After reading these blog posts:
- Linux, OCR and PDF - Problem solved
- Creating a searchable PDF with opensource tools ghostscript, hocr2pdf and tesseract-ocr
- Using Tesseract OCR with PDF scans
and going through the snippet below (from this gist) for Linux, I think I found a method to OCR a multi-page PDF and get a PDF in the output that could also work in OS X. Most of the dependencies are available in homebrew (brew install tesseract
and brew install imagemagick
), except one, hocr2pdf
.
I haven't been able to find a port of it for OS X. Is there one available? If not, how can one OCR a multi-page PDF and get the results back again in a multi-page PDF in OS X, using free, open source tools?
#!/bin/bash
# This is a script to transform a PDF containing a scanned book into a searchable PDF.
# Based on previous script and many good tips by Konrad Voelkel:
# http://blog.konradvoelkel.de/2010/01/linux-ocr-and-pdf-problem-solved/
# http://blog.konradvoelkel.de/2013/03/scan-to-pdfa/
# Depends on convert (ImageMagick), pdftk and hocr2pdf (ExactImage).
# $ sudo apt-get install imagemagick pdftk exactimage
# You also need at least one OCR software which can be either tesseract or cuneiform.
# $ sudo apt-get install tesseract-ocr
# $ sudo apt-get install cuneiform
# To install languages into tesseract do (e.g. for Portuguese):
# $ sudo apt-get install tesseract-ocr-por
echo "usage: ./pdfocr.sh document.pdf ocr-sfw split lang author title"
# where ocr-sfw is either tesseract or cuneiform
# split is either 0 (already single-paged) or 1 (2 book-pages per pdf-page)
# lang is a language as in "tesseract --list-langs" or "cuneiform -l".
# and author, title are used for the PDF metadata.
#
# usage example:
# ./pdfocr.sh SomeFile.pdf tesseract 1 por "Some Author" "Some Title"
pdftk "$1" burst dont_ask
for f in pg_*.pdf
do
if [ "1" == "$3" ]; then
convert -normalize -density 300 -depth 8 -crop 50%x100% +repage $f "$f.png"
else
convert -normalize -density 300 -depth 8 $f "$f.png"
fi
done
rm pg_*.pdf
for f in pg_*.png
do
if [ "tesseract" == "$2" ]; then
tesseract -l $4 -psm 1 $f $f hocr
elif [ "cuneiform" == "$2" ]; then
cuneiform -l $4 -f hocr -o "$f.html" $f
else
echo "$2 is not a valid OCR software."
fi
hocr2pdf -i $f -r 300 -s -o "$f.pdf" < "$f.html"
done
pdftk pg_*.pdf cat output merged.pdf
pdftk merged.pdf update_info_utf8 doc_data.txt output merged+data.pdf
echo "InfoBegin" > in.info
echo "InfoKey: Author" >> in.info
echo "InfoValue: $5" >> in.info
echo "InfoBegin" >> in.info
echo "InfoKey: Title" >> in.info
echo "InfoValue: $6" >> in.info
echo "InfoBegin" >> in.info
echo "InfoKey: Creator" >> in.info
echo "InfoValue: PDF OCR scan script" >> in.info
in_filename="${1%.*}"
pdftk merged+data.pdf update_info_utf8 in.info output "$in_filename-ocr.pdf"
rm -r doc_data.txt in.info merged* pg_*