JPH0537778A - Picture reader - Google Patents

Abstract

PURPOSE:To attain highly accurate color information reading even at read of an original with a higher reflectance than that of a shading correction white board by setting properly a shading correction data being a gradation. CONSTITUTION:In the picture reader, in which an original 1 is lighted by a lighting system, a picture is formed on a face of a read means 6 having a lien sensor via an image forming optical system 5 and the means 6 is used to read the picture, a shading correction white board 4 is provided in the vicinity of an original platen and the white board 4 is read by the means 6 to generate a shading correction data, then a picture processing section 7 adjusts the gradation of the correction data to have a maximum gradation or below and the processing section 7 uses the adjusted shading correction data to read the original. Thus, the correction data is properly set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device, and more particularly, it is effective in reducing the amount of light at the end in the arrangement direction (main scanning direction) of the elements of the reading means including a line sensor (CCD) for image reading. To correct the image information on the document surface with a simple structure and to read with high precision, such as a copying machine,
The present invention relates to an image reading apparatus suitable for facsimiles, image scanners and the like.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus in which image information on a document surface illuminated by an illumination system is read using a reading means such as a line sensor, the document surface is illuminated by a light source such as a fluorescent lamp. Was there. Then, an image on the surface of the original is formed on the surface of the reading means by the reflected light flux from the surface of the original through the imaging optical system, and the electric signal output from the reading means is processed by the image processing section to be read. ing. Then, the two-dimensional image information on the document surface is read by moving the document surface or the image reading means in the sub-scanning direction.

In such an image reading apparatus, for example, the cos ⁴ rule of the image forming optical system makes the light quantity distribution uneven on the reading means surface, and a white plate is used as an original due to variations among the elements of the line sensor. The output distribution from the reading means was not uniform even when used for reading.

Therefore, conventionally, a shading correction white plate is used to perform shading correction in the image processing section so that the output distribution from the reading means becomes uniform. The shading correction at this time is performed so that the output distribution from the reading unit when the shading correction white plate is used has the maximum gradation (for example, gradation 255).

That is, when the i-th output value of the line sensor when reading the shading correction white plate is Xi,
The shading correction value there is set to (maximum gradation / Xi). As a result, after shading correction, the output value when the shading correction white plate as the original is read by the reading unit is set to the maximum gradation (gradation 255) in one line as shown in FIG.

[0006]

In the conventional image reading apparatus, when the shading correction is performed, the output after the shading correction has the maximum gradation as shown in FIG. Therefore, for example, when reading an original having a higher reflectance than the shading correction white plate, for example, an original drawn in a fluorescent color, the output from the line sensor normally exceeds the maximum gradation.

However, since the maximum gradation is not actually exceeded, as a result, when a document such as a fluorescent color having a higher reflectance than such a shading correction white plate is read, the color information cannot be read correctly. There was a problem.

According to the present invention, when the shading correction white plate is used for shading correction, by appropriately setting the output from the reading means, that is, the shading correction data which is the gradation, when reading a document having a higher reflectance than the shading correction white plate. However, it is an object of the present invention to provide an image reading device capable of reading color information with high accuracy.

[0009]

An image reading apparatus according to the present invention illuminates a document placed on a document table with an illumination system, and images the image on a reading unit surface having a line sensor through an imaging optical system. In an image reading apparatus that forms an image and reads the image by the reading unit, a shading correction white plate is provided near the document table, and when the shading correction white plate is read by the reading unit and shading correction data is created, The image processing unit is adjusted so that the shading correction data is equal to or less than the maximum gradation, and the original is read using the shading correction data adjusted by the image processing unit.

[0010]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention.

In FIG. 1, reference numeral 1 denotes a document, on the surface of which a color image is formed, which is placed on the surface of the document table glass 19. Reference numeral 2 is a light source such as a fluorescent lamp or a halogen lamp. Reference numeral 8 denotes a concave mirror, which connects the light source 2 to the platen glass 1
The light flux emitted in the direction opposite to 9 is condensed and guided to the original 1. The light source 2 and the concave mirror 8 form an element of the illumination system.

Reference numeral 20 is an infrared cut filter. An image forming optical system (projection optical system) 5 forms a color image on the surface of the original 1 on the reading means 6 via the mirrors 3a, 3b and 3c and the infrared cut filter 20.

The reading means 6 is composed of three line sensors such as CCDs. The line sensor 3 is monolithically formed on the substrate and has a configuration in which a plurality of light receiving elements are arranged one-dimensionally in the main scanning direction (direction perpendicular to the paper surface in FIG. 1). Further, in front of the three line sensors, color filters R, G, and B for passing predetermined color light for reading a color image, for example, red (R), green (G), and blue (B) are arranged. .

FIG. 2 shows the spectral sensitivities of R, G and B when reading the three line sensors of the reading means 6 at this time. In this embodiment, the color image information of the original 1 is digitally read by the reading means 6 having such a configuration.

A shading correction white plate 4 has a uniform spectral reflectance and is fixed to a part of the document glass 19. An image processing unit 7 processes the electrical image information read by the reading unit 6.

In this embodiment, after shading correction is performed by the method described later, the reflected light flux from the original 1 placed on the surface of the original glass 19 is reflected by the mirrors 3a, 3b and 3c, and the infrared cut filter 20 is used. Imaging optical system 5 via
An image is formed on the surface of the reading unit 6 by means of the above, and the color image on the surface of the original 1 is read. Then, the platen glass 19 is indicated by an arrow 19a, or the mirrors 3a, 3b, 3c are indicated by an arrow 3d.
As described above, the surface of the original 1 is scanned by moving in the sub-scanning direction, and the color image on the surface of the original 1 is two-dimensionally read.

FIG. 3 shows a shading correction white plate 4 according to the present invention and a highlighter pen (red, magenta) used as an example.
It is explanatory drawing of the spectral reflectance characteristic of.

In the figure, 31 is the spectral reflectance of the shading correction white plate 4, and 32 is the spectral reflectance of the highlighter pen. The spectral reflectance 31 of the shading correction white plate 4 is substantially equal to the white level of white paper. The spectral reflectance 32 of the fluorescent pen is higher than that of the shading correction white plate 4 in a part of the wavelength range.

FIG. 4 is an explanatory diagram of an output distribution from one line sensor (1H) when the shading correction white board 4 is read by the apparatus of FIG. 1 before shading correction.

As shown in the figure, the output distribution in the main scanning direction is, for example, the light amount unevenness in the longitudinal direction of the light source (main scanning direction), the variation between the bits of the line sensor (CCD), and the cos ⁴ rule of the imaging optical system. As a result, the output distribution is not uniform within one line.

Therefore, in this embodiment, the platen glass 19 is moved so that the shading correction white plate 4 is positioned within the reading area. And at this time the line sensor (C
The output value from the i-th element of the CD) is Xi
Then, as shown in FIG. 5, the shading correction data Yi becomes Yi = k × (maximum gradation) / Xi (1) when k (k <1) is used as a coefficient. I have to.

The coefficient k may be any number as long as it is 1 or less. For example, when a document having the highest reflectance than the reflectance of the shading correction white plate is read, the i-th output from the line sensor is output. When Zi, k × (Zi / Xi) ≈1. This prevents the output from being saturated when read by the reading means. (In this embodiment, the maximum gradation is set to 255.) Then, the shading correction data at this time is recorded in the image processing unit 7. Then, the document 1 is actually read by the reading means 6
When the image data is read in, the read data is corrected by the image processing unit 7 based on the shading correction data Yi.

The coefficient k in the equation (1) may be any number as long as it is 1 or less, but in this embodiment, k = 0.9 in consideration of the spectral reflectance of the fluorescent pen as the original.

FIG. 6 shows an output distribution from the line sensor when the shading correction white plate after shading correction is used.

As shown in FIG. 6, the maximum gradation (255 (F
F)) is smaller than that and has a uniform gradation 230.

As described above, in this embodiment, shading correction data is created, and when the shading correction white plate is read, the output distribution from the line sensor is corrected so as to be uniform with a value smaller than the maximum gradation. . That is, the white level of the shading correction data is set lower than the maximum gradation.

That is, in the present embodiment, the shading correction is performed with a value smaller than the maximum gradation value of the shading level of the shading correction white plate, so that the spectral reflectance of the spectral reflectance in a certain wavelength range is higher than that of the shading correction white plate of a fluorescent pen or the like. Even when reading a high original, the color information can be read with high accuracy without saturating the output value from the line sensor.

FIG. 7 is an explanatory diagram of the spectral characteristic of the second embodiment of the shading correction white board according to the present invention. In the figure, 71 is the spectral reflectance of the shading correction white plate.

In this embodiment, a shading correction white plate having a spectral reflectance lower than the white level spectral reflectance 72 is used.

Generally, the shading correction white plate has a tendency that dirt and the like in the air adhere to the white plate and stain it to decrease the spectral reflectance with time. For this reason, the shading correction white plate having a slightly lower spectral reflectance than the shading correction white plate having a high spectral reflectance has a smaller reduction rate of the spectral reflectance due to long-term use.

For this reason, in this embodiment, the shading correction white plate having a lower spectral reflectance than that of the first embodiment is used to prevent an increase in the decrease rate of the spectral reflectance with time.

In the present embodiment, the method of determining the coefficient k is such that the reading means does not saturate even when the original having the highest spectral reflectance is read, which is the same as in the first embodiment. is there.

In each of the above-described embodiments, the coefficient k may be variable instead of being fixed, and shading correction data may be created in accordance with the information of the read image and recorded in the image processing unit for use. . According to this, when reading a document such as a fluorescent pen that does not have a portion having a spectral reflectance higher than the white level, it is possible to further reduce the shading error.

[0034]

According to the present invention, as described above, by setting the white level of the output from the reading unit when performing shading correction with the shading correction white plate, that is, the shading correction data to be a gradation, the white level is lower than the maximum gradation. It is possible to achieve an image reading apparatus capable of reading color information with high accuracy even when reading a document having a higher reflectance than the shading correction white plate.

Particularly in the present invention, a line sensor (CCD)
When the output value from the i-th element of the elements is, the shading correction data Yi has k (k <1) as a coefficient, Yi = k × (maximum gradation) / Xi ... ····················································································································································.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a spectral characteristic of the reading unit in FIG.

FIG. 3 is an explanatory diagram of spectral characteristics of a document and a shading correction white plate according to the present invention.

FIG. 4 is an explanatory diagram of an output distribution from the line sensor before shading correction.

FIG. 5 is an explanatory diagram of shading correction data according to the present invention.

FIG. 6 is an explanatory diagram of an output distribution from the line sensor after shading correction.

FIG. 7 is an explanatory diagram of the spectral characteristic of the shading correction white plate according to the second embodiment of the present invention.

FIG. 8 is an explanatory diagram of an output distribution from a line sensor after conventional shading correction.

[Explanation of symbols]

1 manuscript 2 light sources 3a, 3b, 3c mirrors 4 Shading correction white board 5 Imaging optical system 6 reading means 7 Image processing unit 8 concave mirror

Claims (3)

[Claims] 1. A document placed on a document table is illuminated by an illumination system, the image is formed on a reading means surface having a line sensor through an image forming optical system, and the image is read by the reading means. In the image reading apparatus, the shading correction white plate is provided in the vicinity of the document table, and when the shading correction white plate is read by the reading means and the shading correction data is created, the shading correction data is set to be equal to or less than the maximum gradation. An image reading apparatus, wherein the original is read using the shading correction data adjusted by the image processing unit and adjusted by the image processing unit. 2. The image reading apparatus according to claim 1, wherein the original is optically scanned. 3. The image reading apparatus according to claim 1, wherein the reflection surface of the shading correction white plate is gray.