JPH11341502A - Signal processing circuit for solid-state image pickup element and camera system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the signal processing circuit for a solid-state image pickup element that copes with both a case of using an infrared ray cut filter and a case of not using the infrared ray cut filter, where the sensitivity is improved when no infrared ray cut filter is in use and color reproducibility equal to that of using the infrared ray cut filter is maintained and to provide the camera system. SOLUTION: The camera system is provided with a primary color separation circuit 161 that separates an image signal outputted from an imaging device 13 having a color filter into R, G, B primary color signals, a primary color separation matrix constant setting circuit 162 that sets a primary color separate matrix constant to the primary color separation circuit 161 and switches a matrix constant between the case that an infrared ray (IR) cut filter 19 is placed in an optical system to receive an image in the imaging device 13 and the case that the filter 19 is not placed, and white balance amplifiers 165R, 165G, 165B that adjust the gain among the R, G, B primary color signals outputted from the primary color separate circuit 161.

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 solid-state imaging device and a camera system, and more particularly to a signal processing circuit for processing an image signal output from a solid-state imaging device having a color filter, and a camera system using the same. About.

[0002]

2. Description of the Related Art The relative luminous efficiency of a human being is approximately 400 n in wavelength.
m to 700 nm. On the other hand, a solid-state image sensor, for example, a CCD (Charge Coupled Device) image sensor has sensitivity in the infrared region (700 nm or more).
It will be different from human appearance and color. Therefore, when configuring an imaging system using a CCD imaging device having a color filter, an optical system that captures incident light from a subject on the imaging surface of the CCD imaging device usually includes:
An infrared cut filter is provided to improve color reproducibility.

FIGS. 8A and 8B show spectral sensitivity characteristics of complementary color filters (cyan (Cy), yellow (Ye), green (G), and magenta (Mg)) used in a CCD image sensor. Show. Here, the relative luminous efficiency of a human is about 400 nm to 700 in wavelength.
Since it is in the range of nm, only characteristics within that range are shown. As is clear from this spectral sensitivity characteristic, before passing through the infrared cut filter (a), the infrared region (700 nm
), The sensitivity on the long wavelength side including the infrared region decreases after passing through the infrared cut filter (b).

[0004]

As described above, by capturing incident light (image light) from a subject on the imaging surface of the CCD imaging device through the infrared cut filter, the CCD
The sensitivity of the image sensor decreases. Therefore, in an imaging system using a conventional CCD imaging device having a color filter, since an optical system has an infrared cut filter,
There was a limit to improving the sensitivity.

[0005] On the other hand, if the infrared cut filter is removed for the purpose of improving the sensitivity, the color reproducibility deteriorates as described above. In particular, for example, when images are taken under different color temperatures such as indoors and outdoors, the color of the subject is completely different, and the characteristics of the imaging system (camera system) are NG. Here, the color temperature refers to the temperature (K) of a black body having the same chromaticity as the test light source.

[0006] The present invention has been made in view of the above problems, and an object thereof is to cope with both a case where an infrared cut filter is used and a case where an infrared cut filter is not used.
Further, it is an object of the present invention to provide a signal processing circuit and a camera system of a solid-state imaging device which can improve sensitivity when an infrared cut filter is not used and can maintain color reproducibility equivalent to the case where the filter is used.

[0007]

According to the present invention, there is provided a signal processing circuit for a solid-state imaging device, comprising: a primary color separation circuit for separating an image signal output from a solid-state imaging device having a color filter into R, G, and B primary color signals; A primary color separation matrix constant is set for this primary color separation circuit, and a primary color separation matrix constant setting circuit capable of switching the matrix constant is provided between the primary color separation circuit and an R, G, B primary color signal output from the primary color separation circuit. And a white balance amplifier that performs gain adjustment.

In the signal processing circuit of the solid-state image sensor having the above-described configuration, the primary-color separation matrix constant of the primary-color separation circuit can be switched by the setting circuit. By setting optimized values for the case where the infrared cut filter is placed and the case where the infrared cut filter is not placed in the optical system that captures the incident light, it is equivalent to the case where the infrared cut filter is not placed Color reproducibility is obtained.

A camera system according to the present invention comprises a solid-state image pickup device having a color filter, an optical system for taking in incident light from a subject on an image pickup surface of the solid-state image pickup device, and an image signal for R, G, B primary color signals. And a primary color separation matrix for setting a primary color separation matrix constant for the primary color separation circuit and switching the matrix constant between when an infrared cut filter is arranged in the optical system and when it is not arranged. The configuration includes a constant setting circuit and a white balance amplifier that performs gain adjustment between the R, G, and B primary color signals output from the primary color separation circuit.

In the camera system having the above configuration, when an infrared cut filter is arranged in the optical system, the sensitivity on the long wavelength side including the infrared region is reduced. And good color reproducibility can be obtained. On the other hand, when the infrared cut filter is not provided in the optical system, the sensitivity can be improved and the cost can be reduced, but the color reproducibility deteriorates. At this time, by setting an optimized value as the primary color separation matrix constant of the primary color separation circuit, the same color reproducibility as when the infrared cut filter is provided can be obtained even when the infrared cut filter is not provided.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a camera system according to the present invention. As is clear from the figure,
The camera system 10 includes, as an example, a lens 11, an optical low-pass filter (LPF) 12, an image sensor 13, a preamplifier 14, an A / D converter 15, a digital signal processing circuit 16, an optical detector 17, and a system controller 18. It has a configuration. In addition,
After the optical low-pass filter 12, if necessary,
An infrared (IR) cut filter 19 is provided.

In the camera system 10 having the above configuration,
The lens 11 transmits incident light (image light) from a subject (not shown) through an optical low-pass filter 12 to an image sensor 13.
Is imaged on the imaging surface of. As the imaging device 13, CC
A solid-state imaging device such as a D imaging device is used. The imaging device 13 has a color filter (not shown) of a complementary color or a primary color, converts an image formed on the imaging surface into an electric signal, and supplies the electric signal to the preamplifier 14 as an analog image signal.

The preamplifier 14 samples and holds an analog image signal output from the image pickup device 13 to extract necessary data, and performs gain control in order to adjust the signal to an appropriate level. The analog image signal that has passed through the preamplifier 14 is supplied to an A / D converter 15. The A / D converter 15 converts the output signal of the preamplifier 14 from an analog signal to a digital signal, and supplies the digital signal to a digital signal processing circuit 16.

The digital signal processing circuit 16 includes, for example, a primary color separation circuit 161, a primary color separation matrix constant setting circuit 1
62, a changeover switch 163, an attenuator 164, white balance amplifiers 165R, 165G, 165B, a gamma correction circuit 166, a color difference matrix circuit 167, an encoder 168, and a D / A converter 169.

Note that it is possible to adopt a configuration in which the A / D converter 15 is provided in the digital signal processing circuit 16, and it is also possible to adopt a configuration in which the D / A converter 169 is provided outside the digital signal processing circuit 16. is there.

In the digital signal processing circuit 16, the primary color separation circuit 161 converts the digital image signal supplied from the A / D converter 15 into R (red), G (green), and B (blue) primary color signals. Sr1, G signal Sg1 and B signal Sb1.
65R, 165G, 165B. In the camera system 10, the primary color separation circuit 161 separates R, G, and B primary color signals from the luminance signal Y and the two color difference signals Cr and Cb based on the following equation.

R = Cr + RMATY × Yr + RMATC × Cb G = Y + Cr + Cb B = Cb + BMATY × Yb + BMATC × Cr where RMATY, RMATC, BMATY, BMAT
C is a primary color separation matrix constant.

This primary color separation matrix constant RMATY,
RMATC, BMATY, and BMATC are set by the primary color separation matrix constant setting circuit 162. The primary color separation matrix constant setting circuit 162 is provided for the primary color separation matrix constants RMATY, RMATC, and BMAT in a system in which the infrared cut filter 19 is disposed after the optical low-pass filter 12 and in a system in which the infrared cut filter 19 is not disposed.
The configuration is such that different values optimized for each are set by switching between Y and BMATC.

Of the R signal Sr1, G signal Sg1, and B signal Sb1 output from the primary color separation circuit 161, the R signal S
A changeover switch 163 is inserted in the signal path to the white balance amplifier 165R of r1. In the case of a system in which an infrared cut filter 19 is arranged downstream of the optical low-pass filter 12, the changeover switch 163 directly outputs the R signal Sr 1 to the white balance amplifier 1.
In the case of a system in which the infrared cut filter 19 is not provided, the R signal Sr1 is attenuated by a predetermined amount by the attenuator 164 and supplied to the white balance amplifier 165R.

The white balance amplifier 165R receives an R gain signal Sr supplied from the system controller 18.
2, the gain of the R signal Sr1 supplied from the primary color separation circuit 161 is adjusted and supplied to the gamma correction circuit 166 as an R signal Sr3. White balance amplifier 1
65G is G provided from the system controller 18.
The gain of the G signal Sg1 supplied from the primary color separation circuit 161 is adjusted based on the gain signal Sg2, and the G signal Sg
The number 3 is supplied to the gamma correction circuit 166. The white balance amplifier 165B adjusts the gain of the B signal Sb1 supplied from the primary color separation circuit 161 based on the B gain signal Sb2 supplied from the system controller 18, and supplies the same to the gamma correction circuit 166 as the B signal Sb3.

That is, the white balance amplifier 165
In R, 165G, and 165B, based on the R gain signal Sr2, the G gain signal Sg2, and the B gain signal Sb2 given from the system controller 18, the ratios of the R signal Sr1, the G signal Sg1, and the B signal Sb1 are made equal. White balance is obtained by adjusting each gain.

The gamma correction circuit 166 outputs the R signal Sr3,
Gamma (γ) correction for faithful color reproduction is performed based on the G signal Sg3 and the B signal Sb3. After that, the color difference matrix circuit 167 performs color difference matrix processing, and the encoder 168 combines the Y signal (not shown) with a Y signal (not shown) to convert it into a video signal. Then, the D / A converter 169 converts the digital signal into an analog signal. R signal Sr3 passing through white balance amplifiers 165R, 165G, 165B
The G signal Sg3 and the B signal Sb3 are also supplied to the optical detector 17.

FIG. 2 shows an example of the circuit configuration of the optical detector 17. As can be seen from the figure, the optical detector 17 includes a subtractor 171 for subtracting the G signal from the R signal and a subtractor 17 for subtracting the G signal from the B signal.
2 and an integrating circuit 173 that integrates the color difference signals, ie, the RG signal and the BG signal, which are the output signals of the subtracters 171 and 172, for each field.

As shown in FIG. 3, the integrating circuit 173 has different integration ranges divided into a high-luminance portion and a normal-luminance portion according to the integration slice level based on the luminance level. Only the high-luminance data (RG, BG) is integrated, and the data (RG, B-G) having a luminance lower than the integration slice level in the normal luminance portion.
Integrate only G). However, when the luminance is extremely high, it is determined that the luminance is saturated, and the data that is equal to or higher than the high luminance limiter level is not integrated. In addition, data having a luminance that is too low is regarded as noise, and integration is not performed on data that is lower than the low luminance limiter level.

As described above, the optical detector 17
In various cases, various limiters and special processing are performed so that white balance processing does not malfunction under special conditions (for example, conditions such as full-color monochrome). Then, the integrated value data (RG, BG) obtained by integrating in different integration ranges of the high luminance portion / normal luminance portion for each field is supplied to the system controller 18 at the next stage.

In the present embodiment, the color difference signals RG and BG are generated from the R, G and B signals, and thereafter the color difference signals R and G are generated.
-G and BG are integrated, but the R, G and B signals are integrated first, and then the color difference signals RG and BG are generated from the integrated R, G and B signals. It is also possible.

The system controller 18 to which the above-described optical detector 17 is supplied with each of the R, G, and B integrated value data is constituted by, for example, a microcomputer. FIG. 4 shows an example of a functional block of the system controller 18.

As apparent from FIG. 4, the system controller 18 has a configuration including a comparison circuit 181, an adder 182, a subtractor 183, and a gain setting circuit 184. The comparison circuit 181 is an optical detector 1
7, the integrated value data (RG, B
-G) and the integrated value data (RG, B-
G) and outputs the integrated value data closer to 0.

The adder 182 adds the RG integrated value data and the BG integrated value data selected by the comparison circuit 181 to generate R + B-2G data, and outputs the data to a gain setting circuit. 184. The subtractor 183 calculates R-
The BG integrated value data is subtracted from the G integrated value data to generate RB data.
To supply. The gain setting circuit 184 outputs the R + B-2G data output from the adder 182 and the subtractor 183
Gain signal Sr2, G gain signal Sg2 and B gain signal Sb2 based on RB data output from
Generate

Here, the system controller 18 according to the present embodiment has a configuration in which each function of the comparison circuit 181, the adder 182, the subtractor 183, and the gain setting circuit 174 is executed by software, for example. A program 18 'for implementing these functions
Are built in the system controller 18 as shown in FIG.

As described above, in the system controller 18, R supplied from the optical detector 17 is
A simple arithmetic process of addition and subtraction is performed by converting each integrated value data obtained by integrating each of the color difference signals of -G and BG into data of R + B-2G and RB by an addition / subtraction process. Since the data can be converted only by the software, the load on the software can be reduced.

In this embodiment, the calculation of each data of R + B-2G and RB is executed by software according to a program 18 'built in the system controller 18. The comparison circuit 181, the adder 182, the subtractor 183, and the gain setting circuit 184, which are blocks, can be configured by hardware. In this case, the load on software can be reduced.

The R generated by the system controller 18
The gain signal Sr2, the G gain signal Sg2, and the B gain signal Sb2 are output to the white balance amplifiers 165R, 165G, 165B in the digital signal processing circuit 16 described above.
(See FIG. 1), the white balance amplifiers 165R, 165G, 16
5B is controlled. That is, the white balance gains (R gain, G gain, B gain) obtained by the system controller 18 are reflected on the white balance amplifiers 165R, 165G, 165B.

In the camera system 10 described above, in an optical system that captures incident light (image light) from a subject on the image pickup surface of the image pickup device 13 and forms an image, the optical system may be disposed downstream of the optical low-pass filter 12 as necessary. An infrared cut filter 19 is provided. In the case of a camera system that does not use the infrared cut filter 19, the sensitivity of the infrared cut filter 19 does not decrease, so that the sensitivity of the entire system can be improved, and the cost of the entire system can be reduced by the price of the infrared cut filter 19. it can.

Here, the color reproducibility when the infrared cut filter 19 is not used will be considered. FIG. 5 shows an example of color reproduction on a vectorscope when the infrared cut filter 19 is not used. This is a coordinate system when a color bar chart of seven colors is imaged, and the horizontal axis represents the color difference signal B.
The vertical axis indicates the amplitude (gain) of the color difference signal RY, and the origin is white (W).

In this coordinate system, magenta (Mg), red (R), and yellow (Ye) are in the second quadrant, and green (G) and the fourth quadrant are in the third quadrant. Are cyan (Cy) and blue (B). The black circle (●) in the coordinate system is about 3,2.
The color reproduction at a relatively low color temperature of 00K (for example, an incandescent light bulb), and the open circle (（) is the color reproduction at a high color temperature of about 10,000K (for example, at the sea or a ski resort).

Here, in configuring the camera system,
An important condition is that color reproducibility is good at both the low color temperature and the high color temperature. Ideally, color reproduction should not change between low color temperature and high color temperature.
If the infrared cut filter 19 is not provided, a large change occurs. Thus, for example, when an image is captured under conditions where the color temperature is different between indoor and outdoor, the color of the subject becomes completely different.

Therefore, in the present embodiment, even when the infrared cut filter 19 is not provided, the color reproducibility is improved similarly to the case where the infrared cut filter 19 is provided, and the change in color reproduction is reduced with respect to the color temperature change. For this purpose, the primary color separation matrix 16
Primary color separation matrix constant R used for primary color separation at 1.
Set MATY, RMATC, BMATY, BMATC to optimized values. The optimization of the primary color separation matrix constant is performed using a color reproduction simulator from the viewpoint of both color reproducibility and color temperature change.

As described above, in the camera system 10 in which the infrared cut filter 19 is not disposed (is not used), the primary color separation matrix constants RMATY, RMATC, and BMAT used in the primary color separation by the primary color separation circuit 161 are used.
By optimizing Y and BMATC, the same color reproducibility as when the infrared cut filter 19 is used is maintained.
At the same time, a change in color reproduction can be reduced with respect to a change in color temperature.

FIG. 6 shows the color reproduction on the vectorscope when the infrared cut filter 19 is not used (a) and when the primary color separation matrix constant is optimized (b). FIG. 7 shows spectral sensitivity characteristics after primary color separation before optimization (a) and after optimization (b) of the primary color separation matrix constant. As is apparent from FIG. 7B, by optimizing the primary color separation matrix constant, the spectral sensitivity on the long wavelength side can be suppressed.

In a signal path of the R signal Sr1 output from the primary color separation circuit 161 to the white balance amplifier 165R, the changeover switch 163 is used in a system in which the infrared cut filter 19 is not provided (not used). The signal level of the signal Sr1 is reduced by the attenuator 164.
And supply it to the white balance amplifier 165R. The reason will be described below.

First, when a CCD image pickup device is used as the image pickup device 13, the CCD image pickup device operates in the infrared region (700n).
m-), the infrared cut filter 19
By not using, the energy on the long wavelength side increases. As a result, when the entire balance is obtained, the white balance shifts to the red (long wavelength) side, and the white balance shifts, so that the signal level of the R signal is suppressed.

Further, even if the primary color separation matrix constant is optimized, the spectral sensitivity on the long wavelength side cannot be completely suppressed, so that the energy of the long wavelength component increases at a low color temperature. Therefore, at low color temperatures, the R gain must be reduced, and the white balance amplifier 16
The adjustment lower limit of 5R will soon be reached. Therefore, by suppressing the signal level of the R signal before being input to the white balance amplifier 165R, the gain adjustment range of the white balance amplifier 165R can be expanded.

On the other hand, in a camera system in which the infrared cut filter 19 is disposed (used), the primary color separation matrix constant setting circuit 162 is different from the conventional primary color separation matrix constant RMAT by the primary color separation matrix constant RMAT.
Y, RMATC, BMATY, and BMATC are set, and the changeover switch 163 uses the R signal Sr1 output from the primary color separation circuit 161 as it is as the white balance amplifier 16
Supply to 5R. Thus, although the sensitivity of the entire system is reduced by the reduction in sensitivity of the infrared cut filter 19, excellent color reproducibility can be obtained.

The camera system according to the present invention is applicable to consumer, business and industrial cameras having an auto white balance function. Thus, when a system that does not use an infrared cut filter is configured, the sensitivity of the entire system can be improved,
The cost of the entire system can be reduced.

[0047]

As described above, according to the present invention,
In processing an image signal output from a solid-state imaging device having a color filter, a primary color separation matrix constant of a primary color separation circuit can be switched, and as the matrix constant,
When an infrared cut filter is arranged in an optical system that captures incident light from a subject on the imaging surface of a solid-state imaging device and when it is not arranged, by setting optimized values for each, When an infrared cut filter is arranged in the optical system, good color reproducibility is obtained by its action, while when an infrared cut filter is not arranged in the optical system, sensitivity can be improved and cost can be reduced. The same color reproducibility as when an infrared cut filter is provided can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a camera system according to the present invention.

FIG. 2 is a circuit block diagram illustrating an example of a configuration of an optical detector.

FIG. 3 is a diagram showing an integration range in an integration circuit in an optical detector.

FIG. 4 is a functional block diagram illustrating an example of a system controller.

FIG. 5 is a diagram showing color reproduction on a vector scope when an infrared cut filter is not used.

FIG. 6 is a diagram showing color reproduction on a vector scope;
(A) shows the case where there is no infrared cut filter, and (b) shows the case where the primary color separation matrix constant is optimized.

FIG. 7 is a diagram showing spectral sensitivity characteristics after primary color separation,
(A) shows the characteristics before optimization of the primary color separation matrix constant,
(B) shows characteristics after optimization of the primary color separation matrix constant.

FIG. 8 is a diagram illustrating spectral sensitivity characteristics of a complementary color filter;
(A) shows the characteristics before passing through the infrared cut filter,
(B) shows the characteristics after passing through the infrared cut filter.

[Explanation of symbols]

10 camera system, 12 optical low-pass filter,
13 ... image sensor, 16 ... digital signal processing circuit, 17 ...
Optical detector, 18: system controller, 19: infrared (IR) cut filter, 161: primary color separation circuit, 162: primary color separation matrix constant setting circuit, 163: changeover switch, 164: attenuator, 165
R, 165G, 165B ... White balance amplifier

Claims (5)

[Claims] 1. A signal processing circuit for processing an image signal output from a solid-state imaging device having a color filter, wherein the image signal is converted into primary color signals of R (red), G (green), and B (blue). A primary color separation circuit for separating, a primary color separation matrix constant for the primary color separation circuit, and a primary color separation matrix constant setting circuit capable of switching the matrix constant; and the R and G output from the primary color separation circuit. , B, and a white balance amplifier for adjusting the gain between the primary color signals of the solid-state imaging device. 2. The method according to claim 1, wherein the primary color separation matrix constant setting circuit includes a matrix for determining whether or not an infrared cut filter is disposed in an optical system that captures incident light from a subject on an imaging surface of the solid-state imaging device. 2. The signal processing circuit according to claim 1, wherein the constant is switched. 3. The R output from the primary color separation circuit.
In the signal path of the primary color signal to the white balance amplifier, the R
2. The signal processing circuit according to claim 1, further comprising means for selectively lowering the signal level of the primary color signal. 4. A solid-state imaging device having a color filter, an optical system for capturing incident light from a subject on an imaging surface of the solid-state imaging device, and R (red), G (green), and B ( A primary color separation circuit that separates the primary color signal into a primary color signal, and a primary color separation matrix constant for the primary color separation circuit. A camera system comprising: a primary color separation matrix constant setting circuit for switching constants; and a white balance amplifier for adjusting a gain between the R, G, and B primary color signals output from the primary color separation circuit. . 5. The R output from the primary color separation circuit.
In the signal path of the primary color signal to the white balance amplifier, the R
5. The camera system according to claim 4, further comprising means for selectively lowering the signal level of said primary color signal.