Viewing Stereo
Passive Stereo
As was the case with active stereo, users of passive stereo systems must wear special glasses. Unlike the active stereo glasses, however, passive stereo glasses are simple, inexpensive, very lightweight, and have no embedded electronics. Two primary types of passive systems have been developed:
- Anaglyphs: The image for one eye is drawn in red, and the image for the other eye is drawn in blue or green. The user wears glasses with a corresponding red lens over one eye and a blue (or green) lens over the other. The color filtering then ensures that only the correct image arrives at each eye. A clear disadvantage of this approach is that only monochrome images are possible.
- Light polarization: Full color left and right eye images can be presented at the same time on the display, but with two different polarizations. The passive glasses have corresponding polarized lenses, thus ensuring that each eye only receives the image intended for it. The obvious advantage is that full color stereo is possible. An early problem was that the light polarization process resulted in darker images. Projectors today tend to be much brighter, however, hence this problem has more or less disappeared. To work effectively, a special polarization-preserving screen must be used. The glasses are quite inexpensive. The ones on the left vary from about a dollar a pair (top) to fifteen or so (bottom).
