Image Processing Software Helps Preserve Ancient Art

Flavio Fontana

Artifacts from the city of Ravenna, Italy, which in the fifth century saw the sunset of the Western Roman Empire, have played an important role in developing a multispectral imaging technique. The technique exploits The MathWorks' MATLAB image processing technology and could prove to be of invaluable help in preserving and restoring ancient mosaics and other art.

Italian mosaics in the church of St. Apollinare Nuovo undergo analysis before restoration begins.

A research group, formed by L. Seccia, A. Iannucci, N. Santopuoli and B. Vernia, is doing the work under the auspices of CIRAM at the University of Bologna and the Superintendence for Architectural Goods.

Seccia and his colleagues developed multispectral measurements in which advanced optical processing techniques were an integral part. The primary aim of the project was to determine the status of the early Byzantine mosaics in the Church of St. Apollinare Nuovo and to investigate the techniques to repair this artwork.

The key innovation in the group's approach has been the synergic use of three techniques: reflectography, thermography and photogrammetry. MATLAB software along with the Image Processing Toolbox have enabled customization and modification of the techniques used for this uncommon application.

Reflectographic images were acquired with a low-cost monochrome charge-coupled device (CCD) camera using specific optical filters from the near-UV to the near-IR. The subsequent interpretation of these images allowed identification of subtle features of the mosaics that could not be seen by the naked eye. The accuracy of the Image Processing Toolbox software made it possible to distinguish original pieces from those added in restorations.

Other valuable information has been collected by using a mid-IR camera to determine the thermal response of the mosaics to heat excitation. The mapping of the underlying support, consisting of plaster coats, provides the restorer with a powerful tool for locating, for example, the presence of detachments.

The third technique, photogrammetric mapping, allowed the researchers to represent the mosaics in three dimensions with 1.5-mm accuracy. This has made possible correlation of the first two measurements with the physical displacement of the mosaic surface. Comparison of the data obtained by the three methods and their interpretation through software codes developed for this purpose have provided an objective overview of the condition of the artwork. This process enables future monitoring and provides an insight into the secrets of the artists who created them centuries ago.

The researchers collaborated closely with CCD instrumentation maker Spectra Electronica SaS of Milan. They plan to analyze other mosaics in the Ravenna area and to use the techniques for quality control in industry.