SURGEONS and designers could soon be manipulating 3D moving images floating
in mid-air rather than on computer screens, say engineers at DERA, Britain鈥檚
soon-to-be-privatised defence research lab. They say designers will be able to
extend a car鈥檚 bodywork just by waving a stylus, and almost instantly see what
it looks like鈥攐r surgeons could twist a brain scan around to locate an
injury.
鈥淲e can create a real image floating in 3D space,鈥� 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鈥檛
require people to wear cumbersome headgear to see the image, and prolonged use
doesn鈥檛 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.
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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 鈥渋nside鈥� the hologram that鈥檚
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鈥檛 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. 鈥淵ou very quickly get into
gigabytes of image data that you have to compute, store and display. It鈥檚 a
gargantuan feat,鈥� he says.
DERA developed the screen on which the hologram is formed. Called an 鈥渁ctive
tiling modulator鈥�, 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.