IEEE Spectrum November, 2014 - 54

We have solved all these problems with a new
projector system that reflects light precisely back
along the path it has just taken. By doing this,
we can project the correct image, in its proper
apparent position, directly at the observer-
provided that the projector is close enough
to the observer's eyes. In order to do this, we
can place it on the person's head or mount the
projector on the ceiling and have it track the
person's movements.
Our retroreflective projection technology, or
RPT, uses a screen coated in 50-micrometer glass
beads, which produces a very bright reflection.
What's more, the system uses one projector for
each eye, so it can create a stereoscopic effect

how to make a rolling theater in the round
A crouching boy becomes visible to
a driver when she looks back. In this, the
latest refinement of the authors' system,
the projector is placed on the floor rather
than the ceiling and projects an image of
the boy up to a half mirror. Some of the
rays bounce to a special, retroreflective
screen on the backseat, which returns them
directly to the driver's eye. Some rays (not
shown, for simplicity's sake) also proceed
upward to produce a copy of the image on
a ceiling retroreflector. This image is also
reflected by the half mirror to the driver's
eye, ensuring that she will see the boy even
if someone is sitting in the backseat.

computer

with a single screen. No shutter glasses or any
other movie-house 3-D equipment are required.
here's how iT works: The projector directs the outgoing
beam to a half mirror in front of the observer. Part
of the beam goes on to illuminate the special screen,
which reflects most of it directly back through the
half mirror and straight into the observer's eyes.
The reflection is bright because the tiny beads
that make up the retroreflective coating work very
efficiently. When illuminated by 1 lux of light, the
reflective brightness is roughly 500 candelas per
lux per square meter. Multiplying this value by
0.25 to account for the reduction caused by passing to and fro through the half mirror gives a final
54

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NOV 2014

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NOrth americaN

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retroreflective
screen
video camera

half mirror

SPectrUm.ieee.OrG

projector



http://SPectrUm.ieee.OrG

Table of Contents for the Digital Edition of IEEE Spectrum November, 2014

IEEE Spectrum November, 2014 - Cover1
IEEE Spectrum November, 2014 - Cover2
IEEE Spectrum November, 2014 - 1
IEEE Spectrum November, 2014 - 2
IEEE Spectrum November, 2014 - 3
IEEE Spectrum November, 2014 - 4
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IEEE Spectrum November, 2014 - 73
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IEEE Spectrum November, 2014 - 75
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IEEE Spectrum November, 2014 - 82
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IEEE Spectrum November, 2014 - 84
IEEE Spectrum November, 2014 - 85
IEEE Spectrum November, 2014 - 86
IEEE Spectrum November, 2014 - 87
IEEE Spectrum November, 2014 - 88
IEEE Spectrum November, 2014 - Cover3
IEEE Spectrum November, 2014 - Cover4
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