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Weird ring artifact with DSS but not ASTAP or Siril (animated gif inside)

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#1 acrh2

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Posted 02 October 2022 - 12:50 AM

So I'm looking for suggestions on why this happens and maybe if there's a setting to fix this.

 

I just get a new mono setup, and this is the first I have seen of this artifact:

 

1) It only appears in a DSS stack, not in ASTAP or Siril stacks.

2) It doesn't appear in single lights, darks, biases, flats, master dark, master flat or master bias.

3) It gradually appears the more light subs you add for stacking, so if you stack half the subs, it's half as pronounced.

4) It only appears in Ha data, not in LRGB data.

5) My current reducer WO Flat6aiii and my current reflector Apertura 72EDR don't mix - stars in corners have significant coma.

6) My attempts to change stacking method or kappa value in DSS produced no change.

 

This is an image from Siril Histogram viewing mode - it's an extreme stretch that's meant to show the entire range of data at the same time.

These are stacks of about 3 hours of 4 min subs of Ha data.

 

52397830777_9a9b1c7222_o.gif

 

Any thoughts?

 

Thanks.

 

 

 



#2 sharkmelley

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Posted 02 October 2022 - 02:11 AM

It's possible it's caused by some post-processing in DSS. To prevent this, it is recommended to save a DSS stack with settings embedded but not applied.



#3 acrh2

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Posted 02 October 2022 - 02:15 AM

It's possible it's caused by some post-processing in DSS. To prevent this, it is recommended to save a DSS stack with settings embedded but not applied.

No settings were applied. Like I said, LRGB filters showed no artifacts, only Ha. 



#4 KlausKlaus

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Posted 02 October 2022 - 03:50 AM

DSS Forum: https://groups.io/g/...yStacker/topics



#5 Tapio

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Posted 02 October 2022 - 04:19 AM

Sorry but why not just use ASTAP more instead of DSS?
It's better and more versatile software anyway.

#6 acrh2

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Posted 02 October 2022 - 04:29 AM

Sorry but why not just use ASTAP more instead of DSS?
It's better and more versatile software anyway.

It's 3 times slower than DSS according to Nebula Photos.

https://www.youtube....h?v=fbzE1YcICGU

But now I'm thinking I kinda have to.


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#7 Tapio

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Posted 02 October 2022 - 06:08 AM

If you are in a hurry I hear that Siril is really fast.
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#8 KlausKlaus

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Posted 02 October 2022 - 07:44 AM

76AC5CAB-062B-4E55-ABFF-E6F8B9544FFA.jpeg



#9 PhilHoyle

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Posted 03 October 2022 - 09:42 AM

Are you using the latest version of DSS? If not, try it.

#10 AngryBear

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Posted 03 October 2022 - 10:24 AM

Best results over speed any time. If you can get both then great else, start the process and go get your favorite beverage. 



#11 Mike in Rancho

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Posted 03 October 2022 - 11:09 AM

There are quite a few possibilities.

 

Were these images both made with identical subs, freshly run to allow each program to generate its own masters?  Which subs were used and how did you use them?

 

The first difference could come from Siril's histogram stretch itself, which as you say is extreme and would be based on the file's statistics.  So the stretches would not necessarily be equivalent.  In fact you can see the stretch difference in your animated gif.

 

DSS and ASTAP use a different calibration workflow, most especially regarding the use of bias.  In DSS it is subtracted from everything.  In ASTAP, it is only for flats.  To match them, you'd have to put bias into DSS's dark flats tab.

 

DSS also offers quite a few options for combining calibration subs, ASTAP does not.

 

I believe ASTAP also forces background normalization when using sigma rejection, which you cannot disable.  In DSS it is optional, and several algorithms to do so are offered if one uses it.

 

Those are the major differences I can think of right now off the top of my head...


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#12 acrh2

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Posted 03 October 2022 - 04:23 PM

There are quite a few possibilities.

 

Were these images both made with identical subs, freshly run to allow each program to generate its own masters?  Which subs were used and how did you use them?

 

The first difference could come from Siril's histogram stretch itself, which as you say is extreme and would be based on the file's statistics.  So the stretches would not necessarily be equivalent.  In fact you can see the stretch difference in your animated gif.

 

DSS and ASTAP use a different calibration workflow, most especially regarding the use of bias.  In DSS it is subtracted from everything.  In ASTAP, it is only for flats.  To match them, you'd have to put bias into DSS's dark flats tab.

 

DSS also offers quite a few options for combining calibration subs, ASTAP does not.

 

I believe ASTAP also forces background normalization when using sigma rejection, which you cannot disable.  In DSS it is optional, and several algorithms to do so are offered if one uses it.

 

Those are the major differences I can think of right now off the top of my head...

Thanks for the insight, Mike. I already spent way too much time on this, but your post gave me some new ideas, so I'm gonna try some new things.



#13 acrh2

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Posted 03 October 2022 - 04:24 PM

Where did you get this, sir?



#14 WizzieFoggs

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Posted 03 July 2023 - 08:29 AM

I have this kind of result in ASTAP. It has certain pattern over the image with Sigma Clip Average stacking method with sigma set to 2.0.

The images with "overcorrecting" in DSS are here: https://www.cloudyni...2#entry12787801

Attached Thumbnails

  • wflat_astap.jpg

Edited by WizzieFoggs, 03 July 2023 - 08:33 AM.


#15 rj144

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Posted 03 July 2023 - 10:37 AM

Where did you get this, sir?

https://www.cloudyni...age-statistics/

 

Whoops... just realized this is an old thread.  Nonetheless...


Edited by rj144, 03 July 2023 - 10:39 AM.

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