Advice on using star masks in GIMP or paint.net

[sharkbite]

Hi Folks - hoping someone could help me.

Just starting on this deep sky lark, i have managed to get a decent stack of Eta Carina subs, stacked them in DSS and created a star mask.

As i am way too tight to pay for photoshop...

I was hoping someone might be able to give me some practical instructions on
how to use star masks in either GIMP, paint.net (or perhaps another freeware tool) to reduce the brightness of the stars while increasing that of any nebulosity...

Google is supposed to be my friend, but i have only found tutorials on photoshop...

Any help would be most appreciated.

[ZeroID (Brent)]

GIMP is remarkably ppowerfull so don't discount it. I'm no GIMP expert, nor Photoshop for that matter, but most of the principles and functions are the same. You may have to 'translate' some of the tools names etc but watching the Photoshop videos may give you some clues as to what to look for in Gimp.
Sorry I can't be much more help than that.

[janoskiss (Steve H)]

Gimp would do fine but you need the 16-bit colour version for serious editing (v2.9 iirc), which is still in beta and a pain to install. Otherwise quantisation noise will get you with only 8-bits per colour. This is the biggest shortcoming of Gimp and has been for a long time. I think the developers have their priorities wrong or maybe there simply just aren't enough developers. (Users have been crying out for more than 8-bit colour support for a decade or more.) The Gimp is okay for the final stages of editing and some basic stuff but not for serious work. At least not the current stable release v2.8.

Imagemagick is a lot more powerful (and will do 32-bit colour, int or float) but also a lot less user friendly. Sorry I don't have a straight answer to your question. Just thought you should be aware of the gimp's limitations before you invest too much time. But if do you get v2.9 working I'd like to hear about it.