JPS6030256A - Image reader - Google Patents

Abstract

PURPOSE:To improve subscanning-directional resolution by deforming an image so that the formed image is longer in the subscanning direction than in a main scanning direction when the image is focused on an image sensor. CONSTITUTION:A subject image obtained by light irradiation from a light source 1 is converged by a lens 3 and focused on the photodetection part of the image sensor 4 through a convex cylindrical mirror 5. At this time, the direction of the curvature center axis 11 of the cylindrical mirror 5 is set at right angles to the optical axis of the lens 3 and subscanning direction V so that light from the lens 3 changes in path. Thus, the cylindrical lens 5 is positioned to obtain an image which has the same magnification as an image at a position A in the main scanning direction H and is magnified by X (>N) corresponding to the enlargement of an image of a focal position B corresponding to the curvature radius R of the surface of the mirror 5 in the subscanning direction on the photodetection part of the image sensor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for reading images using a solid-state image sensor.

Conventionally, in devices that irradiate light onto a subject such as microfilm, use a lens to form an image on the light receiving section of a solid-state image sensor (such as a COD image sensor), and convert the optical image into an electrical signal, an image sensor is used. Several problems have arisen regarding the shape of the second light receiving section. As shown in FIG. 1, the light receiving section of a solid-state image sensor (1, for example, a CCI image sensor) is constructed by arranging 1,000 to 2,000 square-shaped individual light receiving elements S in a row. In the figure, a is the length of one side of the light-receiving element S, and Wl, . . . , Wn indicate the numbers assigned to the light-receiving element S. When reading an image of a subject by dividing it into individual light-receiving elements S, the resolution in the main scanning direction 11 (meaning the direction in which 1000 to 2000 light-receiving elements S are lined up) is determined by the number of light-receiving elements S. . Then, in the sub-scanning direction (
The resolution of the direction of scanning performed using means for moving the object or image sensor, or the direction in which the image flows and moves (usually perpendicular to the above-mentioned main scanning direction), is the resolution of the light receiving element. It is determined by the length a of one side of S. Therefore, in a device that repeatedly moves and stops the subject or image sensor for sub-scanning and reads image information only when it stops, the relative speed between the image sensor and the subject is zero at the time of reading. Therefore, the resolution is the same in both the main scanning direction and the sub-scanning direction.

However, in this case, the feed of the sub-scanning must be stopped when reading, and it takes a long time for the sub-scanning, so it cannot satisfy the demands of the times for speed reduction. . Therefore, in order to increase the speed of sub-scanning, it is necessary to read images while always moving the subject or the image sensor at a constant speed.

However, if the sub-scanning speed is kept constant, a problem arises in that the resolution in the sub-scanning direction decreases for the reason shown in Pope. For example, FIG. 2 shows a case where a certain number of light receiving elements S sub-scan the image plane of the subject at a constant speed (however, they do not move in the main scanning direction). Here, 11 or 12 is a line indicating a hypothetically set area by dividing the image plane in the sub-scanning direction, and it is assumed that the width of this line is determined to be, for example, the vertical side a of the light receiving element S. Also, in order to fully read the information on each line,
- Set the reading time for each line as L3-t+ (constant). First, at time L1, the light receiving element S reads the image information of the first line 41. Next, time L2 (=(L3
+E1)/2), the upper half of the light receiving element S reads the image information of the lower half of the second line 12, and the lower half of the light receiving element S reads the image information of the upper half of the second line 4□. Also read. Furthermore, at time L3, the light receiving element S is completely switched to the second state.
Read the information on line 12. That is, when sub-scanning is performed at a constant speed, the light-receiving element S reads the information of both the first and second lines in a substantially overlapping manner within the - reading time L3-11, and as described above, The angular image accuracy in the sub-scanning direction is reduced by half compared to the case where sub-scanning is stopped sequentially.

Therefore, a method has been devised to read image information in a pseudo-stopped state. For example, there is a method that utilizes momentary light emission from a light emitting device such as a strobe. However, in this case, the amount of light received by the CCD image sensor is generally the intensity of light (
Since it is determined by the product of the light receiving time (AX) and the light reception time ([n), the intensity of the light must be increased in order to obtain the necessary amount of light.

For this purpose, the structure of the machine becomes complicated, and the electrical hardware also becomes complicated. Furthermore, in order to obtain a light-emitting device that can be used for high-speed reading, it is necessary to increase the blinking frequency and improve the sensitivity of the light-receiving element to cope with it (overcoming the large amount of flashing). There must be.

The present invention has been made to eliminate the above drawbacks, and when forming an image on an image sensor, for example, a convex cylindrical mirror or a concave cylindrical lens is used between the image forming lens and the image sensor.
By distorting the image to be formed so that its length in the sub-scanning direction is longer than the length in the main-scanning direction, the resolution in the sub-scanning direction can be improved. An object of the present invention is to provide an image reading device that enables improved image reading.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic diagram showing essential parts of an embodiment of the present invention. Here, the light source 1 is for irradiating a subject 2 such as a microfilm with light. The lens 3 is designed to focus the light image obtained by the light irradiation and form the light onto a light receiving portion of an image sensor 4 such as a CCD image sensor. Also, radius 1
A convex cylindrical mirror 5 having a curvature of t is placed in such a position that its central axis of curvature 11 is perpendicular to the optical axis of the lens 3 and the sub-scanning direction V, and the path of light from the lens 3 is changed. Furthermore, if the arrangement direction of the light receiving elements of the image sensor 4, that is, the main scanning direction 1'1, is parallel to the central axis of curvature 11 of the convex cylindrical mirror 5, and the surface of the mirror 5 is flat, the light from the lens 3 will be focused. The image sensor 4 is placed at a position N where it will connect.

First, in the conventional state where the convex cylindrical mirror 5 is not provided, the image on the subject 2 is assumed to be an N-times image, for example, and formed at the entry position according to the lens 30 magnification. Therefore, as mentioned above, by providing the convex cylindrical mirror 5 at a flexible position, the light receiving section of the image sensor 4 is displayed at the same magnification (N times) as the image at the above-mentioned position in the main scanning direction I. And, in the sub-scanning direction V perpendicular to the main-scanning direction '1], for example, N times (X> N).In other words, the convex cylindrical mirror 5
As the name suggests, the image has a cylindrical mirror surface, so there is no image distortion in the main scanning direction 11, and the image is distorted by a factor of X only in the sub-scanning direction (2).

Therefore, the case where image information on a subject is read according to this embodiment will be described below using FIG. 4. Here, it is assumed that image information within a virtual line 71+72 set at a constant interval on the image plane is read under the same conditions as in the conventional example (FIG. 2), that is, at a constant sub-scanning speed. Also, here, since the image is magnified by X times in the sub-scanning direction (■) and formed on the light receiving section, the virtual line l11+11.2 set on the image plane is
Expanded twice, the interval is a', (-N a )
Therefore, compared to the conventional example (Fig. 2), X/N (> 1
) will be doubled.

Then, first, at time [1, the light receiving element S is on the first line 1
Read the information within the area of axa at the lower end of 1.

Next, at time t2 (−(t3+tt) 72 ), the light receiving element S reads information within the area of axa near the center of the line 11. Furthermore, at time L3, the light receiving element S reads the information within the second line 12, but the amount of information is only within a small area of a><a, and this amount of information is This is a very small amount compared to the total information amount of axa' (-aXa XN ).

Therefore, in the conventional example described above, one line is read out once.
In contrast, in the above embodiment, in addition to the information on line 11, all the information on line 12 is read over the information on line 12, which is useless information. Only (<1) times as much information is read, and the resolution can be improved to the extent that the amount of wasted information is reduced.

FIG. 5 is a schematic diagram showing essential parts of another embodiment of the present invention. This is an optical system substantially equivalent to the embodiment shown in FIG. 3, in which a concave cylindrical lens 6 is used in place of the convex cylindrical lens 50. Here, the third
The light receiving part of the image sensor 4 is arranged at the same position as the position A in the figure, and a concave cylindrical lens 6 with a certain curvature is placed between the lens 3 and the image sensor 4, and its optical axis is It is arranged parallel to the optical axis of the lens 3, and its central axis of curvature 12 is parallel to the main scanning direction 1 of the image sensor 4. Furthermore, a correction lens 7 is provided for correcting the focal position shift caused by the lens 6, CCI), and image distortion in the longitudinal direction. Then, based on the same principle as the embodiment shown in FIG. 2, the magnification in the main scanning direction II is the same as when the concave cylindrical lens 6 is not used, and the magnification is constant only in the sub-scanning direction (2) depending on the size of the curvature. Each light receiving element of the image sensor 4 reads the enlarged and distorted image. Therefore, the principle of reading image information shown in FIG. 4 can be applied as is, and therefore the same effect as the embodiment shown in FIG. 3 can be obtained.

In the embodiment shown in FIG. 3, instead of the convex cylindrical mirror 5, a concave cylindrical mirror is arranged so that its central axis of curvature is perpendicular to the central axis of curvature of the mirror 50, and the main scanning of the image is performed. A similar effect can be obtained by conversely decreasing the magnification in the direction.

Furthermore, in the embodiment shown in FIG. 5, instead of the concave cylindrical lens 6, a convex cylindrical lens is arranged so that its central axis of curvature is perpendicular to the central axis of curvature of the lens 60, and the main scanning of the image is performed. Even if the magnification in the direction is made smaller, the same effect can be obtained.

Further, although the present invention is mainly applied to devices that read images of objects such as microfilm using transmitted light, it is also applicable to devices that read images by reflecting light onto them, such as facsimile machines and RI copying machines. It is also applicable to

As explained above, the present invention allows an image to be read by an image sensor to be read by an image sensor so that the length of the image in the sub-scanning direction on the screen is longer than the length in the main scanning direction.
By distorting, the amount of unnecessary information read in the sub-scanning direction is reduced, and the image can be read without reducing the resolution in the sub-scanning direction even with a constant-velocity sub-scanning method, which is an extremely excellent effect. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the light receiving section of a CCD image sensor, FIG. 2 is a diagram of the operating principle of image reading according to the conventional example, FIG. 8 is a schematic diagram showing the main parts of an embodiment of the present invention, and FIG. The figure is a diagram of the operating principle of image reading according to the present invention, and FIG. 5 is a schematic diagram showing the main part of another embodiment of the present invention. J...Light source 2...Subject 3...Lens 4...Image sensor 5...Convex cylindrical mirror 6...Concave cylindrical lens 7...Correction lens Figure 1 Figure 2 Figure 1 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] An image reading device that reads an image using a solid-state image sensor, wherein the image formed on the sensor is distorted in the sub-scanning direction.