JPH11234482A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image reader that has a uniform resolution of an image and eliminates the need for a memory for software processing by focusing with a constant magnification in synchronism with a scanning of a scanning means. SOLUTION: The rotating mirror 22 of an image pickup camera section acts like a scanning means and is driven to scan an original image in the subscanning direction by a driver. An image pickup lens 23 is driven by the driver to form an image on a line sensor 21 and is focused without changing an image pickup magnification even when the distance from the image forming position to an original face is changed. The focusing with a constant magnification is performed in synchronism with a scanning by the rotating mirror 22. Two-dimensional image reading is conducted by reading in the subscanning direction and reading in the main scanning direction by the line sensor 21 itself. Thus, even when the height of a book original B differs for each read position, the read image is not distorted like a barrel and an image equivalent to an original image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a face-up type image reading apparatus for reading an image on a front surface of a book document or the like with its facing side facing upward.

[0002]

2. Description of the Related Art Conventionally, in a face-up scanner device for reading a two-dimensional image of a book document or the like by optical scanning using a line sensor, the height of the spread surface of the book document is measured in advance, and the height data is obtained. Originally, a clear image is obtained by performing focusing in synchronization with scanning.

FIG. 4 shows an optical system of a conventional image reading apparatus of this type. The image of the target object 101 is
An image is formed on the line sensor 103 by the optical system including the image sensor 2. The longitudinal direction of the line sensor 103 is in the plane of the paper. The taking lens 102 focuses on a change in the object distance by moving the entire lens as usual. D
Is the length of the object in the main scanning direction of the line sensor 103, x is the change in the height of the object, and d and d 'are the lengths of the object image on the line sensor 103 when the object height is low and high. It is.
As can be seen from the figure, as the height of the object increases (the distance decreases), the shooting magnification changes from a / b to a ′ /
It changes to b '.

FIG. 5 shows a read image when a book original with its facing surface facing upward is focused by the above-described normal lens extension method. As described above, since the magnification of a high portion of the document is increased, the read image 104 has a shape as if two barrels are connected as shown in FIG.

[0005]

As described above, in the conventional book document reading method, the magnification changes in accordance with the height of the book document, so that the read image is distorted in a barrel shape. However, in order to obtain an image similar to the original image, in addition to the need for software processing, the density of the finally obtained image becomes the pixel density at the position where the image is most reduced, and the image The resolution will be reduced. In addition, there is a problem that a memory is required for software processing.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. In a face-up reading apparatus that reads a book document using a line sensor, the height of the book document differs at each reading position. Also, the read image is not distorted in a barrel shape, an image similar to the original image is obtained, and software processing for correcting distortion is unnecessary, and therefore, the resolution of the image is uniform and does not decrease. It is another object of the present invention to provide an image reading apparatus which does not require a memory for software processing.

[0007]

According to a first aspect of the present invention, there is provided an image reading apparatus for reading an upward original by optical scanning from above, a line sensor for reading the original image, and a line sensor for reading the original image. An imaging lens for forming an image on a sensor, and scanning means for relatively moving the original image by the line sensor and the imaging lens,
The imaging lens is a lens capable of focusing without changing magnification even when the distance from the image forming position to the document surface changes, and performs magnification-invariant focusing in synchronization with scanning by the scanning unit. is there. In the above configuration, when the line sensor scans the original image and reads a two-dimensional image, the imaging lens performs focusing without changing the magnification in synchronization with the scanning, thereby distorting the image in the main scanning direction of the line sensor. Can be eliminated.

According to a second aspect of the present invention, in the configuration described in the first aspect, the change in the distance from the image forming position to the document surface includes a change in the distance due to the scanning method of the scanning unit. In the above configuration, an image similar to the original image can be obtained even when the original is scanned using the rotating mirror.

According to a third aspect of the present invention, in the configuration according to the first or second aspect, the original to be read is a three-dimensional object, and the shape of the object is measured in advance, and the imaging lens is used. Is to perform magnification-invariant focusing on the surface of a three-dimensional object using the measurement data during scanning. In the above configuration, it is possible to accurately perform magnification-invariant focusing based on data (distance height) from the imaging position to the document surface obtained in advance.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the image reading apparatus. The image reading apparatus includes a platen 10 on which a document B such as a book or a file is placed facing upward.
Above the document table 10, an imaging camera section 20 for reading the document B by optical scanning is provided.
The imaging camera section 20 has a CCD line sensor 21 as an imaging element, a folding rotary mirror 22 as an optical system for forming an original image on the line sensor 21, and a photographing lens 23. Document B is located on the upper back side of platen 10.
An illumination unit 30 that illuminates the document table 10 is provided.
0 and a height measuring mirror 50 that captures the shape of the upper end of the document B. Further, a start key 60 for causing the apparatus to start reading an image is provided on the platen 10 at each of left and right target positions.
Are provided.

The rotating mirror 22 of the imaging camera unit 20 functions as a scanning unit, and is driven by a driving device (not shown) so as to scan the original image in the sub-scanning direction. The imaging lens 23 is driven by a driving device (not shown) so as to form an image on the line sensor 21, and performs focusing without changing the photographing magnification even when the distance from the image forming position to the document surface changes. (Details described later). This constant magnification focusing is synchronized with the scanning of the rotating mirror 22. Reading in the sub-scanning direction and line sensor 2
The two-dimensional image is read by reading in the main scanning direction by itself.

FIG. 2 is a front view showing a state in which the upward facing surface of the book document is scanned by the rotating mirror 22. The longitudinal direction of the line sensor 21 is perpendicular to the drawing. From a state in which a point P on the document surface (actually, a line passing through the point P and perpendicular to the drawing, but referred to as a point in the drawing) is rotated, the rotating mirror 22 swings by an angle θ, and When the upper point Q is scanned, the distance from the photographing lens 23 to the object (original surface) is
It becomes shorter by x than the distance when the point P is scanned.

FIGS. 3A and 3B are diagrams showing the configuration of the photographing lens 23, and correspond to a state in which the points P and Q are read, respectively. The photographing lens 23 is composed of two groups, and it is assumed that the object plane and the image plane are arranged at the focal position of each group. That is, in FIG.
Consider a lens system including a lens group 1 on the object side having a focal length corresponding to the object distance f1 and a lens group 2 (fixed) on the image plane side with a focal length f2. Is formed. As shown in FIG.
When the object 3 moves to the lens side by x, the focus can be achieved by moving the lens group 1 on the object side to the right by x. Moreover, the magnification is represented by -f1 / f2, and is constant regardless of the object distance.

Therefore, the height data of the book document B is collected in advance and converted into the distance from the rotation center O of the rotating mirror 22 shown in FIG. The angle θ of the rotating mirror 22 is replaced with the position data.
A table of position data of the lens group 1 on the object side corresponding to (scan angle) is prepared, and based on this, the lens group 1 on the object side is moved in synchronization with the scanning angle θ to focus. The magnification can be unchanged. In this way, focusing can be performed at a constant magnification in synchronization with the scanning in accordance with the height of the spread of the book document, and an image with a constant reading density can be obtained regardless of the scanning position.

In the present embodiment, for simplicity of description, the taking lens 23 is composed of two groups of lenses.
The object plane and the image plane have a configuration such that they are at the focal position of each group. In this configuration, it is necessary to move the lens group 1 on the object side by the same amount as the change in the object distance. For example, US Pat. No. 5,383,059
The use of a lens as disclosed in Japanese Patent Application Laid-Open No. H11-27995 makes it possible to focus with a compact configuration while keeping the magnification unchanged regardless of the object distance.

In the present invention, a mirror rotation method has been described as a scanning method. However, in this scanning method, the object distance changes with scanning even for a flat original.
In addition to the change in the height of the book document, the focus is unchanged. Other scanning methods can be adopted as long as they can focus while keeping the magnification unchanged.

[0017]

As described above, according to the image reading apparatus of the present invention, when scanning a book original using a line sensor to read a two-dimensional image, focusing at a constant magnification is performed in synchronization with the scanning. Therefore, even if the height of the book document is different for each reading position, the read image does not distort in a barrel shape, an image similar to the original image is obtained, and a software-based method for correcting the distortion is provided. No processing is required. Therefore, the resolution of the image is uniform and does not decrease, and a memory is not required for software processing.

Further, even in a simple scanning method in which a mirror is rotated as a scanning means, an image similar to the original image can be obtained. Furthermore, by performing constant-magnification focusing in synchronization with scanning based on height data of a book manuscript obtained in advance, not only software processing and memory are not required, but also a finally obtained image is obtained. The density can also be higher.

[Brief description of the drawings]

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

FIG. 2 is a front view illustrating a state in which an upward facing surface of a book document is scanned by a rotating mirror;

FIGS. 3A and 3B are diagrams illustrating a configuration of a photographing lens. FIGS.

FIG. 4 is a diagram showing an optical system of a conventional image reading apparatus.

FIG. 5 is a diagram illustrating a read image when a book document is focused by a normal lens extension method.

[Explanation of symbols]

 21 CCD line sensor 22 Rotating mirror (scanning means) 23 Photographing lens

Claims (3)

[Claims] An image reading apparatus for reading an upward original by optical scanning from above, a line sensor for reading an original image, an imaging lens for forming an original image on the line sensor, and an original image formed by the line sensor and the imaging lens And a scanning means for relatively moving the imaging lens, wherein the imaging lens is a lens capable of focusing without changing the magnification even if the distance from the image forming position to the document surface changes, and An image reading apparatus, wherein magnification-invariant focusing is performed in synchronization with scanning. 2. The document reading apparatus according to claim 1, wherein the change in the distance from the image forming position to the document surface includes a change in the distance by the scanning method of the scanning unit. 3. An original to be read is a three-dimensional object, and the shape of the object is measured in advance, and the imaging lens uses the measurement data during scanning to adjust the magnification of the surface of the three-dimensional object. 3. The document reading apparatus according to claim 1, wherein focusing is performed.