ACM Reference Format Brown, B., Toler–Franklin, C., Nehab, D., Burns, M., Dobkin, D., Vlachopoulos, A., Doumas, C., Rusinkie- wicz, S., Weyrich, T. 2008. A System for High–Volume Acquisition and Matching of Fresco Fragments: Reassembling Thetan Wall Paintings. ACM Trans. Graph. 27, 3, Article 84 (August 2008), 9 pages. DOI = 10.1145/1360612.1360683 http://doi.acm.org/10.1145/1360612.1360683. Copyright Notice Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or direct commercial advantage and that copies show this notice on the first page or initial screen of a display along with the full citation. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, to redistribute to lists, or to use any component of this work in other works requires prior specific permission and/or a fee. Permissions may be requested from Publications Dept., ACM, Inc., 2 Penn Plaza, Suite 701, New York, NY 10121-0701, fax +1 (212) 869-0481, or permissions@acm.org. © 2008 ACM 0730-0301/2008/03-ART84 $5.00 DOI 10.1145/1360612.1360683 http://doi.acm.org/10.1145/1360612.1360683 A System for High-Volume Acquisition and Matching of Fresco Fragments: Reassembling Theran Wall Paintings Benedict J. Brown ∗ Corey Toler-Franklin ∗ Diego Nehab † Michael Burns ∗ David Dobkin ∗ Andreas Vlachopoulos ‡ Christos Doumas § Szymon Rusinkiewicz ∗ Tim Weyrich ∗ Figure 1: Our acquisition system, deployed at the Akrotiri Excavation, Thera. We use a flatbed scanner to capture high-resolution images and normals of wall painting fragments (shown at left), and multiple 3-D scanners to acquire geometry. A single user can operate up to four scanners simultaneously, while a second user operates the flatbed scanner and verifies processing results. This yields a throughput of approximately 10 fragments per hour. Our matching algorithm correctly finds the only two matches in this data set using the scanned 3-D geometry. Abstract Although mature technologies exist for acquiring images, geom- etry, and normals of small objects, they remain cumbersome and time-consuming for non-experts to employ on a large scale. In an archaeological setting, a practical acquisition system for routine use on every artifact and fragment would open new possibilities for archiving, analysis, and dissemination. We present an inexpensive system for acquiring all three types of information, and associated metadata, for small objects such as fragments of wall paintings. The acquisition system requires minimal supervision, so that a single, non-expert user can scan at least 10 fragments per hour. To achieve this performance, we introduce new algorithms to robustly and au- tomatically align range scans, register 2-D scans to 3-D geometry, and compute normals from 2-D scans. As an illustrative applica- tion, we present a novel 3-D matching algorithm that efficiently searches for matching fragments using the scanned geometry. 1 Introduction Computer-based acquisition and processing of 3-D shape and re- flectance data has proven its potential to revolutionize certain kinds of research in the humanities and social sciences. However, previ- ous “computational humanities” projects have necessarily involved significant manual labor and nontrivial participation by computer scientists. This is because the tools for high-throughput 3-D scan- ning, calibrated reflectance measurement, systematic organization ∗ Princeton University. {bjbrown,ctoler,mburns,dpd,smr,tweyrich}@cs.princeton.edu † Microsoft Research. nehab@microsoft.com, work conducted while at Princeton University ‡ Akrotiri Excavation, Thera § National University of Athens and Akrotiri Excavation, Thera of acquired data, and applications such as 3-D shape search have been in the realm of research, rather than production. As these technologies mature, their availability to non-computer experts can be broadened by solving the crucial problems of scalability and us- ability. This paper focuses on the associated technical challenges. We describe how to integrate acquisition and processing tools recently developed in the computer graphics field into a system suit- able for large-scale archaeological documentation and reconstruc- tion. Although we present our work in the context of a case-study, described below, our methods for rapid acquisition by non-experts, automatic and robust 3-D reconstruction, user-focused workflow, and scalable 3-D search are applicable to many archaeological ex- cavations and cultural heritage projects, and could be deployed broadly with minimal incremental development effort. We focus on the specific problem of documenting and recon- structing fragments of wall paintings from the site of Akrotiri on the volcanic island of Thera (modern-day Santorini, Greece). An eruption destroyed the ancient civilization, burying the remains of a flourishing Late Bronze Age (c. 1630 B.C.) settlement in ash, similar to Pompeii. Excavations have yielded an unparalleled trove of artifacts and information from the prehistoric Aegean, includ- ing numerous wall paintings ranging from naturalistic and narrative scenes to abstract motifs [Doumas 1992]. Uniquely, much of the original plaster material remains at Akrotiri; from the tens of thousands of small lime-plaster fragments uncovered at the site (typically less than 10 cm across and less than 1 cm thick), it is possible to largely reconstruct interior walls of buildings and thereby recover important clues to the culture, tech- nology, and architecture of ancient Thera. The fragments tested in this paper come from a huge wall painting (approximately 5.20 m × 3.20 m) depicting symmetrical pairs of spirals (Figure 15); the original wall was not preserved at all. Thus, the restoration of this composition is also important to studying the architecture and func- tion of the collapsed third floor of the building [Vlachopoulos 2008, 454, Figure 41.47–50]. At Akrotiri, as at other excavations, recent computer graphics research may significantly improve the quality of artifact documen- tation and reduce the human labor involved in matching the “jigsaw puzzle” of fragments (currently estimated at 75% of the total human effort at the site), freeing up time for other important tasks includ- ing conservation and restoration. For example, 3-D scanning may provide more complete documentation of the state of excavated fragments; registration algorithms may be used to align the 3-D ACM Transactions on Graphics, Vol. 27, No. 3, Article 84, Publication date: August 2008.