3-D gadgets without the glasses
Fancy watching a movie on your mobile phone, where figures leap out from the screen in 3-D, rather as Princess Leia did in that scene from Star Wars?
That's the claim made by US researchers, who on Wednesday reported they had made a display which gives a three-dimensional image that can be viewed without special glasses and is intended for cellphones, tablets and watches.
Unlike the holographic projection used in George Lucas' movie fantasy, their small prototype display is flat and backlit. It uses a technology called diffractive optics to give 3-D images that can be viewed from multiple angles, even if the device is tilted.
"Unlike a lot of technology out there that only does so-called horizontal parallax, which means that you only see 3-D when you move your head left and right, we actually are talking about a technology that gives 3-D for full parallax," said David Fattal, who led a team at Hewlett-Packard Laboratories in Palo Alto, California.
"For example, if you were to display a 3-D image of planet earth with the North Pole facing out from the screen, by turning your head around the display, you would actually be able to have a view of any country on the globe, you would be able to see all the way around," Fattal said.
Diffractive optics meet a challenge posed by the human anatomy, according to the study, published by the journal Nature.
Humans view the world stereoscopically, meaning that our two eyes see two slightly different images because they are separated by about six centimetres.
Two-dimensional screening provides only a single flat image, which means the two eyes both see the same picture on the screen.
Three-dimensional imaging, therefore, has to present a slightly different image to each eye.
Glasses-based systems work by having two lenses that each polarise the light in different directions, or by having lenses of red and green.
In the first case, the display has two simultaneous images, each with different polarisation; in the second, the two images have red and green outlines.
Current glasses-free systems, including some mobiles, use thin lenses called lenticules or parallax barriers that send an image towards each eye.
But the 3-D effect is limited and can only be perceived if the viewer is positioned in a narrow zone.
The new "autostereoscopic multiview display" uses a backlight whose surface has been etched with tiny refractors.
Each of these microscopic deflectors send individual points of light in specific directions.
These individual pixels, put together, comprise the different images sent to each eyeball.