Studies of photographic grain in a coherent optical system: Signal-dependence and its implications

The signal-dependence of photographic grain is easily demonstrated by studying the first order statistics (mean and variance) of the scattered light in a coherent optical spectrum analyzer. It is shown empirically and from simple theoretical considerations that the granularity of the photographic material can be determined using a coherent measurement and can be interpreted as an inverse signal to noise ratio. The traditional linear Fourier domain filter can be shown by simple considerations to be ill-suited for dealing with the signal-dependence of photographic grain.