3D holo video arrives
Technology Research News
Although three-dimensional video has long
been imagined -- Princess Lea's recorded plea to Obi-Wan Kenobi in the
1977 Star Wars movie comes to mind -- it has been slow to show up in the
real world. This is because three-dimensional video is orders of magnitude
more complicated than ordinary video.
Researchers from the University of Texas have devised a three-dimensional
video system that cuts down the compute power needed to project three-dimensional
images by using an 800,000-mirror device designed for two-dimensional
digital projectors as a sort of holographic film. "Our system provides
a simulated hologram capable [of] dynamic, truly holographic 3D images
like 3D movies," said Michael Huebschman, a research physicist at the
University of Texas Southwestern Medical Center at Dallas.
The approach could be used to make three-dimensional heads-up
displays, medical images, and computer games. It could eventually lead
to three-dimensional movies and television.
Our sense of sight depends on the way light reflected from an
object's surface hits our eyes. Light from a dark area of the object has
a smaller amplitude than light from a bright area. Light waves also interfere
with each other. When waves are in opposite phases, meaning the crest
of one light wave coincides with the trough of another, the waves cancel
each other. When two crests coincide, they are in phase and they reinforce
each other. And how out of phase two light waves are determines the amplitude
of the point where they intersect.
A hologram is a representation on a single plane of all of the
phase information, or interference pattern, of the light coming from an
object. It creates a three-dimensional image by projecting the interference
pattern reflected by a real object.
Holograms are made by bouncing a laser beam off an object and
having a second laser beam intersect the reflected light. The laser beams
interfere with each other, producing the requisite pattern of bright and
dark areas. The pattern is captured in a light-sensitive medium. Holograms
are seen when light hits the storage medium at the same angle as when
the hologram was recorded.
The researchers hit on the idea for their holographic video when
they realized that the mirrors of a digital micromirror device could function
like the light-sensitive grains of holographic storage media, said Huebschman.
In the researchers' system, the hologram is stored as information in a
computer rather than physically stored in a medium. The computer controls
the digital micromirror device.
In their original use projecting two-dimensional digital video,
the micromirrors project light waves of different amplitudes. The researchers
modified the device so that the mirrors projected the phase interference
pattern of a hologram. "The inspiration was realizing that the micromirrors
of the DMD are just large grains in a piece of film, and if a suitable
hologram could be computed and that image placed on the DMD, it would
interact with coherent light and then should function like a film hologram,"
The digital micromirror device is made up of 800,000 mirrors that
are 16 microns across, which is about three times the size of a red blood
cell. It is connected to a computer that controls the angles of the mirrors.
Any of 256 shades of gray can be projected onto each of the mirrors at
any time, providing a black and white holographic projection that can
be controlled in real-time to make three-dimensional video. "The mirrors...
being off or on are like the grains in a film emulsion being exposed or
not," said Huebschman. "The shades of gray on the DMD hologram are analogous
to the shades of gray of the grains in the emulsion hologram," he said.
One challenge to getting the device working as a holographic projection
system was the size of the mirrors, according to Huebschman. Despite their
relatively small size, the mirrors are larger than the grains of material
that make up film, which limits the available projection angles.
The method can eventually be used in several types of three-dimensional
displays, according to Huebschman. It is especially appropriate for heads-up
displays in aircraft, military control systems and air traffic control
systems, he said.
These applications have three things in common, said Huebschman.
A three-dimensional view would allow a viewer to gain an additional element
of information from a device he ordinarily uses; the device can be updated
quickly; and all that needs to be projected to provide the extra information
is a simulated object.
Further down the road, with better three-dimensional resolution,
the method could be used to bring three-dimensional images to scientific
workstations, computer games, flight simulators, x-rays and other types
of medical imaging, and movies.
The combination of the device and real-time digital hologram recording
equipment, which is yet to be developed, would make three-dimensional
live television possible, said Huebschman.
Several other research projects are also aimed at providing three-dimensional
video. A system developed by Actuality Systems, Inc. projects pixels in
space to build a three-dimensional scene. These pixels are timed to reflect
off a rotating plate so that they scatter to the correct locations at
the right times. The University of Texas method takes less compute power
than the three-dimensional pixel system because it uses the hologram to
organize light patterns, said Huebschman. "That information is already
available in a hologram," he said.
Another method developed at the Massachusetts Institute of Technology
converts holograms into a pair of two-dimensional stereo views, then projects
the images onto a user's eyes. "We start with a similar computer-generated
hologram but rather than using complex opto-electric elements to project
a stereo image, we project the image which results from the defraction
of... light by the hologram," Huebschman said.
The Texas work takes a new approach to three-dimensional holographic
video, said Hiroshi Yoshikawa, an associate professor of electronics and
computer science at Nihon University in Japan. The interesting point is
that the researchers are using phase modulation rather than amplitude
modulation to achieve the dynamic three-dimensional projections, he said.
The researchers' next steps are making color holograms, improving
the display equipment, and making a mobile, heads-up virtual image viewer,
said Huebschman. "We are ultimately aiming for 3D TV," he said.
One of the main challenges is making larger arrays of digital
micro mirror devices that have smaller mirrors, Huebschman added.
The method could yield practical three-dimensional heads-up displays
in one to two years, x-ray machines in two to three years, workstations
and flight simulators in three to five years, medical imaging equipment
and movies in five to ten years, and live TV in 10 to 15 years, according
Huebschman's research colleagues were Bala Munjuluri and Harold
R. Garner. The work appeared in the March 10, 2003 issue of Optics Express.
The research was funded by the Texas Board of Higher Education Advanced
Research Program, the University of Texas Southwestern Center for Biomedical
Inventions and the National Cancer Institute.
Timeline: 1-2 years, 2-3 years, 3-5 years,
5-10 years, 10-15 years
Funding: Government, University
TRN Categories: Data Representation and Simulation; Optical
Computing, Optoelectronics and Photonics
Story Type: News
Related Elements: Technical paper, "Dynamic Holographic
3D Image Projection," Optics Express March 10, 2003.
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