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P P E N D I X
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Q
U A L I T Y A N D
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O N T E N T
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© 1999 Biometric Identification, Inc.
Quality
The quality score is based on how well the ridge pattern is defined within the
fingerprint image that was enrolled. In other words, quality measures how clearly
the Veriprox imaged the fingerprint. Poor quality enrollments can result in an
elevated rate of false rejection making it difficult for the user to verify reliably.
The score is given in stars (
) and ranges from zero to five stars, with five being
the best quality (rarely obtained) and zero being the worst. Quality scores of three
stars and higher perform well with the BII verification algorithm. In this range, the
algorithm readily compensates for differences in fingerprint quality. It statistically
is still true that the larger the quality score the better the performance of an
enrollment.
As a general rule of thumb, quality scores less than three stars require
intervention on the part of the enroller or administrative software. Sources of low
scores include dry fingers and dirty sensors.
If the quality score falls below three stars, BII recommends the following options:
•
Ensure that the sensor and finger are clean.
•
If the finger and sensor are clean and a dry finger is suspected, try re-enrolling
one more time, leaving the finger on the sensor for several seconds prior to
enrollment. Frequently finger moisture accumulates over time to provide a
good image.
•
Fingerprint quality can vary among individual fingers for the same person. Try
enrolling an alternate finger to see if the score improves.
•
Alter the security level
for that particular template
by decreasing the threshold
a minimum of 1 level (e.g., change the value from medium [3] to low [4]). This
will offset the false rejection for that template by making it easier to match. If
use of that template indicates that raising the threshold one level still produces
false rejections, try setting the value to its lowest security (level 5).
Warning
:
Decreasing a template’s security may increase the risk of a
false acceptance for that template.
A thorough enrollment procedure will ensure streamlined and reliable verification
for users. It is recommended that all four options be performed in the order listed
above to maximize the performance of the device.
Very Low
Very High