Thanks, your warning is so true! However, it a PDF without a .pdf ending is used, the user deserves whatever happens to it ;^)

I’ll check it and fix it.

tiny comment on the perl script — if the file name doesn’t end with .pdf, the input file will be overwritten. it might be better to check and add _gray at the end anyway, even if there’s no .pdf ending.

I found a way to do it, please see my post:

http://yentaublog.wordpress.com/2012/01/25/convert-pdfs-to-blackwhite-translated-from-chinese/

I can’t really help you. Is there any reason why PDF -> PS -> PDF is not acceptable for you?

I have tried the code you show, and it actually works on PS files, but not PDFs (if we do not convert the input PDF to PS before applying gs, the output PDF is still a color one). It strikes me as funny, since gs should also handle PDFs!

I must also say that your code seems to convert text to B/W, but not images, at least in a couple of tries I’ve made.

pdf2ps color.pdf color.ps

gs \
-o bw-from-color.pdf \
-sDEVICE=pdfwrite \
-c “/setrgbcolor{0 mul 3 1 roll 0 mul 3 1 roll 0 mul 3 1 roll 0 mul add add setgray}def” \
-f color.ps

but how to convert color pdf to monochrome pdf directly(without converting it to ps first)?

is there any way to convert a pdf to pure black & white (monochrome) with ghostscript? Thanks.