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Keeping star colour

carastro
23 Nov, 2015 08:17
Despite having imaged for a number of years, the one thing I have always found to be difficult is keeping star colour.  I use photoshop for post-processing (pixinsight looks totally alien to me).

So just wondered what the secret is to keeping good star colour.

I do mainly mono imaging but still have my trusty DSLR but had the same problem with that too.  Maybe it's my work flow.

Carole
wargrafix
23 Nov, 2015 20:05
Overstretching an image can reveal detail but pushes the color more muted. Its finding the balance. Better to have true color.
RickS
23 Nov, 2015 21:23
Losing star colour is a common problem, Carole, and it's unlikely to be something wrong with your workflow.  Stars are very much brighter than the other objects in our images and tend to turn white (saturated during capture, washed out by heavy stretching, etc.)

One approach is to try to prevent star colour loss during stretching.  In PixInsight the MaskedStretch process is much kinder to star colour than HistogramTransformation. I don't know if it's possible to do something similar in PS to mask and protect the stars while stretching.

Another option (you can do both, of course) is to enhance the colour in the stars after stretching.  There are lots of techniques for this in PI - apply a star mask and use CurvesTransformation to boost saturation, or tweak the CIELAB a* and b* curves, or …  Jay GaBany gave a talk at an imaging conference in Australia about intensifying colour that had many PS techniques.  He also wrote about it in this book: http://www.springer.com/gp/book/9781461478331 That's probably a good place to look for ideas.

Cheers,
Rick.
Edited 23 Nov, 2015 21:24
BjoernH
23 Nov, 2015 21:41
I use the Astronomy Tools for Photoshop and they have an action called "increase star color" which works pretty well. I think it gets the color information from the outer part of the stars and then recolors the entire star in that color. For my humble beginnings in Astrophotography that is absolutely enough. smile
RickS
23 Nov, 2015 23:23
I forgot to mention that PI also has a "Repair HSV Separation" script that can be useful for fixing star colour.
Starry-Eyes
24 Nov, 2015 03:34
I find star colors very easy with DSS, (just for stacking), & StarTools. with a DLSR. When in the StarTools color module just sample stars with a mask. This establishes white balance. Then clear mask, invert mask thus filling it. Simple!
BjoernH
24 Nov, 2015 15:28
PJ Mahany
I find star colors very easy with DSS, (just for stacking), & StarTools. with a DLSR. When in the StarTools color module just sample stars with a mask. This establishes white balance. Then clear mask, invert mask thus filling it. Simple!
Cool, thank you! I didn't know about StarTools. Looks great!
carastro
27 Nov, 2015 16:58
Thanks for your suggestions every-one, I have booked marked this page and will try some of these out next time I get a clear sky!!!!

Or even try re-stacking and processing some old data.
I do have "actions" in photoshop but tend to forget to use them, partly because I feel it is using some-one else's skills, plus I think I have tried it in the past but found it made no difference.

Carole
Edited 27 Nov, 2015 17:00
 
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