JPH0766948A - Image reader - Google Patents

Abstract

(57) [Abstract] [Purpose] When an image is read by a light receiving means using an image pickup device such as a CCD, an image of high quality which does not have a moire phenomenon and is free from uneven interference peculiar to low pass filters is obtained. Getting a reader. In an image reading apparatus for forming an image of an image 1 illuminated by an illuminating means on an image receiving surface of a light receiving means 3 having a plurality of image pickup devices by an image forming means 2 and reading the image, the image reading means is provided between the image forming means and the light receiving means. The optical means 4 including a plurality of low-pass filters 4A, 4B, 4C having a linear pattern is provided in the optical path of the optical path, and the plurality of low-pass filters forming the optical means have their linear patterns all directed in different directions. thing.

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 obtaining an image (color image) by using an image pickup device such as CCD, and particularly, by using a low-pass filter having a linear pattern, a lineup of image pickup devices (pixels). By using an optical means having a plurality of low-pass filters arranged such that the directions of the linear patterns are different from each other with respect to the direction, while removing the moire phenomenon, remove the inherent interference unevenness caused between the low-pass filters, The present invention relates to an image reading device which is capable of reading the image with high accuracy and is suitable for, for example, a color scanner or a color facsimile.

[0002]

2. Description of the Related Art Generally, in a color image reading apparatus using an image pickup device such as a CCD having a discrete pixel structure, image information is optically spatially sampled to obtain an output image.

In this case, if the color image contains high spatial frequency components higher than the sampling frequency, a false signal such as a structure or color tone which the color image does not have occurs.

That is, frequency components that cannot be collected by the output device (reading device) (frequency components exceeding the Nyquist frequency) cannot be reproduced as image information, and a phenomenon called so-called waveform distortion (aliasing) occurs. This causes moire fringes and false colors to be formed in the output image.

Therefore, conventionally, a low-pass filter is arranged in a part of the optical system of the image reading apparatus to limit the high frequency component of the color image to eliminate the influence of aliasing.

FIG. 4 shows a Japanese Patent Application No. 4-
It is a principal part schematic diagram of the image reading apparatus of No. 31369.

In FIG. 1, reference numeral 41 is a reflection type color image (halftone dot original), and 42 is an image forming means for forming a color image on a surface of a light receiving means 43 described later at a predetermined magnification. Reference numeral 43 denotes a light receiving unit, which is composed of, for example, a one-dimensional line sensor (CCD) or the like, and converts image information from the color image 41 into an electric signal. The line sensor 43 has a plurality of image pickup elements (pixels) arranged so as to have spectral sensitivities corresponding to the three primary colors of R (red), G (green), and B (blue), arranged repeatedly on one line. Let me configure it. In the figure, R,
G and B color filters are vapor-deposited to read a color image with three color lights of R, G and B.

Reference numeral 44 denotes an optical means, and two low-pass filters 44 having a linear pattern as shown in FIG.
A and 44B are provided, and two types of low-pass characteristics are obtained by disposing them at positions different from each other on the optical axis, thereby removing both normal moire and folded moire.

In the figure, a color image 41 illuminated by an illumination means (not shown) is passed through a plurality of low-pass filters 44A and 44B by an image forming means 42 to form an image on the surface of the light receiving means 43 at a predetermined magnification. The color image 41 is digitally read by the light receiving means 43 based on predetermined color light. Then, the reading means including the illuminating means (not shown), the image forming means 42, the optical means 44, and the light receiving means 43 are line-scanned obliquely with respect to the paper surface, thereby sequentially reading the color image 41. .

[0010]

In the image reading apparatus shown in FIG. 4, the directions of the linear patterns of the two low pass filters 44A and 44B constituting the optical means 44 are
For example, if they are all arranged in the same direction, the diffracted lights produced by the linear patterns of the low-pass filters 44A and 44B may interfere with each other to generate a unique interference pattern. Therefore, for example, there may be peculiar unevenness that does not depend on the number of lines of the halftone dot document 41.

For example, when the halftone dot document 41 is read by the light receiving means 43 in this arrangement, the low-pass filter 44 is used.
A unique interference pattern is generated from A and 44B, and as a result, a unique uneven pattern is generated in the output image 45 regardless of the placement direction of the halftone dot document 41 as shown in FIG. There was a tendency.

These phenomena become more prominent when an edge enhancement filter is applied in image processing.

The present invention relates to Japanese Patent Application No. 4 proposed by the present applicant.
The image reading apparatus of Japanese Patent Laid-Open No. 31369/1999 is further improved so that a plurality of low-pass filters constituting the optical means are oriented such that the direction of the linear pattern thereof is appropriate to the arrangement direction of the image pickup elements (pixels) of the light receiving means. The image reading device can effectively prevent the generation of an interference pattern due to the interference of diffracted lights generated by the low-pass filter, remove the moire fringes, and obtain a high-quality image without interference unevenness. For the purpose of providing.

[0014]

An image reading apparatus of the present invention is an image reading apparatus for reading an image illuminated by illumination means by forming an image on a light receiving means surface having a plurality of image pickup elements by an image forming means. An optical unit including a plurality of low-pass filters having a linear pattern is provided in an optical path between the image forming unit and the light-receiving unit, and the plurality of low-pass filters forming the optical unit have different directions of the linear patterns. It is characterized by facing in the direction.

In particular, two low pass filters are provided close to each other in the vicinity of the diaphragm of the image forming means so that the linear patterns are orthogonal to each other, and the linear patterns are provided in a direction different from the directions of the linear patterns of the two low pass filters. The low-pass filter is provided at a different position on the optical axis of the image forming means, or the direction of the linear pattern of the low-pass filter provided at a different position on the optical axis of the image forming means depends on the image pickup device of the light receiving means. That is orthogonal to the array direction of
It is characterized in that the surfaces of the plurality of low-pass filters constituting the optical means on the incident side and the emitting side are all formed of the same pattern.

[0016]

Embodiment 1 FIG. 1 is a schematic view of a main part of an image reading apparatus according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 1 is a reflection type color image (halftone dot original), 2 is an image forming means, which has a diaphragm inside, and a light receiving means (one-dimensional line sensor) 3 described later.
The color image 1 is formed on the surface at a predetermined magnification.

Reference numeral 4 denotes an optical means, which is provided in the optical path between the image forming means 2 and the line sensor 3 and has three low pass filters 4A, 4B and 4C having a linear pattern.
Is made up of. Three low pass filters 4A, 4
B and 4C are arranged so that the directions of the linear patterns thereof are different from the arrangement direction of the elements (pixels) of the line sensor 3.

In this embodiment, the low-pass filter 4A and the low-pass filter 4B are arranged close to each other in the vicinity of the diaphragm position of the image forming means 2, and the low-pass filters 4A, 4A,
The 4B linear patterns are arranged so that the directions thereof are orthogonal to each other. Accordingly, in this embodiment, the line sensor 3
The MTF in the element arrangement direction (main scanning direction) and the MTF in the scanning direction (sub-scanning direction) are efficiently equalized.

The low-pass filter 4C is arranged closest to the line sensor 3, and the linear pattern of the low-pass filter 4C is arranged so as to be different from the linear pattern of the low-pass filter 4A and the low-pass filter 4B. Further, they are arranged so as to be orthogonal to the arrangement direction of the elements of the line sensor 3.

The surfaces of the low-pass filters 4A, 4B, and 4C in the present embodiment on the incident side and the exit side are all formed in the same pattern, which facilitates the manufacture and makes it possible to manufacture at low cost. I have to.

The line sensor (CCD) 3 is, for example, R
A plurality of three elements (pixels) set to have a spectral sensitivity corresponding to the three primary colors of (red), G (green), and B (blue) are repeatedly arranged on one line. Further, R, G, and B color filters are vapor-deposited on the respective element surfaces so that a color image can be read with three color lights of R, G, and B. That is, the color image 1 is read by dividing the range corresponding to the read pixels of the color image 1 in the arrangement direction of the elements.

The illuminating means (not shown), the image forming means 2, the optical means 4, and the light receiving means 3 constitute reading means.

In this embodiment, a color image (halftone dot original document) 1 illuminated by illumination means (not shown) is formed into an image forming means 2.
Thus, the light passes through the low-pass filters 4A, 4B, and 4C to form an image on the surface of the light receiving means 3 at a predetermined magnification. Then, the color image 1 is generated by the light receiving means 3 based on the predetermined color light.
Is being read digitally. Then, the reading means scans the color image 1 line by line, thereby sequentially reading the color image 1.

In general, a line sensor used as a light receiving means in an image reading apparatus scans relatively with respect to an image (halftone dot document), so that the MTF in the scanning direction (sub scanning direction) is the element (pixel) of the line sensor. It is lower than the MTF in the arrangement direction (main scanning direction).

Therefore, it is sufficient to provide the low-pass filter 4C having a low-pass characteristic in the direction (sub-scanning direction) orthogonal to the arrangement direction of the elements of the line sensor in order to remove the folding moire phenomenon.

However, in order to efficiently balance the MTF, the linear pattern of the low-pass filter 4C should be centered around the optical axis of the low-pass filter 4C so that the linear pattern of the low-pass filter 4C is not aligned with the linear pattern of the low-pass filters 4A and 4B. It may be rotated for balancing.

FIG. 2 shows the low-pass filters 4A, 4B, 4A, 4B in the array direction of the elements of the line sensor 3 of this embodiment.
It is explanatory drawing which showed the direction of the linear pattern of 4C.

Each low-pass filter 4A in FIG.
The direction of the linear pattern of 4B and 4C is the line sensor 3
The low-pass filter 4C is arranged at 90 °, the low-pass filter 4B is arranged at 45 °, and the low-pass filter 4A is arranged at 135 ° with respect to the arrangement direction of the elements. Low pass filter 4A and low pass filter 4B
Shows that the linear pattern can be rotated in a predetermined direction (clockwise) about the optical axis of the image forming means (not shown) while maintaining the orthogonal state, and is rotated by 45 ° in the figure. ing. As a result, in the present embodiment, the moire phenomenon is removed while the pattern of interference unevenness caused by the interference of the diffracted lights generated by the low-pass filter is effectively removed.

In the present embodiment, as described above, the image forming means while maintaining the linear state of the linear patterns of the two low-pass filters 4A and 4B provided close to the diaphragm position of the image forming means 2 as described above. Of the low-pass filters 4A, 4 while maintaining good MTF frequency characteristics by arranging them so that they are rotated about the optical axis of and are different from the linear patterns of the other low-pass filters 4C.
The moire phenomenon is removed while the inherent interference unevenness between B and 4C is effectively removed. As a result, the color image (halftone dot document) 1 is read with high accuracy and a high quality image is obtained.

In this embodiment, the three low pass filters 4 are arranged so that the directions of the linear patterns are different from each other.
Although A, 4B, and 4C are appropriately arranged on the optical axis to form the optical means 4, the low-pass filters 4A and 4 are provided.
Other low-pass filters may be added so as to be different from the directions of the linear patterns of B and 4C. According to this, the moire phenomenon can be removed more favorably.

FIG. 3 shows each low-pass filter 4 in the arrangement direction of the elements of the line sensor 3 according to the second embodiment of the present invention.
It is explanatory drawing which showed the direction of the linear pattern of A, 4B, 4C.

This embodiment is different from Embodiment 1 described above in that the low-pass filter 4A and the low-pass filter 4B are used.
30 in a predetermined direction (clockwise) about the optical axis of the image forming means (not shown) while maintaining the linear pattern of
It was rotated. Other configurations and optical functions are substantially the same as those in the first embodiment.

That is, in the present embodiment, by rotating the low-pass filter 4A and the low-pass filter 4B in the clockwise direction about the optical axis of the image forming means (not shown) by 30 ° while maintaining the orthogonal relationship of the linear patterns. Also, the same effect as that of the above-described first embodiment is obtained.

The low-pass filter 4 as in this embodiment
The orthogonal relationship of the linear patterns of A and 4B is effective for equalizing the MTF balance between the array direction of the elements of the line sensor 3 and the scanning direction, but for example, the MTF in the scanning direction is arranged in the pixel of the line sensor. When it is desired to lower the MTF in the direction, it is possible by making the rotation angle of the low pass filter 4B 30 ° smaller or the rotation angle 120 ° of the low pass filter 4A larger.
Further, these values are variable depending on design items considering the removal amount of moire and the like.

Also, Japanese Patent Application No. 4-3 previously proposed by the applicant.
As in Japanese Patent No. 1369, each low-pass filter 4A, 4A
By changing the positional relationship of B and 4C on the optical axis, M
The spatial frequency that makes the TF value 0 can also be changed. In addition, each low-pass filter 4A, 4 with the same pattern
Needless to say, the cost can be reduced by changing the direction and arrangement position of the B and 4C linear patterns.

In each of the above embodiments, an example using a reflection type original (color image) is shown. Of course, even if a transmission type original is used, the present invention is applied in the same manner as the above-mentioned embodiments. be able to.

[0038]

According to the present invention, as described above, the image pickup device (pixel) of the light receiving means is provided in the optical path between the image forming means and the light receiving means.
By providing an optical means having a plurality of low-pass filters arranged so that the directions of the linear patterns are different from each other, the diffracted light produced by each low-pass filter interferes with each other while effectively eliminating the moire phenomenon. It is possible to achieve an image reading apparatus capable of removing an interference pattern generated when doing so and obtaining a high-quality image.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing directions of linear patterns of the respective low-pass filters according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing directions of linear patterns of respective low-pass filters according to the second embodiment of the present invention.

FIG. 4 is a schematic view of a main part of a conventional image reading device.

FIG. 5 is an explanatory view of a main part of a conventional low-pass filter.

FIG. 6 is an explanatory diagram when an image is output by a conventional image reading device.

[Explanation of symbols]

 1 image 2 image forming means 3 light receiving means (line sensor) 4 optical means 4A, 4B, 4C low-pass filter

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Claims (4)

[Claims] 1. An image reading apparatus for reading an image illuminated by an illuminating means by forming an image on a light receiving means surface having a plurality of image pickup elements by an image forming means and reading the image between the image forming means and the light receiving means. An image reading device characterized in that an optical means composed of a plurality of low-pass filters having a linear pattern is provided in an optical path, and the plurality of low-pass filters constituting the optical means have all linear patterns in different directions. apparatus. 2. Two low-pass filters are provided close to each other in the vicinity of the diaphragm of the image forming means so that the linear patterns are orthogonal to each other, and the linear patterns are provided in a direction different from the directions of the linear patterns of the two low-pass filters. The image reading apparatus according to claim 1, wherein another low-pass filter is provided at another position on the optical axis of the image forming means. 3. The linear pattern direction of a low-pass filter provided at another position on the optical axis of the image forming means is orthogonal to the arrangement direction of the image pickup elements of the light receiving means. Image reading device. 4. The image reading apparatus according to claim 1, wherein the surfaces of the plurality of low-pass filters forming the optical unit on the entrance side and the exit side all have the same pattern.