Guiding light

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Three-dimensional moving pictures have not changed much over the decades. Even Disney’s latest contribution, ‘Meet the Robinsons’, relies on the audience wearing the same kind of polarising glasses that were used more than 50 years ago. Television has moved on a little more than cinema, but not much. Designs exist for screens that feed separate images to a viewer’s right and left eyes, thus achieving the same effect as the polarising specs. Unfortunately, only one viewer at a time is able to benefit, because he has to sit in line with the centre of the screen in order for it to work.

That may be about to change. A new form of display being developed by Ian Sexton and his colleagues at De Montfort University, in Leicester, England, could allow people to watch 3DTV from anywhere in the room, without having to resort to glasses. Better still, it can be modified to allow a whole family to view, rather than just a lone individual.

All three-dimensional representations of moving images work by fooling the brain into constructing a 3D perception from two slightly different images arriving at different retinas. The brain can be fooled this way because this is how it perceives depth when confronted with the real world rather than a flat screen. Existing 3DTV creates the separate images by showing them as alternating lines across the screen. The light from the lines is directed to the appropriate eye using either tiny lenses or diffraction gratings over each pixel. These are arranged so that one set of rows can be viewed only from the right-hand side, while the other can be seen only from the left.

It sounds clumsy, but it works—for a single viewer. What Dr Sexton and his colleagues have done is to adapt the technique to steer each image in several directions at once. The result is that moving images can be seen in 3D by up to four people, even as they squabble about who should sit where on the sofa.

To make this possible, Dr Sexton has added two new gizmos to the equipment. One is a system that tracks the whereabouts of the audience’s heads. The other is a novel diffraction technique known as holographic projection.