Direction filtering reinforcement method of fingerprint image

Abstract

The invention relates to a direction filter enhancing method for a fingerprint image, which mainly includes a normalization processing of the fingerprint image, the direction estimation and the direction filter enhancement of fingerprint ridges. The normalization processing aims at eliminating the influences of uneven finger pressing on the fingerprint image and making full preparation for accurately extracting the direction information of the ridges. By using a mask method to extract the direction information of the ridges, the method of the invention is provided with high accuracy and lays a solid foundation for the following direction filter enhancement. In the direction filter enhancement of the fingerprint ridges, a smoothing filter template is used for the smoothing of a dermal ridge tangent direction and a sharpening filter template is used for the sharpening along the dermal ridge normal direction after the smoothing by the invention. Therefore, the contrast ratio between the ridge and the river reach of the fingerprint can be obviously enhanced; furthermore, the ridge interruption due to an over-drying finger can be connected and the ridge adhesion due to an excessive wet finger can be removed to obtain a good enhancing effect.

Description

technical field [0001] The invention relates to a fingerprint image preprocessing method before fingerprint image recognition, in particular to a direction filter enhancement method in the fingerprint image preprocessing. Background technique [0002] The preprocessing of fingerprint image is the most important part in automatic fingerprint identification system, and the result of preprocessing will directly affect the reliability and accuracy of identification. Therefore, the preprocessing of fingerprint image has become a research hotspot in the field of fingerprint identification. The preprocessing of the fingerprint image includes a filter enhancement processing of the fingerprint image. In the existing technology, "Acta Electronics" No. 1, 2004 provided a fingerprint image adding method "based on the ridge fingerprint filtering algorithm". The article pointed out that in the process of fingerprint collection, it is inevitable to introduce various noises , when it is se...

AI Technical Summary

Problems solved by technology

[0008] (1) Using extremum filtering and smoothing filtering to remove noise before enhancing the image will lose a lot of detail information of the fingerprint image, which is not desirable

[0009] (2) Before the directional filtering of the image is enhanced, the original fingerprint image is not gray-scale normalized, which cannot eliminate the impact of uneven finger pressure on the fingerprint image (that is, the central color of the fingerprint is often heavy, and the peripheral color is light) situation), which will adversely affect the accuracy of subsequent direction information extraction

[0010] (3) The algorithm of direction field estimation in this method is to calculate the direction angle of each pixel point first, and then quantize the direction of the pixel point to eight directions according to the direction angle, that is to say, from the obtained In the process of converting the direction angle value into the corresponding quantized direction value, there are uncertain factors in the quantization selection. Therefore, the direction value is difficult to be accurate, which will directly affect the effect of ridge filter enhancement according to the eight quantized directions.

[0011] (4) In this method, only smoothing filter templates are designed in the directional filter enhancement, and no sharpening filter templates are designed, and the templates are small, so it is difficult to accurately reflect the characteristics of filtering along the direction of the ridges, and the local direction changes sharply or there are ridges. Adhesive fingerprint image enhancement is less than ideal

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