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I'm trying to understand Adobe Illustrator's color conversion method between RGB/HSB and CMYK. I'm pretty sure they use ICC profiles to do the conversion, and they make a bunch of ICC profiles available for download (http://www.adobe.com/support/downloads/detail.jsp?ftpID=3680).

I can't match the conversion using a combination of those profiles to Illustrator's color picker.

What RGB and CMYK ICC profiles does Illustrator use in its color picker?

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It may be important to realize that, unlike Photoshop, Illustrator does not color manage the color picker.. your OS does. –  Scott Jul 19 '13 at 23:22
The color picker... the box which appears when you double-click the fill color, for example, is OS managed in Illustrator. So yes, it's possible to get different colors on Windows and Mac for the color picker inside Illustrator. The color picker is not as integrated into Illustrator as it is in other Adobe apps. The Color Panel is managed by Illustrator, but not the color picker. –  Scott Jul 20 '13 at 5:29
@Scott understood. So what I'm trying to do is mimic the conversion that Illustrator (I guess the OS in this case) presents to the user, but programmatically on a linux server. How can I figure out what profiles the OS is doing for the conversion? –  ARolek Jul 20 '13 at 16:25
worth pointing out that regardless of what profile or colour picker your apps use, you will always get a shift when moving a document between mac and windows. in fact you are practically guaranteed a shift when moving between 2 macs! –  stephencosh Jul 22 '13 at 19:51

1 Answer 1

This is a pretty old question, but based on its unanswered status and number of up votes and views I thought I'd take a crack at it. Based on your question and the additional comment about doing the conversion on a programmatically on a Linux server, I did some hunting around. There is a Ruby library called ruby-pdf that does colour conversions for handling PDFs. In the docs for the library's colour tools it discusses using the tools for conversion. Interestingly, there is this tidbit:

 # Adobe PDF Display Formula
  r = 1.0 - min(1.0, c + k)
  g = 1.0 - min(1.0, m + k)
  b = 1.0 - min(1.0, y + k)

See here for the reference: http://ruby-pdf.rubyforge.org/color-tools/doc/classes/Color/CMYK.html

Note this comment: "Converts the CMYK colour to RGB. Most colour experts strongly suggest that this is not a good idea (some even suggesting that it’s a very bad idea). CMYK represents additive percentages of inks on white paper, whereas RGB represents mixed colour intensities on a black screen."

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The link is broken –  Rosenthal Sep 14 '14 at 2:44
Very interesting! Although I don't think this models the AI colour picker. Take look at this. C, M, Y, and K values usually go from 0 to 100 but your formula suggests it expect them to be from 0 to 1. No problem. Lets plug CMYK (0,100,100,0), which is "red", using your formula with cmyk (0,1,1,0). It results in rgb (1,0,0). Then we have to project that into the RGB usual values, that go from 0 to 255, so it would end up being RGB (255,0,0) or #ff0000. That is a red, true, but not the one Illustrator comes up with, which is (228, 11, 20) or #e40b14. –  cockypup Mar 12 at 14:19

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