9 November 2019 | New Scientist | 43bounced off the wall. The haphazard nature
of scattering made things difficult, because it
was only possible to get a sphere of possibilities
as to what point on what object’s surface each
photon had come from. But by timing lots
of photons returning from many different
positions on the wall, the researchers ended
up with numerous spheres of possibilities.
Ultimately, the points where these spheres
overlapped in their calculations formed a
crude yet recognisable three-dimensional
image of the hidden manikin.
Accidental cameras
Specialist laser systems like Raskar’s don’t
come cheap, which could limit their
application. Last year, some of his former
group members, now at Stanford University
in California, developed a version of their
algorithm that could be run in conjunction
with more widely available detection
equipment. As the technology shrinks,
they hope it could be integrated into surgical
endoscopes. This might allow surgeons to
see parts of an unhealthy intestine that are
otherwise too tight to probe. It could also
find use in autonomous vehicles, letting them
spot other road users about to hurtle out of
side streets. Exploiting it in CSI-style forensics
will be trickier, because the technology would
have to be incorporated into every CCTV
camera at the manufacturing stage.
And yet, even everyday technology can
be trained to see things outside the frame.
The underlying concept here is different,
relying on the existence of what are now
being called “accidental cameras”, but the
results are equally jaw-dropping.
We normally think of cameras as devices
with glass or plastic lenses, but a camera can
be anything that controls the light falling on
a surface. Take the humble camera obscura,
for example: by allowing light to enter a
darkened room solely through a tiny hole,
only light rays travelling directly from different
points outside can get in. Unadulterated by
any scattered light, these direct rays form
a perfect, if inverted, image of the exterior
scene on the wall opposite the hole.
Such a camera is almost always deliberately
constructed. But as soon as Antonio Torralba
and William Freeman at MIT started looking,
they found unintended cameras almost
everywhere – not just holes, but edges of any
sort. A corner in a corridor, for instance. >