Rotation invariant thinning algorithm to detect ridge bifurcations for fingerprint identification

In this paper we have modified the thinning algorithm proposed by Ahmed and Ward (2002). The unique feature that distinguishes the algorithm is its ability to thin any symbol or fingerprint to its central line taking care that the shape of the symbol is preserved while being rotation invariant. Our modified algorithm also incorporates a process to thin zigzag diagonal lines having a width of two pixels which was not considered in "a rotation invariant rule-based thinning algorithm for character recognition" (Ahmed and Ward, 2002). The algorithm is iterative and makes use of parallel processing to speed up execution. The system has 21 rules in its inference engine which are applied simultaneously to every pixel in each iteration. The algorithm is implemented for thinning fingerprints, fonts and symbols to a single pixel width. We also introduce a 24 rule based mask for detection of ridge bifurcations, which can be helpful for recognition/authentication of fingerprints as a biometric.