Butterfly Nebula - Managing Star glow/halo

m_abukhalid

Well-known member
Jan 20, 2018
63
2
Two nights ago I imaged the Butterfly nebula. The following is a result of stacking 19x5minute calibrated exposures at ISO 200 imaged with the D5500a and a UV cut filter. I applied stock ABE settings to each channel, linear fit red and blue against the predominate green channel (I had an exceptionally strong green due to all the smoke haze, I think) and recombined. Color calibration and background neutralization done in Photometric Calibration and an average neutral SCNR to cut down the green as much as possible. Deconvolution performed through a nebulosity mask generated from a range mask with a star mask subtracted and remaining large stars clone stamped out. Two passes of MTL against luminance and chrominance each. I think the data looks really good for the amount of total integration but the big challenge here is the glow from that blown out star.
butterfly.jpg

Below is a link to both the final linear image above as well as the result of masked stretch which set a target background of 0.2, iterations of 1000 (trial against the usual 100) and target background against the darkest part of the background. If smaller jpeg files would be better let me know:

Next, I normally would use histogram transformation/Curves transformation through the nebulosity mask to create more contrast between the background and the rest of the image. I would then use HDRMT to rescue as much detail as possible, some sharpening through the nebulosity mask and then histo/curves and star reduction for final image. However before I do all that I think I should do something about eliminating all the glow from that star if possible as its making the use of targetted nebulosity masks difficult. Theres some faint data to rescue below it ... Brute approach of using a luminance mask would just emphasize the glow further.

I would appreciate it if someone can have a look at this and give me some advice on how to manage this challenge. All feedback/critcism is welcome. I am using a first generation i7 so trial and error is taking a lot of time. Getting more data thats properly exposed and using HDR process to bring out the details is probably the best way and that will happen later. I would still need to do something about the glow though. Thanks!
 

Juan Conejero

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Sep 2, 2004
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Valencia, Spain
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In my opinion, there is absolutely no problem with Sadr in this image. The halo is perfectly normal, well under control, and a natural consequence of the star's high brightness. The MaskedStretch algorithm has done a fine job here. I don't know why you may want it to look differently, but an HDR combination with short exposures would be the only valid way to handle this 'problem'.
 
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m_abukhalid

Well-known member
Jan 20, 2018
63
2
Thanks Juan! I am just trying to avoid having a big white circle around Sadr by the time Im done enhancing/stretching the nebulosity. A luminance mask will treat glow as part of the luminance and will stretch the glow with the nebulosity. My nebulosity mask is the difference of a range and star mask and then clonestamping the edges and gives me this:
butterfly_badmask.png

If I dont clone stamp and use a simple star mask subtraction I push the smaller stars more than I want and I get the diffraction shadow in Sadr:
butterfly_badmask_simple.png

Im trying to basically understand if there's a way to control the glow of the stars in a clean way or maybe selectively diminish the glow after Im done.
 

m_abukhalid

Well-known member
Jan 20, 2018
63
2
I have processed this to the maximum of my ability... first time using SMI/PIP steps and Im amazed how much detail that brings out. But the colors are now an ugly orange... is there a tutorial I can reference to help bring back the original reds and tease out the blues in there? I tried to use the color saturation tool but Im completely lost as to how to use it.
butterfly_semifinal.jpg