How do I know if PDF pages are color or black-and-white?

Question

Given a set of PDF files among which some pages are color and the remaining are black & white, is there any program to find out among the given pages which are color and whi

Answer 1

It is possible to use the Image Magick tool identify. If used on PDF pages it converts the page first to a raster image. If the page contained color can be tested using the -format "%[colorspace]" option, which for my PDF printed either Gray or RGB. IMHO identify (or what ever tool it uses in the background; Ghostscript?) does choose the colorspace depending on the presents of color.

An example is:

identify -format "%[colorspace]" $FILE.pdf[$PAGE]

where PAGE is the page starting from 0, not 1. If the page selection is not used all pages will be collapsed to one, which is not what you want.

I wrote the following BASH script which uses pdfinfo to get the number of pages and then loops over them. Outputting the pages which are in color. I also added a feature for double sided document where you might need a non-colored backside page as well.

Using the outputted space separated list the colored PDF pages can be extracted using pdftk:

pdftk $FILE cat $PAGELIST output color_${FILE}.pdf

---

#!/bin/bash

FILE=$1
PAGES=$(pdfinfo ${FILE} | grep 'Pages:' | sed 's/Pages:\s*//')

GRAYPAGES=""
COLORPAGES=""
DOUBLECOLORPAGES=""

echo "Pages: $PAGES"
N=1
while (test "$N" -le "$PAGES")
do
    COLORSPACE=$( identify -format "%[colorspace]" "$FILE[$((N-1))]" )
    echo "$N: $COLORSPACE"
    if [[ $COLORSPACE == "Gray" ]]
    then
        GRAYPAGES="$GRAYPAGES $N"
    else
        COLORPAGES="$COLORPAGES $N"
        # For double sided documents also list the page on the other side of the sheet:
        if [[ $((N%2)) -eq 1 ]]
        then
            DOUBLECOLORPAGES="$DOUBLECOLORPAGES $N $((N+1))"
            #N=$((N+1))
        else
            DOUBLECOLORPAGES="$DOUBLECOLORPAGES $((N-1)) $N"
        fi
    fi
    N=$((N+1))
done

echo $DOUBLECOLORPAGES
echo $COLORPAGES
echo $GRAYPAGES
#pdftk $FILE cat $COLORPAGES output color_${FILE}.pdf