JPH06205286A - Exposure controller for electronic camera - Google Patents

Abstract

PURPOSE:To provide the exposure controller for the electronic camera in which consecutive exposure is controlled even when an iris with an aperture stepwise varied by means of a stepping motor is employed. CONSTITUTION:An electric signal read from a CCD 14 is outputted to an AE microcomputer 16 and an AGC amplifier 22. The AE microcomputer 16 obtains a brightness of an object from the received electric signal and calculates number of steps for driving a stepping motor 20 based on a difference between the obtained brightness of object and the brightness of object corresponding to a current iris aperture. Number of pulse signals by the step number is outputted to a drive circuit 18 to drive the stepping motor 20 thereby controlling an iris 12. Thus, stepwise exposure is controlled over a brightness change per one step of the stepping motor. On the other hand, when the difference gets smaller, a gain control signal is outputted to an AGC amplifier 22 to control the amplification factor of the electric signal. Thus, much delicate exposure control is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure control device for an electronic camera, and more particularly to controlling the amount of incident light incident on an image pickup device stepwise, and performing fine adjustment and brightness of an object after the stepwise control. The present invention relates to an exposure control device for an electronic camera that automatically makes adjustments according to subtle changes.

[0002]

2. Description of the Related Art An exposure control device for a conventional electronic camera (especially a movie) automatically controls exposure so that an image having a constant brightness can be obtained regardless of the brightness of a subject. The aperture of the diaphragm is continuously adjusted by current control (meter system) so that proper exposure is achieved. When the light quantity of the subject is insufficient, an image sensor (CCD)
The gain of the amplifier for automatic gain control (AGC) is adjusted so that the signal level of the electric signal converted by the above becomes a standard set value.

In addition, in an electronic camera capable of shooting both movies and still images, there has been proposed an electronic camera in which a diaphragm aperture is adjusted by driving a stepping motor (Japanese Patent Laid-Open No. 63-61569). ).

[0004]

By the way, in the case of adding a function capable of still photography to a movie, and taking print production from the movie into consideration, a stepping mode can be used to accurately determine the aperture opening. It is advantageous to use a diaphragm driven by a motor. On the other hand, when an electronic camera disclosed in Japanese Patent Laid-Open No. 63-61569 is used to take a picture of a movie, the driving of the stepping motor is overshot and the aperture of the diaphragm is stepped. Change in the image level is unnatural. Further, there is a drawback that hunting occurs when the subject brightness slightly changes or when the proper exposure is in the middle of the steps.

The present invention has been made in view of such circumstances, and even if a diaphragm in which the aperture of the diaphragm changes stepwise by a stepping motor is used, the change in the brightness level of the image becomes unnatural and hunting is prevented. An object of the present invention is to provide an exposure control device for an electronic camera that does not occur.

[0006]

In order to achieve the above object, the present invention provides an exposure control device for an electronic camera having an aperture whose aperture opening changes stepwise every time the stepping motor is driven step by step. In the above, the detecting means for detecting the subject brightness, and the aperture control for calculating the driving step number of the stepping motor according to the subject brightness detected by the detecting means and driving the stepping motor by the calculated step number. Means, a variable amplifier for amplifying an electric signal output from the image sensor, and a proper exposure based on a difference between a target aperture value corresponding to the subject brightness and the aperture value controlled stepwise by the aperture control means. And a gain control means for controlling the gain of the variable amplifier so that

[0007]

According to the present invention, the diaphragm control means calculates the driving step number of the stepping motor based on the object brightness detected by the detecting means, and drives the stepping motor by the step number. Further, the gain of the variable amplifier for amplifying the electric signal output from the image pickup device is controlled based on the difference between the target aperture value corresponding to the subject brightness and the aperture value controlled stepwise by driving the stepping motor. . In this way, the aperture is controlled stepwise by driving the stepping motor, and the exposure adjustment between each step is performed by controlling the gain of the variable amplifier. Aperture value of

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an exposure control device for an electronic camera according to the present invention will be described in detail below with reference to the accompanying drawings.
FIG. 1 is a block diagram of an essential part showing an embodiment of an exposure control device for an electronic camera according to the present invention. In the figure, the subject light is transmitted through the taking lens 10 and the diaphragm 12 to the image sensor (CC
D) An image is formed on the light receiving surface of 14. The diaphragm 12 is driven by the stepping motor 20, and the diaphragm opening changes stepwise every time the stepping motor 20 is driven step by step.

The CCD 14 accumulates charges of incident light and reads the accumulated charges in synchronization with a timing pulse applied from a timing generator (not shown). The electric signal read from the CCD 14 in this manner is output to the AE microcomputer 16 and the AGC amplifier 22. The AE microcomputer 16 is based on the input electric signal, at regular intervals,
For example, the subject brightness is obtained every (1/60) seconds, and the number of steps for driving the stepping motor 20 is calculated based on the difference between the subject brightness and the subject brightness corresponding to the current aperture opening. Then, a pulse signal is output to the drive circuit 18 by the calculated number of steps to drive the stepping motor 20 to control the diaphragm 12. As a result, the stepwise aperture control is performed in a step amount equal to or larger than the luminance change amount per step of the stepping motor 20.

As shown in FIG. 2, a stepping motor 20 is provided.
The gain of the AGC amplifier 22 is controlled in order to perform the exposure adjustment within the luminance change amount per step (arrow A). The detailed operation of the AE microcomputer 16 will be described later. The electric signal whose gain is controlled by the AGC amplifier 22 is
After the signal processing circuit 24 performs predetermined signal processing, the signal is output to the recording device 26 as a video signal.

Next, the detailed operation of the AE microcomputer 16 will be described with reference to the flowchart of FIG.
First, when the exposure control is started every predetermined period (step 100), the photometric value is calculated based on the electric signal from the CCD 14 (step 102). Subsequently, the deviation is obtained by subtracting the photometric value (current aperture value) corresponding to the current aperture opening from the calculated photometric value (target aperture value) (step 104). When the absolute value of the deviation is equal to or more than the brightness change amount X per step of the stepping motor, that is, when the aperture control for driving the stepping motor is required (step 10).
6) First, the AGC amplifier 22 is initialized (step 106). Furthermore, when the deviation is zero or more (step 11
2) The deviation is divided by the brightness change amount X, and the maximum integer value that does not exceed the result is set as the stepping motor driving step number n (step 114). On the other hand, when the deviation is less than zero (step 112), the deviation is divided by the luminance change amount X, and a value obtained by adding 1 to the maximum integer value which does not exceed the result is set as the stepping motor driving step number n (step). 116). Then, the pulse signal of the stepping motor driving step number n is output to the drive circuit 18. still,
When the integer value is positive, for example, the stepping motor 20 is normally rotated to move the diaphragm 12 in the closing direction, and when it is negative, the stepping motor 20 is reversed to move the diaphragm 12 in the opening direction. Let

On the other hand, when the absolute value of the deviation becomes smaller than the luminance change amount X (step 106), a gain control signal is output to the AGC amplifier 22 to electrically compensate the deviation (step 108). A specific numerical value will be described below.
Subject brightness is 11.8 EV (target value of step 104)
And the brightness change amount per step is (1/12)
Stepping mode which is EV (deviation of step 104)
Consider the case of shooting with an exposure control device having an aperture driven by a camera. Assuming now that, for the sake of simplicity, the proper exposure when shooting a 12EV subject is obtained at the position of m steps, the proper exposure for a 11.8EV subject is (m-3 ) Step and (m-2) step are almost in the middle.

As described above, the EV corresponding to the step (m-3) in the case of the change from the low luminance side and the EV corresponding to the step (m-2) in the case of the change from the high luminance side. The diaphragm is controlled so that the value becomes the value, and the diaphragm control is stopped. Therefore, when the diaphragm stops at step (m-2), the EV value controlled by this diaphragm is 1
Since it is 1.83 EV, the deviation from the target value (11.8 EV) is 0.03 EV. That is, the AE microcomputer 16
Is set so that the signal level of the electric signal output from the CCD 14 is reduced by 0.03 EV by making it bright.
The gain of the C amplifier 22 is controlled.

Similarly, when the diaphragm is stopped in (m-3) steps, the EV value controlled by this diaphragm is 11.75 EV, so the target value (11.8 EV).
The deviation from and is 0.05 EV. That is, AE microcomputer 1
No. 6 is set so that the signal level of the electric signal output from the CCD 14 is increased by 0.05 EV corresponding to the brightness.
It controls the gain of the GC amplifier 22.

In the above embodiment, the subject brightness is measured based on the electric signal from the CCD 14,
Not limited to this, the photometry may be performed by another photometric means.

[0016]

As described above, according to the exposure control device for an electronic camera of the present invention, continuous exposure control is performed despite stepwise control of the aperture opening by driving a stepping motor. Is possible. Therefore, absolute brightness can be obtained in still and movie.
Further, in the movie, the brightness of the screen does not change stepwise, and the screen does not flicker due to hunting accompanying a slight change in the amount of light.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an exposure control device for an electronic camera according to the present invention.

FIG. 2 is an explanatory view showing a change in brightness due to the aperture 12 of FIG.

FIG. 3 is a flowchart showing a detailed movement of the AE microcomputer 16 of FIG.

FIG. 4 is an explanatory diagram showing a specific operation of the embodiment of FIG.

[Explanation of symbols]

 12 ... Aperture 14 ... Image sensor (CCD) 16 ... AE microcomputer 18 ... Drive circuit 20 ... Stepping motor 22 ... AGC amplifier

Claims (1)

[Claims] 1. An exposure control device for an electronic camera having a diaphragm in which a diaphragm aperture changes stepwise every time the stepping motor is driven step by step, the detecting means detecting object brightness, and the detecting means detecting the brightness. A diaphragm control means for calculating the number of driving steps of the stepping motor according to the subject brightness and driving the stepping motor by the calculated number of steps, and a variable amplifier for amplifying an electric signal output from the image sensor. And gain control means for controlling the gain of the variable amplifier so as to obtain proper exposure based on the difference between the target aperture value corresponding to the subject brightness and the aperture value controlled stepwise by the aperture control means. An exposure control device for an electronic camera, comprising: