Early Animation: Zoetropes, Phi phenomenon and Persistance of vision!

A zoetrope is a device that produces an illusion of action from a rapid succession of static pictures. The term zoetrope is from the Greek words ζωή - zoe, "life" and τρόπος - tropos, "turn". It may be taken to mean "wheel of life".

It consists of a cylinder with slits cut vertically in the sides. Beneath the slits on the inner surface of the cylinder is a band which has either individual frames from a video/film or images from a set of sequenced drawings or photographs. As the cylinder spins the user looks through the slits at the pictures on the opposite side of the cylinder's interior. The scanning of the slits keeps the pictures from simply blurring together so that the user sees a rapid succession of images producing the illusion of motion, the equivalent of a motion picture. Cylindrical zoetropes have the property of causing the images to appear thinner than their actual sizes when viewed in motion through the slits.

The phi phenomenon is a perceptual illusion described by Max Wertheimer in his 1912 Experimental Studies on the Seeing of Motion, in which a disembodied perception of motion is produced by a succession of still images. In discussions of the perception of film and video it is often confused with beta movement, but it is a distinct phenomenon not directly involved in the perception of motion pictures.

The classic phi phenomenon experiment involves a viewer or audience watching a screen, upon which the experimenter projects two images in succession. The first image depicts a line on the left side of the frame. The second image depicts a line on the right side of the frame. The images may be shown quickly, in rapid succession, or each frame may be given several seconds of viewing time. Once both images have been projected, the experimenter asks the viewer or audience to describe what they saw.
At certain combinations of spacing and timing of the two images, a viewer will report a sensation of motion in the space between and around the two lines, even though the viewer also perceives two distinct lines and not the continuous motion of objects referred to as Beta movement. The phi phenomenon looks like a moving zone or cloud of background color surrounding the flashing objects. The discovery of the phi phenomenon was a significant milestone in Gestalt psychology.

Persistence of vision is the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina.