Using CMYK/Transparent images in a PDF file

Question

I am using PDFX / Lualatex to create a PDF/X-4 file. My problem is that the publisher is wanting the images in the file to be CMYK. Some of my images are transparent.

The problem:

• Latex only supports a limited number of image formats and does not allow for TIFF
• PNG images can have transparency, but do not support CMYK colour profiles
• JPG images do support CMYK, but cannot have transparency

So, what is my solution for including a transparent and CMYK image in a PDF file that the publisher will be able to use?

Answer 1

Your only option is to convert the images to PDF which support CMYK and transparency and can by included by LaTeX.

You can do this using ImageMagick:

1. Create a simple transparent PNG (for example only):

   convert magick:logo -transparent white logo.png
   

2. Convert the PNG to a CMYK PDF (choose appropriate profiles for your printing environment):

   convert logo.png \
   -profile /usr/share/color/icc/sRGB_v4_ICC_preference_displayclass.icc \
   -profile /usr/share/color/icc/ISOcoated_v2_eci.icc logo.pdf
   

3. Test with the following TeX file (tex_logo.tex):

   \documentclass{standalone}
   \usepackage[cmyk]{xcolor}
   \usepackage{tikz}
   
   \begin{document}
   \begin{tikzpicture}[inner sep=0pt]
     % put a small grey square behind image to show the transparency
     \fill [black!20] (-1,-1) rectangle (1,1);
     \node at (0,0) {\includegraphics[width=54.19mm]{logo.pdf}};
   \end{tikzpicture}
   \end{document}
   

4. Use the GhostScript tiffsep device to produce separations and check that everything looks like it should:

   gs -dSAFER -dNOPAUSE -dBATCH -sOutputFile=tex_logo.tiff -sDEVICE=tiffsep \
   -sCompression=lzw -r300 -dTextAlphaBits=4 -dGraphicsAlphaBits=4 \
   -sDefaultRGBProfile=/usr/share/color/icc/sRGB_v4_ICC_preference_displayclass.icc \
   -sDefaultCMYKProfile=/usr/share/color/icc/ISOcoated_v2_eci.icc \
   -sOutputICCProfile=/usr/share/color/icc/ISOcoated_v2_eci.icc tex_logo.pdf
   

Here's the resulting composite output and separations:

Composite

Cyan separation

Magenta separation

Yellow separation

Black separation