Image reading device

Abstract

The objective is to obtain an image reading device that accurately detects shadow images within the read image and accurately detects the skewness of the document sheet, regardless of the surface brightness of the opposing member of the image sensor. [Solution] The image sensor 31 generates a read image including the image of the document sheet by optically reading an image at a predetermined reading position in the transport path of the document sheet. The sensor roller 32 is an opposing member positioned opposite the image sensor 31 at a predetermined reading position. The skew detection unit detects the skew of the document sheet based on the shadow image of the document sheet that occurs in the read image obtained by the image sensor 31. The skew detection unit then (a) derives a threshold based on the density of the image of the sensor roller 32 in the read image, and (b) detects the shadow image with the derived threshold.

Description

Technical Field

[0001] The present invention relates to an image reading device.

Background Art

[0002] When an image reading device reads a document image from a document sheet using an image sensor, it calculates the skew amount of the document sheet based on the shadow image generated by the document sheet on the opposing member facing the image sensor (see, for example, Patent Document 1). In that image reading device, the sensor gain is changed according to the reading luminance value of the opposing member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described image reading device, depending on the surface brightness of the opposing member, the shadow image in the read image may not be accurately detected. When the surface brightness of the opposing member is high, the density of the shadow image in the read image becomes low, so there is a possibility that the shadow image may not be accurately detected. Also, when the surface brightness of the opposing member is low, the density difference between the shadow image and the background portion other than the shadow image in the read image becomes small, so there is a possibility that the shadow image may not be accurately detected.

[0005] Further, when the sensor gain is changed as described above, the density of the shadow image in the read image changes; thus, it is difficult to appropriately set the threshold value for detecting the shadow image.

[0006] The present invention has been made in view of the above problems, and aims to provide an image reading device that accurately detects shadow images in the read image and accurately detects the skewness of the document sheet, regardless of the surface brightness of the opposing member of the image sensor. [Means for solving the problem]

[0007] The image reading device according to the present invention comprises a transport device that transports a document sheet along a transport path, an image sensor that generates a read image including the image of the document sheet by optically reading an image at a predetermined reading position in the transport path, a counter member positioned opposite the image sensor at the predetermined reading position, and a skew detection unit that detects the skew of the document sheet based on a shadow image of the document sheet occurring in the read image obtained by the image sensor. The skew detection unit (a) derives a threshold value based on the density of the image of the counter member in the read image, and (b) detects the shadow image using the derived threshold value. [Effects of the Invention]

[0008] According to the present invention, an image reading device is obtained that can accurately detect shadow images in the read image and accurately detect the skewness of the document sheet, regardless of the surface brightness of the opposing member of the image sensor.

[0009] The above or other objects, features, and advantages of the present invention will become even more apparent from the following detailed description in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a side view showing the internal configuration of an image reading device according to an embodiment of the present invention. [Figure 2] Figure 2 is a block diagram showing the electrical configuration of the image reading device shown in Figure 1. [Figure 3] Figure 3 illustrates the acquisition of a shadow image by the image sensor 31 in Figure 1. [Figure 4]Figure 4 shows an example of a shadow image in a read image. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the figures.

[0012] Figure 1 is a side view showing the internal configuration of an image reading device according to an embodiment of the present invention. The image reading device shown in Figure 1 is a device such as a scanner, copier, facsimile machine, or multifunction device, and is equipped with an automatic document feeder as a document transport device.

[0013] The image reading device shown in Figure 1 comprises a main unit 1, contact glasses 1a and 1b positioned on the top surface of the main unit 1, an image sensor 2, and a document cover 3. The document cover 3 includes an automatic document feeder 4.

[0014] Contact glass 1a is a transparent component on which the document is placed when image scanning is performed without using the automatic document feeder 4. Contact glass 1b is a transparent component over which the document passes when the document is automatically transported by the automatic document feeder 4 while the document image is scanned.

[0015] Image sensor 2 reads the document image from the document sheet. Specifically, when the document is automatically transported by the automatic document feeder 4 and image reading of the document image is performed, image sensor 2 is a sensor that optically reads the document image of the document as it passes through a predetermined image reading position in the document transport path. Image sensor 2 reads the document image line by line. Image sensor 2 is equipped with a light source (such as a light-emitting diode) and a light-receiving element (such as a line sensor). The light source emits light, and the light-receiving element detects the reflected light reflected from the document or other object via the contact glasses 1a and 1b, and outputs an electrical signal corresponding to the amount of reflected light. The controller 41, described later, receives this electrical signal and generates the document image (i.e., image data of the document image) based on this electrical signal.

[0016] The original document cover 3 is a member that can be placed in surface contact with and rotatably installed on the contact glass 1a. It adheres the original document to the contact glass 1a and prevents ambient light from entering the apparatus interior from the contact glasses 1a and 1b during image reading.

[0017] Also, the automatic document feeder 4 includes a paper feed tray 11 on which the document sheets are placed and a conveying device 21. The conveying device 21 feeds the document sheets one by one from the stack of document sheets on the paper feed tray 11 and conveys them along the conveyance path to the discharge tray 14. The automatic document feeder 4 controls the conveying device 21 to pass the document sheets one by one through the reading position of the image sensor 2 (the position on the contact glass 1b) and discharges them to the discharge tray 14.

[0018] Specifically, the conveying device 21 includes a paper feed unit 12 and conveying rollers 13 along the conveyance path. The paper feed unit 12 feeds the document sheet (the topmost document sheet in the stack of document sheets) and conveys it by the conveying rollers 13. The paper feed unit 12 includes a paper feed roller 12a, a driving roller 12b, a driven roller 12c, a conveying belt 12d, and an auxiliary roller 12e. The paper feed roller 12a feeds the document sheets on the paper feed tray 11 one by one along the conveying belt 12d into the conveyance path.

[0019] Also, the image sensor 2 can change the image reading position by a driving device (not shown). When performing image reading using the automatic document feeder 4, the image reading position of the image sensor 2 is set as the passing position of the document on the contact glass 1b. The image sensor 2 optically reads the image of the document conveyed by the automatic document feeder 4 when passing over the contact glass 1b. Here, the image sensor 2 is a color image sensor and reads the document images of a plurality of colors such as RGB at different image reading positions in the conveyance direction. In this embodiment, a CIS (Contact Image Sensor) is used as the image sensor 2. When performing image reading using the automatic document feeder 4, the image sensor 2 is disposed directly below the contact glass 1b.

[0020] The paper feed roller 12a, the drive roller 12b, and the conveyance roller 13 are driven by a drive device (not shown) such as a motor.

[0021] The discharge tray 14 is located below the paper feed tray 11 and is a tray on which the original document sheets discharged from the discharge port 15 at the end of the conveyance path are stacked. The discharge port 15 discharges the original document sheets to the discharge tray 14 at the end of the conveyance path.

[0022] Furthermore, the image reading device shown in FIG. 1 includes a lift device 22, an image sensor 31, and a sensor roller 32.

[0023] The lift device 22 raises and lowers the paper feed tray 11 by an existing lifting method. Specifically, the lift device 22 includes an electrically operating drive power source (such as a motor, an actuator, etc.), and mechanically raises and lowers the paper feed tray 11 with the driving force generated by the drive power source.

[0024] Also, the image sensor 31 generates a read image including an image of the original document sheet by optically reading an image at a predetermined reading position in the conveyance path for a predetermined period (including the period during which the original document sheet passes). The image sensor 31 is the same as the image sensor 2 and is, for example, a CIS. Here, an image of one of the two sides of the original document sheet is read by the image sensor 31, and an image of the other side is read by the image sensor 2.

[0025] The sensor roller 32 is an opposing member provided opposite to the image sensor 31 at a predetermined position (image reading position) in the conveyance path, and conveys the original document sheet while bringing it into contact with the image sensor 31.

[0026] Also, in this embodiment, the sensor roller 32 is a conveyance roller whose surface is white, and is used as a white reference member for obtaining a white reference value for shading correction by the image sensor 31.

[0027] Figure 2 is a block diagram showing the electrical configuration of the image reading device shown in Figure 1. As shown in Figure 2, the image reading device further includes a controller 41. The controller 41 includes a processor that executes a program, an ASIC (Application Specific Integrated Circuit), etc., and controls the image sensors 2, 31 and the automatic document feeder 4 (transport device 21, lift device 22, etc.) to perform image reading of the document sheet and acquire image data of the image on the document sheet (document image).

[0028] Furthermore, this controller 41 operates as a shading correction unit 41a, a skew detection unit 41b, and a correction processing unit 41b.

[0029] The shading correction unit 41a reads the surface image of the sensor roller 32 using the image sensor 31 when there is no original sheet, sets a white reference value based on the image data (density) of the read image obtained therefrom, stores it in a non-volatile memory (not shown), and uses this white reference value to perform shading correction on the read image (image of the original sheet).

[0030] The skew detection unit 41b detects skew of the document sheet based on the shadow image of the document sheet that occurs in the read image obtained by the image sensor 31.

[0031] Figure 3 illustrates the acquisition of a shadow image by the image sensor 31 in Figure 1. Figure 4 shows an example of a shadow image in a scanned image. For example, as shown in Figure 3, the image sensor 31 includes a first light source 51 and a second light source 52 arranged along the transport path, and further includes an image sensor element 53 as a light-receiving element. The second light source 52 is positioned upstream of the first light source 51 in the transport path. A shadow image 102 is formed in front of the document sheet 101 due to the thickness of the document sheet 101. Therefore, for example, as shown in Figure 4, if the document sheet 101 is tilted at an angle of obliqueness A, the image 201 and shadow image 202 of the document sheet 101 appear tilted at the angle of obliqueness A in the scanned image 200.

[0032] The oblique detection unit 41b (a) derives a threshold based on the density of the image 203 (image of the area where no shadow image is generated) of the sensor roller 32 (opposing member) in the read image 200, and (b) detects the shadow image 202 with the derived threshold. Here, image 203 is, for example, the image at a predetermined height at the beginning of the read image 200, as shown in Figure 4.

[0033] For example, the oblique detection unit 41b generates a binarized image by binarizing the read image 200 using a derived threshold, and then searches along the sub-scanning direction from the leading edge of the binarized image to detect the first band-shaped image as a shadow image.

[0034] In Embodiment 1, the skew detection unit 41b uses a specific test sheet as the original document to derive the threshold value described above in advance, and then detects skew by detecting a shadow image at that threshold value on the user's original document (i.e., the original document to be scanned). Specifically, the specific test sheet is a thin sheet (for example, a blank sheet with a basis weight of about 35 to 50 grams) that is less likely to generate a shadow image 102 (i.e., the height of the shadow image is small), and the skew detection unit 41b derives the threshold value described above based on the density of the image 203 of the sensor roller 32 (opposing member) in the read image 200 for that specific test sheet and the density of the shadow image 202 of the specific test sheet in the read image.

[0035] For example, if the lowest density value in the density range of image 203 is Dmin, and the highest density value in the density range of shadow image 202 is Dmax, then the average of Dmax and Dmin is given as the threshold Th, as shown in the following equation.

[0036] Th = (Dmax + Dmin) / 2

[0037] For example, in the case of 8-bit RGB data, the density range is 0 to 255. When the density range (density distribution) of the image 203 on the surface of the sensor roller 32 is 220 to 230, and the density range of the shadow image 202 is 210 to 214, the minimum density value Dmin of image 203 is 220, the maximum density value Dmax of shadow image 202 is 214, and the threshold Th mentioned above is set to an average value of 217.

[0038] On the other hand, if the brightness of the surface of the sensor roller 32 is high (i.e., the reflectance of light from the image sensor 31 is high), for example, if the density range (density distribution) of image 203 is 234 to 244 and the density range of shadow image 202 is 218 to 222, then the minimum density value Dmin of image 203 will be 234, the maximum density value Dmax of shadow image 202 will be 222, and the threshold Th mentioned above will be an average value of 228.

[0039] In this way, the threshold is set higher the higher the surface brightness of the sensor roller 32. Therefore, even if the density of the shadow image decreases due to the high brightness of the sensor roller 32 surface (i.e., even if the RGB values ​​of the shadow image increase), the threshold (RGB values) is set high, and the shadow image is accurately detected.

[0040] Furthermore, the skew detection unit 41b determines the skew angle A of the original sheet 101 based on the read image 200 described above. Specifically, as shown in Figure 4 for example, the angle between the direction in which the shadow image 202 extends in the read image 200 (the direction of the long edge of the shadow image 202) and the main scanning direction is determined as the skew angle A.

[0041] Then, the correction processing unit 41c corrects the image 201 of the original sheet in the scanned image 200 by rotating it by an angle A in the opposite direction to the skew direction, and outputs the corrected image 201.

[0042] Next, the operation of the image reading device described above will be explained.

[0043] The oblique detection unit 41b derives the threshold value described above based on the density of the image 203 of the sensor roller 32 (opposing member) in the read image, as described above.

[0044] Subsequently, when the user's original sheet 101 is placed in the paper feed tray 11 and a predetermined user operation is detected, the controller 41 starts the image reading operation (scan job) of the original sheet. Once the image reading operation starts, the controller 41 uses the transport device 21 to transport the original sheets 101 on the paper feed tray 11 one by one along the transport path to the output tray 14, and performs image reading with the image sensor 31 or the like.

[0045] In this process, the skew detection unit 41b acquires a read image 200 from the image sensor 31, detects a shadow image 202 in the read image using the threshold described above, and determines whether or not there is skew or derives the skew angle A based on the shadow image 202.

[0046] Then, if the skew detection unit 41b determines that the original sheet 101 is skewed, the correction processing unit 41c rotates the original image (image 201 of the original sheet 101) in the scanned image 200 based on the derived skew angle A.

[0047] As described above, according to Embodiment 1, the image sensor 31 generates a read image 200 including an image 201 of the document sheet by optically reading an image at a predetermined reading position in the transport path of the document sheet. The sensor roller 32 is an opposing member positioned opposite the image sensor 31 at its predetermined reading position. The skew detection unit 41b detects the skew of the document sheet based on the shadow image 202 of the document sheet that occurs in the read image 200 obtained by the image sensor 31. The skew detection unit 41b then (a) derives a threshold based on the density of the image 203 of the sensor roller 32 in the read image 200, and (b) detects the shadow image 202 with the derived threshold.

[0048] As a result, regardless of the surface brightness of the opposing member of the image sensor 31 (in this case, the sensor roller 32), shadow images in the scanned image are accurately detected, and the skewness of the document sheet is accurately detected.

[0049] Embodiment 2.

[0050] In Embodiment 2, the oblique detection unit 41b adjusts the threshold value based on the difference between the brightness of the image read from the adjustment chart of known predetermined brightness (i.e., brightness under the illumination light conditions of the image sensor 2) and the predetermined brightness.

[0051] Specifically, the skew detection unit 41b acquires a reading image of the adjustment chart from the image sensor 31, identifies the brightness of the reading image (the adjustment chart portion), derives the difference between the identified brightness and a known predetermined brightness, and adjusts the threshold by increasing or decreasing it by a correction amount corresponding to that difference. If the reading image is RGB data, the reading image is L * a * b * The data is converted, and the brightness (L) of the read image is determined. * ) is derived.

[0052] For example, if the above-mentioned difference (brightness difference) is 2.0 or greater, the correction amount is set to +2; if the above-mentioned difference (brightness difference) is 1.0 or greater and less than 2.0, the correction amount is set to +1; if the above-mentioned difference (brightness difference) is 0.0 or greater and less than 1.0, the correction amount is set to 0; if the above-mentioned difference (brightness difference) is -1.0 or greater and less than 0.0, the correction amount is set to -1; if the above-mentioned difference (brightness difference) is -2.0 or greater and less than -1.0, the correction amount is set to -2; and if the above-mentioned difference (brightness difference) is -3.0 or greater and less than -2.0, the correction amount is set to -3.

[0053] For example, in Embodiment 1, when the threshold Th is set to an average value of 217, and the brightness difference for the adjustment chart is -1.9 and the correction amount is -2, the threshold Th is adjusted to 215.

[0054] The other configurations and operations of the image reading device according to Embodiment 2 are the same as those of Embodiment 1, so their description will be omitted.

[0055] Embodiment 3.

[0056] In Embodiment 3, the shading correction unit 41a (a) derives a correction coefficient based on the color of the read image and the predetermined color for an adjustment chart of known predetermined colors (i.e., the color under the illumination light conditions of the image sensor 2), and (b) corrects the image of the original sheet by multiplying the image of the original sheet after shading correction by the correction coefficient.

[0057] Therefore, the shading correction unit 41a corrects the read image (image of the original sheet) according to the following formula.

[0058] Corrected image data (pixel value) = (Uncorrected image data (pixel value) - Black reference value for each pixel) / (White reference value for each pixel - Black reference value for each pixel) × Correction coefficient

[0059] Here, the shading correction unit 41a uses the ratio of the G value in the RGB values ​​of the color in the adjustment chart to the G value in the RGB values ​​of the image read from the adjustment chart as the correction coefficient.

[0060] For example, the color of the adjustment chart is L * a * b * If the values ​​are (94.0, 0.4, -1.5), the corresponding RGB values ​​are (237, 237, 240). In this case, if the RGB values ​​of the image read from the adjustment chart are (232, 231, 233), the correction factor is 1.03 (= 237 / 231).

[0061] In the third embodiment, the skew detection unit 41b adjusts the threshold by multiplying the threshold by the correction coefficient.

[0062] For example, in Embodiment 1, if the threshold Th is set to an average value of 217, and the correction coefficient is 1.03, the threshold Th will be adjusted to 224.

[0063] The other configurations and operations of the image reading device according to Embodiment 3 are the same as those of Embodiments 1 or 2, so their description will be omitted.

[0064] Various changes and modifications to the embodiments described above will be obvious to those skilled in the art. Such changes and modifications may be made without deviating from the spirit and scope of the subject matter and without diminishing the intended advantages. In other words, such changes and modifications are intended to be included in the claims.

[0065] For example, in embodiments 1 to 3 described above, skew detection is performed by the image sensor 31, but skew detection may also be performed by the image sensor 2. In that case, the opposing member of the image sensor 2 may be a press plate that holds down the document sheet. [Industrial applicability]

[0066] The present invention can be applied, for example, to an image reading device. [Explanation of Symbols]

[0067] 21 Conveying device 31 Image Sensor 32. Sensor roller (an example of an opposing member) 41a Shading Correction Section 41b Oblique detection unit 41c Correction Processing Unit

Claims

1. A transport device that transports the original document sheet along a transport path, An image sensor generates a read image including the image of the original sheet by optically reading an image of a predetermined reading position in the transport path, A counter member positioned opposite the image sensor at the predetermined reading position, The system includes a skew detection unit that detects the skew of the document sheet based on the shadow image of the document sheet that occurs in the read image obtained by the image sensor, The oblique detection unit (a) derives a threshold based on the density of the image of the opposing member in the read image, and (b) detects the shadow image using the derived threshold. An image reading device characterized by the following.

2. The image reading device according to claim 1, characterized in that the skew detection unit derives the threshold based on the density of the image of the opposing member in the read image for a specific test sheet and the density of the shadow image of the specific document sheet in the read image.

3. The image reading device according to claim 1, characterized in that the skew detection unit adjusts the threshold based on the difference between the brightness of the read image on the adjustment chart of predetermined brightness and the predetermined brightness.

4. The system further includes a shading correction unit that performs shading correction on the image of the aforementioned manuscript sheet. The shading correction unit (a) derives a correction coefficient based on the color of the read image and the predetermined color for an adjustment chart of predetermined colors, and (b) corrects the image of the original sheet by multiplying the image of the original sheet after shading correction by the correction coefficient. The oblique detection unit adjusts the threshold by multiplying the threshold by the correction coefficient.

5. Further equipped with a correction processing unit, The skew detection unit determines the skew angle of the document sheet based on the read image, The correction processing unit corrects the image of the document sheet by rotating the image of the document sheet in the read image by the angle of skew in the opposite direction to the skew direction. The image reading device according to claim 1, characterized by the following:

Images