II.

Persistence of Vision

The perception of on-screen movement is caused by a phenomenon called “persistence of vision”: when presented with a series of rapidly changing images, the human brain cannot process them fast enough to see each image separately and instead perceives a single continuous moving image. In standard cinematic films there are 24 frames (images) per second—24 fps. The set speed of television systems varies in different countries and is either 25 fps or 30 fps. Animation created for playback on a computer, CD-ROM, or DVD requires 14 fps or more for fluid movement and depends on the available random access memory (RAM) and speed of the computer’s processor or CD-ROM/DVD drive. At a low speed of 8 fps or less, the moving image will appear jerky or the illusion of movement may be lost altogether.