Image reading device

Abstract

To provide an image reading device that corrects the difference between front and rear reading values without being affected by the difference in paper quality and paper thickness.SOLUTION: An image reading device 200 has: a conveying unit 86 that conveys a document to a conveyance path; a front face image reading unit 14 that reads a front face of the document conveyed by the conveying unit 86; a rear face image reading unit 15 that is arranged on the opposite side of the front face image reading unit 14 across the conveyance path and reads a rear face of the document; and an image processing unit 78 including an area selection unit that specifies a specific area that is the same area in a first read image obtained by the front face image reading unit 14 reading a first face of the document and a second read image obtained by the rear face image reading unit 15 reading the first face of the document, a peak calculation unit that calculates the peak of density in the specific areas in the first read image and the second read image, and a density correction value generation unit that generates, by using the peak of density, a correction value for performing correction so that the peak of density in the first read image and the peak of density in the second read image have the same value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image reading device such as a digital copying machine, a facsimile machine, or a scanner, and more particularly to an image reading device having a double-sided simultaneous reading configuration that reads both sides of an original simultaneously in one conveyance. [Background technology]

[0002] Recently, there are scanning devices equipped with a scanning mechanism capable of scanning the front and back sides of a document separately, enabling the scanning of both sides in a single document feed. However, this type of scanning device has a problem in that the read values ​​obtained when scanning the front side of a document differ from the read values ​​obtained when scanning the back side of the document. Possible causes of this include differences in the sensitivity of the scanning sensor, optical differences in the optical system, and deterioration of the components that make up the scanning sensor over time. Furthermore, some scanning devices of this type are capable of feeding documents made of various materials and thicknesses, and the influence of these materials and thicknesses may also be a factor.

[0003] Patent document 1 discloses a technology for reducing the difference between the front and back read values ​​by using gain correction values ​​and offset correction values ​​based on read data obtained by reading a density reference document prepared in advance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4785690 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the paper quality or thickness of a document is different, the distance from the document to the reading sensor in the conveyance path is different for the front and back sides. Therefore, the technology of Patent Document 1 uses a density reference document prepared in advance, and therefore cannot completely correct the difference between the read values ​​of the front side and the back side when the paper quality or thickness of the document that the user actually wants to convey is different. This means that there is a need to develop a system that can adjust the read values ​​of the front and back images of a document to match the document that the user actually uses. [Means for solving the problem]

[0006] In view of the above, the image processing device according to the present invention comprises: a conveying unit that conveys the document to a conveying path; a front image reading unit that reads the front surface of the document conveyed by the conveying unit; a back image reading unit that is disposed on the opposite side of the transport path from the front image reading unit and that reads the back side of the document; an area selection unit that identifies a specific area that is the same area in a first read image obtained by reading a first side of the document with the front image reading unit and a second read image obtained by reading the first side of the document with the back image reading unit; a peak calculation unit that calculates a density peak in the specific region of the first read image and the second read image; The image forming apparatus is characterized by having a density correction value generation unit that generates a correction value using the density peak to correct the density peaks of the first read image and the second read image so that they have the same value. [Effects of the Invention]

[0007] According to the image reading device of the present invention, it is possible to correct the difference between the front and back read values ​​without preparing a reference document in advance for generating correction values ​​and without being affected by differences in paper quality or thickness. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a partial cross-sectional view schematically showing the configuration of an image reading apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of the main part of the image reading device. [Figure 3] 1 is a block diagram of an image reading apparatus according to an embodiment of the present invention; [Figure 4] FIG. 2 is a block diagram of an image processing unit according to an embodiment of the present invention. [Figure 5] 6 is a flowchart of a density adjustment process of the front and back image reading unit according to the first embodiment of the present invention. [Figure 6] 1 is an example of a read document according to an embodiment of the present invention. [Figure 7] 5 is a density histogram of a read image read by a front and back image reading unit according to the first embodiment of the present invention. [Figure 8] 4 is a graph of input / output concentration characteristics according to the first embodiment of the present invention. [Figure 9] 10 is a flowchart of a density adjustment process of a front and back image reading unit according to a second embodiment of the present invention. [Figure 10] 10 is a density histogram of an image read by a front and back image reading unit according to a second embodiment of the present invention. [Figure 11] 10 is a density histogram of an image read by a front and back image reading unit according to a second embodiment of the present invention. [Figure 12] 10 is a density histogram of an image read by a front and back image reading unit according to a second embodiment of the present invention. [Figure 13] 10 is a graph showing input / output concentration characteristics according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are examples of the present invention, and the present invention is not limited to the following embodiments. The present invention should be appropriately modified or changed depending on the configuration of the device in which the present invention is used and various conditions, without departing from the spirit of the present invention.

[0010] First Embodiment First, an image reading apparatus according to a first embodiment of the present invention will be described.

[0011] Fig. 1 is a partial cross-sectional view schematically showing the configuration of an image reading device 200 according to a first embodiment of the present invention. Fig. 2 is a partial cross-sectional view schematically showing the configuration of a main part of a document transport unit of the image reading device 200 according to the first embodiment of the present invention.

[0012] 1 and 2, an image reading device 200 of this embodiment includes a sheet intake device (sheet feeding device) 101. A plurality of sheets are stacked on a sheet stacking table (sheet placing table) 1, and the sheet stacking table 1 is configured to be freely raised and lowered by an elevation section 2. A sheet stacking detection sensor 12 detects that a sheet (original) is stacked on a sheet stacking surface 1a of the sheet stacking table 1.

[0013] A pickup roller 4 (taking-in means) as an example of a sheet pickup section sends out a sheet on the sheet stacking table 1 to a conveying path from the sheet stacking table 1. The pickup roller 4 is driven by a pickup roller up / down motor 5 and can move to a sheet taking-in position and a retracted position above the sheet taking-in position shown in Fig. 1, and is moved to the sheet taking-in position when taking in a sheet, and is moved to the retracted position after taking in is complete.

[0014] The control unit 900 issues instructions to rotate the pickup roller 4 and to move between the sheet take-in position and the retracted position. The control unit 900 has a CPU, ROM, RAM, etc. (not shown), and the CPU executes programs stored in the ROM to realize various controls. The control unit 900 will be described later. The image reading device according to this embodiment may further include a sheet feed roller 6, a separation roller 7, a feed motor 8, a separation motor 9, and a nip gap adjustment motor 11.

[0015] The conveying motor 10 drives other rollers (sheet conveying units) to convey the separated sheet to an image reading position where the image on the sheet is read by a plurality of image reading sensors (image reading units) made up of the front image reading unit 14 and the back image reading unit 15 located on the opposite side of the conveying path, and further to a discharge position. The conveying motor 10 also drives each roller so that the sheet conveying speed can be changed according to settings such as the optimum speed for reading the sheet and the sheet resolution.

[0016] The pre-registration sensor 32 (first detection means) is arranged upstream of the registration roller pair consisting of registration rollers 17 and 18 in the sheet conveyance direction, and detects the fed sheet. The post-registration sensor 33 is arranged downstream of the registration roller pair consisting of registration rollers 17 and 18, and detects the conveyed sheet. The double feed detection sensor 30 is arranged between the pre-registration sensor 32 and the registration roller pair, and detects double feeding of sheets. The image reading device according to this embodiment may further include a registration clutch 19 and document conveying rollers 20-25.

[0017] When the post-registration sensor 33 (second detection means) detects the sheet, the control unit 900 issues an instruction to the image reading unit to read the image, and the image on the sheet being conveyed is read. The image of the sheet read by the image reading unit is transmitted to an external device such as an information processing device via an interface unit (not shown).

[0018] The basic configuration of the image reading device 200 of this embodiment will be described with reference to Figures 3 and 4. Figure 3 is a block diagram of a control unit 900 and its periphery in the image reading device 200. Figure 4 is a block diagram of an image processing unit 78 in the image reading device 200.

[0019] The image reading device 200 basically comprises a front image reading unit 14, a back image reading unit 15, an image control unit 71, a sending unit 73, an image processing unit 78, a control unit 900, a conveying unit 86, and a detection sensor unit 87. The front image reading unit 14 and the back image reading unit 15 turn on their light-emitting elements and scan one line at the timing instructed by the image control unit 71. The image control unit 71 performs A / D conversion, shading correction, and other processes on the image signals output from the front image reading unit 14 and the back image reading unit 15 in response to instructions from the control unit 900, and sends the signals to the image processing unit 78 in the subsequent stage.

[0020] The image data processed by the image processing unit 78 is transmitted to the transmission unit 73. The transmission unit 73 has a function of communicating with an external device 300 such as a host PC outside the image reading device 200, and transmits image data at the request of the external device 300. The image data transmitted to the external device 300 is stored in an image data storage unit 79 using a storage device such as a hard disk drive inside the external device 300. The external device 300 further includes an operation unit 201 and a display unit 202. In addition, transmission and reception between the external device 300 and the control unit 900 is performed via the transmission unit 73.

[0021] The control unit 900 comprehensively controls the operation of the entire image reading device 200. The transport unit 86 is made up of a plurality of drive units and transmission units, etc., shown in Fig. 1, and is driven and controlled by instructions from the control unit 900. The detection sensor unit 87 is made up of sensors that detect sheets, such as the double feed detection sensor 30, pre-registration sensor 32, and post-registration sensor 33, shown in Fig. 1. The control unit 900 grasps the current state and position of the sheet based on information from these sensors.

[0022] FIG. 4 is a diagram showing the details of the inside of the image processing unit 78.

[0023] The image processing unit 78 receives the image data sent from the image control unit 71, and the area selection unit 74 selects a specific area from the received image data. The area may be selected by selecting a predefined area, or by selecting an arbitrary area by the user. The specific area may be identified from the relative positional relationship based on a feature point in the image data, such as a corner of a sheet.

[0024] A density histogram is calculated in a histogram calculation unit 75 based on the result of the region selection unit 74. A density peak is calculated from the calculated density histogram in a peak calculation unit 76. A density correction value generation unit 77 generates a correction value from the calculated density peak so that the density peak of the image acquired by the image reading unit has the same density value.

[0025] Details of the control of image processing unit 78 of this embodiment will be described with reference to the control flow in Fig. 5 and Figs. 6 to 8. Fig. 5 is a flowchart of the density adjustment process in the front and back image reading units, Fig. 6 is an example of a read image, Fig. 7 is a density histogram of each of the read images read by the front and back image reading units, and Fig. 8 shows the density input / output characteristics of the image reading unit in this embodiment.

[0026] In this embodiment, the input value and the output value have a linear relationship, and this relationship is called a density linearity characteristic. In this embodiment, the density histogram is adjusted using the density values ​​obtained by converting the acquired image to gray. Note that similar processing may be performed on each RGB color component of a color image without performing gray conversion.

[0027] The user sets the document A on the sheet stacking tray 1 and feeds it into the image reading device 200 so that the first side (the front side in this embodiment) of the document A faces the front side image reading unit 14 of the image reading device 200 (S101). After the sheet stacking detection sensor 12 detects that the document A has been set and the document A is fed (S101), reading of the document A begins. The front side image reading unit 14 reads the front side of the document A to obtain a first read image (S102), and the document A is discharged from the image reading device 200 (S103).

[0028] The ejected document A is set again on the sheet stacking tray 1 by the user so that the front side of document A faces the backside image reading unit 15 of the image reading device 200, and is fed to the image reading device 200 (S104). In other words, the user sets document A upside down from when it was set in step S101. At this time, the user may use the display unit 202 or the like to notify the user to set document A so that the front side faces the backside image reading unit 15. After the sheet stacking detection sensor 12 detects that document A has been set again and document A is fed (S104), reading of document A begins.

[0029] The back side image reading unit 15 reads the front side of the document A to obtain a second read image (S105), and the document A is then ejected from the image reading device 200 (S106). In this way, by reading the same side of the same document with the image reading unit, the same image can be obtained in the front side image reading unit 14 and the back side image reading unit 15, and the respective images can be compared.

[0030] From the first read image and the second read image read by the image reading unit, the control unit 900 uses the area selection unit 74 in the image processing unit 78 to select arbitrary areas and create density histograms A' and B' (S107). Density histogram A' represents the histogram of the first read image, and density histogram B' represents the histogram of the second read image. The area may be the entire image (entire area), or an arbitrary area (selected area) as shown by the dotted line in FIG. 6. As described above, the area is identified from the relative position based on feature points contained in the image, such as the corners of the document or specific patterns or designs contained in the document.

[0031] In addition, since it is possible that the document is set so that the leading edge and trailing edge are facing in opposite directions in steps S101 and S104, the area may be specified including a rotation process. Also, although not illustrated in the present embodiment, it is possible that the user does not set the document A upside down, so it is possible to determine whether the first read image and the second read image are read from the same side of the same document, and if it is determined that they are not the same side, it is possible to not execute the subsequent processes and to issue an instruction to the user to restart from step S101 again. For these reasons, it is preferable to use a document whose image characteristics differ between the front and back sides.

[0032] In this embodiment, a density histogram is created from an image in which the region indicated by the dotted line in Fig. 6 is selected. From the selected region, density histograms A' and B', which indicate the number of pixels for each density value, as shown in Fig. 7, are created using a histogram calculation unit 75. From the created histograms, the density value (peak) with the largest number of pixels is calculated using a peak calculation unit 76 (S108).

[0033] The peaks (P and P' shown in FIG. 7) of the first and second read images obtained from the calculation results are compared to check whether there is a difference in the peaks (S109). If there is a difference in the peaks (Yes in S109), it is determined that there is a difference in the density values ​​of the first and second read images. Therefore, using the density correction value generation unit 77, a back-side density correction value is generated (S110) that is configured by offset adjustment or gain adjustment so that peak P' of the density linearity characteristic of the second read image matches peak P of the density linearity characteristic of the first read image, as shown in FIG. 8. If there is no substantial difference in the peaks (No in S109), it is determined that there is no difference in the density values ​​of the first and second read images, and no back-side density correction value is generated.

[0034] In this embodiment, the method for generating the back surface density correction value is described as offset adjustment or gain adjustment, but the back surface density correction value does not have to be only one of the above and may include both. Also, although it was described that the back surface density correction value is not generated if the result of step S109 is No, this is equivalent to setting the back surface density correction value to a default value that does not apply correction to the back surface image.

[0035] By performing these processes, when the original document is read, there is no difference in density between the first read image and the second read image, as shown in Figure 12, and images of the same density can be output from the image reading units on the front and back.

[0036] <Second embodiment> In the first embodiment described above, the density value with the largest number of pixels is calculated in the processing flow to generate a correction value, but in this embodiment, two density values ​​with the largest number of pixels are calculated and correction processing is performed.

[0037] The control flow will be explained using Figures 9 and 10 to 13. Figure 9 is a flowchart of the density adjustment process in the front and back image reading units, Figures 10 to 12 show density histograms of the images read by the front and back image reading units in the second embodiment, and Figure 13 shows input / output density characteristics.

[0038] The processing performed in steps S201 to S207 in the control flow of Fig. 9 is the same as the processing performed in steps S101 to S107 in the control flow of Fig. 5, and therefore a description thereof will be omitted. Also, a description of the same reference numerals as those in the first embodiment will be omitted.

[0039] From an image in which an arbitrary region such as that indicated by the dotted line in FIG. 6 is selected, density histograms A' and B', which indicate the number of pixels for each density value, as shown in FIG. 10, are created using the histogram calculation unit 75. To calculate peaks in regions of different density from the created histogram, two arbitrary regions, a first density range (X region) and a second density range (Y region), are set (S208). The peak calculation unit 76 calculates the density value with the largest number of pixels in the X region (peaks P and P') and the density value with the largest number of pixels in the Y region (peaks Q and Q') (S209). The density peaks P and P', and Q and Q' obtained in the X region and Y region are compared from the calculated results, and the comparison results are stored (S210).

[0040] From the stored results, a correction value is first generated by offset adjustment or gain adjustment so that the peaks of density histogram A' and density histogram B' in region X have the same density value (S211). In this embodiment, the correction value is generated so that peak Q' of density histogram B' has the same density value as peak Q of density histogram A', as shown in FIG.

[0041] Using the density values ​​Q and Q' that coincide with each other in step S211 as a reference, a correction value is generated by offset adjustment or gain adjustment so that the peaks of density histogram A' and density histogram B' in the Y region have the same density value (S212). In this embodiment, the correction value is generated so that peak P' of density histogram B' has the same density value as peak P of density histogram A', as shown in FIG.

[0042] By performing these processes, it is possible to generate correction values ​​that make the density histograms the same for the front and back image reading units, and the density linearity characteristics of the first read image and the second read image as shown in Fig. 13 also become the same for the front and back image reading units. As a result, when the document is read, there is no difference in the density values ​​of the first read image and the second read image, and it becomes possible to output images with the same density for the front and back image reading units.

[0043] In the first and second embodiments described above, the front side of document A is read by the front and back image reading units, and processing is performed based on the histogram of the first read image. However, the reverse may also be done, where the back side of document A is read by the front and back image reading units, and processing is performed based on the histogram of the second read image.

[0044] In the first and second embodiments described above, the histogram of the read image read by the back image reading unit was matched to the histogram of the read image read by the front image reading unit, but the opposite process may also be performed, that is, the histogram of the read image read by the front image reading unit may be matched to the histogram of the read image read by the back image reading unit.

[0045] Furthermore, in the above first and second embodiments, an example of the density correction value for the back side of the document A is shown, but, for example, it is also possible to obtain a plurality of density correction values ​​(here, combinations of offset correction values ​​and gain correction values) that make peak P and peak P' the same density value and peak Q and peak Q' the same, obtain a correlation coefficient between the density histogram of the back side density image corrected with each combination of density correction values ​​and the density histogram of the front side, and use the combination of density correction values ​​with the highest correlation as the final density correction value.

[0046] In the first and second embodiments, the image processing unit and the image data storage unit 79 are provided outside the image reading device, but they may be provided inside the image reading device.

[0047] Furthermore, if the difference in the peak density values ​​between the first and second scanned images calculated in the first and second embodiments is large, the control unit 900 may determine that the scanned image is in an abnormal state, and may notify the user of this fact via the display unit 202 or a notifying unit (not shown). The difference in density values ​​at this time may be a predetermined value set in advance, or may be set by the user. [Explanation of symbols]

[0048] 1 seat loading platform 4 Pickup roller 5 Pickup roller up / down motor 12 Sheet stacking detection sensor 14 Surface image reading unit 15 Back side image reading unit 30 Double feed detection sensor 71 Image control unit 73 Transmission Department 74 Area selection section 75 Histogram calculation section 76 Peak calculation section 77 Density correction value generation unit 78 Image Processing Unit 79 Image data storage unit 86 Conveyor 87 Detection sensor part 200 Image reader 201 Operation section 202 Display section 300 External device 900 control section

Claims

1. a conveying unit that conveys the document to a conveying path; a front image reading unit that reads the front surface of the document conveyed by the conveying unit; a back image reading unit that is disposed on the opposite side of the transport path from the front image reading unit and that reads the back side of the document; an area selection unit that identifies a specific area that is the same area in a first read image obtained by reading a first side of the document with the front image reading unit and a second read image obtained by reading the first side of the document with the back image reading unit; a peak calculation unit that calculates a density peak in the specific region of the first read image and the second read image; and a density correction value generation unit that generates a correction value using the density peak to correct the density peaks of the first read image and the second read image so that they have the same value.

2. 2. The image reading apparatus according to claim 1, further comprising a histogram calculation unit that calculates density histograms in the specific regions of the first read image and the second read image, respectively, and calculates peaks from the density histograms.

3. 2. The image processing device according to claim 1, wherein the density correction value generation unit corrects the density of the first read image and the second read image based on a density value having a large number of pixels in a first density range and a density value having a large number of pixels in a second density range so that an output value for an input value to the front image reading unit or the back image reading unit becomes the same value.

4. 2. The image reading device according to claim 1, wherein the density correction value generating unit generates a correction value for either the entire area or a selected area of ​​the first read image and the second read image selected by the area selecting unit.

5. The image reading device according to claim 1, characterized in that, when the difference in density value between the density peak of the first read image and the density peak of the second read image is greater than a predetermined value, the density correction value generation unit does not generate the correction value and notifies the user that the density difference is large.

Images