Chapter | 6 Processing of Handwriting and Sketching Dynamics
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nition, sketching, gesturing all the way to biometric user recognition
by signature analysis. This chapter provides an overview to technical
concepts of the most common sensors today, reviews principles for the
analysis of signals derived from writing and drawing dynamics and
discusses different recognition objectives. Finally, we briefly review
algorithms for two exemplary applications: pen-based sketches for
interactive interface design [5] and similarity search in databases of
handwriting digital documents [6].
6.3 BASICS IN ACQUISITION, EXAMPLES FOR
SENSORS
The variety of sensors for sampling pen-based dynamics, also referred
to as digitiser tablets, which is available today is based on different
physical phenomena. This section provides a short review of acquisi-
tion technologies and sensors, based on optical, electromagnetic and
resistive/capacitive film methods.
Besides the aforementioned light pen technology, there exists at
least one more concept for optically tracing the pen movement, which
is based on a defined pattern structure, which encode the position by
almost invisible patterns on pre-printed paper. In this technology,
pens are equipped with tiny digital cameras, integrated in the pen
tip, which continuously perform video recordings of the area below
the pen tip. A pattern recognition algorithm, executed by a computer
device embedded in the pen, determines the pen position based on
co-ordinates encoded by the patterns printed on the pen surface. Sen-
sors of this type have been developed, commercialised and licensed
to other organisations for example by a company named Anoto AB
(www.anoto.com).
Besides more exotic methods based on ultrasonic triangulation,
acceleration and force sensors attached to the writing surface, today
the majority of digitiser tablets are either electromagnetically oper-
ated or are based on resistive/capacitive film technology. The first
category is typically based on inductive coupling between an induc-
tor in the pen tip and a matrix of circuit tracks embedded in the writing
surface (e.g., the tablet PC display), powered by AC voltage at differ-
ent frequencies. By frequency analysis of the voltage induced at the
pen tip, the pen position can be determined. Tablets based on resistive

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