kraken is a turn-key OCR system forked from ocropus. It is intended to rectify a number of issues while preserving (mostly) functional equivalence.

If you already got a model trained for ocropus you can always expect it to work with kraken without all the fuss of the original ocropus tools.


kraken’s main features are:

Currently missing or underdocumented are:

  • Tests
  • New training interface

All functionality not pertaining to OCR and prerequisite steps has been removed, i.e. no more error rate measuring, etc.

Pull requests and code contributions are always welcome.



A vagrant virtual machine is also available on the hashicorp atlas. Run vagrant init openphilology/kraken && vagrant up to install without doing any compiling yourself.

kraken requires some external libraries to run. On Debian/Ubuntu they may be installed using:

# apt install libpangocairo-1.0 libxml2 libblas3 liblapack3 python-dev python-pip


It is no longer necessary to install the clstm python bindings manually. There are binary wheels (automatically installed) that should work for most Linux systems on PyPi; for non-x86 systems that need to build from source the dependencies listed in the clstm documentation need to be installed.

Because the build behavior of pip versions older than 6.1.0 interferes with the scipy build process numpy has to be installed before doing the actual install:

$ pip install numpy

Install kraken either from pypi:

$ pip install kraken

or by running pip in the git repository:

$ pip install .


While kraken is Python 2/3 compliant, there are limits to its compatibility. For various reasons it is not possible to use pickled models under Python 3. As the vast majority of models are still in the legacy format it is recommended to use Python 2.7. On the other hand all models in the central repository are converted to the fully upward compatible pronn format.

Finally you’ll have to scrounge up an RNN to do the actual recognition of characters. To download ocropus’ default RNN converted to the new format and place it in the kraken directory for the current user:

$ kraken get default

A list of libre models available in the central repository can be retrieved by running:

$ kraken list

Model metadata can be extracted using:

$ kraken show arabic-alam-al-kutub
name: arabic-alam-al-kutub.clstm

An experimental model for Classical Arabic texts.

Network trained on 889 lines of [0] as a test case for a general Classical
Arabic model. Ground truth was prepared by Sarah Savant
<> and Maxim Romanov <>.

Vocalization was omitted in the ground truth. Training was stopped at ~35000
iterations with an accuracy of 97%.

[0] Ibn al-Faqīh (d. 365 AH). Kitāb al-buldān. Edited by Yūsuf al-Hādī, 1st
edition. Bayrūt: ʿĀlam al-kutub, 1416 AH/1996 CE.
alphabet:  !()-.0123456789:[] «»،؟ءابةتثجحخدذرزسشصضطظعغفقكلمنهوىي ARABIC


Recognizing text on an image using the default parameters including the prerequisite steps of binarization and page segmentation:

$ kraken -i image.tif image.txt binarize segment ocr
Loading RNN     ✓
Processing      ⣻

To binarize a single image using the nlbin algorithm:

$ kraken -i image.tif bw.tif binarize

To segment a binarized image into reading-order sorted lines:

$ kraken -i bw.tif lines.json segment

To OCR a binarized image using the default RNN and the previously generated page segmentation:

$ kraken -i bw.tif image.txt ocr --lines lines.json

All commands and their parameters are documented, just add the standard --help flag for further information.

Training Tutorial

There is a training tutorial at Training a kraken model.


Kraken is provided under the terms and conditions of the Apache 2.0 License retained from the original ocropus distribution.