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How can I generate a monochrome pdf file from a color pdf file?

I have tried ImageMagick's convert, but with bad results.

A direct conversion

convert -monochrome file.pdf file-bw.pdf

produces dithered images.

Going through png

convert -monochrome -background white -geometry 2048 file.pdf file-bw.png

stubbornly keeps the background to some shade of gray.

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2 Answers

up vote 6 down vote accepted

You can do this easily in Preview:

  1. Open the PDF in Preview.
  2. Go to File > Export...
  3. From the Quartz Filter drop-down box, select Black & White.
  4. Save and you're done.
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You can also use Ghostscript to transform color into grayscale PDFs. The most recent version is v. 9.05, which is the recommended one for this task.

Commandline:

 gs \
   -o grayscale.pdf \
   -sDEVICE=pdfwrite \
   -dPDFSETTINGS=/prepress \
   -sColorConversionStrategy=Gray \
   -sColorConversionStrategyForImages=Gray \
   -sProcessColorModel=DeviceGray \
   -dCompatibilityLevel=1.4 \
   /path/to/input.pdf
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