JPH08289307A - Signal processing circuit for single plate color image pickup device - Google Patents

Abstract

PURPOSE: To reduce the quantization noises of color signals and at the same time to suppress the dark-time FPN (fixed pattern noises) by providing a dark- time FPN suppression circuit to the signal processing circuit of a single plate color image pickup device. CONSTITUTION: When the data are read out a solid state image pickup element 1 in a 2-line reading system, the image pickup signals S1 and S2 including the dark-time FPN components are outputted to the signal lines 1a and 1b respectively. Then the color signals including the dark-time FPN components are produced when the difference is calculated by a color signal generation subtracter 3 between both signals S1 and S2. Then the element 1 is shaded by a shading filter 9, and the data corresponding to the dark-time signals of the 1st and 2nd image pickup signals outputted to the lines 1a and 1b are stored in the dark-time signal data memories 13 and 14 respectively. Then the switches 10 and 11 are connected to the side (b), and the image pickup signals including the suppressed FPN are acquired by the subtracters 16 and 17. At the same time, the color signal data free from the dark-time FPN components are acquired through the subtracters 18 and 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for a single-chip color image pickup device, and more particularly to a signal processing circuit capable of suppressing dark fixed pattern noise (FPN).

[0002]

2. Description of the Related Art Conventionally, in a single-chip color image pickup device in which image pickup light is emitted to a solid-state image pickup element through a color separation filter, when A / D conversion is performed on an image pickup signal, color is generated by quantization noise. In order to prevent the S / N of the signal from deteriorating, as shown in FIG. 5, the color signal generated from the difference between the image pickup signal and the pixel is separately A / D converted. There is. In FIG. 5, 1 is a two-line readout type solid-state imaging device, 2 is a preamplifier, 3 is a color signal generation subtractor, 4 and 5 are imaging signal A / D converters, and 6 is a color signal A / D. A converter, 7 is an image pickup signal switch, and 8 is a color separation filter. As is well known, in the two-line reading method as described above, the output signals of both the solid-state image sensor 1 and thus the preamplifier 2 are output from each successive adjacent pixel belonging to the same horizontal line, and these outputs S1 , S2, the digital data corresponding to S2 are sequentially and alternately switched by the image pickup signal switch 7 and output, and the luminance signal Y corresponding to the scanning of the horizontal line is derived from the output side of the image pickup signal switch 7. Further, in this method, the color signal (data) C is derived as the difference between the outputs S1 and S2 of the two.

In the signal processing circuit of the single-plate color image pickup device having such a structure, when an internal amplification type photoelectric conversion element is used as a unit pixel of the solid-state image pickup element, a dark FPN or a dark FPN based on variations in dark characteristics between pixels is used. , The dark FPN based on the dark shading becomes conspicuous. In such a case, generally, an FPN suppressing circuit having a configuration as shown in FIG. 6 (corresponding parts to FIG. 5 are indicated by the same reference numerals) is provided to suppress the dark FPN. ing.

That is, a light-shielding filter 9, changeover switches 10, 11, 12 and subtractors 16, 17, 18 and dark signal data memories 13, 14, 15 are provided, and light-shielding filter 9 shields light before imaging. State, changeover switch 10, 11, 12
Is connected to the a side, and the dark signal data is stored in the dark signal data memories 13, 14 and 15, and the changeover switches 10, 11 and 12 are connected to the b side at the time of imaging, and the subtracters 16 and 17 are connected. ， 18
From the imaging signal data to the dark signal data memory 13, 1
By subtracting the dark signal data stored in 4 and 15, the dark FPN is suppressed.

[0005]

By the way, when such an FPN suppression circuit is provided, since the color signal generated from the difference between the image pickup signal and the pixel is subjected to the signal processing in parallel, the color signal for the color signal is not processed. A signal data memory in the dark is required,
It has the disadvantage of high cost.

The present invention has been made to solve the above problems when a dark FPN suppressing circuit is provided in a signal processing circuit of a conventional single-plate color image pickup device. Each invention does not require a dark signal data storage unit for a color signal and can perform a dark FPN suppressing operation while reducing a quantization noise of a color signal. For the purpose of providing
A fourth aspect of the invention is to further reduce the quantization noise in the signal processing circuit of the single-plate color image pickup device according to the first to third aspects.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a solid-state image pickup device having an internal amplification type photoelectric conversion element as a unit pixel through a color separation filter. Image signals obtained from a single-plate color image pickup device that emits image pickup light and color signals generated from the difference between pixel signals of the image pickup signals by A / D converters. In a signal processing circuit of a single-plate color image pickup device that performs D conversion to perform signal processing,
Immediately after resetting the charges stored in the light-shielded state or in the solid-state image sensor, or while resetting, the dark-time signal data storage unit for image signal for reading and dark-converting the dark time signal for A / D conversion, and storing the dark signal. Read from A / D
A dark FPN suppressing subtraction means for an image pickup signal for subtracting dark signal data accumulated in the storage means from the converted image signal data, and the image signal dark signal data storage for the A / D converted color signal data. A dark signal FPN suppressing subtracting means for subtracting color signal dark signal data generated based on the dark signal data accumulated in the means is provided.

According to a second aspect of the present invention, in the signal processing circuit of the single-plate color image pickup device according to the first aspect, the image pickup signal is obtained from the single-plate color image pickup device by a two-line reading method. And the second image pickup signal, the dark signal data storage means for the image pickup signal comprises first and second dark signal data storage means for the image pickup signal, and the dark FPN suppressing subtraction means of the image pickup signal is Darkness FPN suppression subtraction means for the first and second image pickup signals, wherein the color signal is formed by a difference signal between the first and second imaging signals, and the color signal darkness FPN suppression subtraction means Is configured to subtract the difference data of the dark signal data stored in the first and second image signal dark signal data storage means from the A / D converted color signal data.

According to a third aspect of the present invention, in the signal processing circuit of the single-plate color image pickup device according to the first aspect, the image pickup signal is a signal obtained from the single-plate color image pickup device by a one-line reading method. And the color signal is generated by a difference between the image pickup signal and the delayed image pickup signal obtained through the delay means, and the dark signal FPN suppressing subtraction means for the color signal has the image signal dark signal data. The difference data between the dark signal data accumulated in the storage means and the delayed dark signal data obtained through the delay means is inputted as dark signal data.

In the signal processing circuit of the single-plate color image pickup device thus constructed, the dark signal data stored in the image signal dark signal data storage means is used to subtract the dark FPN suppression of the color signal. The operation of the means is performed. Therefore, the dark signal data storage means for the color signals is not required, and the dark FPN is reduced while reducing the quantization noise of the color signals.
Can be suppressed.

The invention according to claim 4 is the same as claims 1 to 3.
In the signal processing circuit of the single-chip color image pickup device described above, the FPN in the preceding stage of the A / D converter for the color signal and in the dark state of the color signal
A multiplier that multiplies a constant is arranged in front of the suppression subtraction means. With this configuration, it is possible to further reduce the quantization noise of the color signal.

[0012]

EXAMPLES Next, examples will be described. FIG. 1 is a circuit configuration diagram showing a first embodiment of a signal processing circuit of a single-plate color image pickup device according to the present invention, and the same or corresponding members as those of the conventional example shown in FIG. , The description is omitted. This embodiment differs from the conventional example shown in FIG. 6 in that it has no memory means corresponding to the memory 15 of the conventional example shown in FIG. . The subtractor 19 obtains the difference between the dark signal data stored in the first image signal dark signal data memory 13 and the second image signal dark signal data memory 14 to obtain a color signal. This subtractor 19 forms the dark signal data for
The difference data formed in (4) is input to the subtracter 18 for FPN suppression during dark of color signals. Then, the subtractor 18 subtracts the difference data of the dark signal data of the image pickup signal from the color signal data A / D converted by the A / D converter 6 to remove the FPN from the color signal. ing.

Next, the operation of the first embodiment thus constructed will be described with reference to the signal waveform diagram shown in FIG. In addition, (C1), (C2), (D), and
(E) is an analog representation of a waveform corresponding to each corresponding digital value. First, when read out from the solid-state image sensor 1 by the two-line reading method, the first and second signal lines 1a and 1b are connected to the first and second signal lines 1a and 1b via the preamplifier 2.
As shown in (A1) and (A2) of FIG. 2, first and second image pickup signals S1 = (S11 + N11) and S2 = (S21 + N21) including the dark FPN components N11 and N21, respectively, are output. In the color signal generation subtractor 3, each signal line 1
By taking the difference between the first and second image pickup signals S1 and S2 of a and 1b, the dark FPN as shown in FIG.
Color signal including component (N11-N21) {(S11 + N11)-
(S21 + N21)} is formed.

Next, the solid-state image pickup device 1 is shielded from light by the light-shielding filter 8, the switches 10 and 11 are connected to the side a, and the first and second switches shown in (C1) and (C2) of FIG. The dark signal N of the first image pickup signal output to the signal lines 1a and 1b
Data corresponding to the dark signal N21 of the 11th and 2nd image pickup signals are stored in the 1st and 2nd image pickup signal dark signal data memories 13 and 14, respectively.

Next, the switches 10 and 11 are connected to the b side, the light-shielding filter 8 is removed, and the image pickup light is made incident on the solid-state image pickup device 1 and the first signal line 1a, 1b contains a dark FPN component. And the second image pickup signals S1 and S2 are output. At the same time, the dark signal data memory for the first and second imaging signals
The dark signals N11 and N21 stored from 13 and 14 are read out, and the subtractors 16 and 17 subtract the data corresponding to the imaging signals S1 and S2 from the dark signal data N11 and N21.
An image pickup signal in which FPN is suppressed can be obtained.

Simultaneously with this operation, the subtracter 19 converts the dark signal data N11, N21 read from the image signal dark signal data memories 13, 14 as shown in FIG. Difference data (N11-N21) is formed, and this difference data (N11-N21) is input to the negative side of the dark-time FPN suppressing subtractor 18 for color signals. Then, in the subtracter 18, the dark FPN component (N
Color signal including (11-N21) {(S11 + N11)-(S21 +
N21)} From the corresponding data, the difference data (N11-N2
By subtracting 1), as shown in FIG. 2E, color signal data (S11-S21) in which the dark FPN component (N11-N21) is removed, that is, FPN is suppressed is obtained. To be

Next, a second embodiment will be described. FIG.
2 is a circuit configuration diagram showing a second embodiment. The same or corresponding members as those in the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, between the color signal generating subtractor 3 and the color signal A / D converter 6 in the first embodiment,
In addition, multipliers 21 and 22 for multiplying a predetermined constant α between the subtractor 19 and the dark signal FPN suppressing subtractor 18 respectively.
It is configured by interposing.

As described above, by interposing the multipliers 21 and 22, it is possible to suppress the FPN of the color signal while further reducing the quantization noise by the A / D converter 6 for the color signal.

Next, a third embodiment will be described. FIG.
Is a circuit configuration diagram showing a third embodiment. The same or corresponding members as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. This embodiment is configured to read from the solid-state image pickup device 1 by a one-line reading method, and a color signal is obtained from an image pickup signal output to a single signal line 1a and a delay line 31 to the signal line 1a. The delayed image pickup signal is subtracted by the subtractor 3 to be formed. Further, the subtracter 19 includes the dark signal data from the dark signal data memory 13 for imaging signals and the dark signal data memory 13 similarly.
From the delayed dark signal data obtained via the delay line 32 from the delay line 32 and the difference between them is calculated to obtain the dark signal F of the color signal.
It is configured to be input to the PN suppressing subtractor 18.

With this configuration, even if the signal read from the solid-state image pickup device is a one-line read system, the FPN of the color signal can be suppressed while similarly reducing the quantization noise due to A / D conversion. You can

Also in this embodiment, the quantization noise can be further reduced by interposing a multiplier as in the second embodiment. Further, in each of the above-described embodiments, the configuration in which the dark signal is read out by using the light shielding filter is shown, but without using the light shielding filter, immediately after resetting the accumulated charge of the solid-state image sensor or while resetting. The dark signal may be read in the absence of photocharge.

[0022]

As described above on the basis of the embodiments,
According to the invention described in claims 1 to 3, by using the dark signal data accumulated in the dark signal data storage means for the imaging signal,
A low-cost signal processing circuit capable of suppressing dark FPN while reducing quantization noise of color signals without using the dark signal data storage means for color signals can be obtained. According to the invention described in claim 4, in the signal processing circuit of the single-plate color imaging device according to claims 1 to 3, it is possible to further reduce the quantization noise of the color signal.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a signal processing circuit of a single-plate color imaging device according to the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the first embodiment shown in FIG.

FIG. 3 is a circuit configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit configuration diagram showing a third embodiment of the present invention.

FIG. 5 is a diagram showing a configuration example of a signal processing circuit of a conventional single-plate color imaging device.

FIG. 6 is a diagram showing a configuration example of a signal processing circuit of a single-chip color imaging device including a conventional FPN suppression circuit.

[Explanation of symbols]

 1 Solid-state imaging device 2 Preamplifier 3 Color signal generation subtractor 4, 5 Imaging signal A / D converter 6 Color signal A / D converter 7 Imaging signal switch 8 Color separation filter 9 Light-shielding filter 10, 11, 12 Switches 13 and 14 Dark signal data memory for imaging signals 15 Dark signal data memory for color signals 16 and 17 Dark FPN suppression subtractor for imaging signals 18 Dark FPN suppression subtractor for color signals 19 Subtractor 21 , 22 Multiplier 31, 32 Delay line

Claims (4)

[Claims] 1. An image pickup signal obtained from a single-plate color image pickup device in which an image pickup light is emitted to a solid-state image pickup element having an internal amplification type photoelectric conversion element as a unit pixel through a color separation filter, The color signals generated from the difference between the pixel signals of the image pickup signals are respectively A / D converted by A / D converters.
In a signal processing circuit of a single-plate color image pickup device which performs D conversion to perform signal processing, a dark signal in a light-shielded state or immediately after resetting the accumulated charge of a solid-state image pickup device or while there is no photocharge while resetting is performed. Dark signal data storage means for image pickup signals for reading and A / D converting and accumulating;
Dark-time fixed pattern noise suppression subtraction means for subtracting the dark-time signal data stored in the storage means from the A / D-converted imaging signal data read from the solid-state image sensor, and the A / D-converted color signal data From the dark signal data storage means for the imaging signal, the dark signal data of the color signal generated based on the dark signal data of the dark signal is subtracted. A signal processing circuit for a single-chip color image pickup device characterized by the above. 2. The image pickup signal is composed of first and second image pickup signals obtained by the two-line reading method from the single-plate color image pickup device, and the dark signal data storage means for the image pickup signal is first and second. The second dark signal data storage means for image pickup signal, the dark fixed pattern noise suppression subtraction means for the image pickup signal comprises dark fixed pattern noise suppression subtraction means for the first and second image pickup signals, and The color signal is the first
And a difference signal between the second image pickup signal, and the dark-time fixed pattern noise suppressing subtraction unit of the color signal, the dark signal for the first and second image-pickup signals from the A / D-converted color signal data. 2. The signal processing circuit for a single-chip color image pickup device according to claim 1, wherein the signal processing circuit is configured to subtract difference data of dark signal data respectively stored in the data storage means. 3. The image pickup signal is a signal obtained by the one-line reading method from the single-chip color image pickup device, and the color signal is composed of the image pickup signal and a delayed image pickup signal obtained through a delay unit. The subtraction unit for suppressing the fixed pattern noise in the dark of the color signal, which is generated by the difference, is stored in the dark signal data storage unit for the image pickup signal in the dark signal data and the delayed dark time obtained through the delay unit. The signal processing circuit of the single-chip color image pickup device according to claim 1, wherein the differential data from the signal data is input as dark signal data. 4. A multiplier for multiplying a constant is arranged before the color signal A / D converter and before the color signal dark time fixed pattern noise suppression subtraction means. 4. The signal processing circuit of the single-plate color imaging device described in any one of 3 above.