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Configuring OCR engine

OpenKM can work with several OCR engines, like Tesseract.

Tesseract

Section titled “Tesseract”

Tesseract is an open-source OCR engine adopted by Google. It works really well. OCR can natively read TIFF documents and has a high recognition rate with images of 300 dpi resolution that are converted to lineart (1-bit color).

The supported image formats are:

  • TIFF
  • PNG
  • JPG
  • GIF

Installation

Section titled “Installation”
OS Description
Ubuntu and Debian bash<br>$ apt install tesseract-ocr<br>
The default installed language is English, so depending on your locale you may want to install another language file.
For example, to install the Spanish language pack:
bash<br>$ apt install tesseract-ocr-spa<br>
You can check the installed languages this way:
bash<br>$ tesseract --list-langs<br>
More information at:
- https://github.com/tesseract-ocr/tesseract
- https://tesseract-ocr.github.io/tessdoc/Installation.html
Red Hat and CentOS On CentOS, you can install Tesseract from the EPEL repository:
bash<br>$ yum install epel-release<br>$ yum install tesseract<br>
The default installed language is English, so depending on your locale you may want to install another language file.
For example, to install the Spanish language pack:
bash<br>$ yum install tesseract-langpack-spa<br>
You can check the installed languages this way:
bash<br>$ tesseract --list-langs<br>
On Red Hat, we recommend contacting Red Hat support for more information.
More information at:
- https://tesseract-ocr.github.io/tessdoc/Installation.html
Windows Download from https://tesseract-ocr.github.io/tessdoc/Installation.html and follow the installation wizard.

Check installation

Section titled “Check installation”

From the command line, execute (where image.jpg should be an existing image file):

Terminal window
$ tesseract image.jpg text

Configuration

Section titled “Configuration”

Go to Administration > Configuration parameters and edit the parameter named system.ocr:

OS
Linux /usr/bin/tesseract ${fileIn} ${fileOut}
or
/usr/bin/tesseract ${fileIn} ${fileOut} -l esp
The parameter -l esp indicates that the Spanish language support must be used while executing OCR.
To see all Tesseract options, execute:
bash<br>$ tesseract<br>
Windows c:\Tesseract-ocr-3.0.2\tesseract.exe ${fileIn} ${fileOut}
or
c:\Tesseract-ocr-3.0.2\tesseract.exe ${fileIn} ${fileOut} -l spa
The parameter -l esp indicates that the Spanish language support must be used while executing OCR.
To see all Tesseract options, execute:
bash<br>c:\Tesseract-ocr-3.0.2> tesseract.exe<br>
  • The parameter ${fileIn} will be replaced internally by the image document to be processed.
  • The parameter ${fileOut} will be replaced internally by a temporary text file.
  • You can set other additional parameters like the -l spa parameter in the example.

Additional information

Section titled “Additional information”

Dictionary

Section titled “Dictionary”

You can also use an OpenOffice.org dictionary to enhance the OCR process. You can find these language-specific dictionaries at OpenOffice.org Dictionary Repository.

Configuration

Section titled “Configuration”

Go to Administration > Configuration parameters and edit the parameter named system.openoffice.dictionary:

OS
Linux /home/openkm/dictionary/en-GB.zip
Windows c:\tomcat-8.5.69\dictionary\en-GB.zip

OCR rotate configuration

Section titled “OCR rotate configuration”

There’s a configuration parameter that forces OCR on rotated documents.

Configuration

Section titled “Configuration”

Go to Administration > Configuration parameters and edit the parameter named system.ocr.rotate:

Property Description
system.ocr.rotate The parameter is a collection of degrees separated by the character “;”.
90;180;270;

Additional information:

Section titled “Additional information:”