Patent Publication Number: US-2009219579-A1

Title: Image reading device, apparatus, and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application No. 2008-050328, filed on Feb. 29, 2008 in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments of the present invention relate to an image reading device, an image forming apparatus including the image reading device, and an image reading method. 
     2. Description of the Background 
     In reading an image from a document, some conventional image reading devices allow a user to vary and select a desired level of productivity (number of document sheets read per unit time) and image quality. 
     For example, one conventional image reading device allows a user to select either an automatic reverse document feed (ARDF) reading mode or a sheet-through document feed (DF) reading mode. In the ARDF mode, a document feeder automatically feeds a document from a document tray to a document reading table and a carriage reads an image from the document on the document reading table while moving. In the sheet-through DF reading mode, the carriage remains stationary and reads an image from a document while the document is being fed. The ARDF reading mode and the sheet-through DF reading mode are also associated with reading resolutions of 1200 dpi (dot per inch) and 600 dpi, respectively, so that a user can select either an image-quality priority mode or a productivity priority mode. 
     Another similar conventional approach relates to an image reading system in which an image reading device is connected to an output device via a network. The image reading system automatically optimizes various control operations in accordance with an image reading speed of the image reading device, an image output speed of the output device, and an effective speed of the network. 
     However, the above-described conventional image reading device needs two reading units corresponding to the two reading modes, i.e., the sheet-through DF reading mode and the ARDF reading mode, resulting in an increased manufacturing cost. Further, a user cannot specify a particular reading mode (e.g., the sheet-through DF reading mode capable of providing high-speed reading) to increase the productivity of the reading mode. Since a user cannot also select either an image-quality priority mode or a productivity priority mode and the resolution differs between the image-quality priority mode and the productivity priority mode, the conventional image reading device may not provide an image having a resolution requested from a user. 
     At least in the sheet-through DF reading mode, in order to read a document at a high resolution, the document must be transported at a relatively low speed compared to when the document is read at a standard resolution. By contrast, when a document is read at a low resolution, the document can be transported at a relatively high speed compared to when the document is read at a standard resolution. 
     In other words, the lower the resolution, the higher the document transport speed and the higher the reading productivity. Conversely, the higher the resolution, the lower the reading productivity. It is to be noted that the resolution here is that of a document image in the sub-scanning direction, that is, a direction in which the document is transported. On the other hand, the resolution of a document image in the main-scanning direction depends on a CCD (charge-coupled device) and is thus assumed to be constant. 
     In terms of image quality, an image read at a high resolution (low speed) can more finely reproduce the original document than an image read at a low resolution (high speed) and interpolated by digital image processing. Accordingly, low-speed reading can increase the resolution of a document image, resulting in an excellent image quality. 
     However, in order to increase the reading productivity without reducing the reading resolution, the conventional image reading device needs a mechanism for feeding a document at a high speed and additional circuitry and components for increasing the light intensity of a light source to read a document. 
     Alternatively, the above-described conventional image reading system also has disadvantages in that a user cannot select a desired level of productivity/image quality because the productivity of the image reading system as a whole is determined by capabilities of the output device. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides an image reading device, an image reading method, and an image forming apparatus allowing a user to adjust the balance between productivity and image quality. 
     In one illustrative embodiment, an image reading device reads a document using a plurality of reading modes including a sheet-through reading mode for reading a document at a fixed reading position while the document is automatically fed. The image reading device includes a first resolution changer, a second resolution changer, and a resolution setting unit. The first resolution changer changes a linear velocity at which the document is fed or a traveling speed of a reading carriage to change a resolution at which the document is read in a sub-scanning direction. The second resolution changer electrically interpolates image data output from the first resolution changer to change a resolution of the image data. The resolution setting unit provides a plurality of combinations of resolution change rates between the first resolution changer and the second resolution changer as a plurality of resolution change modes and sets the first resolution changer and the second resolution changer to one of the combinations of resolution change rates. 
     In another illustrative embodiment, an image forming apparatus includes an image reading device for reading a document using a plurality of reading modes including a sheet-through reading mode for reading a document at a fixed reading position while the document is automatically fed. The image reading device includes a first resolution changer, a second resolution changer, and a resolution setting unit. The first resolution changer changes one of a linear velocity at which the document is fed and a traveling speed of a reading carriage to change a resolution at which the document is read in a sub-scanning direction. The second resolution changer electrically interpolates image data output from the first resolution changer to change a resolution of the image data. The resolution setting unit provides a plurality of combinations of resolution change rates between the first resolution changer and the second resolution changer as a plurality of resolution change modes and sets the first resolution changer and the second resolution changer to one of the combinations of resolution change rates. 
     In still another illustrative embodiment, a method of reading a document using a plurality of reading modes including a sheet-through reading mode for reading the document at a fixed reading position while automatically feeding the document includes changing, interpolating, providing, and setting. The changing changes one of a linear velocity at which the document is fed and a traveling speed of a reading carriage using a first resolution changer to change a resolution at which the document is read in a sub-scanning direction. The interpolating electrically interpolates image data output from the first resolution changer using a second resolution changer to change a resolution of the image data. The providing provides a plurality of combinations of resolution change rates between the first resolution changer and the second resolution changer as a plurality of resolution change modes. The setting sets the first resolution changer and the second resolution changer to one of the combinations of resolution change rates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily acquired as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a sectional view illustrating a structure of an image reading device according to an illustrative embodiment of the present disclosure; 
         FIG. 2  is a block diagram illustrating a schematic configuration of an image forming apparatus including an image reading device according to an illustrative embodiment; 
         FIG. 3  is a schematic view illustrating a structure of a document reading section in a platen reading mode; 
         FIG. 4  is a schematic view illustrating a structure of the document reading section in a document-feed reading mode; 
         FIG. 5  is a block diagram illustrating a basic configuration of a read-signal processing unit illustrated in  FIG. 2 ; 
         FIG. 6  is a block diagram illustrating a detailed configuration of the read-signal processing unit illustrated in  FIG. 2 ; 
         FIG. 7A  is a block diagram illustrating a configuration of an image processing unit illustrated in  FIGS. 1 and 5 ; 
         FIG. 7B  is an illustration for explaining processing performed in a first image processing section of the image processing unit; 
         FIG. 7C  is an illustration for explaining processing performed in a second image processing section of the image processing unit; 
         FIG. 8  is a diagram illustrating density adjustment performed in a gamma conversion unit of the first image processing section; 
         FIG. 9  is a diagram illustrating an example of a look-up table used for density adjustment; and 
         FIG. 10  is a block diagram illustrating a functional configuration of an image reading device according to an illustrative embodiment. 
     
    
    
     The accompanying drawings are intended to depict illustrative embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results. 
     Although the illustrative embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the present invention and all of the components or elements described in the illustrative embodiments of this disclosure are not necessarily indispensable to the present invention. 
     Below, an image reading device  100  and an image forming apparatus  200  including the image reading device  100  according to an illustrative embodiment of the present disclosure are described with reference to the drawings. In the following description, for example, a sheet-through DF (document feed) reading mode represents a mode in which a carriage remains stationary and reads an image from a document while the document is being fed. A platen reading mode represents a mode in which a document is placed on a document reading table and a carriage reads an image from the document while moving. An automatic reverse document feed (ARDF) reading mode represents a mode in which a document feeder automatically feeds a document from a document tray to a document reading table and a carriage reads an image from the document on the document reading table while moving. 
       FIG. 1  is a sectional view illustrating a structure of the image reading device  100  according to the present illustrative embodiment. 
     In  FIG. 1 , the image reading device  100  according to the present illustrative embodiment includes a device body  1 , a document feeder  2 , and a document reading table  3 . 
     The device body  1  includes a scanning optical unit  9 . The scanning optical unit  9  further includes a first carriage  4 , a second carriage  5 , a lens  6 , a photoelectric transducer  7 , and a carriage stepping motor  8 . The first carriage  4  includes a light source  4   a  and a mirror  4   b.  The light source  4   a  may be, for example, a xenon lamp or fluorescent light. The second carriage  5  includes a first mirror  5   a  and a second mirror  5   b.  The photoelectric transducer  7  is, for example, a one-dimensional CCD (charge-coupled device) and, in the following description, is assumed to be a three-line CCD (hereinafter “CCD  7 ”) for reading a color image. The carriage stepping motor  8  drives the first carriage  4  and the second carriage  5 . 
     The document feeder  2  is provided with an SDF (sheet document feeder) unit  10  and a document tray  11 . The SDF unit  10  includes a document-feed stepping motor  12  for feeding a document. On an upper portion of the document reading table  3  is pivotally mounted a document cover plate  14 , under which a document  13  is set. At an end portion of the document reading table  3  is disposed a reference white board  15  for shading correction. 
       FIG. 2  is a block diagram illustrating a schematic configuration of the image forming apparatus  200  including the image reading device  100  according to the present illustrative embodiment. Although the image forming apparatus  200  is illustrated as a color MFP (multi functional peripheral) in  FIG. 2 , the image forming apparatus according to the present invention is not limited to the color MFP illustrated in  FIG. 2  but may be any other suitable type of image forming apparatus. 
     In  FIG. 2 , the image forming apparatus  200  includes the light source  4   a,  the CCD  7 , the document-feed stepping motor  12 , a document-feed motor driver  20 , the carriage stepping motor  8 , a carriage-motor driver  28 , a control CPU (central processing unit)  16 , a light-source driver  17 , a CCD driver  18 , a read-signal processing unit  25 , an image processing unit  19 , a memory  27   b,  a memory controller  27   a,  a write-signal processing unit  26   a,  an LD (laser diode)  26   b,  and an LD driving unit  26   c.    
     [Configuration of Document Reading Section] 
       FIG. 3  is a schematic view illustrating a structure of a document reading section in the platen reading mode.  FIG. 4  is a schematic view illustrating a structure of the document reading section in the sheet-through DF reading mode. 
     The document reading modes according to the present illustrative embodiment include, for example, the platen reading mode, in which image data is read from a document placed on the document reading table  3  as illustrated in  FIG. 3 , and the sheet-through DF reading mode, in which image data is read from a document at a fixed reading position while the document is being fed using the document feeder  2 . A description is given below of examples of operations in the platen reading mode and the sheet-through DF reading mode. 
     [Operation in the Platen Reading Mode] 
     As illustrated in  FIG. 3 , in the platen reading mode, the document  13  is set on the document reading table  3 , which is disposed below the document cover plate  14 . The control CPU  16  activates the light-source driver  17  to turn the light source  4   a  on. The CCD  7  driven with the CCD driver  18  scans the reference white board  15  to read light signals, and an A/D (analog-digital) converter of the image processing unit  19  converts the read signals to digital data. The read-signal processing unit  25  retains the digital data as white reference data on a RAM (random access memory), such as a line buffer  36  illustrated in  FIG. 6 , provided in the image processing unit  19  for shading correction. 
     The control CPU  16  controls the carriage-motor driver (driving unit)  28  to activate the carriage stepping motor  8 , so that the first carriage  4  travels toward the document  13 . When the first carriage  4  scans the surface of the document  13 , the CCD  7  performs photoelectric conversion on image data of the document  13 . 
     [Operation in Sheet-Through DF Reading Mode] 
     Unlike the above-described platen reading mode in which a carriage scans a document placed on the table, for the document-feed reading (so-called sheet-through) mode, the first carriage  4  stopping at a certain position scans a document fed with the document feeder  2 . 
     As illustrated in  FIG. 4 , in the sheet-through DF reading mode, the control CPU  16  controls the first carriage  4  to scan the reference white board  15  at a constant speed and stop at a sheet-through document reading position. The control CPU  16  controls the document-feed motor driver  20  to drive the document-feed stepping motor  12  for feeding the document. 
     The document  13  set on the document tray  11  is fed to a predetermined reading position of the first carriage  4  using separation rollers  29  and conveyance rollers  30 . At this time, while the document  13  is being fed at a constant speed, the CCD  7  photoelectrically converts image data of the document  13  with the first carriage  4  stopping at the sheet-through document reading position. 
     [Read-Signal Processing Unit] 
       FIG. 5  is a block diagram illustrating a basic configuration of the read-signal processing unit  25  illustrated in  FIG. 2 .  FIG. 6  is a block diagram illustrating a more detailed configuration of the read-signal processing unit  25 . 
     The read-signal processing unit  25  illustrated in  FIG. 5  includes an analog-video processing unit  21  and a shading-correction processing unit  22 , and processes an input analog-video signal “a” to generate digitally-converted data and transmits the digitally-converted data to the image processing unit  19 . 
     After the analog-video processing unit  21  performs digital conversion on the analog-video signal “a” having been photoelectrically converted through the CCD  7 , the digitally-converted data is corrected using the shading-correction processing unit  22  for the document reading section and transmitted to the image processing unit  19  for various types of image processing. 
     The analog-video processing unit  21  illustrated in  FIG. 5  includes, for example, a preamplifier circuit  31 , a variable amplifier circuit  32 , and an A/D (analog-to-digital) converter  33  illustrated in  FIG. 6 . The shading-correction processing unit  22  includes a black calculation circuit  34 , a shading-correction calculation circuit  35 , and the line buffer  36 . The line buffer  36  is a memory to retain the above-described white-reference data used as reference data of the shading correction. 
     As illustrated in  FIG. 6 , light emitted from the light source  4   a  is reflected by the document  13  placed on the document reading table  3 , passes through a shading adjustment plate  37 , is condensed through the lens  6  and focused on the CCD  7 . The shading adjustment plate  37  adjusts the amount of the reflected light so as to reduce a difference between a middle portion and end portions of the CCD  7 . If the difference in the amount of reflected light is too large, only a calculation result including large distortion might be obtained in the shading-correction processing unit  22 . Hence, according to the present illustrative embodiment, such a difference in the amount of reflected light is reduced before shading-correction calculations are performed. Incidentally, in  FIG. 6 , a mirror for turning the reflected light back is omitted for simplicity. 
     [Image Processing Unit] 
       FIG. 7A  is a block diagram illustrating a configuration of the image processing unit  19  illustrated in  FIGS. 1 and 5 .  FIG. 7B  is an illustration for explaining a process executed in a first image processing section  40   a  of the image processing unit  19 .  FIG. 7C  is an illustration for explaining a process executed in a second image processing section  40   b  of the image processing unit  19 .  FIG. 8  is an illustration for explaining density adjustment performed in a gamma conversion unit  41   c  of the first image processing section  40   a.    FIG. 9  is an illustration of an example of a look-up table used for the density adjustment. 
     As illustrated in  FIG. 7A , the image processing unit  19  includes the first image processing section  40   a  and the second image processing section  40   b,  each of which is implemented by an ASIC (application-specific integrated circuit). 
     [First Image Processing Section] 
     As illustrated in  FIG. 7B , the first image processing section  40   a  performs interline correction, magnification change (resolution change), gamma conversion, filtering, and color conversion on image data from the read-signal processing unit in an interline-correction unit  41   a,  a magnification change unit  41   b,  a gamma conversion unit  41   c,  a filtering unit  41   d,  and a color conversion unit  41   e,  respectively. 
     The interline correction unit  41   a  corrects a line deviation between red (R), green (G), and blue (B), which is caused by a difference in mount positions between RGB in the CCD  7 . For example, when a blue (B) line is used as a reference line, the interline correction unit  41   a  corrects the amount of line deviation between RGB. The magnification change unit  41   b  converts the resolution of image data read from the document  13  to a desired resolution. The gamma conversion unit  41   c  mainly performs conversion processing on density adjustment, and, for example, as illustrated in  FIG. 8 , outputs image data input with a given density as image data with a desired different density. 
     As illustrated in  FIG. 9 , such density adjustment may be performed using a look-up table containing information on a plurality of pairs of input and output densities. The filtering unit  41   d  performs filtering calculations for MTF (modulation transfer function) correction, sharpening, and smoothing. The color conversion unit  41   e  converts the RGB color space to a color space of an output device, for example, CMYK (cyan, magenta, yellow, black) color space. For a color image, the above-described processing of the first image processing section  40   a  is performed on each of the RGB components. By contrast, for a monochrome image, the above-described processing may be performed on only one component using, for example, a path to G data of the RGB. 
     [Second Image Processing Section (in the Case in which a Fixed Threshold is Binarized in Gradation Conversion)] 
     As illustrated in  FIG. 7C , the second image processing section  40   b  performs gradation conversion in a gradation conversion unit  42   c.  When the gradation conversion unit  42   c  of the second image processing section  40   b  performs gradation conversion on image data before storing the image data on, for example, the memory  27   b  or any other suitable storage, the number of gradations may be set relatively small to reduce the amount of stored data. The following example assumes that binary gradation conversion is selected, and more specifically, the gradation conversion is performed by binarizing a fixed threshold when a write unit is capable of outputting up to one bit, that is, two gradations. 
     When a binary image is requested, the gradation conversion unit  42   c  of the second image processing section  40   b  illustrated in  FIG. 7C  converts each of CMYK images of eight bits, i.e., 256 gradations to binary image data of two gradations, and transmits the binary image data as image data “b” to the memory controller (ASIC)  27   a.    
     Here, an example of processing on such a fixed threshold is described below. 
     For example, when the threshold is 128, the second image processing section  40   b  binarizes the pixel data of an input image in the following manner. 
     When 0≦pixel data&lt;128 is true, the second image processing section  40   b  outputs 0; and 
     when 128≦pixel data≦255 is true, the second image processing section  40   b  outputs 1. 
     [Second Image Processing Section (in the Case in which a Fixed Threshold is Quaternized in Gradation Conversion)] 
     Next, a description is given of gradation conversion performed by quaternizing a fixed threshold when the write unit can output up to two bits, i.e., four gradations. 
     When a quaternary image is requested, the gradation conversion unit  42   c  of the second image processing section  40   b  illustrated in  FIG. 7C  converts each of CMYK images of eight bits, i.e., 256 gradations to quaternary image data of four gradations, and outputs the quaternary image data as image data “b” to the memory controller (AISC)  27   a.    
     For processing on such a fixed, quaternary threshold, for example, the second image processing section  40   b  quaternizes the pixel data of an input image in the following manner. 
     When 0≦pixel data&lt;64 is true, the second image processing section  40   b  outputs 0; 
     when 64≦pixel data&lt;128 is true, the second image processing section  40   b  outputs 1; 
     when 128≦pixel data&lt;192 is true, the second image processing section  40   b  outputs 2; and 
     when 192≦pixel data≦255 is true, the second image processing section  40   b  outputs 3. 
     Thus, the second image processing section  40   b  quaternizes the input image. 
     [Image-Data Storage] 
     In the above-described examples of gradation conversion, the gradation conversion unit  42   c  converts CMYK image data into one-bit or two-bit image data. Such converted image data is temporarily stored on the memory  27   b  via the memory controller  27   a.    
       FIG. 10  is a block diagram illustrating a functional configuration of an image reading device according to an illustrative embodiment of the present disclosure. 
     As illustrated in  FIG. 10 , the image reading device according to the present illustrative embodiment includes, for example, a first resolution changer  101 , a second resolution changer  102 , and a resolution setting unit  103 . The first resolution changer  101  changes the traveling speed of a carriage to change the reading resolution of image data in the sub-scanning direction of the image reading device. The second resolution changer  102  interpolates the image data using an electric circuit, such as an ASIC, to change the resolutions of the image data in the main- and sub-scanning directions. The resolution setting unit  103  sets the first resolution changer  101  and the second resolution changer  102  to magnifications (resolution change rates) of image data. 
     The first resolution changer  101  includes, for example, the light-source driver  17 , the document-feed motor driver  20 , and the carriage motor driver  28 . The second resolution changer  102  performs processing in the magnification change unit  41   b  in the image processing unit  19  and operates as a module for changing the resolutions of image data in the main- and sub-scanning directions. The resolution setting unit  103  is a module implemented by the CPU  16 . 
     In the present illustrative embodiment, when the image reading device  100  outputs an image with resolutions of 600 dpi (dot per inch) and 600 dpi in the main- and sub-scanning direction, a combination of magnifications between the first resolution changer  101  and the second resolution changer  102  is predetermined for each productivity mode, as described in the following example. 
     In the following description, the traveling speed at which a carriage reads an image at a resolution of 600 dpi in the sub-scanning direction is referred to as “standard-resolution speed”. The operation of the CCD  17  at the standard-resolution speed for 600 dpi is used as a reference to control the driving of the CCD  17 . 
     Productivity Mode 1 (Productivity Priority Mode) 
     First resolution changer: 50% magnification and 300-dpi reading (at a speed twice the standard-resolution speed) 
     Second resolution changer: 200% magnification 
     Productivity Mode 2 (Productivity/Image-Quality Balance Mode) 
     First resolution changer: 100% magnification and 400-dpi reading (at a speed 1.5 times the standard-resolution speed) 
     Second resolution changer: 150% magnification 
     Productivity Mode 3 (Image-Quality Priority Mode) 
     First resolution changer: 100% magnification and 600-dpi reading (at the standard-resolution speed) 
     Second resolution changer: 100% magnification 
     Next, a description is given of an operation performed when a user requests an image resolution of 600 dpi and the productivity mode 1 (productivity priority mode) is selected as the productivity mode. 
     In such a case, the resolution setting unit  103  instructs the first resolution changer  101  to move the carriage of the document reading section at a speed twice the standard-resolution speed. The resolution setting unit  103  also instructs the second resolution changer  102  to change the sub-scanning resolution of image data to 200%. 
     According to the instructions, the carriage travels to read a document, and the first resolution changer  101  outputs image data with main- and sub-scanning resolutions of 600 dpi and 300 dpi, respectively. The second resolution changer  102  changes the sub-scanning resolution of the image data output from the first resolution changer  101  to 200%, and outputs the image data with main- and sub-scanning resolutions of 600 dpi and 600 dpi to the subsequent step. 
     At this time, in theory the reading productivity becomes about twice the productivity of the productivity mode 3 (image-quality priority mode) described below, and thus the time required for reading the document in the productivity mode 1 is about half the reading time in the productivity mode 3. In fact, however, since it takes time to feed the document to the reading position, the reading time in the productivity mode 1 may not be precisely half the reading time in the productivity mode 3. 
     Next, a description is given of an operation performed when a user requests a resolution of 600 dpi and the productivity mode 2 (productivity/image-quality balance mode) is selected as the productivity mode. 
     In such a case, the resolution setting unit  103  instructs the first resolution changer  101  to move the carriage at a speed 1.5 times the standard-resolution speed. The resolution setting unit  103  also instructs the second resolution changer  102  to change the sub-scanning resolution of image data to 150%. 
     According to the instructions, the carriage travels to read a document, and the first resolution changer  101  outputs image data with main- and sub-scanning resolutions of 600 dpi and 400 dpi, respectively. The second resolution changer  102  changes the sub-scanning resolution of the image data output from the first resolution changer  101  to 150%, and outputs the image data with main- and sub-scanning resolutions of 600 dpi and 600 dpi to the subsequent step. 
     At this time, the reading productivity becomes about 1.5 times the productivity of the productivity mode 3 (image-quality priority mode), and thus the time required for reading the document in the productivity mode 2 is about two thirds of the reading time in the productivity mode 3. In fact, however, since it takes time to feed the document to the reading position, the reading time in the productivity mode 2 may not be precisely two-thirds of the reading time in the productivity mode 3. 
     Next, a description is given of an operation performed executed when a user requests an image resolution of 600 dpi and the productivity mode 3 (image-quality priority mode) is selected as the productivity mode. 
     In such a case, the resolution setting unit  103  instructs the first resolution changer  101  to move the carriage at the standard-resolution speed. The resolution setting unit  103  also instructs the second resolution changer  102  to change the sub-scanning resolution of image data to 100%, that is, so as not to change the sub-scanning resolution. 
     According to the instructions, the carriage travels to read a document, and the first resolution changer  101  outputs image data with main- and sub-scanning resolutions of 600 dpi and 600 dpi, respectively. The second resolution changer  102  changes the sub-scanning resolution of the image data output from the first resolution changer  101  to 100% and outputs the image data with main- and sub-scanning of 600 dpi and 600 dpi to the subsequent step. 
     At this time, the reading productivity becomes about half of the productivity of the productivity mode 1 (productivity priority mode), and thus the time required for reading the document in the productivity mode 3 is about twice the reading time in the productivity mode 1. In fact, however, since it takes time to feed the document to the reading position, the reading time in the productivity mode 3 may not be precisely twice the reading time in the productivity mode 1 but may be slightly greater than twice. 
     In the above-described examples, the image resolution requested from a user is assumed to be 600 dpi. Next, a description is given of an operation performed in each of the productivity modes 1 to 3 when the image resolution requested from a user is 300 dpi. 
     First, a description is given of an operation performed when a user requests an image resolution of 300 dpi and the productivity mode 1 (productivity priority mode) is selected as the productivity mode. 
     In such a case, the resolution setting unit  103  instructs the first resolution changer  101  to move the carriage at a speed four times the standard-resolution speed. The resolution setting unit  103  also instructs the second resolution changer  102  to change the main- and sub-scanning resolutions of image data to 50% and 200%, respectively. 
     According to the instructions, the carriage travels to read a document, and the first resolution changer  101  outputs image data with main- and sub-scanning resolutions of 600 dpi and 150 dpi, respectively. The second resolution changer  102  changes the main- and sub-scanning resolutions of the image data output from the first resolution changer  101  to 50% and 200%, respectively, and outputs the image data with main- and sub-scanning resolutions of 300 dpi and 300 dpi to the subsequent step. 
     At this time, the reading productivity becomes about twice the productivity of the productivity mode 3 (image-quality priority mode), and thus the time required for reading the document in the productivity mode 1 is about half the reading time in the productivity mode 3. In fact, however, since it takes time to feed the document to the reading position, the reading time in the productivity mode 1 may not be precisely twice the reading time in the productivity mode 3. 
     Next, a description is given of an operation performed when a user requests an image resolution of 300 dpi and the productivity mode 2 (productivity/image-quality balance mode) is selected as the productivity mode. 
     In such a case, the resolution setting unit  103  instructs the first resolution changer  101  to move the carriage at a speed three times the standard-resolution speed. The resolution setting unit  103  also instructs the second resolution changer  102  to change the main- and sub-scanning resolutions of image data to 50% and 150%, respectively. 
     According to the instructions, the carriage travels to read a document, and the first resolution changer  101  outputs image data with main- and sub-scanning resolutions of 600 dpi and 200 dpi, respectively. The second resolution changer  102  changes the main- and sub-scanning resolutions of the image data output from the first resolution changer  101  to 50% and 150%, respectively, and outputs the image data with main- and sub-scanning resolutions of 300 dpi and 300 dpi to the subsequent step. 
     At this time, the reading productivity becomes about 1.5 times the productivity of the productivity mode 3 (image-quality priority mode), and thus the time required for reading the document in the productivity mode 2 is about two thirds the reading time in the productivity mode 3. In fact, however, since it takes time to feed the document to the reading position, the reading time in the productivity mode 2 may not be precisely two thirds the reading time in the productivity mode 3. 
     Next, a description is given of an operation performed when a user requests an image resolution of 300 dpi and the productivity mode 3 (image-quality priority mode) is selected as the productivity mode. 
     In such a case, the resolution setting unit  103  instructs the first resolution changer  101  to move the carriage at a speed twice the standard-resolution speed. The resolution setting unit  103  also instructs the second resolution changer  102  to change the main- and sub-scanning resolutions of image data to 50% and 100%, respectively. 
     According to the instructions, the carriage travels to read a document, and the first resolution changer  101  outputs image data with main- and sub-scanning resolutions of 600 dpi and 300 dpi, respectively. The second resolution changer  102  changes the main- and sub-scanning resolutions of the image data output from the first resolution changer  101  to 50% and 100%, respectively, and outputs the image data with main- and sub-scanning resolutions of 300 dpi and 300 dpi to the subsequent step. 
     At this time, the reading productivity becomes about half the productivity of the productivity mode 1 (productivity priority mode), and thus the time required for reading the document in the productivity mode 3 is about two thirds the reading time in the productivity mode 1. In fact, however, since it takes time to feed the document to the reading position, the reading time in the productivity mode 3 may not be precisely twice the reading time in the productivity mode 1 but may be slightly greater than twice. 
     In the above-described examples, the image resolution requested from a user is assumed to be 600 dpi or 300 dpi. It is to be noted that, according to the present illustrative embodiment, a user can set a given image resolution and variably set a combination of magnifications (resolution change rates) between the first resolution changer  101  and the second resolution changer  102 . 
     Next, a description is given of a user&#39;s operation to read a document. For example, a user performs the operation in the following manner. 
     (1) A user determines which should have priority, image quality (resolution in the sub-scanning direction) or reading speed, in reading a document and selects one productivity mode through an operation unit. 
     (2) The user places a plurality of document sheets on the document tray of the document feeder. 
     (3) The user presses a reading start button of an operation panel to start reading the document sheets. 
     As described above, for example, the sheet-through DF reading mode and the platen reading mode may be used as the reading mode of a document image. According to the present illustrative embodiment, combinations of the reading modes and the productivity modes may be predetermined, and information on the combinations is stored on the memory  27   b  or any other suitable storage. Such a configuration allows a document to be automatically read, for example, in the productivity mode 1 when a user selects the sheet-through DF reading mode or in the productivity mode 3 when a user selects the platen reading mode. 
     Next, the reading operation using such predetermined combinations of reading modes and productivity modes is described with reference to examples of the combination of the sheet-through DF reading mode and the productivity mode 1 (productivity priority mode) and the combination of the platen reading mode and the productivity mode 3 (image-quality priority mode). 
     A user performs the reading operation, for example, in the following manner. 
     (1) A user determines which should have priority, image quality or reading speed, in reading a document. 
     (2) If image quality is given priority, the user places the document on the document reading table. 
     (3) The user presses the reading start button of the operation panel to start reading the document. 
     (4) Alternatively, if reading speed is given priority, the user places the document on the document tray of the document feeder. 
     (5) The user presses the reading start button of the operation panel to start reading the document. 
     As described above, examples of the reading mode of a document image includes the ARDF reading mode. According to the present illustrative embodiment, the combinations of the reading modes including the ARDF reading mode and the productivity modes may be predetermined, and information on the combinations may be stored on the memory  27   b  or any other suitable storage. Such a configuration allows a document to be automatically read, for example, in the productivity mode 1 when a user selects the sheet-through DF reading mode, in the productivity mode 2 when a user selects the ARDF reading mode, or in the productivity mode 3 when the user selects the platen reading mode. 
     Next, the reading operation using predetermined combinations of reading modes and productivity modes is further described, taking examples of the combination of the sheet-through DF reading mode and the productivity mode 1 (productivity priority mode), the combination of the ARDF reading mode and the productivity mode 2 (productivity/image-quality balance mode), and the combination of the platen reading mode and the productivity mode 3 (image-quality priority mode). 
     A user performs the reading operation, for example, in the following manner. 
     (1) A user determines which should have priority, image quality or reading speed, in reading a document. 
     (2) If image quality is given priority, the user places the document on the document reading table. 
     (3) The user presses the reading start button of the operation panel to start reading the document. 
     (4) Alternatively, if the reading speed is given priority, the user places the document on the document tray of the document feeder. 
     (5) If the user uses the automatic document feeder, the user selects either the sheet-through DF reading mode or the ARDF reading mode through the operation unit. 
     (6) The user presses the reading start button of the operation panel to start reading, the document. 
     Although in the above description the combinations of reading modes and productivity modes are predetermined, according to the present illustrative embodiment, the combinations of magnifications between the first resolution changer  101  and the second resolution changer  102  may be associated with image-quality modes. Each of the image-quality modes includes a group of parameters of digital image processing, such as gamma conversion, filtering, or color conversion. In the following description, for example, the term “text mode” represents an image-quality mode in which digital-processing parameters are set so as to provide an image quality suitable for a document mainly including text. The term “photographic mode” represents an image-quality mode in which parameters suitable for a photographic document are set. The term “text/photographic mode” represents an image-quality mode in which intermediate parameters between the text and photographic modes are set. 
     A description is given below of examples in which a productivity mode is set corresponding to an image-quality mode selected by a user instead of a reading mode. In the following example, the document reading section is assumed to output an image with main- and sub-scanning resolutions of 600 dpi and 600 dpi. Examples of the combination of image-quality mode and productivity mode are as follows. 
     EXAMPLE 1 
     Text Mode and Productivity Mode 1 
     First resolution changer: 50% magnification and 300-dpi reading (at a speed twice the standard-resolution speed) 
     Second resolution changer: 200% magnification 
     EXAMPLES 2 
     Text/Photographic Mode and Productivity Mode 2 (Priority and Image-Quality Balanced) 
     First resolution changer: (⅔×100) % magnification and 400-dpi reading (at a speed 1.5 times the standard-resolution speed) 
     Second resolution changer: 150% magnification 
     EXAMPLE 3 
     Photographic Mode and Productivity Mode 3 (Image-Quality Priority Mode) 
     First resolution changer: 100% magnification and 600-dpi reading (at the standard-resolution speed) 
     Second resolution changer: 100% magnification 
     A user performs a reading operation, for example, in the following manner. 
     (1) A user selects the text mode for a document mainly containing text as the image-quality mode. 
     (2) The productivity mode 1 is automatically selected corresponding to the text mode. 
     (3) The user selects the sheet-through DF reading mode to read a plurality of document sheets and places the plurality of document sheets on the automatic document feeder. 
     (4) The user presses the reading start button of the operation panel to start reading the document sheets. 
     Alternatively, according to the present illustrative embodiment, an image-quality mode and a productivity mode may be automatically set corresponding to a reading mode selected by a user. Examples of the combination of reading mode, image-quality mode, and productivity mode are as follows. 
     Example 1 
     Sheet-Through DF Reading Mode, Text Mode, and Productivity Mode 1 (Productivity Priority Mode) 
     First resolution changer: 50% magnification and 300-dpi reading (at a speed twice the standard-resolution speed) 
     Second resolution changer: 200% magnification 
     Example 2 
     Platen Reading Mode, Photographic Mode, and Productivity Mode 3 (Image-Quality Priority Mode) 
     First resolution changer: 100% magnification and 600-dpi reading (at the standard-resolution speed) 
     Second resolution changer: 100% magnification 
     Next, with respect to the above-described combination examples, a description is given of an operation performed when a user instructs the image reading device to read a document image using the sheet-through DF reading mode or the platen reading mode. For example, when a user selects the sheet-through DF reading mode and places a document on the automatic document feeder, the text mode and the productivity mode 1 are automatically selected to read the document. Alternatively, when a user selects the platen reading mode, the photographic mode, and the productivity mode 3 are automatically selected to read the document. 
     A user performs such an operation, for example, in the following manner. 
     (1) A user places a document on the document tray of the document feeder. 
     (2) The text mode and the productivity mode 1 are automatically set in response to the reading mode selected through the CPU. 
     (3) The user presses the reading start button of the operation panel to start reading the document. 
     According to the above-described illustrative embodiment, the image reading device includes the first and second resolution changers. The first resolution changer changes the linear velocity at which a document is fed or the traveling speed of the carriage for reading a document to change a resolution at which the document is read in the sub-scanning direction. The second resolution changer electrically interpolates the image data output from the first resolution changer to change the resolution of the image data. The image reading device can change the combination of magnifications (resolution change rates) in the first and second resolution changers, and further includes the resolution setting unit to set the combination as a predetermined mode. Such a con figuration allows a user to select either an image-quality priority mode or a productivity priority mode, thus improving convenience for users. 
     Further, although in the platen reading mode it may take a user longer to replace document sheets or pages, a user may not require increased reading productivity. Further, when the document is not a bound book or magazine but a cut sheet, a user who wants increased reading productivity can select the sheet-through DF reading mode. Thus, according to the above-described illustrative embodiment, a user may use the platen reading mode to read a magazine or book and the sheet-through DF reading mode to read a cut-sheet document often used in an office environment. 
     According to an illustrative embodiment, a given combination of a reading mode and a reading productivity may be fixed depending on a user&#39;s situation. Such a configuration allows a user to set such a desired reading productivity in a fixed manner without re-setting a productivity mode for each operation, thereby improving convenience for users. 
     Among a plurality of reading modes used in the image reading device, the highest productivity value may differ depending on the performances of actuators used. For example, an actuator for feeding a document in the automatic document feeder may differ from an actuator for moving a carriage in the platen reading mode because of constraints on mechanical layout or cost of the image reading device. Alternatively, even if the actuators are the same type, a difference between the mechanism for feeding the document and the mechanism for moving the carriage may result in a difference in the upper limitation of the reading speed. Thus, in the platen reading mode as well, a user may want to increase reading productivity per document sheet. 
     Hence, to meet such a demand for a higher reading productivity per document sheet, the image reading device according to the present illustrative embodiment may associate settings of a productivity mode capable of achieving the highest reading productivity with a productivity mode capable of reading at the highest speed. 
     Such a configuration can effectively improve the reading, productivity. Further, a user can easily use a reading productivity in the most effective combination by only selecting a desired reading mode, thus improving convenience for users. For an actuator compatible with one reading mode, when the actuator is assumed to be used at a fixed reading speed, it is easier to select components than when the actuator is assumed to be used at a variable reading speed, thereby increasing development efficiency. Accordingly, when an actuator is assumed to be used at a fixed reading speed in one reading mode, the above-described advantages can be more easily obtained. 
     As described above, in a typical office environment, a plurality of cut-sheet documents are often used and, among various reading modes, the sheet-through DF reading mode can provide the highest reading productivity at a relatively low cost. 
     Accordingly, according to an illustrative embodiment, a productivity mode (a combination of magnifications between the first resolution changer and the second resolution changer) capable of achieving the highest reading productivity may be associated with the sheet-through DF reading mode capable of relatively easily providing a high reading productivity in view of cost and mechanism. Such a combination of the sheet-through DF reading mode and a productivity mode having a high productivity can more effectively achieve a high productivity at a relatively low cost. 
     Generally, there is a demand for reading a photographic document at a high image quality. Among a plurality of reading modes, the platen reading mode may provide a relatively high image quality than the sheet-through DF reading mode. One reason is that, in the sheet-through DF reading mode, since a document is read during travel, document skew or color misalignment may appear, resulting in image degradation. For such a reason, the platen reading mode may be used to meet a demand for a higher image quality. 
     Hence, according to an illustrative embodiment, a productivity mode capable of providing a high image quality at the lowest productivity may be associated with the platen reading mode. Thus, among a plurality of selectable reading modes, a productivity mode capable of achieving the highest image quality is combined with a reading mode (the platen reading mode) capable of achieving the highest image quality, allowing a user to easily obtain a high image quality without considering a productivity mode. 
     Although in the above-described example the platen reading mode is associated with the productivity mode in which image quality is given priority, a user may request to associate a document type (image-quality mode), rather than such a reading mode, with a productivity mode. 
     For example, when a user tries to read an image from a bound document mainly containing text, the user uses the platen reading mode because the bound document is not a cut-sheet type. Further, because the document mainly contains text, a user may not put a priority on image quality. In such a case, when the user tries to read as many document sheets or pages as possible, the unique correspondence between the reading modes and the productivity modes as described in the above-described example may not meet a user&#39;s request. This is the case with the sheet-through DF reading mode and, when a photographic document is read in the sheet-through DF reading mode, an image-quality priority mode at a low productivity is not selected in the above-described example. 
     Hence, according to an illustrative embodiment, image-quality modes may be associated with productivity modes. Such a configuration allows a user to easily select an optimal productivity and image quality level without being puzzled by the selection of the productivity mode, thus improving convenience for users. 
     As described above, in a typical office environment, a plurality of cut-sheet documents is relatively often used and, among a plurality of reading modes, the sheet-through DF reading mode can achieve the highest reading productivity at a relatively low cost. 
     Hence, according to an illustrative embodiment, a productivity mode (a combination of resolution change rates between the first resolution changer and the second resolution changer) capable of achieving the highest productivity may be fixedly associated with the sheet-through DF reading mode capable of relatively easily achieving a high productivity in view of cost and mechanism. Such a configuration can achieve the highest productivity among a plurality of selectable reading modes at a relatively low cost. Further, the productivity modes may be associated with the image-quality modes. Such a configuration allows a user to select an image-quality mode and a productivity mode by selecting only one reading mode. As a result, a user need not instruct an image-quality mode and a productivity mode through the operation unit, thus further improving convenience for users. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein. 
     With some embodiments of the present invention having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications are intended to be included within the scope of the present invention. 
     For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     Further, as described above, any one of the above-described and other methods of the present invention may be embodied in the form of a computer program stored in any kind of storage medium. 
     Examples of such a storage medium include, but are not limited to, flexible disk, hard disk, optical discs, magneto-optical discs, magnetic tapes, nonvolatile memory cards, ROM (read-only-memory), etc. 
     Alternatively, any one of the above-described and other methods of the present invention may be implemented by ASIC, prepared by interconnecting an appropriate network of conventional component circuits or by a combination thereof with one or more conventional general purpose microprocessors and/or signal processors programmed accordingly.