A Clearer Picture

Looking beneath the surface of paintings no longer means

simply searching for hidden implications within the artwork. New image

processing technology can now unmask a painting quite literally, revealing what

it looked like when the painter first completed it.

Take Da Vinci's masterpiece, the Mona Lisa, which hangs at

the Louvre in Paris, summoning millions to the museum from all over the globe

and inspiring hundreds of years of scholarship. The painting no longer looks the

way it did when Da Vinci finally laid down his brush. Layers of brown varnish,

an extensive network of fine cracks and repeated restoration efforts have left

their mark. Physicist John F Asmus of the University of California at San Diego

has spent the last few years applying computer image processing techniques to a

high-resolution photograph of the painting to recover faint or lost details.

Asmus and his colleagues first converted the photograph into

a digital image composed of 6 mn pixels for each of the three colors: red,

green, and blue. Then, they measured the amount of light at various wavelengths

transmitted by a piece of ancient varnish. Using a mathematical procedure, they

subtracted the effect of the varnish from the digital image to create a

brighter, more natural picture. When they enhanced the contrast and brought out

underlying patterns using false colours, startling discoveries were made. There

was a string of spots below her neck, indicating a possible necklace that the

artist eventually decided to paint over. In the picture's background was a

faint, distant mountain ridge that may have been erased by a restorer. However,

there are still mysteries left to be solved. We are yet to know how much of the

lady's legendary smile was actually created by Da Vinci and how much is the

result of tampering by restorers. Thanks to digital technology, the answers will

not remain buried for long.

In fact, digital imaging has led to a whole new era in the

study and conservation of art. Film photography, being a chemical process, had

introduced many uncontrollable variations in images. In the mid-90s itself,

several museums the world over began to use digital photography to archive their

works. However, the advancement to digital imaging has provided an entirely new

source of information to art historians. The National Gallery, London, is one of

the pioneering museums to use this technology. In collaboration with Hewlett

Packard, they have developed a series of specialist cameras for art. These

cameras win over digital photography in three respects: high resolution, low

noise, and color accuracy. Their latest camera, MARC 2, takes a 100Mpixel image,

as against the 5Mpixel of mainstream consumer photography. In order to capture a

larger area, the camera moves the small sensor over a large area in a series of

'tiles', which are then automatically 'stitched' together. The National

Gallery camera minimizes electrical noise by using wholly digital interconnect

and by turning off the power to the motorization system, which micro-moves the

sensor, for the exposure of every tile. Furthermore, the system is color

calibrated with great care before every image capture, using specific lighting

of a known color temperature. "The image colors finally reproduced are

within 4 delta-E of the original," says Huw Robson, manager, Digital Media

Department, Hewlett Packard Laboratories (Europe). "To all intents and

purposes, this difference is close to imperceptible to the human visual

system."

Capturing accurate copies of paintings is only one of the

benefits of this new digital technology. Since imaging can also be achieved with

non-visible light, infrared rays are used to see through the pigment to the ink

or charcoal underneath, revealing the original ideas of the artist. In addition,

scientists can now study the amount a painting fades from year to year as well

as the wear and tear due to transport, using the color accuracy provided by this

technology. Conservators and restorers can view paintings at full size at

different stages of restoration. "In one case, restorers practiced their

painting on a printed reproduction before working on the original", says

Robson. Several museums are also using digital technology to create interactive

guides that allow the visitor to zoom in on brushstrokes within a painting,

which can then also be printed on demand.

"The National Gallery is the only museum I know of that

has digitally captured its entire collection," states Robson. "Many

galleries have high-quality photographic transparencies of their collection and

many have scanned these in for a digitally accessible record, but this is

time-consuming, costly, and (critically) nowhere near as accurate." The

leading galleries of the world can easily afford the equipment for capture. More

than 225,000 paintings and 36,000 three-dimensional objects at the Louvre,

Paris, are scanned and stored in a multi-resolutional form that allows

enthusiasts to browse through pictures online and appreciate the minutest

brushwork. Three of the finest museums in the world, Museo del Prado (Madrid),

Uffizi Gallery, (Florence), and Accademia Carrara (Bergamo) worked with the

University of Milan on cooperative infrared imaging of their collections in

order to see the original sketches on the canvas. The National Gallery of Modern

Art in New Delhi is also in the process of digitizing its collection. Art lovers

can now access the works of Raja Ravi Varma, Amrita Shergill, Rabindranath

Tagore, and other modern Indian painters online.

Art galleries across the globe are realizing the benefits of

this new technology. Digitising art is simply the next step in art scholarship.

From viewing a painting closely, to bending over it with a magnifying glass, to

blowing up a photograph of it, scholars have constantly been searching for new

ways to get a clearer picture. Digital technology has made it possible to go

beyond the visible and to understand the intent and purpose behind every

brushstroke. It has brought us closer than ever to the actual workings of the

artist's mind.

Himani Dalmia