JP3303643B2 - Exposure amount control device for imaging device for mobile object - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure control apparatus for a moving object imaging apparatus, and more particularly to an apparatus for determining an optimum exposure amount at a next imaging timing from an obtained image.

[0002]

2. Description of the Related Art Conventionally, a technique for controlling an exposure amount of an imaging device such as a CCD camera has been known. For example, in the exposure control apparatus disclosed in Japanese Patent Application Laid-Open No. H4-6966, when taking an image under illumination such as a fluorescent lamp whose brightness periodically fluctuates, the following control is performed based on the integrated value of the amount of incident light within a predetermined time. A configuration for controlling an exposure time required to obtain a target image output is described.

[0003]

However, the above prior art is based on the fact that the brightness of the light source changes periodically. Therefore, the prior art is mounted on a moving body such as a vehicle to acquire a surrounding image. There is a problem that cannot be applied to a situation where brightness changes aperiodically or discontinuously. In particular,
When considering a vehicle, if a tunnel or the like exists ahead of the vehicle path, the surrounding area changes discontinuously at the tunnel point, so the exposure time is controlled based on the current amount of incident light before the tunnel. However, there was a problem that a desired image could not be obtained and the real-time property was impaired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to realize a real-time operation even in a situation where the brightness of the surroundings is discontinuously changed when mounted on a moving body such as a vehicle. An object of the present invention is to provide an exposure amount control device of a moving object imaging device capable of reliably acquiring a desired image without any loss.

[0005]

According to a first aspect of the present invention, an image pickup apparatus mounted on a moving body and an optimum exposure amount at a specific point on a path of the moving body are calculated in advance. The image processing apparatus further includes an arithmetic unit and an exposure amount adjusting unit that sets an exposure amount of the imaging device to the previously calculated optimal exposure amount when the moving body reaches the specific point.

According to a second aspect of the present invention, in the first aspect, a speed detecting means for detecting a speed of the moving body, and a direction for detecting a traveling direction of the moving body. Detecting means for calculating a position in an image at which a moving object is estimated to be present at the next imaging timing of the imaging apparatus based on the detected speed and direction; The means calculates the optimal exposure amount using the position in the image of the moving object at the next imaging timing as the specific point.

Further, in order to achieve the above object, a third
According to a second aspect of the present invention, in the second aspect, the calculation means corresponds to a target image output based on a relationship between an image output near a position in an image of the moving object at a next imaging timing and a current exposure amount. It is characterized in that the optimum exposure amount is calculated.

As described above, in the present invention, the optimum exposure amount at a specific point on the course of the moving object, specifically, at the position where the moving object will be present at the next imaging timing is calculated in advance, and the actual exposure amount is calculated. When the body reaches that point, the exposure of the imaging device is adjusted with this optimal exposure.

Therefore, even if a tunnel or the like exists in front of the moving body, the optimum exposure amount at the point is determined in advance, so that as soon as the vehicle enters the tunnel or the like, the optimum exposure amount is set around the moving body. The situation can be photographed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of this embodiment. A CCD camera 10 as an imaging device is provided at a predetermined position of a vehicle as a moving body. The CCD camera 10 includes a CCD sensor 12 and a CCD control circuit 14 for adjusting the exposure time of the CCD sensor 12. A video signal obtained by the CCD camera 10 is output to an ECU 20, which is an image processing microcomputer. On the other hand, a vehicle speed sensor 16 for detecting the speed of the vehicle, and a direction sensor 18 for detecting the traveling direction of the vehicle are also provided.
Each detection signal is output to the ECU 20. In addition, as the direction sensor 18, a magnetic sensor, a steering angle sensor, or the like can be used. The image processing ECU 20 stores a video signal A / D 22 for converting a video signal output from the CCD camera 10 into a digital signal, an input unit 24 for inputting a detection signal from a sensor, a CPU 26, and an optimum exposure amount determination program described later. ROM 28, frame memory 30 for storing the video signal digitized by video signal A / D 22, and output unit 3 for outputting the operation result
2 is included. CPU 26 is a frame memory 3
The optimum exposure amount determination program stored in the ROM 28 is executed by using the image data stored in the image data 0, and an image output near the position where the vehicle is present at the next imaging timing (specifically, after 33 ms) is extracted. Based on the extracted output amount, the optimum exposure amount at that position is determined and output to the output unit 32. This output is supplied from the output unit 32 to the CCD control circuit 14 of the CCD camera 10 as an electronic shutter time control signal, and the CCD control circuit 14 controls the exposure amount of the CCD 12 based on the electronic shutter time. The timing at which the output unit 32 outputs the electronic shutter time control signal to the CCD camera 10 is the timing at which it is determined that the vehicle, which is a moving body, has reached the specific point where the optimal exposure has been calculated. It is determined based on a count-up signal from a timer that does not perform the operation or based on a position detection signal from a navigation system.

FIG. 2 shows an image processing EC according to this embodiment.
A detailed processing flowchart of U20 is shown. In the figure, when the power is first turned on (S101), the image processing ECU 20 sets arbitrary electronic shutter times t1 and t2 to C
The voltage is supplied to the CD camera 10, and the output voltage from the CCD camera 10 at these two points is measured (S102). This output voltage measurement is for measuring the output characteristics of the CCD camera 10, and the slope of the output voltage with respect to the electronic shutter time and the offset voltage are calculated based on the time and the output voltage (S103, S104).

FIG. 3 shows the relationship between the electronic shutter exposure time and the CCD output voltage in a general CCD camera. In general, even if the exposure time is 0, a predetermined offset voltage is generated from the CCD, and the output voltage increases as the exposure time increases. The slope of the increase changes according to the surrounding brightness, that is, the amount of incident light, and the greater the brightness, the greater the slope. Therefore, the electronic shutter exposure time at a certain brightness is set at two points, the CCD output voltage at each point is measured, the slope of the straight line is obtained, and the offset voltage is extrapolated by extrapolating the CCD output voltage at the electronic shutter time 0. It can be determined uniquely. The slope and offset voltage at each brightness calculated in this way are stored in the memory of the CPU 26.

After the CCD output characteristics at each brightness are obtained, the CCD camera 10 photographs a predetermined area in front of the vehicle, and supplies a video signal to the image processing ECU 20 (S1).
05). The image processing ECU 20 converts the input video signal into a digital signal using the video signal A / D 22 and stores the digital signal in the frame memory 30. Then, a target electronic shutter time calculation process is performed based on the stored image data (S106). This target electronic shutter time calculation processing is mainly composed of the following two steps. That is, (1) Estimate the position of the vehicle at the next imaging timing (after 33 msec). (2) Estimate the brightness from the relationship between the electronic shutter exposure time and the CCD output voltage at the estimated position, and obtain the desired CC.
Determining Target Electronic Shutter Time Required to Obtain D Output Voltage Note that the above step (1) further includes the following two steps. Calculate the position of the vehicle on the road at the next imaging timing based on the current speed and traveling direction of the vehicle. Calculate the position in the image corresponding to the calculated position on the road. A specific processing flowchart of the calculation processing is shown. First, the CPU 26 inputs the vehicle speed signal from the vehicle speed sensor 16 and the traveling direction data from the direction sensor 18 via the input unit 24, and detects the vehicle speed and the traveling direction (S201). Next, based on these data, the CPU 26 calculates the position of the vehicle on the road at the next imaging timing T (ie, 33 msec) (S202). The position of the vehicle on the road after T seconds is (X, Z). Next, the position (x, y) in the image corresponding to the calculated position (X, Z) on the road of the vehicle is calculated (S203).

FIG. 5 shows an example of a coordinate system used for calculating a position in an image from a position on a road. In the figure, the coordinate system representing the position on the road is XYZ
And the road surface is parallel to the XZ plane and at the position of Y = -H. The origin of XYZ is the center of the lens of the CCD camera 10, and the image plane xy is arranged at a position separated by a distance F (F is a focal length). In such a coordinate system, an arbitrary point Q (X, -H, Z) located on the road surface
(X, y) in the image plane can be expressed as follows.

[0016]

X = F · X / (Zcosθ−Hsinθ) y = −F (Zsinθ + Hcosθ) / (Zcosθ−
Hsin θ) Therefore, by using the above formula, the position in the image corresponding to the position on the road of the vehicle after T seconds calculated in S202 can be uniquely calculated. FIG. 6 shows a position 100 in the image at the next imaging timing calculated in this way.
In the figure, the position 200 in the image on which the current brightness control is based is also shown for comparison. After the position in the image of the vehicle at the next imaging timing is calculated, the CPU 26 reads the output voltage data at this position from the frame memory 30 and evaluates the brightness at that point based on the electronic shutter time data at that time. In the present embodiment, as shown in FIG. 3, the brightness is evaluated in three levels of large, medium, and small, and the brightness at a specific point is evaluated in any of these three levels. It is determined. After the inclination of the position and the offset voltage at the next imaging timing are calculated, C
From the CD target output voltage required at that point, the PU 26 calculates the required electronic shutter exposure time using these slope and offset voltage data (S2).
04). For example, when the brightness at the next imaging timing is small and the desired CCD output voltage is Vd, the electronic shutter exposure time corresponding to this Vd is td, so that the CPU 26 Td is calculated as the exposure amount.

As described above, the processing in S106
That is, after the target electronic shutter time calculation processing is executed, the image processing ECU 20 determines whether or not the vehicle has reached that point, that is, whether or not 33 msec has elapsed from the previous imaging timing. If it is determined that the vehicle has reached that point, the output unit 32 outputs the C
The calculated electronic shutter exposure time as the optimal exposure amount is output to the CD control circuit 14, and the surroundings of the vehicle are photographed with the exposure time. Note that the electronic shutter control signal transmission timing may be configured to transmit the electronic shutter control signal to the CCD camera 10 when it is determined that the vehicle has reached the point based on the position detection signal from the navigation system.

Further, in the present embodiment, the specific position is the vehicle position at the next imaging timing, but the optimum exposure amount of the vehicle position at the next imaging timing may be calculated in advance.

In addition, not a vehicle position at the next imaging timing as a specific point, but a point on the path of the vehicle in the image where the brightness is greatly changed is extracted, and an estimated travel time to that point is extracted. May be calculated to output the optimal exposure amount.

[0020]

As described above, according to the exposure control apparatus of the imaging apparatus for a mobile object of the present invention, the optimum exposure at a specific point on the vehicle course is calculated in advance, and when the point is reached, Since the photographing is performed with the optimal exposure amount, it is possible to cope with a discontinuous change in the incident light amount, and it is possible to reliably obtain a desired image.

In particular, even at a point where the amount of incident light changes sharply, such as in a tunnel, a clear image can be obtained without a time delay.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention.

FIG. 2 is an overall processing flowchart in the embodiment.

FIG. 3 is a graph showing a relationship between an electronic shutter exposure time and a CCD output voltage in the embodiment.

FIG. 4 is a flowchart of a target electronic shutter time calculation process in the embodiment.

FIG. 5 is an explanatory diagram showing a relationship between a position on a road and a position in an image.

FIG. 6 is an explanatory diagram showing a position in an image of the vehicle at a next imaging timing in the embodiment.

[Explanation of symbols]

10 CCD camera, 16 vehicle speed sensor, 18 direction sensor, 20 image processing ECU.

Claims (3)

(57) [Claims] An imaging device mounted on a moving object; a calculating unit for calculating an optimum exposure amount at a specific point on a path of the moving object in advance; and an image pickup device when the moving object reaches the specific point. An exposure amount adjusting means for setting an exposure amount of the apparatus to the optimum exposure amount calculated in advance; 2. The exposure amount control device for a moving body imaging apparatus according to claim 1, further comprising: speed detecting means for detecting a speed of the moving body; direction detecting means for detecting a traveling direction of the moving body; Based on the detected speed and direction, a position calculation unit that calculates a position in an image at which a moving object is estimated to be present at the next imaging timing of the imaging device. An exposure amount control device for an imaging device for a moving body, wherein an optimal exposure amount is calculated using a position in an image of the moving body at the next imaging timing as the specific point. 3. The exposure amount control device for a moving body image pickup apparatus according to claim 2, wherein the calculating unit is configured to determine a relationship between an image output near a position in an image of the moving body at a next imaging timing and a current exposure amount. An exposure amount control device for an imaging device for a mobile object, which calculates an optimum exposure amount corresponding to a target image output based on the image data.