Faking Hair

Shakespeare described it like "golden threads" and Pablo Neruda said it was "the same hair, only in different colors." Hair has always been a source of muse for the creative types. Capturing that exact description in a line of poetry or the precise shimmer on a canvas has been a favorite challenge for artists through the ages. Now the challenge is to get hair right on the computer screen.

Computers are capable of creating the three-dimensional structure of hair. It's the light that they can't get right. Through the process of "rendering," the computer algorithms can process how light is reflected from the structures to make an image.

The computations for rendering are complex and take into account the scattering of light. These work well for dark hair colors. But when it comes to blondes, the computer just can't get the color right, because light traveling through a mass of blond hair is not only reflected off the surfaces of the hairs, but passes through the hairs and emerges in a diffused form, from there to be reflected and transmitted some more.

But a newly developed rendering process for digital hair promises faster, and better hair color for blondes and other light colored manes by taking into account the multiple scattering of light through the hair.

"The model that's been around since the '80s works for black hair, and a model we introduced in 2003 in collaboration with workers at Stanford gets brown hair right and makes blond hair better," said Steve Marschner, an award-winning computer graphics expert "Using that model with our new work provides the first practical method to use physically realistic rendering for blond hair and still get the right color."

The technology behind the new rendering process will be detailed at the 2006 SIGGRAPH computer graphics conference from July 30 to Aug. 3.

--Sara Goudarzi

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Credit: Marschner lab, Cornell University