JPH08321917A - Image reader - Google Patents

Abstract

PURPOSE: To provide an image reader capable of stably reading an image even when the condition of numerical number is revised by revising a correction characteristic of an image signal associated with the adjustment of the number of openings of light emitted to an original copy. CONSTITUTION: A cylindrical scanning type image reader is provided with a lighting optical system E and an image forming optical system F. The lighting optical system E is an optical system allowing light to irradiate a lighting area of an original copy 2 to lead the light from a secondary light source P30 to the original and provided with a collector lens 40, a field lens 43, a relay system lens 44 and a condensor lens 49. Furthermore, a variable visual field aperture AS is arranged at a position in optical conjugation with a position of a pupil of the condensor lens 49. The image forming optical system F forms an image of a read area of the original 2 onto an image forming face by a pickup lens 27 and the light passing through a hole of a main aperture plate 25 arranged on the image forming face is read by an photo multiplier 21. In this image reader, when the numerical number of openings of the light is revised, the aperture size of the aperture As is revised and the correction characteristic of a correction lookup table to correct the image signal outputted from the photo multiplier 21 is revised.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus which illuminates an original document and photoelectrically reads the image of the original document.

[0002]

2. Description of the Related Art FIG. 10 is a diagram showing an example of an image reading apparatus as a background art of the present invention, showing an input scanning optical system of a scanning head. In this image reading apparatus, as shown in the figure, a pickup lens 1 provided on a scanning head with light from a document 102 attached to a document cylinder 101.
03, the real image of the original 102 is imaged at the position of the main aperture plate 104 having a plurality of holes (apertures) of different sizes, and the main aperture plate 1
Light passing through one hole (aperture) 04 is incident on the photomultiplier tube 105 and converted into an electric signal. When changing the reading resolution, the hole diameter (aperture size) of the main aperture plate 104 through which light passes is changed according to the reading resolution.

In order to read the original 102 with the image reading apparatus configured as described above, it is necessary to illuminate the original 102 under appropriate conditions. Therefore, conventionally, various illumination optical systems have been proposed and incorporated in the image reading apparatus. In this illumination optical system, a light source lamp 106 and a collector lens 107 that takes in light from the light source lamp 106.
And the field stop 108 are arranged in this order, and the light from the light source lamp 106 is emitted through the collector lens 107 and the field stop 108 into the ray pipe 111 extending parallel to the rotation axis of the original cylinder 101. .

Inside the ray pipe 111, an aperture stop 109 and a mirror 112 are arranged. After the light incident on the ray pipe 111 passes through the aperture stop 109,
It is reflected by the mirror 112. Then, the reflected light is applied to the original 102 on the original cylinder 101 via the condenser lens 110 fixed to the surface of the ray pipe 111. The aperture diameter of the aperture stop 109 (aperture size)
The numerical aperture of the illumination light can be changed by changing.

If the surface of the original 102 has irregularities or scratches, or if the original has a rough graininess, the numerical aperture of the illumination light is increased to irradiate the original with diffused illumination light, and an image is displayed without being affected by scratches or the like. Can be read. On the contrary, if there is no unevenness or scratches on the surface of the original, or if the original has a fine grain,
By reducing the numerical aperture of the illumination light to prevent flare,
You can scan images that are true to the original.

[0006]

However, when the numerical aperture of the illumination light is adjusted, the measured density changes according to the numerical aperture due to the variation of the so-called Q factor (the value obtained by dividing the parallel density by the diffusion density). . FIG. 11 is a graph showing density characteristics when the density measured by a densitometer is plotted on the horizontal axis and the density measured by an image reading apparatus capable of adjusting the numerical aperture of illumination light is plotted on the vertical axis.

Since the density measured by the densitometer coincides with the density measured when the numerical aperture of the illumination light in the image reading apparatus is made sufficiently large, this density is used as a reference. As shown in this figure, the smaller the numerical aperture, the more the density tends to be recognized, and the larger the numerical aperture, the closer to the density measured by the densitometer.

Therefore, even if the original is the same, if the numerical aperture of the illuminating light is adjusted, the measured density will change.
It becomes impossible to read stable image density.

An object of the present invention was made in view of the above problems, and it is an object of the present invention to provide an image reading apparatus capable of stably reading an image even if the numerical aperture of illumination light is adjusted.

[0010]

An image reading apparatus according to claim 1, wherein an illumination optical system for illuminating an original with illumination light, a numerical aperture adjusting means for adjusting a numerical aperture of the illumination light, and an image of the original are displayed. A photoelectric conversion unit for reading and outputting an image signal; and a correction unit for correcting the image signal based on a correction characteristic and outputting a corrected image signal. Further, the correction according to the numerical aperture of the illumination light. Further provided is a changing means for changing the characteristic.

An image reading apparatus according to a second aspect is the image reading apparatus according to the first aspect.
In the above, the correction characteristic is such a characteristic that the smaller the numerical aperture of the illumination light is, the lighter the density represented by the corrected image signal is compared with the image signal.

According to a third aspect of the present invention, in the image reading apparatus according to the first aspect, the illumination optical system includes a light source, a lens that condenses light from the light source onto a document, a pupil position of the lens, or an optical system including the pupil position. And a variable aperture stop disposed at a conjugate position, and the numerical aperture of the illumination light is adjusted by adjusting the aperture size of the variable aperture stop.

[0013]

In the image reading apparatus according to the first aspect of the present invention, the illumination optical system illuminates the original with illumination light, guides the light from the original to the photoelectric conversion means, reads the image of the original, and outputs an image signal. This image signal outputs a corrected image signal based on the correction characteristic of the correction means. When the numerical aperture of the illumination light is adjusted by the numerical aperture adjusting unit according to the state of the surface of the original or the degree of graininess, the changing unit adjusts the numerical aperture, and the changing unit outputs the image signal output from the photoelectric converting unit. Change the correction characteristics to correct. Therefore, it is possible to correct the fluctuation of the image signal caused by the adjustment of the numerical aperture of the illumination light.

In the image reading apparatus according to the second aspect, the fluctuation of the image signal due to the adjustment of the numerical aperture of the illumination light tends to be read darker as the numerical aperture of the illumination light is smaller. The smaller the numerical aperture, the lighter the density represented by the corrected image signal is compared with the image signal.

According to another aspect of the image reading apparatus of the present invention, the variable aperture stop is arranged at the pupil position of the lens for condensing the light from the light source or at a position optically conjugate with the pupil position, and the aperture of the variable aperture stop is arranged. By adjusting the size, the numerical aperture of the illumination light can be adjusted with a simple configuration.

[0016]

【Example】

<Cylindrical Scanning Image Reading Device> FIGS. 1 and 2 are a perspective view and a plan view showing an embodiment of an illumination optical system E and an imaging optical system F of a cylindrical scanning image reading device according to the present invention, respectively. Is.

As shown in FIG. 1, the illuminating optical system E illuminates the original 2 mounted on the original cylinder 1 and the transmissive optical system ET for illuminating the original 2 from the direction opposite to the transmissive optical system ET. And a reflection optical system ER. The illumination optical system E (transmission optical system ET and reflection optical system ER) described below should also be applied to a device that reads an image by placing the original 2 on a transparent flat plate such as a glass plate. You can

In the transmission optical system ET, a light source 30 and a collector lens 40 are arranged inside the lamp house 28 (see FIG. 2). A ray pipe 29 extending in the sub-scanning direction Y is connected to the lamp house 28. Inside the ray pipe 29, a field lens 43, a relay lens 44, a mirror 48, and a condenser lens 4 are connected.
9 and are provided.

In the light source 30, as shown in FIG. 1, a perforated elliptical mirror 32 is arranged so as to surround a light source lamp 31 such as a xenon lamp or a halogen lamp. A part of the light emitted from the light source lamp 31 is reflected by the elliptical mirror 32, guided to the reflection optical system ER, and irradiated on the original 2.
Further, a hole 32S is formed on the side surface of the elliptic mirror 32, and a part of the light emitted from the light source lamp 31 has a hole 3S.
After passing 2S, it is condensed at a predetermined position P30 by a secondary light source forming lens system 35 including two lenses 33 and 34,
A secondary light source is formed. In addition, reference numeral 36 reflects the light emitted from the secondary light source forming lens system 35 to reflect the light source lamp 3
It is a mirror for guiding the light from 1 to the collector lens 40.

As described above, in this embodiment, the light source 30 is constituted by the elements 31 to 35, the light emitted from the light source lamp 31 is divided into two optical paths, and the reflection optical system ER and the transmission optical system are respectively provided. It is incident on the system ET. In addition, in this embodiment, since the light from the light source lamp 31 is distributed in two directions orthogonal to each other by using the perforated elliptical mirror 32 configured as described above, the light from the light source lamp 31 is distributed. Can be used spatially and efficiently.

When the transparent original is used as the original 2, the transparent optical system ET is used, and when the reflective original is used, the reflective optical system ER is used, so that the optical path selectively enters each optical path. A shutter (not shown) is provided.

Further, in this embodiment, as can be seen from FIGS. 1 and 2, since the secondary light source forming lens system 35 is composed of a focal type optical system, the optical path is different from that in the case of using an afocal system. The length of the light source 30 can be shortened.
Can be made compact.

As shown in FIG. 2, the collector lens 40 is configured to collect the light emitted from the light source 30 and guide it to the field lens 43.

FIG. 3A is a diagram showing an optical configuration of the transmission optical system ET. In this optical system, a variable aperture stop AS is arranged at a position P30 where the secondary light source is formed. The variable aperture stop AS is formed with a plurality of apertures (holes) having different aperture sizes (hole diameters), and the aperture of the aperture stop is rotated by a predetermined angle by the aperture stop motor 7 (see FIG. 2). The size (pore diameter) can be appropriately changed. Along with this, the numerical aperture of the illumination light with which the document 2 is irradiated can be adjusted. In addition,
The variable aperture stop AS and the aperture stop motor 7 correspond to the numerical aperture adjusting means of the present invention.

The collector lens 40 is arranged at a position separated from the secondary light source by the focal length f41S of the lens 40, and takes in the light from the secondary light source through the mirror 42,
The parallel light is emitted to the field lens 43 side. On the rear side of the collector lens 40, a variable field stop FS is arranged in a positional relationship conjugate with the original 2. The hole diameter (size) of the variable field diaphragm Fs can be adjusted by the field diaphragm motor 6 (see FIG. 2).

Further, in this embodiment, the light source image of the light source lamp 31 is formed at the pupil position 99 of the condenser lens 49, and this illumination optical system is a Koehler illumination system.

Next, returning to FIG. 1, the collector lens 4
The process until the light emitted at 0 is applied to the original 2 will be described. The emitted light enters the relay lens 44 via the field lens 43. The relay lens 44 is composed of two lenses 45 and 46. The two lenses 45 and 46 are arranged so as to be separated from each other by a distance obtained by adding the focal lengths thereof, so that a so-called afocal optical system is formed. Here, by using the relay system 44 lens as an afocal optical system, it is possible to perform good relaying without being affected by dust or the like adhering to the lens surface as compared with the case of forming with a focal system. That is,
For focal optics, the light source image (or field stop image)
Are formed in or on the surface of the lens, and when dust or the like is attached to the lens surface of the lens, the light source image (or the field stop image) is disturbed, which adversely affects the image. In contrast,
When the relay system is formed by the afocal optical system as in this embodiment, the light source image and the field stop image are formed in the space area between the lenses, so that they are not affected by dust on the lens surface and are excellent. The light source image is on the condenser lens 49 side,
Then, the field stop image can be transmitted onto the original 2.

The light emitted from the relay lens 44 is reflected by a mirror 48 and then condensed by a condenser lens 49, and the original 2 on the original cylinder 1 (see FIG. 2).
Is irradiated.

In such an illumination optical system E, the original 2
By adjusting the hole diameter (size) of the field stop FS arranged at a position conjugate with, it is possible to change the illumination area on the original 2 where the light source 30 is irradiated with light.

Next, the reflection optical system ER will be described with reference to FIG. As shown in FIG. 1, the reflection optical system R is composed of a bundle fiber 130 for guiding the light from the light source 30 to the vicinity of the original cylinder 1.
The one end 131 of the bundle fiber 130 faces the opening 32R of the perforated elliptical mirror 32, and the perforated elliptic mirror 32 is provided.
Of the light emitted through the opening 32R from the one end 131 of the bundle fiber 13
After being incident on 0 and guided to the other end (not shown),
The light is emitted from the other end toward the original 2. Thus, the illumination for reflecting the original 2 is performed.

As shown in FIGS. 1 and 2, the image forming optical system F includes a main aperture plate 25 and a pickup lens 27 for forming an image of the original 2 on the main aperture plate 25. The main aperture plate 25 is arranged on the image forming surface on which the image of the document 2 is formed by the pickup lens 27. A plurality of holes (apertures) having different diameters are formed in the main aperture plate 25 similarly to the variable aperture stop AS of the illumination optical system described above, and the main aperture motor 5 (see FIG. 2) allows One is selected from a plurality of holes (apertures), and the main aperture plate 25 is rotated so as to be located on the optical axis of the pickup lens 27. The light that has passed through the hole (aperture) of the main aperture plate 25 is collimated by the collimator lens 24.
Are converted into parallel light beams by the two dichroic mirrors 23R and 23B and the mirror 23G, and are separated into three primary colors. Further, through the color filters 22R, 22B and 22G, photomultiplier tubes 21R which are photoelectric conversion elements, respectively. ，
Guided to 21B and 21G.

In such an imaging optical system F, by changing the hole diameter (size) of the main aperture plate 25, it is possible to change the reading area according to the reading resolution.

FIG. 4 is a control block diagram of an image reading apparatus including the illumination optical system E and the image forming optical system F.

The image reading device is controlled by a main controller 55 which is mainly composed of a microcomputer and the like. Main controller 55
Is composed of a CPU, a ROM, a RAM, and the like, and the CPU controls each load based on a control program stored in the ROM, control data stored in the RAM, and information from the operation panel 54.

Further, the photomultiplier tubes 21R, 21B, 21
The image signals R1, B1 and G1 respectively output from G are
The current-voltage conversion circuit 50 converts the voltage value, the LOG conversion circuit 51 performs logarithmic conversion, and the A / D conversion circuit 52 converts the voltage value into digital data. The sampling clock CL is input to the A / D conversion circuit 52, and A / D conversion is performed at the timing of the sampling clock CL. Therefore, the reading resolution in the main scanning direction X can be changed by adjusting the frequency of the sampling clock CL. For example, if the frequency of the sampling clock CL is multiplied by N, the reading resolution will be multiplied by N.

Image signal R converted into digital data
2, B2, and G2 are corrected to a corrected image signal R3, B3, and G3 by a correction lookup table 53 (hereinafter referred to as correction LUT 53). In FIG. 5, the image signal R2
And the image signal R3. As shown in this figure, the correction characteristic of the correction LUT 53 corresponds to the inverse characteristic of the characteristic shown in FIG. 11, and the image signal R2 is plotted on the horizontal axis.
In the graph in which the corrected image signal is plotted on the vertical axis, the characteristic is represented by a downward convex curve. The correction characteristics are prepared in accordance with a plurality of selectable numerical apertures NA, and the smaller the numerical aperture NA, the lighter the image signal R2 becomes. The relationship between the image signal B2 and the corrected image signal B3 and between the image signal G2 and the corrected image signal G3 is basically the same as the relationship between the image signal R2 and the corrected image signal R3. It is a characteristic indicated by a curve. A correction characteristic corresponding to information about the numerical aperture of the illumination light designated by the operator is selected from the plurality of correction characteristics. Therefore, the correction characteristic is changed from the correction LUT 53 according to the numerical aperture of the illumination light, and the corrected image signal R
Outputs 3, B3 and G3. The correction LUT 53 corresponds to the correction means of the present invention.

The magnification control circuit 56 controls the sub-scanning speed data V
y is output to the sub-scanning control circuit 58, and the sub-scanning motor 4 is driven at that speed. Further, it outputs a selector signal SEL that changes according to the reading resolution RES to the reading area control circuit 59. The reading area control circuit 59 drives the main aperture motor 5 and the field stop motor 6 so that the reading area corresponds to the reading resolution RES. The document cylinder 1 controls the speed of the main scanning motor 3 via the main scanning control circuit 57 so that it rotates at a constant peripheral speed Vx regardless of the reading resolution.

When the operator inputs information on the numerical aperture NA of the illuminating light from the operation panel 54, the main control unit 55 changes the selection signal SEL for selecting the correction characteristic of the correction LUT 53 according to the information and the variable. The drive signal DAS output to the aperture stop control circuit 60 for adjusting the aperture size of the aperture stop AS is output. The correction LUT 53 is
A correction characteristic is selected based on the selection signal SEL. Therefore, the image signal is corrected based on the selected correction characteristic. On the other hand, the aperture stop control circuit drives the aperture stop motor 7 based on the drive signal DAS to adjust the aperture size of the aperture stop AS. The main controller 55 corresponds to the changing means of the present invention.

Information regarding the numerical aperture NA of the illumination light is given by the operator. When the original has scratches or irregularities, the aperture size (hole diameter) of the variable aperture stop AS is increased to increase the numerical aperture of the illumination light. On the contrary, when the original 2 has no scratches or irregularities, the operation panel 5 has information that reduces the aperture size of the variable aperture stop AS and reduces the numerical aperture of illumination light.
4 to the main controller 55.

The relationship between the hole diameter dA of the variable aperture stop AS and the numerical aperture NA of the illumination light is as shown in FIG. In this figure, for convenience of explanation, it is assumed that the aperture stop AS is placed at the pupil position of the condenser lens 49. Assuming that the angle formed by the light beam passing through the periphery of the aperture stop and the optical axis is θ and the distance between the principal point position of the condenser lens 49 and the original 2 is f49, the numerical aperture NA is NA = sin θ = dA / (f49 + dA) 1 It can be represented by / 2. Therefore, the numerical aperture NA of the illumination light
In order to change, the hole diameter dA of the variable aperture stop As may be changed. For example, in order to increase the numerical aperture NA of the illumination light, the hole diameter dA may be increased according to the above relational expression.

As described above, based on the information about the numerical aperture of the illumination light instructed by the operator, the variable aperture diaphragm A
Adjusting the aperture size of S, correcting the image signal based on the correction characteristics corresponding to that information, and outputting a corrected signal to obtain a stable image signal even if the numerical aperture of the illumination light changes. You can

In this embodiment, as can be seen from FIG. 3A, the field lens 43 and the condenser lens 49 are arranged so as to form an afocal optical system. An afocal relay lens 44 is arranged between the field lens 43 and the condenser lens 49. Moreover, as described above, since the collector lens 40 is arranged at the position separated from the secondary light source by the focal length, the transmission optical system ET is image-side telecentric, so that the original 2 can be satisfactorily read. Can be illuminated.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made.

In this embodiment, the variable aperture diaphragm AS is arranged at the position where the secondary light source is formed, but the arrangement position of the variable aperture diaphragm AS is not limited to this, and the light source image or it It may be located at any conjugate position, in other words, at the pupil position of the condenser lens 49 or at a position conjugate therewith. However, when it is arranged at the position P30 where the secondary light source is formed as described above, the variable aperture stop AS is located in the lamp house 28, and the aperture size (hole diameter) of the aperture stop AS is automatically changed. There is an advantage that it is easy to incorporate an automatic adjustment mechanism (such as a drive source and a driving force transmission unit) for On the other hand, when the aperture stop is arranged at a position conjugate with the light source image and closest to the original 2 (in this embodiment, the pupil position (AS ′) of the condenser lens 49), the influence of vibration of the ray pipe 29 or the like is caused. It can be minimized, and the document 2 can be illuminated stably.

Further, in this embodiment, the transmission optical system T is a so-called Koehler illumination system, but a critical illumination system is obtained by adjusting the intervals between the optical elements without changing the basic constituent elements. Is also possible,
Even in this case, the same effect as that of the Koehler illumination system can be obtained.

Further, the transmission optical system T according to this embodiment.
Is equipped with a relay lens 44, but this relay lens 44 is not an essential component of the present invention, and as shown in FIG. The optical system T can be configured,
The same effect as that of the first embodiment can be obtained. In this case, the position of the variable aperture stop AS may be provided at the position AS where the light source image is formed or at the pupil position (AS ′) of the condenser lens 49 as in the case of FIG. Further, as shown in FIG. 3C, the light source lamp 31 may be arranged at the position of the secondary light source of the above-mentioned embodiment. At this time, aperture stop A
The position of S may be provided at the pupil position (AS ′) of the condenser lens 49.

Further, in this embodiment, the condenser lens 49 is used as a part of the illumination optical system E in FIGS. 3A to 3C, but a zoom lens may be used instead. In this case, by changing the magnification of the zoom lens while the size of the field stop FS is fixed, the illumination area can be changed as in the above embodiment.

Further, in the above embodiment, the reading resolution in the main scanning direction X was realized by adjusting the frequency of the sampling clock CL, but the sampling clock CL
This can also be realized by keeping the frequency of 1 constant and adjusting the rotation speed Vx of the original cylinder 1. It can also be realized by adjusting both the sampling clock and the rotation speed Vx of the original cylinder.

<Flat Scanning Image Reading Device> FIGS. 7 and 8 show an embodiment of an illumination optical system E and an imaging optical system F of a flat scanning image reading device according to another embodiment of the present invention. FIG. 3 is a perspective view and a plan view showing FIG. Note that FIG.
9A and 9B are a cross-sectional view in the main scanning direction X and a sub-scanning direction Y, respectively. The planar scanning type image reading device has the same basic principle and configuration as the cylindrical scanning type image reading device, except that the reading area is changed from a spot shape to a slit shape.

This image reading device, as shown in FIG.
An illumination optical system E for illuminating the original 12 placed on the original table 11 and an image forming optical system F for reading an image of the original are provided.

The illumination optical system E includes a linear light source 80 made of a fluorescent lamp, a collector lens 81 made of a cylindrical lens, a variable field stop Fs, a mirror 88, and a variable aperture stop A.
s, condenser lens 8 consisting of a cylindrical lens
9 are arranged in order. The variable field stop FS is arranged at a position optically conjugate with the original 12 with respect to the condenser lens 89. The variable aperture stop AS is arranged at the pupil position of the condenser lens 89. In this illumination optical system E, the slit width (size) of the variable field stop FS
The illumination area on the original 12 can be adjusted by adjusting. Further, by adjusting the slit width (opening size) of the variable aperture stop AS, the original 1
It is possible to adjust the numerical aperture of the illumination light with which the light is irradiated on the second light.

Further, in the image forming optical system F, a mirror 76, a zoom lens 77, and a line sensor 71 which is a photoelectric conversion element are arranged in order. The line sensor 71 is, for example, C
The sensor is a CD or the like, and is arranged on the image plane which is an optically conjugate position with respect to the zoom lens 77. Therefore, the line sensor 71 can read the image on the line of the document 12.

In the image forming optical system F, when the reading resolution is changed, the image forming magnification of the zoom lens 77 is adjusted by the magnification converting motor 15 in the main scanning direction X, so that the line sensor 71 is connected. The image magnification to be imaged can be changed. Regarding the sub-scanning direction, by adjusting the relative speed (sub-scanning speed) between the document 2, the optical system 70 including the imaging optical system F, and the illumination optical system E, as in the above-mentioned cylindrical scanning type image reading apparatus. realizable.

FIG. 9 shows a plan view of the variable field stop FS. The variable field stop FS adjusts the slit width Δd formed by the pair of slit plates 91a and 91b by driving the field stop motor 16. Slit plate 9
1 has blocks 92a and 92b fixed to both ends thereof, and a screw 93 is attached to one of the blocks 92,
Rails 94 pass through the other side, respectively. The screw 93 is divided into upper and lower parts and the forming direction of the screw is changed. Therefore, when the screw 93 is rotated, the slit 91
a and 91b move in opposite directions. Therefore, the slit width Δd can be adjusted by rotating the field stop motor 16. The variable aperture stop AS has the same structure as the variable field stop FS, and the aperture stop motor 17
The slit width (aperture size) of the variable aperture stop AS can be changed, that is, the numerical aperture of the illumination light can be adjusted by rotating.

The control block diagram of this plane scanning type image reading device has substantially the same basic configuration as the control block diagram of the cylindrical scanning type image reading device. Photomultiplier tubes 21R, 21
In place of B and 21G, a line sensor 71 is replaced and the main scanning control circuit 57, the main scanning motor 3 and the main aperture motor 5 are deleted. Therefore, the operation of the plane scanning type image reading apparatus will be described with reference to FIG.

The operator checks the original document 12 for scratches, irregularities, and graininess. If the document 12 has scratches, irregularities, or coarse graininess, the operator inputs information to the operation panel 54 such that the slit width of the aperture stop is wide. To do. In the opposite case, the information that narrows the slit width of the aperture stop is input. The slit width of the aperture stop AS is adjusted by controlling the drive of the aperture stop motor 17 based on this information. Further, the correction characteristic of the correction LUT 53 is selected. As a result, the numerical aperture of the illumination light is adjusted and the image signal is corrected based on the correction characteristic corresponding to the numerical aperture. Therefore, a stable image signal can be read regardless of the adjustment of the numerical aperture of the illumination light.

[0057]

According to the first aspect of the invention, since the correction characteristic of the image signal is also changed in accordance with the adjustment of the numerical aperture of the illumination light,
An image can be stably read even if the numerical aperture of the illumination light is adjusted.

According to the invention of claim 2, it is possible to surely correct the fluctuation of the image signal due to the adjustment of the numerical aperture of the illumination light.

According to the third aspect of the invention, the numerical aperture of the illumination light can be easily adjusted by adjusting the aperture size of the variable aperture stop.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an illumination optical system and an imaging optical system of a cylindrical scanning type image reading device according to the present invention.

FIG. 2 is a plan view showing the outline of an illumination optical system and an imaging optical system of a cylindrical scanning type image reading device according to the present invention.

3A is a diagram showing an optical configuration of the illumination optical system of FIG. 1, FIG. 3B is a diagram showing an optical configuration of an illumination optical system of another embodiment, and FIG. It is a figure which shows the optical structure of the illumination optical system of the Example.

FIG. 4 is a control block diagram of the image reading apparatus according to the present invention.

FIG. 5 is a diagram showing the relationship between the hole diameter dA and the numerical aperture NA of the variable aperture stop AS.

FIG. 6 is a graph showing a correction characteristic of a correction LUT.

FIG. 7 is a perspective view showing an example of an illumination optical system and an imaging optical system of a plane scanning type image reading device.

FIG. 8A is a sectional view of a plane scanning type image reading apparatus, and FIG. 8B is a sectional view.

FIG. 9 is a front view showing the configurations of a field stop and an aperture stop.

FIG. 10 is a diagram showing an illumination optical system and an imaging optical system of a conventional image reading apparatus.

FIG. 11 is a graph showing density characteristics that change according to the numerical aperture of illumination light.

[Explanation of symbols]

 1 Document Cylinder 2, 12 Document 5 Main Aperture Motor 6,16 Field Aperture Motor 7,17 Aperture Stopper Motor 11 Document Plate 15 Magnification Conversion Motor 20 Scanning Heads 21R, 21G, 21B Photomultiplier Tube 25 Main Aperture Plate 27 pickup lens 30 light source 31 light source lamp 35 secondary light source forming lens system 40 collector lens 43 field lens 44 relay system lens 49 condenser lens 50 current-voltage converter 51 LOG conversion circuit 52 A / D conversion circuit 53 correction LUT 54 operation panel 55 Main control unit 59 Reading area control circuit 60 Aperture stop control circuit 70 Optical system 71 Line sensor 77 Imaging lens 80 Light source 81 Collector lens 89 Condenser lens 99 Pupil position FS Field stop AS Aperture stop E Illumination optical system ER anti Optical system ET Transmission optical system F Imaging optical system RES Reading resolution SEL selection signal DAS drive signal NA Numerical aperture of illumination light dA Variable aperture diaphragm aperture size R2, B2, G2 Image signal R3, B3, G3 Corrected image signal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kizo Takao 5 No. 5 Higashikujo Minami Ishida-cho, Minami-ku, Kyoto City Dai Nippon Screen Mfg. Co., Ltd., Jujo Plant Climbing 4-chome Tenjin Kitamachi No. 1 1 Dainippon Screen Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. An illumination optical system for irradiating an original with illumination light, a numerical aperture adjusting means for adjusting the numerical aperture of the illumination light, a photoelectric conversion means for reading an image of the original and outputting an image signal, the image. An image reading apparatus comprising: a correction unit that corrects a signal based on a correction characteristic and outputs a corrected image signal, further comprising a changing unit that changes the correction characteristic according to a numerical aperture of the illumination light. Image reading device. 2. The correction characteristic is such a characteristic that the smaller the numerical aperture of the illumination light is, the lighter the density represented by the corrected image signal is compared with the image signal. Image reading device. 3. The illumination optical system includes a light source, a lens for condensing light from the light source onto an original, and a variable aperture stop arranged at a pupil position of the lens or at a position optically conjugate with the pupil position. The image reading apparatus according to claim 1, further comprising: and adjusting a numerical aperture of the variable aperture stop to adjust a numerical aperture of the illumination light.