JPS6326065A - Image reader - Google Patents

Abstract

PURPOSE:To remove moire by placing a lentucular plate on the plane of light incidence of solid-state image pickup elements in which photodetectors are arranged one- dimensionally to make the direction of arrangement of element lenses conform with the direction of arrangement of photodetectors and making the amount of blur caused by the lenticular plate about double as much as the intervals of the photodetectors. CONSTITUTION:In the case of an optical system in which incident light 10 forms an image at a point P on an image pickup element 7, the luminous flux 10 is divided by each element of a lenticular plate 9, and each small luminous flux forms an image at a point P' and is diverged and spread to an area A on the color image pickup element 7 and causes blur at the image forming point P. The amount of blur DELTAbecomes the same in primary approximation for each element lens of the lenticular plate 9. The first zero cross frequency of response function of the lenticular plate 9 is 1/DELTA, and by making it 1/2 of sampling frequency, that is, making it equal to Nyquist frequency, the occurrence of more can be eliminated. In taking it into consideration that it is an unmagnification system, Nyquist frequency becomes 1/(2d) (d is the interval of photodetectors of the image pickup element), and accordingly, it is sufficient when 1/DELTA=1/(2d).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device, and particularly to an image reading device that prevents moiré using compact means.

(Prior Art) As shown in FIG. 10, a conventional image reading device includes a platen glass 1 on which an original is placed, a light source 2 that illuminates the original, and a light source that reflects light reflected from the original. a first mirror 3, a second mirror 4, and a third mirror 5 that form a predetermined optical path; a spherical lens 6 that focuses the reflected light;
The image pickup device 7 converts the light focused by the spherical lens 6 into an electrical signal.

The image sensor 7 is of an array type in which a plurality of light receiving elements are arranged, such as a one-dimensional CCD sensor.

Now, in an image reading device having such a configuration,
When reading a document placed on platen glass 1, light source 2 and first mirror 3 are scanned in the sub-scanning direction (arrow A direction). On the other hand, the image sensor 7 converts the input document information into electrical signals line by line at a predetermined period.

By repeating this operation, reading of the document information progresses.

(Problem that the invention attempts to solve) The above-mentioned conventional technology had the following problems.

That is, if there is a high frequency component in the document information, a beat component such as moiré will occur between the sampling frequency of the reading device and the quality of the reproduced image will be significantly degraded.

An object of the present invention is to eliminate the problems of the prior art described above and to make it possible to prevent the occurrence of moiré with a compact means.

(Means and operations for solving the problems) In order to solve the above problems, the present invention provides an image reading device using a solid-state image sensor having a plurality of light-receiving elements arranged one-dimensionally. A lenticular plate is arranged on the light incident surface of the solid-state image sensor so that the arrangement direction of the element lenses thereof coincides with the arrangement direction of the light receiving elements, and the amount of blur caused by the lenticular plate is approximately 2 times the distance between the light receiving elements. The feature is that moiré can be removed with a compact device by doubling the size.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a schematic diagram of an embodiment of the present invention.

In the figure, 1 is a platen glass on which the original is placed; 2
is a light source that illuminates the original; 3 is a mirror that reflects light reflected from the original; 8 is a rod lens array; 4 is a mirror; 9
7 is a lenticular plate according to the present invention, and 7 is the one-dimensionally arranged image pickup device described above.

A perspective view of the lenticular plate 9 and the image sensor 7 is shown in FIG. In this embodiment, as shown in the figure, the element lenses of the lenticular plate 9 are provided in the same direction as the arrangement direction of the light receiving elements of the image sensor 7, and the distance l between the two satisfies the following formula. There is.

1 = d
The photodetector is in a pinch.

Next, the reason why the present embodiment can prevent the occurrence of moiré will be explained.

Now, as shown in FIG. 3, it is assumed that there is an optical system in which the incident light beam 10 forms images on two points on the image sensor 7''.

At this time, when the lenticular plate 9 is inserted as shown in FIG. 4, the light beam 10 is divided into each element of the lenticular plate 9, and each small light beam forms an image at a point P' and further diverges, resulting in color imaging. It spreads over area A on element 7. In other words, the original image forming point P will be blurred.

If this amount of blur is Δ, the amount of blur Δ will be the same for any element lens of the lenticular plate 9 in a first-order approximation. Therefore, it is sufficient to consider one element lens of the lenticular plate 9 when calculating the amount of displacement.

Therefore, focusing on FIG. 5, the distance between the lenticular plate 9 and the image plane 7a on the image sensor 7 is 1, the distance from the lenticular plate 9 to the imaging point P' is 1', and the curvature of the element lens is 1'. If rl is the pitch, Pl is the refractive index of the lenticular plate 9, then the following equation holds true.

1/l-1/1 --(n-1)/r Here, if the refractive index n of the lenticular plate 9 is set to n-1,5, the above equation becomes as follows.

1/1-1/1 =--1/ (2r) Therefore, the following formula holds true.

1--2 r 1/ (2r+ 1) = -(2J Furthermore, the amount of displacement Δ is expressed by the following formula.

Δ-PIX(1-1-)/l-...(3) Said (
Substituting equation (2) into equation (3) yields the following.

Δ-1/ f2 X (r/P)l ・・・・・・
(4) Next, the response function of the lenticular plate 9 is given by the following equation in the X direction, since if the element lens is considered to have no aberration, the light beam emitted from the - point spreads by Δ in the X direction. expressed.

sin (πΔf)/πΔf Here, f is the spatial frequency.

The first zero crossing frequency of this response function is 1/Δ
If this is made equal to 1/2 of the sampling frequency, that is, the Nyquist frequency, the occurrence of moiré can be eliminated. Here, if we take into account that it is an isometric system,
Since the Nyquist frequency is 1/(2d) (where d is the distance between the light receiving elements of the image sensor), the following equation should be satisfied.

1/Δ−1/(2d) Substituting the above equation (4) into this Δ and finding d yields the following.

d=l/f4X(r/P)1 Therefore, 1=dx4　x　(r/P)-15) becomes.

Therefore, moiré can be removed by arranging the lenticular plate 9 so as to satisfy equation (1).

Next, a specific example of the image reading device of this embodiment will be described.

In this specific example, an equal-width contact type image sensor that performs sampling at 16 dots/mm, that is, an image sensor with a distance d between light receiving elements of 62.5 urn (-1/16 mm) is used. In addition, a lenticular plate 9 with r/P = 20
Use. When these values are substituted into the above equation (1), the distance 1 between the lenticular plate 9 and the light receiving element becomes as follows.

1 m 5 mm When a document is read in continuous feed mode with this image reading device,
It was possible to obtain a good image reading device free of moiré in both the main scanning direction and the sub-scanning direction.

Next, regarding the second embodiment of the present invention, FIGS.
This will be explained with reference to the figures. FIG. 6 is a plan view of this embodiment, and FIG. 7 is a sectional view taken along the line A--A in FIG. 6.

In the figure, 11 is a ceramic substrate, 12 is a staggered photosensitive pixel array formed on the ceramic substrate, and 13 is a dust-proof lenticular plate cover fixed to the ceramic substrate 11 with an adhesive.

The lenticular plate cover 13 is integrally molded, for example, with a resin having a refractive index of 1.5, and the arrangement direction of the element lenses of the lenticular plate is aligned with the arrangement direction of the photosensitive pixel row 12. Further, the distance l between the light receiving surface of the photosensitive pixel array 12 and the lower surface of the lenticular plate cover 13 is set to a value determined by the above equation (1).

The device of this embodiment is provided in the optical path of the light reflected by the mirror 4 in FIG. In this embodiment, as in the first embodiment, l = 5 in, and r/P-2
When the lenticular plate cover 13 of No. 0 was used, a good reproduced image without moiré could be obtained.

According to this embodiment, since the lenticular plate is formed integrally with the dustproof cover, a support for installing the lenticular plate in the optical path is not required, and the structure becomes more compact.

Next, a third embodiment of the present invention will be described with reference to FIGS. 8 and 9. FIG. 8 is a schematic configuration diagram of this embodiment, FIG. 9 is an enlarged view of the main part, and 15 is a lenticular plate 1.
6 shows the mirror surface formed on the back surface of the device. Further, other symbols indicate the same or equivalent items as in FIG. 2.

According to this device, the incident light source is first applied to the lenticular plate 1.
6, the light is reflected by the mirror surface 15, and passes through the lenticular plate 16 again toward the image pickup device 7. That is, the incident light passes through the lenticular plate 16 twice. Further, the incident angle and exit angle to the lenticular plate 16 are 45°.

Taking these two points into consideration, the above equation (1) can be transformed as follows.

d-2Xv'Txl/ (4X (r/P)1-1
/ J7
μm), and the distance l between the lenticular plate and the image sensor
When 5 mm, r/P=57, and if an image reading device satisfying these values was created, a good reproduced image without moiré could be obtained.

According to this embodiment, since the lenticular plate is formed integrally with the mirror that reflects light, there is no need for a support for installing the lenticular plate in the optical path, resulting in a compact design.

In addition, each of the above-mentioned embodiments is disclosed in, for example, Japanese Patent Application No. 59-1815.
A color image sensor of the type disclosed in Publication No. 68,
That is, it goes without saying that the present invention can also be applied to a color image sensor in which color filters of the same shape are arranged on a parallelogram-shaped photosensitive pixel array.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

According to the present invention, the occurrence of moiré can be prevented using the lenticular plate, so that the image reading device can be manufactured compactly. Furthermore, if the lenticular plate is formed integrally with the dustproof cover of the image sensor or with a mirror that reflects light reflected from the original to form a predetermined optical path, a support for the lenticular plate is not required. Therefore, there is an effect that the image reading device can be made even more compact.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view of essential parts of a first embodiment of the present invention, and FIG. 2 is a schematic diagram of an image reading device to which this embodiment is applied. FIG. 4 is an explanatory diagram of the light beam incident on P. FIG. 4 is an explanatory diagram of the optical path when a lenticular plate is inserted into the optical system.
The figure is an explanatory diagram of the amount of radiation by one element lens of the lenticular plate, and Figures 6 and 7 are, respectively,
A plan view and a sectional view of the main parts of the second embodiment of the present invention, No. 8
The figure shows a schematic configuration diagram of a third embodiment of the present invention, FIG. 9 shows an enlarged view of the main part thereof, and FIG. 10 shows a schematic configuration diagram of a conventional image reading device. 7... Image sensor, 9, 16... Lenticular plate,
13...Lenticular plate cover, 15...Mirror surface agent Patent attorney Michito Hiraki 18 Figure 1 Figure 2 Figure 3 Figure 4 Figure n 5.

Claims (3)

[Claims] (1) In an image reading device using a solid-state image sensor formed by one-dimensionally arranging a plurality of light-receiving elements, a lenticular plate is provided on the light incident surface of the solid-state image sensor, and the array direction of the element lens is aligned with the light-receiving element. An image reading device characterized in that the lenticular plate is arranged so as to match the arrangement direction of the light receiving elements, and the amount of blur caused by the lenticular plate is approximately twice the distance between the light receiving elements. (2) The image reading device according to claim 1, wherein the lenticular plate is integrally formed with a dustproof cover of the solid-state image sensor. (3) The image reading device according to claim 1, wherein the back surface of the lenticular plate is mirror-finished, and the lenticular plate is installed in place of a reflecting mirror in the optical path.