M31 & M33 again

[imakebeer]

I'm continuing to hone my skills in all respects and had another go last night at M31 & M33, and I feel like it's an improvement over the last attempts here. I think the M31 pic is less noisythan before and the stars in particular seeem really bright though I'm not sure why.

M31: 81 lights at 60s & ISO 400 + 10 each darks, biases and flats.

M33: Only 18 lights at 60s &ISO 800 + 10 each darks, biases and flats - not for the first time I was undone by a flat battery in the camera! 😭😭😭 Have now ordered a dummy battery!

Stacked in Sequator and fiddled with in GIMP - @Rallemikken I took your advice and tried Siril, but at the moment I just seem to get better results from Sequator. The Siril tutorials are good though, and I can see it's a very powerful tool - I think part of the problem is I'm not sure at what stage to switch over from Siril to GIMP. The learning journey continues.....

[Rallemikken]

26 minutes ago, imakebeer said:

I think part of the problem is I'm not sure at what stage to switch over from Siril to GIMP

This is how I do it; first I set up the environment in a temporary folder:

- I make one Siril-compatible folder complete with subfolders and files for lights and calibration files, lets call it "M31"

- I make one folder for results, both temporary and finsihed images, lets call it "M31-results"

- Inside "M31-results" I make a subfolder named "png"

- I do one or more semiautomatic stacks in Siril. Once you have converted and registrered the stack itself takes only minutes. I give the fits-files names that tell me something about what options I chose during the stack. Then I move the resulting .fits-files into "M31-results".

- I often also do a stack in DSS. Better do that last, it will fill up the "M31"-folder with crap. I rename the Autosave.fit and move it to "M31-results".

- About file names: Take a look at http://www.agle.no/astro/bilder/M81_M82-Siril-SC_25_25-kalib-bextr-asinh.jpg  This is M81 and M82, stacked in Siril, Sigma Cappa 2.5 high and 2.5 low, color calibrated (not photometric this time), background extracted and asinh stretched, all this inside Siril. I usuallly save a .tif-file for each incremental step, all to the "-result"-folder, with a little more added to the file name. If I have several .fits-files to start with, I might end up with a lot of tif's. Same for the original Autosave.fit from DSS: I open it in Siril, do my things, and saves as tif's, but this time I name them i.e. "M81_DSS_Siril_kalib-bextr-asinh.tif" and so on. In tis way I can see that this image was stacked in DSS (opposed to the rest, which all are stacked in Siril) and I can see what mods I did to it in Siril. 

This is what I do in Siril, not necesarrily all these steps, but most often in this order: Color calibration OR photometric color calibration. Crop. If you do the final crop as early as possible, you can easily blend several images based on the same fits. If you do a galaxy, and one version has really nice colors but bloated stars, you can blend parts of it with another version that hasn't been so heavily processed, and where the background is better preserved. Takes some experience, and it's NOT cheating, as long as you use the same  file to start with. After crop I do background extraction, if needed. The new routine on this offer a preview, and you get fingertip control when you set or delete points. Works REALLY WELL! DOES NOT introduce noise or destroy details! Then I blow up the image in Autostretch-mode and take a peek at the background. If it's much noise, I do a Median Filter, most often 5x5. Sliders midway. In the end, I always do a gentle Asinh stretch. I have my own way on this: I start whit a value of 7, 6 or 5, and work my way down to 2. This will requiere experience. After a run from 5 (via 4 and 3) to 2, I save, do 4 "undo"'s, and start from 6. Same procedure. Sounds weird, but it works for me. And I ends up with several versions I can continue on.

In this way you have a "M31-results" with a handful of original fits-files, not tampered or modified in any way. In the same folder you have some more tif-files, with names that tells you what it is, where it was stacked, how it was stacked, and what has been done in Siril afterwards. Note that the "png"-folder is empty. This is where you will export your images after you have done your magic in Gimp. PNG is lossless, but does not support layers. I always keep my final images in PNG, and export as JPG for internet, facebook and such.  And as said earlier, two images of the same object is easy to blend (or merge) as long as they come from the same tif in the first place.