[AI] Fat fingers can become dainty for touch screens

Sanjay ilovecold at gmail.com
Wed Apr 14 02:25:11 EDT 2010

          Touch-screen devices could be smaller if they could read how you
          use your fingers

by Colin Barras

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 "fat finger" problem - 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 Christian Holz and
Patrick Baudisch 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 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 Movie Camera .

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 - defined by the
three-dimensional axes of pitch, roll and yaw.

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 to 3 millimetres across.

"Touch input is very precise for a specific roll, pitch and yaw," says
Baudisch. That precision has gone unappreciated because each precise
cluster is located at a slightly different region beneath the finger
"so those many small distributions together make a big mess."

The pair reasoned that if the touch-screen device "knew" 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 'em
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 - dubbed Ridgepad - finds the centre of the fingerprint
for each touch on a screen, and compares it with a database to
calculate the finger's 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.

"This work clearly helps to provide some guidance as to how to improve
selection accuracy with touch devices," says Daniel Wigdor at
Microsoft Research in Redmond, Washington.

Andrew Wilson, also at Microsoft Research, agrees, but notes that
optical fingerprint scanning technology isn't compatible with thin
touch-screen devices. "[The success of this] would depend on whether
we can develop thin and cheap touch sensors with the fidelity
necessary to pick up fingerprints," he says.

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