LaTeX color and ICC color profiles

Question

I have a (pdf|Xe)LaTeX document and trying to keep it CMYK. For some documents, I use a certain color for it's elements, which is RGB #BDCDDA. As my final document should be using the Adobe CMYK profile "CoatedFOGRA39.icc", I need to manually convert that RGB value to e.g. this:

\DefineNamedColor{named}{mycolor}{cmyk}{0.3203,0.1602,0.1172,0.0000}

But, if in the future I want to switch to a different CMYK color profile for maybe another printing company, I have to edit the color definition again, as for example an USWebCoatedSWOP version of RGB #BDCDDA has different CMYK values.

Ideally, I would like to write something like

\DefineNamedColor{named}{mycolor}{/path/to/CoatedFOGRA39.icc}{#BDCDDA}

and have the color auto-converted from RGB (can be considered to be sRGB colorspace) to the correct CMYK value.

Can any LaTeX package help me here, or do I have to set up an external workflow to pre-generate LaTeX snippets with correct CMYK color definitions?

Sidenote: this question is not about embedded figures/pictures, but about using named colors for text and background.

Answer 1

I think the simplest is to put your definitions in a local package so they can easily be shared between documents and customised to different profiles.

In your document put something like

  \usepackage[CoatedFOGRA39]{mycolor}

if you specify a profile that you have set up, relevant definitions are made, otherwise you get an error. mycolor.sty could look something like this:

\RequirePackage{color}

\DeclareOption{CoatedFOGRA39}{\def\mycolor{CoatedFOGRA39}}
\def\mycolorprofileA{CoatedFOGRA39}
\ProcessOptions\relax

\ifx\mycolor\@undefined
\PackageError{mycolor}{No color profile declared}{declare a color profile}
\fi


\ifx\mycolor\mycolorprofileA
\DefineNamedColor{named}{mycolor}{cmyk}{0.3203,0.1602,0.1172,0.0000}
\fi

The above just declares one colour in one profile, but it could be extended...

Answer 2

After a close look this question does not make sense. Why? If you care about correct colours, RGB #BDCDDA is not a colour. It becomes a colour together with an RGB colour profile (sRGB and AdobeRGB being popular ones). But it does not become a colour together with a CMYK profile because for a conversion you need a start and a destination profile. Here we can guess because of the web-like hex style of the colour values that the source profile probably is sRGB. But likely the one who gave you the values does not master colour management otherwise he/she/they would have told you the profile.

I see three solutions how to handle this correctly:

1 RGB based colour managed document

\documentclass{book}
\usepackage{xcolor}
\usepackage{luatex85}

%Create an OutputIntent in order to correctly specify colours
\immediate\pdfobj stream attr{/N 3} file{sRGB.icc}
\pdfcatalog{%
  /OutputIntents [
    <<
      /Type /OutputIntent
      /S /GTS_PDFA1
      /DestOutputProfile \the\pdflastobj\space 0 R
      /OutputConditionIdentifier (sRGB)
      /Info (sRGB)
    >>
    <<
      /Type /OutputIntent
      /S /GTS_PDFX
      /DestOutputProfile \the\pdflastobj\space 0 R
      /OutputConditionIdentifier (sRGB)
      /Info (sRGB)
    >>
  ]
}

\DefineNamedColor{named}{mycolor}{HTML}{BDCDDA}

\begin{document}
\textcolor{mycolor}{light blue text}
\end{document}

If this does not look as an answer because it's an RGB document keep in mind that every good print shop does a colour conversion anyway specifically for their machine. As long as they know the source profile they can handle it.

2 CMYK based colour managed document

\documentclass{book}
\usepackage[cmyk]{xcolor}
\usepackage{luatex85}

\immediate\pdfobj stream attr{/N 4} file{ISOcoated_v2_300_eci.icc}
\pdfcatalog{%
  /OutputIntents [
    <<
        /Type /OutputIntent
        /S/GTS_PDFA1
        /DestOutputProfile \the\pdflastobj\space 0 R
        /OutputConditionIdentifier (Coated FOGRA39)
        /Info(FOGRA39L)
    >>
    <<
        /Type /OutputIntent
        /S/GTS_PDFX
        /DestOutputProfile \the\pdflastobj\space 0 R
        /OutputConditionIdentifier (Coated FOGRA39)
        /Info(FOGRA39L)
    >>
  ]
}

\DefineNamedColor{named}{mycolor}{cmyk}{0.3203,0.1602,0.1172,0.0000}

\begin{document}
\textcolor{mycolor}{light blue text}
\end{document}

This will work too. On a calibrated screen viewed with a colour management capable viewer you will see the correct colours. This under the assumption that the conversion of the values you have made is correct.

3 CMYK OutputIntent with RGB text object

\documentclass{book}
\usepackage[cmyk]{xcolor}
\usepackage{luatex85}

\immediate\pdfobj stream attr{/N 4} file{ISOcoated_v2_300_eci.icc}
\pdfcatalog{%
  /OutputIntents [
    <<
        /Type /OutputIntent
        /S/GTS_PDFA1
        /DestOutputProfile \the\pdflastobj\space 0 R
        /OutputConditionIdentifier (Coated FOGRA39)
        /Info(FOGRA39L)
    >>
    <<
        /Type /OutputIntent
        /S/GTS_PDFX
        /DestOutputProfile \the\pdflastobj\space 0 R
        /OutputConditionIdentifier (Coated FOGRA39)
        /Info(FOGRA39L)
    >>
  ]
}

\DefineNamedColor{named}{mycolor}{HTML}{BDCDDA}

\begin{document}
\textcolor{mycolor}{light blue text}
\end{document}

Even if you declare an OutputIntent for the whole PDF you could assign a different colour profile to certain text objects as in this MWE. But I don't know which internal conversion algorithm is applied so I don't recommend this way.

For all three ways I recommend using the full PDF/A and/or PDF/X standard, not just the MWE I show here. Here I show how such a document would look like.

I used a dual OutputIntent in my examples because a viewer can apply the A or X. There will be colour unmanaged viewers too. If you use both with the same profile you are on the safe side.