Convert a PDF file to black and white (not grayscale)

Convert a PDF file to black and white (not grayscale)

# The first approach that I found was to convert using a virtual device using Ghostscript.
# The virtual device, pdfwrite, supports parameters to convert the original PDF file to another PDF file in grayscale.
# In my case, I wanted only black and white, so this was not enough.

#!/bin/bash

gs \
 -sOutputFile=output.pdf \
 -sDEVICE=pdfwrite \
 -sColorConversionStrategy=Gray \
 -dProcessColorModel=/DeviceGray \
 -dCompatibilityLevel=1.4 \
 -dNOPAUSE \
 -dBATCH \
 $1
 
# I didn't find any solution that worked for my case, so I had to create my own.
# A question at StackOverflow asked the same question, the response was:

gs -o <output-file.pdf> -sDEVICE=pdfwrite \
-c "/osetcolor {/setcolor} bind def /setcolor {pop [0 0 0] osetcolor} def" \
-f <input-file.ps>

# What this does is redefine the setcolor function from PostScript to always set the color to black (0, 0, 0).
# This should work, but there are other functions that also set colors in PostScript.
# After some evaluation, I found that my PostScript file used setrgbcolor.
# The adapted solution is this:

gs -o output.pdf -sDEVICE=pdfwrite \
-c "/setrgbcolor {pop pop pop 0 setgray} bind def"  \
-f $1 

# I redefined setrgbcolor to pop all the previous parameters and to use the setgray function to set the color as black (0).