Scan single or multi-page document, post-process it and convert to OCR'ed PDF

scandoc

#!/bin/bash -eu

# Usage: scandoc [expected number of pages]
# Eg:
#   scandoc 1    # Scan one page, then process
#   scandoc 5    # Scan 5 pages, then process
#   scandoc      # Scan until page 99 or other action triggers end
#
# Description:
#   Scandoc interactively scans a number (1 or more) of pages, runs
#   post-processing   operations on each page, runs OCR on the high quality
#   version and generates a new, lower quality PDF. The OCR from the high
#   quality version and the images from the low quality version are then
#   merged into a single PDF.
#
#   This final PDF should be fairly low size, very readable, and contain
#   accurately recognized text.
#
# Requires:
#   - scanimage for scanning
#   - unpaper for rectifying, removing background
#   - imagemagic merging, resampling and compressing
#   - tesseract for OCR
#   - qpdf to merge image and text pdf
#
#   Use scanimage -L to get a list of devices.
#   e.g. device `genesys:libusb:006:003' is a Canon LiDE 210 flatbed scanner
#   then copy/paste genesys:libusb:006:003 into SCANNER below.

PAGES=${1:-99} # Parameter: number of pages; defaults to 99 (which is equivalent to 'unlimited')

# Parameters based on environment variables
# Sensible defaults are set for me
# You can set your own defaults per shell by exporting them, or
# eg. add them to your ~/.bashrc

: ${SCANNER:="brother4:bus9;dev1"} # My USB scanner
: ${OCR_LANG:=nld}                 # Tesseract language
: ${SCAN_DPI:=300}                 # A good resolution for OCR
: ${FINAL_RES:=1240x}              # A good resolution for PDF
: ${SHOW:=0}                       # Show the result
: ${NICE:=10}                      # Priority of this process - this prevents Tesseract from hogging your machine
: ${UNPAPER:=1}                    # Whether to run unpaper
: ${FILENAME:=AUTO}                # If no FILENAME is set, or set to 'AUTO': make one up based on time

if [[ "${FILENAME}" == "AUTO" ]]; then
  FILENAME=$(date "+%F_%T" | sed 's/:/-/g').pdf # Don't use ':' because of Windows
fi

for command in unpaper scanimage convert tesseract qpdf; do
  if ! command -v "${command}" &>/dev/null; then
    echo "Missing command: '${command}'"
    command "${command}"
    exit 1
  fi
done

re='^[0-9]+$' # Check if PAGES is a number
if ! [[ ${PAGES} =~ $re ]]; then
  echo "error: Usage: $0 filename number_of_pages" >&2
  exit 1
fi

TMP_DIR=$(mktemp -d)
trap "{ rm -vrf "${TMP_DIR}"; }" EXIT

echo "Scanning to: '${FILENAME}'"

PAGE=0

while [[ "${PAGE}" -lt "${PAGES}" ]]; do
  PAGE=$((PAGE + 1))

  echo "Please, place page ${PAGE}/${PAGES} on the scanner"
  cat <<EOF
Press:
  [enter] to scan,
  [q] to stop scanning and start parsing,
  [l] to scan one more page and then start parsing,
  [m] to scan and increase the total number of pages (${PAGES} -> $((PAGES + 1)))
  [ctrl+c] to abort"
EOF

  read ACTION
  [[ "${ACTION}" == "q" ]] && break
  echo "Start scanimage..."

  filename="${TMP_DIR}/page_$(printf "%03d" "${PAGE}").tiff"
  scanimage -p -d "${SCANNER}" \
    --format=tiff \
    --resolution "${SCAN_DPI}" \
    --output-file "${filename}"

  if [[ "${UNPAPER}" == "1" ]]; then
    unpaper -q --dpi 300.0 "${filename}" "${filename%.tiff}-unpaper.pnm" &
  fi
  [[ "${ACTION}" == "l" ]] && break
  if [[ "${ACTION}" == "m" ]]; then
    PAGES=$((PAGES + 1))
  fi
done

echo "Changing priority to '${NICE}' (higher is lower)"

echo "Waiting for unpaper to finish..."
wait
renice -n "${NICE}" $$

echo "Merging pages..."

if [[ "${UNPAPER}" == "1" ]]; then
  convert "${TMP_DIR}"/page_*-unpaper.pnm "${TMP_DIR}/combined.tiff"
else
  convert "${TMP_DIR}"/page_*.tiff "${TMP_DIR}/combined.tiff"
fi

convert "${TMP_DIR}/combined.tiff" -scale "${FINAL_RES}" -compress jpeg -quality 75 "${TMP_DIR}/combined.pdf"

echo "Running OCR..."
tesseract -l "${OCR_LANG}" -c textonly_pdf=1 "${TMP_DIR}/combined.tiff" "${TMP_DIR}/ocr" pdf

qpdf "${TMP_DIR}/combined.pdf" --underlay "${TMP_DIR}/ocr.pdf" -- "${FILENAME}"

echo "Scan of '${FILENAME}' is done"

rm -rf ${TMP_DIR}

if [[ "${SHOW}" == "1" ]]; then
  xdg-open "${FILENAME}"
fi