JPH10333204A - Exposure controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control exposure just after the duration of the large fluctuation of incident light quantity even when the incident light quantity is largely fluctuated for a short time by performing control corresponding to the fluctuation only when the fluctuation of the incident light quantity is kept for a longer time than a set time which is set in advance. SOLUTION: A microprocessor 10 controls a diaphragm 2 corresponding to the fluctuation when the fluctuation of the quantity of light made incident through a photographing lens 1 is kept for the longer time than the set time which is set in advance based on a signal transmitted from an optical detector circuit 9. When the fluctuation is kept only for the time <= the set time, the control of the diaphragm 2 is performed by judging that the fluctuation is not caused. By setting a non-acting period being a fixed time for the remarkable disturbance of the incident light quantity occurring in the midst of photographing, a situation that the exposure is not accurately controlled just after the duration of the temporary remarkable disturbance and a video is swung as shown in the conventional one is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an exposure control device for controlling an exposure amount in an electronic camera such as a video camera.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an electronic camera, such as a video camera, having a photographic lens and an image pickup device such as a so-called CCD disposed on an image plane of the photographic lens. In such an electronic camera, the amount of light incident through the photographic lens, that is, the amount of light received by the image sensor is measured, and based on the measurement result, the exposure amount control means for controlling the amount of light incident on the photographic lens is controlled. An exposure control device is provided.

As the exposure control means, there are a mechanical iris diaphragm and a so-called electronic shutter for limiting a time during which a light receiving element corresponding to each pixel constituting an image pickup element receives light.

That is, in an electronic camera having such an exposure control device, an appropriate exposure amount is calculated for an object to be photographed in accordance with a change in brightness of the object to be photographed, and the aperture and the speed of an electronic shutter are controlled. .

[0005]

In the above-described exposure control apparatus for an electronic camera, a change in the amount of light incident through the photographing lens, that is, a disturbance is detected, and then the aperture and the electronic shutter are controlled. It takes a predetermined time to make the exposure amount appropriate.

[0006] Therefore, when a strong disturbance occurs for a short time, after the disturbance leaves, a large fluctuation of the exposure amount occurs in response to the disturbance, and the exposure amount immediately after the disturbance is not accurately controlled. Would.

For example, if a car light crosses the shooting range during dark shooting, the aperture is stopped down in response to the brightness of the light immediately after passing the light,
The dark image during shooting becomes very dark. Conversely, if a person or car crosses the shooting range during daytime shooting and a shadow is formed, the aperture opens immediately in response to the darkness of the person or car just after passing the person or car. The daytime video during the shooting becomes very bright.

Therefore, the present invention has been proposed in view of the above-mentioned circumstances, and even when the amount of light incident through a photographing lens in an electronic camera fluctuates drastically for a short time, this fluctuation has been eliminated. It is an object of the present invention to provide an exposure control device in which the exposure amount is accurately controlled immediately thereafter.

[0009]

In order to solve the above-mentioned problems, an exposure control apparatus according to the present invention comprises an exposure amount control means for controlling the amount of light incident on a photographic lens based on the amount of light incident through the photographic lens. The control circuit unit for controlling is characterized in that the control corresponding to the change in the amount of light incident through the photographing lens is performed only when the change lasts for a longer time than a preset time. Is what you do.

[0010]

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

As shown in FIG. 1, the exposure control apparatus according to the present invention automatically controls the amount of light incident through the photographing lens 1 in an electronic camera, that is, the amount of exposure, and forms a control circuit. A microprocessor 10 is provided. The microprocessor 10 includes a program RAM 14 storing programs and a RAM 15 storing various data.
It operates according to the programs and data stored in M14 and RAM15. This microprocessor 10
An arithmetic unit 13 for performing arithmetic processing is provided.
In step 3, a predetermined calculation process is performed. The microprocessor 10 exchanges data with an external circuit via an I / O port 11 and controls the external motor 6 via a PWM circuit. The I / O port 11 of the microprocessor 10 includes a TG, that is, a timing generator 7, a D / A, that is, a digital-to-analog converter 8, and an OPD serving as a photometric unit.
That is, the optical detector circuit 9 is connected.

The amount of light incident through the photographing lens 1 is controlled by a stop 2 serving as an exposure amount control means.
The aperture 2 is driven by a motor 6 controlled by a microprocessor 10. The light incident on the photographing lens 1 whose light amount is controlled by the diaphragm 2 forms an image on the light receiving surface of the CCD, that is, the solid-state imaging device 3. The solid-state imaging device 3 has a function of an electronic shutter by controlling the time during which the light-receiving device corresponding to each pixel receives incident light by the timing generator 7 connected to the microprocessor 10.

The output signal from the solid-state imaging device 3 is S / H
The signal is sent to the AGC, that is, the automatic gain control amplifier 5 via the circuit 4. The automatic gain control amplifier 5 is controlled by the microprocessor 10 via the digital / analog converter 8. The output signal from the auto gain control amplifier 5 is sent to a signal processing circuit (not shown) and also sent to an optical detector circuit 9. From the optical detector circuit 9, a signal corresponding to the integrated value of the amount of light incident on the solid-state imaging device 3 is sent to the microprocessor 10.

In this exposure control apparatus, the microprocessor 10 compares the signal sent from the optical detector circuit 9 with a signal indicating the target value of the exposure control to set the aperture 2 to an appropriate aperture value. Control is performed.

In the above-described exposure control apparatus, a predetermined time is required from when light is incident on the photographic lens 1 to when it is subjected to electrical conversion, comparison, and correction value correction by aperture control. Therefore, if the input light amount fluctuates for a short time, that is, if a temporary disturbance occurs, after the disturbance leaves, the disturbance is reflected on the control of the diaphragm 2, and there is a possibility that accurate exposure control may not be performed. is there. Therefore, this exposure control apparatus is adapted to cope with a strong disturbance of the incident light amount that causes a problem in an image obtained by imaging without reducing the response speed of the exposure control.

That is, in this exposure control device,
Based on the signal sent from the optical detector circuit 9, the microprocessor 10 controls the diaphragm 2 according to the fluctuation of the amount of light incident through the photographing lens 1 when the fluctuation continues for a longer time than a preset time. Is performed, and when the fluctuation lasts only for a time equal to or shorter than the set time, the diaphragm 2 is controlled assuming that there is no fluctuation. The set time is preferably set according to the use environment, for example, 100 msec to 1000 msec.
It is about msec.

As shown in the flowchart of FIG. 2, when the exposure control is started in step st1, the microprocessor 10 fetches a signal corresponding to the integrated value of the incident light amount from the optical detector circuit 9 in step st2. Then, in step st3, a difference between the integrated value obtained from the signal sent from the optical detector circuit 9 and the integrated value used in the previous processing is obtained, and this difference is set to a preset set value, that is, a threshold level. Is determined. If the difference exceeds the threshold level, it is determined that the disturbance is severe, and the process proceeds to step st4. If the difference does not exceed the threshold level, it is not determined that the disturbance is severe, and step st
Proceed to 6.

In step st4, the timer is started while the exposure control operation is stopped. This timer is activated during the duration of the disturbance and will measure the duration of the disturbance. In step st5, it is determined whether or not the duration of the disturbance, that is, the timer measurement value is equal to or longer than a preset time. If the timer measurement value is equal to or longer than the set time, the process proceeds to step st6. If the timer measurement value is less than the set time, the process proceeds to step st7. Step st6
Then, a normal exposure control operation is performed, and the process proceeds to step st8. In step st8, the process returns to the main routine.

In step st5, if the duration of the disturbance is a temporary one that is shorter than the set time, the exposure control operation remains stopped, so that the image immediately after the disturbance is not disturbed.
Then, in step st7, in order to prevent the response speed of the exposure control from being lowered by stopping the exposure control operation, the correction value is weighted in proportion to the duration of the disturbance, that is, the timer value, and the degree of the disturbance. Then, the exposure control operation is gradually started from a completely stopped state, and the process proceeds to step st8.

[0020]

As described above, in the exposure control apparatus according to the present invention, a certain period of non-operation is provided for a remarkable disturbance of the incident light amount which occurs during photographing, so that the conventional exposure control apparatus is seen. Immediately after the passage of such a temporary intense disturbance, the amount of exposure is not accurately controlled and the image does not go up.

In particular, when a constant environment such as a surveillance camera is continuously photographed, an effect is expected because an optimum threshold value is easily determined uniquely for the condition.

That is, according to the present invention, even when the amount of light incident through the photographing lens in an electronic camera fluctuates drastically for a short time, the exposure amount is accurately controlled immediately after the fluctuation has left. An exposure control device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an exposure control device according to the present invention.

FIG. 2 is a flowchart showing an operation of the exposure control device.

[Explanation of symbols]

1 shooting lens, 2 aperture, 3 CCD, 10 microprocessor

Claims (1)

[Claims] 1. A light meter for measuring a light amount incident through a photographing lens, an exposure amount controller for controlling a light amount incident on the photographing lens, and controlling the exposure amount controller in accordance with a light measurement result by the light metering unit. And a control circuit unit, based on the measurement result by the photometric means,
When the fluctuation of the amount of light incident through the photographing lens lasts for a longer time than the preset time, the exposure amount control means is controlled in accordance with the fluctuation, and the fluctuation is limited to the time equal to or less than the predetermined time. An exposure control device that controls the exposure amount control means assuming that the fluctuation does not occur when it does not continue.