JPH0998350A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce various kinds of noise signal from an image signal without being affected by ambient temperature change. SOLUTION: A controller 13 obtains an image pickup signal with shut light and an image pickup signal without shut light for each field time from a CCD image sensor 3. An image pickup signal via a CDS circuit 5 and an image pickup signal delayed by one field time via a field memory 9 are fed to a switching circuit 11 and switched based on the controller 13. A difference detection circuit 12 detects a difference between picture signals fed from the switching circuit 12 to obtain the image pickup signal only from which the noise component is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device capable of reducing noise generated from a solid-state image pickup element, and more particularly to reducing noise or the like generated or changed during photographing due to temperature change of the solid-state image pickup element. The present invention relates to a solid-state image pickup device.

[0002]

2. Description of the Related Art Generally, a solid-state image pickup device converts an optical image of a subject into electric three primary color signals by a solid-state image pickup element.
The three primary color signals are adjusted to a predetermined standard signal by, for example, γ correction, knee correction, white balance adjustment, or the like.

Prior to such adjustment of color signals, the solid-state image pickup device has a random noise generated in the solid-state image pickup element,
Various types of noise such as shading, blemishes and smears must be reduced.

Therefore, in the solid-state image pickup device, a correlated double sampling (hereinafter, referred to as CDS: Correlated Double Sampling)
Circuit) is used to reduce random noise.
However, the CDS circuit cannot reduce various noises such as shading, blemishes, and smear.

In order to solve such a problem, the conventional solid-state image pickup device uses not only the CDS circuit but also other noise reduction circuits.

For example, as shown in FIG. 5, a conventional solid-state image pickup device 100 includes a liquid crystal shutter 101 and a solid-state image pickup element 1.
02 and a CDS circuit 10 for reducing random noise
3, an analog / digital (hereinafter referred to as A / D) converter 104, a switching circuit 105, a noise memory 106 for storing only data of a noise component, and a difference detection circuit 10.
7 and a controller 108 that controls the liquid crystal shutter 101 and the switching circuit 105. When a shutter switch (not shown) is pressed, the controller 108
Closes the liquid crystal shutter 101 to shield the solid-state image sensor 102 from light, and simultaneously switches the switching circuit 105 to the noise memory 106 side. Then, the solid-state image sensor 1 when shielded from light
The image pickup signal obtained from 02 is subjected to so-called random noise reduction in the CDS circuit 103, and converted into image pickup data in the A / D converter 104. The imaged data is the switching circuit 1
It is stored in the noise memory 106 via 05.

Next, the controller 108 opens the liquid crystal shutter 101 and switches the switching circuit 105. Then, in the image pickup signal of the subject obtained from the solid-state image pickup device 102, random noise is reduced by the CDS circuit 103.
The image is converted by the / D converter 104 into image pickup data. The image pickup data is sent to the difference detection circuit 107 via the switching circuit 105.
Is supplied to. The difference detection circuit 107 detects the difference between the imaged data of the subject and the imaged data stored in the noise memory 106. As a result, the difference detection circuit 107
Can cancel noise that could not be reduced by the CDS circuit 103 and output an image pickup signal with sufficiently reduced noise.

[0008]

However, the solid-state image pickup device 100 cannot reduce the blemisch noise or the like that is generated later due to a temperature change or the like during image pickup.

In particular, the dark current which causes the blemisch noise flows from the solid-state image sensor due to the influence of the ambient temperature even when the shutter is closed to block the light entering the solid-state image sensor, and noise is generated. To do. This dark current has a constant value without the signal charge obtained from the photosensitive element becoming zero even when the light to the photosensitive element is blocked. This value varies with the ambient temperature and is usually
It doubles when the temperature rises by 8-10 ° C. Therefore, when a dark current flows in the image pickup signal, the dynamic range of the image pickup signal decreases as the temperature rises, and the S / N ratio also decreases, resulting in increased sensitivity unevenness.

Therefore, in the solid-state image pickup device 100, the image pickup data stored in the noise memory 106 must be exchanged in order to reduce the Bremish noise or the like that is generated or changed subsequently. Since the liquid crystal shutter 101 has to be closed once for this replacement of the image pickup data, the photographing must be stopped once, which is troublesome.

Further, like a broadcasting camera device,
Although there is a solid-state imaging device provided with a Blemish correction circuit in advance, such a solid-state imaging device has insufficient temperature followability and it is difficult to accurately adjust the correction level.

The present invention has been made in view of such circumstances, and outputs various kinds of noise from an image pickup signal and outputs an image pickup signal having a good image quality, without being affected by temperature changes due to the environment. It is an object of the present invention to provide a solid-state imaging device that does

[0013]

In order to solve the above-mentioned problems, a solid-state image pickup device according to the present invention includes a solid-state image pickup device which outputs image pickup signals of all pixels corresponding to image pickup light every one field period. The imaging signal output from the solid-state imaging device is set to 1
Shutter means for controlling an image pickup signal which is shielded and an image pickup signal which is not shielded for each field period, a delay means which delays and outputs an image pickup signal outputted from the solid-state image pickup element for one field period, and a solid-state image pickup element Difference detecting means for detecting the difference between the image pickup signal output from the solid-state image pickup device and the image pickup signal output from the solid-state image pickup device, and the image pickup signal and the light-shielding image pickup signal shielded from the solid-state image pickup device for each field period. And a control means for controlling the shutter means.

In this solid-state image pickup device, the control means controls the shutter means to obtain an image pickup signal and a non-light-shielded image pickup signal for each field period from the solid-state image pickup device. The difference detection unit can obtain only the image pickup signal in which the noise component is reduced by detecting the difference between the image pickup signal obtained from the solid-state image pickup unit and the image pickup signal delayed for one field period by the delay unit.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of a solid-state image pickup device according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, for example, the solid-state image pickup device 1 includes a liquid crystal shutter 2, a two-line type CCD image sensor 3 for reading out image pickup signals of all pixels in one field period, registers 4 and 6, and an image pickup device. Correlated double sampling (hereinafter referred to as CD
S: Correlated Double Sampling) Circuits 5, 7
An analog / digital (hereinafter referred to as A / D) converter 8, a field memory 9 functioning as a delay circuit, a D / A converter 10, a switching circuit 11 for switching an imaging signal, and an imaging A difference detection circuit 12 for reducing a noise component from the signal and a controller 13 for controlling the liquid crystal shutter 2 and the switching circuit 9 are provided.

When the image pickup of the subject is started, the controller 13 controls the liquid crystal shutter 2 so as to close one field period in one frame period as shown in the timing chart of FIG.

Since the CCD image sensor 3 outputs the image pickup signals of all pixels in one field period, when the liquid crystal shutter 2 is opened, for example, the register 4 contains dark current noise at the current ambient temperature. The image pickup signals of pixels in odd fields are output, and the image pickup signals of pixels in even fields including dark current noise are output from the register 6, for example. When the liquid crystal shutter 2 is closed, the CCD image sensor 3 outputs an image pickup signal as an offset which is a noise component due to a dark current in each field. Here, the CCD image sensor 3 switches the fields to be read by the registers 4 and 6 every time all pixels are read. CC in this way
The image pickup signal output from the D image sensor 3 is supplied to the CDS circuits 5 and 7 via the registers 4 and 6, respectively.

The CDS circuit 5 reduces random noise from the supplied image pickup signal and supplies it to the switching circuit 11.

The CDS circuit 7 reduces random noise from the supplied image pickup signal and supplies it to the A / D converter 8.
The A / D converter 8 converts the supplied image pickup signal into image pickup data and supplies the image pickup data to the field memory 9. The field memory 9 stores the supplied image pickup data of the subject once, then reads the image pickup data, and supplies the image pickup data to the D / A converter 10. Here, the field memory 9 takes one field period to store and read the imaging data. For this reason, the field memory 9 functions as a delay circuit. The D / A converter 10 converts the supplied image pickup data into an image pickup signal and supplies the image pickup signal to the switching circuit 11.

The switching circuit 11 is connected from the CDS circuit 5 to terminals a and d, connected to the D / A converter 10 to terminals b and c, and connected from the difference detection circuit 12 to each other. Two switches 11a and 1 that meet each other
1b, the switch 11b is switched to the terminal c when the switch 11a is at the terminal a, and the switch 11b is switched to the terminal d when the switch 11a is at the terminal b.

An image pickup signal A as shown in FIG. 2A is supplied to the terminals a and b of the switching circuit 11,
An imaging signal B as shown in FIG. 2B, for example, is supplied to the terminals b and c. The switching circuit 11 distributes the image pickup signal by performing switching by the controller 13 for each one-field period, and the difference detection circuit 1
Feed to 2. The difference detection circuit 12 detects the difference between the supplied image pickup signals, so that the image pickup signal C of each field in which the dark current noise is reduced as shown in FIG. 2C.
Is detected.

That is, as shown in FIG. 2, the image pickup signal ev
Focusing on en1 and the image pickup signal even2, these image pickup signals are image pickup signals that are shifted by one field. Therefore, the dark current noise does not change rapidly though it depends on the temperature. Therefore, if the difference between the image pickup signal even1 and the image pickup signal even2 is obtained, as shown in FIG. 2C, the dark current noise of the even field is reduced. Imaging signals e1-e2 are obtained. Similarly, the dark current noise is reduced by obtaining the difference between the image pickup signal odd3 and the image pickup signal odd2, the difference between the image pickup signal even3 and the image pickup signal even4, the difference between the image pickup signal odd5 and the image pickup signal odd4, ... It is possible to obtain a field imaging signal o3-o2, an even field imaging signal e3-e4, an odd field imaging signal o5-o4, ....

That is, when the image pickup signal A and the image pickup signal B delayed by one field period are supplied to the image pickup signal A, the difference detection circuit 12 detects the difference between the image pickup signals of only the noise component from the image pickup signal of the subject. Thus, the image pickup signal C for each field with reduced noise is obtained. That is, considering that the Blemish noise does not change abruptly in a short time, the difference detection circuit 12 obtains the difference between the image pickup signals that are shifted by one field period, so that the noise changed due to a temperature change during image pickup or the like. The noise can be reduced by following the change.

The image pickup signal thus read out is
For example, it is output as a standard signal of the NTSC system via a color separation circuit, a process circuit, an encoder and the like (not shown).

As described above, in the solid-state image pickup device 1,
Not only can various types of noise such as shading, blemishes, and smear be reduced, but also noise changes due to changes in environmental temperature and blemishes and other noise that have occurred subsequently can be reduced. In addition, since it is not necessary to adjust the correction level during image capturing, it is convenient and convenient.

Next, the second solid-state image pickup device according to the present invention will be described.
The embodiment will be described.

The solid-state image pickup device 20 includes a liquid crystal shutter 2
1, a line-sequential CCD image sensor 22 for reading out all pixels in one field period, and A / D converters 24, 2
8 and a frame memory 25 that functions as a delay circuit by storing and reading the image pickup signal of one frame,
29, D / A converters 26 and 30, a difference detection circuit 27 that reduces noise components from the image pickup signal, and a controller 31 that controls the shutter 21 and the frame memory 29.

When an image of a subject is picked up by the solid-state image pickup device 20, the controller 31 controls the liquid crystal shutter 21 so as to close one field period in one frame period, as shown in the timing chart of FIG.

Since the CCD image sensor 22 outputs the image pickup signals of all pixels in one line in one field period, when the liquid crystal shutter 21 is open, one frame including dark current noise is included. Output an image pickup signal. Further, when the liquid crystal shutter 21 is closed, the CCD image sensor 22 outputs an image pickup signal as an offset which is a noise component due to the dark current of each frame.
In this way, the CCD image sensor 22 detects the output image pickup signal D from the difference detection circuit 27 as shown in FIG. 4D.
And A / D converter 24 respectively.

The A / D converter 24 converts the supplied image pickup signal into image pickup data and supplies the image pickup data to the frame memory 25. The frame memory 25 stores the supplied imaging data once, then reads it out, and supplies it to the D / A converter 26. At this time, the frame memory 25
Takes one field period from once storing the imaging data to reading it. Therefore, the frame memory 25 functions as a delay circuit. D
The / A converter 10 converts the supplied image pickup data into an image pickup signal and supplies the image pickup signal E to the difference detection circuit 27 as shown in FIG. 4E.

When the image pickup signal D and the image pickup signal E delayed by one field period are supplied to the image pickup signal D, the difference detection circuit 27 detects the difference of the image pickup signal E from the image pickup signal D,
An image pickup signal F for each frame with reduced noise is obtained. That is, considering that the Blemish noise depends on the temperature change but does not change abruptly in a short time, the difference detection circuit 27 obtains the difference between the image pickup signals which are shifted by one field period from each other, thereby changing the temperature during the image pickup. Even if the noise is changed due to such reasons, the noise can be reduced by following the change.

Image signal F obtained by the difference detection circuit 27
Is supplied to the A / D converter 28. A / D converter 28
Converts the supplied image pickup signal F into image pickup data and supplies the image pickup data to the frame memory 29.

The frame memory 29 stores the supplied image pickup data, and the image pickup data is read out under the control of the controller 31. For example, the controller 31
The image data of one frame shown in FIG. 4F is divided into the image data G for every two fields shown in FIG. 4G and read. Here, the controller 31 reads 1 (odd and even), 3 (odd and even), 5 (odd and even) of the imaging data G as shown in FIG. 4G when reading the imaging data stored in the frame memory. ... are read out in one frame period. Further, the controller 31 may read the imaging data stored in the frame memory as shown in FIGS. 4H and 4I when reading the imaging data.

The image data read out in this way is supplied to the D / A converter 30 and converted into an image signal, and is passed through a color separation circuit, a process circuit, an encoder and the like (not shown), for example, the NTSC system. Is output as the standard signal of.

As described above, the solid-state image pickup device 20 can not only reduce various noises such as shading, blemishes, smears, but also noises due to changes in environmental temperature and blemishes that are generated later. Noise can also be reduced. In addition, since it is not necessary to make adjustments during imaging, it is convenient and convenient.

An electronic shutter may be used instead of the liquid crystal shutter of the solid-state image pickup device according to the present invention. The electronic shutter performs a shutter operation by forcibly discarding the image pickup signal read from the solid-state image pickup element, and can pick up an image of a high-speed moving object without blurring. By using an electronic shutter, this solid-state imaging device can extremely effectively reduce random noise other than noise that depends on the shutter speed.

As described above, the solid-state image pickup device according to the present invention detects only the difference between the image pickup signal and the image pickup signal delayed by the delay means for a predetermined time to obtain only the image pickup signal in which the noise component is reduced. be able to. That is,
This imaging device can reduce not only various so-called fixed noises, but also noises generated later due to temperature changes and the like.

[0039]

As is apparent from the above description, in the solid-state image pickup device according to the present invention, an image pickup signal and a non-light-shielding image pickup signal are obtained from the solid-state image pickup device at predetermined time intervals, and the image pickup signal and the delay means are provided. By detecting the difference from the image pickup signal delayed by a predetermined time, it is possible to obtain only the image pickup signal in which the noise component is reduced. That is, this image pickup device can not only reduce so-called fixed noise, but also noise that is generated or changed subsequently due to temperature change or the like.

Even if the noise changes due to a change in temperature or the like, the noise can be reduced by following the change, so that it is possible to take an image for a long time.

Further, since it is not necessary to adjust the correction level for reducing the noise, the operation is free from trouble.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration in a first embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a timing chart for explaining an operation state of the solid-state imaging device according to the first embodiment.

FIG. 3 is a block diagram showing a circuit configuration of the solid-state imaging device according to a second embodiment.

FIG. 4 is a timing chart for explaining an operating state of the solid-state imaging device according to the second embodiment.

FIG. 5 is a block diagram showing a circuit configuration of a conventional solid-state imaging device.

[Explanation of symbols]

 2 Liquid crystal shutter 3 CCD image sensor 9 Field memory 12 Difference detection circuit 13 Controller

Claims (3)

[Claims] 1. A solid-state image sensor that outputs an image-capturing signal of all pixels according to image-capturing light for each one-field period, and an image-capturing signal that is shielded and one that is not shielded every one-field period from the solid-state image sensor. The shutter means for controlling the shutter means, the shutter means for controlling the image pickup signal output from the solid-state image pickup device into the image pickup signal which is shielded and the image pickup signal which is not shielded every one field period, and the solid-state image pickup A delay unit that delays the image pickup signal output from the device by one field period and outputs the image pickup signal, an image pickup signal output from the solid-state image pickup device via the delay unit, and an image pickup signal output from the solid-state image pickup device And a difference detection unit that detects a difference between the solid-state imaging device and the solid-state imaging device. 2. The shutter means is a liquid crystal shutter that shields the imaging light incident on the solid-state imaging device, and the control means shields the imaging light incident on the solid-state imaging device for each field. The solid-state imaging device according to claim 1, wherein the liquid crystal shutter is controlled as described above. 3. The shutter means is an electronic shutter for forcibly discarding the image pickup signal read from the solid-state image pickup device, and the control means sets the image pickup signal from the solid-state image pickup device to 1
The solid-state image pickup device according to claim 1, wherein the solid-state image pickup device is read out and controlled so as to be discarded field by field.