Animation is a dynamic medium in which images or objects are manipulated to appear as moving images. In traditional animation the images were drawn (or painted) by hand on cels to be photographed and exhibited on film. Nowadays most animations are made with computer-generated imagery (CGI). Computer animation can be very detailed 3D animation, while 2D computer animation can be used for stylistic reasons, low bandwidth or faster real-time renderings. Other common animation methods apply a stop motion technique to two and three-dimensional objects like paper cutouts, puppets or clay figures. The stop motion technique where live actors are used as a frame-by-frame subject is known as pixilation.
Commonly the effect of animation is achieved by a rapid succession of sequential images that minimally differ from each other. The illusion-as in motion pictures in general-is thought to rely on the phi phenomenon and beta movement, but the exact causes are still uncertain. Analog mechanical animation media that rely on the rapid display of sequential images include the phenakisticope, zoetrope, flip book, praxinoscope and film. Television and video are popular electronic animation media that originally were analog and now operate digitally. For display on the computer, techniques like animated GIF and Flash animation were developed.