Reconstructing the Thera Frescoes: Automated Digitization and Matching of Fragments

The archaeological site of Akrotiri on the island of Thera (modern-day Santorini) has proven a treasure trove of information about Aegean civilization and culture. Among its most valued artifacts are wall paintings (frescoes), which have been preserved in the volcanic ash since the sixteenth century BCE. The frescoes, however, are typically recovered in fragments of a few centimeters to a few tens of centimeters in length, and reconstructing complete wall sections from the fragments occupies a major portion of the effort at Akrotiri. We propose to build a system that will assist archaeologists and conservators by digitizing excavated fragments and automatically proposing matches on the basis of color, 3-D shape, and other cues. Such systems have been researched before, for objects including frescoes, pottery shards, and inscribed marble slabs. For this project, however, our overriding goal is to leave an ongoing legacy: a combination of equipment and computer software that is sufficiently practical and easy to use that it will become an everyday part of excavation activities at Akrotiri. The system will have three major components: • Acquisition equipment. Beginning with commercially-available color and 3-D scanners, we will build a hardware configuration for capturing the color texture of each fragment, together with its thickness and 3-D shapes of the edges. We will write custom software to control the scanners, ensuring that capture is easy (may be performed by non-computer-experts) and fast (no more than a few minutes per fragment). All captured data will be stored together with semantic information about the fragment, as well as any annotations provided by archaeologists and conservators. • Matching algorithms. Building on recent research results, we will develop a system for computing candidate matches between fragments, and proposing them to the user for verification. We will explore different cues for performing this matching, including the 3-D shape of edges, fragment thickness, color and edges on the surface, any user-supplied annotations, and arbitrary combinations of different cues. • User interface. We will build a computer program that allows users to move fragments or groups of fragments on the screen, easily evaluating the proposed matches. The software will keep track of all information associated with each fragment, as well as with each match. The software will also include features such as revision control and support for concurrency, allowing multiple users to work either simultaneously or serially. On the basis of our past experience, we believe that such a system will successfully allow for a more rapid and more complete reconstruction of the wall paintings, with less handling of the physical fragments. The project will be carried out in cooperation with archaeologists and conservators at Akrotiri, led by the director of excavations, Christos Doumas. We propose to carry out the work beginning early in 2007, with major development complete by the beginning of the summer. Software development will be carried out by researchers and graduate students at Princeton University, and will be coordinated with a course taught at Princeton during the spring semester. This proposal describes in detail the components of the hardware and software systems that we will develop, together with our educational plan.