JPH06189200A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To provide superior picture quality by surely removing the fixed pattern noise of an image pickup element corresponding to photographing conditions without enlarging a device. CONSTITUTION:Dummy lines not connected to photosensitive picture elements are provided in a part of the photosensitive part of the image pickup element 1 and also a line buffer 4 for storing noise component data is provided. Signals outputted from the dummy lines are taken into the line butter 4 and used as the noise component data and the noise is corrected. Thus, the device can be prevented from being enlarged with the noise corrected by using a small memory and also the fixed pattern noise can be surely removed without receiving the influence of the photosensitive picture elements.

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 used in a video camera or the like.

[0002]

2. Description of the Related Art In a solid-state image pickup device used in a video camera or the like, it is known that noise is generated due to various factors in the process of signal processing. inside that,
As fixed pattern noise in a solid-state image pickup device, two types of noise are conventionally known: random uneven noise that produces an image like frosted glass and streak noise arranged vertically or horizontally.

As a method of correcting these noises,
Conventionally, a method using a circuit as shown in FIG. 9 has been used. That is, the noise component data of the image sensor for one screen is stored in the frame memory 52 in advance.
Then, when the image pickup signal generated by the image pickup element 51 is output to the process circuit 7, the noise component stored in the frame memory 52 is subtracted from the image pickup signal by the subtractor 6 and then output.

[0004]

However, in the above-mentioned conventional example, in order to store the noise component data of the image pickup device, a frame memory for one screen having a large memory amount is required, which increases the size of the entire apparatus. And the problem of cost increase was invited. By the way, noise may be corrected by using a line buffer capable of saving the memory amount in order to downsize the device. But,
In such a case, there were the following problems. That is, in general, streak-like noise is most noticeable among fixed pattern noises, and therefore it is necessary to effectively remove this noise. However, when the line buffer is used, it is affected by uneven noise, which is another fixed pattern noise of the image pickup device, so that there is a problem that the streak noise cannot be accurately corrected. .

Further, since the noise component data of the image pickup device stored in the frame memory is fixed, it is not possible to effectively remove dark current uneven noise which changes in accordance with a change in temperature. There was a problem. Further, in the above-mentioned conventional example, even if it is not necessary to correct the image pickup signal, the correction is uniformly performed. Therefore, in that case, the image quality is not improved.
On the contrary, there was a problem of deterioration.

The present invention has been made in order to solve the above problems, and makes it possible to surely remove noise components in an image pickup device without increasing the size of the entire apparatus and to reduce the noise during photography. The purpose is to enable appropriate noise correction according to the state.

[0007]

In the solid-state image pickup device of the present invention, a signal line not connected to a photosensitive pixel is provided in a part of the image pickup element, and noise component data used for correcting noise of the image pickup element. Is provided, and when the noise component data is taken into the line buffer, a signal line to which the photosensitive pixel is not connected is selected.

Another feature of the present invention is that an image sensor for generating an image signal by photoelectric conversion, an image memory for storing the image signal generated by the image sensor, and noise correction for the image sensor. And a subtractor for subtracting the noise component data generated by the noise generation unit from the image signal stored in the image memory, and the image signal is converted into the image signal. After storing in the memory, noise component data is generated by the noise generating means, and the noise component data is subtracted from the image signal by the subtractor and output.

The noise generating means includes the image pickup device,
The noise component data is generated by the image sensor in a dark state in which the light from the subject is shielded by the light shielding unit. Good.

Further, there may be provided a deciding means for deciding whether or not to carry out the subtraction processing according to the state of the image signal stored in the image memory. Further, the subtraction processing may be performed without fail when increasing the gain of the image signal stored in the image memory.

[0011]

As described above, according to the present invention, a signal line to which a photosensitive pixel is not connected is provided in a part of the image pickup device, and a signal output from this signal line is used as noise component data of the image pickup device. , It is possible to perform noise correction that is not affected by the photosensitive pixels, and it is possible to capture noise component data line by line.
A line buffer with a small amount of memory is sufficient as a memory for storing the noise component data.

Further, by providing noise generating means for generating noise component data of the image pickup device and generating the noise component data for each photographing of one screen, it is possible to obtain the noise component data according to the photographing situation. Therefore, it is possible to perform noise correction according to the noise state at the time of shooting. Furthermore,
Decide whether to perform noise correction according to the state of the image signal of the subject.If noise correction is not necessary, do not perform noise correction.Always make noise correction when increasing the gain of the image signal. By doing so, it is possible to perform optimum noise correction according to the state of the photographed subject.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the solid-state image pickup device of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a block diagram of a solid-state imaging device showing a first embodiment of the present invention. It should be noted that in FIG. 1, the portions to which the same reference numerals as those of the conventional solid-state imaging device shown in FIG. 9 are attached have the same functional portions as those of the conventional one.

The image pickup device 1 is driven by a driver 8. The driver 8 is driven by the drive pulse PDR generated from the synchronization signal generation circuit 9. The output signal from the image pickup device 1 is switched by the switch 2, and when the movable terminal 2a is switched to the fixed terminal A side, the terminal A
Is applied to one end of the subtracter 6 as the image pickup output Y _S.
When the movable terminal 2a is switched to the fixed terminal B side, the output signal from the image pickup device 1 is A / D from the terminal B.
It is input to the converter 3 and stored in the line buffer 4 as digital noise component data.

This noise component data is D / A converted by the D / A converter 5, and analog noise component data Y
It is input to the other end of the subtractor 6 as _N. Then, the noise component data Y _N is subtracted from the above-mentioned image pickup output Y _S , and the correction signal Y is obtained. The correction signal Y generated in this way is input to the process circuit 7 and subjected to processing such as white clip and aperture correction, and then the video signal S.
It is output as v.

FIG. 2 is a diagram showing a detailed configuration of the image pickup device 1, and here, a MOS type image pickup device is taken as an example. That is, one pixel is composed of a MOS-FET (MOS type field effect transistor) 11 and a photodiode 12. A predetermined number of pixels are regularly arranged in the horizontal direction and the vertical direction to form the photosensitive portion. The charges generated in the photosensitive section are read out via the horizontal signal line 13 and the vertical signal line 14 connected to each pixel.

To explain this charge reading operation in a little more detail, first, in the vertical direction, the address signal ADR designating a read line is input to the decoder 15, and the designated read line is transmitted to the vertical register 16. Then, the horizontal line 13 thus designated is sequentially scanned according to the address signal ADR. Next, in the horizontal direction, the signal of each pixel connected to one horizontal line designated by the address signal ADR is transferred to the horizontal register 1 via the vertical signal line 14.
It is sequentially output by the action of 7.

The present embodiment is characterized in that a dummy line 18 to which no photosensitive pixel is connected is provided at the top of this horizontal line. The dummy line 18 is designated at the time of capturing fixed pattern noise in the vertical direction, which will be described later.

Next, the overall operation of the solid-state image pickup device of this embodiment shown in FIG. 1 will be described in detail with reference to the timing chart of FIG.

In FIG. 3, (a) shows the vertical synchronizing signal VD.
And (b) shows the vertical blanking signal VB. First, when the timing enters the vertical blanking period as shown in FIG. 3B, the address signal ADR changes to FIG.
As shown in (c), the dummy line 18 shown in FIG. 2 is designated. As described above, since no photosensitive pixel is connected to the dummy line 18, the signal output from the dummy line 18 is only a noise component and is used as fixed pattern noise of the image sensor 1.

In the vertical blanking period,
As shown in FIG. 3D, the switch signal PSW is applied to the switch 2 so that the movable terminal 2a selects the fixed terminal B side. As a result, the noise component data output from the image sensor 1 is input to the A / D converter 3. Furthermore,
The A / D converter pulse PCNT1 is turned on as shown in FIG. 3 (e), and the A / D converter 3 starts to operate. As a result, the noise component data for one horizontal line is A / D converted and stored as a digital signal in the line buffer 4.

Next, when the vertical blanking period is ended and the effective period is entered, the switch signal PSW is sent to the switch 2 so that the movable terminal 2a selects the fixed terminal A side as shown in FIG. 3 (d). Given. As a result, the imaging output Y _{S on} the valid line designated by the address signal ADR during this valid period is input to one end of the subtractor 6.

Further, within this effective period, the D / A converter pulse PCNT2 for driving the D / A converter 5 is
As shown in FIG. 3 (f), it is turned on, and the noise component data accumulated in the line buffer 4 during the vertical blanking period is converted into analog noise component data Y _N and input to the other end of the subtractor 6. To be done. In the subtractor 6, Y =
Y _S -Y _N becomes operation is performed, thereby the fixed pattern noise correction signal Y component is removed is obtained. Then, the correction signal Y is input to the process circuit 7, where a synchronizing signal and the like are added and output as a video signal Sv.

In the above-described first embodiment, the case where the subtraction process in the subtractor 6 is performed using an analog signal has been described, but it may be performed using a digital signal. FIG. 4 is a diagram showing a solid-state imaging device as a second embodiment in which the subtraction processing is digitally performed in this way. Note that, in FIG. 4, the same functional portions as those of the solid-state imaging device shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 4, the output signal from the image pickup device 1 is A / D converted by the A / D converter 3 into a digital signal. The output signal from the image pickup device 1 is the image pickup output or the noise component data of the image pickup device 1 which is switched and output at the operation timings shown in FIGS. 3A to 3D, as in the above-described embodiment. .

When the digital signal output from the A / D converter 3 is obtained by A / D converting the image pickup output of the image pickup device 1, the digital signal is picked up at one end of the subtractor 20 by switching the switch 19. Directly input as output Y _SD . In addition, the digital signal output from the A / D converter 3 converts the noise component data of the image sensor 1 into the A / D
In the case of being converted, this digital signal is input to the line buffer 4 by switching of the switch 19 and once stored, and then is subtracted as the noise component data Y _{ND by the} subtracter 20.
Is input to the other end of.

Then, the subtracter 20 outputs the above-mentioned image pickup output Y _SD.
This noise component data Y _ND is subtracted from
_D is obtained. The correction signal Y _D is input to the D / A converter 5 after being added with a synchronizing signal or the like in the process circuit 7, converted into an analog signal and output as a video signal Sv.

In the above-described first and second embodiments, the number of times noise component data is fetched from the dummy line 18 has not been described in detail, but this is not limited to once. For example, more accurate noise component data can be obtained by increasing the number of times of capturing and taking the average value.

As described above, according to the first and second embodiments, the signal obtained from the dummy line 18 to which the photosensitive pixel is not connected on a line-by-line basis is smaller in line memory 4 than the frame memory. Since it is stored as noise component data in the memory and noise correction is performed based on the noise component data, it is possible to perform noise correction that is not affected by the photosensitive pixels without enlarging the device unnecessarily. Image quality can be obtained.

Next, a third embodiment of the present invention will be described. FIG. 5 is a block diagram showing the solid-state imaging device of this embodiment. First, the overall operation of this embodiment will be briefly described with reference to FIG.

In FIG. 5, when a shutter button (not shown) is turned on, the light shield plate 31 is opened, and an object image is formed on the image pickup surface of the CCD 32 by an optical system (not shown) provided in front of the light shield plate 31. It is imaged and photoelectrically converted by the CCD 32. The image pickup signal thus obtained is A / D converted by the A / D converter 33 and then stored in the frame memory 34 as an image signal.

Next, the light shielding plate 31 is closed and photoelectric conversion is performed by the CCD 32 in the dark state. The image pickup signal obtained in this way is obtained by photoelectric conversion performed by blocking any light from the outside of the CCD 32, and is used as noise component data S _N of fixed pattern noise of the CCD 32.

The noise component data S _N obtained in this manner is directly input to one end of the subtractor 36 without undergoing the A / D conversion processing by the A / D converter 33. Note that the noise component data S _N is not read when it is determined to be unnecessary by the determination operation described later.

Then, in synchronization with the input of the noise component data S _N to the subtractor 36, the frame memory 34
The image signal of the subject stored in the D / A converter 35
Is D / A converted by and is input to the other end of the subtractor 36 as an analog image signal S _D. Then, in the subtractor 36, S =
The subtraction process S _D -S _N is performed, and the correction signal S from which the noise component of the CCD 32 is removed is obtained.

This correction signal S is applied to the terminal B of the switch 37.
Entered in. Further, the uncorrected image signal S _D is input to the terminal A of the switch 37, and the system controller 42
Depending on the judgment, either the corrected signal S or the uncorrected signal S _D is selected. The method of this determination will be described later. Then, the selected signal is given to the recording device 39 and recorded after being subjected to predetermined processing in the process circuit 38.

Next, the method of determining the terminal selection of the switch 37 by the system controller 42 will be described with reference to FIG.
This will be described with reference to the flowchart of. First, step S1
When the shutter is turned on in step S2, the light shielding plate 3
1 is opened, photoelectric conversion of the subject is performed in step S3, and the image pickup signal (subject data) is stored in the frame memory 34.
Is taken into.

In step S4, the histogram processing of the luminance distribution of the captured object data is performed, and the highlight point HP and the dark point DP of the image are determined from the processing result. FIG. 7 is a diagram showing an example of the result of this histogram processing. The processing result is obtained by classifying the pixels into 256 steps based on the captured subject data and arranging them in order of brightness. The value of 99% of the whole is set as the highlight point HP, and the value of 1% is set as the dark point DP.

Further, the index (INDEX) is determined from the combination of the highlight point HP and the dark point DP obtained in this way, for example, based on the chart shown in FIG. Where the index is O
In the case of N, the noise component is read, and in the case of the index being OFF, the noise component is not read.

Next, the index is turned on in step S5.
Or OFF is determined. When it is determined that the index is ON, the process proceeds to step S6, the light shielding plate 31 is closed, and the noise component data S _N of the CCD 32 is read and input to one end of the subtractor 36 in step S7. Next, in step S8, the movable terminal 37a of the switch 37 is switched to the terminal B side, whereby the subtractor 3
The correction signal S generated in 6 is selected, and the correction signal S is recorded in the recording device 39 in step S10.

In step S5, the index is OF
If it is determined that the value is F, the process proceeds to step S9 without reading the noise component data S _N in steps S6 and S7, and the uncorrected signal S _D is selected by switching the movable terminal 37a to the terminal A side. This uncorrected signal S _D is recorded in the recording device 39 in S10.

In the above description of the present embodiment, the image pickup signal itself in the dark state captured at one time is taken by the CCD3.
The case where the noise component data S _N of 2 is used has been described, but the present invention is not limited to this. For example, the effect of random noise can be reduced by averaging image signals in a dark state captured a plurality of times using a line buffer or the like and using this to perform noise correction.

The selection of whether or not to read the noise component data S _N has been described based on the result of the histogram processing. However, when the gain of the image signal is increased, the noise component data S _N is selected. You may make it always read and always perform noise correction. Also, the subtraction operation in the subtractor 36 may be performed digitally, as in the case of the second embodiment described above.

As described above, according to the third embodiment, the image pickup signal in the dark state generated by closing the light shielding plate is used as the noise component data of the image pickup device, and the fixed pattern noise of the image pickup device is corrected based on this. So I did
It is possible to obtain noise component data according to the shooting condition for each shooting of one screen, and it is possible to perform optimum noise correction according to the noise state at the time of shooting. Furthermore, it is determined whether or not noise correction is performed according to the state of the image signal stored in the frame memory, and noise correction is not performed when correction is not necessary, so excessive correction is prevented. Optimal noise correction can be performed, and the time for shooting one image can be shortened.

[0044]

As described above, according to the present invention, a signal line to which a photosensitive pixel is not connected is provided in a part of the image pickup device, and a signal output from this signal line is used as noise component data of the image pickup device. Since it is used, it is possible to perform noise correction that is not affected by the photosensitive pixels, and thus it is possible to obtain good image quality in which fixed pattern noise of the image sensor is reliably removed. Further, since the signal line to which the photosensitive pixel is not connected is provided and the noise component data is obtained from the signal line, it is possible to take in the noise component data on a line-by-line basis, thereby using a frame memory having a large memory amount. There is no need, and the device can be downsized.

Further, a noise generating means for generating noise component data and a determining means for determining whether or not to perform noise correction according to the state of the image signal of the subject are provided, and the noise generating means is used for one screen. Noise correction is performed based on the noise component data generated for each shooting, and noise correction is not performed when it is determined that correction is not necessary based on the image signal of the subject. Also, it is possible to perform optimum noise correction according to the state of the image signal of the subject, and thereby always obtain good image quality. Further, when noise correction is not performed, there is an effect that the shooting time for one screen can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing a solid-state imaging device according to a first embodiment.

FIG. 2 is a diagram showing a detailed configuration of an image sensor.

FIG. 3 is a timing chart showing the overall operation timing of the solid-state imaging device.

FIG. 4 is a block diagram showing a solid-state imaging device according to a second embodiment.

FIG. 5 is a block diagram showing a solid-state imaging device according to a third embodiment.

FIG. 6 is a flowchart for explaining the operation of the third embodiment.

FIG. 7 is a diagram showing an example of a result of histogram processing.

FIG. 8 is a diagram showing indexes determined from the result of histogram processing.

FIG. 9 is a block diagram showing a configuration of a conventional solid-state imaging device.

[Explanation of symbols]

 1 Image Sensor 2 Switch 2a Movable Terminal 3 A / D Converter 4 Line Buffer 5 D / A Converter 6 Subtractor 7 Process Circuit 9 Sync Signal Generation Circuit 13 Horizontal Signal Line 14 Vertical Signal Line 18 Dummy Line 19 Switch 20 Subtractor 31 Light Shading Plate 32 CCD 33 A / D Converter 34 Frame Memory 35 D / A Converter 36 Subtractor 37 Switch 37a Movable Terminal 38 Process Circuit 39 Recording Device 42 System Controller

Claims (5)

[Claims] 1. A signal line to which a photosensitive pixel is not connected is provided in a part of an image sensor, and a line buffer for storing noise component data used for correcting noise of the image sensor is provided. Is taken into the line buffer, a signal line to which the photosensitive pixel is not connected is selected. 2. An image sensor for generating an image signal by photoelectric conversion, an image memory for storing the image signal generated by the image sensor, and noise for generating noise component data for noise correction of the image sensor. And a noise subtraction unit for subtracting the noise component data generated by the noise generation unit from the image signal stored in the image memory, storing the image signal in the image memory, and then generating the noise. A solid-state imaging device, wherein noise component data is generated by the means, and the noise component data is subtracted from the image signal by the subtractor and output. 3. The noise generating means is constituted by the image pickup device and a light shielding means for shielding light from the subject to the image pickup device, and the noise component data includes light from the subject by the light shielding means. The solid-state image pickup device according to claim 2, wherein the solid-state image pickup device is generated by the image pickup device in a dark state shielded from light. 4. The solid-state image pickup device according to claim 2, further comprising a determination unit that determines whether or not to perform the subtraction processing according to a state of an image signal stored in the image memory. . 5. The solid-state image pickup device according to claim 2, wherein the subtraction process is performed without fail when increasing the gain of the image signal stored in the image memory.