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Advanced 3D Displays
by Juan C. DĂĽrsteler [message nş 88]

Visualisation in 3D, typically associated to special goggles and bulky devices, has begun to break its bounds with the appearance of 3D display systems that can be used with the naked eye.

The launch of the latest episode of the “Star Wars” saga, has exposed us again to the iconography that George Lucas has made us fond of. One of the classic devices of these movies is the volumetric display where princess Leia and so many other characters save their 3D messages in which they appear in full size, sometimes scrambled with some strips, always victims of some imperial interference (space is not what it used to be). 

But it doesn’t seem that we’ll have to wait for along time in order to enjoy similar 3D displays to those of George Lucas’ movies. For some time different researchers and companies have been experimenting with displays systems that do not need special goggles. Their work has led to several types of technologies, some of them already available commercially

  • Autoestereoscopic or Parallax Displays: are computer screens, similar to the traditional ones, where you can see in 3D without needing polarising or coloured filters. Some systems have selective shutters that show only some columns of pixels that correspond to the image of one of the eyes while occluding the columns corresponding to the other one’s image, for a given position of the user’s head. For this reason they are typically associated to an infrared head tracker. (For more information see for example the excellent Java demos of the New York University.) 

    Other systems, like those of 4d-Vision emit light in different angles depending on their colour. Red, green and blue light is deflected in different directions in order to build views for the right and left eye in eight different view planes. This allows you to see in 3D independently of the user’s position, not requiring a head tracker and allowing different users to see the same display in 3D.

    produces autoestereoscopic displays based on a technology called lenticular screen. The prices of all these devices begin in the range of $6000 .
  • Volumetric displays: systems that show the information in a predefined volume. In the same way that a TV screen is capable of illuminating selectively each and every one of the pixels on its surface, a volumetric display is able to do the same for all the voxels (pixels in 3D) that make up its volume.
  • There are 3 main types:

    • Varifocal mirror: a mirrored membrane that oscillates becoming a variable focal distance mirror reflecting the image of a screen. By synchronising the image shown on the screen with the optical power of the mirror, any point of a given volume can be scanned (and illuminated). Still quite an experimental system.

    • Emissive volume: a given volume filled with a medium that is able to emit light from any part of its interior as a result of an external excitation, for example by different wavelength lasers. Very experimental, the main problem is finding the appropriate substrate. 

    • Rotating screen: a flat screen rotates at around 600 rpm. For every angular position of the screen in a predetermined set an optical system projects onto it the image of an object corresponding to the perspective associated to that angle. The final result is the 3D image of the object, viewable in 360 degrees. 
ActualityDNA.jpg (27359 bytes) PerspectaExploded.gif (19140 bytes)
Perspecta Spatial 3D, a rotating screen Volumetric display by Actuality systems.

Image courtesy of Actuality Systems, Inc. (Burlington, Mass., USA)

Scheme of the Perspecta Spatial 3D display. Click on the image to enlarge it.

Image courtesy of Actuality Systems, Inc. (Burlington, Mass., USA)

Some of these rotating systems are already commercially available for a relatively affordable price of $45,000 , like the system called Perspecta Spatial 3D from Actuality that is the subject of the US Patent 6,183,088

Perspecta, possibly the most advanced of these types of systems gives a resolution of over 100 Million voxels. It’s made of a spherical transparent dome that gives it a characteristic “crystal ball” appearance. Inside it a flat screen rotates at 730 rpm. A projector illuminates the screen successively with up to 198 images of 768x768 pixels each, showing one or the other depending on the screen’s rotating angle.

Every one of the images corresponds to a “slice” of the object as if we cut it through a vertical axis, and it’s refreshed 24 times per second. The persistence of retinal vision converts the stack of 2D images into a sharp 3D perception of the object.

The advantage of this device relies on the fact that the objects appear to be floating within the transparent dome and can be seen from any angle or position. It’s probably the closest device to the R2D2 projector of Star Wars.

Many ends are still loose. Once 3D images “take themselves off” the computer screen without the need for goggles or special devices we will want to interact with them, touch and modify them. A new field in the human computer interface will or open.

Maybe soon we will act as the sorcerer’s apprentice with our hi tech crystal ball… 

For more information about these systems see the interesting article interesting article on autoestereoscopy or the  3dcgi list. 

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