Want to know the principle of the fingerprint access control system ? Let me tell you.
Professor Bo Taichai of the University of Paris, France, classifies the details of fingerprints into four categories: starting point, ending point, difference, and combination. When performing fingerprint comparison, the four features are extracted and saved, and the feature points of the two fingerprints are compared. Through the translation, rotation and transformation ratio, when the maximum feature point of the coincidence is greater than a certain number, two The fingerprints are the same.
In the actual comparison, the fingerprint collected on the spot is compared with the existing template fingerprint feature points to judge, and the principle block diagram is as follows.
Figure 1 Block diagram of fingerprint identification
Image preprocessing also includes: fingerprint image quality control, pattern classification, calculation direction field, image enhancement, binarization, refinement and detail feature pruning. The effect of image processing at each stage of the fingerprint comparison process is as follows:
Original fingerprint image screenshot for central point filtering processing binary, refinement and feature point extraction
In Fig. 2, the original fingerprint image is 240*320, 256-level gray-scale BMP image; the processing of the fingerprint image is performed according to the fingerprint direction field established by the fingerprint texture feature, and the finally extracted fingerprint feature point is a vector. Its component includes the Cartesian coordinates and direction of the point (the tangential direction of the fingerprint ridgeline at that point). The on-site fingerprint feature point set and the template fingerprint feature point set are compared according to the principle that the fingerprint structure features are unchanged under the translation and rotation transformation, and the comparison result is determined by setting the corresponding comparison threshold.
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