JP6079196B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus including a noise source and an imaging element.

  There is known an image pickup apparatus in which an autofocus lens and a camera shake correction mechanism are installed around an image pickup device. The imaging device captures a subject image and outputs an image signal. However, noise generated by a noise source such as a motor or a coil included in an autofocus lens or a camera shake correction mechanism may be included in the image signal. In order to prevent noise from being mixed into the image signal, the motor of the autofocus lens is driven when a pixel that does not constitute an image out of the pixels included in the image sensor outputs a charge (Cited Document 1). In addition, a configuration is known in which the frequency of the drive clock of the power supply is reduced during the period in which the image sensor outputs an image signal in order to prevent noise from entering from the power supply (Cited document 2).

JP 2008-118378 A JP 2010-245747 A

  However, since there are a small number of pixels that do not form an image among the pixels included in the image sensor, the period during which the motor can be driven is limited, and there is a possibility that the period necessary for focusing cannot be secured. That is, if the motor is driven in accordance with the timing of the image sensor, the autofocus lens and the camera shake correction mechanism may not function sufficiently. Even if the frequency of the drive clock of the power supply is set to a low speed, the power supply voltage fluctuates when the motor is driven, and noise due to this may be mixed into the image signal.

  The present invention has been made in view of these problems, and an object of the present invention is to obtain an imaging apparatus that removes noise from an image signal output by an imaging element while exhibiting the function of a mechanism that constitutes a noise source.

  An imaging device according to a first invention of the present application includes an imaging device that captures a subject image and outputs an image signal, a first processing unit that receives and processes an image signal from the imaging device, and an image signal when operating. A noise source for adding noise, and a first recording means for previously recording the noise source operation state and the noise added to the image signal in association with each other. Is read from the first recording means and subtracts the noise from the image signal, corresponding to the situation in which the noise source is operating in the first period from when the first signal is received until the first processing unit receives the image signal. It is characterized by that.

  The imaging device includes a plurality of lines. The line includes a plurality of photoelectric conversion elements that receive a subject image and convert it into an image signal. During the first period, the photoelectric conversion elements included in the line receive the subject image. The first processing unit preferably subtracts noise from the image signal for each line in a period from when the processing unit receives the image signal generated by the line.

  The imaging device includes a plurality of lines. The line includes a plurality of photoelectric conversion elements that receive a subject image and convert it into an image signal. During the first period, the photoelectric conversion elements included in the line receive the subject image. It is a period until the first processing unit receives an image signal generated by the line after that, and the operation state is preferably a ratio of a period during which the noise source operates in the first period.

  An image pickup apparatus according to a second invention of the present application includes an image pickup device that picks up a subject image and outputs an image signal, a second processing unit that receives and processes the image signal from the image pickup device, and an image signal when operating. A noise source that adds noise to the image sensor, and a second recording unit that records an operation state of the noise source in a second period from when the image sensor receives the subject image until the second processing unit receives the image signal; The noise source reads the operation status recorded by the second recording means and operates according to the operation status, and the image sensor completely shields light during the period when the noise source is operating according to the operation status In this state, imaging is performed to output a signal, and the second processing unit receives the signal to create a dark exposure signal, and subtracts the dark exposure signal from the image signal.

  The image sensor includes a plurality of photoelectric conversion elements that receive a subject image and convert it into an image signal. Image signals output from all the photoelectric conversion elements constitute one frame, and the second period includes This is the period from when the included photoelectric conversion element starts receiving the subject image until the second processing unit finishes receiving all the image signals. The second processing unit subtracts noise from the image signal for each frame. It is preferable to do.

  The imaging device includes a plurality of lines, the line includes a plurality of photoelectric conversion elements that receive a subject image and convert it into an image signal, and the operation state is after the photoelectric conversion element included in the line receives the subject image. This is the ratio of the period during which the noise source operates in the first period until the second processing unit receives the image signal generated by the line, and the second recording means displays the operation status of the noise source for each line. The noise source operates for each line according to the operation status of each line, outputs a signal by performing imaging in a state where the line corresponding to the line is completely shielded, and the second processing unit It is preferable to generate the dark exposure signal by receiving the signal from all the lines.

  An image pickup apparatus according to a third invention of the present application includes an image pickup device that picks up a subject image and outputs an image signal, a sensitivity setting unit that sets shooting sensitivity according to the subject image, and receives and processes an image signal from the image pickup device. A first processing unit and a second processing unit that perform the operation, a noise source that adds noise to the image signal during operation, and an operation state of the noise source and noise added to the image signal are recorded in advance in association with each other. A first recording unit, and a second recording unit that records an operation state of the noise source in a second period from when the image sensor receives a subject image until the processing unit receives an image signal. When the setting unit sets the photographing sensitivity to a low sensitivity, the first processing unit generates a noise source in a first period from when the image sensor receives a subject image until the first processing unit receives an image signal. Noise corresponding to the situation where the When reading out from the first recording means and subtracting noise from the image signal and the sensitivity setting unit sets the photographing sensitivity to high sensitivity, the noise source operates by reading out the operation status recorded by the second recording means It operates according to the situation, and during the period when the noise source is operating according to the operation situation, the imaging device captures an image while being completely shielded from light and outputs a signal, and the second processing unit receives the signal. Then, a dark exposure signal is created, and the dark exposure signal is subtracted from the image signal.

  According to the present invention, it is possible to obtain an imaging apparatus that removes noise from an image signal output from an imaging element while exhibiting the function of a mechanism that constitutes a noise source.

It is the block diagram which showed the imaging device roughly. 3 is a timing chart showing a relationship between a charge reading timing and a coil driving timing in the image sensor. It is the flowchart which showed the 1st imaging process. 3 is a timing chart showing a relationship between a charge reading timing and a coil driving timing in the image sensor. It is the flowchart which showed the 2nd imaging process.

  Hereinafter, an imaging apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a digital camera 100 that is an embodiment of an imaging apparatus. The configuration of the digital camera 100 will be described with reference to FIG.

  The digital camera 100 includes a DSP 110 having a signal generation unit, a CMOS 121 that forms an imaging device (CIS), a noise reduction SR (Shake Reduction) block 122, a gyro sensor 123, a first recording unit, and a second recording unit. It mainly includes a memory 124, a recording medium 125, an operation member 126, a monitor 127 that forms a warning unit, and a photographing lens 130 that is a noise source.

  The photographing lens 130 includes a lens 131 and a lens driving motor 132, and is attached to the digital camera 100 so as to be detachable. The taking lens 130 forms a subject image on the CMOS 121. The lens drive motor 132 includes a coil or a magnetic material, and generates electrical noise during operation.

  The CMOS 121 includes a plurality of pixels arranged in the vertical direction and the horizontal direction. The pixel includes a photoelectric conversion element, and the pixel image received by the imaging lens 130 is received by the pixel, converted into an electric charge, and accumulated. The accumulated charge is output to the DSP 110 as an image signal. This procedure will be described in detail. The plurality of pixels arranged in a line in the horizontal direction simultaneously convert the subject image connected by the photographing lens 130 into electric charges and store them. This operation is sequentially performed from the upper side to the lower side in the vertical direction. When this is finished, a plurality of pixels arranged in a line in the horizontal direction simultaneously output the accumulated charges. This operation is sequentially performed from the upper side to the lower side in the vertical direction. Thereby, the CMOS 121 outputs an image signal to the DSP 110. A plurality of pixels arranged in a line in the horizontal direction is called a horizontal line.

  The DSP 110 includes an SR control unit 111 that controls the SR block 122, a CIS control unit 112 that controls the CMOS 121, a motor control unit 113 that controls the lens driving motor 132, and an image that forms a first processing unit and a second processing unit. A processing unit 114 is provided.

  The image processing unit 114 receives an image signal from the CMOS 121, performs image processing while using the memory 124 as a temporary storage area, and generates an image or an image file. The image is displayed on the monitor 127 and the image file is stored in the recording medium 125. The storage medium is an SD card, for example, provided so as to be detachable from the digital camera 100.

  The motor control unit 113 receives the image from the image processing unit 114 and determines the in-focus state of the subject image based on the contrast of the image. Then, the lens drive signal is transmitted to the lens drive motor 132 and driven in accordance with the in-focus state. When driving the lens driving motor 132, the motor control unit 113 also transmits a lens driving signal to the image processing unit 114.

  The gyro sensor 123 detects vibration applied to the digital camera 100, that is, angular velocity, and transmits the detected vibration to the SR control unit 111. The SR control unit 111 determines whether or not the angular velocity is greater than or equal to a threshold value when the CMOS 121 is performing exposure. And when it is more than a threshold value, the drive amount required in order to cancel the vibration applied to the digital camera 100 is calculated. Then, the drive amount is transmitted to the SR block 122 and the image processing unit 114 as an SR drive signal.

  The SR block 122 includes a voice coil motor 122a. The SR block 122 that has received the drive amount from the SR control unit 111 energizes the voice coil motor 122a in accordance with the drive amount, and moves the CMOS 121 using the force generated by the voice coil motor 122a. As a result, the CMOS 121 moves so as to cancel the vibration applied to the digital camera 100. The voice coil motor 122a includes a magnetic body and a coil, and generates a force by changing the magnitude of a current flowing through the coil. The voice coil motor 122a fixes the position of the CMOS 121 by keeping the magnitude of the current flowing through the coil constant. When the current flowing in the coil is constant, the electrical noise generated by the voice coil motor 122a is extremely small and has a constant value. On the other hand, when the current flowing through the coil changes, the voice coil motor 122a generates electrical noise.

  The CIS control unit 112 transmits a read signal to the CMOS 121. The charges accumulated in the pixels of the CMOS 121 are output in response to the read signal.

  During the exposure period of the CMOS 121 and the output period of the image signal, the image processing unit 114 stores the duty ratio of the SR drive signal and the lens drive signal. Details of this operation will be described later.

  The memory 124 stores in advance noise corresponding to the duty ratio of the SR drive signal and the lens drive signal in association with the duty ratio. While driving the SR block 122 or the lens drive motor 132, noise is created by capturing the image with the CMOS 121 completely shielded from light. If imaging is performed while the CMOS 121 is completely shielded from light, noise caused by the operation of the CMOS 121 and noise generated by the operation of the SR block 122 or the lens drive motor 132 are included in the image signal. That is, the image signal output from the CMOS 121 thereby makes noise. Noise is generated according to the duty ratio of the SR drive signal or the lens drive signal during a period in which the pixels included in one horizontal line accumulate charges. For example, noise is generated every 5% from 0% to 100%. If the noise corresponding to the duty ratio of the SR drive signal or the lens drive signal at the time of actual imaging is subtracted from the charge output by the horizontal line at the time of actual imaging, the noise can be removed for each horizontal line.

  Next, with reference to FIGS. 1 and 2, the relationship between the timing at which a pixel outputs charge and the drive signal when noise is removed for each horizontal line will be described.

  When the level of the horizontal synchronization signal (HD) transmitted from the CIS control unit 112 to the CMOS 121 is temporarily lowered from Hi to Lo, a plurality of pixels arranged in a row in the horizontal direction are connected by the photographing lens 130. The subject image is simultaneously converted into electric charge and accumulated. This operation is sequentially performed from the upper side to the lower side in the vertical direction. This is called a rolling shutter. Hereinafter, a period in which an image of one frame is captured using the rolling shutter is referred to as an exposure period. In the exposure period, the SR control unit 111 transmits a drive amount necessary for canceling the vibration applied to the digital camera 100 to the SR block 122 and the image processing unit 114 as an SR drive signal. The SR block 122 that has received the SR drive signal drives the CMOS 121 according to the drive amount. During the exposure of the CMOS 121, the image processing unit 114 measures and stores the duty ratio of the SR drive signal. More specifically, the image processing unit 114 obtains the duty ratio of the SR drive signal during a period in which the pixels included in one horizontal line are accumulating charges, and stores the duty ratio in association with the horizontal line.

  When the CIS controller 112 lowers the level of the vertical signal (VD) from Hi to Lo again, the pixel starts to output charges. That is, a plurality of pixels arranged in a line in the horizontal direction simultaneously output accumulated charges. By performing this operation in order from the upper side to the lower side in the vertical direction, an image signal is output from the CMOS 121 to the DSP 110. A period from when the first pixel starts outputting charges to when all the pixels finish outputting charges is called a reading period. During the readout period, the SR control unit 111 transmits an SR drive signal for fixing the position of the CMOS 121 to the SR block 122 and the image processing unit 114. The SR block 122 that has received this SR drive signal fixes the CMOS 121 at the current position. That is, the position of the CMOS 121 is fixed during the reading period, and the electrical noise generated by the voice coil motor 122a is extremely small and constant.

  On the other hand, when the gyro sensor 123 detects an angular velocity greater than or equal to the threshold during the readout period, the SR control unit 111 calculates a drive amount and transmits an SR drive signal to the SR block 122 and the image processing unit 114. In response to this, the SR block 122 energizes the voice coil motor 122a. The period during which the voice coil motor 122a is energized is represented as period A in FIG. As a result, the amount of current to the voice coil motor 122a changes, the CMOS 121 is moved so as to cancel the vibration applied to the digital camera 100, and the voice coil motor 122a generates noise. When the external force is no longer applied to the digital camera 100 and the angular velocity detected by the gyro sensor 123 becomes less than the threshold value, the SR control unit 111 outputs the SR drive signal for fixing the position of the CMOS 121 to the SR block 122 and the image. The data is transmitted to the processing unit 114. Thereby, the amount of current to the voice coil motor 122a becomes constant, the position of the CMOS 121 is fixed, and the voice coil motor 122a does not generate noise. In the readout period, the image processing unit 114 stores the duty ratio of the SR drive signal. More specifically, the pixels included in one horizontal line simultaneously output charges, and the image processing unit 114 stores the duty ratio of the SR drive signal for each horizontal line.

  When the image processing unit 114 finishes receiving the image signal from the CMOS 121, the image processing unit 114 obtains a duty ratio for each horizontal line and reads out noise corresponding to the obtained duty ratio from the memory 124. Then, noise is subtracted for each horizontal line.

  When receiving the lens drive signal from the motor control unit 113, the image processing unit 114 obtains the duty ratio and receives the noise corresponding to the obtained duty ratio from each horizontal line in the same manner as when received from the SR control unit 111. Subtract.

  Next, the first imaging process will be described with reference to FIG. The first imaging process is configured to remove noise for each horizontal line, and is executed when a shutter release button provided in the operation member 126 is operated.

  In the first step S31, a return mirror (not shown) is raised and a shutter (not shown) is opened.

  In the next step S32, the CMOS 121 starts exposure, that is, enters an exposure period. In the exposure period, the plurality of pixels arranged in a line in the horizontal direction simultaneously convert the subject image connected by the photographing lens 130 into electric charges and accumulate them. This operation is sequentially performed from the upper side to the lower side in the vertical direction. The image processing unit 114 stores the duty ratio of the SR drive signal for each horizontal line. Then, the shutter is closed and the return mirror is lowered to complete the exposure period.

  In the next step S33, the image processing unit 114 reads out noise corresponding to the duty ratio stored in step S32 from the memory 124.

  In the next step S34, the image processing unit 114 subtracts noise for each horizontal line from the image signal to create a corrected image. Then, the process ends.

  Since the noise can be removed for each horizontal line by executing the first imaging process, the noise can be removed from the image signal according to the operation state of the SR block 122. In addition, since noise that has been created in advance is used, it is possible to remove noise faster than the second imaging process described later.

  Next, with reference to FIGS. 1 and 4, the relationship between the timing at which a pixel outputs charge and the drive signal when noise is removed for each image will be described. The description of the same configuration as that shown in FIG. 2 is omitted.

  When the level of the vertical signal (VD) transmitted from the CIS control unit 112 to the CMOS 121 is temporarily lowered from Hi to Lo, the subject image connected by the photographing lens 130 is converted into charges and accumulated. In the exposure period, the SR control unit 111 transmits a drive amount necessary for canceling the vibration applied to the digital camera 100 to the SR block 122 and the image processing unit 114 as an SR drive signal. The SR block 122 that has received the SR drive signal drives the CMOS 121 according to the drive amount. During the period when all the pixels are exposed, the image processing unit 114 stores the duty ratio of the SR drive signal. More specifically, the image processing unit 114 calculates and stores the duty ratio of the SR drive signal for the entire exposure period.

  When the CIS controller 112 lowers the level of the vertical signal (VD) from Hi to Lo again, the pixel starts to output charges. That is, the CMOS 121 outputs an image signal to the DSP 110.

  On the other hand, when the gyro sensor 123 detects an angular velocity equal to or higher than the threshold during the reading period, the SR control unit 111 calculates a drive amount, and the SR block 122 energizes the voice coil motor 122a accordingly. The period during which the voice coil motor 122a is energized is represented as period A in FIG. As a result, the amount of current to the voice coil motor 122a changes, the CMOS 121 is moved so as to cancel the vibration applied to the digital camera 100, and the voice coil motor 122a generates noise. When the external force is no longer applied to the digital camera 100 and the angular velocity detected by the gyro sensor 123 becomes less than the threshold value, the SR control unit 111 outputs the SR drive signal for fixing the position of the CMOS 121 to the SR block 122 and the image. The data is transmitted to the processing unit 114. Thereby, the amount of current to the voice coil motor 122a becomes constant, the position of the CMOS 121 is fixed, and the voice coil motor 122a does not generate noise. In the period during which the CMOS 121 outputs an image signal, and in the readout period, the image processing unit 114 stores the duty ratio of the SR drive signal. More specifically, the image processing unit 114 stores the duty ratio of the SR drive signal during a period in which an image signal corresponding to one image is output.

  When the image processing unit 114 finishes receiving the image signal from the CMOS 121, the image processing unit 114 causes the SR control unit 111 to drive the SR block 122 based on the duty ratio in the exposure period and / or the readout period. At this time, the CMOS 121 captures an image while being completely shielded from light and outputs a signal, and the image processing unit 114 receives the signal and creates a dark exposure signal. This dark exposure signal makes noise. Then, the image processing unit 114 subtracts the dark exposure signal, that is, noise from the image signal. Thereby, noise can be removed in image units.

  When receiving the lens drive signal from the motor control unit 113, the image processing unit 114 obtains the duty ratio and creates a dark exposure signal corresponding to the obtained duty ratio in the same manner as when received from the SR control unit 111. To subtract from the image.

  Next, the second imaging process will be described with reference to FIG. The second imaging process is configured to remove noise for each image, and is executed when a shutter release button provided in the operation member 126 is operated.

  In the first step S51, a return mirror (not shown) is raised and a shutter (not shown) is opened.

  In the next step S52, the CMOS 121 starts exposure, that is, enters an exposure period. During the exposure period, all the pixels convert the subject image connected by the photographing lens 130 into electric charges and accumulate them. The image processing unit 114 stores the duty ratio of the SR drive signal during the exposure period. Then, the shutter is closed and the return mirror is lowered to complete the exposure period.

  In the next step S53, while the SR block 122 is moved again at the duty ratio stored in step S32, the CMOS 121 is completely shielded from the light and imaging is performed to create noise.

  In the next step S54, the image processing unit 114 subtracts the noise created in step S53 from the image signal to create a corrected image. Then, the process ends.

  By executing the second imaging process, noise can be removed from the image signal in accordance with the operation status of the SR block 122. In addition, since noise is newly created, noise can be removed more accurately.

  The first imaging process and the second imaging process can be selectively executed. The first imaging process is used when the digital camera 100 captures images with low imaging sensitivity, for example, ISO 100, and the second imaging process is used when images are captured with high imaging sensitivity, for example, ISO 3200. The photographing sensitivity is set by the user operating a sensitivity setting unit provided in the operation member 126. The image processing unit 114 adjusts the gain of the image signal according to the shooting sensitivity set by the user. When the sensitivity is low, the gain is adjusted low, and when the sensitivity is high, the gain is adjusted high. When shooting at a low shooting sensitivity, noise on the image signal is smaller than when shooting at a high shooting sensitivity, but noise can be removed at high speed by using the first imaging process. On the other hand, when shooting with high shooting sensitivity, noise on the image signal increases, but noise can be removed with high accuracy by using the second imaging process.

  According to the present embodiment, the noise can be removed from the image signal output by the CMOS while the SR block and the lens driving motor constituting the noise source sufficiently operate their functions.

  A solid-state imaging device such as a CCD may be used instead of the CMOS 121.

  Further, the first and second imaging processes may be configured so that noise in a period in which the CMOS 121 outputs an image signal is subtracted from the image signal in addition to noise in the period in which the CMOS 121 is imaging. . That is, the image processing unit 114 stores the duty ratio of the SR drive signal and the lens drive signal, and subtracts noise generated in accordance with the duty ratio from the image signal.

  It has been described that the first imaging process is used for low imaging sensitivity and the second imaging process is used for high imaging sensitivity. However, the first imaging process may be used with high imaging sensitivity, and the first imaging process may be used with low imaging sensitivity. Two imaging processes may be used.

100 digital camera 110 DSP
111 SR Control Unit 112 CIS Control Unit 113 Motor Control Unit 114 Image Processing Unit 121 CMOS
122 SR block 122a Voice coil motor 123 Gyro sensor 124 Memory 125 Recording medium 126 Operation member 127 Monitor 130 Shooting lens 131 Lens 132 Lens drive motor

Claims (7)

An image sensor that has a plurality of lines each having a plurality of photoelectric conversion elements that receive a subject image and convert the image signal into the image signal;
A first processing unit that receives and processes the image signal from the imaging device;
A noise source that adds noise to the image signal when operating;
Different operating conditions of the noise source in the first period from when the photoelectric conversion element of one line receives the subject image to when the first processing unit receives the converted image signal , and accordingly, and a noise added to the image signal, a memory for storing in advance in association,
The first processing unit, line by line before Symbol image signal, the noise corresponds to the situation where the noise source is operated in the first period is read out from said memory, said noise from said image signal for each line Imaging device that subtracts. The imaging apparatus according to claim 1 , wherein noise generated by an operation of the noise source when imaging is performed with the imaging element completely shielded from light, is stored in the memory . Before SL operation situation, the imaging device according to claim 1 or 2 noise sources in the first period is the percentage of time to work. An image sensor that captures a subject image and outputs an image signal;
A second processing unit for receiving and processing the image signal from the imaging device;
A noise source that adds noise to the image signal when operating;
Second recording means for recording, in a memory, an operation state of the noise source in a second period from when the imaging element receives a subject image until the second processing unit receives the image signal. ,
The noise source reads an operation state recorded in the memory by the second recording unit and operates in accordance with the operation state, and the imaging element is operated during a period in which the noise source is operating in accordance with the operation state. Takes an image in a completely shielded state and outputs a signal, and the second processing unit receives the signal to create a dark exposure signal, and subtracts the dark exposure signal from the image signal . The image sensor includes a plurality of photoelectric conversion elements that receive a subject image and convert the image into the image signal.
The image signals output from all the photoelectric conversion elements constitute one frame,
The second period is a period from when the photoelectric conversion element included in the imaging element starts to receive a subject image to when the second processing unit finishes receiving all the image signals.
The imaging apparatus according to claim 4, wherein the second processing unit subtracts the noise from the image signal for each frame. The image sensor includes a plurality of lines,
The line includes a plurality of photoelectric conversion elements that receive a subject image and convert the image into the image signal.
In the operation state, a noise source operates in a first period from when a photoelectric conversion element included in the line receives a subject image until the second processing unit receives an image signal generated by the line. Is the percentage of the period,
The second recording unit records an operation state of the noise source for each line, and the noise source operates for each line according to the operation state for each line, and a line corresponding to the line. The imaging apparatus according to claim 4 or 5, wherein imaging is performed in a state where light is completely shielded and a signal is output, and the second processing unit receives the signal from all lines and creates a dark exposure signal. . An image sensor that captures a subject image and outputs an image signal;
A sensitivity setting section that sets the shooting sensitivity according to the subject image;
A first processing unit and a second processing unit that receive and process the image signal from the imaging device;
A noise source that adds noise to the image signal when operating;
First recording means for pre-recording the operation state of the noise source and the noise added to the image signal in association with each other;
Second recording means for recording an operation state of the noise source in a second period from when the image sensor receives a subject image until the second processing unit receives the image signal;
When the sensitivity setting unit sets the photographing sensitivity to a low sensitivity, the first processing unit includes a period from when the image sensor receives a subject image until the first processing unit receives the image signal. Reading out noise corresponding to the situation in which the noise source is operating in the first period from the first recording means, and subtracting the noise from the image signal;
When the sensitivity setting unit sets the photographing sensitivity to high sensitivity, the noise source reads the operation status recorded by the second recording unit and operates according to the operation status, and the noise source During the period of operation according to the operation status, the image sensor captures an image while being completely shielded from light and outputs a signal, and the second processing unit receives the signal and creates a dark exposure signal. An imaging device that subtracts the dark exposure signal from the image signal.

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