True stylus support requires an extra layer of sensors built into a device's display, which adds costs. If the new Microsoft stylus concept were to become available, it would allow precise stylus use on any display, even on those that aren't already touch-sensitive.
Andreas Nowatzyk and colleague Anoop Gupta hit upon the idea of using the grid of pixels that make up a digital display as a navigational system for their backwards-compatible stylus. In their design, a small camera inside the stylus looks down at the display and counts off pixels as they pass by to track its movement. That is fed back to the device via a wireless link, much as a wireless mouse reports its motion to a computer. The way the stylus tracks its motion is similar to the way "smart pens" such as the LiveScribe, a device for aiding note-taking, use a camera to track dots on special paper
However, for the stylus to work, it also needs to know precisely where on the screen it is at any time. The Microsoft researchers' solution was to have the related software "massage" the color of the blue pixels in a display so that their pattern of brightness encodes their position; the stylus then knows where it is. "Blue is chosen because the human eye doesn't have many blue cones in the fovea," the area of the retina used for our central vision, says Nowatzyk.
In his design, the stylus needs to note the average brightness of around five groups of four pixels to learn exactly where it is. It can constantly report that back to the computer, which can update its display and react appropriately. Matched images of a Windows desktop with and without that tweaking of blue pixels shows that it isn't noticeable. The software needed to alter a device's blue pixels to include the location signal could be bundled with its driver, says Nowatzyk.
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