Reproducing this effect in computer graphics has always been a challenge. Computers can create three-dimensional structures resembling hair, but the process of rendering, in which the computer figures out how light will be reflected from those structures to create an image, requires complex calculations that take into account the scattering between hairs. Current methods use approximations that work well for dark hair and passably for brown, but computer-generated blondes still don't look like they're having more fun. But now Cornell researchers have developed a new and much quicker method for rendering hair that promises to make blond (and other light-colored) hair more realistic.
The problem is that light travelling 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. The only method that can render this perfectly is "path-tracing," in which the computer works backward from each pixel of the image, calculating the path of each ray of light back to the original light source. Since this require hours of calculations, computer artists resort to approximations. The result, in a test rendering of a swatch of blond hair, appears almost identical to a rendering by the laborious path-tracing method. Path tracing for the test required 60 hours of computation, while the new method took only 2.5 hours, the researchers report.
More information:
http://www.sciencedaily.com/releases/2006/07/060720095452.htm
More information:
http://www.sciencedaily.com/releases/2006/07/060720095452.htm