The basis of all film falls on the brain’s ability, or lack thereof, to process what the eyes perceive. By presenting a still image in quick enough succession, the brain will fail to see the motion of the images passing and create an illusion of motion of the actual image.
This is the persistence of vision. The brain retains an image for 1/15 of a second. When the brain processes 10-12 individual images a second, the brain replaces this as movement. The phenakistoscope was invented by Joseph Plateau. The slot was used to stop the image, making the motion easier to perceive. Projectors use this same principal by using an intermittent movement, something we will discuss in the future.
Persistence of vision is an optical phenomenon. At 10 frames a second, the brain still sees the space between the images. In the 18th century, they learned that 24 frames a second provoked smooth motion. Flip books at this time used 24 frames.
Lucretius in 70BC-80BC era first mentions the concept. Ptolemy describes the idea around 165AD. Porphyry, Ibn Al-Haytham, Da Vinci, Newton, & Patrick D’Arcy all contributed to the concept.
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German theorists Max Wetheimer specifically discovered that the movement is created behind the retina. The eye splits incoming information as light, color, depth, form and motion. They also learned that it is not how long the brain retains the image, rather how the brain interacts with it. Multiple images become interpreted as one as the brain cannot keep track of each individual image. The brain begins processing the information as motion of one object as it cannot cope with it otherwise.
In simple terms, light bounces from a two dimensional image into your eyes. Your brain perceives this light as an object in space. Should the image move, the brain perceives this as motion. If you control what light the eye receives by a narrow viewport, your brain will perceive motion only within the portal, the surrounding light is still. If one passes sequential photographs faster than 10 images a send, that light confuses the brain into thinking it is a still object again. At 24 sequential images a second, the brain perceives the light as smooth motion of the object in the portal. Change the sequential images into one continuous film strip, project a light through the strip to create an image on a surface, the eye will collect this reflected light from the surface and the brain perceives a large continuously moving still imagery.
This sounds complex but it is simple enough you can do this with a toddler. a disk suspended between two strings, an image on either side, and spin. There you go.
Future blogs will touch on this concept again. It is intrinsically part of the movie going experience.
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