Fingerprint Analysis (part 2) Pavel Mrázek

Local ridge frequency

Image enhancement / binarization General rule: –Smooth along ridges –Enhance ridge-valley contrast –Separate fingerprint from background (segmentation) Various methods: –Convolution –PDEs –Morphology –Gabor filters –…

Gabor filters Several orientations Several frequencies At each position, –select orientation –select frequency –filter using the appropriate Gabor filter

Gabor filters

Coherence enhancing shock filter Shock filter: Regularized:

Coherence enhancing shock filter Use direction estimate: w … dominant eigenvector of the structure tensor

Examples Coherence enhancing shock filter

Ridge thinning Thinning: morphological operation Pixel value set to background if ridge connectivity not affected Structuring element: typically 3x3 window 9 pixels, 512 possible configurations, look-up

Singular point detection Methods for core and delta detection: –Poincaré index –Irregularity of orientation field, curvature –Partitioning of orientation field Reliability problems

Texture features

Feature extraction summary Extract features, store a template Prepare representation useful for matching –minutiae –… Reduce memory requirements (typical size 500 B – 30 kB) Privacy: fingerprint not stored

Enrollment Register user, store data into a database

Verification Compare to enrolled template, accept / reject a match

Identification Recover identity, 1-to-N match

References Maltoni et al.: Handbook of Fingerprint Recognition. Springer Maltoni. A tutorial on fingerprint recognition. In LNCS 3161, Springer Hong, Wan, Jain. Fingerprint image enhancement: algorithm and performance evaluation. IEEE PAMI Zhou, Gu. A model-based method for the computation of fingerprints’ orientation field. IEEE TIP Weickert. Coherence enhancing shock filters. DAGM Contact: mrazekp -at- cmp.felk.cvut.cz