Symbol recognition by error-tolerant subgraph matching between region adjacency graphs

In this paper, we propose an error-tolerant subgraph isomorphism algorithm formulated in terms of Region Adjacency Graphs (RAG). A set of edit operations to transform one RAG into another one are defined. Regions are represented by polylines and string matching techniques are used to measure their similarity. The algorithm follows a branch and bound approach driven by the RAG edit operations. This formulation allows matching computing under distorted inputs and also reachong a solution in a near polynomial time. The algorithm has been used for recognizing symbols in hand drawn diagrams.