JPH06291945A - Picture reader - Google Patents

Abstract

PURPOSE:To solve problems such as precision in manufacture of a shading correction plate (standard white board) and deposition of dust in the picture reader having an original lighting means, a solid-state image pickup element in which light receiving elements are arranged in a line, and an image forming optical system forming an image of the original onto the solid-state image pickup element or the like. CONSTITUTION:In the picture reader having a lighting means lighting an original, a solid-state image pickup element in which light receiving elements are arranged in a line, an image forming optical system forming an image of the original to the solid-state image pickup element, and a shading correction plate (standard white board), when the image of the standard white board 1 to the solid-state image pickup element, the optical system is defocused by using a diffusion board 8 or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to correction of light in an image reading apparatus that reads a document with a linear solid-state image sensor.

[0002]

2. Description of the Related Art Next, a conventional technique will be described.

<Conventional Example 1> In Conventional Example 1 shown in FIG. 7, the image reading apparatus includes a shading correction plate 1, a document table glass 2, an illumination optical system 3, a full speed mirror 4, a half speed mirror 5, and an imaging lens 6. , CCD line sensor 7.
As shown in FIG. 8, a CCD line sensor generally has a plurality of pixels arranged in a horizontal row at a pixel pitch of 6 to 7 μm. The lens 6 is generally provided so as to form an image on the CCD sensor 7 at a magnification of 1/10. A document (not shown) is placed on the document table glass 2. Lighting system 3
Is configured to move in parallel with the full-speed mirror 4 from left to right in the figure, and at the same time, the half-speed mirror 5 is configured to move from left to right in the figure at half the speed of the full-speed mirror 4. The original is linearly imaged on the CCD 7 from left to right. Since the CCD 7 outputs an electric signal according to the light energy that has entered each pixel within a unit time, the output for the image of the original can be sequentially obtained.

When a manuscript having a uniform density is read, C
The output of each pixel of the CD is not constant as shown in FIG. FIG. 9 shows the output of each pixel of the CCD at a certain point of time, with the horizontal axis indicating the pixel and the vertical axis indicating the output.

This is because uniform illumination without any unevenness is impossible, the amount of light at the end portion decreases due to the cos 4th power of the imaging lens, and the sensitivity unevenness of each pixel of the CCD is generally about ± 10%. The reason is that it changes with the usage time of the device.

As a means for solving this problem, "shading correction" is generally performed. In FIG. 7, a uniform white (standard white) shading correction plate 1 is provided, the standard white of 1 is read before reading the original, and the CCD output at the time of reading the original is corrected based on this information. is there. Specifically, the output S _ij of the CCD reading (i-th pixel, j unit time, i = 1, 2, 3, ...
n, j = 0, 1, 2, ... M, where j = 0 is standard white data and j > 1 is original data)

[0007]

[Equation 1]

A correction calculation of (η is a correction constant) is performed as an output of the apparatus.

<Prior Art 2> For a copying machine, a facsimile machine, and an image input apparatus for inputting image information to a computer, etc., an original is illuminated by a light source, and the reflected light is converted into an electric signal by a line image scanner. An image reading apparatus of a type that moves an image reading line in the sub-scanning direction while converting is used. The original is illuminated very brightly at the center of the line of such line-type image reading, but the amount of light that hits the original at both ends is small, and an unbalance in illuminance occurs between the center of the original and both ends of the original. There is a problem. Conventionally, in order to solve this problem, as shown in FIG. 11 (b), one kind of light amount correction plate, which is shown by a slant line, has a narrow central opening and wide opening at both ends as a light source and a CCD. Was installed in the optical path of.

[0010]

However, the above-mentioned conventional example has the following problems.

That is, the conventional example 1 has the following problems. This is because if the uniformity of the white plate is not sufficient, the data of S _{ko in} the above equation will be inadequate, and S _{kj of the} device output signal will also be inadequate, and streaks will appear in the portion corresponding to S _kj of the output image. As a result, the uniform accuracy of the white plate is currently becoming severe.

The resolution of the current reader is 400 DP
I is the mainstream, and the reading width per pixel at this time is 6
It is about 0 μm, and development of higher resolution is required. Therefore, even if a uniform white plate is manufactured, 60μ
It is required to make the concentration uniform in a small area of m order or less,
Extreme difficulty and high cost. Also, the uniformity of surface roughness is becoming severe. Further, the allowable size of dust or the like that adheres to the white color when assembling the device is considerably reduced, and a great amount of labor is required to clean the white plate. In addition, minute dust that adheres when the device is used poses a problem.

Further, in the above-mentioned conventional example 2, when three types of light sources are sequentially turned on to perform R reading, G reading, and B reading, there are the following problems.

In FIG. 15, the light amount distribution on the original surface of the G light source is represented by a solid line u, and the B light source is represented by a dotted line v.
The R light source is represented by a one-dot broken line w. The light amount distributions of the three types of light sources on the original surface are different. The different factors include, for example, that the distances between the light source and the document surface are different depending on the three types of light sources.

Further, due to the spectral sensitivity characteristics of the line type light receiving element (CCD), the CCD output value of the reflected light obtained by illuminating the original with the R, G, B light sources differs for each R, G, B. The output value may be small. In order to improve the shortage of the R output value, only the tube diameter of the R light source is increased to increase the amount of light on the document surface. Even if the tube diameter is changed, the light amount distribution on the document surface also changes.

In the conventional light quantity correction plate, as shown in FIG. 11B, one kind of light quantity correction plate having a hatched opening is provided in the optical path between the light source and the CCD. . This light quantity correction plate has a different light quantity distribution on the original surface.
Of the types of light sources, for example, the light amount distribution of the G light source shown in FIG. 15u and c of the imaging lens as shown in FIG.
The aperture shape is made in consideration of the light distribution distribution characteristic according to the os4 power law.

Therefore, as shown in FIG. 16, when the document is illuminated by the G light source, a good C as shown by the solid line u'is obtained.
The CD output waveform can be obtained, but when illuminated with the B light source,
There was a drawback that the output was higher in the peripheral area than in the central area.

On the contrary, when illuminated by the light source for R, the peripheral part of the image is largely dropped compared to the central part, the electric shading correction range must be expanded, the SN ratio is lowered, and a high-performance image is obtained. It was a hindrance to reading.

The present invention solves the above problems,
It is an object of the present invention to provide an image reading device that operates well and is reliable.

[0020]

In order to achieve the above-mentioned object, the solution means according to the present invention comprises at least an illuminating means for illuminating an original, a solid-state image pickup device having light receiving elements arranged in a line, and an original. In an image reading apparatus having an image forming optical system for forming an image on the solid-state image sensor and a shading correction plate (standard white plate), the optical system is defocused when the standard white plate is formed on the solid-state image sensor. It is characterized by having done. According to the solving means, when the standard white plate for shading correction is read, dust and density unevenness are detected and good correction is achieved.

Further, another solution of the present invention is to provide an image reading device which forms three types of light sources for illuminating an original document and reflected light from the original document on a line type light receiving element through an imaging lens. In the above, the light source comprises three types of light sources for R reading, G reading, and B reading, and the three types of light sources are sequentially turned on, and in the optical path between the light source and the line type light receiving element, It is characterized in that a light amount correction means is provided corresponding to the light distribution distribution characteristics of the three types of light sources. According to the solving means, good CCD output can be obtained by providing the light quantity correcting means in the optical path between the light source and the CCD in accordance with the light distribution distribution characteristics of the three types of light sources on the original surface. To

[0022]

EXAMPLES Next, examples of the present invention will be described.

<First Embodiment> FIGS. 1 and 2 show a first embodiment of the present invention. The image reading apparatus according to the embodiment includes a shading correction plate (standard white plate) 1, a document table glass 2, an illumination optical system 3, a full speed mirror 4, a half speed mirror 5, an imaging lens 6,
It has a CCD line sensor 7 and a diffusion plate 8. In the CCD line sensor, as shown in FIG. 8, a plurality of pixels are arranged in a horizontal row. Lens 6 is a CC for manuscripts at 1 / 10th magnification
It is provided so as to form an image on the D sensor 7. Lighting system 3
Moves in parallel with the full-speed mirror 4 from left to right in the figure, and at the same time, the half-speed mirror 5 moves from left to right in the figure at half the speed of the full-speed mirror 4, and the original is linearly moved from left to right. Images are sequentially formed on the CCD 7 to the right. Since the CCD 7 outputs an electric signal in accordance with the light energy that is incident within a unit time, the output of the image of the original is sequentially obtained from the device.

In FIG. 1, a white plate 1 having a uniform density is illuminated with 3, and an image is formed on a CCD 7 by a lens 6 through 4, 5. In FIG. 2, the diffusion plate 8 is moved to the optical path in order to deteriorate the image of the white plate 2. The marginal rays l _1, l ₂ is shown in FIG. 2 as a representative example of the imaging rays, l ₁
, L ₂ are scattered by the diffuser plate 8, so that the image of the white plate is blurred. For this reason, the density of the image due to white density unevenness and dust is relaxed to form an image, and erroneous recognition of the CCD is reduced.

The degree of diffusion of the diffusion plate 8 should not be so great. If the degree of diffusion is large, the uneven illumination lens c
This is because the uneven light amount due to the os power law is also canceled.

When reading a document, the diffusion plate 8 is moved out of the optical path.

Illuminance unevenness due to the illumination system, lens cos4
The change in the light amount due to the reduction of the light amount at the end portion according to the power law is not abrupt due to the uneven density of the white plate and the change in the image light amount due to dust, and therefore is not affected by this configuration.

<Embodiment 2> FIG. 3 shows another embodiment. In the figure, 9 is a flat glass plate. If you insert a flat glass plate into the optical path,

[0029]

[Equation 2]

Since the optical path changes by (n: refractive index d: thickness), the focus position changes. Therefore, the image is out of focus on the CCD. At this time, a rapid change in the light amount of the image due to uneven density of the white plate and dust is alleviated. On the other hand, variations in the illuminance of the illumination system and changes in the amount of light at the edge due to the cos 4 power law of the lens are less affected by this configuration, are reflected in the illuminance on the image plane, and are corrected for shading.

The glass 9 has a function and a function of being inserted into the optical path when reading the white plate and being put out of the optical path during reading the original.

<Embodiment 3> In this embodiment, the CCD sensor 7 is defocused at the time of reading the white plate and is installed at the position 7 '. Therefore, the image of the white plate is CC
A blurred image is formed on the D sensor 7 '. Therefore, CC
The image is out of focus on D. At this time, a rapid change in the light amount of the image due to uneven density of the white plate and dust is alleviated. On the other hand, the unevenness of illuminance of the illumination system and the change in the light amount due to the reduction of the light amount at the end portion due to the cos 4 power law of the lens are not easily affected in this configuration, and are reflected in the image plane illuminance to perform shading correction.

The CCD 7 is constructed so as to move to the position 7'when reading a white plate and to the position 7 when reading a document as shown in FIG.

<Embodiments 4 and 5> FIGS. 5 and 6 show other embodiments.

In each case, a part of the image forming optical system is moved to deteriorate the image formation on the CCD 7.

In FIG. 5, the imaging lens 6 is replaced by the CCD 7
Are moving to the side. Further, in FIG. 6, the half-speed mirror 5 is moved in a direction away from the CCD 7. Therefore, in both cases, the optical path system changes and the image formation relationship collapses.
The image of the white plate is blurred on the CCD 7. The following operation is the same as that of the third embodiment.

The lens 6 shown in FIG. 5 and the half-speed mirror 5 shown in FIG. 6 are constructed so as to return to their normal positions when reading a document.

<Sixth Embodiment> FIGS. 10 to 11 show a sixth embodiment.
FIG. The original 104 placed on the original table surface 105 is illuminated by three types of light sources, an R light source 103, a G light source 102, and a B light source 101.

First, the R light source 103 is turned on, and the original 1
04, the reflected light is reflected by the folding mirror 106,
The imaging lens 11 is bent by 107 and 108.
After passing through 0, an image is formed on the CCD 111. Mirror 10
6 is the velocity V in the sub-scanning direction, and the mirrors 107 and 108 are
By moving at a speed of 1/2 V, the entire surface of the document is scanned. Similarly, the G light source 102 and the B light source 101 are sequentially turned on, and R reading, G reading, and B reading are completed.

A light quantity correction plate 109 is arranged in the optical path between the light source and the CCD.

When the R light source 103 having the light distribution characteristic as shown by w in FIG. 15 is turned on, the light amount correction plate having the shape shown in FIG. 11C is arranged.

As shown in FIG. 15, when the G light source, which has a smaller amount of light drop around the center than the R light source 103, is turned on, as shown in FIG. ) The light amount correction plate is switched to the light amount correction plate having an opening shape with a smaller amount of spread around the center of the opening of the light amount correction plate.

Further, when the B light source is turned on, the B light source is switched to a light amount correction plate having a smaller peripheral spread amount with respect to the center than the light amount correction plate arranged for the G light source.

As described above, these three types of light sources R,
By switching the three kinds of light amount correction plates by the switching means according to the lighting of G and B, a good CCD output as shown by u ′ in FIG. 16 is always obtained, and high-performance image reading is possible. Became.

<Embodiment 7> Another embodiment will be described. Sixth
In the embodiment, the three types of light amount correction plates were replaced according to the lighting of the three types of light sources for R, G, and B. In the seventh embodiment, as shown in FIG. 12, it is possible to obtain a good CCD output by changing the distance from the lens 110 with one type of light amount correction plate according to the switching of the light source.

For example, of the three types of R, G, and B light sources having the light distribution characteristics shown in FIG. 15, one type of light quantity correction plate shown in FIG. When lit,
It is used at the O position indicated by the solid line, and when the B light source with a smaller amount of light loss around the G light source is turned on, it is moved to the P position further away from the lens 110, which is indicated by the broken line, and used. .

On the contrary, when the light source for R, in which the amount of light loss around the light source for G is larger than the light source for G, is turned on, it is moved to the position of Q shown by the broken line for use. 115 represents the pupil of the lens 110,
Reference numeral 114 denotes a light beam which is imaged on the CCD 111 by the lens 110.

In the case of the light quantity correction plate having the same size of the central opening, the light beam 114 can be moved from the O position to the Q position.
If the light source for R, which has a larger amount of light loss around the G light source than the G light source, is turned on, the final C
In the CD output, a good output waveform that is almost uniform in the central portion and the peripheral portion can be obtained.

On the contrary, in the case of the light source for B in which the light amount in the peripheral portion is smaller than that in the light source for G, if the light amount correction plate is moved away from the lens 110, the cut amount of the light flux 114 in the central portion is reduced, and the good C
A CD output waveform is obtained.

<Embodiment 8> An eighth embodiment will be described with reference to FIG. When the G light source is turned on, the light amount correction plate 109 having an opening shape as shown in FIG. 11B is used at the Q position. When the R light source in which the amount of light drop around the G light source is larger than the G light source is turned on, the light amount correction plate 109 moves to the Q position.

When the B light source is turned on, another type of light amount correction plate 113 having a shape different from that of the light amount correction plate 109 is inserted between the lens 110 and the CCD 111.

As described above, one type of light amount correction plate is moved in the optical axis direction by the switching means in response to lighting switching of three types of light sources, and another type of light amount correction plate having a different shape is switched. By inserting / removing, similar to the sixth and seventh embodiments described above, a good CCD output waveform can be obtained.

[0053]

As described above, according to the first to sixth aspects of the present invention, when the standard white plate for shading correction is read, it is detected that there is little influence on dust and density unevenness of the white plate. Performance is improved.

According to the invention of claims 7 to 9, 3
By providing the light amount correction means corresponding to the lighting switching of the light sources of different types between the light source and the CCD, it is possible to obtain a good CCD output waveform regardless of which light source is turned on.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an image reading apparatus according to the present invention.

FIG. 2 is an enlarged view of a main part of the first embodiment of the image reading apparatus according to the present invention.

FIG. 3 is a diagram showing a second embodiment of the image reading apparatus according to the present invention.

FIG. 4 is a diagram showing a third embodiment of the image reading apparatus according to the present invention.

FIG. 5 is a diagram showing a fourth embodiment of the image reading apparatus according to the present invention.

FIG. 6 is a diagram showing a fifth embodiment of the image reading apparatus according to the present invention.

FIG. 7 is a diagram showing an example of a conventional image reading apparatus.

FIG. 8 is a diagram showing another example of a conventional image reading apparatus.

FIG. 9 is a diagram showing still another example of the conventional image reading apparatus.

FIG. 10 is a diagram showing a sixth embodiment of the image reading apparatus according to the present invention.

FIG. 11 is a diagram showing a light correction plate having a shape corresponding to a light source.

FIG. 12 is a diagram showing a seventh embodiment of the image reading apparatus according to the present invention.

FIG. 13 is a diagram showing an eighth embodiment of the image reading apparatus according to the present invention.

FIG. 14 is a diagram showing a cos 4 power law of a lens.

FIG. 15 is a diagram showing a light distribution characteristic of a light source.

FIG. 16 is a diagram showing an output waveform of a CCD

[Explanation of symbols]

1 ... Shading correction plate (standard white plate) 2 ... Platen glass 3 ... Illumination system 4 ... Full speed mirror 5 ... Half speed mirror 6 ... Lens 7 ... CCD line sensor 8 ... Diffusion plate 9 ... Glass flat plate 101 ... B light source 102 ... G light source 103 ... R light source 104 ... Original document 105 ... Original platen glass 106, 107, 108 ... Folding mirror 109 ... Light amount correction plate 110 ... Imaging lens 111 ... CCD 113 ... Light amount correction plate 114 ... Luminous flux 115 ... Pupil

Claims (9)

[Claims] 1. An illumination unit for illuminating at least a document,
A solid-state image sensor having light-receiving elements arranged in a line, and an image-forming optical system for forming an image of a document on the solid-state image sensor,
An image reading device having a shading correction plate (standard white plate), wherein an optical system is defocused when an image of the standard white plate is formed on a solid-state image sensor. 2. The image reading apparatus according to claim 1, having a function of inserting a diffusion plate between the image forming device and the solid-state image pickup device when forming an image of the standard white plate on the solid-state image pickup device. 3. The image reading device according to claim 1, wherein the solid-state imaging device is moved in the optical axis direction for defocusing. 4. The image reading device according to claim 1, wherein the image forming element is moved in the optical axis direction for defocusing. 5. The image reading apparatus according to claim 1, wherein the standard white plate is installed at a position moved in the optical axis direction for defocusing. 6. The solid-state imaging device and the imaging device according to claim 1, wherein the solid-state imaging device and the imaging device are moved in the optical axis direction for defocusing.
An image reading apparatus characterized in that a standard white plate is installed at a position moved in the optical axis direction. 7. An image reading device for forming three types of light sources for illuminating an original and an image of reflected light from the original on a line type light receiving element through an imaging lens, wherein the light source is for R reading. The light source includes a light source, a G reading light source, and a B reading light source, and the three types of light sources are sequentially turned on, and the light distributions of the three types of light sources are arranged in the optical path between the light source and the line type light receiving element. An image reading apparatus characterized in that a light amount correction means is provided in accordance with characteristics. 8. A means for switching between the light sources and the line type light receiving element, which switch the light amount correction plates having different opening shapes, corresponding to the switching of lighting of the three types of light sources. An image reading device provided. 9. The light amount correction plate provided between the light source and the line type light receiving element according to claim 7,
An image reading apparatus characterized in that a distance between the light quantity correction plate and the imaging lens is changed in response to lighting switching of a kind of light source.