GUN at the ready, you are picking your way through an alien world, tracking an adversary. Spotting your chance, you launch an attack. It takes your foe by surprise, and you鈥檝e got him cold.
It鈥檚 the sort of scenario you鈥檒l find in any first-person shooter game, but this one is different. For a start, the virtual world is displayed in stunning 3D. And then there鈥檚 the fact that the player whose on-screen character you have just dispatched is sitting right next to you. Though your opponent is looking at the same screen as you are, they see an entirely different view, tailored to their own virtual character.
Perhaps best of all, neither of you is wearing the clunky spectacles normally required for 3D viewing.
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The technology to make most of this happen is already up and running in developers鈥� labs. It relies, like any 3D illusion, on sending a slightly different view of a scene to each eye. In today鈥檚 3D movie theatres and the first 3D TV sets, this is done by giving viewers glasses whose lenses let different images through to each eye. But within the next few months the first glasses-free or 鈥渁utostereoscopic鈥� 3D systems are due to go on sale. One of these will be Nintendo鈥檚 hand-held games machine.
鈥淎ny 3D illusion relies on sending a slightly different view of a scene to each eye鈥�
鈥淚t is widely rumoured that the 3DS will use 鈥榩arallax barrier鈥� 3D technology,鈥� says , a computer vision researcher at the Massachusetts Institute of Technology鈥檚 Media Lab. This involves dividing the images destined for each eye into thin vertical strips, and displaying strips from alternate images side by side, or 鈥渋nterlaced鈥�, on an LCD. In front of this is a second LCD displaying opaque stripes that act as a barrier to ensure that each eye sees only the sections the interlaced image intended for it. The technique is based on a century-old system that uses a fixed vertical grid.
Nintendo鈥檚 solution is not without its problems, however. It only works when the viewer is a certain distance from the screen: stray further away or closer, and the barrier strips are no longer aligned with the image strips, resulting in a blurry mess. That isn鈥檛 too much of a problem for a hand-held gaming device, which most people will hold at reading distance, but applying the technology to a wall-mounted TV would be far more complicated.
The electronics manufacturer Toshiba is also pursuing glasses-free 3D TV, and in April it . It is not giving any details of how the 3D effect will be produced, beyond admitting that it will work only within a narrow viewing angle.
Slightly further in the future are a generation of glasses-free 3D displays that do away with such limitations, including the 鈥� short for 鈥渉igh-efficiency laser-based multi-user multi-modal 3D鈥�. In the prototype being developed by an international consortium the image is projected onto a flat screen by a laser mounted behind it. An LCD mask between the projector and the screen separates the left and right images, and the screen itself has a built-in lens array that focuses each image directly into the left or right eye of the viewer, as appropriate 鈥� removing the need for 3D glasses.
Above the screen is a camera connected to an image-processing system that monitors the position of the viewer鈥檚 head. If the viewer moves, information from the head tracker is used to adjust the mask to ensure that the appropriate image is still sent to each eye.
By targeting separate left and right images to several viewers simultaneously, Helium3D displays could eventually allow people sitting side by side to experience entirely different views. 鈥淔riends could play a 3D game against each other on the same screen with each other鈥檚 view kept secret,鈥� says at University College London, a member of the Helium3D team. The technology would also make it possible for a single viewer to peer around the side of a virtual object by moving to their left or right. Lanman says that the big challenge with this design, as ingenious as it is, will be to cram the components into a flat-screen display.
An alternative 3D display system, known as the , is being developed by Microsoft. The image is produced from a rectangular slab of transparent acrylic which tapers to a point from about halfway up (see diagram).
Light projected through the bottom face of the wedge-shaped slab travels upwards in the same way as light travels through an optical fibre 鈥� bouncing at a shallow angle off its front and rear faces. As the light travels upwards and the slab tapers, however, the rays are deflected so that they hit the front surface of the slab at an ever-steeper angle.
Eventually the rays reach the critical angle at which they are no longer reflected but instead exit from the front of the slab. The shallower the angle at which light enters the bottom of the wedge, the further up the screen it travels before exiting. Using two suitably angled projectors, the Wedge can be used to send different images to the viewer鈥檚 left and right eye, creating a glasses-free 3D effect.
So far, this only works for a viewer positioned straight in front of the screen, as with Toshiba鈥檚 3D TVs, but , who created the Wedge, says that with the help of the kind of technology used in Helium3D, it can be modified to work over a wider angle.
Travis suggests fitting an array of cheap projectors to the base of the sheet and coupling these to head-tracking cameras. The viewer鈥檚 position would dictate which pair of projectors to use to optimise the 3D effect. As with Helium3D, it may be possible to cater for several viewers, or provide different 3D images to a pair of gamers.
