Hi Steve,
I've had a chance to look at your TIFFs now. The darker patterns are definitely a feature of your data. Sometimes they can be detail (dust lanes, variations in stellar density), but they can also be artefacts of some sort (under or over correction by your flat frames, some type of noise reduction, failure to dither properly).
For what it's worth, without having seen the progression and the "appearance" of the structures in the various TIFFs I was successful in seeing them from the start (which I consciously tried to do).
True Gaussian (and - by approximation - the Poisson noise we mostly deal with in AP) exhibits random noise at all scales, its amplitude becoming smaller and smaller (and thus harder to detect) as scale increases. You can see this effect in the Denoise module's first step - which exploits exactly this - where StarTools asks you to specify the size of noise grain beyond which you can't see its existence anymore; StarTools is filtering out bigger and bigger scales as you increase the noise grain parameter.
Given the Poisson nature of the noise we tend to deal with, noise reduction in StarTools indeed deals with noise grain at different scales (and cleverly exploiting psycho-visual effects that go along with that). Correlating detail at bigger scale tends to show on a smaller scale, but much less often the other way around. In your images, we see correlation at larger scales that doesn't appear to be present at smaller scales; somewhat suspicious.
Looking at the Veil data again, there is definitely "clumping" (e.g. correlation at large scales"). There's actually a filter in the Layer module that seeks out this "clumping" across the 3 channels called ("Local Maximum Entropy RGB Selection"). Turn it on and you'll see something like this;
-
- scr.png (477.58 KiB) Viewed 5587 times
The clumping appears to be somewhat elongated (diagonally), which leads me to believe we're looking at a dithering problem; the dithering displacement may not have been sufficient or the frames that were selected during stacking were to heavily weighted towards one particular amount of displacement.
I'd probably suggest using an amount of dithering that is much larger than what you're currently using, while making sure that if you stack frames a good distribution of frames are selected for stacking across the full displacement range (e.g. if you're spiralling out, make sure you don't just stack the frames from one part of the spiral because the seeing happened to be best then).
Let us know how you go!
