Touch-less touchscreen : An Insight

THE popularity of touch-screens on mobile phones means that a swipe, tap or a flick comes as naturally these days as the click of a mouse. But existing touch-screens have their limits. Those relying on changes in electrical resistance tend to have poorer resolution than is needed for modern applications, while those that rely on capacitance require an ungloved finger.

Consequently, a new generation of touch-screens, known as optical liquid crystal displays, is emerging. Optical LCDs embed tiny light sensors next to many of the screen’s pixels. In the brief moments between each successive screen image, the backlight is turned off. In these periods of darkness, undetectable to the human eye, sensors are able to pick up light coming from outside the device.

Although such sensors are designed to detect only the presence or absence of a finger touching the screen, Ramesh Raskar, a researcher at the Massachusetts Institute of Technology, wondered whether this new type of device could be turned into not a touch, but a touchless screen by using the sensors to detect more distant objects as well.

His idea was to treat each sensor as if it were a pinhole camera. He (or, rather, his software) would then stitch the two-dimensional images from each pinhole together to obtain a three-dimensional picture. This could then be used to determine which bit of the screen a distant finger is pointing at.

Dr Raskar and his colleagues lack the resources to fabricate an optical LCD of their own to test this idea, so they have created a mock-up that uses individual liquid crystals as makeshift pinholes, and this seems to work. They call it a bidirectional (or BiDi) display. Its name comes from the fact that it uses an ordinary LCD, but in a way that allows light to pass in either direction through some of the liquid crystals in the screen.

When the backlight is off, those crystals act as pinholes. In place of the light sensors that would be engineered into a production version, Dr Raskar uses a diffuser placed behind the screen, upon which the tiny images from the individual pinholes are cast. These images are monitored by a digital camera positioned behind the diffuser. The result is an array of images, each formed from a slightly different perspective. These different perspectives are then combined to form into a three-dimensional image by a computer using a trick from astronomical analysis known as MURA (modified uniformly redundant array). The result of the MURA processing is that the computer knows where the user’s hand is, and the user can thus control objects on the screen with a wave of that hand.

If the principle can indeed be extended to devices that employ optical LCDs, screens of the future will be able to harness the power of mere gestures. Zooming in on an image, and then out again, will be as easy as moving a hand closer or further away from the screen. A hovering finger or a simple movement will be able to press virtual buttons.

These features will, no doubt, be of particular appeal to those who dislike the perpetually greasy and smeared appearance of touch-screen computers and mobile phones. So, even though yet another set of skills will need to be mastered to control these screens, they may well be the wave of the future.

Posted in: Technology