Star Halo from HorseHead Nebula

General discussion about StarTools.
Post Reply
sandconp
Posts: 30
Joined: Tue Dec 03, 2019 6:59 pm

Star Halo from HorseHead Nebula

Post by sandconp »

I have a very large Star Halo from a very bright star (Altinak) in my astronomy image of B33 and I was wondering how to remove the Halo using Star Tools? I also own Affinity Pro (very similar to Photoshop) and was wondering if that would also be an option?

I will provide the URL for the TIFF file if you are willing to help take a look at my image and help me eliminate the halo. I am basically very happy with everything else.

https://www.dropbox.com/s/z95dohtqxxvxzrc/B33.tiff?dl=0
User avatar
admin
Site Admin
Posts: 2683
Joined: Thu Dec 02, 2010 10:51 pm
Location: Melbourne
Contact:

Re: Star Halo from HorseHead Nebula

Post by admin »

Hi,

This definitely would fall firmly into the realm of photo retouching and is not generally something you would use StarTools for.
Alnitak will always be a problem, and please understand some of your peers may frown on retouching images like this.

Of course, though, it can be done in StarTools;
B33.jpg
B33.jpg (426.39 KiB) Viewed 912 times
The procedure is not trivial, nor does it have a specific formula or technique rooted in proper signal processing, but it is as follows;

Launch the heal module and go into the mask editor. Lasso the halo as close as well as possible, making sure to include all offending pixels.
Back in the heal module;
Parameter [New Darker Than Old] set to [Yes]
Parameter [New Must Be Darker Than] set to [65 %] or thereabouts for this image.
This should yield a fairly neutral patch.

We are now going to make use of the fact that this particular halo increases in intensity towards the edges.

Launch the Layer module. Go into the Mask editor and Invert the mask (leaving a "hole").
Put the original image with the halo in the background (either from the undo buffer, or by loading it into the foreground and then swapping background and foreground).
Set Brightness Mask Mode to "Where fg is light, use bg", and Brightness Mask Power to maximum (5.0). This will protect the star's core from dimming due to what we are about to do.

Set Mask Fuzz to maximum. You should notice the halo's edge being reduced.
Now it's just a matter of doing this a few iterations more (e.g. use this output as the input for another round).

Copy, Paste Bg
Copy, Paste Bg
Copy, Paste Bg
Copy, Paste Bg

Hope this helps!

EDIT: You can even go all the way and restore the stars that were dimmed a little, by layering them back in from the original.
Ivo Jager
StarTools creator and astronomy enthusiast
sandconp
Posts: 30
Joined: Tue Dec 03, 2019 6:59 pm

Re: Star Halo from HorseHead Nebula

Post by sandconp »

Thanks Ivo.
Post Reply