The virtual worlds in computer games provide a realistic backdrop to the action. But step too close and the effect is lost – you'll see that textures and patterns are usually displayed on flat surfaces that look dull and artificial.

A simpler way to add depth to textured surfaces could change that.

The new technique can reconstruct the depth of a surface simply by taking two photos of it – one with a flash and one without (see video, right). Merely analysing the resulting shading patterns can capture the surface's 3D texture.

Until now making realistic textures required the use of bulky and expensive laser scanners, says Mashhuda Glencross at the University of Manchester, UK. And the process is really time-consuming, she adds.

3D in a flash

Glencross and the Manchester team worked with Gregory Ward at Dolby Canada in Vancouver to develop their quick and cheap alternative.

At the heart of the technique is the assumption that the brightness of a pixel in the image is related to its depth in the real scene. Parts of the surface deep in a crack or pit receive light from a restricted area of the sky, and appear relatively dark.

By contrast, protruding parts of the surface receive more light and appear brighter in a photo.

Correct colours

But the colour of the surface also affects its brightness in a photo. With the same illumination, light-coloured spots appear brighter than dark ones.

Taking a photo using the flash removes that effect. The surface is flooded with light and the camera can record the true colour of every part it can see, even those in cracks and pits.

The flashlight image is paired up with a photo taken without extra lighting. Software then compares the brightness of every matching pair of pixels in the two images and calculates how much of a pixel's brightness is down to its position, and how much is due to its colour.

That information is used to produce a realistic rendering of a surface's texture. By altering the direction of illumination on the virtual surface the system can generate realistic shadow effects.

Spot the difference

To test the realism of the results, the researchers asked 20 volunteers to compare images of a surface made using two photos to versions of the same surface rendered using lasers. The volunteers couldn't tell the difference.

The new technique is already being used to add depth and realism to the ancient carvings that will appear in Maya Skies – a full-dome digital projection for planetariums that tells the story of the Mayan people. Maya Skies will be released in 2009.

Glencross and Ward presented their results at the SIGGRAPH conference in Los Angeles last week.