1. Department of Algorithms And Their Applications, Faculty of Informatics, Eötvös Loránd University, Pázmány Péter sétány 1/C, H-1117, Budapest, Hungary. nhantos@inf.u-szeged.hu
2. Department of Image Processing and Computer Graphics, University of Szeged, Árpád tér 2. H-6720, Szeged, Hungary. pbalazs@inf.u-szeged.hu