When animators want to capture the realism of a live object’s motion, a technique called rotoscoping is used. In traditional film animation, film footage of the motion is rear-projected, one frame at a time, onto a frosted screen that is mounted on the animators worktable.

The artist traces the frames onto cels. This process is called rotoscoping.

The video equivalent is called keying or matting. Digital rotoscoping has recently become possible. Here, the frame buffer is used to hold the incoming action, and software picks out the image of interest from the background, assuming the subject was shot against a solid color.