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HMM-Based Lexicon-Driven and Lexicon-Free Word Recognition for Online Handwritten Indic Scripts
April 2012 (vol. 34 no. 4)
pp. 670-682
S. Madhvanath, Genesys Telecom Labs., Chennai, India
A. Bharath, Hewlett-Packard Labs., Bangalore, India
Research for recognizing online handwritten words in Indic scripts is at its early stages when compared to Latin and Oriental scripts. In this paper, we address this problem specifically for two major Indic scripts-Devanagari and Tamil. In contrast to previous approaches, the techniques we propose are largely data driven and script independent. We propose two different techniques for word recognition based on Hidden Markov Models (HMM): lexicon driven and lexicon free. The lexicon-driven technique models each word in the lexicon as a sequence of symbol HMMs according to a standard symbol writing order derived from the phonetic representation. The lexicon-free technique uses a novel Bag-of-Symbols representation of the handwritten word that is independent of symbol order and allows rapid pruning of the lexicon. On handwritten Devanagari word samples featuring both standard and nonstandard symbol writing orders, a combination of lexicon-driven and lexicon-free recognizers significantly outperforms either of them used in isolation. In contrast, most Tamil word samples feature the standard symbol order, and the lexicon-driven recognizer outperforms the lexicon free one as well as their combination. The best recognition accuracies obtained for 20,000 word lexicons are 87.13 percent for Devanagari when the two recognizers are combined, and 91.8 percent for Tamil using the lexicon-driven technique.

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Index Terms:
natural language processing,handwritten character recognition,hidden Markov models,image representation,Tamil word samples,HMM based lexicon driven word recognition,lexicon free word recognition,online handwritten Indic scripts,Latin scripts,oriental scripts,hidden Markov models,phonetic representation,bag-of-symbols representation,handwritten Devanagari word,symbol writing orders,Writing,Hidden Markov models,Feature extraction,Handwriting recognition,Character recognition,Shape,Ink,Tamil.,Online handwriting recognition,word recognition,lexicon driven,lexicon free,bag of symbols,symbol order variation,Devanagari
S. Madhvanath, A. Bharath, "HMM-Based Lexicon-Driven and Lexicon-Free Word Recognition for Online Handwritten Indic Scripts," IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 34, no. 4, pp. 670-682, April 2012, doi:10.1109/TPAMI.2011.234
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