Making a PDF grayscale with ghostscript
September 30th 2008
A request from a friend made me face the problem of converting a color PDF into a grayscale one. Searching the web provided some ways of doing so with Adobe Acrobat, via some obscure menu item somewhere.
However, the very same operation could be undertaken with free tools, such as ghostscript. I found a way to do it in the YANUB blog, and I will copy-paste it here, with a small modification.
Assuming we have a file called color.pdf, and we want to convert it into grayscale.pdf, we could run the following command (all in a single line, and omitting the “\” line continuation marks):
% gs -sOutputFile=grayscale.pdf -sDEVICE=pdfwrite \
-sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray \
-dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH color.pdf
I prefer the above to YANUB’s version below (in red what he lacks, in blue what I lack), because a shell operation is substituted by some option(s) of the command we are running:
% gs -sOutputFile=grayscale.pdf -sDEVICE=pdfwrite \
-sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray \
-dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH color.pdf < /dev/null
A sample Perl script to alleviate the tedious writing above:
#!/usr/bin/perl -w
use strict;
my $infile = $ARGV[0];
my $outfile = $infile;
$outfile =~ s/\.pdf$/_gray.pdf/;
system "gs -sOutputFile=$outfile -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH $infile"
Assuming we call the Perl script “togray.pl”, and that we have a color file “input.pdf”, we could just issue the command:
% togray.pl input.pdf
and we would get a grayscale version of it, named “input_gray.pdf”.
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1 Comment »
Jose on 06 Nov 2008 at 4:19 am #
Hi,
Great post and it also works in Windows with Ghostview (http://pages.cs.wisc.edu/~ghost/doc/GPL/gpl863.htm).
The only thing that I had to change was the exe.
gswin32.exe -sOutputFile=grayscale.pdf -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH color.pdf
I did try the perl script but it should work also.
Thanks,
Jose.