Color Calibration is difficult!

[Emanuele]

I am having an impossibly hard time color calibrating my M31 image.

It's all yellow and if I select the previews for the white reference (the core of the galaxy) and background reference, it gets green and blue and yellow all over.

Am I missing something?

[Emanuele]

okay, here's the best I could get, and it is still horrible.
I am not sure what I am doing wrong. The colors of the stars appear to be okay, but the galaxy is all yellow.... why is that?
I tried using eXcalibrator with the registered FITs but PI truncates the header and they can't be read anymore....

[Juan Conejero]

Hi Emanuele,

Select the whole M31 galaxy as white reference, not just the core. If you select just the core, or an elliptic galaxy as you've done in the screenshot, then the white reference will be too red. You must use a relatively nearby spiral galaxy as white reference, as it will provide a source for all possible stellar populations and is not significantly reddened.

Let me know if it works better this way. If you wish, I'd be glad to give it a try if you can upload the image. It could be a nice firum tutorial.

[harist]

ColorSaturation is an equally important tool in need of a forum tutorial!

Tasos

[Emanuele]

Juan, thank you so much for your reply and offer! I will gladly accept:

the image suffers from:

light frames with light pollution gradient (Red and Green - the blue is fine)
Dust donuts.

where can i upload the original linear-image ?