Reseach On The Method Of Three Dimensional Fingerprint Image Acquisition And Processing

Fingerprint is currently one of the most widely used biometric technologies.Fingerprint technologies have been researched and developed several decadeswhich have been focused on touching fingerprint recognition.For touching fingerprint recognition, a finger touches or rolls onto sensorsurface, the elastic skin is easily deformed which caused the different quality offingerprint images and directions by the different pressure of users. The skinconditions of different moisture also caused inconsistent fingerprint images.Hence, the representation of the same fingerprint changes every time the finger isplaced on the sensor platen, increasing the complexity of fingerprint matchingand representing a negative influence on system performance. As a result, a newapproach to capture fingerprints has been proposed. This approach, referred to astouchless or contactless fingerprint, tries to overcome the above-cited problems.Because of the lack of contact between the finger and sensor surface, the skindoes not deform during the capture. Therefore, contactless fingerprint on thefingerprint identification can get better results.In this paper, the three-dimensional fingerprint image is acquired based onthe method of Fourier transform profilometry which is one of the structured-lightthree dimensional measurement methods. Besides, we set up a three-dimensionalfingerprint image acquisition system by laser light source, CCD camera, grating,microobjective and computer etc. The deformation stripe images produced by thefinger surface height variations are acquired by using a camera after projectingthe fringe pattern of grating self-imaging to the surface of a finger by using the microscope objectives. Finally surface3-D shape of the finger is restructured byprocessing the pattern in computer and demodulating the phase information.In this paper, a detailed introduction of the principle of Fourier transformprofilometry is given and how it can obtain three-dimensional of fingerprintimage. Besides, the techniques of measurement, such as pretreatment, and phaseunwrapping for strip pattern were investigated. Useful fundamental frequencycomponent is obtained by using wavelet de-noising method to eliminate theeffects of high frequency noise in the images of the stripes and by adoptingwavelet transform to eliminate the stripe of zero frequency spectral components.After that, inverse Fourier transform is applied to acquire the principal valuephase map. For the problem of phase in the phase principle value figure isinterceptive, the traditional phase unwrapping algorithms are analyzed andsummarized, and in the final, select the domain neighbourhood antinoisealgorithm. This method can detect the noise in the phase principle value figure,make phase unwrapping process be valid only in effective data points, reduce thenoise influence on phase unwrapping effectively, and improve the precision ofphase unwrapping. The experimental results show that the method of Fouriertransform profilometry can get the height value of each point on the surface offinger.An ellipsoid fitting three dimensional fingerprint image processing methodis given in this paper. The three-dimensional fingerprint image is fit to theellipsoid model, and projected onto a two-dimensional plane. This paperintroduced the three-dimensional fingerprint image ellipsoid fitting process. Theexperimental results indicate that the fingerprint image and the ellipsoid can fitwell.