Everything You Need to Know About Touchscreen Tablets


Microsoft first introduced the Tablet PC in the early 2000’s, but it is only in the past year has the concept of a slate computer caught the public’s fancy. Apple stoked the fire with the long rumored iPad, and last year tablet computers started to appear in all sizes. Many companies are currently working to produce slate devices, and one thing they all have in common is the touchscreen. Slate devices provide a natural use for operation by touch, so this is only logical. But there are a lot of misconceptions about touchscreens that are important to address, as not all slates will be as useful as many think they will.

The term touchscreen has become distorted to the point that it is often misused. Tablet PCs as introduced by Microsoft require a special digitizer and pen to operate; they do not work by touch normally. These Tablet PCs often are thought to have touchscreens, even though that is not the case. There are three types of “touchscreens” or digitizers in common use currently, and each has specific uses.

Active digitizer. This is the screen type used in the Microsoft Tablet PC. Active screens do not recognize touch at all, and only hovering or contact with the special pen that is supplied registers interaction with the screen. While these are not touchscreens, the proliferation of the other two types of digitizers have created a huge misconception about active digitizers. These are the only type of digitizer that have been successfully leveraged for handwriting on the computer screen.

Resistive digitizer. These screens have been around since the early PDA days, and were specifically developed to be used with a plastic stylus. A precise tap on the screen is required for accurate sensing by the digitizer, thus the stylus requirement. Touching such screens with a finger nail is also precise enough, enabling touch without a stylus.

Recently, light touch versions of the resistive digitizer have been incorporated in screens that have more sensitive response to touch. These do not interpret handwriting on the screen well like the active digitizer, due to the lower precision of the sensing and the inability to rest the hand on the screen. Resting the hand on the screen for writing on a device with a resistive digitizer results in an effect called “vectoring”, as any touch on these screens is interpreted as a deliberate action. This inability to rest the hand on the screen is the reason that most Microsoft Tablet PCs do not use resistive digitizers. UMPCs designed primarily for touch control aside, only one Fujitsu Tablete PC model line incorporated a resistive digitizer, the P16xx series. This required special “palm rejection” technology to ignore the hand resting on the screen while handwriting with a plastic stylus.

Capacitive digitizer. When we think of touchscreens currently, the capacitive screen is what commonly comes to mind. This is the type of touchscreen brought into the mainstream by the iPhone, and is by nature the only type in use capable of multitouch. The “pinch and zoom” feature of the iPhone is made possible due to the capacitive digitizer. This is the type of touchscreen in the iPad.

Capacitive digitizers work by sensing skin contact by the touching action. They do not work with pressure as the other two types; they require actual touch to register an action. This prevents the use of these touchscreens for handwriting on the screen, unless a special stylus is employed that fools the digitizer into thinking it has been touched by skin.

What does this mean in the real world?

Currently only Tablet PCs with active digitizers can effectively be used for “inking”, or handwriting on the computer screen. Attempts to produce tablets capable of properly allowing handwriting using resistive digitizers have not been successful, with the one exception by Fujitsu noted. Even that was not a complete success, as the inking on the screen was prone to skips due to the palm rejection technology.

Resistive digitizers have largely fallen by the wayside since the appearance of the capacitive type. The resistive type of touchscreen is still being used in many tablets being produced today, from those based on Android to many running Windows. These tablets cannot be used for handwriting on the screen in a productive environment. This is a big misconception that some have about tablets in general, that they can all be used for handwriting on the screen. There will be many people unhappy when they buy a slate using a resistive screen only to discover they cannot write on the display.

Capacitive digitizers can be used for handwriting if software is designed to handle the special stylus required. There are such apps on the iPhone, and when coupled with the stylus (also available through third parties) it is possible to write ink notes on the screen. This is not widely used nor has the capability been developed to the point of providing a full inking experience. Capacitive digitizers are more expensive than resistive types, and prior to the iPad no manufacturer has used one in a device larger than a phone. The true multitouch screen has been relegated to phone devices as a result, with the exception of expensive Tablet PCs that use two digitizers.

Dual digitizer systems incorporate both an active and a capacitive digitizer to provide the best of inking and touch. These require special technology that turns off the touch digitizer when the active pen gets close to the screen for inking, to prevent the erroneous sensing of the hand that results in vectoring. Touch the pen to the screen, and touch is totally turned off until the pen raises from the screen. This works well in Tablet PCs like the ThinkPad x200 I am evaluating, but it is not cheap to implement.

So what does this mean to you, the consumer interested in the tablets flooding the market? With just a few exceptions, virtually every tablet you see running Android or Windows is likely running a resistive digitizer capable of “light touch” sensing. These are good touch tablets, but do not expect these tablets to handle writing on the screen. The technology just can’t handle it.

The iPad is upping the touchscreen game by using a large capacitive digitizer. The multitouch experience is likely to be superb, but the OS used on the iPad is not designed to handle inking, even with a special stylus capable of it. There will need to be third party apps written to capitalize on this unintended capability, so it will not handle it out of the box.

Tablet PCs that run Windows 7 and have dual digitizers are the only devices currently available that can handle both touch (multitouch, too) and handwriting on the screen. These devices are much more expensive than the cheap tablets garnering a lot of attention recently, but you get what you pay for. The important thing to remember is if handwriting on the screen is vital to your needs, the cheap tablets are not going to handle it well, if at all.

To provide a full handwriting on the screen experience, the platform must natively handle it properly. Currently, only Windows 7 and Windows Vista have the capability. Microsoft doesn’t offer Windows XP Tablet Edition any longer, so any tablet with XP will not handle inking at all. Android is starting to appear on slates this year, but it has no native ability to handle handwriting on the screen. It will have to be developed by either Google or third parties to leverage that ability fully. The iPad doesn’t have the ability to handle handwriting either, but I wouldn’t be surprised to see companies produce solutions down the road.

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