JPS6281882A - Camera diaphragm control system in automatic reader vehicle number - Google Patents

Abstract

PURPOSE:To attain an exact reading fully responded to an environmental change by calculating and deciding whether a view field is against or for the light from a camera from the direction of the sun and the image pickup direction of the camera, and controlling the diaphragm of the camera. CONSTITUTION:A video signal image-picked up with camera 2.8 is added to detectors 2.1, and there, the video signal is converted to a voltage level, and the representative value E of the brightness of a video is obtained. Also, the output of a timepiece 2.3 and a sensor signal from a vehicle sensor are inputted to a control circuit 2.2, and from the two signals, the direction of the sun and the image pickup direction of the camera are found, a decision whether the view field is against the light or not being performed. And a decided result is sent to a motor 2.5 through a motor driver 2.4, and the diaphragm 2.7 of the camera 2.8 is adjusted. Thereby, the exact reading for the vehicle number responded to the environmental change can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a camera aperture control system in an automatic vehicle number reading device.

C Conventional technology and 1! ! When a television camera is installed outdoors for purposes such as monitoring, there are large changes in brightness, and automatic control of the camera's aperture is essential.

The EE method is a typical control method. FIG. 6 is a diagram explaining the principle of the EE method. The video signal detected by the camera 1.7 is converted into a voltage level by the detector 1.1, and a representative value E of the brightness of the video is determined. E is the maximum value, average value, or intermediate value of image brightness (typical value such as +11. Comparator 1.2), r, handedness is compared with A, and if E>A+α, aperture IG As if to relax, E<
For A-α, input to motor and driver 1.3 to open the aperture, move motor 1.4 9 times, and open IE-A.
If l≦α, the stone moves. Note that α is a constant determined by A.

In other words, this EE method is an aperture method that attempts to always keep the representative value E of image brightness constant.

However, since this method performs aperture control based only on the video signal (Jl), the following problems arise when automatically reading the vehicle number.

FIG. 2 shows an example of the configuration of an automatic vehicle number reading device. When sensing No. 45 is received from the double sensors 3 and 1, the i-most image control circuit 3
．． 4 captures a static 11-image from TV cameras 3 and 2;
An image processing circuit 3.5 cuts out the plate, and a character identification circuit 3.6 reads the vehicle number.

The field of view of the screen of an automatic vehicle number reader is approximately 1.5 m in the horizontal direction, which is relatively narrow. Therefore, the images will be completely different depending on whether the vehicle is present on the screen or not. Now, let's consider the change in image brightness due to double passing with a fixed aperture. Figure 3 is an example. (a) is an example of the passing of the own system illumination (both vehicles), which is brighter than the road surface, and (b) is an example of passing a black system vehicle, which is darker than the road surface.Here, considering the aperture control using the EE method described above, When a black car passes, the aperture is closed, and when a black car passes, the aperture is opened. However, because license plates are standardized regardless of the color of the car, the aperture is adjusted depending on the color of the car. If the opening and closing changes, the plate will not be imaged clearly. In other words, it is insufficient to control the aperture only by changing the aperture in response to environmental changes that affect the illuminance of the plate, such as when the sun is obscured by movement of clouds. It is.

Next, the influence of the position of the sun will be explained using FIG.

As in (a), when the TV camera and the sun are in the same direction with respect to l(, it is called a frontlight condition.) As in (b), when the TV camera and the sun are in opposite directions, it is called a backlight condition. In front light conditions, direct sunlight hits the plate, but in back light conditions, the plate is shaded by light rain and no sunlight hits the plate.

Therefore, in order to take a clear image of the plate, it is necessary to change the F-number of the aperture depending on whether it is in a front-lit or back-lit situation, even in the same environment.

However, in terms of the overall brightness of the image, if it is sunny,
There is no big difference between the front-light condition and the back-light condition, and it is difficult to distinguish between them. Also, of course, before determining whether the person is blind or backlit,
It is necessary to judge whether it is sunny or not, but in the EE method, since the representative value of the image brightness is always kept constant, the image within the field of view (1 degree is unknown, I can't judge.

[Means for resolving the problem] As explained above, the conventionally used EE method cannot sufficiently respond to changes in the environment and accurately read license plates. This is to improve the aperture control method.

The present invention adopts the aperture control method of a television camera to automatically read the vehicle number, but it is calculated from the sensing signal from the vehicle sensor, the brightness of the image, and the position information of the aperture drive motor. A control circuit that determines a combination of the illuminance within the field of view of the camera calculated from the aperture value, the position of the sun with respect to the camera and the brightness of the image calculated from the date and time indicated by a clock, and instructs the drive of the aperture drive motor. In preparation for this, the aperture is opened and closed.

"fart, - The aperture control method of the present invention will be explained with reference to FIG.

As shown in the figure, 2.8 is the camera, 2.6 is the lens, 2.7 is the aperture, and 2.1 is the detection unit that converts the video signal into a voltage level and calculates the representative value E of the brightness of the video. It is a vessel.

Further, 2.2 is a control circuit, and the output of the clock 2.3 and the sensor from the vehicle sensor are input to this control circuit 2.2. 2,4 are motor drivers, 2.5 are motors, , motor 2
．． 5 drives the aperture 2.7, but at the same time outputs motor position information and sends it back to the control circuit 2.2.

Here, the aperture control of the present invention will be explained with reference to the aperture control flowchart shown in FIG. In addition, the following ■, [phase],
The diaphragm opening/closing operation in (2) shall be changed by a unit angle determined by the characteristics of the motor. Furthermore, this control is always executed unless some kind of interruption occurs.

Referring to the automatic vehicle number reading device shown in FIG. 2, check whether the vehicle is detected or not. When the vehicle is detected, the aperture does not open or close at all.

■Calculate the illuminance within the field of view. If the F value of the diaphragm calculated from the position information of the E1 motor is the representative value of the brightness of the image and is f, then L=kf''E.

(k is a proportional constant) ① Compare the illuminance and L+ (constant). If L≦L1, it is determined that the environment requires lighting for imaging, such as at night.

■、■、If the aperture's F number is the minimum, the aperture is already fully open, so do nothing. Otherwise, open the aperture by one unit.

(2) Instruct the imaging control circuit that illumination is necessary for imaging.

If it is determined that it is daytime based on ■ and ■, then the illuminance and L2
Compare (constant). If L≦L2, it is determined that sunlight is not shining on the road surface due to cloudy weather, etc., and the process proceeds to ■.

If it is determined that it is sunny based on (1) and (2), the position of the sun is calculated from the date and time information obtained from the clock, and by comparing it with the installation conditions of the television camera, it is determined whether the sun is in front light or back light.

(2), [Phase], and (2), set reference values suitable for each condition, ie, A and α for cloudy conditions, front lighting, and back lighting. Note that A is the base bet value and α is the reference blind value.

Opening/closing of the aperture is determined by the magnitudes of O20, ■, and E.

If IE-AI≦α, it is assumed that the brightness of the image is appropriate and nothing is done.

If it is ERA-α, it is determined that the image is too dark than the standard value, and the aperture is set to l! Open 11th place.

If E>A+α, it is determined that the image is too bright than the reference value, and the aperture is closed by one unit.

INDUSTRIAL APPLICABILITY The present invention is applied to aperture control of a camera of a device that images the license plate of a vehicle running or stopped on a road surface and automatically reads the vehicle number.

[Operations and Effects] In the present invention, the illuminance within the field of view of the camera is calculated,
This is compared with a standard value that distinguishes between day and night to determine whether it is day or night, and if it is daytime, it is further compared with a standard value that distinguishes between cloudy or sunny. It compares the standard value and the brightness of the actual image to control the opening and closing of the camera's aperture, and if it is sunny, the date and time are determined by the clock.
Is the sun directly in front of the camera's imaging direction?
Calculates whether the situation is backlit, determines whether it is frontlit or backlit, and compares the actual image brightness with the reference value for either backlighting or backlighting, and then adjusts the aperture. The opening and closing of the door is controlled. Further, when the illuminance within the field of view of the camera is compared with the reference value and it is determined that it is night or a state close to night, the aperture is fully opened and the illumination device shown in FIG. 2 is turned on.

In the present invention, the double-sided sensor detects the range that is always in the camera's field of view only when the vehicle is not within the camera's field of view, especially in sunny conditions, and the field of view is either backlit or in front of the camera. Or, the camera's aperture is controlled based on the direction of the sun calculated from the date and time on the clock and the imaging direction of the camera to distinguish between frontlight and backlight. When entering the building, you can clearly see the plate number, and the overall body color is 11, avoiding the effects of direct sunlight and the position of the sun.

[Brief explanation of drawings]

FIG. 1 shows in block diagram form an embodiment of the invention. FIG. 2 shows a block diagram of an example of an automatic vehicle number reading device. Figure 3 (a) is an illustration of the brightness variation in the image when a white vehicle, which is brighter than the road surface, passes by, and Figure 3 (b) is an illustration of the variation in image brightness when a black vehicle, which is darker than the road surface, passes. It is a diagram. FIGS. 4(a) and 4(b) are diagrams explaining the influence of the sun's position. FIG. 5 is a flowchart of the aperture control method of the present invention. FIG. 6 is a block diagram of an automatic control system for the aperture of a general camera. 2.1...Detection W, 2.2...Control circuit, 2.3.
・・Clock, 2.4・・Motor driver, 2.5・
...Motor, 2.8...Lens, 2.7...Aperture, 2.8...Camera. Figure 1 Figure 2 Figure 3 Seat 4 Figure 5 Figure

Claims (1)

[Claims] (1) The illuminance within the field of view is calculated from the aperture value calculated from the detection signal from the vehicle sensor, the brightness of the image, and the position information of the aperture drive motor, and the position of the sun relative to the camera is calculated from the date and time indicated by the clock. A camera aperture control system in an automatic vehicle number reading device, comprising a control circuit that makes a judgment based on a combination of the brightness of the image and the brightness of the image, and instructs the drive of the aperture drive motor.