Author Topic: Is it possible to do a CMYK combine in Pixinsight  (Read 2052 times)

Offline goofisd

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Is it possible to do a CMYK combine in Pixinsight
« on: 2015 January 13 10:30:46 »
I thought I saw a pixel math technique to combine CMYK monochrome images into a color image. But I can't find it now.
Does anyone know if this is possible?

Essentially, if you imagine I shot subs with a cyan, magenta and yellow filter, then integrated them into separate masters, how do I combine them to get accurate/semi-accurate color?

Offline oldwexi

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Re: Is it possible to do a CMYK combine in Pixinsight
« Reply #1 on: 2015 January 13 11:37:07 »
Very interesting.
Where did you get CMY astrophotography filters ???
Which camera delivers CMY Images ???

However,
My thinking to solve your question, maybe wrong,   is:
C consists of GB
M consists of RB
Y consists of RG

So logically the PixelMath Expression i would use is:
in the line of RGB/K:                  (Y*0.5) +  (M*0.5)
in the line of G:                         (Y*0.5) +  (C*0.5)
in the line of B:                         (M*0.5) + (C*0.5)

In the Destination area:
tag          create new image...
Set Color space to     RGB Color

Gerald

Offline goofisd

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Re: Is it possible to do a CMYK combine in Pixinsight
« Reply #2 on: 2015 January 13 12:34:31 »
Gerald, thanks for that - I was thinking along those lines as a fallback.

I never said I had the CMYK filters  :) ... I just suggested them for illustration.
(I'm working on a crazy narrowband issue and I think I can deal with it better in CMYK)

Offline Geoff

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Re: Is it possible to do a CMYK combine in Pixinsight
« Reply #3 on: 2015 January 13 13:28:55 »
Very interesting.
Where did you get CMY astrophotography filters ???

Just as an interesting aside I tried to see where these could be sourced.  Maybe here http://www.edmundoptics.com/products/sort_by_spec.cfm?productid=1734&sort=attrib_27563&order=DESC&accsort=accRoHS&accOrder=DESC
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Offline oldwexi

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Re: Is it possible to do a CMYK combine in Pixinsight
« Reply #4 on: 2015 January 13 15:57:35 »
@Geoff!
Thanks for the link to the filters.

@gofisd
Can you talk about the CYM narrowband Project?
I would be very interested to hear about these technics.

Gerald

Offline Geoff

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Re: Is it possible to do a CMYK combine in Pixinsight
« Reply #5 on: 2015 January 13 18:35:17 »
I think expressions of the following form are the way to do it
R=M+Y-C (=[R+B]+[R+G]-[G+B])
G=C+Y-M
B=C+M-Y

I have ignored the factors of 2.  I don't think they matter as long as you rescale your results.
Geoff

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Offline goofisd

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Re: Is it possible to do a CMYK combine in Pixinsight
« Reply #6 on: 2015 January 14 08:06:21 »
Gerald, the basics are adding select Stromgren filters to my narrowband collection and getting better/more accurate colors in my narrowband imaging ... especially stars.

What I'd really like is being able to set the particular hue for each monochrome master and combine them based on what their center wavelength is. But I think that's asking too much (although someone has pointed me at some pixel math tutorials that just might make it possible).