JPH06325159A - Image illuminance adjusting method - Google Patents

Abstract

PURPOSE:To obtain an image with proper illuminance by adjusting a stop on the basis of an obtained image of a vehicle which runs on a path when the image is continuously photographed. CONSTITUTION:When the image is inputted (step 2), a license plate tries to be extracted (step 3) and when a white ground plate is found (step 4), a light/ dark decision on the plate surface is made (step 5); when the plate is absent, a screen light/dark decision is made (step 6) and a stop adjustment signal is generated (step 7) on the basis of the results of the respective light/dark decisions. Consequently, the image with excellent illuminance is obtained irrelevantly to the direction of the sun and even under the influence of artificial lighting and a shadow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the illuminance of an image of a vehicle traveling on a road.

[0002]

2. Description of the Related Art When taking an image of a vehicle running on an outdoor road, it is necessary to adjust the illuminance of the image taken because of the influence of natural light or artificial light depending on the time of day. In order to meet such a demand, image illuminance adjusting methods and apparatuses as shown in FIGS. 6 and 7 have been conventionally proposed.

FIG. 6 is a diagram showing the overall structure of a conventional image illuminance adjusting device. An optical sensor 48 for detecting ambient brightness and generating a light intensity signal 58 proportional to the brightness, an aperture adjusting means 7 for producing an aperture adjustment signal 57 from the light intensity signal 58, and an aperture according to the aperture adjustment signal 57. It is composed of a camera 47 that opens and closes.

FIG. 7 is a flow chart showing a diaphragm adjusting method of the diaphragm adjusting means 7 of FIG. After setting the initial values of brightness and aperture to BRS and IRS respectively in step 49,
It is determined whether or not the light intensity signal is valid (step 50), and if it is not valid, the process ends. If the light intensity signal is valid, the intensity value is substituted into BR (step 51), and BR is
And BRS are compared (step 52). If BR> BRS in step 52, IRS is the minimum aperture value IRSMI.
Judge whether N or less (step 53), and IR at step 53
When S> IRSMIN, BRS is incremented and IRS is decremented in step 55, a signal for closing the aperture by one step is generated (step 38), and the process returns to step 50 to continue the processing. If IRS ≦ IRSMIN, the process returns to step 50 without doing anything. BR ≦ B in step 52
When it is judged as RS, IRS is the maximum aperture value IRSMA
It is judged whether it is X or more (step 54), and IRS <IRSMA
If X, decrement BRS and I in step 56.
Increment RS, generate a signal to open the aperture one step (step 39), and return to step 50 IRS ≧ IR
In the case of SMAX, nothing is done and the process returns to step 50 and continues.

Since the conventional image illuminance adjusting method operates as described above, the diaphragm is adjusted so as to be in inverse proportion to the intensity of the light detected by the optical sensor.

[0006]

Since the light intensity detected by the optical sensor depends on the direction in which the sensor is installed, it is not always proportional to the ambient brightness depending on the direction of the sun. In addition, the light intensity detected by the optical sensor and the brightness on the road may be different when the shadow of a building extends on the road or when the road is illuminated by artificial lighting. It was not possible to obtain an image with high illuminance.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an image with an appropriate illuminance even under the influence of the direction of sunlight, artificial lighting, shadows and the like. Is.

[0008]

According to the image illuminance adjusting method according to the present invention, an image is appropriately determined based on the brightness of the entire image of an actually photographed image or the brightness of a white background portion of a license plate. The illuminance of the image is adjusted by determining whether or not the illuminance is present and opening and closing the diaphragm.

[0009]

According to the present invention, when the brightness of the entire screen of the photographed image or the white background of the license plate is darker or brighter than the preset threshold value, the aperture of the camera is opened and closed.

[0010]

【Example】

Example 1. FIG. 1 is a flow chart showing the overall procedure of an image illuminance adjusting method according to the present invention. In step 1,
It is determined whether or not the image capturing is completed, and if the image capturing is completed, the process is terminated. If the image pickup is continued, it is checked in step 2 whether there is an image input. If not, the process returns to step 1 to repeat the process. When the image is input, the license plate is extracted in step 3, and it is determined whether the white plate is extracted (step 4). When the white plate is extracted, the lightness / darkness of the white portion of the plate surface is determined in step 5. Done, if not extracted,
In step 6, the lightness / darkness of the entire screen is determined. After the aperture adjustment signal is generated and the aperture is adjusted in step 7 based on the lightness / darkness determination result, the process returns to step 1 to continue the processing.

FIG. 2 is a flow chart showing the plate surface lightness / darkness determination procedure 5 of FIG. In step 8, the initial value 0 is set to the brightness / darkness determination result flag FLAG and the plate surface concentration integrated value SUM
Is substituted. In step 9, the coordinates of the white area of the plate are calculated, the X coordinate of the left end is STX, and the X coordinate of the right end is ED.
Substitute X with the Y coordinate of the upper end for STY and the Y coordinate of the lower end for EDY. X and Y counters I and J
Initial values STX and STY are respectively substituted into (step 1
0), the density of the pixel at the coordinates (I, J) is added to the SUM (step 11). It is determined whether the counter I in the X direction is equal to the final value EDX (step 12). If not, step 13 is incremented by 1 and step 11 is repeated. When I is equal to EDX, it is judged whether the counter J in the Y direction is equal to the final value EDY (step 14). If not equal, the initial value STX is substituted for I in step 15 and J is incremented. 11
repeat. If J is equal to EDY, it is determined in step 16 whether SUM is smaller than a certain threshold value TH1, and if it is smaller, -1 is assigned to the brightness / darkness determination result flag FLAG (step 20). When SUM is greater than or equal to TH1, in step 17, SUM is set to another threshold value TH.
It is determined whether or not it is larger than 2, and if it is larger, 1 is assigned to the brightness / darkness determination result flag FLAG in step 19. If SUM is less than or equal to TH2, 0 is assigned to the lightness / darkness determination result flag FLAG in step 18 to indicate that it is appropriate.

FIG. 3 is a flow chart showing the screen brightness determination procedure 6 of FIG. In step 21, the counter CO
Substitute an initial value of 0 for each of UNT, I, and J. In step 22, the density of the pixel at coordinates (I, J) is the threshold value BT.
If it is larger than H, it is judged to be C in step 23 if larger.
Increment OUNT and do nothing if not large. It is determined whether or not the counter I in the X direction is equal to the screen width which is the final value (step 24). If they are not equal, I is incremented in step 13 and the process returns to step 22. I
Is equal to the screen width, it is determined whether the counter J in the Y direction is equal to the final screen height (step 25). If not, the initial value 0 is substituted for I in step 26, and J
Is incremented and the process returns to step 22. If J is equal to the screen height, then in step 27, COUNT is equal to the threshold value C.
It is determined whether or not it is larger than TH1, and when it is larger, -1 indicating dark is substituted in the light / dark determination result flag FLAG.
When COUNT is less than or equal to CTH1, it is determined whether or not COUNT is smaller than another threshold value CTH2 (step 28). If it is smaller, 1 is assigned to the brightness / darkness determination result flag FLAG (step 19). COUNT is CTH
If it is 2 or more, 0 indicating that it is appropriate is substituted into the brightness / darkness determination result flag FLAG (step 18).

FIG. 4 is a flow chart showing the aperture adjustment signal generation procedure 7 of FIG. In step 29, variables I and VAL
Substitute the initial value 0 into. In step 1, it is determined whether or not the image capturing is completed. If the image capturing is completed, the process is completed. If the shooting is continued, the image waiting for the result of the lightness / darkness determination is waited for (step 30), and if there is input, I is incremented (step 13) to indicate that the lightness / darkness determination result flag is dark-1. Is determined (step 3). FLAG
If −1, the variable VAL is decremented (step 33). When FLAG is not -1, it is determined whether FLAG is equal to 1 indicating that it is bright (step 32), and if it is equal, VAL is incremented, and if not, nothing is done. After that, it is determined whether or not I becomes equal to the preset number of data DMAX (step 35). If not equal, it returns to step 1 and repeats the processing. I
Is equal to DMAX, it is determined whether VAL is smaller than the threshold value VTH1 (step 36), and if it is smaller, a signal for closing the aperture by one step is generated (step 38).
When VAL is VTH1 or more, VAL is another threshold value V
It is determined whether or not it is larger than TH2 (step 37), and if it is larger, a signal for opening the aperture by one step is generated (step 3).
9) If it is not big, do nothing. Then I and VAL
The initial value 0 is substituted for (step 29) and the process returns to step 1.

Example 2. FIG. 5 shows another embodiment of the aperture adjustment signal generation procedure 7 of FIG. In step 40, the clock counter and the data number counter I are initialized. In step 41, it is determined whether or not a certain period of time has passed. If not, it is checked in step 42 whether or not the brightness / darkness determination result has been input. If there is no input, the process returns to step 41. If there is an input, it is determined in step 31 whether the lightness / darkness determination result flag is -1, and if -1, it is VAL.
Is decremented (step 33), and if not -1, V
It is determined whether AL is 1 (step 32), and if it is 1, VAL is incremented, and if it is not 1, nothing is done.
After that, I is incremented, and the process returns to step 41. If it is determined in step 41 that the fixed time has elapsed, it is checked whether or not the image capturing is completed (step 1). If the image capturing is completed, the process ends. If imaging continues, VA
L is divided by the number of data I (step 43). V after division
If AL is smaller than the threshold value ATH1 44, a signal for opening the aperture by one step is generated (step 38). If ATH1 or more, or if it is larger than another threshold value ATH2 (step 45), a signal for closing the aperture by one step is generated (step 39). After that, the clock counter and the data number counter I are initialized and the process returns to step 41.

[0015]

As described above, according to the present invention, the iris of the camera is adjusted according to the brightness of the entire screen of the actually photographed image or the surface of the white background plate. You can adjust the illuminance of the image including the effect of. Further, since the white background plate surface with relatively little disturbance of illuminance change is used as the light / dark judgment data, more accurate illuminance adjustment can be performed.

[Brief description of drawings]

FIG. 1 is a flowchart showing a screen illuminance adjusting method according to an embodiment of the present invention.

FIG. 2 is a flow chart showing a plate surface lightness / darkness determination method according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a method for determining screen brightness according to the embodiment of the present invention.

FIG. 4 is a flowchart showing a diaphragm adjustment signal generating method according to an embodiment of the present invention.

FIG. 5 is a flowchart showing a diaphragm adjustment signal generating method according to an embodiment of the present invention.

FIG. 6 is a diagram showing an overall configuration of a conventional screen illuminance adjustment device.

FIG. 7 is a flowchart showing a conventional screen illuminance adjusting method.

[Explanation of symbols]

 1 Image capture end determination procedure 2 Image input presence / absence determination procedure 3 License plate extraction procedure 4 White background plate presence / absence determination procedure 5 Plate surface brightness / darkness determination procedure 6 Screen brightness / darkness determination procedure 7 Aperture adjustment signal generation procedure 8 FLAG, SUM initialization procedure 9 Plate white background area Coordinate calculation means 10 Counter I, J initialization procedure 11 Density value integration procedure 12 I, EDX comparison procedure 13 I increment procedure 14 J, EXY comparison procedure 15 I, STX substitution, J increment procedure 16 SUM, lower threshold Comparison procedure 17 SUM, upper threshold comparison procedure 18 FLAG, 0 substitution procedure 19 FLAG, 1 substitution procedure 20 FLAG, -1 substitution procedure 21 COUNT, I, J initialization procedure 22 Concentration, threshold comparison procedure 23 COUNT in Clement procedure 24 I, Screen width comparison procedure 25 J, Screen height Comparison procedure 26 I initialization, J increment procedure 27 COUNT, upper threshold comparison procedure 28 COUNT, lower threshold comparison procedure 29 I, VAL initialization procedure 30 Bright / darkness determination result input waiting procedure 31 FLAG, -1 comparison procedure 32 FLAG, 1 comparison procedure 33 VAL decrement procedure 34 VAL increment procedure 35 I, DMAX comparison procedure 36 VAL, lower threshold comparison procedure 37 VAL, upper threshold comparison procedure 38 Aperture "closed" signal generation procedure 39 Aperture "Open" signal generation procedure 40 Time counter initialization procedure 41 Fixed time elapsed determination procedure 42 Bright / dark determination presence / absence determination procedure 43 VAL average value calculation procedure 44 VAL, lower threshold comparison procedure 45 VAL, upper threshold comparison procedure 46 Vehicle 47 Camera with aperture function 48 Optical sensor

Claims (2)

[Claims] 1. An image illuminance adjusting method for an apparatus for continuously photographing a grayscale image of a vehicle traveling on a road using a camera, extracting a license plate from the photographed image,
When a white background plate is extracted, find the average density of the white background part, and when the average density exceeds the upper threshold,
If it is judged to be too dark, and if it is below the lower threshold, it is judged to be bright, and if a white plate is not extracted, the number of pixels with a darker density than a certain density value is calculated in the entire screen, and the If the integrated value exceeds a certain threshold value, it is judged to be dark, and if it falls below a certain threshold value, it is judged to be bright. The image illuminance adjustment method that opens the aperture of the camera by one step and opens the aperture of the camera by one step when the number of units judged to be dark exceeds a certain value. 2. An image illuminance adjusting method for an apparatus for continuously photographing grayscale images of a vehicle traveling on a road using a camera, extracting a license plate from the photographed images,
When a white background plate is extracted, the average density of the white background portion is obtained, and when the average density exceeds the upper threshold value, it is determined that it is too dark, and when it is below the lower threshold value, it is determined that it is bright. If the white plate is not extracted,
In the entire screen, calculate the number of pixels with a darker density than a certain density value, and if the integrated value exceeds a certain threshold, it is determined to be dark, and if it falls below a certain threshold, it is determined to be bright,
If the number of cars judged to be bright exceeds a certain percentage of the data for a certain period of time, the camera aperture should be stopped by one step, and if the number of cars judged to be dark exceeds a certain percentage, the camera diaphragm should be opened one stage. Image illuminance adjustment method.