JP2003070009A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve color reproducibility by eliminating the effect of infrared rays, if an infrared cut filter is not provided. SOLUTION: In a color difference signal generating section of a signal processing means 3, it is detected as to whether an R-Y signal is positive or negative. If the R-Y signal is positive where the effect of the infrared rays becomes large, a correction amount of the R-Y signal is calculated, only the correction amount is subtracted from the R-Y signal and the signal is outputted, and a color difference signal is generated, on the basis of the reduced R-Y output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device suitable for a vehicle-mounted camera and a doorphone camera capable of taking a picture even in low illuminance.

[0002]

2. Description of the Related Art As a method of improving sensitivity in a low-illuminance state in a color image pickup device using a solid-state image pickup device, it is generally known to remove an infrared cut filter arranged in front of the solid-state image pickup device. . When a black-and-white image is generated, no major problems occur, but when a color image is generated by this method, the infrared light component that is not the original color is captured and signal processed, and the color reproducibility is significantly deteriorated. To do.
In particular, this deterioration becomes remarkable at low illuminance such as in the evening.

As a technique for solving this, Japanese Patent Laid-Open No. 2001-2001
-69519 uses an image sensor equipped with a filter that transmits light in the near-infrared region and a filter that does not transmit light in the near-infrared region, and Japanese Patent Laid-Open No. 2000-59798 discloses an infrared cut filter. It has been proposed to switch positions.

[0004]

In the former technique, an image pickup device having sensitivity in the near infrared region is used,
There is a problem that a general image pickup device cannot be used, and the latter technique requires a mechanism for switching filters, which is a cost disadvantage.

In view of the above, it is an object of the present invention to provide an image pickup apparatus which can improve the sensitivity and color reproducibility at low illuminance at low cost.

[0006]

According to the present invention, there is provided an image pickup device having a plurality of types of color filters,
A signal processing means for generating a luminance signal and a color difference signal from an output signal of the image pickup device, and the signal processing means for eliminating the influence of infrared light, the signal processing means One of the correction for reducing the value, the correction for reducing the value of the luminance signal, and the correction for reducing the value of the luminance signal and the value of the color difference signal is performed.

Further, the signal processing means performs correction for reducing the value of the output signal of the color component which is easily affected by infrared light. Note that this correction may be performed independently,
It is also possible to combine each of the above corrections.

The color filters are complementary color filters of magenta, green, cyan and yellow. When using these color filters, if you do not provide an infrared cut filter,
The output values of the magenta and yellow color components increase due to the influence of infrared light. Therefore, in the correction of the color difference signal, the RY signal that is greatly affected by the infrared light is corrected. In addition, in the correction of the output signal of the color component, the correction of the output values of magenta and yellow is performed.

Here, the degree of influence of infrared light corresponds to the magnitude of the RY signal. Therefore, the correction of the color difference signal is
This is performed according to the magnitude of the RY signal. That is, since the output of the R signal increases due to the influence of infrared light, R-
The Y signal also moves in the positive direction as a whole. Therefore,
The positive / negative of the RY signal is detected, correction is performed to reduce the RY signal when the RY signal is positive, and a color difference signal is generated based on the RY output in which the influence of the infrared light is eliminated. Similarly, for the luminance signal, correction is performed to reduce the value of the luminance signal when the RY signal is positive. When the RY signal is negative or 0, it means that there is little or no influence of infrared light. In this case, therefore, it is not necessary to perform correction, and the color difference signal and the luminance signal are generated as they are. Therefore, it is possible to generate a color difference signal and a luminance signal in which the influence of infrared light is eliminated, and it is possible to realize an image with improved color reproducibility.

As the degree of influence of the infrared light, the intensity of the infrared light may be detected by the infrared sensor, and if the ratio of reducing the color difference signal and the luminance signal is determined according to the detected intensity. Good.

Further, in the output signals of the color components, the output of the magenta and yellow color components becomes large due to the influence of infrared light. Therefore, correction is performed to reduce the output values of the magenta and yellow color components. The influence of infrared light is eliminated from the color difference signals generated based on the output signals of these color components.

Therefore, by eliminating the infrared cut filter, the output of the luminance signal is increased, and the sensitivity can be increased at low illuminance. At this time, due to the influence of infrared light, red and other images are displayed with high brightness,
Although the image is different from the color of the subject, the color reproducibility can be prevented from being lowered by outputting the corrected color difference signal and the luminance signal as a video signal.

Each of the above corrections may be performed when an infrared cut filter is attached to the image pickup device. In this case, the degree of decrease of each output signal may be made smaller than that in the case without the infrared cut filter, and the color reproducibility can be improved. In particular, it is suitable when using an infrared cut filter having a characteristic of passing an infrared light region to some extent.

[0014]

FIG. 1 shows the configuration of an image pickup apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is an image pickup device composed of CCD or CMOS, 2 is an image pickup device driving means, 3
Is a signal processing means, 4 is a synchronizing signal generating means, and 5 is a lens.

Light from the subject is imaged on the light receiving surface of the image pickup device 1 through the lens 5, and the output signal of each pixel of the image pickup device 1 is read out according to the drive signal from the image pickup device driving means 2. , To the signal processing means 3. The signal processing means 3 is
The color difference signal generation unit and the luminance signal generation unit are provided, and the luminance signal and the color difference signal are generated from the output signal of the image sensor 1 and the horizontal synchronization signal and the vertical synchronization signal generated by the synchronization signal generation unit 4 are superimposed. As a result, a video signal is generated and output.

A plurality of types of color filters are attached to the image pickup device 1. This color filter is a complementary color filter, and as shown in FIG. 2, corresponding to each pixel, magenta (Mg), green (G), cyan (Cy), and yellow (Ye).
Each color filter is arranged two-dimensionally. Note that the illustrated arrangement is an example, and the present invention is not limited to this. Of the color filters, Mg transmits blue and red light, G transmits green light, Cy transmits green and blue light, and Ye transmits green and red light. Therefore, the relationships Mg = R + B, Cy = G + B, Ye = G + R are established.

In this image pickup apparatus, an infrared cut filter is not provided between the image pickup element 1 and the lens 5. FIG. 3 shows an example of the spectral sensitivity characteristic of the color filter depending on the presence or absence of the infrared cut filter. In FIG. 3, (a) shows the case where there is an infrared cut filter, (b) shows the case where there is no infrared cut filter, the horizontal axis represents the wavelength (nm), and the vertical axis represents the sensitivity. As is clear from this figure, without the infrared cut filter, the color components of Mg and Ye are particularly affected by infrared light.

Generally, a luminance signal (Y = Ye + Mg + Cy)
Since + G) is generated by averaging the output signals of the light that has passed through the respective color filters, it is possible to take in the infrared light component and raise the level of the luminance signal. When a red subject is photographed, the brightness tends to be higher than that of other colors.

The color difference signals Cr and Cb are generally generated according to the following equations. In addition, Cr is R
Cb is a color difference signal corresponding to -Y and Cb. Cr = Ye + Mg- (Cy + G) (1) Cb = Cy + Mg- (Ye + G) (2)

From equations (1) and (2), Mg and Ye, which are easily affected by infrared light, cancel each other out in Cb,
Although the influence is small, it is doubled for Cr, and it can be seen that the influence of infrared light is great.

Therefore, in order to eliminate the influence of infrared light,
In the color difference signal generation unit of the signal processing means 3, correction is performed to reduce the value of the color difference signal affected by infrared light. That is, the color difference signal generator is provided with a selector 1 as shown in FIG.
A color difference signal correction circuit including 0, a multiplier 11 and a subtractor 12 is provided.

First, the magnitude of the RY signal calculated from the output signal of the image pickup device 1 is detected, and if the RY signal is positive, the RY signal is output from the selector as it is to the multiplier 11 in the subsequent stage. Sent to. The multiplier 11 multiplies the RY signal by an arbitrary ratio (parameter) set by the user according to his / her preference, and calculates a correction amount (RY correction rate) of the RY signal.
Any ratio here is a value after the decimal point. Subtractor 12
In, the calculated correction amount is subtracted from the RY signal, and the result is output as the RY output. A color difference signal is finally generated based on the corrected RY output and BY output.

When the RY signal is negative or 0, the selector outputs 0, and the correction in the correction circuit is invalidated.
In this case, the RY signal remains unchanged, and the color difference signal is generated based on this. When the RY signal is negative or 0 in this way, it means that the influence of infrared light is small, and thus no correction is performed.

By the way, the image pickup device has a function of adjusting the white balance, and by using this function, basically, the reproducibility of colors can be secured to some extent. However, when an infrared cut filter is not provided in the filter of the image sensor 1 and a color filter is used, signals of the color components of Mg and Ye become large due to the influence of infrared light, so that the RY output value is high. Will be. As a result, red or the like is displayed with high brightness, or an image having a color different from the color of the subject is displayed. As described above, the influence of infrared light can be eliminated and the color reproducibility can be improved by reducing the color difference signal according to the magnitude of the RY signal, particularly the sign thereof.

Further, in order to eliminate the influence of infrared light on the luminance signal, the luminance signal generating section of the signal processing means 3 carries out correction for reducing the value of the luminance signal. That is,
A brightness signal correction circuit including a multiplier 13 and a subtractor 14 as shown in FIG. 5 is provided in the brightness signal generation unit. The luminance signal correction circuit is arranged in the subsequent stage of the color difference signal correction circuit.

In the above circuit, the correction amount (RY correction rate) of the RY signals obtained by the color difference signal correction circuit is used to set an arbitrary ratio (luminance) set by the user according to his / her preference. Parameter) for multiplying the Y signal. Subtractor 14
In, the correction amount of the Y signal calculated by the multiplier 13 is subtracted from the Y signal, and the result is output as the Y output to generate the luminance signal. When the RY signal is negative or 0, the influence of infrared light is small, and therefore the luminance signal is not corrected.

As described above, by decreasing the value of the luminance signal according to the magnitude of the RY signal, it is possible to mitigate the phenomenon that the luminance of the red portion becomes high and improve the color reproducibility. It should be noted that, as compared with the correction in which the correction amount of the RY signal is directly reduced from the Y signal, the correction amount obtained by multiplying the correction amount of the RY signal by the parameter as described above is reduced from the Y signal. Then, the decrease amount of the Y output becomes small, and the effect of increasing the output of the luminance signal without the infrared cut filter becomes remarkable.

Therefore, by not providing the infrared cut filter, the output of the luminance signal can be increased, and the sensitivity can be increased at low illuminance. By eliminating the influence of infrared light by correcting the color difference signal and the luminance signal, it is possible to adjust the balance of color reproducibility, and it is possible to provide an image according to the taste of the user.

Next, another embodiment will be described. In general, the output signal from the image sensor 1 is separated for each color filter at the time of color separation and sent to the next stage. Therefore, attention is paid to color components that are easily affected by infrared light, and correction is performed to reduce the output values of these color components. Specifically, in the signal processing means 3, in order to perform a correction for reducing the output values of the color components of Mg and Ye, which are greatly affected by infrared light, the signal processing means 3 uses a multiplier 15 and a subtracter 16 as shown in FIG. A color component correction circuit is provided. The basic configuration of the image pickup device is the same as that of the above embodiment.

When the output signal of each pixel of the image pickup device 1 is input to the signal processing means 3, an arbitrary ratio (luminance parameter) set by the user according to his preference for the Mg + Ye signal.
Is multiplied by the Mg + Ye signal. In the subtractor 16, the correction amount of the Mg + Ye signal calculated by the multiplier 15 is subtracted from the Mg + Ye signal, and the result is output to the luminance signal generation unit and the color difference signal generation unit as the Mg + Ye output, and based on the reduced Mg + Ye output. To generate a luminance signal and a color difference signal.

As described above, by reducing the output value of the output signal of the color component which is easily influenced by infrared light, the influence of infrared light can be eliminated before the generation of the luminance signal and the color difference signal, and the color reproducibility can be improved. Can be improved. Also, Cy,
Since there is no correction effect on the G color component, R-
The color reproducibility is improved as compared with the case where the Y output is corrected.

The present invention is not limited to the above embodiment, and it goes without saying that many modifications and changes can be made to the above embodiment within the scope of the present invention. Three circuits of a color difference signal correction circuit, a luminance signal correction circuit, and a color component correction circuit may be combined, or a color difference signal correction circuit and a color component correction circuit or a brightness signal correction circuit and a color component correction circuit may be combined. It should be noted that the color component correction circuit is arranged in a stage before the color difference signal correction circuit.

Further, each circuit may be independent, and in this case, the luminance signal correction circuit judges whether the R + Y signal is positive or negative, and when it is positive, the Y signal is multiplied by an arbitrary ratio (parameter) to obtain a correction amount. Will be calculated. No parameter may be used in the correction of the Y output. That is,
Instead of multiplying the correction amount of the RY signal, the correction amount of the RY signal may be subtracted from the Y signal as it is.

In each correction of the R-Y output, the Y output, and the Mg + Ye output, an arbitrary ratio (parameter) is set by the user, but it may be set automatically, for example, during the daytime. When normal color reproducibility is desired, the degree of output reduction is set to be large, and when high luminance is desired such as at night, the degree of output reduction is set to be small.

Further, in each of the above embodiments, the infrared cut filter is not provided, but it is also applied to the case where an infrared cut filter, particularly an infrared cut filter having a characteristic of passing an infrared light region to some extent is provided. be able to. That is, it is suitable when the characteristics of the infrared cut filter are changed and the sensitivity of the output signal is increased and the color reproducibility is harmonized. Even in such a case, the color reproducibility can be further improved. .

[0036]

As is apparent from the above description, according to the present invention, an image pickup apparatus which is not provided with an infrared cut filter or an image pickup which uses an infrared cut filter having a characteristic of passing an arbitrary region of the infrared light region is used. By correcting the luminance signal, the RY output, and the Mg + Ye output, which are greatly affected by infrared light, in the device, it is possible to mitigate the phenomenon that the color difference signal becomes large and the luminance becomes high in the red portion of the image. Therefore, it is possible to provide an image pickup apparatus which can balance the improvement of color reproducibility and the increase of sensitivity at low illuminance at low cost without using a special image pickup element or mechanism.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image pickup apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement of color filters.

FIG. 3 is a spectral sensitivity characteristic diagram of color filters with and without an infrared cut filter.

FIG. 4 is a block diagram of a color difference signal correction circuit.

FIG. 5 is a block diagram of a luminance signal correction circuit.

FIG. 6 is a block diagram of a color component correction circuit.

[Explanation of symbols]

1 Image sensor 2 Image sensor driving means 3 Signal processing means 4 synchronization signal generation means 5 lenses

Claims (9)

[Claims] 1. An image pickup device provided with a plurality of types of color filters, and signal processing means for generating a luminance signal and a color difference signal from an output signal of the image pickup device, wherein the signal processing means emits infrared light. An image pickup apparatus, wherein correction is performed to reduce the value of a color difference signal according to the degree of influence of infrared light on the color difference signal in order to eliminate the influence. 2. An image pickup device provided with a plurality of types of color filters, and a signal processing means for generating a luminance signal and a color difference signal from an output signal of the image pickup device, wherein the signal processing means emits infrared light. An image pickup apparatus, wherein correction is performed to reduce a value of a luminance signal according to a degree of influence of infrared light on the color difference signal in order to eliminate an influence. 3. An image pickup device provided with a plurality of types of color filters, and signal processing means for generating a luminance signal and a color difference signal from an output signal of the image pickup device, wherein the signal processing means emits infrared light. An image pickup apparatus, wherein correction is performed to reduce the value of the luminance signal and the value of the color difference signal according to the degree of influence of infrared light on the color difference signal in order to eliminate the influence. 4. The image pickup apparatus according to claim 1, 2 or 3, wherein the signal processing means performs correction for reducing a value of an output signal of a color component which is easily influenced by infrared light. 5. The image pickup apparatus according to claim 1, wherein the color filter is a complementary color filter of magenta, green, cyan, and yellow, and the color difference signal RY is corrected. 6. The image pickup apparatus according to claim 1, wherein the correction is performed when the value of the color difference signal is positive, and the correction is not performed when the value is negative. 7. An image pickup device provided with a plurality of types of color filters, and signal processing means for generating a luminance signal and a color difference signal from output signals of respective color components of the image pickup device, wherein the signal processing means is red. An image pickup apparatus, wherein correction is performed to reduce a value of an output signal of a color component that is easily affected by outside light. 8. The color filter is a complementary color filter for magenta, green, cyan, and yellow, and corrects the output signals of the color components for magenta and yellow.
Alternatively, the image pickup device according to item 7. 9. The image pickup device according to claim 1, wherein an infrared cut filter is attached to the image pickup element.