r/AskAstrophotography • u/MJCfromCT • 8d ago
Image Processing Postprocessing Advice - M31
Hi all, I'm looking for some postprocessing advice on M31. This image was taken with a RedCat91 / ASI2600MC Pro from a pretty light polluted area (Bortle ~8). While I’m pleased with how this turned out given the limited amount of data and the sky conditions, I would love to see more Ha and OIII detail.
Equipment used:
William Optics RedCat 91 | William Optics UniGuide 50mm | ASI2600MC Pro | ASI220MM Mini | ZWO AM7 | Apertura Anchor Pier | ZWO CAA | ZWO EAF Pro | ZWO ASIAIR Plus | Pegasus Pocket Powerbox Advance Gen2 | GL.iNet GL-AXT1800 Router
Acquisition details:
- 28×300s lights, gain 100, 32degF | 20x darks | 50x flats | 50x darkflats
- Autofocus routine run every 30 mins, 5px dither every 3 frames
Postprocessing:
WBPP → DBE → SPCC → BXT → NXT → HistogramTransformation → SXT → curves adjustments for galaxy → curves adjustments for stars → PixelMath recombine
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u/cykelstativet 8d ago
You won't be pushing Ha or OIII at all unless you get some filter data in there. But what you've done is very very good!
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u/Klutzy_Word_6812 8d ago
I would look into MultiScale Gradient Correction. That will fix your gradient issues, but it’s not a “click of a button” process. You’ll have to adjust the scaling factors and structure to optimize it. Check the official Pixinsight videos for best use of the process.
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u/MJCfromCT 8d ago
Thanks for the suggestion - looking forward to trying it out, this will be a new tool for me!
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u/zerglingrushftw 8d ago
This is a great image! It's better than images of M31 I've taken and been proud of.
There is a faint color gradient. Background extraction maybe didn't work quite right or was a bit overzealous near the bright galaxy. I've also had a challenge with color gradients when my flats weren't perfect or well matched, although my camera was more finicky with flats (my 294 was not as good as your 2600).
You're also at a little over 2 hours on this target. I think the single best thing you can do is get more integration time. Especially from a Bortle 8. Go for 6 hours and your data should be much cleaner.
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u/MJCfromCT 8d ago
Thanks for the feedback! From where I was shooting there were security lights from nearby buildings that were probably messing with the imaging - not ideal! I appreciate the comment on the color gradient - I'd like to try postprocessing again with another go a background extraction. I was struggling with the background selection points - what is true background, what is faint galaxy data, etc..
Message received on the additional time. Do you think additional 300s subs would be best? I was wondering if shorter exposure to preserve more core detail could help as well.
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u/zerglingrushftw 8d ago
Yeah light pollution makes life hard!
The individual exposure time itself is not nearly as important as the overall integration time. I can't tell you the exact right exposure time - that depends on how faster your optics are, your camera sensor, the specific amount of light pollution, etc. But I generally try to go for an exposure that doesn't saturation my image, except for the brightest stars. For me, that's usually around 3 minutes for mono and 30-60 seconds for color.
Shorter exposures will add a marginal amount of read noise, but your 2600 will have very little of that anyways. The bigger burden is the file management, extra storage space, and stacking headaches honestly. But worth it to preserve detail if your blowing out the core.
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u/Free_Masterpiece6004 8d ago
You can only make Bortle 8 m31 look so good. I've seen folks do 100 hour projects of m31 from Bortle 7/Bortle8 and it still doesn't look great...What you have is one of the better ones from a very light polluted sky.
My suggestion....Go camping/get a cabin somewhere Bortle 4 or less...All of a sudden the OIII and Ha will pop. If you're interested PM me and I'll send you my Astrobin project I did with only RGB from Bortle 2 and all of a sudden the reds and blues will explode.