No nonsense, affordable astro software that just works.
The two aspects - colour and luminance - of your image are neatly separated thanks to StarTools' signal evolution Tracking engine.
Signal bias is a fixed background levels which, contrary to a gradient, affects the whole image evenly.
In the Auto mask generator, set the parameters you need to generate your mask.
You can convert everything you see to a format you find convenient. Give it a try!