U3.6 Fingerprint

U3.6 Fingerprint

1. Uses ridges on the skin, Ridges = lines. Valleys = Spaces between

2. Major and Minor features

   • 3 Major Features
     • Arch, Loop, Whorl
       • Major features used to classify fingerprints so they are more easily searchable
         • Only look in or compare to Arch records etc.
   • Minor features = Minutiae
     • Minutiae are the distinguishing features
       • Ridge endings and burifications in fingerprint pattern
       • Most algorithms are based on munutiae

3. Fingerprint processing involves several steps

   • Image is captured by sensor
     • noise is reduced IE:dirt, dryness, scars. definition against the valleys is enhanced
       • Image is binarised = reduced to black or white
         • Thinning is performed = reduction of ridges down to a single pixel to help detect ridge endings and burifications in the pattern
           • Ridges are traced,endings are found at termination points of the ridges and burifications are found at the junction of lines
             • Extracted features consists of the sequence of bits representing for each minutuae, type of minutiae (ridge or burification) its location and direction
               • Matching is done by comparing extracted features against the reference template
                 • Like comparing the shape of 2 graphs, if the graphs are similar enough according to the tolerance threshold the result is a match
                   • Some FP recognition can be done without the minutiae instead using pattern matching

4. Advantages

   • Mature technology, lots of development, investment and research. Takes up 2/3 of Biometric Market
   • Easy to use, non intrusive
   • High levels of accuracy, low error rates, low FMR, low FNMR
   • Long term stability of FP over a lifetime
   • Ability to enrol multiple fingers

5. Disadvantages

   • Inability to Enrol some users IE elderly, manual workers, thin fingerprints (Asian)
   • Accuracy affected by skin condition
   • Association with forensic applications
     • Privacy issues with users

6. Sensors

   • Optical
     • Oldest / most mature
       • Finger placed on glass and Image taken using optical device (camera)
         • Not much further development
   • Ultrasound
     • Uses ultrasound for capturing images
       • Un affected by dirt grease moisture etc
         • Better than optical but can only operate between 10c -32 c. Mainly used indoors
   • Chip Based
     • Capacitive
       • Most widely used chip based sensor
     • E-field
       • reads sub surface of skin, not affected by skin surface issues
     • Direct Optical Scanning
       • Robust fibre optic sensor
     • Thermal
       • Uses the fingers natural heat, no optic or light source required