CLS filter colour balance

Questions and answers about processing in StarTools and how to accomplish certain tasks.

CLS filter colour balance

Postby alacant » Thu May 11, 2017 10:27 am

I'm getting a cyan cast and/or maybe too much red... Any tips for curing this? Here's an example of an image of m101:
http://2.bp.blogspot.com/-URlNEztSmqM/WRAerH7L1WI/AAAAAAAAubY/_mlJPpxbkL4cPhfzX0pb535mi3RnnBqHACK4B/s1600/101-3.jpg
TIA and clear skies,
Steve
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Re: CLS filter colour balance

Postby admin » Sat May 13, 2017 4:13 am

Hi Steve,

You may find the following information useful;
Colour balancing of data that was filtered by a light pollution filter


Colour balancing of data that was filtered by a light pollution filter is fundamentally impossible; narrow (or wider) bands of the spectrum are missing and no amount of colour balancing is going to bring them back and achieve proper colouring. A typical filtered data set will show a distinct lack in yellow and some green when properly colour balanced. It's by no means the end of the world - it's just something to be mindful of.


Correct colouring may be achieved however by shooting deep luminance data with light pollution filter in place, while shooting colour data without filter in place, after which both are processed separately and finally combined. Colour data is much more forgiving in terms of quality of signal and noise; the human eye is much more sensitive to noise in the luminance data that it is in the colour data. By making clever use of that fact and performing some trivial light pollution removal in Wipe, the best of both worlds can be achieved.


Does this help?
Ivo Jager
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Re: CLS filter colour balance

Postby alacant » Sun May 14, 2017 8:15 am

Hi Ivo
Yes, that confirms what I'm experiencing. The point is that with the cheap and cheerful moon and skyglow filter, ST did a great job of colour balance out of the box. Now I've got this inline cls thing, it' doesn't do so well. The reason why I want the cls is that it gives me much longer light frames before the histogram moves right of centre and also the 2" screw on skyglow filter produces rings around stars.

Anyway, as you say, I have to bear in mind the impossibility of colour balancing with filters. I'll do my best. Promise!
Thanks again and clear skies,
Steve
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Re: CLS filter colour balance

Postby brasspoodle » Tue Aug 08, 2017 7:42 am

I'm finding with a CLS-CCD filter on my Modded DSLR I can get reasonable colour corrections if I process star colour (via a mask) and background/object (via the inverted star mask) separately. I find I normally have to reduce the default 200% saturation and sometimes the object needs very little colour correction anyway. My stars without colour correction are generally blue and red, so just a case of capping green to yellow and lowering the red and, to a lesser extent the blue. I can do this while still tracking so happy with that :-)
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