Caught in action: a workshop on Motion Capture

Vinnie Reddy, Founder and CEO of Animoto Studio conducted a very interesting session on Motion capture on day 3 of Anifest India '08. Motion capture, also known as mocap, is the process of recording/tracking real life movements as sequences of co-ordinates in 3D space with the help of sensors attached to the actor's body. Motion Capture which emerged as a technique in the '70s, is now being used in animation, live action movies, gaming, medical simulations, television and sports.

Owing to the increasing importance of mocap, Hollywood has lots of set-ups dedicated completely to mocap. Considering it's a process that burns holes in the producers' pockets, why choose it? This is why: 24 frames per second in animation is one hell lot to produce, and motion capture can make this process four times faster! That should be good news to all those producers who had the passion for animation but shied away from it just because it is time consuming as opposed to live action. Motion capture lets an actor play multiple roles; it gives more fluidity and a realistic edge to the movements in the final output: be it VFX or animation. It lets one use any camera angle that would be used in live action films.

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There are a couple of systems for capturing movements. One of them is optical system which is bone driven, as in the sensors are targeted to the bones and placed on the joints of the actor. The joint movements are then transferred to the 3D character. An action clip from Mission Impossible II explained this further. A lot of actors were performing the action with the help of suspension wires, wearing suits and sensors. The optical system noted all their kicks and twirls which were later used in action sequences in the movie. Another system used is the marker system which has ping-pong sized markers and the set up has six or more cameras in a circle all pointing to the spot where the actor is performing, thus giving many angles of the action.

Games, moving more towards cinema with their character driven storylines, revived the use of mocap in the '80s when people had started giving up on the complex and messy technique. Now-a-days, intense usage of the technique can be seen in movies like Beowulf where around 600 cameras were used to track the body and facial movements of around 12-24 actors, which generated some 17 hours of footage to produce a 2-hour movie!! Also movies like Titanic used mocap for long shots. Others like Polar Express, Final Fantasy, Shrek also made notable use of mocap. Indian cinema too is seen utilizing this facility for a lot of upcoming films like Chotta Bheem by Piccaso studio, Yash Raj banner's Roadside Romeo, Rajnikant's Sultan. Even Ghatotkach used mocap for three of its song sequences.

Though it might be expensive to use mocap, its advantage is that it compresses the amount of time the same content would have taken had it been made by a team of animators. Also keeping the costs in mind, not all stories should and can use mocap. One needs to consider if the sequence can be better rendered through any other medium. For example, traditional animation will give an output with stretch and squash which cannot be rendered by mocap which is the best option only when the desired movement is realistic.

Excerpts from the Q&A:

While acting for mocap does one have to hold the props for example if it is a shooting scene, would one have to hold guns?
It would better to hold some prop, even if it's a fake or a wooden block. It helps the movement as it gives it a sense of weight.

Does the physique of the actor performing have to be similar to character in 3D?
More or less the physique should be similar, as in if there is a fat guy acting for a lean guy in 3D that might cause distortions or minimizations. In optical systems, as only the bones are targeted, the body fat would not matter too much. Hence the amount of distortion would hardly be anything. But a lean person might have a certain amount of flexibility to which a fat actor might not do justice.

Are animals ever motion captured?
Yes. For video games mostly domestic animals like horse and dogs are traced. It depends on how well the animals have been trained to perform the actions desired.

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