Convert color image pdf to black and white pdf.

smaller.sh

#!/bin/bash
INPDF=$1
OUTDIR=$2
ROT=$3
CONVOPTS=$4
INBASE=$(basename ${INPDF} .pdf)
TMP=$(mktemp -d)
pdfimages -j ${INPDF} ${TMP}/${INBASE}  # emits ppm,pbm or jpg
for i in $(ls ${TMP}/${INBASE}-*.*)
do
  convert ${CONVOPTS} -colorspace Gray -threshold 40% $i -compress zip $i.pdf
done
pdftk ${TMP}/${INBASE}-*.pdf cat output ${TMP}/${INBASE}-cat.pdf
[ ! -z $ROT ] && pdftk ${TMP}/${INBASE}-cat.pdf cat 1-end${ROT} output ${OUTDIR}/${INBASE}.pdf