A lot more environments were created for the third Ice Age film, including the Lost World where they encounter dinosaurs. All images © Twentieth Century Fox.

Where to go next with the third Ice Age (opening today from Fox)? That was the challenge for Blue Sky and director Carlos Saldanha. (Blue Sky recently moved from New York to Connecticut to improve efficiency and expand resources. For one thing, animation is now located on the same floor).

Well, adding stereoscopic 3-D opened up a range of artistic possibilities, along with the addition of dinosaurs, a love interest for the ever-popular Scrat and a weasel-like character for more comic relief. Plus, Manny (Ray Romano), Diego (Denis Leary) and Sid (John Leguizamo) are maturing into responsible parents and caretakers.

"I would say it's comforting because you know how these guys are supposed to move around and act, but it's also a challenge to find new things to animate to so they're still fun to watch on screen," suggests Galen Tan Chu, the supervising animator that has worked on all the Blue Sky features.

So what was it like working in 3-D, which has taken animation by storm?

For its first venture into stereoscopic 3-D, Blue Sky had to learn all about creating a proper sense of depth.

"Where you have Z-depth sensitivity to really tell whether there's something in front of or behind someone, you can't cheat the way you can in 2-D," Chu offers. "And I remember having to kick back a few shots to my department. Let's say a hand looked like it was grabbing the tip of the acorn, except that the animator only did that from the camera. So that when you look at that in stereo space, it looks completely wrong: like the acorn is 10 feet behind the hand. And I know in previous movies there were some shots where we got away with that. So the concept of real space needs to be more respected.

"Similarly, with the eye lines, with real space you're going to be able to tell whether characters are actually looking at each other. A lot of times animators will cheat the eye lines so that it looks fine in camera space, in stereo space we're a little bit more conscious of that.

"And, with arm stretching, you have to be really careful in showing [proper spatial relation to camera]. Also, as far as characters in relation to the borders of the camera, if you have a character that's protruding forward in stereo, it starts to tamper with the illusion of depth if the eyes are getting cropped off by the top portion of the camera. And so we were a little bit more conscious about keeping characters in frame to get the full stereo effect."

By working with stereo as early as possible, though, they were able to create more of a thrill ride experience. "There was a sequence where a few of our characters rode a Pterodactyl flying through the Lost World, and we were very stereo sensitive to make sure that elements were coming from and away from camera and to camera; really playing with the Z space to get the most out of the medium. It's definitely changed the way we approach our process."