JP2010177930A - Image reader and image formation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance an S/N ratio while reducing a step in an output level, generated by a plurality of line sensors for reading a plurality of areas formed by dividing one line of a document, respectively. <P>SOLUTION: A determination means determines whether the maximum value among output levels of the line sensors determined by a second determination means exceeds a predetermined lower-limit target level. A step reducing means reduces the step in output level at a boundary of the plurality of line sensors after adjustment of the output level by a second gain control means is completed. When the maximum value among the output levels of the line sensors determined by the second determination means exceeds the lower-limit target level, even when adjustment of the output level by the second gain control means is not performed, the step reducing means does not reduce the step. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image reading apparatus and an image forming system for optically reading a document.

  An image reading apparatus generally includes an analog gain circuit that performs gain adjustment on an analog image signal output from an image sensor, an offset correction circuit that performs offset adjustment, and an analog-to-digital conversion unit that converts the analog signal into a digital signal. ing. These circuits are called analog processors. The analog gain circuit adjusts the amplification amount (gain) in the amplification circuit that amplifies the image signal.

  Conventionally, an analog gain circuit, an offset correction circuit, and an analog-digital conversion unit exist as independent circuits for each readout channel of an image signal. However, in recent years, with the high integration of semiconductors, analog processors in which these are integrated into one chip have appeared. In an analog processor made into one chip, output characteristics between a plurality of channels are stable, and a difference between the output characteristics is expected to be small.

By the way, in order to increase the reading speed of the image reading apparatus, there has been proposed an invention in which a linear image sensor is divided into a plurality of areas and pixel signals are read out in parallel from each area (Patent Document 1). In the invention described in Patent Document 1, a step occurs in the signal level (output level) of the pixel signal at the boundary of the region. Therefore, Patent Document 1 employs output level adjusting means that operates so as to reduce the level difference of the output level.
JP 2001-211297 A

  Incidentally, in a conventional image reading apparatus such as Patent Document 1, a linear light source (linear light source) such as a xenon lamp, a fluorescent lamp, or a cold cathode tube has been used. Light from these linear light sources is input to an image sensor such as a CCD via a lens.

  FIG. 12 is a diagram for explaining the luminance distribution and the connecting step in the line light source. The horizontal axis indicates the main scanning position, and the vertical axis indicates the output level of the pixel signal. As shown in FIG. 12, in the line light source, the central area of one line is brightest. The luminance at the edge is lower than that in the central area. Here, the linear image sensor is divided into a first half area and a second half area, and the center is a boundary between them.

  On the other hand, an image reading apparatus provided with an LED light source configured by arranging a plurality of LEDs in the main scanning direction due to an improvement in the luminance of the LEDs has been studied. However, when the LED light source and the lens are combined, the luminance at the end portion is lowered as in the case of the line light source. Therefore, it is conceivable to increase the luminance at the end by arranging more LEDs at the front end and the rear end in the main scanning direction than at the center.

  FIG. 13 is a diagram for explaining the luminance distribution and the connecting step in the LED light source. The horizontal axis indicates the main scanning position, and the vertical axis indicates the output level of the pixel signal. Since the LEDs are unevenly arranged, the central portion is dark and the end portions are bright.

  As can be seen from a comparison between FIG. 12 and FIG. 13, a step occurs in the brightest portion of the line light source, and a step occurs in the darkest portion of the nonuniformly arranged point light sources. In particular, the step in the unevenly arranged point light source tends to be larger than the step in the line light source. This is due to the gain adjustment itself. Since the line light source has the maximum output level in the central region in the main scanning direction, gain adjustment is executed based on the output level in the central region. Therefore, after gain adjustment, the connecting step generated at the boundary between the first half area and the second half area becomes relatively small.

  However, in an unevenly arranged LED light source, the output level is highest at the output level at the end in the main scanning direction. Therefore, gain adjustment is performed independently in the first half area and the second half area in accordance with the output level at the end. That is, after the gain adjustment, adjustment for matching the output level of the first half area and the output level of the second half area is not executed, and therefore the connecting step tends to be large.

  FIG. 14 is a diagram for explaining gain adjustment and step correction in the related art. The horizontal axis indicates the main scanning position, and the vertical axis indicates the output level of the pixel signal. In this related technology, the gain adjustment value is determined based on the highest output level of the output level of the first half region and the output level of the second half region, and the determined gain adjustment value is determined for both the first half region and the second half region. Set to analog gain circuit. Thereby, as FIG. 14 shows, a connection level | step difference becomes small. However, if the gain adjustment value in the first half area and the gain adjustment value in the second half area are the same, the S / N ratio of the image tends to deteriorate when the difference in output level increases. This is because the output level difference is digitally raised by a shading circuit or the like.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. For example, an object of the present invention is to improve an S / N ratio while reducing a step of an output level generated in a plurality of line sensors that respectively read a plurality of areas obtained by dividing one line of a document. Other issues can be understood throughout the specification.

  The image reading apparatus of the present invention includes, for example, a plurality of line sensors, a first determination unit, a first gain adjustment unit, a second determination unit, a determination unit, a second gain adjustment unit, and a step reduction unit. The plurality of line sensors respectively read a plurality of areas obtained by dividing one line of the document. The first determining means determines the maximum value of the output level in each of the plurality of line sensors, and determines the line sensor that has output the image signal at the maximum output level. The first gain adjusting means increases the output gain of the plurality of line sensors until the maximum value of the output level of the line sensor determined by the first determining means reaches a predetermined upper limit target level. The second determining means determines the maximum value of the output level in each of the plurality of line sensors after the adjustment of the output gain by the first gain adjusting means is completed, and is the largest of the maximum values in the plurality of line sensors. A line sensor that outputs an image signal with a small maximum value is determined. The determining means determines whether or not the maximum value of the output level of the line sensor determined by the second determining means exceeds a predetermined lower limit target level. If the maximum value of the output level of the line sensor determined by the second determining unit does not exceed the lower limit target level, the second gain adjusting unit determines that the determined maximum value of the output level of the line sensor is the lower limit target level. The output gain of the determined line sensor is increased until it exceeds. The level difference reducing unit reduces the level difference of the output level at the boundary between the plurality of line sensors after the adjustment of the output level by the second gain adjusting unit is completed. If the maximum value of the output level of the line sensor determined by the second determining unit exceeds the lower limit target level without executing the output level adjustment by the second gain adjusting unit, the step reducing unit Do not perform reduction.

  According to the present invention, it is possible to improve the S / N ratio while reducing the level difference of the output level generated in a plurality of line sensors that respectively read a plurality of areas obtained by dividing one line of a document.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

  FIG. 1 is a schematic cross-sectional view of an image reading apparatus according to an embodiment. The image reading apparatus may be called an image scanner, an image reader, or a scanner apparatus. Further, there are an image reading apparatus that is used by being connected to a personal computer and an image reading apparatus that is used as a part of an image forming system. Examples of the image forming system include a copying machine, a multifunction machine, and a system in which a personal computer and a printer are combined. As described above, the image forming system includes an image reading device and an image forming device that forms an image read by the image reading device on a recording medium.

  In FIG. 1, an ADF 100 is an automatic document feeder. The pickup roller 1 picks up the document bundle S set on the document tray 20 and feeds it to the separation unit 2. The separating unit 2 separates the originals one by one from the original bundle S. The document is conveyed to the reading position R by the first registration roller 3, the second registration roller 4, and the first conveyance roller 5. The reader unit 200 reads an image of a document while being conveyed at the reading position R. The second transport roller 6 and the paper discharge roller 8 discharge the document onto the paper discharge tray 21.

  The reader unit 200 optically reads image information recorded on a document, photoelectrically converts it, and outputs it as image data. The reader unit 200 includes an ADF platen 201, a book platen glass 202, a scanner unit 209 having a lamp 203 and a first mirror 204, a second mirror 205, a third mirror 206, a lens 207, an image sensor unit 208, and the like. ing. The lamp 203 is a line light source such as a xenon lamp, a fluorescent lamp, or a cold cathode tube, or a plurality of point light sources. In particular, in the present embodiment, the lamp 203 is a plurality of LEDs (light emitting diodes) that are non-uniformly arranged in the main scanning direction. The main scanning direction is a direction substantially parallel to one line of the document. The direction orthogonal to the main scanning direction is called the sub scanning direction. As described in the background art section, a plurality of LEDs may be arranged more at the end portion than at the central portion in the main scanning direction. In such an unevenly arranged LED light source, the output level is highest at the end in the main scanning direction. In this case, the connecting step is easily noticeable after gain adjustment. The lens 207 is an optical component for forming an image of light from the original on the line sensor.

  A white plate 210 is disposed between the ADF platen 201 and the book platen glass 202. The image sensor unit 208 reads the reflected light from the white plate 210 to perform light amount sampling, shading correction, and the like.

  When reading an image of a document conveyed from the ADF 100, the reader unit 200 moves the scanner unit 209 below the ADF platen 201 and stops there. The reader unit 200 reads image information while a document is being conveyed on the reading position R. When reading an image of a document placed on the book platen glass 202, the reader unit 200 moves the scanner unit 209 in the sub-scanning direction to read image information.

  The lamp 203 is lit when reading image information and illuminates the document. The reflected light from the document is input to the image sensor unit 208 via the first mirror 204, the second mirror 205, the third mirror 206, and the lens 207. The image sensor unit 208 includes, for example, three line sensors for color reading and one line sensor for black and white reading. These line sensors are, for example, linear image sensors.

  FIG. 2 is a block diagram illustrating a control unit for controlling the ADF 100 and the reader unit 200. The CPU 300 is a central processing unit and comprehensively controls each unit of the image reading apparatus. The ROM 301 is a read-only memory and stores a control program and the like. The RAM 302 is a random access memory and functions as a work area for the CPU 300.

  The CPU 300 is connected to the image control ASIC 303 via a bus. The image control ASIC 303 is connected to the lamp driving circuit 304, the line sensor driving circuit 305, the analog processor 306, and the image interface 308. The lamp driving circuit 304 controls the irradiation lamp 203 to turn on / off the irradiation lamp 203. The line sensor drive circuit 305 drives the image sensor unit 208. The analog processor 306 electrically performs offset correction and amplification correction on the output value of the image data from the image sensor unit 208.

  According to the present embodiment, the CPU 300 controls the lamp 203, the image sensor unit 208, and the analog processor 306 via the image control ASIC 303 including the image processing circuit 307. In other embodiments, the CPU 300 may directly control the lamp 203, the image sensor unit 208, and the analog processor 306. The image interface 308 is an interface for further outputting image data output from the image processing circuit 307 to an external device.

  FIG. 3 is a diagram showing a 4-line image sensor. The image sensor unit 208 is the 4-image sensor unit shown in FIG. 1 applied in the present embodiment. The image sensor unit 208 includes four line sensors 401, 402, 403, and 404. Light (original image) from the original is imaged on each line sensor by the lens 207. Each line sensor converts incident light into electric charge and outputs it as an image signal.

  The line sensors 401, 402, and 403 are color line sensors, and a color filter is attached to the light receiving surface. For example, the line sensor 401 for red has a red (R) filter. The line sensor 402 for green has a filter for green (G). The blue line sensor 403 has a blue (B) filter. A full-color image can be obtained by synthesizing R / G / B image signals output from the line sensors 401, 402, and 403 for each pixel.

  The line sensor 404 is a line sensor dedicated to reading monochrome images. Therefore, the image signal output from the line sensor 404 is monochrome image data. The monochrome line sensor 404 is driven by a transfer clock faster than the color line sensors 401, 402, and 403. The monochrome line sensor 404 may not include a filter, or may include a lighter color filter than the R / G / B filter.

  FIG. 4 is a diagram for explaining a shift register provided only in the monochrome line sensor 404. A shift register is provided to increase the transfer rate of black and white image data. Thereby, it is possible to transfer the first half area 510 and the second half area 520 of one line of the document in parallel. In other words, the single line sensor 404 has imaging elements from the first pixel to the Nth pixel as a whole. Among these, the first pixel to the N / 2 pixel constitute the first half area 510, and the (N / 2 + 1) pixel to the N pixel constitute the second half area 520. Therefore, the monochrome line sensor 404 functions as a plurality of line sensors that respectively read a plurality of areas obtained by dividing one line of the document. Of the black and white line sensor 404, the first half area 510 can be called a first black and white line sensor, and the second half area 520 can be called a second black and white line sensor. The first half area 510 of the monochrome line sensor 404 is a first line sensor that reads a first area obtained by dividing one line of a document. The second half area 520 is a second line sensor that reads the remaining second area obtained by dividing one line of the document.

  Thus, the merit of dividing a single linear image sensor into a plurality is that the transfer rate of image data is increased. The transfer amount in each area of the monochrome line sensor 404 is half of the transfer amount of the R / G / B line sensors 401, 402, and 403. Therefore, it is possible to shorten the output time of the image data from the image sensor unit 208 at the time of monochrome reading.

  In the present embodiment, the black and white line sensor 404 is divided into two regions for the sake of brevity. That is, the first half area 510 and the second half area 520 of the line sensor 404 for black and white are configured by dividing a single linear image sensor into a plurality of parts. However, it goes without saying that the monochrome line sensor 404 may be divided into three or more regions. That is, when the line sensor 404 is divided into three or more regions, the first gain adjustment for each region is executed according to the maximum value of the output level of the entire line sensor 404. When the first gain adjustment is completed, the maximum value is measured for each region. For the region corresponding to the maximum value not exceeding the lower limit target level, the second gain adjustment and the step reduction process are performed. Executed.

  FIG. 5 is a diagram for explaining the analog processor 306. Image signals from the line sensors 401, 402, 403, and 404 are input to the analog processor 306 via the image control ASIC 303.

  In the full color image reading mode, the analog processor 306 employs R / G / B image signals from the line sensors 401, 402, and 403. In the monochrome image reading mode, the analog processor 306 employs image signals from the first half area 510 and the second half area 520 of the line sensor 404.

  The analog processor 306 includes a first analog processor 610, a second analog processor 620, and a third analog processor 630. The first analog processor 610 is a first image processing circuit that performs image processing on an image signal that is alternatively selected by the first image signal selector 640 from the R image signal or the black and white first half area 510. The second analog processor 620 is a second image processing circuit that performs image processing on an image signal that is alternatively selected by the second image signal selector 641 from the G image signal or the black and white second half area 520. The third analog processor 630 is a third image processing circuit that processes the B image signal. The R image signal is an image signal from the color line sensor for red, the G image signal is an image signal from the color line sensor for green, and the B image signal is an image signal from the color line sensor for red. .

  In the present embodiment, two image signal selectors are employed, but a single image selector having a similar switching function may be employed. As described above, the first image signal selector 640 and the second image signal selector 641 alternatively select image signals from a plurality of line sensors for reading a black and white image and image signals from a plurality of color line sensors. It functions as a selection means for selecting. The first analog processor 610 and the second analog processor 620 are a plurality of image processing circuits that perform image processing on the image signal selected by the selection unit.

  The first analog processor 610 includes a first offset circuit 611, a first gain circuit 612, and a first AD conversion circuit 613. The first offset circuit 611 corrects the black offset in accordance with a preset offset value for the image signal output from the first image signal selector 640. The first gain circuit 612 amplifies the image signal according to a preset gain adjustment value. The first AD conversion circuit 613 converts an analog signal into a digital signal.

  The second analog processor 620 also includes a second offset circuit 621, a second gain circuit 622, and a second AD conversion circuit 623. The third analog processor 630 also includes a third offset circuit 631, a third gain circuit 632, and a third AD conversion circuit 633. The function of each circuit is the same as that of the circuit included in the first analog processor 610. Note that the offset correction value and the gain adjustment value are set by the CPU 300. The digital image signal output from each analog processor is input to the image control ASIC 303.

  FIG. 6 is a diagram for explaining the operation of the image processing circuit 307 included in the image control ASIC 303. The image processing circuit 307 includes a first shading circuit 711, a second shading circuit 721, and a third shading circuit 731. The first shading circuit 711 receives the image signal sent from the first analog processor 610 and executes shading correction. The second shading circuit 721 receives the image signal sent from the second analog processor 620 and executes shading correction. The third shading circuit 731 receives the image signal sent from the third analog processor 630 and executes shading correction. Shading correction is performed for each pixel.

  The image processing circuit 307 further includes a level difference correction circuit 701. Since the level difference correction is necessary only for the black and white image data, the first shading circuit 711 and the second shading circuit 721 are connected.

  The level difference correction circuit 701 includes a first LUT 702 and a second LUT 703 corresponding to each line. LUT is an abbreviation for lookup table. The step correction circuit 701 uses the first LUT 702 and the second LUT 703 to perform output (luminance) level linearity correction (step correction). Note that the CPU 300 can control the step correction circuit 701 so as not to execute the step correction. In this case, the first LUT 702 and the second LUT 703 pass through the image data from the corresponding shading circuit to the subsequent stage without correction.

  Conversely, during black and white reading, the CPU 300 controls the first LUT 702 and the second LUT 703 so that the first LUT 702 and the second LUT 703 function effectively. The image data in the first half area 510 passes through the first analog processor 610, and the image data in the second half area 520 passes through the second analog processor 620. Therefore, when the gain adjustment values of the first gain circuit 612 and the second gain circuit 622 are different, there is a possibility that an output level step occurs at the boundary between the first half area 510 and the second half area 520. Therefore, by effectively functioning the first LUT 702 and the second LUT 703 of the step correction circuit 701, the step at the boundary between the first half area 510 and the second half area 520 can be corrected.

  FIG. 7 is a flowchart showing gain adjustment and step correction according to the embodiment. Here, gain adjustment and step correction are executed for the monochrome line sensor 404.

  In step S801, CPU 300 starts gain adjustment in the black and white mode. The gain adjustment in the monochrome mode is executed when the reader unit 200 is activated or when reading has not been performed for a predetermined time or more since the previous reading. The CPU 300 moves the scanner unit 209 below the white plate 210 in order to read the white plate 210 using the monochrome line sensor 404.

  In step S802, the CPU 300 sets the first gain adjustment value GA of the first gain circuit 612 for adjusting the gain of the first half area 510 to an initial value (for example, 0). Similarly, the CPU 300 sets the second gain adjustment value GB of the second gain circuit 622 for adjusting the gain of the second half area 520 to an initial value (for example, 0).

  In step S803, the CPU 300 determines a gain target level. The gain target level includes an upper limit target level X and a lower limit target level Y. These gain target levels are held in the RAM 302. Each shading circuit compares the output level of each pixel signal stored in the built-in shading RAM with the gain target level, and executes shading correction. Assuming that the gradation of the image is 255 gradations, the upper limit target level X is determined to be 240 or the like. The lower limit target level Y is determined to be lower than the upper limit target level X by a predetermined value. For example, the lower limit target level Y is determined to be 230 or the like. Note that the determination method of the upper limit target level X and the lower limit target level Y is appropriately determined according to the combination of the image sensor, the analog processor, the shading circuit, and the like.

  In step S804, the CPU 300 enables the black and white line sensor 404 to be valid. This is because the white plate 210 is read using the line sensor 404 for black and white. For example, the CPU 300 switches the first image signal selector 640 so that the image signal output from the first half area 510 of the monochrome line sensor 404 is input to the first analog processor 610. The CPU 300 switches the second image signal selector 641 so that the image signal output from the second half area 520 of the monochrome line sensor 404 is input to the second analog processor 620.

  In step S805, the CPU 300 activates the image sensor unit 208. The CPU 300 sends a command to the line sensor driving circuit 305 so that the image sensor unit 208 starts outputting an image. Further, the CPU 300 sends a command for turning on the lamp 203 to the lamp driving circuit 304.

  In step S806, the CPU 300 waits until the light amount of the lamp 203 and the output from the image sensor unit 208 are stabilized. You may wait until these actually stabilize, or you may wait only for a predetermined fixed time. When the output of the image sensor is stabilized, the process proceeds to step S807.

  In step S807, CPU 300 searches and determines the maximum value (maximum output level MA) among the output levels of the pixel signals corresponding to the first half area 510. For example, the CPU 300 samples the image data corresponding to the first half area 510 among the elements included in the monochrome line sensor 404 from the shading RAM included in the first shading circuit 711. Next, the CPU 300 compares the sampled output levels and determines the maximum output level MA based on the comparison result.

  In step S808, CPU 300 searches and determines the maximum value (maximum output level MB) among the output levels of the pixel signals corresponding to second half area 520. For example, the CPU 300 samples the image data corresponding to the second half area 520 from the elements included in the monochrome line sensor 404 from the shading RAM included in the second shading circuit 721. Next, the CPU 300 compares the sampled output levels and determines the maximum output level MB based on the comparison result.

  In step 809, the CPU 300 compares the maximum output level MA of the first half area 510 with the maximum output level MB of the second half area 520, and determines whether or not MA is larger than MB. If MA is larger than MB, the process proceeds to step S810.

  In step S810, the CPU 300 sets the maximum output level MA of the first half area 510 to a larger maximum value M, and sets the maximum output level MB of the second half area 520 to a smaller maximum value N. Thereafter, the process proceeds to step S812.

  On the other hand, if it is determined in step S809 that MA is not greater than MB, the process proceeds to step S811. In step S812, the CPU 300 sets the maximum output level MB of the second half area 520 to a larger maximum value M, and sets the maximum output level MA of the first half area 510 to a smaller maximum value N. Thereafter, the process proceeds to step S812.

  In step S812, the CPU 300 compares the larger maximum value M with the upper limit target level X, and determines whether or not the larger maximum value M is smaller than the upper limit target level X. The image quality increases when the maximum value M is as close as possible to the upper limit target level X. Therefore, if the larger maximum value M is smaller than the upper limit target level X, the process proceeds to step S813 to adjust the gain.

  In step S813, CPU 300 adds the same value to gain adjustment value GA set in first gain circuit 612 and gain adjustment value GB set in second gain circuit 622, respectively. Thereafter, the process returns to step S806. In accordance with the gain adjustment value increased by one step, the processes after step S806 are executed. Finally, if it is determined in step S812 that the larger maximum value M is equal to or higher than the upper limit target level X, the process proceeds to step S814. As described above, the CPU 300 increases the output gain common to the plurality of line sensors by one step until the maximum value of the output level of the line sensor reaches the predetermined upper limit target level. Therefore, the CPU 300 functions as a first gain adjustment unit.

  In step S814, the CPU 300 compares the smaller maximum value N with the lower limit target level Y, and determines whether or not the smaller maximum value N is larger than the lower limit target level Y. If the smaller maximum value N is larger than the lower limit target level Y, step correction is not necessary, and the process proceeds to step S815. In step S815, the CPU 300 stores in the RAM 302 information indicating that the step correction is not performed. At this time, GA set in the first gain circuit 612 and GB set in the second gain circuit 622 have the same gain adjustment value.

  FIG. 8 is a diagram showing the luminance distribution of one line acquired by the monochrome line sensor 404 when the smaller maximum value N is larger than the lower limit target level Y. It can be seen that MB which is the maximum value of the second half area 520 is larger than the upper limit target level X, and MA which is the maximum value of the first half area 510 is larger than the lower limit target level Y.

  On the other hand, if it is determined in step S814 that the smaller maximum value N is not greater than the lower limit target level Y, that is, less than the lower limit target level Y, the process proceeds to step S816. In step S816, the CPU 300 stores in the RAM 302 information indicating that the level difference needs to be corrected.

  FIG. 9 is a diagram showing the luminance distribution of one line acquired by the monochrome line sensor 404 when the smaller maximum value N is not larger than the lower limit target level Y. It can be seen that MB, which is the maximum value in the second half area, is larger than the upper limit target level X, and MA, which is the maximum value in the first half area, is smaller than the lower limit target level Y.

  In step S817, CPU 300 determines whether or not smaller maximum value N is equal to maximum output level MA of the first half area. Here, it is determined whether the maximum value of the output level in one whole line is the maximum value produced from the first half area 510 or the maximum value produced from the second half area 520. If the smaller maximum value N is equal to the maximum output level MA of the first half area, the smaller maximum value N is produced from the first half area, and the larger maximum value M is produced from the second half area. move on.

  In step S818, CPU 300 searches for and determines the maximum value (maximum output level MA) among the output levels of the pixel signals corresponding to first half area 510. This process is the same process as step S807.

  In step S <b> 819, the CPU 300 compares the MA and the lower limit target level Y, and determines whether or not the MA is lower than the lower limit target level Y. If MA is smaller than the lower limit target level Y, the process proceeds to step S820.

  In step S820, CPU 300 substitutes MA for N, and further adds a predetermined value to the value of gain adjustment value GA in first half area 510. In step S821, the CPU 300 waits for the output of the line sensor 404 to stabilize, and then returns to step S817. The processing from step S817 to step S821 is repeatedly executed until MA becomes equal to or higher than the lower limit target level Y. If it is determined in step 819 that MA is equal to or higher than the lower limit target level Y, the process proceeds to step S826.

  In step S826, CPU 300 determines a step from MA, which is the maximum value of first half area 510, and MB, which is the maximum value of second half area 520. For example, the step is a difference between MA and MB. The calculated level difference is stored in the RAM 302.

  On the other hand, if the smaller maximum value N is not the maximum output level MA of the first half area in step S817, the process proceeds to step S822. In this case, a smaller maximum value N is produced from the second half area.

  In step S822, CPU 300 searches for and determines the maximum value (maximum output level MB) among the output levels of the pixel signals corresponding to second half area 520. This process is the same process as step S808.

  In step S823, the CPU 300 compares the MB with the lower limit target level Y, and determines whether the MB is smaller than the lower limit target level Y. If MA is smaller than the lower limit target level Y, the process proceeds to step S824.

  In step S824, CPU 300 substitutes MB for N, and further adds a predetermined value to the value of gain adjustment value GB in second half area 520. In step S825, the CPU 300 waits for the output of the line sensor 404 to stabilize, and then returns to step S817. Steps S817, S822 to S825 are repeated until MB reaches the lower limit target level Y. If it is determined in step 823 that MB is equal to or higher than the lower limit target level Y, the process proceeds to step S826. In step S826, a step is calculated as described above.

  FIG. 10 is a diagram showing the luminance distribution of one line acquired by the monochrome line sensor 404 when there is a step. The maximum value MB of the second half area 520 is larger than the upper limit target level X, and the maximum value MA of the first half area 510 is larger than the lower limit target level Y. However, it can be seen that there is a step in the central region. Therefore, it is necessary to calculate and correct the step.

  When the gain adjustment for the monochrome line sensor 404 is completed, the step correction value calculated in step S826, the gain adjustment value GA for the first half area in the monochrome image sensor unit, and the gain adjustment value GB for the second half area are obtained. Is fixed.

  According to this embodiment, the maximum value (MA, MB) of the output level is determined for each of the plurality of line sensors (S807, S808), and the line sensor that outputs the image signal at the maximum output level is determined. (S809). Therefore, the CPU 300 functions as a first determination unit. Furthermore, according to the present embodiment, the output gains of the plurality of line sensors increase until the maximum value of the output level of the line sensor determined by the first determining unit reaches a predetermined upper limit target level (S812). , S813). Therefore, the CPU 300 functions as a first gain adjustment unit. Further, after the adjustment of the output gain by the first gain adjusting means is completed, the line sensor that outputs the image signal at the output level of the smallest maximum value (N) among the respective maximum values in the plurality of line sensors is determined. (S810, S811). Therefore, the CPU 300 functions as a second determination unit. Further, the CPU 300 functions as a determination unit that determines whether or not the maximum value of the output level of the line sensor determined by the second determination unit exceeds a predetermined lower limit target level (Y) (S814). The maximum value of the output level of the line sensor determined by the second determination unit may not exceed the lower limit target level. In this case, the CPU 300 increases the output gain of the determined line sensor until the determined maximum value of the output level of the line sensor exceeds the lower limit target level (S820, S824). Therefore, the CPU 300 functions as a second gain adjustment unit. The step correction circuit 701 functions as a step reduction unit that reduces the step of the output level at the boundary between the plurality of line sensors after the output level adjustment by the second gain adjustment unit is completed. On the other hand, if the maximum value of the output level of the line sensor determined by the second determination unit exceeds the lower limit target level without executing the output level adjustment by the second gain adjustment unit (S814), the CPU 300 Therefore, the level difference correction circuit 701 does not reduce the level difference.

  FIG. 11 is a flowchart showing the monochrome image reading process. The monochrome image reading process is started when a monochrome reading job is instructed from an operation unit (not shown).

  In step S1101, the CPU 300 reads the gain adjustment value GA from the RAM 302, sets the gain adjustment value GA in the first gain circuit 612, and sets the gain adjustment value GB in the second gain circuit 622. In step S1102, the CPU 300 sets the monochrome line sensor 404 to be valid. This process is the same as step S804.

  In step S <b> 1103, the CPU 300 refers to information indicating whether or not there is a level difference correction stored in the RAM 302 and determines whether level difference correction is necessary. If step correction is necessary, the process proceeds to step 1104. In step S1104, the CPU 300 reads out the step values stored in the RAM 302 and sets them in the first LUT 702 and the second LUT 703, respectively, thereby determining the step correction value. Thus, the step correction value of the first half area 510 is determined from the step value and the first LUT 702. Similarly, the step correction value of the second half area 520 is determined from the step value and the second LUT 703. In the first LUT 702, step correction values for steps having different values are determined through experiments or the like and stored in advance. Similarly, in the second LUT 703, step correction values for steps having different values are determined through experiments and stored in advance.

  On the other hand, if the information stored in the RAM 302 indicates that the step correction is not necessary, the process proceeds to step S1105. In step S1105, the CPU 300 sets the step correction circuit 701 so that the input image data is output as it is without performing step correction. This is called through setting. The through setting is a setting for not performing luminance conversion processing on image data. Therefore, compared with the case where the level difference correction circuit 701 is set to be effective, the read image can be reproduced without deteriorating. In the present embodiment, the first LUT 702 and the second LUT 703 included in the level difference correction circuit 701 are set to through, but a switch and a detour are provided for bypassing the image signal so that the image signal does not pass through these LUTs. Also good.

  In step S1106, the CPU 300 activates the image sensor unit 208. The CPU 300 sends a command to the line sensor driving circuit 305 so that the image sensor unit 208 starts outputting an image. Further, the CPU 300 sends a command for turning on the lamp 203 to the lamp driving circuit 304.

  In step S1107, the CPU 300 waits until the light amount of the lamp 203 and the output from the image sensor unit 208 are stabilized. When the output is stabilized, the process proceeds to step S1108. In step S1108, the CPU 300 uses the line sensor 404 to read a document conveyed from the ADF 100 or a document on the book platen glass 202 as a monochrome image.

  In step S <b> 1109, the CPU 300 determines whether there is an original document remaining on the original document tray 20 of the ADF 100. If it is determined that the document remains, the process returns to step S1108, and the CPU 300 reads the next document again. If no document remains, CPU 300 ends the reading process.

  As described above, according to the present embodiment, the S / N ratio is improved while reducing the step of the output level generated in the plurality of line sensors that respectively read the plurality of areas obtained by dividing one line of the document. It becomes possible to make it. In particular, if the maximum value (N) of the output level of the line sensor determined by the second determination means exceeds the lower limit target level (Y) without adjusting the output level in steps S817 to S825, the level difference The correction circuit 701 does not perform step reduction. In general, when the step is reduced, the S / N ratio may be deteriorated. Therefore, by executing the level difference correction only when necessary, it is possible to improve the S / N ratio while reducing the level difference of the output level.

  In particular, the CPU 300 determines whether the first half area 510 and the second half area 520 have a maximum value (M) of the maximum value MA of the first half area 510 and the maximum value MB of the second half area 520 reaches the upper limit target level X. Increase each output gain by one step. Thereby, each S / N ratio of the first half area 510 and the second half area 520 is improved.

  In the present embodiment, the monochrome line sensor for reading a monochrome image has been described. However, it goes without saying that the technical idea of the present invention can be applied to a line sensor for reading a color image when the area is divided.

  In general, color image reading and black-and-white image reading are performed alternatively. Therefore, by providing an image signal selector, the first analog processor 610 and the second analog processor 620 can be shared for reading color images and reading monochrome images. As a result, the manufacturing cost and the circuit scale can be reduced.

  In particular, in the present embodiment, a plurality of point light sources are arranged more at the end than at the center in the main scanning direction. Further, the light from the original is imaged on the line sensor by using imaging means such as a lens. In the image reading apparatus adopting such a configuration, the step is likely to be prominent, and thus it is worth applying the present invention.

1 is a schematic cross-sectional view of an image reading apparatus according to an embodiment. 2 is a block diagram showing a control unit for controlling the ADF 100 and a reader unit 200. FIG. It is the figure which showed 4 line image sensor. It is a figure for demonstrating the shift register provided only in the line sensor 404 for monochrome. 4 is a diagram for explaining an analog processor 306. FIG. It is a figure for demonstrating operation | movement of the image processing circuit 307 contained in image control ASIC303. It is the flowchart which showed the gain adjustment and level | step difference correction which concern on embodiment. It is the figure which showed the luminance distribution of 1 line acquired by the line sensor 404 for black-and-white when the smaller maximum value N is larger than the target level Y of a minimum. It is the figure which showed the luminance distribution of 1 line acquired by the line sensor 404 for black-and-white when the smaller maximum value N is not larger than the target level Y of a minimum. It is the figure which showed the luminance distribution of 1 line acquired by the line sensor 404 for black-and-white when a level | step difference exists. It is the flowchart which showed the monochrome image reading process. It is a figure for demonstrating the luminance distribution in a linear light source, and a connection level | step difference. It is a figure for demonstrating the luminance distribution in a LED light source, and a connection level | step difference. It is a figure for demonstrating gain adjustment and level | step difference correction in related technology.

Claims (12)

An image reading device,
A plurality of line sensors that respectively read a plurality of areas obtained by dividing one line of a document;
First determining means for determining a maximum value of an output level in each of the plurality of line sensors and determining a line sensor that outputs an image signal at the output level of the maximum value;
First gain adjusting means for increasing the output gain of the plurality of line sensors until the maximum value of the output level of the line sensor determined by the first determining means reaches a predetermined upper limit target level;
After the output gain adjustment by the first gain adjusting means is completed, the maximum value of the output level is determined in each of the plurality of line sensors, and the smallest maximum of the maximum values of the plurality of line sensors is determined. Second determining means for determining a line sensor that outputs an image signal at a value output level;
Determination means for determining whether or not the maximum value of the output level of the line sensor determined by the second determination means exceeds a predetermined lower limit target level;
If the maximum value of the output level of the line sensor determined by the second determination means does not exceed the lower limit target level, the determined maximum value of the output level of the line sensor exceeds the lower limit target level. Second gain adjusting means for increasing the output gain of the determined line sensor until
A step reducing means for reducing a step of the output level at the boundary of the plurality of line sensors after the adjustment of the output level by the second gain adjusting means is completed;
If the maximum value of the output level of the line sensor determined by the second determination unit exceeds the lower limit target level without adjusting the output level by the second gain adjustment unit, the step difference reduction unit An image reading apparatus, wherein the step reduction is not executed.   The first gain adjusting means sets the output gains of the plurality of line sensors to one level until the maximum value of the output level of the line sensor determined by the first determining means reaches a predetermined upper limit target level. The image reading apparatus according to claim 1, wherein the image reading apparatus increases each time.   The image reading apparatus according to claim 1, wherein the plurality of line sensors are a plurality of monochrome line sensors for reading a monochrome image. A plurality of color line sensors for reading color images;
A selection means for alternatively selecting image signals from a plurality of line sensors for reading the monochrome image and image signals from the plurality of color line sensors;
The image reading apparatus according to claim 3, further comprising: a plurality of image processing circuits that perform image processing on the image signal selected by the selection unit. The plurality of color line sensors include a color line sensor for red, a color line sensor for blue, and a color line sensor for green,
The first image processing circuit of the plurality of image processing circuits alternatively performs image processing on the image signal from the red color line sensor and the image signal from the first black and white line sensor. ,
Of the plurality of image processing circuits, a second image processing circuit alternatively performs image processing on the image signal from the green color line sensor and the image signal from the second monochrome line sensor. ,
The image reading apparatus according to claim 4, wherein a third image processing circuit among the plurality of image processing circuits performs image processing on an image signal from the blue color line sensor.   4. The image reading apparatus according to claim 1, wherein the plurality of line sensors are configured by dividing a single linear image sensor into a plurality of parts. 5. It further comprises a plurality of point light sources arranged unevenly in the main scanning direction,
The image reading apparatus according to claim 1, wherein a plurality of the point light sources are arranged at an end portion rather than a central portion in the main scanning direction.   The image reading apparatus according to claim 1, further comprising a lens configured to form an image of light from the original on the line sensor. An image reading device,
A first line sensor for reading a first area formed by dividing one line of a document;
A second line sensor for reading the remaining second area obtained by dividing one line of the original;
A first determination means for comparing a maximum value of the output level of the first line sensor with a maximum value of the output level of the second line sensor and determining a line sensor corresponding to a larger maximum value;
The output gain of the first line sensor and the output gain of the second line sensor until the maximum value of the output level of the line sensor determined by the first determination means reaches a predetermined upper limit target level. First gain adjusting means for increasing
After the adjustment of the output gain by the first gain adjusting means is completed, the maximum value of the output level of the first line sensor and the maximum value of the output level of the second line sensor are compared again, and the smaller Second determining means for determining a maximum value of
Determining means for determining whether the smaller maximum value exceeds a predetermined lower target level; and
If the smaller maximum value does not exceed the lower target level, the line corresponding to the lower maximum value until the smaller maximum value exceeds the lower target level. Second gain adjusting means for increasing the output gain of the sensor;
Level difference reducing means for reducing the level difference between the output levels of the two elements located at the boundary between the first line sensor and the second line sensor after the output level adjustment by the second gain adjusting means is completed. And
Even if the output level is not adjusted by the second gain adjusting means, if the smaller maximum value exceeds the lower limit target level, the step reduction by the step reducing means is not executed. An image reading apparatus. An image reading device,
A plurality of line sensors that respectively read a plurality of areas obtained by dividing one line of a document;
A plurality of amplifying means provided corresponding to the plurality of line sensors and amplifying image signals from the plurality of line sensors;
First gain adjusting means for adjusting a common output gain in the plurality of amplifying means so that the maximum value of the output level of any of the plurality of line sensors exceeds a predetermined upper limit target level;
After the output gain is adjusted by the first gain adjusting means, if the maximum value of the output level of any of the plurality of line sensors is below a predetermined lower limit target level, the maximum output level of the line sensor Second gain adjusting means for adjusting an output gain of the amplifying means corresponding to the line sensor so that a value exceeds the lower limit target level;
An image reading apparatus comprising: a step reducing unit that reduces a step of an output level at a boundary between the plurality of line sensors when an output gain is adjusted by the second gain adjusting unit.   The step reduction means does not reduce the step when the maximum value of the output level of the plurality of line sensors exceeds the lower limit target level after the output gain is adjusted by the first gain adjustment means. The image reading apparatus according to claim 10. An image forming system,
An image reading device according to any one of claims 1 to 11,
An image forming system comprising: an image forming apparatus that forms an image read by the image reading apparatus on a recording medium.

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