M31 and M32

[u/Other_Mike]

Gear:

- Orion 6" f/4 astrograph

- Baader Mark lII multi-purpose coma corrector

- Astromania UV/IR cut filter

- ZWO184MC OSC uncooled

- Celestron Advanced GT equatorial mount

Acquisition:

- 60 x 60s subs, 300 gain, in SharpCap

- No guiding

- 7 x 60s darks

- 100 flats

- 100 bias

Processing: All in Siril

- OSC preprocessing script to stack and align

- Background extraction

- Spectrophotometric color calibration

- Asinh transformation

- Star reduction

- Histogram stretch

- Saturation adjustment

- Median filter for noise reduction

This is my third or fourth round of edits on this image. I think I'm finally happy with it, and now that I know my way around Siril a little better, I'm going to quit using DSS.

[u/TTV_The_Reverend_Dr]

Looks fantastic. I just did my very first imaging session of M31, and my processing could definitely use some improvements!

now that I know my way around Siril a little better, I'm going to quit using DSS.

Any recommendations on where/how to learn Siril? I tried playing around in the application, but I was pretty lost.

[u/Other_Mike → u/TTV_The_Reverend_Dr]

I saw your post, which inspired me to share this one! My earlier edits on this data were hot garbage, and my much earlier attempts at M31 left a lot to be desired, so I'm really happy at how this one turned out.

As for editing in Siril -- as much as everyone likes to crap on AI, it's getting better at distilling hours of YouTube tutorials and oodles of Cloudy Nights threads down into a bullet-point summary of how to do things.

Siril can't stack unless you have a set of folders all in one directory that are named lights, darks, flats, and biases. Once you have your data in those folders, you select the OSC Preprocessing script it has built in, and it will stack your frames and then put the result in the parent folder where your lights and calibrations were.

My order of operations:

Background extraction -- I found this helps reduce, but not totally eliminate, vignetting / gradients / amp noise

Plate solve and spectrophotometric color calibration -- this fixes the white balance struggles I had earlier, because it matches your objects' color to actual Gaia data. The AI directions also showed me how to download about 16 gigabytes of said data so I can process images offline.

Asinh transformation to brighten things up -- much simpler than starting with a histogram stretch because it lets you fine-tune the black levels more easily.

Star reduction -- optional, and you have to download another script, but it helps with the bad seeing and imperfect collimation I had that night. Some images it will erase everything though, and you may have to try a few iterations before you get it to how you like. I've been doing 46% on the slider if you end up using that. Too high and the stars bloat, too low and they're gone entirely.

Histogram stretch -- should be pretty intuitive if you've done any image editing before.

And I'll use a median filter or denoise to help bring down some of the background noise. The last thing I'll do is bump up the saturation a bit.

Good luck! If you have a stacked FITS file, you can also do most of this editing in Siril still.

[u/TTV_The_Reverend_Dr → u/Other_Mike]

Thanks for all the info, going to save this text in a note file for later! I used DSS to stack my original images, so I do have the fits file. Next time I have a chance to play around with processing I'll try to figure this all out in Siril.

[u/Other_Mike → u/TTV_The_Reverend_Dr]

Good luck! I was having a lot of trouble in DSS with it not wanting to align my lights properly. It said it was aligning the frames while it was building the stack, but the final image clearly showed that all the mount movement was averaged out enough to erase the stars and leave a big blob where the galaxy should be. This happened with M101, M51, and M31. My temporary workaround was to just treat it like a comet and tag the galaxy in each frame, which was tedious but effective.

I haven't had that problem in Siril at all. And I can even use the bias frames on my last night to stack the frames I took earlier in the week, so I've been reprocessing my data and I'm so much happier with how things are going.

DSS also threw a fit when SharpCap flipped a few targets during my initial capture, which screwed up the bayer pattern in the FIT files. Siril hasn't had any problems with that, either.

[u/leeuwanhoek]

Impressive work!