So Neri, Carli and Jacovitti solicited the help of Sanjit Mitra at the University of California at Santa Barbara. Both Neri and Carli had worked as visiting scientists in Mitra's research lab, which specializes in color filtering, or correcting, and color matching. "When Marco explained last summer that they were doing a pixel-based analysis, I suggested they also use texture," Mitra recalls. "In other words, not just one pixel but blocks of pixels. Blocks afford a much more robust approach, so that the process of searching and sorting is faster."

Mitra's group has explored this sort of texture-based sorting in the hopes of developing novel Internet search engines for the future. "Give me a barking dog or a rotating yellow bowl," offers Serkan Hatipoglu, a graduate student in Mitra's lab, by example, "but search not by using words but image features." Hatipoglu has spent four years on the problem, "trying to find features to distinguish images, so that I don't have to look at all the image information. I just extract features from texture patterns and compare those features to find similar images in a database."

In the case of the ruined frescoes, Hatipoglu applied this texture-based sorting to pick out plain cement. The team was thus able to quickly subtract from the fragments' images all those broken edges and three-dimensional faces that were not part of the original fresco¿a simplification that should make the task to matching up colors and details much easier.

If they ever get to that point. So far the scientists have had little contact with the actual restoration project in Assisi. Neri and Carli say that perhaps some of the restoration professionals found the idea of using computers distasteful. At any rate, based on their work with the Assisi frescoes, the researchers suggest that all earthquake-prone countries place on file extensive photographic surveys of their priceless works of art; should disaster strike, computers and image-processing techniques might then come to the rescue.

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