JPH03276069A - Automatic vehicle number reader with speed measuring function - Google Patents

Abstract

PURPOSE:To offer speed information on a vehicle by providing photographing means which photograph a road, vehicle head detecting means which detect the head of the vehicle plural times by image processing, and speed detecting means which find the vehicle speed from the movement distance of the vehicle head. CONSTITUTION:The reader consists of an automatic vehicle number reader main body 1, lighting devices 2a and 2b, a camera device 3, etc., and the automatic vehicle number reader main body 1 consists of an A/D converting circuit 11, an edge detecting circuit 12, a binary coding circuit 13, a 1st memory 14, an image processor 15, a 2nd memory 16, and a general processor 17. Namely, the reader is equipped with photographing means 2a, 2b, and 3 which photograph the road, vehicle head detecting means 11-15 which detect the head of the vehicle plural times by processing a series of photographed images, and the speed detecting means 16 and 17 which finds the speed of the vehicle from the movement distance of the detected vehicle head. Then the head of the vehicle is detected plural times by the image processing to calculate the movement distance of the vehicle head, thereby calculating the speed of the vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an automatic vehicle number reading device with a speed measurement function that automatically identifies the plate number of a running vehicle.

<Prior Art> The importance of identifying vehicles traveling on the road has recently become more and more important.

Therefore, automatic vehicle number reading devices have been developed that install television cameras on the road, optically capture vehicle license plates, and identify the number through image processing.

For example, a position sensor that detects the presence of a vehicle is installed at a predetermined position on the road, and a lighting device and automatic vehicle number reader are installed downstream from the installation location, and the position sensor detects the passing of the vehicle. A method has been proposed in which, when detected, the vehicle is illuminated with a lighting device and photographed with a camera equipped with an automatic vehicle number reader. A plate portion of the photographed image is cut out by plate cutting processing, a character portion therein is cut out by character cutting processing, and character recognition processing is performed by character recognition processing.

However, the above method has a drawback in that a position sensor must be installed separately from the automatic vehicle number reader.

Therefore, in order to omit the need for a position sensor, a method has been developed in which images are constantly taken with a camera and a license plate is extracted from the video information regardless of the presence or absence of a vehicle. However, for example, the number of frames capturing a vehicle traveling at 120 km/h is approximately 5.8 frames, assuming a vertical field of view of 3 and a 2 ms screen scanning rate of 60 frames/sec. These five frames of the screen must be examined at high speed within the time limit, ie, within 1/12 seconds. I wanted to,
This requires extremely high-speed image processing to cut out license plates. Therefore, it is necessary to simplify the plate cutting process. In other words, there is a problem in that it is necessary to increase the speed at the cost of reducing the accuracy of plate cutting.

Therefore, the applicant has filed a patent application for an automatic vehicle number reader that can read vehicle numbers with sufficient accuracy without installing a position sensor or simplifying the plate cutting process. March 15, 2015 “Automatic car number reading device”
).

The automatic vehicle number reading device according to this application has a photographing means for photographing the road and a vehicle head detecting means for detecting the head of the vehicle by processing the photographed image, and cuts out the plate only when the head of the vehicle is detected. , which performs character extraction and recognizes the extracted characters.

<Problems to be Solved by the Invention> However, according to the automatic vehicle number reading device described above, it is possible to detect the entrance of a vehicle without using a position sensor by detecting the head of the vehicle through image processing. It is not possible to detect the speed of

Although vehicle speed information is often required together with license plate information, conventionally it could only be measured using a separate speed measurement device.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an automatic vehicle number reading device with a speed measurement function that can detect not only the entry of a vehicle but also the speed of the vehicle.

<Means for Solving the Problems> To achieve the above object, the automatic vehicle number reading device with a speed measurement function of the present invention uses a photographing means for photographing a road and a series of photographed images. The vehicle head detection means includes a vehicle head detection means for detecting the vehicle head multiple times, and a speed detection means for determining the speed of the vehicle from the detected travel distance of the vehicle head.

<Operation> According to the automatic vehicle number reading device with speed measurement function configured as described above, by detecting the vehicle head multiple times through image processing,
It is possible to calculate the distance traveled by the head of the vehicle and calculate the speed of the vehicle based on the number of frames on the screen during that time. I wanted to,
In addition to vehicle number information, vehicle speed information can also be provided.

<Example> Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments.

FIG. 2A and FIG. 2B are a plan view and a front view showing an installation example of an automatic vehicle number reading device with a speed measurement function. The automatic vehicle number reading device with a speed measurement function consists of an automatic vehicle number reading device body 1, lighting devices 2a and 2b, a camera device 3, etc. The camera device 3 is installed on the side of the road together with the lighting devices 2a and 2b. It is attached to the upper part of the arm of Pole 4. The automatic vehicle number reading device main body 1 is attached to the side of the installation pole 4. In addition, traffic lights, pedestrian bridges, etc. may be used instead of installed poles.

The camera device 3 is mounted at a predetermined angle of inclination so that the field of view of the camera device 3 is set in a predetermined area R on the road.

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

An image signal captured by the camera is A/D converted by an A/D conversion circuit 11. The converted digital data is supplied to edge detection circuit 12. The edge detection circuit 12 detects portions (edges) where the density of the image changes. The output signal of the edge detection circuit 12 is
3, and is binarized using a predetermined threshold value as a reference.

The binarized signal is stored in the first memory 14 as a preprocessed image. The data stored in the first memory 14 is supplied to an image processor 15, where a profile (vertical projection) is created. This profile is stored in the second memory 16. The data stored in the second memory 16 is input to the general-purpose processor 17,
Here, vehicle head detection processing, plate cutting out processing, character cutting out processing, and character recognition processing are performed.

More specifically, the edge detection circuit 12 extracts only the outline of the vehicle by performing two-dimensional differentiation on an image in which the vehicle or the like is shown. The binarization circuit 13 makes the outline of the vehicle even clearer by binarizing it. The binarized image is shown in FIG. 4A. A profile of the binarized image is created by the image processing processor 15.

This profile is shown in Figure 4B. Vertical axis y in Figure 4B
is in the direction of vehicle travel.

A flowchart (first
(see figure). First, the original image is captured (step (1)), and the head of the vehicle is detected based on the profile shown in FIG. 4B (step (2)). This vehicle head detection process is
This is a process in which the profile is scanned from below and the position y1 where the added number of pixels exceeds the threshold value A is determined to be the head of the vehicle. When the head of the vehicle is detected (step (3)), it is already -
The original image is imported (step (4)). This step (4
) and the time at which the original image is captured in step (1) above corresponds to the scanning time for one frame of the image.

This is because, in this embodiment, the vehicle head detection process is completed within the scanning time of one frame, but if the vehicle head detection process is completed within the scanning time of n (n≧2) frames. If completed, the difference between the time to capture the original image in step (4) and the time to capture the original image in step (1) above will correspond to the scanning time for n frames of the image.

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

That is, the moving distance on the screen is calculated from the vehicle head yt and y2 that have already been determined. This moving distance is calculated as L-y2-yl. If L<0, the vehicle is traveling in the opposite direction, so the calculation is terminated.

If L≧0, L is compared with a threshold value Lo (step (8)). If L<LO, the moving distance is too small and the influence of the vehicle head detection error will be greatly affected by the speed calculation, so the process returns to step (4) without performing the speed calculation and captures the next original image.

If L≧Lo, the moving distance is assumed to be sufficiently large and the speed is calculated (step (9)). Also, in parallel with this, a car number reading process is performed. This vehicle number reading process limits the range in the front α and rear β of the vehicle head y to the plate cutting range. Next, when the plate is cut out in this limited range, the characters are extracted. In this process, characters are extracted, and finally character recognition is performed to identify the number.

In step (9), the moving distance on the screen is converted into the actual moving distance of the vehicle on the road. Conversion method 5th
The explanation will be based on the diagram. The height of the camera device 3 is H1, the angle of inclination is θ, the road surface is CO1, the average height of the vehicle head is ΔH, and the vertical field of view of the screen photographed 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 position of the vehicle head is ED, respectively.
Let G be the approach position of the vehicle head when -yi, and F be the approach position of the vehicle head when Y=Y2. Further, J is the distance between y2 and A on the screen.

Ac-HY (kl -Y cos θ) sin θ DE-(H-ΔH) Y (HY cos θ) sin θ holds true.

Similarly, DF-(H-ΔH)J (H-J cos θ) sin θDG-(H-Δ
H) (L-+l) (H(L+ j ) eos θ) sin θ holds, and GF-DE-DF is found. The speed of the vehicle can be determined by dividing GF by "the difference between the time at which the original image is captured in step (4) and the time at which the original image is captured in step (1)."

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

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. For example, in a vehicle head detection process, a portion of the road surface whose brightness is lower than the standard brightness is recognized as a shadow of the vehicle. It may be detected and used for vehicle entry (see Japanese Patent Laid-Open No. 174199/1983). Various other design changes can be made without changing the gist of the present invention.

<Effects of the Invention> As described above, according to the automatic vehicle number reading device with speed measurement function of the present invention, by detecting the head of the vehicle multiple times through image processing, the distance traveled can be calculated, and the speed of the vehicle can be calculated. I can do it. Therefore, it is possible to provide vehicle speed information in addition to vehicle number information without using a special device for detecting speed.

[Brief explanation of the drawing]

Figure 1 is a flowchart showing vehicle head detection processing and speed calculation processing, Figure 2A is a plan view showing an installation example of an automatic vehicle number reader with speed measurement function, Figure 2B is a front view of the same, and Figure 3 is speed measurement. A block diagram of the circuit configuration of an automatic vehicle number reading device with a function; Fig. 4A is an image of a vehicle that has been binarized by edge detection; Fig. 4B is a profile obtained by adding the number of pixels in the vehicle running direction; Fig. 5 The figure is an explanatory diagram showing a speed calculation method. Fig. 1 1...Automatic vehicle number reading device with speed measurement function, 3...
Camera device, 15... Image processing processor, 17... General purpose processor

Claims (1)

[Scope of Claims] 1. An automatic vehicle number reading device that automatically identifies the plate number of a vehicle traveling on the road, comprising a photographing means for photographing the road, and a plurality of vehicle fronts by processing a series of photographed images. 1. An automatic vehicle number reading device with a speed measurement function, comprising: a vehicle head detecting means for detecting the vehicle head; and a speed detecting means for determining the vehicle speed from the detected travel distance of the vehicle head. 2. The vehicle head detection means extracts pixels representing edges with a high density change rate based on the photographed image, counts the number of pixels in the traveling direction of the vehicle, and calculates a predetermined number of pixels with this counted number of pixels. 2. The automatic vehicle number reading device with a speed measurement function according to claim 1, wherein the vehicle head is detected by comparing the vehicle head with a threshold value.