Game Development Reference
In-Depth Information
Given the way that eyes focus light, we are born seeing the world upside
down! After a few days, our brains instinctively flip the images over so
that the motion of our hands matches the motion that we observe. There
have even been tests where people wearing glasses that invert your vi‐
sion will eventually see the images right side up. When they take off the
glasses, everything looks upside down again until their brain has time
to correct the image.
Binocular fusion is also a learned behavior of the brain. The visual cortex takes the
independent visual information from each eye and fuses it into a single image. Your
brain does this as a way of organically calculating the distance to objects so that you can
efficiently interact with the three-dimensional world. The exact process by which your
brain accomplishes this is an area of active research. In fact, researchers have found that
two images need not have any geometrical disparity in order to be fused. That is, if you
take the exact same photograph of the same object and the same angle, but with different
lighting, the shadows being cast can also cause the brain to recreate the object in three
dimensions.
Parallax is the distance an object moves between the left- and right-eye images. You can
easily demonstrate it by holding your thumb six inches from your face and closing one
of your eyes. Block some of the words on this page with your thumb. Now open that
eye and close the other one. The words that were behind your thumb should now be
visible. This is because your eyes are not in the same position, so the different angles
provide slightly different pictures of the page. This distance your thumb appeared to
move is the parallax at that distance from your eye.
Fusion is a little harder to achieve, but Figure 24-1 provides an interesting example. The
two circles are set a specific distance apart and show the top of a truncated cone coming
out of the page. The top of the cone is offset compared to the bottom. This offset is in
opposite directions, mimicking how your eyes would see it if you were directly over the
cylinder.
Figure 24-1. Cone stereopair
The best way to view the stereopair shown in Figure 24-1 is to begin by looking above
this topic at a far-off object. Now lower your gaze without refocusing your eyes and
stare between the two sets of circles. With some trying, your brain should be able to fuse
the images so that there are now three sets of circles. The original two will be out of
 
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