使用免费的开放源代码工具在OS X中的PDF上进行OCR

阅读这些博客文章后：

• Linux，OCR和PDF-已解决问题
• 使用开源工具ghostscript，horc2pdf和tesseract-ocr创建可搜索的PDF
• 将Tesseract OCR与PDF扫描结合使用

并要通过下面的代码段（从这个 GIST）的Linux，我想我找到OCR的方法多页PDF和得到的输出，可以在依赖OS X.大多数也工作在自制可用PDF （brew install tesseract和brew install imagemagick），但其中一个除外hocr2pdf。

我找不到OS X的端口。有没有可用的端口？如果不是，如何使用免费的开放源代码工具OCR编写多页PDF，并在OS X中以多页PDF重新获得结果？

#!/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_*

Tesseract 3.03+内置了对PDF输出的支持。需要安装leptonica。您可以使用： brew install tesseract --HEAD获得最新版本的tesseract。您还将需要安装ghostscript，但不需要hocr2pdf。

以下脚本使用ghostscript将PDF拆分为JPEG，使用tesseract对JPEG进行OCR，并输出单个PDF页面，最后再次使用ghostscript将页面重新组合为一个PDF。

#!/bin/sh

y="`pwd`/$1"
echo Will create a searchable PDF for $y

x=`basename "$y"`
name=${x%.*}

mkdir "$name"
cd "$name"

# splitting to individual pages
gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=jpeg -r300 -dTextAlphaBits=4 -o out_%04d.jpg -f "$y"

# process each page
for f in $( ls *.jpg ); do
  # extract text
  tesseract -l eng -psm 3 $f ${f%.*} pdf
  rm $f
done

# combine all pages back to a single file
gs -dCompatibilityLevel=1.4 -dNOPAUSE -dQUIET -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile="../${name}_searchable.pdf" *.pdf

cd ..
rm -rf "${name}"

# Adapted from: http://www.morethantechnical.com/2013/11/21/creating-a-searchable-pdf-with-opensource-tools-ghostscript-hocr2pdf-and-tesseract-ocr/
# from http://www.ehow.com/how_6874571_merge-pdf-files-ghostscript.html
# bash tut: http://linuxconfig.org/bash-scripting-tutorial
# Linux PDF,OCR: http://blog.konradvoelkel.de/2013/03/scan-to-pdfa/

我tesseract也在os x上使用。在这里简要地介绍一下如何使其自动化。