Page 221 - DCAP504_Computer Graphics

Computer Graphics

Persistence of Vision
Persistence of vision is a phenomenon of the eye where an afterimage is thought to persist for one
twenty-fifth of a second on the retina of the eye. In the visual perception phenomenon, the eye is not
considered as a camera. The phi phenomenon has a more constructionist approach towards cinema
while persistence of vision is a realistic approach.
Today, persistence of vision is an accepted phenomenon in the history of cinema. In the early days, it
was determined that a frame rate of less than 16 frames per second had enabled the mind to see flashing
images. Audiences, sometimes interpret motion at ten frames per second or even slower. The modern
theatrical films run at 24 frames per second.
The two perceptual illusions are:
1. Phi Phenomenon: This method is an optical illusion defined by Max Wertheimer in the Gestalt
psychology in 1912. It is based on the principle that the human eye is able to perceive movements
based on pieces of information. This is similar to the succession of images. The speed of the images
per second can be observed for the phi phenomenon. The figure 14.1 shows the phi phenomenon
and depicts how an object moves in a circular motion with constant speed.

Figure 14.1: Phi Phenomenon

Source: http://en.wikipedia.org/wiki/Phi_phenomenon
2. Beta Movement: The beta movement is considered to be a perceptual illusion where the brain
merges two more still images, imaginatively to be in motion. This phenomenon creates an illusion
of motion both towards and away from the viewer. Consider phenomenon of a viewer watching a
screen. This screen is projected with two images in succession. The first image shows a ball on the
left side of the frame, while the second image shows a ball on the right side of the frame. These
images are shown in rapid succession. Thus, as a viewer you can see one ball moving from the left
towards the right but not two balls flashing in succession. When the two objects are of different
size that is when the first image is large and the second image is small. As a viewer, you can only
view that the object is moved away from us.

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