Persistence of Vision is the theory that the human eye sees images 1/25th of a second after we stop looking at them. This is what creates the idea of motion perception, so when humans look at stop motion images being played next to one another they see the illusion of the images being one continuous loop. If a stop motion video is shot in less than 16fps then our minds will interpret separate images and will see through the illusion. A very early example of stop motion images in 24fps, so that our eyes can interpret everything as a full video, is the ‘Galloping Horse’ animation, made in 1878. Separate images are played next to one another so quickly that the human eye will begin to perceive the separate still images as being one continuously flowing video.
A screenshot from ‘Galloping Horse’
Different tools are used so that humans can see images quickly enough for them to be perceived as a moving image. These include the Zoetrope and Praxinoscope, which both work by being spun around on a pivot very quickly. A Zoetrope, (left), and a Praxinoscope, (right).
As cameras have developed, they have been able to start shooting in higher frame rates. This effectively means that more images (frames) will be played per second. This means that the eye will see more images and will perceive the moving illusion to be more smooth as it closer to the frame rate in which the eye sees things in real life. This means that the use of animation in film and television is improving as it is becoming easier for filmmakers to produce a higher frame rate with their better equipment.