Reader

Abstract

To provide a reading device capable of preferably detecting an edge of a manuscript.SOLUTION: A back surface reading deice 42 is provided immovably while facing a manuscript passing plate 41 below the manuscript passing plate 41. Above the manuscript passing plate 41, a white film 49 adhered to a lower surface of a pressing member 46 is provided while facing the manuscript passing plate 41. By reading out the white film 49 by the back surface reading deice 42, a pixel value output from the back surface reading deice 42 is created. When a back surface of a manuscript is read out by the back surface reading deice 42, a pixel value output from the back surface reading deice 42 is subjected to gray scale conversion by a first gradation conversion function and a second gradation conversion function in accordance with a histogram, and an edge of the manuscript is detected by a region separation by using the pixel value after the gray scale conversion.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005]

[0001] The present invention relates to a reading device.

Background Art

[0002] Conventionally, a reading device that includes an ADF (Auto Document Feeder) and reads the front and back surfaces of a document while transporting the document by the ADF using a front surface reading device and a back surface reading device, respectively, is known (see, for example, Patent Document 1). In addition, some reading devices can read images of documents placed on a contact glass in a FB (Flat Bed) method in addition to reading in the ADF method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When reading a document in the ADF method in a reading device that employs both methods, the document is transported along a transport path, and during the transport, the back surface of the document contacts the contact glass for back surface reading, and the front surface of the document contacts the contact glass for front surface reading. Since the front surface reading device needs to reciprocate in the same direction as the movement direction of the document on the contact glass below the contact glass for front surface reading, it is provided slightly spaced apart from the contact glass. On the other hand, the back surface reading device is provided in close contact with the contact glass for back surface reading.

[0005] Due to this structure, factors such as the use of high-brightness LEDs (Light Emitting Diodes) as light sources for the front and back scanning devices may cause the scanned image to become brighter than expected. In such cases, the edges of the scanned image of the document may become blurred, potentially leading to a failure in edge detection.

[0006] The objective of the present invention is to provide a reading device that can accurately detect the edges of scanned images from a document. [Means for solving the problem]

[0007] To achieve the above objective, the reading device according to the present invention comprises a transparent plate, a reading device positioned opposite the transparent plate from one side, emitting light from a light source toward the transparent plate, receiving reflected light from a reading target located on the other side of the transparent plate, and outputting a pixel value corresponding to the amount of light received, a white area positioned opposite the transparent plate from the other side, a storage unit, and a control unit. The storage unit stores a grayscale conversion function for converting the pixel values ​​output from the reading device into grayscale values. The control unit causes the reading device to read the white area, creates a histogram of pixel values ​​corresponding to the grayscale of each pixel using the pixel values ​​output from the reading device as a result of this reading, causes the reading device to read the original document located between the transparent plate and the white area, inputs the pixel values ​​output from the reading device as a result of this reading into a grayscale conversion function corresponding to the histogram, obtains the pixel values ​​after grayscale conversion by the grayscale conversion function, performs region separation using the pixel values ​​after grayscale conversion, and detects the edges of the original document.

[0008] In this configuration, a reading device is provided on one side of the transparent plate, facing the transparent plate, and a white area is provided on the other side of the transparent plate, facing the transparent plate. The reading device reads the white area, and a histogram of the pixel values ​​output from the reading device (horizontal axis: pixel value, vertical axis: frequency) is created. When the original document is read by the reading device, the pixel values ​​output from the reading device are converted in grayscale using a grayscale conversion function corresponding to the histogram, and the edges of the original document are detected by region separation using the converted pixel values. In the grayscale conversion using the grayscale conversion function corresponding to the histogram, for example, the pixel values ​​of the white area are converted to lower values, so that pixel values ​​that clearly show the edges of the scanned image of the original document can be obtained. As a result, the edges of the scanned image of the original document can be detected well from the converted pixel values. [Effects of the Invention]

[0009] According to the present invention, the edges of the scanned image of the document can be detected well. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view illustrating the configuration of a reading device according to one embodiment of the present invention. [Figure 2] This is a block diagram showing the electrical configuration of a reading device. [Figure 3] This diagram shows the flow of image data processing in a reading device. [Figure 4] This figure shows the first grayscale conversion function used for grayscale conversion. [Figure 5] This figure shows the second-tone conversion function used for grayscale conversion. [Figure 6] This figure shows an example of a histogram of pixel values ​​obtained by reading a white film. [Figure 7] This is a flowchart showing the flow of the function determination process. [Figure 8] This figure shows an example of an image of the edges of a document, demonstrating a state where the edges are sharp. [Figure 9]A diagram showing an example of an image of the edge of a document, indicating a state where the edge is unclear. [Figure 10] A diagram showing an example of an image of the edge of a document, indicating a state where the edge is clear. [Figure 11] A diagram showing an example of an image of the edge of a document, indicating a state where the edge is unclear.

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0012] <Configuration of the Reading Device> The reading device 1 shown in FIG. 1 is a device for reading a document, and includes a housing 2 and a document cover 3. The reading device 1 is configured to be able to read a document by both the FB (Flat Bed) method and the ADF (Auto Document Feeder) method. An ADF 4 is provided on the document cover 3 of the reading device 1.

[0013] For the following description, the front, rear, left, and right of the reading device 1 are defined based on the state of the reading device 1 as viewed from its front side. Also, the up and down directions are defined in the state where the reading device 1 is installed on a horizontal plane. FIG. 1 shows a cross-section of the reading device 1 cut along a cutting plane line extending in the left-right direction.

[0014] The housing 2 has a substantially rectangular parallelepiped shape. As shown in FIG. 2, a first opening 12 and a second opening 13 are provided on the top plate 11 of the housing 2.

[0015] The first opening 12 has edges extending in the front-rear direction and the left-right direction, and is formed in a rectangular shape that is longer in the left-right direction than in the front-rear direction. A document placement plate 14 is provided so as to close the first opening 12 from below. The document placement plate 14 is formed in a flat plate shape using a transparent material.

[0016] The second opening 13 has an edge extending in the front-back direction and the left-right direction on the left side of the first opening 12, and is formed in a rectangular shape that extends细长ly in the front-back direction. A document passing plate 15 is provided so as to close the second opening 13 from below. The document passing plate 15 is formed in a flat plate shape using a transparent material.

[0017] As shown in FIG. 1, inside the housing 2, a surface reading device 21 (an example of a second reading device) is provided below the document placement plate 14 and the document passing plate 15 (an example of a second transparent plate) and is movable in the sub-scanning direction which is the left-right direction. In order to be movable in the sub-scanning direction, the surface reading device 21 is arranged with a gap between it and the lower surfaces of the document placement plate 14 and the document passing plate 15. The surface reading device 21 is in the form of a CIS (Contact Image Sensor) unit and includes a light source 22, a light guide 23, a rod lens array 24, and an image sensor 25 inside the housing.

[0018] The light source 22 includes three-color LEDs (Light Emitting Diodes) of red, green, and blue. The lighting of the light source 22 is controlled by pulse width modulation.

[0019] The light guide 23 is a member that propagates the light of the light source 22 and is made of a transparent material. The light guide 23 is arranged in front of the light source 22 and extends in the main scanning direction which is the front-back direction orthogonal to the sub-scanning direction.

[0020] The rod lens array 24 is arranged with its position shifted in the left-right direction from the light guide 23, for example, on the left side of the light guide 23. The rod lens array 24 includes a number of rod lenses (an example of a lens) arranged in alignment in the main scanning direction. The rod lens is a refractive index distribution type lens with a magnification of unity.

[0021] The image sensor 25 comprises a predetermined number (for example, 12) sensor IC chips. The sensor IC chips are arranged in a single row in the main scanning direction. Each sensor IC chip comprises a row of light-receiving elements. The row of light-receiving elements is composed of multiple light-receiving elements arranged in a single row at equal pitch in the main scanning direction. Each light-receiving element comprises, for example, R (red), G (green), and B (blue) color filters and a photodiode, and outputs an electrical signal corresponding to the intensity of each RGB color component contained in the incident light.

[0022] Light from the light source 22 is irradiated onto the object to be read on the document placement plate 14 or document passage plate 15 through the light guide 23, and the reflected light from the object to be read passes through the rod lens array 24 and enters the image sensor 25. One rod lens, for example, forms a 1:1 image on the light-receiving surfaces of multiple light-receiving elements. Photoelectric conversion is performed at each light-receiving element, and an electrical signal is output from each light-receiving element, thereby enabling the surface reading device 21 to read one line in the main scanning direction.

[0023] A pressing member 26 is provided above the document passage plate 15. The pressing member 26 has a pressing surface on its lower surface that is parallel to the document passage plate 15, and a guide surface that is inclined or curved so that it moves further away from the document passage plate 15 as it moves to the left from the pressing surface. The pressing member 26 is elastically biased toward the document passage plate 15 by an elastic member 27. In addition, a white film 28 (an example of a second white part) is attached to the lower surface of the pressing member 26.

[0024] The document cover 3 is designed to open and close. When the document cover 3 is in the closed position, it covers the entire top surface of the housing 2. The document cover 3 is displaced to the open position by lifting the front side from the closed position. When the document cover 3 is in the open position, the entire top surface of the housing 2 is exposed.

[0025] The ADF4 includes a supply tray 31 and an output tray 32. The supply tray 31 and the output tray 32 are arranged to overlap with a gap between them vertically. A transport path 33 is formed inside the ADF4. One end of the transport path 33 is open over the left end of the supply tray 31, extends to the left, curves in a U-shape and folds back to the right, passes between the document passage plate 15 and the presser member 26, and the other end is open to the right between the supply tray 31 and the output tray 32. Inside the ADF4, along the transport path 33, a supply roller 34, a separation roller 35, a transport roller 36, a reversing roller 37, and an output roller 38 are provided in this order from the supply tray 31 side.

[0026] Between the transport roller 36 and the reversing roller 37, a document passage plate 41 (an example of a first transparent plate) is provided on the lower side of the transport path 33. The document passage plate 41 is formed in a flat shape using a transparent material, and its upper surface extends along the transport path 33.

[0027] Below the document feed plate 41, a back-side reading device 42 (an example of a first reading device) is provided. The back-side reading device 42 has the same configuration as the front-side reading device 21, and includes a light source 43, a light guide 44, a rod lens array 45, and an image sensor 46 within its housing. The back-side reading device 42 is fixedly positioned, and the upper surface of the housing of the back-side reading device 42 is in contact with the lower surface of the document feed plate 41. The specific configurations of the light source 43, light guide 44, rod lens array 45, and image sensor 46 are the same as those of the light source 22, light guide 23, rod lens array 24, and image sensor 25 of the front-side reading device 21, respectively, so their explanation is omitted.

[0028] Light from the light source 43 is irradiated onto the object to be read on the document pass-through plate 41 through the light guide 44, and the reflected light from the object to be read passes through the rod lens array 45 and enters the image sensor 46. Photoelectric conversion is performed at each light-receiving element, and an electrical signal is output from each light-receiving element. This electrical signal is converted into a pixel value, thereby enabling the back-side reading device 42 to read one line in the main scanning direction.

[0029] A pressing member 47 is provided above the document passage plate 41. The pressing member 47 has a pressing surface on its lower surface that is parallel to the document passage plate 41, and a guide surface that is inclined or curved so that it moves further away from the document passage plate 41 as it moves to the right from the pressing surface. The pressing member 47 is elastically biased toward the document passage plate 41 by an elastic member 48. In addition, a white film 49 (an example of the first white part) is attached to the lower surface of the pressing member 47.

[0030] When scanning a document using the FB method, the document cover 3 is opened to the open position, and the document is placed on the upper surface of the document tray 14. At this time, the document is positioned so that its left edge contacts the left edge of the first opening 12 from the right side, and its rear edge contacts the rear edge of the first opening 12 from the front side. Then, the document cover 3 is closed to the closed position, and the document is covered from above by the document cover 3. Then, in response to the command to execute a scan, the surface reading device 21 moves to a position corresponding to the starting reading position at the beginning of the reading range, and as it moves in the sub-scanning direction from that position, the surface reading device 21 reads the document on the document tray 14 line by line in the sub-scanning direction, thereby achieving document scanning.

[0031] On the other hand, when scanning a document using the ADF method, the document is placed on the supply tray 31 of the ADF 4. The front-side reading device 21 is stopped in a position where it faces the document passage plate 15 from below. Then, in response to the command to execute a scan, the document is transported by the supply rollers 34. The document is separated one by one by the separation rollers 35 and transported along the transport path 33 by the transport rollers 36 and the reversing rollers 37. As the document passes between the document passage plate 15 and the holding member 26, the front-side reading device 21 reads the back side of the document line by line, thereby achieving the reading of the front side of the document. As the document passes between the document passage plate 41 and the holding member 47, the back-side reading device 42 reads the back side of the document line by line, thereby achieving the reading of the back side of the document.

[0032] Furthermore, as shown in Figure 2, the reader 1 includes a CPU (Central Processing Unit) 51, a non-volatile memory 52 (an example of a storage unit) such as flash memory or E2PROM that can be rewritten, and a volatile memory 53 such as SDRAM. The CPU 51, non-volatile memory 52, and volatile memory 53 are connected to a bus 54 for data communication.

[0033] The CPU 51 (an example of a control unit) controls various parts of the reading device 1, such as the ADF 4 and the moving mechanism 55 that moves the surface reading device 21 in the sub-scanning direction, by executing programs for various processes. The non-volatile memory 52 stores programs executed by the CPU 51 and various data. The volatile memory 53 is used as a work area when the CPU 51 executes programs.

[0034] The moving mechanism 55 includes a carriage that carries the surface reading device 21, a stepping motor that can rotate in both forward and reverse directions, a drive pulley that is rotationally driven by the stepping motor, a driven pulley that is paired with the drive pulley, and a belt that is wrapped around the drive pulley and the driven pulley. The drive pulley and the driven pulley are spaced apart from each other in the left-right direction, and their respective axes of rotation extend in the front-rear direction. The middle portion of the belt is fixed to the carriage. As the drive pulley rotates, the belt moves, and as the belt moves, the carriage carrying the surface reading device 21 moves in a sub-scanning direction that coincides with the left-right direction.

[0035] The reader 1 is also equipped with an operation panel 56. The operation panel 56 includes an operation section for various settings and a display section for displaying information. The operation section and the display section may be provided separately, or they may be in the form of a touch panel where the operation section, such as a pressure-sensitive or capacitive transparent film switch, is superimposed on a display section such as a liquid crystal display.

[0036] <Image data processing> The CPU 51 is incorporated into, for example, an ASIC (Application Specific Integrated Circuit), which, as shown in Figure 3, substantially comprises a scan circuit 61, a skew correction circuit 62, an image processing circuit 63, a JPEG encoder 64, a scan device circuit 65, and an edge detection image processing circuit 66. Each of the circuits, the scan circuit 61, the skew correction circuit 62, the image processing circuit 63, the JPEG encoder 64, the scan device circuit 65, and the edge detection image processing circuit 66, may be implemented entirely or partially by hardware such as logic circuits, or the parts not implemented in hardware may be implemented in software through program processing, or all of them may be implemented in software through program processing. The program processing is executed by the CPU 51.

[0037] For example, when a command to read both sides of a document is input to the reading device 1, the CPU 51 controls the front-side reading device 21, the back-side reading device 42, and the moving mechanism 55, etc., to perform processing for reading both the front and back sides of the document. The instruction to read the document is input from the control panel, for example, by the user operating the control panel 56.

[0038] The electrical signals output from the front-side reading device 21 and the back-side reading device 42 (hereinafter collectively referred to as "reading devices 21 and 42") are input to the scan circuit 61. The scan circuit 61 includes an A / D conversion circuit 71, a black correction circuit 72, and a shading correction circuit 73.

[0039] The A / D conversion circuit 71 has, for example, an 8-bit (0-255) resolution, and for each RGB color, the electrical signals output from each reading device 21, 42 are converted into digital pixel values ​​(pixel data). For example, electrical signals below the lower limit reference voltage (lower limit) are uniformly converted to "0", electrical signals exceeding the upper limit reference voltage (upper limit) are uniformly converted to "255", and electrical signals within the range from the lower limit to the upper limit are converted into pixel values ​​according to the magnitude of their voltage.

[0040] In the black correction circuit 72, black correction is performed on the pixel values ​​after A / D conversion by the A / D conversion circuit 71 to remove noise from each pixel.

[0041] In the shading correction circuit 73, shading correction is performed on the pixel values ​​after black correction to reduce density unevenness between pixels due to the characteristics of the optical system. The CPU 51 stores the pixel values ​​after shading correction in the volatile memory 53 (see Figure 2).

[0042] In this embodiment, an example of the "reading device" of the present invention is configured by the reading devices 21 and 42 and the scanning circuit 61.

[0043] Subsequently, the CPU 51 reads the pixel values ​​after shading correction from the volatile memory 53 and inputs these read pixel values ​​to the skew correction circuit 62. If the document is transported along the transport path 33 (see Figure 1) at an angle relative to the transport direction, the scanned image consisting of the pixel values ​​after shading correction will be tilted with respect to the directions (coordinate axes) corresponding to the main scanning direction and sub-scanning direction. The skew correction circuit 62 performs skew correction processing to correct the tilt of the scanned image. The tilt of the scanned image is detected, for example, by detecting the leading edge of the scanned image and determining the tilt angle of that leading edge with respect to the main scanning direction. The detection of the leading edge will be described later. The CPU 51 stores the pixel values ​​after the skew correction processing in the volatile memory 53.

[0044] Subsequently, the CPU 51 reads the pixel values ​​after the skew correction process from the volatile memory 53 and inputs the read pixel values ​​to the image processing circuit 63. In the image processing circuit 63, the pixel values ​​after the skew correction process are converted into Y component (luminance), Cb component (chrominance), and Cr component (chrominance) values ​​according to a predetermined conversion formula. The CPU 51 stores the Y, Cb, and Cr component values ​​in the volatile memory 53.

[0045] Subsequently, the CPU 51 reads the values ​​of the Y, Cb, and Cr components from the volatile memory 53 and inputs these values ​​to the JPEG encoder 64. The JPEG encoder 64 creates JPEG (Joint Photographic Experts Group) compressed data from the values ​​of the Y, Cb, and Cr components. The CPU 51 then saves the JPEG compressed data to the volatile memory 53.

[0046] Meanwhile, the CPU 51 inputs the pixel values ​​after shading correction, which are generated from the electrical signals output by the back-side reading device 42, to the scan device circuit 65. The scan device circuit 65 includes a main scan filter circuit 81, a main scan reduction circuit 82, and a grayscale conversion circuit 83.

[0047] In the main scanning filter circuit 81, each pixel value is sequentially treated as a target pixel value from one end to the other in the main scanning direction, and processing is performed using a 3x3 or 5x5 smoothing filter (moving average filter) centered on that target pixel value.

[0048] The main scan reduction circuit 82 performs a decimation process to reduce the read image by simply decimating pixels at regular intervals. Alternatively, the main scan reduction circuit 82 may also perform an area averaging process to reduce the read image by replacing the pixel values ​​within a predetermined range (for example, 2x2, 3x3) with their average value.

[0049] In the grayscale conversion circuit 83, grayscale conversion (grayscale conversion) using a grayscale conversion function converts the pixel values ​​after the main scan reduction process for each RGB color into pixel values ​​that change the grayscale of the read image consisting of those pixel values. The CPU 51 stores the output pixel values ​​output from the grayscale conversion circuit 83, that is, the pixel values ​​of each RGB color after grayscale conversion, in the volatile memory 53.

[0050] The non-volatile memory 52 stores, for example, two types of tone conversion functions: a first tone conversion function and a second tone conversion function.

[0051] The first tone conversion function takes the form of a piecewise linear tone curve, as shown in Figure 4. In grayscale conversion using the first tone conversion function, when the input pixel value input to the tone conversion circuit 83 is in the first range, which is less than or equal to a predetermined value A, the output pixel value is 0 regardless of the input pixel value. When the input pixel value is in the second range, which has a predetermined value A as the lower limit and a predetermined value B greater than A as the upper limit, the output pixel value increases linearly with a first slope as the input pixel value increases. When the input pixel value is in the third range, which has a predetermined value C greater than B as the lower limit and a maximum value (255) as the upper limit, the output pixel value increases linearly with a second slope greater than the first slope as the input pixel value increases. When the input pixel value is in the fourth range between the second and third ranges, that is, the range between predetermined value B and predetermined value C, the output pixel value is a constant value regardless of the input pixel value.

[0052] As shown in Figure 5, the second tone conversion function has a different form from the first tone conversion function, being a piecewise linear tone curve. In grayscale conversion using the second tone conversion function, when the input pixel value is within the range of a predetermined value A or less, the output pixel value becomes 0 regardless of the input pixel value. Furthermore, in the range where the input pixel value is greater than the predetermined value A, the output pixel value increases linearly with a constant slope as the input pixel value increases.

[0053] In creating the first grayscale conversion function, the CPU 51 causes the back-side reading device 42 to read the white film 49 (see Figure 1) in monochrome reading mode. The white film 49 is read in monochrome, and 256 grayscale pixel values ​​are obtained. Subsequently, the CPU 51 creates a histogram of the pixel values ​​obtained by reading the white film 49 (horizontal axis: pixel value, vertical axis: frequency). Then, from the histogram, the CPU 51 identifies the range BC (the range between a predetermined value B and a predetermined value C) of pixel values ​​whose frequency is greater than or equal to a predetermined value. The first tone conversion function is created by modifying the correspondence between input and output pixel values ​​in the range between predetermined values ​​B and C in the second tone conversion function so that the output pixel value remains constant regardless of the input pixel value, and then modifying the correspondence between input and output pixel values ​​in a third range with predetermined value C as the lower limit so that the output pixel value increases linearly with increasing input pixel value from the output pixel value corresponding to the modified predetermined value C up to the upper limit of the output pixel value.

[0054] The CPU 51 stores the pixel values ​​of each RGB color after grayscale conversion in the volatile memory 53, and then, at an appropriate timing, reads the pixel values ​​of each RGB color after grayscale conversion from the volatile memory 53 and inputs the read pixel values ​​to the edge detection image processing circuit 66. The edge detection image processing circuit 66 includes a YIQ conversion circuit 84, a region separation circuit 85, a main scan size setting circuit 86, a leading edge detection circuit 87, and a trailing edge detection circuit 88.

[0055] In the YIQ conversion circuit 84, the pixel values ​​of each RGB color after grayscale conversion are converted to the Y component (luminance), I component (chrominance), and Q component (chrominance) values ​​according to a predetermined conversion formula.

[0056] The Y component value is input to the region separation circuit 85 as the density value of a grayscale digital image. In the region separation circuit 85, the Y component value is binarized. That is, a predetermined threshold is used, and Y component values ​​below the threshold are uniformly converted to "0", while Y component values ​​above the threshold are uniformly converted to "255". Then, in the region separation circuit 85, for example, an edge detection method using a Sobel filter is used to detect (extract) the image edges represented by the binarized values.

[0057] In the main scan size setting circuit 86, the size of the document in the main scan direction is set based on the edges detected by the region separation circuit 85. The CPU 51 stores the size of the document in the main scan direction in the volatile memory 53.

[0058] The document leading edge detection circuit 87 detects the coordinates of the two vertices of the leading edge of the document in a Cartesian coordinate system, where arbitrary straight lines extending in the main scanning direction and arbitrary straight lines extending in the sub-scanning direction are used as coordinate axes, and the intersection of these lines is the origin.

[0059] In the document trailing edge detection circuit 88, the coordinates of the two vertices at the trailing edge of the document in the same coordinate system as the document leading edge detection circuit 87 are detected from the edge detected by the region separation circuit 85.

[0060] The CPU 51 stores the coordinates of the two vertices at the leading edge of the document and the coordinates of the two vertices at the trailing edge of the document in the volatile memory 53. The tilt of the scanned image, which consists of pixel values ​​after shading correction (the tilt angle of the leading edge relative to the main scanning direction), can be determined from the coordinates of the two vertices at the leading edge of the document.

[0061] <Function determination process> In order to determine whether to use the first or second grayscale conversion function for grayscale conversion in the scan device circuit 65 (see Figure 3), the CPU 51 executes the function determination process shown in Figure 7.

[0062] In the function determination process, as described above, when the front and back sides of the original document are read by the front reading device 21 and the back reading device 42, respectively, the CPU 51 inputs the shading-corrected pixel values ​​generated from the electrical signal output by the back reading device 42, from among the shading-corrected pixel values ​​output from the shading correction circuit 73 (see Figure 3), to the scan device circuit 65. At this time, the scan device circuit 65 (grayscale conversion circuit 83) uses the second grayscale conversion function, which is a standard grayscale conversion function (S1). Then, the edge detection image processing circuit 66 detects the edges of the image on the back side of the original document read by the back reading device 42 (S2).

[0063] After the image on the back of the document has been read, the CPU 51 instructs the back-side reading device 42 to read the white film 49 (see Figure 1) in monochrome reading mode (S3). The electrical signal output from the back-side reading device 42 is input to the scan circuit 61, where A / D conversion, black correction, and shading correction are performed to obtain 256 gradation pixel values ​​for each pixel. Subsequently, the CPU 51 creates a histogram of the pixel values ​​obtained by reading the white film 49 (horizontal axis: pixel value, vertical axis: frequency), finds the mode from the histogram, and obtains that mode as the white film pixel value.

[0064] Subsequently, the CPU 51 compares the white film pixel value with a predetermined threshold. If the white film pixel value is greater than the threshold (S4:YES), the CPU 51 sets the first grayscale conversion function to be used for grayscale conversion when scanning documents in the future (S5). As a result, when the brightness of the reflected light on the white film 49 is as high as the brightness of the reflected light on the surface of the document, the pixel values ​​read from the exposed portion of the white film 49 (the portion not covered by the document) can be kept low when scanning documents in the future, and pixel values ​​that clearly show the edges of the image on the back of the document can be obtained, as shown in Figure 8. As a result, the edges of the scanned image on the back of the document can be detected well.

[0065] On the other hand, if the second tone conversion function is used for tone conversion when scanning a document in subsequent scans, even though the white film pixel value is greater than the threshold, the pixel value read from the exposed portion of the document on the white film 49 will be large, and as shown in Figure 9, the edges of the image on the back of the document may be broken, making it difficult to detect the edges properly.

[0066] If the white film pixel value is below the threshold (S4:NO), the CPU 51 sets the system to use the second tone conversion function for tone conversion when scanning documents in the future (S6). If the white film pixel value is below the threshold and the first tone conversion function is used for tone conversion when scanning documents in the future, the output pixel value (density) for the input pixel value between predetermined value B and predetermined value C (see Figure 4) will overlap with the edge density, and as shown in Figure 10, the density difference in that area will disappear, which may cause the edges of the image on the back of the document to be broken and make it difficult to detect the edges properly.

[0067] Therefore, the second grayscale conversion function is used for grayscale conversion when scanning documents in the future. As a result, the edges of the image on the back side of the document can be detected well, as shown in Figure 11.

[0068] <Effects and Effects> As described above, the front-side scanning device 21 is mounted below the document placement plate 14 and the document passage plate 15, and is movable in the sub-scanning direction, which is the left-right direction. The back-side scanning device 42 is mounted below the document passage plate 41, facing the document passage plate 41, and is immovable. Furthermore, the front-side scanning device 21 is positioned with a gap between it and the lower surface of the document passage plate 15, while the back-side scanning device 42 is positioned in contact with the document passage plate 41. In this configuration, the image scanned by the back-side scanning device 42 is brighter than the image scanned by the front-side scanning device 21, and the edges of the scanned image on the back side of the document tend to become blurred.

[0069] Above the document passage plate 41, a white film 49 attached to the lower surface of the pressing member 47 is provided facing the document passage plate 41. The back-side reading device 42 reads the white film 49, and a histogram of the pixel values ​​output from the back-side reading device 42 is created. When the back side of the document is read by the back-side reading device 42, the pixel values ​​output from the back-side reading device 42 are converted in grayscale using a grayscale conversion function (first grayscale conversion function or second grayscale conversion function) corresponding to the histogram, and the edges of the document are detected by region separation using the pixel values ​​after grayscale conversion. For example, if the brightness of the reflected light on the white film 49 is as high as the brightness of the reflected light on the surface of the document, grayscale conversion using the first grayscale conversion function is performed, and the pixel values ​​of the parts of the white film 49 not covered by the document are converted to lower values. This makes it possible to obtain pixel values ​​that clearly show the edges of the scanned image of the back side of the document. As a result, the edges of the scanned image of the back side of the document can be detected well from the pixel values ​​after grayscale conversion.

[0070] <Variation> Although embodiments of the present invention have been described above, the present invention can also be implemented in other forms.

[0071] For example, in the above-described embodiment, when both the front and back sides of a document are read, the pixel values ​​after shading correction, which are generated from the electrical signal output by the back-side reading device 42, are input to the scan device circuit 65 from the shading correction pixel values ​​output from the shading correction circuit 73.

[0072] In addition to this, when both the front and back sides of the document are read, the pixel values ​​after shading correction output from the shading correction circuit 73, which are generated from the electrical signal output by the front reading device 21, may be input to the scan device circuit 65. Also, when only the front side of the document is read, the pixel values ​​after shading correction generated from the electrical signal output by the front reading device 21 are naturally input to the scan device circuit 65.

[0073] When the shading-corrected pixel values ​​generated from the electrical signals output by the surface reading device 21 are input to the scan device circuit 65, the second grayscale conversion function is used for grayscale conversion, and the first grayscale conversion function, which is created based on the histogram of pixel values ​​obtained by reading the white film 49, is not used.

[0074] Furthermore, in the above-described embodiment, the CPU 51 causes the back-side reading device 42 to read the original document, then causes the back-side reading device 42 to read the white film 49, creates a histogram of the pixel values ​​output from the back-side reading device 42 by reading the white film 49, and when the back-side reading device 42 performs the reading of the next document, it inputs the pixel values ​​output from the back-side reading device 42 into a grayscale conversion function corresponding to the histogram, and obtains the pixel values ​​after grayscale conversion by the grayscale conversion function.

[0075] The CPU 51 may, however, have the back-side reading device 42 read a white film 49 before reading the original document, create a histogram of the pixel values ​​output from the back-side reading device 42 by reading the white film 49, and then, when the back-side reading device 42 reads the original document, input the pixel values ​​output from the back-side reading device 42 into a grayscale conversion function corresponding to the histogram to obtain the pixel values ​​after grayscale conversion by the grayscale conversion function.

[0076] Alternatively, the CPU 51 may, before the reading device 1 is shipped from the factory, have the white film 49 read by the back-side reading device 42, create a histogram of the pixel values ​​output from the back-side reading device 42 by reading the white film 49, and when the original document is read by the back-side reading device 42, input the pixel values ​​output from the back-side reading device 42 into a grayscale conversion function corresponding to the histogram to obtain the pixel values ​​after grayscale conversion by the grayscale conversion function.

[0077] Furthermore, the histogram may be created when the power to the reading device 1 is turned on, when the back-side reading device 42 is replaced, when the light source 43 or image sensor 46 provided in the back-side reading device 42 is replaced, or when the white film 49 is replaced, etc.

[0078] In the grayscale conversion using the first grayscale conversion function, when the input pixel value input to the grayscale conversion circuit 83 is within the fourth range between a predetermined value B and a predetermined value C, the output pixel value is assumed to be constant regardless of the input pixel value. However, the output pixel value may increase linearly with a slope smaller than the first slope in response to an increase in the input pixel value, or it may increase nonlinearly.

[0079] Furthermore, various design modifications can be made to the aforementioned configuration within the scope of the matters described in the patent claims. [Explanation of symbols]

[0080] 1: Reader 15,41:Manuscript passage board 21: Surface reading device 22,43:Light source 28,49: White film 42: Backside reading device 51:CPU 52: Non-volatile memory

Claims

1. A transparent plate and A reading device is positioned opposite the transparent plate from one side, emits light from a light source toward the transparent plate, receives reflected light from a reading target located on the other side of the transparent plate, and outputs a pixel value corresponding to the amount of light received. The transparent plate has a white portion positioned opposite it from the other side, Memory unit and, It comprises a control unit and, The storage unit stores at least a first grayscale conversion function as a grayscale conversion function for converting the pixel values ​​output from the reading device to grayscale. The first grayscale conversion function is designed such that, in a first range where the input pixel value is less than or equal to a predetermined value, the pixel value after grayscale conversion becomes 0; in a second range where the input pixel value is lowered by the predetermined value, the pixel value after grayscale conversion increases linearly with a first slope as the input pixel value increases; in a third range where the input pixel value is uppered by the maximum value of that pixel value, the pixel value after grayscale conversion increases linearly with a second slope as the input pixel value increases; and in a fourth range between the second and third ranges, the value increases linearly, nonlinearly, or takes a constant value as the input pixel value increases. The control unit, The reading device is made to read the white area, and a histogram of pixel values ​​corresponding to the intensity of each pixel is created using the pixel values ​​output from the reading device as a result of this reading. The mode of the histogram is compared with a predetermined threshold. If the mode is greater than the threshold, the first tone conversion function is set to be used for tone conversion. If the mode is less than or equal to the threshold, a tone conversion function other than the first tone conversion function is set to be used for tone conversion. The reading device is made to read the original document located between the transparent plate and the white area, and the pixel values ​​output from the reading device as a result of this reading are input into a grayscale conversion function set by comparing the mode and the threshold, thereby obtaining the pixel values ​​after grayscale conversion by the grayscale conversion function. A reading device that performs region separation using pixel values ​​after grayscale conversion and detects the edges of the scanned image of the original document.

2. A reading device according to claim 1, The memory unit stores a first tone conversion function and a second tone conversion function as the tone conversion function. The first grayscale conversion function is created such that, in the fourth range, it increases with a slope smaller than the first slope or takes a constant value in response to an increase in the input pixel value. The second grayscale conversion function is designed such that, when the input pixel value is less than or equal to a predetermined value, the pixel value after grayscale conversion becomes 0, and when the input pixel value is greater than the predetermined value, the pixel value after grayscale conversion increases linearly with a constant slope as the input pixel value increases. The control unit compares the mode of the histogram with a predetermined threshold and, if the mode is greater than the threshold, uses the first grayscale conversion function for grayscale conversion; if the mode is less than or equal to the threshold, uses the second grayscale conversion function for grayscale conversion.

3. A reading device according to claim 2, A reading device in which a slope smaller than the aforementioned certain slope is considered 0.

4. A reading device according to claim 2 or 3, The transparent plate includes a first transparent plate and a second transparent plate, The reading device is A light source is positioned opposite the first transparent plate from the first side and emits light toward the first transparent plate, and a first reading device receives reflected light from a reading target located on the second side opposite to the first side of the first transparent plate and outputs a pixel value corresponding to the amount of light received. The device includes a light source positioned opposite the second transparent plate from the third side and emitting light toward the second transparent plate, and a second reading device that receives reflected light from a reading target located on the fourth side opposite to the third side relative to the second transparent plate and outputs a pixel value corresponding to the amount of light received, The aforementioned white part is, The first transparent plate has a first white portion positioned opposite it from the second side, The second transparent plate includes a second white portion that is positioned opposite to it from the fourth side, The control unit, The first reading device is made to read one side of the original document located between the first transparent plate and the first white area, and the mode of the histogram is compared with a predetermined threshold. If the mode is greater than the threshold, it is decided to use the first grayscale conversion function for grayscale conversion. If the mode is less than or equal to the threshold, it is decided to use the second grayscale conversion function for grayscale conversion. The pixel values ​​output from the first reading device by reading the one side of the original document are input to the determined first grayscale conversion function or second grayscale conversion function to obtain the pixel values ​​after grayscale conversion by the first grayscale conversion function or second grayscale conversion function. A reading device that causes the second reading device to read the other side of the original document located between the second transparent plate and the second white area, inputs the pixel values ​​output from the second reading device as a result of this reading into the second grayscale conversion function, and obtains the pixel values ​​after grayscale conversion by the second grayscale conversion function.

5. A reading device according to claim 4, The first reading device is positioned in contact with the first transparent plate, The second reading device is a reading device that is positioned with a gap between it and the second transparent plate.

6. A reading device according to any one of claims 1 to 3, The transparent plate includes a first transparent plate and a second transparent plate, The reading device is A light source is positioned opposite the first transparent plate from the first side and emits light toward the first transparent plate, and a first reading device receives reflected light from a reading target located on the second side opposite to the first side of the first transparent plate and outputs a pixel value corresponding to the amount of light received. The device includes a light source positioned opposite the second transparent plate from the third side and emitting light toward the second transparent plate, and a second reading device that receives reflected light from a reading target located on the fourth side opposite to the third side relative to the second transparent plate and outputs a pixel value corresponding to the amount of light received, The aforementioned white part is, The first transparent plate has a first white portion positioned opposite it from the second side, The second transparent plate includes a second white portion that is positioned opposite to it from the fourth side, The control unit, The first reading device is made to read one side of the original document that is located between the first transparent plate and the first white portion. A reading device that causes the second reading device to read the other side of the original document that is located between the second transparent plate and the second white portion.

7. A reading device according to claim 6, The first reading device is positioned in contact with the first transparent plate, The second reading device is a reading device that is positioned with a gap between it and the second transparent plate.

8. A reading device according to any one of claims 1 to 7, The control unit is a reading device that, when causing the reading device to read the document, causes the reading device to read the white area before reading the document, and creates the histogram.

9. A reading device according to any one of claims 1 to 7, The control unit, When the aforementioned document is read by the reading device, the reading device is made to read the white area and create the histogram. A reading device that causes the reading device to read the next document, inputs the pixel values ​​output from the reading device as a result of this reading into a grayscale conversion function corresponding to the histogram created when the document was read, and obtains the pixel values ​​after grayscale conversion by the grayscale conversion function.

10. A reading device according to any one of claims 1 to 7, The control unit is a reading device that, before the reading device is shipped from the factory, causes the reading device to read the white area and creates the histogram.

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