Today's digital movie characters are more realistic, interactive, and endearing than ever before. But creating them is still expensive and labor-intensive. Most are either hand-drawn frame by frame with digital pen and ink (and computers that fill in some gaps), or they are based on "motion capture" techniques, which record and digitally mimic the movements of live actors to create on-screen characters. But as movies and video games pack more and more digital creatures onto the screen, animators are turning to physics and new artificial-intelligence methods for faster, more efficient ways to bring their stories to life.

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