Warning: This document is for the development version of kraken. The latest version is 0.10.0.

kraken

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

Features

kraken’s main features are:

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.

Installation

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

# apt install libpangocairo-1.0 libxml2 libblas3 liblapack3 python3-dev python3-pip

pip

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:

$ pip3 install numpy

Install kraken either from pypi:

$ pip3 install kraken

or by running pip in the git repository:

$ pip3 install .

conda

If you are running Anaconda/miniconda, use:

$ conda install -c mittagessen kraken

Models

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
<sarah.savant@aku.edu> and Maxim Romanov <maxim.romanov@uni-leipzig.de>.

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
MADDAH ABOVE, ARABIC HAMZA ABOVE, ARABIC HAMZA BELOW

Quickstart

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.

License

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