Module 1: Roots of Animation

1.3 Persistence of Vision

So, how does animation work? What causes a still image to appear to move smoothly across a scene? Are your eyes playing tricks on you? Yes, in a way they are. A simple theory known as persistence of vision offers an explanation. As you'll recall, the Greek astronomer Ptolemy discovered this principle back in 130 A.D. This principle has evolved since then, as a result of further studies about light and observations of human eye anatomy and behavior. Let's examine how this principle serves as the basis of animation.

The retina captures and holds an image for one-tenth of a second before processing the next image. If images are flashed before the eye at at least 10 frames per second, the brain thinks it is seeing a single moving image. The number of frames per second, or FPS, directly correlates to how smooth the movement appears. If the frame rate is too slow, the motion will look awkward and jerky. If the frame rate is too high the motion will blur. We will discuss frames and frame rates in more detail in the next module.


Figure 1.3 Frame Animation Comparison

Roll your cursor over the 5fps and 12fps images shown above.




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