Why Won't My Stylus Work On My Tablet

Microsoft's prototype stylus can work on any screen

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Black and white stylus resting on a screen

Before capacitive touchscreens and multitouch support became popular, touch interaction was performed using the stylus -– which is essentially a pen with no ink. Everything from mobile PDAs to CAD workstations used styluses to allow for more tactile computer input. However, relatively recently the Apple iPhone helped to catalyze cheaper capacitive screens that allowed users to skip the pen altogether and interact with the screen directly using one or more fingers. Since then, most mobile devices and slate laptops have moved away from stylus-friendly resistive touchscreens in favor of the capacitive variety.

As a result, the stylus has been relegated to a rather niche input device that is generally only used by artistic professionals with specialty hardware like the Wacom pens. Microsoft has not forgotten about the once ubiquitous stylus, however. A team of researchers within the company has been hard at work developing a new prototype stylus. Not only are they designing it around the ability to work on any display, but to do so with a high level of accuracy.

Currently, it is possible to get stylus accessories that have capacitive tips and are able to work with most touchscreens. The issue with such styluses though is accuracy, because they are essentially a workaround for capacitive panels that are calibrated to track finger input — a pointer that generally has a much larger area than the tip of a stylus.

The stylus that Microsoft is proposing forgoes trying to work with touch panels and instead uses the LCD display output itself to track movement. Using a camera that is mounted in the stylus at a slight angle, it captures images of the LCD display at a resolution of 512×512 pixels. Depending on which pixels are in and out of focus, software is able to determine the angle that the stylus is being held at. It also employs that same camera for motion tracking: By using the grid of pixels that make up the display itself, the stylus is able to to count the pixels as they move past the camera's field of view in order to precisely track movement in any direction.

Using a camera to track movement on a pen is not a new technique, however. It has been used with actual pens, such as Livescribe, to electronically save copies of written notes when the camera-equipped pen is paired with special paper that has (small) dots large enough that a camera is able to pick up on and use to track movement. Software then translates that physical movement to draw out the image digitally.

A photo of display showing the individual pixels. What makes the Microsoft version different is that it's pushing for an imaging sensor that is small enough to be integrated into a pen but powerful enough to accurately track individual pixels on an LCD display, which can be very small depending on physical screen size and resolution. According to Technology Review, Microsoft currently has engineering teams working on such an image sensor.

One of the hurdles that they run into with the camera-based approach is determining the stylus's absolute (as opposed to relative) position on the physical screen. While traditional touch panels are able to electrically determine position when the stylus physically makes contact with the panel and closes a circuit that corresponds to a calibrated (x,y) point on the screen, non-touchscreen displays obviously lack that hardware. The company's answer to that problem is to use the same camera that counts pixels for movement to determine position. A piece of software is installed on the smartphone, computer, or other device that slightly tweaks the blue colors that are output by the display to create a sort of map that a camera is sensitive enough to pick up on, but the human eye does not notice — just like the dots-on-paper method.

As the resolution (and specifically pixels-per-inch, PPI) of the display increases, the more accurate the stylus would become. That is very promising as it means that it can be very accurate and would not require an expensive touchscreen panel to do so. Using such a stylus, you could use it with all your screen-equipped devices for accurate pen input including your desktop or workstation which traditionally are not set up for touch input. As Windows 8 gets closer to release and smartphones continue the march for all touch-based input, the stylus may well make a comeback for situations that require more accurate input than a relatively large finger can provide, especially on smaller screens that continue to ramp up the resolution.

HTC Touch 2 used with stylus. There is one flaw, though: pressure sensitivity. Especially in the case of displays that are fused to thin layers of glass (like the Retina Display MacBook Pro), you risk cracking the display if you press down on it with the stylus. In that respect, the Microsoft prototype is not likely to take on the Wacom (and similar professional-grade) styluses that encourage you to apply pressure to the input pad and are able to accurately translate that physical pressure to the digital image (which can be extremely helpful in drawing applications).

For general input though, this sounds like an accurate solution that is not tied to a specific computer or other device-side hardware. Such a stylus could make artistic endeavors all that much easier to do digitally, as well as helping to make the paperless office a reality by allowing all the employees to e-sign and add notes to digital documents (which can eliminate the print, sign, scan hassle) easily and without the company needing to spring for touchscreen-equipped devices. I can also see the stylus being a good device for students, making annotating digital textbooks and notes just as easy as the dead tree version.

Not to mention that you could have a single stylus that you could use with any of your devices, and that would be easy enough to replace if lost (no need to track down a specific Dell stylus for your laptop, for example). Microsoft's camera-based stylus is still in development, and we have no data on when it might be released commercially — but let's hope it's soon.

[Image credit: Kprateek88, Asim Saleem]