JP2007286890A - Fingerprint input device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent composition of an abnormal fingerprint image from slice images inputted by a sweep type fingerprint sensor. <P>SOLUTION: This fingerprint input device 100 having a sensor 101 sequentially reading a fingerprint from a moving finger is provided with a means 102A storing partial images of the fingerprint, which are read by the sensor in association with a reading sequence, in a storage device 104, a means 102B finding a mean value of differences between mutually corresponding pixels for each pair of partial images sequentially read, a means 102C determining propriety of moving speed of the finger based on a history of the found mean value, and a means 102D outputting the determination result to an output device 103. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for inputting a fingerprint image used for personal authentication, and more particularly to a technique for processing an image acquired by a sweep type fingerprint sensor.

  Conventionally, a sweep type sensor is known as a kind of sensor for reading a fingerprint. In general, a sweep type sensor has a rectangular sensor surface slightly wider than the width of a finger, and reads a fingerprint of a finger sliding on the sensor surface with a plurality of lines. A fingerprint to be read is input as a slice image at each reading timing, and a whole image of one fingerprint is formed by a combination of the plurality of slice images.

For example, there is a technique described in Patent Document 1 (described later) with respect to a process for constructing a fingerprint image input by the above sweep type sensor. Japanese Patent Application Laid-Open No. H10-228667 describes a technique of obtaining a sweep speed based on a fingerprint image in the context of reading and correcting distortion of an image portion having a speed fluctuation.
JP 2002-216116 A

  In the conventional technique described in Patent Document 1, fingerprint image configuration processing is performed on the premise that there is an overlapping portion between the current slice image and the immediately preceding slice image. However, this method has the following problems.

  Conventionally, when fingerprint slice images are sequentially input, as shown in FIG. 6, the error of pixel values between images in the context of input is calculated, and the position where the error is the smallest is the overlapping position of both images. It is determined.

  However, if the finger is swept faster than the reading period of the sensor, the reading process will not be in time, making it difficult to read the entire fingerprint. As a result, as shown in FIG. 7, an overlapping region is not obtained between slice images input continuously, and a fingerprint portion is lost on the image.

  Even in such a situation, the conventional technique forcibly superimposes and outputs the input fingerprint images, so that an abnormal fingerprint image as shown in FIG. 8 may be output. When personal authentication is performed using an abnormal fingerprint image, even if the subject is a valid subject, authentication may fail.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for preventing an abnormal fingerprint image from being configured from a slice image input by a sweep type fingerprint sensor.

  The fingerprint input device according to the present invention is a fingerprint input device including a sensor for sequentially reading fingerprints from a moving finger, and stores the partial images of the fingerprints read by the sensors in a storage device in association with the reading order. A means for obtaining an average value of differences between pixels corresponding to each other for each pair of partial images in which the reading order is continuous, a means for judging suitability of finger movement speed based on a history of the obtained average values, Means for outputting a result of the determination by an output device.

  According to the present invention, it can be immediately fed back to the subject that the moving speed of the finger with respect to the sensor is inappropriate. Further, since the validity of the input fingerprint can be verified prior to the fingerprint collation processing, useless processing of using an inappropriate slice image for collation can be prevented. Thereby, the processing of the apparatus is made efficient and it is possible to avoid waiting for the subject for a long time.

  FIG. 1 shows the configuration of an embodiment of the present invention. The fingerprint input device 100 of this embodiment includes a conventionally known sweep type line fingerprint sensor 101. The reading format of the line fingerprint sensor 101 may be any of an optical detection type, a capacitance type, and a pressure sensitive type. In order to input a fingerprint from the line fingerprint sensor 101, as shown in FIG. 2, a finger 202 in a state where the fingerprint 201 is in contact with the sensor surface (101) is moved in a direction orthogonal to the longitudinal direction of the sensor surface (101). That is, it is slid in the illustrated sweep direction 203.

  As shown in FIG. 1, the fingerprint input device 100 includes a CPU (Central Processing Unit) for processing a slice image of a fingerprint read by the line fingerprint sensor 101 and a computer 102 including a program, an LCD (Liquid Crystal Display) or A display device 103 such as a CRT (Cathode Ray Tube) and a storage device 104 including a RAM (Random Access Memory) and a ROM (Read Only Memory) are provided.

  A slice image storage area operation module 102A, a pixel difference average value calculation module 102B, a sweep speed determination module 102C, and a result display module 102D are installed in the computer 102 as programs executed by the CPU. The operation of these programs will be described later.

  The storage device 104 stores the current slice image storage area 104_1 for storing the latest input slice image, the immediately preceding slice image storage area 104_2 for storing the slice image input immediately before, and the latest and immediately preceding slices. A pixel difference average value storage area 104_3 for storing a pixel difference average value (to be described later) relating to the image is provided.

  The operation of the fingerprint input device 100 will be described with reference to the flowchart shown in FIG. When the finger is placed on the line fingerprint sensor 101 and the sweep is started, the slice image storage area operation module 102A of the computer 102 stores the data for one slice image acquired from the line fingerprint sensor 101 in the immediately preceding slice image storage area 104_2. (Step S1).

  Subsequently, when the slice image storage area operation module 102A acquires new slice image data from the line fingerprint sensor 101, the slice image storage area operation module 102A stores it in the current slice image storage area 104_1 (step S2). At this time, the first slice image and the next slice image after the start of input are stored.

  The pixel difference average value calculation module 102B recognizes an overlapping area U between the slice image in the immediately previous slice image storage area 104_2 and the slice image in the current slice image storage area 104_1. This overlapping region U is determined and recognized by a known method. Then, with respect to this overlapping region U, the combination of overlapping pixels is recognized, and the difference of the pixel value ν in each combination is calculated. Further, an average value A is obtained by averaging the calculated differences in the overlapping region U (step S3).

  The calculation of the average value A will be specifically described with reference to FIG. In the overlapping area U of the current slice image S (t) (S: slice image, t: time) and the previous slice image S (t-1), N (“1” to “N”) as shown in the figure. When there is a combination of pixels, the difference between the pixel values ν is calculated for each of “1” to “N”.

  For example, in the case of the pixel “1”, the pixel value ν (t) of “1” in the current slice image S (t) and the pixel value ν (“1” of the previous slice image S (t−1). Find the difference from t-1). After obtaining the differences for all of “1” to “N” in this manner, the average value A of the differences in the overlapping region U is calculated. Therefore, the average value A can be obtained by the following [Equation 1].

  The pixel difference average value calculation module 102B stores the obtained average value A in the pixel difference average value storage area 104_3 of the storage device 104 (step S4). Further, in preparation for processing of the subsequent slice image, the slice image currently in the slice image storage area 104_1 is moved to the immediately preceding slice image storage area 104_2 (step S5).

  The sweep speed determination module 102C determines the suitability of the finger sweep speed in the line fingerprint sensor 101 based on the history of the average value A stored in the pixel difference average value storage area 104_3. In the determination, first, a reference value ε set in advance for the determination of the sweep speed is compared with the above-described average value A (step S6). Then, it is determined whether or not the comparison result (A> ε) that the average value A exceeds the reference value ε is continuously output (step S7).

  The number of continuous times as the threshold value for the determination is set in advance according to the accuracy required for determination, such as 3 times or 5 times. Further, as the reference value ε to be compared with the average value A, for example, a value as shown in FIG. 5 can be applied. The illustrated graph represents the relationship between the presence or absence of the overlapping region U and the average value A by a frequency distribution. Using this graph, the average value corresponding to the intersection of the two frequency distributions regarding the overlapping region is adopted as the reference value ε.

  As a result of the above determination, if the average value A does not exceed the reference value ε or exceeds the reference value ε but is not continuous (step S7: No), it is determined that the sweep speed is appropriate (step S8). Here, it is the initial stage of input of the slice image, and the history number of the average value A is one. Therefore, it is determined that there is no problem in the sweep speed at this stage.

  Thereafter, each time a new slice image is input, it is stored in the current slice image storage area 104_1 (step S2), and the average value A is calculated according to the above procedure and compared with the reference value ε (steps S3 to S6). . In the process, when the input of the slice image is completed without the average value A continuously exceeding the reference value ε (step S9: Yes), the process is terminated assuming that the input of the fingerprint is normally performed all the time. The slice image input normally is used for the subsequent fingerprint collation process.

  On the other hand, when it is detected that the average value A continuously exceeds the reference value ε (step S7: Yes), the result display module 102D is activated and displays a warning screen indicating that the sweep speed is inappropriate, that is, too fast. The information is displayed on the device 103 (step S10). The warning content is a content that prompts the subject to input again while reducing the sweep speed. For example, “input error: finger moving too fast. Please input again slowly” is displayed. At that time, the fingerprint input process is interrupted, and the slice image input this time is invalidated.

  According to the embodiment described above, it is possible to immediately feed back to the subject that the sweep speed of the finger with respect to the line fingerprint sensor 101 is inappropriate and should be input again. Further, since the validity of the input fingerprint can be verified prior to the fingerprint collation processing, useless processing of using an inappropriate slice image for collation can be prevented. Thereby, the processing of the apparatus is made efficient and it is possible to avoid waiting for the subject for a long time.

  In the above-described embodiment, an arithmetic expression ([Equation 1]) that averages the absolute value of the difference between two pixel values has been presented for calculating the average value A. 2] may be used to average the square error values. Since the square error value does not become a negative value, the determination condition can be simplified.

  In the above embodiment, all the pixels in the overlapping area are used for calculating the average value A, but the averaging target may be a part of the pixels in the overlapping area. Thereby, calculation time can be shortened.

  Furthermore, in the above embodiment, a warning about the sweep speed is notified on the screen, but instead, for example, a warning may be given by voice guidance using a speaker, or a screen display and voice guidance may be used in combination.

It is a block diagram which shows the structure of the fingerprint input device of embodiment of this invention. It is explanatory drawing regarding the fingerprint input with respect to the line fingerprint sensor in embodiment. It is a flowchart which shows the operation | movement procedure of embodiment. It is explanatory drawing regarding calculation of the average value A in embodiment. It is explanatory drawing regarding the setting of the reference value (epsilon) in embodiment. It is explanatory drawing regarding the conventional fingerprint input method. It is explanatory drawing regarding the conventional fingerprint input method. It is explanatory drawing regarding the conventional fingerprint input method.

Explanation of symbols

100 fingerprint input device
101 line fingerprint sensor
102 computer
102A slice image storage area operation module
102B pixel difference average value calculation module
102C sweep speed judgment module
102D result display module
103 Display device
104 Storage device
104_1 Current slice image storage area
104_2 Previous slice image storage area
104_3 Pixel difference average value storage area

Claims (9)

A fingerprint input device including a sensor for sequentially reading fingerprints from a moving finger,
Means for storing a partial image of a fingerprint read by the sensor in a storage device in association with a reading order;
Means for obtaining an average value of differences between pixels corresponding to each other for each pair of partial images in which the reading order is continuous;
Means for determining the suitability of the moving speed of the finger based on the obtained average value history;
And a means for outputting the result of the determination by an output device.   2. The fingerprint input device according to claim 1, wherein, when obtaining the average value, a calculation is performed to average the absolute value of the difference between the pixels in regions corresponding to each other of the pair of partial images.   2. The fingerprint input device according to claim 1, wherein, when obtaining the average value, a calculation is performed to average a square value of a difference between pixels in regions corresponding to each other of the pair of partial images.   4. The fingerprint input device according to claim 1, wherein when the average value history indicates that the average value continuously exceeds a reference value, it is determined that the finger moving speed is inappropriate. 5.   A program for causing a computer to function as the fingerprint input device according to any one of claims 1 to 4. A fingerprint input device having a sensor for sequentially reading fingerprints from a moving finger,
Storing a partial image of a fingerprint read by the sensor in a storage device in association with a reading order;
Obtaining an average value of differences between pixels corresponding to each other for each pair of partial images in which the reading order is continuous;
Determining whether or not the finger moving speed is appropriate based on the obtained average value history;
And a step of outputting the result of the determination by an output device. In the step of obtaining the average value by the fingerprint input device,
The fingerprint input method according to claim 6, wherein an operation of averaging absolute values of differences between pixels in a region corresponding to the pair of partial images is performed. In the step of obtaining the average value by the fingerprint input device,
The fingerprint input method according to claim 6, wherein a calculation is performed to average a square value of a difference between pixels in regions corresponding to each other of the pair of partial images. In the step in which the fingerprint input device determines whether or not a finger moving speed is appropriate,
The fingerprint input method according to claim 6, wherein when the average value history indicates that the average value continuously exceeds the reference value, it is determined that the finger moving speed is inappropriate.

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