Keeping star colour - Forums

Topic starter

Nov 23, 2015

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

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wargrafix

Nov 23, 2015

Overstretching an image can reveal detail but pushes the color more muted. Its finding the balance. Better to have true color.

Rick Stevenson

Nov 23, 2015 · Edited: Nov 23, 2015

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.

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Björn Hoffmann

Nov 23, 2015

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.

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Rick Stevenson

Nov 23, 2015

I forgot to mention that PI also has a "Repair HSV Separation" script that can be useful for fixing star colour.

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PJ Mahany

Nov 24, 2015

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!

Björn Hoffmann

Nov 24, 2015

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!

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Carastro

Topic starter

Nov 27, 2015 · Edited: Nov 27, 2015

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

Rich Sky

Jul 21, 2019 · Edited: Aug 25, 2019

Hi
Thank you for letting me know this was an old discussion.
R

Hunter Harling

Jul 21, 2019

I use Arcsinh stretch for RGB images and it seems to give great color.

Carastro

Topic starter

Jul 21, 2019

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.

Carole

Eckhard Völcker

Aug 31, 2019

Maybe you can share how you did it, Carole,

Carastro

Topic starter

Sep 15, 2019 · Edited: Sep 15, 2019

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.

Carole

Stephen Charnock

Sep 15, 2019

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.

Steve

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Carastro

Topic starter

Sep 18, 2019

That's pretty similar to what I am doing, except I haven't been saving the star layer for future use.

Carole