Master Dark using SC Capture Darks problem

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stubblejumper
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Master Dark using SC Capture Darks problem

Post by stubblejumper » Mon Oct 08, 2018 5:29 am

Master Darks created via SharpCap v3.1 and 3.2 beta cause the calibration routines in Pixinsight and Images Plus to basically wipe out the lights. If I capture individual frames and then combine them to create a master dark in PIS it works as expected. My best guess is the PIS and IP+ are not interpreting the Master Dark correctly. Any suggestions? What is different in SC's Master Dark?

stubblejumper
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Re: Master Dark using SC Capture Darks problem

Post by stubblejumper » Mon Oct 08, 2018 5:32 am

Sorry. I should have mentioned ASI1600MM Pro, Windows 10. There is no log that I am aware of. Since SC didn't crash, it likely wouldn't be helpful anyway.

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admin
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Re: Master Dark using SC Capture Darks problem

Post by admin » Mon Oct 08, 2018 3:54 pm

Can you share a single dark frame, a single light frame and the two master dark frames (the SharpCap one and the PI one). I'm sure the answer will be in the FITS headers somewhere but not sure quite where.

For large files the easiest way to share is to upload to dropbox, google driver, etc and then share a link to the files.

cheers,

Robin


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Re: Master Dark using SC Capture Darks problem

Post by admin » Tue Oct 09, 2018 9:19 pm

Hi, it looks as though your light frames are saved with the 'Save 10/12/14 bit images in FITS files without stretching to 16 bit' option turned on, meaning that they are 12 bit images with a range of 0..4095. See https://docs.sharpcap.co.uk/3.2/#Saving%20Options.

The master dark created by SharpCap is a 16 bit image with a range of 0..65536. PixInsight doesn't like this combination.

You should turn the 'without stretching' option off really - the only valid use case I know of for this option is for use with certain Astrometry software that dislikes images stretched to the full 16 bit range. For any other use case this option causes problems rather than cures them. I have already strengthened the wording to discourage casual use of this option in SharpCap 3.2, but I think I will make it even more clear cut now!

For existing data you can just work with your master dark from PixInsight, or you could probably get a working process by scaling up the light frames in PIxInsight by multiplying them by 16 before doing the dark subtraction.

It's also worth being aware that I (and others) have found cases where the 'Optimize' option in PixInsight for the MasterDark causes problems - if used it seems to cause dark subtraction to be less effective on sensors with visible amp glow. I've not been able to find what the true effect of the 'Optimize' option is, so it's hard to be sure why it has this effect, but it's certainly worth trying with this turned off.

cheers,

Robin

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oopfan
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Re: Master Dark using SC Capture Darks problem

Post by oopfan » Tue Oct 09, 2018 11:11 pm

May I suggest a warning on this option: "Unless you are a photometrist leave this option off!"

Brian

stubblejumper
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Re: Master Dark using SC Capture Darks problem

Post by stubblejumper » Wed Oct 10, 2018 5:02 pm

I know I process my lights as 32bit XISF in Pixinsight. The lights/darks/flats are captured using Sharpcap with 16 bit option. I wasn't aware of a setting "saving as 10/12/14".

I'll go look for it.

Don

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Re: Master Dark using SC Capture Darks problem

Post by oopfan » Wed Oct 10, 2018 5:11 pm

Don,

File | SharpCap Settings...

Brian
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