Displaying 3D Without Glasses

Sharp builds 3D screens in which an additional, switchable-barrier level provides stereoscopic vision.

Using a lattice with thin slits, it's possible to have each of the viewer's eyes see different pixels on the screen, allowing construction of screens that look three-dimensional without glasses. The problem is of course that the display's construction defines the viewing position - in terms of both viewing angle and distance.

If the viewer moves their head to one side, the eye soon starts to see pixels that are intended for the other eye. And if the viewer comes too close to the screen, the angle of the lattice is no longer correct - likewise if the viewer moves too far away. There have been attempts to balance out this effect with "head tracking", using a camera attached to the screen. Some companies have also tried to use this method to achieve the 3D effect for several viewers at once.

With liquid-crystal technology, it's possible to make the lattice switchable, so that it can take on more or less any structure. This also means you can switch the lattice off altogether, allowing the screen to switch between 2D and 3D.

Advantages:
No glasses necessary; well suited to LCD displays; screen can switch from normal to 3D mode.

Disadvantages:
Only works for one person; requires specific viewing distances and positioning; resolution is halved.

Optical systems such as prisms or lenticular lenses can also control emission in a way that means both eyes see different images. As with the parallax process, this only works in certain positions and at certain viewing distances.

The process is also used to make more than two perspectives visible; up to eight viewing angles are currently possible, making the 3D effect visible for several positions and for more viewers. Philips has already produced a working model with 46 perspectives. 3D hologram projection works using emission that varies depending on direction, whereby the differing emissions are produced by refraction in a flat layer.

Advantages:
Easily achieved with all types of screen.

Disadvantages:
Only useable at certain viewing distances; resolution is halved or - for multiple viewing perspectives - reduced even more strongly.

A lenticular lens can produce a number different perspectives, two of which will reach the eyes of the viewer.

If an image is projected onto a surface that's rotating quickly, it will produce actual 3D images; similar methods include projection onto suspended particles, such as a curtain of steam, or into objects made up of numerous holographic layers. Rotating objects fitted with LEDs can also produce spatial depictions.

Advantages:
Looks like a real, 3D object.

Disadvantages:
Limited to relatively small objects; currently mostly in the prototype stage.

It's also possible to produce images that appear to be three-dimensional and which change depending on the position of the viewer's head. While objects on a two-dimensional screen don't change in relation to one another as the user moves, these systems must generate new images depending on the viewer's position - so-called "head tracking" or "eye tracking".

This requires a sensor to record the movements of the viewer's head, along with information about the spatial arrangement of the displayed objects. The system is therefore easiest to realize with games and other material produced by computers. The picture then resembles the impression you get, for example, if you keep one eye closed and move your head while looking through a window.

Advantage:
Works with every screen type and without glasses.

Disadvantages:
Not really stereoscopic; only effective for one person; requires a lot of real-time processing and a sensor. Currently mostly seen in DIY solutions, using the Wii remote, for example.

Clever image processing can achieve a three-dimensional, psycho-optical effect (an optical illusion), for example, using edge processing or contrast differentiation.

Advantage:
Possible with all screen types.

Disadvantage:
Not real 3D.

Apart from volumetric displays, all of these processes have one serious disadvantage in common: They don't produce genuine three-dimensional images, but rather an approximation of such on a two-dimensional screen.

The problem here is essentially that they don't address other senses that contribute to spatial perception. In particular, there is no focusing of the eyes on nearby objects (the eye's focus must always remain set to the distance of the screen), and with head-movements, the objects on the screen retain their position relative to one another (except in head tracking), which they would not do in the real world.

To make stereoscopic images look realistic, the camera crew, CGI specialists, and directors have to work very carefully. Not all scenes that work perfectly in 2D can be recorded in three dimensions.

Philips uses prism systems that enable viewers to experience the 3D effect from various positions.