Can you mask Part of an Image Manually Selecting that Part?

[jerryyyyy]

In my LRGB images I always have some LP remnants in the background that if I clip out I will clip out the central object, say a galaxy like M101.  Is there a way to manually select what I want to mask, e.g. the galaxy?  The RangeMask also masks the LP. 

[NGC7789]

The PixInsight methodology frowns on arbitrary masks.

The correct way to attack your problem in PI is to attack the gradient caused by the LP with either DBE or ABE.

Perhaps you could put a FITs file up on dropbox or somewhere so folks could see what you are seeing and then more precise techniques can be recommended.

-Josh

[jerryyyyy]

Yes, I have attacked these gradients with great vigor using DBE and ABE.  Problem is that given the amount of LP where I live there is always a lof of what I interpret to be sky glow or whatever noise that approximate the signal in the edges of nebula and galaxies.  Last couple of weeks i have processed and reprocessed a of of data on M101. 

I started out here:



and eventually got here:



I have tried all sorts of settings with the DBE and eventually I decided that a lot of samples (30) of small size (6) avoiding the DSO was best at getting rid of the gradients... but as I use DBE I see the noise rising the in the background. 

I also have to improve my flats.

Am shooting some new targets with better flats. 

Anyway, thanks for the comments. 

[pfile]

background noise after DBE is pretty normal - if you subtract a smooth model of the background sky, what is left is the shot noise from the background.

i think your final image looks pretty good but has too much green; either SCNR to green or just pulling down the green channel with the curves tool will improve things a lot.

this field should be pretty easy to DBE as there's not much going on except for the galaxy.

rob