The Delaunay Document Layout Descriptor

Security applications related to document authentication require an exact match between an authentic copy and the original of a document. This implies that the documents analysis algorithms that are used to compare two documents (original and copy) should provide the same output. This kind of algorithm includes the computation of layout descriptors from the segmentation result, as the layout of a document is a part of its semantic content. To this end, this paper presents a new layout descriptor that significantly improves the state of the art. The basic of this descriptor is the use of a Delaunay triangulation of the centroids of the document regions. This triangulation is seen as a graph and the adjacency matrix of the graph forms the descriptor. While most layout descriptors have a stability of 0% with regard to an exact match, our descriptor has a stability of 74% which can be brought up to 100% with the use of an appropriate matching algorithm. It also achieves 100% accuracy and retrieval in a document retrieval scheme on a database of 960 document images. Furthermore, this descriptor is extremely efficient as it performs a search in constant time with respect to the size of the document database and it reduces the size of the index of the database by a factor 400.