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I have a colour PDF file, and I'm going to print it out and then photocopy it in black and white. I'd like to know what it's like in B&W before photocopying it. Is it possible to 'greyscale' a PDF on the command line using free software? I'm using Ubuntu 9.10.

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36

ImageMagick can do this.

convert -colorspace GRAY color.pdf gray.pdf

via this email

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  • 27
    That significantly reduces quality. @goyinux' solution is better. – Johannes Weiss Feb 12 '13 at 16:41
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    Convert will actually rasterize the contents of the pdf. So unless the pdf already encapsulates only raster images (e.g. a scanned document), this approach is a big no-no. – m000 Sep 19 '14 at 12:24
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    Unless you use -density 400 -quality 100 parameters - that works well – burtek Dec 13 '15 at 20:51
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    Really, is there anything ImageMagick can't do? :) – BalinKingOfMoria Aug 18 '17 at 3:02
  • -density 400 -quality 100 creates HUGE files. +1 for @goyinux's solution. – Stanimir Stoyanov Jun 27 '18 at 10:45
156

Better:

gs \
 -sOutputFile=output.pdf \
 -sDEVICE=pdfwrite \
 -sColorConversionStrategy=Gray \
 -dProcessColorModel=/DeviceGray \
 -dCompatibilityLevel=1.4 \
 -dNOPAUSE \
 -dBATCH \
 input.pdf
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    Agreed, this gives much better results than convert, but sometimes it rotates the pdf which is a bit annoying! – tdc Aug 7 '12 at 18:08
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    Just realised you can disable that with -dAutoRotatePages=/None – tdc Aug 7 '12 at 18:15
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    I just ran this command on a 58MB PDF that was already greyscale (came from a scanner) and the resulting output was 10MB and looked exactly the same. Nice! – Archie Dec 19 '12 at 2:33
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    Works well on Windows, too! Just remove the `\` and put everything on the same line. – ixe013 Aug 19 '14 at 4:23
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    In fact, this fails with this error GPL Ghostscript 9.10: Unable to convert color space to Gray, reverting strategy to LeaveColorUnchanged. – jjmerelo Dec 15 '15 at 17:56
13

Here’s a little script which in addition to the grayscale conversion can concatenate multiple input files. To use the script, put the following lines in a file, e.g. "convert2gray.sh"

#!/bin/bash
gs -sOutputFile=converted.pdf -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibiltyLevel=1.4 -dNOPAUSE -dBATCH $@

and make it executable

chmod +x convert2gray.sh

Then

./convert2gray.sh input1.pdf input2.pdf … lastinput.pdf

will produce a single PDF "converted.pdf", which contains all pages from the input files converted to grayscale.

I had to print out mutliple files all in grayscale and found this the easiest way, since you can print out everything after inpection with one command.

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  • FWIW, pdftk can concatenate PDFs, too. – user1338062 Jun 14 '18 at 7:07

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