Techniche 5th issue (Read-Only) - College of Technology, Pantnagar

Page 22
Techtonic
Biometric Fingerprint Reader
T
he CCF got up and running in no time and now it embraces
a technology (not yet implemented though!)
that’s known to all but how much do we know about
it? Biometric computerized fingerprint scanner used in
CCF and the one used in your laptop have since decades
evolved from the mainstay of spy thrillers to embodiments
of exotic technology of the real world. The purpose
of this device is simple- “Instead of, or in addition
to, a password, you need your distinctive print to gain
access.”
Human beings happen to have built-in easily accessible
unique identity cards, at our fingertips. Fingerprints
are formed due to tiny pattern of ridges and valleys
formed in our fingers through a combination of genetic
and environmental factors. The genetic
code in the DNA along with
many other factors determine the
development of skin in a foetus and
pattern of ridges in fingers. Consequently,
fingerprints are a unique
marker for a person even an identical
twin.
A fingerprint scanner’s job is to
take place of an analyst which collects
fingerprint sample and compares
it to other samples in the record.
A fingerprint reader system has
two basic jobs— it needs to get an
image of your finger, and it needs to determine whether
the pattern of ridges and valleys in this image matches
the pattern of ridges and valleys pre-scanned images.
There are number of ways to get an image of somebody’s
finger. The most common methods today are
optical scanning (the one the CCF scanner uses), and
capacitance scanning.
The heart of an optical scanner is a charge coupled
device (CCD), the same light sensor system used in camcorders
and digi- cams. A CCD is simply an array of sensitive
diodes called photosites, which generate an electrical
signal in response to light photons. Each photosite
records a pixel, a tiny dot representing the light that hit
the spot. Collectively, the light and dark pixels form an
image of the scanned finger. Typically, an analog -todigital
converter in a scanner system processes the ana-
The CCF Revolution
log electrical signal to generate a digital representation
of the image. The scanning process starts when you
place your finger on a glass plate, and a CCD camera
takes a picture. The scanner has its own light source,
typically an array of light emitting diodes to illuminate
the ridges of finger, with darker areas representing
more reflected light (the ridges of the finger) and
lighter areas representing less reflected light (the valleys
between the ridges). Before comparing the print to
stored data, the scanner processor makes sure that the
CCD has captured a clear image. It checks the average
pixel darkness, it rejects the image if it is too dark or
light, and then tries to scan again.
When the darkness level is adequate, the scanner
system goes on to check the image
definition (how sharp the fingerprint
scan is). The processor looks
at several straight lines moving
horizontally and vertically across
the image. If the fingerprint image
has good definition, a line running
perpendicular to the ridges will be
made up of alternating sections of
very dark pixels and very light pixels.
If the processor finds that the
image is crisp and properly exposed,
it proceeds to comparing
the captured fingerprints with fingerprints
on file.
Most fingerprint scanner systems compare specific
features of fingerprints called minutiae. These are
points where ridge lines end or split into two
(bifurcations). To get a match, the scanner system doesn’t
have to find an entire pattern of minutiae both in the
sample, and in the print on record. It simply has to find
a sufficient number of minutiae patterns that the two
prints have in common. The exact number varies according
to scanner programming.
So, in the future if you find yourself without your
ID in the CCF, then your index finger may come to
your rescue.
Mayank Tilara
II Year, Civil Engineering