Ligature modeling for online cursive script recognition

Online recognition of cursive words is a difficult task owing to variable shape and ambiguous letter boundaries. The approach proposed in this paper is based on hidden Markov modeling of letters and inter-letter patterns called ligatures occurring in cursive script. For each of the letters and the ligatures we create one HMM that models temporal and spatial variability of handwriting. By networking the two kinds of HMMs, we can design a network model for all words or composite characters. The network incorporates the knowledge sources of grammatical and structural constraints so that it can better capture the characteristics of handwriting. Given the network, the problem of recognition is formulated into that of finding the most likely path from the start node to the end node. A dynamic programming-based search for the optimal input-network alignment performs character recognition and letter segmentation simultaneously and efficiently. Experiments on Korean character showed correct recognition of up to 93.3 percent on unconstrained samples. It has also been compared with several other schemes of HMM-based recognition to characterize the proposed approach.