By Suzzanne Rebello
3D artist and CG specialist Suzzanne Rebello shares some of the latest trends in motion capture and the challenges faced by manufacturers in this field
Motion Capture or Mocap is a relatively primitive, but widely used technique, for transforming live action performances into computer animated images. Hulk, Final Fantasy, The Mummy, King Kong, Narnia- The Lion, The Witch & The Wardrobe are some of the popular movies, which have used Mocap extensively.
This technique is used widely in games and big movie productions. Video games often use motion capture to animate athletes, martial artists, and other in-game characters involving character animations, which require realistic animation. The process begins with actors and stunt people rehearsing scenes including highly choreographed dances or fights with guns, knives, whips and other objects. The real people are then dressed head to toe in leotards like body suits, which are then studded with reflectors (silver markers, about the size of gumballs), allowing the gestures to be recorded as points in space.
More than 40 cameras are set along the studio walls at various heights to record the action, picking up points of light from the markers attached to the suits. The movements are then mapped onto a digitised 3D model, and a skeleton of every character and object in motion is created. Later physical features, clothes and backgrounds are filled in to create animated sequences.
Mocap works brilliantly for capturing the larger moves like the leaps and the somersaults or even dance sequences like the one in James Bond- Tomorrow Never Dies, or the Hulk. Director Ang Lee got into a special Mocap suit and pretended to be Hulk, to show the computer team exactly how he wanted the Hulk to move.
Lee’s actions were directly transferred realtime onto the Hulk in 3D space as he was stomping, smashing and lifting cars.
Mocap now includes face, fingers and captures subtle expressions, often referred to as performance capture.
In 2004, a new approach was taken by special effects wizard Ken Ralston and Robert Zemeckis’ to capture Tom Hank’s subtleties and finer shift of facial expressions in the movie Polar Express. This is when a proprietary Mocap process that Sony calls Imagemotion was formed. This was followed by Beowulf, an attempt make animation appealing to adults, with real movements and real textures. It was a huge success. The movie A Christmas Carol, starring Jim Carrey who plays four roles is setto release this Christmas and is the next big Mocap production to watch out for.
Mocap is used extensively in game development as well. In games, typically two types of 3D character animations are used - Realtime and Cinematics. Realtime allows player to choose from preset library moves such as crouch, jump andcrawl whereas, Cinematics involves fully rendered movies that are used for game intros and cut-scenes.
Realtime (RT) motion is becoming more and more popular for live TV broadcasts. Mocap is used to place virtual characters with a real scene or vice versa. For RT, mock-ups are required for non-standard human features such as tails or big bellies. When combining live elements with virtual ones, the real world cameras must share the same properties as the virtual cams. RT could be useful for training simulations, visual perception tests, or performing a virtual walk-through in a 3D environment.
The use of Mocap for ongoing character animation based series is another trend that is picking up in order to cut down costs or the scheduling and the renting out of Mocap studios. Gypsy is a commonly used setup.
It is easy to use and transport, and works well in most environments. The use of Phasespace optical motion combined with Motion Builder makes it easy to use. Mocap is ideal for small set-ups and could prove to be cost-effective and quick as opposed to paying expensive rentals to studios.
Another newer solution is FacePro, a Facial Motion capture toolset plug-in that is used with the VICON Blade system. SkinFlex is an additional feature that helps deal nuances like how the skin rolls as it stretches and moves and captures every lip curl and purse. Digital Concepts Group’s FacePro has helped take facial motion capture to the next generation of game, film, television and advertising media.
Alternatively, Motion capture data can be purchased off the net, and is very common with medium to small-sized production and special effects studios. You have various file formats, e.g. .bvh, .bip, .fbx that can be read by most of the software apps that are commonly used by artists.
MoCap for Artists: Workflow and Techniques for Motion Capture by Midori Kitagawa
Understanding Motion Capture for Computer Animation and Video Games: by Alberto Menache
3D Game Animation for Dummies: by Kelly L. Murdock
The Animator’s Motion Capture Guide: Organizing, Managing, Editing by Matt Liverman