StarExterminator and keeping background stars in M33

Richard Lewis

I'm processing M33 and after running StarExterminator I can see that a lot of the galaxy's stars are pulled. I want to keep them in so I need a mask of some sort. I was thinking of doing an elliptical mask covering the entire galaxy with GAME, run STX. On the "starless" image then create another mask using MLT to only pick out the smallest stars which should be mostly background? Then apply that mask to the original image and run STX again? 

I suppose what would be nice is script of some sort that lets me create a mask specifying the largest FWHM of the stars I want to mask out. 

BlockHead

I think your idea is on the right track. Using MLT can certainly pick up on star-like structures. 

You can also try the GAME script in one go. 

You can make an ellipse around the galaxy and see what GAME pickup up for "stars" within the ellipse.

Use the "Star Mask" option... you might like what it does and it might simplify your work.

-the Blockhead

Richard Lewis

Seems I can get (sort of) I want by using the GAME script to create a star mask. I invert it and apply to the image. However the star mask only contains the larger stars and since it's a gradient mask leave stuff behind. Maybe use PixelMath to combine a binary mask with stars mask. 

BlockHead

Exactly... you did it correctly. 

You can use a binary mask... in combination and it will give you what you want. But, you can't control the amount of star-like objects. It was worth a shot though. 

You can do what you originally described for great control. You can also use the Clone Stamp process and paint on objects in the galaxy to create the mask directly. But the MLT method is really a good wholesome way to achieve what you want. 

-the Blockhead

Richard Lewis

Thanks Adam, used FAME from Seti Astro to create a binary mask around the galaxy. Used the freehand tool to trace around the spiral arms. FAME is cool because there is a paint brush object as well that gives a lot of control over mask generation. Still a WIP but a lot closer to what I'm after. The image is with a GT81 WIFD and ASI2600MM

Watching your videos now on processing M83 LRGB. 

Before your videos I almost gave up on PixInsight. 

Richard Lewis

Removing the HA and O-III channels I get a better result. I also learned that LRGBCombination works much better with non-linear images