JPH0670833B2 - 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,
An object of the invention is to provide a license plate reading device capable of shortening processing time and improving reading accuracy.

[Means for Solving Problems] In order to solve the above problems and achieve the object, the present invention provides
It is characterized by taking the following measures. That is, an ultrasonic transmitter / receiver that transmits ultrasonic waves and receives reflected waves from the car body is installed on both sides of the vehicle body of the vehicle, and the vehicle width of the vehicle is determined from the time difference data between the ultrasonic wave transmission time and the reception time by the transmitter / receiver. Value and the distance from the transceiver to the vehicle body are measured, the installation position of the license plate of the vehicle is estimated based on the measured value information, and the image information of the vehicle imaged by the imaging means based on the estimated position information It is characterized in that a license plate is read by cutting out a part of the image and performing predetermined image processing on the cut out image.

[Operation] By taking such a means, the license plate position in the vehicle is promptly estimated, only the license plate portion is extracted from the estimated position and the vehicle front image, and the image is extracted from the extracted portion. Since the processing is performed, 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.
A pair of vehicle type identification devices 3, 3 and a shutter device sandwiching the
4 and 4 are arranged facing each other. Vehicle type identification device
3 and 3 are vehicle separators 5 and 5 each of which is composed of a plurality of photo-emitters and receivers of photocells for detecting passage of a vehicle, and an ultrasonic sensor is provided to the vehicle detection signals of the vehicle separators 5 and 5. In response to this, ultrasonic waves are transmitted to both sides of the vehicle body of the passing vehicle, the reflected wave from the vehicle body is received, and the time difference t2-t1 between the reception time t2 and the transmission time t1 is measured by electrical means, and based on this time difference data. Ultrasonic type vehicle width measuring device 6,6 that measures the vehicle width of a passing vehicle
It has and. The shutter devices 4 and 4 have the same structure and function as the vehicle separators 5 and 5, 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 television camera 8 has a visual field range indicated by A in the figure, and is set so that at least the license plate N of the vehicle 1 is within the visual field range A. Further, the television camera 8 is equipped with an infrared flash 9 which is filtered so as to emit light of a long wavelength which cannot be visually recognized by humans. 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 4 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 facing distance of the devices 4, 5 and 6 installed opposite to each other on the lane 2 is L, the vehicle width of the vehicle 1 is W, the visual field width of the TV camera 8 is X, and the vehicle width measuring devices 6 and 6 are installed at positions. To the both sides of the vehicle body, l1 and l2, the distance from the shutter devices 4, 4 to the end of the field of view A of the TV camera 8 is l3, the distance from the end of the field of view of the TV camera 8 to the center of the vehicle 1. Xn
Then, there is a relation of l3 + Xn = 1l + (W / 2) ... (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 ... (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 a normal passenger car is (X1, Y1) = (Xn1 ± x1, Yn1 ± y1) (3). Also, the license plate existence area for large vehicles is (X2, Y2) = (Xn2 ± x2, Yn2 ± y2) (4).

FIG. 5 is a block structure diagram of the license plate reader of the present embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals. The vehicle type identification device 3 inputs the identification information from the license plate identification device 10 for the passing vehicle 1, the vehicle width information from the vehicle width measurement device 6, the vehicle passage detection information from the vehicle separator 5 and the shutter device 4, and these The vehicle type of the passing vehicle 1 is determined based on the information. The license plate discriminating apparatus 10 measures the position of the license plate of the passing vehicle 1, discriminates the size of the license plate N, and encodes the plate number. The vehicle width measuring device 6 transmits / receives ultrasonic waves to / from both side surfaces of the vehicle body of the passing vehicle by using the first and second ultrasonic sensors 6a and 6b, and the vehicle width W of the vehicle and the vehicle width concerned are determined from the time difference. It measures the distances l1 and l2 from the measuring device to the car body. The shutter device 4 sends a vehicle detection signal to the television camera 8 and the infrared flash 9 when the vehicle 1 reaches the mounting position.

FIG. 6 is a control block diagram of the vehicle type identification device 3.
The CPU circuit 31 connects each interface 3 through the bus line 32.
Vehicle detection information from the vehicle separator 5 and shutter device 4, vehicle width measurement information from the vehicle width measurement device 6, and shutter device, which are connected to 3, 34, 35 and are input via these interfaces 33, 34, 35 Based on the license plate discrimination information from the license plate discrimination device 10 that operates in response to the vehicle detection signal from the vehicle 4, the vehicle type discrimination processing of the passing vehicle 1 is controlled. Further, the vehicle type discrimination processing unit 36, the memory circuit 37, and the host model input / output interface 38 are connected to the CPU circuit 31 via the bus line 32. The vehicle type identification processing unit 36 determines the vehicle type of the passing vehicle 1 according to a predetermined vehicle type identification processing program by the arithmetic control of the CPU circuit 31, and the memory circuit 37 stores the vehicle type identification processing program and the like. Therefore, the vehicle type identification signal obtained by this device is sent to the upper model 39 such as the data processing device through the upper model input / output interface 38.

FIG. 7 is a block diagram of the ultrasonic type vehicle width measuring device 6. The CPU circuit 61 uses the bus line 62 to
Each ultrasonic sensor 6a, 6b measured by the second measuring unit 63, 64
The vehicle width calculation unit 65 controls the vehicle width calculation processing by inputting the distance information l1, l2 from the vehicle side surface to the vehicle body side surface. The vehicle width calculation unit 65 calculates the vehicle width value W of the passing vehicle from the relationship of W = L- (l1 + l2) (5). Therefore, the information on the vehicle width value W and the distances l1 and l2 calculated by this device is input to the vehicle width measuring device input / output interface 34 of the vehicle type identification device 3 via the input / output interface 66. There is.

FIG. 8 is a control block diagram of the license plate discriminating apparatus 10. In the figure, an A / D converter 101 converts an analog image signal from the television camera 8 into a digital image signal of, for example, 512 × 512 × 8 bit gradation,
The digital image signal converted here is distributed by the distributor 102 to the frame memory 103 and the differentiating circuit 104. The frame memory 103 stores an original image of 8-bit gradation. On the other hand, the differentiating circuit 104 takes the difference between the shades of pixels adjacent in the horizontal direction and outputs the absolute value thereof.
This absolute value output is binarized by the binarization circuit 105. The output of the binarization circuit 105 is distributed by the distributor 106 to the differential binary image memory 107 and the feature extraction circuit 108. The differential binary image memory 107 stores the binarized differential binary image. On the other hand, the feature extraction circuit 108 extracts the feature of the differential binary pixel, and the extracted signal is the feature memory 109.
Memorized in.

In the figure, a CPU circuit 110 controls arithmetic processing necessary for discriminating a license plate, and the bus line 11
1 through the frame memory 103, differential binary image memory 1
07, the characteristic memory 109 is connected, and further, the vertical histogram memory 112, the horizontal histogram memory 113, the license plate discrimination processing unit 114, and the license plate position memory 115 are connected. Vertical histogram memory 112
Is a memory that scans the coordinate of the differential binary image memory 107 in the X and Y directions and counts and records the frequency of the black level "1" in the vertical direction. Similarly, the horizontal histogram memory 113 is a memory for scanning the differential binary image memory 107 in the coordinates X and Y to count and record the frequency of the horizontal black level "1". Also, the license plate discrimination processing unit 114
Has a storage area for storing a reference value of a license plate and a reference value such as an encoded license plate number in advance, and the reference value and each memory according to a predetermined processing program under the control of the CPU circuit 110. 103,107,
By comparing the stored contents of 109, 112, and 113, the size of the license plate N of the traveling vehicle 1 is discriminated and the plate number is coded. The license plate position memory 115 is for taking in and storing the license plate position information obtained by the vehicle type identification device 3 via the input / output interface circuit 116. The input / output interface 116 exchanges signals between the CPU circuit 110 and the vehicle type discriminating apparatus 3, that is, license plate position information is given from the vehicle type discriminating apparatus 3, and the CPU circuit 110
From, a license plate size discriminating signal and a plate number coding signal are given.

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 5, 5, a vehicle detection signal is sent from the vehicle separators 5, 5 to the vehicle separator interface 33 of the vehicle type identification device 3. (ST1). Further, in response to the vehicle detection signal, the vehicle width measuring devices 6, 6 are notified of the start of vehicle width measurement (ST
2). Then, ultrasonic waves are emitted to both sides of the vehicle body of the vehicle 1 by the action of the ultrasonic sensors 6a and 6b, the first sensor 6a measures the distance l1 from the sensor 6a to the vehicle body 1, and the second sensor 6b measures the sensor. The distance l2 from 6b to the car body 1 is measured. The measurement is completed before the vehicle 1 reaches the installation position of the shutter devices 4, 4.

Next, when the vehicle 1 comes across the shutter devices 4, 4, a vehicle detection signal is sent from the shutter devices 4, 4 to the vehicle separator interface 33 (ST3). Further, in response to the vehicle detection signal, the license plate determination device 10 is notified of the start of vehicle front portion imaging (ST4). Then, the image capture signal is sent to the television camera 8 and the front image of the vehicle 1 is captured. 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 4,4, the vehicle width measuring device 6,6 is notified of the vehicle width measuring operation termination by the operation of the vehicle type identification device 3 (ST5). Next, the vehicle width measurement device 6,6 sends the vehicle width measurement value W of the vehicle 1 and the distance information l1, l2 to the vehicle type discrimination device 3,3 (ST6).
As a result, the vehicle type identification device 3 calculates the position of the license plate N based on each measured value, and the calculated value and the vehicle width measured value W are used for the expression (3) (for a normal vehicle) or the above (4). The position of the license plate N of the vehicle 1 is estimated from the formula (in the case of a large vehicle) (ST7). Then,
The license plate position information estimated by the vehicle type identification device 3 is transmitted to the license plate identification device 10 (ST
8).

Then, the license plate discriminating apparatus 10 discriminates the size of the license plate N or encodes the plate number (ST9). That is, in FIG. 8, the field of view A is illuminated by the infrared flash 9 when the passing vehicle 1 reaches the installation position of the shutter devices 4, 4, and the image at this time is captured by the television camera 8 and A / It is sent to the D converter 101. Then, the A / D converter 101 converts the analog video signal from the television camera 8 including the license plate N on the front surface of the vehicle into a digital value and distributes it to the frame memory 103 and the differentiating circuit 104.
In the frame memory 103, for example, a digital image showing an area of the visual field A of 512 × 512 × 8 bits is stored in one screen. It should be noted that this screen is not rewritten unless an image is newly input. On the other hand, the differentiation circuit
In 104, the difference between the densities of the pixels adjacent in the horizontal direction of the digital image is calculated, and the absolute value thereof is binarized.
Is output to. This can be easily constructed by a known technique, and the output data is 512 × 512 × 8 bits.

In the binarization circuit 105, 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". After being compressed into binary image data of 1-bit pixel, it is distributed to the differential binary image memory 107 and the feature extraction circuit 108. In the feature extraction circuit 108, the part of the differential binary image where the change is large is extracted and stored in the feature memory 109.

Then, in the CPU 110, based on the license plate position information from the vehicle type identification device 3, the frame memory 103
Original image and differential image memory from 107 and feature memory 1
Only the license plate portion is extracted from the differential binary image from 09, and predetermined arithmetic processing is performed on the memory contents of only this portion. 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 112 and the horizontal histogram memory 113, respectively, and the license plate discrimination processing unit 114 determines the license plate N according to the stored contents of these memories. Is discriminated and the plate number is encoded. The determination result is sent to the vehicle type determination device 3.

Then, the vehicle type is discriminated by the function of the CPU 31 of the vehicle type discriminating device 3 based on the result of discriminating the size of the license plate and the vehicle width value W of the vehicle 1 (ST10). Then, this vehicle type information is notified to the high-end model 39 such as the data processing device (ST
11).

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,
The position of the passing vehicle 1 is measured by the vehicle width measuring device 6,6,
The license plate position is estimated from this vehicle position information, and the license plate information is read by processing only the limited image of the license plate portion, so 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, the toll collection work can be speeded up and the accuracy can be improved, 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.

[Effects of the Invention] As described in detail above, the present invention provides an ultrasonic wave transmitter / receiver for transmitting ultrasonic waves and receiving reflected waves from the vehicle body on both side surfaces of a vehicle body, and the ultrasonic wave transmitter / receiver transmits ultrasonic waves. The vehicle width value of the vehicle and the distance from the transceiver to the vehicle body are measured from the time difference data between the time and the reception time, and the installation position of the license plate of the vehicle is estimated based on the measurement value information, and the estimated position The license plate is read by cutting out a part of the image information of the vehicle imaged by the imaging means based on the information and performing a predetermined image processing on the cut out image.

Therefore, according to the present invention, the license plate position in the vehicle is promptly estimated, only the license plate portion is extracted from the estimated position and the vehicle front image, and the image processing is performed on the extracted portion. ,
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 9 are views showing an embodiment of the present invention, in which FIG. 1 is a schematic view showing the 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 schematic block configuration diagram of the present device. FIG. 7 is a control block diagram of the vehicle type discriminating device, FIG. 7 is a control block diagram of the vehicle width measuring device, FIG. 8 is a control block diagram of the license plate discriminating device, and FIG. 9 is a flow chart for explaining the operation of the present device. . 1 ... Vehicle, 3 ... Vehicle type discriminating device, 4 ... Shutter device, 5 ... Vehicle separator, 6 ... Vehicle width measuring device, 8 ... TV camera, 10 ... License plate discriminating device.

Claims (1)

[Claims] 1. A device for reading license plate information by performing predetermined image processing on the image information of a vehicle imaged by an image pickup means, transmitting ultrasonic waves to both side surfaces of the vehicle body of the vehicle and receiving reflected waves from the vehicle body. And an ultrasonic transmitter / receiver, measuring means for measuring the vehicle width value of the vehicle and the distance from the transmitter / receiver to the vehicle body from the time difference data between the ultrasonic wave transmitting time and the receiving time by the transmitter / receiver, and the measuring means. Position estimation means for estimating the installation position of the license plate of the vehicle based on the value information and preset license plate existing area information for each vehicle type, and the position estimation from the image information of the vehicle imaged by the imaging means The image cutting-out means for cutting out a part corresponding to the license plate installation position estimated by the cutting-out means and the image cut-out by this cutting-out means Only the license plate reading apparatus characterized by comprising an image processing means for reading the number plate information by performing a predetermined image processing.