JP2010021727A - Image reading device and control method thereof - Google Patents

Abstract

An image reading apparatus and a control method therefor are provided that can realize a reduction in size and cost of a reading unit for reading a document, and that appropriately correct a color shift in a sub-scanning direction.
A correction coefficient corresponding to a main scanning position of a pixel of interest in an image reading apparatus that reads a document using a plurality of off-axial reflecting surfaces having different incidence directions and emission directions of a reference axis ray and having a curvature. And the image data are used to correct a color shift in the sub-scanning direction with respect to the target pixel. If the correction coefficient corresponding to the main scanning position of the target pixel is not stored in advance, color misregistration correction is executed by linear interpolation.
[Selection] Figure 6

Description

  The present invention relates to an image reading apparatus such as a copying machine that optically reads a document and a control method thereof.

  Image reading apparatuses such as copying machines, facsimile machines, and image scanners are provided with a so-called reduction optical system reading apparatus for reading a document. Such a reduction optical system reading apparatus forms an image of reflected light obtained when scanning a document surface in a scanning optical system including an exposure lamp and a folding mirror on a photoelectric conversion element via a lens, and outputs an electric signal. Convert to

However, in a reading device using a reduction optical system and a CCD line sensor, if the angle of view of the lens is widened, the image distortion off-axis becomes remarkable, so it is necessary to take a long optical path. Was getting bigger. Therefore, in Patent Document 1, as an optical system of a reading unit that meets demands for cost reduction and miniaturization, the imaging optical system has a plurality of off-states in which the incident direction and the reflection direction of the reference axis light beam are different and have a curvature. An image reading apparatus using an imaging optical element including an axial reflection surface has been proposed.
JP 2002-335375 A

  However, the conventional techniques have the following problems. For example, in a conventional reduction optical system, the amount of color misregistration in the sub-scanning direction is substantially uniform with respect to the main scanning position, and the color misregistration in the sub-scanning direction is corrected by correcting the main scanning position with a constant value. It was solved. However, in an image reading apparatus using an off-axial optical system as described in Patent Document 1, a read image may be distorted due to a dimensional error that occurs during the manufacturing process of the off-axial reflecting surface. In particular, when this distortion occurs as a color misregistration in the sub-scanning direction, it varies depending on the main scanning position. Therefore, the conventional correction method using a uniform correction value at the main scanning position is sufficient to correct the color misregistration in the sub-scanning direction. The effect of was not obtained. For this reason, the location where sufficient color misregistration correction cannot be performed has been a factor of erroneously determining the color / monochrome determination of a document or black characters and color characters.

  The present invention has been made in view of the above-described problems, and achieves downsizing and cost reduction of a reading unit for reading a document, and also appropriately corrects color misregistration in the sub-scanning direction. And it aims at providing the control method.

  The present invention can be realized, for example, as an image reading apparatus including a reading unit that reads a document using a plurality of off-axial reflecting surfaces having different curvatures of the incident direction and the emitting direction of the reference axis light beam. The image reading apparatus includes a storage unit that stores correction coefficients for correcting color misregistration in the sub-scanning direction in the image data read by the reading unit for each of a plurality of main scanning positions in the main scanning direction, and color misregistration correction. Corresponding to the main scanning position of the target pixel, holding means for holding image data read in the main scanning line that is different by one line in the sub-scanning direction in the sub-scanning direction with respect to the main scanning line including the target pixel of interest. Color misregistration correcting means for correcting color misregistration in the sub-scanning direction with respect to the pixel of interest using the correction coefficient stored in the storage means and the image data held in the holding means.

  In addition, the present invention is realized as a control method for an image reading apparatus including a reading unit that reads a document using a plurality of off-axial reflecting surfaces having different curvatures, for example, the incident direction and the emitting direction of the reference axis light beam. it can. The control method includes a correction coefficient for correcting color misregistration in the sub-scanning direction in the image data read by the reading unit, corresponding to the main scanning position of the target pixel to be corrected for color misregistration, and the target pixel. And a step of correcting a color shift in the sub-scanning direction with respect to the pixel of interest using image data read in the main scanning line which is different from the main scanning line by one line before and after in the sub-scanning direction. .

  The present invention can provide, for example, an image reading apparatus that can reduce the size and cost of a reading unit for reading a document, and that appropriately corrects color misregistration in the sub-scanning direction, and a control method therefor.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as superordinate concepts, intermediate concepts and subordinate concepts 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.

  Hereinafter, the present embodiment will be described with reference to FIGS. 1 to 7. FIG. 1 is a cross-sectional view illustrating an example of a reading device of an image reading device according to the present embodiment. Reference numeral 101 denotes a reading device for reading a document according to the present embodiment.

  The reading apparatus 101 includes a reading unit 102, a guide shaft 103, a frame body 117, and a document table glass 118. The reading unit 102 includes a light source 104, reflection mirrors 105, 106, and 107, an imaging unit 113, a CCD line sensor 114, a signal processing board 115, and a coupling member 116 in order to scan an image of a document. Further, the imaging unit 113 includes imaging mirrors 108, 109, 110, 111 and a mirror holding member 112.

  The guide shaft 103 guides the reading unit 102 when the reading unit 102 scans in the left-right direction in FIG. The light source 104 is an example of an illumination unit for illuminating a document. The reflection mirrors 105, 106, and 107 guide the light diffused by the document surface to the imaging unit 113.

  The imaging mirrors 108, 109, 110, and 111 image the light guided by the reflection mirrors 105, 106, and 107. The imaging mirrors 108 to 111 according to the present embodiment include off-axial reflecting surfaces having different curvatures in the incident direction and the emitting direction of the reference axis light beam. The mirror holding member 112 holds the imaging mirrors 108 to 111 at a predetermined relative position.

  The CCD line sensor 114 photoelectrically converts the light imaged by the imaging unit 113. The signal processing board 115 drives the CCD line sensor 114 and processes a signal output from the CCD line sensor 114. The coupling member 116 couples the CCD line sensor 114 and the signal processing board 115 to the frame body 117 of the reading apparatus 101. The document table glass 118 is a table for placing a document. The pressure plate 119 pushes the document onto the document table glass 118. The reading unit 102 moves and scans the image of the document placed on the platen glass 118.

  When reading a document image, the light source 104 illuminates the document, and the light diffused on the document surface is guided to the imaging mirrors 108 to 111 by the reflection mirrors 105, 106, and 107 and imaged on the CCD line sensor 114. . The CCD line sensor 114 photoelectrically converts the imaged light and processes the obtained electric signal by the signal processing board 115. By these processes, the image of the document is read as an electrical signal.

  Next, a control configuration of the reading apparatus 101 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a control configuration of the reading apparatus 101 according to the present embodiment. Here, the control block related to the present invention will be mainly described. Therefore, the reading apparatus 101 may be configured to include other control blocks.

  The image reading apparatus according to the present embodiment includes an analog processing circuit 201, an AD converter 202, a shading circuit 203, a color misregistration correction unit 204, a timing generation circuit 205, an EEPROM 206, a CPU 207, and a line memory 208 as control configurations. Each control block is connected by a signal line.

  The CCD line sensor signal output from the CCD line sensor 114 is sent to the subsequent stage through an emitter follower circuit (not shown) for impedance conversion. The analog processing circuit 201 samples an output signal from the CCD line sensor 114 by a technique such as CDS, and performs offset adjustment, gain adjustment, and the like on the sampled data. The AD converter 202 converts the output signal from the analog processing circuit 201 into digital data.

  The shading circuit 203 performs white shading correction for correcting the sensitivity variation for each pixel of the CCD line sensor 114 and the edge light amount drop, and black shading correction for correcting the black level (dark portion) variation. In addition, the shading circuit includes a memory that holds white shading coefficients and black shading coefficients, and a memory for averaging multiple lines when white shading coefficients and black shading coefficients are calculated.

  The line memory 208 holds image data for two lines, and can hold image data for two lines for each color of RGB. Specifically, the line memory 208 holds image data read in a main scanning line that is different by one line in the sub-scanning direction with respect to the main scanning line including the target pixel that is a color misregistration correction target. The EEPROM 206 stores processing parameters of the color misregistration correction unit 204 and the like. The color misregistration correction unit 204 performs color misregistration correction using the input image data and the image data held in the line memory 208. Details of the color misregistration correction will be described later.

  The CPU 207 comprehensively controls image processing, and instructs each control block to set the operation mode of each block, read / write of the EEPROM 206, processing timing, and the like. The timing generation circuit 205 generates an operation signal for each block. Each block operates in synchronization with a signal output from the timing generation circuit 205.

  Next, setting information stored in the EEPROM 206 will be described with reference to FIG. FIG. 3 is a diagram showing parameters for color misregistration correction stored in the EEPROM 206 according to the present embodiment.

  Reference numeral 301 shown in FIG. 3 indicates information on six main scanning positions. Reference numeral 302 denotes a RED color misregistration correction coefficient set corresponding to each main scanning position. Reference numeral 303 denotes a BLUE color misregistration correction coefficient set corresponding to each main scanning position. These pieces of information are stored in advance in association with the EEPROM 206. The correction coefficient set includes three values and is a coefficient used for the correction calculation. Details of the coefficient will be described later.

  Here, the reason why the correction coefficients are prepared for the six main scanning positions is to correct color shifts that differ at the main scanning positions according to the main scanning positions. In each coefficient set, a correction coefficient set corresponding to the amount of color misregistration in the sub-scanning direction of the reading unit is set in advance. As these setting values, a predetermined chart is read at the time of factory shipment, and a correction value calculated based on the result is written. In addition, after shipment, a service person may input the correction value added to the reading unit using the operation panel.

  As shown in FIG. 3, no correction coefficient for the G signal is prepared. This is because the processing is not performed using the G signal as a reference, but the color shift of the R signal and the B signal is corrected to match the RGB sub-scanning positions. However, it is not necessary to limit the reference signal to the G signal, and other colors may be used.

  Further, when processing is performed only on the R signal and the B signal, the G signal sub-scanning MTF (Modulated Transfer Function) increases with respect to the R signal and the B signal, and the RGB balance of the sub-scanning MTF increases. There is. In this case, it is desirable to adjust the RGB balance of the sub-scanning MTF by setting the set values of the correction factors A1, A2, and A3 for the G signal so as to lower the MTF.

  Next, the operation of the color misregistration correction unit 204 will be described with reference to FIG. FIG. 4 is a diagram showing image data for three lines. As shown in FIG. 4, the color misregistration correction in the color misregistration correction unit 204 uses image data for three sub-scanning lines. Reference numeral 401 denotes image data of the (n-1) th line. Reference numeral 402 denotes image data of the nth line. Reference numeral 403 denotes image data on the (n + 1) th line.

Image data 401 and 402 are image data held in the line memory 208, and image data 403 is current read image data input to the color misregistration correction unit 204. The color misregistration correction unit 204 generates an output signal Yn from the following formula using the pixel values Xn−1 and Xn + 1 of one line before and after the target pixel position Xn in the main scanning.
Yn = {A1 * (Xn-1) + A2 * Xn + A3 * (Xn + 1)} / 128 (Formula 1)
Here, A1, A2, and A3 are the three correction coefficients held in the EEPROM 206 as described above, and are registered in the color misregistration correction unit 204 by the CPU 207. The color misregistration correction amount can be changed by changing the values of the correction coefficients A1, A2, and A3. The correction coefficients A1, A2, and A3 can be set to values from 0 to 128, and are set so that the total of the set values is 128. Expression 1 is performed independently for each of the RGB colors, and a calculation unit for realizing the above calculation is prepared for each of the RGB colors.

  Next, the color misregistration amount and the correction coefficient will be described with reference to FIG. FIG. 5 is a diagram showing the relationship between the actual color misregistration amount and the correction coefficient setting value according to the present embodiment. The horizontal axis indicates the main scanning position, and the vertical axis indicates the color misregistration amount.

  A solid line 501 indicates the actual color misregistration amount, and a white circle (◯) indicates the color misregistration correction amount corresponding to each main scanning position set in FIG. FIG. 5 shows only one color of image data, and the same applies to signals of other colors.

  A dotted line 502 indicates a color shift amount to be corrected. The color misregistration correction amount between the main scanning positions where the color misregistration correction amount is set, that is, between the white circle and the white circle, is generated by linear interpolation using the calculation result in the correction coefficient set set by the white circle. As described above, by linearly interpolating the color misregistration correction amount, the color misregistration correction can be performed smoothly while reducing the memory consumption, and a read image with higher accuracy can be obtained.

  Next, the details of the color misregistration correction unit 204 will be described with reference to FIG. FIG. 6 is a block diagram illustrating a configuration example of the color misregistration correction unit 204 according to the present embodiment. Here, an example of correcting the RED signal among the RGB signals will be described. However, the correction method for other signals is the same as the method described below.

  The color misregistration correction unit 204 includes a counter 601, a coefficient selection unit 602, a first correction unit 603, a second correction unit 604, and a linear interpolation unit 606. The counter 601 performs a counting operation based on the pixel clock signal generated from the clock signal of the timing generation circuit 205.

  In the coefficient selection unit 602, a correction coefficient set held in the EEPROM 206 and a main scanning position corresponding to the correction coefficient set are set. When the coefficient selection unit 602 receives the output of the counter 601 and the set main scanning position matches the counter value, the coefficient selection unit 602 gives the corresponding color to the first correction unit 603 and the second correction unit 604 in the subsequent stage. Select the deviation correction coefficient and output it. For example, when the counter value of the counter 601 reaches 1500, the coefficient selection unit 602 outputs the correction coefficient set R2 to the first correction unit 603 and outputs the correction coefficient set R3 to the second correction unit 604. To do.

  A correction coefficient is input to the first correction unit 603 and the second correction unit 604 by the coefficient selection unit 602. Further, the first correction unit 603 and the second correction unit 604 are input with the image data for three lines of the image data for two lines from the line memory 208 and the image data input by the color misregistration correction unit 204. Is done. Using the input information, the first correction unit 603 and the second correction unit 604 perform the correction calculation of Expression 1.

  Thereafter, the calculated values of the first correction unit 603 and the second correction unit 604 are input to the subsequent linear interpolation unit 606. The linear interpolation unit 606 uses the output value of the counter 601 and the main scanning position data held in the coefficient selection unit 602 to perform linear interpolation on the calculated values of the first correction unit 603 and the second correction unit 604. Execute and output the final color misregistration correction value.

  Here, the linear interpolation calculation will be described. For example, when the 1900th pixel indicated by the arrow in FIG. 5 is corrected, first, the first correcting unit 603 corrects the 1900th pixel image data with the correction coefficient set R2 set at the main scanning position 1500 pixels. . Similarly, the second correction unit 604 corrects and calculates the image data of the 1900th pixel with the correction coefficient set R3 set at the main scanning position of 2900 pixels.

  The calculation outputs of the first correction unit 603 and the second correction unit 604 are output to the linear interpolation unit 606, where linear interpolation calculation is performed. The output of the first correction unit 603 is multiplied by 1000 which is a difference (first difference) between the main scanning position 2900 of the correction coefficient set R3 and the main scanning position 1900 to be corrected. On the other hand, the output of the second correction unit 604 is multiplied by 400, which is a difference (second difference) between the main scanning position 1500 of the correction coefficient set R2 and the main scanning position 1900 to be corrected. Further, the linear interpolation unit 606 adds two values (the first multiplication result and the second multiplication result), and uses the addition result between the main scanning position of the correction coefficient set R2 and the main scanning position of the correction coefficient set R3. Divide by 1400 which is the difference and output.

  Thus, for the main scanning position for which no correction coefficient is set, correction calculation is performed using correction coefficient sets set before and after the target main scanning position. Thereafter, linear interpolation is performed on the calculation result based on the difference between the main scanning position where the correction coefficient set is set and the main scanning position to be corrected. Thereby, color misregistration correction is performed, color misregistration correction is performed smoothly in each area in the main scanning direction, and uniform color misregistration correction is realized in all areas in the main scanning direction.

  Next, a control flow of the color misregistration correction unit 204 will be described with reference to FIG. FIG. 7 is a flowchart showing a processing procedure of color misregistration correction according to the present embodiment. In the process described below, the color misregistration correction process for one image signal is described for each RGB image signal.

  First, in step S <b> 701, the color misregistration correction unit 204 determines whether a correction coefficient corresponding to the main scanning position of the target pixel is stored in the EEPROM 206. If it is stored, the process proceeds to step S702. If it is not stored, the process proceeds to step S704. Specifically, the color misregistration correction unit 204 searches for the value of the main scanning position 301 shown in FIG. 3 using the value indicating the main scanning position as a search keyword. If there is a value corresponding to the main scanning position 301, it is determined that a correction coefficient corresponding to the main scanning position of the target pixel is stored in the EEPROM 206.

  In step S <b> 702, the color misregistration correction unit 204 obtains the correction coefficient corresponding to the main scanning position of the target pixel stored in the EEPROM 206 and the image data corresponding to the main scanning position of the target pixel held in the line memory 208. get. Thereafter, in step S703, the color misregistration correction unit 204 corrects the color misregistration in the sub-scanning direction at the target pixel using the acquired data.

  On the other hand, in step S704, the color misregistration correction unit 204 corresponds to two correction coefficients different from the main scanning position of the target pixel stored in the EEPROM and the main scanning position of the target pixel held in the line memory 208. Image data to be acquired. Here, one of the two correction coefficients is a correction coefficient (first correction coefficient) corresponding to the main scanning position stored in the EEPROM 206 that is smaller than the value indicating the main scanning position of the target pixel and is the closest value. It becomes. The other is a correction coefficient (second correction coefficient) corresponding to the main scanning position stored in the EEPROM 206 that is larger than and closest to the value indicating the main scanning position of the target pixel.

  Next, in step S705, the color misregistration correction unit 204 performs color misregistration correction for each of the two correction coefficients by the first correction unit 603 and the second correction unit 604. Subsequently, in step S706, the color misregistration correction unit 204 performs color misregistration correction on the target pixel by linearly interpolating the correction results of the first correction unit 603 and the second correction unit 604 with the linear interpolation unit 606. finish.

  As described above, the image reading apparatus according to the present embodiment corrects the color shift in the sub-scanning direction with respect to the target pixel using the correction coefficient corresponding to the main scanning position of the target pixel and the image data. As a result, even in a reading apparatus that reads a document using a plurality of off-axial reflecting surfaces having different incidence directions and emission directions of the reference axis light beam, the optimum correction coefficient for each main scanning position is used. Color misregistration correction can be performed. Therefore, the present image reading apparatus can employ a reading unit using a plurality of off-axial reflecting surfaces that is advantageous for miniaturization / cost reduction without degrading the quality of the read image.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, when the image reading apparatus does not hold a correction coefficient corresponding to the main scanning position of the target pixel, linear interpolation is performed using a correction coefficient corresponding to another main scanning position different from the main scanning position. Thus, the color shift of the target pixel may be corrected. As a result, the image reading apparatus need not store correction coefficients corresponding to the entire area of the main scanning position, and need only store a number of correction coefficients that can realize sufficient color misregistration correction by linear interpolation in advance. Therefore, this image reading apparatus can reduce the memory consumption related to the color misregistration correction.

  In addition, the image reading apparatus may perform color misregistration correction processing only on the B (Blue) signal and the R (Red) signal with respect to the read image data, for example, based on the G (Green) signal. As a result, the image reading apparatus can minimize the decrease in the sub-scanning MTF due to the color shift in the sub-scanning direction.

It is sectional drawing which shows an example of the reading apparatus of the image reading apparatus which concerns on this embodiment. It is a block diagram which shows the control structure of the reader 101 which concerns on this embodiment. It is a figure which shows the parameter for color misregistration correction | amendment stored in EEPROM206 which concerns on this embodiment. It is a figure which shows the image data for 3 lines. It is a figure which shows the relationship between the actual color shift amount and correction coefficient setting value which concern on this embodiment. It is a block diagram which shows the structural example of the color shift correction | amendment part 204 which concerns on this embodiment. It is a flowchart which shows the process sequence of the color misregistration correction which concerns on this embodiment.

Explanation of symbols

101: Reading device 102: Reading unit 103: Guide shaft 104: Light sources 105, 106, 107: Reflecting mirrors 108, 109, 110, 111: Imaging mirror 112: Mirror holding member 113: Imaging unit 114: CCD line sensor 115 : Signal processing board 116: coupling member 117: frame 118: platen glass

Claims (5)

An image reading apparatus comprising reading means for reading a document using a plurality of off-axial reflecting surfaces having different curvatures of the incident direction and the emitting direction of the reference axis ray,
Storage means for storing a correction coefficient for correcting color misregistration in the sub-scanning direction in the image data read by the reading means for each of a plurality of main scanning positions in the main scanning direction;
Holding means for holding image data read in different main scanning lines by one line before and after in the sub-scanning direction with respect to the main scanning line including the target pixel to be corrected for color misregistration;
A color shift that corrects a color shift in the sub-scanning direction with respect to the target pixel using the correction coefficient stored in the storage unit and the image data stored in the holding unit, corresponding to the main scanning position of the target pixel. An image reading apparatus comprising: a correction unit.   When a correction coefficient corresponding to the main scanning position of the target pixel is not stored in the storage unit, linear interpolation is performed using a correction coefficient corresponding to another main scanning position different from the main scanning position, The image reading apparatus according to claim 1, further comprising an interpolation unit that corrects a color shift of the target pixel. A first correction coefficient corresponding to the main scanning position stored in the storage means that is smaller than the value indicating the main scanning position of the target pixel and that is the closest value is used to correct color misregistration in the sub-scanning direction. 1 correction means;
A color correction in the sub-scanning direction is corrected using a second correction coefficient corresponding to the main scanning position stored in the storage unit that is larger than and closest to the value indicating the main scanning position of the target pixel. 2 correction means,
The interpolation means includes
A first multiplication result obtained by multiplying a correction result of the first correction unit by a first difference which is a difference between a value indicating the main scanning position of the target pixel and a value indicating the main scanning position of the first correction coefficient. And a second result obtained by multiplying the correction result of the second correction unit by a second difference that is a difference between a value indicating the main scanning position of the target pixel and a value indicating the main scanning position of the second correction coefficient. The image according to claim 2, wherein linear interpolation is performed by adding a multiplication result and dividing the addition result by a value obtained by adding the first difference and the second difference. Reader.   The correction coefficient does not include a correction coefficient for one color with respect to the read image data, and includes only a correction coefficient for each color for correcting the image data of another color. The image reading apparatus according to any one of claims 1 to 3. A control method for an image reading apparatus including a reading unit that reads a document using a plurality of off-axial reflecting surfaces having different curvatures of an incident direction and an exit direction of a reference axis ray, and having a curvature,
A correction coefficient for correcting color misregistration in the sub-scanning direction in the image data read by the reading unit corresponding to the main scanning position of the target pixel to be corrected for color misregistration, and main scanning including the target pixel An image including a step of correcting a color shift in the sub-scanning direction with respect to the target pixel by using image data read in a main scanning line which is different by one line before and after the line in the sub-scanning direction. A method for controlling a reader.

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