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Fingerprint Basics
 Fingerprints
are one of those bizarre twists of nature. Human beings happen to
have built-in, easily accessible identity cards.
You
have a unique design, which represents you alone, literally at your
fingertips. How did this happen?
People
have tiny ridges of skin on their fingers because this particular
adaptation was extremely advantageous to the ancestors of the human
species. The pattern of ridges and "valleys" on fingers make it
easier for the hands to grip things.
There
are several ways a security system can verify that somebody is an
authorized user. Most systems are looking for one or more of the
following:
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“what you have” system - Requires "token," such
as an identity card with a magnetic strip. |
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“what you know” system - Requires you to enter a
password or PIN number. |
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“who you are” system - Is actually looking for
physical evidence that you are who you say you are -- a
specific fingerprint, pattern. |
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“
Who you are" systems like fingerprint scanners have a number of
advantages over other systems. To name few: |
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Physical attributes are much harder to fake than
identity cards. |
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You can't guess a fingerprint pattern like you can guess
a password. |
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You can't misplace your fingerprints, like you can
misplace an access card. |
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You can't forget your fingerprints like you can forget a
password. |
Fingerprint Enrollment is to register the fingerprint template for
later recognition. A good enrollment is crucial for all reliable
fingerprint recognition systems.
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Factors influencing Finger Enrollment |
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Finger Position |
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Finger Rotation |
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Finger Area |
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Finger Condition |
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Finger Pressure |
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How it works |
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When the user places their finger on
Fingerprint Recognition Device (FRD) for the first time, the
fingerprint is scanned and a 3-D fingerprint image is
captured. All the fingerprints contain a number of unique
physical characteristics called minutiae which includes
certain visible aspects of fingerprints such as ridges, ridge
endings, and bifurcation (forking) of ridges. Most of the
minutiae are found in the core points of fingerprints, and the
core points themselves are found near the center of the
fingerprint on the fleshy pad. |
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Fig. A-1 Core Points on different
fingerprint patterns. A core point is defined as the topmost
point on the innermost upward recurving ridge line. |
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The user is enrolled, or registered, in the database after a
special minutiae based algorithm extracts key minutiae points
from a live image at the time of acquisition and converts the
data into a unique mathematical template comparable to a
60-digit password. |
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This unique template is then encrypted and stored – it is
important to note that no actual image of the fingerprint is
stored, only the minutiae- based template. The next time a new
fingerprint image for an individual is scanned by the FRD,
another template is created and the two templates are compared
to verify user’s identity. |
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Getting good fingerprint images |
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The quality of fingerprint image is relative to the number of
minutiae points captured. If the number of locations of the
minutiae remain consistent whenever an individual’s
fingerprint image is scanned and captured, the fingerprint
image is successfully matched to the pre-existing template.
Fingerprint images do not possess an adequate number of
minutiae points may be unusable. |
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Fig. A-2 Poor- quality fingerprints |
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Figure A-2 shows poor-quality fingerprints, characterized by
smudged, faded or otherwise distorted areas on the
fingerprint. These conditions can be caused by excessive
dryness or wetness, or scarring of the skin at the fingertip |
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The Fingerprint matching algorithm is capable of extracting
the correct minutiae even without benefit of a perfect print.
However, the positioning of the finger and the relative
wetness or dryness of the fingerprint when it is placed on the
optic window for scanning are both important factors in
getting a match. |
Correcting wet/dry fingerprint images
When
the temperature is low, or just after washing hands, the fingerprint
is often dry. In this case, the user may moisturize their
fingerprint simply by breathing on it before applying it to the
optic window. If the fingerprint is too wet, the ridges and valleys
are rendered indistinguishable. The lack of minutiae data causes wet
fingerprints to be rejected. This can be remedied simply by swiping
the fingerprint on a clean towel or cloth.
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Position of the Fingerprint |
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In
order to capture the most minutiae, maximize the surface area of the
fingerprint on the fingerprint input window. |
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Contrast with Figure, which illustrates the most common mistakes
made during the initial phase of enrollment. |
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How
much pressure is required for a good-quality fingerprint? |
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If too much pressure is applied to the sensor window, the
ridges adhere to each other and are rendered
indistinguishable. In this case, the net effect is similar to
the hard-to-find minutiae of the wet fingerprint image. On the
other hand, if too little pressure is applied the resulting
image is similar to the dry fingerprint. |
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Issues related to pressure are easily addressed, however. A
little practice is all that is needed for users to get the
feel of it. |
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Common Problems and Solutions
Most
verification failures occurs because of the following problems: |
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Finger Positioned Incorrectly |
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Finger moved during reading |
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Pressing too heavily or lightly |
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Wrong finger using one that doesn’t have a template stored on
the token |
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Finger too wet or dry |
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Cut finger or otherwise changed |
All
these problems are easily solved or avoided with proper training
during enrollment and capturing quality prints from one than one
finger or thumb.
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A
Comparison : Optical vs. Capacitive (Semiconductor)
Fingerprint Sensors |
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Optical
Sensors |
Capacitive
Sensors |
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Sensor
Type |
Optical |
Capacitive
(Semiconductor or chip) |
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Performance |
Good for all type of fingers |
Poor results for dry type finger |
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Sensor
Surface |
No special treatments or maintenance
required |
Usually needs surface treatments,
including ESD and other protective coatings
Coatings may be uneven, wear out over time, degrade
performance, and shorten product lifetime |
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Overall
Durability |
Scratch-proof, unbreakable glass platen
made of material as hard as quartz
Resistant to shock, ESD, and extreme weather |
Corrodes easily from repeated handling
and everyday exposure
Susceptible to damage by electrostatic discharge
Thin silicon chips are inherently fragile and susceptible
to damage by hard external impact and scratches |
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Imaging
Area, Resolution, and Size |
Large imaging area (0.5 inch x 0.6 inch)
High resolution (500 dpi)
Large image size (78,000 pixels) |
Usually smaller imaging area, image size,
and resolution due to greater cost of manufacturing larger,
high quality chips |
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Cost-Effectiveness |
Initial high cost,
But long life, no maintenance required
So on the long run more economical
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Low manufacturing cost
Consistent quality surface coatings may
be expensive to produce
Replacement, maintenance, and downtime costs can add up |
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Advantages |
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Small compact |
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Less power consumption |
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Rugged alternative for > 10 users |
Cheaper alternative for < 10 users |
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Good for general public use
Like access control; attendance |
Good for personal use like PDA; mobile
phone etc i.e battery powered equipments |
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Disadvantages |
Bulky |
Highly Fragile can be easily damaged |
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Consume more power |
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