JPH0670834B2 - Number plate reader - Google Patents

Description

TECHNICAL FIELD The present invention relates to a license plate reader suitable for use in a toll collection system for toll roads or a toll collection system in toll parking lots.

[Prior Art] In recent years, as a toll collection system for toll roads, a system has been considered in which a license plate of a vehicle is read, a vehicle type is discriminated from the read information, and a toll is calculated based on the vehicle type information. Here, the reading of the license plate of the vehicle is performed as follows by utilizing the software processing by the computer. That is, the front shape of the vehicle is imaged by an image pickup means such as a television camera, the image information is A / D-converted, then taken into a frame memory, and image processing is performed in accordance with a predetermined program procedure to determine the size of the license plate or The plate number is encoded and used as vehicle type identification information.

[Problems to be Solved by the Invention] However, as described above, in the conventional license plate reading apparatus, image processing is performed on all the images in the frame memory in accordance with a program procedure built in the computer in advance. . Therefore, it takes a long time to complete the entire process. When applying this license plate reader to the entrance gate unmanned system as an example of a toll collection system for toll roads, the vehicle type is selected while the vehicle is traveling from the position of the license plate reader to the position of the automatic ticket issuing device. You have to determine. Therefore, it takes a long time to process the license plate reader, which has been a serious problem in unmanning the entrance gate. In addition, since the vehicle front image stored in the frame memory includes the headlight and other parts in addition to the license plate, the accuracy of the image processing of the license plate part is deteriorated. There was a risk of misdecoding.

The present invention has been made based on such circumstances,
It is an object of the invention to provide a license plate reading device capable of shortening the processing time and improving the reading accuracy.

[Means for Solving Problems] In order to solve the above problems and achieve the object, the present invention provides
The wheel distance and the passing position of the vehicle are measured by the output from the wheel distance measuring device that is sensitive to the wheel treading of the vehicle, and the vehicle's license plate mounting position is estimated based on these measured value information. Based on this, a part of the image information of the vehicle imaged by the imaging means is cut out, and the license plate information is read by performing a predetermined image processing on the cut out image.

[Operation] By taking such a means, since the license plate is mounted at the center position of the vehicle, the license plate mounting position on the vehicle can be promptly estimated,
According to this estimated position, only the license plate portion is extracted from the front image of the vehicle and image processing is performed, so that it is not necessary to perform image processing of a portion unnecessary for reading the license plate.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a state diagram showing an arrangement example when the license plate reading device of the embodiment is installed at a toll gate on a toll road. In the figure, a vehicle 1 having a license plate N attached at least on the front side travels along a toll gate entrance lane 2 in the direction of arrow F in the figure.
The vehicle separators 4 and 4 of the vehicle type identification device 3 and the shutter devices 5 and 5 are arranged so as to face each other, with the vehicle separator 4 in between. Further, the wheel distance measuring device 6 of the vehicle type discriminating device 3 is embedded in the lane 2. The vehicle separators 4 and 4 are composed of a plurality of phototube light-emitters and light-emitters to detect passage of each vehicle and output a vehicle detection signal. The wheel-distance measuring device 6 is sensitive to wheel treading of the vehicle. However, the wheel distance of the vehicle and the pedaling position of the wheel are measured. Further, the shutter devices 5 and 5 have the same structure and function as the vehicle separators 4 and 4, and the shutter of the TV camera 8 mounted on the roof 7 of the toll gate on the lane 2 has a vehicle detection signal. It becomes a timing signal for instructing on. The TV camera 8 is A in the figure.
It has a visual field range indicated by, and is set so that at least the license plate N of the vehicle 1 falls within the visual field range A. Further, the television camera 8 is provided with an infrared flash 9 which is filtered so as to emit long-wavelength light that cannot be visually recognized by humans, and the television camera 8 has an image sensor which is particularly sensitive in the infrared region. Are using. A license plate discriminating device 10 discriminates the license plate N mounted on the front surface of the passing vehicle 1 based on the output signals from the vehicle type discriminating device 3, the shutter device 5 and the television camera 8. .

Here, the positional relationship between the mounting position and the passing position of the license plate N of the vehicle 1 with respect to the present device is as shown in FIG. That is, the wheel distance of the vehicle 1 is W, and the distances from both ends of the wheel distance detector 6, that is, from the road shoulder to both side surfaces of the wheel are respectively.
l1 and l2, if the distance from the road shoulder to the end of the field of view A of the TV camera 8 is l3 and the distance from the end of the field of view of the TV camera 8 to the center of the vehicle 1 is Xn, then l3 + Xn = l1 + (W / 2) There is a relationship of (1). Therefore, assuming that the license plate N is attached to the central portion of the vehicle 1, when the one end P of the field of view A of the television camera 8 is used as a reference point, the position of the license plate N, that is, Xn, is Xn = (l1 + W / 2) -l3 is represented by (2).

The positional relationship of the license plate N with respect to the vehicle 1 is as shown in FIG. That is, if the vertical coordinate axis with respect to the vehicle body is Y, the horizontal coordinate axis is X, and the lane 2 at one end P of the visual field A of the television camera 8 in FIG. 2 is the reference point (0,0), the license plate N The position of is represented by (Xn, Yn).

Here, generally, the mounting position of the license plate N differs depending on the vehicle type as shown in FIG. That is, the license plate of a normal passenger vehicle is within the range α in FIG. 4, and the license plate of a large vehicle is within the range β in the figure. If these are expressed by the above-mentioned coordinate relationship, the license plate existence area of the ordinary passenger car is (X1, Y1) = (Xn1 ± x1, Yn1 ± y1) (3). In addition, the license plate existence area for large vehicles is (X2, Y2) = (Xn2 ± x2, Yn2 ± y2) (4).

On the other hand, the wheel distance measuring device 5 is composed of left and right contact bodies 50, 50 'as shown in FIG. 5, and each contact body 50, 50' is composed of two flat metal such as stainless steel. Top contact 51,5
1'and a plurality of metallic lower contacts 52, 52 'which are arranged immediately below these upper contacts 51, 51' at predetermined intervals.
And resistance elements 53, 53 'for electrically connecting adjacent contacts in each of the lower contacts 52, 52'.

Then, the left and right wheels T, T'of the vehicle 1 are connected to the contact bodies 50, 50 '.
If the resistance value between a and b and between a'and b'of the contact body 50, 50 'when not pressing is R, the wheels T, T'press the contact body 50, 50'. When the upper contacts 51, 51 'are deformed and short-circuited with the predetermined lower contacts 52, 52', the resistance values are represented by (R-r1) and (R-r2), respectively. However, r1 and r2 are the total values of the resistance elements 53 and 53 'in the portions where current cannot flow due to a short circuit. Therefore, the distances l1 and l2 from both side surfaces of the wheels T and T'to the road shoulder and the wheel distance W are expressed by the following equations (5) to (7).

l1 = G (R-r1) (5) l2 = G (R-r2) (6) W = G (r1 + r2) (7) (where G is a constant) FIG. It is a control block diagram of. In the figure, an A / D converter 61 converts an analog image signal from the television camera 8 into a digital image signal of, for example, 512 × 512 × 8 bit gradation, and the converted digital image signal is a distributor. It is distributed to the frame memory 63 and the differentiation circuit 64 by 62. The frame memory 63 stores the original image of 8-bit gradation. On the other hand, the differentiating circuit 64 takes the difference between the densities of pixels adjacent in the horizontal direction and outputs the absolute value, and this absolute value output is binarized by the binarizing circuit 65. That is,
The value of 8 bits per pixel is compared with a predetermined threshold value, and if the value is larger than the threshold value, it is set to "1", and if the value is smaller than the threshold value, it is set to "0". Compress to. The output of the binarization circuit 65 is distributed by the distributor 66 to the differential binary image memory 67 and the feature extraction circuit 68. Differentiation 2
The value image memory 67 stores the binarized differential binary image. On the other hand, the feature extraction circuit 68 extracts a portion of the differential binary image with many "1/0" changes, that is, a portion with many density changes of the original image. Specifically, the position information of the license plate is extracted. This extracted signal is stored in the feature memory 69. The frame memory 63, the differential binary image memory 67, and the feature memory 69 are composed of the same storage element.

In the figure, a CPU circuit 70 controls arithmetic processing necessary for discriminating license plates, and a bus line 71
Through the frame memory 63, the differential binary image memory 67,
A characteristic memory 69 is connected, and further a vertical histogram memory 72, a horizontal histogram memory 73, a license plate processing unit 74, a license plate position memory 75 and an input / output interface circuit 76 are connected. The vertical histogram memory 72 vertically scans the image stored in the feature memory 69 including the license plate cut out by the license plate position information stored in the license plate position memory 75 in the X and Y directions. This is a memory for counting and recording the frequency of the black level "1" in the direction. Similarly, the horizontal histogram memory 73 is a memory for scanning the image including the license plate in the feature memory 69 in the X and Y directions of coordinates and counting and recording the frequency of the black level "1" in the horizontal direction. Further, the license plate discrimination processing unit 74 has a storage area for storing the reference value of the license plate and the reference value of the encoded license plate number in advance, and a predetermined processing program under the control of the CPU circuit 70. According to the above reference values and memory 6
By comparing the stored contents of 3,67,69,72, and 73, the size of the license plate N of the passing vehicle 1 is discriminated and the plate number is encoded. The license plate position memory 75 receives and stores the license plate position information obtained based on the output signal from the vehicle type identification device 3 via the input / output interface circuit 76.
The input / output interface 76 exchanges signals between the CPU circuit 70 and the vehicle type discriminating device 3 and the shutter device 5, that is, from the vehicle type discriminating device 3, vehicle detection information, wheel distance and vehicle passing position information. Given, CPU
The circuit 70 provides license plate size information and plate number coding information.

Next, the operation of the license plate reader of this embodiment will be described with reference to the flow chart shown in FIG.
Now, when the passing vehicle 1 enters the toll gate and reaches the installation position of the vehicle separators 4, 4, a vehicle detection signal is sent from the vehicle separators 4, 4 to the input / output interface circuit 76 of the license plate discrimination device 10. Will be done (ST1). Then, in response to the vehicle detection signal, the wheel distance measuring device 6 is notified of the passage position of the vehicle and the start of measuring the wheel distance (ST2). Next, vehicle 1
The shutter device 5,5, the shutter device 5,5
A vehicle detection signal is sent from the input / output interface circuit 76 (ST3). Then, in response to this vehicle detection signal, the television camera 8 is notified of the start of the vehicle front surface photography. (ST4). Then, using the TV camera 8, the vehicle 1
The front image is captured and the captured image is taken into the license plate discriminating apparatus 10. (ST5). At this time, the infrared flash 9 illuminates the visual field A.

On the other hand, in response to the vehicle detection signal from the shutter devices 5, 5, the wheel distance measuring device 6 is notified of the termination of the measurement operation such as the wheel distance (ST6). Thereafter, the wheel distance measuring device 6 sends the wheel distance W of the vehicle 1 and the passing position information 1 to the input / output interface circuit 76 of the license plate discriminating device 10 (ST
7). As a result, in the license plate discrimination device 10, the position of the license plate N is calculated based on each measured value by the arithmetic processing of the CPU 70 according to a program predetermined in the license plate discrimination processing unit 74, and the calculated value and the wheel distance W The position of the license plate N of the vehicle 1 is estimated from the formula (3) (for a normal car) or the formula (4) (for a large car) and stored in the license plate position memory 75 (ST8). .

On the other hand, the analog video signal of the vehicle front portion including the license plate N captured and captured by the TV camera 8 is A
It is converted into a digital value by the / D converter 61 and distributed to the frame memory 63 and the differentiating circuit 64. Frame memory
In 63, for example, a digital image showing an area of the visual field A of 512 × 512 × 8 bits is stored in one screen. In addition,
This screen is not rewritten unless a new image is input. On the other hand, in the differentiating circuit 64, the difference between the densities of adjacent pixels in the horizontal direction of the digital image is calculated, and the absolute value is output to the binarizing circuit 65. This can be easily constructed by a known technique, and the output data is 512 × 512 × 8 bits.

In the binarization circuit 65, the value of 8 bits for one pixel is compared with a predetermined threshold value, and if the value is larger than the threshold value, it is "1", and if it is smaller than the threshold value, it is "0" and 1 After being compressed into binary image data of 1-bit pixel, it is distributed to the differential binary image memory 67 and the feature extraction circuit 68. Feature extraction circuit 68
In (1), a large change in “1/0” of the differential binary image, that is, a large change in density of the original image is extracted and stored in the feature memory 69.

Then, in the CPU 70, only the license plate portion is extracted from the differential binary image from the characteristic memory 69 based on the license plate position information stored in the license plate position memory 75 (ST9), and only this portion of the memory is extracted. A predetermined memory scan is performed on the contents (ST1
0). As a result, the histograms of the binary images of the vertical and horizontal directions of the coordinates are stored in the vertical histogram memory 72 and the horizontal histogram memory 73 (ST11), and the license plate discrimination processing unit 74 determines the stored contents of these memories. The size of the license plate N is discriminated and the plate number is encoded (ST12).

Thus, the license plate N is recognized and notified to the higher-level model such as the data processing device as the vehicle type identification information (ST
13).

According to the present embodiment having such a configuration, the license plate information is not read by performing image processing over the entire area of the visual field A of the television camera 8,
By measuring the wheel distance and the passing position of the passing vehicle 1 by the wheel distance measuring devices 6, 6, estimating the license plate position from these information, and processing only the limited image of the license plate portion, the license plate Since the information is read, image processing can be performed at high speed. Further, since noise parts such as headlights are cut off, highly accurate reading is possible. Therefore, by applying this embodiment to a toll road toll collection system,
Toll collection work can be speeded up and highly accurate, and unmanned toll gates can be realized.

The present invention is not limited to the above embodiment,
For example, it can be applied to a pay parking lot.

[Effect of the Invention] As described in detail above, according to the present invention, the license plate mounting position with respect to the vehicle is promptly estimated, and only the license plate portion is extracted from the vehicle front image according to the estimated position, Since image processing is performed,
It is possible to provide a license plate reader that can shorten the processing time and improve the reading accuracy.

[Brief description of drawings]

1 to 7 are views showing an embodiment of the present invention, in which FIG. 1 is a schematic view showing an installation situation of this device at a tollgate, and FIG. 2 is a passage position between a license plate and a vehicle. FIG. 3 is a diagram showing the relationship, FIG. 3 is a diagram showing the positional relationship between the vehicle and the license plate, FIG. 4 is a diagram showing the license plate mounting position by vehicle type, and FIG. 5 is a specific configuration of the wheel distance measuring device. FIG. 6 is a schematic block diagram of the license plate discriminating apparatus, and FIG. 7 is a flow chart for explaining the operation of the apparatus. 1 ... Vehicle, 3 ... Vehicle type identification device, 4 ... Vehicle separator,
5 ... Shutter device, 6 ... Wheel distance measuring device, 8 ... TV camera, 10 ... License plate discrimination device.

Claims (1)

[Claims] 1. An apparatus for reading license plate information by subjecting image information of a vehicle imaged by an image pickup means to predetermined image processing, and a wheel distance measuring apparatus which is sensitive to wheel tread pressure of the vehicle, and this wheel distance measuring apparatus. Based on the output from the measuring means for measuring the wheel distance and the passing position of the vehicle, and the number plate attachment of the vehicle based on the measurement value information by the measuring means and the preset license plate existence area information for each vehicle type. Position estimation means for estimating the position, image cutout means for cutting out a part corresponding to the license plate mounting position estimated by the position estimation means from the image information of the vehicle imaged by the image pickup means, and the cutout means Image processing means for reading license plate information by performing predetermined image processing only on the cut out image. License plate reader, characterized in that.