Once one has obtained some stereoscopic (a.k.a. "3D") content, how is it to be displayed? This is indeed a rapidly evolving area, with strong interest in devleoping hardware for the consumer market. Large-scale uptake is some way off yet... we will discuss some of the basic principles, as well as some hardware which is currently in use.

The basic requirement is that each of the viewer's eyes must receive the image that is intended for it- and only that image. The most common way to achieve this is via the use of glasses which somehow allow or block the left or right image as required. That is, the right eye must see oinly the image intended for the right eye; and similarly for the left eye. It is the job of the "3D glasses" to make this happen.

There are several methods for achieveing this, some of which we'll now look at briefly.

Colour separation

Anaglyph The viewer's glasses have different colour filters for each eye, a common example being red and cyan. The left and right images are processed so that their colour content matches the range of colours admitted by the corresponding eye filter. Typically, these red/cyan images can be composited into a single image, so that an anaglyph image can be presented as a single image that's encoded with the stereo information.

Infitec A refinement of the anaglyph method, this projection method uses matched filters for the projectors and viewer's glasses. Each left or right filter covers segments of the entire visual range of colours; the transmission curve resembles a comb filter, rather than the broad block or pass of traditional anaglyph filters. Two projectors are required.

Polarised

Two projectors are used, each with a polarising filter (usually in front of the lens). The planes of polarisation of the filters are crossed. The viewer's glasses have matching filters, and thus each eye sees only the matching projector's image.

Shutter glasses

A single projector (or monitor) alternately displays the left and right images. The viewer wears glasses which contain LCD panels which are alternately opaque and clear (that is, when the left panel is opaque, the right is clear, and vice versa). The glasses operate in synchronism with the projector; when the left image is displayed, the left eye panel is clear and the right opaque, and vice versa. This is done at a rate sufficiently rapid that most people do not perceive any flickering in the image.

Glasses-free displays

Currently suited only to much smaller numbers of viewers than any of the above methods, it is possible to produce monitor displays which simultaneuosly display both the left and right images, yet ensure that each of the viewer's (or viewers') eyes see only the correct image without the use of glasses.