Make clean PDFs look like they were scanned

clean2scan.sh

#!/bin/sh
#
# clean2scan.sh -- make clean PDFs look like they were scanned
#
# Usage: clean2scan.sh <file>
#
# This is a simple script that uses ImageMagick and Ghostscript to
# distort and transform pages in a PDF to mimick scanned PDFs.
#
# Requires: convert(1) and gs(1)
#

[ "$*" ] || {
    echo >&2 "usage: ${0##*/} <file>"
    exit 1
}

tmpdir="$(mktemp -d)"
trap 'rm -rf "$tmpdir" >/dev/null 2>&1' EXIT
trap 'exit 2' HUP INT QUIT TERM

# Target resolution (DPI).
resolution=192

# Generate random real numbers in the range [-arg, arg].
random() {
    [ "$1" ] || set -- 1.0
    awk "BEGIN { srand(); print -$1 + 2.0 * $1 * rand(); exit; }"
}

# Split PDF into individual pages.
convert -density "$resolution" "$1" "${tmpdir}/%010d.pdf"

# Add a little bit of multiplicative noise, random rotation, barrel
# distortion, and convert each page to grayscale.
for pdf in "$tmpdir"/*.pdf
do
    convert -density "$resolution"                    \
            "$pdf"                                    \
            -rotate "$(random 1.5)"                   \
            -attenuate 0.3                            \
            +noise Multiplicative                     \
            -distort Barrel "$(random 0.005) 0.0 0.0" \
            -colorspace Gray "${pdf%.*}.scan.pdf"
done

# Merge the distorted pages to a single PDF and optimize using
# Ghostscript.
convert -density "$resolution" "$tmpdir"/*.scan.pdf "$tmpdir/merged.pdf"
gs -sDEVICE=pdfwrite                                 \
   -dCompatibilityLevel=1.4                          \
   -dPDFSETTINGS=/printer                            \
   -dNOPAUSE                                         \
   -dQUIET                                           \
   -dBATCH                                           \
   -sOutputFile="${1%.*}.scan.pdf"                   \
   "$tmpdir/merged.pdf"