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Rejecting bleeding stars: Deepskystacker vs. PixInsight

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#1 justusliebig

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Posted 17 November 2019 - 02:05 PM

Dear all,

 

i haven't been looking around here, but that is just because I have been mostly happy with my AP game and I didn't have to troubleshoot for some time. However, now that Orion is up, I am actually suffering from too bright stars. I get column errors and my idea was to average them out by rotating the camera. This is the my starting point:

 

 

8TGXAmd.jpg

 

But rotating did only add more of those nasty defects. I used Windsorized sigma clipping in PI (left) and kappa-sigma in DSS (right).

 

O2ybylr.png

ozx1gKY.png

The version from DSS looks way better. I played with the rejection values in PI but to now avail. What does DSS do different?! Thanks



#2 Moreflying

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Posted 17 November 2019 - 03:32 PM

I'm not sure I have an answer to that but I notice something else in your image with Windsorized sigma clipping in PI that I had. If you look at some of your brighter stars (low in the image) look at how they are eroded away missing pixels on the left sides. Do you see it? I had the exact same problem and could never figure it out. Here I see it with someone else's image. The PI gurus need to look into that IMO.



#3 james7ca

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Posted 17 November 2019 - 06:21 PM

In PI you may have to apply the Large-Scale Pixel Rejection.



#4 pfile

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Posted 17 November 2019 - 06:37 PM

also the difference i think is that PI has 3 as the default # of sigmas to reject on the high side, but DSS has 2 sigmas as default. if you cranked PI down to 2 on the high slider you might see comparable results.

 

PI 1.8.8 has a new rejection algorithm called ESD - "Generalized Extreme Studentized Deviate Test" - god knows what that really means - but it might be worth a try here. it's supposed to be better at identifying outlying pixels. but the tooltip does say it needs 25-50 subs to really work best.

 

also i agree with james that the LS rejection could help.

 

rob



#5 justusliebig

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Posted 17 November 2019 - 06:38 PM

In PI you may have to apply the Large-Scale Pixel Rejection.

Thanks for the hint, no difference with various permutations/combinations

 

MOhT7OY.png



#6 james7ca

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Posted 17 November 2019 - 08:00 PM

How many subs are you stacking? Windsorized sigma clipping works best when you have a relatively large number of subs (greater than 15?). Percentile Clipping should work better if you have a smaller number of subs.



#7 justusliebig

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Posted 17 November 2019 - 08:04 PM

How many subs are you stacking? Windsorized sigma clipping works best when you have a relatively large number of subs (greater than 15?). Percentile Clipping should work better if you have a smaller number of subs.

30+ from 3 different sessions/rotations :/ Lowering the sigma helped at the expense of a lot signal, yet still not as good what DSS produces




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