How to convert PDF to Grayscale

I scanned a document in color to PDF, and I don't want to re-scan it.

How can I convert this PDF document to grayscale (preferably without loss of other information)?

My usual toolset of doPDF, pdfsam and the Neevia online converter don't work here. I was thinking I could simply print to PDF and select the Grayscale color option, but doPDF doesn't have that option.

I'm using Windows, but I can probably handle a solution for any OS.

palswim

Posted 2011-08-03T16:54:04.050

Reputation: 2 793

Answers

I found a solution in a blog post:

With GhostScript (and Windows users can access gs via cygwin), you can do it with the following command:

gs \
  -o grayscale.pdf \
  -sDEVICE=pdfwrite \
  -sColorConversionStrategy=Gray \
  -dProcessColorModel=/DeviceGray \
  -dCompatibilityLevel=1.4 \
   source.pdf

This will convert source.pdf to grayscale.pdf and not put you into a GhostScript shell (due to the -o option instead of the -sOutputFile= option).

palswim

Posted 2011-08-03T16:54:04.050

Reputation: 2 793

1OMG!, what a complicated workaround for avoiding the Ghostscript command prompt to stay up after the processing! A more simple solution is to add -dNOPAUSE -dBATCH to the commandline. The -dNOPAUSE part spares you from hitting [return] after each page, and the -dBATCH part saves you from typing 'quit' at to exit the GS> prompt. And even shorter: just use -o grayscale.pdf for specifying the output file; this -o ... implicitly also sets -dBATCH -dNOPAUSE... – Kurt Pfeifle – 2011-08-08T20:14:35.797

It appears this no longer works with recent versions of Ghostscript: http://ghostscript.com/pipermail/gs-bugs/2012-May/025904.html says "'Gray' is not a documented legal value for ColorConversionStrategy"

– AnC – 2013-02-21T17:01:20.083

Sounds like a job for Imagemagick. Windows and Linux versions are available.

http://www.imagemagick.org/script/index.php

This should do the trick at the command line:

convert -colorspace GRAY original.pdf grayscale.pdf

Linker3000

Posted 2011-08-03T16:54:04.050

Reputation: 25 670

@nodiscc: you should be aware that ImageMagick employs Ghostscript as its delegate to render and interpret the PDF input file... (So without a working Ghostscript installation on the same system it won't work.) – Kurt Pfeifle – 2011-08-08T20:09:43.040

Just install PDFCreator. It has a small footprint and adds a PDF printer to Windows. And as you've mentioned, just select grayscale when printing to it.

Traveling Tech Guy

Posted 2011-08-03T16:54:04.050

Reputation: 8 743

Not that this would make your answer invalid, but do PDF prints lose information on each print? – palswim – 2011-08-03T21:43:52.787

I believe not, but you could just try - it's free :) – Traveling Tech Guy – 2011-08-04T03:33:11.723

Sejda.com has an online tool for Converting PDF docs to Grayscale.

Go to https://www.sejda.com/grayscale-pdf and upload your doc
Click Convert PDF to Grayscale and then Download to save your grayscaled document.

The online grayscale converter is free to use 3 times per hour, for files up to 50Mb or 200 pages.

There's also an offline version of the same tool that you can install and work locally, without uploading your files: https://www.sejda.com/desktop

Disclaimer: I'm one of the developers.

Edi

Posted 2011-08-03T16:54:04.050

Reputation: 532

You can just use the free service at http://greyscalepdf.com to convert any PDF to greyscale.

python_noob

Posted 2011-08-03T16:54:04.050

Reputation: 109

Nice; good find! Some people have sensitive information in their PDFs and don't want to use an online conversion service, though. – palswim – 2013-01-14T22:06:24.113