Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sun!imagen!atari!portal!cup.portal.com!dan-hankins
From: dan-hankins@cup.portal.com (Daniel B Hankins)
Newsgroups: comp.sys.amiga
Subject: Re: Coke 3D
Message-ID: <14489@cup.portal.com>
Date: 10 Feb 89 00:33:23 GMT
References: <8902071540.AA02699@terra.oscs.montana.edu>
Organization: The Portal System (TM)
Lines: 53


     It is entirely possible, and in fact not difficult at all, to obtain
on the Amiga the same kind of 3D effects observed during Superbowl
halftime.

     The effect is based on a phenomenon known as the Pulfrich effect,
named after its discoverer.  He discovered that when one eye is covered
with a dark glass, that a pendulum swinging left and right would appear to
take on a circular motion.  The reason for this was discovered some time
later.
     When light strikes the retina of the eye, a chemical reaction takes
place which causes a signal to be transmitted to the brain.  There is a
measurable delay between the time the light strikes the retina and the time
that the reaction progresses far enough for the signal to be sent.  As one
might expect, the speed of this reaction is in proportion to the energy
received.  What this means in practical terms is that a dim light causes
the signal to be generated later than a bright light.

     Suppose that wearing a dark glass over the right eye causes an
additional delay of 1/60th of a second in reception of any given signal. 
Now suppose that you are watching the pendulum as it swings from left to
right.  Your left eye sees where the pendulum is now, and your dimmer right
eye sees where the pendulum was 1/60th of a second ago - slightly to the
left of where it is now.  To focus both eyes on the object, the right eye
must be focused slightly to the left of the focus of the left eye.  Here's
a grossly exaggerated diagram:

                                direction of motion
                                  -------------->

    Pendulum 1/60th of a second ago -> *   * <- Pendulum now
                                        \ /
                                         * <- apparent position of pendulum
                                        / \
                                       ^   ^
                                left eye   right eye (dim)

     So while swinging from left to right, the pendulum appears to be
closer than it actually is.  While swinging from right to left, the
pendulum would appear to be farther away than it actually is.  Voila!  3D
effect.

     How to do this sort of thing on the Amiga is fairly clear:  Close
objects should move from left to right, medium range object should be
stationary, and far objects should move from right to left.  The dark lens
should be worn over the right eye.

     One caution:  prolonged usage of this technique can cause a splitting
headache (eyestrain) in some people, for the same reason that other stereo
vision techniques do.


Dan Hankins