I can see clearly now

Evolution, you have to admit, came up with some real innovations. It gave us two eyes, for example, so we could perceive depth. Very handy for our ancestors: is that angry sabre-tooth tiger very far away, or just very small?

Then suddenly, movies, television and computer screens arrived, managing to render millions of years of evolution redundant and returning us to a two-dimensional world. People have quite rightly felt that something important was taken away from them, and so giving a third dimension to cinema and computer screens has long been something of a holy grail. We all know the lengths the industry has gone to; remember the red and green glasses we were supposed to wear in an attempt to fool ourselves that this indeed could be a three-dimensional medium?

Computer and television screens are trickier prospects; the red/green filter trick can work, but it's never been anything more than a gimmick. There was also a time when cinemas tried to use polarised lenses to pull off the same trick, but that just doesn't work on computer screens because you can't polarise light coming off them.

I should point out that I'm not talking about virtual reality and 3D environments on the Web, which are essentially different ways to overcome the same limitations but which by no means give an illusion of depth.

Computers were entirely responsible for the next big 3D gimmick: "Magic Eye" stereograms. You probably remember the craze from about five years ago when they briefly deposed Take That from adolescents' bedroom walls, with images of spheres, cones, the Statue of Liberty and even, if I remember correctly, a sabre-tooth tiger.

There's a site listed below that goes into detail about how they work; but essentially one saw a slightly blurry but indisputably 3D image. You can still pick them up for a few quid from poster sellers on street corners and markets.

There's a stereogram on this page that I constructed from a program downloaded from the Net, just in case you'd forgotten what they're like. There are a number of programs around for doing this; they let you render a greyscale image into a stereogram so that the darker the area on the image, the further away it appears to the viewer.

People on the Web have also made other attempts to overcome the limitations of computer screens. Ray's web page has 3D versions of his holiday snaps. They take a little time to get your eyes round it but they're worth a look.

One thing, however, is clear: we're not much closer to three-dimensional screens than we were, say, 10 years ago. But at least we can console ourselves with the fact that when the time does come, Microsoft won't try to sell us some new piece of equipment - we were all born with two eyes. And with the stuff you'll find around at the moment, the worst that can really happen is that you'll end up with the mother of all migranes.

www.microsoft.com/mind/0197/sirds/sirds.htm

An essay on the principles of stereograms and how to go about making them.

www.peanutsw.com

Download "3D Dots", a stereogram maker for Macs

www.ray3d.com

Ray's web page: 3D holiday snaps and home movies