Sigma Clipping setting during Live Stacking

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
sandconp
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Sigma Clipping setting during Live Stacking

Post by sandconp » Wed Apr 08, 2020 1:46 pm

Does Sharpcap Pro support Sigma Clipping and if so, where is this set and the values?

I have an image that has a satellite streak through it and I would like to prevent this from happening in the future.

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Re: Sigma Clipping setting during Live Stacking

Post by admin » Wed Apr 08, 2020 4:19 pm

Hi,

Yes, sigma clipped stacking is supported – see the documentation here https://docs.sharpcap.co.uk/3.2/#Stacking%20Tab

Cheers, Robin

sandconp
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Re: Sigma Clipping setting during Live Stacking

Post by sandconp » Wed Apr 08, 2020 5:20 pm

Any suggestions for settings?

rbgdmd@gmail.com
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Re: Sigma Clipping setting during Live Stacking

Post by rbgdmd@gmail.com » Tue Jun 16, 2020 2:55 am

What is your suggestion on how to set the "Sigma Low Limit (%)?

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Re: Sigma Clipping setting during Live Stacking

Post by admin » Tue Jun 16, 2020 10:05 pm

Hi,

leave it at default unless you are getting a very high number of pixels rejected by the sigma clipping algorithm with no obvious cause. That control is primarily intended deal with potential problems with cameras that have very low noise levels – it would be possible for the initial sigma determination stage to calculate a very low expected noise level and then start rejecting pixels on a massive scale if the image value change slightly. The sigma low limit control puts a lower bound on the calculated sigma values for pixels to avoid this happening.

Cheers, Robin

donstim
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Re: Sigma Clipping setting during Live Stacking

Post by donstim » Wed Jun 17, 2020 11:55 pm

I've been unable to prevent satellite streaks during live stacking. Last night I got several streaks before sigma clipping had a chance to build its calibration. So, I cleared the stack then got a streak after the 10 frames had been acquired. Essentially no pixels rejected (maybe 0.0001%).

ZWO ASI 294MC Pro camera, gain 121, exposure 15 seconds on an 8-inch SCT with f/6.3 reducer corrector.

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Re: Sigma Clipping setting during Live Stacking

Post by admin » Thu Jun 18, 2020 8:41 pm

Hi,

Did you capture the raw frames by any chance? If you did we could replay in the folder monitor camera and see if adjusting the settings would have helped or if we need to go further and make changes to the code.

Thanks, Robin

donstim
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Re: Sigma Clipping setting during Live Stacking

Post by donstim » Fri Jun 19, 2020 8:18 am

No, sorry I did not. Next time!

Don

poolemarkw
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Re: Sigma Clipping setting during Live Stacking

Post by poolemarkw » Fri Jun 19, 2020 3:12 pm

Just to clarify, does the Sigma Clipping function remove an entire frame when it sees the abnormal pixels, or include the frame but ignore those abnormal pixels?

Thanks,

Mark

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Re: Sigma Clipping setting during Live Stacking

Post by admin » Fri Jun 19, 2020 7:45 pm

Hi,

it only excludes the pixels that have a abnormal values – so inferior for satellite streak is in one of the images then the right pixels from the satellite should get added to the stack, but all the rest of the data in the image should.

Thanks, Robin

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