JP2801247B2 - Exposure control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic exposure device, and more particularly to a method for smoothly controlling an aperture.

(Background Art) In recent years, the development of video equipment such as video tape recorders (hereinafter abbreviated as VTRs) has been remarkable, and in particular, automatic exposure adjustment devices have become standard equipment, especially in camera-integrated VTRs. .

A conventional exposure control method in such a camera-integrated VTR will be described below with reference to FIG.

The amount of light incident from the optical system 1 is adjusted by an exposure adjusting mechanism (hereinafter referred to as an iris) 2 to form a subject image on an image sensor 3. The signal obtained from the image sensor 3 is input to a camera signal processing circuit 4 where it is subjected to processing such as gamma correction, separated into a luminance signal and a chrominance signal. Is converted into a television signal. The image luminance signal Y obtained before the gamma correction obtained by the camera signal processing circuit 4 is subjected to integration processing by an integrator 6 and an arithmetic unit 7 generates a difference signal from a reference value 8. The difference signal is used as an exposure control signal, and the driver 9 and the actuator 10 control the iris 2 (exposure adjusting aperture mechanism) so that the relationship between the output of the integrator 6 and the preset reference value 8 becomes constant. The opening amount is controlled.

(Problems to be Solved by the Invention) However, in the conventional control method, only the linear processing is performed on the aperture control signal, and the amount of movement of the actuator with respect to the amount of change in the aperture control signal is relative to the amount of iris aperture. And becomes smaller on the open side, and becomes larger if the aperture is narrowed down.

Therefore, considering the feedback system including the video signal, the loop gain of the feedback loop increases as the iris is narrowed down from the open state, and the loop gain of the feedback loop increases as the iris opens up from the narrowed down state. Will be lower. That is, when the aperture is close to the open side, the change in the amount of light is small even if the aperture of the aperture changes, but even when the aperture of the aperture slightly changes toward the small aperture, the image is captured. Since the brightness on the surface greatly changes, and the responsiveness of the feedback loop of iris control changes due to this change, the movement amount of the actuator tends to increase as the iris is narrowed down. This not only causes hunting on the small aperture side, but also causes a problem that aperture control is not performed smoothly.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and according to the invention described in claim (1), drives the diaphragm and drives the diaphragm. An aperture driving means for changing the exposure amount, a detecting means for detecting the position of the aperture and outputting it as aperture value information, and an aperture control signal for controlling the aperture driving means to drive the aperture. Control means for calculating, and aperture correction data set in advance for each of the plurality of aperture value information of the aperture, and aperture correction data corresponding to the aperture value information detected by the detection means to the control means. The exposure control apparatus further includes a correction unit that controls the change in the exposure state with respect to the driving amount of the aperture driving unit so as to be substantially constant by supplying and correcting the aperture control signal.

According to the invention described in claim (2) of the present application, there is provided a lens unit detachable from a camera body, the diaphragm, diaphragm driving means for driving the diaphragm to change an exposure amount, and Detecting means for detecting the position of the aperture and outputting it as aperture value information; and calculating an aperture control signal for driving the aperture by controlling the aperture driving means based on a control signal from the camera body. Control means, and aperture correction data set in advance for each of the plurality of pieces of aperture value information of the aperture, and supplying aperture correction data corresponding to the aperture value information detected by the detection means to the control means. The lens control unit corrects the aperture control signal in such a manner that the amount of change in the exposure state with respect to the driving amount of the aperture driving means is controlled to be substantially constant.

According to the invention described in claim (3) of the present application, there is provided a camera system including a camera body and a lens unit detachable from the camera body. A camera-side control unit for detecting a control signal regarding brightness and transmitting the control signal to the lens unit; an aperture, an aperture driving unit for driving the aperture and changing an exposure amount, on the lens unit side; Detecting means for detecting the position of the aperture and outputting it as aperture value information; and calculating an aperture control signal for driving the aperture by controlling the aperture driving means based on a control signal from the camera body. Control means; and aperture correction data set in advance for each of the plurality of aperture value information of the aperture, and aperture correction data corresponding to the aperture value information detected by the detection means. And a correction unit that controls the amount of change in the exposure state with respect to the driving amount of the aperture driving unit to be substantially constant by supplying the aperture control signal to the control unit and correcting the aperture control signal. Features.

(Operation) With this, in the feedback control system that controls the opening amount of the diaphragm based on the change in the amount of incident light passing through the diaphragm, it is possible to reversely correct the change caused by the change in the diaphragm value of the loop gain of the feedback loop. This makes it possible to keep the apparent loop gain constant regardless of the aperture value.

(Embodiment) Hereinafter, an embodiment in which the automatic exposure apparatus according to the present invention is shown in each drawing will be described in detail.

FIG. 1 is a block diagram showing a first embodiment of the automatic exposure apparatus according to the present invention.

In the figure, the same components as those of the above-described conventional example are denoted by the same reference numerals, and description thereof will be omitted.

A subject image formed on an imaging surface of an imaging device 3 such as a CCD from a lens optical system 1 via an iris 2 is photoelectrically converted by the imaging device 3 and output as an imaging signal. An image pickup signal is supplied to a signal processing circuit 4 and subjected to gamma conversion and the like, and a color signal C and a luminance signal Yγ are extracted as a video signal. It is output from the camera unit in the form of a signal or the like.

A luminance signal Y output from the camera signal processing circuit generates a control signal for controlling the iris 2 for obtaining an appropriate exposure according to the luminance state of the screen.
After being input to the integration circuit 6 and integrated, it is compared with a reference value 8 by an arithmetic unit 7 to generate a difference signal. This difference signal is supplied as an exposure control signal to an actuator 10 via a driver 9, and the iris 2 is controlled based on the difference signal so that the difference signal becomes constant.

On the other hand, the opening amount of the iris is detected by an iris encoder 11, the detected value is amplified to a predetermined level by a buffer amplifier 12, and then the iris control signal is corrected by a multiplier 13. This iris encoder 11,
The buffer amplifier 12 and the multiplier 13 constitute an inverse correction circuit for a change in the loop gain of the feedback loop of the iris control system which is a feature of the present invention.

Here, a general example of the optical characteristics of the iris 2 is shown in FIG. 2, where the relationship between the amount of movement of the iris driving actuator and the aperture value is non-linear, and is closer to the smaller aperture side. As the actuator moves slightly, the aperture value changes greatly. In other words, the loop gain of the feedback loop on the small-aperture side is increased, and the actuator is largely moved even with a small change in the light amount. It can be seen that hunting easily occurs. Curve A in FIG. 3 is a characteristic curve showing the relationship between the aperture value and the loop gain of the feedback loop for iris control.

In the present invention, on the premise of such conditions, the second
When using an iris with optical characteristics as shown in the figure,
The operation of the correction circuit for controlling the gain of the iris control system will be described.

The voltage output from the encoder 11 for detecting the aperture of the iris, that is, the aperture value, is input to the buffer amplifier 12, amplified at a predetermined amplification rate and given a predetermined bias, and then guided to the multiplier 13. I will The multiplier 13 takes the product of the difference signal from the reference value 8 output from the arithmetic unit 7 and the voltage output from the buffer amplifier 12 according to the aperture value. As described above, on the small aperture side, a change in the amount of light is large even for a slight change in the aperture value. As a result, the loop gain of the control system increases on the small aperture side.
Therefore, the output voltage of the buffer amplifier 12 is set so as to be large in the vicinity of the open state of the iris and to decrease as the iris is closed, so as to change according to the aperture value.

Since the output of the buffer amplifier 12 is multiplied by the amount of movement of the iris driving actuator 10, the amount of movement of the actuator becomes smaller as the amount of light changes greatly toward the small aperture side even if the movement is slight. And hunting hardly occurs. Output voltage of this buffer amplifier 12 (corresponding to the correction value of the movement amount of the actuator 10)
FIG. 4 shows the relationship between the aperture value and the aperture value.

That is, the voltage applied to the driver 9 varies depending on the aperture value of the iris 2 even when the light amount changes, and when the iris 2 is in the open state, the output voltage of the buffer amplifier 12 is large. Therefore, the amount of movement of the iris 2 increases.

On the other hand, since the output voltage of the buffer amplifier 12 decreases as the iris 2 is narrowed, the amplification factor is substantially reduced by multiplying the output voltage of the arithmetic unit 7 by the multiplier 13. Accordingly, the operation amount of the actuator 10 is corrected so as to be small.

This control operation will be further described with reference to FIG. FIG. 5 uses the aperture value of iris 2 as a parameter,
FIG. 4 is a characteristic diagram showing a relationship between an iris control output voltage of a calculator 7 and an actual movement amount of an actuator 10.

In the same figure, a computing unit 7 corresponding to the reference value 8
With reference to the output voltage and the movement amount of the actuator at this time, the increase and decrease from each reference value are indicated by positive and negative values.

According to the conventional iris control system having no correction system, the relationship between the output voltage of the arithmetic unit 7 and the amount of movement of the actuator does not always change, regardless of the aperture value, and is controlled in a fixed relationship. This characteristic is shown by a single characteristic curve drawn by a dashed line in FIG. Therefore, the curve must have a characteristic that guarantees stable operation without hunting even at the state of the smallest aperture.The slope of the curve becomes smaller, and as a result, the response becomes closer to the maximum aperture value. It turns out that it becomes slow.

On the other hand, according to the present invention, the above-described gain correction is applied to the output of the arithmetic unit 7 according to the aperture value, so that the relationship between the multiplier 7 and the actuator movement amount changes according to the aperture value. . That is, on the side where the aperture value is small, the slope of the characteristic curve is reduced by decreasing the gain, and the amount of movement of the actuator 10 with respect to the change in the output of the calculator 7 is reduced. This makes it possible to perform stable iris control without causing a hunting side even on the small aperture side.

Conversely, as the aperture value of the iris moves toward the open side, the gain is corrected so as to increase, so that the slope of the characteristic curve increases, and the actuator 10 responds to a change in the output of the arithmetic unit 7. It can be seen that the amount of movement increases. In other words, on the open aperture side where the sensitivity decreases,
Iris response is improved by increasing the loop gain.

Further, in the figure, for convenience of explanation, both the output of the arithmetic unit 7 and the movement amount of the actuator 10 are shown as drive characteristics in a minute range where linearity is maintained.

In this way, for the same change in the amount of light, the amount of movement is controlled to be large when the iris 2 is in the open state, and is controlled to decrease as the iris 2 is closed. As a result, the loop gain of the iris control feedback loop is reduced. , And becomes a substantially constant value as shown by a curve B in FIG. The moving amount of the iris driving encoder 10 has such a characteristic that it becomes smaller as it goes toward the smaller aperture as shown in FIG. 4 in the entire variable range of the aperture value.

With the above operation, in the feedback loop in which the iris control is performed based on the change in the video signal level obtained by photoelectrically converting the incident light whose light amount is controlled by the iris 2 by the image pickup device 3, the change in the loop gain with respect to the aperture value In this way, it is possible to perform the reverse correction and keep the apparent loop gain with respect to the aperture value constant, and perform the iris control smoothly regardless of the aperture value.
Stable control without hunting or the like can be performed.

Next, a second embodiment of the present invention will be described with reference to FIG.

This embodiment is an embodiment in which the present invention is applied to a case where a conversion lens is realized for a video camera or the like.

In the figure, the same components as those in FIG. 1 described above are denoted by the same reference numerals, and description thereof will be omitted. LS indicates a lens unit and a CM camera unit, respectively, and are connected by a mount part MT. Also, in this mount,
A data communication path 21 for exchanging data between the camera and the lens is formed by electric contacts (not shown). The communication between the camera unit CM and the lens unit LS is performed in synchronization with Vsync (vertical synchronization signal) for the sake of convenience corresponding to the television signal on the camera unit side.

In the camera unit CM, the configurations of the image pickup device 3, the camera signal processing circuit 4, the camera encoder 5, and the integrator 6 are the same as those in FIG. In this embodiment, the output of the integrator 6 is supplied to an image camera-side control microcomputer (hereinafter referred to as a camera microcomputer) 14 which has been converted into digital information via an A / D converter 16. The reference value 8 for iris control is also supplied to the camera microcomputer 14 via the A / D converter 18.

On the other hand, when it comes to the lens unit LS, a lens-side control microcomputer (hereinafter referred to as a lens microcomputer) 15 is provided, and an iris control calculated based on control information transmitted from the camera microcomputer 14 via the communication path 21 is provided. The data is supplied to the driver 9 via the D / A converter 17 to perform iris control.
The output signal of the buffer amplifier 12 that supplies correction data according to the aperture value detected by the iris encoder 11 is also converted to a digital signal by the A / D converter 16 and then supplied to the lens microcomputer 15. The above-described loop gain correction operation is performed by arithmetic processing in the lens microcomputer 15.

That is, according to the present embodiment, the correction circuit including the buffer amplifier 12 and the multiplier 13 of the first embodiment shown in FIG. 1 is performed by the lens microcomputer 15, and a part of the correction circuit is incorporated in the camera microcomputer 14. is there.

In the first embodiment, a predetermined amplification factor is set by adjusting the bias and the amplification factor, and the control signal is amplified by the multiplier 13. In this embodiment, the camera microcomputer is used without using the multiplier.
The video signal, the reference signal, and the encoder output signal, which have been converted into digital data by the A / D converters 16, 18, and 19, respectively, are input to the camera microcomputer 14 and the lens microcomputer 15, and are processed in the camera and the lens microcomputer. The calculation process in this case is the first
In addition to the linear processing same as that of the embodiment, the inverse correction can be performed even when the iris 2, the driver 9, the actuator 10, the iris encoder 11, the buffer amplifier 12, and the like have an element having a non-linear characteristic.

Hereinafter, FIG. 6 will be described in detail. As in the first embodiment, the video signal obtained by the integrator 6 is converted to an A / D converter 16.
Is input to the camera microcomputer 14 after digital conversion. The camera microcomputer 14 converts the reference voltage 8 into the A / D converter 1
The reference value digitally converted by 8
The calculation is performed in the same manner as in the embodiment.

The result calculated by the camera microcomputer 14 is the communication line
Communication is made to the lens microcomputer 15 through a predetermined procedure via 21.

The lens microcomputer 15 outputs the iris control data transmitted from the camera microcomputer 14 to the iris aperture value encoder 11 and amplifies the data to a predetermined amplification rate by the buffer amplifier 12 and converts the data into digital data by the A / D converter 17. The amplified signal is amplified to a predetermined amplification factor determined by the iris aperture information and output.

As described above, the amplification factor at this time may not be linear with respect to the iris aperture value. For example, as shown in FIG. 7, the aperture value is divided into areas and a gain corresponding to the aperture value is used. What is necessary is just to amplify. The number of divided areas and the gain can be appropriately selected according to the characteristics of an iris and an encoder to be used, and may be stored as a data table in the lens microcomputer 15 in advance.

 Other processes are the same as in the first embodiment.

FIG. 8 is a flowchart for explaining the operation of the second embodiment.

First, as processing on the camera side, # 1: the output obtained by integrating the luminance signal output by the camera signal processing circuit 4 by the integration circuit 6 is converted into a digital signal by the AD converter 16 and taken into the camera microcomputer 14.

♯2: The reference level is converted into a digital signal by the AD converter 18 and taken into the camera microcomputer 14.

♯3: The camera microcomputer 14 calculates (integrated value of video signal−reference level).

♯4: Wait until input timing of a predetermined Vsync (video vertical synchronization signal).

♯5: Set chip select signal.

# 6: The iris data is converted from parallel to serial and transmitted from the camera side to the lens side via the communication path 21.

♯7: Reset chip select signal.

Thus, transmission of one packet of the iris control information to the lens is completed. This transmission is periodically repeated.

Next, the processing on the lens unit LS side performed based on the data transmitted from the camera side will be described.

♯8: Check chip select input.

# 9: The iris data is taken into the lens microcomputer 15 by the serial-parallel conversion.

Step # 10: At the same time, after the aperture value detected by the iris encoder 11 is amplified to a predetermined level by the buffer amplifier 12, the data converted into digital data via the A / D converter 19 is taken into the lens microcomputer 15.

♯11: The lens microcomputer 15 collates the received aperture value data with a conversion table pre-configured in the lens microcomputer 15 to obtain iris drive data, and supplies the iris correction data supplied from the A / D converter 19. The data is referred to a correction table for the aperture value and the gain shown in FIG. 7 to determine a correction value, and the iris drive data is corrected based on the correction value.

♯12: The corrected iris drive data is supplied to the D / A converter 17.

By repeating the above control flow at a predetermined cycle, communication of control information is performed between the camera unit and the lens unit, whereby various controls including iris control are executed.

Hereinafter, as described above, on the lens side, the output of the encoder 11 that detects the aperture value is supplied to the lens microcomputer 15 via the buffer amplifier 12 and the A / D converter 19, and the first embodiment differs from the first embodiment. Similarly, an operation of correcting the loop gain of the feedback loop for iris control to a constant value is performed. In this embodiment, the same control operation as in the first embodiment is performed except that the processing is performed in the microcomputer.

FIG. 9 is a characteristic curve showing the relationship between the aperture value and the loop gain before and after the correction of the iris control loop. FIG. 10 is a diagram showing the case where the iris control is performed by using a data table in the lens microcomputer 15. 9 is a characteristic curve showing a relationship between an aperture value and an output of the buffer amplifier 12 (an output of the A / D converter 19, which corresponds to a correction value of the actuator 10). First Embodiment of Analog Control (FIG. 3, FIG.
(Fig.), The actuator movement amount for each aperture value,
It can be seen that the correction of the loop gain is controlled by discrete values.

According to the present embodiment, since an information table for iris control and correction can be formed on the lens microcomputer side, in the case of an interchangeable lens, control information corresponding to the characteristics of each iris is provided for each lens. It is a very effective means of compatibility because it can be prepared for a complete expression.

(Effects of the Invention) As described above, according to the exposure control device of the present invention, a specific aperture, a specific aperture,
In accordance with the characteristics of the aperture drive actuator and the aperture value detection encoder, the control system has a reverse characteristic correction system that corrects the nonlinearity based on the aperture value of the loop gain of the control system, regardless of the aperture value. In addition, a substantially constant loop gain can be obtained, the drive characteristics greatly differ depending on the aperture value, and operability is not deteriorated. In particular, hunting on the small aperture side can be prevented, and the operation is smooth and stable. Aperture control can be realized.

Also, by programming the correction characteristics of the aperture control system in advance on a table in the microcomputer, the aperture control can be smoothly performed, and even when the lens is formed into an interchangeable lens as in the above-described second embodiment, It is only necessary to store control and correction data on the lens unit side in accordance with the characteristics of the aperture lens optical system, which has a great effect on lens compatibility.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention, FIG. 2 is a diagram showing characteristics of an iris used in the embodiment of the present invention, and FIG. 3 is an iris control system in the embodiment of the present invention. FIG. 4 is a diagram showing the characteristics of the iris correction system in the embodiment of the present invention, and FIG. 5 is a relationship between the control voltage of the arithmetic unit and the movement amount of the iris control actuator in the embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of the second embodiment of the present invention. FIG. 7 is a diagram showing a data table for explaining the iris control operation of the second embodiment. 9 is a flowchart for explaining the operation of the second embodiment of the present invention. FIG. 9 is a diagram showing characteristics of an iris control system in the embodiment of the present invention. FIG. 10 is an iris correction system in the embodiment of the present invention. Diagram showing the characteristics of FIG. 11, FIG. Is a block diagram showing an exposure control device in a conventional VTR.

Claims (3)

(57) [Claims] An aperture driving means for driving the aperture to change an exposure amount; a detecting means for detecting a position of the aperture and outputting it as aperture value information; and controlling the aperture driving means. Control means for calculating an aperture control signal for driving the aperture, and aperture correction data preset for each of a plurality of pieces of aperture value information of the aperture, and aperture value information detected by the detection means. Correction means for supplying aperture correction data corresponding to the above to the control means and correcting the aperture control signal so as to control the amount of change in the exposure state with respect to the drive amount of the aperture drive means to be substantially constant; and An exposure control device, comprising: 2. A lens unit detachable from a camera body, an aperture, aperture driving means for driving the aperture to change an exposure amount, and detecting a position of the aperture to obtain aperture value information. Detecting means for outputting, based on a control signal from the camera body side, controlling means for controlling the aperture driving means to calculate an aperture control signal for driving the aperture, and a plurality of aperture values of the aperture By providing preset aperture correction data for each piece of information, by supplying aperture correction data corresponding to aperture value information detected by the detection means to the control means, and correcting the aperture control signal, A correction unit that controls the amount of change in the exposure state with respect to the drive amount of the aperture drive unit to be substantially constant. 3. A camera system comprising a camera body and a lens unit detachable from the camera body, wherein a control signal relating to brightness for controlling an aperture is detected on the camera body side. A camera-side control unit for transmitting to the unit, an aperture, an aperture driving unit for driving the aperture to change an exposure amount, and detecting a position of the aperture on the lens unit side, and detecting aperture position information as aperture value information. Detecting means for outputting, control means for calculating an aperture control signal for driving the aperture by controlling the aperture driving means based on a control signal from the camera body, and a plurality of aperture values of the aperture Aperture correction data set in advance for each piece of information is provided, and aperture correction data corresponding to the aperture value information detected by the detection means is supplied to the control means. Camera system comprising by correcting the aperture control signal, that the variation in the exposure state with respect to the drive amount of the diaphragm driving means and a correction means controlled to be substantially constant.