Digital Image Noise

Bob,

If I understand your method, you are reading "dark noise" from the image sensor - noise resulting from sources other than signal (light). As you mention, noise in a phtographic image is dominated by shot noise which is related to signal intensity. Dark noise represents the foor above which signal + shot noise must rise in order to give useable image data.

I believe your formula computes the mean of the recorded signal (dark noise in your setup) - and perhaps should be described as such.

Shot noise is related to signal (light) intensity, and is quantified as the dispersion (e.g. std. dev.) about the mean signal intensity.

Dark noise is related to other factors, including photodiode circuitry, temperature and length of exposure.

Indeed, the 'hot pixels' would remain a constant throughout the samples.

Dear Woody,

So far as I understand it, that is exactly what I am trying to characterize - the dark noise. The images that I start with as candidates are taken in a darkened room with the lens cap on.

Actually, I am re-considering my algorithm at the moment. If I make the change that I am considering, the result would result in a much greater spread in values as ISO and shutter duration change. You will note that my equation divides by the total number of pixels in the image that have a non-zero value. Instead, I think I should be dividing by the total number of pixels in the image. Using that formula results in much lower values for Digital Noise Figure when the ISO and shutter duration are low in value.

I have just uploaded Version 2.0 of the software, which now displays the resulting Digital Noise Level in deciBels (dB) relative to an average scene (18% gray card).

A Noise Level of -40 dB, for example, means that the average noise level is approximately 1/100th (1%) of the average signal level in an average scene.

To download your copy of the Noise Level program (approx. 1.4 MB), go to
http://zaffora.f2o.org​/W9DMK/Programs
and then from the list of software downloads, right click on NoiseLevel.zip and select "Save Target as.."

After unzipping run the setup program to install the program.