JP2010231536A - Method of detecting optimum position for imaging subject - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of determining whether a finger to be imaged is located at a position suitable for imaging only by use of captured image data without using a hardware component. <P>SOLUTION: The position detecting method includes steps of; detecting an area brighter than a specific brightness from a captured image; calculating the size and position of the detected area; and comparing the calculated area and position with a preset first threshold and second threshold, respectively, and determining, when there is an area whose brightness exceeds the first threshold and the area is located in a position within a range determined by the second threshold, that the object to be imaged is placed in a proper shooting position. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and apparatus for determining whether or not an object photographed by a camera is placed at an optimal position.

In recent years, personal authentication devices using finger veins, that is, the finger is irradiated with near infrared light (near infrared light), the transmitted light or reflected light is photographed, and the finger vein pattern is extracted from the image data. Devices for use in authentication are becoming widespread.
Conventionally, there is a personal authentication device disclosed in Patent Document 1 below.

JP2007-133623A

What is important in photographing the finger vein is that the distance between the device and the finger is always taken at the same interval. However, since it is practically extremely difficult to stop the finger at a fixed interval, it is often operated so that the finger is placed at a position where the finger is lightly touched.
As a method of determining whether or not a finger is touching the device, there is a method of mounting hardware parts such as a touch sensor, but there is a problem that the number of parts of the device increases, which is disadvantageous in terms of cost. There is.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method that can determine whether or not a finger to be imaged is in a position suitable for imaging based only on captured image data without using hardware components. There is.

In order to solve the above-described problem, an optimal shooting position detection method for a shooting target object according to the present invention is such that a shooting target object is placed at an appropriate position from an image shot by illuminating illumination light on a side surface of the shooting target object. An optimal shooting position detection method in a device for detecting whether or not
The device is
A step of detecting an area brighter than a specific brightness from the captured image; a step of calculating the size and position of the detected area; and a first threshold value for which the calculated area and position are preset; When there is an area whose brightness is larger than the first threshold and the area is in a position within a range defined by the second threshold, the object to be imaged is appropriately captured. It is characterized by comprising the step of determining that it is placed at a position.
Further, the illumination light is near infrared light.

The optimum shooting position detection measure for a shooting target object according to the present invention is an apparatus that detects whether a shooting target object is placed at an appropriate position from an image shot by irradiating the side surface of the shooting target object with near infrared rays. There,
Means for detecting an area brighter than a specific brightness from the photographed image; means for calculating the size and position of the detected area; and a first threshold value set in advance for each of the calculated areas and positions. When there is an area whose brightness is larger than the first threshold and the area is in a position within a range defined by the second threshold, the object to be imaged is appropriately captured. And a means for determining that it is placed at a position.
Further, the illumination light is near infrared light.

The present invention has the following effects.
(1) Since it can be determined whether or not the distance between the device and the finger is suitable for photographing only with the photographed image data, it is not necessary to install hardware such as a touch sensor.

It is a block block diagram which shows embodiment of the apparatus using the optimal imaging | photography position detection method of this invention. It is explanatory drawing which shows the example of the relationship between an illuminating device and a finger | toe when the finger | toe which is a imaging | photography subject is put in the optimal position, and a picked-up image. It is explanatory drawing which shows the example of the relationship between an illuminating device and a finger | toe in case the finger | toe which is a imaging | photography subject is put a little away from the optimal position, and a picked-up image. It is explanatory drawing which shows the example of the relationship between an illuminating device and a finger | toe when the finger | toe which is a imaging | photography subject is placed considerably away from the optimal position, and a picked-up image. It is a figure explaining the scanning method of an image. It is a figure explaining the counter provided in order to detect the optimal imaging position. It is a flowchart which shows the optimal imaging | photography position detection method of this invention. It is a flowchart which shows the continuation of FIG. It is a figure which shows the example of the image placed in the optimal imaging position, and the example of the image which is not placed.

Hereinafter, an embodiment of an optimum photographing position detection method to which the present invention is applied will be described.
FIG. 1 is a configuration diagram of a system that implements an optimal photographing position detection method according to the present invention, and an infrared illumination device 2 irradiates a finger to be photographed with near infrared rays with an output specified by a control unit 1. In this state, the camera 3 that has received an instruction from the control unit 1 captures a finger, outputs image data of the finger to the storage device 5, and further stores the optimum position determination device 4 that has received the instruction from the control unit 1. The image data of the finger stored in the device 5 is read out and image processing is performed to detect whether or not the finger position is at the optimum position.

FIG. 2A is a diagram showing the positional relationship between the infrared illuminating device 2 that implements the optimum photographing position detection method according to the present invention, the camera, and the finger, and is a top view of the finger 201 viewed from the top surface side (back side of the hand). It is.
As shown in the top view of FIG. 2, a plurality of near infrared light emitting diodes (LEDs) 202 having directivity are arranged on the left and right side surfaces of the finger 201 in the axial direction.
The cross-sectional view of FIG. 2B shows the positional relationship between the finger 201 and the near-infrared light emitting diode 202, and the near-infrared rays are emitted toward a position 204 (a portion indicated by a thick line) on the side of the finger 201 slightly downward. I try to irradiate.
The camera 3 captures the surface of the finger 201 irradiated by the near infrared light emitting diode 202 and outputs image data. The optimum position 203 indicates a position most suitable for the camera 3 to photograph the finger 201.
When the finger 201 is placed at the optimum position 203, the near-infrared diode 202 irradiates the portion at the position 204 (the portion indicated by a bold line) particularly strongly due to its directivity.
A captured image 210 in FIG. 2C is an example of an image captured in this state, and a region 211 corresponding to the position 204 is captured particularly brightly.

The cross-sectional view of FIG. 3A shows a state where the finger 201 is placed at a position slightly away from the optimum position 203, and the near-infrared diode 202 has a position 205 (part indicated by a bold line) due to its directivity. Irradiate the part of
A photographed image 310 in FIG. 3B is an example of an image photographed by the camera 3 in this state, and a portion of an area 311 corresponding to the position 205 is photographed particularly brightly. Compared with the image of FIG.2 (c), the area of a bright part increases.

4A shows a state where the finger 201 is placed at a position considerably away from the optimum position 203, and the near-infrared light emitting diode 202 cannot irradiate the finger 201. FIG.
A photographed image 410 in FIG. 4B is an example of an image photographed by the camera 3 in this state, and the area of a brightly photographed part is larger than the photographed image 210 in FIG. 2 and the photographed image 310 in FIG. And very little

As described above, in order to perform position detection according to the present invention using a photographed image, the photographed image is processed as follows to detect whether the finger 201 is placed at the optimum position.
An image 501 in FIG. 5 is an image in a state where the finger 201 is placed at the optimum position.
The center line 502 indicates the center of the shooting range in the y direction (the center line of the shooting range in the finger axis direction). The origin of the coordinates is the upper left of the image data, the right side is positive in the x direction, and the lower side is positive in the y direction.
In the present invention, as shown in FIG. 6, an upper y coordinate discovery counter 604, a lower y coordinate discovery counter 605, an upper y coordinate integration counter 606, a lower y coordinate integration counter 607, an upper pixel number integration counter 608, a lower side A pixel number integration counter 609 is provided. Then, the imaging range is scanned in the y direction from the position of H / 2 (H = size in the y direction of the image data), which is the center position in the y direction. When the scanning is completed, the x coordinate position is changed to x = x + 1. Then, the process of scanning in the y direction is repeated until x = W (W = the size of the imaging range in the x direction) is reached.

In the process of repeating this scanning, the upper y-coordinate discovery counter 604 and the lower y-coordinate discovery counter 605 count how many pixels exceeding a specific brightness Br exist in the y direction.
More specifically, the lower y coordinate discovery counter 605 counts the number of pixels exceeding a specific brightness Br when scanning downward from the center position in the y direction (position of H / 2). If a pixel exceeding the brightness Br is found, yc1 = yc1 + 1 is set, and the number of pixels exceeding the specified brightness Br when scanning upward from the H / 2 position is determined by the upper y-coordinate discovery counter 604. If a pixel exceeding a specific brightness Br is found, yc0 = yc0 + 1 is set.

If a pixel exceeding a specific brightness Br is found, the information on the y-coordinate position is accumulated by the lower y-coordinate integrating counter 607 and the upper y-coordinate integrating counter 606, and yg1 = yg1 + i and yg0 = yg0 + i, respectively. To do. Here, i is a y-coordinate value of a pixel exceeding a specific brightness Br. For example, when scanning in the downward direction and y = 100 and y = 101 and the specific brightness Br is exceeded, yg1 = 100 + 101 = 201.
Further, the lower pixel number integration counter 609 and the upper pixel number integration counter 608 integrate the continuous number of pixels exceeding a specific brightness Br. For example, assuming that the coordinates of the pixel 504 exceeding the specific brightness Br in FIG. 5 to the pixel 505 falling below Br are y0 and y1, respectively, ctr0 = ctr0 + 1 = y0−y1 is integrated in the upper pixel number integration counter 608.

  Similarly, if the coordinates of the pixel 506 exceeding the specific brightness Br in FIG. 5 to the pixel 507 lower than Br are y2 and y3, respectively, ctr1 = ctr1 + 1 = y3−y2 is integrated in the lower pixel number integration counter 609. .

  According to the count values ctr0 and ctr1 of the upper pixel number integration counter 608 and the lower pixel number integration counter 609, when the image is as shown in FIG. 9A, the specific brightness Br is continuously exceeded. Since the number of pixels is small, the count values ctr0 and ctr1 are lower than the threshold value Ba, so that it can be regarded as an inappropriate photographing position.

  Also, as shown in FIG. 9B, when the image has few portions exceeding the specific brightness Br, the count values yc0 and yc1 of the upper y-coordinate discovery counter 604 and the lower y-coordinate discovery counter 605 are the threshold values. It will be below Ya, and it can be considered that it is an inappropriate photographing position.

  Further, in the case of an image as shown in FIG. 9C, the difference “yg1 / yc1−yg0 / yc0” from the average value yg1 / yc1, yg0 / yc0 of the coordinate values of the pixels exceeding the specific brightness Br Is smaller than the threshold value Yw, and if it falls below this, it can be regarded as an inappropriate photographing position.

  Further, in the case of an image as shown in FIG. 9D, the count values yc0 and yc1 of the pixels in which the number of pixels continuously exceeding the specific brightness Br exceeds the threshold value Ba and exceeds the specific brightness Br. Since the difference between the average value yg1 / yc1 and yg0 / yc0 of the coordinate values of pixels in which the threshold value Ya exceeds the threshold value Ya and the specific brightness Br exceeds the threshold value Yw, the appropriate photographing position Can be seen.

7 and 8 are flowcharts for determining whether or not the position is optimum in the apparatus to which the optimum photographing position detection method according to the present invention is applied.
Step 701 captures an image of a finger. The width of the image obtained at this time is W, and the height is H.
Step 702 initializes a counter necessary for the determination process.
yg0 and yg1 are upper and lower y-coordinate integration counters, yc0 and yc1 are upper and lower y-coordinate discovery counters, and ctr0 and ctr1 are upper and lower pixel count integration counters, which are counted in step 702. Initialize to value = 0.

Step 703 is to initialize a counter value j for performing scanning in the x direction in the lower image scanning.
In step 704, it is determined whether or not scanning in the x direction has ended. If the value of j is smaller than the width W of the image, scanning in the x direction has not ended, and the process proceeds to step 705. .
In step 705, the counter value i for scanning in the y direction is initialized to a value that is ½ of the image height H.

In step 706, it is determined whether or not scanning in the y direction has been completed. The counter values i and H are compared. If i <H, the scanning in the y direction has not been completed. move on.
Step 707 determines whether or not the pixel of interest (x position = j, y position = i) exceeds a specific brightness Br.

  Step 708 carries out a process of counting the discovery of y coordinates exceeding a specific brightness Br and a process of integrating the found y coordinates.

Specifically, yc1 = yc1 + 1 and yg1 = yg1 + i (i = scanning coordinate position in the y direction). For example, when the first pixel exceeding a specific brightness Br is found at the scanning coordinate position y = 100, yc1 = 1 and yg1 = 100.
In step 709, it is determined whether or not scanning in the y direction has been completed. If i <H, scanning in the y direction has not been completed, and thus the process proceeds to step 710.

Step 710 determines whether or not the pixel of interest (x position = j, y position = I) is less than the specific brightness Br (is darker than the specific brightness), and is not darker than the specific brightness Then, go to Step 711. If it is darker than the specific brightness, the process proceeds to step 715.
Step 711 is a process of counting the number of pixels exceeding a specific brightness, and ctr1 = ctr1 + 1.

  Step 712 is a process of incrementing the counter value i for scanning in the y direction, i = i + 1. After incrementing, the process returns to step 709 to determine whether i <H. If i <H, the scanning in the y direction has not been completed. Therefore, the processing in steps 710 to 712 is repeated again, and the specific brightness Br is determined. Accumulate the number of consecutive bright pixels.

If i <H and the scanning in the y direction is completed, the process proceeds to step 714, where j = j + 1 and the scanning position in the x direction is incremented.
If a pixel darker than the specific brightness Br appears at the stage where the scanning in the y direction has not ended, the process proceeds from step 710 to step 714 to increment the counter value j for scanning in the x direction.
Step 713 is a process of incrementing the count value i for y-direction scanning to i + 1.
Step 714 is a process of incrementing the counter value j for scanning in the x direction.
This completes the scan in the lower side in the y direction.

In step 715, a counter value j for performing scanning in the x direction in the upper image scanning is initialized.
Step 716 determines whether or not the scanning in the x direction has been completed. If j <W, the scanning in the x direction in the upper image scanning has not been completed, and the process proceeds to step 717.
Step 717 initializes the initial position of the y-direction scan.
Step 718 determines whether or not scanning in the y direction in the upper image scanning has been completed. If i ≧ 0, scanning in the y direction in the upper image operation has not been completed, and the process proceeds to step 719.

Step 719 determines whether the pixel of interest (x position = j, y position = I) exceeds a specific brightness Br. If the target pixel exceeds a specific brightness Br, Step 720 is performed. Proceed to
Step 720 includes a process of updating the upper y-coordinate discovery counter yc0 that counts that the y-coordinate exceeding the specific brightness Br is found to yc0 = yc0 + 1, and a process of accumulating the found y-coordinates yg0 = yg0 + 1. Is what you do.
Step 721 determines whether or not the scanning in the y direction has been completed (whether i ≧ 0). If i ≧ 0 and the scanning in the y direction has not been completed, the process proceeds to step 722. .
Step 722 determines whether or not the pixel of interest (x position = j, y position = i) is below a specific brightness Br. If it is below the specific brightness Br, the process goes to Step 726. If YES, go to step 723.
Step 723 is a process of counting the number of pixels exceeding a specific brightness, and updates the upper pixel number integration counter ctr0 by +1.

Step 724 is a process of incrementing the counter value i for scanning in the y direction. After the update, the process returns to step 721 and repeats the process of counting the continuous number of pixels exceeding the specific brightness Br.
Step 725 is a process of incrementing the counter for scanning in the y direction.
Step 726 is a process for incrementing a counter for x-direction scanning, and is executed every time the y-direction scanning is completed. If j> W, the x-direction scanning is completed. Proceed to

Step 727 is a process for determining whether the count value yc0 or yc1 of the y-coordinate discovery counter is below the threshold value Ya for the upper scanning area and the lower scanning area. It is determined that the position is not optimal.
Step 728 determines whether or not the count value of the counter ctr0 or ctr1 that counts the number of consecutive pixels having a specific brightness Br exceeds the threshold value Ba for the upper scanning area and the lower scanning area. If it is lower than the process, it is determined that the position is not the optimum position.
Step 729 is to determine whether or not the difference between the average value yg0 / yc0 of the upper y-coordinate and the average value yg1 / yc0 of the lower y-coordinate of the pixel exceeding the specific brightness Br exceeds the threshold Yw. If it is below, it is determined that the position is not the optimum position.

In the present invention, the image is scanned in the lower direction and the upper direction around the center line in the y direction of the imaging range, and the number of pixels brighter than the specific brightness Br and the specific brightness Br appear. The number of pixels brighter than the average y-direction coordinate and the specific brightness Br is detected, and based on the detection result, it is determined whether the position of the finger to be photographed is at the optimum photographing position. Whether it is a finger or an adult's finger, it can be determined whether it is the optimum photographing position.
That is, the position where a pixel brighter than the specific brightness Br appears is a range that does not fall below the threshold value Yw on both the left and right sides of the center line in the axial direction of the finger, and the size (or area) of the bright region is the threshold value Ba. If it does not exceed the size determined by, it is determined that it is placed at the optimum position.
According to this, in the image of FIG. 3B, the size of the area brighter than the specific brightness Br is larger than the threshold value Ba, but the position where a pixel brighter than the specific brightness Br appears is lower than the threshold value Yw. Since it is a range position and the width of the band-like dark region is small, it can be determined that the band is placed at an inappropriate position away from the optimum photographing position.
In addition, as in the image of FIG. 2C, when a dark region having a predetermined width is sandwiched between both sides of the center in the axial direction of the finger, a region brighter than a specific brightness is present on both sides less than a predetermined size. Therefore, it can be determined that it is placed in the optimum position regardless of whether it is an adult or a child.
In the embodiment, image data obtained by photographing a finger is scanned in a direction orthogonal to the axial direction of the finger. However, the present invention is not limited to this, and is configured to scan in the axial direction. be able to.
In addition, the illumination light is near-infrared light for capturing a finger vein image. However, if the object to be imaged is another object, illumination light other than near-infrared light can be used.

DESCRIPTION OF SYMBOLS 1 Control part 2 Infrared illumination device 3 Camera 4 Optimal position determination apparatus 201 Finger of imaging | photography object 202 Near-infrared LED
203 Optimal position 210 Photographed image

Claims (4)

An optimal shooting position detection method in an apparatus for detecting whether a shooting target object is placed at an appropriate position from an image shot by irradiating illumination light on a side surface of the shooting target object,
The device is
A step of detecting an area brighter than a specific brightness from the captured image; a step of calculating the size and position of the detected area; and a first threshold value for which the calculated area and position are preset; When there is an area whose brightness is larger than the first threshold and the area is in a position within a range defined by the second threshold, the object to be imaged is appropriately captured. A method for detecting an optimum photographing position of a photographing object, comprising a step of determining that the object is placed at a position.   The method according to claim 1, wherein the illumination light is near infrared light. A device that detects whether a shooting target object is placed at an appropriate position from an image shot by irradiating the side surface of the shooting target object with near infrared rays,
Means for detecting an area brighter than a specific brightness from the photographed image; means for calculating the size and position of the detected area; and a first threshold value set in advance for each of the calculated areas and positions. When there is an area whose brightness is larger than the first threshold and the area is in a position within a range defined by the second threshold, the object to be imaged is appropriately captured. An apparatus for detecting the optimum photographing position of a photographing object, characterized by comprising means for determining that the object is placed at a position.   The apparatus according to claim 1, wherein the illumination light is near infrared light.

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