JPH1188621A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide with an inexpensive configuration an image reader, in which a focused image is formed on an image sensor without lowering the resolution, even in the case of an original of a large size. SOLUTION: In an image reader that is provided with a light source 2 as a light-emitting means emitting a light on an original 8 by a prescribed slit width, an image sensor 5 where read pixels with a number causing required resolution are arranged on a line with a length equivalent nearly to a maximum width of the original, and a lens means focusing the reflected light from the original 8 onto read pixels 4, an image-forming leans 9 is arranged to the lens means so that the image-forming magnification is almost equal to a range of read pixel number of 10,000-45,000.

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 for digitally reading an original image, and more particularly to an image reading apparatus suitable for reading a wide original at a high resolution.

[0002]

2. Description of the Related Art Conventionally, an image of the same-size image sensor scanning system in which the length of an image sensor is linearly arranged to a length corresponding to the reading width of a document, and the image data of the document is read by scanning at the same magnification A reading device 1 is known. This method is
As shown in FIG. 3, a linear light source 2 such as an LED array arranged in the width direction of the document, a selfoc lens 3 for forming an image of reflected image data of the document, and a line for photoelectrically converting the image data are arranged. And an image sensor 5 such as a CCD having a plurality of read pixels 4.

For example, an original is sub-scanned at a constant speed on a transparent original platen glass 6, and reflected light from a light source 2 illuminated on the original is received by a selfoc lens 3 and focused on an image sensor 5. The image is formed in the state. The reflected light of the imaged document is digitized by the image sensor 5, subjected to image processing by the image processing unit 7, and then output to an image forming apparatus such as a copying machine or a printer (not shown) or an image forming unit. Then, an image is formed.

The read pixels of the image sensor have the desired number of resolutions. For example, if a document is 36 inches wide and a resolution of 400 dpi (dots per inch) is required, 14400 pixels are required. Pixels are required, and if the effective reading width and an error region due to mechanical alignment are included, about 15,000 read pixels are required.

On the other hand, as shown in FIG. 4, as a method of scanning by an image sensor such as a CCD, a linear light source 2 extending in the width direction of a document, a document 8 to be scanned, and a document 8
A reduced image sensor 10 having a length considerably shorter than the width of
2. Description of the Related Art A reduced image sensor scanning type image reading apparatus having an imaging lens 9 for forming image data from a reflected original 8 on a reduced image sensor 10 is known. The linearly illuminated light source 2 such as a fluorescent lamp irradiates a document to be sub-scanned, and the reflected light is received by an imaging lens 9 to form an image on a reduced image sensor 10. The formed reflected light is digitized, subjected to image processing by the image processing unit 7, and then output to an image forming apparatus or an image forming unit such as a copying machine or a printer (not shown) to form an image.

[0006] The reduced image sensor 10 has a plurality of read pixels arranged in a line. For example, the read pixels in an image sensor having a size of 1728 to 5000 pixels are commercially available. A reduced image sensor having a number of pixels of less than 10,000 is available on the market, though it cannot be made cheaper than the reduced image sensor 10 of 5000 pixels.
The higher the number of pixels, the lower the yield and the higher the cost.

The maximum size of a document is determined by the relationship between the number of read pixels of the reduced image sensor to be used and the required resolution. For example, when a resolution of 400 dpi is required using an image sensor of 5000 pixels, the maximum size of a document corresponds only to A3.

[0008] In the image reading apparatus of the reduced image sensor scanning system, in order to cover a document of 36 inch size,
For example, a resolution of 400 dpi or more can be maintained by arranging two 7500-pixel reduced image sensors. However, since the distance between pixels is as small as a few microns, there is no reliable method for accurate matching between pixels at a joint portion of two image sensors.

[0009]

In the above-described image reading apparatus of the same-magnification type image sensor scanning system, the size and weight are reduced. However, since a selfoc lens is used as the lens means, the focal point becomes small. There is a problem that the depth becomes shallow. For example, when moving a document on the document glass table, it is necessary to move the document so as to be in close contact with the document glass. If the document is moved up and down by 0.1 mm or more, the focus of the reflected light to the image sensor will be shifted. You will not be able to form a sharp image. In particular, when a thick document such as a book is targeted, the central portion when the book is opened is separated from the platen glass, resulting in an out-of-focus image.

The above-mentioned image reading apparatus of the reduced image sensor scanning type is preferably used when a small-sized document such as A4 or A3 size is used.
Further, since the image forming lens is used in the optical system, the depth of focus is deeper than that of the image reading apparatus of the same-size image sensor scanning method described above, and even if the original is displaced by about 1 mm in the optical axis direction, it is sharp. An image can be formed on the image sensor.

For example, when the number of pixels of the reduction type image sensor is 5000 pixels, the size of the original to be used is A4 size, and when the original is read vertically, the image data becomes 210 mm in length, so that the resolution is about 600 dpi. Can be obtained. However, if the document size is A0
If the size of the document becomes large, the width of the document
Since it is 41 mm, the resolution is as low as about 150 dpi.

In such a case, the problem can be solved by increasing the number of pixels of the reduced image sensor. However, only image sensors having a number of pixels less than 10,000 are commercially available. It is impossible to read the above document at a high resolution. That is, in the case of A1 size, when the resolution becomes 600 dpi, 1
The number of pixels of 4000 is required, and it cannot be supported by a commercially available reduced-size image sensor having less than 10,000 images. In the case of the A0 size, when the resolution becomes 400 dpi, the number of pixels is required to be 13000, which cannot be supported by a commercially available reduced image sensor. Furthermore,
In the case of A2 size, when the resolution becomes 1200 dpi, 13
000 pixels are required, and a commercially available reduced-size image sensor cannot be used.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and can form an in-focus image on an image sensor without lowering the resolution even for a large-size document. It is an object to provide an image reading device with an inexpensive configuration.

[0014]

In order to solve the above-mentioned problems, the present invention provides a light irradiating means for irradiating a relatively moving original with a predetermined slit width, and a light irradiating means for providing a required resolution. An image reading apparatus comprising: an image sensor in which a number of read pixels are arranged in a line in a length substantially corresponding to the width of a maximum original; and lens means for focusing reflected light from the original on the read pixels. The number of read pixels is in the range of 10,000 to 45000, preferably 13,000.
-30,000, wherein an imaging lens is arranged in the lens means so that an imaging magnification is substantially equal.

Further, the maximum size of the document is not less than A1 size.

Further, an optical path from the original to the image sensor is folded by a plurality of reflecting means, and the imaging lens is provided so as to be movable in an optical axis direction of the reflected light. It is characterized in that the magnification can be changed above.

Still further, the image forming lens is provided so as to be movable in the direction of the optical axis of the reflected light, and the optical path length of the image sensor is variably provided from the document so that the image can be scaled on the image sensor. Features.

In such a configuration, light from a linear light source is projected onto a large-size document that moves relatively. The reflected light from the document is folded by a plurality of reflecting means on the way, and forms an image on a read pixel on an image sensor by an image forming lens. The read pixels are set at a density so as to have a desired resolution.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an image reading apparatus 1 according to the present invention.
1 shows a schematic side sectional view of FIG. The image reading apparatus 1 includes a linear light source 2 that irradiates light toward a document surface, a reflection unit 11 that folds reflected light of the document, and a maximum size document that can absorb mechanical positioning errors. Slightly wider than the width,
Further, the image sensor 5 includes an image sensor 5 in which read pixels 4 having a predetermined resolution are arranged in a line, and an imaging lens 9 set so that the imaging magnification on the image sensor 5 is substantially equal.

In the embodiment, reference numeral 6 denotes a platen glass, and a document is conveyed at a predetermined speed by a document conveying means (not shown). As the light source 2, a linear LED array or a lamp such as a fluorescent lamp is used, and at least one line of light sources is arranged along the width direction of the document. Since the reflected light of the large-size document is formed on the image sensor 5 at a substantially equal magnification, the optical path length becomes extremely long. For this reason, the reflection means 11 is provided in at least one place, and the reflected light from the document is folded. In the embodiment, the configuration in which the reflecting means 11a, 11b, and 11c are provided at three places is shown. However, the number is not limited, and the position of the reflecting means 11a, 11b, and 11c may be either in front of or behind the imaging lens 9. May be the side.

The imaging lens 9 is a single lens or a combination of a plurality of lenses, and an aspheric lens is preferably used so that the reflected light from the document is accurately imaged.

FIG. 2 is a schematic front view of the image reading apparatus.
Although the reflection means and the light source are omitted in the drawing, the reflected light reflected from the document is imaged on the image sensor 5 through the imaging lens 9 at substantially the same magnification.

In the case where zooming is possible by using a zoom lens as the imaging lens 9 in FIG.
Is moved in the direction of the optical axis, and the image is appropriately focused on the image sensor 5 to form an image, whereby digital image data having a desired resolution can be obtained.

Further, the imaging lens is moved in the direction of the optical axis so as to have a desired magnification in FIG. 1, and, for example, the reflecting means 11a and 11b are moved in the direction of the optical axis to change the optical path length to form an image. Is made variable. By this operation, an in-focus and enlarged image is formed on the image sensor 5, and high-resolution digital image data can be obtained.

FIG. 5 shows an example of an image reading apparatus capable of performing the above-described scaling. A part of the width of the maximum size document or a document smaller in size than the maximum size document is used, and the image is enlarged to a desired magnification and imaged on the image sensor 5 using the effective reading width of the image sensor. Thus, high-resolution digital image data can be obtained.
For example, when the width of the maximum original 8 is A0 size (841 mm) and the resolution of 400 dpi is maintained, about 1
An image sensor 5 having a length corresponding to the A0 size having 3000 pixels is required. In such an image reading apparatus, an A2 size (420 mm)
The reflected light corresponding to the original 8 is scaled by the above-described method using substantially the entire effective length of the image sensor to form an image on the image sensor 5. As a result, an A2 size original can be read as digital image data having a high resolution of 800 dpi. In the embodiment, almost the entire effective length of the image sensor is used. However, a part of the image sensor may be used.
It is also possible to obtain a resolution of 600 dpi using almost two thirds of the image sensor.

1 and 2, the operation will be described with reference to FIGS. 1 and 2. The light emitted from the light source 2 toward the moving original 8 is reflected by the image forming lens 9 as reflected image data from the original 8. An image is formed on the image sensor 5 on the read pixels 4 arranged in a line after passing through. At this time, the light is folded a plurality of times by the reflecting means 11 provided in the optical path from the surface of the document 8 to the read pixel 4. The image data formed on the image sensor 5 is photoelectrically converted sequentially from the leading end to the trailing end of the read pixel 4, and is read line by line so as to have a predetermined resolution. The read N-line digital image data is subjected to image processing by the image processing unit 7 for each line, and is output to an image forming unit or an image forming apparatus (not shown) to obtain an output image.

In reading a document, scanning is performed from the front end to the end of the image sensor.
The image sensor may be divided into a plurality of blocks, read for each block, and then connected to be converted into one-line digital image data.

As an example, the maximum width of the original is 36
The size was an inch size (914 mm). In this case, the length of the image sensor is slightly longer than the size of the original,
When the resolution is set to 400 dpi, the number of pixels is about 1
There are 5000 pixels. Further, for example, if the resolution is 1200d
pi, about 36 inches, about 4
The number of pixels is 5000 pixels. A0 size (841m
In the case of m), when the resolution of 400 dpi is maintained, a minimum number of pixels of 13000 is required.

Although the embodiment has been described with reference to a document transport type image reading apparatus for transporting a document onto a document glass surface, a document fixed type image reading type in which image data of the document is read while the document is fixed. It may be a reading device.

[0030]

Focusing on the fact that a 1: 1 image sensor is easier to produce than a reduced image sensor in the case of a wide image, it is suitable for reading a document image of a large format document with a resolution of 400 dpi or more. Inexpensive and stable image reading with a deep depth of focus, provided that the number of read pixels is within the range of 10000 to 45000 pixels, preferably 12000 to 30000 according to the size of the document. Is performed, and a sharp image with focus can be read.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view showing an image reading apparatus according to the present invention.

FIG. 2 is a schematic front view showing an image reading apparatus according to the present invention.

FIG. 3 is a schematic sectional side view showing a conventional image reading apparatus using a unit-size image sensor.

FIG. 4 is a schematic diagram showing an image reading apparatus using a conventional reduced image sensor.

FIG. 5 is a schematic front view showing an image reading apparatus according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading apparatus 2 Light source 3 Selfoc lens 4 Reading pixel 5 Image sensor 6 Document glass 7 Image processing unit 8 Document 9 Imaging lens 10 Reduction image sensor 11, 11a, 11b, 11c Reflecting means

Claims (6)

[Claims] 1. A light irradiating means for irradiating a relatively moving document with light at a predetermined slit width, and a number of read pixels of a required resolution to substantially correspond to a width of the maximum document. In an image reading apparatus having an image sensor arranged in a row and lens means for focusing reflected light from the original on the read pixels, the number of read pixels is in a range of 10,000 to 45000, An image reading apparatus, wherein an image forming lens is arranged on a lens means so that an image forming magnification is substantially equal. 2. The method according to claim 1, wherein the number of read pixels is 13000 to 3000.
2. The image reading apparatus according to claim 1, wherein the value is in a range of 0. 3. The image reading apparatus according to claim 1, wherein the maximum size of the document is at least the A1 size. 4. The image reading apparatus according to claim 1, wherein an optical path from the document to the image sensor is folded by a plurality of reflection units. 5. The image reading apparatus according to claim 1, wherein the imaging lens is provided so as to be movable in a direction of an optical axis of the reflected light, and is variable in magnification on the image sensor. 6. The image forming lens is provided so as to be movable in the direction of the optical axis of the reflected light, and the optical path length of the image sensor from the document is variably provided so that magnification can be changed on the image sensor. The image reading device according to any one of claims 1 to 4, wherein