OCR with OpenCV and Tesseract (Installation Guide)

Introduction

Tesseract OCR provides some powerful algorithms for recognizing text in images. The text can be small, big, or skewed and this is managed through some flags in the algorithm. Another good feature is the ability to extract confidence values not only for the whole text, but to individual words and even letters.

OpenCV can be viewed as the state-of-the-art library for managing anything related to computer vision. It can be used to read in static images or ones from a camera, transform them to a form suitable for the OCR algorithm and apply it.

Note:

Since OpenCV 3.0, the Tesseract OCR has been integrated into the text module. For more information look at the official documentation (most likely here).

Installation

Installing OpenCV is relatively easy. It can be done either by using the version added to the PPA and using a package manager such as synaptic to install it. To compile the library from source, follow the instructions on their website.

To install Tesseract, you can either try

sudo apt-get install libtesseract-dev 

Or can compile it from source. To do so, you can use the following instructions (assuming you have 8 virtual core, otherwise calling to make should be done with the number of cores the current platform has):

  1. Initially, we need to install the base libs
sudo apt-get install libpng-dev libjpeg-dev libtiff-dev zlib1g-dev  
sudo apt-get install gcc g++  
sudo apt-get install autoconf automake libtools
  1. Getting Leptonica
wget http://www.leptonica.org/source/leptonica-1.70.tar.gz  
tar -zxvf leptonica-1.70.tar.gz  
cd leptonica-1.70  
./configure  
make -j8 -l8  
sudo make install  
sudo ldconfig
  1. Finally, installing Tesseract OCR
svn checkout http://tesseract-ocr.googlecode.com/svn/trunk/  
cd trunk/  
./autogen.sh  
./configure  
make -j8 -l8  
sudo make install  
sudo ldconfig  
sudo make install-langs

After following the instructions, the commands

pkg-config tesseract --libs 

and

pkg-config opencv --libs

should return something similar to

\-L/usr/local/lib -ltesseract  
# and  
/usr/local/lib/libopencv\_calib3d.so /usr/local/lib/libopencv\_contrib.so /usr/local/lib/libopencv\_core.so /\* and continue with all other modules \*/

 Sample Application

Now that we have everything installed, we need to test that it’s working. An easy way would be to construct a sample application. This will be done in the next article!

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Daniel Angelov
PhD Student Robotics and AI

Making actual robots smarter.

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