What is Persistence of Vision in Film?
During the production of animated films, the illusion of movement is frequently referred to as the persistence of vision. This phenomenon is said to result from the residual image. Which is ingrained within the retina of the eye as the next image is shown creating an optical illusion. Causing the brain to perceive motion in instances in which there is technically not a fluid movement or motion occurring. But what is persistence of vision in film and how can it be explained?
Understanding Persistence of Vision in Film
The persistence of vision phenomenon basically results when the eyes see a single non-moving image. Which is printed on the retina for a period of just 1/25 of a second. As the brain looks to perceive an image, even after exposure to the image has since discontinued.
The eye continues to see it for that very brief period of time. When another image is shown, such as in a flip book, where the static image is very similar to the previous image but has shifted slightly. Persistence of vision will cause the eye to see an illusion of movement.
Thus, when several static frames are shown in succession at a fast rate one after another. The illusion of movement can be reproduced due to persistence of vision for the human eyes.
You might recall the early use of flip book animations? The use of rapidly changing frames, with very minimal changes within the frame can create the perceived look of altered movement or motion. Despite the frames being static and no actual movement occurring.
How is Persistence of Vision in Film Used?
In the film industry, persistence of vision is used to fool the audience into perceiving motion. Knowing that the eye will see an image for 1/25 of a second.
It’s safe to assume that the succession of pictures at a speed of at least 20 frames/sec will create visual fluidity. Such that the human eye cannot perceive the rigidity or lack of succession in images that are shown.
Likewise, if a projector were to show frames that flashed at 20 frames/sec or less, the eyes would notice the scrolling of the images and the lack of persistent fluidity would be noticeable.
In other words, the eyes would be able to recognize the changing of images from one to the next. Because of the slow succession below 20fps. But anything over 20fps would result in good visual fluidity.
In Summary
Thus, persistence of vision in film has been used for nearly 100 years to produce the illusion of motion by showing the succession of static images, one after another. And only with rapid projection of these images has the illusion of movement become fluid and natural appearing.
Which is why most films are shown at about 24fps. It’s also why, for exceptional quality and the highest fluidity, films can be shown at 30 to 60 fps for greater persistence of vision in film