film techniques - What is a "performance capture" animation movie?

The recent movie The Adventures of Tintin: The Secret of the Unicorn is a performance capture animated movie. What is a "performance capture" movie and what is the need for this technology when the same effects could be visualized using normal animation (think movies like Ice Age)?

Answer

Performance capture generally refers to the practice of capturing very subtle movements from real actors and using those in animation. Movies like Ice Age are fine without performance capture because the characters aren't realistic.

The problem you run into when trying to make realistic human animations is that the human brain is wired to detect very subtle cues in facial patterns and if an animator makes even minor errors, we tend to be uncomfortable with the animation, associating the problem with a physical defect, illness or death. That phenomenon is usually called the uncanny valley.

Steve Perlman explains how one version of the technology was improved to bridge the uncanny valley in this excellent video.

One thing you can theoretically do with this performance capture technology is record a broad array of facial expressions with a famous actor, and continue featuring that performance in new movies long after their ultimate demise. That seems even a little creepier to me than bad animation, but to each his own I guess.

Ultimately though, the reason for the technology is to capture an actor's well honed "art" as opposed to something an animator can realistically replicate.