Now, various firms are beginning to make displays for unencumbered viewing of desktop-scale 3D images commercially available. The technologies involved differ, but they all aspire to the eye-catching brightness and depth-of-field of holograms, still the gold standard for in-depth imaging.
Anyone who has ever witnessed a laser-burnished holographic image floating in air at a museum or lab or art gallery remains haunted by its ghostly presence. Even if you've only seen the original Star Wars movie and its depiction of Princess Leia's secret message projected holographically by R2D2, you're probably hooked. In 1977, when director George Lucas crudely synthesized his 3D holographic film clip, it seemed the most imminent of the futuristic technologies in Star Wars. Nearly a quarter-century later, a full-color in-depth holographic display with real-time animation is still largely a thing of fantasy. In fact, the only holograms widely available today are the thumbnail-size foil-embossed ones on credit cards-hardly what the medium is capable of projecting.
A true hologram employs two beams of monochromatic laser light to create an interference pattern that under the right illumination can reproduce the full depth of an object. As an optical phenomenon, it can replicate the entire visual content of a real-world scene-in some cases, down to the microscopic level. To display real-time computer-generated 3D color data sets from CAD/CAM models, medical scans, or animated entertainment clips requires huge computing overhead for rendering all those points simultaneously.
|Voxel's laser-based holographic technology, one of several that now allow viewers to see in stereo without special glasses, is the basis of a commercial application for displaying medical scans.|
The current crop of holographic-type displays offers usable alternatives to as yet unattainable large-scale real-time holographic imaging by employing perceptual or technological compromises. Except for purists, the distinction between the vivid unencumbered images obtained with low-tech white light and mirrors as opposed to high-tech lasers becomes less important than the display devices' practicality in specific applications and environments. Regardless of their underlying technologies, these easy-to-view in-depth displays are now generically referred to as "holographic"-even if many of them actually aren't.
Just how deeply holography has entered public perception was demonstrated a few years ago when ABC News anchor Peter Jennings introduced a report about an innovative medical imaging prototype by describing it as a hologram. "We told his producers that this wasn't a true hologram," recalls Alan Sullivan, chief technology officer for the device's maker, Dimensional Media Associates. "They said that to the general public a 3D image is a hologram, and that's all that mattered, even if we knew better."
This display reflected a computer graphics model of a human heart from a projection LCD display onto a heart-shaped plastic form. Though seemingly simple, this imaging system nonetheless provided a useful technology for modeling cardiac anomalies with a realistic sense of depth. In addition to giving would-be surgeons an accurate-looking visualization, it also responded to a "digital scalpel"-a device providing force feedback to replicate the feel of manipulating or even cutting into the heart. This proof-of-concept prototype was funded by the US Defense Department's DARPA agency, under its telemedicine research program.
In the current generation of Dimensional Media's in-depth displays, it's all literally done with mirrors. With Dimensional's technology, which the firm calls "high-definition volumetric display" (HDVD), tabletop or kiosk-size enclosures containing spherical glass mirrors and high-quality white lightbulbs are used in point-of-sale displays to converge the reflected light beams from an object-like client Pepsi's new blue can-12 to 16 inches into mid-air to catch consumers' attention. Six different models are available, ranging in price from $3500 to $7500. Such applications generate the cash flow necessary to develop more advanced displays.
Recently, the firm has begun producing HDVD systems to project computer graphics from a standard video screen into a free-standing 3D viewing field. For mens fashion designer Hugo Boss, Dimensional used its optical arrays to create a floating computer-animated talking head that goes into its spiel whenever passers-by trigger a motion-sensing device (see "Ghostly Guests," pg. 20, February 2001). This mirror system is somewhat similar to one used 10 years ago in a videodisc-based arcade game some readers may remember-Sega's "holographic" Time Traveler.
|Dimensional Media's mirror-based "holography" helps make a Pepsi can jump out at potential customers passing by a soft-drink machine. |
In addition to mirrors, Sullivan and his researchers are at work on another holographic-like technology, embodied in the Hypercube-Dimensional Media's 20-inch diagonal 3D display intended as a benchmark for the hologram workstations of tomorrow. At the heart of the Hypercube (expected to sell for $15,000) is a "multiplanar volumetric display," a horizontal stack of transparent LCD screens (the prototype uses 25 layers) that flicker on and off to create the illusion of a Z-depth axis extending from 6 inches to more than 50 feet out of the screen. "We could have the display available as a plug-and-play peripheral for workstations and PCs as early as the summer of 2002," says Sullivan.
An even larger holographic-like display using mirrors to project a 3D viewing field embodies the theories of Scottish scientist John Logie Baird, who in 1926 was the first to broadcast a television image of a human face. Baird's biographer, Dr. Peter Waddell, a professor of mechanical engineering at the University of Strathclyde in Glascow, Scotland, has headed up efforts to create 4-foot-diameter mirrors capable of projecting brilliant three-foot-high images.
The core technology is a stretchable membrane mirror (SMM) that weighs much less than traditional glass mirrors. It uses a silvered Mylar film stretched across a kettle drum-size frame. An analog-to-digital computer controls a vacuum system that induces in the membrane a parabolic lens-like curvature, optimized for projecting an image beyond its viewing plane. This plastic mirror system is remarkably stable, according to its maker, and costs one twentieth of its glass counterpart.
Licensing the technology for commercial introduction, US-based Ethereal Technologies will market SMMs as part of its Vis4D volumetric imaging system, a workstation capable of displaying autostereo video or real-time animations of 3D computer models. Left- and right-eye views are displayed on a pair of LCD screens and projected via beam-splitters into the mirror's sweet spot, from which images are reflected outward into an autostereoscopic field.
|A holographic triptych measuring 4 by 30 feet greets visitors to a Texas airport. "Muse," "Technology," and "Nature are holographic images from Zebra Imaging.|
Ethereal has just deployed its first Vis4D beta versions, with partial funding from the Interactive Visualization Program, a special project of the Department of Defense. A system for the US Army will create computer-generated training simulations of tank turrets. The Navy's system will enlist telepresence for close-up video inspections of submarines at sea, transmitted to a land-based workstation. At United Technologies' research labs, telepresence is being tested for consulting on repairs of mechanical assemblies, like jet engine components manufactured by its Pratt&Whitney division. Still another Vis4D beta system went to Daimler Chrysler's design division, for modeling new automotive parts. Ethereal founder and president Bob Andrews says he expects to start offering his mirror displays commercially later this year.
The commercial development of laser-based holographic imaging has long been dependent on finding successful business models to defray the cost of the equipment involved, including top-of-the-line computer systems, expensive lab-grade lasers, and isolation gear to prevent image-ruining physical vibrations. "You want an application where you're not just making pretty 3D pictures, but where there's a cost-justifying need to understand spatial relationships," notes Stephen Hart, chief scientist for display technology developer Voxel.
In a technique pioneered by Hart, imaging slices from medical CT or MRI scans of patients' bones or brains are computer-synthesized into a full 3D model that can be recorded holographically via a laser onto a 14- by 17-inch sheet of film. When displayed in an office or operating room, this white-light readable hologram provides a surgeon or other specialist with an in-depth visualization for delicate medical procedures. Instead of depending on a series of hard-to-read films of 2D slices on a light box on the operating room wall, the doctor can clearly see on a monitor-size viewer a one-to-one reproduction of a fracture or a tumor-with high enough fidelity for the image to be accurately measured. Such technology can provide invaluable information during a difficult operation.
Currently, Voxel acts as a service bureau, offering same-day holographic imaging for diagnostic scans sent from hospitals and doctors' offices over the Net in the standard DICOM 3.0 medical imaging file format. "We've now produced more than 8000 holograms for some 3000 patients," says Hart. The firm's printer, working with a Macintosh 840AV computer, produces 5 to 10 images per hour. Voxel's fee is $200 per Voxgram print, delivered via overnight express to the doctor's office.
Viewing the film also requires a $2000 light box, with a diffraction grating aligning the beams from a bright white light to cast from the holographic film an image half projecting forward from the film plane, and half behind it. Though hardly state-of-the-art, the glowing, monochromatic images have revealed otherwise unseen medical anomalies, saving dozens of lives, including Voxel chief technology officer John Wright's daughter, diagnosed with a brain tumor and successfully operated on at age 2 -1/2.
|The brewing company's well-known Clydesdales are making their holographic debut courtesy of Zebra Imaging's "hogel" technology.|
Laser-etched holograms don't all have to be serious, life-or-death visualizations. For example, the technology used to produce the largest digitally mastered, true-color full-parallax holograms could be appearing soon at a tavern near you. "We've just made 500 holograms of the Budweiser Clydesdales for Anheuser-Busch and 500 holograms for Guinness. We could end up replacing neon beer signs in bars and restaurants," says Alejandro Ferdman, CEO and co-founder of Zebra Imaging, which is commercializing technology developed at the University of Texas (see "Degrees of Freedom," pg. 36, May 2001).
A Zebra hologram is composed of many small holograms, each about two millimeters square and called a "hogel." Each hogel is computed to represent a digital image from a particular angle of view and rendered as a pattern on a liquid crystal display, in turn illuminated and printed by green, red, and blue lasers in step-and-repeat fashion on a flat, square 2- by 2-foot tile of polymer film. Such tiles can be assembled adjacent to others to create holographic images of unlimited size. For display, instead of a fancy light box, all that's needed is a halogen bulb placed at a 45 degree angle above the viewing plane. The 3D effect is visible across a horizontal viewing angle of greater than 100 degrees, a far wider range than most conventional holograms.
The largest display hologram to date is a 4- by 30-foot triptych of art pieces created by Zebra-"Muse," "Technology," and "Nature"-which made its debut in September at Austin Bergstrom International Airport in Austin, Texas. The largest hologram ever shown before that, a 4- by 10-foot wall-filler by Zebra, depicted Ford's red P2000 concept car with simulated animation. Composed of more than 900,000 voxels, this hologram alone contained more digital information than the film Titanic.
Ford's latest commitment to holographic displays is a joint venture called Holographic Imaging, in partnership with the UK's Defense Evaluation and Research Agency (DERA) in Malvern, Worcestershire. (DERA, long an innovator in electro-optics, holds the principal patent for liquid crystal displays.) The announced goal of the new company, to be headquartered in California, is no less than the full holographic display-the first laser-based in-depth 3D equivalent of today's 2D workstation monitors, using DERA's computer-generated holography (CGH) technology.
"Ford has been long been looking at volumetric displays as the next step in visualization," explains Holographic Imaging's COO Tom Scott, previously director of advanced design for Ford and the auto firm's most vocal champion for funding holography research.
The first CGH prototype is housed in a 6-foot high frame, resembling an old-fashioned roofed wishing well. In the base is a laser light source and a high-resolution liquid-crystal display known as a spatial light modulator (SLM), which renders holographic interference patterns computed by a Macintosh G4-level computer. The resulting holographic image is reflected into a 3D field hovering outside the display's frame.
Defining every point holographically in a three-dimensional model 12 inches deep would require immense computing power. But, "the technical breakthroughs in the electronic holography challenge are clever algorithms that reduce computing overhead without losing perceived image quality," Scott says. He anticipates an off-the-shelf CGH monitor within two years. In addition to targeting automotive engineers, Holographic Imaging's initial sales will also be aimed at oil and and gas exploration geologists, medical diagnosticians, and industrial designers.
|The newly formed Holographic Imaging venture is already producing prototypes for laser-based holographic workstation monitors.|
The technologies used to create these and other displays may be disparate, but given all the commercial activity behind their development, the dream of a vivid glasses-free in-depth display for every professional application and workstation appears about to come true.
Steve Ditlea is a freelance journalist based in Spuyten Duyvil, New York. He has been reporting on holography since 1976.
In recent months, numerous other glasses-free 3D display technologies, most of them non-holographic in nature, have made their debuts. A few of these products display free-floating imagery, but the majority of them make three-dimensional imagery appear to project from the screen of a conventional-looking monitor.
An example of this latter type is Dynamic Digital Depth's 3D TV software, which converts 2D content to 3D and allows it to be viewed in 3D without glasses. The cost of the software with a 50-inch plasma monitor is $28,000.
StereoGraphics Corp. makes a flat-panel monitor, the SynthaGram, which incorporates a lenticular lens optical device that likewise allows viewers to see digital content that appears to project from the screen. The SynthaGram is available now for $6000.
The Dresden 3D display (created in Germany, but called the Elsa Ecomo 4D in the US) is yet another example. The Dresden flat panel, which costs approximately $14,000, uses proprietary eye-tracking technology to allow a user not only to see 3D without special eyewear, but to move from side to side in front of the monitor without noticing a decline in image quality.
|Display technologies such as Dynamic Digital Depth's 3D TV allow users to see 3D imagery that appears to project from the monitor, without having to wear viewing aids such as glasses or visors. |
Last in this jumping-out-at-you-from-a flat-screen category is Dimension Technologies' Virtual Window LCD displays, which use a special active substrate between the LCD and its backlighter that makes images on the display appear in 3D. This substrate can be turned off, and the monitors also used for conventional 2D viewing. In the next couple of months, we'll review at least one of these kinds of stereo displays to see what it's like to actually do some modeling with one.
In an Internet vein, Provision Interactive Technologies has developed a more holographic-style display called Holovision, which makes 3D models appear to hover in midair in front of a kiosk-type display. Holovision is currently partnering with Web content developer Cycore to display models created with Cycore's Cult3D software.
Still other displays take the "bell jar" approach, in which the monitor is a transparent dome. An example still in development is Actuality Systems' spherical display monitor, for the time being codenamed Helios. Within this 20-inch-diameter globe floats volumetric imagery that can be viewed by multiple users from any angle around it. The product is slated for commercial availability in 2002.
Actuality Systems · www.actuality-systems.com
Dimensional Media Associates · www.3dmedia.com/flash/flash.html
Dimension Technologies · www.dti3d.com
Dresden 3D · www.dresden3d.com
Dynamic Digital Depth · www.ddd.com
Ethereal Technologies · vis4d.ncms.org/ethereal.html
Provision Interactive Technologies · www.provisionentertainment.com
StereoGraphics Corp · www.stereographics.com
Voxel · www.voxel.com
Zebra Imaging · www.zebraimaging.com