JP4847281B2 - Imaging apparatus, control method therefor, and imaging system - Google Patents

Description

  The present invention relates to an imaging apparatus having a photoelectric conversion unit, a control method thereof, and an imaging system.

  Conventionally, a solid-state image sensor has been used in an imaging apparatus such as an electronic camera. As such a solid-state imaging device, there is one in which an amplifying device is incorporated in each pixel, such as a CMOS image sensor. As described above, in the solid-state imaging device in which the amplifying element is incorporated in each pixel, there is a problem that fixed pattern noise is generated due to variation in characteristics of the amplifying element. On the other hand, a method of removing fixed pattern noise by taking a difference between a signal (S signal) imaged in a state where light enters and a signal (N signal) imaged in a state where light does not enter is used. Yes. However, with such a technique, when high-intensity light exceeding the signal saturation level is incident, the output signal falls from the saturation level, and the high-intensity subject portion of the captured image appears to sink black (hereinafter referred to as “high-intensity”). There is a problem that the “black sun phenomenon” occurs.

  In order to solve such a problem, there is a technique of clipping the N signal to a set value (see Patent Document 1).

Patent Document 1 discloses a technique of using a predetermined voltage as a reset voltage when the voltage output to the common signal line after the reset suddenly drops.
JP 2000-287131 A

  However, in the invention of Patent Document 1, means for detecting the level of the voltage output to the common signal line and means for using a predetermined voltage as the voltage at the time of reset must be added to the imaging device. There was a problem that the scale increased. Further, if the N signal has a large noise signal that is equal to or higher than the clip level, the noise signal is also clipped to a predetermined level, and the noise signal cannot be completely removed.

  The present invention has been made in view of the above problems, and an object of the present invention is to effectively remove a noise signal and suppress the occurrence of a high-intensity black sun phenomenon without increasing the circuit scale.

The first aspect of the present invention has a pixel portion having a photoelectric conversion unit, relates an optical signal generated by the pixel unit, an imaging apparatus for generating a captured image based on a difference component of a noise signal, prior to reading the first stored optical signals to the pixel unit in the imaging, it reads the first accumulation time Ma蓄 product with noise signals, the noise signal from the optical signal read out after readout of the noise signal Prior to reading the optical signal accumulated in the pixel unit in the second imaging after the first imaging, the first captured image generation means for generating a first captured image by subtracting reading a long second accumulation time Ma蓄 product was noise signal than the first accumulation time, generates a second captured image by difference the noise signal from the optical signal read out after readout of the noise signal Second to An image the image generation means, a difference image generating means for generating a difference image between the first captured image and the second captured image, from the differential image, the pixel signals of the pixels constituting the said difference image is set in advance and an image region extracting means for extracting a region which is closed by the pixel having a threshold or more output values, in either one of the first captured image and the second picked-up image, extracted by the previous SL image region extracting means Image correction means for replacing a pixel signal in an area corresponding to the set area with a pixel signal corresponding to a saturation level of the pixel portion .

  A second aspect of the present invention relates to an imaging system, and includes an optical system and the imaging device described above.

A third aspect of the present invention includes a pixel having a photoelectric conversion unit, relates to a control method for an imaging apparatus for generating a captured image based on the difference amount between the optical signal and the noise signal generated by the pixel unit The noise signal accumulated in the first accumulation time is read before reading the optical signal accumulated in the pixel unit in the first imaging , and the noise signal is read from the optical signal read after the noise signal is read. generating a first captured image by subtracting the, prior to the reading of the stored optical signals to the pixel unit in the second imaging after the first imaging, than the first accumulation time reading a noise signal was also accumulated in the long second accumulation time, and generating a second captured image by difference the noise signal from the optical signal read out after readout of the noise signal, the second Generating a difference image between the captured image and the second captured image, from the difference image, the pixel signals of the pixels constituting the said difference image is closed by the pixel having a preset threshold value or more output values a step of extracting a region, in one of the first captured image and the second captured image, a pixel signal in the region corresponding to the region issued extracted, the saturation level of the pixel portion And a step of replacing it with a corresponding pixel signal .

  According to the present invention, it is possible to effectively remove a noise signal and suppress the occurrence of a high-luminance black sun phenomenon without increasing the circuit scale.

  Hereinafter, an imaging device according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The embodiment described below is an example as means for realizing the present invention, and should be appropriately modified or changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, the present invention is not limited to the following embodiment.

  FIG. 1 is a circuit diagram of an imaging unit according to a preferred embodiment of the present invention.

  In the imaging unit according to the preferred embodiment of the present invention, a plurality of unit pixels 1 are two-dimensionally arranged. Each unit pixel 1 includes a photodiode 2, a transfer switch 3, a reset switch 4, a row selection switch 5, a pixel amplifier 6, and a floating diffusion layer FD7. The photodiode 2 is a photoelectric conversion unit that converts light into signal charges and accumulates them. The transfer switch 3 transfers the signal charge generated by the photoelectric conversion of the photodiode 2 according to the pulse PTX. The floating diffusion layer FD7 accumulates the signal charge transferred by the transfer switch 3. The reset switch 4 resets the floating diffusion layer FD7 connected to the gate of the pixel amplifier 6 to the voltage level of SVDD according to the reset pulse PRES. The pixel amplifier 6 functions as a source follower and amplifies the signal charge accumulated in the floating diffusion layer FD7. The row selection switch 5 selects a row pixel selected by a vertical scanning circuit (not shown) according to a selection pulse PSEL.

  The signal of the row pixel selected by the row selection switch 5 is output to the vertical output line 22 connected to the load current source 21 via the pixel amplifier 6. Of the signals output to the vertical output line 22, the optical signal (S signal) is stored in the storage capacitor CTS 27 via the transfer gate 25 which is turned on in response to the signal output pulse PTS. Further, the noise signal (N signal) is stored in the storage capacitor CTN26 via the MOS transistor 24 turned on by the noise output pulse PTN. Next, a noise signal is accumulated in the capacitor CHN30 and an optical signal is accumulated in the capacitor CHS31 via the transfer switches 28 and 29 by control signals PHS and PHN from a horizontal scanning circuit (not shown). Next, the differential amplifier 32 outputs a captured image based on the difference between the two.

  FIG. 2 is a timing chart showing the first drive timing in the imaging unit of FIG.

  At time t1, the signal HD indicating the start of one horizontal scanning period changes from L (low level) to H (high level). At this time, since the PSEL signal and the PRES signal are H, both the reset switch 4 and the selection switch 5 are ON. Therefore, the potential SVDD is output to the vertical output line 22.

  At time t2, the PRES signal becomes L and the selection switch 5 is turned OFF. Further, the PTS signal and the PTN signal become H, and the transfer gate 25 and the MOS transistor 24 are turned on. As a result, the potential SVDD output to the vertical output line 22 is supplied to the storage capacitor CTN26 and the storage capacitor CTS27 as the signal storage unit, and the storage capacitor CTN26 and the storage capacitor CTS27 are reset.

  At time t3, the PRES signal becomes L and the reset switch 4 is turned OFF. As a result, the floating diffusion layer FD7 enters a floating state, and the floating diffusion layer FD7 holds a noise signal.

  At time t4, the PSEL signal becomes H and the selection switch 5 is turned on. As a result, the source follower circuit constituted by the selection switch 5 and the load current source 21 is activated, and a noise output corresponding to the reset potential of the floating gate of the pixel amplifier 6 is made on the vertical output line 22.

  At time t5, the PTS signal and the PTN signal become L, the transfer gate 25 and the MOS transistor 24 are turned off, and the storage capacitor CTN26 and the storage capacitor CTS27 are in the initial state.

  At time t6, the PTN signal becomes H, the MOS transistor 24 is turned on, and the noise signal stored in the floating gate of the pixel amplifier 6 is stored in the storage capacitor CTN26.

  At time t7, the PTN signal becomes L, the MOS transistor 24 is turned off, and the accumulation operation of the noise signal from the pixel amplifier 6 to the storage capacitor CTN26 is completed.

  Next, the mixed signal of the optical signal and noise signal generated in the photodiode 2 is accumulated. First, the vertical output line 22 is reset to a constant potential by a circuit (not shown).

  At time t8, the PTS signal becomes H and the transfer gate 25 is turned on.

  At time t9, the PTX signal becomes H, the transfer switch 3 is turned on, and the optical signal stored in the photodiode 2 is transferred to the floating gate of the pixel amplifier 6. At this time, since the PSEL signal is H, the above-described source follower circuit is in an operating state, and an “optical signal + noise signal” is output on the vertical output line 22 according to the potential of the floating gate of the pixel amplifier 6. Is made. Accordingly, the “light signal + noise signal” output to the vertical output line 22 is stored in the storage capacitor CTS 27 via the transfer gate 25.

  At time t10, the PTX signal becomes L, the transfer switch 3 is turned off, and the transfer operation to the floating gate of the pixel amplifier 6 is completed.

  At time t11, the PTS signal becomes L, the transfer gate 25 is turned off, and the accumulation operation in the storage capacitor CTS27 is completed.

  Thus, during the period from t8 to t11 including the period from t9 to t10, the storage capacitor CTS27 is connected to the vertical output line 22 by setting the PTS signal to H, and “optical signal + noise signal” is stored in the storage capacitor. It is held in CTS27.

  As described above, the “noise signal” for one row and the “light signal + noise signal” generated by the photodiode 2 are accumulated in the CTN 26 and the CTS 27, respectively.

  Next, these two signals are transferred to the capacitors CHN30 and CHS31 in response to a control pulse PH controlled by a horizontal shift register (not shown).

  Then, the “noise signal” and “optical signal + noise signal” accumulated in the capacitors CHN 30 and CHS 31 are output as “optical signal + noise signal” − “noise signal” = optical signal by the differential amplifier 32. The

  In FIG. 1, when the amount of incident light is large and the photodiode 2 is saturated, the saturated charge may overflow into the floating diffusion layer FD7 even if the transfer switch 3 is turned off. In this case, as shown in FIG. 7A, since the S signal has reached the saturation level, the signal level does not become higher than that. Therefore, the signal level of the S signal is constant regardless of the presence or absence of charge leaking into the floating diffusion layer FD7. On the other hand, the N signal is performed during an accumulation time Tn1 from the completion of resetting of the floating diffusion layer FD7 shown in FIG. 2A to the completion of transfer to the storage capacitor CTN26 by the PTN signal shown in FIG. The accumulation time Tn1 is a time sufficient for the charge corresponding to the N signal of the floating diffusion layer FD7 to be transferred to the storage capacitor CTN26 almost completely, and a short period is set to shorten the read time. Is done. If the amount of light that saturates the photodiode 2 is incident during the accumulation time Tn1, the charge amount of the floating diffusion layer FD7 and the charge transfer destination storage capacitor CTN26 cannot maintain the reset level due to the overflowing charge. To increase. As a result, as shown in FIG. 7B, the output signal, which is the difference signal between the S signal and the N signal, rapidly decreases as the N signal increases, and a high-intensity black sun phenomenon occurs.

  FIG. 3 is a diagram illustrating a timing chart showing the second drive timing in the imaging unit of FIG. Description of operations similar to those in FIG. 2 is omitted.

  The second drive timing shown in FIG. 3 is a drive timing used together with the first drive timing when the high-luminance black sun phenomenon occurs.

  A period Tn2 from the reset completion time A ′ to the N signal transfer end time B ′ at the second drive timing shown in FIG. 3 is set to be longer than the accumulation time Tn1 at the first drive timing. The timing after the N signal transfer end timing B 'is shifted backward by Tn2-Tn1.

  As shown in FIG. 3, in the case of the second imaging using the second driving timing, the N signal transfer time is set longer than that of the first imaging using the first driving timing. Therefore, charge overflow due to saturation of the photodiode 2 is likely to occur. That is, the black sun occurrence area in the output image at the time of the second imaging is larger than that at the time of the first imaging.

In the preferred embodiment of the present invention, as described later, a difference image between the first captured image in the first imaging and the second captured image in the second imaging is used. Therefore, the time from the start of exposure to the start of the horizontal scanning period is made the same for the first imaging using the first drive timing and for the second imaging using the second drive timing . Since the accumulation time Tn1 and the accumulation time Tn2 are very short compared to the time from the start of exposure to the start of the horizontal scanning period, the exposure times of the first imaging and the second imaging can be considered to be substantially the same. .

  FIG. 4 is a diagram for explaining the principle of the present embodiment.

  FIG. 4A is an example of an image in which a high-luminance black sun phenomenon has occurred during the first imaging using the first drive timing described in FIG.

  FIG. 4B is an example of an image in which a high-luminance black sun phenomenon has occurred during the second imaging using the second drive timing described in FIG. 3, and the same subject as that in FIG. It is a thing. The second picked-up image at the time of the second image pickup shown in FIG. 4 (b) has a larger black sun occurrence region than the first picked-up image at the time of the first image pickup shown in FIG. 4 (a). You can see that

  FIG. 4C is a difference image obtained by subtracting the second captured image in FIG. 4B from the first captured image in FIG. In the first imaging and the second imaging, since the exposure time is substantially the same, there is almost no difference between the two imaging for a general subject. Therefore, the difference image shown in FIG. 4C has a value near 0 (black level). On the other hand, since the size of the area where black sun is generated differs between FIG. 4A and FIG. 4B, black sun does not occur in FIG. 4A. In FIG. 4B, the region where the black sun has occurred becomes a positive output in FIG. 4C. In addition, the area where the black level is blacked down in both FIGS. 4A and 4B is a value near 0 (black level) in FIG. 4C. As described above, as shown in FIG. 4C, the difference image between FIG. 4A and FIG. 4B is an image in which a donut-shaped output exists around a high-luminance subject.

  Here, it is possible to determine that the closed region (region having a value near 0) surrounded by the donut-shaped output in FIG. 4C is a region where black sun is generated. Therefore, the address of this closed region may be stored, and the output value at the same address of the first captured image in FIG. 4A may be replaced with a saturation level value. Since the area where the black sun is generated and the periphery thereof are considered to be sufficiently saturated areas, the value to be replaced in this way may be the value of the saturation level.

  In the above description, the output value of the predetermined area of the first captured image is replaced with the saturation level value. However, the output value of the predetermined area of the second captured image may be replaced with the saturation level value. Good. That is, the region where the black sun is generated in FIG. 4B corresponds to both the region where the positive output is made in FIG. 4C and the closed region surrounded by this region. Therefore, the address of the area obtained by combining the area where the plus output is made in FIG. 4C and the closed area is stored, and the output value of the same address of the second captured image shown in FIG. 4B is saturated. It may be replaced with a level value. The same applies to the flowchart of FIG. 5 described later.

  FIG. 5 is a flowchart illustrating the operation of the imaging unit according to the preferred embodiment of the present invention. The following processing can be performed, for example, when the system control unit 214 executes a program or the like stored in the ROM 215.

  In step S101, first imaging is performed at the first drive timing.

  In step S102, it is determined whether or not there is a region that has reached the saturation level in the image captured in step S101. If it is determined that there is a region that has reached the saturation level (“Yes” in step S102), the process proceeds to step 103, and if it is determined that there is no region that has reached the saturation level (“No” in step S102). ”), The process proceeds to Step 108.

  In step S103, the second imaging at the second drive timing is performed.

  In step S104, a difference image is generated by subtracting the second captured image obtained by the second imaging from the first captured image obtained by the first imaging.

  In step S105, it is determined whether or not there is an area having an output value greater than or equal to the set value in the difference image generated in step S104. If it is determined that there is an area greater than the set value in the difference image (“Yes” in step S105), the process proceeds to step S106, and if it is determined that there is no area greater than the set value in the difference image (step “No” in S105), the process proceeds to step S108.

  In step S106, the address of the closed region surrounded by a region having an output value equal to or larger than the set value in the difference image generated in step S104 is stored.

  In step S107, the first captured image is corrected by replacing the output value of the address stored in step S106 in the first captured image obtained in step S101 with a value corresponding to the saturation level of the main imaging unit.

  In step S108, if it is determined in step S105 that there is an area greater than the set value in the difference image, the corrected first captured image is output as an output image. On the other hand, if it is determined in step S105 that there is no region greater than the set value in the difference image, the first captured image acquired in step S101 is output as it is as an output image.

  In FIG. 5, first, it is determined whether or not there is a saturated portion in the shooting screen, and the high-intensity black sun determination is performed only when there is a saturated portion, but the present invention is not limited to this. For example, the determination of the presence or absence of a saturated portion may be performed once every several frames, or the determination of high-intensity black sun may be performed every frame without determining the presence or absence of a saturated portion.

  Next, an imaging system incorporating an imaging unit according to a preferred embodiment of the present invention will be described. FIG. 6 is a diagram showing an imaging system according to a preferred embodiment of the present invention.

  The imaging system according to this embodiment includes an optical system 201 and an imaging device. An imaging apparatus according to this embodiment includes a mechanical shutter (represented as “mechanical shutter” in FIG. 6) 202, an imaging unit 203, an AGC circuit 204, an A / D converter 205, a timing signal generation circuit 206, and the above-described embodiment. A drive circuit 207 is provided. The imaging apparatus according to the present embodiment also includes a signal processing circuit 208, an image memory 209, an image recording medium (represented as “recording medium” in FIG. 6) 210, a recording circuit 211, an image display apparatus 212, a display circuit 213, and system control. The unit 214 is provided. The imaging apparatus according to the present embodiment also includes a nonvolatile memory (ROM) 215 and a volatile memory (RAM) 216.

  The optical system 201 has a lens and a diaphragm. The AGC circuit 204 performs analog signal processing. The A / D converter 205 converts an analog signal into a digital signal. The timing signal generation circuit 206 generates a signal for operating the imaging unit 203, the AGC circuit 204, and the A / D converter 205. The drive circuit 207 drives the optical system 201, the mechanical shutter 202, and the imaging unit 203. The signal processing circuit 208 performs signal processing necessary for the captured image data. For example, the signal processing circuit 208 can function as a difference image generation unit that generates a difference image. Also, for example, the signal processing circuit 208 extracts image area determination means for determining whether or not there is an area in which the absolute value of the pixel signal is equal to or greater than a set value from the difference image, and image area determination means extraction for extracting the determined area. It can also function as a means. For example, the signal processing circuit 208 can also function as an image correction unit that replaces the value of the pixel signal in the captured image with a set value. The image memory 209 stores the image processed image data. The image recording medium 210 is a recording medium that can be detached from the imaging apparatus. The recording circuit 211 records the signal-processed image data on the image recording medium 210. The image display device 212 displays the image data subjected to signal processing. The display circuit 213 displays an image on the image display device 212. The system control unit 214 controls each unit of the imaging apparatus. The ROM 215 stores a control program executed by the system control unit 214, control data such as parameters and tables used when executing the program, and correction data such as a scratch address. The RAM 216 transfers and stores the program, control data, and correction data stored in the ROM 215, and is used when the system control unit 214 controls the imaging apparatus.

  Hereinafter, a photographing operation using the mechanical shutter 202 using the imaging device configured as described above will be described.

  Prior to the photographing operation, necessary programs, control data, and correction data are transferred from the ROM 215 to the RAM 216 when the operation of the system control unit 214 is started, such as when the imaging apparatus is turned on. These programs and data are used when the system control unit 214 controls the imaging apparatus. Further, if necessary, additional programs and data are transferred from the ROM 215 to the RAM 216, or the system control unit 214 directly reads out and uses the data in the ROM 215.

  First, the optical system 201 drives a diaphragm and a lens according to a control signal from the system control unit 214 to form a subject image set to an appropriate brightness on the imaging unit 203.

  Next, during still image shooting, the mechanical shutter 202 is driven by the control signal from the system control unit 214 so as to shield the image capturing unit 203 in accordance with the operation of the image capturing unit 203 so that a necessary exposure time is obtained. Is done. At this time, when the imaging unit 203 has an electronic shutter function, it may be used together with the mechanical shutter 202 to ensure a necessary exposure time. Note that the mechanical shutter 202 is always open during the shooting operation when shooting in a mode in which the exposure time is controlled only by the electronic shutter function of the imaging unit 203 without using the mechanical shutter 202 during movie shooting and still image shooting. Keep the state.

  The imaging unit 203 is driven by a driving pulse based on the operation pulse generated by the timing signal generation circuit 206 controlled by the system control unit 214, converts the subject image into an electrical signal by photoelectric conversion, and outputs the signal as an analog image signal. . The analog image signal output from the imaging unit 203 is subjected to an operation pulse generated by the timing signal generation circuit 206 controlled by the system control unit 214, and the AGC circuit 204 removes the clock synchronization noise, and the A / D converter In 205, it is converted into a digital image signal.

  Next, in the signal processing circuit 208 controlled by the system control unit 214, as described in the flowchart of FIG. 5, a series of black sun suppression processing such as generation of a difference image, extraction of black sun dark areas, and correction of the dark areas. I do. The digital image signal is subjected to image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, and image compression processing.

  The image memory 209 is used to temporarily store a digital image signal during signal processing or to store image data that is a digital image signal subjected to signal processing. Further, the image memory 209 temporarily stores the “first captured image”, the “second captured image”, and the difference image generated by the difference processing in the signal processing circuit 208 in the description of the flowchart of FIG. be able to.

  The image data signal-processed by the signal processing circuit 208 and the image data stored in the image memory 209 are converted into data suitable for the image recording medium 210 (for example, file system data having a hierarchical structure) in the recording circuit 211. Are recorded on the image recording medium 210. Further, such image data is subjected to resolution conversion processing in the signal processing circuit 208, and then converted into a signal suitable for the image display device 212 (for example, an NTSC analog signal or the like) in the display circuit 213 for image display. It may be displayed on the device 212.

  Here, the signal processing circuit 208 may output the digital image signal as it is to the image memory 209 or the recording circuit 211 without performing signal processing by the control signal from the system control unit 214. Also, the signal processing circuit 208, when requested by the system control unit 214, information of digital image signals and image data generated in the signal processing process, for example, the spatial frequency of the image, the average value of the designated area, the compression Information such as the amount of image data or information extracted from the information is output to the system control unit 214. Furthermore, the recording circuit 211 outputs information such as the type and free capacity of the image recording medium 210 to the system control unit 214 when requested by the system control unit 214.

  Further, a reproduction operation when image data is recorded on the image recording medium 210 will be described. The recording circuit 211 reads out image data from the image recording medium 210 in response to a control signal from the system control unit 214, and the signal processing circuit 208 similarly in response to a control signal from the system control unit 214 indicates that the image data is a compressed image. Performs image decompression processing and stores it in the image memory 209. The image data stored in the image memory 209 is subjected to resolution conversion processing by the signal processing circuit 208, converted to a signal suitable for the image display device 212 by the display circuit 213, and displayed on the image display device 212. .

  Note that the imaging apparatus according to the present invention may be configured to perform the first imaging and the second imaging in one frame and to determine and correct the high-intensity black sun for each frame. Or it is good also as a structure which calculates | requires a sunken part from the comparison with the image of a previous frame by making each of 2 continuous frames into 1st and 2nd imaging.

  In the description of the principle of the present embodiment described with reference to FIG. 4, the address of the closed region that is output in the difference image is used as the correction region of the black sun image. However, an area that is slightly larger than the closed area may be set as a correction area in consideration of variations in captured images.

  As described above, in a preferred embodiment of the present invention, an area where a black sun phenomenon due to a high-intensity subject occurs from a difference image between two images with different N signal (reset signal) transfer times. Discriminate and replace the output value of the corresponding area with the saturation level. With such a configuration, it is possible to suppress the occurrence of a high-intensity black sun phenomenon without adding extra components and without degrading the basic performance as a solid-state imaging device.

FIG. 3 is a circuit diagram of an imaging unit according to a preferred embodiment of the present invention. It is a figure which shows the timing chart which shows the 1st drive timing in the imaging part of FIG. It is a figure which shows the timing chart which shows the 2nd drive timing in the imaging part of FIG. It is a figure for demonstrating the principle of this embodiment. It is a figure which shows the flowchart which shows operation | movement of the imaging part which concerns on suitable embodiment of this invention. 1 is a diagram illustrating an imaging system according to a preferred embodiment of the present invention. It is a figure which shows transition of an output signal level.

Explanation of symbols

2 Photodiodes 26, 27 Storage capacitor 208 Signal processing circuit

Claims (4)

An imaging apparatus that includes a pixel unit having a photoelectric conversion unit and generates a captured image based on a difference between an optical signal generated by the pixel unit and a noise signal,
Prior to reading the optical signal accumulated in the pixel unit in the first imaging, the noise signal accumulated for the first accumulation time is read, and the noise signal is subtracted from the optical signal read after the noise signal is read. A first captured image generation means for generating a first captured image by
Prior to reading out the optical signal accumulated in the pixel portion in the second imaging after the first imaging, a noise signal accumulated for a second accumulation time longer than the first accumulation time is read, and the noise Second captured image generation means for generating a second captured image by subtracting the noise signal from the optical signal read after reading the signal;
Differential image generation means for generating a differential image between the first captured image and the second captured image;
Image area extracting means for extracting, from the difference image, an area closed by a pixel having an output value equal to or greater than a preset threshold value of a pixel signal constituting the difference image;
In either one of the first captured image and the second captured image, a pixel signal in a region corresponding to the region extracted by the image region extraction unit is a pixel signal corresponding to the saturation level of the pixel unit. Image correction means to replace with,
An imaging apparatus comprising: Determination means for determining whether or not there is a region that has reached a saturation level in the first captured image;
The said 2nd captured image generation means produces | generates the said 2nd captured image according to having determined that the area | region which has reached the saturation level exists by the said determination means. The imaging device described. Optical system,
The imaging apparatus according to claim 1 or 2 ,
An imaging system comprising: A control method for an imaging apparatus that includes a pixel having a photoelectric conversion unit and generates a captured image based on a difference between an optical signal and a noise signal generated by the pixel unit,
Prior to reading out the optical signal accumulated in the pixel section in the first imaging, the noise signal accumulated in the first accumulation time is read out, and the noise signal is read from the optical signal read out after the noise signal is read out. Generating a first captured image by subtracting; and
Before reading out the optical signal accumulated in the pixel unit in the second photographing after the first photographing, the noise signal accumulated in the second accumulation time longer than the first accumulation time is read, Generating a second captured image by subtracting the noise signal from the optical signal read after reading the noise signal;
Generating a difference image between the first captured image and the second captured image;
Extracting from the difference image a region closed by a pixel having an output value equal to or greater than a preset threshold value of a pixel signal of the pixel constituting the difference image;
A step of replacing a pixel signal in a region corresponding to the extracted region with a pixel signal corresponding to a saturation level of the pixel unit in any one of the first captured image and the second captured image;
A method for controlling an imaging apparatus, comprising: