JP3041859B2 - Imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus that automatically controls an aperture value and AGC controls a level of an image pickup signal.

[Conventional technology]

2. Description of the Related Art As an imaging device such as a television camera, a device that includes an automatic aperture control device and an AGC circuit and that automatically controls an imaging signal to an appropriate level is known. FIG. 2 shows an example of such a conventional imaging device.

The imaging light passing through the lens 1 and the aperture 2 is incident on a solid-state imaging device 3 such as a CCD. On the light receiving surface of the solid-state imaging device 3, a color filter of three primary colors or complementary colors is provided. The signal component of each pixel of the solid-state imaging device 3 is supplied to the sample and hold circuit 4, and the sample and hold circuit 4 outputs an imaging signal at the timing of raster scanning.

This imaging signal is supplied to the AGC amplifier 5 and the detection circuit 6. From the detection circuit 6, an average value of the imaging signal is extracted. The output signal of the detection circuit 6 is supplied to the comparison circuit 7,
A comparison output corresponding to the difference between the average value of the imaging signal and the reference voltage source 8 is formed from the comparison circuit 7, and the value of the diaphragm 2 is controlled by the comparison output. Although not shown, the value of the aperture 2 is controlled by an aperture control motor. As the level of the imaging signal increases, the value of the aperture 2 increases, and the imaging signal output from the sample and hold circuit 4 is controlled to a predetermined signal level or lower.

The output signal of the AGC amplifier 5 is taken out as an imaging output and supplied to the detection circuit 9. Detection circuit 9 to AG
An average value of the output signal of the C amplifier 5 is obtained, and the average value and the reference voltage source 10 are supplied to the comparison circuit 11. Comparison circuit 11
Generates a control signal for controlling the gain of the AGC amplifier 5.

In an imaging apparatus in which automatic aperture control and AGC control are applied to an image signal, aperture control is usually given priority over AGC control in order to improve the S / N of the image signal.
That is, even if the aperture 2 is opened to the maximum, when the subject is dark and the amount of light is insufficient, the gain of the AGC amplifier 5 is controlled to increase.

[Problems to be solved by the invention]

The conventional imaging device shown in FIG.
In order to control the AGC amplifier 5, the detection circuits 6, 9, the comparison circuits 7, 10, and the reference voltage sources 8, 11 are required, respectively, and the circuit configuration has a disadvantage that the circuit configuration is complicated.

In order to solve such a problem, the present applicant has already proposed an imaging device capable of controlling an aperture and an AGC amplifier with one control signal as shown in Japanese Patent Application No. 63-208825. I have.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved imaging device of the type proposed above.

[Means for solving the problem]

The present invention has a diaphragm for limiting the amount of incident light incident on an image sensor, and a variable gain control circuit for correcting a signal level of an image signal from the image sensor, and a level of an output signal of the variable gain control circuit. In the imaging apparatus, the output of the variable gain control circuit is compared with a reference value, and the output of the variable gain control circuit is compared with a reference value. And a variable gain control circuit for controlling the aperture with the output of the integration circuit for the aperture control signal, and the variable gain control with the output of the integration circuit for the variable gain control circuit. When the subject is bright, the gain of the variable gain control circuit is fixed and the amount of incident light is controlled by the aperture. When the subject is dark, the control circuit of the variable gain control circuit is controlled. Forming a flop is obtained to perform the control of the signal level by the variable gain control circuit.

[Action]

A position detector is provided in connection with the stop 2, and a detection signal of a level corresponding to the state of the stop 2 is obtained from the position detector. Based on this detection signal, a predetermined opening range, for example, a maximum open state is detected. Until this detection is performed, the variable gain control circuit 5 is fixed so as to have the minimum gain.
Therefore, the aperture control is given priority over the gain control.
When the diaphragm 2 is fully opened, a gain control signal corresponding to the level of the imaging signal is supplied to the variable gain control circuit 5. Thereby, the level of the imaging signal is maintained at an appropriate level.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a lens system, 2 denotes an aperture, and 3 denotes a solid-state imaging device such as a CCD. A position detector 21 for detecting the opening state of the diaphragm 2 is provided. Although not shown, the aperture state of the aperture 2 can be controlled by a motor, and an aperture control signal SC1 is supplied to the motor. As the aperture stop 2 is opened from the position detector 21, a detection signal whose level increases is obtained. Position detecting element 21
For example, a magnet provided in connection with a motor for changing the aperture and a Hall element arranged in close proximity to the magnet can be used.

The output signal of the solid-state imaging device 3 is applied to a sample-and-hold circuit 4
, And an image pickup signal is output from the sample and hold circuit 4 at the timing of raster scanning. The output signal of the sample hold circuit 4 is supplied to the AGC amplifier 5. The gain of the AGC amplifier 5 is controlled by the AGC control signal SC2 so that the output signal has a predetermined level. The output signal of the AGC amplifier 5 is output as an image signal and supplied to the A / D converter 22. The output signal of A / D converter 22 is integrated circuit 2
Supplied to 3. The integration circuit 23 digitally integrates the imaging signal converted into a digital signal, and an output signal corresponding to an average value of the imaging signal is obtained from the integration circuit 23.

The output signal of the integration circuit 23 is supplied to the subtraction circuit 24, and is subtracted from the reference data REF2 from the reference data generation circuit 25.
The subtraction circuit 24 is provided for comparing the output signal of the integration circuit 23 with the reference data REF2 from the reference data generation circuit 25. The output signal of the subtraction circuit 24 is supplied to the integration circuits 26 and 27.

The output signal of the integration circuit 26 is supplied to the D / A converter 28, and the A / D
An analog aperture control signal SC1 is generated from the converter 28, and the aperture control signal SC1 is supplied to a control motor (not shown) of the aperture 2. The output signal of the integration circuit 27 is supplied to one input terminal b of the switch circuit 29. Switch circuit 29
The reference data REF1 from the reference data generation circuit 30 is supplied to the other input terminal a. The output signal of the switch circuit 29 is supplied to the D / A converter 31, and the analog AGC control signal SC2 from the D / A converter 31 is supplied to the AGC amplifier 5. When the reference data REF1 is supplied to the AGC amplifier 5 as the control signal SC1, the AGC amplifier 5 is set to have the minimum value of the gain change range.

The switch circuit 29 is controlled by an output signal of the comparison circuit 32. The output signal of the position detector 21 is supplied to one input terminal of the comparison circuit 32, and the reference voltage source 33 is supplied to the other input terminal. The value of the reference voltage source 33 is set to be equal to the level of the detection signal when the diaphragm 2 is opened at the maximum. The comparison circuit 32 generates a binary output signal according to the magnitude relationship between the detection signal and the reference voltage source 33. That is,
When the relationship (detection signal <reference voltage source 33) is satisfied, the switch circuit 29 selects the input terminal a. When the relationship is (detection signal ≧ reference voltage source 33), the switch circuit 29 selects the input terminal b. I do.

In the above-described embodiment, the level of the output signal of the position detector 21 increases as the aperture 2 is opened, and the output signal of the comparison circuit 32 is inverted when the aperture 2 is fully opened. Therefore, when the subject is bright, the switch circuit 29 selectively supplies the reference data REF1 on the input terminal a side to the D / A converter 31, so that the gain of the AGC amplifier 5 is fixed to the minimum value. In this state, the aperture 2 is controlled by the aperture control signal SC1 corresponding to the output signal of the subtraction circuit 24, so that the aperture control operation is given priority over the AGC operation.

When the light amount of the subject is small and the aperture 2 is fully opened, the output signal of the comparison circuit 32 is inverted, and the switch circuit 29 selects the input terminal b. Therefore, the AGC operation is performed, and the average level of the imaging signal is held at a predetermined level.

In the above embodiment, the AGC is performed until the throttle is fully opened.
Although the gain of the amplifier 5 is fixed, the gain of the AGC amplifier 5 may be controlled from a state slightly before the fully open state. Further, the control signal of the aperture 2 or the AGC amplifier 5 is not limited to being formed according to the average value of one image.
One image may be divided into a plurality of regions, an average value of the imaging signals of each region may be obtained, and weighting may be performed according to the region. For example, by increasing the weight of the average value in the central region, the adverse effect due to backlight may be removed. Further, digital control may be performed by software processing of a microcomputer. Of course, the control signal for the aperture and the AGC amplifier may be formed by an analog circuit.

〔The invention's effect〕

According to the present invention, the gain of the AGC amplifier is fixed to the minimum value until the aperture is sufficiently opened, so that the aperture control operation is given priority over the AGC operation. Further, according to the present invention, since the aperture and the AGC amplifier are controlled by one control signal, there is an advantage that the circuit configuration is simple. Further, the present invention has separate integrating circuits for the aperture control signal and the AGC amplifier control signal, respectively.
The gain of the amplifier is fixed and the amount of incident light is controlled by the aperture. When the subject is dark, a control loop of the AGC amplifier is formed to control the signal level by the AGC. This simplifies the circuit configuration by sharing the comparison circuit for the aperture control and the control of the AGC amplifier, and has the effect of selecting an integration circuit having the optimum characteristics for each control. Have.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of a conventional imaging apparatus. Description of main reference numerals in the drawings 2: aperture, 3: solid-state imaging device, 5: AGC amplifier, 21: position detector, 29: switch circuit, 32: comparison circuit.

────────────────────────────────────────────────── ─── Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 5/222-5/257

Claims (1)

(57) [Claims] A variable gain control circuit for correcting a signal level of an image signal from the image sensor; and an output signal of the variable gain control circuit. An imaging device configured to control the aperture and the gain of the variable gain control circuit based on the level of the variable gain control circuit. And an integration circuit for the variable gain control circuit, and the aperture is controlled by the output of the integration circuit for the aperture control signal. The output of the integration circuit for the variable gain control circuit is output by the integration circuit for the variable gain control circuit. When the subject is bright, the gain of the variable gain control circuit is fixed and the amount of incident light is controlled by the aperture. When the subject is dark, the variable gain control circuit is controlled. An imaging apparatus, wherein a control loop of a control circuit is formed to control a signal level by the variable gain control circuit.