Colour Mottling / Background Noise (M31)

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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yewyuee
Posts: 3
Joined: Tue Dec 07, 2021 10:01 am

Colour Mottling / Background Noise (M31)

Post by yewyuee »

Greetings,

This is my first post. Firstly, a BIG THANK YOU to Ivo & Mike (in Rancho) who were extremely helpful (personal workflow in C N forums message). I am since an adopter of StarTools and with it the start of a learning process.

To recap: the subject is M31. Untracked fixed tripod imaging. Integration only an hour. 2,250 lights of 1.6sec sub exposure with some darks, bias, & flats to go with it. ISO 1600. Partly cloudy, Bortle 8 sky.

I have two things I hope to be enlightened at this moment.
<< The attached is my first StarTools post processed image which I am rather pleased >>

(1)Colour mottling (did I get the right term... those dark ugly patches everywhere).
I suppose it's a combination of heavy gradient (removal) from the light pollution, high ISO, & very short sub-exposure (1.6s).
In the photoshop world, I could probably "hide" these artefacts by slightly clipping the black point (darken the background).
How do I go about "improving (not artificially darken) this background noise" .. i.e. under which particular module. Or did I "overdo some modules"?

(2)The colours of M31.
I tried two methods; both the default and by sampling (tried various sampling points but mainly near the core).
Main query being: given my limited data set, is the colour of M31 authentic enough (compared to the usual golden brown we see in the internet everywhere).

Thank you.

eddie

The stack from DSS
https://www.dropbox.com/s/27nbf9oz20fjc ... S.FTS?dl=0

My attempt using StarTools
https://ibb.co/vVZ77NT
Mike in Rancho
Posts: 1141
Joined: Sun Jun 20, 2021 10:05 pm
Location: Alta Loma, CA

Re: Colour Mottling / Background Noise (M31)

Post by Mike in Rancho »

Hi Eddie,

This is the same dataset as before on CN?

The overall general coloring is reasonably in the ballpark. I think I do recall having some slight issues with balancing going either too blue or too green, but a middle ground of sorts was found.

Yeah, that mottling is pretty common with beginning datasets, mine included, and can have several causes. One is just the walking of pattern noise from sub to sub. I suppose this can kind of happen using a static tripod, as you are just letting the target "walk" up the screen until you reset.

Otherwise this often happens from stretching data well past what it can actually handle, such that you bring out the background noise and then often start enhancing it in the modules. Then towards the end of processing, things like SS and denoise can end up coagulating it all into all those mottles. Yuck! Boy I can't count the number of my early images that ended up like that. :lol:

I suppose I would be much more conservative with the AutoDev. Because it's M31 possibly stronger on the Wipe using a mask to indicate where the feature detail is, but that's something to experiment with either way. You might consider the correlation filter. A significant bin. Smash down the dynamic range of the shadows in A/D and/or Contrast, whilst preserving the target. Avoid enhancing too much of the highlights in anything like HDR and particularly Sharp, if you even use them. And don't overdue deconvolution such that background noise brightens. In Color, go easy on the dark saturation, which is often in the background. Use SS to push the background back. Don't overdue denoise, and in fact maybe even feed some even grain back in with that parameter so that it looks more balanced.

That's what I might try, anyway.

Oh...and tracking! :!:

I started out with a static tripod too. Tried it maybe 3 or 4 times before I had enough and was ordering my HEQ5. :)
hixx
Posts: 250
Joined: Mon Sep 02, 2019 3:36 pm

Re: Colour Mottling / Background Noise (M31)

Post by hixx »

Hi Eddie,
to cover up "black holes", you may try using the Skyglow parameter in Filmdev module at the very end of your workflow. Use 1% up to 3% black or blue depending on taste. The resulting background will be lifted to a higher minimum value.
clear skies,
jochen
fmeireso
Posts: 367
Joined: Mon Sep 28, 2020 8:46 pm
Location: Belgium

Re: Colour Mottling / Background Noise (M31)

Post by fmeireso »

To me looks like it just needs more integration time. More integration time will let more color come out as i learn this year myself. Naste gradient indeed but wipe took mostly take care of that.Anyhow way better then my first try about 3 years ago...
M31_500.jpg
M31_500.jpg (493.94 KiB) Viewed 3497 times
Last edited by fmeireso on Sun Dec 12, 2021 7:00 pm, edited 2 times in total.
fmeireso
Posts: 367
Joined: Mon Sep 28, 2020 8:46 pm
Location: Belgium

Re: Colour Mottling / Background Noise (M31)

Post by fmeireso »

About over 3 -4 hrs off integration time might lead to this ...
M31500kb.jpg
M31500kb.jpg (498.47 KiB) Viewed 3497 times
yewyuee
Posts: 3
Joined: Tue Dec 07, 2021 10:01 am

Re: Colour Mottling / Background Noise (M31)

Post by yewyuee »

Thank you everyone, for the tips and encouragement.
Will experiment with all the above techniques/parameters and hopefully squeeze more out of it.

Shall try to add another hour’s worth of data when M31 comes around again next October (low in my sky now). It’s difficult to do more than two hours worth untracked; an hour is already taking close to 15 hours of DSS stacking and 500gb.

Best regards All.
ionia23
Posts: 62
Joined: Fri Jul 16, 2021 7:39 pm

Re: Colour Mottling / Background Noise (M31)

Post by ionia23 »

What was said earlier about stretching data past usability? There you go. That's a big one I struggled with.
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It seems all these little bits of data that are stretched unintentionally rear their ugly bits as soon as you get to the super structure module. Sure, you can use that and tracked noise reduction to deal with those, but you end up with "false" nebula clouds and/or an image that is overall too blurred.

More integration time will help with noise making stretching easier. I don't shoot less than 100 for each object that I shoot with my OSC.
ionia23
Posts: 62
Joined: Fri Jul 16, 2021 7:39 pm

Re: Colour Mottling / Background Noise (M31)

Post by ionia23 »

Oh, one more tip about combating mottled backgrounds.

Assume the following workflow in Startools starting with your stacked image.
Open as Linear, not white balanced, and so on so you can process luminance and color in tandem, sort of.

1. Autodev. Whatever default settings load. Keep it.
2. Go do any necessary cropping for stacking artifacts and weird pixels on the edge.
3. Binning (if needed)
4. Wipe. Do what you need to do for a darker, smooth background but don't go overboard with Gradient Aggressiveness.
5. Filmdev. Redo global stretch.

I find that using the "home in" option is a good guide to maximize your stretch, but watch for the moment when background "mottling" just starts to appear. As soon as you see that, start bumping up the "Skyglow" setting. Bring up up until it starts washing out mottling. You'll need no more than 5%, 10 on slightly overstretched or somewhat poorly calibrated images.

6. Contrast. Don't be surprised if the default settings immediately emphasize the object and darken and smooths the background beautifully. You may need to ramp down the Locality setting. If you do this, make sure you do the same to the same to the setting to the right (shadow linearity?). You also may have to turn off Expose Dark Areas in case it brings up noise.

At this stage, continue on whatever workflow you need for the object you're working on.
decay
Posts: 430
Joined: Sat Apr 10, 2021 12:28 pm
Location: Germany, NRW

Re: Colour Mottling / Background Noise (M31)

Post by decay »

Hi, just for security reasons: 1.6sec sub exposure time seems to be quite short, even at ISO 1600 (you did not mention what lens?); did you check the histogram of a single sub? The sky background should be bright enough - some people say the peak of the histogram should be at about 25% from the left side.

Best regards, Dietmar.
yewyuee
Posts: 3
Joined: Tue Dec 07, 2021 10:01 am

Re: Colour Mottling / Background Noise (M31)

Post by yewyuee »

Thank you very much everyone.
Have a great year ahead!
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