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Processing Tips for Altinak? [Deep Sky] Processing techniques · Nick Martin · ... · 8 · 294 · 1

nm_martin 0.00
Nick Martin
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So, I've thought it was a great idea to make a 4-panel mosaic of the horse head nebula region using my 8 inch edge HD scope at native focal length. Little was I prepared for the reflections that Altinak would cause, and I really don't know what I can do to deal with it. Below is a dropbox link to the XISF that I'm working with here. Very little has been done to this file. It is still in its linear state. I have just combined the RGB channels, performed a SPCC to calibrate the colors, and used the SGC to remove the gradients. I haven't done anything else to it at this point while I try to figure out how to handle these reflections, and also deal with the stray light in the upper left corner resulting from a nearby street lamp.

Anyone have any thoughts on how I can approach this?

https://www.dropbox.com/scl/fi/eqpvkahysun2n5jn3gylz/Image10.xisf?rlkey=vtuipkcy5p1wynya6hes3zrf9&st=79rv4039&dl=0
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Gondola 8.11
Tony Gondola
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Too many hops to download, can you just post an inline  jpg?
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nm_martin 0.00
Nick Martin
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I haven't stretched it, so taking a straight JPG out of Pixinsight wouldn't show much. Here is a screenshot of the STF autostretch applied. The dropbox link shouldn't require anything beyond clicking download if you want to see the full xisf.

Screenshot 2024-12-22 204917.jpg
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Gondola 8.11
Tony Gondola
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Are you shooting in broadband? If so, it might help to go narrowband on this target. That would help to cut back the star brightness and tame that street light too, doing short subs would also help. Other then that I can't think of what else you can do. This is an issue for anyone that shoots this field so at some point you just have to accept it as part of the image. The real problem is that SCTs make those darned donut reflections, hopefully the above will help.
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nm_martin 0.00
Nick Martin
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Thanks. I know I can do narrowband but this region seems to be better in broadband. I haven't really seen any good narrowband images of this region. I was hoping there would be some technique I could use to edit out the reflections. I wouldn't mind the brightness of the star of it weren't for the reflections.
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Gondola 8.11
Tony Gondola
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Yeah, I'm with you on that.
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daveshow07 3.15
David Foust
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Lots of careful masking is how I'd approach it:
  • Gradient correct, background extract, color correct, and stretch how you'd normally stretch.
  • Open SetiAstro's Freehand Adaptive Mask Editor (FAME) script.
  • Utilize the freehand mask option and I'd probably select the "lightness" mask option over the "binary" option, and set the blur to about 10-15.
  • Mask each color reflection individually and repeat the process for each color. (You can do multiple individual masks with the FAME tool, so mask all the reflections with the same color at a time.) Generate the mask.
  • Hover over one of the reflections and look at the RGB levels on the bottom information bar. It should tell you the intensity of each color. Open the curves tool, and play around. Make sure the real time preview window is open so you can see how changes you make affect it. If it's a red reflection, open the Red curve, and make some reductions around the level that the information bar indicated. You may also need to make minor adjustments to Gand B to get the color balance you want. Eventually you should be able to find a  level adjustment that helps it blend in to the area around it without reflections.
  • Repeat for the other colors.

Note that You may need to mask each color of each individual reflection as they may not be uniform in intensity.

I would handle the bright reflection on the top left corner the same way, but I might wait until I've stitched together the mosaic to do it, so it's easier to balance it with the data in the other panels. I suppose the same could be said for Alnitak's reflections too, since we're only seeing 3 of what I presume to be 4 reflections on Alnitak.

I went through this exercise to patch up some nasty gradients on one panel of my M33 HOORGB mosaic. Not sure what happened with flats in the stacking process (the other panel was perfect), but gradient correction didn't fix it, so I had to make this type of an adjustment for the final corrections.

Lots of time and patience will be needed for this, so be patient and don't hesitate to take a break and start the process over if needed! I did about 5 times! 

Good luck!
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nm_martin 0.00
Nick Martin
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Thanks for the insight. Would it be easier to correct in the channels before combining them?

Since my window for adding to this mosaic is more or less gone at this point, I may set this target aside for a bit but I want to play around with some processing options in the mean time.
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daveshow07 3.15
David Foust
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I only work in OSC, so I haven't tried correcting in each channel first, but I don't see why you couldn't! Honestly, it would probably be easier working in each color channel before combining. You may still need to make some final tweaks in the combined image anyway, but getting the heavy lifting done before combining makes sense. In principle it's the same process, but instead of tweaking the R, G, and B curves individually, you'll instead tweak the RGB/k curve (or perhaps the L curve) in the curves tool.
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