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Volumetric display
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A volumetric display device is a graphical display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. One definition offered by pioneers in the field is that volumetric displays create 3-D imagery via the emission, scattering, or relaying of illumination from well-defined regions in (x,y,z) space.
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Encyclopedia
A volumetric display device is a graphical display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. One definition offered by pioneers in the field is that volumetric displays create 3-D imagery via the emission, scattering, or relaying of illumination from well-defined regions in (x,y,z) space. Though there is no consensus among researchers in the field, it may be reasonable to admit holographic and highly multiview displays to the volumetric display family if they do a reasonable job of projecting a three-dimensional light field within a volume.
Most, if not all, volumetric 3-D displays are autostereoscopic; that is, they create 3-D imagery visible to the unaided eye. Note that some display technologists reserve the term “autostereoscopic” for flat-panel spatially-multiplexed parallax displays, such as lenticular-sheet displays. However, nearly all 3-D displays other than those requiring headwear, e.g. stereo goggles and stereo head-mounted displays, are autostereoscopic. Therefore, a very broad group of display architectures are properly deemed autostereoscopic.
Volumetric 3-D displays embody just one family of 3-D displays in general. Other types of 3-D displays are: stereograms / stereoscopes, view-sequential displays, electro-holographic displays, parallax "two view" displays and parallax panoramagrams (which are typically spatially-multiplexed systems such as lenticular-sheet displays and parallax barrier displays), re-imaging systems, and others.
Although first postulated in 1912, and a staple of science fiction, volumetric displays are still under development, and have yet to reach the general population. With a variety of systems proposed and in use in small quantities—mostly in academia and various research labs—volumetric displays remain accessible only to academics, corporations, and the military.
Types of volumetric displays
Many different attempts have been made to extend the dynamic 2D representation of the cathode ray tube to three dimensions. There is no officially accepted "taxonomy" of the variety of volumetric displays, an issue which is complicated by the many permutations of their characteristics. For example, illumination within a volumetric display can either reach the eye directly or via an intermediate surface; likewise, the surface, which need not be tangible, can undergo motion such as reciprocation or rotation. One categorization is as follows:
Swept-volume display
Swept-surface (or "swept-volume") volumetric 3-D displays rely on the human persistence of vision to fuse a time-series of regions of the ultimate 3-D region into a single 3-D image. A variety of swept-volume displays have been created.
For example, the 3-D scene is computationally decomposed into a series of "slices," which can be rectangular, disc-shaped, or helical cross-sectioned, whereupon they are projected onto or from a display surface undergoing motion. The image on the 2D surface (created by projection onto the surface, LEDs embedded in the surface, or other techniques) changes as the surface rotates. Due to the persistence of vision humans perceive a volume of light. The display surface can be reflective, transmissive, or a combination of both.
Another type of 3-D display which is a candidate member of the class of swept-volume 3-D displays is the varifocal mirror architecture. One of the first references to this type of system is in 1966, in which a vibrating mirrored drumhead re-images a series of patterns from a high frame rate 2-D image source, such as a vector display, to a corresponding set of depth surfaces.
Static volume
So-called static volume volumetric 3-D displays create imagery without any macroscopic moving parts in the image volume. It is unclear if the rest of the system must remain stationary for membership in this display class to be viable.
This is probably the most 'direct' form of volumetric display. In the simplest case, an addressable volume of space is created out of active elements that are transparent in the off state but are either opaque or luminous in the on state. When the elements or voxels are activated they show a solid pattern within the space of the display.
Several static-volume volumetric 3-D displays use laser light to encourage visible radiation in a solid, liquid, or gas. For example, some researchers have relied on two-step upconversion within a rare earth-doped material when illuminated by intersecting infrared laser beams of the appropriate frequencies.
Another technique uses a focused pulsed infrared laser (about 100 pulses per second; each lasting a nanosecond) to create balls of glowing plasma at the focal point in normal air. The focal point is directed by two moving mirrors and a sliding lens, allowing it to draw shapes in the air. Each pulse creates a popping sound, so the device crackles as it runs. Currently it can generate dots anywhere within a cubic metre. It is thought that the device could be scaled up to any size, allowing for 3D images to be generated in the sky.
Candidate: Highly multiview displays
Parallax panoramagrams, such as parallax barrier displays, generate an approximation of a desired 3-D light field. For a sufficient angular density of "view" directions, the synthesized 3-D light field becomes nearly equivalent to a volumetric image. Some researchers state that even a flat-panel 3-D display that projects over 30 views within a 30-degree horizontal field of view evokes an accommodation response in the viewer. Therefore, multiview displays with a high angular view density might be rightful members of the class of volumetric 3-D displays.
Candidate: Holograms and electro-holographic
The realistic imagery of holograms and electro-holographic displays make them contenders for membership in the class of volumetric 3-D displays, as well.
Human-computer interfaces
The unique properties of volumetric displays, which may include: 360-degree viewing, agreement of converge and accommodation cues, and their inherent "three-dimensionality," enable new user interface techniques. There is recent work investigating the speed and accuracy benefits of volumetric displays (Van Orden et al, 2000), new graphical user interfaces (Grossman et al, 2004), and medical applications enhanced by volumetric displays (Med., 2005; Wang et al, 2005)...
Also, software platforms exist which deliver native and legacy 2-D and 3-D content to volumetric displays (Chun et al, 2005).
Artistic Use
An artform called Hologlyphics has been explored since 1994, combining elements of holography, music, video synthesis, visionary film, sculpture and improvisation. Volumetric movies have been shown to live audiences at film festivals, art galleries and music events. Multiple Volumetric Displays and multi-loudspeaker arrays surround an audience. The movies are shown in conjunction with music, either live or recorded with the volumetric animations.
The original intent was to combine Holography with Music, and finally Volumetric Displays were settled on as an artistic medium. Many traditional film & video special effects have been adapted to Hologlyphic Movies, plus many more special effects unique to Volumetric Displays have been developed. These include volumetric wipe effects, raster bending, morphing, kaleidoscope & mirroring effects, experimental rotations, spatial warping effects and image sequencing.
The Hologlyphic movies can also be performed in real-time, like a video synthesizer, controlled by musical keyboards, motion sensors, control panels, and acoustic instruments. The image generation system is mostly digital, but some of the original image generators and processors were analog and remain in use.
Drawbacks
Known volumetric display technologies also have several drawbacks that are exhibited depending on trade-offs chosen by the system designer.
It is often claimed that volumetric displays are incapable of reconstructing scenes with viewer-position-dependent effects, such as occlusion and opacity. This is a misconception; a display whose voxels have non-isotropic radiation profiles are indeed able to depict position-dependent effects. To-date, occlusion-capable volumetric displays require two conditions: (1) the imagery is rendered and projected as a series of "views," rather than "slices," and (2) the time-varying image surface is not a uniform diffuser. For example, researchers have demonstrated spinning-screen volumetric displays with reflective and/or vertically diffuse screens whose imagery exhibits occlusion and opacity. One system (Cossairt et al, 2004; Favalora, 4 Aug. 2005) created HPO 3-D imagery with a 360-degree field of view by oblique projection onto a vertical diffuser; another (Otsuka et al, 2004) projects 24 views onto a rotating controlled-diffusion surface; and another (Tanaka et al, 2006) provides 12-view images utilizing a vertically oriented louver.
So far, the ability to reconstruct scenes with occlusion and other position-dependent effects have been at the expense of vertical parallax, in that the 3-D scene appears distorted if viewed from locations other than those the scene was generated for.
One other consideration is the very large amount of bandwidth required to feed imagery to a volumetric display. For example, a standard 24 bit per pixel, 1024×768, flat/2D display requires about 165 MB/s to be sent to the display hardware to sustain 70 frames per second, whereas a 24 bit per voxel, 1024×768×1024 (1024 "pixel layers" in the Z axis) volumetric display would need to send about three orders of magnitude more (165 GB/s) to the display hardware to sustain 70 volumes per second. As with regular 2-D video, one could reduce the bandwidth needed by simply sending fewer volumes per second and letting the display hardware repeat frames in the interim, or by sending only enough data to affect those areas of the display that need to be updated, as is the case in modern lossy-compression video formats such as MPEG. Furthermore, a 3-D volumetric display would require two to three orders of magnitude more CPU and/or GPU power beyond that necessary for 2-D imagery of equivalent quality, due at least in part to the sheer amount of data that must be created and sent to the display hardware.
Furthermore, volumetric displays could easily be replaced with Virtual retinal displays (VRD), using 2 to 3 orders of magnitude less of processing power, being a 2D display simulating a 3D environment. The cost of a volumetric display is also a great deal more than this competing technology, producing hundreds of times the amount of light, and undoubtedly hundreds of times the power, for the same effect.
See also
External links
- - developer of Perspecta volumetric displays (old website)
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- — by USC Institute for Creative Technologies
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- — a small volumetric display composed of 6x6x6 voxels, each represented by a 2-color LED
- - developer of Cheoptics360 volumetric displays
- - 2005 presentation by QinetiQ
- — Article about Perspecta displays at The Future of Things
- — 1996 summary of volumetric displays by Mark Lucente
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