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October 27, 2008

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Computer helps reassemble a lost past

Aug. 15, 2008
Courtesy Princeton University
and World Science staff

For dec­ades, ar­chae­o­lo­gists in Greece have been slowly re­assem­bling wall paint­ings from The­ra, an is­land civ­il­iz­a­tion bur­ied by vol­can­ic ash mil­len­nia ago.

The Her­cu­le­an jig­saw puz­zle—more than a cen­tu­ry of fur­ther work at the cur­rent pace—may soon get much eas­i­er, thanks to an com­put­er sys­tem be­ing de­vel­oped by Prince­ton Uni­ver­s­ity sci­en­tists work­ing with ar­chae­o­lo­gists in Greece.

A reassembled art­work from Thera, which was bu­ried under vol­can­ic ash more than 3,500 years ago. (Cour­tesy Prince­ton Graph­ics Group)
The sys­tem is still be­ing per­fected but has yielded prom­is­ing re­sults so far, sci­en­tists said: when tested on some frag­ments from one large paint­ing, it found 10 out of 12 al­ready known matches, and two more pre­vi­ously un­known.

The tech­nol­o­gy could “change the way peo­ple do ar­chae­o­lo­gy,” said com­put­er sci­ent­ist Da­vid Dob­kin, dean of the Prince­ton fac­ul­ty. Dob­kin and col­leagues re­port­ed on the work in a pa­per pre­sented Aug. 15 in Los An­ge­les at the As­socia­t­ion of Com­put­ing Machin­ery’s an­nu­al SIG­GRAPH con­fer­ence on com­put­er graph­ics.

Dobkin got the in­spira­t­ion for the proj­ect af­ter a 2006 vis­it to the site of Ak­ro­tiri The­ra, an an­cient cul­ture bur­ied more than 3,500 years ago at an is­land now known as San­to­rini. The Prince­ton team worked with the ar­chae­o­lo­gists and con­ser­va­tors at Ak­ro­tiri.

Re­build­ing an shattered fres­co, mo­sa­ic or si­m­i­lar ar­ti­fact is like solv­ing a gi­ant jig­saw puz­zle, but with no re­fer­ence pic­ture, thou­sands of ti­ny pieces—many badly erod­ed—and other frag­ments mis­sing.

Oth­er re­search­ers have tried to cre­ate com­put­er sys­tems to au­to­mate parts of the pro­cess, but re­lied on ex­pen­sive, un­wieldy equip­ment that had to be op­er­ated by com­put­er ex­perts, ac­cord­ing to the Prince­ton team. The new sys­tem, they said, uses inex­pen­sive, off-the-shelf hard­ware and is de­signed to be worked by ar­chae­o­lo­gists and con­ser­va­tors. The sys­tem mim­ics pro­ce­dures tra­di­tion­ally fol­lowed by ar­chae­o­lo­gists.

It “could re­duce the time needed to re­con­struct a wall from years to months,” free­ing up re­search­ers for oth­er im­port­ant work such as restora­t­ion and study, said Szy­mon Ru­sin­kie­wicz, a com­put­er sci­ent­ist whose re­search team led the Prince­ton ef­fort.

The team plans to return to the site this fall to per­ma­nently in­stall the sys­tem, said Prince­ton’s Tim Wey­rich, tech­ni­cal lead re­searcher on the proj­ect. But the sys­tem will nev­er re­place the ex­pe­ri­ence, con­tex­tu­al knowl­edge and “soft skills” of con­ser­va­tors and ar­chae­o­lo­gists, he added. “The com­put­er takes over the la­bo­ri­ous parts of the pro­cess while leav­ing the im­por­tant, in­tu­i­tive de­ci­sions to the hu­mans.”

* * *

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 Front image: Tim Weyrich, a postdoctoral teaching fellow in computer science at Princeton, examines fresco fragments in Santorini. (Cour­tesy Prince­ton Graph­ics Group)

 

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For decades, archaeologists in Greece have been slowly reassembling wall paintings from the Thera, an island civilization buried by volcanic ash millennia ago. The Herculean jigsaw puzzle—more than a century of further work at the current pace—may soon get much easier, thanks to an computer system being developed by Princeton University scientists working with archaeologists in Greece. The system is still being perfected but has yielded promising results so far, scientists said: when tested on some fragments from one large painting, it found 10 out of 12 already known matches, and two more previously unknown. The technology could “change the way people do archaeology,” said computer scientist David Dobkin, dean of the Princeton faculty. Dobkin and fellow researchers report on the work in a paper presented Aug. 15 in Los Angeles at the Association of Computing Machinery’s annual SIGGRAPH conference on computer graphics. Dobkin got the inspiration for the project after a 2006 visit to the site of Akrotiri Thera, an ancient culture buried more than 3,500 years ago at an island now known as Santorini. The Princeton team worked with the archaeologists and conservators working at Akrotiri. Rebuilding an excavated fresco, mosaic or similar artifact is like solving a giant jigsaw puzzle, but with thousands of tiny pieces—many badly eroded and lacking clear color, pattern or texture. Other researchers have tried to create computer systems to automate parts of the process, but relied on expensive, unwieldy equipment that had to be operated by computer experts, according to the Princeton team. The new system, they said, uses inexpensive, off-the-shelf hardware and is designed to be worked by archaeologists and conservators. The system mimics procedures traditionally followed by archaeologists. It “could reduce the time needed to reconstruct a wall from years to months,” freeing up researchers “for other valuable tasks such as restoration and ethnographic study,” said Szymon Rusinkiewicz, a computer scientist whose research team led the Princeton effort. The team is planning another trip to the site this fall to permanently install the system, said Princeton’s Tim Weyrich, technical lead researcher on the project. But the system will never replace the experience, contextual knowledge and “soft skills” of conservators and archaeologists, he added. “The computer takes over the laborious parts of the process while leaving the important, intuitive decisions to the humans.”