Configuring OCR engine
OpenKM can work with several OCR engines, like Tesseract.
OpenKM can be integrated with any OCR engine that can be executed from the command line.
Tesseract
Check the list of supported languages at https://tesseract-ocr.github.io/tessdoc/Data-Files-in-different-versions.html
More information about installation on different operating systems and Linux distros at https://tesseract-ocr.github.io/tessdoc/Installation.html
Tesseract is an open-source OCR engine adopted by Google. It works really well. OCR can read TIFF documents natively and has a high recognition rate with images at 300 dpi resolution that have been converted to line art (1-bit color).
The supported image formats are:
- TIFF
- PNG
- JPG
- GIF
Installation
| OS | Description |
|---|---|
|
Ubuntu and Debian |
$ apt install tesseract-ocr 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: $ apt install tesseract-ocr-spa You can check the installed languages this way: $ tesseract --list-langs More information at: |
|
Red Hat and CentOS |
In CentOS you can install Tesseract from the EPEL repository: $ yum install epel-release 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: $ yum install tesseract-langpack-spa You can check the installed languages this way: $ tesseract --list-langs In Red Hat, we recommend contacting Red Hat support for more information. More information at: |
|
Windows |
Download from https://tesseract-ocr.github.io/tessdoc/Installation.html and follow the installation wizard. |
Check installation
From the command line, execute (where image.jpg should be an existing image file):
$ tesseract image.jpg text
The file image.jpg is an image file.
If all goes well, a file named text.txt that contains the extracted text will be created.
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 should be used when executing OCR. To see all Tesseract options, execute: $ tesseract
|
|
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 should be used when executing OCR. To see all Tesseract options, execute: c:\Tesseract-ocr-3.0.2> tesseract.exe |
|
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. Each parameter is separated by a single space. |
|
Once configured, please go to Administration > Utilities > Plugins, choose com.openkm.plugin.extractor.TextExtractor from the Select menu and enable the TesseractTextExtractor plugin
Additional information
- http://code.google.com/p/tesseract-ocr/
- Tesseract - Summary & first experiences.
- Tesseract OCR Google Groups
- First Interactions with Tesseract OCR on Ubuntu Linux
- http://code.google.com/p/tesseract-ocr/wiki/ReadMe
- http://code.google.com/p/tesseract-ocr/wiki/FAQ
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
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 |
Dictionaries come in .zip or .oxt format. You can use both.
OCR rotate configuration
There's a configuration parameter that forces OCR on rotated documents.
The feature is useful, for example, for upside-down scanned pages, where standard OCR would fail.
When the feature is enabled, the operation will be performed on all OCR extractions, which can have undesired effects on the OCR templates feature.
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; |
