JP3078717B2 - Image input 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 image input apparatus, and more particularly to an image input apparatus for reducing moire of a read image so as not to affect reading quality.

[0002]

2. Description of the Related Art Conventionally, in an image input device using a CCD or other solid-state image pickup device, moire may be generated when a picture original or the like which shows gradation by halftone dots or the like is read like a printed matter. This moiré occurs when the original contains a pattern of a pattern with periodicity, and a new striped light and shade pattern that does not exist in the original is detected in a portion where the pattern is read. In order to suppress the occurrence of such moiré, a technique of disposing a light-transmitting plate on the optical path to generate defocus and reduce moiré is disclosed in Japanese Patent Application Laid-Open No. 61-269460.
No., published in Japanese Unexamined Patent Publication No.

[0003]

However, when the thickness of the light-transmitting plate for eliminating moiré becomes large, the space increases, and the arrangement and specifications of other optical components are restricted. It will be. In particular, in an image input apparatus of a movable optical system, a mirror is usually provided between the original and the imaging lens, and the mirror scans the original. There is a problem that space is restricted and the configuration of the device is complicated.
Further, when the thickness of the light transmitting member is increased, it is difficult to drive the light transmitting member quickly and accurately, which causes a problem that the cost is increased.

[0004] In addition, when the thickness of the light-transmitting member becomes large, the transmittance decreases and the effect of the inhomogeneity of the material increases, so that the optical performance of the device deteriorates. There is also.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image input apparatus having an optical system capable of easily and surely reducing moiré in a space-saving manner so as not to affect reading quality.

[0006]

According to a first aspect of the present invention, there is provided an image input apparatus for reading an image by projecting an image of a document onto an image sensor with an imaging lens. Depending on the magnification of the imaging lens, the thickness of the translucent member on the optical axis between the original and the imaging lens and on the optical axis between the imaging lens and the image sensor is increased.
A light- transmitting member for moiré elimination is arranged on one of the thinned members.

According to a second aspect of the present invention, the magnification of the imaging lens is (1-1 / (Ld + 1) when the required number of resolution lines on the document surface is L and the pupil diameter of the imaging lens is d. )) The light transmitting member is larger than ^1/2 , and the translucent member is arranged so as to be freely inserted and removed on the optical axis between the document and the imaging lens.

According to a third aspect of the present invention, the magnification of the imaging lens is (1-1 / (Ld + 1) when the required number of resolution lines on the document surface is L and the pupil diameter of the imaging lens is d. )) Characterized in that the light transmitting member is smaller than ^1/2 , and is disposed so as to be freely inserted and removed on the optical axis between the imaging lens and the image sensor.

According to a fourth aspect of the present invention, the imaging lens has a variable magnification, and the translucent member has a required number of resolution lines L on the original surface and a pupil diameter d of the imaging lens. The magnification of the imaging lens is (1-1 / (Ld + 1)) ^1/2
When the magnification is larger than (1-1 / (Ld +
1)) When it is smaller than ^1/2 , it is arranged on the optical axis between the imaging lens and the image sensor.

[0010]

[Action] In the image input device according to claim 1, of the optical axis between the document and the imaging lens in accordance with the magnification of the imaging lens, the optical axis between the imaging lens and the image sensor , Translucent part
Since the light-transmitting member for moiré elimination is arranged on one of the sides, which can reduce the thickness of the material, the thickness of the light-transmitting member for moiré elimination regardless of the magnification of the imaging lens Can be made thinner. As a result, the light-transmitting member can be accommodated in a small space, the driving of the light-transmitting member can be facilitated, and the cost of the light-transmitting member can be reduced.

In the image input device according to the second aspect, the magnification of the imaging lens is larger than (1-1 / (Ld + 1)) ^1/2 ,
Since the translucent member is removably disposed on the optical axis between the original and the imaging lens, the translucent member is disposed on the optical axis between the imaging lens and the image sensor for the reason described later. The thickness of the translucent member can be further reduced as compared to the case where the light transmitting member is disposed.

In the image input device according to the third aspect, the magnification of the imaging lens is smaller than (1-1 / (Ld + 1)) ^1/2 ,
Since the translucent member is removably disposed on the optical axis between the imaging lens and the image sensor, the translucent member is disposed on the optical axis between the original and the imaging lens for a reason described later. The thickness of the translucent member can be further reduced as compared to the case where the light transmitting member is disposed.

In the image input device according to the present invention, the light transmitting member is configured such that the magnification of the variable magnification imaging lens is (1-1 / (Ld +
1)) When it is larger than ^1/2 , it is arranged on the optical axis between the original and the imaging lens, and the magnification of the imaging lens is (1-1 / 1).
(Ld + 1)) When it is smaller than ^1/2 , it is disposed on the optical axis between the imaging lens and the image sensor. Therefore, even when the magnification of the imaging lens is variable, the thickness of the light transmitting member is Can be minimized.

[0014]

FIG. 1 is a perspective view showing the structure of an image input apparatus according to a first embodiment. The document 2 is relatively moved in the AB direction with respect to the imaging unit 3 by a sub-scanning mechanism not shown. Image light from the linear scanning area 2a of the document 2 sequentially passes through the projection imaging lens 13 and the moire eliminating light transmitting member 23 arranged on the optical axis OA of the imaging unit 3. Incident on a CCD 33 serving as an image sensor.

The imaging lens 13 has a magnification m of (1-1).
/ (Ld + 1)) ^1/2 . Here, L means the required number of resolution lines (lines / mm) on the document 2, and d means the pupil diameter (mm). This (1-1 / (Ld +
1)) The meaning of ^1/2 will be described later in detail.

The light transmitting member 23 is made of a parallel plate glass, and reduces the occurrence of moire due to the defocus effect to such an extent that the reading quality is not affected. The translucent member 23 can be reciprocated in the CD direction by an advancing and retreating mechanism (not shown). That is, the advancing / retracting mechanism enables the light transmitting member 23 to reciprocate between an operating position on the optical axis OA and a retracted position deviated from the optical axis OA,
The translucent member 23 can be freely inserted and removed on the optical axis OA.

The direction of insertion and removal of the translucent member 23 is not limited to the CD direction, but may be arranged to be freely insertable and removable in the EF direction.

The output of the CCD 33 is read out in synchronization with the movement of the document 2, and is processed by a CCD drive circuit and a signal processing circuit (not shown).

FIGS. 2 and 3 show (1-1 / (Ld +
1)) The meaning of ^1/2 is explained. When the magnification of the imaging lens 13 is lower than this value, the light transmitting member 23 is arranged on the optical axis OA between the imaging lens 13 and the CCD 33. This explains that the thickness of the light transmitting member 23 can be reduced.

As shown in FIG. 2, when the light transmitting member 23 is inserted on the optical axis OA between the imaging lens 13 and the light receiving surface 33a of the CCD 33, the optical path of the image light is changed before the light transmitting member 23 is inserted. Changes from the one indicated by the principal ray PL1 to the one indicated by the principal ray PL2 after the light transmitting member 23 is inserted. As a result, the position of the imaging plane 34a is CC
It moves backward from its original position on the light receiving surface 33a of D33.

In this case, the required thickness t1 of the light transmitting member 23
Is given by the following equation as described in detail below.

T1 = δFn (1 + m) / (n-1) where δ represents the diameter of a circle of confusion, and F represents the imaging lens 13
, M indicates the magnification of the imaging lens 13, and n indicates the refractive index of the light transmitting member 23.

The above equation giving the thickness t1 of the light transmitting member 23 is as follows:
It is determined as follows. That is, the diameter δ of the circle of confusion is δ = d · Δb / b from the geometric relationship in FIG.

Here, d indicates the pupil diameter (here, approximately the diameter of the light beam passing through the main plane) as described above, and b indicates the pupil plane of the imaging lens 13 (here, approximately the main plane). From the image to the light receiving surface 33a which is an image surface. Therefore, assuming that the focal length of the imaging lens 13 is f, d = f / F and b = f
The relationship of (1 + m) holds. Δb is the distance b
Indicates the amount by which the distance from the principal point of the imaging lens 13 to the image plane varies due to the insertion of the light transmitting member 23. Therefore, Δb =
The relationship of t1 (1-1 / n) is established.

Therefore, the following relationship holds: δ = d · Δb / b , δ = ft1 (1-1 / n) / Ff (1 + m), δ = t1 (n−1) / Fn (1 + m) The thickness t1 of the member 23 is given by the following equation.

[0026]

(Equation 1)

FIG. 3 shows a case where the light transmitting member 23 is assumed to be the imaging lens 1.
FIG. 4 is a diagram illustrating an image forming state when the image is inserted on the optical axis OA between the scanning area 3 and the scanning area 2a of the original 2; The optical path of the image light is
The state changes as indicated by the principal ray PL1 before the insertion of the light transmitting member 23 to the state indicated by the principal ray PL3 after the insertion of the light transmitting member 23. As a result, the image plane 3
The position of 4b moves behind the position of the light receiving surface 33a of the CCD 33.

In this case, the required thickness t2 of the light transmitting member 23
Is given by the following equation as described in detail below.

T2 = δFnf (1 + m) / m (n-1)
(Mf + δF) The above equation that gives the thickness t2 of the translucent member 23 is obtained as follows. That is, the diameter δ of the circle of confusion is given as follows from the geometric relationship in FIG.

[0030]

(Equation 2)

In the above equation, d = f / F, b
= F (1 + m). Further, the light transmitting member 23
When the effective magnification of the imaging lens 13 after insertion is m ′,
The following relationship is established by moving the imaging position.

[0032]

(Equation 3)

[0033]

(Equation 4)

Here, a indicates the distance from the pupil plane (here, approximately the main plane) of the imaging lens 13 to the original image plane of the original 2, and Δa indicates the distance a of the light transmitting member 23. Indicates the amount that varies with insertion. Therefore, Δa = −t 2 (1-1
/ N) holds. Therefore, the relational expression of Expression 4 is modified as follows.

[0035]

(Equation 5)

Accordingly, the effective magnification m 'is given by the following equation.

[0037]

(Equation 6)

From Equations 6 and 3, Δb is given by the following equation.

[0039]

(Equation 7)

Further, from the relationship of Equation 2, the diameter δ of the circle of confusion
Is modified as follows.

[0041]

(Equation 8)

Accordingly, the thickness t2 of the light transmitting member 23 is given by the following equation.

[0043]

(Equation 9)

Hereinafter, the magnification of the imaging lens 13 is assumed to be the same,
An arrangement in which the thickness of the light transmitting member 23 inserted between the imaging lens 13 and the CCD 33 is reduced under the condition that the required number of resolution lines L on the document 2 is the same is considered.

The thickness t2 of the light transmitting member 23 inserted on the optical axis OA between the imaging lens 13 and the scanning area 2a of the original 2.
And the thickness t1 of the translucent member 23 inserted on the optical axis OA between the imaging lens 13 and the light receiving surface 33a of the CCD 33, are given by the following equations from Equations 1 and 9. .

[0046]

(Equation 10)

Here, since the diameter δ of the circle of confusion is expressed by δ = m / L using L, which is the required number of resolution lines on the document 2, Equation 10 is modified as follows. You.

[0048]

[Equation 11]

Therefore, if the condition of-(f + F / L) m ² + f> 0 is satisfied, t2−t1> 0. That is, − (fL / ( fL + F ) ) ^1/2 <m <(fL / ( fL +
F ) ) If the condition of ^1/2 is satisfied, t2-t1> 0. here,
Since m> 0, if the condition of m <(fL / ( fL + F ) ) ^1/2 is satisfied, t2−t1> 0. here,
Using the relationship of F = f / d, when the following relational expression is satisfied, t1 <t2.

[0050]

(Equation 12)

This means that the imaging lens 13 and the CCD 33
In order to reduce the thickness t1 of the translucent member 23 inserted between them, it means that the magnification m of the imaging lens 13 needs to satisfy the conditional expression (12). Therefore,
When the magnification m of the imaging lens 13 satisfies the conditional expression 12, it is not desirable to insert the translucent member 23 between the imaging lens 13 and the document 2. When the magnification m of the imaging lens 13 is equal to (1-1 / (Ld + 1)) ^1/2 , the light transmitting member 23 is connected between the imaging lens 13 and the CCD 33 and between the imaging lens 13 and the CCD 33. The thickness of the light transmitting member 23 does not change regardless of whether the light transmitting member 23 is inserted.

An example of specific specifications of the image input device according to the first embodiment will be described below. For example, assuming that a lens focal length: f = 150 mm, an F number: F = 8, a confusion circle diameter: δ = 0.05 mm, an optical magnification: m = 0.3, and a refractive index of a light transmitting member: n = 1.52, From Expression 1, the thickness t1 of the light transmitting member 23 inserted between the imaging lens 13 and the CCD 33 is 1.51 mm. From Expression 9, the thickness t2 of the light transmitting member 23 inserted between the imaging lens 13 and the document 2 is 16.74 mm.

FIG. 4 is a perspective view showing the configuration of the image input device according to the second embodiment. The original 2 is imaged by the sub-scanning mechanism (not shown) as in the first embodiment.
3 relative to the direction AB. The image light from the linear scanning area 2a of the document 2 passes through the moire eliminating light transmitting member 123 and the projection imaging lens 113 arranged on the optical axis OA of the imaging unit 103. Mirror 14
At 3, the light is split into three light beams and incident on three CCDs 133a, 133b, and 133c, which are image sensors.

The light transmitting member 123 is made of a parallel plate glass, and reduces the occurrence of moire due to the defocus effect to such an extent that the reading quality is not affected. In addition, this light transmitting member 123 moves the light transmitting member 123 between the operating position on the optical axis OA and the optical axis O.
It can be inserted and removed by an advancing / retracting mechanism (not shown) that reciprocates between a retracted position deviated from A.

The magnification m of the imaging lens 113 is (1−1).
1 / (Ld + 1)) greater than ^1/2 . The reason will be described below.

Referring again to FIG. 2 and FIG. 3, when the relationship of Expression 12 derived in the description of the first embodiment is satisfied, t1 <t2, and the imaging lens 13 and CC
Light-transmitting member 23 inserted between light-receiving surface 33a of D33
Becomes thinner. In other words, when the following relational expression is satisfied, t2 <t1 and the translucent member 23 inserted between the imaging lens 13 and the scanning area 2a of the document 2 is satisfied.
Means that the thickness becomes thinner.

[0057]

(Equation 13)

This is because, as in the second embodiment shown in FIG.
Light transmitting member 1 inserted between image forming lens 113 and document 2
In order to reduce the thickness of 23, it means that the magnification m of the imaging lens 113 needs to satisfy the conditional expression (13). Therefore, when the magnification m of the imaging lens 113 satisfies the conditional expression (13), it is not desirable to insert the translucent member 123 between the imaging lens 113 and the CCDs 133a to 133c.

The outputs of the CCDs 133a, 133b, and 133c are processed by a CCD drive circuit and a signal processing circuit (not shown). At this time, each CCD 133a, 1
By compensating for positional deviation and shading at the portions corresponding to the joints at the ends of 33b and 133c, joint processing is performed on these image signals. Thereby, each CCD 133
It is possible to obtain the same one-dimensional image signal as when a, 133b, and 133c are set to the same sensitivity and are arranged without a break on a straight line.

FIG. 5 is a perspective view showing the structure of the third embodiment. The third embodiment is a modification of the imaging unit 3 of the first embodiment, and the same portions are denoted by the same reference numerals and description thereof will be omitted.

The imaging lens 213 has a magnification m of (1−1).
A burr that varies between a relatively low magnification state smaller than 1 / (Ld + 1)) ^1/2 and a relatively high magnification state whose magnification m is larger than (1-1 / (Ld + 1)) ^1/2. It is a focal lens.

The first light transmitting member 223a is made of parallel plate glass, and reduces the occurrence of moire due to the defocus effect to such an extent that the reading quality is not affected. The first light transmitting member 223a is insertable into and removable from the optical axis OA. That is, the first light transmitting member 223a is driven by the advance / retreat mechanism 323a, and the imaging lens 213 and the CCD
33 between the operating position on the optical axis OA and the retracted position deviated from the optical axis OA.

The second light transmitting member 223b is also made of parallel flat glass, and reduces the occurrence of moire due to the defocus effect to such an extent that the reading quality is not affected. The second light transmitting member 223b is also insertable into and removable from the optical axis OA. That is, the translucent member 223b is driven by the reciprocating mechanism 323b to reciprocate between an operation position on the optical axis OA between the imaging lens 213 and the document 2 and a retracted position deviated from the optical axis OA. I do.

Referring again to FIGS. 2 and 3 of the first embodiment, in order to reduce the thickness of the light transmitting member 23 inserted between the imaging lens 13 and the light receiving surface 33a of the CCD 33,
It is necessary that the magnification m of the imaging lens 13 satisfies the conditional expression (12). In order to reduce the thickness of the light transmitting member 23 inserted between the imaging lens 13 and the scanning area 2a of the document 2, the magnification m of the imaging lens 13 must satisfy the conditional expression 13 Is required. This means that in the third embodiment shown in FIG. 5, when the magnification m of the imaging lens 213 is in a relatively low magnification state satisfying the conditional expression (12),
By driving the first light transmitting member 223a, the imaging lens 213 and C
The thickness of the first light transmitting member 223a can be minimized by moving it to the operating position on the optical axis OA between the CD 33 and driving the second light transmitting member 223b to the retracted position. Means Conversely, the imaging lens 2
When the magnification m of 13 is in a relatively high magnification state that satisfies the conditional expression 13, the second light transmitting member 223b is driven to move the imaging lens 213 and the original 2 to the operating position on the optical axis OA. This means that the thickness of the second light transmitting member 223b can be minimized by moving and driving the first light transmitting member 223a to the retracted position.

[0065]

As described above, according to the image input apparatus of the first aspect, on the optical axis between the original and the imaging lens, and between the imaging lens and the image sensor according to the magnification of the imaging lens. The thickness of the translucent member on the optical axis between
Since the translucent member for moire off to either capable Rukoto are arranged, it is possible to reduce the thickness of the light transmitting member for size irrespective moiré erase the magnification of the imaging lens . As a result, the light-transmitting member can be accommodated in a small space, the driving of the light-transmitting member can be facilitated, and the cost of the light-transmitting member can be reduced.

According to the image input device of the second aspect,
Since the magnification of the imaging lens is larger than (1-1 / (Ld + 1)) ^1/2 and the translucent member is disposed on the optical axis between the original and the imaging lens so as to be freely inserted and removed, The thickness of the light transmitting member can be reduced more than when the light transmitting member is arranged on the optical axis between the imaging lens and the image sensor.

According to the image input device of the third aspect,
Since the magnification of the imaging lens is smaller than (1-1 / (Ld + 1)) ^1/2 and the translucent member is disposed on the optical axis between the imaging lens and the image sensor so as to be freely inserted and removed. The thickness of the light transmitting member can be further reduced as compared with the case where the light transmitting member is arranged on the optical axis between the document and the imaging lens.

According to the image input device of the fourth aspect,
When the magnification of the variable magnification imaging lens is (1-1 / 1 /
(Ld + 1)) when it is larger than ^1/2 , it is arranged on the optical axis between the original and the imaging lens, and the magnification of the imaging lens is smaller than (1-1 / (Ld + 1)) ^1/2 Sometimes, the light transmitting member is disposed on the optical axis between the imaging lens and the image sensor, so that the thickness of the light transmitting member can be minimized even when the magnification of the imaging lens is variable.

[Brief description of the drawings]

FIG. 1 is a perspective view of an image input device according to a first embodiment.

FIG. 2 is a diagram for explaining the operation of the image input device of the first embodiment.

FIG. 3 is a diagram for explaining the operation of the image input device of the first embodiment.

FIG. 4 is a perspective view of an image input device according to a second embodiment.

FIG. 5 is a diagram illustrating an image input device according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 3 imaging unit 13 imaging lens 23 light transmitting member 33 CCD 103 imaging unit 113 imaging lens 123 light transmitting members 133a to 113c CCD 213 image forming lenses 223a, 223b first and second light transmitting members 323a, 323b advance / retreat mechanism

Claims (4)

(57) [Claims] An image input apparatus for projecting an image of a document onto an image sensor with an image forming lens and reading the image, wherein an image between the document and the image forming lens is provided in accordance with a magnification of the image forming lens. On the optical axis and on the optical axis between the imaging lens and the image sensor, the thickness of the light-transmitting member is reduced.
An image input apparatus, wherein a light- transmitting member for moiré elimination is disposed on one of the light-transmitting members. Wherein the magnification of the imaging lens, the number of necessary resolution line of the document surface to the pupil diameter of the imaging lens is L when the d (1-1 / (Ld + 1 )) 1 / ^Greater than ² ,
2. The image input device according to claim 1, wherein the translucent member is disposed so as to be freely inserted and removed on an optical axis between the document and the imaging lens. Wherein the magnification of the imaging lens, the number of necessary resolution line of the document surface to the pupil diameter of the imaging lens is L when the d (1-1 / (Ld + 1 )) 1 / ^Less than ² ,
2. The image input device according to claim 1, wherein the translucent member is disposed on an optical axis between the imaging lens and the image sensor so as to be freely inserted and removed. 4. The imaging lens has a variable magnification, and the translucent member has a required number of resolution lines on the document surface of L.
When the pupil diameter of the imaging lens is d and the magnification of the imaging lens is greater than (1-1 / (Ld + 1)) ^1/2 , the distance between the original and the imaging lens is And the magnification of the imaging lens is (1-1 / (Ld
2. The image input device according to claim 1, wherein the image input device is arranged on the optical axis between the imaging lens and the image sensor when the ^value is smaller than +1)) ^1/2 .