Effects of Signal-Dependent Granularity*

Abstract

The effect of the dependence of grain-noise level on signal level is considered for a coherent optical-processing system. It is shown that even when all spatial frequencies associated with image detail are removed by high-pass filtering, the square-law rectification of grain noise reproduces a recognizable image. A similar effect is shown to occur for halftone images. A simple explanation is provided for halftones which agrees well with experiment. A linear theory is also given for the case of granularity. Experimental results, relating macroscopic density measurements in the original and the filtered image, show argeement to the theory for fine-grain films, while results for coarse-grain films suggest minor deviations.