CAPS was the technology used to combine hand-drawn and computer-generated imagery in Disney's 1989 The Little Mermaid.
CAPS stands for Computer Animation Production System. Developed by Disney and Pixar, it digitized hand-drawn animation and allowed artists to add computer-generated elements, color, camera movement, and compositing more efficiently than traditional painted cels.
The Little Mermaid is often associated with the transition from Disney’s older cel-animation process to digital production. CAPS was used experimentally near the end of the film, including for the rainbow effect in the closing sequence. It became the standard production system for later Disney animated features.
A common mix-up is naming Pixar’s RenderMan, which is a rendering system rather than Disney’s production and compositing workflow. Deep Canvas was a later Disney technology used notably for three-dimensional backgrounds in Tarzan, not the system identified with The Little Mermaid’s early digital work.