Warning: This document is for an old version of kraken. The latest version is 0.10.0.


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:

  • Clean public API
  • Tests
  • New training interface (certainly only for CLSTM)

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

Pull requests and code contributions are always welcome.


While kraken does not require a working C compiler on run-time anymore numpy and scipy compilation still requires build-essential or your distributions equivalent and some dependencies.

# apt-get install gcc gfortran python-dev libblas-dev liblapack-dev libpangocairo-1.0

If clstm support is desired (highly recommended) the associated python extension has to be build and 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


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.txt 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.txt


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