foxit-readerpdfpdf-reader
I have a large color PDF that I can easily view greyscale in Foxit Reader:
Unfortunately various bits of text end up in ridiculously light shades of grey.
Similar, but not direct, questions include:
How can I force a PDF to display only in pure black and white?
In Foxit
Tools -> Preferences -> Documents -> Document Colors Options
The last suggestion indeed only converts to grayscale and then only works if the underlying doc uses setrgbcolor. This did not work for me, since I had a doc, that used setcolor.
I had success with redefining setcolor to always set the color to 0,0,0:
gs -o <output-file.pdf> -sDEVICE=pdfwrite \
-c "/osetcolor {/setcolor} bind def /setcolor {pop [0 0 0] osetcolor} def" \
-f <input-file.ps>
It has been 15+ years since I did any PostScript hacking, so the above may be lame, incorrect or even accidental - if you know how to do better, please suggest.
Best Answer
ImageMagick is free and cross-platform. This command should work:
For example:
You'll have to set the threshold to taste.