FILM GRAIN NOISE IN PARTIALLY COHERENT IMAGING

Optical image formation (and processing) is strongly affected by film grain noise. The noise effects depend on the spatial coherence of the illumination. These phenomena are analyzed for the case of Kohler illumination. The effective transmittance of any photographic image is instrument dependent due to diffusion by the grain (Callier effect). Thus the question arises: what is the meaningful physical quantity in image formation? The Callier effect directly influences the contrast of weak modulations, which happens to be maximum in symmetric partially coherent illumination. Ultimately, the detection of weak modulations is not limited by the contrast but by the sur. Using statistical assumptions for the noise behavior, the optimal conditions for weak modulation detection are discussed. This study is devoted to imaging, but its results may be extended to double-slit microdensitometry.