IEEE Spectrum November, 2014 - 55
retroreFlectors return an incident ray of light directly to its source,
allowing a projector to display the appropriate image to the driver no matter
where she may be directing her gaze. The reflectors are coated with tiny
beads, whose internal optics do the trick. Because retroreflective screens
convey light to the eye efficiently, they are very bright.
brightness of around 125 cd/lx/m2. A similarly
illuminated movie screen, by comparison, would
typically have a reflective brightness on the order
of 1 cd/lx/m2.
In other words, our RPT system's projection is
at least 100 times as bright as that achieved using
normal screens. And because the reflection is along
the axis of projection, there is no distortion of the
image even when it's projected on a screen of a
complex shape.
This system can also work as a kind of optical
camouflage, one that could make a person disappear into the background, for instance. The military might not come running, though, because this
trick works only if the person being camouflaged
is wearing clothes covered in
retroreflective beads. Also, the
observer must peer through a
half mirror while the projector
is fed data from a video camera
behind the camouf laged person. A computer uses imagebased rendering techniques to
calculate the appropriate perspective and to transform the
captured image into the image
to be projected onto the subject,
who then blends seamlessly into
the background. It is quite an
amusing effect.
Another possible use of the
RPT system is to capture data
from an X-ray machine or an
MRI scan, render it into an image,
and then superimpose it onto a
patient undergoing surgery. This
would be particularly useful for
minimally invasive surgery, the
kind conducted through a "keyhole" in the body. By superimposing ultrasonic data, the projector could also
display the body's inner organs in real time.
In a factory, a skilled craftsman might wear a glove
made of retroreflective material. An image could
be projected onto the glove showing tiny objects-
such as those involved in the testing of circuits-that
would otherwise be obscured by the craftsman's
hand. The possibilities of our see-through technology abound.
so far we have Been describing a system that caters to
just one person. But there is no reason not to equip
all the people in a car with this apparatus. Indeed,
it is quite possible to project multiple images on
the same screen.
illustrAtion by
James Provost
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Table of Contents for the Digital Edition of IEEE Spectrum November, 2014
IEEE Spectrum November, 2014 - Cover1
IEEE Spectrum November, 2014 - Cover2
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IEEE Spectrum November, 2014 - Cover3
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