CN111639555B - Finger vein image noise accurate extraction and adaptive filtering denoising method and device - Google Patents

Finger vein image noise accurate extraction and adaptive filtering denoising method and device Download PDF

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CN111639555B
CN111639555B CN202010414619.2A CN202010414619A CN111639555B CN 111639555 B CN111639555 B CN 111639555B CN 202010414619 A CN202010414619 A CN 202010414619A CN 111639555 B CN111639555 B CN 111639555B
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赵国栋
张烜
蓝师伟
李学双
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Holy Point Century Technology Co ltd
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Abstract

The invention relates to a finger vein image noise accurate extraction and self-adaptive filtering denoising method and device, wherein the method comprises the following steps: 1) Calculating a multidirectional curvature response value of the finger vein image based on the two-dimensional Gaussian template; 2) Setting a maximum curvature response value threshold T 1 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Determining a noise area according to the curvature response value distribution condition and extracting a noise area image; 3) And filtering the noise area by a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image. The device comprises a calculation module, a noise area extraction module and a noise area filtering module. The method can realize accurate and effective detection of the noise of the finger vein image, realize accurate and rapid filtering processing on the detected noise area, effectively improve the recognition performance of the finger vein image containing the noise, and improve the actual use experience of the finger vein recognition system.

Description

Finger vein image noise accurate extraction and adaptive filtering denoising method and device
Technical Field
The invention belongs to the technical field of biological feature recognition in information security, and particularly relates to a finger vein image noise accurate extraction and adaptive filtering denoising method and device.
Background
The finger vein recognition technology belongs to the biological characteristic recognition technology and is a typical technology in the second generation biological characteristic recognition technology. The outstanding technical characteristics are that the collected biological characteristics are in the body, and compared with traditional biological characteristics such as fingerprints, faces and the like, the biological characteristics have higher safety and irreproducibility. The characteristic acquisition relies on the absorption of hemoglobin in blood to near infrared light, so that living body identification is fundamentally ensured, and meanwhile, the finger vein lines have uniqueness and long-term invariance, so that the method is a biological characteristic with high safety and great research value.
It is found that cracks on the finger, peeling areas or dust on the acquisition window are all reflected in the finger vein image, and the gray value of the dust is generally lower than that of the finger vein line area, and the dust belongs to a noise area in the finger vein image. When noise exists in the finger vein image, instability of the noise can cause great problems for the practical use experience of the finger vein recognition system: when the noise of the image is excessive, the verification passing rate may be reduced, and even verification success may not be possible. Therefore, when noise exists in the finger vein image, detection and filtering denoising are needed to be carried out on the noise area, so that the success rate of verification of the image containing the noise is improved.
The finger vein recognition method disclosed in patent number CN110119724A comprises the following steps: performing ROI positioning on an image acquired by a high-definition camera; carrying out gray scale normalization processing on different parts of the image; carrying out mean filtering and Gaussian filtering on the image to eliminate noise; judging the center position of the grain by using curvature detection; enhancing the contrast of the gray scale map through gamma transformation; judging edge pixel points by using a refinement method based on an index table; fusing, expanding and smoothing the extracted finger vein skeleton; finger vein recognition was performed by template matching, hu invariant moment, improved Zernike moment.
In the prior art, the method for eliminating noise by carrying out mean filtering and Gaussian filtering on the image has the following defects: the noise area is not positioned accurately enough, and the filtering processing speed is not fast enough.
Disclosure of Invention
The invention aims to solve the defects of inaccurate positioning of a noise region of a finger vein image and insufficient filtering processing speed in the finger vein recognition process in the prior art, and provides a finger vein image noise accurate extraction and self-adaptive filtering denoising method and device.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the invention relates to a finger vein image noise accurate extraction and self-adaptive filtering denoising method, which comprises the following steps:
1) Calculating a multidirectional curvature response value of the finger vein image based on the two-dimensional Gaussian template;
2) Setting a maximum curvature response value threshold T 1 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Determining a noise area according to the curvature response value distribution condition and a threshold value, and extracting a noise area image;
3) And filtering the noise area by a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image.
Preferably, the specific step of step 1) includes:
1.1 Constructing a curvature calculation operator in the 8 direction according to a two-dimensional Gaussian function, wherein the two-dimensional Gaussian function is as follows:
Figure BDA0002494489590000021
wherein x and y represent the length and width of the template, respectively;
1.2 Calculating a multidirectional curvature, the calculation of curvature involving the calculation of a first partial derivative, the calculation of a second partial derivative and the calculation of a gaussian function in a straight line L θ First and second directional derivatives in the direction, wherein,
the calculation formula of the first partial derivative is as follows:
Figure BDA0002494489590000022
the calculation formula of the second partial derivative is as follows:
Figure BDA0002494489590000023
calculating the Gaussian function in the straight line L θ The calculation formulas of the first-order and second-order directional derivatives in the direction are as follows:
Figure BDA0002494489590000031
wherein θ represents an included angle introduced, which is a certain straight line L θ An included angle with the positive direction of the x-axis;
1.3 Calculating a multidirectional curvature response value, wherein the calculation formula is as follows:
Figure BDA0002494489590000032
preferably, the step 2) specifically includes:
2.1 Setting a maximum curvature response value threshold T 1 According to the maximum curvature response value threshold T 1 Screening suspected noise points;
2.2 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold are set 2 According to the rate response value threshold S and the number threshold T exceeding the curvature response value threshold 2 Determining a noise area;
2.3 A noise area image is extracted.
Preferably, the rate response value threshold S is smaller than the maximum curvature response value threshold T 1
Preferably, the magnitude of the rate response value threshold S is: s=t 1 /2。
Preferably, the step 3) specifically includes:
3.1 Setting a proportion value eta of the noise point, and calculating the maximum median filtering template size according to the proportion value eta;
3.2 According to the maximum median filtering template size, performing circle-by-circle median filtering from outside to inside to obtain a denoised finger vein image.
Preferably, the specific step of calculating the maximum median filtering template size in the step 3.1) includes:
3.1.1 Setting the template as a square template, wherein the initial side length of the template is 1;
3.1.2 Calculating the proportion of noise points in all points in the current template size;
3.1.3 If the proportion of noise points in all points in the current template size is smaller than eta, the current template size is determined to be the best matched median filtering template size, if the proportion of noise points in all points in the current template size is larger than or equal to eta, the side length is increased on the basis of the side length of the current template, and the step 3.1.2 is returned.
Preferably, in the step 3.1.3), the increase of the side length is 1 each time.
Preferably, the specific way of the circle-by-circle median filtering from outside to inside in the step 3.2) is as follows: the median filtering is defined as one pass in four directions, namely from top to bottom, from bottom to top, from left to right, and from right to left, wherein only one noise point is processed each time, after the first pass is executed, the outermost noise point of the noise area in the image is filtered, the noise point is marked as a normal point at the moment, the next pass is performed, and the size of the maximum median filtering template needs to be recalculated every time the next pass is performed.
The invention also relates to a finger vein image noise accurate extraction and self-adaptive filtering denoising device, which comprises:
1) The calculating module is used for calculating a multidirectional curvature response value of the finger vein image based on the two-dimensional Gaussian template;
2) A noise region extraction module for setting a maximum curvature response value threshold T 1 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Determining a noise area according to the curvature response value distribution condition and extracting a noise area image;
3) And the noise region filtering module is used for filtering the noise region through a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image.
Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects:
the invention provides a finger vein image noise accurate extraction and self-adaptive filtering denoising method, which comprises the steps of firstly calculating a multidirectional curvature value of a finger vein image based on a two-dimensional Gaussian template, then extracting a noise area according to the curvature value, filtering noise points through median filtering of a circle-by-circle self-adaptive size, and realizing noise area detection and noise filtering of the finger vein image.
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FIG. 1 is a flow chart of a method for accurately extracting vein image noise and adaptively filtering and denoising;
FIG. 2 is a gray scale image of a finger vein containing noise;
FIG. 3 is a threshold T 2 Judging a suspected noise area image;
FIG. 4 is an image after adaptive turn-by-turn median filtering;
FIG. 5 is an illustration of gray scale images of the finger veins in different noise patterns;
FIG. 6 is a denoised image of a library of differently noisy images;
fig. 7 is a block diagram showing accurate extraction of vein image noise and adaptive filtering denoising.
Detailed Description
The invention will be further understood by reference to the following examples which are given to illustrate the invention but are not intended to limit the scope of the invention.
Example 1
Referring to fig. 1, the accurate extraction and adaptive filtering denoising method of finger vein image noise comprises the following steps:
1) For a finger vein gray scale image, as shown in fig. 2, the image size is 320×140, it is obvious that noise points with low gray scale value and more dispersed distribution exist in the image, and the multidirectional curvature response value of the finger vein image is calculated based on a two-dimensional gaussian template, and the specific steps include:
1.1 Constructing a curvature calculation operator in the 8 direction according to a two-dimensional Gaussian function, wherein the two-dimensional Gaussian function is as follows:
Figure BDA0002494489590000051
wherein x and y represent the length and width of the template, respectively, the two-dimensional gaussian template selected in this embodiment is a 9×9 square template, and x=y=9;
1.2 Calculating a multidirectional curvature, the calculation of curvature involving the calculation of a first partial derivative, the calculation of a second partial derivative and the calculation of a gaussian function in a straight line L θ First and second directional derivatives in the direction, wherein,
the calculation formula of the first partial derivative is as follows:
Figure BDA0002494489590000052
the calculation formula of the second partial derivative is as follows:
Figure BDA0002494489590000053
calculating the Gaussian function in the straight line L θ The calculation formulas of the first-order and second-order directional derivatives in the direction are as follows:
Figure BDA0002494489590000054
wherein θ represents an included angle introduced, which is a certain straight line L θ The included angle with the positive direction of the x-axis, the angle parameter θ in this embodiment takes the value of 0 °,22.5 °,45 °,67.5 °,90 °,112.5 °,135 °,157.5 °;
1.3 Calculating a multidirectional curvature response value K θ The calculation formula is as follows:
Figure BDA0002494489590000061
2) Setting a maximum curvature response value threshold T 1 Curvature responseA value threshold S and a number threshold T exceeding a curvature response value threshold 2 Determining a noise area and extracting a noise area image according to the curvature response value distribution condition and a threshold value, wherein the specific steps are as follows:
2.1 Since the curvature value of the noise region is generally large and since the continuity thereof is poor, there are large values above a plurality of direction angles, the maximum curvature response value threshold T is set first 1 T in the present embodiment 1 280, according to the maximum curvature response value threshold T 1 Screening suspected noise points, i.e. when the maximum curvature value of a point is greater than T 1 When the noise points are suspected noise points;
2.2 A rate response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Wherein the magnitude of the rate response value threshold S is smaller than the maximum curvature response value threshold T 1 In the present embodiment, s=t 1 Number threshold T exceeding curvature response value threshold 2 Is 5, according to the rate response value threshold S and the quantity threshold T exceeding the curvature response value threshold 2 The noise area is determined, namely, the condition that the curvature response value exceeds 140 and the maximum curvature response value exceeds 280 is required to be satisfied at least in 5 directions, the current point is considered to be the determined noise area, the noise area image shown in fig. 4 is extracted, and compared with fig. 2 and 3, the extracted noise area image can accurately reflect the noise distribution condition in the image, so that accurate detection is realized.
3) After obtaining an accurate noise area image, filtering the noise area by a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image, wherein the specific steps comprise:
3.1 Because the size of the median filtering template has direct influence on the filtering effect and efficiency, the noise area in the finger vein image has different sizes, and if the whole image uses a larger median filtering template, the filtering time is longer; if smaller templates are used, the filtering effect is not good for some large noisy areas. It is therefore necessary to determine its optimal median filtering template size for a certain noise point. The median filtering principle is to select the intermediate value after sorting all the values in the template to replace the current value, if a certain point is a noise point, the gray value of the point is an edge area of all the value sorting in the template size, the median is to be ensured to be close to the normal gray range, the proportion of the noise point number in the point in the current template is required to be ensured not to be too high, therefore, when the template size of median filtering is determined, the proportion value eta of the noise point is required to be set, in the embodiment, the proportion value eta is 30%, namely, the proportion of the noise point in the template participating in median filtering at present is ensured to be not to exceed 30%, the filtering effect at the moment is better, and the maximum median filtering template size is calculated according to the proportion value eta, namely
3.1.1 Setting the template as a square template, wherein the initial side length of the template is 1;
3.1.2 Calculating the proportion of noise points in all points in the current template size;
3.1.3 If the proportion of noise points in all points in the current template size is smaller than eta, the current template size is determined to be the best matched median filtering template size, if the proportion of noise points in all points in the current template size is larger than or equal to eta, the side length is increased on the basis of the side length of the current template, the increment of the side length each time is 1, and the step 3.1.2) is returned, and the maximum median filtering template side length of the embodiment is 6 is obtained through the method;
3.2 According to the maximum median filtering template size, carrying out circle-by-circle median filtering from outside to inside to obtain a denoised finger vein image, wherein the specific mode is as follows: the median filtering is defined as one time in four directions, namely one time from top to bottom, from bottom to top, and from left to right, and from right to left, wherein only one noise point is processed each time, after the first time is executed, the outermost noise point of a noise area in an image is filtered, and is marked as a normal point at the moment, and then the next time of filtering is carried out; it should be noted that: for each filtering, the size of the maximum median filtering template needs to be recalculated, the filtered image is shown in fig. 4, and compared with fig. 2, the noise area in the image is basically filtered out, the vein lines become the main areas with low gray values in the image, and the vein features are obvious.
In order to analyze the denoising effectiveness of the method, a plurality of noise image libraries of different types are selected, and as shown in fig. 5, a total of 3 noise type images are used as comparison images, and 1 group of normal acquisition image libraries which do not contain noise are saved and used as template images. The situation after denoising of the 3 kinds of noise image libraries is shown in fig. 6, and the method has good filtering effects on noise with different distribution forms at different degrees. The comparison test was based on the 4 image libraries described above, each image library containing 100 fingers, 5 images per finger. And taking the normal image input system as a template, directly inputting 3 groups of noise image libraries into the system as verification images to obtain verification results without denoising, and inputting the 3 groups of noise image libraries into the system as verification images after denoising by the method to obtain the verification results after denoising, wherein the verification passing rate and the false recognition rate are respectively counted, and when the false recognition rate is counted, the finger templates are shielded and only the rest 99 finger templates are compared. For each noise image library, the number of results of statistical verification success rate is 1500, and the number of results of statistical false verification rate is 1500. The success rate before and after denoising and the false recognition rate are compared as shown in table 1.
Table 1: comparison of success rate before and after denoising and false recognition rate
Figure BDA0002494489590000081
As is clear from the results in table 1, the recognition rate was reduced to different degrees when the finger vein image included noise, and the more serious the noise was, the more the recognition rate was reduced. After the noise image is denoised, the recognition rate of the noise image can be obviously improved, for 3 noise image libraries with different degrees, the recognition rate is respectively improved by 12.40 percent, 15.53 percent and 15.60 percent, and for images with more serious noise, the recognition rate is improved more, and no new false recognition is performed after the noise is removed in the aspect of false recognition rate, so that the overall recognition performance of the noise image library can be improved by the denoising method.
Example two
Referring to fig. 7, the present embodiment relates to a finger vein image noise accurate extraction and adaptive filtering denoising apparatus, including:
1) The calculating module is used for calculating a multidirectional curvature response value of the finger vein image based on the two-dimensional Gaussian template; the computing module is a module for realizing the function of the step 1) in the embodiment.
2) A noise region extraction module for setting a maximum curvature response value threshold T 1 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Determining a noise area according to the curvature response value distribution condition and extracting a noise area image; the noise region extraction module is a module for realizing the function of step 2) of the embodiment.
3) And the noise region filtering module is used for filtering the noise region through a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image. The noise region filtering module is a module for realizing the function of the step 3) in the embodiment.
The present invention has been described in detail with reference to the embodiments, but the description is only the preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. All equivalent changes and modifications within the scope of the present invention should be considered as falling within the scope of the present invention.

Claims (9)

1. A finger vein image noise accurate extraction and self-adaptive filtering denoising method is characterized in that: which comprises the following steps:
1) Calculating a multidirectional curvature response value of a finger vein image based on a two-dimensional Gaussian template, wherein the method specifically comprises the following steps of:
1.1 Constructing a curvature calculation operator in the 8 direction according to a two-dimensional Gaussian function, wherein the two-dimensional Gaussian function is as follows:
Figure QLYQS_1
(1),
in the method, in the process of the invention,xandyrespectively representing the length and the width of the template;
1.2 Calculating a multidirectional curvature, the calculation of curvature involving the calculation of a first partial derivative, a second partial derivativeCalculation of the order partial derivative and calculation of the Gaussian function in a straight lineL θ First and second directional derivatives in the direction, wherein,
the calculation formula of the first partial derivative is as follows:
Figure QLYQS_2
(2),
the calculation formula of the second partial derivative is as follows:
Figure QLYQS_3
(3),
calculating the Gaussian function in straight lineL θ The calculation formulas of the first-order and second-order directional derivatives in the direction are as follows:
Figure QLYQS_4
(4),
in the method, in the process of the invention,θindicating the included angle of introduction, which is a straight lineL θ And (3) withxAn included angle in the axial direction;
1.3 Calculating a multidirectional curvature response value, wherein the calculation formula is as follows:
Figure QLYQS_5
(5);
2) Setting a maximum curvature response value threshold T 1 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Determining a noise area according to the curvature response value distribution condition and a threshold value, and extracting a noise area image;
3) And filtering the noise area by a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image.
2. The method for accurately extracting and adaptively filtering and denoising finger vein image noise according to claim 1, wherein the method comprises the following steps of: the step 2) specifically comprises the following steps:
2.1 Setting a maximum curvature response value threshold T 1 According to the maximum curvature response value threshold T 1 Screening suspected noise points;
2.2 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold are set 2 According to the curvature response value threshold S and the number threshold T exceeding the curvature response value threshold 2 Determining a noise area;
2.3 A noise area image is extracted.
3. The finger vein image noise accurate extraction and adaptive filtering denoising method according to claim 2, wherein: the curvature response value threshold S is smaller than the maximum curvature response value threshold T 1
4. The method for accurately extracting and adaptively filtering and denoising finger vein image noise according to claim 3, wherein the method comprises the following steps of: the curvature response value threshold S is as follows: s=t 1 /2。
5. The method for accurately extracting and adaptively filtering and denoising finger vein image noise according to claim 1, wherein the method comprises the following steps of: the step 3) specifically comprises the following steps:
3.1 Setting the proportion value of noise pointsηAccording to the ratio valueηCalculating the size of a maximum median filtering template;
3.2 According to the maximum median filtering template size, performing circle-by-circle median filtering from outside to inside to obtain a denoised finger vein image.
6. The method for accurately extracting and adaptively filtering and denoising finger vein image noise according to claim 5, wherein the method comprises the following steps of: the specific step of calculating the maximum median filtering template size in the step 3.1) comprises the following steps:
3.1.1 Setting the template as a square template, wherein the initial side length of the template is 1;
3.1.2 Calculating the proportion of noise points in all points in the current template size;
3.1.3 If the proportion of noise points in all points in the current template size is smaller thanηThe current template size is determined to be the best matched median filtering template size, if the proportion of noise points in all points in the current template size is greater than or equal toηAnd (3) increasing the side length on the basis of the side length of the current template, and returning to the step 3.1.2).
7. The method for accurately extracting and adaptively filtering and denoising finger vein image noise according to claim 6, wherein the method comprises the following steps of: the increase of the side length in the step 3.1.3) is 1 each time.
8. The method for accurately extracting and adaptively filtering and denoising finger vein image noise according to claim 5, wherein the method comprises the following steps of: the specific mode of the circle-by-circle median filtering from outside to inside in the step 3.2) is as follows: the median filtering is defined as one pass in four directions, namely from top to bottom, from bottom to top, from left to right, and from right to left, wherein only one noise point is processed each time, after the first pass is executed, the outermost noise point of the noise area in the image is filtered, the noise point is marked as a normal point at the moment, the next pass is performed, and the size of the maximum median filtering template needs to be recalculated every time the next pass is performed.
9. The utility model provides a finger vein image noise accurate extraction and self-adaptation filtering denoising device which characterized in that: it comprises the following steps:
1) The calculation module calculates a multidirectional curvature response value of the finger vein image based on a two-dimensional Gaussian template, and specifically comprises the following steps:
1.1 Constructing a curvature calculation operator in the 8 direction according to a two-dimensional Gaussian function, wherein the two-dimensional Gaussian function is as follows:
Figure QLYQS_6
(1),
in the method, in the process of the invention,xandyrespectively representing the length and the width of the template;
1.2 Calculating a multidirectional curvature, the calculation of the curvature involving the calculation of a first partial derivative, the calculation of a second partial derivative, and the calculation of a gaussian function in a straight lineL θ First and second directional derivatives in the direction, wherein,
the calculation formula of the first partial derivative is as follows:
Figure QLYQS_7
(2),
the calculation formula of the second partial derivative is as follows:
Figure QLYQS_8
(3),
calculating the Gaussian function in straight lineL θ The calculation formulas of the first-order and second-order directional derivatives in the direction are as follows:
Figure QLYQS_9
(4),
in the method, in the process of the invention,θindicating the included angle of introduction, which is a straight lineL θ And (3) withxAn included angle in the axial direction;
1.3 Calculating a multidirectional curvature response value, wherein the calculation formula is as follows:
Figure QLYQS_10
(5);
2) A noise region extraction module for setting a maximum curvature response value threshold T 1 A curvature response value threshold S and a number threshold T exceeding the curvature response value threshold 2 Determining a noise area according to the curvature response value distribution condition and extracting a noise area image;
3) And the noise region filtering module is used for filtering the noise region through a circle-by-circle self-adaptive median filtering method to obtain a denoised finger vein image.
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