Why are the latest touch-screen devices often larger than the push-button gadgets they replace? It has long been assumed the culprit is the so-called 鈥渇at finger鈥� problem 鈥� when touch targets are packed too close together, a fingertip may be too wide to hit the right one.
But the real reasons for touch-screen mishits are finger orientation and variation between users, suggests a study by and at the Hasso Plattner Institute in Potsdam, Germany. More importantly, they can be corrected.
The fat finger problem is the main reason why icons on hand-held touch-screen devices are generally around 10聽millimetres across. In recent years numerous ways around the problem have been explored, including the combination of a touch screen with a touch-sensitive pad on the rear of the device.
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To get a handle on the problem, Holz and Baudisch asked 12 volunteers to repeatedly touch a target on a touch screen, but to do so with their finger held at a specific angle 鈥� defined by the three-dimensional axes of .
Tight spots
They found that the touch screen registered distinct clusters of touch points for different finger orientations. In some cases those distinct clusters were just 2聽to 3聽millimetres across.
鈥淭ouch input is very precise for a specific roll, pitch and yaw,鈥� says Baudisch. That precision has gone unappreciated because each precise cluster is located at a slightly different region beneath the finger 鈥渟o those many small distributions together make a big mess.鈥�
The pair reasoned that if the touch-screen device 鈥渒new鈥� the orientation of the finger as it touched the screen, it should be possible to define much smaller targets on the screen than previously thought possible.
Print 鈥檈m
Holz and Baudisch asked another 12 volunteers to conduct a similar experiment, but this time they used an eight-camera rig to accurately capture the precise orientation of the finger on the screen. By enabling their system to take that information into account they tripled the precision of the touch interaction.
Fingerprints can reveal finger orientation, so the researchers adapted a type of fingerprint scanner used at international borders to see if their system could work without cameras.
Their system 鈥� dubbed Ridgepad 鈥� finds the centre of the fingerprint for each touch on a screen, and compares it with a database to calculate the finger鈥檚 orientation. Applying the cluster region associated with a specific orientation gave the system twice as much accuracy as traditional touch technology, says Baudisch.
At present, however, the fingerprint scanner technology could not be built into portable devices such as phones because its components are too big.
鈥淭his work clearly helps to provide some guidance as to how to improve selection accuracy with touch devices,鈥� says at Microsoft Research in Redmond, Washington.
, also at Microsoft Research, agrees, but notes that optical fingerprint scanning technology isn鈥檛 compatible with thin touch-screen devices. 鈥淸The success of this] would depend on whether we can develop thin and cheap touch sensors with the fidelity necessary to pick up fingerprints,鈥� he says.
