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When I include certain graphics in my LaTeX book, compile the tex file with pdflatex and then flatten the PDF, all the text on pages with either png or pdf graphics ends up grey instead of black.

Text on pages without graphics, and on pages with jpeg graphics, comes out black as it should.

The problem doesn't appear until the PDF file is flattened (for flattening I'm using the second method at http://www.ncl.ucar.edu/Support/talk_archives/2011/0681.html), but even if I don't flatten the PDF file before uploading the file to the printing service, the printing service will flatten the PDF file themselves and I end up with these unusual grey dithered pages in the printed hard copy.

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    We will have to see a minimal code of yours and maybe that certain graphic. PNG and PDFs do work fine, normally. How do you compile your document? I do not know flattening yet, sorry. Does this also happen, when you insert such an image too say Word and produce a PDF there? If yes, it would be off-topic and we have to search the error in imagemagic – LaRiFaRi Apr 17 '15 at 8:10
  • One example of a problematic graphic would be the png Creative Commons logo provided on the creative commons website: mirrors.creativecommons.org/presskit/icons/cc.large.png - there is nothing special about the way I'm including the graphics, I just use a simple \includegraphic command. Flattening means reducing the PDF file's content to a single layer, which is something a lot of professional printing companies require. – dwk Apr 18 '15 at 10:13
  • @dwk: Flattening can mean all sort of things; typically it's the process of removing any transparency features and producing PDF 1.3. – Reinstate Monica - M. Schröder Apr 21 '15 at 17:53
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The problem appears to be related to the transparency of the PNG and PDF graphics I was using. I solved the problem by flattening the PDF graphics before inserting them, and opening the PNG files in gimp to remove the alpha channel from those files.

(It would appear that pdflatex is invisibly spreading the transparent layer of transparent graphics across the whole page rather than confining it to the size of the graphic, and nobody notices a problem unless they attempt to flatten the resulting PDF.)

  • I'm reasonably sure that the treatment of transparency by pdfTeX is correct. Can you provide some conformation for your claim (like a report by Adobe Acrobat Preflight or similar tools)? – Reinstate Monica - M. Schröder Apr 21 '15 at 17:52
  • Well this is odd; although I've had this problem with two separate ~500pg documents I've worked on, when I try to replicate the problem with a small/minimal document, the problem fails to manifest. Another question on here seems very much related though: tex.stackexchange.com/questions/71001/… – dwk Apr 23 '15 at 9:15
  • If you can reducide this to a test case, please file a bug with the pdfTeX maintainer. – Reinstate Monica - M. Schröder Apr 23 '15 at 11:54

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