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Abstract
The photographic image of an extended object possessing complex fine structure is “degraded” by three effects. The first is the limited resolution of the photographic objective. The second is the spread of the image due to scattering of light by the grains of the undeveloped emulsion. The third is a statistical fluctuation in the effective photographic response (sensitivity) from one small region of the emulsion layer to another, due to statistical fluctuations in the density of the silver grains in the developed emulsion.
It results from the presence of these fluctuations that the Shannon information content of the photographic image of a member of any statistically characterized object set is infinite; in particular this is true for a member of a low-contrast random object set. It is described in general terms how the mean information content of the images in the last-mentioned case can be evaluated with the help of contrast transmission theory and can be used as an assessment of photographic image quality. A brief explanation of the physical meaning of Shannon information in terms of entropy-reduction is also given.