JP2011061695A - Image reading apparatus and method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus capable of improving precision of a background luminance detection value in a top end portion of a document and removing a background equivalent to an intermediate portion of the document. <P>SOLUTION: When an instruction to read images on a surface of a document is received, images within a predetermined range on the rear side of the document are read by a reading unit 106 for reading images on the rear side of the document and a background luminance on the rear side of the document read by the reading unit 106 is detected. Images on a front side of the document are read by a reading unit 114 disposed at a position different from that of the reading unit 106, and while using the detected background luminance, background luminance on the front side of the read document is detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image reading apparatus and method capable of reading images from the front and back sides of a conveyed document, and a program, and more particularly to a technique for detecting background luminance of a read document image.

  As an apparatus for digitizing office documents, there is an increasing demand for an image reading apparatus that reads a document as digital image data. In particular, in recent years, in order to pursue high productivity, an image reading apparatus capable of simultaneously reading images on the front and back sides of a document in substantially the same time as the reading time on one side of the document has become mainstream.

  Patent Document 1 describes a method of configuring an area sensor dedicated to document determination as means for providing data for optimizing image processing to an image processing unit of a document to be read. Further, in Patent Document 2, in an apparatus having a double-sided simultaneous reading function, sensors for reading an image are arranged at positions facing each other across a document in order to make the reading start timings of the front and back surfaces the same. Points are listed.

  In some image reading apparatuses having a double-sided simultaneous reading function, the image reading sensor for the front surface and the image reading sensor for the back surface are not disposed at positions facing each other, but are disposed at positions shifted from each other. The reason for this is that when two image reading sensors are simply arranged at opposing positions, the mutual interference of light emitted from the light sources on the front and back surfaces affects the read image. Patent Document 3 describes that the wavelength of light emitted by each light source is not the same on the front surface and the back surface in order to avoid the influence of mutual interference of light.

  On the other hand, many image reading apparatuses have a function of removing the background of a read original image. One reason for removing the background of the document is to clarify a significant portion of the read document image and to improve the image quality.

  As a background removal method, there is generally a method of converting pixel data having a background luminance level or less into white pixels. In addition, there is a method in which the background luminance used as a reference is compared with the input pixel level, and if there is a difference, it is brought closer to the input pixel in a certain level unit.

  FIG. 11 is a diagram illustrating the luminance level of the background output to the input pixel.

  L1 is a background luminance initial value, and L2 indicates the background luminance of the input image. P1, P2, P10, and P11 indicate the level of the first input pixel, the level of the second input pixel, the level of the tenth input pixel, and the level of the eleventh input pixel, respectively. Further, BgLevel indicates the background luminance output with respect to the input pixel level.

  When the first pixel is input, the levels P1 and L1 of the first input pixel are compared. If the level of P1 is lower, the background luminance is lowered by a certain level. When the next pixel is input, the second input pixel level P2 is compared with the current background luminance. If the level of P2 is lower, the background luminance is further lowered by a certain level. Similarly, since the input pixel level is lower than the background brightness up to P9, the background brightness decreases in order. Since the level P10 of the tenth pixel is higher than the background brightness, the background brightness increases by a certain level. Since the level P11 of the eleventh pixel is lower than the background luminance again, the background luminance is lowered again by a certain level. In this way, the input pixel level and the background brightness are constantly compared, and the background brightness can be brought close to the actual background brightness L2 by increasing or decreasing the background brightness.

  In the illustrated example, the actual background brightness has reached the tenth pixel, but the background brightness of a general document may be several tens of lines. In the background removal process, the background brightness obtained in this way is used as a reference value, and a pixel having a value near the reference value is regarded as a background color and converted into a white value to perform background removal.

JP 2005-94680 A JP 9-321947 A JP 2001-320557 A

  Conventionally, as described above, when a difference between the input pixel level and the output background luminance is detected, if the value for increasing or decreasing the output background luminance is set large, the pixel required to reach the actual background luminance from the initial value The number decreases.

  However, the background brightness is greatly shaken by pixels other than the background (significant pixels) in the image, and the background brightness after the significant pixels greatly deviates from the actual background brightness. As a result, the background remains around the significant pixels and the image quality is degraded. For this reason, when the difference between the input background brightness and the output background brightness is detected, the level width for increasing / decreasing the output background brightness is usually designed to be small. As a result, some pixels are required at the leading edge of the document until the output background brightness approaches the actual background brightness. Meanwhile, there is a problem that the base cannot be removed accurately.

  12A is a diagram illustrating an example of a document image, and FIG. 12B is a diagram illustrating a result of performing background removal processing by reading the document image of FIG. 12A with a conventional image reading apparatus. It is.

  The document image shown in FIG. 12A has a background color on the entire surface. In FIG. 12B, reference numeral 1200 represents the background luminance in each line of the document image as a darkness. 1201 is a range until the output background luminance reaches the actual background luminance, and 1202 is a range after the output background luminance reaches the actual background luminance.

  Conventionally, the background removal processing is performed with reference to a value slightly deviated from the actual background brightness until the background brightness detected from the leading edge of the document reaches the actual background brightness (1201). For this reason, when the read image data is used for a copying operation, the background removal at the leading edge of the document is not effective and the background is printed. As an example in which there is a background from the leading edge, there are a large number of various documents such as newspaper or manuscript paper colored, printed matter having a background color, and the like.

  Further, since there are many single-sided originals in office documents, the operation rate of the image sensor on the back side is not so high, and there is a problem that it is not efficiently used as an image reading apparatus.

  The present invention has been made in view of the above problems, and provides an image reading apparatus and method, and a program capable of improving the accuracy of the background luminance detection value at the leading edge of the document and removing the background equivalent to the middle portion of the document. The purpose is to do.

  In order to achieve the above object, an image reading apparatus of the present invention is an image reading apparatus capable of reading images of a first surface and a second surface of a document by a plurality of image reading means while conveying the document. When receiving an image reading instruction on one side of the document, a first image reading unit that reads an image in a predetermined range on the first side of the document, and a first image of the document read by the first image reading unit. First detection means for detecting the background luminance of the second surface, second image reading means for reading an image on the second surface of the document, which is disposed at a position different from the first image reading means, and the first And a second detection unit for detecting the background luminance of the second surface of the document read by the second image reading unit using the background luminance detected by the first detection unit.

  According to the present invention, when reading an image on one side of a document, the background luminance of the surface opposite to the surface to be read is used as an initial value, thereby improving the accuracy of detecting the background luminance at the leading end of the surface to be read.

1 is a diagram illustrating a schematic configuration of an image reading apparatus according to an embodiment of the present invention. It is a figure which shows schematic structure of the periphery of the reading unit 106 in FIG. It is a figure which shows schematic structure of the periphery of the reading unit 114 in FIG. 2A is a diagram showing a detailed configuration of a CIS device that constitutes the reading unit 106, and FIG. 2B is a diagram showing a detailed configuration of a CCD device that constitutes the reading unit 114. FIG. 3 is a block diagram illustrating a functional configuration of an image processing unit in the image reading apparatus. FIG. (A) is a diagram showing the situation when the document reaches the reading start position of the reading unit 106, and (b) is a diagram showing the situation when the document reaches the reading start position of the reading unit 114. (A) is a figure which shows the time-dependent change of the light quantity of the light source at the time of double-sided reading of a document, (b) is a figure which shows the time-dependent change of the light quantity of the light source at the time of single-sided reading of a document. 6 is a flowchart illustrating an example of an image reading process executed by the image reading apparatus. It is a flowchart which shows the back surface background removal process performed with an image reading apparatus. It is a flowchart which shows the surface background removal process performed with an image reading apparatus. It is a figure which shows the luminance level of the background output with respect to an input pixel in a background removal process. (A) is a diagram showing an example of a document image, and (b) is a diagram showing a result of performing background removal processing by reading the document image with a conventional image reading apparatus.

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

  FIG. 1 is a diagram showing a schematic configuration of an image reading apparatus according to an embodiment of the present invention. In the figure, only the main part related to the present invention is shown, and the other components are omitted.

  In FIG. 1, reference numeral 100 denotes an image reading apparatus such as a scanner having a double-sided simultaneous reading function, and includes the following units. Reference numeral 101 denotes an ADF (Auto Document Feeder) document placement unit that transports the documents 102 placed on the apparatus one by one. Reference numeral 103 denotes a conveyance path of the document 102 in the image reading apparatus 100.

  Reference numeral 104 denotes a feed roller, which is rotationally driven by a motor (not shown), and feeds the originals 102 placed on the original placement unit 101 to the conveyance path 103 one by one. Reference numeral 105 denotes a sensor that detects the leading and trailing ends of the document 102 fed on the conveyance path 103 and outputs a detection signal to a control unit described later.

  A reading unit 106 reads an image on the back surface (example of the first surface) of the document 102 when the upward side of the document 102 placed on the document placement unit 101 is the front surface (example of the second surface). (First image reading means). Since the reading unit 106 is disposed inside the ADF where there is no sufficient space around the reading unit 106, the reading unit 106 includes a contact image sensor (CIS) that does not require a long optical path length.

  Reference numeral 107 denotes a light source that supplies light necessary for image reading by the reading unit 106. When the reading unit 106 is configured by CIS, it is configured by a light emitting diode (LED) or the like. Reference numeral 108 denotes a white plate on which an image is read by the reading unit 106 in order to create a reference value for shading correction.

  Reference numerals 109, 110, 111, and 112 are transport rollers that are driven to rotate synchronously by a motor (not shown) and transport the document 102 along the transport path 103. Reference numeral 113 denotes a glass plate on which the document 102 is placed when image reading by ADF is not performed.

  Reference numeral 114 denotes a reading unit (second image reading unit) that is arranged at a position different from the reading unit 106 and reads an image on the front side of the original that is different from the back side of the original read by the reading unit 106. Since the reading unit 114 is arranged not on the ADF but on the apparatus main body side where a sufficient space exists around the reading unit 114, the reading unit 114 is configured by a CCD (Charge Coupled Device) of a reduction optical system capable of taking an optical path length.

  Reference numeral 115 denotes a light source that supplies light necessary for image reading by the reading unit 114. When the reading unit 114 is constituted by a CCD, it is constituted by a fluorescent tube, an LED, or the like. Reference numeral 116 denotes a white plate on which an image is read in order to create a reference value for shading correction. When reading the entire surface of the document placed on the glass plate 113, the reading unit 114 and the light source 115 are moved by a driving mechanism (not shown) to scan the entire surface of the document.

  A paper discharge roller 117 discharges the document 102 that has been read to a paper discharge tray 118.

  FIG. 2 is a diagram showing a schematic configuration around the reading unit 106 in FIG.

  In FIG. 2, reference numeral 201 denotes a lens that receives reflected light emitted from the light source 107 to the document 102. Reference numeral 202 denotes a CIS device that converts optical information collected by the lens 201 into an electrical signal. A detailed configuration of the CIS device 202 is shown in FIG.

  In FIG. 4A, reference numeral 301 denotes a device that converts optical information collected by the lens 201 into an electrical signal, and includes a plurality of sensor devices 302 arranged in the lateral direction. Each of the sensor devices 302 outputs an electrical signal, so that pixel values constituting the main scanning direction of the document 102 are determined. Many CIS devices do not include a filter for color discrimination. Therefore, the sensor device 302 only converts the light level as an electrical signal regardless of the color component.

  When reading an image of a monochrome document, the light source 107 emits monochromatic light based on the time required for the CIS device 202 to convert input optical information as an electrical signal level. The light source color that the light source 107 develops when reading an image of a monochrome original is green.

  When an image of a color original is read, the color component value of light collected by the lens 201 must be determined. As described above, the CIS device 202 only outputs the input light level as an electric signal level, so that each component value can be output by switching the light source color. That is, when reading the red component, the light source color of the light source 107 is red (hereinafter referred to as “R”). Similarly, when reading the green component, the light source color of the light source 107 is green (hereinafter referred to as “G”), and when reading the blue component, the light source color of the light source 107 is blue (hereinafter referred to as “G”). B ”).

  Therefore, when reading an image of a color document, it is possible to adjust the CIS device 202 to an electric signal level by adjusting so that the document does not move during reading of one line of the document while also controlling a motor (not shown). The reading operation is performed after ensuring. Reading an image for one line of a color document requires three times the reading time compared to reading a monochrome document image (in the case of monochromatic irradiation).

  FIG. 3 is a diagram showing a schematic configuration around the reading unit 114 in FIG.

  In FIG. 3, 401, 402, and 403 are mirrors that guide the reflected light that the light source 115 irradiates the document 102 to the lens 404. The lens 404 is a lens that collects light reflected by the mirror 403. In a reading unit using a CCD device, the light source color used as the light source is often white. Further, as a light source used, an LED, a fluorescent tube, or the like is used. Reference numeral 405 denotes a unit configured with a sensor that receives optical information collected by the lens 404, and includes a CCD 406 that is a sensor device. A detailed configuration example of the CCD 406 is shown in FIG.

  In FIG. 4B, a CCD 406 is a CCD device configured by a sensor array for three lines. In the case of a CCD device, a sensor element that converts input optical information into an electrical signal is configured with a filter that extracts only a component to be read. That is, a sensor element that wants to read the R component includes an R component extraction filter. Similarly, a sensor element that wants to read the G component includes a G component extraction filter, and a sensor element that wants to read the B component includes a B component extraction filter. Thus, since the sensor element includes a color component filter for reading, white having no color dependency is adopted as the light source color of the light source 115. For example, 501 is an array of sensor elements 504 that read R components, 502 is an array of sensor elements 505 that read G components, and 503 is an array of sensor elements 506 that read B components.

  Therefore, unlike the reading unit 106 including the CIS device 202, the reading unit 114 including the CCD 406 can simultaneously obtain the reading values of the respective components constituting the color original by reflected light based on light irradiation of the same light source color. is there. Since a plurality of sensor elements are arranged so that each color component can be read simultaneously, the lines read by each sensor element array (sensor element arrays 501, 502, 503) are not the same line. That is, a physical arrangement distance exists between the arrangement position of the sensor element array 501 and the arrangement position of the sensor element array 502. Therefore, the distance must be handled as a delay between lines in the reading unit 114 using the CCD 406.

  The correction of the delay between lines at the time of reading is performed using a memory (not shown) that stores the read original. That is, the line data of each read color component is temporarily stored in the memory, and the pixels constituting the line are generated by reading out the components constituting the same line.

  FIG. 5 is a block diagram illustrating a functional configuration of the image processing unit in the image reading apparatus 100.

  In FIG. 5, reference numeral 1400 denotes a control unit that controls the entire image reading apparatus 100. The control unit 1400 controls each unit described below. A surface light source lighting control unit 1401 performs lighting control of the light source 115, and a light source lighting control signal 1402 is output from the surface light source lighting control unit 1401. Reference numeral 1403 denotes image data read by the reading unit 114, and 1404 denotes a surface input image data i / f unit that controls input of the image data 1403.

  A surface image processing unit 1405 performs, for example, shading correction processing using a reading value when the reading unit 114 reads the white plate 116 as a reference value. In addition, the surface image processing unit 1405 performs image processing other than the background removal processing, such as processing for converting the read device-dependent color space image data into image data in a standardized color space (for example, sRGB space). .

  Reference numeral 1407 denotes a surface background luminance detection unit for detecting the surface background luminance, and outputs the surface background luminance 1408 with reference to the output image data of the surface image processing unit 1405. A surface background removal processing unit 1409 refers to the surface background luminance 1408 output from the surface background luminance detection unit 1407, and converts pixels determined to be the background from the output image data of the surface image processing unit 1405 to white pixels. The background removal process is performed. Reference numeral 1406 denotes a surface output image data i / f portion, which sequentially outputs the image data processed by the surface background removal processing portion 1409.

  Reference numeral 1410 denotes a back light source lighting control unit that performs lighting control of the light source 107, and reference numeral 1411 denotes a light source lighting control signal output from the back light source lighting control unit 1410. Reference numeral 1412 denotes image data read by the reading unit 106, and reference numeral 1413 denotes a back side input image data i / f portion for performing input control of the image data 1412.

  Reference numeral 1414 denotes a back surface image processing unit, which performs, for example, shading correction processing using a read value when the reading unit 106 reads the white plate 108 as a reference value. Further, the back image processing unit 1414 performs image processing other than the background removal processing, such as processing of converting the read device-dependent color space image data into image data of a standardized color space (for example, sRGB space). .

  Reference numeral 1416 denotes a back surface background luminance detection unit that detects the back surface background luminance, and outputs the back surface background luminance 1417 with reference to the output image data of the back surface image processing unit 1414. Reference numeral 1418 denotes a back surface background removal processing unit that refers to the back surface background luminance 1417 output from the back surface background luminance detection unit, and converts pixels determined to be the background from the output image data of the back surface image processing unit 1414 to white pixels. The background removal process is performed at. Reference numeral 1415 denotes a back surface output image data i / f unit, which sequentially outputs the image data processed by the back surface background removal processing unit 1418.

  Next, the double-sided reading operation of the document 102 in the image reading apparatus 100 will be described with reference to FIGS. 6 (a) and 6 (b).

  FIG. 6A is a diagram illustrating a situation when the document 102 reaches the reading start position of the reading unit 106, and FIG. 6B illustrates a time when the document 102 reaches the reading start position of the reading unit 114. FIG.

  In FIG. 6A, the document 102 placed on the document placement unit 101 is sequentially transported in the transport direction on the transport path 103 by driving the feeding roller 104. When the leading edge of the document 102 reaches the sensor 105, the sensor 105 outputs a detection signal to the control unit 1400. Upon receiving the detection signal from the sensor 105, the control unit 1400 performs driving control of the feeding roller 104 for a predetermined time, and then performs lighting control of the light source 107 by the back light source lighting control unit 1410 in preparation for image reading on the back side of the document. . After the light source 107 is turned on and the amount of light is stabilized, image reading on the back side of the document 102 by the reading unit 106 is started. Thereafter, the control unit 1400 drives and controls the conveyance rollers 109 to 111 to convey the document 102. When the reading operation mode is color original image reading, the control unit 1400 performs the image reading operation while switching the light source color of the light source 107 by the back light source lighting control unit 1410.

  When the control unit 1400 receives the detection signal from the sensor 105, after the drive rollers 109 to 111 are driven and controlled for a predetermined time, the surface light source lighting control unit 1401 turns on the light source 115 to prepare for image reading on the document surface. Take control. After the light source 115 is turned on and the amount of light is stabilized, image reading on the surface of the document 102 by the reading unit 114 is started. FIG. 6B shows a state in which the image reading operation on the front surface and the back surface of the document 102 is performed.

  When the trailing edge of the document 102 passes the sensor 105, the sensor 105 outputs a detection signal to the control unit 1400. Upon receiving the detection signal from the sensor 105, the control unit 1400 obtains the remaining number of lines for reading the image on the back side of the document and the remaining number of lines for reading the image on the surface of the document. This is calculated from the distance on the conveyance path 103 from the detection position of the sensor 105 to the reading start position of the reading unit 106 or the reading start position of the reading unit 114 and the document conveyance speed. Then, the control unit 1400 performs image reading control on the back side of the document only for the number of lines from the detection position of the sensor 105 to the reading start position of the reading unit 106.

  The control unit 1400 controls the light source 107 to be turned off by the back side light source lighting control unit 1410 after a predetermined time has elapsed after the image reading on the back side of the document is completed. On the other hand, even when the image reading on the back side of the document is completed, the image reading on the surface of the document is performed by the reading unit 114. Therefore, the control unit 1400 continues to convey the original 102 by drivingly controlling the conveyance rollers 109 to 111 and 112. At the same time, image reading control on the surface of the document is also performed. When the reading of the image on the surface of the original by the reading unit 114 is completed, the control unit 1400 controls the light source 115 to be turned off by the surface light source lighting control unit 1401 after a predetermined time has elapsed.

  Next, lighting control of the light source 107 and the light source 115 at the time of reading both sides of the document 102 will be described with reference to FIG.

  FIG. 7A is a diagram showing a change with time of the light amounts of the light sources 107 and 115 when reading both sides of the document 102.

  In the illustrated example, the horizontal axis represents the elapsed time, and the vertical axis represents the light amount of the light source 107 or 115. A solid line indicates a change in the light amount of the light source 107, and a broken line indicates a change in the light amount of the light source 115. Further, T0 to T7 indicate times when the light amount of the light source 107 or 115 changes. L0 indicates the maximum level of the light amount of the light source 107, and L1 indicates the maximum level of the light source 115.

  When reading is started (Ts: reading start timing), first, the light source 107 is turned on at timing T0. Image reading on the back side of the document is started at timing T1 when the light amount of the light source 107 is stabilized. Image reading on the back side of the document is started at timing T1 when the light amount of the light source 107 is stabilized. Then, at the timing T2, the surface light source 115 is turned on. Image reading on the surface of the document is started at a timing T3 when the light amount of the light source 115 is stabilized. Thereafter, the image reading of the original 102 is performed in a state where the light amounts of the light source 107 and the light source 115 are kept constant.

  Timing T4 indicates the timing when the reading of the back side of the document is completed. Timing T5 indicates the timing when the light source 107 is turned off. Timing T6 indicates the timing when the image reading on the surface of the document is completed. Timing T7 indicates the timing when the light source 115 is turned off.

  In FIG. 7A, the maximum light amounts of the light source 107 and the light source 115 are L0 and L1, and a difference (L0> L1) is given between L0 and L1. The maximum value of the light amount of the light source 107 and the light source 115 is determined as a range in which the image data of the surface where reading is not performed is not input to the reading unit on the reading side due to the influence of transmitted light or the like when the document 102 is irradiated. It is. Therefore, the light amount of the light source 107 for the back surface is not necessarily large. In general, the amount of light varies depending on the paper quality of the original 102 and is controlled.

  Next, the single-sided reading operation of the document 102 in the image reading apparatus 100 will be described.

  In a conventional image reading apparatus, when performing single-sided reading of a document (for example, image reading of a document surface), lighting control of a light source for the back surface or reading control by a reading unit on the back surface side is not performed. In the image reading apparatus 100 according to the present embodiment, even when performing single-sided reading of a document, lighting control of the light source 107 for the back side and reading control of the reading unit 106 that performs image reading on the back side are performed.

  FIG. 8 is a flowchart illustrating an example of an image reading process executed by the image reading apparatus 100.

  In the image reading apparatus 100, when the user receives an instruction to start a reading operation from an operation unit (not shown), the control unit 1400 starts reading control. The controller 1400 determines whether or not the reading operation mode set by the user is the single-sided reading mode (step S401). If it is determined that the mode is not the single-sided reading mode but the double-sided reading mode, the process proceeds to step S402. If the single-sided scanning mode is determined, the process proceeds to step S409.

  In step S402, the control unit 1400 drives and controls the feeding roller 104 to convey the document 102 on the document placement unit 101 to the reading start position of the reading unit 106 (see FIG. 6A). When it is determined that the document 102 has reached the reading start position of the reading unit 106 (YES in step S403), the control unit 1400 instructs the back light source lighting control unit 1410 to turn on the light source 107 (step S404). After the light source 107 is turned on, the reading unit 106 reads the image on the back side of the document 102 (step S405). Here, the image reading operation in step S405 will be described.

  When the light source 107 is turned on, the reflected light of the document 102 enters the reading unit 106. Incident light is converted into an electrical signal by the CIS device 202 in the reading unit 106 and output. The output electrical signal is input to the back side input image data i / f unit 1413 as image data 1412.

  The back side input image data i / f unit 1413 outputs the input image data to the back side image processing unit 1414. The back image processing unit 1414 performs predetermined image processing on the input image data. Specifically, the input image data is subjected to processing such as shading correction using the image reading value of the white plate 108 as a reference value, and conversion to predetermined color space data. When the output data of the back surface image processing unit 1414 is input to the back surface background luminance detection unit 1416, the back surface background luminance detection unit 1416 detects the background luminance by the background luminance detection method described with reference to FIG.

  On the other hand, the back surface background removal processing unit 1418 removes the background from the input image data according to the background brightness level output by the back surface background brightness detection unit 1416. The image data whose background has been removed by the back surface background removal processing unit 1418 is held in a storage unit such as a memory (not shown) via the back surface output image data i / f unit 1415. The above is a series of image reading operations in step S405.

  Next, in step S <b> 406, the control unit 1400 conveys the document 102 by drivingly controlling the conveyance rollers 109 to 111. After the image reading on the back side of the document is completed (YES in step S407) and a predetermined time has elapsed, the control unit 1400 outputs a turn-off instruction to the back-side light source lighting control unit 1410 to control the turning off of the light source 107 (step S408). ). Thereafter, in the same manner as described above, the image reading process (step S416) of the document surface by the reading unit 114 is executed, and this process is terminated. Note that whether or not the image reading on the back side of the document in step S407 has been completed is performed by, for example, detection of the trailing edge of the document by the sensor 105, drive control of the feed roller 104, and the like. There may be.

  On the other hand, in step S409, the control unit 1400 drives and controls the feeding roller 104 to convey the document 102 on the document placement unit 101 to the reading start position of the reading unit 106 (see FIG. 6A). When it is determined that the document 102 has reached the reading start position of the reading unit 106 (YES in step S410), the control unit 1400 instructs the back light source lighting control unit 1410 to turn on the light source 107 (step S411). After the light source 107 is turned on, the reading unit 106 reads an image on the back side of the document 102 (step S412). Step S412 is an example of a first reading unit, for example. Then, the control unit 1400 conveys the document 102 by driving control of the feeding roller 104 and the conveying rollers 109 to 111 (step S413).

  Next, the control unit 1400 determines whether or not the reading of the document is completed (step S414). The document reading completion determination is made based on whether or not the leading edge of the document 102 has reached the reading start position of the reading unit 114. The arrival at the reading start position is performed based on, for example, whether the document 102 has been conveyed for a predetermined time with reference to the time when the sensor 105 detects the leading edge of the document 102. When it is determined that the front end of the document 102 has not reached the reading start position of the reading unit 114, the control unit 1400 continues document reading control (step S412) and conveyance control (step S413).

  On the other hand, when it is determined that the leading edge of the document 102 has reached the reading start position of the reading unit 114 (YES in step S414), the process proceeds to step S415. In step S415, the control unit 1400 terminates image reading by the reading unit 106 and controls the light source 107 to be turned off (see t3 in FIG. 7B), and proceeds to step S416.

  In the above processing, the reading time of the back side of the document by the reading unit 106 at the time of single-sided reading is the time from when the leading edge of the document 102 reaches the reading start position of the reading unit 106 to the reading start position of the reading unit 114. It is. That is, the reading range of the back side of the document by the reading unit 106 at the time of single-sided reading is limited to a predetermined range from the front end of the document, not the entire back side of the document. This predetermined range is a range until the detected background luminance reaches the actual background luminance, and is defined according to the distance on the conveyance path from the reading start position of the reading unit 106 to the reading start position of the reading unit 114. Is done.

  Next, lighting control of the light source 107 and the light source 115 when reading one side of the document 102 will be described with reference to FIG.

  FIG. 7B is a diagram showing a change with time of the light amounts of the light sources 107 and 115 when reading one side of the document 102.

  In the illustrated example, the horizontal axis represents the elapsed time, and the vertical axis represents the light amount of the light source 107 or 115. A solid line indicates a change in the light amount of the light source 107, and a broken line indicates a change in the light amount of the light source 115. Further, t0 to t11 indicate times when the light amount of the light source 107 or the light source 115 changes. L0 indicates the maximum level of the light amount of the light source 107, and L1 indicates the maximum level of the light source 115.

  When reading is started (Ts: reading start timing), first, at the timing t0, the light source 107 is turned on (timing when step S411 is executed). Image reading on the back side of the document is started at timing t1 when the light amount of the light source 107 is stabilized (timing when step S412 is executed for the first time). At timing t2, the surface light source 115 is turned on. Image reading on the document surface is started at timing t3 when the light amount of the light source 115 is stabilized.

  In the original single-sided reading, the light source 107 for the back side is turned off at the timing t3 (the timing when step S415 is executed), and the reading of the image of the front end portion of the original 102 by the reading unit 106 is completed (step S415). Timing t5 indicates the timing when the light source 107 is turned off.

  Reading by the reading unit 114 is continuously performed even after reading by the reading unit 106 is completed. The light source 115 is turned off when the last line of the document 102 is read (t6). Timing t7 indicates the timing when the light source 115 is turned off.

  Next, the back surface background removal process and the front surface background removal process in the image reading apparatus 100 will be described.

  FIG. 9 is a flowchart showing the back surface background removal process executed by the image reading apparatus 100. This process is a process executed in parallel with the process of FIG.

  In step S500, as in steps S402 and S409 in FIG. 8, the control unit 1400 controls the drive of the feeding roller 104, and reads the document 102 on the document placement unit 101 from the reading start position (back side scanning) of the reading unit 106. Transport to the start position. When it is determined that the document 102 has reached the back side scanning start position of the reading unit 106 (YES in step S501), the control unit 1400 sets a preset specified value as an initial value of the background luminance (step S502). Then, the reading unit 106 reads the image on the back side of the document 102 and inputs image data (step S503).

  The input image data is input to the back surface background luminance detection unit 1416 via the back surface input image data i / f unit 1413 and the back surface image processing unit 1414 shown in FIG. Here, the back background luminance detection unit 1416 compares the current initial value of the background luminance with the first input pixel value. As a result of comparison, when the input pixel value is large, the value of the back surface background luminance 1417 output from the back surface background luminance detection unit 1416 is increased, and when the input pixel value is small, the value of the back surface background luminance 1417 to be output is decreased. Luminance detection is performed (step S504). Step S504 is, for example, first detection means.

  Next, the control unit 1400 determines whether or not the reading operation mode set by the user is the single-sided reading mode (step S505). If it is determined that the single-sided reading mode is set, the process proceeds to step S506. On the other hand, if it is determined that the duplex reading mode is set, the control unit 1400 performs background removal processing by the back surface background removal processing unit 1418 based on the output value (back surface background luminance 1417) of the back surface background luminance detection unit 1416 in step S504. This is performed (step S508). The image data processed by the back surface background removal processing unit 1418 is output by the back surface output image data i / f unit 1415.

  Next, the control unit 1400 determines whether or not reading of the image on the back side of the document is completed (step S509). Step S509 is the same as step S407 in FIG. 8 described above.

  In step S506, the control unit 1400 determines whether the leading end of the document 102 has reached the reading start position of the reading unit 114, as in step S414 in FIG. If the result of this determination is that it has arrived, this processing is terminated. If it has not been reached, processing proceeds to step S507. In step S507, the control unit 1400 conveys the document 102 by the feeding roller 104 and the conveyance rollers 109 to 111, and returns to step S503.

  As described above, as the back surface background removal processing, the background luminance detection (step S504) is performed in units of pixels on the input image data even when reading a single-sided document. The same process is repeated until the leading edge of the document reaches the front surface reading start position of the reading unit 114 when reading a single-sided document, and until the image reading of the back side of the document is completed when reading a double-sided document.

  FIG. 10 is a flowchart showing the surface background removal process executed by the image reading apparatus 100. This process is a process executed in parallel with the process of FIG.

  In step S <b> 601, the control unit 1400 controls driving of the feeding roller 104 and the conveyance rollers 109 to 111 and conveys the document 102 to the reading start position (front surface reading start position) of the reading unit 114. When it is determined that the document 102 has reached the front surface reading start position of the reading unit 114 (YES in step S602), the control unit 1400 determines whether or not the reading operation mode set by the user is the single-sided reading mode (step). S603).

  As a result of the determination in step S603, when it is determined that it is in the single-sided reading mode, the process proceeds to step S604, whereas when it is determined that it is in the double-sided reading mode, the process proceeds to step S610. In step S610, the control unit 1400 sets a preset specified value as the initial value of the current background luminance of the surface background luminance detection unit 1407, and proceeds to step S605.

  In step S604, the control unit 1400 sets the output value of the back surface background luminance detection unit 1416 (back surface background luminance 1417) as the initial value of the background luminance of the front surface background luminance detection unit 1407, and proceeds to step S605. In step S605, the reading unit 114 reads an image on the surface of the document 102 and inputs image data. Step S605 is, for example, a second reading unit.

  Next, in step S606, background luminance detection is performed as in step S504 described above. Here, the input image data is input to the surface background luminance detection unit 1407 via the surface input image data i / f unit 1404 and the surface image processing unit 1405 shown in FIG. Here, the surface background luminance detection unit 1407 compares the initial value of the current background luminance with the first input pixel value. The initial value of the current background luminance is a predetermined value set in advance in the case of step S610 (in the case of the double-sided reading mode).

  On the other hand, in the case of step S604 (in the case of the single-sided reading mode), the output value (back surface background luminance 1417) of the back surface background luminance detection unit 1416 is obtained. As a result of comparison, when the input pixel value is large, the value of the surface background luminance 1408 output by the surface background luminance detection unit 1407 is increased, and when the input pixel value is small, the value of the output surface background luminance 1408 is decreased. Perform luminance detection.

  In the case of single-sided scanning, the output value of the back surface background brightness detection unit 1416 (back surface background brightness 1417) is used as an initial value when detecting the surface background brightness, so that the accuracy of the background brightness detection value at the leading edge of the document can be improved. It is possible to perform background removal equivalent to that in the middle portion of the document. Step S606 is, for example, second detection means.

  Next, in step S607, the background removal processing is performed by the surface background removal processing unit 1409 based on the output value (surface background luminance 1408) of the surface background luminance detection unit 1407 in step S606. The image data processed by the surface background removal processing unit 1409 is output by the surface output image data i / f unit 1406.

  Next, the control unit 1400 determines whether or not the image reading on the surface of the document has been completed (step S608). On the other hand, when the image reading on the surface of the document is not completed, the control unit 1400 transports the document 102 by the transport rollers 109 to 111 and returns to step S605.

  According to the above-described embodiment, using the fact that the arrangement of the reading unit 106 for the back surface and the reading unit 114 for the front surface is different on the conveyance path 103, when receiving a single-side reading instruction, the output value of the back surface background luminance detection unit Is used in the surface background luminance detection unit. As a result, when reading an image on one side of the original, the accuracy of the background luminance detection value at the leading end of the reading surface can be improved, and appropriate background removal is possible. Further, by limiting the image reading range on the back side of the document when detecting the background brightness of the surface opposite to the surface to be read, it is possible to reduce excessive lighting of the light source 107 and suppress the power consumption of the apparatus. .

  Note that the image reading apparatus in the above embodiment may be a single scanner or a multifunction machine having a scanning function, a printing function, and the like.

  The object of the present invention can also be achieved by executing the following processing. That is, a storage medium in which a program code of software that realizes the functions of the above-described embodiments is supplied to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus is stored in the storage medium. This is the process of reading the code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the program code and the storage medium storing the program code constitute the present invention.

DESCRIPTION OF SYMBOLS 100 Image reading apparatus 102 Original 105 Sensor 106,114 Reading unit 107,115 Light source 1400 Control part 1407 Front surface brightness | luminance detection part 1409 Front surface background removal processing part 1416 Back surface background brightness detection part 1418 Back surface background removal processing part

Claims (6)

In an image reading apparatus capable of reading images of a first surface and a second surface of a document by a plurality of image reading means while conveying the document,
A first image reading unit that reads an image in a predetermined range on the first side of the original when receiving an image reading instruction on one side of the original;
First detection means for detecting a background luminance of a first surface of a document read by the first image reading means;
A second image reading means for reading an image on the second side of the document, which is disposed at a position different from the first image reading means;
And second detection means for detecting the background brightness of the second surface of the document read by the second image reading means using the background brightness detected by the first detection means. An image reading apparatus.   The first image reading means includes a light source for irradiating the original with light and a conversion means for converting reflected light from the original into an electric signal, and a predetermined range of the first surface of the original. The image reading apparatus according to claim 1, wherein when the image is read, lighting control of the light source is performed according to the range.   The predetermined range is defined according to a distance on a conveyance path of the document from a reading start position of the first image reading unit to a reading start position of the second image reading unit. Item 3. The image reading apparatus according to Item 1 or 2.   4. The image reading apparatus according to claim 1, wherein the predetermined range is a range until a detected background luminance reaches an actual background luminance. 5. In a reading method of an image reading apparatus capable of reading images of a first surface and a second surface of a document by a plurality of image reading means while conveying the document,
A first reading step of reading an image in a predetermined range on the first side of the original by the first image reading means when receiving an image reading instruction on one side of the original;
A first detection step of detecting a background luminance of the first surface of the document read by the first image reading means;
A second reading step of reading an image on the second surface of the document by a second image reading means arranged at a different position from the first image reading means;
And a second detection step of detecting the background brightness of the second surface of the document read by the second image reading means using the background brightness detected by the first detection means. Image reading method.   A computer-readable program for causing a computer to execute the image reading method according to claim 5.