JP2998166B2 - Automatic car number reading device with speed measurement function - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle number automatic reading device with a speed measurement function, which automatically identifies a plate number of a running vehicle.

BACKGROUND ART The importance of identifying vehicles traveling on a road has become increasingly important recently.

Therefore, an automatic vehicle number reading device has been developed in which a television camera is installed on the road, the license plate of the vehicle is optically captured, and the number is identified by image processing.

For example, a position sensor that detects the presence of a vehicle is installed at a predetermined position on a road, and an illuminating device and a vehicle number automatic reading device are installed at a downstream position distant from the installation position, and the vehicle passes by the position sensor. A system has been proposed in which, when detected, the vehicle is illuminated by a lighting device and photographed by a camera provided with an automatic car number reading device. A plate portion is cut out from the photographed image by a plate cutout process, a character portion is cut out by a character cutout process, and a character recognition process is performed by a character recognition process.

However, the above method has a disadvantage that a position sensor must be provided separately from the automatic car number reading device.

Therefore, in order to omit the position sensor, a technique has been developed in which a camera is constantly photographed and a license plate is cut out from the video information regardless of the presence or absence of a vehicle.
However, for example, the number of screens capturing a vehicle traveling at 120 km / h is about 5.8 frames when the vertical field of view is 3.2 m and the number of screen scans is 60 frames / sec. You have to look at these 5 frames at high speed in 12 seconds. Therefore, it is necessary to cut out the license plate by very high-speed image processing. For this reason, the plate cutting process must be simplified.
That is, there is a problem that it is necessary to increase the speed until the accuracy of plate cutting is reduced.

Therefore, the applicant has not installed the position sensor, and
A patent application has been filed for a vehicle number automatic reading device capable of reading the vehicle number with sufficient accuracy without simplifying the plate cutting process (March 15, 1990, "Automatic Vehicle Number Reading Device").

The car number automatic reading device according to the present application has photographing means for photographing a road, and vehicle head detecting means for detecting a vehicle head by processing a photographed image, and performs plate cutting only when a vehicle head is detected. , And performs character extraction to recognize the extracted character.

<Problems to be Solved by the Invention> However, according to the above-described vehicle number automatic reading device, the approach of the vehicle can be detected without a position sensor by detecting the head of the vehicle by image processing. Can not detect the speed of Although the speed information of the vehicle is often required together with the information of the license plate, conventionally, it can only be measured by a separately provided speed measuring device.

Therefore, an object of the present invention is to provide a vehicle number automatic reading device with a speed measurement function capable of detecting the speed of the vehicle as well as detecting the entry of the vehicle.

<Means for Solving the Problems> To achieve the above object, a vehicle number automatic reading device with a speed measuring function according to the present invention comprises: a photographing means for photographing a road; A head detecting means for detecting the head of the vehicle a plurality of times, and a speed detecting means for obtaining the speed of the vehicle from the difference between the detected moving distance of the head and the detection time, the head detecting means based on a captured image, A pixel representing an edge having a high density change rate is extracted, the number of pixels is counted in the traveling direction of the vehicle, and the head count is detected by comparing the counted number of pixels with a predetermined threshold value. Yes, the speed detection means,
Using the head moving distance L on the screen, the head moving distance is expressed by the following formula: (H−ΔH) HL / [(H− (L + 1) cos θ) (H−1 cos θ) sin θ] (H: Height, ΔH: average head height, θ: dip,
1: difference on the screen between the approach position of the head of the vehicle and the position of the road surface corresponding to the dip angle θ).

<Operation> According to the vehicle number automatic reading device with the speed measurement function having the above configuration, the head distance is calculated by detecting the head multiple times by image processing, and based on the number of frames on the screen during that time. The speed of the vehicle can be calculated. Therefore, vehicle speed information can be provided in addition to vehicle number information.

<Example> Hereinafter, an example will be described in detail with reference to the accompanying drawings.

2A and 2B are a plan view and a front view showing an installation example of a vehicle number automatic reading device with a speed measurement function. The car number automatic reading device with the speed measurement function includes a car number automatic reading device main body 1, lighting devices 2a and 2b, a camera device 3, and the like. The camera device 3 is installed alongside the lighting devices 2a and 2b along the road. It is attached to the upper part of the arm of the pole 4. The car number automatic reading device main body 1 is attached to the side of the installation pole 4. In addition, a traffic light, a pedestrian bridge, or the like may be used instead of the installation pole.

The camera device 3 is attached with a predetermined inclination so that the field of view of the camera device 3 is set in a predetermined region R on the road.

FIG. 3 is a block diagram showing an internal circuit configuration of the vehicle number automatic reading device main body 1. As shown in FIG. The car number automatic reading device main body 1
It comprises an A / D conversion circuit 11, an edge detection circuit 12, a binarization circuit 13, a first memory 14, an image processor 15, a second memory 16, and a general-purpose processor 17.

The image signal captured by the camera is sent to the A / D conversion circuit 1
A / D conversion is performed by 1. The converted digital data is supplied to the edge detection circuit 12. The edge detection circuit 12
A portion (edge) of the image having a change in density is detected. The output signal of the edge detection circuit 12 enters the binarization circuit 13 and is binarized based on a predetermined threshold. The binarized signal is stored in the first memory 14 as a preprocessed image. First
The data stored in the memory 14 is transferred to the image processor 15
Where a profile (vertical projection) is created. This profile is stored in the second memory 16
Is stored in The data stored in the second memory 16 is input to a general-purpose processor 17 where a vehicle head detection process, a plate cutout process, a character cutout process, and a character recognition process are performed.

More specifically, the edge detection circuit 12 extracts only the outline of the vehicle by performing two-dimensional differentiation on an image showing the vehicle and the like. The binarization circuit 13 further clarifies the outline of the vehicle by binarization. The binarized image is shown in FIG. 4A. The profile of the binarized image is created by the image processor 15.
This profile is shown in FIG. 4B. The vertical axis y in FIG. 4B is in the vehicle traveling direction.

The flowchart of the processing performed by the general-purpose processor 17 (first
This will be described with reference to FIG. First, an original picture is fetched (step (1)), and a vehicle head is detected based on the profile of FIG. 4B (step (2)). This head-of-head detection process is a process of determining the position y1 at which the number of pixels obtained by scanning and adding the above profile from below the threshold value A exceeds the threshold value A as the head of the vehicle. When the head of the vehicle is detected (step (3)), the original image is captured again (step (4)). This step (4)
The difference between the time at which the original image is captured and the time at which the original image is captured in step (1) corresponds to the scanning time for one frame of the image. This is because, in this embodiment, the vehicle head detection processing is completed within one frame of scanning time, but if the vehicle head detection processing is performed within n (n ≧ 2) frames of scanning time. If completed, the difference between the time at which the original picture is taken in step (4) and the time at which the original picture is taken in step (1) corresponds to the scanning time for n frames of the image.

After taking in the original image of step (4), the vehicle head detecting process is performed again (step (5)), and the vehicle head y2 is detected. If the vehicle head cannot be detected (step 6), the process returns to the beginning. If the vehicle head can be detected, the moving distance on the screen is calculated (step (7)).

That is, the moving distance on the screen is calculated from the heads y1 and y2 already obtained. This moving distance L is obtained by L = y2-y1. If L <0, since the vehicle is traveling in the reverse direction, the calculation is terminated.

If L ≧ 0, L is compared with a threshold Lo (step (8)). If L <Lo, the travel distance is too small, and the influence of the head-of-vehicle detection error greatly appears in the speed calculation. Therefore, the flow returns to step (4) without calculating the speed, and the next original image is fetched.

If L ≧ Lo, it is determined that the moving distance is sufficiently large, and the speed calculation is performed (step (9)). In addition, a vehicle number reading process is performed in parallel. In this car number reading process, the range within the front α and the rear β of the head y is limited to the play and cut-out range. Next, when the plate is cut out in this limited range, the characters are This is a process of extracting characters to be extracted and finally performing character recognition to identify numbers.

In step (9), the moving distance L on the screen is converted into the actual moving distance of the vehicle on the road. The conversion method will be described with reference to FIG. Assume that the height of the camera device 3 is H, the dip angle is θ, the road is CO, the average height of the vehicle head is ΔH, and the vertical field of view of the screen captured by the camera device 3 is Y.

The positions on the road surface corresponding to both ends B and A of the vertical field of view of the screen are C and A, respectively, and the approach positions of the head of the vehicle are E and D, respectively. The approach positions of the head when y = y1 are G and y = Let F be the approach position of the head at y2. Also, is y2 and A
Is the distance on the screen.

Holds.

Likewise Holds, and GF = DG−DF is obtained. The speed of the vehicle can be obtained by dividing GF by "the difference between the time at which the original picture is taken in step (4) and the time at which the original picture is taken in step (1)".

The obtained speed data is output to the outside of the automatic vehicle number reading device and used for determining the speed of the vehicle.

Although the present invention has been described based on the embodiment above, the present invention is not limited to the above embodiment, for example, as a vehicle head detection process, a portion having a brightness lower than the reference brightness of the road surface portion as a shadow of the vehicle. It may be detected and used for approaching the vehicle (see Japanese Patent Application Laid-Open No. 63-174199).
Various other design changes can be made without departing from the scope of the present invention.

<Effect of the Invention> As described above, according to the vehicle number automatic reading device with the speed measurement function of the present invention, the moving distance is calculated by detecting the head of the vehicle a plurality of times by the image processing, and the speed of the vehicle is calculated. Can be. Therefore, the speed information of the vehicle can be provided in addition to the vehicle number information without using a special device for detecting the speed.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a vehicle head detection process and a speed calculation process. FIG. 2A is a plan view showing an example of installation of a car number automatic reading device with a speed measurement function. FIG. 2B is a front view thereof. FIG. 4A is an image of a vehicle binarized by detecting an edge, FIG. 4B
The figure shows a profile obtained by adding the number of pixels in the vehicle traveling direction, and FIG. 5 is an explanatory diagram showing a speed calculation method. 1 ... Automatic car number reading device with speed measurement function 3 ... Camera device 15 ... Image processing processor 17 ... General purpose processor

Claims (1)

(57) [Claims] 1. A vehicle number automatic reading device for automatically identifying a plate number of a vehicle running on a road, a photographing means for photographing a road, and a vehicle head being detected a plurality of times by processing a series of photographed images. The vehicle head detecting means includes: a head detecting means; and a speed detecting means for obtaining a speed of the vehicle from a difference between the detected moving distance of the head and the detection time. The head detecting means includes an edge having a high density change rate based on a captured image. And detecting the head of the vehicle by counting the number of pixels in the traveling direction of the vehicle and comparing the counted number of pixels with a predetermined threshold value. Is calculated by using the head moving distance L on the screen, using the following formula: (H−ΔH) HL / [(H− (L + 1) cos θ) (H−1 cos θ) sin θ] (H: shooting Height of means, ΔH: average height of head, θ : Dip,
1: A vehicle number automatic reading device with a speed measurement function, which is obtained based on a difference between an approach position of a vehicle head and a position of a road surface corresponding to a dip angle θ on a screen).