JPH05189598A - Number plate information reader - Google Patents

Abstract

PURPOSE:To surely read number plate information of a number plate attached to a vehicle. CONSTITUTION:This device is provided with a front plate image pickup part 10 which picks up the image of the number plate attached to the front part of the vehicle, a rear plate image pickup part 12 which picks up the image of the number plate attached to the rear part, a number plate information detecting part 14 and a number plate information recognizing part 16 which obtain number plate information from images obtained by the front plate image pickup part 10 and the rear plate image pickup part 12, and a number plate information comparing part 18 which compares number plate information obtained from the image picked up by the front plate image pickup part 10 and that obtained by the image picked up by the rear plate image pickup part 12 with each other to settle the final read result (number plate information)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention captures a scene image including a vehicle number plate from a television camera, detects a number plate area from the captured scene image, and detects the information written on the number plate. The present invention relates to a number plate information reading device for reading.

[0002]

2. Description of the Related Art Generally, number plate information recorded on a number plate attached to a vehicle such as an automobile is
In Japan, the format is as shown in FIG.
In other words, a serial vehicle number a represented by 4 or less digits of Arabic large numbers, a classification number b represented by 2 or less digits of Arabic small numbers, a kanji code c indicating the Land Transport Bureau, whether or not it is used for transportation business This is the kana / romaji code d.

For example, in a parking lot where automatic management is performed, the above-mentioned number plate information is read. In this case, the entrance time is calculated by comparing the number plate information read at the entrance and exit of the parking lot, and the parking fee is calculated by calculating the parking time from the entrance time and the exit time.

Such reading of the number plate information is generally performed on the front plate of the vehicle because the rear plate is easily soiled and the imaging timing is easy.

[0005]

Conventionally, in the automatic reading of the number plate information, there are always unreadable and erroneous readings. This is due to the limitation of the recognition technology, and the number plate failure, that is, the number plate's damage or stain is a major factor. Recently, there are cases where the number plate on the front of the vehicle is removed and the vehicle is brought into the vehicle. In some cases, such a defective plate cannot read the information even if it is visible to the naked eye. Moreover, the plate brought in the car,
I couldn't capture because of privacy issues.
It will be difficult to read them no matter how the recognition technology advances in the future.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a number plate information reading device capable of surely reading the number plate information of a number plate attached to a vehicle. To do.

[0007]

According to the present invention, first number plate information recorded on the number plate is obtained based on the image obtained by capturing an image including a number plate attached to the front part of a vehicle. A first reading means for recognizing
A second image capturing method, which captures an image including a number plate attached to a rear front portion of the vehicle and recognizes second number plate information recorded in the number plate based on the obtained image.
Reading means, the first numbering plate information obtained by the first reading means and the second numbering plate information obtained by the second reading means are compared, and based on a result of the comparison, And comparing means for determining number plate information for the vehicle, and outputting the number plate information decided by the comparing means.

[0008]

According to this structure, the recognition accuracy can be improved by comprehensively handling the reading result by the first reading means and the reading result by the second reading means, and either one of them can be improved. It is possible to obtain the number plate information even if the plate is defective and cannot be read.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the number plate information reading device according to the embodiment. As shown in FIG. 1, the number plate information reading device includes a front plate imaging unit 10, a back plate imaging unit 12, a number plate information detection unit 14, a number plate information recognition unit 16, a number plate information comparison unit 18, and a timer unit. 20, memory unit 22,
And a CPU 24 are provided, each of which is a general-purpose bus 2
Connected to 6. Further, the front plate imaging unit 10, the rear plate imaging unit 12, the number plate information detection unit 1
4 and the number plate information recognition unit 16 are connected to the image bus 2
8 is connected.

The front plate image pickup unit 10 and the rear plate image pickup unit 12 detect a running vehicle, irradiate a near-infrared flash, for example, and display a vehicle image including a number plate from the front direction and the rear direction of the vehicle, respectively. Image. The detailed configuration will be described later.

The number plate information detection unit 14 analyzes the images picked up by the front plate image pickup unit 10 and the rear plate image pickup unit 12, and an area for each number plate information described in the number plate, that is, a series vehicle number a,
The respective areas in which the classification number b, the kanji code c, and the kana / romaji code d are recorded are detected. The number plate information recognition unit 16 performs a recognition process on each of the areas corresponding to the detected number plate information, and reads characters.

The number plate information comparison unit 18 compares the read result of the image picked up by the front plate image pickup unit 10 with the read result of the image picked up by the rear plate image pickup unit 12 to determine the final read result. To do.

The timer section 20 has a clock function for obtaining time information. The memory unit 22 is a general-purpose storage unit used for processing. The CPU 24 mainly controls the entire processing. The general-purpose bus 26 is a data bus used for general-purpose data transfer, and the image bus 28 is a data bus used exclusively for image data transfer.

Next, the details of the front plate image pickup section 10 and the rear plate image pickup section 12 will be described. As shown in FIG. 2, the front plate imaging unit 10 includes the television camera 1
0a (hereinafter abbreviated as a TV camera), a flash device 10b, a detection sensor 10c, an A / D conversion unit 10d, and an image storage unit 10e. The rear plate image capturing unit 12 is similar to the front plate image capturing unit 10 in that the television camera 12a, the flash device 12b, and the detection sensor 12 are included.
c, the A / D conversion unit 12d, and the image storage unit 12e. The front plate imaging unit 10 and the rear plate imaging unit 12 are installed on an elevated structure as shown in FIG. 3, for example.

The detection sensors 10c and 12c detect that the running vehicle has reached a predetermined position by a light beam, an ultrasonic wave, a Doppler radar system, or the like, and output a vehicle detection signal indicating this to the CPU 24. .. CPU2
In accordance with the received vehicle detection signal, 4 causes the flash devices 10b and 12b to irradiate a near infrared flash, for example, and causes the television cameras 10a and 12a to capture a vehicle image including a number plate.

The front plate image pickup section 10 picks up a vehicle image including a plate (front plate) attached to the front portion of the vehicle as shown in FIG. A vehicle image including the same plate (rear plate) as the front plate attached to the rear portion of the vehicle is captured from the rear direction of the vehicle.

The flash devices 10b and 12b use, for example, a near infrared flash that is irradiated as a night light to stabilize the lighting conditions because the visible light flash hinders the operation. Of course, a permanent light such as a halogen lamp may be used instead of the near infrared flash.

The images captured by the television cameras 10a and 12a are processed by the A / D converters 10d and 12d.
For example, it is converted into an 8-bit digital signal and temporarily stored in the image storage units 10e and 12e. Needless to say, the quantization precision is not limited to 8 bits.

Next, details of the number plate information detecting section 14 will be described. Number plate information detection unit 14
5, the binarization processing unit 14a, the series vehicle number candidate detection unit 14b, the classification number detection unit 14c, the Kanji code detection unit 14d, and the Kana / Romaji code detection unit 14e.
Composed by.

The binarization processing section 14a includes image storage sections 10e of the front plate image pickup section 10 and the rear plate image pickup section 12,
The captured image accumulated in 12e is converted into, for example, a binary image in which the character portion is "1" and the background portion is "0".

When there is a contrast between characters (number plate information) and the background like a number plate image, binarization by contrast detection is effective. As a binarization method by such contrast detection, for example, the method previously filed by the applicant of the present application as Japanese Patent Application No. 63-300744 can be used.

According to such a binarization method, the contrast image is obtained as a binary image as shown in FIG. Of course,
Needless to say, the processing can be performed by a binarization method using normal threshold processing.

The series vehicle number candidate detection unit 14b detects the candidate area of the series vehicle number that is most easily found in the number plate information. In order to detect a candidate region of a series of vehicle numbers, for example, a labeling process is performed on a binary image, a connected region connected by “1” in the binary image is detected, and then the vertical / horizontal size of each detected connected region and each It is performed based on the analysis result such as how to arrange the connected regions.

In the labeling process, as shown in FIG. 7, each connected area is labeled, and the coordinate indicating the position of the circumscribing rectangle (two diagonal points) is obtained as the accompanying information for each connected area. As shown in FIG. 7, when there are four connected areas, xs1 to 4, ys corresponding to each connected area
The respective coordinates of 1 to 4, xe1 to 4, and ye1 to 4 are obtained.

Since the binary image is obtained by imaging the vehicle when the vehicle reaches a predetermined position by the detection sensors 10c and 12c, even if the vehicle is different, it is imaged at substantially the same point. The size of a series of vehicle numbers on the image is almost within a certain fluctuation range.

The arrangement is based on the format shown in FIG. 8. Therefore, by analyzing the individual size and area of the connected area and the arrangement of the connected areas, the image portion (series of vehicle number candidates) related to the series of vehicle numbers is analyzed. Area) can be detected. Of course, such a character string detecting means is not limited to the method of detecting the connected area using labeling, and may be projection information for the X and Y axes, which is a general character string detecting method. Note that FIG. 8A shows the style (size rule) of the middle plate of the number plate, and FIG.
Indicates the style (size rule) of the number plate. As shown in FIG. 8, the sizes of the middle plate and the large plate are different, but the styles are defined for each.

Other information such as the classification number can be easily detected from the relative positional relationship based on the format of FIG. The classification number detection unit 14c, the Kanji code detection unit 14d, and the Kana / Romaji code detection unit 14e are based on the relative positional relationship based on the coordinate information of the series vehicle number candidate area obtained by the series vehicle number candidate detection unit 14b. For example, the image portion (area) relating to each component is detected by using a means similar to the detection of the series vehicle number candidate.

The area detection of these constituent elements simultaneously serves as verification means for a series of vehicle number candidates. That is, when the areas of the series vehicle number, the classification number, the kanji code, and the kana / romaji code are obtained, each area is output as a true area corresponding to each component.

Next, the number plate information recognition section 16
For example, recognition processing is performed on the detected number plate information by a pattern matching method or a structure analysis method.
Such character recognition technology is described in "Image Processing Handbook".
It is described in P468-473. For example, according to the pattern matching method, a number / character pattern is cut out in accordance with the coordinate information obtained from the number plate information detection unit 14,
The similarity is obtained by comparing the cutout pattern and the reference pattern.

The degree of similarity is a numerical measure indicating how similar the input pattern and the reference pattern are to each other. Here, the degree of similarity equal to or higher than an empirically determined threshold is calculated up to the top n. It is output as a recognition result together with the corresponding character code.

Next, the operation of the embodiment will be described with reference to the drawings shown in FIGS. First, the front plate is processed according to the procedure of the flowchart shown in FIG.

When the traveling vehicle reaches the detection sensor 10c of the front plate image pickup section 10, the detection sensor 10c
The vehicle detection signal is output to the CPU 24 via the general-purpose bus 26 (step A1). The CPU 24 operates the flash device 10b and the television camera 10a to capture a front vehicle image with the front plate attached (step A2). At this time, the CPU 24 causes the timer unit 2 to
Time information is read from 0 (step A3).

The captured image is stored in the image storage section 10e via the A / D conversion section 10d. The binarization processing unit 14a of the number plate information detection unit 14 performs binarization processing on the image (multi-valued image) stored in the image storage unit 10e. The series vehicle number candidate detection unit 14b, the classification number detection unit 14c, the Kanji code detection unit 14d, and the Kana / Romaji code detection unit 14e each are number plate information, that is, a series vehicle number, from the binary image obtained by the binarization process. Areas of candidate a, classification number b, kanji code c, and kana / romaji code d are detected (step A
4).

The number plate information recognition unit 16 performs character recognition recognition for each character based on each area of the detected number plate information (step A5). The number plate information recognizing unit 16 then recognizes the recognition result having the highest degree of similarity for each character to the nth position, and the timer unit 20.
The time information thus obtained is sequentially stored in the memory unit 22 as a reading result as shown in FIG. 9 (step A).
6). Here, the read result (stored information i, i = 0 to n) stored in the memory unit 22 is referred to as a read result F for convenience.

Next, the rear plate is processed according to the procedure of the flowchart shown in FIG. The traveling vehicle is a detection sensor 12c of the rear plate imaging unit 12.
When reaching, the detection sensor 12c outputs a vehicle detection signal to the CPU 24 via the general-purpose bus 26 (step B1). The CPU 24 operates the flash device 12b and the television camera 12a to capture a vehicle image in the rear direction with the rear plate attached (step B2). At this time, the CPU 24 reads the time information from the timer unit 20 (step B3).

The captured image is the A / D conversion unit 12d.
Image storage unit 12e (not shown) via (not shown)
Memorized in. The binarization processing unit 14a of the number plate information detection unit 14 performs binarization processing on the image (multivalued image) stored in the image storage unit 12e.

The series vehicle number candidate detecting unit 14b, the classification number detecting unit 14c, the Kanji code detecting unit 14d, and the Kana / Romaji code detecting unit 14e are respectively number plate information, that is, number plate information, from the binary image obtained by the binarization process. A region of a series of vehicle number a candidates, classification number b, kanji code c, and kana / romaji code d is detected (step B
4).

The number plate information recognition section 16 performs character recognition recognition for each character based on each area of the detected number plate information (step B5). As a result, a reading result having the highest degree of similarity in each character of the number plate information can be obtained. Here, this read result is referred to as a read result B for convenience.

The number plate information comparison section 18 compares the read result B with the read result F stored in the memory section 22 in the number plate information recognition section 18.
First, the number plate information comparison unit 18 is stored in the memory unit 22.
The stored information 0 (reading result F) stored in the memory is read (steps B6 and B7), and it is determined whether the reading result F and the reading result B match based on the following evaluation formula (step B8). ).

N1 / na> t1 (1) n2 / na> t2 (2) n1 ... The number of characters in which the recognition results of the first places match each other. Except for n2 ... n1, the number of characters for which there is a match with the recognition result of the 1st to nth positions of each other. na ... total number of characters. t1 ... predetermined threshold value t1 ... predetermined threshold value.

The number plate information comparing section 18 determines that the read result F and the read result B match when the above expressions (1) and (2) are both satisfied. If it is determined that they do not match, the number plate information comparison unit 18 sequentially reads the stored information i (read result F) from the memory unit 22 (steps B9 and B10) and compares the read result F with the read result B. (Step B7,
B8).

As a result, when the read result B does not match any of the read results F stored in the memory unit 22, the read result B is taken as the final read result together with accompanying information such as imaging time information. Output (Step B
11).

On the other hand, when the result of the comparison shows that a matching read result F (stored information i) is present, the read result F is output as a final read result together with accompanying information such as imaging time information (step B12), the memory unit 22
Is deleted from (step B13).

The stored information i stored in the memory unit 22 is processed according to the procedure shown in the flowchart of FIG. That is, if the read result B and the read result F do not match as a result of the comparison in step B8, the read result B is output as the final read result in step B11. Therefore, the original read result F corresponding to the read result B output here remains in the memory unit 22. Further, the read result F remains in the memory unit 22 even when the front plate image pickup unit 10 picks up the image and the rear plate image pickup unit 12 does not pick up the image. This processing is for coping with these cases.

First, the CPU 24 sequentially reads out the time information from the timer unit 20 (step C1), and when it is determined that a predetermined time has elapsed (step C2), the memory unit 2
The read result F (stored information i) stored in 2 is read out, and the imaging time information is checked (step C3).

If a certain time has not passed since the image was picked up (step C4), it is left in the memory section 22 as it is, and the image pickup time information is similarly checked for other accumulated information i (steps C5 and C3).

If it is determined in step C4 that the predetermined time or more has elapsed, this accumulated information (read result F) is output together with accompanying information such as imaging time information and deleted from the memory section 22 (step C7). ).

In this manner, the number plate information of the front plate attached to the front part of the vehicle and the rear plate attached to the rear part of the vehicle is imaged by the front plate imaging part 10 and the rear plate imaging part 12, respectively. Then, the final read result is output by comparing the two. Therefore, the number plate information can be reliably obtained even if the number plate is severely damaged or soiled, or even if the front plate is brought into the vehicle and the image cannot be picked up.

The evaluation formula used for the comparison in step B8 treats each element of the series vehicle number a, the classification number b, the kanji code c, and the kana / romaji code d in a limited manner according to the application field. It is also possible to enhance the effect by weighting each element.

[0050]

As described above, according to the present invention, the first reading means for reading the number plate information of the number plate mounted on the front side of the vehicle from the front direction, and the first reading means mounted on the rear side of the vehicle from the rear direction. A second reading means for reading the number plate information of the number plate, and comparing the reading result by the first reading means and the reading result by the second reading means to determine the number plate information, The recognition accuracy can be improved, and the number plate information will be correct even if one of the plates is a marked defective plate due to dirt or damage, or if the front plate is removed and brought into the vehicle. It is readable.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a number plate information reading device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an imaging unit.

FIG. 3 is a diagram illustrating an installation state of an imaging unit.

FIG. 4 is a diagram for explaining the format of a number plate.

FIG. 5 is a block diagram showing a configuration of a number plate information detection unit.

FIG. 6 is a diagram showing an example of a contrast image.

FIG. 7 is a diagram for explaining labeling processing.

FIG. 8 is a diagram for explaining the size rule of the number plate.

FIG. 9 is a flowchart for explaining an operation of a front plate reading process.

FIG. 10 is a memory map diagram showing accumulation of read information.

FIG. 11 is a flowchart for explaining the operations of the rear plate reading and comparison processing.

FIG. 12 is a flowchart for explaining an operation of accumulated information processing.

[Explanation of symbols]

10 ... Front plate imaging unit, 10a ... TV camera, 10
b ... Flash device, 10c ... Detection sensor, 10d ... A
/ D conversion unit, 10e ... Image storage unit, 12 ... Rear plate imaging unit, 14 ... Number plate information detection unit, 14a ... 2
Quantization processing unit, 14b ... Serial vehicle number candidate detection unit, 14c
... Classification number detection unit, 14d ... Kanji code detection unit, 14e
... Kana / Romaji code detection unit, 16 ... Number plate information recognition unit, 18 ... Number plate information comparison unit, 20 ...
Timer section, 22 ... Memory section, 24 ... CPU, 26 ... General-purpose bus, 28 ... Image bus.

Claims (3)

[Claims] 1. A first reading means for capturing an image including a number plate attached to a front portion of a vehicle and recognizing first number plate information recorded on the number plate based on the obtained image. And an image including a number plate attached to the rear front part of the vehicle, and recognizing the second number plate information recorded in the number plate based on the obtained image.
Reading means, the first numbering plate information obtained by the first reading means and the second numbering plate information obtained by the second reading means are compared, and based on a result of the comparison, A number plate information reading device comprising: a comparison unit that determines number plate information for a vehicle; and outputs the number plate information determined by the comparison unit. 2. When the result of the comparison by the comparison means determines that the first number plate information and the second number plate information match, the first number plate information is output, The number plate information according to claim 1, wherein when it is determined that the first number plate information and the second number plate information do not match, the second number plate information is output. Reader. 3. The first number plate information obtained by the first reading means is sequentially stored for each vehicle, and when there is the first number plate information which has been stored for a certain time or more, The number plate information reading device according to claim 1, wherein the corresponding number plate information is output.