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 command line.
OpenKM comes with a TextExtractor plugin for each OCR engine. Only must be a single TextExtractor enabled based on your current OCR engine.
List of OCR TextExtractors:
- com.openkm.extractor.Tesseract3TextExtractor ( can be used for tesseract version 3.x and 4.x )
- com.openkm.extractor.Tesseract2TextExtractor
The most common configuration is to only have enabled the plugin com.openkm.extractor.Tesseract3TextExtractor.
More information about plugins at Administration > Utilities > Plugins
Tesseract
Check the list of supported languages at https://tesseract-ocr.github.io/tessdoc/Data-Files-in-different-versions.html
Tesseract is an Open Source OCR engine adopted by Goggle. It works really well. The OCR natively can read TIFF documents and has hight ratio of recognition with images 300 dpi of resolution and converted to lineart (1 bit color).
The supported image formats are:
- TIFF
- PNG
- JPG
- GIF
Installation
| OS | Description |
|---|---|
|
Ubuntu and Debian |
$ apt-get install tesseract-ocr tesseract-ocr-eng Depending on your locale you would like to install other language file. More information at: |
|
Red Hat and CentOS |
More information at: |
|
Windows |
Download from https://code.google.com/p/tesseract-ocr/ and follow the installation wizard. |
Check installation
From 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 right a file named text.txt what 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 indicate must be used the Spanish language support while 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 indicate must be used the Spanish language support while executing OCR. To see all tesseract options execute: c:\Tesseract-ocr-3.0.2> tesseract.exe |
|
Parameter ${fileIn} will be replaced internally by image document to be processed. Parameter ${fileOut} will be replaced internally by temporal text file. Can set other additional parameters like -l spa parameter in example. Each parameter is separated by a single "white space". |
|
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. 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-7.0.61\dictionary\en-GB.zip |
Dictionaries comes in .zip or oxt format. Can use both.
OCR rotate configuration
There's a configuration parameter that force document ocr on rotated document.
The feature is useful for example in upside down scanned pages, where standard OCR direction will fails.
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 character ";" 0;90;180;270; |