102

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.

3 Answers 3

40

ImageMagick can do this.

convert -colorspace GRAY color.pdf gray.pdf

via this email

9
  • 37
    That significantly reduces quality. @goyinux' solution is better. Feb 12, 2013 at 16:41
  • 8
    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, 2014 at 12:24
  • 4
    Unless you use -density 400 -quality 100 parameters - that works well
    – burtek
    Dec 13, 2015 at 20:51
  • 2
    Really, is there anything ImageMagick can't do? :) Aug 18, 2017 at 3:02
  • 1
    -density 400 -quality 100 creates HUGE files. +1 for @goyinux's solution. Jun 27, 2018 at 10:45
212

Better:

gs \
 -sOutputFile=output.pdf \
 -sDEVICE=pdfwrite \
 -sColorConversionStrategy=Gray \
 -dProcessColorModel=/DeviceGray \
 -dCompatibilityLevel=1.4 \
 -dNOPAUSE \
 -dBATCH \
 input.pdf
8
  • 2
    Agreed, this gives much better results than convert, but sometimes it rotates the pdf which is a bit annoying!
    – tdc
    Aug 7, 2012 at 18:08
  • 21
    Just realised you can disable that with -dAutoRotatePages=/None
    – tdc
    Aug 7, 2012 at 18:15
  • 2
    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, 2012 at 2:33
  • 1
    Works well on Windows, too! Just remove the `\` and put everything on the same line.
    – ixe013
    Aug 19, 2014 at 4:23
  • 1
    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, 2015 at 17:56
16

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.

1
  • FWIW, pdftk can concatenate PDFs, too. Jun 14, 2018 at 7:07

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