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10.4. Summary 255
screens, there are no problems, but the challenge is to accommodate stere-
opsis under such conditions. Each individual will have a slightly different
viewpoint, point of focus etc., and these effects amplify the differences. Re-
volving and providing solutions to VR-specific issues such as this are still at
the research stage, and no definitive or obvious answer has emerged. Some
experiments have been done by using shutter eye systems that display two
images for every participant in the room. Unfortunately, this will involve
operating the display and polarizing shutters at much higher frequencies.
At present, systems that can accommodate three people have been demon-
strated, and in one case even a revolving mechanical disk acting as a shutter
that sits in front of a projector has been tried. It would seem, however, that
the most promising approach involves trying to improve the LCD shutter
technology and projection systems. Fortunately, to a first approximation, the
effect on individuals of rendering a generic stereoscopic viewpoint from the
center of the cave does not introduce a distortion that is too noticeable. The
overwhelming sensation of depth perception outweighs any errors due to the
actual point of focus not being the one used to generate the stereoscopic view.
We will not take this discussion any further here, but we suggest that you
keep an eye on the research literature that appears at conferences such as the
SPIE [2] annual meeting on electronic imaging.
10.3.7 Front or Back Projection
All the illustrations used so far have depicted front projection. There is no
particular reason for this. Back projection works equally well for stereopsis.
Sometimes the term used to describe back-projection stereopsis is a stereo wall.
If there a re any drawbacks, they are purely in terms of space, but even this can
be overcome by using a mirror with the projectors mounted in a number of
different possible configurations. Back projection has the major advantage
that anyone working in the stereo environment can go right up to the screen
without blocking out the light from the projector.
10.4 Summary
This chapter has introduced the concept, notation and hardware of stereop-
sis. We have looked at both low-cost (e.g., stereo glasses) and high-cost (e.g.,
head-mounted displays) hardware and how they work to achieve the stereo
effect. So regardless of your VR budget, you should be able to develop a
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256 10. Stereopsis
stereoscopic working environment which considerably enhances the VR ex-
perience.
What we have not considered in the chapter is the topic of display adap-
tors and how they are intrinsically linked to the creation of stereo output.
However, we shall return to this topic and also examine some practical appli-
cation programs and how they are constructed in Chapter 16. There we will
also look at how to use two simple webcams to record stereoscopic images
and play stereoscopic movies.
Bibliography
[1] C. Bungert. “HMD/Headset/VR-Helmet Comparison Chart”. http://www.
stereo3d.com/hmd.htm.
[2] IS&T and SPIE Electronic Imaging Conference Series. http://
electronicimaging.org/.
[3] LightSpace Technologies. “DepthCube”. http://www.lightspacetech.com/.
[4] R. Wangsness. Electromagnetic Fields, Second Edition. New York: John Wiley
& Sons, 1986.
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