Game Development Reference
In-Depth Information
Frames
The animation (and motion pictures as a whole) is based on the human ability to per-
ceive the so called
apparent motion
. It is not based on the real continuous move-
ment of an object, which should exist on each point of the motion trajectory, but on the
phase positions of an object, which exist only on the extreme positions of the traject-
ory. Everything in between is imagined by the brain (when the visual system creates
the in betweens at wrong positions, illusions such as the wagon-wheel effect occurs).
A good example of the apparent motion is the rail crossing semaphore with two al-
ternately flashing lamps. The signal may look like lights moving left and right, although
in reality, there is no physical movement of the lamps. Recall any neon sign with, for
example, moving chains of lamps or animated flipping topics. Thence, it is quite easy
to convince a person that something is moving because the vision system is very du-
bious and always tries to catch clues that something changes its positions.
Vilayanur S. Ramachandran
and
Stuart M. Anstis
in their article
The Perception of
Apparent Motion
, published in
Scientific American
(
June, 1986, Vol. 254, No. 6
), gave
the following pictorial explanation of the apparent motion's origin:
"In the real world anything that moves is a potential predator or prey. Hence being
able to quickly detect motion and determine what moved, and in what way, is crucial
for survival. For example, the ability to see apparent motion widely separated images
may be particularly important when detecting the motion of animals that are seen in-
termittently, as when they move behind a screen of foliage or a tree trunk."
The following figure shows how apparent motion works:
The
phi
phenomenon, which was defined by psychologist
Max Wertheimer
in 1912
and later became the basis for the cinema theory, is a special case of the apparent
motion and it directly describes the principle of motion pictures: a series of separate
still imageswith somecommonelements appearing rapidlycreates anillusion of com-
