Advances in Fingerprint Technology.pdf

Number of Positionings and Comparisons
The value of any fingerprint for identification is inversely proportional to the
chance of false association. This chance depends on the number of comparisons
that are attempted. Each attempt carries a potential for chance correspondence;
and the greater the number of attempts, the greater the overall
chance of false association. “Attempt” means both the number of possible
positionings on one individual and the number of different individuals with
which the print is compared. A fingerprint model should address this issue
and provide a means to determine the number of attempted comparisons.
Description of the Stoney and Thornton Model
Minutia Description and Survey
After proposing their set of model features, Stoney and Thornton performed
a systematic study of epidermal ridge minutiae 22 using a ridge-based minutia
description method. 51 The study was based on a survey of minutiae from the
distal portions of 412 thumbprints (pairs of right and left thumbs, all from
males, including 147 Whites, 56 Blacks, and 3 Asians). For each thumbprint,
a centrally located focal minutia was chosen and neighboring minutiae were
sampled.
The distal portion of thumbprints was chosen by Stoney and Thornton
because prints of this area are commonly encountered and because of the
absence of pattern type characteristics in this region. Regardless of the pattern
type, ridges on the distal portions of the digits show similar ridge flow,
conforming to the digital outline, flowing in an arch from one side of the
finger to the other.
The focal minutia was selected in a systematic way. A minutia was sought
in the most central portion of the ridge having a 5 mm radius of curvature.
If there was a single minutia on this ridge, within 45° of the center, then this
minutia was chosen. If more than one minutia was present, then the minutia
closest to the center line was chosen. If there was no minutia present on the
ridge, then successively more distal ridges were examined until a minutia was
found.
Once the focal minutia was chosen, neighbor minutiae were sampled within
the arc 45° on either side of the minutia, and with ridge counts of up to six
ridges proximally and nine ridges distally. The pattern type of the print was also
determined, along with measurements of the minutia and ridge densities.
For each neighbor minutiae, the type, orientation, ridge count, and
angular distance from the focal minutia was recorded. The minutia types
allowed were forks, ending ridges, and dots. Other “compound” forms of
minutiae were considered as closely spaced combinations of these three basic
minutia types.