JP2003169258A - Imaging unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging unit that can prevent a false signal from being superimposed on a signal around a white level while reserving a dynamic range of an image signal maximally. <P>SOLUTION: The imaging unit provided with an image pickup device 13 for imaging an object, a first memory 17 for storing the imaging signal obtained by exposing the object by the image pickup device 13 in a non-light shield state, a second memory 18 for reading a signal at a dark state of the image pickup device 13 in a light shield state and storing it, an adder circuit 19 for subtracting storage information (dark state signal) of the memory 18 from storage information (bright state signal) in the memory 17, is provided with a white level clip circuit 23 that clips a white level with respect to the imaging signal whose dark state signal is suppressed depending on a level of the dark state signal stored in the second memory 18. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as an electronic still camera (digital camera) or a video camera, and more particularly to an image pickup apparatus having a fixed pattern noise removing function.

[0002]

2. Description of the Related Art In recent years, electronic still cameras have been developed mainly for capturing and recording still images. Since the image sensor used in this type of camera has fixed pattern noise (hereinafter, referred to as FPN), if the output signal of the image sensor is used as it is, this FPN is superimposed on an effective signal component, resulting in image quality. It causes deterioration. For this reason,
The FPN of each pixel of the image sensor is detected in advance and stored in the memory, and the FPN is removed from the output signal of the image sensor to obtain an image signal with the FPN removed.

Here, the dynamic range of the image signal is limited by the characteristics of the image signal itself, the performance of the A / D converter, etc., and if the FPN is subtracted from the saturated signal, it is originally clipped. The FPN will be superimposed on the level that should be constant. Therefore, the white level has been set to a level slightly lower than the level of the saturated signal.

However, since the FPN signal includes a portion that depends on temperature and time, in order to clear the above problem under all conditions, it is necessary to set the white level to a considerably low value in consideration of the worst condition. in this case,
Since the maximum value of the level of the image signal is reduced, there is a problem that the dynamic range of the signal is narrowed.

[0005]

As described above, in the conventional method of removing the FPN from the output signal of the image pickup device in order to improve the image quality of the image signal obtained by the image pickup device, the set value of the white level to be clipped is set. By
There are problems that a false signal is generated and the dynamic range is reduced.

The present invention has been made in consideration of the above circumstances, and an object thereof is to prevent a false signal from being superimposed in the vicinity of a white level while ensuring the maximum dynamic range of an image signal. An object of the present invention is to provide an image pickup apparatus that can prevent the above.

[0007]

(Structure) In order to solve the above problems, the present invention adopts the following structure.

That is, according to the present invention, an image pickup device for picking up an image of a subject, a dark signal storage means for reading a dark signal of the image pickup device in a light-shielded state and storing it in a storage means, and an image pickup device in a non-light-shielded state An image pickup device provided with a dark signal suppressor that suppresses a dark signal by subtracting a dark signal stored in the dark signal storage unit from an image signal obtained by exposure with an element, ) Computation means for computing the level of the dark signal stored in the dark signal storage means based on photographing conditions, and the white level of the image pickup signal in which the dark signal is suppressed by the dark signal suppression means, White level clipping means for clipping based on the level of the dark signal calculated by the calculating means is provided.

(2) Computation means for computing the level of the dark time signal stored in the dark time signal storage means based on photographing conditions, and defect based on the dark time signal stored in the dark time signal storage means Defective pixel detection means for detecting a pixel, and a white level for clipping the white level of the image pickup signal in which the dark signal is suppressed by the dark signal suppressing means based on the level of the dark signal calculated by the calculating means. It is characterized by further comprising clipping means and defective pixel compensating means for replacing the signal level of the defective pixel detected by the defective pixel detection means with the signal level of the adjacent effective pixel.

(3) Computation means for computing the level of the dark signal stored in the dark signal storage means on the basis of photographing conditions, and an image signal obtained by exposing the image sensor in a non-light-shielded state. , The analog gain adjusting means for adjusting the analog gain so that the white level is not clipped by the subsequent circuit, and the white level of the image pickup signal in which the dark signal is suppressed by the dark signal suppressing means match the original level. Thus, the digital gain adjusting means for adjusting the digital gain is provided.

(Operation) According to the present invention, by clipping the white level of the image pickup signal in which the dark signal is suppressed by the dark signal suppressing means based on the level of the dark signal by the white level clipping means, The white level can be optimally set according to the level of the dark signal. Specifically, when the dark signal is small, the white level can be increased to increase the dynamic range, and when the dark signal is large, the white level can be decreased to suppress the generation of the false signal. As a result, it is possible to prevent the false signal from being superimposed in the vicinity of the white level while ensuring the maximum dynamic range of the image signal.

In addition to the above configuration, a defective pixel detecting means for detecting a defective pixel based on the dark signal stored in the dark signal storage means, and a signal level of the defective pixel detected by the defective pixel detecting means. By providing a defective pixel compensating unit that replaces with the signal level of the adjacent effective pixel, it is possible to suppress the generation of a false signal due to the defective pixel, in addition to the above effects.

Further, instead of optimally setting the white level according to the level of the dark signal on the digital side, the white level is not clipped by the post-stage circuit with respect to the image signal obtained by exposure by the image sensor. An analog gain adjusting unit that adjusts the gain and a digital gain adjusting unit that adjusts the digital gain so that the white level matches the original level of the image pickup signal in which the dark signal is suppressed by the dark signal suppressing unit are provided. By providing the same, it is possible to prevent the false signal from being superimposed on the white level while securing the maximum dynamic range of the image signal as in the above case.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below with reference to the illustrated embodiments.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
2 is a block diagram showing a basic configuration of a digital camera according to the embodiment of FIG.

In the figure, 11 is a light blocking filter for selectively blocking the light from the object, 12 is a lens system consisting of various lenses, 13 is a CCD color image pickup device, and the image of the object is the light blocking filter 11 and the lens 12. An image is formed on the light receiving surface of the image pickup device 13 via.

Reference numeral 14 is a temperature sensor for detecting the temperature of the image pickup device 13, 15 is a gain control amplifier for amplifying the image pickup signal of the image pickup device 13, and 16 is an A / D converter for A / D converting the image pickup signal. Is. Although not shown in the figure, a grayscale compression circuit for selectively grayscale-compressing the A / D converted signal is provided.

Reference numeral 17 is a first memory for storing an explicit signal (a signal obtained by performing normal image pickup by the image pickup device in the non-light-shielded state), and 18 is a dark signal (a signal obtained by the image pickup device in the light-shielded state). ) A second memory for storing
Reference numeral 19 is an adder circuit, and 21 is an offset circuit for inputting an offset amount. In the adder circuit 19, in response to the explicit signal stored in the first memory 17, the second memory 18
The dark signal stored at is subtracted and an offset is added.

Reference numeral 22 is a changeover switch, and 23 is a white level clip circuit. Either the explicit signal stored in the first memory 17 or the signal added by the adder circuit 19 is selected by the changeover switch 22 and input to the white level clipping circuit 23, which clips the white level. It

Reference numeral 24 is a pixel defect detection circuit, 25 is a defect memory, and 26 is a pixel defect compensation circuit. Second memory 18
A defect is detected by the pixel defect detection circuit 24 based on the dark signal stored in, and the address of the defect is recorded in the defect memory 25. Then, based on the information stored in the defect memory 25, the pixel defect compensation circuit 26 compensates the defective pixel for the signal whose white level is clipped by a method such as adjacent complement. The compensated data is recorded in the memory card 27 such as CompactFlash (registered trademark). When the A / D converted output is gradation-compressed, the defect-compensated image data is expanded by a gradation expansion circuit (not shown).

In the figure, 30 is a CPU for controlling each part, 31 is a timing generator (TG) for controlling the drive timing of the CCD image pickup device 13, and 32 is a TG.
31 shows a signal generator (SG) for driving 31.

2 to 4 are flow charts for explaining the operation of this embodiment.

First, as shown in FIG. 2, the gain value for the image pickup signal, the shutter speed at the time of image pickup, and the temperature are calculated (step S1). For these calculations, as shown in FIG. 3, first, a white clip value is calculated (S1).
-1). At this time, the accumulation time t is 1 second and the gain g is 1
Double, the clip level C, which is the pp value when the temperature T is 25 ° C., is set to 128, and the clip level C is defined as C = 128 × t × g × 2 ^{(T-25) / 8} . However, the maximum value of C is 512.

Next, the offset value is calculated (S1-
2) The gain value and the shutter speed at the time of bright and dark photography are calculated (S1-3). Further, the number of times the dark signal is captured is calculated (S1-4). In the calculation of the dark signal acquisition times, the accumulation time t is 1 second, the gain g is 1, and the temperature T is 25.degree.
Is defined as N = t × g × 2 ^{(T-25) / 8} . However, N is a positive integer, and the maximum value of N is 8.

Subsequently, after calculating the gain value at the time of calculation (S1-5), the defect detection is judged (S1-6). Here, the accumulation time t is 1 second, the gain g is 1 time, and the temperature T is 2
The detection threshold level K at 5 ° C. is 128, and the detection threshold level K is defined as K = 128 × t × g × 2 ^{(T-25) / 8} . If K ≦ 128, no defect is detected. If K> 128, defect is detected.

Next, it is determined whether or not the noise cancel mode is set (S2). When the noise cancel mode is not set, normal photographing is performed (S3), and defect compensation calculation is further performed (S4). Then, the image signal is recorded in the memory card 27 (S12). Here, when the noise cancel mode is not set, gradation compression may be performed as in a normal image processing system. However, as will be described later, gradation compression is not performed when the noise cancel mode is set.

On the other hand, when the noise cancel mode is set in the determination of S2, the main exposure photographing is performed with a predetermined gain value and shutter speed (S5), and then the light shielding filter 1 is used.
With the light shielded by 1 (S6), the bright signal is read from the image sensor 13 and temporarily stored in the first memory 17 (S7).

Next, photographing is performed in a light-shielded state (S8),
The dark signal is read from the image sensor 13 and the second memory 1 is read.
It is temporarily stored in S8 (S9). Then, it is determined whether the dark signal is captured many times (S10), and if it is a sufficient number of captures, a noise cancellation calculation is performed (S11).

In the noise canceling operation, as shown in FIG. 4, first, a dark signal is read from the second memory 18 (S
11-1). Then, it is determined whether or not the defect detection is performed again (S11-2). This determination is made depending on whether or not the conditions such as the gain value, the shutter speed, and the temperature are changed. When the defect detection is performed again, the pixel defect detection circuit 24
Then, a defect detection calculation is performed according to the above, and defect data is stored in the defect memory 25 (S11-3). Then, the bright signal is read from the first memory 17 (S11-4), the dark signal is subtracted from the bright signal, and the offset is further calculated (S11-5). Further, after setting the clip level according to the level of the dark signal, the white level clipping circuit 23 clips the white level (S11-6). Then, the pixel defect compensation circuit 26 performs a defect compensation calculation based on the defect data to obtain image data (S11-7).

When the noise canceling calculation in S11 or the defect compensating calculation in S4 is completed, the image data is recorded in the memory card 27. However, in the case of S11, it is recorded as it is, but in the case of S4, since gradation compression processing has been performed in advance, it is recorded after decompression processing.

Next, the principle of suppressing fixed pattern noise in this embodiment will be described.

First, the conventional method will be described with reference to FIG. As shown in FIG. 5A, a portion having a large bright signal is cut off because it is out of the dynamic range of the A / D converter or the like. By subtracting the dark signal as shown in FIG. 5B from the bright signal, a signal as shown in FIG. 5C is obtained. In this signal, the dark signal is subtracted even in the vicinity of the maximum level value that is cut including the dark signal, so that a false signal component remains in the vicinity of the maximum level value. Therefore, by further clipping the vicinity of the maximum level value, the false signal component can be removed as shown in FIG.

When the fixed pattern noise is comparatively small, the method of FIG. 5 does not cause any problem, but when the fixed pattern noise is large as shown in FIGS. 6A and 6B, as shown in FIG. The false signal in the signal obtained by subtracting the dark signal from the bright signal becomes large. In this case, as shown in FIG. 6 (d), a false signal remains even after clipping. Figure 6
As shown in (e), if the clip level is set sufficiently high in advance, the false signal can be removed, but in this case, the dynamic range of the signal becomes small.

On the other hand, in the present embodiment, the adder circuit 19
With respect to the image pickup signal in which the dark signal is suppressed by, the white level of the dark signal is variably set by the white level clip circuit 23 based on the level of the dark signal stored in the second memory 18. The white level can be optimally set according to the level. That is, when the dark signal is small, the white level can be increased to increase the dynamic range, and when the dark signal is large, the white level can be decreased to suppress the generation of the false signal.

On the other hand, if a pixel defect exists, the result shown in FIG.
As shown in (a), the bright signal includes a dark signal and a defect component due to a defective pixel. When a dark signal (including a defect) as shown in FIG. 7 (b1) is subtracted from this signal and further clipped at a predetermined level,
As shown in 1), false signals due to pixel defects remain near the maximum level. In this case, Figure 7 (b2)
If the pixel defect is complemented by the adjacent pixel as shown in FIG. 7, the false signal can be eliminated as shown in FIG. 7 (c2).

However, as shown in FIGS. 8 (a) and 8 (b),
When the signal due to the pixel defect becomes large due to the temperature and other conditions, the level of the defect which has not been recognized as a defect until now becomes large. Therefore, even if the complementary process by the adjacent pixel is performed, as shown in FIG. 8C. In addition, a false signal due to a pixel defect remains. If the threshold value of the pixel defect is set to be sufficiently small in advance, it is possible to remove this false signal, but in this case, the number of defects becomes extremely large, and the load of the complementing process and the capacity of the defect memory are increased. growing.

The pixel defect will be further described.

9 and 10, (a) shows a bright signal, (b) shows a dark signal, and (c) shows a signal obtained by subtracting the dark signal from the bright signal and clipping it. When the level of the pixel defect is relatively small, the dark signal shown in FIG. 9 (b1) is subtracted from the bright signal shown in FIG. 9 (a1), and the defect is replaced to obtain the signal shown in FIG. 9 (c1). As shown, it is possible to suppress the generation of false signals.

However, when the level of the pixel defect becomes high due to the temperature rise or the like, if the defect detection is not performed again, as shown in FIG.
Even if the dark signal shown in FIG. 9 (b2) is subtracted from the bright signal shown in (a2) and the defect is replaced, the generation of the false signal cannot be suppressed as shown in FIG. 9 (c2).

Therefore, in this embodiment, as shown in FIGS.
When the defect level becomes large due to the temperature rise as shown in 1), the defect detection is performed again and the clip level for the signal after subtraction of the dark signal is lowered. As a result, even if the defect level becomes large due to the temperature rise,
As shown by 0 (c1), it is possible to suppress the generation of false signals.

Further, when the defects are detected again according to the temperature rise and the like, if there are too many detected defects, there is a problem that the defect position memory becomes insufficient, and the replacement cannot be corrected. In such a case, FIG. 10 (a2) (b
By raising the pixel defect threshold value according to the defect level as shown in 2), it is possible to suppress the generation of false signals while reducing the replacement of defective pixels, as shown in FIG. 10 (c2).

The reason why gradation compression is not performed when noise is canceled will be described with reference to FIG. Without gradation compression, subtracting the dark signal shown in FIG. 11B2 from the bright signal shown in FIG.
As shown in 1 (c2), a signal with no dark component is obtained.
However, in the case of gradation compression, the bright signal is compressed as shown in FIG. 11 (a1), but the dark signal is not compressed as shown in FIG. 11 (b1). Is subtracted, a false signal remains as shown in FIG. 11 (c1). Therefore, when the noise cancel mode is set, gradation compression is not performed. This switching can be performed by the changeover switch 22.

FIG. 12 is a timing chart for explaining the sheath sequence in this embodiment.

Mechanical shutter (shield filter 1 in FIG. 1)
Imaging is performed with 1) opened, and a bright signal is accumulated for a predetermined time. Then, after closing the mechanical shutter, the bright signal is read out and stored in the first memory 17. Further, the image is taken again with the mechanical shutter closed, and the dark signal is read out and stored in the second memory 18. First
From the light signal stored in the memory 17 of the second memory 1
An image signal is obtained by subtracting the dark signal stored in 8. Then, by performing the above-described white level clipping and pixel defect compensation on this image signal, an FPN and defect-corrected high-quality image signal can be obtained.

The digital camera is usually equipped with a display element such as a liquid crystal display for displaying a real-time image. When the dark signal is accumulated and read in addition to the normal bright signal accumulation and readout as in the present embodiment, the dark signal is read during the period in which the dark signal is read and stored. The image read out from the image pickup device before being read out is displayed on the display device provided in the camera body. Thereby, it is possible to prevent the display from being interrupted during the dark signal storage and the dark signal from being displayed on the display element.

(Second Embodiment) In the previous embodiments, the white level to be clipped for the signal after subtracting the dark signal from the bright signal is optimally set. Instead of this, the analog gain is lowered and the digital gain is raised during the FPN cancel operation.

Specifically, as shown in FIG. 13 (a),
The analog gain is lowered so that the maximum value of the bright signal falls within the dynamic range of the A / D converter. The gain control amplifier 15 shown in FIG. 1 may be used for this gain adjustment. At the same time, as shown in FIG. 13B, the analog gain is also reduced for the dark signal. In this case, even if the dark signal is subtracted from the bright signal after A / D conversion, no false signal is generated as shown in FIG. However, the dynamic range of the signal itself is small. Therefore, the digital gain is increased so that the white level matches the original level. For this gain adjustment, the gain of a digital amplifier (not shown in FIG. 1) that amplifies the digital signal after A / D conversion may be adjusted. As a result, as shown in FIG. 13D, the vicinity of the maximum value of the signal is clipped by the white level of the digital circuit.

Also in this embodiment, noise can be canceled while ensuring the ISO sensitivity value (gain value) and the dynamic range of the signal. Therefore, the same effect as that of the first embodiment can be obtained.

(Third Embodiment) When there are many pixel defects in the image pickup device, there are problems that the processing time for defect detection becomes long, the memory capacity for storing defects becomes large, and the like.

In this embodiment, whether or not to detect a pixel defect is determined according to the level of the bright signal. In particular,
For the bright signal as shown in FIG.
As shown in (b), only the area where the level of the bright signal is high is set as the defect detection area. Then, as shown in FIG. 14C, in a region where the level of the bright signal is high, defect detection is performed and replacement with an adjacent pixel is performed.

Here, the noise component due to the pixel defect is generally included in the dark signal as well as the bright signal. Therefore, in a region where the level of the bright signal is not so high, the abnormal signal due to the pixel defect is suppressed by subtracting the dark signal from the bright signal. Therefore, as in the present embodiment, a sufficient effect can be obtained even if the defective pixel is compensated only in the region where the bright signal level is high.

In this embodiment, since the number of detected defects is reduced,
It is possible to shorten the processing time and the memory capacity. In addition, when the subject image is entirely white, the above-described effect cannot be obtained because all the bright signal levels are high. In such a case, it is sufficient to detect the entire surface white and raise the defect threshold level when the average value is above a certain level.

The present invention is not limited to the above-described embodiments, and various modifications can be carried out without departing from the scope of the invention.

[0054]

As described above in detail, according to the present invention, the white level to be clipped is set for the image pickup signal in which the dark signal is suppressed based on the level of the dark signal. Can be optimally set. Therefore, it is possible to prevent the false signal from being superimposed on the white level while ensuring the maximum dynamic range of the image signal. In addition to this, by detecting defective pixels and compensating for defective pixels, it is possible to suppress the generation of false signals due to defective pixels.

Further, instead of optimally setting the white level according to the level of the dark signal on the digital side, the analog gain is lowered and the digital gain is raised for the image pickup signal obtained by exposure by the image pickup device. Similarly to the above, it is possible to prevent the false signal from being superimposed on the white level while ensuring the maximum dynamic range of the image signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a digital camera according to a first embodiment.

FIG. 2 is a flowchart showing the overall operation of the first embodiment.

FIG. 3 is a flowchart showing an operation for calculating a gain value for an image pickup signal, a shutter speed at the time of image pickup, and a temperature.

FIG. 4 is a flowchart showing the operation of noise cancellation calculation.

FIG. 5 is a diagram for explaining an FPN cancel operation according to a conventional method.

FIG. 6 is a diagram for explaining a problem when fixed pattern noise is large.

FIG. 7 is a diagram for explaining a case where a pixel defect exists.

FIG. 8 is a diagram for explaining a problem when a pixel defect becomes large.

FIG. 9 is a diagram for explaining a problem when a pixel defect becomes large.

FIG. 10 is a diagram for explaining an FPN cancel operation according to this embodiment.

FIG. 11 is a diagram showing a state of a signal when gradation compression is performed with and without noise cancellation.

FIG. 12 is a timing chart for explaining a sheath sequence according to the first embodiment.

FIG. 13 is a diagram for explaining an FPN cancel operation according to the second embodiment.

FIG. 14 is a diagram for explaining an FPN cancel operation according to the third embodiment.

[Explanation of symbols]

11 ... Shading filter 12 ... Lens system 13 ... CCD color image sensor 14 ... Temperature sensor 15 ... Gain control amplifier 16 ... A / D converter 17 ... First memory 18 ... second memory 19 ... Adder circuit 21 ... Offset circuit 22 ... Changeover switch 23 ... White level clip circuit 24 ... Pixel defect detection circuit 25 ... defective memory 26 ... Pixel defect compensation circuit 27 ... Memory card 30 ... CPU 31 ... Timing generator (TG) 32 ... Signal generator (SG)

Claims (15)

[Claims] 1. An image pickup device for picking up an image of a subject, a dark signal storage means for reading a dark signal of the image pickup device in a light-shielded state and storing it in a storage means, and a dark signal storage means for storing the dark signal. Calculating means for calculating the level of the dark signal based on the photographing condition, and subtracting the dark signal stored in the dark signal storing means from the image pickup signal obtained by exposing with the image pickup device in a non-shielded state Then, the dark signal suppressing means for suppressing the dark signal and the white level of the image pickup signal in which the dark signal is suppressed by the dark signal suppressing means are set to the level of the dark signal calculated by the calculating means. An image pickup apparatus comprising: a white level clipping unit that clips on the basis of a white level clipping unit. 2. An image pickup element for picking up an image of a subject, a dark signal storage means for reading out a dark signal of the image sensor in a light-shielded state and storing it in a storage means, and a dark signal storage means for storing the dark signal. Defective pixel detecting means for detecting a defective pixel based on a dark signal, calculating means for calculating the level of the dark signal stored in the dark signal storage means based on photographing conditions, A dark signal suppressor that suppresses a dark signal by subtracting a dark signal stored in the dark signal storage from an image pickup signal obtained by exposure with an image pickup device, and the dark signal suppressor. White level clipping means for clipping the white level of the image pickup signal in which the dark signal is suppressed based on the level of the dark signal calculated by the calculating means; and a defect detected by the defective pixel detecting means. The signal level of the unit, the image pickup apparatus characterized by comprising a, a defective pixel compensation means for replacing the signal level of the effective pixel adjacent. 3. A temperature detecting means for detecting the temperature of the image pickup device, wherein the calculating means calculates the level of a dark signal based on the temperature detected by the temperature detecting means. The imaging device according to claim 1 or 2. 4. The image pickup apparatus according to claim 1, wherein the calculation means calculates the level of the dark signal based on the charge storage time of the image pickup element. 5. A gain control means for controlling the gain of the output signal of the image pickup device is provided, and the calculation means calculates the level of the dark signal based on the gain controlled by the gain control means. The image pickup apparatus according to claim 1 or 2, characterized in that. 6. The image pickup apparatus according to claim 1, wherein the output signal of the image pickup device is read out a plurality of times and the dark signal of the image pickup device is obtained by adding the read signals. 7. An image read from said image pickup device before reading said dark time signal from said image pickup device during the period in which said dark signal is stored in said dark signal storage means, comprising display means for displaying an image. The image pickup apparatus according to claim 1 or 2, characterized in that is displayed on the display means. 8. The image pickup apparatus according to claim 2, wherein the defective pixel detecting means determines a pixel in which the level of the dark signal is equal to or higher than a predetermined threshold value as a defective pixel. 9. A temperature detecting means for detecting the temperature of the image pickup device, wherein the defective pixel detecting means changes the threshold value based on the temperature detected by the temperature detecting means. The imaging device according to claim 8. 10. A gain control unit for controlling a gain of an output signal of the image pickup device, wherein the defective pixel detection unit changes the threshold value based on the gain controlled by the gain control unit. The imaging device according to claim 8, wherein 11. The image pickup apparatus according to claim 8, wherein the defective pixel detection means changes the threshold value based on a charge storage time of the image pickup element. 12. A selection means for selecting whether or not to operate the dark-time signal suppressing means, and a gradation compression means for gradation-compressing an image signal, and an image when the dark-time signal suppressing means is not operated. 3. The image pickup apparatus according to claim 1, wherein the gradation compression of the signal is performed, and the gradation compression of the image signal is not performed when the dark signal suppression unit is activated. 13. An image pickup device for picking up an image of a subject, a dark signal storage means for reading a dark signal of the image pickup device in a light-shielded state and storing it in a storage means, and an exposure by the image pickup device in a non-light-shielded state. For the image pickup signal obtained by the analog gain adjusting means for adjusting the analog gain so that the white level is not clipped by the subsequent circuit, and the image pickup signal obtained by adjusting the analog gain,
A dark signal suppressor that subtracts the dark signal stored in the dark signal storage unit to suppress the dark signal, and an image pickup signal in which the dark signal is suppressed by the dark signal suppressor, An image pickup apparatus comprising: a digital gain adjusting unit that adjusts a digital gain so that a white level matches an original level. 14. An image pickup device for picking up an image of a subject, a dark time signal storage means for reading a dark time signal of the image pickup device in a light-shielded state and storing it in a storage means, and a dark time signal storage means for storing the dark signal. Calculating means for calculating the level of the dark signal based on the photographing condition, and subtracting the dark signal stored in the dark signal storing means from the image pickup signal obtained by exposing with the image pickup device in a non-shielded state Then, the dark signal suppressing means for suppressing the dark signal and the white level of the image pickup signal in which the dark signal is suppressed by the dark signal suppressing means are set to the level of the dark signal calculated by the calculating means. White level clipping means for clipping based on the above, and defective pixel detection for detecting a defective pixel based on the dark signal stored in the dark signal storage means in a region where the level of the image pickup signal is a predetermined value or more. Stage and the signal level of the detected defective pixels by the defective pixel detector means, the imaging characterized by comprising a defective pixel compensation means for replacing the signal level of the effective pixel adjacent, the device. 15. The defective pixel detection means determines a pixel in which the level of the dark signal is equal to or higher than a predetermined threshold value as a defective pixel, and the average value of the levels of the image pickup signals is a predetermined value. 15. The image pickup apparatus according to claim 14, wherein the threshold value is increased in the above cases.