Create scanned looking PDFs with adjustable DPI/quality support

scan_effect.sh

#!/usr/bin/env bash

set -Eeuo pipefail

SCRIPT_NAME="$(basename "$0")"
INPUT=""
OUTPUT="scanned_output.pdf"
DPI="130"
QUALITY="65"
INSTALL_DEPS="false"

usage() {
  cat <<USAGE
Usage:
  ./$SCRIPT_NAME [options] input.pdf [output.pdf]

Options:
  -d, --dpi NUMBER       Output resolution. Default: 130
  -q, --quality NUMBER   JPEG quality from 1 to 100. Default: 65
      --install          Try to install missing dependencies, then continue
  -h, --help             Show this help message

Examples:
  ./$SCRIPT_NAME input.pdf output.pdf
  ./$SCRIPT_NAME --dpi 130 --quality 65 input.pdf output.pdf
  ./$SCRIPT_NAME -d 150 -q 72 input.pdf scanned.pdf
  ./$SCRIPT_NAME --install input.pdf output.pdf
USAGE
}

error() {
  echo "Error: $*" >&2
}

info() {
  echo "$*"
}

is_number() {
  [[ "$1" =~ ^[0-9]+$ ]]
}

parse_args() {
  while [[ $# -gt 0 ]]; do
    case "$1" in
      -d|--dpi)
        [[ $# -ge 2 ]] || { error "Missing value for $1"; exit 1; }
        DPI="$2"
        shift 2
        ;;
      --dpi=*)
        DPI="${1#*=}"
        shift
        ;;
      -q|--quality)
        [[ $# -ge 2 ]] || { error "Missing value for $1"; exit 1; }
        QUALITY="$2"
        shift 2
        ;;
      --quality=*)
        QUALITY="${1#*=}"
        shift
        ;;
      --install)
        INSTALL_DEPS="true"
        shift
        ;;
      -h|--help)
        usage
        exit 0
        ;;
      --)
        shift
        break
        ;;
      -* )
        error "Unknown option: $1"
        usage
        exit 1
        ;;
      *)
        if [[ -z "$INPUT" ]]; then
          INPUT="$1"
        elif [[ "$OUTPUT" == "scanned_output.pdf" ]]; then
          OUTPUT="$1"
        else
          error "Too many arguments: $1"
          usage
          exit 1
        fi
        shift
        ;;
    esac
  done

  while [[ $# -gt 0 ]]; do
    if [[ -z "$INPUT" ]]; then
      INPUT="$1"
    elif [[ "$OUTPUT" == "scanned_output.pdf" ]]; then
      OUTPUT="$1"
    else
      error "Too many arguments: $1"
      usage
      exit 1
    fi
    shift
  done
}

validate_args() {
  if [[ -z "$INPUT" ]]; then
    usage
    exit 1
  fi

  if [[ ! -f "$INPUT" ]]; then
    error "Input file not found: '$INPUT'"
    exit 1
  fi

  if ! is_number "$DPI" || [[ "$DPI" -lt 72 || "$DPI" -gt 600 ]]; then
    error "DPI must be a number between 72 and 600. Current value: $DPI"
    exit 1
  fi

  if ! is_number "$QUALITY" || [[ "$QUALITY" -lt 1 || "$QUALITY" -gt 100 ]]; then
    error "Quality must be a number between 1 and 100. Current value: $QUALITY"
    exit 1
  fi
}

missing_dependencies() {
  local missing=()

  command -v pdftoppm >/dev/null 2>&1 || missing+=("pdftoppm")
  command -v img2pdf >/dev/null 2>&1 || missing+=("img2pdf")

  if ! command -v magick >/dev/null 2>&1 && ! command -v convert >/dev/null 2>&1; then
    missing+=("imagemagick")
  fi

  printf '%s\n' "${missing[@]}"
}

install_command_hint() {
  cat <<'HINT'
Install commands:
  Ubuntu/Debian:
    sudo apt update
    sudo apt install -y poppler-utils img2pdf imagemagick

  Fedora:
    sudo dnf install -y poppler-utils img2pdf ImageMagick

  Arch Linux:
    sudo pacman -S --needed poppler img2pdf imagemagick

  macOS with Homebrew:
    brew install poppler img2pdf imagemagick
HINT
}

try_install_dependencies() {
  info "Trying to install missing dependencies..."

  if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update
    sudo apt-get install -y poppler-utils img2pdf imagemagick
  elif command -v dnf >/dev/null 2>&1; then
    sudo dnf install -y poppler-utils img2pdf ImageMagick
  elif command -v pacman >/dev/null 2>&1; then
    sudo pacman -S --needed poppler img2pdf imagemagick
  elif command -v brew >/dev/null 2>&1; then
    brew install poppler img2pdf imagemagick
  else
    error "No supported package manager found. Please install dependencies manually."
    install_command_hint
    exit 1
  fi
}

check_dependencies() {
  local missing
  missing="$(missing_dependencies | tr '\n' ' ')"

  if [[ -z "${missing// }" ]]; then
    return 0
  fi

  error "Required dependency/dependencies are not installed: $missing"

  if [[ "$INSTALL_DEPS" == "true" ]]; then
    try_install_dependencies

    local missing_after
    missing_after="$(missing_dependencies | tr '\n' ' ')"

    if [[ -n "${missing_after// }" ]]; then
      error "Still missing after install attempt: $missing_after"
      install_command_hint
      exit 1
    fi

    info "Dependencies installed successfully."
  else
    install_command_hint
    echo ""
    echo "Or run this script with --install:"
    echo "  ./$SCRIPT_NAME --install --dpi $DPI --quality $QUALITY '$INPUT' '$OUTPUT'"
    exit 1
  fi
}

get_imagemagick_command() {
  if command -v magick >/dev/null 2>&1; then
    echo "magick"
  else
    echo "convert"
  fi
}

main() {
  parse_args "$@"
  validate_args
  check_dependencies

  local im_cmd
  im_cmd="$(get_imagemagick_command)"

  local workdir pages_dir scanned_dir
  workdir="$(mktemp -d)"
  pages_dir="$workdir/pages"
  scanned_dir="$workdir/scanned"

  cleanup() {
    rm -rf "$workdir"
  }
  trap cleanup EXIT

  mkdir -p "$pages_dir" "$scanned_dir"

  info "Splitting PDF into JPEG pages... DPI=$DPI, QUALITY=$QUALITY"
  pdftoppm -r "$DPI" "$INPUT" "$pages_dir/page" -jpeg -jpegopt quality="$QUALITY",progressive=y,optimize=y

  info "Applying scan effect..."

  local i=0 rotate output_page
  shopt -s nullglob
  for f in "$pages_dir"/page-*.jpg; do
    i=$((i + 1))

    if [[ $((i % 2)) -eq 0 ]]; then
      rotate="0.35"
    else
      rotate="-0.25"
    fi

    output_page="$scanned_dir/$(basename "$f")"

    "$im_cmd" "$f" \
      -rotate "$rotate" \
      -attenuate 0.05 +noise Gaussian \
      -blur 0x0.18 \
      -brightness-contrast 1x5 \
      -strip \
      -interlace JPEG \
      -sampling-factor 4:2:0 \
      -quality "$QUALITY" \
      "$output_page"
  done

  if [[ "$i" -eq 0 ]]; then
    error "No pages were generated from the input PDF."
    exit 1
  fi

  info "Creating compressed PDF..."
  img2pdf "$scanned_dir"/page-*.jpg -o "$OUTPUT"

  info "Done: $OUTPUT"
}

main "$@"