A fundamental limitation to the quality of wavefront reconstruction images is noise generated by the granular structure of the recording medium. Predictions of the signal-to-noise ratios that can be achieved in wavefront-reconstruction imaging are based on the checkerboard and overlapping circular-grain models of the recording medium. When the object consists of a multitude of resolvable point sources, the signal-tonoise ratio is found to be proportional to the space-bandwidth product of the recording medium; when the object is a diffuse surface, the signal-to-noise ratio is found to be independent of that space-bandwidth product. The quantum limit to signal-to-noise ratio is approachable only with a judicious choice of reference exposure and a recording medium free of other classical noise sources.
J. W. GOODMAN, "Film-Grain Noise in Wavefront-Reconstruction Imaging," J. Opt. Soc. Am. 57, 493-502 (1967)