During enrollment and subsequent identification processes, your fingerprint is typically displayed on a computer or video display monitor. The display contains a reference circle to aid you in positioning of your print consistently. This visual feedback is provided to help you address all of the quality control issues which are covered in this technical brief.

Centering your print: Before proceeding with enrollment or identification, place your finger into the finger guide on a fingerprint reader. Position it so that the pattern area is fairly centered on the monitor's display. Next, locate a point of interest (common line-type) in your print that can be easily recognized. Practice lifting and replacing your finger on and off the unit until you can consistently find this point of interest and are comfortable with the process.

To ensure consistent positioning you should select a point of interest which is in the reference circle and make sure that the feature is consistently placed relative to this reference circle.

Under normal tuning, BIO-key allows a placement deviation of +/- 150 pixels during the scan process. This equates to a total placement derivation of approximately 1/3 of the image provided for print display.

Print rotation: Print rotations greater than 20 degrees could be rejected. At best, the computer model will not consistently match the live scan. (BIO-key allows system administrators to set tolerances based on application security requirements.)

Print image quality: Print image quality should be controlled, not too dry, not too wet, and only minor scars.

Pressure: Pressure distortion should be minimized. Simply place the finger using light to normal pressure. Do not push or pull your finger to center it, because this can distort your print. Anytime repositioning is required, lift your finger slightly and then set it back down.

BIO-key uses an algorithm called Vector Segment Technology™ (VST) to enroll and identify users. VST starts by taking a scan of your finger at an effective resolution of 500 dots per inch (DPI). It then makes several passes on the image to optimize it. This is followed by a vector conversion process. In short, VST intelligently converts pixels into vectors that are used to catalogue the print.

Because VST generalizes fingerprints, it is very tolerant of micro feature changes or print contamination. This built-in tolerance allows BIO-key to be used in applications where other identification systems would be unreliable.

VST analyzes and categorizes prints in the same manner that a fingerprint expert would, only better and faster. It identifies all of the common print features described on pages 1 and 2, as well as other pertinent distinguishing marks or relative characteristics of the scanned image. In addition, the pattern area can be classified according to industry accepted rules.

Following analysis, VST generates an encrypted finger model for optional transmission to a central site for verification. This model represents an access key to the central database for one-to-one (1:1) or one to many (1:N) lookups. The system consistently maps a scanned print into a fixed coordinate system so that the print always has the same general origin. With this feature, BIO-key systems can be used to generate index keys for large existing fingerprint databases. These indexes in turn allow for very fast real time personal identification.