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Information Processing & Management
Volume 41, Issue 1, January 2005, Pages 139-160
An Asian Digital Libraries Perspective
 
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doi:10.1016/j.ipm.2004.04.011    
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Copyright © 2004 Elsevier Ltd. All rights reserved.

Off-line isolated handwritten Thai OCR using island-based projection with n-gram model and hidden Markov models*1

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Thanaruk TheeramunkongCorresponding Author Contact Information, E-mail The Corresponding Author, a and Chainat WongtapanE-mail The Corresponding Author, b, 1

a Information Technology Program, Sirindhorn International Institute of Technology, Thammasat University, Pathumthani 12121, Thailand

b Department of Computer Science, Faculty of Science, Payap University, Chiangmai, Thailand


Available online 15 June 2004.

Abstract

Many traditional works on off-line Thai handwritten character recognition used a set of local features including circles, concavity, endpoints and lines to recognize hand-printed characters. However, in natural handwriting, these local features are often missing due to rough or quick writing, resulting in dramatic reduction of recognition accuracy. Instead of using such local features, this paper presents a method called multi-directional island-based projection to extract global features from handwritten characters. As the recognition model, two statistical approaches, namely interpolated n-gram model (n-gram) and hidden Markov model (HMM), are proposed. The experimental results indicate that the proposed scheme achieves high accuracy in the recognition of naturally-written Thai characters with numerous variations, compared to some common previous feature extraction techniques. Another experiment with English characters also displays quite promising results.

Author Keywords: Thai character recognition; Island-based projection; n-gram model; Hidden Markov models

Article Outline

1. Introduction
2. Previous feature extraction methods
3. Multi-directional island-based projection
3.1. Raw feature extraction
3.2. Numerosity reduction using clustering
4. n-gram and HMM for character recognition
4.1. Basic formulation of character recognition problem
4.2. Statistical approach
4.3. n-gram models for character recognition
4.4. HMMs for character recognition
5. The recognition scheme
6. Experimental results
6.1. Data set & model parameters
6.2. Basic experiments
6.3. Comparison to other feature extraction methods
6.4. Effect of the number of clusters and states
6.4.1. Application to English character recognition
7. Summary and result analysis
8. Conclusion and future works
Appendix A. Discussion materials
References















Corresponding Author Contact InformationCorresponding author. Tel.: +66-2-501-3505-20x2004; fax: +66-2-501-3524

*1 An earlier version of the paper was presented at the ICADL Conference.

1 Tel.: +66-53-304805x453.


Information Processing & Management
Volume 41, Issue 1, January 2005, Pages 139-160
An Asian Digital Libraries Perspective
 
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