Picture escapes from the box: Thorn-EMI's variation on a Victorian 3-D illusion promises new depth for TV and computer games

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COMPUTER displays are about to acquire some spooky attributes. Thorn EMI has devised a system for suspending images in space that, in the best ghostly tradition, you can put your hand through. The first application will be to heighten the realism of computer games.

The technique - a hi-tech version of a Victorian fairground trick done with mirrors - produces images which give the impression of being three- dimensional, even when they are derived from two-dimensional originals.

In the Victorian version a half-silvered mirror, set at an angle to the source image, reflects half its light on to a flat reflector that directs the light back through the mirror to the viewer. This gives the impression that the source image is hanging in front of the mirror. Because only some of the light reaches the viewer's eyes, the image is unfocused and dim.

A team from Thorn EMI's Central Research Laboratory (CRL) has refined this device with a special type of mirror called a beam splitter, adding another reflecting surface. This and another refinement under development will mean that the light directed into the suspended image will be increased by more than 200 per cent.

The source of the image can be a still or moving picture, on a television or computer screen, or it can be a real object - or person - illuminated by a bright light and hidden from the viewer.

The suspended image is as bright as its source and visible in daylight. The optical equipment which makes up the system fits into a 'black box' that can be linked to a standard TV or computer monitor. In the video games prototype, the TV lies on its back under a table, and the image is seen floating above the table. The CRL has talked to several games manufacturers about commercialising the technology, called the Suspended Image System.

John Holden, CRL's principal engineer, said there had also been approaches from advertising and exhibition companies after a demonstration at a recent trade show in which images of Coke cans and Barbie dolls were suspended in space.

CRL has also been demonstrating the system with the Philips interactive compact disc game Seventh Guest, which is designed to look 3-D on a standard television screen.

The CRL system produces images which can be seen from a wide field of view. The biggest image achieved with the prototype was 61cm (24in) across the diagonal. Mr Holden and the team of six, who have so far spent five years working on the project, believe it will be possible to create larger images.

The suspended-image technology is expected to breathe new life into existing television programmes and films. Once they are freed from the cue for two-dimensional flatness, prompted by the edges of the TV screen, three-dimensional cues will come into play, creating an impression of depth.

'For example, if people are standing in front of a building, your brain sees the illusion of depth, because it knows that the building is further away than the people,' Mr Holden said. A similar impression is achieved at present by wearing glasses with one red and one green lens to view special pictures split into slightly red and slightly green images. Each eye sees a slightly different picture, giving a stereographic effect.

Suspended images could also be used to bring a new perspective to the family photograph album. Or the three- dimensional qualities of the images would be a useful addition to certain business software, especially computer modelling packages in which the designs could be displayed in the 3-D format.

CRL is now developing a system which would allow the user to interact with the suspended image by touching it.

According to Mr Holden, suspended images would have all the attributes of virtual reality displays without requiring users to wear headsets and goggles. An added advantage of the technology is that the computer displays would not emit electromagnetic radiation, nor would there be any glare from reflected light as there is from a standard computer screen.

(Photograph omitted)