Colour Stack, one channel individuals

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
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GammaCassiopeiae
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Colour Stack, one channel individuals

Post by GammaCassiopeiae » Mon Jul 22, 2019 10:25 pm

Greetings,

I'm a relatively new user of Sharpcap... I took a set of 50 images with a brand new ZWO ASI294MC Pro camera on Friday night. They were live stacked in Sharpcap, and the result appeared quite good. I had selected "Save Individual Frames". Output format is FITS.

https://www.astrobin.com/416285/

In close inspection I see that there is a faint airplane or satellite track in the stacked image. Scanning the individual frames I can see the one image that causes the problem. I'm viewing them in FITS Liberator 3. I would like to stack again, discarding this bad frame.

Here's the problem: In FITS Liberator the stacked image has three image "planes" or colours. The individual frames, however, have only one image plane each. The file sizes match: The individuals frames are roughly one-third of the size. I seem to have saved only one "plane" of the individual frames, so cannot re-stack the images.

This particular imaging session is not the biggest concern... how do I avoid this problem in the future? Am I ONLY able to live-stack with SharpCap, with no option to re-stack later???

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admin
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Re: Colour Stack, one channel individuals

Post by admin » Wed Jul 24, 2019 7:11 pm

Hi,

The individual frames that you have captured are saved in raw format. This is the raw data that comes off the camera sensor before it is processed to generate a full-colour image. Many different types of software can perform this processing for you – see viewtopic.php?t=254.

SharpCap automatically performs the processing of the raw images into full-colour images before the stacking process in order to allow things like alignment and the rotation to work correctly, but saves the raw images to allow you to get the best possible results if you decide to post process. You'll find applications like deep sky stacker will be able to deal with these images correctly providing you have the settings adjusted properly.

Cheers, Robin

GammaCassiopeiae
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Re: Colour Stack, one channel individuals

Post by GammaCassiopeiae » Wed Jul 24, 2019 10:10 pm

Thanks for the reply.

The stacked files are "FITS" format in a directory …/capture/00_00_11, and the raw frames are FITS format, in a directory called …/capture/00_00_11/rawframes. The raw frame FITS files are one-third the size of the stacked ones, and clearly don't contain the colour information.

One thing I thought of is that the three colours are saved in three separate FITS files, but the metadata indicates that each (greyscale) FITS file is captured at a different time. Should I be saving the rawframes in a different format?

GammaCassiopeiae
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Re: Colour Stack, one channel individuals

Post by GammaCassiopeiae » Wed Jul 24, 2019 10:13 pm

I should add that I have DSS and can stack the raw frames successfully to make a nice greyscale image...

GammaCassiopeiae
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Re: Colour Stack, one channel individuals

Post by GammaCassiopeiae » Thu Jul 25, 2019 2:02 am

Whoops.. I'll check out that link properly!

GammaCassiopeiae
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Re: Colour Stack, one channel individuals

Post by GammaCassiopeiae » Thu Jul 25, 2019 3:35 am

Did I mention I was a beginner?

!

This was very helpful. I managed to de-bayer the apparent greyscale files to create colour versions. Then I managed to stack them. Since much of this was done for the first time I'm not sure the new version is better, but at least I have the principals down now.

Thanks again!

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Re: Colour Stack, one channel individuals

Post by admin » Thu Jul 25, 2019 9:01 pm

Good to hear that you got it working – unfortunately the box that you need to take in DSS to make the colour work is fairly hidden away, which is why it's good that Dave posted that thread with full details of how to find it.

Cheers, Robin

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