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I agree

Keeping star colour

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.

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.
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: That's probably a good place to look for ideas.

Edited 23 Nov, 2015 21:24
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
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.
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!
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!
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.

Edited 27 Nov, 2015 17:00
21 Jul, 2019 18:20
Thank you for letting me know this was an old discussion.
Edited 25 Aug, 2019 16:14
21 Jul, 2019 18:52
I use Arcsinh stretch for RGB images and it seems to give great color.
21 Jul, 2019 23:08
This thread is nearly four years old.  In the meantime I have found ways to preserve star colour.  I did have a workflow for Arcsinh stretch in Photoshop, but after a few goes when it worked well, it stopped working, so I gave up and worked out my own plan.

Thanks for the thoughts though guys.

31 Aug, 2019 04:24
Maybe you can share how you did it, Carole,
15 Sep, 2019 12:54
Oh dear, only just found this reply as I have been on holiday.  Sorry for the delay.

Well basically I use photoshop, so this will be no use to the Pixinsight people.

When I start stretching in levels and curves, I normally select and feather the stars and increase the star colour using image/adjust/Match colour.  I do this BEFORE levels and curves washes out the star colour, sometimes I have to do this more than once.

Hope that makes sense.

Edited 15 Sep, 2019 13:29
15 Sep, 2019 18:50
One of the best ways to preserve star colour in PS is to save the stars to a layer early on in the stretch process before they get washed out.  When the stars  are not washed out make a selection of stars (number of techniques for doing this).  Once you have just the stars in your selection you can then save the selection for future use as well as a create a layer just out of stars which you can put back on top of your final layered image.

18 Sep, 2019 07:14
That's pretty similar to what I am doing, except I haven't been saving the star layer for future use.

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