JP2766139B2 - Image reading 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 reading apparatus,
The present invention relates to an image reading apparatus that reads an original by dividing the original into a plurality of areas in a main scanning direction.

[0002]

2. Description of the Related Art For example, a planar scanning type image reading apparatus such as a scanner reads a picture original having a gradation such as a photograph or a picture and a line drawing original having no gradation such as a character. 2. Description of the Related Art As an image reading apparatus of this type, there is known an image reading apparatus which divides a main scanning direction into a plurality of areas and reads an original. As such an image reading apparatus, for example, Japanese Patent Publication No. Sho 62
In Japanese Patent No.-52506, a document placement section for placing a document, a light source for irradiating the document with light, a large number of solid-state imaging devices arranged in the main scanning direction and corresponding to pixels, and A plurality of lenses that are arranged in the main scanning direction and form an image of light from a document on a solid-state imaging device.

[0003]

In the above-mentioned conventional configuration,
When reading a picture original, so-called moire may occur. This moiré occurs when a document includes a pattern with periodicity, and a new striped moiré that does not exist in the document occurs at a portion where the pattern is read.

In order to prevent this, it is conceivable to attach a low-pass filter to each lens. However, when a low-pass filter is arranged in each lens, the degree of moiré removal by each low-pass filter differs, which causes a problem that image quality varies between image forming regions. An object of the present invention is to remove moiré uniformly and suppress variations in image quality between image forming regions.

[0005]

An image reading apparatus according to the present invention is an apparatus for reading an original by dividing the original into a plurality of areas in the main scanning direction. This device includes a document placement unit, a light source, a number of solid-state imaging devices, a plurality of lenses, and a light transmitting member.
The document placement section is for placing a document. The light source irradiates the original with light. Many solid-state imaging devices are arranged in the main scanning direction. Multiple lenses
It is arranged in the main scanning direction corresponding to a plurality of regions, and forms light from a document on a solid-state image sensor. The light transmitting member has a light diffusing property disposed between the lens and the document so as to collectively cover the optical path of the lens.

[0006]

In the image reading apparatus according to the present invention, when light from a light source irradiates a document placed in a document placement section, light from a plurality of areas divided in the main scanning direction passes through a light transmitting member. Light is incident on a plurality of lenses corresponding to a plurality of regions. Light incident on the plurality of lenses forms an image on a solid-state image sensor.

Here, since the light transmitting member is disposed so as to collectively cover the optical paths of the plurality of lenses, the degree of moire removal between the lenses is made uniform. This makes it possible to suppress variations in image quality between the image forming regions, as compared with a case where the light-transmitting members are individually arranged on the lenses.

[0008]

FIG. 1 shows an image reading apparatus (hereinafter referred to as a scanner) 1 according to an embodiment of the present invention. The scanner 1 has a lower frame 2 and an upper frame 3. An original placing device 4 is arranged on the upper surface of the lower frame 2. As shown in FIG. 2, a transmission light source 7 for slit exposure of a transmission original is vertically movably disposed below the original placing device 4 in the center of the lower frame 2. The document placing device 4 includes a document table 5 that can move in the sub-scanning direction indicated by an arrow in FIG. 2, and a drive mechanism 13 that drives the document table 5. Platen 5 is 483 mm x 646 m
The original 6 can be placed up to m, and the original is sandwiched between a pair of upper and lower glass plates.

On the upper frame 3, there are arranged a reflection light source 8 for slit exposure of a reflection original, an optical system 9, and a light receiving element 10 comprising a CCD line sensor. The light receiving element 10 is configured by arranging four CCD line sensors in series in the main scanning direction (the depth direction in FIG. 2).
Each CCD line sensor has, for example, a CC of 7500 pixels.
It is composed of a D element (an example of a solid-state image sensor).

The optical system 9 is, as shown in FIG. 3, for reflecting light from the original 90 degrees in the horizontal direction and a reflecting mirror 11 long in the main scanning direction, and for forming an image of the light from the original on the light receiving element 10. Lens 12. The lens 12 is
As shown in FIG. 3, four CCD sensors are arranged in parallel corresponding to the CCD line sensors. The lens 12 is arranged on the image reading line 22 of the document table 5 so that its fields of view overlap.

As shown in FIG. 2, each light receiving element 10
A light shielding plate 15 is provided between the lens 12 corresponding to each CCD line sensor as the light receiving element 10 to prevent flare. That is, the light receiving element 10 and the lens 12 are integrated by the light shielding plate 15. A long-pass filter 14 that is long in the main scanning direction and covers the optical paths of all the lenses 12 is disposed between the reflection mirror 11 and the lens 12. The low-pass filter 14 is a light transmitting member having a light diffusing property. When the low-pass filter 14 diffuses light, only light having a low spatial frequency enters the lens 12 and moire can be removed. The low-pass filter 14 can be moved up and down with respect to the optical path by a drive motor 21 via a link 20. The low-pass filter 14 retreats from the optical path when reading a line drawing original, and advances on the optical path when reading a picture original.

The low-pass filter 14 is a filter having a large number of small circles.
Is the focal length of f, the cutoff frequency is S ₁ , and the wavelength of light is λ, the diameter φ of the small circle can be determined by φ = f · λ · S ₁ For example, f = 100 mm, λ = 540n
m, S ₁ = 10 lines / mm, the diameter φ of the small circle
Becomes 0.546 mm. FIG. 4 shows an example of the frequency characteristic at this time. The vertical axis in FIG. 4 is the contrast, and the horizontal axis is the spatial frequency.

The low-pass filter 14 allows a low frequency component of the spatial frequency to pass, and blocks a high frequency region. For this reason, the high frequency component is removed from the light incident on the lens 12, the pitch of the picture is blurred, and moire does not occur. In addition, since the low-pass filter 14 is disposed so as to cover the optical path of the lenses 12 at a time, there is little variation in filtering conditions between the lenses 12.

Next, the operation of the above embodiment will be described. When the document 6 is mounted on the document table 5 and the operator instructs to start scanning, the light source 7 or the light source 8 is turned on, and the document table 5 is turned on.
Moves in the left-right direction (sub-scanning direction) in FIG. 2 to start scanning. When the scanning is started, the light transmitted or reflected with respect to the original 6 is reflected in the horizontal direction by the reflection mirror 11 and enters the lens 12 via the low-pass filter 14. The light incident on the lens 12 forms an image at the light receiving element 10 and is converted into an electric signal corresponding to an image.

Here, since the high-frequency component of the light incident on the lens 12 is removed by the low-pass filter 14, a moire image is less likely to be generated on the light receiving element 10. Further, since the low-pass filters 14 are arranged so as to collectively cover the optical paths of the lenses 12, the state of filtering light incident on each lens 12 becomes uniform, and moire is uniformly removed. For this reason, there is no variation in image quality between the respective image forming regions, and stable image quality can be obtained.

In the above embodiment, the light receiving element 10 and the lens 12 are integrated by the light shielding plate 15, and the low-pass filter 18 is located outside the light receiving element 10 and the lens 12. Even during maintenance such as replacement, it can be easily performed without adjusting the distance between the light receiving element 10 and the lens 12. [Other Embodiments] Instead of the low-pass filter, non-glare glass having light diffusing properties may be used. For example, a non-glare glass may be arranged 2 to 10 mm above the document 6 to lower the resolution of the document image. FIG. 5 shows the frequency characteristics at this time. Here, the contrast is slightly lower on the high frequency side than on the low frequency side. The present invention can be similarly implemented in such a configuration.

[0017]

In the image reading apparatus according to the present invention, since the light transmitting member which covers the optical path of the lens is disposed between the original and the lens, the moire is uniformly removed, and the distance between the image forming areas is reduced. Variation in image quality can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view thereof.

FIG. 3 is a schematic perspective view of an upper frame.

FIG. 4 is a graph showing frequency characteristics of a low-pass filter.

FIG. 5 is a diagram corresponding to FIG. 4 of another embodiment.

[Explanation of symbols]

 Reference Signs List 1 scanner 5 platen 6 document 7 and 8 light source 10 light receiving element 12 lens 14 low-pass filter

Claims (1)

(57) [Claims] 1. An image reading apparatus for reading a document by dividing the document into a plurality of areas in a main scanning direction, a document placement unit for placing the document, a light source for irradiating the document with light, A large number of solid-state imaging devices arranged in a scanning direction, and arranged in the main scanning direction corresponding to the plurality of regions;
A plurality of lenses for imaging light from the document on the solid-state imaging device; and a light-diffusing translucent member disposed between the lens and the document so as to collectively cover an optical path of the lens. An image reading device comprising: