Optical enhancement of degraded fingerprints

The similarities and differences between fingerprints enable degraded fingerprints to be optically enhanced for the purpose of identification. A coherent optical processing system was used to locate and analyze the spectra of features that uniquely identify fingerprints. The spectra of these ridges and ridge characteristics (minutiae) are located in harmonic bands of spatial frequencies for all types of fingerprints. A general set of simple filters was developed to enhance the identifying features of degraded fingerprints. Simple binary filters (lowpass, bandpass, highpass, and contrast reversal) use the circular symmetry of fingerprint spectra to enhance the degraded fingerprints. Schlieren and Laplacian filters perform an edge enhancement on the fingerprint ridges. These techniques improved the identifiability of degraded fingerprints while maintaining the generality of the procedure and the integrity of the fingerprints.