Information Technology Reference
In-Depth Information
2.7 Head Mounted Displays
A head mounted display [29] is a display device worn on the head or as part of a
helmet that has a small display optic in front of both eyes in case of a binocular
HMD (monocular HMDs also exist but unable to produce 3D images). A typical
HMD has two small displays with lenses embedded in a helmet or eye-glasses.
The display units are miniaturized and may include CRT, LCDs, LCOS, or OLED.
Some HMDs also allow partial see-through thus super-imposing the virtual scene
on the real world. Most HMDs also have head tracking functionality integrated.
From the 3D vision point of view, they are equivalent to glasses based systems.
HMD manufacturers include Cybermind [30], I-O [31], Rockwell Collins [32],
Trivisio [33], Lumus [34].
3 Autostereoscopic Displays
Autostereoscopic displays provide 3D perception without the need for wearing
special glasses or other head-gear, as separation of left / right image is imple-
mented using optical or lens raster techniques directly above the screen surface. In
case of two views, one of the two visible images consists of even columns of pix-
els; the second image is made up of odd columns (other layouts also exist). The
two displayed images are visible in multiple zones in space. If the viewer stands at
the ideal distance and in the correct position he or she will perceive a stereoscopic
image (sweet spot). Such passive autostereoscopic displays require the viewer to
be carefully positioned at a specific viewing angle, and with her head in a position
within a certain range, otherwise there is a chance of the viewer being in the
wrong position (invalid zone) and seeing an incorrect image. This means that the
viewer is forced to a fixed position, reducing the ability to navigate freely and be
immersed.
To overcome the problem of invalid zones head and/or eye tracking systems
can be used to refresh the images whenever the viewer is about to enter such a
zone and experience an incorrect 3D image [35]. Even though there could be la-
tency effects, such a system provides the viewer with parallax information and it
is, therefore, a good solution for single user applications. Multi-user extensions of
this technique are also developed [36].
Some autostereoscopic displays show stereoscopic 3D (consisting of two im-
ages), others go beyond that and display multiview 3D (consisting of more than
two views). Multiview displays [37] project different images to multiple zones in
space. In each zone only one image (view) of the scene is visible. The viewer's
two eyes are located in different zones, seeing different images thus 3D perception
is enabled. When the user moves, entering different zones will result in different
views, thus a somewhat limited horizontal motion parallax effect is achieved. As
the number of views ranges from 4 to 9 in current multiview displays, the transi-
tion to adjacent zones is discrete, causing „jumps” as the viewer moves. Multiview
displays allow multiple simultaneous viewers, restricting them, however, to be
within a limited viewing angle. The image sequences are periodically repeated in
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