Perspective Projection - Transformations and Projections in Computer Graphics - page 127

3.13 Viewing a Stereoscopic Image

A stereoscopic image consists of a pair (right-eye, left-eye) of images. To see this pair
in three dimensions, we have to view it in a special way. The guiding principle is that
our brain must receive from our eyes the same signals it receives when we watch a real
three-dimensional image. Given a stereoscopic pair of images on paper or on a screen,
the most common techniques to view it are as follows:
1. View it through a stereoscope. This is a simple device that can easily be built
at home.
2. Thecross-eyetechnique. Thetwoimagesofapairarelaidsidebysideandthe
viewer has to cross his eyes in order to slide the images and see them fused into a single
image.
3. The parallel-view technique. This is similar to the cross-view method but is
appropriate for small images.
4. The anaglyph method. The two original images are combined into a single image
where they are painted different colors. Special glasses are used to make sure each eye
sees only one color.
5. Page-flipped techniques, where the left and right pictures are continually flipped
on the screen.
6. Line alternate methods, where the left-eye and right-eye pictures are interleaved
on the screen. These are popular with head-mounted displays.
There are other, more sophisticated techniques, such as the Pulfrich effect and dot
stereograms. We follow with detailed descriptions of the most common methods.
Stereoscope
A stereoscope (Figure 3.48) is a simple device for viewing a stereo pair. It can easily be
made at home from cardboard, wood, and two lenses. In a piece of cardboard, cut two
circular holes with a diameter of about 1.5 in each and with about 6.5 cm separation
between their centers. Place a lens with a focal length of 4 in in each hole. Look at a
stereo pair located about 4 in away through the lenses, using another piece of cardboard
to make sure each eye sees only one image. More sophisticated devices are available
from several sources, such as [StereoGraphics 05] and [Edmund Scientific 05].
The Cross-Eye View Technique
Note . If you wear glasses, keep them on when trying this method.
The right and left images should be displayed side by side, with the right image on
the left and the left image on the right, as illustrated here:
RL right eye left eye

Start by staring at the center point between the two images. Slowly cross your eyes
and watch the two images slide closer. With a little patience and practice, you should
be able to make the two images overlap. You will then see three images, as illustrated
here: