Command-line tool to OCR PDFs

ocrpdf.sh

#!/bin/bash
# OCR a PDF using Tesseract and Ghostscript
# (brew install tesseract, brew install ghostscript using Homebrew on a Mac)
# Usage: ocrpdf input.pdf output.pdf

# Copyright (c) 2017 Matthew Wigginton Conway
#
# 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.

TEMP=`mktemp -d`
INPDF="$1"
OUTPDF="$2"

# Split the original PDF to page images, as Tesseract does not handle input PDFs and can only
# handle one png at a time
# https://stackoverflow.com/questions/653380
gs -sDEVICE=pngalpha -o "$TEMP/page-%04d.png" -r300 "$INPDF"

# OCR each page image
NFILES=`ls "$TEMP" | wc -l`
CURFILE=0

for png in "$TEMP"/*.png; do
  let "CURFILE=CURFILE+1"
  echo OCRing page $CURFILE / $NFILES
  tesseract $png $png pdf
done

# Merge the pages
# https://stackoverflow.com/questions/8158584
gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress "-sOutputFile=$OUTPDF" "$TEMP"/*.pdf

# Clean up
rm -rf "$TEMP"