JP2001346011A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader capable of holding quality of an image as high by obtaining a reference signal for shading correction at high precision irrespective of stain with time of a rear side surface member to read an original. SOLUTION: The maximum value within a range of a original passing area L2 is detected by a peak hold circuit 24 and a gain of an amplifier 32 is controlled so that the detected maximum output value of an A/D converter 11 reaches a preset target value 224. A reading signal of the original passing area L2 in the main scanning direction is detected at timing when a reference original 1a is on a rear side surface roller 14 and the reading signal (reference reflection signal) of the original passing area L2 at the time is used for calculation of initial reference data. A reading signal of a non-passing area L1 of the original is stored as a correction signal (reference reflection correction signal) of the initial reference data whenever the non-passing area L1 of the original is read.

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 such as a digital copying machine, a facsimile, and a scanner for correcting an output image signal when a document is read.

[0002]

2. Description of the Related Art In recent years, an image reading apparatus that exposes an original with a light source, reads the intensity of the reflected light with a light receiving element, converts the read intensity into an electric signal, and outputs the electric signal has been widely used. For example, Japanese Patent No. 2822674 has a main scanning reference plate and a sub-scanning reference plate, and a reference voltage of an A / D (analog / digital) converter is supplied with a signal from the sub-scanning reference plate via an amplifier. The amplification degree of the amplifier is determined from the characteristics of the image signal in the main scanning direction, so that even if the illuminance distribution and reading characteristics in the main scanning direction change, an appropriate A
An image reading device capable of obtaining a reference voltage of a / D converter is described.

[0003] Also, Japanese Patent No. 2872236 discloses that
The white member outside the image reading area was read from the ratio of the signals read from the white members outside the area and the white member outside the image reading area and the optimum peak output value. The target value at the time is calculated, and the gain of the image signal amplifier is adjusted so that the value at the time of reading the white member outside the image reading area becomes the target value. An image reading apparatus that can obtain an appropriate gain of an image signal amplifier even when it changes is described. Further, Patent No. 287
Japanese Patent No. 5279 discloses that a reference signal in the main scanning direction read from a main scanning reference plate is subjected to median arithmetic processing and then used as a shading correction signal to obtain an appropriate shading correction signal even if the main scanning reference plate becomes dirty. An image reading device is described that can be used.

[0004]

However, the correction of the image signal in the conventional image reading apparatus is performed by the reference white plate on the same surface as the document passage surface. In some cases, the image quality is deteriorated due to the influence of the surface being stained with time.

Accordingly, a first object of the present invention is to provide an image reading apparatus capable of obtaining a high-precision reference signal for shading correction regardless of the contamination with time of a back member for reading a document and maintaining a high quality image. It is to provide. A second object of the present invention is to provide an image reading apparatus capable of preventing a surface on which a correction signal of initial reference data for calculating a reference signal for shading correction is obtained from being stained.

A third object of the present invention is to provide an image reading apparatus capable of replacing a reference reflection member for obtaining initial reference data for calculating a reference signal for shading correction. A fourth object of the present invention is to provide an image reading apparatus capable of improving the accuracy of correcting an image signal with respect to aging and preventing deterioration of the image signal. A fifth object of the present invention is to provide an image reading apparatus capable of preventing the reading quality from being deteriorated due to a change in the reading characteristics of the image reading apparatus.

[0007]

According to the first aspect of the present invention, a light source for illuminating a member on an installation glass, a first conveying means for conveying a member illuminated by the light source, and A second conveying means formed at one end;
Reading means for reading, as an image signal, reflected light from a member conveyed by the first conveying means; storage means for storing the image signal read by the reading means as initial reference data; Image signal output means for outputting an image signal being output, detection means for occasionally detecting reflected light from the second transport means illuminated by the light source as a correction signal, and correction signal detected by the detection means. Correction means for correcting the initial reference data stored in the storage means based on the image signal based on the initial reference data stored in the storage means and the correction signal detected by the detection means Providing shading correction means for performing shading correction on the image signal output by the output means. To achieve the first object.

According to a second aspect of the present invention, in the first aspect of the present invention, the second transporting means is provided in a region other than a passage area of the member transported by the first transporting device or in a non-contact state of the transported member. By being a region, the second object is achieved.

According to a third aspect of the present invention, in the first or the second aspect of the present invention, the member serving as the initial reference data stored in the storage means is an insertion opening for inserting a member into the installation glass, or an installation opening. The third object is attained by being installed directly on the glass.

According to the invention described in claim 4, in the invention described in any one of claims 1, 2, and 3,
The initial reference data stored in the storage unit is updated each time a reading operation is performed by the reading unit, the storage unit stores the updated initial reference data as reference data, and the shading correction unit includes the storage unit. By executing the shading correction of the image output by the output unit based on the reference data stored in the and the correction signal detected by the detection unit,
The fourth and fifth objects are achieved.

According to a fifth aspect of the present invention, in the first aspect of the present invention, when the storage means stores initial reference data, The reflected light from the second transport unit illuminated by the light source is stored as initial correction data, and the correction unit is configured to execute the correction based on a ratio between the initial correction data and a correction signal detected as needed by the detection unit. By correcting the initial reference data stored in the storage means,
The fourth and fifth objects are achieved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a diagram showing a configuration of the image reading apparatus according to the present embodiment. In the image reading apparatus of FIG. 1, the drive source and the drive transmission system are omitted. The image reading apparatus includes a document table 2 on which a document 1 is placed, a document insertion sensor 3, document feed rollers 4a and 4b, and guide plates 5 and 6 (including a plurality of guide plates not numbered in the drawing). Registration sensor 7, registration rollers 8a and 8b,
A linear sensor (reading sensor) 9, a selfoc lens array 10, document illumination light sources 11a and 11b, document conveying rollers 12a and 12b, a contact glass 13, a back roller 14, document discharge rollers 16a and 16b, and a document receiver 17 are provided. . The back roller 14 is used for the reference reflection member 1.
4a and a reading back member 14b.

FIG. 2 is a block diagram showing a reading control section of the image reading apparatus of FIG. The reading control unit includes an analog processing circuit 21, an A / D (analog / digital) converter 22, a timing generation circuit 23, a peak hold circuit 24, a control unit 25, and a shading correction circuit 2.
6, a memory 27, an operation unit 28, and a D / A (digital / analog) converter. The analog processing circuit 21 samples and holds the signal section of the analog image signal from the linear sensor 9.
0, a level adjustment circuit 31 for DC reproduction of an analog image signal and level adjustment and an amplifier 32 with variable gain.

The A / D converter 22 converts an image signal, which is an analog signal, into an 8-bit digital image signal. The timing generation circuit 23 outputs a clock signal, a gate signal, an address signal, and the like to each circuit block based on the control of the control unit 25. Peak hold circuit 24
Detects the maximum value in the range determined by the control unit 25, and the value is updated every main scanning. AGC (auto gain control) by the reading control unit in FIG. 2 is performed for the reference original 1 inserted in the same manner as the normal original 1 is inserted.
a is not on the back roller 14, the A / D converter 2
The gain of the amplifier 32 is controlled so that the maximum value of the output No. 2 in the main scanning direction becomes a predetermined target value (hereinafter, the target value is set to 224 as an example).

The shading correction circuit 26 detects variations in the distribution of the illumination light amount of the original in the main scanning direction and the linear sensor 9.
The variation of the image signal in the main scanning direction caused by the output characteristics from the A / D converter 22 to the A / D converter 22 is corrected. First, A /
The output value of the D converter 22 is multiply averaged for each of the 128 pixels in the main scan, and stored in the memory 27 as initial reference data for shading correction. The operation unit 28
A key is provided for recognizing that the reference document 1a is to be inserted into the image reading apparatus before the reference document 1a is inserted.

FIG. 3 is a diagram showing the positional relationship of the back roller in the main scanning direction. The reference document 1a is usually a paper document having a width equal to or larger than the document 1 that can be read by the image reading device and having no white stain. The back roller 14 includes a reference reflecting member 14a corresponding to the document non-passing area L1 and a reading back member 14b corresponding to the document passing area L2. In addition, the normal reflectance of the back roller 14 is
It is assumed that the value is close to the reflectance of a white document. The reading width of the linear sensor 9 includes the document non-passing area L1 and the document passing area L2 of the back roller 14;
The output of the linear sensor 9 corresponds to both the document non-passing area L1 and the document passing area L2 of the back roller 14. The read signal 40 is a signal for reading a document corresponding to one main scan after analog processing.

FIG. 4 is a view showing a modified example of the back roller. As shown in FIG. 4, the reference reflection member 14a, which is the document non-passing area L1, is provided on the back roller 14 on a different surface from the reading back member 14b, which is the document passing area L2, so that the It is less susceptible to the effects of the resulting contamination over time. Also, the reference reflection member 1
4a is separated from the extended portion of the surface of the reading roller 14b of the back roller 14 through which the document passes, so that it is less affected by dirt.

Next, shading correction in the image reading apparatus will be described. The reading operation of creating the initial reference data for shading correction in the image reading device is as follows.
The initial reference data capture key on the operation unit 28 is pressed,
It is started after the insertion of the reference original 1a. Then, the reading control unit executes the AGC operation of the reference original 1a and captures the initial reference data. First, at the timing when the reference document 1a is on the back roller 14 as an AGC operation, the peak value within the range of the document passage area L2 is detected by the peak hold circuit 24, and the detected output maximum value of the A / D converter 22 is detected. Is a preset target value 22
The gain of the amplifier 32 is controlled so as to be 4.

After the maximum output of the A / D converter 22 is matched with the target value 224 in the range of the document passage area L2, the gain of the amplifier 32 is used to adjust the reference document 1a on the back roller 14 in the main scanning direction. Of the document passing area L2 is detected. The detected document passage area L2
Is used for calculating initial reference data. The reading of the document non-passing area L1 is always performed, and each time the reading signal of the document non-passing area L1 is stored as a correction signal (reference reflection correction signal) of the initial reference data. Reference document 1a is back roller 1
4, the document passing area L in the main scanning direction
When detecting the second read signal and calculating the initial reference data, the read signal of the document non-passage area L1 in the calculated initial reference data is also stored as the initial correction data.
When the initial reference data is updated, the initial correction data is also updated to a read signal of the document non-passage area L1 detected when the initial reference data is updated.

The initial reference data based on the read signal of the first original scanning area L2 in the main scanning direction detected at the timing when the reference original 1a is on the back roller 14 is stored in the memory 27 as the previous initial reference data. This is used when calculating and updating the initial reference data. The initial reference data uses a read signal main scan of 128 lines and the following (1)
It is calculated by the formula and stored in the memory 27. Initial reference data = (7 × previous initial reference data + current read signal) / 8 (1)

Reference data for shading correction is calculated by the shading correction circuit 26 according to the following equation (2) based on the initial reference data, the initial correction data, and the correction signal at the time of document reading, and is stored in the memory 27. Reference data = initial reference data × initial correction data / correction signal (2) The original image signal is corrected by the shading circuit 26 in units of pixels in accordance with the following equation (3). Original image signal after correction = Original image signal × Maximum value when standard document 1 is read / Reference data (3)

Note that, instead of adjusting the gain of the amplifier 32, which is the AGC operation, the control can be performed by adjusting the reference voltage of the A / D converter 22. The reference voltage is supplied from the D / A converter 29. For the analog output of the D / A converter 29, the gain of the amplifier 32 is determined by the digital output of the control unit 25 so that the maximum output value of the A / D converter 22 becomes the target value 224. Further, in the present embodiment, in order to calculate the initial reference data, the first reference document 1 to be read is a white paper document. However, the present invention is not limited to this. Should be fine. It should be noted that the above-mentioned initial reference data can be taken in when the image reading apparatus is manufactured, when there is an abnormality (part replacement, etc.), and when the number of read originals reaches a predetermined value.

[0023]

According to the first aspect of the present invention, based on the initial reference data stored in the storage means and the correction signal detected by the detection means, the image signal output by the image signal output means is determined. And shading correction means for executing shading correction, so that the accuracy of image signal correction can be improved even if the surface of the document back member becomes dirty.

According to the second aspect of the present invention, the second conveying means is a region other than the passing region of the member conveyed by the first conveying unit or the non-contact region of the conveyed member, so that the surface for obtaining the correction signal is provided. Can be prevented, and the accuracy of image signal correction can be improved by using the reference reflection correction signal detected from the surface.

According to the third aspect of the present invention, the member serving as the initial reference data stored in the storage means is placed directly on the insertion opening for inserting the member into the installation glass or directly on the installation glass. Even if the surface becomes dirty, the accuracy of image signal correction can be improved.

According to the fourth aspect of the present invention, the initial reference data stored in the storage means is updated each time a reading operation is performed by the reading means, and the storage means stores the updated initial reference data as reference data, and performs shading. The correction means performs shading correction of the image output by the output means based on the reference data stored in the storage means and the correction signal detected by the detection means, thereby improving the accuracy of the image signal correction. Can be.

According to the fifth aspect of the present invention, when the storage means stores the initial reference data, the second illuminated by the light source is used.
The reflected light from the conveyance means is stored as initial correction data, and the correction means converts the initial reference data stored in the storage means based on the ratio between the initial correction data and the correction signal detected as needed by the detection means. Since the correction is performed, the temporal variation of the image reading device can be detected by the change rate of the reference reflection correction signal, and the reference reflection signal can be corrected according to the change rate, so that the accuracy of the image signal correction can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image reading apparatus according to an embodiment;

FIG. 2 is a block diagram illustrating a reading control unit of the image reading apparatus of FIG. 1;

FIG. 3 is a diagram illustrating a positional relationship of a back roller in a main scanning direction.

FIG. 4 is a view showing a modified example of the back roller.

[Explanation of symbols]

 1a Reference document 9 Linear sensor 14 Back roller 14a Reference reflection member 14b Reading back member 21 Analog processing circuit 22 A / D (analog / digital) converter 23 Timing generation circuit 24 Peak hold circuit 25 Control unit 26 Shading correction circuit 27 Memory 28 Operation Section 29 D / A (Digital / Analog) Converter 30 Sample Hold Circuit 31 Level Adjustment Circuit 32 Amplifier

Claims (5)

[Claims] A light source for illuminating a member on the installation glass; a first conveying unit for conveying a member illuminated by the light source; a second conveying unit formed at one end of the first conveying unit; Reading means for reading reflected light from a member conveyed by the first conveying means as an image signal; storage means for storing the image signal read by the reading means as initial reference data; stored in the storage means An image signal output unit that outputs an image signal that has been detected, a detection unit that occasionally detects reflected light from the second transport unit illuminated by the light source as a correction signal, and a correction signal that is detected by the detection unit. Correction means for correcting the initial reference data stored in the storage means on the basis of the initial reference data stored in the storage means, and the detection means Therefore on the basis of the detected correction signal, the image reading apparatus characterized by comprising a shading correction means for performing shading correction on the image signal output by said image signal output means. 2. The image according to claim 1, wherein the second transport unit is a region other than a passage region of the member transported by the first transport unit or a non-contact region of the transported member. Reader. 3. A member serving as initial reference data stored in the storage means, an insertion opening for inserting the member into the installation glass,
The image reading apparatus according to claim 1, wherein the image reading apparatus is installed directly on a setting glass. 4. The initial reference data stored in the storage means is updated each time a reading operation is performed by the reading means, and the storage means stores the updated initial reference data as reference data, and the shading correction means And performing shading correction of an image output by said output means based on reference data stored in said storage means and a correction signal detected by said detection means. The image reading device according to any one of claims 2 and 3. 5. When the storage means stores initial reference data, reflected light from the second transport means illuminated by the light source is stored as initial correction data, and the initial correction data and the detection means are stored. The correction means corrects the initial reference data stored in the storage means based on a ratio with a correction signal detected at any time by the control means. Item 5. The image reading device according to any one of Items 4.