Ensembles for Graph-Based Keyword Spotting in Historical Handwritten Documents

Keyword Spotting (KWS) offers a convenient way to improve the accessibility to historical handwritten documents by retrieving search terms in scanned document images. The approach for KWS proposed in the present paper is based on segmented word images that are represented by means of different types of graphs. The actual keyword spotting is based on matching a query graph with a set of document graphs using the concept of graph edit distance. In particular, we propose to employ ensemble methods for KWS with graphs. That is, a query graph is not matched against one but several different graphs representing the same document word. Eventually, we use different strategies to combine these individual graph dissimilarities. In an experimental evaluation on two benchmark datasets, the proposed ensemble methods outperform the individual ensemble members as well as four state-of-the-art reference systems based on dynamic time warping.