JP2005269189A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus with an inexpensive configuration for reading color image information and monochromatic information without causing image deterioration. <P>SOLUTION: The image reading apparatus 10 is provided with: a light source 13a for emitting white light to an original; an image forming lens 15 for receiving light reflected in the original and forming an image of the reflected light to obtain an optical image; a photoelectric conversion section (photoelectric conversion element) 16 for applying photoelectric conversion to the optical image to obtain image data, and the photoelectric conversion section includes color image read sensor sections (line sensors) 16a to 16c and a monochromatic image read sensor section (line sensor) 16d. A BPF 18 is inserted onto an optical path 17 at a pre-stage of the photoelectric conversion section in a monochromatic image read mode to provide only a particular wavelength component in the reflected light to the photoelectric conversion section. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus that is used in an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and that reads an image by irradiating an object to be read such as an original with light.

  In general, in an image reading apparatus capable of reading a color image (hereinafter referred to as a color image reading apparatus), a white light source having a uniform irradiation spectrum distribution in a visible light range is used as a light source, and each line sensor is used as an image sensor. A so-called three-line image sensor is used on which a filter having sensitivity distributions for the three primary colors of red (R), green (G), and blue (B) is used, and can be read accurately with a single scan. Like to do.

  In such a three-line image sensor, for example, when a monochrome document is read and monochrome image data is output, one color of R, G, B color image data is substituted for the monochrome image data. In this case, only a part of the spectral component of the white light source is used by the filter formed in the three-line image sensor 5, and the light emission of the light source The sensitivity and the S / N ratio are reduced as compared with a monochrome image read-only scanner using a green light source having the highest efficiency and conversion efficiency of the image sensor.

  For this reason, an image sensor to which a monochrome image reading line is added is known. For example, an R line sensor, a G line sensor 27G, and a B line sensor in which color separation filters having different wavelength selectivity are formed on the image sensor. And a monochrome line sensor in which no color separation filter is formed, color image information is read from the original by the R line sensor, G line sensor, and B line sensor, and at the same time, monochrome image information is read by the monochrome line sensor. (See Patent Document 1).

  Here, in addition to the first light receiving element array in which the light receiving portion of the image sensor is provided with color separation filters for three lines of R, G, and B, the second light reception in which no color separation filter is formed. Each color image information is read by the first light receiving element array from the reflected light of the specific spectral component having the element array and selected by the color separation filter, and the second light is reflected from the reflected light of all the spectral components of the light source. Monochrome image information is read by the light receiving element array.

Japanese Patent Laid-Open No. 2001-144900 (pages 8 to 12, FIGS. 1 to 9)

  By the way, in the conventional image reading apparatus, the second light receiving element array that is a monochrome image reading line has sensitivity to all wavelengths of RGB, that is, receives light of all wavelengths of the white light source. The resolution (MTF performance) deteriorates due to the influence of chromatic aberration in the imaging lens.

  In particular, in an imaging lens having a large chromatic aberration of magnification, which is one of the chromatic aberrations of the imaging lens, the MTF performance is greatly deteriorated, and when the second light receiving element array reads monochrome image information, image degradation occurs. There is a problem of doing it.

  In addition, when correcting the chromatic aberration of the imaging lens, many parameters such as the number of lens materials constituting the imaging lens, their types, and combinations must be taken into account. If the number of pixels is set to about 3 pixels, the number of lens materials constituting the imaging lens has to be increased, resulting in an increase in cost.

  SUMMARY OF THE INVENTION Accordingly, in view of the problems of the prior art, the present invention has an object to provide an image reading apparatus capable of reading color image information with an inexpensive configuration and reading monochrome image information without causing image deterioration. And

  Accordingly, in order to solve the above problems, the present invention is used when reading an image on an object to be read to obtain image data, and a light source for irradiating the object to be read with white light, and the object to be read An imaging lens body that receives reflected light from a body and forms an image of the reflected light to form an optical image; and a photoelectric conversion unit that photoelectrically converts the optical image to obtain the image data, and the photoelectric conversion unit Is an image reading device having a color image reading sensor unit and a monochrome image reading sensor unit, which is selectively inserted on an optical path in front of the photoelectric conversion unit and includes only a specific wavelength component of the reflected light. And a filter unit that allows passage and a control unit that inserts the filter unit on the optical path in the monochrome image reading mode.

  In the present invention, it is desirable that the filter means is selectively inserted on an optical path in front of the imaging lens body.

  In the present invention, the control means receives a mode selection signal indicating whether it is a color image reading mode or a monochrome image reading mode, and if the mode selection signal is a mode different from the previous reading mode, the mode selection signal The image data is obtained by performing gain control according to the indicated reading mode.

  In the present invention, the color image reading sensor unit is formed with color separation filters for the three primary colors of red, green, and blue, and the monochrome image reading sensor unit is not formed with a color separation filter. The means cuts a component having a longer wavelength than the component corresponding to the green wavelength from the reflected light, and allows only the specific wavelength component to pass.

  In the present invention, the control means selects the output of the color image reading sensor unit in the color image reading mode, and selects the output of the monochrome image reading sensor unit in the monochrome image reading mode. To.

  As described above, in the image reading apparatus of the present invention, the filter unit is selectively inserted on the optical path upstream of the photoelectric conversion unit, and the filter unit allows only a specific wavelength component of the reflected light to pass. In addition, since the filter means is inserted on the optical path in the monochrome image reading mode, only a specific wavelength component is given to the photoelectric conversion unit via the imaging lens body in the monochrome image reading mode. Thus, image degradation does not occur during monochrome image reading. In addition, since the filter means is removed during color image reading, color image reading can also be performed. Further, since it is only necessary to selectively insert the filter means on the optical path, it is not necessary to increase the accuracy of the imaging lens body, and the cost is rarely increased.

  In the present invention, since the filter means cuts a component having a wavelength longer than the component corresponding to the green wavelength from the reflected light, the light source that irradiates the green wavelength component as a light source in the monochrome image reading mode. As in the case of using this, there is an effect that image degradation at the time of monochrome image reading can be prevented with an inexpensive configuration.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  Referring to FIG. 1, the illustrated image reading apparatus 10 is used together with an image forming apparatus (not shown) such as a copying machine. The image reading apparatus 10 includes a transparent document placing table (contact glass) 11, and an image reading unit (image scanner unit (ISU)) 12 is disposed immediately below the contact glass 11.

  The image scanner unit 12 includes first and second scanner bodies 13 and 14, an imaging lens body 15, and a photoelectric conversion element (charge coupled element (CCD)) 16. The scanner body 13 includes a white light source (hereinafter simply referred to as a light source) 13a and a mirror 13b, and the second scanner body 14 includes mirrors 14a and 14b.

  When reading an image on a document, a document (not shown) is placed on the contact glass 11 with the image surface facing downward, and the light source 13a is moved along a shaft body (not shown) (that is, not shown). The light is emitted from the light source 13a. The light reflected by the image plane (reflected light) is sequentially reflected by the mirror 13 b and the mirrors 14 a and 14 b and is imaged on the CCD 16 by the imaging lens body 15. Then, the CCD 16 photoelectrically converts the reflected light, and the original image is read by the CCD 16 to obtain image data.

  When the light source 13a moves, the mirror 13b moves together with the light source 13a, and the mirrors 14a and 14b move in the same direction as the light source 13a at half speed. As a result, the length of the optical path 17 (optical path length) from the document to the CCD 16 is kept constant. In the example shown in the figure, a filter (bandpass filter (BPF)) 18 that is selectively inserted on the optical path 17 is provided upstream of the imaging lens body 15, and the operation of this BPF 18 will be described later. To do.

  As shown in FIG. 2, the CCD 16 has four line sensors 16a to 16d, and the line sensors 16a to 16c each have sensitivity distributions for the three primary colors of red (R), green (G), and blue (B). The line sensor 16d is not formed with a color separation filter. In the following description, the line sensors 16a to 16c are referred to as an R line sensor 16a, a G line sensor 16b, and a B line sensor 16c, respectively, and the line sensor 16d is referred to as a monochrome line sensor 16d.

  The image data output from the CCD 16 is converted into digital data by an image processing unit (not shown), and then, for example, for each color (for example, yellow, cyan, magenta, black) to a laser scanner unit (LSU: not shown). Then, laser light corresponding to each color image data is output from the LSU, and an image carrier such as a photosensitive drum for each color is exposed by the laser light to form an electrostatic latent image. Then, the electrostatic latent image is developed by a developing device (not shown) to form each color toner image on the image carrier.

  Thereafter, for example, each color toner image is sequentially transferred onto a recording sheet to form a color toner image on the recording sheet, the recording sheet is sent to a fixing unit (not shown), and the toner image on the recording sheet is fixed. , Eject the recording paper. In the case of a monochrome image, a toner image is formed on an image carrier corresponding to black and transferred onto a recording sheet.

  As shown in FIG. 3, the monochrome line sensor 16d receives light of all wavelengths of white light, which is reflected light of the light source 13a, because it has sensitivity to all wavelengths of RGB. Therefore, as described above, if the chromatic aberration of magnification is large in the imaging lens body 15, as shown in FIG. 4, if the chromatic aberration of magnification is 1 pixel or more on the monochrome line sensor 16d surface, the imaging performance is improved. It will drop greatly.

  In FIG. 4, the relationship between the original position and the chromatic aberration of magnification is shown for R, G, and B with G as a reference. The curve indicated by reference numeral L1 indicates RG, and the straight line indicated by reference numeral L2 indicates the straight line. G-G is shown, and the curve indicated by the symbol L3 shows BG.

  Now, the imaging performance of the imaging lens body 15 will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram showing the lens imaging performance when the light source 13a is a white light source, and FIG. It is a figure which shows the lens image formation performance in case the light source 13a is a G light source which radiates | emits only green (G) wavelength light. 5 and 6, the horizontal axis indicates defocus (the distance between the CCD 16 and the imaging lens body 15, and the minus direction is a predetermined distance between the CCD 16 and the imaging lens body 15 with zero as a reference (predetermined distance). And the plus direction represents a state in which the CCD 16 and the imaging lens body 15 are moved away from each other by a predetermined distance), the curve L4 indicates the imaging performance of the vertical line at the center of the image, and the curve L5 indicates The imaging performance of the horizontal line in the image end is shown. A curve L6 indicates the imaging performance of the vertical line at the image end.

  5 and 6, when the allowable CTF (%) is 30%, the G light source has a wider defocus than the white light source, and the distance accuracy between the CCD 16 and the imaging lens body 15 is higher. It turns out that there is no need to do. That is, in a white light source, good lens imaging performance cannot be obtained unless the distance between the CCD 16 and the imaging lens body 15 is set accurately.

  Therefore, when the white light source is used when the CCD 16 shown in FIG. 2 is used, the monochrome line sensor 16d may cause image deterioration in the monochrome image unless the lens imaging performance is good. Considering that the range is narrow, that is, considering that it is difficult to accurately define the distance between the CCD 16 and the imaging lens body 15, image deterioration in a monochrome image cannot be avoided.

  Therefore, in the first embodiment of the present invention, as described above, the BPF 18 is disposed in the front stage of the imaging lens body 15 and the BPF 18 is selectively inserted into the optical path 17. One end of the BPF 18 is supported by a shaft body 18a, and the shaft body 18a is rotationally driven by a drive source (not shown) such as a motor. The motor is controlled by a control device (not shown) as will be described later.

  The BPF 18 is a filter that blocks light on the R wavelength side (long wavelength side), and has, for example, a filter part formed in a film shape and a frame body that supports the filter part. The white light source has the spectral characteristics shown in FIG. 7. In FIG. 7, the portion indicated by reference numeral M1 corresponds to G, and the portions indicated by reference signs M2 and M3 correspond to B and R, respectively. The spectral transmission characteristics of the BPF 18 have, for example, the characteristics shown in FIG. 8, have a high transmittance for B to G, have a steep slope of the spectral transmission characteristics, and absorb the R side (long wavelength side light). As such a filter, for example, a color correction filter manufactured by ISUZU GLASS is known, and trade names include IEC-508 and ICE552.

  1 and 9, an original is set on the contact glass 11 of the image reading apparatus 10 (scan original setting: step S1), and an operation panel (not shown) provided in the image forming apparatus is provided. ) To select a print mode (scan mode) (step S2). Now, when the color (COLOR) mode is selected, the control device receives the mode selection signal, thereby recognizing the color mode selection, and then the control device determines whether or not the BPF 18 exists on the optical path 17. Determine (step S3).

  As described above, the BPF 18 is driven by the motor, but the BPF 18 is selectively positioned at the first position located on the optical path 17 and the second position located outside the optical path 17. By driving and controlling the motor, the BPF 18 is positioned at the first position or the second position. At this time, the control device rotates the motor forward or backward to position the BPF 18 at the first position or the second position. Based on the rotation direction and the rotation amount of the motor, the control device detects that the BPF 18 has the first and first positions. It is possible to recognize which of the two positions. That is, the rotation direction and rotation amount in the previous motor drive control are stored as motor information, and based on this motor information, the control device determines whether or not the BPF 18 exists on the optical path 17.

  If it is determined that the BPF 18 is positioned on the optical path 17, the previous printing mode is recognized as monochrome (MONO), and the control device drives and controls the motor to move the BPF 18 to a second position outside the optical path 17. (Move it to the position indicated by the broken line block in FIG. 1: Step S4). Then, the control device selects the outputs of the R line sensor 16a, the G line sensor 16b, and the B line sensor 16c (color CCD output selection: step S5).

  Further, as described above, since the control device recognizes that the previous print mode was monochrome (that is, recognizes that the monochrome mode has been switched to the color mode), the gain set corresponding to the color printing is set. Control (AGC: shading) is performed (step S6), and then color printing is executed in accordance with the image data obtained from the image reading apparatus 10 as described above (start of scan image forming process: step S7). .

  On the other hand, when the control device determines in step S3 that the BPF 18 does not exist on the optical path 17, the control device recognizes that the previous print mode was color, and the control device recognizes the R line sensor 16a, the G line sensor 16b, and the B line sensor. The output of 16c is selected (color CCD output selection: step S8). Further, as described above, the control device recognizes that the previous print mode was color (that is, since the color mode is continuously performed), so the gain control set corresponding to the color printing is performed. Without performing, in step S7, color printing is executed in accordance with the image data obtained from the image reading apparatus 10.

  When the monochrome mode is selected in step S2 (when the mode selection signal indicates the monochrome mode), the control device similarly determines whether or not the BPF 18 exists on the optical path 17 (step S2). S9). If it is determined that the BPF 18 is positioned on the optical path 17, the previous printing mode is recognized as the monochrome mode, and the control device selects the output of the monochrome line sensor 16d (monochrome CCD output selection: step S10).

  Further, as described above, the control device recognizes that the previous print mode was the monochrome mode. Therefore, in step S7, the image reading device 10 does not perform the gain control set corresponding to the monochrome print. Color printing is executed according to the image data obtained from the above.

  In the monochrome mode, as a result of the BPF 18 being positioned on the optical path 17, when the reflected light from the mirror 14 b passes through the BPF 18, the long wavelength component is cut and incident on the imaging lens body 15, and from the imaging lens body 15. Is imaged on the monochrome line sensor 16d. As a result, the monochromatic line sensor 16d forms an image of reflected light when the G light source is used as the light source 13a through the imaging lens body 15, and the lens imaging performance is improved as described above. The image quality is kept good, and image deterioration does not occur during monochrome image printing.

  If it is determined in step S9 that the BPF 18 is not on the optical path 17, the control device recognizes that the previous printing mode was the color mode, and the control device controls the drive of the motor so that the BPF 18 is in the first path on the optical path 17. Move to position (step S11). Then, the control device selects the output of the monochrome line sensor 16d (monochrome CCD output selection: step S12). Furthermore, as described above, the control device recognizes that the previous print mode was the color mode (that is, recognizes that the color mode has been switched to the monochrome mode), and is thus set for monochrome printing. Gain control is performed (AGC: step S13), and then color printing is executed according to the image data obtained from the image reading apparatus 10 in step S7.

  In this way, in the monochrome mode, the BPF 18 is inserted in front of the imaging lens body 15 to cut off the long wavelength component such as the R component, and only the G component and its nearby components are formed. 15 is effective in reading color image information with an inexpensive configuration and reading monochrome image information without causing image deterioration.

  In the example shown in FIG. 1, the example in which the BPF 18 is inserted before the imaging lens body 15 has been described. However, the BPF 18 is inserted between the imaging lens body 15 and the CCD 16 to connect the G component and the like to the CCD 16. However, if the BPF 18 is inserted between the imaging lens body 15 and the CCD 16, the magnification and the focal point change depending on the thickness of the BPF 18. Therefore, the BPF 18 may be inserted before the imaging lens body 15. preferable.

  As a result of inserting a filter that allows passage of a specific wavelength component at the time of monochrome image reading into the front stage of the photoelectric conversion unit, image deterioration does not occur at the time of monochrome image reading, and an image forming apparatus such as a copying machine It can be applied to image reading.

1 is a diagram schematically illustrating a first embodiment of an image reading apparatus according to the present invention in a cutaway manner. FIG. FIG. 2 is a perspective view showing an example of a charge coupled device (CCD) used in the image reading apparatus shown in FIG. 1. It is a figure which shows the spectral sensitivity of the monochrome line sensor shown in FIG. FIG. 2 is a diagram showing a relationship between a document position and a chromatic aberration of magnification in the imaging lens body shown in FIG. It is a figure for demonstrating the relationship between a defocus at the time of using a green light source (green lamp) and CTF. It is a figure for demonstrating the relationship between a defocus at the time of using a white light source (white lamp) and CTF. It is a figure which shows the spectral characteristic of a white light source. It is a figure which shows an example of the spectral transmission characteristic of the band pass filter (BPF) shown in FIG. 3 is a flowchart for explaining an image reading operation in the image reading apparatus shown in FIG. 1.

Explanation of symbols

10 Image Reading Device 11 Document Placement Table (Contact Glass)
12 Image reading unit (Image Scanner Unit (ISU))
13, 14 Scanner body 15 Imaging lens body 16 Photoelectric conversion element (charge coupled device (CCD))
17 Optical path 18 Band pass filter (BPF)
13a White light source 13b, 14a, 14b Mirror 16a-16d Line sensor

Claims (6)

Used when reading an image on the object to be read to obtain image data, and a light source for irradiating the object to be read with white light and the reflected light from the object to be read is imaged. An imaging lens body that is an optical image, and a photoelectric conversion unit that photoelectrically converts the optical image to obtain the image data. The photoelectric conversion unit includes a color image reading sensor unit and a monochrome image reading sensor unit. An image reading apparatus comprising:
Filter means that is selectively inserted on the optical path in front of the photoelectric conversion unit, and that allows only a specific wavelength component of the reflected light to pass through;
An image reading apparatus comprising: control means for inserting the filter means on the optical path in a monochrome image reading mode.   The image forming apparatus according to claim 1, wherein the filter unit is selectively inserted on an optical path upstream of the imaging lens body.   The control means receives a mode selection signal indicating whether it is a color image reading mode or a monochrome image reading mode, and when the mode selection signal is a mode different from the previous reading mode, the reading indicated by the mode selection signal 3. The image reading apparatus according to claim 1, wherein the image data is obtained by performing gain control according to a mode.   2. The color image reading sensor unit is formed with color separation filters for the three primary colors red, green, and blue, and the monochrome image reading sensor unit is not formed with a color separation filter. The image reading apparatus according to any one of claims 1 to 3.   5. The filter unit according to claim 4, wherein the filter means cuts a component having a longer wavelength than the component corresponding to the green wavelength from the reflected light, and allows only the specific wavelength component to pass. Image reading device.   The control means selects the output of the color image reading sensor unit in the color image reading mode, and selects the output of the monochrome image reading sensor unit in the monochrome image reading mode. The image reading apparatus according to claim 3 or 5, wherein the image reading apparatus is an image reading apparatus.

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