Produce a PDF document from scanned images

pdf-from-images.sh

#!/usr/bin/env bash

# pdf-from-images.sh is licensed under the MIT License  (a.k.a. the "Expat
# License"), details of which are below. Comments and code contributions are
# welcome at <https://gist.github.com/shoogle/3dc1604e4930f07523728d3795a66ec8>
#
# MIT License
#
# Copyright (c) 2018 Peter Jonas
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

readonly output_page_width_mm=210
readonly output_page_height_mm=297

readonly output_page_margin_mm=5
readonly output_page_footer_mm=5
readonly text_height_mm=3 # must be smaller than footer

function print_help() {
  cat <<EOF
pdf-from-images.sh - produce a PDF from scanned images prepared by Scan Taylor

Usage:    pdf-from-images.sh title images [...]

Example:  pdf-from-images.sh "My Scanned Document" scan-01.png scan-02.png

Input images are assumed to be monochrome and have no margins (i.e. tightly
cropped in Scan Taylor or similar program). The script outputs a PDF which has:

  - One input image per page, with images scaled to fit A4 (no resampling).
  - Title and page number displayed at the bottom of each page.
  - Small ${output_page_margin_mm}mm margins for safe printing.
  - Maxium lossless compression to optimize file size.
  - PDF filename set to title passed in on the command line.
EOF
}

function image_info() {
  local image_file="$1" info
  info="$(identify -units PixelsPerCentimeter -format "%wx%h %xx%y\n" "$1")"
  size="${info% *}"
  width="${size%x*}"
  height="${size#*x}"
  density="${info#* }"
  densityX="${density%x*}"
  densityY="${density#*x}"
}

function calculations() {
  readonly output_area_width=$((output_page_width_mm-2*output_page_margin_mm))
  readonly output_area_height=$((output_page_height_mm-2*output_page_margin_mm-output_page_footer_mm))

  max_width=0
  max_height=0

  for img in "$@"; do
    image_info "${img}"
    if ((width > max_width)); then max_width=${width}; fi
    if ((height > max_height)); then max_height=${height}; fi
  done

  readonly max_width max_height

  output_densityX="$(bc -l <<<"${max_width}0/${output_area_width}")"
  output_densityY="$(bc -l <<<"${max_height}0/${output_area_height}")"

  if [[ "$(bc -l <<<"${output_densityX} > ${output_densityY}")" == "1" ]]; then
    output_density="${output_densityX}"
  else
    output_density="${output_densityY}"
  fi

  readonly output_page_margin_px="$(bc <<< "${output_density} * ${output_page_margin_mm} / 10")"
  readonly output_page_footer_px="$(bc <<< "${output_density} * ${output_page_footer_mm} / 10")"
  readonly text_height_px="$(bc <<< "${output_density} * ${text_height_mm} / 10")"
  readonly output_page_width_px=$((max_width+2*output_page_margin_px))
  readonly output_page_height_px=$((max_height+2*output_page_margin_px+output_page_footer_px))

  # Recalculate density to adjust for rounding errors in height and width

  output_densityX="$(bc -l <<<"${output_page_width_px}0/${output_page_width_mm}")"
  output_densityY="$(bc -l <<<"${output_page_height_px}0/${output_page_height_mm}")"

  if [[ "$(bc -l <<<"${output_densityX} > ${output_densityY}")" == "1" ]]; then
    output_density="${output_densityX}"
  else
    output_density="${output_densityY}"
  fi

  readonly output_density output_densityX output_densityY
  }

function image_convert() {
  local in="$1" out="$2" i="$3" n="$4" title="$5" label
  label="${title} - $i of $n"
  try convert -units PixelsPerCentimeter -background White \
    "${in}" -density "${output_density}" \
    -gravity Center -extent "${max_width}x${max_height}" \
    -gravity South -splice "0x${output_page_footer_px}" \
    -fill Black -size "x${text_height_px}" label:"${label}" -composite \
    -gravity Center -extent "${output_page_width_px}x${output_page_height_px}" \
    -type BiLevel "${out}"
}

# sometimes imagemagick fails to allocate memory, but works if we try again...
function try() {
  # keep trying to execute a failing command until it succeeds or we get bored
  local i=0 n=5 command="$1"
  while ! "$@"; do
    ((i++))
    if ((i < n)); then
      echo >&2 "$0: ${command} failed $i times, trying again... (max $n times)"
      sleep 0.1 # wait before trying again, maybe free some memory
    else
      echo >&2 "$0: ${command} failed $n times. Giving up now."
      exit 1
    fi
  done
}

function main() {
  if [[ "$1" =~ ^-+h ]]; then
    print_help
    exit
  fi
  local title="$1" tmp="$(mktemp -d)"
  trap "rm -rf \"${tmp}\"" EXIT
  shift
  echo >&2 "Computing page dimensions..."
  local images=("$@") i=0
  calculations "${images[@]}"
  echo >&2 "Processing images..."
  for img in "${images[@]}"; do
    local out="${tmp}/$(basename "${img%.*}.png")"
    output[$i]="${out}"
    ((i++))
    string="$i of ${#images[@]}"
    echo >&2 "${img} (${string})"
    image_convert "${img}" "${out}" $i ${#images[@]} "${title}"
  done
  echo >&2 "Creating PDF..."
  try convert "${output[@]}" -type BiLevel -compress Fax "${title}.pdf"
}

main "$@"