JP2017183964A - Reading device and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reading device capable of reducing a reading linearity difference of the front and back surfaces of an original without using any special original such as a density reference original.SOLUTION: A reading device (100) comprises: a front surface side CIS(Contact Image Sensor) 126 for reading the front surface image of an original; a back surface side CIS 128 for reading the back surface image of the original; shading correction circuits 400, 401 for performing shading correction to image data of the original on the basis of a gain adjustment value and an offset adjustment value for shading correction determined on the basis of a reading result obtained when the front surface side and back surface side CISs respectively read shading white boards (α, β); and a gain correction value calculation circuit (402) for correcting the gain adjustment value and an offset correction value calculation circuit (403) for correcting the offset adjustment value such that a reading characteristic difference of the front surface side and back surface side CISs is reduced on the basis of reading data obtained when white paper is read by controlling light quantity of LED light sources 130, 132.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technology of a reading device that reads image information recorded on a document.

For example, a reading apparatus that reads an image of a document generally reads a white reference document or white reference plate in order to correct reading unevenness due to variations in characteristics of optical systems, light emitting elements, and image sensors included in the reading unit. Shading correction.
Also, in a reading device used in a copying machine or the like, so-called “flow reading” is performed, in which a document is transported one page at a time on a platen glass and an image of the document is read by a reading unit fixed to the transport path. Things are known. In addition, there is known a device in which two reading devices are provided to improve productivity and the front and back of a document are read at a time.

  When reading the front and back sides of a document with a single conveyance, there may be a variation in the amount of light due to a difference in reading position when reading a document image. In addition, there is a problem that the reading value of the front side document and the reading value of the back side document are different, and the reproduced color and density are different.

  To solve this problem, for example, using a density reference document having density patterns of at least two different densities, the difference between the front and back reading characteristics (linearity difference) is reduced by the gain correction value and the offset correction value based on the front and back reading data. There is a technique to do this (for example, Patent Document 1).

Japanese Patent Laid-Open No. 2008-078798

However, in the technique disclosed in Patent Document 1, it is necessary to use a special document such as a density reference document in order to reduce the difference in linearity between the first and second reading units.
If the reading characteristics of the reading device change due to deterioration over time, or if the density reference original is not sufficiently managed and scratches or dirt are generated, there remains a problem that correction processing cannot be performed normally. Further, when the original is clogged in the reading apparatus during the flow reading and the density reference original is damaged, the correction process cannot be normally performed. Furthermore, there is a problem that a new density reference document must be procured when the density reference document is scratched, stained, or damaged.

  It is a main object of the present invention to provide a reading apparatus that can reduce a difference in reading linearity between the front and back sides of a document without using a special document such as a density reference document. An image forming apparatus having the reading device is also provided.

  In the reading apparatus of the present invention, a first reading unit that reads a front image of a document, a second reading unit that reads a back image of the document, and the first and second reading units read a white reference member, Shading for performing shading correction on the image data of the document read by the first and second reading means based on the gain adjustment value and offset adjustment value for shading correction determined based on the reading result A correction means and a reading characteristic difference between the first reading means and the second reading means are reduced based on reading data obtained by controlling a light amount of a light source and reading a document having a uniform in-plane density on the front surface and the back surface. And a data correction means for correcting the gain adjustment value and the offset adjustment value.

  According to the present invention, the difference in reading linearity between the front and back sides can be reduced by using a document having a uniform in-plane density (for example, white paper) without using a special document such as a density reference document having a plurality of density patterns. Can be planned.

1 is a schematic longitudinal sectional view illustrating an example of a configuration of a reading apparatus according to an embodiment. 6 is a flowchart illustrating an example of a reading process for reading a double-sided document performed by a reading device. FIG. 3 is a block diagram illustrating an example of a main functional configuration of a reading device. The figure for demonstrating an example of the circuit structure of image processing ASIC. FIG. 6 is a diagram for explaining shading correction performed by a reading device. The figure which shows an example of the blank paper image which is a result of the brightness | luminance acquisition process via the surface side CIS. The flowchart which shows an example of the brightness | luminance acquisition process procedure via the surface side CIS. The figure which shows an example of the relationship between the light emission rate and brightness | luminance of CIS of the front and back side in the center part of a reference | standard original. The flowchart which shows an example of the procedure of a shading correction process. The figure for demonstrating an example of the average brightness | luminance of 1 point | piece contained in the range of a high luminous rate, and the average brightness | luminance of 1 point | piece contained in the range of a low luminous rate. The graph for demonstrating an example of the processing result of the front-back matching performed by a reader.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Further, a case where the present invention is applied to a reading device that reads a document image will be described as an example. This reading apparatus is configured to be connectable to the image forming apparatus.

[Example Embodiment]
FIG. 1 is a schematic longitudinal sectional view showing an example of the configuration of the reading apparatus according to the present embodiment.
A reading device 10 shown in FIG. 1 includes an automatic document feeder 100 and a device main body 99 that reads an image of a document.

A document tray 101 stacks documents 102. A paper feed roller 103 is disposed above the document tray 101. The paper feed roller 103 is connected to the same drive source as the separation conveyance roller 104, and rotates with the rotation to feed the original 102.
The paper feed roller 103 is normally retracted to an upper position, which is the home position, so that the original 102 is not obstructed. When the paper feeding operation is started, the paper feeding roller 103 descends and comes into contact with the upper surface of the document 102. The paper feed roller 103 is pivotally supported by an arm (not shown), and moves up and down when the arm swings.

  The separation conveyance driven roller 105 is disposed on the side opposite to the separation conveyance roller 104 and is pressed toward the separation conveyance roller 104 side. The separation conveyance driven roller 105 is formed of a rubber material or the like that has slightly less friction than the separation conveyance roller 104, and cooperates with the separation conveyance roller 104 to copy one original 102 fed by the paper supply roller 103. Feed the paper one by one.

  The registration roller 106 and the registration driven roller 107 align the front end of the original 102 fed by the separation unit, abut the front end of the original 102 separated toward the nip portion of the stationary registration roller pair, and the original 102 Make a loop on the top and align its tip. The read roller 108 and the read driven roller 109 flow the original 102 toward the reading glass 116.

A front-side CIS (contact image sensor) 126 reads image information on the surface of the document 102 that passes on the flow reading glass 116 (first image reading unit).
The back side CIS 128 reads image information on the back side of the document 102 that passes through the flow reading glass 129 (second image reading unit).
After the reading of the front surface and the back surface is finished, the document 102 is scooped up from the flow reading glass 116 by the jump table 117 and then discharged to the discharge tray 114 via the lead discharge roller 111, the lead discharge driven roller 112 and the discharge roller 113. Is done.

  FIG. 2 is a flowchart illustrating an example of a reading process for reading a double-sided document performed by the reading device 10. Hereinafter, the operation of the reading apparatus 10 will be described with reference to FIG. The reading process by the reading device 10 is mainly controlled by a CPU (Central Processing Unit) 500 described later.

  The reading apparatus 10 starts feeding the document 102 placed on the document tray 101 (S201). The reading device 10 reads the image information on the surface of the document 102 passing through the flow reading glass 116 via the front surface side CIS 126 (S202). The reading apparatus 10 reads the image information on the back side of the document 102 via the back side CIS 128 (S203). The reading apparatus 10 discharges the document 102 for which reading of the front surface and the back surface is completed to the paper discharge tray 114 (S204).

FIG. 3 is a block diagram illustrating an example of a main functional configuration of the reading device 10.
The reading device 10 includes a CIS line sensor 126a included in the front side CIS 126, a front side CIS line sensor driving circuit 302 that drives and controls the LED, a LED light source 130 that is a light source included in the front side CIS 126, and an LED control circuit 131 that controls the LED light source 130. Have The A / D converter 303 converts analog data output from the front side CIS 126 into digital data, and a shading correction circuit 400 for the output signal. The shading correction circuit 400 functions as a first shading correction unit.

The back side CIS 128 has the same configuration as the front side CIS 126.
The reading device 10 includes a CIS line sensor 128a included in the back side CIS 128, a back side CIS line sensor driving circuit 306 that drives and controls the LED light source 132 that is a light source included in the back side CIS 128, and an LED control circuit 133 that controls the LED light source 132. Have The A / D converter 307 converts analog data output from the back side CIS 128 into digital data, and a shading correction circuit 401 for the output signal. The shading correction circuit 401 functions as a second shading correction unit.

The reading apparatus 10 also includes an image processing ASIC 304 that performs image processing of image signals from the shading correction circuits 400 and 401, and an SDRAM 305 that temporarily stores image data. Note that image data that has undergone image processing including shading correction in the image processing ASIC 304 is sent to an image forming apparatus (not shown).
The reading apparatus 10 also includes a CIS moving motor 501 that moves the front side CIS 126 to the flow reading position, and a document conveyance motor 502 that conveys the document during the flow reading. The CPU 500 controls each functional configuration of the reading device 10.

FIG. 4 is a diagram for explaining an example of the circuit configuration of the image processing ASIC 304.
The image processing ASIC 304 includes a gain correction value calculation circuit 402 (first data correction unit) that determines a gain correction value described later based on image data stored in an SDRAM 305 described later. Further, an offset correction value calculation circuit 403 (second data correction unit) that determines an offset correction value is provided.
Hereinafter, shading correction for correcting variation for each pixel of image data output from the front side CIS 126 and the back side CIS 128 will be described with reference to FIG.

FIG. 5 is a diagram for explaining the shading correction performed by the reading device 10.
The shading data is obtained by irradiating light from the LED light source 130 of the front side CIS 126 and reading the white shading plate α (white reference member α) existing on the flow reading glass 116. Similarly, also on the back side CIS 128, the shading data is obtained by irradiating light from the LED light source 132 and reading the white shading plate β (white reference member β) below the flow reading glass 116. In this way, reading is performed through the flow-reading glasses 129 and 116, and the white reference of the front side CIS 126 and the back side CIS 128 is determined, and based on this, the offset adjustment value and the gain adjustment value are determined. Hereinafter, this point will be described in detail.

The offset adjustment value is determined as follows. The LED light sources 130 and 132 corresponding to the front side CIS 126 and the back side CIS 128 are turned off.
In this state, the shading correction circuits 400 and 401 perform offset adjustment for each pixel so that each pixel value of data output from the front side CIS 126 and the back side CIS 128 becomes an arbitrary target value (for example, luminance value 5). This adjustment value is stored in the SDRAM 305 as an offset adjustment value.

  The gain adjustment value is determined as follows. The gain value is adjusted for each pixel so that each pixel value of the shading data of the front surface side CIS 126 and the back surface side CIS 128 becomes an arbitrary target value (for example, a luminance value 245). The gain adjustment value is stored in the SDRAM 305. Note that it is desirable to use the same reference white plate for the front side CIS 126 that reads an image on the front side of the document and the back side CIS 128 that reads an image on the back side of the document.

  Then, the shading correction circuits 400 and 401 perform predetermined processing on the image data output from the front side CIS 126 and the back side CIS 128 by reading the image of the document 102. In the processing by the shading correction circuits 400 and 401, the output luminance value is adjusted for each pixel based on the offset adjustment value and the gain adjustment correction value stored in the SDRAM 305 for the image data. In this way, shading correction is performed on image data output from each of the front side CIS 126 for reading the front side image of the original and the back side CIS 128 for reading the rear side image of the original.

  Note that the reading characteristics of the front surface side CIS 126 and the rear surface side CIS 128 do not always match the reading characteristics of the front surface side CIS 126 due to the difference in characteristics between the front surface reading glass 116 and the back surface flow reading glass 129. Therefore, a reading characteristic difference (linearity difference) may occur between the front side and the back side. Therefore, in the reading apparatus 10 according to the present embodiment, processing for reducing the linearity difference between the front and back sides (referred to as front-to-back fitting processing) is performed. Hereinafter, this point will be described in detail.

Image data used for correction processing performed by the reading device 10 will be described.
In the reading apparatus 10, correction processing is performed using a document with uniform in-plane density on the front and back surfaces, for example, white paper (white paper). The lighting time of the LED light source 130 irradiated during the shading correction processing of the front side CIS 126 is Ta1, an arbitrary time ta (> 0), and an integer X (≧ 1), and the lighting time TaX is calculated by the following equation (1).

TaX = Ta1- (X-1) * ta, (X ≧ 1) Formula (1)

  When the front side CIS 126 scans blank pages, first, an image corresponding to the number of main scanning lines L (for L lines) arbitrarily determined for blank pages in the state of the lighting time Ta1 (X = 1) is read. Next, the lighting time Ta2 (X = 2) is controlled via the LED control circuits 131 and 133, and the image for L lines is read again. The above processing is repeated with Ta3, Ta4, Ta5,..., And when the lighting time Taend is set to an arbitrarily determined light emission rate of 0, the image is read until the lighting time TaX reaches Taend, and the processing is terminated. This series of processing is referred to as luminance acquisition processing for each light emission amount.

  FIG. 6 is a diagram illustrating an example of a blank image (hereinafter referred to as a reference document) that is a result of the luminance acquisition processing via the front side CIS 126. As shown in FIG. 6, by changing the lighting times Ta1, Ta2 (= Ta1-ta), Ta3 (= Ta1-2ta)... Taend, it is possible to obtain the luminance corresponding to each lighting time. it can.

FIG. 7 is a flowchart showing an example of a luminance acquisition processing procedure via the front side CIS 126. Note that each processing shown in FIG. 7 is mainly performed by the CPU 500.
When X = 1 (S800), the CPU 500 calculates the lighting time TaX based on the equation (1) (S801). The CPU 500 reads an image for L lines at the lighting time TaX (S802). The CPU 500 calculates an average luminance value of data for L lines via the image processing ASIC 304 (S803). The CPU 500 determines whether TaX is Taend (S804). When TaX is not Taend (S804: No), the CPU 500 updates X = X + 1 (S805), and returns to the process of step S801. If not (S804: Yes), the process is terminated.

  The same processing is also performed on the back side CIS128. The lighting time of the LED light source 132 irradiated during the shading correction processing of the back side CIS 128 is Tb1, an arbitrary time tb (> 0), and an arbitrarily determined lighting time Tbend of 0, and TbX by the following equation (2) Is calculated. The luminance acquisition processing procedure via the back side CIS 128 is the same processing procedure as the luminance acquisition processing of the front side CIS 126 described above.

TbX = Tb1− (X−1) * tb, (X ≧ 1) Expression (2)

  Further, the light emission rate Ka of the front surface side CIS 126 can be calculated by the following equation (3), and the light emission rate Kb of the back surface side CIS128 can be calculated by the following equation (4).

Ka = (TaX−Taend) / (Ta1−Taend) (3)
Kb = (TbX−Tbend) / (Tb1−Tbend) (4)

FIG. 8 is a diagram showing an example of the relationship between the CIS light emission rate and the luminance on the front side and the back side in the center of the reference document. The vertical axis of the graph shown in FIG. 8 represents luminance, and the horizontal axis represents the light emission rate of the light source.
As shown in FIG. 8, it can be seen that there is a difference in linearity even when the front side and the back side have the same light emission rate. This linearity difference is caused by the difference between the reading luminance on the front surface side and the reading luminance on the back surface side.
In the following, a process for reducing the front / back linearity difference (front / back matching process) based on the luminance value of the reference document will be described with reference to FIG.

FIG. 9 is a flowchart illustrating an example of the procedure of the shading correction process. Each process shown in FIG. 9 is mainly performed by the CPU 500. Further, an example will be described in which the reading characteristics on the back side are matched with the reading characteristics on the front side (processing for reducing the linearity difference between the front and back sides) based on the reference document (FIG. 6).
Further, the processes in steps S901 to S905 shown in FIG. 9 are different depending on whether the process is through the front side CIS 126 or the back side CIS 128, and the same process is performed. The process is not limited to being performed.

The CPU 500 reads the shading white plates α and β via the front side CIS 126 and the back side CIS 128, and starts shading correction via the shading correction circuits 400 and 401 based on the read result (S901).
The CPU 500 starts the blank page reading by the front side CIS 126 and the back side CIS 128 (S902), and performs a luminance acquisition process (S903). The CPU 500 calculates an average luminance value for L lines corresponding to each light emission rate, and stores the calculation result in the SDRAM 305 as correction data (S904). When the luminance acquisition process is completed, the CPU 500 ends the blank page reading (S905).

  The CPU 500 determines a gain correction coefficient a for correcting the gain adjustment value and an offset correction coefficient b for correcting the offset adjustment value (S906). For example, the correction coefficient may be calculated using all the correction data stored in the SDRAM 305 in the process of step S904. However, in this case, since it is necessary to refer to a lookup table (LUT) or the like, the circuit scale becomes large and the reference backup data becomes enormous. For this reason, it may be difficult to realize with limited memory resources.

  Therefore, in the reading device 10 according to the present embodiment, one point included in the range of the high light emission rate (H1) and one point included in the range of the low light emission rate (H2) out of the halftone light emission rates of the light source. The brightness is adjusted using only a total of two points. Hereinafter, this point will be described with reference to FIG.

FIG. 10 is a diagram for explaining an example of the average luminance of one point included in the range of the high luminous rate (H1) and the average luminance of one point included in the range of the low luminous rate (H2).
FIG. 10 is a chart showing the average luminance of the front and back surfaces at two light emission rates, and an example in which the luminance is adjusted using two gradation patches (luminance patterns of two different light amounts) in the center of the chart. Cite. Actually, it is necessary to adjust the brightness in each of the corresponding areas on the front and back sides.

  From the correction data stored in the SDRAM 305 in the process of step S904 shown in FIG. 9, the read luminance data (average luminance x1) of the high emission rate H1 on the surface side obtained through the surface side CIS 126, and the low emission rate H2 Read luminance data (average luminance x2). Further, read luminance data (average luminance y1) of the high emission rate H1 on the back side and read luminance data (average luminance y2) of the low emission rate H2 acquired through the back side CIS128 are read. The read data is as shown in Table 1 below.

  The CPU 500 determines the gain correction coefficient a for correcting the gain adjustment value via the gain correction value calculation circuit 402. Further, the offset correction coefficient b for correcting the offset adjustment value is determined via the offset correction value calculation circuit 403. When each value is set as shown in Table 1 above, the gain correction coefficient a and the offset correction coefficient b on the back surface side with respect to the front surface side can be obtained by the following equations (5) and (6), respectively.

  Returning to the description of FIG. 9, the CPU 500 determines the gain adjustment value corrected based on the gain correction coefficient a, that is, the gain adjustment value after the front-to-back matching process. Further, the offset adjustment value corrected based on the offset correction coefficient b, that is, the offset adjustment value after the front-to-back matching process is determined (S907). As described above, the gain adjustment value and the offset adjustment value are corrected so as to reduce the reading characteristic difference between the front and back sides based on the read data having the brightness patterns of at least two different light amounts obtained by reading the white paper.

FIG. 11 is a graph for explaining an example of the result of front-to-back matching performed by the reading device 10. The vertical axis of the graph shown in FIG. 11 represents luminance, and the horizontal axis represents the light emission rate of the light source.
As shown in FIG. 11, when comparing the graph before the front / back matching process and the graph after the front / back matching process, the luminances X1 and X2 on the front side at the light emission rates H1 and H2 after the front / back matching process are as follows. It can be seen that the difference between the luminances Y1 and Y2 on the back side is reduced. That is, the back-side linearity difference can be reduced by matching the back-side reading characteristics to the front-side reading characteristics by the front-back matching process.

As described above, in the reading apparatus 10 according to the present embodiment, the amount of light is adjusted using a document (for example, white paper) having a uniform in-plane density to acquire image data, and gain correction data is acquired based on the acquired image data. (Gain correction coefficient) and offset correction data (offset correction coefficient) are generated.
Thereby, instead of using a special document such as a density reference document having a plurality of density patterns, a linearity difference between the front and back sides can be reduced by using a document (for example, a white paper) having a uniform in-plane density.

  In the above description, the case of reading a single color (black) document has been described as an example. In addition, even when the document has multiple colors, for example, the same processing as that described above may be performed for each color of RED, GREEN, and BLUE. Further, the image forming apparatus connected to the reading apparatus 10 may be configured according to the specifications.

  The embodiment described above is for explaining the present invention more specifically, and the scope of the present invention is not limited to these examples.

  DESCRIPTION OF SYMBOLS 10 ... Reading apparatus, 99 ... Reading apparatus main body, 100 ... Automatic document feeder, 101 ... Document tray, 102 ... Document, 103 ... Paper feed roller, 104 ... Separation / conveying roller, 105... Separation / conveying driven roller, 106... Registration roller, 107... Followed roller, 108. 113 ... paper discharge roller, 114 ... paper discharge tray, 116, 129 ... flow-reading glass, 117 ... jump stand, 126 ... front side CIS (reading means), 126a, 128a,. -CIS line sensor, 128 ... back side CIS (reading means), 130, 132 ... LED light source, 131, 133 ... LED control circuit, 302, 306 ... line sensor Drive circuit 303, 307 ... A / D converter 304 ... Image processing ASIC 305 ... SDRAM 400, 401 ... Shading correction circuit 402 ... Gain correction value calculation circuit 403 ... Offset correction value calculation circuit, 500... CPU, 501... CIS moving motor, 502.

Claims (8)

First reading means for reading a surface image of a document;

Second reading means for reading a back side image of the original;
The first and second reading means read the white reference member, and based on the gain adjustment value and the offset adjustment value for shading correction determined based on the reading result, the first and second reading means Shading correction means for performing shading correction on the image data of the original read by
The gain adjustment is performed so as to reduce a difference in reading characteristics between the first and second reading means based on read data obtained by controlling a light amount of a light source and reading a document having a uniform in-plane density on the front and back sides. Data correction means for correcting the value and the offset adjustment value,
Reader. The data correction means reads the first and second reading means based on read data having luminance patterns of at least two different light quantities obtained by reading a document having a uniform in-plane density on the front and back surfaces. The gain adjustment value and the offset adjustment value are corrected so as to reduce a characteristic difference,
The reading device according to claim 1. The white reference member includes a first white reference member that determines a white reference of the first reading unit, and a second white reference member that determines a white reference of the second reading unit,
The shading correction unit reads the first white reference member by the first reading unit, and based on the gain adjustment value and the offset adjustment value for shading correction determined based on the reading result, A first shading correction unit that performs shading correction on the image data of the document read by the first reading unit; and the second reading unit reads the second white reference member, and based on the reading result. Second shading correction means for performing shading correction on the image data of the document read by the second reading means based on the determined gain adjustment value and offset adjustment value for shading correction. It is characterized by
The reading device according to claim 1 or 2. The light source is a first light source that irradiates light toward the front surface of the document and a second light source that irradiates light toward the back surface of the document,
By controlling the light amounts of the first light source and the second light source, reading data corresponding to the front surface side and the back surface side having at least two different light intensity patterns respectively on the front surface side and the back surface side is obtained. It has a control means to control to,
The reading device according to claim 1, 2 or 3. The data correction unit corrects the gain adjustment value and the offset adjustment value of the second reading unit with reference to the reading characteristic of the first reading unit to read the reading characteristics of the first and second reading units. Characterized by reducing the difference,
The reading device according to any one of claims 1 to 4. A document feeding means for feeding the document,
The control means controls the light amounts of the first and second light sources when reading the original having a uniform in-plane density fed from the original feeding means, and at least each of the front side and the rear side Control is performed so as to acquire read data corresponding to the front side and the back side, each having a luminance pattern of two different light quantities,
The reading device according to claim 4 or 5. The document having a uniform in-plane density is white paper,
The reading device according to claim 1. An image forming apparatus having a reading device for reading a document image,
The reader is
First reading means for reading a surface image of a document;
Second reading means for reading a back side image of the original;
The first and second reading means read the white reference member, and based on the gain adjustment value and the offset adjustment value for shading correction determined based on the reading result, the first and second reading means Shading correction means for performing shading correction on the image data of the original read by
The reading characteristic difference between the first and second reading means is determined based on reading data having brightness patterns of at least two different light amounts obtained by controlling the light amount of the light source and reading a document having a uniform in-plane density. Data correction means for correcting the gain adjustment value and the offset adjustment value so as to reduce,
Image forming apparatus.