Knowledge based search of character strings in line drawings

In this paper, we present a system for singling out character strings from line drawings. Characters, candidate according to a preliminary selection, are replaced with rectangles preserving information about character size, position and orientation. Rectangles are clustered on the basis of a set of criteria. Each cluster is seen as a graph whose nodes represent rectangles, while arcs represent their possible connections, established on the basis of properly defined visibility criteria. Strings within clusters are searched, in a proper state space, according to a hierarchy derived from the knowledge of the problem, injected by means of models representing the most common configurations of strings in terms of their topological and geometrical properties. The system is implemented in an object-oriented fashion. Experimental results on a large set of documents of different types are reported