Image reading device and image forming device

Abstract

To solve the problem in which: when an ADF is attached to an image reading device and shipped, the position of the ADF with respect to the image reading device may be changed due to vibration during transport after shipping, which results in a reduction in the accuracy of determining the amount of inclination of a document.SOLUTION: An edge detection unit 206 sets a gain to a first value when a luminance value when a reading unit 109A reads a guide plate 116 is larger than a predetermined value, and sets the gain to a second value smaller than the first value when the luminance value when the reading unit 109A reads the guide plate 116 is smaller than the predetermined value. As a result of this, a reduction in the accuracy of detecting a shadow of a leading end of a document can be prevented.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a technique for correcting image data representing an image read by an image reading device. [Background technology]

[0002] An image reading device reads an image on a document by irradiating the document with light and detecting the reflected light with a reading unit. Some image reading devices read an original document conveyed by an automatic document feeder (ADF) with a reading unit.

[0003] In such an image reading device, variations in the nip pressure and rotation speed of the rollers that transport the document can cause the document to skew and the document position to vary in a direction perpendicular to the transport direction (hereinafter referred to as the main scanning direction).Patent Document 1 describes a configuration that detects the shadow of the leading edge of the document in the transport direction from image data that represents the reading result, and performs rotation correction on the image data based on the tilt angle of the detected shadow of the leading edge of the document with respect to the main scanning direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-118911 A Summary of the Invention [Problem to be solved by the invention]

[0005] The ADF has a guide plate at a reading position where the transported document is read, which serves as a background when the reading device reads the document. The ADF is attached to the image reading device so that the distance between the guide plate and the image reading device is a predetermined distance. However, if the ADF is shipped in a state where it is attached to the image reading device, the position of the ADF relative to the image reading device may change due to vibrations during shipping and transportation. As a result, the distance between the guide plate and the image reading device deviates from the predetermined distance, and the accuracy of detecting the shadow of the leading edge of the document decreases. As a result, the accuracy of determining the amount of inclination of the document decreases.

[0006] In view of the above-mentioned problems, an object of the present invention is to suppress a decrease in accuracy in determining the amount of skew of a document. [Means for solving the problem]

[0007] In order to solve the above problem, an image reading device according to the present invention has a loading section on which documents are loaded, a feeding section which feeds the documents loaded on the loading section, a transport section which transports the documents fed by the feeding section to a reading position, a light source which emits light, a reading section which reads an image of the document by receiving reflected light from the document passing the reading position, an opposing member which is provided on the opposite side of the light source with respect to a transport path along which the document is transported and which faces the document passing the reading position, a detection means which detects a shadow cast on the opposing member by the light emitted from the light source and the document being transported based on image data including an image of the document read by the reading section, a determination means which determines an amount of inclination corresponding to an angle of inclination of a side of a leading end of the document in a transport direction in which the document is transported with respect to a predetermined direction perpendicular to the transport direction based on the shadow detected by the detection means, and a correction means which corrects the image data so that the amount of inclination is reduced, By Reading the opposing member The brightness value in the main scanning direction perpendicular to the conveying direction of the document is compared with a threshold value, and if the brightness value is greater than the threshold value, the gain is reduced by a predetermined value. This adjustment operation is repeated until the brightness value becomes equal to or less than the threshold value. It is characterized by: Effect of the Invention

[0008] According to the present invention, it is possible to suppress a decrease in accuracy in determining the amount of inclination of a document. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a control configuration diagram of the image reading device according to the first embodiment. [Diagram 3] 5 is an explanatory diagram of acquisition timing of image data stored in an image memory. FIG. [Figure 4] 5A to 5C are explanatory diagrams of processing in an edge detection unit according to the first embodiment. [Diagram 5] 13 is a diagram showing an image obtained by reading an original document by the reading unit in a state in which the original document feeder is attached in a position displaced from a predetermined position relative to the reading unit; FIG. [Figure 6] FIG. 2 is an explanatory diagram of manuscript information according to the first embodiment. [Figure 7] 5A to 5C are explanatory diagrams of a registration correction process according to the first embodiment. [Figure 8] 5 is a flowchart of a document reading process according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Preferred embodiments of the present invention will be described below with reference to the drawings. However, the shapes of the components and their relative positions described in the embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and the scope of the present invention is not intended to be limited to the following embodiments.

[0011] [First embodiment] [Image forming device] 1 is a cross-sectional view showing the configuration of a monochrome electrophotographic copying machine (hereinafter referred to as an image forming apparatus) 100 used in this embodiment. Note that the image forming apparatus is not limited to a copying machine, and may be, for example, a facsimile machine, a printing machine, a printer, etc. Furthermore, the recording method is not limited to an electrophotographic method, and may be, for example, an inkjet method, etc. Furthermore, the type of the image forming apparatus may be either a monochrome type or a color type.

[0012] The configuration and functions of the image forming apparatus 100 will be described below with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 100 has an image reading device 200 including an original feeding device 201 and a reading device 202, and an image printing device 301. The original feeding device 201 is rotatable with respect to the reading device 202.

[0013] <Image reader> Pickup roller 103 as a feeding section feeds originals 101 loaded on tray 102 as a loading section into the inside of original feeding device 201. Separation rollers 104 and 105 are provided to prevent pickup roller 103 from feeding multiple originals 101 at the same time. Originals 101 fed to the transport path are transported toward reading position A by transport roller 106 and lead roller 107. Separation rollers 104, 105, transport roller 106, and lead roller 107 are included in the transport section.

[0014] A transparent glass 108 is disposed at the reading position A, and a reading unit 109A is provided on the opposite side of the glass 108 to the transport path. The reading unit 109A has an LED 110, an image sensor 111, and an optical component group 112. The image sensor 111 has a plurality of pixels that receive R (red), G (green), and B (blue) light in the main scanning direction.

[0015] The reading unit 109A reads an image of the front surface (first surface) of the original 101 as follows. Specifically, the LED 110 as a light source irradiates (emits) light onto the front surface of the original 101 through the glass 108. The optical component group 112 guides the reflected light from the original 101 received through the glass 108 to the image sensor 111. The image sensor 111 outputs analog image data based on the received reflected light. The image sensor 111 simultaneously reads one line of image across the main scanning direction. Therefore, by reading one line of image multiple times by the image sensor 111 while conveying the original 101, the image sensor 111 can output image data including the entire original 101. An A / D conversion unit (not shown) of the reading unit 109A converts the analog image data into digital image data and outputs it to the controller 200 (FIG. 2).

[0016] A detection sensor 113 for detecting the original 101 is provided upstream of the reading position A in the transport direction of the original 101. The controller 200 determines the timing for the reading unit 109A of the original 101 to start reading based on the timing at which the detection sensor 113 detects the original 101.

[0017] Presser rollers 114 and 115 press the original 101 toward the glass 108. A white guide plate 116 is disposed as an opposing member at a position directly opposite the reading unit 109A between the presser rollers 114 and 115, that is, on the opposite side of the reading unit 109A with respect to the transport path along which the original is transported.

[0018] Original 101 that has passed reading position A is transported by transport rollers 117 toward reading position B. Transparent glass 118 is disposed at reading position B, and reading unit 109B is provided on the opposite side of glass 118 to the transport path. Reading unit 109B has a similar configuration to reading unit 109A, and reads an image on the back side (second surface) of original 101. The timing at which reading unit 109B starts reading is also determined based on the timing at which detection sensor 113 detects the original. A white guide plate 119 is disposed in a position directly opposite reading unit 109B.

[0019] The document 101 that has passed the reading position B is discharged onto a discharge tray 121 by a discharge roller 120 .

[0020] On the right side of the glass 108, a white reference plate 122 is provided as a reference reading member for acquiring shading data.

[0021] <Image printing device> Inside the image printing device 301, sheet storage trays 302 and 304 are provided. Different types of recording media can be stored in the sheet storage trays 302 and 304. For example, A4 size plain paper is stored in the sheet storage tray 302, and A4 size thick paper is stored in the sheet storage tray 304. Note that the recording media refers to media on which an image is formed by the image forming device, and examples of the recording media include paper, resin sheets, cloth, overhead projector sheets, labels, etc.

[0022] The recording medium stored in the sheet storage tray 302 is fed by a pickup roller 303 and sent to a registration roller 308 by a conveying roller 306. The recording medium stored in the sheet storage tray 304 is fed by a pickup roller 305 and sent to a registration roller 308 by conveying rollers 307 and 306.

[0023] Image data output from the image reading device 200 is input to an optical scanning device 311 including a semiconductor laser and a polygon mirror. In addition, the outer peripheral surface of the photosensitive drum 309 is charged by a charger 310. After the outer peripheral surface of the photosensitive drum 309 is charged, a laser beam corresponding to an image signal input from the document reading device 200 to the optical scanning device 311 is irradiated onto the outer peripheral surface of the photosensitive drum 309 from the optical scanning device 311 via the polygon mirror and mirrors 312 and 313. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 309.

[0024] The electrostatic latent image is then developed by toner in a developing device 314 serving as an image forming section, and a toner image is formed on the outer peripheral surface of the photosensitive drum 309. The toner image formed on the photosensitive drum 309 is transferred to a recording medium by a transfer charger 315 provided at a position (transfer position) facing the photosensitive drum 309. Registration rollers 308 feed the recording medium to the transfer position in accordance with the transfer timing at which the image is transferred to the recording medium by the transfer charger 315.

[0025] As described above, the recording medium onto which the toner image has been transferred is sent to the fixing device 318 by the conveyor belt 317, and is heated and pressurized by the fixing device 318, so that the toner image is fixed onto the recording medium. In this manner, an image is formed on the recording medium by the image forming apparatus 100.

[0026] When an image is formed in a single-sided printing mode, the recording medium that has passed through the fixing device 318 is discharged to a discharge tray (not shown) by discharge rollers 319 and 324. When an image is formed in a double-sided printing mode, the recording medium is conveyed to a reversing path 325 by discharge rollers 319, conveying rollers 320, and reversing rollers 321 after a fixing process is performed on the first side of the recording medium by the fixing device 318. The recording medium is then conveyed again to the registration rollers 308 by conveying rollers 322 and 323, and an image is formed on the second side of the recording medium by the method described above. The recording medium is then discharged to a discharge tray (not shown) by discharge rollers 319 and 324.

[0027] Furthermore, when the recording medium with an image formed on its first side is discharged face-down to the outside of image forming apparatus 100, the recording medium that has passed through fixing device 318 is conveyed through discharge rollers 319 toward conveying rollers 320. Thereafter, just before the rear end of the recording medium passes through the nip portion of conveying rollers 320, the rotation of conveying rollers 320 is reversed, and the recording medium is discharged to the outside of image forming apparatus 100 via discharge rollers 324 with the first side of the recording medium facing downward.

[0028] The configuration and functions of image forming apparatus 100 have been described above.

[0029] <Control configuration> 2 is a block diagram showing an example of a control configuration of the image forming apparatus 100. First, the control configuration of the image printing apparatus 301 will be described.

[0030] 2, the system controller 151 includes a CPU 151a, a ROM 151b, and a RAM 151c. The system controller 151 is also connected to an analog-to-digital (A / D) converter 153, a high voltage control unit 155, a motor control device 600, sensors 159, and an AC driver 160. The system controller 151 is capable of transmitting and receiving data and commands to and from each of the units connected thereto.

[0031] The CPU 151a reads out and executes various programs stored in the ROM 151b to execute various sequences related to a predetermined image formation sequence.

[0032] The RAM 151c is a storage device and stores various data such as set values ​​for the high voltage control unit 155, command values ​​for the motor control device 600, and the like.

[0033] System controller 151 receives signals from sensors 159, and sets the set value of high voltage control unit 155 based on the received signals.

[0034] A high voltage control unit 155 supplies a necessary voltage to a high voltage unit 156 (charger 310, developer 314, transfer charger 315, etc.) in accordance with a set value set by the system controller 151.

[0035] The motor control device 600 controls the motor 509 that drives a load provided in the image printing device 301 in response to a command output from the CPU 151a.

[0036] The A / D converter 153 receives a detection signal detected by a thermistor 154 for detecting the temperature of the fixing heater 161, converts the detection signal from an analog signal to a digital signal, and transmits the digital signal to the system controller 151. The system controller 151 controls the AC driver 160 based on the digital signal received from the A / D converter 153. The AC driver 160 controls the fixing heater 161 so that the temperature of the fixing heater 161 becomes a temperature required for performing the fixing process. The fixing heater 161 is a heater used in the fixing process, and is included in the fixing unit 318.

[0037] As described above, the system controller 151 controls the operation sequence of the image forming apparatus 100 .

[0038] Next, a description will be given of the control configuration of the image reading device 200. The CPU 203 controls the image reading device 100 by executing a program stored in the non-volatile memory 209.

[0039] The transport motor 201 is a drive source for each roller provided in the document feeder 201 , and is rotationally driven under the control of the controller 200 .

[0040] The operation unit 202 provides a user interface. The CPU 203 controls the operation unit 202 so as to display an operation screen for the user to set the type of recording medium to be used (hereinafter referred to as paper type) on a display unit provided in the operation unit 202. The CPU 203 receives information set by the user from the operation unit 202 and outputs the information set by the user to the system controller 151.

[0041] The system controller 151 transmits information indicating the status of the image forming apparatus to the operation unit 202. The information indicating the status of the image forming apparatus is, for example, information regarding the number of images formed, the progress of the image forming operation, and information regarding sheet jams and multiple feeds in the image printing device 301 and the document feeding device 201. The operation unit 202 displays the information received from the system controller 151 on the display unit.

[0042] The reading units 109A and 109B output digital image data to the controller 200. The image data has a higher numerical value as the intensity of the reflected light increases. This numerical level is hereinafter referred to as a brightness level. In addition, the image data output by the reading unit 109A is hereinafter referred to as the front image data, and the image data output by the reading unit 109B is hereinafter referred to as the back image data.

[0043] The front side image data output by the reading unit 109A is input to the shading circuit 204A, and the back side image data output by the reading unit 109B is input to the shading circuit 204B. The shading circuits 204A and 204B perform addition / subtraction and multiplication / division on the image data to correct the effects of non-uniformity in the amount of light from the LED 110 and uneven sensitivity for each pixel of the image sensor 111 (shading correction), and generate image data that is uniform in the main scanning direction.

[0044] The front side image data after the shading correction by the shading circuit 204A is stored in the image memory 205. On the other hand, the back side image data after the shading correction by the shading circuit 204B is input to the image inversion circuit 210.

[0045] The image inversion circuit 210 inverts the main scanning direction of the back side image data. This is because in this embodiment, the reading units 109A and 109B have the same configuration, and the main scanning direction of the image read by the reading unit 109B is inverted with respect to the image read by the reading unit 109A. The back side image data processed by the image inversion circuit 210 is stored in the image memory 205. That is, the image scale 205 functions as a first storage unit.

[0046] FIG. 3 is an explanatory diagram of the timing of acquiring the front image data and the back image data stored in the image memory 205. After the conveyance of the document 101 is started at time t0, the detection sensor 113 detects the leading edge of the document 101 at time t1. The CPU 203 determines the time t2 before the document 101 reaches the reading position A based on the time t1, for example, based on the conveying speed at which the document 101 is conveyed. Then, the CPU 203 stores the front image data output by the reading unit 109A in the image memory 205 for a predetermined period from the time t2. Note that the predetermined period is at least the period until the rear end of the document 101 leaves the reading position A. This predetermined period is obtained based on the conveying speed of the document 101. Similarly, the CPU 203 determines the time t3 before the document 101 reaches the reading position B based on the time t1. Then, the CPU 203 stores the back image data output by the reading unit 109B in the image memory 205 for a predetermined period from the time t3. CPU 203 may start reading by reading unit 109A at time t2 and store the front side image data in image memory 205, or may store the front side image data of reading unit 109A that has been reading since before time t2 in image memory 205. CPU 203 may start reading by reading unit 109B at time t3 and store the back side image data of reading unit 109B that has been reading since before time t3 in image memory 205. In the following description, the image indicated by the front side image data will also be referred to as the front side image, and the image indicated by the back side image data will also be referred to as the back side image.

[0047] 2, the front image data output from the shading circuit 204A is also input to the edge detection unit 206. In addition, the back image data output from the image inversion circuit 210 is also input to the edge detection unit 206. In the following, correction of the front image data will be described, but the back image data is corrected in the same manner.

[0048] FIG. 4 is an explanatory diagram of the process by the edge detection unit 206. FIG. 4 shows an image in which a row of pixels in the main scanning direction obtained by the reading unit 109A at every predetermined time from time t2 is combined in the sub-scanning direction perpendicular to the main scanning direction. As described above, the surface image data input to the edge detection unit 206 is from time t2 before the leading edge of the document 101 in the transport direction reaches the reading position A. That is, when the reading unit 109A starts reading an image, the guide plate 116 is read first. Thereafter, the image of the document 101 is read as the document 101 is transported. That is, the surface image data input to the edge detection unit 206 includes image data indicating the guide plate 116 and image data indicating the leading edge side of the document 101.

[0049] The edge detection unit 206 performs binarization processing on the surface image data, with a region of 9 pixels in total, 3 pixels in the main scanning direction and 3 pixels in the sub-scanning direction, as one block. In the following, the number of pixels in the main scanning direction of the reading units 109A and 109B is assumed to be 7488, and the reading units 109A and 109B perform reading 12000 times during the predetermined period. The pixel position in the main scanning direction is represented as n (0≦n≦7487), and the pixel position in the sub-scanning direction is represented as m (0≦m≦11999). The luminance values ​​of the 9 pixels in one block are represented as px (x=0 to 8), and the maximum and minimum values ​​are represented as pmax and pmin.

[0050] At a location where all nine pixels are the guide plate 116 (white) as at point A in FIG. 4A, all nine pixels are white pixels, so the difference between pmax and pmin is small. On the other hand, at a boundary between the guide plate 116 (white) and the shadow (gray) of the leading edge of the document 101 as at point B in FIG. 4A, white pixels and gray pixels are mixed among the nine pixels, so the difference between pmax and pmin is large. Therefore, if the difference between pmax and pmin is greater than a predetermined threshold pth, it can be determined that there is a pixel (hereinafter referred to as a candidate pixel) within the block that is a candidate for the shadow caused by the leading edge of the document 101. In this embodiment, if the difference between pmax and pmin within a block is greater than a predetermined threshold pth, the center pixel of the block (pixel at coordinates (n, m)) is determined to be a candidate pixel. The edge detection unit 206 performs this determination process for each n and m except for n=0, n=7487, m=0, and m=11999. In this embodiment, one scale mark on the x-axis and y-axis corresponds to the distance between the center positions of two adjacent pixels.

[0051] Fig. 4(A) is an image represented by 8-bit (brightness level: 0 to 255) image data, and Fig. 4(B) is an image represented by image data obtained by binarizing the image data of the image of Fig. 4(A) using a threshold value pth=14. White in Fig. 4(B) indicates pixels determined by the above process as candidates for a shadow caused by an edge on the leading edge side of the document 101. Of the multiple candidate pixels shown in Fig. 4(B), the row of candidate pixels in the main scanning direction that is located furthest to the leading edge in the sub-scanning direction (the row of pixels in the main scanning direction that are first determined to be candidate pixels in the sub-scanning direction) is determined to be a shadow caused by an edge on the leading edge side of the document 101.

[0052] FIG. 5 is a diagram showing an image obtained by reading an original document by reading unit 109A in a state in which original document feeder 201 is attached in a position displaced from a predetermined position relative to reading unit 202. As shown in FIG.

[0053] Fig. 5(a) is a diagram showing an image obtained by reading an original document with a predetermined gain by the reading unit 109A. As shown in the right diagram of Fig. 5(a), when an original document is read while floating above the glass, the difference between pmax and pmin in a block becomes smaller than a predetermined threshold value pth due to an increase in the luminance value of the shadow caused by the leading edge of the original document. In other words, the leading edge of the original document cannot be detected. As a result, the accuracy of determining the inclination of the original document with respect to the main scanning direction decreases.

[0054] Fig. 5(b) is a diagram showing an image obtained by reading an original document with a gain smaller than that of Fig. 5(a) by the reading unit 109A. As shown in the right diagram of Fig. 5(b), by lowering the gain, it is possible to lower the brightness values ​​of the guide plate 116, which had been blown out, and the shadow areas, which had been shifted to the bright side. This makes it possible to increase the dynamic range of the brightness values ​​of the guide plate 116 and the shadow areas. As a result, a difference in brightness between the front guide plate 116 and the shadow areas has occurred.

[0055] As shown in Fig. 2, the binary data output by edge detection unit 206 is input to document information determination unit 207. Fig. 6 shows an image indicated by the binary data input to document information determination unit 207. The image indicated by the binary data input to document information determination unit 207 is an image within the range indicated by the dotted line in Fig. 5, and includes document 101. The range of this dotted line is n = 0 to 7487, and m = 0 to 11999.

[0056] The document information determination unit 207 determines the document information of the front side (hereinafter, front document information) based on the inputted binary data. The document information determination unit 207 also determines the distance (width) W in the main scanning direction between the two corners on the leading edge side of the document 101. The document information determination unit 207 then outputs the front document information and the width W to the CPU 203. Here, the front document information is information including the position and angle of the document in the front image. The position of the document 101 is the position (x1, y1) of the first position of the document 101 in the front image. In this embodiment, this first position is one of the two corners on the leading edge side of the shadow generated by the document 101 (left side in FIG. 5). The angle of the document 101 is the angle of a predetermined side of the document 101 in the front image with respect to the reference direction of the front image. In this embodiment, the predetermined side is the shadow generated by the leading edge side of the document 101, and the reference direction is the main scanning direction (predetermined direction). That is, the angle of the original 101 is θ1 in Fig. 5. Note that when the shadow created by the edge on the leading edge of the original 101 inclines upstream from the position (x1, y1) in the transport direction, the angle θ1 takes a negative value, and when the shadow created by the edge on the leading edge of the original 101 inclines downstream from the position (x1, y1), the angle θ1 takes a positive value.

[0057] The CPU 203 outputs the front side document information, that is, the position (x1, y1) and the angle θ1, to the correction unit 208.

[0058] The correction unit 208 reads out the front surface image data stored in the image memory based on the position (x1, y1) and the angle θ1, and outputs the data to the system controller 151. Specifically, the correction unit 208 reads out the image data along a direction parallel to the shadow cast by the edge on the leading edge side of the position original 101, starting from the read start position (x1, y1).

[0059] As described above, the correction unit 208 reads the front side image data stored in the image memory up to the rear side of the document. That is, the correction unit 208 functions as a reading unit.

[0060] Fig. 7 is a diagram showing an image read by the correction unit 208. As shown in Fig. 7, image data is read in an amount corresponding to the width W along a direction parallel to the shadow, so that the edge on the leading edge side of the document becomes parallel to the main scanning direction. Note that the same process is performed on the back side image data.

[0061] The system controller 151 cuts out the image area to be printed from the image data output from the correction unit 208. Specifically, for example, the system controller 151 cuts out the image data based on the position (0,0) of the image data shown in FIG. 7 output from the correction unit 208 according to the size of the recording medium set by the user using the operation unit 202. More specifically, for example, when the document shown in FIG. 7 is A4 size and the size of the recording medium set by the user using the operation unit 202 is A4 size, the system controller 151 can cut out the image of the document excluding the shadow at the right end and the shadow at the rear end of the document. The system controller 151 controls the image printing device 301 to perform printing based on the cut-out image data. That is, the system controller 151 functions as an external device. Note that the external device includes not only the system controller 151 provided in the image forming device 100 but also a smartphone, a tablet, a PC, and the like.

[0062] 8 is a flowchart of an image reading process according to the present embodiment. The process of the flowchart shown in FIG.

[0063] When a request to start reading a document is made, the reading unit 109A moves to the reading position A in S701.

[0064] In S702, the guide plate 116, which is the background portion that reflects the shadow of the document, is read by the reading unit 109A with a preset digital gain, and the luminance value of the guide plate 116 is calculated.

[0065] In S703, if the maximum brightness value of the entire main scanning area of ​​the guide plate 116 is less than or equal to 245, the process proceeds to S604. If the maximum brightness value of the entire main scanning area of ​​the guide plate 116 is greater than or equal to 245, the process proceeds to S705.

[0066] In S704, the current digital gain value for edge extraction is determined to be optimal, and the flow ends.

[0067] In S705, if the number of times the maximum brightness value in the entire main scanning area of ​​the guide plate 116 has been confirmed is 15 or less, the process proceeds to S706. If the number of times the maximum brightness value has been confirmed is 15 or more, an error is displayed on the operation unit 202 and the flow ends.

[0068] In S706, the digital gain for edge extraction is reduced by 2%, and the luminance of the guide plate 116 is acquired.

[0069] As described above, in this embodiment, before reading of the document by the reading unit 109A is started, the edge detection unit 206 adjusts the gain for detecting the edge on the leading edge side of the document based on the result of reading the guide plate 116 by the reading unit 109A. Specifically, the edge detection unit 206 sets the gain to a first value when the luminance value when the reading unit 109A reads the guide plate 116 is greater than a predetermined value, and sets the gain to a second value smaller than the first value when the luminance value when the reading unit 109A reads the guide plate 116 is less than the predetermined value. As a result, it is possible to suppress a decrease in the accuracy of detecting the shadow of the leading edge of the document. In other words, it is possible to suppress a decrease in the accuracy of determining the amount of inclination of the document. [Explanation of symbols]

[0070] 102 Tray 103 Pickup roller 104, 105 Separation roller 106 Transport roller 107 Lead Roller 110 LED 111 Image Sensor 116 Guide plate 200 Controller 203 CPU 206 Edge detection unit 207 Manuscript Information Judgment Unit 208 Correction Section

Claims

1. a loading section on which documents are loaded; a feeding section for feeding the originals loaded on the loading section; a transport unit that transports the document fed by the feeding unit to a reading position; A light source that emits light; a reading unit that reads an image of the document by receiving reflected light from the document passing through the reading position; an opposing member that is provided on an opposite side of the light source with respect to a transport path along which the document is transported, and that faces the document passing through the reading position; a detection unit that detects a shadow generated on the facing member by the light emitted from the light source and the document being transported based on image data including an image of the document read by the reading unit; a determining unit that determines an amount of inclination corresponding to an angle of inclination of a leading edge side of the document relative to a predetermined direction perpendicular to the transport direction in a transport direction of the document, based on the shadow detected by the detecting unit; a correction means for correcting the image data so as to reduce the amount of tilt; having The detection means compares a luminance value in a main scanning direction perpendicular to the transport direction in which the original is transported, obtained by reading the opposing member with a threshold value, and if the luminance value is greater than the threshold value, an adjustment operation is performed to lower the gain by a predetermined value, repeatedly until the luminance value becomes equal to or less than the threshold value.

2. 2. The image reading device according to claim 1, wherein the opposing member is white.

3. The image reading device according to claim 1 or 2, an image forming unit that forms an image on a recording medium based on the image read by the image reading device; An image forming apparatus comprising:

Images