JP2000299822A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically switch a shutter speed in response to illuminance of an object while keeping stability of the lightness of an image in a fluorescent light flicker prevention mode. SOLUTION: A CPU 18 of this image pickup device sets an AGC gain variable GC so as to make photometry data DT constant on the basis of photometry data DT from a photometry circuit 17 to control an automatic gain control circuit 14. Furthermore, when a combination between a shutter speed variable ST and the AGC gain variable GC satisfies a switching condition, the dynamic range of the illuminance of the object to activate automatic gain control for stabilizing the lightness of the image is extended by selecting the shutter speed variable ST from a 1st shutter speed (1/50 sec) to a 2nd shutter speed (1/100 sec) or vice versa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, and more particularly to a technique for switching the shutter speed of an electronic shutter in an image pickup device for preventing flicker of fluorescent light.

[0002]

2. Description of the Related Art It is well known that in a situation where the field frequency of an image pickup apparatus is different from the frequency of a commercial power supply, an image is picked up under a fluorescent light and a fluorescent light flicker occurs. For example, in the case of an imaging device having a field frequency of 60 Hz, when imaging is performed under a fluorescent lamp in an area where the commercial power frequency is 50 Hz, fluorescent lamp flicker occurs. When the commercial power frequency is 50 Hz, the fluorescent lamp repeats blinking at 100 Hz. Since the fluorescent lamp blinking frequency of 100 Hz is not an integral multiple of the field frequency of 60 Hz, the amount of light incident on the solid-state imaging device fluctuates during one field period, and fluorescent lamp flicker occurs. Therefore, when fluorescent lamp flicker occurs, a method of fixing the electronic shutter speed to 1/100 sec is adopted. Expressing this electronic shutter speed in terms of frequency is 10
0 Hz. This is referred to as “frequency description electronic shutter speed” in this specification. Since the electronic shutter speed of 100 Hz described in the frequency description is synchronized with the fluorescent lamp blinking frequency of 100 Hz, no matter how the phase of the electronic shutter operation is shifted from the phase of the fluorescent lamp blinking, the fixed electronic shutter speed is 1/1/3. The amount of light incident on the solid-state imaging device during 100 seconds is kept constant, so that flicker of the fluorescent lamp does not occur. For such background art, for example, JP-A-5-91373 and JP-A-6-125495 can be referred to. However, the techniques disclosed in these publications are not related to the problem to be solved by the present invention.

Here, 1/100 of the electronic shutter speed is used.
Consider sec. Commercial power frequency is 50Hz
In order to prevent the flicker of the fluorescent lamp at the time of (1), it is conceivable to set the electronic shutter speed to 1/200 sec or 1/50 sec in addition to 1/100 sec corresponding to the fluorescent lamp blinking frequency of 100 Hz. But,
1/200 sec is too fast, and the amount of light incident on the solid-state imaging device is insufficient, so that it is difficult to adopt. 1 / 50se
In the case of c, if the field frequency is 60 Hz, it becomes physically impossible. This is because the electronic shutter speed cannot be made larger (slower) than one field cycle. Therefore, generally, the commercial power frequency is 50 Hz.
In this case, 1/100 sec is set as the electronic shutter speed for preventing the flicker of the fluorescent lamp.

[0004] Now, a description of the related art related to the present invention will be given. In recent years, in order to input an image to an information processing device such as a personal computer, 30 Hz
Driven imaging devices have been developed. It is different from the NTSC system that displays in the interlaced system.
30Hz moving image display has become mainstream, and 30Hz
This is because a non-interlaced drive can sufficiently recognize a moving image. Therefore, an imaging device driven at 30 Hz corresponding to the frame frequency in the NTSC system is used.

[0005] In an imaging apparatus driven at 30 Hz, a commercial power supply frequency of 60 Hz at which a fluorescent lamp blinking frequency is 120 Hz is used.
No fluorescent lamp flicker occurs in imaging in the area z. This is because 120 Hz is an integral multiple of the field frequency of 30 Hz. However, the flickering frequency of the fluorescent lamp in a region where the commercial power supply frequency is 50 Hz is 100 Hz, which is not an integral multiple of 30 Hz of the field frequency of the image pickup device, so that fluorescent lamp flicker occurs.

In order to prevent the flicker of the fluorescent lamp, a mode in which the electronic shutter speed is fixed to 1/100 sec or 1/50 sec is provided even in an imaging apparatus driven at 30 Hz.

As described above, there is a restriction that the electronic shutter speed described in the frequency cannot be made larger (slower) than the one-field cycle. However, in the case of an imaging device driven at 30 Hz, the one-field cycle is 1/1. 30Hz
Therefore, as the electronic shutter speed for preventing the flicker of the fluorescent lamp, 1/5
0 sec can be adopted. The electronic shutter speed of 50 Hz in the frequency description is one of the fluorescent lamp blinking frequencies.
Since the frequency is an integral multiple of 00 Hz, it is possible to prevent fluorescent lamp flicker. When the electronic shutter speed is set to 1/50 sec, the amount of incident light is increased as compared with the case of 1/100 sec, and there is an advantage that the S / N ratio is improved.

Here, the mechanical aperture mechanism of the imaging lens will be described. What is described here has nothing to do with flicker flicker prevention for the time being.
When the subject moves fast, the electronic shutter speed is increased. In this case, since the exposure time in the solid-state imaging device is shortened, the S / N ratio of the image tends to decrease. Therefore, when the electronic shutter speed is high, it is preferable to increase the aperture of the aperture mechanism as much as possible. Conversely, when the movement of the subject is slow or stationary, the electronic shutter speed is reduced. In this case, since the exposure time in the solid-state imaging device becomes longer, the S / N ratio of the image is improved. However, when the subject is too bright, the solid-state imaging device may be electronically saturated and the image may be whitish. In such a case, it is preferable to limit the amount of incident light by reducing the aperture of the aperture mechanism.

The relationship between the prevention of flicker of fluorescent light and the mechanical diaphragm mechanism will now be described. In an imaging apparatus driven at 30 Hz, when the electronic shutter speed is fixed to 1/100 sec in order to prevent flicker of fluorescent light, it is preferable to increase the opening amount of the mechanical diaphragm mechanism in view of the decrease in the amount of incident light. . When the electronic shutter speed is fixed to 1/50 sec, it is preferable to make the aperture of the aperture mechanism smaller as the subject becomes brighter.

In recent years, in order to reduce the cost of the main body of the image pickup apparatus, a mechanical diaphragm mechanism has been eliminated, and an image pickup apparatus configured to perform exposure control only with an electronic shutter built in a solid-state image pickup device. Equipment research is ongoing.

In an image pickup apparatus without such a mechanical aperture mechanism, a solid-state image sensor is used as a measure for keeping the brightness of an image constant irrespective of a change in illuminance of a subject when preventing flicker of fluorescent light. Automatic gain control (AGC: Auto Gain Control) for the signal output from the image sensor
It is conceivable to devise it.

The relationship between the illuminance of the subject, the AGC gain, and the image brightness in the automatic gain control will be considered below. Here, the image brightness may be regarded as an average luminance value over the entire surface of the solid-state imaging device.

When the illuminance of the object is low, the signal obtained by the solid-state imaging device is greatly amplified by setting the AGC gain to a high value, and as a result, the image brightness is maintained at a required level. Conversely, when the illuminance of the subject is high, the degree of amplification of the signal obtained by the solid-state imaging device is suppressed by setting the AGC gain low, and as a result, the image brightness is maintained at a required level. As a general tendency, in a certain range of the subject illuminance, the image brightness can be kept constant by adjusting the AGC gain in a state in inverse proportion to the subject illuminance.

[0014]

In an image pickup apparatus which does not have the above-mentioned mechanical diaphragm mechanism and performs automatic gain control also for preventing flicker of fluorescent light, the brightness of an image is controlled irrespective of the fluctuation of the illuminance of the object. It can be made constant only when the subject illuminance is within a certain range, and there is a limit to the applicable subject illuminance range.

FIG. 13A shows the relationship between the illuminance of the subject and the AGC gain in a mode in which 1/50 sec is selected and fixed as the electronic shutter speed in order to prevent flicker of the fluorescent lamp.
FIG. 13B shows the relationship between the subject illuminance and the image brightness.
Shown in Also, 1 / 100s as the electronic shutter speed
ec and illuminance and AGC in fixed mode by selecting ec
FIG. 14A shows a relationship between gains, and FIG. 14B shows a relationship between subject illuminance and image brightness.

In the mode in which the electronic shutter speed is 1/50 sec, the exposure time of the image sensor is long and the amount of incident light is relatively large, so that the illuminance of the subject is the same as in the mode in 1/100 sec. Then, the AGC gain may be lower. Electronic shutter speed 1/50 sec
13A when the characteristic line CL11 of the AGC gain of FIG. 13A is the electronic shutter speed of 1/100 sec.
(A) is closer to the lower illuminance side than the AGC gain characteristic line CL12.

There is naturally a limit to the AGC gain in automatic gain control. The upper limit is the gain upper limit value AGCMAX
And The lower limit is zero.

First, the electronic shutter speed is 1/50 sec.
The state in the mode c will be discussed based on FIGS. 13 (a) and 13 (b). In this mode, the subject illuminance H is H11
The automatic gain control is set to operate in the range of ≤H≤H13. Since the substantial exposure time of the image sensor is as long as 1/50 sec, the amount of incident light is relatively large. Therefore, the subject illuminance range in which the automatic gain control operates is set to a relatively low illuminance range [H11 to H13]. H11
At lower subject illuminance, the AGC gain is
Since the image is fixed at the GCMAX, the image brightness decreases as the illuminance decreases. However, this does not have to be a problem in a range where the subject illuminance is too low.

The problem is on the side where the illuminance of the subject is high. When the subject illuminance is higher than H13, the AGC gain is fixed at the gain lower limit value of zero, and the image brightness increases with the increase in the illuminance. If a mechanical aperture mechanism is provided, it is possible to reduce the amount of incident light to maintain the image brightness at a constant level. However, since there is no mechanical aperture mechanism, the image brightness increases. Hs1 is the illuminance of the subject when the image brightness reaches the saturation level. Even if the fluorescent lamp flicker can be prevented, at this level, the solid-state imaging device is electronically saturated and the image becomes whitish.

Next, the electronic shutter speed is reduced to 1 / 100s.
The state in the ec mode will be discussed with reference to FIGS. 14 (a) and 14 (b). In this mode, the subject illuminance H is H
The automatic gain control is set to operate in the range of 12 ≦ H ≦ H14. Since the substantial exposure time of the image sensor is as short as 1/100 sec, the amount of incident light is relatively small. Therefore, the subject illuminance range in which the automatic gain control operates is set to a relatively high illuminance range [H12 to H14]. H14 is higher than H13 in the case of FIG. In FIG. 14, H
When the subject illuminance is higher than 14, the AGC gain is fixed at the gain lower limit value of zero, and there is no mechanical aperture mechanism. Therefore, the image brightness increases as the illuminance increases. Hs2 is the illuminance of the subject when the image brightness reaches the saturation level. At this level, the solid-state imaging device is electronically saturated and the image is whitish.

H12 is higher than H11 in FIG. In FIG. 14, when the illuminance of the subject is lower than H12, the AGC gain is fixed at the gain upper limit value AGCMAX, so that the image brightness decreases with the decrease in the illuminance. Hd is the illuminance of the subject when the image brightness becomes zero. The subject illuminance Hd, when projected on FIG. 13, is located within the range of [H11 to H13] in which the automatic gain control functions. When the subject illuminance is in the range [Hd to H12], the brightness of the image is reduced. When the electronic shutter speed is fixed at 1/100 sec because of the fast movement of the subject, fluorescent light flicker can be prevented, but if the subject illuminance is low,
Good quality images cannot be obtained.

In the case of the prior art, even if the shutter speed has both a mode operating at 1/100 sec and a mode operating at 1/50 sec, both modes are automatically switched. This is not the case, and the operability is poor because it is planned to manually switch the shutter speed when the user recognizes that a defect has occurred in the image quality. In addition, the conditions for switching depend on human intuition and experience,
There is a problem that the image quality is not always good.

The present invention has been made in order to solve the above-mentioned problems, and has as its object to extend the range of subject illuminance in which a high-quality image can be captured.

[0024]

According to a first aspect of the present invention, there is provided an image pickup apparatus, comprising: an automatic gain control means for maintaining photometric data substantially constant based on photometric data obtained from an output of an image sensor;
Shutter speed switching means for switching the shutter speed of the electronic shutter of the image sensor between a first shutter speed and a second shutter speed; and determining whether a combination of a gain and a shutter speed for the automatic gain control means satisfies a switching requirement. When the switching requirement is satisfied, a switching instruction is given to the shutter speed switching means, and the automatic gain control means is provided with a switching determination instruction means for giving a predetermined gain. The operation of this configuration is as follows. It is assumed that the first shutter speed is lower than the second shutter speed. When the subject illuminance increases and the gain decreases while operating at the first shutter speed and the switching requirement is satisfied, the shutter speed is increased to the second shutter speed.
At the same time as the shutter speed, and raise the gain higher. As a result, automatic gain control operates even in a range where the illuminance of the subject is higher. Switching between the first and second shutter speeds is automatic.

According to a second aspect of the present invention, there is provided an imaging apparatus according to the first aspect, wherein a predetermined gain to be provided when switching from the first shutter speed to the second shutter speed (this is described in an embodiment to be described later). Startup gain AGC
LH) and a predetermined gain given when switching from the second shutter speed to the first shutter speed (this is a fall gain A in an embodiment described later).
(Corresponding to GCHL), and the shutter speed switching of the electronic shutter is provided with hysteresis. This means the following. That is, the illuminance of the subject when switching from the first shutter speed to the second shutter speed, and the second
The subject illuminance at the time of switching from the shutter speed to the first shutter speed is shifted. Therefore, the shutter speed does not change frequently.

According to a third aspect of the present invention, there is provided an image pickup apparatus according to the first and second aspects, wherein a nonvolatile storage means for storing a current shutter speed, and a last storage means stored in the storage means when the power is turned on. Means for reading the shutter speed and instructing the shutter speed switching means as an initial value of the shutter speed.
The operation of this configuration is as follows. If the conditions of the previous use of the imaging device and the conditions of the current use are the same or similar, it is considered that the illuminance of the surroundings is also similar, and it is not necessary to calculate the shutter speed based on the photometry data again when the power is turned on. Also gets better.

According to a fourth aspect of the present invention, in the first to third aspects, the shutter speed is set to the first shutter speed and the second shutter speed based on photometric data obtained from the output of the imaging device when the power is turned on. It is characterized in that a means for initial setting to one of the shutter speeds is provided. An accurate shutter speed is initially set according to the current use conditions, regardless of the previous use conditions.

According to a fifth aspect of the present invention, there is provided the imaging apparatus according to the first to fourth aspects, wherein the first shutter speed is set to approximately 1 unit.
/ 50 sec, and the second shutter speed is set to approximately 1/100 sec. Although this is an example, flickering of the fluorescent light is prevented in imaging under the fluorescent light in a region where the commercial power frequency is 50 Hz.

According to a sixth aspect of the present invention, in the first to fifth aspects, the predetermined gain is set to a value that keeps the image brightness constant before and after switching the shutter speed. It is. Although it is conceivable to slightly change the image brightness before and after the switching of the shutter speed, it is still preferable to stabilize the image brightness at any shutter speed. According to this configuration, the image brightness does not change before and after the switching of the shutter speed, and the image brightness is stabilized in the entire range of the subject illuminance where the automatic gain control operates.

[0030]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus according to the present invention. In the embodiments described below, a CCD camera using a solid-state imaging device driven at 30 Hz will be described as an example. This 30
The Hz driven CCD camera is for taking image data into a personal computer or the like. that is,
For example, it is effective for a video conference held via a network.

When the 30 Hz driven CCD camera is used in the Kansai region where the commercial power supply frequency is 60 Hz, flicker does not occur even if the electronic shutter speed is set to an arbitrary value, but the commercial power supply frequency is 50 Hz. The electronic shutter speed is set to 1/50 sec in order to prevent flickering of fluorescent lamps even when used locally.
And two modes of 1/100 sec. Further, in consideration of cost reduction, no mechanical aperture mechanism is provided.

[Embodiment 1] FIG. 1 is a block diagram showing an electrical configuration of an imaging apparatus according to Embodiment 1. In FIG. 1, reference numeral 11 denotes a solid-state imaging device (CCD) on which an optical image of a subject is formed via an optical system (not shown), and reference numeral 12 denotes a solid-state imaging device 11 in response to an electronic shutter control signal ST.
A timing signal generating circuit also referred to as a timing generator (TG) for generating a timing signal T for driving the semiconductor device; a CDS 13 for converting a discontinuous analog video signal from the solid-state imaging device 11 into a continuous analog video signal
(Correlated Double Sampling) A correlated double sampling circuit 14 amplifies an analog video signal, and the gain of the amplification is controlled in response to a gain control signal GC (AGC circuit: Auto). Gai
n), 15 is an A / D converter for converting an analog video signal into a digital image signal PD, and 16 is an image which performs various processes such as luminance processing or color processing on the digital image signal PD to generate a video signal VS. A signal processing circuit 17 receives a luminance component signal YL from the video signal processing circuit 16 and integrates the signal to output photometric data DT corresponding to the illuminance of the subject. Based on the measured photometric data DT,
The gain control signal GC is output to the automatic gain control circuit 14 so that the value is always constant, and the electronic shutter control signal S is output to the timing signal generation circuit 12.
CPU (Central Processing Unit) that outputs T, 19 is CP
A main memory including a ROM (read only memory) storing a program for calculation and control by U18 and a RAM (random access memory) as a working area for assisting calculation and control and storing data; Reference numeral 20 denotes a non-volatile memory such as an EEPROM that stores various video processing data and stores various data such as the final electronic shutter speed STlast and the AGC gain when the electronic shutter speed is switched. The non-volatile memory 20 corresponds to “non-volatile storage means” in the claims.

The solid-state image pickup device 11 forms an optical image of a subject incident through an optical system. Solid-state imaging device 11
Is driven in response to the timing signal T from the timing signal generation circuit 12 to generate and output an analog video signal corresponding to the optical image formed. Solid-state imaging device 11
Although the analog video signal output from is discontinuous, the correlated double sampling circuit 13 converts the analog video signal into a continuous analog video signal. This continuous analog video signal is amplified by the automatic gain control circuit 14. In this case, the automatic gain control circuit 14 amplifies the analog video signal according to the gain control signal GC from the CPU 18. The analog video signal thus amplified is converted into a digital image signal PD by the A / D converter 15 and then input to the video signal processing circuit 16. Video signal processing circuit 16
In the digital imaging signal PD, required processes are performed on a luminance component and a color component. The video signal VS obtained by processing by the video signal processing circuit 16 is output to another circuit in the imaging device. On the other hand, the video signal processing circuit 16 sends out the luminance component signal YL to the photometry circuit 17. The luminance component signal YL input in the photometric circuit 17 is integrated, and photometric data DT as a measured value of the subject illuminance is sent to the CPU 18. The CPU 18 generates a gain control signal GC so that the value of the photometric data DT becomes constant and sends it to the automatic gain control circuit 14. Further, it sends out an electronic shutter control signal ST to the timing signal generation circuit 12 as needed. Further, the CPU 18 stores image processing data, shutter speed data, and AGC gain data (switching gain AGC
LH, falling gain AGCHL, marginal gain AGCl
mt, final shutter speed STlast, etc.).

Before describing the operation according to the flowchart, the characteristic line of the AGC gain shown in FIG. 7A will be described in advance. This characteristic line corresponds to a CPU
18 is realized. The horizontal axis represents the subject illuminance, the vertical axis represents the AGC gain, and the shutter speed is also shown in correspondence with the subject illuminance on the horizontal axis. The object illuminance H2 or less corresponds to 1/50 sec, which is the first shutter speed, and the object illuminance H2 or more corresponds to 1/100 sec, which is the second shutter speed. That is, the subject illuminance H2 corresponds to a switching point of the shutter speed. When the illuminance of the object is equal to or less than H1, the AGC gain is the gain upper limit value AGCMAX. When the subject illuminance is in the range of [H1 to H2], A
This is a first negative characteristic line CL1 in which the GC gain linearly decreases from the upper limit value AGCMAX to 0. When the illuminance of the subject is just H2, the AGC gain is set to 0 and the start-up gain
Can be switched between This is the AGC gain switching characteristic line CLch1. The AGC gain switching characteristic line CLch1 is perpendicular to the horizontal axis. When the subject illuminance is in the range of [H2 to H3], the second negative characteristic line CL2 in which the AGC gain linearly decreases from the rising gain AGCLH to 0 is formed.

The value of the AGC gain rising gain AGCLH corresponding to the top of the AGC gain switching characteristic line CLch1 is determined as follows. That is, the value of the photometric data DT when the point A, that is, the shutter speed is 1/50 sec and the AGC gain is 0, and the value of the photometric data DT when the point B, that is, the shutter speed is 1/100 sec and the AGC gain is the rising gain AGCLH. The startup gain AGCLH is set to a value that makes the value of DT the same. The value of the start-up gain AGCLH is obtained by adjustment or the like in advance, and is stored in the non-volatile memory 20 before the product shipment of the imaging device.

Hereinafter, the operation of the imaging apparatus configured as described above will be described with reference to the flowcharts of FIGS.

FIG. 2 is a flowchart showing a main processing routine by the CPU 18. The main processing routine is roughly divided into an initial setting routine R1, an AGC control routine R2, a shutter speed switching determination routine R
3 and shutter speed / gain switching routine R4
It is composed of

In the initial setting routine R1, an initial shutter speed is determined when the power is turned on. In the AGC control routine R2, the photometric data DT from the photometric circuit 19 is
Is controlled so as to fall within the convergence range. In the shutter speed switching determination routine R3, it is determined whether or not the relationship between the shutter speed and the AGC gain satisfies the shutter speed switching requirement. In the shutter speed / gain switching routine R4, the shutter speed is increased from 1/50 sec to 1/100 s.
ec or 1/100 sec to 1/50 sec
Switch to.

Initial setting routine R in the first embodiment
FIG. 3 shows a specific example of No. 1. In step SP11,
The startup gain AGCLH is read from the non-volatile memory 20 and stored at a predetermined address in the RAM of the main memory 19, and in step SP12, the final shutter speed S at the time of the previous use before the power was turned on from the non-volatile memory 20
Tlast is read, and in step SP13, the shutter speed variable S set in the RAM of the main memory 19 is set.
The last final shutter speed STlast is set to T. This is the initial data of the shutter speed.
Next, the process proceeds to the first step of the AGC control routine R2.

When this initial setting routine R1 is used, the installation location of the imaging device is fixed, and the conditions of the previous use and the conditions of the current use are similar, and the illuminance around the imaging device changes so much. Valid when not. That is, each time the power is turned on, there is no need to measure the surrounding illuminance and calculate an appropriate shutter speed according to the illuminance, and the process of setting the initial value of the shutter speed can be performed quickly. The initial setting routine R1 in FIG. 3 corresponds to “means for instructing an initial value of the shutter speed”.

FIG. 4 shows a specific example of the AGC control routine R2 in the first embodiment. The CPU 18 determines in step S
At P21, the photometric data DT is read from the photometric circuit 17. In step SP22, it is determined whether or not the value of the photometric data DT is larger than the maximum value DTmax of the convergence range. If the value of the photometric data DT is equal to or less than the maximum value DTmax and the above determination is negative, the process proceeds to step SP24.
, But the value of the photometric data DT is the maximum value DTm
If it is larger than ax and the above determination is affirmative, the process proceeds to step SP23, in which the AGC gain variable GC set in the RAM of the main memory 19 is decremented by a certain amount α, and then proceeds to step SP24.

In step SP24, the photometric data DT
Is smaller than the minimum value DTmin of the convergence range. If the value of the photometric data DT is equal to or greater than the minimum value DTmin and the above determination is negative, the AGC
The control routine R2 ends and the process proceeds to the first step of the shutter speed switching determination routine R3.
When the value of T is smaller than the minimum value DTmin and the above judgment is affirmative, the routine proceeds to step SP25, where A
The GC gain variable GC is incremented by a certain amount α,
Next, the process proceeds to the first step of the shutter speed switching determination routine R3.

By repeating the AGC control routine R2, the value of the photometric data DT converges within a convergence range defined by the minimum value DTmin and the maximum value DTmax.

The above is described with reference to FIG.
Means that the AGC gain is controlled along the negative characteristic line CL1 or the second negative characteristic line CL2. In FIG. 7B, the image brightness is maintained at a constant value. Means that.

The function of the AGC control routine R2 by the CPU 18, the automatic gain control circuit 14 and the photometric circuit 17
Corresponds to “automatic gain control means” in the claims.

FIG. 5 shows a specific example of the shutter speed switching determination routine R3 in the first embodiment. CPU1
8 is the shutter speed variable S in step SP31.
It is determined whether or not the value set in T is 1/50 sec. If the determination is affirmative, the process proceeds to step SP32, where the value set in the AGC gain variable GC becomes 0. It is determined whether or not the shutter speed / gain switching routine R4 is affirmative. Step SP
If the determination in step 31 or step SP32 is negative, the process proceeds to step SP33, in which it is determined whether the value set in the shutter speed variable ST is 1/100 sec. Proceeds to step SP34, determines whether or not the value set in the AGC gain variable GC is the start-up gain AGCLH. If the determination is affirmative, the first step of the shutter speed / gain switching routine R4 Proceed to. If the determination is negative in step SP33 or SP34, the AGC control routine R2
Return to the first step of. The shutter speed switching determination routine R3 in FIG. 5 corresponds to a part of “switching determination instructing means”.

The significance of the above operation will be described. Step S
If both P31 and step SP32 are positive, the shutter speed variable ST is 1/50 sec and A
This means that the GC gain variable GC is 0, which corresponds to the fact that the first negative characteristic line CL1 has been lowered to the point A in FIG. And
In this case, the shutter speed is increased from 1/50 sec to 1/50 sec.
In order to switch to 100 sec, the process proceeds to the first step of the shutter speed / gain switching routine R4. Further, when both step SP33 and step SP34 are affirmative, it means that the shutter speed variable ST is 1/100 sec and the AGC gain variable GC is the start-up gain AGCLH, which is shown in FIG. This corresponds to the fact that the second negative characteristic line CL2 has risen to the point B. In this case, the shutter speed is increased from 1/100 sec to 1/50
In order to switch to sec, the process proceeds to the first step of the shutter speed / gain switching routine R4. In other than the two cases, the switching of the shutter speed is not performed. Step SP33 of determining whether or not the shutter speed variable ST is set to 1/100 sec may be omitted in practice and may be omitted. That is, when the determination in step SP31 is negative, the shutter speed variable ST becomes 1 /
This is because it is 100 sec.

FIG. 6 shows a specific example of the shutter speed / gain switching routine R4 in the first embodiment. CP
U18 determines whether or not the value of the shutter speed variable ST is set to 1/50 sec in step SP41, and if the determination is affirmative, the process proceeds to step SP41.
Proceed to 42 and set the shutter speed variable ST to 1/50 sec.
And sets it to 1/100 sec, and further sets the value of the AGC gain variable GC to 0 in step SP43.
And set it to the startup gain AGCLH,
Next, the routine proceeds to step SP46. Step SP4
If the determination of 1 is negative and the value of the shutter speed variable ST is set to 1/100 sec, the process proceeds to step SP44, where the shutter speed variable ST is set to 1/10.
Switching is performed from 0 sec and set to 1/50 sec, and in step SP45, the AGC gain variable GC is switched from the gain AGCLH and set to 0. In step SP46, the value of the currently set shutter speed variable ST is stored in the non-volatile memory 2.
0 at a predetermined address, and the AGC control routine R2
Return to the first step of.

Steps SP42 and SP43 are the same as those in FIG.
(A) corresponds to switching the AGC gain from point A to point B on the AGC gain switching characteristic line CLch1. In addition, steps SP44 and SP45
This corresponds to switching the AGC gain from point B to point A on the GC gain switching characteristic line CLch1. The shutter speed / gain switching routine R4 in FIG. 6 corresponds to a part of the "switching determination instructing means".

The CPU 18 sends the value of the shutter speed variable ST after switching to the timing signal generation circuit 12 as an electronic shutter control signal ST. The timing signal generation circuit 12 controls a shutter speed of an electronic shutter in the solid-state imaging device (CCD) 11 based on the received electronic shutter control signal ST. This C
The function of the PU 18 and the function of the timing signal generation circuit 12 correspond to “shutter speed switching means” in the claims.

The rising gain AGCLH is determined in advance as described above, and the change in image brightness can be suppressed even when the shutter speed is switched.

By repeating the AGC control routine R2, the shutter speed switching determination routine R3, and the shutter speed / gain switching routine R4 described above, exposure control is performed to keep the image brightness constant.

FIG. 7A shows a shutter speed of 1/50 s.
The relationship between the illuminance of the subject and the AGC gain corresponding to switching between ec and 1/100 sec is shown. FIG.
(B) shows the relationship between subject illuminance and image brightness. The imaging device operates at a shutter speed of 1/50 sec when the illuminance of the subject is equal to or lower than H2, and operates at a shutter speed of 1/100 sec when the illuminance of the subject is higher than H2.
In the range of the subject illuminance [H1 to H2], the relationship between the subject illuminance and the AGC gain is a first negative characteristic line CL1, and the image brightness is kept constant by automatic gain control during this period. In the first negative characteristic line CL1, the AGC gain decreases linearly as the illuminance of the subject increases, and the AGC gain becomes 0 when the illuminance of the subject is H2, that is, at the point A.

If the illuminance of the subject becomes slightly higher than H2 along the first negative characteristic line CL1, the AGC gain is fixed to 0 in the case of the prior art. Start to increase as shown. However, in the first embodiment, the AGC gain is switched when the AGC gain drops to the first negative characteristic line CL1 and becomes zero. That is, the AGC gain is raised at a stretch along the AGC gain switching characteristic line CLch1 to the gain AGCLH, that is, the point B.

When the illuminance of the subject further increases than H2, the AGC gain falls from the rising gain AGCLH toward 0 along the second negative characteristic line CL2. That is, the state in which the automatic gain control is effective continues toward the higher illuminance side. When the illuminance of the object is in the range of [H2 to H3], the AGC gain rises along the second negative characteristic line CL2 and the rising gain AGCLH, that is, B
At this point, the AGC gain is switched. That is, the AGC gain is dropped to 0, that is, the point A at a stretch along the AGC gain switching characteristic line CLch1.

When the illuminance of the subject is in the range [H1 to H2] on the low illuminance side, the shutter speed is 1/50 sec. When the illuminance of the subject increases and the AGC gain reaches point A, the shutter speed is reduced. Automatically switches to 1/100 sec and AGC gain rises to gain AGC
Since the mode is switched to LH, it is possible to cope with even higher subject illuminance. In comparison with the prior art, if the subject illuminance exceeds H13 (corresponding to H2) when the shutter speed is 1/50 sec in FIG. 13, the image brightness starts to increase. Then, it was necessary to manually switch the shutter speed to 1/100 sec.

In FIG. 7, when the illuminance of the object is in the range [H2 to H3] on the low illuminance side, the shutter speed is 1/1.
00 sec, the illuminance of the subject decreases and the AG
When the C gain reaches the point B of the start-up gain AGCLH, the shutter speed is automatically switched to 1/50 sec and the AGC gain is switched to 0, so that it is possible to cope with even lower object illuminance. In comparison with the prior art, if the subject illuminance falls below H12 when the shutter speed is 1/100 sec in FIG. 14, the image brightness starts to decrease as indicated by the broken line B. Then, manually set the shutter speed to 1/50
It was necessary to switch to sec.

According to the imaging apparatus of the first embodiment, such manual switching is not required, and the switching can be performed automatically. Further, the image brightness can be kept constant regardless of the switching of the shutter speed.

In summary, the range of the subject illuminance in which the image brightness is kept constant even if the subject illuminance increases is [H
1 to H3]. This means that, based on 1/50 sec, [H11 to H11 in FIG.
13] is equivalent to being extended to the higher illuminance side. Alternatively, on the basis of 1/100 sec, this corresponds to expansion to a lower illuminance side than [H12 to H14] in FIG.

In this manner, the dynamic range of the illuminance of the subject in which the automatic gain control for stabilizing the image brightness can be performed can be extended. On the extended high illuminance side, there is an effect of suppressing an increase in image brightness due to an increase in the subject illuminance, and on the extended low illuminance side, a decrease in the S / N ratio due to a decrease in the subject illuminance is suppressed. effective.

[Second Embodiment] In the second embodiment, the switching of the shutter speed has hysteresis. The basic configuration of the imaging device according to the second embodiment is the same as that shown in FIG. 1 in the case of the first embodiment. In the second embodiment, the programs stored in the main memory 19 and the control operation of the CPU 18 are different from those in the first embodiment. That is, the switching of the shutter speed has hysteresis.

Before describing the operation according to the flowchart, the characteristic line of the AGC gain shown in FIG. 11A will be described in advance. This characteristic line corresponds to CP
This is realized by the operation of U18. 1/50
For the first negative characteristic line CL1 when operating in sec and the AGC gain switching characteristic line CLch1 for switching from 1/50 sec to 1/100 sec,
This is the same as FIG. 7A in the case of the first embodiment. CLch
1 is referred to as a first AGC gain switching characteristic line.

A second negative characteristic line when operating at 1/100 sec is indicated by a symbol CL3, and the second negative characteristic line CL3 is the second negative characteristic line CL3 in the first embodiment shown in FIG. This corresponds to a line obtained by linearly extending the negative characteristic line CL2 straight to the low illuminance side and the high gain side.

Although the subject illuminance H4 is lower than H2, when the subject illuminance is in the range [H4 to H2], the limit gain AGClmt at the subject illuminance H4 corresponding to the point C is obtained.
, A second negative characteristic line CL3 that decreases linearly to 0 when the subject illuminance is H3. When the illuminance of the subject is just H4, the AGC gain is switched from the limit gain AGClmt at the point C to the falling gain AGCHL at the point D with the switching of the shutter speed from 1/100 sec to 1/50 sec. Switching from point C to point D is performed by the second AGC gain switching characteristic line CLch2.
It is. The second AGC gain switching characteristic line CLch2 is perpendicular to the horizontal axis similarly to the first AGC gain switching characteristic line CLch1. Point D is the intersection of the first negative characteristic line CL1 and the second AGC gain switching characteristic line CLch2, and point B is the intersection of the second negative characteristic line CL3 and the first AGC gain switching characteristic line CLch1. It is an intersection.
In general, the slope of the second negative characteristic line CL3 will be equal to the slope of the first negative characteristic line CL1. The shape surrounded by points A, B, C, and D indicates that this characteristic has hysteresis.

The shutter speed is shown in two states in accordance with the illuminance of the object on the horizontal axis. One is point A / B
1/50 sec on low illuminance side with H2 corresponding to point as boundary
And the high illuminance side is set to 1/100 sec.
This means that the first negative characteristic line CL1 drops from point E to point A, the first AGC gain switching characteristic line CLch1 rises, and the second negative characteristic line CL2 drops from point B to point F. Corresponding to the transition. The other is to set the low illuminance side to 1/50 sec with H4 corresponding to point C and point D as the boundary,
The high illuminance side is set to 1/100 sec. This means that the second negative characteristic line CL3 rises from point F to point C, the second AGC gain switching characteristic line CLch2 falls, and the first negative characteristic line CL1 rises from point D to point E. Corresponding to the transition.

AGC gain limit gain A corresponding to point C
The value of GClmt is determined as follows. That is, the end point H4 of the subject illuminance on the low hysteresis side is set to an arbitrary value lower than H2. The second negative characteristic line CL2 in FIG. 7A is linearly extended to the low illuminance side, the point at which the object illuminance H4 is set to C, and the point from point F to point C is the second point in the second embodiment. 2, the AGC gain at the point C is the limit gain AGClmt. The value of the AGC gain fall gain AGCHL corresponding to the point D is determined as follows. That is, the value of the photometric data DT when the point C, that is, the shutter speed is 1/100 sec, and the AGC gain is the limit gain AGClmt, and the value at the point D, that is, when the shutter speed is 1/50 sec and the AGC gain is the falling gain AGCHL. Falling gain A to a value that makes the value of photometric data DT the same
GCHL is defined. How to determine the start-up gain AGCLH is the same as in the first embodiment. The values of the rising gain AGCLH, the limit gain AGClmt, and the falling gain AGCHL are obtained by adjustment or the like in advance, and are stored in the nonvolatile memory 20 before shipment of the imaging device from a product.

Hereinafter, the operation of the imaging apparatus configured as described above will be described with reference to the flowcharts of FIGS. The form of the main processing routine is the same as that of FIG. 2 in the case of the first embodiment, and an initial setting routine R1, an AGC control routine R2, a shutter speed switching determination routine R3, and a shutter speed / gain switching routine R
Four. However, the contents of each routine except the AGC control routine R2 are different from those of the first embodiment.
Each is shown in FIGS.

Initial setting routine R in the second embodiment
FIG. 8 shows a specific example of No. 1. In step SP51,
The rising gain AGCLH, the falling gain AGCHL, and the limit gain AGClmt from the nonvolatile memory 20
Is read and stored at a predetermined address in the RAM of the main memory 19, and in step SP52, the nonvolatile memory 2
From 0, the final shutter speed STlast at the time of the previous use before the power is turned on is read, and in step SP53, the shutter speed variable ST set in the RAM of the main memory 19 is set to the last shutter speed STlas of the previous time.
Set t. This is the initial data of the shutter speed. Next, the process proceeds to the first step of the AGC control routine R2.

The AGC control routine R2 is the same as in FIG. 4 in the case of the first embodiment, and the description is omitted.

FIG. 9 shows a specific example of the shutter speed switching determination routine R3 in the case of the second embodiment. CPU1
8 is the shutter speed variable S in step SP61.
It is determined whether or not the value set in T is 1/50 sec. If the determination is affirmative, the process proceeds to step SP62 where the value set in the AGC gain variable GC becomes 0. It is determined whether or not the shutter speed / gain switching routine R4 is affirmative. Step SP
If the determination in step SP62 or step SP62 is negative, the process proceeds to step SP63, in which it is determined whether the value set in the shutter speed variable ST is 1/100 sec. If the determination is positive. Proceeds to step SP64, determines whether or not the value set in the AGC gain variable GC has reached the limit gain AGClmt. If the determination is affirmative, the routine proceeds to the first step of the shutter speed / gain switching routine R4. move on. If the determination is negative in step SP63 or step SP64, the process returns to the first step of the AGC control routine R2. FIG. 9 differs from FIG. 5 in that the value of step SP64 is a limit gain AGClmt instead of the start-up gain AGCLH. The shutter speed switching determination routine R3 in FIG. 9 corresponds to a part of "switching determination instructing means" in claims.

The significance of the above operation will be described. Step S
If both P61 and step SP62 are affirmative, the shutter speed variable ST is 1/50 sec and A
This means that the GC gain variable GC is 0, which corresponds to the fact that the first negative characteristic line CL1 has been lowered to the point A in FIG. Then, at this time, in order to switch the shutter speed from 1/50 sec to 1/100 sec, the process proceeds to the first step of the shutter speed / gain switching routine R4. Step SP63 and step SP6
4 is affirmative, the shutter speed variable S
T is 1/100 sec and the AGC gain variable GC is the limit gain AGClmt, which means that
This corresponds to the fact that the second negative characteristic line CL3 has risen to the point C in FIG. In this case, the shutter speed is increased from 1/100 sec to 1/100 sec.
In order to switch to 50 sec, the process proceeds to the first step of the shutter speed / gain switching routine R4. In other than the two cases, the switching of the shutter speed is not performed. Step SP63 of determining whether or not the shutter speed variable ST is set to 1/100 sec may not be actually present and may be omitted for the same reason as described above.

FIG. 10 shows a specific example of the shutter speed / gain switching routine R4 in the second embodiment. C
The PU 18 determines whether or not the value of the shutter speed variable ST is set to 1/50 sec in step SP71, and if the determination is affirmative, the process proceeds to step S71.
Proceed to P72 to set the shutter speed variable ST to 1/50 sec
The value of the AGC gain variable GC is switched from 0 in step SP73 to be set to the start-up gain AGCLH. The above is step SP41 in the case of the first embodiment,
This is the same as SP42 and SP43. Step SP
If the determination at 71 is negative and the value of the shutter speed variable ST is set to 1/100 sec, the process proceeds to step SP74, where the shutter speed variable ST is set to 1/1.
Switch from 00 sec, set to 1/50 sec,
Further, in step SP75, the AGC gain variable GC
Is switched from the limit gain AGClmt to the fall gain AGCHL. In the case of the first embodiment, the AGC gain variable GC is set to 0 in step SP45, but the fall gain AGCHL is set in step SP75.
The difference is that it is set to And step SP
At 76, the value of the currently set shutter speed variable ST is stored at a predetermined address of the nonvolatile memory 20, and the process returns to the first step of the AGC control routine R2.

Steps SP72 and SP73 are the same as those in FIG.
In (a), the first AGC gain switching characteristic line CL
This corresponds to switching the AGC gain from point A to point B on ch1. Steps SP74 and SP75
Is A on the second AGC gain switching characteristic line CLch2.
This corresponds to switching the GC gain from point C to point D. The shutter speed / gain switching routine R4 shown in FIG.
Is equivalent to a part of

The rise gain AGCLH and the fall gain AGCHL are predetermined as described above, and the change in image brightness can be suppressed even when the shutter speed is switched.

By repeating the AGC control routine R2, the shutter speed switching determination routine R3, and the shutter speed / gain switching routine R4 described above, exposure control is performed so as to keep the image brightness constant.

FIG. 11A shows that the shutter speed is 1/50.
The relationship between the subject illuminance and the AGC gain corresponding to switching between sec and 1/100 sec is shown. FIG.
1 (b) shows the relationship between the subject illuminance and the image brightness.

First, the situation when the shutter speed is switched from 1/50 sec to 1/100 sec will be described. When operating along the first negative characteristic line CL1, the shutter speed is 1/50 sec. The AGC gain decreases linearly as the illuminance of the subject increases on the first negative characteristic line CL1,
The AGC gain is 0 when the subject illuminance is H2, that is, at the point A. When the subject illumination is slightly higher than H2,
The AGC gain is switched. That is, the first AG
AGC at once along C gain switching characteristic line CLch1
The gain is raised to the gain AGCLH, that is, the point B.

When the illuminance of the subject further increases than H2, the AGC gain falls from the rising gain AGCLH toward 0 along the second negative characteristic line CL3. That is, the state where the automatic gain control is effective continues toward the high illuminance side.

Next, when the shutter speed is 1/100 sec.
The situation when switching from the state of FIG. 1 to 1/50 sec will be described. When operating along the second negative characteristic line CL3, the shutter speed is 1/100 sec.
It has become. In the second negative characteristic line CL3, the AGC gain linearly increases as the subject illuminance decreases, and the AGC gain becomes the limit gain AGClmt when the subject illuminance is H4, that is, at the point C. When the illuminance of the subject becomes slightly lower than H4, the AGC gain is switched. That is, the second AGC gain switching characteristic line CL
AGC gain drops at a stretch along ch2 and gain AG
It falls to CHL, that is, point D.

The operation with such hysteresis produces the following effects as compared with the first embodiment. In the case of Embodiment 1, in FIG.
If the illuminance of the subject slightly fluctuates near H2, hunting may occur. That is, if H2 is slightly exceeded from H2 or less, the shutter speed is switched from 1/50 sec to 1/100 sec.
From the above, if the shutter speed falls slightly below H2, the shutter speed becomes 1
Since the switching from / 100 sec to 1/50 sec, such a situation is repeated alternately and the shutter speed is frequently switched, hunting occurs in which the image brightness fluctuates slightly.

On the other hand, in the second embodiment, since the operation is accompanied by hysteresis, the illuminance of the subject fluctuates around H2 after the switching to the second negative characteristic line CL3 at H2. However, as long as the shutter speed does not drop to H4, the shutter speed is kept at 1/100 sec. Also, once the line is switched to the first negative characteristic line CL1 at H4, even if the illuminance of the object fluctuates near H4, the shutter speed is reduced to 1/5 unless it rises to H2.
It is kept at 0 sec. Therefore, hunting in which the image brightness fluctuates rapidly due to frequent switching of the shutter speed is prevented.

Embodiment 2 with this hysteresis
In the same manner as in the first embodiment, the shutter speed is set to 1/50 sec and 1/50 according to the change in the illuminance of the subject.
It can be switched automatically between 100 sec.
There is no need for manual switching as in the prior art. Then, despite the switching, the image brightness can be kept constant.

[Third Embodiment] A third embodiment relates to another mode of the initial setting routine R1. The basic configuration of the imaging device according to the third embodiment is the same as that shown in FIG. 1 in the case of the first embodiment. FIG. 12 shows a specific example of the initialization routine R1 in the third embodiment.
Shown in

When the power is turned on, the CPU 18 reads the rising gain AGCLH, the fixed gain AGCfix, and the criterion value DTHL from the non-volatile memory 20 in step SP81 and stores them in a predetermined address of the RAM of the main memory 19, AGC at SP82
AGCfix is set to the gain variable GC, and step S
1 / 100s for shutter speed variable ST in P83
Set ec. That is, the initial value of the AGC gain and the initial value of the shutter speed when the power is turned on are temporarily fixed to predetermined values.

Next, in step SP84, the photometric data DT is read from the photometric circuit 17, and
85 is the reference value DTH
It is determined whether or not the shutter speed variable ST is smaller than the reference value DTHL.
ec is set, and then the process proceeds to the first step of the AGC control routine R2. That is, since the amount of light incident on the solid-state imaging device 11 becomes insufficient, the shutter speed is reduced. When the photometric data DT is equal to or greater than the reference value DTHL, the process proceeds to the first step of the AGC control routine R2 without switching the shutter speed. The initial setting routine R1 in FIG. 12 corresponds to "means for instructing an initial value of the shutter speed based on photometric data".

The third embodiment may be applied to the first embodiment or the second embodiment.

A television broadcasting system in Japan and the United States, NTSC (National Television System Committe)
In the case of e), the field frequency is 60 Hz.
In this case, if the commercial power frequency is 50 Hz, fluorescent lamp flicker occurs. Therefore, in each of the above embodiments, for example, when configuring an imaging device driven at 30 Hz, the first shutter speed for preventing flicker of fluorescent light is 1/50 sec, and the second shutter speed is 1/1.
00 sec.

In the case of PAL (Phase Alteration by Line), which is a television broadcasting system in Germany and the United Kingdom, the field frequency is 50 Hz. In this case, if the commercial power frequency is 60 Hz, fluorescent lamp flicker occurs. For example, when configuring an imaging device driven at 25 Hz, the first shutter speed for preventing flicker of fluorescent light is 1/30 sec, and the second shutter speed is 1/6.
0sec or 1st shutter speed 1 / 60s
ec, the second shutter speed may be set to 1/120 sec.

In the above-described embodiment, an imaging apparatus having no mechanical aperture mechanism has been described in consideration of cost reduction. However, it is also possible to apply the present invention to an imaging apparatus having such an aperture mechanism. .

[0090]

The first aspect of the present invention is to prevent fluorescent lamp flicker.
According to the first aspect of the present invention, the dynamic range of the illuminance of the subject in which the automatic gain control for stabilizing the image brightness can be operated is fixed. can do. In addition, since the switching of the shutter speed is performed automatically, the operability can be improved as compared with the case where manual operation is performed. Also, the image quality can be stabilized by switching.

According to the second aspect of the present invention, the gain characteristic of the automatic gain control with respect to the illuminance of the subject has a hysteresis, so that the shutter speed does not change frequently and the hunting in which the image brightness flickers is prevented. hand,
Image quality can be improved.

According to the third aspect of the present invention, the condition of the previous use of the imaging device and the condition of the present use are the same or similar,
If the surrounding illuminance is similar, it is not necessary to calculate the shutter speed again based on the photometric data when the power is turned on, and the last shutter speed can be used as the initial value of the shutter speed, which is unnecessary. The convergence time until image brightness becomes stable can be shortened by eliminating a switching operation of the shutter speed.

According to the fourth aspect of the present invention, even if the current use condition of the imaging apparatus is different from the previous use condition, it is possible to initialize an accurate shutter speed according to the current use condition.

According to the fifth aspect of the present invention, it is possible to prevent the flicker of the fluorescent lamp in the imaging under the fluorescent lamp in the area where the commercial power supply frequency is 50 Hz.

According to the sixth aspect of the present invention, the image brightness does not change before and after the switching of the shutter speed, and the image brightness can be stabilized in the entire range of the illuminance of the subject on which the automatic gain control operates.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electrical configuration according to first to third embodiments of the present invention.

FIG. 2 is a flowchart of a main processing routine according to the first to third embodiments;

FIG. 3 is a flowchart of an initial setting routine according to the first embodiment;

FIG. 4 is a flowchart of an AGC control routine according to the first to third embodiments.

FIG. 5 is a flowchart of a shutter speed switching determination routine according to the first embodiment;

FIG. 6 is a flowchart of a shutter speed / gain switching routine according to the first embodiment;

FIG. 7 is a characteristic diagram showing a relationship between the subject illuminance, the AGC gain, and the image brightness in the imaging device according to the first embodiment;

FIG. 8 is a flowchart of an initialization routine in the second embodiment.

FIG. 9 is a flowchart of a shutter speed switching determination routine according to the second embodiment.

FIG. 10 is a flowchart of a shutter speed / gain switching routine according to the second embodiment.

FIG. 11 is a characteristic diagram showing a relationship between subject illuminance, AGC gain, and image brightness in the imaging device according to the second embodiment;

FIG. 12 is a flowchart of an initialization routine according to the third embodiment.

FIG. 13 is a characteristic diagram showing the relationship between the subject illuminance, the AGC gain, and the image brightness when the shutter speed is 1/50 sec in the conventional imaging apparatus.

FIG. 14 is a characteristic diagram showing the relationship between the subject illuminance, the AGC gain, and the image brightness when the shutter speed is 1/100 sec in the conventional imaging apparatus.

[Explanation of symbols]

11: solid-state imaging device (CCD), 12: timing signal generation circuit, 13: correlated double sampling circuit, 14: automatic gain control circuit, 15: A / D converter, 16: video signal processing circuit, 17: photometric circuit , 18 CPU, 19 main memory, 20 non-volatile memory (EEPROM), PD
Digital imaging signal, VS: video signal, YL: luminance component signal, DT: photometric data, GC: gain control signal (AGC)
Gain variable), ST: electronic shutter control signal (shutter speed variable), T: timing signal, AGCLH: rising gain, AGCHL: falling gain, AGCl
mt: limit gain, STlast: last shutter speed, AGCfix: fixed gain, DTHL: reference value, DTmax: maximum value, DTmin: minimum value, CL1
... first negative characteristic line, CL2 ... second negative characteristic line, CL
3 ... second negative characteristic line, CLch1 ... first AGC gain switching characteristic line, CLch2 ... second AGC gain switching characteristic line

Claims (6)

[Claims] 1. An automatic gain control means for keeping photometric data substantially constant based on photometric data obtained from an output of an image sensor, and a first shutter speed and a second shutter for controlling a shutter speed of an electronic shutter of the image sensor. Shutter speed switching means for switching to a speed, and determining whether or not a combination of a gain and a shutter speed for the automatic gain control means satisfies a switching requirement, and when the switching requirement is satisfied, issues a switching instruction to the shutter speed switching means. And a switching determination instructing means for giving a predetermined gain to the automatic gain control means. A predetermined gain provided when switching from the first shutter speed to the second shutter speed and a predetermined gain provided when switching from the second shutter speed to the first shutter speed. 2. The image pickup apparatus according to claim 1, wherein a hysteresis is provided for switching the shutter speed of the electronic shutter differently. 3. A non-volatile storage means for storing a current shutter speed, and a last shutter speed stored in the storage means when power is turned on, and the shutter speed switching means as an initial value of the shutter speed. The imaging apparatus according to claim 1, further comprising: an instruction unit. 4. A power supply system comprising: means for initially setting a shutter speed to one of a first shutter speed and a second shutter speed based on photometric data obtained from an output of the image sensor at power-on. The imaging device according to any one of claims 1 to 3, wherein 5. The method according to claim 1, wherein the first shutter speed is approximately 1/5.
0 sec, and the second shutter speed is almost 1 /
The imaging device according to claim 1, wherein the imaging time is 100 seconds. 6. The imaging apparatus according to claim 1, wherein the predetermined gain is a value that keeps image brightness constant before and after switching of a shutter speed.