RU2395840C1 - Method of forming fingerpring biometrical code - Google Patents

Abstract

FIELD: information technology. ^ SUBSTANCE: when processing an electronic image of a ridge pattern, the said image undergoes binarisation through filtration, joining false discontinuities on the image, removal of false lime merging and levelling pixels of the electronic image relative a given pixel intensity threshold, after which the skeleton of the binary electronic image is formed by thinning its lines to given thickness. After determination of munitia coordinates on the skeleton of the ridge pattern, their centre of mass is calculated. In order to define arguments of the biometrical code function, cores of the ridge pattern are isolated, for which distance from the centre of mass is calculated for each munitia. The core is the munitia with the shortest distance from the centre of mass. A tree is constructed from each core to the rest of the munitia. The length of the branches of each tree is calculated and the values are graded. Munitia concentration arguments are calculated and the values are used to form the biometrical code of the ridge pattern. ^ EFFECT: more reliable fingerprint biometrical code, reduced number of operations when comparing codes and formation of the code taking into account increase in probability of occurrence of false munitia moving from the centre of the fingerprint image. ^ 9 cl, 9 dwg

Description

The invention relates to the field of recognition, presentation and reproduction of data, namely, methods for reading and recognizing printed or written characters or pattern recognition, in particular fingerprints and the formation of their biometric codes.

A known method of generating a biometric code (application US 2007/0036401 A1 "System for recognition fingerprint image, method and program for the same", February 15, 2007), which provides for the conversion of the papillary pattern of the fingerprint into electronic form, processing of its electronic image, determination of arguments functions of the biometric code of the papillary pattern - coordinates of the minutes.

The disadvantage of this method is that the biometric code is generated in the form of a set of coordinates of the minutes in pure form, and therefore, a large number of computational operations must be performed at the stage of comparing biometric codes. Another disadvantage of this method is the instability to uniform compression / stretching of the print image.

A known method of generating a biometric code (application US 2004/0252868 Al "Method and device for matching fingerprints", December 16, 2004), which provides for the conversion of the papillary pattern of the fingerprint into electronic form, processing of its electronic image, determining the arguments of the function of the biometric code of the papillary pattern - square areas of electronic image.

The disadvantage of this method is that the biometric code is formed in the form of a set of square image areas, and therefore, a large number of computational operations must be performed at the stage of comparing biometric codes. Another disadvantage of this method is the instability to rotation of the image of the print.

The closest in technical essence is the method of generating a biometric code according to the international application WO 2008/030166 A1 "A method, an apparatus, and a computer program product within fingerprint matching". The prototype method consists in converting the papillary pattern of the fingerprint into electronic form, processing its electronic image, determining the coordinates of the minutes of the papillary pattern, storing them, determining the function arguments of the biometric code of the papillary pattern, which form its biometric code.

Compared with analogues, the prototype method provides resistance to uniform compression / stretching of the image and the rotation of the print.

However, the closest analogue has a relatively low reliability of the code, due to the fact that it does not take into account the increase in the likelihood of false minutes when the fingerprint is removed from the center of the electronic image, and low reliability is associated with the need to perform a large number of operations at the stage of comparing biometric codes and the absence of redundancy.

The purpose of the claimed technical solution is to develop a method for generating a biometric fingerprint code that provides higher code reliability, reducing the number of operations performed at the stage of code comparison, generating a code taking into account that the probability of false minutes increases with increasing distance from the center of the electronic image of the fingerprint.

Для определения аргументов функции биометрического кода выделяют 2≤K≤N сердцевин папиллярного узора, для чего для n-й минуции вычисляют ее удаление S_n от центра масс С, а в качестве K сердцевин принимают K минуций с наименьшими значениями их удалений S от центра масс С. Затем от каждой k-й сердцевины, где k=1, 2, _…, K, строят деревья к остальным J=N-l минуциям, вычисляют длины ребер

каждого k-го дерева, где j=1, 2, _…, J, и ранжируют их, рассчитывают аргументы кучности минуций с сердцевинами путем вычисления соотношений длин ребер

каждой k-й сердцевины и углов

между j-м и r-м ребром, а биометрический код папиллярного узора формируют в виде

, причем значение r и r' выбирают равным j+1.This goal is achieved by the fact that in the known method of generating a biometric fingerprint code containing N minutes, which consists in converting the papillary pattern of the fingerprint into electronic form, processing its electronic image, determining the coordinates of the minutes of the papillary pattern, storing them, determining the arguments of the biometric function code papillary pattern, which form its biometric code, when processing an electronic image of a papillary pattern (PU) binarize it. Binarization of the image of a PU consists in filtering it, splicing the false gaps on it, removing false line merges and aligning the pixels of the electronic image with respect to a predetermined intensity threshold And _pore pixels, which is selected within 60 ÷ 100, and pixels with an intensity below a predetermined threshold And _{pores are} converted to black, and pixels with an intensity above a predetermined threshold And _{pores are} converted to white. Then form the skeleton of a binary electronic image by thinning its lines to a predetermined thickness Δ = 1. After determining the coordinates x _n , y _n N minutes, where n = 1, 2, _... , N, on the skeleton of the papillary pattern, the center of mass C is calculated by the formula

To determine the arguments of the biometric code function, 2≤K≤N cores of the papillary pattern are distinguished, for which for the nth minute its distance S _n from the center of mass C is calculated, and K minutes are taken with K cores with the smallest values of their distances S from the center of mass C. Then, from each k-th of the core, where k = 1, 2, _..., k, to the other building trees J = Nl Minutius, calculated lengths of the edges

of each k-th tree, where j = 1, 2, _... , J, and rank them, calculate the arguments of accuracy of minutes with cores by calculating the ratio of the lengths of the edges

every kth core and corners

between the jth and rth edges, and the biometric code of the papillary pattern is formed in the form

moreover, the value of r and r 'is chosen equal to j + 1.

Thanks to the new combination of features, the claimed method reduces the likelihood of false minutes, since the code formation takes into account several cores located in the central part of the electronic image of the PU, as well as the necessary computational operations before comparing the codes, which improves the reliability of the biometric fingerprint code.

The claimed method is illustrated by images that show:

figure 1 - image of a fingerprint in electronic form.

figure 2 - image of a fingerprint after filtering.

figure 3 - image of a fingerprint after splicing false gaps and removal of false mergers.

4 is a binary image of a fingerprint.

5 is a skeleton of a binary image of a fingerprint.

6 - minutes on the skeleton of a binary image of a fingerprint.

7 is a core on the skeleton of a binary image of a fingerprint.

Fig.8 is a tree from the core to the remaining minutes.

Fig.9 is a biometric code in a matrix representation.

The claimed method is implemented as follows.

Known methods for generating a biometric fingerprint code, as a rule, are based on determining the coordinates of the minutes and converting their values into some data set (David Maltoni "Handbook of fingerprint recognition", ed. Springer 2003, p. 83). As a rule, false minutes may appear in the image structure, and with a probability that increases with an increase in the offset from the center of the image, codes are simplified to increase the processing speed, while at the verification stage a large computational load appears, and the reliability of the code decreases.

The aforementioned indicates the existence of a problem in the development of technical solutions that ensure the formation of a biometric code taking into account a decrease in the accuracy of the coordinates of the minutes with an increase in their distances from the center of the image, an increase in the reliability of the code and all settlement operations prior to verification of the code.

The marked problem is solved in the claimed method as follows.

The electronic view of the image of the papillary pattern of the fingerprint, shown in figure 1, is a raster image with pixel intensities in the range 0 ÷ 255 (see ANSI standard, www.ansi.com. Appeal 19.01.2009), in which pixels with lower intensity the grooves of the print are represented - the lines of the papillary pattern 1, and the background with pixels with higher intensity. The original image contains high-frequency noise - noise and false line breaks 2 and false merges of lines 3 (see figure 2), caused by a loose fit of the finger to the surface of the scanning device.

Image noise removal technology is known. To do this, it is treated with a low-pass filter, for example, with a Gaussian core (see L. Shapiro, J. Stockman "Computer Vision", published by BINOM, 2006, p.196). The result of this conversion is presented in figure 2.

Well-known technology is used to correct false line breaks of lines 2 and false merges of lines 3 (see Sharat Chikkerur, Alexander N. Cartwright "Fingerprint image enhancement using STFT analysis". Center of unified biometrcis and sensors, University at Buffalo, NY, USA, 2003 .): determine the local orientation of the lines and perform filtering by the Gabor core, the result of which is shown in Fig.3.

To equalize the intensities of the pixels, threshold image processing is performed (see L. Shapiro, J. Stockman "Computer Vision", published by BINOM, 2006, p.116), the result of which is presented in Fig.4. In this case, pixels with an intensity below a predetermined threshold are converted to black, and pixels with an intensity above a predetermined threshold are converted to white. Based on the range of possible values of pixel intensities, the best quality of a binary image is achieved with AND _then = 60 ÷ 100.

Then, to simplify the process of searching for minutes, the skeleton of the binary image shown in FIG. 5 is constructed by thinning its lines to a predetermined thickness Δ. The thickness of the lines of the skeleton 8 is usually chosen equal to one pixel (Y. A. Furman, A. N. Yuryev, V. V. Yashin “Digital methods of processing and recognition of binary images”, Publishing house of the Krasnoyarsk University, 1992, p. 192).

On the skeleton of the binary image, the coordinates of the minutes 9 (x _n , y _n ) are determined, located at the points where the skeleton lines of the skeleton 8 are bifurcated or terminated (see ANSI standard, www.ansi.com, accession 01/19/2009), their coordinates are remembered. The size of the coordinate grid is determined by the intervals x _n = 0, 1, X _max , y _n = 0, 1, ..., Y _max , where X _max and Y _max are selected in the interval 200–500 pixels (see the FBI standard, www.fbi. com, appeal January 15, 2009).

Чтобы внести избыточность, повышающую надежность кода, для определения аргументов функции биометрического кода выделяют 2≤K≤N сердцевин 10 папиллярного узора, показанных на фиг.7 в виде концентрических кругов, для чего для n-й минуции 9 вычисляют ее удаление S_n от центра масс 11, а в качестве К сердцевин 10 принимают минуции с наименьшими значениями их удалений S от центра масс 11.In order to have the greatest influence on the biometric code, the minutes located closer to the center of the electronic image have the greatest impact, the center of mass of the minutes 11 shown in Fig. 7 is calculated by the formula

In order to introduce redundancy that increases the reliability of the code, 2≤K≤N cores 10 of the papillary pattern shown in Fig. 7 in the form of concentric circles are allocated to determine the arguments of the function of the biometric code, for which its distance S _n from the center is calculated for the nth minute 9 masses 11, and as K cores 10 take minutes with the smallest values of their distances S from the center of mass 11.

каждого k-го дерева, где j=1, 2, …, J, и ранжируют их. Рассчитывают аргументы кучности минуции с сердцевинами путем вычисления соотношений длин ребер 12

каждой k-й сердцевины и углов

между j-м и r-м ребром, а биометрический код папиллярного узора формируют в виде

, который представляет собой матрицу размерности K×J, показанную на фиг.9.Then, so that all the parameters that make up the biometric code are relative, which makes the code resistant to rotations, shifts and uniform compression / stretching of the electronic image of the PU, from each k-th core 10, where 1, 2, ..., K, construct the edges of the trees 12 to the remaining J = N-1 minutes 9. One of these trees is shown in Fig. 8. Calculate the lengths of the ribs 12

each k-th tree, where j = 1, 2, ..., J, and rank them. The arguments of accuracy of mining with cores are calculated by calculating the ratio of the lengths of the ribs 12

every kth core and corners

between the jth and rth edges, and the biometric code of the papillary pattern is formed in the form

which is a K × J matrix shown in FIG. 9.

Due to the choice of cores, the generated biometric code is more susceptible to the influence of minutes located closer to the center of the electronic image. All the parameters that make up the biometric code are relative, which makes the code resistant to rotations, shifts, and uniform compression / stretching of the electronic image of the control panel, and also eliminates the need for computational operations at the stage of code comparison. This is the reason for achieving the formulated technical result - ensuring a higher code reliability, reducing the number of operations performed at the stage of code verification, generating the code, taking into account the fact that the probability of false minutes increases when the fingerprint is removed from the center of the electronic image.

Claims (9)

1. The method of generating a biometric fingerprint code containing N minutes, which consists in converting the papillary pattern of the fingerprint into electronic form, processing its electronic image, determining the coordinates of the minutes of the papillary pattern, storing them, determining the function arguments of the biometric code of the papillary pattern, by which form its biometric code, characterized in that when processing an electronic image of a papillary pattern binarize it by filtering, splicing available on m of false gaps, removal of false line merges and pixel alignment of the electronic image relative to a predetermined threshold of pixel intensity, and then form the skeleton of the binary electronic image by thinning its lines to the specified thickness Δ, and after determining the coordinates x _n , y _n N minutes, where n = 1, 2, ..., N, x _n = 0, 1, ..., X _max , y _n = 0, 1, ..., Y _max , the center of mass C is calculated on the skeleton of the papillary pattern, moreover, to determine the arguments of the biometric code function 2≤K≤N cores of the papillary pattern are distinguished, for which, for of the nth minute, calculate its distance S from the center of mass C, and as K cores, take K minutes with the smallest values of their distances S from the center of mass C, then from each kth core, where k = 1, 2, ..., K build trees to the remaining J = Nl minutes, calculate the lengths of the edges

of each k-th tree, where j = 1, 2, ..., J, and rank them, calculate the arguments of accuracy of minutes with cores by calculating the ratio of the lengths of the edges

, each kth core and corners

between the jth and rth edges, and the biometric code of the papillary pattern is formed in the form

2. The method according to claim 1, characterized in that the thickness of the lines of the skeleton of the binary image Δ is chosen equal to one pixel of the electronic image of the papillary pattern. 3. The method according to claim 1, characterized in that the center of mass of the minutes is calculated by the formula

. 4. The method according to claim 1, characterized in that to equalize the intensities of the pixels of the electronic image of the papillary pattern, pixels with an intensity below a predetermined threshold are converted to black, and pixels with an intensity above a predetermined threshold are converted to white. 5. The method according to claim 1, characterized in that the predetermined threshold of the intensity of the pixels is selected in the range of 60 ÷ 100. 6. The method according to claim 1, characterized in that the value of r is chosen equal to j + 1. 7. The method according to claim 1, characterized in that the value of r 'is chosen equal to j + 1. 8. The method according to claim 1, characterized in that the value of X _max selected in the range of 200 ÷ 500 pixels. 9. The method according to claim 1, characterized in that the value of Y _max selected in the range of 200 ÷ 500 pixels.

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