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Virtual puzzle
reconstructs archaeological pieces
Software developed at IC recomposes relics from digitized photographs

MANUEL ALVES FILHO

EAmid countless activities linked to teaching and research, professor Jorge Stolfi, from Unicamp's Computing Institute (IC), still finds time to dedicate himself to puzzles. These are not, however, games that can be found in any toy store, although they bear some similarity to them. The teacher's “hobby”, guided by extreme scientific rigor, represents a new stage in relation to a study developed for the doctoral thesis of one of his students, Helena Cristina da Gama Leitão, defended in 1999. With the help of software and using digitized photos of fragments of archaeological pieces, Stolfi seeks to virtually recompose relics that, despite their eventual material value, help tell a part of Brazil's history. Without the computational tool, which was successfully tested on flat surfaces and is now beginning to be used to assemble images in three dimensions (3D), the tendency would be for many of these objects to never have the chance to regain their shape.

Fragments of historical relics belonging to the Brazilian Archaeological Institute (IAB): pieces are being photographed from 12 different positions and angles, so that software developed by Unicamp's Computing Institute (IC) can find the corresponding pairs and the object has the chance to be virtually reconstituted

Stolfi says that the idea of ​​developing the computer program arose from a practical problem, frequently faced by archaeologists. Much of the material found at an archaeological site is made up of ceramic fragments. Not infrequently, these shards are left on site, as it would be very expensive to remove them, or they are collected and stored in boxes or bags, which end up in the basements of museums, due to the difficulty of fitting them together and forming a complete piece again. . “Often, a single vase is fragmented into thousands of pieces, many of which are similar. To put this object back together would take a long time and require properly trained personnel,” he explains. With this in mind, the professor proposed to his postgraduate student that she develop software, whose function would be precisely to identify, in a collection of fragments, which of them matched each other.

To do this, Stolfi and his student carried out a controlled experiment. In other words, they produced artificial fragments from common ceramics used in construction. Because they were flat, the pieces were placed directly on the scanner, thus generating digitized images. Then, the shards had their contours outlined, so that they could be compared to each other. “As our interest was to solve a computing problem, we had to develop a method that had two important characteristics. First, it was capable of analyzing thousands of fragments. Second, that a real marriage could be found between two couples, even if this marriage was not perfect, due to the damage they normally present”, he explains.

The challenge was finally overcome and the software proved to be efficient in finding the real pairs and thus reconstituting the piece virtually. From the image on the computer screen, says the IC professor, it is also possible to reconstruct the piece on the material plane, numbering each fragment. “In other words, the puzzle is easy to put together, as piece number one fits with piece number two and so on”, teaches Stolfi. The tool, therefore, reduces the time that would be spent if the work was done manually, based on trial and error. It should be noted that, as the number of fragments is multiplied by ten, the time required to find the real pairs manually is 100 times greater.

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Third dimension

Professor Jorge Stolfi: model allows analysis of thousands of fragments

The doctoral thesis that generated the software also gave rise to an article that was published earlier this year. The text, according to Professor Stolfi, had a good response among the international scientific community. Now, the IC professor is faced with a new challenge, which is to use the tool to try to recompose archaeological pieces in the third dimension. The work has the collaboration of now professor Helena Cristina, who teaches at the Fluminense Federal University (UFF). She is photographing the ceramics collection at the Brazilian Archaeological Institute (IAB) with a digital camera. Each piece is being photographed at least 12 times, from several different angles, in order to record its three-dimensional shape.

Once this work is completed, the software will also identify matching pairs. The expectation is that some pieces will begin to have their three-dimensional format virtually recomposed within a year. Eventually, some objects may also be reconstructed on the material plane. “This is important, as a vase, a statue or a fresco is capable of revealing, for example, aspects of the culture and level of development of a certain people, at a given time”, analyzes Stolfi. Currently, according to the IC professor, archeology has used database technology to try to reassemble historical relics. In this approach, the archaeologist manually codes the fragments by colors, figures or other attributes, and the tool points out the corresponding fittings. “But this has not been useful for ceramic objects, as the colors vary a lot within the same piece.”

In Egypt, for example, archaeologists recently found a tomb in which the ceiling frescoes had collapsed. Because of this, they gave up on entering the site to preserve it. “As these fragments were not damaged, it is quite possible that our method would work in this case and help reconstruct these frescoes”, predicts Stolfi. According to him, the technique put at the service of archeology could also be used by bioinformatics, to find pairs of fragments in a protein sequence. The research conducted by the IC professor and his colleague from UFF has, in recent years, received financial support from Faperj, Capes and CNPq.

 

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