The observed density of a photographic record is dependent on the aperture of the illuminating and imaging optics. This effect, due to the scattering by the photographic emulsion, is analyzed using as few assumptions as possible. The results show a reasonable agreement with experiments on Callier effect found in the literature. In the realm of a study about noise and coherence in image processing, the influence of the Calier effect on image contrast is discussed. It is found in particular that contrast variations may be large (over a factor of 10 in some cases) and that the best contrast is obtained for a certin partially coherent illumination.