“Life is cruel,” he points out, adding, “Why should the afterlife be any different?” The blasphemous splendor of that question resounds through the movie, spawning a mass of morbid detail and thus bolstering one’s conviction that computer-generated images, while constitutionally unfit for certain textures—all seas look fake, as do all healthy humans—grow ever more attuned to the monstrous, the decaying, and the deceased. ... Domestic drama has nothing to gain from the new technology; horror has nothing to lose. [Link, for now.]How long will it be before breakthroughs render this delicious statement obsolete? Cornell researcher Steve Marschner, who shared an Academy Award for Gollum's transluscent skin in "Lord of the Rings," has just announced a breakthrough in the rendering of computer-generated hair:
Poets and novelists often describe hair as "shining" or "shimmering." Dark hair has a "sheen"; blond hair "glows." All this comes about because of the complex scattering of incident light off of individual hairs and from one hair to another. ...Another iteration of the perennial clash between those who believe technology can never offer a convincing simulacrum of all that is good in the world and those who believe it is only a matter of time before it does just that. The most interesting questions, as with all such dichotomies, lie between these two perspectives: Technology may advance towards our expectations, but insofar as we live in a world dependent on technology, our expectations are shaped by its possibilities as well. The physical medium and language of film take copious liberties with reality, but we have internalized them - that is to say, they have disappeared, and contribute to our taking in of the world itself. At some point, animation that strives to be "true" to reality will meet an increasingly virtual society barrelling towards it from the opposite direction.
The problem [in reproducing this effect] is that 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. 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.
"People do something reasonable for one bounce and then assume it reflects diffusely," Marschner explained. In other words, he said, they assume that hair is opaque. "In light-colored hair it's important to keep track of the hair-to-hair scattering," he said.
Marschner and Moon's algorithm begins by tracing rays from the light source into the hair, using some approximations of the scattering and producing a map of where photons of light can be found throughout the volume of hair. Then it traces a ray from each pixel of the image to a point in the hair and looks at the map to decide how much light should be available there. [Link.]