Signal = ideal (image) noise = difference between ideal and what's actually recorded
Now let's try an experiment. We expose the film to a uniform source of light. As an average on the whole frame, the "signal" is good, i.e. we got an average level of gray that corresponds to the exposure. Now let's take a smaller aperture - 1mm x 1mm. The recorded signal varies inside this area, due to the presence of grain. Basically that's how they measure RMS - they take a small aperture and measure the variance of signal when they move that aperture along a uniformly exposed area. What I was asking is if this could be expressed as a s/n ratio instead of the classic "RMS" value.
cheers, caveman
Bruce Rubenstein wrote:
Squeaky would like to know what value of "no noise" you are using, since S/N is a ratio. I would like to know why you are using a ratio for something that is constant? The grain for a given film doesn't vary from one part of the film to another. S/N ratio is useful for quantifying a dynamic range. Squeaky and I both think that there are good reasons for not expressing grain as a S/N ratio.
