I have a colour PDF file, and I'm going to print it out and then photocopy it in black and white. I'd like to know what it's like in B&W before photocopying it. Is it possible to 'greyscale' a PDF on the command line using free software? I'm using Ubuntu 9.10.
ImageMagick can do this.
convert -colorspace GRAY color.pdf gray.pdf
via this email
Here’s a little script which in addition to the grayscale conversion can concatenate multiple input files. To use the script, put the following lines in a file, e.g. "convert2gray.sh"
gs -sOutputFile=converted.pdf -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibiltyLevel=1.4 -dNOPAUSE -dBATCH $@
and make it executable
chmod +x convert2gray.sh
./convert2gray.sh input1.pdf input2.pdf … lastinput.pdf
will produce a single PDF "converted.pdf", which contains all pages from the input files converted to grayscale.
I had to print out mutliple files all in grayscale and found this the easiest way, since you can print out everything after inpection with one command.
In my case I am keeping signed document scans in color, but need reprint it without gray noice. For this case works well
convert -density 300 -threshold 75% input.pdf output.pdf
(based on the answer)
Range between 50%-75% works fine in circumstances when you have color scan PDF (text as image) with original resolution 300dpi.
In case of text saved as PDF (not image) you will get huge increasing of output file size.