Author Topic: Debayer of images resulting in pink star cores  (Read 1908 times)

Offline chrisvdberge

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Debayer of images resulting in pink star cores
« on: 2015 July 18 03:14:01 »
I have a problem with the star cores in my images, for saturated stars.
At first I thought it was a problem of using MaskedStretch which is protecting the cores of the stars. But using the Repaired HSV Seperation didn't solve anything.
I then noticed that linear version of the image has pink stars, no matter what I do with ColorCalibration. Of course this causes the MaskedStretch to result in weird star cores.

I inspected an individual frame, uncalibrated and there the stars are white. The calibrated frame has pink stars.
I then tested the Debayering of an individual frame without calibration; same problem; pink stars.
I tested all kinds of settings for debayering, but I'm pretty sure it should be RGGB and other settings are no good either..

Anyone any suggestions on what is going wrong here?

I'm using a Nikon D600 for imaging by the way.



Offline akulapanam

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Re: Debayer of images resulting in pink star cores
« Reply #1 on: 2015 July 20 15:30:56 »
I had the same issue on one of my images.  In my case I was getting pink rings around stars and the issue turned out to be that my red frames were slightly out of focus compared to the other two channels.  This was surprising because I use a OSC Atik 490 color.  Try extracting the individual channels and look at the size of the stars in the red channel compared to the blue and green channels.

Offline chrisvdberge

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Re: Debayer of images resulting in pink star cores
« Reply #2 on: 2015 July 21 05:28:39 »
hmm that is interesting. However, I would have to see this effect in the RAW file right? If I open up these files in another viewer everything is correct (white stars.) Only when I debayer in PI I get this reddish/pinkish stars....

EDIT: Took another look with Preview on Mac on a single RAW file and I must say I DO see a darker core in the blown out stars. Seems grey in this preview, but this could be the problem..

I shot these images with rented equipment at astrofarm Kiripotib, so not much to solve in the setup anymore, but good to know for the future ;)

Offline akulapanam

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Re: Debayer of images resulting in pink star cores
« Reply #3 on: 2015 July 21 08:23:28 »
How are you stacking your images? The other thing I have seen that causes this problem is hot pixel removal in DSS. 

Since you tool these images in Africa on thing you might do to try and save them is use either superpixel or individual channel extraction. Both will loose resolution but superpixel might help cover up the issue and you might be able to use a star core shrink or even fill in the holes on the individual channel that is out of focus.

Offline chrisvdberge

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Re: Debayer of images resulting in pink star cores
« Reply #4 on: 2015 July 21 09:46:39 »
I can see it happen when I debayer one RAW image in PI, so I doubt it has anything to do with the stacking :)

Offline akulapanam

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Re: Debayer of images resulting in pink star cores
« Reply #5 on: 2015 July 21 10:54:50 »
Yep focus issue then :(. Try the superpixel or channel extract method then

astropixel

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Re: Debayer of images resulting in pink star cores
« Reply #6 on: 2015 July 23 14:19:25 »
What are your calibration steps prior to deBayer?

Offline chrisvdberge

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Re: Debayer of images resulting in pink star cores
« Reply #7 on: 2015 July 24 01:15:38 »
I don't think the calibration steps matter, since I see this happening when I debayer a single exposure straight from the camera