The Incredibles and The Polar Express are two recent animated features that achieve remarkable creative results using different styles of
human character animation. The Incredibles is an example of first-class keyframe cartoon character computer animation that integrates 2D
traditional styles with the 3D computer style that we have come to expect from Pixar projects. The Polar Express offers an innovative
approach that animates computer-generated virtual characters by applying realtime human performances and keyframe touch-ups.
Comedy and Action Through Squash-and-Stretch
Two aspects of The Incredibles represent significant departures from the topic and style of earlier Pixar movies: the human characters are
central to the storyline and they are animated with considerable squash-and-stretch. To make the later possible the technical character
team and the animators joined forces to develop new tools for animating squash and stretch humans in real time. The design and ease of
use of the character setup rigs was driven by the animators' needs, and keeping the overall look-and-feel similar to earlier versions of Pixar
animation software was an important consideration.
One of the main characteristics of the software tools used to animate The Incredibles was the layering of two key stages in the animation
process: the bone and muscle calculations, and the squash-and-stretch system. Without the layering of these two stages it would have been
difficult to provide animators with realtime feedback. In simple terms, the first stage of this layered process started by running the bone and
muscle calculations through all the character's positions in a shot. Using statistical analysis the software determined the most significant
changes in the character's skin throughout the shot, and "baked" those deformations into the model so that they could effectively be used as
blend shapes. (Without the baking animated models played back at rates of eight to 10 frames per second.) After doing the first pass
animation the animators saw the baked geometry and did not have to deal directly with the bone and muscle system. The second stage of
the layered animation process consisted of applying the squash-and-stretch to the baked geometry as a post-process, and animators were
able to visualize this in realtime.
Geometry decimation was another technique used to keep the playback as close as possible to 24 frames per second. Animators were
involved in the process of hand-crafted decimation that brought some meshes to about 25% of the full geometry but kept, for example, the
full and decimated silhouette shapes of each character identical. Each character had a decimated version, with most of the savings
occurring in the body geometry and not the face. Decimated models did everything that full models did, and the deformation hierarchies
remained the same but with much less overhead. Shots got finalized during the animation stage using the decimated version but the final
rendering used the full geometry.