Virtually Yours Source: New Scientist December 16, 2000.
SURGEONS and designers could soon be manipulating 3D
moving images floating in mid-air rather than on computer screens, say
engineers at DERA, Britain's soon-to-be-privatised defence research
lab. They say designers will be able to extend a car's bodywork just
by waving a stylus, and almost instantly see what it looks like--or
surgeons could twist a brain scan around to locate an injury.
"We can create a real image floating in 3D space," says
Chris Slinger, head of holography at the Defence Evaluation and
Research Agency in Malvern, Worcestershire. Working in a joint venture
with the Ford Motor Company, DERA says it plans to have its first
products based on advanced computer generated holography (CGH) on the
market in 2003.
Unlike other techniques, such as stereography or virtual
reality, CGH doesn't require people to wear cumbersome headgear to see
the image, and prolonged use doesn't lead to any ill effects. Users
manipulate images using tools that exist partly as real objects and
partly as virtual tools. It is like nothing else we have seen before,
claims Slinger.
CGH is based on the same principle as the holograms
invented by Dennis Gabor in 1949. A hologram is essentially an
interference pattern generated from the object being depicted. When
light strikes the hologram it is diffracted, forming a series of
wavelets. Interference between these wavelets produces wavefronts that
simulate the light that would have come from the original object.
In a normal hologram, the image appears to be "inside"
the hologram that's producing it. But with a computer generated
hologram it is possible to produce interference patterns that simulate
the waves from an object hanging in empty space. This means an image
can be projected in front of the screen, Slinger says (see Diagram).
In the DERA/Ford device, a mirror focuses the image so that it can be
seen from a range of angles. There is a another key difference, too:
as well as displaying images of real objects, the CGH system can
create 3D images of imaginary objects.
The main problem with previous computer-generated
holograms has been that they don't have enough pixels to produce an
image of a useful size, says Stephen Benton of the Massachusetts
Institute of Technology. Benton says roughly a billion pixels are
needed to produce a 3D image. "You very quickly get into gigabytes of
image data that you have to compute, store and display. It's a
gargantuan feat," he says.
DERA developed the screen on which the hologram is
formed. Called an "active tiling modulator", it uses ferro-liquid
crystals to create vast numbers of pixels that form a hologram. The
system is modular and can be scaled up or down to the required image
size. Previously, this had been too complex and computationally
demanding, says Benton.
by Duncan Graham-Rowe
http://www.newscientist.com/news/news.jsp?id=ns226914