JP2011071690A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of almost equalizing the brightness of an original image read in different original read modes. <P>SOLUTION: The image reader includes: a gain adjusting means for adjusting, to a target value, first output in which a first original read means reads a third white reference plate and outputs it, and second output in which a second original read means reads a second white reference plate and output it; and a correction means for correcting data for shading correction or a correction coefficient to be multiplied with image data before or after shading correction, in which the first original read means reads the third white reference plate and the second original read means reads the second white reference plate, according to the read mode by three pieces of data that are first and third read data for correction in which the first and third white reference plates are read by the first original read means adjusted by the gain adjusting means and second read data for the correction in which the second white reference plate is read by the second original read means adjusted by the gain adjusting means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an original reading apparatus for reading an original, and more particularly, an image reading provided with a flow reading mode in which an image of a conveyed original is read by an original reading means and a fixed reading mode in which an original placed on a contact glass is read by an original reading means. It relates to the device.

This type of image reading apparatus has a configuration in which a light source that illuminates a document and reflected light of the document illuminated by the light source is read by a line sensor. For this reason, if the light quantity of the light source varies, spots are generated in the read image. Therefore, in general, the acquisition of shading correction correction data for correcting the variation in the amount of light depending on the reading position of the document with reference to the reference white plate is performed before the reading is started, and the shading correction is performed based on the acquired correction data based on the image processing. It is done as a pre-processing.

For example, the “shading correction technique” disclosed in Patent Document 1 always sets an optimal shading correction by automatically setting shading correction accuracy in order to output a document read by a scanner [image reading apparatus] with high reproducibility. Like to do.

Further, as disclosed in Patent Document 2, the image reading apparatus has a flow reading mode in which an image of a conveyed document is read by a document reading unit, and a fixed reading mode in which a document placed on a contact glass is read by a document reading unit. An image reading apparatus is known.

Normally, in the image reading apparatus having the two reading modes as described above, as shown in FIG. 9, the contact glasses CG1 to CG3 are obtained by processing the same glass material into a desired size, and the contact glass CG2 is used. A white reference plate WB2 is disposed in the vicinity of CG3, and a white reference plate WB3 is disposed in the vicinity of CG3. The white reference plates WB1 and WB3 are used to pass the respective contact glasses to perform shading correction of the document reading means RD1 and RD2. . Naturally, in the flow reading mode, when the original is read with the original reading means RD1 stopped moving below the contact glass CG1, the transmittance of the contact glass CG1 and the contact glass CG3 is the same, so the original reading means RD1. These shading corrections are the same under the above correction conditions and do not need to be adjusted.

Furthermore, in recent years, the resolution of reading has tended to increase sharply in order to read a high-quality image more clearly than a printed document, and reading in the scanning reading mode has become the mainstream instead of reading in the fixed reading mode. As an automatic document feeder that transports documents, it strives to improve transport performance.

JP-A-10-341337 JP 2002-182437 A

However, paper used as a document on which high-quality images are printed is often coated with a surface close to that of photographic printing paper. It is difficult to slip and difficult to transport accurately without transport spots.

Therefore, in order to accurately convey the sheet without conveyance unevenness, it has been possible to apply an antistatic coating to at least the conveyance original surface of the contact glass used in the flow-reading mode. The transmittance decreases, and there is a difference with the transmittance of contact glass that is not coated. Due to this difference in transmittance, images read by simultaneous double-sided scanning are particularly bright and dark, and an output image faithful to the original is obtained. The problem of being unable to do so arises. The reason for this is that, in the apparatus configuration shown in FIG. 9, since the dedicated white reference plate is not disposed on the contact glass CG1, the gain adjustment of the document reading means RD1 that reads one side of the document in the flow reading mode is fixed reading. This is performed using the white reference plate WB3 used in the mode. As a result, a difference occurs in the gain between the document reading unit RD1 and the document reading unit RD2 due to the difference in transmittance due to the coating process, and even if the same document is read, a difference in brightness appears that one is bright and the other is dark. it is conceivable that. Although the above-mentioned problem can be solved by coating the contact glass CG3 in the same manner as the contact glasses CG1 and CG2, the contact glass CG3 is one size larger than the maximum size of the document to be handled, and the coating processing cost This is not practical because it increases the price of the equipment.

The present invention has been made to solve the above-described problems, and an object of the present invention is to correct the brightness of an original image obtained by reading in each original reading mode by correcting shading correction data in different original reading modes. An object of the present invention is to provide an image reading apparatus which can be made substantially equal.

In order to solve the above-described problem, an image reading apparatus according to the present invention includes a first document reading unit that is arranged across a document transport path and reads a transported document through a first contact glass, and a second contact glass. A second original reading unit that reads the conveyed original via the image, and supports the first original reading unit movably along the placed original surface, and the image of the conveyed original traveling along the conveyance path A scanning mode in which one or both of the first and second document reading units are scanned, and an image is read by scanning the first document reading unit while the document is placed on the third contact glass. In the image reading apparatus provided with the control means for controlling the fixed reading mode, the first and second contact glasses are parallel flat glasses whose surfaces are coated, and the third contact glass is a front surface. The coating treatment using a parallel flat glass without straining facilities in,
A first white reference plate disposed on the first contact glass for acquiring data of the first document reading means; and the first and second contacts disposed on the second and third contact glasses. Second and third white reference plates for adjusting the output gain of the document reading means, a first output by which the first document reading means reads and outputs the third white reference plate, and the second document Gain adjusting means for adjusting a second output for the reading means to read and output the second white reference plate to a target value; and the first document reading means for the third white reference plate and the second output. The first original reading means in which the correction coefficient to be multiplied by the shading correction data or the image data before or after the shading correction read by the original white reading plate is adjusted by the gain adjusting means. By the above The first and third correction read data read from the first and third white reference plates and the second white reference plate read from the second original reading means adjusted by the gain adjusting means. It is characterized by comprising a correcting means for correcting according to the above-mentioned reading mode with three pieces of data, ie, two correction reading data.

The first white reference plate is disposed in the transport path of the transported document, and after the first to third correction read data is acquired by the first and second document reading units, the transport path is used. The adjustment jig member is removable from the inside.

Further, the gain adjustment by the first and second gain adjusting means is corrected by the decrease in transmittance due to the coating process.

Further, the shading correction data of the first document reading means for reading the transported document through the first contact glass in the flow reading mode is obtained by the first document reading means using the third white reference plate. Consists of read shading correction data.

According to the present invention, the first original reading unit reads and outputs the third white reference plate, and the second original reading unit reads and outputs the second white reference plate. Gain adjusting means for adjusting the second output to a target value is provided, wherein the first original reading means is the third white reference plate, and the second original reading means is the second white reference plate. The first and third white reference plates are read by the first document reading means adjusted by the gain adjusting means for the correction coefficient to be multiplied by the read shading correction data or image data before or after shading correction. The first and third correction read data and the second correction read data obtained by reading the second white reference plate by the second document reading unit adjusted by the gain adjusting unit. By providing the correction means for correcting according to the reading mode with the three data, the first and second contact glasses subjected to the coating process and the third not subjected to the coating process in the assembly process of the image reading apparatus. A white reference plate is disposed on each contact glass, and after the correction coefficients of the first and second document reading means are stored and set according to different reading modes, the white reference plate disposed on the first contact glass is removed. Then, in the reading process of reading the document image in each reading mode, using the white reference plate arranged on the second and third contact glasses, immediately before the start of reading according to each document reading mode of the first and second document reading means The shading correction data can be read and adjusted based on the correction coefficient stored in the shading correction data. Read can be made substantially equal to the brightness of the original image obtained at, it is possible to provide an image reading apparatus capable of obtaining a faithful output image on the document.

1 is a cross-sectional view illustrating an image reading apparatus including an automatic document feeder according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a main part of a document reading mechanism unit in FIG. 1. It is a block diagram which shows schematic structure of a process control part. It is a gain adjustment process diagram. It is a correction coefficient acquisition process figure. It is a shading correction process drawing. FIG. 6 is an enlarged cross-sectional view of a main part of an automatic document feeder according to a second embodiment of the present invention. It is sectional drawing to which the principal part of the automatic document feeder which concerns on 3rd embodiment of this invention was expanded. It is the schematic for demonstrating the shading correction method in the conventional image reading apparatus.

[First embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an image reading apparatus provided with an automatic document feeder, and FIG. 2 is an enlarged sectional view of a main part of the document reading mechanism.

The image reading device SC includes a flat bed scanner IR that reads an image by scanning the first document reading unit with the document placed on the third contact glass, and a flat bed scanner IR that is placed above the flat bed scanner IR. And an automatic document feeder DF that is attached by a hinge or the like so as to be freely opened and closed, and that automatically separates the document and conveys it to the reading position of the flatbed scanner IR.

First, in the flat bed scanner IR, a contact glass CG1 and a contact glass CG3 are disposed horizontally adjacent to the upper surface of the apparatus frame BD1. A guide rail GD is drawn inside the apparatus frame BD1, and the first document reading means RD1 is supported along the guide rail GD so as to be movable in parallel to the document surface of the placed document. Placed on the contact glass CG3, the movement position P1 positioned in the flow reading mode, the movement position P2 facing the white reference plate WB3 via the contact glass CG3 in order to acquire the shading correction data of the first document reading means RD1. It moves between a reading start position P3 to a reading end position P4 for reading the placed document in the fixed reading mode. Further, the image reading device SC includes a control unit CU that reads image data and stores various data.

The contact glass CG1 is used for reading one side of a transported document transported by the automatic document transport device DF. The material is float glass, the thickness t1 is 2.8 ± 0.1 mm, and the refractive index n is 1.5. Parallel plane glass is coated with antistatic coating for static electricity generated by sliding contact with the transported document on the surface, antifouling coating to prevent dirt, scratches, etc. due to sliding contact with the transported document. ing. Further, the contact glass CG3 is used for reading an original placed by a person one by one, and a parallel flat glass substantially the same as the contact glass CG1 is used. The contact glass CG3 needs to be subjected to a coating process depending on the usage form. There is no coating treatment.

The first document reading means RD1 includes a light source LD1 in which a plurality of LEDs are arranged in the main scanning direction for illuminating the read document, reflection mirrors MR1 to MR4 that reflect reflected light from the read document, and reflection mirrors MR1 to MR4. The optical lens LE1 that condenses the guided reflected light, the light receiving element CCD1 disposed on the focus surface of the reflected light collected by the optical lens LE1, and a memory RM that stores output data read by the light receiving element CCD1. A data transfer cable terminal for transmission control is provided.

Next, the automatic document feeder DF stacks and stores the documents, the conveyance guide path 2 for conveying the documents on the sheet feed tray 1, and the document discharged from the conveyance guide path 2. A paper discharge tray 3 is provided. In addition, the conveyance guide path 2 is formed with an opening for sliding the document on the contact glass CG1 and an opening for placing the contact glass CG2 across the guide path on the opposite side of the contact glass CG1. ing. Further, it comprises second document reading means RD2 that reads the document passing through the surface of the contact glass CG2 through the contact glass CG2. The contact glass CG2 includes a white reference plate WB2 that is movably supported at an insertion position positioned on the document reading surface and a retracted position retracted from the document reading surface.

The contact glass CG2 is formed of the same material as the contact glass CG1, is made of float glass, is a plane parallel glass having a thickness t1 of 2.8 ± 0.1 mm and a refractive index n of 1.5, and is conveyed on the surface. Coating processing such as antistatic coating for static electricity generated by sliding contact with the surface, antifouling coating for preventing contamination and scratches due to sliding contact with the conveyed document, and scratch protection coating are performed.

The second document reading unit RD2 has substantially the same optical system configuration as the first document reading unit RD1, and includes a light source LD2 in which a plurality of LEDs are arranged in the main scanning direction for illuminating the read document, and a read document. Reflective mirrors MR5 to MR7 for reflecting the reflected light, an optical lens LE2 for condensing the reflected light guided by the reflective mirrors MR5 to MR7, and light reception arranged on the focus surface of the reflected light collected by the optical lens LE2. A device CCD2 and a control unit CU for controlling transmission of output data read by the light receiving device CCD2 to the memory RM are provided. The second document reading unit RD2 is provided to enable double-sided reading in which images on both sides of the document conveyed together with the first document reading unit RD1 can be read simultaneously.

Next, the control unit CU will be described with reference to FIG. As shown in the figure, the control unit CU includes a document presence / absence sensor, a home position sensor of the document reading means RD1, input of various sensor signals of the automatic document feeder DF, communication control with an external I / F, and a flatbed scanner IR. Control of a drive circuit for driving conveyance of the document reading means RD1, driving of document conveyance of the automatic document conveyance device DF, and control of the image processing unit are performed. In the image processing unit, input image data is subjected to shading correction as preprocessing of image processing, and is output from an external I / F to a host PC or the like through subsequent image processing. Further, the shading correction unit performs correction according to the reading mode by multiplying the shading correction data or the image data before or after the shading correction by the correction coefficient set by the control unit.

Next, each reading specification of the first and second document reading units RD1 and RD2 is adjusted within a permissible value for gain adjustment (step 1), a correction coefficient acquisition method for shading correction (step 2), and shading correction (step). 3) will be described with reference to FIGS.

[About gain adjustment]
First, the gain adjustment step 1 will be described with reference to FIG. 4 in which each reading specification of the first and second document reading units RD1 and RD2 is within an allowable value. The first and second document reading means RD1 and RD2 have different output values even when the same white reference is read using the same light source due to the number of reflection mirrors MR and the sensitivity variation of the light receiving element CCD. It is necessary to perform gain adjustment that suppresses the output value within a predetermined range. This gain adjustment is effective when the brightness of the image scanned in the scanning mode is different from the brightness of the image scanned in the fixed scanning mode, or when both sides of the document are scanned in the scanning mode. Is to correct the difference.

As shown in FIG. 4, in the apparatus that has been assembled (the state shown in FIG. 1), the apparatus power is turned on and the light amounts of the light sources LD1 and LD2 of the first and second document reading means RD1 and RD2 are stabilized. , The white reference plate WB3 is read by the light receiving element CCD1 of the first document reading means RD1, the output value of the light receiving element CCD1 is detected, and the output value is used as the gain data 1, and the gain of the control unit CU shown in FIG. Temporarily store in the adjustment memory RM0. At the same time, the white reference plate WB2 is read by the light receiving element CCD2 of the second document reading means RD2, the output value of the light receiving element CCD2 is detected, and the output value is similarly used as gain data 2 in the gain adjustment memory RM0 of the control unit CU. Memorize temporarily.

The gain adjustment memory RM0 temporarily stores the two gain data 1 and 2 using a gain adjustment arithmetic circuit (not shown), and the output data is obtained based on the smaller output data in the two gain data 1 and 2. As the maximum output, 95% is set as the adjustment target value, and the gain adjustment of the first and second document reading means RD1 and RD2 is performed so that the values of the two gain data 1 and 2 become the adjustment target value. The gain adjustment values 1 and 2 are stored in the gain adjustment memory RM0 of the control unit CU. This gain adjustment is always executed not only in the apparatus assembly process but also whenever the apparatus power is turned on every time an image is read, and captures changes in the light source, environmental temperature, and the like, and the first and second originals. Gain adjustment of the reading means RD1 and RD2 is performed.

[About the correction coefficient acquisition method and its storage]
Next, the first adjustment process step 2 relating to the acquisition and storage of the correction coefficient will be described with reference to FIG. After the gain adjustment of each of the first and second document reading means RD1 and RD2 within the permissible value in step 1 above, the flatbed scanner IR if the power is turned on and before gain adjustment data is acquired. The control CPU of the control unit CU mounted on the computer determines that the gain adjustment data is not yet acquired, and activates the gain adjustment correction coefficient acquisition mode in step 1 shown in FIG. At that time, the automatic document feeder DF is opened upward, and a white reference plate (adjustment jig member) WB1 prepared in advance is temporarily placed on the first contact glass CG1, and automatically in the temporarily placed state. The document conveying device DF is slowly lowered downward, and the white reference plate WB1 is disposed between the first contact glass CG1 and the conveying guide path 2 using the gap in the conveying guide path 2.

At the start of step 2, the first document reading means RD1 is moved and adjusted to the moving position P2 (see FIG. 1) facing the white reference plate WB3, the illumination light source LD1 is turned on, and the light quantity of the illumination light source LD1 is changed. Waiting for a stable time, the light receiving element CCD1 acquires the light quantity distribution data in the main scanning direction of the reflected light from the white reference plate WB3. First, the gain of the light receiving element CCD1 is adjusted by the acquired data, and the acquired data is adjusted after the adjustment. The correction coefficient calculation data 3 is temporarily stored in the correction coefficient storage memory RM1 managed by the control CPU.

Subsequently, the first document reading unit RD1 is moved and adjusted to the moving position P1 (see FIG. 1) opposite to the previously placed white reference plate WB1 (see the dotted line in FIG. 2), and the illumination light source LD1 is turned on again. The light receiving element CCD1 obtains the light quantity distribution data in the main scanning direction of the reflected light from the white reference plate WB1 after waiting for the light quantity of the illumination light source LD1 to stabilize, and the obtained data is controlled as the correction coefficient calculation data 1 Temporarily stored in the correction coefficient storage memory RM1 managed by the CPU.

At the same time, the second document reading means RD2 facing the white reference plate WB2 turns on the illumination light source LD2, waits for a time for the light amount of the illumination light source LD2 to stabilize, and then the amount of reflected light from the white reference plate WB2 in the main scanning direction. The distribution data is acquired by the light receiving element CCD2, and the gain of the light receiving element CCD1 is first adjusted by the acquired data. After the adjustment, the acquired data is temporarily stored in the correction coefficient storage memory RM1 managed by the control CPU as the correction coefficient calculation data 2. store.

As described above, after the temporary storage of the correction coefficient calculation data 1, 2, and 3 is completed in the correction coefficient storage memory RM1, the control CPU calculates the correction coefficient from the correction coefficient calculation data 1, 2, and 3, and adjusts the gain. The correction coefficients 1, 2, and 3 are stored and stored in the correction coefficient storage memory RM1 shown in FIG.

The correction coefficients 1, 2, and 3 are in a state in which a decrease in transmittance of the first and second contact glasses due to the coating process described above is reflected. Further, after the gain adjustment is completed, the white reference plate WB1 temporarily placed as an adjustment jig member is removed from the first contact glass CG1. If the adjustment time and adjustment effort are ignored, the white reference plate WB1 can be replaced with other white reference plates WB2 and WB3.

[Shading correction according to each scanning mode]
Next, the process control unit CPU that has determined that the correction coefficients 1, 2, and 3 are stored in the correction coefficient storage memory RM1 activates the shading correction adjustment mode in step 3 shown in FIG. In this shading correction adjustment mode, the first and second document reading means RD1 and RD2 that have been gain-corrected in consideration of the light quantity deterioration of the illumination light sources LD1 and LD2 and changes in the apparatus environment temperature in the previous gain adjustment process are actually used. This is executed for each reading mode immediately before the reading operation.

In the following description, the conditions in this embodiment are as follows.
First contact glass CG1: with coating treatment Transmittance 95%
Second contact glass CG2: With coating treatment Transmittance 95%
Third contact glass CG3: without coating treatment, transmittance 98%
Four reflecting mirrors with 94% reflectance in the first document reading means RD1 Three reflecting mirrors with 94% reflectance in the second document reading means RD2 90% reflectance of the white reference plate WB2
90% reflectance of white reference plate WB3
This is the case.

<Adjustment method in fixed reading mode>
When the document is placed on the third contact glass CG3, a document detection sensor (not shown) detects that the document is placed on the third contact glass CG3, and gives a signal to the processing control unit CPU. In response to the signal, the fixed reading mode of the processing control unit CPU is activated. By this activation, the first document reading means RD1 is moved and adjusted to the moving position P2 facing the white reference plate WB3, the illumination light source LD1 is turned on, and the white reference is waited for a time for the light quantity of the illumination light source LD1 to stabilize. Each light quantity value in the main scanning direction of the reflected light from the plate WB3 is acquired by the light receiving element CCD1 as shading correction data, and the acquired data is stored and stored in the shading correction memory RM2 shown in FIG. Then, the shading correction data 1 is corrected using the data value of the correction coefficient 3 stored and stored in the correction coefficient storage memory RM1.

<Adjustment method for single-sided scanning mode>
When a document is placed on the paper feed tray 1 of the automatic document feeder DF, a document detection sensor (not shown) detects that the document is placed on the paper feed tray 1 and gives a signal to the processing control unit CPU. In response to this signal, the flow reading mode of the processing control unit CPU is activated. As a result of this activation, a selection screen for single-sided scanning or double-sided simultaneous scanning is displayed on the connected personal computer screen. When single-sided scanning is selected, the first document reading means RD1 once moves to the moving position P2 facing the white reference plate WB3. The light source LD1 is turned on and the light amount value in the main scanning direction of the reflected light from the white reference plate WB3 is acquired by the light receiving element CCD1 as shading correction data after waiting for a time for the light amount of the illumination light source LD1 to stabilize. Then, the acquired data is stored and stored in the shading correction memory RM2 shown in FIG. Then, the shading correction data 1 is corrected using the data value of the correction coefficient 1 previously stored and stored in the correction coefficient storage memory RM1. In this state, the first document reading means RD1 is moved and set to the moving position P1, which is a one-side flow reading position, and reads the surface of the conveyed document conveyed by the automatic document conveying device DF.

<Adjustment method for simultaneous scanning mode duplex scanning>
On the other hand, when the double-sided simultaneous reading is selected, the first original reading unit RD1 is similarly moved and adjusted once to the moving position P2 facing the white reference plate WB3, the illumination light source LD1 is turned on, and the illumination light source LD1 is turned on. Waiting for a time for the amount of light to stabilize, each light amount value in the main scanning direction of the reflected light from the white reference plate WB3 is acquired as shading correction data by the light receiving element CCD1, and the acquired data is shown as shading correction data 1 in FIG. Store and store in the shading correction memory RM2. At the same time, the second original reading unit RD2 turns on the illumination light source LD2, waits for a time for the light amount of the illumination light source LD2 to stabilize, and uses each light amount value in the main scanning direction of the reflected light from the white reference plate WB2 as shading correction data. Obtained by the light receiving element CCD2, the obtained data is stored and stored in the shading correction memory RM2 shown in FIG. Then, the shading correction data 1 and 2 are respectively corrected using the data values of the correction coefficient 1 and the correction coefficient 2 stored and stored in the correction coefficient storage memory RM1. In this state, waiting for the first document reading means RD1 to move and set to the moving position P1, which is the one-side flow reading position, the conveyance of the document is started by the automatic document feeder DF. The original reading means RD1 and RD2 simultaneously read both sides of the conveyed original.

[Specific adjustment method]
When the gain of the reflectance of the white reference plate at the light receiving unit and the A / D output maximum value of white reference plate reading is actually adjusted to 220/255, the adjustment is performed as follows. Note that FB indicates the CCD1 correction adjustment in the fixed reading mode, the ADF table indicates the CCD1 correction adjustment in the scanning reading mode front side reading, and the ADF back indicates the CCD2 correction adjustment in the scanning reading mode back side reading.
FB 90% x 98% x 94% to the fourth power ≒ 68.9% A / D output maximum value: 220
ADF back 90% × 95% × 94% to the third power ≒ 71.0% A / D output maximum value: 220
(When reading ADF front jig 90% x 95% x 94% to the fourth power ≒ 66.8% A / D output: 213)
Similarly, the reflectance and A / D output when scanning a document with a reflectance of 50% are:
FB 50% x 98% x 94% to the fourth power ≒ 38.3% A / D output maximum value: 50/90 x 220
≒ 122
ADF table 50% × 95% × 94% to the fourth power ≒ 37.1% A / D output maximum value: 50/90 × 213
≒ 118
ADF back 50% x 95% x 94% to the third power ≒ 39.5% A / D output maximum value: 50/90 x 220
≒ 122
When shading correction is performed in this state,
FB 122 / 220≈55.5% 256 gradations: 122/220 × 255≈141
ADF table 118 / 220≈53.6% 256 gradations: 118/220 × 255≈137
ADF back 122 / 220≈55.5% 256 gradations: 122/220 × 255≈141
Thus, there is a difference in each numerical value, and there is also a difference from the actual reflectance of the original.
Therefore, in order to correct this difference and the white reference plate reflectance (90%), a correction coefficient is calculated as follows.
FB 220 / a × 90% 256 gradations: 220 / a × 90% × 255
ADF table 220 / b × 90% 256 gradations: 220 / b × 90% × 255
ADF back 220 / c × 90% 256 gradation: 220 / c × 90% × 255
It should be noted that a and c are the maximum values of read data that is not subjected to shading correction of the white reference plate of the machine, and b is the maximum value of read data that is not subjected to shading correction of the white reference plate jig of the machine.
If a, b, and c are 220, 213, and 220, the correction coefficient is
FB 90% (when expressed in 256 gradations, it is 230)... Correction coefficient 1
ADF table 93% (256 gradations gives 237)
... Correction factor 2
Back of ADF 90% (when expressed in 256 gradations, it becomes 230)
... Correction coefficient 3
When this is multiplied by the 50% shading corrected data,
FB 55.5% × 90% ≈50% 256 gradations: 141 × 230 / 255≈127
ADF table 53.6% × 93% ≈50% 256 gradations: 137 × 237 / 255≈127
ADF back 55.5% x 90% ≒ 50% 256 gradations: 141 x 230/255 ≒ 127
And the difference in the configuration of the reading unit and the reflectance of the white reference plate can be corrected. For simplicity of explanation, the offset level is set to 0. Since there is actually an offset level, it is necessary to consider that amount in the calculation.

[Second Embodiment]
FIG. 7 is an enlarged cross-sectional view of a main part of an automatic document feeder according to the second embodiment of the present invention. In the first embodiment described above, when the correction coefficient is acquired, the white reference plate (adjustment jig member) WB1 prepared in advance is temporarily placed on the first contact glass CG1. However, if possible in the device configuration, by processing the same coating material processed into the first contact glass CG1 at the end of the third contact glass CG3 as shown in the figure in a strip shape in the main scanning direction, The step performed using the white reference plate (adjustment jig member) WB1 can be performed without using the white reference plate (adjustment jig member) WB1.

[Third embodiment]
FIG. 8 is an enlarged cross-sectional view of a main part of an automatic document feeder according to the third embodiment of the present invention. In this embodiment, the glass width of the first contact glass CG1 is widened and arranged under the white reference plate WB3 arranged in the third contact glass CG3. As in the second embodiment, The step performed using the white reference plate (adjustment jig member) WB1 can be performed without using the white reference plate (adjustment jig member) WB1.

SH Document CG1 First contact glass CG2 Second contact glass CG3 Third contact glass RD1 First document reading means RD2 Second document reading means WB1 First white reference plate WB2 Second white reference plate WB3 First 3 white reference plate ST1 gain adjusting means (gain adjusting step <step 1>)
ST2 Correction coefficient acquisition means (correction coefficient acquisition adjustment step <Step 2>)
ST3 Shading correction means (shading correction step <Step 3>)
CU control means (control unit)
WB1 First white reference plate (adjustment jig member)
WB2 Second white reference plate WB3 Third white reference plate

Claims (5)

A first document reading unit that is disposed on the front and back of the transported document and reads the transported document through the first contact glass; and a second document reading unit that reads the transported document through the second contact glass;
Supporting the first document reading means movably along the placed document surface;
A flow reading mode in which an image of a transported document traveling along the transport path is read by one or both of the first and second document reading units, and the document is placed on a third contact glass. In an image reading apparatus comprising a control means for controlling a fixed reading mode for reading an image by scanning one original reading means,
The first and second contact glasses use parallel flat glass whose surface is coated, and the third contact glass uses parallel flat glass whose surface is not coated,
A first white reference plate disposed on the first contact glass for acquiring data of the first document reading means; and the first and second contacts disposed on the second and third contact glasses. Second and third white reference plates for adjusting the output gain of the document reading means;
A first output for reading and outputting the third white reference plate by the first document reading unit; and a second output for reading and outputting the second white reference plate by the second document reading unit. A gain adjusting means for adjusting to a target value;
The shading correction data or the image data before or after shading correction obtained by the first original reading unit reading the third white reference plate and the second original reading unit reading the second white reference plate, respectively. First and third correction read data obtained by reading the first and third white reference plates by the first document reading unit adjusted by the gain adjustment unit, and the gain adjustment unit. Correction means for correcting according to the reading mode with three data including the second correction reading data obtained by reading the second white reference plate by the second original reading means adjusted by An image processing apparatus. The first white reference plate is disposed in the transport path of the transported document, and after the first to third correction read data is acquired by the first and second document reading means, from the transport path. The image processing apparatus according to claim 1, wherein the image processing apparatus is a detachable adjustment jig member. The image processing apparatus according to claim 1, wherein gain adjustment by the first and second gain adjusting units is corrected by a decrease in transmittance due to the coating process. The image processing apparatus according to claim 1, wherein the coating process comprises an antistatic coating. For the shading correction data of the first document reading unit that reads the transported document through the first contact glass in the flow reading mode, the first document reading unit reads the third white reference plate. The image processing apparatus according to claim 1, comprising shading correction data.