THE most maddeningly difficult jigsaw puzzle would be a walkover for a new
software package. Its authors say it could piece together priceless frescoes
destroyed by an earthquake in 1997. The frescoes by Giotto were shattered when
an earthquake hit the 13th-century Basilica of St Francis in Assisi, about 130
kilometres north of Rome.
Anyone who has put a jigsaw together knows how difficult it is to match up
pieces containing similar colours. In the smashed frescoes, the task of figuring
out where each tiny piece belongs could take years.
A computer, however, might do it in a matter of minutes with the right
program. So after digitally scanning every broken shard, researchers attempted
to match the digital image to detailed photographs taken before the earthquake
happened.
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But the first attempts fell short. The computer struggled to match the
photographs, which were taken under various lighting conditions, with the
crumbled, irregularly shaped shards. For example, the computer failed to
discriminate between pale greyish fragments of cement on the shards and greyish
images such as clouds, says Serkan Hotipoglu, who conducted the research with
Sanjit Mitra at the University of California at Santa Barbara, and Marco Carli
and Alessandro Neri at the University of Rome. The results were presented last
week at the Symposium on Image and Signal Processing and Analysis in Pula,
Croatia.
To improve the algorithm, Hotipoglu tweaked it to examine regions of pixels
rather than individual pixels. The computer could then evaluate not only the
colour of the pixel but also repeat patterns that convey textured surfaces such
as wood or clouds. By scanning for textures, the computer can distinguish
between similarly coloured objects.
After the computer finds an area of distinct colour and texture, the
algorithm matches it to features in photos taken before the quake. The algorithm
could be used for reconstructing any type of digital image, says Hotipoglu.
But despite the system鈥檚 efficacy, not everyone is impressed. 鈥淲hile
computers might be appropriate for this particular situation, nothing can
replace the human touch,鈥� said Mathew Szczepanowski, who is owner and head
conservator of the Conservation Studio for Art in Philadelphia, Pennsylvania.