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SHREK 2

Raising The Bar...Again

There is perhaps no artistic arena in which the term "state-of-the-art” is more fleeting than computer animation. Advancements in the field have come so far and so fast, it seems almost impossible to fathom that the first computer-animated feature was released less than 10 years ago. In fact, much of what is seen in "Shrek 2” could not have been achieved with the very same tools that were considered state-of-the-art on "Shrek.”

Bielenberg states, "We definitely tried to raise the bar across the board on ‘Shrek 2.' We wanted to push the envelope to deliver something entirely new for audiences.”

Once again, DreamWorks' Preferred Technology Provider, Hewlett Packard (HP), made it possible to take computer animation to the next level, providing the computing infrastructure for the animation studio. "Shrek 2” employed more than 300 HP workstations, giving the various artists unprecedented interactive control and flexibility in the creation of the movie. A 3000-processor render farm of HP servers was also utilized to address the massive computing requirement of the production.

The two most important technological breakthroughs on "Shrek 2” both had to do with light: the bounce shader, a form of global illumination; and subsurface scattering, which lent a natural translucence to the characters' skin.

Developed at PDI/DreamWorks, the bounce shader is modeled on the way light naturally bounces from one surface to another, ad infinitum. To illustrate, a dark room with only one tiny light source seems to grow more illuminated because the light is bouncing off of the various surfaces in the room. Similarly, the bounce shader is able to take one light and gauge where the bounces would take it. In the past, the visual effects team would have to place virtual lights all over the set to achieve a similar result in the computer, and it still would not look as natural.

Bielenberg explains that, in addition to set lighting, the bounce shader had significant applications for lighting characters. "It is often difficult to get light under a character's chin with a key light coming in from above. The bounce shader figures out how much light is actually reflecting off of the character's chest and fills it in under the chin, giving you a natural, softer feel.”

While the bounce shader lit the characters more naturally from without, subsurface scattering gave their skin a natural translucence from within. Bielenberg points out, "Most of us don't realize how much light is penetrating our skin, refracting and re-emerging. It's like when you take a flashlight and put it against the palm of your hand. You can see the light coming through your hand, seeming to make it almost transparent. We've implemented a technique that simulates the translucency our skin has, and that's what we call subsurface scattering. Without that translucence, our characters' skin would look hard and opaque, like plastic or metal.”

PDI/DreamWorks' Academy Award®-winning facial animation system was the breakthrough that allowed "Shrek” to be the first computer-animated film to put human characters in leading roles. The complex layering system enabled the animators to convey emotions through facial expressions as never before. Nevertheless, "Shrek 2,” with its much larger cast, required that the facial animation system be brought up a notch…or two.

The basics of the facial animation system did not change from the first movie to the sequel. The character technical directors, supervised by Lucia Modesto and Lawrence D. Cutler, essentially built a head in the computer, beginning with the skull and then layering on muscles and finally skin. The skin is programmed to respond to the manipulations of the muscles beneath in different combinations, enabling the animators to capture the desired expressions.

For "Shrek 2,” the technical directors added more muscles to the faces—Shrek's face alone had

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