JP3348275B2 - Fingerprint image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fingerprint image processing apparatus for capturing a fingerprint image. Fingerprints are placed on the impression table, illuminated by a light source, and the fingerprint image is picked up by a camera. There is a case. Even under such difficult conditions, there is a demand to increase the possibility of fingerprint registration and collation.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of a conventional fingerprint image processing apparatus in which a finger placed on a prism 42 constituting a fingerprint imprinting table is illuminated by a light source 41 such as a light emitting diode or an incandescent lamp. The fingerprint image of the finger is captured by a camera 44 such as a CCD camera via an optical system such as a lens 43, and the image capturing unit 45 transfers an image capturing signal from the camera 44 to the arithmetic processing unit 46 together with a synchronization signal and the like. I do.

[0003] The arithmetic processing unit 46 digitizes the image pickup signal and transfers it to the fingerprint processing main unit 47. The fingerprint processing main unit 47 has a fingerprint registration function, a fingerprint collation function, or both of them. At the time of fingerprint registration, for example, a digital image signal is generated so that ridges and valleys of a fingerprint can be identified. Binarization is performed to extract a plurality of feature points including ridge branch points and the like, and to register the fingerprint points together with the fingerprint registrant's identification number in the file as a fingerprint image of the fingerprint registrant.

At the time of fingerprint collation, a fingerprint image previously registered is read out from a file based on the identification number of the fingerprint collator, and the fingerprint fingerprint placed by the fingerprint collator on the prism 42 and captured by the camera 44 is taken. The image is compared with feature points by performing the same processing as at the time of registration, and if more than a predetermined number of feature points match, a fingerprint match corresponding to the identification number at registration and the identification number at matching is made. The confirmation is performed, and the door can be opened and closed and various devices can be operated based on the identity confirmation.

[0005]

The fingerprint image picked up by the camera 44 at the time of fingerprint registration or fingerprint collation is affected by the curved state of the finger placed on the fingerprint impressing table, the collapse of ridges, the pressing force, and the like. As a result, it becomes partially unclear. It is also affected by the dryness of the skin of the finger. For example, it is more difficult to obtain a captured fingerprint image of a desired brightness in the case of a completely dry finger, as compared to the case where the skin contains some water. Becomes In addition, when the finger is strongly pressed on the fingerprint imprinting table, the brightness of the captured fingerprint image is slightly increased, but the brightness of the captured fingerprint image of the dried finger is hardly improved.

Therefore, at the time of fingerprint registration or fingerprint collation, the fingerprint imaging operation is repeated until the fingerprint is registered or the fingerprint collation result is obtained. In the worst case, fingerprint registration cannot be performed or fingerprint collation cannot be performed. There was a problem that could occur. An object of the present invention is to enable a desired fingerprint image to be obtained by performing a plurality of fingerprint imaging operations even when a desired captured fingerprint image cannot be obtained.

[0007]

According to the present invention, there is provided a fingerprint image processing apparatus comprising: (1) a CCD camera or the like which illuminates a finger placed on an impression table 2 composed of a prism or the like with a light source 1 such as a light emitting diode to image the finger; And a fingerprint image input unit 3 having an image capturing unit 8 for capturing a captured image signal from the camera 7, and a captured fingerprint image from the image capturing unit 8 of the fingerprint image input unit 3 is normal. Arithmetic processing unit 4 including image capture determining unit 10 and gain adjustment determining unit 11 for determining whether or not
A fingerprint processing main unit 5 for performing fingerprint registration / fingerprint collation based on the captured fingerprint image when the image capturing determination unit 10 of the arithmetic processing unit 4 determines that the fingerprint image is a normal captured fingerprint image; There is provided a gain control unit 6 for controlling a gain for a captured image signal from the fingerprint image input unit 3 to the image capture determination unit 10 of the arithmetic processing unit 4 according to the determination result of the gain adjustment determination unit 11.

[0008] Then, the image capture determining unit 10 divides one screen into blocks composed of a plurality of pixels, calculates the average value of the luminance values of the pixels in the blocks for each block, and calculates the average luminance value of each block. The first luminance reference value is compared with the first luminance reference value.
And the first number of missing blocks and the first number
When the first number of missing blocks is less than the first threshold, the captured fingerprint image is captured. When the first number of missing blocks is equal to or greater than the first threshold, the luminance average value and the first Is compared with a second luminance reference value smaller than the second luminance reference value, a block having a luminance average value smaller than the second luminance reference value is set as a second defective block, and the number of the second defective blocks and a second threshold value are set. And when the second number of missing blocks is less than the second threshold, the gain adjustment determining unit 11 instructs the gain control unit 6 to perform gain control, and the second number of missing blocks is equal to the second threshold. At the time of the above, a function of instructing fingerprint image capturing by the fingerprint image input unit 3 is provided.

(2) The gain control section 6 includes a counter section 17 for counting the number of times the gain control has been instructed from the gain adjustment determination section 11 of the arithmetic processing section 4, and a gain adjustment determination section 11.
A gain value is calculated in accordance with the gain control instruction from the fingerprint image input unit 3 and the image capture determination unit 10 of the arithmetic processing unit 4
And a gain value calculating unit 19 that stops the gain control when the counter unit 17 reaches a preset count value and returns the content of the gain control to the initial state. Have.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an embodiment of the present invention. Reference numeral 1 denotes a light source composed of a light emitting diode, an incandescent lamp, etc. Reference numeral 4 denotes an arithmetic processing unit, 5 denotes a fingerprint processing main unit for performing fingerprint registration and fingerprint collation, and 6 denotes a gain control unit.

The fingerprint image input section 3 includes a camera 7 for picking up a fingerprint imprinted on the fingerprint impressing table 2 and an image capturing section 8. The arithmetic processing section 4 includes an A / D conversion section. 9 and
The configuration includes an image capture determination unit 10, a gain adjustment determination unit 11, and switching circuits (SW) 12, 13. The fingerprint processing main unit 5 includes an image memory 14, an image processing unit 15,
The configuration includes a registration / collation processing unit 16. The gain controller 6 includes a counter 17, a control signal transmitter 18,
The configuration includes a gain value calculator 19. The configuration and function of each unit described above can be realized by an arithmetic processing function of a computer, a memory, and the like.

A captured image signal obtained by capturing a fingerprint by the camera 7 is transferred from the image capturing unit 8 to the arithmetic processing unit 4, and the A / A
In the D converter 9, each pixel is converted into a digital image signal indicating a luminance value by a plurality of bits. The image capture determining unit 10 divides one screen of the captured fingerprint image into a plurality of blocks, and calculates an average value of luminance values of pixels in each block.

For example, as shown in FIG. 2A, when a finger 22 is impressed on the fingerprint imprinting table 21, one screen of the captured fingerprint image is divided into a plurality of blocks, and the luminance values of the pixels in each block are divided. When the average value is calculated, the result is indicated by 23 in (B). In this case, the block 24 corresponds to the background, and the average value of the luminance values of the pixels is the lowest value. The block 26 corresponds to the pad portion of the finger, and the average value of the luminance values of the pixels is the largest value, but is usually different from each other. The block 25 corresponds to the peripheral portion of the finger, and the average value of the luminance values of the pixels is an intermediate value, and the variation is large.

The image capture determining section 10 compares the average luminance value of each block with the first luminance reference value. A block less than the first luminance reference value is defined as a first defective block. For example, the block 24 corresponding to the background portion is a first missing block, and the block 26 corresponding to the peripheral portion of the finger includes a block serving as the first missing block. In addition, the block 25 corresponding to the abdomen of the finger hardly includes a missing block in the case of a normal captured fingerprint image. Therefore, the number of first defective blocks in one screen is counted, and the first number of defective blocks is compared with a first threshold.

If the first number of missing blocks is less than the first threshold value, it is determined that the captured fingerprint image has a desired luminance, and the switching circuit 13 is switched to the fingerprint processing main unit 5 to change the captured fingerprint image. To transfer. When the first number of missing blocks is equal to or greater than the first threshold value, the captured fingerprint image has brightness lower than desired brightness. Therefore, the second luminance smaller than the first luminance reference value
Is compared with the average luminance value of each block, and the blocks whose average luminance value is less than the second luminance reference value are compared to the second luminance reference value.
Of the missing block. The second number of missing blocks is compared with a second threshold. If the second number of missing blocks is less than the second threshold, the first missing block may be less than the first threshold by gain adjustment. If it is determined that the probability is high, and if the second number of missing blocks is equal to or greater than the second threshold, it is determined that fingerprint imaging needs to be performed again. Note that the second threshold can be set to a value equal to the first threshold, and the first and second thresholds are set to different values in consideration of the characteristics of the camera 7 and the characteristics of the optical system. can do.

When the second number of missing blocks is less than the second threshold, the gain adjustment judging section 11 instructs the gain control section 6 to perform gain control via the switching circuit 12. The gain control unit 6 uses the counter unit 17 to control the gain adjustment determination unit 1
The gain value calculation unit 19 counts the number of times of the gain control instruction from 1 and calculates the gain value corresponding to the difference between the average luminance value of the block and the second luminance reference value, or sets the gain value in advance. A gain value is calculated based on the gain increment, and a gain control signal is added from the control signal transmitting unit 18 to the fingerprint image input unit 3 or the arithmetic processing unit 4 via a path indicated by a dotted line.

The fingerprint image input unit 3 opens, for example, the aperture of the camera 7 according to the gain control signal, or the image capturing unit 8
Increase the gain of the amplifier. Thus, in the case of a captured fingerprint image having a low average luminance value, the fingerprint image captured next has a desired luminance. When the gain of the arithmetic processing unit 4 is controlled according to the gain control signal, for example, A / D
In the process of converting the digital signal into a digital signal in the conversion unit 9, a fingerprint image having a desired luminance is obtained by adding a value corresponding to the gain control signal.

Further, as described above, the image capture determining unit 10
The first average number of defective blocks is obtained by comparing the average luminance value of the block with the first luminance reference value. If the first number of defective blocks is less than the first threshold value, the determination and switching of capturing a fingerprint image are performed. By controlling the circuit 13, the fingerprint image is stored in the fingerprint processing main unit 5.
And if the first number of defective blocks is not less than the first threshold, the switching circuit 1
3 is a function of performing a process of transferring the average luminance value of the block to the gain adjustment determining unit 11 by controlling the block 3. Further, the gain adjustment determination unit 11 is connected to the image capture determination unit 1 via the switching circuit 13.
A second defective block is obtained by comparing the average luminance value of the block transferred from 0 with the second luminance reference value.
Is compared with the second threshold to determine whether gain control is possible. If the second number of blocks is equal to or greater than the second threshold, the fingerprint image input unit 3 is switched via the switching circuit 12. The second function is to send a gain control instruction to the gain control unit 6 via the switching circuit 12 when the second number of defective blocks is less than the second threshold value. it can.

Further, it is also possible to adopt a configuration in which the functions of the image capture determining section 10 and the gain adjustment determining section 11 are put together.
Further, the configuration may be such that the counter section 17 in the gain control section 6 is omitted. Further, as described above, the gain value calculating section 19 obtains an added value in the A / D conversion section 9 corresponding to the gain at the time of the gain control for the arithmetic processing section 4, and uses this as a gain control signal, The data can be transferred from the transmission unit 18 to the A / D conversion unit 9 along the dotted line path.

Alternatively, the gain control section 6 can transmit a gain control signal from the control signal transmitting section 18 as a control signal for the light source 1 and can control the luminance of the light source 1 to be increased. In this case, the light-emitting diodes constituting the light source 1 are arranged corresponding to blocks obtained by dividing one screen of the fingerprint image or to a plurality of blocks, and the gain value calculator 19 calculates the gain corresponding to the blocks of the fingerprint image, and It is also possible to adopt a configuration in which the luminance of the light emitting diode corresponding to a block or a plurality of blocks is controlled based on the same. Alternatively, it is also possible to control the luminance of the light emitting diode corresponding to a block or a plurality of blocks by identifying the distribution of the first and second defective blocks.

FIG. 3 is a flow chart of the embodiment of the present invention, in which a fingerprint image is captured by the camera 7 (A1).
The captured fingerprint image is divided into blocks (A2). That is, one screen of the captured fingerprint image converted into a digital signal by the A / D converter 9 of the arithmetic processing unit 3 is divided into a plurality of blocks.

Next, the average luminance value of the block is calculated (A
3). That is, in the image capture determination unit 10, for example, 5
One screen consisting of 12 × 512 pixels is divided into blocks of 16 × 16 pixels, and the luminance values of the pixels in each block are added and divided by 256 to obtain an average luminance value of the blocks. Since the luminance average value in this case does not need to be highly accurate, it can be calculated by processing such as truncation after the decimal point in accordance with the calculation accuracy.

The average luminance value is compared with the first luminance reference value, and a block having a value less than the first luminance reference value is determined as a first defective block, and the number of the first defective blocks is obtained (A
4). Next, it is determined whether the first number of missing blocks is less than a first threshold (A5). If less than the first threshold,
It is determined that the image is a captured fingerprint image having a desired luminance, and the image is captured (A
11). That is, the captured fingerprint image is transferred from the image capture determination unit 10 to the image memory 14 of the fingerprint processing main unit 5 via the switching circuit 13.

If the first number of defective blocks is not less than the first threshold value, the second luminance reference value smaller than the first luminance reference value is compared with the luminance average value of the block, and the second luminance reference value is compared with the second luminance reference value. A block less than the value is set as a second missing block, and the second missing block number is obtained (A6). Next, a second threshold having the same or different value as the first threshold is compared with the second number of defective blocks, and it is determined whether or not the second number of defective blocks is less than the second threshold (A7). If it is not less than the second luminance reference value, it means that a desired fingerprint image cannot be obtained even by the gain control, so that the process proceeds to step (A1) to perform the fingerprint imaging operation from the beginning. That is,
In the fingerprint image input unit 3, the fingerprint imaging process is performed again.

If the second number of missing blocks is less than the second threshold, the counter 17 increments the gain control instruction count by one (A8), and determines whether the instruction count has exceeded the count threshold (A8). A9) If exceeded, the gain is returned to the initial state (A12), and a step of capturing a fingerprint image (A1)
Move to If not, the brightness of the captured fingerprint image is increased by gain control (A10), and step (A3).
Move to

That is, the brightness of the captured fingerprint image for one screen input to the image capture determining unit 10 is increased in accordance with the gain control signal due to the gain of the camera 7 and the like, the gain of the A / D converter 9 and the like. From the determination (A5) based on the first number of missing blocks, it is determined whether or not the fingerprint image can be captured. If the fingerprint image cannot be captured, gain control is performed based on the determination (A6) based on the second number of missing blocks. By repeating this, a fingerprint image having a desired luminance can be obtained and captured.

In this case, steps (A8) and (A9) are omitted, and the process proceeds from step (A7) to step (A10) along a dotted line. In this step (A10), the average luminance value of the block is calculated. By calculating a gain value corresponding to the difference from the second luminance reference value, controlling the gain in the fingerprint image input unit 3 or the arithmetic processing unit 4, and increasing the average luminance value of each block, the first By reducing the number of missing blocks of the above and making the first number of missing blocks less than the first threshold value, a fingerprint image with a desired luminance can be obtained.

Also, as in steps (A8) and (A9),
When including a step of counting the number of times of gain control instruction and determining whether or not the number of times exceeds the number threshold, a step of increasing the gain by gain control is set in advance, and the gain is gradually increased. When the gain control instruction count exceeds the above, even if the gain is excessively increased and the average luminance value of the first defective block in the fingerprint image can be increased, the average luminance value of the normal block increases excessively, resulting in an unclear image. . Therefore, when the gain control instruction count exceeds the threshold count, the fingerprint imaging operation is performed from the beginning without performing any further gain control.

The present invention is not limited to the above-described embodiment. For example, an image memory for one screen is provided in the image capturing unit 8 of the fingerprint image input unit 3, and the gain control is performed by the arithmetic processing unit. 4, when the gain control does not result in a fingerprint image having a desired luminance, the captured image signal is read out from the image memory again, and the captured image signal is re-read in accordance with the control signal. The signal can be converted into a digital signal in the A / D converter 9 that has performed gain control.

[0030]

As described above, according to the present invention, the arithmetic processing unit 4 divides one screen of a captured fingerprint image into a plurality of blocks, and calculates the average luminance value of the blocks and the first luminance reference value. Are compared to obtain a first missing block, and it is determined whether or not this first missing block number is less than a first threshold value.
If it is less than the first threshold value, it is determined that the fingerprint image has the desired brightness and the image is captured. If it is not less than the first threshold value, the fingerprint image is lower than the desired brightness. A second missing block is obtained by comparing with a small second luminance reference value, the second number of missing blocks is compared with a second threshold, and the second number of missing blocks is less than the second threshold. In addition, the gain of the gain controller 6 controls the brightness of the captured fingerprint image to be increased, whereby a fingerprint image with a desired brightness can be obtained without repeating the fingerprint imaging operation. The fingerprint image of the person who has made it possible to take in the fingerprint image, and there is an advantage that the operation in fingerprint registration or fingerprint collation can be facilitated.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a captured fingerprint image according to the embodiment of the present invention.

FIG. 3 is a flowchart of the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional fingerprint image processing apparatus.

[Explanation of symbols]

 Reference Signs List 1 light source 2 fingerprint printing stand 3 fingerprint image input unit 4 arithmetic processing unit 5 fingerprint processing main unit 6 gain control unit 7 camera 8 image capture unit 9 A / D conversion unit 10 image capture determination unit 11 gain adjustment determination unit 17 counter Unit 18 control signal transmission unit 19 gain value calculation unit

Claims (2)

(57) [Claims] 1. A fingerprint image input unit comprising: a camera for illuminating a finger placed on an impressing table with a light source to capture an image; an image capturing unit for capturing an image signal from the camera; An arithmetic processing unit including an image capture determining unit and a gain adjustment determining unit for determining whether the captured fingerprint image from the image capturing unit of the input unit is normal, and the image capturing of the arithmetic processing unit When the determination unit determines that the fingerprint image is a normal captured fingerprint image, the fingerprint registration /
A fingerprint processing main unit that performs fingerprint collation, and a gain for the captured image signal from the fingerprint image input unit to an image capture determination unit of the arithmetic processing unit according to the determination result of the gain adjustment determination unit of the arithmetic processing unit. The image capture determination unit divides one screen into blocks of a plurality of pixels, calculates an average value of luminance values of pixels in the blocks for each block, and Comparing the average luminance value of each of the images with the first luminance reference value, and setting a block having a luminance average value less than the first luminance reference value as a first defective block;
The first number of missing blocks is compared with a first threshold value, and when the number of the first missing blocks is less than the first threshold value, the captured fingerprint image is captured. At the time of a threshold or more, the luminance average value is compared with a second luminance reference value smaller than the first luminance reference value, and a block having a luminance average value less than the second luminance reference value is defined as a second defective block. Comparing the second number of missing blocks with a second threshold,
When the second number of missing blocks is less than a second threshold, the gain adjustment determining unit instructs the gain control unit to perform gain control, and when the second number of missing blocks is equal to or greater than a second threshold, A fingerprint image processing apparatus having a function of instructing a fingerprint image by the fingerprint image input unit. 2. The gain control section calculates a gain value according to a gain control instruction from the gain adjustment determination section, the counter section counting the number of gain control instructions from a gain adjustment determination section of the arithmetic processing section. Controlling the gain of the captured image signal from the fingerprint image input unit to the image capture determining unit of the arithmetic processing unit, and stopping the gain control when the counter unit reaches a preset count value 2. The fingerprint image processing apparatus according to claim 1, further comprising a gain value calculating section for returning the content of the gain control to an initial state.