Algorithm for Decreasing the Error Rate of Data Entered On a Touch-Sensitive Terminal
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Kalendra, PW: AUTHOR [+1]
This article discloses a technique for use in a computer system which decreases the error rate of data entered at a touch screen terminal by creating hysteresis in the borders of touch targets to minimize jitter and problems during finger lift.
Algorithm for Decreasing the Error Rate of Data Entered
On a Touch-
discloses a technique for use in a computer
system which decreases the error rate of data entered at a touch
screen terminal by creating hysteresis in the borders of touch
targets to minimize jitter and problems during finger lift.
Touch-sensitive applications acquire input from users by
comparing touch information received from the hardware versus "touch
targets" created and maintained by the application or some layer of
its device driver software. The touch targets are usually square or
rectangular fields presented on the screen as bordered boxes
containing prompts. They are highlighted by changing their video
attributes, for example, by switching to inverse video as they are
selected by touch with a finger or other type of stylus. The box
touched at the time the stylus is lifted from the screen is taken by
the application to be the user's selection.
which can occur are jitter and non-perpendicular
lift. Jitter appears when the stylus is positioned at the border of
a touch target, and the touch values being returned from the hardware
differ by one or more counts from one scan to the next; i.e., the
value returned as the horizontal coordinate of the touch position may
oscillate between two values. The same may happen for the vertical
coordinate or for both at the same time. Jitter appears to the user
as instability where one or more touch targets appear to flicker. At
its worst, jitter can cause four separate touch targets to appear
selected when the stylus is placed at their common intersection, as
illustrated in Fig. 1. Lifting the stylus while jitter is occurring
will result in essentially random results. It is not predictable
which of the flashing targets will be selected.
Non-perpendicular lift is an error mechanism unique to infrared
(IR) touch technology and is caused by the fact that the user may not
lift the stylus away from the screen in a direction perpendicular to
the screen. If the stylus is moved parallel to the display screen
while it is being lifted, it may actually pass into an adjacent touch
target zone before it is high enough to clear the IR beams. When
this happens, the wrong touch target is selected, as illustrated in
Both of these
situations can be dramatically improved by doing
two things in the software which manages and interprets touch input
1. Change the size of the touch target zone dynamically to provide
hysteresis in the borders of each touch zone.
2. Provide audible feedback to the user to indicate touches which
fall within a valid touch zone and those which do not.
Fig. 3 shows
a touch target as it might appear on the video
display. The dotted line shows an invisible touch zone which is
created by software as the range of touch input required for the
software to recognize that this targ...