darks/flats saving as incorrect color space

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stobiewankenobi
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darks/flats saving as incorrect color space

#1

Post by stobiewankenobi »

Hello,

I purchased a sharpcap pro license, and would like to use sharpcap to take my darks/flat images. The issue I'm seeing is using RAW16 and taking a dark saves it as RAW16/Grey, which DSS will not stack with a RAW16/RGB light image.

I have the same issue with flats.

Any advice on what I'm doing wrong? How do I get a good dark/flat image that can be used by DSS?

Thanks in advance!
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Re: darks/flats saving as incorrect color space

#2

Post by admin »

Hi,

This seems to work fine for me – I set the camera into RAW12 mode (or RAW16 depending on your model of camera), ensure that the preferred still file format is set to fits in the SharpCap settings and then capture lights, darks and flats.

In deep sky stacker, ensure that the checkbox at the top of the fits files settings pages checked (the one that makes it treat 16-bit fits files as raw colour files that need to be debayered).

Once those settings are all correct when you select the files of whichever type into DSS, they will show up in the list as grey 16-bit, but in the previous column titled CFA you should see a yes to indicate that there really colour files.

Hopefully that makes sense, if it doesn't help then please share screenshot of the file list in DSS and a small set of sample files via dropbox, one drive or similar.

Cheers, Robin
stobiewankenobi
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Re: darks/flats saving as incorrect color space

#3

Post by stobiewankenobi »

Hey @robin.

Sure, so I have attached screenshots showing all the settings are correct.

I am imaging in Sharpcap with FITS outputs using the Capture darks feature (I pay for pro). I select RAW16 and set gain, exposure, tmp to the same values.

In DSS in FITS I force RGGB, and import the dark file, it shows as Grey 16, and when I try to stack I get the error message you can see in the screenshot.

https://imgur.com/a/t19sqwy

Please let me know if you see something obvious that I'm doing incorrectly. My camera model is QHY 247c.

Thanks!
stobiewankenobi
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Re: darks/flats saving as incorrect color space

#4

Post by stobiewankenobi »

Also here is a folder with the files I am working with: https://drive.google.com/drive/folders/ ... sp=sharing
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Re: darks/flats saving as incorrect color space

#5

Post by admin »

Hi,

Okay, I see what you're doing – you are using the live stacking functionality to capture a number of shorter frames and stack them and then trying to process the stacked images in deep sky stacker and trying to apply dark frames.

Unfortunately that's a processing workflow that can't work correctly if you are using the alignment feature of live stacking (which is the main point of using it for most people). When the alignment feature is turned on, each frame that is captured is adjusted (rotated and/or offset) to align it correctly with the image already in the stack. In order to do that correctly first of all the image has to be converted from RAW mode to full-colour mode before the alignment. Also any dark subtraction has to be applied before the alignment is done – that means you must use the dark subtraction functionality in SharpCap to make this work rather than trying to subtract the darks after the stacking is complete.

To explain why this is vital, imagine that your camera has a hot pixel. Your dark image will also have a hot pixel at that point, so dark subtraction would remove the hot pixel. But, if you use stacking with the alignment turned on then the adjustments made to each frame to do the alignment will mean that the extra incorrect signal from the hot pixel will be spread out in the stacked image – often as a faint line if you have a slight drift. As you can imagine subtracting a dark frame that has a single hot pixel a particular point from the stacked image won't correct properly for the effects of the hot pixels in the light frames.

Hope that makes sense, Robin
stobiewankenobi
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Re: darks/flats saving as incorrect color space

#6

Post by stobiewankenobi »

Ah OK I see.

So is the solution to tick the "save individual frames" when doing live stacking? I Love the view and ability to see what I'm imaging live as I get more data. If I save each frame individually rather than saving the resulting .fits file from the stacking process, then stacking those individual frames along with my darks should that work? I will test tonight if so.

Thank you.
stobiewankenobi
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Re: darks/flats saving as incorrect color space

#7

Post by stobiewankenobi »

So I tried this tonight, and while it did stack, it resulted in an image with almost no data. I am not sure if this is sharpcap doing something in the way it creates darks or what. But this is the image I get after stacking 60m worth of subs with a sharpcap created dark. If I remove the dark all my data is fine.

https://imgur.com/a/b1e7MTC

Without the dark I get a pretty clear image of the veil nebula (although obviously dim as it's narrowband). But with this dark in plan, the histogram is pretty much non existent.
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Re: darks/flats saving as incorrect color space

#8

Post by admin »

Hi,

Yes you are right that the theory is to tick the box to save the individual images which saved them before the dark and flat corrections are applied, allowing you to reprocess them later in software of your choice.

In order to work out why the inclusion of darks is causing you a problem I would suggest starting by looking at the individual frames and the dark frames in fits Liberator to see what the maximum pixel values are – sometimes people managed to get into a situation where for one reason or another the image frames are 12 bit and the darks are 16-bit or similar and then the dark subtraction can cause this sort of problem.

Cheers, Robin
stobiewankenobi
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Re: darks/flats saving as incorrect color space

#9

Post by stobiewankenobi »

@robin All the images are 16 bit. And the dark is 16bit. All the lights have good data (over 800 score) and when I stack them without a dark they stack fine. It's only when I use the dark from Sharpap that I get the loss in data. Any ideas?
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Re: darks/flats saving as incorrect color space

#10

Post by admin »

Hi,

Please can you share the dark frame that SharpCap created an about three image frames (both in fits format). They will be too big to upload here so the best bet is to put them on Google Drive or somewhere like dropbox and share a link. I presume that you are using DSS for stacking since you mentioned earlier in the thread.

Cheers, Robin
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