JP2000316805A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide images of good performance at all times by giving a positional relationship that reduces the influence of moire in consideration of specifications of various fiberscopes, television cameras, and CCDs. SOLUTION: In this image pickup device, an image created by an image guide fiber 2 and composed of a plurality of spatially discrete points is formed on a solid image pickup element 12, and an image obtained by means of the solid image pickup element 12 is displayed on an external display device 14. The relative positions of a regular arrangement A of images and the basic arrangement B of the solid image pickup elements are made to deviate from each other by a rotational angle of α so that the frequency spectrum of a discrete image formed on the solid image pickup element 12 on a two-dimensional frequency space is discrete from a sampling point produced by the solid image pickup element 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device,
In particular, the present invention relates to an image pickup apparatus in which an image composed of a plurality of spatially discrete points using an image guide fiber or the like is displayed on an external display device such as a monitor for observation.

[0002]

2. Description of the Related Art For example, an image guide fiber is often used as an image composed of a plurality of discrete points spatially. In the image guide fiber, an image is formed by light transmitted through a plurality of optical fiber cores having a certain regular arrangement and spatially discrete. A typical example of obtaining an image using the image guide fiber is an endoscope called a so-called fiberscope.

[0003] Observation with a fiberscope is usually
A subject image is formed on the end surface of the image guide fiber by the objective optical system provided at the distal end, and the image is transmitted to the other end of the image guide fiber, and this image is enlarged by the eyepiece optical system. ing.

However, in many cases, this image is observed not only visually but also on a monitor. In this case,
This is achieved by attaching a television camera having a built-in solid-state imaging device typified by a so-called CCD or the like to the fiberscope eyepiece.

The configuration of such an endoscope imaging apparatus will be described with reference to FIG. The observation system of the fiberscope 1 is
The image transmission system includes an image guide fiber 2, an objective lens 5 disposed at the distal end, a field mask 3 disposed on an eyepiece 7, and an eyepiece 6. The visual field mask 3 is usually provided with an index such as a notch as a mark so that the vertical direction of the observation image can be recognized. A television camera 15 attached to the eyepiece 7 of the fiberscope 1 has a built-in imaging lens 10, a low-pass filter 11, and a solid-state imaging device 12.

When such a fiberscope 1 is used, illumination light transmitted by a light source and a light guide fiber (not shown) irradiates an object M, and this object image is formed on an end surface of the image guide fiber 2 by an objective lens 5. This image is transmitted to the other end of the image guide fiber 2. Then, an image is formed on the solid-state imaging device 12 through the eyepiece 6, the imaging lens 10 in the television camera, and the low-pass filter 11, signal processing is performed through the camera control unit 13, and an external display device such as a television monitor 14 is projected as an image.

FIG. 2 shows an example of a configuration in which an eyepiece is not arranged in the fiberscope 1. In this example, an image formed by the image guide fiber 2 is formed directly on the solid-state imaging device 12 by the imaging lens 9 provided on the television camera 15 side.

The image transmitted by the image guide fiber 2 onto the solid-state image sensor 12 has the following characteristics.

FIG. 3A shows an end face of the image guide fiber 2 having a hexagonal close-packed structure. In the figure, reference numeral 2a denotes a core of an optical fiber constituting the image guide fiber 2, and 2b denotes a clad. Arrow A indicates the direction in which the image guide fibers 2 are stacked. Also, FIG.
The solid-state imaging device 12 has a three-dimensional array, and an arrow B indicates the horizontal scanning direction.

When the end face image of the image guide fiber 2 is picked up by such a solid-state image pickup device 12, if the fiber interval P _f of the image guide fiber 2 and the imaging magnification β are:
Has a very strong first-order spatial frequency spectrum ν _sc ,
_sc = 1 / (P _f × β × sin 60 °) Here, the imaging magnification β indicates the magnification of the entire optical system between the end surface of the image guide fiber 2 and the solid-state imaging device 12.

If the stacking direction of the image guide fibers 2 is taken on the horizontal axis, this frequency spectrum exists in six directions on a two-dimensional frequency space as shown in FIG. Each frequency spectrum has a structure in which an angle of 60 ° is sequentially formed.

When a solid-state image sensor is used to spatially discretely sample an image of an object, if the object image contains a high-frequency component equal to or higher than the Nyquist limit of the solid-state image sensor, the high-frequency component is sampled. A false signal called moiré or the like occurs due to the beat with the frequency. When this moiré occurs, the original object image becomes difficult to see.

Hereinafter, a CCD will be specifically described as an example of the solid-state imaging device. As a CCD, the horizontal pixel pitch is P _x , the vertical pixel pitch is _Py, and G
(Green), Cy (cyan), Mg (magenta), Y
Consider a complementary color mosaic type in which each color filter of e (yellow) is arranged in a checkered pattern as shown in FIG. 5 and an image signal is created by simultaneous reading of two pixels and two lines. Then, on the two-dimensional spatial frequency plane as shown in FIG. 6, the coordinates (1 / 2P _x , 0), (− ／)
_{P x, 0), (1} / 2P x, 1 / 4P y), (- 1/2
P _x ,-／ P _y ), (１ ／ P _x ,-／ P _y )
_{(-1 / 2P x, 1 /} 4P y) to the sampling point occurs. Such sampling points vary depending not only on the pixel pitch but also on the configuration and arrangement of the color filters, the signal reading method, and the like. If there is an image containing a frequency spectrum near these sampling points, strong moiré will occur. FIG.
In FIG. 7 and in FIG. 7, the sampling point is indicated by a large double circle. However, even if the position of the frequency spectrum of the image guide fiber is slightly away from the sampling point, if it is within this circle, This conceptually indicates that moiré occurs and, in that case, the level of moiré is relatively strong.

In the following figures, only the positions of the sampling points are shown.

[0015] Using such a solid-state imaging device, when a photographic image guide fiber image as described above, as an example, is represented as two-dimensional frequency characteristic f _F as shown in FIG. 7. Normally, the relationship between the arrangement direction of the image guide fibers and the pixel arrangement direction of the CCD is often as shown in the figure. Further, since the image guide fiber has a regular structure and its frequency spectrum is often close to the sampling point, moire is very likely to occur.

If only a specific fiberscope is used, one frequency spectrum is determined. However, since the fiber spacing and the eyepiece magnification of the image guide fiber differ depending on the type of fiberscope, various frequency values are set for each fiberscope. Take. Therefore, even if the same television camera is used, the frequency spectrum of the image guide fiber has a certain width.

Furthermore, even when a plurality of television cameras having different imaging magnifications are used, or when the imaging lens is a zoom lens, the frequency of the image guide fiber often takes various values, as shown in FIG. Has a certain frequency width in the major axis direction of the ellipse. Note that the direction is a direction indicated by an arrow in FIG. 4 and is a fixed direction as described above. The ellipse indicated by f _F in FIG. 7 is an example of the frequency band, and is shown as a two-dimensional frequency characteristic f _F.

Also, in the following figures, the frequency by the image guide fiber is given a width for such a reason.

When moire occurs, the image becomes very difficult to see, so it is necessary to remove the moire.
For this purpose, conventionally, a frequency spectrum near a sampling point due to the occurrence of moiré is attenuated by using an optical low-pass filter including a birefringent plate such as a quartz filter.

However, if the moiré is sufficiently removed, the low-pass characteristics are strengthened by increasing the number of low-pass filters, for example, so that the image is blurred and the image quality is deteriorated. In particular, as the pixel pitch of the CCD becomes smaller and the resolution becomes higher, the effect of the low-pass characteristic on the image becomes very large. Conversely, if moire removal is insufficient, it is difficult to perform moire removal at a delicate level, for example, an image that is very difficult to see due to moire. Furthermore, since a space for arranging a crystal filter or the like is required, the number of components or the like may be limited. In addition, if a sufficient space is taken, the entire apparatus becomes large, which is not preferable.

Therefore, there is a case where moire is removed in combination with a method other than an optical low-pass filter such as a quartz filter. One of them is to shift the relative position between the regular arrangement of the image guide fiber images and the basic arrangement of the solid-state imaging device by a predetermined amount. As previously mentioned,
Normally, the image guide fiber has a regular structure, and its frequency spectrum is often close to the sampling point of the CCD, so that moire is very likely to occur. Therefore, for example, the positional relationship is shifted as shown in FIG.
Moire can be reduced by separating the spatial spectrum f _F of the image guide fiber and the sampling point in the frequency space.

Conventionally, for example, with a fiberscope attached to a television camera, via a mechanical connection,
The fiberscope itself or the television camera itself was being rotated. However, in this case, every time the fiberscope is attached, it is necessary to adjust the rotation direction of the fiberscope or the television camera while watching the image, which is troublesome and very troublesome. Furthermore, the lighting system of the fiberscope, the cables of the television camera, and the like often protrude from the side or oblique direction of the fiberscope, and depending on the direction, the operation may be hindered.

Therefore, as described above, the same effect can be obtained by displacing the positional relationship in advance, instead of rotating the object directly at the time of observation, as described above.
No. 4 and Japanese Patent Application Laid-Open No. H6-254044 have been proposed.

Japanese Patent Application Laid-Open No. 6-254444 discloses an image guide fiber used in a fiberscope in which the stacking direction of the image guide fiber is inclined by ± 15 ° with respect to the index of the scope mask. At the time of combination, the positional relationship rotates ± 15 ° relative to the normal case. In this case, unless the system is limited to the types and combinations of fiberscopes, for example, another fiberscope that does not tilt the conventional image guide fiber for a TV camera optimized for such a fiberscope In such a case, moire cannot be removed with the combination with the fiberscope, and the television camera cannot be used. As a user, it is necessary to purchase a dedicated fiberscope besides the television camera, which imposes a heavy burden on cost and storage space. Of course, a television camera that can be used successfully even when combined with such another fiberscope can be used, but this eliminates the need to change the stacking direction of the image guide fibers of the fiberscope.

Further, as described above, the appearance of moire naturally changes depending on the relationship between the sampling points of the CCD and the frequency spectrum of the image guide fiber array. However, in the prior art, since the basic arrangement of the solid-state imaging device and the regular stacking direction of the image guide fibers are set to a fixed angle of ± 15 °,
In this case, it is hard to say that the optimization has been performed in various cases, and it cannot be said that moiré has been sufficiently removed in terms of performance. Further, in general, since the sampling point of the CCD and the frequency spectrum of the image guide fiber array are close to each other and moiré is easily generated, it is practical to remove moiré only by such a rotation effect without an optical low-pass filter. difficult.

Japanese Patent Application Laid-Open No. 6-86754 discloses a stacking direction of image guide fibers in order to optimize moire caused by a color subcarrier frequency of a composite signal existing near the frequency spectrum of the image guide fibers. Alternatively, it is shown that the CCD is inclined by 30 °. In recent years, with the reduction in the size of the CCD pixel, a finer image has been obtained.
There are many signal input methods to the external display device, such as RGB input and Y / C component input, and the color subcarrier frequency is not much of a problem. As described above, the moiré removal at the sampling point is not optimized, and even if this is applied, the moiré cannot be removed.

As described above, in the prior art, the general C
It was not known how to set the angle to remove moiré generated in relation to the CD sampling point.

[0028]

As described above, as described above,
In the prior art, it is not clear how much the positional relationship between them and the rotation should be changed in consideration of the specifications of the used fiberscope, television camera or CCD. For this reason, even in combination with various fiberscopes, it has not been possible to provide an image pickup apparatus that can remove moire well and can always obtain high-quality images.

The present invention has been made in view of these problems of the prior art,
Considering the specifications of various fiberscopes, TV cameras and CCDs, that is, the frequency spectrum of the image guide fiber and the sampling points of the CCD, etc., by giving a relative positional relationship that reduces the influence of moiré, the performance is always good. It is an object to provide an imaging device capable of obtaining an image.

[0030]

An image pickup apparatus according to the present invention for achieving the above object forms an image spatially constituted by a plurality of discrete points on a solid-state image sensor, and obtains the image by the solid-state image sensor. An image display device for displaying an image displayed on an external display device, wherein a relative position between the regular arrangement of the images and the basic arrangement of the solid-state imaging device is shifted by a predetermined amount.

Hereinafter, the imaging apparatus of the present invention will be described. As conceptually shown in FIG. 12, the image pickup apparatus of the present invention comprises a CCD 12 or C
By rotating the CD part by a certain angle with respect to the stacking direction of the image guide fibers 2, an optimum relative positional relationship between the pixel array of the CCD 12 and the regular stacking direction of the image guide fibers 2 is given. It is said to reduce.

This will be described in detail below. As shown in FIG. 7, since the sampling point of the CCD 12 and the frequency spectrum of the image guide fiber 2 are very close to each other, moire tends to occur. On the other hand, the direction of the frequency spectrum by the image guide fiber 2 exists only in a certain direction with respect to the stacking direction of the image guide fiber 2. Therefore, if the sampling points and the frequency spectrum of the image guide fiber 2 are discrete in the frequency space, the occurrence of moire can be reduced.

Therefore, in the following, for clarity,
The sampling point of the CCD 12 is fixed as a coordinate reference, and the first quadrant and the fourth quadrant will be described in detail in consideration of the symmetry in the two-dimensional frequency space. Note that (0, １ ／ P _y ), (0,-／ P _y )
Although there are other sampling points, these are not considered here because they are slightly discrete in frequency from the frequency spectrum of the image guide fiber 2.

Therefore, the stacking direction A of the image guide fibers 2 is rotated counterclockwise with respect to the CCD array B by a rotation angle α as shown in FIG. 8 to shift the relative positional relationship. Then, the frequency spectrum of the image guide fiber in the first quadrant deviates from the sampling point of (1 / 2Px, 1 / 4Py). On the other hand, if the frequency spectrum of the image guide fiber in the fourth quadrant is given a certain rotation angle, (1 / 2P _x , 0)
Approaching the sampling point, but (1 /
2P _x , − ／ P _y ).

That is, in the first state, the frequency spectrum of the image guide fiber is (１ ／ P _x , １ ／).
Although moiré occurred due to the influence of the sampling points of (P _y ) and (１ ／ P _x , − ／ P _y ), after rotation, (モ ア P _x , ４P _y ) and ( 1/2
By dispersing from the sampling point of (P _x , − ／ P _y ), it is difficult to receive these effects, and the moiré level can be suppressed. Conversely, (1 / 2P _x , 0)
Is more susceptible to the influence of the sampling point, but if the frequency is discrete as in other cases, the influence can be relatively reduced.

Although the frequency in the direction of the ν _y axis originally approaches the sampling point in the oblique direction such as (xP _x , ／ P _y ), the frequency is sufficiently discrete compared with the others. And there is not much impact.

Further, it is needless to say that the second and third quadrants can be similarly considered.

Next, (1 / 2P _x , 1 / 4P _y ), (1
/ 2P _x, 0) and (1 / 2P _x, the frequency relationship between the frequency spectrum of each sampling point and the image guide fiber -1 / 4P _y) will be described.

Assuming that the fiber spacing P _f of the image guide fiber and the imaging magnification β are, the frequency spectrum ν _sc of the image guide fiber is ν _sc = 1 / (P _f × β × s
in 60 °).

First, the frequency spectrum in the first quadrant
P and (1 / 2P_x, 1 / 4P_y), (1 / 2P_x, 0)
The spatial frequency difference L between each sampling point
Confuse. (1 / 2P_x, 1 / 4P_y) Sampling poi
Frequency difference L ₁Is represented by the following equation.

[0041] _{^{L 1 2 = ν x 2 +}} ν y 2 + ν sc 2 -2
ν _sc (ν _x cosA + ν _y sinA) The spatial frequency difference L _{2 at} the sampling point of (の P _x , 0) is expressed by the following equation.

[0042] _{^{L 2 2 = ν x 2 +}} ν sc 2 -2ν x ν sc cosA Similarly, the frequency spectrum Q in the fourth quadrant (1 /
2P _x, 0), we obtain a spatial frequency differences L between the sampling points of _{(1 / 2P x, -1 /} 4P y). (1
/ 2P _x, 0 spatial frequency difference L ₃ at a sampling point) is expressed by the following equation.

[0043] The _{^{L 3 2 = ν x 2 +}} ν sc 2 -2ν x ν sc cosB, (1 / 2P x, -1 / 4P y) spatial frequency difference L ₄ at the sampling point is expressed by the following equation.

[0044] _{^{L 4 2 = ν x 2 +}} ν y 2 + ν sc 2 -2
ν _sc (ν _x cosB + ν _y sinB) where ν _x = １ ／ P _x , ν _y １ ／ P _y , A = 3
0 + α, B = 30−α.

Therefore, it is necessary to determine the rotation angle α so that each value becomes sufficiently large under the above conditions 1 to 5. That is, it is necessary to determine the rotation angle α such that the minimum value is the largest value among the values.

Next, the angle φ _CCD of the sampling point in the oblique direction with respect to the ν _x direction in the horizontal axis direction in the two-dimensional frequency space is as follows.

[0047] φ_CCD= Tan^-1(Ν_y/ Ν_xNote that the frequency of the sampling point in the oblique direction is ν
_CCDThen ν_x= V _CCDcosφ_CCD, Ν_y= V
_CCDsinφ_CCD, Ν_CCD ^Two= V_x ^Two+ Ν_y ^TwoBecomes

The relationship between the frequency spectrum of the image guide fiber and the sampling point can be considered in several cases depending on the angle of φ _CCD . The frequency spectrum is set for one specific condition, but has a certain width in the following description and the drawings.

(1) φ_CCD<30 ° In consideration of FIG. 9, (1 / 2P_x, 1 / 4P_y)
And (1 / 2P_x, 0)
The number spectrum P is far apart. (1 / 2P_x, −
1 / 4P_y) Frequency spectrum at sampling point
Le Q leaves after approaching, (1 / 2P_x, 0)
Approaching the sampling point. For this reason,
The wave number spectrum Q is (1 / 2P_x,-1 / 4P_y),
(1 / 2P _x, 0) from each sampling point
It is necessary that they are equal as the inter-frequency difference. In other words, before
= In the conditional expression, that is, L_Three ^Two
= L _Four ^TwoIt is necessary to be. By this conditional expression
When the roll angle α is obtained, ν_y(Ν_y-2ν_scsinB) =
0 and ν_ySince ≠ 0, ν_y-2ν_scsinB = 0
It is. Also, since B = 30−α, α = 30−sin^-1(Ν_y/ 2ν_sc).

(2) When φ _CCD = 30 ° Considering as shown in FIG. 10, the frequency spectrum P is far away from the sampling point of (１ ／ P _x , 0). The frequency spectrum P from the sampling point _{(1 / 2P x, 1 /} 4P y) moves away. Further, the frequency spectrum Q moves away from the sampling point of (1 / 2P _x ,-／ P _y ),
(P _x , 0). Therefore, the frequency spectrum Q is (1 / 2P _x, -1 /
4P _y ) and (１ ／ P _x , 0) need to be equal as the spatial frequency difference from each sampling point.

In this case, (1 / 2P _x , １ ／)
P _y ) from the sampling point
Spatial frequency difference in the _{(1 / 2P x, -1 /} 4P y)
The spatial frequency difference in the frequency spectrum Q from the sampling point is also equal.

That is, in the above conditional expression, ==
L₁ ^Two= L_Three ^Two= L_Four ^TwoMust be
become.

[0053] Here, L ₃ ² = L ₄ when obtaining the rotation angle α from the ^{second _{condition, ν y 2 -2ν sc ν y}} sinB = 0 _{becomes, ν y (ν y -2ν sc} sinB) = 0, Since ν _y ≠ 0, ν _y -2ν _sc sinB = 0. Also, B = 3
Since 0-α, α = 30−sin ⁻¹ (ν _y / 2ν _sc ), which is the same as the conditional expression.

(3) When φ _CCD > 30 ° Considering as shown in FIG. 11, the frequency spectrum P is far away from the sampling point of (ポ イ ン ト P _x , 0). Further, the frequency spectrum Q moves away from the sampling point of (1 / 2P _x , − ／ P _y ). However, the frequency spectrum P moves away after approaching the sampling point of (1 / 2P _x , 1 / 4P _y ), and the frequency spectrum Q approaches the sampling point of (1 / 2P _x , 0). These become problems in relation to the sampling point.

Therefore, in order for each frequency spectrum to be discrete from each sampling point most mutually in this contradictory relationship, it is necessary to set = in the above conditional expression. In other words, it spatial frequency difference each other are equal, it is required to be L ₁ ² = L ₃ ^2. When the rotation angle α is determined by this conditional expression, ν _y ² −2ν _sc (ν
_x cosA + v _y sinA−v _x cos B) = 0, and considering A = 30 + α and B = 30−α, v _sc (2ν _x −√3ν _y ) sin α−ν _sc v _y co
sα + ν _y ² = 0. A rotation angle α that satisfies this equation may be obtained.

It should be noted that the rotation direction may be either clockwise or counterclockwise since the same concept can be applied.

As described above, from the relationship between the frequency spectrum of the image guide fiber and the sampling point of the solid-state image pickup device such as a CCD, the relative frequency spectrum of the image guide fiber and the sampling point are set to be less affected by the sampling point. The positional relationship can be clarified. That is, it is possible to clarify how much the relative positional relationship between the stacking direction of the image guide fibers and the arrangement of the CCDs, that is, how much to rotate, can reduce the influence of moiré.

[0058]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an imaging apparatus according to the present invention will be described based on embodiments.
(Example 1) CCD pixel pitch is set to P_x= 4.0 [μ
m], P_y= 4.0 [μm], ν_x= 1 / 2P
_x= 125.0 [books / mm], ν_y= 1 / 4P_y= 6
2.5 [lines / mm]
Int angle φ_CCDIs φ_CCD= Tan^-1(Ν_y/ Ν_x)
= Tan^-1(62.5 / 125.0) = 26.6 [°]
Becomes Also, the frequency of the sampling point in the oblique direction
Number ν_CCDIs ν_CCD= √ (ν_x ^Two+ Ν_y ^Two) = 139.8
[Book / mm].

Here, assuming that each fiber scope has, for example, 124 [lines / mm] and 97 [lines / mm] as the frequency spectrum ν _sc of the image guide fiber, φ _CCD <30 °. When the rotation angle α is obtained from the calculation formula, when ν _sc = 124 [lines / mm], α = 30−sin ⁻¹
(62.5 / 2 x 124) = 15.40 [°] When ν _sc = 97 [lines / mm], α = 30-sin
⁻¹ (62.5 / 2 × 97) = 11.21 [°].

As described above, since various rotation angles are taken in accordance with the value of the frequency spectrum ν _sc of the image guide fiber, it is sufficient if the rotation angle can be finely adjusted for each type of the fiber scope, but it is desired to fix the rotation angle to a constant angle. By the way. For this purpose, it is necessary to determine the final angle from the overall balance while observing the moire level for each fiberscope to be used. For simplicity, it is preferable to calculate the average value of the whole and determine the angle while observing the moiré level within a range of about ± 5 ° around the average value. The average rotation angle α ′ in the above case is α ′ = 13.31 [°].

However, if there is another different frequency spectrum, this average value also changes. Also,
It is not always necessary to perform averaging, and it may be set so as to optimize for a specific frequency spectrum.

(Embodiment 2) When the CCD pixel pitch is P _x =
Assuming that 4.0 [μm] and P _y = 3.464 [μm],
ν _x = １ ／ P _x = 125.0 [lines / mm], ν _y = 1
/ 4P _y = 72.2 [lines / mm], and the angle φ _CCD of the oblique sampling point is φ _CCD = tan
⁻¹ (ν _y / ν _x ) = tan ⁻¹ (72.2 / 125.0)
= 30.0 [°]. The frequency ν _CCD of the sampling point in the oblique direction is ν _CCD = _CCD (ν _x ² + ν _y
² ) = 144.3 [lines / mm].

Here, assuming that the frequency spectrum ν _sc of the image guide fiber is, for example, 124 [lines / mm] and 97 [lines / mm], φ _CCD = 30 °. When the rotation angle α is obtained from the calculation formula, when ν _sc = 124 [lines / mm], α = 13.007
[°] When ν _sc = 97 [lines / mm], α = 8.15 [°]. The average rotation angle α ′ is α ′ = 1.61
[°].

(Embodiment 3) When the CCD pixel pitch is P_x=
3.8 [μm], P_y= 2.7 [μm], ν_x
= 1 / 2P_x= 131.6 [lines / mm], ν_y= 1/4
P_y= 92.6 [lines / mm], and a diagonal sump
Ring point angle φ_CCDIs φ_CCD= Tan^-1(Ν_y
/ Ν_x) = Tan^-1(92.6 / 131.6) = 35.
1 [°]. Also, the sampling point in the oblique direction
Frequency ν_CCDIs ν_CCD= √ (ν_x ^Two+ Ν_y ^Two) = 1
60.9 lines / mm.

Here, assuming that each fiber scope has a frequency spectrum ν _sc of, for example, 124 [lines / mm] and 97 [lines / mm], φ _CCD > 30 °. When the rotation angle α is obtained from the calculation formula, when ν _sc = 124 [lines / mm], α = 12.33
[°] When ν _sc = 97 [lines / mm], α = 2.30 [°]. The average rotation angle α ′ is α ′ = 7.17
[°].

For example, in the first embodiment, the image guide
Frequency spectrum of fiber _sc= 300 [books / m
m], α = 30−sin^-1(62.5 / 2 ×
300) = 24.02 [°], and the rotation angle is considerably large.
growing. However, originally the frequency of the sampling point
Number and the frequency spectrum of the image guide fiber
They are far apart in frequency.

In this case, the frequency spectrum of the image guide fiber is 2.1 times the frequency of the sampling point in the oblique direction and 2.4 times the frequency of the sampling point in the horizontal direction. In such a case, if only the rotation is used as the moiré removing means, aliasing distortion occurs at a frequency that is an integral multiple of the original sampling point, which is affected.
If an optical low-pass filter or the like using a crystal filter is formed, the influence in such a high frequency range can be reduced, and the influence of moire from a low frequency point is reduced, so that it is not necessary to take a sufficient rotation angle. Usually, when the frequency spectrum of the image guide fiber includes a frequency band of about 0.5 to 1.5 times the frequency of the sampling point, it is effective to rotate the image guide fiber.

However, even in such a case, the rotation angle is 2 degrees.
In some cases, the index of the field mask 3 of the fiberscope rotates as shown in FIGS. 13A and 13B depending on the difference in the rotation angle direction, and the index shifts from the vertical direction of the monitor. There is not much problem if the angle is small,
If the angle is large, the operation may be slightly more difficult than in a normal case. The same applies to the case where such a visual field mask is not provided, for example, in the case of an ultrafine system having an image guide fiber diameter of about φ0.5 mm or less.

For this reason, if the rotation angle is up to about 17 °, there is not much problem in practical use. However, the visual impression of the monitor image is not so good, and it is desired that the angle be smaller than 15 ° if possible. However, it is not always possible to set such an angle, and from this point, it is necessary to use a moiré removing means other than rotation.

Next, a case where the optical low-pass filter is used in combination with the rotation described above will be described.

(Embodiment 4) FIG. 14 (a) shows this case.
The characteristics in the two-dimensional frequency space will be described. CCD pixel
Switch P_x= 5.0 [μm], P_y= 5.0 [μm]
Then, ν_x= 1 / 2P_x= 100.0 [books / mm],
ν_y= 1 / 4P_y= 50.0 [lines / mm]
Angle of sampling point in direction φ_CCDIs φ_CCD= T
an^-1(Ν _y/ Ν_x) = Tan^-1(50.0 / 100.
0) = 26.6 [°]. Also, the diagonal sump
Ring point frequency ν_CCDIs ν_CCD= √ (ν_x ^Two
+ Ν _y ^Two) = 111.8 [lines / mm].

Here, assuming that each fiber scope has, for example, 124 lines / mm and 97 lines / mm as the frequency spectrum ν _sc of the image guide fiber, φ _CCD <30 °. When the rotation angle α is obtained from the calculation formula, when ν _sc = 124 [lines / mm], α = 18.37
[°] When ν _sc = 97 [lines / mm], α = 15.06 [°]. Further, the average rotation angle α ′ = 16.72 [°].

Here, as shown in FIG. 14B, an optical low-pass filter composed of a single crystal filter 16 is arranged in the image pickup apparatus, and the characteristic in the two-dimensional frequency space shown in FIG. As is clear from FIG. 1, one trap line passes near each sampling point. As a result, the response at each sampling point decreases, so that the influence of moire can be reduced,
The rotation angle is as small as about 13 °.

The crystal filter 16 has a crystal axis direction of 0 ° with respect to the horizontal scanning direction of the CCD, and a thickness of 0.85 mm.

In the following, arrows indicating the crystal axis direction of the crystal filter in the figure are provided at both ends, which indicates that either direction may be used.

(Embodiment 5) This is also a CCD sampler.
Point and image guide fiber frequency spec
The torque is the same as in the fourth embodiment. However, FIG.
(B) As shown in FIG.₁, 16
_TwoOptical low-pass fill composed of λ / 4 plate 17 and λ / 4 plate 17
In which an imager is arranged in an imaging device. In this case, the figure
It is clear from the characteristics in the two-dimensional frequency space of FIG.
In particular, (1 / 2P_x, 1 / 4P _y), (1/2)
P_x,-1 / 4P_y) Oblique sampling points
Two trap lines pass near the gate.

When the response in the vicinity of the sampling point in the oblique direction is reduced as described above, the influence of moire on the point is reduced, so that it is not necessary to increase the rotation angle and the spatial frequency difference. Therefore, even when the rotation angle is smaller than the above calculated value and the frequency spectrum of the image guide fiber is close to the oblique sampling point, the effect of moiré can be at a level that does not cause a practical problem. For this reason, the rotation angle is about 10 °
And not too much rotation.

The crystal filters 16 ₁ and 16 ₂ are C
The crystal axis directions are each 0 ° with respect to the CD horizontal scanning direction,
The λ / 4 plate 17 is interposed between the 90 ° configuration.

The thicknesses of the quartz filters 16 ₁ and 16 ₂ were sequentially set to about 0.85 mm and 1.7 mm. The order of arrangement may be reversed.

(Embodiment 6) This is also the same as Embodiment 5, but as shown in FIG. 16B, two crystal filters 16 ₁ and 16 ₂ whose crystal axis directions are at 45 ° to each other. An optical low-pass filter consisting of: is disposed in an imaging device. In this case as well, as is clear from the characteristics in the two-dimensional frequency space of FIG. 16A, since two trap lines pass near the sampling point in the oblique direction, the response near the sampling point in the oblique direction is reduced. The rotation angle is reduced to about 10 °.

The quartz filters 16 ₁ and 16 ₂ are C
Each crystal axis direction is ± 2 with respect to the horizontal scanning direction of CD.
It has a 45 ° configuration of 2.5 °.

The thickness of each of the quartz filters 16 ₁ and 16 ₂ was 0.92 mm. The order of arrangement may be reversed.

(Embodiment 7) This is also the same as Embodiment 6, but as shown in FIG. 17 (b), the crystal filters 16 ₁ and 16 ₁ whose crystal axis directions are successively at 45 ° to each other.
_2, 16 ₃ of the optical low-pass filter consisting of three in which was placed in an imaging device. Also in this case, FIG.
As is clear from the characteristics in the two-dimensional frequency space of (a), since two trap lines pass near the sampling point in the oblique direction, the response near the sampling point in the oblique direction is reduced, and the rotation angle is reduced. It is as small as 10 °.

The crystal filters 16 ₁ , 16 ₂ , 16
No. ₃ has a 45 ° configuration in which the crystal axis directions are respectively 75 °, 60 °, and 15 ° with respect to the horizontal scanning direction of the CCD.

The crystal filters 16 ₁ , 16 ₂ , 1
6 ₃ thickness was constructed sequentially 1.1 mm, 1 mm, as 1 mm. The order of arrangement may be reversed.

Thus, (（P _x ,)
P _y ) and (レ ス ポ ン ス P _x ,-／ P _y ) reduce the response at oblique sampling points.
Because the effect of moiré on this point is reduced,
It is not necessary to increase the rotation angle and the spatial frequency difference. Therefore, the rotation angle can be made smaller than the above calculated value, and even when the frequency spectrum of the image guide fiber is close to the oblique sampling point, the effect of moiré can be made to a level that does not cause a practical problem.

For this purpose, it is preferable that a trap line formed by at least two quartz filters passes near these sampling points. In this case, when the oblique direction of the sampling frequency by the image sensor and [nu _CCD, it is desirable to configure a trap lines within around this frequency of 0.3Nyu _CCD passes. But,
Because if configured by the plurality of trap lines frequency response is reduced by the synergistic effect, 0.4ν _CCD
If there is a trap line within the range, it is practically applicable.

However, if the number of surplus trap lines increases, a blurred image having reduced resolving power is obtained. Therefore, there is a relationship with the rotation angle, and the resolving power is not reduced as much as possible without increasing the number of constituent crystal filters. It is necessary. In particular, when using a high-resolution solid-state imaging device with a small pixel pitch, if moiré is removed using only an optical low-pass filter, the image will be blurred and deteriorated, and high resolution cannot be used. Since it does not decrease, when used in combination, a very large effect can be obtained without deteriorating the image.

Although the optical low-pass filter using the quartz filter and the moiré removal by the rotation of the CCD have been described above, it may be used together with the defocusing performed by moving the imaging lens or the CCD. If the defocus amount can be adjusted, the moire level can be finely adjusted, which is very convenient.

The image is not limited to the image guide fiber, but is also useful when a display screen such as a monitor having a regular discrete structure such as a cathode ray tube or a liquid crystal display device is photographed by a solid-state image sensor such as a CCD. . In such a case, the frequency band corresponding to the frequency spectrum of the image guide fiber does not have much width, so that a more optimal rotation angle can be configured. The present invention is not limited to this, and it is needless to say that, when a discrete image is captured by the solid-state imaging device, the present invention effectively works as moiré removal.

The observation unit using the image guide fiber and the television camera do not need to be separate from each other, and may be an integrated imaging device in which the observation unit using the image guide fiber and the television camera are integrally formed. Absent. The fiberscope may be of any form as long as it uses an image guide fiber, and may be a flexible endoscope or a rigid endoscope.

The configuration of the mosaic filter of the CCD is not limited to the complementary color type as in the present invention.
A primary color type composed of three colors of G (green) and B (blue) may be used. Further, other solid-state imaging devices other than the CCD may be used. However, if the configuration of the solid-state imaging device, the way of signal processing, and the like are different, the sampling point at which moire occurs varies, but it goes without saying that the same can be applied based on the concept of the present invention.

The above-described imaging apparatus of the present invention can be configured, for example, as follows: [1] An image composed of a plurality of spatially discrete points is formed on a solid-state imaging device, and In an imaging device configured to display an image obtained by an imaging device on an external display device, a relative position between a regular array of the images and a basic array of the solid-state imaging device is shifted by a predetermined amount. Imaging device.

[2] In an image pickup apparatus in which an image formed spatially by a plurality of discrete points is formed on a solid-state image pickup device, and an image obtained by the solid-state image pickup device is displayed on an external display device. A regular arrangement of the images and a basic arrangement of the solid-state imaging device such that a frequency spectrum of the discrete image generated on the solid-state imaging device in a two-dimensional frequency space is discrete from a sampling point generated by the solid-state imaging device An imaging apparatus characterized in that the relative position of the imaging device is shifted by a rotation angle α.

[3] The above in a two-dimensional frequency space
Sampling in the oblique direction to the horizontal scanning direction of the solid-state image sensor
Angle φ between ring points_CCDIs φ_CCD> 30 °
When ν_sc(2ν_x−√3ν_y) Sinα-ν_scν_yc
osα + ν_y ^Two= 0 that the rotation angle α satisfies
The imaging device according to the above [2], which is characterized in that: Where ν _xIs
At the sampling point in the oblique direction of the solid-state imaging device
Horizontal frequency component, ν_yIs the vertical frequency
Component, ν_scIs the frequency spectrum of the discrete image.

[0096] [4] the solid angle phi _CCD in an oblique direction of the sampling points with respect to the horizontal scanning direction of the imaging device on a two-dimensional frequency space, when _{φ CCD ≦ 30 °, α =} 30-sin -1 (ν _y / 2ν _sc ), wherein the rotation angle α satisfies the condition [2]. Here, ν _x is a frequency component in a horizontal direction with respect to a sampling point in an oblique direction of the solid-state imaging device,
ν _y is the frequency component in the vertical direction, and ν _sc is the frequency spectrum of the discrete image.

[5] In an image pickup apparatus in which an image formed spatially by a plurality of discrete points is formed on a solid-state image pickup device, and an image obtained by the solid-state image pickup device is displayed on an external display device. Reducing the frequency response near the sampling point of the solid-state imaging device by an optical low-pass filter provided in the imaging device, and the relative position between the regular arrangement of the images and the basic arrangement of the solid-state imaging device An imaging device characterized in that is shifted by a rotation angle α.

[6] The imaging apparatus according to the above [5], wherein the rotation angle α is smaller than 15 °.

[7] A birefringent plate is used as the optical low-pass filter, and at least two trap lines pass near the oblique sampling point of the solid-state imaging device. 5] or the imaging device according to [6].

[0100] [8] wherein when the diagonal sampling frequency is [nu _CCD by the solid-state imaging device, above, characterized in that configured to pass trap lines within the center 0.4Nyu _CCD this frequency [7] The imaging device according to the above.

[0101]

[9] The method according to any of [2] to [7], wherein the frequency spectrum of the discrete image is included in the range of 0.5 to 1.5 times the frequency with respect to the plurality of sampling points. The imaging device according to claim 1.

[10] The method according to [2], wherein the discrete image has a hexagonal close-packed structure using image guide fibers.

The imaging device according to any one of [9].

[11] Assuming that the fiber spacing P _{f of} the image guide fiber and the imaging magnification β of the entire optical system interposed between the end surface of the image guide fiber and the solid-state image sensor,
The frequency spectrum ν _sc becomes ν _sc = 1 / (P _f × β × s
(10 °), which is a primary frequency spectrum represented by (in 60 °).

[12] The rotation angle α is an angle between the horizontal scanning direction of the solid-state imaging device and the stacking direction of the image guide fibers with respect to the horizontal scanning direction. An imaging device according to any one of the preceding claims.

[13] The solid-state imaging device is a mosaic type CCD in which complementary color filters are respectively arranged on the entire surface of the light receiving section, and the horizontal pixel pitch of the solid-state imaging device is P _x and the vertical pixel pitch is P _y . Then, the sampling point in the oblique direction by the solid-state imaging device is 2
On dimensional frequency space _{(1 / 2P x, 1 /} 4P y), (-
_{1 / 2P x, -1 / 4P} y), (1 / 2P x, -1 / 4
The imaging device according to any one of the above [2] to [12], wherein the imaging device is represented by (P _y ) and (− ／ P _x , ４P _y ).

[0106]

As is apparent from the above description, various fiberscopes, television cameras, and C
The use of a CD, that is, a relative positional relationship in which the influence of moire is reduced in consideration of the frequency spectrum of the image guide fiber, the sampling point of the CCD, and the like,
That is, since the rotation angle can be given, the effect of moire is small, and an image with high resolution and good performance can be obtained.

Further, in the present invention, since the solid-state image pickup device such as a CCD is rotated, an image having good performance can be obtained even in combination with various conventional fiberscopes.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of an endoscope imaging apparatus.

FIG. 2 is a diagram illustrating a configuration example of an endoscope imaging apparatus when an eyepiece is not arranged in a fiberscope.

FIG. 3 is a diagram for explaining an end face of an image guide fiber having a hexagonal close-packed structure and an arrangement of solid-state imaging devices in a two-dimensional arrangement.

FIG. 4 is a diagram showing the direction of the primary frequency spectrum of an image guide fiber in the case of a hexagonal close-packed structure.

FIG. 5 is a diagram showing an arrangement of color filters of a CCD.

FIG. 6 is a diagram showing sampling points of a CCD.

FIG. 7 is a diagram showing a sampling point of a CCD and a frequency spectrum of an image guide fiber.

FIG. 8 is a diagram for explaining shifting a positional relationship between a sampling point of a CCD and a frequency spectrum of an image guide fiber.

FIG. 9: φ is a sampling point in the oblique direction of the CCD
It is a figure for explaining the case of _CCD <30 degrees.

FIG. 10 is a diagram for explaining a case where the sampling point in the oblique direction of the _CCD is φ _CCD = 30 °.

FIG. 11 is a diagram for explaining a case where the sampling point in the oblique direction of the _CCD is φ _CCD > 30 °.

FIG. 12 is a diagram for explaining a relative positional relationship between a pixel array of CCDs and a regular stacking direction of image guide fibers in the imaging apparatus of the present invention.

FIG. 13 is a diagram showing how a field mask of a fiberscope on a monitor looks when a CCD is rotated.

FIG. 14 is a diagram for explaining characteristics in a two-dimensional frequency space and a configuration of an optical low-pass filter according to a fourth embodiment of the present invention.

FIG. 15 is a diagram for explaining characteristics in a two-dimensional frequency space and a configuration of an optical low-pass filter according to a fifth embodiment of the present invention.

FIG. 16 is a diagram for explaining characteristics in a two-dimensional frequency space and a configuration of an optical low-pass filter according to a sixth embodiment of the present invention.

FIG. 17 is a diagram for explaining characteristics in a two-dimensional frequency space and a configuration of an optical low-pass filter according to a seventh embodiment of the present invention.

[Explanation of symbols]

M ... Object 1 ... Fiberscope 2 ... Image guide fiber 3 ... Field mask 5 ... Objective lens 6 ... Eyepiece 7 ... Eyepiece 10 ... Imaging lens 11 ... Low pass filter 12 ... Solid state imaging device 13 ... Camera control unit 14 ... External display device 15 TV camera 16, 16 ₁ , 16 ₂ , 16 ₃ Quartz filter 17 λ / 4 plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4C061 AA00 BB02 CC07 DD03 FF02 FF46 JJ06 LL03 NN01 PP01 PP08 TT08 5C024 AA01 AA18 CA02 DA01 EA04 EA09 FA01 GA11 HA27 5C065 AA04 BB13 CC03 DD03 DD20 EE05 EE07

Claims (3)

[Claims] 1. An imaging apparatus configured to form an image spatially formed by a plurality of discrete points on a solid-state imaging device and to display an image obtained by the solid-state imaging device on an external display device. An image pickup apparatus, wherein a relative position between a regular arrangement of the images and a basic arrangement of the solid-state imaging device is shifted by a predetermined amount. 2. An image pickup apparatus wherein an image formed spatially by a plurality of discrete points is formed on a solid-state image pickup device, and an image obtained by the solid-state image pickup device is displayed on an external display device. The regular arrangement of the images and the basic arrangement of the solid-state imaging device so that the frequency spectrum of the discrete image generated on the solid-state imaging device on the two-dimensional frequency space is discrete from sampling points generated by the solid-state imaging device. The relative position of the rotation angle α
An imaging device characterized by being shifted. 3. An angle φ _CCD formed by a sampling point in a diagonal direction with respect to a horizontal scanning direction of the solid-state imaging device on a two-dimensional frequency space is φ _CCD > 30 °.
ν _sc (2ν _x −√3ν _y ) sinα−ν _sc ν _y cosα
3. The imaging apparatus according to claim 2, wherein the rotation angle α satisfies + ν _y ² = 0. Here, ν _x is a frequency component in a horizontal direction with respect to a sampling point in an oblique direction of the solid-state imaging device, ν _y is a frequency component in a vertical direction, ν
_sc is the frequency spectrum of the discrete image.