NASA Jet Propulsion Laboratory, California Institute of Technology

Space scientists at JPL working with art conservators at the Los Angeles County Museum of Art have developed new technique for separating paintings hidden beneath master works.

The effort resulted in the first successful use of image enhancement techniques to separate X-ray images of paintings where two or more works exist on the same surface, according to museum officials.

The technique, derived from computer-processing of photographs from NASA's unmanned spacecraft, will allow art conservators and museum curators to better evaluate earlier compositions often found underneath easel paintings.

William R. Leisher, head of conservation at the Los Angeles County Museum of Art (LACMA), asked JPL investigators to separate and enhance painting found to exist beneath the 17th century oil painting "The Crucifixion," by an unidentified Flemish painter.

Astronomer Dave Glackin and scientist Don Lynn, both image processing specialists, and computer analyst Raim Quiros, in collaboration with Jium Druzik and Dr. Pieter Meyers of the museum, developed computer programs for subtracting the top painting from the botto so that the hidden painting may be seen in detail.

"The Crucifixion," painted on paper, shows Jesus Christ being lowered from the cross by group of followers. The bottom painting, painted directly on the 16-by-24 inch wooden panel, shows scene of man and woman seated at table. The two are dressed in l7th century clothing, and the room is lighted by sunlight shining through window.

Art conservators commonly use X-ray photography to examine paintings. The X-ray photos may often show that paintings or sketches exist beneath top painting, but the works are not automatically delineated. The two works usually are fused in an X-ray photo and appear as blurred, double image.

"What we sometimes find is completely different composition underneath," said Druzik, associate conservator at the museum. When that happens, he said, "there will always be question in the curator's mind as to whether or not an unknown masterpiece exists under the top painting layer."

In order to separate the two images, the JPL team first designed computer programs to minimize the appearance of the grain pattern of the wood on which the original work was painted.

Next, photograph of the top painting was matched with the X-ray image. Any brushstrokes from the X-ray version that matched the top painting were subtracted. Consequent subtractions removed most traces of the top painting, while the remaining bottom painting was computer-enhanced to bring out detail.

The pioneering development of the painting subtraction technique could lead to future systems designed uniquely for discerning and separating multiple X-ray images of paintings with designs under the surface. Such systems, said Druzik, "will be another invaluable tool for conservators and curators."

"This project is good example of the applications of space technology to other problems of great public interest," said Dave Glackin of JPL. Glackin and Kurt Liewer of JPL, working with LACMA conservators, are undertaking new task, using high-resolution spacecraft photography system and JPL's image processing facility to study the condition of the museum's _C_o_d_e_x__H_a_m_m_e_r, treatise on the nature of water by Leonardo da Vinci. Results from the project, supported by grant from the Armand Hammer Foundation, should determine how to best preserve the works.

Future applications of computer processing to art conservation might include techniques to date paintings by determining the age of wood on which compositions were painted. Dendrochronology, the science of dating wood based on the number and character of tree rings, usually requires shaving wood away from the edge of the original wood panel. Computer enhancement of the wood grain of panel would eliminate the need to remove original support material in order to date it.

The $35,000 painting subtraction project was funded by the Caltech President's Fund. JPL is operated for NASA by Caltech.

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