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First Person: Pre-animation for Motion Capture

Jan 1, 1999 12:00 PM, Mike Fallows

Donkey Kong Country (DKC) was the first CGI cartoon series produced primarily with 3D characters rendered in realtime. Medialab created 70 percent of the animation using its proprietary Clovis performance capture system. The makers of the series reinvented the production process, and established a formal chain of fabrication to allow seamless integration of real-time animation.

The production pipeline divides into four stages: design, preparation of an episode, animation, and final rendering. The animation stage involves three phases: pre-animation, real-time shoot, and post-animation. Pre-animation is essential to optimizing the real-time shoot and overcoming the inherent limitations of performance capture.

Designers initiate pre-animation by breaking down each episode into sequences, scenes, and shots. Sequences-groups of successive shots-serve no other purpose than to break the episode up into manageable pieces. For DKC, the production team re-defined the term "scene" to denote a group of shots involving real-time 3D characters where place and action unite in a similar fashion. In real-time shooting, which is like live action in that it involves different takes and rushes, the set-up costs represent a large part of the overall cost of a shoot. Therefore, it is more effective to optimize the shoot by recording many shots where there is a common denominator in a scene.

Next, it is crucial to analyze the sequences carefully and prepare certain elements before the real-time shoot. For example, in order to avoid down time during the real-time shoot, artists working on DKC had to check that the displacement of each character in the real-time scene remained contained in a circle four meters in diameter. At the time, this was the limit of the motion-capture area. (It has since increased and continues to increase as the motion-capture technology evolves.)

Also during pre-animation, artists create a real-time set in order to position the performance. Since it is not possible to have the entire set on the screen during the real-time session, artists select the elements that are absolutely necessary to the action. They then decide the degree to which they must define the elements. For example, if a character is playing the piano, artists must define the piano to make the keys visible. However, if the character simply passes by the piano, then artists need to only define the piano by its bounding box.

Artists must also create background images during pre-animation to help the performer correctly position the character. The choice of the temporary background image is important because it provides a guide for positioning the other characters for animation.

Pre-animation (or preanims) created during this phase also allow the easy integration of real-time animation into the production process. DKC evolved into a hybrid series because preanims are actually key-framed elements that serve to bridge real-time elements.

On DKC, the preanims separate into two main types: preanims on background elements (including camera moves, camera cuts, and any element of the set) and preanims on elements that then go through the motion-capture process (i.e., preanims on characters created in Softimage).

Preanims have artistic and technical purposes. Artistic preanims enhance real-time animation and, figure early in my decisions as a director when I analyze an episode. For example, when a door opens and a character appears, the door animation must be complete during the real-time shoot so that the actor can interact with the movement of the door. Artists must pre-animate the door action.

Additionally, a character cannot grasp an object in realtime. Therefore, artists key-framed Donkey Kong's banana. Then the storyboard artists came up with ways for him to grab or drop the banana out of the frame so that the change in the state of his hand occurred off screen. Vehicles such as Funky's plane, Bluster's copter, or King K. Rool's mine carts were all preanims. (On the other hand, doors smashed open, coconuts thrown, and any other props that do not have characters attached to them we post animated.)

Technical preanims come into play in three different ways. In scenes where a character is walking a long distance for an extended period of time, artists key-frame the character from approximately the waist down. They then animate the character's upper body in realtime, keeping the performer at the center of the stage and overwriting parts of the preanim to insure a seamless connection between upper and lower body. A second, similar application for technical preanims allows characters to travel in key-framed vehicles.

Animators have also developed a technique to "teleport" characters. They do this by establishing a character in one long pre-animation frame that acts on the coordinates of the character. For example, Cranky was able to appear next to his organ, exit the field, and then enter the field in the next shot 25 meters away from the organ. During the camera cut, his coordinates were changed to allow this.

Preanims are essential to overcome the limitations of motion capture and allow real-time animation to be at the heart of the production process. Real-time animation gives directors enormous control and flexibility over production because they can be present throughout the process. Directors can work with actors to develop subtle characterizations through physical details (such as how a character walks). The ability to adjust these nuances on the fly makes characters more believable and lifelike, which is, after all, the goal-even for cartoons.

Mike Fallows is the director of Donkey Kong Country. Medialab has offices in Paris, Los Angeles, and Tokyo.

© 2008 Penton Media, Inc.