Character recognition techniques associate a symbolic identity with the image of character. Character recognition is commonly referred to as optical character recognition (OCR), as it deals with the recognition of optically processed characters. The modern version of OCR appeared in the middle of the 1940’s with the development of the digital computers. OCR machines have been commercially available since the middle of the 1950’s. Today OCR-systems are available both as hardware devices and software packages, and a few thousand systems are sold every week.
In a typical OCR systems input characters are digitized by an optical scanner. Each character is then located and segmented, and the resulting character image is fed into a preprocessor for noise reduction and normalization. Certain characteristics are the extracted from the character for classification. The feature extraction is critical and many different techniques exist, each having its strengths and weaknesses. After classification the identified characters are grouped to reconstruct the original symbol strings, and context may then be applied to detect and correct errors.
Optical character recognition has many different practical applications. The main areas where OCR has been of importance are text entry (office automation), data entry (banking environment) and process automation (mail sorting).
The present state of the art in OCR has moved from primitive schemes for limited character sets, to the application of more sophisticated techniques for omnifont and handprint recognition. The main problems in OCR usually lie in the segmentation of degraded symbols which are joined or fragmented. Generally, the accuracy of an OCR system is directly dependent upon the quality of the input document. Three figures are used in ratings of OCR systems; correct classification rate, rejection rate and error rate. The performance should be rated from the systems error rate, as these errors go by undetected by the system and must be manually located for correction.
In spite of the great number of algorithms that have been developed for character recognition, the problem is not yet solved satisfactory, especially not in the cases when there are no strict limitations on the handwriting or quality of print. Up to now, no recognition algorithm may compete with man in quality. However, as the OCR machine is able to read much faster, it is still attractive.
In the future the area of recognition of constrained print is expected to decrease. Emphasis will then be on the recognition of unconstrained writing, like omnifont and handwriting. This is a challenge which requires improved recognition techniques. The potential for OCR algorithms seems to lie in the combination of different methods and the use of techniques that are able to utilize context to a much larger extent than current methodologies. May be exchanged electronically or printed in a more computer readable form, for instance barcodes.
The applications for future OCR-systems lie in the recognition of documents where control over the production process is impossible. This may be material where the recipient is cut off from an electronic version and has no control of the production process or older material which at production time could not be generated electronically. This means that future OCR-systems intended for reading printed text must be omnifont.
Another important area for OCR is the recognition of manually produced documents.
Within postal applications for instance, OCR must focus on reading of addresses on mail produced by people without access to computer technology. Already, it is not unusual for companies etc., with access to computer technology to mark mail with barcodes. The relative importance of handwritten text recognition is therefore expected to increase.
[Source]: Line Eikvil, "Optical Character Recognition", available at: “citeseer.ist.psu.edu/142042.html".