$ find /dir/to/search -name *.tif -size -90M -exec ls -lh {} \;

Get just the size and path and write to a file:

$ find /dir/to/search -name *.tif -size -90M -exec ls -lh {} \; | awk '{print $5 , $8}' > output.txt

Useful for finding images that might have been scanned at the wrong resolution/bit depth/etc.

I remembered seeing a few years ago that HP had open-sourced their OCR engine, Tesseract, development of which has now been taken over by Google. Tesseract is supposedly very good at what it does, namely, recognizing characters in images.

Tesseract does not, however, have many essential features found in modern OCR software, including document layout analysis and output formatting. That’s where OCRopus comes in. I think of it as a wrapper around Tesseract, capable of doing the layout analysis and providing formatted output. In truth, it can do much more than that, and different OCR engines and other components can be plugged into OCRopus, but the preceding simplification works for my purposes.

Usage

Use OCRopus with a simple call from the command line:

$ ocroscript recognize /path/to/file.png > /path/to/output.html

OCRopus will work its magic on file.png and give you an hOCR file. hOCR uses class and title attributes in an otherwise simple HTML file to embed layout information into the recognized text. I hope soon to create a script to transform the hOCR into a PDF; I’ll post more when it’s ready.

Installation

The trickiest part of using OCRopus is the installation. There are quite a few dependencies and some inaccurate documentation, so I made a few wrong turns along the way. Fortunately, I remembered to document what I was doing as I went. The instructions below represent the necessary steps to have an operable installation of OCRopus on Linux Mint as of 2009-03-27. For the record, I’m starting in /var/tmp.

Install Tesseract

As mentioned above, Tesseract is the OCR engine that powers OCRopus.

$ svn checkout http://tesseract-ocr.googlecode.com/svn/trunk/ tesseract-ocr-read-only
$ cd tesseract-ocr-read-only
$ ./configure
$ make
$ sudo make install
$ cd ..

Install iulib

iulib provides some basic image processing libraries used by OCRopus.

$ svn checkout http://iulib.googlecode.com/svn/trunk/ iulib
$ cd iulib
$ sudo apt-get install scons
$ sudo apt-get install libpng12-dev libjpeg62-dev libtiff4-dev libavcodec-dev libavformat-dev libsdl-gfx1.2-dev libsdl-image1.2-dev
$ sudo apt-get install imagemagick
$ scons
$ sudo scons install
$ cd ..

Install Leptonica

Leptonica provides more image processing and layout analysis capabilities.

$ wget http://leptonica.googlecode.com/files/leptonlib-1.60.tar.gz
$ tar xvzf leptonlib-1.60.tar.gz
$ cd leptonlib-1.60
$ ./configure
$ make
$ sudo make install
$ cd ..

Install OpenFST

OpenFST provides language modeling code to OCRopus. Note that this takes a while (a couple of hours for me) to compile.

$ wget http://mohri-lt.cs.nyu.edu/twiki/pub/FST/FstDownload/openfst-1.1.tar.gz
$ tar xvzf openfst-1.1.tar.gz
$ cd openfst-1.1
$ ./configure
$ make
$ sudo make install
$ cd ..

Install OCRopus

We now have all our dependencies installed, so it’s time to install OCRopus.

$ sudo apt-get install libeditline-dev
$ svn checkout http://ocropus.googlecode.com/svn/trunk/ ocropus
$ cd ocropus
$ ./configure
$ make
$ sudo make install

Update (2009-04-01): OCRopus is still young and has many bugs. One particularly annoying bug, one that is quite easy to fix: the Doctype declaration for the hOCR file was missing some quotes, rendering the XHTML invalid. I’ve submitted a patch. So, some slightly revised installation instructions, picking up in the ocropus directory:

$ wget http://xplus3.net/downloads/fix_ocropus_doctype.diff
$ patch -p0 -i fix_ocropus_doctype.diff
$ ./configure
$ make
$ sudo make install

Rather than wiping a hard disk, or even dual-booting, I opted to go with a less committed approach. I’ve set up a virtual computer to run within Windows Vista. I tried Microsoft Virtual PC first, but I never got past the boot stage (on several Linux distributions) before it collapsed into a whimpering heap of self-contradiction. Not dissuaded, I gave Sun’s VirtualBox a try, and it worked admirably.

So I now have Linux Mint 6 installed within VirtualBox within Vista. From what I’ve read about the distribution, it’s a lot like Ubuntu, with a few additional tools to make it easier for the uninitiated to use. I have two monitors, so I’ve pretty much just dedicated one to displaying Windows and one to displaying Linux.

So far, my experience has been pretty good. For basic basic usage (i.e., Internet browsing, word processing, etc.), it seems as easy to use as Windows. mintInstall, the software installation program that comes bundled with Linux Mint, makes installation of the thousands of common software packages very easy, and apt-get fills in where mintInstall leaves off. I had XChat running happily withing moments, something I still haven’t figured out how to do on Vista. I still have a bit of learning to do inside the terminal, but I’m making progress.

As I run across obstacles, I’ll try to post them here (with their solutions, I hope) so I can remember how to do things again later.