JP3916233B2 - Image pickup device and digital image pickup apparatus including the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image sensor that converts received object light into an electrical signal and an image pickup apparatus including the image sensor, and more particularly to an image sensor that reduces the influence of shading and a digital image pickup apparatus including the image sensor.
[0002]
[Prior art]
2. Description of the Related Art In recent years, digital cameras and digital video cameras that include an image sensor composed of a CCD that converts received light of an object into an electrical signal and digitally record a captured image have become widespread.
By the way, in this kind of digital image pickup device, light incident on the image pickup device via the optical lens system is reduced in the peripheral portion compared to the center of the screen, and so-called shading is generated in which the signal output in the peripheral portion is reduced. To do.
In particular, when the image sensor is further miniaturized and the aperture size of a plurality of photodiodes constituting the image sensor is reduced, this shading becomes remarkable.
As a method for reducing the shading, a method of optimizing optically by shifting the position of an on-chip microlens provided in the image sensor from the center of the photodiode is generally used (see Patent Documents 1 to 3).
In addition, recently, a method for correcting by digital arithmetic processing is being carried out instead of only optical correction as described above (see Patent Document 4).
[0003]
[Patent Document 1]
JP-A-6-140609 [Patent Document 2]
Japanese Patent Laid-Open No. 10-125887 [Patent Document 3]
JP 2001-160973 A [Patent Document 4]
Japanese Patent Laid-Open No. 2000-324505
[Problems to be solved by the invention]
By the way, in the method of optically reducing shading, there is a limit to the optimization of the position of the microlens, so that it is difficult to cope with further miniaturization of the image sensor. In particular, since the light of each color having a dominant wavelength for each color has a different refractive index, it is difficult to accurately reduce shading for each color by simply shifting the microlenses.
Further, in the method of correcting shading in a digital arithmetic process, if the number of pixels increases due to further miniaturization, the time required for the calculation increases and extra processing time is required. In addition, the noise feeling of the image varies between the central portion and the peripheral portion of the image, and the image quality is degraded.
[0005]
The present invention has been made in view of the above circumstances, and provides an image pickup device capable of accurately reducing shading and obtaining a high-quality image without taking extra processing time, and a digital image pickup apparatus including the image pickup device. It is intended to provide.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an image pickup device according to claim 1 includes a light receiving portion having a plurality of light receiving devices that receive incident subject light and convert it into an electrical signal, and a color filter stacked on the light receiving portion. The transmittance of the color filter of at least one color is adjusted in accordance with a change in subject light due to shading, and the output of the light receiving unit is adjusted.
According to the image pickup device having this configuration, the output of the light receiving unit is adjusted by adjusting the transmittance of the color filter in accordance with the shading, so that the shading of each color having a different wavelength is accurately reduced and a high quality image is obtained. Obtainable.
[0007]
The image pickup device according to claim 2 is characterized in that the transmittance is adjusted by adjusting the density of the color filter.
According to the imaging device having this configuration, by adjusting the transmittance of the color filter by adjusting the density of the color filter, it is possible to easily adjust the output of the light receiving unit and accurately reduce the shading of each color having different wavelengths. An image can be obtained.
[0008]
The image pickup device according to claim 3 is characterized in that the transmittance is adjusted by adjusting the thickness of the color filter.
According to the image sensor of this configuration, by adjusting the transmittance by adjusting the thickness of the color filter, the output of the light receiving unit can be easily adjusted to accurately reduce the shading of each color with different wavelengths and achieve high quality Can be obtained.
[0009]
A digital imaging device comprising the imaging device according to claim 4, creates an image data from a lens, an imaging unit that converts subject light incident through the lens into an electrical signal, and an output signal from the imaging unit A digital imaging apparatus having a digital signal processing unit, wherein the imaging element according to any one of claims 1 to 3 is used for the imaging unit.
According to the digital image pickup apparatus including the image pickup device having this configuration, it is possible to obtain a high-quality image without taking extra processing time as compared with the case where the output is corrected in terms of arithmetic processing.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image sensor according to an embodiment of the present invention and a digital image pickup apparatus including the same will be described with reference to the drawings.
Here, a digital camera will be described as an example of the digital imaging device.
FIG. 1 is a diagram illustrating a configuration of a digital camera. The lens 11 attached to the digital camera 10 is a single focal lens having a fixed focal length and a fixed imaging angle of view. The digital camera 10 condenses light from the subject via the lens 11, and the light is received by the imaging unit 12 whose condensing surface is disposed at the focal position of the lens 11. The imaging unit 12 is configured by an imaging element called a honeycomb CCD provided with a plurality of light receiving elements each having an octagonal shape. Each light receiving element converts the received light into an electric signal according to the amount of light received, and the obtained electric signal is output to the amplifier 13 via the vertical transfer path (VCCD) and the horizontal transfer path (HCCD) according to the transfer pulse. Is done. Details of the imaging unit 12 will be described later.
[0011]
The amplifier 13 is an amplifier that amplifies the electrical signal sent from the imaging unit 12 with a predetermined amplification factor. Thereafter, the electric signal is converted into a digital signal by the A / D converter 14 and sent to the pass line 20. A CPU 21, a digital signal processing unit 22, a compression processing unit 23, a recording medium controller 24, a display unit 25, and a RAM 26 are connected to the pass line 20.
The digital signal processing unit 22 is a signal processing unit that applies various correction processes to the digital signal sent from the A / D converter 14. Specifically, in response to an instruction from the CPU 21, the digital signal processing unit 22 performs white balance adjustment and white balance adjustment by multiplying the digital value of each color signal by a predetermined adjustment value based on the integrated value for each color. Digital image data is created by performing gamma correction for converting input / output characteristics such that the RGB signals have desired gamma characteristics, YC processing for generating luminance signals and chroma signals, and the like.
[0012]
The compression processing unit 23 compresses the image data created by the digital signal processing unit 22 based on a predetermined compression method such as a JPEG method, and generates compressed data of a predetermined format. Conversely, the compression processing unit 23 also performs an operation of decompressing data compressed into a predetermined format in accordance with an instruction from the CPU 21.
The recording medium controller 24 is an interface that is connected to a removable recording medium 30 such as a smart medium and transmits signals to and from the recording medium 30. The recording medium controller 24 reads data from the recording medium 30 and writes or erases data on the recording medium 30 in accordance with instructions from the CPU 21.
The display unit 25 has a monitor that displays image data. For example, the display unit 25 is attached to the back surface of the housing of the digital camera 10, and data written in the recording medium 30 is read out to the RAM 26 and displayed on a monitor on the display unit 25 in accordance with an instruction from the CPU 21. Is done.
[0013]
FIG. 2 is a perspective view showing an image sensor that constitutes the imaging unit 12 of the digital camera 10.
As described above, the imaging device 30 includes a plurality of honeycomb-shaped light receiving elements 31 arranged in a honeycomb arrangement, a vertical transfer path (VCCD) 32a for transferring an electric signal from the light receiving elements 31, and a horizontal transfer path. (HCCD) 32b. An RGB color filter 34 and a microlens 35 are arranged in this order immediately above each light receiving element 31 of the light receiving unit 33.
[0014]
The subject light incident from the lens 11 first enters the microlens 35. The microlens 35 condenses the subject light incident through the lens 11 and efficiently condenses the light on the light receiving element 31. The subject light that has passed through the microlens 35 passes through the color filter 34 and enters the light receiving element 31.
[0015]
The color filter 34 is obtained by arranging any one of R, G, and B in a predetermined arrangement for each light receiving element 31, and subject light collected by the microlens 35 is emitted from the color filter 34. And enters the light receiving element 31. Thereafter, the subject light is converted into an electric signal by the light receiving element 31, and this electric signal is transferred to the amplifier 12 via the vertical transfer path 32a and the horizontal transfer path 32b.
[0016]
Here, when the light incident through the lens 11 is reduced in the peripheral portion due to shading compared to the center of the screen, the output level of the electrical signal from the light receiving portion 33 gradually increases toward the peripheral portion with respect to the screen center. descend.
Further, since this output level generally changes greatly in light having a long wavelength, as shown in FIG. 3, the output level of the RGB primary colors increases in the order of B, G, and R, and appears at the periphery of the screen. May be cyan blue.
[0017]
For this reason, in the color filter 34, the density is adjusted according to the change in the output level of each color in the light receiving unit 33 due to shading, and the transmittance is adjusted.
As a method of adjustment, as shown in FIG. 4, the density of each color of RGB of the color filter 34 is dark at the center of the screen and gradually decreases toward the periphery. Thereby, the non-uniformity of the light receiving level between the light receiving element in the central part and the light receiving element in the peripheral part is eliminated, and the entire transmission amount of the subject light is made uniform. That is, when the same amount of light should be received, the problem that the light receiving level is lower in the peripheral portion than in the central portion is solved. In this way, as shown in FIG. 5, the output from the light receiving unit 33 is made uniform, and the influence of shading is mitigated to achieve optimization.
[0018]
As described above, according to the imaging device 30 described above, since the output of the light receiving unit 33 is adjusted by adjusting the transmittance of the color filter 34 in accordance with the shading, the shading of each color having different wavelengths can be accurately reduced. And high quality images can be obtained.
And according to the digital camera 10 provided with this image pick-up element 30, compared with what corrects an output by arithmetic processing, a high quality image can be obtained, without taking extra processing time.
[0019]
The method for adjusting the density of each color of the color filter 34 is not limited to the above example as long as uneven color of the image due to shading can be suppressed.
[0020]
In FIG. 6, among the color filters 34, the density of the R color, which is most affected by shading, is adjusted and brought close to the output level of other colors. In this way, even if correction is performed only for R, the difference in the light reception level between the peripheral portion and the central portion is reduced as compared with before correction, and the captured image looks better than before adjustment. can get.
[0021]
In the color filter 34 shown in FIG. 7, the density of the R and G colors is adjusted to be close to the output level of the B color that is not significantly affected by shading. As described above, when adjustment is performed so that the attenuation levels of the respective colors coincide with each other, the difference between the light reception levels of the peripheral portion and the central portion is reduced, and the ratio of each color at the time of RGB composition is included in the light emitted from the subject. Therefore, a better image than before the adjustment can be obtained.
[0022]
In FIG. 8, among the color filters 34, the density of each of the R color that is most affected by shading and the B color that is not significantly affected by shading is adjusted. The R and B color output levels are brought close to the G color output level without adjustment. By performing such adjustment, the same effect as that of the filter shown in FIG. 7 can be obtained.
[0023]
As described above, according to the adjustment methods shown in FIGS. 6 to 8, the output levels of the respective colors can be made uniform to reduce the difference, and the color unevenness of the image due to shading can be suppressed.
[0024]
In the above example, the density of each color of the color filter 34 is adjusted and the output level in the light receiving unit 33 is adjusted according to the shading. However, as shown in FIG. 9, the thickness of the color filter 34 is adjusted according to the shading. The same effect can be obtained even if the adjustment is made.
[0025]
In the above example, the density of each color of the color filter 34 is adjusted according to the shading in which the output change gradually occurs from the center of the screen toward the peripheral portion. In the case of shading, it goes without saying that the density of each color of the color filter 34 is adjusted in accordance with the output change due to this shading.
In addition, the lens 11 of the above embodiment is not limited to a focus lens, and may be a zoom lens such as a telephoto lens.
In the above example, a so-called digital camera that captures a still image is described as an example of the digital imaging device. However, the present invention is applied to a digital imaging device that includes a digital video camera that continuously captures images and generates moving images. Is also applicable.
[0026]
【The invention's effect】
As described above, according to the image pickup device of the present invention, the output of the light receiving unit is adjusted by adjusting the transmittance of the color filter in accordance with the shading, so that the shading of each color having a different wavelength is accurately reduced. High quality images can be obtained.
And according to the digital camera provided with this image sensor, it is possible to obtain a high-quality image without taking extra processing time as compared with the case where the output is corrected in arithmetic processing.
[Brief description of the drawings]
FIG. 1 is a functional block diagram illustrating a configuration of an image sensor according to an embodiment of the present invention and a digital image pickup apparatus including the image sensor.
FIG. 2 is an exploded perspective view of the image sensor for explaining a schematic structure of the image sensor.
FIG. 3 is a graph illustrating a change in output of a light receiving unit due to shading.
FIG. 4 is an explanatory diagram of how to adjust the density of a color filter.
FIG. 5 is a graph illustrating how to adjust the output of the light receiving unit.
FIG. 6 is a graph illustrating another example of how to adjust the output of the light receiving unit.
FIG. 7 is a graph illustrating another example of how to adjust the output of the light receiving unit.
FIG. 8 is a graph illustrating another example of how to adjust the output of the light receiving unit.
FIG. 9 is an explanatory diagram of how to adjust the thickness of the color filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Digital imaging device 11 Lens 12 Imaging part 30 Imaging element 31 Light receiving element 33 Light receiving part 34 Color filter

Claims (4)

An image sensor comprising a light receiving unit having a plurality of light receiving elements that receive incident subject light and convert it into an electrical signal, and a color filter composed of a plurality of colors stacked on the light receiving unit,
An imaging device, wherein the transmittance of at least one color filter is adjusted in accordance with a change in subject light due to shading, and an output of the light receiving unit is adjusted. The imaging device according to claim 1, wherein the transmittance is adjusted by adjusting a density of the color filter. The imaging device according to claim 1, wherein the transmittance is adjusted by adjusting a thickness of the color filter. A digital imaging apparatus comprising: a lens; an imaging unit that converts subject light incident through the lens into an electrical signal; and a digital signal processing unit that creates image data from an output signal from the imaging unit, A digital imaging apparatus using the imaging device according to any one of claims 1 to 3 in an imaging unit.

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