JP2863447B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging apparatus provided with an optical low-pass filter arranged in an incident optical path of a solid-state imaging device such as a CCD or a MOS for performing two-dimensional sampling and suppressing the influence of carrier components. .

[0002]

2. Description of the Related Art FIG. 1 shows the arrangement of picture elements and apertures of a solid-state image sensor, for example, a one-chip CCD image sensor. In FIG.
Indicates the vertical direction. One of two adjacent lines has
Green filter 1G and a blue filter 1B is disposed alternately in the horizontal direction of the pixel spacing P _{x (e.g.} 17 .mu.m), the other of the green filter 2G and red filters 2R is P
_It is arranged alternately at intervals of _x . Picture element interval of the vertical direction is a _{P y} (e.g., 13 .mu.m). The imaging light is sampled by such a lattice-shaped opening pattern.

[0003] sampling the output of the CCD image sensor described above, as shown in the spatial frequency spectrum of FIG. _{2, (f x = 0,} f y = 0) baseband component positioned centered in (2G, R, B))
Multiple harmful carrier components are generated. The horizontal axis _{f x,} vertical axis _{f v} in FIG 2 represents the horizontal frequency and vertical frequency normalized by respective _P x / 2 [pi and _P y / _2π.

[0004] Carrier component generated about a position of _{(f x = 1, f y} = 0) gives rise to moiré when fine stripes made of stripes of black and white vertically extending,
Position carrier component generated about the _{(f x = 1/2,} f y = 0) , at the time of slightly rough vertical stripe, causing cross-color phenomenon green and magenta is generated. (F
_A carrier component generated around the position of _x = 0, f _y = 1) causes moire when a fine horizontal stripe is formed.

[0005]

Therefore, it is necessary to construct an optical low-pass filter having a trap point at the position of these harmful carrier components. However, if the high frequency component of the baseband component is also attenuated, the resolution is reduced. Therefore, an optical low-pass filter having the above-mentioned position as a trap point and not attenuating the baseband component is preferable. For example, with respect to the horizontal direction, as shown in FIG. 3A, _{(f x
= 1/2) (f x} = 1) and a trap point, (f
In the range of _{x = 0) ~ (f x} = 1/2), preferably it is sufficiently low loss characteristics.

The frequency characteristic of an optical low-pass filter using one birefringent quartz plate is represented by cos as shown in FIG. 3B.
The frequency characteristic of an optical low-pass filter in which two birefringent quartz plates are stacked is represented by a cos ² curve as shown in FIG. 3C. The frequency characteristic of the cos curve does not attenuate the baseband component and does not cause a decrease in resolution, but has a small effect of suppressing the influence of the carrier component. The cos ² curve can suppress the influence of the carrier component, but loses the baseband component, resulting in a reduction in resolution.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical low-pass filter having a characteristic capable of removing the influence of a carrier component without reducing a high frequency component of a base band component.
An object of the present invention is to provide an imaging device including

Another object of the present invention is to use only three quartz plates, so that the process of attaching the quartz plates can be simplified and a thin optical low-pass filter is provided. It is to provide an imaging device .

[0009]

SUMMARY OF THE INVENTION This invention provides an imaging apparatus that performs a two-dimensional spatial sampling of the object image from the imaging device of the picture element structure of the vertical pixel pitch in the horizontal pixel pitch P _x was P _y, It has at least three birefringent plates for separating one incident light into eight light beams, and the diagonal scanning direction of the image sensor is changed by a separation point by four of the eight light beams. One side is {2 / 2P _x (／
2 means the square root of 2. ), And is formed of a square of the same size as the first square by a separation point by the other four rays among the eight rays, and is formed into a first square. the second to form a square, that the three birefringent plate was continuously laminated on the front surface of the imaging element that is shifted a distance of the horizontal pixel pitch P _x in the scanning direction of the imaging device for It is an imaging device characterized by the following.

[0010]

[0011]

[Action] first birefringent plate, the distance between the ordinary ray and the extraordinary ray and (√2 / 2) P _x, the second birefringent plate, the distance between the ordinary ray and the extraordinary ray and P _x , The third birefringent plate,
The distance between the ordinary ray and the extraordinary ray and (√2 / 2) _{P x.} Since these birefringent plates are stacked, incident light is separated into eight light beams. By the separation distance described above,
Eight rays form two squares. With such a configuration, in order to suppress harmful carrier components, frequency characteristics having at least three trap points can be realized by three birefringent plates.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is used to explain the optical characteristics of the first quartz plate 11, the second quartz plate 12, and the third quartz plate 13 in this embodiment. In FIG.
The incident light that has passed through the imaging lens is supplied to the quartz plates 11, 12, and 13 in a direction perpendicular to the sheet surface of the drawing.

The quartz plate 11 separates incident light into ordinary rays and extraordinary rays, and a main surface 14 extending perpendicularly to the paper surface of the drawing where these ordinary rays and extraordinary rays are present has a horizontal scanning direction H.
Is at an angle of θ ₁ (for example, + 45 °). The main surface 15 of the quartz plate 12 where the ordinary and extraordinary rays are present coincides with the horizontal scanning direction. The main surface 16 of the quartz plate 13 is θ with respect to the horizontal scanning direction H.
₂ (eg, -45 °). These three quartz plates 11, 12 and 13 correspond to the second quartz plate 12.
Are laminated and stuck so that is located in the middle. Further, the quartz plate 13 is arranged in the incident optical path such that the quartz plate 13 comes to a position closest to the solid-state imaging device side.

Here, the angles formed by the main surfaces of the three quartz plates 11, 12, and 13 are relative to each other. For example, as shown by a broken line in the crystal plate 11, (θ ₁ = −45 °)
If the crystal plate 13 is indicated by a broken line, (θ
₂ = + 45 °). Therefore, as a method of combining the three quartz plates 11, 12, and 13, the quartz plate 1
The two main surfaces 15 are 0 ° and 180 °, respectively, so that two combinations are possible.

The crystal plate 11 has a horizontal pixel interval of P _x
When the distance between the ordinary ray and the extraordinary ray is (√2 / 2)
P _x (√2 means a square root of 2; the same applies hereinafter). Quartz plate 12 is for the separation distance between P _x, the crystal plate 13, the separation distance (√2
/ 2) it is an _{P x.} Such setting of the separation distance can be performed by selecting the thickness dimension of the quartz plates 11, 12, and 13.

Light incident on the first crystal plate 11 is firstly split into an ordinary ray o ₁ and an extraordinary ray e ₁ having the same intensity and being parallel. The two rays are incident on the second quartz plate 12 to be divided into an ordinary ray and an extraordinary ray, respectively. From the quartz plate 12, the ordinary ray o ₁ secondary to the ordinary ray o ₁ is generated.
o ₂ and the extraordinary ray _o 1 _{e 2} and extraordinary ray ordinary ray originating from _{e 1} secondarily _e 1 _{o 2} and the extraordinary ray _e 1 _{e 2} of the four
A ray of light results. After passing through the second quartz plate 12, this 4
The rays of the book are parallel. The intensities of the four light beams vary depending on the angle θ ₁ formed by the main surfaces of the quartz plates 11 and 12.
As shown in Figure 5A, when the major surface of both are allowed to theta ₁ rotated from the position parallel, the intensity of the four light beams, becomes the following equation.

[0017] _{o 1 o 2 = o 1 cosθ} 1 o 1 e 2 = o 1 sinθ 1 e 1 o 2 = e 1 sinθ 1 e 1 e 2 = e 1 cosθ 1

When these four rays are incident on the third quartz plate 13, a total of eight ordinary rays and extraordinary rays are generated from each ray three-dimensionally. Figure 5B ray _o 1 ordinary ray generated from _{o 2} to 3-order _o 1 _o 2 _{o 3} and the extraordinary ray _o 1 o
₂ e _3, and shows the relationship between the ray _o 1 ordinary rays _o resulting from _{e 2} to 3-order 1 _e 2 _{o 3} and the extraordinary ray _o 1 _e 2 _{e 3,}
These are the major surface of each of the crystal plates 12 and 13 an angle and theta _2, it becomes the strength shown by the following formula.

O₁o₂o₃= O₁o₂cos θ₂= O₁cos θ₁cos θ₂  o₁o₂e₃= O₁o₂sin θ₂= O₁cos θ₁sin θ₂  o₁e₂o₃= O₁e₂sin θ₂= O₁sin θ₁sin θ₂  o₁e₂e₃= O₁e₂cos θ₂= O₁sin θ₁cos θ₂

FIG. 5C shows the tertiary rays e ₁ e ₂ o ₃ and the extraordinary ray e ₁ e ₂ e ₃ , which are generated tertiarily from the rays e ₁ e _2, and the tertiary rays which are generated from the rays e ₁ o ₂ . Ordinary ray e ₁ o ₂ o ₃
And the relationship between the extraordinary rays e ₁ o ₂ e ₃ , which have the strength shown by the following equation.

E₁o₂o₃= E₁o₂cos θ₂= E₁sin θ₁cos θ₂  e₁o₂e₃= E₁o₂sin θ₂= E₁sin θ₁sin θ₂  e₁e₂o₃= E₁e₂sin θ₂= E₁cos θ₁sin θ₂  e₁e₂e₃= E₁e₂cos θ₂= E₁cos θ₁cos θ₂

In the above equation, (θ₁= 0) (θ2 =
0) That is, the main surfaces of the three quartz plates 11, 12, and 13 are parallel.
Assuming that₁= O₁o₂= O₁o₂o₃  e₁= E₁e₂= E₁e₂e₃  And the primary ray o₁And extraordinary ray e₁But
It exits through the quartz plates 12 and 13 as it is. This one embodiment
Then, (θ₁= 45 °) (θ₂= 45 ゜)
First, the eight light rays generated from the quartz plate 13 are (1/2)
o₁Or (1/2) e₁Of the strength of (o₁=
e₁), The intensity of these eight rays is equal to each other.
It will be something new.

Referring to FIG. 6, a description will be given of the direction and distance at which one light beam incident on the origin is separated. Due to the first quartz plate 11, the incident light within its main surface 14 (１４
2/2) is only the separation distance _{P x.} The following crystal plate 12, are separated by a distance of P _x within that major surface 15 (shown in phantom). Further, the next crystal plate 13 separates the main surface 16 (indicated by a dashed line) _by a distance of (√2 / 2) Px. Finally, the above-mentioned eight rays are shown in FIG.
And is incident on the solid-state imaging device. Two light beams o ₁ e ₂ o ₃ and e ₁ o ₂ e ₃ overlap.

One embodiment of the present invention comprising the three quartz plates 11, 12, 13 is shown in FIG.
As shown in, with a distance of P _x in the horizontal direction H, the optical low-pass filter for separating the ordinary and extraordinary rays, as shown in FIG. 7B, 1 pieces of the light beam (√2 / 2) P _x Can be considered as a combination of an optical low-pass filter that divides the light into four rays at the positions of the vertices of a diamond having a length of.

The optical low-pass filter shown in FIG.
As shown in FIG. 8, the horizontal _{direction, (f} x = 1 /
₂₎ (having a f x = 3/2) cos curve the frequency characteristic 21 having a trap point at a point ..., 7B
Optical low-pass filter shown in _{the, (f x = 1) (} f x
= 3) cos having a trap point at point
^It has a frequency characteristic 22 of ^two curves. Accordingly, one embodiment of the present invention has a pass characteristic 23 obtained by combining the frequency characteristics 21 and 22, as shown by hatching in FIG.

The embodiment of the present invention has a frequency characteristic 24 of a cos ² curve shown in FIG. 9 similar to the optical low-pass filter shown in FIG. 7B in the vertical direction. Here, the frequency _{f y} in the vertical direction, CC shown in FIG. 1
Those determined by the pixel spacing _{P y} in the vertical direction of the opening pattern of the D image _{sensor, (P x = 17μm, P} y =
(13 μm), (1 / P _x ) <(1 / P _y ), and a trap point is generated at a position smaller than (f _y = 1). _Therefore, it is possible to suppress the influence of harmful carrier components occurring in the position of _{(f x = 0, f y} = 1/2).

From the horizontal frequency characteristic 23 and the vertical frequency characteristic 24 described above, the spatial frequency is shown in FIG.
In, _{f y} axis parallel to the straight line 25, 26 and _f x,
form an angle of 45 ° with each axis of f _y , (f _x = 1)
_(F x = -1) linearly inclined through the position of ... 27,
A trap point indicated by 28 occurs, and a baseband component indicated by oblique lines is obtained.

In this embodiment, since the openings of the solid-state imaging device such as a CCD image sensor are arranged in a rectangular repetition, (θ ₁ = 45 °) (θ ₂ = −45 °). However, the values of [theta] ₁ and [theta] ₂ need not coincide with +45 [deg.] And -45 [deg.], But may be in the vicinity of them. The separation distance between the quartz plates 11, 12, and 13 is P
_x , (√2 / 2) P _x may be substantially equal to the value of _x .

[0029]

Effects of the Invention According to the present _{invention, (f} x, _{f y)} is (1 / 2,0), (1,0), (0,1 / 2), (0,
1) An image pickup apparatus having an optical low-pass filter having trap points at points such as (1/2) and (1/2) to suppress the influence of a carrier component and to reduce the loss of a baseband component. Can be realized.

According to the present invention, the number of required quartz plates is three.
And the number of sheets can be reduced.
It can be simplified and thin optical low-pass
Can be a filterThe size of the imaging device can be reduced.
You.

[Brief description of the drawings]

FIG. 1 is an enlarged plan view of an example of an aperture pattern of a CCD image sensor to which the present invention can be applied.

FIG. 2 is a spatial frequency spectrum used for describing the present invention.

FIG. 3 is a frequency characteristic diagram used for describing an optical low-pass filter.

FIG. 4 is an optical low-pass filter used in one embodiment of the present invention ;
FIG. 3 is a schematic diagram for explaining optical characteristics of each crystal plate of the filter .

FIG. 5 is an optical low-pass filter used in an embodiment of the present invention ;
FIG. 3 is a schematic diagram for explaining optical characteristics of a filter .

FIG. 6 is an optical low-pass filter used in one embodiment of the present invention ;
FIG. 3 is a schematic diagram for explaining optical characteristics of a filter .

FIG. 7 is an optical low-pass filter used in an embodiment of the present invention.
FIG. 3 is a schematic diagram for explaining optical characteristics of a filter .

FIG. 8 shows an optical low-pass filter used in an embodiment of the present invention.
5 is a graph used to explain a filter frequency characteristic.

FIG. 9 is an optical low-pass filter used in one embodiment of the present invention.
5 is a graph used to explain a filter frequency characteristic.

FIG. 10 shows an optical low-pass used in one embodiment of the present invention.
5 is a graph used to explain a frequency characteristic of a filter .

[Explanation of symbols]

 11 first quartz plate 12 second quartz plate 13 third quartz plate

Claims (1)

(57) [Claims] 1. A imaging apparatus for performing two-dimensional spatial sampling of the object image from the imaging device of the picture element structure of the vertical pixel pitch in the horizontal pixel pitch is P _x was P _y, 8 present a single incident light And at least three birefringent plates for splitting the light into two light beams, and a separation point by four of the eight light beams defines a scanning direction of the image sensor as a diagonal direction and a side of √2 / 2P _x (√2 means the square root of 2), and the first square is formed by the separation point of the other four rays among the eight rays. It is composed of the same size of the square and square, so as to form a second square, which is shifted a distance of the horizontal pixel pitch P _x in the scanning direction of the imaging device relative to the first square, The above three birefringent plates are Imaging device according to claim continuously be laminated placed were on the surface.