ANSI/NIST-ITL 1-2011 - NIST Visual Image Processing Group ...

ANSI/NIST-ITL 1-2011Data Format for the Interchange of Biometric and Forensic InformationTable 28: EFS Methods of determining center point of reference locationsCode Name DescriptionL01Lateral centeronlyUppermost pointof the ridge withgreatestcurvatureOverallfingerprint focalpointThe center location is defined laterally (across thefinger) but is not meaningful in the other dimension(longitudinally, or along the finger). Lateral center ismost frequently used for defining the center line ofarches, tips, and lower joints. Lateral center is onlymeaningful if the orientation (Field 9.301) is known;the point marked is the center with respect to theorientation angle.For a fingerprint with a known or estimated orientation,the center point is determined by finding the highestpoint of each ridge that is convex pointing upward, andmeasuring the curvature/peak angle by following theridge 1.63mm (0.064in) in both directions from thatpoint. The point with the minimum angle (greatestcurvature) is the center point of reference.The overall fingerprint focal point is the point wherethe lines perpendicular to ridge flow converge. Thepoint of convergence is determined in terms of leastsquares (see, e.g., Novikov and Kot (1998) 26 )4.26 Novikov S.O and Kot V.S.; “Singular Feature Detection and Classification of Fingerprints using Hough Transform”;Proc. Of SPIE (Int. Workshop on Digital Image Processing and Computer Graphics (6 th ): Applications in Humanities andNatural Sciences); vol 3346, pp 259-269, 199892DRAFT 2