Section
1.2:
FEATURES, FEATURE VECTORS, AND CLASSIFIERS
3
communicate and exchange information. Thus, the goal of building intelligent
machines that recognize
spoken
information
has been a long-standing one for
scientists and engineers as well as science fiction writers. Potential applications
of
such machines are numerous. They can be used, for example, to improve efficiency
in a manufacturing environment,
to
control machines in hazardous environments
remotely, and to help handicapped people to control machines by talking to them.
A
major effort, which
has
already had considerable success,
is
to enter data into
a computer via a microphone. Software, built around a pattern (spoken sounds
in this case) recognition system, recognizes the spoken text and translates it into
ASCII
characters, which are shown on
the
screen and can be stored
in
the memory.
Entering information by “talking” to a computer is twice as fast as entry by a skilled
typist. Furthermore, this can enhance our ability to communicate with deaf and
dumb people.
The foregoing are only four examples from a much larger number of possible
applications. Typically, we refer
to
fingerprint identification, signature authenti-
cation, text retrieval, and face and gesture recognition. The last applications have
recently attracted much research interest and investment in an attempt to facilitate
human-machine interaction and further enhance the role of computers
in
office
automation, automatic personalization
of
environments, and so forth. Just to
pro-
voke imagination, it
is
worth pointing out that the
MPEG-7
standard includes
provision for content-based video information retrieval from digital libraries
of
the type: search and find all video scenes in a digital library showing person
“X
laughing. Of course, to achieve the final goals in all of these applications,
pattern recognition is closely linked with other scientific disciplines, such as
linguistics, computer graphics, and vision.
Having aroused the reader’s curiosity about pattern recognition, we will next
sketch the basic philosophy and methodological directions in which the various
pattern recognition approaches have evolved and developed.
1.2
FEATURES, FEATURE VECTORS, AND CLASSIFIERS
Let us first simulate
a
simplified case “mimicking” a medical image classification
task. Figure
1.1
shows two images, each having a distinct region inside it. The
two regions are also themselves visually different. We could say that the region of
Figure 1.1 a results from a benign lesion, class
A, and that of Figure 1.1
b
from
a
malignant one (cancer), class
B.
We will further assume that these are not the only
patterns (images) that are available to us, but we have access to an image database
with a number of patterns, some of which are known to originate from class
A
and
some from class
B.
The first step
is
to identify the measurable quantities that make these two
regions
distinct
from each other. Figure
1.2
shows
a
plot of the mean value of the intensity
in each region of interest versus the corresponding standard deviation around