MIT Media Lab PhD students create BiDi, an LCD screen-based multi-touch and motion detecting interaction system.

Natal's camera-based approach to sensing depth and motion struggles to detect motions close to the screen itself. BiDi, on the other hand, features light sensors as part of its screen, allowing more direct control. It was created by a team consisting of Matthew Hirsch, Henry Holtzman and Ramesh Raskar from MIT Media Lab, and Douglas Lanman from Brown University.

A video demonstration of BiDi shows a 3D TIE Fighter and X-Wing being turned in space, with the user selecting other Star Wars craft by moving their hand close to the screen.

It was inspired by a new generation of LCD displays from manufacturers including Sharp which feature light sensors among the display pixels to provide relatively cheap to produce multi-touch capabilities. But because they're positioned close to the screen, they can only sense objects on its surface.

MIT's team adapted the system by positioning the light-detecting sensors around 2.5cm behind the LCD layer, which allows the sensors to detect objects around 50cm away from it.

By placing a mask with many pin-sized holes in the LCD layer, the light sensing layer receives many different images, each slightly different depending on the angle they receive them. The system can analyse these in order to determine depth.

At the moment, BiDi captures motion at the rate of around 10 frames a second, which leads to a degree of lag, though the team claims the effect can be mitigated by using more powerful computing hardware.

Moreover, at 50cm, BiDi can hardly achieve the room-based motion sensing that Natal is designed for. But with further development it could contain the nucleus for a new model for motion-sensing control schemes which boast a closer relationship between gestures and the screen and don't require a separate unit of hardware to operate.

More information on BiDi is available on its website.