The Art & Science of Movie Special Effects

Persistence of Vision

Look at a bright light for a few seconds and then abruptly close your eyes. The image of the light seems to stay in your eyes a little longer even though your eyes are closed.

This phenomenon is termed as Persistence of Vision because the vision seems to persist for a brief moment of time.

When the retina of the eyes are excited by light, they send impulses to the brain which are then interpreted as an image by the visual cortex in the brain. The cells in the retina continue to send impulses even after the incident light is removed. This continues for a few fractions of a second till the retinal cells return back to normal. Until that time, the brain continues to receive impulses from the retina, and hence seems to perceive an image of the source of light, giving rise to the phenomenon called Persistence of Vision.
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Principle of Motion Picture

The Principle of Motion Picture is totally based on the phenomenon of Persistence of Vision. Without it, motion picture as we know it simply would'nt exist. Our eyes can retain a picture for a fraction of a second after seeing one. Before this time frame expires, if a another similar picture is shown in its place, the eyes see it as a continuation of the first picture, and don't perceive the gap between the two.

If a series of still pictures depicting progressively incrementing action is flashed before the eyes in rapid succession, the eyes see it as a scene depicting smooth, flowing action. All visual media (Movies, TV, Electronic Displays, Laser Light Shows, etc) exploit this phenomenon.

Thanks to Persistence of Vision, our entertainment industry could make a transition from perpetual live shows like dance and dramas, to recordable entertainment like movies.
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What is Motion

Motion of an object is the continuous displacement of the object in space with reference to another object. In the absence of a reference object, motion ceases to be apparent. What this means is that motion is always measured in relation to another object, which is used as a reference point.

When we drive, the road & the surroundings move past us. Thus we get the sensation of motion. So the road & surroundings are our reference points. When we fly, the earth beneath us is our reference point. But as you can see, the closer the reference point, the more acute the sense of motion. That's why astronauts in orbit seldom sense speed (though they are moving at thousands of miles an hour ) because earth, their only reference point is quite far away.

OK, but what has this got to do with Special Effects ?! A Sfx technique called Compositing totally relies on the way our mind perceives motion. Compositing is one of the most useful tools in a Sfx technician's bag of tricks. Keep these two in mind; the object, and its reference point(s); both of these are necessary to perceive motion in a scene.
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Story Board :
A series of sketches based on the final draft of the script depicting various scenes in the story, which the director, cameraman and the art department use to plan for each scene.
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Types of Special Effects :
There is a wide range of effects that is used in the industry. You have front / back projection, compositing, cel animation, computer animation, rotoscoping, stop-motion & go-motion animation, puppetry, pyrotechnics, miniature / model making, matte paintings, makeup effects, stunt effects, sound effects and a host of other effects techniques. The list keeps growing as time goes by. Sometimes older techniques give way to newer and more sophisticated ones. And as stated earlier, Special Effects range from highly sophisticated techniques like visual effects or photo special effects to the mundane effects like special effects make up or even special effects hair dye.
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