Also called
3D displays or
spatial displays, autostereoscopic
displays are
stereoscopic displays which do not require any special viewing devices, such as shutter glasses or polarized glasses. An autostereoscopic display -- one which can display high-fidelity, three-dimensional, moving pictures -- is in some sense the
Holy Grail of display technology.
There are several approaches to autostereoscopic displays currently being researched. They include video holography (at MIT's Media Lab), integral photography (at NHK's STRL), parallax barrier methods (at the NYU Media Research Lab), and methods using diffractive optical elements (at the University of Alabama at Huntsville).
Two of the major roadblocks to the creation of the ultimate autostereoscopic display are (1) the unavailability of high resolution light emitters (current technologies, like LCDs and CRT's just don't cut it) and (2) the extremely high bandwidth required to send the data to the display. Some estimate the bandwidth requirement as 1 gigapixels/frame, which for a 24-bit, 30 frames/s display would be 720 Gbps. By comparison, Firewire transfers data at a measly 400 Mbps. Obviously, some sort of lossy compression is necessary to make this sort of display possible in the near future.
In some sense, the term 3D display is a misnomer. Autostereoscopic displays work by reconstructing the plenoptic function, which is a five-dimensional function describing the distribution of light in a space. In most cases, however, the reconstruction of the full 5D function is impossible or impractical, so the 4D simplification is used.
Finally, the projection constraint for autostereoscopic displays states that there must be some element of the display along the line from the viewer's eye to a point in the spatial image. This means that if you're looking at a spatial image produced by an autostereoscopic display, then some part of the display must be behind all parts of the image from your viewpoint -- you should not be able to see the viewer on the other side of the image looking at the image in the reverse direction (unless, of course, the display is transparent).
References
- David F. McAllister (editor), Stereo computer graphics and other true 3D technologies, Princeton University Press, 1993
-
Michael McKenna and David Zeltzer, "Three Dimensional
Visual Display Systems for Virtual Environments,"
Presence: Teleoperators and Virtual Environments, 1992, 1(4):421–458.
- Takanori Okoshi, Three-dimensional Imaging Techniques, Academic Press, 1976