Document image decoding using iterated complete path search

The computation time of Document Image Decoding can be significantly reduced by employing heuristics in the search for the best decoding of a text line. By using a cheap upper bound on template match scores, up to 99.9% of the potential template matches can be avoided. In the Iterated Complete Path method, template matches are performed only along the best path found by dynamic programming on each iteration. When the best path stabilizes, the decoding is optimal and no more template matches need be performed. Computation can be further reduced in this scheme by exploiting the incremental nature of the Viterbi iterations. Because only a few trellis edge weights have changed since the last iteration, most of the backpointers do not need to be updated. We describe how to quickly identify these backpointers, without forfeiting optimality of the path. Together these improvements provide a 30x speedup over previous implementations of Document Image Decoding.