•Over the
years several coefficients have been developed to provide a normalised scale of similarity.
•All
are f(a,b,c,d) where
–a = count of on-bits unique to fingerprint
A
–b = count of on-bits unique to fingerprint
B
–c = count of on-bits common to both
fingerprints A and B
–d = count of off-bits common to both
fingerprints A and B
•A
list of the common ones are here
•The most
common coefficient is that due to Tanimoto, but others are now being seriously investigated and are available.
•Given the
nature of Daylight fingerprints it is inappropriate to use measures with the common off-bits d, as this value can be arbitrarily altered by adjusting the size.