JP2990488B2 - Fingerprint collation device and fingerprint imprint determination method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fingerprint collating apparatus and a fingerprint imprint determining method for preventing erroneous determination in fingerprint collation. A fingerprint matching device is known in which a fingerprint is registered in advance and a fingerprint is imaged by a fingerprint imaging unit when performing identity verification, and a fingerprint matching device that matches the registered fingerprint is known. It is necessary to determine whether

[0002]

2. Description of the Related Art FIG.
Denotes a camera, 22 denotes a light source, 23 denotes a prism, 24 denotes an elastic film, and 25 denotes a finger for imprinting a fingerprint. The camera 21 can be, for example, a CCD camera, and is arranged at an angle equal to or smaller than the critical angle θ with respect to the printing surface (the surface of the elastic film 24), and illuminates the printing surface via the prism 23 from the light source 22. ,
When the finger 25 is not placed, the reflected light does not enter the camera 21. When the finger 25 is placed on the elastic film 24 on the impression surface, the ridges and valleys forming the fingerprint of the finger 25 are formed. Is incident on the camera 21 and the camera 2
1 outputs a signal obtained by imaging the fingerprint.

[0003] The elastic film 24 is for improving the adhesion to the finger 25 so that a clear fingerprint can be picked up even with a dry finger, and a certain degree of wear resistance is required. is there.
Therefore, there is no usable colorless and transparent material. Therefore, when strong light is incident on the impression surface from outside, the elastic film 2
4 scattered light by itself may be generated and incident on the camera 21. When the elastic film 24 is scratched or dust adheres, the light from the light source 22 generates reflected light and enters the camera 21.

In the fingerprint collation device, a finger 25 is placed on a fingerprint imprinting surface (on the elastic film 24), and a fingerprint is imaged by the camera 21 for processing. It is necessary to determine whether or not this is the case. Therefore, in the conventional fingerprint matching device,
For example, (a) when a finger is placed on the impression surface, the reflected light from the finger is incident on the camera 21. Therefore, the average luminance in a determination area used for fingerprint collation or the like in an imaged screen by the camera 21 is obtained. When the average luminance exceeds a preset threshold value, it is presumed that the reflected light from the finger 25 has entered the camera 21, it is determined that the fingerprint is imprinted, the captured image signal at that time is captured, and fingerprint registration and registration are performed. A method for performing fingerprint collation is known.

[0005] (b) A method is also known in which the judgment area is divided into a plurality of blocks, and when the number of blocks in each of which the average luminance exceeds a threshold value is equal to or greater than a predetermined value, the state of imprinting is determined. . If the number of blocks in the determination area is j, the number of pixels in the block is m, and the luminance of the pixels in the determination area is P _qn , the average luminance A _q of a certain block is A _q = (Σ _{n = 1} ^{n = m} P _qn ) / m (1) Then, for a certain threshold value a, the total number of blocks in which the above-mentioned average luminance _satisfies A _q > a is obtained, and N
When the total number N satisfies the relationship of N> b with respect to a certain threshold value b, there is also known a method of determining that a fingerprint is imprinted.

[0006]

The above-mentioned prior art (a)
When the average luminance in the determination area exceeds the threshold value, the fingerprint is determined to be a fingerprint imprint. When strong light is incident on the fingerprint imprint surface, such as direct sunlight, the scattered light of the elastic film 24 is generated by the camera 21. , The entire screen becomes a white screen as a whole, and the average luminance increases. That is, an error occurs in the seal determination.

In the conventional example (b), a method of determining a number N where the average luminance of each block in the determination area exceeds the threshold value a, and when the number N exceeds the threshold value b, determines that the fingerprint is imprinted. Even if the illumination unevenness of 22 can be remedied, the conventional example (a)
As in the case of (1), if strong light is incident on the impression surface, the average luminance of each block increases, and an error occurs in the impression determination. An object of the present invention is to provide a fingerprint collation device and a fingerprint imprint determination method which prevent such an error in imprint determination.

[0008]

According to the present invention, there is provided a fingerprint collating apparatus and a fingerprint imprint judging method, wherein a fingerprint image pickup unit 1 configured to enter an image by reflecting light from illumination from a light source, and a plurality of fingerprint judging areas. The block is divided into blocks, and the average luminance within the block is calculated based on the multi-valued image signal from the fingerprint imaging unit 1. The average luminance within the block is calculated from the average luminance within the block. And a luminance deviation calculating and arranging unit 3 for calculating the number of pixels corresponding to the deviation, and a pixel corresponding to the deviation from the luminance deviation calculating and arranging unit 3. With respect to the number, when the number of pixels within a predetermined range whose deviation is close to zero does not exceed the threshold value, a fingerprint determining unit 4 that determines that the fingerprint imaging unit 1 is in a fingerprint stamping state, Judge the stamping state And a fingerprint verification unit 5 for fingerprint identification based on multi-valued image signal from the fingerprint image pickup unit 1 when.

In the fingerprint imprint determining method in the fingerprint collating apparatus, an average luminance is obtained for each of a plurality of blocks in a fingerprint determining area based on a multi-valued image signal picked up by the fingerprint image pick-up unit 1. The deviation between the average luminance of the block and the luminance of the pixels in the block is determined, the number of pixels corresponding to the deviation is determined for the entire determination area, the horizontal axis is the deviation, and the vertical axis is the number of pixels. From a predetermined value centered on a point shifted by a predetermined value in the horizontal axis direction from the threshold value, and determines whether or not the number of pixels has exceeded a threshold value. It is a thing.

[0010]

The multi-valued image signal from the fingerprint imaging unit 1 including a CCD camera and the like is applied to the average brightness calculation unit 2 in the block via the interface unit 6. Is divided into a plurality of blocks, and the average luminance in each block is calculated. The luminance deviation calculating and arranging unit 3 calculates a deviation between the average luminance in the block and the luminance of each pixel in the block, processes all the pixels in the determination area, and obtains a correspondence between the deviation and the number of pixels. The impression determining unit 4 determines that external light has entered the fingerprint imaging unit 1 when the number of pixels within a predetermined range near zero is greater than the threshold, and determines that the external light has not exceeded the threshold. Is determined to be in the fingerprint imprinting state, the multi-valued image signal from the fingerprint imaging unit 1 at that time is binarized in the binarization unit 7, and the binarization registration registered in the storage unit 8 is performed. The fingerprint is collated with the fingerprint collation unit 5 and a collation judgment is output.

The embossing determination method is to determine an average luminance for each of a plurality of blocks in a fingerprint determination area, determine a deviation between the luminance of each pixel of this block and the average luminance in the block, and then determine the entire determination area. , The relationship between the deviation and the number of pixels is obtained. Assuming that the horizontal axis is the deviation and the vertical axis is the number of pixels, when external light is incident, or conversely, when the light incident on the fingerprint imaging unit 1 is only a small amount of reflected light, most of the pixels are within the block. The deviation from the average luminance becomes zero or close to it,
The number of pixels near the deviation of zero increases to a degree exceeding the threshold. On the other hand, in the case of the fingerprint imprinting state, the reflected light corresponding to the fingerprint is incident on the fingerprint imaging unit 1, so that the number of pixels near the zero deviation is reduced, and the bimodal characteristic around the zero deviation is the center. As a pixel number distribution, the number of pixels near zero deviation does not exceed the threshold value. In addition, corresponding to the electrical characteristics of the fingerprint imaging unit 1 and the configuration of each unit, the pixel number distribution characteristic with respect to the deviation is not symmetrical with respect to the zero deviation, so that the characteristic is distributed in the horizontal axis direction from the zero deviation point. A determination is made as to whether or not the number of pixels within a predetermined range has exceeded a threshold value, with the point shifted by the predetermined value as the center.

[0012]

FIG. 1 is an explanatory view of a fingerprint collating apparatus according to an embodiment of the present invention. 1 is a fingerprint imaging unit, 2 is an average luminance calculation unit in a block, 3 is a luminance deviation calculation and arraying unit, and 4 is an impression. Judgment part,
Reference numeral 5 denotes a fingerprint collating unit, 6 denotes an interface unit, 7 denotes a binarizing unit, and 8 denotes a storage unit. As shown in FIG. 5, the fingerprint imaging unit 1 includes a camera 21, a light source 22, a prism 23, and an elastic film 2.
4 is included.

The multi-valued image signal from the fingerprint imaging unit 1 is
For example, the signal is converted into a digital signal in the interface unit 6 and is added to the average luminance calculating unit 2 in the block.
The in-block average luminance calculator 2, the luminance deviation calculator, the arrayer 3, and the seal determiner 4 can be realized by logic circuits of respective functions, but can also be easily realized by an arithmetic processing function by a microprocessor or the like. Can be realized.

FIG. 2 is a flow chart of the embodiment of the present invention. The steps (a) to (f) show the operation of fingerprint imprint determination, which will be described below with reference to FIG. The captured multi-valued image captured by the fingerprint imaging unit 1 is captured via the interface unit 6 (a), and the average brightness in each block in the determination area is calculated in the average brightness calculation unit 2 in the block (b).

For example, the imaging area 11 shown in FIG.
Assuming a 2 × 512 pixel configuration, the determination area 12
May have, for example, a 400 × 320 pixel configuration, and divide the determination area 12 into a plurality of blocks 13. Each block 13 can have, for example, a 16 × 16 pixel configuration.

As described above, if the number of blocks 13 in the decision area 12 is j, the number of pixels in the block is m, and the luminance of the pixels in the decision area 12 is P _qn , the average luminance A _q in the block is It can be determined by equation (1). As described above, the number of pixels in the determination area 12 is set to 400 × 32
0, the number of pixels of the block 13 is 16 × 16, j =
500, m = 256.

The average luminance in the block is obtained (b).
The difference between the luminance of each pixel and the average luminance in each block is determined, and the number of pixels having the same difference is determined (c). That is, the luminance deviation calculating, in the sequencing unit 3 obtains a brightness P _qn and variance of each pixel in the block and block average luminance A _q, seeking each deviation for all the pixels in the determination area 12, The number of pixels having the same deviation is obtained.

Then, a pixel number distribution with respect to the deviation is obtained such that the horizontal axis represents the deviation and the vertical axis represents the number of pixels. That is, the luminance deviation calculating and arranging unit 3 accumulates the number of pixels having the same deviation, and arranges the number of pixels corresponding to the deviation using a table or the like. FIG. 4 shows an example of the pixel number distribution with respect to the deviation. Curve A in FIG. 4 shows the case where external light is incident, and curve B shows the case of fingerprint imprinting. That is, when external light is incident, each block 13 in the determination area 12 has almost the same luminance.
The number of pixels near the deviation 0 increases. Therefore, it has a single-peak characteristic. Ideally, if the determination area 12 has uniform brightness, the number of pixels having a deviation of 0 is 128000 in the above-described case, and the number of pixels having other deviations is 0. As described above, when the fingerprint is not imprinted, if the threshold is set to σ, the characteristic becomes a single peak, and thus exceeds the threshold σ.

When a fingerprint is picked up, the luminance distribution corresponds to the minute pattern of the ridges and valleys of the fingerprint, so that the number of pixels near the deviation 0 is relatively small. That is, the number of pixels having the same luminance as the average luminance in the block is reduced, and the distribution of the number of pixels corresponding to the deviation is obtained over a relatively wide range of the deviation. Characteristics. In this case, the maximum number of pixels does not exceed the threshold value σ.

In practice, the relationship between the deviation and the number of pixels depends on the characteristics of the fingerprint imaging unit 1, the amplification characteristics of the interface unit 6, etc., the digitization characteristics of the multi-valued image signal, etc. The valley of the curve B does not coincide with the position of the deviation 0. Therefore, a range of ± β is set around a point shifted in the horizontal axis direction by a predetermined value α corresponding to the characteristic from the position of the deviation 0, and it is checked whether or not the number of pixels within this range exceeds the threshold σ ( Step (d) in FIG. 2). FIG. 4 shows a case where the position shifts from the position of the deviation 0 in the direction of the negative deviation. However, the position may shift in the direction of the positive deviation depending on the characteristics of each part. The value of ± β is selected in consideration of the shapes of the curves A and B, and includes the range in which the number of pixels near the deviation 0 of the curve B is small and the number of pixels near the deviation 0 of the curve A. By setting so as to include a large range, it is possible to reduce determination errors.

Then, it is determined whether or not there is a pixel number exceeding the threshold value σ within the range of ± β (step (e) in FIG. 2).
If there is a pixel number exceeding the threshold σ, it is not due to the fingerprint imprinting state, but due to external light, etc., and the process proceeds to step (a). If there is no pixel number exceeding the threshold σ, it is determined that the fingerprint is imprinted. Then, fingerprint registration and collation processing is performed (f). That is, the processing of step (e) is performed by the impression determining unit 4, and when it is determined that the fingerprint is imprinted, the image is binarized by the binarizing unit 7. At the time of collation, the registered fingerprint is read from the storage unit 8, collated by the fingerprint collation unit 5, and a collation determination output as to whether or not the identity is verified is obtained.

[0022]

As described above, the fingerprint collating apparatus of the present invention comprises a fingerprint imaging unit 1 and an average brightness calculation unit 2 in a block.
And a luminance deviation calculating and arranging unit 3; a stamping determining unit 4; and a fingerprint collating unit 5. The deviation between the average luminance in each block of the determination area and the luminance of each pixel is determined, and pixels having the same deviation are determined. The number of pixels is determined to determine whether or not the number of pixels exceeds a threshold value σ. If the number of pixels does not exceed the threshold σ, the fingerprint is determined to be in a fingerprint-printed state, and fingerprint collation is performed. When incident, or conversely, when nothing is incident, since the number of pixels near the deviation 0 increases, there is an advantage that the state of fingerprint imprinting can be reliably determined.
Also at the time of fingerprint registration, it can be determined whether or not the fingerprint has been read correctly.

Also, a fingerprint imaging unit 1, an average luminance calculation unit 2 within a block, a luminance deviation calculation / arrangement unit 3, and a stamp determination unit 4
In the fingerprint collation device including, the deviation between the average luminance of each of a plurality of blocks in the determination area and the luminance of the pixels in the block was determined, the deviation was plotted on the horizontal axis, and the number of pixels with the same deviation was plotted on the vertical axis. Sometimes, when the number of pixels within a range of ± β does not exceed a threshold value σ around a point shifted by a predetermined value α in the horizontal axis direction from the point of deviation 0, it is determined that the fingerprint is imprinted. By selecting the shift value α and the determination range β in accordance with the above characteristics, there is an advantage that the fingerprint imprint state can be correctly determined.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a fingerprint matching device according to an embodiment of the present invention.

FIG. 2 is a flowchart of an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a determination area.

FIG. 4 is an explanatory diagram of an impression determination according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fingerprint imaging unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fingerprint imaging part 2 Average luminance calculation part in a block 3 Luminance deviation calculation and arrangement part 4 Impression judgment part 5 Fingerprint collation part 6 Interface part 7 Binarization part 8 Storage part

Claims (2)

(57) [Claims] A fingerprint imaging unit configured to capture an image by reflecting light from illumination from a light source; dividing a fingerprint determination area into a plurality of blocks, based on a multi-valued image signal from the fingerprint imaging unit; Calculating an average luminance in the block, calculating an average luminance in the block; calculating a deviation between the average luminance in the block from the average luminance calculation in the block and the luminance of each pixel in the determination area; A brightness deviation calculating and arranging unit for obtaining the number of pixels corresponding to the pixel value, and regarding the number of pixels corresponding to the deviation from the brightness deviation calculating and arranging unit, the number of pixels within a predetermined range where the deviation is close to zero exceeds a threshold value. When there is no fingerprint imprinting unit, a fingerprint judging unit that judges that the fingerprint imprinting state has been obtained, and a fingerprint based on the multi-level image signal from the fingerprint imaging unit when the fingerprint imprinting state is judged by the embossing judging unit. Fingerprint illumination for collation A fingerprint matching device comprising: 2. An average luminance is calculated for each of a plurality of blocks in a fingerprint determination area based on a multi-valued image signal captured by a fingerprint imaging unit, and an average luminance of each block and a luminance of a pixel in the block are calculated. Is obtained, the number of pixels corresponding to the deviation is obtained for the entire determination area, and the horizontal axis is the deviation, and the vertical axis is the number of pixels. Determining whether the number of pixels within a predetermined range centered on the point shifted by the threshold value exceeds a threshold value, and if not, determining that the fingerprint is in a fingerprint imprinting state. Fingerprint imprint determination method in the device.