JP2000050013A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader capable of providing image data with exact magnification and high resolution. SOLUTION: An image reader 1 forms the image of an original 5 at an original reading position A through an optical system 2 having a zoom lens 9 onto an imaging device 10. The focal distance of the zoom lens 9 is set corresponding to the designated magnification. A reference pattern 11 is provided at a position parallel with the original reading position A. The image of the reference pattern 11 is formed through the optical system 2 onto the imaging device 10, and the resolution of image of this reference pattern 11 is detected. The distance between the zoom lens 9 and the imaging device 10 or focal distance of the zoom lens 9 is corrected so that the resolution can exceed a fixed reference value. Electric magnifying processing is applied to the output signal of the imaging device 10 so as to cancel the practical magnification change of the optical system 2 with the correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image reading device. More specifically, the present invention relates to an image reading apparatus such as an image scanner that optically reads an image of a document.

[0002]

2. Description of the Related Art An image reading apparatus of this type is known which forms an image of a document placed at a document reading position on an image pickup device (photoelectric conversion device) via an optical system having a zoom lens. Have been. Image data is obtained from the output signal of the image sensor. When changing the magnification of reading, the focal length changing mechanism changes the focal length of the zoom lens of the optical system according to the magnification specified by the operator.

[0003]

If an accurate magnification can be obtained simply by setting the focal length of the zoom lens, the resolution of the optical system is determined according to the obtained magnification. However, there is a problem that it is not possible to obtain an accurate magnification and, consequently, an accurate resolution simply by setting the focal length of the zoom lens.

An object of the present invention is to provide an image reading apparatus capable of obtaining image data with accurate magnification and high resolution.

[0005]

According to a first aspect of the present invention, there is provided an image reading apparatus, comprising: an image sensor; and an image of a document located at a document reading position on the image sensor via a zoom lens. In an image reading apparatus including an optical system for forming an image and magnification changing means for setting a focal length of a zoom lens of the optical system according to a designated magnification, a reference provided at a position aligned with the document reading position A pattern, an image of the reference pattern is formed on the image sensor through the optical system, and resolution detection means for detecting the resolution of the image of the reference pattern, such that the resolution exceeds a certain reference value. Resolution correcting means for correcting the distance between the zoom lens and the imaging element or the focal length of the zoom lens, and substantially double the optical system associated with the correction by the resolution correcting means. So as to cancel the change, characterized by comprising an electrical variable magnification means for performing an electrical magnification change processing to the output signal of the image pickup device.

In the image reading apparatus according to the first aspect, first, the magnification changing means sets the focal length of the zoom lens of the optical system according to the specified magnification. Prior to reading the image of the original document, the resolution detecting means forms an image of the reference pattern provided at a position aligned with the document reading position on the image pickup device via the optical system, and Detect the resolution of the image. When the resolution is lower than a certain reference value, the resolution correcting means sets the distance between the zoom lens and the imaging device or the focal length of the zoom lens so that the resolution exceeds the certain reference value. to correct. Thereby, a high resolution is realized. Then, the electric scaling unit performs an electric scaling process on the output signal of the image sensor so as to cancel a substantial change in magnification of the optical system accompanying the correction by the resolution correcting unit. The image represented by the signal (image data) after the scaling process accurately corresponds to the specified magnification. Therefore, with the correction by the resolution correcting unit and the scaling process by the electric scaling unit, the image of the original document placed at the document reading position is transferred to the image sensor via the zoom lens of the optical system. In this case, image data can be obtained with accurate magnification and high resolution.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the image reading apparatus of the present invention will be described in detail.

FIG. 1 shows a schematic sectional configuration of an image reading apparatus 1 according to one embodiment, and FIG. 2 shows a block configuration of a signal processing system of the image reading apparatus 1.

As shown in FIG. 1, this image reading apparatus 1
Includes a transparent glass (hereinafter, referred to as “document glass”) 4 disposed horizontally at an upper portion of the main body, and a photoelectric conversion element 10 as an image pickup device and an optical system 2 inside the main body.

An original reading position A is placed on the original glass 4.
Are determined, and are arranged in line with the document reading position A.
A reference pattern 11 described later is provided. The operator places the document 5 at the document reading position A downward.

The optical system 2 includes a light source 6 extending in a direction perpendicular to the cross section of FIG. 1 (this is referred to as a “main scanning direction”).
It includes a reflector 7, mirrors 8a, 8b and 8c, and a zoom lens 9 provided at the lower part of the main body. The light source 6 is formed of a lamp having a cylindrical outer shape. The reflector 7
The light source 6 is disposed on the right side in FIG. 1 and has an arc-shaped cross section facing the light source 6. Light source 6
Is reflected by the reflector 7 and is irradiated in a line toward the original 5 placed on the original glass 4. The mirror 8a is located below the light source 6 and the reflector 7,
In the horizontal direction in FIG. 1 (referred to as the “sub-scanning direction”), the mirror is arranged at a position inclined 45 ° with respect to the original glass 4 with the mirror surface facing upward in the position between these members 6 and 7. I have. The mirror 8b is disposed at a position to the left of the mirror 8a in a posture parallel to the mirror 8a with the mirror surface facing down. The mirror 8c is disposed at a position directly below the mirror 8b in a posture perpendicular to the mirror 8b with the mirror surface facing upward. Light reflected by the original 5 (indicated by a dashed line in FIG. 1)
Are sequentially reflected by mirrors 8a, 8b, and 8c, and further enter photoelectric conversion element 10 through zoom lens 9. As a result, the image of the original 5 is formed on the photoelectric conversion element 10, and the image is read in the main scanning direction. The light source 6, the reflector 7, the mirrors 8a, 8b and 8c
Are supported by a slide mechanism (not shown) and are moved in parallel in the sub-scanning direction. Specifically, when the light source 6, the reflector 7, and the mirror 8a are moved at the speed V, the mirrors 8b and 8c are moved synchronously at the speed V / 2. Thereby, scanning in the sub-scanning direction is performed while maintaining the conjugate length of the zoom lens 9, and image reading in the sub-scanning direction is performed.

The zoom lens 9 is mounted on the optical block 3 together with the photoelectric conversion element 10. As shown in FIG. 2, the image reading apparatus 1 includes a CPU (Central Processing Unit) 20 for controlling the operation of the entire apparatus. The focal length of the zoom lens 9 is variably set by a known type of focal length changing mechanism 16 including a stepping motor under the control of the CPU 20. That is, the CPU 20 and the focal length changing mechanism 16 function as magnification changing means. The photoelectric conversion element 10 is a so-called line sensor (a photodiode arranged in a line).
The longitudinal direction of the photoelectric conversion element 10 is arranged so as to coincide with the main scanning direction. The optical block 3 is a CPU
Under the control of 20, the optical block moving mechanism 17 including a stepping motor translates in the main scanning direction. For example, as shown in FIG. 6, the optical block moving mechanism 17 moves the zoom lens 9 and the photoelectric conversion element 10 to the center position in the main scanning direction X (FIG.
(Shown by a broken line in FIG. 6) to a position shifted by a solid line (shown by a solid line in FIG. 6). At the same time, the focal length changing mechanism 1
6, the distance between the zoom lens 9 and the photoelectric conversion element 10 is changed. As a result, it is possible to enlarge a part of the document 5 and read it with high accuracy.

FIG. 3 shows the original glass 4 shown in FIG.
The upper reference pattern 11 is shown in an enlarged manner. The reference pattern 11 is a line pattern 11 formed in a row on a strip-shaped substrate (white background) which is elongated in the main scanning direction X.
a and a ladder pattern 11b. Both the line pattern 11a and the ladder pattern 11b
"-"-Shaped black lines are formed at a constant pitch (spatial period) in the main scanning direction X and arranged in parallel with each other. The pitch of the line pattern 11a is set to be sufficiently large compared to the width of one line, while the pitch of the ladder pattern 11b is set to twice the width of one line (31p / mm in this example).

The image reading apparatus 1 operates as follows as a whole.

First, a document 5 is placed at a document reading position A on a document glass 4 shown in FIG.
The reading magnification is specified. Then, the CPU 20 controls the focal length changing mechanism 16 (FIG. 2) to set the focal length of the zoom lens 9 according to the specified magnification.

Subsequently, prior to reading the original image of the original, the CPU 20 controls the above-mentioned slide mechanism so that the light source 6, the reflector 7, the mirror 8a, etc. of the optical system 2 convert the image of the reference pattern 11 into an image. It is moved to the position where the image is taken in, and the image of the reference pattern 11 is
Image on top. The output signal of the photoelectric conversion element 10 is A
The digital signal is converted by a / D converter 18 into a digital signal,
Is input to

Here, the output signal of the photoelectric conversion element 10 (A
Indicates the digital signal after / D conversion. The same applies hereinafter. )
The line pattern 11a and the ladder pattern 1b are as shown in FIGS. As can be seen from FIG. 4, periodic drop pulses I ₁ , I ₂ ,... Corresponding to each line of the line pattern 11a appear in the output signal of the photoelectric conversion element 10. Since the coordinates of each line of the line pattern 11a in the main scanning direction X are known, the CPU 20 calculates the address difference Δ between the drop pulses I ₁ and I ₂ on the main scanning address and the pixel pitch.
The magnification of reading can be recognized. When the image of the reference pattern 11 is read in a state where the optical block 3 is set at the reference position and the focal length of the zoom lens 9 is set so as to have the reference magnification, the drop pulses I ₁ and I ₂ are designed. The position shift amount of the optical block 3 can be recognized based on the difference between the address at which appears and the address at which the drop pulses I ₁ and I ₂ actually appear. As can be seen from FIG. 5, the output signal of the photoelectric conversion element 10 includes the maximum value MAX and the minimum value MIN corresponding to the white line (white background) and the black line alternately arranged in the ladder pattern 11b. Appear alternately. The CPU 20 functions as a resolution detecting means, and calculates the resolution of the image of the ladder pattern 11b using the maximum value MAX and the minimum value MIN according to the following equation (1). (Resolution) = (MAX−MIN) / (MAX + MIN) (1)

Next, the CPU 20 determines whether or not the resolution of the image of the ladder pattern 11b exceeds a certain reference value (for example, 0.5). When the resolution of the image of the ladder pattern 11b is lower than the reference value, the CPU
20 serves as a resolution correcting means, and the ladder pattern 11
The focal length changing mechanism 16 shown in FIG. 2 is controlled to control the zoom lens 9 so that the resolution of the image b exceeds the reference value.
Is corrected. Thereby, a high resolution can be realized.

Then, the CPU 20 controls the electric zooming unit 21 as an electric zooming unit to control the zoom lens 9.
A magnification parameter (magnification) for the electric magnification unit 21 is set so as to cancel a substantial change in magnification of the optical system 2 accompanying the correction of the focal length. As can be seen, based on this scaling parameter, when the electrical scaling unit 21 performs an electrical scaling process on the output signal of the photoelectric conversion element 10,
The image represented by the signal (image data) after the scaling process exactly corresponds to the magnification specified by the operator.

Thereafter, the CPU 20 controls the above-mentioned slide mechanism to scan the light source 6, the reflector 7, the mirror 8a, etc. of the optical system 2 in the sub-scanning direction, and
The original image of the original 5 is formed on the photoelectric conversion element 10 via the optical system 2 with the correction of the focal length.
Then, the electric variable power section 21 is connected to the photoelectric conversion element 10.
Is subjected to electrical scaling processing according to the scaling parameter. The signal (image data) after the scaling process is
It is stored in the image memory 14 shown in FIG. In this way, image data can be obtained with accurate magnification and high resolution.

When the resolution of the image of the ladder pattern 11b exceeds the reference value, the focal length of the zoom lens 9 is not corrected. The output signal of the photoelectric conversion element 10 is stored in the image memory 14 without undergoing scaling processing.

In the above example, the focal length of the zoom lens 9 is corrected to increase the resolution. Instead, the distance between the zoom lens 9 and the photoelectric conversion element 10 is corrected. Is also good. Also in this case, the CPU 2
A magnification parameter (magnification) for the electric magnification unit 21 is set such that a change in the magnification of the optical system 2 caused by the correction of the distance between the zoom lens 9 and the photoelectric conversion element 10 is offset by 0. ) And subjecting the electric scaling unit 21 to a scaling process in accordance with the scaling parameter, image data can be obtained with accurate magnification and high resolution.

In the above example, an optical block moving mechanism 17 is provided for enlarging a part of the area of the original 5 and reading it with high accuracy, and the optical block having the zoom lens 9 and the photoelectric conversion element 10 mounted thereon. 3 can be translated in the main scanning direction, but the present invention is not limited to this. FIG.
As shown in (b), two sets of zoom lenses and photoelectric conversion elements may be arranged in the main scanning direction X. A set of the zoom lens 9A and the photoelectric conversion element 10A reads an image of a substantially half area 5A of the document 5, and a set of the zoom lens 9B and the photoelectric conversion element 10B reads an image of the remaining substantially half area 5B of the document 5. Read (a slight crossover is provided between the read areas). In this case, the reference pattern 11 'has ladder patterns 11c and 11d at the center positions of the two regions 5a and 5b, that is, at positions corresponding to the optical axes of the zoom lenses 9A and 9B. Then, before reading the original image of the original 5, the resolutions of the images of the ladder patterns 11c and 11d are detected, and the zoom lenses 9A and 9A are adjusted so that the two detected resolutions exceed a certain reference value and coincide with each other. The focal length of 9B (or the distance between the zoom lens and the photoelectric conversion element) is corrected. Further, the optical system 2 associated with this correction
In order to cancel the change in the substantial magnification of
A scaling parameter (magnification) for 1 is obtained, and the electric scaling unit 21 performs scaling processing according to the scaling parameter. As a result, image data can be obtained with accurate magnification and high resolution. In addition, the resolution levels of the two regions 5a and 5b of the document 5 can be made uniform without relying on mechanical positioning by using expensive components.

[0024]

As is clear from the above, according to the image reading apparatus of the first aspect, it is possible to obtain image data with accurate magnification and high resolution.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a cross-sectional structure of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a signal processing system of the image reading apparatus.

FIG. 3 is a view showing a reference pattern provided on a document glass of the image reading apparatus.

FIG. 4 is a diagram illustrating an output signal of a photoelectric conversion element when a line pattern is read.

FIG. 5 is a diagram illustrating an output signal of a photoelectric conversion element when a ladder pattern is read.

FIG. 6 is a view for explaining how to move the optical block in the main scanning direction.

FIG. 7 is a diagram showing a modification of the image reading apparatus.

[Explanation of symbols]

 2 Optical system 4 Document glass 5 Document 9, 9A, 9B Zoom lens 10, 10A, 10B Photoelectric conversion element 11, 11 'Reference pattern

Claims (1)

[Claims] 1. An image pickup device, an optical system for forming an image of a document at a document reading position on the image pickup device via a zoom lens, and a focal point of the zoom lens of the optical system according to a designated magnification. An image reading apparatus comprising: a magnification changing unit that sets a distance; a reference pattern provided at a position aligned with the document reading position; and an image of the reference pattern formed on the image sensor via the optical system. Resolution detecting means for detecting the resolution of the image of the reference pattern, and correcting the distance between the zoom lens and the imaging element or the focal length of the zoom lens so that the resolution exceeds a certain reference value. A resolution correcting unit that performs an electrical scaling process on an output signal of the image sensor so as to cancel a substantial change in magnification of the optical system accompanying the correction by the resolution correcting unit. Image reading apparatus is characterized in that a to electrical zooming means.