JP2003143613A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device that can capture an image with excellent image quality by simplifying the configuration of its optical low-pass filter so as to reduce the cost increase and the manufacturing difficulty. SOLUTION: The image pickup device is characterized in that it has imaging elements 3 to which a plurality of kinds of color filters are horizontally and vertically arranged with an equal pitch and the optical low-pass filter 6 combining two double refractive optical elements in which the elimination band B with respect to an object light made incident onto the imaging elements 3 with an angle of 45-degrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for converting an image into electronic information using a photoelectric conversion element, and more particularly to an image pickup element in which color filters and pixels of Bayer array are arranged at equal pitches in horizontal and vertical directions. The present invention relates to an imaging device having the same.

[0002]

2. Description of the Related Art Conventionally, many image pickup apparatuses using an image pickup element having a so-called Bayer array color filter have been proposed.

FIG. 5 is a block diagram showing a configuration of a conventional image pickup apparatus. In FIG. 5, 1 is a lens which is an image pickup optical system, 2 is an optical low pass filter, 3 is an image pickup element, 4 is an image processing circuit, Reference numeral 5 is a color filter.

The operation will be described with reference to the drawings.

A subject image (not shown) formed on the image pickup device 3 by the lens 1 through the optical low-pass filter 2 is
After being photoelectrically converted by the image sensor 3 and output as an electric signal, the image processing circuit 4 performs a predetermined process and outputs as an image signal.

A color filter 5 is provided on the image forming plane of the image pickup device 3 as shown in FIG.

FIG. 6 is a diagram showing the arrangement of the color filters of the image pickup device.

Here, C1, C2, C3, and C4 are first, second, third, and fourth color filters, respectively, and the color filter 5 is arranged such that each color filter has one pixel in both horizontal and vertical directions. It is arranged every other time.

Here, there are cases where filters of the same color are used for C1 and C4 or C2 and C3.

One example is the Bayer array.

Each color filter is arranged in accordance with the pixel pitch of the image pickup device, and Ph is a horizontal pixel pitch,
Pv is a vertical pixel pitch.

Due to such an arrangement, the color information of the subject image is sampled at random, and when the image processing circuit 4 interpolates the color information, the image has horizontal and vertical high frequency components. When doing so, a color signal called a false color is generated due to aliasing, which significantly deteriorates the image quality.

FIG. 7 shows the sampling intervals of the image pickup device in the frequency plane and the appearance of false colors.

HL is horizontal luminance folding, VL is vertical luminance folding, HF is horizontal false color, and VF is vertical false color.

In order to suppress such false colors HF and VF, an optical low pass filter 2 using a birefringent optical element such as artificial quartz has been inserted immediately before the image pickup element.

In particular, horizontal and vertical pixel pitches Ph, P
In an image pickup apparatus using image pickup elements having the same v, the spatial frequency to be removed by the optical low-pass filter is to prevent spurious colors HF and VF from being generated as much as possible while keeping the band of the luminance signal. For example, it is set as (1) or (2) in FIG.

FIG. 8 is a two-dimensional frequency plan view showing the state of the elimination band of the conventional optical low pass filter.

B is a removal band of the optical low pass filter.

As shown in FIG. 8 (1), an optical element having two kinds of vertical and horizontal orthogonal removal bands B may be combined.

Further, as shown in FIG. 8 (2), when the pixel pitches of the image pickup elements are equal in the horizontal and vertical directions, an optical element having two types of elimination bands B orthogonal to each other at an angle of 45 ° may be combined. .

[0021]

However, in the optical low-pass filter 2 using the birefringent optical element used in the above-mentioned conventional image pickup apparatus, the light ray passing through the birefringent optical element is polarized. Even if one birefringent optical element is inserted after another birefringent optical element so that the removal zones B are orthogonal to each other, the predetermined performance cannot be obtained.

For this reason, a phase plate for returning the polarized light between the two birefringent optical elements or another birefringent optical element having a rejection band B having an angle of 45 ° with the two birefringent optical elements is used. Since the optical element has to be inserted, the manufacturing cost has increased due to the increase in the cost of the parts and the increase in the bonding of the engineering parts.

The present invention has been made in view of the problems of the above-described conventional example, and is an image pickup apparatus that can capture an image with good image quality while simplifying the configuration of the optical low-pass filter and reducing costs and manufacturing difficulties. The purpose is to provide a device.

[0024]

Therefore, the present invention is intended to achieve the above object by providing an image pickup device shown in any one of the following items (1) to (3). is there.

(1) An image pickup device in which a plurality of types of color filters are arranged at equal pitches in the horizontal and vertical directions, and two birefringences in which the elimination bands for subject light incident on the image pickup device form an angle of 45 ° with each other. An image pickup apparatus comprising: an optical low-pass filter in which optical elements are combined.

(2) The optical low-pass filter has a false color reducing circuit for reducing false color in a high frequency portion in the horizontal direction of the signal output from the image pickup device, and the optical low pass filter has a removal band with respect to a horizontal array of pixels. 2. The image pickup apparatus according to (1) above, which has a configuration in which two birefringent optical elements forming an angle of 22.5 ° and forming an angle of 45 ° are combined with each other.

(3) The optical low-pass filter has a false color reduction circuit for reducing false color of a high frequency portion of a signal output from the image pickup device in a vertical direction, and the optical low-pass filter has a removal band with respect to a vertical array of pixels. 2. The image pickup apparatus according to (1) above, which has a configuration in which two birefringent optical elements forming an angle of 22.5 ° and forming an angle of 45 ° are combined with each other.

That is, a circuit for reducing false color is added to the image processing circuit for processing the signal output from the image pickup device, and an optical low-pass combining two birefringent optical devices each having a removal band of 45 °. Use a filter.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to a plurality of examples.

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. The same components as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

Further, 6 is two birefringent optical elements according to the present embodiment, in which the elimination bands form an angle of 22.5 ° with respect to the horizontal array of pixels and form an angle of 45 ° with each other. Is a signal processing circuit, and 8 is a horizontal false color reducing circuit included in the signal processing circuit 7 for reducing false colors in a high frequency portion in the horizontal direction.

The operation will be described with reference to the drawings.

A subject image (not shown) formed on the image pickup device 3 by the lens 1 through the optical low pass filter 6,
After being photoelectrically converted by the image pickup device 3 and output as an electric signal, the signal processing circuit 7 performs a predetermined process and outputs as an image signal.

Further, a color filter 5 is provided on the image forming surface of the image pickup device 3 as in the above-mentioned conventional example.

When the signal processing circuit 7 performs the interpolation processing of the color information, among the false colors due to the high frequency components contained in the image, the one due to the vertical high frequency components is as shown in FIG. It is suppressed by the filter 6.

Further, the optical low-pass filter 6 of the present invention.
Also suppresses the aliasing distortion of the luminance in the horizontal direction.

FIG. 2 is a two-dimensional frequency plan view showing a state of aliasing of false colors and brightness when the optical low pass filter according to the first embodiment of the present invention is used.

Similar to the conventional example, HL represents horizontal luminance folding, VL represents vertical luminance folding, HF represents horizontal false color, and VF.
Is a vertical false color, and B is a removal band of the optical low-pass filter.

The remaining horizontal false color HF in FIG.
Is a horizontal false color reduction circuit 8 provided in the signal processing circuit 7.
Therefore, the image quality is not deteriorated because it is reduced by using the characteristics of the image signal. The horizontal false color reduction circuit 8 interpolates color information by using a pixel vertically adjacent to a target pixel in order to suppress a false color in the horizontal direction that occurs when an object having vertical stripes is imaged. To do.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention. The same components as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

Reference numeral 7'denotes a signal processing circuit, and reference numeral 9 denotes a signal processing circuit according to the present embodiment. An optical low-pass filter 10 in which a plurality of birefringent optical elements are combined is a vertical false color reduction circuit included in the signal processing circuit 7'to reduce false color in a high frequency portion in the vertical direction.

The operation will be described with reference to the drawings.

An unillustrated subject image formed on the image pickup device 3 by the lens 1 through the optical low-pass filter 9 is
After being photoelectrically converted by the image pickup device 3 and output as an electric signal, the signal processing circuit 7'performs a predetermined process and outputs as an image signal.

Further, a color filter 5 is provided on the image plane of the image pickup device 3 as in the above-mentioned conventional example.

When performing the interpolation processing of color information in the signal processing circuit 7 ', among the false colors due to the high frequency components contained in the image, those due to the horizontal high frequency components are as shown in FIG.
It is suppressed by the optical low pass filter 9 of this embodiment.

Furthermore, the optical low-pass filter 9 of the present embodiment also suppresses the aliasing distortion of the luminance in the vertical direction.

FIG. 4 is a two-dimensional frequency plan view showing how aliasing of false colors and luminances occurs when the optical low pass filter of the second embodiment of the present invention is used.

Similar to the conventional example, HL represents horizontal luminance folding, VL represents vertical luminance folding, HF represents horizontal false color, and VF.
Is a vertical false color, and B is a removal band of the optical low-pass filter.

The remaining vertical false color VF in FIG.
Is reduced by the vertical false color reduction circuit 10 provided in the signal processing circuit 7'using the characteristics of the image signal, so that the image quality is not deteriorated. The vertical false color reduction circuit 8
For example, in order to suppress a false color in the vertical direction that occurs when a horizontal stripe object is captured, color information is interpolated using pixels that are horizontally adjacent to the target pixel.

[0052]

As described above, according to the present invention, an image pickup apparatus having a Bayer array color filter and an image pickup element in which pixels are arranged at equal pitches in both horizontal and vertical directions is used. By adding a false color reducing circuit for reducing false color in the horizontal direction to the image processing circuit to be processed, and by using an optical low pass filter in which two birefringent optical elements each having a removal band of 45 ° are combined, It is possible to provide an imaging device that can obtain an image without image quality deterioration while simplifying the configuration of the optical low-pass filter.

[Brief description of drawings]

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

FIG. 2 is a two-dimensional frequency plan view showing how aliasing of false color and luminance is performed when the optical low-pass filter according to the first embodiment of the present invention is used.

FIG. 3 is a block diagram showing a configuration of an image pickup apparatus according to a second embodiment of the present invention.

FIG. 4 is a two-dimensional frequency plan view showing a state of aliasing of false colors and luminances when the optical low pass filter according to the second embodiment of the present invention is used.

FIG. 5 is a block diagram showing a configuration of a conventional imaging device.

FIG. 6 is a diagram showing an arrangement of color filters of an image sensor.

FIG. 7 is a two-dimensional frequency plan view showing how aliasing of false colors and luminance occurs when a conventional optical low-pass filter is used.

FIG. 8 is a two-dimensional frequency plan view showing a state of a removal band of a conventional optical low pass filter.

[Explanation of symbols]

1 lens 2 Conventional optical low-pass filter 3 image sensor 4 Image processing circuit 5 color filters 6 Optical low-pass filter of the first embodiment 7 Signal processing circuit 7'Signal processing circuit 8 Horizontal false color reduction circuit 9 Optical low-pass filter of the second embodiment 10 Vertical false color reduction circuit HL Horizontal brightness folding VL Vertical brightness folding HF horizontal false color VF vertical false color B Optical low-pass filter rejection band

Claims (3)

[Claims] 1. An image sensor in which a plurality of types of color filters are arranged at equal pitches in both horizontal and vertical directions, and two birefringent optics in which a rejection band for subject light incident on the image sensor forms an angle of 45 ° with each other. An image pickup apparatus comprising: an optical low-pass filter in which elements are combined. 2. A false color reduction circuit for reducing false color of a high frequency portion in a horizontal direction of a signal output from the image pickup device, wherein the optical low-pass filter has a removal band for each horizontal array of pixels. 2. The image pickup apparatus according to claim 1, wherein the birefringent optical elements that form an angle of 22.5 ° and form an angle of 45 ° are combined with each other. 3. A false color reduction circuit for reducing false color of a high frequency portion in a vertical direction of a signal output from the image pickup device, wherein the optical low-pass filter has a removal band for each vertical array of pixels. 2. The image pickup apparatus according to claim 1, wherein the birefringent optical elements that form an angle of 22.5 ° and form an angle of 45 ° are combined with each other.