Hi Sven,
Yes Dietmar is correct - the verbotten-for-ST procedure is histogram channel alignment, which can have various other names such as neutralization, normalization, background this-or-that, etc., but can also sometimes use terms like RGB. As it does in DSS.
What you are discussing however is a
spatial channel alignment, which DSS has a different term for and is also on a different tab. That is perfectly okay, if needed, since the overall white balance is not being affected. Basically, the three channels are split/extracted, and then registered or star aligned (which is why if done in DSS after-the-fact, it is good to run a sufficient new star-sensing registration), and put back together.
Another potential cause I suppose is saturated cores. It is the AutoDev that results in this look. If you ran FilmDev (otherewise not optimal), it is likely you would not see it. Or, an AutoDev where you draw an ROI that does not contain any such stars (use long thin slice if needed to otherwise cover the rest of the image's total dynamic range), and maybe usage of some IFD, would also eliminate or at least minimize the effect.
My guess is, that due to the way AutoDev is built, bright and/or oversatured cores and surrounding pixels get somewhat of an "HDR" effect imposed on them, revealing a little ringing. I'm not entirely sure what AutoDev's full saturation or clipping handling algorithms are, but we know Ivo warns us of the potential pitfalls of blown star cores. Not that they are fully avoidable of course, with my 6" Newt and at f/3.8, I will probably blow the cores of any decently bright star in about, oh, one second.
![Laughing :lol:](./images/smilies/icon/lol.gif)
In NINA I usually aim for saturated pixels in the low 100's (across 26MP APS-C), which is a fairly common rule-of-thumb.
Also, depending on severity of any such ringing, it's possible that they will somewhat process out, particularly following a good deconvolution as the center resolves inward. Then double check what things look like after getting to Color, and see what Highlight Repair might do too.
On the Airy Disk / stellar profile theory, my guess is no, but I can't guarantee that. My impression has always been that those fading concentric rings due to diffraction are difficult to see except in really good seeing, usually needing high magnification, and often lucky imaging techniques.
![Shrug :confusion-shrug:](./images/smilies/confusion/shrug.gif)