fake pdf scanner.

convert-pdf2scan.sh

#!/usr/bin/env bash
set -e # exit on error
################################################
#
# Prerequisits:
#   ensure ImageMagick is installed
#
# Usage:
#   convert-pdf2scan [--gray] files...
#
################################################
if [ "$1" == "--gray" ]
then
  colorspace="Gray"
  shift 
fi

tilt_min=0.02
tilt_max=0.06
density=100
noise=0.15

for input in "$@"
do

  build_dir="$(mktemp -d "${TMPDIR:-/tmp}"/pdf2scan.XXXX)"
  output_file="$(basename "$input" .pdf)_scan.pdf"
  
  # process each page
  page_count=$(identify -ping "$input" | wc -l | bc)
  page_range="0..$(bc <<< "$page_count - 1")"
  for (( page_index=0; page_index<$page_count; page_index++ ))
  do
    echo "process page $(bc <<< "$page_index + 1")/$page_count ..."
    
    # randomize tilt
    tilt=$(bc -l <<< "$tilt_min + ($tilt_max - $tilt_min) * ($RANDOM/32767)")
    if [ $(($RANDOM % 2)) = 0 ]
    then
      tilt=-$tilt
    fi
    
    convert \
      -density $density \
      "${input}[${page_index}]" \
      -background none \
      -rotate $tilt \
      -attenuate $noise \
      +noise Multiplicative \
      ${colorspace:+-colorspace $colorspace} \
      -sharpen 0x1.0 \
      "$build_dir/page_${page_index}.pdf"
  done
  
  # merge pages
  echo "merge pages into '$output_file' ..."
  IFS=$'\n' scan_pages=($(ls -1 "$build_dir/page_"* | sort -V))
  convert \
    -density $density \
    -compress jpeg -quality 80 \
    "${scan_pages[@]}" \
    "$output_file"
  
  echo "done!"
done