Even better than the real thing?

A revolution has taken place in the world of making images.

It happened when workers here at the National Gallery in London placed a replica of "The Magdalen Reading" alongside several other paintings by 15th-century Flemish painter Rogier van der Weyden. This incredibly accurate digital copy sums up a decade-long search for electronic tools that curators, conservators, and art historians can use to catalog, restore, and reinterpret art.

The process is expected to be used more and more by museum restorers and art historians. As it is, it will make art more accessible to everyone.

"You may never visit the National Gallery, the Louvre, or the Uffizi, but you can print a life-size reproduction that allows you to view the painting as if you were standing next to the original," says Joyce Farrell, a scientist at Hewlett-Packard Laboratories in Palo Alto, Calif., the National Gallery's partner in the project.

The National Gallery is leading the way in this unchartered territory. Its scientists have harnessed a digital camera, a computer workstation, and a large-format printer to capture, store, and reproduce "The Magdalen Reading" with breathtaking accuracy. The original panel and the printed reproduction have been on display side-by-side at the National Gallery in London.

"It demonstrates what complete faith we have in this photographic reproduction to place it so close to the original," says Lorne Campbell, curator of the van der Weyden exhibit.

To accurately reproduce van der Weyden's rich palette of colors, National Gallery scientists photographed the painting, stored the image in computer memory, and sent it to a large-format printer. The printer translated numerical values using a color map to a precise reproduction of this work of art.

Digital images help in restoration

For most of this century, photographers have captured restored paintings to record a lasting image. But film negatives deteriorate over time. Digital copies will allow the National Gallery to keep a permanent record for each restoration.

Jill Dunkerton, a conservator here at the National Gallery, says digital copies of a painting recorded during restoration and full-scale prints will mean her successors will be able to accurately compare the painting she restores in this century with the painting they will inherit from her in the next.

If she faces a painting that's faded or deteriorated, she can test her ideas for restoration on the printout.

"I can actually paint on the full-sized printout of the original using watercolors," Ms. Dunkerton explains. "So before I start work on a painting, I have a sure idea of what I am setting out to do."

The digital camera and infrared video also can show conservators the undersurface of a painting. "X-radiography and infrared examination of paintings have been going on for a long time," Dunkerton says, "but photographic negatives are unwieldy." Conservators have pasted them on large boards next to the painting to compare images they see to the painting itself.

Now, with the press of a button on her computer, she can project "an image that contains an X-ray or infrared reflectogram on the surface layer of the painting," Dunkerton says.

"Together, they reveal the changes an artist made between the careful underdrawing and what he decided to paint."

Trading images electronically

Typically, conservators travel between museums to acquaint themselves with works of an artist whose painting they are restoring. Now, they can trade images electronically.

"There will be enormous value to restorers as museums build up bodies of digital images," Dunkerton says. "Sending digital paintings to one another through the Internet will be immensely helpful."

Recently, scientists at the Doerner Institute in Munich and the National Gallery exchanged images of a painting by Albrecht Drer over the Internet.

David Saunders, a scientist at the National Gallery, compared a color map from an image he captured five years ago with one made weeks before the exhibit opened. Mr Saunders could determine changes in light, saturation, and hue.

"We are convinced that our combination of digital camera, computer workstation, and large-format printer is perfectly able to detect and display changes that occur during the lifetime of a painting," he says. Conservators can print an exact replica of the painting to compare areas where the computer measured changes to the painting itself.

Eventually, every painting in the National Gallery collection will be catalogued using this digital imaging. So far, Saunders and his team have captured 400 of the gallery's 2,300 paintings.

When green fades to brown

John Cupitt, another National Gallery scientist, created a way for art historians to use these digital images to reinterpret art. Mr. Cupitt can use the workstation to adjust the color of the image to show, for example, that a hillside that is now brown, once was green. Curators can print a full-scale image of the work of art for display or send the restored digital image directly to a publisher for printing.

"Sometimes pigment changes color," Cupitt says.

"Conservators can't restore the picture to its original color. [But] using image processing, they can show others what the picture might have looked like when it was first painted," he says.