I have a pretty simple question that I hope has a simple answer.
When I process my astrophotos, I've been using Nebulosity to stack and do basic processing like level-stretching and curves - and afterward, I'll toss them into GIMP (2.8, I believe) and do some more basic contrasty, curve-y, level-y stuff too.
But as I was looking back recently at some exposures shot with an older William Optics ZenithStar 80 (non-Apo) I see that there are some blue/violet halos from chromatic aberration around the brighter stars. In most cases, these are pics are already flattened as JPGs. I'm not sure where the original RAW stacks are.
By the way, the attached file is just a cropped screen shot of the original JPG, not the whole shootin' match.
Anyway, is there a simple method in GIMP to get rid of those violet halos? I'll admit that I've seen an example or two on YouTube, but they don't look so simple to me. I've never used layers or masks or anything like that in the past. I'm sure I'm just missing something in there.
Remember, the question is regarding a simple, free solution that does not include buying an APO! (As much as I would like to...)