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

ANSI/NIST-ITL 1-2011Data Format for the Interchange of Biometric and Forensic InformationFigure 20: EFS Minutia placement when type is unknown. 31There are three confidence values used to define how precisely the minutia canbe defined: confidence in existence, direction, and location. Each of theseoptional information items contains a positive integer value from “1” to “100”indicating the percentage confidence in the existence of the minutia. If theconfidence value is determined by a human examiner, the only valid values shallbe “100” (certain) or “50” (debatable); automated algorithms may use the fullrange.This field consists of six information items:• The first information item (‘x’ coordinate / MXC) is expressed in units of10 micrometers (0.01mm). 32• The second information item (‘y’ coordinate / MYC) is expressed in unitsof 10 micrometers (0.01mm).• The third information item (Theta / MTD) is expressed in degrees. 33• The fourth information item (Type / MTY) is selected from Field 9.324Distinctive Features / DIS. 34Brad Wing 6/23/10 1:09 PMComment: Rewritten for consistencyofpresentation30The center of the ridge ending should be at the "Y" of the valley. The theta angle should run up the ridge.•31 The minutia is placed as for a ridge ending, type is set to unknown, and the radius of uncertainty isdefined to include possible points of intersection with neighboring ridges.•32 Ridge endings are located at the fork of the midpoint of the valley (see Figure 19), and bifurcations are at thefork of the midpoint of the ridge (Figure 18). Unknown types are marked as for ridge endings, but with the radius ofuncertainty also defined.•33 The angle of the minutia is determined by constructing three virtual rays originating at the minutia andextending 1.93mm (0.064” – about three ridge widths) along each ridge (for a bifurcation) or valley (for a ridge ending).The smallest of the three angles formed by the rays is bisected to indicate the minutiae direction.•34 The type of minutia shall be set if the examiner/encoding process is confident as to type: the “either” typeshall be used for all minutiae that are not clearly identifiable as a ridge ending or a bifurcation. Because of the frequencywith which minutiae appear to be ridge endings in one impression and bifurcation in another, even in clear images, it isrecommended that the minutiae type be used as supporting evidence rather than as a basis for exclusion. All complexminutiae types (crossovers/trifurcations etc) should be marked as combinations of bifurcation/endings. Unusuallydistinctive types/combinations of minutiae should be marked as unusual minutiae/groups of minutiae in Field 9.32497DRAFT 2