JPH10224571A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of the correction of the read value of an original. SOLUTION: First white data obtained by reading a platen roller 6 by a CCD 1 are divided into plural blocks and the maximum value of the first white data inside the divided respective blocks is computed. A second white reference member 12 is inserted to an area illuminated by an exposure lamp 3 at the lower part of a platen glass 4 on the optical axis of the CCD 1 and the second white reference member 12 is read by the CCD 1. A shading correction coefficient is computed for respective picture elements based on the maximum value of the first white data, second white data obtained by reading the second white reference member 12 and a predetermined coefficient and the read value of reading the original 5 is shading-corrected by the computed shading correction coefficients of the respective picture elements.

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, and more particularly, to an image reading apparatus that reads an original and a reference member and corrects the read value of the original based on the read value of the reference member.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus forms an image of a document in a main scanning direction by forming reflected light from the document on a CCD through a slit by an image forming lens. It is read every line. Then, the CCD outputs an image signal having a level corresponding to the density of the original image.

By the way, it is desirable that the output level corresponding to each photosensitive portion of the CCD is uniform over the entire reading area if the density of the original image is constant.

However, variations in the sensitivity of each photosensitive portion of the CCD, variations in the light amount distribution of the exposure lamp in the main scanning direction, changes over time of the variations, and variations in the amount of transmitted light in the main running direction of the imaging lens, etc., cause the CCD. The output of each photosensitive unit varies, and is not uniform over the entire reading area.

Therefore, conventionally, an image reading apparatus has been equipped with a CC.
Shading correction is performed so as to make the variation in the output of each photosensitive portion D uniform. Shading correction is
A shading correction coefficient is calculated based on the read value of the white reference plate, and the read value of the document is corrected using the calculated shading correction coefficient. Note that, as the white reference plate, a plate-shaped white platen and a white platen roll that are read at a position where a document is read are generally used.

However, in a large-format original reading apparatus that reads an original while transporting the original, the dirt carried by the original causes
The plate-shaped white platen or the white platen roll is easily stained. For this reason, as shown in JP-A-7-107283, a white reference plate is inserted into the platen portion before reading a document, and the inserted white reference plate is read. I have.

By the way, the platen glass may be contaminated with dirt such as glue of a cut and pasted document, or the platen glass may be damaged by impact or the like. As described above, when the platen glass has dirt or scratches, the document reading device reads the inserted white reference plate through the dirt or scratches. For this reason, as shown in FIG. 6, a low-level portion (see symbols A and B) locally occurs in the image signal of one line in the main scanning direction due to dirt or scratches. The value of the low level part becomes an error of the shading correction coefficient. The error of the shading correction coefficient becomes an image error as it is, and the same error occurs in all the lines, so that it appears as an unsightly and conspicuous vertical stripe in the image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to propose an image reading apparatus in which the accuracy of correction of a read value of a document is improved.

[0009]

According to a first aspect of the present invention, there is provided a first reference member which is read at a document reading position and a second reference member which is read at a position other than the document reading position. Illumination means for illuminating a document read at the document reading position, the first reference member, and the second reference member; and the document, the first reference member,
Reading means for reading the second reference member by dividing the second reference member into a plurality of pixels;
The read value of the reference member is processed in such a manner that the influence of the dirt on the document reading position is reduced, the read value of the second reference member read by the reading unit, and a predetermined coefficient. Correction means for correcting the read value of the document read by the reading means using a correction coefficient determined for each pixel.

According to a second aspect of the present invention, in the first aspect of the invention, the correcting means divides the plurality of read values of the first reference member into a plurality of blocks, and sets a maximum value in each of the divided blocks. By adopting the value as the read value in each block, the read value of the first reference member is processed so as to reduce the influence of the deterioration of the document reading position.

That is, the illuminating means according to the first aspect of the present invention includes a document read at the document reading position, a first reference member read at the document reading position, and a second reference member read at a position other than the document reading position. Illuminate the reference member.

Here, the colors of the first reference member and the second reference member are reference colors such as white and black.

The reading means reads the document, the first reference member, and the second reference member by dividing them into a number of pixels. That is, the reading means has a large number of photosensitive units, and reads the original, the first reference member, and the second reference member by each photosensitive unit. Therefore, the original, the first reference member, and the second reference member are read by the respective photosensitive units, and the read values of the original, the first reference member, and the second reference member are read by the respective photosensitive units (pixels). Corresponds to each.

Here, the first reference member is arranged at the original reading position in advance, or is arranged at the original reading position when necessary by moving means or the like, and is read at the original reading position by the reading means. Similarly, the original is read at the original reading position by the reading means in such a manner that the original is previously arranged at the original reading position, or is arranged at the original reading position by a moving means when necessary. In this case, the illumination unit illuminates the first reference member and the original by illuminating the original reading position.

On the other hand, when the reading means reads the second reference member at a position other than the document reading position, for example,
At least one of the reading unit and the illuminating unit and the second reference member may be relatively moved to read the second reference member at a position other than the document reading position.

That is, the reading means and the illuminating means are fixed, and the second reference member is moved to a position other than the document reading position (a position readable by the reading means), or the second reference member is moved to a position other than the document reading position. The reference member is fixed, and the second
The reading means and the illuminating means may be moved to a position where the reference member is read, or both the reading means and the illuminating means and the second reference member may be moved.

In this case, the illuminating unit illuminates the second reference member by illuminating a position other than the document reading position.

In addition, when the second reference member is previously arranged at a position other than the document reading position, and the reading means reads the second reference member, the illumination light from the illumination means is used by the second reference member using an optical system. The second reference member may be illuminated by irradiating the second reference member, and the reflected light from the second reference member may be incident on the reading unit by an optical system.

Here, if the original reading position is deteriorated due to dirt or damage, the read value of the first reference member read by the photosensitive portion of the reading means corresponding to the deteriorated portion of the original reading position is The value is different from the read value of the first reference member read by the photosensitive unit of the reading unit corresponding to a position other than the deteriorated portion of the document reading position. Therefore, if the correction coefficient used for correcting the read value of the document is obtained as it is, the read value of the first reference member read by the photosensitive unit corresponding to the deteriorated portion of the document reading position becomes an error. The error of the correction coefficient becomes an image error as it is, and the read value of the document cannot be accurately corrected.

Therefore, the correcting means processes the read value of the first reference member read by the reading means so as to reduce the influence of the deterioration of the document reading position. Here, the correcting means divides the plurality of read values of the first reference member into a plurality of blocks as described above, and calculates the maximum value in each of the divided blocks in each block. , The read value of the first reference member may be processed so as to reduce the influence of stains on the document reading position. Alternatively, the average value of the read values in each divided block may be adopted as the read value in each block.

Since the read value of the first reference member is merely processed so as to reduce the influence of the deterioration of the original reading position, the read value of the first reference member is affected by the deterioration of the original read position. It has not been treated to disappear completely.

On the other hand, the read value of the second reference member
Is read at a position other than the document reading position, so there is no influence of the deterioration of the document reading position. However, since the second reference member is not read at the document reading position, the second reference member is illuminated and read with a light amount different from the light amount with which the document is illuminated. Therefore, the read value of the second reference member includes the effect of being illuminated with a light amount different from the light amount with which the document is illuminated.

As described above, the read value of the first reference member is processed only so as to reduce the influence of the deterioration of the reading position of the document, or the read value of the second reference member is used as the value of the document. The reading cannot be corrected.

On the other hand, as a result of a number of experiments, the present inventor has been able to accurately correct the read value of the original and to determine the correction coefficient for correcting the read value of the original. The value obtained by processing the read value so as to reduce the influence of the deterioration of the document reading position and the coefficient of the read value of the second reference member could be determined in advance.

In view of this, the correcting means processes the read value of the first reference member so as to reduce the influence of the deterioration of the document reading position, the read value of the second reference member read by the reading means, and Using a correction coefficient determined for each pixel according to a predetermined coefficient, the read value of the document read by the reading unit is corrected.

As described above, the read value of the first reference member is processed according to the value obtained by processing so as to reduce the influence of the stain on the document reading position, the read value of the second reference member, and a predetermined coefficient. The correction value of the document read at the document reading position is corrected using the correction coefficient determined for each pixel, so that the influence of the deterioration of the document reading position can be reduced and the accuracy of the correction of the document reading value is improved. Can be done.

[0027]

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

The image reading apparatus according to the present embodiment is configured as a large-sized image reading apparatus that scans a drawing or the like to create a recording sheet, and is provided in a copying machine (not shown).

As shown in FIG. 1, a document transport mechanism 100 and a document transport mechanism 200 are provided on both sides of the optical reading unit 300 in the document transport direction. The document transport mechanism 100 includes two upper and lower guide plates 51 a and 51 forming a document transport path L for transporting the document 5.
b, a feed roller 8a for feeding a document, and a driven roller 7, and the document feeding mechanism 200 includes guide plates 51a and 51b, a feeding roller 8b, and a driven roller 7.

Document transport mechanism 100 on the upstream side in the document transport direction
Is provided with a document insertion detecting sensor 20 for detecting that a document has been inserted. The original insertion detection sensor 20 includes a light emitting element that emits light and a light receiving element that receives light emitted from the light emitting element. Then, a detection signal is output.

The optical reading unit 300 is provided between the lower guide plates 51b of the original transport mechanisms 100 and 200.
A platen glass 4 is provided, and a platen roller 6 as a first reference member is provided directly above the platen glass 4. The platen roller 6 is formed by baking and painting a steel pipe in white, and is supported by the main body via a bearing.

Below the platen glass 4, there are provided a CCD 1 as a reading means and a lens 2 for forming an image of the original conveyed to a position where the platen roller 6 of the platen glass 4 comes into contact (original reading position) on the CCD 1. ing. This lens 2 is composed of, for example, a Selfoc lens. In the present embodiment, the CCD 1 is configured by arranging photosensitive units of about 14,400 pixels in a direction (main scanning direction) orthogonal to the document conveying direction so that a document having a width of 36 inches (914 mm) can be read at a resolution of 400 dpi. I have. Therefore,
The CCD 1 reads a document every one line in the main scanning direction.

A pair of exposure lamps 3 as illuminating means for illuminating the original are provided at both sides of the lens 2 in the original conveying direction. Each exposure lamp 3 uses a fluorescent lamp and is arranged so that the longitudinal direction of the fluorescent lamp is the main scanning direction, and illuminates a document reading position.

In a space below the platen glass 4 and above the exposure lamp 3, a second reference member
The white reference plate 12 is provided. The second white reference plate 12 is formed by baking a steel plate with white.

The second white reference plate 12 moves in a space below the platen glass 4 and above the exposure lamp 3 by the moving mechanism 18 shown in FIG. That is, the moving mechanism 18 includes the guide 14 arranged in the document conveying direction. A holding portion 13 is connected to the guide 14. The holding portion 13 is provided with a rack portion 15 that meshes with a gear 16, and a second white reference plate 12 is attached to the rack portion 15.

By the forward and reverse rotation of the gear 16, the rotational force of the gear 16 is transmitted to the rack 15, and the rack 15 moves. With the movement of the rack unit 15, the holding unit 13
4 so that the second white reference plate 12
Moves in the direction opposite to the document transport direction.

A white reference plate insertion detection sensor 22 is disposed below the platen glass 4 and at a first position P ₁ where light from the exposure lamp 3 does not enter. The white reference plate insertion detection sensor 22 includes a light emitting element that emits light and a light receiving element that receives light emitted from the light emitting element. The second white reference plate 12 is inserted into the optical axis of the CCD 1. Detect that it has been done.

[0038] That is, the second white reference plate 12 is moved, the distal end of the second white reference plate 12 (moving mechanism 18 and the opposite side) is received in the light by being located in a first position P ₁ blocked In this case, the light receiving element outputs a detection signal. Therefore, it can be detected from the detection signal that the second white reference plate 12 has been inserted into the optical axis of the CCD 1.

A white reference plate retreat detection sensor 24 is disposed below the platen glass 4 and at a second position P ₂ where light from the exposure lamp 3 does not enter. The white reference plate retreat detection sensor 24 includes a light-emitting element that emits light and a light-receiving element that receives light emitted from the light-emitting element, and the second white reference plate 12 is moved from the optical axis of the CCD 1 Detects evacuation.

The second white reference plate 12 moves in the document conveying direction, and the leading end of the second white reference plate 12 (the side opposite to the moving mechanism 18) passes through the _second position P2, so that light is transmitted. The light receiving element that has started receiving light outputs a detection signal. Therefore,
It is possible to detect from the detection signal that the second white reference plate 12 has been retracted from the optical axis of the CCD 1.

In the initial state, the second white reference plate 1
Reference numeral 2 denotes a position retracted from the optical axis of the CCD 1.

Next, a control system of the image reading apparatus according to this embodiment will be described. As shown in FIG. 3, the control system includes the document insertion detection sensor 20 and the white reference plate insertion detection sensor 2 described above.
2. White reference plate retreat detection sensor 24, A (analog) / D (digital) converter 26 connected to CCD 1, feed roller 8a, transport roller 8b, and driver 28 for rotating gear 16. , CPU30, R
An OM 32, an SRAM 34, and a signal processing circuit 36 are provided, and these are connected to a bus 38. Although not shown, the exposure lamp 3 is also connected, and when the power is turned on, the exposure lamp 3 is turned on. The CPU 30 and the signal processing circuit 36 constitute a correction unit of the present invention.

FIG. 4 shows a control routine which starts when the insertion of the original 5 is detected by the original insertion detection sensor 20. In step 52, the original is conveyed to the position just before the platen glass 4 and stopped. Prior to reading the original, the platen roller 6 is read. That is, image data obtained by reading the platen roller 6 from the CCD 1 via the platen glass 4 is fetched as first white data (reflectance) R1 and written in a predetermined area of the SRAM 34 in step 54. The first white data R1 is a digital value obtained by digitally converting the image signal from the CCD 1 by the A / D converter 26 (in the present embodiment, the image data is composed of image data of 144000 pixels).

Here, the first white data R1 includes a CCD
Of the sensitivity of each photosensitive portion, and the variation of the light amount distribution of the exposure lamp in the main scanning direction (as shown in FIG. 6, the light amount at positions corresponding to both ends of the exposure lamp at the document reading position corresponds to the center of the exposure lamp). In addition to the variation in light amount at the position), the variation with time of the variation, the variation in the amount of transmitted light in the main running direction of the lens, and the variation due to stains and scratches on the platen roller 6 are locally included (reference A in FIG. 6). , B).

In step 56, the first white data R1 written in a predetermined area of the SRAM 34 is read, and in step 58, the first white data (image data for 14400 pixels) is converted into image data of 144 pixels each. The block is divided into a total of 100 blocks, and the maximum value R1MAX of the image data in the block is calculated for each block.

In step 60, the second white reference plate is set to a CCD
The second white reference plate 12 is read by inserting it into the first optical axis. That is, image data (digital value) obtained by reading the second white reference plate 12 from the CCD 1 is taken in as second white data (reflectance) R2, and the second white reference plate is retracted from the optical axis of the CCD 1. In step 62, the SRAM
34 is written in a predetermined area.

Here, the second white data R2 includes a CCD
The variation in the sensitivity of each photosensitive portion, the variation in the light amount distribution of the exposure lamp in the main scanning direction, the variation with time of the variation, and the variation in the transmitted light amount in the main running direction of the lens. It does not include the variation that caused it.

In step 64, the second white data R2 written in a predetermined area of the SRAM 34 is read.

In step 66, the difference between the first white data and the second white data is calculated, and it is determined whether the calculated difference is equal to or greater than a predetermined value. 2
It is determined whether the white data is normal. If each data is not normal, the process returns to step 52 to execute the above processing (steps 52 to 66).

On the other hand, if the data is normal, the shading correction coefficient of each pixel is calculated in step 68.

Here, the processing in step 68 will be described with reference to FIG. That is, in step 72 of FIG. 5, a variable X for identifying a pixel is initialized, and in step 74, the variable X is set to 1
Increment, at step 76, the shading correction coefficient R White _{x of} pixel X (the pixel identified by the variable X)
Is calculated based on the expression (1).

[0052]

R white _x = (R 1MAX _bx ) × α + (R 2 _x ) × β (1) where R1MAX _bx is the maximum of the first white data in the block to which the X-th pixel belongs. R2 _X indicates the second white data of the X-th pixel. Further, α and β are predetermined coefficients, which are obtained by a number of experiments, and which enable the shading correction to be described later to be executed with high accuracy. The shading correction coefficient R White _x of the pixel X is the maximum value of the first white data. And the second white data are weighted average values.

In step 78, the calculated shading correction coefficient R White _x of the pixel X is stored.

In step 80, the variable X is set to the total number of pixels X.
By determining whether it is equal to or greater than ₀ (14400 in the present embodiment), it is determined whether or not the shading correction coefficient R White _x for all pixels has been calculated and stored.

If the variable X is not equal to or greater than the total number of pixels X ₀ , the flow returns to step 74 to execute the above processing (step 74).
Step 80) is executed. If the variable X is equal to or greater than the total number of pixels X ₀ , the shading correction coefficients R White _x for all the pixels have been calculated and stored, so this subroutine ends and the routine proceeds to step 70 (see FIG. 4).

At step 70, the original is read. That is,
By rotating the feed roller 8a, the original is transported to the platen glass 4, and the CCD 1 is moved while the original is moved.
Is read for each line in the main scanning direction. The output of the CCD 1 (original reading signal R Data _{x of} each pixel) is sent to the signal processing unit 36. The signal processing unit 36 performs shading correction by multiplying the document read signal R Data _x of each pixel read for each line in the scanning direction by 1 / R White _x of each pixel for each pixel. A signal (corrected reflectance) that has been subjected to shading correction is output as a Video signal through processing such as density level correction.

The reason why the shading correction coefficient is calculated by using the maximum value of the first white data and the second white data, and the shading correction coefficient is not calculated only by the second white data is that the second white reference. Since the plate is exposed at a position near the exposure lamp, the light amount distribution on the second white reference plate is more averaged than the light amount distribution at the position where the original is read. That is, the difference between the light amount at the position corresponding to the center of the exposure lamp at the document reading position and the light amount at the positions corresponding to both ends of the exposure lamp is smaller than the original difference. Therefore, when the shading correction coefficient is calculated using only the second white data, the positions corresponding to the both ends of the exposure lamp at the original reading position are dark, so that what should be shading-corrected so as to be bright originally should be darkened. This is because shading correction is performed.

As described above, in the present embodiment, the first white data is divided into a plurality of blocks, and the maximum value of the first white data of each pixel in the block is calculated for each block. Then, the calculated maximum value is used. For this reason,
It is possible to reduce the influence of a locally large variation included in the first white data due to stains and scratches on the platen roller and the platen glass. Therefore, the maximum value can obtain a light amount distribution that is easily changed mainly by environmental conditions such as the temperature of the document reading unit.

On the other hand, since the second white data is not obtained by reading the second white reference plate through the platen glass, the second white data is not affected by stains on the platen glass.

Accordingly, since the shading correction coefficient is obtained from the maximum value of the first white data and the second white data, the influence of the local stain on the platen glass 4 can be almost eliminated. As a result, the interval at which the operator cleans the platen glass 4 can be lengthened, and the stability of the apparatus can be improved.

Incidentally, the light quantity of the exposure lamp changes one by one under the influence of the temperature inside the apparatus and the ambient temperature of the use environment. However, in the above-described embodiment, the control routine (FIG. 4) described above is started each time insertion of a document is detected by the document insertion detection sensor, and shading correction is performed each time a document is read. Shading correction can be performed properly without being affected by changes in temperature or ambient temperature of the use environment.

In the embodiment described above, the second reference plate is moved in a space below the platen glass 4 and above the exposure lamp 3, but the present invention is not limited to this. Alternatively, the CCD may be moved, or the second reference plate and the CCD may be relatively moved such that the second reference plate is read by the CCD in the space.

In the above-described embodiment, the image data of the platen roller is divided into a plurality of blocks, and the maximum value of the image data in each block is obtained for each block. The invention is not limited to this, and an average value of image data in a block may be obtained.

Further, in the above-described embodiment, the platen roller is read. However, the present invention is not limited to this, and a plurality of plates parallel to the axial direction of the platen roller are provided around the platen roller. A reference plate formed of a flat surface and rotatable about the axis of the platen roller may be provided, and one surface of the reference plate may be used as a white surface serving as a white reference, and the white surface may be read.

In the above-described embodiment, an example in which the image reading apparatus is provided in the copying machine has been described. However, the present invention is not limited to this, and may be provided in a printer, a facsimile, or the like. .

[0066]

As described above, according to the present invention, the read value of the first reference member is processed so as to reduce the influence of dirt on the document reading position, the read value of the second reference member, The correction value determined for each pixel in accordance with the determined coefficient is used to correct the read value of the document read at the document reading position, so that the influence of the deterioration of the document reading position can be reduced, and This has the effect that the accuracy of reading value correction can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an image reading apparatus according to an embodiment.

FIG. 2 is a perspective view showing a moving mechanism for moving a second white reference plate.

FIG. 3 is a block diagram illustrating a control system according to the present embodiment.

FIG. 4 is a flowchart illustrating a control routine according to the present embodiment.

FIG. 5 is a flowchart showing a subroutine of step 68 in FIG. 4;

FIG. 6 is a graph showing the distribution of the main scanning of the CCD output.

[Explanation of symbols]

 Reference Signs List 1 CCD (reading means) 3 Exposure lamp (illumination means) 5 Document 6 Platen roller (first reference member) 12 Second white reference plate (second reference member)

Claims (2)

[Claims] A first reference member that is read at a document reading position; a second reference member that is read at a position other than the document reading position; a document that is read at the document reading position; and the first reference member Illuminating means for illuminating the second reference member; reading means for reading the document, the first reference member, and the second reference member by dividing the pixel into a plurality of pixels; A value obtained by processing the read value of the first reference member read so as to reduce the influence of the deterioration of the document reading position, a read value of the second reference member read by the reading unit, and a predetermined value. An image reading apparatus comprising: a correction unit configured to correct a read value of a document read by the reading unit using a correction coefficient determined for each pixel according to a coefficient. 2. The method according to claim 1, wherein the correcting unit divides a plurality of read values of the first reference member into a plurality of blocks, and adopts a maximum value in each of the divided blocks as a read value in each block. 2. The image reading apparatus according to claim 1, wherein the reading value of the first reference member is processed so as to reduce the influence of the deterioration of the document reading position.