Caricatured or not, the enormous number of balloons needed to carry Carl's house to South America required a more robust rigid body simulation as well as a little cheating. All images © Disney/Pixar.

Fusing The Wizard of Oz, It's a Wonderful Life, Hayao Miyazaki and Joe Grant, among others, is reason enough to rejoice after seeing what Pete Docter has conjured with Up, Pixar's 10th feature (opening tomorrow from Disney). It's as wild and funny and unpredictable and daring an adventure as you might expect. But there's something more -- there always is with Pixar, isn't there? There's something joyous and redemptive in Carl Fredricksen's quest to fly his house to Paradise Falls in South America to complete the childhood dream he shared with his late wife Ellie. Up may not be as flashy as Pixar's greatest hits, but it achieves a grace and maturity that may be longer lasting. If ever there was really a case to be made for Pixar breaking out into the live-action Best Picture Oscar category, Up offers the best one yet with, literally, its most touching, human story.

Docter and Supervising Animator Scott Clark (who got his start at Pixar on Monster's, Inc.) recently discussed the secret sauce behind Up: the notion of "Simplexity," coined by Art Director Ricky Nierva.

"What it means is: we wanted everything on first read to have very simple shapes: squares, circles, etc.," Docter explains. In other words, Carl is shaped like a box, which represents the past, while Ellie and Russell, the young, enthusiastic Wilderness Explorer and sidekick, are very round, denoting the future.

"It's a very nice, clean, caricatured look. But as you go deeper you see textures and enough details and flexibility to be able to carry us through the film -- the range of expressions that we would need or the level of detail to make the jungle seem believable, for example.

A trip to the real Tepui provided the primeval and other-worldly look captured in this concept of Paradise Falls (from The Art of Up, Chronicle Books, Lou Romano/Don Shank).

"I've always been interested in how far you can push things to be simplified. And that's especially difficult with computer animation, at least the way we use it here at Pixar, in terms of the level of detail and texture and lighting. But I believe that's what animation really does well: that sense of simplification and caricature, in the same way that [Al] Hirschfeld will reduce the likeness of someone in just a few lines, the same can be done through design and movement and stripping away anything that's not that gesture that you're trying to portray."

For instance, they deliberately made Carl's house look like a dollhouse. "So things like the texture of the material on the chair was really scaled up compared to a life size chair," Docter adds. "And the corners of tables are more rounded, so we wanted a handmade kind of feel [to make the house] feel warm and cozy and comfortable and small. And the other extreme is when you get to Paradise Falls down in South America, where you really need to feel these grand vistas and the wind sweeping your face. You don't want it to look like a model or you just won't believe it."

However, Clark suggests that the significance of Simplexity runs deeper. "I think Simplexity [also] applies to an acting choice. How much you say with how little you do. For instance, with Carl, he's a very simple man from the animation side of things. He's very boxy and he's old, so he's going to have physical and emotional limitations. So what can we say with one expression instead of zipping him around like a cartoon? I think there's an exaggeration in what you don't animate as opposed to what you do animate. People tend to get into animation because they like to push and exaggerate things and you can have fun moving stuff around. And we had a lot of fun not moving things around.

"The easiest example is the gag when Carl is slowly moving down the stairwell in his chair. He's just in one pose and is moving down this rail with a scowl on his face. He's accepted his lot in life at this point. We animated that and they put a pose in there and some blinks and some head movement, and we looked at it and said, 'No, it's funnier if you take the head movement out but maybe add some shaking in the chair that wobbles his fingers a little bit to make it more believable.' We really stripped away the number of blinks and used them sparingly. The more minimal it got, the funnier it got to us. But it took just as much discipline to go that direction and understand that it was better than over animating it. We found that the best choice was having Carl look at Russell, show no expression and then just blink. That really said it all. This is in sharp contrast to Buzz Lightyear or Heimlich or Mr. Incredible."

Although there were no Holy Grails achieved technically on Up (though it marks Pixar's first foray into stereoscopic 3-D), there were still some incremental improvements worth touting.

"I feel like we've reached a point where we can do almost anything we want," Clark admits. "We can caricature a human and it looks pretty appealing. Most of the technical achievements are almost boring. The thing that excited me the most was how to get the foot to detect where the ground is. As an animator, I didn't have to eyeball where the foot contact was. It's amazing what a difference it makes when you have four-legged creatures running around on a craggy Tepui rock. And we had some improvements in hair and cloth simulation. Nobody's thinking about Carl's jacket when they're watching the movie, but his proportions are bizarre. He's three heads high so when we started putting cloth sim on top of that model, he looked like a little person and his arms and legs would get lost in the cloth and it didn't feel like the caricature of an old man that we were drawing. As animators, we said we needed to see the break in the elbow. We needed to see the breaks in the knees so we could get straights and breaks. Believe it or not, they had to build in all these cheats on top of this cloth sim. For the balloons, they actually calculated how many millions of balloons it would take to lift a house. Of course, the house would have to be a speck, so we pulled back to the caricature of it."