JP2005006066A - Color filter for solid-state image pickup element and color image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a camera which can be continuously used day and night by making the color reproducibility in the daytime and the sensitivity at night compatible without providing a mechanical mechanism for turning ON/OFF an infrared cutoff filter. <P>SOLUTION: One G filter among the four pixels of RGBG constituting one unit of a normal Bayer array is replaced with an IR filter. RGB filters are distributed for a first mode. The IR filter is distributed for a second mode. The infrared cutoff filter is applied to the three pixels of RGB. And, when it is relatively bright such as in the daytime, the pixel interpolation is executed by mainly using the three pixels of RGB in the first mode. When it is relatively dark such as at night, the pixel interpolation is executed by mainly using one pixel of the IR in the second mode. As a result, it is possible to make the improvement of the color reproducibility with a bright object, and the improvement of the sensitivity with a dark object compatible only by the software type switching. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color filter for a solid-state imaging device and a color imaging device using the same, and is particularly suitable for a camera that can be used both day and night.
[0002]
[Prior art]
In recent years, in order to improve image quality in digital cameras, mobile phones, and the like, technological innovations in image sensors have advanced. Up to now, the main focus has been on increasing the number of pixels. However, in addition to the number of pixels, efforts have been made to improve image quality.
[0003]
Generally, one color filter is attached to each image sensor. As shown in FIG. 6A, one using three primary colors of red (R), green (G), and blue (B) (so-called Bayer array), as shown in FIG. 6B, cyan (Cy), Some use four complementary colors of magenta (Mg), yellow (Ye), and green (G). The primary color system has excellent color reproducibility, and the complementary color system has excellent sensitivity.
[0004]
In order to generate an image using a signal imaged by the image sensor, luminance information is required in addition to color information. When a primary color Bayer array is used as the color filter, since green has a wavelength intermediate between red and blue, the green filter transmits a little amount of red and blue light. For this reason, conventionally, luminance information has been obtained using signals picked up by green pixels. As shown in FIG. 6A, since the green pixels are present in the horizontal and vertical lines, the horizontal resolution and the vertical resolution are relatively high.
[0005]
By the way, in a color imaging device using an imaging device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), the entire image plane is caused by light scattering or reflection by the imaging device or the like when light enters the optical system. In order to prevent flare, which is a phenomenon of fogging, and to improve color reproducibility, an infrared cut filter that cuts infrared components is often disposed in front of the image sensor. However, since sensitivity decreases when an infrared cut filter is used, when importance is placed on sensitivity, sensitivity is improved by capturing light in the infrared region without using an infrared cut filter.
[0006]
In addition, an imaging apparatus that can turn on / off the use of an infrared cut filter is also provided as a method for achieving both of flare prevention and improvement of color reproducibility and improvement of sensitivity. In this type of image pickup apparatus, the infrared cut filter is turned on during daytime when the illuminance is sufficient, and is used as a color camera. On the other hand, at night when the illuminance is insufficient, the infrared cut filter is turned off, and it can be used as a monochrome camera using light in the infrared region.
[0007]
[Problems to be solved by the invention]
However, in the above conventional technique, it is necessary to provide a mechanism for mechanically moving the filter in order to turn on / off the infrared cut filter. For this reason, there has been a problem that the reduction in size and weight of the imaging apparatus is hindered and the cost is increased. There is also a problem of reliability in the operation performance and durability of the mechanical movable part.
[0008]
The present invention has been made to solve such a problem, and provides daytime color reproducibility and nighttime sensitivity without providing a mechanical mechanism for turning on / off the infrared cut filter. It aims at making it possible to use it day and night continuously.
[0009]
[Means for Solving the Problems]
The color filter for a solid-state imaging device of the present invention is a combination of a red, green, and blue primary color filter and an infrared filter having sensitivity at least in the infrared region. Specifically, a first line in which a green filter and another color (for example, blue) filter are alternately arranged, and a remaining one color (for example, red) filter and an infrared filter are alternately arranged. A second line, and the first line and the second line are alternately arranged.
[0010]
Preferably, an infrared cut filter for blocking infrared light is further arranged at a pixel position where the three primary color filters are arranged. Or, instead of further arranging an infrared cut filter in addition to the color filter, a color obtained by multiplying the spectral characteristics of red, green and blue by the spectral characteristics of the infrared cut filter as the spectral characteristics of red, green and blue A filter may be configured and the color filter may be arranged.
[0011]
The infrared filter is composed of, for example, a white filter. In another aspect, it is constituted by an infrared transmission filter having spectral characteristics only in a substantially infrared region.
[0012]
In addition, the color imaging device of the present invention interpolates the color filter for the solid-state imaging device described above, the solid-state imaging device on which the color filter for the solid-state imaging device is disposed, and the signal of each pixel captured by the solid-state imaging device A plurality of signal processing means for generating image data, and a plurality of image data generated by pixel interpolation calculation with different utilization ratios of the information of the pixel in which the color filter is arranged and the information of the pixel in which the infrared filter is arranged And a mode control means for switching the mode.
The color imaging device of the present invention may include a light emitting element for infrared illumination.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a digital camera 10 that implements a color imaging apparatus according to the present invention.
[0014]
As shown in FIG. 1, the digital camera 10 of this embodiment includes an optical system 1 including a shutter 1a, a lens 1b, and an iris 1c, an image sensor 2 such as a CCD or a CMOS, an analog signal processing unit 3, and an A A / D converter 4, an image processing unit 5, a controller 6 that controls the entire digital camera 10, and an operation unit 7 are provided. On the front surface of the image sensor 2, the color filter 2a of the present embodiment is disposed.
[0015]
In the digital camera 10 configured as described above, the incident light to the optical system 1 is imaged by the imaging device 2 via the shutter 1a, the lens 1b, and the iris 1c. The image sensor 2 photoelectrically converts the incident light that has been imaged to generate an analog image signal corresponding to the incident light. The analog signal generated here for each pixel is subjected to noise removal by the analog signal processing unit 3 and then supplied to the A / D converter 4 to be converted into a digital signal for each pixel.
[0016]
The digital signal obtained by the A / D converter 4 is supplied to the image processing unit 5. The image processing unit 5 performs various signal processing including color interpolation processing and color correction processing on the digital signal for each pixel. Since each pixel of the image sensor 2 can only detect the intensity of light after passing through the color filter 2a, there is only one color information per pixel at this time. The image processing unit 5 determines the color for each pixel by interpolating the signal of each pixel, and generates image data.
[0017]
There are various interpolation calculation methods, and any method can be applied in the present embodiment. For example, when determining the color of a certain pixel, it is possible to apply bilinear interpolation such as calculating the average value of the surrounding pixels. As will be described in detail later, in this embodiment, an infrared filter is arranged in the first mode in which the interpolation calculation is mainly performed using information on pixels in which the three primary color color filters are arranged. A second mode in which interpolation information is mainly used by using pixel information, and the mode can be switched under the control of the controller 6. The mode to be switched can be specified by the user operating the operation unit 7, for example.
[0018]
In the above configuration, the analog signal processing unit 3, the A / D converter 4, and the image processing unit 5 constitute the signal processing means of the present invention. The controller 6 constitutes the mode control means of the present invention.
[0019]
FIG. 2 is a diagram showing a filter arrangement of the color filter 2a. In a normal Bayer arrangement, as shown in FIG. 6A, RGB three primary color filters are arranged in a mosaic pattern, and one unit is formed by four RGBG pixels. On the other hand, as shown in FIG. 2, the color filter 2a of the present embodiment is configured by replacing one G filter of RGBG with an infrared filter (IR filter) having sensitivity at least in the infrared region. .
[0020]
That is, the color filter 2a of the present embodiment includes a first line in which G filters and B filters are alternately arranged when viewed in the horizontal direction, and a second line in which R filters and IR filters are alternately arranged. Each filter is configured in a mosaic pattern by alternately arranging the first lines and the second lines. When viewed in the vertical direction, the first line in which the G filter and the R filter are alternately arranged and the second line in which the B filter and the IR filter are alternately arranged are alternately arranged. Yes.
[0021]
Here, the three primary color filters may be used as they are, but preferably an infrared cut (IRC) filter for blocking infrared light is further arranged at the pixel position where the three primary color filters are arranged. To do. Alternatively, instead of arranging the color filters of the three primary colors and the infrared cut filter in an overlapping manner, a color filter having characteristics obtained by multiplying each of the RGB spectral characteristics by the spectral characteristics of the infrared cut filter is configured. They may be arranged (respective spectral characteristics of the RGB filter and spectral characteristics of the IRC filter are shown in FIG. 3).
[0022]
On the other hand, the infrared filter may be one in which both visible light and infrared light have spectral characteristics (for example, a white filter), or smear (high-intensity light) when shooting a bright subject in the daytime. In order to prevent the occurrence of a phenomenon in which the charges overflowing from the pixel on which the incident light flows into the signal line or the transfer section and a false false signal appears in the vertical direction from the pixel, spectral characteristics are given only to the infrared region. It may be a thing. When spectral characteristics are given only to the infrared region, an infrared transmission filter that transmits only infrared light may be used, or spectral characteristics that provide maximum sensitivity near 800 nm, which is the peak wavelength of infrared illumination. A filter provided with may be used. Since the infrared region is not cut by the infrared cut filter, the spectral sensitivity in the infrared region is made as high as possible.
[0023]
4 and 5 are diagrams showing spectral characteristics of the three primary color filters and the infrared filter. 4 shows a case where a white filter is used as the infrared filter, and FIG. 5 shows a spectral characteristic when an infrared transmission filter is used as the infrared filter. The white filter has a spectral characteristic that transmits all the visible light of RGB and also transmits light in the infrared region. In addition, the infrared transmission filter has spectral characteristics such that RGB visible light is hardly transmitted, but only light in the infrared region is transmitted.
[0024]
When using a white filter, an ND (neutral density) filter is placed in front of the white filter to prevent the occurrence of smears because the sensitivity of infrared light is too good compared to the sensitivity of visible light. By reducing the amount of transmitted external light, the sensitivity of visible light and the sensitivity of infrared light may be approximately the same. Also, instead of arranging the white filter and the ND filter in an overlapping manner, a filter having a characteristic obtained by multiplying the spectral characteristic of the white filter by the spectral characteristic of the ND filter is configured and arranged as an IR filter. Also good.
[0025]
As described above, the image processing unit 5 in FIG. 1 performs the interpolation calculation under any mode switched by the control of the controller 6 according to the operation of the operation unit 7. In the first mode, the interpolation calculation is performed mainly using the photoelectric conversion signal of visible light, that is, the information of the pixel on which the RGB color filter (multiplied by the spectral characteristics of the infrared cut filter) is arranged. . Here, “mainly used” means that the utilization ratio of the pixel in which the color filter is arranged is larger than the utilization ratio of the pixel in which the infrared filter is arranged. For example, the interpolation calculation is performed using only the information of the pixel in which the color filter is arranged. This first mode has good color reproducibility and is suitable for daytime photography.
[0026]
On the other hand, in the second mode, the interpolation calculation is performed mainly using the photoelectric conversion signal of infrared light, that is, the information of the pixel in which the infrared filter is arranged. Here, “mainly used” means that the usage ratio of the pixel in which the infrared filter is arranged is larger than the usage ratio of the pixel in which the color filter is arranged. For example, the interpolation calculation is performed using only the information of the pixel in which the infrared filter is arranged. This second mode has high sensitivity and is suitable for night photography.
[0027]
In addition, when the pixel information of the infrared filter is not used at all in the first mode, there is only one G filter pixel for extracting luminance information in one unit of four pixels. Even when the pixel information of the color filter is not used at all in the second mode, only one IR filter pixel from which luminance information is extracted exists in one unit of four pixels. For this reason, both the horizontal and vertical resolutions are halved compared to the normal Bayer array.
[0028]
However, recent digital cameras have dramatically increased the number of pixels, and a large resolution can be secured by the number of pixels themselves. Therefore, there is not much problem even if the resolution is halved. For example, when considering a CCD with 1.3 million pixels (horizontal 1280 × vertical 1024), the effective resolution is (horizontal 640 × vertical 512), which is in VGA (Video Graphics Array) or NTSC (National Television System Committee standard) format. Sufficient resolution can be obtained for use.
[0029]
As described above in detail, according to the present embodiment, one G filter of four pixels constituting one unit of the Bayer array is replaced with an IR filter, and the RGB filter is used for the first mode and the IR filter is used for the first filter. Sort for 2 modes. When the day is relatively bright, the first mode mainly uses pixel interpolation of three RGB pixels, and when the night is relatively dark, the second mode mainly uses one IR pixel. Pixel interpolation is performed. Thus, by performing the interpolation process according to the photographing conditions, it is possible to achieve both daytime color reproducibility improvement and nighttime sensitivity improvement.
[0030]
Further, in the present embodiment, the filter arrangement of the color filter 2a is devised so that the infrared cut filter is applied only to the three RGB pixels and the infrared cut filter is not applied to one IR pixel. Since which pixel is mainly used in the interpolation calculation is determined by software, it is not necessary to provide a mechanical mechanism for turning on / off the infrared cut filter, and the imaging apparatus can be reduced in size. Weight reduction, cost reduction, and improvement in reliability can be achieved.
[0031]
In the above-described embodiment, the example in which only the pixel information of the color filter is used in the first mode and only the pixel information of the infrared filter is used in the second mode is described. However, the present invention is not limited to this example. That is, in the first mode, if the usage ratio of the pixel information of the color filter is larger than the usage ratio of the pixel information of the infrared filter, the pixel information of the infrared filter may be used somewhat. Similarly, in the second mode, if the use ratio of the pixel information of the infrared filter is larger than the use ratio of the pixel information of the color filter, the pixel information of the color filter may be used somewhat.
[0032]
Moreover, although the said embodiment demonstrated the example which switches a 1st mode and a 2nd mode by operating the operation part 7 by a user, you may make it switch automatically. For example, the ambient illuminance is detected based on the amount of light received by the image sensor 2, and the mode is automatically switched to the first mode when the illuminance is greater than a predetermined threshold and to the second mode when the illuminance is smaller than the threshold. Also good. Instead of the image sensor 2, a dedicated light receiving element for detecting illuminance may be provided.
[0033]
In the above embodiment, the color imaging device 10 is configured as shown in FIG. 1, but in addition to these components, a light emitting element for infrared illumination (such as an infrared light emitting LED) may be further provided. . In the second mode that uses pixel information of an infrared filter that has a very strong sensitivity to infrared light, shooting a subject that is darker than previously possible by shooting the subject by irradiating the subject with infrared light ( For example, shooting in the dark is possible.
[0034]
In the above embodiment, switching between the first mode and the second mode has been described. However, three or more modes may be switched. For example, the first to nth (n ≧ 3) modes are provided. In the first mode, pixel interpolation is performed using only pixel information of the color filter. In the second mode, pixel interpolation is performed by adding some pixel information of the infrared filter to the pixel information of the color filter. In the third mode, the use ratio of the pixel information of the infrared filter is gradually increased so that the pixel interpolation is performed with the use ratio of the pixel information of the infrared filter larger than that in the second mode. In the nth mode, it is possible to perform pixel interpolation using only the pixel information of the infrared filter.
[0035]
Moreover, although the said embodiment demonstrated the example which applies the color filter of this embodiment to a digital camera, it is not limited to this. For example, the present invention can also be applied to a digital video camera, a mobile phone with a camera, a surveillance camera, a PDA (Personal Digital Assistant) with a camera, and the like. These terminals are suitable for applying this embodiment because there are many opportunities to shoot a dark subject at night from a bright subject in the daytime.
[0036]
The image sensor 2 described above can be applied to both a progressive method (all pixel readout method) and a frame readout method as a photoelectric conversion signal readout method.
[0037]
In addition, each of the above-described embodiments is merely an example of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. In other words, the present invention can be implemented in various forms without departing from the spirit or main features thereof.
[0038]
【The invention's effect】
As described above, according to the present invention, it is not necessary to provide a mechanical mechanism for turning on / off the infrared cut filter, and it is possible to improve color reproducibility in a bright subject and improve sensitivity in a dark subject. Thus, it is possible to provide a color imaging device that can be used continuously day and night. By eliminating mechanical mechanism parts, it is possible to reduce the size and weight of the imaging device, reduce costs, and improve reliability.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of a digital camera that implements a color imaging apparatus according to the present invention.
FIG. 2 is a diagram illustrating a filter arrangement of a color filter according to the present embodiment.
FIG. 3 is a diagram illustrating spectral characteristics of a color filter and an infrared cut filter.
FIG. 4 is a diagram illustrating spectral characteristics of a color filter and an infrared filter.
FIG. 5 is a diagram illustrating spectral characteristics of a color filter and an infrared filter.
FIG. 6 is a diagram showing a filter arrangement of a conventional color filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical system 1a Shutter 1b Lens 1c Iris 2 Image pick-up element 2a Color filter 3 Analog signal processing part 4 A / D converter 5 Image processing part 6 Controller 7 Operation part 10 Digital camera

Claims (7)

A first line in which green filters and other one color filters among the three primary colors composed of red, green, and blue are alternately arranged;
A second line in which a filter of the remaining one of the three primary colors and an infrared filter having sensitivity at least in the infrared region are alternately arranged;
A color filter for a solid-state imaging device, comprising a mosaic filter in which the first lines and the second lines are alternately arranged. 2. The color filter for a solid-state imaging device according to claim 1, further comprising an infrared cut filter for blocking infrared light at a pixel position where the three primary color filters are arranged. The color filter having the three primary colors is a color filter having characteristics obtained by multiplying each spectral characteristic of red, green, and blue by a spectral characteristic of an infrared cut filter that blocks infrared light. Color filters for solid-state image sensors. The color filter for a solid-state imaging device according to claim 1, wherein the infrared filter is a white filter. The color filter for a solid-state imaging device according to claim 1, wherein the infrared filter is an infrared transmission filter having spectral characteristics only in a substantially infrared region. A color filter for a solid-state imaging device according to any one of claims 1 to 5,
A solid-state image sensor on which the color filter for the solid-state image sensor is disposed;
Signal processing means for generating image data by interpolating signals of each pixel imaged by the solid-state imaging device;
A mode for switching and controlling a plurality of modes for generating the image data by pixel interpolation calculation with different utilization ratios of the information of the pixels in which the color filters of the three primary colors are arranged and the information of the pixels in which the infrared filters are arranged And a color imaging apparatus comprising: a control unit; The color imaging apparatus according to claim 6, further comprising a light emitting element for infrared illumination.

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