Explained: How our eyes see videos or moving images
When we see movie, animation or TV, i.e. video in any format, we are actually looking at a rapidly displayed series of stills. Does this mean that video is actually just a collection of photos? Confusing, but yes, that’s how it works. How do we manage to see a bunch of photos as video, and how is it so smooth that we cannot make out each image separately? It’s because of a phenomenon called persistence of vision. Let’s know a bit more about this.
What is persistence of vision?
The eye and brain retain a visual impression for about 1/30th of a second, even after the object itself is removed. The exact time of image retention depends on the brightness of the image. And this ability of the eye to retain an image in the brain is known as persistence of vision. Different technologies take advantage of human persistence of vision to help us see video. For example, when we watch a movie, it feels like a continuous experience of seeing motion smoothly, even though the screen is dark about half the time. Movies show 24 or 25 still images per second. Depending on the film, each frame is shown twice or three times during this period. The eye retains the image of each frame long enough to give us an illusion of smooth motion. TV, animation, computer monitors and smart phone videos take advantage of our failure to notice the constantly refreshing images right in front of us, since the brain is holding on to the same image.
How do moving images form inside the eye?
Whenever light strikes the retina, the brain retains the impression of that light for about 1/10th of a second, depending on how bright it is, even after the source of that light is removed from the eye. This is due to a prolonged chemical chain reaction inside us. As a result, the eye cannot clearly distinguish changes in light that occur faster than the light retention period. The changes either go unnoticed or they appear to be one continuously lit image to the human eye. And that’s how we see images ‘moving’ or ‘video’.