First Person: Pre-animation for Motion Capture

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

The production pipeline divides into four stages: design, preparation of anepisode, animation, and final rendering. The animation stage involves threephases: pre-animation, real-time shoot, and post-animation. Pre-animationis essential to optimizing the real-time shoot and overcoming the inherentlimitations of performance capture.

Designers initiate pre-animation by breaking down each episode intosequences, scenes, and shots. Sequences-groups of successive shots-serve noother 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 shotsinvolving real-time 3D characters where place and action unite in a similarfashion. In real-time shooting, which is like live action in that itinvolves different takes and rushes, the set-up costs represent a largepart of the overall cost of a shoot. Therefore, it is more effective tooptimize the shoot by recording many shots where there is a commondenominator in a scene.

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

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

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

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

On DKC, the preanims separate into two main types: preanims on backgroundelements (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 enhancereal-time animation and, figure early in my decisions as a director when Ianalyze 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 theactor can interact with the movement of the door. Artists must pre-animatethe door action.

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

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

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

Preanims are essential to overcome the limitations of motion capture andallow real-time animation to be at the heart of the production process.Real-time animation gives directors enormous control and flexibility overproduction because they can be present throughout the process. Directorscan work with actors to develop subtle characterizations through physicaldetails (such as how a character walks). The ability to adjust thesenuances 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 officesin Paris, Los Angeles, and Tokyo.