My apologies for diverting the thread away from FPN with what I thought was an innocent comment about signal and noise. You will have to judge for yourselves whether the "fairly basic book for amateurs" is accurate or inaccurate in its treatment of signal and noise as it applies to CCD images and calibration. If you find it inaccurate(albeit incomplete as FPN is not covered) please let us all know how and why.
Two quick quotations:
Taken together, these artifacts are called pattern noise. In some cameras the pattern is the same in every bias frame; in others the pattern is different in every bias frame. Repeating pattern noise is better than changing pattern noise but all pattern noise is bad... In some the pattern noise is larger than readout noise.
So he is referring to fixed variations in "signal" as pattern noise. That is Richard Berry from https://manualzz.com...ews-the-qsi-532
But my favorite quotation on this stuff is from a pioneer in maximum entropy and Bayesian methods in image processing:
The concept of noise is always defined in a specific context. As a consequence, what is considered noise in one case may be considered "signal" in another. One man's weed is another man's wildflower.
That's a graduate level text on optics and imaging, "Probability, Statistical Optics, and Data Testing" by B. R. Frieden. It's a rare text where the author actually takes the time to make this point. Normally it is assumed and not stated. As Bob alluded - it would be hard to write out any SNR expression if you had to fret about the distinction in terms of the causes of the terms. In fact I can put most anything in a context where it is a "signal."
So if you want to go by Richard Berry, then clearly he is happy to refer to undesirable modulations of signal as a noise term. It sounds like you feel that breaks Berry's own rules on this stuff - but he uses the term noise.
I think there is a fairly established convention in professional technical writings in experimental science and engineering - and that is to focus on the thing you are trying to measure as signal and anything that obfuscates it as noise. Only in amateur writings do I see people trying to distinguish them - and it is a lost cause because most anything can be regarded as "signal."
But the way Berry Burnell talk about dark current pattern noise is ok in that they do describe it as ultimately due to variations in what we normally view as a "signal" - i.e. dark current. And on top of it there is Poisson noise. That's fine - but the problem is when you say since it is inherently a signal it is always a signal - but obviously they don't really believe it because Berry himself calls it noise. The real problem for beginners learning this stuff is that I have seen people try to wrestle in their minds that calibration only increases noise. So why do it? Well it actually decreases noise - when you allow your vocabulary to include terms like "pattern noise" - as Berry does. It's a noise term that adds in quadrature with all the others - and it is reduced by master dark subtraction - and applying flats.
And that book makes no mention of dithering at all. That's when you would really get tongue tied trying to say you want to dither to reduce the signal. Instead all those undesirable things are noise terms and there are ways to reduce them. There is no need to think noise only grows when you do all this calibration stuff.