αρογη ´- A System for the Virtual Aided Recomposition of Fragmented Frescos

Abstract. The paper describes a digital system for the virtual aided recomposition of fragmented frescos, an innovative approach that is being developed and proved on the St. Matthew’s fresco, painted by Cimabue in the Upper Church of St. Francis in Assisi which had an extension of 35 squared meters and broke into more than 140.000 pieces during the earthquake in 1997. The base level of the designed system transposes the traditional recomposition process in a digital way: the laboratory of fragments in Assisi, used for the traditional recomposition, becomes a client-server architecture that can be geographically distributed. Several operators can jointly work on the same fresco from different clients connected over Internet to a server, situated in our Institute in Bari, where a database has been designed and realized to contain the digital image of each single fragment. Several further features have been added to improve the efficiency and efficacy of the recomposition process. The database is indexed using a query-by-example approach applied to suitable sample images (fragments and/or details extracted from the reference image of the whole fresco). Colour and texture has been used as features to describe the pictorial content of fragments. Since the only available picture of the whole fresco has been acquired in unknown conditions and exhibits colours significantly different from those of fragments, it has been necessary to estimate and apply suitable and specific colour transformations to different regions of the reference image to make meaningful their comparison. The restorers of the Central Institute for Restoration, which cooperates in this project, are very interested in this strongly innovative approach. They are working on the St. Matthew’s fresco using the system and have pointed out several advantages that the system brings into their work as long as many new features that can enrich its possibilities. 1