JP2002238000A - Imaging device and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device that conducts smooth exposure control with respect to an illuminance change of an object, while securing proper S/N in a photographing under low illuminance conditions. SOLUTION: The imaging device 1 is provided with a lens section 11, that photographs the image of an object, a CCD 12 that applies photoelectric conversion to an incident light from the lens section, an S/H(sample and hold) circuit 13 that applies sampling and holding to the signals obtained through photoelectric conversion, a gain amplifier AGC 14 that adjust signal level, a signal processing circuit 15 that obtains a video signal, a shutter drive circuit 18 that adjusts the storage time of the electric charges of the CCD 12, and a control section 16 that sorts exposure control by gain adjustment and exposure control by storage time control, on the basis of a sorting pattern.

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 an image pickup method, and more particularly, to exposure control that smoothly changes the illuminance of a subject while ensuring a good S / N ratio even when photographing under low illuminance conditions. The present invention relates to an image capturing apparatus and an image capturing method.

[0002]

2. Description of the Related Art In a conventional image pickup apparatus, when the illuminance of a subject is low, a signal obtained by photoelectrically converting the image of the subject requires more gain adjustment, so that the ratio of noise to the signal (S / N ratio) is reduced. become worse. It is generally known that at such low illuminance, the gain adjustment can be suppressed and the S / N ratio can be improved by setting the charge storage time of the photoelectric conversion element to be equal to or longer than the image capturing cycle. Here, the charge accumulation time corresponds to the shutter open time, and the case where the charge accumulation time is equal to or longer than the image capturing cycle
For example, in the case of a video image captured at a period of 1/30 second, this corresponds to making the exposure time longer than 1/30 second of opening the shutter. In addition, opening the shutter for a longer time than the imaging cycle and performing exposure is expressed as a slow shutter, and in the case of an exposure time within the imaging cycle,
Expressed as a normal shutter.

FIG. 8A shows a state in which a conventional imaging apparatus adjusts a gain according to the illuminance of a subject. FIG. 8B shows a state in which the conventional imaging apparatus controls the exposure time according to the illuminance of the subject. FIG.
8A and 8B, the horizontal axis indicates the illuminance (AE_LEVEL) of the subject, and the horizontal axis indicates an area where exposure control is performed by gain adjustment in order of low illuminance and an area where exposure control is performed using a slow shutter. And a region where exposure control is performed by a normal shutter. That is, it is predetermined that the imaging apparatus performs exposure control by any one of gain adjustment control, slow shutter control, and normal shutter control according to the illuminance.

As shown in FIGS. 8 (a) and 8 (b), the conventional image pickup apparatus controls the exposure by changing the gain adjustment value when the illuminance is low, and changes the shutter opening time when the illuminance is high. Exposure is controlled.

As described above, the conventional imaging apparatus combines the accumulation time control within the imaging cycle, the slow shutter control, and the gain adjustment in accordance with the illuminance of the subject, thereby reducing the S / N ratio even at low illuminance. It holds and realizes appropriate exposure control.

[0006]

However, in the conventional imaging apparatus, especially in an area where exposure control is performed by slow shutter control, exposure is performed for a longer time than a normal imaging cycle. As a result, the image is blurred and the smoothness of the image is impaired.

More specifically, FIG. 9A shows the relationship between illuminance and exposure time, and FIG. 9B shows the relationship between illuminance and frame rate. That is, the conventional imaging device is
When the illuminance of the subject decreases, the exposure time is lengthened to perform the exposure control. However, the frame rate at this time is
It decreases as the exposure time becomes longer. In particular, when the illuminance of the subject frequently moves between the boundary positions between the normal shutter region and the slow shutter region, there is a problem that a change in the frame rate is large and the obtained image is coarse and coarse.

Accordingly, the present invention has been proposed in view of such a conventional situation. In photographing under a low illuminance condition, a good S / N ratio is ensured and a change in the illuminance of a subject is smoothly performed. It is an object of the present invention to provide an imaging apparatus and an imaging method that can perform exposure control on an image.

[0009]

In order to achieve the above-mentioned object, an image pickup apparatus according to the present invention controls conversion means for photoelectrically converting an image of a subject and accumulation time of electric charges stored in the conversion means. Storage time control means, gain adjustment means for adjusting the gain of the signal converted by the conversion means, and illuminance detection means for detecting the illuminance of the subject, and charges the conversion means over the imaging cycle of the image of the subject. In an imaging apparatus having a mode for setting an accumulation period, when a decrease in the illuminance value is detected by the illuminance detection unit in the mode, exposure control is preferentially performed by the gain adjustment unit, and adjustment of the gain adjusted by the gain adjustment unit is performed. Control means for switching from exposure control by the gain adjustment means to exposure control by the charge accumulation time in the accumulation time control means in accordance with the duration of the period in which the value is greater than zero Provided.

In such an image pickup apparatus, when a decrease in the illuminance value is detected by the illuminance detection means in the mode, exposure control is performed by preferentially performing gain adjustment, so that the gain adjustment value is larger than zero. Switching is performed from exposure control by gain adjustment to exposure control by charge accumulation time according to the duration of a certain period. In particular, the control means performs the distribution of the exposure control by the gain adjustment and the exposure control by the accumulation time control based on the distribution pattern.

[0011] In order to achieve the above object, an imaging method according to the present invention comprises a conversion step of photoelectrically converting an image of a subject;
A storage time control step of controlling the storage time of the charges stored in the conversion step, a gain adjustment step of adjusting the gain of the signal converted in the conversion step, and an illuminance detection step of detecting the illuminance of the subject; In an imaging method having a mode for setting a period for accumulating charges beyond the imaging cycle of the image, when detecting a decrease in the illuminance value in the illuminance detection step in this mode, preferentially controls exposure by a gain adjustment step, Control for switching from exposure control by gain adjustment in the gain adjustment step to exposure control by charge accumulation time in the accumulation time control step in accordance with the duration of a period in which the gain adjustment value adjusted in the gain adjustment step is greater than zero Process.

In such an imaging method, when a decrease in the illuminance value is detected in the illuminance detection step in the mode, exposure control is performed by preferentially performing gain adjustment, and the gain adjustment value is larger than zero. Switching is performed from exposure control by gain adjustment to exposure control by charge accumulation time according to the duration of a certain period. In particular, in the control step, the distribution between the exposure control by the gain adjustment and the exposure control by the accumulation time control is performed based on the distribution pattern.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image pickup apparatus shown as one configuration example of the present invention includes a photoelectric conversion element for photoelectrically converting an image of a subject and an accumulation time control means for controlling an accumulation time of electric charges accumulated in the photoelectric conversion element. And a gain adjustment unit that adjusts the gain of the signal converted by the photoelectric conversion element, and an illuminance detection unit that detects the illuminance of the subject.

This image pickup apparatus performs gain adjustment preferentially when the illuminance detector detects a decrease in illuminance value in a mode in which the shutter is opened and exposed beyond the imaging cycle of the image of the subject, particularly when the illuminance is detected. Even when the illuminance condition of the subject fluctuates, the exposure control is performed, and the exposure control based on the gain adjustment is switched from the exposure control based on the gain adjustment to the exposure control based on the shutter speed in accordance with the duration of the period in which the gain adjustment value is greater than zero. Smooth exposure control can be performed with respect to a change in the illuminance of the subject while ensuring a good S / N ratio.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The imaging device 1 is 1/30
This is an imaging device that captures frames (images) at intervals of seconds.
As shown in FIG. 1, an imaging device 1 includes a lens unit 11 that images a subject and a photoelectric conversion device (Charge Coupled Device) (hereinafter, a CCD) that photoelectrically converts incident light from the lens unit.
It is written. ) 12, a sampling / hold circuit (hereinafter, referred to as an S / H circuit) 13 for sampling and holding a signal obtained by photoelectric conversion, a gain amplifier AGC 14 for adjusting a signal gain, and a video signal. And a signal processing circuit 15 for obtaining the same. Each of these parts
Each circuit is generally controlled by a control unit 16. The imaging device 1 further includes a shutter drive circuit 18 that adjusts the charge accumulation time of the CCD 12. In FIG. 1, solid lines indicate signals of incident light from a subject and photoelectrically converted incident light, and broken lines indicate control lines.

Light incident from a subject is electrically accumulated in the CCD 12 via the lens 11. CCD1
The signal representing the image of the subject photoelectrically converted in step 2 is subjected to double-layer correlation sampling processing in the S / H circuit 13 to reduce noise of accumulated charges in the CCD 12. Subsequently, the signal is sent to the gain amplifier AGC 14 and the signal level is adjusted. Subsequently, the signal representing the image of the subject photoelectrically converted by the CCD 12 is subjected to camera signal processing in a signal processing circuit 15 to become a video signal 17 of the subject. Further, the signal processing circuit 15 has a function as illuminance detection means for detecting the illuminance of the subject.

The control section 16 obtains a detection value 19 of the illuminance detected by the signal processing circuit 15 and adjusts the gain of the signal in the gain amplifier AGC 14 and the accumulation time in the CCD 12 in accordance with the detection value 19. Exposure is appropriately controlled by controlling the drive circuit 18. When the signal detection circuit 15 detects a decrease in the illuminance of the subject in the mode in which the charge accumulation period in the CCD 12 is set beyond the imaging cycle of the subject image, the control unit 16 first gives priority to the gain amplifier AGC14. The exposure control is switched from the exposure control by the gain amplifier AGC 14 to the exposure control by adjusting the charge accumulation time in the CCD 12 in accordance with the period in which the gain adjustment value is larger than zero. Here, the exposure control by adjusting the charge accumulation time in the CCD 12 can be considered as the control of the shutter open time.

Exposure control (AE control) in control section 16
Will be described with reference to FIG. The control unit 16 can be considered to have a configuration as specifically shown in FIG. That is, the control unit 16 stores a reference AE storage unit 21 that stores a level serving as a reference for exposure (AE), an amplifier 22 that multiplies a detection value 19 of illuminance by a predetermined gain, and a detection value that is further multiplied by a coefficient. Integrate the illuminance of the subject (AE_L
It has an integrator 23 for calculating EVEL) and a distribution pattern storage unit 24 for storing a distribution pattern representing distribution between exposure control by gain adjustment and exposure control by charge accumulation time control. These components are collectively controlled by the CPU 25.

The control section 16 multiplies the error amount of the detection value 19 with respect to the reference level of exposure from the reference AE storage section 21 by the gain in the amplifier 22 to obtain a control amount for each frame. Subsequently, the control unit 16 calculates the illuminance of the subject by integrating the control amount for each frame. The control unit 16 determines the adjustment value of the gain in the gain amplifier AGC 14 and the exposure time in the shutter drive circuit 18 according to the illuminance, and controls the exposure. Here, the control unit 16
Is performed on the basis of a distribution pattern giving distribution of exposure control by gain adjustment and exposure control by accumulation time control.

For example, FIG. 3 shows one of the distribution patterns of the exposure control based on the gain adjustment according to the illuminance and the exposure control based on the accumulation time control, that is, the exposure control in the gain amplifier AGC 14 and the exposure control based on the shutter open time. . Note that the normal shutter means that the shutter opening time is within the imaging cycle, and the slow shutter means that the shutter opening time exceeds the imaging cycle.

FIG. 3A shows the relationship between the gain amplifier AGC 14 shown as pattern 1 (hereinafter referred to as an initial pattern) and the illuminance, and FIG. 3B shows the relationship between the shutter open time and the illuminance. It is shown. In the initial pattern shown in FIG. 3, when the illuminance is large, the exposure is controlled by the shutter open time, and when the illuminance is less than a predetermined illuminance, the shutter is opened for 1/30 second, and the exposure is controlled by the gain adjustment in the gain amplifier AGC14. It is a pattern.

FIG. 4 shows a second distribution pattern different from the initial pattern. FIG. 4A shows the gain amplifier AG in the second distribution pattern.
The relationship between C14 and illuminance is shown, and FIG.
The relationship between the shutter open time and the illuminance in the distribution pattern of FIG. The second distribution pattern is
When the illuminance is large, the exposure is controlled by the shutter open time, and when the illuminance is equal to or less than a predetermined illuminance, the exposure is controlled by the gain adjustment in the gain amplifier AGC 14, with the shutter open time as the predetermined value of the slow shutter.

FIG. 5 shows a third distribution pattern different from the initial pattern and the second distribution pattern. FIG. 5A shows the relationship between the gain amplifier AGC 14 and the illuminance in the third distribution pattern, and FIG. 5B shows the relationship between the shutter open time and the illuminance in the third distribution pattern. It is shown.
In the third distribution pattern, when the illuminance is large, the exposure is controlled by the shutter open time, and when the illuminance is equal to or less than a predetermined illuminance, the exposure is adjusted by a gain adjustment in the gain amplifier AGC14 as a predetermined value of a slow shutter with a longer shutter open time. This is the pattern to be controlled.

Referring to FIG. 6, a description will be given, with reference to FIG. 6, of a process in which the control section 16 sorts exposure control by gain adjustment and exposure control by accumulation time control based on the sorting pattern.

In step S1, the controller 16 determines whether or not the shutter release time is in the slow shutter area. If the shutter release time is not in the slow shutter region in step S1, the control unit 16 determines in step S2 whether the gain adjustment value is 0 dB by the gain amplifier AGC14. When the gain adjustment value is 0 dB, the control unit 16 returns the distribution pattern to the initial pattern in step S3, sets the shutter open time according to the illuminance according to the behavior of the initial pattern, and sets the setting signal. To the shutter drive circuit 18.

The control unit 16 determines that the shutter release time is not in the slow shutter region and the gain adjustment value is 0 dB.
If not, in step S4, a timer for measuring a period during which the gain adjustment value is larger than 0 dB is started. In step S5, if the preset time has been reached, the distribution pattern is changed in step S6, and the shutter opening time according to the illuminance and the gain adjustment value according to the illuminance are changed according to the behavior of the changed pattern. The setting signal is sent to the shutter drive circuit 18 and the gain amplifier AGC 14.

If the shutter release time is in the slow shutter area in step S1, the control unit 16 determines in step S7 whether the gain adjustment value of the gain amplifier AGC 14 is 0 dB. When the gain adjustment value is 0 dB, the control unit 16
Ends the process without changing the distribution pattern.

On the other hand, the control unit 16 determines in step S1 that the shutter release time is in the slow shutter area and the gain adjustment value in the gain amplifier AGC 14 is 0.
If not, the process of step S6 is performed.

Since the processing shown in FIG. 6 is periodically executed, the processing pattern of the exposure control is always switched according to the illuminance, the adjustment value of the gain at the illuminance, and the shutter open time.

Here, the above three patterns have been described. However, the control unit 16 performs the above-described distribution showing the relationship between the exposure control by adjusting the illuminance and the gain and the exposure control by adjusting the shutter open time in more detail. A plurality of patterns are stored. The control unit 16 enables stable exposure control by switching these plurality of distribution patterns stepwise at a speed that does not affect the response time of the exposure control.

FIG. 7 shows the behavior of the exposure control in the image pickup apparatus 1 when the illuminance of the subject actually changes in time series.
This will be described with reference to FIG. 7A shows a time-series change in the illuminance of the subject, FIG. 7B shows a time-series change in the shutter open time, and FIG. 7C shows a gain amplifier AGC.
The time series change of the gain adjustment value at 14 is shown.

When the illuminance of the detected subject decreases, the image pickup apparatus 1 controls the exposure by extending the shutter open time (period A). When the shutter open time becomes 1/30 second corresponding to one frame, the shutter open time temporarily becomes constant, the mode is switched to gain adjustment, and the timer starts counting (period B). At this time, the control unit 16 performs a process corresponding to step S3 in FIG. That is, under the control of the control unit 16, the gain amplifier AGC 14 performs gain adjustment according to the decrease in illuminance based on the distribution pattern. In period B, the since there is no change in illuminance in b _2, but also the gain adjustment value with it has become a constant value, the illuminance in b ₂ can be considered of course be reduced. In that case, the behavior such as continued adjustment value of the gain is increased in b ₂ is obtained.

When the timer counts the predetermined period T, the control of the shutter open time is started (period C). The adjustment value of the gain in the gain amplifier AGC14 decreases based on the distribution pattern, and the adjustment of the shutter open time is performed until the gain adjustment value becomes 0 dB. This corresponds to the processing of steps S4 to S6 shown in FIG.

In the period D, when the detected illuminance of the subject again decreases, the gain amplifier AGC 14 adjusts the gain to execute exposure control, and the timer starts counting. At this time, the control unit 16 determines in step S7 in FIG.
From step S6. That is, under the control of the control unit 16, the gain amplifier AGC 14 performs gain adjustment according to the decrease in illuminance based on the distribution pattern.

When the timer counts the predetermined period T, control of the shutter opening time is started (period E). Based on the distribution pattern, the adjustment value of the gain in the gain amplifier AGC 14 decreases and the shutter opening time is adjusted until it becomes 0 dB. Here, since the shutter speed reaches the minimum value before the gain adjustment value becomes 0 dB, the gain that is not reduced remains.

When the detected illuminance of the subject starts to recover, the imaging apparatus 1 controls the gain adjustment value to return to 0 dB, and then executes the exposure control by shortening the shutter open time. .

As described above with reference to FIGS. 6 and 7, the imaging apparatus 1 switches to the slow shutter after a predetermined time has elapsed after the gain adjustment is performed by the gain amplifier AGC 14, and gradually reduces the shutter speed. I do. That is, the exposure time is lengthened. The imaging device 1 includes a gain amplifier AG
Until the gain adjustment at C14 becomes 0 dB, exposure control by gain adjustment and exposure control by accumulation time control are simultaneously performed based on the distribution pattern. Imaging device 1
Switches from exposure control by gain adjustment to exposure control by accumulation time control according to the length of the period in which exposure control is performed by gain adjustment. That is, the imaging apparatus 1 responds to the instantaneous change in the illuminance of the subject by adjusting the gain of the signal from the CCD 12, and controls the charge accumulation time according to the length of the period in which the gain is adjusted. Is supported by

The conventional image pickup apparatus has a problem that, particularly in an area where the exposure control is performed by the slow shutter control, the frame rate decreases as the illuminance decreases, so that the image is blurred and the smoothness of the image is impaired. Was. In particular, when the illuminance of the subject frequently moves between the boundary positions between the normal shutter region and the slow shutter region, the change in the frame rate becomes large, and the smoothness of the obtained image is lost. On the other hand, the imaging apparatus 1 performs exposure control by gain adjustment and exposure control by accumulation time control based on the distribution pattern according to the illuminance by the above-described processing, thereby stabilizing the illuminance change of the subject. Exposure control is possible. Also,
According to the imaging device 1, a good S / N ratio can be secured under low illuminance without abruptly changing the frame rate according to the illuminance change of the subject. Therefore, smooth exposure control can be performed with respect to the change in the illuminance of the subject.

Further, according to the image pickup apparatus 1, since the exposure can be controlled in accordance with the change in illuminance without using a mechanism such as an iris (aperture), the number of parts is reduced, thereby reducing the manufacturing cost. In addition, the size and weight of the imaging device itself can be reduced.

It should be noted that the present invention is not limited to only the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

[0041]

As described above in detail, the image pickup apparatus according to the present invention comprises a conversion means for photoelectrically converting an image of a subject;
A storage time control unit configured to control a storage time of charges stored in the conversion unit; a gain adjustment unit configured to adjust a gain of a signal converted by the conversion unit; and an illuminance detection unit configured to detect illuminance of the subject. In the imaging apparatus having a mode for setting a period for accumulating charges in the conversion means beyond the imaging cycle of the image of the image, when the illuminance detection means detects a decrease in the illuminance value in this mode, the gain adjustment means preferentially performs exposure. Control for switching from exposure control by the gain adjusting means to exposure control by the charge accumulation time in the accumulation time control means in accordance with the duration of the period in which the gain adjustment value adjusted by the gain adjustment means is greater than zero. Means.

In such an image pickup apparatus, when a decrease in the illuminance value is detected by the illuminance detection means in the mode, exposure control is performed by preferentially performing gain adjustment, so that the gain adjustment value is larger than zero. Switching is performed from exposure control by gain adjustment to exposure control by charge accumulation time according to the duration of a certain period. In particular, the control means performs the distribution of the exposure control by the gain adjustment and the exposure control by the accumulation time control based on the distribution pattern.

Therefore, the image pickup apparatus according to the present invention can smoothly perform exposure control with respect to a change in illuminance of a subject while securing a good S / N ratio even when photographing under low illuminance conditions. Become. Further, according to the imaging apparatus of the present invention, it is possible to perform exposure control according to changes in illuminance without using a mechanism such as an iris (aperture). A reduction in size and weight is realized.

Further, according to the imaging method of the present invention, there is provided a conversion step of photoelectrically converting an image of a subject, a storage time control step of controlling a storage time of charges stored in the conversion step, and a signal converted in the conversion step. A gain adjusting step of adjusting the gain of the subject, and an illuminance detecting step of detecting the illuminance of the subject, and an imaging method having a mode for setting a period for accumulating charges beyond the imaging cycle of an image of the subject, When a decrease in the illuminance value is detected in the illuminance detection step, the exposure is preferentially controlled by the gain adjustment step, and the gain is adjusted according to the duration of the period in which the adjustment value of the gain adjusted in the gain adjustment step is larger than zero. A control step is provided for switching from exposure control by gain adjustment in the adjustment step to exposure control by charge accumulation time in the accumulation time control step.

In such an imaging method, when a decrease in the illuminance value is detected in the illuminance detection step in the mode, exposure control is performed by preferentially performing gain adjustment, and the gain adjustment value is larger than zero. Switching is performed from exposure control by gain adjustment to exposure control by charge accumulation time according to the duration of a certain period. In particular, in the control step, the distribution between the exposure control by the gain adjustment and the exposure control by the accumulation time control is performed based on the distribution pattern.

Therefore, according to the imaging method of the present invention, it is possible to control the exposure smoothly with respect to the change in the illuminance of the subject, while securing a good S / N ratio even when photographing under low illuminance conditions. It becomes possible. Further, according to the imaging method of the present invention, it is possible to perform exposure control according to a change in illuminance without using a mechanism such as an iris (aperture), and therefore, an imaging apparatus to which the imaging method of the present invention is applied is manufactured. Manufacturing costs are reduced. Further, the size and weight of the imaging device itself can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an imaging device according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a control unit of the imaging device according to the present invention.

FIG. 3 is a diagram showing a distribution pattern for distributing exposure control by a gain amplifier and exposure control by a shutter.

FIG. 4 is a diagram showing a distribution pattern for distributing exposure control by a gain amplifier and exposure control by a shutter.

FIG. 5 is a diagram showing a distribution pattern for distributing exposure control by a gain amplifier and exposure control by a shutter.

FIG. 6 is a flowchart illustrating a process in which the imaging apparatus according to the present invention switches between exposure control using a gain amplifier and exposure control using a shutter according to illuminance.

FIG. 7A is a diagram illustrating a time-series change in illuminance of a subject, and FIG. 7B is a diagram illustrating a change in a shutter open time when the illuminance of the subject changes in a time-series; FIG. 7C is a diagram illustrating a change in the gain adjustment value when the illuminance of the subject changes in a time series.

FIG. 8A shows an AGC in a conventional imaging apparatus.
FIG. 8B is a diagram showing the relationship between the illuminance of the subject and the illuminance of the subject.
FIG. 7 is a diagram illustrating a relationship between an exposure time and illuminance of a subject in a conventional imaging device.

FIG. 9A is a diagram showing a relationship between an exposure time and an illuminance with a subject in a conventional imaging apparatus, and FIG.
FIG. 3 is a diagram illustrating a relationship between a frame rate and illuminance of a subject in a conventional imaging device.

[Explanation of symbols]

1 imaging device, 11 lens unit, 12 CCD, 13
S / H circuit, 14 gain amplifier AGC, 15 signal processing circuit, 16 control unit, 17 video signal, 18 shutter drive circuit, 19 detection value, 21 reference AE storage unit, 22
Amplifier, 23 integrator, 24 distribution pattern storage, 25 CPU

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 5/235 H04N 5/235

Claims (6)

[Claims] A converting means for photoelectrically converting an image of a subject;
Accumulation time control means for controlling the accumulation time of the electric charge accumulated in the conversion means, gain adjustment means for adjusting the gain of the signal converted by the conversion means, and illuminance detection means for detecting the illuminance of the subject An imaging apparatus having a mode for setting a period for accumulating charges in the conversion means beyond the imaging cycle of the image of the subject, wherein the gain is set when the illuminance detection means detects a decrease in illuminance value in the mode. Exposure control is preferentially performed by the adjustment means, and the exposure control by the gain adjustment means is performed by the accumulation time control means in accordance with the duration of the period in which the gain adjustment value adjusted by the gain adjustment means is greater than zero. An imaging apparatus, comprising: control means for switching to exposure control based on charge accumulation time. 2. An image pickup apparatus according to claim 1, wherein said control means performs exposure control based on a distribution pattern representing distribution between exposure control by said gain adjustment means and exposure control by said accumulation time control means. apparatus. 3. The control means according to claim 1, wherein said control means controls a plurality of distribution patterns in which exposure control by said gain adjustment means and exposure control by said accumulation time control means are performed stepwise in accordance with an illuminance value in said illuminance detection means. 3. The imaging apparatus according to claim 2, wherein exposure control is performed by continuously switching. 4. A conversion step of photoelectrically converting an image of a subject,
An accumulation time control step of controlling the accumulation time of the electric charge accumulated in the conversion step, a gain adjustment step of adjusting the gain of the signal converted in the conversion step, and an illuminance detection step of detecting the illuminance of the subject. An imaging method having a mode for setting a period for accumulating charges beyond the imaging cycle of the image of the subject, wherein, when a decrease in the illuminance value is detected in the illuminance detection step in the mode, priority is given to the gain adjustment step. Exposure control, and the charge control in the accumulation time control step from the exposure control by gain adjustment in the gain adjustment step in accordance with the duration of the period in which the gain adjustment value adjusted in the gain adjustment step is greater than zero. An imaging method comprising: a control step of switching to exposure control based on the accumulation time of the image. 5. The exposure control according to claim 4, wherein in the control step, the exposure control is performed based on a distribution pattern representing the distribution of the exposure control in the gain adjustment step and the exposure control in the accumulation time control step. Imaging method. 6. The control step includes: distributing a plurality of distribution patterns in which exposure control in the gain adjustment step and exposure control in the accumulation time control step are performed stepwise in accordance with an illuminance value in the illuminance detection step. 6. The imaging method according to claim 5, further comprising a step of performing exposure control by continuously switching.