What could be more routine
than an action scene in a movie, or someone talking on TV?
Often we forget that when we see images moving in these two media that
are so central to our social lives, we are actually the victims
of a motion illusion.
The moving images that you see when
you go to the movies are not really caused by the continuous
movement of anything in the images themselves. On the contrary,
what you are really watching is a series of still photographs
(or "frames") that are separated from each other
by thin black strips. When the movie was being filmed, the
movie camera shot several of these frames per second (in
today's movie cameras, 24), so that the position of the people
and objects that were moving differs slightly from one frame
to the next. Television and video cameras work differently,
but they are still capturing a succession of still images.
When a film is shown, to give the impression
of fluid rather than jumpy motion, the projector cannot just run
the film continuously. Instead, it must stop each frame between
the projector lamp and the projector lens for a fraction of a second.
In between frames, a shutter closes between the lamp and the film
to darken the screen so that you cannot see the film moving from
one frame to the next.
But if all you saw was 24 frames and 24 intervals
of darkness per second, your eyes would still notice a bit of flicker
from the alternating light and darkness. Starting at about 50 images
per second, however, you stop noticing the darkness and begin perceiving
the light as continuous. The shutter therefore closes not just
once between frames, but also once while each frame remains in
position. Thus, what you are actually seeing each second is 48
images alternating with 48 intervals of darkness.
It was long thought that the reason we stop perceiving flicker at around 50 images
per second was a phenomenon called "retinal persistence". For decades,
books about motion pictures also said that retinal persistence was responsible
for the illusion of movement that we experience on the big screen. But now it
would appear that the real explanation for these two phenomena is
quite different.
The French physician and
inventor Étienne-Jules Marey was the first person
to use photographs taken in rapid
succession to record the phases of locomotion in
animals and humans. In 1877, the British/American photographer
Eadweard James Muybridge took a series of 24 photos of
a running horse, then mounted them on a device that projected
them at a sufficient speed to create the illusion that
the horse was galloping.
The first public screening of motion
pictures took place on December
28, 1895 in Paris, using the Cinematograph
projector invented by brothers Louis and
Auguste Lumière. The screening consisted
of a few short silent films shot by the
Lumière brothers themselves, including Train
Arriving at La Ciotat Station (see
below).
Still from the film Train
Arriving at La Ciotat Station,
by Louis Lumière (1895)
The period until the late 1920s was
the era of silent films. There was no
sound to accompany the images except, sometimes, a pianist
playing music live while the movie was being shown. Sound entered
the movies in 1927 when the film The Jazz Singer came
out in the United States.
The date when colour was introduced into
motion pictures is harder to pin down. The first great
popular colour films were The Wizard of Oz and Gone
With the Wind, both of which came out in 1939. But
a silent film called Cupid Angling was shot in
colour back in 1918, and various experiments with hand
colouring were attempted prior to 1908.
Lastly, on January 27, 1926, the Scottish inventor John
Baird gave the first public demonstration of his process
for receiving images on a cathode-ray tube—the ancestor
of television.
