JP2010200089A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an imaging apparatus capturing a sharp image with an excellent S/N ratio even in low-illuminance environment. <P>SOLUTION: An imaging apparatus includes: a slow-shutter function for outputting charges photo-electrically converted by a solid-state imaging sensor after accumulating the charges for a fixed period of time, and an electronic amplification function for amplifying and outputting the charges photo-electrically converted by the solid-state imaging sensor. When the slow-shutter function is in operation, an exposure time is switched in accordance with illuminance measured by an illuminance measuring part, to change multiplication of electronic amplification in accordance with the exposure time and the illuminance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus having an electron multiplication function and a slow shutter function for adjusting the brightness of a captured image captured using a solid-state imaging device.

In conventional imaging devices, an electron multiplication function that improves the sensitivity of captured images in a dark environment by multiplying and outputting the charge accumulated in the solid-state imaging device as a high-sensitivity function in a low-light environment And a slow shutter function that makes it possible to capture even weak light by extending the charge accumulation time of the solid-state imaging device by taking an image with an extended shutter time (exposure time).
When such an electronic multiplication function and a slow shutter function are used in the same imaging device, the electronic multiplication function and the slow shutter function are controlled independently as separate brightness control modes. During operation, the exposure time is fixed and the multiplication factor of electron multiplication is changed.When the slow shutter function is activated, the exposure time is gradually increased as the image becomes darker, and the multiplication factor of electron multiplication is fixed to a constant value. It was common.

  Further, as a conventional technique, by reading AGC (Auto Gain Control) correction data corresponding to the magnification of the exposure time of the slow shutter function and correcting the AGC value, the amount of change in the brightness of the subject entering from the lens There is a television camera apparatus that matches the amount of change in an output video signal due to a change in the magnification of the exposure time of the slow shutter function (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-75007 (page 4-5, FIG. 1)

In the conventional imaging device, the exposure time of the slow shutter function is extended stepwise by 2 times, 4 times, 6 times, etc., so the resolution of the convergence luminance amplification level is low, and the image is overexposed. There was a problem that the image was blackened and a clear captured image could not be obtained.
Further, Patent Document 1 aims to match the amount of change in brightness of a subject entering from a lens with the amount of change in an output video signal due to a change in the magnification of the exposure time of the slow shutter function. The problem that a clear captured image cannot be acquired due to the low resolution of the convergence luminance amplification level of the slow shutter function in the apparatus cannot be solved.

  The present invention has been made in order to solve the above-described problems, and it is an object of the present invention to obtain an imaging apparatus capable of acquiring a clear captured image with a good S / N ratio even in a low illumination environment. It is the purpose.

  An image pickup apparatus according to the present invention includes a solid-state image pickup device that photoelectrically converts light to generate electric charges and outputs the output, an amplifier that amplifies the electric charges output from the solid-state image pickup device and outputs the electric signals, and the amplifier outputs A video signal processing unit that generates and outputs a video signal based on the electrical signal, a video signal output unit that converts the video signal output by the video signal processing unit into a video format for display, and an external An illuminance measuring unit that measures the illuminance of the image, and a control unit that adjusts the brightness of the captured image when the video signal is displayed, and the charge that has been photoelectrically converted by the solid-state imaging device is accumulated for a certain period of time and then output. When the slow shutter function is in operation, the control unit has an electron multiplication function for multiplying and outputting the photoelectrically converted electric charge of the solid-state imaging device. Switches the exposure time according to the illuminance measured by the illuminance measurement unit, in which the multiplication factor of the photomultiplier was set to vary depending on the exposure time and the intensity.

  Since the imaging device according to the present invention switches the exposure time according to the illuminance measured by the illuminance measurement unit during the slow shutter function operation, and changes the multiplication factor of the electron multiplication according to the exposure time and the illuminance, There is an effect that a captured image having a clear and good S / N ratio can be obtained even in a low illumination environment.

1 is a block diagram illustrating a configuration of an imaging apparatus according to Embodiment 1. FIG. It is a figure which shows the relationship between the brightness | luminance control mode in the conventional imaging device, and each setting value at the time of each brightness | luminance control mode operation | movement. It is a figure which shows the relationship between the luminance control mode in a conventional imaging device, and a luminance amplification level. It is a figure which shows the relationship between the luminance control mode in the imaging device of this invention and each setting value at the time of each luminance control mode operation | movement. 6 is a diagram illustrating a relationship between an exposure time in a slow shutter control mode and a multiplication factor of electron multiplication in the imaging apparatus according to Embodiment 1. FIG. 6 is a diagram illustrating a relationship between a luminance control mode and a luminance amplification level in the imaging apparatus according to Embodiment 1. FIG. It is a figure which shows the relationship between the exposure time at the time of slow shutter control mode in case the sensitivity of the electron multiplication of CCD2 which concerns on Embodiment 2 varies, and a luminance amplification level. 6 is a block diagram illustrating a configuration of an imaging apparatus according to Embodiment 2. FIG. It is a data block diagram which shows an example of the data structure of the data table 16 which concerns on Embodiment 2.

Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating a configuration of the imaging apparatus according to the first embodiment. In the figure, light incident through a lens 1 is imaged by a CCD (Chaage Coupled Device) 2 as a solid-state imaging device, and an optical image of a subject is generated. The CCD 2 photoelectrically converts this optical image to generate electric charge, and outputs it to a CDS (Correlated Double Sampling) 3. The CDS 3 removes the noise of the electric charge output from the CCD 2, and the amplifier 4 amplifies the electric charge from which the noise has been removed and outputs it as an electrical signal. The analog signal is converted into an analog signal by the A / D (Analog to Digital) converter 5. A certain electric signal is converted into a digital signal. The digital signal converted by the A / D converter 5 is output to the video signal processing unit 6. The video signal processing unit 6 performs various types of image processing on the input digital signal to generate a video signal. The video signal output from the video signal processing unit 6 is converted into a predetermined video format by the video signal output unit 7 and output to an external display unit (not shown). The video signal converted into a predetermined video format is displayed on the display unit as a captured image.

  A luminance level detection circuit 8 as a luminance level detection unit detects the luminance level of the video signal generated by the video signal processing unit 6. The microprocessor 9 serving as a control unit is responsible for various controls of the imaging apparatus, and also adjusts the brightness of the captured image when the video signal is displayed. The I / F unit 10 is for realizing a command interface with the outside. When a command is input from the I / F unit 10, the microprocessor 9 discriminates the input command and stores the command in the imaging apparatus. Each block is controlled to determine the operation of the imaging apparatus.

  The electron multiplication control circuit 11 determines the multiplication factor of the electron multiplication based on the signal output from the microprocessor 9, and the CCD drive circuit 12 determines a predetermined value based on the multiplication factor determined by the electron multiplication control circuit 11. Are supplied to the CCD 2. Based on a predetermined drive pulse supplied from the CCD drive circuit 12, the CCD 2 multiplies the photoelectrically converted charge and outputs it to the CDS 3.

  The timing generator 13 determines the exposure time based on the signal output from the microprocessor 9, and the CCD drive circuit 12 supplies a predetermined drive pulse to the CCD 2 based on the exposure time determined by the timing generator 13. Based on a predetermined drive pulse supplied from the CCD drive circuit 12, the CCD 2 accumulates the photoelectrically converted charge for a certain period and outputs it to the CDS 3. Further, the video data for one field is stored in the memory circuit 14, and the video signal processing unit 6 stores the video data in the memory circuit 14 when the slow shutter function is operating and there is a period in which the video signal is not output. The output video data is output to the video signal output unit 7 as complementary video data.

  The lens driving circuit 15 drives the lens 1 based on a signal from the microprocessor 9.

Here, in order to compare with the imaging apparatus according to the present invention, the luminance control operation of the conventional imaging apparatus will be described.
First, FIG. 2 shows three brightness control modes which are types of control modes for adjusting the brightness (brightness) of a captured image in accordance with the external illuminance (environmental illuminance) and increasing the sensitivity in the conventional imaging device. It is a figure which shows the relationship with each setting value of the aperture_diaphragm | restriction in each brightness | luminance control mode operation | movement, the multiplication factor of electron multiplication, and exposure time.

  The brightness control mode transitions in the order of aperture control mode, electron multiplication control mode, and slow shutter control mode as the imaging environment changes from a bright state to a dark state.

The microprocessor 9 drives the aperture control mode when the environmental illuminance measured by the illuminance measurement unit (not shown) is higher than the illuminance A (the outside is bright). In the aperture control mode, the microprocessor 9 includes an aperture (not shown) incorporated in the lens 1 via the lens driving circuit 15 so that the amount of light incident on the lens 1 increases as the outside becomes darker (the ambient illuminance decreases). Control the aperture to close the aperture so that the amount of light incident on the lens 1 decreases as the outside becomes brighter, and the captured image will appear white when it is bright or the subject of the captured image when it is dark The brightness (brightness level) of the captured image is adjusted so that the image is not easily seen.
In the aperture control mode, the multiplication factor for electron multiplication is a minimum value, and the exposure time is fixed (for example, fixed to 1/60 seconds).

Next, when the ambient illuminance is between illuminances A and B where sufficient brightness is not obtained in the captured image by the control in the aperture control mode, the microprocessor 9 drives the electron multiplication control mode and operates the electron multiplication function. Let In the electron multiplication control mode, when the microprocessor 9 outputs a control signal to the electron multiplication control circuit 11 based on the ambient illuminance, the electron multiplication control circuit 11 performs the electron multiplication based on the control signal input from the microprocessor 9. Determine the multiplication factor. Based on the multiplication factor determined by the electron multiplication control circuit 11, the CCD drive circuit 12 supplies a predetermined drive pulse to the CCD 2. When the CCD 2 accumulates and outputs charges obtained by photoelectrically converting the optical image formed on the CCD 2, the accumulated charges are output by multiplying the charges based on the drive pulse from the CCD drive circuit 12. The sensitivity of the captured image in a dark environment can be increased.
In the electron multiplication control mode, the aperture is in the open state, and the exposure time is fixed as in the aperture control mode.

Further, when the ambient illuminance is lower than the illuminance B state (the outside is dark), the microprocessor 9 drives the slow shutter control mode because sufficient brightness cannot be obtained in the captured image even by the control in the electron multiplication control mode. , Operate the slow shutter control mode. In the slow shutter control mode, the microprocessor 9 increases the luminance amplification level of the image pickup device by increasing the accumulation time when accumulating the photoelectrically converted charge by the CCD 2 to 2 times, 4 times, 6 times, and so on. The image can be captured even with weak light.
In the slow shutter control mode, the aperture is in the open state, and the multiplication factor of the electron multiplication is the maximum value.

  FIG. 3 is a diagram illustrating the relationship between three luminance control modes and luminance amplification levels in a conventional imaging apparatus. In the figure, the horizontal axis represents three luminance control modes that are switched according to the ambient illuminance, and the vertical axis represents the luminance amplification level controlled according to the luminance control mode.

Since the aperture and the multiplication factor of the electron multiplication are controlled by the microprocessor 9, they are often controlled with a resolution of 256 or 1024 that can be easily processed by the microprocessor 9. Therefore, the luminance amplification level in the aperture control mode and the electron multiplication control mode changes almost continuously, so that the visual luminance level also changes smoothly.
On the other hand, since the exposure time in the slow shutter control mode changes stepwise by a value of 2 times, 4 times, 6 times,..., A step occurs in the luminance amplification level as shown in FIG. Due to the low resolution of the luminance amplification level in the slow shutter control mode, there has been a phenomenon that the image flies white or sinks black.

  Next, FIG. 4 is a diagram showing the relationship between the three brightness control modes and the set values when operating in each brightness control mode of the imaging apparatus according to the present invention. As in FIG. 2, the brightness control mode transitions in order of the aperture control mode, the electron multiplication control mode, and the slow shutter control mode as the imaging environment changes from a bright state to a dark state.

  The aperture in the aperture control mode and the electron multiplication control mode, the multiplication factor for electron multiplication, and the exposure time are the same as those in FIG. In the slow shutter control mode, the exposure time changes to 2 times, 4 times, 6 times,... As the darker, and the aperture is opened, but the multiplication factor of the electron multiplication is variable.

  FIG. 5 is a diagram illustrating the relationship between the exposure time in the slow shutter control mode and the multiplication factor of the electron multiplication in the imaging apparatus according to the first embodiment. In the figure, the horizontal axis represents the exposure time in the slow shutter control mode that switches according to the environmental illuminance, and the vertical axis represents the multiplication factor of the electron multiplication controlled according to the exposure time and the environmental illuminance.

  When the ambient illuminance decreases and transitions from the electron multiplication control mode to the slow shutter control mode, the microprocessor 9 outputs a control signal to the timing generator 13 so as to double the exposure time. When the exposure time is doubled, the overall luminance amplification level of the image pickup apparatus is also doubled. Therefore, the microprocessor 9 supplies the electron multiplication control circuit 11 with the multiplication factor of the electron multiplication and the minimum value of the electron multiplication control mode. The control signal is output so as to be a half value (setting value A in FIG. 5) between the maximum value (setting value B in FIG. 5). Thereafter, the microprocessor 9 outputs a control signal to the electron multiplication control circuit 11 so as to gradually increase the multiplication factor of the electron multiplication until the set value B is reached as the ambient illuminance decreases.

  When the ambient illuminance further decreases, the microprocessor 9 outputs a control signal to the timing generator 13 so that the exposure time is quadrupled. When the exposure time is quadrupled, the overall luminance amplification level of the image pickup apparatus is 4/2 times, so the microprocessor 9 sets the electronic multiplication control circuit 11 to a minimum value and a set value B. A signal is output so as to be 2/4, that is, a value of 1/2. Thereafter, the microprocessor 9 outputs a control signal to the electron multiplication control circuit 11 so as to gradually increase the multiplication factor of the electron multiplication until the set value B is reached as the ambient illuminance decreases.

Further, when the ambient illuminance decreases, the microprocessor 9 outputs a signal to the timing generator 13 so as to increase the exposure time by six times. When the exposure time is 6 times, the overall luminance amplification level of the image pickup device is 6/4 times, so that the microprocessor 9 sets the electron multiplication control circuit 11 to a minimum value and a set value B. A signal is output so that the value becomes 4/6, that is, 2/3. Thereafter, the microprocessor 9 outputs a control signal to the electron multiplication control circuit 11 so as to gradually increase the multiplication factor of the electron multiplication until the set value B is reached as the ambient illuminance decreases.
Thereafter, the multiplication factor of the electron multiplication is similarly changed according to the environmental illuminance.

  As described above, as a result of increasing the resolution of the convergence luminance amplification level in the slow shutter control mode, the luminance amplification level in the slow shutter control mode changes almost continuously as shown in FIG. The upper luminance level can be changed smoothly.

  In the first embodiment, even when the exposure time of the imaging apparatus changes stepwise from 2 times, 4 times, and 6 times, the multiplication factor of the electron multiplication is gradually changed according to the ambient illuminance. As a result, the brightness amplification level can be changed smoothly, and a captured image with a clear and good S / N ratio can be obtained.

Embodiment 2. FIG.
In the first embodiment, the multiplication factor of the electron multiplication is gradually changed based on the exposure time and the ambient illuminance. However, the sensitivity of the electron multiplication of the charge multiplication type CCD 2 is the individual difference of the CCD 2 or the CCD 2. It is known that it varies due to reasons such as secular change, and when such a variation occurs, a deviation occurs between the assumed luminance amplification level and the actual luminance amplification level, It becomes difficult to perform good brightness control.
In the second embodiment, even when the sensitivity of the electron multiplication of the charge multiplying CCD 2 varies, the luminance control can be performed satisfactorily, and the captured image with excellent visibility can be acquired. The apparatus will be described.

  As described in the first embodiment, when the exposure time is changed, the multiplication factor of the electron multiplication is set to a predetermined value corresponding to the exposure time, and then the multiplication factor of the electron multiplication is reduced as the ambient illuminance decreases. Is gradually increased until reaching the set value B, if the sensitivity of the electron multiplication of the CCD 2 is as expected, the result is as shown in FIG. It will not be continuous. However, when the sensitivity of the electron multiplication of the CCD 2 varies in the direction in which the sensitivity is larger than the expected value, the luminance amplification level becomes larger than expected, and in the case in which the sensitivity is smaller, the luminance amplification level is larger than expected. Therefore, the brightness amplification level becomes discontinuous before and after the exposure time is switched.

  FIG. 7 shows the relationship between the exposure time and the luminance amplification level in the slow shutter control mode when the sensitivity of the electron multiplication of the CCD 2 varies in the direction larger than the assumed value in the imaging apparatus according to the second embodiment. FIG. In the figure, the horizontal axis represents the exposure time in the slow shutter control mode that switches according to the environmental illuminance, and the vertical axis represents the luminance amplification level controlled according to the exposure time and the environmental illuminance.

  As the luminance amplification level becomes discontinuous in this way, the luminance of the video signal varies when the exposure time is switched. When switching to increase the exposure time, if the sensitivity of electron multiplication varies in the direction that increases, the brightness decreases, and if the sensitivity of electron multiplication decreases, the brightness increases. Because of the fluctuations, when the exposure time is switched, the captured image displayed on the display suddenly becomes brighter or darker, and hunting (the captured image becomes brighter or darker) is repeated. The brightness is not stable).

  FIG. 8 is a block diagram illustrating a configuration of the imaging apparatus according to the second embodiment. In the figure, the same components as those in FIG. 1 are denoted by the same numbers. Unlike FIG. 1, in FIG. 8, the microprocessor 9 is provided with a data table 16 and a learning means 17 that store a set value string of multiplication factors for electron multiplication set in the slow shutter control mode.

FIG. 9 is a data configuration diagram illustrating an example of a data configuration of the data table 16 according to the second embodiment. The data table 16 stores the theoretical value sequence of the multiplication factor of electron multiplication and the set value sequence of the multiplication factor of electron multiplication in the first embodiment in association with each other.
The set value of the multiplication factor for electron multiplication should be corrected so that the luminance level index value, which is the luminance level input from the luminance level detection circuit 8, is the same as the target luminance level in the slow shutter control mode. This is a value after correction of the multiplication factor of electron multiplication, and is determined by the difference between the target luminance level and the luminance level index value.

First, when transitioning from the electronic multiplication control mode to the slow shutter control mode, the data table 16 stores a set value sequence of multiplication factors for electron multiplication set in the slow shutter control mode.
When transitioning to the slow shutter control mode, the microprocessor 9 acquires the current brightness level from the brightness level detection circuit 8, and generates the data table 16 using this brightness level as the brightness level index value. For example, if the target luminance level is 10 and the luminance level index value is 11 at the time of transition in the slow shutter control mode, the sensitivity of the electron multiplication of the CCD 2 varies in a direction that is larger than the assumed value. The sensitivity is 1.1 times (11/10) of the assumed value. Therefore, as shown in FIG. 9, the setting value of the multiplication factor of the electron multiplication in the data table 16 is corrected to be a value obtained by dividing the theoretical value of the multiplication factor of the electron multiplication by 1.1. Good. In FIG. 5 of the first embodiment, when the multiplication factor setting value B for electron multiplication is doubled, the setting value A is 1.5 times, but FIG. 9 shows the multiplication factor for electron multiplication. This is a data table 16 when the set value B is doubled, and is not set to a value greater than the set value B or less than the set value A. The range is up to twice.

Next, the microprocessor 9 determines the set value of the multiplication factor of the electron multiplication based on the theoretical value of the multiplication factor of the electron multiplication and the generated data table 16, and sends a control signal to the electron multiplication control circuit 11. Output.
Thereafter, in the slow shutter control mode, the microprocessor 9 determines the set value of the multiplication factor of the electron multiplication on the basis of the theoretical value of the multiplication factor of the electron multiplication and the data table 16, and controls the control by the electron multiplication control circuit 11. Output a signal.

  As described above, since the multiplication factor of the electron multiplication in the slow shutter control mode is determined based on the target brightness level in the slow shutter control mode and the brightness level index value acquired from the brightness level detection circuit 8, the CCD 2 Even when the sensitivity of electron multiplication varies due to individual differences, the brightness amplification level before and after switching of the exposure time changes almost continuously, and the captured image displayed on the display section suddenly becomes brighter. It won't be dark and will not hunting.

Next, every time the learning unit 17 switches to increase the exposure time, the amount of change in the luminance level of the video signal is detected, and the electronic increase stored in the data table 16 is prevented so that the luminance level does not change. An operation for rewriting the set value string of the double multiplication factor will be described.
First, the microprocessor 9 acquires the luminance level from the luminance level detection circuit 8 immediately before switching to increase the exposure time. Thereafter, when the microprocessor 9 determines the set value of the multiplication factor of the electron multiplication based on the theoretical value of the multiplication factor of the electron multiplication and the current data table 16, and outputs a control signal to the electron multiplication control circuit 11. The microprocessor 9 acquires the brightness level from the brightness level detection circuit 8 again. This luminance level is the luminance level of the video signal that has been subjected to the electron multiplication by the setting value of the multiplication factor of the electron multiplication determined based on the data table 16 by extending the exposure time.

Next, the learning means 17 compares the brightness levels before and after switching of the exposure time. If there is no change in the brightness level, the learning means 17 determines that the sensitivity of the electron multiplication of the CCD 2 is correctly corrected, and then sets the exposure time. The data table 16 is not updated until switching to make it longer.
If there is a variation in the brightness level, the learning means 17 updates the set value string of the multiplication factor of the electron multiplication in the data table 16 so that the sensitivity of the electron multiplication of the CCD 2 can be corrected correctly according to the variation amount. For example, when the luminance level before switching of the exposure time is 10 and the luminance level after switching is 9, the correction value by the set value of the multiplication factor of the electronic multiplication in the data table 16 Is too large, and its sensitivity is 0.9 times (9/10) before switching. Therefore, the setting value of the multiplication factor of the electron multiplication in the data table 16 of FIG. 9 is recorrected and updated so as to be a value obtained by dividing the setting value of the multiplication factor of the electron multiplication by 0.9.
Thereafter, the microprocessor 9 determines the set value of the multiplication factor of the electron multiplication based on the theoretical value of the multiplication factor of the electron multiplication and the updated data table 16, and outputs a control signal to the electron multiplication control circuit 11. To do.

  Thus, when switching to increase the exposure time in the slow shutter control mode, the setting value of the multiplication factor of the electronic multiplication in the data table 16 is corrected to the optimum value based on the amount of change in the luminance level before and after the switching. By providing a learning function to be updated, it is possible to obtain a good captured image with a stable brightness level even when the sensitivity of the electron multiplication of the charge multiplying CCD 2 varies due to aging of the CCD 2 or the like. And a captured image with excellent visibility can be acquired.

  In the above embodiment, the configuration in which the multiplication factor of the electron multiplication in the slow shutter control mode is set with reference to the data table 16, but the theoretical value and the setting of the multiplication factor of the electron multiplication in the data table 16 has been described. You may make it comprise the arithmetic processing by the arithmetic expression which shows the relationship with a value sequence, or combining arithmetic processing and the data table 16. FIG.

  In addition, a plurality of pattern values of electron multiplier multiplication value setting values are stored in the data table 16, and an optimum electron multiplication factor multiplication value setting value string pattern is obtained based on the target luminance level and the luminance level index value. You may make it select.

  Alternatively, a plurality of setting value sequences of multiplication factors for electron multiplication may be stored in the data table 16 so that the user can select the installation value sequence via the I / F unit 10. The range of the degree of freedom of tuning corresponding to the imaging environment of the place is widened, and it becomes possible to change to an installation value having a hysteresis characteristic that does not frequently change the exposure time.

1 Lens 2 CCD
3 CDS
4 Amplifier 5 A / D Converter 6 Video Signal Processing Unit 7 Video Signal Output Unit 8 Luminance Level Detection Circuit 9 Microprocessor 10 I / F Unit 11 Electron Multiplication Control Circuit 12 CCD Drive Circuit 13 Timing Generator 14 Memory Circuit 15 Lens Drive Circuit 16 Data table 17 Learning means

Claims (6)

A solid-state imaging device that photoelectrically converts light to generate charges and outputs them;
An amplifier that amplifies the electric charge output from the solid-state imaging device and outputs the electric charge as an electric signal;
A video signal processing unit that generates and outputs a video signal based on the electrical signal output by the amplifier;
A video signal output unit that converts the video signal output by the video signal processing unit into a video format for display and outputs the video signal;
An illuminance measurement unit that measures external illuminance;
A controller that adjusts the brightness of the captured image when the video signal is displayed;
It has a slow shutter function that outputs the charge that has been photoelectrically converted by the solid-state image sensor for a certain period and an electron multiplication function that multiplies and outputs the charge that has been photoelectrically converted by the solid-state image sensor,
The control unit switches the exposure time according to the illuminance measured by the illuminance measurement unit when the slow shutter function is operating, and sets the multiplication factor of the electron multiplication according to the exposure time and the illuminance. An imaging apparatus characterized by being changed.   When switching the exposure time of the slow shutter function to be longer, the control unit controls to reduce the multiplication factor of the electron multiplication according to the switched exposure time, and then sets the exposure time of the slow shutter function to 2. The imaging apparatus according to claim 1, wherein control is performed so that the multiplication factor of the electron multiplication is gradually increased according to the illuminance measured by the illuminance measurement unit until switching to be longer.   3. The multiplication factor of the electron multiplication when the exposure time of the slow shutter function is switched is a value obtained by dividing the exposure time before switching by the exposure time after switching. Imaging device. A data table for storing the electron multiplication factor and the electron multiplication factor correction value in association with each other;
The imaging apparatus according to claim 1, wherein the control unit corrects a multiplication factor of the electron multiplication when the slow shutter function is operating based on the data table. A luminance level detection unit for detecting the luminance level of the video signal generated by the video signal processing unit;
The correction value for the multiplication factor of the electron multiplication is determined based on a target luminance level when the slow shutter function is operating and a luminance level detected by the luminance level detection unit. Imaging device.   The luminance level detection unit detects a luminance level before and after switching so that an exposure time of the slow shutter function becomes long, and when the two luminance levels change, the two luminance levels change. 6. The imaging apparatus according to claim 5, wherein a correction value of the multiplication factor of the electron multiplication is updated so as not to occur.

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