SHORT PAPER Matching Islamic patterns in Kufic images Damla Arifoglu • Emre Sahin • Hande Adiguzel • Pinar Duygulu • Mehmet Kalpakli Received: 2 October 2011 / Accepted: 16 November 2014 / Published online: 21 January 2015 Ó Springer-Verlag London 2015 Abstract In this study, we address the problem of matching patterns in Kufic calligraphy images. Being used as a decorative element, Kufic images have been designed in a way that makes it difficult to be read by non-experts. Therefore, available methods for handwriting recognition are not easily applicable to the recognition of Kufic pat- terns. In this study, we propose two new methods for Kufic pattern matching. The first method approximates the con- tours of connected components into lines and then utilizes chain code representation. Sequence matching techniques with a penalty for gaps are exploited for handling the variations between different instances of sub-patterns. In the second method, skeletons of connected components are represented as a graph where junction and end points are considered as nodes. Graph isomorphism techniques are then relaxed for partial graph matching. Methods are evaluated over a collection of 270 square Kufic images with 8,941 sub-patterns. Experimental results indicate that, besides retrieval and indexing of known patterns, our method also allows the discovery of new patterns. Keywords Cultural heritage  Calligraphy  Kufic  Sequence matching  Graph matching 1 Introduction Decorative inscriptions have been used both in Western and Eastern cultures throughout the history. As depicting humans in art is discouraged in Islam, geometric patterns and calligraphy have been the main form of artistic expression in Islamic cultures. 1 Kufic is one of the oldest calligraphic forms of the various Islamic scripts. Kufic derives its name from the city of Kufa, where it was developed around the eighth century, and until about the eleventh century, it was the main script used to copy Qur’ans. It has been mainly used as a deco- rative element in manuscripts, pottery, coins, architecture, stone inscriptions, and wooden work for several centuries [1–4], with the proverbs and passages from the Qur’an being used as dominant sources. Its influence on European art during the Middle Ages or the Renaissance can also be recognized, and the resulting style is known as pseudo- Kufic or Western-Kufic. Among the three Kufic scripts-written, Ma’qeli Kufic, also known as square Kufic, has been the most common Kufic types used in decoration and encountered in many different forms at historical buildings [5] (see Fig. 1). Analysis of Kufic scripts may shed light to a relatively unknown era in history and therefore is of interest to scholars around the world. Moreover, for a regular person visiting a historical site, it is the taste of a treasure hunt to discover repeating words and phrases in complex Kufic patterns (see Fig. 2). However, even for a person whose D. Arifoglu (&)  E. Sahin  H. Adiguzel  P. Duygulu Department of Computer Engineering, Bilkent University, Ankara 06800, Turkey e-mail: damla.arifoglu@gmail.com E. Sahin e-mail: i.emre.sahin@gmail.com H. Adiguzel e-mail: handee.a@gmail.com P. Duygulu e-mail: pinar.duygulu@gmail.com M. Kalpakli Department of History, Bilkent University, Ankara 06800, Turkey e-mail: kalpakli@bilkent.edu.tr 1 http://en.wikipedia.org/wiki/Islamic_calligraphy. 123 Pattern Anal Applic (2015) 18:601–617 DOI 10.1007/s10044-014-0437-z